解析TD—LTE系统干扰

1、解析TDLTE系统干扰【摘 要】文章对TD-LTE的系统内外干扰的机理进行了系统分析，并结合标准中的设备性能最低要求计算出典型情况下系统间隔离度要求，以及隔离度的实现方法。Articles 【 pick to 】 the system inside and outside interference mechanism of td-lte has carried on the system analysis, combined with the standard minimum requirements of the equipment properties calculated typical

2、ly isolation between system requirements, and the realization of the isolation methods.【关键词】TD-LTE 干扰 隔离度【 key words 】 td-lte interference isolation ratio1 概述1 overview随着TD-LTE标准的冻结、设备的成熟以及移动互联网业务飞速发展，TD-LTE已经成为业界的关注焦点。而TD-LTE系统内外干扰问题是网络部署时必须要考虑的关键问题之一。As the td-lte standards to freeze, the mature o

3、f the equipment as well as the rapid development of mobile Internet business td-lte has become the focus of concern of the industry. But td-lte system inside and outside interference problem is a network deployment must be one of the key issues to consider.TD-LTE系统面临的干扰包括噪声Pn、系统内干扰Iintra-system和系统间干

4、扰Iinter-system，下面将分别对这三种干扰进行分析。Td-lte system faced by interfering in Pn, system including noise interference Iintra Iinter - system - between the system and the system interference, the following will respectively analyze the three interference.2 噪声2 the noise噪声可以按照来源分为接收机内部噪声和外部噪声。接收机内部噪声包括导体的热噪声和放

5、大器的噪声放大；外部噪声是指来自接收机以外的非移动通信发射机的电磁波信号，可以分为自然噪声和人为噪声。Noise can be divided into internal noise and external noise receiver according to the source. Internal noise including conductors of heat receiver and amplifier's noise amplification; External noise is from outside of the mobile transmitter rece

6、iver of electromagnetic signals, can be divided into natural and man-made noise.一般在进行分析时主要考虑接收机内部噪声，可通过以下式子计算得到：The receiver when carries on the analysis of main consideration internal noise, can be calculated by the following formula:Pn=KTB+NF （1）Pn + NF = (KTB (1)其中：Among them:K：波尔兹曼常数（Boltzmann c

7、onstant），1.380662×10-23JK-1；K: Boltzmann constant (the Boltzmann constant), 1.380662 x 10-23 jk - 1;T：开尔文绝对温度，一般计算中取常温290K；T: kelvin, the absolute temperature, general computation of normal temperature 290 k;B：接收机有效带宽；B: receiver bandwidth effectively;NF：接收机的噪声系数，标准中一般取基站的噪声系数分别为7dB。NF: receive

8、r noise coefficient, a standard generally take the noise coefficient of base stations in the 7 db respectively.由于LTE系统带宽在1.4MHz20MHz可变，并且采用OFDMA/SC-FDMA的多址方式，用户实际只占用系统带宽中的一部分。因此，信道的热噪声水平也会随着占用带宽的变化而变化。Due to the LTE system bandwidth in 1.4 MHz to 20 MHz variable, and the OFDMA/SC - FDMA multiple acc

9、ess methods, users really only part of the system bandwidth. Therefore, channel thermal noise level also will change as the change of bandwidth.3 系统内干扰3 interference within the system系统内干扰是本移动通信系统内各无线网元收发单元之间的干扰。Interference in the system is in this system for mobile communications interference betw

10、een each wireless network transceiver unit.3.1 同频干扰3.1 same frequency interferenceTD-LTE系统同小区下的不同用户下行采用OFDMA、上行采用SC-FDMA的多址方式，不同用户占用不同的、相互正交的子载波，因此不存在3G系统中的同小区不同用户的多址干扰问题。LTE系统中的同频干扰主要是同频的其他小区的干扰，这也是LTE系统中干扰协调、抑制技术要解决的问题。Td-lte system with area under different user downlink OFDMA uplink the SC - FDM

11、A, multiple access methods, different users occupy different, mutually orthogonal sub-carrier, so there is no in the 3 g system with multiple-access interference problems of different users. The same frequency interference in LTE system is mainly same frequency interference from the other village, c

