JP2008141545A - Receiver in m-ary communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain SN ratio estimation in a receiver of an M-ary communication system. <P>SOLUTION: The receiver 200 in the M-ary communication system is provided with: a code sequence generation part 13 which generates M (M is an integer ≥ 2) code sequences; M correlators 1a-Ma which perform a correlation operation between a code sequence represented by a receiving signal of a receiving part 12 and the M code sequences to generate M correlation values and an SN ratio estimation part 22 and periodically receives synchronizing signal representing a code sequence for synchronization. The SN ratio estimation part 22 estimates SN ratio on the basis of output of a correlator corresponding to the code sequence for synchronization in receiving timing of the synchronizing signal. Otherwise, noise components are estimated from output of the correlators except the one corresponding to the code sequence for synchronization in the receiving timing of the synchronizing signal while estimating signal components from output of the correlator corresponding to the code sequence for synchronization in the receiving time of the synchronizing signal and the SN ratio is estimated from the signal components and the noise components. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiving apparatus of an M-ary communication system that performs communication using an M-ary / SS communication system (M-ary spread spectrum communication system), and more particularly to an SN ratio estimation method in the receiving apparatus.

  In recent years, an M-ary / SS communication system has been proposed as a communication system with good frequency utilization efficiency, and application to future AV fields is expected (for example, see Patent Documents 1 and 2 below). A conventional M-ary communication system employing this communication method will be briefly described.

  The transmission apparatus in the M-ary communication system includes a code sequence generation unit that generates M code sequences, and selects one code sequence according to transmission data (M is an integer of 2 or more). For example, when transmitting 2-bit information, four code sequences are required. In these M code sequences, the cross-correlation between different code sequences is substantially zero.

  On the other hand, a receiving apparatus in the M-ary communication system includes a code sequence generating unit that generates the same M code sequences as that on the transmitting side and M correlators. Each of these code sequences is received from the transmitting apparatus. Correlation calculation with the code sequence is performed to obtain M correlation values.

  When the correlation calculation is performed using the same code sequence as the code sequence selected by the transmission device, the correlation value is large, but the correlation calculation is performed using a code sequence different from the code sequence selected by the transmission device. In this case, the correlation value is very small because the cross-correlation between different code sequences is substantially zero as described above.

  Therefore, the receiving apparatus performs correlation calculation between all the code sequences used by the transmitting apparatus and the received code series, and estimates that the data corresponding to the code series that can obtain the largest correlation value is the transmission data. can do. Since the transmission device and the reception device share information representing the correspondence relationship between the code sequence and the data, the reception device can estimate such transmission data.

JP-A-4-35332 JP 2006-74196 A JP 2004-254003 A

  On the other hand, SN ratio (signal-to-noise ratio) estimation is an important technique in wireless communication. For example, antenna directivity control is performed based on the SN ratio. Further, power control for minimizing transmission power for the purpose of reducing power consumption and interference can be performed based on the SN ratio.

  One technique for estimating the S / N ratio is a blind S / N ratio estimation technique that does not use a pilot signal (reference signal). As a blind SN ratio estimation method, there are a method using a second-order moment and a fourth-order moment, a method using a higher-order moment, and a method using a maximum likelihood estimation algorithm. However, both of these methods are intended for communication systems in which signal components exist constantly. In the M-ary / SS communication system, it is difficult to estimate which of the M correlators contains a signal component, and the conventional blind SN ratio estimation method cannot be used as it is.

  Note that the method described in Patent Document 3 is an SN ratio estimation method applied to an M-phase PSK (Phase Shift Keying) method, and is not applied to an M-ary / SS communication method.

  Therefore, an object of the present invention is to provide a receiving apparatus in an M-ary communication system that can realize the SN ratio estimation.

In order to achieve the above object, a receiving apparatus in an M-ary communication system according to the present invention includes a receiving unit that receives a transmitted signal in accordance with an M-ary communication scheme that includes a specific code sequence at a specific position; A code sequence generator for generating a code sequence of M (M is an integer of 2 or more);
A reception apparatus in an M-ary communication system, comprising: a correlation unit that generates M correlation values representing a correlation between a code sequence represented by a reception signal of the reception unit and each of the M code sequences In addition, an SN ratio estimation unit that estimates an SN ratio based on a correlation value corresponding to the specific code sequence is provided.

  As a result, the SN ratio can be estimated in the receiving apparatus in the M-ary communication system.

  Specifically, for example, the receiving unit receives the specific code sequence at a specific timing corresponding to the specific position.

For example, when the correlation value corresponding to the specific code sequence is called a specific correlation value among the M correlation values, and the other correlation values are called non-specific correlation values,
The SN ratio estimation unit estimates the SN ratio based on the specific correlation value and the non-specific correlation value at the specific timing.

