2 research outputs found
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Performance of MC-CDMA with pilot code and blind equalization algorithm
Various methods and techniques have been introduced and applied to advance the state of the art of mobile wireless communications technology. For example, some techniques are applied to overcome the problem of multipath caused by the mobile environment. Multipath produces replicas of the wanted signal which arrive at the receiver with different time delays. If not dealt with properly, this environment will greatly deteriorate the quality of the wanted signal. The so-called multiuser feature of many wireless communication systems will also add some interference to the signal of interest. This thesis makes an attempt to improve the performance of wireless communication systems that use either pilot-based or blind equalization techniques to obtain channel side information. Specifically, these techniques are concerned with the estimation of multipath parameters in order to improve system performance. By inserting some pre-defined code which is called a pilot code on each pre-defined segment of a data block, we can recover the signal by pilot-based methods. Using an adaptive method, some knowledge of the channel characteristics and input source, we can achieve acceptable error rate using blind equalization as an alternate solution to pilot-based. Finally, new enhancements are added to blind equalization to improve its performance further
A two-stage CMA-based receiver for blind joint equalization and multiuser detection in high data-rate DS-CDMA systems
The paper deals with the problem of blind mitigation of intersymbol interference (ISI) as well as multiple-access interference (MAI) in asynchronous high data-rate direct-sequence code-division multiple-access systems. A blind adaptive multiuser receiver based on the constant-modulus algorithm (CMA) is proposed, which demodulates each desired user by exploiting only the knowledge of its spreading code, without requiring estimation of the users's channels and timings. In order to overcome the CMA interference capture problem, which arises in a multiuser scenario, a two-stage adaptive receiver is adopted: In the first stage, partial MAI and ISI suppression is blindly achieved by exploiting the desired user signature structure properties; in the second stage, the residual MAI and the ISI are removed by using the CMA, and the information symbols of the desired user are reliably recovered. Theoretical analysis and simulation results show that the first stage is an effective blind adaptive strategy which allows the CMA detector in the second stage to lock on the desired-user symbol, at a particular delay. The proposed blind receiver achieves a significant performance gain in comparison with existing blind methods