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Capability of the TETRA Equalizer on Multi-path Interference

I'm designing an indoor TETRA coverage making use of a Bi-Directional Amplifer (BDA). Due to the client's requirements, the designed coverage for the outdoor carpark is having both direct line-of-sight (LOS) from donor celllsite and its repeated signal from BDA. LOS and repeated signals are similar in strength. The BDA unit has a round-trip system delay of 15us while feeder propagation time is negligible. So, the time difference between LOS and repeated signal can assume 15us. This scenario can be regarded as multi-path interference.

Knowing that the User Equipment (UE) deploys the equalizers to handle the multi-path effect, I'm unable to find the equalizer capability requirement in the GSM Specification. For a common 2G UE of TERA or GSM, what's the minimum time spread on multi-path signals that the equalizer is able to handle?

Parents
  • 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?    

Reply
  • 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?    

Children
  • 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.