Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
  • H04B7/0802—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection
  • H04B7/0822—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection according to predefined selection scheme
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/022—Site diversity; Macro-diversity
  • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems

Definitions

• Embodiments of the present invention relate to the field of multi-user
• MIMO Multiple Output Multiple Input
• embodiments of the present invention relate to a Blind Interference Alignment (BIA)-based Multi-User MIMO communication system in which each active base station operates an identical BIA code structure across the cell topology in a given transmission resource.
• BIA Blind Interference Alignment
• DoFs Degrees of Freedom
• SU-MIMO Single User MIMO
• TX transmission
• RX receive
• SU-MIMO Single User MIMO
• TX transmission
• RX receive
• SU-MIMO Single User MIMO
• TX transmission
• RX receive
• These DOFs can under certain conditions be used to improve throughput by a factor that grows linearly with min(N t , N r ).
• Such benefits of MIMO, and increased DoFs underlie much of the interest in using MIMO in new and future systems.
• CSI Channel State Information
• CSIT Bit Interleaved Coded Modulation
• CSIR D-BLAST
• MU-MIMO can, for example, be used to improve throughput linearly with min(N t , K).
• many MU-MIMO techniques (in fact most if not all of the prevailing MU-MIMO techniques used and studied for standards) require knowledge of CSIT.
• MU-MIMO based on CSIT unlike SU-MIMO based on CSIR, requires additional overheads to estimate CSI and feedback CSI to transmitters before the transmission can take place.
• MU-MIMO is of practical interest since it has the benefit over SU-MIMO of being able to grow the DoFs without having to add many receive antennas, radio frequency (RF) chains, or increase processing (e.g., decoding) complexity to portable or mobile devices.
• RF radio frequency
• the value F CS i is often defined either by the system or by necessity given the coherence of channels in time and/or frequency. As the state of channels changes more rapidly in time and/or frequency, a larger effective fraction of resources may need to be used to estimate and keep track of CSI.
• LTE Long Term Evolution
• 8 symbols in a resource block of 12x14 OFDM symbols are used to support downlink pilots for each of the N t antennas.
• the net spectral efficiency increases have to account for the fraction of resources used for CSI overhead.
• the net spectral efficiency growth is in fact less than that of individual data symbols as only a fraction, e.g. no more than (1- N t xF CS i), of symbols can be used for data.
• the channels seen between the transmitting BS and the K users being served must be jointly changing in a predetermined way (with respect to the blind interference alignment scheme).
• This joint variation can be accomplished by having multiple antenna modes. This can be implemented by employing many (physical) antenna elements at each user, or by having a single antenna element that can change its physical characteristic, e.g. orientation, sensitivity pattern, etc.
• the system requires only that one mode be active at a given time slot.
• the single active receive antenna is a multi-mode antenna, able to switch between, e.g., N t modes in a pre-determined fashion. Having a single RF chain keeps decoding complexity in line with conventional single-antenna mode MU-MIMO systems.
• the modes must be able to create independent (e.g., linearly independent) CSI vectors for the single user. Transmission also has to be confined to a suitable coherence interval in time over which the CSI in a given mode, though unknown to the system, is assumed to be effectively constant and different from mode to mode.
• the BIA technique works by creating a suitable antenna mode switching and combined data transmission vector over the K information bearing streams that are to be sent to the K users (one stream carries the intended information for one user). Such information bearing stream themselves are vectors. These are sent in various arithmetic combinations simultaneously thus using the extra DoFs provided by the antenna mode switching.
• the antenna- switching pattern of that user ensures that the user observes that symbol through all its N t antenna modes (thereby in an N t dimensional space) and can thus decode it;
• the antenna- switch patterns of the rest of the users are such that the transmission of this N t dimensional symbol only casts an 1 -dimensional shadow to their receivers. This is accomplished by ensuring that each of these receivers uses the same antenna mode in all the N t dimensional symbol is transmitted.
• BIA techniques do have some inherent challenges and limitations in the scenarios in which they can be used.
