12 research outputs found
2-User Multiple Access Spatial Modulation
International audienceSpatial modulation (SM) is a recently proposed approach to multiple-input-multiple-output (MIMO) systems which entirely avoids inter-channel interference (ICI) and requires no synchronisation between the transmit antennas, while achieving a spatial multiplexing gain. SM allows the system designer to freely trade off the number of transmit antennas with the signal constellation. Additionally, the number of transmit antennas is independent from the number of receive antennas which is an advantage over other multiplexing MIMO schemes. Most contributions thus far, however, have only addressed SM aspects for a point-to-point communication systems, i.e. the single-user scenario. In this work we seek to characterise the behaviour of SM in the interference limited scenario. The proposed maximumlikelihood (ML) detector can successfully decode incoming data from multiple sources in an interference limited scenario and does not suffer from the near-far problem
Detect-and-forward relaying aided cooperative spatial modulation for wireless networks
A novel detect-and-forward (DeF) relaying aided cooperative SM scheme is proposed, which is capable of striking a flexible tradeoff in terms of the achievable bit error ratio (BER), complexity and unequal error protection (UEP). More specifically, SM is invoked at the source node (SN) and the information bit stream is divided into two different sets: the antenna index-bits (AI-bits) as well as the amplitude and phase modulation-bits (APM-bits). By exploiting the different importance of the AI-bits and the APM-bits in SM detection, we propose three low-complexity, yet powerful relay protocols, namely the partial, the hybrid and the hierarchical modulation (HM) based DeF relaying schemes. These schemes determine the most appropriate number of bits to be re-modulated by carefully considering their potential benefits and then assigning a specific modulation scheme for relaying the message. As a further benefit, the employment of multiple radio frequency (RF) chains and the requirement of tight inter-relay synchronization (IRS) can be avoided. Moreover, by exploiting the benefits of our low-complexity relaying protocols and our inter-element interference (IEI) model, a low-complexity maximum-likelihood (ML) detector is proposed for jointly detecting the signal received both via the source-destination (SD) and relay-destination (RD) links. Additionally, an upper bound of the BER is derived for our DeF-SM scheme. Our numerical results show that the bound is asymptotically tight in the high-SNR region and the proposed schemes provide beneficial system performance improvements compared to the conventional MIMO schemes in an identical cooperative scenario.<br/
Adaptive OFDM Index Modulation for Two-Hop Relay-Assisted Networks
In this paper, we propose an adaptive orthogonal frequency-division
multiplexing (OFDM) index modulation (IM) scheme for two-hop relay networks. In
contrast to the traditional OFDM IM scheme with a deterministic and fixed
mapping scheme, in this proposed adaptive OFDM IM scheme, the mapping schemes
between a bit stream and indices of active subcarriers for the first and second
hops are adaptively selected by a certain criterion. As a result, the active
subcarriers for the same bit stream in the first and second hops can be varied
in order to combat slow frequency-selective fading. In this way, the system
reliability can be enhanced. Additionally, considering the fact that a relay
device is normally a simple node, which may not always be able to perform
mapping scheme selection due to limited processing capability, we also propose
an alternative adaptive methodology in which the mapping scheme selection is
only performed at the source and the relay will simply utilize the selected
mapping scheme without changing it. The analyses of average outage probability,
network capacity and symbol error rate (SER) are given in closed form for
decode-and-forward (DF) relaying networks and are substantiated by numerical
results generated by Monte Carlo simulations.Comment: 30 page
Extension and practical evaluation of the spatial modulation concept
The spatial modulation (SM) concept combines, in a novel fashion, digital modulation and
multiple antenna transmission for low complexity and spectrally efficient data transmission.
The idea considers the transmit antenna array as a spatial constellation diagram with the transmit
antennas as the constellation points. To this extent, SM maps a sequence of bits onto a
signal constellation point and onto a spatial constellation point. The information is conveyed
by detecting the transmitting antenna (the spatial constellation point) in addition to the signal
constellation point. In this manner, inter-channel interference is avoided entirely since transmission
is restricted to a single antenna at any transmission instance. However, encoding binary
information in the spatial domain means that the number of transmit antennas must be a power
of two. To address this constraint, fractional bit encoded spatial modulation (FBE—SM) is
proposed. FBE–SMuses the theory of modulus conversion to facilitate fractional bit rates over
time. In particular, it allows each transmitter to use an arbitrary number of transmit antennas.
Furthermore, the application of SM in a multi-user, interference limited scenario has never
been considered. To this extent, the average bit error rate (ABER) of SM is characterised in
the interference limited scenario. The ABER performance is first analysed for the interference-unaware detector. An interference-aware detector is then proposed and compared with the cost
and complexity equivalent detector for a single–input multiple–output (SIMO) system. The
application of SM with an interference-aware detector results in coding gains for the system.