  By also using the non-specific correlation value at the specific timing, it is possible to realize the SN ratio estimation with a desired accuracy in a relatively short period of time.

  Specifically, for example, the signal-to-noise ratio estimation unit includes a signal component estimation unit that estimates a signal component in the signal-to-noise ratio based on the specific correlation value at the specific timing, and the non-specific correlation value at the specific timing. And a noise component estimator for estimating a noise component in the S / N ratio, and the S / N ratio is estimated from the signal component and the noise component.

  Further, specifically, for example, the receiving apparatus periodically receives a synchronization signal corresponding to the specific code sequence, and the specific timing is a reception timing of the synchronization signal.

  More specifically, for example, the correlation unit generates the M correlation values by performing a correlation calculation between the code sequence represented by the received signal and each of the M code sequences.

  ADVANTAGE OF THE INVENTION According to this invention, the receiver in a M-ary communication system which can implement | achieve SN ratio estimation can be provided.

  The significance or effect of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely one embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. .

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description regarding the same part is omitted in principle.

  The M-ary communication system according to the embodiment of the present invention includes the transmission device 100 in FIG. 1 and the reception device 200 in FIG. The transmission device 100 and the reception device 200 communicate using the M-ary / SS communication method (M-ary spread spectrum communication method).

[Fig. 1: Configuration of transmitter and basic operation]
FIG. 1 is a functional block diagram of the transmission device 100. The transmission apparatus 100 includes a code sequence generation unit 1, a selector 2, a transmission unit 4, and an antenna 5.

  The code sequence generator 1 generates a total of M code sequences for M-ary / SS communication and outputs them to the selector 2 (M is an integer of 2 or more). These M code sequences are from code sequences C1, C2,..., And CM (hereinafter referred to as “code sequences C1 to CM”. The same applies to other code sequences and correlators). Composed. In the code sequences C1 to CM, the code sequences C1 to CM are determined so that the cross-correlation between different code sequences becomes substantially zero.

  The selector (selection unit) 2 selects one of the code sequences C1 to CM received from the code sequence generation unit 1 according to the transmission data to be transmitted to the receiving device 200 of FIG. The sequence is output to the transmission unit 4.

  The transmitter 4 modulates the code sequence selected by the selector 2 to generate a modulated signal. Then, the transmitter 4 performs a frequency conversion process on the modulated signal to generate a radio signal, and outputs the radio signal via the antenna 5.

[Fig. 2: Configuration of receiver and basic operation]
FIG. 2 is a functional block diagram of the receiving device 200. The receiving apparatus 200 includes an antenna 11, a receiving unit 12, a code sequence generating unit 13, a data receiving correlation unit 14, a maximum value detecting unit 15, a data estimating unit 16, a synchronization control unit 17, and a selector 21. And an S / N ratio estimation unit 22. The data reception correlator 14 includes M correlators 1a, 2a,...

  The receiving unit 12 receives a radio signal transmitted from the transmission device 100 via the antenna 11 and performs a frequency conversion process on the received radio signal to generate a modulated signal. Then, the receiving unit 12 demodulates the modulated signal to generate data representing a code sequence selected and transmitted by the transmission apparatus 100 (hereinafter referred to as code sequence data), and receives the code sequence data as data reception To the correlation unit 14 and the synchronization control unit 17.

  The code sequence generator 13 generates and outputs M code sequences C1a to CMa (that is, C1a, C2a,..., And CMa) having a common phase Pa. The phase Pa is determined according to the synchronization control signal from the synchronization control unit 17.

  The code sequences C1a to CMa are the same code sequences (or similar as described later) to the code sequences C1 to CM generated by the code sequence generation unit 1 of the transmission device 100, respectively.

  The correlators 1a, 2a,..., And Ma in the data reception correlator 14 are code sequences C1a, C2a,..., And CMa received from the code sequence generator 13 and codes received from the receiver 12, respectively. Performs correlation with series data. The correlators 1a to Ma output the correlation values obtained by the correlation calculation to the maximum value detection unit 15, respectively.

  Here, the correlation calculation is the multiplication of the code sequence received from the code sequence generator 13 and the code sequence data, and the integration value obtained by integrating the multiplication result for a period of one bit of the transmission data. The processing to be obtained as the correlation value shall be said. The obtained correlation value represents the magnitude of the correlation between the code sequence received from the code sequence generating unit 13 and the code sequence represented by the code sequence data, and the correlation value obtained as the correlation increases. Will grow.

  When the correlation calculation is performed using the same code sequence as the code sequence selected by transmission apparatus 100, the correlation value is large, but the correlation calculation is performed using a code sequence different from the code sequence selected by transmission apparatus 100. As described above, the correlation value in the case of performing is a very small value because the cross-correlation between different code sequences is substantially zero.

