Range Test Comparison Between WLR089U Module and SAMR34 Chip-Down XPRO

Overview

A range test in wireless communications generally refers to the distance covered by a wireless link between a transmitter and a receiver, with acceptable packet loss and without breaking the link. The higher the operating frequency the lower the range will be, as high-frequency signals are more attenuated by free space than low-frequency signals are (e.g.: 2.4 GHz signals are attenuated more than Sub-1 GHz signals). So, if two signals (2.4 GHz and Sub-1 GHz) of the same Tx power are transmitted, the Sub-1 GHz signal (915 MHz or 868 MHz) will reach a longer distance than the 2.4 GHz signal. There is another factor that affects the range: antenna size. High-frequency signals (2.4 GHz) need a smaller antenna than lower-frequency signals (915 MHz) as the antenna size (e.g.: λ/4 for monopole antenna) is directly proportional to the wavelength of a signal and the wavelength is inversely proportional to the operating frequency. λ/4 is the required length for a monopole antenna to achieve long range. If a λ/10 size antenna is used for that application, the range will be reduced.

Next, the range of the same Tx & Rx differs based on the test environments (free space, office, industry, hospital, etc.) as there will be different obstacles that affect the signal strength by reflection, diffraction, and scattering; the range will be different for different environments. Here, we focused on two methods of measurement. The first one is based on a conducted test setup using cables and attenuators in between Tx and Rx DUTs placed within Gigahertz Transverse Electro Magnetic (GTEM) Cells. The communication link between the GTEM cell’s input port and Device Under Test (DUT) is radiated. The second one has been measured in an open area in a suburban environment, which is one of the real use cases.

• Link budget measurement by GTEM cell
  • Calculated range from the link-budget
• Better range projection by real range measurement
  

Link budget measurement by GTEM cell

Test Setup

GTEM cells are used for link budget measurement including Antenna Gains (Tx & Rx)

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RF Path Loss Description

• TEM Cell Path Loss (TCPL): 868 MHz: ~18 dB, 915 MHz:~19 dB
• Insertion loss of the variable attenuator (IL_VA): ~6 dB
• Total Coaxial Cable Loss (CL): ~2 dB
• Link budget = 2* TCPL + IL_VA+ the attenuation of the variable attenuator + CL + 30 dB
• 868 MHz Link budget = 74 dB + the attenuation of the variable attenuator
• 915 MHz Link budget = 76 dB + the attenuation of the variable attenuator

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WLR089U and SAMR34 XPRO Settings

• Power level: 15 @868 MHz, 20 @915 MHz
• Spread factor: SF12
• LoRA bandwidth: 125 kHz
• No. of packets: 100
• 1% Packet error rate

Both WLR089 XPro and SAMR34 Xplained Pro have similar performance in the Link Budget measurement.

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Formula

Friis equation in decibel form:
PR (dB) =−20log(4πλ)−10nlog(d)+GT+GR+PT
Link budget = 20log(4πλ)+10nlog(d)+Fm

Fm= Fading margin, at least 15 dB
d=distance (in m), n=2.5 for open field
For 915 MHz and 868 MHz, 20log(4πλ) = ~32 dB

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Calculated range from the link-budget

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Better Range Projection by Real Range Measurement at 1.5 km

1.5 km RSSI test :

Read the average Received Signal Strength Indicator (RSSI) value in RX at a distance of 1.5 km from TX. Next, calculate the sensitivity margin to estimate the range. DUT is placed at a height of 1.5 m from the ground.

• The sensitivity with SF12 for 915 MHz and 868 MHz is -136 dBm.
• The average RSSI reading for both WLR089U and SAMR34 XPro is ~ -103 dBm at 915 MHz and ~ -105 dBm at 868 MHz.
• The sensitivity margin is 33 dB at 915 MHz and 31 dB at 868 MHz.
• sensitivity margin = 10nlog(d1500), where n = 2.8 for suburban environment
• The range for 915 MHz is ~ 22.7 km and 868MHz is ~ 18.9 km.

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Recommended Range Test Setup

It is suggested to test in an open area with fewer to no obstacles between Tx and Rx.

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Tested Samples

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Antenna Used in the Measurement

Used antenna in WLR089U:

• RFA-S1-C55H1-150D034 from ALEAD technology
• Peak antenna gain: 2 dBi

Used antenna in SAMR34 XPro:

• RFA-ZW-C55-B-RP-D034 from ALEAD technology
• Peak antenna gain: 2 dBi

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Learn More

• Range calculation application note
   

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