US20080020790A1

US20080020790A1 - Diversity Code Allocation for Distributed Transmit Diversity

Info

Publication number: US20080020790A1
Application number: US11/613,680
Authority: US
Inventors: Wanshi Chen; Alpaslan Savas; Rath Vannithamby
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2005-04-14
Filing date: 2006-12-20
Publication date: 2008-01-24
Also published as: CN101199154A; CN101199154B; US7787552B2; US20060233275A1

Abstract

A method of allocating diversity codes to sectors in a mobile communication network achieves a favorable code balance for all mobile terminals a predetermined percentage of the time. The method comprises allocating diversity codes to each sector in a cluster of sectors for a first time period according to a diversity code pattern, rotating said diversity code pattern relative to said cluster, and allocating diversity codes to each sector in said cluster for a second time period according to said rotated diversity code pattern.

Description

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/106,092 titled “Distributed Transmit Diversity in a Wireless Communication Network” and filed on Apr. 14, 2005, which is incorporated herein in its entirety by reference.

BACKGROUND

The present invention relates generally to distributed transmit diversity for mobile communication systems, and more particularly, to a method of allocating diversity codes to sectors in a mobile communication system.
The design of radiocommunication systems for high data rates is made difficult by the nature of the radio propagation channel. One phenomenon which makes radio communications more difficult than some other forms of communication is multi-path fading. In most radiocommunication systems, there is no direct line of sight between the base station and mobile terminal. The presence of buildings, trees, hills, and other objects in the environment surrounding the mobile terminal reflect and scatter radio waves transmitted by the base station. Thus, a signal transmitted by the base station may arrive at the mobile terminal from many different directions with different propagation delays. One effect of multi-path propagation is that the various multipath components of a received signal exhibit varying degrees of distortion, particularly in phase and amplitude. The multipath components of the transmitted signal may combine in a variety of ways, causing fluctuations in signal strength. This phenomenon is known as multipath fading. For example, if two reflected signals are 180 degrees out-of-phase with one another, the two signals will cancel each other out. In effect, the signal disappears. Other partial out-of-phase relationships among multiple copies of a received signal produce lesser reductions in received signal strength. The degree of fading will fluctuate as the mobile moves around in the network.
Transmit diversity is a commonly used countermeasure to combat multipath fading. The concept of transmit diversity is relatively simple. If several replicas of a signal are transmitted simultaneously over independently fading channels, the likelihood that at least one of the received signals will not be severely degraded by fading increases. Even in circumstances where each replica experiences fading, the multiple replicas may be combined in such a manner to create a usable signal.
There are many forms of transmit diversity, including frequency diversity, time diversity, and space diversity. In frequency diversity, the signal is transmitted using different carrier frequencies that are spaced sufficiently apart from each other to provide independently fading versions of the signal. In time diversity, the same message signal is transmitted in differing time periods. In space diversity, multiple transmitting or receiving antennas are used with spacing between adjacent antennas chosen so as to assure the independence of fading events.
Transmit diversity systems may sometimes employ coding to improve the diversity gain. For example, space-time diversity codes are known in which different coded versions of a signal are transmitted from different antennas. One well-known space-time code is the Alamouti code. Space-frequency diversity codes are also known.
Use of space-time and space-frequency codes has been proposed for delivering broadcast multicast services (BCMCS) in Code Division Multiple Access (CDMA) systems. In CDMA systems, a mobile terminal in soft handoff receives signals from two or more different transmitters in different sectors or cells. Thus, CDMA systems inherently achieve a form of distributed transmit diversity (DTD). Space-time diversity can be achieved by transmitting different coded versions of a signal from transmitters located in two or more different sectors or cells. The efficacy of DTD in CDMA systems depends on the degree of balance, in terms of signal strength, between the different coded versions of the signal as seen at the receiver. Therefore, there is a need for ways to improve the code strength balance in CDMA systems that employ DTD.

