Re: [Discuss-gnuradio] Suggestion to Improve Some Digital Modulations Reception

[Johnathan Corgan]

On Tue, Jul 7, 2009 at 08:14, Firas A.<address@hidden> wrote:

>...some digital modulations (for example GMSK)
> reception can be improved by using a scrambling engine which is something I
> used before many years ago to improve data reception circuitry performance.

Pseudo-randomizing bit sequences to prevent long runs is a standard
radio technique, as you mention.

GNU Radio has gr.scrambler() and gr.descrambler() blocks to do this.
The first takes unpacked bits in and feeds them through a configurable
LFSR; the second undoes this operation to return the original bits.
See the 'digital-bert' example for how this is used to test the bit
error rate of a BPSK channel.

In the example digital packet radio application, we instead use a
whitener that has a pre-generated sequence of bits that we XOR the
payload with.

Johnathan