- This topic has 13 replies, 1 voice, and was last updated 12 years, 6 months ago by pix.
9th November 2008 at 22:27 #54613abdelGuest
For the same power class MS, 1800 MS have lower output power then the 900 MS.
What is the reason for this?11th November 2008 at 17:13 #54614pixGuest
both bands use different “bit” codes for their power class. I don’t know the actual reason behind, but it sure is very messy !!12th November 2008 at 12:58 #54615abdelGuest
regarding the previous question,I have another question.
Now for the same TRX power class, which band TRX have highest output power? 1800 BTS or 900 BTS?
And I also found that,for 1800 MS,receiver sensitivity is higher then 900 MS.(Means 1800 downlink received level have to be better then 900 to receive coverage).I can’t understand the reason also for that.12th November 2008 at 15:31 #54616pixGuest
I don’t know about the TRX power class, but i can just tell you that usually a 1800 TRX has a max power output which is slightly less than 900 TRX. By 1 or 2dB usually.12th November 2008 at 19:15 #54617pixGuest
the rx sensitivity is the same between 1800 and 900, the only difference is in the propagation. Usually, one assumes 10dB difference between 900 and 1800.
For instance, in urban area, one antenna transmits:
GSM900 at 45dBm
DCS1800 at 45dBm
at 1km, a MS measures:
GSM900 = -80dBm
DCS1800 = -90dBm
(this is just an example)
a MS is supposed to be able to understand a GSM900 and DCS1800 signal down to -102dBm at least.13th November 2008 at 14:28 #54618abdelGuest
ya level must be worse in 1800, compare to 900 as 1800 have higher path loss.
As coverage is poorer in 1800 compare to 900,what is the meaning of less TRX output power in 1800? I mean as pathloss is higher,so TRX output power should be more to enhanced the coverage.13th November 2008 at 15:28 #54619pixGuest
i agree with you, but the TRX power is not only a matter of what “should” be done. More often, it is driven by cost.
If you want a high power TRX in DCS1800, it exists, but it’s more expensive. Power supply is bigger, etc.
A TRX1800 at the same price than a TRX900 will always have a bit less output power. I know that 1dB is not neglictible, but i doubt you that anyone has deliberately chosen to have 1dB less in DC1800 ! It’s just engineering constraint for the same cost.13th November 2008 at 15:40 #54620abdelGuest
thanx again Pix.13th November 2008 at 19:45 #54621AbdelGuest
Hey who is that guy using my name. kkkk then from now I am Abdel33 from Somalia.
Abdel3314th November 2008 at 08:15 #54622yanGuest
can you please tell me what are the things make 1800 less than 900 by 10 dB.14th November 2008 at 08:45 #54623RHGuest
Free space path loss=32.44+20Log(f)+20Log(d)
d=distance between MS and BTS.
So,you can see from tha formula that,as f (Frequency) is higher,path loss will be higher.
So,at a same distance,1800 band should have lower coverage then 900 band due to higher path loss.14th November 2008 at 10:41 #54624pixGuest
free space loss will tell you that there is a delta of 6dB.
then you add 3dB of additional loss (more attenuation by trees, buildings, etc.)
then you add 1dB due to TX difference
regards,15th November 2008 at 08:23 #54625YanGuest
the TX is 3 dB difference or 1?16th November 2008 at 17:39 #54626pixGuest
TX difference is purely vendor dependent. For Alcatel, it’s about 1dB difference (comparing within the same family of TRX).
For others, it might more, or less.