Vol.:(0123456789) Wireless Personal Communications https://doi.org/10.1007/s11277-020-07180-x 1 3 Performance Analysis of Cooperative Underlay Spectrum Sharing System in Co‑channel Interference Limited Environment Varsha Vimal Sood 1  · Kavita Vij Bindra 1  · Rajesh Khanna 1  · Surbhi Sharma 1 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract In this paper, performance analysis of an asynchronous distributed space time block coded system with optimum combining at the cognitive radio receiver (CR-Rx) has been done in a cooperative underlay cognitive Internet of Things network under the infuence of multiple co-channel primary users (PUs) interferers. The transmit power strategy being employed at the CR-Tx considers the PIP (peak interference power) at the PU-Rx and peak transmit power constraints at the CR-Tx, respectively. We have derived the probability density func- tion of the signal-to-interference ratio (SIR) at the destination for the proposed system. The system is numerically and mathematically analyzed in terms of average post processed SIR (APPSIR), ergodic capacity ( C erg ), average bit error rate (ABER) and outage probability. All the numerical outcomes are in corroboration with its simulation counterpart. Keywords Amplify and forward (AF) · Cognitive radios · Cooperative communication · Delay tolerant codes · Linear dispersion (LD) codes · Optimum combining 1 Introduction With the rising demand in wireless mobile applications, the conventional spectrum allo- cation policies lead to the under utilisation of electromagnetic spectrum. The national agency such as FCC (Federal communication commission) has found that the allo- cated spectrum is poorly used according to geographical and temporal variations. As a result, cognitive radio (CR) [1] is a promising candidate which aims at efcient uti- lisation of the available spectrum. CR provides fexible spectrum access schemes such as interweave, overlay and underlay [2]. By taking into consideration the advantages of all the spectrum access strategies, we employed underlay spectrum sharing scheme. In underlay spectrum sharing access, both the licensed and unlicensed user shares the same frequency spectrum by keeping interference from CR network to PU below some predefned limit [3, 4]. The proposed system aims at improving overall system * Kavita Vij Bindra kavita.bindra@thapar.edu 1 ECED, TIET, Patiala, Punjab, India