Study Of Coding And Modulation Techniques In Ultra-Wideband Communications

Ultra-Wideband (UWB) radio is a promising technique for short range wireless communication and has widely application range in both military and civil fields, as it has many advantages such as low transmit power, high processing gain, high multipath resolution ability, high data rate, large capacity, etc. At the same time, as a new-emerging communication technique, it also faces many challenges. In this thesis, the coding and modulation techniques in UWB communications are studied.The time hopping pulse position modulation (TH-PPM) UWB communication system is studied and simulated with MATLAB. There are many factors that affect the system performance, such as pulse parameters, channel encoding scheme and so on. Their affections are observed via simulations. The UWB indoor channel model proposed by IEEE and Rake receiver employed in multipath channel environment are also studied.Aiming at the unbalanced bit error rate of different transmitted data symbols when TH-PPM is employed as the modulation method in multipath environment, a balance encoding scheme, which is enlightened from Manchester code and also refers to the conventional repetition code used in UWB system, is proposed to solve the problem. It is shown by computer simulation that the bit-error-rate performance of different symbols can be balanced via encoding the transmitted data symbol with balance code and then optimal reception can be achieved.Pulse position amplitude modulation (PPAM) is a new modulation scheme that combines pulse position modulation (PPM) and pulse amplitude modulation (PAM) together. The application of PPAM in UWB system is studied and the performances of 22-PPAM UWB system and 2-PPM UWB system are compared. It is shown by simulation that, comparing with 2-PPM scheme, the 22-PPAM scheme can improve the data rate considerably.Based on the respective studies of balance encoding scheme and PPAM modulation, the combination of the two techniques is studied. Simulation shows that the UWB system which combines balance encoding scheme with PPAM can get higher data rate, while can also get optimal reception at the same time.