Selecting an Antenna and Improving Cellular Signal Strength in IoT Application

Photo by Vyacheslav Shatskiy on Unsplash

Every single Internet of Things (IoT) device needs an antenna. The importance of an IoT product’s antenna cannot be overstated. It is the interface to the outside world. The antenna is one part of a system that conveys RF energy from a transmitter to a receiver. The antenna is crucial: it may make or break the communication with your devices. A good antenna will give you a good wireless range. A bad antenna may cause your devices to not even be reachable in the field.

IoT devices are typically small and often have a severely limited power budget to operate for long periods from a small energy source such as a primary coin cell. An antenna that may be suitable on paper is not guaranteed to perform well in practice. Proper selection and design-in are both essential to ensure a reliable wireless connection, covering the desired communication distance, while driving the antenna at the lowest possible input power to minimise demand on the device’s precious energy supply.

Antenna selection

Among the challenges that must be dealt with, selecting and integrating a suitable antenna has a significant impact on the RF-subsystem and consequently affects the system performance in terms of communication range, overall power consumption, and battery life.

To choose an antenna, the search can be focused on according to frequency range or wireless standard. Antennas are available for single-band applications or multi-band antennas designed for multiple feeds.

Type of antennaExamplesApplications
Wire AntennasDipole antenna, Monopole antenna, Helix antenna, Loop antennaPersonal applications, buildings, ships, automobiles, space crafts
Aperture AntennasWaveguide (opening), Horn antennaFlush-mounted applications, air-craft, space craft
Reflector AntennasParabolic reflectors, Corner reflectorsMicrowave communication, satellite tracking, radio astronomy
Lens AntennasConvex-plane, Concave-plane, Convex-convex, Concaveconcave lensesUsed for very highfrequency applications
Micro strip AntennasCircular-shaped, Rectangularshaped metallic patch above the ground planeAir-craft, space-craft, satellites, missiles, cars, mobile phones etc.
Array AntennasYagi-Uda antenna, Micro strip patch array, Aperture array, Slotted wave guide arrayUsed for very high gain applications, mostly when needs to control the radiation pattern

Check out the antennas you can use in IoT projects

Important parameters to choose

  • Shape and size of antenna
  • To check Mounting option, whether it is RF connector mount, or PCB mount etc.
  • Frequency of operation
  • Coverage requirement
  • Omni-directional or directional operation
  • Gain of Antenna

Understanding LTE Signal Strength Values

Below are explanations of the LTE signal strength values:

  • SINR/SNR – The signal-to-noise ratio of the given signal. The higher the SNR the better your signal quality will be. The SNR reading will be automatically calculated by the base station in dB.
  • RSRP – The average power received from a single Reference signal, and Its typical range is around -44dbm (good) to -140dbm(bad).
  • RSRQ – In dB, Indicates quality of the received signal, and its the ratio of usable signal to noise and interference measured in dBm. RSRQ=RSRP-RSSI.
  • RSCP — In the UMTS cellular communication system, Received Signal Code Power (RSCP) denotes the power measured by a receiver on a particular physical communication channel.
  • RSSI – In dBm, The Receive Strength Signal Indicator measures the average total received power of the whole band.

Causes of Poor Signal

There are many different factors that influence signal strength and quality; these factors include, but are not limited, to the following:

  • Distance from the Cellular Tower
  • Physical barriers (mountains, buildings, trains, etc.)
  • Building Structures ( brick, concrete, metal roofs, etc.)
  • Interference
  • Network Issues
  • Network Congestion
  • Weather

Signal strength and signal quality numbers do not incorporate all of the relevant factors. Keep in mind that measurements of signal strength and signal quality for a specific moment do not reflect on the stability of a connection, as these values will vary as conditions change.

Interpreting Signal Values

Signal measurement values are provided by the cellular modules at any time. The following modules (also available on Sixfab) show how to interpret the signal strengths.

