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Method and Apparatus for Extending an Incremental Redundancy (IR) Process at the Physical Layer by use of an Auxiliary Process initiated above the Physical Layer

IP.com Disclosure Number: IPCOM000205887D
Publication Date: 2011-Apr-06
Document File: 21 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Related People

Jeremy J. Tucker: ATTORNEY

Abstract

Embodiments of the invention include a combined method and apparatus that is able to lower the code rate achieved by the PHY without changing the channel code or the core of the existing IR scheme. It works in conjunction with the existing code and core IR processes by adding an auxiliary channel code (AUX-code) before such processes. With proper control layer signaling, and additional decoding functions for the AUX-code at the receiver, the system is able to use either a parallel HARQ-IR process, or a single serial TTI process, or a bundled TTI process, to support use of the AUX-code.

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1.  TITLE OF THE INVENTION

Method and Apparatus for Extending an Incremental Redundancy (IR) Process at the Physical Layer by use of an Auxiliary Process initiated above the Physical Layer

2.  INVENTOR(S) INFORMATION

Sean A. Ramprashad

Sayandev Mukherjee

3. FIELD OF THE INVENTION

Embodiments of the invention focus on the Physical (PHY) Layer design of systems such as that of 3GPP’s Long Term Evolution (LTE) which includes within the physical layer an Incremental Redundancy (IR) scheme.   Such an IR scheme is also known as a Hybrid ARQ-IR (HARQ-IR) process. The performance and effectiveness of such a scheme depends on the lowest coding rate achievable by the channel code used at the PHY layer.   Embodiments of the invention effectively lower the code rate achieved by the PHY without changing the channel code at the PHYor any of the core functions of the existing IR scheme.   It does so by exploiting the IR process itself in conjunction with new packets generated at the RLC layer or above.  By doing so it expands the operational capability of the PHY allowing it to target users that require lower code rates.  It also enables the system to support more aggressive use of IR over a wider range of effective rates and a larger number of IR transmissions.

4. BACKGROUND OF THE INVENTION

Embodiments of the invention focus on the Physical (PHY) Layer design of systems such as 3GPP’s Long Term Evolution (LTE) which includes within the physical layer an Incremental Redundancy (IR) scheme.   This incremental redundancy scheme allows the PHY layer to progressively, over many transmissions, lower the effective code rate applied to the information stream, thus making it progressively easier for a user to receive and decode  the stream.  It follows that the performance, operational range, and effectiveness of such a scheme depends on the lowest coding rate of the channel code used at the PHY layer.    In LTE (and other systems), the physical layer code rate is rate 1/3.  As will be seen in examples to follow, this can often severely limit the effectiveness of IR after the third (progressive) transmission.

To illustrate the operation of such a system we briefly review the design in 3GPP LTE (up to Release 9).   Details are known to those familiar with the state of the art.  Such details also apply to many systems other than LTE.  Many texts and standard documents are available to provide such details.  

Figure 1 shows the typical process used in many systems (including LTE) whereby a packet at the Radio Link Control (RLC) Layer is then encoded at the PHY layer before transmission using a channel code.  In Figure 1 the channel code is a so-called turbo code.  The design of turbo coders is well-known to those familiar in the art.  In LTE the two convolutional codes used in the turbo code are the same design, differing only in the interleavers at their inputs.  The rate of each convolutional code is ½, so each covolutional encoder ...