27 research outputs found
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
On the energy efficiency of spatial modulation concepts
Spatial Modulation (SM) is a Multiple-Input Multiple-Output (MIMO) transmission technique
which realizes low complexity implementations in wireless communication systems. Due the
transmission principle of SM, only one Radio Frequency (RF) chain is required in the transmitter.
Therefore, the complexity of the transmitter is lower compared to the complexity of
traditional MIMO schemes, such as Spatial MultipleXing (SMX). In addition, because of the
single RF chain configuration of SM, only one Power Amplifier (PA) is required in the transmitter.
Hence, SM has the potential to exhibit significant Energy Efficiency (EE) benefits. At
the receiver side, due to the SM transmission mechanism, detection is conducted using a low
complexity (single stream) Maximum Likelihood (ML) detector. However, despite the use of a
single stream detector, SM achieves a multiplexing gain.
A point-to-point closed-loop variant of SM is receive space modulation. In receive space modulation,
the concept of SMis extended at the receiver side, using linear precoding with Channel
State Information at the Transmitter (CSIT). Even though receive space modulation does not
preserve the single RF chain configuration of SM, due to the deployed linear precoding, it
can be efficiently incorporated in a Space Division Multiple Access (SDMA) or in a Virtual
Multiple-Input Multiple-Output (VMIMO) architecture.
Inspired by the potentials of SM, the objectives of this thesis are the evaluation of the EE of
SM and its extension in different forms of MIMO communication. In particular, a realistic
power model for the power consumption of a Base Station (BS) is deployed in order to assess
the EE of SM in terms of Mbps/J. By taking into account the whole power supply of a BS and
considering a Time Division Multiple Access (TDMA) multiple access scheme, it is shown that
SM is significantly more energy efficient compared to the traditional MIMO techniques. In
the considered system setup, it is shown that SM is up to 67% more energy efficient compared
to the benchmark systems. In addition, the concept of space modulation is researched at the
receiver side. Specifically, based on the union bound technique, a framework for the evaluation
of the Average Bit Error Probability (ABEP), diversity order, and coding gain of receive space
modulation is developed. Because receive space modulation deploys linear precoding with
CSIT, two new precoding methods which utilize imperfect CSIT are proposed. Furthermore, in
this thesis, receive space modulation is incorporated in the broadcast channel. The derivation of
the theoretical ABEP, diversity order, and coding gain of the new broadcast scheme is provided.
It is concluded that receive space modulation is able to outperform the corresponding traditional
MIMO scheme. Finally, SM, receive space modulation, and relaying are combined in order
to form a novel virtual MIMO architecture. It is shown that the new architecture practically
eliminates or reduces the problem of the inefficient relaying of the uncoordinated virtual MIMO
space modulation architectures. This is undertaken by using precoding in a novel fashion. The
evaluation of the new architecture is conducted using simulation and theoretical results
A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals
Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility
Scaling up virtual MIMO systems
Multiple-input multiple-output (MIMO) systems are a mature technology that has been incorporated
into current wireless broadband standards to improve the channel capacity and link
reliability. Nevertheless, due to the continuous increasing demand for wireless data traffic new
strategies are to be adopted. Very large MIMO antenna arrays represents a paradigm shift in
terms of theory and implementation, where the use of tens or hundreds of antennas provides
significant improvements in throughput and radiated energy efficiency compared to single antennas
setups. Since design constraints limit the number of usable antennas, virtual systems can
be seen as a promising technique due to their ability to mimic and exploit the gains of multi-antenna
systems by means of wireless cooperation. Considering these arguments, in this work,
energy efficient coding and network design for large virtual MIMO systems are presented.
Firstly, a cooperative virtual MIMO (V-MIMO) system that uses a large multi-antenna transmitter
and implements compress-and-forward (CF) relay cooperation is investigated. Since
constructing a reliable codebook is the most computationally complex task performed by the
relay nodes in CF cooperation, reduced complexity quantisation techniques are introduced. The
analysis is focused on the block error probability (BLER) and the computational complexity for
the uniform scalar quantiser (U-SQ) and the Lloyd-Max algorithm (LM-SQ). Numerical results
show that the LM-SQ is simpler to design and can achieve a BLER performance comparable to
the optimal vector quantiser. Furthermore, due to its low complexity, U-SQ could be consider
particularly suitable for very large wireless systems.
