JP5658187B2 - Wireless communication apparatus, wireless communication system, and wireless communication method - Google Patents

Description

  The present invention relates to a wireless communication apparatus, a wireless communication system, and a wireless communication method that perform noise estimation in cooperative relay transmission.

  In recent years, cooperative communication schemes that improve communication characteristics by making cooperative relay transmissions to radio stations other than a source station and a destination station have attracted attention, and much research has been conducted on cooperative relay transmission. The system model of the communication method in cooperative relay transmission is mainly determined by the three elements of the relay station forward method, the cooperative system configuration (topology), and the cooperative protocol.

  The relay station forward method indicates what kind of signal processing is performed on a signal received by the relay station from the source station and transmitted to the destination station. The most representative relay station forward methods are the DF (Decode-and-Forward) method and the AF (Amplify-and-Forward) method. The DF method is a method of reproducing a signal received by a relay station and transmitting the reproduced signal to a destination station. The AF method is a method of amplifying a signal received by a relay station and transmitting the amplified signal to a destination station.

  Further, the cooperative system configuration (topology) includes the number of communication devices as a source station, a relay station, and a destination station that configure a wireless communication system using the cooperative communication method, and cooperative relay hops performed in the wireless communication system. Indicates a number. For example, the simplest configuration of a wireless communication system using a cooperative communication system includes a source station (Source), a relay station (Relay) that relays a signal transmitted by the source station, and a destination station (Destination). 1-Relay2-HOP (1R2H) configuration. In the 1R2H configuration, generally, one slot of radio resources (time and frequency) is allocated to transmission / reception from the transmission station to the relay station and transmission / reception from the relay station to the destination station. In many cases, one period is set to two slots. The cooperative protocol indicates a combination of transmission / reception relationships between communication devices (source station, relay station, and destination station) in one cycle of the wireless communication system.

  Next, with reference to FIG. 3, the cooperation protocol I (for example, refer nonpatent literature 1) in the radio | wireless communications system which has 1R2H structure is demonstrated. FIG. 3 is an explanatory diagram showing the operation of the cooperation protocol I in the wireless communication system having the 1R2H configuration. The wireless communication system includes a transmission station S, a relay station R, and a destination station D. One cycle of the wireless communication system is divided into two slots, a first slot and a second slot. In the first slot, the source station S performs broadcast transmission to the relay station R and the destination station D, and in slot 2, the relay station R transmits to the destination station D. Destination station D receives a signal (subpacket P1) transmitted from source station S in slot 1, and receives signals (subpackets P1 and P2) transmitted from source station S and relay station R in slot 2. .

  Hereinafter, the transmission / reception relationship of the source station S, the relay station R, and the destination station D when the protocol I is applied as the cooperative protocol in the wireless communication system will be described. FIG. 4 is a block diagram showing a configuration of a wireless communication system having a 1R2H configuration.

  The transmitting station S includes a transmission data signal generation unit 1, a training signal generation unit 2, an OFDM (orthogonal frequency division multiplexing) modulation unit 3, and a transmission unit 4. The transmission data signal generation unit 1 modulates the information bit string and generates a transmission data signal. The training signal generation unit 2 generates a training signal and outputs it to the OFDM modulation unit 3. Here, the training signal is a known signal for calculating a channel frequency response described later. The OFDM modulation unit 3 combines the training signal and the data signal to generate a packet signal, and transmits the packet signal via the transmission unit 4.

  The relay station R includes a switch unit 11, a received signal storage unit 12, a signal amplification unit 13, and an amplification coefficient information generation unit 14. The switch unit 11 switches the flow of signals in the circuit so that a common antenna for transmission and reception performs reception in the first slot and transmission in the second slot. The received signal storage unit 12 stores the value of the signal received in the first slot for signal transmission in the second slot. The signal amplifying unit 13 amplifies the received signal by attenuation. The amplification coefficient information generation unit 14 generates information to notify the destination station D of the amplification coefficient of the relay station R.

