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

2. 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

3. 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

4. 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

5. 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

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

7. Cells

8. 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

9. FDMA

10. 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.

11. 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

12. TDMA

13. 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

14. An Overview of Cellular Technologies

15. 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

16. 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

17. 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

18. 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

19. The Wireless Spectrum

20. 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.

21. 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

22. 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.

23. Cellular Call Completion

24. Call Completion

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

26. Time Division Multiple Access (TDMA)

27. 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.

28. 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.

29. Emerging Third Generation (3G) Technologies
The promise of these technologies is that a user can access all her telecommunication services from one mobile phone.
CDMA 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.

30. 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.

31. 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.

32. 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.