Scheduled Data Message Transmission in APCO P25 Systems
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Solution Overview
Problem
In communication systems, especially those following APCO Project 25 standards, unscheduled data message transmissions often result in message deterioration or loss due to multiple devices trying to transmit simultaneously, and confirmation messages consume significant bandwidth on outbound packet data channels.
Innovation Solution
A system and method for transmitting scheduled data messages on a controlled access packet data channel, where communication units append a header with time specifications to data messages, ensuring transmission at predetermined times, thereby avoiding contention and allowing unconfirmed message transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple communication units transmit data messages simultaneously on the same packet data channel, then the data transmission capacity is improved, but message deterioration or loss occurs due to contention
Solution Approach 1:
The system performs preliminary scheduling of data message transmissions by the zone controller, assigning specific time slots and channels to different communication units before transmission occurs. This preliminary allocation prevents simultaneous transmissions on the same channel, eliminating message deterioration while maintaining high data transmission capacity through efficient resource utilization.
2Reliability
If confirmation messages are sent to verify data message receipt, then message delivery reliability is improved, but bandwidth consumption on outbound packet data channel increases significantly
Solution Approach 1:
The invention extracts the confirmation function from the outbound packet data channel and relocates it to the inbound packet data channel. Communication units send confirmation messages back to the zone controller on the inbound channel, which has available capacity since it is primarily used for upstream transmissions. This separation allows reliable delivery confirmation without consuming additional outbound channel bandwidth.
3Speed
If unscheduled data transmission is used to allow immediate message sending, then transmission speed is improved, but message loss increases due to channel contention
Solution Approach 1:
The zone controller performs preliminary scheduling of data transmissions, assigning communication units to specific time slots and channels in advance. This allows communication units to transmit immediately when their scheduled time arrives without contention, as the channel is reserved exclusively for them. The scheduling information is provided beforehand, enabling fast transmission while guaranteeing message integrity through dedicated channel allocation.
Data Source
AI summary
A system and method for enabling scheduled data messages to be transmitted within a communication system on a controlled access packet data channel. When a scheduled data message is to be transmitted, a mobile device generates the data message, appends a predetermined type of header to the data message, and passes the data message to a communication unit. The header comprises an hour field, a minute field, and a slot field indicative of a specific time when the data message is to be transmitted on the controlled access packet data channel. After receiving a data message from the mobile device, the communication unit parses the received data message to determine whether the received data message should be processed as a scheduled data message on the controlled access packet data channel, and transmits the data message to a fixed network at a specific time based on the hour, minute, and slot fields in the header.