2,351 research outputs found
Approximation of L\"owdin Orthogonalization to a Spectrally Efficient Orthogonal Overlapping PPM Design for UWB Impulse Radio
In this paper we consider the design of spectrally efficient time-limited
pulses for ultrawideband (UWB) systems using an overlapping pulse position
modulation scheme. For this we investigate an orthogonalization method, which
was developed in 1950 by Per-Olov L\"owdin. Our objective is to obtain a set of
N orthogonal (L\"owdin) pulses, which remain time-limited and spectrally
efficient for UWB systems, from a set of N equidistant translates of a
time-limited optimal spectral designed UWB pulse. We derive an approximate
L\"owdin orthogonalization (ALO) by using circulant approximations for the Gram
matrix to obtain a practical filter implementation. We show that the centered
ALO and L\"owdin pulses converge pointwise to the same Nyquist pulse as N tends
to infinity. The set of translates of the Nyquist pulse forms an orthonormal
basis or the shift-invariant space generated by the initial spectral optimal
pulse. The ALO transform provides a closed-form approximation of the L\"owdin
transform, which can be implemented in an analog fashion without the need of
analog to digital conversions. Furthermore, we investigate the interplay
between the optimization and the orthogonalization procedure by using methods
from the theory of shift-invariant spaces. Finally we develop a connection
between our results and wavelet and frame theory.Comment: 33 pages, 11 figures. Accepted for publication 9 Sep 201
Nonresonant self-injection seeding of a gain-switched diode laser
We demonstrate step-tunable single-mode operation of a gain-switched diode laser by nonresonant self-injection seeding from an uncoated glass slide used as an external cavity reflector. A spectral bandwidth reduction from 11 mn to 0.05 nm and wavelength tunability has been achieved for picosecond (near-transform-limited) pulses with little effect on other laser characteristics. Good agreement with numerical simulations based on a compound-cavity laser model is also reported
On the theoretical aspects of multi-carrier spread spectrum systems.
by Tsan-Fai Ho.Thesis (M.Phil.)--Chinese University of Hong Kong, 1996.Includes bibliographical references (leaves 64-68).Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Review on spread spectrum communications --- p.1Chapter 1.2 --- The spread spectrum techniques --- p.2Chapter 1.2.1 --- Direct Sequence (DS) Systems --- p.2Chapter 1.2.2 --- Frequency Hopping (FH) Systems --- p.2Chapter 1.2.3 --- Time Hopping (TH) Systems --- p.4Chapter 1.2.4 --- Hybrid Systems --- p.4Chapter 1.3 --- Existing Applications of the spread spectrum systems --- p.5Chapter 1.4 --- Organization of the thesis --- p.6Chapter 2 --- The Concept of Duality --- p.7Chapter 2.1 --- Multi-Carrier Systems - An Overview --- p.7Chapter 2.2 --- Orthogonal Frequency Division Multiplexing --- p.8Chapter 2.2.1 --- Bandwidth Efficiency --- p.9Chapter 2.2.2 --- Spectral Efficiency --- p.10Chapter 2.2.3 --- Effects of fading --- p.11Chapter 2.3 --- Applications of OFDM in multiple access --- p.13Chapter 2.3.1 --- ST-CDMA --- p.13Chapter 2.3.2 --- MC-DS-CDMA --- p.14Chapter 2.3.3 --- OFDM-CDMA --- p.15Chapter 2.4 --- Duality - Time-Frequency Interrelation --- p.16Chapter 3 --- Performance of Multi-Carrier CDMA System --- p.17Chapter 3.1 --- System Model --- p.17Chapter 3.2 --- Performance Analysis --- p.20Chapter 3.2.1 --- Gaussian Channel --- p.20Chapter 3.2.2 --- Fading Channel --- p.24Chapter 3.3 --- Performance with Pulse Shape --- p.33Chapter 3.4 --- Appendix --- p.34Chapter 4 --- Signal Design Criteria for MC-CDMA System --- p.36Chapter 4.1 --- Existence of Signal Distortion --- p.37Chapter 4.2 --- Measures of the Signal Envelope Fluctuation --- p.38Chapter 4.3 --- Complementary Sequences --- p.41Chapter 4.4 --- Crest Factors --- p.42Chapter 4.4.1 --- Time-limited Pulse --- p.43Chapter 4.4.2 --- Ideally Band-Limited Pulses --- p.43Chapter 4.4.3 --- Shaped Pulses --- p.45Chapter 4.5 --- Spectrally Efficient Complementary (SEC) Sequences --- p.48Chapter 4.6 --- Construction of Spectrally Efficient Complementary(SEC) Sequences --- p.50Chapter 4.7 --- Generalized Multiphase Spectrally Efficient Complementary Sequences --- p.55Chapter 5 --- Summary and Future Extensions --- p.58Chapter 5.1 --- Summary of the Results --- p.58Chapter 5.2 --- Topics for Future Research --- p.59AppendixChapter A --- Exhaustive search of MPSEC sequences --- p.61Chapter B --- Papers derived from this thesis --- p.63Bibliography --- p.6
Land Mobile Radio Systems - A Tutorial Exposition
An in-depth tutorial on land mobile radio system
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