HK1083949A1 - Beacon signaling in a wireless system - Google Patents

Description

Beacon signaling in a wireless system

Background

Spread spectrum OFDM (orthogonal frequency division multiplexing) multiple access is an example of a spectrally efficient wireless communication technique. OFDM may be used to provide wireless communication services.

In an OFDM spread spectrum system, the total spectral bandwidth is typically divided into a number of orthogonal tones, i.e., subcarrier frequencies. In a cellular network, the same bandwidth is typically reused in all cells of the system. Those tones are frequency hopped across the bandwidth for channel (frequency) diversity and interference averaging. Tone hopping follows a predefined tone hopping sequence so that the hopping tones of a given cell do not collide with each other. The tone hopping sequences used in adjacent cells may be different in order to average out the interference between cells.

One exemplary form of tone hopping sequence is

In the above equation, N is the total number of tones, t is the OFDM symbol index, j is the index of one tone hopping sequence, j 1_j(t) is the index of the tone occupied by the jth tone hopping sequence at time t. SLOPE is a cell specific parameter that uniquely determines the tone hopping sequence used in a given cell. Neighboring cells may use different values of SLOPE.

Information (control and data) is transmitted through various physical channels. One physical channel corresponds to one or more tone hopping sequences defined in equation (1). Thus, those tone hopping sequences are sometimes referred to as data tone hopping sequences. In one physical channel, the basic transmission unit is one channel segment (segment). A channel segment includes a plurality of tones, typically corresponding to a plurality of OFDM symbols, corresponding to a hopping sequence of data tone(s) of a data channel over a time interval.

In addition to data tone hopping sequences, OFDM spread spectrum systems may use a pilot (pilot) in the downlink to facilitate various operations, which may include synchronization and channel estimation. A pilot typically corresponds to one or more pilot tone hopping sequences. As disclosed in US patent application 09/551,791, a typical form of a pilot tone hopping sequence is

Pilot_j(t)＝SLOPE·t+O_jmodN (2)

By using different values of SLOPE, different pilot sequences will occur. Different pilot sequences may be used in different cells.

In the above equations, N, t and SLOPE are the same parameters as used in equation (1), j is the index of a Pilot tone hopping sequence, Pilot_j(t) is the index of the tone occupied by the jth pilot tone hopping sequence at time t, and O_jIs a fixed offset of the jth pilot tone hopping sequence. Usually cells in a system use the same set of offsets O_j}。

In an OFDM spread spectrum system, the pilot and data tone hopping sequences are typically periodic, with the same period, and use the same value for the parameter SLOPE. The time interval of one period of a tone hopping sequence is sometimes referred to as a superslot. Thus, a super slot corresponds to a period after which a pilot sequence is repeated. The structure of the pilot, physical channel and channel segments is typically repeated from one super slot to another, so that these structures can be uniquely determined once the super slot boundaries have been identified.

Fig. 1 shows a frequency versus time diagram 100 that describes the general concept of data and pilot tone hopping sequences, control and data traffic channels, channel segments, and superslots.

Fig. 1 includes a first row 102, a second row 104, a third row 106, a fourth row 108, and a fifth row 110. Each row 102, 104, 106, 108, 110 corresponds to a different orthogonal frequency tone in the frequency domain.

Fig. 1 also includes a first column 112, a second column 114, a third column 116, a fourth column 118, a fifth column 120, a sixth column 122, a seventh column 124, an eighth column 126, a ninth column 128, and a tenth column 130. Each column 112, 114, 116, 118, 120, 122, 124, 126, 128, 130 corresponds to one OFDM symbol time in the time domain.

In the example of fig. 1, the superslots 133, 135 each have a period equal to the period of the tone hopping sequence. The first superslot 133 has one period of five OFDM symbol times represented by the first through fifth columns 112, 114, 116, 118, 120 and bounded by vertical time domain boundary lines 111 and 121. The second superslot 135 also has one period of five OFDM symbol times. The superslot 135 corresponds to the sixth through tenth columns 122, 124, 126, 128, 130 and is bounded by vertical time domain boundary lines 121 and 131.

During the first superslot (columns 112, 114, 116, 118, 120), a data tone hopping sequence is displayed for a first traffic segment. Three tones are dedicated to the first traffic segment in each symbol period. The data tone hopping sequence of the first example traffic channel segment is depicted by the diagonal shading that descends from left to right in fig. 1. During the second superslot (columns 122, 124, 126, 128, 130), a data tone hopping sequence is displayed for a second traffic segment. The data tone hopping sequence repeats in each superslot 133, 135. The data tone hopping sequence of the second example traffic channel segment is depicted by the rising diagonal shading in fig. 1. During the OFDM time intervals represented by the first column 112 and the sixth column 122, traffic channel data is shown to include frequency tones represented by the first row 102, the second row 104, and the third row 106. During the OFDM time interval represented by the second column 114 and the seventh column 124, traffic channel data is represented as including frequency tones represented by the first row 102, the third row 106, and the fifth row 110. During the OFDM time interval represented by the third column 116 and the eighth column 126, traffic channel data is shown to include frequency tones represented by the second row 104, the fourth row 108, and the fifth row 110. During the OFDM time interval represented by fourth column 118 and ninth column 128, traffic channel data is shown to include frequency tones represented by first row 102, third row 106, and fourth row 108. During the OFDM time interval represented by the fifth column 120 and the tenth column 130, traffic channel data is shown to include frequency tones represented by the second row 104, the third row 106, and the fourth row 108.

Fig. 1 also shows a pilot tone hopping sequence. The pilot tone hopping sequence repeats in each superslot 133, 135. The pilot tone hopping sequence is depicted in fig. 1 by shading with small horizontal lines. During the OFDM time interval represented by the first column 112 and the sixth column 122, pilot tones are allocated to the frequency tones represented by the fifth row 110. During the OFDM time interval represented by second column 114 and seventh column 124, pilot tones are allocated to frequency tones represented by fourth row 108. During the OFDM time interval represented by the third column 116 and the eighth column 126, pilot tones are allocated to the frequency tones represented by the third row 106. During the OFDM time interval represented by fourth column 118 and ninth column 128, pilot tones are allocated to the frequency tones represented by second row 104. During the OFDM time interval represented by the fifth column 120 and the tenth column 130, pilot tones are allocated to the frequency tones represented by the first row 102.

In some OFDM spread spectrum systems, traffic channels are assigned on a segment-by-segment basis. In particular, traffic channel segments may be independently assigned to different wireless terminals. A scheduler determines the amount of transmit power and burst data rate associated with a particular channel coding and modulation scheme to be used in each traffic channel segment. The transmit power and burst data rate may be different for different traffic channel segments.

Zoning is a popular method of increasing the capacity of a wireless system. For example, fig. 2 depicts a cell 200 that includes three sectors (sectors): sector 1201, sector 2203, and sector 3205. Cell 200 also includes a base station 207 that employs a 3-sector antenna including antenna sector 1209, antenna sector 2211, and antenna sector 3213. The sectorized antenna provides some isolation between the sectors 201, 203, 205. In an ideal system, the same spectrum can be reused in all sectors 201, 203, 205 without interfering with each other, thereby tripling the system capacity (over a full cell) in the 3-sector system shown in fig. 2. Unfortunately, ideal signal separation is not possible in the real world, which generally complicates the use of partitions in some systems.

Theoretically, integrating partitions into one OFDM spread spectrum system would improve overall system performance. Interference between sectors due to limited antenna isolation and reflection from objects may limit the practical capability obtained on a full cell. It can therefore be appreciated that there is a need for methods and apparatus: allows the use of partitions in an OFDM system and in a manner that increases the capacity of such a system while avoiding many of the interference problems associated with partitions.

Disclosure of Invention

According to the present invention, the same frequency spectrum, e.g., frequency, may be reused in each sector of a cell in a sectorized OFDM system. In some embodiments of the invention, sectors of a cell are synchronized according to tone frequency, OFDM symbol timing, data tone hopping sequence, channel segment, and super slot boundary. In some embodiments less synchronization of transmission characteristics or parameters is used. Indeed, certain features of the present invention, such as the beacon (beacon) signals discussed below, may be used in situations where frequency synchronization between sectors of a cell is minimal or non-existent.

In various embodiments, symbol timing between sectors of a cell is substantially synchronized, e.g., symbol transmission start times are synchronized to within the duration of a cyclic prefix contained in the transmitted symbol. As is known in the art, it is common to add a cyclic prefix (e.g., a copy of a portion of a symbol so that the same data is on both ends of the symbol being transmitted). The cyclic prefix provides some protection against timing errors and can be used as a buffer in an acceptable amount of timing difference that may occur between sectors.

The different cells in the system may, but need not, be synchronized with respect to transmission characteristics such as frequency. In the synchronized sector embodiment, for any control or data traffic channel in a particular sector, there is a corresponding control or data traffic channel in each of the other synchronized sectors of the same cell. Corresponding channels in different sectors will have identically configured frequency tones and time intervals, e.g., transmission frequency and symbol transmission time. For transmission, the channel is divided into segments. Thus, the corresponding channel will have a corresponding channel segment. Because of the high degree of inter-sector synchronization in a fully synchronized sector embodiment, inter-sector interference is concentrated between corresponding channel segments in such an embodiment. Non-corresponding channel segments will see relatively little inter-sector interference with each other.

In some embodiments, the SLOPE values of the pilots used in each sector of a cell are the same, but the offsets are different. This results in the repeated pilot tone sequence being the same in each sector, but the starting point of the sequence is different in time. Thus, at any point in time, the steering in different sectors of a cell may be different.

When the sectorized OFDM spread spectrum system is used in a cellular network, different values of SLOPE may be used by neighboring cells to determine pilot and channel tone hopping sequences in accordance with the present invention. The slope offset settings in different cells may be the same. The different cells need not and need not be synchronized according to tone frequency, OFDM symbol timing, tone hopping sequence, channel segment, or super slot boundary.

In accordance with a feature of the invention, in some embodiments, the transmit power of corresponding channel segments (if channel segments are active) allocated to different sectors of a cell is substantially the same in each sector. In this case, the difference between the transmit powers of the corresponding active channel segments in the sectors of one cell is not greater than Delta, where Delta is a value used to control the channel power difference between the sectors. Different deltas may be used for different channels. In one embodiment, Delta is set to a constant, e.g., zero, for at least one channel. In another embodiment, Delta may be different between different groups of corresponding channels, different groups of corresponding channel segments, or may be a function of the burst data rate used in the corresponding channel segment, or some other criteria. A scheduler may be used to coordinate power allocation in different sectors of a cell in a centralized manner. According to the present invention, the dynamic range of allocated power between traffic channels in the same sector may be large, while the dynamic range of allocated power between corresponding traffic channels in different sectors is limited. In some embodiments, the difference between corresponding channels of different sectors is kept below a 3dB relative power difference for the channel segments actively used in each sector of a cell.

To facilitate signal discrimination of channel segments corresponding to different sectors, different scrambling bit sequences may be used in different sectors, and sometimes do so, in generating the transmit signals in the respective sectors. A wireless terminal receiver may use a particular scrambled bit sequence to selectively demodulate signals transmitted from an intended sector of a base station. Alternatively, the wireless terminal receiver may use multiple scrambled bit sequences to simultaneously demodulate multiple sector transmissions from one base station or signals from multiple base stations.

The channel condition of a wireless terminal can be described as being in one of two characteristic regions. In the first region, the SIR is not limited by inter-sector interference. When in the first region, the base station may increase the received SIR by allocating a high transmit power, thereby providing an increased SIR. In the second region, the SIR is limited by inter-sector interference, in which case assigning a high transmit power may not significantly increase the received SIR, since the inter-sector interference increases as the channel power increases uniformly in each sector's corresponding channel.

