Handover Failure due to same BCCH-BSIC Limited available radio frequency ARFCN owned by mobile operators would often increase challenge of RF planning and optimization. Beside difficulty when assigning frequency, one of impact of this is high handover failure due to configuring same BCCH and BSIC on the neighbor. We can simply identify such impact by make a special query that meet such condition: “High handover failure in one direction AND 1st tier + 2nd tier neighbor have same BCCH-BSIC”
On this situation, mobile station would be “fooled” during composing measurement report to observed cell and handover shall be wrong be triggered and possibly increases handover failure. Wireless network optimization can be started with network configuration audit which cover inspection of high handover failure rate in one direction with above mentioned situation is met.
Uplink Interference Identification
Frequency clearance is mandatory requirement in designing, implementing and optimizing radio frequency for cellular networks. Though a good frequency plan has been
defined to ensure acceptable of internal interference level, an external interference sometime disturbs the radio networks not only in the operational phase but also when the mobile operator optimizing their radio networks. Continuous radio performance quality monitoring activities should cover major KPIs as well as interference level in the network. Identification on interference level can be performed through BSS performance statistic such as radio quality issues relate to handover activities and signaling and traffic channel drops analysis. There are many reasons causing radio quality problem such as defective RF module on the BTS, non optimized coverage design, bad frequency planning, external interference, etc. Unluckily, not all of root causes of the radio quality problems can be easily identified by the RF engineers, especially when the problem occurred due to external interference on the uplink direction. At the end, a field measurement test has to be conducted, e.g. using spectrum analyzer.
To ease the field measurement test in identifying interference sources in office interference level analysis shall be initialized using dedicated mode or idle mode performance data. Measurement Reports send by MS is common statistic data used by radio networks during dedicated mode, and specific vendor RF feature like Idle Interference Measurement is available as well for idle interference analysis. Through geographical information system application available in market such as MapInfo, those RF measurement statistic data can be easily manipulated using data interpolation thus become useful information for RF engineer to conduct external interference sources identification.
Fractional Load Planning
Fractional Load Planning is one of specific radio design task that evaluating and analyzing available frequency spectrum and transceiver against traffic load, thus able to determine design of radio frequency assignment strategy to maintain quality service at desired level. At early stage of activity, gathering performance measurement data and network configuration is required to allow evaluation of current relation between network load and performance. The evaluation should lead to frequency spectrum efficiency preliminary analysis which deliver initial frequency allocation and hopping scheme. Using advanced planning tool, the initial RF strategy can be simulated and evaluated through intensive coverage and interference analysis.
The simulation would let us know whether further adjustment would be required or not, thus most suitable and benefit strategy can be determine. Once we able to find it, detail RF configuration data for new hopping system shall be defined. On implementation of the new RF strategy derived from fractional load planning, fine tuning might be required, including consideration of activation and fine-tuning of interference controlling feature such as Power Control and DTX.
Ping Pong Handover As the cellular network growing, it requires addition of new sites to expand capacity and or coverage services. New mobile operators were expecting to grow their network in exponential order to gain market share against mature competitors. Without any intensive network performance maintenance, common problem such ping pong handover would be degrade user experience like bad voice quality ( SQI speech quality index, MOS mean opinion score ) or even dropped call.
Ping Pong handover is shown from the successful handover back to old cell within pre-defined time of total handover, e.g. less than 10 seconds. Since not all BSS vendors provide such performance counters it might be identified by simple metric that shall be expressed as total successful handover over number of call or connection, e.g. more than 200% indicates ping pong handover. The actual ping pong handover is easily identified through drive test with sense of optimization engineer without require any calculation. Coverage holes might lead to Ping-Pong handover especially for slow moving mobiles. It may be cause by shadowing by high building. Several possible equal signals from two or more base stations might lead to Ping-Pong handover as well which is so called not optimized cell dominance. The following action items shall be used for optimization solutions:
•
Check the parameter setting such as hysteresis, offset, priority layer in dual-band case, etc. If poor parameters setting found, then correct the related parameters. Compare to default parameters design. • Check the output power BSPWR and BSPWRT which normally put on maximum value or compare to design. • Check path balance on transceiver link, e.g. loss in uplink and downlink chain. Defective RF modules might be the reason of imbalanced link. • Check the site location such as possible coverage holes or no dominant cells. • Perform drive test on that particular area to check the signal strength, if the average of signal strength of the neighbors are the same, no dominant cell is found. • For Long term action if no dominant cell shall be adding new site, while short term action shall be uptilt the most dominant cell as the serving cell for that area and reduce coverage for others.
