Zucheng Zhou

A computationally efficient exact ML sphere decoder

Low-complexity tree search based exact maximum-likelihood (ML) detectors have gained attention for optimum signal detection in multiple-input multiple output (MIMO) wireless systems. In this paper, taking a fresher look at the closet lattice point search problem, we propose a new fast exact ML sphere decoder with ever-increasing radius (IR-SD). It is shown that IR-SD visits minimum number of tree nodes and is more computationally efficient than existing sphere decoders. IR-SD is also faster and requires less storage than ML stack detector. An upper-bound of expected computation and storage complexity of IR-SD independent of tree radius is derived. Numerical results validate that IR-SD greatly speeds up the ML detection than other sphere detectors while requiring less storage than ML stack algorithm. A factor-of-2.5 speed-up is observed over the depth-first Schnorr-Euchner sphere decoders when utilizing IR-SD in 16-QAM 10/spl times/10 complex MIMO system.

An energy diffserv and application-aware MAC scheduling for VBR streaming video in the IEEE 802.15.3 high-rate wireless personal area networks

Pseudo-static time division multiple access (pTDMA) channel access is adopted in the IEEE 802.15.3 specification of high-rate wireless personal area networks. However, in the pTDMA, unnecessary transceiver startup and idle listening of destination devices consume much energy. Furthermore, the pTDMA is not efficient for variable bit rate video flows. In this paper, we propose an energy diffserv and application-aware scheduling (EDAS) algorithm in the medium access control layer for delay-sensitive variable bit rate streaming video. The proposed EDAS scheme takes energy efficiency, quality of service, and fairness into considerations. It includes a channel time partition mechanism, an application-aware dynamic channel time allocation algorithm, as well as a flow admission control mechanism. The EDAS scheme also provides an energy differentiated service to the devices with different remaining-energy levels. Simulation results show that the proposed EDAS scheme outperforms the IEEE 802.15.3 pTDMA significantly in terms of fraction of decodable video frames and energy efficiency.

Joint ML channel estimation and data detection for STBC via novel sphere decoding algorithms

Space-time block codes (STBC) are very effective and simple schemes to utilize the diversity gain in multiple-input multiple-output (MIMO) wireless systems. In previous research on STBC data detection, channel state information is usually assumed to be known at the receiver side, which enables simple maximum-likelihood (ML) decoding at the receiver. We consider the problem of joint ML channel estimation and data detection for STBC systems when the channel state information is not available at the receiver. It is shown that the joint ML channel estimation and data detection for complex STBC system is an integer least-square optimization problem for constant-modulus modulation. We propose novel sphere decoders which provide a low-complexity exact optimal solution to this optimization problem. The proposed sphere decoder visits the minimum number of tree nodes in finding the ML solution. In addition, by modifying the novel sphere decoder, we provide efficient exact ML joint channel estimation and data detection for STBC wireless systems employing non-constant modulus modulation schemes. Considerable performance gain and complexity reduction are achieved with these methods.

Performance evaluation of MIMO systems in a mixture of Gaussian noise and impulsive noise

Most of the analyses of multiple-input multiple-output (MIMO) systems so far have been based on the ideal Gaussian noise model. In this paper, performance analysis of MIMO systems is performed in a mixture of Gaussian noise and impulsive noise modeled as a symmetric alpha stable process. Three typical MIMO systems are considered: 1) zero-forcing (ZF) system, 2) maximum likelihood (ML) system and 3) space time block coding (STBC) system. The symbol-error-rates (SER) or the upper bound of SER of each system is derived. Simulations are performed in the mixed noise with different impulsive intensity and impulsive level and the results show that the performances of all the systems are degraded greatly in the mixed noise and STBC has no performance gain over ZF and ML when high impulsive noise appears.

