摘要
随着移动通信的发展,高速的数据传输成为各大标准追求的目标,而提高传输速率无疑是从提高频谱效率和扩大带宽两个角度进行。同时作为宽带无线技术的逐渐成熟,3GPP需要在宽带方面有一个自己的且具有竞争力的标准,为了迎合这一发展理念,3GPP于2004年提出了更有竞争力的,更具革命性的系统概念——LTE长期演进计划。
为了实现较高的频谱效率和较高的容量,LTE系统需要有效的方案处理系统中的干扰。LTE系统采用OFDM技术,OFDM可以提供正交性非常好的载波资源,从而能有效的克服小区内的干扰。但是为了提高频谱效率,充分的利用宝贵的频谱资源,LTE中各个小区复用全部的频谱资源。小区间的干扰成了无法避免的问题,这种情况下,干扰水平关系着整个系统的性能和效率。所以小区间的干扰抑制问题成为了3GPP会议中讨论的热点,也成为关系到LTE能否实现的关键问题。
业界针对小区间的干扰问题提出了各种方案,其中最早也是最基本的方案是频率复用相关的方案,随着研究的深入讨论的重点又转移到了功率控制方面。从这两个方面解决小区间的干扰问题也成为LTE标准中的主流手段。本文针对这两个方面进行了深入研究,重点更倾向于其中的功率控制方面。我们通过仿真比较了三种功控方法的性能,并在此基础上引入小区间的干扰信息作为功率控制的调整因子,改善系统的干扰水平并改善吞吐性能。因为负载指示符也是表示小区间干扰的一种方式,所以我们对该信令格式进行了优化,并仿真这种优化对性能的改善情况。随着LTE讨论的基本完结,LTE-A的技术讨论也逐渐开始了。随着新节点的引入,系统内的干扰场景有所变化,根据不同的场景会有不同的解决办法。新节点的引入改变了小区内的传播环境,原有的接入方法可能并不适用,这里我们根据现有的系统模型提出新的有效的接入判决的备选方案,同时给出仿真效果图。
Along with the development of mobile communication, high data-rate transmission becomes the target that several standard organizations pursuit. And improving efficiency and expanding the spectrum can helps to reach such a goal. As broadband wireless technology mature gradually, the 3GPP need to have a broadband standard of its own. In order to cater to such development concept, a more competitive and more revolutionary concept, the Long Term Evolution system was put forward by 3GPP in 2004.
In order to realize the target of high frequency efficiency and capacity, LTE system needs efficient solutions to deal with the interference within the system. OFDM technology adopted by the LTE system can provide orthogonal sub-carriers, so intra-cell interference can be avoided. However, due to the limited frequency resources, the cells in the LTE system need to reuse the frequency resources, and the inter-cell interference is unavoidable. The inter-cell interference relates to the whole system performance and efficiency. So the inter-cell interference problem has become a hot points during the 3GPP meetings, also it will affect the realization of LTE system.
Different kinds of inter-cell interference management schemes have been proposed by many companies. The schemes proposed first were mostly based on the frequency reuse. As the deepening of the research, the emphasis is transferred to power control schemes. Thereafter, the methods based on the power control or frequency reuse have become the main means to depress the interference. In this paper we studied from this two aspects, and put more emphasis on the power control. We compare three different power control algorithms, then simulate and analyze their performances. Based on the intra-cell power control algorithm, we propose a novel power control scheme on the basis of inter-cell interference information. The simulation results show that the scheme we proposed can improve the system capacity and the performance of the cell-edge users. For the Overload Indicator is one of the signaling carrying the interference information, we optimize the format of OI and simulate the performance differences. The work for LTE-Advanced standardizing begins as soon as the standard work of LTE has been finished. Due to new service points such as relay introduced, the interference environment of the system varied. New methods were proposed for different occasions. We propose that the original access method could not fit the new system, for the new service points change the interference environment a lot. We suggest another three methods to replace the original one and give the simulation results.
引文
[1]3GPP Technical Specification Group Radio Access Network, TR25.913 v8.0.0, Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN) [S], Sep.2008.
[2]3GPP Technical Specification Group Radio Access Network, TR25.912, Feasibility study for evolved UTRA and UTRAN [S],2005.
