It is useful to review the basic architecture of a 2G mobile telephone, such as a GSM phone. This will enable us to understand what the basic building blocks are of a digital communications device, particularly the modem aspects such as the RF, analog and digital baseband modules, and to see how DSP processors are really at the heart of digital cellular (and wireless) devices.

In Figure 10.9, we can see in the basic components of a digital cellular device, such as a GSM phone. Just for completeness, we shall now briefly explain the functional blocks shown in the figure, though it is not really our intention to examine digital wireless modems in any more depth that this in this book.


Figure 10.9 2G digital cellular phone architecture.

10.6.1 Radio Frequency (RF)

Modulator/Power Amplifier The raw bitstream that we wish to transmit is used to create a corresponding pattern in the RF transmission from the antenna that can be detected by a receiver at the base station. This pattern in the RF gets created by varying the frequency slightly about a central value, such that at certain points in time, corresponding to the bit rate, the RF signal has a certain characteristic that enables the receiver to detect the underlying bit values at corresponding bit intervals. The modulated signal is fed into a power amplifier that drives the signal into ...

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