SMART ENERGY WEIGHTLESS AND WHITE SPACE COMMUNICATION By Professor William Webb, FREng, FIET FIEEE, CEO of Weightless SIG Spend a couple of minutes right now on a popular internet search engine with terms like “internet of things”, “smart meters” and “smart grids” and you’ll be met with hundreds of millions of hits; enormous global shifts are obviously taking place in machine communications – the world is changing and fast. But hold on, this ‘brand new’ phenomenon has been happening for decades, hasn’t it? Well, the answer is yes and no. We have been forecasting a connected world but it just hasn’t happened. If it had, then we wouldn’t even be considering the reasons and we’d be enjoying the utopian Shangri-La today. Conventionally M2M solutions have been developed around traditional legacy cellular technologies but for most applications they are not optimal. Cellular technologies do provide sufficiently good coverage for some applications but the hardware costs can be $20 or more depending on the generation of cellular used and the subscription costs are often closer to $10 per month than $10 per year. Battery life cannot be extended much beyond a month. Cellular networks are often ill-suited to the short message sizes in machine communications, resulting in extremely significant overheads associated with signalling in order to move terminals from passive to active states, report on status and more. So while cellular can capture a small percentage of the market which can tolerate the high costs and where devices have external power, it cannot meet the requirements of the 50 billion plus device market, nor the billion dollar global smart meter opportunity. Indeed, if it could, it would have done so already and there would be no further debate about the need for new standards. WHITE SPACE IS THE PARADIGM SHIFT The value in machines having wireless communications has long been understood and a large market predicted for many years. That this has not transpired has been because of the difficulty of meeting all the requirements within the constraints of the available radio spectrum. These constraints changed significantly with the advent of white space – the unused portions of the spectrum band in and around TV transmissions – which provides near-perfect spectrum with free access. White space meets all of the requirements for M2M communications. It is unlicensed and so access to it is free. It is plentiful, with estimates of around 150 MHz of spectrum available in most locations – more than the entire 3G cellular frequency band. It is globally harmonized since the same band is used for TV transmissions around the world. And, it is in the perfect low frequency band which enables excellent signal propagation delivering long range and excellent in-building penetration without the need for inconveniently large antennas in the devices. This is why white space is the paradigm shift. Access to white space provides the key input needed to make the deployment of a wide-area machine network for smart meters (and other devices) economically feasible. White space access requires devices with the following characteristics: 54 • Relatively low output power. The FCC has specified 4W EIRP for base stations and 100 mW EIRP for terminals – an order of magnitude lower than legacy GSM/3G/LTE based technologies. • Stringent adjacent channel emissions. White space devices must not interfere with existing users of the spectrum, predominantly TV signal transmissions. The energy that they transmit must remain almost entirely within the channels they are allowed to use. The FCC has specified that adjacent channel emissions need to be 55 dB lower than in-band emissions, a specification much tighter than most of today’s wireless technologies. • The need to frequently consult a database to gain channel allocation. Devices need to rapidly vacate a channel if it is needed by a licensed user. Interference can be problematic in white space. Many channels have residual signals from TV transmissions. These can be in-band emissions from distant, powerful TV masts that are too weak for useful TV reception but are still significantly above the noise floor. Or they can be adjacent channel emissions from nearby TV transmitters, some of which are transmitting in excess of 100 kW. In addition, since the band is unlicensed, other users might deploy equipment and transmit on the same channels as the machine network, causing local interference problems. These are not insurmountable issues. But no legacy technology has been designed to operate in such an environment and so would be sub-optimal at best. For example, we have shown that in the UK that an optimized technology could access around 90 MHz of white space after all the interference issues are taken into account, whereas an existing technology such as Wi-Fi or WiMax could only access around 20 MHz. White space spectrum provides the key to unlock the machine network problem. However, the combination of the unique and unusual nature of the spectrum access and the very different characteristics of machine traffic compared to human traffic means that using any existing standard is far from optimal. Hence, the need for a standard designed specifically for machine communications within white space. That new standard has been developed, named Weightless. WEIGHTLESS – A GAME CHANGER There are many short range technologies that come closer to the price points needed in the M2M sector. These include Wi-Fi, Bluetooth, ZigBee and others. However, being short range these White space signals have good range and immunity from obstacles such as trees in rural areas SMART ENERGY & METERING INTERNATIONAL ISSUE - 1 | 2013