Dissertations / Theses on the topic 'CSMA/CA MAC protocol'

The idea of wireless distributed computing (WDC) is rapidly gaining recognition owing to its promising potential in military, public safety and commercial applications. This concept basically entails distributing a computationally intensive task that one radio device is assigned, among its neighboring peer radio devices. The added processing power of multiple radios can be harnessed to significantly reduce the time consumed in obtaining the results of the original complex task. Since the idea of wireless distributed computing depends on a radio device forming a network with its peers, it is imperative and necessary to have a medium access control (MAC) protocol for such networks which is capable of scheduling channel access by multiple radios in the network, ensuring reliable data transfer, incorporating rate adaptation as well as handling link failures. The thesis presented here elaborates the design and implementation of such a MAC protocol for WDC employed in a practical network of radio devices configurable through software. It also brings to light the design and implementation constraints and challenges faced in this endeavor and puts forward viable solutions.
Master of Science

IEEE 802.15.4 is a standard defined for wireless sensor network applications with limited power and relaxed throughput needs. The devices transmit data during two periods: Contention Access Period (CAP) by accessing the channel using CSMA/CA and Contention Free Period (CFP), which consists of Guaranteed Time Slots (GTS) allocated to individual devices by the network coordinator. The GTS is used by devices for cyclic data transmission and the coordinator can allocate GTS to a maximum of only seven devices. In this work, we have proposed two algorithms for an efficient GTS allocation. The first algorithm is focused on improving the bandwidth utilization of devices, while the second algorithm uses traffic arrival information of devices to allow sharing of GTS slots between more than seven devices. The proposed schemes were tested through simulations and the results show that the new GTS allocation schemes perform better than the original IEEE 802.15.4 standard.

Este trabalho apresenta um modelo analítico para a análise de vazão (throughput) da camada MAC do IEEE 802.11. A proposta se diferencia da maioria dos desenvolvimentos realizados na área por apresentar uma modelagem de ambientes com estações não-saturadas, levando em consideração o perfil do tráfego gerado pelas camadas superiores ao nível de enlace. Dessa maneira, o modelo permite uma análise do desempenho de aplicações reais sobre redes sem fio, a partir de resultados provenientes de um modelo matemático, enquanto diversos outros trabalhos avaliam somente situações de saturação das estações. Simulações utilizando Network Simulator 2 e comparações com resultados obtidos em trabalhos análogos desenvolvidos por outros pesquisadores validam o modelo proposto. Cenários com variações na quantidade de estações e carga oferecida à rede são avaliados utilizando o modelo teórico e comparados aos resultados simulados, provendo uma análise do comportamento dos limites de vazão do sistema. As estruturas do IEEE 802.11 MAC foram estudadas a fim de embasar o desenvolvimento do modelo proposto. Também foi realizada uma pesquisa a respeito de Cadeias de Markov, que serve como estrutura básica para a descrição do IEEE 802.11 DCF.
This work provides an analytical model to compute the IEEE 802.11 DCF throughput. The proposed analysis differs from most of the related work by presenting scenario modeling with unsaturated stations, accounting for the traffic characteristics generated by the upper layers to the data link layer. As a consequence, the proposed model allows for an accurate analysis of real applications over wireless networks, based on mathematical model results, while several other researches evaluate only saturate stations situations. Simulations ran using Network Simulator 2 and comparisons with results obtained on similar works developed by other researchers are used to validate the proposed model. Scenarios with different number of stations and offered loads are evaluated using the theoretical model and compared to the simulated results, providing an analysis on the behavior of the maximum throughput provided by the network. A study was made on the structures and mechanisms of IEEE 802.11 MAC in order to support the development of the proposed model. A research on Markov Chains was also done, since it is the basic structure used to describe the IEEE 802.11 DCF.

This thesis proposes and studies a Medium Access Control (MAC) protocol for networks of tags deployed over an industrial machine using THz communications. Despite the great advantages of these frequencies, there are drawbacks that cannot be ignored, such as propagation delays that, even at small distances, are of the same order of magnitude as packet transmission times. For this reason, the mathematical models developed for Contention-Free and Contention-Based protocols take into account the propagation delay. The main focus of this thesis is on the CSMA/CA protocol, which introduces channel sensing to reduce collisions and increase performance. The performance of the protocol are compared with two benchmarks, based on Polling and Aloha, considering an industrial machine scenario and accounting for physical and MAC layers features.

