US20080192857A1 - Wireless Receiving Apparatus, Wireless Transmitting Apparatus, and Interference Signal Removing Method - Google Patents

Wireless Receiving Apparatus, Wireless Transmitting Apparatus, and Interference Signal Removing Method Download PDF

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US20080192857A1
US20080192857A1 US11/722,856 US72285605A US2008192857A1 US 20080192857 A1 US20080192857 A1 US 20080192857A1 US 72285605 A US72285605 A US 72285605A US 2008192857 A1 US2008192857 A1 US 2008192857A1
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interference
signal
section
subcarriers
interference signal
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Kenichi Miyoshi
Akihiko Nishio
Daichi Imamura
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InterDigital Patent Holdings Inc
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Matsushita Electric Industrial Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining

Definitions

  • the present invention relates to a radio receiving apparatus, radio transmitting apparatus and interference signal cancellation method.
  • Multicarrier communication such as OFDM (Orthogonal Frequency Division Multiplexing) is focused as one of counter techniques of frequency selective fading.
  • Multicarrier communication is a technique of transmitting data using a plurality of carriers (subcarriers) with transmission rates suppressed to such an extent that frequency selective fading does not occur, which results in high-speed transmission.
  • the OFDM scheme utilizes a plurality of subcarriers which are orthogonal each other and where data is arranged, provides high frequency use efficiency in multicarrier communication, can be implemented with relatively simple hardware, is particularly focused and is variously studied.
  • AAA adaptive array antenna
  • Patent Document 1 discloses a technique for estimating an optimum weight promptly and precisely in a receiving apparatus where the OFDM scheme and AAA technique are combined.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 2003-218759
  • the AAA technique can cancel interference signals corresponding to the number of antennas minus one in principle.
  • the receiving apparatus disclosed in Patent Document 1 requires N+1 antennas.
  • M is the number of multipath for interference signal sources
  • the receiving apparatus disclosed in Patent Document 1 requires a large number (N ⁇ M+1) of antennas.
  • the receiving apparatus disclosed in Patent Document 1 requires a large number of antennas for canceling interference signals, it naturally follows that it is actually difficult to mount the receiving apparatus disclosed in Patent Document 1 in a radio communication mobile station apparatus (referred to as a mobile station) for which miniaturization is increasingly demanded in recent years.
  • a radio communication mobile station apparatus referred to as a mobile station
  • a radio receiving apparatus of the invention adopts a configuration including a receiving section that receives a multicarrier signal including a plurality of subcarriers on which a plurality of same symbols are mapped; and an interference cancellation section that cancels an interference signal from the multicarrier signal using the plurality of same symbols.
  • FIG. 1 is a concept diagram showing an OFDM signal
  • FIG. 2A is a concept diagram showing a symbol of subcarrier # 1 ;
  • FIG. 2B is a concept diagram showing a symbol of subcarrier # 2 ;
  • FIG. 2C is a concept diagram showing a symbol of subcarrier # 3 ;
  • FIG. 2D is a concept diagram showing a symbol of subcarrier # 4 ;
  • FIG. 3 is a diagram illustrating the operating principle of AAA technique
  • FIG. 4 is a diagram illustrating the operating principle of the present invention.
  • FIG. 5 is a block diagram showing a configuration of a base station according to Embodiment 1 of the present invention.
  • FIG. 6 is a block diagram showing a configuration of a mobile station according to Embodiment 1 of the present invention.
  • FIG. 7 is a diagram showing a mapping pattern according to Embodiment 1 of the present invention.
  • FIG. 8 is a block diagram showing a configuration of a base station according to Embodiment 2 of the present invention.
  • FIG. 9 is a diagram showing a mapping pattern according to Embodiment 2 of the present invention.
  • FIG. 10 is a diagram showing a mapping pattern according to Embodiment 2 of the present invention.
  • FIG. 11 is a block diagram showing a configuration of a mobile station according to Embodiment 3 of the present invention.
  • FIG. 12 is a diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 13 is a diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 14 is d diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 15 is a diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 16 is a diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 17 is a diagram showing a mapping pattern according to Embodiment 4 of the present invention.
  • FIG. 18 is a configuration diagram of a mobile communication system according to Embodiment 5 of the present invention.
  • FIG. 19 is a diagram showing a mapping pattern according to Embodiment 5 of the present invention.
  • FIG. 20 is a block diagram showing a configuration of a base station according to Embodiment 6 of the present invention.
  • FIG. 21 is a configuration diagram showing a mobile communication system according to Embodiment 7 of the present invention.
  • FIG. 22 is a block diagram showing a configuration of a mobile station according to Embodiment 7 of the present invention.
  • FIG. 23 is a block diagram showing a configuration of an interference cancellation section according to Embodiment 7 of the present invention.
