Imran Zaka

Minimum bit error rate multiuser detection for OFDM-SDMA using particle swarm optimization

The Minimum Bit Error Rate (MBER) detectors outperform the conventional Minimum Mean Squared Error (MMSE) detector by minimizing the Bit Error Rate (BER) directly. In this paper an MBER multiuser detector for Orthogonal Frequency Division Multiplexing-Space Division Multiple Access (OFDM-SDMA) system is proposed employing Particle Swarm Optimization (PSO) for finding the optimum weight vectors. Simulation results show that the proposed system achieves faster convergence with lower complexity as compared to Genetic Algorithms (GA) with same Bit Error Rate (BER) performance.

An MBER–BLAST algorithm for OFDM–SDMA communication using particle swarm optimization

A multiple antenna-aided, minimum bit error rate–Bell Laboratories-layered space–time (MBER–BLAST) multiuser detection algorithm is proposed for uplink orthogonal frequency division multiplexing–space division multiple access (OFDM–SDMA) communication to increase the capacity of the system. The proposed algorithm overcomes the limitations of the conventional detectors when the number of users exceed the number of receiver antennas. A particle swarm optimization (PSO) algorithm is employed for finding the optimum weight vectors for MBER detector. PSO is well suited for physically realizable, real-time applications, where low complexity and fast convergence are of absolute importance, while an optimum maximum likelihood (ML) detection using an exhaustive search method is prohibitively complex. The proposed algorithm outperforms the MBER detector and is capable of achieving performance close to that attained by ML detector at a significantly lower complexity, especially under high user loads. Simulation results show that MBER–BLAST detector promises substantially improved performance compared with the existing systems and offers a good performance–complexity trade-off. It supports a large number of users by exploiting the capacity advantages of multiple antenna systems in rich scattering environments. Copyright

Multicode Multicarrier Interleave Division Multiple Access Communication

A new mulitcode multicarrier interleave division multiple access (MC-MC-IDMA) system is proposed and analyzed in frequency selective channels. The system supports different modulation schemes for variables data rates. Each user transmits his message by choosing a sequence from an orthogonal code-set. An MC-MC-IDMA system achieves spreading gains both in time and frequency domains. Bit error rate of the system is derived and simulation results are presented.

Multicarrier Interleave Division Multiple Access Communication with Adaptive Subchannel Allocation

A low complexity multicarrier interleave division multiple access (MC-IDMA) system operating in multipath fading channels with adaptive subchannel allocation for uplink transmission is described. Instead of transmitting chips over a number of subchannels uniformly, chips are transmitted over subchannels which have largest fading amplitudes among all the subchannels. Concatenated Zigzag codes are used as Forward Error Correcting Codes (FEC). Simulation results show that the adaptive subchannel allocation scheme used in conventional MC-IDMA system greatly improves the bit error rate (BER) performance of the system.

PSO- AND GA-BASED NARROWBAND JAMMER EXCISION IN CDMA

Narrowband jammer excision is formulated as an optimization problem in this paper. Optimal filter weights are calculated/searched for by the computational intelligence techniques. We compare the error rate performance, complexity, and implementation issues of various computational intelligence techniques like Particle Swarm Optimization (PSO), Genetic Algorithm, and Least Mean Square (LMS). These techniques update the excision filter weights iteratively till the convergence criteria has been achieved. Bit Error Rate performance shows these techniques effectively suppress the Narrow Band Interference. It has been observed that PSO-based algorithm with tuned parameters outperforms other schemes of PSO and the other algorithms. It approaches the optimum performance in fewer iterations with ease in implementation.

Narrowband Jammer Excision in CDMA Using Particle Swarm Optimization

We formulate the narrowband jammer excision as an optimization problem and present a new algorithm that is based on Particle Swarm Optimization (PSO). In this paper particle positions represent the filter weights and particle velocity represents the updating increment of the weighting matrix. Simulation and numerical results show that PSO based algorithm is a feasible approach for jammer excision. It approaches the optimum performance in fewer iterations with lower complexity. The performance improvement is shown by plotting the Bit Error Rate (BER) as a function of Signal to Interference and Noise Ratio (SINR).

Combined Equalization and Channel Estimation for MC-IDMA Uplink Transmissions

Combined equalization based on combination of pre and post equalizations in a multicarrier interleave division multiple access (MC-IDMA) system, is described. The channel pre-equalization is constrained to keep transmitted power unchanged. Combined-equalization requires explicit channel state information (CSI) both at the mobile station and the base station. A low complexity uplink channel estimation strategy is developed at the base station for post-equalization. CSI at the mobile is made available for pre-equalization, by exploiting channel reciprocity between down and uplinks in time division duplex (TDD) mode. It is shown that system with combined equalization improves the bit error rate (BER) significantly as compared to the corresponding systems with pre and post equalizations alone.

Iterative multiuser detection of CDMA in fading channels

A new multiuser detection technique is proposed which is based on Gaussian approximation. The system uses conventional reverse link CDMA transmitter and a proposed receiver. In the receiver, the interference rejection block, known as Signal Reliability Estimator (SRE) and the decoder (DEC), exchange extrinsic information in an iterative manner. The system is analyzed in Rayleigh fading channels. It is observed from simulation results that Bit Error Rate (BER) of the system is almost independent of the number of users.

Intelligent interleaver for PAPR reduction

In orthogonal frequency division multiplexing (OFDM) systems, one of the major problems to be tackled is high peak to average power ratio (PAPR). In this paper a PAPR reduction scheme for OFDM system is proposed that takes the advantage of the classification capability of learning vector quantization (LVQ) networks. The symbols are distributed in different classes and interleaved by a different interleaver, to achieve minimum PAPR before they are transmitted. A tremendous reduction in number of computations is achieved to get the required reduction in PAPR values.

Comparison of Jammer Excision Techniques

In communication receivers, jamming mitigation techniques play a critical role in improving its performance. These mitigation techniques try to remove or reduce the effect of jamming and are employed at a pre-processing stage in the receiver. In this paper we compare the performance of several techniques in presence of broadband jammer signal. Simulation results are presented showing comparison of signal to noise ratio enhancement and bit error rate improvement