The Study On Implementation Of DSP Software Algorithm Of Wireless MODEM Based On OFDM

This paper studies a new type of MODEM to transmit data over a mobile radio channel. It's based on a new technology called COFDM, which means Coded Orthogonal Frequency Division Multiplexing. The whole system Of COFDM/FM MODEM is realized on digital signal processing (DSP). Concretely, TMS320C5402 is selected to be the core processor, and all the main functions and algorithms of the MODEM.is realized on the platform of CCS2.0,provided by TI company.In the scheme, original binary data are received in the form of data files, then are treated by RS coding, interleaving in frequency field and the trellis coded modulation (TCM) to form the 16-QAM modulated signals.Then safeguard interval and cylic prefix are inserted to the modulated signals. Through careful arrangement of sub-channels for useful data and zero, a frame of COFDM signals is made up of many sub-channels with the form of 16-QAM. OFDM is realized by IFFT and coherent demodulation is by FFT. In the receiver, synchronization algorithm is based on safeguard interval and is completed by the algorithm of maximal likelihood (ML),which avoids the waste of bandwidth and power if pilots are used for synchronization. In demodulation part, the soft-decision Viterbi decoding algorithm is selected, so is deinterleaving and RS decoding. Some parameters such as the depth of interleaving and selection of sub-channels can be planned depending on the reality to achieve the optimization. All the functions and algorithms are achieved by software, so it is an all-digital programmable MODEM. The experiments indicate that the half-duplexing MODEM suitable for the existing standard FM channel with about 9600b/s, can be achieved by a TMS320C5402 aided by few peripheral circuits.