n be configured prior to shipment or are often unknown, a flexible receiver platform capable in the field for the air interface required. Although it may of rapid self-adjustment is a benefit. Since SDRs can not be practical to look to standards of the past in and of rapidly be reconfigured, they are ideal for the in- themselves, systems of the future are prime candidates. terception of wireless communications [3]. Additionally, With the competing 3G standards a manufacturer with since they already employ high-speed DSP, the DSP can limited resources could build a single system capable of Analog Control Loops Channel Channel Filter 1 Filter 1 Filter 2 Antenna Output Tuning Control Loops Figure 2.3-3 Super-heterodyne SDR. Software defined radio CHAPTER 2.3 SDR A SDR B SDR C Figure 2.3-4 Interoperability. supporting either CDMA2000 or UMTS while con- [5,6]. Other architectures such as direct conversion tinuing to support the legacy standards from which these both for transmit and receive are seeing some popularity have evolved. From a user point of view, such a system is in applications that are not as demanding. Currently also valuable because if the user should want to change direct conversion (Tx and Rx) is found in user terminals standards, all that is required is that the system be for cellular communications as well as for Tx on the base reprogrammed for the new standard, preserving all of the station side. It is possible that future developments will investment made in the original equipment. enable direct conversion on the receive side as well. Of course, other areas could also benefit from the Until then, the super-heterodyne architecture will con- economies of scale offered here. Other such areas in- tinue to be used in one form or another. clude devices for the reception of competing satellite broadcast of audio and video content and two-way Receiver communications systems, to name a few [4]. High-performance SDR receivers are typically con- Architectures structed from some variant of the super-heterodyn