Improved Pilot-Aided Channel Estimation in Zero Padded MC-CDMA Systems

Abstract

This paper considers two simple procedures to improve the channel frequency response estimate for uplink Zero Padded MC-CDMA systems. The first approach uses a precomputed matrix that projects the original discrete frequency response onto the subspace where the true frequency response lies. The second uses a constrained MMSE optimization that forces the estimate to belong to this subspace. Analytical expressions for the mean square error and its upper and lower bounds are presented for the conventional and the two improved channel estimators. Numerical results show significant reduction in both the multiple access interference and the noise terms of the estimation error when using the improved estimators. Simulation results indicate that MMSE receivers using each of the improved procedures achieve gain in bit error rate performance.

Performance Analysis of a Simple Subspace Projection-Based Channel Estimate Improver for Multicarrier CDMA Systems

“…Looking from a different perspective [29], [30], [31], [32], it can be shown that this procedure is equivalent to projecting the original channel frequency response estimate in the subspace generated by the first L columns of the DFT matrix F M,M . Note that by virtue of (3) the true frequency response of the channel has to lie in this subspace.…”

“…where λ min and λ max are the minimum and maximum eigenvalues of D w F as defined in (30), respectively. The comparison of (27) and (31) motivates the defintion of the MAI reduction factor η as:…”

“…where {d w i,j } are the elements of matrix D w F in (30), which depends only on DFT coefficients and on the spreading codes in use.…”

“…In fact, the simple yet improved channel estimator introduced in [28] is based on the idea of retaining the most significant taps of the channel impulse response. In this paper, in order to investigate and compare the performance of these estimators, we reformulate the improved estimator [28] in light of a subspace projection approach [29], [30], [31], [32].…”

Estimação de Canal Melhorada Baseada em Projeção em Subespaço para Sistemas MC-CDMA

“…Estimadores de canal já são bem conhecidos na literatura para sistemas CDMA [5] e, também, já apresentados para modulações OFDM [6]. Para o sistema MC-CDMA, foco deste trabalho, a novidade consiste em, partindo de [6], explorar um novo enfoqueàquela idéia por meio de uma matriz de projeção que projeta a estimativa de canal no subespaço onde a verdadeira resposta de frequência do equivalente discreto do canal está contida [7], [8], [9]. São apresentadas análises estatísticas e expressões para limitantes do erro médio quadrático dos estimadores, que independem das características do canal.…”