Análise de técnicas de equalização de canal para SC-FDMA

Abstract

As for the main problems found in wireless digital communication systems, the multipath phe- nomenon stands out, as it could cause severe distortion on the transmitted signal, possibly com- promising the system’s whole functioning. This paper presents the study and implementation of

the main channel equalization schemes existent in literature, as a way to compensate multipath

effects, applied to SC-FDMA (Single Carrier - Frequency Division Multiple Access). The SC- FDMA standard specified for the Uplink of the 4th Generation LTE (Long Term Evolution) was

implemented, as also three channel estimation and channel equalization techniques. The first one, channel estimation by Linear Interpolation, uses the reference symbols for the interpolation process, being the classic technique used for SC-FDMA systems. The rest of the implemented

techniques, CMA(Constant Modulus Algorithm) and CMA-DD Concurrent (Constant Modu- lus Algorithm - Direct Decision), are blind channel equalization techniques, proposed for single

carrier systems.

The implemented techniques were evaluated for different operation scenarios, with low, me- dium and high dispersion, considering the user moving at different speeds: a low speed pedes- trian, a medium speed vehicle and a high speed vehicle, all defined by the 3GPP (3rd Generation

Partnership Project), through the EPA, EVA and ETU channels. The performance comparison of

the Linear Interpolation, CMA e Concurrent techniques were analyzed through the SER (Sym- bol Error Rate) results. The algorithm’s convergence time and residual error were evaluated for

the adaptive techniques, using the MSE (Mean Squared Error). The Concurrent equalizer had superior performance compared to the other techniques for all the cases considered in terms of SER, presenting values up to two orders inferior when compared to the other equalizers,

even when in a critical operation scenario (EVA and ETU channels). Besides, the classic Li- near Interpolation technique showed a significantly inferior performance compared to the other

techniques for all scenarios considered.