OVERVIEW: iDEN Voice Compression Technology

algorithms and one digital-signal processor (DSP) to perform voice compression/decompression and RF modulation/demodulation.

Base Station Control Channel

 

Transmitting 6 of 6 slots continually.

 

 

 

 

 

 

 

 

 

 

 

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Portable Unit

 

When turned on, scans for control station, then transmits one slot every six slots.

 

 

 

 

 

 

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Figure 1-2. i DEN TDMA Format

1.2i DEN Voice Compression Technology

Voice is converted into a digital bit stream by sampling the voice signal at a high rate and converting the samples into numbers, which are represented by bits. A sample consists of 8 bits. Approximately 8000 samples per second (64 Kbps) are required to maintain a reasonable quality.

Voice compression reduces the number of bits per second while maintaining the voice at an acceptable quality level. The iDEN system uses a coding technique called Vector Sum Excited Linear Prediction (VSELP) to compress voice to 4.2 or 8.0 Kbps. The compressed voice-data bits modulate the RF signal. The compression rate is based on the type of call (dispatch or interconnect) and the network configuration established by the local service provider.

Adding error-correction bits to the coded-voice bits increases the required RF-transmission bit rate to approximately 7.4 Kbps for the 4.2 Kbps voice coder and 14.8 Kbps for the 8.0 Kbps voice coder.

1.2.1RF Transmission Bursts

All RF transmissions within an iDEN system occur in 15-millisecond blocks called bursts. An

iDEN base station transmits bursts continuously on each RF frequency it uses. Transmission bursts from the stations are synchronized in time by signals received from the global positioning satellite

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Motorola i860 manual DEN Voice Compression Technology, RF Transmission Bursts