74 research outputs found
Adaptive and Iterative Multi-Branch MMSE Decision Feedback Detection Algorithms for MIMO Systems
In this work, decision feedback (DF) detection algorithms based on multiple
processing branches for multi-input multi-output (MIMO) spatial multiplexing
systems are proposed. The proposed detector employs multiple cancellation
branches with receive filters that are obtained from a common matrix inverse
and achieves a performance close to the maximum likelihood detector (MLD).
Constrained minimum mean-squared error (MMSE) receive filters designed with
constraints on the shape and magnitude of the feedback filters for the
multi-branch MMSE DF (MB-MMSE-DF) receivers are presented. An adaptive
implementation of the proposed MB-MMSE-DF detector is developed along with a
recursive least squares-type algorithm for estimating the parameters of the
receive filters when the channel is time-varying. A soft-output version of the
MB-MMSE-DF detector is also proposed as a component of an iterative detection
and decoding receiver structure. A computational complexity analysis shows that
the MB-MMSE-DF detector does not require a significant additional complexity
over the conventional MMSE-DF detector, whereas a diversity analysis discusses
the diversity order achieved by the MB-MMSE-DF detector. Simulation results
show that the MB-MMSE-DF detector achieves a performance superior to existing
suboptimal detectors and close to the MLD, while requiring significantly lower
complexity.Comment: 10 figures, 3 tables; IEEE Transactions on Wireless Communications,
201
Multi-carrier transmission techniques toward flexible and efficient wireless communication systems
制度:新 ; 文部省報告番号:甲2562号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2008/3/15 ; 早大学位記番号:新470
From the conventional MIMO to massive MIMO systems: performance analysis and energy efficiency optimization
The main topic of this thesis is based on multiple-input multiple-output (MIMO) wireless communications,
which is a novel technology that has attracted great interest in the last twenty
years. Conventional MIMO systems using up to eight antennas play a vital role in the urban
cellular network, where the deployment of multiple antennas have significantly enhanced the
throughput without taking extra spectrum or power resources. The massive MIMO systems
“scales” up the benefits that offered by the conventional MIMO systems. Using sixty four or
more antennas at the BS not only improves the spectrum efficiency significantly, but also provides
additional link robustness. It is considered as a key technology in the fifth generation
of mobile communication technology standards network, and the design of new algorithms for
these two systems is the basis of the research in this thesis.
Firstly, at the receiver side of the conventional MIMO systems, a general framework of bit error
rate (BER) approximation for the detection algorithms is proposed, which aims to support
an adaptive modulation scheme. The main idea is to utilize a simplified BER approximation
scheme, which is based on the union bound of the maximum-likelihood detector (MLD),
whereby the bit error rate (BER) performance of the detector for the varying channel qualities
can be efficiently predicted. The K-best detector is utilized in the thesis because its quasi-
MLD performance and the parallel computational structure. The simulation results have clearly
shown the adaptive K-best algorithm, by applying the simplified approximation method, has
much reduced computational complexity while still maintaining a promising BER performance.
Secondly, in terms of the uplink channel estimation for the massive MIMO systems with
the time-division-duplex operation, the performance of the Grassmannian line packing (GLP)
based uplink pilot codebook design is investigated. It aims to eliminate the pilot contamination
effect in order to increase the downlink achievable rate. In the case of a limited channel
coherence interval, the uplink codebook design can be treated as a line packing problem in a
Grassmannian manifold. The closed-form analytical expressions of downlink achievable rate
for both the single-cell and multi-cell systems are proposed, which are intended for performance
analysis and optimization. The numerical results validate the proposed analytical expressions
and the rate gains by using the GLP-based uplink codebook design.
Finally, the study is extended to the energy efficiency (EE) of the massive MIMO system, as
the reduction carbon emissions from the information and communication technology is a long-term
target for the researchers. An effective framework of maximizing the EE for the massive
MIMO systems is proposed in this thesis. The optimization starts from the maximization of
the minimum user rate, which is aiming to increase the quality-of-service and provide a feasible
constraint for the EE maximization problem. Secondly, the EE problem is a non-concave
problem and can not be solved directly, so the combination of fractional programming and the
successive concave approximation based algorithm are proposed to find a good suboptimal solution.
It has been shown that the proposed optimization algorithm provides a significant EE
improvement compared to a baseline case
MIMO Systems
In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity
Constrained Detection for Spatial-Multiplexing Multiple-Input–Multiple-Output Systems
A family of detectors that exploit signal constraints is developed for maximum-likelihood detection for multiple-input–multiple-output (MIMO) systems. Real constrained detectors and decision-feedback detectors are proposed for real constellations by forcing the relaxed solution to be real. A generalized minimum mean square error (GMMSE) and constrained least squares MIMO detectors are also developed for unitary and nonunitary signal constellations. Using these constrained detectors, we propose a new ordering scheme to achieve a tradeoff between interference suppression and noise enhancement. Moreover, to mitigate the inherent error propagation, the decision-feedback MIMO detectors are integrated with signal constraints. The simulation results show that our combined detector achieves a significant performance gain over vertical Bell Laboratories layered space-time (V-BLAST) detection
Unified Framework for Multicarrier and Multiple Access based on Generalized Frequency Division Multiplexing
The advancements in wireless communications are the key-enablers of new applications with stringent requirements in low-latency, ultra-reliability, high data rate, high mobility, and massive connectivity. Diverse types of devices, ranging from tiny sensors to vehicles, with different capabilities need to be connected under various channel conditions. Thus, modern connectivity and network techniques at all layers are essential to overcome these challenges. In particular, the physical layer (PHY) transmission is required to achieve certain link reliability, data rate, and latency. In modern digital communications systems, the transmission is performed by means of a digital signal processing module that derives analog hardware. The performance of the analog part is influenced by the quality of the hardware and the baseband signal denoted as waveform. In most of the modern systems such as fifth generation (5G) and WiFi, orthogonal frequency division multiplexing (OFDM) is adopted as a favorite waveform due to its low-complexity advantages in terms of signal processing. However, OFDM requires strict requirements on hardware quality.
