Introduction
Whenever new transport channels
are established then RNC has to inform both the NodeB and the UE about the
permitted transport format combinations. The Calculated Transport Format
Combination (CTFC) is a tool for efficient signalling of transport format
combinations.
Let I be the number of transport
channels that are included in the transport format combination. Each
transport channel TrCHi, i = 1, 2, …, I, has Li transport
formats, i.e. the transport format indicator TFIi can take Li values,TFIi ε
{0,1,2,...,Li-1}
Pi =
|
i-1
∏
j = 0
|
Lj ,
where i=1,2,...,I and L0=1
|
Let TFC(TFI1, TFI2,
…, TFII) be the transport format combination for which TrCH1 has
transport format TFI1, TrCH2 has transport format
TFI2, etc. The corresponding CTFC(TFI1, TFI2,
…, TFII) is then computed as:
For FACH and PCH transport
channels, "TrCH1" corresponds to the transport channel
listed at the first position in IE "FACH/PCH information" in IE
"Secondary CCPCH System Information", "TrCH2"
corresponds to the transport channel listed at the second position in IE
"FACH/PCH information" and so on.
For all other transport channels
in FDD and for all configured transport channels of the same transport
channel type (i.e. DCH, DSCH, USCH) in TDD, "TrCH1"
corresponds to the transport channel having the lowest transport channel
identity in the transport format combination mapped to the TFCI field.
"TrCH2" corresponds to the transport channel having the
next lowest transport channel identity, and so on.
Examples
To understand the above
mathematical equations better, lets take couple of examples
AMR Codec
This example is specified in [2]
in more detail. Also for details about the conversational speech CS RAB in
this example see section 6.10.3.4.1.4 in [4].
In case of a voice call being
setup, the network will make use of an AMR codec. In the AMR codec, there are
3 transport channels to support class A, B and C bits. Also one transport
channel is required to support signalling. Hence we can represent the
transport formats as shown in the table below:
|
AMR
|
Signalling
|
|
Class A
|
Class B
|
Class C
|
|
|
TrCH1
|
TrCH2
|
TrCH3
|
TrCH4
|
L
|
3
|
2
|
2
|
2
|
TFI
|
|
|
|
|
0
|
0
|
0
|
0
|
0
|
1
|
81
|
103
|
60
|
148
|
2
|
39
|
-
|
-
|
-
|
The permitted transport format
combinations are in table below:
TFCI
|
TFI1
|
TFI2
|
TFI3
|
TFI4
|
Explanation
|
1
|
0
|
0
|
0
|
0
|
DTX
|
2
|
1
|
0
|
0
|
0
|
SID
|
3
|
2
|
1
|
1
|
0
|
12.2 Kbps
|
4
|
0
|
0
|
0
|
1
|
Signalling
|
5
|
1
|
0
|
0
|
1
|
SID + Signalling
|
6
|
2
|
1
|
1
|
1
|
12.2kbps + signalling
|
The CTFC for the permitted
combinations will now be calculated as follows:
CTFC for TFCI 1 = (0) + (0*3) +
(0*3*2) + (0*3*2*2) = 0
CTFC for TFCI 2 = (1) + (0*3) +
(0*3*2) + (0*3*2*2) = 1
CTFC for TFCI 3 = (2) + (1*3) +
(1*3*2) + (0*3*2*2) = 11
CTFC for TFCI 4 = (0) + (0*3) +
(0*3*2) + (1*3*2*2) = 12
CTFC for TFCI 5 = (1) + (0*3) +
(0*3*2) + (1*3*2*2) = 13
CTFC for TFCI 6 = (2) + (1*3) +
(1*3*2) + (1*3*2*2) = 23
The following CTFC will now be
sent in the Radio Bearer Setup message: CTFC6,0, CTFC6,1,
CTFC6,11, CTFC6,12, CTFC6,13 and CTFC6,23.
Six bits will be required to send the CTFC from which the table of transport
formats can be contructed by the UE.
PS Data Transfer
Now we take an example of 128Kbps
Interactive or background PS RAB with signalling. We need only one transport
channel for the PS RAB and one transport channel for signalling. The
transport formats are shown in the table below:
|
PS RAB 128 Kbps
|
Signallling
|
|
TrCH1
|
TrCH2
|
L
|
5
|
2
|
TFI
|
|
|
|
0*336
|
0
|
|
1*336
|
148
|
|
2*336
|
-
|
|
4*336
|
-
|
|
8*336
|
-
|
The permitted transport format
combinations are in table below:
TFCI
|
TFI1
|
TFI2
|
|
|
|
1
|
0
|
0
|
|
|
|
2
|
1
|
0
|
|
|
|
3
|
2
|
0
|
|
|
|
4
|
3
|
0
|
|
|
|
5
|
4
|
0
|
|
|
|
6
|
0
|
1
|
|
|
|
7
|
1
|
1
|
|
|
|
8
|
2
|
1
|
|
|
|
9
|
3
|
1
|
|
|
|
10
|
4
|
1
|
|
|
|
The CTFC for the permitted
combinations will now be calculated as follows:
CTFC for TFCI 1 = (0) + (0*5) = 0
CTFC for TFCI 2 = (1) + (0*5) = 1
CTFC for TFCI 3 = (2) + (0*5) = 2
CTFC for TFCI 4 = (3) + (0*5) = 3
CTFC for TFCI 5 = (4) + (0*5) = 4
CTFC for TFCI 6 = (0) + (1*5) = 5
CTFC for TFCI 7 = (1) + (1*5) = 6
CTFC for TFCI 8 = (2) + (1*5) = 7
CTFC for TFCI 9 = (3) + (1*5) = 8
CTFC for TFCI 10 = (4) + (1*5) = 9
The following CTFC will now be
sent in the Radio Bearer Setup message: CTFC4,0, CTFC4,1,
CTFC4,2, CTFC4,3, CTFC4,4, CTFC4,5,
CTFC4,6, CTFC4,7, CTFC4,8, CTFC4,8,
CTFC4,9and CTFC4,10. Four bits will be required to send
the CTFC from which the table of transport formats can be contructed by the
UE.
References
[1] 3GPP TS 25.331: Radio Resource
Control (RRC) protocol specification
[4] 3GPP TS 34.108: Common test
environments for User Equipment (UE) conformance testing
|