Multiple AccessDifferent multiple access methods use different strategies to:Divide the radio spectrum into channels (Tim...
Frequency Division Multiple Access (FDMA)            As AMPS and NMT
Time Division Multiple Access (TDMA)           As GSM and IS-136
Why Do we need new access techniques? Band Saturation More BW efficiency Capacity (more than ½ The population of theglo...
What about SDMA?
CDMA Spread Spectrum  Originally developed for military and navigation purposes           NO More necessary       As Chann...
CDMA Spread Spectrum•Researches started even from 1950’s•Cellular spread-spectrum application was suggested by Cooper and ...
CDMA Spread Spectrum
CDMA Spread Spectrum
CDMA Spread Spectrum
Signal Spreading Preview In DS spreading, the incoming digital speech signal is multiplied by a digital pseudo-noise (PN)...
Signal Spreading Preview Fast frequency hopping    This approach assumes that the two stations have:    A common knowledg...
Signal Spreading Preview Time Hopping     Time hopping assumes that the two stations in communication have:     A common ...
The Strengths of CDMA Increased system capacity. Cell sites can be larger. Enhanced privacy due to digital coding of CD...
Bit Stream Multiplication Concepts Bit stream multiplication is the process where an input bit stream of information (usu...
Bit Stream Multiplication Concepts Consider the difference between spreading and scrambling:
Bit Stream Multiplication Concepts    Data      01110101111010111101    Code      10110101001010101011    Code      101101...
Bit Stream Multiplication Concepts b(t) · c(t) = y(t) b(t) · c(t) · c(t) = b(t)
Spreading and Despreading Remember that spreading occurs when a lower bit rate input signal b(t) is multiplied by a highe...
Spreading and Despreading Cont. despreading takes y(t) and multiplies again by the same spreading PN code c(t) to recover...
Scrambling and Descrambling Scrambling is often used for privacy. When scrambling is used for encryption, then descrambli...
Spreading and Power Spectral Density Spreading does not change total power. Spreading  changes how the power is distribut...
1 1 0 0 1 0 1 0 0 1   1 1 0 0 1 0 1 0 0 10 0 1 1 0 1 0 1 1 0   1 1 0 0 1 0 1 0 0 1
PN Codes A binary sequence with fixed length and has noise-like  randomness Low correlation between shifted versions of ...
Code Generation Circuitry
Code Generation Circuitry          D           D           D      Flip Flop   Flip Flop   Flip Flop
Repeated Spreading and ScramblingCDMA systems use scrambling and spreading in several  ways for: Encryption for privacy ...
Repeated Spreading and Scrambling            C5                 C1  C2                      C1       C3            C4
Quick Review
RF Transmission Delay and its Effect Radio signals typically travel at a rate of about five microseconds to  the mile. As...
RF Transmission Delay and its Effect
Locking On to a Particular PN Sequence Cont.
Locking On to a Particular PN Sequence Cont.
Locking On to a Particular PN Sequence Cont.
Signal Correlation With Offsets Less Than 1 Time Chip
Signal Correlation With Offsets Less Than 1 Time Chip
Signal Correlation
Multi-User Downlink Overview
Multi-User Downlink Overview
Multi-User Downlink Overview   C3
Multi-User Uplink Overview
System PerformanceTraditional Systems Performance is measured by signal-  to-noise ratio (S/N). The desired users signal v...
System Performance
Frequency Reuse
Multipaths and Delay Spread
Non-RAKE CDMA Reception
Non-RAKE CDMA ReceptionDifferential Delay > 1 Tc
Non-RAKE CDMA Reception Differential Delay < 1 Tc
RAKE Receiver Operation
RAKE Receiver Less multipath effect No ISI problem Better signal reception Less power needed
Ch1 intro to cdma
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Ch1 intro to cdma

  1. 1. Multiple AccessDifferent multiple access methods use different strategies to:Divide the radio spectrum into channels (Time or Freq.)Allocate those channels among users (One channel or more)Identify different users on an RF carrier (Fixed or dynamic)
  2. 2. Frequency Division Multiple Access (FDMA) As AMPS and NMT
  3. 3. Time Division Multiple Access (TDMA) As GSM and IS-136
  4. 4. Why Do we need new access techniques? Band Saturation More BW efficiency Capacity (more than ½ The population of theglobe use mobile phones)
  5. 5. What about SDMA?
