GeoDTN<Emphasis Type="Bold">+</Emphasis>Nav: Geographic DTN Routing with Navigator Prediction for Urban Vehicular Environments

Position-based routing has proven to be well suited for highly dynamic environment such as Vehicular Ad Hoc Networks (VANET) due to its simplicity. Greedy Perimeter Stateless Routing (GPSR) and Greedy Perimeter Coordinator Routing (GPCR) both use greedy algorithms to forward packets by selecting relays with the best progress towards the destination or use a recovery mode in case such solutions fail. These protocols could forward packets efficiently given that the underlying network is fully connected. However, the dynamic nature of vehicular network, such as vehicle density, traffic pattern, and radio obstacles could create unconnected networks partitions. To this end, we propose GeoDTN+Nav, a hybrid geographic routing solution enhancing the standard greedy and recovery modes exploiting the vehicular mobility and on-board vehicular navigation systems to efficiently deliver packets even in partitioned networks. GeoDTN+Nav outperforms standard geographic routing protocols such as GPSR and GPCR because it is able to estimate network partitions and then improves partitions reachability by using a store-carry-forward procedure when necessary. We propose a virtual navigation interface (VNI) to provide generalized route information to optimize such forwarding procedure. We finally evaluate the benefit of our approach first analytically and then with simulations. By using delay tolerant forwarding in sparse networks, GeoDTN+Nav greatly increases the packet delivery ratio of geographic routing protocols and provides comparable routing delay to benchmark DTN algorithms.     

Making transmission schedules immune to topology changes inmulti-hop packet radio networks

Transmissions scheduling is a key design problem in packet radio networks, relevant to TDMA and CDMA systems. A large number of topology-dependent scheduling algorithms are available, in which changes of topology inevitably require recomputation of transmission schedules. The need for constant adaptation of schedules to mobile topologies entails significant, sometime insurmountable, problems. These are the protocol overhead due to schedule recomputation, performance penalty due to suspension of transmissions during schedule reorganization, exchange of control message and new schedule broadcast. Furthermore, if topology changes faster than the rate at which new schedules can be recomputed and distributed, the network can suffer a catastrophic failure. The authors propose a robust scheduling protocol which is unique in providing a topology transparent solution to scheduled access in multi-hop mobile radio networks. The proposed solution adds the main advantages of random access protocols to scheduled access. Similarly to random access it is robust in the presence of mobile nodes. Unlike random access, however, it does not suffer from inherent instability, and performance deterioration due to packet collisions. Unlike current scheduled access protocols, the transmission schedules of the proposed solution are independent of topology changes, and channel access is inherently fair and traffic adaptive     

Supporting service differentiation for real-time and best-effort traffic in stateless wireless ad hoc networks (SWAN)

We propose SWAN, a stateless network model which uses distributed control algorithms to deliver service differentiation in mobile wireless ad hoc networks in a simple, scalable and robust manner. The proposed architecture is designed to handle both real-time UDP traffic, and best effort UDP and TCP traffic without the need for the introduction and management of per-flow state information in the network. SWAN supports per-hop and end-to-end control algorithms that primarily rely on the efficient operation of TC/IP protocols. In particular, SWAN uses local rate control for best-effort traffic, and sender-based admission control for real-time UDP traffic. Explicit congestion notification (ECN) is used to dynamically regulate admitted real-time sessions in the face of network dynamics brought on by mobility or traffic overload conditions. SWAN does not require the support of a QoS-capable MAC to deliver service differentiation. Rather, real-time services are built using existing best effort wireless MAC technology. Simulation, analysis, and results from an experimental wireless testbed show that real-time applications experience low and stable delays under various multihop, traffic, and mobility conditions.     

Energy-efficient Routing of Multimedia Traffic in Frequency-Hop Packet Radio Networks

Conservation of energy is important in a packet radio network, but reliance on energy-efficient routes for all types of traffic leads to large delays and low success probabilities in many situations. We describe and evaluate protocols that select routes according to the service priorities of the traffic. Energy conservation is emphasized for delay-tolerant traffic but sacrificed for delay-intolerant traffic, which gives good performance for both types of traffic.This paper was presented in part at the IEEE Wireless Communications and Networking Conference, Atlanta, March 2004.     