SUMMARY

The present invention provides a method of allocating dynamic diversity codes to a group of sectors in a mobile communication network such that code balance is achieved for all mobile terminals in the network a predetermined percentage of the time. According to one exemplary embodiment of the present invention, a base diversity code pattern is defined for allocating diversity codes in sequential time periods. For a first time period, the diversity codes are allocated according to the base diversity code pattern. For each additional time period, the base diversity code pattern is rotated and the diversity codes are allocated based on the rotated diversity code pattern. Thus, the diversity codes allocated for each sequential time period correspond to a different relative rotation of the diversity code pattern. In one exemplary embodiment, the diversity code pattern is selected such that any three mutually-adjacent sectors will include two or more different diversity codes in any given time period. Thus, a mobile terminal receiving information signals transmitted from three mutually-adjacent sectors will always receive at least two different diversity coded versions of the information signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a communication network implement a diversity code allocation scheme according to an exemplary embodiment of the present invention.
FIG. 2 illustrates an exemplary diversity code pattern for a 7-sector cluster.
FIG. 3 illustrates a static diversity code allocation scheme for a 7-sector cluster.
FIG. 4 illustrates an alternating diversity code allocation scheme for a 7-sector cluster.
FIG. 5 is a flow diagram illustrating an exemplary method of allocating diversity codes.
FIG. 6 illustrates an exemplary diversity code pattern for a 19-sector cluster.
FIG. 7 illustrates an exemplary diversity code pattern for a 21-sector cluster.
FIG. 8 illustrates an exemplary diversity code pattern for a 57-sector cluster.
FIG. 9 illustrates an exemplary diversity code pattern for a 21-sector cluster.
FIG. 10 illustrates an exemplary distributed transmit diversity network with a centralized diversity coding circuit.
FIG. 11 illustrates an exemplary distributed transmit diversity network with a distributed diversity coding circuit.
FIG. 12 is a block diagram of one embodiment of a radio base station configured for diversity coding.
FIG. 13 is a block diagram of one embodiment of a radio base station controller configured to diversity coding.
FIG. 14 is a block diagram of a distributed transmit diversity network in another embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates an exemplary mobile communication network 10 implementing a diversity code allocation scheme according to one embodiment of the present invention. The network 10 may comprise, for example a Code Division Multiple Access (CDMA) network. The geographic area of the mobile communication network 10 is divided into a plurality of cells 12. The cells 12 may be further divided into a plurality of sectors 14, or may comprise a single sector 14. Each cell 12 includes at least one transmitter 16 that is typically located at the center of the cell 12. If the cell 12 is divided into two or more sectors 14, a separate transmitter 16 is typically provided for each sector 14. In the remaining discussion, the term sector 14 is used to describe the diversity code allocation scheme. It should be understood that the term sector 14 as used below includes a cell 12 comprising a single sector 14.
In CDMA networks, a mobile terminal 20 in soft handoff is served by multiple sectors 14 at the same time. In the exemplary embodiment, it is assumed that the mobile terminal 20 may be served simultaneously by up to three adjacent cells 12 or sectors 14. The active set for a mobile terminal 20 comprises the set of cells 12 or sectors 14 that are currently serving the mobile terminal 20. Thus, in the exemplary embodiment, the mobile terminal 20 can have an active set of size 1, 2, or 3.
For distributed transmit diversity, diversity coded information signals for the mobile terminal 20 are transmitted from two or more sectors 14 to the mobile terminal 20. Each sector 14 codes the information signal according to an assigned diversity code. A variety of diversity codes can be used, including space-time diversity codes (e.g. Alamouti code) and space frequency diversity codes. In the following discussion, it is assumed that the set of available diversity comprises two diversity codes, denoted herein as C₀and C₁. It should be understood, however, that the set of available diversity codes could, in some embodiments, comprise more than two diversity codes. Regardless of the number of diversity codes, the mobile terminal 20 should preferably receive diversity-coded information signals coded using each one of the available diversity codes. In the exemplary embodiment with two diversity codes C₀and C₁, the mobile terminal 20 should receive diversity-coded information signals coded using both codes C₀and C₁.
