Wired technologies are the eldest ones, as the first smart home implementations were based on the existing home infrastructure (Power Lines). They provide more secure communications with limited interference.

This technology is well-known and used in the US. As presented in “Smart Home Automation in the IoT Era: A Communication Technologies Review” ^[1][45], it is a specification based on three major characteristics. It can provide connectivity with the use of various wired communication technologies and is wireless with the collaboration of EnOcean technology ^{[2][3][4][5][6][7]}[43,44,46,47,48,49].

Dupline is a wired home automation technology mostly known in the EU. It uses powerlines or twisted pairs for exchanging information. The maximum number of devices that can be connected in this system is 128, whilst its packet size is very small (14 Bytes), achieving data rates up to 9.6 Kbps ^{[1][8][9][10]}[30,45,50,51].

Ethernet is one of the most well-known technologies introduced by Bob Metcalfe and his team ^[11][52], who allied. It is known for interconnecting network devices such as computers and PLCs through its RS586 port. It is a proprietary technology, standardized with backward compatibility. It uses twisted pair or fiber optics as a data exchange medium while achieving very high data rates ^{[1][12][13][14][15][16][17][18]}[45,53,54,55,56,57,58,59].

These technologies take advantage of both wired and wireless technologies in home automation through communication redundancy and provide high availability.

KNX (aka KONNEX) is a very popular worldwide open standard technology. It supports powerline and ethernet cabling for wired communications and provides wireless connectivity as well. Furthermore, it can collaborate with other known wireless technologies such as EnOcean, WiFi, and Zigbee. According to the medium used, it can provide data rates from 9.6 Kbps up to 100 Gbps with a packet size of 16 Bytes ^{[1][12][19][20][21][22][23]}[31,45,53,60,61,62,63].

This technology was presented by the Echelon Corporation Company in 1991. It first originated as BACnet’s competitor; therefore, compatibility is provided between them. LonWork is an abbreviation of “Local Operating NetWORK”. Its’ innovation is that each device has an embedded Neuron Chip, along with transceivers and electronics for application. In detail, it has an SoC (System on a chip) implementation containing many microprocessors, ROM (Read Only Memory), RAM (Read Access Memory) modules, and I/O (Input/Output) interface ports. Moreover, an electronic module is provided for physical interface connections with other devices.

It is a multi-medium technology, as it can provide connections through:

• Twisted pair;
• Ethernet;
• Fiber Optics;
• RF;
• BACnet.

The message size is 228 Bytes, while the data rates provided can reach up to 1.25 Mbps. Regarding coverage, it can reach distances up to 2700 m in wired connections.

Devices or systems can be separated into smaller groups of intelligent elements, called nodes, creating a smart network ^[24][25][26][64,65,66].

It is one of the oldest home automation systems, as it was introduced in 1975. This technology is open-sourced and used for remotely controlling X-10’s compliance transmitters and receivers. It has two modes for connections:

• Wired: powerlines already pre-installed in every home;
• Wireless: RF.

Short messages (commands) are used and broadcasted by transmitters to the receiving unit and processed by a unique ID. Receivers read this information and compare it with the receiving ID to determine if it matches their own. If the condition is met, then the whole message is downloaded and processed.

Due to the nature of this technology, data rates of 60 bps are provided, covering distances up to 30 m. Therefore, it is mostly used in automation networks such as lightning, home appliance, and security sensors ^[2][27][43,67].

This technology is X10’s successor; it provides backward compatibility with all existing devices supporting the technology (operating in 132 KHz) despite the commands not being similar. Its network consists of both wired and wireless connections providing MESH connections between them and ensuring connection redundancy ^{[2][3][24][26][28]}[38,43,44,64,66].

These technologies are introduced to solve the need for interfacing with the existing home infrastructure and to provide a low-cost, high-efficiency solution for device communication. They can be divided into two major categories, according to the distance they cover.

Short-range technologies can be used primarily on small buildings and homes, providing high-speed and high-availability connections between devices.

IPv6 over low-power wireless personal area networks is used for home automation systems and is characterized by its simplicity and low cost. It provides wireless connectivity where serious power constraints are needed. It makes use of IEEE 802.15.4 standard in the lowest OSI-7 layers ^[12][53] and IPv6 (IP version six) protocol for communications.

This technology is characterized as WPAN (Wireless Personal Area Network), exchanging data packets of 100 bit, while achieving data rates up to 250 Kbps and covering distances up to 200 m. It also provides mesh capabilities, but with a device making multiple wireless concurrent connections with more than one neighboring device. If its primary connectivity is lost, communication can still be established through another connection in the same network.