Cost analysis of mobility protocols

Increasing demand for mobility in wireless data network has given rise to various mobility management schemes. Most of the analysis on mobility protocols used Random Waypoint mobility model However, the analysis done earlier ignored some major costs, resulting in an incomplete estimation and used random waypoint model which fails to represent realistic movement pattern. In this paper, we have developed an analytical cost model considering all possible costs related to mobility management, and have used city section mobility model, a realistic mobility model, to compute the total costs of two mobility protocols: HIMPv6 and SIGMA. We have defined two novel performance metrics, normalized overhead and efficiency, for mobility protocols based on the signaling costs and used them to evaluate the performance of SIGMA and HMIPv6 protocols varying network size, mobility rate and traffic rate. Results show that the total cost of SIGMA is much less than HMIPv6 due to the higher cost of packet tunneling, even though the mobility signaling cost of SIGMA is higher than HMIPv6. Moreover, mobility signaling costs of both the protocols using city model and random waypoint model are found to be much different, demonstrating the fact that random waypoint model cannot be used as an approximation to a realistic scenario. The analytical framework presented in this paper can be used by the network professionals to estimate amount of load on the network due to mobility protocols and compare them based on the proposed performance metrics to select the best protocol.     

Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/G^Y/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.     

Development of Mobile Communications Systems Beyond Third Generation

Second generation mobile radio systems have been successfully deployed worldwide. These systems are evolved to higher data rates and packet transmission. Third generation mobile radio systems will be initially deployed in 2001 and 2002 in different regions of the world. Advanced multimedia services are under development and first services are already being offered in second generation systems. Due to the megatrend of the rapid growth of Internet type services packet oriented traffic is exceeding circuit switched traffic. Therefore, communication systems will be developed and optimized for packed oriented traffic. This paper presents a vision of a system beyond third generation mobile communications, which comprises a combination of several optimized access systems on a common IP based medium access and core network platform. These different access systems will interwork by horizontal and vertical handover, service negotiation and global roaming. The different access systems are allocated to different mutually complementing cell layers with respect to cell size, coverage and mobility to provide globally optimized seamless services to users.     

System aspects of smart-antenna technology in cellular wirelesscommunications-an overview

In this paper, we surveyed the three main system aspects of smart-antenna (SA) technology in wireless communications, i.e., SA receiver, wireless network control, and planning with SAs. A classification of SA receivers and their algorithms is given in order to simplify orientation in a very large amount of structures and algorithms. We discuss system integration of SA receivers, taking into consideration expected propagation conditions, user mobility, and offered traffic. Several radio network planning and upgrading concepts associated with SAs are evaluated. We describe possible radio networks architectures when SAs are used at the mobiles, base stations, or at both ends. Radio network control functions with SAs at different layers are briefly examined. Existing experimental and commercially available SAs and their performance are surveyed     

Cognitive medium access control protocols for secondary users sharing a common channel with time division multiple access primary users

The unused time slots in a primary time division multiple access (TDMA) network are regarded as the potential channel access opportunities for secondary users (SUs) in cognitive radio (CR). In this paper, we investigate the medium access control protocols that enable SUs to access a common TDMA channel with primary users (PUs). The primary traffic is assumed to follow a Bernoulli random process. A two‐state Markov chain is used to model the secondary traffic, and two different scenarios are considered. The first scenario assumes that the secondary packet arrivals are independent and follow a Bernoulli random process and a cognitive carrier sensing multiple access (Cog‐CSMA) protocol is proposed. A Rayleigh fading channel is considered in evaluating Cog‐CSMA, and its throughput expression is derived in this paper. The second scenario assumes that the packet arrivals follow a correlated packet arrival process and a cognitive packet reservation multiple access (Cog‐PRMA) protocol is proposed. A Markov chain is used to model the different system states in Cog‐PRMA and derive the throughput. Numerical results show that the Cog‐CSMA and Cog‐PRMA protocols achieve the objective of supporting secondary transmissions in a TDMA network without interfering the PUs' transmissions and improve the network bandwidth utilization. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficient and adaptive congestion control for heterogeneous delay-tolerant networks

