Search

Problem statement: Vehicular Ad hoc Networks (VANET) is one of the most challenging research area in the field of Mobile Ad Hoc Networks. Approach: In this research we proposed a dynamic power adjustment protocol that will be used for sending the periodical safety message. (Beacon) based on the analysis of the channel status depending on the channel congestion and the power used for transmission. Results: The Beacon Power Control (BPC) protocol first sensed and examined the percentage of the channel congestion, the result obtained was used to adjust the transmission power for the safety message to reach the optimal power. Conclusion/Recommendations: This will lead to decrease the congestion in the channel and achieve good channel performance and beacon dissemination. Key words: Power control, piggyback, safety message, BPC protocol, congestion avoidance, INTRODUCTION VANET has attracted a wide range of research effort these days, aiming to reach road safety, infotainment and a comfort driving experience, all these benefits in low cost. In [...]

Problem statement: As group key management extended into the area of large dynamic networks, complex issues emerged involving the many operations that run over several network topologies. The issues that occurred due to multiple topologies were also compounded by differing views of the network, taken at different time slices or positions within the network. This was especially complex when figuring in mobile, ad-hoc networks. View synchrony is the current operational technique, or assumption, applied to group key exchange protocols. However, before this analysis view synchrony was just that, an assumption and the literature for group key exchange lacked an inquiry into what could happen when view synchrony was removed. Current group key management protocols rely on view synchrony and yet all protocols vary in requisite operational descriptions and performance measures. In this study, a framework for group key management protocol operations and performance measures was defined and examined how that framework could be used to compare and contrast existing protocols with and, more importantly, without view synchrony. Approach: Current literature lacked categories by which to quantify the performance metric of the protocols. This study first defined the dynamic key operations that all protocols share. By these definitions, group key management protocols were directly compared. Once definitions existed, this study assembled a list of costs that every protocol requires to establish and share keys across the dynamic group. These results provided an understanding of view synchrony's role and whether or not it should be solely relied on in these current protocols. Results: The prior conclusion that view synchrony was an integral part of all group key management protocols was shattered, when seen through the lens of communication costs and assumptions in wireless ad-hoc networks. View synchrony, as an assumed part of all group key management was previously inconsistently portrayed. The ability to see this before did not exist because a framework upon which to evaluate the costs did not exist. Now, literature can proceed with clearly defined understandings of what values exist in group key management protocols. Conclusion/Recommendations: Better communication in group key management will be a benefit to the entire field. Now that costs can be analyzed, procedure and security can be improved and protocols can be implemented for wireless ad-hoc networks. In addition, it led two authors of this study to create a new protocol, DTEGK, to maximize the most efficient communication, as view synchrony was hindering the effectiveness of previous protocols. Without the hindrance of view synchrony and a quantitative list of defined communication costs, protocols can also now be extended into the wireless, ad-hoc realm of group key management. Key words: Group key management, cryptography, wireless, ad-hoc networks, INTRODUCTION In 1976, Diffie and Hellman (1976) introduced an implementation of two-party key exchange protocol that allowed two participants to create a private cryptographic key through the use of publicly [...]

The wireless Greedy Primal-Dual (wGPD) protocol for congestion control and scheduling in multihop wireless networks is described. This protocol keeps buffer occupancies smaller and reduces the probability of packet drops by spreading loads among multiple queues.

This paper discusses the impact that communication will have on the electric power grid in the future. Recent efforts, such as UCA 2.0 and IEC 61850, are establishing a standard way for electric power substations, intelligent electronic devices, and other apparatus to communicate over data networks. These efforts pave the way to a future where protection and control of the electric power grid will migrate towards a common utility intranet. The intranet will almost certainly be based on Internet standards due to their widespread use, low cost, and easy migration path over time. A utility intranet, common to the utilities but separate from the Internet, will allow for the eventual connection of regional substations, equipment, and control centers throughout the grid. The transition will allow capabilities beyond what is currently available, but it requires a careful understanding of the implications for network capacity constraints, protocol selections, and quality-of-service technologies. This paper discusses the benefits of utility communication, the likely pitfalls in the use of Internet technology for protection and control systems, and technologies that can help to mitigate those pitfalls. This paper also introduces a model for the expected background traffic that will be present in a utility intranet. Experimental results illustrate the use of different communications protocols in representative power situations in the face of different levels of background traffic in the electric power and communication synchronizing simulator simulation environment. Index Terms--Background traffic, protection and control, quality of service (QOS), simulation, utility intranet.