In some embodiments, the wireless terminal estimates its channel condition characteristics and informs the base station so that the base station can make reasonable scheduling decisions based on power and burst data rate allocations. The channel condition information may include information that distinguishes between inter-sector interference and other interference. In accordance with the present invention, the base station scheduler may utilize reported channel condition characteristics for the wireless terminal, including power information, signal strength, and SIR, to match the wireless terminal to the appropriate channel in each sector. The decision to provide additional power or to allocate a segment of a wireless terminal to a channel with high power may be made based on an inter-sector interference indication relative to other interference. In this manner, wireless terminals that may benefit from higher transmit power, e.g., wireless terminals that experience low inter-sector interference, may be assigned to high power channels in preference to wireless terminals that experience relatively high inter-sector interference. The allocation of high power channel segments may be used to load balance the system, improve or optimize system performance and/or increase throughput by evaluating and reducing inter-sector and inter-cell interference.

According to one embodiment of the invention, if a wireless terminal is operating within a cell boundary region of a sector and is assigned a channel segment, the cell's scheduler may cause tones corresponding to channel segments in sectors adjacent the boundary region to be unassigned to reduce or eliminate inter-sector interference. In accordance with the present invention, partition isolation between wireless terminals in non-sector boundary regions can be managed by a scheduler selectively assigning channel segments corresponding to channels having different power levels to different wireless terminals. Low power channel segments are typically assigned to wireless terminals that are close to the transmitter, while high power channel segments are assigned to wireless terminals that are far from the base station. The number of low power channels in a sector typically exceeds the number of high power channels, such that in many cases, the portion of the total transmit power of the sector allocated to relatively few high power channels is more than the portion allocated to a large number of low power channels.

The base station may frequently and/or periodically transmit a beacon signal, e.g., a relatively high power signal on one or several tones, over a period of time, e.g., a symbol period. During beacon transmission, the transmit power is concentrated on one or a few tones, e.g., the tones of the beacon signal. This high concentration of power may result in 80% or more of the total transmit power of one sector being allocated in the beacon tones. In one embodiment, the beacon signal is transmitted for a fixed OFDM symbol duration (e.g., the first or last OFDM symbol) of a super-slot and may be repeated on every super-slot or every few super-slots. In this case, a beacon signal is used to indicate the super slot boundary. Thus, once the time location of the beacon signal is located, the boundary of the super slot can be determined. According to the invention, the beacon signals may be allocated to perform different tasks, e.g. conveying different types of information. Beacons may be assigned to utilize a fixed predetermined frequency, which itself may convey information, e.g., the boundaries of a frequency band or frequency may correspond to an index number, e.g., a sector index number. Other beacons may be assigned multiple or varying frequencies that may relate to one or more index numbers used to convey information, where the information may be, for example, a slope value used to determine the frequency hopping sequence of the cell to which the beacon is transmitted. The set of tones carrying the high power in the beacon signal may be selected from a predetermined group of beacon tone sets according to the information to be transmitted. The use of different sets of beacon tones in the beacon signal may indicate specific system information such as the value of SLOPE, the boundaries of the frequency band, and the sector index.

In one embodiment of the invention, the type of beacon transmitted varies as a function of transmission time, alternating in the time domain, for example. In another embodiment of the invention, the beacon frequency tone allocation may be reconfigured if a failure or problem occurs once at a particular tone frequency. By utilizing both the time and frequency domains to vary the information transmitted and conveyed by the beacon signal, a large amount of information can be conveyed to the mobile device in an efficient manner. This information may be used, for example, to determine the sector/cell location of the mobile device, to offload certain functions required by the pilot (e.g., synchronization to superslot boundaries), to reduce the time required for the pilot to traverse, to evaluate the strength of reception, and to provide useful information to predict and improve the efficiency of handoffs between sectors and cells.

In some embodiments, the frequency, symbol timing and super slot structure of an uplink signal is subordinate to the frequency, symbol timing and super slot structure of a downlink signal and is synchronized in different sectors of a cell in accordance with the present invention. In one embodiment, the data tone hopping sequences and channel segments are synchronized across sectors of a cell. In another embodiment, the data tone hopping sequences and channel segments are random among sectors of a cell so that one channel segment in one sector can interfere with multiple channel segments in another sector of the same cell.

One embodiment of the beacon feature of the present invention is directed to a method of operating a base station transmitter in a frequency division multiplexed communication system. The base station transmitter utilizes a set of N tones to communicate information to a first area, e.g., a sector of a cell, over a first time period using a first signal, said first time period being at least two seconds long, where N is greater than 10, and said method includes transmitting a second signal comprising a set of X tones during a second time period, where X is less than 5, and at least 80% of a maximum average total base station transmit power used by said base station transmitter for transmission into said first area during any 1 second period during said first time period is allocated to said set of X tones. The first time period may be a large time interval, such as minutes, hours or days. In some cases, the first period of time is at least 30 minutes long. In particular implementations X is equal to one or two. The second time period may be a time period, for example, a symbol transmission time period in which a beacon signal is transmitted. In some cases, during a second time period, at least half of the N-X tones in said set of N tones but not in said set of X tones are unused during said second time period. In some implementations none of the N-X tones in the set of N tones, but not in the set of X tones, are used for transmission into the first region during the second time period. In other implementations, a plurality of N-X tones in the set of N tones, but not in the set of X tones, are used in the first region during the second time period. The base station may be part of a communication system, wherein the communication system is an orthogonal frequency division multiplexing system. In some OFDM implementations, the second time period is a time period for transmitting an orthogonal frequency division multiplexing symbol. The second time period, e.g., a beacon transmission time period, may be repeated periodically during said first time period. The method in this example may further comprise transmitting a third signal comprising a set of Y tones during a third time period, wherein Y < N, each tone in said third set of Y tones having 20% or less of said maximum average total base station transmit power used by said base station transmitter for transmission into said first region during any 1 second period during the first time period, said third time period being equal in duration to said second time period. In some embodiments, the third time period may be a symbol time in which the data signal, pilot signal, and/or control signal is transmitted. The third time period may be different from the second time period or overlap the second time period. When the third time period overlaps or is the same as the second time period, a small fraction of the total power transmitted during the time period may be used by data, pilot and/or control signals modulated on the Y tones, for example, the small fraction may be 20% or less since the beacon signal(s) (e.g., high power tone (s)) in the first region consume at least 80% of the power. High power tones, such as one or more beacon tones, may be, and in various embodiments are, transmitted at a predetermined fixed frequency. The predetermined frequency may, and typically does, have a fixed frequency offset of > 0 relative to the lowest frequency tone in the set of N tones. This allows the beacon signal to provide an indication of the boundary of the N tone sets.

In various embodiments, at least one of the X tones (e.g., beacon tones) is transmitted in the first region at a frequency determined as a function of at least one of a base station identifier and a sector identifier. In many implementations, for each repetition of said second time period in said first time period, there are Z repetitions of said third time period in said first time period, where Z is at least 10, e.g., the number of data transmission symbol time periods is much greater than the number of beacon signal symbol time periods. In some cases Z is at least 400, e.g., there are at least 400 data transmission symbol times for each beacon transmission signal time. In some implementations, a fourth signal comprising G tones is transmitted into the first region during a fourth time period, wherein G is less than 5, and at least 80% of said maximum average total base station transmitter power used by said base station transmitter for transmission into the first region during any 1 second period during said first time period is allocated to said G tones. The G tones may correspond to, for example, one symbol transmission time in which one beacon signal different from the beacon signal transmitted in the second time period is transmitted. In one embodiment, the frequency of at least one of said G tones is a function of at least one of a base station identifier and a sector identifier, and said at least one of said G tones is not one of said set of X tones. In various implementations, the second and fourth time periods are repeated periodically during said first time period. In some embodiments, a base station includes a transmitter control routine that includes a module, such as a software module or code block, that controls the generation and transmission of signals during each of the first, second, third and fourth transmission time periods. When the first signal period is entirely composed of the second, third and fourth signal transmission periods and the transmission is controlled by the control modules of these periods, a separate control module may not be used for the first signal period. Thus, the emission control means may comprise one or more software modules, each of which controls a different emission characteristic, such as a separate emission characteristic of the invention as set out in one of the pending claims. Thus, while only a single transmitter control routine may be present in a base station, the single routine may, and often does, include a plurality of different control modules. The beacon transmission method of the present invention can be applied to each sector of a multi-sector cell.

A method of communication in a base station for a sectorized cell will now be described for the various synchronization features of the present invention. According to which a base station transmits symbols, e.g., modulated symbols, into a plurality of sectors of the cell using orthogonal frequency division multiplexing symbols. The frequency division multiplexing symbols are generated by: information is modulated on one or more symbols and in most cases a cyclic prefix is added to form the modulated symbol to be transmitted. In one embodiment, the method includes operating each sector to transmit a plurality of orthogonal frequency division multiplexing symbols with one set of tones, each orthogonal frequency division multiplexing symbol. The symbol is transmitted at a symbol transmission start time. Thus, each transmitted symbol has a symbol transmission start time. Each sector is controlled to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start time in accordance with the present invention. In various embodiments, each of the orthogonal frequency division multiplexing symbols includes a cyclic prefix having a cyclic prefix length. In some of these embodiments, the substantially same symbol transmission start times are such that: the difference between the symbol transmission start times of any two adjacent sectors is at most the amount of time used to transmit one cyclic prefix. A set of frequency hopping sequences is typically used to assign tones to a first set of communication channels in a first sector of the cell. The same set of hopping sequences is used to assign tones to a corresponding set of communication channels in each of the other sectors of the cell. Each hopping sequence has a start time. In one embodiment, the start time of each hopping sequence in said set of hopping sequences in each said sector is the same. To allow the device to distinguish between signals corresponding to different sectors of a cell with different information to be transmitted, for example, the modulated symbols may be subjected to a scrambling operation prior to transmission. Different scrambling sequences are used in different sectors. The scrambling sequence thus provides a way to distinguish between data corresponding to different sectors. Thus, in at least one embodiment, scrambling of modulation symbols is performed prior to transmitting said modulation symbols with said transmitted symbols, wherein a different scrambling sequence is used in each sector of the cell. The communication channels in each sector of a cell are typically divided into segments, with segments of the corresponding channels in each sector of the cell having the same segment division and having substantially the same segment start time, such that for one segment of one channel in one sector there is another segment of the corresponding channel, where both segments use the same set of hopping sequences and the same segment start time. In some embodiments, the difference between the segment start times of segments of the same channel in different cells is no greater than the time used to transmit one cyclic prefix. Pilot tones are typically transmitted in each sector of a cell. The method of the present invention in various embodiments includes transmitting a portion of pilot tones in each sector of a cell according to a pilot tone hopping sequence, using the same pilot tone hopping sequence in each sector, but using a different fixed tone offset in each sector of a cell. The pilot tone hopping sequence can be a slope hopping sequence. In such an implementation, neighboring cells may use different slope values to determine the slope hopping sequence to use. In some implementations, the pilot tones in each sector of the cell are transmitted according to a set of pilot tone hopping sequences, the same set of pilot tone hopping sequences being used in each sector, but a different fixed tone offset being used in each sector of the cell. In this case, the pilot tone hopping sequences in a set of pilot tone hopping sequences corresponding to a sector are typically offset with respect to each other, the offset being a corresponding set of pre-selected offsets that are the same in each sector of the cell. Also in this case, the set of pilot tone hopping sequences used by any two adjacent sectors of the cell may not be the same, due to the use of different fixed tone offsets in the adjacent sectors. Because different fixed tone offsets are used for the pilot tone hopping sequences in adjacent sectors, the set of pilot tone hopping sequences used in any two adjacent sectors of a cell need not be, and sometimes are not, the same.

