Communications using frequency modulated signals have been in existence since the early years of radio communications. In a frequency modulated system, information is modulated in a frequency domain and placed on a carrier for transmission to at least one receiver. In commercial broadcast FM transmission, the transmitted signal bandwidth is quite large relative to the modulation bandwidth because a high modulation index is used. For example, in conventional FM broadcast communications the transmitted signal bandwidth used is on the order of 200 kilohertz, while the modulation bandwidth is only 25 or 30 kilohertz. This large disparity between signal bandwidth and modulation bandwidth is desirable in commercial applications since it increases the signal to noise ratio at the receiver at the expense of frequency use efficiency as well as transmitter station complexity. This enables the inexpensive production of portable FM receivers which have high audio reproduction capability.
As digital electronics continue to decrease in cost, it has become desirable to utilize digital electronics in applications previously performed only by analog electronics. This is especially true in the area of radio communications including commercial FM broadcast receivers. However, given the large modulation index used in commercial FM broadcast equipment, a digital signal processor designed to operate in a high modulation index FM environment must perform mathematical manipulations on sampled versions of a received signal at a rate equal to or greater than two times the signal bandwidth. Thus, when used for signal processing of conventional high (200 kilohertz) FM signals, this necessitates that the signal processor perform mathematical manipulations on signal components sampled at a rate equal to or greater than 400 kilosamples per second or 200 kilosamples per second in a quadrature baseband configuration. Even with digital electronics decreasing in cost, it is still problematic to use digital signal processors that operate at this speed. Such high speed digital signal processors have the disadvantages of consuming comparatively large amounts of power, as well as being difficult to build. These factors have a significant impact on the ability to build portable FM communications receivers based on digital signal processing technology. Therefore, what is needed are a method and system for reducing the power consumption and complexity of digitally implemented FM broadcast receivers, without significantly degrading the audio reproduction capability of the FM receiver.
USPTO Backgrounds
USPTO Backgrounds