Ghost RACH or Phantom RACH
Phantom RACH is a process when specific mobile is sending Random Access burst to a serving cell (cell which specific mobile is camping on). The Random Access burst contains TSC (Training Sequence) the TSC is derived from BCC number which is part of BSIC transmitted on Synchronization Channel (SCH) on BCCH TRX i.e. TSC=BCC for BCCH TRX. Now when mobile transmits Random Access burst, this transmission is OMNI directional i.e. transmitted not only toward serving cell but to all surrounding cells as well. When network utilizes a very tight BCCH reuse (less than 25 BCCH in use) in urban area, then the BCCH reused with in the limited geographical area many times and BCCH allocation requires proper allocation of BCC in order to prevent BCCH/BCC (not BSIC) reuse. More over the Phantom RACH is related to UL performance of the cell. The UL performance of the cell is 100% depends on antenna configuration i.e. antenna type and tilt. Correctly designed antenna configuration will prevent appearance of Phantom RACH as well.
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Post subject: Re: What is Phantom RACH? Posted: Thu Sep 09, 2010 4:06 pm
* BCCH Freq is frequency channel that is used to carry or transmit BCCH. Bronze Member
One Cell has one BCCH. * BSIC (Base Station Identity Code) is Code that is used to distinguish Co-
Joined: Wed Apr 14, 2010 5:33 pm
Channel BTSs. It is comprised of NCC(Network Color Code) + BCC(Bas Station
Posts: 53
Color Code).
Cash on hand: 505.00
If there are two BTSs are close each others with different BCCH and different BSIC, It will not be a problem. Each BTS will erceive RACH from its own MSs. But If those two BTSs have different BSICs but have same BCCHs, It may cause Phantom RACH. MS will transmit a RACH to those two BTSs with just one certain BSIC. The BTS who has this BSIC will responce this RACH, but the other BTS who doesn’t have this BISC will not response RACH. This is what we call Phantom RACH or Ghost RACH.
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Post subject: Re: What is Phantom RACH? Posted: Wed Sep 15, 2010 12:37 pm
Occurs primarily due to sporadic noise and interference, channel requests from distant MS can be affected by such noise when MS output power is low Joined: Wed Sep 15, 2010 12:09 pm Posts: 3
and if MS output power is high could cause interference to other coadjacent channel cells.....the channel coder decodes the message on the
Cash on hand:
RACH from the radio if message is decoded channel request is forwarded to
30.00
Layer 1 of the BTS (Layer 1 does no filtering of RACH) --> BTS Abis recieves the channel request and determines valid establishment cause value and if determined forwards the channel request to Call Processing --> Call Processing does no filtering of channel request and attempts to allocate an SDCCH if MS does not respond to immediate assignment that is no MS ever existed for RACH or MS is far away or turned off "CHANNEL REQUEST MS FAIL" is pegged..........
Dear experts, I do not wish to be stupid, I am learner. can I ask a simple question: What would happen if one site, three different NCC, for ex: cellA 51, CellB 62, CellC 73. Or neighbors cells have a different NCC from parent. RF engineer 2010-05-25, 12:52 AM Dear experts, I do not wish to be stupid, I am learner. can I ask a simple question: What would happen if one site, three different NCC, for ex: cellA 51, CellB 62, CellC 73. Or neighbors cells have a different NCC from parent. different NCC there will be no problem if BCC not the same nofelet different NCC there will be no problem if BCC not the same
2010-05-25, 01:38 PM
OK, but another question, if BCCs are the same? danikd OK, but another question, if BCCs are the same?