In recent years, time-triggered communication protocols have been developed to support time-critical applications for in-vehicle communication. In this respect, the FlexRay protocol is likely to become the de facto standard. In this paper, we investigate the scheduling problem of periodic signals in the static segment of FlexRay. We identify and solve two subproblems and introduce associated performance metrics: 1) The signals have to be packed into equal-size messages to obey the restrictions of the FlexRay protocol, while using as little bandwidth as possible. To this end, we formulate a nonlinear integer programming (NIP) problem to maximize bandwidth utilization. Furthermore, we employ the restrictions of the FlexRay protocol to decompose the NIP and compute the optimal message set efficiently. 2) A message schedule has to be determined such that the periodic messages are transmitted with minimum jitter. For this purpose, we propose an appropriate software architecture and derive an integer linear programming (ILP) problem that both minimizes the jitter and the bandwidth allocation. A case study based on a benchmark signal set illustrates our results. Index Terms--FlexRay, integer programming, real time, scheduling, vehicular communication networks.

The FlexRay communication protocol is expected to be the de facto standard for high-speed, in-vehicle communication. In this paper, we formally investigate the scheduling problem for the dynamic segment (DS) of FlexRay. We take the bounds on the generation times and the timing requirements of the signals into consideration to propose a reservation-based scheduling approach that preserves the flexible medium access of the DS. To obtain efficient schedules, we formulate a nonlinear integer programming problem (NIP) that minimizes the required duration of the DS. This NIP is then decomposed into two linear binary integer programming problems to facilitate the computation of feasible message schedules. An experimental study illustrates our message scheduling approach for the DS of FlexRay. Index Terms--FlexRay, integer programming, real time, scheduling, vehicular communication networks.

A grid-powered Web Geographical Information Science (GIS)/Web Processing Service (WPS) system has been developed for archiving and distributing large volumes of geospatial data. However, users, WPS servers, and data resources are always distributed across different locations, attempting to access and archive geospatial data from a GIS survey via conventional Hypertext Transport Protocol, Network File System Protocol, and File Transfer Protocol, which often encounters long waits and frustration in wide area network (WAN) environments. To provide a 'local-like' performance, a WAN/grid-optimized protocol known as 'Grid Jet' developed at our lab was used as the underlying engine between WPS servers and clients, which utilizes a wide range of technologies including the one of paralleling the remote file access. No change in the way of using software is required since the multistreamed Grid Jet protocol remains fully compatible with the existing IP infrastructures. Our recent progress includes a real-world test that PyWPS and Google Earth over the Grid Jet protocol beat those over the classic ones by a factor of two to eight, where the distribution/archiving distance is over 10 000 km. Index Terms--Bulk data transfer, data archiving, geodata set, grid computing, Web Processing Service (WPS).

As the transport layer protocol of the Space Communication Protocol Standard (SCPS) suite, SCPS-Transport Protocol (SCPS-TP) is actually transmission control protocol (TCP), with a set of extensions aimed at improving TCP performance in space communications. Some work has been done on the performance evaluation of SCPS-TP in comparison with TCP. However, those works have been done by testing SCPS-TP via emulation test-beds. We present the file transfer experimental work of testing the SCPS protocol stack over NASA's geostationary orbit (GEO) Advanced Communications Technology Satellite (ACTS). Considering that space communication channels in practice are frequently asymmetric in terms of channel bandwidth, our work is concentrated on the evaluation of the effectiveness of SCPS-TP in coping with channel rate asymmetry. We conclude that SCPS-TP is better suited than TCP over long-delayed, asymmetric, satellite channels with a throughput advantage of over 30 Kbyte/s for the transmission of a 10 Mbyte file. A hybrid of the channel rate control and acknowledgment frequency reduction mechanisms makes significant contributions to the performance enhancement of SCPS-TP over asymmetric space channels.

