BER & SNR

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IMPROVEMENT OF BER & SNR OF WIRELESS COMMUNICATION USING MAXIMAL RATIO COMBINING TECHNIQUE

Submitted By

Md. Alamgir Hossain ID: ECE 090300139

Rehenuma Tarannum ID: ECE 090100130 Supervised By

Ashraful Arefin Assistant Professor Department of Electrical & Electronic Engineering Northern University Bangladesh

December 2014 Department of Electronics and Communication Engineering

NORTHERN UNIVERSITY BANGLADESH

DECLARATION We hereby declare that the work presented in this thesis is the outcome of the research work performed by us under the supervision of Ashraful Arefin, Assistant Professor, Department of Electrical & Electronic Engineering, Northern University Bangladesh.

We also declare that no part of this project and thereof has been or is being submitted elsewhere for the award of any degree or Diploma.

Signature

Md. Alamgir Hossain ID: ECE 090300139

Rehenuma Tarannum ID: ECE 090100130

Countersigned

Ashraful Arefin Assistant Professor Department of Electrical & Electronic Engineering Northern University Bangladesh

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APPROVAL This is to certify that the Project and Thesis on “Improvement of BER & SNR of Wireless Communication using Maximal Ratio Combining Technique” by Md. Alamgir Hossain, ID: ECE 090300139, and Rehenuma Tarannum, ID: ECE 090100130, has been carried out under our supervision. The project has been carried out in partial fulfillment of the requirements for the degree of Bachelor of Science (B.Sc.) in Electronics and Communication Engineering in the year of 2014 and has been approved as to its style and contents.

Board of Examination

Ashraful Arefin (Supervisor) Assistant Professor Department of Electrical & Electronic Engineering Northern University Bangladesh

Lecturer Department of Electrical & Electronic Engineering Northern University Bangladesh

Engr. Md. Badiuzzaman Associate Professor and Head Department of Electronics & Communication Engineering Northern University Bangladesh

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ABSTRACT Communication is very important in this world. We have two types of communication such as wired communication and wireless communication. Wireless communication is divided into mobile communications and fixed wireless communications. It has gained exponential growth of subscribers during last 10 to 12 years and continues to expand everyday with new technology invention. To reduce the fading problem of wireless communication we have different type’s diversity techniques. In the new generation of mobile communication systems, high data transmission rate and low bit error probability have been common requirements. Higher performance of the mobile terminals is needed. In diversity technique Maximum Ratio Combining (MRC) is the one of the most important method. In MRC all the branches are used simultaneously. Each of the branch signals is weighted with a gain factor proportional to its own SNR. Co-phasing and summing is done for adding up the weighted branch signals in phase. Maximal ratio combining will always perform better than either selection diversity or equal gain combining because it is an optimum combiner. The information on all channels is used with this technique to get a more reliable received signal.

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ACKNOWLEDGEMENT Thanks to Almighty, the Creator and Sustainer who has given us strength and opportunity to complete the Thesis, “Improvement of BER & SNR of Wireless Communication using Maximal Ratio Combining Technique”.

We would like to express our gratitude and appreciation our supervisor, Ashraful Arefin, for his guidance in the execution of the thesis, for keeping us on our toes, and for his kind understanding. Our acknowledgment also goes out to the thesis presentation assessor.

We would like to thanks our Honorable Head, Faculty of Science and Engineering also. Finally, we express our greetings to all our friends and teachers who have influenced and encouraged of us to develop this project.

The Authors December 2014

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TABLE OF CONTENTS Declaration ……………………………………………………………...................................... Approval……………………………………………………………………………………….. Abstract………………………………………………………………….................................... Acknowledgment…………………………………………......................................................... Table of Contents………………………………………………………………………............. List of Figure………………………………………………………….......................................

i ii iii iv v viii

Chapter 1: Introduction 1.1 1.2

Introduction…………………………………………………………………............. Overview of Combining Method…………………………………………………….

01 02

1.3

Maximum Ratio Combining (MRC)…………………………………………...........

02

1.4

General Block Diagram of Antenna Diversity Scheme…….......................................

