MXPA06006018A - Code channel management in a wireless communications system - Google Patents

Abstract

Systems and techniques are disclosed relating to communications. The systems and techniques involve separating a plurality of subscriber stations into first and second groups, a different first code from a plurality of orthogonal codes to each of the subscriber stations in the first group, assigning each of the subscriber stations in the first group either its allocated first code or a first sub-code derived from its allocated first code, to support a dedicated channel, and assigning a second sub-code derived from one of the first codes to support a communications channel to one of the subscriber stations in the second group. A second code may be used to support a dedicated channel to the second subscriber station.

Description

HANDLING OF CODE CHANNELS IN A WIRELESS COMMUNICATION SYSTEM Field of the Invention The present invention relates generally to communications, and more specifically, to systems and techniques for handling assignments of code channels in a wireless communication system.

BACKGROUND OF THE INVENTION Modern communication systems are designed to allow multiple users to share a common means of communication. Such a communication system is a Multiple Division Code Access (CDMA) system. The CDMA communication system is a modulation and multiple access scheme based on propagated spectrum communications. In a CDMA communication system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different code that modulates a carrier, and therefore propagates the signal over the entire spectrum. The transmitted signals can be separated in the receiver by a correlator using a corresponding code to disprogate the desired signal. Unwanted signals, whose codes do not match, contribute only to noise. In propagated spectrum communications, the fixed base stations are generally dispersed through an access network to support wireless communications with various user devices. The access network can be divided into regions known as cells with a base station serving each cell. In applications with high traffic content, the cell can be further divided into sectors with a base station serving each sector. In this configuration, the base station can allocate one or more dedicated channels using alsh codes to each user within their cellular region to support voice and data communications over a non-return link transmission. A non-return link transmission refers to a transmission from the base station to a user and a return link transmission refers to a transmission from the user to the base station. One or more shared channels can also be used by the base station with its own distinct Walsh code. Additional Walsh code assignments can be reserved for various signaling and system support functions. There is a limited number of Walsh codes available for any given base station, and thus the number of channels, which include dedicated and shared channels, is limited to a given code space. In past CDMA systems, the capacity of the non-return link was limited only by mutual interference between multiple users, and therefore, the code space was sufficient for the number of channels it could support. However, recent advances in technology have reduced the effects of interference, allowing additional simultaneous users, and thus the increasing demand for more codes to support additional channels. In addition, with the tremendous increase in wireless communications over the past few years, there has always been a growing demand for higher data rate services to support web browsing, video applications, and the like. This demand is often satisfied by using multiple dedicated channels to carry data from the base station to the user with each channel having a different Walsh code. In some cases, high data rate services can be supported by Walsh variable propagation. The Walsh variable propagation requires the use of shorter length Walsh codes for higher data rate transmissions. Using a Walsh code of shorter length, however, avoids using all the longer codes of the chip model of the shorter code, thus exhausting the multiple Walsh codes. The increased demand for codes, reduced available codes, or a combination of the two could result in an insufficient number of Walsh codes to channel the non-return link. Thus, the capacity of the system may be limited in situations where, due to advances in interference mitigation, otherwise additional users and / or increased data throughput may be available. Accordingly, there is a need in the art for an efficient methodology for handling code assignments.

BRIEF DESCRIPTION OF THE DRAWINGS Aspects of the present invention are illustrated by way of example, and not by way of limitation, in the accompanying drawings, wherein: Figure 1 is a conceptual block diagram of a modality of the communication system of CDMA; Figure 2 is a conceptual diagram illustrating the creation of orthogonal codes; Figure 3 is a conceptual diagram illustrating a hierarchical tree structure used to model a Walsh code that has a length of 64; Figure 4 is a conceptual diagram illustrating a hierarchical tree structure used to illustrate an example of Walsh code assignments for a subscriber station in temporary transfer; Figure 5 is a conceptual diagram illustrating a hierarchical tree structure used to illustrate an example of Walsh code assignments for a subscriber station with good geometry for a service base station; Figure 6 is a simplified functional block diagram illustrating one embodiment of several subsystems for a CDMA communication system; Figure 7 is a flow chart illustrating a mode of a processor algorithm used to assign Walsh codes in a CDMA communication system; and Figure 8 is a flow diagram illustrating an alternative embodiment of a processor algorithm used to assign Walsh codes in a Walsh communication system.