12、oordination, this also is in the LTE system interference suppression techniques to solve the problem.3.2 LTE TDD系统上下行链路间干扰3.2 TDD LTE TDD system has link between interferenceLTE TDD系统采用时分双工的方式，上下行信道工作在相同的频点，通过上下行转换点设置上下行信道可占用的时隙。上行与下行之间由于时间转换点不一致、基站之间不同步或无线信号传播时延等，可能出现“重叠”（同时存在上行链路和下行链路）的时间点，引起eNode

13、 B小区间或终端用户间的干扰。LTE TDD system USES time division duplex mode, has work in the same frequency channel, TDD by has TDD point set has channel occupancy time slot. Between upward and downward due to the time point of inconsistencies, the sync between base stations or wireless signal propagation delay, e

14、tc., may appear "overlap" (both uplink and downlink link) the point in time, cause interference eNode B district or the end user.（1）相邻小区间或同小区不同频率间的上下行转换点不一致(1) the neighboring cells or with TDD community between different frequency has breaking point如果相邻小区第二转换点设置不同，在上下行配置不同的时隙，会出现一个小区eNode

15、B发射时，另一个小区eNode B正在接收的情况，因而将出现比较严重的上下行链路间干扰，如图1所示：If adjacent area the second point of setting, configuration of TDD in has different time slot, will appear a neighborhood eNodeB launch another village eNode B are receiving, so there will be interference between TDD serious has link, as shown in fig

16、ure 1:为了避免该类干扰，规划中应注意：To avoid this kind of interference, the planning should be paid attention to:1）结合各区域的上下行业务量需求特点，尽量在成片的区域内采用同一时隙分配方案；TDD 1) combined with the regional has traffic demand characteristics, as far as possible use in the area of the piece of the same time slot allocation scheme;2）在采

17、用不同时隙分配方案的区域交界处，相邻两个采用不同时隙分配方案的小区中，应有一个闭塞发生重叠的时隙，或者两个相邻小区通过检测重叠时隙上的干扰强度，决定是否将用户继续分配在该重叠时隙上。2) in different time slot allocation scheme area at the junction, adjacent to the two different time slot allocation scheme in the neighborhood, there should be a block overlap time slot, and two neighboring c

18、ells by detecting overlapping time slot on the interference intensity, users decide whether to continue to distribute on the overlap time slot.（2）相邻小区间失同步(2) loss of synchronization between neighboring cells在相邻的小区之间同步基准不一致时，即使小区间采用相同的转换点设置方案，由于起始时刻不同，也会有“重叠”时间点出现，如图2所示：In synchronous datum inconsist

19、encies between adjacent area, even if the same point of setting scheme between zones, due to the different starting point, also can have the "overlapping" point in time, as shown in figure 2:LTE的eNode B之间一般采用外接参考时钟源（如GPS或伽利略卫星系统）实现同步。当外接参考时钟源故障，以及同步过程误差过大时，都有可能出现Node B之间失同步。根据3GPP TS36.133

20、要求，采用相同频率、且有重叠覆盖区域的相邻Node B之间，帧起点的时间误差应小于或等于3s（覆盖距离小于3km）；如果满足该要求，则相邻小区间的上下行干扰时间很短，对网络的性能影响不大。LTE eNode B between generally USES an external reference clock source (such as GPS and Galileo satellite system). When an external reference clock source fault, as well as the synchronization error is too l

21、arge, will likely lose synchronization between the Node B. According to 3 GPP TS36.133 requirements, using the same frequency, and there are overlapping coverage area between adjacent Node B, frame start time error should be less than or equal to 3 mu s (covering distance is less than 3 km); If meet

22、 the requirements, TDD is between adjacent area has interference time is short, and impact on the performance of the network.在规划LTE TDD系统的基站间同步时，应满足该要求。In planning LTE TDD system synchronization between the base station should meet the requirements.（3）无线传播时延大于转换点保护时隙(3) wireless transmission delay t

23、ime slot is greater than the point of protection在无线信号传播过程中，随着传播距离的增加会形成传播时延。此外，在采用移动通信直放站延伸小区覆盖距离时，也会引入直放站设备的时延。传播距离产生的时延为：In the process of the wireless signal transmission, with the increase of propagation distance will form the propagation delay. In addition, when using mobile communication repea

