Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/30—Transmission power control [TPC] using constraints in the total amount of available transmission power
  • H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/0001—Arrangements for dividing the transmission path
  • H04L5/0003—Two-dimensional division
  • H04L5/0005—Time-frequency
  • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A) or DMT
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/24—Cell structures
  • H04W16/30—Special cell shapes, e.g. doughnuts or ring cells

Definitions

• Embodiments of the present invention are related to the field of coordinated transmission in wireless communication systems; more particularly, embodiments of the present invention are related to varying the transmit power of base stations in clusters in a coordinated manner across a multi base station environment, so that different base stations within a cluster operate together to transmit over multiple frequencies, bands and/or channels at different power levels, and so that the variations are jointly coordinated across all the clusters.
• Emerging and future wireless systems require ever increasing efficiency in the utilization of the radio frequency spectrum in order to increase the data rate achievable within a given transmission bandwidth. Increases in the throughput achievable per unit bandwidth can be accomplished by employing multiple transmit and receive antennas combined with signal processing. Indeed, a number of recently developed techniques and emerging standards are based on employing multiple antennas at a base station to improve the reliability of data communication over wireless media without compromising the effective data rate of the wireless systems. Alternatively, the multiple antennas can be used to increase the data rates achievable per unit bandwidth.
• Such MIMO schemes form the basis of what are referred to as single-user MIMO systems.
• channels corresponding to a distinct set of time-frequency slots are used to send multiple streams to a single user by coding an information bearing stream into a signal that is transmitted over the multiple antennas on the allocated channel.
• a scheduler is then used to schedule the transmissions for different users on different channels, in a similar way that it is done in a SISO transmission.
• very high sum-rates i.e., the sum of the rates of the users who are being transmitted to
• Multi-User MIMO Multi-User MIMO
• MU-MEVIO Multi-User MIMO
• zero-forcing or block zero-forcing
• MU-MIMO precoders use knowledge of all the channels between transmit/receive antenna pairs in order to linearly precode the users' signals that are to be transmitted, so that the receiver of each user "sees" its own signal in noise.
• LTE Long Term Evolution
• SU-MIMO Single-User MIMO
• base stations or controllers
• the same set of antennas the power levels across channels remain unchanged over time and the same set of users for scheduling.
• a method and apparatus for varying transmit power patterns in a multi-cell wireless transmission environment.
• the method comprises varying transmit power coordination patterns for base stations in the wireless communication system to jointly vary base station power over a set of virtual channels over base stations within a cluster and across clusters of base stations; and jointly transmitting by groups of the base stations to one or more user terminals in their respective clusters based on the transmit power coordination patterns.
• Figure 1 illustrates an example layout of clusters of size 3 with three subchannels per cluster.
• Figure 2 illustrates a frequency power allocation in the arrangement of Figure 1.
• Figure 3 is a flow diagram of one embodiment of a process for controlling a base station.
• Figure 4 illustrates a two-channel power/user scheduling allocation pattern for 4 controllers.
• Figure 5 illustrates a three channel power/user scheduling allocation pattern.
• Figure 6 illustrates a power/scheduling set allocation pattern over two channels.
• Figure 7 illustrates a 4-channel power/user-set allocation pattern for 4 controllers.
• Figure 8 illustrates a power allocation pattern for a sequence of controllers.
• Figure 9 is a block diagram of one embodiment of a base station.
• Figures 10-12 illustrate examples of transmit power patterns. DETAILED DESCRIPTION OF THE PRESENT INVENTION
• Embodiments of the present invention include multi-cell deployments that systematically coordinate resources and users among a set of controllers.
• each controller is part of a cluster, or a base station.
• the coordination of resources occurs in a time-varying manner (e.g., a periodically time varying manner).
• these schemes coordinate the use of the following: (i) the set of transmit antennas controlled by each controller; (ii) the transmit power limitations imposed on the antennas controlled by each controller; (iii) the set of users considered for scheduling per controller.
• Embodiments of the present invention jointly vary the power- level patterns applied to each channel over time/frequency slots and for each controller.
• the base station transmit power levels are allocated over the channels over the base stations in a cluster and over other clusters of base stations. That is, the power of the base stations within a cluster are a priori chosen but jointly with associated powers of base stations in other clusters, and are all jointly varied over a set of channels 1, 2, ..., F, such that the transmit power level allocations are not independent from the associated allocations in other (including neighboring) clusters. This results in increased throughputs for all users and a fairer performance between cell users and edge users without much increase in complexity compared to a non-coordinated system.