DETAILED DESCRIPTION The detailed description set forth in the following with the accompanying drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention can be practiced. Each mode described in this description is provided only as an example or illustration of the present invention, and should not necessarily be taken as preferred or advantageous over other modalities. The detailed description includes specific details for the purpose of providing a complete understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without these specific details. In some cases, well-known structures and devices are shown in block diagram form so as to avoid obscuring the concepts of the present invention. Acronyms and other descriptive terminology may be used only for convenience and clearly not intended to limit the scope of the invention. In the following description, various systems and techniques will be described in the context of a CDMA communication system that uses Walsh codes to channel the non-return link. While these techniques may be well suited for use in this type of application, those skilled in the art will readily appreciate that these systems and techniques can be applied to any propagated spectrum communication environment. Accordingly, any reference to a Walsh code management methodology in a CDMA communication system is only intended to illustrate various inventive aspects of the present invention, with the understanding that these inventive aspects have a wide range of applications. Figure 1 is a conceptual block diagram of a modality of a CDMA communication system. An access network 102 can be used to support wireless communications, with multiple user devices 104a-104c. The access network 102 may also connect to additional networks external to the access network, such as the Internet, corporate intranet, a Public Switched Telephone Network (PSTN), or the like. The user device 104, commonly referred to as a subscriber station, can be any type of device that can communicate with the access network 102 including a mobile telephone, a computer, a modem, a personal digital assistant, or any other similar device . The access network 102 is shown with a Base Station Controller (BSC) 106 which supports several base stations 108a-108c dispersed throughout a geographic region. The geographic region can be subdivided into smaller regions known as cells with a base station serving each cell. In high traffic content applications, the cell can be further divided into sectors with a base station serving each sector. Although not shown in Figure 1, the access network 102 may employ numerous BSCs each supporting any number of base stations to extend the geographic range of the access network 102. The BSC 106 can be used to coordinate the activities of multiple base stations, as well as provide an interconnection to the networks external to the access network 102. In CDMA communication systems, Walsh codes are commonly used to separate multiple subscriber stations in communication with a base station. Each subscriber station can be assigned a different Walsh code during call set-up to support non-return link communications over a dedicated traffic channel. The Walsh code can be of any length depending on the particular application and the general design restrictions. A short Walsh code reduces the processing time while a long Walsh code increases the code gain. The length of the Walsh code also has an impact on the capacity of the system. There are as many Walsh codes as there is code length. Thus, if a Walsh code length of 64 is used, which is very common in today's CDMA communication systems, then there are only 64 Walsh codes available. This limits the number of channels available in the non-return link. Traditionally, the length of the Walsh code has been selected to accommodate the data rate of the non-return link communications. In variable data rate systems, the length of the Walsh code can be selected to accommodate the maximum proportion of data. This procedure, however, can result in resources of Walsh codes that are not used much for lower data rates. A sufficient methodology for assigning Walsh codes in a variable data rate system can be used to reduce or eliminate the minimum use potential of the Walsh code space for low data rates. A CDMA communication system that uses a variable rate speech encoder is just one example of a system that could benefit from the various systems and techniques described throughout this description to efficiently handle the Walsh code assignments. A variable rate speech encoder is typically used to reduce mutual interference between multiple users operating in the same cellular region by transmitting voice with the least amount of data to sustain acceptable speech quality. An Enhanced Variable Rate Encoder-Decoder (EVRC) is a common example. An EVRC transmits voice using frames of one eighth, one quarter, one half and the whole proportion. During periods of silence, frames of an eighth of proportion can be transmitted. The power required to transmit frames of an octave of proportion, and in this way the interference presented in the cellular region, is lower than when transmitting frames of greater proportion. During periods of active conversation, a variety of frames of higher proportion can be transmitted. As it increases, on average, one-eighth-ratio and full-proportion frames are predominantly used, and less than one-quarter and one-half proportion frames are frequently used. A Selective Mode Voice Signal Encoder (SMV) is another example of a vocal signal encoder. The SMV makes more efficient use of half-proportion frames (ie, one-quarter and one-half proportions), thereby reducing the frequency of full-ratio frames. The result is that the average ratio of an SMV can be less than the average proportion of an EVRC. From an interference point of view, capacity can be improved.

As more efficient speech encoders become standard technology, further improvements in system capacity can be realized through reduced energy use by lowering the average voice rate. Still, with today's technology, these speech encoders use completely the same amount of resources in terms of Walsh code space because their required peak rate remains unchanged. To more efficiently use the Walsh code space, various systems and techniques will be described to handle the Walsh code assignments in a way that takes into account the data rate of the non-return link communications. Although these systems and techniques will be described in the context of a variable rate speech encoder, those skilled in the art will readily be able to apply these principles to any variable rate data scheme. Furthermore, these systems and techniques are not limited to handling the Walsh code assignments in the non-return link, but they can be applied to any type of code assignments in either the non-return or return link. Before describing the various systems and techniques for handling Walsh code assignments, it is useful to briefly discuss certain fundamental principles of Walsh codes. The Walsh codes are orthogonal codes. This means that the Walsh codes have zero cross-correlation. The zero cross correlation is obtained if the product of the two codes, added over the length of the codes, is zero. With reference to FIGURE 2, the Walsh codes can be easily generated by starting with a germ value "0", which repeats the "0" horizontally and vertically and complements the "0" diagonally, to generate two Walsh codes 202 that they have a length of two. This is often referred to as a Walsh 2x2 code. A Walsh 4x4 code 204 can then be generated by repeating the 202 Walsh code 2x2 horizontally and vertically, and complementing the 202 Walsh code 2x2 diagonally. This process can be repeated until a Walsh code that has the desired length is derived. In the case of many conventional CDMA communication systems, that may be a Walsh 64x64 code. In variable rate speech encoder applications, the Walsh code length may be selected to support a full proportion frame. The proportion of frames is a measure of the volume of information that is transmitted, typically measured in bits per second. Depending on the coding and modulation scheme, one or more symbols can be generated for each voice bit. The volume of the symbols that are transmitted is commonly referred to as the proportion of symbols and corresponds to the proportion of frames. The proportions of lower symbols can use longer Walsh codes to maintain a constant chip ratio. Accordingly, a 1/2 ratio speech frame can be propagated with a Walsh code that is twice as large as the Walsh code for a full proportion speech frame. By way of example, if a full proportion speech frame is propagated with a Walsh code having a length of 64, then a speech frame of 1/2 of proportion can be propagated with a Walsh code having a length of 128. Similarly, a 1/4 ratio voice frame can be propagated with a Walsh code having a length of 256, and a 1/8 ratio voice frame can be propagated with a Walsh code having a length of 512. The tree structure for recursively constructing Walsh codes of successfully longer lengths can be exploited to efficiently assign Walsh codes in a variable rate speech encoder environment. This concept is well understood with reference to FIGURE 3. FIGURE 3 is a hierarchical tree structure used to model a full-ratio Walsh code that has a length of 64. A Walsh code W?,, index / is located in a node in the tree structure identified by the length (L) and an index (index), which identifies one of the Walsh codes of a particular length. Any particular Walsh code is orthogonal to all other Walsh codes in the tree structure, except for those of greater length that are derived from the Walsh code and conversely, for those of shorter length from which the Walsh code is derived. . In this way, for example, four codes of Walsh W25S;? - W25s, with a length of 256 can be assigned. This means that a single Walsh code can be used to support four 1/4 proportion speech frames. Alternatively, if you assign a Walsh code that has a length of 128, w? 2?,? for example, then only two Walsh codes with a length of 256 remain available: 256.3 and 256.4-Walsh codes that are derived from the assigned Wi28 code ,? with greater lengths are not orthogonal to the Walsh W12a code ,? assigned, and therefore, can not be used to spread to other channels. Walsh codes not available include W64 / ?, W256,?, W256,2 W512 1, W512 /, w5i2,3 / and W5i2, - Thus, in this second example with Walsh code? 28 ,? being assigned, the remaining possible Walsh code assignments include a number of possibilities that are given in Table 1 below.