Another area of interest involves using SM for relaying systems. The aptitude of SM to replace
or supplement traditional relaying networks is analysed and its performance is compared with
present solutions. The application of SM to a fixed relaying system, termed dual-hop spatial
modulation (Dh-SM), is shown to have an advantage in terms of the source to destination ABER
when compared to the classical decode and forward (DF) relaying scheme. In addition, the
application of SM to a relaying system employing distributed relaying nodes is considered and
its performance relative to Dh-SM is presented.
While significant theoretical work has been done in analysing the performance of SM, the implementation
of SM in a practical system has never been shown. In this thesis, the performance
evaluation of SM in a practical testbed scenario is presented for the first time. To this extent,
the empirical results validate the theoretical work presented in the literature
On the Performance of Full-duplex Two-way Relay Channels with Spatial Modulation
In this paper, the spatial modulation (SM) technique
is employed at the source and relay nodes in a full-duplex twoway
relay channel (FD-TWRC) to support spectral-efficient bidirectional
communications while guaranteeing a low cost implementation.
Maximum likelihood (ML) detectors are employed at
each node that is subject to an intrinsic self-loop interference (SI).
We first propose a tight upper bound on the average bit error
probability (ABEP). Then based on the ABEP upper bound, an
asymptotic ABEP expression is derived in the high SNR regime.
Exploiting the asymptotic ABEP, an exact SNR threshold for the
selection between FD-TWRC-SM and half-duplex (HD)-TWRCSM
is derived in a closed form, which sheds light on when it is
beneficial to select the FD (or HD) mode. In addition, the power
allocation (PA) among sources and relay is investigated, through
which an optimal PA factor in terms of ABEP is obtained. All
analytical results derived in this paper are verified by Monte
Carlo simulations, from which some new insights are obtained
on the performance of FD-TWRC-SM
Precoding-Aided Spatial Modulation for the Wiretap Channel with Relay Selection and Cooperative Jamming
We propose in this paper a physical-layer security (PLS) scheme for dual-hop cooperative networks in an effort to enhance the communications secrecy. The underlying model comprises a transmitting node (Alice), a legitimate node (Bob), and an eavesdropper (Eve). It is assumed that there is no direct link between Alice and Bob, and the communication between them is done through trusted relays over two phases. In the first phase, precoding-aided spatial modulation (PSM) is employed, owing to its low interception probability, while simultaneously transmitting a jamming signal from Bob. In the second phase, the selected relay detects and transmits the intended signal, whereas the remaining relays transmit the jamming signal received from Bob. We analyze the performance of the proposed scheme in terms of the ergodic secrecy capacity (ESC), the secrecy outage probability (SOP), and the bit error rate (BER) at Bob and Eve. We obtain closed-form expressions for the ESC and SOP and we derive very tight upper-bounds for the BER. We also optimize the performance with respect to the power allocation among the participating relays in the second phase. We provide examples with numerical and simulation results through which we demonstrate the effectiveness of the proposed scheme
Dual-Hop Spatial Modulation (Dh-SM)
Print ISBN: 978-1-4244-8332-7International audienceIn this paper, we introduce Dual-hop Spatial Modulation (Dh-SM).We look at the effect that Dh-SMhas on the required signal to noise ratio (SNR) at the destination and how it can help alleviate the multi-hop burden in the system. Initial biterror- ratio (BER) results comparing the performance of Dh-SM with orthogonal decode-and-forward (DF) are presented where Dh-SM is shown to have up to a 10 dB SNR advantage
Spatial Modulation for Generalized MIMO:Challenges, Opportunities, and Implementation
A key challenge of future mobile communication research is to strike an attractive compromise between wireless network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, especially on multiple-input-multiple-output (MIMO) technologies. This motivates the proposal of an emerging wireless communications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communications, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Furthermore, it has received sufficient research attention to be implemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field
Mitigation techniques through spatial diversity combining and relay-assisted technology in a turbulence impaired and misaligned free space optical channel.
Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban, 2018.In recent times, spectrum resource scarcity in Radio Frequency (RF) systems is one of the
biggest and prime issues in the area of wireless communications. Owing to the cost of
spectrum, increase in the bandwidth allocation as alternative solution, employed in the recent
past, does no longer offer an effective means to fulfilling high demand in higher data rates.
Consequently, Free Space Optical (FSO) communication systems has received considerable
attention in the research community as an attractive means among other popular solutions to
offering high bandwidth and high capacity compared to conventional RF systems. In
addition, FSO systems have positive features which include license-free operation, cheap and
ease of deployment, immunity to interference, high security, etc. Thus, FSO systems have
been favoured in many areas especially, as a viable solution for the last-mile connectivity
problem and a potential candidate for heterogeneous wireless backhaul network. With these
attractive features, however, FSO systems are weather-dependent wireless channels.
Therefore, it is usually susceptible to atmospheric induced turbulence, pointing error and
attenuation under adverse weather conditions which impose severe challenges on the system
performance and transmission reliability. Thus, before widespread deployment of the system
will be possible, promising mitigation techniques need to be found to address these problems.
In this thesis, the performance of spatial diversity combining and relay-assisted techniques
with Spatial Modulation (SM) as viable mitigating tools to overcome the problem of
atmospheric channel impairments along the FSO communication system link is studied.
