Throughput

Throughput is the number of bits of real data transmitted per a unit of total transmission time, typically expressed in kilobits per second (kbps). In addition to the transmitted data, there is usually some overhead, which is additional control and/or address data that must be sent with every data packet. You must include that overhead when calculating the throughput. 

As an example, assume that you transmit 8 bits of overhead and 25 bits of data in 33 µs.

Throughput = 25 bits / 33 µs = 0.757 bits/ µs (which you can also interpret as 757,000 bps or 757 kbps). 

Effect of Packet Loss on Throughput

Packet loss decreases the data received, thus lowering effective throughput. A packet error rate (PER) of 0% does not decrease the throughput, and a PER of 100% results in a throughput of 0. The relationship is linear, and the throughput is easily scaled by a factor of 1-PER.

Throughput in X8721A

The X8721A can measure the effective throughput of a Bluetooth Low Energy device in both Active Scan and Connected modes. These modes are handled slightly differently, but the general principle is that the throughput is the number of bits of data (payload) delivered in a unit of time. In both cases, the result it scaled by 1-PER to account for lost packets.

Active Scan Mode

In Active Scan mode the tester considers the data packets in both the advertisements and the scan response data.  The total amount of payload data is divided by the transmit time. 

Connected Mode

Connected mode supports four different data rates, but the throughput calculations are the same: the payload data received is divided by the time it took to send the data. Of course, there are four different throughputs expected.