HK1067830B - Method and apparatus for transmitting the sync channel message in a multi-carrier communication system - Google Patents

Description

Method and apparatus for transmitting synchronization channel message in multi-carrier communication system

The present application is a divisional application entitled "method and apparatus for transmitting a synchronization channel message in a multicarrier communication system" having an application date of "21/4/2000", and an application number of "00806609.4".

Technical Field

The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for transmitting and receiving broadcast information in a multi-carrier CDMA communication system.

Background

The application of Code Division Multiple Access (CDMA) modulation techniques is one of several techniques that facilitate communications in which there are many system users. Other multiple-access communication system techniques, such as Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA), are well known in the art. However, for multiple access communication systems, spread spectrum modulation techniques for CDMA have greater advantages than these modulation techniques. The use of CDMA techniques in a MULTIPLE access communication SYSTEM is disclosed in U.S. patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE access communication SYSTEM USING SATELLITE OR terrestrial repeaters," which is assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. The use of CDMA techniques IN multiple access communication SYSTEMs is further disclosed IN U.S. patent No. 5,103,459 entitled "SYSTEM and METHOD FOR generating signal WAVEFORMS IN a CDMA CELLULAR TELEPHONE SYSTEM" (SYSTEM AND METHOD FOR GENERATING SIGNAL waverms IN ACDMA cell TELEPHONE SYSTEM), which is assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. CDMA has been standardized in interim standards IS-95A and IS-95B of the telecommunications industry association entitled Mobile Station-Base Station Compatibility Standard for dual Mode Spread Spectrum Systems (hereinafter collectively referred to as IS-95) for dual Mode Spread Spectrum Systems.

In the IS-95 communication system, channels of information transmitted from a common base station are distinguished from each other by orthogonal spreading codes. Each channel is spread by a unique orthogonal spreading sequence. The channels transmitted by the IS-95 base station include: a pilot channel, a synchronization channel, at least one paging channel, and a dedicated traffic channel. A mobile station in the coverage area of a base station uses a pilot channel to provide a phase reference for the relative demodulation of other channels. The synchronization channel carries overhead information such as timing information, pilot PN offset information, and other information that allows other overhead channels to be received. The paging channel informs the mobile station of the mobile station's termination of a call directed to the mobile station in the area. The dedicated traffic channel provides information directed to users of particular mobile stations in the coverage area of the base station.

In IS-95, when the base station sends a synchronization channel message, it will use the fixed length message format of table 1 below:

TABLE 1

Field(s)	Length (position)
		MSG_TYPE(‘00000001’)	8
P_REV	8
		MIN_P_REV	8
SID	15
		NID	16
PILOT_PN	9
		LC_STATE	42
SYS_TIME	36
		LP_SEC	8
LTM_OFF	6
		DAYLT	1
PRAT	2
		CDMA_FREQ	11

MSG _ TYPE message TYPE

Extent of P _ REV protocol modification

MIN P REV minimum protocol modification degree. The base station sets this field to prevent mobile stations that the base station cannot support from accessing the system.

And (4) identifying the SID system. The base station shall set this field to the system identification number of the system.

The NID network identification. This field serves as a sub-identifier for the system defined by the owner of the SID.

PILOT _ PN PILOT PN sequence offset identification (index). The base station should set this field to the pilot PN sequence offset for this base station in units of 64 PN chips.

LC _ STATE long code STATE. The base station should set the SYS TIME field of the message to the long code state for the TIME given by this field.

SYS _ TIME system TIME. The base station shall set this field to system time as 4 sync channel superframes (320 ms) after the end of the last superframe (including any portion of the sync channel message) minus the pilot PN sequence offset in units of 80 ms.

LP _ SEC is the number of skip seconds that have occurred since system time.

LTM _ OFF local time offset to system time. The base station should set this field to the binary complement (two's complement) of the offset of local time to system time in units of 30 minutes.

DAYLT daytime savings time indicator. If daytime time savings are effective, the base station should

PRAT paging channel data rate. The base station should set this field to the PRAT field value shown in table 2, corresponding to the data rate used by the paging channel in the system.

TABLE 2 paging channel data Rate

PRAT field (binary system)	Number of paging channelsData rate
		00	9600 bps
01	4800 bps
		10	Retention
11	Retention

CDMA _ FREQ frequency allocation. For CDMA channels including the original paging channel, the base station should set this field to the CDMA channel number corresponding to the CDMA frequency assignment.

In the IS-95 system, each base station transmits a pilot channel covered only by a short PN sequence. In the IS-95 system, the short PN sequence repeats every 26 milliseconds. The pilot signal transmissions from each base station are distinguished from each other by phase shifts between each other. In particular, each base station associated with a single base station controller is at least 64 PN chips out of phase.

Under normal operation, the mobile station first acquires a pilot signal. The pilot signal carries no data and is a simple all-zero sequence spread by a common short code that also spreads all other channels transmitted by the base station. After acquiring the pilot channel, the mobile station receives the above information from the synchronization channel. The frame and interleaver timing on the synchronization channel is aligned with the pilot PN sequence. The zero state of the short PN sequence marks the starting point of the sync channel frame and the interleaver.

In the Personal Communications System (PCS) spectrum of the united states, CDMA channel number N designates the carrier frequency of the forward link and reverse link channels. In particular, channel number N corresponds to a reverse link carrier frequency of (1850+0.05N) and a forward link carrier frequency of (1930+0.05N), where N varies from 0 to 1199. The bandwidth of each CDMA channel is 1.25 MHz. Thus, the channel numbers of adjacent CDMA channels differ by at least 25(25 × 0.05MHz to 1.25 MHz). Certain carrier frequencies are assigned as preferred frequency allocations to facilitate initial acquisition by the mobile station. Referring to fig. 1, for an IS-95B CDMA system in the a block of the PCS band, the channel numbers for the preferred frequency allocations are 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, and 275. Upon power up, the mobile station will first search for a preferred frequency allocation.

