Performance Prediction and Tuning for Symmetric Coexistence of WiFi and ZigBee Networks

Due to the explosive deployment of WiFi and ZigBee wireless networks, 2.4GHz ISM bands (2.4GHz-2.5GHz) are becoming increasingly crowded, and the co-channel coexistence of these two networks is inevitable. For coexistence networks, people always want to predict their performance (e.g. throughput, energy consumption, etc.) before deployment, or even want to tune parameters to compensate unnecessary performance degradation (owing to the huge differences between these two MAC protocols) or to satisfy some performance requirements (e.g., priority, delay constraint, etc.) of them. However, predicting and tuning performance of coexisting WiFi and ZigBee networks has been a challenging task, primarily due to the lack of corresponding simulators and analytical models. In this dissertation, we addressed the aforementioned problems by presenting simulators and models for the coexistence of WiFi and ZigBee devices. Specifically, based on the energy efficiency and traffic pattern of three practical coexistence scenarios: disaster rescue site, smart hospital and home automation. We first of all classify them into three classes, which are non-sleeping devices with saturated traffic (SAT), non-sleeping devices with unsaturated traffic (UNSAT) and duty-cycling devices with unsaturated traffic (DC-UNSAT). Then a simulator and an analytical model are proposed for each class, where each simulator is verified by simple hardware based experiment. Next, we derive the expressions for performance metrics like throughput, delay etc., and predict them using both the proposed simulator and the model. Due to the higher accuracy of the simulator, the results from them are used as the ground truth to validate the accuracy of the model. Last, according to some common performance tuning requirements for each class, we formulate them into optimization problems and propose the corresponding solving methods. The results show that the proposed simulators have high accuracy in performance prediction, while the models, although are less accurate than the former, can be used in fast prediction. In particular, the models can also be easily used in optimization problems for performance tuning, and the results prove its high efficiency

Evaluation of the impact of mobility models on handover in WLAN indoor environments

Nowadays, mobility models are used to simulate realistic movements produced by the users of a wireless or a mobile network. The aim of this project is to evaluate the impact of mobility models on handover process in Wireless Local Area Networks (WLAN) indoor environments, using the network simulator NS-2. This document contains a previous theoretical characterization of the basic mobility models and their application in the network simulator NS-2, a study of the infrastructure mode support and a modification of the current handover algorithm. The study focuses on two mobility models in WLAN indoor environments: one where movements are completely random (i.e. Random Waypoint) and another one where next step depends on previous movements (i.e. Gauss-Markov). In order to support infrastructure mode operation in WLAN, a new patch with modifications of the source code is applied. Furthermore, a first approach for the development of a new handover algorithm is presented. Simulations are run in two different scenarios: one with 4 Access Points (APs) offering full coverage in the simulated area, and another one with 8 APs, simulating overcoverage in order to guarantee higher capacity for a higher density of users. Results are presented showing a comparative of the cell residence time (CRT) for each scenario. From the results obtained, it is possible to see that the CRT changes depending on the algorithm and the mobility model applied, being lower when the Random Waypoint model is applied. On the other hand, the new handover algorithm designed from the current implementation leads to a decrease in the average CRT