TABLE 1 The use of longer Walsh codes to support lower proportion speech frames tends to increase the user's capacity for a given Walsh code space. The increase in capacity will be determined by the average frame ratio of the subscriber stations that operate within the cellular region of the base station. By way of example, if the average frame ratio is equal to 1/2, the base station will be able to support, on average, 128 subscriber stations with a Walsh code 64x64. In reality, a number of Walsh codes may be required to support overload and signaling functions, leaving fewer Walsh codes available to support the non-return link traffic. However, the number of subscriber stations that can be supported must still be significantly greater than the number of Walsh codes. As a result, significant improvements in user capacity can be achieved through efficient management of Walsh code resources. A Walsh code management scheme can be implemented in any number of. shapes . Several examples will be presented in the following in the context of CDMA communication systems with a Walsh code of 64x64 to channel the non-return link. Probably, the clearest procedure in terms of complexity involves an arbitrary assignment of Walsh codes to each of the subscriber stations based on the proportion of speech frames. Thus, if a subscriber station is in need of a Walsh code to support a frame ratio of 1/2, all 64 full-rate Walsh codes could be searched in an arbitrary manner until a Walsh code is found. available to have a length of 128. In order to effectively handle the Walsh code assignments based on the proportion of frames of the speech encoder for each subscriber station, the Walsh codes may need to be reassigned on a frame basis per frame. The re-assignment of Walsh codes on a raster-based basis, however, tends to consume valuable resources.

By way of example, additional power of the non-return link may be required to signal the Walsh code assignments to the subscriber stations. To minimize the demand on the resources, a Walsh code management scheme can be implemented where only a portion of the subscriber stations are signaled with the Walsh code assignments on a frame-by-frame basis. Walsh code signaling on a frame-by-frame basis can be limited to those subscriber stations that have good geometry with the service base station to reduce the power overload. This can include all subscriber stations that are not actively engaged in a temporary transfer. Temporary transfer is the process of establishing communications with a new base station before breaking existing communications with the original base station. Referring again to FIGURE 1, the temporary transfer process may be initiated when the subscriber station 104a moves away from its service base station 108a along discontinuous line 110 and toward an objective base station 108b. More specifically, the temporary transfer process may be initiated by detecting, at the subscriber station 104a, an increase in the resistance of a pilot signal from the target base station 108b when the subscriber station moves away from its service base station 108a. When the pilot signal resistance reaches a threshold, the subscriber station 104a reports this information back to the BSC 106 through its service base station 108a. The target base station 108b can then be added to an active set maintained in the BSC 106. The BSC 106 can then direct the target base station 108b to establish communications with the subscriber station 104a. As a result, the subscriber station 104a can communicate with the BSC 106 through both the service and target base stations 108a and 108b. Communications from both the service and target base stations 108a and 108b may be combined in the substation station 104a to increase the processing gain. This communication mode may continue until the signal strength of the pilot signal from the service base station 108a decreases to a level which causes the BSC 106 to remove the service base station 108a from the active set and instruct the base station 108a of service to destroy communications with the subscriber station 104a. Each subscriber station coupled in temporary transfer can be assigned a full ratio Walsh code by its service base station from which all Walsh code assignments are formed from frame to frame. With reference to FIGURE 4, the assignment of Walsh codes from each base station can be fixed in the furthest to the left of the subtree rooted in the full-ratio Walsh code. By means of the example, if a frame ratio of 1/2 is transmitted, the Walsh code Wi28, a can be assigned, if a frame ratio of 1/4 is transmitted, the Walsh code W256 (1 can be assigned, and if a ratio of 1/8 frames is transmitted, the Walsh code W512, a can be assigned to each of these Walsh codes W128,?, W2S8 / 1, and W512? l can be derived by concatenating multiple copies of the code from Full-proportion Walsh W64;? Since each frame ratio has a unique Walsh code, there is no ambiguity in the subscriber station in terms of the Walsh code assignment once the frame ratio is determined. Once the Walsh code assignments have been made to those subscriber stations in temporary transfer, the remaining Walsh code space can be assigned in a timely manner to the remaining subscriber stations. By way of example, if the Walsh code 28 is assigned to a subscriber station coupled in temporary transfer ,? from its full-proportion Walsh code assigned to support a ratio of 1/2 frames, then the Walsh code wi28.2 may be available for assignment to one of the remaining subscriber stations. The Walsh W128.2 code assignment can be signaled at that subscriber station at the beginning of the frame or at some other appropriate time. In some cases, one or more of the remaining subscriber stations may require a full proportion frame. In that case, the unused Walsh space of two or more full-proportion Walsh codes can be used. This procedure provides a high degree of flexibility in Walsh code assignments, although it can significantly increase signaling overhead. In order to reduce signaling overhead without significantly compromising flexibility, the Walsh code assignments to each of the remaining subscriber stations can be restricted to a full-proportion Walsh code. The full-ratio Walsh code can be signaled at the subscriber station from the service base station on a frame-by-frame basis. A dedicated non-return link traffic channel can be assigned to each of the remaining subscriber stations to handle the overflow. A Walsh code having a length of 512, or any other length, can be used to support the dedicated non-return link traffic channel. An example of Walsh code assignments for a remaining subscriber station will now be described in conjunction with FIGURE 5. FIGURE 5 is a hierarchical tree structure used to model a full-ratio Walsh code that has a length of 64. In In the following example, the remaining subscriber station is assigned a dedicated Walsh code that has a length of 512 to support a dedicated non-return link traffic channel. The Walsh code dedicated to the subscriber station in this example is designated (W5? 2 /?) ?, where the index. { ) x means the first in the 64 Walsh codes of full proportion. The dedicated non-return link traffic channel is sufficient to carry 1/8 ratio voice frames. However, if the voice transmitted to the subscriber station requires a higher proportion of frames, unused Walsh codes of a full proportion Walsh code assigned to a subscriber station in temporary transfer may be assigned to support the traffic channels. of no return link. In this case, the full-ratio Walsh code can be signaled at the subscriber station by the service base station. The subscriber station can use blind proportion and code detection to find the Walsh code assignments. Assume that a subscriber station coupled in temporary transfer is assigned a Walsh code (W512,1) 2, where the index () 2 means the second of the 64 full-rate Walsh codes, the possible combination of assignments of Walsh codes to support the dedicated and non-return link traffic channels is given in Table 2 below.

