Wireless Communication and Networks

• Wireless communication involves transmitting signals without physical wires.

Elements of a Wireless Network

• Wireless networks often include a mix of wired and wireless components.
• Wireless hosts include laptops, smartphones, and IoT devices.
• These hosts may be stationary or mobile
• Mobility isn't always required for wireless communication
• Base stations connect to wired networks and relay data between the wired network and wireless hosts in their "area"
• Cell towers and 802.11 access points are examples of base stations.
• A wireless link is used to connect mobiles to a base station and acts as a backbone link.
• The wireless link employs multiple access protocols to coordinate link access.
• Wireless links have various transmission rates and distances, and operate on different frequency bands.

Network Modes

• Infrastructure mode relies on a base station to connect mobile devices to a wired network.
• Handoffs occur in infrastructure mode when a mobile device switches base stations to maintain its connection to the wired network.
• Ad hoc mode operates without base stations.
• Nodes in ad hoc mode can only transmit to other nodes within their link coverage.
• Nodes self-organize into a network and route data among themselves.

Wireless Network Taxonomy

• Single hop infrastructure networks allow hosts to connect directly to a base station (WiFi, cellular)
• Multiple hop infrastructure networks require hosts to relay through multiple wireless nodes (mesh net)
• Single hop infrastructure allows hosts to connect to a larger internet
• No infrastructure networks like Bluetooth or ad hoc networks do not require base stations, and have no direct connection to the internet.
• No infrastructure multiple hop networks (MANET, VANET) don't have base stations, and require relaying to reach a given wireless node.

Wireless Link Characteristics: Attenuation

• Wireless radio signals lose power (attenuate) over distance due to free space "path loss."
• Free space path loss is proportional to (frequency * distance)^2, denoted by (fd)².
• Higher frequencies or longer distances result in greater path loss.

Wireless Link Characteristics: Multipath Fading

• Multipath propagation happens as radio signals reflect off objects and the ground.
• Signals arrive at the destination at slightly different times using different routes:
  • Direct (line of sight)
  • Reflected paths

Wireless Link Characteristics: Multipath

• Multipath propagation, where radio signals reflect off objects and the ground, causing signals to arrive at slightly different times.
• Coherence time is the amount of time a bit is present in the channel to be received.
  • Influences the maximum possible transmission rate because coherence times cannot overlap.
  • Inversely proportional to frequency and receiver velocity

Wireless Link Characteristics: Noise

• Interference from external sources, like motors and appliances, can disrupt wireless network frequencies.
• Signal-to-Noise Ratio (SNR) measures the strength of the desired signal relative to background noise.
• A larger SNR makes it easier to extract the signal from noise.
• SNR versus Bit Error Rate (BER) Tradeoff:
  • When the physical layer is given, increasing power increases SNR and decreases BER.
  • SNR changes with mobility, requiring dynamic adaptation of the physical layer
  • Dynamic modulation techniques and rates can change the SNR

Channel Characteristics

• Shadow fading is a large-scale fluctuation of the signal strength caused by large objects obstructing the signal's path between transmitter and receiver

Channel Characteristics: Doppler Shift

• Positive (+) Doppler shift if the mobile moves toward the base station.
• Negative (-) Doppler shift if the mobile moves away from the base station.
• Doppler frequency shift requires compensation for correct frequency synchronization

Fundamentals of Wireless Communication

• Combined signal loss is the overall degradation of signal strength

Receiver Characteristics

• Received signal is characterized by the Signal-to-Noise Ratio (SNR).
• SNR is calculated by dividing the signal power by the noise power.
• SNR is dimensionless but measured in dB (decibels).
• A variation of SNR is the Signal-to-Interference-&-Noise Ratio (SINR).

Wireless Transmission Issues

• The role of an antenna involves its gain and signal propagation across environments
• The lost power when signals are transmitted.

Antennas

• Antennas convert electric current to electromagnetic waves.
• Waves operate within the radio and microwave bands of 3 KHz to 300 GHz.
• Antenna characteristics are identical for sending or receiving signals.
• Direction and wave propagation depend on antenna shape.
  • Isotropic: Power propagates equally in all directions (spherical pattern, ideal).
  • Omni-directional: Power propagates in all directions on one plane (donut shape).
  • Directional: Power is concentrated in a specific direction.
• Isotropic antenna 2D examples use a 1m radius circle around the antenna
• Directional antenna use different antenna strength at different angles

History

• First telephone by Alexander G. Bell in 1880
• First car mounted radio telephone by Bell labs in 1921
• First commercial mobile radio telephone service by Bell labs and AT&T in 1946, which was half duplex
• Mobile telephone network R&D continued in 50s and 60s that established local and limited systems, like MTA and MTB by Ericsson
• First commercially successful mobile telephone network was ARP in Finland, 1971.
  • Autoradiopuhelin - car phone radio
  • Also known as zero-generation cellular networks
  • The system had cells but roaming was not seamless, and it was not a handheld device
• First handheld cellular phone: 1973 by Motorola
  • Motorola DynaTAC
• Trial "real" GSM networks: 1978
  • Matured as 1G (first generation) in 80s"
  • Included automatic handover, analog signal
• 2G (second generation) - 1990
  • Included digital technology adopted in the 90s
  • GSM and CDMA networks
• Now 3G, 4G, LTE, 5G, and beyond

