In ad hoc networks, the hidden- and the exposed-terminal problems can severely reduce the network capacity on the MAC layer. To address these problems, the ready-to-send and clear-to-send (RTS/CTS) dialogue has been proposed in the literature. However, MAC schemes using only the RTS/CTS dialogue cannot completely solve the hidden and the exposed terminal problems, as pure "packet sensing" MAC schemes are not safe even in fully connected networks. We propose a new MAC protocol, termed the dual busy tone multiple access (DBTMA) scheme. The operation of the DBTMA protocol is based on the RTS packet and two narrow-bandwidth, out-of-band busy tones. With the use of the RTS packet and the receive busy tone, which is set up by the receiver, our scheme completely solves the hidden- and the exposed-terminal problems. The busy tone, which is set up by the transmitter, provides protection for the RTS packets, increasing the probability of successful RTS reception and, consequently, increasing the throughput. This paper outlines the operation rules of the DBTMA scheme and analyzes its performance. Simulation results are also provided to support the analytical results. It is concluded that the DBTMA protocol is superior to other schemes that rely on the RTS/CTS dialogue on a single channel or to those that rely on a single busy tone. As a point of reference, the DBTMA scheme out-performs FAMA-NCS by 20--40% in our simulations using the network topologies borrowed from the FAMA-NCS paper. In an ad hoc network with a large coverage area, DBTMA achieves performance gain of 140% over FAMA-NCS and performance gain of 20% over RI-BTMA.

This paper presents a new carrier sensing mechanism called DVCS (Directional Virtual Carrier Sensing) for wireless communication using directional antennas. DVCS does not require specific antenna configurations or external devices.

Wireless networks are built upon a shared medium that makes it easy for adversaries to launch jamming-style attacks. These attacks can be easily accomplished by an adversary emitting radio frequency signals that do not follow an underlying MAC protocol. Jamming attacks can severely interfere with the normal operation of wireless networks and, consequently, mechanisms are needed that can cope with jamming attacks. In this paper, we examine radio interference attacks from both sides of the issue: first, we study the problem of conducting radio interference attacks on wireless networks, and second we examine the critical issue of diagnosing the presence of jamming attacks. Specifically, we propose four different jamming attack models that can be used by an adversary to disable the operation of a wireless network, and evaluate their effectiveness in terms of how

In this paper, we propose a CSMA-based medium access control protocol for multihop wireless networks that uses multiple channels and a dynamic channel selection method. The proposed protocol uses one control channel and # data channels, where # is independent of the number of nodes in the network. The source uses an exchange of control packets on the control channel to decide on the best channel to send the data packet on. Channel selection is based on maximizing the signal-to-interference plus noise ratio at the receiver. We present performance evaluations obtained from simulations that demonstrate the effectiveness of the proposed protocol. 1

We describe a new carrier–sense multiple access (CSMA) protocol for multihop wireless networks, using multiple channels and a distributed channel selection scheme. The proposed protocol divides the available bandwidth intoÆchannels where the transmitting station selects an appropriate channel for packet transmission. The selection criterion is based on the interference power measurements on the channels. We show via simulations that this multichannel CSMA protocol provides a higher throughput compared to its single channel counterpart by reducing the packet loss due to collisions. 1

Wireless networks are built upon a shared medium that makes it easy for adversaries to launch denial of service (DoS) attacks. One form of denial of service is targeted at preventing sources from communicating. These attacks can be easily accomplished by an adversary by either bypassing MAC-layer protocols, or emitting a radio signal targeted at jamming a particular channel. In this paper we present two strategies that may be employed by wireless devices to evade a MAC/PHY-layer jamming-style wireless denial of service attack. The first strategy, channel surfing, is a form of spectral evasion that involves legitimate wireless devices changing the channel that they are operating on. The second strategy, spatial retreats, is a form of spatial evasion whereby legitimate mobile devices move away from the locality of the DoS emitter. We study both of these strategies for three broad wireless communication scenarios: two-party radio communication, an infrastructured wireless network, and an ad hoc wireless network. We evaluate several of our proposed strategies and protocols through ns-2 simulations and experiments on the Berkeley mote platform.

Recent research in sensor networks, wireless location systems, and power-saving in ad hoc networks suggests that some applications' wireless traffic be modeled as an event-driven workload: a workload where many nodes send traffic at the time of an event, not all reports of the event are needed by higher-level protocols and applications, and events occur infrequently relative to the time needed to deliver all required event reports. We identify several applications that motivate the event-driven workload, and propose a protocol that is optimal for this workload. Our proposed

In order to realize real-time communication over Ethernet or fast Ethernet, one must be able to bound the medium access time within an acceptable limit. The multiple access nature of an Ethernet makes it impossible to guarantee a deterministic medium access time (hence packet delivery deadlines) to individual stations. However, one can bound the medium access time statistically by limiting the packet arrival rate at the medium access control (MAC) layer. While focusing on automated manufacturing systems as the main application, this paper considers the connection admission control (CAC) problem for statistically bounding the medium access time of Ethernet. Specifically, a packet is guaranteed to have a medium access time smaller than a predefined bound with a certain probability if the instantaneous packet arrival rate is kept below a certain threshold. Through an analysis, we first derived such a threshold. In order to keep the packet arrival rate under the given threshold, we employ a middleware which (i) resides between the transport layer and Ethernet datalink layer and (ii) smooths packet streams between them. The implementation of this middleware requires only a minimal change in the OS kernel without any modification to the current standard of Ethernet MAC protocol or TCP or UDP/IP stack. In order to solve the CAC problem, we derived the probability of transmitting a packet successfully upon each trial by modeling the MAC protocol, 1-persistent CSMA/CD, and the collision resolution protocol, Binary Exponential Backoff, of Ethernet. Using a simulation study, we have shown this analytic model to provide a reasonably accurate estimate of packet-loss (or deadline-miss) rate over Fast Ethernet. Finally, we implemented the middleware on the Linux OS, experimentally dem...

Abstract—Ultra-wideband (UWB) transmission is an emerging wireless communication technology with unique potential merits such as high-rate, low-transmission power, immunity to multipath propagation, and capability in precise positioning. It has received significant interests for future wireless communications from both academia and industry. In UWB wireless networks, medium access control (MAC) is essential to coordinate the channel access among competing devices. The unique UWB characteristics not only pose significant challenges but also offer great opportunities in efficient UWB MAC design. This paper presents a comprehensive overview of UWB MAC development on four important aspects: multiple access, overhead reduction, resource allocation, and quality of service (QoS) provisioning, and identifies some future research issues. Index Terms—Medium access control (MAC), quality of service (QoS), resource allocation, ultra-wideband (UWB) transmission, wireless personal area network (WPAN). I.

Abstract-The channel throughput for a finite number of packet paper, we give an exact throughput analysis in the case of a broadcasting users is analyzed for random access protocols, including finite population for all of the above-listed protocols. Arthurs slotted persistent carrier sense multiple access (CSMA) with and without and Stuck [ 1] also provide an analysis of throughput for slotted collision detection and unslotted persistent CSMA with and without and unslotted persistent CSMA with collision detection based on collision detection. We consider both p- and 1-persistent CSMA. Our models different from ours. (A difference between our model results can be extended to infinite population cases (by taking the proper and theirs involves the way in which one disposes of a packet, limit), where they agree with available. the known throughput expressions when the transmission of which is suppressed as a result of packets sensing a busy channel. In our model, similar to [6], they are dismissed from the system at the beginning of the next trans-I.