JP2012231227A - Receiver and reception method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement frequency deviation detection effectively by a receiver in a communication system using STBC system or DSTBC system.SOLUTION: A receiver for receiving a signal coded based on STBC system or DSTBC system includes a reference signal memory 152 for storing data representing a predetermined synchronization signal coded based on STBC system or DSTBC system, a channel response calculator 151 for estimating transmission path response by comparing the data associated with the synchronization signal on the received signal and data stored in the reference signal memory 152, frequency deviation calculators 153-1 and 153-2 for respectively detecting frequency deviation from calculated values on a series of transmission path response, and a selector 154 for selecting one value from the two detected frequency values.

Description

  The present invention relates to a receiver and a reception method that perform communication using a space-time block coding (STBC) method or a differential space-time block coding (DSTBC) method.

In a mobile communication system, there is a transmission diversity system using STBC, which is one of MIMO (Multi Input Multi Output) techniques, as means for improving communication quality by increasing resistance to fading.
For example, in a communication system in which a signal is weighted according to a channel response (channel response) on the transmitter side in order to obtain a diversity effect using a plurality of transmission antennas, the transmitter side preliminarily transmits channel state information (CSI: You need to know Channel State Information. Here, CSI specifically means response characteristics between the transmission antenna and the reception antenna.

On the other hand, in the case of the STBC method, there is no need to know CSI on the transmitter side, and there is an advantage that the transmission diversity effect can be easily obtained. However, on the receiver side, CSI is necessary when performing STBC decoding as in other MIMO schemes. For this purpose, known signals called pilots with predetermined patterns are periodically arranged. The method is generally taken. An appropriate arrangement period of pilots is determined by the speed of time fluctuation of a propagation path to be handled, that is, a fading frequency, and it is necessary to shorten the arrangement period as the fading frequency increases. That is, in the case of high-speed fading, information transmission efficiency may be significantly impaired.
Therefore, a transmission diversity method using DSTBC has been proposed as a method that does not require CSI on the receiver side. The DSTBC system has the disadvantage of sacrificing anti-noise characteristics due to differential conversion on the receiver side, but has the advantage that it does not require a pilot or the like and can easily cope with high-speed fading.

Incidentally, automatic frequency control (AFC) is a basic function to be provided in a receiver used in a mobile communication system. This detects a deviation (error) between the transmission frequency and the reception frequency, and controls the reception frequency to match the transmission frequency. The accuracy of this AFC strongly depends on the frequency deviation detection accuracy.
As a frequency deviation detection method, CSI is observed multiple times at a certain time interval, and the frequency deviation is obtained from the phase change of CSI under the assumption that the fluctuation of CSI due to fading is sufficiently gradual. Is generally done. In particular, in OFDM (Orthogonal Frequency Domain Multiplex) transmission, a method of obtaining a frequency deviation from a phase change in an OFDM symbol using an inserted guard interval is also used.

JP 2009-303086 A

  As described above, it is effective to observe CSI at a certain time interval in order to detect the frequency deviation. Currently, the system to which the STBC scheme is applied is often based on OFDM transmission. Similar to other MIMO schemes, when transmitting pilots to observe CSI from individual transmission antennas, the transmission from other transmission antennas is performed. So as not to interfere with other pilots, the signals are transmitted separately on the frequency axis or the time axis. In the case of single carrier transmission, separation on the frequency axis is impossible, and in order to separate on the time axis, two symbol times are required to transmit one pilot, and transmission efficiency decreases. . That is, in single carrier transmission, there are currently few frequency deviation detection methods suitable for the STBC method or the DSTBC method.

  The present invention has been made in view of such a conventional situation, and proposes a technique for effectively detecting a frequency deviation by a receiver in a communication system using the STBC method or the DSTBC method. The purpose is to do.

In the present invention, when a signal including a predetermined synchronization signal is encoded by the STBC method or the DSTBC method and received by the receiver, the receiver stores in advance data corresponding to the synchronization signal in the received signal. The channel response is estimated by comparing with the encoded data representing the synchronization signal.
That is, in a receiver that receives a signal encoded by the STBC method or the DSTBC method, a storage unit that stores data representing a predetermined synchronization signal encoded by the STBC method or the DSTBC method, and the above-described signal in the received signal Data corresponding to the synchronization signal is input, and estimation means for comparing the input data with data stored in the storage means to estimate a propagation path response is provided.

