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7/27/2019 03 Channel Structure and Function 44
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WR_BT03_E1_1
Channel Structure and Function
ZTE University
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Objectives
• At the end of this course, you will be able to
master:
– Classification of channels
– Structure and Function of channels
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Classification of channels
Structure and Function of channels
Physical layer procedure
Content
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RNS RNS
CN
RNC RNC
Iu Iu
Iur
Iub Iub Iub Iub
Architecture of UMTS
UE
NodeB NodeB NodeB NodeB
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Channel Type
Physical channel Transport channel
Logical channel
Node BRNC
Physical channel
Transport channel
Logical channel
UE
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Concept of channel
PHY layer
MAC layer
RLC layer
Transport channel
Physical channel
Logical channel
L1
L2
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Channel Type
Logical channels: Describe what is transported (i.e., the information to
be transmitted)
Transport channels:
Describe how the logical channels are to betransmitted.
Physical channels:
Represent the “transmission media” providing the
platform through which the information is actually
transferred.
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Protocol stack of the Uu interface
L3
c o n t r o l
c o n t r o l
c o n t r o l
c o n t r o l
Logical
Channels
Transport
Channels
C-plane signalling U-plane information
PHY
L2/MAC
L1
RLC
DCtGC
L2/RLC
MAC
RLCRLC
RLCRLC
RLC
RLCRLC
Duplication avoidance
UuS boundary
BMCL2/BMC
control
PDCPPDCP L2/PDCP
DCtGC
Radio
Bearers
RRC
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Logical Channels
Control Channel (CCH) Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
Dedicated Control Channel (DCCH)
Common Control Channel (CCCH)
Traffic Channel (TCH)Dedicated Traffic Channel (DTCH)
Common Traffic Channel (CTCH)
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Transport Channel
Random Access Channel (RACH)
Broadcast Channel (BCH) Paging Channel (PCH)
Forward Access Channel (FACH) Common Packet Channel (CPCH)
Common Transport Channels
Dedicated Transport Channels Downlink Shared Channel (DSCH) Dedicated Channel (DCH)
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Physical Channel
Dedicated Physical Channel (DPCH)
Physical Random Access Channel (PRACH) Physical Common Packet Channel (PCPCH)
Uplink Physical Channels
Secondary Common Control Physical Channel (S-CCPCH)
Common Pilot Channel (CPICH)
Primary Common Control Physical Channel (P-CCPCH)
Synchronization Channel (SCH)
Physical Downlink Shared Channel (PDSCH)
Downlink Physical Channels
Acquisition Indication Channel (AICH)
Page Indication Channel (PICH)
Dedicated Physical Channel (DPCH)
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Logic
Channel
Transport
Channel
CCCH DCCH DTCH
RACH CPCH DCH
Uplink Downlink
PCCH BCCH DCCH DTCH CCCH CTCH
PCH BCH FACH DSCH DCH
Mapping relationship
Transport
Channel
CCCH DCCH DTCH
RACH CPCH DCH
Uplink Downlink
PCCH BCCH DCCH DTCH CCCH CTCH
PCH BCH FACH DSCH DCH
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Mapping relationship
Transport Channels DCH
RACH CPCH
BCH FACH PCH DSCH
Physical Channels Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH) Physical Random Access Channel (PRACH) Physical Common Packet Channel (PCPCH) Common Pilot Channel (CPICH) Primary Common Control Physical Channel (P-CCPCH) Secondary Common Control Physical Channel (S-CCPCH)
Synchronization Channel (SCH) Physical Downlink Shared Channel (PDSCH) Acquisition Indication Channel (AICH) Page Indication Channel (PICH)
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Classification of channels
Structure and Function of channels
Physical layer procedure
Content
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WCDMA frame structure
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Physical Channels(1)
The physical channel is in a 3-layer structure by thetime:
Superframe
One superframe lasts 720ms, and consists of 72 radio
frames.
radio frame
One radio frame has a period of 10ms, and comprises
15 timeslots with the same length. Corresponding to
38400 chips, it is a basic unit of the physical layer.
