Code Division Multiple Access(CDMA); 1. Frequency Division Multiple Access (FDMA). Standard. 1. GSM (TDMA); 2. IS (CDMA); 3. American Mobile Phone. GSM Vs. CDMA An Overview. Bhushan G. Jagyasi. Lecturer, Elex & Tele Comm Dept. Thadomal Shahani Engineering College. Classification Of Existing. GSM f7 7 cell re-use pattern f6 f1 f5 f3 f2 f6 f1 f5 f4 f7 f2 f4 ncy Reuse. Division Multiple Access CDMA is a "spread spectrum" technology – Spreads the information contained in a particular signal of interest over a much greater bandwidth than.
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Frequency-hopping spread spectrum - Wikipedia
As a result, bandwidth can be used more efficiently. Military use[ edit ] Spread-spectrum signals are highly resistant to deliberate jammingunless the adversary has knowledge of the spreading characteristics.
Military radios use cryptographic techniques to generate cdma pdf ppt channel sequence under the control of a secret Transmission Security Key TRANSEC that the sender and receiver share in advance. By itself, frequency hopping provides cdma pdf ppt limited protection against eavesdropping and jamming.
Most modern military frequency hopping radios also employ separate encryption devices such as the KY Speech Security Equipment.
Despite the name's similarity to the FRS allocationthe system is a proprietary design, rather than cdma pdf ppt official FCC allocated service. Frequency-hopping spread spectrum technology is also used in many hobby RC radio controlled transmitters and receivers used for model cars, airplanes, and drones.
CDMA - Introduction
Technical considerations[ edit ] The overall bandwidth required for frequency hopping is much wider than that cdma pdf ppt to transmit the same information using only one carrier frequency. However, because transmission occurs only on a small portion of this bandwidth at any given time, the effective interference bandwidth is really the same.
While providing no extra protection against wideband thermal noisethe frequency-hopping approach does reduce the degradation caused by narrowband interference sources. One of the challenges of frequency-hopping systems is to synchronize the transmitter and receiver.
One approach cdma pdf ppt to have a guarantee that the transmitter will use all the channels in a fixed period of time.
The cdma pdf ppt can then find the transmitter by picking a random channel and listening for valid data on that channel. The transmitter's data is identified by a special sequence of data that is unlikely to occur cdma pdf ppt the segment of data for this channel, and the segment can also have a checksum for integrity checking and further identification.
The transmitter and receiver can use fixed tables of channel sequences, so that once synchronized they can maintain communication by following the table. On each channel segment, the transmitter can send its current location in the table. Both frequency hopping and direct sequence systems can transmit cdma pdf ppt 1 Watt, a thousand-fold increase from the 1 milliwatt limit on non-spread-spectrum systems.
The Federal Communications Commission FCC also prescribes a minimum number of channels and a maximum dwell time for each channel.
In a real multipoint spread spectrum radio system, space allows the possibility of multiple transmissions on the same frequency cdma pdf ppt multiple radios in a geographic area.
This creates the possibility cdma pdf ppt system data rates that are higher than the Shannon limit for a single channel. Spread spectrum systems do not violate the Shannon limit. Spread spectrum systems rely on excess signal to noise ratios for sharing of spectrum.
Beam steering and directional antennas also facilitate increased system performance by providing isolation between remote radios. Multiple cdma pdf ppt edit ] In Guglielmo Marconi experimented with frequency-selective reception in an attempt to minimise interference.
Frequency-hopping spread spectrum
Assume we have a cdma pdf ppt students gathered in a classroom who would like to talk to each other simultaneously. Nothing would be audible if everyone starts speaking at the same time. Either they must take turns to speak or use different languages to communicate.
The second option is quite similar to CDMA — cdma pdf ppt speaking the same language can understand each other, while other languages are perceived as noise and rejected.
Similarly, in radio CDMA, each group of users is given a shared code.