Wai Ho Mow
Hong Kong University of Science and Technology, ECE, Faculty Member
Research Interests:
Research Interests:
Research Interests:
Abstract Lattice decoding algorithms have been proposed for implementing the maximum likelihood detector (MLD), which is the optimal receiver for multiple-input multiple-output (MIMO) channels. However the computational complexity of... more
Abstract Lattice decoding algorithms have been proposed for implementing the maximum likelihood detector (MLD), which is the optimal receiver for multiple-input multiple-output (MIMO) channels. However the computational complexity of direct implementation of the lattice decoding algorithm is high and the throughput is variable. In this work, a K-best algorithm is proposed to implement the lattice decoding. It is computational inexpensive and has fixed throughput. It can be easily implemented in a pipelined fashion and has similar ...
Research Interests:
Abstract Assuming perfect channel state information (CSI), linear precoding/decoding for multiple-input multiple-output (MIMO) systems has been considered in the literature under various performance criteria, such as minimum total... more
Abstract Assuming perfect channel state information (CSI), linear precoding/decoding for multiple-input multiple-output (MIMO) systems has been considered in the literature under various performance criteria, such as minimum total mean-square error (MSE), maximum mutual information, and minimum average bit error rate (BER). It has been shown that these criteria belong to a set of reasonable Schur-concave or Schur-convex objective functions of the diagonal entries of the system mean-square error (MSE) matrix.
Abstract In this paper, the problem of index assignments for quantizers with uniform encoders and channel-optimized decoders for M-PSK schemes is studied. The analytical expressions of MSD (Mean-Squared Distortion) for such quantizers... more
Abstract In this paper, the problem of index assignments for quantizers with uniform encoders and channel-optimized decoders for M-PSK schemes is studied. The analytical expressions of MSD (Mean-Squared Distortion) for such quantizers with the natural, zigzag and NBC-Gray mappings, respectively, have been derived.
Abstract In this paper, we propose low-complexity lattice detection algorithms for successive interference cancelation (SIC) in multi-input multi-output (MIMO) communications. First, we present a dual-lattice view of the vertical Bell... more
Abstract In this paper, we propose low-complexity lattice detection algorithms for successive interference cancelation (SIC) in multi-input multi-output (MIMO) communications. First, we present a dual-lattice view of the vertical Bell Labs Layered Space-Time (V-BLAST) detection. We show that V-BLAST ordering is equivalent to applying sorted QR decomposition to the dual basis, or equivalently, applying sorted Cholesky decomposition to the associated Gram matrix.
Abstract From a lattice viewpoint, Clarkson, Sweldens and Zheng significantly reduced the complexity of multiantenna differential decoding. Their approximate decoding algorithm, however, has not unleashed the full potential of lattice... more
Abstract From a lattice viewpoint, Clarkson, Sweldens and Zheng significantly reduced the complexity of multiantenna differential decoding. Their approximate decoding algorithm, however, has not unleashed the full potential of lattice decoding. In this paper, we present several improved algorithms, generally referred to as differential lattice decoding (DLD), for multiantenna communication.
Abstract Bit-interleaved coded modulation with iterative decoding (ID) is an effective scheme for both AWGN and fading channels because it simultaneously realizes large Euclidean distance and high diversity. In the literature, ID schemes... more
Abstract Bit-interleaved coded modulation with iterative decoding (ID) is an effective scheme for both AWGN and fading channels because it simultaneously realizes large Euclidean distance and high diversity. In the literature, ID schemes with hard-decision feedback (HDF), as well as soft-decision feedback (SDF), have been investigated. While HDF/ID exhibits a performance inferior to SDF/ID, it is much simpler to implement.
Abstract The idea of formulating the detection of a lattice-type modulation, such as M-PAM and M-QAM, transmitted over a linear channel as the so-called universal lattice decoding problem dates back to at least the early 1990s. The... more
Abstract The idea of formulating the detection of a lattice-type modulation, such as M-PAM and M-QAM, transmitted over a linear channel as the so-called universal lattice decoding problem dates back to at least the early 1990s. The applications of such lattice decoders have proliferated in the last few years because of the growing importance of some linear channel models such as multiple-antenna fading channels and multi-user CDMA channels.
Abstract The performance analysis of multi-input-multi-output (MIMO) systems with M-ary quadrature amplitude modulation (MQAM) and a space-time block code (STBC) over flat Rayleigh fading channels for imperfect channel state information... more
Abstract The performance analysis of multi-input-multi-output (MIMO) systems with M-ary quadrature amplitude modulation (MQAM) and a space-time block code (STBC) over flat Rayleigh fading channels for imperfect channel state information (CSI) is presented. In this paper, the optimum fading gain switching thresholds for attaining maximum spectrum efficiency (SE) subject to a target bit-error rate (BER) and an average power constraint are derived.
