What limits BLE throughput?

PHY data rate (1M or 2M), connection interval (how often data is sent), DLE (Data Length Extension, max 251 bytes/PDU vs 27 default), MTU (application payload per ATT transaction), and the number of packets per event. Without DLE: max ~236 kbps on 1M. With DLE + 2M PHY: up to ~1.4 Mbps.

Data Length Extension (BLE 4.2+) increases the maximum PDU payload from 27 to 251 bytes. Without DLE, each packet carries only 20 bytes of ATT data after L2CAP/ATT headers. With DLE: 244 bytes per packet. This dramatically reduces per-byte overhead and increases throughput by 3-5x.

Why is real throughput lower than PHY rate?

The 1 Mbps PHY rate is the raw over-the-air bit rate including preamble, access address, headers, CRC, and inter-frame spacing. Application throughput deducts these overheads plus connection event scheduling gaps. Maximum practical throughput is approximately 800 kbps on 1M PHY with optimal settings.

Wireless Protocols

BLE Throughput

BLE Throughput is the application-layer data rate achievable over a BLE connection, typically ranging from 2 kbps (long CI, no DLE) to ~1.4 Mbps (7.5 ms CI, DLE, 2M PHY, multiple packets/event). Key factors: PHY data rate, connection interval, Data Length Extension (DLE), MTU size, and packets per connection event. Maximizing throughput requires optimizing all parameters simultaneously.

Category: Wireless Protocols

Max: ~1.4 Mbps (2M+DLE)

Understanding BLE Throughput

Without DLE, each BLE packet carries only 20 bytes of ATT payload (27-byte PDU minus 7 bytes of L2CAP/ATT headers). With DLE enabled, the PDU extends to 251 bytes, carrying 244 bytes of ATT data per packet. This reduces overhead from 35% to under 3%, multiplying effective throughput 3-5×.

Multiple packets can be sent per connection event if both sides support it. With 7.5 ms CI, DLE, and 2M PHY, approximately 6 packets fit in one event, yielding ~1.4 Mbps. Real-world throughput also depends on the mobile OS: iOS and Android impose different limits on packets per event.

Throughput Estimation

Throughput = (Payload/packet) × (Packets/event) / CI

No DLE, 1M PHY, CI=7.5 ms:
20 B × 6 pkts / 7.5 ms = 128 kbps

DLE, 2M PHY, CI=7.5 ms:
244 B × 6 pkts / 7.5 ms ≈ 1.4 Mbps

Throughput by Configuration

PHY	DLE	CI	Pkts/Event	Throughput
1M	No (20 B)	7.5 ms	6	~128 kbps
1M	Yes (244 B)	7.5 ms	4	~800 kbps
2M	Yes (244 B)	7.5 ms	6	~1.4 Mbps
1M	Yes (244 B)	30 ms	4	~200 kbps

Common Questions

Frequently Asked Questions

What limits throughput?

PHY rate, CI, DLE (27 vs 251 B PDU), MTU, and packets/event. Without DLE: max ~236 kbps. With DLE+2M: ~1.4 Mbps.

What is DLE?

Data Length Extension (BLE 4.2+): PDU from 27 to 251 bytes. ATT payload from 20 to 244 bytes. 3-5× throughput improvement.

Real vs PHY rate?

1 Mbps PHY includes all overhead. Max app throughput ~800 kbps on 1M. Overhead: preamble, headers, CRC, IFS, scheduling gaps.

Related Terms

← Supervision Timeout BLER →

BLE Performance

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