1. 網路多媒體研究所 1 WCDMA Technology Past, Present and Future Part II: CDMA Technology Overview

2. 網路多媒體研究所 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. 網路多媒體研究所 3 Typical Communication System

4. 網路多媒體研究所 4 Radio Channel Features Path Loss Shadowing Multipath Fading Noise

5. 網路多媒體研究所 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. 網路多媒體研究所 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. 網路多媒體研究所 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. 網路多媒體研究所 8 Typical Ways to Overcome Fading Diversity Equalization Forward error correcting codes and interleaving Increasing power RAKE Receiver

9. 網路多媒體研究所 9 Impact of Radio Channel on System Design (1/2)

10. 網路多媒體研究所 10 Impact of Radio Channel on System Design (2/2)

11. 網路多媒體研究所 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. 網路多媒體研究所 12 Digital Modulation Techniques ASK (Amplitude Shift Keying) PSK (Phase Shift Keying) FSK (Frequency Shift Keying) QAM (Quadrature Amplitude Modulation) Etc…

13. 網路多媒體研究所 13 BPSK and QPSK

14. 網路多媒體研究所 14 16-QAM and 64-QAM

15. 網路多媒體研究所 15 Modulation/Demodulation Block Diagram Modulator Demodulator

16. 網路多媒體研究所 16 Cellular Concept Cell –Virtual Boundary of Radio Coverage –Possible Issues Handover Interference Capacity

17. 網路多媒體研究所 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. 網路多媒體研究所 18 FDMA and TDMA FDMA TDMA N 2 1 W Ts Time Frequency Ws W NTs Time Frequency N Ts2Ts 1 12

19. 網路多媒體研究所 19 CDMA CDMA N Code N Code 2 1 Code 1 2 Frequency Ts Code N 1 2 Time W

20. 網路多媒體研究所 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. 網路多媒體研究所 21 FDD and TDD FDD TDD UPLINK DOWNLINK Ts Time Frequency Wdl Wul W NTs Time Frequency Ts2Ts UPLINKUPLINK UPLINKUPLINK DOWNLINKDOWNLINK DOWNLINKDOWNLINK

22. 網路多媒體研究所 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. 網路多媒體研究所 23 Hard Handover

24. 網路多媒體研究所 24 Soft Handover RNC Cell 1 Cell 2

25. 網路多媒體研究所 25 Softer Handover

26. 網路多媒體研究所 26 Interference Inter Symbol Interference Co-Channel Interference Adjacent Channel Interference

27. 網路多媒體研究所 27 Inter-Symbol Interference (ISI)

28. 網路多媒體研究所 28 Co-channel Interference (CCI) & Adjacent Channel Interference (ACI)

29. 網路多媒體研究所 29 Illustration of Cellular Frequency Reuse Concept Reuse Efficiency = i 2 +i  j+j 2

30. 網路多媒體研究所 30 Interference Contributions from Other Cells IS-95 Air Interface Standards

31. 網路多媒體研究所 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. 網路多媒體研究所 32 CDMA Concept CDMA N Code N Code 2 1 Code 1 2 Frequency Ts Code N 1 2 Time W

33. 網路多媒體研究所 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. 網路多媒體研究所 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. 網路多媒體研究所 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. 網路多媒體研究所 36 Wideband CDMA Era 1995, WCDMA, CDMA2000 2000, TD-SCDMA

37. 網路多媒體研究所 37 Concept of Spread Spectrum

38. 網路多媒體研究所 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. 網路多媒體研究所 39 Spread/Depread Spectrum Spectrum After Spreading/Before Despreading Spectrum After Despreading/Before Spreading frequency …… B SS BTBT frequency ……

40. 網路多媒體研究所 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. 網路多媒體研究所 41 Principle of S.S. (1/4)

42. 網路多媒體研究所 42 Principle of S.S. (2/4)

43. 網路多媒體研究所 43 Principle of S.S. (3/4)

44. 網路多媒體研究所 44 Principle of S.S. (4/4)

45. 網路多媒體研究所 45 Spreading/Despreading Data Spreading code Spread signal = Data x code Spreading code Data = Spread signal x code 1 1 1 1 1 Symbol Chip

46. 網路多媒體研究所 46 Block Diagram of a Typical S.S. System

47. 網路多媒體研究所 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. 網路多媒體研究所 48 Classification of CDMA

49. 網路多媒體研究所 49 Time/Freq. Occupancy of DS, FH, and TH Signals Frequency Time Frequency Time x x x xx x DSFH TH x x

50. 網路多媒體研究所 50 RAKE Receiver

51. 網路多媒體研究所 51 Maximal Ratio Combining (MRC) in RAKE Radio channel consist of many multipaths Each multipath change the amplitude and the phase of the transmitted signal The data in QPSK signal is in phase Energy splitted to many fingers detected by the mached filter MRC corrects the phase with channel amplitude estimate

52. 網路多媒體研究所 52 Challenges in CDMA System Design Soft Handover Power Control –Open loop –Closed loop (Inner and Outer loop) Code Design –Synchronization codes –Channelization codes –Scrambling codes Baseband Design –Synchronization (Frame/Slot/Symbol/Chip) –Searcher (find and maintain qualified paths) –AFC, AGC, and Clock Recovery –RAKE receiver (Channel estimation, RAKE fingers, and Maximal-ratio combining) –Channel codec (convolutional codes, concatenated codes, turbo code

53. 網路多媒體研究所 53 Conclusion: Features of S.S and CDMA Features of CDMA –High spectrum efficiency –Release from frequency management –Low mobile station transmit power –Soft-handover –Path Diversity (RAKE Fingers) –Security –Anti-jamming capability Features of Wideband Spreading –High and wide variety of data rates –Improvement of multipath resolution –Statistical multiplexing efficiency