The international telecommunications union has recently requested proposed methods for providing high-rate data and high-quality voice services over wireless communication channels. The first of these recommendations was promulgated by the telecommunications industry association entitled "cdma 2000 ITU-R RTT candidate submission" (hereafter cdma 2000). cdma2000 proposes increasing the throughput of the forward link signal by transmitting portions of the information over three frequency bands, each having a bandwidth of 1.2288 MHz. This method is described as a "multi-carrier" method.

In CDMA2000, a multi-carrier CDMA system is defined that uses three adjacent 1.25MHz rf (radio frequency) channels, the spacing between which is also equal to 1.25 MHz. Referring to fig. 2, a multi-carrier CDMA system in block a of the PCS band may be spread with a center channel over channels 50, 75, 100, 125, 150, 175, 200, 225, or 250. Channels 50 and 250 are typically avoided to prevent interference to adjacent frequency bands on the reverse link. In the proposed cdma2000 description, the reverse link can be directly extended with a chip rate of 3.6864Mcps, which is more difficult to meet the radiation limit requirements than a chip rate of 1.2288 Mcps.

Upon power up, the mobile station searches for a pilot signal on the preferred frequency. If no pilot is found in the current channel, it changes its channel and searches again. Once a pilot is acquired, the mobile station demodulates the synchronization channel associated with the pilot to receive timing information, pilot PN offset, and other information that makes it possible to receive other additional channels.

In the multi-carrier method, one method of providing sync channel data is to divide the sync channel message into three parts and place one third of the message on each of the three parts of the multi-carrier signal. If the synchronization channel of a multi-carrier system is spread over three channels, the mobile station must know the correct channel to use by the system in order to reliably demodulate the synchronization channel. Since the correct channel is not known a priori, the mobile station must attempt many combinations to receive the synchronization channel message. If the preferred number of channels, the elapsed time, exceeds in such an experiment, the initial acquisition time of the mobile station is therefore reduced. Accordingly, there is a need in the art for a method of minimizing the search time of a mobile station.

Disclosure of Invention

The present invention is a novel and improved method and apparatus for transmitting broadcast information in a multi-carrier communication system. The proposed invention transmits the synchronization channel of the multi-carrier system with a channel bandwidth of 1.25MHz (i.e., on a single carrier) and specifies the preferred channel transmitted by the synchronization channel to replace the preferred channel of the entire multi-carrier system. The synchronization channel message will indicate the center frequency of the multi-carrier system, if any, in the frequency band and the frequency of the single-band system, if any.

Considering again block a of the PCS band, the preferred channels for synchronization channel transmission may be selected as channels 75, 150 and 225. This choice ensures that any multi-carrier system will always use one of the preferred channels regardless of the location of its center channel. Upon power-up, the mobile station first searches for a synchronization channel on the preferred channel. Once the pilot signal is acquired on any of these channels, the mobile station demodulates the synchronization channel on the channel. The mobile station knows the location of the multi-carrier and single carrier systems in the frequency band from the synch channel message if each system is present. It can be readily seen that by using the recommendations in this disclosure, both the number of channels searched and the number of hypotheses tested are greatly reduced. As a result, the initial acquisition time of the mobile station is improved.

According to a first aspect of the present invention there is provided a multi-frequency channel base station for operating within a predetermined set of frequency channels, wherein data components of forward link data are transmitted simultaneously on a plurality of frequency bands, each frequency band representing a frequency channel and having a carrier frequency, the base station comprising: means for transmitting a synchronization channel message on a single frequency channel within a predetermined set of frequency channels, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single channel system, wherein the center frequency channel is used for receiving signals by a device receiving the synchronization channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; and means for transmitting the remaining components of said forward link data on another frequency channel of a predetermined set of frequency channels.

According to a second aspect of the present invention, there is provided a multi-frequency channel mobile station comprising: control means for controlling operation of the plurality of receiver subsystems in accordance with frequency information indicated in a received synchronization channel message, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single-channel system, wherein the center frequency channel is used to receive signals and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; receiving means for receiving the synchronization channel message on a single frequency channel and providing the synchronization channel message to the means for controlling and for receiving a first portion of a multi-channel signal; and receiving means for receiving an additional portion of the multi-channel signal on another frequency channel.

According to a third aspect of the present invention, there is provided a method of transmitting a data component of forward link data in a communication system, comprising: transmitting a synchronization channel message on a single frequency channel within a predetermined set of frequency channels, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single-channel system, wherein the center frequency channel is used for receiving signals by a device receiving the synchronization channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; and transmitting the remaining components of the forward link data on another frequency channel of a predetermined set of frequency channels.

According to a fourth aspect of the present invention, there is provided a method of receiving a data component of forward link data in a communication system, comprising: receiving a synchronization channel message and a first portion of a multi-channel signal on a single frequency channel, wherein the synchronization channel message indicates one of a center frequency channel of the multi-channel system and a single channel system, wherein the center frequency channel is used to receive the signal and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; controlling operation of a plurality of receiver subsystems in accordance with frequency information indicated in the received synchronization channel message; and receiving an additional portion of the multi-channel signal on another frequency channel.

According to a fifth aspect of the present invention, there is provided an apparatus operable in at least one of a single carrier system and a multi-carrier system, comprising: a multiplexer that multiplexes the forward link signal into a forward link data stream containing broadcast channel data including a synchronization channel message; a first transmit subsystem, coupled to the demultiplexer, that transmits a first portion of the forward link data stream on a first carrier frequency; a second transmit subsystem, coupled to the multiplexer, that transmits a second portion of the forward link data stream on a second carrier frequency; and a third transmit subsystem, coupled to the multiplexer, transmitting a third portion of the forward link data stream at a third carrier frequency, wherein the sync channel message is transmitted on a preferred channel by a transmit subsystem selected from the first, second and third transmit subsystems, the selected transmit subsystem for transmitting on a carrier frequency selected from the first, second and third carrier frequencies, and wherein the preferred channel is for receiving signals by a device receiving the sync channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the preferred channel.