As described above, in the present invention, in a configuration in which a synchronization signal that is not normally encoded by the STBC method or the DSTBC method is encoded and transmitted, the data portion corresponding to the synchronization signal in the received signal and the reference signal (stored in the storage unit) (Data) has a certain relationship, and the propagation path response can be estimated using this.
As a result, it is possible to obtain a deviation (error) between the transmission frequency and the reception frequency from the estimated value of the propagation path response. For example, the frequency deviation can be effectively detected even in single carrier transmission.

  ADVANTAGE OF THE INVENTION According to this invention, the detection of the frequency deviation by a receiver can be performed effectively in the communication system using a STBC system or a DSTBC system.

It is a figure which shows the structural example of the STBC transmission system which concerns on one Example of this invention. It is a figure which shows the structural example of a frequency deviation detector. It is a figure which shows the structural example of a frequency deviation calculator. It is a figure which shows an example of a frame structure. It is a figure which shows the structural example of the DSTBC transmission system which concerns on one Example of this invention.

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of an STBC transmission system which is a communication system using the STBC scheme. In this example, it is assumed that QPSK (Quadrature Phase Shift Keying) is used as a modulation scheme, but other modulation schemes may be used.
The STBC method is a method for calculating two symbols as one processing unit for time-series data to be transmitted and recombining and transmitting signals from two antennas in the time domain and the spatial domain. Two types of orthogonal sequences are output.
The STBC transmission system of the present example includes a transmitter that encodes and transmits time-series data to be transmitted by the STBC method, and receives and decodes a signal encoded by the STBC method, and transmits the time-series data to be transmitted. Having a receiver to get.

The transmitter of this example includes an input unit 101, a serial-parallel converter 102, a symbol mapper 103, an STBC encoder 104, transmission baseband units 105-1 and 105-2, transmission RF units 106-1 and 106-2, A frequency oscillator 107 and transmission antennas 108-1 and 108-2 are provided.
The receiver of this example includes a reception antenna 121, a reception RF unit 122, a frequency oscillator 123, a reception baseband unit 124, a serial-parallel converter 125, an STBC decoder 126, a symbol demapper 127, a parallel-serial converter 128, An output unit 129 is provided, and a frequency deviation detector 130 and a frequency control unit 131 are further provided.

The transmitter of this example generally performs the following processing.
That is, when a bit string (transmission bit string) of time-series data to be transmitted is given to the input unit 101, the serial-parallel converter 102 bundles the transmission bit string input from the input unit 101 every 4 bits and forms a symbol mapper. To 103. The symbol mapper 103 performs symbol mapping by QPSK modulation for every 2 bits on the 4-bit transmission bit string input from the serial-parallel converter 102 and collects 2 symbols (1 symbol: 2 bits). The set is output to the STBC encoder 104. The STBC encoder 104 performs STBC encoding on the input symbol set, and outputs the result to the transmission baseband units 105-1 and 105-2.
Specifically, in the STBC encoder 104, when the input symbol set is s ₁ , s ₂ , symbol sequences in the order of s ₁ , -s ₂ ^* are transmitted to the transmission baseband unit 105-1. And outputs a symbol sequence in the order of s ₂ and s ₁ ^* to the transmission baseband unit 105-2. Here, x ^* is a conjugate complex of x.

  Transmission baseband section 105-1 performs processing such as waveform shaping on the symbol sequence input from STBC encoder 104, generates a baseband signal, and outputs the baseband signal to transmission RF section 106-1. Transmission RF section 106-1 performs processing such as frequency conversion and power amplification on the baseband signal input from transmission baseband section 105-1, and outputs the result to transmission antenna 108-1. The transmission antenna 108-1 transmits the signal input from the transmission RF unit 106-1 to the receiver by radio.

