Because Bluetooth works in the ISM frequency band, it has strict requirements on its frequency range . There are such requirements in the output frequency range of Bluetooth. The measurement standard is the power spectral density of -80dBm/Hz . If the RBW is set to 100K, then it is - 30dBm. The Bluetooth duplex mode is TDD. Power is divided into 3 levels
Class1:0dBm-20dBm;
Class2:-6dBm-4dBm;
Class3:0dBm
The common one is Class2, and the power is generally around 0dBm . In addition, I also heard that there is Class 1.5 , but it is not a standard value, and the power is between Class1-2 .
There are three modulation methods of Bluetooth, GFSK , π/4-DQPSK , 8DPSK . For the parameters of the standard modulation signal, please refer to the spec .
The settings before the test include whether the test mode is loopback or transmission mode, whether frequency hopping is required , whether the packet is a single-slot packet or a multi-slot packet, and whether the packet's payload is PRBS9 or 00001111/01010101 .
The basic test items of Bluetooth TX include
Output power, power spectral density, power control, frequency range, 20dB bandwidth, adjacent channel power, modulation characteristics, initial carrier tolerance, carrier frequency offset .
The basic test items of RX are
Sensitivity, carrier-to-interference performance, blocking performance, intermodulation characteristics and maximum input level .
Then there is the EDR test, which is nothing more than a different modulation method.
For the adjacent channel power, it is a little different from TD or W, and the test range specified in the specification is relatively wide. Specifically, the channel of +-2 is less than -20dBm, and for +-3 and all other channels, it should be -40dBm, and 3 fail points are allowed, but the power of the fail point cannot exceed -20dBm. For the test of the carrier-to-interference ratio, there is such a problem. In the requirement list, for the same frequency, the required signal is 11dB larger than the interference. 0dB at 1M, -30dB at 2M, and -40dB at greater than 3M. But for an image frequency point, the requirement is -9dB. The specification states that this image frequency point is given by the chip manufacturer. In addition, the frequency points that do not meet the requirements are called spurious response points, and 5 such points are allowed beyond the frequency of 2M greater than the useful signal, but these points must meet the C/I greater than -17dB.
Because some people will ask what is the meaning of DH1 , 2-DH3 , etc., so let's talk about the problem of data grouping mode. The bluetooth system supports real-time synchronous directional connection and non-real-time asynchronous non-directional connection, which become SCO respectively. Link ( Synchronous Connection-Oriented Link ) and ACL link ( Asynchronous Connection-Less Link ), the former mainly transmits real-time information such as voice, and transmits it in the specified time slot, while the latter is mainly data, which can be used at any time. time slot transmission. However, when the ACL transmission occupies the reserved time slots of the SCO , once the system needs the SCO transmission, the ACL will automatically give up these time slots to ensure the real-time performance of the SCO . There are several forms of ACL packets, such as our more common DH1, DH3, DH5 , DM1, DM3, DM5 . The numbers that follow indicate the number of time slots supported. The difference between DH and DM is that DH does not add FEC , that is, forward error correction code. Therefore, the anti-interference performance is poor, but the transmission rate is higher thanDM be quick. For 2-DH1 and 3-DH1 that appeared in the test , it is the difference of the modulation method, 2 corresponds to π/4-DQPSK , and 3 corresponds to 8DPSK . SCO 's data package includes HV1, HV2, HV3 , DV, EV3, EV4, EV5 , but in reality, it is all test data services, so everyone knows this is OK .
1. Launch test
(1) Output power
The link is frequency hopping, the EUT is set to loopback mode or send mode, the payload PN9 is sent, and the packet type is the maximum length supported (DH1, 3 or 5).
The tester measures peak and average power over the entire burst range at low, mid and high frequencies.
The specification requires peak power and average power to be less than 23dBm and 20dBm, respectively, and to meet the following requirements:
If the power level of the EUT is 1, 0dBm<average power<20dBm;
If the power level of the EUT is 2, -6dBm<average power<4dBm;
If the power level of the EUT is 3, the average power is <0dBm.
(2) Power density
The link is frequency hopping, the EUT is set to loopback mode or send mode, the payload PN9 is sent, and the packet type is the maximum length supported (DH1, 3 or 5).
The tester finds the frequency point corresponding to the maximum power in the 240MHz frequency band by sweeping the frequency, and then performs a time domain scan (scanning time is 1 minute) at this frequency point, and measures the maximum value, which is required to be less than 20dBm/100kHz.
(3) Power control
The initial state is non-frequency hopping, and the test mode is loopback mode or transmit mode. Send the payload PN9, the packet type is DH1. The maximum output power of the DUT is -40dBm.
The EUT works at three frequency points of low, medium and high respectively, and sends back the DH1 packet whose modulated signal is PN9. The tester controls the EUT output power through LMP signaling, and tests the range of the power control step size, which is between 2dB and 8dB as required by the specification.
