[Opinion] 2×2:2 MIMO in Smartphones

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? (more…)

Wi-Fi Riddles: Faster speeds require weaker signals?

A discussion of my previous post in the 802.11 Wireless professionals group lead to a discovery of a new bit of overlooked knowledge! Many thanks to Eduard Garcia-Villegas and Mike Rex, who turned my attention to this one.

Ever wondered why faster rates have smaller effective distance? It was always attributed to signal fading – higher rates require more complex modulation, which, in turn, requires higher SNR (Signal-to-Noise Ratio) value. So at greater distances, with lower SNR, one has to use lower rates. Simple.

Turns out, in addition to that the transmitters may as well lower their power when transmitting at higher rates! This is done because at higher power values transmitters are more likely to introduce errors in the signal they create due to non-linearity in their behaviour (if you want more details – just go to the discussion). Here’s an example from a datasheet that Eduardo provided (the numbers are Tx Power, dBm):

Tx Power: HT20, 2.4GHzTx Power: HT20, 5GHz

Note how the power falls as MCS number increases. Also note how this is different in 5GHz depending on channel number.

Mike Rex added, that the users of alternative consumer WLAN router firmwares (such as DD-WRT and Tomato) sometimes suffer from strange performance and link reliability issues, as these firmwares allow varying radio power levels (and other power settings) beyond what manufacturer has intended, resulting in poor Tx signal quality. This mainly is just a result of the shortcomings and compromises in hardware design (even if the APs are built on the same chipset), but certainly not something a non RF engineer would suspect first! 😉

Well, I learned something – this blog already pays off. 🙂 Many thanks to Eduard, Mike and all others, who tool part in the discussion. This bit has been rolled into the original post to keep all things together.

RFID Gen2 v1.2 and v2.0 standard specifications

Cover page of EPC Global Gen2 v2.0 standard
Cover page of EPC Global Gen2 v2.0 standard

Somehow, I missed the fact that EPC Global Gen2 v2.0 standard was passed end of last year (it appears, I missed a lot of things end of last year). Anyway, for those interested:

  • Here’s the v2.0 spec.
  • Here’s the v2.0 fact sheet (what’s new compared to v1.2 on a very high level).
  • Here’s the v1.2 spec (for in-depth comparison).
  • In 2014 the v2 spec should ratified as ISO/IEC 18000-63 standard.

The main enhancements are

  • Cryptographic authentication of tags and readers, to verify identity and provenance, reduce the risk of counterfeiting and unauthorized access.
  • Enhanced User Memory for supplementary encodings (such as maintenance logging) during a product’s life cycle.
  • Untraceable function to hide portions of data, restrict access privileges and reduce a tag’s read range.
  • “Non-removable” flag for embedded tagging of electronics and sewn-in tagging of apparel, to indicate that a tag cannot easily be removed without compromising the tagged product’s intended functionality

More information can be found on the GS1 Gen 2 page (EPC Global is a subsidiary of GS1). For those that are far away from the topic, the barcodes in supermarket, for example, are also standardised by GS1.