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e. Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth).
DS-CDMA (Direct-Sequence Code Division Multiple Access) is a multiple access scheme based on DSSS, by spreading the signals from/to different users with different codes. It is the most widely used type of CDMA. Cordless phones operating in the 900 MHz, 2.4 GHz and 5.8 GHz bands; IEEE 802.11b 2.4 GHz Wi-Fi, and its predecessor 802.11-1999.
For the case of MC-DS-CDMA where OFDM is used as the modulation scheme, the data symbols on the individual subcarriers are spread in time by multiplying the chips on a PN code by the data symbol on the subcarrier. For example, assume the PN code chips consist of {1, −1} and the data symbol on the subcarrier is −j.
Conceptually, OFDM is a specialized frequency-division multiplexing (FDM) method, with the additional constraint that all subcarrier signals within a communication channel are orthogonal to one another. In OFDM, the subcarrier frequencies are chosen so that the subcarriers are orthogonal to each other, meaning that crosstalk between the sub ...
Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by beginning transmission only after the channel is sensed to be "idle". [1][2] When they do transmit, nodes transmit their packet data in its entirety.
Channel access method. In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. [1] Examples of shared physical media are wireless networks, bus networks, ring networks and point-to-point ...
Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. [1] The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same ...
Chip (CDMA) In digital communications, a chip is a pulse of a direct-sequence spread spectrum (DSSS) code, such as a pseudo-random noise (PN) code sequence used in direct-sequence code-division multiple access (CDMA) channel access techniques. In a binary direct-sequence system, each chip is typically a rectangular pulse of +1 or −1 amplitude ...