24、ter station extension region coverage distance, will delay introduction of repeater station equipment. Delay of transmission distance are as follows:=d/c （2） tau = d/c (2)其中，d是传播距离，c是光速。Where d is the propagation distance, c is the speed of light.在一个小区内如果传播时延过大，也会引起终端的上行链路对附近其他终端的下行链路接收形成干扰。为了在eNode

25、 B接收端实现各终端的上行信号同步，终端必须提前一定的时间发送上行的UpPTS和子帧2。如图3所示，以eNode B发射端的时间作为基准，该时间提前量应该等于终端到eNode B的无线传输时延，也就等于Node B发射的下行信号到达终端的无线传输时延。如果以终端接收到的下行信号时间作为基准，该时间提前量就是两倍的无线传输时延（2）。Within a community if the propagation delay is too big, can also cause the terminal to uplink downlink link received form other termi

26、nal near interference. For the eNode B receiving end realize the uplink signal synchronization of each terminal, the terminal must be a certain amount of time in advance to send up the UpPTS and sub frame 2. As shown in figure 3, to launch the eNode B time as a benchmark, the time schedule should be

27、 equal to the terminal to the eNode B wireless transmission delay tau, the launch of the downlink signal is equal to the Node B reaches the terminal of the wireless transmission delay. If the terminal receives the downlink signal time as a benchmark, the nc is twice the wireless transmission delay (

28、2 tau).相对于接收到的下行信号基准，由于终端需要以2的时间提前量发送上行UpPTS和子帧2，如果2大于DwPTS和UpPTS之间的保护间隔GP，就会引起该终端的上行UpPTS信道干扰附近其他终端接收来自Node B的DwPTS信道。因此，按照以下公式可确定不产生上下行干扰的最大传输距离（即最大覆盖距离）：Relative to the downlink signal received by the benchmark, due to the terminal need to send 2 tau nc uplink UpPTS and sub frame 2, if tau is gre

29、ater than 2 DwPTS and UpPTS protection interval between GP and uplink UpPTS channel interference can cause the terminal near other terminal receiving DwPTS channel from the Node B. Therefore, according to the following formula can be set for TDD does not produce has interference of maximum transmiss

30、ion distance (i.e., maximum coverage range) :（3）(3)其中，tgap是保护时间间隔。Among them, the tgap is to protect the time interval.根据标准中的特殊子帧配置，可计算得出不同特殊子帧配置格式下TD-LTE基站的最大覆盖距离，如表1所示：According to the standard of the special child frame configuration, can be calculated under different special subframe configurati

31、on format td-lte base station maximum coverage range, as shown in table 1:如果存在移动通信直放站等转发设备，由于直放站设备内部的滤波器件固有时延和光纤介质中的信号传播时延，会导致上述时延保护间隔对应的最大覆盖距离进一步缩小。If there is a forward equipment such as mobile communication repeater stations, repeater station equipment due to the internal filter of the inherent t

32、ime delay and fiber optic medium signal propagation delay, lead to the delay protection interval corresponding to the maximum coverage range narrowed.考虑到该干扰信号经过远距离的传播损耗后，信号功率已经比较微弱，工程中一般较少考虑该干扰的影响。Considering the interference signal after long-distance transmission loss, it is comparatively weak sig

33、nal power, engineering in general, less consider the impact of the interference.（4）邻频干扰(4) adjacent frequency interference由于设备滤波特性的非理想性，干扰也存在于使用相邻频率的各方之间。Because of interference device non ideal filter characteristics, also exist in the use of adjacent frequency between parties.假设不同频率上的终端数量和位置分布相同，从

34、3GPP标准中对接收机的ACS和ACLR指标要求来看（一般在30dB以上），相对于同频干扰，邻频干扰对接收机的影响小30dB以上，即邻频干扰比同频干扰弱1000倍以上，可以忽略。Assumes that the terminal number and location distribution of different frequency are the same, the receiver from the 3 GPP standard requirements of ACS and ACLR index (generally in more than 30 db), compared wi

35、th the same frequency interference, adjacent frequency interference influence on receiver's little more than 30 db, the adjacent frequency interference more than 1000 times weaker than the same frequency interference, and can be ignored.4 系统间干扰Interference between 4 system4.1 系统间干扰类型4.1 system i

