Bluetooth, a wireless technology based on a frequency-hopping physical layer, enables portable devices to form short-range wireless ad hoc networks. Bluetooth hosts are not able to communicate unless they have previously discovered each other through synchronization of their timing and frequency-hopping patterns. Thus, even if all nodes are within proximity of each other, only those nodes which are synchronized with the transmitter can hear the transmission. To support any-to-any communication, nodes must be synchronized so that the pairs of nodes, which can communicate with each other, form a connected graph. Using Bluetooth as an example, we first provide deeper insights into the issue of link establishment in frequency-hopping wireless systems. We then introduce an asynchronous distributed protocol that begins with nodes having no knowledge of their surroundings and terminates with the formation of a connected network topology satisfying all constraints posed by Bluetooth. An attractive protocol feature is its ease in implementation using the communication primitives offered by the Bluetooth Specification.

Wireless ad hoc networks have been a growing area of research. While there has been considerable research on the topic of routing in such networks, the topic of topology creation has not received due attention. This is because almost all ad hoc networks to date have been built on top of a single channel, broadcast based wireless media, such as 802.11 or IR LANs. For such networks the distance relationship between the nodes implicitly (and uniquely) determines the topology of the ad hoc network. Bluetooth is a promising new wireless technology, which enables portable devices to form short-range wireless ad hoc networks and is based on a frequency hopping physical layer. This fact implies that hosts are not able to communicate unless they have previously discovered each other by synchronizing their frequency hopping patterns. Thus, even if all nodes are within direct communication range of each other, only those nodes which are synchronized with the transmitter can hear the transmission. To support any-to-any communication, nodes must be synchronized so that the pairs of nodes (which can communicate with each other) together form a connected graph. Using Bluetooth as an example, this paper first provides deeper insights into the issue to link establishment in frequency hopping wireless systems. It then introduces the Bluetooth topology construction protocol (BTCP), an asynchronous distributed protocol for constructing scatternets which starts with nodes that have no knowledge of their surroundings and terminates with the formation of a connected network satisfying all connectivity constraints posed by the Bluetooth technology. To the best of our knowledge, the work presented in this paper is the first attempt at building Bluetooth scatternets using distributed logic and is quite "practical" in the sense that it can be implemented using the communication primitives offered by the Bluetooth 1.0 specifications.

To enhance the throughput of a slotted ALOHA control channel in a radio communication system, we present and analyze a method for estimating the number of remote stations that are attempting to transmit to a central base station. Each of the contending remote stations randomly chooses to transmit with probability p. Our novel contribution is the use of information concerning the number of successful packet transmissions that arrive without retransmission (i.e., that are successfully received on their first transmission attempt), as a metric for accurately and robustly estimating the number of contending remote stations. This estimate is determined at the base station and then used to compute the optimal transmission probability p that is used as feedback to the remote stations for their use. The proposed estimation method is analyzed and shown to provide good steady-state performance. While we analyze a slotted ALOHA type of access protocol here, these results can be applied to more complex reservation multiple access protocols in which the slotted ALOHA protocol is used for the reservation channel.

The probability of capture under a model (for a land mobile radio direct sequence spread spectrum system) based on the ratio of the largest received power to the sum of interference powers is examined in the limit of a large number of transmitting stations. It is shown in great generality that the limit depends only on the capture ratio threshold and the roll-off exponent of the distribution of power received from a typical station. This exponent is insensitive to many typical channel effects such as Rician or Rayleigh fading and log-normal shadowing. The model is suitable for large systems with noncoherently combined interference.

With the growth of wireless personal communications networks and wireless local area networks (WLAN's), the need for increased reliability of the radio link has become evident. The use of diversity techniques, such as dual receiving antennas, helps mitigate the effect of multipath fading in both the in-building and land mobile radio environments. A significant issue in the design of such systems is the degree to which correlation between the two or more diversity signals can be tolerated. In this paper, we consider the use of diversity techniques in radio systems that are subject to correlation. Rayleigh fading, lognormal shadowing, and the radio capture effect. In the presence of two simultaneously transmitting stations, the throughput, conditioned on the local-mean power, is determined exactly for the case of a dual diversity receiving station. The insight gained from the two-station analysis is used to develop an accurate approximation for cases with more than two stations. The degree to which correlation can be tolerated without significant performance loss relative to the case of independent diversity signals is quantified, as are the effects of different system parameters (i.e., the capture ratio, power roll-off coefficient, and the amount of shadowing). Furthermore, the relationship between the envelope and power correlation coefficients is presented. An application of the capture results to the slotted ALOHA protocol is also included.

