Robust time and frequency synchronization for OFDM systems with maximum spectrum flexibility

Each Orthogonal Frequency Division Multiplexing (OFDM) system comprises a number of spectrally distributed subcarriers which are either allocated with data or left unused. This choice can be made specifically for each subcarrier and completely independently of each other. Thus, extensive spectrum shaping is possible, which makes OFDM ideal for Cognitive Radio (CR) and related technologies. However, in classical OFDM systems, the subcarrier flexibility is applicable anywhere but not to the synchronization preamble. This paper proposes a novel time and frequency synchronization technique on basis of the Hiperlan/2 preamble which was made spectrally fully flexible. Its robustness and accuracy was proven with simulations and measurements on an FPGA-based Software Defined Radio (SDR) implementation. The synchronization can compete with popular unflexible algorithms under AWGN and Rayleigh channels, while the impact of any subcarrier reallocation is negligible.