KEY USER BENEFITS OF TDMA

• Real-time mobile tracking with either Real Time Kinematic or standard DGPS accuracy
• System provides continuous location of all mobile units ‘at a glance’
• Auto adaptive repeater mode extends operating range in areas where direct communications is obstructed
• Advanced technology permits reliable signal transmission in difficult conditions without operator intervention
• Use of messaging facility for the broadcast of navigational instructions such as waypoints and guard zones reduces voice

TDMA is an intelligent data network system which operates at UHF and VHF frequencies permitting continuous real-time messaging from a wide variety of applications. Operating on a Time Division Multiple Access principle the system is extremely flexible in configuration, giving the mobile data system integrator complete control over messaging rates and content. Each mobile unit within the TDMA system is allocated a unique identity code and transmits its position or other data in a time slot assigned to it. Transmission timing is synchronised by GPS and revised by the control centre as required. All transmitted data carries a tag identifying its origin and destination and this enables other mobile units in the operating area to monitor the data network and automatically forward messages if direct transmission is blocked. This unique technology enhances communication reliability and can significantly extend the operational range of the TDMA system beyond the normal line of sight restrictions.TDMA is ideal for real-time tracking applications allowing the reporting of GPS position of mobile units back to a control centre display system. At the same time, Differential GPS corrections can be broadcast through the network for precise positioning applications. The system operates on a single UHF or VHF frequency and can handle up to 250 mobile reports per radio channel although this capacity can be expanded by the use of additional channels in a cellular configuration.

TECHNICAL CAPABILITIES

Data Communication Between Units
As well as position reporting to a control centre and the distribution of RTCM data, messages can be routed from one mobile to another. Selective or group messaging is possible from the control centre as is the facility for units to be configured dynamically. Voice radio traffic can be reduced and communications in crowded frequencies made faster as a result.

Auto Adaptive Repeater Mode

Any TDMA unit in a system can operate intelligently as a repeater. Each mobile unit monitors the communications status of all other units in its local area, and should the path between 2 units be obscured, the unit will automatically deduce which path is blocked and undertake to pass on the message during the next time slot allocated to the originator of the message. In this way messages can be re-broadcast to circumvent radio line of sight limitations or to relay messages made from beyond the network’s normal radio range.

System Capacity

Transmission of data within a ‘cell’ is via a single radio channel. Each unit’s access to the network is configured during initial set-up. A typical mobile reporting interval would be 10 seconds, depending on priority, which would allow spare capacity to be allocated to fast mobiles and any dedicated repeaters. The frequency of position reports from mobile units can be changed by the control centre enabling it to focus on units involved in critical activities.