CN1689259A - Code channel allocations in a wireless communications system - Google Patents

Abstract

Systems and techniques are disclosed relating to communications. The systems and techniques involve spread-spectrum communications using a scheduler, or similar component, configured to maintain a plurality of spreading sequence assignments and a plurality of available spreading sequences each being orthogonal to the assigned spreading sequences. The scheduler may also be configured to select a spreading sequence from a group of the available spreading sequences having the same length, the selected spreading sequence being generated from a block of codes and being selected based on the number of the available spreading sequences that can be generated using the same block of codes.

Description

Coded Channel Allocation in Wireless Communication Systems

Claiming priority under 35 U.S.C. §119

This patent application claims priority to Provisional Patent No. 60/409,528, entitled "CODECHANNEL ALLOCATIONS IN A WIRELESS COMMUNICATIONS SYSTEM," filed September 9, 2002, assigned to the assignee of the present invention and incorporated by reference combined here.

background

technical field

The present invention relates generally to communications, and more particularly to systems and techniques for managing coded channel assignments in wireless communications systems.

Background technique

Modern communication systems are designed to allow multiple users to share a common communication medium. One such communication system is a Code Division Multiple Access (CDMA) system. CDMA communication system is based on spread spectrum communication modulation and multiple access scheme. In a CDMA communication system, a large number of signals share the same frequency spectrum, resulting in increased user capacity. This is accomplished by sending each signal with a different code that modulates a carrier, thereby spreading the signal across the frequency spectrum. The transmitted signal can be separated in the receiver by a correlator which uses the corresponding code to despread the desired signal. Undesired signals with mismatched codes become just noise.

In spread spectrum communications, a base station controller (BSC) is typically used to connect a wireless network to a communications infrastructure, such as a wide area network (WAN) or a local area network (LAN). A wireless network includes a number of base stations, each configured to serve all users within a geographic area called a cell. In this configuration, orthogonal sequences called Walsh codes can be used in the forward link to separate multiple users operating in the same cell area. The forward link refers to the signal transmission from the base station to the user.

With the dramatic increase in wireless communications over the past few years, there has been a need for higher data rate services to support web browsing, video applications, and the like. Typically, this requirement is met by carrying traffic from the base station to the user using multiple forward channels, each with a different Walsh code. Unfortunately, this approach tends to introduce additional complexity in the user equipment requiring multiple Walsh codes to demodulate.

Another approach for providing high data rate services that avoids the complexity of demodulating multiple Walsh channels involves the use of spreading sequences derived from one or more Walsh codes. However, once a Walsh code is used, it cannot be used again to generate a subsequent spreading sequence for lack of orthogonality. Therefore, an efficient method or algorithm is needed for spreading sequence allocation to avoid missing Walsh codes required for constructing higher speed channels.

Contents of the invention

In one aspect of the invention, a spread spectrum communication apparatus includes a scheduler configured to maintain a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences corresponding to the assigned spreading sequence The sequences are orthogonal, the scheduler is also configured to select a spreading sequence from a set of available spreading sequences with the same length, the selected spreading sequence is generated from a coding block and based on the available spreading sequences that can be generated with the same coding block number to choose.

In another aspect of the invention, a spread spectrum communication system apparatus includes means for maintaining a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence, and selection means for selecting a spreading sequence from a set of available spreading sequences having the same length, the selected spreading sequence being generated from a coding block and being selected based on the number of available spreading sequences that can be generated with the same coding block.

In yet another aspect of the invention, a spread spectrum communication system apparatus includes means for maintaining a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence; The apparatus selects a spreading sequence from a set of available spreading sequences having the same length, the selected spreading sequence being generated from a coding block and based on the number of available spreading sequences that can be generated with the same coding block.

