51 research outputs found
Efficient Spectrum Sharing in the Presence of Multiple Narrowband Interference
In this paper, we study the spectrum usage efficiency by applying wideband
methods and systems to the existing analog systems and applications. The
essential motivation of this work is to define the prospective coexistence
between analog FM and digital Spread Spectrum systems in an efficient way
sharing the same frequency band. The potential overlaid Spread Spectrum (SS)
system can spectrally coincide within the existing narrowband Frequency
Modulated (FM) broadcasting system upon several limitations, originating a key
motivation for the use of the FM radio frequency band in many applications,
encompassing wireless personal and sensors networks. The performance of the SS
system due to the overlaying analog FM system, consisting of multiple
narrowband FM stations, is investigated in order to derive the relevant bit
error probability and maximum achievable data rates. The SS system uses direct
sequence (DS) spreading, through maximal length pseudorandom sequences with
long spreading codes. The SS signal is evaluated throughout theoretical and
simulation-based performance analysis, for various types of spreading
scenarios, for different carrier frequency offset ({\Delta}f) and
signal-to-interference ratios, in order to derive valuable results for future
developing and planning of an overlay scenario
Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application
With the explosive growth of bandwidth requirement in optical fiber communication
networks, optical code division multiple access (OCDMA) has witnessed tremendous
achievements as one of the promising technologies for optical access networks over the
past decades. In an OCDMA system, optical code processing is one of the key
techniques. Rapid optical code reconfiguration can improve flexibility and security of
the OCDMA system. This thesis focuses on advanced optical modulations and
en/decoding techniques for applications in fast reconfigurable OCDMA systems and
secure optical communications.
A novel time domain spectral phase encoding (SPE) scheme which can rapidly
reconfigure the optical code and is compatible with conventional spectral domain phase
en/decoding by using a pair of dispersive devices and a high speed phase modulator is
proposed. Based on this scheme, a novel advanced modulation technique that can
simultaneously generate both the optical code and the differential-phase-shift-keying
(DPSK) data using a single phase modulator is experimentally demonstrated. A
symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using
a similar setup for both the transmitter and receiver is further proposed, based on which
a bit-by-bit optical code scrambling and DPSK data modulation technique for secure
optical communications has been successfully demonstrated. By combining optical
encoding and optical steganography, a novel approach for secure transmission of time
domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over
public wavelength-division multiplexing (WDM) network has also been proposed and
demonstrated.
To enable high speed operation of the time domain SPE/SPD scheme and enhance the
system security, a rapid programmable, code-length variable bit-by-bit optical code
shifting technique is proposed. Based on this technique, security improvements for
OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable
optical codes of up to 1024-chip have been achieved.
Finally, a novel tunable two-dimensional coherent optical en/decoder which can
simultaneously perform wavelength hopping and spectral phase encoding based on
coupled micro-ring resonator is proposed and theoretically investigated. The techniques
included in this thesis could be potentially used for future fast reconfigurable and secure
optical code based communication systems
Radar and Communication Co-existence: an Overview
Increased amounts of bandwidth are required to guarantee both
high-quality/high-rate wireless services (4G and 5G) and reliable sensing
capabilities such as automotive radar, air traffic control, earth geophysical
monitoring and security applications. Therefore, co-existence between radar and
communication systems using overlapping bandwidths has been a primary
investigation field in recent years. Various signal processing techniques such
as interference mitigation, pre-coding or spatial separation, and waveform
design allow both radar and communications to share the spectrum. This article
reviews recent work on co-existence between radar and communication systems,
including signal models, waveform design and signal processing techniques. Our
goal is to survey contributions in this area in order to provide a primary
starting point for new researchers interested in these problems.Comment: Submitted to IEEE Signal Processing Magazin
Dynamic Spectrum Refarming with Overlay for Legacy Devices
The explosive growth in data traffic is resulting in a spectrum crunch
forcing many wireless network operators to look towards refarming their 2G
spectrum and deploy more spectrally efficient Long Term Evolution (LTE)
technology. However, mobile network operators face a challenge when it comes to
spectrum refarming because 2G technologies such as Global System for Mobile
(GSM) is still widely used for low bandwidth machine-to-machine (M2M) devices.
