Title :
LDPC-based space-time coded OFDM systems over correlated fading channels: Performance analysis and receiver design
Author :
Lu, Ben ; Wang, Xiaodong ; Narayanan, Krishna R.
Author_Institution :
Dept. of Electr. Eng., Texas A&M Univ., College Station, TX, USA
fDate :
1/1/2002 12:00:00 AM
Abstract :
We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system with multiple transmitter and receiver antennas over correlated frequency- and time-selective fading channels. It is shown that the product of the time-selectivity order and the frequency-selectivity order is a key parameter to characterize the outage capacity of the correlated fading channel. It is also observed that STCs with large effective lengths and ideal built-in interleavers are more effective in exploiting the natural diversity in multiple-antenna correlated fading channels. We then propose a low-density parity-check (LDPC)-code-based STC-OFDM system. Compared with the conventional space-time trellis code (STTC), the LDPC-based STC can significantly improve the system performance by exploiting both the spatial diversity and the selective-fading diversity in wireless channels. Compared with the previously proposed turbo-code-based STC scheme, LDPC-based STC exhibits lower receiver complexity and more flexible scalability. We also consider receiver design for LDPC-based STC-OFDM systems in unknown fast fading channels and propose a novel turbo receiver employing a maximum a posteriori expectation-maximization (MAP-EM) demodulator and a soft LDPC decoder, which can significantly reduce the error floor in fast fading channels with a modest computational complexity. With such a turbo receiver, the proposed LDPC-based STC-OFDM system is a promising solution to highly efficient data transmission over selective-fading mobile wireless channels
Keywords :
OFDM modulation; channel capacity; computational complexity; correlation methods; data communication; decoding; demodulators; diversity reception; error detection codes; error statistics; fading channels; land mobile radio; modulation coding; optimisation; radio receivers; receiving antennas; transmitting antennas; trellis codes; turbo codes; LDPC-based STC; LDPC-based space-time coded OFDM; MAP-EM demodulator; computational complexity; correlated fading channels; correlated frequency-selective fading channels; correlated time-selective fading channels; data transmission; error floor reduction; fast fading channels; interleavers; low-density parity-check code; maximum a posteriori expectation-maximization; multiple receiver antennas; multiple transmitter antennas; multiple-antenna correlated fading channels; orthogonal frequency-division multiplexing; outage capacity; pairwise error probability; performance analysis; receiver complexity; receiver design; selective-fading diversity; selective-fading mobile wireless channels; soft LDPC decoder; spatial diversity; system performance; turbo receiver; turbo-code-based STC; wireless channels; Convolutional codes; Fading; Frequency division multiplexing; OFDM; Parity check codes; Receiving antennas; System performance; Transmitters; Transmitting antennas; Turbo codes;
Journal_Title :
Communications, IEEE Transactions on