Detecting and dealing with congestion in delay-tolerant networks (DTNs) is an important and challenging problem. Current DTN forwarding algorithms typically direct traffic towards more central nodes in order to maximise delivery ratios and minimise delays, but as traffic demands increase these nodes may become saturated and unusable. We propose CafRep, an adaptive congestion aware protocol that detects and reacts to congested nodes and congested parts of the network by using implicit hybrid contact and resources congestion heuristics. CafRep exploits localised relative utility based approach to offload the traffic from more to less congested parts of the network, and to replicate at adaptively lower rate in different parts of the network with non-uniform congestion levels. We extensively evaluate our work against benchmark and competitive protocols across a range of metrics over three real connectivity and GPS traces such as Sassy [44], San Francisco Cabs [45] and Infocom 2006 [33]. We show that CafRep performs well, independent of network connectivity and mobility patterns, and consistently outperforms the state-of-the-art DTN forwarding algorithms in the face of increasing rates of congestion. CafRep maintains higher availability and success ratios while keeping low delays, packet loss rates and delivery cost. We test CafRep in the presence of two application scenarios, with fixed rate traffic and with real world Facebook application traffic demands, showing that regardless of the type of traffic CafRep aims to deliver, it reduces congestion and improves forwarding performance.     

Cluster Based Routing Protocol for Mobile Nodes in Wireless Sensor Network

Mobility of sensor nodes in wireless sensor network (WSN) has posed new challenges particularly in packet delivery ratio and energy consumption. Some real applications impose combined environments of fixed and mobile sensor nodes in the same network, while others demand a complete mobile sensors environment. Packet loss that occurs due to mobility of the sensor nodes is one of the main challenges which comes in parallel with energy consumption. In this paper, we use cross layer design between medium access control (MAC) and network layers to overcome these challenges. Thus, a cluster based routing protocol for mobile sensor nodes (CBR-Mobile) is proposed. The CBR-Mobile is mobility and traffic adaptive protocol. The timeslots assigned to the mobile sensor nodes that had moved out of the cluster or have not data to send will be reassigned to incoming sensor nodes within the cluster region. The protocol introduces two simple databases to achieve the mobility and traffic adaptively. The proposed protocol sends data to cluster heads in an efficient manner based on received signal strength. In CBR-Mobile protocol, cluster based routing collaborates with hybrid MAC protocol to support mobility of sensor nodes. Schedule timeslots are used to send the data message while the contention timeslots are used to send join registration messages. The performance of proposed CBR-Mobile protocol is evaluated using MATLAB and was observed that the proposed protocol improves the packet delivery ratio, energy consumption, delay and fairness in mobility environment compared to LEACH-Mobile and AODV protocols.     

ID/Locator Split-Based Distributed Mobility Management Mechanism

We have designed the heterogeneity inclusion and mobility adaptation through locator ID separation (HIMALIS) architecture to support mobility natively in the New Generation Network. This paper proposes a new distributed mobility scheme in the HIMALIS architecture for supporting seamless mobility for the host moving across access networks of different network-layer protocols. The proposed scheme also supports mobility of an access network. It includes a signaling procedure to redirect downstream traffic from the previous gateway (or previous access router) to the new gateway (or new access router) to minimize the service disruption or packet losses during a handover. The performance results obtained from a testbed implementation in Linux validate the effectiveness of the proposal. The results demonstrate that it can achieve seamless (no packet loss) handovers if overlapped wireless access networks are available.     

