Date: Wed, 23 Jul 2008 09:44:07 -0700 From: "Maksim Yevmenkin" <maksim.yevmenkin@gmail.com> To: "awnish upadhyay" <awnishupadhyay@gmail.com> Cc: freebsd-bluetooth@freebsd.org Subject: Re: bluetooth link quality and rssi ? Message-ID: <bb4a86c70807230944k4ec35059u32f518a1f41451a5@mail.gmail.com> In-Reply-To: <c162203e0807230736n7750db22u832303c20ab8fde9@mail.gmail.com> References: <c162203e0807230736n7750db22u832303c20ab8fde9@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 7/23/08, awnish upadhyay <awnishupadhyay@gmail.com> wrote: > Hi , > > In BlueZ, what does 'hcitool rssi <address>' 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 <address>' return this difference or > does it give the exact RSSI value which is compared with the GRPR? <quote> 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. </quote> > 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? <quote> 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. </quote> > 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 > <address>' 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 <address>) 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bb4a86c70807230944k4ec35059u32f518a1f41451a5>