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trgput kbps / tbf>kbps / pdch

  • This topic has 10 replies, 1 voice, and was last updated 8 years ago by bill.
Viewing 11 posts - 1 through 11 (of 11 total)
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  • #63602 Reply
    Paul
    Guest

    Dear Optimizers,

    Is there anyone know why the indicator of throughput kbit/s per tbf has higher value than that of kbit/s per PDCH? This indicator was shown in ALU GPRS Telecom NPO.

    As we know, 1 user has 1 TBF (minimum), but also can have more than 1 TBFs (of course it gives higher throughput). In ALU parameter, we have MAX_DL_TBF_per SPDCH,also MAX_UL_TBF_per_SPDCH and MAX_PDCH_per_TBF.

    What is the correlation with throughput?

    Thanks,

    Paul

    #63603 Reply
    Pix
    Guest

    Hi,

    I think you are confusing the terms. The TBF is the group of PDCHs allocated to one user.
    The PDCH is one GPRS timeslot.

    The throughput of the PDCH depends on the coding schemes. If 2 users are sharing one PDCH, with user 1 using it 50% of the time at 30kbps and the other user using it 50% of the time at 40kbps, then the PDCH throughput is 35kbps.

    One user can have for example 4 PDCH at 50kbps each.? In this case, the TBF throughput is 200kbps.

    Hope it clarifies the concept.

    Regards
    pix

    #63604 Reply
    ALU
    Guest

    Dear Pix,
    What about the indicator “Kbit/sec per cell”(GTRPDDCLA GPRS_DL_useful_throughput_radio_cell_avg)? How is it ocmputed? and also as far as I know, its value is not reliable in NPO especially on Cellzone level?Your comments in this regard would be highly appreciated.
    Thank you.

    #63605 Reply
    pix
    Guest

    hi,

    i forgot how it is computed, but you can check the formula. at cell level, the value should be the total amount of bytes transfered on the whole cell (sum of PDCH RLC bytes) per hour.
    At cell zone, the aggregation could be wrong. It should be an average aggregation,not a “sum”.

    the throughput per cell is not very useful anyway (imo), perhaps it can be used to dimension the abis (but I know better indicators for that).

    regards
    pix

    #63606 Reply
    Paul
    Guest

    Dear Pix,

    1. According to 1 TBF for one user, then if we set MAX_UL_TBF_per_SPDCH =4, then in 1 PDCH can be used up to 4 users right (in high PDCH Utilization at that time)?
    So if user A has 20% of time at rate 30kbps, user B has 30% of time at 40 kbps, user C has 30%of time at rate 60 kbps, and the last user D has 20% at rate 50 kbps, then the PDCH throughput would be ==> (0.20*30 kbps + 0.3*40kbps + 0.3*60kbps +0.20*50)
    ==> 6 kbps + 12 kbps + 18 kbps + 10 kbps = 46 kbps. But for the TBF throughput of each user is : user A has TBF throughput 6 kbps, User B 12 kbps, User C 18 kbps, user D 10 kbps.
    The average TBF troughput would be 46 kbps/4=11.5 kbps.
    Please correct me if I’m wrong.

    2. Then, if we set MAX_PDCH_per_TBF=5, it means that 1 user can have PDCH timeslot up to 5 PDCHs.Well, i guess that this condition could be reached when there are still many idle PDCHs (no high PDCH utilization at that time).
    Then if the rate is 50 kbps at each, then that user can have TBF throughput 250 kbps, but the PDCH only 50 kbps. Please correct me if I’m wrong.

    3. Well, I’m actually a little bit confused. You stated :”The TBF is the group of PDCHs allocated to one user”. But you gave an example “If 2 users are sharing one PDCH”. Does it mean that in that 1 PDCH, there are 2 TBFs (1 user 1 TBF) ?

    From my understanding, and based on ALU parameters, it means that 1 TBF can have many PDCHs (no.2) and 1 PDCH can have many TBF (no.1).

    Feel free to discus Pix, I would be grateful to know your response.

    Anyway, thank you so much:)

    Please help me to answer no 1 and 2, I’m asked by my boss to count how many users (max) can be allocated in 1 BTS/Cells.

    Regards,

    Paul

    #63607 Reply
    pix
    Guest

    paul,

    1 : 100% correct
    2 : 100% correct
    3 : as you said
    1 TBF can have many PDCHs (no.2) and 1 PDCH can have many TBF (no.1).

