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Fixedrank Rayleigh quotient maximization by an MPSK sequence,” submitted to
 IEEE Trans. Commun
, 2013
"... Abstract—Certain optimization problems in communication systems, such as limitedfeedback constantenvelope beamforming or noncoherent Mary phaseshift keying (MPSK) sequence detection, result in the maximization of a fixedrank positive semidefinite quadratic form over the MPSK alphabet. This for ..."
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Abstract—Certain optimization problems in communication systems, such as limitedfeedback constantenvelope beamforming or noncoherent Mary phaseshift keying (MPSK) sequence detection, result in the maximization of a fixedrank positive semidefinite quadratic form over the MPSK alphabet. This form is a special case of the Rayleigh quotient of a matrix and, in general, its maximization by an MPSK sequence is NPhard. However, if the rank of the matrix is not a function of its size, then the optimal solution can be computed with polynomial complexity in the matrix size. In this work, we develop a new technique to efficiently solve this problem by utilizing auxiliary continuousvalued angles and partitioning the resulting continuous space of solutions into a polynomialsize set of regions, each of which corresponds to a distinct MPSK sequence. The sequence that maximizes the Rayleigh quotient is shown to belong to this polynomialsize set of sequences, thus efficiently reducing the size of the feasible set from exponential to polynomial. Based on this analysis, we also develop an algorithm that constructs this set in polynomial time and show that it is fully parallelizable, memory efficient, and rank scalable. The proposed algorithm compares favorably with other solvers for this problem that have appeared recently in the literature. Index Terms—Algorithms, maximum likelihood detection, MIMO systems, noncoherent communication, optimization methods, phase shift keying, Rayleigh quotient, sequences. I. PROBLEM STATEMENT, PRIOR WORK,
Multiuser Signature Quantization With TreeStructured Codebook in DSCDMA
"... Abstract—We consider a signature quantization scheme for a group of users in a reverselink direct sequence (DS)code division multiple access (CDMA). Assuming perfect channel knowledge, a receiver selects the set of signatures that maximizes an average signaltointerference plus noise ratio (SINR) ..."
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Abstract—We consider a signature quantization scheme for a group of users in a reverselink direct sequence (DS)code division multiple access (CDMA). Assuming perfect channel knowledge, a receiver selects the set of signatures that maximizes an average signaltointerference plus noise ratio (SINR) from a random vector quantization (RVQ) codebook, which consists of independent isotropically distributed unitnorm vectors. The quantized signatures are relayed from the receiver to users via noiseless ratelimited feedback channels. Previously, we have proposed to organize entries of RVQ codebook into a tree structure (TS) to speed up a search for the optimal entry. Here we extend the TS scheme for a multiuser signature quantization. Numerical results show that for a given performance, a TSRVQ codebook can be an order of magnitude less complex than an RVQ codebook. I.
Quantized Transmit Beamforming With Antenna Selection in a MIMO Channel ∗
"... For a pointtopoint multiinput multioutput (MIMO) wireless channel, we propose a feedback scheme, which consists of transmitantenna selection algorithm and beamforming quantization. A feedback, which is relayed from a receiver to a transmitter via a feedback channel, specifies a set of active tr ..."
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For a pointtopoint multiinput multioutput (MIMO) wireless channel, we propose a feedback scheme, which consists of transmitantenna selection algorithm and beamforming quantization. A feedback, which is relayed from a receiver to a transmitter via a feedback channel, specifies a set of active transmit antennas and associated beamforming vector, which contains transmit antenna coefficients. Assuming perfect channel knowledge, the receiver selects the set of transmit antennas that maximizes the largest eigenvalue of a channel covariance matrix and then, chooses the beamforming vector that maximizes the capacity, from a random vector quantization (RVQ) codebook. Entries in the RVQ codebook are independent isotropically distributed and was previously shown to perform close to the optimum. We derive
Statistical Precoder Design for SpaceTimeFrequency Block Codes in Multiuser MISOMCCDMA Systems
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On the Performance of MIMO Nullforming with Random Vector Quantization Limited Feedback
"... Abstract—This paper analyzes the performance of random vector quantization (RVQ) for limited feedback nullforming in multiinput multioutput (MIMO) communication systems with and without receiver coordination. A singlestream scenario is considered in which one or more primary receivers request nul ..."
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Abstract—This paper analyzes the performance of random vector quantization (RVQ) for limited feedback nullforming in multiinput multioutput (MIMO) communication systems with and without receiver coordination. A singlestream scenario is considered in which one or more primary receivers request nulls by providing limited feedback to the transmitter. Without receiver coordination, each primary receiver informs the transmitter of its best beamforming precoding vector. The transmitter then selects a zeroforcing precoding vector orthogonal to all of the beamforming precoding vectors. With receiver coordination, the primary receivers feed back the common precoding vector that minimizes the average interference. In both cases, secondary receivers in the network do not provide feedback and experience channels statistically equivalent to a singleantenna fading channel. Analytical results show that, for a system with K primary receivers and random codebooks with N = 2B precoding vectors, the mean received power at the primary receivers is upper bounded by N−1/K = 2−B/K with or without receiver coordination. Exact results are also derived for the K = 1 receiver case. Numerical results verify the scaling and also show that systems with receiver coordination outperform those without receiver coordination by a constant gap for large N in terms of average interference. Index Terms—Antenna arrays, nullforming, zeroforcing, limited feedback, random vector quantization, MIMO communication, interference mitigation. I.
MIMO Nullforming with RVQ Limited Feedback and Channel Estimation Errors
"... Abstract—This paper explores limited feedback nullforming techniques based on random vector quantization (RVQ) with and without receiver coordination. The availability of receiver coordination affects the type and amount of feedback required to select an appropriate precoding vector. Approximate upp ..."
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Abstract—This paper explores limited feedback nullforming techniques based on random vector quantization (RVQ) with and without receiver coordination. The availability of receiver coordination affects the type and amount of feedback required to select an appropriate precoding vector. Approximate upper and lower bounds are developed for the mean received power at primary receivers with and without receiver coordination. Numerical results confirm the analysis and show that the channel estimation errors effectively establish a floor on the achievable performance of RVQ nullforming. The size of the RVQ codebook can be selected to approach this floor without excessive overhead. Index Terms—antenna arrays, nullforming, zeroforcing, limited feedback, random vector quantization, MIMO communica
University of Alberta Imperfect Channel Knowledge for Interference Avoidance
"... In every way that matters, anything the mind imagines, exists. The existence stems either from an external idea perceived by the mind, or an internal notion initiated by ones own creativity. ..."
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In every way that matters, anything the mind imagines, exists. The existence stems either from an external idea perceived by the mind, or an internal notion initiated by ones own creativity.