Differential Modulation In Ofdm Systems Technology And Its Realization

Nowadays, the improvement of people's living standard accelerates the updating speed of communication technology and has greater needs for its reliability and rates. OFDM (Orthogonal Frequency Division Multiplexing) deserves more and more researcher's passion for its extreme high frequency efficiency and good anti-multipath fading ability. For this, OFDM has become one of the main technologies of the fourth generation of mobile communication. Differential modulation technology also deserves our patience for its no needs for channel estimation and easier ways for hardware realization. Based on the above reason, this paper has researched the combination of OFDM technology and differential modulation technology. There are two solutions for this combination: OFDM time domain differential modulation and OFDM frequency domain differential modulation. So this paper will discuss the key problems and performances of the above two solutions, and then focus on the hardware realizations, debugging the two systems and testing their performances. The main attention of this paper has been focused on the hardware realization of DBPSK (Differential Binary Phase Shift Keying), DQPSK (Differential Quaternary Phase Shift Keying), D8PSK (Differential 8-ary Phase Shift Keying) in the OFDM system.On the other hand, the traditional design method for hardware realization can not keep up in order to respond to market demands as quickly as we can. So in this paper another new design method is employed that can short the development cycle: model based design. According to the above discussion, this paper has finished the following tasks:First, a brief overveiw of the related theory of OFDM and the above three kinds of differential modulation is presented which is the foundation of the following hardware realizaion of the above two systems.The main attention has been focused on how to solve the fixed phase difference problem which is caused by multi-path effect in the OFDM frequency domain differential system.In this paper,there are two methods have been proposed:estimation by inserting pilot and cascade differential modulation. But the above problem does not exist in the OFDM time domain differential system, so it is easier for the latter to hardware realization.And then, the hardware realization of the above two systems is detailed discussed. Because the model based design method is used and lots of signal processing units of the systems have their corresponding blocks, the main attention has been focused on the design of the system models and their timings not but the realization of the relative theory. This paper has employed the SFF SDR development platform produced by Lyrtech technology in Canada because this platform supports model-based design method.Finally, both of the above systems' performances have been tested which run in the SFF SDR development platform. The results show that the performance of OFDM time domain differential system is better than OFDM frequency domain differential system's.