• the first inherent problem is that BIA schemes often require high Signal to Noise Ratios (SNRs) to operate effectively, e.g. the original BIA scheme may require up to 20 dB of SNR. This is due to a property of the interference alignment process, which results in noise being amplified in the resulting interference-aligned streams. As a consequence of this, the original BIA technique has limited application to many users in a cellular environment.
• SNRs Signal to Noise Ratios
• SINRs Signal-to-Interference-plus-Noise-Ratios
• the wireless communication system comprises a plurality of receivers, wherein each receiver in the plurality having a multi-mode antenna with a single radio frequency (RF) chain that is operable in a plurality of antenna modes, and further wherein each receiver shifts between the plurality of antenna modes in a predetermined manner.
• RF radio frequency
• the wireless communication system also includes a plurality of base stations in a cell topology to perform downlink transmissions to the plurality of receivers, each base station in the plurality of base stations having one or more transmitters having a transmit antenna and being operable to communicate with one or more of receivers in the plurality of receivers using a multi-user MIMO (MU-MIMO)-based blind interference alignment (BIA) scheme, wherein each active base station in the plurality of base stations operates an identical BIA code structure in a given transmission resource.
• MU-MIMO multi-user MIMO
• BIOA blind interference alignment
• Figure 1A illustrates a 1 -dimensional illustration of a cluster transmission strategy indicating locations of stations (triangles), locations of cell-center and cell- edge users (solid ovals), and clusters for a cluster size of 2 base-stations (dashed ovals).
• Figure IB illustrates one embodiment of a cell-based network.
• Figure 10 illustrates a multi-mode antenna receiver.
• Figures 11 and 12 illustrate examples of codes addressing user populations with different mobility levels.
• Embodiments of the present invention relate to a class of techniques known as Blind Interference Alignment (BIA) that can be used to support Multi- User MIMO transmission.
• BIA Blind Interference Alignment
• multiple users each having a few receive antenna elements are able to simultaneously receive multiple data streams (at least one intended for each user) over the same transmission resource.
• the BIA techniques allow transmission and alignment of interference between the streams to be done without the transmitter needing to know the instantaneous channel state information (CSI) between transmitter and receiver.
• CSI channel state information
• One aspect of embodiments of the invention focuses on adjusting the power allocations across users, across alignment blocks, across transmit antennas, and across clusters of antennas performing simultaneous transmission of parallel BIA processes to further improve system performance.
• Another aspect of embodiments of the invention focuses on jointly varying these power allocations together with the transmission architecture across clusters and the groups of users jointly scheduled for transmission across the multisite deployments.
• embodiments of the invention include techniques for coordinating groups of users within a cluster that are scheduled for joint multiuser BIA transmission, as well as the individual code assignments of users within the BIA scheme and the associated transmit power allocations throughout the alignment scheme.
• Another aspect of embodiments of the invention includes coordinated assignments of scheduling groups, BIA codes, and user power allocations across clusters of stations. These assignments control the distribution of user SINRs across deployments and can be tailored and optimized in a semi-static fashion to optimize system performance.
• the present invention also relates to apparatus for performing the operations herein.
• This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer.
• a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus.
• a machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer).
• a machine -readable medium includes read only memory ("ROM");
• RAM random access memory
• magnetic disk storage media magnetic disk storage media
• optical storage media flash memory devices
• Embodiments of the invention include techniques for coordinated
• BIA transmissions across cellular and beyond-cellular networks enable improved system-wide performance by coordinating transmissions initiated by distinct clusters of base-stations.
• parallel synchronous BIA schemes are deployed across clusters, and embodiments of the invention coordinate any subset of the following: a method based on which sets of users are scheduled for parallel BIA transmission across clusters; a re-assignment method of each of the BIA codes across clusters to cluster-users; a power allocated to the user streams on each of the BIA codes from each base-station in the cluster; and a way the power allocated to the user streams on a fixed BIA coding structure is varied across clusters.
• the original BIA scheme well-known by those skilled in the art. For information, see C. Wang, et al, "Aiming Perfectly in the Dark - Blind Interference Alignment through Staggered Antenna Switching", February 2010, (hereinafter "Wang”).
