Scrambling

The scrambler is used in 5G to randomize the bits to remove the long consecutive occurrence of 1’s and 0’s. A scrambler generates the random sequence which is xor-ed with information bit bit-wise. The scrambling is performed for two purposes:

• Randomize the bit sequence or alter the probability distribution of the information bits.

• Reduces impact of inter-cell interference by decorrelating the interference across neighbouring cells.

The scrambling is carried out for all the uplink abd downlink physical channel. For each channel, the seed used to generate the scrambling sequence is different. The seed is computed using parameters relevant to a particular physical chain. The details of the scrambling used in 5G is provided in table-1.

Table 32 Table-1: Scrambling and Scrambling parameters in 5G

Physical chain	Parameters	Comments
PBCH	\(L_{max}\), SFN, SSB-Index	Aka \(1^{nd}\) Scrambling
PBCH	Cell-ID, SSB-Index	Aka \(2^{nd}\) Scrambling
PDCCH	scambling-ID, RNTI	NA
PDCCH	RNTI	Aka RNTI masking
PSCH	scambling-ID, codeword index, RNTI	PRACH

The receiver performs the inverse process of the scrambling called de-scrambling. Descrambling undo the affect of scrambling to recover exact transmission bits. The details about the scrambling, descrambling and RNTI making is provided in upcoming section.

Table of Contents

• Scrambler
  • Scrambler
• Descrambler
  • DeScrambler
• RNTI Masking
  • RNTImasking