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Worldwide interoperability for microwave access (WiMAX) is a promising technology for last-mile Internet access, particularly in the areas where wired infrastructures are not available. In a WiMAX network, call admission control (CAC) is deployed to effectively control different traffic loads and prevent the network from being overloaded. In this paper, we propose a framework of a 2-D CAC to accommodate various features of WiMAX networks. Specifically, we decompose the 2-D uplink and downlink WiMAX CAC problem into two independent 1-D CAC problems and formulate the 1-D CAC optimization, in which the demands of service providers and subscribers are jointly taken into account. To solve the optimization problem, we develop a utility- and fairness-constrained optimal revenue policy, as well as its corresponding approximation algorithm. Simulation results are presented to demonstrate the effectiveness of the proposed WiMAX CAC approach. Index Terms--Call admission control (CAC), optimization, orthogonal frequency-division multiple access (OFDMA), time-division duplex (TDD), worldwide interoperability for microwave access (WiMAX).

Due to the collaborative nature of sensor nodes, time synchronization is critical for many sensor network operations. For sensor networks deployed in hostile environments, security is critical to the success of time synchronization. Over the past few years, a number of secure time-synchronization schemes have been proposed for sensor networks. However, these schemes are designed for homogeneous sensor networks and may incur large communication/computation overhead or may cause accumulated synchronization errors (due to multihop relays of time reference messages). Several works have shown that better performance and security can be achieved in heterogeneous sensor networks (HSNs). In this paper, we presenta secure and efficient time synchronization scheme for HSNs by utilizing powerful high-end sensors. We implement the time-synchronization scheme in real sensor nodes, and the experiments show that our scheme achieves higher synchronization accuracy than a popular sensor time-synchronization scheme. The analyses demonstrate that our scheme is resilient to various attacks and significantly reduces communication overhead. Index Terms--Heterogeneous sensor networks (HSNs), security, time synchronization.

Wireless-communication technology can be used to improve road safety and to provide Internet access inside vehicles. This paper proposes a cross-layer protocol called coordinated external peer communication (CEPEC) for Internet-access services and peer communications for vehicular networks. We assume that IEEE 802.16 base stations (BS) are installed along highways and that the same air interface is equipped in vehicles. Certain vehicles locating outside of the limited coverage of their nearest BSs can still get access to the Internet via a multihop route to their BSs. For Internet-access services, the objective of CEPEC is to increase the end-to-end throughput while providing a fairness guarantee in bandwidth usage among road segments. To achieve this goal, the road is logically partitioned into segments of equal length. A relaying head is selected in each segment that performs both local-packet collecting and aggregated packets relaying. The simulation results have shown that the proposed CEPEC protocol provides higher throughput with guaranteed fairness in multihop data delivery in vehicular networks when compared with the purely IEEE 802.16-based protocol. Index Terms--External peer communication (EPC), IEEE 802.16, multihop, scheduling algorithm, vehicle-to-roadside communication (VRC), vehicular networks.

This paper presents a multicarrier code-division multiple-access (CDMA) system architecture that is based on complete complementary orthogonal spreading codes. The architecture has several advantages as compared to conventional CDMA systems. Specifically, it offers multiple-access interference-free operation in additive white Gaussian noise channels, reduces cochannel interference significantly, and has the potential of higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an 'offset stacked' spreading modulation technique. To maintain good performance in the presence of fading, the offset stacked modulator is followed by a quadrature-amplitude modulation map, which is designed to optimize performance in a fading environment. This new modulation scheme also simplifies the rate-matching algorithms that are relevant for multimedia services and Internet Protocol-based applications. Index Terms--Complete complementary orthogonal (CCO) codes, fading channels, multicarrier code-division multiple access (MC-CDMA), quadrature-amplitude modulation (QAM).

In mobile ad hoc wireless LANs, it is very difficult to maintain a targeted network utilization due to the time-varying nature of the contention-based medium access control protocol and the lack of a central control. Furthermore, previous research has been mainly focusing on the aspect of optimizing the performance at each station. But doing so may result in a very low overall network utilization. Therefore, self-regulating network utilization is very important to provide quality-of-service (QoS) in mobile ad hoc wireless networks. Through self-disciplining its own behaviors locally, each station will optimize its protocol parameters to meet the targeted overall network utilization, which is very important for QoS provisioning to multimedia services. This paper proposes and evaluates a fully distributed scheme for each station to self-regulate its behaviors through adapting the local protocol parameters to meet the targeted overall network utilization with the changes in the network environment such as the number of stations and channel quality. Index Terms--Mobile wireless ad hoc network, network utilization, self-regulation.

A complete complementary code based direct sequence code division multiple access (CC/DS-CDMA) system has been proposed recently as a potential candidate for beyond third generation (B3G) wireless communications. This paper addresses the issues that design of efficient code assignment schemes should be based on a flexible physical layer support, which is extremely important for emerging cross-layer designs in future wireless applications. The study in this paper considers a CC/DS-CDMA system with multiple time slots, three traffic classes and two dynamic code-flock assignment schemes, namely random assignment (RA) and compact assignment (CA). Simulation results show that the CC/DS-CDMA system has variable capacity property (VCP), which is sensitively affected by different code-flock assignment schemes. In general, CA can offer lower blocking probability, whereas RA can offer a larger mean system capacity and higher throughput when offered traffic is heavy. Index Terms--Code division multiple access (CDMA), complete complementary codes, resource allocation.

This paper proposes an analytical method to study multipacket capture effects in a code-division multiple-access (CDMA) communication system considering both signal-to-interference ratio (SIR) levels and packet arrival delay offsets. Single-and double-packet capture probabilities are derived explicitly based on CDMA cochannel interference threshold, which can be generalized to study n-packet capture effect in a CDMA packet data network. Performance of a common coded spread-spectrum (SS) packet network is taken as an example to exemplify the validity of derived analytical model for studying double-packet power-delay capture. It is concluded from the analytical results of this paper that the n-packet-capture capability can significantly enhance performance of an SS packet data network, which is usually underestimated in the literature otherwise. Index Terms--Capture-effect, code division multiple access (CDMA), spread spectrum (SS), wireless packet network.

In this paper, joint power-delay double-capture probabilities of a spread-spectrum packet network are derived. What we mean in terms of 'double-capture' is that a receiver can simultaneously capture the first two incoming packets (from different transmitters) encoded by the same spreading code. The power capture model concerned takes into account multiuser interference, multipath Rayleigh fading, shadowing, and propagation path loss. To derive delay capture probability with an arbitrary arrival delay, a discrete-time approximation is applied. The method of deriving double-capture probability can also be extended to calculating multiple-packet (more than two) capture probabilities. Performance of a common-code slotted ALOHA system is evaluated with the double-capture effect and the results are compared with those of a traditional ALOHA system. It is shown that the channel impairing factors can be greatly mitigated by exploiting joint power-delay double-capture effect. Index Terms--Code division multiple access (CDMA), joint delay-power capture effect, wireless packet network.