1,631 research outputs found
Iterative Multipacket Detection for High Throughput Transmissions in OFDM Systems
This paper presents a multipacket detection technique
for dealing with packet collisions in OFDM schemes (Orthogonal
Frequency Division Multiplexing). Instead of discarding
collided packets as it is done in traditional MAC approaches
(Medium Access Control) additional packets are transmitted
and separated using Multiple Input Multiple Output (MIMO)
based techniques. Reliable detection and high throughputs can
be achieved as long as different interleavers are used for different
retransmissions. We also include a method for estimating the
users involved in the collision
RCFD: A Novel Channel Access Scheme for Full-Duplex Wireless Networks Based on Contention in Time and Frequency Domains
In the last years, the advancements in signal processing and integrated
circuits technology allowed several research groups to develop working
prototypes of in-band full-duplex wireless systems. The introduction of such a
revolutionary concept is promising in terms of increasing network performance,
but at the same time poses several new challenges, especially at the MAC layer.
Consequently, innovative channel access strategies are needed to exploit the
opportunities provided by full-duplex while dealing with the increased
complexity derived from its adoption. In this direction, this paper proposes
RTS/CTS in the Frequency Domain (RCFD), a MAC layer scheme for full-duplex ad
hoc wireless networks, based on the idea of time-frequency channel contention.
According to this approach, different OFDM subcarriers are used to coordinate
how nodes access the shared medium. The proposed scheme leads to efficient
transmission scheduling with the result of avoiding collisions and exploiting
full-duplex opportunities. The considerable performance improvements with
respect to standard and state-of-the-art MAC protocols for wireless networks
are highlighted through both theoretical analysis and network simulations.Comment: Submitted at IEEE Transactions on Mobile Computing. arXiv admin note:
text overlap with arXiv:1605.0971
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
Versatility Of Low-Power Wide-Area Network Applications
Low-Power Wide-Area Network (LPWAN) is regarded as the leading communication technology for wide-area Internet-of-Things (IoT) applications. It offers low-power, long-range, and low-cost communication. With different communication requirements for varying IoT applications, many competing LPWAN technologies operating in both licensed (e.g., NB-IoT, LTE-M, and 5G) and unlicensed (e.g., LoRa and SigFox) bands have emerged. LPWANs are designed to support applications with low-power and low data rate operations. They are not well-designed to host applications that involve high mobility, high traffic, or real-time communication (e.g., volcano monitoring and control applications).With the increasing number of mobile devices in many IoT domains (e.g., agricultural IoT and smart city), mobility support is not well-addressed in LPWAN. Cellular-based/licensed LPWAN relies on the wired infrastructure to enable mobility. On the other hand, most unlicensed LPWANs operate on the crowded ISM band or are required to duty cycle, making handling mobility a challenge.
In this dissertation, we first identify the key opportunities of LPWAN, highlight the challenges, and show potential directions for future research. We then enable the versatility of LPWAN applications first by enabling applications involving mobility over LPWAN. Specifically, we propose to handle mobility in LPWAN over white space considering Sensor Network Over White Space (SNOW). SNOW is a highly scalable and energy-efficient LPWAN operating over the TV white spaces. TV white spaces are the allocated but locally unused available TV channels (54 - 698 MHz in the US). We proposed a dynamic Carrier Frequency Offset (CFO) estimation and compensation technique that considers the impact of the Doppler shift due to mobility. Also, we design energy-efficient and fast BS discovery and association approaches. Finally, we demonstrate the feasibility of our approach through experiments in different deployments.
Finally, we present a collision detection and recovery technique called RnR (Reverse & Replace Decoding) that applies to LPWANs. Additionally, we discuss future work to enable handling burst transmission over LPWAN and localization in mobile LPWAN
Multipacket reception in LTE femtocell networks
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresDriven by the growing demand for high-speed broadband wireless services, LTE technology
has emerged and evolve, promising high data rates to the demanding mobile users.