  6. 6. CDMA Spread Spectrum Originally developed for military and navigation purposes NO More necessary As Channel BW get smaller  More Capacity
  7. 7. CDMA Spread Spectrum•Researches started even from 1950’s•Cellular spread-spectrum application was suggested by Cooper and Nettleton in 1978•IS-95, the narrow band CDMA mobile network, has been standardized in 1993 andcommercial networks were introduced in 1995•3G wideband CDMA systems, such as CDMA2000 in U.S. and European WCDMAdeveloped from 1990s and still ongoing
  8. 8. CDMA Spread Spectrum
  9. 9. CDMA Spread Spectrum
  10. 10. CDMA Spread Spectrum
  11. 11. Signal Spreading Preview In DS spreading, the incoming digital speech signal is multiplied by a digital pseudo-noise (PN) code through a process called bit stream multiplication. The result of DS spreading is an encoded, spread spectrum, CDMA signal.
  12. 12. Signal Spreading Preview Fast frequency hopping This approach assumes that the two stations have: A common knowledge of the frequency hopping plan. Synchronized clocks
  13. 13. Signal Spreading Preview Time Hopping Time hopping assumes that the two stations in communication have: A common knowledge of the time-hopping "plan." Synchronized clocks
  14. 14. The Strengths of CDMA Increased system capacity. Cell sites can be larger. Enhanced privacy due to digital coding of CDMA signals. Enhanced call quality
  15. 15. Bit Stream Multiplication Concepts Bit stream multiplication is the process where an input bit stream of information (usually a digital speech signal) called b(t) is multiplied by a pseudo-noise (PN) code called c(t) to produce a new composite output signal called y(t).
  16. 16. Bit Stream Multiplication Concepts Consider the difference between spreading and scrambling:
  17. 17. Bit Stream Multiplication Concepts Data 01110101111010111101 Code 10110101001010101011 Code 10110101001010101011 Not Data 00110101001010101001
  18. 18. Bit Stream Multiplication Concepts b(t) · c(t) = y(t) b(t) · c(t) · c(t) = b(t)
  19. 19. Spreading and Despreading Remember that spreading occurs when a lower bit rate input signal b(t) is multiplied by a higher chip rate spreading code c(t) as shown. Bit Chip
  20. 20. Spreading and Despreading Cont. despreading takes y(t) and multiplies again by the same spreading PN code c(t) to recover the digital information signal b(t).
  21. 21. Scrambling and Descrambling Scrambling is often used for privacy. When scrambling is used for encryption, then descrambling is used for decryption.
  22. 22. Spreading and Power Spectral Density Spreading does not change total power. Spreading changes how the power is distributed over frequency.The following formulas hold true: G (processing gain) = Fc/Fb SF(Spreading Factor)=Rc/Rb =Tb/Tc
  23. 23. 1 1 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0 10 0 1 1 0 1 0 1 1 0 1 1 0 0 1 0 1 0 0 1
  24. 24. PN Codes A binary sequence with fixed length and has noise-like randomness Low correlation between shifted versions of the sequence Low correlation with other user signals (interference) and noise Good autocorrelation properties with own signal in synchronization
  25. 25. Code Generation Circuitry
  26. 26. Code Generation Circuitry D D D Flip Flop Flip Flop Flip Flop
  27. 27. Repeated Spreading and ScramblingCDMA systems use scrambling and spreading in several ways for: Encryption for privacy Channel identification Base station identification
  28. 28. Repeated Spreading and Scrambling C5 C1 C2 C1 C3 C4
  29. 29. Quick Review
  30. 30. RF Transmission Delay and its Effect Radio signals typically travel at a rate of about five microseconds to the mile. Assuming that a mobile is ten miles away from the base station, a 50 microsecond (µs) delay would be the result. 192 Chip = 260.4 nsec
  31. 31. RF Transmission Delay and its Effect
  32. 32. Locking On to a Particular PN Sequence Cont.
  33. 33. Locking On to a Particular PN Sequence Cont.
  34. 34. Locking On to a Particular PN Sequence Cont.
  35. 35. Signal Correlation With Offsets Less Than 1 Time Chip
  36. 36. Signal Correlation With Offsets Less Than 1 Time Chip
  37. 37. Signal Correlation
  38. 38. Multi-User Downlink Overview
  39. 39. Multi-User Downlink Overview
  40. 40. Multi-User Downlink Overview C3
  41. 41. Multi-User Uplink Overview
  42. 42. System PerformanceTraditional Systems Performance is measured by signal- to-noise ratio (S/N). The desired users signal versus noise.CDMA Systems Performance is measured by signal-to- interference ratio (S/I). The desired users signal versus interference from other users signals.
  43. 43. System Performance
  44. 44. Frequency Reuse
  45. 45. Multipaths and Delay Spread
  46. 46. Non-RAKE CDMA Reception
  47. 47. Non-RAKE CDMA ReceptionDifferential Delay > 1 Tc
  48. 48. Non-RAKE CDMA Reception Differential Delay < 1 Tc
  49. 49. RAKE Receiver Operation
  50. 50. RAKE Receiver Less multipath effect No ISI problem Better signal reception Less power needed

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