Friday, October 3, 2014
If one does not know to which port one is sailing, no wind is favourable. - Seneca the Younger
The Mycenaean Greeks did not win the Trojan War by strength and courage, but thru the dark art of guile. Odysseus, king of Ithaca (portrayed in the mosaic above), known to the Romans as Ulysses, was the chief architect of their victory. It was he who dreamt up the scheme of the Trojan Horse and was the leader of a select band of fifty warriors ensconced within the wooden construction. Thru his cunning, the people of Troy were tricked into dragging the wooden horse into the city as an act of piety. Deep in the night, the hidden soldiers emerged from within the statue, the Trojan night watch was overwhelmed and Troy's gates were thrown open, allowing the Mycenean army, returning under cover of night, to sack the fabled city.
Yet fortune did not smile upon Odysseus. The wrath of the sea god Poseidon cursed him to wander the Mediterranean, with the winds seemingly against him for a full decade until the goddess Athena pleaded with Zeus on his behalf. Subsequently, Zeus sent Hermes to command the nymph Calypso to release Odysseus from his captivity on the island of Ogygia. Despite her protestations, Calypso bowed to the will of Zeus and, providing Odysseus with a small craft and provisions, set him free, whereupon the Zephyr at last filled his sail and drove his skiff east to return him to his wife and home, both of which he had not seen since the legendary thousand ships had set sail for Troy two decades earlier.
The winds, though, do not determine only the destinies of doom-driven heroes from mythology, but acutely affect the High Tech industry as well. In fact, the winds are of particular significance to us, as they carry the wireless bands that are so centrally important to the future of our industry.
In one of my earlier blog posts on the IoT, I mentioned that developments in the wireless spectra would be key to tracking the evolution of the market. There is, in fact, quite a lot happening in this sector that will have far-reaching implications, as a grand battle of wireless standards is currently underway.
The gratitude of every home in our Island, in our Empire, and indeed throughout the world, except in the abodes of the guilty, goes out to the British airmen who, undaunted by odds, unwearied in their constant challenge and mortal danger, are turning the tide of the World War by their prowess and by their devotion. Never in the field of human conflict was so much owed by so many to so few. - Winston Churchill, speech to the House of Commons during the Battle of Britain, August 1940
So who is battling for control of the airwaves in the IoT market? There are three primary contenders at the moment, each with their own historical antecedents.
Based directly on the 802.11 standard, Wi-Fi Direct is a Peer-to-Peer (P2P) version of the venerable protocol. It allows direct communication between Wi-Fi equipment without an access point acting as intermediary. The standard potentially eliminates the need for Wi-Fi devices to have an access point to a LAN at all, as one of the participants in the ad-hoc network can serve that function. As an example, a smartphone could serve as an access point for a group of Wi-Fi enabled sensors.
Another feature of the standard is that it does not require all Wi-Fi appliances to be upgraded to participate. All it takes is one device to be enabled for Wi-Fi Direct so that it can serve as the host for other Wi-Fi devices in the vicinity.
The genius of the standard is in the simplicity of its implementation. The entire access point functionality has been transferred from hardware to software. When two Wi-Fi devices encounter each other and at least one is a Wi-Fi Direct agent, they negotiate to determine which of them will serve as the access point (typically the strongest computational device will win) and then engage in an automated protected setup that eliminates the necessity of user intervention to manage the details.
There are functional enhancements built into the standard in the form of services that make the protocol attractive beyond Wi-Fi's existing ubiquity. Tasks such as data streaming for multimedia and file sharing for printing or social sharing are captured as automated routines.
One area of extra focus by the standards group has been the matter of power consumption. The committee took a serious crack at improving power requirements for mobile or otherwise battery-powered applications and defined a set of power management features which are claimed to improve battery life by 15-40%. There are some engineers testifying that they are regularly observing battery charge duration for various applications on the order of several months out to a full year. Yet at the moment this appears to be confined to conventional AA or AAA batteries and not coin cell versions - a significant limitation to the applicability of the standard to the full range of IoT applications.
Despite this, Wi-Fi Direct is seeing adoption in consumer electronics, including many of the products for the Digital Home such as desktop and laptop PCs, mice, keyboards, scanners, printers, headsets, displays, speakers and the like. The near-instant association between devices that ensures very quick response times to user inputs has been a key trait to Wi-Fi Direct's growth in popularity.
