Convolutive superposition for multicarrier cognitive radio systems

TL;DR

This paper introduces a convolutive superposition method for multicarrier cognitive radio systems, allowing secondary users to transmit efficiently over primary OFDM channels by convolving their signals with primary data, enhancing data rates.

Contribution

It extends single-carrier spectrum-sharing schemes to multicarrier OFDM systems, proposing a novel convolutive superposition technique and analyzing its information-theoretic performance.

Findings

Improved ergodic capacity over conventional schemes

Effective transmission over unused and used subcarriers

Enhanced secondary user data rates

Abstract

Recently, we proposed a spectrum-sharing paradigm for single-carrier cognitive radio (CR) networks, where a secondary user (SU) is able to maintain or even improve the performance of a primary user (PU) transmission, while also obtaining a low-data rate channel for its own communication. According to such a scheme, a simple multiplication is used to superimpose one SU symbol on a block of multiple PU symbols.The scope of this paper is to extend such a paradigm to a multicarrier CR network, where the PU employs an orthogonal frequency-division multiplexing (OFDM) modulation scheme. To improve its achievable data rate, besides transmitting over the subcarriers unused by the PU, the SU is also allowed to transmit multiple block-precoded symbols in parallel over the OFDM subcarriers used by the primary system. Specifically, the SU convolves its block-precoded symbols with the received PU data in the time-domain, which gives rise to the term convolutive superposition. An information-theoretic analysis of the proposed scheme is developed, which considers different amounts of network state information at the secondary transmitter, as well as different precoding strategies for the SU. Extensive simulations illustrate the merits of our analysis and designs, in comparison with conventional CR schemes, by considering as performance indicators the ergodic capacity of the considered systems.