Abstract Lattice decoding algorithms have been shown to have the similar performance as the optimal maximum likelihood decoder for MIMO wireless systems. To reduce the high complexity of the lattice decoding algorithm and to achieve a... more
Abstract Lattice decoding algorithms have been shown to have the similar performance as the optimal maximum likelihood decoder for MIMO wireless systems. To reduce the high complexity of the lattice decoding algorithm and to achieve a regular fixed throughput, a K-best algorithm and the corresponding VLSI architectures have been proposed for the practical implementation of the lattice decoding algorithm.
Abstract In this paper, we describe a low complexity orthogonal frequency-division multiplexing (OFDM) receiver using Log-FFT for coded OFDM system. The complexity of the Log-FFT depends on the size of the look-up table, which is... more
Abstract In this paper, we describe a low complexity orthogonal frequency-division multiplexing (OFDM) receiver using Log-FFT for coded OFDM system. The complexity of the Log-FFT depends on the size of the look-up table, which is determined by the bit width of logarithmic number systems (LNS) representation. In coded OFDM system, simulation results show that there is no degradation in bit error rate performance when only two fractional bits are used for the LNS.
Abstract By employing spatial multiplexing, multiple-input multiple-output (MIMO) wireless antenna systems provide increases in capacity without the need for additional spectrum or power. Zero-forcing (ZF) detection is a simple and... more
Abstract By employing spatial multiplexing, multiple-input multiple-output (MIMO) wireless antenna systems provide increases in capacity without the need for additional spectrum or power. Zero-forcing (ZF) detection is a simple and effective technique for retrieving multiple transmitted data streams at the receiver. However the detection requires knowledge of the channel state information (CSI) and in practice accurate CSI may not be available.
Abstract Non-linear amplitude distortion may be the key impairment in some practical multiple-input multiple-output (MIMO) communications systems. However, there are only a few past investigations addressing its impact on the system... more
Abstract Non-linear amplitude distortion may be the key impairment in some practical multiple-input multiple-output (MIMO) communications systems. However, there are only a few past investigations addressing its impact on the system performance.
Abstract This paper analyzes the average bit error rate (BER) performance of singular value decomposition-based multiple-input multiple-output systems with channel estimation error and feedback delay over uncorrelated Ricean fading... more
Abstract This paper analyzes the average bit error rate (BER) performance of singular value decomposition-based multiple-input multiple-output systems with channel estimation error and feedback delay over uncorrelated Ricean fading channels. By utilizing marginal unordered eigenvalue distributions of complex noncentral Wishart matrices, we derive exact closed-form BER expression under the assumption of equal power allocation.
Abstract Link adaptation allows the transmitter to adapt to changing channel conditions. Critical to the design of link adaptation is the accuracy of channel state information at the transmitter. In this paper, we investigate the effect... more
Abstract Link adaptation allows the transmitter to adapt to changing channel conditions. Critical to the design of link adaptation is the accuracy of channel state information at the transmitter. In this paper, we investigate the effect of imperfect channel state information and feedback delay on the performance of a multiple-input multiple-output zero-forcing receiver with adaptive power allocation.
Abstract Two simple but effective methods for reducing the average complexity (and power consumption) of the conventional turbo-cyclic-redundancy-check decoding scheme with negligible performance degradation in a wideband direct-sequence... more
Abstract Two simple but effective methods for reducing the average complexity (and power consumption) of the conventional turbo-cyclic-redundancy-check decoding scheme with negligible performance degradation in a wideband direct-sequence code-division multiple-access (W-CDMA) environment are introduced. When applied to a W-CDMA turbo code with frame length 640 b at a bit-error rate (BER) of 10-6, the resultant modified schemes can save up to 73% of the average decoding complexity, relative to the conventional scheme.
Abstract In this paper we perform a minimum distance analysis of a class of two dimensional intersymbol interference channels. In particular, some important cases of multitrack multihead magnetic recording systems fall into the studied... more
Abstract In this paper we perform a minimum distance analysis of a class of two dimensional intersymbol interference channels. In particular, some important cases of multitrack multihead magnetic recording systems fall into the studied class. Previously, Soljanin and Georghiades have studied the same problem as we do. The results derived in this paper are more conclusive and they improve upon theirs. The fundamental proof technique that we will use is to transform the channel into an equivalent minimum phase channel.
