Instrumentation & Measurement Magazine 23-9 - 30

Table 2 - Values of Tpacket (total transmission time of the LoRa packet), expressed in ms, versus Bw and SF,
with CR = 1, implicit header (IH = 1), CR = 1, cyclic redundancy check (CRC) = 1, payload of 10 bytes
SF
Bw

7

8

9

10

11

12

125

37.12

64

128

256

430.08

860.16

250

18.56

32

64

128

215.04

430.08

500

9.28

16

32

64

107.52

215.04

network life cycle. In the design stage, measurements conducted at the PHY layer are useful to characterize properties
of the wireless channel. Once the network is operative, crosslayer measurements can be efficiently exploited to gather
information about possible causes of quality-of-service (QoS)
degradation when the latter is observed at higher layers. As
stated above, LoRa technology adopts a CSS scheme that is
particularly robust to narrowband signal interference, while it
is weak towards interferences coming from other LoRa nodes
that are not perfectly orthogonal (same SF) or when the interference is due to modulated signals having wide bandwidth
and noise-like spectrum. Therefore, the authors' attention has
been focused on the correlation between PLR, a well-known
key higher layer parameter, and values that characterize major
PHY quantities, such as different configurations of the LoRa
signal and intentional AWGN powers. In the following, details
about the testbed and operative procedure of the considered
measurement scenario are provided.

Measurement Setup
Experiments have been conducted using a proper measurement setup, emulating a common scenario. The measurement
setup consists of: (i) a LoRa technology wireless link, made by
two SX1272 LoRa Semtech Demoboards, acting as LoRa Transceiver and LoRa Receiver respectively; (ii) the AWGN source,
to emulate typical interference phenomena of a real-world
environment that corrupts the communication (Fig. 2). The
AWGN interference is generated by a signal generator and
conveyed in the direction of the LoRa receiver
by means a horn antenna
connected to the signal
generator through a coaxial cable.
AWGN power is suitably varied in order to
assess LoRa communication at different levels
of SNR (measured close
to LoRa Receiver). The
signal at LoRa Receiver
is captured by an omnidirectional antenna,
which is connected to the
real-time spectrum anaFig. 2. Cross-Layer Measurement Setup.
lyzer through a coaxial
30	

cable. Measurements are carried out according to a cross-layer
approach. In particular, the following parameters are considered: LoRa signal configuration (SF, Bw, CR, CRC, Preamble,
Header, Payload Length) and signal-to-noise power ratio
(SNR) at PHY layer, packet loss ratio (PLR) at transport Layer.
Experiments have been conducted inside a protected and controlled environment, that is a shielded semianechoic chamber
compliant with electromagnetic compatibility requirements.
The semianechoic chamber reduces or eliminates the influence
on measurements of perturbing phenomena in the propagation channel like fading, shadowing, and multipath, thus
making the analysis focused only on the effects caused by the
superposition of the AWGN interference over the useful LoRA
signal. In the following, the measurement procedure is described according to what is shown in Fig. 2. First, by means of
PC1 and PC2, Tx and Rx LoRa devices are set with the desired
values of configuration parameters, thus establishing the PHY
layer characteristics of the LoRa wireless communication channel. Moreover, PC1 sets also the signal generator to provide the
AWGN interference, with the desired power level. Once the
configuration of the testbed is completed, SNR is estimated in
two steps, a preliminary measurements campaign carried out
with the support of the omnidirectional antenna placed close
to the LoRa Rx antenna and connected to the real-time spectrum analyzer. In the first step, the useful signal power inside
the LoRa wireless channel is measured during the only LoRa
data transmission between LoRa Tx and Rx devices. In the second step, the AWGN interference power level at the receiver

IEEE Instrumentation & Measurement Magazine	

December 2020



Instrumentation & Measurement Magazine 23-9

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