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