256 research outputs found
Lightly synchronized Multipacket Reception in Machine-Type Communications Networks
Machine Type Communication (MTC) applications were designed to monitor and control
elements of our surroundings and environment. MTC applications have a different
set of requirements compared to the traditional communication devices, with Machine to
Machine (M2M) data being mostly short, asynchronous, bursty and sometimes requiring end-to-end delays below 1ms. With the growth of MTC, the new generation of mobile communications has to be able to present different types of services with very different requirements, i.e. the same network has to be capable of "supplying" connection to the user that just wants to download a video or use social media, allowing at the same time MTC that has completely different requirements, without deteriorating both experiences.
The challenges associated to the implementation of MTC require disruptive changes at
the Physical (PHY) and Medium Access Control (MAC) layers, that lead to a better use of the spectrum available. The orthogonality and synchronization requirements of the PHY layer of current Long Term Evolution Advanced (LTE-A) radio access network (based on glsofdm and Single Carrier Frequency Domain Equalization (SC-FDE)) are obstacles for this new 5th Generation (5G) architecture. Generalized Frequency Division Multiplexing (GFDM) and other modulation techniques were proposed as candidates for the 5G PHY layer, however they also suffer from visible degradation when the transmitter and receiver are not synchronized, leading to a poor performance when collisions occur in an asynchronous MAC layer. This dissertation addresses the requirements of M2M traffic at the MAC layer applying multipacket reception (MPR) techniques to handle the bursty nature of the traffic and synchronization tones and optimized back-off approaches to reduce the delay. It proposes a new MAC protocol and analyses its performance analytically considering an SC-FDE modulation. The models are validated using a system level cross-layer simulator developed in MATLAB, which implements the MAC protocol and applies PHY layer performance models. The results show that the MAC’s latency depends mainly on the number of users and the load of each user, and can be controlled using these two parameters
Short Range Gigabit Wireless Communications Systems: Potentials, Challenges and Techniques
In this paper, we discuss multi-gigabits per second wireless networks in the 60GHz millimeter wave frequency band. Despite the large unlicensed bandwidth offered by the 60GHz frequency band, severe technical challenges exist towards making multi-Gbps a reality. We discuss the challenges in three different layers: PHY, MAC and the application layers. We also discuss some important technologies in overcoming these challenges, including antenna array beamforming, baseband modulation, data aggregation. The worldwide 60GHz regulatory and the ongoing standardization efforts are reviewed as well
Protocol for Extreme Low Latency M2M Communication Networks
As technology evolves, more Machine to Machine (M2M) deployments and mission critical
services are expected to grow massively, generating new and diverse forms of data
traffic, posing unprecedented challenges in requirements such as delay, reliability, energy
consumption and scalability. This new paradigm vindicates a new set of stringent requirements
that the current mobile networks do not support. A new generation of mobile
networks is needed to attend to this innovative services and requirements - the The fifth
generation of mobile networks (5G) networks. Specifically, achieving ultra-reliable low
latency communication for machine to machine networks represents a major challenge,
that requires a new approach to the design of the Physical (PHY) and Medium Access
Control (MAC) layer to provide these novel services and handle the new heterogeneous
environment in 5G. The current LTE Advanced (LTE-A) radio access network orthogonality
and synchronization requirements are obstacles for this new 5G architecture, since
devices in M2M generate bursty and sporadic traffic, and therefore should not be obliged
to follow the synchronization of the LTE-A PHY layer. A non-orthogonal access scheme
is required, that enables asynchronous access and that does not degrade the spectrum.
This dissertation addresses the requirements of URLLC M2M traffic at the MAC layer.
It proposes an extension of the M2M H-NDMA protocol for a multi base station scenario
and a power control scheme to adapt the protocol to the requirements of URLLC. The
system and power control schemes performance and the introduction of more base stations
are analyzed in a system level simulator developed in MATLAB, which implements
the MAC protocol and applies the power control algorithm.
Results showed that with the increase in the number of base stations, delay can be
significantly reduced and the protocol supports more devices without compromising
delay or reliability bounds for Ultra-Reliable and Low Latency Communication (URLLC),
while also increasing the throughput. The extension of the protocol will enable the study
of different power control algorithms for more complex scenarios and access schemes that
combine asynchronous and synchronous access
An FPGA implementation of OFDM transceiver for LTE applications
The paper presents a real-time transceiver using an
Orthogonal Frequency-Division Multiplexing (OFDM)
signaling scheme. The transceiver is implemented on a
Field-
Programmable Gate Array (FPGA) through Xilinx System
Generator for DSP and includes all the blocks needed
for the
transmission path of OFDM. The transmitter frame can be
reconfigured for different pilot and data schemes. In the
receiver, time-domain synchronization is achieved thr
ough a
joint maximum likelihood (ML) symbol arrival-time and
carrier frequency offset (CFO) estimator through the
redundant information contained in the cyclic prefix (CP).