TABLE 2 FIGURE 6 is a simplified functional block diagram illustrating a modality of several subsystems for a CDMA communication system. The BSC 106 may include many selector elements, although only one selector element 602 is shown for simplicity. A selector element is dedicated to communications with each subscriber station through one or more base stations. When a call is initiated, a call element 604 can be used to induce the base station 108 to establish a connection between the selector element 602 and the subscriber station 104. During the exchange of signaling messages, the subscriber station 104 may report back to the selector element 602 the pilot signals detected from several base stations. The selector element 602 can be used to maintain the active set for the subscriber station 104. The active set includes each base station whose pilot signal resistance exceeds a threshold. The call element 604 can be used to couple each base station in the active set to support communications between the selector element 602 and the subscriber station 104. As part of the call set-up procedures, a processor 606 in the base station 108 may be used to assign the subscriber station to one of two groups depending on the temporary transfer status of the subscriber station. The temporary transfer status of the subscriber station 104 can be assured from the active set in the BSC 106. If the active set for the subscriber station 104 includes multiple base stations, then the processor 606 can determine that the subscriber station 104 initiates will be in temporary transfer and will assign the subscriber station 104 to a group of subscriber stations in temporary transfer. If, on the other hand, the active set for the subscriber station 104 includes only one base station, then the processor 606 can determine that the subscriber station 104 initially will not be coupled in temporary transfer and will assign the subscriber station 104 to a group of subscriber stations with good geometry. The processor 606 can then re-assign the full-ratio Walsh codes to each subscriber station in the temporary transfer group. The processor 606 may also re-assign the low-proportion Walsh codes to each of the subscriber stations in the group of good geometry to support dedicated non-return link traffic channels. The base station 108 can then signal the new allocations and assignments to the various subscriber stations in its cellular region. The signaling of the new Walsh code assignments of full proportion to the subscriber stations involved in temporary transfer can add certain complexities to the Walsh code management scheme. Due to the poor geometry of these subscriber stations, the signaling power may need to be increased. Alternatively, the processor 606 can divide the subscriber stations involved in temporary transfer into multiple groups, with each group being served by common base stations. By grouping together the subscriber stations in communication with the common base stations, the signaling from the base stations can be the same, and therefore, be combined at the subscriber station to increase the processing gain. This can be achieved by a processor algorithm in each base station that makes the same assignments of logical Walsh codes to each subscriber station in the group. The allocation of physical Walsh codes from each base station can then be mapped into the logical Walsh code at the individual subscriber stations. The processor 606 can also be configured to periodically monitor and change the composition of the groups to accommodate a changing communications environment. The composition of the groups can be changed when a subscriber station served by the base station 108 enters a temporary transfer with a target base station, or a subscriber station completes a temporary transfer at the base station 108. These events can be detected by the processor 606 by monitoring the active set in the BSC 106 for each subscriber station in the cellular region of the base station. The composition of the groups can also be changed when the call processor 604 induces the base station 108 to terminate an existing call with a subscriber station. Each time the composition of the groups is changed, the processor 606 can re-assign full-ratio Walsh codes to each subscriber station in the temporary transfer group, and re-assign low-proportion Walsh codes to each subscriber station. Subscriber in the group of good geometry. Low-ratio Walsh codes can be used by the subscriber stations in the good geometry group to support the dedicated non-return link traffic channels. The base station 108 can then signal the new allocations and assignments to the various subscriber stations. The selector element 602 can also be configured to receive voice communications for the subscriber station 104 in a Pulse Code Modulation (PCM) format from the access network. The selector element 602 may include a variable rate speech signal encoder (not shown) configured to convert the PCM voice into speech frames using any known speech compression algorithm. The speech frames can be provided from the selector element 602 to the base station 108. The base station 108 may include a voice queue 608 that buffer the voice frames of the selector element 602 prior to transmission to the subscriber station 104. Voice frames can be released from queue 608 and provided to a channel element 610. The channel element 610 can be configured to determine the various frame proportions of the voice frames freed from the queue and provide this information to the processor 606. Alternatively, the speech signal encoder in the BSC 106 can be used to provide the various proportions of speech. frames to processor 606. Either way, processor 606 can use this information to assign Walsh codes on a frame-by-frame basis. The Walsh code assignments may depend on the state of the temporary transfer of the subscriber station 104. If the subscriber station 104 is coupled in temporary transfer, then the processor 606 may assign the subscriber station 104 a Walsh code from its assigned full-rate Walsh code based on the proportion of frames of each voice frame. Conversely, if the subscriber station 104 does not actively engage in temporary transfer, then the processor 606 can respond in one of two ways. Voice frames that have a frame ratio of 1/8 may not likely receive a Walsh code assignment. These voice frames can be carried in the dedicated non-return link traffic channel. Voice frames having a frame ratio of more than 1/8 may be assigned one or more Walsh codes from the Walsh space not used to support one or more supplementary non-return link traffic channels. The channel element 610 can provide various signal processing functions such as convolutional coding which includes functions of Cyclic Redundancy Check (CRC), interleaving, scrambling with a long Pseudo-random Noise (PN) code, and modulation using Modulation by Quadrature Phase Displacement (QPSK), 8-PSK, 16-QAM or any other modulation scheme known in the art. The modulated speech frames can then be propagated with Walsh codes, combined with other Walsh code channels and modulated in quadrature with short PN codes. The result of the channel element 610 can be provided to a transmitter 612 for filteringamplification and upconversion to a carrier frequency before transmission over the non-return link from the base station 108 to the subscriber station 104 via an antenna 614. The way in which the modulated speech frames in the element 610 are handled channel may depend on the state of the temporary transfer of the subscriber station 104. If the subscriber station 104 is coupled in temporary transfer, then the modulated speech frames may propagate with their respective Walsh code assignments on a frame-by-frame basis. Conversely, if the subscriber station 104 does not actively engage in temporary transfer, then the modulated speech frames can be handled in one of two ways. The channel element 610 can propagate the modulated speech frames having a ratio of 1/8 frames with a low rate Walsh code assigned to support a dedicated non-return link traffic channel. Voice frames that have higher proportions can be separated into multiple streams of data. The first data stream can be propagated with the low-rate Walsh code assigned to the dedicated non-return link traffic channel, and the remaining data streams can be propagated with the Walsh codes assigned for the non-return link traffic channels supplementary The full-ratio Walsh code from which the Walsh codes that support the supplementary non-return link traffic channels are derived can be signaled at the subscriber station 104. Alternatively, the subscriber station 104 may use blind proportion and code detection to access the supplementary non-return link traffic channels. In this embodiment, the complexity of the subscriber station 104 can be reduced by limi blind proportion and code detection to a small group of full-proportion Walsh codes. This group of full-ratio Walsh codes can be signaled in the subscriber station 104 concurrently with the low-rate Walsh code used to support the dedicated non-return link traffic channel. Full-rate Walsh code signaling to a subscriber station which is not actively engaged in temporary transfer can be achieved in any number of ways. By way of example, the full-ratio Walsh code can be signaled at the subscriber station in the dedicated non-return link traffic channel. The signaling information can be included in an extension indicator added to the payload. The length of the extension indicator will depend on the number of Walsh codes of full proportion. In the modalities described so far, the extension indicator can be 6-bits to cover 26 full-ratio Walsh codes. The extension indicator can be set to a certain predetermined value to indicate a ratio of 1/8 frames. This means that the entire payload is carried on the dedicated non-return link traffic channel, and that no supplementary non-return link traffic channels are allocated. The extension indicator can be set to some other value to indicate a higher frame ratio and identify the full-ratio Walsh code that supports the supplementary non-return link traffic channels. The channel element 610 can be configured to multiplex the payload between dedicated and supplementary non-return link traffic channels in many different ways. In the case of a full-ratio frame, the dedicated non-return link traffic channel may need to carry a portion of the payload because the supplementary non-return link traffic channels can only support a frame ratio of 7 / 8 This limitation is the result of mapping the supplementary non-return link traffic channels into the unused Walsh codes into a single full-rate Walsh code., and can be easily seen from Table 2. A subscriber station in temporary transfer will need at least one Walsh code of 1/8 proportion of its Walsh code of full proportion to support its payload, leaving only a frame ratio capacity of 7/8 for the assignment to a subscriber station with better geometry. In the case of a ratio of 1/2 or 1/4 frames, the multiplexing options may increase. Referring again to Table 2, one can easily see that the payload for a 1/2 proportion voice frame can be fully supported by a supplementary non-return link traffic channel using a Walsh code (W? 2s , 2) 2 having a length of 128. Alternatively, the payload can be multiplexed between the dedicated and supplementary non-return link channels. The same is valid for a 1/4 ratio voice frame. The payload for a 1/4 ratio voice frame can be fully supported by a supplementary non-return link using any of the following 256 Walsh codes of length (W256.2) 2 (W25S, 3) 2 O (W256.4) 2, OR can be multiplexed between the dedicated and non-return link channels.