03

1.5

Outline of Thesis……………………………………………………………..............

03

Chapter 2: Wireless Communication 2.1

Overview of Wireless Communication………………………………………………

04

2.2

Characteristics of Wireless Communication Channel……….....................................

05

2.3

First Generation Technologies……………………………………………….............

07

2.4

Second Generation Technologies…………………………………………………….

08

2.5

Second-plus Generation Technologies……………………………………….............

08

2.6

Third Generation Technologies………………………………....................................

09

2.7

Fourth Generation Technologies………………………………..................................

13

2.8

Cellular CDMA…………………………………………………................................

15

2.9

Synchronous DS: Downlink………………………………………………….............

16

2.10

IS-95 Forward link (‘down’)…………………………………....................................

16

2.11

Challenges of Wireless Communication……………………………………………..

16

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2.12

Channel Spreading…………………………………………………………………...

18

2.13

Fading…………………………………………………………………………...........

19

2.14

Fading Channels………………………………………………………………...........

20

2.15

Classification of Fading Channels……………………………………………………

21

Chapter 3: Diversity and Diversity Techniques 3.1

Diversity……………………………………………………………………………..

23

3.2

Diversity Requirements………………………………………...................................

23

3.3

Motivation of Diversity………………………………………………………...........

23

3.4

Types of Diversity……………………………………………………………...........

24

3.5

Diversity Techniques…………………………………………...................................

28

3.6

Diversity Combining Techniques……………………………………………………

29

Chapter 4: Maximal Ratio Combining 4.1

Principle of Maximal Ratio Combining……………………………………………...

33

4.2

Assumptions…………………………………………………………………............

33

4.3

Combining Techniques for Reducing Random Phase……………………….............

34

4.4

Array and Diversity Gain…………………………………………………………….

34

4.5

Diversity Combining…………………………………………………………...........

35

4.6

Highlights of Channel Coding……………………………………………….............

35

4.7

Main Points of MRCs………………………………………………………………..

35

4.8

BER Performance improvement using diversity with maximal ratio combining……

36

4.9

BER Performance improvement using diversity with maximal ratio combining……

38

4.10

Improvement of SNR using diversity with maximal ratio combining……………….

40

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Chapter 5: Conclusion 5.1

Conclusion…………………………………………………………………………...

44

5.2

Future Work………………………………………………………………………….

44

References...….…………………………………………………….................…………………………...46 Appendix A……………………………………………………………………………………………….47 Appendix B……………………………………………………………………………………………….48 Appendix C……………………………………………………………………………………………….49

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LIST OF FIGURES 1.1

General block diagram of antenna diversity scheme…………………………...........

03

2.1

Seamless Multimedia Networks with Mobility and Freedom from Tethers…............

04

2.2

1st Generation most common mobile phone service…………………………...........

08

2.3

Second Generation Technologies…………………………………………………….

09

2.4

Satellite orbits………………………………………………………………………...

11

2.5

Satellite categories………………………………………………................................

11

2.6

Satellite orbit altitudes…………………………………………………………..........

11

2.7

Satellites in geostationary orbit………………………………………………............

12

2.8

Orbits for global positioning system (GPS) satellites………………………………..

12

2.9

LEO satellite system………………………………………………………………….

12

2.10

3G Evolution to All-IP Network……………………………………………………..

11

2.11

A basic RF/IF block diagram showing a typical RF/IF section for a transceiver……

14

2.12

A high level block diagram of transceiver baseband processing section in 4G wireless design……………………………………………………………………….

15

2.13

Phase shifts…………………………………………………………………………...

19

2.14

Slow fading versus fast fading……………………………………………………….

22

3.1

Frequency Diversity………………………………………………………………….

24

3.2

Time Diversity………………………………………………………………………..

25

3.3

Space Diversity………………………………………………………………………

26

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3.4

Receiver Space Diversity…………………………………………………………….

27

3.5

Transmitter Space Diversity………………………………………………………….

27

3.6

Diversity Combining Techniques…………………………………………………….

29

3.7

Switching Combining Technique…………………………………………………….