Drawings

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

figure 1 is a schematic frequency band diagram of a PCS system of a 1 (1x) communication system;

figure 2 is a schematic frequency band diagram of a PCS system of a 3 (3x) communication system;

FIG. 3 is a flow chart illustrating the capture method of the present invention;

FIG. 4 is a block diagram illustrating the major elements in a wireless communication system;

fig. 5 is a simplified block diagram of a multi-carrier transmission system;

fig. 6 is a block diagram of a CDMA modulation system;

fig. 7 is a simplified block diagram of a multicarrier receiver system; and

fig. 8 is a block diagram of a CDMA demodulation system.

Detailed Description

Figure 1 shows a typical frequency band diagram of a multi-band communication system. In currently contemplated wireless communication systems, a mobile station attempting to initiate service will tune to each possible frequency in the preferred set of frequencies and determine whether a system is available at that frequency. In fig. 1, the channel numbers of the preferred frequency allocations are 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, and 275, each corresponding to a frequency band 200a, 200b, 200c, 200d, 200e, 200f, 200g, 200h, 200i, 200j, and 200 k. In the exemplary embodiment, each of these bands IS 1.25MHz wide and IS used to carry IS-95 CDMA transmissions.

Fig. 2 shows a possible center frequency band for a three-component multi-carrier communication system contemplated in cdma2000 (also referred to as IS-2000). In a multi-carrier communication system, a mobile station tunes to each possible group of three adjacent channels and attempts to receive a synchronization channel message. In the current design of multi-carrier systems, the synchronization channel message will be divided into three component parts, each of which will be transmitted separately and simultaneously on different carriers of the multi-carrier frequency band. The mobile station first attempts to receive a synchronization channel message over a multi-carrier system comprising frequency bands 300b, 300c, 300 d. If unsuccessful, the mobile station attempts to acquire a synchronization channel on the multi-carrier system including frequency bands 300c, 300d, and 300 e. This continues for each possible three-band system until the mobile station checks for a multi-carrier system comprising bands 300h, 300i and 300 j. For the above reasons, the frequency bands 300a and 300k in the multi-carrier are not used in the exemplary embodiment.

This method of receiving the synchronization channel message is inefficient and time consuming. If the mobile station is capable of operating in multi-carrier or single-carrier mode, the mobile station will have the potential to perform 11 searches of one or bands 200a-200k and 7 multi-carrier searches using center frequencies 300c-300 i. In a CDMA communication system, each frequency band searched requires the mobile station to test a large number of PN offsets to detect the presence of a pilot signal. Therefore, this capture method requires a considerable period of time.

The present invention clearly provides a more efficient method for capturing the required system parameters in a potential mixed bandwidth communication system. In the present invention, a synchronization channel is always transmitted in one frequency band (1 × band). In the preferred embodiment, the preferred channels are channels 75, 150 and 225. Therefore, in order to acquire information necessary for acquiring a preferred system of the mobile station, the mobile station can receive the sync channel message in one bandwidth only by performing 3 searches at the maximum. The present invention greatly reduces acquisition time in a mixed bandwidth communication system. In addition, providing sync channel messages only on the preferred channel reduces the capacity impact of providing overhead messages on more channels.

The reason for the better channel allocation of the present invention is to provide the maximum flexibility in the devices of the multi-carrier system. The preferred channel is assigned to channel numbers 75, 150 and 220(300c, 300f and 300j) and the multi-carrier system will include one of the preferred channels if anywhere in the band including bands 300a-300 k. A multi-carrier system including bands 300a, 300b, and 300c would include preferred channel 300 c. A multi-carrier system including bands 300b, 300c, and 300d would include preferred channel 300 c. A multi-carrier system including bands 300c, 300d, and 300e would include preferred channel 300 c. A multi-carrier system including bands 300d, 300e, and 300f would include a preferred channel 300 f. Any combination of the three adjacent bands will include a preferred channel on which the mobile station will be able to receive the system parameters required for operation.

In the present invention, the mobile station tunes to the preferred channel (300c, 300f or 300i) and attempts to detect the pilot signal on that band. If a pilot signal is detected, the mobile station receives, demodulates and decodes the synchronization channel message. In the present invention, the sync channel message will provide information identifying the center frequency of the multi-carrier system (if one exists) in the current band group, and identifying the frequency of one band (if one exists) in the current band group.

The mobile station selects a system for which the need or capability is appropriate based on the information received in the synchronization channel. If the mobile station prefers to use a multi-carrier system, the mobile station tunes the multi-carrier system using the center frequency of the multi-carrier system indicated in the synchronization channel message and receives a Broadcast Channel (BCH) message. The broadcast channel message will indicate to the mobile station the Common Control Channel (CCCH) number currently used by the system. The mobile station takes the common control channel number and uses a predetermined shot algorithm to determine which code channel it will use to receive paging messages from the transmitting base station.

If the mobile station chooses to operate in a single-band system, the mobile station uses the information received in the synchronization channel message to tune to the appropriate frequency of the single-band system. The mobile station then receives a general paging channel message on the original paging channel. The general paging channel message provides the paging channel number used by the single-band system. The mobile station uses a predetermined hash function to determine the code channel on which the mobile station will receive the paging message of the transmitting base station.

The invention can equally be applied to a system comprising 3 direct extension communication systems. In this embodiment, the sync channel message will include additional information whether the 3 systems are direct extension systems or multi-carrier systems. The synchronization channel message may also provide information about whether the system uses a form of diversity transmission, such as Orthogonal Transmit Diversity (OTD). If a method of transmit diversity is possible in a multi-band communication system, the specification of the means of transmit diversity greatly reduces the number of hypotheses that must be tested to obtain the system.

These changes to the synchronization channel message can be recommended without extending the synchronization channel message used in IS-95B and above. There are a number of reserved bits in the current sync channel message that can be used to provide additional information.

Fig. 3 is a flow chart illustrating the capture operation of the present invention. In block 2, the mobile station tunes to the preferred channel (300c, 300f or 300 i). It will be appreciated that the invention is disclosed in the context of the PCS band of frequencies and can be readily extended to other bands such as the cellular band. Furthermore, the selected set of preferred channels, while preferred for 3 carriers, will be different for multi-carrier systems with different numbers of carriers.

