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-\chapter{Communication protocols for IoT devices in 4G/5G mobile networks}
-
-\section{Current situation}
-
-It is estimated that currently (2023/2024) there are two actively connected Internet-of-Things (IoT) devices per each person living on the planet Earth and the number will almost double furthermore until 2030, reaching nearly 30 billion connected IoT devices worldwide\cite{statista}.
-
-At the same time, complexity of the IoT devices rises every year and so is their requirements on the underlying network infrastructure and protocols, originally designed predominantly for completely different mobile applications (text messages and voice / video streaming). Need for new IoT-related protocols started to be prominent with wide-spreading and anticipated new use-cases of IoT devices, for which \ac{GSM} and original \ac{LTE} networks were not originally intended and soon found unsuitable in terms of power efficiency, connection reliability and ability to accommodate billions of small devices with tiny average data rates.
-
-IoT devices today are not only simple single-purpose meteo sensors, but more and more frequently this category includes very complex vehicles and machinery, such as autonomous cars with multiple \ac{RADAR}/\ac{LIDAR} sensors or cooperative industrial robots, needing to communicate with the central command \& control facility and with each other in real time and with very high reliability. On the other hand large widespread of massive quantities of very low power devices in possibly critical application can also be expected. Related requirements on communication data volumes, response latency and network reliability far exceed capacity and technical possibilities of older mobile networks. Larger bandwidths, data speeds and lower latencies brought by 4G and especially 5G mobile networks are necessary for providing the appropriate working space for these new IoT devices.
-
-The necessary communication protocols for 4G and 5G mobile networks are being standardized under an umbrella of \ac{3GPP} - an association of national telecommunication standardization agencies and commercial partners. \ac{3GPP} has agreed upon and released several communication protocols (so-called „releases“) for the new generations of mobile networks, unfortunately with some ambiguities in their numbering and labeling. For example, Long-term evolution (LTE) was first introduced as a 3G technology standard but it later become a 4G standard. LTE was followed by LTE-Advanced labeled as „true 4G“ or 4.5G and LTE-Advanced Pro (LTE-A Pro) that is considered 5G but sometimes it is labeled as 4.9G \cite{nokia49g}.
-
-\section{4G IoT networks (LPWAN)}
-
-%IoT has become a large part of every day life and is now crucial to many both critical and non-critical applications. With planed shutdown of 2G and 3G networks [] it is important to look on protocols that are suposed to replace them and enhance their capabilities.
-
-Low-power wide-area network (LPWAN) protocols are 4G LTE wireless communication technologies that enable long-range transmission among IoT devices. LPWAN protocols are designed to meet the diverse requirements of IoT applications, mainly low power consumption, wide coverage range, capacity for large number of devices, and high reliability \cite{gsmalpwan}.
-
-\subsection{NB-IoT}
-NB-IoT (Narrowband Internet of Things) is a cellular LPWAN standard that was developed by \ac{3GPP} for IoT devices and services in 2016 under \ac{3GPP} Release 13 and updated in 2017 with \ac{3GPP} Release 14 \cite{erf}.
-
-NB-IoT focuses on providing extended coverage, enhanced capacity, reduced complexity, and increased battery life for IoT devices that transmit small amounts of data infrequently \cite{rohdenbiot}.
-
-NB-IoT operates on the licensed spectrum and uses a subset of the LTE bands with peak data rate of 26 kb/s for downlink and 16.9 - 66 kb/s for uplink using Cat NB1. Newer standard of Cat NB2 allows maximum peak rate of 127 kb/s for downlink and 159 kb/s for uplink. NB-IoT uses orthogonal frequency division multiplexing (OFDM) modulation for downlink communication and single carrier frequency division multiple access (SC-FDMA) for uplink communication.
-
-Single NB-IoT communication channel corresponds to a single 180 kHz LTE frequency block \cite{ltebook}. This enables the following operation modes \cite{rohdenbiot}:
-
-\begin{itemize}
-	\item In-band operation - NB-IoT operates on standard LTE frequencies among other types of LTE communication
-	\item Guard band operation - Communication takes place in LTE guard-band without any other LTE communication
-	\item Stand alone operation - A theoretically possible scenario when mass adaption of technology will occur. This mode plans to utilize frequency allocation of current GSM networks.
-\end{itemize}
-
-\begin{figure}[!h]
-	\begin{center}
-		\includegraphics[width=0.9\textwidth]{obrazky/nbiotmodes.png}
-	\end{center}
-	\caption[NB-IoT modes]{NB-IoT modes of operation \cite{rohdenbiot}}
-	\label{fig:nbiotmodes}
-\end{figure}
-
-As of writing this thesis (December 2023) NB-IoT is supported in Czechia by all three national mobile operators. Vodafone is declaring universal coverage across the whole country \cite{vodafonemap}, T-Mobile in selected larger cities and O2 only in Moravian-Silesian region \cite{narowbandcoverage}.
