07-07-2012, 01:17 PM
SEMINAR ON CDMA/FDMA/TDMA
[attachment=27114]
International Cocktail Party
FDMA – Large room divided up into small rooms. Each pair of people takes turns speaking.
TDMA – Large room divided up into small rooms. Three pairs of people per room, however, each pair gets 20 seconds to speak.
CDMA – No small rooms. Everyone is speaking in different languages. If voice volume is minimized, the number of people is maximized.
Advantages of TDMA
Flexible bit rate
No frequency guard band required
No need for precise narrowband filters
Easy for mobile or base stations to initiate and execute hands off
Extended battery life
TDMA installations offer savings in base station equipment, space and maintenance
The most cost-effective technology for upgrading a current analog system to digital.
Disadvantages to using TDMA
Requires network-wide timing synchronization
Requires signal processing fro matched filtering and correlation detection
Demands high peak power on uplink in transient mode
Multipath distortion
Advantages of FDMA
If channel is not in use, it sits idle
Channel bandwidth is relatively narrow (30kHz)
Simple algorithmically, and from a hardware standpoint
Fairly efficient when the number of stations is small and the traffic is uniformly constant
Capacity increase can be obtained by reducing the information bit rate and using efficient digital code
No need for network timing
No restriction regarding the type of baseband or type of modulation
Disadvantages to using FDMA
The presence of guard bands
Requires right RF filtering to minimize adjacent channel interference
Maximum bit rate per channel is fixed
Small inhibiting flexibility in bit rate capability
Does not differ significantly from analog system
Advantages of CDMA
Many users of CDMA use the same frequency, TDD or FDD may be used
Multipath fading may be substantially reduced because of large signal bandwidth
No absolute limit on the number of users
Easy addition of more users
Impossible for hackers to decipher the code sent
Better signal quality
No sense of handoff when changing cells
Disadvantages to using CDMA
As the number of users increases, the overall quality of service decreases
Self-jamming
Near- Far- problem arises
[attachment=27114]
International Cocktail Party
FDMA – Large room divided up into small rooms. Each pair of people takes turns speaking.
TDMA – Large room divided up into small rooms. Three pairs of people per room, however, each pair gets 20 seconds to speak.
CDMA – No small rooms. Everyone is speaking in different languages. If voice volume is minimized, the number of people is maximized.
Advantages of TDMA
Flexible bit rate
No frequency guard band required
No need for precise narrowband filters
Easy for mobile or base stations to initiate and execute hands off
Extended battery life
TDMA installations offer savings in base station equipment, space and maintenance
The most cost-effective technology for upgrading a current analog system to digital.
Disadvantages to using TDMA
Requires network-wide timing synchronization
Requires signal processing fro matched filtering and correlation detection
Demands high peak power on uplink in transient mode
Multipath distortion
Advantages of FDMA
If channel is not in use, it sits idle
Channel bandwidth is relatively narrow (30kHz)
Simple algorithmically, and from a hardware standpoint
Fairly efficient when the number of stations is small and the traffic is uniformly constant
Capacity increase can be obtained by reducing the information bit rate and using efficient digital code
No need for network timing
No restriction regarding the type of baseband or type of modulation
Disadvantages to using FDMA
The presence of guard bands
Requires right RF filtering to minimize adjacent channel interference
Maximum bit rate per channel is fixed
Small inhibiting flexibility in bit rate capability
Does not differ significantly from analog system
Advantages of CDMA
Many users of CDMA use the same frequency, TDD or FDD may be used
Multipath fading may be substantially reduced because of large signal bandwidth
No absolute limit on the number of users
Easy addition of more users
Impossible for hackers to decipher the code sent
Better signal quality
No sense of handoff when changing cells
Disadvantages to using CDMA
As the number of users increases, the overall quality of service decreases
Self-jamming
Near- Far- problem arises