Simulcast packet transmission in ad hoc networks

In previous work, unequal error-protection techniques have been applied to improve the throughput of a wireless communication system in which a transmission is received by several radios with different capabilities. For instance, these capabilities may correspond to differences in path loss, fading, or interference. By taking advantage of the broadcast nature of the channel, additional messages for the more-capable receivers can be included on transmissions to the less-capable receivers at very little cost (in terms of required energy at the transmitter or error probabilities at the receivers). This technique has been termed simulcasting or multicast signaling. In this paper, we consider the use of these techniques in an ad hoc network. These techniques impact the link throughput, end-to-end throughput, and network connectivity. We investigate how the choice of parameters for the simulcasting technique affects these network performance metrics. The results indicate that a properly chosen simulcasting technique can improve the link and end-to-end throughput in wireless ad hoc networks with only a slight degradation in other metrics, such as network connectivity.     

Hierarchical routing overhead in mobile ad hoc networks

Hierarchical techniques have long been known to afford scalability in networks. By summarizing topology detail via a hierarchical map of the network topology, network nodes are able to conserve memory and link resources. Extensive analysis of the memory requirements of hierarchical routing was undertaken in the 1970s. However, there has been little published work that assesses analytically the communication overhead incurred in hierarchical routing. This paper assesses the scalability, with respect to increasing node count, of hierarchical routing in mobile ad hoc networks (MANETs). The performance metric of interest is the number of control packet transmissions per second per node (/spl Phi/). To derive an expression for /spl Phi/, the components of hierarchical routing that incur overhead as a result of hierarchical cluster formation and location management are identified. It is shown here that /spl Phi/ is only polylogarithmic in the node count.     

Authentication and consensus overhead in vehicular ad hoc networks

Vehicular ad hoc networks aim at increasing passenger safety by exchanging warning messages between vehicles wirelessly. A main challenge is to resist to various malicious abuses and security attacks. However, any security mechanism comes with overhead. We analyze how the authentication algorithm ECDSA and the consensus mechanism impact the vehicular network performance and the braking distance. Processing and communication overheads, decision methods for consensus, are analyzed by analytical models and intensive simulations. We propose a formula to assess the total time overhead of the authentication. Results conclude that the authentication key size should be chosen carefully, and the decision method should be adapted to the context.     

低开销的MANET网络按需路由协议

针对简单泛洪效率低的问题,提出了一个限制洪泛的高效的路由广播算法,通过Euclidean距离来限制路由发现过程中请求分组被转发的次数;研究了减少路由维护开销,并降低路由发现的频率的方法,提出了一个基于节点高度的路由修复与优化算法,该算法使用节点监听来对链路断裂的路由进行修复与优化.基于限制泛洪的高效的路由广播算法和路由修复优化算法,提出了一种新的低开销的MANET网络按需路由协议LOOR(low overhead on-demand routing).仿真结果表明,新协议增强了路由的顽健性,减少了路由跳数,降低了路由发现的频率,提高了数据分组递送率,并显著地降低了路由控制开销.     

Nash equilibria of packet forwarding strategies in wireless ad hoc networks

In self-organizing ad hoc networks, all the networking functions rely on the contribution of the participants. As a basic example, nodes have to forward packets for each other in order to enable multihop communication. In recent years, incentive mechanisms have been proposed to give nodes incentive to cooperate, especially in packet forwarding. However, the need for these mechanisms was not formally justified. In this paper, we address the problem of whether cooperation can exist without incentive mechanisms. We propose a model,based on game theory and graph theory to investigate equilibrium conditions of packet forwarding strategies. We prove theorems about the equilibrium conditions for both cooperative and noncooperative strategies. We perform simulations to estimate the probability that the conditions for a cooperative equilibrium hold in randomly generated network scenarios.. As the problem is involved, we deliberately restrict ourselves to a static configuration. We conclude that in static ad hoc networks where the relationships between the nodes are likely to be stab le-cooperation needs to be encouraged.     

On the scalability of ad hoc networks

We investigate the inherent scalability problem of ad hoc networks originated from the nature of multihop networks. First, the expected packet traffic at the center of a network is analyzed. The result shows that the expected packet traffic at the center of a network is linearly related with the network size, that is, the expected packet traffic at the center of a network is O(k), where k is the radius of a network. From the result, the upper bound of the diameter of a network D=2k, that guarantees the network is scalable, is obtained. The upper bound is given by C/r-1, where C is the channel capacity available to each node and r is the packet arrival rate at each node.     

