Re: [Discuss-gnuradio] Alamouti coding

[Vanessa Gardellin]

Sure,
I am using the code on the trodeau repository and the ofdm 1tx-1rx
works, however when I try to use the 2tx-1tx with the alamouti it
doesn't.
I am not using USRPs now, but just 2 channel models without noise and offset.
The tx codes 2 consecutive symbols as the alamouti says and add 1
preamble for each antenna:
first tx: |0...0preamble10...0| |0...0|
second tx: |0...0| |0...0preamble20...0|
length preamble1 = length preamble2 = 200 occupied tones
lenght |0...0preamble10...0| = 512 = fft legth
length |0...0| = 512 = fft legth
preamble1 is created as in the ofdm 1tx-1rx i.e. it contains 1s, -1s and 0s
preamble2 contains 1s and -1s

The rx performs synchronization and alamouti decoding taking 2
consecutive symbols each time.

Sometimes the rx is able to decode the header and the pkt length, and
the first 18 character of the payload. The length of the pkt is 400
bytes.

The first error that I can notice is that when it is decoding the
payload sometimes it finds the SYNC signal which means that it finds a
preamble at a certain point of the payload before the length of 400
bytes.

So I think that the problem is in the synchronisation process but it
can be also in the equalizer computation.
Moreover the course frequency is different from 0, but how can this be
possible if I do not introduce offset in the channel?

Can someone helps me in understanding at which stage the error is?

Thank you so much

Vanessa


On Fri, Nov 18, 2011 at 1:29 AM, Kyle Zhou <address@hidden> wrote:
>> Dear all,
>>
>> I am loosing my mind trying to implement alamouti code between 2 tx and
>> 1 rx.
>> I downloaded the trodeau repository but I cannot make the alamouti
>> works.
>>
>> Any help will be appreciated, really, ANY!
>>
>>
>> Thank you
>>
>>
>> Vanessa
>>
> Would you tell us what the problem is before we can help?
> KZ
>
>



-- 
Vanessa GARDELLIN, Ph.D.
Researcher
Institute for Informatics and Telematics (IIT),
Italian National Research Council (CNR)
Via G. Moruzzi 1
56124 Pisa - ITALY
Phone: +390503153267
Room: B65/c
E-mail: address@hidden
WWW: http://www.iit.cnr.it/staff/vanessa.gardellin/
Skype: gardellin.vanessa