The ABR point-to-multipoint connection is now playing a more important role. Many consolidation algorithms have been proposed to solve the consolidation noise problems and the slow transient response problem. But few timeout algorithms are proposed to handle the ¡§non-responsive¡¨ branches problems for the multicast connections. We proposed a timeout algorithm which can handle the ¡§non-responsive¡¨ branches problems and with a lower implementation complexity. Simulation results also show that the proposed timeout algorithm can efficiently handle the ¡§non-responsive¡¨ branches and can use the available bandwidth within a small period of time.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / It is always desirable to transmit several data signals simultaneously. This paper discusses how one transmitter can transmit several data signals to several receivers at the same time in a Point to Multipoint communication system. Two novel schemes are proposed. One is communication with Multiple Phase Shift Keying(MPSK,e.g.8PSK),another is communication with Direct-Sequence Spread-Spectrum Multiple-Access(DS/SSMA). Their models are presented and their operations are illustrated. It is proved theoretically that the communication properties of DS/SSMA are better than those of another.

Applications such as video and audio streaming, online gaming, video conferencing, Voice over IP (VoIP) and File Transfer Protocol (FTP) demand a wide range of QoS requirements such as bandwidth and delay. Existing wireless technologies that can satisfy the requirements of heterogeneous traffic are very costly to deploy in rural areas and “last mile” access. Worldwide Interoperability for Microwave Access (WiMAX) provides an affordable alternative for wireless broadband access supporting a multiplicity of applications. The IEEE 802.16 standard provides specification for the Medium Access Control (MAC) and Physical (PHY) layers for WiMAX. A critical part of the MAC layer specification is scheduling, which resolves contention for bandwidth and determines the transmission order of users. It is imperative for a scheduling algorithm to have a multi-dimensional objective of satisfying QoS requirements of the users, maximizing system utilization and ensuring fairness among the users. In this thesis, we categorize and study various scheduling algorithms for the uplink traffic in WiMAX in view of these objectives. The algorithms are studied under different mixes of traffic and for various characteristics of the IEEE 802.16 MAC layer such as uplink burst preamble, frame length, bandwidth request mechanisms etc. Simulation results indicate that legacy algorithms are not suitable for the multi-class traffic in WiMAX as they do not explicitly incorporate the WiMAX QoS parameters. We provide recommendations for enhancing existing scheduling schemes in WiMAX, and shed light on some of the open issues that need to be addressed. / Thesis (Master, Computing) -- Queen's University, 2007-12-29 18:21:21.521

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / At present, multiple mobile targets will be remote controlled in many remote control and telemetry system, in which multiple access technology will be applied. This paper proposes a communication scheme to remote control multiple mobile targets using Coded-Division Multiple Access(CDMA) technique. It's feasibility, advantage and shortcoming are analyzed. Moreover, the key techniques of Direct-Sequence Spread Spectrum(DS/SS) system, i.e. the correlation detection and delay lock-on techniques, are studied and stimulated on the experimental model. The results of theoretical analysis show that the CDMA system has the peculiar advantage over the conventional multiple access system, such as FDMA and TDMA.

Asynchronous Transfer Mode (ATM) network is being deployed in carrier backbone. ATM can transmit a wide variety of traffic, such as video, voice, and data. Available Bit Rate (ABR) service is one of six ATM services, which is now under intensive research for its closed loop feedback control feature. ABR service supports two types of connections: unicast and multicast. There are also three types of multicast connections: point-to-multipoint, multipoint-to-point, and multipoint-to-multipoint. Multipoint communication is the exchange of information among multiple senders and multiple receivers, forming a multicast group. Examples of multicast applications include audio and video conferencing, video on demand, tele-metering, distributed games, and data distribution applications. In this dissertation, we focus on queuing and packet scheduling management for multipoint-to-point ABR connections. Although there are so many proposed fairness definitions for all ABR sources in a multipoint-to-point connection, there are still problems about queue lengths, queuing delays, and throughputs, when ABR sources are with variable-length packets. From the nature of VC-merge scheme on merged points in a multipoint-to-point connection, merged switches cannot transmit cell-stream of a packet out until the packet is completely and totally queued. If there is no complete packets queued, the switch can then choose an incomplete packet for cut-through forwarding for efficiency. Therefore, if the switch chooses a long packet from a branch that has smaller cell input rate, for cut-through forwarding, the throughput of output ports will experience severe oscillations. At the same time, ABR queue lengths will be also occupied with severe growth, and ABR cells will be experienced long queuing delays. We proposed a scheme, named MWTF (Minimum Waiting Time First), which is architecture-independent of any rate allocation schemes and fairness definitions, to resolve the problems by providing length of each packet to merged switches. Thereby the scheduler can choose an appropriate incomplete packet for cut-through forwarding, by selecting the packet that has the smallest packet waiting time. Simulation results show that merged switch has good performances. Throughput will be no severe oscillations and will be getting smoother. Also cells have smaller and smoother queuing delays in average, and the switches have much smaller queue lengths and smoother variations.