The power control method of the present invention may be used alone or in combination with other features and/or methods of the present invention. According to an exemplary power control method of the present invention, one tone set is used in one cell. A transmitter in said cell transmits into a first sector of said cell using tones from said set of tones over a plurality of symbol times. The cell includes a second sector adjacent to the first sector. The transmitter transmits to said second sector in first and second communication channels, the first communication channel including a first subset of said set of tones during each of a first subset of said plurality of symbol times, the second communication channel including a second subset of said set of tones during each of said first subset of said plurality of symbol times, said first subset of said set of tones and said second subset of said set of tones being different from each other during each symbol time. In one such implementation, the exemplary method includes operating a transmitter to transmit into the first sector on the first and second channels in a manner synchronized with the transmission of the transmitter into the second sector; and controlling a total transmit power of tones corresponding to the first channel in the first sector during said first subset of said plurality of symbol times to be greater than 20% and less than 500% of a total power of tones corresponding to the first channel transmitted into the second sector. In some implementations, controlling the total transmit power of the tones corresponding to the first channel includes limiting the total power used in said first subset of symbol times to a fixed fraction of no more than a maximum average total transmit power used by said transmitter in the first sector during any 1 hour period, said fixed fraction being further used to limit the total transmit power of the tones corresponding to the first channel in the second sector during the first subset of symbol times to no more than said fixed fraction of a maximum average total transmit power used by said transmitter in the second sector during any 1 hour period, said fixed fraction being less than 100%. In some implementations, the symbol time is a symbol transmission time period of orthogonal frequency division multiplexing. The tones are typically orthogonal frequency division tones in this case. The set of tones may be, and often is, different during at least two symbol times. The symbols transmitted at different times may correspond to different symbol constellations. In some implementations, the transmitter transmits symbols corresponding to a first constellation onto the first channel during the first subset of symbol times into the first sector and transmits symbols corresponding to a second constellation during a second subset of the plurality of symbol times, the second constellation including more symbols than the first constellation, in which case the method includes controlling a total transmit power corresponding to the first channel in the first sector during the second subset of the plurality of symbol times to be greater than 50% and less than 200% of a total power corresponding to tones of the first channel transmitted in the second sector during the second subset of the plurality of symbol times. In another embodiment, said transmitter transmits symbols onto said first channel into said first sector at a first channel coding rate during said first subset of said plurality of symbol times and transmits symbols onto said first sector at a second channel coding rate during a second subset of said plurality of symbol times, said second channel coding rate being higher than said first channel coding rate. In this implementation, the method further includes controlling a total transmit power of tones corresponding to the first channel in the first sector during the second subset of the plurality of symbol times to be greater than 50% and less than 200% of a total power of tones corresponding to the first channel transmitted in the second sector during the second subset of the plurality of symbol times. The total transmit power of the transmitted tones in the first sector corresponding to the first channel during the first subset of the plurality of symbol times may be, and in some implementations is, equal to the total transmit power of the transmitted tones in the first channel in the second sector during the first subset of the plurality of symbol times. In many cases, the first subset of the plurality of symbol times will include a number, e.g., at least 14, of consecutive symbol times. The method further includes controlling a total power of tones transmitted in the first sector corresponding to the first channel during a fourth subset of the plurality of symbol times to be greater than 200% or less than 50% of a total power of tones transmitted in the first sector corresponding to the second channel during the fourth subset of the plurality of symbol times. In some implementations, the power control method includes a total power of tones transmitted in the first sector corresponding to the first channel during a fourth subset of the plurality of symbol times being greater than 200% or less than 50% of a total power of tones transmitted in the first sector corresponding to the second channel during the fourth subset of the plurality of symbol times. The fourth subset of the plurality of symbol times sometimes includes at least 14 consecutive symbol times and in some cases is greater than 40. In some implementations, the first and second sectors use a third communication channel during a second subset of the plurality of symbol times, the third communication channel including a third subset of the set of tones during each of the second subset of the plurality of symbol times. In this case, the power control method often further includes the step of controlling the transmitter during the second subset of the plurality of symbol times to limit the total transmit power on the tones corresponding to the third communication channel transmitted by the transmitter to less than 10% of the total transmit power used by the transmitter to transmit the tones corresponding to the third channel into the second sector during the second subset of the plurality of symbol times. In some cases, to limit interference between sectors, e.g., segments, used to transmit control signals, the method includes controlling the transmitter during the second subset of the plurality of symbol times to limit total transmit power on tones corresponding to the third communication channel transmitted by the transmitter to zero. In various implementations, the method of the present invention is further directed to assigning control resources (e.g., segments) corresponding to the third communication channel to the wireless terminal. In this implementation, the method includes operating the base station or an apparatus included therein to identify wireless terminals in a boundary region corresponding to a boundary between the first and second sectors; and allocating resources (e.g., channel segments) corresponding to said third channel to at least one of said identified wireless terminals. Identifying wireless terminals in the boundary region may include receiving, from a wireless terminal, first information indicative of an amount of inter-sector interference measured by the wireless terminal and second information indicative of an amount of background interference measured by the wireless terminal. Identifying wireless terminals in the border area may alternatively or additionally comprise receiving a signal (e.g. a location signal) from a wireless terminal in said border area, a signal indicating that said wireless terminal is in said border area. In some power control embodiments, said first and second sectors use said third communication channel during a third subset of said plurality of symbol times, said third subset of said plurality of symbol times being different from said second subset of said plurality of symbol times. In this case, the method may further comprise controlling a total transmit power used by said transmitter on tones corresponding to said third communication channel transmitted by said transmitter into the first sector during said third subset of said plurality of symbol times to be at least 1000% of a total transmit power used by said second sector to transmit tones corresponding to the third channel into the second sector during said third subset of said plurality of symbol times. This 1000% represents power used for 10 times the power in the second sector. This power difference is often sufficient so that the inter-sector interference seen in the first sector is a relatively small component of the signal interference. In some implementations, the first and second sectors use the third communication channel during a third subset of the plurality of symbol times, the third subset of the plurality of symbol times being different from the second subset of the plurality of symbol times. In this implementation the method further comprises: controlling said transmitter during said third subset of said plurality of symbol times to use a total transmit power on tones corresponding to said third communication channel transmitted by said transmitter into said first sector of at least 1000% of the total transmit power used by said second sector during said third subset of said plurality of symbol times to transmit tones corresponding to said third channel into said second sector. In the power control implementation just discussed, one base station control routine may include different code segments to perform each of the stated control operations. In addition, while the base station transmitter's antenna or other elements may differ in each sector, in many implementations common control logic and control functions associated with the base station are responsible for controlling transmissions in different sectors in accordance with one or more features of the present invention.

Additional features, benefits and embodiments of the present invention are discussed in the detailed description that follows.

Drawings

Fig. 1 depicts the general concept of data and pilot tone hopping sequences, control and data traffic channels, channel segments, and superslots.

Figure 2 shows a three sector cell with a base station employing a 3 sector antenna.

Fig. 3 shows a three sector cell with one base station depicting the concept of inter-sector boundary interference regions.

Fig. 4 depicts an exemplary communication system utilizing cell partitions in accordance with the present invention.

Fig. 5 depicts an exemplary access node that may be used in the communication system of fig. 4 in accordance with the present invention.

Fig. 6 depicts an exemplary end node that may be used in the communication system of fig. 4 in accordance with the present invention.

Fig. 7 depicts frequency tone synchronization throughout sectors of a cell in accordance with the present invention.

Fig. 8 depicts OFDM symbol time synchronization throughout sectors of a cell in accordance with the present invention.

Fig. 9 depicts that the tone frequencies occupied by the jth tone hopping sequence at any OFDM time are the same and the superslot boundaries are the same in all sectors of a cell in accordance with the present invention. Fig. 9 further illustrates the concept of corresponding control or data channel segments within a sector of a cell in accordance with the present invention.

Fig. 10 shows a typical case where frequency tones are distributed over two traffic channels. In accordance with the present invention, the tone hopping sequence at any OFDM time over three typical sectors of a cell is the same for each control or data traffic channel.

Fig. 11 depicts an exemplary pilot tone hopping sequence with the same slope value but with a different offset value in each sector of a cell in accordance with the present invention.

Fig. 12 depicts the concept of puncturing the data sequence of fig. 10 by the pilot tone hopping sequence of fig. 11 in accordance with the present invention.

Fig. 13 shows a table that describes exemplary power allocations between different traffic channel segments in the same sector of a cell and corresponding traffic channel segments in all sectors of a cell in accordance with an embodiment of the invention.

Fig. 14 shows a plot of power versus frequency tone for each tone of a normal OFDM signal.

Fig. 15 shows a plot of power per tone versus frequency tone with respect to the time of beacon signal transmission, where the total power is concentrated on only two tones in accordance with one implementation of the present invention.

Figure 16 shows a plot of power per tone versus frequency tone with respect to the time of beacon signal transmission, where the total power is concentrated on only one tone in accordance with one implementation of the present invention.

Fig. 17 shows a plot of power per tone versus frequency tone for the time of beacon signal transmission, depicting a predetermined beacon signal group according to one embodiment of the invention.

Fig. 18 shows a graph of frequency versus OFDM symbol time, which describes the concept of different functions of successive beacons in the time domain, according to one embodiment of the invention.

Fig. 19 shows a graph of frequency versus OFDM symbol time, which describes the concept of transmitting alternating beacon types in the time domain, according to one embodiment of the invention.

Detailed Description

For an OFDM spread spectrum system, the tones used in a particular cell are all orthogonal. Thus, the data hopping sequence and the physical channel do not interfere with each other. Given the propagation characteristics of a wireless channel, a wireless terminal may experience a large dynamic range of channel conditions, depending on its location, where the channel conditions are measured in terms of signal-to-interference ratio (SIR) or signal-to-noise ratio (SNR). Such a property may be exploited to enhance system capabilities. For example, in accordance with the present invention, a scheduler can optimally balance power in traffic channels by simultaneously serving wireless terminals with very different radio channel conditions. In this case, one wireless terminal with a bad radio channel condition may be allocated a large part of the transmission power and may be allocated a small part of the bandwidth, thereby obtaining service robustness, while another wireless terminal with a good radio channel condition may be allocated a small part of the transmission power and may be allocated a large part of the bandwidth, still enabling a high burst data rate.

The OFDM spread spectrum system of the present invention can be combined with sectorized antennas to improve overall system performance. But in reality antenna isolation is never perfect. A signal transmitted into one sector may leak into another sector with an attenuation factor, causing inter-sector interference, e.g., inter-sector interference. Inter-sector interference may reduce acquisition of power and burst data rate allocations. For example, in the absence of inter-sector interference, a wireless terminal with a good radio channel condition may be allocated a fraction of the transmit power and still achieve a high burst data rate. In the presence of inter-sector interference, the wireless terminal may not be able to achieve the same high burst data rate with the same amount of transmit power. This situation becomes particularly acute when the inter-sector interference originates from a traffic channel that is transmitted at a much higher power, e.g., to serve another wireless terminal with poor channel conditions.