Performance modelling and enhancement of wireless communication protocols

In recent years, Wireless Local Area Networks(WLANs) play a key role in the data communications and networking areas, having witnessed significant research and development. WLANs are extremely popular being almost everywhere including business,office and home deployments.In order to deal with the modem Wireless connectivity needs,the Institute of Electrical and Electronics Engineers(IEEE) has developed the 802.11 standard family utilizing mainly radio transmission techniques, whereas the Infrared Data Association (IrDA) addressed the requirement for multipoint connectivity with the development of the Advanced Infrared(Alr) protocol stack. This work studies the collision avoidance procedures of the IEEE 802.11 Distributed Coordination Function (DCF) protocol and suggests certain protocol enhancements aiming at maximising performance. A new, elegant and accurate analysis based on Markov chain modelling is developed for the idealistic assumption of unlimited packet retransmissions as well as for the case of finite packet retry limits. Simple equations are derived for the through put efficiency, the average packet delay, the probability of a packet being discarded when it reaches the maximum retransmission limit, the average time to drop such a packet and the packet inter-arrival time for both basic access and RTS/CTS medium access schemes.The accuracy of the mathematical model is validated by comparing analytical with OPNET simulation results. An extensive and detailed study is carried out on the influence of performance of physical layer, data rate, packet payload size and several backoff parameters for both medium access mechanisms. The previous mathematical model is extended to take into account transmission errors that can occur either independently with fixed Bit Error Rate(BER) or in bursts. The dependency of the protocol performance on BER and other factors related to independent and burst transmission errors is explored. Furthermore, a simple-implement appropriate tuning of the back off algorithm for maximizing IEEE 802-11 protocol performance is proposed depending on the specific communication requirements. The effectiveness of the RTS/CTS scheme in reducing collision duration at high data rates is studied and an all-purpose expression for the optimal use of the RTS/CTS reservation scheme is derived. Moreover, an easy-to-implement backoff algorithm that significantly enhances performance is introduced and an alternative derivation is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Finally, an additional performance improvement scheme is proposed by employing packet bursting in order to reduce overhead costs such as contention time and RTS/CTSex changes. Fairness is explored in short-time and long-time scales for both the legacy DCF and packet bursting cases. AIr protocol employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium access. A 1-dimensional Markov chain model is constructed instead of the bi-dimensional model in order to obtain simple mathematical equations of the average packet delay.This new approach greatly simplifies previous analyses and can be applied to any CSMA/CA protocol.The derived mathematical model is validated by comparing analytical with simulation results and an extensive Alr packet delay evaluation is carried out by taking into account all the factors and parameters that affect protocol performance. Finally, suitable values for both backoff and protocol parameters are proposed that reduce average packet delay and, thus, maximize performance

On a Joint Physical Layer and Medium Access Control Sublayer Design for Efficient Wireless Sensor Networks and Applications

Wireless sensor networks (WSNs) are distributed networks comprising small sensing devices equipped with a processor, memory, power source, and often with the capability for short range wireless communication. These networks are used in various applications, and have created interest in WSN research and commercial uses, including industrial, scientific, household, military, medical and environmental domains. These initiatives have also been stimulated by the finalisation of the IEEE 802.15.4 standard, which defines the medium access control (MAC) and physical layer (PHY) for low-rate wireless personal area networks (LR-WPAN). Future applications may require large WSNs consisting of huge numbers of inexpensive wireless sensor nodes with limited resources (energy, bandwidth), operating in harsh environmental conditions. WSNs must perform reliably despite novel resource constraints including limited bandwidth, channel errors, and nodes that have limited operating energy. Improving resource utilisation and quality-of-service (QoS), in terms of reliable connectivity and energy efficiency, are major challenges in WSNs. Hence, the development of new WSN applications with severe resource constraints will require innovative solutions to overcome the above issues as well as improving the robustness of network components, and developing sustainable and cost effective implementation models. The main purpose of this research is to investigate methods for improving the performance of WSNs to maintain reliable network connectivity, scalability and energy efficiency. The study focuses on the IEEE 802.15.4 MAC/PHY layers and the carrier sense multiple access with collision avoidance (CSMA/CA) based networks. First, transmission power control (TPC) is investigated in multi and single-hop WSNs using typical hardware platform parameters via simulation and numerical analysis. A novel approach to testing TPC at the physical layer is developed, and results show that contrary to what has been reported from previous studies, in multi-hop networks TPC does not save energy. Next, the network initialization/self-configuration phase is addressed through investigation of the 802.15.4 MAC beacon interval setting and the number of associating nodes, in terms of association delay with the coordinator. The results raise doubt whether that the association energy consumption will outweigh the benefit of duty cycle power management for larger beacon intervals as the number of associating nodes increases. The third main contribution of this thesis is a new cross layer (PHY-MAC) design to improve network energy efficiency, reliability and scalability by minimising packet collisions due to hidden nodes. This is undertaken in response to findings in this thesis on the IEEE 802.15.4 MAC performance in the presence of hidden nodes. Specifically, simulation results show that it is the random backoff exponent that is of paramount importance for resolving collisions and not the number of times the channel is sensed before transmitting. However, the random backoff is ineffective in the presence of hidden nodes. The proposed design uses a new algorithm to increase the sensing coverage area, and therefore greatly reduces the chance of packet collisions due to hidden nodes. Moreover, the design uses a new dynamic transmission power control (TPC) to further reduce energy consumption and interference. The above proposed changes can smoothly coexist with the legacy 802.15.4 CSMA/CA. Finally, an improved two dimensional discrete time Markov chain model is proposed to capture the performance of the slotted 802.15.4 CSMA/CA. This model rectifies minor issues apparent in previous studies. The relationship derived for the successful transmission probability, throughput and average energy consumption, will provide better performance predictions. It will also offer greater insight into the strengths and weaknesses of the MAC operation, and possible enhancement opportunities. Overall, the work presented in this thesis provides several significant insights into WSN performance improvements with both existing protocols and newly designed protocols. Finally, some of the numerous challenges for future research are described

