Chapter 10

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Oct 30, 2023

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Chapter 10: Wireless Wide Area Networks Cellular Telephony - Cellular phones are quickly replacing traditional land-based telephone lines for large groups - Cellular technology is probably one of the most complex of all wireless communications technologies - Governments auction off part of the wireless spectrum  Collect billions of dollars in leasing fees 蜂窝电话 - 蜂窝电话正在迅速取代大型团体的传统陆地电话线 - 蜂窝技术可能是所有无线通信技术中最复杂的技术之一 - 政府拍卖部分无线频谱 - 收取数十亿美元的租赁费 Cellular Telephone Technology - Today, practically all cellular phone networks are based on digital instead of analogy transmission technology - Today’s smartphones can be used for many sophisticated applications  Beyond simply browsing the web or sending and receiving messages and email 蜂窝电话技术 - 如今，几乎所有蜂窝电话网络都采用数字传输技术，而不是类比传输技术 - 如今的智能手机可用于许多复杂的应用领域 - 除了浏览网页或收发信息和电子邮件之外 How Cellular Telephony Works - Keys to Cellular Telephone Works  Cells o Typical call ranges from a few thousand feet to approximately 10 square miles o At the centre of each cell is a cell transmitter connected to a base station o Each base station is connected to a mobile telecommunications switching office (MTSO)  Link between the cellular network and the wired telephone world (public switched telephone network or PSTN)  Controls all transmitters and base stations - Keys to cellular telephone networks (con’d)  Transmitters and cell phones operate at low power o Enables the signal to stay confined to the cell o Signal at a specific frequency does not go far beyond the cell area  Same frequency can be used in other cells at the same time  Except in adjacent cells  Cell phones have special codes o Codes are used to identify the phone, phone’s owner, and carrier or service provider

- Some cellular phones require a SIM card to be installed before they can be used  SIM (subscriber identity module) card – very small electronic card used to associate the phone with the user’s account and with the carrier  SIM cards have between 64KB and 512KB of ROM, between 1KB and 8KB of RAM, and between 64KB and 512KB of EEPROM  Users can move the card between one phone and another and use different phones without reprogramming - When a user moves within the same cell  Transmitter and base station for that cell handle all of the transmissions - As the suer moves toward the next cell  A handoff process occurs - Roaming  User moves from one cellular network to another - Steps to receive a call  Cell phone listens for the SID being transmitted by the abse station on the control channel  Phone compares SID with its programmed SID o If they match, phone is in a network owned by carrier  If SIDs do not match, phone is roaming  When a call comes in, MTSO locates the phone through the registration request  User can move to another cell  Phone and transmitter can change frequencies as required Evolution of Cellular Technology - 1G (First Generation)  Uses analog signals modulated using FM  Based on Advanced Mobile Phone Service (AMPS) o Operates in the 800-900 MHz frequency spectrum o Each channel is 30 KHz wide with a 45 KHz passband o There are 832 frequencies available o Uses Frequency Division Multiple Access (FDMA) o FDMA allocates a single cellular channel with two frequencies to one user at a time - 1G networks use circuit-switching technology - 2G (second Generation)  Transmits data between 9.6 Kbps and 14.4 Kbps o In the 800 MHz and 1.9 GHz frequencies  2G networks are also circuit-switching  2G systems use digital tranmissions - Digital transmissions  Use the frequency spectrum more efficiently  Over long distances, the quality of the voice transmission does not degrade  Difficult to decode and offer better security - Digital transmissions (cont’d)

