Apparatus and method for allocating memory space in a mobile communication system

An apparatus and method for receiving data when an HS-SCCH is not used in a mobile communication system are provided. In the apparatus and method, retransmission data is received, parameters including information about initial transmission data are acquired from the retransmission data, the initial transmission data is retrieved from a second-rate dematching input buffer based on the information about the initial transmission data, second-rate dematching is performed on the initial transmission data and the retransmission data, and first output data is generated by soft-combining the second rate-dematched initial transmission data with the second rate-dematched retransmission data. Accordingly, memory usage can be reduced.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Aug. 20, 2007 and assigned Serial No. 2007-83318, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for optimizing the size of a memory in a Mobile Station (MS). More specifically, the present invention relates to an apparatus and method for optimizing the size of a buffer that an MS allocates for soft-combining of retransmitted data when it operates in a High-Speed Shared Control Channel-less mode (HS-SCCH-less mode) according to an asynchronous mobile communication system standard, the 3rd Generation Partnership Project (3GPP) REL-7 standard.

2. Description of the Related Art

The HS-SCCH-less mode is defined in the 3GPP REL-7 standard. The HS-SCCH-less mode is a technique in which, when small-size Transport Blocks (TBs) are transmitted, their initial transmission version is transmitted without the HS-SCCH, to thereby increase cell capacity.

FIG. 1illustrates a conventional operation for transmitting channels in the HS-SCCH-less mode.

Referring toFIG. 1, a Base Station (BS) transmits initial transmission data to an MS without using an HS-SCCH, i.e. in the HS-SCCH-less mode. That is, upon receipt of Channel Quality Information (CQI) from the MS in step A), the BS transmits initial High-Speed Downlink Shared CHannel (HS-DSCH) data to the MS on a High-Speed Physical Downlink Shared CHannel (HS-PDSCH) without using the HS-SCCH in step B).

The HS-PDSCH transmission has the following features in the HS-SCCH-less mode. Only Quadrature Phase Shift Keying (QPSK) is used as a modulation scheme and only four TB formats or sizes are available. The BS notifies the MS of these TB sizes before transmitting the HS-PDSCH. The HS-PDSCH has a 24-bit Cyclic Redundancy Check (CRC) that is MS-specific like that of the HS-SCCH.

Up to two HS-PDSCH channelization codes are available to the MS. The BS preliminarily allocates an HS-PDSCH channelization code before transmitting the HS-PDSCH to the MS and the MS receives the HS-PDSCH using the allocated HS-PDSCH channelization code. Then the MS performs blind decoding on the HS-PDSCH by sequentially applying the four TB sizes to the HS-PDSCH. If the CRC of the HS-PDSCH indicates an error during the decoding, the MS requests a retransmission of the HS-PDSCH. However, there are restrictions regarding Hybrid Automatic Repeat reQuest (HARQ) as a retransmission scheme as follows.

Up to two retransmissions are allowed. Redundancy Versions (RVs) that are available are semi-fixedly defined according to retransmission numbers. Table 1 below lists transmission numbers versus redundancy versions.

When a retransmission is requested in the HS-SCCH-less mode, the BS transmits the following information to the MS on an HS-SCCH of type2.

(1) 2-bit TB size Information indicating the size of a retransmitted HS-DSCH TB;

(2) a 3-bit Pointer to the previous transmission (PTR) indicating the position of the previously transmitted data, i.e. the position of an Incremental Redundancy (IR) buffer at which there is data to be soft-combined with a retransmitted bit stream; and

(3) 1-bit second or third transmission information indicating a current retransmission number. If the second or third transmission information is 0, this indicates a second transmission and if the second or third transmission information is 1, this indicates a third transmission.

FIG. 2is a timing diagram of a conventional MS operation.

Referring toFIG. 2, after entering the HS-SCCH-less mode, the MS operates as follows.

First, the MS demodulates a received HS-PDSCH and determines whether the HS-PDSCH is type1. If the HS-PDSCH is neither type1nor type2, the MS blind-decodes the HS-PDSCH with respect to all available TB sizes. Herein, type2means retransmission.