In both scenarios, better efficiency can be achieved by confining the payload in a supplementary non-return link traffic channel, thereby freeing the dedicated non-return link traffic channel for another use. However, to effectively exploit this method, the extension indicator must be placed on a separate channel. In addition, the extension indicator channel may be able to be disabled. The extension indicator channel may also include a dedicated code indicator that indicates whether the dedicated non-return link traffic channel is enabled or disabled. The possible cases (A, B and C) are given in the following in Table 3.

TABLE 3 The possible Walsh code assignments are given in Table 4 below using the principles in FIGURE 5. The proportions of non-applicable frames are referred by N / A. TABLE 4 An alternative scheme can be implemented that tends to reduce the power consumed by the extension indicator channel. This can be achieved by assigning a full-ratio Walsh code by default to each subscriber station that has good geometry with the service base station (i.e., subscriber base stations not actively coupled in temporary transfer). The full ratio Walsh code by default can be any full proportion Walsh code, but typically it can be a full proportion Walsh code assigned to a subscriber station in temporary transfer. When the unused Walsh codes of the full-ratio Walsh code by default are sufficient to support a supplementary non-return link traffic channel, which together with the dedicated non-return link traffic channel, can handle the proportion of frames , then the extension indicator channel can be disabled. The possible cases (A, B, C, D and E) are given in the following in Table 5.

TABLE 5 The possible Walsh code assignments are given in Table 6 below using the principles of FIGURE 5. Frame proportions not applicable for each case are referenced by N / A. The index identification outside the parentheses has been modified to indicate whether the Walsh code is derived from the Walsh code of full proportion by default (.def) or extension (ext.).

