Baseband

Baseband is a signal that has a very narrow frequency range, i.e. a spectral magnitude that is nonzero only for frequencies in the vicinity of the origin (termed f = 0) and negligible elsewhere. In telecommunications and signal processing, baseband signals are transmitted without modulation, that is, without any shift in the range of frequencies of the signal, and are low frequency - contained within the band of frequencies from close to 0 hertz up to a higher cut-off frequency or maximum bandwidth. Baseband can be synonymous with lowpass or non-modulated, and is differentiated from passband, bandpass, carrier-modulated, intermediate frequency, or radio frequency (RF).

Various uses

Baseband bandwidth

A baseband bandwidth is equal to the highest frequency of a signal or system, or an upper bound on such frequencies, for example the upper cut-off frequency of a Lowpass filter. By contrast, passband bandwidth is the difference between a highest frequency and a nonzero lowest frequency.

Base Band 5

Base Band 5, abbreviated as BB5, is the current mobile baseband generation implemented on Nokia mobile phones and the replacement for prior DCT (Digital Core Technology) generations.

This generation of Nokia phone basebands uses a new range of chipsets, bus systems and components as well as enhanced security mechanisms preventing manipulations of firmware and system configurations. The phones' system interface has changed over from previous generations to allow, for instance, flashing of the device via USB.

Unlocking

The system is designed to prevent unlocking of certain key capabilities of the handsets (such as usable network or installation of unsigned operating system), which has not been approved by Nokia or the network. Just like the DCT-4 (DCT generation 4) locking system, the unlocking code is unique to each handset and not stored inside the handset, but a hash signature, calculated by a secret algorithm and the phone uses only part of it to verify the code. However, unlike earlier DCT-4 baseband, where it was possible to run custom code, the BB5 generations uses Texas Instrument processor with TrustZone, the unlock code hash checking is implemented into special PA_xx applet, executed by the CPU in protected mode. The idea behind this approach is that will not be possible to patch the simlock applet and fooling the phone of accepting wrong code.