CDMA

Base Station Variable Rate Vocoder

The base station uses a slightly different scheme when the vocoder moves to lower rates. First, EIA/TIA-95-B CDMA base stations do not pulse their transmissions. Rather, base stations repeat the...
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How Forward Link Traffic Channel Physical Layer in CDMA

Voice data at 9600 bps or 14400 bps (full rate) is first passed through a convolutional encoder, which doubles the data rate for the 9600 bps case or increases it...
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CDMA Vocoders how and why

Vocoders Convert Voice to/from Analog Using Data Compression There are Three CDMA Vocoders: IS-96A  Variable Rate (8 kbps maximum) CDG  Variable Rate (13 kbps maximum) EVRC  Variable Rate (improved 8...
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How Frame Formats in CDMA

Once the analog voice is compressed by one of the vocoder processes, some additional data is added to produce a frame. Each frame in CDMA is 20 milliseconds regardless of...
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How Forward Error Protection in CDMA

Uses Half-Rate Convolutional Encoder Outputs Two Bits of Encoded Data for Every Input Bit Unlike many digital cellular systems, CDMA provides powerful error correction to all voice data bits. This...
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How Traffic Channel Forward Link Modifications in CDMA

In an effort to provide CDMA with even greater voice quality, the CDG (CDMA Development Group) has proposed and implemented a new vocoder. This new vocoder uses and improved, higher...
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CDMA System Time

For both mobiles and base station in direct sequence CDMA must be synchronized. In the IS-95A system, synchronization is based on the Global Positioning Satellite system time. How Does CDMA...
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How Long Code Generation and Scrambling in CDMA

All base stations digital transmissions are referenced to a common CDMA system-wide time scale that uses the GPS time scale, which is traceable to and synchronous with Universal Coordianted Time...
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Closed Loop Power Control Puncturing in CDMA

Once the data has been scrambled with the user specific long code, the closed loop power control data is then punctured into the data stream. Remember that the power control...
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why the data needs to be scrambled again at the same rate

After all of the coding used so far in the forward channel, you’re probably wondering why the data needs to be scrambled again at the same rate. If all cells...
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How Auto Correlation in CDMA

Auto-correlation is simply a comparison of a signal against itself. For a digital sequence, such as the short codes used in EIA/TIA-95-B, this comparison is a measure of the number...
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How Forward Link Channel Format in CDMA

The Base Station transmitter signal is, however, the composite of many channels (with a minimum of four). The Pilot channel is unmodulated (Walsh code 0); it consists of only the...
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