Mode selection in device-to-device communications

Device-to-Device (D2D) communication refers to a technology that enables devices to communicate directly with each other, without sending data to the base station and the core network. This technology has the potential to improve system performance, enhance the user experience, increase spectral efficiency, reduce the terminal transmitting power, reduce the burden of the cellular network, and expand cellular applications. In D2D communication UEs are enabled to select among different Transmission Modes (TM)s which are defined based on the frequency resource sharing. Dedicated mode where the D2D communication is direct and data is transmitted through the D2D link by the orthogonal frequency resources to the cellular users so there is not any interference. Reuse mode where data is transmitted through the D2D link by reusing the same frequency resources that are considered for a cellular user or another D2D link so reused mode causes interference at receivers however, the system spectrum efficiency and user access rate may be increased. Cellular mode where the D2D communication is relayed via eNB and it is treated as cellular users. In this work, we aim to reach the optimal mode selection policy, and we use the Markov Decision Process (MDP) method with the objective of maximizing the total expected reward per connection. We present and analyse optimal mode selection policy for several scenarios with different rewards and cost for cellular, dedicated and reused mode. In our study of mode selection issues in D2D enabled network we propose an algorithm for the case when the cellular UE moves in the network. We use QoS parameters, mobility parameters and Analytic Hierarchy Process (AHP) method to define new mobility based mode selection algorithm. To evaluate our proposed algorithm, we considered SNR and delay

Mode selection map in device-to-device communication

One of the recent features presented by the Long Term Evolution - Advanced (LTE-A) standard is enabling the network User Equipments (UEs) to directly communicate with each other without routing the signal through evolved-Node B (eNB). This is called the Device-to-Device (D2D) transmission and it brings different types of gains to the network. The UEs are enabled to choose their transmission mode among the reuse, dedicated, and cellular modes. For a network consisting of a pair of D2D enabled UEs, a cellular UE, and an eNB, the mode selection procedure indicates the best mode to be chosen by the D2D pair while the cellular UE is in communication with the eNB. The reuse and dedicated modes are direct transmission while the cellular mode is the traditional cellular transmission. In the reuse mode the same frequency resources are used by the D2D pair and the cellular user. However, in the dedicated and cellular modes, different resources are allocated for the D2D and cellular transmission. In this work, we show that there are certain regions in the network that if the moving UE stays in them, a specific transmission mode is always selected for the transmission between D2D pair. The set of these regions is called the mode selection map of the network. We use our mode selection map models to propose a handover mechanism when the moving UE leaves a specific region in the map and enters to a neighboring region. For mode selection map derivation, we present an analytical framework for a simple D2D enabled network for two different channel conditions: 1) Line-of-Sight (LoS) path-loss channel; 2) fading channel. The overall throughput of the network for the reuse, dedicated, and cellular modes is calculated and presented in three different equations. When the channel’s model is LoS path-loss, to find the mode selection map, these equations are equalized two by two and the resulted equation is solved. For the fading channel scenario, due to the probabilistic variation of the channels the expectation of the overall throughput of the network is calculated for three Transmission Modes (TMs) and the resulted functions are equalized two by two and solved. In our study of handover issues in D2D enabled network we propose an algorithm for the case when the cellular UE moves in the network while the communication channels are fixed. The algorithm relies on two decision parameters, i.e. distance from the boundaries of the map and intersection with the boundaries of the map, which are analytically computed. To evaluate the performance of the handover mechanism we develop an analytical approach to calculate two performance metrics, denoted as handover rate and sojourn time, using the mode selection map