Cognitive interference-minimizing code assignment for underlay CDMA networks in asynchronous multipath fading channels

Abstract

We propose a secondary CDMA network that operates as an underlay for a primary CDMA network where the code assignment for the secondary network is done cognitively. A code assignment criterion that minimizes interference from primary users and existing secondary users is formulated. The primary user codes as well as bit boundaries are unknown to the secondary network. The problem is initially formulated as a constrained optimization problem. Exhaustive search has complexity that is exponential in the spreading factor. The constraints are therefore relaxed to obtain a near-optimal solution with a complexity that is linear in the spreading factor and performance very close to the exhaustive search method. We consider the different cases where the primary users are bit-and chip-synchronous, chipsynchronous but bit-asynchronous, and chip-asynchronous over multi-path fading channels. We propose a method for blind epoch acquisition by processing the covariance matrix of the received signal. In all cases the performance improvement of the interference-minimizing code assignment over random code assignment is significant reaching over 3 dB for coded systems.

A survey on MAC protocols for complex self-organizing cognitive radio networks

“…They calculated the SUs' transmission probabilities and developed a framework to maximize the number of admitted SUs for the given fairness constraints. Elezabi et al (2009) proposed a scheme for the SUs in underlay cognitive radio networks, which aims to minimize the interference to the PUs. focused on the CDMA-based underlay cognitive radio systems where the PUs can increase transmission power to counter-balance the harmful interference caused by the SUs.…”

Multicarrier Spread Spectrum Modulation Schemes and Efficient FFT Algorithms for Cognitive Radio Systems

“…In [33,34], the authors have proposed an interference-minimizing code assignment strategy for the secondary users in the CDMA underlay cognitive radio networks. The interference caused from the existing primary and secondary users is minimized by minimizing the mean square cross-correlations between the candidate codes and the received signal.…”

Performance Analysis of Uplink Cognitive Radio Transmission based on Overloaded MC-DS-CDMA

“…In underlay CR systems, the secondary users utilize the spectrum of the primary user, provided the interference caused by the secondary users is less than the maximum interference limit that is tolerable by the primary users. A range of spectrum sharing approaches for CDMA-based CR systems have been proposed [4][5][6][7][8][9][10][11][12][13][14][15]. In [4,5], the authors proposed an interference-minimizing code assignment strategy for secondary users in CDMA underlay CR networks.…”