JP4270377B2 - Demodulator and demodulation method - Google Patents

Description

  The present invention relates to a demodulation device and a demodulation method suitable for a mobile radio communication terminal such as a mobile phone.

  Conventionally, an adaptive modulation method is known as one of modulation methods used in a mobile radio communication system such as a mobile phone system. In the following, an adaptive modulation scheme will be described with reference to an HSDPA (high speed downlink packet access) scheme of W-CDMA (Wideband Code Division Multiple Access) as an example.

  In the W-CDMA HSDPA system, the channel quality is obtained by adaptively switching between the QPSK (Quadrature Phase Shift Keying) modulation system and the 16 QAM (Quadrature Amplitude Modulation) modulation system according to the channel quality. However, it is possible to provide high-speed data communication while sacrificing noise durability characteristics for mobile radio communication terminals with good quality, and high while sacrificing communication speed for mobile radio communication terminals with poor propagation path quality. Application of an adaptive modulation scheme that can provide low-speed data communication with noise durability characteristics has been studied (see, for example, Patent Document 1).

  Here, the adaptive modulation scheme is realized by the following basic procedure.

  First, as a first procedure, the mobile radio communication terminal measures the reception quality of the signal transmitted from the base station.

  Next, as a second procedure, the mobile radio communication terminal notifies the base station of the reception quality measurement result.

  Next, as a third procedure, the base station determines transmission parameters such as a coding rate and a modulation frequency based on the reception quality measurement result reported from the mobile radio communication terminal.

  Next, as a fourth procedure, the base station transmits the transmission parameter to the mobile radio communication terminal and transmits data encoded and modulated based on the transmission parameter.

  Thereafter, as a fifth procedure, the mobile radio communication terminal receives transmission parameters from the base station and receives data, and performs demodulation and decoding processing of received data based on the transmission parameters.

  Then, data transmission / reception is continued by periodically repeating the first to fifth procedures.

Since 16QAM is not only phase-modulated but also amplitude-modulated, when a 16QAM-modulated signal is sent from the transmitting side, a demodulator on the receiving side needs a threshold for amplitude demodulation. . Therefore, conventionally, when a 16QAM modulated signal is transmitted from the base station side, the threshold information is also transmitted to the mobile radio communication terminal side.
JP 2003-198426 A (FIG. 6)

  However, in the latest specification of 3rd generation partnership project (3GPP), which is a standardization project for third-generation mobile phone systems, the system has been changed to a mechanism that does not transmit any threshold-related information necessary for QAM demodulation.

  Therefore, the receiving side has to calculate a threshold necessary for QAM demodulation by itself. That is, the reception side can perform QAM demodulation by calculating a threshold value for each slot (slot: 0.667 ms), which is the minimum unit of the wireless communication channel, for example.

  However, when the threshold value is calculated for each slot, it is not preferable because the demodulation processing time becomes long and the power consumption increases.

  The present invention has been made in view of such problems, and does not impair the characteristics of the receiving demodulator on the receiving side of the mobile radio communication system in which threshold-related information for amplitude demodulation is not transmitted from the transmitting side at all. An object of the present invention is to provide a demodulation device and a demodulation method that can reduce the processing time and power consumption required for demodulation.

  The demodulating device of the present invention includes a threshold value calculating means for calculating a threshold value necessary for amplitude demodulating at least a received signal subjected to amplitude modulation, and a calculation frequency for controlling the frequency of threshold value calculation based on the reception quality of the received signal. Control means and demodulation means for performing amplitude demodulation of the received signal using the calculated threshold value.

  Here, the calculation frequency control means estimates the Doppler frequency from the fluctuation level per time of the amplitude of the received signal, and controls the threshold calculation frequency according to the Doppler frequency. The calculation frequency control means controls the frequency of threshold calculation according to the number of rake reception paths of the reception signal.

  The demodulation method of the present invention includes a step of calculating a threshold necessary for amplitude-demodulating at least a received signal subjected to amplitude modulation, a step of controlling the frequency of threshold calculation based on the reception quality of the received signal, And performing amplitude demodulation of the received signal using the calculated threshold value.

