Date: Wed, 23 Jul 2008 17:33:44 +0100 (BST) From: Iain Hibbert <plunky@rya-online.net> To: awnish upadhyay <awnishupadhyay@gmail.com> Cc: freebsd-bluetooth@freebsd.org Subject: Re: bluetooth link quality and rssi ? Message-ID: <1216830824.448647.547.nullmailer@galant.ukfsn.org> In-Reply-To: <c162203e0807230736n7750db22u832303c20ab8fde9@mail.gmail.com> References: <c162203e0807230736n7750db22u832303c20ab8fde9@mail.gmail.com>
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On Wed, 23 Jul 2008, awnish upadhyay wrote: > In BlueZ, what does 'hcitool rssi <address>' 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 <address>' 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
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