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Re: [Discuss-gnuradio] gr_unpack_k_bits_bb, its inverse, and higher orde

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] gr_unpack_k_bits_bb, its inverse, and higher order constellations
Date: Wed, 3 Mar 2010 13:00:40 -0800
User-agent: Mutt/1.5.20 (2009-08-17)

On Wed, Mar 03, 2010 at 11:25:56AM +0100, Mattias Kjellsson wrote:
> Hi list,
> I have been trying to send and receive higher order constellations than
> bpsk (qpsk, qam16, ...). The way I'm currently implementing this (in
> c++) is that I have a custom "pack_k_bits_bb(int bits_per_symbol)"-
> block and then feed the result into a "gr_chunks_to_symbols_bc"- block,
> and then onward in the transmitting chain.
> On the receiving side, I use a "constellation_decoder_cb"- block
> followed by a "gr_unpack_k_bits_bb"- block to get the bits back.
> This approach assumes that there are less than 8 bits per symbol, and
> that the input to the transmitting chain is unpacked bytes, which is
> also produced by the receiver.
> The question is now, how do you produce constellations with more than 1
> bit per symbol? Is there a better way to do this? Sure if one want to,
> for instance, read from a file/device the input should be packed bytes,
> but if the input to the transmitting chain is a "gr_scrambler_bb"-
> block... This is one way of doing it.

I assume that you mean 1 byte per symbol.
I suggest that you create *_ci and *_ii versions that handle 32-bits.

> Comments and suggestions on how to do this in other ways are most
> appreciated.
> BR
> //Mattias

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