It is understood that other embodiments of the invention will become apparent to those skilled in the art from the following detailed description, which shows and describes exemplary embodiments of the invention by way of illustration only. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modifications in various other respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

Description of drawings

Aspects of the invention are illustrated by way of example, not limitation, in the accompanying drawings:

Fig. 1 is a conceptual block diagram of a CDMA communication system;

Figure 2 is a simplified functional block diagram illustrating the basic subsystems of a CDMA communication system;

Fig. 3 is the form of a 64 * 64 Walsh code matrix;

Figure 4 is a conceptual diagram illustrating the composition of a communication pipeline with multiple Walsh codes;

Figure 5 is a conceptual diagram illustrating the hierarchical organization of spreading sequences generated from Walsh codes; and

6A-6C are functional block diagrams of algorithms for assigning spreading sequences to multiple users.

A detailed description

The detailed description set forth below in conjunction with the accompanying drawings is a description of various embodiments of the present invention, rather than merely showing the embodiments that the present invention can implement. The various embodiments described herein are presented by way of illustration or illustration only, and should not be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the invention.

FIG. 1 is a conceptual block diagram of a CDMA communication system. BSC 102 may be used to connect wireless network 104 to communication infrastructure 106, such as a wide area network (WAN) or a local area network (LAN). The wireless network includes a plurality of base stations 108a-d, each assigned to a cell area 110a-d. Through one or more base stations 108a-d under the control of BSC 102, subscriber station 112 may access communication infrastructure 106, or communicate with other subscriber stations (not shown).

FIG. 2 is a simplified functional block diagram illustrating the basic subsystems of the exemplary CDMA communication system of FIG. 1 . BSC 102 includes many selector elements, only one selector element 202 is shown for simplicity. One selector element is dedicated to communicating with each subscriber station via one or more base stations. Call processor 204 may be used to establish a connection between selector element 202 and subscriber station 112 when initiating a call. Scheduler 206 may then assign subscriber station 112 a Walsh code to identify forward link transmissions to subscriber station 112 on the connection. Depending on the data requirements of the subscriber stations 112, the scheduler may assign multiple Walsh codes to the subscriber stations 112 to support high data rate services. Alternatively, scheduler 206 may assign to subscriber station 112 a spreading sequence derived from a plurality of Walsh codes in a manner further detailed below. For purposes of describing the present invention, the term "data" shall be taken to include data, voice, video and/or any other type of information. "Walsh code assignment" shall also be considered to include a Walsh code assignment, multiple Walsh code assignments, and/or spreading sequences derived from multiple Walsh codes. Walsh code assignments may be sent from the BSC 102 to the subscriber station 112, exchanging signaling messages during call setup.

The selector element 202 is configured to receive data from the communication infrastructure 106 . The selector element 202 may then forward the data to various base stations in communication with the indicated subscriber station 112 . Base station 108 may include a data queue 208 that buffers data from selector element 202 prior to transmission to subscriber station 112 over the forward link. Data in data queue 208 may be provided to channel element 210 . Channel element 210 may provide various signal processing functions such as convolutional coding, scrambling with long pseudorandom noise (PN) codes, interleaving, and modulation. The resulting modulated data is then spread with an assigned Walsh code or spreading sequence, combined with an overhead channel, and quadrature modulated with a short PN code. The short PN code is the second layer of coding, which is used to isolate the cell areas from each other. This approach enables repeated use of Walsh codes in each cell area. The output of channel element 210 may be provided to transmitter 212, filtered, amplified, and upconverted to a carrier frequency prior to transmission over the forward link from base station 108 via antenna 214 to subscriber station 112.

The location of scheduler 206 depends on whether a centralized or distributed scheduling function is desired. For example, a distributed scheduling scheme may use a scheduler in each base station. In this configuration, the scheduler of each base station determines Walsh code assignments for subscriber stations within its cell independently of Walsh code assignments within other cells. In contrast, a centralized scheduling scheme may use a single scheduler 206 in the BSC 102 to coordinate Walsh code assignments for multiple base stations. In either case, scheduler 206 is responsible for the allocation of Walsh codes in the forward link to support high data rate services as well as conventional voice services.

