Multilevel Differential Modulation Techniques (64-DAPSK) for Multicarrier Transmission Systems

摘要

In Digital Video Broadcasting (DVB) applications the objective is to transmit a high data rate of 34.368 Mbit/s in a single channel. For terrestrial digital transmission the considered radio channel bandwidth is 7 or 8 MHz. In this paper we analyse the performance of a multicarrier transmission technique, the well-known Orthogonal Frequency Division Multiplexing (OFDM) method, and consider the system parameters for this DVB application. For the OFDM transmission technique an absolute modulation scheme (64-QAM) has been suggested. In this case and in frequency-selective interference situations a channel estimation process and a channel equalization are necessary [4]. The equalization process can be realized by a multiplier bank at the FFT output in the receiver, a so-called frequency-domain equalizer. Alternatively, a multilevel differential modulation technique, the so-called Differential Amplitude and Phase Shift Keying (64-DAPSK) is proposed in this paper, in which the phase and the amplitude are used simultaneously for differential modulation. A differential modulation technique does not require any explicit knowledge about the radio channel properties in the differential channel equalization process. In an OFDM/64-DAPSK receiver it is therefore not necessary to implement a frequency-domain equalizer, which reduces the computation complexity. The performance of both modulation techniques has been analysed in the uncoded case referring to Gaussian and frequency-selective Rayleigh fading channels. The results are described in this paper.