The “WLAN in Disaster Emergency Response” (WIDER) project has developed and implemented an emergency communication system. It provides network and communication services to relief organizations. In order to guarantee the stable and efficient connectivity with a high quality of service (QoS) for the end user, and to make the WIDER system more adaptive to the disaster area, the IEEE 802.16 specification based broadband wireless access solution is adopted. This thesis work aims at evaluating and testing the WIDER system integrated with WiMAX. By learning and analyzing the technology, the benefits and perspective for WIDER using WiMAX are described. A WiMAX solution was configured and integrated into the WIDER system. A series of tests and measurements provide us the performance of the WiMAX solution in throughput, QoS, and reality. The tests helped us to learn and verify the improvements for WIDER due to WiMAX. / “WLAN in Disaster Emergency Response” (WIDER) projektet har utvecklat och implementerat ett kommunikationssystem för katastrof situationer. Systemet tillhandahåller nätverk- och kommunikationstjänster för hjälporganisationer. För att garantera en stabil och effektiv anslutning med hög Quality of Service för användarna samt göra WIDER systemet mer anpassbart för katastrofområden, kommer Broadband wireless access som är baserade på IEEE 802.16 specifikationen att användas. Det här examensarbetet har som målsättning att utvärdera och testa WIDER med WiMax tekniken, vi beskriver olika fördelar och synvinklar med att använda WiMax genom att lära oss och analysera tekniken. En WiMax lösning konfigurerades och integrerades i WIDER systemet. En rad tester och mätningar visar WiMax-lösningens prestanda i form av throughput, Quality of Service och realitet. Testerna lärde oss och hjälpte oss att verifiera förbättringarna i WIDER i och med användningen av WiMax.

First-generation, line-of-sight (LOS) fixed broadband wireless access techniques have been around for several years. However, services based on this technology have been limited in scope to service areas where transceivers can communicate with their base stations, unimpeded by trees, buildings and other obstructions. This limitation has serious consequences in that the system can deliver only 50% to 70% coverage within a given cell radius, thus affecting earned revenue. Next generation broadband fixed wireless access techniques are aimed at achieving a coverage area greater than 90%. To achieve this target, these techniques must be based on a point-to-multipoint (PMP) cellular architecture with low base station antennas, thus possessing the ability to operate in true non-line-of-sight (NLOS) conditions. A possible limiting factor for these systems is link degradation due to interference. This thesis presents a new model to estimate the levels of co-channel interference for such systems operating within the 3.5 GHz multichannel multipoint distribution service (MMDS) band. The model is site-specific in that it uses statistical building/roof height distribution parameters obtained from practically modeling several metropolitan cities in the U.S. using geographic information system (GIS) tools. This helps to obtain a realistic estimate and helps analyze the tradeoff between cell radius and modulation complexity. Together, these allow the system designer to decide on an optimal location for placement of customer premises equipment (CPE) within a given cell area. / Master of Science

Given the current developments and advances in the scientific and technological aspects of human knowledge and introducing new approaches in various fields of telecommunication technologies and industries, there has been an increasing growth in its players' plans and a positive change in their outlooks in order to achieve the target of "anywhere and anytime access". Recent developments of WiMAX (Worldwide interoperability for Microwave Access) networks, as a sign of increasing needs and demands for new telecommunication services and capabilities, have led to revolutions in global telecommunication which should be perceived properly in terms of the commercial and technical aspects in order to enjoy the new opportunities. Most experts believe that WiMAX technology is a preliminary step to develop Fourth Generation networks known as 4G technologies. It has not only succeeded in the utilization of several of the latest telecommunication techniques in the form of unique practical standards, but also paved the way for the quantitative and qualitative developments of high-speed broadband access. IEEE 802.16 Standard introduces several advantages, and one of them is the support for Quality of Services (QoS) at the Media Access Control (MAC) level. For these purposes, the standard defines several scheduling classes at MAC layer to treat service flow in a different way, depending on QoS requirements. In this thesis, we have proposed a new QoS framework for Point-to-Multi Point (PMP) 802.16 systems operating in Time Division Duplexing (TDD) mode over a WirelessMAN-OFDM physical layer. The proposed framework consists of a Call Admission Control (CAC) module and a scheduling scheme for the uplink traffic as well as a simple frame allocation scheme. The proposed CAC module interacts with the uplink scheduler status and it makes its decision based on the scheduler queue status; on the other hand, the proposed scheduling scheme for the uplink traffic aims to support realtime flows and adapts the frame-by-frame allocations to the current needs of the connections, with respect to the grants boundaries fixed by the CAC module. Extensive OPNET simulation demonstrates the effectiveness of the proposed architecture.