 Use less transmitter power  Enable smaller and less expensive individual receivers and transmitters - Multiple access technologies  Time Division Multiple Access (TDMA)  CDMA  Global System for Mobile communications (GSM) o Uses a combination of FDMA and TDMA technologies - 2.5 Generation (2.5G)  Interim step between 2G and 3G  Operates at a maximum speed of 384 Kbps  Primary difference between 2G and 2.5G: o 2.5G networks are packet-switched  Advantages of packet switching o Much more efficient  Can handle more transmissions over a given channel o Permits an always-on connection - Three 2.5G network technologies  General Packet Radio Service (GPRS) o For TDMA or GSM 2G networks o Uses eight time slots in a 200 KHZ spectrum and four different coding techniques to transmit at 114 Kbps  Enhanced Data rates for GSM Evolution (EDGE) o Can transmit up to 384 Kbps o Based on a modulation technique called 8-PSK  CDMA2000 1xRTT o Operates on two 1.25 MHz-wide frequency channels o Supports 144 Kbps packet data transmission - Third Generations (3G)  Intended to be a uniform and global standard for cellular wireless communication - Standard data rates  144 Kbps for a mobile user  386 Kbps for a slowly moving user  2 Mbps for a stationary user - 3G network technologies  CDMA2000 1xEVDO o For 2.5G CDMA2000 1xRTT networks - 3G network technologies (con’d)  CDMA2000 1xEVDV is the successor of CDMA2000 1xEVDO  Wideband CDMA (W-CDMA) o For 2.5G EDGE networks  High-Speed Donwlink Packet Access (HSDPA) o Beyond W-CDMA o Uses a 5t MHz W-CDMA channel, variety of adaptive modulation, multiple in multiple out (MIMO) antennas, and hybrid automatic repeat request (HARQ)  HSPA+ (also called Evolved HSPA) – successor to HSDPA

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o Provides theoretical data rates up to 168 Mbps on the downlink and 22 Mbps on the uplink o Provides an upgrade path to latest-generation o Technology: LTE (Long Term Evolution)  LTE (also known as 4G) o LTE Advanced: expands on LTE by allowing carriers to combine up to five 20-MHz-wie frequency channels o Maximum downlink data rate: up to 1 Gbps  LTE (con’d) o Uses OFDM on the downlink and a technique called orthogonal frequency division multiple access (OFDMA) o Uses single-carrier FDMA (SC-FDMA) on the uplink  Assigns a single subcarrier in the same OFDM stream to each user communicating with the same tower o Many cellular networks worldwide have been upgraded to LTE as well as to the latest evolutions, LTE Advanced and Voice over LTE (VoLTE)  LTE Advanced expands LTE by allowing carriers to combine up to five 20-MHz-wide frequency channels and raise maximum downlink data rate to 1 Gbps  With VoLTE, carriers will move to a totally packet- switched network  5G (fifth generation) o Still not fully approved but being tested by some carriers o Employs a blend of GSM, HSPA+, WiMAX, and Wi-Fi to make use of as much spectrum as possible o Users cognitive radios that “learn” and adapt to the RF environment o Has the ability of many devices to communicate with each other, distributing the responsibility of the processing information around the RF environment Digital Cellular Challenges and Outlook - Cellular telephony has signigicantly changed the way people work and communicate - If 5G’s design is successful  It might reduce the need for the wired telephone infrastructure  Saving carriers the cost of deploying and maintaining much of the able infrastructure Satellite Broadband Wireless - Satellites provide GPS, communication to remote areas of the planet, and radio transmissions/TV signals that reach anyone in real time - Satellite use falls into three broad categories  Satellites are used to acquire scientific data and perform research in space  Satellites look at Earth from space

 Satellites are used as reflectors that bounce or relay signals from one point on Earth to another o Wireless communications falls under this use of satellites Satellite Transmissions - Satellites generally send and receive on one of four frequency bands - Frequency band affects the size of the antenna - Class and Type of Service  Consumer class service o Shares the available bandwidth between the users  Business class service o Offers dedicated channels with dedicated bandwidth o More expensive - Types of connectivity  Point-to-point, point-to-multipoint, and multipoint-to- multipoint - Modulation techniques  Binary phase shift keying (BPSK) – Shifts the starting point of a carrier wave by 180 degrees  Quadrature phase shift keying (QPSK) – Shifts the starting point of the carrier wave by 90 degrees  Eight-phase shift keying (8-PSK) – Can transmit up to 3 bits per symbol  16-level quadrature amplitude modulation (16-QAM)  Primarily used for sending data downstream; considered efficient but is susceptible to interference - Multiplexing techniques – Satellite systems employ two multiplexing techniques, FDMA and TDMA, along with specialized techniques:  Permanently assigned multiple access (PAMA) – a frequency channel is permanently assigned to a user  Single channel per carrier (SCPC) – Assigns a frequency channel to a single source  Multi-channel per carrier (MCPC) uses TDM to consolidate traffic from different users on to each carrier frequency  Demand assigned multiple access (DAMA) – allocated bandwidth on a per-call session  Satellite systems are classified according to the type of orbit they use  Three orbits: o Low earth orbit (LEO) o Medium earth orbit (MEO) o High earth orbit (HEO)  Most HEO satellites fall into a subclass called geosynchronous each orbit (GEO) - Low earth orbit (LEO) satellites  Circle Earth at altitudes between 200 to 900 miles  Must travel at high speeds o So earth’s gravity will not pull them back into the atmosphere