30

3.8

Switching Combining Technique…………………………………………………….

31

3.9

Selection Combining Technique……………………………………………………..

31

3.10

Maximal Combining Ratio……………………………………………………...........

33

4.1

Maximal Combining Ratio……………………………………………………...........

34

4.2

BER Performance improvement using diversity with maximal ratio combining…...

39

4.3

BER Performance improvement using diversity with maximal ratio combining……

41

4.4

Improvement of SNR using diversity with maximal ratio combining……………….

43

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Chapter 1 Introduction 1.1. Introduction Three techniques are used independently or in tandem to improve receiver signal quality equalization compensates for ISI created by multipath with time dispersive channels (W>BC).Linear equalization, nonlinear equalization diversity also compensates for fading channel impairments, and is usually implemented by using two or more receiving antennas. To overcome the effect of fading dips, diversity techniques are introduced. Usually the diversity is applied in receiver site providing wireless link improvement at relatively low cost. The key idea of diversity is artificially creating several independent replicas of the original path. If one path undergoes a deep fade, another independent path may have a strong signal. By having more than one path to select from under some selection schemes, both the instantaneous and average SNRs at the receiver may be improved. Each path or channel is called a diversity branch. Time varying Fading. The phenomenon is described as the constructive/destructive interference between signals arriving at the same antenna via different paths, and hence with different delays and phases, resulting in random fluctuations of the signal level at the receiver. When destructive interference Occurs, the signal power can be significantly reduced and the phenomenon is called as Fading. Deep fades that may occur at particular time or frequency or in space result in severe degradation of the quality of the signal at the receiver making it impossible to decode or detect. Multipath fading arises due to the non-coherent combination of signals arriving at the receiver antenna. Theoretically, the most effective, the most effective may to mitigate multipath fading in wireless channel is transmitter power control. If channel conditions as experienced by the receiver on one side of the link are known at the transmitter on the other side, the transmitter can preprocessed the signal in order to overcome the effects of the channel. But there are some problems in this method .They are the dynamic range of transmitter and if the uplink and down link frequencies are different then transmitter does not have the knowledge of channel experienced by the transmitter. Hence, the channel information has to be fed back from the receiver to the transmitter.

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Overview of Combining Method The introduction of diversity and diversity technique are described in chapter-01.The idea of diversity is to combine several copies of the transmitted signal, which undergo independent fading, to increase the overall received power. Different types of diversity call for different combining methods. Here, we review several common diversity combining methods. Other effective technique is to provide some form of diversity. In the new generation of mobile communication systems, high data transmission rate and low bit error probability have been common requirements. Higher performance of the mobile terminals is needed, accomplishing by increasing capacity or reducing multipath interference. The issue of signal fading in a multi-path environment still stands as a major problem which can be overcome using antenna diversity techniques. The implementation of antenna diversity can increase the channel capacity and reduce the multi-path interference at the expense of adding extra equipment (antenna, combiner) to the receiver but no extra spectrum is consumed.

Maximum Ratio Combining (MRC) In diversity technique Maximum Ratio Combining (MRC) is the one of the most important method. In MRC, all the branches are used simultaneously. Each of the branch signals is weighted with a gain factor proportional to its own SNR. Co-phasing and summing is done for adding up the weighted branch signals in phase. The gain associated with the ith branch is decided by the SNR of the corresponding branch. Both branches are weighted by their respective instantaneous voltage-to-noise ratios. The branches are then co-phased prior to summing in order to insure that all branches are added in phase for maximum diversity gain. The summed signals are then used as the received signal and connected to the demodulator. The advantage is that improvements can be achieved with this configuration even when both branches are completely correlated.

The disadvantage of maximal ratio is that it is complicated and requires accurate estimates of the instantaneous signal level and average noise power to achieve optimum performance with this combining scheme. Maximal ratio combining will always perform better than either selection diversity or equal gain combining because it is an optimum combiner. The information on all channels is used with this technique to get a more reliable received signal.

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1.2. General Block Diagram of Antenna Diversity Scheme

Figure: 1.1: General block diagram of antenna diversity scheme.