  • FIG. 24 is a diagram showing a mapping pattern according to Embodiment 8 of the present invention.
  • FIG. 25 is a block diagram showing a configuration of a mobile station according to Embodiment 8 of the present invention.
  • FIG. 26 is a diagram showing a mapping pattern according to Embodiment 8 of the present invention.
  • An OFDM symbol which is a multicarrier signal, has an extremely low symbol rate and an OFDM symbol received in a multipath environment is received as a signal where signals of a plurality of paths are combined regardless of the number of multipaths. Accordingly, when, in the OFDM scheme, a desired signal and an interference signal are received in a mobile station through multipath, the mobile station receives, as shown in FIG. 1 , both the desired signal and the interference signal as the signal where signals of a plurality of paths are combined.
  • characteristics of an OFDM received signal include providing, even in a multipath environment where, in single-carrier transmission, a signal subjected to frequency selective fading is received, an OFDM received signal influenced by Rayleigh fading per subcarrier.
  • features of the AAA technique require N+1 antennas receiving a signal where one desired signal and N interference signals are combined to cancel N interference signals.
  • signals received at N+1 antennas include the desired signal and interference signals.
  • the signals received at the antennas are multiplied by a weight obtained by MMSE processing so that, by combining signals after weight multiplication, it is possible to cancel N interference signals from the received signal and obtain one desired signal.
  • the characteristics of the OFDM received signal and AAA technique include having subcarriers # 1 to # 4 shown in FIG. 1 as antennas in the AAA technique, mapping the same symbols as desired signals on four subcarriers of subcarriers # 1 to # 4 constituting an OFDM symbol and subjecting subcarriers # 1 to # 4 to MMSE processing as in the AAA technique so that, even when a number of multipaths in OFDM-scheme radio communication occurs, a mobile station can cancel all the interference signals transmitted from three interference signal sources. Further, the mobile station does not require a plurality of antennas but requires only one antenna regardless of the number of multipaths, so that the mobile station can cancel all the interference signals transmitted from three interference signal sources. In other words, when a plurality of multipaths occur, OFDM communication requires one antenna in a mobile station and N+1 subcarriers where the same symbols are mapped as desired signals for canceling interference signals transmitted from N interference signal sources from a received signal.
  • the present invention cancels the interference signal included in the OFDM symbol by using the plurality of subcarriers on which the plurality of same symbols are mapped as a plurality of antennas in AAA technique and by performing MMSE processing on the plurality of same symbols in the frequency domain.
  • a received signal R n at the antenna n is represented by equation 1, where D is a desired signal, U is an interference signal, h Dn is a channel estimation value of the channel of the desired signal at an antenna n, and h Un is a channel estimation value of the channel of the interference signal at the antenna n.
  • a received signal Q m in the subcarrier m is represented by equation 4, where D is a desired signal, U is an interference signal, h Dm is a channel estimation value of the channel in a subcarrier m of the desired signal, and h Um is a channel estimation value of the channel in the subcarrier m of the interference signal.
  • the received signal in the subcarriers is obtained by equation 6.
  • the antenna number n is replaced with the subcarrier number m and the other numbers are represented by the same equations.
  • this is equivalent to that it is possible to cancel an interference signal from an OFDM symbol by utilizing a plurality of subcarriers of the OFDM symbol as a plurality of antennas in the AAA technique and and by subjecting the plurality of subcarriers of the OFDM symbol received at one antenna to MMSE processing as in the AAA technique.
  • FIG. 5 shows a configuration of a radio communication base station apparatus (referred to as a “base station”) 100 according to the present embodiment. Further, FIG. 6 shows a configuration of mobile station 200 according to the present embodiment.
  • base station a radio communication base station apparatus
  • coding section 101 encodes transmission data (bit sequence) and outputs encoded transmission data to modulating section 102 .
  • Modulation section 102 modulates the encoded bit sequence, generates a symbol and outputs the symbol to repetition section 103 .
  • RF repetition factor
  • S/P section 104 Every time S/P section 104 receives K symbols corresponding to a plurality of subcarriers, # 1 to #k constituting an OFDM symbol that is a multicarrier signal inputted in series from repetition section 103 , S/P section 104 transforms the symbols into parallel symbols and outputs the transformed symbols to IFFT section 105 .
  • IFFT section 105 subjects the symbols inputted from S/P section 104 to IFFT (Inverse Fast Fourier Transform), maps (arranges) the transformed symbols on subcarriers # 1 to #k according to a predetermined mapping pattern (arrangement pattern) and generates an OFDM symbol. Further, IFFT section 105 subjects a pilot symbol (PL) to IFFT at the beginning of the frame, maps the transformed pilot symbols on subcarriers # 1 to #k and generates the OFDM symbol.
