Research On Relay-assisted Device-to-device Technology In Cellular Network

With the popularity of smart mobile phone and many mobile phone applications, the business of wireless communication network keeps in-creasing. In future wireless network, the number of user equipment and data speed will increase by one hundred times. The data traffic will in-crease by ten hundred times. The current 4G technology can not satisfy increasing requirements, so the 5th-Generation communication technolo-gy (5 G) is emerging. As a key technology of 5G, device-to-device(D2D)communication can make two users in proximity to communicate directly without going through base station(BS). Using D2D technology in cellu-lar network can increase data speed and improve throughput of network.It also has the potential to increase network throughput. Because the transmission power of mobile phone is low, a main issue of D2D tech-nology is limited range of communication. Introducing relay to D2D can expand the range of D2D communication. Especially, relay-assisted D2D technology has the potential to improve data speed, so it has been paid more and more attentions.Firstly, this thesis introduces two kinds of relay-assisted D2D com-munication scenarios. One is user-to-user relay scenario and another is BS-to-user relay scenario. Especially, this thesis introduces the models,assumptions and applications of two scenarios. The three key issues of relay-assisted D2D communication are relay selection, resource alloca-tion and throughput balance. Then, for the first scenario, a two stages re-lay selection and resource allocation joint method is proposed. This me-thod can improve system performance with a pretty low complexity. For the second scenario, some relay selection methods are proposed. The performances of those methods are analyzed through simulation.To solve the throughput unbalance problem in relay-assisted D2D communication system, throughput balance scheme is researched in this thesis. Firstly, this thesis analyzes the reason of throughput unbalance in relay-assisted D2D communication. Then, eight kinds of throughput bal-ance options are introduced in details. Based on those eight options, three complete throughput balance schemes are proposed. The simulation re-sults show that three throughput balance schemes can improve system performance in different points of focus.