As a rough guide, it defines the following quality measure for the quality of the connection between the mentioned modules and the and cell tower:

RF QualityRSRP (dBm)RSRQ (dB)SINR(dB)
Excellent>= -80>= -10>= 20
Good-80 to -90-10 to -1513 to 20
Fair to poor-90 to -100-15 to -200 to 13
No signal< -100< -20<= 0

RSSI for LTE is a calculated from several other signal related measurements:

RSSI = wideband power = noise + serving cell power + interference power
RF QualityRSSI(dBm)Description
Excellent>-65Strong signal with maximum data speeds
Good-65 to -75Strong signal with good data speeds
Fair-75 to -85Fair but useful, fast and reliable data speeds may be attained, but marginal data with drop-outs is possible
Poor-85 to -95The performance will drop drastically
No signal<= -95Disconnection

It should be noted that all reported measurement values will be evaluated individually.

Quectel BG96 Cat M1/NB1/EGPRS Module

For Quectel BG96 AT+QCSQ AT command can be used:

AT+QCSQ

This will return a string like: Check out the antennas you can use in IoT projects

+QCSQ: <sysmode> ,<value1> ,<value2> ,<value3> , <value4>

<sysmode> → A string type value indicating the service mode in which the MT will unsolicitedly report the signal strength
<value1> ,<value2> ,<value3> , <value4> → the following table lists the signal strength type corresponding to each service mode.

<sysmode><value1><value2><value3><value4>
“NOSERVICE”
“GSM” mode<gsm_rssi>
“CAT-M1” mode<lte_rssi><lte_rsrp><lte_sinr><lte_rsrq>
“CAT-NB1” mode<lte_rssi><lte_rsrp><lte_sinr><lte_rsrq>

<gsm_rssi>,<lte_rssi> : An integer indicating the received signal strength. These parameters are available for GSM and LTE mode respectively.
<lte_rsrp> : An integer indicating the reference signal received power (RSRP). This parameter is available for LTE mode.
<lte_sinr> : An integer indicating the signal to interference plus noise ratio (SINR). Logarithmic value of SINR. Values are in 1/5th of a dB. The range is 0-250 which translates to -20dB – +30dB.
<lte_rsrq> : An integer indicating the reference signal received quality (RSRQ) in dB.

Example:

+QCSQ: “GSM”,-74

For 2G mode RSSI is the only measure. RSSI is a negative value, and the closer to 0, the stronger the signal.

+QCSQ: “CAT-M1”,-52,-81,195,-10

For CAT-M1 and CAT-NB1 there are many measures (RSSI, RSRP, SINR, RSRQ).

Quectel EC25 Mini PCle Module

For Quectel EC25 AT+CSQ AT command can be used.

The command indicates the received signal strength <rssi> and the channel bit error rate <ber>.

This will return a string like:

+CSQ: <rssi>,<ber>

<rssi>
0-113dBm or less
1-111dBm
2…30-109dBm… -53dBm
31-51dBm or greater
99Not known or not detectable
100-116dBm or less
101-115dBm
102…190-114dBm…-26dBm
191-25dBm or greater
199Not known or not detectable
100~199Extended to be used in TD-SCDMA indicating received signal code
power (RSCP)

<ber>
0…7As RXQUAL values in the table in 3GPP TS 45.008 subclause 8.2.4
99Not known or not detectable

Example:

+CSQ: 25,99

The received signal strength is –63dBm and channel bit error rate is 99.

ValueRSSI(dBm)Condition
2-109Marginal
3-107Marginal
4-105Marginal
5-103Marginal
6-101Marginal
7-99Marginal
8-97Marginal
9-95Marginal
10-93OK
11-91OK
12-89OK
13-87OK
14-85OK
15-83Good
16-81Good
17-79Good
18-77Good
19-75Good
20-73Excellent
21-71Excellent
22-69Excellent
23-67Excellent
24-65Excellent
25-63Excellent
26-61Excellent
27-59Excellent
28-57Excellent
29-55Excellent
30-53Excellent

Telit LE910C1 Mini PCIe Module

AT+CSQ and AT+CESQ AT commands are available for the Telit LE910C1.