  • PL pilot symbol
  • one OFDM symbol is constituted of eight subcarriers # 1 to # 8 .
  • a mapping pattern in the present embodiment is as shown in FIG. 7 , for example.
  • the same symbols are mapped onto four different subcarriers and transmitted to mobile station 200 .
  • Mobile station 200 as shown in FIG. 6 receives an OFDM symbol transmitted from base station 100 through antenna 201 .
  • the received OFDM symbol includes the desired signal transmitted from base station 100 and interference signals transmitted from interference signal sources.
  • These interference signals include OFDM symbols having the same frequencies as frequencies # 1 to # 8 of the OFDM symbols transmitted from base station 100 , such as OFDM symbols transmitted from base stations other than base station 100 and OFDM symbols transmitted from mobile stations other than mobile station 200 .
  • antenna 108 of base station 100 is a sector antenna constituted of a plurality of antennas
  • interference signals include OFDM symbol transmitted from antennas of sectors other than the sector where mobile station 200 is located.
  • the OFDM symbol including the desired signal and interference signals are subjected to predetermined radio processing such as down-conversion in RF receiving section 202 , removed the guard interval in GI removing section 203 and inputted to FFT section 204 .
  • FFT section 204 subjects the OFDM symbol inputted from GI section 203 to FFT (Fast Fourier Transform) and obtains the symbols mapped onto subcarriers # 1 to # 8 . These symbols are inputted to selecting section 205 .
  • FFT Fast Fourier Transform
  • Channel estimating section 206 obtains channel estimation values of subcarriers # 1 to # 8 using the input pilot symbols. Then, channel estimating section 206 generates and outputs a P vector using the channel estimation values to MMSE processing section 208 . For example, at t 1 selecting section 205 selects four symbols S 1 mapped onto subcarriers # 1 to # 4 and channel estimating section 206 generates a P vector shown in equation 7 using channel estimation values h 1 to h 4 of subcarriers # 1 to # 4 . The flow is the same for symbols S 2 to S 16 . In addition, the channel estimation value is calculated based on the pilot symbol at the beginning of the frame and the same channel estimation values are used over a one frame per subcarrier.
  • Correlation value calculating section 207 obtains cross-correlation values between subcarriers of the same symbol. For example, when the four symbols S 1 mapped onto subcarriers # 1 to # 4 are inputted, correlation value calculating section 207 obtains cross-correlation values of these four symbols among subcarriers # 1 to # 4 . Then, correlation value calculating section 207 generates an R matrix from the cross-correlation values, obtains the inverse matrix of the R matrix and outputs the obtained inverse matrix to MMSE processing section 208 .
  • correlation value calculating section 207 generates an R matrix represented by equation 8 using cross-correlation values X 11 to X 44 among subcarriers # 1 to # 4 .
  • the flow is the same for symbols S 2 to S 16 .
  • MMSE processing section 208 subjects the P vector (P) inputted from channel estimating section 206 and inverse matrix (R ⁇ 1 ) of the R matrix inputted from correlation value calculating section 207 to MMSE processing using matrix operation represented by equation 9, obtains weights W (W 1 to W 4 ) and outputs the weights to multipliers 209 - 1 to 209 -N.
  • the flow is the same for symbols S 2 to S 16 .
  • Multipliers 209 - 1 to 209 -N multiply the symbols selected in selecting section 205 with the weights obtained in MMSE processing section 208 .
  • Combining section 210 combines symbols after weight multiplication and generates a combined signal.
  • the same symbols combined in combining section 210 are the symbols mapped onto a plurality of different subcarriers so that it is possible to cancel the interference signals from symbols S 1 to S 16 by combining the symbols among the subcarriers.
  • interference cancellation section 213 has correlation value calculating section 207 , MMSE processing section 208 , multipliers 209 - 1 to 209 -N and combining section 210 .
  • the mobile station does not require a large number of antennas as the conventional AAA technique but requires only one antenna for canceling interference signals, so that, regardless of the number of multipaths, it is possible to avoid making the apparatus larger for canceling interference signals.
  • the AAA technique increases the number of receiving antennas based on increase in the number of interference signal sources and the number of multipaths, even when interference signal sources increase, regardless of an increase of multipaths, it is possible to efficiently cancel interference signals by only increasing RF.
  • the present embodiment is effective particularly in a mobile communication system where a communication area (cell) that one base station covers is divided into a plurality of sectors in the angular directions by sector antennas having directivity. Signals transmitted to the plurality of divided sectors are transmitted from a plurality of antennas of one base station and an interference signal level is likely to be higher in interferences between sectors than interferences between cells regardless of a place where the mobile station is positioned.