• the original BIA scheme describes a method for simultaneously communicating information bearing signals to K receivers from a set of M transmit antennas. Each receiver has M physical antennas, but only a single RF chain. An example of one such receiver is shown in Figure 10 where single RF chain 1001 switches between various antenna 1000 and interfaces antennas 1000 with receiver processing 1002.
• the BIA alignment block of length L comprises two sub-blocks that are referred to herein as alignment blocks 1 and 2.
• Alignment block 1 has length N(M - 1) .
• the transmitter transmits the sum of K vector symbols, one M- dimensional symbol per user. Which symbol (out of the N symbols) that is transmitted for each user is selected in a systematic way to ensure that all symbols are decodable at each user. Examples will illustrate this point.
• Alignment block 2 Block 2 has length NK. In each slot of alignment block 2, the transmitter transmits only a single M dimensional symbol. In particular, the transmitter uses N slots in alignment block 2 per user to transmit each of the N user symbols one at a time, and it does so for each of the K users.
• each user has to cycle through its set of M antenna modes in a predetermined and user- specific manner.
• the lxM channel vector between the M transmit antennas and the m-th receive antenna mode of the k-t user (where the m-th antenna mode of a user corresponds, for example, to activating the m-th receive antenna for that user).
• the index of the antenna mode selected by user k in slot t for t ⁇ , 2, L. Then the following lxL vector captures the sequence of modes cycled by user k within a given alignment block:
• a stream s is a vector of two dimensions of the form where >1 ⁇ 2 is the i th information bearing stream supporting data intended for user k.
• each "symbol” can refer to a single numerical value, or can signify a block of such symbols.
• symbols can refer to either case.
• Block 2 a [ 1] [i 2 1 ⁇ ⁇ ⁇ ]
• receiver k has a measurement signal of the form:
• the power of for m ⁇ M is K times as large as that of z ⁇ .
• BlP ⁇ M,K, ⁇ l k] ,q l k] ⁇ denotes the BIA scheme that arises as a power variation of the original BIA scheme described in Wang, according to which:
• J scheme is the use of the associated antenna-cycling mode vector by user k, defining the precise pattern of antenna mode combinations that the BIA scheme requires each user k to cycle its antennas, in order to be able to cancel interference from all other users symbols and decode its own user streams.
• User X is the m-th user in the BIA ⁇ M ⁇ -jp 1 q J J- J scheme.
• the BIA scheme transmits the M symbol- streams destined for user X using powers given by £ m while in block it transmits the same streams at power levels given by the product of and q ⁇ m ⁇ .
• user X uses the antenna-cycling mode pattern
• the interference cancellation algorithm at each user is in general different as it depends on the set J cancellation algorithm at each user however is the same for two BIA schemes that differ in their 's.
• Embodiments involving BIA Schemes Using Inter- Alignment Block Power Variations may be presented using examples. These power allocation examples have two components. The first component relates to the relative power ratio between the power allocated to a user' s scalar stream in alignment block 1 and that in alignment block 2.
• each symbol of the form in alignment block 1 is replaced with f k ⁇ ⁇ where > 0 is a possibly user-specific scalar. Thus, scaling does not prevent one from performing alignment.
• this variation is parameterized in terms of the scalar and denotes the ratio of the transmit power in block 1 of the km user's stream on any antenna divided by the power of the same user/antenna stream in block 2.
• Block 2 a [ 1] [i 2 1 ⁇ ⁇ ⁇ ]
• z m represents noise.
• z represents the sum of K noise terms.
• the power of the noise terms are still not equal, in particular, the power of z ⁇ is 2K-1 times as large as > or, equivalentl , the power of z ⁇ i s 1/(2K-1) times that of z ⁇ ⁇
• l Mxl is a Mxl vector of ones
• P slot represents the per-channel transmit power constraint (on the totality of the transmit antennas implementing the BIA scheme).