Scheduler 206 can be implemented in a variety of ways depending on the particular application and overall design requirements. In an embodiment, Walsh code assignments may be determined from call origination requests from subscriber stations 112 . When a user initiates a call, or loads an application for initiating a call, subscriber station 112 may generate a call origination request identifying the type of service requested by the user and the desired quality of service. For example, a call origination request may indicate that the user has initiated a video application requiring 64 kilobits per second. In this embodiment, the call origination request may be sent from the subscriber station 112 to the base station 108 over a control channel and provided to the scheduler 206 in the BSC 102. The scheduler 206 then makes Walsh code assignments based on the call origination request as well as other system constraints such as: quality of the forward link, maximum transmit power available at the base station, current Walsh codes of other subscriber stations, etc. code allocation and/or other related factors. The Walsh code assignment may be provided to base station 108 where it is sent to subscriber station 112 over a paging channel.

Walsh channel assignments may be made by scheduler 206 using various algorithms. The algorithm can be optimized to provide Walsh channel allocations that minimize the likelihood of restricting high-speed channel allocations to subsequent subscriber stations. To illustrate this concept, the algorithm will be described in conjunction with a 64x64 Walsh code matrix. However, the inventive concepts described in this invention can be used with Walsh code matrices of arbitrary size. Furthermore, variations on this algorithm for use with other spreading codes such as PN codes will be apparent to those skilled in the art. .

Referring to the 64x64 Walsh code matrix shown in Figure 3, the scheduler can assign one of 64 different possible Walsh codes to a subscriber station. Once a Walsh code is assigned, it is not available for assignment to other subscriber stations within the same cell. If a call origination request from a subscriber station requires a high-speed channel, the scheduler can respond in a number of ways. The scheduler can assign two or more available Walsh codes to subscriber stations to transmit forward link data. Alternatively, the scheduler can derive shortened spreading sequences from multiple Walsh codes. By allocating a shortened spreading sequence to subscriber stations, the Walsh codes used to derive the spreading sequence become unusable. These Walsh codes are said to be "virtually" assigned because although they are not technically assigned to subscriber stations, they have been removed from the category of available Walsh channels. For example, a shortened spreading sequence consisting of 32 zeros can be constructed by combining the 32-chip common sequences from the two Walsh codes. As shown in FIG. 3, Walsh codes (W0) 302 and (W32) 304 each have a common chip sequence of 32 zeros as the most significant chip. Thus, a spreading sequence of 32 zeros results in a virtual allocation of Walsh codes (W0) 302 and (W32) 304 . The virtual assignment of Walsh codes (W0) and (W32) is required to maintain orthogonality. Extending this concept to a shortened spreading sequence of 16 zeros results in a virtual assignment of Walsh codes (W0)302, (W16)306, (W32)304 and (W48)308.

FIG. 4 is a schematic diagram showing a Walsh code space of a 32×32 Walsh code matrix. To further illustrate the benefits and utility of using shortened spreading sequences derived from Walsh codes, the concept of communication pipelines will be introduced. A separate pipe is used to support forward link communications from the base station to the various subscriber stations. For voice and low-speed data applications, 32 pipes are available from the 32×32 Walsh code matrix. Each of the 32 pipes is constructed with a different Walsh code having 32 chips and is defined as a 1x pipe. Higher capacity pipelines can be constructed with shortened spreading sequences derived from multiple Walsh codes. For example, a shortened spreading sequence consisting of 4 chips can be constructed from the 8 Walsh codes shown in FIG. 4 . The high-capacity pipeline 402 is eight times (8x) faster than the 1x pipeline, but results in 8 Walsh codes being virtually allocated and not available for future allocations. The 8x pipeline 402 can be split into two 4x pipelines 404 and 406 using a split pipeline operation 408 . Each 4x pipe 404 and 406 includes a shortened spreading sequence consisting of 8 chips and constructed from 4 Walsh codes with a Walsh code space of 32/4 or 8. Instead, the two 4x chips 404 and 406 can be merged back into the 8x pipeline 402 using the merge pipeline operation 410 . However, if the 8x pipe 402 is allocated to a subscriber station, neither of the two 4x pipes 404 and 406 are available for future allocation to other subscriber stations. In a manner further detailed below, split pipeline operations and merge pipeline operations may be used to optimize Walsh code allocation so as to minimize the likelihood of splitting available high-capacity pipelines. In general, a pipeline whose spreading sequences are derived from 2n Walsh codes can be split into two smaller pipelines, each with spreading sequences derived from 2n-1 Walsh codes.

