Wireless sensor networks offer easy implementation, flexibility and mobility of hand held devices. Sensors consist of an internal power source, which is the great limitation for the life time and the usage of sensor networks. To increase the life time, sensors should stay in energy saving sleep mode as long as possible, because in sleep mode the radio is either shut down or working with less energy. Better energy handling is implemented in different power saving mechanism of common Medium Access Control protocols, which are evaluated and analyzed and further extensions and ideas to improve the energy efficiency are presented. Slotted PSM is simulated with the NS2 and compared to the WLAN 802.11 PSM technology and the results show that energy efficiency and power consumption are much better implemented and life time increases with the use of Slotted PSM.

Recent technological advancements are enabling the vision of pervasive or ubiquitous computing to become a reality. Service discovery is vital in such a computing paradigm, where a great number of devices and software components collaborate unobtrusively and provide numerous services. Current service-discovery protocols do not make use of contextual information in discovering services, and as a result, fail to provide the most appropriate and relevant services for users. In addition, current protocols rely on keyword-based search techniques and do not consider the semantic description of services. Thus, they suffer from poor precision and recall. To address the need for a discovery architecture that supports the envisioned scenarios of pervasive computing, we propose a context-aware service-discovery protocol that exploits meaningful contextual information, either static or dynamic, to provide users with the most suitable and relevant services. The architecture relies on a shared, ontology-based, semantic representation of services and context to enhance precision and recall, and to enable knowledge sharing, capability-based search, autonomous reasoning, and semantic matchmaking. Furthermore, the architecture facilitates a dynamic service-selection mechanism to filter and rank matching services, based on their dynamic contextual attributes, which further enhances the discovery process and saves users time and effort. Our empirical results indicate the effectiveness and feasibility of the proposed architecture.

Vehicular communication has been an emerging topic among current wireless research. The vehicular communication can be classified to Inter-Vehicle Communication (IVC) and Road-to-Vehicle Communication (RVC). IVC and RVC support applications mainly on two aspects: safety applications aiming to reduce dangers on the road, and data applications aiming to provide information and entertainment to people on traveling. Vehicles nearby form Vehicular Ad hoc Networks (VANETs) without any fixed infrastructures. Due to the characteristics of vehicular networks such as quickly changing and unstable network topology, IVC has special requirements to the network protocols. Several MAC protocols have been appeared or improved based on previous work for IVC. But these protocols are designed either for QoS guaranteed data service or for reliable message broadcast. There is not a protocol including both application requirements and inexpensive to implement as well. MAC protocol for vehicular communication hasn’t been finalized. In this thesis, an overlay token ring protocol (OTRP) is proposed which can work on MAC layer with broadcast function and taking into the IVC features into consideration. In OTRP, vehicles are grouped to overlapped rings with a token passed in each ring as the sole right for transmission. The ring is dynamically updated in a distributed manner based on smart algorithm at each node. OTRP provides bounded delay by assigning maximum token holding time for each node. It also reduces collisions by decreasing the number of contention nodes by times of ring size. Fair and high throughput is obtained as well. Furthermore, it provides reliable and prompt broadcast of emergency messages by pre-emptively transmitting while applying the token as an acknowledgement. The time nodes reliably receive the message is within limit. Theoretical analysis is provided and simulation results are given to evaluate the performance of OTRP under saturated traffic conditions both in safety and data applications.

