SUMMARYA 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.
Combined equalization based on combination of pre much attention [9]. In the case of downlink, a good Bit Error and post equalizations in a Multicarrier Interleave Division Rate (BER) performance can be achieved using frequency Multiple Access (MC-IDMA) system, is described. The channel domain equalization at the receiver. However, in the case of pre-equalization is constrained to keep transmitted power uplink, each user's signal goes through independent fading unchanged. Combined-equalization requires explicit Channel channels, and the orthogonality among users is lost. The State Information (CSI) both at the mobile station and the base resulting Multiple Access Interference (MAI) degrades the station. A low complexity uplink channel estimation strategy is BER performance. As shown in [10][11][12], the use of Frequency developed at the base station for post-equalization. CSI at the Domain Equalization (FDE) at the receiver cannot suppress the mobile is made available for pre-equalization, by exploiting NIAI. Pre-equalization techniques at the transmitter can be channel reciprocity between down and uplinks in Time Division adopted to counter the multipath and M\AI effects [13][14][15]. In Duplex (TDD) mode. It is shown that system with combined pre-equalization, the gain assigned to each subcarrier can be equalization improves the Bit Error Rate (BER) significantly as varied so that the signal at the receiver appears undistorted. The compared to the corresponding systems with pre and post performance can be further increased by post equalization atthe receiver [16].In this paper we describe the concept of combined Channel estimation; equalization for MC-IDMA system under the constraint of keeping the transmit power the same. As combined I. INTRODUCTION equalization requires channel state information (CSI) at the Wireless communication has been facing the demands for transmitter and the receiver, a low complexity channel high data transfer rates. The greatest current challenge for estimation strategy is developed at the receiver for post future wireless communication systems is to provide broadband equalization. CSI at the transmitter can be made available in mobile data access as high as possible. Single carriers systems Time Division Duplex (TDD) system exploiting channel are limited by Inter Symbol Interference (ISI) due to frequency reciprocity between alternative channel downlink and uplinks. selectivity of wireless channels. Multicarrier systems avoid ISI It is shown that systems with combined-equalization significantly by transmitting data in parallel with longer symbol outperform the systems with pre or post equalizations alone. durations [1]. This offers possibilities for alleviating many of Rest of the paper is organized as follows. Next section the problems encountered in the single carrier systems, and describes the uplink MC-IDMA system model and develops a besides the inspired performance in multipath channels, it combined equalization approach. Channel estimation is exhibits other favorable properti...
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.
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