System and method for bit interleaving of full-rate speech data

Details System and method for bit interleaving of full-rate speech data System and method for bit interleaving of full-rate speech data

2000-05-26

2001-11-27

Dorvil, Richemond (Department: 2641)

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

C704S200000

Reexamination Certificate

active

06324504

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of interleaving bits for coding, transmission, or storage, and more specifically to implementations of the bit re-ordering table for full-rate speech, Table 1 in GSM 05.03.
2. Description of Related Art
A method for encoding full rate speech is specified in the Global System for Mobile Communications' technical specification 05.03 (GSM 05.03) “Digital cellular telecommunications system (Phase 2+); Channel coding” version 5.1.0, May 1996. This publication is hereby incorporated by reference as though completely set forth herein.
The encoding method includes an interleaving process which is carried out in order to combat the burst errors that occur due to the mobile channel. Interleaving helps to separate out the individual errors within any error bursts and thereby effectively randomize the bit errors that are present. Then it is the job of a random error correcting code such as a convolutional code to correct as many of the errors as possible. The interleaver operates to reorder and spread bits from forward error correction (FEC) coded frames into data blocks for time division multiple access (TDMA) data bursts.
Prior art interleaving is performed by taking a single, current speech frame and distributing the bits throughout eight data blocks. Consequently, this prior art method requires that eight data blocks be simultaneously maintained in memory while speech frame bits are distributed among them.
SUMMARY OF THE INVENTION
The present invention provides a memory-efficient system and method for generating data blocks “on demand” for TDMA data bursts. This system and method feature a novel approach which treats the problem not as one of having one speech frame comprising a plurality of bits to encode and then for each bit finding the destination in one of a plurality of data blocks for TDMA data bursts, but rather the reverse, i.e. to consider each TDMA burst individially and then to find in each of a plurality of speech frames the source bits to be used. In one embodiment of the present invention, a GSM transmitter module converts forward error correction (FEC) coded full-rate speech frames into TDMA data blocks. The transmitter module includes a memory configured to store the FEC coded frames in a current frame buffer and a previous frame buffer, an address generator configured to generate addresses of words in the current frame buffer during even clock cycles and addresses of words in the previous frame buffer during odd clock cycles. To generate the word addresses, the address generator operates on word offsets provided by a bit position generator, which also generates intra-word bit offsets. The memory provides the data words requested by the address generator to a multiplexer, which the selects a bit from each of the data words as indicated by the intra-word bit offsets from the bit position generator. The stream of bits from the multiplexer forms the bit reordered and frame interleaved data for the data blocks.
In a preferred embodiment, the present invention comprises a method for bit reordering and frame interleaving for full rate speech in a GSM system. The method includes receiving two frames of forward error correction coded speech data and storing each frame in a separate buffer. The method also includes transferring bits from the buffers to a TDMA block. Each bit transfer includes determining the base address of one of the buffers, calculating a word offset within the selected buffer, calculating a bit offset within the selected word, and transferring the selected bit to a bit position in the TDMA block.


REFERENCES:
patent: 5084891 (1992-01-01), Ariyavisitakul et al.
patent: 5603081 (1997-02-01), Raith et al.
patent: 6035434 (2000-03-01), Sazzad et al.
Global System for Mobile Communications' Technical Specification 05.03 (GSM 05.03) Digital cellular telecommunications system (Phase 2+); Channel coding: version 5.1.0, May 1996, pp. 1-31.

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