Abstract A current-mode binary-search sensing scheme for a 4-state one-transistor one-magnetic tunnel junction (1T1MTJ) magneto-resistive random access memory (MRAM) is proposed. By using the switched-current technique, it is able to read... more
Abstract A current-mode binary-search sensing scheme for a 4-state one-transistor one-magnetic tunnel junction (1T1MTJ) magneto-resistive random access memory (MRAM) is proposed. By using the switched-current technique, it is able to read data non-destructively with a magneto-resistive (MR) ratio of as low as 5%. The circuit is designed using a 0.18 mm CMOS process and the performance is verified by HSPICE.
The group structure of the 2-dimensional sidelobe-invariant transformations for binary arrays is characterized. The design of an efficient exhaustive backtracking search algorithm, which exploits such group structure to reduce the search... more
The group structure of the 2-dimensional sidelobe-invariant transformations for binary arrays is characterized. The design of an efficient exhaustive backtracking search algorithm, which exploits such group structure to reduce the search space and, in the meantime, applies the partially determined autocorrelation values as backtracking conditions, is presented. As a consequence of applying the algorithm, all optimal binary arrays with minimum peak sidelobe levels consisting of up to 49 elements are obtained and tabulated.
Abstract This paper analyzes bit error rate (BER) and outage probability of singular value decomposition-based multiple-input multiple-output systems with channel estimation error and feedback delay over uncorrelated Ricean fading channels.
Abstract In this paper, we present a new view of the vertical Bell Labs layered space-time (V-BLAST) system by interpreting the detection process on the dual lattice, and propose two O (N 3)-complexity ordering algorithms. One algorithm... more
Abstract In this paper, we present a new view of the vertical Bell Labs layered space-time (V-BLAST) system by interpreting the detection process on the dual lattice, and propose two O (N 3)-complexity ordering algorithms. One algorithm updates the dual basis by using the backward Greville formula; the other is to apply the sorted Gram-Schmidt orthogonalization to the dual basis. We demonstrate the connection between the two algorithms as well as their relations with existing algorithms.
Abstract The detriment arising from strong and frequently occurring impulses over an Orthogonal Frequency Division Multiplexing system is paramount because signals on sub-carriers appear to be corrupted simultaneously. To overcome this... more
Abstract The detriment arising from strong and frequently occurring impulses over an Orthogonal Frequency Division Multiplexing system is paramount because signals on sub-carriers appear to be corrupted simultaneously. To overcome this obstacle, clipping has been reported as an effective approach.
Abstract Motivated by the noncoherent subspace coding approach and the low-complexity sparse coding approach to realize random linear network coding, we consider the problem of characterizing the probability of having a full rank (or... more
Abstract Motivated by the noncoherent subspace coding approach and the low-complexity sparse coding approach to realize random linear network coding, we consider the problem of characterizing the probability of having a full rank (or nonsingular) square transfer matrix over a finite field, for which the probability of choosing the zero element is different from that of choosing a nonzero element.
Abstract Cognitive radio technology facilitates spectrum reuse and alleviates spectrum crunch. One fundamental problem in cognitive radio is to avoid the interference caused by other communication systems sharing the same frequency band.... more
Abstract Cognitive radio technology facilitates spectrum reuse and alleviates spectrum crunch. One fundamental problem in cognitive radio is to avoid the interference caused by other communication systems sharing the same frequency band. However, spectrum sensing cannot guarantee accurate detection of the interference in many practical situations. Hence, it is crucial to design robust receivers to combat the in-band interference. In this paper, we first present a simple pilot aided interference detection method.
In this paper, codes which reduce the peak-to-average power ratio (PAPR) in multi-code code division multiple access (MC-CDMA) communication systems are studied. It is known that using bent functions to define binary codewords gives... more
In this paper, codes which reduce the peak-to-average power ratio (PAPR) in multi-code code division multiple access (MC-CDMA) communication systems are studied. It is known that using bent functions to define binary codewords gives constant amplitude signals. Based on the concept of quarter bent functions, a new inequality relating the minimum order of terms of a bent function and the maximum Walsh spectral magnitude is proved, and it facilitates the generalization of some known results.
Barker sequences have been used in many existing communications and ranging systems. Unfortunately, the longest known biphase and quadriphase Barker sequences are of lengths 13 and 15, respectively. In this paper, we introduce the... more
Barker sequences have been used in many existing communications and ranging systems. Unfortunately, the longest known biphase and quadriphase Barker sequences are of lengths 13 and 15, respectively. In this paper, we introduce the so-called quasi-Barker sequences which achieve the minimum peak sidelobe level one within a certain window centered at the mainlobe.
