Classifications

• • 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

Definitions

• the present invention relates to the field of wireless data communication, cellular systems, and coding; more particularly, the present invention relates to sending information via silent symbol coding over under-utilized channels in wireless systems.
• Broadband wireless systems are typically designed for per cell capacity maximization with some fairness constraints for individual users. Even when the fairness constraints are taken into account, the basic assumption is that the allocated rate can be fully utilized.
• practical systems have limitations in terms of smallest chunks of bandwidth allocation. For instance, in HSDPA systems, the smallest time unit a given channel (e.g., spreading code, frequency band, etc.) dedicated to a particular user (say Alice) is 2 milliseconds long. Suppose B bits are waiting in Alice's transmission queue and Alice's channel quality is such that this smallest unit can deliver W bits, which is strictly more than B bits. Therefore, the system wastes (W-B) bits by either going into an idle mode for the remainder of the time slot or by sending padded bits. Note that the main problem here is that the system cannot reassign the channel to another user and partially reuse since the scheduling decisions are done on a per slot basis in this example.
• a method for use in a cellular system in which a channel allocated to a primary user is underutilized at times comprises: creating a unique 0-1 valued permutation code to transmit bits of a secondary user on a channel of the primary user; creating one or more codewords based on a first set of symbols to be transmitted for the primary user and the permutation code; and transmitting the one or more codewords on the channel.
• Figure 1 illustrates, in a typical wireless system, a given base station allocating each of its users a set of channels in the form of frequency bands, time slots, and spreading codes in a scheduling interval.
• Figure 2A illustrates the message blocks for Alice (primary user) and Bob (secondary user) being used together to create a permutation of Bob's symbols padded by silent symbols to completely fill the available symbol locations.
• Figure 2B illustrates an alternative embodiment of a coding arrangement that uses silent symbol coding.
• Figure 3 illustrates a block diagram of high-level actions at a primary user's receiver.
• Figure 4 illustrates a block diagram of high-level actions at a secondary user's receiver.
• Figure 5 illustrates a block diagram of high-level actions at a secondary user's receiver with an extra signal processing operation when z 2 can be decoded.
• Figure 6A illustrates a single cell scenario.
• Figure 6B illustrates a multiple-cell scenario.
• Figure 6C illustrates a multiple-cell scenario and the coordination of resource allocation based on queue backlogs and channel state information.
• Figure 7 illustrates decoding at a secondary user's receiver using permutation coding to learn about the interference and perform interference cancellation to boost up its own reliability or capacity over the same channel.
• Figure 8 illustrates decoding at a secondary user's receiver in which interference cancellation is used over the primary channel of the secondary user, where primary and secondary channels are orthogonal to each other.
• Figure 9 illustrates a block diagram of one embodiment of a base station.
• DETAILED DESCRIPTION OF THE PRESENT INVENTION [0006] New techniques are disclosed herein for utilizing partially utilized wireless channel resources to send more information to other users who observe congestion. Embodiments of the invention achieve such utilization by inserting silent symbols between the symbols to be actually transmitted over the partially used wireless channel. The positions of the silent symbols in a resource block carry information to a user other than the user to whom the particular resource block is addressed.
• a result of using the techniques disclosed herein is to assist wireless users who do not get enough data rates from the resources allocated to them at a given base station (or equivalently wireless access point or wireless transmitter) by sending them more information over under-utilized resources at the same and/or other base station(s).
• 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.
• FIG. 1 a wireless system with a scheduling frame of T time slots and F frequency sub-bands is depicted.
• a given base station allocates each of its users a set of channels in the form of time slots, frequency bands, and spreading codes within a scheduling frame.
• the blocks 101 are assigned to a particular user (say Alice) by the base station A.
• Base station A communicates with Alice by mapping her bit- stream into a non-zero sequence of symbols and sending individual symbols over the allocated resources with each symbol having the same symbol duration T sym .
