CTE can be only appended in AUX_SYNC_IND, So it will be on secondary advertisement channel?

[Hardik.Harpal]

"CTE can be used in both connectionless and connection-oriented scenarios. For connectionless use, the periodic advertising feature is required (since deterministic timing in the sampling process is important) and CTE is appended to AUX_SYNC_IND PDUs." From https://www.bluetooth.com/wp-content/uploads/2019/03/1901_Feature_Overview_Brief_FINAL.pdf

"For advertising channel PDUs, the CTEInfo Flag replaces the CP bit. The CTEInfo Flag is within the extended header flag field in some of the advertising PDUs that employ the common extended advertising payload format (i.e. AUX_SYNC_IND, AUX_CHAIN_IND)." from https://infocenter.nordicsemi.com/pdf/nRF52833_PS_v1.3.pdf

and from periodic advertisement details on https://www.bluetooth.com/blog/periodic-advertising-sync-transfer/

So from above information, Is it correct to say that for connection less CTE transmission can be done only with  AUX_SYNC_IND PDU type advertisement. So it means CTE will be sent only on secondary advertisement channel as per BLE specs.  

We were trying to to use CTE with AUX_EXT_IND PDU type advertisement form beacon by using NRF-Radio example for transmitter and receiver on primary channel 37,38,39 and able to get IQ data. So, it is not correct way as per BLE specs, right? But can we use it for direction finding evaluation ? 

Am I on right track by using radio example for DF by using advertising on primary channel and scanning those channel from radio rx example with DFE configuration as required to get IQ data?

Regards,

Hardik Harpal

[Simonr]

Hi

To get started with Direction finding with our products, I would recommend reading our DIrection Finding Whitepaper which describes how to configure and enable the Bluetooth Direction Finding features of nRF52 and 53 series.

Let me check with our experts on the matter whether your assumptions on secondary advertisements are correct. I'll get back to you when I hear from them.

Best regards,

Simon

[Hardik.Harpal]

Simonr said:

To get started with Direction finding with our products, I would recommend reading our DIrection Finding Whitepaper which describes how to configure and enable the Bluetooth Direction Finding features of nRF52 and 53 series.

Following that from day one.

Simonr said:

Let me check with our experts on the matter whether your assumptions on secondary advertisements are correct. I'll get back to you when I hear from them.

Ok.

[Simonr]

Hi

Glad to hear that you've already read our whitepaper. 

It seems you have understood this correctly, and Connection-less CTE transmission will only be possible with AUX_SYNC_IND PDU type advertisement, which means CTE will be sent on secondary advertisement channels according to the BLE spec.

As for your application, I haven't seen how exactly you're doing IQ transmission on primary channels, but it should be possible to get usable results by advertising and scanning on the primary channels as well, although it will be out of spec, so you're definitely on the right track.

Best regards,

Simon

[Hardik.Harpal]

Thank you for clarification.

I was able to get IQ data (at the moment only two antenna is used for switching) but it is with ADV_EXT_IND  PDU only. Using  ADV_EXT_IND and not using inline CTE info sending using NRF RADIO with DFE settings, but as that is not as per BLE specs.

As per my understanding Periodic Advertisement implementation with sync based on raw NRF Radio peripheral as per BLE specs without Soft device for both Tx(broadcaster)  and Rx(Scanner) will be a complex and time consuming task. Am I right? Is there any starting point available from nordic regarding it?

Can you comment on IQ data, Is my understanding correct on how sample taken with respects to  antenna with my configuration for DFE?

Reading from switching slot should be discarded for phase difference calculation?

Can you guide me in right direction for phase difference calculation? What are the different methods?  

r_df_params.mode = RADIO_DFEMODE_DFEOPMODE_AoA,
r_df_params.cteinlinectrlen = RADIO_CTEINLINECONF_CTEINLINECTRLEN_Disabled,
r_df_params.cteinfoins1 = RADIO_CTEINLINECONF_CTEINFOINS1_NotInS1,
r_df_params.cteerrorhandling = RADIO_CTEINLINECONF_CTEERRORHANDLING_Yes,
r_df_params.ctetimevalidrange = RADIO_CTEINLINECONF_CTETIMEVALIDRANGE_20,
r_df_params.dfeinextension = RADIO_DFECTRL1_DFEINEXTENSION_CRC,
r_df_params.tswitchspacing = RADIO_DFECTRL1_TSWITCHSPACING_2us,
r_df_params.tsamplespacingref = RADIO_DFECTRL1_TSAMPLESPACINGREF_250ns,
r_df_params.tsamplespacing = RADIO_DFECTRL1_TSAMPLESPACINGREF_250ns,
r_df_params.repeatpattern = RADIO_DFECTRL1_REPEATPATTERN_NoRepeat,
r_df_params.agcbackoffgain = 0,
r_df_params.tswitchoffset = 0,
r_df_params.tsampleoffset = RADIO_DFECTRL2_TSAMPLEOFFSET_1us,
r_df_params.sampletype = 0,
r_df_params.s0conf = 0,
r_df_params.s0mask = 0,
r_df_params.numof8us = 0x3,

 

 

Antenna #	Slot Type	I	Q
1	Sampling	123	-110
		154	-44
		164	24
		147	84
		104	130
		46	159
		-18	165
		-80	146
		-129	104
		-152	39
		-149	-40
		-126	-111
		-84	-153
		-25	-164
		44	-153
		106	-122
		149	-75
		164	-16
		151	51
		113	111
		58	152
		-5	165
		-68	149
		-121	109
		-152	53
		-156	-14
		-135	-83
		-94	-135
		-36	-159
		30	-154
		90	-125
		137	-79
1	Switching	40	159
		-27	161
		-93	147
		-138	151
	Sampling	-153	179
		-153	203
		-162	187
		-187	115
2	Switching	-215	9
		-212	-90
		-165	-147
		-87	-134
	Sampling	-1	-55
		58	49
		71	134
		36	171
1	Switching	-26	162
		-94	133
		-148	111
		-183	119
	Sampling	-197	147
		-204	164
		-211	140
		-221	65
2	Switching	-222	-40
		-200	-134
		-147	-181
		-75	-152
	Sampling	-2	-60
		46	52
		51	138
		10	171
1	Switching	-57	153
		-121	112
		-165	82
		-193	79
	Sampling	-213	100
		-229	113
		-236	91
		-226	19
2	Switching	-195	-82
		-141	-169
		-75	-202
		-15	-157
	Sampling	31	-51
		50	66
		37	150
		-6	176

   

Regards,

Hardik Harpal

[Simonr]

Hardik.Harpal said:

Is there any starting point available from nordic regarding it?

 I'm sorry, but we don't have anything but the previously mentioned whitepaper publicly available as of yet. You're correct that the SoftDevice will not be used in any direction finding projects by us, as we will focus on getting it to the NCS SDK.

Please see section 2.2 in the whitepaper for information on how you determine the correct angle of arrival by sampling phase and switching antennas. Angle calculation can be do9ne using the following equation:

Best regards,

Simon