  Transmission baseband section 105-2 performs processing such as waveform shaping on the symbol sequence input from STBC encoder 104, generates a baseband signal, and outputs the baseband signal to transmission RF section 106-2. Transmission RF section 106-2 performs processing such as frequency conversion and power amplification on the baseband signal input from transmission baseband section 105-2, and outputs the result to transmission antenna 108-2. The transmission antenna 108-2 transmits the signal input from the transmission RF unit 106-2 to the receiver by radio.

Here, the frequency conversion by the transmission RF units 106-1 and 106-2 is performed on the basis of the signal of the frequency f _TX that is the output of the frequency oscillator 107. Transmission frequency of the RF signal which is a result of the frequency conversion are those identical in transmission RF section 106-1 and 106-2, which is referred to as _{F TX.}

The receiver of this example generally performs the following processing.
That is, when the signal transmitted from the transmitter is received via the reception antenna 121, the reception RF unit 122 performs processing such as amplification, frequency conversion, and band limitation on the signal received by the reception antenna 121. The baseband signal is generated and output to the reception baseband unit 124. The reception baseband unit 124 performs processing such as waveform shaping including band limitation on the baseband signal input from the reception RF unit 122 and then converts the serial-parallel converter 125 as a complex discrete signal with a symbol period. Output to. The serial-parallel converter 125 collects the signals input from the reception baseband unit 124 two symbols at a time and outputs them to the STBC decoder 126. The STBC decoder 126 performs a decoding process corresponding to the STBC encoding on the signal of each two symbols input from the serial-parallel converter 125 and outputs the result to the symbol demapper 127.

ここで、（式１）において、ｈ_１は送信アンテナ１０８−１から受信アンテナ１２１に至る伝搬路についての伝搬路応答であり、ｈ_２は送信アンテナ１０８−２から受信アンテナ１２１に至る伝搬路についての伝搬路応答であり、パイロットや同期ワード等を用いて伝搬路応答推定器（図示せず）により求められる。
シンボルデマッパ１２７は、ＳＴＢＣ復号器１２６から入力される信号ｑ_１，ｑ_２に対して、ＱＰＳＫ変調に対応したビット判定を行い、４ビット分の信号をまとめてパラレル−シリアル変換器１２８に出力する。パラレル−シリアル変換器１２８は、シンボルデマッパ１２７から入力される４ビット分の信号をシリアル変換して出力部１２９に出力する。 Specifically, in the STBC decoder 126, when the values of the signals input by two symbols are r ₁ and r ₂ , respectively, the decoding process is performed using (Equation 1), and the signal q _{1 of the} decoding result is obtained. , Q ₂ are output to the symbol demapper 127.

Here, in (Equation 1), h ₁ is a propagation path response for a propagation path from the transmission antenna 108-1 to the reception antenna 121, and h ₂ is a propagation path from the transmission antenna 108-2 to the reception antenna 121. And is obtained by a propagation path response estimator (not shown) using a pilot, a synchronization word, or the like.
The symbol demapper 127 performs bit determination corresponding to QPSK modulation on the signals q ₁ and q ₂ input from the STBC decoder 126, and collectively outputs signals for 4 bits to the parallel-serial converter 128. To do. The parallel-serial converter 128 serially converts the 4-bit signal input from the symbol demapper 127 and outputs the converted signal to the output unit 129.

Here, the frequency conversion performed by the reception RF unit 122 is performed based on the signal of the frequency f _RX output from the frequency oscillator 123. The reception frequency of the RF signal which is a result of the frequency conversion to F _RX.
In order for communication between the transmitter and the receiver to be performed properly, the reception frequency F _RX needs to match the transmission frequency F _TX , or the difference must be within a certain tolerance. In order to provide the function for realizing this, that is, the AFC, in the receiver of this example, the output of the serial-parallel converter 125 is input to the frequency deviation detector 130 to obtain the estimated frequency deviation, and the result is subjected to frequency control. To the unit 131. The frequency control unit 131, based on the estimated frequency deviation is input from the frequency deviation detector 130, a frequency as (the error (deviation) between the transmission frequency F _TX and the reception frequency F _RX) becomes smaller frequency deviation The output frequency f _RX of the oscillator 123 is controlled.