TABLE 6 The processor 606 may be configured to implement any number of algorithms to perform Walsh code assignments on a frame-by-frame basis. An example of an algorithm will be described in conjunction with the Walsh code assignment scheme illustrated in Tables 5 and 6. With reference to FIGURE 7, the processor can divide the subscriber stations into three groups in step 702. The first group includes all subscriber stations coupled in temporary transfer. Each subscriber station in the first group can be assigned the full proportion Walsh code. The second group includes a portion of the subscriber stations that are not coupled in temporary transfer. Each subscriber station in the second group can be assigned the full proportion Walsh code by default. The third group includes the remaining subscriber stations that are not coupled in temporary transfer. Subscriber stations in this group do not receive a full-proportion Walsh code by default. The processor can be configured to assign the highest geometry subscriber stations in the third group. In step 704, the processor can create a remaining queue and place all the subscriber stations in the third group in the remaining queue. In step 706, the processor may assign to each subscriber station in the first group a Walsh code of its respective assigned full-rate Walsh code. In stage 708, the processor may attempt to assign to each subscriber station in the second group, with a complete frame ratio requirement, the Walsh codes of its Walsh code of full proportion by respective defect according to Case C in Table 6 Subscriber stations in the second group that require a full frame ratio not supported by their full-proportion Walsh code by default can be placed at the end of the remaining queue. In step 710, the processor may attempt to assign to each subscriber station in the second group, with a frame ratio requirement of 1/2, the Walsh codes of its Walsh code of full proportion by respective default according to Case B in Table 6. The subscriber stations in the second group that requires a ratio of 1/2 frames not supported by their Walsh code of full proportion by respective defect can be placed at the end of the remaining queue. In step 712, the processor may attempt to allocate to each subscriber station in the second group, with a frame proportion requirement of 1/4, the Walsh codes of its Walsh code of full proportion by respective default according to case B in Table 6. Subscriber stations in the second group that requires a ratio of 1/4 frames not supported by their Walsh code of full proportion by respective defect can be placed at the end of the remaining queue. The processor may then attempt to assign the Walsh codes of any Walsh code of full proportion to the subscriber stations in the remaining queue. First, in step 714, the processor may attempt to assign each subscriber station in the remaining queue, with a full frame proportion requirement, the Walsh codes of any Walsh code of full proportion according to the case E in Table 6. Then, in step 716, the processor may attempt to assign each subscriber station in the remaining queue, with a frame proportion requirement of 1/4, the Walsh codes of any full-proportion Walsh code. according to case D or E in Table 6. Finally, in step 718, the processor may attempt to assign each subscriber station in the remaining queue, with a frame proportion requirement of 1/4, the codes of Walsh of any full-ratio Walsh code according to case D or E in Table 6. Another algorithm that can be implemented by the processor to perform the Walsh code assignments on a frame basis per frame will be described in conjunction with FIGURE 8. With reference to FIGURE 8, the processor can divide the subscriber stations in its cellular region into three groups in step 802. The criteria for constructing the groups can be the same as described. previously together with FIGURE 7. In step 804, the processor can create a remaining queue, and place all the subscriber stations in the third group in the remaining queue. In step 806, the processor may assign to each subscriber station in the first group a Walsh code of its respective assigned full-rate Walsh code. In step 808, the processor may attempt to assign each subscriber station in the second group, with a complete frame ratio requirement, which Walsh codes of its Walsh code of full proportion by default according to the case C in Table 6. Subscriber stations in the second group that requires a full frame ratio not supported by their full-proportion Walsh code by default can be placed at the end of the remaining queue. In step 810, the processor may attempt to allocate to each subscriber station in the remaining queue, with a full frame proportion requirement, the Walsh codes of any full-ratio Walsh code in accordance with E in Table 6. In step 812, the processor may try to assign each subscriber station in the second group, with a frame ratio requirement of 1/2, the Walsh codes of its Walsh code of full proportion by default according to case B in the Table 6. Subscriber stations in the second group that require a ratio of 1/2 frames that may not be supported by their full-ratio Walsh code by default can be placed at the end of the remaining queue. In step 814, the processor may attempt to assign to each subscriber station in the second group, with a frame proportion requirement of 1/4, the Walsh codes of its Walsh code of full proportion by default according to the case B in Table 6. Subscriber stations in the second group that requires a ratio of 1/4 frames that could not be supported by their full-ratio Walsh code by default can be placed at the end of the remaining queue. In step 816, the processor may attempt to allocate to each subscriber station in the remaining queue, with a frame ratio requirement of 1/2, the Walsh codes of any Walsh code of full proportion according to case D or E in Table 6. In step 818, the processor may attempt to assign each subscriber station in the remaining queue, with a frame ratio requirement of 1/4, the Walsh codes of any Walsh code of proportion complete according to the case D or E in Table 6. Although the procedures for making Walsh code assignments on a frame by frame basis have been illustrated through a sequence of steps, those skilled in the art will appreciate that the order of the stages is established by means of the example only and not by means of limitation. These stages can be carried out in different orders, with some stages being carried out in parallel. In addition, one or more of these steps may be omitted or may be combined with any other techniques known in the art. In the embodiments of the CDMA communication systems described so far, the processor 606 has been located at the base station 108. However, the location of the processor 606 may ultimately depend on whether the Walsh code space handling is part of a centralized or distributed system. By way of example, a distributed system may use a processor 606 at each base station 108. In this configuration, the processor 606 for each base station 108 determines the Walsh code assignments for the subscriber stations 104 within its cellular region. Conversely, a centralized system can use a single processor 606 in the BSC 106 to coordinate the Walsh code assignments for the multiple base stations 108. As a practical matter, the processor 606 can be located at each base station to reduce the load on the reverse path interface between the BSC 106 and the base stations. However, the processor 606 can be located anywhere in the access network. For purposes of clarity, the processor 606 will reside in a communication station