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Re: [Discuss-gnuradio] use of CCSDS 27 encode/decode

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] use of CCSDS 27 encode/decode
Date: Mon, 30 May 2016 08:45:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

Hi Ekko,

CCSDS27 is really old. In fact, it was really just discussed hours ago to remove it from future versions of GNU Radio; so if you feel like it might not be the right FEC for your application, feel encouraged to use other stuff!
However, there's two things happening to your source:

1. Four byte offset:
From the decoder documentation:
This block is designed for continuous data streaming, not packetized data. The first 32 bits out will be zeroes, with the output delayed four bytes from the corresponding inputs.

2. half your bits are interepreted as erased bits. For that, decoding performance is not half bad:
The input is a stream of (possibly noise corrupted) floating point values nominally spanning [-1.0, 1.0], representing the encoded channel symbols 0 (-1.0) and 1 (1.0), with erased symbols at 0.0.
But you're feeding it 0 and 1 instead of -1 and 1 ! So, use a scale=2 in your char_to_float, and add_const -1

Best regards,

On 30.05.2016 05:58, Ekko wrote:
hello all
i want to use CCSDS 27 encode/decode ,so i write a grc to test these two block without hardware,
but i got he dest data is not same with the source data,
so is there some wrong in my grc.

these is the source file and dest file in my  grcand my grc file

thank you


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