If some ome cell ells are frequ requen enttly seen een as poll pollu uter ters (e.g. .g. >8% time) should ould be mark marked ed and inves investig tigate ated d. Usually, the max number of active cell is 3, so if number of strong pilot is more than han 3,th 3,then en it is a pilot ilot poll pollut utiion point oint.. If (CPI (CPICH CH_R _RSC SCP P 1st - CPIC CPICH_ H_RS RSCP CP4th) < 5 dB ,it means the best serve cell ell is not not domi domina nant nt
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According to the conditions condi tions of Pilot Pollut ion, the SC4,SC5,SC6 are Pilot Pollution, the RSCP of SC6 is more then 5dB lower than the best serve cell, so it is not Pilot Pollution Margin is 5 dB
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Looking at the estimated active set based on the scanner data is a useful measurement of pilot pollution , In order to see areas of excessive SHO candidates, the estimated active set size is allowed to exceed maximum of 3 . Locations where there are more than 3 pilots in the active set should be marked and sources of the interference should be identified. This can be done in conjunction with the Pilot pollution analysis.
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An example of pilot pollution results is provided pro vided in the Table. Table . This shows the % of time each cell was seen as a pilot polluter. Cells which are frequently seen as polluters (e.g. >8) should be marked and investigated.
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Due Due to res restric tricti tion on to site site loca locati tion on and and comp comple lex x geog geogra raph phic ic env environ ironm ment, ent, cell distribution might be improper. Improper cell distribution causes weak covera erage of some ome are areas and and covera erage by multi ltiple ple strong ong pilot ilots s in same same areas. areas. If a NodeB is constructed in a position higher than around buildings, most areas will be with in the line-o e-of sight range. Therefore signals are widely transmitted. Over high site cause difficult control of cross-c s-cell cove covera rage ge,, whic which h caus causes es pilo pilott poll pollut utio ion n. The sect ector azimuth of eac each ant antenna enna is set to cooper opera ate with eac each othe otherr. If the azimuth is improperly set ,might lead to pilot pollution Therefore we must ust adju adjust st the the ante antenn nna a acc accordi ording ng to actu actual al prop propag agat atio ion. n. If the antenna down tilt is improper, signals are received in the areas which are covered by this site. Therefore interferences to other areas caus causes es pilo pilott poll pollut utio ion n . Even Even wors worse, e, inte interf rfer eren ence ces s migh mightt caus cause e call call drop. drop. When the NodeBs are densely distributed with a small planned coverage range and the CPICH power is over high, the pilot covers an area area larg larger er than than the the plan planne ned d area area.. This This caus causes es pilo pilott poll pollut utio ion. n.
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Mult Multip iple le stro strong ng pilo pilots ts inte interf rfer eres es usef useful ul func functi tion onal al sign signal als, s, so Io incr increa ease ses, s, Ec/I Ec/Io o decr decrea ease ses, s, BLER BLER incr increa ease ses, s, and and netw networ ork k qual qualit ity y decl declin ines. es. More ore than three strong ong pil pilots ots or no primar imary y pilo pilott exi exists in multi ltiple ple pilo ilots, ts, frequent handover occurs among these pilots. This might cause call drop. The inter nterfferenc ence of the areas eas with pilot ilot poll pollu utio tion inc increases ases,, the the system capacit capacity y declines. declines.
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Star Startt Assi Assist stan ant. t. Anal Analyz yze e scan scanne ner-b r-bas ased ed RSCP RSCP for for 1st 1st Best Best Serv Servic iceC eCel elll and EcIo for 1st Best Serv erviceCell. ell. Select ect the are areas with high igh RSCP and poor poor Ec/I Ec/Io o as candi andida date te area areas s with with pilo pilott poll pollut utio ion. n. Analyze scanner-based scanner -based Whole PP. PP. Select the areas corresponding to candi andida date te area areas s as the the key area areas s with with pilo pilott poll pollut utio ion. n. Locate the cells that cause pilot pollution of the key areas. Based on RSCP for 1st Best Service Cell, judge whether the pilot pollution is caused by existence of multiple strong pilots or lack of a strong pilot. For the former cause, you can solve the problem by weakening other strong pilots. For the latter cause, you can solve the problem by strengthening some strong pilot. Based on the actual environment, analyze the specific causes to pilot pollution. For specific causes, provide solutions to pilot pollution. While eliminating pilot pollution in an area, consider the influence to other areas and avoid causing pilot pollution or coverage voids to other areas. After the adjustment, we should take retest and analyze a nalyze RSCP, Ec/Io and Whole PP. If they cannot meet KPI requirements, requirements, re -optimize -optimize the network by selecting new key areas until KPI requirements are met.
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According to the test, change pilot signal strength of an area with pilot poll olluti ution by adj adjust usting anten ntenna na dow down tilt and and azim azimut uth. h. This chang hanges es the distribution of pilot signals in the area. The principle for adjustment is enha enhanc ncin ing g prim primar ary y pilo pilott and and weak weaken enin ing g othe otherr pilo pilots. ts. Pilot pollution is caused by the coverage by multiple pilots. A direct method to solve the problem is to form a primary pilot by increasing the powe ower of a cell ell and and decre ecreas asiing the pow power of other her cells. ells. If adjusting power and antenna is not effective to solving pilot pollution, use RRU or micro cells. Using RRU or micro micro cells aims to bring a strong strong -signal coverage coverage in the area with pilot pollution, so the relative strength of other signals decreases.
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