Wireless Communication Technologies

Wireless Networking Problems

• Signal interference/loss:
  • Attenuations (rain, water, dust).
  • Reflections (water body, fog).
  • Diffractions (hills, buildings, obstructions).
• Physical constraints (e.g., antenna icing, zoning restrictions).
• Mobile device power consumptions (e.g., IoT, CPS (Cyber Physical Systems) sensors).
• Cryptography.

Wireless LAN (WLAN) and IEEE 802.11 WiFi

• Standardized by IEEE.
• The most common standard is IEEE 802.11 WiFi.
• WiFi was first adopted in 1997.
  • The technology was developed by researchers from CSIRO, Australia in early 1990s, with patents obtained in 1992 and 1996.
• Since its first adoption, new versions were released.
  • Versions a, b, g, n, h, I, ac, ad, af, ah, ai, aj, aq, ax, ay and so forth.
• Currently, WiFi generation 6 (e.g., IEEE 802.11ax) provides the maximum link rate of 600-9608 Mbit/s.

IEEE 802.11 Variants

• Wi-Fi 1, Wi-Fi 2, and Wi-Fi 3 are not being branded because they are older technologies and their usage is low.

IEEE 802.11

• Part of the IEEE 802 set of local area network (LAN) technical standards.
• Specifies the set of medium access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer communication.

WLAN Goals

• Ease of use
• Easy to set up network
• Easy to connect to network
• Easy to roam across networks
• Power efficiency
• Cheap
• License-free operation
• Robust to noise
• Environmental
• Other license-free systems
• Global usability
• Secure
  • Hard to access network without permission
  • Hard to access others’ transmissions

ISM Band

• The ISM (Industrial, Scientific, and Medical) band refers to a specific range of frequencies that are designated for unlicensed devices to communicate wirelessly.
• The ISM band typically operates in the range of 2.4 GHz to 2.4835 GHz, with some additional frequency ranges like 900 MHz and 5 GHz.

IEEE 802.11 Types

• Two types of WLAN:
  • Ad hoc: stations (computers) directly connect.
  • Infrastructure: with an access point (AP) that connects to a wired LAN and usually a MAN/WAN.
• Distributed coordination is required between stations due to collisions.
  • Carrier sense multiple access/collision avoidance (CSMA/CA) protocol is used.
• Wireless environment is very noisy.
  • Frames are fragmented into small frames so retransmission, which is frequent, is more efficient.
• Unlike 802.3 wired connection that uses CSMA/CD (collision detection), 802.11 uses CSMA/CA (collision avoidance).
• The basic idea is that before transmitting data frames, the sender and receiver must first exchange additional control frames before the 'true' data frames.

CSMA/CA

• Consider a situation of 4 nodes: C, A, B, D from left to right.
  • A wishes to communicate with B.
  • C can hear only A.
  • D can hear only B.
• A observes an idle medium, and initially sends a Request to Send (RTS) frame to B.
• This frame includes a field indicating how long (in microseconds) the actual data frame will be i.e. how long the sender wishes to hold the medium.
• When B receives the RTS it replies with a Clear to Send (CTS) frame, also carrying the length of the data frame.
• Any other node hearing the RTS frame (e.g. C) knows that A is making a request, and should not transmit until the indicated length/time has elapsed. A Time B C D RTS CTS NAV
• Any node hearing the CTS frame (e.g. D) must be close to the receiver (B) and therefore should also not transmit for the indicated length of time. A Time B C D RTS CTS NAV NAV
• Any node that hears the RTS frame, but not the CTS frame, knows that it is not close enough to the receiver to interfere, and so is free to transmit – but must first transmit its own RTS A Time B C D RTS CTS NAV NAV There are two final considerations 1. When the receiver (B) successfully receives a data frame, it must reply with an ACK frame. All other nodes must wait for this ACK frame before transmitting. A Time B C D RTS CTS NAV NAV
• The additional ACK frames were not defined in the early MACA protocols, but added to the Wireless MACA -> MACAW protocol used today. ACK NAV There are two final considerations 2. If two nodes simultaneously issue an RTS and they are not in range, we can have two transmission sequences in the same medium. If the two RTS frames collide, then any receivers will not be able to guess what they were, and no CTS frame will be issued. • When no CTS arrives at the senders, they assume a collision and undergo the standard 802.3b binary exponential back-off algorithm.