  That is, according to the present invention, the calculation frequency of the threshold value for amplitude demodulation can be controlled, and the processing time and power consumption required for demodulation can be reduced by reducing the threshold calculation frequency. Further, according to the present invention, the threshold calculation frequency is controlled based on the reception quality of the received signal. For example, if the threshold calculation frequency is lowered only when the reception quality is good, the demodulation characteristic is improved. It will not be damaged.

  In the present invention, by controlling the calculation frequency of the threshold for amplitude demodulation based on the reception quality of the received signal, the processing time and power consumption required for demodulation are maintained while maintaining the characteristics of the receiving demodulator. Can be reduced.

  Hereinafter, as an embodiment of the present invention, a demodulating apparatus and a demodulating method of the present invention will be described by taking as an example the latest specification of 3GPP that is configured to transmit no threshold-related information necessary for QAM demodulation.

[Configuration of mobile radio communication system]
FIG. 1 shows a schematic configuration of a mobile radio communication system according to an embodiment of the present invention. In FIG. 1, illustration and description of a general configuration such as a radio antenna and an RF circuit are omitted, and only main parts according to the present invention are shown.

  In FIG. 1, in the transmission side apparatus 1 which is a base station, an information signal to be transmitted is encoded by an encoder 11 and sent to a modulator 12. The modulator 12 adaptively switches between the QPSK modulation scheme and the 16QAM modulation scheme in accordance with the radio channel quality. The output signal of the modulator 12 is sent to the multiplexer 13.

  The pilot signal generator 14 receives compensation information used for compensation of a coding rate at the time of coding by the encoder 11, a modulation frequency at the modulator 12, and amplitude and phase fluctuations generated in the wireless communication channel. Transmission parameters for notifying the side apparatus 2 are output as pilot signals and sent to the multiplexer 13. According to the latest specification of 3GPP, even when a 16QAM modulated signal is transmitted from the transmission side device 1, a threshold for amplitude demodulation is not transmitted from the transmission side device 1 to the reception side device 2. . Therefore, the threshold value for amplitude demodulation is not included in the pilot signal.

  The multiplexer 13 multiplexes the signal from the modulator 12 and the pilot signal from the pilot signal generator 14. The output signal from the multiplexer 13 is transmitted to the receiving side apparatus 2 via an RF circuit, an antenna, etc. (not shown) and further via a wireless communication path.

  Here, in FIG. 2, user data D (D 1, D 2, D 3,...) Is transmitted from the transmission side apparatus 1 that is the base station of FIG. 1 to the reception side apparatus 2 that is a mobile radio communication terminal. , And the downlink control channel through which the pilot signal P (P1, P2, P3,...) Is transmitted.

  In FIG. 2, the receiving side apparatus 2 receives downlink control channel data to which a pilot signal P is added before receiving user data D of the downlink user data channel, demodulates the pilot signal, and transmits transmission parameters. Thus, the compensation information of the coding rate, the modulation frequency, the amplitude and the phase applied to the user data D of the downlink user data channel is detected.

  Returning to FIG. 1, the receiving side device 2 receives a signal transmitted from the transmitting side device 1 through a wireless communication path via a receiving means such as an antenna or an RF circuit (not shown), and receives the received signal. Input to demodulator 21.

  The demodulator 21 extracts the pilot signal from the received signal, and switches appropriately between QPSK demodulation and 16QAM demodulation based on the modulation frequency of the transmission parameter demodulated from the pilot signal, while based on the transmission parameter compensation information. Thus, the amplitude and phase fluctuations generated in the wireless communication path are compensated.

  Further, when a 16QAM modulated signal is transmitted from the transmission side device 1, the demodulator 21 calculates a threshold for amplitude demodulation from the received signal as described later, and performs amplitude demodulation using the threshold. . The received signal demodulated by the demodulator 21 is sent to the decoder 22.

  The decoder 22 decodes the output signal from the demodulator 21 based on the coding rate of the transmission parameter, thereby extracting the information signal transmitted from the transmission side device 1.

