Throughput Maximization in Unmanned Aerial Vehicle Networks

The use of Unmanned Aerial Vehicles (UAVs) swarms in civilian applications such as surveillance, agriculture, search and rescue, and border patrol is becoming popular. UAVs have also found use as mobile or portable base stations. In these applications, communication requirements for UAVs are generally stricter as compared to conventional aircrafts. Hence, there needs to be an efficient Medium Access Control (MAC) protocol that ensures UAVs experience low channel access delays and high throughput. Some challenges when designing UAVs MAC protocols include interference and rapidly changing channel states, which require a UAV to adapt its data rate to ensure data transmission success. Other challenges include Quality of Service (QoS) requirements and multiple contending UAVs that result in collisions and channel access delays. To this end, this thesis aims to utilize Multi-Packet Reception (MPR) technology. In particular, it considers nodes that are equipped with a Successive Interference Cancellation (SIC) radio, and thereby, allowing them to receive multiple transmissions simultaneously. A key problem is to identify a suitable a Time Division Multiple Access (TDMA) transmission schedule that allows UAVs to transmit successfully and frequently. Moreover, in order for SIC to operate, there must be a sufficient difference in received power. However, in practice, due to the location and orientation of nodes, the received power of simultaneously transmitting nodes may cause SIC decoding to fail at a receiver. Consequently, a key problem concerns the placement and orientation of UAVs to ensure there is diversity in received signal strength at a receiving node. Lastly, interference between UAVs serving as base station is a critical issue. In particular, their respective location may have excessive interference or cause interference to other UAVs; all of which have an impact on the schedule used by these UAVs to serve their respective users

MAC Protocols for Wireless Mesh Networks with Multi-beam Antennas: A Survey

Multi-beam antenna technologies have provided lots of promising solutions to many current challenges faced in wireless mesh networks. The antenna can establish several beamformings simultaneously and initiate concurrent transmissions or receptions using multiple beams, thereby increasing the overall throughput of the network transmission. Multi-beam antenna has the ability to increase the spatial reuse, extend the transmission range, improve the transmission reliability, as well as save the power consumption. Traditional Medium Access Control (MAC) protocols for wireless network largely relied on the IEEE 802.11 Distributed Coordination Function(DCF) mechanism, however, IEEE 802.11 DCF cannot take the advantages of these unique capabilities provided by multi-beam antennas. This paper surveys the MAC protocols for wireless mesh networks with multi-beam antennas. The paper first discusses some basic information in designing multi-beam antenna system and MAC protocols, and then presents the main challenges for the MAC protocols in wireless mesh networks compared with the traditional MAC protocols. A qualitative comparison of the existing MAC protocols is provided to highlight their novel features, which provides a reference for designing the new MAC protocols. To provide some insights on future research, several open issues of MAC protocols are discussed for wireless mesh networks using multi-beam antennas.Comment: 22 pages, 6 figures, Future of Information and Communication Conference (FICC) 2019, https://doi.org/10.1007/978-3-030-12388-8_

Efficient detection and scheduling for MIMO-OFDM systems

Multiple-input multiple-output (MIMO) antennas can be exploited to provide high data rate using a limited bandwidth through multiplexing gain. MIMO combined with orthogonal frequency division multiplexing (OFDM) could potentially provide high data rate and high spectral efficiency in frequency-selective fading channels. MIMO-OFDM technology has been widely employed in modern communication systems, such as Wireless Local Area Network (WLAN), Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). However, most of the conventional schemes either are computationally prohibitive or underutilize the full performance gain provided by the inherent merits of MIMO and OFDM techniques. In the first part of this dissertation, we firstly study the channel matrix inversion which is commonly required in various MIMO detection schemes. An algorithm that exploits second-order extrapolation in the time domain is proposed to efficiently reduce the computational complexity. This algorithm can be applied to both linear detection and non-linear detection such as ordered successive interference cancellation (OSIC) while maintaining the system performance. Secondly, we study the complexity reduction for Lattice Reduction Aided Detection (LRAD) of MIMO-OFDM systems. We propose an algorithm that exploits the inherent feature of unimodular transformation matrix that remains the same for relatively highly correlated frequency components. This algorithm effectively eliminates the redundant brute-force lattice reduction iterations among adjacent subcarriers. Thirdly, we analyze the impact of channel coherence bandwidth on two LRAD algorithms. Analytical and simulation results demonstrate that carefully setting the initial calculation interval according to the coherence bandwidth is essential for both algorithms. The second part of this dissertation focuses on efficient multi-user (MU) scheduling and coordination for the uplink of WLAN that uses MIMO-OFDM techniques. On one hand, conventional MU-MIMO medium access control (MAC) protocols require large overhead, which lowers the performance gain of concurrent transmissions rendered by the multi-packet reception (MPR) capability of MIMO systems. Therefore, an efficient MU-MIMO uplink MAC scheduling scheme is proposed for future WLAN. On the other hand, single-user (SU) MIMO achieves multiplexing gain in the physical (PHY) layer and MU-MIMO achieves multiplexing gain in the MAC layer. In addition, the average throughput of the system varies depending on the number of antennas and users, average payload sizes, and signal-to-noise-ratios (SNRs). A comparison on the performance between SU-MIMO and MU-MIMO schemes for WLAN uplink is hence conducted. Simulation results indicate that a dynamic switch between the SU-MIMO and MU-MIMO is of significance for higher network throughput of WLAN uplink

