In many cases, data from ad hoc wireless and sensor networks are routed through a cellular infrastructure or a wired network such as an Internet. To meet the quality of service (QoS), one has to ensure performance guarantees not only from the wireless network side but also from the wired network. In the previous chapter, admission-controller design was covered for wired networks so as to meet a desired level of QoS. In this chapter, we treat QoS performance for wireless cellular networks via transmitter power, active link protection, and admission-controller designs. For wireless networks, besides throughput, packet loss, and endto-end delay guarantee, energy efficiency is another QoS performance metric. Energy efficiency, to a certain extent, can be attained by controlling transmitter power, which is the central theme of this chapter.