Firstly, the performance analysis of a heterodyne FSO-SM system with different diversity
combiners such as Maximum Ratio Combining (MRC), Equal Gain Combining (EGC) and
Selection Combining (SC) under the influence of lognormal and Gamma-Gamma
atmospheric-induced turbulence fading is presented. A theoretical framework for the system
error is provided by deriving the Average Pairwise Error Probability (APEP) expression for
each diversity scheme under study and union bounding technique is applied to obtain their
Average Bit Error Rate (ABER). Under the influence of Gamma-Gamma turbulence, an
APEP expression is obtained through a generalized infinite power series expansion approach
and the system performance is further enhanced by convolutional coding technique.
Furthermore, the performance of proposed system under the combined effect of misalignment
and Gamma-Gamma turbulence fading is also studied using the same mathematical approach.
Moreover, the performance analysis of relay-assisted dual-hop heterodyne FSO-SM system
with diversity combiners over a Gamma-Gamma atmospheric turbulence channel using
Decode-and-Forward (DF) relay and Amplify-and-Forward (AF) relay protocols also is
presented. Under DF dual-hop FSO system, power series expansion of the modified Bessel
function is used to derive the closed-form expression for the end-to-end APEP expressions
for each of the combiners under study over Gamma-Gamma channel, and a tight upper bound
on the ABER per hop is given. Thus, the overall end-to-end ABER for the dual-hop FSO
system is then evaluated. Under AF dual-hop FSO system, the statistical characteristics of AF
relay in terms of Moment Generating Function (MGF), Probability Density Function (PDF)
and Cumulative Distribution Function (CDF) are derived for the combined Gamma-Gamma
turbulence and/or pointing error distributions channel in terms of Meijer-G function. Based
on these expressions, the APEP for each of the under studied combiners is determined and the
ABER for the system is given by using union bounding technique. By utilizing the derived
ABER expressions, the effective capacity for the considered system is then obtained.
Furthermore, the performance of a dual-hop heterodyne FSO-SM asymmetric RF/FSO
relaying system with MRC as mitigation tools at the destination is evaluated. The RF link
experiences Nakagami-m distribution and FSO link is subjected to Gamma-Gamma
distribution with and/or without pointing error. The MGF of the system equivalent SNR is
derived using the CDF of the system equivalent SNR. Utilizing the MGF, the APEP for the
system is then obtained and the ABER for the system is determined.
Finally, owing to the slow nature of the FSO channel, the Block Error Rate (BLER)
performance of FSO Subcarrier Intensity Modulation (SIM) system with spatial diversity
combiners employing Binary Phase Shift Keying (BPSK) modulation over Gamma-Gamma
atmospheric turbulence with and without pointing error is studied. The channel PDF for MRC
and EGC by using power series expansion of the modified Bessel function is derived.
Through this, the BLER closed-form expressions for the combiners under study are obtained
Spatial modulation: theory to practice
Spatial modulation (SM) is a transmission technique proposed for multiple–input multiple–
output (MIMO) systems, where only one transmit antenna is active at a time, offering an increase
in the spectral efficiency equal to the base–two logarithm of the number of transmit
antennas. The activation of only one antenna at each time instance enhances the average bit
error ratio (ABER) as inter–channel interference (ICI) is avoided, and reduces hardware complexity,
algorithmic complexity and power consumption. Thus, SM is an ideal candidate for
large scale MIMO (tens and hundreds of antennas). The analytical ABER performance of SM
is studied and different frameworks are proposed in other works. However, these frameworks
have various limitations. Therefore, a closed–form analytical bound for the ABER performance
of SM over correlated and uncorrelated, Rayleigh, Rician and Nakagami–m channels is proposed
in this work. Furthermore, in spite of the low–complexity implementation of SM, there
is still potential for further reductions, by limiting the number of possible combinations by exploiting
the sphere decoder (SD) principle. However, existing SD algorithms do not consider
the basic and fundamental principle of SM, that at any given time, only one antenna is active.
Therefore, two modified SD algorithms tailored to SM are proposed. It is shown that the proposed
sphere decoder algorithms offer an optimal performance, with a significant reduction of
the computational complexity. Finally, the logarithmic increase in spectral efficiency offered
by SM and the requirement that the number of antennas must be a power of two would require
a large number of antennas. To overcome this limitation, two new MIMO modulation systems
generalised spatial modulation (GNSM) and variable generalised spatial modulation (VGSM)
are proposed, where the same symbol is transmitted simultaneously from more than one transmit
antenna at a time. Transmitting the same data symbol from more than one antenna reduces
the number of transmit antennas needed and retains the key advantages of SM.
In initial development simple channel models can be used, however, as the system develops it
should be tested on more realistic channels, which include the interactions between the environment
and antennas. Therefore, a full analysis of the ABER performance of SM over urban
channel measurements is carried out. The results using the urban measured channels confirm
the theoretical work done in the field of SM. Finally, for the first time, the performance of SM
is tested in a practical testbed, whereby the SM principle is validated