with the understanding that the communication station can be a base station, a BSC or any other structure within the access network that hosts the processor 606. The processor 606 it can be represented in software capable of running on a general purpose processor, a specific application processor, or in any other software execution environment. In these embodiments, any reference to the term processor shall be understood to mean software alone or software in combination with the purpose processor -general, specific application processor or software execution environment. The software may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM or any other storage means known in the art. Alternatively, the processor can be implemented in hardware or in any combination of hardware and software. By means of the example, the processor can be implemented with a specific application integrated circuit (ASIC), field programmable gate arrangement (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, any combination thereof, or any equivalent or non-equivalent structure designated to perform one or more of the functions described herein. It will be understood that any reference to the term processor to handle Walsh code assignments may encompass all possible applications described herein as well as other modalities that may be apparent to those skilled in the art. Referring again to FIGURE 6, the transmission of the non-return link from the base station 108 may be received by an antenna 616 at the subscriber station 104 and coupled to a receiver 618 for filtering, amplifying, and downconverting to a signal of baseband The baseband signal may be coupled to a demodulator 620 which provides various demodulation functions including quadrature demodulation using the short PN code, despreading to recover the speech frames and demodulation using the inverse modulation scheme employed in the base station ( that is, QPSK, 8-PSK, 16-QAM or any other known modulation scheme). A decoder 622 can be used to provide various signal processing functions in demodulated voice frames such as descrambling using the long PIN code, deinterleaving, decoding and performing a CRC check function in the decoded speech frames. A speech encoder 624 can be used to convert speech frames to PCM speech using a decompression algorithm compatible with the speech encoder in the BSC 106. The despreading function can depend on whether the subscriber stations 104 are coupled in temporary transfer. The temporary transfer status of the subscriber station may be available through the overload message. If the subscriber station 104 is coupled in temporary transfer, then it can combine the communications of the various base stations during the decoding process to increase the processing gain. Although base stations may have assigned different full-ratio Walsh codes to subscriber station 104, the blind rate and code detection may be used to de-propagate the baseband signal without increasing complexity beyond what currently exists. for the legacy equipment as long as the voice frame of each base station has the same proportion assignment. This is possible even when the proportion assignments are carried out independently as long as the proportion allocation algorithm is standardized. Assuming that the proportion of frames is the same, there is no ambiguity regarding the assignment of Walsh codes of each base station. The process of blind proportioning and code detection for a subscriber station that is not actively engaged in temporary transfer can be significantly different, and depend on the Walsh code assignment scheme used in the service base station. By way of example, the dedicated non-return link traffic channel may be demoted using the low rate Walsh code assigned to the subscriber station 104. If an extension indicator is embedded in the dedicated non-return link traffic channel, then the demodulator 620 may be able to determine whether a portion of the payload is carried by one or more of the supplementary non-return link traffic channels. . Alternatively, the demodulator 620 can access an overload channel to recover the extension indicator. If the extension indicator channel is enabled, then the demodulator 620 can obtain the full-proportion Walsh code that supports one or more of the supplementary non-return link traffic channels. The demodulator 620 may also be able to access a dedicated code indicator in the extension indicator channel to determine if the dedicated non-return link traffic channel is being used. If, on the other hand, the extension indicator is disabled, then the demodulator 620 can determine that the entire payload is carried by the dedicated non-return link traffic channel. In any case, the demodulator 620 may be able to determine the location of the payload within the confines of the Walsh code space. The depropagation function is rather trivial if the payload is confined to the dedicated non-return link traffic channel. Scrambler 620 simply uses the low rate Walsh code assigned to subscriber station 104 to extract the voice frame from the dedicated non-return link traffic channel. However, demodulator 620 can also be configured to access one or more of the supplementary non-return link traffic channels. The Walsh code of the full proportion identified from the extension indicator can be searched by the demodulator to find the appropriate Walsh codes. More specifically, demodulator 620 can perform blind proportion and code detection by despreading the baseband signal with the different Walsh codes derived from the full ratio Walsh code identified by the extension indicator. For each of these Walsh codes, the de-propagated baseband signal may be provided to the decoder 622. If the CRC check function is valid for the baseband signal, this means that a supplementary non-return link traffic channel has been provided. detected. This process continues until all Walsh codes are searched. The payload portions of each of the dedicated and non-return link traffic channels may then be combined and may be provided to the voice signal encoder 62. The various illustrative blocks, modules, algorithms and circuits described in conjunction with the embodiments described herein may be implemented or implemented with a general purpose processor, a digital signal processor (DSP), a specific application integrated circuit (ASIC), a programmable field gate (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but alternatively, the processor may be any conventional processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors together with a DSP core, or any other configuration. The methods or algorithms described in conjunction with the embodiments described herein may be represented directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM or any other form of storage means known in the art. An exemplary storage medium is attached to the processor so that the processor can read the information from and write the information to, the storage medium. Alternatively, the storage medium can be an integral part of the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside anywhere in the access network. Alternatively, the processor and the storage medium can reside anywhere as discrete components in the access network. The above description of the embodiments described is provided to enable any person skilled in the art to make or use the present invention. The 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 departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but will be in accordance with the broadest scope consistent with the principles and novel features described herein.

