Page 73 - From GMS to LTE

Global System for Mobile Communications (GSM) 59

Memory
(RAM, FLASH)

Analog module, Base band
modulator,… processor

Display
Power Keypad
management External Loudspeaker
interfaces
Microphone
Charger Vibration alarm
Battery
Data interfaces
SIM-card
(e.g. USB, Bluetooth, infrared)
Figure 1.46 Basic architecture of a mobile phone.

GPRS management and GPRS data flow;
●
parts of the transmission chain, like channel coder, interleaver and cipherer (dedicated
●
hardware component in some designs);
mobility management (network search, cell reselection, location update, handover,
●
timing advance, etc.);
connections via external interfaces like Bluetooth, infrared and Universal Serial
●
Bus (USB);
user interface (keypad, display, graphical user interface).
●
As many of these tasks have to be performed in parallel, a multitasking embedded
real‐time operating system is used on the RISC processor. The real‐time component of
the operating system is especially important as the processor has to be able to provide
data for transmission over the air interface according to the GSM frame structure and
timing. All other tasks like keypad handling, display update and the graphical user
interface, in general, have a lower priority.
In most devices, the baseband processor is based on the ARM Reduced Instruction
Set (RISC) architecture that allows clock speeds of up to 2 GHz today. Such processors
are built by several manufacturers that have obtained a license from ARM. For simple
devices, ultra‐low‐power versions are used with a clock rate of only a few megahertz.
Such chips are very power efficient and require only little energy while in sleep mode
and while periodically observing the PCH. As a consequence, it is possible to reach
standby times of well over a week. Also, the amount of RAM and ROM for such a device
is very small by today’s standards, usually in the order of only a few hundred kilobytes.
The DSP is another important component of a GSM chipset. Its main task is the
decoding of the incoming signal and FR, EFR, HR or AMR speech compression. In
GSM, signal decoding starts with the analysis of the training sequence of a burst (see