Radio transmitting apparatus and radio transmitting method in multicarrier communication

A radio transmitting apparatus wherein unnecessary consumption of transmission power can be suppressed and PAPR (Peak to Average Power Ratio) can be reduced in multicarrier communication. In the apparatus, a repetition part (105) replicates (repeats) each symbol outputted from a modulating part (103) to generate and output a plurality of identical symbols to an S/P part (107), which converts the symbol sequence outputted in series from the repetition part (105) into parallel symbol sequences and outputs them to an interleaver (109). The interleaver (109) then reorders the symbol sequences outputted from the S/P part (107) and outputs them to a mapping part (111), which removes, in accordance with the propagation path quality of each of subcarriers constituting OFDM symbols that are multicarrier signals, some of the identical symbols as replicated by the repetition part (105) and then maps the rest of the symbols onto subcarriers for application to an IFFT part (113).

TECHNICAL FIELD

The present invention relates to a radio transmitting apparatus and radio transmitting method in multicarrier communication.

BACKGROUND ART

Recently, in radio communication, more particularly, in mobile communication, various information such as images and data, in addition to sound, have been an object of transmission. It is expected that necessity of high-speed transmission will further increase in the future, and therefore a radio transmission technology is required that realizes high transmission efficiency using limited frequency resources efficiently in order to perform high-speed transmission.

As one of such radio transmission technologies, OFDM (Orthogonal Frequency Division Multiplexing) can be cited (for example, see Non-patent document 1). It is known that the OFDM has a high frequency usage efficiency, a low interference between symbols under a multipath environment, and so on, and is effective for improving transmission efficiency.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In OFDM, qualities every subcarrier are greatly fluctuated by frequency selectivity fading caused by multipath. In this case, a quality of a signal allocated to a subcarrier on a trough of the fading is lowered, and demodulation of the signal becomes difficult. Therefore, quality improvement is required so that demodulation is possible.

As a technology for improving the quality in the OFDM, there exists a so-called repetition technology. The repetition technology is a technology that replicates a symbol to generate a plurality of identical symbols, maps the symbols onto a plurality of subcarriers to transmit them, and then combines the symbols on the receiver side to obtain a diversity effect.

In this repetition technology, when each of the identical symbols is mapped onto only a subcarrier having excellent propagation path quality, excess quality arises on the receiver side regarding the symbol, and meanwhile unnecessary transmission power is consumed on a transmitter side.

It is therefore an object of the present invention to provide a radio transmitting apparatus and radio transmitting method capable of suppressing unnecessary consumption of transmission power and reducing PAPR (Peak to Average Power Ratio).

Means for Solving the Problem

The radio transmitting apparatus of the present invention employs a configuration having: a replication section that replicates a symbol to generate a plurality of identical symbols; a mapping section that removes at least one symbol among the plurality of identical symbols in accordance with propagation path quality of each of the plurality of subcarriers and maps the rest of the plurality of identical symbols onto the plurality of subcarriers; a generation section that generates the multicarrier signal from an output of the mapping section; and a transmission section that transmits the multicarrier signal.

Advantageous Effect of the Invention

According to the present invention, in multicarrier communication, unnecessary consumption of transmission power can be suppressed, and PAPR can be reduced.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. A radio transmitting apparatus/radio receiving apparatus described below transmits/receives a multicarrier signal formed with a plurality of subcarriers, and is mounted on, for example, radio communication base station apparatus or radio communication terminal apparatus for use in mobile communication systems.

In the radio transmitting apparatus shown inFIG. 1, coding section101adds an error detection code and performs an error correction coding processing on inputted transmission data.

Modulating section103modulates an output from coding section101by a modulation scheme such as QPSK or 16QAM and generates a symbol.

Repetition section105replicates (i.e. repetition) each symbol outputted from modulating section103to generate a plurality of identical symbols, and outputs them to S/P section (Serial/Parallel conversion section)107. In the following description, the plurality of identical symbols will be set as one unit and referred to as a repetition unit.

S/P section107converts a symbol sequence outputted in series from repetition section105into parallel symbol sequences, and outputs them to interleaver109.

Interleaver109rearranges the symbol sequences outputted from S/P section107and outputs them to mapping section111. That is, interleaver109interleaves the symbol sequences outputted from S/P section107.