[3]3GPP Technical Specification Group Radio Access Network, TS23.246, Multimedia Broadcast/Multicast Service (MBMS) Architecture and functional description [S],2007.
[4]L.J.Cimini, Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing [J], IEEE Trans. Inform. Theory, pp.665-75, July 1985.
[5]胡广书.数字信号处理-理论、算法与实现[M].北京：清华大学出版社,1997.
[6]A.Pled, A.Ruiz. Frequency domain data transmission using reduced computational complexity algorithms [C]. Proc. IEEE Int. Conf. Acoust Speech Signal Processing, pp.964-967.1980.
[7]Motorola, R1-050246, Downlink Multiple Access for EUTRA,3GPP TSG RAN1#40bis Meeting, China, April 2005.
[8]TSG RAN WG4, R1-071211, Response to LS on FDSS,3GPP TSG RAN WG1 Meeting #48 USA, February,2007
[9]Jianhua Zhang, Chen Huang, Guangyi Liu, etc, Comparison of the Link Level Performance between OFDMA and SC-FDMA [C], page(s):1-6, Oct.2006
[10]WiMAX System Evaluation Methodology V1.0 Created on 11/12/2007
[11]Huawei, R1-050507, Soft Frequency Reuse Scheme for UTRAN LTE,3GPP TSG RAN WG1 Meeting#41, Athens, Greece,9-13 May,2005.
[12]Ericsson, R1-050764, Inter-cell Interference Handling for E-UTRA,3GPP TSG RAN WG1 Meeting #42,London, UK, August 29-September 2,2005.
[13]Siemens, R1-050476, "Evolved UTRA uplink scheduling and frequency reuse",3GPP TSG RAN WG1 Meeting #41, Athens, Greece,9-13 May,2005
[14]Alcatel, R1-050593, "Interference coordination for evolved UTRA uplink access",3GPP TSG RAN WG1 AdHoc on LTE, Sophia Antipolis, France,20.-21. June 2005
[15]Huawei, R1-050629, "Inter-cell Interference Mitigation",3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, June 20th-21st 2005
[16]Siemens, R1-050738, Interference mitigation-Considerations and Results on Frequency Reuse, TSG-RAN WG 1 Meeting #42, London, UK, August 29-September 2,2005.
[17]Mohammad Abaii, Gunther Auer, Feroz Bokhari, etc, Interference avoidance concepts, IST-4-027756 WINNER Ⅱ D4.7.2 v1.0, June 30,2007.
[18]CATT, Ericsson, LGE, etc, R1-073224, Way Forward on Power Control of PUSCH 3GPP TSG-RAN WG1 #49-bis, Orlando, USA, June,2007
[19]Anil M.Rao. Reverse Link Power Control for Managing Inter-cell Interference in Orthogonal Multiple Access Systems. IEEE Vehicular Technology Conference, Sept.30-Oct.3 2007, Page(s):1837-1841.
[20]3GPP Technical Specification Group Radio Access Network, TR25.814 v.7.1.0, "Physical Layer Aspects for Evolved Universal Terrestrial Radio Access" [S], Sep.2008.
[21]TSG RAN WG3,3GPP R3-070702, Reply LS to R3-070527/R1-071242 on Backhaul (X2 interface) Delay,3GPP TSG-RAN-WG3 Meeting #55bis,St. Julian's, Malta, March,2007
[22]Nokia Siemens Networks, Nokia, Ericsson,Alcatel-Lucent, etc, R1-074477, Way forward on UL ICIC/Overload Indicator for LTE,3GPP TSG RAN WG1 #50bis meeting, Shanghai, China, October 8th-12th,2007
[23]Sharp, R1-081242, On overload indicator triggering and reporting format,3GPP TSG-RAN WG1 Meeting #52bis, Shenzhen, China,31 Mar-04 Apr,2008.
[24]ZTE, R1-081765, Discussions on report format for overload indicator,3GPP TSG RAN WG1 Meeting #53, Kansas City, MO, USA,5-9 May,2008.
[25]Li Ping, Lihai Liu, Keying Wu, et al. Interleave-Division Multiple-Access [J]. IEEE Trans. on Wireless Commu., pp.938-947, April 2006.