A faster ML sphere decoder with competing branches

A novel fast recursive sphere decoder with parallel competing branches (P-SD) is proposed for exact maximum-likelihood (ML) detection in multiple-input multiple-output (MIMO) systems. P-SD introduces a novel competition mechanism which makes P-SD dynamically choose the targeted branch to perform a bounded search among the competing parallel branches. In P-SD, the search radius shrinks to the minimum Euclidean distance as early as possible. Numerical results show that P-SD achieves considerable computational complexity reduction even compared with the Schnorr-Euchner enumeration (SEE) based sphere decoder (SE-SD).

Receiver design of MIMO systems in a mixture of Gaussian noise and impulsive noise

In this paper, the receiver design of MIMO systems is performed in a mixture of Gaussian noise and impulsive noise modeled as a symmetric alpha stable process. Both spatial multiplexing systems (SM-systems) and diversity based systems are considered. The optimal receiver and several suboptimal receivers are developed and the related problems, such as performance and robustness, are discussed. Simulation shows that the proposed receivers can achieve much better performance than the traditional MIMO receivers in the mixed noise.

A flexible near-optimum detector for V-BLAST

V-BLAST is an important multiple input and multiple output (MIMO) space-time architecture for future high data rate wireless communication system. In this paper, a novel computation-efficient metric-guided (MG) algorithm is proposed for V-BLAST signal detection. This algorithm can achieve near maximum likelihood (ML) detection performance with tractable detection complexity which is inherently adaptive to channel signal-noise ratio (SNR). Through adjusting the value oof one parameter, MG algorith offers the flexibility of achieving any in-between performance-complexity tradeoff between an efficient near-ML detection and original nulling/cancelling algorithm for V-BLAST. Simulation results show that proposed algorithm can offer near-ML detection performance with complexity even less than that of the Schnorr-Euchner sphere decoder (M. O. Damen et al., 2003) and stack algorithm (S. Baro et al., 2003).

A power efficient M-ary orthogonal pulse polarity modulation for TH-UWB system using modified OVSF codes

An M-ary orthogonal pulse polarity modulation (OP/sup 2/M) using modified orthogonal variable spreading factor codes (OVSF), i.e., a set of orthogonal Walsh codes, for time hopping ultra wideband (TH-UWB) communication systems is proposed. Under FCC power spectrum density (PSD) constraint for UWB, the proposed M-ary OP/sup 2/M system proves to be more power efficient than traditional bi-phase shift-keying (BPSK) modulation, binary and M-ary pulse position modulation (PPM) systems. OVSF codes are modified in OP/sup 2/M to smooth the signal PSD for meeting FCC PSD mask for UWB system. Reduced complexity receiver architecture provides tractable system complexity. Analytical and simulation results show that the proposed 32-ary OP/sup 2/M TH-UWB system is more power efficient than previous PPM and BPSK modulations.

A novel approach to signal detection in MIMO-OFDM systems combining coding and joint detection techniques

Multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) techniques are combined to attain high capacity or good performance over frequency selective channels (FS). Joint detection (JD) techniques, as one class of the multiuser detection techniques, are originally used in CDMA systems to combat multiple-access and intersymbol interference. A novel method of combining coding and JD techniques for signal detection in MIMO-OFDM systems is proposed in this paper. Compared with the spatially multiplexing OFDM (SM-OFDM) systems, such as VBLAST-OFDM, this method can attain better performance. Compared with common space-frequency coding OFDM (SFC-OFDM) systems, this method can achieve the full code rates even for more than two transmit antennas with complex constellations. The performances of the approaches using different JD algorithms are analyzed and compared. Simulation shows this method performs well.

A new successive interference cancellation for asynchronous CDMA

This paper introduces a new multi-user detection method, successive interference cancellation based on the order of log-likelihood-ratio (LLR-SIC), for asynchronous code division multiple access (CDMA) systems. LLR-SIC operates on the fact that the most reliable user, i.e. the user with the largest log- likelihood-ratio (LLR) absolute value, should be first detected and cancelled from received signal. Simulation results show that LLR-SIC significantly outperforms partial parallel interference cancellation (P-PIC) over multi-path Rayleigh fading channels. And the results also show that LLR-SIC can even support overloaded systems in which the number of users is greater than the spreading factor.