An improved synchronization scheme for OFDMA systems with initial ranging transmissions

In initial ranging process, it is crucial to estimate multi-user´s multiple parameters such as ranging code, timing and frequency offsets and to pair up these parameters for each user. This paper presents an improved parameter estimation and pairing algorithm for initial ranging process in OFDMA uplink systems by exploiting multidimensional harmonic retrieval (HR) technique. Unlike most existing techniques that estimate each parameter independently and associate the ranging codes with the estimated parameters manually, the proposed method estimates multiple users´ ranging codes, timing and frequency offsets simultaneously, and pair up all parameters automatically. The simulation results confirm that the proposed technique not only improves the ranging code detection capability and adjusts the acquisition range of the estimators, but also increases the maximum number of resolvable users for a given samples.