K.Y. Wu

Interleave division multiple-access

This paper provides a comprehensive study of interleave-division multiple-access (IDMA) systems. The IDMA receiver principles for different modulation and channel conditions are outlined. A semi-analytical technique is developed based on the density evolution technique to estimate the bit-error-rate (BER) of the system. It provides a fast and relatively accurate method to predict the performance of the IDMA scheme. With simple convolutional/repetition codes, overall throughputs of 3 bits/chip with one receive antenna and 6 bits/chip with two receive antennas are observed for IDMA systems involving as many as about 100 users.

On interleave-division multiple-access

This work provides a comprehensive study of IDMA systems. We first outline the basic IDMA principles in single-path and multi-path environments. We then describe a simple semi-analytical technique to assess the performance of IDMA systems, based on which we develop a power allocation scheme for performance optimization. We also discuss the use of low-rate codes to further enhance the power efficiency of IDMA systems. Simulation results demonstrate the advantages of the IDMA scheme in terms of both bandwidth and power efficiencies. For example, with simple convolutional/repetition codes an overall throughput of 8 bits/chip is achieved in single antenna systems. With turbo-Hadamard codes, performance at 1.4 dB away from the theoretical limit is demonstrated in a Gaussian MAC.

Approaching the capacity of multiple access channels using interleaved low-rate codes

We show that the capacity of a Gaussian multiple access channel can be approached by interleaved low-rate codes together with a simple chip-by-chip iterative decoding strategy. Based on a rate /spl ap/ 1/69 code and with a total of 35 simultaneous users (the aggregate rate /spl ap/ 1/2), performance of BER=10/sup -5/ is observed at E/sub b//N/sub 0/ /spl ap/ 1.4 dB, which is close to the corresponding capacity limit (E/sub b//N/sub 0/ /spl ap/ 0 dB).

A simple, unified approach to nearly optimal multiuser detection and space-time coding

Techniques using interleaving as the basic means for signal separation are introduced for both multiple access systems and multiple transmit antenna systems. A very low-cost chip-by-chip iterative detection algorithm is presented. The proposed schemes can achieve nearly optimal performance for system with a large numbers of users or transmit antennas.

A Quasi-Random Approach to Space–Time Codes

This paper presents a quasi-random approach to space-time (ST) codes. The basic principle is to transmit randomly interleaved versions of forward error correction (FEC)-coded sequences simultaneously from all antennas in a multilayer structure. This is conceptually simple, yet still very effective. It is also flexible regarding the transmission rate, antenna numbers, and channel conditions (e.g., with intersymbol interference). It provides a unified solution to various applications where the traditional ST codes may encounter difficulties. We outline turbo-type iterative joint detection and equalization algorithms with complexity (per FEC-coded bit) growing linearly with the transmit antenna number and independently of the layer number. We develop a signal-to-noise-ratio (SNR) evolution technique and a bounding technique to assess the performance of the proposed code in fixed and quasi-static fading channels, respectively. These performance assessment techniques are very simple and reasonably accurate. Using these techniques as a searching tool, efficient power allocation strategies are examined, which can greatly enhance the system performance. Simulation results show that the proposed code can achieve near-capacity performance with both low and high rates at low decoding complexity.

A simple approach to near-optimal multiple transmit antenna space-time codes

This paper presents a family of space-time codes employing interleavers to separate signals form different antennas. Noticeable performance improvement has been observed compared with existing schemes. An interactive detection algorithm is derived. The complexity involved is very low, and increases only linearly with the number of transmit antennas.

Multilayer turbo space-time codes

This letter describes a multilayer turbo space-time coding scheme. Based on a carefully designed power allocation strategy, performance reasonably close to the theoretical limits can be achieved at a rate of two bits per channel use with very low complexity.

An improved two-state turbo-SPC code for wireless communication systems

This letter presents an improved two-state turbo single-parity-check code for applications with rates around 1/3. The new code is compared with the (15,13)/sub 8/ turbo code used in the Third Generation Partnership Project. Simulation results demonstrate that the proposed code can achieve similar performance at reduced decoding complexity.

Multi-layer turbo space-time codes for high-rate applications

We study a multi-layer space-time code, based on random interleaving and proper power allocation. We show that, theoretically, the proposed code can achieve capacity for any transmission rate by superimposing many ideal low-rate codes. We also show that, with practically available codes, the proposed scheme can achieve performance close to the theoretical limit.

High-rate interleave-division-multiplexing space-time codes

We propose a family of simple multi-layer space- time codes based on random interleaving and power allocation techniques. We show that the optimal space-time coding problem can be effectively resolved by superimposing several ideal low-rate codes for an AWGN channel. Simulation results demonstrate that the proposed high-rate space-time codes can achieve performance close to the theoretical limit. I. INTRODUCTIONS