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Training sequence codes

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  • #41969 Reply
    Alok Aggarwal
    Guest

    What is the significance of training sequence codes in GSM.

    #41970 Reply
    Venkatraman D
    Guest

    I think, it ll be used in Error correction (in synchronisation burst) and determining signal strength (like measurement reports and RX_QUAL)

    #41971 Reply
    alexander
    Guest

    training sequence codes is a part of Air interface burst, MS knows training sequence code, so in particular part of burst MS knows what should be received, so in case of signal degradation in Air interface MS adjust it’s own digital filter such way that it reconstruct received signal to training sequence code, so degraded incoming signal reconstructed to receive correct sequence, so all other information bits also cerrectly received even in case if high bit error ration in Air interface (if bit error ration < 12.8 % then every simbol 100% reconstructed) Alex http://www.dx200.biz

    #41972 Reply
    kobe
    Guest

    why the need to set the TSC to BCC when cell is frequency hopping?

    #41973 Reply
    Sayan Patel
    Guest

    What is its relation with BCC in GSM ??

    #41974 Reply
    Paul
    Guest

    Dear all,

    @Alok :
    What need to know about Training sequence code :
    1. TSC is known both by transmitter and receiver
    2. TSC is to maintain timing and equalize the channel (Syncrhonization) as to reduce the ISI or multipath fading effects
    3.TS is very important e.i when a mobile is about to handover to neighbouring cell, it will listen to the BCCH of the neighboring cell, then it will give information to the BTS about the signal strenght, timing advance, etc. This information is brought by a set of burst timeslot. That is Trainig sequence. The receiver will examoines the received training sequence and compares it with a known one in an adaptive equalisation process and the outcome of this comparison is used to correct the transmitted information bits. That informaiton is like as signal strenght, TA, etc.

    @kobe :

    Please correct me if I’m wrong :
    – Hopping frequency (SFH) is a method where BCCH channel freq is hopped, but not the TCH.
    -Baseband Hopping (BBH) => all TCHs and BCCH are hopped.

    As we know, TSC brings the information which is carried through BCCH. The reason why we need to set TSC to BCC in freq hopping, maybe is the TSC’s functionality itself, that is TSC for BCCH, CCCH, & CBCH in which BSS sets the TSC to the O&M parameter of BCC(this requires a mandatory value where TSC value is equal to BCC value).

    I think we need more opinion about it ๐Ÿ™‚

    Dear Pix,

    Perhaps you could clarify my opinion. I’m still a little bit confuse.

    BR,

    PAul

    #41975 Reply
    Mania
    Guest

    Hi,
    As for the TSC it is sent in the Assignment Command and the Handover Command so that the MS can be in Sync. Its finction is same as explained by Paul, I does not necessarily need to be equal to the BSIC as some vendors allow you to set it to other value.
    As for BBH and SFH the difference is only in hopping procedure adapted at the BTS for the MS it has to transmit each frame on a new frequency in both cases.
    In BBH a single call’s baseband signal is hopped between different physical radios ( each of the physical radio is transmitting on a fixed frequency assigned to it) so the call hops on the frequency by hopping on different radios.
    For SFH the physical radios hop on the MAL frequency and A call runs on a single physical radio until a handover / intra-cell HO is trigerred.
    For SFH having 1 BCCH and 1 Frequency in MAL hopping cannot be enabled on any radio.
    for BBH with 1 BCCH and 1 MAL frequency both radios can hop on a MAL that is the collection of both. PWRC is set to cater for correct RxLEv Reporting

    #41976 Reply
    Pix
    Guest

    Paul,

    Just a little correction : TSC is not used when the MS measures the neighbour cells. It is only used on the dedicated channel.