• 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”); random access memory (“RAM”); magnetic disk storage media; optical storage media; flash memory devices; etc.
• the method comprises varying transmit power coordination patterns for base stations in the wireless communication system to jointly vary base station transmit power over a set of virtual channels over base stations within a cluster and across clusters of base stations and jointly transmitting by groups of the base stations to one or more user terminals in their respective clusters based on the jointly varied transmit power coordination patterns.
• the transmit power of the base stations within a cluster are chosen but jointly with associated transmit powers of base stations in other clusters, and are all jointly varied over a set of virtual channels.
• the virtual channels may be frequency sub-bands, time-frequency slots, or other transmission resources, such as for example, spreading codes.
• varying the transmit power coordination patterns among the first plurality of clusters comprises assigning a transmit power pattern to each cluster of base stations in a manner that ensures that the transmit power of at least two base stations in a cluster is different for at least one of the virtual channels.
• transmit power coordination patterns are assigned so that base stations at edges of adjacent clusters transmit over at least one virtual channel at different power levels.
• transmit power coordination patterns are assigned to cause centrally located base stations (or, any base-station for which all of its neighboring base-stations belong to the same cluster as the base station) for all or a group of clusters to transmit at the same power level.
• the transmit power allocation patterns are varied over different channels.
• base station clusters and each of the allocated power levels for the base stations in four adjacent clusters for the two frequencies may be as follows:
• the power levels for transmitting within each different frequency band for each cluster are allocated in a non-uniform manner in which none of the transmit powers are the same for each base station for the same frequency.
• One advantage of these techniques is that by judiciously jointly varying the transmit power-allocation patterns over different channels (and the choice of these power patterns is optimized via offline optimization), together with the user sets for scheduling and, potentially, the antenna sites controlled by each controller, scalable multiuser MIMO deployments with many of the performance benefits of the (impractical) fully coordinated multiuser MIMO systems can be obtained.
• Good sets with such power/user set/antenna-site-set assignment patterns can be a priori generated offline or (regenerated periodically) and stored in lookup tables at the base station controllers.
• these user-sets are (although not necessarily) disjoint across controllers over any given channel, but can be jointly varied from one channel to another.
• the transmit power levels allocated to different controllers are also systematically and jointly varied.
• the antennas controlled by a single controller and the transmit power allocated to these antennas, individually, or in groups) can also vary over time and/or over frequency bands.
• base stations (or transmit antennas) are grouped in clusters and power levels are assigned to each cluster for each frequency, channel or subband, such that the base stations within a cluster operate in a coordinated fashion in which the transmit power is jointly varied for different clusters.
• all base stations in a cluster are fully coordinated. That is, their antennas act effectively as a single MIMO transmitter with CN T antennas, subject to a per-base station sum-power constraint.
• This can be implemented in practice by connecting the base station in each cluster to a cluster controller (processor) that collects all channel state information measurements from all user terminals in the cluster and, at each new time frame, schedules the set of users to be simultaneously served in the downlink and the corresponding beamforming vectors, power allocation and user codewords.
• the cluster joint processing involves only a limited number of base stations per each cluster controller (processor). In this way, the system complexity is bounded even when in the limit when a large number of base stations are used to provide coverage over a very large area(iV fa — > ⁇ ) .
• the chart of Figure 2 shows the allocation of clusters and base- station power allocation coefficients (referred to as "power mask” for purposes herein) to frequency subchannels.
• the total downlink system bandwidth is divided into 3 subbands, corresponding to 3 different clustering layouts.
• an overlapped, or intertwined, coordination architecture is obtained by shifting the basic layout of Figure 1.
• Each shift is assigned to a subband.
• cluster 1 for the "shift 1" arrangement is ⁇ 2,4,7 ⁇ , while cluster
• shift s any set of adjacent 3 base stations needs to be connected to a cluster processor.
• each controller treats jointly only 3 base stations at a time. Therefore, in one embodiment, the high-speed interconnections necessary for joint transmission scheme involve only local links.
• each cluster subband is further divided into subchannels
• the coefficients ⁇ , ⁇ , and ⁇ are repeated in each column of P.
• each cluster makes use of the whole system bandwidth (full frequency reuse).
