OFDMA Initial Ranging for IEEE 802.16e Based on Time-domain and Frequency-domain Approaches

In this paper, we propose and compare two ranging methods for the OFDMA uplink system prescribed by IEEE 802.16e, including multi-user ranging code detection, timing, frequency and power synchronization. In Method I, timing offset estimation is based on the auto-correlation and cross-correlation in time-domain, and an adaptive threshold is defined to detect transmitted ranging codes. The time-domain algorithm has a similar counterpart in the frequency-domain described in Method II, which is more accurate since it bears less interference by extracting the sub-carriers used for ranging from data sub- carriers. Moreover, Method II needs fewer computations since it shares the FFT calculations with the data demodulation process. However, Method I has the advantage of a flexible correlation window size. Simulations confirm that both methods perform well even in the condition of low SNR values and several simultaneous ranging users. To obtain the 90% probability of successful detection, Method II requires an SNR about 3.5 dB less than Method I. Simulations also show that both methods are better, compared with some existing methods.