You are right the value received from the cc2420 is the average correlation
and not LQI, by the way, do you know why it is commonly called LQI ?
In my understanding this correlation value is the average correlation value
of the first eight symbols, we get the correlation of each symbol at the
output of the correlators (16 ?, we have 16 different chips sequences, in
theory we need 16 correlators) . It is the correlation of the symbol that is
supposed to be received and the symbol actually received (S+N), where each
symbol is represented by 32 chips, (see Figure 16 at page 36 of the cc2420
datasheet. )
Regards,
Oziel
Message: 1
Date: Wed, 05 Mar 2008 18:59:25 +0000
> From: Rodolfo de Paz Alberola <[EMAIL PROTECTED]>
> Subject: [Tinyos-help] LQI and corr values
> To: tinyos-help <tinyos-help@Millennium.Berkeley.EDU>
> Message-ID: <[EMAIL PROTECTED]>
> Content-Type: text/plain
>
> Hi,
>
> I have seen in tinyos-2.x you compute the lqi as:
>
> CC2420ReceiveP.nc:
>
> metadata->crc = buf[ length ] >> 7;
> metadata->rssi = buf[ length - 1 ];
> metadata->lqi = buf[ length ] & 0x7f;
>
> CC2420PacketC.nc:
>
>
> async command error_t CC2420Packet.getLqi( message_t* p_msg ) {
> return getMetadata( p_msg )->lqi;
> }
>
> However,in the cc2420 datasheet says that this is the correlation
> value of the 8 first symbols following the SFD, which ranges [50,110],
> and it represents somehow a "chip error rate". LQI value must be later
> calculated by software to convert this value to a range of 0-255
> (either using a combination of RSSI and corr or using PER measurements).
>
> So, what I understand is that this value from tinyos is the correlated
> value of this 8 symbols instead of the LQI of 802.15.4. Is that right?
> And what this correlated value is exactly? My understanding is that is
> a correlation between the chip that is suposed to be received in the
> receiver and the chip received (signal + noise). Does that make sense
> for you?
>
> Regards,
>
> ----
> Rodo
>
>
>
> ------------------------------
>
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>
> End of Tinyos-help Digest, Vol 59, Issue 25
> *******************************************
>
--
Oziel Hernández Salgado
Cell: +52 1 (81) 157 350 61
Home: +52 (81) 821 412 02
[EMAIL PROTECTED]
www.WiseMx.com
"If we knew what it was we were doing, it would not be called research,
would it ?"
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