1. Introduction

One of the primary and long-standing goals of the Federal Communications Commission (FCC) has been to promote more efficient use of spectrum for the radiofrequency (RF) wireless radio transmission. The FCC’s 1999 Spectrum Policy Statement highlighted that “with increased demand of a finite supply of spectrum, the Commission’s spectrum management activities must focus on allowing spectrum markets to become more efficient”; and the Strategic Plan for Fiscal Year 2003–2008 (published in 2002) indicated its general spectrum management goal was to “encourage the highest and best use of spectrum” [1]. Even though there are other, different metrics, one of the accepted common spectrum efficiency metrics for wireless communications is in terms of bits/second/hertz. To approach this goal, many government organizations and commercial communications companies have adopted advanced modulation and amplification transmission techniques to utilize spectrum more efficiently and as much as possible.