IEEE 802.11 Architecture

• Designed so that most decisions distributed to mobile stations
  • Fault tolerant
  • Eliminates bottlenecks
• Components of an 802.11 system includes:
  • Stations
  • Access point (AP)
  • Basic service set (BSS)
  • Extended service set (ESS)
  • Distribution system (DS)

Station

• Component that connects to the wireless medium
  • Contains 802.11 MAC and PHY layers
  • E.g., laptops, smartphones, tablets, printers, and Wi-Fi-enabled IoT devices
• Stations can be classified into:
  • Access Points (APs) – which provide connectivity to other stations.
  • Client stations – like laptops or phones that connect to APs.
• Supports “station services” including:
  • Authentication
  • De-authentication
  • Privacy
  • Delivery of data

Basic Service Set (BSS)

• Set of stations that communicate with each other
  • Independent BSS (IBSS)
    • When all stations in a BSS are mobile and there is no connection to a wired network
    • Typically short-lived with a small number of stations
    • Ad-hoc in nature
    • Stations communicate directly with one another
    • No relay capabilities–nodes must be in direct range
• Set of stations that communicate with each other
  • Infrastructure BSS (BSS)
    • Includes an Access Point (AP)
    • All mobiles communicate directly to AP
    • AP provides connection to wired LAN and relay functionality
    • AP provides central control, allows packet buffering, etc.

Extended Service Set (ESS)

• An ESS is a set of interconnected BSSs with a common SSID (Service Set Identifier or simply network name) e.g Unifi
• Set of infrastructure BSS’s
  • AP’s communicate with each other
  • Forward traffic from one BSS to another
  • Facilitate movement of stations from one BSS to another
• Extends range of mobility beyond reach of a single BSS

Distribution System (DS)

• The DS is the backbone that connects the APs in an ESS.
• Mechanism that allows APs to communicate with each other and wired infrastructure (if available).
• Backbone of the WLAN
• May contain both wired and wireless networks
• Functionality in each AP that determines where received packet should be sent
  • To another station within the same BSS
  • To the DS of another AP (e.g., sent to another BSS)
  • To the wired infrastructure for a destination not in the ESS

ESS & DS (Summary)

IEEE 802.11 Services

• Services divided into
  • Station services
    • Authentication
    • De-authentication
    • Privacy
    • Data delivery
  • Distribution services
    • Association
    • Disassociation
    • Re-association
    • Distribution
    • Integration

Station Services

• Authentication
  • Used to prove identity of one station to another
  • Station must be authenticated in order to access WLAN for data delivery
• De-authentication
  • Used to remove previously authenticated station
  • De-authenticated station cannot access WLAN for data delivery
• Privacy
  • Prevents message contents from being read by unintended recipient
  • Wired equivalency protocol (WEP)–designed to provide same level of protection as found on wired networks
    • 1997, considered insufficient now.
    • WEP, WPA (wifi Protected Access), WPA2, WPA3
    • Only protects data over wireless links, not end-to-end
• Data delivery
  • Provides reliable delivery of data from MAC of one station to MAC of other stations

Distribution Services

• Provide services to allow station mobility within ESS and allow connections to wired networks
• Association service
  • Makes logical connection between station and AP
  • Allows DS of AP to know where to deliver data to station
  • Allows AP to accept data from station
  • AP must allocate channel resources for station
  • Typically association only invoked when station first enters WLAN
• Re-association service
  • Used when station moves to new BSS (new AP)
  • Allows new AP to contact old AP to get packets that may be buffered there for the station

Distribution Services (cont.)

