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What is spreading in CDMA?
A spreading sequence is a binary sequence that appears random but can be reproduced in a deterministic manner by intended receivers. These spreading sequences are used to encode and decode a user’s signal in asynchronous CDMA in the same manner as the orthogonal codes in synchronous CDMA (shown in the example above).
What is spreading in data communication?
In DSSS, a spreading code is used to map each data bit in the original signal to multiple bits in the transmitted signal. The pseudorandom code (spreading code) spreads the input data across a wider frequency range compared with the input frequency. In the frequency domain, the output signals appear as noise.
How is spread spectrum used in CDMA?
In Code Division Multiple Access (CDMA) systems all users transmit in the same bandwidth simultaneously. Communication systems following this concept are “spread spectrum systems”. In this transmission technique, the frequency spectrum of a data-signal is spread using a code uncorrelated with that signal.
What is CDMA explain its working?
Code Division Multiple Access (CDMA) is a sort of multiplexing that facilitates various signals to occupy a single transmission channel. It optimizes the use of available bandwidth. The technology is commonly used in ultra-high-frequency (UHF) cellular telephone systems, bands ranging between the 800-MHz and 1.9-GHz.
What are the advantages of CDMA?
One of the main advantages of CDMA is that dropouts occur only when the phone is at least twice as far from the base station. Thus it is used in the rural areas where GSM cannot cover. Another advantage is its capacity; it has a very high spectral capacity that it can accommodate more users per MHz of bandwidth.
Why do we need to spread a signal?
There are several potential advantages to spreading the spectrum of a signal: Security advantages—The spread signal has many properties in common with noise, and, if the spectral density is low, it can be difficult to detect the presence of the signal unless the spreading sequence is known.
Where is CDMA used?
In the US, Verizon, US Cellular, and the old Sprint network (now owned by T-Mobile) use CDMA. AT and T-Mobile use GSM. Most of the rest of the world uses GSM. The global spread of GSM came about because in 1987, Europe mandated the technology by law, and because GSM comes from an industry consortium.
What is the uses of CDMA?
CDMA allows for greater development and use of broadband devices such as GPS units, PDA’s, wireless laptop modems, Internet capable cell phones, and other innovative devices.
What are the applications of CDMA?
How is the spread factor of a CDMA signal calculated?
The ratio between the user symbol time and the chip time is called the spread factor. The transmit signal occupies a bandwidth that equals the spread factor times the bandwidth of the user data. Figure: A DS-CDMA signal is generated by multiplication of a user data signal by a code sequence. Source: Jack Glas, T.U. Delft.
What are the advantages and disadvantages of CDMA?
Use of wide bandwidth: CDMA, like other spread spectrum technologies uses a wider bandwidth than would otherwise be needed for the transmission of the data. This results in a number of advantages including an increased immunity to interference or jamming, and multiple user access.
How is a DS-CDMA transmit signal generated?
The transmit signal occupies a bandwidth that equals the spread factor times the bandwidth of the user data. Figure: A DS-CDMA signal is generated by multiplication of a user data signal by a code sequence. Source: Jack Glas, T.U. Delft.
How are data rate bit sequences used in CDMA?
Data to be transmitted is multiplied with a high data rate bit sequence and then modulated onto an RF carrier to produce a signal with a much wider bandwidth than data alone. To reconstitute the data at the receiver the same high data rate bit sequence is used to extract the data from the signal.