Simultaneous operation of different wireless applications in the same geographical region and the same frequency band gives rise to undesired interference issues. Since licensed (primary) applications have been granted priority access to the frequency spectrum, unlicensed (secondary) services should avoid imposing interference on the primary system. In other words, secondary system’s activity in the same bands should be in a controlled fashion so that the primary system maintains its quality of service (QoS) requirements. In this thesis, we consider collocated point-to-multipoint primary and secondary networks that have simultaneous access to the same frequency band. Particularly, we examine three different levels at which the two networks may coexist: pure interference, asymmetric co-existence, and symmetric co-existence levels. At the pure interference level, both networks operate simultaneously regardless of their interference to each other. At the other two levels, at least one of the networks attempts to mitigate its interference to the other network by deactivating some of its users. Specifically, at the asymmetric co-existence level, the secondary network selectively deactivates its users based on knowledge of the interference and channel gains, whereas at the symmetric level, the primary network also schedules its users in the same way. Our aim is to derive optimal sum-rates (i.e., throughputs) of both networks at each co-existence level as the number of users grows asymptotically and evaluate how the sum-rates scale with the network size. In order to find the asymptotic throughput results, we derive two propositions; one on the asymptotic behaviour of the largest order statistic and one on the asymptotic behaviour of the sum of lower order statistics. As a baseline comparison, we calculate primary and secondary sum-rates for the time division (TD) channel sharing. Then, we compare the asymptotic secondary sum-rate in TD to that under simultaneous channel sharing, while ensuring the primary network maintains the same sum-rate in both cases. Our results indicate that simultaneous channel sharing at both asymmetric and symmetric co-existence levels can outperform TD. Furthermore, this enhancement is achievable when user scheduling in uplink mode is based only on the interference gains to the opposite network and not on a network’s own channel gains. In other words, the optimal secondary sum-rate is achievable by applying a scheduling strategy, referred to as the least interference strategy, for which only the knowledge of interference gains is required and can be performed in a distributed way.

Simultaneous operation of different wireless applications in the same geographical region and the same frequency band gives rise to undesired interference issues. Since licensed (primary) applications have been granted priority access to the frequency spectrum, unlicensed (secondary) services should avoid imposing interference on the primary system. In other words, secondary system’s activity in the same bands should be in a controlled fashion so that the primary system maintains its quality of service (QoS) requirements. In this thesis, we consider collocated point-to-multipoint primary and secondary networks that have simultaneous access to the same frequency band. Particularly, we examine three different levels at which the two networks may coexist: pure interference, asymmetric co-existence, and symmetric co-existence levels. At the pure interference level, both networks operate simultaneously regardless of their interference to each other. At the other two levels, at least one of the networks attempts to mitigate its interference to the other network by deactivating some of its users. Specifically, at the asymmetric co-existence level, the secondary network selectively deactivates its users based on knowledge of the interference and channel gains, whereas at the symmetric level, the primary network also schedules its users in the same way. Our aim is to derive optimal sum-rates (i.e., throughputs) of both networks at each co-existence level as the number of users grows asymptotically and evaluate how the sum-rates scale with the network size. In order to find the asymptotic throughput results, we derive two propositions; one on the asymptotic behaviour of the largest order statistic and one on the asymptotic behaviour of the sum of lower order statistics. As a baseline comparison, we calculate primary and secondary sum-rates for the time division (TD) channel sharing. Then, we compare the asymptotic secondary sum-rate in TD to that under simultaneous channel sharing, while ensuring the primary network maintains the same sum-rate in both cases. Our results indicate that simultaneous channel sharing at both asymmetric and symmetric co-existence levels can outperform TD. Furthermore, this enhancement is achievable when user scheduling in uplink mode is based only on the interference gains to the opposite network and not on a network’s own channel gains. In other words, the optimal secondary sum-rate is achievable by applying a scheduling strategy, referred to as the least interference strategy, for which only the knowledge of interference gains is required and can be performed in a distributed way.