Fig. 3 depicts a typical cell 300, which includes 3 sectors: sector 1301, sector 2303 and sector 3305, and a base station 307 including a 3-sector antenna. The base station 307 may communicate with terminal nodes (e.g., mobile nodes or mobile terminals) located anywhere within the cell 300 via wireless links. From an interference perspective, a cell can be considered to be composed of sector boundary regions where interference from one neighboring sector can be a serious problem, and non-sector boundary regions. In the depiction of cell 300 in fig. 3, the non-sector boundary regions are distinguished from the boundary regions. Cell 300 includes non-sector boundary region 1309, non-sector boundary region 2311, and non-sector boundary region 3313. Cell 300 also includes sector boundary regions: sector 1-2 boundary region 315, sector 2-3 boundary region 317, and sector 3-1 boundary region 319. The degree of partition isolation can be described in terms of the amount of leakage between the non-sector boundary regions 309, 311, and 313. For example, if a mobile node is located in non-sector boundary region 1309, leakage may occur due to signals intended for sector 2303 and signals intended for sector 3305. The leakage in the non-sector boundary regions 309, 311, 313 is typically-13 dB to-15 dB and may depend on factors such as the antenna type of the base station 307. In the sector boundary region (sometimes referred to as the 0dB region), regions 315, 317, and 319, the signal strength from two adjacent sector antennas at the point of reception may be nearly equal. Methods and apparatus are described for improving system capacity when used in the configuration of a partition.

For purposes of illustration and description, a 3-sector cell 300 is used in the subsequent examples of fig. 3 and fig. 7, 8, 9, 10, 11, 12, and 13. However, it is to be understood that the present invention is applicable to other partitioning schemes. In a sectorized cell, sectors are indexed. For example, in the 3-sector cell 300 of fig. 3, the sector indices may be 1, 2, and 3.

Fig. 4 depicts an exemplary communication system 400 that employs cell sectorization and wireless communication in accordance with the present invention. Communication system 400 includes a plurality of cells, cell 1438, cell N440. Cell 1438 represents a coverage area of AN Access Node (AN)1402 located in cell 1438. Access node 1402 can be, for example, a base station. Cell 1438 is subdivided into a plurality of sectors, sector 1442, sector Y444. A dashed line 446 represents the boundary between sectors 442, 444. Each sector 442, 444 represents an intended coverage area for a sector corresponding to a sectorized antenna located at access node 1402. Sector 1442 includes a plurality of End Nodes (ENs), EN (1)422, EN (x)424, connected to AN1402 by wireless links 423, 425, respectively. Similarly, sector Y444 includes a plurality of End Nodes (ENs), EN (1 ') 426, EN (X') 428 connected to AN1402 by wireless links 427, 429, respectively. ENs 422, 424, 426, 428 may be, for example, mobile nodes or mobile terminals, and may move throughout system 400.

Cell N440 is subdivided into a plurality of sectors, sector 1448, sector Y450, with sector boundary 446'. Cell N440, like cell 1438, includes one access node M402 ', and a plurality of ENs 422', 424 ', 426', 428 'connected to AN M402' by wireless links 423 ', 425', 427 ', 429', respectively.

The access nodes 402, 402' are connected to a network node 406 by network links 412, 414, respectively. Network node 406 is connected to other network nodes, such as other access nodes, intermediate nodes, home agent nodes, or Authentication Authorization Accounting (AAA) server nodes, through network link 420. Network links 412, 414, 420 may be, for example, fiber optic cables.

Fig. 5 illustrates AN exemplary access node 500 of the present invention that may be used in the communication system 400 of fig. 4, such as the AN1402 of fig. 4. The access node 400 includes a processor 502 (e.g., CPU), a wireless communication interface 504, a network/internet interface 506, and a memory 508. The processor 502, wireless communication interface 504, network/internet interface 506, and memory 508 are coupled together by a bus 510, and the elements 502, 504, 506, 508 may exchange data and information over the bus 510.

The processor 502 controls the operation of the access node 500 by executing routines and using data within the memory 528 to operate the interfaces 504,506, to perform the processing necessary to control the basic functions of the access node 500, and to implement features and improvements employed in a partitioned system in accordance with the present invention.

The wireless communication interface 504 includes one receiver circuit 512 and one transmitter circuit 514 connected to sectorized antennas 516, 518, respectively. The receiver circuit 512 includes a descrambler circuit 520 and the transmitter circuit 514 includes a scrambler circuit 522. Sectorized antenna 516 receives signals from one or more mobile nodes, such as EN1422 of fig. 4. Receiver circuitry 512 processes the received signals. If the mobile node utilizes scrambling at the time of transmission, receiver circuitry 512 utilizes its descrambler 520 to remove the scrambling sequence. The transmitter circuit 514 includes a scrambler 522 that may be used to randomize the transmitted signal in accordance with the present invention. The access node 500 may transmit a signal to the mobile node on its sectorized antenna 518, e.g., EN1422 of fig. 4.

The network/internetwork interface 506 includes a receiver circuit 524 and a transmitter circuit 526, which enable the access node 500 to be connected to, and exchange data and information with, other network nodes, e.g., other access nodes, AAA servers, home agent nodes, etc., via network links.

The memory includes routines 528 and data/information 530. The routines include signal generation routines 532 and a scheduler 534. Scheduler 534 includes routines such as an inter-sector interface routine 536, an inter-cell interface routine 538, a power allocation routine 540, and a wireless terminal/service & segment matching routine 542. Data/information 530 includes data/control information 544, pilot information 546, beacon information 548, tone frequency information 550, OFDM signal timing information 552, data tone hopping sequence 554, channel segment 556, superslot boundary information 558, slope value 560, pilot value 562, delta564, burst data rate 566, MN channel condition information 568, power information 570, and MN sector information 572. Tone frequency information 550 includes a set of tones for different signals: a set of N tones for an OFDM signal, a set of X tones for certain beacon signals, a set of Y tones for an OFDM signal and a set of G tones for other beacon signals, and repetition rate information associated with each set of tones. The power information 570 includes wide and narrow inter-sector transmission power control range information, inter-channel transmission power allocation range information, boundary transmission power range information, and power levels allocated for channels in each sector.

Signal generation routine 532 utilizes data/information 530, such as superslot boundary information 558, tone frequency information 550, and/or OFDM symbol timing information 552 to perform signal synchronization and generation operations. The signal generation routine 532 also implements data/control hopping and pilot hopping sequences using data/information, such as data tone hopping sequences 554, data/control information 544, pilot information 546, pilot values 562, and/or sector information 572. Further signal generation routines 532 may utilize data/information 530, such as beacon information 530, to generate beacon signals in accordance with the present invention.

The inter-sector interface routine operates using the methods and data/information 530 of the present invention, e.g., pilot information 546, MN channel condition information 568, and MN sector information 572, to estimate and reduce inter-sector interference within a particular cell. Inter-cell interface routine 536 utilizes the methods and data/information 530 of the present invention, such as reported MN channel condition information 568 and slope value 560 to estimate and reduce the effects of inter-cell interference. Power allocation routine 540 utilizes the methods and data information of the present invention, such as power information 570 and delta564, to control power allocation to various traffic channels, e.g., to optimize performance. Wireless terminal/traffic and segment matching routine 542 utilizes data/information 530, such as MN channel condition information 568, power information 570, channel segment 556 and burst data rate 566, to allocate the wireless terminal to an appropriate channel segment as a function of its power requirements in accordance with the present invention.

Various specific functions and operations of the access node 500 will be discussed in more detail below.

Fig. 6 depicts an exemplary End Node (EN)600, such as a wireless terminal, e.g., Mobile Node (MN), mobile device, mobile terminal, mobile device, fixed wireless device, etc., as might be used in the exemplary communication system of fig. 4 in accordance with the present invention. In this application, end nodes, such as wireless terminals, mobile nodes, mobile devices, mobile terminals, fixed wireless devices, etc., may be referred to in various locations by different terminology and with different exemplary embodiments of the end nodes; it is to be understood that the apparatus and methods of the present invention are also applicable to other embodiments, variations and descriptions of the terminal node. The end node 600 includes a processor 602 (e.g., CPU), a wireless communication interface 604, and a memory 606. The processor 602, wireless communication interface 604, and memory 606 are coupled together by a bus 608, and the components 602, 604, 606 may exchange data and information over the bus 608.

The processor 602 controls the operation of the terminal node 600 by executing routines and utilizing data within the memory 606 to operate the wireless communication interface 604 to perform the processing necessary to control the basic functions of the terminal node 600 while implementing the features and improvements employed in a partitioned system in accordance with the present invention.

The wireless communication interface 604 includes a receiver circuit 610 and a transmitter circuit 612 coupled to antennas 614, 616, respectively. The receiver circuit 610 includes a descrambler circuit 618 and the transmitter circuit 612 includes a scrambler circuit 620. Antenna 614 receives a broadcast signal from AN access node, such as AN1402 of fig. 4. Receiver circuitry 610 processes the received signal and, if the access node utilizes scrambling at the time of transmission, receiver circuitry 610 may remove the scrambling using its descrambler 618 (e.g., a decoder). The transmitter circuit 612 includes a scrambler 620 (e.g., encoder) that may be used to randomize the transmitted signal in accordance with the present invention. The terminal node 600 may transmit the encoded signal to the access node on its antenna 616.

Memory 606 includes routines 622 and data/information 624. Routines 622 include a frequency hopping sequence routine 626, a channel condition monitoring/reporting routine 628, and a beacon signal routine 630. Data/information 624 includes MN channel condition signals 632, power information 634, tone frequency information 636, OFDM signal timing information 638, data tone hopping sequences 640, channel allocation information 642, super slot boundary information 644, slope values 646, pilot values 648, slope indices 650, beacon information 652, sector identification 654, and cell identification 656.

The frequency hopping routine 626 includes a data/control hopping sequence routine 634 and a pilot hopping sequence routine 632 which utilize the methods and data/information 624 of the present invention, e.g., tone frequency information 636, OFDM signal timing information 638, data tone hopping sequence 640, channel allocation information 642, super slot boundary information 644, slope values 646 and/or pilot values 648, to perform operations to process received data, identify the cell 656 and sector 654 in which the mobile device 600 operates, and the corresponding access node 500 in fig. 5 in communication with the end node 600. Channel condition monitoring/reporting routine 628 operates using the methods of the present invention and data information 624, such as MN channel condition information 632, power information 634 and channel assignments 642, to estimate the status and quality of the radio link to access node 500 and then report this data back to access node 500 for scheduling. Beacon information routine 630 performs operations related to beacon signals in accordance with the present invention. Beacon signal routine 630 utilizes data/information 624, e.g., beacon information 652, power information 634, tone frequency information 636, super slot boundaries 644, and/or slope index 650 to perform power such as synchronization of super slot boundaries, determine band boundaries and sector index 654, determine slope value 646, determine cell location 656, and pilot value 648.

Various specific functions and operations of the end node 600 will be discussed in more detail below.

The physical layer full synchronization over the sectors will now be explained.

According to the present invention, the same frequency spectrum is reused in each sector in one cell of a sectorized OFDM spread spectrum system. Furthermore, according to a specific exemplary embodiment of the present invention, the sectors of a cell are perfectly synchronized in terms of tone frequency, OFDM symbol timing, data tone hopping sequences, channel segments, and superslot boundaries. While such synchronization is desirable, certain aspects of the present invention may be used in systems where synchronization between sectors in a cell is not as complete, as is the case in certain exemplary embodiments. Specifically, in each sector of a cell, the same set of tones is used, with the exact same set of tone frequencies included in each set. The OFDM symbol timing is also identical. Fig. 7700 depicts a set of tone frequencies in each of 3 sectors used to form a cell. Horizontal axis 707 of fig. 7 corresponds to frequency. Each vertical arrow represents a frequency tone.

Rows 701, 703, 705 each correspond to a different sector of a typical cell. The same set of N tones is used in each sector, the tones used in each sector being indexed by 0 through N-1.

