Hi,

I have a quite specific question. Perhabs somebody with technical insight
can help me:

The EFR algorithm converts 20 ms. of voice (which would be 160 bytes in
plain G711 encoding) into 244 bits = 30.5 bytes.
In the GSM specification however, two additional bytes are added. One byte
is used to protect the 65 most important bits with a CRC, the other byte is
used to to add redundancy for 4 selected bits.
These 4 bits are transmitted in 12 bits repeating each bit two times.

OK - this was the information. Now the question:

How should these redundant bits be treated? In my world redundancy means
identical. However, I have seen the T68i from SonyEricsson to produce a
strange pattern - for instance 101 or 110. I think the only valid pattern
should be 111 or 000.
Does anybody have a comment? - Or perhabs point me to the right group if
there's a better forum for my question.

Kind regards and thanks in advance
Kim Hyldgaard

Hi Kim,

According to my knowledge, the 16 redundancy bits are created from the
CRC and repetition bits.

For more details, please refer to the relevant ETSI/3GPP standard, which
in this case is GSM 05.03.

You can access the specification for example here:

http://www.3gpp.org/ftp/Specs/latest...s/0503-621.zip

I hope this answer is of some value to you.

Regards,
Antti


Kim Hyldgaard wrote:
>
> Hi,
>
> I have a quite specific question. Perhabs somebody with technical insight
> can help me:
>
> The EFR algorithm converts 20 ms. of voice (which would be 160 bytes in
> plain G711 encoding) into 244 bits = 30.5 bytes.
> In the GSM specification however, two additional bytes are added. One byte
> is used to protect the 65 most important bits with a CRC, the other byte is
> used to to add redundancy for 4 selected bits.
> These 4 bits are transmitted in 12 bits repeating each bit two times.
>
> OK - this was the information. Now the question:
>
> How should these redundant bits be treated? In my world redundancy means
> identical. However, I have seen the T68i from SonyEricsson to produce a
> strange pattern - for instance 101 or 110. I think the only valid pattern
> should be 111 or 000.
> Does anybody have a comment? - Or perhabs point me to the right group if
> there's a better forum for my question.
>
> Kind regards and thanks in advance
> Kim Hyldgaard