Simulation and algorithm design of robust coding for a DVB-S based multimedia wireless system

This research focuses on the design of a novel adaptive robust coded modulation system and interference recovery system for a 42GHz Digital Video Broadcasting-Satellite (DVB- S) based Multimedia Wireless System (MWS) based on the Nottingham Trent University Campus MWS trial. The proposed systems have been designed to extend the usable range of Carrier-to-Noise ratio (C/N) and Carrier-to-Interference (C/I) conditions whilst remaining compatible with DVB-S systems. This is achieved through embedding spreading codes such as Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK), to cope with heavy rain and severe interference conditions. Such systems are particularly applicable when operating in a Single Frequency Network (SFN) environment. The major link impairments that influence the performance of 42GHz MWS systems have been reviewed. These factors contribute to a reduction of the nominal C/N, especially in heavy rain events, which could lead to service provision outage. As a consequence of the cellular reuse of MWS systems, co-channel interference also contributes to the overall link budget. This research indicates that most of the current adaptive MWS systems are designed for C/N and C/I conditions above 6 dB usually based on a dual frequency network, but do not cover the poor C/N or C/I conditions, below 6 dB, that can arise from ad-hoc multi-cellular systems with high system availability requirements in a SFN infrastructure. The proposed systems could be applied to a telephony service which may require availability of 99.999 %, whilst providing high data-rate transmission to other services. A MATLAB shell DVB-S testing platform and CCK simulation model were designed and built to facilitate simulations in the following areas; (i) performance analysis of the DVB-S system in noise and interference environments. The performance of low rate codes are shown to be improved using half-symbol timing alignment; (ii) exploration of new interference resistant coding using concatenated 1/4 CCK codes, which extends the minimum C/I of DVB-S threshold as low as -2 dB; (iii) algorithm design of a novel adaptive robust coded modulation system and interference recovery system for MWS systems. The interference recovery system has been shown to allow the reception of interfering signal as low as 3 dB. The performance of the proposed system in the interference-limited environment is analysed mainly through high-level simulations. Coding gain of 4dB was obtained using 1/2 CCK compared to uncoded Quadrature Phase Shift Keying (QPSK) under the same interference-limited channel. This led to an investigation of the concatenation of 1/4 CCK with convolutional coding to enhance the current DVB-S system performance at very low C/N and C/I conditions. The proposed technique achieves at least 2 dB spreading gain over 1/2 rate Binary Phase Shift Keying (BPSK) system. A novel embedded spreading code for DVB-S packets is also proposed, which supports a high-rate (e.g. 7/8 rate) downlink transmission to the majority of users whilst providing a more robust coded signal (e.g. DSSS) to the minority users with low C/N or C/I conditions. The proposed embedded coding demonstrates backward compatibility with existing DVB-S systems, providing robust modulation in high interference sectors and heavy rain situations. Various areas of potential further works are discussed, including transferring MATLAB codes into actual FPGA implementation and the further investigation of new robust coded modulation to fit this platform.