Timeslot A timeslot is a unit composed of a bit domain,
corresponding to 2560 chips. The bit number and
structure of a timeslot depends on the specific type of
the physical channel.
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Physical Channels(2)
The frame structure of the physical channels is shown:
Tslot #1 Tslot #2 Tslot #I Tslot #15
Ttimeslot= 2560 chip
Frame #0 Frame #1 Frame #I Frame #71
Tframe=10 ms
Tsuperframe=720 ms
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Uplink physical channel
2 UL Dedicated physical channel (DPDCH andDPCCH)
2 UL Common physical channel (PRACH and
PCPCH)
UL Common physical
channel
UL Dedicated physical
channel
Dedicated physical
Control channel DPCCH
Dedicated physical
data channelDPDCH
Physical random Access channel
PRACH
Physical common
Packet channel
PCPCH
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Uplink Dedicated physical channel
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PRACH
Physical Random Access Channel PRACH consists preamble part and message part
Random access transmit 1or more 4096 chips length
preambles and 10ms or 20ms length message part.
Message partPreamble
4096 chips 10 ms (one radio frame)
Preamble Preamble
Message partPreamble
4096 chips 20 ms (two radio frames)
Preamble Preamble
PRACH transmitted structure
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PRACH
Physical Random Access Channel
10ms message part is split into 15 timeslots, each timeslot
consists of 2560chips.
Each timeslot includes data part and control part. They are
transmitted in parallel .
Data part :SF=32~256 , control part: SF=256.
PilotNpilot bits
DataNdata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 10*2
k
bits (k=0..3)
Message part radio frame TRACH = 10 ms
Data
ControlTFCI
NTFCI bits
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Downlink physical channel
DL physical channel include Dedicated physicalchannel、1 Shared physical channel and five
Common control channels.
DPCH
SCH
CPICH
PICH
AICH
CCPCH
PDSCH
DL common physical
channel
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Downlink dedicated physical channel
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CPICH
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CPICH
There is 2 types of CPICH:P-CPICH and S-PICH
P-CPICH: P-CPICH of different cell uses the same Cch,256,0 OVSF code to
spread ,the bit rate of P-CPICH is also fixed.
The P-CPICH is scrambled by the primary scrambling code.
There is one and only P-CPICH per cell.
The P-CPICH is broadcast over the entire cell. it is used to
search cell primary scrambling code during cell selection procedure. And it is also
used for measurement and estimation during handover, cellselection and cell re-selection.
S-CPICH:
A arbitrary channelization code of SF=256 is used for the S-CPICH.
A S-CPICH is scrambled by either the primary or a secondaryscrambling code.
There may be 0,1 or several S-CPICH per cell.
A S-CPICH may be transmitted over the entire cell or part of thecell. It is may be a phase reference for a dl DPCH, but it isdecided by high layer signalling.
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P-CCPCH
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SCH (1)
The Synchronization Channel (SCH) is a downlink signal used
for cell search.
The SCH consists of two sub channels, the Primary and
Secondary SCH.
The 10 ms radio frames of the Primary and Secondary SCH
are divided into 15 slots, each of length 2560 chips.
Structure of synchronization channel
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SCH (2)
P-SCH
The Primary SCH consists of a modulated code of length256 chips. The modulated code need not spreading andscrambling.
The primary synchronization code (PSC) is transmittedonce every slot
The PSC is the same for every cell in the system.
S-SCH
The Secondary SCH consists of repeatedly transmitting alength 15 sequence of modulated codes of length 256 chips.
the Secondary Synchronization Codes (SSC), transmittedin parallel with the Primary SCH.
Each SSC is chosen from a set of 16 different codes of length 256.
This sequence on the Secondary SCH indicates which of the code groups the cell's downlink scrambling codebelongs to.
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S-CCPCH
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PICH
PICH carries PI(
Page Indication),
SF=256,
radio frame=10ms,consists 300bits,288 bits for
paging indication,12 bits Tx Off 。
PICH relates to S-CCPCH which mapping to PCH。
b1b0
288 bits for paging indication12 bits (transmission
off
One radio frame (10 ms)
b287 b288 b299
PICH frame structure
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Classification of channels
Structure and Function of channels
Physical layer procedure
Content
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Cell Search
UE has to get the system information before itregisters with the network and access to services.
