Several enabling technologies such as ultra-densification, millimetre wave communications, massive Multiple Input Multiple Output (MIMO), full duplex technology, and dynamic spectrum access are being investigated in industrial and academic communities in order to foster the deployment of the fifth generation (5G) of wireless communications. In this regard, time has come to think about how Cognitive Radio (CR) principles, which have been investigated in the community for almost one and a half decade, can be incorporated in 5G wireless communications.
CR technology, which can address the spectrum scarcity problem by means of dynamic spectrum access and spectrum sharing, has been motivated by the fact that a significant amount of the wireless spectrum remains under-utilized over a wide range of radio frequencies in the temporal and spatial domains. In addition, this solution does not require the acquisition of the additional expensive radio frequency resource, hence reducing the overall capital and operational expenditure for a wireless operator.
Although recent technical advances in the areas of Software Defined Radio (SDR), and wideband transceivers have led to the possibility of utilizing the available spectrum in a dynamic manner, there are still several challenges to be addressed from the deployment perspective. In one hand, there are technical issues in dealing with several practical imperfections such as noise uncertainty, channel/interference uncertainty, signal uncertainty, transceiver hardware imperfections, and synchronization issues. On the other hand, there are several regulatory and business challenges in order to realize dynamic spectrum access in future wireless networks. In this context, this blog provides a framework on how CR principles can be incorporated in 5G wireless networks without the need of significant upgrades in the existing network architecture.
One way of incorporating CR principles in 5G wireless networks is to enable the spectral coexistence of two or more than two heterogeneous wireless networks in different dimensions such as time, frequency, spatial, polarization, and geographical space by utilizing several advanced interference mitigation and dynamic resource allocation techniques such as cognitive beamforming, cognitive interference alignment, adaptive power control, carrier aggregation, dynamic carrier/bandwidth allocation.
Various practical coexistence scenarios can be considered under this application category: (i) Coexistence of small cells and Macrocells, (ii) Coexistence of unlicensed-WiFi and small cells, (iii) Coexistence of C-band satellite system with LTE/WiMax networks, (iv) Coexistence of future cellular with Ka-band Fixed Satellite Service (FSS) system, (v) Coexistence of terrestrial microwave backhaul links with the FSS satellite, (vi) Coexistence of satellite backhaul links with the terrestrial backhauls, (vii) Coexistence of COMPASS (Radio determination satellite service + Radio navigation satellite service) and TD-LTE, (viii) Coexistence of TVWS (Digital Terrestrial Television (DTT) + Program Making and Special Events (PMSE) services) with different terrestrial services, (ix) Coexistence of radar and communication systems, and (x) Coexistence of geostationary and non-geostationary satellite systems.
Another promising way to benefit from CR principles is to incorporate intelligence in different segments of future wireless networks such as relay nodes, and base stations. Future small/micro/pico/femto-cell base stations can be made intelligent by introducing spectrum awareness capability which will enhance the overall system capacity by reducing the effect of interference and noise. Furthermore, smart antenna capabilities such as source localization and adaptive three dimensional beamforming will not only boost the system capacity, but will also help in enhancing the energy efficiency of future wireless networks.
The widely discussed Licensed Shared Access (LSA) can be implemented in a dynamic manner by taking recent advances in CR techniques, and subsequently allowing spectrum sharing on a frequency, location and time basis. Also, CR principles can be utilized in incorporating full-duplex capability in a wireless node, for example self-backhauling in cellular networks. Moreover, self-organizing small cells (wireless nodes), which are capable of carrying out self-configuration, self-optimization, and self-resilience, can be considered as important enablers for future intelligent wireless systems.
