4.8 Coding for E‑DCH
25.2123GPPMultiplexing and channel coding (FDD)Release 17TS
Figure 21 shows the processing structure for the E‑DCH transport channel mapped onto a separate CCTrCH.
If UL_MIMO_Enabled is not set to TRUE, or UL_MIMO_Enabled is set to TRUE and UL_CLTD_Active is not 1, data arrives to the coding unit in form of a maximum of one transport block once every transmission time interval (TTI).
If UL_MIMO_Enabled is set to TRUE and UL_CLTD_Active = 1, data arrives to the coding unit in form of a maximum of two transport blocks once every TTI.
– If a single transport block arrives to the coding unit in a TTI, the transport block is processed as when UL_MIMO_Enabled is not set to TRUE.
– If two transport blocks arrive to the coding unit in a TTI, each transport block is separately processed as when UL_MIMO_Enabled is not set to TRUE, with the exception of the rank-dependent determinations of SF, modulation, number of E-DPDCHs and S-E-DPDCHs, and the physical channel mapping.
The following coding steps can be identified:
– Add CRC to the transport block
– Code block segmentation
– Channel coding
– Physical layer hybrid ARQ and rate matching
– Physical channel segmentation
– Interleaving
– Physical channel mapping
The coding steps for E-DCH transport channel are shown in the figure below.
Figure 21: Transport channel processing for E-DCH
In the following the number of transport blocks per TTI and the number of transport channels is always one i.e. m=1 and i=1. When referencing non E-DCH formulae which are used in correspondence with E-DCH formulae the convention is used that transport block subscripts may be omitted (e.g. X_{1} may be written X).
4.8.1 CRC attachment for E-DCH
CRC attachment for the E-DCH transport channel shall be performed according to the general method described in 4.2.1 above with the following specific parameters.
The CRC length shall always be L_{1}=24 bits.
4.8.2 Code block segmentation for E-DCH
Code block segmentation for the E-DCH transport channel shall be performed according to the general method described in 4.2.2.2 with the following specific parameters.
There is a maximum of one transport block. The bits input to the block are mapped to the bits directly. It follows that X_{i} = B_{i}. Note that the bits x referenced here refer only to the internals of the code block segmentation function. The output bits from the code block segmentation function are o_{ir1}, o_{ir2}, o_{ir3}, …, o_{irK}.
The value of Z = 5114 for turbo coding shall be used.
4.8.3 Channel coding for E-DCH
Channel coding for the E-DCH transport channel shall be performed according to the general method described in clause 4.2.3 above with the following specific parameters.
There is a maximum of one transport block, i=1. The rate 1/3 turbo coding shall be used.
4.8.4 Physical layer HARQ functionality and rate matching for E-DCH
The hybrid ARQ functionality matches the number of bits at the output of the channel coder to the total number of bits of the E-DPDCH or S-E-DPDCH set to which the E-DCH transport channel is mapped. The hybrid ARQ functionality is controlled by the redundancy version (RV) parameters.
Figure 22: E‑DCH hybrid ARQ functionality
4.8.4.1 Determination of SF, modulation scheme and number of E-DPDCH PhCHs needed
The maximum amount of puncturing that can be applied is
– 1-PL_{non-max} if the modulation scheme or the number of code channels is less than the maximum allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{mod}__{switch} if the modulation scheme is BPSK, the number of E-DPDCH code channels equals to 4 and the usage of 4PAM is allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{mod}__{switch_2} if the modulation scheme is 4PAM, the number of E-DPDCH code channels equals to 4 and the usage of 8PAM is allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{max} if the modulation scheme and the number of code channels equals to the maximum allowed by the UE capability and restrictions imposed by UTRAN.
The number of available bits per TTI of one E-DPDCH for all possible spreading factors and modulation schemes is denoted by N_{256}, N_{128}, N_{64}, N_{32}, N_{16}, N_{8}, N_{4},_{ }N_{2}, M_{4}, M_{2}, L_{4} and L_{2 }where the index refers to the spreading factor. N refers to BPSK modulation, M to 4PAM modulation and L to 8PAM modulation.