The effectiveness of the distributed transmit diversity will depend on the code balance of the diversity-coded signals. Code balance refers to the relative strengths of the different diversity-coded signals received by the mobile terminal 20. Distributed transmit diversity is most effective when the mobile terminal 20 receives each of the diversity-coded signals with the same signal strength.
When the active set for the mobile terminal 20 comprises 2 sectors 14, two different code balance outcomes are possible. The mobile terminal 20 may receive two different diversity coded versions of the signal from two different sectors 14. This circumstance is most favorable. Alternatively, the mobile terminal 20, may receive the same diversity coded signal from both sectors 14. This circumstance is not favorable and should be avoided as much as possible.
When the active set of the mobile terminal comprises 3 sectors 14, it can be assumed that the signal strength will be different from all three sectors 14. Thus, if s₁>s₂>s₃, where “s_m” represents the signal strength from sector m, three different code balance outcomes are possible. Based on this signal scenario, the most favorable code balance (CB₁) is when the mobile terminal 20 receives one diversity coded signal from S1, and the other diversity coded signal from S2 and S3. A less favorable code balance (CB₂) is when the mobile terminal 20 receives one diversity coded signal from S2 and the other from S1 and S3. The code balance is least favorable (CB₃) when the mobile terminal 20 receives one diversity coded signal from S3 and the other diversity coded signal from S1 and S2.
The present invention provides a diversity code allocation scheme that achieves a favorable diversity code balance for all mobile terminals 20 a predetermined percentage of the time. According to one exemplary embodiment, the sectors 14 are grouped to form clusters. As used herein, the term cluster refers to a grouping of cells 12 or sectors 14. For each cluster, a diversity code pattern is defined for allocating diversity codes to sectors 14 in the cluster in sequential time periods. According to embodiments of the present invention, the diversity code allocation is changed over time by rotating the diversity code pattern relative to the cluster. Thus, each sector 14 will be assigned a diversity code sequence for use during sequential time periods (e.g. every n frames, where n>=1). Each diversity code in a diversity code sequence corresponds to a different time period. As a consequence, the diversity codes transmitted from a given sector 14 may change over time. It should be understood that some sectors 14 may use the same diversity code all of the time, while others may change diversity codes over time. For example, a sector 14 assigned the sequence {0,0,0} will use the same diversity code all of the time, and a sector 14 assigned the sequence {0,1,1} will change over time. The diversity code pattern is preferably designed so that any three mutually adjacent sectors 14 include both possible diversity codes in any given time period. In operation, each sector 14 encodes information signals for transmission according to its assigned diversity code sequence.
Assuming that mobile terminals 20 are distributed uniformly throughout the network 10, diversity code balance cannot be ensured for all the mobile terminals 20 all of the time. Some diversity-code allocation schemes may favor certain mobile terminals 20 over others at any given time. Changing the diversity code allocation will improve reception conditions for some mobile terminals 20 and degrade reception conditions for others. The diversity code allocation scheme according to the present invention attempts to achieve a level of fairness for all mobile terminals 20 by ensuring that a favorable code balance will be achieved for all mobile terminals 20 a predetermined percentage of the time.
FIG. 2 illustrates a particular diversity code pattern using two diversity codes C₀and C₁for a 7-sector cluster 18. FIG. 2 illustrates the diversity code allocation at three different time instances, denoted herein as T₁, T₂, and T₃. At any given time, C₀is assigned to four sectors 14 and C₁is assigned to three sectors 14. It should be noted that the diversity code pattern is the same at all three time instances; however, the rotation of the diversity code pattern is different at all three time instances. The relative rotation of the diversity code pattern is 0° at time T₁, 120° at time T₂, and 240° at time T₃. Thus, cell G will use C₁at time T₁, C₁at time T₂, and C₀at time T₃. Similarly cell B will use C₁at time T₁, C₀at time T₂, and C₁at time T₃. These sequences repeat recursively over time.
Table 1 below illustrates the diversity code allocation and diversity code sequence for all sectors 14 of a 7-sector cluster 18. Each row in the table represents the allocation of the diversity codes at a given time instance, and each column represents a diversity code sequence transmitted by a given cell to affect the rotation of the diversity code pattern over time.

