Method for physical control format indicator channel mapping

A method of mapping symbols of a physical control format indicator channel (PCFICH) is described. A start position of a resource element to map the symbols for the PCFICH is determined by flooring a value, obtained by multiplying the number of resource blocks by a variable proportional to a symbol index for the PCFICH and then dividing the multiplied result by 2, wherein the resource blocks are transmitted in downlink. The symbols are mapped in the start position. Therefore, a problem of wasting resource elements or not being able to implement mapping can be solved by applying a simple mapping rule while mapping symbols of the PCFICH.

TECHNICAL FIELD

The present invention relates to a mapping method for frequency and orthogonal frequency division multiplexing (OFDM) symbol regions of a signal transmitted in downlink in a cellular OFDM wireless packet communication system, and more particularly, to a mapping method which is capable of solving a problem of wasting resource elements or not being able to implement mapping by applying a simple mapping rule while mapping symbols of a physical control format indicator channel (PCFICH).

BACKGROUND ART

When transmitting data through downlink of an OFDM wireless packet communication system, if each user equipment is informed of how many OFDM symbols are used to transmit a control channel, the user equipment has many advantages in using information of the control channel. Especially, a 3GPP LTE system defines a channel notifying the number of OFDM symbols used for the control channel as a physical control format indicator channel (PCFICH).

More specifically, in the 3GPP LTE system, the PCFICH is expressed as 2 bits indicating three states according to whether the number of OFDM symbols used to transmit the control channel is 1, 2, or 3. The 2 bits are increased to 32 bits through channel coding and then expressed as 16 quadrature phase shift keying (QPSK) symbols through QPSK modulation. The PCFICH is always transmitted only through the first OFDM symbol of a subframe and a mapping method in a frequency region for transmission is as follows.

y(0), . . . , y(3) are mapped to resource elements starting with a position of k=k0, y(4), . . . , y(7) are mapped to resource elements starting with a position of k=k0+└NRBDLNscRB/4┘, y(8), . . . , y(11) are mapped to resource elements starting with a position of k=k0+└2NRBDLNscRB/4┘, and y(12), . . . , y(15) are mapped to resource elements starting with a position of k=k0+└3NRBDLNscRB/4┘. Here, a value k0for shifting a starting point is k0=(NscRB/2)·(NIDcellmod2NRBDL).

The above additions include a modular operation of NRBDLNscRB, and NIDcelldenotes a physical layer cell identification (ID).

In the above mapping rule, y(0), . . . , y(15) denote 16 QPSK symbols, NRBDLdenotes the number of resource blocks transmitted in downlink, and NscRBdenotes the number of resource elements per resource block. k0is determined according to the cell ID NIDcellwhich varies with each cell. Starting with k0, the symbols are dispersed in four frequency regions comprised of 4 adjacent resource elements which are not used for transmission of a reference signal (RS) to obtain a frequency diversity gain over all downlink frequency bands, and then transmitted. The reason why the 4 adjacent resource elements which are not used for transmission of the reference signal are used is that since other control channels are constructed with a resource element group (REG) comprised of 4 adjacent resource elements which are not used for transmission of the REFERENCE SIGNAL, multiplexing of a PCFICH with other control channels can be efficiently performed using the same mapping method.

However, when mapping symbols for the PCFICH according to the above-described mapping method, there may be the following disadvantages.

First, if and NscRBis 12 in a general subframe structure of a 3GPP LTE system, the second and fourth frequency regions among 4 frequency regions are mapped over 2 REGs when NRBDLis an odd number.

FIG. 1illustrates a conventional mapping method in which 4 symbols are mapped to 2 REGs.

As illustrated inFIG. 1, if NRBDLis an even number, 4 frequency regions for transmission of a PCFICH are identical to units of an REG for transmission of other control channels. However, if NRBDLis an odd number, the second and fourth frequency regions are mapped over 2 REGs. In this case, since an REG is comprised of 4 adjacent resource elements which are not used for transmission of a reference signal, resource elements remaining at both sides of the 4 adjacent resource elements can not be used for transmission of a control channel, thereby wasting resources.

Second, the above-described mapping rule has a region in which mapping can not be implemented.

A frequency mapping region varies with NIDcellwhich is unique for each cell. Hence, cells having adjacent cell IDs may reduce interference caused by transmission of a PCFICH. This NIDcellis comprised of 504 values ranging from 0 to 503 according to a current 3GPP LTE standard. When NRBDLis an odd number, a region in which frequency mapping for PCFICH transmission can not be performed occurs according to NIDcell.

