1. WCDMA Technology Past, Present and Future
Part IV:
Physical Layer on WCDMA

2. Part IV: Physical Layer on WCDMA
Overview on WCDMA Physical Layer
WCDMA Physical Channel
Functions of WCDMA Physical Channel
Spreading in WCDMA Physical Channel
Operations in making a phone call
Baseband Packet Formats
Important Physical Layer Procedures and Issues

3. What is Physical Layer?
Physical layer (PHY) defines how the data (controlling data and the user data = user traffic) has been structured for the transmission over the air interface
In mobile cellular systems the effect of the physical layer is high because of the characteristics of the radio channel (=air interface)
Defines the maximum capacity limits of the system (maximum allowed bit-rate, maximum number of simultaneous users)
In practice the physical layer does not necessary limit the capacity but the implementation of the equipments and the radio channel.
Big impact on equipment complexity,
processing power, algorithms

4. Main Requirements on WCDMA Physical Layer
High bit-rates
Flexible variable bit rate both in uplink and in downlink
Multi-service
Different services have been multiplexed on a single physical connection
Efficient packet data
Support for All IP-RAN
High spectral efficiency

5. WCDMA Radio Interface Protocol Architecture
Control Plane
User Plane
U-plane Radio Bearers L3
RRC
Signalling Radio Bearers
Control
BMC
PDCP L2
Radio Bearers
RLC
Logical Channels
MAC
Transport Channels L1
PHY(W-CDMA)
Physical Channels

6. Physical Channels (1/3) Common Physical Channels:
Synchronization Channels (SCH, DL)
Primary Synchronization Channel (P-SCH)
Secondary Synchronization Channel (S-SCH)
Common Pilot Channel (CPICH, DL)
Common Control Physical Channels (CCPCH, DL)
Primary common physical channel (P-CCPCH)
Secondary common physical channel (S-CCPCH)
Indication Channel
Acquisition Indication Channel (AICH, DL)
Page Indication Channel (PICH, DL)
CPCH Access Preamble Acquisition Indicator Channel (AP-AICH, DL)
CPCH Collision Detection Channel Assignment Indicator Channel (CD/CA-ICH, DL)
CPCH Status Indicator Channel (CSICH, DL)
Physical Random Access Channel (PRACH, UL)
Physical Common Packet Channel (PCPCH, UL)
Dedicated Physical Channels:
Dedicated Physical Data Channel (DPDCH, DL&UL)
Dedicated Physical Control Channel (DPCCH, DL&UL)

7. Physical Channels (2/3)

8. Physical Channels (3/3) Chip rate = 3.84 Mcps
Physical channel is characterize with frequency, code, duration and in uplink with phase shift
1 radio frame (10 ms) includes 15 time slots (one slot equals to power control period, 1/(10ms/15)=1500 Hz)
one time slot = 2560 chips
Slot structure is just for controlling the physical channel and its radio performance 改圖

9. Timing Relationship Between Physical Channels
k:th S -
CCPCH
AICH access
slots
Secondary
SCH
Primary t S
CCPCH,k
10 ms
PICH #0 #1 #2 #3
#14
#13
#12
#11
#10 #9 #8 #7 #6 #5 #4
Radio frame
with
(SFN modulo 2) = 0
(SFN modulo 2) = 1
DPCH,n P
Any CPICH
PICH for k:th
Any PDSCH
n:th DPCH

10. Physical Channel Segmentation, Physical Channel Mapping
Physical Layer Baseband Processing Block Diagram Coding and Multiplexing of Transport Channels
Transport
Channel #1
Transport
Channel #2
Transport
Channel #N
To RF
CRC Attachment,
Channel Coding,
1st Interleaving,
Rate Matching
CRC Attachment,
Channel Coding,
1st Interleaving,
Rate Matching
Modulation
CRC Attachment,
Channel Coding,
1st Interleaving,
Rate Matching
Pulse Shaping
Transport Channel MUX
Scrambling
CCTrCH
I + jQ
(DPDCH)
Physical Channel Segmentation,
2nd Interleaving,
Physical Channel Mapping
PhCH #1
Spreading
&
Gain Weighting I Σ ⊕ j
PhCH #2
PhCH #3 Q
PhCH #4
DPCCH