Next, the configuration of the frequency deviation detector 130 will be described.
Hereinafter, a case where a frame having a structure illustrated in FIG. 4 is used will be described. That is, as an example of a predetermined synchronization signal, a signal string 502 of a synchronization word (SW: Synchronous Word) which is a known symbol sequence is inserted into one frame 501 to be transmitted for 10 symbols. . That is, the frame 501 of this example has a structure in which a data signal sequence, a synchronization word signal sequence 502, and a data signal sequence are arranged in this order, and the entire frame including the synchronization word is STBC encoded. The synchronization word is a fixed bit pattern common to the transmitter and receiver to be synchronized.
In this example, a frame format is used in which a synchronization word is arranged at a position other than the beginning of the frame (a place after the beginning). However, a frame format in which a synchronization word is arranged at the beginning of the frame may be used.

Here, for a time series number n (n = 0, 1, 2, 3, 4) that changes every two symbol times, if the signal sequence 502 of the synchronization word is represented by a (2n), a (2n + 1), STBC The output 503 of the synchronization word portion on the transmission antenna 108-1 side obtained by encoding is a (2n), -a (2n + 1) ^* , and the output of the synchronization word portion on the transmission antenna 108-2 side obtained by STBC encoding. 504 becomes a (2n + 1), a (2n) ^* . Further, the signal sequence 505 corresponding to the synchronization word in the signal received by the receiving antenna 121 is assumed to be r (2n) and r (2n + 1).

FIG. 2 shows a configuration example of the frequency deviation detector 130.
The frequency deviation detector 130 of this example includes a channel response calculator 151, a reference signal memory 152, frequency deviation calculators 153-1 and 153-2, and a selector 154.

Here, in the frequency deviation detector 130 of this example, the signal sequence 505 corresponding to the synchronization word 502 among the signals output from the serial-parallel converter 125 is input by two symbols.
The reference signal memory 152 stores (stores) data representing a known synchronization word 502 encoded with STBC as a reference signal. In the following example, the signal sequence after the STBC encoding is performed on the signal sequence 502 (a (2n), a (2n + 1)) of the synchronization word as a reference signal in the reference signal memory 152, that is, the STBC code Data representing the output 503 (a (2n), -a (2n + 1) ^* ) of the synchronization word portion on the transmission antenna 108-1 side obtained by the conversion, and the synchronization on the transmission antenna 108-2 side obtained by the STBC coding It is assumed that data representing the output 504 (a (2n + 1), a (2n) ^* ) of the word part is stored. Here, a combination of a (2n) and a (2n + 1) may be defined as a state, and each state may be stored with identification information such as a state number.

ここで、（式２）において、スカラ部については、後に伝搬路応答の振幅成分は破棄されるため、省略して“１”とすることが可能である。
また、（式２）において、ａ（２ｎ）^＊，−ａ（２ｎ＋１）は信号列５０３（ａ（２ｎ），−ａ（２ｎ＋１）^＊）の共役複素であり、ａ（２ｎ＋１）^＊，ａ（２ｎ）は信号列５０４（ａ（２ｎ＋１），ａ（２ｎ）^＊）の共役複素であり、参照信号メモリ１５２に保持された参照信号から演算により求められて（式２）に代入される。また、例えば、ａ（２ｎ）とａ（２ｎ＋１）の組み合わせを状態として参照信号メモリ１５２に記憶しておき、これをチャネル応答推定器１５１に与え、チャネル応答推定器１５１において上記の各共役複素を求めるようにしてもよい。すなわち、参照信号メモリ１５２に保持する情報から上記の各共役複素が得られればよい。 The channel response estimator 151 includes a signal sequence 505 (r (2n), r (2n + 1)) input from the serial-parallel converter 125 and a reference signal (synchronization word signal sequence 502) held in the reference signal memory 152. Based on the signal sequence 503 (a (2n), -a (2n + 1) ^* ) and the signal sequence 504 (a (2n + 1), a (2n) ^* )) after STBC encoding is performed on 2) is used to calculate propagation path response (channel response) estimation values h ₁ (2n) and h ₂ (2n), and the transmission antenna 108-1 side propagation path response estimation value h ₁ (2n) is the frequency. Output to deviation calculator 153-1 and output channel response estimated value h ₂ (2n) on transmission antenna 108-2 side to frequency deviation calculator 153-2.