In block 6, the mobile station determines whether the search operation was successful. In the exemplary embodiment, the present invention is incorporated into a CDMA communication system, although the present invention is equally applicable to other mixed bandwidth communication systems. In the exemplary embodiment, the mobile station tunes its RF receiver to the preferred channel (300c, 300f, or 300i) and attempts to detect the presence of the pilot signal. In one embodiment of an IS-95 based CDMA communication system, each base station transmits its pilot signal using a unique pilot signal offset. Thus, the mobile station searches for possible PN offset hypotheses after tuning to a preferred channel (300c, 300f, or 300 i).

Methods and apparatus For detecting pilot signals In CDMA communication systems are well known In the art and are described In detail In U.S. patent No. 5,644,591 entitled Method and apparatus For Performing Search Acquisition In a CDMA communication system, which is assigned to the assignee of the present invention and incorporated herein by reference. The mobile station tests each PN offset hypothesis by calculating the correlation between the received signal in the preferred frequency band and the PN hypothesis being tested. If the correlation energies of all PN hypotheses are less than a threshold, acquisition at the preferred frequency is unsuccessful and operation transfers to block 4. In block 4, the mobile station selects the next preferred channel to be tested (300c, 300f or 300i) and flow moves to block 2 and continues as described above.

Successful acquisition is declared when the mobile station detects sufficient correlation energy between the received signal at the preferred channel frequency and the PN hypothesis. Operation then transfers to block 8. In block 8, the mobile station receives a synchronization channel message. In the present invention, the synchronization channel messages are transmitted in a single one of the frequency bands (300c, 300f or 300 i). In an exemplary embodiment of an IS-95 based CDMA communication system, the synchronization channel frame boundaries and interleaver boundaries are aligned using a short PN sequence for the spread pilot channel signal. Thus, upon successful acquisition of the pilot channel signal, the mobile station has sufficient information to deinterleave and decode the synchronization channel message.

After receiving the synchronization channel message, operation transfers to block 10. The mobile station determines from the synchronization channel message the center frequency of the multi-carrier system in the current band group (if one exists) and the location of the single carrier band in the current band group (if one exists). The mobile station decides whether to operate in the multi-carrier mode or the single channel mode depending on its capabilities and needs.

The operation is transferred to the control block 10. If a mobile station capable of operating in a multi-carrier mode decides to operate in a multi-carrier mode, the flow passes to block 12. In block 12, the mobile station initiates its RF hardware for multi-carrier operation. The mobile station knows from the received sync channel message the center frequency, if one exists, of the multi-carrier system in the current band group. Operation then transfers to block 14 where the mobile station receives a Broadcast Channel (BCH) signal and knows from that channel, along with other information, some common control channel number used by the communication system, in block 14. The mobile station scrambles the common channel number to determine the code channel on which it should use to receive pages.

Returning to block 10, if the mobile station decides to use a single channel system because of a limitation in the mobile station's capabilities or other choices with respect to its service needs, operation transfers to block 16. In block 16, the mobile station initiates its RF hardware for single carrier reception. Operation then transfers to block 18 where the mobile station receives a general page message on a predetermined code channel in block 18. The general paging message will specify the paging channel number used by the system. The mobile station shuffles the paging channel number used to determine the code channel that it will use to receive pages directly from the serving base station.

Fig. 4 introduces elements and terminology of a very simple wireless communication system. The base station 30 transmits a forward link signal 32 to the mobile station 40. The mobile station 40 transmits a reverse link signal to the base station 30.

Fig. 5 is a simplified block diagram illustrating the base station 30 as an exemplary embodiment of a multi-carrier CDMA transmission system having 3 forward link channels. Each transmit subsystem 48 transmits a portion of the forward link signal 32 on a different carrier frequency. The transmit subsystem 48a is at frequency f₁Up-transmits a portion of the forward link signal 32; the transmitting subsystem 48b is at frequency f₂Up-transmits a portion of the forward link signal 32; the transmit subsystem 48c is at frequency f₃Which transmits a portion of the forward link signal 32.

The data transmitted on the forward link signal 32 is provided to a demultiplexer 50. The demultiplexer 50 provides the data to one of the 3 transmit subsystems 48. The present invention IS described in terms of a 3-carrier multi-carrier communication system because each IS-95 carrier, which occupies 1.2288MHz, may be adapted to a bandwidth of 5 MHz. However, those skilled in the art will appreciate that the teachings of the present invention can be readily extended to any number of channels in a multi-carrier system.

The multiplexed data stream is provided to a modulator 52. In an exemplary embodiment, modulator 52 modulates the forward link data according to a CDMA modulation format, such as described in the IS-95 standard and in the aforementioned U.S. patent No. 5,103,459. The forward link data includes dedicated channel data for provision to a given mobile station; and broadcast channel data provided to all mobile stations in the coverage area of the base station 30 or a subset 40 of the mobile stations in the coverage area of the base station 30. The sync channel message is an example of broadcast data transmitted to all mobile stations in the coverage area of the base station 30. In the present invention, a synchronization channel message is provided to designate one of the transmit subsystems 48 for transmission on a designated one of the 3 carriers.

The forward link data modulated by modulator 52 is provided to an upconverter 54. An upconverter 54 upconverts the modulated signal to a carrier frequency (f) generated by a local oscillator (not shown)₁、f₂Or f₃). The upconverted signals are then combined for transmission through an antenna 56.

Fig. 6 illustrates an example embodiment of a modulator 52 that modulates a portion of the forward link signal transmitted on multiple carriers of forward link signal 32. In an example embodiment, a pilot signal is transmitted to allow coherent demodulation of a signal by a receiver, improving the performance of the receiver by providing a phase reference for demodulation. A set of pilot symbols known to both the base station 30 and the mobile station 40 are provided to a walsh spreader 60. Walsh spreader 60 passes walsh sequence W_pilotThe pilot symbols are spread. In an exemplary embodiment, walsh sequences are used to distinguish the channels of data transmitted on a single CDMA carrier. The walsh function may be a fixed number of symbols as described in the IS-95 specification; or may be an Orthogonal function of varying length depending on the data Rate to be transmitted over the channel as suggested in cdma2000 and described in U.S. patent No. 5,751,761 entitled system and Method for Orthogonal Spread Spectrum Sequence Generation in variable data Rate Systems, entitled "system and Method for Orthogonal Spread Spectrum Sequence Generation in variable data rates Systems," which is assigned to the assignee of the present invention and is hereby incorporated by reference.

