Capability of the TETRA Equalizer on Multi-path Interference

I'm afraid I only worked on the later 3G stuff, so I'm a bit shaky on this, but as I understood it. GSM standards don't specify any specific receiver implementation, instead giving a test spec and a performance target, leaving it up to the chip makers to decide how to meet it, but the test waveform is well tailored for 16 state MLSE. In practice all makers do more or less the same, as it's never a good idea to start with a sub optimal designs. From memory the receiver test spec calls up fading with a maximum of 5uS delay, being realistic for reflections in an urban cellular setting - after all a uS is 300metres, so five of them is 1.5km and compares to cell sizes. Any reflection that far away is likely to be noticeably weaker, maybe even comparable to the random chatter from neighboring cells.


This diagram may help you with navigating the standards numbering scheme, it is quite complicated, each team was in charge of a series of standards with a 2 digit start code, and then could create their own index, so 0501 is the first doc written by team 05 for example. There is a lot of it, literally a life's work for about 100 people for each group, and the styles are not fully aligned between groups, - and as above this is before the time I worked on 3G, so I'm not that familiar, but the structure is similar.I'd start with the handset test specs, and look the fading channel and data rates required to pass -I recall 5usec from discusssions, but I'm not sure what decoder performance is mandated with that.>

all the standards are available via the 3GPP website, even though the early GSM stuff "GERAN"
was originally developed under ETSI, it too is made available for free.
If you want a more general intro to the type of equaliser, the following is a good reference in that it contains a thorough treatment of Viterbi equalization for phase modulation in general and GMSK in particular. The book is out of print but if you can get your hands on a used copy, it is easier than the original papers by Viterbi himself. Raymond Steele, Mobile Radio Communications, IEEE Press, 1992, ISBN 0-7803-1102-7.

regards Mike

Hello Mike,

Yes, I also recall from a discussion long, long ago that GSM equalizer is able to overcome a time spread of 5us (10us round-trip) multi-path. BTW, I'll conduct a site acceptance for the new BDA. Let's check if there's some issue in the carpark area.

Thank for your advice.

Joseph

Tetra is different and has a maximum difference between direct and indirect paths of 14 Usec.   Getting enhancers to work means you have to in effect ensure that there is no direct path and only enhanced paths are available. (Tunnels are great for this).  However any car park work or other outdoor areas will struggle.  (Why do you want enhanced coverage outdoors if the direct path is ok already?    

Hello,

This query puzzles me in searching the truths. From the TETRA standard, it only mentions a performance target of 10us on equalizer and leaves it to the equipment vendor to decide the algorithms for realization. And I get the confirmation from our TETRA equipment supplier of portable radio that their testing document guarantees a time delay spread of 6.9us (13.8us round trip). The chipset should perform a little bit beyond the target requirement. That's pretty close to 14us then.

The distributed antenna system is an integrated radio network composing other public security systems, eg 5G, LTE etc. As such, we need to consider other systems' coverage needs. And they may deploy BTS for coverage enhancement.

Last, BDA vendor also revised their system delay to be 4.6us (9.2us round trip) after further lab testing. So, the scenario case should be fine to implement. It would be posted if there's any unexpected popping up during the acceptance.

Thank for all advice.

Best Rgds,

Joseph

And amplifier with even  5us delay presumably has some serious filters - one pole of a few hundred KHz or more likely a few poles and a pass band of a MHz

https://blog.minicircuits.com/rf-group-delay/

Depending on the filter steepness, and the no of filter stages, the delay increases but for all sensible filters is a few times the reciprocal of the bandwidth (in radian frequency), times the no of filter stages.

Filters normally dominate, I can't imagine that the delay in the actual amplifier is more than a few tens of nanoseconds - PCB tracks and matching network delays will be a few feet of cable equivalent.
Mike.