846 research outputs found
Reliable OFDM Receiver with Ultra-Low Resolution ADC
The use of low-resolution analog-to-digital converters (ADCs) can
significantly reduce power consumption and hardware cost. However, their
resulting severe nonlinear distortion makes reliable data transmission
challenging. For orthogonal frequency division multiplexing (OFDM)
transmission, the orthogonality among subcarriers is destroyed. This
invalidates conventional OFDM receivers relying heavily on this orthogonality.
In this study, we move on to quantized OFDM (Q-OFDM) prototyping implementation
based on our previous achievement in optimal Q-OFDM detection. First, we
propose a novel Q-OFDM channel estimator by extending the generalized Turbo
(GTurbo) framework formerly applied for optimal detection. Specifically, we
integrate a type of robust linear OFDM channel estimator into the original
GTurbo framework and derive its corresponding extrinsic information to
guarantee its convergence. We also propose feasible schemes for automatic gain
control, noise power estimation, and synchronization. Combined with the
proposed inference algorithms, we develop an efficient Q-OFDM receiver
architecture. Furthermore, we construct a proof-of-concept prototyping system
and conduct over-the-air (OTA) experiments to examine its feasibility and
reliability. This is the first work that focuses on both algorithm design and
system implementation in the field of low-resolution quantization
communication. The results of the numerical simulation and OTA experiment
demonstrate that reliable data transmission can be achieved.Comment: 14 pages, 17 figures; accepted by IEEE Transactions on Communication
Bayesian Optimal Data Detector for mmWave OFDM System with Low-Resolution ADC
Orthogonal frequency division multiplexing (OFDM) has been widely used in
communication systems operating in the millimeter wave (mmWave) band to combat
frequency-selective fading and achieve multi-Gbps transmissions, such as IEEE
802.15.3c and IEEE 802.11ad. For mmWave systems with ultra high sampling rate
requirements, the use of low-resolution analog-to-digital converters (ADCs)
(i.e., 1-3 bits) ensures an acceptable level of power consumption and system
costs. However, orthogonality among sub-channels in the OFDM system cannot be
maintained because of the severe non-linearity caused by low-resolution ADC,
which renders the design of data detector challenging. In this study, we
develop an efficient algorithm for optimal data detection in the mmWave OFDM
system with low-resolution ADCs. The analytical performance of the proposed
detector is derived and verified to achieve the fundamental limit of the
Bayesian optimal design. On the basis of the derived analytical expression, we
further propose a power allocation (PA) scheme that seeks to minimize the
average symbol error rate. In addition to the optimal data detector, we also
develop a feasible channel estimation method, which can provide high-quality
channel state information without significant pilot overhead. Simulation
results confirm the accuracy of our analysis and illustrate that the
performance of the proposed detector in conjunction with the proposed PA scheme
is close to the optimal performance of the OFDM system with infinite-resolution
ADC.Comment: 32 pages, 12 figures; accepted by IEEE JSAC special issue on
millimeter wave communications for future mobile network
Semidefinite Relaxation-Based PAPR-Aware Precoding for Massive MIMO-OFDM Systems
Massive MIMO requires a large number of antennas and the same amount of power
amplifiers (PAs), one per antenna. As opposed to 4G base stations, which could
afford highly linear PAs, next-generation base stations will need to use
inexpensive PAs, which have a limited region of linear amplification. One of
the research challenges is effectively handling signals which have high
peak-to-average power ratios (PAPRs), such as orthogonal frequency division
multiplexing (OFDM). This paper introduces a PAPR-aware precoding scheme that
exploits the excessive spatial degrees-of-freedom of large scale multiple-input
multipleoutput (MIMO) antenna systems. This typically requires finding a
solution to a nonconvex optimization problem. Instead of relaxing the problem
to minimize the peak power, we introduce a practical semidefinite relaxation
(SDR) framework that enables accurately and efficiently approximating the
theoretical PAPR-aware precoding performance for OFDM-based massive MIMO
systems. The framework allows incorporating channel uncertainties and intercell
coordination. Numerical results show that several orders of magnitude
improvements can be achieved w.r.t. state of the art techniques, such as
instantaneous power consumption reduction and multiuser interference
cancellation. The proposed PAPRaware precoding can be effectively handled along
with the multicell signal processing by the centralized baseband processing
platforms of next-generation radio access networks. Performance can be traded
for the computing efficiency for other platform
Massive MIMO and Waveform Design for 5th Generation Wireless Communication Systems
This article reviews existing related work and identifies the main challenges
in the key 5G area at the intersection of waveform design and large-scale
multiple antenna systems, also known as Massive MIMO. The property of
self-equalization is introduced for Filter Bank Multicarrier (FBMC)-based
Massive MIMO, which can reduce the number of subcarriers required by the
system. It is also shown that the blind channel tracking property of FBMC can
be used to address pilot contamination -- one of the main limiting factors of
Massive MIMO systems. Our findings shed light into and motivate for an entirely
new research line towards a better understanding of waveform design with
emphasis on FBMC-based Massive MIMO networks.Comment: 6 pages, 2 figures, 1st International Conference on 5G for Ubiquitous
Connectivit
Artificial Intelligence-Defined 5G Radio Access Networks
Massive multiple-input multiple-output antenna systems, millimeter wave
communications, and ultra-dense networks have been widely perceived as the
three key enablers that facilitate the development and deployment of 5G
systems. This article discusses the intelligent agent in 5G base station which
combines sensing, learning, understanding and optimizing to facilitate these
enablers. We present a flexible, rapidly deployable, and cross-layer artificial
intelligence (AI)-based framework to enable the imminent and future demands on
5G and beyond infrastructure. We present example AI-enabled 5G use cases that
accommodate important 5G-specific capabilities and discuss the value of AI for
enabling beyond 5G network evolution
Modulation Formats and Waveforms for the Physical Layer of 5G Wireless Networks: Who Will be the Heir of OFDM?