Here, in (Expression 2), since the amplitude component of the propagation path response is discarded later for the scalar part, it can be omitted and set to “1”.
In (Expression 2), a (2n) ^* and −a (2n + 1) are conjugate complexes of the signal sequence 503 (a (2n) and −a (2n + 1) ^* ), and a (2n + 1) ^* and a ( 2n) is a conjugate complex of the signal sequence 504 (a (2n + 1), a (2n) ^* ), and is obtained by calculation from the reference signal held in the reference signal memory 152 and substituted into (Equation 2). Further, for example, a combination of a (2n) and a (2n + 1) is stored in the reference signal memory 152 as a state, and this is given to the channel response estimator 151. You may make it ask. That is, it is only necessary to obtain each conjugate complex from the information held in the reference signal memory 152.

As described above, in the receiver of this example, the STBC-coded known synchronization word (reference signal) to be included in the signal transmitted from the transmitter and the synchronization word in the actually transmitted signal are supported. And a part having a certain relationship with respect to the propagation path response (a relation in which the propagation path response can be estimated by (Equation 2) based on the reference signal and the synchronization word part of the received signal) The estimated value of the response can be obtained.
For example, the reference signal memory 152 stores, as a reference signal, data representing the conjugate complex of the signal sequences 503 and 504 after the STBC encoding is performed on the signal sequence 502 of the synchronization word. You may make it substitute to Formula 2) as it is.

The frequency deviation calculator 153-1 receives the channel response estimation values h ₁ (0), h ₁ (2), h ₁ (4), h on the transmission antenna 108-1 side input from the channel response estimator 151. ₁ (6), h ₁ (8) is used to determine the phase, and the frequency deviation Δf ₁ is calculated from the amount of phase change and output to the selector 154.
The frequency deviation calculator 153-2 receives the channel response estimation values h ₂ (0), h ₂ (2), h ₂ (4), h on the transmission antenna 108-2 side input from the channel response estimator 151. ₂ (6), h ₂ (8) is used to determine the phase, and the frequency deviation Δf ₂ is calculated from the phase change amount and output to the selector 154.
The frequency deviations Δf ₁ and Δf ₂ obtained by the frequency deviation calculators 153-1 and 153-2 are essentially the same, but in the receiver of this example, the selector 154 has a higher accuracy. Is output to the frequency control unit 131.

For example, the selector 154 calculates the channel response powers p ₁ and p ₂ by (Equation 3) based on the frequency deviations Δf ₁ and Δf ₂ input from the frequency deviation calculators 153-1 and 153-2, respectively. If p ₁ ≧ p ₂ , Δf ₁ is selected, otherwise Δf ₂ is selected. Note that this selection criterion is an example, and a method of selecting according to another selection criterion may be adopted.

The internal operation of the frequency deviation calculators 153-1 and 153-2 will be described with reference to FIG.
FIG. 3 shows a configuration example of the frequency deviation calculators 153-1 and 153-2.
The frequency deviation calculators 153-1 and 153-2 of this example have a function of calculating the phase of the input estimated value of the propagation path response and calculating the frequency deviation from the amount of phase change. A delay memory 162, a complex conjugate acquisition unit 163, a phase calculator 164, an integrator 165 composed of an adder 166 and a delay memory 167, and a frequency deviation calculation unit 168 are provided.

ここで、（式４）において、ａｒｇ（ｘ）は、複素数ｘの位相であり、単位を［ｒａｄ］とする。 In the frequency deviation calculators 153-1 and 153-2 of this example, the propagation path response estimated value h (2n) input from the channel response calculator 151 and the propagation path delayed by one timing by the delay memory 162 The estimated value h (2 (n−1)) of the response is multiplied by the conjugate complex value h (2 (n−1)) ^* obtained by the complex conjugate acquisition unit 163 by the multiplier 161, and the phase φ (2n ) Is calculated by the phase calculator 164. The output (phase φ (2n)) by the phase calculator 164 can be expressed by (Expression 4).

