Adaptive Modulation and Coding Using Signal to Noise Ratio Switching Threshold
Orthogonal frequency division multiplexing (OFDM) is one of the key enabling technologies for fourth generation (4G) wireless system. It offers high data rate transmission with high spectral efficiency, immunity to multipath fading and simple implementation using fast Fourier transform (FFT). How...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2009
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/7364/1/FK_2009_53a.pdf |
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| Summary: | Orthogonal frequency division multiplexing (OFDM) is one of the key enabling
technologies for fourth generation (4G) wireless system. It offers high data rate
transmission with high spectral efficiency, immunity to multipath fading and simple
implementation using fast Fourier transform (FFT). However inefficient utilization of
the channel will result when OFDM system is designed for worst-case channel
conditions. Thus adaptive transmission scheme that can be adjusted to channel
conditions is one of the techniques to improve the performance of OFDM systems.
In this thesis, three types of subband adaptive transmission scheme namely adaptive
modulation (AM), adaptive coding (AC) and adaptive modulation and coding (AMC)
based on SNR switching threshold are investigated. The performances of these
systems are evaluated using an efficient adaptation algorithm. The efficient adaptation
algorithm is based on the average value of the SNR of the subcarriers in the subband. First the performance of adaptive modulation using quadrature amplitude modulation
(QAM) and phase shift keying (PSK) system are evaluated. The results obtained
showed that a significant improvements in terms of bit error rate (BER), spectral
efficiency and throughput can be achieved. To further enhance the system,
convolutional coding is employed. However convolutional coding causes the
maximum throughput to be limited. To solve this problem adaptive coding schemes
which provides another area of flexibility is investigated. Finally the combination of
adaptive modulation and adaptive coding is examined.
Simulations results have shown that the performance of adaptive transmission
schemes are superior compared to fixed (nonadaptive) transmission schemes. A high
throughput performance can be achieved without sacrificing the BER. The
performance comparisons of the proposed system with the conservative system
showed that the proposed scheme is able to meet the BER target of 10-3 with a slightly
better throughput performance around 0.3 Bps/Hz. |
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