• Disassociation service
  • Station can use this service to inform AP that it no longer requires service from WLAN
    • 802.11 card being removed
    • Station shutting down
  • AP may force disassociation
    • Cannot support all stations currently associated
    • AP shutting down
  • Station must associate again to access WLAN after disassociation
• Distribution service
  • Determines where to send packets
    • Back to own BSS, to another AP, to wired network

Distribution Services (cont.)

• Integration service
  • Allows 802.11 WLAN to connect to other wireless and wired LANs
  • Translates 802.11 frames to formats for other networks
  • Translates frames in other formats to 802.11 format

WLAN issues

• WiFi (802.11b, 802.11g, 802.11n)
  • Inexpensive, pervasive, reliable, easy to manage
  • Hot spots common, but unscalable for metro area use
  • Range ~100 meters: ok within buildings, campuses
  • Bandwidth: 11 Mbps (b), 54 Mbps (g), 100 Mbps (n)
  • Actual bandwidth often half of nominal due to interference, fading, etc.
  • Half of traffic at many companies is non-work (music or video streaming, Web access, personal email, …)
  • Security is difficult, because signals propagate beyond the building or site

WLAN exercise

• In this building, what type of WLAN would you setup (ad hoc, BSS, ESS), and why?
  • Assume there are people moving in and out frequently
  • Assume there are all different types of furniture that may move around.
• How would you support 25 students streaming video at once using 802.11b?
  • Assume your video requires 2 Mbps (each).

WLAN exercise solution

• In this building, what type of WLAN would you setup (ad hoc, BSS, ESS), and why?
  • Setup an ESS, which will allow handoffs and to connect all devices/stations to the WAN if necessary.
• How would you support 25 students streaming video at once using 802.11b?
  • The total bandwidth needed is $25 * 2 \text{ Mbps} = 50 \text{ Mbps}$.
  • The bandwidth of 802.11b is 11Mbps (practical is half, 5.5).
  • So, you would need 5 BSS (or 10 to be practical).
  • i.e., 5 students will share 1 AP (2.5 students share 1 AP practically, consider interference etc.).

GSM (2G)

• GSM is European standard, adopted worldwide and increasingly in US
  • It’s a 2G (second generation) standard, being superseded by 3G
  • It switches voice calls, like landlines, and is being replaced by voice over IP
• Each voice band is 13 kbps compressed versus 64 kbps fibre.
• Human voice frequency is mostly below 4 kHz.
• According to the Nyquist Theorem, to digitize a signal without loss, you need to sample it at twice its highest frequency — so $2 × 4 \text{ kHz} = 8 \text{ kHz}$.
• 8 bits (1 byte) to represent the amplitude of the voice signal leads to 64 Kbps

GSM (2G)

• Standard GSM has 124 channels
• Each channel is 270.8 kbps (this includes voice data, control, and error correction) carried in 200 kHz
  • 8 users per channel (full-rate speech) using Time Division Multiple Access (TDMA)
  • Not the same frequencies can be reused in adjacent cells but GSM can (re)use 1/3 of channels in each cell, due to good error correction
  • Capacity =~ 124 channels * 8 users/channel * 1/3 reuse= 329 calls (users) per cell
• GSM data is carried over GPRS (General Packet Radio Services), often considered 2.5G

3G wireless

• Worldwide standard, though frequency bands vary by region
  • Roaming phones must use different frequency bands
  • There are a few common frequency bands worldwide
• Designed for many services:
  • Real-time gaming
  • Voice
  • File download and upload
  • Video
  • Web and email
• 3G data protocols are WCDMA (Wideband Code Division Multiple Access) and HSPA(+) High Speed Packet Access (upgrades to WCDMA that bring faster internet)
  • In broad use, continue to evolve new features
  • Will be supported for many years until full 4G usage
  • Data rates of 500 kbps to 1 Mbps typical