On transient behaviours of slotted CSMA protocols

CSMA protocols have been extensively studied under the assumption of an equilibrium condition. The results obtained in this manner provided useful insight for the development of packet radio and local area networks for the transmission of bursty data. The integration of isochronous and bursty traffic in the same network may, however, make the equilibrium assumption unrealistic, for example when fixed-length frames are defined, only a portion of which is devoted to the transmission of bursty data according to a CSMA protocol. In such cases, it is necessary to study the protocol behaviours in fixed-length time segments. This paper presents a technique for the analysis of slotted CSMA protocols in such an environment. Definitions for the transient throughput and transient average packet delay are introduced, and closed form expressions are derived for non-persistent and 1-persistent CSMA and CSMA/CD protocols with arbitrary distribution of the packet length. Numerical results help in the visualization of some interesting phenomena, peculiar to the CSMA operations in finite-length intervals.     

Distributed power control algorithm for cognitive radios with primary protection via spectrum sensing under user mobility

Substantial spectrum gains have been demonstrated with the introduction of cognitive radio however; such gains are usually short lived due to the increased level of interference to licensed users of the spectrum. The interference management problem is herein tackled from the transmitter power control perspective so that transmissions by cognitive radio network does not violate the interference threshold levels at the primary users as well as maintain the QoS requirements of cognitive radio users. We model the cognitive radio network for mobile and immobile users and propose algorithms exploiting primary radio environment knowledge (spectrum use), called power control with primary protection via spectrum sensing. The algorithm is briefly introduced for time invariant systems and demonstrated that it has the ability to satisfy tight QoS constraints for cognitive radios as well as meet the interference constraints for licensed users. We, however, further show that such assumption of terminal immobility in the power control algorithm would fail in cases where user mobility is considered, resulting in increased levels of interference to the primary as well as increased outages in cognitive radio network. We model the link gain evolution process as a distance dependent shadow fading process and scale-up the target signal to interference ratio to cope with user mobility. Since mobility driven power control algorithms for cognitive radios have not been investigated before, we therefore, propose a mobility driven power control framework for cognitive radios based on spectrum sensing, which ensures that the interference limit at the primary receiver is unperturbed at all times, while concurrently maintaining the QoS within the cognitive radio network as compared to static user cases. We also corroborate our algorithms with proof of convergence.     

Congestion control for multimedia applications in the wireless internet

This paper provides a parallel review of two important issues for the next‐generation multimedia networking. Firstly, the emerging multimedia applications require a fresh approach to congestion control in the Internet. Currently, congestion control is performed by TCP; it is optimised for data traffic flows, which are inherently elastic. Audio and video traffic do not find the sudden rate fluctuations imposed by the TCP multiplicative‐decrease control algorithm optimal. The second important issue is the mobility support for multimedia applications. Wireless networks are characterized by a substantial packet loss due to the imperfection of the radio medium. This increased packet loss disturbs the foundation of TCP's loss‐based congestion control. This paper contributes to the ongoing discussion about the Internet congestion control by providing a parallel analysis of these two issues. The paper describes the main challenges, design guidelines, and existing proposals for the Internet congestion control, optimised for the multimedia traffic in the wireless network environment. Copyright © 2004 John Wiley & Sons, Ltd.     

