IT 325: Wireless Networks and LANs

• IT 325 covers the introduction to mobile and wireless networking
• Week 2 focuses on the fundamentals of wireless networking and wireless LANs

Fundamentals of Wireless Networks Topics:

• Trends & Applications
• Definition of a wireless network
• Comparison of wireless, wired, and mobile networks
• Types of wireless networks
• Link characteristics
• Hidden terminal problem
• CDMA (Code Division Multiple Access)

Agenda:

• The basics of wireless communication.
• Differences between wireless and mobile networks.
• The key elements of a wireless network.
• Types of wireless networks and their respective architectures.

Intro to Wireless Networks

• Wireless networks transmit data over electromagnetic waves without physical cables
• A wireless network is one where devices communicate over wireless links

Key Elements of Wireless Networks

• Wireless hosts include smartphones and laptops
• Wireless links include WiFi and cellular
• Base stations include cell towers and access points
• Network infrastructure includes the Internet
• Examples are WiFi, Bluetooth, and cellular networks.
• Key aspects are mobility, scalability, and ease of deployment.

Connectivity

• Wireless technology dominates connectivity in several areas:
• Health and fitness devices
• Virtual reality applications
• UAVs (Unmanned Aerial Vehicles)
• The Internet of Things (IoT)
• Sensors

Demand for Wireless Devices

• Demand is driven by the billions of wireless devices in use.
• Specifically related to the Internet of Things.
• Connected devices reached 50.1 billion in 2020.

Elements of a Wireless Network

• Wireless hosts include laptops, smartphones, and IoT devices which run applications
• Wireless hosts can be stationary or mobile and do not always mean mobility
• Base stations are typically connected to a wired network
• Base stations relay packets between the wired network and wireless hosts within their area
• Examples of base stations include cell towers and 802.11 access points
• Wireless links connect mobile devices to base stations and act as backbone links
• Multiple access protocols coordinate link access.
• Various transmission rates, distances, and frequency bands are utilized.
• Infrastructure mode connects mobile devices into a wired network via a base station
• Handoff occurs when a mobile device switches base stations to maintain a connection to the wired network
• Ad hoc mode does not use base stations
• Nodes can transmit only to other nodes within link coverage

Applications

• News, weather, and road condition updates.
• Communication via GSM.
• GPS-based positioning.
• Local ad-hoc networks can close vehicles to prevent accidents, provide guidance, and ensure redundancy.
• Vehicle data like bus routes/ high speeds get transmitted in advance in case of maintenance.

Emergency Applications

• Early transmission of patient data to hospitals.
• Replacement of infrastructure after disasters, such as earthquakes.
• Use during crises and war

Entertainment and education Applications

• Includes outdoor Internet access in the applications
• Smart travel guides location information
• Ad-hoc network for multi-user gaming.

Devices

• A higher percentage of mobile devices connect to the Internet which are embedded devices
• Standardization across IEEE, 3gpp.org, ietf.org, and ITU

Challenges

• Power consumption limitations of computing, low-quality, small disks because of battery capacity.
• CPU power is limited by internal capacity, supply voltage, clock frequency etc.
• Higher probability of data loss that has to be designed for in advance;
• Limited user interfaces due to size constraints
• Limited fast memory due to memory parts or possible flash memory

Wireless vs Mobile Networks

• Wireless networks focus on untethered connectivity, using WiFi, Bluetooth, and satellite
• Mobile networks involve device movement, handovers which involves cellular networks such as 4G and 5G
• Mobile networks are also wireless

Differences from wired networks

• Wireless networks offer host mobility
• Signal propagation is affected by distance and obstacles.
• Wireless networks have higher error rates.

