Bluetooth BT RF

1. Overview of Bluetooth BT RF

The Bluetooth RF test configuration includes a tester and an EUT (Equipment Under Test), where the tester is the master unit and the EUT is the slave unit. The two can be connected via an RF cable or via an antenna over the air. The tester sends an LMP command to activate the EUT to enter the test mode and configure some parameters of the Bluetooth link between the tester and the EUT. For example, 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 net value of the packet is PN9, 00001111, or 01010101. The test mode is a special state. For safety reasons, the EUT must first be set to the "Enable" state before it can be activated over the air to enter the test mode.

1.1 Bluetooth BT RF transmitter test

(1) Bluetooth RF output power test

The tester sets the initial state as follows: the link is frequency hopping and the EUT is set to loopback. The tester transmits a payload of PN9, and the packet type is a packet of the maximum supported length. The EUT decodes the packet sent by the tester and uses the same packet type to send the payload back to the tester at its maximum output power. The tester measures the peak power and average power in the entire burst range at low, medium and high frequencies. The specification requires that the peak power and average power be less than 23dBm and 20dBm respectively, and meet the following requirements: if the power level of the EUT is 1, the average power > 0dBm; 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 < 0dBm.

(2) Bluetooth BT RF power density test

The initial state is the same as (1). The tester scans the frequency to find the frequency corresponding to the maximum power within the 240MHz frequency band, and then performs a time domain scan at this frequency (scanning time is 1 minute) to measure the maximum value, which is required to be less than 20dBm/100kHz.

(3) Bluetooth BT RF power control test

The initial state is loopback, non-frequency hopping. The EUT works at low, medium and high frequencies respectively, and the return modulation signal is the DH1 packet of PN9. The tester controls the EUT output power through LMP signaling and tests the range of the power control step. The specification requires it to be between 2dB and 8dB.

(4) Bluetooth BT RF frequency range test

The initial state is the same as (3). The tester performs frequency sweep measurement on the DH5 packet with a payload of PN9 returned by the EUT. When the EUT works at the lowest frequency, the tester finds the frequency fL when the power density drops to -80dBm/Hz; when the EUT works at the highest frequency, the tester finds the frequency fH when the power density drops to -80dBm/Hz. For a 79-channel system, fL and fH are required to be within the range of 2.4 to 2.4835GHz.

(5) 20dB bandwidth

The initial state is the same as (3). The EUT works at three frequencies: low, medium and high. The return modulation signal is the DH1 packet of PN9. The tester scans the frequency to find the frequency corresponding to the maximum power, and finds the fL and fH on the left and right sides when the power drops by 20dB. The 20dB bandwidth Df = | fH - fL |, and Df is required to be less than 1MHz.

(6) Bluetooth BT RF adjacent channel power test

The initial state is the same as (3). The EUT works at the 3rd channel, 39th channel and 75th channel, and the return payload is the DH1 packet of PN9. 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 less than -40dBm.

(7) Bluetooth RF BT modulation characteristics

The initial state is the same as (3). The EUT works at three frequencies: low, medium and high. The tester sends a packet with a payload of 11110000 at the maximum supported packet length, and calculates the peak and average frequency offset of the packet sent back by the EUT, which are recorded as Df1max and Df1avg respectively. The tester sends a packet with a payload of 10101010 at the maximum supported packet length, and calculates the peak and average frequency offset of the packet sent back by the EUT, which are recorded as Df2max and Df2avg respectively. The following conditions are required to be met: at least 99.9% of Df1max meets 140kHz< Df1max <175kHz; at least 99.9% of Df2max meets 3115kHz; Df2avg /Df1avg 30.8.

(8) Bluetooth BT RF initial carrier tolerance

The EUT is in loopback state and sends back DH1 with a payload of PN9 to the tester. The tester first sets the link to non-frequency hopping, and the EUT works at low, medium and high frequencies respectively. Then the tester sets the link to frequency hopping. The tester calculates the carrier frequency f0 based on the four preamble codes, and requires that the difference with the nominal frequency fTX is less than 75kHz.

(9) Bluetooth BT RF carrier frequency drift test

The initial state is the same as (3). The EUT works at low, medium and high frequencies respectively, and the return modulation signal is DH1/DH3/DH5 packets with 10101010. The tester first calculates the carrier frequency f0 based on the four preamble codes, and then tests the frequency once every 10 bits of payload. The difference between the frequency and the initial carrier frequency is the instantaneous frequency drift. Finally, the tester turns on frequency hopping and retests the instantaneous frequency drift at all frequencies. The difference between the instantaneous frequency drifts is defined as the drift rate. For DH1 packets, each instantaneous drift is required to be less than 25kHz. For DH3 and DH5 packets, the carrier instantaneous drift is required to be less than 40kHz. The specification also requires that the carrier drift rate be less than 4000Hz/10μs.

