Enhancing Spectral Utilization by Maximizing the Reuse in LTE Network Yuva Kumar S. * , Vanlin Sathya † , Sreenath Ramanath * * Lekha Wireless Solutions, Bangalore, India † University of Chicago, Illinois, USA. e-mail: * [yuva.kumar, sreenath]@lekhawireless.com, † vanlin@uchicago.edu Abstract—Need for increased spectral efficiency is key to improve quality of experience for next generation wireless ap- plications like online gaming, HD Video, etc.,. In our work, we consider a LTE Device-to-device (D2D) network where LTE UEs have primary access to the spectrum and D2D pairs have secondary access. To enhance spectral efficiency, BS can offload the traffic by activating multiple D2D pairs within the serving cell. This ensures that the same radio resource will be reused across the primary LTE UEs and different D2D pairs. In this context, we propose to enable more D2D secondary users in the serving cell, by utilizing neighboring BS spectrum to fairly co- exist with neighboring LTE primary users. We model the system and show via extensive simulations, that the above configuration guarantees good throughput for the D2D pairs in the serving cell while ensuring that the primary LTE throughput demand is not compromised. Index Terms—LTE, Device-to-device (D2D), Cognitive Spec- trum Access. I. Introduction Due to heavy penetration of smartphone and tablets, we have seen a steady rise in the usage of the mobile applications (like YouTube, online gaming, Facebook, Netflix, WhatsApp, etc.) everyday by the cellular users. This situation forces the mobile/cellular operators to increase or reuse the available spectrum. Due to the high capital expenditure (CAPEX) on the spectrum used, reusing the existing (available) spectrum will be a good solution. In this context, one of the feasible solutions would be to deploy more small cells (like Femto or Pico) under a single Macro base station (BS), which will boost the overall spectrum efficiency with the increase of co- channel co-tier interference. An alternate solution to offload mobile traffic at the Macro BS and boost the spectral usage efficiency is to enable/activate more device to device (D2D) communication within the coverage of the BS. In LTE, D2D communications allow UEs to communicate directly without the intervention of eNodeB (eNB). D2D technology has been suggested as a method by the 3GPP for offloading the users traffic and increase the overall spectral efficiency. It also has been included in LTE release 12, as a guidance for implementing. D2D is one of the most promising technology towards 5G for improving resource utilization, enhancing UE throughput and extending battery lifetime. Due to its short-range com- munication, D2Ds have the potential to reuse the same radio resource with different transmission power across different D2D pairs. The challenges involved in enabling D2D com- munications are resource allocation, interference management, handovers, power control, session management, etc. There can be chances where the spectral reuse (in order to efficiently offload the BS traffic using D2D) might not be possible beyond a certain extent (which will result in more interference to the existing cellular users). To overcome this, it is also possible that one can intelligently allocate the neighboring BS spectrum and efficiently reuse the spectrum among D2Ds. Efficient spectrum reuse and co-existence with existing technology is one of the key research topics. As the mobile operators demand for more spectrum, telecom regulatory bodies have been considering release of unused spectrum which has been used in applications such as radars, television, military applications, etc., to operators using cognitive radio technology. During the course of migration there is a need to come up with an alternate mechanism to manage the heavy traffic demands. The work presented in this paper looks into aspects of enhancing overall spectral efficiency. It is proposed that the operator will intelligently use the neighboring BS radio re- sources for assigning it to the additional D2D pairs. Here neighboring BS will be primary user and additional D2D pairs will be the secondary users. Primary user wouldn’t be affected by secondary user transmission because of the relatively large path loss distance. This will boost overall system throughput. Hence, our work focuses on reusing the neighboring spectrum to small cell and D2D in such a way that the overall spectrum efficiency is maximized. As operators are reusing the neighboring BS spectrum among small cells and D2Ds with shorter transmission power in the serving cell, it’ll not interfere with the primary transmissions in the neighboring cell. Hence enabling the additional spectrum for small cell and D2D in a cognitive manner as discussed will tremendously increase the overall spectral reuse efficiency. This paper is organized as follows. Section II describes the overview of the state of art in D2D communications. LTE and D2D co-existence is described in Section III. The system is modelled and analyzed in Section IV. Numerical and simulation results are provided in Section V and the conclusions are provided in Section VI. II. Related Work Telecom industry and research community works on boost- ing the spectrum efficiency by deploying more small cells arXiv:1907.05201v1 [cs.NI] 20 Jun 2019