  The maximum value detection unit 15 detects the maximum value of the correlation value from the correlation values received from the correlators 1a to Ma, and outputs maximum code sequence information representing a code sequence that gives the maximum value to the correlation value.

  The data estimation unit 16 estimates data corresponding to the code sequence represented by the maximum code sequence information as transmission data. The receiving apparatus 200 performs a desired operation according to transmission data obtained by estimation. Note that, since the transmission device 100 and the reception device 200 share information indicating the correspondence between the code sequence and the data (transmission data), the reception device 200 can estimate such transmission data.

  The synchronization control unit 17 performs synchronization acquisition for capturing the initial phase of synchronization and synchronization tracking for maintaining the acquired synchronization between the transmission device 100 and the reception device 200. Various methods have been proposed as a method of synchronization acquisition and synchronization tracking, and the synchronization control unit 17 can employ any of them. As a synchronization tracking method, for example, the method described in Patent Document 1 or 2 can be employed.

  After synchronization acquisition, the synchronization control unit 17 performs synchronization tracking. That is, the synchronization control signal is generated and output so that the phase of the code sequence represented by the code sequence data and the phase Pa of the code sequence C1a to CMa given to the correlators 1a to Ma match.

  With reference to FIGS. 3A to 3C, one method of synchronization tracking will be briefly described. Assuming that the code sequence corresponding to the maximum correlation value matches the code sequence selected on the transmitting apparatus 100 side, the phase of the code sequence represented by the code sequence data and the phase Pa of the code sequences C1a to CMa The characteristic that the maximum correlation value becomes larger as the shift amount of is smaller is utilized.

  Specifically, for example, the synchronization controller 17 is provided with M forward correlators and M backward correlators (both not shown), and the code sequence generator 13 has M common phases Pb. M code sequences C1c to CMc having a code sequence C1b to CMb and a common phase Pc are generated. Here, the phase Pb is advanced from the phase Pc, and the intermediate phase between the phase Pb and the phase Pc is made to coincide with the phase Pa of the code sequences C1a to CMa. The phase difference between the phase Pb and the phase Pc is the phase for one chip of the code sequence (see FIGS. 3A to 3C).

  Each of the M forward correlators performs a correlation operation between the code sequence data and the M code sequences C1b to CMb, and each of the M backward correlators includes the code sequence data and the M code sequences C1c to C1c. Correlation with CMc is performed. After that, among the M correlation values obtained by the correlation calculation of the M forward correlators, the correlation value Vb corresponding to the maximum code sequence information output from the maximum value detection unit 15 is specified, and M Among the M correlation values obtained by the correlation calculation of the backward correlator, the correlation value Vc corresponding to the maximum code sequence information output from the maximum value detection unit 15 is specified. Note that Va represents the maximum correlation value among the M correlation values calculated by the correlators 1a to Ma. Then, the phases Pa, Pb and Pc are controlled so that the correlation values Vb and Vc match.

  That is, when Vb> Vc as shown in FIG. 3B, the phases Pa, Pb and Pc are advanced by the same phase amount, and Vb <Vc as shown in FIG. Delays each phase Pa, Pb and Pc by the same phase amount. On the other hand, when Vb = Vc as shown in FIG. 3A, the phases Pa, Pb, and Pc are not changed.

  Thereby, each phase is adjusted so that the correlation value Vb and the correlation value Vc coincide with each other, and as a result, the correlation value Va is kept in the vicinity of the maximum value that can be taken. That is, a state in which the phase of the code sequence represented by the code sequence data and the phase Pa of the code sequences C1a to CMa are kept in agreement.

  The selector 21 selects a necessary correlation value from the M correlation values calculated by the correlators 1 a to Ma and outputs the selected correlation value to the SN ratio estimation unit 22. Based on the correlation value given from the selector 21, the S / N ratio estimation unit 22 estimates a signal-to-noise ratio (hereinafter, simply referred to as “S / N ratio”) in communication between the transmission device 100 and the reception device 200. The estimated S / N ratio is used for transmission power control of the transmission apparatus 100 and the like.

[Principle of SN ratio estimation]
The receiving apparatus 200 performs characteristic SN ratio estimation using the selector 21 and the SN ratio estimation unit 22. The principle of this SN ratio estimation method will be described. In the following, it is assumed that synchronization acquisition and synchronization tracking are appropriately performed, and the phase of the code sequence represented by the code sequence data and the phase Pa of the code sequences C1a to CMa completely coincide. Consider a case where the code sequence C1 is selected by the transmission apparatus 100. It is assumed that the code sequences C1 to CM and the code sequences C1a to CMa coincide with each other and are simply referred to as a code sequence or M code sequences without distinguishing the two.

