Random Access Preamble Detection in OFDM Systems Using Constant-Amplitude Sequences

In uplink cellular environments, random access preamble detection (RAPD) is achieved by identifying possibly multiple received requesting orthogonal frequency-division multiplexing (OFDM) signals carrying arbitrarily-chosen constant-amplitude (CA) preamble sequences through threshold comparison. Such threshold-based RAPD is analytically studied in terms of false alarm, outage, and false identification probabilities for the receiver operating under independent Rician/Rayleigh multipath channels and in the presence of time offsets among multiple received requesting OFDM signals. The RAPD system is shown to operate under less influence of inter-sequence interference when the preamble sequence set consists of mutually orthogonal CA sequences and contains as many ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible cyclically-shiftable constant-amplitude (CSCA) sequences as possible, where assigning (MPMA) and Zadoff-Chu sequence families, which are <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible CSCA sequences are cyclically shifted from each other with a minimum cyclic-shift-distance ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf> in time domain. The performance characteristics are thus demonstrated for the RAPD systems adopting the modified phase-model-assigning (MPMA) and Zadoff-Chu sequence families, which are comprised of orthogonal and nonorthogonal, respectively, ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible CSCA sequence subfamilies. While constraining upper false-alarm and outage probability bounds, the system adopting the MPMA sequence family is shown to provide much smaller false-identification probability than the system adopting the Zadoff-Chu sequence family.