Introduction to Telecommunications by Gokhale WIRELESS COMMUNICATIONS CHAPTER 5 WIRELESS COMMUNICATIONS Introduction to Telecommunications by Gokhale

Introduction Wireless Communications system in which electromagnetic waves carry a signal through atmospheric space rather than along a wire Most systems use radio frequency (RF, which ranges from 3 kHz to 300 GHz) or infrared (IR, which ranges from 3 THz to 430 THz) waves IR products do not require any form of licensing by the FCC

Timeline of Major Developments Mobile Telephone System (MTS) Introduced in 1946 Simplex (one-way transmission) and manual operation Improved Mobile Telephone System (IMTS) Introduced in 1969 using a 450 MHz band Advanced Mobile Phone Service (AMPS) Introduced in 1983 First system to employ a “cellular” concept

Cellular Topology Cellular network: Cellular network components Series of overlapping hexagonal cells in a honeycomb pattern Cellular network components Base Station:Transmitter, Receiver, Controller, Antenna Cell: Base station’s span of coverage Mobile Switching Center: Contains all of the control and switching elements to connect the caller to the receiver, even as the receiver moves from one cell to another

Personal Communications Systems (PCS) PCS is also called Personal Communications Networks (PCN) Goal of PCS is to provide integrated voice, data and video communications Three categories of PCS: Broadband: cellular and cordless handsets Narrowband: enhanced paging functions Unlicensed: allows short distance operation

Hierarchical Cell Structure Key features of PCS Variable cell size Hierarchical cell structure (picocell, microcell, macrocell, supermacrocell)

Cells

Analog Access Analog Cellular Systems First generation system Based on FDMA (Frequency Division Multiple Access), where frequency band is divided into a number of channels. Each channel carries only one voice conversation at a time. AMPS operates on 800 MHz or 1800 MHz Advantages: Widest coverage Limitations: Inadequate to satisfy the increasing demand Poor security Not optimized for data

FDMA

Digital wireless technologies provide greater system capacity. Digital Access D-AMPS (Digital-AMPS) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access) Digital wireless technologies provide greater system capacity.

TDMA TDMA Second generation system Enables users to access the whole channel bandwidth for a fraction of the time, called slot, on a periodic basis Has applications in satellite communications Advantages Improved capacity

TDMA

CDMA CDMA Third generation system Separates users by assigning them digital codes within a broad range of the radio frequency First technology to use soft-handoff Employs spread spectrum technique Advantages Improved capacity, coverage, voice quality, and immunity from interference

An Overview of Cellular Technologies

Spread Spectrum Technique: FHSS Frequency Hopping Spread Spectrum (FHSS) Resists interference by jumping rapidly from frequency to frequency in a pseudo-random way Advantage Increases the total amount of available bandwidth through the assignment of multiple hopping sequences within the same physical area More flexible than DSSS Application In large facilities especially with multiple floors

Spread Spectrum Technique: DSSS Direct Sequence Spread Spectrum (DSSS) Resists interference by mixing in a series of pseudo-random bits with the actual data Advantage If bits are damaged in transmission, the original data can be recovered as opposed to having to be retransmitted Application Is substituted for point-to-point or multi-point connectivity to bridge LAN segments Limitation Roaming capabilities are less robust

Spread Spectrum Technique: CDPD Cellular Digital Packet Data Allows for a packet of information to be transmitted in between voice telephone calls Enables data specific technology to be tacked onto existing cellular telephone infrastructure

Wireless Applications Cellular Phone High mobility and narrow bandwidth (20 to 30 kHz) Cordless Phone Low mobility and narrow bandwidth (20 to 30 kHz) Wireless LAN Low mobility and high bandwidth (typically 10 Mbps) Wireless Application Protocol (WAP) is a standard for wireless data delivery, loading web pages, and navigation

The Wireless Spectrum

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.

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

Call Completion

Advanced Mobile Pone Service (AMPS) A first generation cellular technology that encodes and transmits speech as analog signals.

Time Division Multiple Access (TDMA)

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.