In accordance with the propagation path quality of each of subcarriers constituting an OFDM symbol that is a multicarrier signal, mapping section111removes some of the identical symbols replicated by repetition section105, maps the rest of the symbols onto the subcarriers, and outputs them to IFFT section113. Subcarriers (blank subcarriers), onto which no symbol is mapped, are generated among the plurality of subcarriers of the OFDM symbol. Moreover, in the following description, some of the identical symbols, which are removed by mapping section111and are consequently not transmitted, will be referred to as “non-transmission symbols.”

Additionally, mapping section111maps a pilot symbol onto each subcarrier and multiplexes it with symbols outputted from interleaver109. However, mapping section111does not map the pilot symbol onto blank subcarriers. In a FDD system, the pilot symbols are used to measure propagation path quality of each subcarrier by the radio receiving apparatus for receiving the OFDM symbol transmitted from the radio transmitting apparatus.

Moreover, in the FDD system, the propagation path quality of each subcarrier inputted to mapping section111is obtained from information obtained from the radio receiving apparatus by measuring the propagation path quality of each subcarrier and returning as feed back the measurement results to the radio transmitting apparatus. In a TDD system, since propagation path quality in transmission is similar to propagation path quality in reception, this propagation path quality is obtained by measuring propagation path quality of each subcarrier of the OFDM symbol transmitted from the radio receiving apparatus by the radio transmitting apparatus. Additionally, as propagation path quality, the propagation path fluctuation level, SNR, SIR, SINR, CIR, CINR or the like is applicable.

IFFT section113subjects the output from mapping section111to Inverse Fast Fourier Transform (IFFT) processing to generate an OFDM symbol that is a multicarrier signal, and outputs it to GI adding section115.

The OFDM symbol outputted from IFFT section113is added a guard interval by GI adding section115, subjected to predetermined radio processing such as up-conversion by transmission R/F section117, and transmitted from antenna119to the radio receiving apparatus.

Next, the radio receiving apparatus for receiving the OFDM symbol transmitted from the radio transmitting apparatus shown inFIG. 1will be described with reference toFIG. 2.

In the radio receiving apparatus shown inFIG. 2, the OFDM symbol received via antenna201is subjected to predetermined radio processing such as down-conversion by reception RF section203, the guard interval is removed by GI removing section205, and the OFDM symbol having no guard interval is inputted to FFT section207.

FFT section207subjects the OFDM symbol to Fast Fourier Transform (FFT) processing, extracts the symbol mapped onto the subcarriers, and outputs a symbol sequence to deinterleaver209. Since some symbols are removed by mapping section111shown inFIG. 1, some symbols in the symbol sequence are missing.

Deinterleaver209rearranges the symbol sequence in the reverse order of the rearrangement performed in interleaver109inFIG. 1, to rearrange the order of the symbol sequence back to the order before the rearrangement by interleaver109. That is, deinterleaver209deinterleaves the symbol sequence. The rearranged symbol sequence is outputted to demapping section211. Further, the pilot symbol mapped onto each subcarrier is outputted to channel estimating section213.

Demapping section211extracts the symbols in repetition units from the symbol sequence and outputs them to combining section215. In this time, demapping section211extracts symbols from the subcarriers other than the blank subcarriers.

Channel estimating section213calculates a channel estimated value (for example, propagation path fluctuation level) of each of subcarriers other than blank subcarriers (i.e. subcarriers onto which symbols are mapped) using the pilot symbols, and outputs them to combining section215.

Combining section215compensates the channel fluctuation of the symbol outputted from demapping section211using the channel estimated value. Then, combining section215assigns weight to each symbol after the channel fluctuation compensation and combines the symbols in the repetition unit.

The symbols after combining are demodulated by demodulating section217, and error correction decoding and error detection are performed by decoding section219. Thus, received data is obtained.

Next, operations of repetition section105, interleaver109and mapping section111will be described in detail. In the following description, one OFDM symbol is formed with sixteen subcarriers, f1to f16.

Here, in the embodiment, as a method of selecting non-transmission symbols in each repetition unit, the following two methods are possible. Hereinafter, the selecting method1and selecting method2will be described respectively. Moreover, in both selecting method1and selecting method2, when a combining result of a plurality of identical symbols in each repetition unit indicates an excess quality, at least one symbol is selected as a non-transmission symbol among the plurality of identical symbols and excluded from mapping.