  • SIR Signal to Interference Ratio
  • the effect of improving SIR is small for interference between sectors than for inter-cell interference when the desired signal level is increased so that it is possible to enhance the effect of improving SIR by suppressing the interference signal level as in the present embodiment.
  • FIG. 8 shows a configuration of base station 300 according to the present embodiment.
  • Base station 300 further has interleaver 301 in the configuration of base station 100 ( FIG. 5 ) according to Embodiment 1.
  • the plurality of same symbols subjected to repetition may be interleaved the frequency domain so that it is possible to improve the diversity effect in the frequency domain. Further, the plurality of same symbols subjected to repetition may be interleaved in the time domain so that it is possible to enhance the diversity effect in the time domain.
  • the mapping pattern of desired signals subjected to repetition onto subcarriers and a mapping pattern of interference signals subjected to repetition onto subcarriers needs to be the same in the frequency domain so that it is possible to obtain a desired signal by canceling interference signals from a received signal in mobile station 200 according to Embodiment 1.
  • the desired signal and interference signal need to be arranged in the frequency domain in the same pattern, so that it is possible to obtain a desired signal by canceling interference signals from a received signal in mobile station 200 according to Embodiment 1.
  • interleaver 301 of the desired signal source and interleaver 301 of the interference signal source need to interleave the same symbols subjected to repetition in the frequency domain according to the same interleaving pattern.
  • interleaver 301 interleaves, as shown in FIG. 9 , symbols shown in FIG. 7 . Then, at this point, the desired signal and interference signal are interleaved in the same pattern in the frequency domain. In contrast, when interleaving is performed in the time domain, interleaver 301 does not interleave symbols, but interleaves OFDM symbols (per column). In this way, the mapping pattern of desired signals subjected to repetition onto subcarriers and the mapping pattern of interference signals subjected to repetition onto subcarriers in the frequency domain become the same, so that it is possible to reliably cancel the interference signals from the received signal.
  • the desired signal and the interference signals may be interleaved in the time domain using different interleaving patterns.
  • mapping pattern of the desired signal source is shown in FIG. 9 and the mapping pattern of the interference signal source is shown in FIG. 10 .
  • the symbol S 1 that is the desired signal is mapped onto subcarriers # 1 , # 3 , # 5 and # 7
  • the symbol S 7 ′ that is the interference signal is also mapped onto subcarriers # 1 , # 3 , # 5 and # 7 .
  • all the combinations of the desired signal and the interference signal in subcarriers # 1 , # 3 , # 5 and # 7 become the same, so that it is possible to prevent a decrease in interference cancellation performance due to a difference in the interleaving pattern in the frequency domain between the desired signal and the interference signal.
  • the present embodiment is effective particularly in a mobile communication system where a communication area (cell) that one base station covers is divided into a plurality of sectors in the angular directions by sector antennas having directivity.
  • a base station has a plurality of sectors, signals are transmitted to adjacent sectors from the one base station, the base station makes it easy to make the interleaving patterns of the interference signal and the desired signal the same in mobile station 200 .
  • signaling is required between base stations in different cells for matching interleaving patterns between the adjacent cells and processing is required in one base station for matching interleaving patterns between adjacent sectors.
  • the interleaving patterns of the desired signal and interference signal different when performing interleaving in the time domain as described above, so that it is possible to make interleaving intervals different in the time domain of symbols for mobile stations. For example, by making the interleaving interval shorter in the time domain for a mobile station with a high moving speed, making delay for interleaving shorter and making the interleaving interval longer in the time domain for a mobile station with a low moving speed, it is possible to enhance reception performance.
  • Mobile station 200 increases the processing amount of matrix operation in MMSE processing, as the RF (Repetition Factor) increases. Therefore, in the present embodiment, MMSE processing is divided and performed.
  • FIG. 11 shows a configuration of mobile station 400 according to the present embodiment.
  • the same components as mobile station 200 ( FIG. 6 ) according to Embodiment 1 are assigned the same reference numerals and are not described.
  • the internal configuration of interference cancellation sections 403 - 1 to 403 - 3 is the same as the internal configuration of interference cancellation section 213 in FIG. 6 .
  • selecting section 401 In case of OFDM symbols at the beginning of the frame in FIG. 7 , selecting section 401 outputs the pilot symbols mapped onto subcarriers # 1 to # 8 to channel estimating section 402 . Further, selecting section 401 selects the plurality of same symbols according to the mapping pattern at the time of generating OFDM symbols in base station 100 and outputs the symbols to interference cancellation sections 403 - 1 and 403 - 2 .
  • selecting section 401 outputs two symbols S 1 mapped onto subcarriers # 1 and # 3 to interference cancellation section 403 - 1 and outputs two symbols S 1 mapped onto subcarriers # 2 and # 4 to interference cancellation section 403 - 2 .
