AOA: Antenna switch pattern and IQ sampling via nrf52833

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

mgl — Thu, 06 Mar 2025 16:34:53 GMT

Where did you get the Direction Finding Antenna Board (PCA2005) from, and how did you connect the DK to the antenna board?

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Zihao — Mon, 06 May 2024 14:22:29 GMT

But for a set of 45 samples, the phase difference between different antennas should be same. However, I calculated this phase difference directly using atan2(I,Q), and found that it fluctuated quite a bit. Of course, the place I'm currently testing is a noisy, multipath office.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

DUMB_GRANT — Mon, 03 Oct 2022 15:44:20 GMT

Hi I am trying to run the example here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_central/README.html#antenna-patterns

I am not sure the use of RFU in antenna switch, can someone explain? I am also not sure about how to use the samples to get the location. I know the one IQ sample gives me one phase.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Gavin — Tue, 07 Jun 2022 06:46:37 GMT

I checked this in version 1.9, what's the currect antenna table do you think ?

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

PaKa — Thu, 26 May 2022 15:05:49 GMT

Did you check this in nRF Connect SDK master? I believe there may have been a mistake in the antenna selection table.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Gavin — Thu, 26 May 2022 07:01:15 GMT

Hi PaKa,

I have read the chapter`NCS -> Antenna Pattern and using ISP1907 Angle of Arrival Demo Kit but still be confused.

Antenna	PATTERN[3:0]
ANT_12	0 (0b0000)
ANT_10	1 (0b0001)
ANT_11	2 (0b0010)
RFU	3 (0b0011)
ANT_3	4 (0b0100)
ANT_1	5 (0b0101)
ANT_2	6 (0b0110)
RFU	7 (0b0111)
ANT_6	8 (0b1000)
ANT_4	9 (0b1001)
ANT_5	10 (0b1010)
RFU	11 (0b1011)
ANT_9	12 (0b1100)
ANT_7	13 (0b1101)
ANT_8	14 (0b1110)
RFU	15 (0b1111)

From the table, every ANT# should map a pattern:

// setting 1
// 11，12，1，2，3，4，5，6，7，8，9，10
static const uint8_t ant_patterns[] = {0x2, 0x0, 0x5, 0x6, 0x1, 0x4,
									   0xC, 0x9, 0xE, 0xD, 0x8, 0xA};
// why not the following: 
// setting 1
// 11，12，1，2，3，4，5，6，7，8，9，10
static const uint8_t ant_patterns[] = {0x2, 0x0, 0x5, 0x6, 0x4, 0x9,
									   0xA, 0x8, 0xD, 0xE, 0xC, 0x1};

// setting 2
// 11，12，1，2，10，3，9，4，8，7，6，5
static const uint8_t ant_patterns[] = {0x2, 0x0, 0x5, 0x6, 0x4, 0x9,
									   0xA, 0x8, 0xD, 0xE, 0xC, 0x1};
// why not the following: 
// setting 2
// 11，12，1，2，10，3，9，4，8，7，6，5
static const uint8_t ant_patterns[] = {0x2, 0x0, 0x5, 0x6, 0x1, 0x4,
									   0xC, 0x9, 0xE, 0xD, 0x8, 0xA};

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

PaKa — Thu, 31 Mar 2022 17:13:05 GMT

For each correctly received package you will get an array of IQ values. The amount of IQ values you get will depend on the length of the CTE event. The standard setting for the example should be 160µs CTE event. This will give you 45 samples (https://infocenter.nordicsemi.com/topic/nwp_036/WP/nwp_036/sample_buffer_config.html). This is 8 values for the reference period and then 37 values from the different antennas in the array (you loop more than once through the pattern with the 160µs CTE period).

The IQ values are stored in a RAM array by the Controller Subsystem, you will need to fetch it to use it in the application space to calculate the angles.Remember these values comes as pairs, one I value and one Q value for each sample. These are signed chars (Bluetooth standard have these as 8 bit values so they are rounded down from the raw radio values).

The sequence for the antenna switching is as given in the PS, https://infocenter.nordicsemi.com/topic/ps_nrf52833/radio.html?cp=4_1_0_5_17_11_5#concept_dfe_antenna_switching. In the default code example we have the 12 antennas and then you will cycle through all entries in the table and then restart from entry 3 and loop like this until the entire CTE period is over.

Note: to be Bluetooth SIG compliant you should always loop through the reference antenna when you loop the pattern. To do this, add the reference antenna also as the last antenna in the pattern.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Miguel Roque — Thu, 31 Mar 2022 14:38:55 GMT

Hello PaKa, thank you for your prompt reply.

I'm sorry but I still confused. First thing, according to the project configuration I'm using a 2us slot time, which means a switch(2us)+sample(2us)=switching_space(4us). I used a logic analyser and in fact, the mux control IOs are changing with a period of 4us, so I assume the configuration is ok. However here comes my first doubt, from my understanding till the moment about AoA, I should receive a IQ sample for each antenna, but what the example plots is just one IQ sample (sometimes based in 45 samples or 1 sample, check the logs bellow). So, how can I despite from each antenna came that precise IQ sample?

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

PaKa — Thu, 31 Mar 2022 12:43:31 GMT

So for the sequence of the antennas, check the table for the antenna pattern and the description in the white paper. The pattern is deterministic so there should be no need to read back the antenna port, this can be calculated instead.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Miguel Roque — Wed, 30 Mar 2022 21:37:34 GMT

Hello all, I'm exactly at same point as @John. Currently I'm printing the IQ data, however I tried to find any info about the antenna ID that produces each IQ data but I didn't get any success until the moment (looking for the bt_df_conn_iq_samples_report struct, I tried to print the parameter rssi_ant_id but the value is allways "2", and in fact I'm using 4 linear antennas from the 12 available on the antenna). Another question that maybe you can help me, based on literature people advise to use external algorithms to decode the sampled data and return an angle, many suggest the MUSIC algorithm, but I didn't find many samples on the internet, or at least any sample easy to implement with the returned data from the devkit, where can I find it?

Best regards, and thank you for your help!

Miguel Soares

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

PaKa — Wed, 30 Mar 2022 14:17:13 GMT

Why do you believe they are not ideal? Have you run them through an algorithm and gotten bad results? Please have in mind the entire purpose with changing the active antenna is to get a change in phase. Since you only get one value from each antenna you can't look at the resulting graph and see if it bad or not.

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Sometimes ever — Wed, 30 Mar 2022 12:31:31 GMT

Thank you！

I have read your whitepaper carefully, but aside from the first 8 samples, I think the remaining data is still not ideal. What is the reason? Is there a way to improve data quality?

RE: AOA: Antenna switch pattern and IQ sampling via nrf52833

Kenneth — Wed, 30 Mar 2022 11:23:39 GMT

Do not look at graphs made of the I data and the Q data as that will always give the wrong impression. Look at the calculated phase and amplitude data only. And remember: the first 8 samples are the reference samples with short spacing and the rest are with much longer gaps between them (so printing them with the same distance in a figure will also be incorrect and most likely just confusing). Please check out:
https://infocenter.nordicsemi.com/topic/nwp_036/WP/nwp_036/intro.html