Even though very large MIMO systems enhance the spectral efficiency of wireless networks,
this comes at the expense of linearly increasing the power consumption due to the use of multiple
radio frequency chains to support the antennas. Thus, the energy efficiency and throughput
of the cooperative V-MIMO system are analysed and the impact of the imperfect channel state
information (CSI) on the system’s performance is studied. Finally, a power allocation algorithm
is implemented to reduce the total power consumption. Simulation results show that
wireless cooperation between users is more energy efficient than using a high modulation order
transmission and that the larger the number of transmit antennas the lower the impact of the
imperfect CSI on the system’s performance.
Finally, the application of cooperative systems is extended to wireless self-backhauling heterogeneous
networks, where the decode-and-forward (DF) protocol is employed to provide a
cost-effective and reliable backhaul. The associated trade-offs for a heterogeneous network
with inhomogeneous user distributions are investigated through the use of sleeping strategies.
Three different policies for switching-off base stations are considered: random, load-based and
greedy algorithms. The probability of coverage for the random and load-based sleeping policies
is derived. Moreover, an energy efficient base station deployment and operation approach
is presented. Numerical results show that the average number of base stations required to support
the traffic load at peak-time can be reduced by using the greedy algorithm for base station
deployment and that highly clustered networks exhibit a smaller average serving distance and
thus, a better probability of coverage
Detection and Resource Allocation Algorithms for Cooperative MIMO Relay Systems
Cooperative communications and multiple-input multiple-output (MIMO) communication systems are important topics in current research that will play key roles in the future of wireless networks and standards. In this thesis, the various challenges in accurately detecting and estimating data signals and allocating resources in the cooperative systems are investigated.
Firstly, we propose a cross-layer design strategy that consists of a cooperative maximum likelihood (ML) detector operating in conjunction with link selection for a cooperative MIMO network. Two new link selection schemes are proposed, along with an iterative detection and decoding (IDD) scheme that utilises channel coding techniques. Simulation results show the performance and potential gains of the proposed schemes.
Secondly, a successive interference cancellation (SIC) detector is proposed for a MIMO system that has dynamic ordering based on a reliability ordering (RO), and an alternative multiple feedback (MF) candidate cancellation method. The complexity of these schemes is analysed and a hard decision feedback IDD system is also proposed. Results show that the proposed detector can give gains over existing schemes for a minimal amount of extra complexity.
Lastly, a detector is proposed that is based upon the method of widely linear (WL) filtering and a multiple branch (MB) SIC, for an overloaded, multi-user cooperative MIMO system. The use of WL methods is explained, and a new method of choosing cancellation branches for an MB detector is proposed with an analysis of the complexity required. A list-based IDD system is developed, and simulation results show that the proposed detector can operate in an overloaded system and provide improved performance gains
Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications
Code-division multiplexing
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 395-404).(cont.) counterpart. Among intra-cell orthogonal schemes, we show that the most efficient broadcast signal is a linear superposition of many binary orthogonal waveforms. The information set is also binary. Each orthogonal waveform is generated by modulating a periodic stream of finite-length chip pulses with a receiver-specific signature code that is derived from a special class of binary antipodal, superimposed recursive orthogonal code sequences. With the imposition of practical pulse shapes for carrier modulation, we show that multi-carrier format using cosine functions has higher bandwidth efficiency than the single-carrier format, even in an ideal Gaussian channel model. Each pulse is shaped via a prototype baseband filter such that when the demodulated signal is detected through a baseband matched filter, the resulting output samples satisfy the Generalized Nyquist criterion. Specifically, we propose finite-length, time overlapping orthogonal pulse shapes that are g-Nyquist. They are derived from extended and modulated lapped transforms by proving the equivalence between Perfect Reconstruction and Generalized