1.3. Outline of Thesis Diversity techniques are the useful methods to reduce fading problem in wireless communications. The best diversity techniques can be selected by analyzing and comparing the different types of diversity techniques. Moreover, different diversity techniques can be combined and used in wireless communication systems to get the best result to mitigate fading problems. The introduction of diversity and diversity technique are described in chapter-01. Description of wireless communications has given in chapter-02. Useful Diversity and Diversity techniques were described in chapter 3. And Maximum Ratio Combining is fully described in chapter 4.It‟s important to combine two or more diversity techniques to get full advantage of diversity techniques. Some diversity combining techniques were described in this chapter

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Chapter 2 Wireless Communication 2.1. Overview of Wireless Communication Wireless Communication Cellular has standards such as first generation cellular system which is an analogue system, second and third generation digital cellular systems. There is one intermediate technology which is called second generation-plus communications system. It supports high speed data transfer over today’s digital cellular systems. Table1 shows the main future of the above technologies. The basics of wireless communication systems are described in chapter 2, based on their services such as speech communication, data transmission, etc. The generations of communication technologies such as 1st generation, 2nd generation, 2nd –plus generation, 3rd generation and 4th generation are described in this chapter. Multiple access formats for wireless communication and their operations are also described briefly at the last section of this chapter.

Wireless Data Vision

Fig: 2.1: Seamless Multimedia Networks with Mobility and Freedom from Tethers.

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Why Wireless Communication?  Freedom from wires  No cost of installing wires or rewiring  No bunches of wires running here and there  “Auto magical” instantaneous communications  without physical connection setup, e.g., Bluetooth,  Wi-Fi

 Global Coverage  Communications can reach where wiring is  infeasible or costly, e.g., rural areas, old buildings,  battlefield, vehicles, outer space (through  Communication Satellites)

 Stay Connected  Roaming allows flexibility to stay connected, anywhere and any time  Rapidly growing market attests to public need for mobility and uninterrupted access.

 Flexibility  Services reach you wherever you go (Mobility).E.g. you don‟t have to go to your lab to check your mail

 Connect to multiple devices simultaneously (no physical connection required)  Increasing dependence on telecommunication services for business and personal reasons

 Consumers and businesses are willing to pay for it  Basic Mantra: Stay connected –anywhere, anytime.

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2.2. Characteristics of Wireless Communication Channel  Wireless Communication has made a tremendous impact on the lifestyle of a human being. Wireless Network provides high speed mobility for voice as well as data traffic.  In radio communications, wireless communication channel works as transmission medium.  Characteristics of wireless communication depend on transmitting signal or information riding on radio.  Radio means electromagnetic wave here. Hence, the information suffers attenuation effects by several reasons which are called fading of radio waves.  These attenuation effects can vary with time. This variation depends on user mobility, which makes wireless a challenging medium of communication.  Uncertainty or randomness is the main characteristic of wireless communication.  Types of randomness are two: randomness in users‟ transmission channels and randomness in users‟ geographical locations.  These factors of user in the wireless network systems lead a signal to random signal attenuation independently through users.  Modulation of electromagnetic (radio) waves is utilized by wireless communication with a carrier frequency. The frequencies vary from a few hundred MHz to several GHz but it depends on the system.  As a result, the behavior of the wireless communication channel is a function of the radio (electromagnetic waves) propagation effects in an environment.

Wireless Channel Impairments:  Noise: Thermal noise (modeled as AWGN).  Path Loss: The loss in power as the radio signal propagates.  Shadowing: Due to the presence of fixed obstacles in the radio path.  Fading: Combines the effect of multiple propagation paths, rapid movement of mobile units and reflectors.