[26]RITT, R1-050608, Inter-cell Interference Mitigation based on IDMA 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France,20-21 June,2005.
[27]Telecom Italia, Ericsson, Alcatel-Lucent, etc, R1-075050, Way forward on UL ICIC/Overload Indicator for LTE,3GPP TSG RAN WG1 #51,Jeju (KR), November,2007
[28]IST-4-027756 WINNER II D4.7.3 v1.0 Smart antenna based interference mitigation [S], June 2007.
[29]C.L. Dolph, "A current distribution for broadside arrays which optimises the relationship between beam width and side-lobe level", Proceedings of the I.R.E and Waves and Electrons, Jan.1946
[30]3GPP Technical Specification Group Radio Access Network, TS 25.214 Physical Layer Procedures (FDD) (Release 7), V7.0.0 (2006-03)
[31]A. Dammann and S. Kaiser, "Standard conformable antenna diversity techniques for OFDM and its application to the DVB-T system," in Proceedings IEEE Global Telecommunications Conference (GLOBECOM 2001), pp.3100-3105, San Antonio, TX, USA, Nov.2001
[32]M. Inoue, T. Fujii, and M. Nakagawa, "Space-time transmits site diversity for OFDM Multi-base station system," in Proceedings IEEE Mobile and Wireless Communication Networks (MWCN 2002), pp.3100-3105, Stockholm, Sweden, Sep.2002
[33]3GPP Technical Specification Group Radio Access Network, TS23.246, Multimedia Broadcast/Multicast Service (MBMS) Architecture and functional description [S],2007.
[34]J. H. Winters, "Optimum combining in Digital Mobile Radio with Cochannel Interference", in IEEE Journal on Selected Areas in Communications, Vol.2, No.4, July 1984
[35]R. G. Vaughan, "On optimum combining at the mobile," IEEE Trans. Veh. Technol., vol.37, no.4, Nov.1988
[36]Nokia & Nokia Siemens Networks, REV-080003, Views for The LTE-Advanced Requirements,3GPP TSG RAN IMT Advanced Worksho, April,2008.
[37]Ericsson, R1-082024, A discussion on some technology components for LTE-Advanced TSG-RAN WG1 #53, Kansas City, MO, USA, May 5-9,2008
[38]IST-2003-507581 WINNER Ⅱ deliverable D3.4, Definition and assessment of relay based cellular deployment concepts for future radio scenarios considering 1st protocol characteristics [S],2005.
[39]IST-4-027756 WINNER Ⅱ deliverable D3.5.1, Relaying concepts and supporting actions in the context of CGs [S],2006.
[40]LG Electronics, REV-080019, Consideration on Technical Candidates for IMT-Advanced [S], 2008.
[41]China Mobile, Vodafone, Huawei, R1-082975.Application Scenarios for LTE-Advanced Relay, TSG-RAN WG1 #54. Jeju, Korea, August 18-22,2008.
[42]Panasonic, R1-082397, Discussion on the various types of Relays, TSG RAN WG1 Meeting #54.Jeju, Korea, August 18-22,2008.
[43]Fujitsu, R1-084297. Relaying with Channel Resource Reuse and SIC for LTE-Advanced, 3GPPTSG-RAN1 #55.Prague, Czech Republic, November 10-14,2008
[44]Panasonic, R1-084232. Discussion on the TD relay and FD relay for FDD system, TSG RAN WG1 Meeting #55.Prague, Czech Republic, November 10-14,2008.
[45]China Mobile, Vodafone, R1-091566, Relay to UE channel model for LTE-Advanced,3GPP TSG-RAN WG1 #56bis, Seoul, Kroea, March 23-27,2009
[46]Qualcomm Europe, R1-091456 "Initial Evaluation of Relay Performance on DL",3GPP TSG-RAN WG1 #56bis,2009.3
[47]3GPP Technical Specification Group Radio Access Network, TR 36.814 v1.0.0 (2008-09), Further Advancements for E-UTRA, Physical Layer Aspects,2008.9.
[48]Ericsson, R1-074444, On Inter-cell Interference Coordination Schemes without/with Traffic Load Indication,3GPP TSG-RAN WG1 Meeting #50bis, Shanghai, China, October 2007.
