531 research outputs found
Dual-Polarized Ricean MIMO Channels: Modeling and Performance Assessment
In wireless communication systems, dual-polarized (DP) instead of
single-polarized (SP) multiple-input multiple-output (MIMO) transmission is
used to improve the spectral efficiency under certain conditions on the channel
and the signal-to-noise ratio (SNR). In order to identify these conditions, we
first propose a novel channel model for DP mobile Ricean MIMO channels for
which statistical channel parameters are readily obtained from a moment-based
channel decomposition. Second, we derive an approximation of the mutual
information (MI), which can be expressed as a function of those statistical
channel parameters. Based on this approximation, we characterize the required
SNR for a DP MIMO system to outperform an SP MIMO system in terms of the MI.
Finally, we apply our results to channel measurements at 2.53 GHz. We find
that, using the proposed channel decomposition and the approximation of the MI,
we are able to reproduce the (practically relevant) SNR values above which DP
MIMO systems outperform SP MIMO systems.Comment: submitted to the IEEE Transactions on Communication
A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles
In recent years, there has been a dramatic increase in the use of unmanned
aerial vehicles (UAVs), particularly for small UAVs, due to their affordable
prices, ease of availability, and ease of operability. Existing and future
applications of UAVs include remote surveillance and monitoring, relief
operations, package delivery, and communication backhaul infrastructure.
Additionally, UAVs are envisioned as an important component of 5G wireless
technology and beyond. The unique application scenarios for UAVs necessitate
accurate air-to-ground (AG) propagation channel models for designing and
evaluating UAV communication links for control/non-payload as well as payload
data transmissions. These AG propagation models have not been investigated in
detail when compared to terrestrial propagation models. In this paper, a
comprehensive survey is provided on available AG channel measurement campaigns,
large and small scale fading channel models, their limitations, and future
research directions for UAV communication scenarios
Characterization of Single- and Multi-antenna Wireless Channels
The wireless propagation channel significantly influences the received signal, so that it needs to be modeled effectively. Extensive measurements and analysis are required for investigating the validity of theoretical models and postulating new models based on measurements. Such measurements, analysis, and modeling are the topic of this thesis. The focus of the included contributions are Multiple-Input Multiple-Output (MIMO) propagation channels and radio channels for sensor network applications. Paper I presents results from one of the first MIMO measurements for a double-directional characterization of the outdoor-to-indoor wireless propagation channel. Such channels are of interest for both cellular and wireless LAN applications. We discuss physical aspects of building penetration, and also provide statistics of angle and delay spreads in the channel. The paper also investigates the coupling between DOD and DOA and the two spectra are found to have non-negligible dependence. We test the applicability of three analytical channel models that make different assumptions on the coupling between DODs and DOAs. Our results indicate that analytical models, that impose fewer restrictions on the DOD to DOA coupling, should be used preferrably over models such as the Kronecker model that have more restrictive assumptions. Paper II presents a cluster-based analysis of the outdoor-to-indoor MIMO measurements analyzed in Paper I. A subset of parameters of the COST 273 channel model, a generic model for MIMO propagation channels, are characterized for the outdoor-to-indoor scenario. MPC parameters are extracted at each measured location using a high-resolution algorithm and clusters of MPCs are identified with an automated clustering approach. In particular, the adopted clustering approach requires that all MPC parameters must be similar in order for the MPCs to form a cluster. A statistical analysis of the identified clusters is performed for both the intra- and inter-cluster properties. Paper III analyzes the spatial fading distribution for a range of canonical sensor deployment scenarios. The presented results are relevant to communicating within, and between, clusters of nodes. Contrary to the widely accepted assumption in published literature that the channel is AWGN at a small-enough distance, our measurements indicate that values of the Rice factor do not, in general, increase monotonically as the Tx-Rx distance is reduced. A probability mixture model is presented, with distance dependent parameters, to account for the distance dependent variations of the Rice factor. A simulation model that includes small- and large-scale fading effects is presented. According to the modeling approach, a sensor node placed anywhere within the spatial extent of a small-scale region will experience the channel statistics applicable to that region. Paper IV presents results characterizing a radio channel for outdoor short-range sensor networks. A number of antennas are placed on the ground in an open area and time-variation of the channel is induced by a person moving in the vicinity of the nodes. The channel statistics of both the LOS path and the overall narrowband signal are non-stationary. We investigate the stationarity interval length to be used for small-scale analysis. Our analysis of the various measured links shows that the Rx signal strength is significantly influenced by a moving person only when the person blocks the LOS path. We present a generic approach for modeling the LOS blockage, and also model the time-variant Doppler spectrum of the channel's scattered components
Empirical Rates Characterization of Wearable Multi-Antenna Terminals for First-Responders
Empirical characterization of the achievable rates for a wearable multi-antenna terminal shows the potential advantages of deploying a large number of antennas at the user end. We focus on the challenges and requirements of the broadband communication in future emergency communication systems, specifically addressing the outdoor-to-indoor propagation scenario, where the first responder is within an underground area such as a garage or basement. The measurement campaign undertaken characterizes the flat fading multiple-input multiple-output (MIMO) channel matrices at 3.5 GHz for a maximum of M = 30 antennas deployed at the base station (BS), and N = 12 wearable antennas at the user. The achievable rates are obtained for two transmission strategies that account for the different levels of channel knowledge. In both cases, all the MIMO processing is carried out at the BS.This work was supported in part by the Spanish Government under Project MIMOTEX (TEC2014-61776-EXP), Project CIES (RTC-2015-4213-7), and Project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE), and in part by the Chilean Government through projects CONICYT under Grant Proyecto Basal FB0821, Grant Fondecyt IniciaciĂłn 11171159, and Grant VRIEA-PUCV 039.462/2017.Publicad
MIMO channel modelling and simulation for cellular and mobile-to-mobile
Recently, mobile-to-mobile (M2M) communications have received much attention due
to several emerging applications, such as wireless mobile ad hoc networks, relay-based
cellular networks, and dedicated short range communications (DSRC) for intelligent
transportation systems (e.g., IEEE 802.11p standard). Different from conventional
fixed-to-mobile (F2M) cellular systems, in M2M systems both the transmitter (Tx)
and receiver (Rx) are in motion and often equipped with low elevation antennas.