The possible number of bits available to the CCTrCH of E-DCH type on all E-DPDCHs, N_{e,data}, then are {N_{256}, N_{128}, N_{64}, N_{32}, N_{16}, N_{8}, N_{4},_{ }2N_{4},_{ }2N_{2}, 2N_{2}+2N_{4}, 2M_{2}+2M_{4}, 2L_{2}+2L_{4}}.
SET0 denotes the set of N_{e,data}_{ }values allowed by the UTRAN and supported by the UE, as part of the UE’s capability. SET0 can be a subset of {N_{256}, N_{128}, N_{64}, N_{32}, N_{16}, N_{8}, N_{4},_{ }2N_{4},_{ }2N_{2}, 2N_{2}+2N_{4}, 2M_{2}+2M_{4}, 2L_{2}+2L_{4}}.
The total number of bits in a TTI on all E-DPDCHs before rate matching with transport format j is N_{e,j}. The total number of bits available for the E‑DCH transmission per TTI on all E-DPDCHs with transport format j, N_{e,data,j}, is determined by executing the following algorithm, where
– PL_{non-max} is signalled from higher layers,
– PL_{mod}__{,switch} is equal to 0.468,
– PL_{mod}__{switch_2} is equal to 0.4,
– PL_{max} is equal to 0.44 , except when the N_{e,data} = 2N_{2}+2N_{4}, 2M_{2}+2M_{4} or 2L_{2}+2L_{4} is allowed by the UTRAN and supported by the UE, in which case PL_{max} is equal to 0.33:
If the UE transmits only one transport block:
SET1 = { N_{e,data} in SET0 such that N_{e,data} – N_{e,j} is non negative }
If SET1 is not empty and the smallest element of SET1 requires just one E-DPDCH then
N_{e,data,j} = min SET1
Else
SET2 = { N_{e,data} in SET0 without 2N_{2}+2N_{4}, 2M_{2}+2M_{4} and 2L_{2}+2L_{4} such that N_{e,data} – PL_{non-max} × N_{e,j} is non negative }
If SET2 is not empty then
Sort SET2 in ascending order
N_{e,data }= min SET2
While N_{e,data} is not the max of SET2 and the follower of N_{e,data }requires only one E-DPDCH do
N_{e,data }= follower of N_{e,data} in SET2
End while
N_{e,data,j} = N_{e,data}
Else
If SET0 includes 2N_{2}+2N_{4}
N_{e,data} = 2N_{2}+2N_{4}
If N_{e,data} / N_{e,j} < PL_{mod_switch} and SET0 includes 2M_{2}+2M_{4}
N_{e,data} = 2M_{2}+2M_{4}
End if
If N_{e,data} is equal to 2M_{2}+2M_{4} and N_{e,data} / N_{e,j} < PL_{mod_switch_2} and SET0 includes 2L_{2}+2L_{4}
N_{e,data} = 2L_{2}+2L_{4}
End if
N_{e,data,j} = N_{e,data} provided that N_{e,data,j} – PL_{max} × N_{e,j} is non negative
Else
N_{e,data,j} = max SET0 provided that N_{e,data,j} – PL_{max} × N_{e,j} is non negative
End if
End if
End if
Else (when UE transmits two transport blocks)
N_{e,data} = 2N_{2}+2N_{4}
If N_{e,data} / N_{e,j} < PL_{mod_switch }and SET0 includes 2M_{2}+2M_{4}
N_{e,data} = 2M_{2}+2M_{4}
End if
If N_{e,data} is equal to 2M_{2}+2M_{4}, N_{e,data} / N_{e,j} < PL_{mod_switch_2} and SET0 includes 2L_{2}+2L_{4}
N_{e,data} = 2L_{2}+2L_{4}
End if
N_{e,data,j} = N_{e,data} provided that N_{e,data} – PL_{max} × N_{e,j} is non negative
End if
While E‑DCH TTI length is 10 ms, if an initial transmission occurs in a compressed frame, or a retransmission occurs in a compressed frame, or a retransmission occurs in a non‑compressed frame for which initial transmission was compressed, the number of available bits per TTI of one E‑DPDCH for all possible spreading factors denoted by N_{256}, N_{128}, N_{64}, N_{32}, N_{16}, N_{8}, N_{4} and N_{2} used in the algorithm above is replaced by k×N_{256}, k×N_{128}, k×N_{64}, k×N_{32}, k×N_{16}, k×N_{8}, k×N_{4} and k×N_{2}. The parameter k is equal to n_{tx1}/15 and n_{tx1} is defined in 4.4.5.1.
