Radio Link Control And Cross Layer Optimization For D2D

The device-to-device (D2D) communication has been considered as an effective technique for complementing and enhancing the conventional cellular systems. Radio Link Control (RLC) Protocol is an important component of Long Term Evolution (LTE), and its main functions are data segmentation and transmission.Compared with wire networks, D2D system have many different characteristics such as higher error rate, longer delay, lower bandwidth,asymmetric channel, frequently mobility and so on, which make the qualities of services in D2D system hard to be guaranteed. The packet losses in traditional wired networks are primarily due to congestion.However, networks with wireless links show a marked increase in losses because of higher bit error rates (BER) and handoffs delay, which involves many layers of network architecture. RLC has three modes: Transparent Mode(TM), Unacknowledged Mode (UM) and Acknowledged Mode (AM)with retransmission function. This article studied the mechanism of designing and realizing radio link control acknowledged mode transmission mode in LTE radio protocol in order to decrease the BER at TCP layer.D2D system is composed of multiple radio links, and every radio link is different in quality. Traditional improved algorithms of TCP cross-layer protocol usually based on cellular network, and the limitation is that they can only measure quality of the radio link which near to the sender. This article put forward an improved algorithm of TCP protocol based on backhaul at RLC layer and cross-layer awareness. The proposed method achieved overall awareness and result delivered back to the sender. As a result, the sender can make adjustments to increase throughput rate at TCP layer.With the NS2, a tool of simulation, the improved algorithm of TCP protocol proposed in the article are confirmed effective. Compared with the original TCP protocol before improvement, it showed that the presented method could improve throughput in D2D system.