The objective of this paper is to investigate the best solution such that on which decision should be made to forward a wireless packet. The decision should be made in such a way to keep the node alive by choosing an alternate path, through those nodes that have more power reserve. Minimizing the consumption of the reserve power will results in an increase in the number of hops the packet must travel. A hybrid solution can be utilized which is a combination of power-aware and minimizing the number of hops to be traveled. Recent research suggests that it should select the node with high power reserve than based on the shortest path. A question arises which is more critical for ad hoc networks the power-aware solution or the shortest path based on the number of hops. This research will investigate these solutions aiming on minimizing power consumption for wireless packets networks and the number of hops to be traveled. Through rigorous empirical analysis based on the p-method and box-space method, we were able to derive critical global properties with respect to end-to-end minimum power consumption routes. Finally, a simulation results are presented to verify the performance of the proposed algorithms. Key words: Box Method, p-method, power-aware routing, wireless communications, ad hoc networks, INTRODUCTION With the increasing dependence on the Internet in many aspects of their daily lives, users demand ubiquitous, high performance Internet access whether they are at work, at home, or [...]

Although many wireless communication standards include multicast as well as unicast traffic in layer 2, most parts of the specifications are limited to unicast methods. In addition, although the existing wireless standards provide reliable unicast methods using an automatic repeat request (ARQ) and a retransmission, multicast packets are not reliably transmitted using these standards. To retransmit a multicast packet, the acknowledgements (ACKs) from the receivers need to be received by the sender to determine whether a retransmission is required. However, transmitting an ACK from each group member degrades the network performance due to the overhead induced by multiple ACK packet transmissions and channel access processes for the ACKs. To solve this problem, in this paper, a medium-access control protocol called the orthogonal frequency division multiplex access (OFDMA) based multicast ACK (OMACK), with minimum ACK overhead over wireless local area networks, is proposed. The proposed scheme uses one orthogonal frequency division multiplex (OFDM) symbol for the ACKs from all member stations (STAs), and each member STA indicates its packet reception status by utilizing a subcarrier within the OFDM symbol. The proposed scheme is thoroughly examined by using simulation and theoretical methods, and the results show that it significantly reduces the aforementioned overhead and, as a consequence, improves the performance of wireless networks. Index Terms--Medium-access control (MAC), multicast, orthogonal frequency division multiplex access (OFDMA), wireless LAN.

Quantum communication is a method that offers efficient and secure ways for the exchange of information in a network. Large-scale quantum communication (1,4) (of the order of 100 km) has [...]

In the interactive communication model, two parties [P.sub.x] and [P.sub.y] possess respective private but correlated inputs x and y, and [P.sub.y] wants to learn x from [P.sub.x] while minimizing the communication required for the worst possible input pair (x, y). Our contribution is the analysis of four nonzero-error models in this correlated data setting. In the private coin randomized model, both players are allowed to toss coins, and [P.sub.y] must learn x with high probability for every input pair. The second and third models are similar to the first one, but the players are allowed to use a common source of randomness and to solve several independent instances of the same problem simultaneously, respectively. In the fourth model, [P.sub.y] is allowed to answer incorrectly for a small fraction of the inputs. We show that one round of communication is nearly optimal for the private coin randomized model. We also prove that the last three models are equivalent and can be arbitrarily better than the original worst case deterministic model when interaction is not allowed. Finally, we show that the deterministic model and all the nonzero-error models are equivalent for a class of symmetric problems arising from several practical applications, although nonzero-error and randomization allow efficient one-way protocols. Index Terms--Communication complexity, interactive communication, nonzero error, randomization, worst case protocols.

There are numerous research challenges that need to be addressed until a wide deployment of vehicular ad hoc networks (VANETs) becomes possible. One of the critical issues consists of the design of scalable routing algorithms that are robust to frequent path disruptions caused by vehicles' mobility. This paper argues the use of information on vehicles' movement information (e.g., position, direction, speed, and digital mapping of roads) to predict a possible link-breakage event prior to its occurrence. Vehicles are grouped according to their velocity vectors. This kind of grouping ensures that vehicles, belonging to the same group, are more likely to establish stable single and multihop paths as they are moving together. Setting up routes that involve only vehicles from the same group guarantees a high level of stable communication in VANETs. The scheme presented in this paper also reduces the overall traffic in highly mobile VANET networks. The frequency of flood requests is reduced by elongating the link duration of the selected paths. To prevent broadcast storms that may be intrigued during path discovery operation, another scheme is also introduced. The basic concept behind the proposed scheme is to broadcast only specific and well-defined packets, referred to as 'best packets' in this paper. The performance of the scheme is evaluated through computer simulations. Simulation results indicate the benefits of the proposed routing strategy in terms of increasing link duration, reducing the number of link-breakage events and increasing the end-to-end throughput. Index Terms--Intervehicular communications (IVC), road-vehicle communications (RVC), stable routing, vehicular ad hoc network (VANET).

