So, Broadcom announced a 2×2:2 (867Mbps) chip for mobile devices, which of course generated lots of excitement.
Let’s see: 867Mbps Wi-Fi, you say?
- Can you sustain such speed with your home Internet connection?
- Have you seen hotspots offering such a high-speed Internet?
Do you have a RAID-enabled NAS at home for file transfers, since even the fastest SSDs do not allow for such read rates?[UPD] Well, clearly got carried away and confused MB and Mb here [/UPD] And if the fastest SSD cannot read that fast,what makes one think their tiny phone will be able to write faster onto their embedded flash (or SD card)? The data I have is 35-65Mbps write rates on average.
- Two antennas means 2x+ power usage of the WLAN module. Can you imagine effect on the battery life?
So, what is the point, then, you say?
For small burst transitions (downloading web pages) that can go directly to memory – this higher speed could be quite useful, as transmission takes less air time. Less air time means better client density on one AP. Less air time also means less power used, and radios don’t stay on for too long (Broadcom claims 25% overall reduction in power use). I am very interested to test this live and see if there is a noticeable difference over “simple” 1-stream 802.11n/ac in real-life scenarios – there’s much more to 802.11 protocol than sending data frames.
- MRC provides better receive sensitivity for the decoder, using math to combine signals from both antennas and extract ‘cleaner’ source data. This can generate ~3dB extra receive gain.
- STBC provide better chances for MRC receiver on the Tx side, by transmitting multiple copies of the same data stream from both antennas in a way (math, again) that MRC receiver can utilize them even better, with potential for another 3dB gain.
- As a result, one gets better rate-over-range (esp, when both AP and client support both technologies), which is very essential for a compact-size device that has it’s WLAN antenna largely covered by a human hand.
So, just like with 802.11ac itself, 2×2 in a phone is not about speed, but rather coexistence and connection quality. And I still believe it’s overkill – I would stop at 1×2:1, probably, for battery life reasons. Expect another wave of spec-selling, just like 800-1000Mhz LCD SmartTVs 🙂