  In this case, as shown in FIG. 4, the output of the correlator 1a includes a noise component and a signal component (information signal component) corresponding to transmission data, and the outputs of the other correlators 2a to Ma include noise. Contains only ingredients.

Consider the noise output from each correlator, where M code sequences are orthogonal sequences and noise is Gaussian noise. M code sequences are represented by α _kl . k represents the type of code sequence and takes an integer satisfying 1 ≦ k ≦ M. l represents the number of data in each code sequence, and takes an integer satisfying 0 ≦ l <Λ. Λ is the code length of each code sequence. In addition, a period in which the l-th data of the code sequence is generated is (l−1) T to lT, and noise generated in this period is ν _l . Then, the noise η _k output from the correlator ka (1 ≦ k ≦ M) is expressed by the following formula (1), and the cross-correlation φ _kj of the noise η _k is expressed by the following formula (2). .

Here, ν ² is the average noise power of ν _l . J represents the type of code sequence, and takes an integer satisfying 1 ≦ k ≦ M and j ≠ k. From equation (2), it can be seen that the noise at the output of each correlator is independent Gaussian noise. Using this property, the symbol correct rate Ψ is obtained. The symbol is unit information (information such as “00” and “01”) of transmission data to be transmitted by the transmission device 100, and the symbol correct answer rate Ψ is that the reception device 200 correctly recognizes the symbol ( (Estimation) probability.

  FIG. 5 shows the output voltage of each phase shifter when it is assumed that there is no noise. Each correlator outputs a voltage signal, and the correlation value is represented by the voltage value of the voltage signal. The output voltage of the correlator 1a to which the signal component is input is the square root of 2, and the output voltages of the other correlators 2a to Ma are 0. Here, the signal power is normalized by 1, and the square root of 2 is the peak value of the output voltage of the correlator 1a.

The variance of noise is represented by σ ² . Then, the following formula (3) is established.

  On the other hand, the existence probability of the correlator output to which no signal component is input is expressed by the following equation (4). Therefore, the symbol correct rate Ψ is expressed by the following equation (5) from the above equations (3) and (4).

  The receiving apparatus 200 estimates a signal-to-noise ratio using a correlator in which a signal component is always included in an output using a part of the transmission signal from the transmitting apparatus 100 whose information is known. Digital communication is performed in units of so-called packets. As shown in FIG. 6, each packet is formed from a synchronization signal for synchronization and a data signal including information such as video information. FIG. 6 shows a packet structure in a transport stream of an MPEG (Moving Picture Experts Group) system. The packet of FIG. 6 is formed from a 1-byte synchronization signal and a 187-byte data signal. The synchronization signal is represented by a synchronization code sequence, and the synchronization code sequence is one of the code sequences C1 to CM.

  The receiving apparatus 200 selects a correlator corresponding to the synchronization code sequence at the timing when the synchronization signal is input, and estimates the SN ratio using the output of the selected correlator. Since the synchronization code sequence is known, the output of the selected correlator includes a signal component.

  Conventionally, as one of blind SN ratio estimation methods that do not use a pilot signal (reference signal), there is a method that uses a second moment and a four-character moment. This method is effective when the phase is uncertain in BPSK (Binary Phase Shift Keying) modulation or the like. On the other hand, in the M-ary / SS communication system, since the signal component is included in the output of the correlator, the SN ratio can be estimated by using the first moment and the second moment.

  A method using the first moment and the second moment will be described. First, the voltage of the signal component included in the output of the correlator corresponding to the code sequence for synchronization is represented by a, and the power of the signal component is represented by S. Further, the voltage of the noise component included in the output of one correlator is represented by n, and the power of the noise component is represented by N. The output voltage of the correlator corresponding to the synchronization code sequence is represented by y. Then, the following formula (6) is established.

Here, the subscript t given to each of y, a, and n represents time. Note that y in this case is different from y in the above formula (4) introduced to show the integral operation. Hereinafter, y (and y _t ) represents the output voltage of the correlator corresponding to the synchronization code sequence.

If y is a random variable and the first and second moments are M ₁ and M ₂ , respectively, a, S and N, and the estimated value a _{e of a} , the estimated values S _e and N of S The estimated value N _e satisfies the following relational expressions (7) to (9).

Here, E () is an average operator, which indicates an average value of random variables (samples) in parentheses. For example, E (y) represents the average value of y. Further, assuming that the signal component voltage a is constant and N1 = E (n ² ), the following equations (10) and (11) are derived from the equations (7) to (9).

Next, consider a case where the estimated value _Se and the estimated value N _e are obtained using a maximum likelihood estimation algorithm (maximum likelihood estimation method). Let the likelihood function be Z (S, N). When the average number is L, the likelihood function Z (S, N) is expressed by the following equation (12).

  When the log likelihood function corresponding to Z (S, N) is LZ (S, N), LZ (S, N) is expressed by the following equation (13).