[Threshold calculation processing for 16QAM demodulation]
Hereinafter, threshold calculation processing necessary for 16QAM demodulation in the demodulator 21 of the reception-side apparatus 2 of the present embodiment will be described.

  First, the concept of 16QAM demodulation will be described with reference to FIG.

  In 16QAM demodulation, each 4-bit data from “0000” to “1111” constituting each received symbol of 16QAM is converted into the 0th bit b0 and the second bit b2 from the left, and the first bit b1 from the left. And demodulating in two stages separately for the third bit b3. Bits b0 and b2 are “0” and “1” determinations using the I and Q axes as determination axes, as in QPSK, and bits b1 and b3 are “0” and “1” using I = 2α and Q = 2α as determination axes. "Determine.

  In the present embodiment, the 2α is a threshold necessary for QAM demodulation. As an example of the calculation method of 2α, a method of using the average amplitude value of the received I and Q signals as shown in Equation (1) can be considered.

この式（１）において、ＩrefはＩ信号の閾値、ＱrefはＱ信号の閾値、Ｍは受信シンボル数、absは絶対値、Ｒｅは実軸、Ｉｍは虚軸、Ｚiは各受信シンボルの値を示している。

In this equation (1), Iref is the I signal threshold, Qref is the Q signal threshold, M is the number of received symbols, abs is the absolute value, Re is the real axis, Im is the imaginary axis, and Zi is the value of each received symbol. Show.

  In so-called soft decision demodulation, in which bits are determined and demodulated so as to have certainty information, the distance from the determination axis may be output as a weight of the data bits.

  The demodulator 21 of the receiving-side apparatus 2 of the present embodiment calculates 2α described above as a threshold necessary for QAM demodulation, and performs amplitude demodulation using the threshold, but at that time, the received signal via the wireless communication path By controlling the calculation frequency of the threshold necessary for the QAM demodulation based on the quality, the processing time and power consumption required for the demodulation can be reduced.

  More specifically, the demodulator 21 of the receiving-side apparatus 2 according to the present embodiment obtains an SN (Signal / Noise) fluctuation amount caused by a signal passing through a wireless communication path as the received signal quality. Then, the calculation frequency of the threshold necessary for the QAM demodulation is controlled based on the SN fluctuation amount.

[Configuration and operation of demodulator]
FIG. 4 shows a configuration of the demodulator 21 according to the embodiment of the present invention that controls the threshold calculation frequency according to the above-described SN fluctuation amount.

  In FIG. 4, the signal transmitted from the transmission side device 1 of FIG. 1 through the wireless communication path to the input terminal 30 of the demodulator 21 and received via the antenna, the RF circuit, or the like of the reception side device 2. Is entered. The demodulator input signal supplied to the input terminal 30 is sent to the input signal buffer 31, the threshold calculation unit 34, and the SN fluctuation estimation unit 33.

  The input signal buffer 31 delays the demodulator input signal by the calculation time performed by the SN fluctuation estimation unit 33 and the threshold value calculation unit 34, and then outputs the signal to the demodulation unit 32.

  The threshold calculation unit 34 calculates a threshold (2α) necessary for QAM demodulation by the calculation of the above-described equation (1) under the control of the SN fluctuation estimation unit 33.

  The SN fluctuation estimation unit 33 estimates the degree of deterioration of the SN ratio generated in the received signal in the wireless communication path by periodically performing the following first to fourth steps during data reception. Based on the estimated value of the SN ratio deterioration degree, the threshold calculation unit 34 generates a calculation frequency control signal for controlling the frequency with which the threshold is calculated.

  First, the SN fluctuation estimation unit 33 calculates a CPICH (Common Pilot Channel) RSCP level (CPICH_RSCP) by the equation (2) as a process of the first step.

なお、式（２）において、cpic_symbiはパスｉの逆拡散後のＣＰＩＣＨ信号、Ｍは受信パス数、ＮpilotはＣＰＩＣＨシンボルの平均サンプル数ある。Ｎpilotは例えばスロット単位（Ｎpilot＝１０）とすれば計算の処理を軽くすることが可能になる。

In equation (2), cpic_symbi is the CPICH signal after despreading of path i, M is the number of received paths, and Npilot is the average number of CPICH symbol samples. If Npilot is, for example, a slot unit (Npilot = 10), the calculation process can be lightened.

