Personal digital assistants (PDAs) are becoming commonplace, and feature continually increasing processing and storage capabilities. Distribution of media through wireless means to these devices is becoming less expensive, but is not yet widespread. The authors describe a novel communication infrastructure to provide distribution of information to PDAs utilizing inexpensive methods; our approach is both scalable and flexible. Most PDAs support infrared (IR) communication, and we focus on this; our infrastructure is not restricted to this, however, and is adaptable to the emerging wireless communication technologies.

This paper presents a solution to the problem of providing quality-of-service (QoS) guarantees in an ATM network with wireless links. The suggested resolution to this problem is through selectable-rate channel coding. In particular, rate-compatible punctured convolutional (RCPC) codes are employed due to their several attractive features that make them favorable for ATM-based applications. In this adaptive scheme, the RCPC code rate is intelligently varied in response to the channel's nonstationary behavior according to the channel state information (CSI). This yields an equivalent stationary channel with a fixed and predetermined bit-error rate (BER) in which QoS can be guaranteed. In order to demonstrate the performance of RCPC codes in providing and maintaining the QoS, a lognormal fading channel model is assumed. An architecture is proposed for the wireless link. This system assumes that accurate CSI is available at the transmitter as well as at the receiver. Bandwidth utilization of the proposed system under various channel conditions is then evaluated, plotted, and discussed.

A method for frame synchronization in a photonic network of time multiplexed space switches is presented. The method, which is based on a feedback scheme, is first introduced for frame synchronization in a single-switch configuration. The feedback scheme is then extended to both hierarchical (tree topology) and nonhierarchical (general topology) multiswitch configurations. Using this feedback scheme has the advantage of providing a mechanism for frame synchronization to be achieved initially, without the need for accurate transmission time measurements, and allowing synchronization to be maintained within very tight bounds. The methods presented require additional electronics at the switches, but electronics only for control purposes, not in the path of the information bits. However, optical delay elements are needed in the path of information bits on some links of the network. The proposed schemes also reduce the amount of synchronization equipment needed, compared to other methods.>

The effects of unbalanced traffic on the performance of the multihop network are discussed. The basic question addressed is how performance might degrade as network size increases. Because unbalanced loads can occur in a multitude of ways, two separate approaches were taken to characterize the effects of imbalance. Present results show that the allowable throughput per user for realistic load patterns is reduced by a factor between about 0.3-0.5 from that predicted for uniform load. Contrary to original fears, this deloading factor is not very sensitive to network size. Although emphasis is on the performance of the multichannel multihop network, the methods presented are applicable to other communication networks which incorporate some type of hopping.>

Communication over a random multiple-access, time-slotted, packet-switched, collision-type, broadcast channel with feedback is considered under a Poisson infinite-user model. The feedback generated by the channel provides some information about the intensity of conflicts. Two conflict-resolution algorithms are discussed for the above channel; they achieve throughputs of 0.334 and 0.369, respectively. The modification technique used to arrive at the second algorithm is emphasized. It is pointed out that the modification technique could be helpful in improving the performance of the conflict-resolution algorithms operating under other types of feedback.>

We study the application of group testing to the design of efficient algorithms for random multiple-access communication systems. Both direct transmission and reservation systems are considered for various types of channel feedback. We propose and analyze algorithms based on conventional and generalized group testing techniques. The proposed algorithms outperform TDMA and algorithms based on binary tree search and possess certain optimality properties.

Communication over a random multiple-access, collision-type, time-slotted, packet-switched channel with binary feedback is considered for a Poisson infinite-user model. Three different types of binary feedback are introduced and confusion resolution algorithms (CRA) are discussed for each. The CRA proposed for the feedback that tells only whether or not there was a collision in the previous slot achieves a throughput of0.442. The CRA proposed for the feedback that tells whether or not the previous slot was empty achieves a throughput of0.279.