Wireless Transmission and Services

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 networks and services

Understand the differences between wireless and wireline local loops

Objectives

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

The Wireless Spectrum

The Wireless Spectrum

The Wireless Spectrum

Unlicensed Frequency Bands

Characteristics of Wireless 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 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

Signal Propagation

Fading and Delay

Fading: 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 - the use of multiple antennas or multiple signal transmissions to compensate for fading and delay.

Signal Propagation

Attenuation - 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.

Fixed vs. Mobile

Fixed vs. Mobile

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 3G - Third generation 4G - Fourth generation (next)

Principles of Cellular Technology

Cells

Figure Radio frequency reuse for cellular towers

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Cellular Call Completion

Components of a signal:

MIN (Mobile Identification Number) - an enclosed representation of the mobile telephone’s 10-digit telephone number.

ESN (Electronic Serial Number) - a fixed number assigned to the telephone by the manufacturer.

SID (System Identification Number) - a number assigned to the particular wireless carrier to which the telephone’s user has subscribed.

Cellular Call Completion

Mobile telephone switching office

Figure 10-4

Central Office

Mobile Switching Office

BSC

BTS

BTS

BTS

BTS

BTS

BSC – Base Station ControllerBTS – Base Transceiver StationsBH – Backhaul

Call Completion

Figure 10-5

Figure 10-6

AMPS (Advanced Mobile Phone Service)

A first generation cellular technology that encodes and transmits speech as analog signals.

TDMA (Time Division Multiple Access)

CDMA (Code Division Multiple Access)

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.

GSM (Global System for Mobile Communications)

A version of TDMA (time division multiple access) 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.

3G (Third Generation) Technologies

In this emerging technology a user can access all telecommunication services from one mobile phone.

CDMA2000 - a packet switched version of CDMA. Maximum throughput is 2.4 Mbps.

W-CDMA (Wideband CDMA) - based on technology developed by Ericson, is also packet-based and its maximum throughput is also 2.4 Mbps.

WLL (Wireless Local Loop)

WLL is 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.

LMDS (Local Multipoint Distribution Service)

A point-to-multipoint, fixed wireless technology that was conceived to supply wireless local loop service in densely populated urban areas to issue television signals.

A disadvantage is that its use of very high frequencies limits making its transmission distance to no more than 4km between antennas.

MMDS (Multipoint Multichannel Distribution System)

Uses microwaves with frequencies in the 2.1 to 2.7 GHz range of the wireless spectrum.

One advantage is its lower frequency range, MMDS is less susceptible to interference.

MMDS does not require a line-of-sight path between the transmitter and receiver.

WLAN Architecture

WLAN Architecture

WLAN Architecture

Wireless Networking Standards

802.11 - IEEE’s Radio Frequency Wireless networking standard committee.

802.11b - uses DSSS (direct sequence spread spectrum) signaling. Uses the 2.4-2.5 GHz frequency range and separates it into 14 overlapping 22-MHz channels – 11 mbps. Mbps 38 meters

802.11g - designed to be just as affordable as 802.11b while increasing its maximum capacity from 11 Mbps through different encoding techniques to 54Mbps. Mbps 38 meters

802.11a - uses multiple frequency bands in the 5 GHZ range. Like 802.11g, 802.11a provides a maximum throughput of 54 Mbps 35 meters

802.11n - developed by the IEEE LAN/MAN Standards Committee (IEEE 802) in the 5 GHz and 2.4 GHz public spectrum bands. 300 Mbit/s (2 streams) 70 meters

Bluetooth

A mobile wireless networking standard that uses DSS (direct sequence spread spectrum) 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 PANs (Personal Area Networks).

Personal Area Networks

Satellite Positioning

The original method for positioning satellites above the earth was in GEO (geosynchronous orbit).

Geosynchronous satellites are positioned approximately 35,800 km (22,300 miles) above the earth’s equator.

An alternative to GEO satellites are LEO (low earth orbiting) satellites.

Satellite Positioning

Satellite Services

Digital broadcasting - To deliver content to subscribers, 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.

GPS (Global positioning service) - 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.

WANs (Wide area networks) - Private companies use satellite transmission to connect multiple locations on their WANs.

