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AMR 5.15 49 54 0 103
AMR 4.75 42 53 0 95
AMR SID 39 0 0 39
6.13 ADAPTIVE MULTIRATE (AMR) CODEC 325


Table 6.13 12.2 kbps transport format parameters
No. of TrChs 3 Comments
Transport block size TrCh 1 0, 39, 81 bits Class A
TrCh 2 103 bits Class B
TrCh 3 60 bits Class C
TFCS 1 1*81, 1*103, 1*60 12.2 kbps speech
2 1*39, 0*103, 0*60 SID
3 1*0, 0*103, 0*60 DTX
1/3 rate convolution + 12-bit CRC
Error protection TrCh 1
TrCh 2 1/3 rate
TrCh 3 1/2 rate
TTI 20 ms



Application
AMR CODEC


A B C
DTCH

RB5 RB6 RB7

RLC



MAC



TB1 TB2 TB3
DCH
TrCh1 TrCh2 TrCh3

Physical




TB1 TB2 TB3
DPDCH
CCTrCH

TFCI
DPCCH


Figure 6.61 Flow of AMR CODEC through the radio link protocol stack

one user listens as the other speaks. In addition, normal speech is punctuated with silent
gaps. All the CODECs also work on silence suppression, where a voice activity detector
determines if the user is silent and whether speech frames should be sent or not. If the
system merely went dead when users ceased talking, it would be rather disconcerting for
the listener; therefore as a reassurance, the receiver side will introduce comfort noise. To
326 UNIVERSAL MOBILE TELECOMMUNICATIONS SYSTEM


assist in the generation of this comfort noise, a Silence Descriptor (SID) frame at a low
rate is sent. This is particularly applicable to environments where there is a relatively
high level of background noise such as, for example, in a car, or if the user has a
radio on.
Since the three classes of bits require different levels of error protection, this means
that their QoS pro¬les are different and cannot therefore be combined at the MAC layer.
This means that each requires a different transport channel (TrCh) which is combined at
the physical layer into a CCTrCH. For simplicity consider only the 12.2 kbps rate, with
the SID. The transport format information is as shown in Table 6.13.
There will be three radio bearers established, each using RLC transparent mode since the
segmentation and reassembly function is not required. At the MAC layer, three different
transport formats are de¬ned for the different error protection schemes, with three transport
blocks delivered to the physical layer every 20 ms. The physical layer performs the CRC
attachment for class A bits, the convolution coding and the rate matching, and combines
all these into a CCTrCH. This process is summarized in Figure 6.61. Note that radio
bearers (RB) 5, 6 and 7 have been chosen for this example.



6.14 CALCULATED TRANSPORT FORMAT
COMBINATIONS

When a connection is established, the RNC must inform both the BTS and the UE of
the parameters for the new or recon¬gured radio link. Part of this parameter set is the
range of permitted transport format combinations, and the identi¬er of each. UMTS pro-
vides a simple, ef¬cient mechanism for transfer of this information through the calculated
transport format combination (CTFC). The CTFC is calculated as follows. Consider that
there are I transport channels (TrCH) that make up the TFC, and that each of these has
L tranport formats, where the TFI of the channel will be TFI = 0, 1, 2, . . ., L ’ 1. For
a given TFC, that is TFC = (TFI1 , TFI2 , . . . , TFII ), the CTFC is calculated as:
I
CTFC = TFIi • Pi
i=1

Where:
i’1
Pi = Lj
j =0

And in this calculation, L0 = 1.
The mathematics here may appear somewhat unwieldy; however, the following example
illustrates their calculation. Consider that a user wishes to make a voice call and that
the network establishes a radio link for this, plus an associated signalling channel. As
discussed, the AMR CODEC generates class A, B and C bits, which each require their own
TrCH, since the QoS pro¬les are different. Therefore, there are four channels established,
three for the call and one for signalling.
6.14 CALCULATED TRANSPORT FORMAT COMBINATIONS 327



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 - - -


Figure 6.62 AMR CODEC transport formats

The voice channels are as shown in Table 6.12, with the inclusion of the signalling
bearer, which is a 3.4 kbps channel, with a TB size of 148 bits sent in a 20 ms TTI. The
transport formats are as shown in Figure 6.62.
The permitted combinations are DTX, SID, 12.2 kbps, signalling, SID + signalling,
12.2 kbps + signalling, as shown in Figure 6.63.
The CTFCs are calculated as follows:

TFC = (TFITrCH1 — L0 ) + (TFITrCH2 — L0 — LTrCH1 )
+ (TFITrCH3 — L0 — LTrCH1 — LTrCH2 )
+ (TFITrCH4 — L0 — LTrCH1 — LTrCH2 — LTrCH3 )

Ignoring L0 since it is always 1, this yields the results shown in Table 6.14.

