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CDMA WIRELESS COMMUNICATONS

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SIVAVARAPRASAD GAMPALA
SIVAVARAPRASAD GAMPALA

CDMA (Code Division Multiple Access) is a cellular technology where each user is assigned a unique code and all users transmit over the same frequency at the same time. It utilizes spread spectrum technology where the message signal is multiplied by a pseudo-random noise code before transmission. This allows all users to be identified by their unique code despite sharing the same frequency band. Some key advantages are high security, lower signal-to-noise ratio requirements, frequency reuse between cells, and entire spectrum availability to each user. However, quality of service can decrease as more users are added due to issues like self-jamming and the near-far problem where distant signals can drown out closer ones.

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CDMA Code Division Multiple Access
Definitions • TDMA – Time Division Multiple Access • FDMA – Frequency Division Multiple Access • CDMA – Code Division Multiple Access
CDMA Technology A cellular system based on code division multiple access (CDMA) has been developed by Qualcomm, Inc. and standardized by the Thlecommunications Industry Association (TIA) as an Interim Standard (15-95). Spread Spectrum technology of channel access used in 3G Comm. N/Ws. Each user uses the same frequency spectrum at the same time
CDMA Access method Accessing to the transmission channel at same frequency and same time Unique Code is assigned to each user for communication by pseudorandom generator Utilization of the B.W of the transmission channel efficiently
CDMA operation • Message Signal • Pseudo random noise code • XOR operation • Orthogonality helps identifying the individual users CDMA in which each channel is assigned a unique PN code which is orthogona' to PN codes used by other users.
CDMA Operation Spread Spectrum Multiple Access Technologies
CDMA Advantages High security due to encryption provided with random codes 1 The ability of CDMA to operate with a much smaller signal-to-noise ratio than conventional narrowband FM techniques 2 CDMA systems to use the same set of frequencies in every cell, which provides a large improvement in capacity 3 Each users is available with entire spectrum hence high voice quality 4
Disadvantages to using CDMA As the number of users increases, the overall quality of service decreases Self-jamming Near- Far- problem arises
Near- Far- problem in CDMA
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CDMA WIRELESS COMMUNICATONS

  • 2. Definitions • TDMA – Time Division Multiple Access • FDMA – Frequency Division Multiple Access • CDMA – Code Division Multiple Access
  • 3. CDMA Technology A cellular system based on code division multiple access (CDMA) has been developed by Qualcomm, Inc. and standardized by the Thlecommunications Industry Association (TIA) as an Interim Standard (15-95). Spread Spectrum technology of channel access used in 3G Comm. N/Ws. Each user uses the same frequency spectrum at the same time
  • 4. CDMA Access method Accessing to the transmission channel at same frequency and same time Unique Code is assigned to each user for communication by pseudorandom generator Utilization of the B.W of the transmission channel efficiently
  • 5. CDMA operation • Message Signal • Pseudo random noise code • XOR operation • Orthogonality helps identifying the individual users CDMA in which each channel is assigned a unique PN code which is orthogona' to PN codes used by other users.
  • 7. CDMA Advantages High security due to encryption provided with random codes 1 The ability of CDMA to operate with a much smaller signal-to-noise ratio than conventional narrowband FM techniques 2 CDMA systems to use the same set of frequencies in every cell, which provides a large improvement in capacity 3 Each users is available with entire spectrum hence high voice quality 4
  • 8. Disadvantages to using CDMA As the number of users increases, the overall quality of service decreases Self-jamming Near- Far- problem arises