M2M devices typically have long life cycles, e.g. smart meters, and it is
expensive to migrate these devices to newer technology since a truck roll will
typically be required to the site where a device is deployed. Furthermore, with
cost of 2G modules several times less than that of LTE, even newly deployed M2M
devices tend to adopt 2G technology. Nevertheless, operators are keen to either
force their 2G M2M customers to migrate so that they can refarm the spectrum or
set aside a portion of the 2G spectrum for continuing operating 2G and only
refarm the rest for LTE. In this paper we propose a novel solution to provide
GSM connectivity within an LTE carrier through an efficient overlay by
reserving a few physical resource blocks for GSM. With this approach, operators
can refarm their 2G spectrum to LTE efficiently while still providing some GSM
connectivity to their low data rate M2M customers. Furthermore, spectrum can be
dynamically shared between LTE and GSM. An approach similar to that proposed in
this paper can also be applied for other narrow band technology overlays over
LTE.Comment: 12 pages, 14 figures, submitted to IEEE Transactions on Wireless
Communication
Investigation of the impact of fibre impairments and SOA-based devices on 2D-WH/TS OCDMA codes
In seeking efficient last-mile solutions for high-capacity, optical code division multiple access (OCDMA) emerges as a promising alternative high-speed optical network that can securely support a multitude of simultaneous users without requiring extensive equipment. This multiplexing technique has recently been the subject of comprehensive research, highlighting its potential for facilitating high-bandwidth multi-access networking. When contrasted with techniques such as wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM), OCDMA offers a more effective and equitable split of available fibre bandwidth among the users. This thesis presents my research focused on the incoherent OCDMA under the influence of optical fibre impairments that uses picosecond multiwavelength pulses to form two-dimensional wavelength hopping time-spreading (2D-WH/TS) incoherent OCDMA codes.
In particular, self-phase modulation, temperature induced fibre dispersion, chromatic dispersion, as well as the impact of semiconductor optical amplifier SOA devices deployment on 2D-WH/TS OCDMA code integrity were investigated. These aspects were investigated using a 17-km long bidirectional fibre link between Strathclyde and Glasgow University. In particular, I investigated the impact of temporal skewing among OCDMA code carriers and the importance of selecting small range of wavelengths as code carriers where wide range manifest high dependency on wavelength. This wavelength dependency is exploited furthermore to measure the induced temperature dispersion coefficient accurately and economically. I have conducted experiments to characterise the impact of SOA-device on 2D OCDMA code carries which is evaluated under different bias conditions. This evaluation addressed the potential challenges and ramifications of the gain recovery time of SOA and its wavelength dependency with respect to gain ratio and self-phase modulation (SPM). The OCDMA code was built using multiplexers and delay lines to create a 2D OCDMA code to allow studying the impact of deploying a SOA under different conditions on each wavelength.