If the CRC of the blind-decoded HS-PDSCH is good, the MS provides packets included in the HS-PDSCH to a Medium Access Control (MAC) layer.

On the other hand, if the blind-decoded HS-PDSCH has a bad CRC with respect to every TB size, the MS buffers the current data, i.e., second rate-dematched data with respect to every TB size at a position computed by equation (1), for soft-combing with later retransmitted data in step A).
IRbuffer offset=[5×CFN+subframe number] mod 13  (1)
where CFN represents Connected Frame Number (CFN).

Then the MS demodulates a received HS-SCCH and, if the HS-SCCH is type2, determines that a retransmission takes place in the HS-SCCH-less mode.

The MS calculates parameters for rate dematching and channel coding of the currently received data by detecting a TB size and a retransmission number from information included in the HS-SCCH in step B).

The MS calculates the IR buffer offset of the initial transmission using a PTR acquired from the HS-SCCH of type2, a current CFN, and a current subframe number by
PreviousIRbuffer offset=[5×CFN+subframe number−6−PTR] mod 13  (2)
where PTR represents “Pointer to the previous transmission”.

After second-rate dematching of the current received data, the MS calculates the previous IR buffer offset by equation (2) and soft-combines the second rate-dematched data of the current bit stream with the data buffered at a position of the IR buffer determined by the TB size in step C).

The MS performs first-rate dematching and channel decoding on the soft-combined data and checks the CRC of the channel-decoded data.

If the CRC indicates no error, the MS provides the decoded data to the MAC layer. Otherwise, the MS requests and waits for a retransmission.

In summary, the MS subjects initial transmission data to blind decoding and sequentially stores second rate-dematched data of the initial transmission data in the IR buffer according to an IR buffer offset and all available TB sizes.

If the initial transmission data turns out bad based on a CRC check with respect to every TB size, the MS keeps the buffered data in the IR buffer. Then, the MS demodulates a received HS-SCCH and if the HS-SCCH is type2, it computes an IR buffer offset and offsets of TBs of all TB sizes, for soft combining.

The MS performs second-rate dematching on currently received data and soft-combines the second rate-dematched data with the data at the buffer position. Then the MS performs first-rate dematching and channel decoding on the combined data.

For satisfactory operation, the IR buffer should meet certain requirements based on the following parameters. The MS applies blind decoding to initial transmission data with respect to every TB size and stores all of second rate-dematched data of the blind-decoded data in the IR buffer, for soft combining with retransmitted data.

Hence, sufficient memory areas should be allocated to buffer second rate-dematched data for all (four) TB sizes during one Transmission Time Interval (TTI). That is, the IR buffer should be able to store the data resulting from blind decoding of 13 successive TTIs for all TB sizes.

If a CRC check indicates that the currently received data from the BS is bad despite blind decoding for every TB size, the MS stores the currently received data for soft-combining with a retransmitted TB.

Since a maximum TB size is 1483 bits, a buffer size that the MS requires in the HS-SCCH-less mode is 231348 bits (=1483 bits×3 (coding rate)×13 (the number of monitoring TTIs)×4 (the number of available TB sizes)).

The 231348-bit buffer size imposes a constraint on the MS when receiving data. Accordingly, there exists a need for an apparatus and method for reducing the buffer size requirement.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and method for allocating a memory space in the case of not using an HS-SCCH in a mobile communication system.

Another aspect of the present invention is to provide an apparatus and method for reducing a required buffer size in HS-SCCH-less mode in a mobile communication system.

In accordance with an aspect of the present invention, a reception method of a receiver when a HS-SCCH is not used in a mobile communication system is provided. The method includes, receiving retransmission data, acquiring parameters, including information about initial transmission data, from the retransmission data, retrieving the initial transmission data from a second-rate dematching input buffer based on the information about the initial transmission data, performing second-rate dematching on the initial transmission data and the retransmission data, and generating first output data by soft-combining the second rate-dematched initial transmission data with the second rate-dematched retransmission data.

