TDCS-Based Cognitive Radio Networks with Multiuser Interference Avoidance

Abstract

For overlay cognitive radio networks (CRNs), transform domain communication system (TDCS) has been proposed to support multiuser communications through spectrum bin nulling and frequency domain spreading. In TDCS-based CRNs, each user is assigned a specific pseudorandom spreading sequence.However, the existence of multiuser interference (MUI) has been seen one of main concerns, due to the non-zero crosscorrelations between any pair of TDCS signals. In this paper, a novel framework of TDCS-based CRNs with the joint design of sequences and modulation schemes is presented to realize MUI avoidance. With the uncertainty of spectrum sensing results in CRNs, we first introduce a sequence design through two-dimensional time-frequency synthesis and obtain a class of almost perfect sequences.That is, periodic autocorrelation and crosscorrelations are identically zero for most circular shifts. These correlation properties are further exploited in conjunction with a specially-designed cyclic code shift keying in order to achieve the advantage of MUI avoidance. Numerical results demonstrate that the MUI-free TDCS-based CRNs are considered as preferable candidates for decentralized CRNs against the near-far problem.

Subcarrier Allocation Based Cooperative Spectrum Sharing with Wireless Energy Harvesting in OFDM Relaying Networks

“…To improve the spectrum utilization, cognitive radio (CR) allows the cognitive users (CUs) access to the licensed spectrum of the primary users (PUs) if it finds the spectrum wholly [1,2,3] or simultaneously transmit with PUs if the interference caused by CUs transmission is under the tolerant value [4]. Numerous works have been conducted to obtain reliable communications for CUs.…”

Constant envelope OFDM RadCom fusion system

“…Single-carrier RadCom signals, in combination with spread-spectrum techniques, can be used for multipleuser communication [4][5][6], whereas its dynamic range remains limited for radar measurements [1]. For multicarrier RadCom waveforms, an additional multiple-access technique is required for multiple-user communication operation [7], and dedicated frequency-domain processing techniques can be exploited to improve the performance of the radar application.…”

Modified WFRFT-based Transform Domain Communication System Incorporating with Spectrum Mismatching

“…These advantages of this technique have aroused extensive concerns in recent years. An unique sequence and a special cyclic code shifting key are designed to establish a novel framework of TDCS-based cognitive radio networks to avoid multiuser interference [3]. The preamble comprising multiple identical training sequence is presented to simplify the estimation of symbol timing offset and carrier frequency offset to solve the synchronization in TDCS [4].…”