June, 2016

Measurements of BLE signal indoors

Posted on Jun 21, 2016 | Comments Off on Measurements of BLE signal indoors

Measurements of BLE signal strength (RSSI) dependency on the range indoors

 

Introduction

There is not much results of Bluetooth Low Energy range measurements to be found on the web. The primary reason is that it’s hard to control for environment, wall and floor materials. That being said, the numerous use cases for Bluetooth LE, from now on BLE, exactly in that type of environment, indoors. We, at Mondevices, decided to fill that gap.

 

Description of Setup

We took various BLE devices that transmit packets about 10 times per second and varied antenna designs. Most of PCBs were based on TI chip CC254x family. We have also included a combination of CC2541 with a power amplifier CC2590 and also used Texas instrument RF Studio with a mounted antenna. Below is a detailed description of the devices used.

Name	UUID	Description
CC2590 MIFA	68:9e:19:18:7a:a0	CC2541+CC2590 amplifier using MIFA antenna
WIRE	20:91:48:4c:9b:c5	CC2540 with vertical 1/4 wave-length antenna
NoBattery	b4:99:4c:74:d6:99	CC2540 with chip antenna and battery removed
CC2590 Wire	68:9e:19:18:83:f7	CC2541+CC2590 amplifier using wire antenna
TiDev	b4:99:4c:64:69:26	TI Smart RF development kit antenna
Roach1	b4:99:4c:74:e8:c5	CC2540 with wire antenna bent like roach antenna
Wire3Coil	b4:99:4c:74:c5:92	CC2540 with wire coiled around circular enclosure
NoBattery	b4:99:4c:74:d6:99	CC2540 with battery far away from PCB
Molex Antenna	b4:99:4c:74:e4:8d	CC2540 with Molex spiral antenna
Roach2	b4:99:4c:74:b7:d5	Roach 2 has antenna bent close to PCB
MIFA	b4:99:4c:74:ef:0a	CC2540 (inverse F) MIFA antenna in the enclosure
CHIP2Louise	b4:99:4c:74:b2:89	CC2540 chip antenna called Louise in the enclosure
CHIP1Molly	20:91:48:4c:a3:8a	CC2540 chip antenna called Molly in the enclosure

We have tried to find the best performing devices that could operate at furthers distances from the office and keep steady connection. We have found that TI RF Dev Kit and CC2590 booster are consistently perform better than other devices. TI Dev Kit has a large wave-length antenna and CC2590 boosts power transmission to 10 dbm, which is 4 times more than current chip antenna at 4 dbm setting or 8-9 times better than CC2541 0 dbm setting.

 

The photo of BLE range test setup describes positioning of all the test devices.

 

We tried all different combinations of antenna while trying to stay as close to same technology stack of TI CC254x family.

The close up of PCB with 1/4 wire antenna, CC2590 combo with MIFA and wire antenna.

Measurements

We have conducted measurement of RSSI strength of advertising packets of all 13 devices using TI Smart RF packet sniffer. We stored the results and parsed them with our custom parser script written in python. The results are attached as plots and tables.

Results

We did several measurements starting within in the same room in the office confines, then outside in the most RF challenging area of the kitchen and outside in the long corridor. The results of RSSI strength measurements of advertising packets are shown below. To avoid clatter on graphs we only display top three and top bottom plots. The tables shows stats for all

the devices. The kitchen area is very typical to every office and home, with metal surfaces of refrigerator, fax and printer machines and surrounding offices with BLE speakers, wearables and printers. Metal surfaces create destructive interference, where BLE signal interfere with itself. Other electronic devices create electromagnetic RF interferences. We counted around 200 BLE devices sending advertisement packets.

In the same room

In the office, same room where we placed all the devices, we can detect all the signals. This is an expected and obvious result. What is interesting that the biggest RSSI values we get from TI Dev Kit, CC2590 booster combo and, most surprising, just a simple vertical 1/4 wave length antenna positioned perpendicular to the PCB plane

The table below shows the stats for all the devices, not just top and bottom three. As one can see devices with power booster, CC2590, shows consistently on top.

UUID	Alias	MeanRSSI	StdDevRSSI	VarianceRSSI	MinRSSI	MaxRSSI	Count	FCSerrors	FCSerror%
68:9e:19:18:83:f7	CC2590 Wire	-37.58	2.86	8.16	-50	-33	187	0	0
68:9e:19:18:7a:a0	CC2590 MIFA	-34.21	3.45	11.9	-47	-30	187	0	0
b4:99:4c:74:e8:c5	Roach1	-44.31	2.95	8.72	-55	-40	186	0	0
20:91:48:4c:a3:8a	CHIP1Molly	-55.22	2.98	8.87	-66	-51	186	2	1.08
b4:99:4c:64:69:26	TiDev	-42.95	3.27	10.71	-54	-38	185	0	0
20:91:48:4c:9b:c5	WIRE	-42.48	3.34	11.17	-54	-36	185	0	0
b4:99:4c:74:b7:d5	Roach2	-57.35	3.13	9.78	-68	-50	176	6	3.41
b4:99:4c:74:e4:8d	Molex Ant	-58.27	3.07	9.45	-68	-51	172	14	8.14
b4:99:4c:74:c5:92	Wire3Coil	-59.29	2.82	7.97	-67	-53	156	10	6.41
b4:99:4c:74:b2:89	CHIP2Louise	-61.53	2.4	5.78	-67	-58	97	28	28.87
b4:99:4c:74:d6:99	NoBattery	-60.29	2.82	7.95	-66	-54	78	18	23.08
b4:99:4c:74:ef:0a	MIFA	-64.29	1.96	3.82	-68	-60	21	17	80.95

As one can see the strongest signals are from CC2590 combo with and without WIRE antenna, and from CC2540 with WIRE antenna. The percentage of FCS errors that demonstrate the data loss is also the least in CC2590+CC2541 combo and in CC2540 with the WIRE antenna.

