6 Physical layer structure
25.2023GPP7.68 Mcps Time Division Duplex (TDD) optionOverall description: Stage 2Release 17TS
6.0 Services offered to higher layers
The 7.68Mcps TDD option supports an identical set of transport channels and indicators to the 3.84Mcps TDD option.
6.1 Frame structure
The 7.68Mcps TDD option frame is of length 10ms and consists of 15 timeslots of duration 5120 * Tc, where Tc is the chip duration (Tc = 1 / 7.68 * 106 = 130.2ns). Any timeslot in the frame can be either uplink or downlink. At least one timeslot in the frame is assigned to the uplink and at least one timeslot in the frame is assigned to the downlink. The frame structure is shown in Figure 6.1.1.
Figure 6.1.1: The 7.68Mcps TDD option frame structure
6.2 Burst structure
The 7.68Mcps burst consists of two data field portions, a midamble portion containing a training sequence and a guard period as shown in Figure 6.2.1. Several bursts can be transmitted at the same time where each burst uses a different OVSF channelisation code, but the same scrambling code.
Figure 6.2.1: 7.68Mcps TDD option burst structure
Three burst types are specified: burst types 1, 2 and 3. The maximum number of training sequences supported in burst types 1 and 3 is either 4, 8 or 16 depending on cell configuration and either 4 or 8 for burst type 2 depending on cell configuration. The lengths of the fields within each burst are defined in Table 6.2.1.
Table 6.2.1: Number of chips within fields of the 7.68Mcps burst
|
Field |
Burst Type 1 |
Burst Type 2 |
Burst Type 3 |
|
Data field 1 |
1952 |
2208 |
1952 |
|
Midamble |
1024 |
512 |
1024 |
|
Data field 2 |
1952 |
2208 |
1760 |
|
Guard Period |
192 |
192 |
384 |
On the downlink, a spreading factor of 32 is supported. Additionally for DPCH, PDSCH and HS-PDSCH, a spreading factor of 1 is supported on the downlink.
On the uplink, spreading factors of 1, 2, 4, 8, 16 and 32 are supported for DPCH, PUSCH and E-PUCH. PRACH and E-RUCCH only support spreading factors 16 and 32 and HS-SICH only supports spreading factor 32.
The spreading factors and burst types supported for different physical channels are defined in Table 6.2.2.
Table 6.2.2: Spreading factors and burst types supported by physical channels
|
Physical channel |
Supported spreading factors |
Supported burst types |
|
UL DPCH |
1, 2, 4, 8, 16, 32 |
1, 2, 3 |
|
DL DPCH |
1, 32 |
1, 2 |
|
P-CCPCH |
32 |
1 |
|
S-CCPCH |
32 |
1, 2 |
|
PRACH |
16, 32 |
3 |
|
PUSCH |
1, 2, 4, 8, 16, 32 |
1, 2, 3 |
|
PDSCH |
1, 32 |
1, 2 |
|
HS-PDSCH |
1, 32 |
1, 2 |
|
HS-SCCH |
32 |
1, 2 |
|
HS-SICH |
32 |
1, 2 |
|
E-PUCH |
1, 2, 4, 8 ,16, 32 |
1, 2, 3 |
|
E-AGCH |
32 |
1, 2 |
|
E-HICH |
32 |
1, 2 |
|
E-RUCCH |
16, 32 |
3 |
Transmission of TPC and TFCI are performed in accordance with the general procedures used for the existing 3.84 Mcps TDD option. Due to the maximum spreading factor being increased from 16 (3.84Mcps) to 32 (7.68Mcps), usage of SF16 for TPC/TFCI is replaced with SF32 where appropriate.
6.3 Midambles
Midambles for burst types 1, 2 and 3 are created using the method applied for 3.84Mcps TDD. The basic midamble code for burst types 1 and 3 is of length 912; for burst type 2 the basic midamble code is of length 456.
Default, common and UE specific midamble modes are supported in the 7.68Mcps TDD option. The characteristics of these midamble allocations at 7.68Mcps are identical to their characteristics at 3.84Mcps. The number of active channelisation codes is signaled via midamble through an extension of the scheme applied at 3.84Mcps TDD (the extension accounts for the higher spreading factor supported at 7.68Mcps).
Midamble transmit powers are allocated as for 3.84Mcps TDD.
The association between midambles and channelisation codes for burst types 1, 2 and 3 are as shown in figure 6.3.1 for Kcell = 16, figure 6.3.2 for Kcell = 8 and figure 6.3.3 for Kcell = 4. Secondary channelisation codes are marked with a *. These associations apply both for UL and DL.