Performance modelling and enhancement of wireless communication protocols

In recent years, Wireless Local Area Networks(WLANs) play a key role in the data communications and networking areas, having witnessed significant research and development. WLANs are extremely popular being almost everywhere including business,office and home deployments.In order to deal with the modem Wireless connectivity needs,the Institute of Electrical and Electronics Engineers(IEEE) has developed the 802.11 standard family utilizing mainly radio transmission techniques, whereas the Infrared Data Association (IrDA) addressed the requirement for multipoint connectivity with the development of the Advanced Infrared(Alr) protocol stack. This work studies the collision avoidance procedures of the IEEE 802.11 Distributed Coordination Function (DCF) protocol and suggests certain protocol enhancements aiming at maximising performance. A new, elegant and accurate analysis based on Markov chain modelling is developed for the idealistic assumption of unlimited packet retransmissions as well as for the case of finite packet retry limits. Simple equations are derived for the through put efficiency, the average packet delay, the probability of a packet being discarded when it reaches the maximum retransmission limit, the average time to drop such a packet and the packet inter-arrival time for both basic access and RTS/CTS medium access schemes.The accuracy of the mathematical model is validated by comparing analytical with OPNET simulation results. An extensive and detailed study is carried out on the influence of performance of physical layer, data rate, packet payload size and several backoff parameters for both medium access mechanisms. The previous mathematical model is extended to take into account transmission errors that can occur either independently with fixed Bit Error Rate(BER) or in bursts. The dependency of the protocol performance on BER and other factors related to independent and burst transmission errors is explored. Furthermore, a simple-implement appropriate tuning of the back off algorithm for maximizing IEEE 802-11 protocol performance is proposed depending on the specific communication requirements. The effectiveness of the RTS/CTS scheme in reducing collision duration at high data rates is studied and an all-purpose expression for the optimal use of the RTS/CTS reservation scheme is derived. Moreover, an easy-to-implement backoff algorithm that significantly enhances performance is introduced and an alternative derivation is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Finally, an additional performance improvement scheme is proposed by employing packet bursting in order to reduce overhead costs such as contention time and RTS/CTSex changes. Fairness is explored in short-time and long-time scales for both the legacy DCF and packet bursting cases. AIr protocol employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium access. A 1-dimensional Markov chain model is constructed instead of the bi-dimensional model in order to obtain simple mathematical equations of the average packet delay.This new approach greatly simplifies previous analyses and can be applied to any CSMA/CA protocol.The derived mathematical model is validated by comparing analytical with simulation results and an extensive Alr packet delay evaluation is carried out by taking into account all the factors and parameters that affect protocol performance. Finally, suitable values for both backoff and protocol parameters are proposed that reduce average packet delay and, thus, maximize performance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Cooperative communication in wireless local area networks