6LowPAN has compatibility with devices using the same standard (802.15.4) and can also communicate to a computer network through Wi-Fi using a gateway ^{[29][30][31][32][33][34][35]}[36,68,69,70,71,72,73].

Bluetooth is a very popular short-range networking technology mostly used in computers, smartphones, and peripheral interconnections. In 2015, the Bluetooth 4.0 standard was introduced ^[36][74]. Described as BLE (Bluetooth Low Energy), it has unlocked its potential to ensure proper communications to the devices in the network whilst improving battery life and data rates ^{[31][36][37][38][39][40][41][42][43][44][45][46][47]}[32,69,74,75,76,77,78,79,80,81,82,83,84].

This technology is a wide-spreading technology, as it provides energy harvesting capabilities in wireless IoT and in-home automation. Every device in this WPAN (Wireless Personal Area Network) does not require any external energy source or battery ^[1][45].

The characteristics of this technology are:

• It can cover distances up to 300 m (outdoors);
• Network speeds up to 125 Kbps;
• 50 μW is required for signal transmission;
• Low band radio, which operates at 868 MHz and 315 MHz radio bands;
• Short telegrams (messages of 4 Bytes) are exchanged between devices;
• It can have heterogeneous connections with other technologies, such as:

  ◦

  Ethernet gateway;

  ◦

  Wi-Fi gateway;

  ◦

  BACnet;

  ◦

  LonWorks;

  ◦

  BLE;

  ◦

  Zigbee.

Furthermore, mesh connectivity is supported while providing quality mechanisms QoS (8-bit CRC) and encryption with the use of VAES (Variable AES) ^{[3][5][20][40][41][48][49][50][51][52][53]}[37,44,47,60,77,78,85,86,87,88,89].

Thread

Thread is a technology that is also based on the 802.15.4 standard, originated by seven companies (ARM (Softbank), Big Ass Fans, Freescale (NXP), Nest Labs (Google), Samsung, Silicon Labs, Yale Locks), which formed the Thread Group Inc. in 2015 ^[1][54][45,90]. It is an open standard technology incorporating many known standards. Therefore, it provides compatibility with other ones like the Nest thermostat and several Zigbee devices ^{[38][41][50][54][55][56][57][58][59][60][61][62]}[39,75,78,86,90,91,92,93,94,95,96,97].

Wi-Fi

This network technology is very popular, as it is known for the interconnection of various everyday devices. The 802.11ac standard (released in 2013) operates at the frequency bands of 2.4 GHz and 5 GHz, achieving data rates from 600 Mbps to 6.93 Gbps. With the introduction of 802.11ax in 2016 (Wi-Fi 6) and the use of M.I.M.O. (Multiple Input, Multiple Output) techniques, the technology can handle multiple connected devices, while providing data rates of 866.6 Mbps, 15 Gbps, 3466 Gbps of up to 9.6 Gbps. The protocol suite used for communications is the TCP/IP (v.4 and v.6), providing mechanisms for QoS (Quality of Service) with 32-bit CRC and security with encryption of AES128. As a well-known and used technology for end-user devices, connections with almost all known home automation technologies are provided by vendors. In 2014, the standard 802.11af of Wi-Fi enhanced its capabilities by improving energy management and efficiency. With the use of the existing WLAN topology, TV White Space frequencies (54 MHz–97 MHz band), and four channels for communications, the area covered remains 100 m, while the data rates can reach or surpass 400 Mbps. 802.11ah (WiFi HaLow) standard, newly introduced by IEEE and released in 2017, is an evolution of the 203.11af and is aimed at IoT devices. It provides many power-constrained stations, up to 100 m of area coverage, using frequencies of 900 MHz and network speeds of 4 Mbps. This technology also supports channels of 1 MHz/2 MHz for use in IoT, which can be increased up to 16 MHz to achieve greater data rates ^{[15][38][63][64][65][66]}[33,56,75,98,99,100].

Z-Wave

Z-Wave is a proprietary technology used by many vendors for home automation and IoT. It is characterized as low-cost, providing low-power transmissions. As described in Paetz (2013) ^[67][101], this technology has static routing and is implemented with a centralized routing table. Routing calculations are embedded into the messages so their forwarding behavior can be indicated (Fuller) ^[68][102]. OpenZwave is a variation of Z-Wave, which is open-source ^[69][103]. It is used in PCs as a USB transceiver dongle, but still, its routing logic is not accessible. It is encrypted in the firmware of the device ^{[3][38][41][44][50][61][68][70][71][72][73]}[35,44,75,78,81,86,96,102,104,105,106].