The concept described above is then extended to the investigation of the SOA’s impact on a 2D-WH/TS OCDMA prime code under high bias current/gain conditions. The overall performance of two different 2D-WH/TS OCDMA systems deploying the SOA was also calculated. I have also investigated the possibility of manipulating chirp in 2D-WH/TS incoherent OCDMA to counteract the self-phase modulation-induced red shift by using single mode fibre and lithium crystals. I have investigated the performance of the picosecond code based optical signal when subjected to temperature variations similar to that experience by most buried fibre systems. I have proposed and demonstrated a novel technique, which I examined analytically and experimentally, that utilises a SOA at the transmitter to create a new code with a new wavelength hopping and spreading time sequences to achieve a unique physical improved secure incoherent OCDMA communication method. A novel fully automated tuneable compensation testbed is also proposed of an autonomous dispersion management in a WH/TS incoherent OCDMA system. The system proposed manipulates the chirp of OCDMA code carriers to limit chromatic dispersion detrimental effect on transmission systems.In seeking efficient last-mile solutions for high-capacity, optical code division multiple access (OCDMA) emerges as a promising alternative high-speed optical network that can securely support a multitude of simultaneous users without requiring extensive equipment. This multiplexing technique has recently been the subject of comprehensive research, highlighting its potential for facilitating high-bandwidth multi-access networking. When contrasted with techniques such as wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM), OCDMA offers a more effective and equitable split of available fibre bandwidth among the users. This thesis presents my research focused on the incoherent OCDMA under the influence of optical fibre impairments that uses picosecond multiwavelength pulses to form two-dimensional wavelength hopping time-spreading (2D-WH/TS) incoherent OCDMA codes.
In particular, self-phase modulation, temperature induced fibre dispersion, chromatic dispersion, as well as the impact of semiconductor optical amplifier SOA devices deployment on 2D-WH/TS OCDMA code integrity were investigated. These aspects were investigated using a 17-km long bidirectional fibre link between Strathclyde and Glasgow University. In particular, I investigated the impact of temporal skewing among OCDMA code carriers and the importance of selecting small range of wavelengths as code carriers where wide range manifest high dependency on wavelength. This wavelength dependency is exploited furthermore to measure the induced temperature dispersion coefficient accurately and economically. I have conducted experiments to characterise the impact of SOA-device on 2D OCDMA code carries which is evaluated under different bias conditions. This evaluation addressed the potential challenges and ramifications of the gain recovery time of SOA and its wavelength dependency with respect to gain ratio and self-phase modulation (SPM). The OCDMA code was built using multiplexers and delay lines to create a 2D OCDMA code to allow studying the impact of deploying a SOA under different conditions on each wavelength.
The concept described above is then extended to the investigation of the SOA’s impact on a 2D-WH/TS OCDMA prime code under high bias current/gain conditions. The overall performance of two different 2D-WH/TS OCDMA systems deploying the SOA was also calculated. I have also investigated the possibility of manipulating chirp in 2D-WH/TS incoherent OCDMA to counteract the self-phase modulation-induced red shift by using single mode fibre and lithium crystals. I have investigated the performance of the picosecond code based optical signal when subjected to temperature variations similar to that experience by most buried fibre systems. I have proposed and demonstrated a novel technique, which I examined analytically and experimentally, that utilises a SOA at the transmitter to create a new code with a new wavelength hopping and spreading time sequences to achieve a unique physical improved secure incoherent OCDMA communication method. A novel fully automated tuneable compensation testbed is also proposed of an autonomous dispersion management in a WH/TS incoherent OCDMA system. The system proposed manipulates the chirp of OCDMA code carriers to limit chromatic dispersion detrimental effect on transmission systems
High Fidelity Satellite Navigation Receiver Front-End for Advanced Signal Quality Monitoring and Authentication
Over the last several years, interest in utilizing foreign satellite timing and navigation (satnav) signals to augment GPS has grown. Doing so is not without risks; foreign satnav signals must be vetted and determined to be trustworthy before use in military applications. Advanced signal quality monitoring methods can help to ensure that only authentic and reliable satnav signals are utilized. To effectively monitor and authenticate signals, the front-end must impress as little distortions upon the received signal as possible. The purpose of this study is to design, fabricate, and test the performance of a high-fidelity satnav receiver front-end for advanced monitoring of foreign and domestic space vehicle signals
Spectrum Sharing Between Cellular and Mobile Ad Hoc Networks: Transmission-Capacity Trade-Off
Spectrum sharing between wireless networks improves the efficiency of
spectrum usage, and thereby alleviates spectrum scarcity due to growing demands
for wireless broadband access. To improve the usual underutilization of the
cellular uplink spectrum, this paper studies spectrum sharing between a
cellular uplink and a mobile ad hoc networks. These networks access either all
frequency sub-channels or their disjoint sub-sets, called spectrum underlay and
spectrum overlay, respectively. Given these spectrum sharing methods, the
capacity trade-off between the coexisting networks is analyzed based on the
transmission capacity of a network with Poisson distributed transmitters. This
metric is defined as the maximum density of transmitters subject to an outage
constraint for a given signal-to-interference ratio (SIR). Using tools from
stochastic geometry, the transmission-capacity trade-off between the coexisting
networks is analyzed, where both spectrum overlay and underlay as well as
successive interference cancelation (SIC) are considered. In particular, for
small target outage probability, the transmission capacities of the coexisting
networks are proved to satisfy a linear equation, whose coefficients depend on
the spectrum sharing method and whether SIC is applied. This linear equation
shows that spectrum overlay is more efficient than spectrum underlay.
