unit 1 - ajaybolar.weebly.comajaybolar.weebly.com/uploads/1/0/1/0/10106930/wireless_unit_1.pdf ·...

10EC81-Wireless Communication

Department of ECE, Canara Engineering College

UNIT 1

1.1 The History and Evolution of Wireless Radio Systems

Early AM wireless systems

A typical wireless transmitter is shown in fig 1.1 . The inductance and capacitance used to tune

the output frequency of the spark-gap.

Due to the nature of the spark-gap emission , maximum power output typically occurred at a

very low frequency with its corresponding long wavelength.

The wireless transmitter shown in fig would emit a signal either long or short duration. The

transmitted signal was the electromagnetic noise produced by the spark gap discharge. The

signal propagated through the air to a receiver located at some distance from the transmitter. At

the receiver the detected signal was interpreted by an operator as either a dot or dash depending

upon its duration.

The next generation of wireless transmitter used more stable RF alternators for their signal

sources.

Figure 1.1 Typical early wireless transmitter

Modern AM

Amplitude modulation is used for low frequency radio broadcasting. Newer uses of AM include

quadrature amplitude modulation . QAM is a hybrid form of amplitude and phase modulation

used for high speed data transmission at RF frequencies. QAM is a digital modulation technique.

QAM is used extensively by broadband cable and wireless systems to achieve bandwidth

efficiency.

The development of FM



AMPS cellular telephone service is an FM based service, FM is used for transmission of FM

broadcast band, TV-broadcasting sound transmission ,direct satellite TV service, cordless

telephones. FM is capable of much more noise immunity than AM

The evolution of digital radio

Advances in microwave digital radio technology and digital modulation techniques provides

increased data rates over the same radio channel.

Many service providers of point to point connectivity are employing microwave and millimeter

wave radio transmission systems that use the most modern digital modulation techniques to

obtain high data rate links. Wireless Internet service providers are using digital radio equipment

for point to point and point to multi-point systems that provide high bit rates internet

connections. Cordless telephones adapted digital radio technology , and all the newest wireless

systems use modern digital modulation technologies to achieve higher data rates and better noise

immunity.

The cellular telephone concept

The cellular concept evolved from earlier mobile radio networks. The mobile phone service

usually consisted of a single, tall, centrally located tower with a high power transmitter that

could only service one user at a time per channel over a particular metropolitan area. Due to the

limited number of frequency allocations, only several dozens of simultaneous users were

possible.

In a cellular system there would be many towers, each low in height , and each with a relatively

low- power transmitter. Each tower could cover a cell . Each tower or cell site would use only a

few of the total number of frequencies available to the entire system. Due to the small cell size ,

these same frequencies could then be reused by other cells at much shorter spacing than

previously possible thus increasing the total number of potential users within the entire system.

As a mobile user moved within the metropolitan area it would be “handed-off” from cell to cell

and different frequencies as assigned to the different cells.

1.1 Different Generations of Wireless Cellular Networks

1G Cellular Systems

Introduction



All first-generation cellular systems used analog frequency modulation schemes for the

transmission of voice messages with two separate bands for downlink(from B.S to M.S) and

uplink( from M.S to B.S) transmissions. This type of system is known as frequency division

duplex (FDD) Also within these two separate bands FDM is used to increase the system

capacity.

Identification numbers were assigned to the cellular system and the subscriber device. These

ID’s were used to determine the mobile status to perform authentication of the mobile, and to

define the mobile’s telephone number for correct operation of the network.

AMPS characteristics

The AMPS system began operation in the 800Mhz band . The down link band was from 824 to

849 Mhz and the uplink was from 869 to 894Mhz. The channel spacing was set at 30 khz and

each B.S’s transmit and receive frequency was separated by 45Mhz.

AMPS channels

The A and B channels consisted of 333channels, Out of these 333 channels , channels 1-312 in

A band are the traffic channels used for the subscribers calls, and the channels 313-333 in the A

band are used for system control functions, These control channels are used by the mobile and

B.S to set up or tear down calls and other network operation such as handoff.

The B band used channels 334-354 for control channels and channels 355-666 for traffic

channels.



Table of AMPS channel numbers and frequencies

AMPS system components and layout

As shown in fig below early AMPS cellular system consisted of the following components

Radio base stations

Communications links

Mobile switching office



The Base station from the cells that provide coverage to mobile subscribers over a particular

geographic area . The base stations are connected to the MTSO that inturn is connected to the

PSTN.

The MSC performs system control by switching the calls to the correct cells, interfacing with the

PSTN , monitoring system traffic for billing, managing the operation of the entire network.

The B.S provides the interface between the MSC and the mobile subscriber

Typical AMPS operation

The AMPS base station uses the dedicated control channels to send a variety of control

information to idle (turned on but not being used) M.S within its cell, and the M.S uses the

corresponding reverse control channel to communicate with the B.S while in the idle mode.

