A New Perspective on the Initial Uplink Synchronization Problem

We explore the frequency domain properties of the signal model associated with the initial uplink synchronization (IUS) problem, and provide some new insights. We show that the adverse effects of carrier frequency offset (CFO) are confined in a small region in the frequency domain. We present a new code design approach that avoids the above mentioned region to cancel the adverse effects of CFO. In this design the codes of different users occupy mutually disjoint intervals on the frequency axis. In this way we minimize the interference between different codes, and thereby, allow considerably large number of simultaneous IUS users in the system. For the proposed codes, we design a simple energy detector. This detector relies on classical results from statistical detection theory. We also propose a simple timing offset estimation technique, which requires us to locate the maximum in a periodogram. The resulting detection-estimation algorithms are simple, non-iterative, fast and accurate. The utility of the proposed design is illustrated using numerical simulation results.