4,326 research outputs found
Scaling up MIMO: Opportunities and Challenges with Very Large Arrays
This paper surveys recent advances in the area of very large MIMO systems.
With very large MIMO, we think of systems that use antenna arrays with an
order of magnitude more elements than in systems being built today, say a
hundred antennas or more. Very large MIMO entails an unprecedented number of
antennas simultaneously serving a much smaller number of terminals. The
disparity in number emerges as a desirable operating condition and a practical
one as well. The number of terminals that can be simultaneously served is
limited, not by the number of antennas, but rather by our inability to acquire
channel-state information for an unlimited number of terminals. Larger numbers
of terminals can always be accommodated by combining very large MIMO technology
with conventional time- and frequency-division multiplexing via OFDM. Very
large MIMO arrays is a new research field both in communication theory,
propagation, and electronics and represents a paradigm shift in the way of
thinking both with regards to theory, systems and implementation. The ultimate
vision of very large MIMO systems is that the antenna array would consist of
small active antenna units, plugged into an (optical) fieldbus.Comment: Accepted for publication in the IEEE Signal Processing Magazine,
October 201
Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions
Massive MIMO is a compelling wireless access concept that relies on the use
of an excess number of base-station antennas, relative to the number of active
terminals. This technology is a main component of 5G New Radio (NR) and
addresses all important requirements of future wireless standards: a great
capacity increase, the support of many simultaneous users, and improvement in
energy efficiency. Massive MIMO requires the simultaneous processing of signals
from many antenna chains, and computational operations on large matrices. The
complexity of the digital processing has been viewed as a fundamental obstacle
to the feasibility of Massive MIMO in the past. Recent advances on
system-algorithm-hardware co-design have led to extremely energy-efficient
implementations. These exploit opportunities in deeply-scaled silicon
technologies and perform partly distributed processing to cope with the
bottlenecks encountered in the interconnection of many signals. For example,
prototype ASIC implementations have demonstrated zero-forcing precoding in real
time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing
of 8 terminals). Coarse and even error-prone digital processing in the antenna
paths permits a reduction of consumption with a factor of 2 to 5. This article
summarizes the fundamental technical contributions to efficient digital signal
processing for Massive MIMO. The opportunities and constraints on operating on
low-complexity RF and analog hardware chains are clarified. It illustrates how
terminals can benefit from improved energy efficiency. The status of technology
and real-life prototypes discussed. Open challenges and directions for future
research are suggested.Comment: submitted to IEEE transactions on signal processin
Quantized vs. Analog Feedback for the MIMO Downlink: A Comparison between Zero-Forcing Based Achievable Rates
We consider a MIMO fading broadcast channel and compare the achievable
ergodic rates when the channel state information at the transmitter is provided
by analog noisy feedback or by quantized (digital) feedback. The superiority of
digital feedback is shown, with perfect or imperfect CSIR, whenever the number
of feedback channel uses per channel coefficient is larger than 1. Also, we
show that by proper design of the digital feedback link, errors in the feedback
have a minor effect even by using very simple uncoded modulation. Finally, we
show that analog feedback achieves a fraction 1 - 2F of the optimal
multiplexing gain even in the presence of a feedback delay, when the fading
belongs to the class of Doppler processes with normalized maximum Doppler
frequency shift 0 <= F <= 1/2.Comment: Submitted to ISIT, January 2007. 5 page
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
On Detection Issues in the SC-based Uplink of a MU-MIMO System with a Large Number of BS Antennas
This paper deals with SC/FDE within a MU-MIMO system where a large number of
BS antennas is adopted. In this context, either linear or reduced-complexity
iterative DF detection techniques are considered. Regarding performance
evaluation by simulation, appropriate semi-analytical methods are proposed.
This paper includes a detailed evaluation of BER performances for uncoded
4-Quadrature Amplitude Modulation (4-QAM) schemes and a MU-MIMO channel with
uncorrelated Rayleigh fading. The accuracy of performance results obtained
through the semi-analytical simulation methods is assessed by means of parallel
conventional Monte Carlo simulations, under the assumptions of perfect power
control and perfect channel estimation. The performance results are discussed
in detail, with the help of selected performance bounds. We emphasize that a
moderately large number of BS antennas is enough to closely approximate the
SIMO MFB performance, especially when using the suggested low-complexity
iterative DF technique, which does not require matrix inversion operations. We
also emphasize the achievable "massive MIMO" effects, even for strongly
reduced-complexity linear detection techniques, provided that the number of BS
antennas is much higher than the number of antennas which are jointly employed
in the terminals of the multiple autonomous users.Comment: 7 pages, 4 figure
Propagation modelling and measurements in a populated indoor environment at 5.2 GHz
There are a number of significant radiowave propagation phenomena present in the populated indoor environment, including multipath fading and human body effects. The latter can be divided into shadowing and scattering caused by pedestrian movement, and antenna-body interaction with bodyworn or hand portable terminals [1]. Human occupants within indoor environments are not always stationary and their movement will lead to temporal channel variations that can strongly affect the quality of indoor wireless communication systems. Hence, populated environments remain a major challenge for wireless local area networks (WLAN) and other indoor communication systems. Therefore, it is important to develop an understanding of the potential and limitations of indoor radiowave propagation at key frequencies of interest, such as the 5.2 GHz band employed by commercial wireless LAN standards such as IEEE 802.11a and HiperLAN 2.
Although several indoor wireless models have been proposed in the literature, these temporal variations have not yet been thoroughly investigated. Therefore, we have made an important contribution to the area by conducting a systematic study of the problem, including a propagation measurement campaign and statistical channel characterization of human body effects on line-of-sight indoor propagation at 5.2 GHz.
Measurements were performed in the everyday environment of a 7.2 m wide University hallway to determine the statistical characteristics of the 5.2 GHz channel for a fixed, transverse line-of-sight (LOS) link perturbed by pedestrian movement. Data were acquired at hours of relatively high pedestrian activity, between 12.00 and 14.00. The location was chosen as a typical indoor wireless system environment that had sufficient channel variability to permit a valid statistical analysis.
The paper compares the first and second order statistics of the empirical signals with the Gaussian-derived distributions commonly used in wireless communications. The analysis shows that, as the number of pedestrians within the measurement location increases, the Ricean K-factor that best fits the Cumulative Distribution Function (CDF) of the empirical data tends to decrease proportionally, ranging from K=7 with 1 pedestrian to K=0 with 4 pedestrians. These results are consistent with previous results obtained for controlled measurement scenarios using a fixed link at 5.2 GHz in [2], where the K factor reduced as the number of pedestrians within a controlled measurement area increased. Level crossing rate results were Rice distributed, considering a maximum Doppler frequency of 8.67 Hz. While average fade duration results were significantly higher than theoretically computed Rice and Rayleigh, due to the fades caused by pedestrians.
A novel statistical model that accurately describes the 5.2 GHz channel in the considered indoor environment is proposed. For the first time, the received envelope CDF is explicitly described in terms of a quantitative measurement of pedestrian traffic within the indoor environment. The model provides an insight into the prediction of human body shadowing effects for indoor channels at 5.2 GHz
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