arXiv subjects

Chau Yuen

Publications and source records attributed to Chau Yuen.

568 records · Page 32Linked to original sources

arXiv2008

Achieving Near-Capacity at Low SNR on a Multiple-Antenna Multiple-User Channel

We analyze the sensitivity of the capacity of a multi-antenna multi-user system to the number of users being served. We show analytically that, for a given desired sum-rate, the extra power needed to serve a subset of the users at low SNR (signal-to-noise ratio) can be very small, and is generally much smaller than the extra power needed to serve the same subset at high SNR. The advantages of serving only subsets of the users are many: multi-user algorithms have lower complexity, reduced channel-state information requirements, and, often, better performance. We provide guidelines on how many users to serve to get near-capacity performance with low complexity. For example, we show how in an eight-antenna eight-user system we can serve only four users and still be approximately 2 dB from capacity at very low SNR.

cs.IT↗

arXiv2008

Power-Balanced Orthogonal Space-Time Block Code

In this paper, we propose two new systematic ways to construct amicable orthogonal designs (AOD), with an aim to facilitate the construction of power-balanced orthogonal spacetime block codes (O-STBC) with favorable practical attributes. We also show that an AOD can be constructed from an Amicable Family (AF), and such a construction is crucial for achieving a power-balanced O-STBC. In addition, we develop design guidelines on how to select the "type" parameter of an AOD so that the resultant O-STBC will have better power-distribution and code-coefficient attributes. Among the new O-STBCs obtained, one is shown to be optimal in terms of power distribution attributes. In addition, one of the proposed construction methods is shown to generalize some other construction methods proposed in the literature.

cs.IT↗

arXiv2008

Optimizing Quasi-Orthogonal STBC Through Group-Constrained Linear Transformation

In this paper, we first derive the generic algebraic structure of a Quasi-Orthogonal STBC (QO-STBC). Next we propose Group-Constrained Linear Transformation (GCLT) as a means to optimize the diversity and coding gains of a QO-STBC with square or rectangular QAM constellations. Compared with QO-STBC with constellation rotation (CR), we show that QO-STBC with GCLT requires only half the number of symbols for joint detection, hence lower maximum-likelihood decoding complexity. We also derive analytically the optimum GCLT parameters for QO-STBC with square QAM constellation. The optimized QO-STBCs with GCLT are able to achieve full transmit diversity, and have negligible performance loss compared with QO-STBCs with CR at the same code rate.

cs.IT↗

arXiv2008

On the Search for High-Rate Quasi-Orthogonal Space-Time Block Code

A Quasi-Orthogonal Space-Time Block Code (QO-STBC) is attractive because it achieves higher code rate than Orthogonal STBC and lower decoding complexity than nonorthogonal STBC. In this paper, we first derive the algebraic structure of QO-STBC, then we apply it in a novel graph-based search algorithm to find high-rate QO-STBCs with code rates greater than 1. From the four-antenna codes found using this approach, it is found that the maximum code rate is limited to 5/4 with symbolwise diversity level of four, and 4 with symbolwise diversity level of two. The maximum likelihood decoding of these high-rate QO-STBCs can be performed on two separate sub-groups of symbols. The rate-5/4 codes are the first known QO-STBCs with code rate greater 1 that has full symbolwise diversity level.

cs.IT↗

arXiv2008

Limited Feedback for Multi-Antenna Multi-user Communications with Generalized Multi-Unitary Decomposition

In this paper, we propose a decomposition method called Generalized Multi-Unitary Decomposition (GMUD) which is useful in multi-user MIMO precoding. This decomposition transforms a complex matrix H into PRQ, where R is a special matrix whose first row contains only a non-zero user defined value at the left-most position, P and Q are a pair of unitary matrices. The major attraction of our proposed GMUD is we can obtain multiple solutions of P and Q >. With GMUD, we propose a precoding method for a MIMO multi-user system that does not require full channel state information (CSI) at the transmitter. The proposed precoding method uses the multiple unitary matrices property to compensate the inaccurate feedback information as the transmitter can steer the transmission beams of individual users such that the inter-user interference is kept minimum.

