A typical application of wireless sensor networks (WSNet) [1] is the following. Given certain regions of interest from the environment, the problem is to design and deploy a WSNet whose sensors monitor the given regions, acquire information, and transmit this information via radio signals to a central location called the base station. There are several critical resources that need to be considered by the designer. (a) Cost: the cost of a WSNet is generally the actual cost of purchasing the sensors. It depends on the number and type of sensor nodes used in the design. (b) Lifetime: the lifetime of a WSNet is the duration of normal operation for the WSNet. Frequently, lifetime is defined as the time until a node in the system becomes inoperative because of an exhausted power supply. (c) Quality of service: additional application specific requirements exists, such as limiting the delay with which data arrive at the base station.