6 Iu Interface User Plane (RAN)
26.2023GPPAdaptive Multi-Rate - Wideband (AMR-WB) speech codecInterface to Iu, Uu and NbRelease 17Speech codec speech processing functionsTS
The data structures exchanged on the Iu interface are symmetrical, i.e. the structure of the uplink data frames is identical to that of the downlink data frames. This facilitates Tandem Free Operation and Transcoder Free Operation.
6.1 Frame structure on the Iu UP transport protocol
6.1.1 Initialisation
At the initialisation of the SMpSDU mode of operation, several parameters are set by the CN. The initialisation procedure is described in 3GPP TS 25.415 [1].
– RFCS:
In the case of UMTS_AMR-WB, the RFCS corresponds to the Active Codec Set (ACS) plus SCR authorised in the communication. Annex A of [1] gives an illustration of the usage of RFCI for UMTS_AMR-WB speech RAB. RFCS used in downlink may differ from that in uplink.
– Delivery of erroneous SDUs:
This parameter shall be set to YES. Erroneous speech frames may be used to assist the error concealment procedures.
The PDU type 0 shall be used for the transport of AMR-WB data.
6.1.2 Time Alignment Procedure
The TC should adjust the timing of the speech data transmission in downlink direction according to the time alignment frame sent by the RNC.
Time alignment procedure shall be dismissed in case of TFO and TrFO.
6.2 Mapping of the bits
The mapping of the bits between the generic AMR-WB frames and the PDU is the same for both uplink and downlink frames.
The following table gives the correspondence of the bit fields between the generic AMR-WB frames at the TC interface and the PDU exchanged with the Iu transport layer.
Table 6-1: Mapping of generic AMR-WB frames onto Iu PDUs
|
PDU field |
Corresponding field within the |
Comment |
|
PDU Type |
N/A |
Type 0 |
|
Frame Number |
N/A |
|
|
FQC |
Frame Quality Indicator |
|
|
RFCI |
Frame Type |
|
|
Payload CRC |
N/A |
|
|
Header CRC |
N/A |
|
|
Payload Fields (N sub-flows) |
Class A or SID payload Class B |
|
|
SDU #1 |
Most important speech bits come first |
Mandatory |
|
SDU #2 |
Next bits follow |
Optional |
|
… |
… |
Optional |
|
SDU #N |
Least important speech bits |
Optional |
The number of RAB sub-flows, their corresponding sizes, and their attributes such as "Delivery of erroneous SDUs" shall be defined at the RAB establishment and signalled in the RANAP RAB establishment request, as proposed in clause 5. The number of RAB sub-flows are corresponding to the desired bit protection classes. The total number of bits in all sub-flows for one RFC shall correspond to the total number given in 3GPP TS 26.201, generic AMR-WB frame, format IF1, for the corresponding Codec Mode respectively Frame Type.
Table 6-2 gives three examples of sub-flow mapping, one for each allowed configuration.
The RFCI definition is given in order of increasing SDU sizes.
In all examples, the sub-flow mapping follows the class division of TS 26.201, with some slight modification: in order to support Blind Transport Format Detection the number of bits in RAB sub-flow 1 is sometimes increased slightly to include not only the Class A bits, but also one or two bits from Class B (the next bits in order of subjective importance according to TS 26.201) . Blind Transport Format Detection requires that RAB sub-flow1 has a different number of bits for each mode. As the 12.65, 15.85, and 23.85 modes all have 72 Class A bits, they would be not be distinguishable if only Class A bits were included in RAB sub-flow1.
– Example 1 describes Codec Type UMTS_AMR-WB, with the three lowest codec modes foreseen in the Active Codec Set (ACS) and provision for Source Controlled Rate operation (SCR).
– Example 2 describes Codec Type UMTS_AMR-WB as in example 1, with codec mode 15.85 in addition. The number of bits allocated to RAB sub-flow 1 in codec mode 15.85 is 73 in order to support Blind Transport Format Detection.
– Example 3 describes Codec Type UMTS_AMR-WB as in example 1, with codec mode 23.85 in addition. The number of bits allocated to RAB sub-flow 1 in codec mode 23.85 is 74 in order to support Blind Transport Format Detection.