In mapping section111, non-transmission symbols are determined in accordance with propagation path quality of f1to f16. In this time, the non-transmission symbols are selected among the identical symbols in each repetition unit. In the present embodiment, as the selecting method1, a method of leaving, among a plurality of identical symbols in each repetition unit, the symbols that are mapped onto subcarriers where propagation path quality is equal to or better than a threshold, selecting at least one symbol among the plurality of identical symbols as a non-transmission symbol, and excluding the non-transmission symbol from mapping, is employed.

For example, when propagation path quality is shown as in the graph ofFIG. 4, subcarriers where propagation path quality is below the threshold, are f1, f4to f9, f11and f12. Additionally, symbols mapped onto these subcarriers by interleaving by the interleaver9are A3, D4, C2, A4, D2, B4, D1, C3and A1. On the other hand, subcarriers, of which each propagation path quality is not less than the threshold, are f2, f3, f10and f13to f16, and the symbols mapped onto these subcarriers are C4, B1, B2, B3, C1, D3and A2.

Here, if there are two identical symbols to be mapped onto subcarriers where propagation path quality is equal to or better than the threshold in a repetition unit, the combining result regarding the repetition unit can sufficiently fulfill desired quality by combining in combining section215of the radio receiving apparatus. That is, if there are two identical symbols to be mapped onto subcarriers where propagation path quality is equal to or better than the threshold, transmitting more identical symbols will result in excess quality in the radio receiving apparatus, and unnecessary transmission power is consumed in the radio transmitting apparatus. So, mapping section111selects symbols causing excess quality in each repetition unit and makes them non-transmission symbols.

To be more specific, focusing on the repetition unit of symbol A (A1to A4), there is one symbol to be mapped onto subcarriers where propagation path quality is equal to or better than a threshold. Similarly, there are three symbols to be mapped onto subcarriers where propagation path quality is equal to or better than a threshold, in the repetition unit of symbol B (B1to B4), there two symbols in the repetition unit of symbol C (C1to C4), and there are one symbol in the repetition unit of symbol D (D1to D4). Therefore, the combining results of the repetition unit of symbol B and the repetition unit of symbol C indicate excess quality in the radio receiving apparatus.

Then, as shown inFIG. 5, mapping section111removes two symbols, B2and B4, among symbols B1to B4, as non-transmission symbols, and maps only the rest of the symbols, B1and B3, onto subcarriers, f3and f13, respectively. Additionally, mapping section111removes two symbols, C2and C3, among symbols C1to C4, as non-transmission symbols, and maps only the rest of the symbols, C1and C4, onto subcarriers, f14and f2, respectively. Mapping section111thus selects non-transmission symbols, prioritizing symbols mapped onto subcarriers where propagation path quality is below a threshold, over symbols mapped onto subcarriers where propagation path quality is equal to or better than the threshold. Moreover, all the symbols A1to A4and D1to D4are mapped onto subcarriers respectively. As a result, f5, f8, f10and f11, become blank subcarriers.

In mapping section111, the non-transmission symbols are determined in accordance with propagation path quality of f1to f16. In this time, the non-transmission symbols are selected among the identical symbols in each repetition unit. In the present embodiment, as selecting method2, a method of selecting, when total of propagation path quality of subcarriers where a plurality of identical symbols are mapped in each repetition unit is equal to or better than predetermined quality, at least one symbol among the plurality of identical symbols as a non-transmission symbol and excluding the non-transmission symbol from mapping.

For example, when propagation path quality is as shown in the graph ofFIG. 6, propagation path quality [dB] of subcarriers f1to f16is as shown inFIG. 6. Additionally, propagation path quality [true value] is obtained by converting [dB] into [true value]. For example, the propagation path quality of f1: −3 [dB] is equal 0.5 in [true value].

Mapping section111first sums up the propagation path quality [true value] of the subcarriers onto which the identical symbols of the repetition unit are mapped respectively. The repetition unit of the symbol A, A1to A4, are mapped onto f1, f6, f12and f16respectively, propagation path quality of f1, f6, f12and f16is 0.5, 0.2, 0.6 and 1.3, respectively, and therefore the total of propagation path quality in the repetition unit of symbol A is 2.6. Similarly, the total of propagation path quality in the repetition unit (B1to B4) of symbol B is 4.8, the total of propagation path quality in the repetition unit (C1to C4) of symbol C is 4.5, and the total of propagation path quality in the repetition unit (D1to D4) of symbol D is 4.6. The total of propagation path quality corresponds to quality of the symbols combined by combining section215of the radio receiving apparatus. That is, this total of propagation path quality corresponds to the quality of each repetition unit in the radio receiving apparatus.

