Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (3.1) (2018) 51-55 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper A Low-Cost Software Defined Radio Based Cognitive Radio Test-Bed for LTE Networks Kolluru Suresh Babu 1 *, Srikanth Vemuru 2 1 Department of CSE, KL University, Andhra Pradesh – 522 502, India. 2 Professor, Department of CSE, KL University, Andhra Pradesh – 522 502, India. *Corresponding author E-mail: kollurusuresh@gmail.com Abstract In this work, we present a low-cost implementation of a Cognitive Radio (CR) test-bed for LTE and LTE-Advanced (LTE-A) Networks. The test-bed setup is implemented using highly integrated Software Defined Radio (SDR) platforms which are well suited for wireless communication. Each transceiver can be configured to work as a primary (resp. secondary) eNodeB or a primary (resp. secondary) user in a Heterogeneous Cognitive Radio framework. In this context, we study the problem of spectrum management in an LTE based hetero- geneous network and propose simple distributed algorithms which the secondary eNodeB can employ to efficiently manage the spectral opportunities that arise in such a network. Experimental validation show significant improvement in the secondary link throughput. Keywords: Software-defined Radio (SDR); Cognitive Radio (CR); 4G; LTE. 1. Introduction Software-defined radio (SDR) [1], [2] is a radio communication technology that is based on software defined wireless communica- tion protocols instead of hardwired implementations. SDR pro- vides an efficient and secure solution to the problem of building multi-mode, multi-band and multi-functional wireless communica- tion devices. Flexibility in reconfiguration of baseband algorithms, software and re-programming of RF parameters has been a key requirement for a generic SDR platform. The evolution of features over several releases of 3GPP and IEEE standards, tactile and proprietary communication systems require scalable baseband algorithms and software. The RF front end requires wider band of operation aggregated over multiple bands to support high data rate communications of the future. WaveGuru [3], [4] is a low cost SDR platform, which addresses the above needs. It can be configured to operate with different waveforms and protocols through dynamic loading of new wave- forms and protocols. Radio frequency spectrum is a finite natural resource that is increasingly in demand for services which encom- passes applications in communication, entertainment, security, military, space, etc. With ever increasing data demands, the avail- able spectrum needs to be optimally utilized. Cognitive radios [5] are spectrum aware radios that enable efficient allocation and utilization of the spectrum. Telecommunication in the 90’s was dominated by voice. Early 2000 onwards, we have seen an exponential growth in data traffic. Recent years have shown a significant data explosion as we have moved into a connected sphere [6]. Moving on to the next genera- tion networks and applications, every available spectral opportuni- ty needs to be identified and effectively utilized. The spectrum usage data analysis indicates that a number of spectrum bands are suitable candidates for reallocation and/or sharing [7]. If we search for RF spectrum at various geographic locations [8] it is observed that i) Some licensed frequency bands by primary users are un- derutilized all the time ii) Some frequency bands are partially utilized iii) Some frequency bands are utilized fully and demand more. Cognitive Radio technology is a prominent technology that enables the improvement of the spectrum use in an efficient man- ner [9]. 2. Mobile communication system capacity can be increased by dense deployment of small cells (Portable low power base stations with a range of few hundred meters) [11], [12]. In a heterogeneous net- work with Macro and small cells, the user can get quality commu- nication by having a downlink channel from macro base station and an uplink channel to low power small cell base station. The cluster of small cells can typically communicate to a macro via a back haul. Long Term Evolution (LTE) [10] is a mature technolo- gy which has been deployed in such heterogeneous scenarios. 3. LTE as part of the 4G technology supports a spectral efficiency three to four times than that of the Release 6 WCDMA in the downlink and two to three times in the uplink. Multiple antennas at the base station and receiver, carrier aggregation, coordinated multi-point and user specific narrow beams are some of the fea- tures that are part of LTE-Advanced to pump in more capacity for data intensive applications. LTE and LTE-Advanced have also been touted as forerunners for next generation of wireless net- works - 5G. 4. The spectrum access by the interested users can be visualized to constitute primary and secondary users. In a specific spectrum access scheme, secondary users may use the primary user's band avoiding any interference during use. Hence, secondary users should detect whether primary users are using the band and decide to let the band free as soon as the primary user wants to use it. This requirement leads to the inclusion of cognitive capabilities for the secondary user to sense and configure the radio. In this context, we deploy a radio test-bed with cognitive capabili- ties to experiment and characterize LTE based Soft-ware Defined Radios. The radios in the test-bed are capable of sensing, re- configuring and optimizing the overall system utility.