Adaptive modulation in ad hoc DS/CDMA packet radio networks

This paper investigates the benefit of adaptive modulation based on channel state information (CSI) in direct-sequence/ code-division multiple-access (DS/CDMA) multihop packet radio networks. By exploiting varying channel conditions, adaptive modulation can be used in ad hoc networks to provide upper layers with higher capacity links over which to relay traffic. Using the /spl alpha/-stable interference model, the distribution of the signal-to-interference ratio (SIR) is obtained for a slotted system of randomly, uniformly distributed nodes using multilevel coherent modulation schemes. Performance is evaluated in terms of the information efficiency, which is a new progress-related measure for multihop networks. Three types of adaptivity are analyzed, differing in the level of CSI available: 1) full knowledge of the SIR at the receiver; 2) knowledge of only the signal attenuation due to fading; and 3) knowledge of only the slow fading component of the signal attenuation. The effect of imperfect channel information is also investigated. Sample results are given for interference-limited networks experiencing fourth-power path loss with distance, Ricean fading, and lognormal shadowing.     

On the connectivity in finite ad hoc networks

Connectivity and capacity analysis of ad hoc networks has usually focused on asymptotic results in the number of nodes in the network. In this letter we analyze finite ad hoc networks. With the standard assumption of uniform distribution of nodes in [0, z], z > 0, for a one-dimensional network, we obtain the exact formula for the probability that the network is connected. We then extend this result to find bounds for the connectivity in a two-dimensional network in [0, z]²     

移动自组网中新的智能丢包区分机制

为了有效区分移动自组网中由于网络拥塞、路由切换和链路错误引起的丢包,通过模糊计算的综合评判模型,在发送端综合端到端往返延时、短期的吞吐量以及乱序数据包3个网络观测参数进行判断。仿真结果表明智能丢包区分算法对丢包原因的判断取得了较好的效果。基于该智能丢包区分算法的TCP改进方案TCP-Fuzzy,能够根据判断出的丢包原因采取恰当的拥塞控制策略,在各种不同的网络环境下都有较好的性能表现。     

Quality of service for packet telephony over mobile ad hoc networks

IP telephony over mobile ad hoc networks is a topic of emerging interest in the research arena as one of the paths toward the fixed-mobile convergence in telecommunications networks. To investigate the performance characteristics of this service, we propose a complete system architecture, which includes a MAC protocol, a routing protocol, and the treatment of voice packets. The telephone system is analyzed in the case of point-to-point calls inside the ad hoc network, and the end-to-end performance is assessed in terms of the percentage of blocked and dropped calls, packet loss and packet delay. The analysis takes into account network scalability by investigating how; the size of the multihop ad hoc network impacts the quality of service. Moreover, the synthetic mean opinion score of the telephone service is evaluated according to the ITU-T E-model.     

Self-organizing packet radio ad hoc networks with overlay (SOPRANO)

The SOPRANO project involves a novel adaptive and scalable wireless network architecture utilizing a mixture of cellular and multihop packet radio system topologies with the potential to support a variety of applications including high-data rate Internet and multimedia traffic at a reasonable degree of implementation complexity. This article discusses the potential benefits of this structure and addresses several relevant issues necessary to support such a network. More specifically, it focuses on connection establishment and self-organization, investigates the formulation of an optimum transmission strategy, and examines some of the techniques by which we can augment the capacity or enhance the system performance in this multihop network. We also present capacity bounds that illustrate how these techniques help in trading off conserved power for a multifold capacity advantage     

HEAP: A packet authentication scheme for mobile ad hoc networks

In mobile ad hoc networks (MANETs) and wireless sensor networks (WSNs), it is easy to launch various sophisticated attacks such as wormhole, man-in-the-middle and denial of service (DoS), or to impersonate another node. To combat such attacks from outsider nodes, we study packet authentication in wireless networks and propose a hop-by-hop, efficient authentication protocol, called HEAP. HEAP authenticates packets at every hop by using a modified HMAC-based algorithm along with two keys and drops any packets that originate from outsiders. HEAP can be used with multicast, unicast or broadcast applications. We ran several simulations to compare HEAP with existing authentication schemes, such as TESLA, LHAP and Lu and Pooch’s algorithm. We measured metrics such as latency, throughput, packet delivery ratio, CPU and memory utilization and show that HEAP performs very well compared to other schemes while guarding against outsider attacks.     

Multiple packet reception in wireless ad hoc networks using polynomial phase-modulating sequences

This paper proposes a blind interference cancellation algorithm that is able to provide multiple packet reception capability for asynchronous random access wireless mobile ad hoc networks. The algorithm exploits the fact that the baseband signal exhibits cyclostationarity properties, which are induced at the transmitters by means of modulating the symbols with polynomial phase sequences. This modulation does not expand the bandwidth and can be considered as a "color code" that can be used to distinguish one transmission from the others (i.e., packets from other users). The proposed technique does not require knowledge of the starting time of transmission of the desired signal and can also be applied to time-dispersive multipath channels. In addition, a practical way of assigning the color codes via the use of a common codebook known to all nodes is proposed, and the impact on local throughput of such a scheme is analyzed. Simulation results illustrate the excellent performance of the proposed approach.     

