Joint transmit/receive one-tap minimum mean square error frequency-domain equalisation for broadband multicode direct-sequence code division multiple access

Abstract

Multicode direct-sequence code division multiple access (DS-CDMA) can flexibly support multimedia services with various data rates simply by changing the code multiplexing order. The use of simple one-tap frequency-domain equalisation (FDE) at a receiver is known to improve the bit error rate (BER) performance of multicode DS-CDMA in a severe frequency-selective fading environment. However, the BER performance improvement is limited due to the presence of the residual inter-chip interference (ICI). The authors propose a joint transmit/receive minimum mean square error (MMSE) FDE, which carries out one-tap transmit FDE and one-tap receive FDE jointly based on the MMSE criterion. The authors theoretically derive a suboptimal set of transmit and receive FDE weights and investigate the BER performance improvement by computer simulation in a freqeuncy-selective Rayleigh fading channel. The proposed scheme improves the received signal-tointerference plus noise ratio after despreading, and consequently, the BER performance can be significantly improved compared to the conventioal receive MMSE-FDE by (a) making the variations in the equivalent channel gain shallower to reduce the residual ICI for large code multiplexing order U and (b) allocating the transmit power to the frequencies having good condition to improve the received signal-to-noise ratio for a small U. This is conformed by the computer simualtion. Recently, multi-carrier (MC) signal transmission (i.e. orthogonal frequency division multiplexing (OFDM) and MC-CDMA) has been attracting attention [4-7]. In

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“…where h q m,n (m ∈ {S, R} and n ∈ {R, D}) is an N c × N c circulant matrix representing the impulse response of the channel from node m to node n at the qth retransmission [9], and π …”

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“…The use of minimum mean square error (MMSE) based frequency-domain equalization (FDE) takes an advantage of channel frequency-selectivity and obtains large frequency diversity gain [5,6]. The use of joint transmit/receive MMSE-FDE [7] can suppress the residual inter-symbol interference (ISI) after FDE and accordingly, it achieves better BER performance than the use of either transmit FDE or receive FDE only.…”

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“…The joint transmit/receive frequency domain equalization (FDE) based on minimum mean square error (MMSE) criterion [9] can be applied to MIMO-ANC.…”