247 research outputs found
Frequency Spreading Equalization in Multicarrier Massive MIMO
Application of filter bank multicarrier (FBMC) as an effective method for
signaling over massive MIMO channels has been recently proposed. This paper
further expands the application of FBMC to massive MIMO by applying frequency
spreading equalization (FSE) to these channels. FSE allows us to achieve a more
accurate equalization. Hence, higher number of bits per symbol can be
transmitted and the bandwidth of each subcarrier can be widened. Widening the
bandwidth of each subcarrier leads to (i) higher bandwidth efficiency; (ii)
lower complexity; (iii) lower sensitivity to carrier frequency offset (CFO);
(iv) reduced peak-to-average power ratio (PAPR); and (iv) reduced latency. All
these appealing advantages have a direct impact on the digital as well as
analog circuitry that is needed for the system implementation. In this paper,
we develop the mathematical formulation of the minimum mean square error (MMSE)
FSE for massive MIMO systems. This analysis guides us to decide on the number
of subcarriers that will be sufficient for practical channel models.Comment: Accepted in IEEE ICC 2015 - Workshop on 5G & Beyond - Enabling
Technologies and Application
Filter Bank Multicarrier for Massive MIMO
This paper introduces filter bank multicarrier (FBMC) as a potential
candidate in the application of massive MIMO communication. It also points out
the advantages of FBMC over OFDM (orthogonal frequency division multiplexing)
in the application of massive MIMO. The absence of cyclic prefix in FBMC
increases the bandwidth efficiency. In addition, FBMC allows carrier
aggregation straightforwardly. Self-equalization, a property of FBMC in massive
MIMO that is introduced in this paper, has the impact of reducing (i)
complexity; (ii) sensitivity to carrier frequency offset (CFO); (iii)
peak-to-average power ratio (PAPR); (iv) system latency; and (v) increasing
bandwidth efficiency. The numerical results that corroborate these claims are
presented.Comment: 7 pages, 6 figure
Pilot Decontamination in CMT-based Massive MIMO Networks
Pilot contamination problem in massive MIMO networks operating in
time-division duplex (TDD) mode can limit their expected capacity to a great
extent. This paper addresses this problem in cosine modulated multitone (CMT)
based massive MIMO networks; taking advantage of their so-called blind
equalization property. We extend and apply the blind equalization technique
from single antenna case to multi-cellular massive MIMO systems and show that
it can remove the channel estimation errors (due to pilot contamination effect)
without any need for cooperation between different cells or transmission of
additional training information. Our numerical results advocate the efficacy of
the proposed blind technique in improving the channel estimation accuracy and
removal of the residual channel estimation errors caused by the users of the
other cells.Comment: Accepted in ISWCS 201
MIMO signal processing in offset-QAM based filter bank multicarrier systems
Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft
PERFORMANCE EVALUATION OF A MULTICARRIER MIMO SYSTEM BASED ON DFT-PRECODING AND SUBCARRIER MAPPING
The ever-increasing end user demands are instigating the development of innovative methods targeting not only data rate enhancement but additionally better service quality in each subsequent wireless communication standard. This quest to achieve higher data rates has compelled the next generation communication technologies to use multicarrier systems e.g. orthogonal frequency division multiplexing (OFDM), while also relying on the multiple-input multiple-output (MIMO) technology. This paper is focused on implementing a MIMO-OFDM system and on using various techniques to optimize it in terms of the bit-error rate performance. The test case considered is a system implementation constituting the enabling technologies for 4G and beyond communication systems. The bit-error rate optimizations considered are based on preceding the OFDM modulation step by Discrete Fourier Transform (DFT) while also considering various subcarrier mapping schemes. MATLAB-based simulation of a 2 × 2 MIMO-OFDM system exhibits a maximum of 2 to 5 orders of magnitude reduction in bit-error rate due to DFT-precoding and subcarrier mapping respectively at high signal-to-noise ratio values in various environments. A 2-3dBs reduction in peak-to-average power ratio due to DFT-precoding in different environments is also exhibited in the various simulations
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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