Synchronization and packet separation in wireless ad hoc networks by known modulus algorithms

In mobile asynchronous ad hoc networks, multiple users may transmit packets at the same time. If a collision occurs, then in current systems both packets are lost and need to be retransmitted, reducing the overall throughput. To mitigate this, we consider to extend the receiver with a small antenna array, so that it can suppress interfering signals. To characterize the signal of interest, we propose to modulate it at the symbol rate by a known amplitude variation. This allows the corresponding multichannel receiver to estimate the beamformer weights that will suppress the interfering sources. We introduce "known modulus algorithms" to achieve this. We also derive synchronization algorithms to estimate the offset of the desired packet in an observation window, among interfering data packets. The algorithms are illustrated via simulations.     

Securing ad hoc networks

Ad hoc networks are a new wireless networking paradigm for mobile hosts. Unlike traditional mobile wireless networks, ad hoc networks do not rely on any fixed infrastructure. Instead, hosts rely on each other to keep the network connected. Military tactical and other security-sensitive operations are still the main applications of ad hoc networks, although there is a trend to adopt ad hoc networks for commercial uses due to their unique properties. One main challenge in the design of these networks is their vulnerability to security attacks. In this article, we study the threats on ad hoc network faces and the security goals to be achieved. We identify the new challenges and opportunities posed by this new networking environment and explore new approaches to secure its communication. In particular, we take advantage of the inherent redundancy in ad hoc networks-multiple routes between nodes-to defend routing against denial-of-service attacks. We also use replication and new cryptographic schemes, such as threshold cryptography, to build a highly secure and highly available key management service, which terms the core of our security framework     

On reducing broadcast redundancy in ad hoc wireless networks

Unlike in a wired network, a packet transmitted by a node in an ad hoc wireless network can reach all neighbors. Therefore, the total number of transmissions (forward nodes) is generally used as the cost criterion for broadcasting. The problem of finding the minimum number of forward nodes is NP-complete. Among various approximation approaches, dominant pruning (Lim and Kim 2001) utilizes 2-hop neighborhood information to reduce redundant transmissions. In this paper, we analyze some deficiencies of the dominant pruning algorithm and propose two better approximation algorithms: total dominant pruning and partial dominant pruning. Both algorithms utilize 2-hop neighborhood information more effectively to reduce redundant transmissions. Simulation results of applying these two algorithms show performance improvements compared with the original dominant pruning. In addition, two termination criteria are discussed and compared through simulation under both the static and dynamic environments.     

An improvement of AODV protocol for the overhead reduction in scalable dynamic wireless ad hoc networks

Wireless Networks - In this paper, the problem of improving reliability and reducing routing overhead in dynamic scalable Wireless Ad hoc NETworks (WANETs) is considered. Having in mind that the...     

On route lifetime in multihop mobile ad hoc networks

One wireless network architecture that has received a lot of attention recently is the mobile ad hoc network (MANET). It is attractive because the network can be quickly deployed without the infrastructure of base stations. One main feature of MANET is that mobile hosts may communicate with each other through a sequence of wireless links (i.e., in a multihop manner). While many routing protocols have been proposed for MANET by considering criteria such as length, quality, bandwidth, and signal strength [S. Agarwal et al., 2000], [D.B. Johnson et al., 2000], [R. Dube et al., Feb. 1997], [Z. Haas and M. Pearlman, 2000], [M. Jiang et al., 1998], [C. Perkins and P. Bhagwat, Sept. 1994], the issue of route lifetime has not been addressed formally. This paper presents a formal model to predict the lifetime of a routing path based on the random walk model. Route lifetime is derived based on a probabilistic model. Through such investigation, we hope to provide further insight into issues such as route selection, route maintenance, and network scalability related to MANETs.     

Security in vehicular ad hoc networks [security in mobile ad hoc]

Vehicular communication networking is a promising approach to facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. One of the ultimate goals in the design of such networking is to resist various malicious abuses and security attacks. In this article we first review the current standardization process, which covers the methods of providing security services and preserving driver privacy for wireless access in vehicular environments (WAVE) applications. We then address two fundamental issues, certificate revocation and conditional privacy preservation, for making the standards practical. In addition, a suite of novel security mechanisms are introduced for achieving secure certificate revocation and conditional privacy preservation, which are considered among the most challenging design objectives in vehicular ad hoc networks.