Here, when a desired quality in the radio receiving apparatus is set to 3.0, the total of propagation path quality of the repetition units of symbols B, C and D each becomes equal to or greater than desired quality. Desired quality is 3.0, and any quality above will be excess quality. Thereupon, mapping section111selects a symbol causing excess quality in each repetition unit and makes the symbol as a non-transmission symbol. Additionally, mapping section111selects non-transmission symbols so that the number of non-transmission symbols becomes maximum in a range of fulfilling the desired quality in each repetition unit, in order to maximize a reduction amount of PAPR.

Concretely, focusing on the repetition unit of symbol B, B1, B4, B2and B3are mapped onto f3, f8, f10and f13, respectively, and propagation path quality of f3, f8, f10and f13is 1.3, 0.6, 1.3 and 1.6, respectively. Therefore, any one of B1to B4is selected as a non-transmission symbol so that the total of propagation path quality becomes more or the desired quality even if the non-transmission symbol is generated. When there thus exist a plurality of candidates of non-transmission symbols, mapping section111selects non-transmission symbols so that resistance against frequency selective fading becomes highest and intervals between subcarriers where identical symbols in each repetition unit are mapped, becomes largest. Since the repetition unit of symbol B (B1to B4) is mapped onto f3, f8, f10and f13, the intervals between the subcarriers become largest when f10is made a blank subcarrier. Therefore, mapping section111selects B2to be mapped onto f10as a non-transmission symbol regarding the repetition unit of symbol B. Thus, the quality of the repetition unit of the symbol B is 3.5.

Further, focusing on the repetition unit of the symbol C, C4, C2, C3and C1are mapped onto f2, f5, f11and f14respectively, and propagation path quality of f2, f5, f11and f14is 1.3, 0.6, 0.6 and 2.0 respectively. Therefore, two symbols, C2and C3, are selected as non-transmission symbols so that the number of non-transmission symbols becomes maximum in a range where the total of propagation path quality fulfills desired quality. Thus, the quality of the repetition unit of symbol C is 3.3.

Furthermore, focusing on the repetition unit of the symbol D, D4, D2, D1and D3are mapped onto f4, f7, f9and f15, respectively, and propagation path quality of f4, f7, f9and f15is 1.0, 1.0, 0.6 and 2.0 respectively. Therefore, either of two symbols, D1and D2, and two symbols, D1and D4, are selected as non-transmission symbols so that the number of non-transmission symbols becomes maximum in a range where the total of the propagation path quality fulfills desired quality. Similar to the above description, mapping section111selects two symbols, D1and D2, as non-transmission symbols so that the intervals between the subcarriers become largest in the repetition unit. Thus, D1and D2are made non-transmission symbols and the quality of the repetition unit of symbol D is 3.0.

Moreover, since the total of propagation path quality of the repetition unit of symbol A is 2.6 and is less than 3.0 of desired quality, all the symbols A1to A4are mapped onto subcarriers.

As described above, in the embodiment, the non-transmission symbols are selected by using the selecting method of either the selection example 1 or selection example 2. In the selection example 1, comparing with the selection example 2, though lighter processing for selecting non-transmission symbols is performed, whether or not excess quality is provided is decided based on rough criteria. On the other hand, in the selection example 2, comparing with the selection example 1, though heavy processing for selecting non-transmission symbols is performed, whether or not excess quality is provided is decided by more precise control. Therefore, either of the selecting methods may be employed in view of processing load to be allowed or quality precision to be required.

According to the present embodiment, symbols causing excess quality in each repetition unit are made non-transmission symbols and blank subcarriers are generated, so that unnecessary consumption of transmission power can be suppressed and PAPR can be reduced without influencing desired quality in the radio receiving apparatus. Additionally, since propagation path environments every cell under a multi-cell environment are different from each other, non-transmission symbols are independently generated every cell and differing blank subcarriers are generated, thereby reducing interference between cells.

Moreover, though the OFDM symbol (namely, FFT size) is employed as the unit of interleaving and deinterleaving in the above description, a frame may be employed as the units to be interleaved and deinterleaved.