4.8.4.1A Determination of SF, modulation scheme and number of S-E-DPDCH PhCHs needed
S-E-DPDCHs are only present when the UE transmits two transport blocks. When present, the number of S-E-DPDCHs is always 4.
The maximum amount of puncturing that can be applied is
– 1-PL_{non-max} if the modulation scheme is less than the maximum allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{mod}__{switch} if the modulation scheme is BPSK and the usage of 4PAM is allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{mod}__{switch_2} if the modulation scheme is 4PAM and the usage of 8PAM is allowed by the UE capability and restrictions imposed by UTRAN.
– 1-PL_{max} if the modulation scheme equals to the maximum allowed by the UE capability and restrictions imposed by UTRAN.
The number of available bits per TTI of one S-E-DPDCH for all possible spreading factors and modulation schemes is denoted by N_{4}, N_{2}, M_{4}, M_{2}, L_{4} and L_{2}, where the index refers to the spreading factor. N refers to BPSK modulation, M to 4PAM modulation and L to 8PAM modulation.
The possible number of bits available to the CCTrCH of E-DCH type on all S-E-DPDCHs, N_{e,data}, then are {2N_{2}+2N_{4}, 2M_{2}+2M_{4}, 2L_{2}+2L_{4}}.
SET0 denotes the set of N_{e,data}_{ }values allowed by the UTRAN and supported by the UE, as part of the UE’s capability. SET0 can be a subset of {2N_{2}+2N_{4}, 2M_{2}+2M_{4}, 2L_{2}+2L_{4}}.
The total number of bits in a TTI on all S-E-DPDCHs before rate matching with transport format j is N_{e,j}. The total number of bits available for the E‑DCH transmission per TTI on all S-E-DPDCHs with transport format j, N_{e,data,j}, is determined by executing the following algorithm, where
– PL_{mod_switch} is equal to 0.468,
– PL_{mod_switch_2} is equal to 0.4,
– PL_{max} is equal to 0.33:
N_{e,data} = 2N_{2}+2N_{4}
If N_{e,data} / N_{e,j} < PL_{mod_switch }and SET0 includes 2M_{2}+2M_{4}
N_{e,data} = 2M_{2}+2M_{4}
End if
If N_{e,data} is equal to 2M_{2}+2M_{4}, N_{e,data} / N_{e,j} < PL_{mod_switch_2} and SET0 includes 2L_{2}+2L_{4}
N_{e,data} = 2L_{2}+2L_{4}
End if
N_{e,data,j} = N_{e,data} provided that N_{e,data} – PL_{max} × N_{e,j} is non negative
4.8.4.2 HARQ bit separation
The HARQ bit separation function shall be performed in the same way as bit separation for turbo encoded TrCHs with puncturing in 4.2.7.4.1 above.
4.8.4.3 HARQ Rate Matching Stage
The hybrid ARQ rate matching for the E-DCH transport channel shall be done with the general method described in 4.2.7.5 with the following specific parameters.
The parameters of the rate matching stage depend on the value of the RV parameters s and r. The s and r combinations corresponding to each RV allowed for the E-DCH are listed in the table below.