• the coefficients are chosen such that a ⁇ ⁇ ⁇ ⁇ ⁇ 0 .
• FIG. 3 is a flow diagram of one embodiment of a process for varying transmit power in a communication system.
• the process is performed by processing logic that may comprise hardware (e.g., dedicated logic, circuitry, etc.), software (such as is run on a general purpose computer system or a dedicated machine), or a combination of both.
• processing logic may comprise hardware (e.g., dedicated logic, circuitry, etc.), software (such as is run on a general purpose computer system or a dedicated machine), or a combination of both.
• the process begins by processing logic dividing a set of channels used by a first cluster of adjacent base stations that operate together as a single distributed multi-antenna transmitter into subchannels (processing block 301).
• the channels are divided into frequency subbands.
• processing logic allocates power for transmission over the subchannels in a non-uniform pattern to each base station in the first cluster jointly within the first cluster and across other clusters (processing block 302).
• allocating power for transmission comprises setting each base station in the first cluster to transmit in at least two of the subchannels as different power levels over each subchannel in a non-uniform manner among the base stations of the first cluster.
• processing logic schedules transmissions for base stations in the first cluster (processing block 303) and causes the joint transmission from base stations in the first cluster to one or more user terminals, including transmitting wireless signals on each of the subchannels whereby the transmit power at each base station and each cluster complies with the pre-as signed power levels of the power coordination patterns (processing block 304).
• the process further comprises shifting a number of base stations into different clusters that each operate together as a single distributed multi-antenna transmitter, and reassigning transmit power coordination patterns to each of the different clusters in a manner that ensures that at least two base stations in a cluster have transmit power levels for at least one of the subchannels that are different.
• the transmit-power-level patterns generate transmit-power variations in a systematic manner over each channel.
• the associated transmit power levels within the cluster and across all clusters within some level of proximity implicitly result in favoring certain users to be chosen by the scheduling/MEVIO transmission algorithm within the cluster.
• the power allocation pattern across the cluster deployment accomplishes this by affecting the signal-to-interference-plus-noise ratio (SINR) of each user.
• SINR signal-to-interference-plus-noise ratio
• the transmit power at the controller serving a user in a given channel affects the large- scale signal level received by any given user, while the associated transmit powers at the controllers controlling neighboring antennas generate interference signals to this user and dictate the large-scale aggregate interference level experienced by that user.
• the techniques attempt to strike a balance between complexity of implementation, scalability, and performance. If the patterns are properly designed, different (and possibly distinct) subsets of users are favored for scheduling over different channels and by different controllers. As a result, the complexity of the scheduler/MIMO algorithm run by each controller can be further reduced (without significantly compromising its performance), by means of restricting the size of the scheduling sets that each controller operates on within any given channel.
• the powermasks "bias" the SINR levels that each user is experiencing within different channels, each user is favored for scheduling (and may only be considered for scheduling) only on a small subset of the channels. As channel state information may be required to consider a user for scheduling within a channel, such power-mask variations can also potentially allow reducing the channel training overhead of the system without appreciable system performance degradation.
• Embodiments of the invention include methods for joint scheduling and physical-layer transmission in the forward link of multicell environments.
• there are multiple controllers each controlling the transmission from a set of transmit antennas, which may be at one site or at multiple sites.
• wideband multiuser transmission is achieved using coded Multiple- Input Multiple- Output (MIMO)/Orthogonal Frequency Division Multiplexing (OFDM).
• MIMO Multiple- Input Multiple- Output
• OFDM Orthogonal Frequency Division Multiplexing
• Joint scheduling/MIMO transmission is performed over groups of time- frequency slots in the OFDM transmission viewed as channels.
• the MIMO transmission technology can be either single-user MIMO or multiuser MIMO.
• the time-frequency slots are mapped (possibly as groups) on to channels.
• each controller is assigned a set of transmit antenna sites, a given transmit power limit, and a subset of user terminals to consider in its scheduling/MIMO transmission algorithm.
• each controller controls one or more base stations that are in a cluster. The controller may be in a base station, a separate unit, or distributed throughout multiple base stations.
• the MIMO transmission algorithm is a multiuser MIMO precoding algorithm (e.g., block zero- forcing precoder).
• the MIMO transmission algorithm is a single-user MIMO algorithm.
• the user selection algorithm could be based on proportional fairness or any other criterion.