• the resource blocks assigned to a user can be represented logically as a sequence of symbols with each symbol having a unique location in the source block.
• the resource blocks assigned to Alice by base station A can be mapped onto n symbol locations.
• base station A makes a dual assignment for a given set of resource blocks.
• Each set of resource blocks are first assigned to a primary user. If the set of resource blocks are under-utilized by the primary user, then they are also assigned to a secondary user.
• the bits of the primary user are mapped onto a sequence of symbols using a constellation with non-zero constellation points (i.e., if S is the constellation and se S, then s H s>0, here s H is the conjugate transpose of the column vector s).
• the primary user symbols and the secondary user bits are then used together to determine a unique permutation codeword where silent symbols are inserted before, after, and/or in between the symbols generated from the primary user bits.
• Base station A transmits the permutation codeword starting from the leftmost symbol: if the next symbol to be transmitted is a silent symbol, base station A does not send anything for the next symbol duration. If the next symbol is not a silent symbol, base station A transmits the signal waveform corresponding to that symbol.
• Figure 2A depicts an example of how primary user (Alice) and secondary user (Bob) information bits are combined together to create such a unique permutation codeword using both primary and secondary user bits. That is, the message block for Alice (primary user) and Bob (secondary user) are used together to create a permutation of Bob's symbols padded by silent symbols to completely fill the available symbol locations.
• L bits that are being sent to Alice are converted into K symbols and M bits being sent to Bob are received by coder 201, which performs a silent symbol (permutation) coding to generate n symbols.
• One method of silent symbol coding performed by coder 201 proceeds as follows. When the primary user's resource blocks are fully utilized, the codeword to be transmitted by the base station includes no silent symbol and only the symbols generated from the primary user's bit stream are sent out. In one embodiment, whenever primary user's resource blocks are under-utilized (n > k), the following set of actions is taken:
• Primary user's message of length L bits waiting in the transmission queue of the base station is mapped onto a bit stream of O's and l's.
• the mapping operation need only be reading L bits from the primary user's queue.
• Primary user's bit stream is mapped onto k modulation symbols Si, S 2 ,..., S k based on the current symbol constellation that the base station is using for the primary user as dictated by the channel state information and rate control algorithm being used in the system.
• M is equal to l+
• CWi,decimai is referred to as the index of CWi and i is used in place of CWi,decimai «
• the index i takes values in the range [0, ⁇ -l] and the set of CW 1 1 S is enumerated as CWi(O), CWi(I),..., CWi(i),..., CWi( ⁇ -l).
• CWi constructed in the previous operation is used to generate a unique codeword X by computing a unique permutation of CWo. Uniqueness here implies that two different codeword in the set of CWi will be mapped to two distinct permutation codes.
• O's represent the silent symbols and l's represent the actual epochs symbols of the primary user is transmitted.
• the coding operation may be performed wherever the baseband processing is performed. This may be in a basestation, access point or other node in the wireless communication system.
• the secondary user knows that data may be sent on the primary user's channel because the base station controller notifies the secondary user when allocating the resources (e.g., channel) to the primary user and tells the both the primary user and the secondary user what coding profile (e.g., permutation coding is enabled or disabled) is to be used. This notification may be performed as part of the profile being provided by the controller to the primary and secondary users.
• resources e.g., channel
• Figure 2B is an alternative embodiment depicting silent symbol/permutation coding.
• L bits to Alice are converted into k symbols 221. These are input into channel coder 240 that performs channel coding that produced encoding symbols 222, which are sent to silent symbol (permutation) coding 210.
• M bits for Bob are input along with an n-bit 0-1 base permutation code into permutation computation block 241.
• the output of permutation computation block 241 is input with n encoding symbols 222 to multiplier 212, which performs symbol-by-symbol multiplication between the output of permutation computation block 241 and n encoding symbols 222, resulting in transmit codewords 223.
• CW denotes the codeword generated at the base station (i.e., sequence of silent symbols interspersed with the actual symbols sent to the primary user)
• zi denotes the possible interference from other radio signals over the same resource blocks CW is sent over
• ni denotes the noise added at the primary user's terminal.
