## 5 Multi-Giga-Hertz Agile Radio Front-End Design
### A Design Example-GigaFront-1 Test-Bed Front-End  
Proposed here is a multi-giga-Hertz agile radio front-end design as an optional design for our laboratorial test-bed called GigaFront-1.  
Philosophy of Design:  
The following aspects are used as guidance in the design.  
* cover all frequencies of interest, namely, the busy TV bands and higher bands up to 5.4 GHz
* reduce RF circuit complexity by using large digital processing bandwidth
* achieve fast subband switching in digital domain
* flexible in system configuration and adding new functions/features
* use as many off-the-shelf products as possible  
The major frequency parameters are listed in Tables 2 and 3. The proposed transmitter front-end and receiver front-end are shown separately. The overall frequency span ranges from 400 MHz through 5.4 GHz, divided into 10 bands in the transmitter and 6 bands in the receiver. Each band can be further divided into a number of subbands in digital domain. The digital processing bandwidth is 500 MHz, which does not put too much pressure on the data conversion section and digital back-end. Band switching can be done by changing the analog switch positions, combined with local oscillator (LO) frequency switching. In the transmitter, the analog mixer generates upper sidebands and lower sidebands, and depending on the position of the second switch (SW2), one of side bands is utilized. This design assumes a minimum transmit subband bandwidth of 10 MHz, and fast switching between the subbands is achieved by changing the frequencies \(f_{0}\), \(f_{1}\) and \(f_{2}\) in digital domain. Note that \(f_{0}\), \(f_{1}\) and \(f_{2}\) range from \(-240\) MHz to 240 MHz, resulting in a maximum frequency shift 480 MHz. It is expected that switching between the subbands is much faster than switching between the bands. There are three quadrature digital processing cores in parallel in either the transmitter or the receiver. The first digital processing core is dedicated to the two lower busy bands ranging from 400 MHz through 1.4 GHz, while the rest two cores are dedicated to the higher bands with a 4 GHz frequency span. The second and third digital processing cores can work simultaneously to cover a 1 GHz frequency range. In the receiver, the bandwidths are 500 MHz for each of the first two bands and 1 GHz for each of the rest of the four bands. This receiver band arrangement tries to reduce band switching effort in the higher frequency range, assuming unbalanced utilizations in the lower and higher frequency ranges.  
\begin{table}
\begin{tabular}{|l|c|c|c|} \hline Band & LO frequency combination & center frequency & SW position \\ \hline
1. 0.4 – 0.9 & 0.65 & 0.65 + \(f_{0}\) & SW1 lower \\ \hline
2. 0.9 – 1.4 & 1.15 & 1.15 + \(f_{0}\) & SW1 upper \\ \hline
3. 1.4 – 1.9 & 3.15, 1.5 & 1.65 + \(f_{1}\) & SW2 lower \\ \hline
4. 1.9 – 2.4 & 3.65, 1.5 & 2.15 + \(f_{2}\) & SW2 lower \\ \hline
5. 2.4 – 2.9 & 3.15, 0.5 & 2.65 + \(f_{1}\) & SW2 lower \\ \hline
6. 2.9 – 3.4 & 3.65, 0.5 & 3.15 + \(f_{2}\) & SW2 lower \\ \hline
7. 3.4 – 2.9 & 3.15, 0.5 & 3.65 + \(f_{1}\) & SW2 upper \\ \hline
8. 2.9 – 4.4 & 3.65, 0.5 & 4.15 + \(f_{2}\) & SW2 upper \\ \hline
9. 4.4 – 4.9 & 3.15, 1.5 & 4.65 + \(f_{1}\) & SW2 upper \\ \hline
10. 4.9 – 5.4 & 3.65, 1.5 & 5.15 + \(f_{2}\) & SW2 upper \\ \hline \end{tabular}
\end{table}
Table 2: Transmitter frequency parameters (GHz).  
Figure 24: Transmitter front-end architecture.