Les exigences de Qualité de Service (QoS) des applications VANET varient selon la nature et le type de l’application. Par conséquent, un protocole de communication VANET doit pouvoir répondre aux diverses exigences de QoS selon le type du trafic. Dans VANET, le canal de transmission est partagé par tous les véhicules en utilisant une même fréquence radio. Une mauvaise exploitation du canal peut donc conduire à des collisions et peut aussi engendrer un gaspillage de la bande passante. Un protocole MAC doit être alors conçu pour partager le canal entre les différents noeuds d’une manière efficace et équitable.Dans cette thèse nous présentons les contributions suivantes :1- Analyse et amélioration de la diffusion dans la norme IEEE 802.11.2- Optimisation de la technique CSMA pour des réseaux 1D et 2D.3- Développement d’un algorithme CSMA de transmission adaptatif qui met à jour le taux de détection de la porteuse en fonction d’une valeur de référence.4- Étude du gain obtenu par l’utilisation d’antennes directionnelles pour Aloha, Aloha non-slotté, et CSMA
Quality of Service (QoS) requirements for VANET applications vary depending on the nature and type of the application. Therefore, a communication protocol in VANETs must be able to meet various QoS requirements according to the type of traffic. In VANET, the transmission channel is shared by all the vehicles using the same radio frequency. A poor exploitation of the channel can therefore lead to collisions and wasted bandwidth. A MAC protocol must therefore be designed to share the channel between the different nodes in an efficient and fair way.In this thesis we present the following contributions:1- Analysis and improvement of diffusion in the IEEE 802.11 standard.2- Optimization of the CSMA technique for 1D and 2D networks.3- Design of an adaptive transmission algorithm that updates the Carrier Sense threshold to reach a target value.4- Study the gain obtained by the use of directional antennas for Aloha, non-slotted Aloha, and CSMA

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
In this paper we introduce an ad hoc distributed supervisory control and data acquisition (SCADA) system, which covers two types of traffic, a small number of slave stations with stream traffic and much larger number of slave stations with burst traffic. To improve the system’s real-time transmission and channel allocation efficiency, a MAC scheme, named Polled-CSMA, is designed by integrating the merits of polling and CSMA protocols. Extensive analysis shows that this MAC protocol meets the system’s QOS requirements.

Industrial wireless sensor network (IWSN) is an application area of WSN used in industrial process monitoring and control with strict time and reliability requirement. WirelessHART standard is the first international standard for IWSN approved by International Electrotechnical Commission (IEC). This is worthwhile to implement this standard on simulator platform. Based on the study of WirelessHART standard, this thesis set up a primary implementation of the MAC layer of WirelessHART standard. To our best knowledge, this is the first comprehensive implementation of WirelessHART using OPNET simulator. The implementation has been evaluated rational. And some improvement of current implementation and standard have also been proposed and implemented. Flexible dedicated slot assignment has also been proposed to reduce the packet loss rate caused by influences of the physical channel.