Making the best use of the Dedicated Short Range Communications multichannel architecture, we propose a cluster-based multichannel communications scheme that can support not only public-safety message delivery but also a wide range of future multimedia (e.g., video/audio) and data (e.g., e-maps, road/vehicle traffic/weather information) applications. Our proposed scheme integrates clustering with contention-free and/or -based medium access control (MAC) protocols. In our scheme, the elected clusterhead vehicle functions as the coordinator to collect/deliver realtime safety messages within its own cluster and forward the consolidated safety messages to the neighboring cluster heads. In addition, the cluster-head vehicle controls channel assignments for cluster-member vehicles transmitting/receiving nonreal-time traffics, which makes the wireless channels more efficiently utilized for vehicle-to-vehicle (V2V) nonreal-time data transmissions. Our scheme uses the contention-free MAC within a cluster and the contention-based IEEE 802.11 MAC among cluster-head vehicles such that the real-time delivery of safety messages can be guaranteed. Under our proposed scheme, we develop an analytical model to study the delay for the consolidated safety messages transmitted by the cluster-head vehicles. Based on this analytical model, we derive the desirable contention-window size, which can best balance the tradeoff between the delay of safety messages and the successful rate of delivering safety messages. The extensive simulation results show that, under various highway traffic scenarios, our proposed scheme can efficiently support the nonreal-time traffics while guaranteeing the real-time delivery of the safety messages. Index Terms--Clustering algorithms, Dedicated Short-Range Communications (DSRC), multichannel medium-access control (MMAC), protocol designs, time--division multiple access (TDMA), vehicle-to-vehicle (V2V) communications, vehicular ad hoc networks (VANETs).

Mobile ad hoc networks(MANET) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self organize into arbitrary and temporary ad-hoc network topologies, allowing people and devices to seamlessly internet work in areas with no preexisting communication infrastructure e.g., disaster recovery environments. An ad-hoc network is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad-hoc paradigm. Recently the introduction of new technologies such as Bluetooth, IEEE 802.11 and hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent revolutions have been generating a renewed and growing interest in the research and development of MANET. To facilitate communication within the network a routing protocol is used to discover routes between nodes. The goal of the routing protocol is to have an efficient route establishment between a pair of nodes, so that messages can be delivered in a timely manner. Bandwidth and power constraints are the important factors to be considered in current wireless network because multi-hop ad-hoc wireless relies on each node in the network to act as a router and packet forwarder. This dependency places bandwidth, power computation demands on mobile host to be taken into account while choosing the protocol. Routing protocols used in wired network cannot be used for mobile ad-hoc networks because of node mobility. The ad-hoc routing protocols are divided into two classes: table driven and demand based. This paper reviews and discusses routing protocol belonging to each category. Keywords: MANET, Routing Protocol, On-demand, active and reactive protocols, INTRODUCTION Wireless network has become very popular in the computing industry. Wireless network are adapted to enable mobility. There are two variations of mobile network. The first is infra-structured network [...]

In distributed database systems the global database is partitioned into a collection of local databases stored at different sites. In this era of growing technology and fast communication media, security has an important role to play. In this paper we presented a secure concurrency control protocol (SCCP) based on the timestamp ordering, which provides concurrency control and maintains security.We also implemented SCCP and a comparison of SCCP is presented in three cases (High, Medium and Low security levels). In this experiment, It is observed that throughput of the system decreases as the security level of the transaction increases, i.e., there is tradeoff between the security level and the throughput of the system. Key Words: Transaction, timestamp, Protocol, and Concurrency, INTRODUCTION A distributed database system is described as 'one in which multiple database sites are linked by a communications system in such a way that the data at any site [...]