• a joint scheduling/MIMO transmission algorithm is run over each controller separately (over the set of users specified by the partition map) with respect to a given scheduling criterion.
• varying base-station cooperation patterns and transmit power masks are implemented as a two-stage operation.
• the following two- stage operation is described in terms of controllers. These controllers may be part of a base station controlling one or more antennas.
• stage 1 a set of parameters that are to be used in stage 2 by each controller are generated. These parameters are stored in a lookup table indexed by a number of (virtual) channels, 1,2, ..., F. For a given channel entry with index f, the lookup table provides parameters for the joint scheduling/MIMO transmission that are to be used by each controller. In one embodiment, once the lookup table is generated, it is pushed to the controllers. In one embodiment, although the entire lookup table could be pushed to each controller, only the subset of parameters pertaining to the operation of that controller is pushed to each controller. Note also, that stage 1 can be a one-shot computation, e.g.
• Stage 2 corresponds to the joint scheduling/transmission operations that are run by each controller.
• the set of controllers perform this operation in parallel.
• each controller first identifies the actual "virtual channel" that this corresponds to in the lookup table, and fetches the corresponding parameters from the lookup table.
• these parameters include: (i) the set of transmit antennas and sites from which the controller is transmitting within this channel; (ii) the transmit power constraints on the controller for this channel; (iii) the set of users that need to be considered for scheduling by the controller's joint scheduling/MIMO transmission algorithm.
• there are one or more repositories of real-time scheduling parameters for each user (containing, e.g. updated versions of the user weights, in the scheduling algorithm).
• each controller accesses the repositories in order to guarantee that it has available the relevant weights/parameters for all the users it will be considering for scheduling within the given channel. Consequently, the joint scheduling/transmission algorithm is implemented, a subset of users is chosen and served, and information is pushed in the repositories to update the weights of all the users in the serving set. In one embodiment, this update occurs locally at each controller, in which case, updated weights/parameters for the controller user- scheduling set are pushed to the associated repositories. In another embodiment, sets of parameters summarizing the users served and their rates can be pushed back to the repositories, where the updated weights/parameters are computed and stored.
• step 2d i.e., the joint scheduling/transmission algorithm would be performed on every channel
• the operations 2c and 2e above need not occur on every single use of the joint-scheduling algorithm.
• mappings that show how controllers are allocated transmit antenna sites, transmit powers and user sets for scheduling.
• groups of time-frequency slots are mapped into a set of "channels" in a periodically time- varying fashion. It is then assumed that the mapping provided in each example is used to determine on each such channel the transmit powers levels that would be used by each controller on this channel (group of time-frequency slots), the antenna sites controlled by each controller, and the subset of users out of which each controller will select the subset that it schedules in each instance.
• the mapping lists which antennas are controlled by the given controller, the total power available to that controller for signal transmission, and the subset of users over which the joint scheduling-transmission algorithm will be implemented.
• one-dimensional deployment examples are used in which, a finite number of antenna sites are uniformly spaced over a line segment that wraps around, i.e., the left end of the segment is viewed to be the same point as its right end.
• the M antenna sites are enumerated as So, S 1 , ..., S M - I -
• the left and right neighboring antenna sites to S 1 are sites Si -1 and S 1+1 , respectively, except when "i" is equal to 0 or to M-I.
• the left and right neighbors of So are sites S M and S 1 , respectively, while the left and right neighbors of S M - I are sites S M - 2 and So , respectively.
• FIG 4 illustrates a two-channel power/user scheduling allocation pattern for four controllers (CO, ..., C3) controlling each of 4 antenna sites (SO, ..., S3).
• U 1 denotes all the users "associated" with antenna site S 1
• this association is distance-based (i.e., path-loss based). More generally, it can be based on large-scale signal-to-interference-plus- noise power ratios (SINRs).
• SINRs signal-to-interference-plus- noise power ratios
• the set U 11 C corresponds to the subset of users that are sufficiently close to S 1 (and thus referred to herein as "center users"), while the set U 11E corresponds to the subset of users that are sufficiently far from S 1 (and thus referred to herein as "edge users").
• U 11C , and U 11E can be overlapping sets (although in the figure these two sets are shown to be non-overlapping).
• U 11E may correspond, e.g., to the whole set U 1 .
• the split between "center” and “edge” users may not be based on distance, but rather, nominal large-scale SINR levels.