The focus of this research is to investigate the effects of bursts of errors and packet collisions on the performance of the medium access control (MAC) portion of the IEEE 802.11 wireless local area network (LAN) protocol.An important ingredient in rapid expansion of wireless networks is the seamless transition between wired and wireless systems. The IEEE standards group in charge of developing the widely used IEEE 802.3 LAN standard has developed the IEEE 802.11 wireless LAN standard. IEEE 802.11 remains hidden from the upper levels of the network, thus allowing a seamless transition between networks. The foundation protocol for the IEEE 802.11 standard, known as Distributed Foundation Wireless Medium Access Control (DFWMAC), operates at the MAC level of the Data Link Layer. The protocol bases its access control mechanism on a principle called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), which is an adaptation of the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol used by IEEE 802.3 standard. The collision avoidance scheme in CSMA/CA allows data packets to be transferred via the wireless medium with lower probability of packet collision. In a slotted multi-access wireless system, performance parameters are affected by the bit error rates on the communication channel. These errors occur as a result of noise introduced by the radio channel or data packet collisions. Collisions occur when two or more stations select the same time slot to transmit their data, thus causing corruption in data packets. In this research, a simulation model coded in Microsoft's Visual Basic programming environment is utilized to investigate the effects of bit errors and packet collisions on performance in CSMA/CA. Performance parameters used in this study include throughput, medium utilization, collisions and station data queue lengths. In the simulation model, error bursts in the communication channel are modeled using a simple Gilbert model with two states, good (G) and bad (B). State G is error free, thus errors can only occur while the model is in state B. Collisions are simulated by two or more stations starting to transmit data packets in the same time slot. Therefore, as the number of stations increases, more and more stations compete for the medium, resulting in an increase in the number of collisions. Collisions are also increased by the amount of traffic that each station introduces into the system. Station load is defined here as the number of data packets per unit time that are released by the higher network protocol layers.The results in Chapter 5 demonstrate that higher network throughput can be achieved when the aggregate load on the network is distributed. For example, 30 stations offering 20 kilobits per second (kbps) of load for a total of 600 kpbs, results in a network throughput of 585 kbps. However, three stations offering 200 kbps of load for a total of 600 kbps offered load, results in a network throughput of 486 kbps. The distributed load is serviced at a 17 percent higher rate. However, once the network becomes saturated at above 40 stations for this model, collisions will more than offset the performance gains produced by the distribution of load.Furthermore, reducing the packet size by 50 percent under an approximately 19.5 percent packet error rate results in a 12 percent gain in throughput. This is primarily due to higher utilization of the network by shorter packets. However, as the packet error rate is reduced, the performance gap between the two packet sizes is reduced. Once the errors are removed completely from the communications channel, the longer packets produce a higher throughput than the shorter packets.
Master of Science

Generally, collisions between packets are undesired in wireless networks. We design this scheme, Cooperative Jamming in Wireless Networks (CJWN), to make use of collision to protect secret DATA packets from being sniffed by a nearby eavesdropper. We are intending to greatly increase the Packet Error Rate (PER) at the eavesdropper when the PER at the receiver is maintained at an acceptable level. This scheme is not intended to completely take the place of various encryption/decryption schemes which are working based on successfully received packets. Adding CJWN to the popular CSMA/CA adopted in IEEE 802.11 will add more security even the key for encryption/decryption is already exposed. Because the overhead of CJWN is very big, we do not suggest using it on every transmission. When some secret packets have a high requirement of confidentiality, CJWN is worth trying at the cost of throughput performance and power.

Wireless local area networks (WLANs) and wireless sensor networks (WSNs) technologies have been comprehensively developed and deployed during recent years. Since commercial WLAN and WSN products share the same free of license frequency band, the low power, low rate ZigBee based WSNs are vulnerable to the interference from Wi-Fi WLANs. Therefore, it is important to evaluate the performance of ZigBee WSNs that are subjected to interference generated by collocated Wi-Fi WLANs and to design effective counter-measuring techniques should performance improvement is needed. In this research, a versatile testbed for conducting various experiments is established and the ZigBee system’s performance with different clear channel assessment (CCA) modes and energy detection (ED) thresholds are evaluated through extensive experimental measurements in the testbed. It can be concluded from the results that CCA has significant impact on ZigBee’s performance. An existing theoretical analysis approach that is based on the collision time model between ZigBee and Wi-Fi packets is suitably modified to provide analytical evaluation means of the cases we examined. In order to mitigate the interference from the collocated Wi-Fi system, a novel and effective interference-aware adaptive CCA (IAACCA) scheme is proposed and implemented as firmware flashed into Crossbow motes. Experiments confirmed the ability of IAACCA to countermeasure effectively interference generated by Wi-Fi and thus improve the performance of ZigBee WSNs. Finally, a thorough statistical analysis is performed to understand the factors impacting the performance of ZigBee system and is used to further verify our experimental methods.