Zigbee

This technology is quite popular in wireless home automation systems and is one of the base competitors of Z-Wave. Due to the delay in the definition of the Bluetooth standard, several companies started the development of a new WPAN technology, named ZigBee, introduced in 2004 ^{[3][21][38][40][41][42][43][50][52][59][64][72][74][75][76][77][78]}[44,61,75,77,78,79,80,86,88,94,98,105,107,108,109,110,111].

3.2. Long Range

Long-range connections are mostly used for connections in larger buildings or architecture, providing availability without the use of repeaters.

DASH7

Industry-standard DASH7 Alliance Protocol (D7AP) is a standard based on the ISO/IEC 18000-7 and applied in wireless sensors and actuators. As its primary function design, it is based on the BLAST (Bursty, Light Data, Asynchronous Transitive) concept ^[43][80]. It operates on unlicensed low wireless frequencies 433 MHz, 868 MHz (EU), and 916 MHz (US), making the technology capable of reaching distances of 10 Km. Its message length is 256 Byte and provides data rates up to 200 Kbps achieving low latency when connected with moving network-capable objects ^[43][80]. Communication is done instantly (bursty) without containing any heavy data, such as audio or video ^[79][112], making it capable of light data payloads used in conventional applications. Due to its command–response communication method, DASH7 provides asynchronous communication. This is achieved as it requires a periodic “hand-shake” for its network and its’ upload-centric nature in addition to the download-centric other technologies that follow ^{[30][43][65][79][80][81][82][83][84][85][86][87][88]}[68,80,99,112,113,114,115,116,117,118,119,120,121].

LoRa (Long Range)

LoRa (Long Range), as the acronym displays, was first introduced in 2015 by Cycleo ^[89][122] and promoted to consumers by Semtech ^[90][123], is an open standard, used mostly for wireless systems separated by great distances with the use of unlicensed RF bands. It is described as LPWAN (Low Power Wide Area Network) or WWAN (Wireless Wide Area Network) and is used for long-range data transmissions, more than 10 km (up to 20 km), while consuming very low energy. This is achieved due to the low frequencies used, its’ message protocol (LoRaWAN) of 255 Bytes, and the low data rates supported (0.3–50 Kbps). As can be seen, it is suitable for applications exchanging a low set of data for long ranges without having to replace batteries for many years (more than 10 years) ^[91][124]. Mainly, it is used in agriculture, but there are also applications developed for H.A. This technology provides a connection to existing computing networks, such as ethernet and Wi-Fi, through its gateway, providing an administration mechanism. Despite its low data nature, LoRa offers data encryption (AES) but no QoS mechanism ^{[32][44][64][65][75][80][89][92][93][94][95][96][97][98][99][100][101][102]}[70,81,98,99,108,113,122,125,126,127,128,129,130,131,132,133,134,135].

LTE (5G/NB-IoT)

LTE (Long Term Evolution) is a very popular networking technology, well known for mobile phone communications used worldwide. It was introduced by 3GPP in 2008 and is based on the already existing networks GSM/EDGE and UMTS/HSPA, having as its primary objective faster data rates for mobile networking devices. To achieve that, new techniques of digital signal processing were introduced. First, 2G was provided to 90% of the world’s population, but its’ main aim and target was mostly for voice ^[103][136]. Therefore, 3G has been introduced, providing more services than voice for a great amount of data. Emerging new technologies such as smartphones and tablets increased the need for higher data rates and led to its evolution in 2012 (4G). Further, 5G was built on the foundations of its successors, providing even higher data rates of 10 Gbps, reliability (32-bit CRC), and encryption (AES256). For IoT and smart home implementations, special modes of this technology are used, LTE CAT-0, LTE CAT-M, and NB-IoT. These are optimized for IoT and smart buildings, reducing the complexity while covering the same range of the same infrastructure. With the introduction of 3GPP release 12, a new category for UE (User Equipment) is supported. This evolution in Cat 0 (Category 0) devices resulted in a significant increase in their battery life. The most notable changes are:

• The throughput for Uplink and Downlink is reduced to 1 Mbps;
• The number of antennas is now decreased from 2 to 1;
• The UE receiver bandwidth is reduced to 1.4 MHz, which can allow the reduction of substantial complexity;
• UE can still operate in existing LTE system bandwidths up to 20 MHz;
• A UE with a lower power class allows the integration of a power amplifier in a system provided in a single chip.