• any user in U 1 is included in the center group of a site if its average nominal large-scale SINR exceeds a certain threshold, while it is included in the edge group if its nominal SINRlevel is below a certain threshold.
• U 11C (channel 2), while users in U 11C are served in the complimentary channel.
• the sets U 11C and U 11E may or may not be disjoint.
• U 11E U 1
• U 11C c U 1
• edge users can be scheduled on both channels, while center users can only be scheduled when the associated controller transmit power is low.
• U 11 C U 1
• U 11 E c U 1
• center users can be scheduled on both channels, while edge users can only be scheduled when the associated controller transmit power is high.
• Table 1 contains a sample lookup table description for the example in
• the lookup table provides a description of the joint transmit- antenna/transmit-power/user-set pattern allocation across controllers over two channels.
• the channels correspond to distinct OFDM tones over the same OFDM block, or the same tone of distinct OFDM blocks.
• P H and P L have to be chosen in such a way that the nominal SINR levels of the edge users are favorable (i.e., sufficiently large) during the slots (channels) that they are served.
• Table 1 Example of joint transmit-antenna/transmit-power/user-set pattern allocation over two channels and four controllers
• the following three representative examples involve wireless systems comprising a wrapped linear array with 8 transmit antenna sites and 4 controllers. In these cases, a single controller controls antennas at multiple (two in this case) antenna sites.
• U 11C denotes the subset of users among those in U 1 that are the closest to the S 1 's. In this case, however, the "edge" user set is split into two sets: U 11L and U 11R ("left” and "right” edge group, respectively). Note again that, although, the groups have been split in terms of their distance and relative location with respect to S 1 , more relevant large-scale signal-to- interference levels can be used for the user partitioning.
• Figure 5 illustrates a three channel power/user scheduling allocation pattern associated with Table 2. Referring to Figure 5, there are 4 controllers (CO, ..., C3), each controlling 2 antenna sites (controller C3 and the sites S6 and S7 that it controls are not shown in the figure). There are 3 power levels: P 1 , P 2 , and P 3 .
• Three sets of users are generated from the set of users U 1 that is associated with antenna site S 1 : a set of "center” users (U 1 ⁇ ) and a set of "left-edge” users (U 1 ⁇ ), and a set of “right-edge” users (U 11R ). All "center” users are scheduled within Channel 3. All controllers are allocated the same transmit power (P 3 ) in that channel. Channels 1 and 2 serve users in edge sets. In these channels, the controller transmit-power allocations are varied between P 1 and P 2 (with P 1 > P 2 ), such that when the "odd" controllers use power P 1 (P 2 ) the even ones use power P 2 (P 1 ).
• Table 3 Example of joint transmit-antenna/transmit-power/user-set pattern allocation over three channels and four controllers, where each controller controls two antenna sites
• each controller changes from channel to channel (alternatively, they may change over time).
• the transmit power allocated to each controller remains unchanged from channel to channel.
• each of the four controllers controls 2 antenna sites within each channel.
• the antenna sites controlled by the controllers vary across the two channels.
• the transmit power remains unchanged from channel to channel.
• the set of users U 1 associated with antenna site S 1 is split between center users (U 11 C) and edge users (U 1 ⁇ ); the "edge" user set is further split into two sets: U 11L and U 11R ("left" and "right” edge group, respectively).
• the line segment over which antenna sites are spaced wraps around.
• certain users may be considered for scheduling (by some controller) only on one of the channels while others may be considered for scheduling on multiple channels.
• center users may be scheduled over the two channels while edge users are always scheduled on one channel. Notice, however, that scheduled edge-users are considered for scheduling when both neighboring antenna sites are controlled by their controller.
• Table 4 Example of joint transmit-antenna/transmit-power/user-set pattern allocation over two channels and four controllers, where each controller controls two antenna sites which can vary depending on the channel used
• the transmit antenna sites, transmit power and user set to be scheduled by any given controller are all varied from channel to channel.
• each of controllers, (CO, ... , C3) controls 2 antenna sites, where the sites controlled by each controller and their transmit power levels vary across channels.
• the set of all combinations is described the four channel power/BS-to-controller associations shown in Table 5.
• Table 5 Example of joint transmit-antenna/transmit-power/user-set pattern allocation over four channels and four controllers, where each controller controls two antenna sites, and the antenna sites transmit power and user sets vary from channel to channel
• each controller controls only two antenna sites at a time, and oscillates between controlling only two patterns. More antenna sites can be controlled at any time and the controller can be assigned to control many more subsets of antenna sites.
