Wireless Transmission and Services. Chapter 9. Objectives. Associate electromagnetic waves at different points on the wireless spectrum with their wireless services Identify characteristics that distinguish wireless transmission from wire-bound transmission
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Wireless Transmission and Services Chapter 9
Objectives • Associate electromagnetic waves at different points on the wireless spectrum with their wireless services • Identify characteristics that distinguish wireless transmission from wire-bound transmission • Explain the architecture and access methods used in cellular net-works and services • Understand the differences between wireless and wireline local loops • Describe the most popular WLAN standards, including their advantages, disadvantages, and uses • Identify the major satellite positioning schemes and list several telecommunications services that rely on satellite transmission
Antennas • Radiation pattern - the relative strength over a three dimensional area of all the electromagnetic energy the antenna sends or receives. • Directional antenna - issues wireless signals along a single direction
Antennas • Omni-directional antenna - issues and receives wireless signals with equal strength and clarity in all directions.
Signal Propagation • Reflection - the wave encounters an obstacle (problem meet) and bounces back towards its source. • Diffraction - a wireless signal splits into secondary waves when it encounters an obstruction. • Scattering - the diffusion, or the reflection in multiple different directions of a signal.
Signal Propagation • Fading and Delay • Fading (blur/weak): a change in signal strength as result of some of the electromagnetic energy being scattered, reflected, or diffracted after being issued by the transmitter. • Diversity (variety) - the use of multiple antennas or multiple signal transmissions to compensate for fading and delay.
Signal Propagation • Attenuation (reduction/become small)- after a signal has been transmitted, the farther it moves away from the transmission antenna, the more it weakens. • Interference - because wireless signals are a form of electromagnetic activity, they can be hampered by other electromagnetic energy, resulting in interference.
Narrowband, Broadband, and Spread Spectrum Signals • Narrowband - a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies. • Broadband - a type of signaling that uses a relatively wide band of the wireless spectrum. • Spread spectrum - the use of multiple frequencies to transmit a signal.
IQ TEST 1 The _____ is a continuum of electromagnetic waves with varying frequencies and wavelengths that are used for telecommunications. Answer: wireless spectrum 2. An antenna’s _____ describes the relative strength over a three-dimensional area of all the electromagnetic energy that antenna sends or receives. Answer: radiation pattern 3. A(n) _____ issues wireless signals along a single direction. Answer: directional antenna 4. A(n) _____ issues and receives wireless signals with equal strength and clarity in all directions. Answer: omni-directional antenna 5. _____ is the diffusion, or the reflection in multiple different directions of a signal Answer: Scattering
Cellular Communications • Mobile telephone service - a system for providing telephone services to multiple, mobile receivers using two-way radio communication over a limited number of frequencies. • Mobile wireless evolution: • First generation • Second generation • Third generation
Cellular Call Completion • Components of a signal: • Mobile Identification Number (MIN) - an enclosed representation of the mobile telephone’s 10-digit telephone number. • Electronic Serial Number (ESN) - a fixed number assigned to the telephone by the manufacturer. • System Identification Number (SID) - a number assigned to the particular wireless carrier to which the telephone’s user has subscribed.
Cellular Call Completion MTSO: mobile telecommunications switching office- the connection between a cellular network and wired telephones
Advanced Mobile Pone Service (AMPS) • A first generation cellular technology that encodes and transmits speech as analog signals.
Code Division Multiple Access (CDMA) • Each voice signal is digitized and assigned a unique code, and then small components of the signal are issued over multiple frequencies using the spread spectrum technique.
Global System for Mobile Communications (GSM) • A version of time division multiple access (TDMA) technology, because it divides frequency bands into channels and assigns signals time slots within each channel. • Makes more efficient use of limited bandwidth than the IS-136 TDMA standard common in the United States. • Makes use of silences in a phone call to increase its signal compression, leaving more open time slots in the channel.