Claims (38)

1. 5 NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. CLAIMS 1. A communication method, characterized in that it comprises: assigning a first code to a first subscriber station; assign a first subcode derived from the first code to support a dedicated channel to the first subscriber station; assign a second code to support a dedicated channel to a second subscriber station; and assigning a second subcode derived from the first code to support a supplementary channel to the second subscriber station. The method according to claim 1, characterized in that it further comprises assigning a third subcode derived from the first code to support a second supplementary channel to the second subscriber station. The method according to claim 1, characterized in that the first subscriber station is in temporary transfer and the second subscriber station is not in temporary transfer. 4. The method according to claim 1, further comprising separating communications for the second subscriber station in the first and second portions, propagating the first portion of the communications with the second code and propagating the second portion of the communications with the second subcode. 5. The method according to claim 1, characterized in that the first subcode comprises a plurality of concatenated copies of the first code. 6. The method according to claim 1, characterized in that it also comprises signaling in the second subscriber station the first code. 7. A communication method, characterized in that it comprises: separating a plurality of subscriber stations in the first and second groups; assign a different first code of a plurality of orthogonal codes to each of the subscriber stations in the first group; assign to each of the subscriber stations in the first group either its first assigned code or a first subcode derived from its first assigned code, to support a dedicated channel; and assigning a second subcode derived from one of the first codes to support a communication channel to one of the subscriber stations in the second group. 8. The method of compliance with the claim 7, characterized in that it further comprises assigning a second code to support a dedicated channel to one of the subscriber stations in the second group, and in that the communication channel comprises a supplementary channel for supporting overflow communications not supported by the dedicated channel. 9. The method of compliance with the claim 8, characterized in that it further comprises separating communications for one of the subscriber stations in the second group in the first and second portions, propagating the first portion of the communications with the second code and propagating the second portion of the communications with the second subcode. The method according to claim 7, further characterized in that it comprises assigning a third subcode of one of the first codes to support a second communication channel to one of the subscriber stations in the second group. The method according to claim 7, characterized in that the subscriber stations in the first group are in temporary transfer and the subscriber stations in the second group are not in temporary transfer. The method according to claim 7, characterized in that the first subcodes each comprise a plurality of concatenated copies of their respective first code. The method according to claim 7, further characterized in that it comprises signaling to one of the subscriber stations in the second group one of the first codes. 14. A communication method, characterized in that it comprises: receiving information from a base station comprising a first code; search through the first code to locate a subcode; depropagate a supplementary channel from the base station with the subcode; depropagate a dedicated channel from the base station with a second code; and combine communications in the dedicated and supplementary channels. 15. The method according to claim 14, characterized in that the information comprises a plurality of codes that include the first code. 16. The method according to claim 14, characterized in that the information identifies the first code as containing the subcode. 17. The method according to claim 14, characterized in that the information is carried in the dedicated channel. 18. The method according to claim 18, characterized in that the information is carried in an overload channel. 19. A communication station, characterized in that it comprises: a processor configured to assign a first code to a first subscriber station, assign a first subcode derived from the first code to support a dedicated channel to the first subscriber station, assign a second code to support a dedicated channel to a second subscriber station and assign a second subcode derived from the first code to support a supplementary channel to the second subscriber station. The communication station according to claim 19, characterized in that the processor is further configured to assign a third subcode derived from the first code to support a second supplementary channel to the second subscriber station. The communications station according to claim 19, characterized in that the processor is further configured to receive information indicating that the first subscriber station is on temporary transfer and that the second subscriber station is not on temporary transfer, the assignment of the first code to a first subscriber station is based on the first subscriber station that is in temporary transfer, and the allocation of the second code to support the dedicated channel to a second subscriber station is based on the second subscriber station that does not It is in temporary transfer. 22. The communications station according to claim 19, further characterized in that it comprises a modulator configured to separate the communications for the second subscriber station in the first and second portions, propagate the first portion of the communications with the second code and propagate the second portion of the communications with the second subcode. The communications station according to claim 19, characterized in that the processor is further configured to derive the first subcode by concatenating a plurality of copies of the first code. 24. The communication station according to claim 19, characterized in that the processor is further configured to signal the first code in the second subscriber station. 25. A communications station, characterized in that it comprises: a processor configured to separate a plurality of subscriber stations into first and second groups, assigning a first different code of a plurality of orthogonal codes to each of the subscriber stations in the first group, assign to each of the subscriber stations in the first group, either its first assigned code or a first subcode derived from its first assigned code, to support a dedicated channel, and assign a second subcode derived from one of the first codes to support a communication channel to one of the subscriber stations in the second group. 26. The communications station according to claim 25, characterized in that the processor is further configured to assign a second code to support a dedicated channel to one of the subscriber stations in the second group and because the communication channel comprises a channel supplementary used by the processor to support overflow communications not supported by the dedicated channel. 27. The communications station according to claim 26, further characterized in that it comprises a modulator configured to separate communications for one of the subscriber stations in the second group in first and second portions, propagate the first portion of the communications with the second code and propagate the second portion of the communications with the second subcode 28. The communication station according to claim 25, further characterized in that it comprises assigning a third subcode of one of the first codes to support a second communication channel to one of the subscriber stations in the second group. 29. The communications station according to claim 25, characterized in that the processor is further configured to receive information indicating whether each of the subscriber stations is in temporary transfer, and to separate the subscriber stations when placing the subscriber stations. in temporary transfer in the first group and the subscriber stations that are not in temporary transfer in the second group. The communications station according to claim 25, characterized in that the first subcodes each comprise a plurality of concatenated copies of their respective first code. 31. The communication station according to claim 25, characterized in that the processor is further configured to signal one of the first codes to one of the subscriber stations in the second group. 32. A subscriber station, characterized in that it comprises: a demodulator configured to receive information from a base station comprising a first code, search through the first code to locate a subcode, dispropagate a supplementary channel from the base station with the subcode, depropagate a dedicated channel of the base station with a second code and combine communications on the dedicated and supplementary channels. 33. The subscriber station according to claim 32, characterized in that the information comprises a plurality of codes that include the first code. 34. The subscriber station according to claim 32, characterized in that the information identifies the first code as containing the subcode. 35. The subscriber station according to claim 32, characterized in that the information is carried in the dedicated channel. 36. The subscriber station according to claim 32, characterized in that the information is carried in an overload channel. 37. A communication station, characterized in that it comprises: means for assigning a first code to a first subscriber station; means for assigning a first subcode derived from the first code to support a dedicated channel to the first subscriber station; means for assigning a second code to support a dedicated channel to a second subscriber station; and means for assigning a second subcode derived from the first code to support a supplementary channel to the second subscriber station. 38. A communications station, characterized in that it comprises: means for separating a plurality of subscriber stations into first and second groups; means for assigning a different first code of a plurality of orthogonal codes to each of the subscriber stations in the first group; means for assigning to each of the subscriber stations in the first group, either its first assigned code or a first subcode derived from its first assigned code, to support a dedicated channel; and means for assigning a second subcode derived from one of the first codes to support a communication channel to one of the subscriber stations in the second group.