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Hybrid Overlay/Underlay Cognitive Radio Network With MC-CDMA | IEEE Journals & Magazine | IEEE Xplore

Hybrid Overlay/Underlay Cognitive Radio Network With MC-CDMA


Abstract:

Cognitive radio allows secondary users (SUs) to exploit the underutilized radio spectrum of the primary networks. To fully utilize the primary spectrum and maximize spect...Show More

Abstract:

Cognitive radio allows secondary users (SUs) to exploit the underutilized radio spectrum of the primary networks. To fully utilize the primary spectrum and maximize spectral efficiency, overlay and underlay transmissions, which exploit the white and gray spaces, respectively, should be used together. However, for underlay, the SUs need to transmit at low power to avoid causing harmful interference to the primary users (PUs), whereas the PUs will cause high interference to the SUs. Thus, interference mitigation is a major issue in underlay spectrum utilization. In this paper, a hybrid transmission system that exploits both overlay and underlay is proposed using multicarrier code-division multiple access due to its interference rejection and diversity exploitation capabilities. Unlike existing approaches, which separate the use of overlay and underlay spectrum, the proposed schemes utilize the entire spectrum for underlay transmission to minimize the PU interference while using the spectrum holes for overlay transmission to maximize the data rate. Two techniques that operate at full-load and overload scenarios are proposed. The overload system is then extended to the multiuser underlay case to further improve spectrum utilization.
Published in: IEEE Transactions on Vehicular Technology ( Volume: 65, Issue: 4, April 2016)
Page(s): 2038 - 2047
Date of Publication: 27 March 2015

ISSN Information:


I. Introduction

Cognitive radio (CR) is a promising solution to the spectrum underutilization problem by opportunistically accessing the spectrum of the primary network. There are two main spectrum access mechanisms in CR networks: overlay and underlay. Overlay transmission utilizes the spectrum holes by exclusively using the unoccupied spectrum of the primary user (PU) and vacates on PU reoccupancy. On the other hand, underlay transmission can utilize the spectrum at any time by transmitting in the presence of PUs at low power to avoid causing harmful interference. The overlay and underlay CR approaches have been widely investigated in the literature [1]– [4].

References

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