Here, in (Expression 4), arg (x) is the phase of the complex number x, and the unit is [rad].

この位相変化量Φ（２ｎ）、すなわち時刻経過に対する傾きは、伝搬路応答ｈの時間変化が十分緩やかであるという条件の下では、周波数偏差の大きさに対応する。 Next, an integrator 165 including an adder 166 and a delay memory 167 calculates a phase change amount Φ (2n). The output (phase change amount Φ (2n)) by the integrator 165 can be expressed by (Expression 5).

This phase change amount Φ (2n), that is, the inclination with respect to the passage of time, corresponds to the magnitude of the frequency deviation under the condition that the time change of the propagation path response h is sufficiently gentle.

ここで、式（６）において、βは、位相変化量Φ（２ｎ）の時刻ｎ＝０，１，２，３，４に対する傾きである。また、ｆ_ｂはシンボル伝送速度（周波数）である。 Using this, the frequency deviation calculation unit 168 can calculate the frequency deviation using (Equation 6).

Here, in Expression (6), β is the slope of the phase change amount Φ (2n) with respect to time n = 0, 1, 2, 3, 4. F _b is a symbol transmission rate (frequency).

As a specific means for obtaining the slope β, for example, it is calculated from (Equation 7) using a first-order least square approximation method.

Further, considering that n = 0, 1, 2, 3, and 4, the slope β can be easily calculated by using the calculation formula (Formula 8).

  The frequency deviation calculators 153-1 and 153-2 can directly obtain the slope of the input channel response estimation value, but in this case, the phase of the channel response estimation value is wrapping. ) Must be noted.

In the above example, the present invention is applied to the STBC system, but the present invention is also effective for the DSTBC system. Hereinafter, a case where the present invention is applied to the DSTBC system will be described.
In the STBC system, a pilot or the like is originally inserted into a signal in order to perform channel response estimation, and the present invention is not necessarily effective. On the other hand, in the DSTBC system, it is not originally assumed that channel response estimation is performed, and therefore, a pilot or the like is not inserted into the signal. Therefore, in the present invention, a channel response can be estimated using a DSTBC-encoded synchronization word inserted for the purpose of frame synchronization and the like, and a frequency deviation is detected from the estimated value of the channel response. ing.

FIG. 5 shows a configuration example of a DSTBC transmission system that is a communication system using the DSTBC scheme.
The transmitter of this example is obtained by replacing the STBC encoder 104 in the transmitter illustrated in FIG. 1 with a DSTBC encoder 201. The receiver of this example is obtained by replacing the STBC decoder 126 in the receiver illustrated in FIG. 1 with a DSTBC decoder 202.
That is, the transmitter and the receiver of this example are configured to use the DSTBC system instead of the STBC system. Other configurations and operations (except for a portion for fixing a DSTBC encoding result of a synchronization word to be described later) are generally the same as the contents described for the STBC method, and thus description thereof is omitted.

  Here, in the example of the STBC method described above, a synchronization word that is a known symbol sequence is used as illustrated in FIG. 4, but this cannot be applied to the DSTBC method as it is. This is because, by simply performing DSTBC encoding, the pattern of the encoding result changes depending on the data before the encoding target data in the frame, so the data portion preceding the sync word in the frame This is because the encoding result of the synchronization word changes according to the change, and thus the signal pattern after the DSTBC encoding is performed on the synchronization word cannot be determined. For this reason, a device for storing the reference signal in advance on the receiver side is required.

Therefore, in this example, the above problem is solved by using a technique for fixing the result of DSTBC encoding of the bit string immediately before the synchronization word.
The fixation of the result of DSTBC encoding of the bit string immediately before the synchronization word is roughly realized by using the following technique for a transmitter that transmits a signal by the DSTBC method.
That is, a frame in which a synchronization word is arranged at a predetermined location after the head is used.
In the transmitter, the initial value control means has a fixed signal point corresponding to immediately before the synchronization word in the DSTBC encoder that processes the transmission target based on the value before the synchronization word from the beginning of the frame. Thus, the initial value of differential encoding when the frame is processed by the DSTBC encoder that processes the transmission target is set.

