| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

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Introduction to Wireless

Communications

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 1/8 |

Communications

Propagation Summary

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

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Mobile Radio Propagation - Outline

• Introduction

• Radiowave Propagation Challenges– Free Space Attenuation

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 2/8 |

– Free Space Attenuation

– Multipath and Shadowing

– Time Delay Spread

• Radiowave Propagation Mitigation Strategies

• Conclusion

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

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Radiowave Propagation - Summary

Irreducible Error

Caused by two main mechanisms:

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 3/8 |

• Firstly, for the narrowband scenario:

DOPPLER

• Secondly, for the wideband scenario:

DELAY SPREAD

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

_______________________________________________________________________________

Radiowave Propagation - Summary

Doppler

– Amplitude and phase variations of fading channel produce error rate that is directly proportional to users

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 4/8 |

produce error rate that is directly proportional to users speed and frequency of transmission.

– As data rate increases, problems due to Doppler reduce although these are then replaced by difficulties of delay spread.

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

_______________________________________________________________________________

Radiowave Propagation - Summary

Narrowband vs. Wideband

• Data rate at which a channel can be considered wideband varies depending on environment. E.g

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 5/8 |

– GSM is regarded as wideband, data rate = 270 kb/s

– DECT is considered narrowband, data rate = 1.1 Mb/s

– Major difference is the typical rms delay spread:

• DECT delay spread = 100ns. GSM delay spread = 4µs

• If the rms delay spread is normalized to the data rate then DECT = 0.11 (100ns×1.1Mb/s). GSM = 1.08 (4µs×270kb/s).

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

_______________________________________________________________________________

Radiowave Propagation - Summary

Delay Spread

• Generally, normalized delay spread < 0.1 � narrowband:

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 6/8 |

– majority of irreducible errors will arise as a result of the time

variations in the channel.

• Once normalized delay spread > 0.1 � channel starts to

exhibit wideband characteristics

– equalization may be required to maintain a low overall error rate

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

_______________________________________________________________________________

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 7/8 |

| University of Dar es Salaam | Department of Electronics and Telecommunications Engineering |

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Relation

between study

on propagation

and wireless

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| TE 412 Introduction to Wireless Communications | Christine Mwase | 10/03/2014 | Slide 8/8 |

and wireless

communication

system design