Design and Measurement Results for Cooperative Device to Device Communication

Introduction

Every natural calamity reminds us of our heavy dependence on infrastructure for information dissemination, and the lack of easily deployable low cost emergency communication services. In any catastrophic natural calamity, such as earthquake, flood, Tsunami etc., communication services are plagued by last mile connectivity issues and destruction of cellular infrastructure. For instance, after Nepal earthquake in 2015 (Denolle, M. A., 2015) and Siachun earthquake in China (Gupta, H. et.al, 2008), most of the cellular infrastructure such as base station (BS) and switching centers were inoperable within minutes of the earthquake. Even if some of these remains functional they are usually plagued by the acute demand of data and voice traffic during the time of disaster rendering the use of mobile devices.

The above motivates the use of a cellular service that is minimally dependent on network infrastructure. Device-to-device (D2D) communication can be visualized as one such service in which devices have minimal dependency on network infrastructure (Babun L., 2015). In a typical D2D cellular communication scenario, the users who are within the D2D range set up a direct radio link instead of routing through the network control authority (NCA) or BS. The communication can occur in two modes, in the first mode data and control signals are transmitted in the same channel which is also allocated to cellular users whereas in the second mode control signals and data are transmitted on channels which are orthogonal to cellular users (Babun L., 2015). Since, the user equipment (UE) exchange data directly through the D2D link circumventing the BS, it can achieve a higher data rate as compared to conventional cellular services. D2D reduces the load on the network and provides robustness against infrastructure failures (Babun L., 2015). Further, it is also low power consuming and spectrally more efficient, since transmit power and required spectrum for a given coverage area is reduced considerably.

The performance of D2D communication can be further enhanced by taking advantage of proximity to other devices by using a cooperative (a.k.a relay) mode of communication (Babun L., 2015). Inclusion of mobile relays and relay assisted D2D communications can increase the achievable transmission capacity, and also improve the coverage of networks (Singh, V. K., et.al., 2016). Relay transmission improves the coverage area, which will be really useful in case of emergency scenarios. However relay selection and energy efficient resource allocations need to be done in optimize way to enhance the capacity and reliability of D2D communications. A multiuser relay assisted D2D network is given in (Hasan, M., et.al., 2014), which formulated a robust optimization problem for relay selection under channel uncertainties. A power efficient relay selection algorithm has been proposed in (Li., P. et.al., 2013). However algorithm focuses on reducing the complexity involved in relay selection and thus solution is non optimal. In addition to the problem of relay selection, energy efficiency and resource allocation, security is also an essential aspect for the success of D2D communication. Security architecture of D2D communication under 3GPP LTE framework has been analyzed in (Wang., M., et.al., 2015). It analyzes the existing security solutions that can be applied to secure the D2D communication and evaluate the performance based on security requirements.

In this work we have obtained proof-of-concept measurement results for low cost, readily deployable D2D communication prototype testbed. The implemented D2D testbed emulates a portable BS and duplex transceivers which are capable of acting as relays as and when required. The portability of this system enables it to be readily deployed in any emergency scenario in order to have immediate access to communication services.

Figure 1.

A direct D2D communication scenario