Enhanced preamble detection for PRACH in LTE

Abstract

The performance of preamble detection in Physical Random Access Channel (PRACH) for long term evolution (LTE) and its advanced degrades when channels become more time dispersive, such as Extended Typical Urban (ETU). However, the Base Station (BS) target received power is determined by users with time dispersive channels, in order to keep the acceptable performance for most of users in a cell. Motivated by the idea of collecting the energy of multiple paths, the optimal statistic is derived in this paper given the Power Delay Profile (PDP) of Rayleigh fading channels. An analytical framework of performance is also proposed in this paper and verified by simulation. It is shown that the proposed optimal statistic increasingly outperforms the traditional peak detecting when time-dispersion of channels increases. Considering the difficulty of achieving the accurate PDP in some scenarios, a suboptimal but robust solution is further developed. Compared with peak detecting, the suboptimal solution lowers the BS's target received power by over 1.1dB for Format 0 PRACH with both 2 and 4 receive antennas in the ETU channel, significantly reduces the user's power consumption and improves the LTE PRACH coverage.