  Next, the SN fluctuation estimation unit 33 calculates the CPICH ISCP level (CPICH_ISCP) by Expressions (3) and (4) as the process of the second step.

なお、式（３）中のcpichjは、パスｉの逆拡散後のＣＰＩＣＨ信号である。

Note that cpichj in equation (3) is a CPICH signal after despreading of path i.

  Then, CPICH ISCP is an average value of each path and is obtained by calculation of Expression (4).

なお、式（４）中のＮはＣＰＩＣＨシンボルの平均サンプル数であり、Ｍは受信パス数である。Ｎは、例えばスロット単位（Ｎ＝１０）とすれば計算の処理を軽くすることが可能になる。

In Equation (4), N is the average number of CPICH symbol samples, and M is the number of received paths. If N is, for example, a slot unit (N = 10), the calculation process can be lightened.

  Next, the SN fluctuation estimation unit 33 calculates the SN ratio (CPICH_SNR) of CPICH according to Expression (5) as the process of the third step. Here, CPICH_RSCP is equivalent to the power of the signal component, and CPICH_ISCP is equivalent to the power of the interference component. Therefore, the SN ratio of CPICH is obtained by Expression (5).

次に、ＳＮ変動推定部３３は、第４ステップの処理として、式（６）により、ＤＳＣＨのＳＮ比（DSCH_SNR）を算出する。

Next, the SN fluctuation estimation unit 33 calculates the SN ratio (DSCH_SNR) of the DSCH by Expression (6) as the process of the fourth step.

ＳＮ変動推定部３３は、以上の第１ステップ〜第４ステップの処理を周期的に行って求めたＳＮ比から、無線通信路で受信信号に生じたＳＮ比の劣化度合いを推定し、閾値算出部３４にて上記閾値を算出する頻度を制御する算出頻度コントロール信号を生成する。

The SN fluctuation estimation unit 33 estimates the degree of deterioration of the SN ratio generated in the received signal in the wireless communication path from the SN ratio obtained by periodically performing the processes of the first step to the fourth step, and calculates a threshold value. The unit 34 generates a calculation frequency control signal for controlling the frequency of calculating the threshold value.

  More specifically, for example, as shown in FIG. 5, the SN fluctuation estimation unit 33 uses a look-up table that represents the correspondence between the Doppler frequency Fd generated according to the movement of the mobile radio communication terminal and the threshold calculation frequency. The Doppler frequency Fd is estimated from the SN fluctuation level, a threshold calculation frequency corresponding to the estimated Doppler frequency Fd is obtained from the lookup table, and a control signal of the threshold calculation frequency is sent to the threshold calculation unit 34.

  That is, in the example of FIG. 5, when it is estimated that the Doppler frequency Fd generated in the wireless communication channel is equivalent to 240 Hz, the SN fluctuation estimation unit 33 performs control so that the threshold calculation unit 34 calculates the threshold 2α for each slot. To do. Similarly, when the SN fluctuation estimation unit 33 estimates that the Doppler frequency Fd is 80 Hz, the SN fluctuation estimation unit 33 controls the threshold value calculation unit 34 to calculate the threshold value 2α once every two slots, and the Doppler frequency Fd is 6 Hz. When it is estimated that the threshold value 2α is calculated by the threshold value calculation unit 34, control is performed so as to be performed once every three slots.

  Here, FIG. 6 shows a measurement example of the I and Q signal amplitudes of the demodulator input signal when the Doppler frequency Fd is 6 Hz and 240 Hz, for example. As can be seen from the measurement example of FIG. 6, when the Doppler frequency Fd is 6 Hz, the I and Q signal amplitudes hardly change over a plurality of slots, but when the Doppler frequency Fd is 240 Hz, It can be seen that the amplitudes of the I and Q signals change greatly. In an environment where the I and Q signal amplitudes do not change greatly between slots as in the case of Doppler frequency Fd = 6 Hz, the threshold necessary for QAM demodulation calculated in the first slot is applied to the subsequent several slots. Suggests that you can. On the other hand, it becomes difficult in an environment where the I and Q signal amplitudes vary greatly between slots, such as Doppler frequency Fd = 240 Hz.