TFCI TFITrCH1 TFITrCH2 TFITrCH3 TFITrCH4 Explanation


1 0 0 0 0 DTX

2 1 0 0 0 SID

3 2 1 1 0 12.2kbps

4 0 0 0 1 Signalling

5 1 0 0 1 SID+signalling


6 2 1 1 1 12.2kbps+signalling


Figure 6.63 Transport format combinations
328 UNIVERSAL MOBILE TELECOMMUNICATIONS SYSTEM


Table 6.14 Calculation of CTFC
TFCI Calculation CTFC
(0) + (0 — 3) + (0 — 3 — 2) + (0 — 3 — 2 — 2)
1 0
(1) + (0 — 3) + (0 — 3 — 2) + (0 — 3 — 2 — 2)
2 1
(2) + (1 — 3) + (1 — 3 — 2) + (0 — 3 — 2 — 2)
3 11
(0) + (0 — 3) + (0 — 3 — 2) + (1 — 3 — 2 — 2)
4 12
(1) + (0 — 3) + (0 — 3 — 2) + (1 — 3 — 2 — 2)
5 13
(2) + (1 — 3) + (1 — 3 — 2) + (1 — 3 — 2 — 2)
6 23


This means that only these six numerical identi¬ers need to be sent, from which the
table of transport formats can be constructed.



6.15 USE OF DSCH
The downlink shared channel is used in CELL-DCH mode see Section 6.16.1, and can
provide extra variable data rate to a user. For variable rates, it can be more ef¬cient to
allocate many users to share the bandwidth of the DSCH. Consider the following example
for a video streaming application (Sallent et al., 2003). The service provides a basic rate
of 32 kbps which is allocated on a dedicated channel, DSCH. In addition, an enhanced
service at higher rate is allocated on the DSCH, which can vary between an additional
0“128 kbps. This allows the video rate to vary between a minimum of 32 kbps and a
maximum of 140 kbps. This allocation can support a basic service delivery through the
dedicated channel, and then supplement this on the DSCH when resources are available.
However, the service can guarantee that at least 32 kbps will be provided.
For Release 5 of UMTS, the speci¬cation allows for use of advanced transmission
techniques and the introduction of the 16-QAM (quadrature amplitue modulation) scheme
to allow the DSCH to achieve data rates of up to around 10 Mbps. This scheme is referred
to as high-speed downlink packet access (HSDPA).



6.16 RADIO RESOURCE CONTROL (RRC)

RRC is the radio network control protocol and provides the functions related to manage-
ment and control of the radio network transmission resources such as the MAC, RLC
and PDCP layers, etc. The primary purpose of RRC procedures is to establish, maintain
and release radio resource connections between the mobile device and the network. Its
functions include such things as handover procedures and cell reselection. RRC is the
control protocol between the UE and the RNC. The major functions provided by RRC
are listed in Table 6.15.
RRC must interact with each layer to provide control information, and in turn receive
measurement feedback from the layers. Between the UE and UTRAN, RRC is responsible
for the establishment of radio bearers for both transport of signalling and traf¬c, and
6.16 RADIO RESOURCE CONTROL (RRC) 329


Table 6.15 RRC functions
Radio resource control functions
System information broadcast
Establishment, maintenance and release of RRC connection between UE and UTRAN
Assignment, recon¬guration and release of radio bearers
RRC connection mobility
Paging
Outer loop power control
Ciphering control
UE measurement and reporting


UTRAN UE
Radio Resource
Assignment
RRC RRC
Measurement
Reporting
Control




Control
Signalling RBs Signalling RBs
Measurements




Measurements
Control




Control
Retransmission
RLC RLC
Control
Measurements




Measurements
MAC MAC

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