Wireless communication protocols are essential for modern embedded systems, enabling devices to connect and share data without wires. This section covers short-range protocols like Bluetooth and ZigBee, as well as longer-range options like Wi-Fi and LoRa.

Understanding these protocols is crucial for designing connected devices. We'll explore their features, applications, and underlying technologies, building on the serial communication concepts introduced earlier in the chapter.

Short-Range Wireless Protocols

Bluetooth

• Bluetooth is a short-range wireless communication protocol that operates in the 2.4 GHz ISM band
• Enables devices to exchange data over short distances (typically less than 10 meters) with low power consumption
• Uses frequency hopping spread spectrum (FHSS) to avoid interference and ensure secure connections
• Supports various profiles for different applications (Hands-Free Profile for car audio systems, Advanced Audio Distribution Profile for wireless headphones)
• Pairing is the process of establishing a trusted connection between two Bluetooth devices, which involves exchanging security keys and creating a bond

Other Short-Range Wireless Protocols

• ZigBee is a low-power, low-data-rate wireless protocol designed for home automation and IoT applications, operating in the 2.4 GHz, 915 MHz, and 868 MHz bands
• NFC (Near Field Communication) is a short-range wireless technology that enables simple and secure two-way interactions between electronic devices over distances of a few centimeters (typically used for contactless payments and access control)
• RFID (Radio-Frequency Identification) uses electromagnetic fields to automatically identify and track tags attached to objects, with applications in inventory management, asset tracking, and access control
• RFID systems consist of a reader (interrogator) and tags (transponders), which can be passive (powered by the reader's electromagnetic field) or active (battery-powered)

Wi-Fi and IEEE Standards

Wi-Fi

• Wi-Fi is a wireless networking technology that allows devices to connect to the internet or communicate with each other without the need for wires
• Operates in the 2.4 GHz and 5 GHz ISM bands, offering higher data rates and longer ranges compared to short-range wireless protocols like Bluetooth
• Wi-Fi networks are identified by their SSID (Service Set Identifier), which is a unique name assigned to the network
• Security is a critical aspect of Wi-Fi networks, with various encryption methods available (WEP, WPA, WPA2, WPA3) to protect data transmitted over the air

IEEE 802.11 Standards

• IEEE 802.11 is a set of standards that define the physical and MAC layers for wireless local area networks (WLANs)
• Different versions of the 802.11 standard (802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.11ax) offer varying data rates, ranges, and features
• 802.11a operates in the 5 GHz band, while 802.11b and 802.11g operate in the 2.4 GHz band
• 802.11n introduced MIMO (Multiple Input, Multiple Output) technology to improve data rates and range by using multiple antennas
• 802.11ac and 802.11ax (Wi-Fi 6) further enhance performance by utilizing wider channels, higher-order modulation schemes, and improved efficiency

Wireless Communication Techniques

Spread Spectrum

• Spread spectrum is a technique used in wireless communications to spread the signal over a wider frequency band, making it more resistant to interference and harder to intercept
• Two main types of spread spectrum techniques are FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum)
• FHSS involves rapidly switching the carrier frequency among many distinct frequencies in a pseudorandom sequence known to both the transmitter and receiver
• DSSS spreads the signal by multiplying it with a pseudorandom noise sequence (PN code), resulting in a wider bandwidth signal that appears as noise to unintended receivers

ISM Bands and LoRa

• ISM (Industrial, Scientific, and Medical) bands are portions of the radio spectrum reserved internationally for unlicensed use in industrial, scientific, and medical applications
• Common ISM bands include 2.4 GHz, 5.8 GHz, 915 MHz (in the Americas), and 868 MHz (in Europe)
• LoRa (Long Range) is a proprietary wireless communication technology designed for long-range, low-power applications in the IoT domain
• LoRa operates in the sub-GHz ISM bands (typically 915 MHz in the Americas and 868 MHz in Europe) and uses a proprietary spread spectrum modulation technique called Chirp Spread Spectrum (CSS) to achieve long-range communication with low power consumption