This paper addresses initial ranging (uplink synchronization and power control) for TDD OFDMA systems. Exploiting the channel knowledge from the downlink channel together with initial power control, we develop a novel initial ranging method which provides multiuser diversity gain and significant power saving for the subscriber stations. We present new ranging signal designs which enable multiuser diversity gain and facilitate new efficient low-complexity algorithms for multiuser ranging signal detection, timing estimation and power estimation. The advantages of the proposed approach over existing methods in terms of the ranging signal detection performance, the number of ranging frames required to finish the ranging process (latency at the network entry), the timing and power estimation performance, the ranging transmission power saving at the subscriber stations, and the complexity saving at the base station are illustrated by analytical and simulation results.

Several variations of Cramer-Rao bounds for carrier frequency offset (CFO) estimation in frequency-selective fading channels have been used to benchmark practical estimators' performance or to design training signals for CFO estimation. Among them, the extended Miller-Chang bound (EMCB) provides a tighter bound than the CRB for locally unbiased estimators. However, there is no closed-form expression of the EMCB for the CFO estimation in frequency-selective fading channels with an arbitrary training signal. In this letter, we derive a closed-form exact average CRB (the EMCB) valid for any training signal and any signal structure for the CFO estimation over frequency-selective Rayleigh fading channels with uncorrelated or arbitrarily correlated taps. The accuracy and generality of the proposed average CRB expression, and its advantages over the existing expressions are corroborated by numerical and simulation results.

In this paper, we propose new ranging signal designs for time-division duplexing multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. Exploiting the channel knowledge from the downlink channel together with initial power control, we develop three ranging transmission schemes which provide multiuser and multi-antenna diversity gains and significant power saving for the subscriber stations. The advantages of the proposed approach over existing methods in terms of ranging performance, energy saving, and complexity saving are illustrated by analytical and simulation results.

This paper addresses initial ranging (uplink synchronization and power control) for TDD OFDMA systems. Exploiting the channel knowledge from the downlink control channel together with initial power control, we develop a novel initial ranging method which provides multiuser diversity gain and significant power saving for the subscriber stations. We present a new ranging signal design which provides multiuser diversity gain and facilitates new efficient low-complexity algorithms for multiuser ranging signal detection, timing estimation and power estimation. The advantages of the proposed approach over existing methods in terms of the ranging signal detection performance, the number of ranging frames required to finish the ranging process, the timing and power estimation performance, the ranging transmission power saving at the subscriber stations, and the complexity saving at the base station are illustrated by analytical and simulation results.