36、nterference types从形成机理角度可分为邻频干扰、杂散辐射、接收机互调干扰和阻塞干扰。From the perspective of formation mechanism can be divided into the adjacent frequency interference, stray radiation and receiver intermodulation interference and blocking interference.（1）邻频干扰（ACI）(1) adjacent frequency interference (ACI)如果不同的系统分配了相邻

37、的频率，就会发生邻频干扰。由于收发设备滤波性能的非完美性，工作在相邻频道的发射机会泄漏信号到被干扰接收机的工作频段内；同时被干扰接收机也会接收到工作频段以外其他发射机的工作信号。决定该干扰的关键特性指标是发射机的ACLR和接收机的ACS。If the different allocated adjacent frequency system, adjacent frequency interference occurs. Due to imperfect transceiver equipment filtering performance, launch opportunity workin

38、g in adjacent channel leakage signal to interference receiver within the working frequency band; Also interfere with the receiver will receive the signal transmitter work other than working band. Decide the key characteristic of the interference index is the ACLR transmitter and the receiver of the

39、ACS.（2）杂散辐射（Spurious emissions）(2) the stray radiation (Spurious emissions)由于发射机中的功放、混频、滤波等部分工作特性非理想，会在工作带宽以外很宽的范围内产生辐射信号分量（不包括带外辐射规定的频段），包括电子热运动产生的热噪声、各种谐波分量、寄生辐射、频率转换产物以及发射机互调等。Because the transmitter power amplifier, mixer, filter and so on part of the work is not ideal, will be within the scope

40、of the work outside very wide bandwidth to produce radiation signal component (not including specified out-of-band radiation spectrum), including electronic thermal motion produced by thermal noise, harmonic component, stray radiation, frequency conversion and transmitter intermodulation products.邻频

41、干扰和杂散辐射不同，邻频干扰中所考虑的干扰发射机泄漏信号指的是被干扰接收机所处频段距离干扰发射机工作频段较近，尚未达到杂散辐射的规定频段的情况，即有效工作带宽2.5倍以上（或者工作带宽上下边界10MHz以外的频段）。当两系统的工作频段相差带宽2.5倍以上（或者相隔10MHz以上）时，滤波器非理想性将主要表现为杂散干扰。Adjacent frequency interference and the stray radiation is different, considering the interference in the neighboring frequency interference

42、 transmitter leakage signal is interfered with receiver in jammer work frequency spectrum distance, has yet to reach the regulation of stray radiation spectrum, namely the effective working bandwidth of 2.5 times more than 10 MHZ bandwidth fluctuation boundary (or work outside of the band). Differen

43、ce when two system work frequency bandwidth more than 2.5 times (or more than 10 MHZ apart), non ideal filter will be mainly for spurious interference.（3）接收机互调干扰(3) receiver intermodulation interference接收机互调干扰包括多干扰源形成的互调、发射分量与干扰源形成的互调（TxIMD）、交叉调制（XMD）干扰。Receiver intermodulation interference componen

44、t includes many interference sources form intermodulation, launch the intermodulation (TxIMD), formed by the interference sources with cross modulation (XMD) interference.多干扰源形成的互调是由于被干扰系统接收机的射频器件非线性，在两个以上干扰信号分量的强度比较高时所产生的互调产物。Many interference sources of intermodulation is due to nonlinear interfer

45、ence system receiver rf device, in two or more the strength of the interfering signal component of intermodulation products produced during the relatively high.发射分量与干扰源形成的互调是由于双工器滤波特性不理想，所引起的被干扰系统的发射分量泄漏到接收端，从而与干扰源在非线性器件上形成互调。Launch component and the interference sources of intermodulation is not id

46、eal, because the duplexer filter characteristics caused by interference of the component of system leakage to the receiver, thus to form the intermodulation interference sources in the nonlinear devices.交叉调制也是由于接收机非线性引起的，在非线性的接收器件上，被干扰系统的调幅发射信号，与靠近接收频段的窄带干扰信号相混合，将产生交叉调制。Cross modulation caused by no

47、nlinear receiver in nonlinear on the receiving device of the jamming system amplitude modulation signal, and near the receiving frequency narrow-band interference signal mix, will produce cross modulation.（4）阻塞干扰(4) blocking interference阻塞干扰并不是落在被干扰系统接收带宽内的。但由于干扰信号功率太强，而将接收机的低噪声放大器（LNA）推向饱和区，使其不能正常工

