WCDMA Technology Past, Present and Future

1. WCDMA TechnologyPast, 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. U-plane Radio Bearers Signalling Radio Bearers WCDMA Radio Interface Protocol Architecture Control Plane User Plane L3 RRC 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

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

10. Σ ⊕ ⊕ Σ j Physical Layer Baseband Processing Block DiagramCoding 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 PhCH #2 PhCH #3 Q PhCH #4 DPCCH

11. 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

12. Channelisation and Scrambling codes

13. Two code layer scheme, downlink

14. Utilization of Channelisation and Scrambling Codes

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

16. Downlink scrambling code (1/2) • Long scrambling code (2^18-1=262143 codes) • Only 38400 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

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

18. 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.

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

20. 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

21. Physical Layer Operations in making a phone call MS 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

22. Physical Layer Operations in making a phone call MS 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

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

24. 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

25. Cell Search Procedure (2/2)

26. 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

27. 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

28. 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.

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

30. Physical Layer Operations in making a phone call MS 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

31. 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)

32. Physical Layer Operations in making a phone call MS 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

33. 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

34. Secondary CCPCH

35. S-CCPCH Fields

36. 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

37. Physical Layer Operations in making a phone call MS 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

38. 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

39. Spreading and Modulation of PRACH Message Part

40. Structure of the Random Access Message Part

41. Random-access Message Data and Control Fields

42. PRACH access procedure

43. 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

44. Physical Layer Operations in making a phone call MS 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

45. 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

46. 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

47. 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

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

49. 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:

50. Downlink spreading and modulation DPCH