11. Functions of WCDMA Physical Layer
Error detection
Multiplexing (TrCH→CCTrCH), demultiplexing (CCTrCH → TrCH)
Channel coding, interleaving, rate matching
CCTrCH Mapping to physical Channels (PhCH)
Modulation, demodulation
Spreading, despreading
Combination of physical channels
Closed loop power control
Radio frequency processing (RF)
Synchronization (chip, bit, slot, frame)
Measurements
Bit-error ratio (BER), Signal-to-Interference ratio (SIR), Transmission power (TxP),
Macrodiversity (soft(er)-handover)

12. Spreading Codes in WCDMA
Channelisation Codes (Spreading code, orthogonal code)
Length is dependent on spreading factor
Used for channel separation from the single source
Good orthogonality properties => decreased interference
Usage have to be managed: If one code with low spreading factor is used, the code in the same code tree branch can not be used
Same codes in every cell / mobiles and therefore the additional scrambling code is needed
Scrambling Codes
Very long (38400 chips), many codes available
Uplink: to separate different mobiles
Downlink: to separate different cells/sectors
Good correlation properties:
The correlation between two codes (two mobiles) is low
The autocorrelation is low when the phase shift ≠ 0. Then the multipath propagation does not have big impact on the interference levels

13. Channelisation and Scrambling codes改圖

14. Two code layer scheme, downlink改圖

15. Utilization of Channelisation and Scrambling Codes
Uplink
Downlink
Channelisation
Codes
Identify the physical channels for the same user if multi-code is used
Identify the physical channels of each user
Scrambling
Identify the users
Identify the cells

16. Channelization Codes – OVSF Codes
The OVSF (Orthogonal Variable Spreading Factor) code is described as Cch,SF,k, where SF is the spreading factor of the code and k is the code number, 0 ≦ k ≦ SF-1.

17. Downlink scrambling code (1/2)
Long scrambling code (2^18-1= codes)
Only chips from the beginning of the code is used
The DL scrambling code is time aligned with the scrambling code of PCCPCH channel which is the timing reference
From these only 8192 codes, devidid into 512 sets, are used in WCDMA in order to speed up the cell search
Each code set includes 1 primary and 15 secondary scrambling (other PhCH) codes.
512 primary scr. codes has been divided into 64 subgroups
Each cell is allocated one primary scrambling code (carrying P-CCPCH, P-CPICH, PICH, AICH and S-CCPCH)
Other channels can use the primary scrambling code or secondary code from the same set. If the secondary code is used the orthogonality is lost reduction of system performance

18. Downlink Scrambling Code (2/2)
Configuration of DL scrambling code generator.

19. Uplink Scrambling Code
The definition of the nth scrambling code word for the in phase and quadrature components follows as:
C1,n=<xn(0)+y(0), xn(1)+y(1),…, xn(N-1)+y(N-1)>
C2,n=<xn(M)+y(M), xn(M+1)+y(M+1),…, xn(M+N-1)+y(M+N-1)>
where N is the period in chips and M = 16,777,232.
Uplink Capacity

20. Block Diagram of WCDMA PHY
Channel
Encoder
Rate
Matching
Block
Interleaver
Data
Modulator
Spreader
Pulse
Shaping
Filter
I/Q Modulator &
Up-converter
Spreading
Multipath
Fading Channel
Channel
decoder
De-rate
Matching
Block
De-Interleaver
Data
Demodulator
Pulse
Shaping
Filter
Down-converter &
I/Q Demodulator
RAKE
Receiver
Synchronizer
Searcher
AFC
N. B. AGC
SIR-Measurement
W. B. AGC
Despreading

21. Part IV: Physical Layer on WCDMA
Overview on WCDMA Physical Layer
WCDMA Physical Channel
Functions of WCDMA Physical Channel
Spreading in WCDMA Physical Channel
Operations in making a phone call
Baseband Packet Formats
Important Physical Layer Procedures and Issues

22. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search
Listen Broadcast Information
Wait for Paging
Establish a dedicate connection for a call
Data Transmission and Reception
Release connection for a call

23. Physical Layer Operations in making a phone callMS BS
Power on 1.
Cell Search
Listen Broadcast Information
Wait for Paging
Establish a dedicate connection for a call
Data Transmission and Reception
Release connection for a call