  The destination station D includes a receiving unit 21, an OFDM demodulating unit 22, a CFR (channel frequency response) dispersion analyzing unit 23, an amplification coefficient information analyzing unit 24, and a received data signal decoding unit 25. The received signal is input to the OFDM demodulator 22 via the receiver 21. The OFDM demodulator 22 demodulates the received signal and separates the training signal and the data signal. The CFR variance analysis unit 23 calculates the variance of CFR between the relay station R and the destination station D using a known training signal. The amplification coefficient information analysis unit 24 analyzes the information notified from the relay station R to obtain an amplification coefficient value. The noise power ratio can be calculated from the obtained CFR dispersion and amplification coefficient. The received data signal decoding unit 25 decodes the data signal to generate an information bit string. Here, a noise power ratio is required to realize maximum likelihood decoding.

In the following explanation, an orthogonal frequency domain multiplexing (OFDM) transmission system is assumed as an example. When the protocol I is applied as the cooperative protocol, the source station S broadcasts the subpacket P1 to the relay station R and the destination station D in the slot 1. At this time, the received signal Y _{d1, m} [k] of the destination station corresponding to the m-th OFDM symbol k-th subcarrier is expressed as equation (1).

Here, H _sd [k] is the channel frequency response (CFR) of the k-th subcarrier between the source station S and the destination station D, and its variance is L _sd . X _{1, m} [k] is a transmission signal corresponding to the subpacket P1 of the mth OFDM symbol kth subcarrier. W _{d1, m} [k] is additive white Gaussian noise (AWGN) in slot 1 at the destination station, and its noise power is E [| W _{d1, m} [k] ² |] = σ ₁ ² . E [•] represents an average. It is assumed that the noise power of the additional noise generated at each wireless station is σ ₁ ² and that the value is known at each wireless station.

Also, the received signal Y _{r1, m} [k] of the m-th OFDM symbol k-th subcarrier received by the relay station R in slot 1 is expressed as equation (2).

Here, H _sr [k] is a CFR between the transmitting station S and the relay station R, and its variance is L _sr . W _{r1, m} [k] is the additional white Gaussian noise in slot 1 at the relay station, and its noise power is equal to E [| W _{r1, m} [k] ² | ] = Σ ₁ ² .

The relay station amplifies the received signal Y _{r1, m} [k] received in the slot 1 by the amplification coefficient α _r and transmits the amplified received signal to the destination station in the slot 2. The amplification coefficient α _r is determined according to the characteristic that the relay station amplifies the received signal Y _{r1, m} [k]. At this time, the received signal Y _{d2, m} [k] received by the destination station in slot 2 is expressed by equation (3-1).

Here, H _rd [k] is the CFR in the relay station R and the destination station D, and its variance is L _rd . W _{d2, m} [k] is additional noise generated at the destination station D in slot 2, and its noise power is E [| W _{d2, m} [k] ² | ] = Σ ₁ ² . W ′ _{d2, m} [k] is the sum of the additional noise and the noise propagated from the relay station,
W ′ _{d2, m} [k] = H _rd [k] α _r W _{r1, m} [k] + W _{d2, m} [k] (3-2)
It is. At this time, if the noise power is set to E [| W ′ _{d2, m} [k] ² |] = σ ′ ₁ ² = τσ ′ ₁ ² ,
τ = L _rd α _r ² +1 (3-3)
It is. That is, τ is the noise power ratio of the received signals of each radio station and the destination station of slot 2.
When formulas (1) and (3-1) are put together, they can be expressed as formula (4).

となる。 Here, H _srd [k] = H _sr [k] H _rd [k]. In the destination station D, the transmission signals included in the received signals Y _{d1, m} [k] and Y _{d2, m} [k] received in the slot 2 are demodulated and decoded. In order to perform maximum likelihood decoding, it is necessary to normalize the noise power of the first slot and the second slot (Non-Patent Documents 1 and 2), and for that purpose it is necessary to estimate τ. If τ can be estimated and Y _{d2, m} [k] is multiplied by 1 / τ

It becomes.