Table 1 displays the UE categories from the 3GPP Specification number 36.306. The 3GPP releases 13 and 14 are widely known as NB-IoT, and it is mostly used for IoT implementations ^[104][137]. Huawei Technologies Co. Ltd. was one of the major companies focusing on this technology, providing enhanced, long-range coverage with the support of a substantial number of low-throughput devices ^[105][138]. Devices in this network are characterized by enhanced network architecture, low response time, low delay sensitivity, very low cost, and low energy consumption. The main advantage of this technology is the ability, when deployed in authorized frequency bands, to make use again of its core network. As IoT devices do not require high data rates, the size of the message varies according to the network deployment, and transmission speed can be up to 204.8 Kbps and 234.7 Kbps for upload and download, respectively. Messages are encrypted with the AES256 Standard (Advanced Encryption), providing extra security for the information exchanged. Furthermore, this technology provides great data integrity, as it implements SNOW 3G ^[106][139] or ATR-128 CMAC (Cipher-based Message Authentication Code) with 4 Byte MIC (Message Integrity Code) QoS mechanism. Due to its origin, LTE, is supported by many developers creating applications for remote management of systems such as traffic control and home automation ^{[44][65][96][99][101][104][105][107][108][109][110]}[81,99,129,132,134,137,138,140,141,142,143].

Mioty

This is a brand-new, open technology created and developed by Fraunhofer Institute in 2016 according to the ETSI telegram splitting ultra-narrow band (TS-UNB) technical specification for low-throughput networks (TS 103 357) and provided to the public through the Canadian company BehrTech. It is a long-range platform (WWAN) covering distances up to 15 km (without obstacles), with data rates of 512 bps. It provides low consumption and long battery life; therefore, it is characterized as LPWAN.The innovation in mioty is the way that messages are transmitted. They are formatted as short telegrams of packets sizing 10–192 Bytes, but they are not sent simultaneously. Using TSMA (Telegram Spread Multiple Access), a random MAC is used, dividing its’ message transmission into several shorter packages (fragments). Then, these are distributed randomly on different channels and timeslots. This technique, according to its developers, can tolerate packet loss of up to 50%. In Figure 3, the mioty telegram splitting technique is depicted. As Mioty is a new technology, there is not so much information available and open-source developments concerning the design of Gateways and wireless nodes, and therefore it is difficult to analyze in-depth the performance of the technology compared with other LPWAN technologies ^{[80][95][101][111][112]}[113,128,134,144,145].

Sigfox

It is a long-range communications technology created and developed in 2010 in Toulouse, France ^[96][129]. It is defined by the ETSI ERM TG28 standard and characterized as LTN (Low-Throughput Network). Sigfox uses the free, unlicensed bands of:

• 868 MHz (Europe);
• 902 MHz (US);
• 430 MHz globally;
• 2.4 GHz globally.

The distances covered are greater than 10 km, achieving data rates up to 100 bps for uploading and 600 bps for downloading. Its’ message length is 8–12 Bytes and provides heterogeneity as modules are developed, providing a connection of its gateway to BLE and Wi-Fi. Unfortunately, due to its’ slow data rate, QoS is not provided but provides encryption to the packets exchanged. One characteristic that can be pointed out is a feature called spatial diversity. As its terminal is not attached to a single base station, like most mobile cellular systems, when following the right deployment, a message sent by a terminal can be received by many base stations ^{[32][44][65][96][100][101][113]}[70,81,99,129,133,134,146].

4.Technologies’ Comparison and Discussion

In this section, a detailed comparison of the technologies studied in this resviearchw will be presented.

These will be presented in four separate groups to reduce information overloading. The key groups are wired, wireless (short range), wireless (medium–long range), and dual mode (using both wired and wireless communications). The separation of wireless protocols into short-range and medium–long range is done due to the multiple technologies available.

Wireless technologies can be classified according to the distance they cover (Figure 4). These are:

• Contact, also described as Proximity, is used for communications with distances up to 10 m.
• Short, also known as WPAN (Wireless Personal Area Networks), covers areas from 10 m to 100 m.
• Short/Medium networks are characterized as WLAN (Wireless Local Area Networks) and are used for areas from 100 m to 1000 m.
• Medium (1–10 km), also described as WNAN (Wireless Neighborhood Area Networks), covers areas from 1 km to 10 km.
• Long-range (10–100 km), also known as WWAN (Wireless Wide Area Networks), is used for greater distances of coverage from 10 km to 100 km.

Figure 4.

Illustration of existing technologies for wireless networking regarding connectivity range.

Figure 4 illustrates all the technologies according to the distance they can cover.