This thesis presents a protocol for intervehicle communication for use in Vehicular Ad Hoc Networks (VANET). VANET is a natural extension of mobile ad hoc networks (MANET) in which the restrictions related to power and mobility are relaxed. The routing protocols used for MANETs are generally dependent on the state of the network. With changes in the network topology, routing messages are generated so that the states of the routers in the network are updated. In the case of VANETs, in which the level of node mobility is high, message-routing overhead has serious implications for the scalability and throughput of the routing protocol. This thesis introduces criteria that are recommended for use when protocols are designed for VANET applications and presents the Selected Node Geographic Forwarding (SNGF) protocol. The SNGF protocol implements controlled flooding in an efficient manner in order to reduce unnecessary communication overhead. The protocol has a destination discovery mechanism that allows it to initiate correspondence between nodes without reliance on static location services. The protocol avoids formation of clusters by using the concept of selective forwarding, thus providing the advantages of cluster based approaches without actually forming one itself. It effectively deals with blind flooding by introducing a comprehensive retransmission time delay in the nodes. This retransmission delay favors the nodes in the direction of the destination and prevents other nodes from retransmitting the same message. The SNGF protocol does not use routing tables, which require frequent updates in mobile networks, instead it relies on directing the messages to geographic locations which are forwarded by any available intermediary nodes. The protocol also provides techniques for handling network fragmentation which can be a frequent problem in vehicular networks. It is capable of delayed message transmission and multiple route discovery in the case of the non-availability of the shortest path to the destination. To evaluate the performance of the SNGF protocol, an extensive study of mobile networks was conducted using the NS2 simulator. The simulation results demonstrate the reachability of the protocol, its scalability advantages and its total independence from location services. The SNGF protocol allows each participating node to operate independently of other nodes in the network. Nodes in the network are able to communicate with other nodes without ever becoming dependent on intermediary nodes. This feature opens new possibility for individual node based application development in ad hoc networks. The traffic profiling is described as it would be observed by an independent node participating in VANET using the SNGF protocol. The node communicates with other nodes and collects relevant data through the discourse capability of SNGF. The data collected by the node is viewed as a snapshot in time of the traffic conditions down the road based upon which future traffic condition is predicted. Traffic profiling is investigated for different levels of VANET deployment. The simulation results show that the proposed method of traffic profiling in a VANET environment using the SNGF protocol is viable for even lower levels of deployment.

<p>Wireless and mobile systems play an increasingly important role in our lives. Fueled by an array of innovative services and applications, mobile data traffic is surging rapidly. Traditionally, wireless traffic growth is met by acquiring new spectrum. However, wireless spectrum demand is soon going to surpass it's availability. Thus, there is an urgent need for major innovations in wireless network architecture, so that our spectrum utilization can achieve its full potential. Motivated by this problem, we explore an alternative design of physical layer aware wireless systems.</p><p>Typical approaches towards improving wireless performance is confined within the physical (PHY) or link layers of the networking stack, providing only partial so- lutions. In this thesis, we advocate to consider the entire network architecture holis- tically. We show how rich PHY layer information can be utilized to address existing challenges in wireless networking - contention resolution, rate control, interference management, etc. We design, implement, and experimentally evaluate protocols to understand network-wide implications of PHY-aware systems. We also pursue the observation that PHY layer not only encode bits but also contain rich information about the ambience, and hence can be viewed as a sensor. This sensing informa- tion can be further coupled with other phone sensors, thereby benefitting pervasive mobile services and applications. We demonstrate how this synergy can contribute towards designing precise indoor localization systems, an important building block for next generation mobile applications.</p> / Dissertation

Satellite IP networks are characterized by high bit error rates, long propagation delays, low bandwidth feedback links, and persistent fades resulting from varying weather patterns. A new unicast transport protocol is designed to address all the above challenges. Two new algorithms, Jump Start and Quick Recovery, are presented to replace the traditional Slow Start algorithm and to recover rapidly from multiple segment losses within one window of data. The characteristics of satellite IP networks also distinguish satellite multicasting from multicasting in terrestrial wirelined networks. A reliable data multicast transport protocol, TCP-Peachtree, is proposed to solve the acknowledgment implosion and scalability problems in satellite IP networks. Developments in space technology are enabling the realization of deep space missions. The scientific data from these missions need to be delivered to the Earth successfully. To achieve this goal, the InterPlaNetary Internet is proposed as the Internet of the deep space planetary networks, which is characterized by extremely high propagation delays, high link errors, asymmetrical bandwidth, and blackouts. A reliable transport protocol, TP-Planet, is proposed for data traffic in the InterPlaNetary Internet. TP-Planet deploys rate-based additive-increase multiplicative-decrease (AIMD) congestion control and replaces the inefficient slow start algorithm with a novel Initial State algorithm that allows the capture of link resources in a very fast and controlled manner. A new congestion detection and control mechanism is developed and a Blackout State is incorporated into the protocol operation. Multimedia traffic is also one part of the aggregate traffic over InterPlaNetary Internet backbone links and it has additional requirements such as minimum bandwidth, smooth traffic, and error control. To address all the above challenges, RCP-Planet is proposed. RCP-Planet consists of two novel algorithms, i.e., Begin State and Operational State. The protocol is based on a novel rate probing mechanism and a new rate control scheme to update the media rate smoothly based on the observed rate for the probing sequence.

