02- OWA200003 WCDMA Radio Interface Physical Layer ISSUE1.0

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Transcript of 02- OWA200003 WCDMA Radio Interface Physical Layer ISSUE1.0

Course code Course nameISSUE 1.0
The physical layer offers data transport services to higher layers.
The access to these services is through the use of transport channels via the MAC sub-layer.
The physical layer is expected to perform the following functions in order to provide the data transport service, for example Modulation and spreading/demodulation and despreading, Inner - loop power control ..etc.
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TS 25.201 Physical layer-general description
TS 25.211 Physical channels and mapping of
transport channels onto physical channels (FDD)
TS 25.212 Multiplexing and channel coding (FDD)
TS 25.213 Spreading and modulation (FDD)
TS 25.214 Physical layer procedures (FDD)
TS 25.308 UTRA High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2
TR 25.877 High Speed Downlink Packet Acces (HSDPA) - Iub/Iur Protocol Aspects
TR 25.858 Physical layer aspects of UTRA High Speed Downlink Packet Access
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Upon completion of this course, you will be able to:
Understand radio interface protocol Architecture
Understand key technology of UMTS physical layer
Understand UMTS physical layer procedures
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Chapter 2 Physical layer key technology
Chapter 3 Physical Layer Procedures
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UTRAN:UMTS Terrestrial Radio Access Network.
The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network through the Iu.
A RNS consists of a Radio Network Controller and one or more Node Bs. A Node B is connected to the RNC through the Iub interface.
Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network.
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MAC Services to upper layers
- Data transfer. This service provides unacknowledged transfer of MAC SDUs between peer MAC entities. This service does not provide any data segmentation. Therefore, segmentation/reassembly function should be achieved by upper layer.
- Reallocation of radio resources and MAC parameters. This service performs on request of RRC execution of radio resource reallocation and change of MAC parameters, i.e. reconfiguration of MAC functions such as change of identity of UE, change of transport format (combination) sets, change of transport channel type. In TDD mode, in addition, the MAC can handle resource allocation autonomously.
- Reporting of measurements. Local measurements such as traffic volume and quality indication are reported to RRC.
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Channel coding and multiplexing
Spreading and modulation
The data from MAC layer is sent to physical layer through transport channel. First the TBs are coded and then multiplexed and mapped to physical channel. Spreading and modulation process on physical channel before transmission. At last the data should be transmitted on physical channel in the air.
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Spreading consists of 2 steps
Channelization operationwhich transforms data symbols into chips. Thus increasing the bandwidth of the signal, The number of chips per data symbol is called the Spreading FactorSF.The operation is done by multiplying with OVSF code.
Scrambling operation is applied to the spreading signal .
Data bit
Chips after spreading
Spreading is applied to the physical channels. It consists of two operations. The first is the channelization operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. The number of chips per data symbol is called the Spreading Factor (SF). The second operation is the scrambling operation, where a scrambling code is applied to the spread signal.
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OVSF code is used as Channelization code
The channelization codes are uniquely described as Cch,SF,k, where SF is the spreading factor of the code and k is the code number, 0 k SF-1.
SF = 1
SF = 2
SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
The channelization codes of figure are Orthogonal Variable Spreading Factor (OVSF) codes that preserve the orthogonality between a user’s different physical channels. The OVSF codes can be defined using the code tree of the figure.
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Scrambling code period : 10ms ,or 38400 chips.
The code used for scrambling of the uplink DPCCH/DPDCH may be of either long or short type, There are 224 long and 224 short uplink scrambling codes. Uplink scrambling codes are assigned by higher layers.
For downlink physical channels, a total of 218-1 = 262143 scrambling codes can be generated. scrambling codes k = 0, 1, …, 8191 are used.
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Set 0
Set 1
……
8192 scrambling codes
A primary scrambling code and 15 secondary scrambling codes are
included in a set.
Group 0
……
512 primary scrambling codes
Each group consists of 8 primary scrambling codes
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Chapter 2 Physical layer key technology
Chapter 3 Physical Layer Procedures
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Section 1 Physical Channel Structure and Functions
Section 2 Channel Mapping
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WCDMA radio interface has three kinds of channels
In terms of protocol layer, the WCDMA radio interface has three channels: Physical channel, transport channel and logical channel.
