Lamiae
Sommaire: Implementation of radio over fiber ofdm system including a novel optical null steering beamformer
List of Figures
List of Acronyms
CHAPTER 1: INTRODUCTION
1.1. Introduction
1.2. Beam-Steering Concept
1.3. Beamforming in the Electrical Domain
1.4. Optical Beamforming
1.5. Null-Steering
Beamforming
1.6. About This Work
CHAPTER 2 DESIGN AND FABRICATION OF THE ANTENNA ARRAY
2.1. Introduction
2.2. Uniformly Excited Linear Arrays
2.2.1. Pattern Formulations
2.2.2. Half Power Beamwidth
2.2.3. Grating Lobes
2.3. Microstrip Patches
2.3.1. Advantages and Disadvantages
2.3.2. Feed Techniques
2.3.3 . Transmission-Line Model
2.4. Microstrip Antenna Design and Fabrication
2.4.1. Substrate Selection
2.4.2. Radiator Element Design
2.4.3. Impedance Matching
2.4.4. Array Fabrication
2.4.5. Experimental Results for our Designed and Fabricated Array
2.5. Conclusion
CHAPTER 3 OPTICAL BEAMFORMING TECHNIQUES
3.t. Introduction
3.2. Fiber Bragg Grating Technology
3.3. Optical Beamforming Methods
3.3.1. TTD Beamforming Using a Fiber Grating Prism
3.3.2. TTD Beamforming Using CFBG and Multiwavelength Tunable Laser
3.3.3. TTD Beamforming Using Tunable CFBG
3.4. Independent Optical Control over the Phase and Amplitude
3.4.1. tPu and rP/, Control based on Gires-Toumois Filters
3.4.2. A New Design Approach
3.5. Effect of Beamformer Filters on Signal Quality and Radiation Pattern
3.5.1. IEEE 802.11 Modulation Format for WLAN Application
3.5.2. Experimental Verification of the Beamformer Effect on Signal Quality
3. Bearn Squint
3.6. Conclusion
CHAPTER 4 ROF LINK IMPLEMENTATION AND RADIATION PATTERN MEASUREMENT
4.1. Introduction
4.2. ROF Link Architecture and Hardware
4.2.1. Multi-carrier Laser Source
4.2.2. RF-Gain Improvernent and Distortion Compensation by Ernploying MZ Modulator Bias Optimization
4.2.3. FBG Actuators
4.2.4. Appropriate Optical Detection Stage
4.3. Link Calibration
4.4. Radiation Pattern Simulation and Measurement
4.5. Source of Errors in the Optical Domain
4.6. DG-HF Advantages and Disadvantages
4.7. Conclusion
CHAPTER 5 CONCLUSION
REFERENCES
Extrait du mémoire implementation of radio over fiber ofdm system including a novel optical null steering beamformer
Chapter 1: Introduction
1.1. Introduction
The field of wireless communications is growing at an explosive rate, covering many tech nical areas such as digital communication, electronic circuit design, antenna and microwave engineering, wireless networks and recently even optical communication. The worldwide activities in this industry are a sign of its huge economic significance. The demand for wireless communi~ation is anticipated to expand steadily in the number of users, new ser vices and the accessible coverage range [1-2]. This demand and the scarcity of the radio frequency (RF) spectrum lead to the need to develop technologies to overcome its limitations.
Implementation of radio over
The application of antenna arrays to mobile communication systems has been suggested recently to overcome the difficulties of limited bandwidth. Many studies show that antenna arrays improve system performance by increasing channel capacity, extending coverage range, tailoring beam shape and steering multiple beams to track many users. The use of arrays also reduces multipath fading, co-channel interference, system complexity, cost and bit-error-rate (BER). Adaptive antennas and the algorithms to control them are vital for new high-capacity communication networks [1] , [3].
In general, antennas may be classified as omnidirectional, directional and phased arra y. An omnidirectional antenna, also çalled as an isotropic antenna, has identical gain in aIl directions while a directional antenna has more gain in certain directions and conseguently les s in others. A phased-array-antenna (P AA) uses an array of simple antennas, such as omnidi rectional antennas, and combines the signaIs on these antennas to shape the array output.
Each antenna in the array is known as an eleme.nt of the array. The direction where the maximum gain appears is controlled by adjusting the phase between different antennas; the signaIs are added in-phase in the direction where maximum gain is required. This proper phase manipulation is called beam-steering and will result in an array gain equal to the sum of the gains of aIl individual antennas. Taking advantage of beam-steering theory, P AA can transmit data in a narrow beam towards users in one particular direction, and then switch the beam towards another user in a different direction. As a result, using the same frequen cy band and allocating different beam slots for different users provides more service ca pacity with the same bandwidth.
Implementation of radio over
The ability of the P AA to control and optimize the radiation pattern and other transmission parameters translates to other advantages such as obviating mechanical components, in creasing the propagation range, and boosting system security. For beam-steering applications, there is no need to rotate the array physicaIly. Therefore the PAA is able to change the beam direction much faster than mechanically-steered antennas while providing greater reliability. The transmission range is increased since the PAA radiated power is more fo cused (because of the higher directivity) in the direction of the user, instead of being pro pagated over a broad region. FinaIly, wireless network security is boosted, as only potential hackers in the same direction as the user can intercept the transmitted signal.
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