From the course: IoT Foundations: Low-Power Wireless Networking

Wireless communication basics

From the course: IoT Foundations: Low-Power Wireless Networking

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Wireless communication basics

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- [Instructor] Before I introduce the wireless network and technologies we're going to talk about the basics of wireless communications using radio frequency signals to transmit data between a radio transmitter and a radio receiver. First of all, let's look at the signals for wireless data transmissions. In wireless communications we use radio frequency electromagnetic waves to transmit data over the air. Any electromagnetic wave can be categorized by its frequency measured by cycles per second using the unit hertz and electromagnetic waves operating in the radio spectrum are called radio waves or radio frequency waves. With our frequency ranging from 3 hertz to 3 terahertz for wireless communications where the higher frequencies beyond are for infrared and the visible lights. A wireless system often operates in a portion of the entire radio spectrum called the radio frequency band. For example, the FM radio is working in the frequency band in the lower radio spectrum shown on this map, while the LTE cellular networks, wi-fi, Bluetooth, as well as other low power wireless technologies, are operating at a higher frequency band. A frequency band used for a wireless communication system can be split into sub-frequency bands for multiple access. As radio spectrum is a resource regulated nationally we need to get a license to operate at the frequency band, but there's some license exempt, or unlicensed frequency bands to use. Let's list the frequencies that some ride assistance are operating at. Bluetooth networks operate at the 2.4 Ghz band and the current wi-fi networks can work at multiple unlicensed bands. In notion, in the lower radios operate at the subgigahertz bands. In national LTE network needs to operate at the licensed band. Now we're briefly explaining how our data communication happens between two radio interfaces on two IoT devices. One is acting as a radio transmitter and the other is acting as a radio receiver. In this diagram the data message is stored in the memory of an IoT device while being internally pass it to the radio transmitter and then the radio transmitter will transform the data into radio signals and emit those signals into the space over the air through the antenna. Then a radios receiver with the same antenna can receive the radio signals and pass that to the other parts of the IoT device for further processing. There's several essential components in the communication process. The first is the data message itself. The second is transmitter or sender. The third is the receiver. The fourth one is the antenna by which the radio signals can wirelessly emit into the space. It can also be harvested from the space for reception. The fifth one is the wireless channel as the transmission medium. It's a logical connection that a signal operating at a frequency band transfer through. Last but not least it is the communication particle which is a set of rules that a transmitter and the receiver needs to follow. Usually we cannot transmit a signal from the transmitter to a receiver in a long distance as the signals will get attenuated in power strength over long distance and about obstructions and deferred by other signals and affected by noise and other transmission permits. In a network we can simply find the representation of the transmitter or receiver into nodes. And a communication link denoted as the dotted line. There are common types of our communication connection between a radio transmitter and a radio receiver. A transmitter can always communicate with a receiver in one-way with a unidirectional communication connection. Or they can communicate in two-ways with a bidirectional connection at the same time or at different times. The links are sometimes called uplink and downlink if the two nodes have different rows. An example of a cellular network with two nodes one is your mobile phone and other is the cellular bay station. The downlink is the connection when the bay station pushes data like audio streams to your mobile phone. To uplink is the connection for the communication when you send the data like text messages to the bay station. Many IoT devices have the hat work ability of being a transmitter and a receiver. And in this case they're called transceiver. In upcoming video we'll introduce the reference model and the protocols that many wireless networking technologies follow.

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