Diagram 8800 depicts OFDM symbol timing for in 3 sectors. The horizontal axis 807 of fig. 8 represents how time is divided according to symbol time in each sector, e.g., time for transmitting one OFDM symbol. Each division on the horizontal axis 807 marks the beginning of a new symbol time in each sector in a cell. Line 1(801) corresponds to symbol times in sector 1, while lines 2 and 3(803, 805) correspond to symbol times in sectors 2 and 3 of the same cell. Note that the symbol start times are synchronized in the three sectors of the cell. Each sector of the cell derives the data tone hopping sequence with the same OFDM symbol index and the same SLOPE value in equation (1). Thus, in each sector, the tone frequencies occupied by the jth tone hopping sequence at any OFDM time are identical, and the superslot boundaries are also identical.

Furthermore, the physical layer channels and channel segments are constructed in the same manner in each sector of a typical cell. Fig. 9 shows a frequency versus time diagram 900 depicting control and data traffic channels and channel segments in 3 sectors of the exemplary cell shown in fig. 3.

Fig. 9 shows the transmission of symbols in each of the 3 sectors of the exemplary cell shown in fig. 3 in a single super slot. In the example of fig. 9, each horizontal partition corresponds to one symbol transmission time, with a typical super slot corresponding to 5 symbol times.

In the example of fig. 9, one super slot 943, the time interval of one period of the data/control tone hopping sequence, is shown as a concatenation of five OFDM symbol times, represented by first through fifth columns 932, 934, 936, 938, 940, and bounded by vertical time domain boundary lines 931 and 941.

Fig. 9 includes a first group of first through fifth rows 902, 904, 906, 908, and 910 corresponding to a first sector of a cell. Each of rows 902, 904, 906, 908, 910 corresponds to a different orthogonal frequency tone in the frequency domain for sector 1.

A second group of the first through fifth rows 912, 914, 916, 918, and 920 corresponds to a second sector of the cell. Each of rows 912, 914, 916, 918, 920 corresponds to a different orthogonal frequency tone in the frequency domain for sector 2.

A third group of the first through fifth rows 922, 924, 926, 928 and 930 corresponds to a third sector of the cell. Each of rows 922, 924, 926, 928, 930 corresponds to a different orthogonal frequency tone in the frequency domain of sector 3.

The same frequency tone is represented by first row 902 of sector 1, first row 912 of sector 2, and first row 922 of sector 3. Similarly, frequency tones are equally present on three sectors in the following set: (second row 904, second row 914, second row 924), (third row 906, third row 916, third row 926), (fourth row 908, fourth row 918, fourth row 928), (fifth row 910, fifth row 920, fifth row 930).

Fig. 9 also includes first through fifth columns 932, 934, 936, 938, and 940. Each of the columns 932, 934, 936, 938, 940 corresponds to one OFDM symbol time in the time domain.

Shading is used in fig. 9 to describe the segment corresponding to a typical channel within a particular sector. For example, during the OFDM symbol time interval represented by first column 932, one traffic channel for sector 1 corresponds to and uses 3 tone frequencies represented by first row 902, second row 904, and third row 906. In the example of fig. 9, three sectors use the same allocation scheme to allocate tones to channels. So that the same tones are used for the channel in sector 2 and sector 3 as in sector 1.

When the OFDM symbol time varies over the super slot 943, data/control tone hopping occurs and the tone frequencies used by the data/control channel vary. It can be seen that for the data/control traffic channel segments in a particular sector, there is a corresponding data/control traffic channel segment in each of the other 2 sectors, since each sector in the exemplary embodiment has the same frequency tone and time interval configuration. Segments of the 3 sectors corresponding to the same channel are sometimes referred to as "corresponding channel segments".

Fig. 10 shows a frequency versus time diagram 1000 depicting a plurality of corresponding data/control traffic channel segments in 3 sectors.

The first to fifteenth rows 1002, 1004, 1006, 1008, 1010, 1012, 1014, 1016, 1018, 1020, 1022, 1024, 1026, 1028, 1030 of fig. 10 correspond to the same frequency tones as the rows 902, 904, 906, 908, 910, 912, 914, 916, 918, 920, 922, 924, 926, 928, 930 of fig. 9, respectively. The first to fifth columns 1032, 1034, 1036, 1038, 1040 of fig. 10 correspond to the same OFDM symbol times as the first to fifth columns 932, 934, 936, 938, and 940 of fig. 9, respectively. One super slot 1043 delimited by the boundary lines 1031 and 1041 of fig. 10 corresponds to the super slot 943 of fig. 9.

The area with line shading descending from left to right is used to represent a first set of corresponding data/control traffic segments (e.g., segments corresponding to the same channel). The area with line shading rising from left to right represents a second corresponding data/control traffic segment in fig. 10. For example, in the OFDM time interval represented by second column 1034, a first data/control traffic segment in sector 1 uses frequency tones represented by first row 1002, third row 1006, and sixth row 1010, while a second data/control traffic segment in sector 1 uses frequency tones represented by second row 1004 and fourth row 1008.

In the exemplary implementation it can be seen that for any control or data traffic channel segment in a particular sector, there is a corresponding control or data traffic channel segment in each of the other 2 sectors that has the same frequency tone and time interval configuration. Those segments in the 3 sectors are referred to as "corresponding channel segments" in the following discussion. Note that inter-sector interference is concentrated between corresponding channel segments due to full synchronization between sectors. Other channel segments typically see little or negligible inter-sector interference between each other.

Fig. 11 shows a frequency versus time diagram 1100 depicting a pilot tone hopping sequence in 3 sectors.

The first to fifteenth rows 1102, 1104, 1106, 1108, 1110, 1112, 1114, 1116, 1118, 1120, 1122, 1124, 1126, 1128, 1130 of fig. 11 correspond to the same frequency tones as the rows 902, 904, 906, 908, 910, 912, 914, 916, 918, 920, 922, 924, 926, 928, 930 of fig. 9, respectively. The first to fifth columns 1132, 1134, 1136, 1138, 1140 of fig. 11 correspond to the same OFDM symbol time as the first to fifth columns 932, 934, 936, 938, and 940 of fig. 9, respectively. One super slot 1143, which is designated by the boundary lines 1131 and 1141 of fig. 11, corresponds to the super slot 943 of fig. 9.

The pilot tone hopping sequence is represented by horizontal line shading in fig. 11. The pilot tone hopping sequences used in each sector of a cell are not all the same to facilitate sector identification for a mobile node, among other benefits. Thus, in fig. 11, the pilot tone hopping sequence is shown to be different in each sector of a three sector cell. Fig. 11 depicts steering in 3 sectors in one cell with no steering overlap by horizontal shading.

According to the invention, the pilots used in each sector of a typical cell have the same SLOPE value but different bias sets O_j}. These known offsets may be included in the pilot value information 562 and/or the mobile node pilot value offset information 648 stored in the base station. In this example, in a 3-sector cell, sector 1 uses the offset O_j，1Sector 2 uses an offset O_j，2Sector 3 uses an offset O_j，3}. Set of biases { O_j，1}、{O_j，2And { O }_j，3Are not exactly the same, resulting in different frequencies being used for steering in different sectors at the same time. In one embodiment, the bias sets are completely non-overlapping, i.e., no two elements in a bias set are identical. Thus, pilots in different sectors do not interfere with each other. In another embodiment, { O_j，2And { O }_j，3Is from { O }_j，1Derived: for all j, O_j，2＝O_j，1+D₂mod N, and O_j，3＝O_j，1+D₃mod N, where D₂And D₃Are two non-zero constants determined by the sector index.

According to the invention, the pilot hopping sequence and the data hopping sequence are multiplexed. I.e., if a pilot sequence occupies the same tone as another data sequence in a particular OFDM symbol time, that tone is used by the pilot sequence, excluding the data that would have been transmitted on that tone. In practice, the data sequence is punctured (punch) at the OFDM symbol time. Punctured (e.g., ignored) data may be recovered from the transmitted data using error correction codes and error correction techniques.

Fig. 12 shows a frequency versus time diagram 1200, which is a combination or overlay of fig. 10 and 11, depicting the puncturing of the data/control sequence of fig. 10 by the pilot sequence of fig. 11. Each row corresponds to a frequency, with each horizontal segment corresponding to a different symbol transmission time.

The first through fifteenth rows 1202, 1204, 1206, 1208, 1210, 1212, 1214, 1216, 1218, 1220, 1222, 1224, 1226, 1228, 1230 of fig. 12 correspond to the same frequency tones as rows 902, 904, 908, 910, 916, 918, 920, 922, 924, 926, 928, 930 of fig. 9, respectively. The first to fifth columns 1232, 1234, 1236, 1238, 1240 of fig. 12 correspond to the same OFDM symbol time as the first to fifth columns 932, 934, 936, 938, and 940 of fig. 9, respectively. One super slot 1243, delimited by boundary lines 1231 and 1241 of fig. 12, corresponds to super slot 943 of fig. 9.

Line shading falling from left to right is used to describe the segment corresponding to one first data or control channel. The line shading rising from left to right indicates a segment corresponding to one second data or control corresponding channel. The circles on top of the data/control channel segment represent pilot tone puncturing data/control sequences to exclude data that would otherwise be transmitted in that segment.

When a sectorized OFDM spread spectrum system is used in a peak-to-nest network, adjacent cells use different SLOPE values to determine the pilot and data tone hopping sequences in accordance with the present invention. In a typical system of the present invention, the set { O } is biased in each of a plurality of cells of the system_j，1}、{O_j，2And { O }_j，3Are identical. Different cells do not need to, and often do not, depend on tone frequency, OFDM symbol timing, tone hopping sequence, channel segment, or super-timeSlot boundary synchronization even though such features/characteristics may be common in a single cell sector.

The power allocation between and within a sector of a cell according to various features of the present invention will now be described.

The fact that inter-sector interference occurs primarily between corresponding channel segments imposes limitations on the power allocation between corresponding channel segments in a sector of a cell.

For the purposes of this description, it is first assumed that the corresponding channel segments are all active, i.e., are being used to transmit signals. According to one feature of the invention, the transmit power allocated to the corresponding channel segments is substantially the same in each sector of a cell. For example, in a 3-sector system, if all 3 corresponding channel segments are active, the difference between the transmit power of those channel segments in the 3 sectors should be no more than one parameter Delta. In the exemplary embodiment, the scheduler 534 of FIG. 5 is responsible for coordinating the power allocation in each sector of the cell in a centralized manner.

The value of Delta stored in the base station as Delta information 564 affects the effects that may occur due to inter-sector interference. For example, for a large Delta, the transmit power of two corresponding channel segments may be quite different. Thus, inter-sector interference may cause greater interference to the one of the two corresponding channel segments with the smaller transmit power. In one embodiment of the invention, Delta564 is set to a constant, such as zero. In another embodiment of the invention, Delta564 may vary. Indeed, the value of Delta564 for different groups of corresponding channel segments may be different in accordance with the present invention. For example, the Delta for the corresponding control channel segment may, and sometimes does, differ from the Delta for the corresponding data traffic channel segment, reflecting the tolerance of different interference levels on different channels from a policy perspective. In one embodiment of the invention, Delta is a function of the burst data rate used in the corresponding channel segment. For example, consider a corresponding traffic channel segment. If one of the segments uses a high channel coding and modulation rate, for example to support a high burst data rate, a small Delta value is desirable and is employed in accordance with the present invention. As part of its function, the scheduler 534 determines the appropriate value for Delta564 when the scheduler 534 coordinates power allocation and burst data rate allocation in a sector of a cell.

In accordance with the present invention, the scheduler, including routine 542 of fig. 5, may independently select wireless terminals to be scheduled in corresponding data traffic channel segments of sectors of a cell. The burst data rate achieved depends on the power allocation determined by routine 540 of fig. 5 and the channel conditions (e.g., indicated by information 568) of the scheduled wireless terminals, and thus may be different in different sectors of a cell.

