- This topic has 10 replies, 1 voice, and was last updated 11 years ago by Imtiaz.
4th August 2006 at 01:10 #45507SureshGuest
How do we finalise the AMR RLT value.Does it vary with the Band used for GSM like 850/900/1800??4th August 2006 at 01:31 #45508PixGuest
RLT = Radio Link Time-out ? If yes, it is not linked to the frequency band or the codec used…6th August 2006 at 02:55 #45509sureshGuest
wanted to know the values of RLT normally used for EFR, AMR-HR, AMR-FR. I dont think so we can have a single value for all.6th August 2006 at 02:58 #45510sureshGuest
RLT-Radio link timeout…..6th August 2006 at 03:46 #45511PixGuest
in alcatel, the RLT is set identical for all codecs and all frequency bands. I still don’t understand why the RLT is impacted by the codec…
RLT is the timer that tells the maximum time during which MS or BTS are allowed to not receive a good signal (= cannot decode SACCH frames). When this timer expires, ms or bts will emit at full power.10th August 2006 at 05:22 #45512sureshGuest
Due to better coding in AMR, the speech quality is improved but the SACCH degrades. Hence you find that the call drops even though the speech may be good.10th August 2006 at 14:14 #45513VanderleyGuest
I think that SACCH coding is better than AMR FR8 codec anyway. Also the information in SACCH is equally important to EFR; AMR, etc.
There is no reason to have good speech and no TA or system info.11th August 2006 at 02:29 #45514PixGuest
The SACCH degrades ? How come ? It’s nice if you can explain because I’m not familiar with the SACCH frames contents and the way it is processed…14th August 2006 at 14:15 #45515VanderleyGuest
SACCH is the same, the speech improves7th September 2011 at 13:10 #45516Karan SinghGuest
AMR Value for RLT is a little bigger as compared to Non AMR, hence you can find that GSM HR RLT set as 28 & AMR HR set as 32 in few systems, this is because in worse c/i conditions AMR is expected to perform better thereby giving a greater chance to the end user to establish his call again in bad radio.22nd September 2011 at 07:15 #45517ImtiazGuest
This portion from a document may explain why RLT values can depend on codec:
AMR provides robust codecs (e.g. AFS4,75, AFS5,9) that allow the network to operate at low C/R values and still to provide sufficient voice quality. On another side, error protection scheme for SACCH (FACCH) was designed for the network using FR and HR speech traffic that can’t cope with interference level in AMR networks. This performance imbalance between SACCH (FACCH) and lower AMR FR codec modes appears as increased number of call drops due to expiry of the Radio Link Timeout timer while speech quality is reasonably good.
The problem has been solved by introducing RLT counter for UL and DL whose initial values are separately configurable for different Service Groups within Power Control object, e.g.:
– higher value for RLT for AMR calls
– lower value for RLT for non-AMR calls