• a special case of a variable-power BIA scheme that has advantages is in the case the BIA scheme employs transmission from multiple base-stations (or, more precisely from antennas that are not collocated.
• transmission is emanating from two base-stations (antennas at two locations)
• Such unequal power allocations are attractive when serving near "center" cell users, i.e., users in the proximity of one of the base- stations, as depicted by the cyan ovals under each BS in Figure 2.
• placing most of the power on the user symbols transmitted from the nearby station improves the user's rates without affecting the rates of the other users in the alignment scheme.
• p w is optimized and not necessarily the same from user to user.
• a synchronous aligned BIA code structure is used across an extended cellular topology.
• a ID wrapped cellular model as shown in Figure IB is used.
• a single (M, K) code- structure (with M ⁇ N t ) operates across the cellular deployment.
• every active cell on a band operates the same (M, K) BIA code structure synchronously with all the other cells (say within the cyclic prefix constraints of an OFDM design), and each user performs the required alignment operation with respect to this (M, K) structure.
• the result of the aligned operation is that, after zero-forcing intra-cell interference in its receiver, a user obtains effectively a x M SU-MIMO channel.
• the aligned system transmissions from all cells using different BIA-codes (different k) do not interfere. However, transmissions from different cells using the same code k do interfere.
• Table II describes a system that assigns a given code in a regular fashion once every two cells, with each cell using only half of the codes on each band. The power assigned to each code is the same. This corresponds to a code- reuse 2 frequency-reuse 1 case. Note that powers in Table II are doubled compared to Table I so that the average transmit power per band within each cell is the same in both cases.
• Table III shows a conventional frequency reuse 2 system in which all the codes are used for transmission by a base station on its active bands. If users operating under Table II perform the same alignment operations with respect to all K codes, the performance of the schemes in Tables II and III are equivalent. This can be understood by noting that the interference on any given code in both systems is the same, i.e. coming from every other station with all such stations using transmission power 2P S on each code.
• the BIA scheme operates a single (M,K) BIA code, and the BIA code is aligned across BSs.
• M,K BIA code
• base stations (or cluster of base stations) in the topology operate according to power masks in Tables II- IV that specify transmission power to be used by each base station on each codeword on a transmission resourse associated with a BIA code, with the transmission power specified by the power mask varying as a function of base station index for each code index value and each transmission.
• packet *1 re fers to the i th uncoded data packet for user k, MCS the modulation/coding scheme used, and BIA the arithmetic operations required to correctly combine coded symbols for transmission.
• each user has a single data packet that undergoes coding and modulation by coding and modulation (MCS) units 201 and 202, in a manner well- known in the art, to each produce a single coded stream.
• MCS coding and modulation
• For each code stream half of the coded symbols (e.g., odd symbols) are used for transmissions on one antenna 210, and the other symbols (e.g., even symbols) are used for the other antenna 21 1. That is, symbols from the user data stream generated by each of MCS units 201 and 202 are sent to BIA transmitters 203 and 204, respectively, which feed antennas 210 and 211 , respectively.
• each user has two data-packets that undergo coding and modulation by coding and modulation units 21 1-214, which each produce their own coded stream.
• One coded stream drives one antenna, and the other coded stream the
• pacset ⁇ undergoes coding and modulation by MCS unit 21 1 to produce coded data ⁇ 1 and a ket!; ' undergoes coding and modulation by MCS unit 212 to produce coded data u ' .
• coded streams are sent to BIA transmitter 233, which drives antenna 240.
• P ⁇ t.- and P af 3 ⁇ 4**i " are coded and modulated by MCS units 223 and 224, respectively, to produce coded streams and - " ' , respectively.
• These are transmitted by BIA transmitter 234 using antenna 241.
• ergodic rates whereby the coded stream(s) for any user span transmissions across many channel realizations, the performance of the two systems is equivalent. Approximations to such an operation can occur in practice, for example, if coded symbols are applied to different independently fading tones in an OFDM system.
• Figure 2B has a natural extension to operations across clusters as shown in Figure 3.
• the example illustrates one operational benefit of BIA when applied to clusters.
