259 research outputs found
Full Rate L2-Orthogonal Space-Time CPM for Three Antennas
To combine the power efficiency of Continuous Phase Modulation (CPM) with
enhanced performance in fading environments, some authors have suggested to use
CPM in combination with Space-Time Codes (STC). Recently, we have proposed a
CPM ST-coding scheme based on L2-orthogonality for two transmitting antennas.
In this paper we extend this approach to the three antennas case. We
analytically derive a family of coding schemes which we call Parallel Code
(PC). This code family has full rate and we prove that the proposed coding
scheme achieves full diversity as confirmed by accompanying simulations. We
detail an example of the proposed ST codes that can be interpreted as a
conventional CPM scheme with different alphabet sets for the different transmit
antennas which results in a simplified implementation. Thanks to
L2-orthogonality, the decoding complexity, usually exponentially proportional
to the number of transmitting antennas, is reduced to linear complexity
L2 OSTC-CPM: Theory and design
The combination of space-time coding (STC) and continuous phase modulation
(CPM) is an attractive field of research because both STC and CPM bring many
advantages for wireless communications. Zhang and Fitz [1] were the first to
apply this idea by constructing a trellis based scheme. But for these codes the
decoding effort grows exponentially with the number of transmitting antennas.
This was circumvented by orthogonal codes introduced by Wang and Xia [2].
Unfortunately, based on Alamouti code [3], this design is restricted to two
antennas. However, by relaxing the orthogonality condition, we prove here that
it is possible to design L2-orthogonal space-time codes which achieve full rate
and full diversity with low decoding effort. In part one, we generalize the
two-antenna code proposed by Wang and Xia [2] from pointwise to
L2-orthogonality and in part two we present the first L2-orthogonal code for
CPM with three antennas. In this report, we detail these results and focus on
the properties of these codes. Of special interest is the optimization of the
bit error rate which depends on the initial phase of the system. Our simulation
results illustrate the systemic behavior of these conditions
L2 Orthogonal Space Time Code for Continuous Phase Modulation
To combine the high power efficiency of Continuous Phase Modulation (CPM)
with either high spectral efficiency or enhanced performance in low Signal to
Noise conditions, some authors have proposed to introduce CPM in a MIMO frame,
by using Space Time Codes (STC). In this paper, we address the code design
problem of Space Time Block Codes combined with CPM and introduce a new design
criterion based on L2 orthogonality. This L2 orthogonality condition, with the
help of simplifying assumption, leads, in the 2x2 case, to a new family of
codes. These codes generalize the Wang and Xia code, which was based on
pointwise orthogonality. Simulations indicate that the new codes achieve full
diversity and a slightly better coding gain. Moreover, one of the codes can be
interpreted as two antennas fed by two conventional CPMs using the same data
but with different alphabet sets. Inspection of these alphabet sets lead also
to a simple explanation of the (small) spectrum broadening of Space Time Coded
CPM
Separable Implementation of L2-Orthogonal STC CPM with Fast Decoding
In this paper we present an alternative separable implementation of
L2-orthogonal space-time codes (STC) for continuous phase modulation (CPM). In
this approach, we split the STC CPM transmitter into a single conventional CPM
modulator and a correction filter bank. While the CPM modulator is common to
all transmit antennas, the correction filter bank applies different correction
units to each antenna. Thereby desirable code properties as orthogonality and
full diversity are achievable with just a slightly larger bandwidth demand.
This new representation has three main advantages. First, it allows to easily
generalize the orthogonality condition to any arbitrary number of transmit
antennas. Second, for a quite general set of correction functions that we
detail, it can be proved that full diversity is achieved. Third, by separating
the modulation and correction steps inside the receiver, a simpler receiver can
be designed as a bank of data independent inverse correction filters followed
by a single CPM demodulator. Therefore, in this implementation, only one
correlation filter bank for the detection of all transmitted signals is
necessary. The decoding effort grows only linearly with the number of transmit
antennas
Development of a Nanosatellite Software Defined Radio Communications System
Communications systems designed with application-specific integrated circuit (ASIC) technology suffer from one very significant disadvantage - the integrated circuits do not possess the ability of programmability. However, Software Defined Radio’s (SDR’s) integrated with Field Programmable Gate Arrays (FPGA) provide an opportunity to update the communication system on nanosatellites (which are physically difficult to access) due to their capability of performing signal processing in software. SDR signal processing is performed in software on reprogrammable elements such as FPGA’s. Applying this technique to nanosatellite communications systems will optimize the operations of the hardware, and increase the flexibility of the system.
In this research a transceiver algorithm for a nanosatellite software defined radio communications is designed. The developed design is capable of modulation of data to transmit information and demodulation of data to receive information. The transceiver algorithm also works at different baud rates. The design implementation was successfully tested with FPGA-based hardware to demonstrate feasibility of the transceiver design with a hardware platform suitable for SDR implementation
Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy
In the first part of this thesis millimetre-wave interferometric imagers are considered
for short-range applications such as concealed weapons detection. Compared to real
aperture systems, synthetic aperture imagers at these wavelengths can provide improvements
in terms of size, cost, depth-of-field (DoF) and imaging flexibility via digitalrefocusing.
Mechanical scanning between the scene and the array is investigated to
reduce the number of antennas and correlators which drive the cost of such imagers.
The tradeoffs associated with this hardware reduction are assessed before to jointly
optimise the array configuration and scanning motion. To that end, a novel metric is
proposed to quantify the uniformity of the Fourier domain coverage of the array and is
maximised with a genetic algorithm. The resulting array demonstrates clear improvements
in imaging performances compared to a conventional power-law Y-shaped array.
The DoF of antenna arrays, analysed via the Strehl ratio, is shown to be limited even
for infinitely small antennas, with the exception of circular arrays.
In the second part of this thesis increased DoF in optical systems with Wavefront
Coding (WC) is studied. Images obtained with WC are shown to exhibit artifacts
that limit the benefits of this technique. An image restoration procedure employing a
metric of defocus is proposed to remove these artifacts and therefore extend the DoF
beyond the limit of conventional WC systems. A transmission optical microscope was
designed and implemented to operate with WC. After suppression of partial coherence
effects, the proposed image restoration method was successfully applied and extended
DoF images are presented
A Tutorial on Environment-Aware Communications via Channel Knowledge Map for 6G
Sixth-generation (6G) mobile communication networks are expected to have
dense infrastructures, large-dimensional channels, cost-effective hardware,
diversified positioning methods, and enhanced intelligence. Such trends bring
both new challenges and opportunities for the practical design of 6G. On one
hand, acquiring channel state information (CSI) in real time for all wireless
links becomes quite challenging in 6G. On the other hand, there would be
numerous data sources in 6G containing high-quality location-tagged channel
data, making it possible to better learn the local wireless environment. By
exploiting such new opportunities and for tackling the CSI acquisition
challenge, there is a promising paradigm shift from the conventional
environment-unaware communications to the new environment-aware communications
based on the novel approach of channel knowledge map (CKM). This article aims
to provide a comprehensive tutorial overview on environment-aware
communications enabled by CKM to fully harness its benefits for 6G. First, the
basic concept of CKM is presented, and a comparison of CKM with various
existing channel inference techniques is discussed. Next, the main techniques
for CKM construction are discussed, including both the model-free and
model-assisted approaches. Furthermore, a general framework is presented for
the utilization of CKM to achieve environment-aware communications, followed by
some typical CKM-aided communication scenarios. Finally, important open
problems in CKM research are highlighted and potential solutions are discussed
to inspire future work
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