- This topic has 16 replies, 1 voice, and was last updated 17 years, 8 months ago by AlexSh.
22nd February 2003 at 13:56 #35077shaliniGuest
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 GSM24th February 2003 at 13:25 #35078phanesh .kGuest
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 me1st May 2003 at 20:33 #35079ZahidGuest
If to ask another question in the same context , why the uplink is higher frequency than downlink ??3rd May 2003 at 10:35 #35080Sachin AnejaGuest
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.
Sachin6th May 2003 at 10:46 #35081MostafaGuest
BTS has a power of 50 watts
( 47dbm) & not 20 watts.
Regards.7th May 2003 at 04:05 #35082PaulGuest
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.
Paul7th May 2003 at 19:02 #35083MostafaGuest
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)10th May 2003 at 11:52 #35084sachin anejaGuest
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?
Sachin12th May 2003 at 06:31 #35085Kiran KVGuest
I am confirming that 20 watt is not equal to 47 dbm.
47 dbm = 51.10 Watts
For more details click on this link
KV12th May 2003 at 11:16 #35086RobertoGuest
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.12th May 2003 at 13:34 #35087ZahidGuest
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.13th May 2003 at 06:46 #35088Kiran KVGuest
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.14th May 2003 at 16:52 #35089ZahidGuest
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
Zahid16th May 2003 at 16:18 #35090madanGuest
in satellite comunications
the line of sight has to be very accurate hence they use lower frequency for downlink
madhu13th August 2003 at 07:02 #35091sourabhGuest
any body here wud tell me wat is the exact reason why uplink frequency is greater than downlink one