A
least-squares channel estimation retrieves the channel
state
information and a simple zero-forcing scheme has been
implemented for channel equalization. Results show that a
rough implementation of the signal path can be impleme
nted
by using only Xilinx System Generator for DSP
Recent Advances in Wireless Communications and Networks
This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters
Robust Wireless Communication for Multi-Antenna, Multi-Rate, Multi-Carrier Systems
Abstract Today's trend of migrating radio devices from hardware to software provides potential to create flexible applications for both commercial and military use. However, this raises security concerns, as malicious attackers can also be generated easily to break legitimate communications. In this research work, our goal is to design a robust anti-jamming radio framework. We particularly investigate three different aspects of jamming threats: high-power jammers, link attacks on rate adaptation, and jamming in multicarrier systems. The threats of high-power jamming to wireless communications today are realistic due to the ease of access to powerful jamming sources such as the availability of commercial GPS/WiFi/cellular devices on the market, or RF guns built from microwave ovens' magnetron. To counter high-power jamming attacks, we develop SAIM which is a hybrid system capable of resisting jammers of up to 100,000 times higher power than legitimate communication nodes. The system robustness relies on our own antenna structure specially designed for anti-jamming purpose. We develop an efficient algorithm for auto-configuring the antenna adaptively to dynamic environments. We also devise a software-based jamming cancellation technique for appropriately extracting original signals, which is more robust than traditional MIMO approaches, as pilot signals are not required in SAIM. In spite of the robustness of SAIM, our design is more appropriate for malicious environments with powerful jammers, where mechanical steering is feasible, e.g., military applications. Residential and commercial wireless communication systems are still vulnerable to even limited-power jamming, as in today's standard wireless protocols, rate information is exposed to adversaries. Rate-based attacks have been demonstrated to severely degrade the networks at very low cost. To mitigate rate-based attacks, we develop CBM, a system capable of hiding rate and -at the same time -increasing resiliency against jammers up to seven times higher than regular systems, where rate is exposed. We achieve the resiliency boost by generalizing Trellis Coded Modulation to allow non-uniform codeword mapping. We develop an efficient algorithm for finding good non-uniform codes for all modulations in {BPSK, QPSK, 8-PSK, 16-QAM, 64-QAM}. To conceal rate information, we devise an efficient method for generating cryptographic interleaving functions. In recently deployed communication networks such as WiFi and LTE systems, MIMO and OFDM are the two main techniques for increasing bandwidth efficiency. While MIMO increases the channel capacity by spatial processing on multiple received signals, OFDM mitigates impacts of dynamic variations in wide-band channels and allows frequency reuse with overlapping carriers. Synchronization is a key for high-throughput performance in MIMO and OFDM systems. In this work, we study impacts of jamming attacks specifically targeting to control channels in WiFi and LTE networks. Our study focuses on efficient techniques for both jamming and anti-jamming in multicarrier systems
Subcarrier and Power Allocation in WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is one of the latest technologies for providing Broadband Wireless Access (BWA) in a metropolitan area. The use of orthogonal frequency division multiplexing (OFDM) transmissions has been proposed in WiMAX to mitigate the complications which are associated with frequency selective channels. In addition, the multiple access is achieved by using orthogonal frequency division multiple access (OFDMA) scheme which has several advantages such as flexible resource allocation, relatively simple transceivers, and high spectrum efficient. In OFDMA the controllable resources are the subcarriers and the allocated power per subband. Moreover, adaptive subcarrier and power allocation techniques have been selected to exploit the natural multiuser diversity. This leads to an improvement of the performance by assigning the proper subcarriers to the user according to their channel quality and the power is allocated based on water-filling algorithm. One simple method is to allocate subcarriers and powers equally likely between all users. It is well known that this method reduces the spectral efficiency of the system, hence, it is not preferred unless in some applications.
In order to handle the spectral efficiency problem, in this thesis we discuss three novel resources allocation algorithms for the downlink of a multiuser OFDM system and analyze the algorithm performances based on capacity and fairness measurement. Our intensive simulations validate the algorithm performances.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
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