Resource Allocation for Network-Integrated Device-to-Device Communications Using Smart Relays

With increasing number of autonomous heterogeneous devices in future mobile networks, an efficient resource allocation scheme is required to maximize network throughput and achieve higher spectral efficiency. In this paper, performance of network-integrated device-to-device (D2D) communication is investigated where D2D traffic is carried through relay nodes. An optimization problem is formulated for allocating radio resources to maximize end-to-end rate as well as conversing QoS requirements for cellular and D2D user equipment under total power constraint. Numerical results show that there is a distance threshold beyond which relay-assisted D2D communication significantly improves network performance when compared to direct communication between D2D peers

Relay assisted device-to-device communication with channel uncertainty

The gains of direct communication between user equipment in a network may not be fully realised due to the separation between the user equipment and due to the fading that the channel between these user equipment experiences. In order to fully realise the gains that direct (device-to-device) communication promises, idle user equipment can be exploited to serve as relays to enforce device-to-device communication. The availability of potential relay user equipment creates a problem: a way to select the relay user equipment. Moreover, unlike infrastructure relays, user equipment are carried around by people and these users are self-interested. Thus the problem of relay selection goes beyond choosing which device to assist in relayed communication but catering for user self-interest. Another problem in wireless communication is the unavailability of perfect channel state information. This reality creates uncertainty in the channel and so in designing selection algorithms, channel uncertainty awareness needs to be a consideration. Therefore the work in this thesis considers the design of relay user equipment selection algorithms that are not only device centric but that are relay user equipment centric. Furthermore, the designed algorithms are channel uncertainty aware. Firstly, a stable matching based relay user equipment selection algorithm is put forward for underlay device-to-device communication. A channel uncertainty aware approach is proposed to cater to imperfect channel state information at the devices. The algorithm is combined with a rate based mode selection algorithm. Next, to cater to the queue state at the relay user equipment, a cross-layer selection algorithm is proposed for a twoway decode and forward relay set up. The algorithm proposed employs deterministic uncertainty constraint in the interference channel, solving the selection algorithm in a heuristic fashion. Then a cluster head selection algorithm is proposed for device-to-device group communication constrained by channel uncertainty in the interference channel. The formulated rate maximization problem is solved for deterministic and probabilistic constraint scenarios, and the problem extended to a multiple-input single-out scenario for which robust beamforming was designed. Finally, relay utility and social distance based selection algorithms are proposed for full duplex decode and forward device-to-device communication set up. A worst-case approach is proposed for a full channel uncertainty scenario. The results from computer simulations indicate that the proposed algorithms offer spectral efficiency, fairness and energy efficiency gains. The results also showed clearly the deterioration in the performance of networks when perfect channel state information is assumed

Relay Assisted Device to Device Communication Underlaying Cellular Networks

Device-to-Device (D2D) communication underlaying cellular networks is a latest technology of advanced wireless communication which allows two nearby devices to communicate without assistance of Base Station (BS) in cellular network. Device-to-Device (D2D) communication improves Spectral Eciency , Energy Eciency ,link reliability and overall system throughput by permitting nearby devices to communicate directly in licensed spectrum.In this thesis , two device discovery protocols are presented ,one reactive protocol and other proactive protocol which helps in discovering the D2D pairs which intend to communicate with each other.In addition, we propose a mode selection algorithm that decides the mode in which the devices can communicate either through traditional cellular mode or D2D mode. This optimum mode selection maximizes the overall throughput. The benets of D2D communication are limited practically when the distance between D2D users is long and poor channel environment between the D2D users. To overcome these drawbacks, a relay-assisted D2D communication is introduced where additional relay mode is proposed along with existing modes (i.e) cellular mode and D2D mode. A joint mode and relay selection scheme based on Hungarian algorithm is proposed to improve the overall system throughput. The Hungarian algorithm proposed, selects a suitable communication mode for each transmission and also select the relay device that acts as a relay between transmitting user and receiving user for relay mode communication.D2D devices sharing the same spectrum with cellular users results in interference, which requires to be managed in the resource allocation algorithm. A graph theory based resource allocation method for D2D users is proposed to improve the overall system capacity and extend the network coverage area

Joint Power and Channel Allocation for Relay-Assisted Device- to- Device Communications

Relay-assisted D2D (Device-to-Device) communication was proposed as a supplement to direct D2D communications for enhancing traffic offloading capacity in Long Term Evolution-Advanced (LTE-A) systems. In this paper, we formulate the joint power and channel allocation relay-assisted D2D communications problem aiming at maximizing the system sum rate of all cellular and D2D links while guaranteeing the minimum required SINR (Signal to Interference and Noise Ratio) of both links. As it is a MINLP (Mixed Integer Non-linear Programming), which can not be solved in polynomial time, we propose two heuristic algorithm (named Proposed HA1 and Proposed HA2) with different complexity levels to solve our design problems. Monte-Carlo simulation results show that the performances of our proposed algorithms with acceptable complexity have a good performance comparing with the optimal performance