Nyquist criteria. Using binary data modulation format, we measure and analyze the accuracy of various Gaussian approximation methods for spread-spectrum modulated (SSM) signalling ...We study forward link performance of a multi-user cellular wireless network. In our proposed cellular broadcast model, the receiver population is partitioned into smaller mutually exclusive subsets called cells. In each cell an autonomous transmitter with average transmit power constraint communicates to all receivers in its cell by broadcasting. The broadcast signal is a multiplex of independent information from many remotely located sources. Each receiver extracts its desired information from the composite signal, which consists of a distorted version of the desired signal, interference from neighboring cells and additive white Gaussian noise. Waveform distortion is caused by time and frequency selective linear time-variant channel that exists between every transmitter-receiver pair. Under such system and design constraints, and a fixed bandwidth for the entire network, we show that the most efficient resource allocation policy for each transmitter based on information theoretic measures such as channel capacity, simultaneously achievable rate regions and sum-rate is superposition coding with successive interference cancellation. The optimal policy dominates over its sub-optimal alternatives at the boundaries of the capacity region. By taking into account practical constraints such as finite constellation sets, frequency translation via carrier modulation, pulse shaping and real-time signal processing and decoding of finite-length waveforms and fairness in rate distribution, we argue that sub-optimal orthogonal policies are preferred. For intra-cell multiplexing, all orthogonal schemes based on frequency, time and code division are equivalent. For inter-cell multiplexing, non-orthogonal code-division has a larger capacity than its orthogonalby Ceilidh Hoffmann.Ph.D
Interference analysis of broadband space and terrestrial fixed radio communications systems in the frequency range 12 to 30 GHz
This thesis presents research into the principles of spectrum sharing analysis
methods developed for investigating implications of interference from
Nongeostationary Fixed Satellite Service (NGSO FSS) systems into Geostationary
Fixed Satellite Service (GSO FSS) systems and Fixed Service (FS) terrestrial radio
systems operating or planned for operation in the 12 to 30 GHz frequency range.
Spectrum sharing is an effective way of allowing new services to operate without
cancelling the existing allocations in the same part of the spectrum. The use of
spectrum sharing results in re-use of the available spectrum among different services
and, therefore, increases the efficient use of the radio frequencies. However, it is
necessary to carry out extensive feasibility studies into technical or operational
compatibility between the services involved. Often, sharing constraints are placed
on systems, such as the power of emissions and the transmitter and receiver antenna
pointings to reduce the interference into negligible levels.
Traditionally, radio spectrum allocated to GSO FSS has been shared with FS. In
recent years, there has been a growing interest in the use of low Earth orbits and a
number of NGSO FSS constellations has been designed to provide broadband data
services. This has led to the allocation of certain bands used by the FS and GSO
FSS systems to NGSO FSS.
In line with the new allocations, NGSO FSS, GSO FSS and FS systems are required
to co-exist in parts of the 12 to 30 GHz frequency range. The primary objectives of
this research were to identify principal factors affecting the feasibility of spectrum
sharing and to develop spectrum sharing analysis methodologies to examine the
implications of these factors with a view to identifying sharing constraints that
would give rise to an acceptable sharing environment
Variable Rate Transmission Over Noisy Channels
Hybrid automatic repeat request transmission (hybrid ARQ) schemes aim to provide
system reliability for transmissions over noisy channels while still maintaining a reasonably
high throughput efficiency by combining retransmissions of automatic repeat
requests with forward error correction (FEC) coding methods. In type-II hybrid ARQ
schemes, the additional parity information required by channel codes to achieve forward
error correction is provided only when errors have been detected. Hence, the
available bits are partitioned into segments, some of which are sent to the receiver immediately,
others are held back and only transmitted upon the detection of errors. This
scheme raises two questions. Firstly, how should the available bits be ordered for optimal
partitioning into consecutive segments? Secondly, how large should the individual
segments be?
