Code Allocation:
Channelization codes, also called Spreading codes, satisfy two purpose: first, to spread the signal energy evenly over the bandwidth below the noise level ; and second, to separate the transmissions from a single source. These are based on the Orthogonal Variable Spreading Factor (OVSF) technique. Orthogonal codes are the codes that have the property that any two codes in the family, except for those that are connected to it and to the right, when multiplied together bitwise and the results of these multiplication are summed, the result is zero. That is, in mathematical way, codes in the family correlated completely with themselves and have zero crosscorrelation with any of the other codes. However, the zero crosscorrelation property of orthogonal codes works only if the codes are time aligned.
In Uplink, channelization codes are used to distinguish data and control channels from the same UE.
In Downlink, channelization codes are used to distinguish signals for different channels and users within a cell.
Scrambling codes, also called PN scrambling codes, are used to separate users and different base stations. They are used on top of spreading and it does not change the signal bandwidth. Also, scrambling codes are found to have better crosscorrelation property as compared to channelization codes even when codes are not time aligned. PN sequence or Pseudorandom number sequence is a sequence of numbers, algorithmically generated, that are distributed evenly throughout the number space but with no discernible pattern to their distribution.
In Uplink, scrambling codes are used to distinguish UE terminals.
In Downlink, scrambling codes are used to distinguish different cells.
ImportantInformation:
- Each signal is spread with the spreading code, i.e. channelization code x scrambling code
- Uplink codes are not cell specific. Channelization Code is picked by mobile and Scrambling code assigned by RNC. They can be decoded anywhere
- Downlink code is cell specific and UE must decode each of them individually
In Downlink, channelization codes are used to distinguish signals for different channels and users within a cell.
Scrambling codes, also called PN scrambling codes, are used to separate users and different base stations. They are used on top of spreading and it does not change the signal bandwidth. Also, scrambling codes are found to have better crosscorrelation property as compared to channelization codes even when codes are not time aligned. PN sequence or Pseudorandom number sequence is a sequence of numbers, algorithmically generated, that are distributed evenly throughout the number space but with no discernible pattern to their distribution.
In Uplink, scrambling codes are used to distinguish UE terminals.
In Downlink, scrambling codes are used to distinguish different cells.
ImportantInformation:
- Each signal is spread with the spreading code, i.e. channelization code x scrambling code
- Uplink codes are not cell specific. Channelization Code is picked by mobile and Scrambling code assigned by RNC. They can be decoded anywhere
- Downlink code is cell specific and UE must decode each of them individually
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