47,123 research outputs found
Wideband Self-Adaptive RF Cancellation Circuit for Full-Duplex Radio: Operating Principle and Measurements
This paper presents a novel RF circuit architecture for self-interference
cancellation in inband full-duplex radio transceivers. The developed canceller
is able to provide wideband cancellation with waveform bandwidths in the order
of 100 MHz or beyond and contains also self-adaptive or self-healing features
enabling automatic tracking of time-varying self-interference channel
characteristics. In addition to architecture and operating principle
descriptions, we also provide actual RF measurements at 2.4 GHz ISM band
demonstrating the achievable cancellation levels with different bandwidths and
when operating in different antenna configurations and under low-cost highly
nonlinear power amplifier. In a very challenging example with a 100 MHz
waveform bandwidth, around 41 dB total cancellation is obtained while the
corresponding cancellation figure is close to 60 dB with the more conventional
20 MHz carrier bandwidth. Also, efficient tracking in time-varying reflection
scenarios is demonstrated.Comment: 7 pages, to be presented in 2015 IEEE 81st Vehicular Technology
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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
Beam Based Stochastic Model of the Coverage Probability in 5G Millimeter Wave Systems
Communications using frequency bands in the millimeter-wave range can play a
key role in future generations of mobile networks. By allowing large bandwidth
allocations, high carrier frequencies will provide high data rates to support
the ever-growing capacity demand. The prevailing challenge at high frequencies
is the mitigation of large path loss and link blockage effects. Highly
directional beams are expected to overcome this challenge. In this paper, we
propose a stochastic model for characterizing beam coverage probability. The
model takes into account both line-of-sight and first-order non-line-of-sight
reflections. We model the scattering environment as a stochastic process and we
derive an analytical expression of the coverage probability for any given beam.
The results derived are validated numerically and compared with simulations to
assess the accuracy of the model
Coverage prediction and optimization algorithms for indoor environments
A heuristic algorithm is developed for the prediction of indoor coverage. Measurements on one floor of an office building are performed to investigate propagation characteristics and validations with very limited additional tuning are performed on another floor of the same building and in three other buildings. The prediction method relies on the free-space loss model for every environment, this way intending to reduce the dependency of the model on the environment upon which the model is based, as is the case with many other models. The applicability of the algorithm to a wireless testbed network with fixed WiFi 802.11b/g nodes is discussed based on a site survey. The prediction algorithm can easily be implemented in network planning algorithms, as will be illustrated with a network reduction and a network optimization algorithm. We aim to provide an physically intuitive, yet accurate prediction of the path loss for different building types
Insights and approaches for low-complexity 5G small-cell base-station design for indoor dense networks
This paper investigates low-complexity approaches to small-cell base-station (SBS) design, suitable for future 5G millimeter-wave (mmWave) indoor deployments. Using large-scale antenna systems and high-bandwidth spectrum, such SBS can theoretically achieve the anticipated future data bandwidth demand of 10000 fold in the next 20 years. We look to exploit small cell distances to simplify SBS design, particularly considering dense indoor installations. We compare theoretical results, based on a link budget analysis, with the system simulation of a densely deployed indoor network using appropriate mmWave channel propagation conditions. The frequency diverse bands of 28 and 72 GHz of the mmWave spectrum are assumed in the analysis. We investigate the performance of low-complexity approaches using a minimal number of antennas at the base station and the user equipment. Using the appropriate power consumption models and the state-of-the-art sub-component power usage, we determine the total power consumption and the energy efficiency of such systems. With mmWave being typified nonline-of-sight communication, we further investigate and propose the use of direct sequence spread spectrum as a means to overcome this, and discuss the use of multipath detection and combining as a suitable mechanism to maximize link reliability
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