Then, the estimated value S _e and the maximum likelihood value of the estimated value N _e (the maximum likelihood estimator) is the following formula (14) and (15), is uniquely determined. Note that the left side of equation (14) is the partial differentiation of LS (S, N) with respect to variable S when S = S _e and N = N _e, and the left side of equation (15) is S = S _e Further, it is a partial differentiation of LS (S, N) with respect to the variable N when N = N _e .

  From the equations (14) and (15), the following equations (16) and (17) are obtained. These agree with the above formulas (8) and (9) considered using the first and second moments. That is, the estimation results for S and N are the same whether the maximum likelihood estimation algorithm is used or the first and second moments are used.

Next, consider the probability that a signal component is included in the output of the correlator corresponding to the code sequence for synchronization and the probability that the noise component is included in a certain limited section. First, assuming that the variance of noise after averaging with the average number of times L is represented by σ _L ² , the following equation (18) is established. Here, N _M represents the average power of noise.

The probability P _S that the signal component is included in the output of the correlator corresponding to the code sequence for synchronization in _a certain section [S _a , S _b ] is expressed by the following equation (19). In addition, a noise with a variance of 1 (estimated noise) is represented by N2. Then, the probability P _N2 that the noise N2 component is included in the output of the correlator corresponding to the synchronization code sequence in _a certain section [S _a , S _b ] is expressed by the following equation (20). Here, chi (y, L) represents the chi-square distribution for y and L.

また、上記式（１１）におけるＮ１は、下記式（２１）によって表される。尚、相関器の出力から検出される信号値は尖頭値であるため、Ｎ_M×Ｎ２に、２が乗じられる。

Moreover, N1 in the said Formula (11) is represented by following formula (21). Since the signal value detected from the output of the correlator is a peak value, N _M × N2 is multiplied by 2.

The estimated value ρ _e of the S / N ratio is expressed by the following formula (22), whereby N1 is expressed by the following formula (23).

If a _e is a constant, the probability Pρ ′ that the estimated SN ratio exists in the interval [ρ _a , ρ _b ], that is, the probable SN ratio in the interval [ρ _a , ρ _b ] is obtained from the equation (23). The estimated probability Pρ ′ is expressed by the following equation (24). Here, the following expressions (25) and (26) are satisfied.

Considering that a _e is not a constant in reality, if z = a _e and a is a square root of 2, the following equation (27) can be obtained from equation (24) using equations (25) and (26). Led.

[Description of specific SN ratio estimation method]
Specifically, the receiving apparatus 200 may estimate the SN ratio as follows. Below, the 1st and 2nd estimation methods are illustrated. Now, it is assumed that the synchronization code sequence represented by the synchronization signal matches the code sequences C1 and C1a. The transmitting apparatus 100 and the receiving apparatus 200 recognize in advance that the synchronization code sequence matches the code sequences C1 and C1a. The transmission apparatus 100 periodically transmits the above-described packet having the data size of 188 bytes described with reference to FIG. 6 to the reception apparatus 200 using the M-ary / SS communication method.

  The first estimation method will be described. Each of the above formulas is mainly a formula for explaining the first estimation method. In the first estimation method, the selector 21 selects the correlation value of the correlator corresponding to the code sequence C1a (that is, the synchronization code sequence), that is, the correlation value output from the correlator 1a, and selects the selected correlation value as SN. This is given to the ratio estimation unit 22. The SN ratio estimation unit 22 is a timing at which a synchronization signal is received (more specifically, a timing at which a correlation value obtained by a correlation calculation between a synchronization code sequence and a code sequence 1a is output from the correlator 1a, Hereinafter, the S / N ratio is estimated based on the correlation value of the correlator 1a at “specific timing”.

  As illustrated in FIG. 7, the specific timing is repeatedly visited at a predetermined cycle while following a communication protocol defined between the transmission device 100 and the reception device 200. The specific timing is a concept having a time width (in this example, a time width of one byte), and this can also be referred to as a specific period. Of course, the receiving apparatus 200 can recognize the specific timing in a state where synchronization acquisition and synchronization tracking are appropriately performed. FIG. 7 is a diagram in which reception signals of the reception device 200 (or transmission signals of the transmission device 100) are arranged in time series. As illustrated in FIG. 7, when the reception signals of the reception device 200 (or the transmission signals of the transmission device 100) are considered in time series, a synchronization signal representing a synchronization code sequence exists at a specific position of the reception signal.

Specifically, the SN ratio estimation unit 22 regards the output voltage of the correlator 1a at each specific timing as y, and calculates the signal component output from the correlator 1a based on the above equations (16) and (17). The estimated value S _e of the power S and the estimated value N _e of the noise component power N are calculated, and S _e / N _e is estimated as the SN ratio. Each time a synchronization signal is received, one sample y is acquired.