The walsh spread pilot symbols are provided to a complex PN spreader 62. The complex PN spreader 62 is based on two separately generated Pseudo Noise (PN) sequences PN_IAnd PN_QThe pilot symbols are spread. If the two inputs of the complex PN spreader 62 are designated I and Q, the result of the complex spreading operation is two channels I 'and Q' given by the equation:

I’＝PN_II-PN_QQ (1)

Q’＝PN_QI+PN_IQ (2)

the purpose of the complex PN spreading is to distribute the load more evenly over the in-phase and quadrature channels of the QPSK modulator, with the result that the peak-to-average ratio on the power amplifier (not shown) of the base station 30 is reduced, which in turn increases the capacity of the base station 30. The complex PN spreading is described in the CDMA2000 RTT proposal and is described in detail in pending U.S. patent application No. 08/886,604 entitled High Data Rate CDMA wireless communication System, which is assigned to the assignee of the present invention and is incorporated herein by reference. The complex PN spread pilot symbols are provided to a transmitter (TMTR)94, which upconverts, filters, and amplifies the signal for transmission through the antenna 56.

In the exemplary embodiment, the sequence W is spread by a unique orthogonal spreading_syncSpreading to distinguish the sync channel message from other channels of information. In the preferred embodiment of the present invention, the synchronization channel message is sent only through a selected one of the modulators 48a, 48b or 48 c. The selected modulator 48 transmits the synchronization channel message on the preferred channel. In an example embodiment, the synchronization channel message indicates a center frequency of the multi-carrier system in the current frequency band, if one exists; and the frequency of the single carrier system in the current frequency band, if there is one.

The sync channel message is provided to the message formatter 64. In an example embodiment, the message formatter 64 generates one set of Cyclic Redundancy Check (CRC) bits and an optional set of tail bits and adds these bits to the synchronization channel message. The IS-95 system does not add tail bits to the sync channel message. cdma2000 (also known as IS-2000) systems add 8 tail bits to the sync channel message. The sync channel message with the CRC bits and tail bits added is provided to an encoder 66. Encoder 66 encodes the sync channel message, CRC bits, and tail bits in accordance with a predetermined forward error correction coding algorithm, such as convolutional coding.

The encoded symbols are then provided to an Interleaver (INT)68, which reorders the encoded symbols according to a predetermined interleaving format. An interleaver is provided to provide time diversity in the transmitted stream of encoded symbols. The decoder has better error correction performance when the error in the received stream is not a burst error.

The reordered symbols are provided to a walsh spreader 70, which is based on a predetermined code sequence W_syncSpreading the reordered symbols. In an example embodiment, W_syncIs a code sequence that is orthogonal to all other code sequences used to channelize the channel of forward link signal 32. The walsh spread signal is then provided to a complex PN spreader 62 and spread as described above.

The common channel message is transmitted to all subscriber stations or groups of subscriber stations within the coverage area of the base station 30. Examples of common channel messages include: a paging message that alerts the mobile station of an incoming signal; and control channel messages that provide the necessary control information to mobile stations within the coverage area of the base station 30. For illustrative purposes, only a single control channel is shown. Those skilled in the art will appreciate that in actual implementations, the base station 30 will transmit multiple control channels.

The common channel message is provided to a message formatter 74. In an example embodiment, the message formatter 74 generates a group of Cyclic Redundancy Check (CRC) bits and a group of tail bits and adds these bits to the common channel message. The common channel message with the CRC bits and tail bits added is provided to an encoder 76. Encoder 76 encodes the common channel message, CRC bits, and tail bits in accordance with a predetermined forward error correction coding algorithm, such as convolutional coding.

The encoded symbols are then provided to an Interleaver (INT)78, which reorders the encoded symbols according to a predetermined interleaving format. An interleaver is provided to provide time diversity in the transmitted stream of encoded symbols. The decoder has better error correction performance when the error in the received stream is not a burst error.

Warp weighing deviceThe newly ordered symbols are provided to a walsh spreader 82, which operates according to a predetermined code sequence W_ccSpreading the reordered symbols. In an example embodiment, W_ccIs a code sequence that is orthogonal to all other code sequences used to channelize the channel of forward link signal 32. The walsh spread signal is then provided to a complex PN spreader 62 and spread as described above.

The dedicated channel message is transmitted to a specific subscriber station within the coverage area of the base station 30. The dedicated channel message is provided to the message formatter 84. In an example embodiment, the message formatter 84 generates a group of Cyclic Redundancy Check (CRC) bits and a group of tail bits and adds these bits to the frame of dedicated channel data. The frame of dedicated channel data with the CRC bits and tail bits added thereto is provided to the encoder 86. Encoder 86 encodes the frame of dedicated channel data, the CRC bits, and the tail bits according to a predetermined forward error correction coding algorithm, such as turbo coding or convolutional coding.

The encoded symbols are then provided to an Interleaver (INT)88, which reorders the encoded symbols according to a predetermined interleaving format. An interleaver is provided to provide time diversity in the transmitted stream of encoded symbols. The decoder has better error correction performance when the error in the received stream is not a burst error.

The reordered symbols are provided to a walsh spreader 90, which is based on a predetermined code sequence W_TSpreading the reordered symbols. In an example embodiment, W_TIs a code sequence that is orthogonal to all other code sequences used to channelize the channel of forward link signal 32. The walsh spread signal is then provided to a complex PN spreader 62 and spread as described above.

The complex PN spread pilot symbols are provided to a transmitter (TMTR)94, which upconverts, filters, and amplifies the signal for transmission through the antenna 56.

