The data link control (DLC) scheme is essentially needed in the protocol stack of wireless ATM systems in order to overcome the incompatibility between the ATM design assumptions and the characteristics of the physical radio channel. In this paper, the DLC scheme developed for the ACTS project Magic WAND (wireless ATM network demonstrator) is evaluated by taking into account a finite state radio channel model which allows to describe the radio transmission quality by a stochastic process. Due to the fact that the transmission quality for two subsequent time slots becomes correlated, this channel model is especially suited to evaluate the performance of error control and retransmission schemes. In particular, we compared the transmission scheme without error control to a scheme with a limited ARQ (automatic repeat request) mechanism by evaluating the cell loss ratio. When considering network services with different maximum delay requirements, these results allow to determine for which services ARQ schemes are beneficial.

A stochastic radio channel model (SRCM) for broadband indoor mobile systems operating at 5.2 and 17 GHz has been derived within the ACTS project AC085 Magic WAND. The SRCM accurately describes the dispersive nature of real radio channels in time, frequency, direction, and polarization. These effects are important for the design and performance evaluation of advanced receiver structures that exploit the inherent channel diversity, e.g., by means of adaptive antennas. The wideband SRCM takes into account all relevant propagation effects observed in real indoor environments. For example, it includes large-scale fluctuations such as transitions where waves are emerging and vanishing as well as the delay drift of the waves. In the paper, the modeling approach adopted for the SRCM is described and illustrated by simulation results.

A systematic approximation for the mean time to lose lock (MTLL) of a coherent third-order PN-code tracking loop has been derived. Such loops are essential in various spread spectrum systems (Global Positioning System, for example). The computation of the MTLL is based on the singular perturbation method. The application of this method to the coherent delay-locked loop (DLL) yields an approximate expression for the MTLL. Therefore, with the proposed loop model the authors are able to analyze this third-order system at a level that gives a well understanding of the nonlinear loop behavior and the exit phenomenon. The influence of a loop offset due to an acceleration rate (jerk) between transmitter and receiver on the optimal filter parameters is described by comparing MTLL and tracking error performance. As intuitively might be expected it turns out that acceleration rate and code rate are exchangeable in the sense that a lower code rate allows a higher acceleration rate (and vice versa) for the same signal-to-noise ratio in order to maintain the same performance. In a case study, GPS code tracking for objects with high jerk is briefly discussed.>

For the first time an approximation for the mean time to lose lock (MTLL) of a third-order coherent PN-code tracking loop has been derived. Such loops are essential in various spread spectrum systems (Global Positioning System, GPS, for example). The computation of the MTLL is based on the singular perturbation method. The application of this calculus to the coherent delay-locked loop (DLL) yields an algebraic expression for the dominant term of the MTLL. The influence of loop offset due to an acceleration rate (jerk) between the transmitter and receiver as well as the optimal choice of the parameters maximizing the MTLL for the loop filter is described. A case study for code tracking of objects with high jerk guided by the GPS is briefly discussed.>