2010-05-25, 02:53 PM
The problem may occur once you have tight BCCH reuse, see below my explanation (I just copy it from another thread) Enjoy Phantom RACH is a process when specific mobile is sending Random Access burst to a serving cell (cell which specific mobile is camping on). The Random Access burst contains TSC (Training Sequence) the TSC is derived from BCC number which is part of BSIC transmitted on Synchronization Channel (SCH) on BCCH TRX i.e. TSC=BCC for BCCH TRX. Now when mobile transmits Random Access burst, this transmission is OMNI directional i.e. transmitted not only toward serving cell but to all surrounding cells as well. When network utilizes a very tight BCCH reuse (less than 25 BCCH in use) in urban area, then the BCCH reused with in the limited geographical area many times and BCCH allocation requires proper allocation of BCC in order to prevent BCCH/BCC (not BSIC) reuse. More over the Phantom RACH is related to UL performance of the cell. The UL performance of the cell is 100% depends on antenna configuration i.e. antenna type and tilt. Correctly designed antenna configuration will prevent appearance of Phantom RACH as well. RF engineer 2010-05-25, 07:14 PM The problem may occur once you have tight BCCH reuse, see below my explanation (I just copy it from another thread) Enjoy Phantom RACH is a process when specific mobile is sending Random Access burst to a serving cell (cell which specific mobile is camping on). The Random Access burst contains TSC (Training Sequence) the TSC is derived from BCC number which is part of BSIC transmitted on Synchronization Channel (SCH) on BCCH TRX i.e. TSC=BCC for BCCH TRX. Now when mobile transmits Random Access burst, this transmission is OMNI directional i.e. transmitted not only toward serving cell but to all surrounding cells as well. When network utilizes a very tight BCCH reuse (less than 25 BCCH in use) in urban area, then the BCCH reused with in the limited geographical area many times and BCCH allocation requires proper allocation of BCC in order to prevent BCCH/BCC (not BSIC) reuse. More over the Phantom RACH is related to UL performance of the cell. The UL performance of the cell is
100% depends on antenna configuration i.e. antenna type and tilt. Correctly designed antenna configuration will prevent appearance of Phantom RACH as well. This explanation is what i was going to post and plus one more thing is that the surrounding cell may consider this also such a kind of handover so it will deteriorate handover performance for both Co BCCH/BSIC cell. BR RF nofelet
2010-05-26, 01:29 PM Thanks for all, from your suggestions I try to find a more intelligent and reasonable solution. mokone
2010-06-12, 11:05 PM Can this have an effect on te drop call rate,as we downtilted a single sector and the DCR shot up together with the Phantom ranch,we then changed both the BCCH and BSIC,with no eefect,what other solutions are ther to reduce the DCR and Phantom ranches apart from a fallback?
Pix, cn u xplain lil more abt wt JZ has raised in his query/// Hw can BTS B misinterpret BTS A's HO access msg as a channel request even if it is having same BSIC(still BCCH is different rite???)
suresh - 26 Sep 2010 Hi pix, can u explain again if u don't mind if i have two bsc and in one bsc adhoc per sector and another bsc 1*1 fre hopping . so problem is in bordering cell of that bscswhich bcch i have used its use as tch in another bscs bordering cell si will it affect my ho sucess because here i have ho failure problem in bsc-bsc handover?huawei system
pix - 26 Sep 2010 hello, when incoming HO towards a certain TCH/BSIC of cell "A", this will also be heard in the neighbour "B" using same BCCH/BSIC couple as the TCH/BSICof "A". The HO ACCESS in UL on TCH/BSIC A is decoded also as a CHANNEL REQUEST on BCCH/BSIC "B". Cell B is allocating a SDCCH channel for that "ghost". Since there are four consecutive HO ACCESS for each HO attempt, it means that B is allocating 4 SDCCH channel per HO. B will face big SDCCH congestion.
Best regards, pix
QUANT - 25 Sep 2010 if they have common neighbor, even if they are not defined as neighbor. there will be HO failure outgoing from common neighbor. I have faced many SDCCH establishment problem when they have intersection coverage area even if they are no the same LAC.