-
-
-
-%NB-IoT is a cellular LPWAN standard that was developed by the 3rd Generation Partnership Project (\ac{3GPP}) for IoT devices and services and published in 2016 with \ac{3GPP} Release 13[] and its updated version in 2017 with \ac{3GPP} Release 14 []. NB-IoT operates on the licensed spectrum and uses a subset of the LTE bands with peak data rate of $26 kb/s$ for downlink and $16.9 \div 66\;kb/s$ for uplink using Cat NB1. Newer standart of Cat NB2 allow maximum peak rate of $127\;kb/s$ for downlink and $159\;kb/s$ for uplink.
-%NB-IoT uses orthogonal frequency division multiplexing (OFDM) modulation for downlink communication and single carrier frequency division multiple access (SC-FDMA) for uplink communication. NB-IoT focuses on providing extended coverage, enhanced capacity, reduced complexity, and increased battery life for IoT devices that transmit small amounts of data infrequently.
-%
-%As of writing this thesis (December 2023) NB-IoT is supported in Czechia by all tree national mobile operators. Vodafone is declaring universal coverage in whole state \cite{vodafonemap}, T-Mobile in selected larger cities and O2 only in Moravian-Silesian region \cite{narowbandcoverage}.
-%
-%\subsubsection{Modes of operation}
-%
-%Single NB-IoT comunication channel correspondes to single 180 kHz LTE frequency block \cite{ltebook}. This enables following operation modes \cite{rohdenbiot}:
-%\begin{itemize}
-%	\item In-band operation - NB-IoT operates in standart LTE frequencies among other types of LTE comunication
-%	\item Guard band operation - Communication occur in LTE guard-band where no prior LTE communication takes place
-%	\item Stand alone operation - A theoretically possible scenaraio when mass adaption of technology will occur. This mode plans to utilizate frequency allocation of current GSM networks
-%\end{itemize}
-
-\subsection{LTE-M}
-
-LTE-M or LTE-MTC (Long-Term Evolution Machine Type Communication) is a second LPWAN protocol specified in \ac{3GPP} Release 12, with improved specification in Releases 13 and 14. Unlike NB-IoT, LTE-M uses more bandwidth (1.4 - 5 MHz) and is capable of higher communication speeds (1 - 4 Mbit/s for downlink and 1 – 7 Mbit/s for uplink). Another advantage of LTE-M over NB-IoT is an ability to function with movable objects (such as cars or drones). Higher bandwidths however lead to greater circuit complexity and possible higher energy consumption related to it \cite{nordiccompare}.
-
-As of writing this thesis (December 2023) LTE-M is covered in Czechia by O2 in 98.5 \% \cite{o2catm} and locally by Vodafone \cite{vodafonemap}.
-
-%LTE-M or LTE-MTC (Long-Term Evolution Machine Type Communication) is second LPWAN protocol specified in \ac{3GPP} release 12 with improved specification in releaes 13 and 14.
-%
-%Unlike NB-IoT LTE-M uses more bandwidth 1.4-5 MHz and is capable of higher comunication speeds (1-4 Mbit/s for downlink and 1-7Mbit/s for uplik depending on version). Another advantage is ability to function with movable objects (eg. cars or drones). Higher bandwidth leads to grater circuit complexity and higher energy consumption related to it.
-%
-%As of writing this thesis (December 2023) LTE-M is coverted in 98.5 \% in Czechina by O2 \cite{o2catm} and mostly by Vodafone \cite{vodafonemap}.
-
-\section{5G IoT networks}
-5G implementation into the mobile networks can be achieved via two methods \cite{5gnruk}:
-
-\begin{itemize}
-	\item NSA (non-stand alone) - 5G features are achieved by adding new RAN (Radio Access Network) to existing 4G LTE core. This approach implements dynamic spectrum sharing and enables rapid deployment of enhanced mobile broadband in customer market without larger changes in existing infrastructure.
-	\item SA (stand alone) - LTE core and RAN are completely replaced with 5G ones. RAN can however still switch back to LTE air interface to ensure backward compatibility with non-5G devices.
-\end{itemize}
-
-In 2018, \ac{3GPP} Release number 15 laid down 5G specification named 5G NR (New Radio). Unlike LTE-A Pro that has just added more features to 4G LTE and operated in LTE standards and channels, 5G NR introduced a new physical layer in air interface \cite{5gnruk}.
-
-5G NR tries to solve three key aspects of wireless technology \cite{5gnruk}:
-
-\begin{itemize}
-	\item eMBB (Enhanced Mobile Broadband): Data-intensive applications needing large bandwidth for primarily traditional end-user demand, like video streaming. This should be achieved by Gigabit LTE, massive MIMO, mmWave technologies, spectrum sharing techniques and advanced channel coding.
