17 terms

Access and Modulation

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4.615 ms
The length of a frame.
Broadcast Control Channel (BCCH)
One control channel is the broadcast control channel in GSM and provides system information to allow mobiles to attach to the cell.
EDGE
Increases the data rate by using multilevel signalling.
Multilevel Signalling
Enables 3 bits of data to be transmitted in the time it takes to transmit bit in GSM/GPRS.
Frequency Shift Keying
Uses segments from sinusoidal waveforms that have different frequencies (waves closer together and further apart).
On Off Keying
The simplest modulation method for digital signals. A burst of signal (on) is sent to represent data 1 and nothing (off) is sent to represent 0.
Phase Shift Keying
Uses segments of sinusoids that have the same frequency and amplitude but differ in phase (goes up and down, then down and up).
Amplitude-Shift Keying
Uses segments which have different amplitudes to represent on/off (heights of wavelength).
Modulation
The process of turning the data bits (ones and zeros) into transmitted waveforms.
Symbol Rate
Number of symbols per second.
Symbol Period
The duration (time) of the symbol.
Binary Phase Shift Keying (BPSK)
A phase shift of 180 degrees (or half a cycle) means that there can only be two different states. A phase change of 180 degrees is seen as an 'inversion' of the carrier wave and a change of amplitude by -1.
Fast fading
The attenuation happens over a short range. Signal takes two paths, with different lengths due to reflection etc. Signal arrives to received at different times, causing interferences.
Fading
Signal attenuation (loss of intensity) which occurs with increased distance from the base station.
Slow fading
Relatively large changes of distance are required to produce significant variations of received signal strength. One dominant signal is sent.
Doppler Shift
If a device moves closer to the base station, the signal frequency rises. As a device moves away from the base station, the signal frequency drops.
High Speed (Downlink/Uplink)Packet Access Uplink
HS(D/U)PA. Uses QPSK, giving 2bits per modulation symbol. Can be deployed on existing 3G networks with minimum disruption. Backwards compatible with previous releases of 3G. Can be deployed at marginal cost.