To further illustrate the way pipelines are separated and combined across the Walsh coding space, it is helpful to show the Walsh code space in a hierarchical organization using the tree structure shown in Figure 5. The tree structure includes 2n+1 nodes with n+1 levels. The variable n can be determined from the following relation: 2n=Walsh code length. For example, in a 64x64 Walsh code matrix, the tree structure has 7 layers of 128 nodes. At the highest level, root level 502, there is node 516 which represents a 64x pipeline with 1-chip spreading sequences derived from all 64 Walsh codes. The 64x pipe can be split into two smaller capacity 32x pipes, represented by the two nodes 518 , 520 of the second layer 504 . Each 32x pipeline at this layer has a 2-chip spreading sequence derived from 32 Walsh codes. In a similar manner, the third layer 506 includes four 16x pipes, each with a 4-chip spreading sequence derived from 16 Walsh codes; the fourth layer 508 includes eight 8x pipes, each with 4-chip spreading sequences derived from 8 Walsh codes. derived 8-chip spreading sequence; the fifth layer 510 includes 16 4x pipes, each with a 16-chip spreading sequence derived from 4 Walsh codes; the sixth layer 512 includes 32 2x pipes, each with a 16-chip spreading sequence derived from 4 Walsh codes; 32-chip spreading sequence derived from 2 Walsh codes; seventh layer 514 includes 64 1x pipes, each with a 64-chip Walsh code.

The assignment of Walsh codes to nodes can be performed using various conventions. An exemplary convention sets the node at the root level 502 to "0". Descending through the levels of the tree structure, the most significant chip of each child node holds the same value as the parent node. The least significant chip of the left child also holds the same value as the parent, while the least significant chip of the right child is assigned the opposite value of the parent. For example, at level 502, node 516 has a value of "0" and represents a 1-chip Walsh code with a value of "0". At the second level 504, node 518 has a value of "00" and node 520 has a value of "01". A similar pattern can be repeated through the levels of the tree, with the last level having 64 nodes, each with a different 64-chip Walsh code.

The assignment of Walsh codes to subscriber stations corresponds to the assignment of nodes in the tree structure. An algorithm for assigning Walsh codes can be implemented according to a specific program. First, when a node is allocated, the entire subtree rooted at that node is marked as virtually allocated. Second, all parent nodes of the allocated node up to the root of the tree structure are marked as virtually allocated. A virtual assignment of these nodes is made in order to maintain orthogonality. These nodes are also not usable for the lack of orthogonality. If communication with a subscriber station is terminated, nodes may be released within the tree structure for future allocation. In addition, all virtual allocations to the entire subtree rooted at this node and its parent node to the root of the tree structure may also be freed.

The algorithm can then be used to select a node at the lowest level of the tree structure that can support the data rate requirements of the subscriber station. If all nodes at that level are unavailable, the algorithm proceeds to the next lower level to locate previously unassigned nodes. This process continues until a node is selected or the algorithm determines that no nodes are available. Where the algorithm identifies multiple nodes that are available at either tier during the selection process, the nodes can be prioritized to prevent arbitrary allocations that would result in invalid deletion of nodes and detachment of high-capacity pipelines. Thus, the exemplary algorithm can optimize node allocation by allocating nodes from denser subtrees. That is, when searching for available nodes allocated in one layer, the priority of available nodes is distinguished according to the allocation density of the subtrees where they are located. Subtrees with more assigned parent nodes are denser subtrees whose available nodes are given higher priority than nodes on less dense subtrees. This allocation density-based prioritization helps reduce the separation of high-speed pipes by invalid Walsh code allocations.

