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CDMA |
Also found in: Acronyms, Wikipedia | 0.04 sec. |
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(Code Division Multiple Access) A method for transmitting simultaneous signals over a shared portion of the spectrum. The foremost application of CDMA is the digital cellular phone technology from QUALCOMM that operates in the 800 MHz band and 1.9 GHz PCS band. CDMA phones are noted for their call quality. Transmitting from the Base Station Each voice conversation is compressed with a vocoder. The output is doubled by a convolutional encoder that adds redundancy for error checking. Each bit from the encoder is replicated 64 times and exclusive OR'd with a Walsh code that is used to identify that call from the rest. The output of the Walsh code is exclusive OR'd with the next string of bits (PN sequence) from a pseudo-random number generator, which is used to identify all the calls in a particular cell's sector. At this point, there is 128 times as many bits as there were from the vocoder's output. All the calls are combined and modulated onto a carrier frequency in the 800 MHz range. Receiving at the Cellphone The received frequencies are quantized into bits ("chips") by the analog-to-digital converter (ADC). The output is run through the Walsh code and PN sequence correlation receiver to recover the transmitted bits of the original signal. When 20ms of voice data is received, a Viterbi decoder corrects the errors using the convolutional code. The Viterbi output goes to the vocoder and digital-to-analog converter (DAC), which decompresses the bits and turns them back into waveforms (sound).
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| Ericsson (NASDAQ:ERICY) has entered into contracts with China Unicom to deploy Ericsson CDMA infrastructure equipment in seven provinces in China. CHICAGO -- BridgePort Networks, the leader in MobileVoIP convergence, has been awarded a 3G CDMA Industry Achievement Award. QUALCOMM Incorporated (Nasdaq: QCOM), pioneer and world leader of Code Division Multiple Access (CDMA) digital wireless technology, has announced that it has entered into a CDMA modem card license agreement with San Diego-based Cyberlane Inc. |
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