Xperia X10 mini pro passive scanning
I've just realized that stock Android 2.1 on the U20i (so called "mimmi") discovers Wifi networks by passive scanning, and only sends out a few probe requests as an acceleration in case of opening the network list menu after waking up. On the other hand, it seems that both Pulse mini (Huawei U8110 with Android 2.1) and Mango (Xperia mini pro SK17i with Android 4.0.4) use normal active scanning.
Common wisdom tells you that passive scanning potentially uses more power. This can happen because the receiver's low noise amplifier and processor can use as much power as the transmit circuit. This is especially plausible because maximum transmit power usually shouldn't exceed 100mW anyway (actually 20dBm EIRP) which is in the ball park of the wireless chip's total consumption already, let alone the whole chipset or mobile device. Active probing involves sending out a probe request on each channel and listening for a response for a limited short interval. I guess the exact timing is dependent on channel conditions and options regarding preamble and link rate, but empirical analysis puts it between 10-16ms. It also has the potential advantage that only those networks show up on your network list to which you have a potential two-way communication channel.
A device which is doing a passive scan on the other hand, should be listening to each channel for multiple beacon intervals, which is usually set to 100ms, however it could go up to 1000ms. Mimmi updates its network list very rapidly, I would say once every second. I guess it doesn't wait for the maximal duration and perhaps it also relies on channel cross-talk.
According to my observations involving continuous scanning, Mimmi provides a very similar battery life as the Pulse. Mango beats both of them with a huge margin, though it has a much more recent system with JIT. The raw network discovery rate of Mimmi and Mango are in the same ball park, though I'd still need to calculate exact statistics about the overlap to be certain. Both of them beat the very slow scanning of the Pulse which takes more than 5000ms each round. Though when traveling at high speed in a train, Mimmi seems to do a much better job.
Consider the increasing prevalence of Wi-Fi equipped mobile devices. These have less than stellar radio setups and antennae, they are moving randomly and minute variations in user posture and the environment cause wild swings in scattering and the radiation pattern. Although probe requests are very small, they are usually sent at the lowest bitrate. Interfere with preexisting communications taking place is inevitable in this case. Probe response is less problematic in this aspect, however the amplification factor is great - usually eating ten times as much radio time as requests. And this time is usually taken away from where it is usually scarce: inside buildings, where the channels are already crowded.
I'd say that passive scanning is the choice which scales hands down better compared to active scanning.
Common wisdom tells you that passive scanning potentially uses more power. This can happen because the receiver's low noise amplifier and processor can use as much power as the transmit circuit. This is especially plausible because maximum transmit power usually shouldn't exceed 100mW anyway (actually 20dBm EIRP) which is in the ball park of the wireless chip's total consumption already, let alone the whole chipset or mobile device. Active probing involves sending out a probe request on each channel and listening for a response for a limited short interval. I guess the exact timing is dependent on channel conditions and options regarding preamble and link rate, but empirical analysis puts it between 10-16ms. It also has the potential advantage that only those networks show up on your network list to which you have a potential two-way communication channel.
A device which is doing a passive scan on the other hand, should be listening to each channel for multiple beacon intervals, which is usually set to 100ms, however it could go up to 1000ms. Mimmi updates its network list very rapidly, I would say once every second. I guess it doesn't wait for the maximal duration and perhaps it also relies on channel cross-talk.
According to my observations involving continuous scanning, Mimmi provides a very similar battery life as the Pulse. Mango beats both of them with a huge margin, though it has a much more recent system with JIT. The raw network discovery rate of Mimmi and Mango are in the same ball park, though I'd still need to calculate exact statistics about the overlap to be certain. Both of them beat the very slow scanning of the Pulse which takes more than 5000ms each round. Though when traveling at high speed in a train, Mimmi seems to do a much better job.
Consider the increasing prevalence of Wi-Fi equipped mobile devices. These have less than stellar radio setups and antennae, they are moving randomly and minute variations in user posture and the environment cause wild swings in scattering and the radiation pattern. Although probe requests are very small, they are usually sent at the lowest bitrate. Interfere with preexisting communications taking place is inevitable in this case. Probe response is less problematic in this aspect, however the amplification factor is great - usually eating ten times as much radio time as requests. And this time is usually taken away from where it is usually scarce: inside buildings, where the channels are already crowded.
I'd say that passive scanning is the choice which scales hands down better compared to active scanning.
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