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What is CDMA
Technology
Product

CDMA is the fastest growing wireless technology that consistently provides better capacity for voice and data communications than other commercial mobile technologies. It is the platform on which 3G (3rd Generations) technologies are built.

The world is demanding more from wireless communication technologies than ever before.

More people around the world are subscribing to wireless services and consumers are using their phones more frequently.

CDMA is a "spread spectrum" technology, allowing many users to occupy the same time and frequency allocations in a given band/space. As its name implies, CDMA works by converting speech into digital information, which is then transmitted as a radio signal over a wireless networks. Using a unique code to distinguish it from others. In the same spectrum, CDMA enables many more people to share the airwaves at the same time without static cross-talk or interference.

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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 800MHz band and 1.9GHz PCS band. CDMA phones are noted for their excellent call quality and long battery life.

CDMA is less costly to implement, requiring fewer cell sites than the GSM and TDMA digital cell phone systems and providing three to five times the calling capacity. It provides more than 10 times the capacity of the analog cell phone system (AMPS). CDMA has become widely used in north America and is also expected to become the third-generation (3G) technology for GSM.

Unlike the other digital systems that use TDMA, which divides the spectrum into different time slots, CDMA's spread spectrum technique overlaps every transmission on the same carrier frequency by assigning a unique code to each conversation. The often-used analogy for this is the ability for you to discern your own speaking language in a room full of people speaking many other languages.

After the speech codec converts voice to digital, CDMA spreads the voice stream over the full 1.25MHz bandwidth of the CDMA channel, coding each stream separately so it can be decoded at the receiving end. The rate of the spreading signal is known as the "chip rate," as each bit in the spreading signal is called a "chip" (no relation to an integrated circuit). All voice conversations use the full bandwidth at the same time. One bit from each conversation is multiplied into 128 coded bits by the spreading techniques, giving the receiving side an enormous amount of data it can average just to determine the value of one bit. CDMA transmission has been used by the military for secure phone calls. Unlike FDMA and TDMA methods, CDMA's wide spreading signal makes it difficult to detect and jam. For more information, contact the CDMA Development Group (CDG) at www.cdg.org. See BREW, wireless generations, IS-95, CDMA2000, W-CDMA, GSM, FDMA, TDMA, CDPD, CDG and spread spectrum.

How the Technology Works CDMA is a fascinating technology, and the illustration below shows you how calls from a base station are encoded and transmitted to a cell phone.

At the base station, each voice conversation is converted into digital code and compressed with a vocoder. The vocoder 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. At the receiving side, the received signals are quantized (turned into bits) and 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, and that all goes to the vocoder which turns the bits back into waveforms(sound).

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Model C2610
Description
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Main Features
  • Up to 500 messages can be saved in the phone
  • Build-in 31-chord polyphonic ringtones
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Description
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Main Features
  • 262K TFT color display
  • MP3/MP4
  • 1,300K Pixels camera
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Model C2800
Description
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Main Features
  • FM radio with integrated speakerphone
  • Ultra-long standby time
  • 32-chord ring tones and MP3 ring tones
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Model C5300
Description
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Main Features
  • 65536 color display
  • 0.3 mega pixels camera
  • BREW download
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  • WAP 2.0
  • Musical keyboard
  • Large phonebook capacity
  • SMS group sending
  • 16chord and MP3 ringtones
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  • Type-ahead for words and phrases
  • Contact groups
  • Shortcut keys
  • Alarm clock and calendar
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