Figure 6.3.1: Association of Midambles to Spreading Codes for KCell = 16
Figure 6.3.2: Association of Midambles to Spreading Codes for KCell = 8
Figure 6.3.3: Association of Midambles to Spreading Codes for KCell = 4
For PRACH and E-RUCCH, up to 16 midambles and channelisation codes may be supported. The training sequences, i.e. midambles, of different users active in the same time slot are time shifted versions of a basic midamble code, m1, or a second basic midamble code, m2, which is a time inverted version of the basic midamble code m1. A fixed association exists between PRACH/E-RUCCH midambles and channelisation codes.
6.4 Coding and Modulation
Multiplexing and channel coding is aligned with 3.84Mcps TDD with the exception that physical channel sequence numbering and the coding of the channelisation code set information on HS-SCCH and E-AGCH shall account for the support of SF32 at 7.68Mcps.
6.5 Scrambling Codes
The binary scrambling code, , for cell parameter n in the 7.68Mcps TDD option is formed from the concatenation of the binary scrambling codes and shown in Annex A of [4].
6.6 Synchronisation Codes
The synchronisation codes for the 7.68Mcps TDD option are formed by repetition coding of the 3.84Mcps TDD synchronisation code words. Unique modulation sequences are applied to these code words that enable the UE to determine the code group, frame alignment and chip rate of the cell.
The synchronization channel (SCH) is constructed in an identical manner to the construction at 3.84Mcps. The relationship between code group, n, and toffset,n at 7.68Mcps is:
6.7 Transmit diversity
Support for beamforming and transmit diversity are aligned with the 3.84Mcps TDD option.
6.8 Measurements
6.9 Indicator Channels
6.9.1 Paging Indicator Channel (PICH)
The paging indicator channel is spread at SF32, but in other respects is identical to the 3.84Mcps TDD PICH [2].
The PICH block may comprise up to NPICH = 8 frames. The PCH block may comprise up to 2 × NPCH = 2 × 16 frames.
6.9.2 MBMS Indicator Channel (MICH)
The MBMS indicator channel is spread at SF32, but in other respects is identical to the 3.84Mcps TDD MICH [2].
6.10 Mapping of transport channels to physical channels
In the 7.68Mcps TDD option, transport channels are mapped onto physical channels according to figure 6.10.1.
|
Transport Channels |
Physical Channels |
|
DCH |
Dedicated Physical Channel (DPCH) |
|
BCH |
Primary Common Control Physical Channel (P-CCPCH) |
|
FACH |
Secondary Common Control Physical Channel (S-CCPCH) |
|
PCH |
|
|
RACH |
Physical Random Access Channel (PRACH) |
|
USCH |
Physical Uplink Shared Channel (PUSCH) |
|
DSCH |
Physical Downlink Shared Channel (PDSCH) |
|
Paging Indicator Channel (PICH) |
|
|
MBMS Indication Channel (MICH) |
|
|
Synchronisation Channel (SCH) |
|
|
HS-DSCH |
High Speed Physical Downlink Shared Channel (HS-PDSCH) |
|
Shared Control Channel for HS-DSCH (HS-SCCH) |
|
|
Shared Information Channel for HS-DSCH (HS-SICH) |
|
|
E-DCH |
E-DCH Physical Uplink Channel (E-PUCH) |
|
E-DCH Random Access Uplink Control Channel (E-RUCCH) |
|
|
E-DCH Absolute Grant Channel (E-AGCH) |
|
|
E-DCH Hybrid ARQ Indicator Channel (E-HICH) |
Figure 6.10.1: Transport channel to physical channel mapping
The mapping between DCH, BCH, FACH, USCH and DSCH transport channels to physical channels is identical to the mapping at 3.84Mcps TDD.
The mapping between the RACH transport channel and the PRACH physical channel is identical to the mapping at 3.84Mcps TDD.
The mapping between the HS-DSCH transport channel and HS-PDSCH physical channels is identical to the mapping at 3.84Mcps TDD. The association and timing between HS-SCCH, HS-DSCH and HS-SICH is identical to the association and timing at 3.84Mcps TDD with the exception that the UE must monitor up to a maximum of eight HS-SCCH (M=8).
The mapping between the E-DCH transport channel and E-PUCH physical channels is identical to the mapping at 3.84Mcps TDD. The association and timing between E-AGCH, E-PUCH and E-HICH is identical to the association and timing at 3.84Mcps TDD with the exception that up to two channelisation codes for E-HICH are supported for the 7.68Mcps option.
The mapping of E-DCH control information to E-RUCCH when E-PUCH resources are unavailable is identical to that for 3.84Mcps TDD.