• each station can operate using independent data packets and independent coded streams.
• each base station has two BIA transmitters that receive coded data from separate MCS units, which perform coding and modulation on different packets of the same user.
• Embodiments of the invention leverage the superior performance can be obtained by optimizing: the way users are grouped/scheduled for BIA
• the way parallel BIA transmission emanating from different transmitting clusters of base-stations are coordinated; that users are grouped/scheduled for parallel BIA transmissions across clusters; the way BIA codes are re-assigned to different users across clusters in the context of scheduling parallel BIA transmissions; and/or the way the power levels in the BIA codes are allocated to different users across clusters in the context of scheduling parallel BIA transmissions.
• multi-cell deployments multiple cells schedule parallel transmissions to subsets of their users.
• the way these parallel transmissions are coordinated can have a large effect in the delivered per-user rates and the overall system performance.
• embodiments of this invention focus on the case whereby whenever any given base-station (or cluster of base-stations) employs BIA to transmit to its users, all other clusters also employ BIA to transmit to their users.
• Embodiments of the invention include methods for operating in BIA in multisite deployments. In particular, one method considers embodiments regarding two classes:
• Cluster-synchronous BIA transmission schemes in this case, all clusters engage in parallel BIA transmissions, all with the same M, and K values, and all with the same set.
• IP J sets can be varied from cluster to cluster. Note that, on the set of time and frequency slots corresponding to transmitting a single alignment code (such as in the examples below), the values of M, K, and fe t3 ⁇ 4I are the same in all clusters engaging in synchronous BIA transmission, but these parameters can be changed over time and/or frequency, from one alignment code to the next).
• Cluster-asynchronous transmissions schemes in this case each cluster users its own BIA scheme with its own M, and K values. In this case, interference removal within a cluster does not result in any interference removal in neighboring clusters. As a result such schemes provide freedom in terms of letting each cluster separately optimize its BIA scheme towards the group of users it is serving. For instance the values of M and K (and thus N and L) may vary time and frequency within a given cluster independently of all other clusters. In addition the L symbols of an alignment block (or blocks of L-alignment block symbols) may be scrambled across time in a cluster specific way.
• BIA transmission schemes By properly varying the user groups served across clusters and their power parameters, improved BIA deployment schemes can arise, which outperform cluster-synchronous BIA schemes based on a common power allocation, i.e., based on a single static BIA scheme that employs a common
• the user topology is considered in small bins, and users from the i-t bin in cell b are referred to as users from bin (i,b).
• users from bin (i,b) are referred to as users from bin (i,b).
• bin (i,b) For convenience of exposition, it is assumed that all users in bin (i,b) are in the same location. However, the techniques presented do not need such assumptions to provide system performance benefits.
• all clusters assign on their m-th code (for each specific value of m) a user from the same relative location in their cell.
• Example 6 Cellular Transmission with BIA serving groups of same relative-location users in each cell and across cells.
• BS b schedules via a BIA M,K, ⁇ pl Mxl , scheme K users from bin (i, b),
• M K and p can be varied with T, or i(T). Note that M can be at most as large as the minimum of N t and the number of mobile antenna modes.
• the values of M and K are chosen/optimized individually, at each location being served (or over groups of locations being served).
• the "relative frequency" by which users from location i are scheduled (jointly across clusters) is chosen so as to optimize a given system utility function.
• multiple parallel BIA transmissions are multiplexed in frequency, with each band serving possibly a distinct set of users with the same M and K.
• the set of power levels can be chosen to optimize a system utility function, and subject to not violating a transmit-power constraint (as done for instance in example in Figure 6).
• Example 7 Cellular Transmission with BIA serving groups of same relative-location users in each cell but where the relative locations can differ from cell to cell.
• BS b schedules, via a
• M K and ⁇ p t , ⁇ can also be varied with T, or i(T). Note that M can be at most as large as the minimum of N t and the number of mobile antenna modes.
• the values of M and K are chosen/optimized individually, for each pair (or group) of locations (being jointly served).
