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Byline: Lichun Bao (001), J. J. Garcia-Luna-Aceves (001) Keywords: ad hoc networks; directional antenna; channel access scheduling; multi-beam adaptive array (MBAA) Abstract: Directional antennas can adaptively select radio signals of interest in specific directions, while filtering out unwanted interference from other directions. A couple of medium access protocols based on random access schemes have been proposed for networks with directional antennas, using the omnidirectional mode for the transmission or reception of control packets in order to establish directional links. We propose a distributed receiver-oriented multiple access (ROMA) scheduling protocol, capable of utilizing multi-beam forming directional antennas in ad hoc networks. Unlike random access schemes that use on-demand handshakes or signal scanning to resolve communication targets, ROMA computes a link activation schedule in each time slot using two-hop topology information. It is shown that significant improvements on network throughput and delay can be achieved by exploiting the multi-beam forming capability of directional antennas in both transmission and reception. The performance of ROMA is studied by simulation, and compared with a well-know static scheduling scheme that is based on global topology information. Author Affiliation: (001) Computer Engineering Department, School of Engineering, BE 399, University of California, Santa Cruz, CA, 95064, USA Article History: Registration Date: 13/12/2004

Byline: Eun-Sun Jung (001), Nitin H. Vaidya (002) Keywords: power control; energy saving; medium access control; ad hoc network Abstract: This paper presents a power control MAC protocol that allows nodes to vary transmit power level on a per-packet basis. Several researchers have proposed simple modifications of IEEE 802.11 to incorporate power control. The main idea of these power control schemes is to use different power levels for RTS--CTS and DATA--ACK. Specifically, maximum transmit power is used for RTS--CTS, and the minimum required transmit power is used for DATA--ACK transmissions in order to save energy. However, we show that these schemes can degrade network throughput and can result in higher energy consumption than when using IEEE 802.11 without power control. We propose a power control protocol which does not degrade throughput and yields energy saving. Author Affiliation: (001) Department of Computer Science, Texas A&M University, College Station, TX, USA (002) Department of Electrical and Computer Engineering, and Coordinated Science Laboratory, University of Illinois, Urbana, USA Article History: Registration Date: 13/12/2004

Byline: Yuan Xue (1), Klara Nahrstedt (1) Keywords: ad hoc networks; routing protocol; misbehaving node Abstract: Most existing designs of ad hoc networks are based on the assumption of non-adversarial environments, where each node in the network is cooperative and well-behaved. When misbehaving nodes exist in the network, the performance of current routing protocols degrades significantly. Since ad hoc networks, consisting of autonomous nodes, are open and distributed in nature, maintaining a fault-free network environment is extremely difficult and expensive. In this paper, we propose a new routing service named best-effort fault-tolerant routing (BFTR). The design goal of BFTR is to provide packet routing service with high delivery ratio and low overhead in presence of misbehaving nodes. Instead of judging whether a path is good or bad, i.e., whether it contains any misbehaving node, BFTR evaluates the routing feasibility of a path by its end-to-end performance (e.g. packet delivery ratio and delay). By continuously observing the routing performance, BFTR dynamically routes packets via the most feasible path. BFTR provides an efficient and uniform solution for a broad range of node misbehaviors with very few security assumptions. The BFTR algorithm is evaluated through both analysis and extensive simulations. The results show that BFTR greatly improves the ad hoc routing performance in the presence of misbehaving nodes. Author Affiliation: (1) Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, U.S.A. Article History: Registration Date: 29/12/2004

Byline: Tao Wan (1), Asrar U. Sheikh (2) Keywords: multiple access; CSMA/CD; channel throughput; queueing; packet transmission; equilibrium point analysis Abstract: This paper presents a new approximation approach, called tagged user approach (TUA), for the queueing analysis of slotted CSMA/CD systems with a finite user population having either finite or infinite user buffer capacity. By assuming a symmetric channel, the performance analysis of the overall system is determined by the performance of an arbitrarily selected user, called the tagged user. With the further assumption that each user always operates with its equilibrium probability, the packet service time distribution can be obtained using a state flow graph by studying the channel contention scheme. The obtained packet service time distribution is then applied to the queueing analysis of the tagged user using the standard queueing theory. That is, the analysis of the channel contention scheme and the analysis of the user queueing behavior are decoupled in this paper. Hence, TUA can be applied to complicated systems such as those where each user buffer may have bulk packet arrivals and random service discipline as long as the corresponding queueing theory is available. Since a state transition probability matrix is not required in TUA, the required amount of computation is quite small. Simulation results verify the high accuracy of the analysis. Author Affiliation: (1) Nortel Networks, Richardson, TX, U.S.A (2) Department of Electrical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia Article History: Registration Date: 04/10/2004

Byline: Songchar Jiang (1), Wan-de Weng (1) Keywords: CDMA; Markov chains; Integrated Services protocol; throughput; delay Abstract: This paper proposes a performance evaluation approach for integrated voice and data services on a broadband code division multiple access (CDMA) network. For random access schemes, the dynamic behavior of a CDMA channel infers that we must be cautious with a performance judgment. We must be especially careful when choosing a mathematical model that has to include the effect of dynamic error rates. The approach shown in this paper is to employ a Poisson error model that takes the occurrence of errors as a Poisson process with the occurring rate dependent on the channel traffic. Based on this assumption, we developed a continuous-time Markov chain model to evaluate the throughput and delay performance. This approach can certainly apply to the evaluation of many integrated services protocols. Author Affiliation: (1) Department of Electrical Engineering, National Yunlin University of Science and Technology 123, University Road, Section 3, Touliu City, Yunlin, Taiwan, 640, R.O.C. Article History: Registration Date: 14/10/2004

Byline: Jiang-Whai Dai (1) Keywords: capture effect; randomly addressed polling protocol; noiseless Abstract: The capture effect, discussed in this paper, is generally considered to enhance the system's performance in a wireless network. This paper also considers the Randomly Addressed Polling (RAP) protocol in the presence of a fading mobile radio environment. Herein, a deterministic channel, which rules according to inverse [alpha] power propagation law, is established to obtain the probability that one collided packet can capture the channel from distance distribution. Through the probability, we analyze the performance of the RAP protocol by using an embedded Markov chain. According to our results, the performance of the RAP protocol does not obviously change in terms of power control, implying that it can be more aptly applied in power control skill than other protocols. Author Affiliation: (1) Department of Electrical Engineering, National Tsing Hua University, Taiwan, 30043, R.O.C Article History: Registration Date: 14/10/2004