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METHOD FOR FASTER AND LOWER POWER CONSUMPTION OF ITERATIVE DECODING ALGORTIHMS WHEN USING A TYPE-II HYBRID ARQ TRANSMISSION SCHEME.

IP.com Disclosure Number: IPCOM000008990D
Original Publication Date: 2002-Jul-29
Included in the Prior Art Database: 2002-Jul-29
Document File: 4 page(s) / 142K

Publishing Venue

Motorola

Related People

Guillaume VIVIER: AUTHOR [+4]

Abstract

Today's wireless systems must provide reliable data services. For wired links, reliability is traditionally obtained thanks to repetition. A packet is retransmitted when the previous attempt was unsuccessful. Such mechanism is named ARQ (Automatic Repeat Request). In the case of wireless transmissions, because of the poor quality of the link, packets should be protected against the channel noise. Protection is given by forward error coding (FEC), e.g. transmitting additional bits to the packet. However, to provide the same quality as in wired system, FEC overhead could lead to very inefficient transmissions. As a result, hybrid schemes, combining FEC and ARQ has been defined. In parallel, recent classes of FEC, such as the Turbo-Codes or Low Density Parity check (LDPC) have appeared or reappeared thanks to the iterative decoding technique which provides very good protection for an acceptable complexity. These schemes outperforms all classical coding schemes. Combining iterative decoding and ARQ in an efficient way should lead to very powerful schemes to provide efficient packet transmission over a wireless interface.

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Method for faster and lower power consumption of iterative decoding algortihms when using a type-II hybrid ARQ transmission scheme.
Introduction

Today's wireless systems must provide reliable data services. For wired links, reliability is traditionally obtained thanks to repetition. A packet is retransmitted when the previous attempt was unsuccessful. Such mechanism is named ARQ (Automatic Repeat Request). In the case of wireless transmissions, because of the poor quality of the link, packets should be protected against the channel noise. Protection is given by forward error coding (FEC), e.g. transmitting additional bits to the packet. However, to provide the same quality as in wired system, FEC overhead could lead to very inefficient transmissions. As a result, hybrid schemes, combining FEC and ARQ has been defined.

In parallel, recent classes of FEC, such as the Turbo-Codes or Low Density Parity check (LDPC) have appeared or reappeared thanks to the iterative decoding technique which provides very good protection for an acceptable complexity. These schemes outperforms all classical coding schemes.

Combining iterative decoding and ARQ in an efficient way should lead to very powerful schemes to provide efficient packet transmission over a wireless interface.

One of the main drawback of iterative decoding is that several iterations are needed to take a decision, either to accept the decoded code word (when errorless) or to ask the transmitter to transmit additional information when the decoder fails. These iterations might lead to a delay increase and of course are power consuming.

The aim of the invention is to reduce the number of iteration and thus to speed up the iterative algorithm in order to save power and time.

Description of the invention

We analyze the throughput of an idealized protocol for reliable packets communication based on type-II Hybrid Automatic Repeat reQuest (HARQ), a combination of forward error correction (FEC) and automatic repeat request (ARQ); in particular it is based on a Incremental Redundancy scheme when codes, decoded with an iterative technique, are used.

The codeword is divided into ‘M’ bursts each of which is sent during a time slot. Any kind of wireless systems could be used for the transmissions (TDMA, CDMA, FDMA).

The decoder uses an iterative algorithm to decode the codeword. The user starts sending the first burst, if the receiver can decode the complete codeword from this burst, it sends a positive acknowledgment (ACK) and the transmission of the current codeword is stopped. If the decoder detects an error, a negative acknowledgment (NACK) is sent back. In this last case the user sends an other burst of the same codeword. The decoder processes jointly the two received bursts, and so on. Since the codeword has ‘M’ sub-blocks, the message can be transmitted in at most ‘M’ bursts: if successful decoding does not occur after ‘M’ transmitted bursts the message is lost.

In general these codes are well define...