Logical channel: Carrying user services directly. According to the types of the carried services, it is divided into two types: Control channel and service channel.
Transport channel: It is the interface of radio interface layer 2 and physical layer, and is the service provided for MAC layer by the physical layer. According to whether the information transported is dedicated information for a user or common information for all users, it is divided into dedicated channel and common channel.
Physical channel: It is the ultimate embodiment of all kinds of information when they are transmitted on radio interfaces. Each kind of channel which uses dedicated carrier frequency, code (spreading code and scramble) and carrier phase (I or Q) can be regarded as a dedicated channel.
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-The Dedicated Channel (DCH) is an uplink or downlink channel.
Broadcast channel (BCH)
Physical Channel
A physical channel is defined by a specific carrier frequency, code (scrambling code, spreading code) and relative phase.
In UMTS system, the different code (scrambling code or spreading code) can distinguish the channels.
Most channels consist of radio frames and time slots, and each radio frame consists of 15 time slots.
Two types of physical channel:UL and DL
Physical Channel
Frequency,code,phase
Now we will begin to discuss the physical channel. Physical channel is the most important and complex channel. A physical channel is defined by a specific carrier frequency,code and relative phase. In CDMA system, the different code (scrambling code or spreading code) can distinguish the channel. Most channels consist of radio frames and time slots, and each radio frame consist of 15 time slots. There are two types of physical channel:UL and DL. Let’s look at the uplink physical channel first.
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Synchronization Channel (SCH)
Downlink Physical Channel
Downlink physical channel is divided into downlink dedicated physical channel and downlink common physical channel. downlink common physical channel includes:
Common Control Physical CHannel(CCPCH)
Uplink Common Physical Channel
Uplink Physical Channel
Uplink physical channel is divided into uplink dedicated physical channel and uplink common physical channel. Uplink dedicated physical channel is divided into uplink dedicated physical data channel(UL DPDCH) and uplink dedicated physical common channel(UL DPCCH). Uplink common physical channel includes physical random access channel(PRACH) and physical common packet channel(PCPCH).
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SCH- Synchronisation Channel
PRACH-Physical random access channel
HS-SCCH-High speed share control channel
HS-PDSCH-High speed physical downlink share channel
High speed downlink share channels
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Two sub channels: P-SCH and S-SCH.
SCH is transmitted at the first 256 chips of every time slot.
PSC is transmitted repeatedly in each time slot.
SSC specifies the scrambling code groups of the cell.
SSC is chosen from a set of 16 different codes of length 256, there are altogether 64 primary scrambling code groups.
ac
s
i,0
p
ac
p
ac
p
ac
ac
s
i,1
Primary
SCH
Secondary
SCH
One 10 ms SCH radio frame
The Synchronisation Channel (SCH) is a downlink signal used for cell search. The SCH consists of two sub channels, the Primary and Secondary SCH.
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Fixed rate 30Kbps SF=256
The CPICH uses the same channel and scrambling code but different sequences in the case transmit diversity is used on downlink channel
slot #1
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Only one CPICH per cell
Broadcast over the entire cell
The P-CPICH is a phase reference for SCH, Primary CCPCH, AICH, PICH. By default, it is also a phase reference for downlink DPCH.
Secondary CPICH
An arbitrary channel code of SF=256 is used for S-CPICH
S-CPICH is scrambled by either the primary or a secondary scrambling code
There may be zero, one , or several secondary CPICH.
S-CPICH may be transmitted over part of the cell
S-CPICH may be a phase reference for S-CCPCH and downlink DPCH.
The P-CPICH is a phase reference for SCH, Primary CCPCH, AICH, PICH
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Fixed rate30kbpsSF=256
Carry BCH transport channel
The PCCPCH is not transmitted during the first 256 chips of each time slot.
Only data part
Data
(Tx OFF)
The Primary CCPCH is a fixed rate (30 kbps, SF=256) downlink physical channels used to carry the BCH transport channel.
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Paging Indicator Channel (PICH)
PICH is a fixed-rate (SF=256) physical channel used to carry the Paging Indicators (PI).
PICH is always associated with an S-CCPCH to which a PCH transport channel is mapped.