Based on the 3rd Generation Partnership Project (3GPP) speci cations,Long Term Evo-
lution Advanced (LTE-A) telecommunication services predict the existence of macro base
stations, Enhanced Node B (eNB) and micro stations HeNB with low power that complements
the network's coverage. This dissertation studies the complementary use of HeNBs
(femtocells 3GPP terminology) to provide broadband services. It is essential to maintain
the networks performance with the network densi cation phenomenon, which brings
signi cant interference problems and consequently more collisions and lost packets. The
use of SC-FDE in the downlink of a LTE-A femtocell network - speci cally multipacket
reception (MPR), with an IB-DFE receiver employing Multipacket Detection (MPD) and
SIC techniques is proposed. A new telecommunications concept named GC emerged with
the increasing environmental concerns. This dissertation shows the performance results
of an iterative MPR and proposes a green association algorithm to change the network
layout according to the mobile users demands reducing the Base Station (BS)'s negative
contribution to the network total energy consumption. The overall results show that the
technologies employed are a solution to achieve a favorable trade-o between performance
and Energy E ciency (EE), responding to the global demands (high data rates) and concerns
(low energy consumption and carbon footprint reduction).
Keywords: Long Term Evolution(LTE), Single Carrier with Frequency Domain
Equalization (SC-FDE), Iterative Block-Decision Feedback Equalizer (IB-DFE),
Home enhanced Node B (HeNB), Successive Interference Cancellation(SIC),Multipacket
Reception(MPR), Green Communications (GC)FCT/MEC Femtocells(PTDC/EEATEL/120666/2010), OPPORTUNISTIC CR(PTDC/EEA-TEL/115981/2009) and ADIN(PTDC/EEI-TEL/2990/2012) project
A random access MAC protocol for MPR satellite networks
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaRandom access approaches for Low Earth Orbit (LEO) satellite networks are usually incompatible
with the Quality of Service (QoS) requirements of multimedia tra c, especially when hand-held devices must operate with very low power.
Cross-Layered optimization architectures, combined with Multipacket Reception (MPR)schemes are a good choice to enhance the overall performance of a wireless system. Hybrid
Network-assisted Diversity Multiple Access (H-NDMA) protocol, exhibits high energy e ciency, with MPR capability, but its use with satellites is limited by the high round trip time. This protocol was adapted to satellites, in Satellite-NDMA, but it required a pre-reservation mechanism that introduces a signi cant delay.
This dissertation proposes a random access protocol that uses H-NDMA, for Low Earth Orbit (LEO) satellite networks, named Satellite Random-NDMA (SR-NDMA). The protocol addresses the problem inherent to satellite networks (large round trip time and signi cant energy consumption) de ning a hybrid approach with an initial random access plus possible additional scheduled retransmissions. An MPR receiver combines the multiple copies received, gradually reducing the error rate. Analytical performance models are proposed for the throughput, delay, jitter and energy e ciency considering nite queues at the terminals. It is also addressed the energy e ciency optimization, where the system
parameters are calculated to guarantee the QoS requirements.
The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) receiver. Results show that the proposed system is energy e cient and can provide enough QoS to support services such as video telephony
Massive MIMO for Internet of Things (IoT) Connectivity
Massive MIMO is considered to be one of the key technologies in the emerging
5G systems, but also a concept applicable to other wireless systems. Exploiting
the large number of degrees of freedom (DoFs) of massive MIMO essential for
achieving high spectral efficiency, high data rates and extreme spatial
multiplexing of densely distributed users. On the one hand, the benefits of
applying massive MIMO for broadband communication are well known and there has
been a large body of research on designing communication schemes to support
high rates. On the other hand, using massive MIMO for Internet-of-Things (IoT)
is still a developing topic, as IoT connectivity has requirements and
constraints that are significantly different from the broadband connections. In
this paper we investigate the applicability of massive MIMO to IoT
connectivity. Specifically, we treat the two generic types of IoT connections
envisioned in 5G: massive machine-type communication (mMTC) and ultra-reliable
low-latency communication (URLLC). This paper fills this important gap by
identifying the opportunities and challenges in exploiting massive MIMO for IoT
connectivity. We provide insights into the trade-offs that emerge when massive
MIMO is applied to mMTC or URLLC and present a number of suitable communication
schemes. The discussion continues to the questions of network slicing of the
wireless resources and the use of massive MIMO to simultaneously support IoT
connections with very heterogeneous requirements. The main conclusion is that
massive MIMO can bring benefits to the scenarios with IoT connectivity, but it
requires tight integration of the physical-layer techniques with the protocol
design.Comment: Submitted for publicatio
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