When the specific timings come in the order of the (Q−L + 1) th, (Q−L + 2),..., Qth specific timing, and the specific timing at the present time is the Qth specific timing, the current timing is estimated. The values S _e and N _e are the output voltage y of the correlator 1a at the (Q−L + 1) th, (Q−L + 2),..., Qth specific timing, that is, the output voltage y corresponding to the average number L. It is calculated from the first moment and the second moment.

  Next, the second estimation method will be described. In the first estimation method, not only the signal component power S but also the noise component power N is estimated using the output of the correlator 1a corresponding to the synchronization code sequence. However, since only the noise component is included in the output of the correlator other than the correlator 1a at the above specific timing, the power N of the noise component is estimated using the output of the correlator other than the correlator 1a. It is also possible. For this reason, in the second estimation method, the power N of the noise component is estimated using the output of the correlator other than the correlator 1a. The estimated SN ratio is expected to converge earlier in the second estimation method than in the first estimation method.

When the second estimation method is employed, the estimated value N _e of the noise component power N can be expressed by the following equation (28).

Here, y _N represents the output voltage of a correlator other than the correlator 1a. Since the outputs of the correlators other than the correlator 1a are independent from each other, Expression (28) is established. E _M-1 () is an average operator whose average number of times is (M−1) times E (), and indicates an average value of random variables (samples) in parentheses. For example, E _M-1 (y _N ² ) represents the average value of y _N ² with the average number of times being (M-1) L.

In the second estimation method, the probability Pρ ′ that the estimated SN ratio exists in the section [ρ _a , ρ _b ] is expressed by the following equation (29). Here, the following expressions (30) and (31) are satisfied. Further, K = (M−1) L is established.

  When the second estimation method is employed, the S / N ratio estimation unit 22 of FIG. 2 includes a signal component estimation unit 22a and a noise component estimation unit 22b as shown in FIG.

The selector 21 selects a correlation value output from the correlator 1a corresponding to the code sequence C1a (that is, the synchronization code sequence), and provides the selected correlation value to the signal component estimation unit 22a. Signal component estimator 22a on the basis of the correlation value of the correlator 1a in the specific timing, to calculate the estimated value S _e of the power S of the signal components. That is, the signal component estimator 22a, the above equation in accordance with (16), in the same procedure as SN ratio estimation unit 22 in the first estimation method to calculate the estimated value S _e, to calculate the estimated value S _e.

On the other hand, the selector 21 gives each correlation value output from the correlators 2a to Ma to the noise component estimation unit 22b. Noise component estimating unit 22b, based on the correlation value of the correlator 2a~Ma in the specific timing, to calculate the estimated value N _e of the noise component power N.

Specifically, the noise component estimating unit 22b, the respective output voltages of the correlator 2a~Ma at each particular time regarded as y _N, and calculates the estimated value N _e based on the equation (28). In other words, each of the output voltages of the correlators 2a to Ma at each specific timing is treated as the sample y _N with respect to the average operator E _M-1 () of the equation (28), and is estimated based on the above equation (28). The value N _e is calculated. A synchronization signal each time the received one, y _N as specimens, the number fraction of the correlator 2A～Ma, i.e. (M-1) are pieces acquired.

When the specific timings come in the order of the (Q−L + 1) th, (Q−L + 2),..., Qth specific timing, and the specific timing at the present time is the Qth specific timing, the current timing is estimated. The value N _e is the (Q−L + 1) th, (Q−L + 2),..., Output voltage y _N of the correlators 2a to Ma at the Qth specific timing, that is, the average number (M−1) L. It is calculated from the second moment of the output voltage y _N of the minute.

Finally, SN ratio estimation unit 22, based on the estimated value N _e estimated by the signal component estimator 22a estimates estimated by S _e and a noise component estimating unit 22b, the S _e / N _e SN Estimate as a ratio.

[Calculation of convergence of estimated SN ratio]
Next, numerical calculation results for Expression (27) corresponding to the first estimation technique and Expression (29) corresponding to the second estimation technique will be described. The average number of times required for the difference between the estimated S / N ratio and the true S / N ratio to be within ± 0.5 dB with a probability of 95% or more (that is, the number of synchronization signal receptions) was determined for each S / N ratio. .

  In FIG. 9, a curve 301 represents the relationship between the average number of times and the SN ratio obtained for the equation (27), and a curve 303 represents a relationship between the average number of times and the SN ratio obtained for the equation (29). Further, M = 256. For example, when the true S / N ratio is 10 dB, the average number of times required until the S / N ratio of 9.5 to 10.5 dB is estimated with a probability of 95% or more is 1000 for the first estimation method. It is slightly less than 100 times in the second estimation method.

