From owner-freebsd-bluetooth@FreeBSD.ORG Wed Jul 23 15:02:39 2008 Return-Path: Delivered-To: freebsd-bluetooth@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 40056106568C for ; Wed, 23 Jul 2008 15:02:39 +0000 (UTC) (envelope-from awnishupadhyay@gmail.com) Received: from yx-out-2324.google.com (yx-out-2324.google.com [74.125.44.29]) by mx1.freebsd.org (Postfix) with ESMTP id 0394E8FC20 for ; Wed, 23 Jul 2008 15:02:38 +0000 (UTC) (envelope-from awnishupadhyay@gmail.com) Received: by yx-out-2324.google.com with SMTP id 8so390310yxb.13 for ; Wed, 23 Jul 2008 08:02:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:mime-version:content-type; bh=flTPupGVjjA6KNBKzhbhRhhrmVxDaH1cPHeEDIfNpa8=; b=RajGtm1t1rI2cBQu+t8VVaytxTIMf6RCgKtkSVgt6nTzUbyT6OIDHQi8QBEPPaABk+ BwQ/om+YChFUPSZ5KLplFdpCtaxnmLsgi+AQ373Q0tpBV7edVcxhvu82rfE5NfwmfbNv u3o1/0RAQXm8mhT/7wjFNmH+l+Rf/TX1yrdCs= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:mime-version:content-type; b=wHedhncfgUf7t8ronxlnaaVAOkSSNXGvXzPJ08F8S1B/7KHmClTE7wU3qZDayqlLky lXJPmN7RkoLovh6Gk4SZAwPrPAymbPREb2w0Rn3hynrlDGrpYWHDgaieefwQXq90OaPK Hq6FFu1tIYHX9QmcwpKsAX8UEuYpJd7OD/RIo= Received: by 10.151.114.9 with SMTP id r9mr203345ybm.178.1216823815730; Wed, 23 Jul 2008 07:36:55 -0700 (PDT) Received: by 10.150.51.12 with HTTP; Wed, 23 Jul 2008 07:36:55 -0700 (PDT) Message-ID: Date: Wed, 23 Jul 2008 15:36:55 +0100 From: "awnish upadhyay" To: freebsd-bluetooth@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Subject: bluetooth link quality and rssi ? X-BeenThere: freebsd-bluetooth@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Using Bluetooth in FreeBSD environments List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Jul 2008 15:02:39 -0000 Hi , In BlueZ, what does 'hcitool rssi
' return? does it return the actual RSSI value or is the output similar to the result of the HCI_Read_RSSI command as mentioned in the BT spec? The BT spec says that HCI_Read_RSSI will read the value for the difference between the measured Received Signal Strength Indication (RSSI) and the limits of the Golden Receive Power Range for a connection handle to another Bluetooth device. Put in other words, will 'hcitool rssi
' return this difference or does it give the exact RSSI value which is compared with the GRPR? I ran some test between an Nokia, Windows MObile and a Belkin BT USB device. I was measuring the RSSI value as seen by the belkin BT device (connected to a PC) while the mobiles weres moved to different locations (I was not doing any data transfer.. but I had the two devices connected and collected the data in a file). I noticed that the RSSI values were highly variable. Even two sets of observations with identical conditions were giving very different values for RSSI. So, my next question is how accurate is the RSSI value? I know the BT spec says that there can be a 6dB +/- variation. Is the result value in dB? Can I use RSSI to quantify the distance between two BT devices? Meaning lower values of RSSI -> higher distance? I was looking at other parameters (link quality, transmit power) and found that the link quality seemed to be a better indicator of the distance.. with increasing separation between the devices, the command 'hcitool lq
' was giving lower values.. meaning there was a degradation in the link quality. Any comments on this? i wanted to know the unit of link quality.and what is the relation between rssi and link quality ? also can we predict the distance depending upon the link quality and rssi.. In Bluetooth, the transmitted power for a link is adjustable and the LM can change the power of a link depending on the conditions. So again, can the transmit power level (hcitool tpl
