How to Implement Multi-Grant Strategies

This guide explains how to manage multiple concurrent grants per CBSD for improved reliability, channel diversity, and load balancing.

Overview

A single CBSD can hold multiple grants simultaneously on non-overlapping frequency ranges. This enables:

• Primary + backup channels (failover)
• Resilience against DPA activations or interference
• Better overall uptime

Key Bridge SAS Specifics:

• We allow up to 15 concurrent grants per CBSD when interference conditions permit.
• All grants are issued in 10 MHz blocks only — we do not support 5 MHz sub-channels or 20 MHz (or wider) bonded channels.
• Granted frequency ranges will always be multiples of 10 MHz and aligned to the CBRS 10 MHz grid (e.g., 3550-3560, 3560-3570, etc.).

Prerequisites

• Working single-grant flow (registration → inquiry → grant → heartbeat)
• Radio hardware/firmware supporting multiple 10 MHz channels simultaneously
• Persistent storage for multiple grantIds

Step 1: Request Multiple Grants

After registration/inquiry, send separate GrantRequest objects (in one array or sequential requests). Request non-overlapping 10 MHz blocks or the full band — the SAS will assign available 10 MHz channels.

Recommended Strategies

Example: Requesting Full Band + Two Specific 10 MHz Blocks

{
  "grantRequest": [
    {
      "cbsdId": "SAS123/CBSD-001",
      "operationParam": {
        "operationFrequencyRange": { "lowFrequency": 3550000000, "highFrequency": 3700000000 },
        "maxEirp": 37.0
      }
    },
    {
      "cbsdId": "SAS123/CBSD-001",
      "operationParam": {
        "operationFrequencyRange": { "lowFrequency": 3550000000, "highFrequency": 3560000000 },
        "maxEirp": 30.0
      }
    },
    {
      "cbsdId": "SAS123/CBSD-001",
      "operationParam": {
        "operationFrequencyRange": { "lowFrequency": 3650000000, "highFrequency": 3660000000 },
        "maxEirp": 30.0
      }
    }
  ]
}

Tip: Use slightly lower maxEirp on secondary requests to improve approval probability.

Step 2: Manage Multiple Heartbeats

• Run independent heartbeat timer for each grantId
• Send separate HeartbeatRequest per grant
• Track transmitExpireTime and operationState per grant

Example Heartbeat for Two Grants

// Grant 1
{ "heartbeatRequest": [{ "cbsdId": "...", "grantId": "GRANT-789", "operationState": "AUTHORIZED", ... }] }

// Grant 2
{ "heartbeatRequest": [{ "cbsdId": "...", "grantId": "GRANT-790", "operationState": "AUTHORIZED", ... }] }

Step 3: Handle Failover and Termination

On 501 TERMINATED_GRANT:

• Stop transmission on that 10 MHz block immediately
• Relinquish the grant
• Promote highest-priority backup
• Request replacement 10 MHz grant

Radio Management:

• Prioritize grants by EIRP or preferred frequency
• Ensure radio switches cleanly between 10 MHz blocks

Best Practices & Tips

• Target 3–10 grants per CBSD in contested areas (up to our 15-grant limit)
• Combine with grouping and measurements for optimal allocation
• Request full band first — we will assign the best available 10 MHz blocks
• Avoid requesting 5 MHz or 20 MHz ranges — they will be rejected or adjusted
• DPA Neighborhood Strategy: When operating in or near a DPA neighborhood, always maintain at least one active grant in the upper 50 MHz (3650-3700 MHz). Many DPAs protect lower channels first, so upper channels often remain available longer during activations.
• Log grantId, exact frequency range, and EIRP for diagnostics
• Key Bridge SAS: Multi-grant deployments show significantly higher uptime during dynamic events

Common Issues & Troubleshooting

Next Steps

• Implement per-grant state tracking
• Test multi-grant failover in sandbox