Shyue-Win Wei

VLSI architectures for computing exponentiations, multiplicative inverses, and divisions in GF(2/sup m/)

A systolic power-sum circuit designed to perform AB/sup 2/+C computation in the finite field GF(2/sup m/) has been presented recently. Based on the power-sum circuit, a VLSI architecture for performing exponentiations in GF(2/sup m/) is developed. Furthermore, two modified architectures that can be used to compute multiplicative inverses and divisions in GF(2/sup m/) are proposed respectively. All the architectures are constructed by m-1 power-sum circuits. The average computation time of the architectures is only two logic gate delays and the circuit complexity is realizable in present VLSI technology. It should be emphasized at this point that the computation time of two gate delays is the highest computation speed in finite field arithmetic.<<ETX>>

Channel estimation for OFDM system with two training symbols aided and polynomial fitting

A time-varying channel estimation method for orthogonal frequency division multiplexing (OFDM) systems is presented. The presented channel estimation method employs two training symbols in combination with polynomial fitting, thus obtaining accurate estimation results under a large normalized Doppler frequency.

Less Complexity Successive Interference Cancellation for OFDM System

The Vertical Bell Laboratories Layered Space Time (V-BLAST) detection presented for multiple-input multiple- output (MIMO) system can also be used for orthogonal frequency division multiplexing (OFDM) signal detection, and is referred as the successive interference cancellation (SIC) method. In the paper a refined SIC algorithm is first presented. Then, several less complexity modified SIC algorithms for OFDM signal detection in multi-path fading channel are presented. The presented modified SIC algorithms can significantly reduce the computation complexity of SIC and meanwhile maintain excellent performance.

Low complexity qSIC equalizer for OFDM system

A well-known interference cancellation technique called successive interference cancellation (SIC) has been proved to have an excellent performance for mitigating inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) system. However, since the complexity of SIC is proportional to the number of OFDM subcarriers N, the realization of this detector become impractical, especially when large number of subcarriers is considered. A low complexity equalization technique based on SIC is therefore proposed for high mobility OFDM system. The presented low complexity modified SIC algorithm is referred to as qSIC equalizer since only the dominant ICI term is considered. The qSIC algorithm can significantly reduce the computational complexity and meanwhile maintain excellent detection performance.

Channel Estimation for OFDM Systems with Asymmetric Pilot Symbols

A time-varying channel estimation method for orthogonal frequency division multiplexing (OFDM) systems is presented. The proposed method makes use of two asymmetric pilot symbols to improve channel estimation performance and meanwhile obtain a reasonable pilot overhead. Complete simulations illustrate that the proposed method can have precise estimation result even under very large normalized Doppler frequency.

A handover algorithm for broadband wireless access system on railway

For the broadband wireless access system of the railway system, because the trains move forward on the railroad in a fixed direction under a regular path, the mobile stations on the railway trains can only choose the approaching neighboring base stations as unique target base station candidates. This is different from the typical broadband wireless access systems. Using the IEEE 802.16e handover algorithm, a simplified, modified handover procedure is proposed to reduce the memory consumption of paused data buffer during the cell re-selection process and shorten the handover operation time during the handover process.

Spreading code selection methods for MC-CDMA under carrier frequency offset

Carrier frequency offset (CFO) may cause multiple access interference (MAI) among users in multi-carrier code division multiple access (MC-CDMA) system. In the paper the code sensitivity of spreading codes and its correlative to the CFO is observed. An interesting property of orthogonality invariant for spreading codes under CFO has been presented. Based on the properties of code sensitivity, several algorithms of selecting the spread codes that will decrease the MAI caused by frequency offset are proposed. Using the presented code selection methods, the system capacity of MC-CDMA can be effectively increased without increasing the system complexity.

Spreading Code Allocation for Downlink MC-CDMA

The paper illustrates that multiple access interference (MAI) can be reduced by arranging the spreading codes in multi-carrier code division multiple access (MC-CDMA) systems. An effective spreading code allocation procedure using simple least square (LS) channel estimation is presented to reduce the MAI in downlink MC-CDMA systems. Moreover, the spreading codes chosen by the method are in a consistent sequence. Using this code selection method, the system capacity of MC-CDMA can be effectively increased without increasing too much system complexity. Simulation results show that the presented method can work well for both time-invariant and fading channels.

On Step-by-Step Complete Decoding Triple-Error-Correcting Binary BCH Codes

According to the properties found in the algebraic complete decoding method for triple-error-correcting binary Bose-Chaudhuri-Hocquenghem (BCH) codes, a step-by-step complete decoding algorithm of this code is presented.

Modified guard band power detection methods for OFDM frequency offset recovery

Fast and less complexity of modified guard band power detection (GPD) methods for orthogonal frequency division multiplexing (OFDM) coarse carrier offset estimation are presented. Conventional GPD have to be operated after the fine carrier offset recovery. The performance of GPD estimation may be significant degraded due to the induced interchannel interference (ICI) if fine carrier offset is not zero. In the paper, we first show that the accuracy of GPD estimation can be significant improved based on a simple concept of power average. Furthermore, according to the similar idea of reference symbol power adjustment (RPA), two general patterns of subcarrier power adjustment are presented to improve the estimation performance under nonzero fine frequency offset. Based on the simulation results of four COST 207 fading channel models, it is illustrated that the presented modified GPD methods can be operated independent of the fine carrier offset adjustment.