Multiple-input-multiple-output (MIMO) technologies, employing multiple antennas
at both the Tx and Rx, have widely been adopted for the third generation (3G) and
beyond-3G (B3G) F2M cellular systems due to their potential benefits of improving
coverage, link reliability, and overall system capacity. More recently, MIMO has been
receiving more and more attention for M2M systems as well.
Reliable knowledge of the propagation channel obtained from channel measurements
and corresponding channel models serve as the enabling foundation for the design
and analysis of MIMO F2M and M2M systems. Furthermore, the development of
accurate MIMO F2M and M2M channel simulation models plays a major role in the
practical simulation and performance evaluation of these systems. These form the
primary motivation behind our research on MIMO channel modelling and simulation
for F2M cellular and M2M communication systems.
In this thesis, we first propose a new wideband theoretical multiple-ring based MIMO
regular-shaped geometry-based stochastic model (RS-GBSM) for non-isotropic scattering
F2M macro-cell scenarios and then derive a generic space-time-frequency (STF)
correlation function (CF). The proposed theoretical reference wideband model can be
reduced to a narrowband one-ring model, a new closed-form STF CF of which is derived
as well. Narrowband and wideband sum-of-sinusoids (SoS) simulation models
are then developed, demonstrating a good agreement with the corresponding reference
models in terms of correlation functions.
Secondly, based on a well-known narrowband two-ring single-input single-output (SISO)
M2M channel reference model, we propose new deterministic and stochastic SoS simulation
models for non-isotropic scattering environments. The proposed deterministic
simulator is the first SISO M2M deterministic simulator with good performance, while
the proposed stochastic simulator outperforms the existing one in terms of fitting the
desired statistical properties of the corresponding reference model.
Thirdly, a new adaptive narrowband MIMO M2M RS-GBSM is proposed for nonisotropic
scattering environments. To the best of our knowledge, the proposed M2M
model is the first RS-GBSM that has the ability to study the impact of the vehicular
traffic density on channel statistics. From the proposed theoretical reference
model, we comprehensively investigate some important M2M channel statistics including
the STF CF, space-Doppler-frequency power spectral density, envelope level
crossing rate, and average fade duration. A close agreement between some channel
statistics obtained from the proposed reference model and measurement data is
observed, confirming the utility of our model.
Finally, we extend the above narrowband model to a new wideband MIMO M2M RSGBSM
with respect to the frequency-selectivity. The proposed wideband reference
model is validated by observing a good match between some statistical properties of
the theoretical model and available measurement data. From the wideband reference
model, we further design new wideband deterministic and stochastic SoS simulation
models. The proposed wideband simulators can be easily reduced to narrowband
ones. The utilities of the newly derived narrowband and wideband simulation models
are validated by comparing their statistical properties with those of the corresponding
reference models.
The proposed channel reference models and simulators are expected to be useful for
the design, testing, and performance evaluation of future MIMO cellular and M2M
communication systems.Scottish Funding Counci
Massive MIMO Performance - TDD Versus FDD: What Do Measurements Say?
Downlink beamforming in Massive MIMO either relies on uplink pilot
measurements - exploiting reciprocity and TDD operation, or on the use of a
predetermined grid of beams with user equipments reporting their preferred
beams, mostly in FDD operation. Massive MIMO in its originally conceived form
uses the first strategy, with uplink pilots, whereas there is currently
significant commercial interest in the second, grid-of-beams. It has been
analytically shown that in isotropic scattering (independent Rayleigh fading)
the first approach outperforms the second. Nevertheless there remains
controversy regarding their relative performance in practice. In this
contribution, the performances of these two strategies are compared using
measured channel data at 2.6 GHz.Comment: Submitted to IEEE Transactions on Wireless Communications,
31/Mar/201
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