• the "relative frequency" by which users from each pair (group) of locations are scheduled (jointly across clusters) is chosen so as to optimize a given system utility function.
• Example 8 Cellular Transmission with a common BIA code, in which users from multiple locations are being simultaneously served by each BIA scheme but where the k-t BIA code is assigned to the same bin location in each cell.
• BS b uses a
• i k i k (T) .
• M and K are fixed, but p [k] and/or q [k] can be varied with k and T, or with the relative location being served.
• clusters engage in synchronous BIA transmissions, whereby the kt code in each BIA-transmitting cluster is not necessarily assigned to users in the same relative cluster locations.
• Example 9 Cellular Transmission with BIA simultaneously serving relative-location users in a coordinated fashion across cells on the same BIA user
• BS b transmits via a scheme to K users.
• User k is chosen from bin (3 ⁇ 4(3 ⁇ 4 ) ,
• M and K are fixed and p t , is possibly varied with T, or with the relative location being served.
• the method enables BIA cluster-synchronous transmission, by splitting the time-frequency plain in OFDM transmission into blocks of OFDM symbols over time, B], B2, ....
• the base-stations are split into clusters (with the clustering sets possible depending on j), and whereby the c-th cluster of BSs employs a
• M ,X can be used for all transmitting clusters in order to enable cluster-synchronous transmission where each user in each cluster is interfered by the transmission of only one out of K j users in all other clusters.
• the vectors depend on the transmission block index j, the cluster index c and the code index k.
• the vectors are selected a priori, and the c- th cluster of base-stations assigns a subset of its users on its Kj BIA user codes, and independently of all other clusters, using information such as knowledge of the users nominal SINR levels, and/or nominal SNR levels from different BSs (within and outside the cluster), as well as knowledge of the a priori selected vectors used by one or more neighboring clusters of BSs engaging in cluster-synchronous BIA transmissions.
• the clusters are size-1, and each base-station employs two BIA schemes, one on each band (and of the form suggested in e.g., example 9.1 and Figure 10).
• the resulting transmission is a constant-power transmission with power per slot ( ⁇ + ⁇ 2 )/2.
• the neighboring BSs with indices b+1 and b-1 would instead serve high nominal-SINR users with code m in band F m , and use the remaining codes to serve low nominal-SINR users. Due to the choice Fi>F 2 , low nominal-SINR users enjoy a rate benefit at the expense of high nominal- SINR users (much like in conventional sub-band scheduling FFR systems) in every cell, while ensuring a constant power transmission.
• the for fixed k are chosen jointly over all clusters c (or in subsets of clusters), subject to some joint performance metric across all users (or subsets of users) scheduled on the kth user code.
• the kth code is assigned across the deployment to users with the same (or similar) nominal-SINR levels with respect to transmission from their cluster.
• neighboring clusters of one or more transmitting BSs assign on a given user code index k, sets of users with pre-specified but possibly different nominal SINR levels (pairing, e.g., cell- center with cell-edge users) and then choose values for and potentially values to select rate trade-offs among these user pairings.
• each base station may schedule users on a code index and location based on geographic user location and/or large-scale SINR values.
• BIA codes address different mobility levels. For a given number of transmit antennas, the larger number of codewords in the BIA code, the larger the rates provided by the code (i.e., the larger the number of multiplexed users), but also the longer the code. Since the user channels need to stay effectively constant for the duration of the code, the more codewords used, the larger the coherence time requirements on the mobile devices. As a result, in one embodiment, the system operates several BIA codes that span several coherence times (mobility levels) and can provide a range of rate/mobility options.
• Figures 11 and 12 are examples that illustrate when base stations only serve a set of users having a same relative cell location across the topology using codes that vary as frequency bands vary.
• different BIA codes are used to serve users of differnet mobility (rather than different locations).
• BIA Code 1 when using codes to address user populations with different mobility levels, users with coherence time Ti or higher are served on band Bi by BIA Code 1; users with coherence time between T 2 and Ti are served on band B 2 by BIA Code 2; and users with coherence time between T3 and T 2 are served on band B3 by BIA Code 3.

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