JZ - 24 Sep 2010 A network is running baseband hopping (BCCH included) with SDCCH allocated on TCH. Consider two nearby cells: BCCH1=TCH2 and BSIC1=BSIC2. Problems with SDCCH timeouts are encountered and they go away when BSIC1 or BSIC2 is changed. I don't have explanation for this. BSIC is broadcast on BCCH and only co-BCCH/co-BSIC reuse should be relevant. Can anyone comment potential co-BCCH/TCH + co-BSIC reuse? Thank you in advance.
RiMi - 26 Jul 2010 as already have answered.... Co-BCCH and Co-BSIC causes problem if they are in neighbour or defined adjacency for the HO.
Saulat Abbas - 26 Jul 2010 Dear All, BCCH and BSIC pair together can cause co BCCH/BSIC clash and Ghost RACH but independently two same BSIC's do not harm the network. Same BCCH causes interference with the same BSIC the system cannot recognize which cell it is. @ Naseer: If there is no overlapping of these cells then there will be no issue at all till the time they are not added as the neighbor of each other. If they are added as the neighbor then system will again not recognize to which cell it should handover to because HO is based on BCCH and BSIC pair not on the Cell ID.
Tanuj - 4 Jun 2009 As long they dont have any common neighbour between them it wont hamper anything
krish - 18 May 2009 hey can anyone tell if i put qlim 45 in eric then what it will give o/p?
Pix - 18 May 2009 As Aye said, no problem as long as both cells are quite far apart. No common neighbours between them, but more generally, one MS in a cell "x" shall not be able to hear 2 cells having co-bcch/co-bsic.
Rex, This is the most mysterious rule from Alcatel. I've been staring stupidly at this rule for years, and it still dosn't make any sense at all. On top of that, it is said that this rule is based on 3GPP recommendations ! As I said before, the TSC is a sequence of bits used to compute the rxqual. I've read that some TSC sequences are better for that purpose than others, but that was in case of 8PSK EGPRS. I have no idea if that's the idea behind this rule or not. I must admit, I gave up :) -pix
Rex - 12 Dec 2009 Hi guys, I thought there is only one TSC. I didn't know that it's possible give different TSCs in a cell, at least I didn't noticed that in OMCR (Alcatel). Why Alcatel recommends (if I remember well) that TSC shouldn't be equal with BCC when BCC equal 1 and TSC could be equal with BCC when BCC different than 1? Regards, Rex
Bijoy - 12 Dec 2009 Pix I'm sorry if you feel my posts are aggressive. Regarding sync n/w,sync can be done either by GPS or by setting any site's clock as sync source(this is called master site,the most stable site of the cluster).As I said earlier also,in case of sync neighbours,there is no need for the TA information in the phy info message. Regarding TSC,TSC should be same as BCC for the BCCH TRX only,not necessarily for the hopping TRX's. Br\\ Bijoy
Pix - 11 Dec 2009 Bijoy, I just got confirmation that the HO are indeed "synchronous" between cells synchronized by GPS. I wonder how it works though. I'll dig on that subject further. Regarding the TS0, still got more digging to do. And regarding the TSC... I don't really understand why you talk about TSC. Let's see. The TCH are less interfered, especially in case of SFH 1x1, because surrounding sites will never collide with each other (or less often than before, let's be realistic :) ).
TSC is related to the BSIC... thanks to TSC, the MS knows how badly interfered is a burst... I'm sorry, i don't see what is the relationship ? -pix (ps : we're just exchanging thoughts, sorry if there is anything in my posts that you feel is aggressive in any way) (I cannot be hold liable for any misinterpretation of my posts) (No animals were harmed during the writing of this post) (Some babies were, though)
Bijoy - 11 Dec 2009 Please ignore the bracketed statement.it should be TCH burst,not an access burst. Br\\ Bijoy
Bijoy - 11 Dec 2009 Pix Please let me know if you find something.That will sure be a good add in my knowledge bucket. Regarding BCCH/BSIC,sync n/w will for sure improve the HOSR (rather C/I)since TSC's will be different for hopping TRX's(I recon in access burst,it is the TSC which gets transmitted).Regarding RACH success,there will not be any improvement as such neither did I said about this. Br\\ Bijoy
Pix - 10 Dec 2009 Ali, Bijoy, I'm going to get confirmation on that. This point is still not clear for me... It is said that a synchronized network would allow "synchronous HO". If that's the case, then the HO are going to be executed much faster : the MS will ready to communicate onto the target TCH much faster. By execution, I mean : the time between HO COMMAND is sent and the 1st speech frame is received in the target cell. Bijoy, About BCCH/BSIC, I don't think the synchronization will help avoiding collision on TS0 of the TRX BCCH. Therefore it won't allow an easier planning of the BCCH TRX. What matter in the BCCH TRX is the cleanliness of the TS0. If all TS0 are transmitted at the same time, this will lead to more collisions than before (on the RACH especially). It will ease up the FreqPlan only for the other TRXs.