(4) Frequency range
The initial state is non-frequency hopping, and the test mode is loopback mode or transmit mode. Send payload PN9 with packet type DH1, 3 or 5.
When the EUT works at the lowest frequency point, the tester finds the frequency point fL when the power density drops to -80dBm/Hz (-30dBm/100KHz bandwidth); when the EUT works at the highest frequency point, the tester finds that the power density drops as Frequency point fH at -80dBm/Hz (-30dBm/100KHz bandwidth). It is required that fL is located in the range of 2399~2405MHz, and fH is located in the range of 2475~2485MHz.
(5) 20dB bandwidth
Non-frequency hopping, the test mode is loopback mode or transmit mode. Send payload PN9 with packet type DH1, 3 or 5.
The EUT works at three frequency points of low, medium and high respectively, and sends back the modulated signal DH1 packet.
The tester sweeps the frequency to find the frequency point corresponding to the maximum power, and finds the fL and fH corresponding to the power drop of 20dB on the left and right sides. The 20dB bandwidth Df = |fH - fL|, and Df is required to be less than 1MHz.
(6) Adjacent channel power
Non-frequency hopping, the test mode is loopback mode. Send the payload PN9, the packet type is DH1.
The EUT working frequency points are the 0th channel, the 39th channel and the 78th channel respectively, and the DH1 packet with the payload of PN9 is returned. The tester scans the entire Bluetooth frequency band and tests the power of each channel.
The leakage power of the adjacent second channel is required to be less than -20dBm, and the leakage power of the adjacent third channel and above is required to be less than -40dBm.
(7) Modulation characteristics
Non-frequency hopping, the test mode is loopback mode. Send payload 11110000 with packet type DH1, 3 or 5.
The EUT operates at three frequency points: low, medium and high respectively. The tester sends a packet of 11110000 with the maximum packet length supported, and calculates the peak value and average value of the frequency offset for the packets returned by the EUT, which are recorded as Df1max and Df1avg respectively. The tester sends a packet of 10101010 with the maximum packet length supported, and calculates the peak value and average value of the frequency offset for the packets sent back by the EUT, which are recorded as Df2max and Df2avg respectively. <175kHz; at least 99.9% of Df2max 3115kHz; Df2avg /Df1avg 30.8.
(8) Initial carrier tolerance
Frequency hopping, the test mode is loopback mode. Send the payload PN9, the packet type is DH1.
The tester calculates the carrier frequency f0 according to the 4 preambles, and the difference with the nominal frequency fTX is required to be less than 75kHz.
(9) Carrier frequency drift
Frequency hopping, the test mode is loopback mode or transmit mode. Send payload 10101010 with packet type DH1, 3 or 5.
The instantaneous drift of the carrier is required to be less than 40kHz. The specification also requires that the carrier drift rate be less than 4000Hz/10µs.
2. Receive the test
For the reception test, all the indicators of the test are based on the statistics of the bit error rate, and at least 1,600,000 bits must be counted.
(1) Single slot sensitivity
WiMAX (Worldwide Interoperability for Microwave Access)
The EUT works at three frequency points of low, medium and high respectively, and sends back the DH1 packet of the modulated signal. According to the requirements of the Bluetooth specification, the tester controls its output power so that the received power of the EUT is -70dBm. The Bluetooth specification allows the RF signal sent by the EUT to have an initial error of 75kHz and a frequency drift of 40kHz, ie a total allowable error of 115kHz. In addition, errors due to modulation, symbol timing, etc. are also considered. If the receiver performance of the EUT is tested by a tester that outputs a "perfect" signal, and the test results are not sufficient to provide redundancy for a true wireless transmission environment, the user will get an erroneous result regarding the quality of the receiver. Experience tells us that for interference testing, the sensitivity of the Bluetooth receiver will generally deteriorate by 4~10dB, and the specific value is related to the packet length and the type of Bluetooth chip.
The tester must support a dirty transmitter, adding interference to the bluetooth signal sent, one group every 20ms, from the first group to the tenth group, and then back to the first group, repeating continuously. . The tester makes statistics on the bit error rate, and requires the bit error rate BER<0.1%.
(2) Multi-slot sensitivity
Similar to the single-slot sensitivity test, but the packet types are DH3 and DH5.
(3) Maximum input level
That is, the saturation level of the Bluetooth receiver. EUT works at low, medium and high frequency points. The tester sends the DH1 packet signal and controls its transmit power so that the level at the entrance of the EUT receiver is -20dBm. The tester counts the bit error rate and requires BER<0.1%.
Test instrument requirements:
The tester must have a Bluetooth protocol stack; in order to perform Bluetooth wireless testing, the tester must fully support the Bluetooth test mode protocol; must be able to perform 1600 frequency hopping per second; must support "dirty transmitter".