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multiplex.ppt
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STC Systel Training Center 1
Multiple access techniques
• 1-FDMA
• 2-TDMA
• 3-CDMA
• 4-OFDMA
• 5-DATA FRAMES
STC Systel Training Center 7
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications
• Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 8
Outline
• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 9
Multiple Access Techniques
• Lack of resources.• Trying to optimize the usage of the available ones.
STC Systel Training Center 10
Time Division Multiple Access (TDMA)
• The whole system spectrum is allocated for single user for pre-defined burst of time.
STC Systel Training Center 11
Time Division Multiple Access (TDMA)
• Advantages- More efficient use of spectrum, compared to FDMA - No need for precise narrowband filters- Flexible bit rate- Easy for mobile or base stations to initiate and execute hands off- Extended battery life
STC Systel Training Center 12
Time Division Multiple Access (TDMA)
• Disadvantages- Requires network-wide timing synchronization- Multipath distortion
STC Systel Training Center 13
Frequency Division Multiple Access (FDMA)
• Pre-defined band of the system spectrum is allocated for single user all the time.
STC Systel Training Center 14
Frequency Division Multiple Access (FDMA)
• Advantages- Sub-bands can be treated as independent systems - Capacity increase can be obtained by reducing the information bit rate and using efficient digital code- No need for network timing
STC Systel Training Center 15
Frequency Division Multiple Access (FDMA)
• Disadvantages- The presence of guard bands- Requires right RF filtering to minimize adjacent channel interference- Channel bandwidth is relatively narrow (30kHz)- Maximum bit rate per channel is fixed- Idle channels add to spectrum inefficiency
STC Systel Training Center 16
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 17
Code Division Multiple Access (CDMA)
• The whole system spectrum is allocated for single user all the time.
STC Systel Training Center 18
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 19
Spread Spectrum Technique• Spectrum: Power spectrum associated with
the base-band signal.• Spread Spectrum: Spreading the base-band
spectrum over a given bandwidth.• Total energy under the power spectrum curve
remains the same after spreading and amplitude may reach the noise level.
STC Systel Training Center 20
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 23
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 25
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 27
Code Division Multiple Access (CDMA)• Advantages
- Greatest spectrum efficiency - No absolute limit on the number of users- Easy addition of more users- Impossible for hackers to decipher the code sent- No sense of handoff when changing cells “Soft Hand-off”- Simplified frequency planning- Random Walsh codes enhance user privacy- Precise power control increases talk time and battery life for mobile phones
STC Systel Training Center 28
Code Division Multiple Access (CDMA)
• Disadvantages- As the number of users increases, the overall quality of service decreases- Near- Far- problem arises- Low ability of complying with existing systems
STC Systel Training Center 29
Multiple Access Techniques Comparison
TDMA FDMA CDMA
Spectrum Efficiency Medium Low High
Security Low Low High
Backward Compatibility Medium High Low
Ease of Implementation High High Low
Frequency Reuse Same frequency Depends on
interference level Same frequency
Transmission Mode Burst Continuous Continuous
STC Systel Training Center 30
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 31
Applications
• IS-95: The North American DS-CDMA Standard (cdmaOne)
• WCDMA (UMTS)• GPS
STC Systel Training Center 32
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications - Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 35
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications
• Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 37
Basic System Architecture
Serial to parallel
converterIFFT
First Data Symbol
Last Data Symbol
TPS and Pilots
First Pilot sub-carrier
Last Pilot sub-carrier
First TPS sub-carrier
r172
r173 =y0
r206
r1875 =y1511
r1876
r2047
r1877
r171
r0
zeros
zeros
STC Systel Training Center 39
Basic System Architecture
IFFT
Parallel to Serial
Converter
x0
x1535
x1536
x2047
x1536
x2047
STC Systel Training Center 43
Outline• Multiple Access Techniques• Code Division Multiple Access (CDMA)
- Spread Spectrum Technique- Direct Sequence Spreading/De-spreading- PN Sequences and orthogonal codes- Immunity to interference- Applications
• Orthogonal Frequency Division Multiplexing (OFDM)- FDM vs OFDM- Basic System Architecture- Applications
STC Systel Training Center 49
T1 Frame
-- Each T1 line is split into 24 channels referred to as DS0's. Each channel is 8 bits wide and the frame is sent on a 8KHz boundary.
- Every frame has synchronization bit at the beginning (8000 Hz).
The data capacity is therefore (24x8x8000)+8000 = 1.544Mbits/sec.