Does the nRF Distance Measurment application support TX power be increased to 4/8 dBm?

[J0sh1101]

Hi,

I am trying to measure the distance of two objects, which can vary from 20 to 350 meters. We have tried the nRF Distance Measurement with Bluetooth LE discovery, which worked fine up to 120 meters. I would like to increase the range by increasing the transmit power to 8 or at least 4 dBm.

I took this code snippet we found here and added it to the RF Distance Measurement with Bluetooth LE discovery. This is what I added to the code:

	err = service_ddfs_init();
	if (err) {
		printk("DDF Service init failed (err %d)\n", err);
		return 0;
	}
	
	set_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_ADV,0, 4);
	
	err = bt_enable(NULL);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
		return 0;
	}
	

After running the code I got an exception fromt hci core:

*** Booting Zephyr OS build v3.3.99-ncs1 ***
Starting Distance Measurement example
E: ***** MPU FAULT *****
E:   Data Access Violation
E:   MMFAR Address: 0x14d31
E: r0/a1:  0x00000000  r1/a2:  0x00000004  r2/a3:  0x00014d31
E: r3/a4:  0x2000f700 r12/ip:  0x00000022 r14/lr:  0x00032e59
E:  xpsr:  0x21000000
E: s[ 0]:  0x00000000  s[ 1]:  0x00000000  s[ 2]:  0x00000000  s[ 3]:  0x00000000
E: s[ 4]:  0x00000000  s[ 5]:  0x00000000  s[ 6]:  0x00000000  s[ 7]:  0x00000000
E: s[ 8]:  0x00000000  s[ 9]:  0x00000000  s[10]:  0x00000000  s[11]:  0x00000000
E: s[12]:  0x00000000  s[13]:  0x00000000  s[14]:  0x00000000  s[15]:  0x00000000
E: fpscr:  0x00000000
E: Faulting instruction address (r15/pc): 0x0003c76a
E: >>> ZEPHYR FATAL ERROR 19: Unknown error on CPU 0
E: Current thread: 0x20007698 (unknown)
E: Resetting system

After looking in the zehpyhr.lst file to see where the program counter was before the exception occurred, I couldn't find anything helpful:

0003c75e <z_handle_obj_poll_events>:
{
   3c75e:	4603      	mov	r3, r0
	return list->head == list;
   3c760:	6800      	ldr	r0, [r0, #0]
	if (!sys_dlist_is_empty(list)) {
   3c762:	4283      	cmp	r3, r0
   3c764:	d008      	beq.n	3c778 <z_handle_obj_poll_events+0x1a>
	sys_dnode_t *const next = node->next;
   3c766:	e9d0 3200 	ldrd	r3, r2, [r0]
	prev->next = next;
   3c76a:	6013      	str	r3, [r2, #0]
	next->prev = prev;
   3c76c:	605a      	str	r2, [r3, #4]
	node->next = NULL;
   3c76e:	2300      	movs	r3, #0
	node->prev = NULL;
   3c770:	e9c0 3300 	strd	r3, r3, [r0]
		(void) signal_poll_event(poll_event, state);
   3c774:	f7ff bf99 	b.w	3c6aa <signal_poll_event>
}
   3c778:	4770      	bx	lr

I also tried to change the TX  power with configuration flag defined in the prj.conf, but It did not improve or help anything:

CONFIG_BT_CTLR_TX_PWR_PLUS_8=y

Can someone explaine me what is happening?

Thanks for the help!!!

OS: Windows

SDK: 2.4.0

IDE: Visual Studio Code

Hardware: nRF52840 DK

[Michal]

J0sh1101 said:

we have currently purchased the BT840E which can provide +13 dBM TX. I found some posts on this topic, but they did not help me completely (post 1, post 2). I followed the instructions described in one of the posts, but I can't seem to activate the FEM. 

The ranging itself is done with a proprietary NDT protocol, not normal BLE. Those methods are specifically for increasing the BLE range.

J0sh1101 said:

we have currently purchased the BT840E which can provide +13 dBM TX. I found some posts on this topic, but they did not help me completely (post 1, post 2). I followed the instructions described in one of the posts, but I can't seem to activate the FEM. 

Please take a look at our Working with RF front-end modules guide.

Best regards,

Michal

[J0sh1101]

Michal said:

The ranging itself is done with a proprietary NDT protocol, not normal BLE. Those methods are specifically for increasing the BLE range.

Does the NDT protocol not work on top of the BLE. Basically, it uses the advertisement and scanning to estimate the range. Wouldn't increasing the BLE range improve the NDT protocol to some extent?

Michal said:

Please take a look at our Working with RF front-end modules guide.

I did and it describes only to upate the overlay and prj.conf files. Would it possible to know where in the code the pins are set/reset?

[Michal]

J0sh1101 said:

Does the NDT protocol not work on top of the BLE. Basically, it uses the advertisement and scanning to estimate the range. Wouldn't increasing the BLE range improve the NDT protocol to some extent?

No. BLE is only used in the sample for connecting and synchronizing the devices. You theoretically could use another protocol instead for that.

From the documentation:

Where actual ranging is done using the NDT protocol.

J0sh1101 said:

I did and it describes only to upate the overlay and prj.conf files. Would it possible to know where in the code the pins are set/reset?

FEM control is part of the Multiprotocol Service Layer (Front-end module feature). The library itself is unfortunately closed-source, but you can take a look at the API documentation.

Best regards,

Michal

[J0sh1101]

Michal said:

FEM control is part of the Multiprotocol Service Layer (Front-end module feature). The library itself is unfortunately closed-source, but you can take a look at the API documentation.

I did it, although you have to set the chl pin manually to make it work with the SKY66403-11 FEM. I have not found this in the documentation.

Maybe it would be good to update the documentation. I will close the ticket since my question has been answered. Thanks again for the help.