- This topic has 9 replies, 1 voice, and was last updated 14 years, 6 months ago by Huawei RF.
27th January 2008 at 09:53 #50632AjayGuest
Even if the C/I is good, why there is high BLER. How can we reduce BLER? Thank you28th January 2008 at 14:36 #50633PixGuest
Good C/I with bad BLER… it tends to lead to the conclusion that the TRE is faulty.
How good is your C/I ?
Which modulation scheme are you using ?29th January 2008 at 05:06 #50634AjayGuest
C/I is more than 30 and when the BLER is high then it C/I goes down to 20. We are using EDGE.
MCS1-MSC4 -> GMSK
MCS5-MCS9 -> 8PSK
Can you give some idea on TRE. What actually is TRE? Thank you29th January 2008 at 09:49 #50635pixGuest
TRE is the transceiver/receiver in the BTS (the TRX). it’s carrying 8 timeslots..
C/I of 20dB is not so good for 8PSK, especially in MCS7, 8 or 9. With such values, it can be normal to see a high BLER. What BLER do you see at C/I 20dB ?31st January 2008 at 04:32 #50636AjayGuest
In SIEMENS we basically used term TRX. So we are little bit confused in TRE. Now we got it.Well the BLER is 25. In my experience I have never face such problems like the reduction in C/I while using EDGE. Is it likely that the C/I gets reduced while using EDGE in MCS-9?31st January 2008 at 19:51 #50637PixGuest
Ok, what you’re saying now is really different than what you said before…
As soon as the transfer goes to MCS9, you see that the C/I decreases ? What happen if you force the MAX MCS to MCS7 ? The C/I is better ?
In theory, there is no link between the C/I and the MCS : the C/I is the same whichever the MCS.
But in MCS9 you much more sensitive to low C/I. I recall that MCS9 works perfectly at C/I > 29dB. So 20dB is not good enough 🙂 BLER = 25% ? That’s very bad…1st February 2008 at 03:59 #50638AjayGuest
Yes there is no link between C/I and Coding Scheme. Regarding forcing to MCS7 the C/I must be same but however we have not check for that. According to drive test team it was said that the C/I decreases after BLER occur. May be we got the wrong information from the drive test team or may be the C/I was fluctuating. Thank you for your co-operation.1st February 2008 at 15:44 #50639PixGuest
Be careful with your drive test equipment : the way they compute the C/I may be based on the BLER. It might not be a “real” C/I.12th February 2008 at 07:05 #50640What is MCS??Guest
Can you tell me what is MCS please??12th February 2008 at 07:26 #50641Huawei RFGuest
MCS: modulation and coding schemes
and coding schemes (MCSs) are proposed for enhanced packet data communications,providing raw RLC data rates ranging from 8.8 Kbps (minimum value per time slot under the worst radio propagation conditions) up to 59.2 Kbps (maximum value achievable per time slot under the best radio propagation conditions). Data rates above 17.6 Kbps require that 8-PSK modulation be used on the air instead of the regular GMSK modulation.
EDGE for Mobile Internet, 2003 ARTECH HOUSE, Emmanuel Seurre.