  Therefore, in the DSTBC encoder (main line DSTBC encoder) that processes the transmission target, by setting the signal point corresponding immediately before the synchronization word to be a fixed point, for example, from the beginning of the frame to the previous synchronization word Even when the value (for example, a part thereof) changes depending on the data content to be transmitted, the mapping arrangement of the synchronization word can be a fixed mapping pattern, and between the transmitter and the receiver, Communication can be efficiently performed by the DSTBC method.

Here, various frames may be used. For example, a frame in which changeable data such as voice to be transmitted is arranged before the synchronization word from the head is used.
In addition, regarding the setting of the corresponding signal point (symbol value) immediately before the synchronization word to be a fixed point, various points may be used as the fixed point, and are set in advance, for example. .

The following configuration is used as an example of the configuration of the initial value control means of the transmitter related to the fixing.
That is, the S / P conversion means performs serial / parallel conversion on the value before the synchronization word from the beginning of the frame, the symbol mapping means performs symbol mapping on the serial / parallel conversion result, and the differential encoding means Difference when the frame is processed by the DSTBC encoder that performs differential encoding on the symbol mapping result using a predetermined initial value and the initial value updating means processes the transmission target based on the differential encoding result. Update and set the initial value of dynamic encoding.

Moreover, the transmitter concerning the said fixation can also be grasped | ascertained as the following structures.
That is, in a transmitter that transmits a signal by the DSTBC method, first differential encoding means for performing differential encoding on a value immediately before a synchronization word from the beginning of a frame using a predetermined initial value; An initial value setting means for setting an initial value based on a differential encoding result immediately before a synchronization word by one differential encoding means, and the frame to be transmitted using the initial value set by the initial value setting means Second differential encoding means for performing differential encoding as described above.

  Further, the initial value setting means is adapted to perform initial encoding in accordance with a differential encoding result immediately before the synchronization word that can be obtained when differential encoding is performed on a value immediately before the synchronization word from the beginning of the frame. A table in which values are set, and a differential encoding result immediately before a synchronization word by the first differential encoding unit and an initial value used for differential encoding of the second differential encoding unit according to the table Set.

The immobilization uses the following characteristics of the DSTBC method.
1) In the DSTBC method, the encoding result obtained by differentially encoding a signal value by a predetermined arithmetic expression using a predetermined initial value is limited to a finite number regardless of the bit string signal value. being classified. That is, since every signal value is classified as a finite number of states, the signal values can be represented by these finite number of signal values.
2) Then, if an initial value in which the encoding result obtained by differentially encoding the finite number of signal values by the same predetermined arithmetic expression as described above becomes a predetermined target value is known, the encoding result is determined for an arbitrary signal value. Therefore, the target encoding result can be obtained by DSTBC encoding.

  Therefore, in the DSTBC system, based on the encoding result obtained by differentially encoding the signal value from the beginning of the frame to immediately before the synchronization word in the first stage encoding process, the initial value associated with the encoding result in advance. Is determined by referring to the table, and the specified initial value is used as the initial value in the second-stage encoding to perform the entire frame encoding process, thereby obtaining a predetermined encoding result as a target for the synchronization word portion of the frame. Can be obtained.

  With the configuration as described above, in the receiver of the present example, the DSTBC-encoded known synchronization word (reference signal) scheduled to be included in the signal transmitted from the transmitter and the STBC method described above, By utilizing the fact that the part corresponding to the synchronization signal in the actually transmitted signal has a certain relationship (the relationship of (Equation 2)) with respect to the channel response, the channel response without using a pilot or the like. The estimated value of can be obtained.