    I don’t know why TSC should be equal to BCC either… I read it, but I can’t prove it ๐Ÿ™‚

    regards
    pix

    #41977 Reply
    SHELDON
    Guest

    Hi all,

    I think it’s just an easy way of planning the TSC. Since the TSC in a way ‘distinguishes’ different signals(an thus help eliminate interference), it’s best to have a different TSC for cells near to each other. Since the BCC is already planned such that adjacent BTSs have different BCCs, it’s easy to plan the TSC by just equating it to the BCC. This will ensure that adjacent cells have different TSCs, and thus help minimize the effect of interference between adjacent cells.

    This is not a scientific explanation, just my opinion.

    Regards,
    SHELDON

    #41978 Reply
    Pix
    Guest

    Sheldon,

    you are correct, and this is why nobody questions this “rule”. It is a friendly rule that makes our life easier…

    …but the strange thing is that it sounds like if you don’t apply this rule, under certain circumstances, this could actually degrade your quality ! And this is where the mystery lies…

    regards
    pix

    #41979 Reply
    SHELDON
    Guest

    Hi Pix,

    It’s surely a strange rule. I don’t see why you should experience a quality degradation.

    In ericsson, the restriction is only on channel group 0. on other channel groups, you can assign a TSC which is different from the BCC.

    Regards,
    SHELDON

    #41980 Reply
    Paul
    Guest

    Dear Pix,

    So, based on your statement (TSC is not used when the MS measures the neighbor cells. It is only used on the dedicated channel), what signaling is used for Handover? this should be BCCH right? Then, How does the MS listen/know the BCCH of the neighboring cell without Training Sequence? Then, how about re-selection?

    From Mania’s statements, TSC is also sent in the Assignment Command and the Handover Command to syncrhonize. So, I’m a little bit confused about it.

    Could you explain it again Pix?

    Thanks A lot.

    Paul

    #41981 Reply
    pix
    Guest

    paul,

    indeed, it is confusing ๐Ÿ™‚
    a “reduced” TSC is used in normal burst, to help the MS fine-sync : thanks to it, the MS is able to extract the useful contents of the burst and perform equalization.

    the “long” TSC is transmitted on the SCCH (in the BCCH timeslot), and it is used for almost the same purpose : the MS uses this sequence to be in perfect sync with the timeslot “rythm” of the cell. After listening to the TSC, it knows when is the start and end of the BCCH bursts.

    The MS doesn’t “listen” to the neighbour cells, it just “measures” the BCCH level. Once in a whilem it decodes the neighbour BSIC, but it doesn’t try to sync with the neighbours.

    During HO procedure, the BSC sends the HO COMMAND to the MS. In this HO CMD, the TSC is indicated so that the MS is able to find the “reduced” TSC located in the middle of the normal bursts of the neighbour cells. This is needed because the MS didn’t previously listened to the BCCH of the neighbour. Therefore, it cannot know the TSC ๐Ÿ™‚

    I hope it is a little clearer…

    regards
    pix

    #41982 Reply
    Mania
    Guest

    Hi Paul,
    Just to add to your question. The MS usually only measures the level of the BCCH in the faster inner loop and then of the top levels measured it uses the idle TS in Multiframe to decode the BSIC and other information on that BCCH to be reported in UL measurement reports.
    Now my confusion is whether the decoding of neighbours’ BSIC is TSC assisted or unassisted. and if so is it using blind equalization techniques for reading neighbour’s BSIC

    #41983 Reply
    Pix
    Guest

    Mania,

    Quiz Time !!

    On which burst is broadcasted the BSIC ?

    In this same burst, what is the other information ?
    ๐Ÿ™‚

    So I assume that the MS probably uses the TSC to fine-tune and properly decode the BSIC.
    I can’t even start looking for it in the 3GPP, wouldn’t know which doc to look at.
    it is probably hidden between the thick book called “how to build a Mobile Station, Layer 1” and the DVD’s of “Biography of a GSM burst, Complete Seasons 1 to 10”.

    Don’t want to spoil, but the burst eventually dies, and ressucitates as a Scrambling Code.

    Regard,
    pix

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