TABLE 1

Diversity Code Allocation For 7-Sector Cluster

Cell A Cell B Cell C Cell D Cell E Cell F Cell G

T

₁ 0 1 0 1 1 0 1

T ₂ 0 0 1 1 0 1 1

T ₃ 0 1 1 0 1 1 0
With the diversity code allocation scheme described above, code balance will be achieved for all mobile terminals 20 a predetermined percentage of the time. Consider, for example, a mobile terminal 20 having an active set of two sectors 14. When the mobile terminal 20 is receiving diversity coded signals from two adjacent sectors 14 at the same time, code balance is obtained as much as possible a predetermined percentage of the time, i.e., two-thirds of the time. That is, the mobile terminal 20 will receive both C₀and C₁from different sectors 14 two-thirds of the time, and will receive either C₀or C₁from both sectors 14 one-third of the time. When the mobile terminal 20 receives diversity coded signals from three adjacent cells 12, the mobile terminal 20 will realize each of three possible power code balances CB₁, CB₂, and CB₃one-third of the time each.

Table 2 compares the rotating diversity code allocation scheme of the present invention with a static code allocation scheme and an alternating code allocation scheme for a 7-sector cluster 18. The static diversity code allocation scheme is illustrated in FIG. 3. The alternating diversity code allocation scheme is illustrated in FIG. 4. In the static diversity code allocation scheme, the diversity codes assigned to different sectors 14 are fixed and do not change over time. In the alternating diversity code allocation scheme, one or more selected sectors 14 alternate between two different diversity codes while the remaining sectors 14 are have fixed or static diversity code assignments. In the embodiment shown in FIG. 4, cell A alternates between C₀and C₁, while cells B-G have static code assignments.

TABLE 2


Performance Comparison Of Diversity Codee Allocation Schemes

Active
Set Size	Static	Alternating	Rotating

2	⅔^rdMTs receive C₀and C₁	⅓^rdMTs receive C₀and C₁	All MTs receive C₀
	100% of the time;	100% of the time;	and C₀67% of time
	⅓^rdMTs C₀or C₁100% of the time	⅔^rdC₀and C₁50% of the time
3	⅓^rdMTs see CB₁100% of time;	⅓^rdMTs see (50% CB₁, 50% CB₂)	All MTs see
	⅓^rdMTs see CB₂100% of time;	⅓^rdMTs see (50% CB₁, 50% CB₃)	(33.3% CB₁, 33.3% CB₂, 33.3% CB₃)
	⅓^rdMTs see CB₃100% of time	⅓^rdMTs see (50% CB₂, 50% CB₃)