• the MAP rule requires the knowledge of k at the receiver.
• Feedback 310 may be used to notify silent symbol detector 301 when the detection results has not correctly identified the silent symbols. This may occur if too many or too few symbols are identified.
• the decoding at the primary user may be performed by directly decoding the incoming symbol stream assuming no knowledge of the permutation coding. This can be done since the permutation coding is another type of noise (albeit a multiplicative one like fading coefficients). This is described in more detail below.
• the secondary user first performs silent symbol detection using silent symbol detector 401 through hypothesis testing to construct X.
• the detection can be symbol by symbol and, in one embodiment, ML or MAP rules are exactly the same as outlined for the primary user but using the statistics of z 2 +n 2 instead of zi+ni.
• Decoder 402 receives and performs permutation code decoding to generate CWi.
• feedback may be used.
• Figure 5 depicts another case in which the CW term can be treated as interference and Z 2 is decodable at the secondary receiver even when CW is treated as noise.
• Feedback may be used to notify other portions of the receiver where errors in decoding have occurred, such as those mentioned above.
• the secondary user performs permutation code decoding for the input
• the permutation code decoding steps are as follows:
• rCWi is the same as CWi and the bits sent for the secondary user are successfully received.
• the secondary user concatenates all such received codewords and parses the bits to divide the bits into blocks and packets for further processing at the upper layers. Since there is a certain probability of error in the decoding process and some blocks/packets can be corrupted, in one embodiment, error detection codes, error correction codes, and/or erasure coding techniques typically should accompany this permutation code decoding.
• a base station BS is shown communicably coupled to a controller 601 and wirelessly coupled to user terminals, Alice and Bob, with channel states h ⁇ and h 12 respectively, for sending bits R 1 and R 2 respectively. Every user is assigned a set of resource blocks as the primary users in a scheduling interval across time slots, bands, and spreading codes.
• the base station B checks the resources that will be under-utilized given the current backlogs in user queues and the number of bits to be transmitted to each user in the next scheduling interval. Each such resource then is assigned to exactly one secondary user (note that the same user can be secondary users over multiple orthogonal resource blocks). The assignments to secondary users take into account many factors such as channel gain estimates over these set of resources and the queue backlogs.
• u is in U if and only if B u >0.
• p u>1 denote the successful decoding probability of permutation codes over research block i.
• This number typically depends on the channel gains from the base stations to the particular secondary user, the modulation/coding levels being used, noise and other interference power.
• p u, i's can be obtained through upper-bounds, approximations, simulations, empirical offline evaluations, and/or online learning. Given these definitions, one can use many different methods to assign underutilized resource blocks to individual users as described next.
• resource assignment to individual backlogged users is done such that, after the assignment, maximum backlog across users is minimized.
• Each underutilized resource blocks are first placed in an assignment set A that has exactly G elements.
• an ordered set O u is created whose elements are T 1 - p u>1 in descending order.
• the method assigns one resource block from assignment set A as follows.
• the above allocation strategy guarantees stability provided that there exists a strategy that stabilizes the buffers (i.e., no buffer has an average backlog that grows in an unbounded fashion).
• Other methods with different objectives lead to different secondary user assignment strategies.
• One method that tries to maximize the throughput over the secondary use assigns each resource block to the user that has the maximum ry p u>1 among all users over this resource block.
• PFS metric or other metrics are computed per (user, resource block) pair and the one that maximizes the metric becomes the assignment pair, after which the metrics are recomputed with updated metrics over the unassigned resource blocks.
• FIG. 6B depicts a multi-cell scenario where Bob is a primary user for transmissions from its own cell and secondary user for transmission from another cell.
• controller 620 is communicably coupled to base stations BS 1 and BS 2 .
• Base stations BS 1 and BS 2 are communicably coupled wirelessly to user terminals such as Alice and Bob.