Turning to fig. 7, a simplified multicarrier receiver provided in an exemplary embodiment in a mobile station 40 is illustrated. In the exemplary embodiment, mobile station 40 is capable of receiving forward link signals 32 transmitted on up to 3 carrier channels simultaneously. Those skilled in the art will appreciate that the present invention may be extended to multicarrier reception for any number of channels. The received signal is provided to each receive subsystem 105, which downconverts and demodulates a different component of the forward link signal 32 based on a unique carrier frequency.

The forward link signal 32 is received at an antenna 100 and provided to a receiver 102. Each receiver 102a, 102b, and 102c is based on a different frequency f₁、f₂Or f₃The received signal is down-converted, filtered and amplified. The downconverted signal is provided to demodulator 104. In an example embodiment, demodulator 104 demodulates each downconverted signal in accordance with a Code Division Multiple Access (CDMA) modulation format. The implementation of the demodulator 104 is described in detail in the above-mentioned U.S. Pat. No. 5,103,459. The demodulated components of the forward link signal 32 are provided to a Multiplexer (MUX)106, which reassembles the transmit data streams.

In the present invention, the mobile station 40 initially uses only a single receiver 102 and demodulator 104 to demodulate the synchronization channel. The mobile station 40 tunes the selected receiver 102 to a predetermined channel (300c, 300f or 300i) and attempts to acquire a pilot signal at the predetermined channel frequency using a corresponding one of the demodulators 104. If sufficient correlation energy is detected, the acquisition is declared successful. The mobile station then down-converts, demodulates, deinterleaves, and decodes the synchronization channel message, still at only a single frequency. The mobile station 40 determines the center frequency of the multi-carrier system in the current frequency band, if one exists, from the synchronization channel message; and the frequency of the single carrier system in the current frequency band, if there is one.

The mobile station 40 decides whether it will operate in a multi-carrier mode or a single-carrier mode. If the mobile station 40 decides to operate in the multi-carrier mode, the mobile station 40 activates the RF circuitry plus receiver 102, tunes to the appropriate frequency group indicated in the synchronization channel message, and begins receiving forward link signals on multiple carrier frequencies. If the mobile station 40 decides to operate in single carrier mode, the mobile station 40 activates the RF circuitry plus receiver 102, tunes to the appropriate frequency indicated in the synchronization channel message, and begins receiving the forward link signal over the single carrier frequency band.

Fig. 8 shows an apparatus for receiving a forward link signal 32 in an example embodiment of a CDMA communication system. Initially, the mobile station 40 must tune to the preferred channel and attempt to acquire the pilot signal for that channel in the following manner.

The forward link signal 32 is received at an antenna 100 and provided to a receiver 102. Receiver 102 tunes to the preferred channel frequency and downconverts, filters, and amplifies the received signal. In the exemplary embodiment, receiver 102 is a four phase shift keyed receiver and outputs in-phase (I) and quadrature (Q) components of the received signal.

The two components of the received signal are provided to a complex PN despreader 112. The complex PN despreader 112 operates on the basis of two pseudo noise sequences PN_IAnd PN_QThe received signal is despread. In an example embodiment, the PN despreading is a complex PN despreading as described in detail in the above-mentioned U.S. patent application No. 08/886,604. In the exemplary embodiment, a generator polynomial (generator polynomial) common to all base stations 30 is used to generate the PN sequence used to spread forward link signal 32. The spreading from the base station can be distinguished from each other by the offset of the sequence.

Control processor 128 provides the offset hypotheses to complex PN despreader 112. Complex PN despreader 112 bases on the PN offset hypothesis and W provided by control processor 128_pilotThe received signal is despread. The received signal is despread based on the PN offset hypothesis and the resulting signal is provided to the pilot filter 114. The pilot filter 114 is based on the orthogonal sequence W_pilotThe signal from complex PN despreader 112 is despread and the result of complex PN despreader 112 is low pass filtered. In an exemplary embodiment, a walsh sequence comprising all 1 s is used to guide the pilot signal.

The resulting signal from the pilot filter 114 is provided to an energy detector 118 which sums the squares of the resulting samples from the pilot filter 114 to provide a received pilot energy value. The received pilot energy value is provided to the control processor 128 where it is compared to a predetermined threshold value. If the calculated energy exceeds the threshold, successful acquisition is declared and the mobile station begins receiving the synchronization channel message. If the energy falls below the threshold value, acquisition is declared unsuccessful and control processor 128 provides the next PN hypothesis to complex PN despreader 112. A Method And Apparatus For searching For PN offset In a CDMA Communication System is described In detail In U.S. patent No. 5,644,591 entitled Method And Apparatus For Performing search acquisition In a CDMA Communication System, which is assigned to the assignee of the present invention And incorporated herein by reference. Assuming that the received pilot energy cannot exceed the threshold after exhausting the possible PN offsets, the control processor sends a message to the receiver 102 to begin downconverting the received signal on a different preferred frequency channel.

Upon successful acquisition of the pilot channel at the preferred channel frequency, the mobile station 40 demodulates and decodes the synchronization channel message. The signal received from the receiver 102 is despread using the PN offset determined in the pilot search algorithm. The pilot filter 114 processes the pilot signal as described above.

The PN despread signal is also provided to walsh despreader 116. A walsh despreader 116 based on the walsh code sequence W_chanThe received signal is despread. When demodulating the synchronization channel, W_chanIs the walsh sequence assigned to transmit the synchronization channel message. The walsh despreader 116 is based on the orthogonal sequence W_chanThe signal components are despread and the result is provided to the dot product circuit 120.

The unknown phase component is introduced into the received signal as the forward link signal 32 traverses the propagation path to the mobile station 40. The dot product circuit 120 computes the projection of the received signal on the received pilot signal and provides a calibration result without phase errors. The implementation of a Dot product circuit for coherent demodulation is described in detail in U.S. patent No. 5,506,865, entitled Pilot Carrier Dot product circuit (Pilot), which is assigned to the assignee of the present invention and is incorporated herein by reference.

