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Bluetooth radio conformance | Bluetooth Device testing and measurements

This page describes Bluetooth radio conformance testing including physical layer and radio layer. It describes Bluetooth transmitter and receiver measurements as part of Bluetooth Device testing and measurements.

Introduction:
Bluetooth specifications were formalized by Bluetooth SIG (Special Interest Group). IEEE initially standardized bluetooth as IEEE 802.15.1 but no longer maintains the standard. Recently bluetooth SIG has published V5.1 as successor to V5.0.

Following table mentions bluetooth standard versions, data rate, modulation and so on.

Bluetooth Standard Data rate Modulation Description
V1.0 1 Mbps GFSK Initial specification
V1.2 1 Mbps GFSK First FDA approved bluetooth medical system as per this standard has been developed.
V2.0 + EDR 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK EDR specification has been introduced for fast data transfer.
V2.1 + EDR 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK SSP (Secure Simple pairing) and EIR (Extended Inquiry Response) concepts have been introduced in bluetooth devices.
V3.0 + HS 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK
V4.0 (Smart) 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK BLE protocol stack and 128 bit AES have been introduced.
V4.1 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK
V4.2 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK Increased data throughput with data length extension, Increased privacy and so on.
V5.0 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK 2 Mbps PHY for LE, LE Long Range
V5.1 1 Mbps, 2 Mbps, 3 Mbps GFSK, π/4-DQPSK, 8-DPSK Released recently in Jan, 2019, Refer Bluetooth v5.0 versus v5.1 >>

Following figure depicts protocol stack layers in a typical bluetooth device. The bluetooth conformance testing requires to validate all of these protocol layers. The major among them include physical layer and radio frequency layers. Radio layer lies below physical layer.

BLE Protocol Stack

Bluetooth devices operate in 2.4 GHz ISM band which ranges from 2400MHz to 2483.5 MHz.

Bluetooth Smart or BLE frequency channels

The bluetooth uses 40 frequency channels out of which 3 are used as advertising channels and 37 are used as data channels.

List of bluetooth transmitter tests

The common bluetooth transmitter tests include modulation spectrum tests, Spurious tests (in-band, out-of-band), radio frequency tolerance etc. Following table summarizes the bluetooth measurements performed on bluetooth transmitter part during bluetooth radio conformance testing.

Bluetooth transmitter tests Description with limits (if any)
Modulation characteristics • Bluetooth packets use GFSK modulation scheme. In this modulation type, positive frequency deviation represents "binary-1" where as negative frequency deviation represents "binary-0".
• In this test, system verifies frequency deviations of the data bits transmitted in a GFSK packet are within limits or not.
• (Basic rate pass limit:)
• 140 KHz <=Δf1avg <= 175 KHz
• Δf2max >= 115 KHz for at least 99.9 % of all Δf2max
• Δf2avg/Δf1avg >=0.8
• (Low Energy pass limit:)
• 140 KHz <=Δf1avg <= 175 KHz
• At least 99.9% of Δf2max values over 10 test packets >=185 KHz
•  Δf2avg/ Δf1avg >=0.8
Output power Minimum output power : 0.01mWatt (-20 dBm)
Maximum output power : 10 mWatt (+10 dBm)
In band spurious emission • The purpose of this test is to verify that the level of unwanted signals from the transmitter within operating band of the device does not exceed specified limits.
• (Pass limit for Bluetooth Basic rate/EDR:)
PTx-26dB (f) <= PTxref - 26 dB for |M-N| = 1
PTx (f) <= -20 dBm for |M-N| = 2
PTx (f) <= -40 dBm for |M-N| >= 3
• (Pass limit for Bluetooth Low Energy :)
PTx <= -20 dBm for FTx +/- 2 MHz
PTx <= -30 dBm for {FTx +/- [3+n] MHz} ; where n =0,1,2,..
Out-of-band spurious emission The equipment manufacturer is responsible for the ISM out-of-band spurious emissions requirements in the intended countries of sale.
Radio Frequency tolerance • The deviation of the center frequency during the packet shall not exceed +/- 150 kHz, including both the initial frequency offset and drift.
• The frequency drift during any packet shall be less than 50 kHz. • The maximum drift rate is 400 Hz/µs.

List of bluetooth receiver tests

The common bluetooth transmitter tests include actual sensitivity level, Interference performance, Out of Band Blocking, Intermodulation characteristics, Maximum usable level, Reference signal definition etc. Following table summarizes the bluetooth measurements performed on bluetooth receiver part during bluetooth radio conformance testing.

Bluetooth receiver tests Description with limits (if any)
Actual sensitivity level The actual sensitivity level is defined as the receiver input level for which a BER of 0.1% is achieved.
The actual sensitivity level of the receiver shall be less than or equal to -70 dBm.
Interference performance (Carrier to Interference ratio) Both the interfering signal and wanted signal should be GFSK-modulated. Passing Limits for various C/I types are as follows.
(C/Ico-channel) = 21 dB
(C/I1 MHz) = 15 dB
(C/I2 MHz) = -17 dB
(C/I>=3 MHz) = -27 dB
(C/IImage frequency) = -9 dB
(C/IImage +/- 1 MHz) = -15 dB
Out of band blocking • The out-of-band blocking test is performed by generating the signal of interest and then combining it with the interfering signal that is out-of-band.
• The BER of <= 0.1% (or PER better than 30.8% for a minimum of 1500 packets) is still the same passing limit.
• The power of level of the interfering signal varies with frequency.
Intermodulation characteristics The purpose of the receiver intermodulation test is to verify that the receiver can demodulate a Bluetooth signal among unwanted signals nearby in frequency. Passing limits for BR and LE are as follows.
For Basic Rate BER <= 0.1%
For LE PER < 30.8%; minimum of 1500 packets are used during the bluetooth device testing.
Maximum usable level The maximum usable input level the receiver can operate at shall be >= -10 dBm.
BER shall be <= 0.1% at -10 dBm input power.
Reference signal definition The parameters of reference signal are as follows.
Modulation = GFSK
Modulation index = 0.5 ± 1%
BT = 0.5 ± 1%
Bit Rate = 1 Mbps ±1 ppm
Modulating Data for wanted signal = PRBS9
Modulating Data for interfering signal = PRBS15
Frequency accuracy better than ±1 ppm

Bluetooth device testing and measurements

➤Following figure mentions generic test setup used for bluetooth device testing and measurements.
➤As mentioned VSG (Vector Signal Generator) is used to generate bluetooth compliant signals which is fed to receiver part of the bluetooth device in order to test it. This test helps in receiver sensitivity and BER testing.

bluetooth test setup

➤VSA (Vector Signal Analyzer) is used to test transmitter part of bluetooth device. The common tests include power spectrum measurements, leakage test, modulation quality and so on.
➤The 3-port RF circulator at 2.4 GHz band is used to direct signal from VSG to bluetooth device (Rx part) and from bluetooth device(Tx part) to VSA. Refer working of RF Circulator >> for more information.

References:
•  www.bluetooth.com



Bluetooth and BLE Related Links

Also refer bluetooth tutorial covering following sub topics:
Bluetooth tutorial  BLE tutorial  Frequency  PHY Layer  MAC layer  Stack  Power classes  Security  products  versions  Bluetooth Vs BLE 


BLE (Bluetooth Low Energy) Links

Bluetooth v4.2 versus v5.0 >>
Bluetooth v5.0 versus v5.1 >>
BLE states and state diagram >>
BLE advertising and data channels >>
BLE protocol stack architecture >>
BLE connection process >>
BLE advertising and data packet formats >>


RF and Baseband Measurement Links


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