となるので、このとき第一スロットと第二スロットの雑音電力は正規化できている。 The noise terms in the first and second lines of equation (5) are

Therefore, at this time, the noise power of the first slot and the second slot can be normalized.

と表せる。 Estimated values of H _sd [k] and H _srd [k] are generally estimated at the destination station D using a training signal (for example, p.13 of the long training sequence [Non-patent Document 3] for wireless LAN standard IEEE802.11a). Is required. For example, IEEE802.11a long training has 2 symbols, and the transmission / reception relationship of the training signal C [k] is given by equation (4)

It can be expressed.

By performing channel estimation on this equation, estimated values of H _sd [k] and H _srd [k] ^ H _sd [k], ^ H _srd [k] (^ is attached to the head of H, and so on. ) Is obtained. However, as described above, not only ^ H _sd [k] and ^ H _srd [k] but also an estimated value of the noise power ratio τ are necessary for maximum likelihood decoding.

The reception data signal decoding unit 25 performs maximum likelihood determination on the equation (5). In the maximum likelihood determination, the detected value ^ X of the transmission signal is obtained by the equations (8-1) and (8-2).

The detected value ^ X of the transmission signal is demodulated by the reverse operation of the transmitting station, and an information bit string is output. (For example, if X _{1, m} [k] and X _{2, m} [k] are generated by constellation mapping based on gray coding seen in pp. 19-20 of Non-Patent Document 3, ^ X is the same. Demapping by constellation is performed and converted into an information bit string.

RU Nabar, H. Bolcskei, and FW Kneubuhler, “Fading relay channels: Performance limits and space-time signal design,” IEEE J. Sel. Areas Commun., Vol. 22, no. 6, pp. 1099-1109, Jun . 2004. W. Su, A. K. Sadek, and K. J. R. Liu, “Cooperative communicationprotocols in wireless networks: performance analysis and optimum power allocation,“ Wireless Personal Commun., Vol. 44, pp. 181-217, Jan. 2008. Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-speed Physical Layer in the 5GHz band, IEEE Std. 802.11a-1999.

As described above, in order to perform maximum likelihood decoding, the destination station needs not only the channel frequency responses H _sd [k] and H _srd [k] but also estimation information of the noise power ratio τ. τ can be obtained from the equation (3-3) if the amplification coefficient α _r and the variance L _rd of the channel frequency response at the relay station R and the destination station D are known. Therefore, generally, information on α _r and L _rd is notified from the relay station to the destination station. However, since transmitting a signal for notification is overhead, it is desirable that the destination station knows the value of the noise power ratio τ without notification processing.

  The present invention has been made in view of such circumstances, and a wireless communication device, a wireless communication system, and a wireless communication method capable of calculating a noise power ratio only at a destination station without notifying information from a relay station The purpose is to provide.

  In the present invention, a transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, and the packet transmitted by the transmitting station in the first slot is received and received. A relay station that relays packet transmission by transmitting the packet in the second slot; and a noise that is a destination station of the packet and is caused by the destination station included in the received signal of the first slot; The destination in a wireless communication system comprising: a destination station that performs maximum likelihood decoding using a noise power ratio that is a ratio to noise caused by the relay station included in the received signal of the second slot to generate an information bit string A wireless communication device that operates as a station, based on training signals received in each of the first slot and the second slot. Characterized by comprising a noise power ratio estimation unit for estimating the noise power ratio using.

  In the present invention, the noise power ratio estimation unit estimates the noise power ratio by calculating an average of a difference between a first symbol and a second symbol of the training signal received in the second slot. And

  In the present invention, the noise power ratio estimator may determine the first of the training signals received in the first slot from the sum of the first symbol and the second symbol of the orthogonal training signal received in the second slot. The noise power ratio is estimated by obtaining an average of numbers obtained by subtracting twice one symbol.