48、作。被干扰系统可允许的阻塞干扰功率一般要求低于LNA的1dB压缩点10dB。Blocking interference does not fall within the interference system receive bandwidth. But due to the interference signal power is too strong, and the receiver of the low noise amplifier (LNA) to the saturated zone, so that it is not working. Be jamming system ca

49、n allow the barrage jamming power of the general requirements 1 db compression point 10 db below the LNA.根据不同干扰形成的特性，邻频干扰、杂散干扰、互调干扰都是落在被干扰系统接收机内，被其接收而恶化通信质量的；阻塞干扰则是在被干扰系统接收带宽以外，通过将被干扰系统接收机推向饱和而阻碍通信的。According to the characteristics of different interference, adjacent frequency interference, stray in

50、terference, intermodulation interference is fall within the jamming system receiver, receiving them and deteriorating quality of communication; Barrage jamming is received by interference system bandwidth, pushed jamming system receiver through the saturated and obstacles to communication.对于落在被干扰系统的

51、接收带宽内的干扰，可以进行功率上的相加。总的干扰功率为：To fall by interference within the receiver bandwidth jamming system, can be additive on the power. The total interference power is:（4）(4)其中，PACI、PSE、PIMD分别为邻频干扰、杂散干扰、互调干扰，单位为dBm。Among them, the PACI, PSE, PIMD neighbors frequency interference, stray interference, intermo

52、dulation interference, unit for dBm.一般情况下，三种干扰的强度相差较大；合成的干扰功率将主要取决于其中最大的一项。即使在最极端的情况下，三种干扰强度相等，总的干扰功率增加4.5dB，仍符合一般情况下干扰指标留有的余量要求。因此工程中一般分别核算各干扰情况是否满足系统指标要求，以简化分析。In general, three types of interference intensity is large; Synthesis of interference power will be subject to one of the biggest one. Eve

53、n in the most extreme cases, three kinds of interference intensity are equal, the total interference power increase 4.5 dB and still conform to the requirements of the normally disturbances leave some allowance. So generally accounted for separately in each interference whether meet the requirements

54、 of system index, in order to simplify the analysis.4.2 系统间干扰分析方法4.2 system interference analysis method干扰分析的方法很多，3GPP TR36.942中提到有两种：确定性计算方法和仿真模拟方法。Interfere with the analysis of the method are many, 3 GPP TR36.942 mentioned has two kinds: deterministic calculation method and simulation method.（1）确

55、定性计算方法(1) deterministic calculation method也称最小允许耦合损耗MCL（Minimum Coupling Loss）计算方法。确定性计算方法的优点是简单易行，可以较容易地获得理论估计结果，所计算的结果对应于最恶劣的情况，对应的MCL要求较严格。Also known as the Minimum allowable coupling-loss MCL (Minimum Coupling Loss) calculation. Deterministic calculation method has the advantage of simple, can m

56、ore easily obtain theoretical estimation results, the calculation results correspond to the worst case, a strict corresponding MCL.确定性计算方法是基于干扰系统和被干扰系统的有关参数，计算出系统间要实现必要的干扰抑制所需要的最小允许耦合损耗MCL。一般MCL采用以下公式计算：Deterministic calculation method is based on the interference system and interference system rela

57、ted parameters, calculate the system to achieve the necessary interference suppression between the minimum needed to allow the coupling loss MCL. MCL commonly use the following formula:MCL=干扰源输出功率-衰减-允许的干扰电平MCL = source output power attenuation - allow interference level（5）(5)根据收发设备的ACS/ACLR或者杂散信号功率

58、、互调抑制要求等指标，结合其工作带宽和发射功率，可以计算出达到一定干扰抑制要求的MCL。According to ACS/ACLR transceiver equipment or stray indices such as signal power, intermodulation suppression requirements, combined with its working bandwidth and transmission power, can calculate the MCL reaches a certain interference suppression requirement.1）衰减1) the attenuation对不同的干扰类型取定为不同的参数：For different interference types take for different parameters:对邻道干扰是ACIR；ACIR for adjacent-channel interference;对互调干扰是互调抑制比。The i