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E. Fraccaroli and D. Quaglia
but requires the presence of a master which may become a point of failure. CSMA
is preferred where transmission patterns are not regular (e.g., messages triggered by
asynchronous events) and variable delays are not an issue. TDMA is preferred in
closed-loop control systems where messages are scheduled.
3.2.2.5 Physical Layer
It deals with the transmission of bits on the medium. Many IoT applications exploit
radio transmissions by using specific frequency intervals (named frequency bands)
of the electromagnetic spectrum. Transmissions over different frequency bands do
not interfere each other and can go in parallel, but two transmissions cannot be
performed on the same frequency band simultaneously. For this reason, in general,
the allocation of transmissions in the electromagnetic spectrum is regulated by
the government. Frequency bands assigned by the government to specific bodies
(usually telecommunication providers) are named licensed bands. They are used
in cellular networks. Other frequency bands can be freely used without asking
the government for a permit provided that the transmitted radiated power is kept
below a given threshold and the number of sent PDU per time unit is kept under a
given threshold; such bands are named unlicensed bands. Traditionally, local area
networks (and their evolution as personal area network) use unlicensed bands, while
commercial telecommunication networks use licensed bands.
There are unlicensed bands in various positions of the spectrum. Some properties of electromagnetic signals depend on frequency value. Bands below 1 GHz
are named sub-gigahertz bands. Their propagation properties are similar to old
FM transmissions, i.e., radio signals go around obstacles and can propagate for
tens of kilometers. Vice versa at frequencies above 1 GHz (e.g., around 2.4 and
5 GHz as in Wi-Fi) radio signals behave similarly to light rays and require Lineof-Sight (LoS) propagation between transmitter and receiver. However physical
bitrate is proportional to frequency. Communication standards use such different
bands according to their application field. For instance, network architectures for
agricultural monitoring and smart meter reading use sub-gigahertz bands for their
excellent propagation capability considering that the required bitrate is low. Vice
versa 2.4/5 GHz bands are used when the required data rate is high, and deployment
place does not create LoS issues.
3.2.3 Standardization Bodies
Standardization bodies are organizations that coordinate the development of new
standards. Standardization bodies can cover specific areas, like the Institute of
Electrical and Electronics Engineers (IEEE) which gather partners interested mainly
into electrical and electronics engineering and computer science, or a wider
selection of topics, like the International Organization for Standardization (ISO).
E. Fraccaroli and D. Quaglia
but requires the presence of a master which may become a point of failure. CSMA
is preferred where transmission patterns are not regular (e.g., messages triggered by
asynchronous events) and variable delays are not an issue. TDMA is preferred in
closed-loop control systems where messages are scheduled.
3.2.2.5 Physical Layer
It deals with the transmission of bits on the medium. Many IoT applications exploit
radio transmissions by using specific frequency intervals (named frequency bands)
of the electromagnetic spectrum. Transmissions over different frequency bands do
not interfere each other and can go in parallel, but two transmissions cannot be
performed on the same frequency band simultaneously. For this reason, in general,
the allocation of transmissions in the electromagnetic spectrum is regulated by
the government. Frequency bands assigned by the government to specific bodies
(usually telecommunication providers) are named licensed bands. They are used
in cellular networks. Other frequency bands can be freely used without asking
the government for a permit provided that the transmitted radiated power is kept
below a given threshold and the number of sent PDU per time unit is kept under a
given threshold; such bands are named unlicensed bands. Traditionally, local area
networks (and their evolution as personal area network) use unlicensed bands, while
commercial telecommunication networks use licensed bands.
There are unlicensed bands in various positions of the spectrum. Some properties of electromagnetic signals depend on frequency value. Bands below 1 GHz
are named sub-gigahertz bands. Their propagation properties are similar to old
FM transmissions, i.e., radio signals go around obstacles and can propagate for
tens of kilometers. Vice versa at frequencies above 1 GHz (e.g., around 2.4 and
5 GHz as in Wi-Fi) radio signals behave similarly to light rays and require Lineof-Sight (LoS) propagation between transmitter and receiver. However physical
bitrate is proportional to frequency. Communication standards use such different
bands according to their application field. For instance, network architectures for
agricultural monitoring and smart meter reading use sub-gigahertz bands for their
excellent propagation capability considering that the required bitrate is low. Vice
versa 2.4/5 GHz bands are used when the required data rate is high, and deployment
place does not create LoS issues.
3.2.3 Standardization Bodies
Standardization bodies are organizations that coordinate the development of new
standards. Standardization bodies can cover specific areas, like the Institute of
Electrical and Electronics Engineers (IEEE) which gather partners interested mainly
into electrical and electronics engineering and computer science, or a wider
selection of topics, like the International Organization for Standardization (ISO).