In a small test scenario I'm measuring the signal strength at the AP.
Do the client smartphones keep a constant signal strength for probe
requests or are there reasons they are varying it?
thanks in advance
Wolfgang R.
The Question was not clear .Still below are the points i can tell from WLAN Technology.
In WLAN signal strength or RSSI keeps on varying as the medium is wireless.
Clients(Ex: Smart Phones) get RSSI of AP from AP's Beacon or any packets coming from AP.So depending on medium ,how that packet came to client ,client determines the RSSI and keep it for that time.
So coming to your question, there is no chance client gets constant RSSI/Signal Strength.
Related
What is the purpose of the txPower in a Beacon? According to this, How to set Transmitting Speed vs Scanning Speeds for Altbeacon Library, the maximum transmission power is already set by default.
Then what is the meaning of the txPower that can be set when sending the beacon and what are the possible values for it?
The txPower field sets one of the bytes in the over the air beacon advertisement. It indicates what a receiving device should expect the signal strength in RSSI to be when the beacon transmitter is one meter away.
A receiving device can then compare the txPower value to the actual measured signal strength and if it is stronger, that means the beacon is closer than one meter. If it is weaker then the beacon is farther than one meter. These two values (actual signal strength vs txPower) can be plugged in to a formula to get a rough distance estimate.
The reason this is a configurable field in the advertisement is twofold:
Not all transmitters have the same output power, so for best results the value should be set on a per device basis. (In practice this is rarely done.)
Obstructions and reflections of the radio signal can impact the expected signal strength at the receiver. For example, a beacon is installed under a counter or in a cabinet. For this reason, measuring the signal after installation (calibration) is recommended for best results.
The default txPower field for the iPhone 4s (the first phone supporting iBeacon for both reception and transmission.) was -59 dBm. This is fairly typical of mobile phones built since then and dedicated transmitters at the full power allowed by regulatory agencies. But variations of 5dB on specific device models are not uncommon.
Read more in my blog post here: http://www.davidgyoungtech.com/2020/05/15/how-far-can-you-go
If probe response packets announces the capabilities of a network,
then what is the purpose of Beacon frames in wireless 802.11 ?
Among other things, beacons allow a device to passively scan all channels for available Access Points so that a list may be presented to a user showing signal strength. They also allow a device to detect if there is another Access Point on the same network and presumably on a different channel with a better signal.
Apologise for the probably use of the wrong word in my question but for the life of me I can't think of the right one.
Anyway, I've been playing about with the Bluetooth Low Energy and I'm trying to create something that is going to use the RSSI signal strength the BLE device emits. For this, I need it to emit its pulse multiple times per second.
Is there a way I can up the amount of times my devices either scan for a signal, or broadcast their signal through code on iOS devices?
No, there is no API for you to change the advertisement speed or radio power.
This aspect is fully controlled by the system. You can only start and stop the advertisement and add some metadata to the packets: device local name, advertised services, etc. Moreover, the contents of the advertisement packets will differ depending on whether your app is in the background or foreground and, additionally, in background it will be slowed down. These effects have been documented in various SO questions and in the header files.
If your clients are iOS applications, then they should use either the RSSI in the advertisement packets (centralManager:didDiscoverPeripheral:advertisementData:RSSI: method) or when connected, the readRSSI method on the peripheral object (just make sure you don't call it too often).
I'm implementing iOS library that reads heart rate sensor data using Bluetooth 4.0 (AKA Bluetooth Smart AKA BLE).
I noticed that RSSI value is being updated only on demand (readRSSI) - otherwise is't always the same.
My doubt is: "Does reading or RSSI cause additional request to the sensor?".
My consideration is about power saving of the device.
I suppose my question is generally to BLE, don't think it's iOS-specific...
Any thoughts are appreciated.
readRSSI reports the RSSI being averaged over an active connection. So if you have a connection to your sensor, reading RSSI doesn't cause any additional overhead. Even if you aren't exchanging user data, your BT devices are periodically communicating to keep synchronized with an active connection, and RSSI can be measured from this ongoing communication.
If you are tearing down your connection, then yes, you will have to reconnect to actually measure RSSI.
Im trying to measure the signal strength of mobile devices from either existing WLAN routers or creating directional antennas. I want to see what specific routers are picking up the top 3-4 signal strengths from a specific mobile device, and use triangulaiton to gather their locaiton. Any ideas of the best route to do this?
I don't know whether such router exists or not, but can provide you an alternative and convenient way. Wireless channel is symmetric in both direction; this is, if the router transmits signal at 20 dBm and mobile device receives such signal at -30 dBm, the received signal strength at router would be -30 dBm if the mobile phone transmits at 20 dBm (given that environment does not change much). Then simply install WiFi analyzer app on your Android phone and record the signal strength of your normal routers.