Table 6‑2: Examples for UMTS_AMR-WB with SCR and two sub-flows, according to subjective class division indication of 3GPP TS 26.201
|
UMTS_AMR-WB |
RAB sub-flows |
Total number (Mandatory) |
Source rate |
|
|
RFCI |
RAB sub- flow 1 (Optional) |
RAB sub- flow 2 (Optional) |
||
|
Example 1 |
||||
|
1 |
40 |
0 |
40 |
AMR-WB SID |
|
2 |
54 |
78 |
132 |
AMR-WB 6.6 kbps |
|
3 |
64 |
113 |
177 |
AMR-WB 8.85 kbps |
|
4 |
72 |
181 |
253 |
AMR-WB 12.65 kbps |
|
Example 2 |
||||
|
1 |
40 |
0 |
40 |
AMR-WB SID |
|
2 |
54 |
78 |
132 |
AMR-WB 6.6 kbps |
|
3 |
64 |
113 |
177 |
AMR-WB 8.85 kbps |
|
4 |
72 |
181 |
253 |
AMR-WB 12.65 kbps |
|
5 |
73 |
244 |
317 |
AMR-WB 15.85 kbps |
|
Example 3 |
||||
|
1 |
40 |
0 |
40 |
AMR-WB SID |
|
2 |
54 |
78 |
132 |
AMR-WB 6.6 kbps |
|
3 |
64 |
113 |
177 |
AMR-WB 8.85 kbps |
|
4 |
72 |
181 |
253 |
AMR-WB 12.65 kbps |
|
5 |
74 |
403 |
477 |
AMR-WB 23.85 kbps |
6.3 Frame handlers
Iu PDU Frame handling functions are described in 3GPP TS 25.415. This sections describes the mandatory frame handling functions at the AMR-WB Generic frame interface.
6.3.1 Handling of frames from TC to Iu interface (downlink)
The frames from the TC in generic AMR-WB frame format IF1 are mapped onto the Iu PDU as follows.
6.3.1.1 Frame Quality Indicator
The Frame Quality Indicator (FQI) from the TC, respectively from the distant TFO partner, is directly mapped to the Frame Quality Classification (FQC) of the Iu frame according to Table 6-3.
Table 6‑3: FQI AMR-WBto FQC Iu PDU mapping
|
FQI AMR |
FQI value |
FQC PDU |
FQC value |
|
GOOD |
1 |
GOOD |
00 |
|
BAD |
0 |
BAD |
01 |
6.3.1.2 Frame Type
The received Frame Type Index l is mapped onto the RFCI j thanks to the assigned RFCS table: the correspondence between Codec Mode, Frame Type Index l and RFCI j is defined at RAB assignment.
6.3.1.3 Codec Mode Indication
The Codec Mode Indication is not used.
6.3.1.4 Codec Mode Request
Codec Mode Request (CMR) in downlink direction is forwarded to the rate control procedure when it changes, or when it is commanded so by the TC in case of TFO, see 3G TS 28.062.
6.3.1.5 Optional internal 8 bits CRC
The internal AMR-WB codec CRC is not used on the Iu interface.
6.3.1.6 Mapping of Speech or Comfort Noise parameter bits
Let us define the N payload fields of the N sub-flows for RFCI j as follow :
Ui(k) shall be the bits in sub-flow i, for k =1 to Mi
Mi shall be the size of sub-flow i, for i = 1 to N
d(k) shall be the bits of the speech or comfort noise parameters of the corresponding Frame Type 1 in decreasing subjective importance, as defined in the generic AMR-WB frame format IF1, see TS 26.201.
Then the following mapping in pseudo code applies:
U1(k) = d(k-1) with k = 1, … M1
U2(k) = d(k-1 + M1) with k = 1, … M2
U3(k) = d(k-1 + M2) with k = 1, … M3
…
UN(k) = d(k-1 + MN-1) with k = 1 … MN
6.3.2 Handling of frames from Iu interface to TC (uplink)
The uplink Iu frames are mapped onto generic AMR-WB frames, format IF1, as follows.
6.3.2.1 Frame Quality Indicator
At reception of Iu PDU the Iu frame handler function set the Frame Quality Classification according to the received FQC, Header-CRC check, and Payload-CRC check (see 25.415). AMR-WB Frame Type and Frame Quality Indicator are determined according to the following table:
Table 6‑4: FQC Iu PDU type 0 to AMR-WB FQI and AMR-WB Frame Type mapping
|
FQC |
FQC value |
Resulting |
FQI value |
Resulting |
|
GOOD |
00 |
GOOD |
1 |
from RFCI |
|
BAD |
01 |
BAD |
0 |
NO_DATA |
|
BAD Radio |
10 |
BAD |
0 |
from RFCI |
|
Reserved |
11 |
BAD |
0 |
Reserved |
6.3.2.2 Frame Type
The received RFCI j is mapped onto the Frame Type Index l thanks to the RFCS table.
6.3.2.3 Codec Mode Indication
The Codec Mode Indication is not used.
6.3.2.4 Codec Mode Request
The received Downlink Rate Control (DRC) command is mapped onto the Codec Mode Request (CMR) towards the AMR-WB Codec. In case a new DRC is received it is mapped into the corresponding CMR of the generic AMR-WB frame format. It is remembered by the TC until the next DRC is received. In each new frame that is sent to the AMR-WB Codec, the stored CMR is resent, in order to control the Codec Mode for the downlink direction.
6.3.2.5 Optional internal 8 bits CRC
The internal AMR-WB Codec CRC is not used on the Iu interface.
6.3.2.6 Speech and Comfort noise parameter bits
The speech and Comfort noise parameter bits are mapped from the sub-flows to the payload of the generic AMR-WB frames with the reverse function of subclause 6.3.1.6.