When the M.S engaged in a voice call , control and signaling information may also be

transmitted over the traffic channel. Fig below depicts the flow of information over these

channels.

The radio link status information is transmitted by the use of supervisory audio tones (SAT) also

known as analog color code. Three SAT frequencies are used : 5970 hz, 6000 hz, 6030 hz, These

tones gives the B,.S and M.S the ability to keep informed about each others transmitting

capabilities and to confirm the success or failure of certain mobile operations



B.S periodically adds a SAT signal to the FVC .

If a M.S is captured by an interfering B.S or B.S is captured by a interfering M.S, this is detected

by the system due to the return of an incorrect SAT & the mobile receiver will be muted.

Similar function is performed by the transmission of DCC.

Additionally a ST of 10khz can be transmitted over a voice channel to confirm orders and signal

various requests.

FOCC transmits 3 data streams in a TDMultiplexed format.

Stream A

Stream A

Busy-idle stream

The B.S in an AMPS system controls the mobile phone by sending order messages, some of

these order messages are

Alert order message: Used to inform the mobile phone there is an incoming call

Audit order message: Used by the B.S to determine if the mobile is still active in the

system.

Change power order message: Used to alert the mobiles RF o/p power

Intercept order message: Used to inform the user that a procedural error has been made

while placing a call.

Maintenance order message: Used to check the operation of the M.S

Reorder order message: Used to indicate that all facilities are in use.

Send called address order message: Used to inform the M.S that it must send a msg to

B.S with dialed digit information

Stop alert order message: Used to inform that it must stop alerting the user.

AMPS security and identification

The mobile’s electronic serial number (ESN)- is provided by the manufacturer

The mobile service providers system identification number (SID)- 15 bit binary number that

are uniquely assigned to cellular system.



The Mobile stations mobile identification number (MIN) -34 bit binary number derived from

the M.S’s 10 digit telephone number , 24 bit are derived from th 7 digit local number & 10 bits

are derived from 3 digit area code.

Summary of basic AMPS operations

Initialization

AMPS ongoing idle mode tasks

Task 1: Respond to overhead information

Task 2: Page match

Task 3: Order

Task 4: Call initialization

Mobile-to-land calls



Handshaking operations

Signaling operations

Service requests

See Figure 2-6

Land-to-mobile and mobile-to-mobile calls

Paging

ID information exchange

Signaling

Control messages

See Figure 2-7



AMPS network operations

Radio base station operations

Base station control operations

Mobile switching center operations



Handoff operations

This operation occurs in a cellular system when a mobile station moves to another cell.

Handshaking operations

Signal strength measurements

MSC operations during handoff

Confirmation messages

See Figure 2-9



Other 1G systems

TACS cellular

NMT cellular

NTT cellular

Other analog cellular systems

Digital AMPS

D-AMPS technology was introduced to increase the capacity of the original AMPS cellular

system.

2G Cellular Systems



Introduction

The basic difference is that 1st generation systems used analog modulation technique for

transmission of subscribers voice over the traffic channel, All subsequent generations

used digital modulation techniques.

Along with this it employed multiplexing

techniques.

1st generation systems relied on SAT & ST to facilitate system operations, 2

nd generation

systems does t use SAT & ST to facilitate system operations. 2nd

generation systems uses

digital encoding & allows for the use of error detection and correction codes.

1st generation systems did not employ digital encryption. 2

nd generation systems uses

digital encoding & allows for the use of error detection and correction codes.

GSM

CDMA

TDMA

PDC and PCS systems

2.5g Cellular Systems

Evolution of mobile data services

CDPD

HSCSD

GPRS

Packet data over CDMA

3G Cellular Systems



Introduction

3G is used to represent a number of cellular systems that have the ability to support high data

services, advanced multimedia services and global roaming.

3G characteristics

3G is able to provide high speed data transfer from packet network and to be able to permit

global roaming.

They need to support advanced digital services.

3G systems must be able to support varying data rates by providing bandwidth on demand to the

subscriber.

3G subscriber devices will be required to support multimedia technologies



3G Cellular Systems

UMTS

Cdma2000

UWC-136/EDGE

4G Cellular Systems and Beyond

4G involves a mix of new concepts and technologies. The goal of 4G is the coverage of wireless

mobile with wireless communication technologies.

Wireless ATM

The All-IP wireless network

IEEE 802.20x



Answers to Problems and Questions

Chapter 1

Section 1.1

1. Time division duplex is a process by which two users share a un-multiplexed bidirectional

telecommunications channel by alternating the transmission of information (i.e. user one uses the

channel and then user two uses the channel). Walkie-talkies are a good example of this type of

operation.

2. An empirical equation for line-of-sight transmission is given by:

4 4total T Rd h h

Where the heights are in meters and the distance is in km.