cs.IT↗

arXiv2008

Beamforming Matrix Quantization with Variable Feedback Rate

We propose an improved beamforming matrix compression by Givens Rotation with the use of variable feedback rate. The variable feedback rate means that the number of bits used to represent the quantized beamforming matrix is based on the value of the matrix. Compared with the fixed feedback rate scheme, the proposed method has better performance without additional feedback bandwidth.

cs.IT↗

arXiv2008

Full Diversity Blind Signal Designs for Unique Identification of Frequency Selective Channels

In this paper, we develop two kinds of novel closed-form decompositions on phase shift keying (PSK) constellations by exploiting linear congruence equation theory: the one for factorizing a $pq$-PSK constellation into a product of a $p$-PSK constellation and a $q$-PSK constellation, and the other for decomposing a specific complex number into a difference of a $p$-PSK constellation and a $q$-PSK constellation. With this, we propose a simple signal design technique to blindly and uniquely identify frequency selective channels with zero-padded block transmission under noise-free environments by only using the first two block received signal vectors. Furthermore, a closed-form solution to determine the transmitted signals and the channel coefficients is obtained. In the Gaussian noise and Rayleigh fading environment, we prove that the newly proposed signaling scheme enables non-coherent full diversity for the Generalized Likelihood Ratio Test (GLRT) receiver.

cs.IT↗

arXiv2007

Four-Group Decodable Space-Time Block Codes

Two new rate-one full-diversity space-time block codes (STBC) are proposed. They are characterized by the \emph{lowest decoding complexity} among the known rate-one STBC, arising due to the complete separability of the transmitted symbols into four groups for maximum likelihood detection. The first and the second codes are delay-optimal if the number of transmit antennas is a power of 2 and even, respectively. The exact pair-wise error probability is derived to allow for the performance optimization of the two codes. Compared with existing low-decoding complexity STBC, the two new codes offer several advantages such as higher code rate, lower encoding/decoding delay and complexity, lower peak-to-average power ratio, and better performance.

cs.IT↗

arXiv2006

Single-Symbol-Decodable Differential Space-Time Modulation Based on QO-STBC

We present a novel differential space-time modulation (DSTM) scheme that is single-symbol decodable and can provide full transmit diversity. It is the first known singlesymbol- decodable DSTM scheme not based on Orthogonal STBC (O-STBC), and it is constructed based on the recently proposed Minimum-Decoding-Complexity Quasi-Orthogonal Space-Time Block Code (MDC-QOSTBC). We derive the code design criteria and present systematic methodology to find the solution sets. The proposed DSTM scheme can provide higher code rate than DSTM schemes based on O-STBC. Its decoding complexity is also considerably lower than DSTM schemes based on Sp(2) and double-symbol-decodable QOSTBC, with negligible or slight trade-off in decoding error probability performance.

cs.IT↗

arXiv2006

Quasi-Orthogonal STBC With Minimum Decoding Complexity

In this paper, we consider a quasi-orthogonal (QO) space-time block code (STBC) with minimum decoding complexity (MDC-QO-STBC). We formulate its algebraic structure and propose a systematic method for its construction. We show that a maximum-likelihood (ML) decoder for this MDC-QOSTBC, for any number of transmit antennas, only requires the joint detection of two real symbols. Assuming the use of a square or rectangular quadratic-amplitude modulation (QAM) or multiple phase-shift keying (MPSK) modulation for this MDC-QOSTBC, we also obtain the optimum constellation rotation angle, in order to achieve full diversity and optimum coding gain. We show that the maximum achievable code rate of these MDC-QOSTBC is 1 for three and four antennas and 3/4 for five to eight antennas. We also show that the proposed MDC-QOSTBC has several desirable properties, such as a more even power distribution among antennas and better scalability in adjusting the number of transmit antennas, compared with the coordinate interleaved orthogonal design (CIOD) and asymmetric CIOD (ACIOD) codes. For the case of an odd number of transmit antennas, MDC-QO-STBC also has better decoding performance than CIOD.

cs.IT↗