WCDMA Technology Past, Present and Future

1. WCDMA TechnologyPast, Present and Future Part II: CDMA Technology Overview

2. Part II:CDMA Technology Overview • Introduction to Wireless Communication • Radio Channel Characteristic • Modulation • Basic Concepts to Mobile Communication • CDMA Technology Overview • History of CDMA • Introduction to Spread Spectrum • Direct Sequence CDMA (DS-CDMA) • CDMA System Characteristic • Challenges in CDMA System Design

3. Typical Communication System

4. Radio Channel Features • Path Loss • Shadowing • Multipath Fading • Noise

5. What is Fading? • Signals from different paths are received with different delays • due to reflections of buildings, trees, etc. • Each path has different attenuation and time delay (phase delay) • Sometimes the relative phase shifts align, so the signal received from different add constructively, but at other time they cancel each other. • This is called Fading

6. Features of the Fading Component • Path loss (Area-mean): • Hundreds or thousands of meters • Reflection, diffraction, and scattering • Shadowing (Local-mean): • A few tens or hundreds of meters • Caused by obstruction and motion • Multipath fading (Short-term fast fading or small-scale fast fading): • Variation of the signal strength over a short distance on the order of a few wavelengths or over short term duration on the order of seconds • Due to multipath reflections of transmitted wave by local scatters, such as houses, buildings, etc, surrounding a MS

7. Received Signal Characteristics • Received signal consists of many multipath components • Amplitudes change slowly • Phases change rapidly • Constructive and destructive addition of signal components • Amplitude fading of received signal (both wideband and narrowband signals)

8. Typical Ways to Overcome Fading • Diversity • Equalization • Forward error correcting codes and interleaving • Increasing power • RAKE Receiver

9. Impact of Radio Channel on System Design (1/2)

10. Impact of Radio Channel on System Design (2/2)

11. Modulation • Why Modulation ? • Different frequency band has different radio characteristic, like fading, interference, thermal noise, etc… • Convert information bits to waveform of digital signal with a carrier belong to certain frequency band • Modulated signal could be easily transmitted and received than signal without modulating

12. Digital Modulation Techniques • ASK (Amplitude Shift Keying) • PSK (Phase Shift Keying) • FSK (Frequency Shift Keying) • QAM (Quadrature Amplitude Modulation) • Etc…

13. BPSK and QPSK

14. 16-QAM and 64-QAM

15. Modulation/Demodulation Block Diagram Modulator Demodulator

16. Cellular Concept • Cell • Virtual Boundary of Radio Coverage • Possible Issues • Handover • Interference • Capacity

17. Multiple Access Concept • Multiple Access is used to distinguish each user while using Radio Access Service • Multiple Access • FDMA (Frequency Division Multiple Access) • TDMA (Time Division Multiple Access) • CDMA (Code Division Multiple Access)

18. FDMA and TDMA Frequency Frequency N Ws ●●● W 1 1 2 N W ●●● ●●● 2 Ws 1 Ws NTs Ts Ts 2Ts Time Time FDMA TDMA

19. Code Code N ●●● ●●● N N Time ●●● Code 2 2 2 W Code 1 1 1 Ts Frequency CDMA CDMA

20. Duplex Concept • Duplex is provided a two way Radio Access Service for each user • Uplink (reverse link) • Downlink (forward link) • Duplex • TDD (Time Division Duplex) • FDD (Frequency Division Duplex)

21. FDD and TDD Frequency Frequency UPLINK Wul UPLINK DOWNLINK DOWNLINK UPLINK W ●●● ●●● DOWNLINK Wdl NTs Ts 2Ts Ts Time Time FDD TDD

22. Handover • When mobiles travel from cell to cell, changes of channels may occur and this action of changing channels is known as hand-over or hand-off. • It is required that the call already established (or in progress) must not be interrupted

23. Hard Handover

24. Soft Handover Cell 1 RNC Cell 2

25. Softer Handover

26. Interference • Inter Symbol Interference • Co-Channel Interference • Adjacent Channel Interference

27. Inter-Symbol Interference (ISI)

28. Co-channel Interference (CCI) & Adjacent Channel Interference (ACI)

29. Illustration of Cellular Frequency Reuse Concept • Reuse Efficiency = i2+ij+j2

30. Interference Contributions from Other Cells • IS-95 Air Interface Standards

31. Part I:CDMA Technology Overview • Introduction to Wireless Communication • Radio Channel Characteristic • Modulation • Basic Concepts to Mobile Communication • CDMA Technology Overview • What is “CDMA” • History of CDMA • Introduction to Spread Spectrum • Direct Sequence CDMA (DS-CDMA) • Frequency Hopping CDMA (FH-CDMA) • CDMA System Characteristic • Challenges in CDMA System Design

32. Code Code N ●●● ●●● N N Time ●●● Code 2 2 2 W Code 1 1 1 Ts Frequency CDMA CDMA Concept

33. What is CDMA? • A multiple access technique using pseudo-random (PN)codes to spread the spectrum of each user signal. • Signals are shared a common wide-band channel at the same time. • Signals are distinguished from each other by using different PN codes. • Receiver processes only the desired signal. All other user signals appear as interference (multiple-access interference) to the desired signal.

34. Pioneer CDMA Era • 1949, Claude Shannon & Robert Pierce: basic idea of CDMA • 1950, De Rosa-Rogoff: DSSS • 1956, Pierce & Green: RAKE receiver • 1961, Magnuski: Near-far problem • 1970s, Development for military & navigation systems

35. Narrowband CDMA Era • 1978, Cooper & Nettleton: Cellular application of SS • 1980s, Investigation of NB-CDMA for cellular application • 1984, DS-CDMA & hybrid CDMA/FDMA proposal for GSM • 1986, Verdu: Formulation of optimal multiuser detection • 1993, IS-95 standard

36. Wideband CDMA Era • 1995, WCDMA, CDMA2000 • 2000, TD-SCDMA

37. Concept of Spread Spectrum

38. Definition of Spread Spectrum • Spread spectrum is a mean of transmission in which the signal occupies a bandwidth in excess of the minimum necessary to send the information. • Band spread is accomplished by means a code which is independent of the data, and a synchronized reception with the code at the receiver is used for despreading and subsequent data recovery.

39. … … frequency BSS … … BT frequency BSS Spread/Depread Spectrum • Spectrum After Spreading/Before Despreading • Spectrum After Despreading/Before Spreading

40. Pseudorandom Codes • The ideal spreading code would be an infinite sequence of equally likely random binary digits. • In practice, periodic pseudorandom codes are used instead (PN codes). • Specific PN codes include: • maximal-length code • Gold codes

41. Principle of S.S. (1/4)

42. Principle of S.S. (2/4)

43. Principle of S.S. (3/4)

44. Principle of S.S. (4/4)

45. Spreading/Despreading Symbol 1 -1 Data Chip 1 -1 Spreading code 1 -1 Spread signal = Data x code 1 -1 Spreading code 1 -1 Data = Spread signal x code

46. Block Diagram of a Typical S.S. System

47. Advantages of Spread Spectrum • Multiple access capability • Low cross-correlation of the code • Protection against multipath interference • Frequency diversity • Privacy • Only the user knows the spreading code • (NB) Interference rejection • The code will spread the received interference • Anti-jamming capability • The code will spread the received jamming • Low probability of interception (LPI) • Low power spectrum density

48. Classification of CDMA

49. Frequency Frequency Frequency Time Time Time Time/Freq. Occupancy of DS, FH, and TH Signals x DS FH TH x x x x x x x

50. RAKE Receiver