Therefore, for this case,

4 250 3.28 4 6 / 3.28 4 76.2 4 1.83 34.9 5.4 40.3 totald km

Therefore, the range of the system is in the order of 40 km.

3. Hint: Search www.FCC.gov for the Office of Engineering and Technology (OET) and then

search for Technical Bulletin No. 53.

4. Hint: Do an Internet search of cellular phone systems.

Section 1.2

5. Frequency division duplex operation was the technology used by first generation cellular

systems. Two separate frequency bands were assigned to the operators, one for down-link and

one for up-link transmission.

6. From Table 2-1 one can determine the channel spacing as 30 kHz. One can write an equation

for the up-link frequency of channel N as:

825.030 .030Frequency of Channel N MHz N

http://www.fcc.gov/



Therefore, for this example:

825.030 445 .030

445 838.380

Frequency of Channel N MHz

Frequency of Channel MHz

Similarly, the down-link frequency for Channel N is given by:


Or, 45 MHz higher. Therefore, the up-link frequency for channel 445 on the B side is 838.380

MHz while the down-link frequency is 883.380 MHz. These are non-boundary traffic channels.

7. From Table 2-1 one can determine the channel spacing as 30 kHz. One can write an equation

for the up-link frequency of channel N as:


Therefore, for this example:

825.030 326 .030

326 834.810

Frequency of Channel N MHz

Frequency of Channel MHz

Similarly, the down-link frequency for Channel N is given by:


Or, 45 MHz higher. Therefore, the up-link frequency for Channel 326 on the B side is 834.810

MHz while the down-link frequency is 879.810 MHz. These are non-boundary control channels.

8. The Mobile Station and the Base Station provide the AMPS “air interface.”

9. The AMPS supervisory audio tones are used to transmit radio link status messages over active

voice channels.

10. The sequence of events that occurs when an AMPS cellular telephone is first turned on are as

follows:



The cellular phone tunes to the signal of the strongest control channel in its area. It then goes

into its initialization process, etc.

11. The AMPS cellular service provider’s system identification (SID) number is used to

facilitate/determine the roaming status of the mobile phone.

12. For a mobile terminated call, the mobile answers a “paging” message. For a mobile

originated call, the mobile must request radio resources be allocated to it for the purpose of

setting up a call.

13. The event that triggers an AMPS handoff operation is the measurement of insufficient

received signal strength (RSS) from the mobile at the currently serving base station.

14. Supervisory audio tones and a signaling tone are needed for the AMPS system because once

the voice conversation starts over the traffic channel, there is no other way available to transmit

system control signals.

15. An AMPS channel can support three D-AMPS users through time division multiplexing.

Section 1.3

16. The fundamental difference between first generation and second generation cellular systems

is that first generation systems used analog signal transmission and second generation cellular

systems use digital transmission (modulation) technology.

17. Two advantages of the use of digital encoding for cellular telephone systems is the ability to

transmit data over the system and the ability to use digital encryption techniques to increase

system security.

18. Second generation cellular systems support more than one user per channel by using some

form of multiplexing (i.e. TDM or CDMA, etc)



Section 1.4

19. A 2.5G cellular system is one that provides modest data transmission speeds (i.e. 64 kbps)

that are higher than the data speeds allowed by 2G networks.

20. The first implementation of CDMA cellular (IS-95) could support a packet data transfer rate

of 14.4 kbps maximum.

Section 1.5

21. 3G cellular telephone systems provide the following features: high data transfer rate services,

global roaming, and advanced multimedia services.

22. The UMTS 3G cellular system is the migration path that GSM operators have chosen to

follow to 3G. The CDMA operators will migrate to cdma2000 to provide 3G cellular service.

23. Harmonization is a term used to indicate the eventual adoption of a universal wireless

cellular standard that everyone in the cellular telephone industry will embrace as the industry

moves past 3G to the next generation of cellular systems.

Section 1.6

24. The purposed 4G cellular telephone system will be based on an all-IP architecture with data

transfer rates in the 20 mbps range.

25. The IEEE 802.20 standards project proposes the support of data transfer rates in excess of 1

mbps for vehicular speeds up to 250 km/h over licensed bands below 3.5 GHz.

Section 1.7

26. Regional standards organizations serve various regions of the world. Their function is to

receive developed standards from implementation groups and either approve or disapprove the

standards.



27. National standards organizations are associated with individual nations. Their function is to

provide final approval for a national standard.

28. The function of the International Telecommunications Union is to provide the final approval

for an international standard.

29. The function of the TR-34 Committee is to be responsible for the telecommunications

standards for the satellite industry.

30. The American National Standards Institute (ANSI) puts the final stamp of approval on the

IEEE 802.11 wireless LAN standards.

unit 1 - ajaybolar.weebly.comajaybolar.weebly.com/uploads/1/0/1/0/10106930/wireless_unit_1.pdf ·...

Documents