A low complexity two dimensional differential demodulation for OFDM systems

Abstract A novel two dimensional differential demodulation (2D DD) is investigated, which exploits both the time and the frequency dimensions using the orthogonal frequency division multiplexing (OFDM) frame structure. Without changing the transmitter, the proposed 2D DD based on graph attempts to search for a more confident bypass, probably containing multiple DD operations. Simplified soft decision metrics of the amplitude ratio and phase difference are derived by making use of a Gaussian approximation. Two optimal path searching algorithms, based on depth-first search (DFS) and breadth-first search (BFS) respectively, are brought up and analyzed in details. Moreover, a random access memory (RAM) method is combined with DFS and BFS to further simplify the optimal path searching algorithms for a small maximum path length. Taking the 64-differential amplitude and phase shift keying (64-DAPSK) modulation scheme for example, simulation results show that the proposed 2D DD can obtain substantial performance gains with reasonable computational complexity. Among the four optimal path searching algorithms, BFS-RAM algorithm is the most potential one for practical applications with its ability of parallel computation. In addition, 2D DD is advantageous to withstand the Doppler effect, which is hence suitable for high mobile broadband wireless access systems.