  In the present invention, a transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, and the packet transmitted by the transmitting station in the first slot is received and received. A relay station that relays packet transmission by transmitting the packet in the second slot; and a noise that is a destination station of the packet and is caused by the destination station included in the received signal of the first slot; A wireless communication system comprising: a destination station that performs maximum likelihood decoding using a noise power ratio that is a ratio of noise caused by the relay station included in the received signal of the second slot to generate an information bit string; The destination station estimates the noise power ratio using an operation based on the training signal received in each of the first slot and the second slot. Characterized by comprising a noise power ratio estimator.

  In the present invention, a transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, and the packet transmitted by the transmitting station in the first slot is received and received. A relay station that relays packet transmission by transmitting the packet in the second slot; and a noise that is a destination station of the packet and is caused by the destination station included in the received signal of the first slot; Radio performed by a radio communication system including a destination station that performs maximum likelihood decoding using a noise power ratio that is a ratio of noise caused by the relay station included in the received signal of the second slot to generate an information bit string A communication method, wherein the destination station uses an arithmetic operation based on a training signal received in each of the first slot and the second slot. Characterized in that it has a noise power ratio estimating step of estimating the sound power ratio.

  According to the present invention, since the noise power ratio can be calculated in the destination station without the relay station notifying the destination station of the value necessary for calculating the noise power ratio, the overhead can be reduced. Is obtained.

It is a block diagram which shows the structure of one Embodiment of this invention. It is explanatory drawing which shows the operation | movement in the protocol II. It is explanatory drawing which shows operation | movement of the cooperation protocol I in the radio | wireless communications system which has 1R2H structure. It is a block diagram which shows the structure of the radio | wireless communications system which has 1R2H structure.

  Hereinafter, a wireless communication system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In this figure, the transmitting station S includes a transmission data signal generation unit 1, a training signal generation unit 2, an OFDM modulation unit 3, and a transmission unit 4. The transmission data signal generation unit 1 modulates the information bit string and generates a transmission data signal. The training signal generation unit 2 generates a training signal and outputs it to the OFDM modulation unit. Here, the training signal is a known signal for calculating a channel frequency response described later. The OFDM modulation unit 3 combines the training signal and the data signal to generate a packet signal, and transmits the packet signal via the transmission unit 4. The transmitting station S shown in FIG. 1 has the same configuration as that of the transmitting station S shown in FIG.

  The relay R station includes a switch unit 11, a received signal storage unit 12, and a signal amplification unit 13. The switch unit 11 switches the flow of signals in the circuit so that a common antenna for transmission and reception performs reception in the first slot and transmission in the second slot. The received signal storage unit 12 stores the value of the signal received in the first slot for signal transmission in the second slot. The signal amplifying unit 13 amplifies the received signal by attenuation. The relay station R shown in FIG. 1 has the same configuration as the relay force R shown in FIG. 4 except that the amplification coefficient information generation unit 14 shown in FIG. 4 is not provided.

  The destination station D includes a receiving unit 21, an OFDM demodulating unit 22, a noise power ratio estimating unit 26, and a received data signal decoding unit 25. The received signal is input to the OFDM demodulator 22 via the receiver 21. The OFDM demodulator 22 demodulates the received signal and separates the training signal and the data signal. The noise power ratio estimation unit 26 estimates the noise power ratio τ using a known training signal. The received data signal decoding unit 25 decodes the data signal to generate an information bit string. Here, the noise power ratio τ is used to realize maximum likelihood decoding.

  Hereinafter, the calculation operation of the estimated value of the noise power ratio τ in the wireless communication system shown in FIG. 1 will be described. Here, a description will be given assuming a system in which a packet has two or more training symbols (for example, IEEE 802.11a long training symbols T1 and T2 [pp. 12-13 of Non-Patent Document 3]). T1 and T2 are signals having the same pattern.