  • subcarriers # 1 and # 3 are combined and subcarriers # 2 and # 4 are combined because, by combining subcarriers having small correlation, it is possible to reliably generate the inverse matrix of the R matrix in interference cancellation sections 403 - 1 and 403 - 2 .
  • Channel estimating section 402 outputs a P vector generated using channel estimation values of subcarriers # 1 and # 3 to interference cancellation section 403 - 1 and outputs a P vector generated from channel estimation values of subcarriers # 2 and # 4 to interference cancellation section 403 - 2 .
  • interference cancellation sections 403 - 1 and 403 - 2 subject the inverse matrix of the R matrix with two rows and two columns and the P vector with two rows and one column to MMSE processing and output a combined signal to interference cancellation section 403 - 3 .
  • interference cancellation sections 403 - 1 and 403 - 2 subject approximately RF/2 to MMSE processing.
  • interference cancellation section 403 - 1 multiplies channel estimation values of subcarriers # 1 and # 3 with weights W 1 and W 3 obtained by MMSE processing, adds and outputs the results (combined channel estimation value) to interference cancellation section 403 - 3
  • interference cancellation section 403 - 2 multiplies channel estimation values of subcarriers # 2 and # 4 with weights W 2 and W 4 obtained by MMSE processing, adds and outputs the results (combined channel estimation value) to interference cancellation section 403 - 3 .
  • interference cancellation section 403 - 3 subjects remaining RF/2 to MMSE processing.
  • interference cancellation section 403 - 3 performs MMSE processing using the inverse matrix of the R matrix with two rows and two columns generated from two combined signals and the P vector with two rows and one column generated from two combined channel estimation values, and outputs a combined signal to demodulation section 211 .
  • Interference cancellation section 403 - 3 outputs the combined signal as a signal from which interference signal is canceled, as the combined signal outputted from interference cancellation section 213 in FIG. 6 .
  • the present embodiment performs MMSE processing described in Embodiment 1 in two steps so that it is possible to reduce the processing amount of matrix operation in MMSE processing.
  • the present embodiment provide the R matrix with two rows and two columns and the P vector with two rows and one column so that it is possible to achieve the effect of reducing the operation amount significantly.
  • selecting section 401 outputs subcarriers where symbol S 1 ′ in FIG. 12 is provided as the interference signal (that is, two symbols S 1 mapped onto subcarriers # 1 and # 2 ) to interference cancellation section 403 - 1 , and outputs subcarriers where symbol S 2 ′ in FIG. 12 is provided as the interference signal (that is, two symbols S 1 mapped onto subcarriers # 3 and # 4 ) to interference cancellation section 403 - 2 .
  • Channel estimating section 402 outputs a P vector generated using channel estimation values of subcarriers # 1 and # 2 to interference cancellation section 403 - 1 , and outputs a P vector generated using channel estimation values of subcarriers # 3 and # 4 to interference cancellation section 403 - 2 .
  • interference cancellation sections 403 - 1 and 403 - 2 subject the inverse matrix of the R matrix with two rows and two columns and the P vector with two rows and 1column to MMSE processing, and outputs a combined signal to interference cancellation section 403 - 3 .
  • interference cancellation section 403 - 1 multiplies channel estimation values of subcarriers # 1 and # 2 with weights W 1 and W 2 obtained by MMSE processing, and adds the multiplied channel estimation values and outputs the addition result (combined channel estimation value) to interference cancellation section 403 - 3
  • interference cancellation section 403 - 2 multiplies channel estimation values of subcarriers # 3 and # 4 with weights W 3 and W 4 obtained by MMSE processing, and adds the multiplied channel estimation values and outputs the addition result (combined channel estimation value) to interference cancellation section 403 - 3 .
  • interference cancellation section 403 - 3 subjects the inverse matrix of the R matrix with two rows and two columns generated from two combined signals and the P vector with two rows and one column generated from two combined channel estimation values to MMSE processing, and outputs a combined signal to demodulation section 211 .
  • the interference signal can thus be canceled from the desired signal.
  • RF repetition factors
  • the repetition factor and mapping pattern for the base station of the desired signal source and the base station of the interference signal source are determined so that it is possible at the mobile station to cancel the interference signal as described above.
  • the mapping pattern of the desired signal and the mapping pattern of the interference signal are made the same in at least two symbols.
  • the mapping patterns in FIGS. 7 and 13 are interleaved in the frequency domain, the same mapping pattern of the desired signal and the mapping pattern of the interference signal are made the same in at least two symbols include.
  • the mapping pattern of the desired signal and the mapping pattern of the interference signal are made the same I at least two symbols as described above.