24. WCDMA Cell Search One timeslot=625 sec P-CCPCH P-CCPCH Base 1 P-CCPCH
P-SCH
S-SCH
P-CCPCH
P-SCH
S-SCH
P-SCH
Base 1
S-SCH
P-CCPCH
P-CCPCH
P-SCH
S-SCH
P-CCPCH
P-SCH
S-SCH
P-SCH
Base 2
P-CCPCH
S-SCH
P-CCPCH
P-SCH
S-SCH
P-SCH
P-SCH
Base 3
P-CCPCH
S-SCH
P-CCPCH
S-SCH
Mobile Searcher

25. Cell Search Procedure (1/2)
How to do cell search? --> Three steps fast cell search algorithm
Step 1: Slot synchronization
Step 2: Frame synchronization and code-group identification
Step 3: Scrambling code identification

26. Cell Search Procedure (2/2)

27. Synchronisation Channel (SCH)
For initial cell search for the MS
The Synchronisation Channel (SCH):
A downlink signal used for cell search
Consists of two sub channels:
Primary SCH
Secondary SCH 改圖

28. Downlink Common Pilot Channel (CPICH)
Primary and secondary CPICH
Primary CPICH
Unmodulated, fixed rate, fixed power channel scrambled with the cell specific primary scrambling code
Used as a phase reference
15 kbps, SF=256 (Cch,256,0)
Used in handover measurements:
CPICH Ec/I0
Used for channel estimation
Secondary CPICH
Used with multiple antenna beams

29. Modulation Pattern for CPICH in case of Transmit Diversity
In case of Transmit Diversity (open or closed loop), the CPICH shall be transmitted from both antennas using the same channelization and scrambling code. In this case, the pre-defined symbol sequence of the CPICH is different for Antenna 1 and Antenna 2.

30. Downlink spreading code
Typically one channelization code tree per cell: Code tree shared between all downlink users
Code for CPICH = Cch,256,0 and for P-CCPCH = Cch,256,1
Resource manager assigns the channelization code for other channels
Downlink SF does not vary on frame by frame bases, except for DSCH
Data rate variation is taken care of with rate matching or with L1 DTX
In multicode tranmissions (high bit rates > 1 Mbps) the parallel code channels have different channelisation code under the same scrambling code but the same SF

31. Downlink spreading and modulation
P-CPICH
S-CPICH

32. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search 2.
Listen Broadcast Information
Wait for Paging
Establish a dedicate connection for a call
Data Transmission and Reception
Release connection for a call

33. Primary Common Control Physical Channel (P-CCPCH)
Carrying the Broadcast Channel (BCH)
Contains random access codes, code channels of other common channels
Pure DATA channel: channel estimation from Common pilot channel
Needs to be demodulated by all the terminals in the system: High Tx power needed
Fixed data rate (30 kbps=15ksps), channellization code length 256 Cch,256,0
No power control
P-CCPCH and SCH are time multiplexed (SCH used in TxOFF period of above shown figure)

34. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search
Listen Broadcast Information 3.
Wait for Paging
Establish a dedicate connection for a call
Data Transmission and Reception
Release connection for a call

35. Secondary CCPCH The S-CCPCH is used to carry the FACH and PCH.
Forward Access Channel (FACH) and Paging Channel (PCH) which can be mapped to same or different S-CCPCH
There are two types of S-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 parameter k determines the spreading factor SF of the S-CCPCH as SF = 256/2k. The spreading factor range is from 256 down to 4.
No TPC
Active only when data available

36. Secondary CCPCH

37. S-CCPCH Fields

38. Page Indicator Channel (PICH)
A terminal registered to the network is allocated a paging group
When there are paging messages coming for any UEs of that group the Paging Indicator will be send on PICH.
After that UE decodes the next PCH message on S-CCPCH to find out whether there was paging messages intended for it
This procedure decreases the power consumption of the UE

39. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search
Listen Broadcast Information
Wait for Paging 4.
Establish a dedicate connection for a call
Data Transmission and Reception
Release connection for a call

40. Physical Random Access Channel (PRACH)
With Random Access Channel (RACH) power ramping is needed with preambles since the initial power level setting in the mobile is very coarse with open loop power control
Preamble: mobile sends 256 repetitions of 16 chip (1 preamble = 4096 chips) signature sequence with increasing power
L1 acknowledgement: base station acknowledges the sequences received with high enough power level (AICH = Acquisition Indication CH)
Mobile RACH message follows the acknowledgement
Can be used also for Data transmission
Message part length 10 or 20 ms 改圖