の値となる。 In the following processing operation, the noise power estimation unit 26 of the destination station D obtains an estimated value of the noise power ratio τ without the notification process from the relay station R. First, the difference between the first and second training received signals Y _d2,1 [k] and Y _d2,2 [k] is calculated. Here, the value is defined as A ₁ [k]. At this time, A ₁ [k] is

It becomes the value of.

Then, the average of | A ₁ [k] | ² for all subcarriers k = 1, 2,..., K divided by 2σ ₁ ² is the estimated value of τ ^^ (^ is the head of τ) The same shall apply hereinafter).

であり、Ｅ［｜Ａ_１［ｋ］｜^２］が得られればτが計算できることがわかる。 This estimation method of τ is based on the following consideration. When calculating a variance _E of ^{_{A 1 [k] [| 2}} | A 1 [k]]

It can be seen that τ can be calculated if E [| A ₁ [k] | ² ] is obtained.

Therefore, the average of | A ₁ [k] | ² for all subcarriers may be approximated as the variance of A ₁ [k] as shown in the following equation (12).

  Based on the above consideration, the destination station D can obtain the estimated value of τ without the notification process from the relay station R by the equations (9) and (10).

である。 Next, a case where an orthogonal training signal is used will be described. When an orthogonal training signal is used, different signal processing is performed to estimate the noise power ratio τ. The transmission and reception relationship when using an orthogonal training signal is

It is.

の値となる。 Here, A ₂ [k] is defined as A ₂ ≡−2Y _d1,1 [k] + Y _d2,1 [k] + Y _d2,2 [k]. At this time, A ₂ [k] is

It becomes the value of.

Then, the average of | A ₂ [k] | ² for all subcarriers k = 1, 2,..., K divided by 2σ ₁ ² is used as an estimated value of 2 + τ, and 2 is subtracted from that value. To obtain an estimated value τ of τ.

であり、Ｅ［｜Ａ_２［ｋ］｜^２］が得られればτが計算できることがわかる。 This estimation method of τ is based on the following consideration. When calculating a variance _E of ^{_{A 2 [k] [| 2}} | A 2 [k]]

It can be seen that τ can be calculated if E [| A ₂ [k] | ² ] is obtained.

Therefore, the average of | A ₂ [k] | ² for all subcarriers may be approximated as the variance of A ₂ [k] as shown in the following equation (17).

  Based on the above considerations, the destination station can obtain the estimated value of τ by the equations (14) and (15) without the notification process from the relay station.

  In the above description, the case where the protocol I of the cooperative protocol is used has been described as an example, but the protocol II may be used (see Non-Patent Document 1). FIG. 2 is an explanatory diagram showing the operation in protocol II. The signal processing performed at the destination station D in slot 2 may be the same as in protocol I.

  In the above description, the case where OFDM modulation is used as a multicarrier system has been described. However, the present invention is not limited to this, and an orthogonal frequency division multiple access (OFDMA) system, a multicarrier code division multiple, or the like. Connection (Multi Carrier-Code Division Multiple Access; MC-CDMA) may be used.

  Further, not only a 2-hop system but also a multi-hop system may be used. Further, not only one relay system in which only one relay station R exists, but also a multi-relay system in which a plurality of relay stations R exist and performs simultaneous transmission may be used. Furthermore, not only a single antenna system in which each radio station has only one antenna, but also a multi-antenna system having a plurality of antennas may be used.

  As described above, as one form of coordinated transmission in wireless relay, the wireless channel is divided into two time slots, and the transmitting station transmits the first data in the first time slot, and the second time slot. The relay station transfers the first data. In this embodiment, in order to perform maximum likelihood decoding, a noise power ratio that is a ratio of noise power included in the received signal in the first time slot and noise power included in the received signal in the second time slot is calculated. There is a need to. Conventionally, the noise power ratio is calculated based on channel information between the relay station R and the destination station D and the amplification factor at the relay station R. In this method, there is a problem that overhead is increased because signal exchange between the relay station R and the destination station D occurs.