• Figures 10, 11, and 12 show such examples with clusters of size 3. The controllers are designated C 0 -C 3 and the base stations are designated So-S 11 . In the embodiment shown in Figure 10, two channels are employed. Each controller is associated with the same set of base stations over both channels. The center base station in each cluster always transmits at power P M - The edge base stations in each cluster transmit at power P L over one channel and at power P H over the other channel.
• each controller is associated with the same set of base stations over both channels and the center base station in each cluster always transmits at power P M -
• the power of the left edge base station of a cluster at a given channel (1 or 2) equals P H
• the power of the right edge base station of the neighboring cluster to the left is set to P L over the same channel.
• the shaded regions in the figure are meant to qualitatively suggest how the coverage areas over which users are scheduled vary over channel and cluster, assuming P H >P L -
• Figure 12 shows another related embodiment involving 3 channels with clusters of size three.
• the clusters are varied over the three channels (implementing a full shift system).
• the center base station transmits at power P M while the edge base stations transmit at power P L .
• P M the center base station transmits at power P M
• P L the edge base stations transmit at power P L .
• Related embodiments involving two dimensional cellular layouts can be readily designed.
• each controller controls 7 antenna sites at a time.
• the static antenna assignment case whereby the association between controllers and antenna sites is fixed, and where each controller controls a "center" site and its six neighboring sites. If a total of F distinct power- level patterns are employed across controllers, a total of F channels could be employed to depict the associated pattern allocations.
• each controller/ transmit antenna site association changes over channels.
• each controller may oscillate between 7 possible "7 -transmit antenna site" cluster configurations, whereby the central antenna site in the cluster controlled by the controller is periodically varied among a given site and its 6 first- tier neighbors.
• F distinct power-level patterns are employed across controllers, a total of 7F channels could be employed to depict the associated pattern allocations.
• the lookup table parameters for the 7F channels could be generated offline.
• the scheduling of users is performed jointly over channels (or coordination patterns). While assigning disjoint sets of users to different controllers over any given channel, each scheduling algorithm is run independently on each controller.
• the rates of the users across the multicell deployments can still be coupled, however, even though each controller schedules users independently of others within any given channel. Specifically, if deployments are used where on different channels a given user is assigned to different controllers, the scheduling of users is indirectly coupled across controllers. In these cases, even though user selection is conducted independently within each channel and for a given controller, there is information shared across channels (or coordination patterns) and this information is exploited by the controller to update parameters used in the user selection of each of its channels. The information can be the weight associated to each user, when a user was last scheduled, and/or other pertinent scheduling parameters.
• the coupling between rates of users across the multi-cell deployment can occur even in the case that there is a static assignment of transmit-antennas to the controllers.
• such user-rate coupling can be induced by using varying transmit power-level patterns across controllers and by judiciously associating (for scheduling), e.g., "edge" users with different controllers over different channels.
• One such example is illustrated in Figure 8.
• the antenna-to- controller association is the same as in the example of Figure 4. Referring to Figure 8, each of controllers C n , (where only Co, ..., C 3 are shown), controls one antenna site, S n .
• the power levels used by each controller are varied over two channels between a low power (P L ) and a high power (P H )-
• P L low power
• P H high power
• “center” users i.e., users sufficiently close to an antenna site, or users with sufficiently high nominal SINR
• edge users i.e., users sufficiently far from their nearest antenna site
• the power per controller of Figure 8 is varied between a low power and a high power, exactly like in Figure 4. However, the users association to controllers is different in Figure 8 from that in Figure 4.
• Embodiments of the present invention enable the design of low- complexity readily scalable high-performance methods for joint scheduling/MIMO transmission algorithms for downlink multicell deployments.
• a priori design of jointly time-frequency varying patterns of controlled antenna sites, transmit power limits, and user sets to be scheduled can yield MIMO deployments with high sum rates and improved throughputs for users at the cell edges.
• Elements of one embodiment that make these system designs attractive include:
• a set of controllers each of which may control one of multiple antenna sites, each with one or more antennas.
• a coded MIMO/OFDM transceiver along with a family of codes and coding rates. Given a rate for a scheduled user, a code and a coding rate are selected for this particular user and are used to encode a segment of the information- bearing signal for that user. In one embodiment, the resulting signals for all users are summed up and transmitted via OFDM.
