 armed forces. To achieve this goal, the SpeakEasy utilized many of the techniques discussed in this chapter Multimode implies the ability to process several differ- to provide multiband, multi-modes of operations. Al- ent kinds of standards. Examples of standards include though many people contributed to the concept and AM, FM, GMSK, and CDMA but are limited to none of development of SDR, Joe Mitola of Mitre is generally these. An SDR has the ability to work with many dif- credited with being the "father of software-defined ferent standards and be continuously reprogrammed. radio" [2]. Therefore, a better term than multimode, which implies Although the SpeakEasy was a fully developed SDR, it a discrete number of modes, may be variable mode, is fair to say that simpler and more rudimentary forms of which implies a continuously changeable mode of oper- SDR existed before this program. By taking a look at how ation. As with other characteristics, these modes may be systems are being developed in the commercial realm, it sequential or simultaneous, in the case of a multi-carrier is easy to see how they also may have evolved in military radio. and nonmilitary programs. Although there are many enabling technologies that have come online in the last decade, one of the key Multi-rate technical driving forces was the development of low-cost Multi-rate is closely related to multimode. A multi-rate DSPs. From a market point of view, the rapid growth of radio is one that either processes different parts of the the telecommunications industry, particularly cellular signal chain at different samples rates, as in a multi-rate communications, provided a demand for low-cost Software defined radio CHAPTER 2.3 Analog Control Loops Channel Channel Band Filter 1 Band Filter 2 Filter 1 Filter 2 Antenna Output Detector Tuning Control Loops Figure 2.3-1 Traditional super-heterodyne with analog detection. equipment both from a user and an infrastructure point a 200 kHz bandwidth, while an IS-95 system operates on of view. Although first