In accordance with another aspect of the present invention, a receiver for receiving data when a HS-SCCH is not used in a mobile communication system is provided. The receiver includes a controller for acquiring parameters including information about initial transmission data from received retransmission data, for retrieving the initial transmission data from a second-rate dematching input buffer based on the information about the initial transmission data, for performing second-rate dematching on the initial transmission data and the retransmission data, and for generating first output data by soft-combining the second rate-dematched initial transmission data with the second rate-dematched retransmission data, and a storage unit including the second-rate matching input buffer and an IR buffer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention are intended to provide an apparatus and method for allocating a memory space in the case of not using an HS-SCCH in a mobile communication system.

FIG. 3is a block diagram of an MS according to an exemplary embodiment of the present invention.

Referring toFIG. 3, an HS-SCCH type2detector326acquires control information from an HS-SCCH of type2, when a retransmission takes place in HS-SCCH-less mode.

A demodulator318demodulates data received on an HS-PDSCH.

A Transport Format Indication (TFI) detector320detects a TFI during demodulation of the HS-SCCH.

An offset generator for retransmission322decides an offset of a second-rate dematching input buffer324and an offset of an IR buffer310to be accessed, when the retransmission is performed in the HS-SCCH-less mode.

When the CRC determination result of initial transmission data indicates an error after blind decoding with respect to every TB size, the second-rate dematching input buffer324buffers the demodulated initial transmission data.

Since it should store the demodulated data of 13 successive TTIs, the second-rate dematching input buffer324has 13 offsets and an offset to be assessed is determined by the offset generator322for retransmission.

When the retransmission occurs, the IR buffer310, better shown in its expanded illustration311, stores soft-combined data of the initial transmission data and retransmission data and manages the soft-combined data using a different offset for each of the 13 successive TTIs.

When a retransmission is performed, that is, an RV is 3, a second-rate dematcher314(second-rate dematcher0) receives TB information (i.e. TB size information) from the TFI detector320and performs second-rate dematching on a current retransmission TB.

A second-rate dematcher316(second-rate dematcher1) accesses the initial transmission data buffered in the second-rate dematching input buffer324according to an offset and performs second-rate matching on the initial transmission data, when the retransmission occurs.

A soft combiner312soft-combines the data received from second-rate dematcher0and second-rate dematcher1.

A first-rate dematcher308performs first-rate dematching on the data received from the soft combiner312.

A channel decoder306channel-decodes the data received from the first-rate dematcher308.

A CRC checker302determines the CRC of the channel-decoded data.

If the result of the CRC determination indicates an error, an offset generator for writing304determines a position at which to buffer the current soft-combined data in the IR buffer311.

While not shown, the MS is provided with a controller. The controller can control any or all of the offset generator304for writing, the CRC checker302, the channel decoder306, the first-rate dematcher308, the soft combiner312, the second-rate dematcher1316, the second-rate dematcher0314, the TFI detector320, the offset generator for retransmission322, the demodulator318, and the HS-SCCH type2detector326.

Also, the functions of the offset generator304for writing, the CRC checker302, the channel decoder306, the first-rate dematcher308, the soft combiner312, the second-rate dematcher1316, the second-rate dematcher0314, the TFI detector320, the offset generator for retransmission322, the demodulator318, and the HS-SCCH type2detector326can be incorporated in the controller. That is, while these components are shown separately, such illustration is only made in order to describe their functions separately. It is not to be construed as requiring the components to be provided separately.

Therefore, in actual implementation, the MS can be so configured that the controller performs all or part of the functions of the offset generator304for writing, the CRC checker302, the channel decoder306, the first-rate dematcher308, the soft combiner312, the second-rate dematcher1316, the second-rate dematcher0314, the TFI detector320, the offset generator for retransmission322, the demodulator318, and the HS-SCCH type2detector326.

While not shown, the MS is provided with a storage unit. The storage unit may include the IR buffer310and the second-rate dematching input buffer324.

FIG. 4is a timing diagram of an operation of an MS according to an exemplary embodiment of the present invention.