Advanced PHY/MAC Design for Infrastructure-less Wireless Networks

Wireless networks play a key role in providing information exchange among distributed mobile devices. Nowadays, Infrastructure-Less Wireless Networks (ILWNs), which include ad hoc and sensor networks, are gaining increasing popularity as they do not need a fixed infrastructure. Simultaneously, multiple research initiatives have led to different findings at the physical (PHY) layer of the wireless communication systems, which can effectively be adopted in ILWNs. However, the distributed nature of ILWNs demand for different network control policies that should have into account the most recent findings to increase the network performance. This thesis investigates the adoption of Multi-Packet Reception (MPR) techniques at the PHY layer of distributed wireless networks, which is itself a challenging task due to the lack of a central coordinator and the spatial distribution of the nodes. The work starts with the derivation of an MPR system performance model that allows to determine optimal points of operation for different radio conditions. The model developed and validated in this thesis is then used to study the performance of ILWNs in high density of transmitters and when the spectrum can be sensed a priori (i.e. before each transmission). Based on the theoretical analysis developed in the thesis, we show that depending on the propagation conditions the spectrum sensing can reduce the network throughput to a level where its use should be avoided. At the final stage, we propose a crosslayered architecture that improves the capacity of an ILWN. Different Medium Access Control (MAC) schemes for ILWNs adopting MPR communications are proposed and their performance is theoretically characterized. We propose a cross-layer optimization methodology that considers the features of the MPR communication scheme together with the MAC performance. The proposed cross-layer optimization methodology improves the throughput of ILWNs, which is validated through theoretical analysis and multiple simulation results

Performance Analysis of Channel-Aware Media Access Control Schemes

This thesis proposes a new Channel-Aware MAC (CA-MAC) protocol that allows more than two simultaneous transmissions to take place within a single wireless collision domain. In this proposed work, Multiple-Input Multiple-Output (MIMO) system is used to achieve higher spectral efficiency. The MIMO-based PHY layer has been adopted to help in controlling the transmission and to avoid any collisions by using weights gains technique on the antenna transmission, and by recovering any possible collisions using ZigZag decoding. In order to develop CA-MAC algorithm, to exploit the full potential of MIMO system, the library of 802.11x standard has been modified. NS-2 based simulations were conducted to study the performance of the proposed system. Detailed analysis and comparisons with current protocols schemes are presented

Improving the Performance of Wireless LANs

This book quantifies the key factors of WLAN performance and describes methods for improvement. It provides theoretical background and empirical results for the optimum planning and deployment of indoor WLAN systems, explaining the fundamentals while supplying guidelines for design, modeling, and performance evaluation. It discusses environmental effects on WLAN systems, protocol redesign for routing and MAC, and traffic distribution; examines emerging and future network technologies; and includes radio propagation and site measurements, simulations for various network design scenarios, numerous illustrations, practical examples, and learning aids

Cross-Layer design and analysis of cooperative wireless networks relying on efficient coding techniques

2011/2012This thesis work aims at analysing the performance of efficient cooperative techniques and of smart antenna aided solutions in the context of wireless networks. Particularly, original contributions include a performance analysis of distributed coding techniques for the physical layer of communication systems, the design of practical efficient coding schemes that approach the analytic limiting bound, the cross-layer design of cooperative medium access control systems that incorporate and benefit from advanced physical layer techniques, the study of the performance of such solutions under realistic network assumptions, and, finally the design of access protocols where nodes are equipped with smart antenna systems.XXV Ciclo198

Cross-layer Design for Wireless Mesh Networks with Advanced Physical and Network Layer Techniques

Cross-layer optimization is an essential tool for designing wireless network protocols. We present a cross-layer optimization framework for wireless networks where at each node, various smart antenna techniques such as beam-forming, spatial division multiple access and spatial division multiplexing are employed. These techniques provide interference suppression, capability for simultaneous communication with several nodes and transmission with higher data rates, respectively. By integrating different combinations of these multi-antenna techniques in physical layer with various constraints from MAC and network layers, three Mixed Integer Linear Programming models are presented to minimize the scheduling period. Since these optimization problems are combinatorially complex, the optimal solution is approached by a Column Generation (CG) decomposition method. Our numerical results show that the resulted directive, multiple access and multiplexing gains combined with scheduling, effectively increase both the spatial reuse and the capacity of the links and therefore enhance the achievable system throughput. The introduced cross-layer approach is also extended to consider heterogeneous networks where we present a multi-criteria optimization framework to model the design problem with an objective of jointly minimizing the cost of deployment and the scheduling period. Our results reveal the significant benefits of this joint design method. We also investigate the achievable performance gain that network coding (with opportunistic listening) when combined with Successive Interference Cancellation (SIC) brings to a multi-hop wireless network. We develop a cross-layer formulation in which SIC enables concurrent receptions from multiple transmitters and network coding reduces the transmission time-slot for minimizing the scheduling time. To solve this combinatorially complex non-linear problem, we decompose it to two linear sub-problems; namely opportunistic network coding aware routing, and scheduling sub-problems. Our results affirm our expectation for a remarkable performance improvement when both techniques are jointly used. Further, we develop an optimization model for combining SIC with power control (PC). Our model optimally adjusts the transmission power of nodes to avoid interference on unintended receivers and properly embraces undesired interference through SIC. Therefore, it provides a balance between usage of PC and SIC at the transmitting and receiving sides, respectively. Our results show considerable throughput improvement in dense and heavily loaded networks