Frame structure of PICHone frame of length 10ms consists of 300 bits of which 288 bits are used to carry paging indicators and the remaining 12 bits are not defined.
N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72, or 144.
If a paging indicator in a certain frame is set to 1, it indicates that UEs associated with this paging indicator should read the corresponding frame of the associated S-CCPCH.
One radio frame (10 ms)
b
1
b
0
12 bits (undefined)
This is the structure of paging indicator channel.
In a 10ms radio frame, 288bits are used to carry paging indicators and the remain 12 bits are undefined.
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Carry FACH and PCH.
Two kinds of SCCPCH: with or without TFCI. UTRAN decides if a TFCI should be transmitted, UE must support TFCI.
Possible rates are the same as that of downlink DPCH
SF =256 - 4.
FACH and PCH can be mapped to the same or separate SCCPCHs. If mapped to the same S-CCPCH, they can be mapped to the same fame.
Data
bits (k=0..6)
The Secondary CCPCH is used to carry the FACH and PCH. There are two types of Secondary CCPCH: those that include TFCI and those that do not include TFCI. It is the UTRAN that determines if a TFCI should be transmitted, hence making it mandatory for all UEs to support the use of TFCI. The set of possible rates for the Secondary CCPCH is the same as for the downlink DPCH
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The random-access transmission data consists of two parts:
One or several preambleseach preamble is of length 4096chips and consists of 256 repetitions of a signature whose length is 16 chips16 available signatures totally
10 or 20ms message part
Which signature is available and the length of message part are determined by higher layer
Now introduce PRACH and PCPCH simply.
CPCH is like RACH with fast power control and longer allocation time,and with the possibility of using higher bit rates to transfer larger amounts of data with a more controlled access method.
One of CPCH’s main advantages is a short access delay with a high bit rate, which makes it especially suitable for bursty data. Compared to DCH,CPCH can better adapt to data rate changes. On the other hand, CPCH may also degrade capacity,owing to its lack of soft handover.
Since CPCH uses fast power control , it gives better spectrum efficiency and thus better capacity than RACH, which is not power controlled.
SF:
control part of PRACH:256 PCPCH:256
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Preamble
Preamble
Preamble
Preamble
Now introduce PRACH and PCPCH simply.
CPCH is like RACH with fast power control and longer allocation time,and with the possibility of using higher bit rates to transfer larger amounts of data with a more controlled access method.
One of CPCH’s main advantages is a short access delay with a high bit rate, which makes it especially suitable for bursty data. Compared to DCH,CPCH can better adapt to data rate changes. On the other hand, CPCH may also degrade capacity,owing to its lack of soft handover.
Since CPCH uses fast power control , it gives better spectrum efficiency and thus better capacity than RACH, which is not power controlled.
SF:
control part of PRACH:256 PCPCH:256
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Now introduce PRACH and PCPCH simply.
CPCH is like RACH with fast power control and longer allocation time,and with the possibility of using higher bit rates to transfer larger amounts of data with a more controlled access method.
One of CPCH’s main advantages is a short access delay with a high bit rate, which makes it especially suitable for bursty data. Compared to DCH,CPCH can better adapt to data rate changes. On the other hand, CPCH may also degrade capacity,owing to its lack of soft handover.
Since CPCH uses fast power control , it gives better spectrum efficiency and thus better capacity than RACH, which is not power controlled.
SF:
control part of PRACH:256 PCPCH:256
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RACH
Acquisition Indicator Channel (AICH)
Frame structure of AICHtwo frames, 20 ms consists of a repeated sequence of 15 consecutive AS, each of length 20 symbols(5120 chips). Each time slot consists of two partsan Acquisition-Indicator(AI) and a part of duration 1024chips with no transmission.
Acquisition-Indicator AI have 16 kinds of Signature.
CPICH is the phase reference of AICH.
AS #14
AS #0
AS #1
AI part
Unused part
20 ms
AS:access slot.
The AICH is a fixed rate physical channel (SF 256) used to indicate in the cell the reception by the base station of PRACH preambles(signatures). Once the base station has received a preamble, the same signature that has been detected on the PRACH preamble is then sent back to the UE using this channel.
