Mobility Management for LTE-Advanced Relay Systems - Research Paper Example

?? Standardization activities are underway with the aim of achieving a next generation high capa and high-speed mobile communication system. The future wireless communication network is expected to be a heterogeneous environment with different wireless technologies that differ in cost, bandwidth and coverage area. These different technologies can cooperate together In order to improve the user’s quality of service and granting mobile users the ability of roaming across different wireless networks in a seamless manner. However, the different characteristics of each wireless technology with regards to QoS brought many challenges for provisioning the continuous services (e.g. audio/video streaming) in a seamless way. In such a heterogeneous environment, to support mobile user’s requirements, a mobility management mechanism is a key issue. Index Terms— Heterogeneous network, LTE-Advanced, Relay System, Vertical Handoff I. INTRODUCTION With the increase in demand and rapid development of wireless communication quality over the past 3 decades, the initial 1G has run into 4G with a high data rate and better mobility support. The 4G technique-International Mobile Telecommunications-Advanced (IMT-Advanced) systems include new capabilities that go significantly beyond those of the IMT-2000. Key requirements of the IMT Advanced systems, for instance, include improved mobility support and cell edge performance, increased spectral bandwidth and efficiency, reduced handover interruption time and reduced User plane latency and Control [1]. Considered as the main trend in future wireless communications, 3GPP LTE-Advanced has advanced features, for instance coordinated multipoint processing, carrier aggregation. It also considered as one of the top candidates towards achieving the IMT Advanced requirements. In 3GPP, high speed train scenario is agreed as the main scenario in Rel11 study item, mobile relay for E-UTRA. Here, when train rushes at a high speed the channel characteristics change and result in Doppler spread. Also the vehicles are vehicles are more crowded than other areas and therefore passengers are more likely to use high data rate services, for instance, browsing, playing games and watching videos so as to pass time [2]. The high data rate transmission requires strong signal strengths and high throughput, plus better mobility management, so mobile relay station for large vehicles are proposed for Broadband Wireless Access (BWA) system. A relay system may be mobile, which means it is a dedicated network node equipped on the vehicles to provide a fixed access link to those travelling on the vehicles. It is very suitable to solve the capacity gain of the high speed vehicles if it is well deployed. In a conventional cellular network, user equipment (UE) is connected directly to a Base Station (BS), and when a user moves away from the cell center, he/she will get less bandwidth which means lower data rates. However relaying technique has been introduced in 3GPP release 10 & 11 to allow establishing an indirect two-hop link between UE and BS through a Relay Node (RN). Relay nodes can also be used to spread out the cell coverage and increase the coverage outside main area (e.g. at cell edge). The two major challenges addressed in this context are maintaining the throughput and ensure a seamless mobility and service continuity to all UEs. Hence, the objective of this paper is to develop, implement, and evaluate intelligent algorithms for next generation wireless communications systems with focus on throughput and service continuity. Specifically, the paper mainly addresses to the following aspects: Relaying in heterogeneous network, resources and mobility management. The rest of the paper is arranged as follows. Firstly, the overview of fixed and mobile relay system is given is Section II. In Section III, the paper presents a Handoff Analysis. Section IV presents a system level simulation and results. The paper concludes with section V. II. FIXED AND MOBILE RELAY SYSTEMS OVERVIEW A. Background of relay in LTE-Advanced Network Largely speaking, relay is identified as an enhancement for the traditional cellular architecture. Relay Station (RS) plays a key role in the network and is capable of relaying data between base stations (BS) and mobile stations (MS) wirelessly. Normally, relay is likely to perform the following functions: wireless backhaul connections to on-land network, wireless connection service to mobile stations in the cell. The RS-MS link and the BS-RS link are respectively known as access link and backhaul link [3]. Several advantages are provided by relay station. Firstly, RS is expected to be settled in the edge of the cell to cover shadowing area. Since the BS is not able to provide sufficient coverage for edge users, RS improve radio link quality for them with ordinary interference to other users. Secondly, in hotspot area where there may be a high traffic data demand for a certain time, RS can help to offer serviced for some users so as to avoid network overload, for instance in traffic jams. Finally, RS is easy to deploy and maintain since its deployment cost is low and its size is smaller than the BS. In accordance with the moving state the relay station can be divided into fix relay station (FRS) and mobile relay station (MRS). Interest of network operations, academies and equipment manufacturers has been raised because of the advantages mentioned above. Even more interesting is the fact that mobile relays are able to achieve better user seamless mobility experience and handover performance. B. Fixed Relay C. Mobile Relay These are generally mounted on vehicles such as trains or buses. It is known that vehicles with shield carriages can cause penetration loss the radio signals to/from UEs inside the carriage. In order to reduce penetration loss and decrease interference, it is recommended that the mobile relay utilize individual transceiver outside and inside the vehicle separately. The donor antennae is placed at the top of vehicle and the antennae of MRS to UE placed inside the vehicle and down titled to reduce the interruption to the area outside the vehicle. When compared to Fixed Relay System, MRS may comprise some additional features, which means lower cost of equipment and more flexible deployment options. Given the fact that MRS have better antennas to obtain diversity gain, the backhaul link is better than the direct radio link between MS and BS, so that one of the main contributions of the mobile relay system is improving system capacity. As a serving BS for UEs in the vehicle, MRS should support the following BS functions: routing of user plane data towards serving gateway, radio resource management, measurement and reporting configuration for scheduling and mobility [4]. MRS has the ability to perform group handover instead of UE individual mobility procedures. With group mobility, UE will achieve a better handover performance and lower radio link failure. Fig. 1 below shows an application scenario of high speed railway downlink transmission from a BS to a UE via a MRS. III. handoff analysis A. General The process of handoff maintains continuity of a session or call of a mobile station (MS) while moving in and out of the coverage area of different cells. It works by changing the current channel in the current cell to a new channel when the MS shifts into a new cell [5]. Figure 2. below shows a handoff scenario, whereby a MS is connected to a base station BS1. It moves from BS1 to BS 2 while in a call. Handoff is performed when there is an overlapping area between tow BSs, meaning that the MS receives signal from two BSs. Signal strengths of BS1 and BS2 are measured continuously to establish the better one. If signal strength of BS1 is better than that of BS2 and can provide MS with the required needs, then a handoff decision is made and the MS is connected to BS1. Fig. 2. Handoff in wireless networks If for some reason, the new BS cannot support the required resources of the connection, the hand off is denied and connection is then dropped. Call dropping probability is that possibility of a connection being forced to terminate because of the lack of resources in the target BS. IV. simulation and results Scenario: (4 eNodeB, 20 Relay Nodes, 60 UE + UE) Average Bitrate: Packet Loss: Blocking rate: Average Blocking rate (%) Blocking rate (%) Number of Handoffs: LTE-A vs RelayNodes Utilization: kjkjkjkjkj jkjkjkjkjkj kjkjkjkj jkjkjkjkj kjkjkjkjkj kjkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk Read More