  • mapping patterns of a plurality of same symbols in the frequency domain are the same on at least M+1 subcarriers in the base station of the desired signal and the base stations of interference signal sources so that it is possible to cancel interference signals from all interference signal sources.
  • the repetition factor for the desired signal and the repetition factor for the interference signal is different, it is possible to cancel the interference signal from the received signal and obtain the desired signal.
  • FIG. 18 shows a configuration of a mobile communication system according to the present embodiment.
  • the present embodiment include the mobile station MS A that is communicating with the base station BS A and is located near the cell boundary of cell A. Further, the case is described where a cell adjacent to cell A is cell B. Accordingly, in FIG. 18 , for mobile station MS A , the base station BS A is a desired signal source and the base station BS B is an interference signal source.
  • a signal transmitted to the mobile station MS A located in cell A from the base station BS A is a desired signal for mobile station MS A
  • a signal transmitted to the mobile station MS B located in cell B from the base station BS B is a desired signal for the mobile station MS B and an interference signal to the mobile station MS A
  • the base station BS B (interference signal source) and the mobile station MS B have a plurality of antennas (two in FIG. 18 ), and perform MIMO (Multi Input Multi Output) communication.
  • MIMO Multi Input Multi Output
  • the base station BS B of the interference signal source when, in base station BS A of the desired signal source, a mapping pattern is provided as shown in FIG. 7 , the base station BS B of the interference signal source provide a mapping pattern at the antenna on one side as shown in FIG. 15 and provide a mapping pattern at the antenna on the other side as shown in FIG. 19 .
  • the mapping pattern of the desired signal and the mapping patterns of the interference signals transmitted from two antennas the same in the frequency domain, even when the base station BS B of the interference signal source performs MIMO communication, the mobile station MS A can cancel the interference signal from the received signal in the same way as described above.
  • the repetition factor is L
  • L ⁇ 1 interference signals can be canceled so that, when the base station BS B performs MIMO communication using L ⁇ 1 antennas at maximum, it is possible at the mobile station MS A to cancel all the interference signals.
  • the desired signal is not subjected to MIMO transmission and the interference signal is subjected to MIMO transmission
  • the base station when the base station has a plurality of antennas and performs MIMO transmission, it is possible at the mobile station to cancel the interference signal from the received signal and obtain the desired signal.
  • FIG. 20 shows a configuration of base station 500 according to the present embodiment.
  • Base station 500 further provides scrambling section 501 in the configuration of base station 300 ( FIG. 8 ) according to Embodiment 2.
  • Scrambling section 501 subjects an interleaved symbol to complex multiplication with one of OVSF (Orthogonal Variable Spreading Factor) code, GOLD code, PN code and rotation code to complex multiplication, and subjects symbols to scrambling processing.
  • OVSF Orthogonal Variable Spreading Factor
  • the interference signal from base station 500 becomes whitened in the mobile station by scrambling processing so that it is possible to reduce the influence of interference.
  • FIG. 21 shows a configuration of a mobile communication system according to the present embodiment.
  • the present embodiment includes the mobile station MS A that is communicating with the base station BS A and is located near the cell boundary of cell A. Further, the case is described where cells adjacent to cell A are cells B and C. Accordingly, in FIG. 21 , for the mobile station MS A , the base station BS A is a desired signal source, and the base stations BS B and BS C are interference signal sources.
  • a signal transmitted to the mobile station MS A located in cell A from the base station BS A is a desired signal for the mobile station MS A
  • a signal transmitted to a mobile station located in cell B from the base station BS B is an interference signal B for the mobile station MS A
  • a signal transmitted to a mobile station located in cell C from the base station BS C is an interference signal C for the mobile station MS A
  • the mobile station MS A has a plurality of antennas (two in FIG. 21 ). In such a mobile communication system, it is possible at the mobile station MS A to cancel a plurality of interference signals (the interference signals A and B)
  • mapping pattern in the base station BS A of the desired signal source is provided as shown in FIG. 7
  • a mapping pattern in the base station BS B of the interference signal source is provided as shown in FIG. 15 and the mapping pattern in the base station BS B is matched with the mapping pattern of the base station BS A .
  • interference signal B interference signal having the mapping pattern matched with the desired signal
  • interference signal C interference signal having the mapping pattern unmatched with the desired signal
  • FIG. 22 shows a configuration of mobile station 600 according to the present embodiment.
  • the same components as mobile station 200 ( FIG. 6 ) according to Embodiment 1 are assigned the same reference numerals and are not described.
  • antennas 201 - 1 and 201 - 2 , RF receiving sections 202 - 1 and 202 - 2 , GI removing sections 203 - 1 and 203 - 2 , and FFT sections 204 - 1 and 204 - 2 in FIG. 11 are the same as antenna 201 , RF receiving section 202 , GI removing section 203 , and FFT section 204 in FIG. 6 .
