Title :
Reduced complexity in-phase/quadrature-phase M-QAM turbo equalization using iterative channel estimation
Author :
Yeap, Bee Leong ; Wong, Choong Hin ; Hanzo, Lajos
Author_Institution :
Dept. of Electron. & Comput. Sci., Southampton Univ., UK
Abstract :
A reduced complexity trellis-based turbo equalizer known as the in-phase (I)/quadrature-phase (Q) turbo equalizer (TEQ-IQ) invoking iterative channel impulse response (CIR) estimation is proposed. The underlying principle of TEQ-IQ is based on equalizing the I and Q component of the transmitted signal independently. This requires the equalization of a reduced set of separate I and Q signal components in comparison to all of the possible I/Q phasor combinations considered by the conventional trellis-based equalizer. It was observed that the TEQ-IQ operating in conjunction with iterative CIR estimation was capable of achieving the same performance as the full-complexity conventional turbo equalizer (TEQ-CT) benefiting from perfect CIR information for both 4- and 16-quadrature amplitude modulation (QAM) transmissions, while attaining a complexity reduction factor of 1.1 and 12.2, respectively. For 64-QAM, the TEQ-CT receiver was too complex to be investigated by simulation. However, by assuming that only two turbo equalization iterations were required, which is the lowest possible number of iterations, the complexity of the TEQ-IQ was estimated to be a factor of 51.5 lower than that of the TEQ-CT. Furthermore, at BER = 10-3 the performance of the TEQ-IQ 64-QAM receiver using iterative CIR estimation was only 1.5 dB away from the associated decoding performance curve of the nondispersive Gaussian channel.
Keywords :
Gaussian channels; channel estimation; computational complexity; convolutional codes; equalisers; error statistics; iterative decoding; quadrature amplitude modulation; transient response; turbo codes; 16-QAM; BER; I signal components; I/Q phasor combinations; M-QAM turbo equalization; Q signal components; TEQ-CT; TEQ-IQ; TEQ-IQ 64-QAM receiver; complexity reduction factor; convolutional code; decoding performance curve; full-complexity conventional turbo equalizer; in-phase/quadrature-phase turbo equalizer; iterative CIR estimation; iterative channel impulse response estimation; nondispersive Gaussian channel; quadrature amplitude modulation; reduced complexity equalization; trellis-based turbo equalizer; Amplitude estimation; Amplitude modulation; Bit error rate; Channel estimation; Computer science; Equalizers; Intersymbol interference; Iterative decoding; Phase shift keying; Quadrature amplitude modulation;
Journal_Title :
Wireless Communications, IEEE Transactions on
DOI :
10.1109/TWC.2002.806355