An efficient random access scheme for OFDMA systems with implicit message transmission

Abstract

Random access channel (RACH) is usually used for initial channel access, bandwidth request, etc. In this paper, we analyze the throughput and access delay performance of the RACH in an orthogonal frequency division multiple access (OFDMA) system. A closed-form expression of the RACH throughput is presented and its mean access delays under both binary exponential and uniform backoff policies have also been derived. Moreover, to further improve the utilization of RACH in an OFDMA system, we propose a novel message transmission scheme in a shared RACH. The message in the proposed scheme can be sent implicitly in the cyclic-shifted preambles which make the transmission much more reliable in a contention based RACH. Meanwhile, performance of the preamble detection has also been improved by the redundant information conveyed in messages. Finally, simulation results will demonstrate performance gains of the proposed scheme.

Propagation Delay Difference Estimation for Initial Random Access in LTE Compatible Mobile Satellite Communications System

“…So collision may occur among UEs which belong to the same sub-area or different sub-area. Here we consider the collision probability is only analyzed based on Mathematical probability statistics as [7]. However, since contention-free RA occupy part of the sequences, the remaining number of available sequences that can be used for contention-based RA satisfies 64 W ≤ .…”