  It can be seen that in the second estimation method, the average number of times required for convergence decreases as the SN ratio increases. On the other hand, the first estimation method behaves such that the average number of times necessary for convergence is saturated when the SN ratio is high. This is considered to be due to the fact that the term (11) corresponding to the first estimation method includes a term relating to the signal component, and that the influence of this term appears as the SN ratio increases.

[Power control]
The S / N ratio estimated by the first or second estimation method is used for transmission power control of the transmission apparatus 100 or the like. A specific example is given with reference to FIG.

  10, the home server 101 includes the transmission device 100 of FIG. 1, and the display device 201 includes the reception device 200 of FIG. The home server 101 uses the transmission device 100 to transmit AV data including a video signal and an audio signal to the display device 201 by the M-ary / SS communication method. The AV data is transmitted in units of packets as described above, and the transmission signal from the transmission apparatus 100 includes a synchronization signal.

  The display device 201 restores AV data as transmission data using the receiving device 200, and performs video display and audio output based on the restored AV data. At this time, the receiving apparatus 200 estimates the SN ratio as described above using the synchronization signal, and generates control data for minimizing the transmission output power of the transmitting apparatus 100 based on the estimated SN ratio. . The control data is transmitted from the display device 201 to the home server 101, and the transmission device 100 of the home server 101 controls transmission power when transmitting AV data according to the control data.

  More specifically, when the estimated S / N ratio is higher than a predetermined reference S / N ratio, control data instructing a decrease in the transmission power is generated, and the estimated S / N ratio is lower than the reference S / N ratio. In this case, control data for instructing an increase in the transmission power is generated. As a result, the transmission power when transmitting AV data is maintained in the vicinity of the minimum transmission power necessary for obtaining a desired S / N ratio, energy saving is achieved, and interference with other communication signals is reduced to a low level. It can be suppressed. The transmission of control data from the display device 201 to the home server 101 can be performed using the M-ary / SS communication method, or can be performed using other communication methods.

The numerical calculation results regarding such power control are shown below while comparing the first and second estimation methods. Consider a case where power control is performed with a signal error rate of 10 ⁻² as a minimum condition. Further, M = 256. In this case, the signal ^- to-noise ratio at which the signal error rate is 10 ⁻² is about 11 dB. A margin for control is set to about 3 dB, and a reference S / N ratio that is a boundary of increase or decrease in transmission power is set to 14 dB.

Then, the average number of times (that is, the number of receptions of the synchronization signal) required until the probability that the SN ratio is estimated to be 14 dB or more when the true SN ratio is 11 dB is 10 ⁻⁴ or less was obtained. As a result, the average number of times for the first estimation method was 83 times, while that for the second estimation method was four times.

  Taking the packet configuration of 188 bytes shown in FIG. 6 as an example, assuming that the bit rate is 6 Mbps (Mega Bits Per Second) which is a standard image transmission rate, the frequency at which the S / N ratio can be estimated per second is obtained. First, when 6 Mbps is converted into a symbol rate, it becomes 3/4 Mega Symbols Per Second.

  In the first estimation method, 83 data are required for one SN ratio estimation, and taking into account that the frequency of appearance of the synchronization signal (synchronization symbol) is once in 188 times, 3/4 Mega ÷ ( 83 × 188) ≈48, it is possible to estimate the SN ratio about 48 times per second. On the other hand, in the second estimation method, SN ratio estimation can be performed about 997 times per second in the same way. For example, in the IS-95 (Interim Standard-95) standard applied to mobile phones, power control is performed 800 times per second, but almost any desired power control can be realized by adopting the second estimation method. It becomes.

<< Deformation, etc. >>
As modifications or annotations of the above-described embodiment, notes 1 to 6 are described below. The contents described in each comment can be arbitrarily combined as long as there is no contradiction.

[Note 1]
The specific numerical values shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

[Note 2]
2 illustrates the case where the code sequences C1a to CMa generated by the code sequence generator 13 in FIG. 2 are the same as the code sequences C1 to CM generated by the code sequence generator 1 in FIG. It is not limited.

  It is not always necessary for the code sequence generation unit 13 to generate a code sequence that completely matches the code sequences C1 to CM, and a code sequence that is highly similar to the code sequences C1 to CM (in other words, a code having a high correlation). Generation) is sufficient. That is, a part of the code sequence generated by the transmission apparatus 100 and a part of the code sequence generated by the reception apparatus 200 may be different. For example, a part of the code sequence C1 and a part of the code sequence C1a may be different. If there is a difference between the code sequence of the transmitting apparatus 100 and the code sequence of the receiving apparatus 200, the correlation value obtained by the correlation calculation is smaller than when there is no difference, but in the system to which the receiving apparatus 200 is applied. As long as an allowable error rate can be realized, there may be a difference between them.