    Example (using your example)
    User A has 1 TBF w/ 2 PDCH
    User B has 1 TBF w/ 2 PDCH
    User C has 1 TBF w/ 1 PDCH
    User D has 1 TBF w/ 1 PDCH

    on PDCH 1 (= timeslot 1 of the TRX)
    user A has 20% of time at rate 30kbps, user B has 30% of time at 40 kbps, user C has 30%of time at rate 60 kbps, and the last user D has 20% at rate 50 kbps, then the PDCH throughput would be ==> (0.20*30 kbps + 0.3*40kbps + 0.3*60kbps +0.20*50)= 46 kbps

    on PDCH 2 (= timeslot 2 of the TRX)
    user A has 40% of the time at rate 30kbps, user B has 60% at rate 40kbps
    (0.40*30 kbps + 0.6*40kbps) = 36kbps

    PDCH throughput of PDCH 1 = 46kbps
    PDCH throughput of PDCH 2 = 36kbps

    TBF throughput of user A = 0.2*30kbps + 0.4*30kbps = 18kbps
    TBF throughput of user B = 0.9*40 = 36kbps
    TBF throughput of user C = 0.3*60kbps = 20kbps

    Notice that one user will get the same “max” throughput on all of its PDCH. For example user A has a max throughput per PDCH of 30kbps. That depends on the MCS used. If MCS is equal to MCS-4, then it is MCS4 on all the PDCH.

    I think your whole idea of the TBF and PDCH is excellent, so don’t let me confuse you ๐Ÿ™‚

    Best Regards,
    Pix

    #63608 Reply
    Paul
    Guest

    Dear Pix,

    Thank you so much Pix. It becomes easier to understand the throughput of GPRS concept.

    No Pix, your answer doesn’t confuse me. But remember, we are pushed to think and develop ourselves when we meet problem we couldn’t solve ( confusing problem) ๐Ÿ™‚

    Best Regards,

    Paul

    #63609 Reply
    pix
    Guest

    paul,

    you’re right, technical problems are always a challenge…
    but me making myself clear is another kind of problem ๐Ÿ™‚
    human communication through web forums generates confusion by itself.

    I’m waiting for the day when forums will be based on telepathy ! :))

    #63610 Reply
    ALU
    Guest

    Dear Guyz,
    Interesting Q&A Session going on so I decided to drop by.I have a few questions of my own regarding GPRS throughput(slightly irrelevant to the previous discussion but I am sure both of u wouldnt mind slight deviation as long as its related 2 throughput :P). Feel free 2 confuse me aswell coz the questions are already quite confusing ๐Ÿ™‚

    1:The max no of TSs a user can have depends on MS Multislot Class aswell.Now mostly the max TSs that a user can have in one directions is 4(eg 4+1 for Multislot Class 8)[Excluding Multislot class 30-33]. So, even if we increase MAX_PDCH_per_TBF beyond 4 or 5, it will not have any impact in increase in throughput.Am I correct?

    2: Consider a site having 1 E1 and of configuration 4/4/6.So as one TRX requires 2 Abis TSs so total no of Abis Ts’s used would be 31 ie..(14*2=28 for data + 3(or 2)for Signaling).So, it means that we dont have any Extra Abis TSs configured for the site.Now excluding Bonus+Extra Nibbles, we are only left with BASIC Nibbles per cell.
    Now as we know that inorder to achieve MCS9, we need to have around 5GCH(4.49Abis nibbles)
    If we consider
    Cell A(4 TRX):Total Basic Abis nibbles =(4*8)=32
    Max_PDCH_High_load=4
    MS MULTISLOT Class 8(4+1)for all users
    so one user using 4 PDCH would require=(4*4.5)=18Abis Nibbles
    So, with this calculation, we can have only one user using MCS9 simultaneously in this cell? because we dont have another 18 Abis Nibbles(only 14 left).Am i right?

    3:If an MS Multislot Class is 8(4+1), so can that user use less than 4 TSs(PDCH) or is it compulsory for it to use 4(to satisfy its Multislot Class)?

    #63611 Reply
    pix
    Guest

    hello,

    please, join in !
    1/ yes, correct!

    2/ well, your computation is correct BUT why not take into account the bonus nibbles ???
    in a 4/4/6 BTS, you would have 3 BCCH + 7 SDCCH, that’s 10 bonus nibbles !
    Just for clarification :
    – Extra & Bonus nibbles are shareable at BTS level.
    – Basc nibbles are shareable only within the same cell.

    3/ “sub-“optimal allocations are possible, of course. The MFS will try to allocate as many PDCH as possible (up to the multislot class limit). But if it can’t then it will allocate less. The MS is able to support those sub-optimal configurations. It can even support PDCH configurations with holes. example : the MS gets (PDCH 1 + PDCH 2 + PDCH 4) while the Timeslot 3 is used for somebody else.

    regards
    pix

    #63612 Reply
    bill
    Guest

    dears, how can we statistically measure throughput per user or throughput per tbf?

    usually we get statistically is the throughput per timeslot, any ideas?

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