Most of the existing routing protocols for ad hoc networks are designed to scale in networks of a few hundred nodes. They rely on state concerning all links of the network or links on the route between a source and a destination. This may result in poor scaling properties in larger mobile networks or when node mobility is high. Using location information to guide the routing process is one of the most often proposed means to achieve scalability in large mobile networks. However, locationbased routing is difficult when there are holes in the network topology. We propose a novel positionbased routing protocol called Proximity Aware Routing for Ad-hoc networks (PARA) to address these issues. PARA selects the next hop of a packet based on 2-hops neighborhood information. We introduce the concept of 'proximity discovery'. The knowledge of a node's 2-hops neighborhood enables the protocol to anticipate concave nodes and helps reduce the risks that the routing protocol will reach a concave node in the network. Our simulation results show that PARA's performance is better in sparse networks with little congestion. Moreover, PARA significantly outperforms GPSR for delivery ratio, transmission delay and path length. Our results also indicate that PARA delivers more packets than AODV under the same conditions. Keywords: Mobile ad hoc networks, location-based routing, AODV, INTRODUCTION Ad hoc networks consist of autonomous nodes that collaborate in order to forward packets. There is no stationary infrastructure. Thus, each node acts as an end system and a [...]

This paper demonstrates the formal validation process of safety properties of Selective ACKnowledgment (SACK) protocol. SACK is a complex communication protocol as it is used in various types of distributed computer systems and networks. This acknowledgment mechanism is used with sliding window protocol that allows the receiver to acknowledge packets received out of order, but within the correct sliding window. One of the critical property of SACK is its' safety property. In order to validate this property formally by using the Z/Eves theorem prover, we specify the SACK protocol using Z formal specification language. By using theorem prover tool, it helps to reduce time, energy and mistake than in relatively manual theorem proving which can be tedious and error-prone task. Key words: formal validation, Z specification, safety property, protocol communication, SACK, INTRODUCTION Communication protocol is a complex protocol and it is used in many distributed system and networks. Non-formal techniques are successfully used to design the protocol, but it contains unexpected [...]

A hybrid wireless network is an extension to an infrastructure network, where a mobile host may connect to an access point (AP) using multihop wireless routes via other mobile hosts. The APs are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select their operating channels dynamically through channel switching. In this environment, we propose a routing protocol that finds routes to balance load among channels while maintaining connectivity. The protocol works with nodes equipped with a single network interface, which distinguishes our work with other multichannel routing protocols that require multiple interfaces per node. The protocol discovers multiple routes to multiple APs, possibly operating on different channels. Based on traffic load information, each node selects the 'best' route to an AP and synchronizes its channel with the AP. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The protocol assures that every node has at least one route to an AP, where all intermediate nodes are operating on the same channel. Our simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a multichannel protocol with no load balancing. Index Terms--Communication system routing, communication systems, load-balancing, multi-channel, multi-hop, protocols, routing.

Abstract: A mobile Ad-hoc NETwork (MANET) is wireless network composed of mobile nodes that are dynamically and randomly located in such a manner that the interconnections between nodes are capable [...]

Abstract: This study introduces an analysis to the performance of the Enhanced Associativity Based Routing protocol (EABR) based on two factors; Operation complexity (OC) and Communication Complexity (CC). OC can [...]

In the automatic repeat request (ARQ) protocol, the sender keeps retransmitting a code word until it receives a positive acknowledgment from the receiver sent through the feedback channel. This correspondence proposes plain and diversity combining hybrid ARQ protocol communication schemes suitable for the m([greater than or equal to] 2)-ary asymmetric channel using t-asymmetric error correcting/all asymmetric error detecting (t-AEC/AAED) codes. The analysis shows that error correction definitely improves the throughput of the system compared to the ARQ protocol which uses only error detecting codes. The correspondence provides simple analytic expressions for the average number of transmissions of a code word in both plain and diversity combining t-AEC/AAED ARQ (t [greater than or equal to] 0) protocol systems over the m-ary asymmetric channel, m [greater than or equal to] 2. An example is shown on how to get very close to the Z-channel capacity. Index Terms--Asymmetric errors, automatic repeat request (ARQ) protocols, diversity combining, error correcting/detecting codes, m-ary alphabet, optical communication, VLSI systems, Z-channel.