Abstract Data transmission using self-organizing feature map (SOFM) based vector quantizer (VQ) and channel optimized vector quantizer (COVQ) with various space-time trellis codes (STTC) over wireless channels are studied. It is... more
Abstract Data transmission using self-organizing feature map (SOFM) based vector quantizer (VQ) and channel optimized vector quantizer (COVQ) with various space-time trellis codes (STTC) over wireless channels are studied. It is interesting to note that in a SOFM-STTC system, even with a weak STTC, the overall performance in terms of reconstruction error does not degrade a lot, compared with a stronger STTC. Hence, a system of low complexity but satisfactory performance could be built.
Abstract In this paper, we introduce a novel criterion to rank puncturing patterns for rate-compatible LDPC codes. Specifically, based on Gaussian approximation density evolution, a cost function is devised to characterize the degree... more
Abstract In this paper, we introduce a novel criterion to rank puncturing patterns for rate-compatible LDPC codes. Specifically, based on Gaussian approximation density evolution, a cost function is devised to characterize the degree distribution of the punctured code matrices, which are derived from a mother code matrix by matrix transformation. This cost function allows us to effectively compare the expected performance of candidate puncturing patterns and to sort out good ones.
Abstract Recently, lattice-reduction-aided detectors have been proposed for multiple-input multiple-output (MIMO) systems to give performance with full diversity like maximum likelihood receiver yet with complexity similar to linear... more
Abstract Recently, lattice-reduction-aided detectors have been proposed for multiple-input multiple-output (MIMO) systems to give performance with full diversity like maximum likelihood receiver yet with complexity similar to linear receiver. However, these lattice-reduction-aided detectors are based on the traditional LLL reduction algorithm that was originally introduced for reducing real lattice basis, even though the channel matrices are inherently complex-valued.
Abstract Due to the use of commodity software and hardware, crash-stop and Byzantine failures are likely to be more prevalent in today's large-scale distributed storage systems. Regenerating codes have been shown to be a more efficient... more
Abstract Due to the use of commodity software and hardware, crash-stop and Byzantine failures are likely to be more prevalent in today's large-scale distributed storage systems. Regenerating codes have been shown to be a more efficient way to disperse information across multiple nodes and recover crash-stop failures in the literature.
Abstract: This work investigates linear precoding over non-singular linear channels with additive white Gaussian noise, with lattice-type inputs. The aim is to maximize the minimum distance of the received lattice points, where the... more
Abstract: This work investigates linear precoding over non-singular linear channels with additive white Gaussian noise, with lattice-type inputs. The aim is to maximize the minimum distance of the received lattice points, where the precoder is subject to an energy constraint. It is shown that the optimal precoder only produces a finite number of different lattices, namely perfect lattices, at the receiver.
Abstract: The Lenstra-Lenstra-Lov\'asz (LLL) algorithm is the most practical lattice reduction algorithm in digital communications. In this paper, several variants of the LLL algorithm with either lower theoretic complexity or... more
Abstract: The Lenstra-Lenstra-Lov\'asz (LLL) algorithm is the most practical lattice reduction algorithm in digital communications. In this paper, several variants of the LLL algorithm with either lower theoretic complexity or fixed-complexity implementation are proposed and/or analyzed. Firstly, the $ O (n^ 4\ log n) $ theoretic average complexity of the standard LLL algorithm under the model of iid complex normal distribution is derived.
Abstract: Inspired by the application scenarios such as battery-operated wireless sensor networks (WSN), we investigate the design of an easy-to-implement energy-efficient two-way relaying scheme in which two source nodes exchange their... more
Abstract: Inspired by the application scenarios such as battery-operated wireless sensor networks (WSN), we investigate the design of an easy-to-implement energy-efficient two-way relaying scheme in which two source nodes exchange their messages with the help of an intermediate relay node. Due to their efficient decoder hardware implementation, block codes, such as Hamming and BCH codes, instead of convolutional and other sophisticated codes, are adopted in WSN-related standards, such as Bluetooth and IEEE802. 15.6.
Abstract Successive interference cancellation (SIC) has been used in multi-rate code division multiple access (CDMA) systems to eliminate the co-channel interference. In SIC, the required transmission power of a certain user can be... more
Abstract Successive interference cancellation (SIC) has been used in multi-rate code division multiple access (CDMA) systems to eliminate the co-channel interference. In SIC, the required transmission power of a certain user can be reduced if it is detected late in the cancellation order as the interferences caused by the users that are detected before have been cancelled. In this work, we study the power control strategy based on different orderings for the SIC given the knowledge of the battery capacity of the mobiles.