Abstract:Abstract-We present the application of greedy interference avoidance methods to codeword optimization in the uplink of a code division multiple access (CDMA) system in which the channel between a given user and the base station receiver is assumed known and stable for the duration of the transmission. Repeated application of greedy interference avoidance monotonically increases sum capacity and yields an optimal codeword ensemble that satisfies a simultaneous water-filling distribution. However, algorithms for… Show more
“…Another interesting area is signature optimization using limited feedback (e.g., [20], [248], [249], [256], [257], [263], [264], [328], [332], [341]). In fact, spreading code design using randomly generated codes formed the basis behind the development of RVQ ideas [281].…”
Section: A Single Antenna Scheduling and Spectrum Sharingmentioning
Abstract-It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
“…Another interesting area is signature optimization using limited feedback (e.g., [20], [248], [249], [256], [257], [263], [264], [328], [332], [341]). In fact, spreading code design using randomly generated codes formed the basis behind the development of RVQ ideas [281].…”
Section: A Single Antenna Scheduling and Spectrum Sharingmentioning
Abstract-It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
“…We note that while many algorithms are available for obtaining uplink CDMA codewords (see [10][11][12][13] and references therein) only a few algorithms have been proposed for downlink scenarios [14][15][16]. We also note that the uplink CDMA codeword ensembles can be designed to optimize various performance measures such as individual or sum rates and Signal-to-Interference+Noise-Ratios (SINR).…”
“…,pK } which maximizes the sum capacity of the corresponding vector MAC. For general scenarios with non-ideal channels and colored noise, these may be obtained by applying the interference avoidance algorithms discussed in [11][12][13], and the corresponding uplink transmit covariance for a given user in this case is given by…”
In this paper we study the uplink-downlink duality for Gaussian vector channels with colored noise, and we derive the duality transformations (downlink-to-uplink and vice versa) that imply transmit covariance matrices for which user rates in uplink and downlink are identical. These transformations are then applied for transmitter adaptation in Code Division Multiple Access (CDMA) systems to obtain an ensemble of downlink CDMA codewords from an optimal ensemble of uplink codewords.
“…d. Adjust user k's codewords sequentially using the greedy procedure of the basic eigen-algorithm; the codeword corresponding to symbol m of user k is replaced by the minimum eigenvector of the autocorrelation matrix of the corresponding interference-plus-noise process. e. Iterate the previous step until convergence (making use of escape methods [22] if the procedure stops in suboptimal points). 3.…”
Section: Generalizing the Eigenalgorithmmentioning
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