A wireless local area network (WLAN) provides high bandwidth to users in a limited geographical area. This network faces certain challenges and constraints that are not imposed on their wired counterparts. They are: frequency allocation, interference and reliability, security, power consumption, human safety, mobility, connection to wired LAN,service area, handoff and roaming, dynamic configuration and the throughput. But the wireless medium relies heavily on the features of MAC protocol and the MAC protocol is the core of medium access control for WLANs. The available MAC protocols all have their own merits and demerits. In our research works, we propose a hybrid MAC protocol forWLAN. In the design, we have combined the merits of the TDMA and CDMA systems to improve the throughput of the WLAN in a picocellular environment. We have used the reservation and polling methods of MAC protocols to handle both the low and high data traffics of the mobile users. We have strictly followed the standards specified by IEEE 802.11 for WLANs to implement the designed MAC protocol. We have simulated the hybrid TDMA/CDMA based MAC protocols combined with RAP (Randomly Addressed Polling) for Wireless Local Area Networks. We have developed a closed form mathematical expressions analytically for this protocol. We have also studied the power control aspects in this environment and we derived a closed form mathematical expressions analytically for this power control technique. This hybrid protocol is capable of integrating different types of traffic (like CBR,VBR and ABR services) and compiles with the requirements of next-generation systems.The lower traffic arrival is dealt with the Random Access and the higher traffic arrival is with the Polling methods. This enables us to obtain higher throughput and lowmean delay performance compared to the contention-reservation-based MAC schemes. The protocol offers the ability to integrate different types of services in a flexible way by the use of multiple slots per frame, while CDMA allows multiple users to transmit simultaneously using their own codes. The RAP uses an efficient "back-off" algorithm to improve throughput at higher arrival rates of user's data. The performance is evaluated in terms of throughput, delay, and rejection rate using computer simulation. A detailed simulation is carried out regarding the maximum number of users that each base station can support on a lossy channel. This work has analyzed the desired user's signal quality in a single cell CDMA (Code Division Multiple Access) system in the presence of MAI (Multiple Access Interference). Earlier power control techniques were designed to assure that all signals are received with equal power levels. Since these algorithms are designed for a imperfect control of power, the capacity of the system is reduced for a given BER (Bit-Error Rate). We proposed an EPCM (Efficient Power Control Mechanism) based system capacity which is designed for the reverse link (mobile to base station) considering the path loss, log-normal shadowing and Rayleigh fading. We have simulated the following applications for the further improvement of the performance of the designed MAC protocol:Designed protocol is tested under different traffic conditions. The protocol is tested for multimedia traffic under application oriented QoS requirements. Buffer Management and resource allocation. Call Admission Control (hand-offs, arrival of new users). The adaptability to the variable nature of traffic.The propagation aspects in the wireless medium. The proposed MAC protocol has been simulated and analysed by using C++/MATLAB Programming in IBM/SUN-SOLARIS UNIX environment. The results were plotted using MATLAB software. All the functions of the protocol have been tested by an analysis and also by simulation. Call admission control function of the protocol has been tested by simulation and analysis in a multimedia wireless network topology and from analysis we found that at low traffic the throughput is high and at high traffic the throughput is kept constant at a reasonable high value. The simulation results also justify/ coordinate the analysis results. Dynamic channel allocation function of the protocol was tested and analysed and the coordinated results show that at low traffic, high throughput and at high traffic the throughput is constant. Buffer management function of the protocol simulation shows the results that the packet loss can be controlled to a minimum by adjusting the buffer threshold level at any traffic conditions. Maintenance of data transfer during the hand-offs function was simulated and the results show that the blocked calls are less during low traffic and at high traffic the blocked calls can be kept constant at low value. Thus, the proposed model aimed at having high throughput, high spectral efficiency, low delay, moderate BER and moderate blocking probability. We have considered a pico cell with a maximum of several users and studied the power efficiency of combined channel coding and modulation with perfect power controlled CDMA system. Thus our simulation of the "software radio" has flexibility in choosing the proper channel coders dynamically depending upon the variations of AWGN channel.

There are several standards for wireless communication. People that are involved in computers and networking recognize names like Bluetooth, HiperLAN and IEEE 802.11. The last one was standardized in 1997 [2,6]and has begun to reach acceptance as a solid ground for wireless networking. A fundamental part of an IEEE 802.11 node is the Medium Access Controller, or MAC. It establishes and controls communication with other nodes, using a physical layer unit.