Types of Wireless Networks

• Single-hop networks have hosts which connects to a base station (WiFi, cellular) and connects to a larger Internet
• No infrastructure networks connections to larger Internet networks like Bluetooth & ad hoc networks
• Multiple hops relay through several wireless nodes which connects to larger Internet for mesh networking
• No base station in use and connect to others given wireless node MANET, VANET

Wireless Properties

• Wireless networks are subject to interference and bit errors.
• Wireless networks have more sources of corruption vs. the wired networks that results in increase of bit error rate
• Signals weaken over distance (attenuation) which results in path loss
• Signals take different paths due to reflections resulting in multipath propagation issues
• Power trade-offs are very important for mobile, battery-powered devices.
• They work as a broadcast medium, sending the same traffic to everyone nearby

Wireless Links and Network Characteristics

• Radio signal attenuates as it propagates through matter called "path loss"
• Interference occus from other sources due to shared wireless network frequencies; example shared 2.4 GHz from WiFi, cellular
• Multipath propagation bounces signal off various objects that arrives destinations at various times
• Decreased signal strength, interference, and multipath propagation

Fading and Attenuation

• Wireless radio signal attenuates (loses power) as it propagates
• This also increases free space "path loss"

Multipath

• Radio signals reflect off objects arriving at a destination at different times.

Wireless Link Characteristics

• SNR is about signal-to-noise ratio that has a larger SNR the easier it is to extract signal from noise
• SNR is about better error rates
• SNR is related to physical layer requirements while maintaining throughput.

Wireless Link Characteristics Summary:

• Challenges include signal attenuation, interference to devices and multipath propagation overlaps
• Metrics for includes signal-to-noise ratio (SNR) such as signal strength vs noise
• Relationship with error and probability being better SNR = lower BER.

Wireless Transmission Techniques

• Frequency bands are the ISM bands (2.4GHz, 5GHz), cellular (800 MHz - 5GHz)
• Modulation: BPSK, QAM, OFDM
• Access Methods: FDMA, TDMA, CDMA
• In multiple access, the wireless devices connect to the wired network infrastructure as well to work on ad hoc networking.

Hidden Terminal Problem

• Senders (A, C) cannot hear each other but transmit to receiver (B) causing inference
• Two example devices work opposite of a singular base station
• Result is collisions occurs and reduce performance issues
• Solution involves RTS/CTS protocols

Code Division Multiple Access (CDMA)

• CDMA is a channel partitioning protocol where each user has a unique code and all share the signal frequency
• Benefits are multiple users transmitting simultaneously while maintaining interference resistance

CDMA Encoding and Decoding

• The process involves the sender data bit multiplied by Code sequence
• Receiver will decode using the sender's code
• Requires the right code to be correctly decoded

Wireless LANs Topics

• The IEEE 802.11 Wireless LANs
• WiFi Architecture
• Channels and Association
• MAC protocol: CSMA/CA
• Frame structure
• Mobility in WiFi
• Advanced features in WiFi
• PANs: Bluetooth

Agenda

• Understand for IEEE 802.11 WiFi standard
• CSMA/CA and MAC mechanisms
• Frame formats, address fields for 802.11
• Mobility management in WiFi networks

Intro to IEEE 802.11

• Standardization for WLANs defined by IEEE
• Variants within 802.11b/g/n/ac/ax (WiFi 4,5,6)
• Data rates increasing to 11 Mbps to 14Gbps
• Operating frequencies are 2.4GHz or 5GHz
• Multiple access uses CSMA/CA
• Use cases are home, business, campuses

Characteristics in WLAN

• Wireless Links:802.11ax - 14 Gbps, 802.11ac - 3.5 Gbps, 802.11n - 600 Mbps, 802.11g - 54 Mbps, 802.11b -11 Mbps, Bluetooth - 2 Mbps
• Common distances: indoor: 10-30m, outdoor: 50-200M, mid range outdoor 200m - 4KM, Long range outdoor 4KM - 15KM

IEEE 802.11 Wireless LAN standards

• 802.11b had a max transfer rate of 11Mbps on 2.4 GHz
• 802.11g had a max transfer rate of 54Mbps on 2.4 GHz
• 802.11n had a max transfer rate of 600 on 2.4 and 5 GHz GHz
• 802.11ac had a max transfer rate of 3.47Gpbs on 5 GHz
• 802.11ax had a max transfer rate 14Gbps on 2.4 and 5 GHz
• 802.11af has a max data rate of 35 – 560 Mbps on unused TV bands (54-790 MHz)
• 802.11ah has a max data rate of 347Mbps on 900 Mhz
• Multiple access uses CSMA/CA and have base-station and ad-hoc network versions