  As described above, in each configuration example, in the receiver of the communication system using the STBC method or the DSTBC method, the reference signal memory 152 for storing the synchronization word, and the propagation path response from the received signal and the reference signal corresponding to the synchronization word are obtained. Channel response calculator 151 to be calculated, two frequency deviation calculators 153-1 and 153-2 to detect a frequency deviation from a series of propagation path calculated values, and a selection to select one from the two detected frequency values And a frequency deviation detector 130 having a transmitter 154. In each of the frequency deviation calculators 153-1 and 153-2, propagation is performed using a synchronization word string encoded by the STBC method or the DSTBC method. The road response was calculated.

The advantage of encoding the synchronization word will be described.
In a system that employs STBC or DSTBC, a method of embedding a symbol string of a synchronization word in a frame as it is without encoding STBC or DSTBC for the synchronization word is common. On the other hand, in the present invention, it is assumed that STBC or DSTBC encoding is continuously performed on the synchronization word like other data, but this method has the following advantages.

The first advantage is that orthogonality is secured in the receiver to separate the synchronization words transmitted from the two transmitters.
When using synchronization words that are not STBC / DSTBC encoded, the synchronization word transmissions respectively transmitted from the two transmitters need to be provided with means that do not interfere with each other so that they can be separated at the receiver. For this purpose, the method in which one transmitter stops transmitting at the time when one transmitter is transmitting a synchronization word, or in the case of OFDM transmission, one transmitter transmits the synchronization word. For the subcarrier that is being used, the other transmitter may take a method of stopping transmission. The above method has a difficulty in the use efficiency of transmission time or frequency (subcarrier) necessary for transmitting the synchronization word. For the above purpose, it is also possible to set two synchronization word strings orthogonal to each other in advance, and each transmitter transmits each synchronization word string at the same time. According to the STBC or DSTBC coding method of the synchronization word used in the present invention, it is guaranteed that the two synchronization word signals transmitted from the respective transmitters as the coded output are orthogonal to each other by the STBC coding. Therefore, it is not necessary to take the above measures.

  The second advantage relates particularly to DSTBC encoding. Since DSTBC is a method of transmitting 4 bits of transmission information using a signal one time before as a reference signal, for example, when the operation of the encoder is temporarily interrupted at the beginning of a frame, the first 4 bits cannot be decoded. In a general frame configuration, there is no problem because a bit string that does not need to be decoded such as a preamble is arranged at the head. However, if a synchronization word string is arranged in the frame and the operation of the DSTBC encoder is interrupted here, the 4 bits immediately after the synchronization word cannot be decoded. The encoding of the synchronization word used in the present invention avoids such a situation and contributes to the transmission efficiency in that a so-called redundant bit is not required.

Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. It is also possible to provide various systems and devices.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.
In addition, as various processes performed in the system and apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in hardware resources including a processor and a memory. A controlled configuration may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

101: input unit, 102: serial-parallel converter, 103: symbol mapper, 104: STBC encoder, 105-1, 105-2: transmission baseband unit, 106-1, 106-2: transmission RF unit, 107 : Frequency oscillator, 108-1, 108-2: Transmitting antenna,
121: reception antenna 122: reception RF unit 123: frequency oscillator 124: reception baseband unit 125: serial-parallel converter 126: STBC decoder 127: symbol demapper 128: parallel-serial converter 129: Output unit, 130: Frequency deviation detector, 131: Frequency control unit,
151: Channel response calculator, 152: Reference signal memory, 153-1, 153-2: Frequency deviation calculator, 154: Selector,
161: Multiplier, 162: Delay memory, 163: Complex conjugate acquisition unit, 164: Phase calculator, 166: Adder, 167: Delay memory, 165: Integrator, 168: Frequency deviation calculation unit

Claims (2)

In a receiver that receives a signal encoded by the STBC method or the DSTBC method,
Storage means for storing data representing a predetermined synchronization signal encoded by the STBC method or the DSTBC method;
Data corresponding to the synchronization signal in the received signal is input, and an estimation unit that estimates the propagation path response by comparing the input data and the data stored in the storage unit;
A receiver comprising: A reception method in which a signal including a predetermined synchronization signal is encoded by the STBC method or the DSTBC method and received by a receiver,
The receiver compares the data corresponding to the synchronization signal in the received signal with data representing the encoded synchronization signal stored in advance, and estimates a channel response;
And a receiving method.

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