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Optimize over-the-air bandwidth usage with WMX modem status

Raveon’s WMX protocol is the preferred way to communicate over-the-air in advanced or tightly-integrated configurations. As of version D4 of the protocol, it is now possible to closely monitor message queuing, transmission and acknowledgement. This allows bandwidth usage to be optimized for the communication application.

Bit 5 in the WMX control field indicates whether the modem should provide additional message information back to the sender. Setting this bit in a message sent to a modem will cause two messages sent back to the receiver:

  1. A message indicating whether the message was accepted and queued (“Q”) or was rejected due to a full buffer or other condition (“N”)
  2. A message indicating that the message has been transmitted (“T”), processed locally as a command (“L”) or was flushed from the buffer and not processed (“F”)

The messages will indicate the sequence number of the message whose status is being provided.

Number of bytes

Field Name

Data

1

Message Status

ASCII Character Indicating a Message Status. It will be one of:

‘Q’ – Message has been accepted and queued for transmission

‘N’ – Message was not accepted for transmission and has been dropped

‘T’ – Message was sent over-the-air and has been fully processed

‘L’ – Message was processed locally (commands to the local radio)

‘F’ – Message was queued but subsequently flushed and not transmitted

1

Status Separator (,)

1-3

Original Sequence Number

The sequence number of the original message (the message whose status is being provided). ASCII Decimal formatted.

1

Status Separator (,)

1-4

Message TOID

The destination address of the original message (the message whose status is being provided). ASCII Hex formatted.

This information provides insight into bandwidth usage that allows optimization for the particular communication scenario. For instance, an installation using TDMA will queue data to be sent until the modems transmission slot is available. If only a single message or a set amount of data should be queued, the application can wait for the “T”, “L” or “F” messages before providing another message to send over-the-air.

Acknowledgement messages received by the modem also generate special WMX packets. When an acknowledgement is received, a message with frame type 3 will be output from the modem. This message will indicate which sequence number was acknowledged by the remote radio. With a combination of the queue full (“N”), transmit (“T”) and acknowledgement messages, it is possible to send bulk data continuously over-the-air as well as re-transmit any data that is not acknowledged.

Example code for interfacing with our radios using WMX can be found in our public code repository.

For advice on your own system implementation from a Raveon engineer, contact us today.

Filed under: Data Radio Technology, System Design | Posted on July 31st, 2013 by Adam Hickerson

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