Referring toFIG. 4, after entering the HS-SCCH-less mode, the MS operates as follows. First, the MS demodulates an initial transmission HS-PDSCH. If evaluation of the CRC of the demodulated HS-PDSCH indicates an error with respect to every TB size, the MS buffers the demodulated data in the second-rate dematching input buffer in step A).

If a received HS-SCCH is type2, indicating retransmission in step B), the MS retrieves the initial transmission data and soft-combines the initial transmission data with retransmission data using control information acquired from the HS-SCCH in step C).

Then the MS buffers the soft-combined data at a preset offset of the IR buffer in step D).

FIG. 5is a flowchart illustrating an operation of an MS according to an exemplary embodiment of the present invention.

Referring toFIG. 5, the MS receives an HS-SCCH and determines whether the HS-SCCH is type2in step505.

If the HS-SCCH is not type2, which implies an initial transmission, the MS performs blind decoding on a currently received HS-PDSCH with respect to every TB size in step520.

If a CRC determination result of the blind-decoded HS-PDSCH is good in step530, the MS provides data included in the HS-PDSCH to a MAC layer in step535and then completes the process.

If the CRC determination result of the blind-decoded HS-PDSCH is bad in step530, the MS buffers the demodulated data of the HS-PDSCH in the second-rate dematching input buffer in step540.

An offset at which the demodulated data is buffered is computed by
Offset of second-rate dematching input buffer=[5×CFN+subframe number] mod 13  (3)
where CFN represents Connected Frame Number.

After buffering the demodulated data, the MS requests retransmission of the HS-PDSCH in step545.

If it is determined in step505that the HS-SCCH is type2, the MS determines that the currently received data is retransmission data in the HS-SCCH-less mode.

Thus, the MS determines parameters associated with rate dematching and channel decoding based on a TB size, a retransmission number, and a PTR included in the HS-SCCH in step510.

In step515, the MS determines a TB offset associated with the previous transmission using the PTR by
Previous offset of second-rate dematching input buffer=[5×CFN+subframe number−6−PTR] mod 13  (4)
where PTR represents “Pointer to the previous transmission” and CFN represents Connected Frame Number.

In step550, the MS performs second-rate dematching on the retransmission data.

The MS then accesses the second-rate dematching input buffer using the offset computed by equation (4) in step555, retrieves an initial transmission TB from the offset, and performs second-rate dematching on the initial transmission TB in step560.

In step565, the MS soft-combines the retransmission data with the initial transmission data and buffers the soft-combined data in the IR buffer at an offset computed by
Offset of IR buffer=[5×CFN+subframe number] mod 13  (5)
where CFN represents Connected Frame Number.

The MS performs first-rate dematching and channel decoding on the soft-combined data in step570.

The MS determines the CRC of the channel-decoded data in step575. If the CRC determination result is good, the MS provides the channel-decoded data to the MAC layer in step585. Furthermore, if the CRC determination is good, the data stored in the IR buffer in step565may be deleted in step585.

On the contrary, if the CRC determination result is bad in step575, the MS buffers the soft-combined data in the IR buffer at an offset computed by equation (5) in step580.

If the CRC determination result of the data buffered in the IR buffer is also bad and thus a third transmission (i.e. a second retransmission) takes place, soft combining is performed at the IR buffer.

Then the algorithm of the present invention ends.

Compared to the conventional technology that has a buffer size requirement of 231348 bits (1483 bits×3 (coding rate)×13 (the number of monitoring TTIs)×4 (the number of available TB sizes)), exemplary embodiments of the present invention require a buffer size of only 82797 bits ((960 bits (QPSK)×2 (the number of HS-PDSCHs)×13 (the number of monitoring TTIs)=24960 bits)+(1483 bits×3 (coding rate)×13 (the number of monitoring TTIs)=57837 bits).

Therefore, exemplary embodiments of the present invention can save 148551-bits of buffer size, relative to the conventional technology. That is, the buffer size requirement is reduced to about ⅓ of the conventional buffer size requirement.