Evolution GSM

4G wireless

• 4G is also called LTE (long term evolution) and release 8.
  • Standardized by 3GPP (in GSM lineage)
  • Not backward compatible with 3G
  • Entirely IP based; no voice switched traffic
  • Supports spectrum flexibility for worldwide operation
  • Handoffs at 350 km/hr to support high speed rail
  • Any individual phone supports limited spectrum, since RF and filter design are expensive/inflexible
  • Data rates of up to 20 Mbps typical
  • Scarcity of bandwidth resulting in throttling of use (As more users connect and consume data available bandwidth per user can drop).
• CDMA lineage ending
  • Carriers will sunset networks to make more room for LTE, 5G
  • Competitor to LTE was being standardized by 3GPP2 (in CDMA lineage) Another candidate for 4G was WiMAX, which eventually faded out

5G wireless

• Envisioned in 2015, started deployment in 2019
• The aim is to provide three key application areas:
  • Enhanced mobile broadband
  • Ultra-reliable and low latency: real-time, safety, etc.
  • Massive machine type communications
• Been tested throughout
  • E.g. Qualcomm 5G simulations in Europe
  • E.g. at the commonwealth games in 2018 Gold Coast by Telstra

mmWave

• The term “mmWave” (millimetre wave) refers to a specific part of the radio frequency spectrum between 24GHz and 100GHz, which have a very short wavelength.
• This section of the spectrum is pretty much unused, so mmWave technology aims to greatly increase the amount of bandwidth available.

5G Properties

• Peak Data Rate: max rate per user under ideal conditions.
  • 10 Gbps for mobiles, 20 Gbps under certain conditions.
  • 20x better than 4G.
• User experienced Data Rate: Rate across the coverage area per user.
  • 100 Mbps in urban/suburban areas. 1 Gbps hotspot.
  • 10x better than 4G.
• How?
  • High-band (mmWave) resulting in very high data rates.
  • Massive MIMO and beamforming enhance throughput.
  • Wide bandwidths (up to 400 MHz or more) are used compared to LTE's 20 MHz.

Massive MIMO & Beamforming

5G Properties

• Latency: Radio contribution to latency between send and receive
  • The typical latency for a 4G network is around 60 milliseconds, whereas 5G could decrease this to as low as 1 millisecond.
• How ?
  • Shorter Transmission Time Interval (TTI), In 4G: TTI = 1 ms
  • In 5G: TTI can be reduced to 0.125 ms or less
  • This means data packets are scheduled and sent faster and more frequently.
  • 5G uses mini-slots (smaller time units) rather than waiting for full frames.
  • Edge Computing

5G Properties

• Mobility: guaranteed seamless handover and QoS at max speed
  • Seamless handover for up to 500km/h mobility, 1.4x faster than 4G.
• Connection Density: devices per km2
  • Up to 100x more devices per unit area compared to 4G.
  • Around 1 million devices per km2
• Energy Efficiency: network bits/Joule.
  • 90% reduction in network energy usage.
  • Up to 10-year battery life for low power IoT devices, 100x better than 4G.
• Area Traffic Capacity: throughput per m2
  • 10 Mbps/m2

5G Test Results

• Qualcomm 5G simulations
• In Telstra's Gold Coast 5G trials, it achieved network speeds of around 3Gbps using mmWave bands. That's roughly 30 times as a fast as the maximum speed of an NBN 100 connection.

Personal Area Network

Personal Area Network

• Networks that connect devices within a small range
  • Typically on the order of 10 meters or so.
• Application areas
  • Data and voice access points
    • Real-time voice and data transmissions
  • Cable replacement
    • Eliminates need for numerous cable attachments
    • Hook your laptop to your phone, headphones, mouse, keyboard, printer, camera, etc.
  • Ad hoc networking
    • Device with PAN radio can establish connection with another when in range

Bluetooth Standard

• Universal short-range wireless capability
• Bluetooth standardization began in 1998
• Sponsors
  • Initial: Ericsson, Nokia, IBM, Toshiba, and Intel
  • Expanded in 1999 to include 3 Com, Lucent, Microsoft, and Motorola
  • Thousands of companies are now adopters
• Goals of system design
  • Global operation
    • No fixed infrastructure required for
  • network set-up or maintenance
  • Voice and data connections
  • Small, low power radio
  • Low cost: $5-$10 per node

