Wi-Fi Aware

The ability for Wi-Fi enabled devices to automatically discover each other and understand each other’s public Wi-Fi offerings is a powerful enabler for point to point Wi-Fi connectivity. Standards based ad hoc point to point Wi-Fi connections are currently quite a manual arrangement and so have seen little usage. Attempts to initiate such connections using Bluetooth and NFC have lowered the hurdle, but pre-emptively discovered potential connections via Wi-Fi Aware will make it much easier.
As is very often the case the full potential of technology is unlocked by widely or ideally universal standards, so Wi-Fi Aware promises to create new possibilities.

The significance of the ‘MU’ in 802.11ac MU-MIMO

Firstly, what is the ‘MU’ feature in 802.11ac MU-MIMO? Put simply it allows multiple Wi-Fi client devices (e.g. mobile phones, tablets, and laptops) to exchange data with an access point radio, in parallel. Previously only one Wi-Fi client device at a time could exchange data with an access point radio. An important consequence of this is that the aggregate throughput of access points can spend longer at higher levels and so make more efficient use of network resources. Another consequence is that traffic analysis will be more difficult when there are multiple simultaneous talkers.

The number of Wi-Fi client devices that can exchange data simultaneously with an access point radio is limited by the number of spatial streams that each supports. The 802.11ac amendment to the 802.11 standard allows for radios with up to eight spatial streams, although only recently have four stream MU-MIMO processors become available. Each spatial stream is a distinct stream of data that requires an antenna of its own linked to one radio. A connection between an access point and a Wi-Fi client device will use one or more streams. In practical terms this means a four stream 802.11ac processor with MU-MIMO in an access point can communicate in parallel with four single stream client devices, or two single stream client devices and one two stream client device, or two client devices each using two streams, or of course one four stream client device.

At this time a typical 802.11ac setup may use an 80 MHz channel width and an 800 ns guard interval, with connections perhaps achieving MCS 7. If that setup were fully MU-MIMO enabled it would then have a theoretical aggregate throughput of 4*292.5 Mbps i.e. 1.17 Gbps. Out of interest I performed a test as I wrote this in very good RF conditions using a Sony Xperia Z Ultra and Samsung Galaxy NotePRO 12.2 connected to D-Link DAP-2695. I used them for no other reason than they happen to be sitting on the next desk and are all are very current. All of these are 802.11ac devices, but not MU-MIMO. The Sony device achieved a link speed of 325 Mbps with RSSI at -42 dBm; it delivered 205.7 Mbps up and 207.95 Mbps down. The Samsung device achieved a link speed of 866 Mbps with RSSI also at -42 dBm; it delivered 208.87 Mbps up and 413.89 Mbps down. These were the best figures from among a handful of tests on each client device. Some test results achieved only half of these rates or less, but most were similar. These links are clearly 80 MHz, 400 ns, MCS 7 and MCS 9 for the Sony and Samsung respectively, with one and two streams respectively. Anyway, if these devices were MU-MIMO then my best aggregate download throughput for two Xperia and one NotePRO (for example) would be 2*207.95 + 413.89 = 829.79 Mbps. Add a client on a 600 Mbps 2.4 GHz radio and we can see it is possible for an access point to make full use a GbE link. The theoretical throughput of GbE is 118660598 data bytes per second (about 949 Mbps) using a 1460 data bytes Maximum Segment Size in a normal Ethernet frame of 1518 bytes containing a Maximum Transmission Unit (MTU) of 1500 bytes. Using a 9K MTU improves this to about 123916800 data bytes per second i.e. about 991 Mbps. In practice of course these theoretical GbE maximums cannot be achieved, and Wi-Fi transfer rates are likely to be about half of the link speed.

Let us consider how multiple SSIDs relate to this ‘MU’ feature. An access point radio operates on one logical channel at a time. In fact that logical channel may be composed of multiple contiguous channels or discontinuous ‘bonded’ channels that behave as one large channel. These techniques increase the amount of spectrum used by a radio for a logical channel and so its bandwidth. They do not provide distinct parallel streams of data. As SSIDs are configured to a band and thence a radio, so they will all share the same logical channel of their radio. Consequently all SSID traffic has to take a turn on their radio’s configured logical channel, unless that radio is MU-MIMO enabled. In which case SSID traffic might travel over one or more spatial streams, depending on Wi-Fi client device MU-MIMO capability, and so could travel in parallel with other SSID traffic. So, SSIDs provide no innate transmission parallelism; that can only come from MU-MIMO enabled 802.11ac radios.

