Chap 6 wireless networks Flashcards
(37 cards)
Wireless Networks
Networks that use wireless data connections
utilize radio waves /other wireless technologies to transmit data over the air.
Common Uses: Communication between devices, accessing the internet, sharing files and resources, and various other purposes
Wireless Hosts
Any device that can connect to the network without wires. They run applications and can be stationary (non-mobile) or mobile
Types:
▪Client Devices: laptops, smartphones, tablets, gaming consoles, and smart TVs.
▪Wireless Printers.
▪Smart Home Devices: thermostats, security cameras, and doorbells.
▪Wireless Sensors and Wearables: Fitness trackers, smartwatches
Base Station
A central communication hub that connects wireless devices to the network infrastructure.
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Key Characteristics:
* Typically connected to a wired network.
* Facilitates the transmission and reception of data between wireless devices and the wired network backbone.
* Plays a crucial role in enabling wireless communication, providing coverage, and managing network traffic
Wireless Link
communication pathway between wireless devices for transmission of data without physical cables.
Key Characteristics:
* Enables communication over the air using radio waves, infrared, or other wireless technologies.
* Multiple access protocol coordinates wireless link access.
* Factors affecting wireless links are Distance, Radio Frequency (RF), and transmission rates
Infrastructure Mode
networking mode used in wireless networks.
access point acts as a bridge between wireless devices and the wired network infrastructure
Ad Hoc Mode
A networking mode where wireless devices communicate directly with each other without the need for a central access point (AP) or infrastructure.
temp network/ad hoc network
Wireless Network Taxonomy
Categorization of wireless networks based on the number of hops for data transmission
Single Hop
A network where data packets are transmitted directly from the source node to the destination node within a single transmission hop.
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Example: Bluetooth Connections
Multiple Hop
A network where data packets are transmitted from the source node to the destination node through one or more intermediate nodes.
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Example: Wireless Mesh Networks
Fading
The fluctuation in the received signal strength caused by changes in the propagation environment.
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Causes: Phenomena such as reflection, diffraction, scattering, and shadowing, which result in signal attenuation and distortion
Mitigation Techniques: Diversity techniques (e.g., antenna diversity, frequency diversity), equalization, and adaptive modulation
Types of fading
Slow Fading: Changes in signal strength occur gradually over time due to movements of objects or changes in the environment.
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Fast Fading: Rapid fluctuations in signal strength occur over short time intervals, typically caused by multipath propagation
Multipath Propagation
Occurs when signals travel along multiple paths between the transmitter and receiver due to reflection, diffraction, and scattering.
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Effects: Multiple copies of the transmitted signal arrive at the receiver with different delays, phases, and amplitudes. Can cause intersymbol interference (ISI) and fading, leading to degradation in signal quality and performance.
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Mitigation Techniques: Equalization, diversity reception (e.g., spatial diversity, frequency diversity), and adaptive modulation
Noise
Unwanted signals or disturbances that interfere with the desired signal, degrading the signal-to-noise ratio (SNR) and impairing communication performance.
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Common Sources: Thermal noise, atmospheric noise, man-made interference (e.g., electrical appliances, other wireless devices), and quantization noise.
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Impact: Can limit the achievable data rates, increase error rates, and reduce the effective range of wireless communication systems.
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Mitigation Techniques: Signal processing algorithms (e.g., filtering, error correction coding), frequency hopping, spread spectrum modulation, and power control
Hidden Terminals
Wireless devices that are within range of a common access point or receiver but cannot directly communicate with each other due to obstacles or distance.
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Problem: Hidden terminals may interfere with each other’s transmissions, leading to collisions and degraded network performance.
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Occurrence: Can occur in wireless LANs and ad hoc networks, particularly in environments with obstructed line-of-sight or high interference.
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Mitigation Techniques: Carrier sensing mechanisms (e.g., CSMA/CA in Wi-Fi networks), clear channel assessment (CCA), and collision avoidance protocols
Attenuation
Wireless radio signal loses power as it propagates (free space “path loss”).
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Free Space Path Loss: Approximately proportional to (fd)², where f is frequency and d is distance. Higher frequency or longer distance leads to larger free space path loss.
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Impact: Attenuation also causes the “hidden terminal” problem
Code Division Multiple Access (CDMA)
A channel access method used in wireless communication systems. It allows multiple users to share a single frequency band at the same time.
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Key Principle: Each user is assigned a unique code, which is used to spread their data signal over a wider bandwidth. Only receivers with the matching code can decipher the signal, eliminating interference from other users
CDMA Working
- User data is digitized and converted into a spread-spectrum signal using a unique code (chipping sequence).
- The chipping sequence spreads the user’s data signal over a wider bandwidth.
- Multiple spread-spectrum signals from different users are transmitted on the same frequency band
Receiving and De-spreading (CDMA)
- At the receiver, the incoming signal is correlated with the user’s specific chipping sequence.
- Only the signal with the matching code is recovered, while signals from other users are filtered out as noise.
- A high correlation between the received signal and the user’s code allows the receiver to successfully extract the original data by reversing the spreading operation
IEEE 802.11 Wireless LAN (Wi-Fi)
A set of standards that define the protocols for wireless local area networks (WLANs). It specifies how data can be transmitted between devices using radio waves instead of cables
IEEE 802.11 Wireless LAN (Wi-Fi) components
Wireless Devices (Stations - STAs): Laptops, smartphones, tablets, etc., that connect to the wireless network.
Access Points (APs): Devices that act as central hubs for the wireless network, providing connectivity between wireless devices and wired networks (like Ethernet) or the interne
IEEE 802.11 LAN Architecture
Building Blocks:
1. Stations (STAs): Your laptops, smartphones, tablets, etc., that connect to Wi-Fi.
1. Access Point (AP): The central hub (often called a base station) that manages communication and provides wired network or internet access.
1. Basic Service Set (BSS): The core unit of a WLAN, consisting of one AP and multiple STAs associated with it.
Basic Service Set (BSS)
the core unit of a WLAN, consisting of one AP and multiple STAs associated with it.
Two Operation Modes for BSS
Infrastructure Mode (Common): STAs connect to the AP for internet access. The AP acts like a bridge, relaying data between devices and the wired network.
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Ad-Hoc Mode (IBSS): Less common, devices connect directly with each other without an AP, forming a temporary peer-to-peer network
802.11 Channels
- Specific frequency ranges allocated for Wi-Fi communication.
- allow multiple Wi-Fi networks to operate in the same area without causing excessive interference