• a map/lookup table that is jointly used by all controllers, and whose entries are cycled through in unison by all controllers.
• the map lists resource allocations over a set of "channels", which are synchronously visited (or, synchronously cycled through) by all controllers.
• each channel entry provides for each controller the following: (a) the transmit antenna sites that this controller controls (and will thus schedule transmissions) within this channel; (b) the total transmit power to be used by each base station controlled by this controller on this channel; (c) the set of users over which the scheduling/ MIMO precoding algorithm is to be performed by the controller; (d) other pertinent information such as, e.g., the duty cycle of each channel. 5.
• a mapping of time-frequency slots into virtual channels To determine what is transmitted within any time-frequency slot, the slot (or a set of slots) is first mapped into a virtual channel entry. Then all controllers choose their resource allocation parameters according to what is listed for them on that channel entry in the map.
• given to the controller are the following: (a) a transmit power constraint at the controller; (b) a set of users (from which the controller will choose a scheduled set), (c) the user "weights", i.e., the factor by which each users' rate will be weighed in scheduling/optimization criterion; (d) the required channel parameters between the antennas controlled by the given controller and the antennas of each user; (e) the aggregate interference level at each user.
• the controller uses a joint scheduling/MIMO transmission algorithm comprising a scheduling algorithm (e.g., a proportional fair-scheduling algorithm), together with a MIMO transmission scheme.
• a scheduling algorithm e.g., a proportional fair-scheduling algorithm
• the MIMO transmission scheme is either a SU-MIMO algorithm or a multiuser precoding algorithm (i.e., block zero-forcing precoder).
• the scheduling algorithm runs on top of the coordinated patterns. This algorithm results in a subset of users (along with the associated rates) that are to be served within the given channel by the given controller.
• the algorithm also generates the associated parameters for the MIMO transmission scheme. In one embodiment, these include the channel coding parameters, the number of streams per user, and, potentially (e.g., in the case of multiuser MIMO, or closed loop SU-MIMO) the associated precoding matrix. Then the strategy listed in item 2 is used for transmission, and the scheduling parameters of the users are appropriately updated.
• One advantage of embodiments of the invention is that it allows interference management and mitigation for achieving high- sum rates and high edge throughputs, while maintaining the simplicity of schemes that do not employ multi- cell coordination.
• each controller runs its own scheduling/MIMO transmission algorithm, as is the case in the uncoordinated case.
• significant improvements can be obtained in terms of sum-rates and edge-rates without significant increase in complexity.
• the resulting schemes are also readily scalable in: (a) number of antenna sites following the map; (b) number of antenna sites controlled by each controller, (c) number of antennas per site; (d) receive antennas per user; (d) granularity in the transmit power profile.
• FIG. 9 is a block diagram of one embodiment of a base station that performs one or more of the functions described above.
• the base station 900 includes a control 901 coupled to a network interface 902 and baseband processing 903.
• Baseband processing 903 is also coupled to network interface 902 and amplifiers/Tx/Rx 904, which comprises the transmitter(s) and receiver(s) of the base station, along with their amplifiers, and these are coupled to antennas 905.
• a power supply 906 also provides power to components of base station 900.
• All embodiments concern cases where transmission happens jointly from at least two distinct locations. If there is one base station per location, that means transmission JOINTLY happens from multiple base- stations (i.e., one entity collects all channel info, does scheduling and decides what all the base station in the cluster will jointly transmit).
• Control 901 includes a control interface 901(b) to send and receive control information, such as, for example, information specifying coordination patterns and/or information to control other base stations or antenna controllers.
• Processor(s) 901 (a) control, or cause to be controlled, many of the base station's operations (or operations of other base stations), including changes in coordination patterns.
• processor 901 (a) operates as a controller to collect all channel information, perform scheduling and determining which base stations in the cluster will jointly transmit with each other. (Note that alternatively these control functions could be implemented in a device outside of a base station and control all base stations in one (or more) clusters.)
• Memory 901(c) stores instructions to perform the functions described herein and other data, along with pre-defined coordination patterns, such as those described above. In one embodiment, memory 901(c) stores one or more lookup tables as described above.
• a timing/clock unit 901(d) provides timing and/or clocking for the base station, in a manner well-known in the art.

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• 2009
  • 2009-08-10 US US12/538,739 patent/US8705484B2/en active Active
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