Chapter 6 Data Systems
Signal Propagation Propagation - The way in which a wave travels from one point to another L O S (line of sight) - Signal travels in straight line directly from transmitter to receiver When _____________ are in a signal's way, the signal may: Pass through them Be absorbed into them
obstacles
Antennas Wireless signals originate from electrical current traveling along a conductor: Travels from the transmitter to an antenna. ___________ emits the signal as a series of electromagnetic waves into the atmosphere. At the destination, another antenna accepts the signal and a receiver converts it back to current. Two antennas must be tuned to the same frequency in order to use the same channel.
Antenna
__________________ Operates in the radio band of 2.4-2.4835 GHz Hops between frequencies within that band to help reduce interference Requires close proximity to form a connection Exact distance requirements depend on the class of Bluetooth device Before two Bluetooth devices can connect, they must be paired Bluetooth interfaces are susceptible to a range of security risks Bluejacking—A connection is used to send unsolicited data Bluesnarfing—A connection is used to download data without permission
Bluetooth
Channel Management Most wireless devices implement one of two technologies: F H S S (frequency hopping spread spectrum) D S S S (direct sequence spread spectrum) How each wireless standard in the 2.4 GHz range uses its allotted band: Wi-Fi uses _ _ _ _ Bluetooth uses _ _ _ _ ZigBee uses D S S S A N T+ uses a fixed frequency (does not use D S S S or F H S S)
D S S S F H S S
Wireless Standards for the I o T (Internet of Things) _ _ _ - Made up of any device that can be connected to the Internet. Personal monitoring devices - One of the fastest-growing areas of I o T (Ex. Fitbit, Alexa, Ring). Smart home devices - Interlink devices such as locks and lights, security cameras, etc. HAN (home area network) - Connected devices within a home create a type of LAN W PAN (wireless personal area network) - Include short-range wireless technologies such as Bluetooth (headphones, bluetooth on car, a computer mouse) and ZigBee. _________ rarely exceed about 10 meters in any direction. Most common wireless technologies used to connect W PAN and HAN devices are discussed next.
I o T PANs
Wireless networks (W LANs) Networks that transmit signals through the air via _ _ (______ __________) waves. Wired and wireless signals share many similarities. Use of the same Layer 3 and higher protocols. The nature of the atmosphere makes wireless transmission different from wired transmission.
R F (radio frequency)
Radiation pattern Relative strength over three-dimensional area of all electromagnetic energy that antenna sends, receives. Unidirectional (directional antenna) - Issues wireless signals along single direction. Omnidirectional antenna - Issues, receives wireless signals with equal strength, clarity in all directions ____________ - Reachable geographical area
Range
_____________ A smart home protocol that provides two basic types of functions: Signaling to manage wireless connections Control to transmit data and commands between devices A Z-Wave network controller (called a hub) Receives commands from a smartphone or computer and relays the commands to various smart devices on its network Z-Wave transmissions have a range of up to 100 m per hop Can tolerate up to four hops through repeaters
Z-Wave
___________ Based on the 802.15.4 standard A low-powered, battery-conserving wireless technology Designed to handle small amounts of data Ideal for use in I S M (industrial, scientific, and medical) sensors Used in IoT devices for: Building automation, H V A C control, A M R (Automatic Meter Reading), and fleet management
ZigBee
The Wireless Spectrum The ___________________ ________________ is the frequency range of electromagnetic waves used for data/voice communication Spans frequency ranges or bands between 9 kHz and 300 GHz Some bands have only a single frequency (called a fixed frequency) for that band
wireless spectrum
