Search

The IEEE 802.11 medium-access control (MAC) protocol is usually considered to be a default standard in multihop wireless networks. However, in a multihop network with a large interference range, the request-to-send/clear-to-send (RTS/CTS) handshake and virtual carrier sensing mechanism may not be able to eliminate interference or solve hidden- and exposed-terminal problems. This paper proposes two new MAC protocols, i.e., the power-fixed dual (PFD) and power-aware dual (PAD) busy-tone schemes, both of which are able to effectively prevent collision of data/acknowledgment (ACK) packets and are applicable in various open-space environments with different path-loss characteristics. Analytical models are developed to evaluate their performance in terms of the blocking area, saturation throughput, and capability of mitigating aggregate interference of simultaneous transmissions. Numerical examples are presented to show the effectiveness of the proposed MAC protocols and the interaction between performance metrics and key parameters. Analysis and simulation results indicate that both PFD and PAD schemes can achieve a much higher throughput and a lower packet-collision ratio than IEEE 802.11 distributed coordination function (DCF), conservative CTS reply (CCR), and dual busy-tone multiple-access (DBTMA) schemes. Index Terms--Ad hoc network, IEEE 802.11, large interference area, medium-access control (MAC), multihop wireless network, power control.

In mobile ad hoc networks (MANETs), many applications require group-oriented computing among a large number of nodes in an adversarial environment. To deploy these large-scale cooperative applications, secure multicast service must be provided to efficiently and safely exchange data among nodes. The existing literature has extensively studied security protection for a single multicast group, in which all nodes are assumed to have the same security level. However, such an assumption may not be valid in practice because, for many applications, different users can play different roles and thus naturally be classified into multiple security levels. In this paper, we propose a pyramidal security model to safeguard the multisecurity-level information sharing in one cooperation domain. As a prominent feature, a pyramidal security model contains a set of hierarchical security groups and multicast groups. To find an efficient key management solution that covers all the involved multicast groups, we develop the following three schemes for the proposed security model: 1) separated star key graph; 2) separated tree key graph, and 3) integrated tree key graph. Performance comparison demonstrates that the scheme of integrated tree key graph has advantages over its counterparts. Index Terms--Group-oriented computing, key management, mobile ad hoc network (MANET), multicast, pyramidal security model.

In this paper, we propose a group-based location service protocol named GrLS for Mobile Ad hoc NETworks (MANETs). The novelty of GrLS is in its exploitation of group mobility to improve the efficiency of the location service. GrLS uses different location management strategies for single nodes and for groups of nodes. A single node is responsible for recruiting its own location servers and performing location update. On the other hand, in a group of nodes, only the group leader recruits the location servers and updates its location to a specific home region called group home region. Since the location update cost normally dominates the location service cost for all practical purposes, the overhead of the location service protocol is significantly reduced. Furthermore, when the nodes join or leave groups, GrLS can provide seamless location service handoff. To the best of our knowledge, GrLS is the first location service protocol in MANETs that has explored group mobility and developed group location management for mobile nodes. Both theoretical analysis and simulation results show that GrLS can achieve a higher success ratio of location query and better load balance with much lower overhead than the existing protocols without considering group mobility. Index Terms--Group location management, group mobility, location service, Mobile Ad hoc NETworks (MANETs).

All currently available code-division multiple-access (CDMA) technologies used in second-generation and third-generation mobile cellular systems are interference limited and can be appropriately called first-generation CDMA, whereas next-generation CDMA should provide a nearly interference-free performance. This paper addresses the issues on spreading code generation that is suitable for next-generation CDMA systems. The real environment adaptation linearization (REAL) approach is proposed to generate perfectly orthogonal complementary (POC) codes characterized by multiple access interference (MAI)-free and multipath interference (MI)-free operation. The REAL approach takes into account almost all major impairing factors in real applications, such as multipath propagation, asynchronous transmission, random data signs, and burst traffic, such that a CDMA system using them can offer an interference-resist operation. Two important conclusions are drawn in this paper: First, implementation of an interference-free CDMA will not be possible unless using complementary codes, such as the POC codes. Second, to enable interference-free CDMA, the flock size of the signature codes should preferably be equal to the set size of the codes. A fast algorithm to generate supercomplementary codes (a subset of POC codes) is also presented, and their ideal orthogonality is explicitly proven. Index Terms--Multipath effect, multiple access interference (MAI), next-generation code-division multiple access (CDMA), perfectly orthogonal complementary (POC) code.

This paper proposes a cooperation strategy among rational nodes in a wireless cooperative relaying network as an effort to solve two basic problems, i.e., when to cooperate and how to cooperate. First, a symmetric system model comprising two users and an access point (AP) is presented. In this model, each user plays an equal role and acts as a source as well as a potential relay and has the right to decide the amount of bandwidth it should contribute for cooperation. Second, referring to the cooperative game theory, the above problems are formulated as a two-person bargaining problem. Then, a cooperation bandwidth allocation strategy based on the Nash bargaining solution is proposed, in which if a derived condition is satisfied, users will cooperatively work, and each will share a certain fraction of its bandwidth for relaying; otherwise, they will independently work. Simulation results demonstrate that when cooperation takes place, users benefit from the proposed strategy in terms of utility, and those with longer distance to the AP should spend more bandwidth to cooperate with others. Index Terms--Cooperative diversity, cooperative relay, game theory, Nash bargaining solution (NBS).