The omnipresence of Wi-Fi could be rivalled only by another equally pervasive standard such as Bluetooth. Despite its rather severe early deployment difficulties, Bluetooth became ubiquitous in mobile and consumer electronic systems and continues to dominate the PAN (personal area network.)
BT 4.0 shares several features with Wi-Fi Direct, such as the use of the 2.4GHz band, multipoint support in ad-hoc networks, the ability to dynamically switch between master and slave states and the division of the spectrum into multiple channels. The protocol also shares the concept of automated handshake and services support between devices, greatly simplifying usage.
There are some additional features in BT 4.0 that are advantageous in comparison to Wi-Fi Direct, including the daisy chaining of individual ad-hoc networks (though the master-slave relationship gets a little trickier) and, more significantly, a deliberate targeting of applications based on the use of a coin cell battery. It is a standard historically focused on supporting low power applications. Though the protocol does permit line of sight communications up to a full kilometer, the overwhelming majority of implementations are for much shorter ranges with a greatly reduced power consumption profile.
This latest version of Bluetooth does have some drawbacks when compared to Wi-Fi Direct, however. The supported data rates are much lower (though they appear sufficient for currently targeted applications.) A more serious flaw is the lack of backwards compatibility with legacy devices when a BT 4.0 device is in Low Energy mode. This presents obvious difficulties for deployment. Introducing a more advanced technology that requires significant changes to existing infrastructure is always a dicey proposition, and it's a real shame the Bluetooth SIG couldn't find a way to avoid the problem when defining BT 4.0's feature set.
Part of the wireless spectrum has a decidedly checkered history - that of Ultra-Wideband (UWB.) For years, UWB was confined to military applications - in particular, for ground-penetrating radar. The band itself, however, is extraordinary. Spread over a very wide spectrum (3.1-10.6 GHz) and operating at singularly low energy levels, it is an intuitively attractive band that, paradoxically, has seen only very limited use to date.
The width of the band makes it unusually well suited to supporting multiple users simultaneously. Furthermore, its energy profile is so low that spectra with which it overlaps treat it as background noise, automatically eliminating the danger of any signal interference or cross-talk.
A concerted effort to commercialize the band began in the 1990's. At a certain point, however, the 802.15.3a PAN Task Force split into two camps (the UWB Forum and the WiMedia Alliance), each with its own collection of industry backers, over two standards which were virtually identical in performance but mutually exclusive - in particular concerning the method for partitioning the frequency range into channels. The friction eventually devolved into open warfare, with one of the committee directors actually resigning over his disgust with the acrimonious nature of the debate.
The impasse forced a dissolution of the working group towards the end of the 2000's. Yet one faction did not see work cease on its version of a standard for this very promising radio band. A group of companies began working together in the mid-2000's on a wireless version of USB. This group - the Wireless USB Promoter Group - was, along with the Bluetooth SIG and the USB Implementor's Forum, an inheritor of the WiMedia Alliance work on UWB. While the Bluetooth SIG rejected the specification and chose a different path, the Wireless USB Promoter Group forged ahead and developed the Wireless USB standard.
The specification is already seeing implementation in a variety of consumer electronics applications, including game controllers, Flash drives, cameras, printers and the like. Its bandwidth, power consumption and extraordinary connectivity are proving to be highly attractive indeed. A potentially serious flaw, though, is the supported range - apparently no greater than 10m, and as little as 3m for high bandwidth service demands.
How They Stack Up
To the victor belong the spoils. - William L. Marcy
When compared side by side, the three standards show their share of individual strengths and weaknesses. Not all sources agree on the exact values of the parameters listed below; nevertheless, the following table will serve our purposes broadly enough as a general guide.
Is there a clear cut winner from a purely technical standpoint? Clearly not. All are based on older standards that are, at this point, essentially universal. Wi-Fi Direct has clear leadership in range. BT 4.0 and Wireless USB have a great advantage in power. Connectivity and performance favor Wireless USB. BT 4.0 and Wi-Fi Direct have a much more substantial deployment history as wireless standards.
Yet all of them have a glaring weakness - a fatal one, in fact. What that might be, however, is a topic for another post.