Particular station from the received signal.
Fourth and fifth row demonstrates how to get the signal of a normalized isĪssignments to four stations. Station transmit -1, then the result is +2. For example, if in one chip period, three stations transmit +1 and one Two or more stations transmit simultaneously, their bipolar signals gets added For the moment, we assume that all stationsĪre synchronized in time, so all chip sequences begin at the same instant. Sequence, it can transmit a 0 by sending the inverse of its chip sequence, or itĬan be silent and transmit nothing. Also note that, S*(~S) is -1.ĭuring each bit time, a station can transmit a 1 by sending its chip Sequence with itself is 1 This is because each m terms in the inner The normalized inner product with any chip Orthogonal, by which we mean that the normalized inner product of any twoĭistinct chip sequences, S and T (written as S*T, Let us use the symbol S to indicate the m-chip vector for We will show chip sequences in parentheses, so a 1 bit for It is more easier to use a bipolar notation, with binary 0 being -1 andīinary 1 being +1. Reconstruct the code for synchronous detection.
ItĪppears random, but is actually deterministic, so that the receiver can Order to protect the signal, the chip sequence code used is pseudo-random. (assuming no changes in the modulation or encoding techniques). To mb chips/sec can only be done if the bandwidth available is increasedīy a factor of m, making CDMA a form of spread spectrum communication Increasing the amount of information to be sent from b bits/sec = 8, if station A is assigned the chip sequence 00011011, it sends a 1 bit by
To transmit a 0 bit, it sends the one'sĬomplement of its chip sequence. Is assigned a a unique m-bit chip sequence. Typically there are 64 or 128 chips per bit. In CDMA, each bit time is subdivided into m short intervalsĬalled chips. The key to CDMA is to be able toĮxtract the desired signal while rejecting everything else as random Instead, itĪssumes that multiple signals add linearly.
Relaxes the assumption that colliding frames are totally garbled. Multiple simultaneous transmissions are separated using coding theory. In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access For radio systems there are two resources, frequency and time.
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