Sequence Design for Cognitive CDMA Communications under Arbitrary Spectrum Hole Constraint

TL;DR

This paper introduces a new family of sequences for cognitive CDMA that maintain low interference and spectral efficiency under spectrum hole constraints, improving system performance and resilience.

Contribution

It presents a novel quasi-ZCZ sequence family and an optimization algorithm for PAPR and auto-correlation, addressing spectrum hole constraints in cognitive radio.

Findings

Sequences achieve zero cross-correlation and near-zero auto-correlation under spectrum constraints.

Proposed sequences outperform traditional methods in bit-error-rate performance.

Systems using these sequences are more resilient to spectrum sensing mismatch.

Abstract

To support interference-free quasi-synchronous code-division multiple-access (QS-CDMA) communication with low spectral density profile in a cognitive radio (CR) network, it is desirable to design a set of CDMA spreading sequences with zero-correlation zone (ZCZ) property. However, traditional ZCZ sequences (which assume the availability of the entire spectral band) cannot be used because their orthogonality will be destroyed by the spectrum hole constraint in a CR channel. To date, analytical construction of ZCZ CR sequences remains open. Taking advantage of the Kronecker sequence property, a novel family of sequences (called "quasi-ZCZ" CR sequences) which displays zero cross-correlation and near-zero auto-correlation zone property under arbitrary spectrum hole constraint is presented in this paper. Furthermore, a novel algorithm is proposed to jointly optimize the peak-to-average power ratio (PAPR) and the periodic auto-correlations of the proposed quasi-ZCZ CR sequences. Simulations show that they give rise to single-user bit-error-rate performance in CR-CDMA systems which outperform traditional non-contiguous multicarrier CDMA and transform domain communication systems; they also lead to CR-CDMA systems which are more resilient than non-contiguous OFDM systems to spectrum sensing mismatch, due to the wideband spreading.