Multilevel differential modulation techniques (64‐DAPSK) for multicarrier transmission systems

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Abstract
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.

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