41. Spreading and Modulation of PRACH Message Part

42. Structure of the Random Access Message Part

43. Random-access Message Data and Control Fields

44. PRACH access procedure

45. Acquisition Indicator Channel (AICH)
Acqusistion Indicator Channel (AICH)
User for RACH channel indication
For the detection of AICH MS used Common pilot channel
To all MS in the cell: high power, low data rate

46. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search
Listen Broadcast Information
Wait for Paging
Establish a dedicate connection for a call 5.
Data Transmission and Reception
Release connection for a call

47. Dedicated Physical Channel
DPCCH (Dedicated physical control channel) is constant bit rate and carries all the information in order to keep physical connection running
Reference symbols for channel estimation in coherent detection and for SIR estimation in fast power control
Power control signalling bits (TPC)
Transport format information (TFCI) = bit rate, interleaving
DPDCH (Dedicated physical data channel) is variable bit rate and carriers User data
DPDCH bit rate is indicated with TFI bits on DPCCH

48. Downlink dedicated physical channel(1/3)
Time multiplexed DPCCH and DPDCH:
DCH is carried by DPDCH
Discontinuous transmission in DPDCH fields in order to handle variable data rates 改圖

49. Downlink dedicated physical channel(2/3)
The DPDCH and DPCCH have the same power and the same SF
DPDCH spreading factor from 512 (7.5 ksps) to 4 (960 ksps)
For example: SF = 8
3.84x10^6/8/1000=480 ksps=960 kbps
I/Q modulation (QPSK): 2 bit = 1 symbol
Procedure in the UE when receiving DL-DPCH:
Estimate the SIR (Pilot)
Detect TPC and adjust UL Tx power
Detect the used bit-rate and interleaving (TFCI)
Detect the data (Data): needs buffering of the Data field

50. Downlink DPCH Fields
Half Rate Speech
144Kbps
384Kbps

51. Downlink dedicated physical channel(3/3)
DPDCH bit rate can change frame-by-frame (10 ms)
Rate matching done to the maximum bit-rate of the connection
Lower bit rates obtained with discontinuous transmission (no audible interference)
The usable DL bit-rate allocated by the Radio Resource Management (RRM) algorithms (in this case Admission Control)
Discontinuous transmission: 改圖

52. Downlink spreading and modulation
DPCH

53. Uplink dedicated physical channel(1/3)
There can be several uplink DPDCH for one mobile but only one DPCCH
TFCI = Transport Format Combination Indicator
TPC = Transmitted Power Control
FBI = Feedback information (for Tx antenna diversity) 改圖
DPCCH
DPDCH

54. Uplink dedicated physical channel(2/3)
DPDCH spreading factor from 256 (15 ksps) to 4 (960 ksps)
DPCCH spreading factor from 256 (15 ksps) = constant
For example: SF = 16
3.84x10^6/16/1000=240 kbps
I/Q modulation (QPSK): 1 bit = 1 symbol
Procedure in the base station when receiving UL-DPDCH/DPCCH:
Estimate the SIR (Pilot)
Detect TPC and adjust DL Tx power
Detect the used bit-rate and interleaving (TFCI)
Detect the data (Data): needs buffering of the Data field

55. Uplink DPDCH Field 改圖

56. Uplink DPCCH Fields
There are two possible compressed slot formats for each normal slot format. They are labelled A and B and the selection between them is dependent on the number of slots that are transmitted in each frame in compressed mode. The channel bit and symbol rates given in table 2 are the rates immediately before spreading.

57. Uplink dedicated physical channel(3/3)
DPDCH bit rate can change frame-by-frame (10 ms)
Higher bit rate requires more transmission power
Also DPCCH power is higher for higher bit-rates in order to enable accurate channel estimation
Continuous transmission regardless of the bit rate
Admission control in RNC allocates those bit rates that can be used on physical layer 改圖

58. Uplink spreading on dedicated channels

59. Power Control in W-CDMA (1/4)

60. Power Control in W-CDMA (2/4)UE UL UE
Node B
Close loop UL DL
Node B
Open loop

61. Power Control in W-CDMA (3/4)

62. Power Control in W-CDMA (4/4)

63. Illustration of Power Control
Inner Loop
Outer Loop

64. Transmitter Power Control Timing

65. Physical Layer Operations in making a phone callMS BS
Power on
Cell Search
Listen Broadcast Information
Wait for Paging
Establish a dedicate connection for a call
Data Transmission and Reception 6.
Release connection for a call