An example of this process is described with reference to Figure 5, which shows the 64 Walsh codes at level 514, and the individual Extended sequence. First, if a subscriber station requires a 4x pipe, a node at layer 510 can be selected and assigned to the subscriber station. Nodes at layer 510 are generated from Walsh codes residing at the lowest layer 514, as described above. For example, node 522 is generated from a piece of Walsh code 524 . If node 522 is assigned to a subscriber station, the Walsh code of block 524 appears to be unavailable and should therefore be marked as virtually assigned. Likewise, any node that can be generated from one or more Walsh codes in block 524, either alone or in combination with other Walsh codes, can be indicated as unavailable by the assignment of node 522. Therefore, all Walsh codes in nodes 521, 523, 526, 528, 518, and 516 and block 524 should be marked as being virtually allocated.

Then, if the second subscriber station requests, for example, a 16x pipe, then 506 nodes of the layer can be selected and assigned to the second subscriber station. A set of available nodes at layer 506 should therefore be identified. Since the spreading sequence represented by node 528 can be generated from Walsh code block 524 already making node 528 unusable, the only available nodes on layer 506 would be nodes 530 , 532 and 534 . And in fact each of these nodes 530 , 532 and 534 represents a spreading sequence that cannot be generated from the Walsh code block 524 .

After the set of available nodes has been identified, one can be selected for assignment to the second subscriber station. Selecting from the highest density subtree avoids splitting high-speed pipes through invalid Walsh code assignments. By applying this criterion it can be seen that node 530 should be chosen to avoid fragmenting the 32x pipeline represented by node 520 at level 504 . The decision to select a node 520 can be made by evaluating the number of unavailable nodes that can be generated for each available node within the group from its corresponding coded block. In other words, for each available node 530, 532, and 534 on layer 506, the number of unavailable parent nodes is determined, and the largest number of unavailable parent nodes is selected for assignment to the second subscriber station. In this example, it is then determined that node 530 has two unavailable parents (518 and 516); node 532 has one unavailable parent (520); and node 534 has one unavailable parent (520). Node 530 has the largest number of unavailable nodes that can be generated from its corresponding Walsh code block 525, so node 530 is selected and assigned to the second subscriber station. Of course, all nodes that then represent a spreading sequence that can be generated from one or more Walsh codes in block 525 should be marked as virtually allocated.

6A-6C are block flow diagrams illustrating an exemplary algorithm that may be used to implement the basic concepts described in connection with FIG. 5 . As described above, the algorithm is employed to allocate a pipe to support forward link communications from a base station to a subscriber station. The algorithm has three components. The first component 602 identifies the highest capacity pipe available and the second component 604 uses that pipe in the manner briefly described below. If the capacity of the pipe exceeds the capacity requirement of the subscriber station, the second component 604 searches for a pipe with a capacity comparable to the capacity requirement of the subscriber station. If the second component search is successful, a pipe may be assigned to the subscriber station. Otherwise, a third component 606 is used to search for a pipe with the required capacity using split pipe operation.

At block 608, the input to the algorithm is the pipe capacity "j" required to support forward link communications from the base station to the subscriber station. The algorithm is initialized at block 610 by setting index variable "k" to index "N". Since this component of the algorithm is searching the highest capacity pipe available, the index N is the highest level of the Walsh code tree structure. For example, in a 64x64 Walsh code matrix, the tree structure has seven levels, and N=6 at the highest level. At decision block 612, it is determined whether any pipes are available in the current tier "k". If there is a pipeline available at that layer, the algorithm proceeds to component 604, as described below. However, if there is no pipe available at that level, then in block 614, the index variable is decremented to check whether there is an available pipe at the next level in the tree structure. Since "0" is the lowest level of the tree structure, at block 616 the algorithm checks that the index variable does not go below "0" as it repeats the iterative process of checking available pipes as indicated by arrow 618 . If the iteration continues to a point where the index variable is below "0", the algorithm determines that no pipes are available for allocation and the process terminates at block 622 .