FIG. 2illustrates the case where a region in which mapping can not be implemented occurs in a frequency region for PCFICH transmission according to NIDcell. For example, if NRBDLis 25, NIDcellis 12, and NscRBis 12, a frequency region allocated to 4 successive resource elements deviates from a frequency region in which a PCFICH should actually be transmitted. In this case, the PCFICH can not be allocated to a corresponding region.

DISCLOSURE

Technical Problem

An object of the present invention devised to solve the problem lies in providing a method which can solve a problem of wasting resource elements or having difficulty in mapping while mapping symbols for a PCFICH.

Technical Solution

The object of the present invention can be achieved by providing a method of mapping symbols of a PCFICH in units of a resource element group. If the number of resource blocks transmitted in downlink is an even number, a conventional mapping method is used. If the number of resource blocks is an odd number, the method of mapping symbols of a PCFICH is used including determining a start position of a resource element to map the symbols for the PCFICH using a variable obtained by subtracting1from the number of resource blocks, and mapping the symbols in the start position.

The determining may include determining an initial start position according to a physical layer cell ID.

The mapping may include mapping symbols of a first group among four groups to resource elements starting with a position of k=k0, mapping symbols of a second group among the four groups to resource elements starting with a position of k=k0+└(NRBDL−1)NscRB/4┘, mapping symbols of a third group among the four groups to resource elements starting with a position of k=k0+└2(NRBDL−1)NscRB/4┘, and mapping symbols of a fourth group among the four groups to resource elements starting with a position of k=k0+└3(NRBDL−1)NscRB/4┘.

The mapping may include mapping symbols in positions except for resource elements of reference signals in a first OFDM symbol.

In another aspect of the present invention, provided herein is a method of mapping symbols of a PCFICH, including determining a start position of a resource element to map the symbols for the PCFICH by flooring a value, obtained by multiplying the number of resource blocks by a variable proportional to a symbol index for the PCFICH and then dividing the multiplied result by 2, wherein the resource blocks are transmitted in downlink, and mapping the symbols in the start position,

The determining may include determining an initial start position according to a physical layer cell ID.

The mapping may include mapping symbols of a first group among four groups to resource elements starting with a position of k=k0, mapping symbols of a second group among the four groups to resource elements starting with a position of k=k0+└NRBDL/2┘·NscRB/2; mapping symbols of a third group among the four groups to resource elements starting with a position of k=k0+└2NRBDL/2┘·NscRB/2, and mapping symbols of a fourth group among the four groups to resource elements starting with a position of k=k0+└3NRBDL/2┘·NscRB/2.

The mapping may include mapping symbols of a first group among four groups to resource elements starting with a position of k=k0, mapping symbols of a second group among the four groups to resource elements starting with a position of k=k0+└NRBDL/2┘·NscRB/2, mapping symbols of a third group among the four groups to resource elements starting with a position of k=k0+2└NRBDL/2┘·NscRB/2, and mapping symbols of a fourth group among the four groups to resource elements starting with a position of k=k0+3└NRBDL/2┘·NscRB/2.

The mapping may include mapping symbols in positions except for resource elements of reference signals in a first OFDM symbol.

ADVANTAGEOUS EFFECTS

In accordance with the exemplary embodiments of the present invention, a problem of wasting resource elements or not being able to implement mapping can be solved by applying a simple mapping rule while mapping symbols of a PCFICH.

BEST MODE

Reference will now be made in detail to the exemplary embodiments of the present invention with reference to the accompanying drawings. The detailed description is intended to explain exemplary embodiments of the present invention, rather than to show the only embodiments that can be implemented according to the invention.

In an exemplary embodiment of the present invention, a method applying different mapping rules according to NRBDLis proposed.

In a conventional mapping method, the above-described problems do not occur for NRBDLof an even number, so the conventional mapping method is used for NRBDLof an even number and the following mapping method is used for NRBDLof an odd number.

Hereinbelow, y(0), . . . , y(15) denotes 16 QPSK symbols, NRBDLdenotes the number of resource blocks transmitted in downlink, and NscRBdenotes the number of resource elements per resource block.

According to an exemplary embodiment of the present invention, if NRBDLis an odd number, y(0), . . . ,y(3) are mapped to resource elements starting with a position of k=k0, y(4), . . . ,y(7) are mapped to resource elements starting with a position of k=k0+└(NRBDL−1)NscRB/4┘, y(8), . . . ,y(11) are mapped to resource elements starting with a position of k=k0+└2NRBDLNscRB/4┘ or k=k0+└2(NRBDL−1)NscRB/4┘, and y(12), . . . ,y(15) are mapped to resource elements starting with a position of k=k0+└3(NRBDL−1)NscRB/4┘.