World Cellular Market

• The global mobile market has expanded from 2G to 5G
• In 2025, 2.8 billion 5G subscriptions are forecast

Cellular Networks: Comparison of Generations

• 2G (1993):
  • Technology: GSM
  • Access System: TDMA, CDMA
  • Switching Type: Circuit switching for voice and packet switching for data
  • Internet Service: Narrowband
  • Bandwidth: 25 MHz
  • Advantage: Multimedia features (SMS, MMS), internet access and SIM introduced
  • Applications: Voice calls, short messages
• 3G (2001):
  • Technology: WCDMA
  • Access System: CDMA
  • Switching Type: Packet switching except for air interference
  • Internet Service: Broadband
  • Bandwidth: 25 MHz
  • Advantage: High security, international roaming
  • Applications: Video conferencing, mobile TV, GPS
• 4G (2009):
  • Technology: LTE, WIMAX
  • Access System: CDMA
  • Switching Type: Packet switching
  • Internet Service: Ultra broadband
  • Bandwidth: 100 MHz
  • Advantage: Speed, high speed handoffs, global mobility
  • Applications: High speed applications, mobile TV, wearable devices
• 5G (2018):
  • Technology: MIMO, mm Waves
  • Access System: OFDM, BDMA
  • Switching Type: Packet switching
  • Internet Service: Wireless World Wide Web
  • Bandwidth: 30 GHz to 300 GHz
  • Advantage: Extremely high speeds, low latency
  • Applications: High resolution video streaming, remote control of vehicles, robots, and medical procedures

Features of Cellular Networks

• Wide coverageReuse frequencies and expansion of the network are easy
• Deployment Wired communication and connectivity to PSTN
• Large Number of Users Cells are formed by user and Cell size depends on number of users

Cellular Network Growth and First Generation Systems

• Simple growth was achieved by using a single transmitting/receiving station that was heavy, bulky, and expensive
  • No switching between regions, low quality, limited capacity, rapid market saturation
  • Power-hungry transceiver that had an unsafe power level
• First generation included introduction of analog cellular systems in the late 1970s and 1980s
  • Included analog systems, incompatible systems, and limited voice service
  • Lacked encryption, used FM modulation and FDMA transmission technology, and suffered from capacity saturation

Frequency Bands

• First generation frequency band systems include:
  • MCS, NMT 900, AMPS/ NAMPS, TACS, JTACS/ NTACS and more

First Generation Systems

• Includes regional information and access modes, like modulation
  • MCS-L2: Japan, FDMA/PM
  • NMT 450: Scandinavia, FDMA/FM
  • AMPS: North America, FDMA/FM
  • TACS: United Kingdom, FDMA/FM
  • And More

Second Generation

• Second generation includes digital cellular systems (90's) and development of unified international standard for mobile communications
  • Used pan-national roaming, digital encryption, and enhanced range of services (data + voice)
  • Had low power consumption, was light weight, compact and pocket size, and used TDMA transmission technology
  • Has huge capacity

Third Generation

• Third-generation cellular systems
  • Offer multimedia services
  • Are larger BW
  • Have higher bit rate
  • Have more services

Cell Planning

• Cells must be planned so they function
• Cells come in different layouts

Drive Test

• Actual cell coverage must be tested to use the cells

Frequency Reusage in Cells

• Frequency reuse depends on a cellular network

Cell Layouts

• Cluster size can vary
  • Typically, cluster size is 7

Cell sectorization

• Cell sectorization allows the reuse of directional antennas in place of omni-directional antennas
• Layouts are typically 3 sectors

Cell types

• Macrocell
• Microcell
• Picocell

Cellular Network Capacity and Coverage

• Dividing the territory up into cells that each cell is served by a base station
  • The division into cells is not perceptible to the user, with imperceptible transitions between cells
  • The capacity of a cell in Mbit/s does not depend on the size of the cell
• Urban zone = high user density - Base stations are deployed to provide sufficient capacity - Base stations have the capacity in Mbit/s per km2 to match the traffic demand of the customers
• Rural zone = low user density - Base stations are deployed to ensure coverage - Deploy enough base stations at every point in the territory a terminal can connect

PicoCell

• The technology is used for cellular networks

Cell Sizes

• Cell size varies by type, urban and rural are larger, and global has macrocells
• Pico-Cells are contained with in buildings

Channel Allocation Techniques

• Fixed channel assignment has less channels, dynamic has largest channels, compared to hybrid which improves channel speed