Sunday, 19 May 2013

Top 10 Things a WiFi Installer Does Not Want To Hear...


Here are the top 10 things (IMO) you don't want to hear from a customer when you arrive on site to install a new WiFi network (I compiled this rather quickly in a flippant moment - please don't take it too seriously...):
  1. Our networking guy, who was going to be helping you today, isn't available, I'm afraid he's... (choose from the following):
    • On a late shift
    • Off sick
    • On leave
    • Over-slept
    • Double-booked
    • Left the company
    • Had a baby
    • Buying a radiation suit
  2. Oh, you wanted POE ports for those APs?
  3. Our goods-in department has definitely received the kit, they're just not sure which part of the hospital it went to...
  4. Oh, we thought you were bringing the kit with you. No, we haven't received anything.
  5. You know that 500-person call-center where you said we might have issue with personal hot-spots? The good news is, we've introduced a policy of 'no personal hot-spots' in that area! As a sweetener, we gave all of the operatives a bluetooth headset, mouse and keyboard each. We also threw in 5 new microwave ovens for their rest area, together with 10 new security cameras to monitor all that new gear.
  6. We've changed out minds. We'd really like to be able to run video and voice across the network as well. Can you squeeze that in whilst you're here?
  7. Our CEO has a new iPad and he'd really like to be able to use it on the wireless network. I know it wasn't in scope, but it's really important...
  8. Well, the salesman said it would support <insert unsupported feature here>.
  9. We've decided we would like a bit of coverage outside of the building after all (the CEO is a smoker). Can you move a couple of APs a bit closer to the windows near the smokers area?
  10. The cabling guy has assured us that you'll have no issues with 120 metre cable runs...
I'm sure there are plenty of others... :)

Nigel.

Tuesday, 7 May 2013

5GHz - 3 Missing Channels in Europe

Last year, I put up a posting which highlighted the fact that here in the UK (and I suspect all of Europe) we often have 3 channels missing from our allocation of unlicensed channels in the 5GHz band.  Looking at many manufacturer data sheets, channels 120, 124 and 128 are often shown as not being supported. This is despite the fact that they are allocated for use by local regulatory bodies (OFCOM here in the UK).

I recently posted a question about this on a partner forum of a major WiFi vendor that I deal with and finally got a definitive answer on this. In this post, I'll share my findings.

The reason that these particular channels (120 - 128) receive special treatment is that they occupy frequencies that are used by weather radar systems. WiFi systems have to be very careful not to interfere with those systems during their normal operation. Therefore, WiFi equipment has some additional checks and tests imposed on it to make sure that it does not inadvertently cause any interference.

In the ETSI region (Europe), the standard EN 301 893 dictates that any channels operating in the frequency range 5.6GHz to 5.65GHz must wait an additional period of time before using a channel. For most DFS-affected channels, a WiFi device must wait for 60 seconds to verify that no radar is present before commencing operation. However, on the channels in the 5.6GHz to 5.65GHz range, the device (i.e. Access Point) must wait 10 minutes! The table below (taken from Annex D of the standard) details this requirement:


Due to this 10 minute wait period, it seems that many manufacturers have chosen to withdraw support for the channels affected, which are 120, 124 and 128. This makes perfect sense now - who would want an AP to be allocated to a channel and then wait for 10 minutes before it can use it..?

I'm pleased to have finally got to the bottom of this particular grey area, but it seems like bad news for WiFi usage in Europe generally. With the anticipated sharp uptake in 5GHz usage around the globe, as 802.11ac starts to roll out, the loss of 3 channels is quite a chunk of spectrum to lose.

In the UK we have 19 unlicensed channels to use on 5GHz for WiFi. Losing 3 of those channels is a 15% loss in spectrum. This is at a time when we really need to be increasing spectrum availability to cope with the additional channel bonding opportunities that  802.11ac provides to increase WiFi speeds.

Hmmm....let's hope some additional spectrum turns up in the near future.

References:
Update: I've now created a white paper which details 5GHz usage for WiFi in the UK. Find it here

Saturday, 4 May 2013

Samsung Galaxy S4 WiFi Capabilities


With all of the excitement around 802.11ac that is currently unfolding, I was very interested to hear about the support for 11ac by the recently released  Saumsung Galaxy S4. Having a quick scan of the reviews across the web about the new handset, I was intrigued to see claims that it supports 802.11ac, allowing speeds up to 1.3Gbps! Feeling a little sceptical that it would support anything close to those speeds, I did a bit of digging to see what I could find.

My first port of call was a product tear-down over at TechInsights.com. They revealed that the WiFi chip in the S4 is the Broadcom BCM4335


A quick look around the Broadcom site soon revealed the product page for the BCM4335, with an overview of the chipset specification. In summary, it supports:

  • Single stream IEEE 802.11ac solution with data rates up to 433.3 Mbps
  • Full IEEE 802.11a/b/g/n legacy compatibility with enhanced performance
  • Supports 20, 40, and 80 MHz channels with optional SGI (256 QAM modulation)
  • The BCM4335 features advanced idle power consumption performance, which significantly extends mobile device's battery life
  • Broadcom's TurboQAM™ technology implements the highest data-rate 256-QAM mode in 2.4 GHz and enables devices equipped with the BCM4335 to deliver 10 percent faster throughputs than 802.11n speeds when communicating with other 5G WiFi devices
  • Key high-throughput mobility interfaces, including SDIO 3.0, PCIe and HSIC, make it suitable for smartphone, tablet and computing platforms
  • Advanced beamforming (IEEE 802.11ac/n), Low-Density Parity Check (LDPC) code and Space-Time Block Code (STBC) support for better coverage and more reliable connectivity
  • Built-in media processing to off-load host processor
  • Integrated support for Wi-Fi Direct™, Wi-Fi Certified Miracast™ and Wi-Fi Certified Passpoint™ technologies
Some very interesting facts and figures here, but this pretty much quashed the outlandish claims in some articles around the 1.3Gbps top speed, as the chipset cannot go beyond 433mbps.Even so, these potential performance gains over other non-11ac handsets are very impressive. 

Although the chipset itself may support up to 443.3 Mbps, primarily through the 80Mhz-width channel capability, this doesn't mean that the Samsung implementation has actually taken advantage of the full 80Mhz channel width. I still needed more information to find out what the S4 itself was actually capable of.
 
The next stop was the FCC web site (A3L/GTI9505 if you want to take a look yourself) to have a look to see if I could see what speeds and channel widths had been tested during the FCC approval testing process.  


The WLAN testing report shows that the handset was tested on both 2.4GHz (802.11b/g/n) and 5GHz (802.11a/n/ac). Interestingly, it was tested up to 433.3mbps, using an 80Mhz width channel! 


There were also some interesting power levels presented, which seem to suggest that the transmit power level of the device was averaging around 11-13dBm on 5GHz, depending on the data rate and channel. On 2.4GHz, it looks like it has a slightly higher power output, showing figures averaging 12-15dBm.

So, in summary, the S4 is a single stream device, supporting up to 80MHz channels (for 802.11ac ) and has a top speed of around 433Mbps. Don't forget
 these figures will assume ideal conditions (i.e. short guard interval, close proximity to AP, good SNR values etc.), and that these are connection speeds, not throughput speeds that you would see when transferring data. Actual throughput is likely to be a little over half of the top-speed of 433Mbps. 

Also, don't forget that 802.11ac is only supported on the 5GHz band. If you are using it on 2.4GHz, the best you are going to get is the top speed for a single stream 802.11n device  on a 20MHz channel (around 72Mbps connection speed).

All we need now are some 802.11ac APs to use the S4 with :)