user terminals are essential for adapting to the different wireless networks, thereby eliminating the need for separate multiple terminals. The most promising approach is that of the software radio. Unfortunately, the current software radio technology is not completely feasible for all wireless networks due to the following problems: It is impossible to have just one antenna and one LNA to serve the wide range of frequency bands (i.e. to cover all the bands of all 4G networks). One solution could be to use multiple analogue parts to work in different frequency bands. This certainly increases the design and complexity and physical size of a terminal. The existing analogue to-digital converters (ADC) used in mobile stations are not fast enough. The GSM requires at least 17-bit resolution with very high sampling rates. To provide such a bit resolution, the speed of the fastest current ADC is still two or three orders of magnitude slower than required. In order to allow real-time execution of software-implemented radio interface functions, such as fre- quency conversion, digital filtering, spreading and de-spreading, parallel DSPs have to be used, thereby increasing the circuit complexity and high power consumption and dissipation. 5.7.2 Wireless Network To use 4G services, the multimode user terminals should be able to select the target wireless systems. The process of broadcasting messages periodically to mobile stations becomes complicated in 4G het- erogeneous systems because of the differences in wireless technologies and access protocols. One of the possible solutions is to use software radio devices that can scan the available networks and, after scanning, will load the required software and configure themselves for the selected network by downloading the required software models by scanning the available wireless networks. The software can be downloaded from media such as a PC server or over the air (OTA). OTA is the most challenging way to achieve a wireless system discovery, but its availability frees users