) be used as an indicator of the distance? In my tests, I did see a variation in the tpl value for different positions. And one last question.. do any of these values depend on the manufacturer - i.e. for the same distance and identical environmental conditions.. will a 3COM device, Belkin device and say a cisco device give different values? -- Awnish Upadhyay Msc. Mobile and Radio Communication, 07809682838. From owner-freebsd-bluetooth@FreeBSD.ORG Wed Jul 23 16:34:39 2008 Return-Path: Delivered-To: freebsd-bluetooth@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id AF743106564A for ; Wed, 23 Jul 2008 16:34:39 +0000 (UTC) (envelope-from plunky@rya-online.net) Received: from smtp01.one2one.net (smtp01.one2one.net [149.254.200.196]) by mx1.freebsd.org (Postfix) with ESMTP id 5CB168FC12 for ; Wed, 23 Jul 2008 16:34:39 +0000 (UTC) (envelope-from plunky@rya-online.net) Received: from [127.0.0.1] (helo=localhost) by smtpbarns01 with esmtp (Exim 4.50) id 1KLhIG-0004z6-Pe; Wed, 23 Jul 2008 17:34:24 +0100 Received: from smtpbarns01 ([127.0.0.1]) by localhost (smtpbarns01 [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 19005-05; Wed, 23 Jul 2008 17:34:24 +0100 (BST) Received: from [10.36.118.140] (helo=rya-online.net) by smtpbarns01 with smtp (Exim 4.50) id 1KLhID-0004z0-HB; Wed, 23 Jul 2008 17:34:24 +0100 Received: (nullmailer pid 845 invoked by uid 1000); Wed, 23 Jul 2008 16:33:44 -0000 Date: Wed, 23 Jul 2008 17:33:44 +0100 (BST) To: awnish upadhyay In-Reply-To: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Message-Id: <1216830824.448647.547.nullmailer@galant.ukfsn.org> From: Iain Hibbert X-Virus-Scanned: by amavisd-new-20030616-p10 (Debian) at example.com X-SA-Exim-Connect-IP: 127.0.0.1 X-SA-Exim-Mail-From: plunky@rya-online.net X-SA-Exim-Scanned: No (on smtpbarns01); SAEximRunCond expanded to false Cc: freebsd-bluetooth@freebsd.org Subject: Re: bluetooth link quality and rssi ? X-BeenThere: freebsd-bluetooth@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Using Bluetooth in FreeBSD environments List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Jul 2008 16:34:39 -0000 On Wed, 23 Jul 2008, awnish upadhyay wrote: > In BlueZ, what does 'hcitool rssi
' return? does it return the > actual RSSI value or is the output similar to the result of the > HCI_Read_RSSI command as mentioned in the BT spec? > > The BT spec says that HCI_Read_RSSI will read the value for the difference > between the measured Received Signal Strength Indication (RSSI) and the > limits of the Golden Receive Power Range for a connection handle to another > Bluetooth device. > > Put in other words, will 'hcitool rssi
' return this difference or > does it give the exact RSSI value which is compared with the GRPR? (FreeBSD is not BlueZ btw) It returns the value that the controller supplies (from Read_RSSI command) > I noticed that the RSSI values were highly variable. go figure > is how accurate is the RSSI value? I know the BT spec says that there can > be a 6dB +/- variation. Is the result value in dB? it is dB above or below the Golden Receive Power Range (whatever that might be :) > Can I use RSSI to quantify the distance between two BT devices? Meaning > lower values of RSSI -> higher distance? Not with any guarantee of precision. Radio waves bounce off walls and and are absorbed by furniture or human bodies. I think the reasoning for providing this value is that you can use it to compare different links and choose the strongest ones (eg for a mesh network) rather than interpreting it on its own. > And one last question.. do any of these values depend on the manufacturer - > i.e. for the same distance and identical environmental conditions.. will a > 3COM device, Belkin device and say a cisco device give different values? nothing is absolute regards, iain From owner-freebsd-bluetooth@FreeBSD.ORG Wed Jul 23 16:44:08 2008 Return-Path: Delivered-To: freebsd-bluetooth@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 29F65106564A for ; Wed, 23 Jul 2008 16:44:08 +0000 (UTC) (envelope-from maksim.yevmenkin@gmail.com) Received: from rv-out-0506.google.com (rv-out-0506.google.com [209.85.198.227]) by mx1.freebsd.org (Postfix) with ESMTP id 0BB488FC15 for ; Wed, 23 Jul 2008 16:44:07 +0000 (UTC) (envelope-from maksim.yevmenkin@gmail.com) Received: by rv-out-0506.google.com with SMTP id b25so2967360rvf.43 for ; Wed, 23 Jul 2008 09:44:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references; bh=L2/hXQBEqQeektPt6HScgWML8Ae7+w5g6pgRo7s3xB4=; b=Ln85x5R5vbevyMWLa3A+w+UyW9JwyqgowNLUePrEeEOSopBzUdBTJuopdqnd0T0QyC YkrwpSyspBJ6nv/3kzzd5LVht0aLXDIMFXb4zS+I4EXKC5nys+rAqtRv7o/w69er9eFn Vf0j7Q6yp+71I3vt3sF7ZNdh9sYg4wBWerDdk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=hWAg0Xq8zmJwWzwY7ZYnyLWzrr2dNnaSWzren1TJTPAW+iwQesObeBQSD+VXwDzwZz c1POG65O8l7/W6W66FRxKOJnEVl8pXoONyz3u3AydchBXyDtgT80cbrMlzMYMs6wufNa Jsk0a0Trt94wupDEx+EUOM7Nm63WTdX1RzPJM= Received: by 10.140.202.12 with SMTP id