Page 1269 - 5G Basics - Core Network Aspects

Transport aspects 2

D.4.2 CnD(t) encoding and decoding for OPUCn

The cumulative value of CnD(t) (CnD(t)) is encoded in the ODTUCn.ts justification control bytes JC1, JC2, JC3,
JC4, JC5 and JC6. Bits D1 to D18 carry the value of CnD(t). Bit D1 carries the most significant bit and bit D10
carries the least significant bit. As shown in Figure 20-7, bits D1 to D7 are located in bits 2-8 of JC4, bits D8
to D9 are located in bits 1-2 of JC1, bits D10 to D16 are located in JC5, and bits D17 to D18 are located in
bits 1-2 of JC2.
The CRC-9 located in bits 2-8 of JC6 and bits 1-2 of JC3 is calculated over the D1-D18 bits in JC4, JC1, JC5 and
2
3
9
JC2. The CRC-9 uses the g(x) = x + x + x + 1 generator polynomial, and is calculated as follows:
1) The JC4 bits 2-8, JC1 bits 1-2, JC5 bits 2-8, and JC2 bits 1-2 are taken in network transmission order,
most significant bit first, to form an 18-bit pattern representing the coefficients of a polynomial
M(x) of degree 17.
9
2) M(x) is multiplied by x and divided (modulo 2) by G(x), producing a remainder R(x) of degree 8 or
less.
8
3) The coefficients of R(x) are considered to be a 9-bit sequence, where x is the most significant bit.
4) This 9-bit sequence is the CRC-9 where the first bit of the CRC-9 to be transmitted is the coefficient
0
8
of x and the last bit transmitted is the coefficient of x .
The de-mapper process performs steps 1-3 in the same manner as the mapper process, except that here,
the M(x) polynomial of step 1 includes the CRC bits of JC6 and JC3, resulting in M(x) having degree 26. In
the absence of bit errors, the remainder shall be 000000000.
A parallel logic implementation of the source CRC-9 is illustrated in Appendix VI.

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