FIG. 3is a flow chart illustrating a PCFICH mapping method according to an exemplary embodiment of the present invention.

A symbol index i for PCFICH mapping is initialized to 0 (step S310).

Next, a determination is made as to whether NRBDLis an odd number (step S320). If NRBDLis an odd number, positions of resource elements to map 4 symbols of a PCFICH are determined using NRBDL−1 and the 4 symbols are mapped to corresponding positions (step S330).

If NRBDLis an even number, positions of resource elements to map 4 symbols of a PCFICH are determined using NRBDLand the 4 symbols are mapped to corresponding positions (step S340).

If mapping is completed, the symbol index i is increased by 4 (step S350).

If the symbol index i is less than 16 (step S360), the above operations (steps S320to S350) are repeated since symbols to be mapped remain.

Finally, if the symbol index i is equal to or greater than 16 (S360), a procedure is ended.

Meanwhile, another exemplary embodiment of the present invention proposes a single mapping method irrespective of whether NRBDLis an odd number or an even number.

That is, the following mapping rule using a single expression regardless of NRBDLcan solve the conventional problems in mapping symbols for a PCFICH.

According to another exemplary embodiment of the present invention, y(0), . . . ,y(3) are mapped to resource elements starting with a position of k=k0, y(4), . . . ,y(7) are mapped to resource elements starting with a position of k=k0+└NRBDL/2┘·NscRB/2, y(8), . . . ,y(11) are mapped to resource elements starting with a position of k=k0+└2NRBDL/2┘·NscRB/2,and y(12), . . . ,y(15) are mapped to resource elements starting with a position of k=k0+└3NRBDL/2┘·NscRB/2.

In the above method, k0is determined according to NIDcell. If an index indicated by k0collides with an index of a resource element using a reference signal, k0may use an index increased by ‘1’.

FIG. 4is a flow chart illustrating a PCFICH mapping method according to another exemplary embodiment of the present invention.

First, a symbol index i for PCFICH mapping is initialized to 0 (step S410).

A start position of a resource element for PCFICH mapping is determined by flooring a value obtained by multiplying a variable Iiproportional to the symbol index by NRBDLand then dividing the multiplied result by 2 (step S420). The variable may be, for example, I0=0, I4=1, I8=2, and I12=3.

If mapping is completed, the symbol index i is increased by 4 (step S450).

If the symbol index i is less than 16 (step S460), the above operations (steps S420to S450) are repeated since symbols to be mapped remain.

Finally, if the symbol index i is equal to or greater than 16 (S460), a procedure is ended.

The above mapping rule according to another exemplary embodiment of the present invention may be modified as follows.

Namely, y(0), . . . ,y(3) are mapped to resource elements starting with a position of k=k0, y(4), . . . ,y(7) are mapped to resource elements starting with a position of k=k0+└NRBDL/2┘·NscRB/2, y(8), . . . ,y(11) are mapped to resource elements starting with a position of k=k0+2└NRBDL/2┘·NscRB/2,and (12), . . . ,y(15) are mapped to resource elements starting with a position of k=k0+3└NRBDL/2┘·NscRB/2.

FIG. 5illustrates an example of REGs when two or less transmit antennas are used.

In the first OFDM symbol (first line) through which a PCFICH is transmitted, since reference signals of respective antennas are transmitted, one REG is comprised of 6 resource elements. Since no reference signal exists in the second OFDM symbol (second line) when using 2 or less transmit antennas, one REG is comprised of 4 resource elements.

FIG. 6illustrates an example of REGs when 4 transmit antennas are used.

In the first OFDM symbol (first line) through which a PCFICH is transmitted, since reference signals of antennas are transmitted, one REG is comprised of 6 resource elements. When using 4 transmit antennas, since reference signals exist even in the second OFDM symbol (second line), one REG is comprised of 6 resource elements.

FIG. 7illustrates an example of PCFICH mapping according to a cell ID.

InFIG. 7, a system band corresponds to 20 resource blocks. Different start positions are set for 10 cell IDs. Positions denoted by “1” indicate positions of k0in the above-described mapping method. Accordingly, interference between cell IDs is reduced.

INDUSTRIAL APPLICABILITY

The present invention provides a mapping method for frequency and OFDM symbol regions of a signal transmitted in downlink in a cellular OFDM wireless packet communication system and is applicable to a base station, a user equipment, etc. in a 3GPP LTE system.