z12mr162222rvf.186.1216831447536; Wed, 23 Jul 2008 09:44:07 -0700 (PDT) Received: by 10.141.178.21 with HTTP; Wed, 23 Jul 2008 09:44:07 -0700 (PDT) Message-ID: Date: Wed, 23 Jul 2008 09:44:07 -0700 From: "Maksim Yevmenkin" To: "awnish upadhyay" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: Cc: freebsd-bluetooth@freebsd.org Subject: Re: bluetooth link quality and rssi ? X-BeenThere: freebsd-bluetooth@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Using Bluetooth in FreeBSD environments List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Jul 2008 16:44:08 -0000 On 7/23/08, awnish upadhyay wrote: > Hi , > > In BlueZ, what does 'hcitool rssi
' return? does it return the this mailing lists is for discussing bluetooth on freebsd and not linux :) you might be better off to sending your questions to proper linux bluez mailing list. > actual RSSI value or is the output similar to the result of the > HCI_Read_RSSI command as mentioned in the BT spec? i would image it would be the result of the hci read_rssi command. > The BT spec says that HCI_Read_RSSI will read the value for the difference > between the measured Received Signal Strength Indication (RSSI) and the > limits of the Golden Receive Power Range for a connection handle to another > Bluetooth device. > > Put in other words, will 'hcitool rssi
' return this difference or > does it give the exact RSSI value which is compared with the GRPR? read_rssi command returns a measure of the received signal strength indication of a link between the local and a remote bluetooth devices. the returned value provides a relative measure of the rssi and the "golden receive power range." the golden receive power range is the range of desired received signal power resulting in minimal error. a received signal with too little or too much power results in an inability to accurately decode the transmitted signal. > I ran some test between an Nokia, Windows MObile and a Belkin BT USB device. > I was > measuring the RSSI value as seen by the belkin BT device (connected to a PC) > while the mobiles weres moved to different locations (I was not doing any > data > transfer.. but I had the two devices connected and collected the data in a > file). > I noticed that the RSSI values were highly variable. Even two sets of > observations with identical > conditions were giving very different values for RSSI. So, my next question > is how accurate is the RSSI value? I know the BT spec says that there can > be a 6dB +/- variation. Is the result value in dB? theoretically, there exists an inverse proportional relationship between the received signal and the distance from the receiving station that can be represented linearly. unfortunately, various phenomena like multipath fading and shadowing make it impossible to establish a precise relationship. for practical purposes, this technique involves determining the path loss function based on statistical analysis. > Can I use RSSI to quantify the distance between two BT devices? Meaning > lower values of RSSI -> higher distance? please read above. > I was looking at other parameters (link quality, transmit power) and found > that the link quality seemed to be a better indicator of the distance.. > with increasing separation between the devices, the command 'hcitool lq >
' was giving lower values.. meaning there was a degradation in the > link quality. Any comments on this? i wanted to know the unit of link > quality.and what is the relation between rssi and link quality ? > also can we predict the distance depending upon the link quality and rssi.. theoretically. you probably should look at all 3: Get_Link_Quality, Read_RSSI and Read_Transmit_Power_Level value. some of those could be manufacturer specific (imo). > In Bluetooth, the transmitted power for a link is adjustable and the LM can > change the power of a link depending on the conditions. So again, can the > transmit power level (hcitool tpl
) be used as an indicator of the > distance? In my tests, I did see a variation in the tpl value for different > positions. please read above. > And one last question.. do any of these values depend on the manufacturer - > i.e. for the same distance and identical environmental conditions.. will a > 3COM device, Belkin device and say a cisco device give different values? yes, imo. thanks, max