Discontinuous time tracking for OFDMA uplink

Pilot symbols in OFDMA (orthogonal frequency division multiple access) uplink transmission can be used to estimate changes of round-trip delay. The authors evaluate to which extend such estimation can be used to control uplink timing advance and thus reduce random access channel overhead, taking 20 MHz LTE as example. As result, estimation performance is in the order of LTE timing advance granularity if around 10 physical resource blocks are allocated per second. For low-mobility terminals longer averaging in time domain can be used to reduce the influence of receiver noise. If the base station has multiple antennas, maximum ratio combining of receive signals can be used to further improve SNR (signal-to-noise ratio). The estimator could be improved by also taking covariances of pilots of allocations in different time slots into account.