Adaptive full response digital modulation for wireless communication environments

In this thesis the performance of coherently detected Binary Phase Shift Keying (SPSK), Quarternary Phase Shift Keying (QPSK) as well as Square 16 and 64 Quadrature Amplitude Modulation (QAM) are considered as benchmark transmission schemes, and are referred to as fixed modulation schemes. Their performance is evaluated over narrow-band channels, with and without the presence of interference. Interference cancellation is considered for the interfered scenarios. The fixed schemes are compared with an adaptive modulation scheme that switches between various transmission modes depending upon the channel conditions. The transmission modes are 'No Transmission', BPSK, QPSK, Square 16 and 64 QAM and it is proposed that the channel conditions are estimated exploiting the reciprocal nature of a slow fading Time Division Duplex (TDD) channel. An optimised adaptive scheme yields up to 7 dB Eb/N0 and 18 dB Eb/N0 benefit over fixed modulation schemes across slow Rayleigh fading channels for Bit Error Rates (BER) of 1 x 10-2 and 1 x 10-4, respectively, in the absence of interference. It is shown that when latency is constrained to 30 ms and a statistical multiplex algorithm is deployed, and adaptive scheme can support 25% more multi-media users than a fixed modulation scheme, with an additional reduction in BER by as much as 1.5 orders of magnitude.By exploiting adaptive modulation and cancellation of the interference from a single co-channel interferer, it is shown that average BERs of 1 x 10-2 and 1 x 10-4 may be achieved over slow Rayleigh fading channels in the presence of 10 and 20 dB Signal to Interference Ratio (SIR), respectively, for average channel SNRs from 0 to 50 dB. A modified TDD technique, incorporating passive reception, is detailed. This strategy would allow adaptive modulation to be incorporated into the proposed third generation Universal Mobile Telecommunications System (UMTS) protocols. It is shown that Adaptive modulation, in an indoors environment, would achieve its upper-bound performance for mobile speeds below 4.5 ms-1.