  In the present embodiment, the destination station D calculates the noise power ratio τ by performing arithmetic processing on the known signals received in the first time slot and the second time slot, and uses this noise power ratio to calculate the noise power ratio τ. Likelihood decoding is performed. Specifically, when the conventional pilot signal is used, the noise power ratio is calculated by using the average of the difference between the received known signals in the first time slot and the second time slot. In addition, when using an orthogonal type known signal, the sum of the first symbol and the second symbol of the known signal received in the second time slot is twice the first symbol of the known signal received in the first slot. The noise power ratio is calculated by subtracting and averaging. With this configuration, since the noise power ratio can be calculated only by the destination station, overhead can be reduced.

  The program for realizing the function of the processing unit in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed, whereby the noise power ratio is reduced. A calculation process may be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer system” includes a WWW system having a homepage providing environment (or display environment). The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, what is called a difference file (difference program) may be sufficient.

  As mentioned above, although embodiment of this invention has been described with reference to drawings, the said embodiment is only the illustration of this invention, and it is clear that this invention is not limited to the said embodiment. is there. Accordingly, additions, omissions, substitutions, and other changes of the components may be made without departing from the technical idea and scope of the present invention.

  It can be applied to applications where it is essential to perform noise estimation in cooperative relay transmission.

  S ... Originating station, R ... Relay station, D ... Destination station, 26 ... Noise power ratio estimator

Claims (5)

A transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, the packet transmitted by the transmitting station in the first slot, and the received packet A relay station that relays packet transmission by transmitting in the second slot; a destination station of the packet, the noise caused by the destination station included in the received signal of the first slot; and the second slot Operating as the destination station in a wireless communication system comprising a destination station that performs maximum likelihood decoding using a noise power ratio that is a ratio with noise caused by the relay station included in the received signal to generate an information bit string A wireless communication device,
A wireless communication apparatus, comprising: a noise power ratio estimation unit configured to estimate the noise power ratio using a calculation based on a training signal received in each of the first slot and the second slot.   The noise power ratio estimation unit estimates the noise power ratio by calculating an average of a difference between a first symbol and a second symbol of the training signal received in the second slot. The wireless communication device according to 1.   The noise power ratio estimation unit is configured to calculate 2 of the first symbol of the training signal received in the first slot from the sum of the first symbol and the second symbol of the orthogonal training signal received in the second slot. The wireless communication apparatus according to claim 1, wherein the noise power ratio is estimated by obtaining an average of numbers obtained by subtracting a multiple. A transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, the packet transmitted by the transmitting station in the first slot, and the received packet A relay station that relays packet transmission by transmitting in the second slot; a destination station of the packet, the noise caused by the destination station included in the received signal of the first slot; and the second slot A wireless communication system comprising: a destination station that generates an information bit string by performing maximum likelihood decoding using a noise power ratio that is a ratio to noise caused by the relay station included in the received signal;
The destination station is
A wireless communication system, comprising: a noise power ratio estimation unit that estimates the noise power ratio using a calculation based on a training signal received in each of the first slot and the second slot. A transmitting station that transmits a packet in a first slot and a second slot obtained by time-sharing one radio channel, the packet transmitted by the transmitting station in the first slot, and the received packet A relay station that relays packet transmission by transmitting in the second slot; a destination station of the packet, the noise caused by the destination station included in the received signal of the first slot; and the second slot A wireless communication method performed by a wireless communication system including a destination station that performs maximum likelihood decoding using a noise power ratio that is a ratio to noise caused by the relay station included in the received signal and generates an information bit string. And
The wireless communication method according to claim 1, further comprising: a noise power ratio estimation step in which the destination station estimates the noise power ratio using an operation based on the training signal received in each of the first slot and the second slot.

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