-	\item mMTC (Massive Machine Type Communications): Low-power and low-cost applications with small data volumes but potentially large number of these devices in a small footprint. It is built on LTE LPWAN protocols like LTE-M and NB-IoT, making them potentially a core part of 5G.
-	\item URLLC (Ultra-reliable and Low-latency Communication): Mission-critical applications traditionally possible only by direct wire connection, necessary for real-time control of autonomous vehicles and industrial machinery.
-\end{itemize}
-
-As of December 2023, 5G IoT networks are not yet commercially available in Czechia.
-
-%%%%%%
-\subsection{URLLC requirements}
-
-URLLC (Ultra-Reliable and Low-Latency Communication) is a new requirement for 5G networks  for providing real-time communication protocols with very low delays and very high levels of reliability. First attempts to address this were introduced in 4G LTE HRLLC (Higher-Reliability and Low-Latency Communication) in \ac{3GPP} release 15 \cite{5gamericasurllc}. Until this point, aspects of latency and reliability were
-dealt in separately and sometimes were in direct contradiction to each other (reliability was achieved with repeated data redundancy, which multiplied latency). Combination of these two aspects is however essential for several critical applications with different requirements, as shown in table \ref{tab:urllc}:
-
-\begin{table}[!h]
-	\begin{center}
-		\small
-		\begin{tabular}{|l|c|c|c|}
-			\hline
-			Scenario & E2E latency [ms] & Reliability [\%] & Data rate [Mbps] \\\hline\hline
-			Discrete automation						& 10	& 99.99		& 10 \\\hline
-			Process automation – remote control		& 60	& 99.9999	& 100 \\\hline
-			Process automation ‒ monitoring			& 60	& 99.9		& 1 \\\hline
-			Process automation ‒ monitoring			& 40	& 99.9		& 10 \\\hline
-			Electricity distribution – high voltage	& 5		& 99.9999	& 10 \\\hline
-			Intelligent transport systems				& 30	& 99.9999	& 10 \\\hline
-			\hline
-		\end{tabular}
-	\end{center}
-	\caption[Performance requirements for URLLC]{Performance Requirements for Low-Latency and High-Reliability Scenarios \cite{5gamericasurllc}}
-	\label{tab:urllc}
-\end{table}
-
-
-\subsection{Latency}
-With such strict latency requirements, as low as 5 ms end-to-end latency, it is necessary to minimize air interface delay (to 1 ms or less). To achieve such low latency, intensive optimization of air data delivery is necessary.
-
-There are several possible approaches that can lead to reduced communication time and latency \cite{5gamericasurllc}:
-
-\begin{itemize}
-	\item Frequent transmission opportunities
-Downlink control channel used to carry scheduling information for data transmission is not usually monitored by end device for power saving reasons. However to reduce the waiting time for delivering the control information, the end device could do this. For device to start uplink transmission, it needs to send a scheduling request (SR) that allocates a specific transmission slot. To minimize the waiting time, the periodicity of the SR resource configuration should reflect latency requirements. This can be further emphasized by flexible schedulling timing mainly in Time Division Dulex (TDD).
-
-	\item Flexible transmission duration
-This aspect is supported in 5G using larger subcarier spacing. This shortens slot duration and gives bigger oportunity for quicker communication establishment.
-
-	\item Grant-free (or configured grant) uplink transmission
-In cases with very low latency demand, grant-free uplink transition, specific periodic uplink resource for device can be arranged. End device in this scenario does not need to wait for scheduling request and at any time it has data it can transmit in this arranged slot without a need for dynamic grant.
-
-\end{itemize}
-
-Air interface is only partially responsible for total end-to-end latency. Remaining latency is caused by core network, internet network and particular server with which the device is communicating. This is to be solved by new concept of Edge computing. Edge computing is a possibility for a mobile operator or another entity to move services from a remote server closer to the device and to execute necessary task right in 5G core network \cite{3gppurllc}.
-
-Another method of lowering transport network latency is to avoid transport network completly. This is experimented in vehicle-to-vehicle (V2V) protocols and in non-IP based communication \cite{5gamericav2v}.
-
-\subsection{URLLC reliability optimization}
-
-In \ac{3GPP} Release 16, redundant transmission for high-reliability communication was introduced \cite{5gamericasurllc}. With this method, user packets are duplicated and simultaneously transferred to the receiver via two disjoint user plane paths. The redundant packets are then eliminated at the receiver side. This further avoids occasional fails in one path propagation and slims probability of exceding the delay requirements. Other changes can be made in 5G core parameters settings, like QoS Monitoring, dynamic division of Packet Delay Budget and enhancements of session continuity \cite{3gppurllc}.
 
 \chapter{IoT communication modules for 4G/5G networks}