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Uplink Dedicated Physical Channel
DPDCH and DPCCH are I/Q code multiplexed within each radio frame
DPDCH carries data generated at Layer 2 and higher layer
DPCCH carries control information generated at Layer 1
Each frame is 10ms and consists of 15 time slots, each time slot consists of 2560 chips
The spreading factor of DPDCH is from 4 to 256
The spreading factor of DPDCH and DPCCH can be different in the same Layer 1 connection
Each DPCCH time slot consists of Pilot, TFCIFBITPC
Now look at the feature of uplink dedicated physical channel.
Pilot is used to help demodulate
TFCI: transport format combination indicator
FBI:used for the FBTD.
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Pilot
N
pilot
bits
TPC
N
TPC
bits
Data
N
data
bits
DPDCH
DPCCH
FBI
N
FBI
bits
TFCI
N
TFCI
bits
This is the frame structure of uplink DPDCH and DPCCH. The length of 1 radio frame is 10 ms and 1 radio frame consists of 15 time slots. One slot has fixed 2560 chips. So the chip rate is fixed 3.84Mcps.
10 multiplied by 2 power k, k=0 to 6. SF=2 power (8-k)
How to calculate the number of bits of a slot? The number of chips of a slot is fixed 2560. So if the SF is 4, the bits of the slot before spreading spectrum is 640 (2560 divided by 4)
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such as demodulation, power control, etc
Data bearer
at physical layer
Let’s look at the functions of uplink DPDCH and DPCCH.DPDCH is used to bear data at physical layer. DPCCH provide control data for DPDCH, such as demodulation,power control etc.
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Control information includesPilotTPCTFCI(optional).
The spreading factor of DCH can be from 512 to 4,and can be changed during connection
DPDCH and DPCCH is time multiplexed.
Multi-code transmission within one CCTrCH uses the same spreading factor. In this case, the DPCH control information is transmitted only on the first downlink DPCH.
Different CCTrCH can use different spreading factors in the case there are several CCTrCHs for one UE. In this case information of only one DPCCH needs to be transmitted.
This slide introduces the feature of downlink dedicated physical channel.
One UE can transmit only one CCTrCH at once,but multiple CCTrCHs can be simultaneously received in the forward direction(downlink).
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One radio frame, T
Data2
N
data2
bits
DPDCH
TFCI
N
TFCI
bits
Pilot
N
pilot
bits
Data1
N
data1
bits
DPDCH
DPCC
H
DPCCH
TPC
N
TPC
bits
We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and DPCCH is time multiplexed. This is main difference. The chips of one slot is also 2560. Because the SF of downlink DPCH can be 512, so the k can be 7.
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Data bearer
The functions of downlink DPDCH/DPCCH are similar with uplink DPDCH/DPCCH.
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Section 1 Physical Channel Structure and Functions
Section 2 Channel Mapping
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Chapter 2 Physical layer key technology
Chapter 3 Physical Layer Procedures
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Scrambling-code identification
UE uses PSC to acquire slot synchronization to a cell
UE uses SSC to find frame synchronization and identify the code group of the cell found in the first step
UE determines the primary scrambling code through correlation over the CPICH with all codes within the identified group, and then detects the P-CCPCH and reads BCH information
During the cell search, the UE searches for a cell and determines the downlink scrambling code and frame synchronisation of that cell. The cell search is typically carried out in three steps:
Step 1: Slot synchronisation
During the first step of the cell search procedure the UE uses the SCH’s primary synchronisation code to acquire slot synchronisation to a cell. This is typically done with a single matched filter (or any similar device) matched to the primary synchronisation code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.
Step 2: Frame synchronisation and code-group identification
During the second step of the cell search procedure, the UE uses the SCH’s secondary synchronisation code to find frame synchronisation and identify the code group of the cell found in the first step. This is done by correlating the received signal with all possible secondary synchronisation 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 synchronisation is determined.
Step 3: 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 found cell. The primary scrambling code is typically identified through symbol-by-symbol correlation over the CPICH with 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.And the system- and cell specific BCH information can be read.
If the UE has received information about which scrambling codes to search for, steps 2 and 3 above can be simplified.
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AICH access
P
Any CPICH
k:th S
SCH(Primary and secondary),CPICH(Primary and secondary),P-CCPCH,PDSCH have the same frame timing.
S-CCPCH has the time delay of S-CCPCH relative to P-CCPCH. PICH…