processing gain vs spreading gain | difference between processing gain and spreading gain used in CDMA

This page on processing gain vs spreading gain describes difference between processing gain and spreading gain used in CDMA. It also explains spreading factor.

As we know in CDMA transmitter and receiver identical PN sequences are used in order to retrieve the data back. Speading is applied in transmitter and de-spreading in the receiver. The unwanted signal remains spreaded and behaves like noise. Despreading process strengthens desired signal in comparison to other undesired signals.

Processing Gain

For DSSS, bits are known as chips after spreading. The same is depicted in the figure-1. As shown in the figure, Tb is one bit period and Tc is one chip period. 1/Tc is the chip rate which characterise this spread spectrum transmission system.

The ratio of information bit duration to chip duration is known as processing gain(PG).
Processing gain = Tb/Tc
It is also known as spreading factor.
In other words it represents number of chips in one data bit period.

In general it is defined as ratio of signal to noise ratio (SNR) at output to the SNR at the input.
PG (dB) = SNROUT (dB) - SNRIN (dB)

Spreading Factor | Spreading Gain

There is no difference between spreading gain and procesing factor. Both of these terms are used interchangeably. Spreading factor is expressed above. In other words, spreading factor is the ratio of chip rate at the output to the information bit rate at the input of spreading block used in CDMA transmitter.

Higher the spreading factor better and more is the spreading. Hence more codes can be accommodated on the same frequency channel.

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UMTS Tutorial  UMTS architecture  UMTS Stack  UMTS channels 

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