As shown in Table 2, the static allocation scheme favors some mobile terminals 20 over others. When the active set comprises two sectors 14, two-thirds of the mobile terminals 20 will receive both C₀and C₁100% of the time and the remaining one-third will receive a single diversity coded signal C₀or C₁100% of the time. In the alternating scheme, when the active set comprises two sectors 14, one-third of the mobile terminals 20 will receive both diversity coded signals C₀and C₁100% of the time and two-thirds will receive both diversity coded signals C₀and C₁150% of the time. In comparison, the rotating diversity code allocation scheme according to the present invention lets all mobile terminals 18 receive both diversity coded versions of the signal 66.67% of the time.
A similar result is obtained for the static scheme and alternating scheme when the active set comprises three sectors 14. In the case of the static scheme, one-third of the mobile terminals 20 will achieve CB₁100% of the time, one-third will achieve CB₂100% of the time and one-third will achieve CB₃100% of the time. In the case of the alternating scheme, one-third will achieve CB₁50% of the time and CB₂50% of the time, one-third will achieve CB₁50% of the time and CB₃50% of the time, and one-third will achieve CB₂50% of the time and CB₃50% of the time. In comparison, the rotating scheme of the present invention lets all mobile terminals 20 achieve CB₁33.3% of the time, CB₂33.3% of the time, and CB₃33.3% of the time.
FIG. 5 is a flow diagram illustrating an exemplary method of allocating diversity codes according to one exemplary embodiment. A base diversity code pattern is defined for a cluster 18 of sectors 14 (box 102) and the diversity codes are allocated to each of the sectors 14 according to the base diversity code pattern for a first time period (box 104). For each additional time period, the base diversity code pattern is rotated relative to the cluster 18 (box 106) and diversity codes are allocated to each of the sectors 14 according to the rotated diversity code pattern (box 108). In the illustrated embodiments, three rotations including the base diversity code pattern are used.
The diversity code allocation scheme according to the present invention, wherein a diversity code pattern is rotated relative to a cluster 18 of sectors 14, can be applied to large clusters 18. FIGS. 2 and 6-9 illustrate different diversity code allocation schemes for different sized clusters 18. FIG. 2 illustrates a diversity code allocation scheme according to one exemplary embodiment for a cluster 18 comprising 7 sectors. FIG. 6 illustrates a diversity code allocation scheme according to another exemplary embodiment for a cluster 18 comprising 19 sectors 14. FIGS. 7 and 9 illustrate a diversity code allocation scheme according to another exemplary embodiment for a cluster 18 comprising 21 sectors 14. FIG. 8 illustrates a diversity code allocation scheme according to another exemplary embodiment for a cluster 18 comprising 57 sectors 14.
Although rotating the diversity code allocation may be preferable when the mobile terminals 20 are uniformly distributed in the network 10, there may be several circumstances when the static allocation or alternating allocation is more preferable. For example, there may be circumstances where a large number of mobile terminals 20 are located in the same area. This may occur, for example, during a sporting event, concert, or parade. In this case, the static allocation or alternating allocation may provide a greater benefit. Also, there may be circumstances when the service provider may want to favor certain mobile terminals 20 over others. With some feedback from the mobile terminals 20, control logic within the network 10 can determine what type of allocation scheme is best and switch between different diversity code allocation schemes. For example, control logic could be located at a base station controller that controls all of the sectors in said cluster. In one embodiment, the control logic may switch between the dynamic diversity code allocation based on rotating a diversity code pattern as described above and a static diversity code allocation. In another embodiment, the control logic may switch between the dynamic diversity code allocation based on the rotating and alternating diversity code patterns. In another embodiment, the control logic can switch between diversity code allocations based on rotating, alternating, and static diversity code patterns.
The feedback from the mobile terminals 20 may take various forms. In some embodiments, the mobile terminals 20 may feedback the pilot signal strength for each sector 14 in their active set. In this case, the amount of feedback will be large. To reduce the feedback, the mobile terminals 20 may feedback information indicating the 0° ordering of the pilot signals from each sector 14 in their active set from strongest to weakest. Transmitting order information would reduce the feedback as compared to transmitted full pilot strength measurement reports. As a third option, the mobile terminal 20 may simply feedback a change request comprising a single bit indicating whether a change in the code allocation is requested. For example, the mobile terminal 20 may send a “1” to request a change in the diversity code allocation, and a “0” otherwise.
FIG. 10 is a functional block diagram illustrating components of a wireless communication network 10 that implements distributed transmit diversity according to one exemplary embodiment. Each of a number of spaced-apart transmitters 16 receives a different diversity-coded version of the same information signal, from one or more diversity-coding circuits 15, which may be implemented as a separate node within the network 10. As previously described, the transmitters 16 may be located at one radio base station, or may comprise sector transmitters at different radio base stations. Diversity-coding circuit(s) 15 may comprise processing circuits located in a base station controller that is associated with the radio base station(s). The information signal may comprise a dedicated channel signal targeted to a particular mobile terminal 20, or may be a Broadcast-Multicast Services (BCMCS) signal or other type of broadcast signal targeted to a group of mobile terminals 20.