The restriction on power allocation between corresponding channel segments in each sector of a cell does not impose the same restriction on power allocation between different channel segments within a sector. In practice, different channel segments may be allocated considerably different amounts of transmit power in a particular sector. For example, consider a corresponding traffic channel segment. Assume that there are two traffic channel segments at a particular time. Scheduler 534 may assign a wireless terminal with poor channel conditions to the first traffic channel segment in each sector and a wireless terminal with good channel conditions to the second traffic channel segment in each sector via routine 542 of fig. 5. The scheduler 534 can then optimally balance the power allocation among the two traffic channel segments. For example, scheduler 534, via routine 540, allocates a large portion (e.g., 80% or more) of the transmit power to a first traffic channel segment to win service robustness for poor channel wireless terminals and a small portion (e.g., 20% or less) of the transmit power to a second traffic channel segment to achieve high burst data rates. In accordance with the present invention, the dynamic range of allocated power between two traffic channel segments in the same sector can be large, e.g., greater than a 3dB relative power difference, while the dynamic range of allocated power between corresponding traffic channel segments in sectors of a cell is limited, e.g., less than a 3dB relative power difference in some embodiments.

Fig. 13 depicts the power allocation between traffic channel segments in the same sector and between corresponding traffic channel segments for multiple sectors of a cell for a typical case where there are two traffic channel segments and the Delta value is 0. In the table 1300 of fig. 13, a first column 1308 lists traffic segment numbers, a second column 1310 lists sector 1 power allocation information, a third column 1312 lists sector 2 power allocation information, and a fourth column 1314 lists sector 3 power allocation information. The first row 1302 of the table 1300 lists column header information. A second row 1304 lists traffic channel 1 power allocation information on three sectors. The third row 1306 lists traffic channel 2 power allocation information on three sectors. In this example, Delta is 0, i.e., the assignment of the corresponding channels in each sector of the cell is the same, while the power assignment difference between the channels is large, e.g., a 4-fold difference.

Consider the following exemplary embodiment of the present invention, which includes 2 adjacent sectors, including 2 channels in each sector, with base station transmit power control on each channel in each sector of a cell in accordance with the present invention.

The transmitter may be controlled to operate on a first and second communication channel in a synchronized manner such that transmissions are into both the first sector and the second sector.

Typically, the total transmit power (S1PC1) of the tones corresponding to the first channel in the first sector of the cell during a time period (e.g., a subset of the symbol times) is controlled to be greater than 20% and less than 500% of the total power of the transmitted tones corresponding to the first channel (S2PC1) in the second sector. This may be represented by a wide first channel inter-sector transmit power control range: 20% < (S1PC1/S2PC1) < 500%.

In some embodiments, controlling the total transmit power of the tones corresponding to the first channel comprises limiting the total power used in the first subset of symbol times to no more than a fixed fraction of a maximum average total transmit power used by the transmitter in the first sector during any 1 hour period, said fixed fraction further used to limit the total transmit power of the tones corresponding to the first channel in the second sector during the first subset of symbol times to no more than a maximum average total transmit power used by the transmitter in the second sector during any 1 hour period, said fixed fraction being less than 100%.

In some embodiments, the total transmit power of the tones corresponding to the first channel (S1PC1) in the first sector of the cell during a time period (e.g., another subset of symbol times) is controlled to be greater than 50% and less than 200% of the total power of the transmitted tones corresponding to the first channel (S2PC1) in the second sector. This may be represented by a narrow first channel inter-sector transmit power control range: 50% < (S1PC1/S2PC1) < 200%. The base station may monitor the number of symbols in one constellation for one time interval and use this information to determine whether to apply a wide or narrow inter-sector channel control range. When the number of symbols in a constellation is large (e.g., each set is modulated by more elements), the channel is more susceptible to interference noise, and therefore a narrower inter-sector power control range is selected by the base station, allowing the base station to more closely control the degree of interference between users in a sector and keep it to an acceptably low level. The base station may also decide whether to use a wide or narrow inter-sector power control range based on the channel coding rate (e.g., whether the coding rate is a slower or faster coding rate). If the channel uses a faster code rate for a time interval, the base station should use a narrower inter-sector transmit power control range, since a faster range will make the user more susceptible to interference, and if a narrower inter-sector transmit power control range is used, the degree of interference between users can be more closely controlled and managed by the base station to maintain an acceptable level.

In some embodiments, a time interval or period, e.g., a subset of symbol times involving transmission power control on a particular channel of two adjacent sectors using a tighter inter-sector power control range or a narrower inter-sector power control range, comprises at least 14 consecutive symbol times.

In some embodiments, the total transmit power of the tones corresponding to the first channel in the first sector during a time period (e.g., an interval of symbol times) may be equal to the total power of the tones transmitted in the first channel of the second sector. This can be described as: s1PC1 ═ S2PC 1. Fig. 13 depicts an example where the power allocation for sector 1 and sector 2 to traffic segment 1 is 80% (second row 1304, column 21310, and column 31312).

In some embodiments, for a time period, within a particular sector (e.g., the first sector), the total power of the transmitted tones for the first channel in the first sector (S1PC1) may be greater than 200% and less than 50% of the power of the transmitted tones for a second channel in the first sector (S1PC 2). This inter-channel transmission power control range within a sector can be expressed as: ((S1PC1/S1PC2) < 50%) or (S1PC1/S1PC2 > 200%). Such an embodiment is shown in the example of fig. 13, with S1PC1 ═ 80% (second row 1304, second column 1310) and S1PC2 ═ 20% (third row 1306, second column 1310); s1PC1/S1PC2 equals 400%. This allows the base station to employ a wide range of power selection to match users to power levels.

The time interval in which the base station controls the difference in transmit power level between two channels within a particular sector of a cell to be in the range of greater than 200% or less than 50% may be an interval of at least 14 consecutive symbol times.

According to the present invention, a wireless terminal may be identified as being in a border area, e.g., a sector border area. The allocation of communication resources (e.g., channels) to wireless terminals may be controlled. Those resources may include a channel that limits the base station total transmit power of its controlled tones to < 10% of the total transmit power of corresponding tones in the same channel in an adjacent sector of the border wireless terminal sector, in accordance with the present invention. Thus, in this case, the ratio of the total transmit power of the base station on the corresponding tones of the same channel between adjacent sectors will be 10% or less for one sector and 1000% or more for the adjacent sectors. In another embodiment, the < 10% level may be 0%; there is effectively no power transmission on the same channel in the adjacent border sector. These implementations, in which a channel in a sector is allocated little or no power, are useful for wireless terminal operation in sector boundary regions, in which a high degree of interference is typically experienced, such as regions 315, 317 and 319 of fig. 3, in accordance with the present invention.

The identification and classification of wireless terminals 600 of fig. 6 to be in a boundary region (e.g., a sector boundary region) and the allocation or resources according to the identification may be performed by the base station under control routines 528, wherein the control routines 528 include the inter-sector interference routine 536 of fig. 5, the wireless terminal/traffic & segment matching routine 542 and the power allocation routine 540 of fig. 5. The identification of one wireless terminal 600 in one border area may be made from feedback information obtained from the wireless terminal 600 received and processed by the base station 500; the feedback information may include an experienced inter-sector interference, background interference, and a level of location interference. Wireless terminal 600 may collect MN channel condition information 632 under the direction of channel condition monitoring/reporting routines 628 and report such information to base station 500; this information may be used by base station 500 in MN channel condition information 568.

It is next considered that the corresponding channel segments need not all be active. Note that an inactive segment does not cause inter-sector interference to, and is not affected by, inter-sector interference from other corresponding channel segments. Thus, when the scheduler 534 coordinates power allocation in sectors of a cell, only active segments are considered, according to one embodiment of the invention.

If a wireless terminal, such as MN 600 of fig. 6, is located at a sector boundary, such as region 315, 317, or 319 of fig. 3, it may experience a significant amount of inter-sector interference. In one embodiment of the invention, scheduler 534 uses inter-sector interference routines 536 and matching routines 542 to assign a segment of a first traffic channel to a wireless terminal in a sector boundary and to assign the corresponding traffic channel segment to a wireless terminal in a non-sector boundary region in other sectors. In another embodiment of the present invention, scheduler 534 assigns a traffic channel segment to a sector boundary wireless terminal via routines 538 and 542 and keeps one or more corresponding traffic channel segments in other sectors inactive to reduce inter-sector interference. In this case, the frequencies allocated to wireless terminals in sector boundary areas will not experience interference from neighboring sectors because tones are unused in those sectors. In one embodiment, there is a mode of utilizing a particular traffic channel segment, wherein one sector periodically keeps the segment inactive while some other sectors keep the segment active. The pattern may be fixed so that the sectors do not have to coordinate with each other in a real-time manner. For example, one sector (sector a) keeps a traffic segment inactive (i.e., it is not assigned to any wireless terminal in the sector), while the other two sectors (sectors B and C) assign segments to wireless terminals in the sector boundary between a and B and between a and C. In subsequent traffic segments, sector B remains inactive while the other two sectors assign segments to wireless terminals in the sector boundaries between B and a and between B and C. Then, in the subsequent traffic segment, sector C keeps one traffic segment inactive while the other two sectors allocate segments to wireless terminals in the sector boundary between C and a and between C and B. The entire pattern then repeats without explicit and real-time coordination between the three sectors.

One consequence of complete timing and frequency synchronization among sectors of a cell is that a wireless terminal (e.g., MN 600 of fig. 6), particularly near a sector boundary (e.g., boundary 446 or 446' of fig. 4), may have difficulty in ascertaining from which sector 654 of fig. 6 a received channel segment is coming. To distinguish channel segments among sectors, different scrambling bit sequences may be used in different sectors.

Scrambling is a well-known method of randomizing transmitted signals. There are many ways to achieve scrambling. A specific implementation is considered below for purposes of description. It is to be understood that the principles of the present invention are not dependent upon a particular exemplary implementation. At transmitter 514 of fig. 5, at a particular OFDM symbol transmission time, symbols from different channel segments generated by encoders of the individual channel segments are multiplexed to form a symbol vector, which is then used to generate an OFDM symbol signal to be transmitted. The scrambled bit sequence is a random binary sequence and is known to both the transmitter 514 and the receiver 610 of fig. 6. In an exemplary embodiment, the symbol vectors are phase rotated according to the scrambled bit sequence. At receiver 600, the same sequence of scrambled bits is used to de-rotate the received symbols before decoding occurs.

According to one embodiment of the invention, different scrambling bit sequences are used in different sectors and the sector/scrambling information is stored in the mobile device. The base station, 500 of fig. 5, uses different scrambling bit sequences in the 3 sectors to generate their respective transmit signals. The wireless terminal receiver of fig. 6 uses the particular scrambled bit sequence corresponding to the sector in which it is located to selectively demodulate the signal transmitted from an intended sector of base station 500. Alternatively, wireless terminal receiver 600 may use multiple scrambling bit sequences to simultaneously demodulate signals from multiple sector transmissions of one base station 500 or from multiple base stations, where the scrambling sequences used correspond to the scrambling sequences used by the sectors transmitting the recovered signals.

The channel condition measurement and reporting features of the present invention will now be described. To facilitate the scheduling of downlink traffic channel segments, such as power allocation and burst data rate allocation, a wireless terminal 600 of fig. 6 may measure its downlink traffic conditions under the control of routines 628 of fig. 6 and periodically transmit a channel condition report including data/information 632/634 of fig. 6 to base station 500 of fig. 5.