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Table 1: Main futures of cellular technologies First Generation

Second Generation

Second + Generation

Third Generation

Analog

Digital data

Digital data

Digital data

transmission

transmission

transmission

transmission

Mainly for talking

Mainly talking

Mainly talking

talking and video

Voice bands data

Digital data

Increasing digital

Mainly digital data

data Circuit switched

Local systems

Circuit switched

Global roaming facility

Increasingly packet

Mainly packet

switched over IP

switched over IP

network

network

Global roaming

Global roaming

facility

facility with full flexibility

2.3. First Generation Technologies First-generation (1G) mobile communication systems is a basic analog radio communication systems that established the first cellular radio infrastructure. The main problem of 1G mobile communication systems for cellular service providers is that it has less capacity to handle the sheer number of users which demand voice services. Circuit switched connections are used in the analog cellular networks for data transfer. However, the performance of the radio link for data transport is considered marginally because of the limitations creates by the nature of the analog technology. The dynamics of the radio channels like dropouts, fade of signals, and multi-path (multipath can be tolerated during a voice connection), can be disastrous to the subscribers for mobile data transport. Using standard modems with some adaptation can sustain Subscriber data rates of 2400 bits/s or less to the cellular network. Generally, Due to limited available capacities, limitations of data recovery, low security, and the high cost of use for many applications, the analog cellular infrastructure systems are not so efficient of sending data. Some of the widely used standards are discussed as following.AMPS is an analog cellular phone system using FDMA.

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1st Generation most common mobile phone service since early 80’s

Fig: 2.2: 1st Generation most common mobile phone service.

2.4. Second Generation Technologies Second-Generation (2G) mobile communication systems are the most common in the wireless communication industries currently. Digital technologies are used in 2G to provide many advantages for both the voice-based and the data-based mobile communication systems. Available facilities in this technology are the increased system capacity, increased security against eavesdropping, superior cell hand-off, and better radio signal recovery under different conditions. In addition, rather than quality speech these technologies support services such as fax, short messaging service (SMS), and roaming for mobile subscribers.

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Fig: 2.3: Second Generation Technologies.

2.5. Second-plus Generation Technologies The second generation technologies capable to transfer data at the rate of only up to 14.4 Kbps. The high data speeds are needed for video and graphical image transmissions. But this speed is not available on the most mobile phone systems today. Providing such capabilities the technologies are required a highly complex and robust platform that will not be available in most of the countries next few years, according to researchers. An intermediate step to the next generation technologies is second-plus generation or 2.5G technologies. Supporting data transfer rates is 57.6 Kbps or higher in these technologies and offer subscribers access to the internet at speeds that are comparable to a wire-line Integrated Services Digital Network (ISDN) connection or even faster than ISDN sometimes. These technologies include HSCSD (High speed Circuit Switched Data), GPRS (General Packet Radio Services) and EDGE (Enhanced Data Rates for Global Evolution).

2.6. Third Generation Technologies Two common but effective limitations of the second generation communication networks are low bandwidth and limited network capacity. These two limitations impact negatively to the users‟ experience and the reliability of the service. To overcome these limitations, it was very important to initiate a new technology. Third generation or 3G technology took foot step to 9

initiate at such a time and it is a new technological revolution that will offer far more bandwidth and greater data and voice call capacity than today‟s digital mobile networks capable. It is a next big step in wireless communication technology for mobile network development with its goal being full inter-operability and inter-working of mobile communication systems. The 3G will unite the disparate standards those are used in today‟s second generation wireless networks.

Advantages of 3G  New radio spectrum to relieve overcrowding in existing systems.  More bandwidth, security, and reliability.  Interoperability between service providers.  Fixed and variable data rates.  Asymmetric data rates.  Backward compatibility of devices with existing networks.  Always-online devices. 3G will use IP connectivity, IP is packet based (not circuit based)

 Rich multimedia services. Disadvantages of 3G

 

The cost of upgrading base stations and cellular infrastructure to 3G is very high. Requires different handsets and there is the issue of handset availability. 3G Handsets will be a complex product. Roaming and making both data/voice work has not yet been demonstrated. Also the higher power requirements (more bits with the same energy/bit) demand a larger handset, shorter talk time, and larger batteries)

 

Base stations need to be closer to each other (more cost). Tremendous spectrum-license costs, network deployment costs, handset subsidies to subscribers, etc.



Wireless service providers in Germany and Britain who won spectrum licenses in auctions, paid astronomical prices for them. As a result, they have little

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 Satellite orbits

Fig: 2.4: Satellite orbits.