Furthermore, this result also provides insight into the effects of different
network parameters on transmission capacities, including link diversity gains,
transmission distances, and the base station density. In particular, SIC is
shown to increase transmission capacities of both coexisting networks by a
linear factor, which depends on the interference-power threshold for qualifying
canceled interferers.Comment: 23 pages, 7 figures, submitted for publicatio
Optical code-division multiple access system and optical signal processing
This thesis presents our recent researches on the development of coding devices, the
investigation of security and the design of systems in the optical cod-division multiple
access (OCDMA) systems. Besides, the techniques of nonlinear signal processing used
in the OCDMA systems fire our imagination, thus some researches on all-optical signal
processing are carried out and also summarized in this thesis.
Two fiber Bragg grating (FBG) based coding devices are proposed. The first coding
device is a superstructured FBG (SSFBG) using ±π/2-phase shifts instead of
conventional 0/π-phase shifts. The ±π/2-phase-shifted SSFBG en/decoders can not only
conceal optical codes well in the encoded signals but also realize the reutilization of
available codes by hybrid use with conventional 0/Ï€-phase-shifted SSFBG en/decoders.
The second FBG based coding device is synthesized by layer-peeling method, which
can be used for simultaneous optical code recognition and chromatic dispersion
compensation.
Then, two eavesdropping schemes, one-bit delay interference detection and
differential detection, are demonstrated to reveal the security vulnerability of differential
phase-shift keying (DPSK) and code-shift keying (CSK) OCDMA systems.
To address the security issue as well as increase the transmission capacity, an
orthogonal modulation format based on DPSK and CSK is introduced into the OCDMA
systems. A 2 bit/symbol 10 Gsymbol/s transmission system using the orthogonal
modulation format is achieved. The security of the system can be partially guaranteed.
Furthermore, a fully-asynchronous gigabit-symmetric OCDMA passive optical
network (PON) is proposed, in which a self-clocked time gate is employed for signal
regeneration. A remodulation scheme is used in the PON, which let downstream and
upstream share the same optical carrier, allowing optical network units source-free. An
error-free 4-user 10 Gbit/s/user duplex transmission over 50 km distance is reazlied.
A versatile waveform generation scheme is then studied. A theoretical model is
established and a waveform prediction algorithm is summarized. In the demonstration,
various waveforms are generated including short pulse, trapezoidal, triangular and
sawtooth waveforms and doublet pulse.
ii
In addition, an all-optical simultaneous half-addition and half-subtraction scheme is
achieved at an operating rate of 10 GHz by using only two semiconductor optical
amplifiers (SOA) without any assist light.
Lastly, two modulation format conversion schemes are demonstrated. The first
conversion is from NRZ-OOK to PSK-Manchester coding format using a SOA based
Mach-Zehnder interferometer. The second conversion is from RZ-DQPSK to RZ-OOK
by employing a supercontinuum based optical thresholder
- …