As described above, the algorithm proceeds to component 604 when the highest capacity pipe available is identified, as indicated by arrow 624 . It should be noted that when the highest capacity pipe available is identified, all pipes created from the highest capacity pipe available via one or more detach pipe operations are considered unavailable, regardless of whether they were previously allocated. Since it would be ineffective to assign a pipe with a capacity higher than required, component 604 searches for a pipe whose capacity is equal to "j". First, at decision block 626, it is determined whether the required pipe capacity "j" is greater than or equal to the index "k" of the highest capacity pipe available. If so, then at block 628, the algorithm selects the highest capacity pipe identified at component 602 to support forward link transmissions between the base station and the subscriber station, and the process terminates at block 630. Otherwise, at block 632, the index variable "n" is initialized to the current index value "k" and the search for lower capacity pipes begins. At block 634, index "n" is descended one level in the tree structure, and at decision block 636, it is checked whether the shifted index "n" has passed level "0" of the tree structure. If so, the search for a pipe with capacity equal to "j" fails and the algorithm proceeds to component 606 for a split pipe operation. Otherwise, the algorithm determines at decision block 638 whether the pipe at the shifted index "n" level is available. If a pipe for that tier is not available, the determination continues iteratively, as indicated by arrow 640, until an available lower capacity pipe is found. Thus, at decision block 642 it is determined whether the pipe at level "n" after the offset equals the desired pipe capacity "j". If so, then at block 644, the pipe is used to support forward link transmissions between the base station and the subscriber station. Otherwise, it is determined at decision block 648 whether the required pipe capacity "j" is less than the pipe capacity at the offset index "n" level. If not, the algorithm proceeds to component 606 for a split pipeline operation. However, if it is determined that the required pipeline capacity "j" is lower than the pipeline capacity at the offset index "n" level, at block 650 index "k" is set to the current value of the offset index "n", The iterative search process begins again at block 632 . Thus, the search for a pipe with a capacity equal to "j" continues until a pipe is found or the required pipe capacity exceeds the pipe capacity at the offset index "n" level.

In the event that the required pipe capacity "j" exceeds the pipe capacity at the offset index "n" level, the algorithm proceeds to component 606 where it performs a split pipe operation to create smaller pipes within the tree structure. At block 652, a split pipeline operation is performed on the layer indicated by index "k". At block 654, the index "k" is moved down one level in the tree structure, and at decision block 656 the algorithm determines whether the required pipe capacity "j" is equal to the split pipe at the shifted index "k" level. If so, one of the split pipes is assigned to the subscriber station at block 658 and the algorithm terminates at block 660 . Otherwise, as indicated by arrow 662, the split pipe operation continues through an iterative process until a pipe with capacity equal to "j" is found.

Implementation or execution of the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments described herein may be implemented using: a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), an Programmable gate array (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, however, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented by a combination of computing devices, eg, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in both. 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 medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. Alternatively, the storage medium may be integrated with the processor. The processor and storage medium may reside in the ASIC. ASICs may reside anywhere in the communication system. Alternatively, the processor and storage medium may reside as discrete components in the communications system.

The above description of the preferred embodiment enables any person skilled in the art to make or use the 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 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 is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (21)