Table 15D: RV for E-DCH
E-DCH RV Index |
s |
r |
0 |
1 |
0 |
1 |
0 |
0 |
2 |
1 |
1 |
3 |
0 |
1 |
The parameter e_{plus}, e_{minus} and e_{ini} are calculated with the general method for QPSK as described in 4.5.4.3 above. The following parameters are used as input:
N_{sys} = N_{p1} = N_{p2} = N_{e,j}/3
N_{data} = N_{e,data,j}
r_{max} = 2
During uplink compressed frames while E‑DCH TTI length is 10 ms and if N_{data}>N_{e,j}:
– If N_{data} mod 3 = 1, one δ bit is added to the N_{t,sys} bits as the last systematic bit and another δ bit is added to the N_{t,p1} bits as the last N_{t,p1} bit.
– If N_{data} mod 3 = 2, one δ bit is added to the N_{t,sys} bits as the last systematic bit.
4.8.4.4 HARQ bit collection
The HARQ bit collection shall be performed according to the general method for bit collection for turbo encoded TrCHs with puncturing as specified in 4.2.7.4.2 including the removal of the bits with value .
4.8.5 Physical channel segmentation for E‑DCH
When more than one E-DPDCH or S-E-DPDCH is used, physical channel segmentation distributes the bits among the different physical channels. The bits input to the physical channel segmentation are denoted by s_{1}, s_{2}, s_{3}, …,s_{R}, where R is the number of bits input to the physical channel segmentation block. The number of PhCHs is denoted by P.
The bits after physical channel segmentation are denoted u_{p,k} where p is the PhCH number. U(p) is the number of physical channel bits in one E-DCH TTI for the p^{th} E-DPDCH or S-E-DPDCH. The relation between s_{k} and u_{p,k} is given below.
Bits on first PhCH after physical channel segmentation:
k = 1, 2, …, U(1)
Bits on p^{th} PhCH after physical channel segmentation:
k = 1, 2, …, U(p)
4.8.6 Interleaving for E‑DCH
The interleaving is done as shown in figure 22A below, separately for each physical channel. The bits input to the block interleaver are denoted by , where p is PhCH number and U=U(p) is the number of bits in one TTI for one PhCH.
Figure 22A: Interleaver structure for E-DCH
The basic interleaver is as the 2^{nd} interleaver described in Clause 4.2.11.
For 4PAM, there are two identical interleavers of the same size R2×30, where R2 is the minimum integer fulfilling . The output bits from the physical channel segmentation are divided one by one between the interleavers: bit u_{p,k} goes to the first interleaver and bit u_{p,k+1} goes to the second interleaver. Bits are collected one by one from the interleavers: bit v_{p,k} is obtained from the first interleaver and bit v_{p,k+1} is obtained from the second interleaver, where k mod 2=1.
For 8PAM, there are three identical interleavers of the same size R2×30, where R2 is the minimum integer fulfilling . The output bits from the physical channel segmentation are divided one by one between the interleavers: bit u_{p,k} goes to the first interleaver, bit u_{p,k+1} goes to the second interleaver and bit u_{p,k+2} goes to the third interleaver. Bits are collected one by one from the interleavers: bit v_{p,k} is obtained from the first interleaver, bit v_{p,k+1} is obtained from the second interleaver and bit v_{p,k+2} is obtained from the third interleaver, where k mod 3=1.
4.8.7 Physical channel mapping for E‑DCH
The E-DCH structure is described in [2]. The bits input to the physical channel mapping are denoted _{p,1}, _{p,2}, …, _{p,U(p)}. The bits _{p,k} are mapped to the PhCHs such that the bits for each PhCH are transmitted over the air in ascending order with respect to k.
During compressed frames in the uplink and when E‑DCH TTI is 10 ms:
– For the initial transmission the bits shall be consecutively mapped to the non‑idle slots. The UE shall not map any bit to the E‑DPDCH idle slots specified in 4.4.5.1.
– In case a retransmission occurs in a compressed frame or a retransmission occurs in a non‑compressed frame for which initial transmission was compressed:
– If n_{tx1}>n_{max}: The bits shall be consecutively mapped to the n_{max} available slots. The remaining bits are not transmitted.
– If n_{tx1}n_{max}: The bits shall be consecutively mapped to the n_{tx1} non‑idle slots, whilst no bits are mapped to the idle slots.
– The transmission gap position and the parameters n_{tx1} and n_{max} are specified in 4.4.5.2.