why low frequancy is used for uplink and high frequancy is

[hassanmd]

low power uplink

used for downlink?e.g 800 -915 for uplink in gsm and
925 - 960 for downlink?same in DCS!

 

[dipnirvana]

uplink at lower frequency

First understand, lower the frequency more the distance it can travel with given power.

uplink--> when handset transmit-- Battery powered
Downlink--> when DCS transmit-- Mains powered

now , since lower frequency transmitted by the handset ,it can go to higher distance with low power. low power is important bcoz' it's battery power equipment.
And for downlink the frequency is higher hence need more power to travel larger distance but power here is not a problem bcoz' normelly DCS is mains powered.

 

[vfone]

reasons for low uplink level

Is just an arbitrary choice, and doesn’t have anything in common with distance or power management.

 

[hbk2222]

frequency downlink bigger than uplink

the attenuation in the low frequency is less than high ones,so as the mobile has a limited power it uses the lower frequency.

 

[Aya2002]

why lower frequency is use in uplink?

the attenuation in the low frequency is less than high ones,so as the mobile has a limited power it uses the lower frequency.

that is correct

 

[Bhanumurthy]

why uplink use low frequency?

But however itz not the same with satellite commns.Satellite use higher uplink freq.when receiving and lower downlink freq.when transmitting

 

[vfone]

low frequency for uplink

Let’s take an example: GSM900 with 45MHz split between UL and DL, and a distance between Mobile and BS of 2 km.

UpLink = 900MHz => Free space path loss = 97.5dB
DownLink = 945MHz => Free space path loss = 97.9dB

So, is only 0.4 dB difference between UL and DL losses in free space, and probably adding fading and multipath there will be no difference.

In satellite communication is a different story due to greater distances, but not in cellular systems.

 

[hakeen]

higher frequency used for downlink

Yes power loss is the one of the concern and reason why fdown>fup

 

[dipnirvana]

downlink frequency higher than uplink

I agree with Vfone that FSL is not differing much even if u take extreme case of 800MHz(uplink) and 960MHz(downlink) than the difference is 98.07dB-96.48dB ~1.5dB it's nothing.

But may be in initial development of mobile communication , when battery was not so advanced as now. They borrowed the idea from the satellite communication. I am not sure.

 

[ghb]

i agree abirtrarily chosen, the power differences over the band are small