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uplink/downlink

Viewing 15 posts - 1 through 15 (of 17 total)
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  • #35077 Reply
    shalini
    Guest

    i would like to know why there r 2 seperate frequencies and why a guard band between these two frequencies when the whole slot of 890-960 is allocated for GSM

    #35078 Reply
    phanesh .k
    Guest

    The two freq are 890 to 915 is for
    reciver 935 to 960 for transmission
    the guard band is 20 mhz to maintain the isolation between trans and reciver if u need any furthe clarification mail me

    #35079 Reply
    Zahid
    Guest

    If to ask another question in the same context , why the uplink is higher frequency than downlink ??

    #35080 Reply
    Sachin Aneja
    Guest

    hi Zahid,

    Uplink frequency is from MS to BTS and Downlink frequency is from BTS to MS. BTS has o/p power of 20 watt and MS has o/p power of 2Watt.BTS has already higher power than MS, so in order to maintain syncronization between two Uplink frequency is lower than downlink.

    I am not sure this is the right answer of yourquestion so, if u came to know about some other reason for this, then plz tell me also.

    Regards

    Sachin

    #35081 Reply
    Mostafa
    Guest

    Hi, Sachin,

    BTS has a power of 50 watts
    ( 47dbm) & not 20 watts.

    Regards.

    #35082 Reply
    Paul
    Guest

    Response to Mostafa : Actually depends on the equipment you are using. Regulatory bodies in the country may also restrict the maximum EIRP and hence the output power after the PA.

    Response to Sachin : The term syncronization is not correct in the context. The line of thought you were following is correct.

    The higher the frequency, the high the path loss. The power-limiting link when calculating the link budgets for GSM is in most cases (where the BTS has output power far larger than MS)the uplink hence in an attempt to favour the weaker link, the lower frequencies have been assigned to the uplink.

    Note that this is applicable to almost all wireless communications systems.

    Paul

    #35083 Reply
    Mostafa
    Guest

    To paul: The nominal output power is 47dbm for GSM 2 phase, and of course, depending on the link budget you can regulate your power.

    Example from Ericsson :
    RBS 2202 : 47dbm. (nominal)
    RBS micro : 33 dbm. ( nominal)

    #35084 Reply
    sachin aneja
    Guest

    hi paul,

    plz confirm me BTS O/P power. i think i m right that BTS power is 20 Watt.(47dbm). According to mustafa 47dbm =50 watt. is it true.if yes then tell me how?

    Regards

    Sachin

    #35085 Reply
    Kiran KV
    Guest

    Hi sachin,
    I am confirming that 20 watt is not equal to 47 dbm.
    47 dbm = 51.10 Watts
    For more details click on this link
    http://www.hirose.co.jp/cat2002e/300/e30000004.pdf

    regds
    KV

    #35086 Reply
    Roberto
    Guest

    1) First of all,to find out the power in dBm :

    P[dBm]=10*log( P[mW] )

    20W => 10*log(20000 mW)=43dBm
    50’11873W => 10*log(50118’73 mW)=47dBm

    2) The reason for using higher frequencies in the downlink and lower frequencies in the uplink is power saving in the batteries of the mobile station.
    Transmitting in high frequencies involve more power consumption than transmitting in low frequencies.As the battery in MS is limited due to its mobility, power availability in BTS is greater, and low frequencies are used by the MS to transmit.

    In wireless Satellite systems, satellites use low frequencies to transmit in order to save battery.

    #35087 Reply
    Zahid
    Guest

    Hi kiran,thanx for your comments and welcome u,

    also i wold like to thanx buddies like roberto pual ,mostafa,etc.

    plz I would like to say my question in other perspective. i.e. in sattelite communication.
    why the uplink frequency is higher than downlink.

    thank for your time and efforts.

    #35088 Reply
    Kiran KV
    Guest

    In the satellite communications the uplink frequency will always be higher than its downlink. This is because the higher frequencies suffer greater spreading or free space loss than a lower frequency.

    #35089 Reply
    Zahid
    Guest

    Thank you kiran. Can u plz tel me more about that , i mean whats the technical reason behind it. like u said lower frequency offer less resistance , but why??? i mean what r the factors???

    thank you for your time

    Zahid

    #35090 Reply
    madan
    Guest

    in satellite comunications
    the line of sight has to be very accurate hence they use lower frequency for downlink

    regards
    madhu

    #35091 Reply
    sourabh
    Guest

    any body here wud tell me wat is the exact reason why uplink frequency is greater than downlink one

Viewing 15 posts - 1 through 15 (of 17 total)
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