The balance of wired and wireless

Recently I installed a 4G LTE router in a site where there is a poor wired Internet service with no plans for improvement, but a choice of proximate 4G LTE base stations. The resulting wireless throughput is better, the service more reliable, and the prospect of further improvements immanent – partly because of the increasing competition between the wireless Internet service providers (WISPs) offering 4G. Apparently the wired infrastructure is not economically viable to upgrade according to its ISP. This is surprising statement given that the area is very densely populated with consumers and wired infrastructure. Perhaps what they mean is not enough disgruntled customers are leaving for 4G to justify spend on upgrading their service yet. This is not the first area I have come across with that attitude by an ISP. The first time I was told this was also in a build-up area, but it had fewer consumers and more businesses that are probably paying for leased lines anyway, so it was easier to see why there. Anyway, this attitude made me wonder where it is economically viable to put in at least fibre to the cabinet. Obviously the WISP base stations that serve this recent site need to aggregate a lot of data, and at least one of them has no wireless carrier antennas, so I suspect it is using fibre for backhaul. I think this is a case where wired infrastructure can more easily make money. It has the throughput advantage (at the moment) that can justify the cost of digging in a heavily developed area with strong property laws. I expect ISPs to continue to cede customers to WISPs and wired infrastructure to further retrench and focus on highly aggregated throughput.

Now suppose that some clever researcher finds some scrap of information intrinsic in electromagnetic radiation that allows distinct transceivers to be identified, or even just groups of them. This would make a dramatic difference to wireless communication because spectrum becomes less contended. In fact something like that has already been announced in the shape of pCells. I hope for and expect more innovations of this kind. When they arrive they will have a profound effect on wireless communication and wires will retrench further.

Wi-Fi site surveys and two stream Wi-Fi for mobile phones

I recently asked the Ekahau site survey tool maker if they could add a feature that allows visualisation of different qualities of client transceiver. The reason I asked is because the range of Wi-Fi client ability continues to expand. Very soon the new Broadcom BCM4354 chip will deliver two-stream 802.11ac Wi-Fi to smartphones. Meanwhile some very old clients are still in use along with clients that have poor design and/or build quality. Some websites report that the Samsung Galaxy S5 should be available in April using the BCM4354 and that the iPhone 6 will also use it. So the Broadcom BCM4354 will rapidly expand to the range Wi-Fi client ability that WLANs are expected to manage. I think that site survey tools should allow me to deliver reports that visualise this diversity of connection quality. If you have to provide a certain level of Wi-Fi service to a diverse set of clients you need to know what they will experience, not just what can be obtained on the high end equipment that WLAN professionals use.

802.11ac approved

The IEEE has finally announced approval of IEEE 802.11ac amendment to the 802.11 standard.
It seems like we waited forever.
Understandably makers were keen to sell us products that take advantage of it before it was finalised; that created the expectation.
As long as buyers are made aware of the risks associated with early adoption I am happy to have that choice.
802.11ac is expected to be an important step in Wi-Fi, but as it operates in the 5 GHz band only its shorter range will increase system costs where more access points are required to get coverage.

Wireless sensors are coming

The Dash7 Alliance promotes the ISO 18000-7 standard for wireless sensor networking.
On 2013-09-25 it announced the public release of the first version of the DASH7 Alliance Protocol.
Low implementation costs will be important in its competition with Zigbee.
Operating at a lower frequency DASH7 has an inherent range advantage but lower throughput.
Dash7 also specifies lower power usage than Zigbee but lesser security features.
Although Zigbee and Dash7 have overlapping applications their different characteristics should allow both to find a niche.

Wireless Power

Many companies are developing wireless power systems, but one seems to have an advantage.

Ossia Inc. is developing technology they claim can charge devices at up to 30 feet, others claim only millimetres or centimetres.

They say they are in talks to bring their Cota system to market and think it should be in consumer products by 2015.

At Wireless Head our business is the application of wireless technology to business; so if Ossia Inc. can free us from that last wire it is great news to us.

Take a look at this presentation by the founder and CEO of Ossia for TechCrunch.