Synchronization for broadband OFDM mobile ad hoc networking: Simulation and implementation

Broadband wireless services are typically considered usable in limited mobility conditions (fixed access or at pedestrian speeds). In this paper, we present a method for time and frequency synchronization of broadband OFDM for mobile ad hoc networking systems, where each node randomly and rapidly changes location. The proposed method is robust in Rayleigh fading and is computationally tractable for low-power digital signal processor (DSP) implementations. The synchronization method uses a pseudo-noise (PN) preamble sequence, provides low probability of false detection, low probability of missed detection, and exhibits a low peak-to-average power ratio (PAPR). We show that the power spectral density (PSD) of the PN-based preamble, after the digital up-converter shaping filter, fits into a spectral mask similar to that of the OFDM traffic signal's PSD. Efficient implementation is demonstrated using frequency-domain equivalent processing on a fixed-point Texas Instruments DSP and a floating-point Motorola G4 PowerPC with Altivec.