The work has been carried out as final project at Linkopings Universitet, it has been about the improvement of the functions of MAC layer. I have developed some of the required functions that PUM uses to interact with the MAC layer. Because of that, I have implemented the Reception functions of MAC layer, having the possibility of using short control frames RTS/CTS to minimize collision.

Denna rapport behandlar prestandaproblem i den nyligen standardiserade Mesh kommunikationsstandarden (IEEE 802.11s). I denna rapport, undersöker och förbättra vi ett förhållande som resulterar i reduktion av genomströmningen i en kedja av noder topologi. IEEE802.11s är mycket lovande med många fördelar för både IoT-systemen och trådlösa nätverk i båda hemmet och arbete.Vi arbetar med frågan om orättvisa när CSMA/CA tillämpas, vilket orsakar genomströmningsreduktion på grund av paketförluster och indikerar svältning. Vi analyserar konsekvenserna av Collision Avoidance (CA) mekanism och föreslår en ersättning för CA som är både rättvist och samtidigt kan upprätthålla undvikande av kollisioner. Vi implementera detta i en simulator och resultatet visar på betydligt högre end-to-end-genomströmning än standard CSMA/CA och inga paketförluster på grund av buffertspill.
This thesis rapport deals with the performance issues of the newly standardized Wireless mesh protocol (IEEE 802.11s). In this thesis, we work on improving the conditions that results in throughput degradation in a chain of nodes topology. The mesh standard is very promising with many advantages for both IoT systems and home wireless networks.We work on the issue of unfairness when CSMA/CA is applied, which causes throughput degradation due to packet loss and indicates starvation. We analyze the implication of the Collision Avoidance (CA) mechanism and propose a replacement for the CA that is both fair and able to maintain collision avoidance. We implement this in a simulator and the result shows significantly higher end-to-end throughput compared to the original CSMA/CA and no packet loss due to buffer overflow.

No
Supported by the IEEE 802.15.4 standard, embedded sensor networks have become popular and been widely deployed in recent years. The IEEE 802.15.4 medium access control (MAC) protocol is uniquely designed to meet the desirable requirements of the low end-to-end delay, low packet loss, and low power consumption in the low rate wireless personal areas networks (LR-WPANs). This paper develops an analytical model to quantify the key performance metrics of the MAC protocol in LR-WPANs with bursty ONOFF traffic. This study fills the gap in the literature by removing the assumptions of saturated traffic or nonbursty unsaturated traffic conditions, which are unable to capture the characteristics of bursty multimedia traffic in sensor networks. This analytical model can be used to derive the QoS performance metrics in terms of throughput and total delay. The accuracy of the model is verified through NS-2 (http://www.isi.edu/nsnam/ns/) simulation experiments. This model is adopted to investigate the performance of the MAC protocol in LR-WPANs under various traffic patterns, different loads, and various numbers of stations. Numerical results show that the traffic patterns and traffic burstiness have a significant impact on the delay performance of LR-WPANs.

碩士
國立暨南國際大學
電機工程學系
101
In IEEE 802.15.4 networks, routers cannot enter sleep mode to reduce power consumption and runs out of battery power quickly. In addition, the implementation of CSMA/CA protocol in IEEE 802.15.4 is different from that in IEEE 802.11. Because a node does not perform channel sensing during backoff, a collision may occurs when a node transmit a packet. As a result, IEEE 802.15.4 is unsuitable for wireless sensor networks (WSN). In this thesis, we design and implement the CSMA / CA protocol based on IEEE 802.11 by TI CC2530 for wireless sensor networks. For hardware-related programming, we have implemented the RF driver, the MAC Timer driver, the interrupt service routines, the channel sensing mechanism, and the two-way handshaking CSMA/CA protocol. A prototype platform was built and packets are successfully delivered between multiple nodes. In the future, the platform can be extended to a complete media access control (MAC) layer suitable for wireless sensor networks, such as the well-know S-MAC.