In this paper, an optimal topology-transparent reservation time division multiple access (OTTR-TDMA) protocol is proposed for multihop ad hoc networks. Our MAC protocol is based on a slotted TDMA architecture in which every slot is divided into reservation phase and data transmission phase. Every node not only transmits data in its assigned slots that are computed by Chlamtac's algorithm, but it also utilizes free slots among its non-assigned slots through reservation. Through theoretical analysis, we derive the proper parameter for the best performance. We compare our protocol with other TDMA protocols and find that it gives better performance. Simulation results show that they are consistent with our analytical results. Keywords: Time division multiple access (TDMA); Topology-transparent reservation; Ad hoc network

The IEEE 802.11 standard inherently supports multiple data rates at the physical layer. Various rate adaptation mechanisms have been proposed to exploit this multirate capability by automatically adapting the transmission rate to best utilize the wireless spectrum. This study is primarily motivated by the observation that in a wireless network, a multihop high-rate path can potentially achieve better throughput and delay than using a single-hop low-rate path for transmission. Specifically, this paper introduces a relay-aided media access (RAMA) protocol by taking advantage of the existence of such multihop high-rate links. This is demonstrated by replacing one low-rate link with two high-rate links using a relay node. One of the key novelties in the proposed RAMA protocol is that the transmission from the immediate relay node to the destination node is free of contention. Results from analysis and simulations show that RAMA can significantly improve performances in terms of both throughput and delay. Index Terms--IEEE 802.11, media access control (MAC), multirate transmission, wireless networks.

We propose an adaptive hybrid automatic repeat request--forward error correction (ARQ--FEC) erasure-correcting scheme for quality of service (QoS)-driven mobile multicast services over wireless networks. The main features of our proposed scheme include (i) the low complexity achieved by the graph code; (ii) dynamic adaptation to the variations of packet-loss level and QoS requirements. To increase error-control efficiency and support diverse QoS requirements, we develop a two-dimensional (2-D) adaptive error-control scheme that dynamically adjusts not only the error-control redundancy, but also the code mapping structures. By deriving and identifying the closed-form nonlinear analytical expression between the optimal check-node degree and the packet-loss level, we propose the nonuniformed adaptive coding structures to achieve high error-control efficiency. Applying the Markov chain model, we obtain closed-form expressions that derive the error-control redundancy as a function of packet-loss level and the optimal check-node degree in each adaptation step. The convergency of error-control redundancy adaptation is dynamically controlled by different QoS requirements such that a high error-control efficiency can be achieved. Using the proposed 2-D adaptive error control, we design an efficient hybrid ARQ--FEC protocol for mobile multicast services with diverse reliability QoS requirements. The proposed scheme keeps the feedback overhead low by consolidating only the numbers rather than the sequence numbers of the lost packets, which are fed back by multicast receivers. Also conducted is a set of numerical and simulation evaluations that analyze and compare our proposed adaptive scheme with those using nonadaptive graph codes, Reed--Solomon erasure codes (RSE), and the pure ARQ-based approach. The simulation results show that our proposed scheme can efficiently support QoS-driven mobile multicast services and achieve high error-control efficiency while imposing low error-control complexity and overhead for mobile multicast networks. Index Terms--Adaptive hybrid automatic repeat request-forward error correction (ARQ--FEC), error control, graph codes, low-complexity erasure codes, mobile multicast, quality of service (QoS), wireless networks.

The performance of two-phase collaborative communication protocols is studied for wireless networks. All the communication nodes in the cluster are assumed to share the same channel and transmit or receive collaboratively in a quasi-static Rayleigh flat-fading environment. In addition to small-scale fading, the effect of large-scale path loss is also considered. Based on a decode-and-forward approach, we consider various variable-rate two-phase protocols that can achieve full diversity order and analyze the effect of node geometry on their performance in terms of the outage probability of mutual information. For the single-relay node case, it is shown that if the collaborator node is close to the source node, a protocol based on space-time coding (STC) can achieve good diversity gain. Otherwise, a protocol based on receiver diversity performs better. These protocols are also compared with one based on fixed-rate repetition coding and their performance tradeoffs with node geometry are studied. The second part deals with multiple relays. It is known that with N relays an asymptotic diversity order of N + 1 is achievable with STC-based protocols in the two-phase framework. However, in the framework of collaborative STC, those relay nodes which fail to decode remain silent (this event is referred to as a node erasure). We show that this node erasure has the potential to considerably reduce the diversity order and point out the importance of designing the STC to be robust against such node erasure. Index Terms--Collaborative (cooperative) communication, relay channel, space-time coding (STC), spatial diversity, wireless networks.

