Re: [Discuss-gnuradio] gr-lte updated to GNU Radio 3.7 API

[Tom Tsou]

On Thu, Dec 19, 2013 at 3:07 PM, Johannes Demel
<address@hidden> wrote:
> Currently synchronization doesn't support fractional CPs. Besides this,
> reducing the sample rate helps a lot to make it run faster. Only thing to
> keep in mind though, having a different number of blocks than used by the
> base station will only allow you to decode PBCH. But for a start. That's not
> much of a problem.

The fractional CP is a pain to deal with. Performing acquisition at
1.92 Msps, though, is quite reasonable and is appropriate for 1.4 MHz
LTE channels anyways.

UE side LTE decoding is inherently a multirate process. PBCH decoding
should ideally be performed at the reduced sample rate because any
data outside of the inner 6 RBs provides no useful information to the
search and decoding process. The same concept extends to any channel
configurations below the full LTE 30.72 Msps rate. But, since the
channel bandwidth is unknown until PCBH acquisition, the receiver
should, ideally, support all rates and dynamically switch between them
as needed.

Practically speaking, the issue with real-time operation on USRP type
devices is that we can't switch device sample rates without breaking
symbol timing or slot alignment. That means running a fixed device
rate and multiple resampling chains to cover the desired channel
bandwidths.

But yes, sticking with one sample rate avoids all of the above, and is
a much simpler way to start. Perhaps multirate handling is something
to consider for future development. If there were only more hours in a
day...

  -TT