 Satellite categories

Fig: 2.5: Satellite categories.

 Satellite orbit altitudes

Fig: 2.6: Satellite orbit altitudes. 11

 Satellites in geostationary orbit

Fig: 2.7: Satellites in geostationary orbit.

 Orbits for global positioning system (GPS) satellites

Fig: 2.8: Orbits for global positioning system (GPS) satellites.

 LEO satellite system

Fig: 2.9: LEO satellite system. 12

 3G Evolution to All-IP Network

Fig: 2.10: 3G Evolution to All-IP Network.

2.7. Fourth Generation Technologies Growth of science is so fast and wireless communication is not exceptional from it. After a lot of research and implementation works the network providers started to provide 3G services. But some researchers could not be satisfied with this limit of wireless communication. As a result they started to work on more upgraded wireless services which are called 4G. This 4G technology will take mobile communication step forward in integrate radio and television transmissions for all users with flexibility and it will unite world‟s phone standards into one technology with very speed. There are two key elements which are required to deliver a legitimate 4G network. First is the ability to roam across different wireless network standards with the one device; and the second, and most obvious, is a higher level of bandwidth. Why Move Towards 4G?  Limitation to meet expectations of applications like multimedia, full motion video, wireless teleconferencing Wider Bandwidth  Difficult to move and interoperate due to different standards hampering global mobility and service portability  Primarily Cellular (WAN) with distinct LANs‟; need a new integrated network 13

 Limitations in applying recent advances in spectrally more efficient modulation schemes  Need all digital network to fully utilize IP and converged video and data Key 4G Mobility Concepts 

Mobile IP  VoIP  Ability to move around with the same IP address  IP tunnels  Intelligent Internet



Presence Awareness Technology  Knowing who is on line and where



Radio Router  Bringing IP to the base station



Smart Antennas  Unique spatial metric for each transmission.

4G RF/IF Architecture Example

Fig: 2.11: A basic RF/IF block diagram showing a typical RF/IF section for a transceiver. 14

4G Transreceiver Processing Example

Fig: 2.12: A high level block diagram of transceiver baseband processing section in 4G wireless design.

Mobile–Short History  70-th – first mobile networks (analog) – 1G  90-th – digital mobile networks – (2G, GSM)  Beginning of current decade – (2,5G, EGSM)  Expectations – 3G (broadband access, HBRs in air interface)  Exponential grows (some figures)

2.8. Cellular CDMA Advantages of CDMA  Soft handoff  Soft capacity  Multipath tolerance: lower fade margins needed  No need for frequency planning. Near-far Effect and Power Control:  CDMA performance is optimized if all signals are received with the same power.  Frequent update needed.  Performance is sensitive to imperfections of only a dB.

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2.9. Synchronous DS: Downlink In the „forward‟ or „downlink‟ (base-to-mobile): all signals originate at the base station and travel over the same path. One can easily exploit orthogonality of user signals. It is fairly simple to reduce mutual interference from users within the same cell, by assigning orthogonal Walsh-Hadamard codes.

2.10. IS-95 Forward link (‘down’)

     

Logical channels for pilot, paging sync and traffic. Chip rate 1.2288 M chip/s = 128 times 9600 bit/sec Length 64 Walsh-Hadamard (for orthogonality users). Maximum length code sequence (for effective spreading and multipath resistance. Transmit bandwidth 1.25 MHz Convolution coding with rate 1/2.

2.11. Challenges of Wireless Communication 

High Data Rate, seamless and high mobility requirements.



Spectral efficiency challenge (2-10 b/s/Hz).



Frequency selectivity due to large bandwidth requirements



High System Capacity.



Reliable Communications.

First Challenge  Efficient Hardware  Low power Transmitters, Receivers  Low Power Signal Processing Tools  Efficient use of finite radio spectrum  Cellular frequency reuse, medium access control protocols,  Integrated services  Voice, Data, Multimedia over a single network  Service differentiation, priorities, resource sharing

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Multimedia Requirements Voice

Data

Video

Delay