1. A spread spectrum communication device, comprising: a scheduler configured to maintain a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence, the scheduler being further configured to start from A spreading sequence is selected from a set of available spreading sequences having the same length, the selected spreading sequence is generated from a coding block and is selected based on the number of available spreading sequences that can be generated with the same coding block. 2. The apparatus of claim 1, wherein each available spreading sequence in the set is generated from a different coding block, wherein the scheduler is further configured to select a spreading sequence whose has the minimum number of available spreading sequences that can be generated with their corresponding coding blocks. 3. The apparatus of claim 1 , wherein a scheduler selects the spreading sequence to support transmission on a communication channel, the scheduler is further configured to: first determine the length based on the capacity of the communication channel, and then All available spreading sequences of said length are assigned to said group, thereby determining a set of available spreading sequences. 4. The apparatus of claim 1, wherein the selected spreading sequence has a sequence whose common portion is from each code in the block. 5. The apparatus of claim 1, wherein the codes each comprise a Walsh code. 6. The apparatus of claim 1, wherein each available spreading sequence in the set is generated from a different coding block, the scheduler is further configured to identify among all available spreading sequences An available spreading sequence having the shortest length, the selected spreading sequence being one from the group from which the coding block was not generated to generate the identified spreading sequence. 7. The apparatus of claim 1, further comprising a selector element configured to spread communications directed to the wireless device with a selected spreading sequence. 8. A spread spectrum communication device, comprising: a scheduler configured to maintain a plurality of spreading sequences and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence, the scheduler being further configured to select from all available spreading sequences An available spreading sequence having the shortest length is identified in , a target length is determined and compared to the length of the identified spreading sequence, and an available spreading sequence is selected based on the comparison result. 9. The apparatus of claim 8, wherein the length of the selected spreading sequence is greater than or equal to the target length. 10. The apparatus according to claim 8, wherein the scheduler is further configured to select the identified spreading sequence as the selected spreading sequence if the target length is less than or equal to the length of the identified spreading sequence. 11. The apparatus of claim 8, wherein the identified spreading sequence is generated from a coding block, and if the target length is greater than the length of the identified spreading sequence, the scheduler is further configured to: deleting those spreading sequences that can be generated from at least one code in said block, and selecting said spreading sequence from the remaining available spreading sequences if the length of at least one remaining available spreading sequence is equal to the target length. 12. The apparatus of claim 8, wherein the identified spreading sequence is generated from a coding block, and if the target length is greater than the length of the identified spreading sequence, the scheduler is further configured to: Those spreading sequences that can be generated from at least one code in said block are deleted, and if none of the remaining available spreading sequences has a length equal to the target length, one of the deleted spreading sequences is selected. 13. The apparatus of claim 8, wherein a scheduler selects the spreading sequence to support transmission on a communication channel, the scheduler is further configured to determine the target length by measuring the capacity of the communication channel. 14. A spread spectrum communication device, comprising: means for maintaining a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence; and Selection means for selecting a spreading sequence from a set of available spreading sequences having the same length, the selected spreading sequence being generated from a coding block and being selected based on the number of available spreading sequences that can be generated with the same coding block. 15. The apparatus according to claim 14, wherein each available spreading sequence in said set is generated from a different coding block, and said selecting means selects a spreading sequence which has Minimum number of available extension sequences for block generation. 16. The apparatus of claim 14, wherein the spreading sequence is selected to support transmission on a communication channel, the apparatus further comprising means for determining the length by first based on the capacity of the communication channel , and then assign all available spreading sequences with the length to the group, thereby determining a set of available spreading sequences. 17. The apparatus of claim 14, wherein the selected spreading sequence has a sequence whose common portion is from each code in the block. 18. The apparatus of claim 14, wherein the codes each comprise a Walsh code. 19. The apparatus of claim 14, wherein each available spreading sequence in said set is generated from a different coding block, said apparatus further comprising means for: from all available spreading sequences The available spreading sequence with the shortest length is identified in , the selected spreading sequence being one from the group that was generated from the coding block that was not used to generate the identified spreading sequence. 20. The apparatus of claim 14, further comprising means for spreading the communication with the selected spreading sequence. 21. A method of spread spectrum communication, comprising: maintaining a plurality of spreading sequence assignments and a plurality of available spreading sequences, each of the plurality of available spreading sequences being orthogonal to the assigned spreading sequence; and A spreading sequence is selected from a set of available spreading sequences having the same length, the selected spreading sequence being generated from a coding block and based on the number of available spreading sequences that can be generated with the same coding block.

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