Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Software-Defined Radio 333A software-defined radio offers the following features:– The radio can be used everywhere if all major wireless communication standards aresupported. The corresponding standard-specific application software can be downloadedfrom the existing network itself.– The software-defined radio can guarantee compatibility between several wirelessnetworks. If UMTS is not supported in a given area, the terminal station can searchfor another network, e.g. GSM or IS-95.– Depending on the hardware used, SDR is open to adopt new technologies andstandards.Therefore, SDR plays an important role in the success and penetration of 4G systems.A set of examples of the current standards for cellular networks is given in Table 6-3.These standards, following their multi-access schemes, can be characterized as follows:– Most of the 2G mobile communication systems are based on TDMA, while a CDMAcomponent is adopted in 3G systems.– In conjunction with TDMA, many broadband WLAN and WLL standards supportmulti-carrier transmission (OFDM).For standards beyond 3G we may expect that a combination of CDMA with a multicarrier(OFDM) component is a potential candidate. Hence, a generic air interface basedon multi-carrier CDMA using a software-defined radio would support many existing andfuture standards (see Figure 6-34).6.5.2 Basic ConceptA basic implementation concept of a software-defined radio is illustrated in Figure 6-35.The digitization of the received signal can be performed directly on the radio frequencySoftware-controlled configuration unitMulti-carrier-based systemsCDMA-based systemsOther systemsFigure 6-34Software configured air interface