  The same applies to the code sequences C1a to CMa, the code sequences C1b to CMb, and the code sequences C1c to CMc generated by the code sequence generator 13.

[Note 3]
In addition, the number of correlators included in the data reception correlator 14 may be less than M. In this case, by using one correlator in a time division manner, one correlator may be caused to execute a correlation operation corresponding to a plurality of code sequences.

[Note 4]
Although “code sequences C1a to CMa have a common phase Pa” is described in the present specification, “common” regarding the phase does not mean that the phase is strictly common, and the function described above. This is a concept including a slight phase difference that does not cause a significant problem with respect to realizing the above.

  For example, when the phase of the code sequence data input to the correlators 1a to Ma differs between the correlators 1a to Ma due to phase fluctuations due to noise, wiring delay, and other design reasons. In order to cope with this phase difference, the code sequence generation unit 13 may actively generate M code sequences having slightly different phases. The M code sequences in this case are also expressed as having a “common” phase. The same applies to the code sequences C1b to CMb.

[Note 5]
Each of the transmission device 100 and the reception device 200 in FIG. 1 can be realized by hardware or a combination of hardware and software. In particular, the function of the SN ratio estimation unit 22 in FIG. 2 can be realized by hardware, software, or a combination of hardware and software.

[Note 6]
With reference to FIG. 10, the example in which the transmission device 100 and the reception device 200 are mounted on the home server 101 and the display device 201 has been shown, but these are mounted on various communication devices (or electronic devices including communication devices). It is possible. For example, the receiving device 200 is mounted on a mobile phone (not shown), and is used for telephone calls and data reception on the mobile phone.

It is a functional block diagram of the transmission apparatus which concerns on embodiment of this invention. It is a functional block diagram of the receiver which concerns on embodiment of this invention. FIG. 3 is a diagram illustrating a relationship between a phase of a code sequence generated by a code sequence generation unit in FIG. 2 and a correlation value obtained, and is a diagram for explaining a phase control technique by a synchronization control unit in FIG. 2. It is a figure which shows one state of the output of each correlator of FIG. FIG. 5 is a diagram corresponding to FIG. 4 and showing the output voltage of each phase shifter of FIG. 2 when it is assumed that there is no noise. FIG. 3 is a diagram illustrating a configuration of a packet transmitted from the transmission device in FIG. 1 to the reception device in FIG. 2. It is a figure showing the SN ratio estimation timing by the SN ratio estimation part of FIG. It is a figure which shows an example of the internal block diagram of the S / N ratio estimation part of FIG. It is a figure which shows the simulation result in connection with SN ratio estimation of the SN ratio estimation part of FIG. FIG. 3 is a diagram for explaining an application example of the transmission device in FIG. 1 and the reception device in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Transmission apparatus 200 Reception apparatus 11 Antenna 12 Reception part 13 Code sequence generation part 14 Data reception correlation part 15 Maximum value detection part 16 Data estimation part 17 Synchronization control part 21 Selector 22 SN ratio estimation part 1a-Ma correlator

Claims (6)

A receiving unit that receives a transmitted signal according to the M-ary communication method, including a specific code sequence at a specific position;
A code sequence generator that generates M code sequences (M is an integer of 2 or more);
A reception apparatus in an M-ary communication system, comprising: a correlation unit that generates M correlation values representing a correlation between a code sequence represented by a reception signal of the reception unit and each of the M code sequences Because
A receiving apparatus in an M-ary communication system, comprising: an S / N ratio estimation unit that estimates an S / N ratio based on a correlation value corresponding to the specific code sequence. The receiving device in the M-ary communication system according to claim 1, wherein the receiving unit receives the specific code sequence at a specific timing corresponding to the specific position. Among the M correlation values, a correlation value corresponding to the specific code sequence is called a specific correlation value, and other correlation values are called non-specific correlation values,
The receiving apparatus in the M-ary communication system according to claim 2, wherein the SN ratio estimation unit estimates the SN ratio based on the specific correlation value and the non-specific correlation value at the specific timing. The SN ratio estimation unit
A signal component estimator for estimating a signal component in the SN ratio based on the specific correlation value at the specific timing;
A noise component estimation unit that estimates a noise component in the S / N ratio based on the non-specific correlation value at the specific timing,
The receiving apparatus in the M-ary communication system according to claim 3, wherein the SN ratio is estimated from the signal component and the noise component. The receiving apparatus periodically receives a synchronization signal corresponding to the specific code sequence,
The receiving apparatus in the M-ary communication system according to claim 2, wherein the specific timing is a reception timing of the synchronization signal. The correlation unit generates the M correlation values by performing a correlation calculation between the code sequence represented by the received signal and each of the M code sequences. A receiving apparatus in the M-ary communication system according to claim 5.

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