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

On the Design of MAC Protocols for Multi-Packet Communication in IEEE 802.11 Heterogeneous Networks Using Adaptive Antenna Arrays

This paper discusses the design requirements for enabling multiple simultaneous peer-to-peer communications in IEEE 802.11 asynchronous networks in the presence of adaptive antenna arrays, and proposes two novel access schemes to realize multipacket communication (MPC). Both presented solutions, which rely on the information acquired by each node during the monitoring of the network activity, are suitable for distributed and heterogeneous scenarios, where nodes equipped with different antenna systems can coexist. The first designed scheme, called threshold access MPC (TAMPC), is based on a threshold on the load sustainable by the single-node, while the second protocol, called signal-to-interference ratio (SIR) access MPC (SAMPC), is based on an accurate estimation of the SIR and on the adoption of low density parity check codes. Both protocols, which are designed to be backward compatible with the 802.11 standard, are numerically tested in realistic scenarios. Furthermore, the performance of the two schemes is compared to the theoretical one and to that of the 802.11n extension in a mobile environment

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

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

SNR-Based OLSR Routing Protocol for Wireless Mesh Networks

Wireless Mesh Networks (WMNs) consist of a collection of mobile and fixed nodes that form a network. Nodes are capable of communicating with each other either with infrastructure, or infrastructureless, or in a hybrid mode. The major advantages of WMNs over the other wireless networks are the low-cost, self organization, self configuration, last mile internet solution, scalability, and reliability. These advantages have attracted the researcher over the last five years. WMNs technology is gaining an increased attention from the Institute of Electrical and Electronics Engineers (IEEE) community. This led the IEEE organization to emerge a special working group (IEEE 802.11s) in charge of the issues deriving from a completely wireless distribution system used to interconnect different Basic Service Sets (BSSs) through secure and performing links. In a multi-hop networks, like WMN, one of the main factors that influences the performance is the routing protocol. Generally speaking, routing protocols can be classified based-on the routing metric to 1) hop count-based routing protocols, like Adhoc on demand distance vector (AODV) where the optimum path is defined as the path that goes through the minimum number of nodes, 2) the link quality-based routing protocols, like OLSR where some metrics such as the bandwidth and the packet error rate are considered to define the optimum path to the destination. In this work the performances of a three commonly used routing protocols are compared. The main goal of this stag is to study the influence of different routing protocols in WMNs. The comparison is conducted with two scenarios of networks; a high mobility network and a low mobility network. (Open network) OPNET 11.5 modeler is used to build the WMNs. The performance of the network and the routing protocols has been studied in means of network throughput, End-to-End delay, routing protocol overhead and the mobility. The obtained results show that the Optimized link state routing protocol (OLSR) has the highestthroughput overDSR andAODVrouting protocols in WMNs. The unpredictable behavior of the wireless medium in WMNs environment demands the need for a routing protocol that is aware of the link conditions. Unfortunately the routing protocols used such as AODV and Dynamic source routing (DSR) are hop count-based; where the routing algorithm uses the number of nodes to determine the optimum path to the destination. In the second stage of this work a new routing technique for WMNs based-on Signal to noise ratio (SNR) as a new metric for OLSR routing protocol, is developed. The new metric has been implemented on the OLSR routing protocol module using OPNET simulator. The modified OLSR routing protocol is implemented in the comparison scenarios. The obtained results show that, when SNR is used as a routing metric in the OLSR routing protocol, the OLSR is getting the significantly higher network throughput over the DSR and AODV routing protocols. In the same time, the modified OLSR implemented with the SNR metric is showing a high improvement over the OLSR with the traditional hop-count metric. This thesis also studies the affect of different amounts of mobility in WMNs performance. VI

Capacity and performance study of IEEE 802.11e in WLANs and ad hoc networks

This master thesis focuses on the IEEE 802.11e Enhanced Distribution Channel Access (EDCA). The IEEE 802.11e protocol became an IEEE standard in November 2005 and is a very popular research topic. Even though the protocol has been tested for faults and errors a long time there are still research topics to explore. This thesis will try to answer some of those topics. The main topic in this thesis is how the IEEE 802.11e MAC operates in a multihop ad hoc network. We discuss and evaluated the findings along with simulation results, and compare our work with earlier work on the same topic that used the legacy IEEE 802.11 standard. The results we present are interesting throughput results that seem to tell us that the new IEEE 802.11e is better then the original WLAN standard when it comes to multihop ad hoc network forwarding

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