End-to-End Adaptive QoS Provisioning over GPRS Wireless Mobile Network

The General Packet Radio Service (GPRS) offers performance guaranteed packet data services to mobile users over wireless frequency-division duplex links with time division multiple access, and core packet data networks. This paper presents a dynamic adaptive guaranteed Quality-of-Service (QoS) provisioning scheme over GPRS wireless mobile links by proposing a guaranteed QoS media access control (GQ-MAC) protocol and an accompanying adaptive prioritized-handoff call admission control (AP-CAC) protocol to maintain GPRS QoS guarantees under the effect of mobile handoffs. The GQ-MAC protocol supports bounded channel access delay for delay-sensitive traffic, bounded packet loss probability for loss-sensitive traffic, and dynamic adaptive resource allocation for bursty traffic with peak bandwidth allocation adapted to the current queue length. The AP-CAC protocol provides dynamic adaptive prioritized admission by differentiating handoff requests with higher admission priorities over new calls via a dynamic multiple guard channels scheme, which dynamically adapts the capacity reserved for dealing with handoff requests based on the current traffic conditions in the neighboring radio cells. Integrated services (IntServ) QoS provisioning over the IP/ATM-based GPRS core network is realized over a multi-protocol label switching (MPLS) architecture, and mobility is supported over the core network via a novel mobile label-switching tree (MLST) architecture. End-to-end QoS provisioning over the GPRS wireless mobile network is realized by mapping between the IntServ and GPRS QoS requirements, and by extending the AP-CAC protocol from the wireless medium to the core network to provide a unified end-to-end admission control with dynamic adaptive admission priorities.     

The n‐ary stack algorithm for the wireless random access channel

The emergence of wireless and personal communication networks has brought random access protocols for packet radio networks back to the research forefronts. Most such protocols are based on the ever popular ALOHA protocol. Unfortunately, this protocol is inherently unstable and requires sophisticated schemes to stabilize it. Another class of random access schemes, called limited sensing or stack algorithms, has been proposed that is stable and allows for the dynamic incorporation of new stations into the network. In this paper, we will review the simple to implement n-ary stack algorithm, and we will study its performance under various system parameters in the presence of capture, and also in the presence of feedback errors. Finally, we will investigate its maximum system throughput under various traffic generation processes. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Simple Model for Computation of Packet Radio Network Communication Performance

A model is presented that allows the computation of the approximate level of communication performance for an arbitrary packet radio network using one of a variety of protocols. The communication performance is specified in terms of the end-to-end message delays incurred for a given level of end-to-end traffic rates. The network is specified in terms of its link capacities. While the model makes a variety of assumptions to allow simple computation of the performance level, agreement within a factor of two is obtained with results from simulation. As the number of nodes in the network and its connectivity is increased, the model is expected to give better accuracy. Thus, the model should prove to be a useful tool in the design and analysis of large packet radio networks where detailed analysis and simulation would prove too cumbersome.     

A design concept for reliable mobile radio networks with frequency hopping signaling

The design of a packet radio network must reflect the operational requirements and environmental constraints to which it is subject. In this paper, we outline those features that distinguish the High Frequency (HF) Intra Task Force (ITF) Network from other packet radio networks, and we present a design concept for this network that encompasses organizational structure, waveform design, and channel access. Network survivability is achieved through the use of distributed network control and frequency hopping spread-spectrum signaling. We demonstrate how the execution of the fully distributed Linked Cluster Algorithm can enable a network to reconfigure itself when it is affected by connectivity changes such as those resulting from jamming. Additional resistance against jamming is provided by frequency hopping, which leads naturally to the use of code division mutiple access (CDMA) techniques that permit the simultaneous successful transmission by several users. Distributed algorithms that exploit CDMA properties have been developed to schedule contention-free transmissions for much of the channel access in this network. Contention-based channel access protocols can also be implemented in conjunction with the Linked Cluster network structure. The design concept presented in this paper provides a high degree of survivability and flexibility, to accommodate changing environmental conditions and user demands.     

Cross-Layer optimal connection admission control for variable bit rate multimedia traffic in packet wireless CDMA networks

Next generation wireless code division multiple access (CDMA) networks are required to support packet multimedia traffic. This paper addresses the connection admission control problem for multiservice packet traffic modeled as Markov modulated Poisson process (MMPP) with the quality of service (QoS) requirements on both physical layer signal-to-interference ratio (SIR) and network layer blocking probability. Optimal linear-programming-based algorithms are presented that take into account of SIR outage probability constraints. By exploiting the MMPP traffic models and introducing a small SIR outage probability, the proposed algorithms can dramatically improve the network utilization. In addition, we propose two reduced complexity algorithms that require less computation and can have satisfactory approximation to the optimal solutions. Numerical examples illustrating the performance of the proposed schemes are presented.