How to Handle Heartbeat Messages

This guide explains how to implement the Heartbeat procedure as defined in WINNF-TS-0016.

Overview

The Heartbeat is the ongoing "keep-alive" mechanism that maintains an active Grant. It allows the SAS to:

• Authorize transmission (move Grant from GRANTED to AUTHORIZED state)
• Renew the Grant expiration
• Issue directives (e.g., reduce power, suspend, or terminate)

Heartbeats must be sent regularly (typically every 60 seconds, but follow SAS-specified heartbeatInterval).

Failure to heartbeat results in Grant termination.

Prerequisites

• Successful GrantResponse with a valid grantId
• Grant in GRANTED state (after approval)

Step 1: Construct the HeartbeatRequest

Required Parameters

Optional but Recommended

Example JSON (first heartbeat after grant)

{
  "heartbeatRequest": [
    {
      "cbsdId": "SAS123/CBSD-001",
      "grantId": "GRANT-789",
      "grantRenew": true,
      "operationState": "GRANTED",
      "measReport": {
        "rcvdPowerMeasReports": [
          {
            "measFrequency": 3620000000,
            "measBandwidth": 10000000,
            "measRcvdPower": -55.3
          }
        ]
      }
    }
  ]
}

Example JSON (ongoing heartbeat while transmitting)

{
  "heartbeatRequest": [
    {
      "cbsdId": "SAS123/CBSD-001",
      "grantId": "GRANT-789",
      "grantRenew": true,
      "operationState": "AUTHORIZED",
      "transmitExpireTime": "2026-01-07T14:30:00Z"
    }
  ]
}

Step 2: Send the Request

• HTTPS POST to SAS heartbeat endpoint
• Mutual TLS authentication
• Send at intervals specified in previous HeartbeatResponse (heartbeatInterval)

Tip: Start a timer immediately after receiving a successful response. Send the next heartbeat before the interval expires (e.g., 5-10 seconds early as safety margin).

Step 3: Process the HeartbeatResponse

Key Parameters

Critical responseCode Values

Example Successful Response

{
  "heartbeatResponse": [
    {
      "cbsdId": "SAS123/CBSD-001",
      "grantId": "GRANT-789",
      "transmitExpireTime": "2026-01-07T15:00:00Z",
      "heartbeatInterval": 60,
      "response": {
        "responseCode": 0,
        "responseMessage": "Success"
      }
    }
  ]
}

Best Practices & Tips

• Begin transmission only after first successful heartbeat with transmitExpireTime in the future.
• Stop transmission immediately if transmitExpireTime is in the past or upon SUSPENDED/TERMINATED.
• Always honor updated operationParam (e.g., reduced maxEirp).
• Include accurate measReport when configured — improves future grant approvals.
• Implement jitter (random 0-5 seconds delay) to avoid synchronized bursts across many CBSDs.
• Persist grantId and last successful heartbeat state for recovery after reboot.
• Use exponential backoff for transient failures, but do not exceed heartbeatInterval.

Common Issues & Troubleshooting

Next Steps

• Continue heartbeat loop for the lifetime of the Grant
• Monitor for SAS directives and respond promptly