碩士
國立暨南國際大學
電機工程學系
99
The CSMA/CA protocol is commonly used in many wireless networks. When a station receives a packet from its upper layer, it has to sense the channel before transmission. If the channel is idle, it randomly chooses a value according to its current Contention Window as its backoff counter and starts the backoff procedure. When it counts down to zero, the station starts transmission. As the number of nodes increases, the probability that more than one station transmits increases, results in high collision probability and performance degradation. To solve the problem, we propose a new medium assess protocol named contention-free (CF-CSMA) for the infrastructure mode of wireless LANs. In the CF-CSMA scheme, all stations use the channel sequentially according to the order controlled by the Access Point (AP) and packet collision can be totally eliminated. In addition, we implement the CF-CSMA scheme in NS2 to simulate the real networks. Simulation results show that the proposed scheme outperforms traditional schemes in terms of packet delay, collision probability and throughput.

碩士
國立成功大學
資訊工程學系
103
Machine-to-Machine (M2M) communication is a machine-independent communication paradigm that can facilitate wired and wireless communications without the need for human intervention. However, as the number of network devices increases, the occurrence of collisions rises, which results in the efficiency of the MAC layer protocol being degraded and the power consumption being increased. To resolve this problem, this thesis proposes an enhanced IEEE 802.11 CSMA/CA media access scheme designated as CSMA/CA-RBTv, in which RBT denotes the Registered Backoff Time and v denotes vector. In the proposed CSMA/CA-RBTv, when a mobile node transmits data to the AP, it attaches a random number called the RBT, which denotes the next time slot the mobile node would like to transmit its next data packet, to the packet. Once the AP receives the packet, it extracts the RBT and adds it to a Registered-Time-Slot-List (RTSL) used to conduct channel access scheduling. Before transmitting the ACK packet to the mobile node, the AP (1) selects the node with the smallest RBT from the RTSL list as the next one to access the wireless channel and (2) uses RTSL to make a bit vector marking which time slots have been registered/reserved for data transmission, i.e., channel access. Finally, the AP appends the aforementioned two pieces of channel access information to the ACK packet. Since the ACK packet is transmitted in a broadcast manner, all of the mobile nodes which overhear the transmission know which node has the next right to access the channel and which time slots are still available for channel access. Consequently, the occurrence of collisions can be reduced, which also results in decreasing power consuming. The simulation results show that the proposed CSMA/CA-RBTv scheme results in a significant improvement in both the transmission performance and the energy efficiency of the M2M network as the number of mobile nodes increases.

博士
國立成功大學
電機工程學系碩博士班
95
As data traffic increase rapidly, IP over WDM (Wavelength Division Multiplexing) transport will replace conventional SONET transport in current metropolitan area networks. Such networks will require new MAC protocols to efficiently share network bandwidth among multiple network nodes. The thesis describes and evaluates a novel Carrier Sense Multiple Access with Carrier Preemption (CSMA/CP) MAC protocols for IP over WDM ring networks. Moreover since the traditional IP provides the best effort service only, supporting IP packets with QoS (Quality of Service) transfer has become a crucial issue for multimedia transmission. The thesis accordingly proposes QoS-aware CSMA/CP MAC protocol. It uses the concepts of CSMA/CP and the QoS mechanism to support all-optical and QoS-aware transferring of the IP packets of the nodes in the WDM ring networks. Analysis and simulation results show that the proposed MAC protocols are efficient and practical and will be an excellent candidate for next-generation metro networks.

The ad hoc wireless Local Area Network (WLAN) has gained a lot of interest in the research community due to its special properties, such a s deployment flexibility. With current demands, ad hoc WLANs are being developed to provide better quality to users. Firstly, a simulation model is built in C++ programming language with object-oriented method. The software of the WLAN simulator is designed to provide highly detailed and accurate statistical information, and can serve as a general platform for further simulation studies. Secondly, a newly proposed double window algorithm introduces a priority-based window alternative to the standard CSMA/CA. Simulation results demonstrate that networks achieve a better Quality of Service (QoS) by using the new priority-based window. Thirdly, the Pseudo Access Points (PAP) routing protocol is presented to enhance the traditional proactive routing protocols. The simulations confirm that the PAP routing protocol is better than the generic [straight theta] routing protocol under different mobility scenarios. It provides higher throughput, less failed routing, less variance of the hop count, etc, and thus offers a better Quality of Service. The performance evaluation of the PAP routing protocol is also emphasized. The investigation shows that the performance of the PAP routing protocol can be improved through the manipulation of various input parameters.