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Multiple Address (MAS) Radio

URL:      http://www.micronetcom.com/mas.htm

MAS radio has gained popularity in recent years due to its flexibility, reliability and compact size. A basic MAS radio link consists of a master radio transmitter/receiver unit and multiple remote radio transmitter/receiver units. A master unit can access or poll multiple units via a pair of transmit/receive frequencies. The master unit is set up always ready to transmit and receive in order to keep delay due to transmitter keying to a minimum. Each remote unit is set up always in the listening mode until it is polled and then ready to transmit. Each remote unit has a unique address so no two units will try to answer the poll at the same time. This eliminates any contention among the remotes to transmit to the master. The frequency pair used by MAS requires to be licensed by the FCC and the same pair can be re-used elsewhere in the system as long as it does not cause any interference.

For performance reasons, there is a limit to the number of remotes that can be polled by one master radio. This limit is determined by the time delay in the poll and the handshaking required in the response, the data transmission rate and the data collection time set by the system. So, for a large service area, many master radios will need to be used to cover groups of remote units each located in or near a utility owned facility. For difficult-to-reach locations due to topography or limitation of line-of-sight, the same MAS radio can be used as a repeater radio to allow signal transmission over or around large obstructions.

Typically each master radio is located at a site where there is an existing connection to the utility’s control center where data is collected for the entire system. This can be a microwave site or fiber optic network node in a network. MAS radio is the preferred communication medium and has been used widely by utilities for SCADA (supervisory control and data acquisition) systems and DA (distribution automation) systems.

Main Features of Technology

Technology

Radio

Frequency

895 to 960 MHz transmit/receive frequency pair

Bandwidth

25kHz for existing frequencies, 12.5kHz for new frequencies

Operation

Requires line-of-sight, point-to-multipoint for master and remote radios

Capacity

Can be expanded by using more master radios, but will be limited by how fast remotes can be polled and system scan period allowed

Coverage

Each link is typically 15km

Data rate

Up to 4.8kbps, can be increased to 9.6Kbps but coverage will be reduced

No. of channels

Minimum separation between adjacent channels is 25kHz for previous frequency allocations and 12.5KHz for new frequency allocations

Multiplexing/modulation method

Frequency shift keying (FSK)

Power

5W master, 1W remote

Regulatory

Frequency licensing required

Key Advantages

Capacity

Capacity is limited by data speed and system scan time. Also, limited by the number of masters that can be physically installed in the system (location, topography, etc.)  

Coverage

Can typically reach 15 km, can be extended by using repeaters

Data rate

Up to 9.6kbps (with reduced coverage)

Reliability

Can be improved with remote diagnostics, warm standby equipment and redundant architecture 

Interference

Licensed frequencies provide some protection against interference by others

Cost

Relatively low

Key Disadvantages

Operation

Line-of-sight to remotes prone to obstruction

Regulatory

Licensing is time consuming and may not be possible due to lack of available frequencies

Keywords:            Wireless, LAN

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Copyright EPRI 2004