Internet of Things, all things connected. In this era, more and more objects will be connected to the Internet, and eventually to the host / cloud connection. These connections can be implemented using a variety of communication links.
However, the device itself is typically connected wirelessly to the IoT system. This wireless connection is the most important or weak link in the system. Therefore, it is important to choose a wireless technology that matches the device and its surroundings. This article describes several wireless candidate technologies that are most likely to be adopted for new designs.
The device is wirelessly linked to the gateway is a typical IoT connection scenario (Figure). The gateway is an interface that connects to the Internet through a public broadband cable or DSL modem, and then connects to the Internet through an Internet service provider. In another application scenario called machine-to-machine (M2M), the device connection goes through a cellular carrier, then to another carrier, or directly to the Internet.
Figure: Typical wireless connection scenario for IoT (a) and M2M(b) applications
There are many design factors that must be examined in detail when choosing a wireless technology:
• Data rate of the device: video stream, measuring temperature per minute, or other parameters between.
• Range or distance to the gateway: a few inches in the room, or more than a mile in rural areas.
· Environment: Hazardous environment in the factory, outdoor environment exposed to the weather, noise or electromagnetic interference from electronic equipment.
· Need encryption or authentication: What are the requirements for data security?
· Power consumption: battery life, energy efficiency, may need to connect to AC.
Capacity: The number of connected devices.
· Quality of service and reliability.
· Network topology: star, mesh, or other topology.
• Simplex or duplex: one-way or two-way communication.
· Appropriate and available spectrum: licensed or license-free.
• Available ICs, modules and devices.
· Cost: Design, manufacturing or Internet access service fees.
· Development platform: Do you need an operating system? What other software do you need?
Internet access: cellular, digital subscriber line (DSL), cable, satellite.
· Standard license conditions are available.
2G/3G cellular
Many use cases, commonly referred to as machine-to-machine (M2M), are similar to the Internet of Things. Many vendors offer cellular phone modules for embedding into other products, and most major cellular operators offer M2M connectivity services on the standard licensed spectrum. Although 2G technologies such as GSM/GPRS/EDGE are popular, some operators have plans to phase out 2G services.
However, most networks still support 3G technologies such as WCDMA and CDMA2000 with data rates of up to several megabits per second. The range is the distance to the cell site and can be as long as several kilometers. Cellular connectivity is clearly an option, but it is more expensive than the other options described later.
802.15.4
802.15.4 targets short-range, low-mid data rates and low-power use cases and is the basis for several other standards mentioned later. Its main operating spectrum is the 2.4GHz Industrial, Scientific, and Medical (ISM) license-free band, which is sometimes used in the 902MHz to 928MHz and 868MHz bands.
The 802.15.4 standard provides packet-based protocols for the PHY and MAC network layers. Other standards add more layers based on this to provide enhanced network capabilities and performance.
6LoWPAN address node
The 6LoWPAN of the Internet Engineering Task Force (IETF) is short for Internet Protocol version 6 (IPv6) based on low-power wireless personal area networks.
The original target of this standard was 802.15.4, which was later adopted by Bluetooth Smart and low-power HaLow Wi-Fi. Specifically, 6LoWPAN defines a way to adapt IPv6 packets into other protocol frames using encapsulation and header compression techniques.
Bluetooth
Perhaps the most widely used short-range wireless technology is Bluetooth (BT) operating in the 2.4 GHz ISM band. Several different versions offer a variety of different data rates, power levels and ranges. The basic working principle is Frequency Hopping Spread Spectrum (FHSS) technology with different modulation methods.
The latest version of Bluetooth is Bluetooth Smart or version 4.1, also known as Bluetooth Low Energy (BLE). This configuration uses shortened packets with a maximum rate of 1 Mb/s and GFSK modulation. Its biggest benefit is its excellent low power consumption. The transmission power is 10mW and its distance is up to 100 meters. There are multiple software profiles for different purposes, and their interoperability certification is effectively compatible.
LoRa
LoRa (Long Distance) is a technology developed by Semtech. The typical operating frequency is 915MHz in the US, 868MHz in Europe, and 433MHz in Asia. LoRa's physical layer (PHY) uses a unique form of frequency-modulated spread spectrum technology with forward error correction (FEC). This spread spectrum modulation allows multiple radios to use the same frequency band, as long as each device uses a different bandwidth and data rate. The typical range is from 2km to 5km and the longest distance is up to 15km, depending on the location and antenna characteristics.
LTE Cat 0/1
LTE is an abbreviation for Long Term Evolution and is the fourth generation of cellular technology.
LTE Cat 0 and Cat 1 are simplified versions of LTE that are specifically designed to match the low power and low speed requirements of M2M. M2M applications, also known as machine-like communications (MTC), use existing cellular networks in the licensed spectrum rather than short-range wireless and the Internet.
The standard LTE network is too wasteful for most basic monitoring and control applications. LTE Cat 0 and Cat 1 are simplified versions that provide the right solution for M2M applications with maximum data rates of 1Mb/s and 10Mb/s. Cat 0 and Cat 1 use existing LTE bandwidth and orthogonal frequency division multiple access (OFDMA) modulation techniques. This long range solution can support a range of several kilometers.
Narrowband Internet of Things (NB-IoT)
A relatively new variant of using LTE for the Internet of Things is the narrowband Internet of Things. Unlike all 10 MHz or 20 MHz bandwidths using standard LTE, the narrowband IoT uses a 180 kHz wide resource block containing 12 15 kHz LTE subcarriers. The data rate is in the range of 100 kb/s to 1 Mb/s.
This more simplified standard provides very low power consumption for networked devices. In addition, it can be deployed as a software overlay into any LTE network. The resource blocks of the narrowband IoT can be well adapted to the standard LTE channel or guard band. When operators repartition their earlier 2G spectrum, they can also fit into the standard GSM channel. The modulation employs an OFDMA downlink and an SC-FDMA uplink.
SIGFOX
SIGFOX is both a wireless technology and a network service. SIGFOX operates in the ISM band of 868MHz and 902MHz, but consumes very narrow bandwidth or power consumption.
SIGFOX radios employ a technique called ultra-narrowband (UNB) modulation, which only occasionally transmits short messages at low data rates. The maximum length of a message is 12 bytes, and the maximum number of messages a node can transmit per day is 140. Due to its narrow bandwidth and short messages, it can achieve a long transmission distance of several kilometers in addition to its 162dB link budget.
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