[Tinyos-help] Acoustic Localization

[Michael Collett]

Hi Azhar,
 
It's been a while since I worked on this but my understanding is:
 
*The chirps are added on top of each other at the raw data level. This is to increase the signal to noise ratio.
*The sample rate of the microphone is determined by ADC.getContinuousData() and is 15kHZ (I think)
*The Buffer can hold 3000 samples, but more if they are added on top of each other.
*The 850 sample chirp width is what is used to estimate where the acoustic pulse lies in the buffer, and hence it's start point (which is used to estimate the acoustic propagation delay.
 
Hope this is correct and useful,
 
Mike

-----Original Message-----
From: Muhammad Azhar [mailto:leo_az_83 at hotmail.com]
Sent: 29 September 2007 13:11
To: Michael Collett; mnawaz at cse.unsw.edu.au; schip at santafe.edu; janos.sallai at vanderbilt.edu; mmaroti at isis.vanderbilt.edu
Subject: FW: [Tinyos-help] Acoustic Localization


Hi,
 
   Sorry for forwarding this email to you, but I have not received any replies for my question posted below.  As my deadline is coming soon, it'd really be great if you could help me.
   Really waiting to hear from you.  Thank you.
 
Regards,
Azhar





  _____  

From: leo_az_83 at hotmail.com
To: tinyos-help at Millennium.Berkeley.EDU
Subject: RE: [Tinyos-help] Acoustic Localization
Date: Fri, 28 Sep 2007 14:27:16 +0000


I think I might have found some answers to my first question (but I might be wrong!!!).
 
Looking back at OutsideRangingSensorM, if buffer has been filled up for a single chirp (i.e. all 850 samples have been filled), then the next MicADC.dataReady() would return FAIL.  Thus, in AcousticMultiSamplerM, it causes state to be changed to STATE_IGNORING.  It simply waits for tickCount to be decremented to 0 before the next chirp is sampled.  Thus, buffer[i] simply "adds on" to the previous value of the chirp at approximately the same "sound level" since for each interval, the chirp comes before the silence period.  This carries on until all 16 chirps has been sampled, after which f! iltering is done.
 
However, I'm still not too sure how 850 samples was derived for 1 chirp.  Also, I am assuming that the shortest "chirp + silence" period still produces more than 850 samples in order for my above explanation to hold true (but is this assumption correct?).  Basically, the answer to the second question I posted could probably give me a clearer picture.

Looking forward to your advise on this matter.  Thank you.
 
Regards,
Azhar


  _____  

From: leo_az_83 at hotmail.com
To: tinyos-help at Millennium.Berkeley.EDU
Date: Fri, 28 Sep 2007 05:44:39 +0000
Subject: [Tinyos-help] Acoustic Localization

Hi,
 
(Using T1.1.15, micaz)
 
   With regards to the implementation of acoustic localization by Vanderbilt University, I have some queries pertaining to certain issues:
 
- In OutsideRangingSensorM, the processing (i.e. filtering) is done after AcousticMultiSampler.ReceiveDone() is signalled.
  Thus, does it mean that the buffer array, which consists of a maximum of 850 samples, contains the samples of all 16 chirps before filtering is done?
 
- In AcousticMultiSamplerM, when calling MicADC.getContinuousData(), what is the frequency of data that is sampled for 1 chirp approximately?
  I see that 1 jiffy = 1/32768 s.
  Thus, since rate is set to 100, Timer.fired() would be signalled after every 100/32768 s.
  Therefore, since the "longest" silence + chirp period is 27, MicADC.getContinuousData() would return the greatest number of samples for a single chirp within 2700/32768 s.
  (By the way, BUFFER_LENGTH was defined to be 850 - how was this derived?)
  However, I'm still clueless on the sampling frequency of MicADC.getContinuousData().
 
[FYI - I read through AcousticMultiSampler.txt where it was mentioned that "upon receiving an acoustic beacon message, this component (AcousticMultiSampler) will turn off the radio and will sample the microphone at specified time intervals at around! 16 KHz", but I still do not have any idea how these values are derived.]
 
 
  Your help would be very much appreciated. Thanks.
 
Regards,
Azhar



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