947 research outputs found
Modified Threshold-based Spectrum Sensing Approach for VANETs
The Primary User (PU) signal detection in Cognitive Radio (CR) is crucial and is achieved through spectrum sensing techniques. The Energy Detection method is a commonly used technique, and selecting a proper threshold is essential to enhance the efficiency of the CR system. This research paper demonstrates the maximum achievable throughput and validates a Modified Threshold (MT) approach. The authors consider a scenario with multiple antennas at the receiver, where these antennas are correlated and subjected to mobility effects, and they employ the Energy Detection (ED) for spectrum sensing. The study analyzes the system's performance over a Nakagami-m fading channel, considering available correlations among the antenna elements. To compute important statistical values, the Moment Generating Function (MGF) method is employed. The research employs specialized mathematical functions, such as the Lauricella and confluent hypergeometric functions, to derive closed-form expressions for the Probability of Detection when employing the diversity technique. The results indicate a significant enhancement in the performance of the proposed algorithm when utilizing the modified threshold parameter across a wide range of Signal to Noise Ratio (SNR) values. Additionally, increasing the number of branches in the antenna system further improves detection performance. Interestingly, under high fading parameter conditions (m=4), the detection probability is found to be superior with exponential correlation among the L antenna elements compared to other available correlated branches
Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays
Massive MIMO (multiple-input multiple-output) is no longer a "wild" or
"promising" concept for future cellular networks - in 2018 it became a reality.
Base stations (BSs) with 64 fully digital transceiver chains were commercially
deployed in several countries, the key ingredients of Massive MIMO have made it
into the 5G standard, the signal processing methods required to achieve
unprecedented spectral efficiency have been developed, and the limitation due
to pilot contamination has been resolved. Even the development of fully digital
Massive MIMO arrays for mmWave frequencies - once viewed prohibitively
complicated and costly - is well underway. In a few years, Massive MIMO with
fully digital transceivers will be a mainstream feature at both sub-6 GHz and
mmWave frequencies. In this paper, we explain how the first chapter of the
Massive MIMO research saga has come to an end, while the story has just begun.
The coming wide-scale deployment of BSs with massive antenna arrays opens the
door to a brand new world where spatial processing capabilities are
omnipresent. In addition to mobile broadband services, the antennas can be used
for other communication applications, such as low-power machine-type or
ultra-reliable communications, as well as non-communication applications such
as radar, sensing and positioning. We outline five new Massive MIMO related
research directions: Extremely large aperture arrays, Holographic Massive MIMO,
Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive
MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin
Efficient BER simulation of orthogonal space-time block codes in Nakagami-m fading
In this contribution, we present a simple but efficient importance sampling technique to speed up Monte Carlo simulations for bit error rate estimation of orthogonal space-time block codes on spatially correlated Nakagami-m fading channels. While maintaining the actual distributions for the channel noise and the data symbols, we derive a convenient biased distribution for the fading channel that is shown to result in impressive efficiency gains up to multiple orders of magnitude
Uncoded space-time labelling diversity : data rate & reliability enhancements and application to real-world satellite broadcasting.
Doctoral Degree. University of KwaZulu-Natal, Durban.Abstract available in PDF
Massive MIMO with Dual-Polarized Antennas
This paper considers a single-cell massive MIMO (multiple-input
multiple-output) system with dual-polarized antennas at both the base station
and users. We study a channel model that includes the key practical aspects
that arise when utilizing dual-polarization: channel cross-polar discrimination
(XPD) and cross-polar correlations (XPC) at the transmitter and receiver. We
derive the achievable uplink and downlink spectral efficiencies (SE) with and
without successive interference cancellation (SIC) when using the linear
minimum mean squared error (MMSE), zero-forcing (ZF), and maximum ratio (MR)
combining/precoding schemes. The expressions depend on the statistical
properties of the MMSE channel estimator obtained for the dual-polarized
channel model. Closed-form uplink and downlink SE expressions for MR
combining/precoding are derived. Using these expressions, we propose
power-control algorithms that maximize the uplink and downlink sum SEs under
uncorrelated fading but can be used to enhance performance also with correlated
fading. We compare the SEs achieved in dual-polarized and uni-polarized setups
numerically and evaluate the impact of XPD and XPC conditions. The simulations
reveal that dual-polarized setups achieve 40-60\% higher SEs and the gains
remain also under severe XPD and XPC. Dual-polarized also systems benefit more
from advanced signal processing that compensates for imperfections.Comment: 15 pages, 9 figures. To appear in IEEE Transactions on Wireless
Communication
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