AT+CSQ – Signal Quality Execution command returns received signal strength indication and channel bit error rate from the MT.

+CSQ: <rssi>, <sq>

<rssi> – received signal strength indication (3GPP)
0(-113) dBm or less
1(-111) dBm
2..30(-109) dBm. (-53) dBm / 2 dBm per step
31(-51 ) dBm or greater
99Not known or not detectable
<rssi> – received signal strength indication (TDSCDMA)
100(-116) dBm or less
101(-115) dBm
102…191(-114…-26) dBm
191(-25) dBm or greater
199Not known or not detectable
<sq> – signal quality – as mentioned below:

2G (GSM) – RXQUAL [bit error rate (in percent)]

0less than 0.2%
10.2% to 0.4%
20.4% to 0.8%
30.8% to 1.6%
41.6% to 3.2%
53.2% to 6.4%
66.4% to 12.8%
7more than 12.8%
99not known or not detectable

3G (UTRAN) – ECIO(dBm)

0(-1) to (0)
1(-5) to (-2)
2(-8) to (-6)
3(-11) to (-9)
4(-15) to (-12)
5(-18) to (-16)
6(-22) to (-19)
7(-24) to (-23)
99not known or not detectable

4G (LTE) – RSRQ(dBm)

0(-4) to (-3)
1(-6) to (-5)
2(-8) to (-7)
3(-10) to (-9)
4(-13) to (-11)
5(-15) to (-14)
6(-17) to (-16)
7(-19) to (-18)
99not known or not detectable
Note: This command should be used instead of the %Q and %L commands, since GSM/WCDMA relevant parameters are the radio link ones and no line is present, hence %Q and %L have no meaning.

AT+CESQ – Execution command returns received signal quality parameters according to the network on which the module
is registered.

The execution command returns the following message. Its format depends on the network on which the module is registered.

+CESQ: <rxlev>,<ber>,<rscp>,<ecno>,<rsrq>,<rsrp>

<rxlev> – received received signal strength level (see 3GPP TS 45.008 subclause 8.1.4)
0rssi < -110 dBm
1-110 dBm ≤ rssi < -109 dBm
2-109 dBm ≤ rssi < -108 dBm
..
61-50 dBm ≤ rssi < -49 dBm
62-49 dBm ≤ rssi < -48 dBm
63-48 dBm ≤ rssi
99not known or not detectable or if the current serving cell is not a GERAN cell
<ber> – bit error rate (in percent)
0…7As RXQUAL values in the table in 3GPP TS 45.008 subclause 8.2.4
99not known or not detectable or if the current serving cell is not a GERAN cell
<rscp> – received signal code power (see 3GPP TS 25.133 subclause 9.1.1.3 and 3GPP TS 25.123 subclause 9.1.1.1.3).
0rscp < -120 dBm
1-120 dBm ≤ rscp < -119 dBm
2-119 dBm ≤ rscp < -118 dBm
94-27 dBm ≤ rscp < -26 dBm
95-26 dBm ≤ rscp < -25 dBm
96-25 dBm ≤ rscp
255not known or not detectable or if the current serving cell is not a UTRA cell
<ecno> – ratio of the received energy per PN chip to the total
0Ec/Io < -24 dB
1-24 dB ≤ Ec/Io < -23.5 dB
2-23.5 dB ≤ Ec/Io < -23 dB
47-1 dB ≤ Ec/Io < -0.5 dB
48-0.5 dB ≤ Ec/Io < 0 dB
490 dB ≤ Ec/Io
255not known or not detectable or if the current serving cell is not a UTRA cell
<rsrq> – reference signal received quality (see 3GPP TS 36.133 subclause 9.1.7).
0rsrq < -19.5 dB
1-19.5 dB ≤ rsrq < -19 dB
2-19 dB ≤ rsrq < -18.5 dB
..
32-4 dB ≤ rsrq < -3.5 dB
33-3.5 dB ≤ rsrq < -3 dB
34-3 dB ≤ rsrq
255not known or not detectable detectable or if the current serving cell is not a EUTRA cell
<rsrp> – type, reference signal received power (see 3GPP TS 36.133 subclause 9.1.4).
0rsrp < -140 dBm
1-140 dBm ≤ rsrp < -139 dBm
2-139 dBm ≤ rsrp < -138 dBm
95-46 dBm ≤ rsrp < -45 dBm
96-45 dBm ≤ rsrp < -44 dBm
97-44 dBm ≤ rsrp
255not known or not detectable or if the current serving cell is not a EUTRA cell
Note: 4G/3G only products like LM960 does not support GSM access technology.

