RF Contest!

Hi Pix
As far as I Know,SAIC mobile stations were designed to demodulate a GMSK carrier and suppress GMSK- modulated interference. These mobile stations are typically designed to suppress one dominant interferer. They can be used to suppress the second sub-channel in an AQPSK modulated signal and therefore can be used as receivers for the VAMOS technique.

However, the SAIC methodology does not exploit the fact that when AQPSK modulation is used, the second sub-channel has a constant 90 degree phase shift with respect to the first sub-channel. Moreover, a SAIC receiver will experience the second sub-channel as the dominant interference and it will lose effectiveness suppressing additional external interferers,hence low SCPIR compared to VAMOS level 1 MS.

VAMOS level 1 MS exploit knowledge of the two TSC’s. When an ordinary QPSK demodulator or a proper modification of a QPSK modulator to deal with AQPSK is used, then joint detection is performed. This type of receiver offers optimal performance whenever the signal is corrupted by Gaussian white noise only. But such a receiver is unable to effectively suppress any external interference.Hence higher SCPIR compared to SAIC level 1 MS and so comes the need of SAIClevel 2 MS.

Br\\
Bijoy

Hi bijoy,

You are describing the difference between VAMOS-I/SAIC and the VAMOS-II. The latter is able to effectively suppress the AQPSK interferer.

VAMOS level 1 MS is just a SAIC MS which is able to use the TSC Set 2. There is no special interference algorithms based on AQPSK usage. Therefore, their “SCPIR thresholds” are the same.

It can be seen in the 3GPP “MUROS” tech spec. The link level simulations show no difference between SAIC and VAMOS-I, as far as I remember. They both are described as “DARP”, with no further difference.

VAMOS-II on the other hand is much more efficient and can work with SCPIR as low as -10dB !

For SAIC/VAMOS- I, the SCPIR must be greater than -4dB.

Regards,
pix

Yes you are absolutely right, that’s a good & valid point.

But I wonder by how many dB’s the SCPIR is improved ? max 2dB I would say ?

Also, this software enhancement might actually benefit the paired MS too :
If a VAMOS-I MS is paired with a SAIC MS, then both are equally enjoying the orthogonality of their TSC. In this case, the SAIC MS is as efficient as the VAMOS-I.

But when a SAIC is paired with a SAIC, that’s where there is a slight degradation.

It’s great to discuss with you because you are very educated & have a very sharp mind 😉

Regards

hi paraHO,

you snooze, you loose !

“What happens SCPIR in cases where single MS has activated two radio channels?”

Why would a MS have 2 radio channels ?

VAMOS works only for TCH, and therefore each MS needs only one TCH. As if it were in a regular TCH timeslot.

4 MS (a, b, c, d) on one VAMOS TCH timeslot means :
2 MS (a, b) in Half-Rate, paired on the HR-subchannel 0. a is on vamos-subchannel 0, b is on vamos-subchannel 1.

2 MS (c, d) in Half-Rate, paired on the HR-subchannel 1. a is on vamos-subchannel 0, b is on vamos-subchannel 1.

In the physical TCH timeslot, there is two HR subchannels, which are physically independant (as an image : HR0 = even bursts and HR1 = odd bursts).

On HR0 (even bursts), the a and b are tx-ing and rx-ing at the same time.

your turn to shoot, bijoy. I’m so exhausted from work, I need to have fun !

Hi,

Need some information regarding SACCH position for VAMOS :

Shifted SACCH is only for DTX cases?
If above is true then what will be SACCH mapping for User1 if both the
calls are full rate (VAMOS)