With the rapid increase in mobile data traffic (especially video content traffic), the number of content access requests is also increasing. In this context, device-to-device (D2D) communication has been an effective technology in increasing the spectral efficiency and reducing the load by offloading the mobile data traffic in cellular networks. In order to reduce the load on eNodeBs (eNBs), centralized area controller (CAC) has been proposed earlier to take content aware decisions for content access requests. In this paper, we propose to exploit CAC in a distributed manner. Distributed D2D controller (DDC) is responsible for arbitrating and scheduling D2D transfers. Thus, every content access request from a user equipment (UE) is first served by a neighboring DDC and in case the content is not available in the region, the request is forwarded to the eNB. Further, it has been observed that the inclusion of DDCs in the existing D2D architecture reference model requires the addition of new reference points. The same has been highlighted in this paper. Due to the spatiotemporal correlation in the mobile data traffic, a learning algorithm can be employed that determines the number of required resources to fulfill the D2D data rate requirements. Hence, we propose a Q-learning based algorithm that learns the expected number of resource blocks (RBs) required to meet the data rate requirements at each DDC. In addition, a cache content management policy is proposed that exploits the popularity of the contents in order to increase the chances of D2D communication. With extensive simulations, we observe that the proposed Q-learning algorithm indeed learns by reserving near-optimal number of RBs to serve the data rate requirement at each DDC. Further, we observe that the one- and two-hop modes of D2D transfer effectively reduces the load on eNB by transferring a maximum 49% of the required data to the UEs.

With the exponential growth in mobile data traffic, the number of content access requests is increasing and hence, the load on the LTE eNodeB (eNB) is also increasing. In such a scenario, transferring data files using Device- to-Device (D2D) communication helps in offloading cellular data traffic. In order to reduce the load on eNB, Centralized Area Controller (CAC) has been proposed earlier to take content aware decisions for content access requests. CAC uses long range LTE communication for uplink transmission thereby leading to more energy consumption. Additionally, it relies on eNBs for spectral resource allocation thereby increasing the load on the eNBs. In this paper, a Distributed D2D Controller (DDC) deployment for arbitrating and scheduling D2D transfers is proposed. Every content access request from a User Equipment (UE) is first served by a neighboring DDC. In case the content is not available in the region, the request is sent to the eNB. A complete DDC working protocol that explains the above procedure is proposed. The service rate requirement for the DDC to achieve the same expected response time as that of the CAC is calculated. In order to reduce the overall cost of placement of DDCs, a DDC placement algorithm that uses convex hull to determine the locations for placing DDCs is proposed. The performance of DDCs is compared with CAC in terms of the number of content access requests that are serviced using D2D. In addition, we compare the total power consumed in uplink transmission in the case of DDC and CAC. Extensive simulations demonstrate that our proposed distributed controller is more energy efficient from users perspective than that of the centralized controller.

With a wide range of applications, Machine-to-Machine (M2M) communication has become an emerging technology for connecting generic machines to the Internet. To ensure ubiquity in connections across all machines, it is necessary to have a standard infrastructure, such as 3GPP LTE-A network infrastructure, that facilitates such type of communications. However, owing to the huge scale of machines to be deployed in near future and the nature of data transactions, ensuring ubiquitous connections among all the machines will be difficult. Solutions that not only maintain connectivity but also route machine data in a cost effective manner are the need of the hour. In this context, it has been suggested that Device-to-Device (D2D) communication can play a very important role in expanding network coverage and routing the data between source-destination machine pairs. In this paper, we conduct a feasibility study to highlight the impact of multi-hop D2D communication in increasing the network coverage and average rate of a Machine Type Communication (MTC) device. We present a stochastic geometry based framework to analyze the coverage probability and average data rate of a three-hop M2M network deployed along with User Equipments (UEs) and conduct extensive simulations to study the system performance. Our simulation results show that the three-hop M2M network formed from out-of-range MTC devices and UEs can significantly improve the coverage and average rate of the entire network. Due to the mobility of users in the network, design of robust routing mechanisms in such a time evolving network becomes difficult. Hence, we suggest the use of space-time graph built from the predicted user locations to design a cost efficient multi-hop D2D topology that enables routing of MTC data to its destination.

Device-to-Device (D2D) communication as an underlaying cellular network empowers direct communication between two users and helps in offloading network traffic. However, due to interference posed by the D2D transmitters to the primary cellular users, intelligent resource allocation techniques need to be incorporated for the betterment of the overall system. Overlay D2D communication eliminates the interference between cellular users and D2D users by dedicating resources for D2D users. With this approach, interference among D2D users can still pose a potential threat to the overall system performance. To handle this additional interference without significantly affecting the spectrum efficiency, smart assignment of wireless resources is necessary among D2D users. For the first time, we look into this problem and propose an efficient channel assignment scheme that mitigates the interference among D2D users. By meticulously assigning the channels with proper power control, the proposed channel assignment scheme is found to improve the spectrum reuse as well as the energy efficiency of the system. We compare our scheme with Full Reuse (FR) channel assignment scheme where every D2D pair fully shares the channel resources. Extensive simulations demonstrates that our scheme performs better than FR in terms of spectrum reuse, energy efficiency and overall system blocking.