We analyze an efficient medium access control (MAC) protocol for use in a single cell of a wireless local area network (LAN). A fixed frame structure with two periods is used; one period for making reservations using a slotted Aloha protocol and a second period for data transmission. The MAC protocol operates in a centralized manner in which a single station, the base station, accepts reservations (transmission or data requests) that are made by the remote stations, and then schedules the times in which they will transmit or receive data. We consider two different types of client-server traffic models, an open-loop and a closed-loop model. In the open-loop model, a remote station can generate reservation requests for the base station whether or not it has received a response from the base station. In the closed-loop case, the remote station waits for a response before generating a new request. The performance of the MAC protocol was analyzed exactly for both the open and closed-loop traffic models and for cases in which transmission errors and a mean-value type of radio capture model are included. In addition, different policies were considered for the transmission strategy that is used by the remote stations when they attempt to make reservations. We derive exact results for the mean throughput and waiting times as well as for the queue length distributions. We also derive an approximate Markov chain to treat a case in which a fixed-position capture model is used. Several types of behavior are illustrated through the use of numerical examples.>

Presents a new scheduler, the two-dimensional round-robin (2DRR) scheduler, that provides high throughput and fair access in a packet switch that uses multiple input queues. We consider an architecture in which each input port maintains a separate queue for each output. In an N/spl times/N switch, our scheduler determines which of the queues in the total of N/sup 2/ input queues are served during each time slot. We demonstrate the fairness properties of the 2DRR scheduler and compare its performance with that of the input and output queueing configurations, showing that our scheme achieves the same saturation throughput as output queueing. The 2DRR scheduler can be implemented using simple logic components, thereby allowing a very high-speed implementation.>

An efficient medium access control (MAC) protocol for use in a single cell of a wireless local area network (LAN) is analyzed. A fixed frame structure with two periods is used, one period for making reservations using a slotted Aloha protocol and a second period for data transmission. The MAC protocol operates in a centralized manner in which a single station, the base station, accepts reservations (transmission or data requests) that are made by the remote stations, and then schedules the times in which they will transmit or receive data. Two different types of client-server traffic models, open loop and closed loop, are considered. Exact results are derived for the mean throughput and waiting times as well as for the queue length distributions. Several types of behavior are illustrated by numerical examples.>

The author defines and analyzes an M/G/1 vacation model that can be used to describe a single station in the fiber distributed data interface (FDDI). The M/G/1 model uses a service discipline called the exhaustive limited with limit variation discipline. According to this discipline, the server provides service until either the system is emptied or a randomly chosen limit of l frames has been served. The server then goes on a vacation before returning to service the queue again. The model can be used to gain insight into how the varying (timer-controlled) limit on the number of frames that can be transmitted during token visit at a station affects the mean waiting time in the timed-token protocol of FDDI. The analytical results of the M/G/1 vacation model are applied to an FDDI simulation example.>

This correspondence examines integrated-circuit logarithmic arithmetic units which include adders, subtracters, multipliers, and dividers. The design of these arithmetic units is reviewed, and an example arithmetic unit which performs multiplication followed by addition is designed in detail. The design results are used to develop a size and speed comparison of integrated-circuit logarithmic and fixed-point arithmetic units. This comparison is exercised through a video signal processing example. It is concluded from this comparison that logarithmic arithmetic units are smaller than, and as fast as, fixed-point arithmetic units with comparable capabilities in digital signal processing applications characterized by large dynamic range and moderate computational accuracy requirements. Further, this comparison quantitatively illustrates the interaction of digital-signal-processing and integrated-circuit issues in the design of special-purpose digital signal processors.