AliAsgher - 10 Dec 2009
I agree Bijoy, MS will still have to get Sync burst from neighbors to get idea about TA. Handover times should not be reduced.
Bijoy - 10 Dec 2009 Pix I'm still talking about BCCH/BSIC.What did I else be meaning by saying "tighter BCCH reuse".If you are alloted less B/W,will you be of course be offered less NCC as well(TRAI guideline). Regarding synconised n/w,i think you get confused with syncronised neighbours. Even if you say for sync neighbours,the only benefit you get is that MS doesn't need the TA in the phy info message,thats it.As far as tuning to the target cell is concerned,the process & time is similar than that of a non sync HO.The messages are not lesser,the content becomes redundant only
Br\\ Bijoy
Pix - 10 Dec 2009 Bijoy, Well, you talked about BCCH/BSIC. You shouldn't have :) The HO intercell will be executed faster than before : both serving cell and target cells are synchronized. (do I need to explain further ?) Synchronous HO are faster than Asynchronous HO, because there is no need for the MS to resync with the new cell. Less messages....
Hi all , What is the reason of Immediate Assignment failure in idle mode? Dashty Dear, Reasons below: - SDCCH Congestion - Phantom or dummy RACH, - H/W (TRX, Combiner, diplexers, VSWR) - Radio (Coverage, Interference, DL/UL unbalance, ...) I hope can help,
2009-06-24, 04:41 PM
Regards ghassen also we have expired timers and co bcch and co bsic === phantom rach (T10 < T_MSRFPCI), FR call: (T_MSRFPCI Expiry) FR call: (T10 Expiry) Unsuccessful TCH assignment procedure LAPDm I-Frame with ASSIGNMENT COMMAND not acknowledged by MS (T200 Expiry), FR call
2009-06-24, 07:09 PM
RF engineer 2009-06-24, 07:43 PM Totally all the mentioned reasons posted are causes and if you want to be sure why you have this fail it is beteer to check what the requirement for channel request(MOC,MTC,location update,ememrgency,,,,,,,) ao when you find your request is high for one of them you can understand what is causes. BR RF electron Dear friend thanks for your help
2009-06-25, 01:43 AM
Finally i found the problem! Problem was in radio link LOS!! after radio realignment problem solved
Regards ghassen Dear friend thanks for your help
2009-06-25, 02:06 AM
Finally i found the problem! Problem was in radio link LOS!! after radio realignment problem solved
Regards then it was T_MSRFPCI counter EXPIRED??? electron then it was T_MSRFPCI counter EXPIRED???
2009-06-25, 11:45 AM
N200 Expired ! justdream Friends, can you give me some information about Phantom RACH and how to optimize it? RF engineer
2010-02-22, 04:53 PM
2010-02-22, 05:27 PM
Friends, can you give me some information about Phantom RACH and how to optimize it? Phantom RACH is kind of non real channel request some time BTS decode noise as channel request and you can reduce it by change Parameter related to RACH and RX leve access min or RACH access min BR RF justdream 2010-02-22, 05:29 PM Phantom RACH is kind of non real channel request some time BTS decode noise as channel request BR RF Thanks but in this way, can subcounters count the total number of Phantom RACH :confused: RF engineer 2010-02-22, 09:12 PM Thanks but in this way, can subcounters count the total number of Phantom RACH :confused: Yes some vendor have this raw data and they took in to KPI formulation for immediate assignment but for me in huawei this KPI is not exist , make downtilt or change radio parameter as mentioned before the problem will be solved BR RF justdream
2010-02-25, 11:48 PM
Experts, can you give me the formula required to calculate the total number of phantom RACCH UL My vendor is Siemens, kindly help :hug: emahmoud
2010-02-26, 04:05 AM
Hi all , What is the reason of Immediate Assignment failure in idle mode?