Another classification of these technologies’ characteristics is:

• User interaction;
• Technical characteristics;
• Data integrity;
• Energy/Cost.

4.1. User Interaction

According to the information provided in Tables 2–5 of the article, technologies, mostly wired, have been provided to consumers for over 20 years. These are BACnet, Bluetooth, Dupline, Ethernet, KNX, LonWorks, Wi-Fi, and X10. Three of them are known for computer and mobile device networking. These are the most popular ones in building automation. In Europe, the most known technologies in the market are Dupline and KNX, while in the US, they are BACnet, X10, and its successor, Insteon. Among the most recent technologies, are Zigbee and Z-Wave the most known ones.

While there are many solutions regarding home automation in the market, many of them are extending their capabilities by providing support for security systems, remote metering, and medical appliances. Most of them offer an API (Application Programming Interface) to developers for them to include their technology in their products.

4.2. Technical Characteristics

Technical characteristics are an important category to examine the technologies’ capabilities in more detail. According to “Trends in Home Automation Systems and Protocols”  ^[12][53], all of them follow the OSI-7 reference model. According to its specification, it has seven layers named from the bottom up: physical, data link, network, transport, session, presentation, and application.

Of course, the most devices that can be supported by network technology, the more versatile this technology is. Technologies based on the 802.15.4 standard (apart from Thread) can have a significant number of devices in their network, 64,000. Some, such as Bluetooth, Dupline, Z-Wave, and X10, offer a small number of connected devices, while others are capable of a very high number of devices, such as Ethernet, Insteon, Wi-Fi (v.6), LTE, NB-IoT, DASH7, mioty.

Mesh capability is offered by many networking technologies. Another important feature examined has to do with the communication protocols used for their communications. TCP/IP, also used in computer networks, is supported by most of the technologies presented. This is important for data exchanged from one technology to another. Other technologies exchange a very small amount of data; therefore, small frames or telegrams are used.

4.3. Security/Quality

Security is a significant factor for each technology, and the assurance of the information exchanged through these technologies is necessary. Either at a basic level or enhanced, a form of security is provided by almost all of the technologies examined. Old technologies, e.g., Dupline and X10, are the only ones in this resviearchw that do not provide this feature. For wired mediums, BACnet provides encryption to the transport layer with the use of TLS (Transport Layer Security), which is a 256-bit frame used with the rest of the data payload exchanged to provide encryption. 

Technologies using wireless transmission provide encryption to lower OSI layers and physical and data links. The most common method used is 128-bit size AES used by following the 802.15.4 standard. There are also long-range ones, such as Dash7, LoRa, and mioty, which use the same method. Bluetooth, Insteon, LTE, NB-IoT, and WiFi provide enhanced encryption with 256 bit. EnOcean provides a different method of encryption as it uses VAES (Variable AES) for providing extra security. Sigfox, as a low data rate technology, uses as a security mechanism for Key Generation and MAC verification sequence.

4.4. Security/Quality

Energy consumption constitutes one of IoT and home automation’s major goals. Every improvement presented for this technology aims for this characteristic. This feature is most needed for wireless-based technologies, where a component can be in an area without a stable power supply; therefore, batteries must be used. Therefore, there is a need for them to consume a small amount of energy for their operation and to have better efficiency (power loss). All wireless technologies provide this feature except Wi-Fi (802.11 a/b/n/ac/ax) and LTE, as they are mainly used for high data rates (multimedia applications), and therefore more energy is needed. Transmission power is very low in technologies that use short-range (0–100 mW) features that vary according to the obstacles in between transceivers causing interference.

Wired medium technologies, as they are constantly connected to a power supply, are not so focused on low energy consumption. As in wireless, apart from the ones used for high data rates, energy consumption is small.

The best technology regarding power consumption and efficiency is EnOcean. As an energy harvesting technology, the power needed for its operation is produced by it; therefore, the overall number is zero. Its’ transmission power (TX-power) is still the lowest at about 50 μW.

A very important characteristic examined is cost. Almost all of the technologies based on the 802.15.4 standard are open-sourced; therefore, there is no need to buy licenses or extra fees in developing/operating them, so they can be available to everyone. Z-Wave is a proprietary technology, requiring device certification, which adds extra cost to the total value of a product. EnOcean devices are manufactured by a limited number of contractors, as it is not very popular yet. As a result, their value is a little higher than their competition. Wi-Fi and Bluetooth (in many cases) technologies are available in almost every end-user device in the market and can be used without the extra cost of acquiring an extra device or gateway. 

More details are provided in the full article [147]