• base station BS 1 wirelessly communicates with R 1 bits to using a channel with channel state h ⁇ and R 2 bits to Bob using a channel with channel state h 12 .
• base station BS 2 wirelessly communicates with Rl bits to Alice using a channel with channel state h 21 and R2 bits to Bob using a channel with channel state h 22 Unlike the scenario in Figure 6A, the primary and secondary users of a given resource block do not belong to the same cell. If a resource reuse factor of 1 is in place, then in this scenario a user can be both a primary user and a secondary user for the same resource block, but with respect to distinct base stations.
• Figure 6C shows even a more general feasible application scenario in which the techniques described herein can be used. Referring to Figure 6C, a controller node 630 behind the cell tower keep user queues 63 I 1 -OS I M and manages all the resource allocation decisions at each cell.
• Alice and Mark have only assignments as primary users and they are under-utilizing their resource blocks. If their resource block is orthogonal, then Bob can simultaneously listen to both of them in a non-interfering fashion and become a secondary user for more than one resource block assigned at different locations. On top of it, Bob has its own primary resource assignment from his own base station (e.g., this typically means the base station with the strongest signal strength for Bob). [0039] Another method disclosed herein is to use underutilized resources for interference cancellation purposes.
• Figure 7 shows the decoding procedure for the case when a user is both a primary user and a secondary user for the same resource block assigned by different base stations forming an interference channel CW+z 2 +n 2 , where CW is the interference from the other cell, Z 2 is the desired signal from user's base station, and n 2 is the interference.
• the interference channel CW+z 2 +n 2 is input to both silent symbol detector 701 and interference canceller 702.
• the constructed permutation codeword X output from silent symbol detector 701 is input into permutation code decoder 703 and interference replicator 704.
• Permutation code decoder 703 performs permutation code decoding.
• the permutation coding as disclosed herein can be utilized as follows.
• the permutation code carries information about the symbols Si, ..., S k which are the actual interference terms (the rest of n-k symbols in CW are silent and causes no interference). Depending on the achievable rate of the permutation code, all or a subset of these k symbols can be encoded and embedded in CW. Then the decodable portion can be subtracted from CW+z 2 +n 2 by interference canceller 702 mitigating and even (if enough capacity exists) completely eliminating the interference CW at the secondary user, thereby outputting z 2 +n 2 to receiver 705, which generates Z 2 therefrom. This technique can be used towards increasing the reliability or pushing the rate of Z 2 to a higher bit rate to achieve higher capacity over the primary resource of the secondary user.
• Figure 8 shows another interference cancellation scenario where the primary and secondary resource blocks at a receiver are on orthogonal resources.
• receiver is the secondary user for the resource block over which CW+z 2 +n 2 is delivered and it is the primary user for the resource block over which Z 3 +Z 4 +11 3 is sent.
• Z 2 and Z 4 are the interference terms while n 2 and 11 3 are the noise terms over these resource blocks.
• CW carries the permutation code and Z 3 is the information sent to the receiver as the primary users.
• CW is used here to carry information about Z 4 which is a transmission from another cell in the same system.
• Z 4 can be recovered and cancelled from the received signal using silent symbol detector 701, permutation code decoder 703 and interference replicator 704, as is done in Figure 7.
• silent symbol detector 701 permutation code decoder 703 and interference replicator 704, as is done in Figure 7.
• Z 3 can be decoded at a much higher reliability level or a higher capacity constellation/code combination can be utilized to increase the capacity over the primary channel allocation to this user.
• y( n - k) ⁇ can be found that will provide the positions of zeros in a binary sequence of length n, hence a unique permutation. (To be more rigorous, it is shown that y ⁇ n - k ) ⁇
• the location[0, I] function refers to the position of the Z-th zero in the binary sequence of length n and takes values in ⁇ 0, 1, . . . , ( « - 1) ⁇ .
