The extrinsic information transfer (EXIT) functions of Hadamard codes in the context of repeat-zigzag-Hadamard (RZH) codes with parallel decoding are investigated. EXIT functions over both the binary erasure channel (BEC) and the binary-input additive white Gaussian noise (BIAWGN) channel are derived. The application of these EXIT functions in the design of low-rate capacity-approaching irregular RZH (IRZH) codes is also considered. Using the EXIT functions, the bit error rate (BER) for a given code profile can be easily estimated and the differential evolution (DE) technique can be employed to find the optimal degree profile for given design parameters. The EXIT functions derived in this communication can serve as an effective tool for designing low-rate IRZH codes with parallel decoding in both BEC and BIAWGN channels.

In this paper, we propose a new class of low-rate error correction codes called repeat-zigzag-Hadamard (RZH) codes featuring simple encoder and decoder structures, and flexible coding rate. RZH codes are serially concatenated turbo-like codes where the outer code is a repetition code and the inner code is a punctured zigzag-Hadamard (ZH) code. By analyzing the code structure of RZH codes, we prove that both systematic and nonsystematic RZH codes are good codes, in the sense that for an RZH code ensemble, there exists a positive number gamma0such that for any binary-input memoryless channel whose Bhattacharyya noise parameter is less than , the average block error probability of maximum-likelihood (ML) decoding approaches zero. Two decoding algorithms-serial and parallel decoders for RZH codes-are proposed. We then employ the extrinsic information transfer (EXIT) chart technique to design irregular RZH codes. Results show that the optimized irregular RZH codes exhibit a performance that is very close to capacity in the low-rate regime.

We investigate the optimal design of a multihop wireless mesh network equipped with multiple orthogonal wireless channels and multiple radios. Specifically, we focus on solutions that can efficiently utilize the limited resource to support multiple unicast applications by routing and network coding. We propose a cross-layer optimization framework where the broadcasting feature of the wireless environment, which plays an important role in realizing the achievable gain of network coding, is taken into account. Moreover, we propose a network code construction scheme based on linear programming, with which the possible achievable Coding+MAC gain could be significantly increased. Delay constraints are also included in the network code construction formulation so that the possible impact of the extra decoding delay to the TCP/IP performance can be reduced without changing the upper-layer protocols. The proposed network design based on cross-layer optimization results in significant increase in network throughput.

We investigate the extrinsic information transfer (EXIT) functions of Hadamard codes in the context of repeat- zigzag Hadamard (RZH) codes with parallel decoding. The derived EXIT functions can serve as an effective tool for designing low-rate IRZH codes with parallel decoding in BIAWGN channels.

The recently proposed interleave-division multiple-access (IDMA) system is a flexible spread-spectrum air-interface technique featuring low receiver complexity and high spectral efficiency. In IDMA, each user's chip sequence is interleaved by a distinct chip-level interleaver. The receiver employs a simple chip-level iterative multiuser detector to decode the user's data. Here we focus on the analysis and optimization of such an IDMA system. We show that IDMA can be viewed as a limit case of the conventional CDMA employing repetition code and random spreading. Two analytical tools, namely, the large-system performance approximation and the EXIT chart technique are tailored in the context of IDMA chip-level iterative detector to facilitate the system performance analysis and optimization. The spectral efficiencies of a low-rate coded IDMA system with equal power setting in both single-cell and multi-cell scenarios are then analyzed, from which it is seen that the coded IDMA system with turbo receiver is a spectral efficient multiple-access scheme. Finally, we consider optimal power allocation among users in IDMA to maximize the spectral efficiency with finite-alphabet constellation. The differential evolution technique for nonlinear optimization is adopted to solve the power profile optimization problem. With optimized power profiles, the low-rate coded IDMA system can approach the optimal spectral efficiency with finite input constellations

In this paper, we propose a new multi-rate multiple-access wireless system implemented by variable spreading gain and chip-level random interleaving. Optimization across the physical and network layers in the uplink of such a system is also treated. A multi-criterion reinforcement learning (MCRL)-based adaptive call admission control (CAC) method is proposed which can easily handle multiple average QoS requirements

We propose a new class of low-rate error correction codes called repeat-zigzag-Hadamard (RZH) codes. RZH codes are serially concatenated turbo-like codes where the outer code is a repetition code and the inner code is a punctured zigzag-Hadaniard (ZH) code. We prove that RZH codes are good in the sense that for an RZH code ensemble, there exists a positive number 70 such that for any binary-input memoryless channel whose Bhattacharyya noise parameter is less than 70, the average maximum-likelihood (ML) decoder block error probability approaches zero. EXIT charts are used to design irregular codes

We consider a code-spread and chip-interleaved time-hopping (TH) multiple-access scheme for multiuser ultra-wideband (UWB) communications. In such a system, each user's chip sequence is interleaved by a user-specific distinct random interleaver, and the receiver is a low-complexity chip-level iterative multiuser detector (MUD) which performs simple Rake-type combining to collect the energy dispersed in multipath UWB channels. To further reduce the receiver complexity, time reversal (TR), a transmitter preprocessing technique, is also considered. When power control is employed along with TR, a single-tap receiver can be utilized which offers a desirable bit error rate (BER) performance with a significantly reduced sampling rate. Furthermore, the zigzag Hadamard (ZH) code is proposed as the low-rate code for both channel coding and spreading in the code-spread TH-UWB system. With its capacity-approaching capability and low encoding/decoding complexity, the parallel concatenated ZH code is a promising coding scheme for UWB applications.

In this paper, we focus on the analysis and optimization of the interleave-division multiple-access (IDMA) system. The spectral efficiencies of the coded IDMA system are analyzed. Optimal power allocation among users in IDMA, to maximize the spectral efficiency with a finite-alphabet constellation, is also considered. Differential evolution is adopted to solve the power profile optimization problem.

We study the mutual information transfer characteristics of the soft interference cancellation (SIC) multiuser detectors (MUD) for coded code-division multiple-access (CDMA) systems in synchronous additive white Gaussian noise (AWGN) and asynchronous multipath fading channels. Based on the extrinsic information transfer (EXIT) chart technique, we compare the asymptotic (as the block length goes to infinity) performance and the convergence behavior of different joint detection schemes which are highly dependent upon different system parameters and channel conditions. A framework of using the EXIT chart to analyze the coding-spreading tradeoff is also addressed for turbo multiuser detection. Results show that the SIC-minimum mean square error (MMSE) MUD generally provides a higher spectral efficiency than the SIC-match filter (MF) MUD. Moreover, the impact of finite block length on the convergence behavior of turbo MUD is also analyzed using a consistent Gaussian approximation on the distribution of the output extrinsic information.