The channel condition of one wireless terminal 600 may be in two characteristic regions. For the sake of description, it is assumed that channel conditions are measured in terms of SIR (signal to interference ratio). In a first region, e.g., a non-sector boundary region, the SIR is limited by inter-cell interference or radio propagation loss, and inter-sector interference is a small component. In this case, the base station 500 may increase the received SIR of one traffic channel segment to the wireless terminal 600 by allocating high transmit power under the control of routines 538 and 540 of fig. 5. In a second region, e.g., an inter-sector boundary region, the SIR is primarily limited by inter-sector interference. In this case, assigning a high transmit power does not significantly increase the received SIR given the limitations on power assignment (e.g., a small Delta between sectors on corresponding data traffic channel segments in a sector of the cell), since the power of the interference increases with increasing power. The two above regions represent extreme channel condition characteristics. In the real world, the channel conditions of the wireless terminal 600 may be more generally located between the two extreme regions just described.

In accordance with the present invention, the wireless terminal 600, under the control of routines 628, estimates (e.g., measures) its channel condition characteristics and informs the base station 500 of the determined channel condition. This enables the base station 500 to make reasonable scheduling decisions based on power and burst data rate allocation. In one embodiment of the invention, the data 632, 634 of fig. 6 is included in a downlink channel condition report sent to the base station. In some implementations, wireless terminal 600 distinguishes SIR due to inter-sector interference by routine 536 of fig. 5 and SIR due to other types of fading (e.g., inter-cell interference) by routine 536 of fig. 5 and provides such information to the base station. This enables the base station to perform power allocation decisions based on inter-sector feedback information rather than just a single interference indication, which makes it difficult to determine whether allocating more power would have the desired beneficial result.

The use of one or more relatively high power tones, referred to herein as a beacon signal, will now be described. To facilitate various downlink operations, base station 500 of fig. 5 may frequently and/or periodically transmit a beacon signal as a function of information 530 including beacon information 548 under the control of signal generation routines 532 in accordance with the present invention. Each beacon signal is an OFDM signal transmitted over, for example, a single symbol transmission period. When a beacon signal is transmitted, most of the transmit power is concentrated on a few tones, including, for example, one or two tones of the beacon signal. Many or most tones not used for beacon signals may, and often do, not be used. During a beacon signal transmission time (which in some embodiments may be a symbol time), the tones forming the beacon may comprise 80% or more of a maximum average total base station power used by the base station for transmission in a sector. In some embodiments, some additional tones may carry signals simultaneously with the beacon transmission, and the total power level of those tones is less than or equal to 20% of the maximum average base station power used by the base station to transmit in one sector at the time of the beacon transmission.

Diagram 1400 of fig. 14 shows a generic OFDM signal. The vertical axis 1402 represents the power allocated to the tone and the horizontal axis 1404 corresponds to the tone frequency. The individual bars 1406, 1408, 1410, 1412, 1414, 1416, 1418, 1420, 1422, 1424 each correspond to a power level for each of the different typical OFDM frequency tones at a time (e.g., symbol period). It can be seen that the total power is divided relatively equally between the frequency tones.

Fig. 15 is a diagram 1500 illustrating an exemplary beacon signal in accordance with an exemplary embodiment of the present invention. The beacon signal includes two tones 1506, 1508. The majority of the sector transmit power is allocated between the two tones 1506, 1508 of the beacon, each of which is allocated approximately 45-50% of the total power. The vertical axis 1502 represents power per tone and the horizontal axis 1504 corresponds to tone frequency. In the example of fig. 15, this results in the two tones having approximately equal total power as the tones typically used to transmit data. The single bars 1506, 1508 correspond to the power level of each of the two selected OFDM frequency tones at the time of beacon transmission. It can be seen that the total power is concentrated on the two selected frequencies when the beacon is transmitted. The sector transmit power is significantly concentrated on a very limited number of tones, quite unlike conventional pilot tones, where the pilot may be transmitted at a power level slightly higher than the tones used to transmit data.

Fig. 16 is a graph 1600 illustrating an exemplary beacon signal in which total power is allocated primarily to only a single frequency tone allocated approximately 90-100% of the total sector transmission power, in accordance with another embodiment of the present invention. The vertical axis 1602 represents power per tone and the horizontal axis 1604 represents frequency tones. One single bar 1606 corresponds to the power level of a single selected OFDM frequency tone used as a beacon signal. It can be seen that the total power at beacon transmission is concentrated on a single frequency tone, resulting in a beacon tone having a power level at least 5 times the power level of the highest power tone used to transmit data in the sector at other times.

One advantage of this concentration of power to one beacon signal is that a mobile node (e.g., MN 600 of fig. 6) can easily and quickly identify the beacon signal(s). This allows information, such as superslot boundary synchronization information, slope (cell) information, or sector information, to be quickly and/or accurately conveyed to the mobile device at the time a beacon is transmitted. Given the beacon tones have high power, they are easy to detect, and the probability of one data tone being misinterpreted as one beacon tone is relatively low due to the typically large power difference between the beacon tone and the data tone.

In one embodiment of the invention, the beacon signal may be transmitted during a fixed OFDM symbol duration of a super slot, e.g., the first or last OFDM symbol. In this way, one beacon tone may be used to mark a superslot boundary. The beacon signal may repeat every super slot or every few super slots. The beacon signal is easy to detect because it concentrates very high power on a few tones. Thus, once the time position of the beacon signal has been located, the super slot boundary can be quickly determined with a high degree of certainty.

In another embodiment of the present invention, one or more high power tones used as a beacon signal are selected from a predetermined group of beacon tones or sets of tones. The set of tones is used when multiple high power tones form a beacon signal that may vary over time. The set of predetermined beacon tones may be included as part of the beacon information 548 stored in the base station and the beacon information 652 stored by the wireless terminal of fig. 5. This use of different sets of beacon tones as beacon signals can be used to indicate or convey specific system information, including sector identification information. For example, the beacon signal may use 4 tones, as shown in fig. 17. In the graph 1700 of fig. 17, the vertical axis 1702 represents power per tone, while the horizontal axis 1704 represents frequency. Fig. 17 shows a set of four beacon tones: b11706, a11708, a21710 and B21712. Each tone power of each beacon 1706, 1708, 1710 is approximately equal such that each beacon tone is allocated approximately 25% of the total sector transmit power. The frequency locations of the different beacon tones, e.g., the two inner tones a11708 and a21710, are used to indicate the value of SLOPE used in the cell. The frequency locations of certain frequency tones, such as the outer tones B11706 and B21712, are used to indicate the boundaries of the frequency band used in the cell, for transmission purposes and/or optionally for sector indexing. The beacon signals of the neighboring cells will have different inner beacon tone frequency locations a11708 and a21710 to indicate different slope values. Thus, in one particular cell, beacon signals of different sectors may have different B11706 and B21712 tone locations. Assuming that outer beacon tones B11706 and B21706 are used to indicate frequency boundaries, these outer beacon tones may be the same in each sector of a cell, assuming the same frequency band is used in each sector.

The time at which a particular beacon signal is transmitted may be used to indicate something other than the slot boundary. Fig. 18 shows a frequency versus OFDM symbol time diagram 1800 depicting the different types of beacons that may be transmitted in the time domain in accordance with various possible embodiments of the present invention. Vertical axis 1802 represents frequency and horizontal axis 1804 corresponds to OFDM symbol time. Different beacon signals will be described as corresponding to a particular beacon type according to the information that it conveys, alone or in combination with other beacon signals.

A type 1 beacon signal 1806 is shown as being transmitted at the beginning of a superslot. After a time interval 1812 of k superslots (where k is an integer value), a beacon 1808 of type 2 is transmitted. Then after k superslots 1814, a beacon 1810 of type 3 is transmitted. The tone frequencies and/or beacon tone power levels of the three beacons 1806, 1808, 1810 are different. Type 1 beacons 1802 may be used to convey frequency floor information indicating a lower frequency boundary of the frequency band used in a sector. A beacon of type 2 may be used to provide a slope index, e.g., a slope indication, from which a wireless terminal may determine the slope of a cell. Using type 2 beacons to determine the slope enables a wireless terminal to determine in which cell a mobile node is located. A beacon 1810 of type 3 is used to convey sector information (e.g., to allow a mobile device to identify sector locations 1, 2, 3) in the same manner as a beacon of type 2 is used to convey cell information (e.g., slope information) via, for example, an index table of sector numbers or a steering offset corresponding to a particular frequency tone value. As discussed above, different base stations may be preconfigured with different slope values and different pilot offset values in different sectors, which values are used to control the frequency hopping sequence within a cell of one base station.

Fig. 19 shows a frequency versus OFDM symbol time diagram 1900 depicting the concept of transmitting alternating beacon types in the time domain to convey information in accordance with one embodiment of the invention. The vertical axis 1902 represents frequency and the horizontal axis 1904 represents OFDM symbol time. In the example shown in fig. 19, the base station 500 of fig. 5 transmits alternating beacon types in the following sequence: type 1 beacons 1906, type 2 beacons 1908, type 1 beacons 1910, type 2 beacons 1912, type 1 beacons 1914, type 2 beacons 1916, type 1 beacons 1918, type 2 beacons 1920. All type 1 beacons 1906, 1910, 1914, 1918 are on the same frequency tone f₁1922 is transmitted. Type 2 beacons 1908 and 1916 are on frequency tone f_2a1924, while type 2 beacons 1912 and 1920 are transmitted on frequency tone f_2b1926 is transmitted. Type 2 beacons in the time domain on two frequency tones f_2a1924 and f_2b1926 alternately. The mobile node 600 of fig. 6 may identify a type 1 beacon according to the beacon tone frequency. The mobile node 600 can handle two different types of beacons through an index table that frequency translates each tone into an index number that ultimately translates into a slope hop value 646 of fig. 6 that is specific to a particular cell 656 of fig. 6. The mobile node 600 will receive two index numbers, one of which will correspond to the slope index 650. The access node 500 will operate on a fixed number of slope index values with a defined slope indication equation. From the information of this data held by the mobile device, the mobile device 600 can determine which index 650 corresponds to the slope 646.

As an example, consider a slope index range of 0 ≧ X_SNot less than 79, the slope indicates the equation as (X)_S+39)Mod 80。X_SIndicating an index to the slope of access node 500. The access node 500 transmits a type 2 beacon when corresponding to X_SAnd (X)_S+39) alternating between the pitch frequencies of Mod 80. In slope index value ═50, the exemplary access node transmits type 2 beacons with index values of 50 and 9. The mobile node 600 may receive an index 50 beacon followed by an index 9 beacon, or may receive an index 9 beacon followed by an index 50 beacon, depending on when the mobile device 600 first detects a type 2 beacon signal. In order for mobile device 600 to determine which is X_SOr slope index (first beacon), the mobile device 600 will match X with the index of the second beacon_SThe distance is 39 index numbers. If the mobile device 600 receives 9 and then 50 first, the change in the number of index points is 41; thus, the second received index value 50 is the true value to be used for the slope index 650. If the mobile device 600 receives 50 first and then 9, the change in the number of index points is 39, so the first received index value of 50 is the true value to be used for the slope index 650.

By utilizing an index to the slope or slope indication, frequency diversity is provided while allowing reconfiguration in the event of a failure of a particular tone frequency.

Beacons may also be useful for identifying cell and sector locations (656 and 654 of fig. 6) and a more accurate location within a sector of a mobile device 600 receiving the beacon signal(s), thereby being useful for providing handoff alerts and improving the efficiency of handoff operations. Furthermore, the number of pilots and/or pilot power may be reduced by taking over certain functions sometimes performed by utilizing pilot hopping sequences and transmitted pilot signals, such as synchronization to superslot boundaries. So that the time for pilot data puncturing can be reduced and it is also possible to save the power needed to transmit and process the pilot.