5G cellular communications promise to deliver the gigabit experience to
mobile users, with a capacity increase of up to three orders of magnitude with
respect to current LTE systems. There is widespread agreement that such an
ambitious goal will be realized through a combination of innovative techniques
involving different network layers. At the physical layer, the OFDM modulation
format, along with its multiple-access strategy OFDMA, is not taken for
granted, and several alternatives promising larger values of spectral
efficiency are being considered. This paper provides a review of some
modulation formats suited for 5G, enriched by a comparative analysis of their
performance in a cellular environment, and by a discussion on their
interactions with specific 5G ingredients. The interaction with a massive MIMO
system is also discussed by employing real channel measurements.Comment: to appear IEEE Signal Processing Magazine, special issue on Signal
Processing for the 5G Revolution, November 201
A Survey on MIMO Transmission with Discrete Input Signals: Technical Challenges, Advances, and Future Trends
Multiple antennas have been exploited for spatial multiplexing and diversity
transmission in a wide range of communication applications. However, most of
the advances in the design of high speed wireless multiple-input multiple
output (MIMO) systems are based on information-theoretic principles that
demonstrate how to efficiently transmit signals conforming to Gaussian
distribution. Although the Gaussian signal is capacity-achieving, signals
conforming to discrete constellations are transmitted in practical
communication systems. As a result, this paper is motivated to provide a
comprehensive overview on MIMO transmission design with discrete input signals.
We first summarize the existing fundamental results for MIMO systems with
discrete input signals. Then, focusing on the basic point-to-point MIMO
systems, we examine transmission schemes based on three most important criteria
for communication systems: the mutual information driven designs, the mean
square error driven designs, and the diversity driven designs. Particularly, a
unified framework which designs low complexity transmission schemes applicable
to massive MIMO systems in upcoming 5G wireless networks is provided in the
first time. Moreover, adaptive transmission designs which switch among these
criteria based on the channel conditions to formulate the best transmission
strategy are discussed. Then, we provide a survey of the transmission designs
with discrete input signals for multiuser MIMO scenarios, including MIMO uplink
transmission, MIMO downlink transmission, MIMO interference channel, and MIMO
wiretap channel. Additionally, we discuss the transmission designs with
discrete input signals for other systems using MIMO technology. Finally,
technical challenges which remain unresolved at the time of writing are
summarized and the future trends of transmission designs with discrete input
signals are addressed.Comment: 110 pages, 512 references, submit to Proceedings of the IEE
A Low Complexity Near-Maximum Likelihood MIMO Receiver with Low Resolution Analog-to-Digital Converters
Based on a new equivalent model of quantizer with noisy input recently
presented in [23], we propose a new low complexity receiver that takes into
account the nonlinear distortion (NLD) generated by Analog to Digital converter
(ADC) with insufficient resolution. The strength of new model is that it
presents the NLD as a function of only the desired part of input signal
(without noise). Therefore it can easily be used in a variety of NLD mitigation
techniques. Here, as an illustration of this, we use a pseudo-ML approach to
detect the original QAM modulation based on the equivalent transfer function
and exhaustive search. Simulation results for a single user QAM under flat
fading show performance equivalent to a true ML receiver, but with much lower
computational complexity. The excellent performance of our receiver is an
independent validation of the model [23]
Deep Learning-Based Channel Estimation for High-Dimensional Signals
We propose a novel deep learning-based channel estimation technique for
high-dimensional communication signals that does not require any training. Our
method is broadly applicable to channel estimation for multicarrier signals
with any number of antennas, and has low enough complexity to be used in a
mobile station. The proposed deep channel estimator can outperform LS
estimation with nearly the same complexity, and approach MMSE estimation
performance to within 1 dB without knowing the second order statistics. The
only complexity increase with respect to LS estimator lies in fitting the
parameters of a deep neural network (DNN) periodically on the order of the
channel coherence time. We empirically show that the main benefit of this
method accrues from the ability of this specially designed DNN to exploit
correlations in the time-frequency grid. The proposed estimator can also reduce
the number of pilot tones needed in an OFDM time-frequency grid, e.g. in an LTE
scenario by 98% (68%) when the channel coherence time interval is 73ms (4.5ms)
A Framework on Hybrid MIMO Transceiver Design based on Matrix-Monotonic Optimization
Hybrid transceiver can strike a balance between complexity and performance of
multiple-input multiple-output (MIMO) systems. In this paper, we develop a
unified framework on hybrid MIMO transceiver design using matrix-monotonic
optimization. The proposed framework addresses general hybrid transceiver
design, rather than just limiting to certain high frequency bands, such as
millimeter wave (mmWave) or terahertz bands or relying on the sparsity of some
specific wireless channels. In the proposed framework, analog and digital parts
of a transceiver, either linear or nonlinear, are jointly optimized. Based on
matrix-monotonic optimization, we demonstrate that the combination of the
optimal analog precoders and processors are equivalent to eigenchannel
selection for various optimal hybrid MIMO transceivers. From the optimal
structure, several effective algorithms are derived to compute the analog
transceivers under unit modulus constraints. Furthermore, in order to reduce
computation complexity, a simple random algorithm is introduced for analog
transceiver optimization. Once the analog part of a transceiver is determined,
the closed-form digital part can be obtained. Numerical results verify the
advantages of the proposed design.Comment: 13 pages,7 figures, IEEE Signal Processing 201
- …