The scaled output from the dot product circuit 120 is provided to a multiplexer 122 which combines the two received streams into a signal data stream. The data stream is provided from the multiplexer 122 to a deinterleaver 124 that reorders the received symbols according to a predetermined deinterleaving format. The reordered symbols are provided to a decoder 126, which decodes the symbols of the synchronization channel message to provide a received synchronization channel message.

The received synchronization channel message is provided to the control processor 128. In the present invention, control processor 128 determines the channel frequency of the original overhead channel of the single carrier system from the synchronization channel message; or to determine the center frequency of the multi-carrier system. The control processor 128 initiates the correct number of receiving subsystems 105 based on the sync channel message and tunes them to the appropriate channel to receive the forward link signal 32.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (39)

1. A multi-frequency channel base station operating within a predetermined set of frequency channels, wherein data components of forward link data are simultaneously transmitted on a plurality of frequency bands, each frequency band representing a frequency channel and having a carrier frequency, said base station comprising:

means for transmitting a synchronization channel message on a single frequency channel within a predetermined set of frequency channels, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single channel system,

wherein the center frequency channel is used for receiving signals by a device receiving a synchronization channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; and

means for transmitting the remaining components of said forward link data on another frequency channel of a predetermined set of frequency channels.

2. The base station of claim 1 wherein said synchronization channel message is transmitted on a preferred frequency channel in a preferred frequency channel set, wherein the number of channels is less than the number of channels in said predetermined frequency channel set.

3. The base station of claim 2, wherein the predetermined set of frequency channels is a set of frequency channels in a personal communication system block of frequency channels.

4. The base station of claim 3 wherein the channel numbers of the preferred frequency channel group are 75, 150 and 225.

5. The base station of claim 1,

the device for transmitting the synchronous channel message on a single frequency channel in the preset frequency channel group is a first transmitting subsystem; while

Said means for transmitting the remaining components of said forward link data on another frequency channel of a predetermined set of frequency channels is at least one additional transmit subsystem.

6. The base station of claim 5, wherein the synchronization channel message indicates frequency channels of a single channel system in the predetermined set of frequency channels.

7. The base station of claim 5 wherein said synchronization channel message is transmitted on a preferred frequency channel in a preferred frequency channel set, wherein the number of channels is less than the number of channels in said predetermined frequency channel set.

8. The base station of claim 7, wherein the predetermined set of frequency channels is a set of frequency channels in a personal communication system block of frequency channels.

9. The base station of claim 8 wherein the channel numbers of the preferred frequency channel group are 75, 150 and 225.

10. A multi-frequency channel mobile station, comprising:

control means for controlling operation of the plurality of receiver subsystems in accordance with frequency information indicated in a received synchronization channel message, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single-channel system,

wherein the center frequency channel is for receiving signals and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel;

receiving means in said plurality of receiver subsystems for receiving said synchronization channel message on a single frequency channel and providing said synchronization channel message to said means for controlling and for receiving a first portion of a multi-channel signal; and

receiving means in said plurality of receiver subsystems for receiving additional portions of said multi-channel signal on another frequency channel.

11. The mobile station of claim 10,

the control device is a control processor;

the receiving means for receiving the synchronization channel message on a single frequency channel is a first receiver subsystem; while

Said receiving means for receiving an additional portion of said multi-channel signal on another frequency channel is at least one additional receiver subsystem.

12. The mobile station of claim 11, wherein said control means determines whether to operate in a single frequency channel mode or a multi-frequency channel mode; directing the first receiver subsystem to a frequency channel indicated in the synchronization channel message for single frequency channel signal reception when the mobile station decides to operate in single frequency channel mode; directing the at least one additional receiver subsystem to tune to at least one additional frequency channel when the mobile station decides to operate in a multi-frequency channel mode.

13. The mobile station of claim 11 wherein said control means directs said first receiver subsystem to tune to one of said predetermined set of preferred frequency channels.

14. The mobile station of claim 10 wherein said mobile station is operating in a personal communications system, PCS, set of frequency channels, wherein said predetermined set of preferred frequency channels includes frequency channel numbers 75, 150 and 225.

15. The mobile station of claim 11, wherein said control processor determines whether to operate in a single frequency channel mode or a multi-frequency channel mode; directing the first receiver subsystem to tune to a frequency channel indicated in the synchronization channel message for single channel system reception when the mobile station decides to operate in single frequency channel mode; directing the at least one additional receiver subsystem to tune to at least one additional frequency channel when the mobile station decides to operate in a multi-frequency channel mode.

16. The mobile station of claim 11 wherein said control processor directs said first receiver subsystem to tune to a frequency channel of a predetermined set of preferred frequency channels.

17. The mobile station of claim 11 wherein said mobile station is operating in a personal communications system, PCS, set of frequency channels, wherein said predetermined set of preferred frequency channels includes frequency channel numbers 75, 150 and 225.

18. A method of transmitting a data component of forward link data in a communication system, comprising:

transmitting a synchronization channel message on a single frequency channel within a predetermined set of frequency channels, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single channel system,

wherein the center frequency channel is used for receiving signals by a device receiving a synchronization channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel; and

the remaining components of the forward link data are transmitted on another frequency channel of a predetermined set of frequency channels.

19. The method of claim 18, wherein the synchronization channel message is transmitted on a preferred frequency channel in a preferred frequency channel set, wherein the number of channels is less than the number of channels in the predetermined frequency channel set.

20. The method of claim 19, wherein the predetermined set of frequency channels is a set of frequency channels in a personal communication system block of frequency channels.

21. The method of claim 20, wherein the channel numbers of the preferred frequency channel group are 75, 150 and 225.

22. A method of receiving a data component of forward link data in a communication system, comprising:

receiving a synchronization channel message and a first portion of a multi-channel signal on a single frequency channel, wherein the synchronization channel message indicates one of a center frequency channel of a multi-channel system and a single channel system,

wherein the center frequency channel is for receiving signals and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the center frequency channel;

controlling operation of a plurality of receiver subsystems in accordance with frequency information indicated in the received synchronization channel message; and

additional portions of the multi-channel signal on another frequency channel are received.