For supporting the mobile host (MH) to be the multicast receivers on wireless networks, the traditional approaches such as the Hierarchical Remote Subscription (HRS) and Bi-directional Tunneling with Mobile Multicast (BT-MoM) integrate the Mobile IP protocol with the IP multicast technique. However, they inherit intrinsic problems to handle mobility and suffer significant delays to rebuild the multicast tree when the MH moves out of the multicast tree, which results in serious playback interruption and quality of service (QoS) degradation for the ongoing multimedia service especially when the MH are scattered over different kinds of wireless networks. In this paper, we propose a cross-layer framework and the Hierarchical Multicast Session Initiation Protocol (HMSIP), which extend the IETF Session Initiation Protocol (SIP) with the concept of multicast SIP session and integrate the underlying IP Multicast QoS routing protocol and the RSVP resource reservation technique, to support mobile multimedia multicasts. This framework significantly reduces handoff delays and deployment costs and hence achieves end-to-end QoS support for MHs on heterogeneous wireless networks. Further, we mathematically analyze handoff delays of the HRS, BT-MOM and HMSIP schemes. Moreover, simulation results show that the HMSIP can significantly achieve much more stable and lower handoff delays than those of the BT-MOM and HRS only with a small proportion of extra bandwidth than the bandwidth-optimal HRS, thereby supporting higher numbers of handoffs without interrupting multimedia playback of the mobile multicast activity. Tradeoffs between costs for deploying HMSIP Proxies in the framework and corresponding performances of the HMSIP families are discussed. Finally, multimedia QoS improvements of MHs are shown to emphasize advantages by integrating RSVP in this HMSIP framework. Keywords: IP Multicast; Mobile IP; Multimedia QoS; Heterogeneous wireless networks; SIP; HMSIP

Abstract: The Adaptive Reliable Multicast Protocol (ARM) with intermediate node support is introduced to guarantee message delivery to all multicast receivers in mobile ad hoc environment. ARM distributes multicast message [...]

In this paper, three random access control mechanisms based on the well-known Slotted ALOHA, NP-CSMA, and 1P-CSMA protocols are presented. The basic idea is to limit the number of transmissions and retransmissions at high traffic loads in order to minimize collisions while keeping system stability. A new medium-access control protocol called Adaptive Traffic Load (ATL) is proposed. With ATL, all users are assigned authorization of transmission probabilities that vary according to the prevailing average traffic conditions in the system. ATL ensures that the system throughput is kept constant at its maximum value regardless of the traffic load. A mathematical analysis to calculate the probability density function of the access delay in the ATL protocol under the assumption of infinite user population is also presented. Mean access delay follows increases exponentially with respect to the traffic load when conventional random access protocols are used. However, it follows a linear function with respect to the traffic load when ATL is used. The average traffic load of the system is an input of the ATL protocol in order to assign access authorization probabilities to all users attempting to access the network. A simple algorithm for traffic load estimation based on the probability of finding empty slots in the system within an estimation period is proposed in this paper to asses the average traffic load. In the numerical evaluations of ATL, the Enhanced Data for GSM Evolution (EDGE) system is considered as a case study. For high arrival rates, channel utilization can be low in EDGE even if the system has sufficient capacity to serve incoming data users. A mathematical analysis of ATL-Slotted ALOHA as well as ATL-CSMA is presented. In the case of ATL-CSMA, system throughput varies according to the cell size. Hence, the ATL protocol is evaluated in picocell, microcell and macrocell environments as recommended by ITU-R. Also, the performance of EDGE is evaluated in terms of average data rate and packet delay for both S-ALOHA and ATL S-ALOHA considering long range dependent traffic type. Index Terms--Access delay, adaptive traffic load, CSMA, long range dependent (LRD) traffic, S-ALOHA.