  • Mobile station 600 divides and performs interference canceling processing into two steps.
  • interference cancellation sections 601 - 1 to 601 -K separate the interference signal (interference signal C) having the mapping pattern unmatched with the desired signal in the space domain
  • interference cancellation section 213 separates the interference signal (interference signal B) having the mapping pattern matched with the desired signal in the frequency domain.
  • Interference cancellation sections 601 - 1 to 601 -K are provided so as to correspond to a plurality of subcarriers # 1 to #K constituting an OFDM symbol and receives both a signal received at antenna 201 - 1 and another signal received at antenna 201 - 2 , per subcarrier. Then, interference cancellation sections 601 - 1 to 601 -K cancel the interference signal C from the received signal by subjecting the signals to MMSE processing in the space domain.
  • Interference cancellation sections 601 - 1 to 601 -K when in canceling the interference signal C from the received signal, receive a signal (referred to as a “pseudo desired signal”) combining the desired signal and interference signal B as a desired signal in MMSE processing, and subjects the symbol to MMSE processing. Only the interference signal C is first demultiplexed from the received signal by MMSE processing.
  • FIG. 23 shows a configuration of interference cancellation sections 601 - 1 to 601 -K.
  • Signals from FFT sections 204 - 1 and 204 - 2 are inputted to interference cancellation sections 601 - 1 to 601 -K per subcarrier # 1 to #K.
  • channel estimating section 6011 calculates a channel estimation value of the desired signal per antenna and outputs the calculated channel estimation value to combining section 6013 .
  • channel estimating section 6012 calculates a channel estimation value of the interference signal B per antenna and outputs the calculated channel estimation value to combining section 6013 .
  • Combining section 6013 combines the channel estimation value of the desired signal and the channel estimation value of the interference signal B per antenna and outputs the combined channel estimation value to MMSE processing section 6014 .
  • MMSE processing 6014 can subject the pseudo desired signal as a desired signal in MMSE to MMSE processing in the space domain. Then, it is possible to extract the pseudo desired signal from the received signal (a signal where the desired signal and interference signals B and C are mixed) by this MMSE processing. In other words, it is possible to cancel the interference signal C from the received signal. Pseudo desired signals obtained in MMSE processing sections 6014 in interference cancellation sections 601 - 1 to 601 -K are outputted to selecting section 205 .
  • interference cancellation section 213 cancels the interference signal B from the pseudo desired signal and extracts only the desired signal.
  • the repetition factor (RF) is L
  • the present embodiment it is possible to reliably cancel all interference signals when the relationships of M 1 ⁇ N and M 2 ⁇ L hold, where the number of interference signal sources having the mapping pattern matched with the desired signal is M 1 , the number of interference signal sources having the mapping pattern unmatched with the desired signal is M 2 , the number of receiving antennas of the mobile station is N and the repetition factor is L.
  • interference canceling processing may be performed in a single step rather than in two steps in the space domain and the frequency domain, in the present embodiment, by canceling the interference signal (interference signal C) having the mapping pattern unmatched with the desired signal prior to canceling the interference signal (interference signal B) having the mapping pattern matched with the desired signal, it is possible to reduce the number of antennas and the computation amount required for canceling interference. This is because of the reason as described below.
  • the interference signal B is extracted as a pseudo desired signal, not as an interference signal when the interference signal C is canceled from the received signal in the space domain.
  • the number of interference signals that should be canceled in the space domain can be reduced so that it is possible to decrease the number of antennas required for canceling interference and reduce the amount of inverse matrix operation required for canceling interference.
  • the interference signal having the mapping pattern matched with the desired signal and the interference signal having the mapping pattern unmatched with the desired signal are provided, it is possible at the mobile station to cancel the interference signals from the received signal and obtain the desired signal.
  • Embodiment 1 where the mapping patterns in the frequency domain in the base station of the desired signal source and the base station of the interference signal source are the same, a case will be described with the present embodiment where the mapping patterns in the time domain in the base station of the desired signal source and the base station of the interference signal source are the same.
  • Embodiment 1 in consideration of the fact that channel variations in the time domain are generally smaller than channel variations in the frequency domain, maps the plurality of same symbols subjected to repetition in the frequency domain ( FIG. 7 ).
  • channel variations in the time domain can be larger than channel variations in the frequency domain. In such a case, it is effective to map the plurality of same symbols subjected to repetition in the time domain.
  • the base station of the desired signal source have a mapping pattern as shown in FIG. 24 .
  • the base station of the interference signal source uses a mapping pattern matched with the mapping pattern as shown in FIG. 24 as in Embodiment 1.