Dear, i think the problem related to 2 main causes: 1. interference: try out of band on BCCH TRX. 2. TMU HW Failure: Replace it. viswajeet 1. no agch available , full 2. agch message time out
2010-02-28, 07:38 PM
transmission ok ? radio quality good ? if using sattelite need longer timer. :hug: :hug: :hug: radio_network what are all the other statistics to be affected due to phantom rach.
2010-02-28, 08:27 PM
parsarka 2010-03-01, 01:46 AM Yes some vendor have this raw data and they took in to KPI formulation for immediate assignment but for me in huawei this KPI is not exist , make downtilt or change radio parameter as mentioned before the problem will be solved BR RF Hi, Thanks for the vaulable suggestion.Please do the needfull to mention the entire parametrs & their optimal valuse to be used for Huawei system so that my network can be benifited. Regards Raj RF engineer
2010-03-01, 03:30 PM Hi, Thanks for the vaulable suggestion.Please do the needfull to mention the entire parametrs & their optimal valuse to be used for Huawei system so that my network can be benifited. Regards Raj Rx level access min -102, RACH min access level -105 what BSC you are using it . BR RF viswajeet
2010-03-03, 01:12 AM
Experts, can you give me the formula required to calculate the total number of phantom RACCH UL My vendor is Siemens, kindly help :hug: hi justdream, UL Phantom RACH ? hmm.. houw bout maxretrans ? jox101 Hi!
2010-03-17, 04:42 PM
Anyone here knows the difference between rach access min level and rx access min level? bruno hautenfaust 2010-04-06, 11:08 AM The counter for Number of Immediate Assignment Attempts is ImmAssAtt = ATIMASCA[1 ..14] also you can find MBUSYSSP[6] :Receipt of a invalid ESTABLISHMENT INDICATION message (undefined Layer3 message) related for a SDCCH (BTS → BSC) or no receipt of an ESTABLISHMENT INDICATION message after activation of a SDCCH (phantom RACH). BR danikd Friends, can you give me some information about Phantom RACH and how to optimize it?
2010-05-05, 04:01 PM
Phantom RACH is a process when specific mobile is sending Random Access burst to a serving cell (cell which specific mobile is camping on). The Random Access burst contains TSC (Training Sequence) the TSC is
derived from BCC number which is part of BSIC transmitted on Synchronization Channel (SCH) on BCCH TRX i.e. TSC=BCC for BCCH TRX. Now when mobile transmits Random Access burst, this transmission is OMNI directional i.e. transmitted not only toward serving cell but to all surrounding cells as well. When network utilizes a very tight BCCH reuse (less than 25 BCCH in use) in urban area, then the BCCH reused with in the limited geographical area many times and BCCH allocation requires proper allocation of BCC in order to prevent BCCH/BCC (not BSIC) reuse. More over the Phantom RACH is related to UL performance of the cell. The UL performance of the cell is 100% depends on antenna configuration i.e. antenna type and tilt. Correctly designed antenna configuration will prevent appearance of Phantom RACH as well. If you would like to know more...just ask!!!! Nasrin 2010-09-12, 12:08 AM hi all phantom RACH can degrade imm ass fail on sdcch ,what about sd drop?can affect it ? other qusetion when HLR check the channel requset is from MS or not? RF Engr 2010-09-29, 09:02 PM Phantom RACH is a process when specific mobile is sending Random Access burst to a serving cell (cell which specific mobile is camping on). The Random Access burst contains TSC (Training Sequence) the TSC is derived from BCC number which is part of BSIC transmitted on Synchronization Channel (SCH) on BCCH TRX i.e. TSC=BCC for BCCH TRX. Now when mobile transmits Random Access burst, this transmission is OMNI directional i.e. transmitted not only toward serving cell but to all surrounding cells as well. When network utilizes a very tight BCCH reuse (less than 25 BCCH in use) in urban area, then the BCCH reused with in the limited geographical area many times and BCCH allocation requires proper allocation of BCC in order to prevent BCCH/BCC (not BSIC) reuse. More over the Phantom RACH is related to UL performance of the cell. The UL performance of the cell is 100% depends on antenna configuration i.e. antenna type and tilt. Correctly designed antenna configuration will prevent appearance of Phantom RACH as well. If you would like to know more...just ask!!!! Its a great reply.But dont you think interference on uplink can also cause Phantom rach e.g external interference in network causing phantom rach danikd