The system information is beared in the BCH
channel, and its data is mapped into the Primary
CCPCH.
So the cell search procedure is mainly to decode the
data of P-CCPCH.
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Cell search procedure (1)
The cell search is typically carried out in three steps: Step1: Slot synchronization
During the first step of the cell search procedure the
UE uses the SCH channel's primary synchronization
code to acquire slot synchronization to a cell.
This is typically done with a single matched filter (or
any similar device) matched to the primary
synchronization code which is common to all cells.
The slot timing of the cell can be obtained by
detecting peaks in the matched filter output.
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Sketch of Slot Synchronization
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Cell search procedure (2)
Step2: Frame synchronization and code-groupidentification
During the second step of the cell search procedure,
the UE uses the SCH channel's secondary
synchronization code to find frame synchronization
and identify the code group of the cell found in thefirst step.
This is done by correlating the received signal with all
possible secondary synchronization code sequences,
and identifying the maximum correlation value. Since
the cyclic shifts of the sequences are unique the code
group as well as the frame synchronization is
determined.
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…
Downlink Scrambling Code Grouping
No. 511 Scrambling Code Group
8176
8177
8191
8176:PSC
8177:SSC
…
8191:SSC
No. 510 Scrambling Code Group
81608161
8175
8160:主扰码 8161:辅扰码
…
8175:辅扰码
No. 504 Scrambling Code Group
8064
8065
8079
8064:主扰码
8065:辅扰码
…
8079:辅扰码
…
No. 7 Scrambling Code Group
112
113
127
8176:PSC
8177:辅扰码
…
8191:辅扰码
No. 1 Scrambling Code Group
16
17
31
16:PSC
17:SSC
…
31:SSC
No. 0 Scrambling Code Group
0
1
15
0:PSC
1:SSC
…
15:SSC
No.63 Primary Scrambling Code Group
… …
No.0 Primary Scrambling Code Group
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Mapping of the Secondary Synchronization Code
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Cell search procedure (3)
Step3: Scrambling-code identification
During the third and last step of the cell search
procedure, the UE determines the exact primary
scrambling code used by the cell.
The primary scrambling code is typically identified
through symbol-by-symbol correlation over the CPICHwith all codes within the code group identified in the
second step.
After the primary scrambling code has been
identified, the Primary CCPCH can be detected sothat the cell specific BCH information can be read.
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Cell search procedure
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Summary of the process
Channel Synchronizationacquired
Note
Primary SCH Chip, Slot, Symbol
Synchronization
Synchronization 256 chips
The same in all cells
Secondary
SCH
Frame Synchronization,
Code Group
(one of 64)
15-code sequence of secondary synchronizationcodes. There are 16 secondary synchronization
codes. There are 64 S-SCH sequences
corresponding to the 64 scrambling code groups
256 chips, different for different cells and slot
intervals
Common
Pilot CH
Scrambling code (one of 8) To find the primary scrambling code from common
pilot CH
PCCPCH Synchronization,
BCCH info
Fixed 30 kbps channel spreading factor 256
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RACH procedure
UE decodes BCH to find out the available RACH sub-channels
and their scrambling codes and signatures
It selects randomly one of the available sub-channels and
signatures
The downlink power is measured and the initial RACH power
level is set with a proper margin due to open loop inaccuracy
UE transmits 1 ms long preamble with the selected signature
Node B replies by repeating the preamble using Acquisition
Indication Channel (AICH)
UE decodes AICH message to see whether the NodeB has
detected the preamble If AICH is not detected, the preamble is resend with 1 dB
higher transmit power
If AICH is detected, a 10 or 20 ms long message part is
transmitted with the same power as the last preamble
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RACH procedure
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Exercise
pls write down the 3 types of channel and describe
their mapping relations.
One radio frame has a period of ( )ms, and
comprises( ) timeslots with the same length.
Corresponding to ( ) chips, it is a basic unit of the
physical layer.
pls describe the main function of each physical
channel.
pls describe the cell search procedure.
pls describe RACH procedure.
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