  • a mobile station receiving a signal transmitted from the base station having such a mapping pattern has a configuration as shown in FIG. 25 .
  • mobile station 800 according to the present embodiment further has transposing section 801 in mobile station 200 ( FIG. 6 ) according to Embodiment 1 .
  • FIG. 25 the same components as those of FIG. 6 are assigned the same reference numerals and are not described.
  • Transposing section 801 transposes a signal inputted from FFT section 204 between the frequency domain and the time domain. To be more specific, in the mapping pattern shown in FIG. 24 , transposing section 801 transposes data portions between frequencies (subcarriers) # 1 to # 8 and time t 1 to t 8 . As a result, the mapping pattern is transformed as the same one shown in FIG. 7 . Data where mapping pattern is thus transformed is outputted to selecting section 205 .
  • the plurality of same symbols subjected to repetition may be interleaved in the time domain so that it is possible to further enhance the diversity effect in the time domain. Further, the plurality of same symbols subjected to repetition may be interleaved in the frequency domain so that it is possible to enhance the diversity effect in the frequency domain.
  • the mapping pattern of desired signals subjected to repetition onto subcarriers and the mapping pattern of interference signals subjected to repetition onto subcarriers need to be the same in the time domain.
  • the desired signal and the interference signal needs to be arranged in the time domain according to the same mapping pattern. Accordingly, the interleaver of the desired signal source and interleaver of the interference signal source need to interleave the same symbols subjected to repetition in the time domain in the same interleaving patterns.
  • interleavers interleave symbols shown in FIG. 24 .
  • the interleaving patterns of the desired signal and interference signal in the time domain are the same.
  • interleavers interleave per subcarrier (per row) without interleaving per symbol.
  • the interleaving patterns of the desired signal and interference signal are the same in the frequency domain and time domain.
  • the mapping patterns subjected to interleaving are the same in the base station of the desired signal source and the base station of the interference signal source.
  • the interference cancellation algorithm is not limited to MMSE and may use algorithms that are interference cancellation algorithms used in the AAA technique.
  • mobile communication systems increasingly need to perform MIMO reception for enabling fast transmission of data rate and may use the stream division algorithm not only for the stream division algorithm in MIMO reception processing, but also for interference canceling processing by using the stream division algorithm as the interference cancellation algorithm so that it is possible to simplify the circuit configuration of the receiver.
  • the stream division algorithm as the interference cancellation algorithm, it eliminates the necessity of operation of the cross-correlation matrix required for using MMSE so that it is possible to cancel interference signals reliably when the number of symbols of the received signal is small.
  • it is possible to switch adaptively between MIMO reception processing and interference canceling processing according to the propagation environment between the base station and mobile station or the distance between the base station and the mobile station.
  • the mobile station when the mobile station is located relatively near the base station and is moving at low speed, it is possible to improve transmission rate by using the stream division algorithm and performing MIMO reception processing, and when the mobile station is located at the cell edge or sector edge, it is possible to improve SINR by performing interference canceling processing of the present invention using the stream division algorithm.
  • MIMO reception processing calculates stream division weights using channel estimation values per stream and per antenna
  • stream division weights may be calculated using channel estimation values per transmitting station and per subcarrier.
  • the mobile station that is a receiving station has one or two antennas
  • a radio receiving apparatus includes the number of antennas as N and the repetition factor as L, it is possible to cancel N ⁇ L ⁇ 1 interference signals by applying the invention.
  • the base station is a transmitting station (radio transmitting apparatus) and the mobile station is a receiving station (radio receiving station)
  • the base station is a receiving station (radio receiving station)
  • the base station receives a desired signal from a mobile station of a desired signal source and receives an interference signal from a mobile station of an interference signal source simultaneously
  • the base station receives a desired signal from a mobile station of a desired signal source and receives an interference signal from a mobile station of an interference signal source simultaneously
  • the base station, mobile station and subcarrier may be referred to as Node B, UE and tone.
  • communication systems may provide a communication area that one base station covers and is referred to as a “cell site” and an area obtained by dividing the cell site into a plurality of areas in the angular direction and is referred to as a “cell”.
  • the invention is applicable to such communication systems.
  • 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” due to differing extents of integration.
  • circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible.
  • FPGA Field Programmable Gate Array
  • reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.
  • the present invention is preferably used in, for example, a base station and mobile station used in a mobile communication system.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Noise Elimination (AREA)
  • Radio Transmission System (AREA)
US11/722,856 2004-12-28 2005-12-26 Wireless Receiving Apparatus, Wireless Transmitting Apparatus, and Interference Signal Removing Method Abandoned US20080192857A1 (en)

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EP1830502A1 (fr) 2007-09-05

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