A radio transmitting apparatus according to the present embodiment has a plurality of differing interleave patterns and performs interleaving in the interleave pattern whereby the number of non-transmission symbols becomes maximum, among the interleave patterns.

First, configurations of the radio transmitting apparatus and radio receiving apparatus according to the present embodiment will be described with reference toFIG. 8andFIG. 9. However, the same numerals are attached to the same configurations as those of Embodiment 1 (FIG. 1andFIG. 2) respectively, and description of the same configurations will be omitted.

In the radio transmitting apparatus shown inFIG. 8, interleaver301has a plurality of differing interleave patterns1to K, and interleaves a symbol sequence using an interleave pattern selected among the plurality of interleave patterns by selection section303.

Selection section303selects one of interleave patterns1to K in accordance with propagation path quality of each subcarrier, and outputs an interleave pattern number as a selection result, to interleaver301and mapping section111. The interleave pattern selecting method in selection section303will be described below.

To report the selection result in selection section303to the radio receiving apparatus, mapping section111maps the interleave pattern number, as information indicating the selection result, onto one of the subcarriers (here, f1).

On the other hand, in the radio receiving apparatus shown inFIG. 9, deinterleaver401has a plurality of differing deinterleave patterns1to K and deinterleaves a symbol sequence using an deinterleave pattern selected among the plurality of interleave patterns by selection section403. The deinterleave patterns1to K correspond to the interleave patterns1to K, respectively. Deinterleaver401rearranges the order of the symbol sequence rearranged by interleaver301using the interleave patterns1to K, back to the order before the rearrangement at interleaver301, using the deinterleave patterns1to K.

Selection section403learns the selection result in selection section303based on the interleave pattern number mapped onto f1, and therefore selects one of the deinterleave patterns1to K in accordance with the interleave pattern number. Then, selection section403outputs the selection result to deinterleaver401.

Next, the interleave pattern selecting method in selection section303of the radio transmitting apparatus will be described with reference toFIGS. 10 to 12. Moreover, in the following description, the selection example 1 described in Embodiment 1 is employed regarding the method of selecting non-transmission symbols. Additionally, the interleave patterns1to3are employed as the interleave pattern.

FIG. 10shows a case where the interleave pattern1is employed,FIG. 11shows a case where the interleave pattern2is employed, andFIG. 12shows a case where the interleave pattern3is employed. As understood by comparingFIGS. 10 to 12with each other, the generated non-transmission symbols differ from each other in accordance with the interleave patterns in use even if the propagation path quality of the subcarriers is the same. That is, the number of generated non-transmission symbols depends on interleave patterns.

Thereupon, selection section303decides which interleave pattern generates the greatest number of non-transmission symbols, and determines the interleave pattern for use in interleaver301. That is, selection section303selects the interleave pattern whereby mapping section111removes the maximum number of symbols.

According to the present embodiment, the interleave pattern, whereby the number of non-transmission symbols becomes maximum, is selected among the plurality of interleave patterns in accordance with propagation path quality, so that the greatest number of non-transmission symbols can be constantly generated following changes in propagation path quality, and, as a result, consumption of transmission power can be suppressed and PAPR can be reduced.

Moreover, as a plurality of different interleave patterns, a plurality of interleave patterns corresponding to a plurality of different delay spreads respectively or a plurality of interleave patterns corresponding to a plurality of different maximum Doppler frequencies respectively can be employed.

Additionally, though the configuration of reporting the interleave pattern number selected by the radio transmitting apparatus to the radio receiving apparatus is described above, the radio receiving apparatus can select the deinterleave pattern based on propagation path quality without this report. Since propagation path quality in transmission is similar to propagation path quality in reception in the TDD system, the radio receiving apparatus also can select the deinterleave pattern, in accordance with the propagation path quality of each subcarrier similarly to selection of the interleave pattern by the radio transmitting apparatus, by measuring propagation path quality of each subcarrier of the OFDM symbol transmitted from the radio transmitting apparatus.

Additionally, the radio communication base station apparatus and radio communication terminal apparatus in the above embodiments may be referred to as “Node B” and “UE,” respectively. The subcarrier may be referred to as “tone.”

Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC”, “system LSI”, “super LSI”, or “ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.

The present application is based on Japanese patent application No. 2004-231114, filed on Aug. 6, 2004, the entire content of which is expressly incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use for radio communication base station apparatus or radio communication terminal apparatus used in mobile communication systems.