2010-10-03, 05:17 PM Its a great reply.But dont you think interference on uplink can also cause Phantom rach e.g external interference in network causing phantom rach As far as I understand, you are referring to non-GSM signal source that transmits with in the UL GSM band on BCCH frequency? If I understand you right, then the answer is following: The probability that Non-GSM signal will introduce Phantom RACH effect is very low, since in order to be decoded on on BTS side it should be GMSK modulated and should contain Random Access message with Access Cause inside. The external (non-GSM) interference you can recognize by analyzing the ICM (Idle Channel Measurements) statistics. Some GSM vendors like Ericsson, Siemens, Huawei have an efficient features to monitor UL interference for entire band (similar to UMTS UL RTWP measurements). Those features (their results) can be very helpful for external UL interference recognition and identification.
Best regards, danikd 2010-10-03, 05:23 PM hi all phantom RACH can degrade imm ass fail on sdcch ,what about sd drop?can affect it ? other qusetion when HLR check the channel requset is from MS or not? SDCCH drop could not be affected by Phantom RACH effect. Since SDCCH drop counted only after SDCCH assignment by specific mobile (immediate assignment complete and RRM - radio resource management engaged for specific connection). Just to remind Phantom RACH just initiates Immediate Assignment procedure but never competes it. To be more precise - HLR never check channel request. All channel requests are managed on BSS level. HLR is involved only into Authentication procedure. This procedure is a DTAP procedure (Direct Transfer), where BSS side (air-interface, BTS, BSC) are transparent and not involved into transaction (they just used as transport pipe for message).
you're right, a RACH on a BCCH is not "failed" even though there is a poor BSIC-BCCH plan. in my opinion, the only problem could be a RACH sent on a BCCH frequency that is used as well few kilometers away. In this situation, the second cell might receive this RACH with a distance > "rach timing advance".
Bilal - 6 Mar 2008 Got the answer. But it creates another confusion. Successful Random Accesses are all except failed random accesses.The failed random access counter is incremented for a Random access received with too high TA, values that are not used or in case of "software file congestion". That means every RACH attempt with less than max TA and defined cause value is a successful Random Access. But Ericsson says poor BSIC planning can be a cause of bad Random Access Success Rate, how is this? Even a phantom RACH intended for another cell must have a valid cause value and hence it must be treated as a Successful Random Access.Any idea?
Pix - 6 Mar 2008 That's the thing, we don't have those in alcatel. Let's try to guess.. the MS starts with a channel request on RACH, the "Channel Required" reaches the BSC, and then is counted as a "random access attempt". The BSC sends a Channel Activation to the BTS, if the SDCCH is not congested. Counted as a "SDCCH Request". The BTS replies with a Channel Activation Ack (not counted) Then the BSC sends a Immediate Assign Command, counted as a "SDCCH allocated".
Maybe in your formula, this is the ratio CHANNEL ACTIVATION / CHANNEL REQUIRED ? I really cannot be sure... this indicator is not provided by alcatel. it can be computed manually though.
Bilal - 6 Mar 2008 You can give the Alcatel's definition for it, I don't think there will be much difference :)
Pix - 6 Mar 2008 you need to find an ericsson guy... i'm the alcatel guy :)
Bilal - 5 Mar 2008 Hi Guys, Random Access Success Rate has the formula : 100 * No. of successful random accesses / No. of random access attempts. Can anybody tell me what is a successful random access? I mean when this counter is pegged?