The concept of cooperative communication has been proposed to improve link capacity, transmission reliability and network coverage in multiuser wireless communication networks. Different from conventional point-to-point and point-to-multipoint communications, cooperative communication allows multiple users or stations in a wireless network to coordinate their packet transmissions and share each other’s resources, thus achieving high performance gain and better service coverage. According to the IEEE 802.11 standards, Wireless Local Area Networks (WLANs) can support multiple transmission data rates, depending on the instantaneous channel condition between a source station and an Access Point (AP). In such a multi-rate WLAN, those low data-rate stations will occupy the shared communication channel for a longer period for transmitting a fixed-size packet to the AP, thus reducing the channel efficiency and overall system performance. This thesis addresses this challenging problem in multi-rate WLANs by proposing two cooperative Medium Access Control (MAC) protocols, namely Busy Tone based Cooperative MAC (BTAC) protocol and Cooperative Access with Relay’s Data (CARD) protocol. Under BTAC, a low data-rate sending station tries to identify and use a close-by intermediate station as its relay to forward its data packets at higher data-rate to the AP through a two-hop path. In this way, BTAC can achieve cooperative diversity gain in multi-rate WLANs. Furthermore, the proposed CARD protocol enables a relay station to transmit its own data packets to the AP immediately after forwarding its neighbour’s packets, thus minimising the handshake procedure and overheads for sensing and reserving the common channel. In doing so, CARD can achieve both cooperative diversity gain and cooperative multiplexing gain. Both BTAC and CARD protocols are backward compatible with the existing IEEE 802.11 standards. New cross-layer mathematical models have been developed in this thesis to study the performance of BTAC and CARD under different channel conditions and for saturated and unsaturated traffic loads. Detailed simulation platforms were developed and are discussed in this thesis. Extensive simulation results validate the mathematical models developed and show that BTAC and CARD protocols can significantly improve system throughput, service delay, and energy efficiency for WLANs operating under realistic communication scenarios

Evaluation of the impact of mobility models on handover in WLAN indoor environments

Nowadays, mobility models are used to simulate realistic movements produced by the users of a wireless or a mobile network. The aim of this project is to evaluate the impact of mobility models on handover process in Wireless Local Area Networks (WLAN) indoor environments, using the network simulator NS-2. This document contains a previous theoretical characterization of the basic mobility models and their application in the network simulator NS-2, a study of the infrastructure mode support and a modification of the current handover algorithm. The study focuses on two mobility models in WLAN indoor environments: one where movements are completely random (i.e. Random Waypoint) and another one where next step depends on previous movements (i.e. Gauss-Markov). In order to support infrastructure mode operation in WLAN, a new patch with modifications of the source code is applied. Furthermore, a first approach for the development of a new handover algorithm is presented. Simulations are run in two different scenarios: one with 4 Access Points (APs) offering full coverage in the simulated area, and another one with 8 APs, simulating overcoverage in order to guarantee higher capacity for a higher density of users. Results are presented showing a comparative of the cell residence time (CRT) for each scenario. From the results obtained, it is possible to see that the CRT changes depending on the algorithm and the mobility model applied, being lower when the Random Waypoint model is applied. On the other hand, the new handover algorithm designed from the current implementation leads to a decrease in the average CRT

