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Synchronization clock problems

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #42021 Reply
    Abdel
    Guest

    Hi everybody,
    I am new in Telecoms and my company is waiting me to solve everything.My company is a mobile operator, fixed line and internet provider and the whole network has no any clock resource at all, such as a BITS machine or Strantum 1 or 2,
    and we have a lot of unkown problems may be caused by the lack of clock, therefore can anybody tell me the effect of lack of clock?

    #42022 Reply
    cybhert
    Guest

    Its analogous to a human body with no heart beat… no clock? drop calls are rampant… your network would be in chaos… so if synchronization or clocking is present. MOC and Trunk calls would be in error. Call connection would be a major problem, fixed it with attaching or giving your nework with an external clock source. There are equipments there or brands that would be happy to equipt your network with their brand of clock like HP or symmetricom…

    #42023 Reply
    Phaysal
    Guest

    Hi,
    I see everywhere, everyone saying that lack of sync can drastically affect network KPIs. but no one really put that in numbers, or even equations. Can you provide any info in this regards?

    #42024 Reply
    Pix
    Guest

    i’ll just bring my 2 cents :
    if there is no synchronisation between 2 BTS, it will not degrade the KPI of the network. Indeed, it is actually a normal situation ! 2 BTS are usually NOT synchronized. It is the MS that will re-synchronize automatically every time it is performing a HO to another BTS.

    Now, between BTS and BSC and MSC, there is always a synchronization : they can communicate on their interfaces.

    A global synchronization between all network elements is not necessary for normal utilization (voice calls, GPRS, EDGE, SMS, etc..)

    #42025 Reply
    Phaysal
    Guest

    Hi,
    My be i m not getting the point here, but if the two BTS are not synchronized, then how would an handover take place. coz IS-95 imposes 3us/day limit for frequency inaccuracies.

    We know that MS in CDMA may/may not be served by more than on BTS.

    1. How much likely it is, that the MS is served by one BTS only at perticular time instant? This may be the case when MS is located in an area, which is covered by one BTS only, not overlapped with some other BTS’s coverage area?

    2. What if that lone serving BTS goes out-of sync with that network. Although this could be detected by the concerned MSC readily, but what would it do to bring BTS back in sync? and what would happen to those MS served only by this BTS?

    3. What would happen, when this MS goes neal coverage area boundary, it would try to acquire new pilot? would it be able to do so, as the BTS which is already serving that MS is out of sync with the network?

    Thanks!

    #42026 Reply
    heru
    Guest

    1. In CDMA System, MS will handled by BTS that have strong power (if the BTS not have problem)but MS can read 3 Pilot Number (Case in our network), but just using 1 PN and other for handoff.
    2. When BTS out of syncronisation the MS can’t handoff to other BTS (call drop). If happened out of sync. check your GPS antenna or other module that using for time syncronisation.
    3. Just happened call drop when MS On call Busy moving from out of sync BTS to normal BTS (Handoff case). But if MS idle move from out of sync BTS to normal BTS, I think when the MS make a call, BTS will be repaging MS and now MS using normal BTS.

    Please correct if wrong

    thank you.

    #42027 Reply
    Phaysal
    Guest

    Thnx heru,
    those really answered my queries. Can we exchange some emails, and have some more dicussion.
    my email id is faisalkhan1981@hotmail.com

    #42028 Reply
    Pix
    Guest

    my answer was regarding a GSM network, not CDMA… it wasn’t detailed in your question 🙂

    #42029 Reply
    Geoff
    Guest

    Hi, we run Nokia WCDMA and 2G network and synchronisation of the BTS does effect KPI’s. Particularly handovers. The local BTS clock is used to derive the TRX or WCDMA frequency, so if it is off, your cell will be off frequency. Where your off freq cell border occurs is where you will have the issues.

    #42030 Reply
    Phaysal
    Guest

    Hi,
    Geoff, Can we relate these two things i.e. synchronization and KPI degradations mathematically, logically or statistically?..

    like can we say.. a jitter of 100 ns in synchronization would degrdade the handovers by 10% … or anything like that?

    by the way.. where r u located?

    #42031 Reply
    Phaysal
    Guest

    One more thing to be considered here:
    When an MS is served by a BS, it is continously synchronized by BS using sync channel. Now if two BS are serving the same MS, and if of them either has jitters in the clock, or its clock has lost sync, then which BS would control the timing and sync of the served MS?

    Regards

    #42032 Reply
    heru
    Guest

    Hi Phaysal, what you mean lost sync..i think that happened different clock with other (maybe in nano second)?
    if you mean lost sync is no clock in BTS, BTS will off, so all MS will handled by other BTS. In our system BTS have Clock generate (From GPS) ,BSC (From GPS) and MSC (From other Switching or Clock MASTER). and all subsystem have Clock Backup (aproximatly 8 Hours) for handled system if clock source off.

    #42033 Reply
    Geoff
    Guest

    Hi Phaysal, firstly I am based in the UK.

    You need to treat synchronisation in two ways, firstly a gradual degradtion in the synchronisation of the BTS clock, BTS clocks are designed to only allow small changes in clock freq over long periods of time. In Nokia BTS you have DAC words which describe the range of adjustment for the BTS clock and when they get to certain extreme ranges will generate alarms. The KPI’s will generally show a gradual degradation and is likely that you fix the issue and then realise the performance improvements.

    Jitter however we have seen on SDH links with excessive pointer movements, which effect the BTS’s ability to utilise the PCM clock for timing. (All of our BTS’s are E1 fed, but higher bit rate circuits are used between the BTS and BSC)In this case KPI’s are difficult to quantify, depends on how often the changes are occurring.

    Hope this helps?

    #42034 Reply
    Abdel
    Guest

    I am wondering why every Interwave BTSs was using a standalone symettricom GPS. Is it to synchronize the BTSs to help make better handover succes ratio? Some vendors say that external clock is very important to keep synchronize the GSM elements specially for the handovers is this true? From my experience, our GSM network is not using any clock at all and the MSC uses its internal clock, but I have seen a lot of trunk slips at the MSC alarm db, which means there is frequency difference between the local clock and the opposite clock connected with the trunk board which results inconsistent code rates of the two sides.

    #42035 Reply
    Geoff
    Guest

    Abdel, your network should have a hierarchical synchronisation plan, for synch of the MSC, down to the BTS’s as a minimum, this will reduce your slip alarms, and probably show KPI improvements as well. GPS synchronisation of the BTS’s allows synchronised handovers to be configured to adjacent cells not sharing the same transmission/common local clock. It removes any timing differences due to transmission delays I believe. We did try it here for a little while but saw no improvements, however the BSC’s and MSC’s in our network are synchronised to GPS as a primary clock source.

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