Wireless AMR overview
Companies investing in automated meter reading (AMR) will also require a carrier technology, which will support all meters for electricity, gas and water, and wireless radio technologies could well fit the bill. The pros and cons of implementing a wireless AMR solution against other types of technologies need to be assessed on a case-by case basis. However, the most appropriate technology or system architecture is a much wider question.
Wireless radio services fall into two basic categories, those using existing publicly provided services and those requiring the construction of private infrastructure.
Publicly available services
The Global System for Mobile communications (GSM) is an ETSI-developed standard for pan-European public mobile telephony networks, which is now being adopted throughout the world.
Current GSM data services are based on circuit switched technology with a maximum user rate of between 9.6 kb/s and 14.4 kb/s. This service comes with a high level of security provided by both subscriber authentication and by encryption over the air interface. GSM also provides the short message service (SMS) of message length up to 160 characters; however, four separate messages can be concatenated together.
GPRS is the stop-gap technology between conventional GSM and third generation (3G) mobile phone technology. GPRS operates in the same bands as GSM and while GPRS will share base station equipment with GSM a different transceiver will be required.
Third generation phone services will take the packet network approach further with all handsets being permanently connected to the network. 3G will operate at higher frequencies than the existing GSM/GPRS services. Partly as a result of this higher frequency, higher bandwidths will be available, giving a theoretical maximum data capacity of 2 Mb/s.
GPRS and 3G will provide data connection in the form of an ‘always on’ packet data service. This makes GPRS and 3G much more suitable for wireless data services than circuit switched GSM.
Public packet radio
The Mobitex protocol for terminal hardware and software is an open specification. Data streams are broken into packets, which travel through the network independently via diverse routes. This effectively results in increased network capacity, avoids congestion and eliminates the need for end-to-end connection, thus enabling fast call set-up times. Mobitex packet switched services can offer data rates of up to 8 kb/s with packet sizes up to 512 bytes. The use of error detection, correction and automatic positive message acknowledgement, provides a guaranteed data delivery service.
The industry standard CCITT (now ITU-T) uses X.25 packet switching at its core. Access equipment uses standard RS232 (V24) interface using the X.28 protocol. These standard protocols enable any systems integrator or vendor to produce compatible equipment facilitating flexible network deployment. This type of packet switched network can also offer user data rates of between 2,400 bits/s to 8,000 bits/s, with a packet structure of 256 bytes with increments of 64 bytes.
The TSAT service (Telemetry via Satellite) is designed for low data rate communications via satellite to fixed sites. This equipment is more suited to external data concentrators rather than individual domestic meters.
Many utility companies already utilise private radio equipment for a variety of different purposes, such as two-way voice dispatch, telemetry and on-site SCADA communications.
Private mobile radio
Private mobile radio (PMR) services were used extensively until quite recently by the majority of the UK utility companies for two-way voice communications. However, many companies have moved their voice and mobile data across the public mobile telephone operators. This has left redundant infrastructure and frequency spectrum, which could be utilised in some way when implementing AMR.
Scanning radio technology allows the construction of cost-effective private communications networks for high performance telemetry applications. The networks comprise a number of scanner base stations, which communicate in a point-to-multipoint configuration to a number of remote outstation radios. The scanner broadcasts the same information to all its outstations and the outstation radios respond back individually. These systems are generally operated as continuously polled master/slave networks with typically 20-30 outstations per scanner.
Low power (Unregulated)
Low power radio is limited power radio equipment that may be operated without the need for an end-user licence. The devices covered under the capabilities of low power radio include alarms, radio microphones, radio local area networks, telecommand and telemetry. There is often no requirement to obtain an operating licence to operate in the appropriate frequency bands, neither is it a necessity to notify the authorities of the intended use for a particular radio channel. There is, however, a requirement to utilise type-approved equipment in accordance with the appropriate MPT specification.
Having said that there are two distinct categories, the emerging international open standard for short range wireless data exchange, Bluetooth, does not fit comfortably in either. Bluetooth operates in the 2.4 GHz band at very low powers to give a maximum practical range of around 100 metres. The technology will support up to eight devices in a local piconet, thus allowing devices in close proximity to share information with each other and access the outside world via a common portal. (See page 24 for a description of Bluetooth.)
A comparison of the practicalities of the different services is presented in the tables above.
In order to provide a manageable efficient data service, any successful AMR implementation is most likely to utilise a packet-based service, either direct to the meter or to a local concentrator, which would then utilise a low specification connection-based link to the meter.
To construct a regional or national data network dedicated to AMR would be extremely expensive in relation to the returns gained. To overcome this it is most likely that, in ordere to implement a cost effective AMR solution, use will have to be made of existing public or private infrastructure for data transmission back to the utility or billing company. However, a low cost private dedicated local network may be used from local concentrators to individual meters.
New developments in wireless technologies such as Bluetooth will definitely help to facilitate wireless AMR. However, success is most likely to be achieved by those composite solutions which make best use of both existing infrastructure and services utilising the latest open architecture wireless technologies.