 Area of earth coverage (called the footprint) is small - LEO systems have a low latency  Use low-powered terrestrial devices (RF transmitters)  Round trip time: 20 to 40 milliseconds for a signal to bounce from an Earth-bound station to a LEO, then back to an Earth station - LEO satellites groups  Little LEO o Provides pager, satellite telephone, and location services  Big LEO o Carriers voice and data broadband services, such as wireless internet access - In the future, LEOs are expected to be in demand for three markets:  Rural conventional telephone, global mobile digital cellular, and international broadband services - Medium earth orbit (MEO) satellites  Orbit the Earth at altitudes between 1,500 and 10,000 miles  Some MEO satellites orbit in. near-perfect circles  Other MEO satellites revolve in elongated orbits called highly elliptical orbits (HEOs) - Advantages of MEO satellites  MEOs do not have to travel as fast; a MEO can circle the Earth in up to 12 hours  Have a bigger earth footprint - Disadvantage of MEO satellites  Higher orbit increases the latency  Round trip time: 50 to 150 milliseconds - HEO satellites  A type of MEO but with elongated orbits  Have a highapogee (maximum altitude) and a low perigee (minimum altitude)  Can provide good coverage in extreme latitudes  Orbits typically have a 24-hour period - Geosynchronous earth orbit (GEO) satellites  Stationed at an altitude of 22,282 miles  Orbit matched the rotation of the Earth o And moves as the Earth moves  Can provide continuous service to a very large footprint o Three GEO satellites are needed to cover the Earth  Have high latencies of about 250 milliseconds  Require high-powered terrestrial transmitting devices Experimental technologies - NASA experimented with ultra-lightweight, solar-powered, high- flying aircraft - Google (Project Loon) has launched experimental ballons that travel around the planet on the jet stream - Facebook is experimenting with solar-powered frones

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- The Google and Facebook projects are an effort to bring Internet connectivity to as many people around the world as possible Satellite Technology Outlook - Satellites can provide wireless communication  In areas not covered by WWAN technologies - Satellites today are enabling carriers to offer  Internet access and voice calls to passengers and crews across large oceans o And in high latitudes and remote corners of the Earth - Likely that satellite technology will evolve  Along with the experimental technologies to increase reliability and lower costs Summary - Two main WWAN technologies are cellular telephony and satellite communications - In cellular telephone networks, the coverage area is divided into sections called cells - Some cellular phones use SIM cards to store user and carrier information - First Generation (1G) cellular technology uses analogy signals and a circuit-switching technology to transmit data at a maximum speed of 9.6 Kbps - Second Generation (2G) can transmit data between 9.6-14.4 Kbps using digital signals instead of analogy signals - 2.5G networks transmit data at a maximum speed of 384 Kbps and uses a packet-switched technique - 3G networks provide new and expanded capabilities and data applications features to mobile users - 4G networks achieve data rates comparable to wired networks  Long Term Evolution (LTE) technology - 5G is currently under development and is slated to be approved in 2018 - Satellites used for wireless data connectivity  Employ common modulation and multiplexing techniques - Satellite orbit types  LEO satellites  MEO satellites  HEO satellites  GEO satellites Tutorial Of the following types of satellite, which travels at the highest orbital speed? LEO Of the following types of satellite, which has the smallest signal footprint? LEO satellites have the smallest footprints, while GEO satellites have the largest. What type of satellites does a GPS wireless system use? MEO Line-of-sight is NOT a characteristic of what type of system?

Wireless Cellular phone technologies play a crucial role in our daily communications. After delving into this topic. 1. Help your friends to identify the possible reasons and provide solutions for the problems: a) no service, b) wrong SIM, emergency calls only, c)cell SID does not match that in phone. No service: scan frequency band for control channel, but couldn’t find it. Out of range of mobile service. Change to a higher location closer a cell 2. In your own words, describe and explain hwo the cellular technologies evolve from 1G to 4G and up to current 5G