Components & Technologies

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Cisco Aironet 802.11b Client Adapters

2.4 GHz802.11b11 Mbps

IncludePC Card PCI CardLMC CardMini PCI

Example of wireless adapter

5 GHz/802.11a• 54 Mbps

Rate Shifting • 6, 9, 12, 18, 24, 36, 48, or 54

Fixed data rates • User configurable option

5 dBi Patch Antenna

CardBus interface

Transmit power settings:• 20 mW, 10 mW, and 5 mW

Acoustical strength is measured relatively per the dBi scale.

WLAN Topologies

A typical use of wireless technology as an add-on to a traditional LAN.

Building to building wireless connectivity can be more cost effective and can avoid obstacles faced by wired connections.

WAN SolutionsFour main requirements for WLAN solution:

1. High availability

• Through system redundancy

• Redundant AP automatic rate negotiation

2. Scalability

• using multiple APs per coverage area

• using multiple frequencies

• AP using load balancing

3. Manageability (diagnostic tools)

4. Open Architecture

• 802.11a

• 802.11b

Challenges & Issues

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Interference from other Sites

Since the 802.11 standards use unlicensed spectrum:

Interference cannot always be detected until the link is actually implemented.

Changing channels is the best way to avoid interference.

Power Management

Power consumption is always an issue with laptops.

There are 3 modes of power for Cisco PC cards:

1.Constant Awake Mode (CAM)

Mode is best when power is not an issue such as when AC power is available to the device. Default mode

2. Power save mode (PSP)

Mode is used when power conservation is the utmost importance. The wireless NIC card will go to ‘sleep’ after a period of inactivity & periodically awake to retrieve buffered data from the AP.

3. Fast power save mode (FastPSP)

Combination of CAM & PSP. For clients who switch between AC & DC power.

Interference from other Devices

Other devices use these frequencies.

Physical objects also cause interference.

In unlicensed bands, the potential for interference from another unlicensed user is becoming greater. The unlicensed bands are allocated on a shared basis.

Interoperability

Interoperability issues might influence an Admin to use a single vendor for all wireless needs.

Closed networks, such as corporate sites, might choose a single-vendor solution in order to benefit from increased management utilities and vendor accountability.

In an open network such as a college campus, the admin cannot usually dictate hardware selection, and must support a variety of hardware solutions.

Network Security

As wireless networks grow, the threat of intruders from the inside and outside is great. Attackers called war drivers are continually driving around searching for insecure WLANs to exploit.

IEEE Wired Equivalent Privacy (WEP) with Temporal Key Integrity Protocol (TKIP) provides robust authentication options with 802.1X to make 802.11-based wireless LANs secure.

IEEE has adopted the use of the Advanced Encryption Standard (AES) to the data-privacy section of the proposed 802.11i standard.

Installation & Site Design Issues

Obstructions to visual link:Topographic featuresCurvature of the EarthBuildingsTrees

Installation and Site Design Issues—WLAN

HotSpots

Today hot spots exceed 220,000 (Oct 2008)

Wi-Fi Manufactures

• Intel – Wi-Fi chips

• Microsoft

• Cisco; 70% of wired computer networks

• 1999 bought Aironet Wireless Communications for $800 million.

• 2003, paid $480 million for Linksys.

• is now the leading maker of Wi-Fi gear

•Netgear

Health IssuesIn general, living things should not be subjected to RF

energy unnecessarily

Antenna guidelines

Do not touch an active antenna. Do not stand in front of, or close to, an antenna that is

radiating a signal. Stand to the back or side of any dish-type antenna. Always assume that any antenna is currently energized. Small-sized antennas operate at higher frequencies,

which are more potentially hazardous. Maintain at least 5 cm (2 in.) between yourself and a

laptop antenna.

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.

WLANs (Wireless LANs) use the same protocols and a similar architecture as wired LANs.

Your assignment

What is 802.20?What is its purpose?Where is it used ?Where is it now installed?How does it fit in with WiFi?What is its future?

Figure 10-1

Central Office

Figure 10-2 Radio frequency reuse for cellular towers

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Figure 10-3

Figure 10-4

Central Office

Mobile Switching Office

BSCBTS

BTS

BTS

BTS

BTS

BSC – Base Station ControllerBTS – Base Transceiver StationsBH – Backhaul

Figure 10-5

Figure 10-6

Conclusion

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 networks and services

Understand the differences between wireless and wireline local loops

Conclusion

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

END