Esrafil Jedari

Performance of the Pre/Post-FFT Smart Antenna Methods for OFDM-Based Wireless LANs in an Indoor Channel with Interference

The performance of OFDM-based Wireless Local Area Networks (WLANs) is investigated by employing different smart antenna techniques at the receiver. The use of multiple antennas at the Access Point (AP) receiver in IEEE802.11a standard-compliant Single Input Multiple Output (SIMO) configuration, improves the physical layer performance in different channel scenarios and interference that may arise from other stations sharing the same frequency band. For this purpose, a comparative study of smart antenna architectures for IEEE802.11a WLAN system using pre-FFT and post-FFT array processing techniques is presented. Simulations are performed on a new model for IEEE802.11a system using a spatio-temporal channel model which is developed based on a measured wideband channels in the 5GHz band. Bit-Error-Rate (BER) performance for QPSK modulation at LOS, OLOS and NLOS channel scenario along with co-channel interference is evaluated. Simulation results demonstrate the effectiveness of employing the proposed pre-FFT signal processing.

A New Double Counting Cancellation Technique for Three-Dimensional Ray Launching Method

A new efficient algorithm is proposed to avoid the ray double counting problem in the three-dimensional ray launching method. This new method is very simple and is based on the angle between the received rays and the total distance traveled by them. These two parameters have to be saved in every ray launching method and therefore the proposed method does not need any extra memory. Comparison between the simulation results shows the good performance of the proposed method

Reduced Complexity Maximum Likelihood Multiuser Detection for OFDM-Based IEEE 802.11A WLANs Utilizing POST-FFT Mode

Considering the space division multiple access (SDMA) in IEEE 802.11a based systems, in this paper, we propose a new two-step multiuser detection (MUD) algorithms. In the first step, MMSE and MSNIR MUD algorithms are used. In the second step, by using sensitive bits algorithm (SBA) to obtain least reliable bits, maximum likelihood detection (MLD) algorithm is applied only to these bits; as a consequence, the search space is reduced dramatically. In order to reduce the computational complexity of MLD algorithm, an innovative modification named the less complex norm approximation (LCNA) based Euclidean distance is used. The performance and complexity of proposed MUD algorithms are compared with nonlinear MMSE-SIC, MSNIR-SIC and ML MUD algorithms. Results show that with a minimal penalty in performance compared to MLD algorithm, the SBA-based proposed two-step schemes have significant reduction in complexity. Furthermore, it is shown that for a specified number of sensitive bits, the introduced algorithms have approximately the same performance with significant less complexity compared to MMSE-SIC and MSNIR-SIC nonlinear MUD algorithms

Low-Rate Channel Coding Scheme for Replica MT-CDMA Communication System

In this paper, we analyze performance of a special kind of multitone CDMA (MT-CDMA) systems that is Replica MT-CDMA. It is shown that with the same bandwidth, Replica MT-CDMA system outperforms the conventional system that we name it as S/P MT-CDMA. We also propose a low-rate bandwidth efficient channel coding scheme for Replica MT-CDMA communication system so that by using it, coded Replica MT-CDMA system needs to the same bandwidth as the uncoded one. In this paper, we compare low-rate coded and uncoded Replica MT-CDMA systems with S/P MT-CDMA system over uplink and downlink Rayleigh fading channels. Our results show that with the same bandwidth, performance of coded Replica MT-CDMA system with the proposed channel coding scheme is considerably better than performance of both uncoded MT-CDMA systems.

A New Statistical Wideband Spatio-Temporal Channel Model for 5-GHz Band WLAN Systems [Comments and corrections on]

This note points out that the probability density function (pdf) for cluster conditional angle-of-arrival (AOA) in the line-of-sight (LOS) scenario proposed in the above-mentioned paper by C.C. Chong et al. (see IEEE Journal on Selected Areas in Communications, vol.21, no.2, Feb. 2003) has some mathematical errors. A possible correction is presented.

Adaptive Rate and Power Allocation Schemes for OFDM/SDMA Systems

In this paper, adaptive resource allocation approaches, which jointly adapts power distribution and subcarrier allocation according to instantaneous channel conditions, is proposed for uplink OFDM/SDMA-based multiuser system. The first scheme utilizes adaptive algorithm to reduce symbol-error rate. The closed-form algorithm is derived for this idea. The second contribution in this paper deals with constant-rate transmissions over a spatial multiuser OFDM system. In the proposed system, the receiver jointly optimizes rate and power assignments for each user and then informs them to the transmitter via a low-rate feedback channels.

A New Wideband MIMO Channel Model for Simulating 5-GHz Band Indoor WLANs

Considerable interest in the indoor applications of wireless local-area networks (WLANs) demands some powerful simulation methods of these systems. Proper modeling of the physical propagation channel is crucial in this context. A novel simulation method for indoor wideband multi-input multi-output (MIMO) channel at the operating frequency band of IEEE 802.11a, HIPERLAN/2, and the emerging IEEE 802.11n standards is presented in this paper which is suitable for performance analysis of MIMO techniques in these systems. The presented model is developed on the basis of a previously proposed channel representation at the same frequency band. Simulation results for MIMO channel capacity are presented and compared with direct measured data and good agreement is observed, which confirms the validity of the proposed model.

A parametric double-directional wideband model for indoor MIMO channel at 5-GHz band

This paper presents a novel method for simulating indoor wideband MIMO radio channels that is based on SIMO measurements previously reported in the literature. The proposed model is specifically tailored for use in 5-GHz band, which is the operating frequency band of some popular indoor WLANs such as IEEE 802.11a and HIPERLAN/2. The procedure for deriving the impulse response was described and simulation results revealing the ability of proposed method to predict MIMO channel performance were presented