1.2 Bluetooth BT RF Receiver Test

The above introduces the wireless indicators and tests of Bluetooth transmitters. For receiver testing, all indicators are tested based on bit error rate statistics, and at least 1600000 bits must be counted. As we all know, it is meaningless to count bit error rate when the frame error rate is large. Therefore, in order to accurately test the performance of the receiver, the tester must be able to test the FER caused by the following 6 situations: CRC error, incorrect payload length, synchronization word error, HEC error, EUT sends back NACK packet to MT8850A, and does not receive the packet sent by EUT in the expected time slot. The following introduces the test of Bluetooth receiver.

(1) Bluetooth BT RF single time slot sensitivity test

The initial state is the same as 1.1 (3). The EUT works at low, medium and high frequencies respectively, and the modulation signal sent back is DH1 packet of PN9. According to the requirements of the Bluetooth specification, the tester controls its output power so that the EUT's receiving power 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, that is, a total error of 115kHz is allowed. In addition, errors caused by modulation, symbol timing, etc. must also be considered. If the EUT's receiver performance is tested by a tester that outputs a "perfect" signal, its test results are not enough to provide redundancy to adapt to the real wireless transmission environment, and the user will get an erroneous result about the receiver quality. 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 interference transmission (dirty transmitter), see Table 1, add interference to the transmitted Bluetooth signal, one group every 20ms, from the first group to the tenth group, and then back to the first group, and repeat continuously. In addition, the Bluetooth baseband signal is also modulated by a sine wave. The tester counts the bit error rate and requires the bit error rate BER<0.1%. In addition, if conditions permit, it is best to retest in the frequency hopping state.

(2) Bluetooth BT RF multi-slot sensitivity test

Similar to the single-slot sensitivity test, but the packet types are DH3 and DH5.

(3) Bluetooth BT RF C/I performance test

The initial state is the same as 1.1 (3), and the EUT works at low, medium, and high frequencies respectively. The useful signal sent by the tester is the DH1 packet with a payload of PN9, and it also sends a Bluetooth interference signal with a payload of PN15. The power levels of the useful signal and the interference signal are shown in Table 2. The tester performs bit error rate statistics, requiring BER<0.1%.

(4) Bluetooth BT RF blocking performance test

The blocking characteristic refers to the ability of the receiver to receive useful signals when there are large interference signals in other frequency bands. The initial state is the same as 1.1 (3), and the EUT transmits and receives at a frequency of 2460MHz (channel 58). The tester not only sends DH1 packets with a payload of PN9 as useful signals, but also sends continuous wave interference signals with frequencies between 30MHz and 12.75GHz. The power level of the useful signal is 3dB higher than the reference sensitivity. The reference sensitivity refers to the minimum level that the receiver can receive when a certain bit error rate is met. The level of the interference signal is 2dB higher than that given in Table 3. The tester counts the bit error rate. If BER>0.1%, the tester records the frequency of the interference signal at this time, and the number of frequency points is required to be less than 24. Other conditions remain unchanged, only the level of the interference signal is reduced to -50dBm, and the tester records the frequency of the interference signal when BER>0.1%, and the number is required to be less than 5.

(5) Bluetooth BT RF intermodulation performance test

The intermodulation characteristic refers to the receiving ability when there are two or more interference signals with a specific frequency relationship with the useful signal (their intermodulation products just fall within the useful signal band). The initial state is the same as 1.1(3), and the EUT transmits and receives the same frequency points, which are low, medium, and high frequency points respectively. The tester not only sends a DH1 packet with a payload of PN9 as a useful signal, whose power is 6dB higher than the reference sensitivity; it also sends a sine wave interference signal with a power of -39dBm and a frequency of f1, and a Bluetooth interference signal modulated by PN15 with a power of -39dBm and a frequency of f2. The difference between f1 and f2 is exactly equal to the receiving frequency of the EUT, and f2-f1 =3MHz, 4MHz or 5MHz. The tester calculates the bit error rate and requires BER < 0.1%.

(6) Bluetooth BT RF maximum input level test

That is, the saturation level of the Bluetooth receiver. The initial state is the same as 1.1(3), and the EUT works at low, medium and high frequency points. The tester sends a DH1 packet signal with a payload of PN9 and controls its transmission power so that the level at the entrance of the EUT receiver is -20dBm. The tester calculates the bit error rate and requires BER < 0.1%.

In addition, transceivers need to test out-of-band spurious emissions, that is, according to ETS or FCC standards, test the out-of-band spurious emissions of the EUT in the working and standby states within the frequency range of 30MHz to 12.75GHz, including antenna conducted spurious emissions and chassis radiated spurious emissions.