Performance evaluation of the GCR block ACK mechanism in IEEE 802.11aa networks

With the growing demand for multimedia services, video streams have become major traffic sources in the Internet. However, it is challenging to transmit multimedia streams over IEEE 802.11 Wireless Local Area Networks (WLANs) with high performance and reliability. As a solution to improve system efficiency, a new standard, 802.11aa, is introduced to provide much more reliable and robust transfer of video stream by introducing several new service features. In this thesis, we analyze the performance of the Groupcast with Retries (GCR) Block ACK scheme as one of the most important features in this standard based on Markov chain models. The properties of groupcast service and block acknowledgement will be merged together in our model. Besides, we take into account the memory feature of the wireless channel and extend it into multi-receivers in accordance with the standard. In particular, the proposed model is built on fixed block size, a type of communication technique in which the block size is kept as fixed during transmission. Furthermore, the lost position of a packet in the block is taken into consideration for in-depth analysis. Numerical results show that under the groupcast with constant retry limit and fixed block size transmission mechanism, the network throughput will be reduced with the growing number of receiving terminals. Compared with the throughput result for the variable block size mechanism obtained from our previous study, we found that with the increasing number of stations, the performance of the fixed block size mechanism is much more stable with respect to the number of stations and channel memory property. However, the variable block size transmission scheme exhibits much better throughput performance when the number of stations is small

A Channel Assignment and Routing Algorithm for Energy Harvesting Multi-Radio Wireless Mesh Networks

Wireless mesh networks are being deployed all around the world both to provide ubiquitous connection to the Internet and to carry data generated by several services (video surveillance, smart grids, earthquake early warning systems, etc.). In those cases where fixed power connections are not available, mesh nodes operate by harvesting ambient energy (e.g., solar or wind power) and hence they can count on a limited and time-varying amount of power to accomplish their functions. Since we consider mesh nodes equipped with multiple radios, power savings and network performance can be maximized by properly routing flows, assigning channels to radios and identifying nodes/radios that can be turned off. Thus, the problem we address is a joint channel assignment and routing problem with additional constraints on the node power consumption, which is NP-complete. In this paper, we propose a heuristic, named minimum power channel assignment and routing algorithm (MP-CARA), which is guaranteed to return a local optimum for this problem. Based on a theoretical analysis that we present in the paper, which gives an upper bound on the outage probability as a function of the constraint on power consumption, we can guarantee that the probability that a node runs out of power with MP-CARA falls below a desired threshold. The performance of MP-CARA is assessed by means of an extensive simulation study aiming to compare the solutions returned by MP-CARA to those found by other heuristics proposed in the literature.Publicad

Evaluation of IEEE 802.11ah Technology for Wireless Sensor Network Applications

We are entering into a new computing technological era where communications are established not just user to user, or user to machine, but also machine to machine (M2M), machine to infrastructure, machine to environment. This then brings out the idea of acquiring data from the environment, process that data and use it to obtain a benefit, and the way to make this happen is by deploying a network of sensors which will provide an application with the desired sensed data. A sensor network is for practical reasons, nowadays considered as a Wireless Sensor Network (WSN). As we move from static web to social networking and furthermore to ubiquitous computing, the amount of wireless devices out there is increasing exponentially. This has triggered a series of challenges for communications technologies as many new requirements need to be addressed. Low-cost, low-power and long-range coverage are the key requirements when designing a WSN. Since the communications subsystem in a WSN is the one dragging most resources, the WSN market is demanding new communication technologies to improve the performance of their current applications, but also to empower innovation by creating new application possibilities. Consequently, a new technology proposal has emerged as a solution to the previously mentioned requirements; the IEEE 802.11ah. This is an amendment to the well-known legacy IEEE 802.11 technologies and promises coverage for up to 1km with at least 100kbps, and support a large amount of stations. This Master’s Thesis offers an insight to this new technology by evaluating its performance through an analytical model which is first developed and then evaluated in MatLab 2014b. A series of performance metrics have been considered in this work with the intention of evaluating its feasibility for WSNs. Different use cases are presented to give an idea of how this new communications standard would perform in real-life scenarios. Based on the obtained results, it is concluded that the standard would perform well when implemented in WSN. But what differentiates the IEEE 802.11ah from its close competitors is the fact that substantial infrastructure using IEEE802.11ah and its amendments already exists, for which the transition to its use seems to be an easy bet. The IEEE 802.11ah is still under development and is expected to be ready for 2016