802.11 Network Architectures

• Basic Service Set (BSS): set of stations with access point (AP) and AP connects to network with Stations associate with one AP
• Extended Service Set (ESS): Multiple BSSs interconnected
• Ad-Hoc Mode: Peer-to-peer communication with AP

802.11 LAN Architecture

• Wireless hosts uses/communicates with base stations
• Base station acts as the access point (AP)
• BSS Basic Service Set (BSS) uses a Cell is in infrastructure mode
• The infrastructure includes wireless hosts, acces point(AP), base stations in ad hoc mode

Channels and Association

• 11 Channels exist in 2.4 Ghz uses 1,6, 11non-overlapping frequency bands for usage
• Consists of scan for access points and strongest signals and authentication

802.11 Channels

• Spectrum divided into channels between differing frequencies
• Interference can be caused when can can be be the chosen neighbouring AP admin
• AP admins can choose frequencies.

802.11 Association

• Arriving host associates with AP
• Scans channels searching beacons frames to include AP SSID and MAC address
• Then perform identification and AP's subnet

802.11: passive/active scanning

• Consists of probing for active connections against passive connections

IEEE 802.11: multiple access

• Access points may be connected to the wired network or function
• Aiming for prevent and avoiding collisions of nodes transmitting simultaneously
• CSMA - sense before transmitting and dont collide transmission of another
• Difficult to sense signals caused from weak signals because of fading
• Avoid collisions within the signals

Medium Access Control (MAC) protocol in 802.11

• Multiple Access with Collision Avoidance (CSMA/CA)
• Why its important to to listen during Wireless node's transmitting/Hidden and exposed terminal problems

CSMA

• Sense the channel before transmitting and busy signals wait or retry at later time.
• CSMA /CA is for better signals

IEEE 802.11 MAC Protocol: CSMA/CA

• If Senses when channel is idle and transmits the channel and the transmitter
• Begins random backoff and transmits and repeats interval
• Sends random messages

IEEE 802.11 Avoiding collisions (more)

• Transmits request to send packets over small CSMA channels
• RTS's and may collide with one another while BS will send message
• BS broadcasts clear-to-send CTS in response to RTS over short distances
• Sender transmits data frame with defer transmissions

RTS/CTS Mechanism for Collision Avoidance

• Serves to reduce the terminal problems when reserving channels with reduces terminal
• Can allow for long frames and overhead between different connections

IEEE 802.11 Frame Format

• The format has a frame control with type flags
• Duration: setting up reservation transmission
• Address fields: 4 MAC fields designed routing
• Sequence control: organizes transmission and retransmission.
• Frame body: contains data payload
• FCs: insures integrity with error checking

802.11 Frame Addressing

• Contains address of MAC , AP, wireless host and access point.

Mobility in IEEE 802.11 Networks

• It includes for a handoff process for devices that move between APs
• Move between IP address
• Handoff which include Hard handoff as well as Soft handoff with smooth functionality
• Mobility for latency packet and security.

802.11: mobility within same subnet

• H1 remains within the same IP Address and is also connected with the AP
• Switch will recognize the location of which node is used

802.11 Advanced features

• Includes adjusting adaption to adjust to SNR.
• Manage power by entering standby mode.

Personal Area Networks: Bluetooth

• Overview is shot range (10m) and low power
• Ad hoc setup with no infrastructure
• Up too 7 clients
• Frequency-hopping spread spectrum is a method of spread-spectrum telecommunications

Bluetooth Specifications

• Diameter less that 10 meter circumference (mouse, keyboard)
• Cable replacement with mouse and keyboard
• Ad hoc without a lot of infrastructure within radio's
• Master controls clients within small transmissions
• The 2.4 radio band
• Low power usage for sleep modes and saving energy

Bluetooth

• 625 usec sec in an allocated slot
• Sender will transmit to 79 frequency channels
• The known channels are random with each slot
• Parked nodes save power and wake to preserve memory
• Assemble nodes through assembly

Research Areas

• Wireless communication involves transmission errors bandwidth and interference
• Locational data transfer support
• Quality and maintenance

Mobile communications through the Layers:

• Application Layer covers multimedia and applications
• Transport is about congestion Data link layer includes security