The wireless medium is a s=ce shared resource in mobde computing. Consequently, the media access control (MAC) layer influences the fairness and robustness of the wireless network. According to the current MAC protocok, stations are not able to gain access equdy to the shared wireless medium. This problem is conunody known as the fairness problem. The fairness problem occurs mostly bemuse of the existence of hidden stations and the presumption of a non-Wy connected wird=s network topology. This paper addresses solutions to the fairness problem in wireless networks. persistent carrier sense mdtiple access based dgr ithms are proposed in which a fair wirel=s access for each user is accomplished using a precsdtiated N acce~Probabfity, Pij, . .that represents the Eti access probabtity horn station i to j. Lii access probabfities are dcdated at the source station in two ways using connection-based and time-based media access methods. According to the used methods, each active user broadcasts information on either the number of Iogicd connections or the average cent ent ion time to the stations within the communication reach. This information exchange provides partird understanding of the topology of the network to the stations. Each station reserves a specific priority for itse~to gain access to the shared medium. It is suggested that the information is exchanged during the W access discovery procedure for the connection-based method, and periodidy for the time-based method. Link access probabtit ies are modified every time the exchanged information is received. The proposed algorithms are dynamic and sensitive to the changes in the network topology. The sdgoritb have been implemented in a specific media access control protocol [1], but they are app~mble to d media access control protocok.Simdation restits show that the algorithms restit in an order of magnitude performance improvement in terms of throughput in a wirel= network.

We recently demonstrated a high function wrist watch computer prototype that runs the Linux operating system and also X11 graphics libraries. In this paper we describe the unique energy related challenges and tradeoffs we encountered while building this watch. We show that the usage duty factor for the device heavily dictates which of the powers, active power or sleep power, needs to be minimized more aggressively in order to achieve the longest perceived battery life. We also describe the energy issues that percolate through several layers of software all the way from device usage scenarios, applications, user interfaces, system level software to device drivers and the need to systematically address all of them to achieve the battery life dictated by the hardware components and the capacity of the battery in the device.

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