1,021 research outputs found
Power Scaling of Uplink Massive MIMO Systems with Arbitrary-Rank Channel Means
This paper investigates the uplink achievable rates of massive multiple-input
multiple-output (MIMO) antenna systems in Ricean fading channels, using
maximal-ratio combining (MRC) and zero-forcing (ZF) receivers, assuming perfect
and imperfect channel state information (CSI). In contrast to previous relevant
works, the fast fading MIMO channel matrix is assumed to have an arbitrary-rank
deterministic component as well as a Rayleigh-distributed random component. We
derive tractable expressions for the achievable uplink rate in the
large-antenna limit, along with approximating results that hold for any finite
number of antennas. Based on these analytical results, we obtain the scaling
law that the users' transmit power should satisfy, while maintaining a
desirable quality of service. In particular, it is found that regardless of the
Ricean -factor, in the case of perfect CSI, the approximations converge to
the same constant value as the exact results, as the number of base station
antennas, , grows large, while the transmit power of each user can be scaled
down proportionally to . If CSI is estimated with uncertainty, the same
result holds true but only when the Ricean -factor is non-zero. Otherwise,
if the channel experiences Rayleigh fading, we can only cut the transmit power
of each user proportionally to . In addition, we show that with an
increasing Ricean -factor, the uplink rates will converge to fixed values
for both MRC and ZF receivers
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
Time- and Frequency-Varying -Factor of Non-Stationary Vehicular Channels for Safety Relevant Scenarios
Vehicular communication channels are characterized by a non-stationary time-
and frequency-selective fading process due to fast changes in the environment.
We characterize the distribution of the envelope of the first delay bin in
vehicle-to-vehicle channels by means of its Rician -factor. We analyze the
time-frequency variability of this channel parameter using vehicular channel
measurements at 5.6 GHz with a bandwidth of 240 MHz for safety-relevant
scenarios in intelligent transportation systems (ITS). This data enables a
frequency-variability analysis from an IEEE 802.11p system point of view, which
uses 10 MHz channels. We show that the small-scale fading of the envelope of
the first delay bin is Ricean distributed with a varying -factor. The later
delay bins are Rayleigh distributed. We demonstrate that the -factor cannot
be assumed to be constant in time and frequency. The causes of these variations
are the frequency-varying antenna radiation patterns as well as the
time-varying number of active scatterers, and the effects of vegetation. We
also present a simple but accurate bi-modal Gaussian mixture model, that allows
to capture the -factor variability in time for safety-relevant ITS
scenarios.Comment: 26 pages, 12 figures, submitted to IEEE Transactions on Intelligent
Transportation Systems for possible publicatio
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
People-Sensing Spatial Characteristics of RF Sensor Networks
An "RF sensor" network can monitor RSS values on links in the network and
perform device-free localization, i.e., locating a person or object moving in
the area in which the network is deployed. This paper provides a statistical
model for the RSS variance as a function of the person's position w.r.t. the
transmitter (TX) and receiver (RX). We show that the ensemble mean of the RSS
variance has an approximately linear relationship with the expected total
affected power (ETAP). We then use analysis to derive approximate expressions
for the ETAP as a function of the person's position, for both scattering and
reflection. Counterintuitively, we show that reflection, not scattering, causes
the RSS variance contours to be shaped like Cassini ovals. Experimental tests
reported here and in past literature are shown to validate the analysis
Rooftop and indoor reception with transmit diversity applied to DVB-T networks: A long term measurement campaign
Although transmit Delay Diversity (DD) can
provide a gain in indoor and other Non Line of Sight situations (NLOS), it can introduce degradation in rooftop reception. In fact, when the Ricean K factor of the channel
is significantly high (e.g. Line of Sight reception), the channel performs similar to an AWGN channel where the performance degrades due to DD that artificially increase
the fading. This paper investigates through practical evaluation the impacts of Transmit DD on LOS and NLOS stationary reception. Then, it studies 2 techniques to reduce the degradation performance in LOS while aiming
to keep the same diversity gain in NLOS receptio
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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