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摘要：继电保护是一种很有前途的成本效益的解决方案，在3GPP LTE先进的延伸覆盖、提高小区吞吐量。由于中继节点的物理特性和低功耗要求，中继部署具有很高的自由度。网站规划策略制定中的信噪比和信噪比的选择标准。3GPP标准的模拟中继站的规划策略进行比较。结果表明，合适的场地规划产量随着阴影标准差相比，随机部署明显减少eNB RN链路SINR增益显著。Abstract— Relaying is considered a promising cost-efficient solution in 3GPP LTE-Advanced for coverage extension and throughput enhancement. Due to compact physical characteristics and low power requirements of the relay nodes, the relay deployment has a high degree of freedom. In this paper, the impact of site planning on the backhaul performance of relay networks within the LTE-Advanced framework is investigated. The site planning strategies are formulated in terms of SNR and SINR based selection criteria. 3GPP compliant simulations are performed comparing relay site planning strategies. It is shown that proper site planning yields significant SINR gain on the eNB-RN link along with a clear reduction in the shadowing standard deviation compared to random deployment.
I. INTRODUCTION 介绍
先进的长期演进（LTE高级）是第三代合作伙伴计划（3GPP）的候选技术，定义了LTE的进一步发展以满足IMT-Advanced的要求框架（高级国际移动通信）指定ITU（国际电信联盟）。根据这一要求，LTE-Advanced应该支持1 Gbps的下行峰值数据速率（DL）和上行500 Mbps（UL），可扩展到100 MHz带宽，提高频谱效率达15 bps/Hz UL和DL 30 bps/Hz，以及改善小区边缘的能力，如同时降低用户平面和控制平面的潜伏期[ 1 ]。为了满足这些要求，如低信号干扰噪声比（SINR）问题在小区边缘覆盖漏洞由于阴影和非视距（NLOS）连接应解决。部署解码转发中继节点（RNS）是一种很有前途的解决方案，以满足日益增长的需求，该技术的LTE-Advanced网络的一个具有挑战性的覆盖延伸和能力增强[ 2 ] [要求] 3。RNS是相对较小的节点具有功耗低、连接和无线回程网络的核心节点B通过进化（ENB）。此功能使部署的灵活性，消除了一个固定的回程成本高。此外，RNS没有严格的安装指南就辐射、视觉障碍、规划调控。Long Term Evolution-Advanced (LTE-Advanced) is the candidate technology of the 3rd Generation Partnership Project (3GPP) which defines the framework for further advancement in LTE to fulfill the requirements of IMT-Advanced (International Mobile Telecommunications Advanced) specified by ITU (International Telecommunication Union). In accordance with these requirements, LTE-Advanced should support peak data rates of 1 Gbps in downlink (DL) and 500 Mbps in uplink (UL), bandwidth scalability up to 100 MHz, increased spectral efficiency up to 15 bps/Hz in UL and 30 bps/Hz in DL, along with improved cell edge capacity, as well as decreased user and control plane latencies [1]. In order to meet these requirements, problems such as low signalto-interference-plus-noise-ratio (SINR) at the cell edge and coverage holes due to shadowing and non-line-of-sight (NLOS) connections should be tackled. Deploying decode and forward relay nodes (RNs) is a promising solution which is one of the proposed technologies for LTE-Advanced networks to meet the growing demand and challenging requirements for coverage extension and capacity enhancement [2][3]. RNs are relatively small nodes with low power consumption, which connect to the core network with wireless backhaul through an evolved Node B (eNB). This feature enables deployment flexibility and eliminates the high costs of a fixed backhaul. Furthermore, RNs do not have strict installation guidelines with respect to radiation, visual disturbance and planning regulation. Therefore, installing RNs involves lower operational expenditure (OPEX) [4] and faster Jyri H.m.l.inen Aalto University, School of Technology and Science P.O. Box 3000, FIN-02015, Finland jyri.hamalainen@tkk.fi network upgrade when operators aim to improve quality of service (QoS) [5]. Thanks to compact physical characteristics and low power consumption of relays, RNs can be mounted on structures like lamp posts with power supply facility. Cell planning and site selection tools are used routinely by operators to improve the system performance and to provide a satisfactory service with minimal deployment expenditure. In this manner, the deployment flexibility of RNs can be utilized by the operators to enhance the system performance by means of improving the eNB-RN link. This becomes even more pronounced in case of interference limited scenarios, where the RN locations exhibiting higher shadowing towards the dominant interferers can be exploited by site selection strategies. This selection results in a better SINR performance and reduces the impact of shadowing. This paper considers two relay site planning strategies within the LTE-Advanced framework, namely the RN cell selection and the RN site location selection. The aim of these planning strategies is to introduce a simple and practical means that can be used to improve the backhaul link between eNB and RN. Both of these strategies can be analyzed by using network planning tools provided that a realistic modeling of path loss and shadow fading is applied. This discussion has been recently carried out in 3GPP standardization. Consequently, a certain bonus has been added to the channel model that describes the backhaul link between eNB and RN, which accounts for the improvement due to relay site planning [6]-[8]. In this paper, we formulate the different site planning strategies using the selection criteria based either on signal-to-noise-ratio (SNR) or SINR. 3GPP compliant simulations are then performed in order to evaluate the effects of different strategies on the system performance. The remainder of the paper is organized as follows. In Section II, the system model including the relay site planning strategies and the simulation assumptions is presented. The simulation results as well as the system performance evaluation for one-tier relay deployment will be provided in Section III. Finally, Section IV concludes the paper.