23. The method of claim 22, further comprising deciding whether to operate in a single frequency channel mode or a multi-frequency channel mode; tuning to a frequency channel indicated in the synchronization channel message for single frequency channel signal reception when a decision is made to operate in single frequency channel mode; when it is decided to operate in a multi-frequency channel mode, at least one additional frequency channel is tuned.

24. An apparatus operable in at least one of a single carrier system and a multi-carrier system, comprising:

a multiplexer that multiplexes the forward link signal into a forward link data stream containing broadcast channel data including a synchronization channel message;

a first transmit subsystem, coupled to the demultiplexer, that transmits a first portion of the forward link data stream on a first carrier frequency;

a second transmit subsystem, coupled to the multiplexer, that transmits a second portion of the forward link data stream on a second carrier frequency; and

a third transmit subsystem, coupled to the multiplexer, that transmits a third portion of the forward link data stream on a third carrier frequency,

wherein the synchronization channel message is transmitted on a preferred channel through a selected one of first, second and third transmission subsystems for transmission on a selected one of the first, second and third carrier frequencies, and

wherein the preferred channel is for receiving signals by a device receiving the synchronization channel message and is one of a set of preferred frequency channels corresponding to a plurality of frequency bands arranged such that any combination of three adjacent frequency bands includes the preferred channel.

25. The apparatus of claim 24, wherein the first transmission subsystem comprises:

a first modulator that modulates the forward link data signal; and

a first upconverter receives the modulated forward link data signal from the first modulator and upconverts the modulated forward link data signal with the first carrier frequency to generate a first portion of the forward link data stream at the first carrier frequency.

26. The apparatus of claim 25, wherein the second transmit subsystem comprises:

a second modulator that modulates the forward link data signal; and

a second upconverter receiving the modulated forward link data signal from the second modulator and upconverting the modulated forward link data signal with the second carrier frequency to generate a second portion of the forward link data stream at the second carrier frequency.

27. The apparatus of claim 26, wherein the third transmit subsystem comprises:

a third modulator that modulates the forward link data signal; and

a third upconverter that receives the modulated forward link data signal from the third modulator and upconverts the modulated forward link data signal with the third carrier frequency to generate a third portion of the forward link data stream at the third carrier frequency.

28. The apparatus as defined in claim 27, wherein the forward link data flow further comprises:

a stream of pilot symbols;

dedicated channel data specifying the mobile station; and

a common channel message.

29. The apparatus of claim 28 wherein said common channel message comprises a plurality of common channel messages transmitted to at least one group of subscriber stations within a coverage area of said apparatus.

30. The apparatus of claim 24, wherein the channel number of the preferred channel is at least one of 75, 150, and 225.

31. The apparatus of claim 24, wherein the synchronization channel message is distinguished from other channel information by spreading by a unique first predetermined code sequence.

32. The apparatus of claim 30, wherein the synchronization channel message is transmitted through only a selected one of the first, second and third modulators.

33. The apparatus of claim 32, wherein the multi-carrier system comprises a plurality of frequency bands arranged such that any combination of three adjacent frequency bands comprises a preferred channel, wherein if a center frequency of the multi-carrier system exists in a current frequency band, the center frequency of the multi-carrier system in the current frequency band is indicated by the synchronization channel message.

34. The apparatus of claim 33, wherein a frequency of a single carrier system is indicated by the synchronization channel message if the frequency exists in a current band group.

35. The apparatus as claimed in claim 28, wherein said first modulator for modulating a forward link data signal comprises:

a first walsh spreader receives the pilot symbol stream and spreads the pilot symbol stream using a walsh sequence.

36. The apparatus as recited in claim 35 wherein said first modulator for modulating a forward link data signal further comprises:

a first message formatter that receives the synchronization channel message and generates a first set of cyclic redundancy check, CRC, bits and adds the first set of CRC bits to the synchronization channel message to generate a formatted synchronization channel message;

a first encoder for encoding said formatted synchronization channel message using a first predetermined forward error correction coding algorithm and generating first encoded symbols;

a first interleaver that interleaves the first encoded symbols with a first predetermined interleaving format to produce first reordered symbols; and

a second walsh spreader receives the first reordered symbols and spreads the first reordered symbols according to a first predetermined code sequence to generate a first walsh spread signal.

37. The apparatus as claimed in claim 36, wherein said second modulator for modulating a forward link data signal comprises:

a second message formatter that receives the common channel message and generates a second set of cyclic redundancy check, CRC, bits and adds the second set of CRC bits to the common channel message to generate a formatted common channel message;

a second encoder for encoding said formatted common channel message using a second predetermined forward error correction coding algorithm and generating second encoded symbols;

a second interleaver that interleaves said second encoded symbols with a second predetermined interleaving format to produce second reordered symbols; and

a third walsh spreader receives the second reordered symbols and spreads the second reordered symbols according to a second predetermined code sequence to generate a second walsh spread signal.

38. The apparatus as claimed in claim 37, wherein said third modulator for modulating a forward link data signal comprises:

a third message formatter receiving the dedicated channel data and generating a third set of Cyclic Redundancy Check (CRC) bits, and adding the third set of CRC bits to the dedicated channel data to generate a frame of dedicated channel data;

a third encoder for encoding the dedicated channel data frame using a third predetermined forward error correction coding algorithm and generating third encoded symbols;

a third interleaver that interleaves the third encoded symbols with a third predetermined interleaving format to generate third reordered symbols; and

a fourth walsh spreader receiving said third reordered symbols and spreading said third reordered symbols according to a third predetermined code sequence to generate a third walsh spread signal.

39. The apparatus of claim 38, further comprising:

a complex PN despreader for despreading said walsh-spread pilot symbol stream, first walsh-spread signal, second walsh-spread signal, and third walsh-spread signal with two separately generated pseudonoise PN sequences to produce complex PN-spread data; and

and the transmitter is used for receiving the complex PN spreading data and carrying out up-conversion, filtering and amplification on the complex PN spreading data.