 

In the RF dead zone – the kitchen

The kitchen is one of the most challenging from RF interference perspective environments. Here  only a few devices survived.

The table below shows the stats for all the devices in the kitchen.

UUID	Alias	MeanRSSI	StdDevRSSI	VarianceRSSI	MinRSSI	MaxRSSI	Count	FCSerrors	FCSerror%
68:9e:19:18:83:f7	CC2590 Wire	-60.59	1.87	3.5	-66	-57	133	0	0
20:91:48:4c:9b:c5	WIRE	-64.62	1.7	2.87	-70	-58	125	6	4.8
b4:99:4c:74:e8:c5	Roach1	-68.07	1.45	2.1	-73	-65	114	10	8.77
68:9e:19:18:7a:a0	CC2590 MIFA	-68.44	2.94	8.63	-76	-62	114	14	12.28
b4:99:4c:74:b7:d5	Roach2	-74.67	1.28	1.65	-77	-72	63	33	52.38
b4:99:4c:64:69:26	TiDev	-75	1.68	2.83	-79	-71	48	21	43.75
b4:99:4c:74:e4:8d	Molex Ant	-75.98	1.01	1.02	-79	-73	46	34	73.91
b4:99:4c:74:c5:92	Wire3Coil	-76.94	1.48	2.18	-80	-75	32	25	78.13
b4:99:4c:74:d6:99	NoBattery	-77	2.6	6.77	-81	-71	13	7	53.85
b4:99:4c:74:b2:89	CHIP2Louise	-80	0	0	-80	-80	4	4	100
b4:99:4c:74:ef:0a	MIFA	-79.67	0.47	0.22	-80	-79	3	3	100
20:91:48:4c:a3:8a	CHIP1Molly	-80	1	1	-81	-79	2	1	50

Again in the kitchen are the strongest signal and lowest errors are in CC2590 combos and in WIRE antenna.

When we tried to walk beyond the kitchen table we only observed CC2590 combo surviving the distance and kitchen interference with high rate of data errors.

In the long corridor

We also did measurements in the corridor far away from the kitchen we got slightly better results.

UUID	Alias	MeanRSSI	StdDevRSSI	VarianceRSSI	MinRSSI	MaxRSSI	Count	FCSerrors	FCSerror%
68:9e:19:18:7a:a0	CC2590 MIFA	-66.67	2.92	8.52	-78	-63	87	1	1.15
20:91:48:4c:9b:c5	WIRE	-71.19	2.89	8.33	-81	-68	68	7	10.29
b4:99:4c:74:d6:99	NoBattery	-74.62	1.74	3.04	-83	-72	60	13	21.67
68:9e:19:18:83:f7	CC2590 Wire	-73.67	3.28	10.76	-80	-67	52	7	13.46
b4:99:4c:64:69:26	TiDev	-72.45	3.06	9.34	-79	-67	42	4	9.52
b4:99:4c:74:e8:c5	Roach1	-75.35	1.85	3.4	-78	-71	34	9	26.47
b4:99:4c:74:c5:92	Wire3Coil	-77.6	0.8	0.64	-79	-76	15	4	26.67

Not surprisingly the strongest signals and lowest FCS errors are from CC2590 combo with and without WIRE antenna, and from CC2540 with WIRE antenna.

Walking towards the advertising devices

The last test in this document we have walked from the area past the kitchen towards the advertising devices. Below is the graph that shows graphs and tables with RSSI values.

UUID	Alias	MeanRSSI	StdDevRSSI	VarianceRSSI	MinRSSI	MaxRSSI	Count	FCSerrors	FCSerror%
68:9e:19:18:7a:a0	CC2590 MIFA	-58.8	10.72	115.02	-74	-34	51	2	3.92
68:9e:19:18:83:f7	CC2590 Wire	-58.66	11.73	137.62	-77	-34	50	5	10
20:91:48:4c:9b:c5	WIRE	-61.04	9.8	95.95	-76	-38	45	3	6.67
b4:99:4c:64:69:26	TiDev	-58.64	12	144.09	-77	-30	42	3	7.14
b4:99:4c:74:e8:c5	Roach1	-59.68	9.36	87.57	-78	-43	31	2	6.45
b4:99:4c:74:d6:99	NoBattery	-61.81	12.61	159.04	-80	-42	27	3	11.11
b4:99:4c:74:e4:8d	Molex Ant	-61.61	10.48	109.8	-82	-47	23	4	17.39
b4:99:4c:74:b7:d5	Roach2	-62.95	8.07	65.09	-76	-51	21	1	4.76
b4:99:4c:74:c5:92	Wire3Coil	-64.68	7.5	56.22	-77	-50	19	4	21.05
b4:99:4c:74:ef:0a	MIFA	-59.94	8.04	64.68	-74	-49	16	1	6.25
b4:99:4c:74:b2:89	CHIP2Louise	-64	4.55	20.67	-72	-58	12	2	16.67
20:91:48:4c:a3:8a	CHIP1Molly	-63.5	6.95	48.25	-75	-52	12	5	41.67

Just like in previous experiments, we can see that the strongest signals and lowest data errors levels are in CC2590 combos.

Conclusions

We have conducted experiments indoors using different antenna configurations and designs on CC254x IoT SoC technology.

We have consistently observed that the strongest signals that survived both RF interference and distance are

• CC2590+CC2541 combo
• WIRE antenna

 

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