II. SYSTEM MODEL系统模型
In this section, the relay site planning strategies are analyzed in detail. In addition, the system model is presented and the LTE-Advanced compliant simulation framework is introduced. 978-1-4244-2519-8/10/$26.00 .2010 IEEE
Figure 1. Different RN deployment scenarios. The eNB on the left is the donor, if the selection is done according to the distance, and the other eNB is typically the interferer. The shadow fading is visualized by the houses. A. Relay Site Planning Strategies In the following, the basis for different site planning strategies is explained using Fig. 1. In this figure, the RN is typically served by the closer eNB (eNB1) and the other eNB (eNB2) is typically the interfering eNB. Some of the backhaul links from the eNBs to the relay positions RN1-RN4 are impacted by shadow fading due to obstacles which are illustrated by the buildings. By selecting a proper RN location, the performance of the backhaul link can be enhanced compared to the case, where a random deployment is used. As can be seen in Fig. 1, both RN1 and RN4 are favorable locations with respect to eNB1 as they experience a better signal quality from eNB1. On the other hand, in order to optimize the SINR, it is also possible to select RN locations that exhibit a higher shadowing towards the dominant interferer like RN3 and RN4 in Fig. 1. If the deployment is noise limited, such a strategy doesn’t provide gain. However, for typical cellular deployments interference will have an impact and there is an incentive to select RN sites accordingly. Both of the above-mentioned approaches can be combined in order to select the location with the best SINR. In Fig. 1 this corresponds to RN4, since it experiences a good signal from the serving eNB1 and at the same time it is not severely interfered by the eNB2. Although it is assumed that the eNB1 in Fig. 1 is always the closest eNB for the RNs, due to shadowing there might be a case such that an RN receives stronger signal from the eNB2 as the eNB1 is shadowed. This effect is most pronounced for RN2 because it suffers from the shadowing towards the eNB1 but not towards the eNB2. In such a case, the RN may select eNB2 as the serving eNB. Following the above-explained arguments, two main relay site planning strategies are considered: A) RN cell selection: There are two options: . (A1): RN always connects to the closest eNB regardless of the shadowing. . (A2): RN is allowed to connect to the best eNB around taking also shadowing into account. B) RN site location selection: Options are now: . (B1): There is only one possible location for RN. . (B2): RN site location can be selected out of M alternatives. Figure 2. Example with an initial location and four other candidate locations. There are totally M=5 alternatives for the RN location. As a result, we obtain four different approaches, namely (A1,B1), (A2,B1), (A1,B2) and (A2,B2). Either SNR or SINR can be used as a criterion for the performance measure for each of these approaches. These criteria are of the form: PkSNRm,k = , (1)PLNm,k Pk Lm,k SNRm,kSINRm,k = = , (2) PN + ΣPk ' Lm,k '1+ ΣSNRm,k ' k '≠kk '≠k where P denotes the signal power, PN is the noise power, L is the path-loss including the shadowing, m refers to the m-th RN candidate location, where m is an integer from the set of [1, M] and k refers to the k-th eNB. We note that k=1 corresponds to the reference eNB and m=1 corresponds to the reference RN location initially deployed in the sector as shown in Fig. 2. In addition, it can be stated that compared to SNR based criterion the SINR based selection criterion takes into account not only the benefit of improving the reception from the serving eNB but also the benefit of reducing the interference caused by other eNBs. Following these criteria the above-mentioned approaches can be expressed as: . (A1,B1): Neither cell selection nor RN site location selection. This is the reference case. SNR(A1,B1) = SNR1,1 , SINR(A1,B1) = SINR1,1 . (A2,B1): Cell selection according to the best eNB, no RN site location selection. SNR1, k0 = max{ SNR1, k }, SINR1, k0 = max{ SINR1, k } . (A1,B2): No cell selection but RN site location selection. SNRm0, 1 =max{SNRm,1}, SINRm0,1=max{SINRm,1} . (A2,B2): Both cell selection to the best eNB and RN site location selection. SNRm0, k0 =max{SNRm, k}, SINRm0, k0=max{SINRm,k} Note that, in (A1,B1) and (A2,B1) both SNR and SINR based criteria will lead to the same result in the selection procedure due to the restriction in site location selection. |