FIG. 11 is a functional block diagram illustrating another exemplary embodiment wherein the diversity coding circuits 15 are distributed and co-located with the transmitters 16. Diversity-coding circuits 15 may be incorporated into each of the transmitters 16, such that diversity coding is implemented by the transmitters 16 as part of transmit processing, at least for selected ones of the signals being transmitted by them. With the embodiment of FIG. 11, a given information signal may be distributed to the transmitters 16 by one or more base station controllers (not shown). The particular code(s) used at each one of the transmitters 16 can be fixed by design, set according to network provisioning information stored at the transmitters 16, or communicated to the transmitters 16 from the base station controller(s) associated with them, for example. In that latter case, the code(s) used by each transmitter 16 can be fixed by base station controller provisioning information, or can be dynamically assigned.
The functionality of the transmitters 16 and the diversity-coding circuit(s) 15 may be implemented in a radio base station embodiment, as shown in FIG. 12. The illustrated radio base station (RBS) 22 is configured for diversity-coding one or more information signals received from an associated base station controller 30, for example. The RBS 22 comprises interface/control circuits 24, which include diversity-coding circuits 26, and a plurality of sector transmitters 28. The RBS 22 may be configured for operation according to a variety of wireless communication network standards, including those based on CMDA or Orthogonal Frequency Division Multiplexing (OFDM) signal types.
In one embodiment, the RBS 22 can be configured to employ diversity coding for mobile terminals 20 that are in softer handoff with it. That is, in circumstances where the same information is being transmitted to a given mobile terminal 20 from two or more of the sector transmitters 28 at the same RBS 22, the RBS 22 sends a different diversity-coded version of the information signal from two or more different sector transmitters 28. Such diversity coding can be managed at the RBS-level, via the included diversity-coding circuits 26. Diversity coding circuit 26 may also determine the type of diversity code allocation scheme to use based on feedback from the mobile terminals 20 as previously described.
For soft handoff conditions on the forward link, wherein a given mobile terminal 20 is being served from two or more sectors 14 located at different RBSs 22, diversity coding may be implemented by one or more base station controllers (BSCs) 30 associated with the involved RBSs 22. FIG. 13 illustrates an embodiment of a BSC 30 that is configured for BSC-level diversity coding of information signals. The BSC 30 comprises communication/control circuits 32, which include diversity-coding circuits 34, and RBS interface circuits 36.
Note that with the BSC-level implementation of diversity coding shown in FIG. 13, the diversity-coding circuits 26 may be omitted from the RBS 22. However, leaving the RBSs 22 with their own diversity coding circuits 26 may offer advantages for softer handoff scenarios, and may reduce the BSC-RBS communication load in certain scenarios. For example, if a given information signal is to be transmitted from two or more sectors 14 of a given RBS 22, it can be sent from the BSC 30 to the RBS 22 as a single information signal, and the RBS 22 can generate the multiple, diversity-coded versions of that signal for transmission. In the alternative, where the diversity coding is done at the BSC-level (or higher), each of the different diversity-coded versions of the same information signal is sent from the BSC 30 to the RBS 22. Obviously, the latter embodiment offers certain advantages regarding a more centralized approach in the network 10 to diversity coding, but comes at the expense of requiring potentially more communication resources between the different network entities.
In at least one embodiment, the diversity-coding circuits 26 are located at the RBS 22 for both softer and soft handoff. In soft handoff scenarios, the BSC 30 directs the diversity coding of the RBS 22 (e.g., the BSC 30 tells the RBS 20 which codes or type of codes to use). The BSC 30 may also determine the type of diversity code allocation scheme to employ based on feedback from the mobile terminals 20 as previously described.
In other embodiments, at least a portion of the diversity-coding circuit(s) 26 reside at higher levels in the network hierarchy, and/or comprise centralized resources that provide for full or partial diversity coding control across a number of other network nodes, e.g., across BSCs 30 and/or RBSs 22. FIG. 14 illustrates an exemplary network 10 comprising a Radio Access Network (RAN) 40, which includes a number of BSCs 30 and RBSs 22, and further includes a centralized node 42 configured for diversity-coding at least some types of information signals. The centralized node 42 may also determine the type of diversity code allocation scheme to use based on feedback from the mobile terminals 20. The network 10 further includes a Packet Switched Core Network (PSCN) 44 and/or a Circuit Switched Core Network (CSCN) 46, that communicatively couple mobile terminals 20 being supported by the RAN 40 to one or more external networks. Such external networks may comprise a Public Data Network (PDN) 50, such as the Internet, or may comprise the Public Switched Telephone Network (PSTN) 52.
With the above range of variations in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims, and their legal equivalents.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