Many devices are equipped with simplified analog hardware to reduce the cost. In this case, OFDM does not work properly as a result of its high peak-to-average power ratio (PAPR) and sensitivity to synchronization errors. To tackle these problems, many waveforms design have been recently proposed in the literature. Some of these designs are modified versions of OFDM or based on conventional single subcarrier. Moreover, multicarrier frameworks, such as generalized frequency division multiplexing (GFDM), have been proposed to realize varieties of conventional waveforms. Furthermore, recent studies show the potential of using non-conventional waveforms for increasing the link reliability with affordable complexity. Based on that, flexible waveforms and transmission techniques are necessary to adapt the system for different hardware and channel constraints in order to fulfill the applications requirements while optimizing the resources.
The objective of this thesis is to provide a holistic view of waveforms and the related multiple access (MA) techniques to enable efficient study and evaluation of different approaches. First, the wireless communications system is reviewed with specific focus on the impact of hardware impairments and the wireless channel on the waveform design. Then, generalized model of waveforms and MA are presented highlighting various special cases. Finally, this work introduces low-complexity architectures for hardware implementation of flexible waveforms. Integrating such designs with software-defined radio (SDR) contributes to the development of practical real-time flexible PHY.:1 Introduction
1.1 Baseband transmission model
1.2 History of multicarrier systems
1.3 The state-of-the-art waveforms
1.4 Prior works related to GFDM
1.5 Objective and contributions
2 Fundamentals of Wireless Communications
2.1 Wireless communications system
2.2 RF transceiver
2.2.1 Digital-analogue conversion
2.2.2 QAM modulation
2.2.3 Effective channel
2.2.4 Hardware impairments
2.3 Waveform aspects
2.3.1 Single-carrier waveform
2.3.2 Multicarrier waveform
2.3.3 MIMO-Waveforms
2.3.4 Waveform performance metrics
2.4 Wireless Channel
2.4.1 Line-of-sight propagation
2.4.2 Multi path and fading process
2.4.3 General baseband statistical channel model
2.4.4 MIMO channel
2.5 Summary
3 Generic Block-based Waveforms
3.1 Block-based waveform formulation
3.1.1 Variable-rate multicarrier
3.1.2 General block-based multicarrier model
3.2 Waveform processing techniques
3.2.1 Linear and circular filtering
3.2.2 Windowing
3.3 Structured representation
3.3.1 Modulator
3.3.2 Demodulator
3.3.3 MIMO Waveform processing
3.4 Detection
3.4.1 Maximum-likelihood detection
3.4.2 Linear detection
3.4.3 Iterative Detection
3.4.4 Numerical example and insights
3.5 Summary
4 Generic Multiple Access Schemes 57
4.1 Basic multiple access and multiplexing schemes
4.1.1 Infrastructure network system model
4.1.2 Duplex schemes
4.1.3 Common multiplexing and multiple access schemes
4.2 General multicarrier-based multiple access
4.2.1 Design with fixed set of pulses
4.2.2 Computational model
4.2.3 Asynchronous multiple access
4.3 Summary
5 Time-Frequency Analyses of Multicarrier
5.1 General time-frequency representation
5.1.1 Block representation
5.1.2 Relation to Zak transform
5.2 Time-frequency spreading
5.3 Time-frequency block in LTV channel
5.3.1 Subcarrier and subsymbol numerology
5.3.2 Processing based on the time-domain signal
5.3.3 Processing based on the frequency-domain signal
5.3.4 Unified signal model
5.4 summary
6 Generalized waveforms based on time-frequency shifts
6.1 General time-frequency shift
6.1.1 Time-frequency shift design
6.1.2 Relation between the shifted pulses
6.2 Time-frequency shift in Gabor frame
6.2.1 Conventional GFDM
6.3 GFDM modulation
6.3.1 Filter bank representation
6.3.2 Block representation
6.3.3 GFDM matrix structure
6.3.4 GFDM demodulator
6.3.5 Alternative interpretation of GFDM
6.3.6 Orthogonal modulation and GFDM spreading
6.4 Summary
7 Modulation Framework: Architectures and Applications
7.1 Modem architectures
7.1.1 General modulation matrix structure
7.1.2 Run-time flexibility
7.1.3 Generic GFDM-based architecture
7.1.4 Flexible parallel multiplications architecture
7.1.5 MIMO waveform architecture
7.2 Extended GFDM framework
7.2.1 Architectures complexity and flexibility analysis
7.2.2 Number of multiplications
7.2.3 Hardware analysis
7.3 Applications of the extended GFDM framework
7.3.1 Generalized FDMA
7.3.2 Enchantment of OFDM system
7.4 Summary
7 Conclusions and Future work
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