This thesis aims to provide an answer to both of these questions for the transmission
of convolutional and Turbo Codes over additive white Gaussian noise (AWGN),
inter-symbol interference (ISI) and Rayleigh channels. Firstly, the ordering of bits is
investigated by simulating the transmission of packets split into segments with a size of
1 bit and finding the critical number of bits, i.e. the number of bits where the output of
the decoder is error-free. This approach provides a maximum, practical performance
limit over a range of signal-to-noise levels. With these practical performance limits, the
attention is turned to the size of the individual segments, since packets of 1 bit cause
an intolerable overhead and delay. An adaptive, hybrid ARQ system is investigated,
in which the transmitter uses the number of bits sent to the receiver and the receiver
decoding results to adjust the size of the first, initial, packet and subsequent segments
to the conditions of a stationary channel
Decentralized Ultra-Reliable Low-Latency Communications through Concurrent Cooperative Transmission
Emerging cyber-physical systems demand for communication technologies that enable seamless interactions between humans and physical objects in a shared environment. This thesis proposes decentralized URLLC (dURLLC) as a new communication paradigm that allows the nodes in a wireless multi-hop network (WMN) to disseminate data quickly, reliably and without using a centralized infrastructure. To enable the dURLLC paradigm, this thesis explores the practical feasibility of concurrent cooperative transmission (CCT) with orthogonal frequency-division multiplexing (OFDM). CCT allows for an efficient utilization of the medium by leveraging interference instead of trying to avoid collisions. CCT-based network flooding disseminates data in a WMN through a reception-triggered low-level medium access control (MAC). OFDM provides high data rates by using a large bandwidth, resulting in a short transmission duration for a given amount of data.
This thesis explores CCT-based network flooding with the OFDM-based IEEE 802.11 Non-HT and HT physical layers (PHYs) to enable interactions with commercial devices. An analysis of CCT with the IEEE 802.11 Non-HT PHY investigates the combined effects of the phase offset (PO), the carrier frequency offset (CFO) and the time offset (TO) between concurrent transmitters, as well as the elapsed time. The analytical results of the decodability of a CCT are validated in simulations and in testbed experiments with Wireless Open Access Research Platform (WARP) v3 software-defined radios (SDRs). CCT with coherent interference (CI) is the primary approach of this thesis.
Two prototypes for CCT with CI are presented that feature mechanisms for precise synchronization in time and frequency. One prototype is based on the WARP v3 and its IEEE 802.11 reference design, whereas the other prototype is created through firmware modifications of the Asus RT-AC86U wireless router. Both prototypes are employed in testbed experiments in which two groups of nodes generate successive CCTs in a ping-pong fashion to emulate flooding processes with a very large number of hops. The nodes stay synchronized in experiments with 10 000 successive CCTs for various modulation and coding scheme (MCS) indices and MAC service data unit (MSDU) sizes. The URLLC requirement of delivering a 32-byte MSDU with a reliability of 99.999 % and with a latency of 1 ms is assessed in experiments with 1 000 000 CCTs, while the reliability is approximated by means of the frame reception rate (FRR). An FRR of at least 99.999 % is achieved at PHY data rates of up to 48 Mbit/s under line-of-sight (LOS) conditions and at PHY data rates of up to 12 Mbit/s under non-line-of-sight (NLOS) conditions on a 20 MHz wide channel, while the latency per hop is 48.2 µs and 80.2 µs, respectively. With four multiple input multiple output (MIMO) spatial streams on a 40 MHz wide channel, a LOS receiver achieves an FRR of 99.5 % at a PHY data rate of 324 Mbit/s. For CCT with incoherent interference, this thesis proposes equalization with time-variant zero-forcing (TVZF) and presents a TVZF receiver for the IEEE 802.11 Non-HT PHY, achieving an FRR of up to 92 % for CCTs from three unsyntonized commercial devices. As CCT-based network flooding allows for an implicit time synchronization of all nodes, a reception-triggered low-level MAC and a reservation-based high-level MAC may in combination support various applications and scenarios under the dURLLC paradigm