nee Enhancement of a Dual-Signal Receiver System for ltaneous Reception of two Go-Channel S Applying Error Correction Coding
Klaus Witrisal, Frank van Wijk · 1997
The Dual-Signal Receiver (DSR), proposed for simultaneous reception of two narrowband modulated co-channel signals, shows large performance degradation when both signals have about equal strength. In this paper, performance enhancement of the DSR using Binary Phase Shift Keying (BPSK) modulation is obtained with Forward Error Correction WC) coding. Rather short hear block codes were evaluated using hard and soft decision decoding techniques. With soft decision decoding, large coding gains are obtained in the channel with co-channel interference and Additive White Gaussian Noise (AWGN). The gain for the channel with interference is larger than for the AW6N-channel, but the absolnte performance is worse. Hard decision decoding gives no significant enhancement. The coding gain for the small signal is about the same as for the large signal due to the occurrence of correlated errors. L INTRODUCTION High spectral efficiency is an important issue in mobile communications systems in order to allow a large number of users to operate in the limited bandwidth available. A method to make a system more efficient is frequency reuse, i.e., to reuse the same bandwidth in areas which are sufsciently apart in space. This is the basic principle of cellular communications systems. The capacity of such systems is increased by reducing the frequency reuse factor which means decreasing the distance between base stations using the same fkequencies. CO-channel interference is the main limiting factor of this principle. Further enhancement of efficiency can be obtained with signal cancellation techniques, as implemented in the receiver system investigated in this paper. In (l), the Dual-Signal Receiver @SR) concept has been proposed for simultaneous reception of two narrowband Binary Phase Shift Keying @PSK) modulated co-channel signals. The receiver concept is based on cancellation of the large signal sly the small signal s, remains with less interference and can be demodulated. The DSR can be used to improve the perfonnance of one desired BPSK-modulated signal in the presence of co-channel interference, as well as it enables simultaneous reception of two co-channel signals. In (2), an alternative scheme using differential phase shifi keying (DPSK) with differential detection is proposed. Unforhmately, the performance of the DSR degrades when the difference in signal strength is small. In this paper, application of Forward Error Correction (FEC) coding is investigated and evaluated to improve the performance of the DSR in case of signal-to-interference ratio SIR The paper is organised as follows: The DSR and its performance without coding are presented in Section II. In Section III, linear block codes are applied and analysed using hard decision decoding. Soft decision decoding is analysed for the quantized- and unqmtized case in Section IV. Computational results and conclusions are given in Sections V and VI, respectively. 0 dB.