In a wireless LAN, due to a radio wave condition and/or coexistence of several specifications, there exist some terminals of various transmission rates. Under the standard IEEE 802.11b/g protocol, all the terminals can achieve the same throughput since they equally obtain the channel access opportunities. In such a case, high-speed terminals cannot show their transmission abilities. To solve that problem, this paper proposes a channel access method which provides the access privileges to the high-speed terminals. Under an employment of the proposed method, the access point rejects the RTS frames origined from the low-speed terminals in a certain condition. Via simulation, the proposed method achieves appropriate throughput to each terminal. Furthermore, as compared with the standard and previously proposed methods, our method provides smaller file transfer delay for low-speed terminals.
Various methods for improving the robustness of adaptive backstepping control systems have been proposed. One of such methods uses an adaptive law with the parameter projection algorithm which realizes a projection action by changing the integral kernel of the adaptive law to another function. It is known that a stable adaptive backstepping control system is achieved based on the overparameterization scheme or high gain non-linear damping scheme when the change type projection algorithm is used for parameter projection. However, in the former scheme, the adaptive controller may be complex for a high order and high relative degree plant. A peculiar problem to high gain feedback such as actuator saturation and difficulty of numeric realization may be caused in the latter scheme. This paper shows that the change type projection algorithm cannot be applied to the tuning functions scheme. On the basis of the fact, this paper proposes a new design method for tuning functions scheme with non-change type projection algorithm. Also, it is shown that the proposed method can solve the problems of the conventional method.
This paper addresses a sensor scheduling problem for large-scale networked sensor systems. Sensor scheduling is required to achieve power saving or to make efficient use of communication channels. The scheduling problem is formulated as a model predictive control problem with single sensor measurement per time. It is assumed that all sensors have the same characteristics and they have state dependent noise. We propose a fast and optimal sensor scheduling algorithm for a class of systems with a sensor characteristics. Computation time of the proposed algorithm is proportional to the number of sensors, and it is independent of the prediction horizon. In addition, a fast sensor scheduling algorithm is presented for a class of systems with a mild condition.