Suwich Kunaruttanapruk

V-BLAST technique for uplink MC-CDMA systems in rich scattering environment

In this paper, we propose a new approach for MC-CDMA system in rich scattering environment. For our proposed system, an efficient MIMO technique, called as V-BLAST (vertical Bell Laboratories layered space-time), is applied in order to increase the capacity of uplink multi-carrier code division multiple access (MC-CDMA) system. High speed transmission can also be achieved by using a low spreading factor. In this system, different users can use the same spreading code, so system capacity can be increased significantly. Different from most of the V-BLAST related researches which assume the perfect knowledge of the channel, we also consider the effect of the practical channel estimation to the system performance. In this paper, we investigate the performance of this system in both rich scattering channel and low scattering channel. We show that this system can be used efficiently in rich scattering environment. In low scattering environment, the performance of this system is too close with original MC-CDMA system. In addition, the result of the simulation with the estimation error shows that this system is suitable for practical implementation.

RLS channel estimation with forgetting factor adaptation for the downlink of MC-CDMA system

In this paper, two pilot-aided-channel-estimation schemes modified from the ordinary recursive least squares (RLS) algorithm for the downlink of multicarrier code division multiple access (MC-CDMA) are proposed. Both techniques employ the method of adjusting the adaptive weigh (forgetting factor) of RLS algorithm for utilizing the correlation in time domain of the channel response in order to improve the estimation accuracy and tracking capability of the system. The simulation results show that our proposed algorithms outperform the customary RLS algorithm channel estimation schemes in both BER performance and tracking capability over the frequency selective fading channel.

Optimum Pulse Shape Design for UWB Systems with Timing Jitter

This paper proposes a novel technique in designing the optimum pulse shape for ultra wideband (UWB) systems under the presence of timing jitter. In the UWB systems, pulse transmission power and timing jitter tolerance are crucial keys to communications success. While there is a strong desire to maximize both of them, one must be traded off against the other. In the literature, much effort has been devoted to separately optimize each of them without considering the drawback to the other. In this paper, both factors are jointly considered. The proposed pulse attains the adequate power to survive the noise floor and at the same time provides good resistance to the timing jitter. The proposed pulse also meets the power spectral mask restriction as prescribed by the Federal Communications Commission (FCC) for indoor UWB systems. Simulation results confirm the advantages of the proposed pulse over other previously known UWB pulses. Parameters of the proposed optimization algorithm are also investigated in this paper.

PERFORMANCE EVALUATION OF UWB SYSTEMS USING DIFFERENT ORDER OF GAUSSIAN PULSES

The ultra-wideband impulse radio (UWB-IR) transmits information by using extremely short pulses that are very sensitive to the timing error. In this paper, the contribution of pulse shapes to the timing error tolerance is considered. Three well known Gaussian derivative pulses are investigated. The simulation results show that different pulse shapes cause substantial difference in achievable bit error rate. The pulse with lower derivative order tends to offer better performance

Iterative partial soft interference cancellation with MMSE multiuser detection for uplink turbo-coded MC-CDMA system

In this paper, we improve the conventional iterative soft interference cancellation by introducing the partial cancellation technique and minimum mean square error (MMSE) multiuser detection technique in an uplink turbo-coded multicarrier code division multiple access (MC-CDMA) system. The performance of our proposed receiver is evaluated in Rayleigh multipath fading channel by using computer simulation. Simulation results demonstrate the advantages of the proposed technique over the conventional technique.

The novel decision feedback equalizer for OFDM system with insufficient cyclic prefix

If the multipath delay difference is greater than the duration of a cyclic prefix, the performance of an orthogonal frequency division multiplexing (OFDM) system suffers severe degradation. The insufficient cyclic prefix phenomenon incurs two adverse interferences, intersymbol interference (ISI) from the adjacent symbols and intercarrier interference (ICI) from other subcarriers in the same OFDM symbol interval. We propose a novel decision feedback equalizer (DFE) receiver to improve the performance of an OFDM system with insufficient cyclic prefix. The proposed receiver does not require knowledge of the channel impulse response. Simulation results confirm the advantages of our proposed receiver over the TEQ technique.

Power allocation optimization for uplink MC-CDMA systems

In this paper, we consider the joint transmitter and receiver for uplink MC-CDMA systems. The equation of the MMSE joint transmitter-receiver is expressed. We apply an optimization technique by rewriting the equation of the joint transmitter and receiver for uplink MC-CDMA systems as second-order cone programming (SOCP) which can efficiently be solved numerically by the existing polynomial convergence software packages. Numerical examples show that the joint transmitter-receiver optimization yields the lower BER compared with the MMSE receiver for both perfect channel estimation and imperfect channel estimation case

Joint Interference Suppression and Frequency Offset Compensation Techniques for a Reverse Link MC-CDMA System

This paper addresses several relevant issues in detection process of a reverse link multicarrier code division multiple access system with frequency offset. Due to the presence of frequency offsets, power of a group of subcarriers is spread to all the available subcarriers. In order to collect all the scattered signal power, we propose a two stages receiver. First stage of the proposed receiver performs maximum ratio combining. Following from the first stage, multiple access interference is suppressed in the second stage. We propose various multiple access interference suppression techniques, having different complexity and performance. Simulation results demonstrate the advantage of the proposed receiver. We also investigate the performance of 2 major subcarrier assignment schemes, namely continuous subcarrier assignment scheme and interleaved subcarrier assignment scheme, in both ideal independent fading channel and practical correlated fading channel.

Optimum training sequences for the uplink of MIMO MC-CDMA systems

In wireless communication systems, the use of multiple antennas at both transmitter and receiver, called multiple-input multiple-output (MIMO) architecture, is one of the most promising techniques to improve spectral efficiency and performance communication links. This paper proposed a new scheme of training sequence transmission for estimating the time-varying channel in the MIMO MC-CDMA system. Such training sequences can be regarded as an optimal manipulation by mean of orthogonal design. The proposed scheme can support more number of users than the conventional scheme. The optimum training sequences reduce the complexity of the channel estimation at the compensation of a negligible performance degradation. The proposed estimator was evaluated by computer simulations to demonstrate the merits of proposed technique.

Parameter Acquisition Techniques for Multiuser Detection with ISI Cancellation in a Quasi-Synchronous Reverse Link MC-CDMA System

In a quasi-synchronous reverse link multicarrier code division multiple access system, the signal detection is vulnerable to the interference due to the insufficient guard interval. A multiuser detection with intersymbol interference cancellation is a potential solution to overcome this problem. In this paper, we proposes a parameter acquisition technique based on a specially designed training sequence for the receiver. The concerned parameters are the transformed signature sequences and the ISI generation sequences. We analyze a criterion for the training sequences to achieve the minimum mean square error and propose the systematic generation of the optimum training sequences. We also propose the noise variance estimator for providing information about noise variance to some classes of multiuser detection. Simulation results prove relevant benefits of the proposed techniques and give useful insights into the system designs.