Bluetooth Standard

• Low power
  • 1 mW transmit power to get 10 m range
  • Can amplify signal to 100 mW transmit power to get 100 m range
  • 50-100 mW active power
  • Standby current < 0.3 mA -> 3 months
  • Voice mode = 8-30 mA -> 75 hours
  • Data mode averages 5 mA(20 kbps) -> 120 hours
• Specifies the physical, link, and MAC layers of the protocol stack
• Applications built on top of Bluetooth using HCI—host controller interface
  • Specifies how to “talk” to Bluetooth device
  • Contains sets of commands for hardware
• Defined in a global band (2.45 GHz ISM band)
  • Bluetooth devices should work anywhere in the world (mostly)
  • Devices within 10 m can share up to 865 kbps of capacity
    • In comparison, your led lightbulb at home would be around 5-10 W.

Bluetooth Standard

• Network topology
  • Master-slave connection.
  • Several slaves and a master form a piconet.
  • Several piconets form a scatternet.
• Frequency-hopped spread spectrum
  • Low cost, low power implementations possible.
  • Better immunity to near-far problem than direct sequence spread spectrum.
  • Error correction schemes used to provide protection against interference on the same narrowband channel.

Bluetooth Standard

• Radio Parameters
  • RF band: 2.4 GHz, ISM band
  • Modulation: BFSK
  • Peak data rate: 1 Mb/s
  • Number of hopping channels: 79
  • Carrier spacing: 1 MHz
  • Peak Tx power: ≤20 dBm
• See additional materials for BFSK (Binary Frequency Shift Keying).

Bluetooth Low Energy (BLE)

• BLE is a wireless communication technology designed to consume significantly less power than traditional Bluetooth while maintaining similar functionality.
• It's ideal for applications where devices need to operate on small batteries for extended periods, like wearable fitness trackers, medical devices, and IoT devices.

Bluetooth channel

• 79 1 MHz channels
• Channel divided into 625 μs slots
• Hop occurs after each packet transmitted
• Packets can be 1, 3, or 5 slots in length
• 1600 hops / second
• Time division duplex
  • Transmit and receive in alternate time slots
  • Master-slave architecture
    • Master transmits in a slot
    • Slave transmits in following slot
• Master schedules all traffic
  • Master must poll slaves explicitly or implicitly by sending a master-to-slave data/control packet
  • Master can dynamically adjust scheduling algorithm
  • Scheduling algorithm not specified in Bluetooth standard

Network Architecture

• Piconets
  • Master and up to seven slave devices
  • Paging unit that established connection becomes piconet master by default
  • Slaves must synchronize to master
    • Master announces its clock and device ID to slaves
  • Master-slave switch
    • Slave can take on role of master if desired
  • Can only be one master per piconet
• Hopping pattern determined by master’s 48-bit Bluetooth Device Address
• Phase in hopping pattern determined by master clock
• Piconet access code determine by master ID

Scatternets

• Slaves within a piconet share 1 MHz bandwidth
• Piconets can co-exist by hopping independently
  • Each piconet can access 1 MHz bandwidth
  • Increase capacity compared with all nodes sharing 1 MHz channel
• Scatternets share 79 MHz bandwidth among different piconets
• Data from a nearby piconet not received by nodes in another piconet
• Nodes can belong to multiple piconets
  • Time division multiplexing
  • Can be a slave in two different piconets
  • Can be a master in one piconet and a slave in another piconet
  • Currently no standard for synchronization between different piconets
    • Inefficient use of resources
    • Can cause connections to be dropped

Wireless Network Configurations

• Image showing:
  • Cellular system
  • Conventional ad hoc systems
  • Scatternets

Summary

• WLAN with newer versions to improve data transfer rate
  • Also need to ensure the reliability, safety, security etc.
• Cellular network getting faster too
  • Where will we be heading in the near future?
• Satellite communications have less and less use, but still provides some fundamental services.
• PAN is becoming more and more used as IoT is being deployed quickly.
  • Technology used also needs to cope with the demand.