Unformatted text preview: tage of blocked calls) Channel 1 Bandwidth Channel 2 Channel 3 Channel 4 Time Time Division Multiple Access (TDMA) The whole channel is assigned to each user, but the users are multiplexed in time during communication. Each communicating user is assigned a particular time slot, during which it communicates using the entire frequency spectrum The data rate of the channel is the sum of the data rates of all the multiplexed transmissions There is always channel interference between transmission in two adjacent slots because transmissions tend to overlap in time. This interference limits the number of users that can share the channel Channel 3 Channel 3 Channel 3 Channel 2 Channel 2 Channel 1 Channel 1 Channel 2 Channel 2 Channel 4 Channel 4 Channel 1 Bandwidth Time Code Division Multiple Access (CDMA) CDMA, a type of a spread-spectrum technique, allows multiple users to share the same channel by multiplexing their transmissions in code space. Different signals from different users are encoded by different codes (keys) and coexist both in time and frequency domains A code is represented by a wideband pseudo noise (PN) signal When decoding a transmitted signal at the receiver, because of low crosscorrelation of different codes, other transmissions appear as noise. This property enables the multiplexing of a number of transmissions on the same channel with minimal interference The maximum allowable interference (from other transmissions) limits the number of simultaneous transmissions on the same channel
Bandwidth All channels share bandwidth Time Code Division Multiple Access (CDMA) Spreading of the signal bandwidth can be performed using
- Direct Sequence (DS): the narrow band signal representing digital data is multiplied by a wideband pseudo noise (PN) signal representing the code. Multiplication in the time dom...
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This note was uploaded on 08/25/2011 for the course EEL 5937 taught by Professor Staff during the Spring '08 term at University of Central Florida.
- Spring '08