Efforts are currently underway in standards organizations to define energy efficiency metrics for wireless networks. This effort reflects current industry interest in producing networks that are as "green" as possible. Candidate metrics examine radiated base station power normalized to area and carried traffic load, e.g., Watts/Erlang/km~2 or Watts/(bits/sec)/km~2. While these measures appear to be a natural way of assessing efficiency, they are in fact inappropriate for use in a wireless system. Targeting such metrics is counter to prudent system operation, as well as misleading in design. We demonstrate these facts both from a theoretical and empirical perspective, noting limits based on the physics of propagation as well as analyzing field data gathered from a large Code Division Multiple Access (CDMA) network. We also use this information to suggest requirements for methods of assessing "green-ness" that are better suited to the wireless domain.
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