Research On Relay Selection Algorithm In TD-LTE-Advanced System

In order to achieve the ITU’s goals for4G which acquires reaching the100Mbit/s, as one of the4G technology, TD-LTE-A introduces the relay technologyto get higher transmission rate. Relay has many advantages such as lower cost,lower power and easy to deploy. It can greatly enhance the system performance ifyou choose it properly among many relays which locate between the eNode-B andUEs. But if the UE chooses a bad one, it brings more interference which caninfluence the system performance. Also the spectrum resource will be wasted. Sohow to select the relay nodes reasonably is very important. This paper will focus onrelay selection algorithm in the TD-LTE-A system. It will give the best relayposition and come up with an improved method for relay selection in mobile relaysystem in order to decreasing the relay switching times.By estimating the throughput performance of TD-LTE-A system whichintroduces relay technology based on the system level simulation, there are fourconclusions obtained. Firstly, the throughput performance can be improved by relaysgreatly. Secondly, in the same scenario it gives a best fixed relay position by usingsystem level simulation, the position locates the middle of the angle betweenantenna direction of main lobe which own to the adjacent of sectors, the distancebetween eNode-B and relay is2/3times of cell radius. With the location of relayplacing in the best fixed relay position, the relay uses can get the highest throughputgain.A new improved method for relay selection in mobile relay system is alsointroduced in this paper. It applies to use in mobile relay system. The main idea ofthe method is as follows. A relay candidate domain is introduced and the relay canbe only selected in the relay candidate domain. If the chosen relay does not moveout of the relay candidate domain, then it will also be chosen in the next time slot.By analyzing the result of the system level simulation, the improved method notonly can improve the uses’ throughput gain, but also decrease the relay switchingtimes. So it can save a lot of resource overhead by using the improved method. Thispaper also research on the performance influenced by the size of relay candidatedomain. From the simulation result, the size of the relay candidate domain isinversely proportional to the average relay user throughput, while the duration ofcommunication which is using the same relay is proportional to the size of the relaycandidate domain. So the size of the relay candidate domain must be chosen by the actual condition. If it needs larger throughput gain, the candidate domain can bechosen smaller, if it want to increase the duration of communication, the candidatedomain must be chosen larger.