Various base station signaling methods of the present invention for different levels of strength and different repetition rates on a per tone basis for use in a typical frequency division multiplexed communication system (e.g., an OFDM system) will be illustrated and discussed. Four signals will be described, possibly a first signal comprising a normal OFDM signal as shown in figure 14, a second signal having a high power level (e.g. a beacon signal as shown in figure 15), a third signal comprising a signal having a normal OFDM signal power level which may comprise, for example, user data or, if contemporaneous with a beacon, a power level which utilizes the power remaining after beacon allocation, and a fourth signal having a level comparable to the high power of the second signal (e.g. another beacon signal as shown in figure 16). Base station transmitter 514 of fig. 5 utilizes a set of N tones, where N is greater than 10, such as included in tone information 550 of fig. 5, to communicate information with the first signal over a first time period, where the first time period is at least two seconds long, and in some embodiments, the first time period is at least 30 minutes. The first signal may comprise, for example, user data on a traffic channel and may be transmitted by using the data tone hopping sequence 554 of fig. 5. A second signal, sometimes referred to as a beacon signal, may be transmitted during a second time period, where the beacon signal includes a set of X tones included in tone information 550, where X is less than 5, and at least 80% of a maximum average total base station transmit power used by the base station to transmit signals into the first area during any 1 second time period during the first time period is allocated to the set of X tones forming the beacon signal. In some embodiments, the second time period for transmitting the second (beacon) signal may be, for example, the time period for transmitting one OFDM symbol 552 of fig. 5. In some embodiments, the second time period, e.g., the beacon time period, is repeated periodically during the first time period. Some of the X tones (beacons) may be at a predetermined fixed frequency; such a fixed frequency (see fig. 17) may be used to convey information such as sector location. Some of the X tones (beacons) may have a fixed frequency offset ≧ 0 from the lowest frequency tone in the set of N tones; in this manner, the second signal (beacon signal) may be used to convey frequency boundary information to wireless terminal 600. Some of the X tones (beacons) may be transmitted at a frequency determined as a function of at least one of a base station identifier and a sector identifier. This may allow a wireless terminal to quickly identify the cell and sector in which it is operating, quickly acquire data and pilot hopping sequences, and quickly synchronize with a base station. In some embodiments, the number of X in the second (beacon) signal is one (see fig. 16) or two (see fig. 16). So that the second (beacon) signal of the base station, which is transmitted at a relatively high power and with energy concentrated on one or a few tones, is readily detected by the wireless terminal. In some embodiments, at least half of the N-X tones in the set of N tones, but not in the set of X tones, are unused during the beacon transmission period. In other embodiments, none of the N-X tones in the set of N tones, but not in the set of X tones, are used during the beacon transmission time. By limiting the transmission of non-X (beacon) tones during the second signal (beacon tone interval), the level of the second (beacon) signal can be increased and confusion with other signals can be reduced, which provides better detection and identification of beacon signals by the wireless terminal.

The third signal may also be transmitted over a third time interval. The third signal may comprise a set of Y tones included in tone frequency information 550, wherein Y ≦ N, wherein each tone in the third set of Y tones possesses 20% or less of the maximum average base station transmit power used by the base station transmitter to transmit signals into the first region during any 1 second period during the first time period. The third time period may have the same duration as the second time period, e.g., occur simultaneously with one beacon signal. In some embodiments, at least two of the data, control, and pilot signals may be modulated on at least some of the set of Y tones. In some embodiments, the repetition rate of the set of Y (third signal) tones is at least 10 times the repetition rate of the set of X (second or beacon signal) tones, while in other embodiments, the repetition rate of the set of Y (third signal) tones is at least 400 times the repetition rate of the set of X (second or beacon signal) tones.

A fourth signal may also be transmitted by base station 500 during a fourth time period. The fourth signal includes G tones contained in tone frequency information 550 of fig. 5, where G is less than 5, and at least 80% of the maximum average total base station power used by the base station to transmit signals into the first region during any 1 second period during the first time period is allocated to the G tones. At least one of the G tones is not in the set of X tones (the second set of signal tones), and the frequency of at least one of the G tones is a function of at least one of a base station identifier and a sector identifier. The fourth signal may also be repeated periodically during the first time interval. The fourth signal may be considered a second beacon signal that is transmitted at a different time than the second signal and conveys different information.

According to the invention the beacon signal is constructed to a relatively high power level in the set on a few tones. During the beacon transmission time, the non-beacon tones may not carry information, or in some cases, some of the non-beacon tones may carry signals, but at a much lower intensity than the beacon tones. By their nature, beacon tones are easy to detect and can quickly convey information, such as cell and/or sector information, frequency boundary information, and/or synchronization information, to wireless terminals.

The uplink problem will now be explained. According to the invention, the frequency, symbol timing and superslot structure of an uplink signal generated by a wireless terminal can be slaved to these characteristics of the downlink signal. With full synchronization of the downlink signals in each sector, tone frequencies, OFDM symbol timing, and super slot boundaries synchronized with the uplink signals in each sector of a cell can ensure similar synchronization in the uplink, which is subordinate to the downlink.

In a preferred embodiment of the present invention, the data tone hopping sequences and channel segments are synchronized across sectors of a cell. In this case, inter-sector interference is concentrated between corresponding channel segments.

In another embodiment of the present invention, the data tone hopping sequence is determined as a function of both the SLOPE parameter and the sector index. In this case, there is no concept of a corresponding channel segment. A channel segment in one sector may interfere with multiple channel segments in other sectors of the same cell.

The present invention may be implemented in hardware and/or software. For example, certain aspects of the invention may be implemented as program instructions executed by a processor. Alternatively or additionally, certain aspects of the invention may be implemented as an integrated circuit, such as an ASIC. The control means controlling one or more transmitters in different embodiments may be implemented as a software module of a control routine. The apparatus of the present invention is directed to software, hardware and/or a combination of software and hardware. Machine-readable media containing instructions for controlling a machine to implement one or more method steps in accordance with the present invention are contemplated and are considered to be within the scope of certain embodiments of the present invention.

Claims (33)

1. A method of operating a base station transmitter in a frequency division multiplexed communication system, said base station transmitter utilizing a set of N tones for transmitting information into a first region utilizing a first signal over a first time period, said first time period being at least two seconds long, where N is greater than 10, and said method comprising:

transmitting a second signal comprising a set of X tones into said first region during a second time period, wherein X is less than 5, and at least 80% of a maximum average total base station transmit power used by said base station transmitter to transmit signals into said first region during any 1 second period during said first time period is allocated to said set of X tones.

2. The method of claim 1, wherein said first area is a sector of a cell.

3. The method of claim 1, wherein X is equal to one or two.

4. The method of claim 1, wherein at least half of the N-X tones in said set of N tones but not in said set of X tones are unused during said second time period in said first region.

5. The method of claim 4, wherein none of the N-X tones in said set of N tones but not in said set of X tones are used during said second time period in said first region.

6. The method of claim 4, wherein a plurality of tones in said N sets of tones but not in N-X tones in said X sets of tones are used during said second time period in said first region.

7. The method of claim 1, wherein the first step is carried out in a single step,

wherein said first area is a sector of a cell; and is

Wherein the communication system is an orthogonal frequency division multiplexing system and the second time period is a time period for transmitting an orthogonal frequency division multiplexing symbol.

8. The method of claim 7, wherein said second time period is repeated periodically during said first time period.

9. The method of claim 7, wherein the method further comprises:

transmitting a third signal comprising a set of Y tones into said first region during a third time period, wherein Y ≦ N, each tone in said third set of Y tones having 20% or less of said maximum average total base station transmit power used by said base station transmitter for transmission into said first region during any 1 second period during said first time period, said third time period equal in duration to said second time period.

10. The method of claim 9, wherein said third time period overlaps said second time period, and said method further comprises:

at least two of the data, control, and pilot signals are modulated on at least some of the set of Y tones.

11. The method of claim 9, wherein said third time period and said second time period are disjoint, and said method further comprises:

at least two of the data, control, and pilot signals are modulated on at least some of the set of Y tones.

12. The method of claim 7:

wherein at least one of said X tones is transmitted at a predetermined fixed frequency; and is

Wherein said at least one of said X tones is transmitted at a frequency having a fixed frequency offset of 0 or greater relative to the lowest frequency tone of said set of N tones.

13. The method of claim 7, wherein at least one of said X tones is transmitted at a frequency determined as a function of at least one of a base station identifier and a sector identifier.

14. The method of claim 9, wherein for each repetition of said second period of time in said first period of time, there are at least Z repetitions of said third period of time in said first period of time, wherein Z is at least 10.

15. The method of claim 14, wherein Z is at least 400.

16. The method of claim 7, further comprising:

transmitting a fourth signal comprising G tones into said first region in a fourth time period, wherein G is less than 5, and at least 80% of said maximum average total base station transmitter power used by said base station transmitter for transmission into said first region during any 1 second period during said first time period is allocated to said G tones.

17. The method of claim 16, wherein the first step is carried out in a single step,

wherein the frequency of at least one of said G tones is a function of at least one of a base station identifier and a sector identifier, and

wherein said at least one of said G tones is not one of said X set of tones.

18. The method of claim 17, wherein said second and fourth time periods are repeated periodically during said first time period.

19. The method of claim 1, wherein the first period of time is at least 30 minutes.

20. A base station for use in a frequency division multiplexed communication system, said base station comprising

A transmitter for transmitting information into a first region using a set of N tones;

first control means connected to said transmitter for controlling said transmitter to transmit into said first region with a first signal over a first time period, said first time period being at least two seconds long, wherein N is greater than 10; and

second control means connected to said transmitter for controlling said transmitter to transmit a second signal comprising a set of X tones into said first region during a second time period, wherein X is less than 5, and at least 80% of a maximum average total base station transmit power used by said base station transmitter for transmission into said first region during any 1 second period during said first time period is allocated to said set of X tones.

21. The base station of claim 20, wherein said first period of time is at least 30 minutes; and wherein said first area is a first sector of a cell comprising first and second sectors.

22. The base station of claim 20 wherein said first and second control means are different portions of a control routine; and is

Wherein X is equal to one or two.

23. The base station of claim 20, wherein at least half of the N-X tones in said set of N tones but not in said set of X tones are unused in said first region during said second time period.

24. The base station of claim 23, wherein none of the N-X tones in said set of N tones but not in said set of X tones are used in said first region during said second time period.

25. The base station of claim 23, wherein during said second time period, a plurality of N-X tones in said set of N tones but not in said set of X tones are used.

26. The base station of claim 20, wherein said communication system is an orthogonal frequency division multiplexing system, and wherein said second time period is a time period for transmitting an orthogonal frequency division multiplexing symbol.

27. The base station of claim 26, wherein said second time period repeats periodically during said first time period.

28. The base station of claim 26, further comprising:

third control means for controlling the transmitter to transmit a third signal comprising a set of Y tones into said first region during a third time period, wherein Y ≦ N, each tone in said third set of Y tones used by said base station transmitter to transmit signals into said first region during any 1 second period of said first time period of 20% or less of said maximum average total base station transmit power, said third time period equal in duration to said second time period.

29. The base station of claim 28, wherein said third time period is disjoint from said second time period, and at least two of data, control, and pilot signals are modulated on at least some tones in said set of Y tones.

30. The base station of claim 26, wherein at least one of said X tones is transmitted at a predetermined fixed frequency.

31. The base station of claim 26, further comprising:

fourth control means for controlling said transmitter to transmit a fourth signal comprising G tones into said first region during a fourth time period, wherein G is less than 5, and at least 80% of said maximum average total base station transmitter power used by said base station transmitter to transmit tones into said first region during any 1 second time period during said first time period is allocated to said G tones.

32. The base station of claim 31, wherein the base station is further configured to,

wherein the frequency of at least one of said G tones is a function of at least one of a base station identifier and a sector identifier, and

wherein said at least one of said G tones is not one of said set of X tones.

33. The base station of claim 32 wherein said second and fourth time periods repeat periodically during said first time period.