The objective of this research is to investigate and develop an efficient and seamless data transport protocol for a heterogeneous wireless mobile network. In next-generation network, most of heterogeneous wireless mobile networks will be combined and complementarily constitute a hierarchical network. To integrate different networks, many challenging issues should be solved. In this thesis, an efficient and seamless data transport mechanisms are explored. We investigate the problems that the current transport control protocol (TCP) will experience within the heterogeneous mobile network. In a heterogeneous network, a mobile host experiences drastic changes in network condition during a session. Traditional TCP struggles with abrupt network changes by intersystem handoff and cannot work efficiently in this environment. We propose a TCP scheme to be tailored to the heterogeneous mobile network to support seamless data transport. In the proposed scheme, a TCP is informed the impending handoff events and works differently based on a handoff type. Simulation results present the proposed algorithm improves throughput, stabilizes data transmission rapidly, and provides a seamless data transfer. We also propose an adaptive resource management scheme within a 3G cellular network based on a users priority level to reduce the call dropping and blocking rates. In a heterogeneous network, a network that provides smaller bandwidth may struggle with handed-off calls being served with a higher bandwidth. Therefore, a resource management algorithm should be defined so that an ongoing call is not dropped by a handoff and provides seamless data transfer. We propose an adaptive resource management scheme based on downgrading the quality of some existing services in a 3G cellular network. We analyze the system capacity, call blocking rate and call dropping rate of the proposed algorithm, and simulate the performance variation of the downgraded traffic. The results show that the proposed scheme increases system capacity, and decreases the call dropping rate at the cost of small delay of the downgraded data traffic.

With the wireless mesh network in the embedded systems related applications booming in recent years, the demand of enhancing the overall end to end network traffic and ensuring a stable connection is growing. We proposed a Dynamic Multi-channel Multi-path Routing Protocol (DMMR Protocol) to decompose contending traffics over different channel, different time and different paths to enhance the end to end network traffic. Choosing channel dynamically according to the channel usage around node in the process of finding paths can avoid inter-flow and intra-flow channel competition. We tend to choose paths with less intersection nodes to reduce the probability of multiple paths are broken at same time when a single node cannot work. We can enhance end to end network traffic further by using multiple interfaces at one node. We use NS2 to test DMMR Protocol, and analyzing the overall end to end traffic when multiple connections are setting up in the network. If the network can accept a new connection, the increment of end to end traffic is same as the traffic of the new connection. In connection robust test, a single path broken will not affect other flows in same connection and the end to end traffic in the connection will recovery immediately when the broken path is repaired.

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The IEEE 802.11a has become the mainstream protocol used in modern wireless communication system due to its high propagation rate of data (54 Mb/s). To meet high propagation rates, the communication devices used in IEEE 802.11a protocol usually present a high conversion gain and a high linearity (denoted as third order intercept point, IIP3). The IIP3 of conventional up- and down-conversion mixers are only about 0 dBm and -5 dBm, which fail to achieve a high propagation rate of data. This thesis utilizes the TSMC 0.18 £gm CMOS technology to design and fabrication up- and down-conversion mixers with very high linearity for IEEE 802.11a application. The proposed high-linearity up-conversion mixer with 1.01 mm ¡Ñ 0.85 mm chip size and its wide bandwidth (5~6 GHz) is well suited for IEEE 802.11a application. To enhance the linearity and bandwidth, a transconductor stage with gm-boosted structure, a switch stgae with LO-body grounded structure and a load stage with shunt peaking structure are adopted in this research. Under 5.2/5.4/5.8 GHz operating frequencies, the implemented up-conversion mixer demonstrates a high conversion gain of 6.8/7.1/6.3 dB and a high linearity of 8.9/9/13.2 dBm, respectivly. In addition, a moderate consuming power (6.86 mW) of such mixer can be achieved at 1.2 V supply voltage. On the other hand, this thesis also designed and fabricated a high-linearity down-conversion mixer with chip size of 1.02 mm ¡Ñ 0.86 mm and 5.2 GHz center frequency. To improve the linearity and isolation and reduce the high-order noise, a transconductor stage with dual-gate structure and a load stage with RC-tank structure are adopted in this research. According to the EM-simulation resutls, the proposed down-conversion mixer presents a moderate conversion gain of 6 dB and a high linearity of 0.8 dBm. Additionly, a moderate consuming power (6.75 mW) of such mixer can be achieved at 1.8 V supply voltage.