1. A method of allocating dynamic diversity codes in a mobile communication network, said method comprising:

allocating diversity codes to each sector in a cluster of sectors for a first time period according to a diversity code pattern;

rotating said diversity code pattern relative to said cluster; and

allocating diversity codes to each sector in said cluster for a second time period according to said rotated diversity code pattern.

2. The method of claim 1 wherein said diversity code pattern is formed from a set of diversity codes.

3. The method of claim 2 wherein said diversity codes are space-time diversity codes.

4. The method of claim 3 wherein said space-time diversity codes are Alamouti codes.

5. The method of claim 2 wherein said diversity codes are space-frequency diversity codes.

6. The method of claim 2 wherein said diversity code pattern is such that any three mutually adjacent sectors will include at least two different diversity codes.

7. The method of claim 6 wherein said set of diversity codes comprises two diversity codes and wherein said diversity code pattern is such that any three mutually adjacent sectors in said cluster will include each of said diversity codes in said set of diversity codes.

8. The method of claim 1 further comprising dynamically changing said diversity code allocation.

9. The method of claim 8 wherein dynamically changing said diversity code allocation comprises changing from said dynamic diversity code allocation based on said rotating diversity code pattern to a static diversity code allocation.

10. The method of claim 8 wherein dynamically changing said diversity code allocation comprises changing from said dynamic diversity code allocation based on said rotating diversity code pattern to a dynamic code allocation based on an alternating diversity code allocation.

11. The method of claim 8 wherein said diversity code pattern is dynanmically changed based on feedback from said mobile stations.

12. A mobile communication network implementing dynamic diversity codes, said mobile communication network comprising:

a plurality of sectors forming a cluster;

wherein each sector in said cluster is assigned a sequence of diversity codes for use during sequential time periods according to a predetermined diversity code pattern, and

wherein said assigned diversity code sequences effects a rotation of said diversity code pattern over said sequential time periods.

13. The mobile communication network of claim 12 wherein said diversity code pattern is formed from a set of diversity codes.

14. The mobile communication network of claim 13 wherein said diversity codes are space-time diversity codes.

15. The mobile communication network of claim 14 wherein said space-time diversity codes are Alamouti codes.

16. The mobile communication network of claim 13 wherein said diversity codes are space-frequency diversity codes.

17. The mobile communication network of claim 13 wherein said diversity code pattern is such that any three mutually adjacent sectors will include at least two different diversity codes.

18. The mobile communication network of claim 17 wherein said set of diversity codes comprises two diversity codes and wherein said diversity code pattern is such that any three mutually adjacent sectors in said cluster will include each of said diversity codes in said set of diversity codes.

19. A mobile communication network comprising a plurality of sectors forming a cluster, wherein each sector in said cluster is assigned a sequence of diversity codes for use during sequential time periods according to a predetermined diversity code pattern, and wherein said assigned diversity code sequences effects a rotation of said diversity code pattern over said sequential time periods.

20. The mobile communication network of claim 19 further including at least one diversity coding circuit for encoding information signals for transmission according to said assigned diversity codes.

21. The mobile communication network of claim 20 wherein each sector includes a separate diversity coding circuit for encoding information signals for transmission from said sector according to said assigned diversity codes.

22. The mobile communication network of claim 20 wherein said diversity coding circuit encodes information signals transmitted from a group of sectors according to said assigned diversity codes.

23. The mobile communication network according to claim 22 wherein said diversity coding circuit is located at a radio base station and encodes information signals from a group of sectors controlled by said radio base station.

24. The mobile communication network according to claim 22 wherein said diversity coding circuit is located at a base station controller.

25. The mobile communication network according to claim 22 including a centralized diversity coding circuit that encodes information signals transmitted by all sectors in a cluster.

26. The mobile communication network of claim 19 further comprising control logic to dynamically change said diversity code allocation.

27. The mobile communication network of claim 26 wherein said control logic dynamically switches between said dynamic diversity code allocation based on said rotating diversity code pattern and a static diversity code allocation.

28. The mobile communication network of claim 26 wherein said control logic dynamically switches between said dynamic diversity code allocation based on said rotating diversity code pattern and a dynamic diversity code allocation based on an alternating diversity code allocation.

29. The mobile communication system of claim 26 wherein said control logic changes the diversity code pattern based on feedback from said mobile terminal