Re: [Discuss-gnuradio] 3G on USRP

[Chris Kilgour]

tss ooty wrote:

> Dear GNU Radio Team & Members,
>
>   I am looking for using USRP as my development kit for 
> implementation of 3G standards 1xEvDO and 1xRTT.
>
>  
>
>   I would like to know if there is any work already done in 
> developing the CDMA2000 PHY on the USRP kit.
>   It would even be very helpful if someone points out any 
> feasibility of making cdma2000 protocol work on USRP. Is there any 
> feature or limitation on the USRP board that makes it suitable or 
> unsuitable for 3G standards 1xEVSO and 1xRTT?
>  
IMHO, your biggest challenges stem from needing custom logic, generally 
because CDMA2000 is a synchronous system with fairly tight timing 
requirements.  For example, one requirement will be power-control which 
requires the reverse channel to react to a recovered power-control bit 
from the forward channel (and hence alter the reverse power by up to 
1dB) within 500us, every 1250us.  Given the buffering latencies at each 
stage of hardware, USB, and processing time in the host, you'll probably 
have to accomplish this power control in the FPGA.  In order to extract 
power-control bits in logic you'll need a quadrature despreader and 
(masked) long-code generator there too.  The despreader will have to be 
syncronized to the network according to a pilot searcher, and if you 
hope to support soft-handoff then it will basically have to be a whole 
rake receiver done in logic.  Continuing on that line, soon you realize 
that most of the whole PHY design requires custom logic. 

If you can find a way to reduce the latencies to an acceptable level, 
then it may be possible to avoid the custom logic.  An interesting 
starting point might be a forward-only "monitor" implementation, which 
of course could be done purely in software since there would be no 
tightly-timed reverse transmissions to make. 

>  Please help me out in this regard since I am finding it very 
> difficult to evaluate the same and wondering why there is already not 
> existing an implementation in the OpenSDR project...
>
>  TIA a lot for all your help.
>
> regards,
> ./tss
>