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| 2. |
- Holland, Ian, et al.
(författare)
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Performance of an Adaptive QAM Scheme over Correlated Rayleigh Fading with Non-zero Delay
- 2004
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Konferensbidrag (refereegranskat)abstract
- Link adaptation techniques have recently been proposed as a spectrally efficient method of obtaining high quality service for mobile communication systems. These schemes aim to better utilise channel capacity compared to fixed transmission schemes, by adapting signal transmission parameters, such as modulation constellation and transmit power. Adaptive modulation schemes, which adapt the modulation constellation, have gained considerable favour for exploiting time-varying channel conditions without increasing the level of co-channel interference. However, the traditional adaptive modulation schemes are designed assuming zero delay between the channel estimation and the modulation mode adaptation. In the case of non-zero delay, the transmitter would update the modulation mode based on outdated channel state information from the receiver. In this paper, we investigate an adaptive quadrature amplitude modulation (AQAM) scheme, which by way of retransmissions, allows a targeted reliability level to be met even in the presence of non-zero delay. The effect of non-zero delay on performance is then investigated. Closed form expressions for the average number of bits per symbol (BPS) throughput and the average bit error rate (BER) of the proposed scheme are derived.
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| 3. |
- Shaheem, Asri, et al.
(författare)
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Channel Reliability Metrics for Flat Rayleigh Fading Channels Without Channel State Information
- 2004
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Konferensbidrag (refereegranskat)abstract
- In this paper, iterative decoding of block turbo codes (BTCs) over flat Rayleigh fading channels is considered. The signal is modulated using binary phase shift keying (BPSK) and coherently detected. An exact channel reliability metric that should be passed to the iterative decoder to achieve optimum performance, when no channel state information (CSI) is available at the receiver, is developed. A low complexity cubic approximation to the exact metric, which has no performance loss, is presented. The numerical results obtained using (10,9)^2 single parity check (SPC) BTC, show that the conventional approach, which uses a linear approximation to the channel reliability metric, results in a 27dB penalty at BER of 10^-5 compared to the case where perfect CSI is available. On the other hand, the use of the proposed reliability metric outperforms the existing metric and results in only a 1.1dB performance loss at BER of 10^-5 compared to the use of the metric when the CSI is perfectly known.
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