• INPUT An index number i e 0 - 1
• STEP-I Remove L bits from the head of the primary user's backlogged data and map onto k symbols ⁇ si, . . . , sk ⁇ .
• the unique index value i for this codeword is
• i can be any integer in the
• Iog2 Else if Iog2 is not an integer and log 2 -th bit is 0, k k
• mapping can be done using Algorithm A2. Denote by location ⁇ , j] the location of j-th zero and location[l, j] the location of j-th one.
• n-k i.e., silent symbols correspond to zeros of the permutation code constructed in STEP-3
• Algorithm A3 describes the encoding algorithm assuming that s/ s are scalars. If s/s are complex numbers, one can apply the algorithm by first considering the real part of s/s and then the imaginary parts as the following example presents.
• the following steps are involved in the decoding operation in each degree of freedom:
• STEP-2 Run Algorithm Al to find the index j e 0 -1
• M- th most significant digit is zero, discard the M-th digit and pass the first (M - 1) bits as the decoded bits with the least significant bit as the first bit being received. If M- th digit is one, declare all M bits as the decoded bits again with the least significant bit as the first bit being received.
• the first strategy (referred to as uncoded strategy) solely relies on making a correct hypothesis testing at each symbol epoch, whereas the second strategy (referred to as coded strategy) try to mimic some of the elements of the encoding strategy used by random permutations, albeit with finite length deterministic coding followed by suboptimum decoding.
• ML-rule becomes: Decide Ho if and only if 4
• ⁇ fails in any of the n epochs, then a wrong permutation II is decoded. This creates a false decoding operation at the secondary user (unless the device uses an error detection/correction capability in the permutation coding layer). After receiving full MAC packets, such errors can be detected by the CRC codes employed at the MAC layer of the secondary user. Wrong permutation decisions at the primary user, however, do not necessarily mean that the actual symbols cannot be recovered. To be more specific, if the false permutation leads to an error correctable by the channel code used for the primary user's payload, the primary user is not impacted. For
• STEP-2 Take ko source symbols ⁇ si, . . . , s t o ⁇ of the primary user and expand it to n encoding symbols ⁇ s ⁇ , . . . , S n ⁇ using a (ko, ⁇ ) forward error correction (FEC) code.
• FEC forward error correction
• MDS maximum distance separable
• each chunk can enumerate up to ⁇ distinct permutation codes.
• a source block of length m Iog2 is obtained or equivalently a source block of length "m with
• the permutation code erases the encoding symbols generated for the primary user in a unique pattern.
• k denotes the actual number of transmissions from the sender side and the notation fc 0 is introduced in the coded case to differentiate the actual number of payload symbols for the primary user.
• the target utilization k ⁇ ko impacts the decoding performance as it will be more rigorously stated in the next section.
• two different channel codes are applied; one for the primary user at STEP-2 and one for the secondary user at STEP-6.
• the code used for the primary user helps in bypassing the hypothesis testing stage completely.
• the code used for the secondary user can be though of boosting the performance of the hypothesis testing stage that is needed to perform permutation code decoding.
• Algorithm A5 makes a rate-error performance tradeoff ⁇ through the parameters k, m, and m :
• the primary user skips the hypothesis testing stage in the decoding operations.
• the receiver directly attempts to perform channel decoding as if no permutation coding were present.
• the permutation coding simply acts as another (non-Gaussian) error source.
• each chunk is labeled as erasure or received using the implicit error detection capability of the permutation codes: each chunk must have in - k) non-silent symbols. Therefore, one can readily label a chunk as
• FIG. 9 is a block diagram of one embodiment of a base station that includes a network interface 1001, baseband processing 1102 and front and/RF unit signal block 1003.
• Baseband processing 1002 encodes the signals for transmission, including the encoding baseband above.
• Signal block 1003 includes the upconverter to upconvert signals at intermediate frequency up to a frequency from transmission.
• Signal block 1003 also includes down converter to down convert received signals to intermediate frequency, which are input to baseband processing 1002 for decoding.

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• 2010
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