Emerging Third Generation (3G) Technologies • The promise of these technologies is that a user can access all her telecommunication services from one mobile phone. • CDMA2000 - a packet switched version of CDMA. • Wideband CDMA (W-CDMA) - based on technology developed by Ericson, is also packet-based and its maximum throughput is also 2.4 Mbps.
Wireless Local Loop (WLL) • A generic term that describes a wireless link used in the PSTN to connect LEC central offices with subscribers. • Acts the same as a copper local loop. • Used to transmit both voice and data signals.
Local Multipoint Distribution Service (LMDS) • A point-to-multipoint, fixed wireless technology that was conceived to supply wireless local loop service in densely populated urban areas and later on a trial basis to issue television signals. • A disadvantage is that its use of very high frequencies limits its signal’s transmission distance to no more than 4km between antennas.
Multipoint Multichannel Distribution System (MMDS) • Uses microwaves with frequencies in the 2.1 to 2.7 GHz range of the wireless spectrum. • One advantage is that because of its lower frequency range, MMDS is less susceptible to interference. • MMDS does not require a line-of-sight path between the transmitter and receiver.
Wireless Networking Standards • 802.11 - IEEE’s Radio Frequency Wireless networking standard committee. • 802.11b - uses direct sequence spread spectrum (DSSS) signaling. Also used the 2.4 - 2.4835 GHz frequency range and separates it into 14 overlapping 22-MHz channels. • 802.11g - designed to be just as affordable as 802.11b while increasing its maximum capacity from 11 Mbps through different encoding techniques. • 802.11a - uses multiple frequency bands in the 5 GHZ range. Like 802.11g, 802.11a provides a maximum throughput of 54 Mbps.
Bluetooth • A mobile wireless networking standard that uses direct sequence spread spectrum (DSS) signaling in the 2.4 GHz band to achieve a maximum throughput of less than 1 Mbps. • Designed to be used on small networks composed of personal communications devices, also known as personal area networks.
Satellite Positioning • The original method for positioning satellites above the earth was in geosynchronous orbit. • Geosynchronous satellites are positioned approximately 35,800 km (22,300 miles) above the earth’s equator. • An alternative to GEO satellites are low earth orbiting (LEO) satellites.
Satellite Services • Digital broadcasting - To deliver content to subscribers, networks (or other multimedia providers) uplink their audio and video signals to a satellite, which then downlinks the signals, in a broadcast fashion, to earth. • Analog broadcasting - Traditional analog television and radio signals can be issued from a terrestrial transmitter to a satellite and then downlinked to another terrestrial location within seconds. • Mobile Wireless - Services such as cellular telephone, paging, and other PCS applications are well suited to LEO or MEO satellite transmission.
Satellite Services • Tracking and monitoring - Two-way satellite communications can be used to monitor the whereabouts and condition of wildlife, mobile weather sensors, marine vessels, and so on anywhere in the world. • Global positioning service (GPS) - A service that expands on remote monitoring functions, GPS allows a mobile station on earth to exchange signals with a satellite to determine its precise location. • Wide area networks - Private companies use satellite transmission to connect multiple locations on their WANs.
IQ TEST 2 1. _____ is a generic term that describes a wireless link used in the PSTN to connect LEC central office with subscribers. Answer: Wireless local loop (WLL) 2. A(n) _____ is a data network that uses wireless signaling for communication between nodes within a limited geographical area. Answer: wireless LAN (WLAN) 3. _____ is a wireless networking specification that uses DSSS in the 2.4 GHz frequency band to achieve a maximum of 10 Mbps throughput. Answer: HomeRF 4. A(n) _____ is a number assigned to the particular wireless carrier to which the telephone’s user has subscribed. Answer: System Identification Number (SID)
Summary • The wireless spectrum, the range of frequencies within the electromagnetic spectrum that are used for telecommunications services, starts at 9 KHz and ends at 300 GHz. • Cellular telephone service is distinguished from other mobile two-way radio services by its use of cells to reuse limited frequencies within a certain geographical area. • Wireless LANs (WLANs) use the same protocols and a similar architecture as wire-bound LANs.