Weightless Wireless M2M White Space Communications
- an overview of the 'Weightless' standard for white space technology for machine to machine, M2M wireless communications.
Weightless is the name for the new standard for machine to machine, M2M communications using white space wireless technology.
With M2M communications set to grow dramatically during the new few years, and with requirements for many systems for a low cost system with ultra-low power and excellent coverage, the new Weightless standard and associated technology has been developed to meet these needs.
While cellular networks will carry the data for many M2M communications, there is also a need for a low cost means of carrying this data. This is where the Weightless standard for M2M wireless communications in white space areas can apply. This white space technology is focussed on providing communications in these areas while still providing widespread coverage.
The name 'Weightless' was chosen to reflect the light-weight nature of the protocols used within the standard. The data overhead per transmission has been minimised for devices that want to communicate just a few bytes of data.
Weightless M2M application areas
The Weightless M2M white space communications technology is aimed at the low cost machine to machine application areas where wide area coverage is required. There are a number of applications that need this form of low cost wireless communications technology. Areas where the Weightless M2M technology may be used include:
- Home and consumer goods
- Energy related communications - in particular smart metering
- Healthcare - in particular the mHealth applications that are starting to be developed
- Transportation - this can include the automotive management
- Retail including point of sale, shelf updating, etc
Weightless M2M requirements
As with the development of any system, there are a number of highlight requirements that the Weightless M2M white space communications system aims to fulfil. These chief aims are summarised below:
- Low cost: Many M2M communications require a very low cost solution. Often the 'machines' will be very low cost themselves and therefore the overall system would not be able to withstand a high cost wireless solution. A cost of around $2 per chip or less is necessary.
- Low power: As many machines are remote and may not have a mains power supply and will therefore need to run from batteries, an aim of a ten year battery life is required for the system in many instances.
- Widespread coverage: For many applications almost complete country coverage is required. For example one major application is likely to be smart metering. As meters will be located wherever power is used, coverage will be required for all areas where meters are located.
- Reliable: One essential requirement is that the message or data delivery must be reliable. Although speed of message delivery for the applications anticipated for the Weightless M2M system, reliable message delivery is key.
- Secure: With the growing threat of hacking and unauthorised compromising of systems, security is an issue high on the agenda of many users.
- Support of large number of terminals: With machine to machine communications growing it is anticipated that a single cell may need to serve between 100 000 and 1 million devices. A national network could easily contain over 1 billion devices if predicted rates of growth are maintained.
- Low cost of service: With the machines in the M2M networks being low cost, a similarly low cost of service must be provided otherwise the business case become significantly less attractive.
- Broadcast message capability: There will be instances where broadcast messages may be needed. The system must be able to accommodate this type of message
- Small data bursts: As many machines will send amounts of data at a time, the system must be able to efficiently handle packets of around 50 bytes.
What is white space?
The Weightless standard for M2M communications aims to use white space for its spectrum usage. However it is necessary to define exactly what is meant by white space.
Most of the radio frequency spectrum is allocated for specific uses. With the growing level of usage of radio spectrum, there is increased pressure on the use of the available spectrum. While one option is to use higher frequencies, this pushes the limits of technology, particularly in terms of producing equipment at prices that meet the cost requirements of the users.
The other alternative is to use the spectrum at lower frequencies more effectively. In general, the frequencies between 300 MHz and 3 GHz (UHF - Ultra High Frequency portion of the radio spectrum) provide the most attractive areas to use. Propagation characteristics are favourable and the antennas are a convenient size.
While there is significant pressure on the assignments for the UHF portion of the radio spectrum, the actual usage levels are relatively low. In some areas it can be as low as 20%. There are many reasons for this. Often sufficient distance needs to be left between broadcast transmitters for example to ensure interference is low. For business users interference needs to be low and again this results in low levels of usage.
The case of television broadcasting which uses much of the UHF portion of the spectrum is particularly interesting. While signals may be able to be received by high gain antennas that are sufficiently high, it is also possible to use these white spaces without causing interference if much lower gain, lower height antennas are used with lower power transmitters, and modulations schemes that are unlikely to cause undue interference.
Effectively white space technologies utilise the spectrum that would otherwise lay dormant to provide the "guard distances" between high power transmitters to ensure minimum interference levels.
Weightless M2M basics
'Weightless' is an open wireless standard that provides the ability for exchanging data between a base station and machines using radio transmissions in unoccupied TV transmission channels - white space.
The remote terminals or machines transmit and receive to and from a base station over the air interface.
The Weightless base stations have a data backhaul route or connection that may be the Internet to the network manager and synchronisation database.
The Weightless specification covers the air interface, i.e. radio system and also the base station interface. This will enable multiple vendors to all supply equipment that interoperates.
In terms of the radio interface, the Weightless standard uses either phase shift keying or quadrature amplitude modulation together with a scheme of 'Whitening' to make the spread the signal and make it look more like white noise to reduce any levels of interference that may be caused. In addition to this this the system uses time division duplex, TDD to enable both uplink and downlink transmissions to use the same channel.
|Weightless M2M Wireless Communications
|Modulation||BPSK, QPSK & 16-QAM|
|Uplink & downlink||Configurable to meet requirements|
|High data rate downlink||~500 kbps - 16 Mbps|
|Low data rate downlink||~ 2.5 kbps - 500 kbps|
In order to develop the specification and standard for the Weightless SIG - Special Interest Group was formed. Its aims are to coordinate and enable all the activities required to deliver the new Weightless standard for M2M communication in white space.
In addition to developing the standard the Weightless SIG also aims to manage its on-going development , promote the standard, manage testing, certification and ensure interoperability. The SIG also aims to provide a forum for influencing regulators to enable access to white space radio spectrum.
By Ian Poole
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