Telit ME910C1-WW Mini PCle Module

AT+CSQ and AT+CESQ AT commands are available for the Telit LE910C1 module.

AT+CSQ – Signal Quality Execution command returns received signal strength indication and channel bit error rate from the MT.

2G Networks The execution command returns the following message:

+CSQ: <rssi>, <ber>

<rssi> – received signal strength indication
0(-113) dBm or less
1(-111) dBm
2..30(-109) dBm. (-53) dBm / 2 dBm per step
31(-51 ) dBm or greater
99Not known or not detectable
<ber> – bit error rate (in percent)
0less than 0.2%
10.2% to 0.4%
20.4% to 0.8%
30.8% to 1.6%
41.6% to 3.2%
53.2% to 6.4%
66.4% to 12.8%
7more than 12.8%
99not known or not detectable

4G Networks The execution command returns the following message:

+CSQ: <rssi>,<rsrq>

<rssi> – Received Signal Strength Indication.

For to be compliant with 3GPP TS27.007 specification, levels are mapped to range 0…31.

0(-113) dBm or less
1(-111) dBm
2..30(-109) dBm. (-53) dBm / 2 dBm per step
31(-51 ) dBm or greater
99Not known or not detectable
<rsrq> – Reference Signal Received Quality.

For levels are mapped to range 0…7.

0-4…-3 dB
1-6…-5 dB
2-8…-7 dB
3-10…-9 dB
4-13…-11 dB
5-15…-14 dB
6-17…-16 dB
7-19…-18 dB
99not known or not detectable

AT+CESQ – Execution command returns received signal quality parameters according to the network on which the module
is registered.

The execution command returns the following message. Its format depends on the network on which the module is registered.

2G Networks The execution command returns the following message:

+CESQ: <rxlev>,<ber>,255,255,255,255

LTE Networks The execution command returns the following message:

+CESQ: 99,99,255,255,<rsrq>,<rsrp>

<rxlev> – received signal strength level, see 3GPP TS 45.008 subclause 8.1.4.
0rssi < -110 dBm
1-110 dBm ≤ rssi < -109 dBm
2-109 dBm ≤ rssi < -108 dBm
61-50 dBm ≤ rssi < -49 dBm
62-49 dBm ≤ rssi < -48 dBm
6348 dBm ≤ rssi
99not known or not detectable or if the current serving cell is not a GERAN cell
<ber> – channel bit error rate.
0…7As RXQUAL values in the table in 3GPP TS 45.008 subclause 8.2.4
99not known or not detectable or if the current serving cell is not a GERAN cell
<rsrq> – reference signal received quality, see 3GPP TS 36.133 subclause 9.1.7.
0rsrq < -19.5 dB
1-19.5 dB ≤ rsrq < -19 dB
2-19 dB ≤ rsrq < -18.5 dB
..
32-4 dB ≤ rsrq < -3.5 dB
33-3.5 dB ≤ rsrq < -3 dB
34-3 dB ≤ rsrq
255not known or not detectable detectable or if the current serving cell is not a EUTRA cell
<rsrp> – type, reference signal received power (see 3GPP TS 36.133 subclause 9.1.4).
0rsrp < -140 dBm
1-140 dBm ≤ rsrp < -139 dBm
2-139 dBm ≤ rsrp < -138 dBm
95-46 dBm ≤ rsrp < -45 dBm
96-45 dBm ≤ rsrp < -44 dBm
97-44 dBm ≤ rsrp
255not known or not detectable or if the current serving cell is not a EUTRA cell




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