  For this reason, the demodulator 21 of the present embodiment uses a look-up table that represents the correspondence between the SN fluctuation width of the wireless communication path and the threshold calculation frequency necessary for QAM demodulation, as shown in FIG. By switching and selecting the threshold calculation frequency according to the reception status (that is, the Doppler frequency level), the threshold calculation frequency is minimized and the processing time and power consumption required for demodulation are reduced without degrading the QAM demodulation performance. It is possible. Accordingly, the terminal cost can be reduced.

  Note that the demodulator 21 according to the embodiment of the present invention may generate a threshold calculation frequency control signal according to the number of reception paths that are combined with a rake, as well as the Doppler frequency as described above. .

  In this case, the demodulator 21 obtains the number of paths taken when the signal propagates through the wireless communication path, in other words, the number of paths to be rake-combined as the received signal quality, and is necessary for the QAM demodulation based on the number of paths Control the frequency of calculation of the correct threshold.

  As described above, the demodulator 21 when generating the threshold value calculation frequency control signal according to the number of reception paths includes a reception path number detection unit instead of the SN fluctuation estimation unit 33 of FIG. The reception path number detection unit uses, for example, a lookup table representing the correspondence between the number of Rake reception paths and the threshold calculation frequency as shown in FIG. 7, and calculates the threshold calculation frequency corresponding to the number of Rake reception paths from the lookup table. The control signal of the threshold calculation frequency is sent to the threshold calculation unit 34.

  That is, in the example of FIG. 7, when the number of Rake reception paths is “1”, the reception path number detection unit controls the threshold calculation unit 34 to calculate the threshold 2α for each slot. Similarly, when the number of Rake reception paths is “3”, the reception path number detection unit controls the threshold value calculation unit 34 to calculate the threshold 2α once every two slots, and the number of Rake reception paths is In the case of “6”, control is performed so that the threshold value 2α is calculated once every three slots by the threshold value calculation unit 34.

  That is, when the number of received paths is small, such as when the number of Rake received paths is “1”, for example, it is considered that the change in signal amplitude obtained by Rake combining is large. The calculation is performed for each slot. On the other hand, when the number of reception paths is large, such as when the number of Rake reception paths is “6”, it is considered that the change in signal amplitude obtained by Rake synthesis is small. Therefore, the threshold value calculation by the threshold value calculation unit 34 is reduced and performed once every three slots.

  As described above, in the demodulator 21 according to the present embodiment, the lookup table indicating the correspondence between the number of Rake reception paths and the threshold calculation frequency shown in FIG. The threshold calculation frequency can be switched. Therefore, the threshold calculation frequency can be minimized, the processing time and power consumption required for demodulation can be reduced without deteriorating QAM demodulation performance, and the terminal cost can be reduced. .

  Returning to FIG. 4, the threshold obtained by the threshold calculation unit 34 whose threshold calculation frequency is controlled as described above is sent to the demodulation unit 32.

  The demodulator 32 demodulates the signal that has passed through the input signal buffer 31 using the threshold obtained by the threshold calculator 34. Then, the output signal from the demodulator 32 is sent from the terminal 35 to the decoder 22 of FIG.

  FIG. 8 shows a timing chart of the demodulator 21 of FIG. 4 when the threshold value calculation unit 34 calculates the threshold value 2α for each slot.

  In FIG. 8, the threshold value calculation unit 34 calculates a threshold value 2α in each slot by sampling the demodulator input signal from the head of the slot. Then, the calculated 2α is passed to the demodulator 32.

  At the same time, the demodulator input signal is passed to the input signal buffer 31, and the time required for the processing in the SN fluctuation estimation unit 33 and the threshold calculation processing in the threshold calculation unit 34 (for example, for one slot) in the input signal buffer. Only buffered).

  The signal buffered by the input signal buffer 31 is transferred to the demodulator 32 and demodulated by the demodulator 32 using the threshold 2α.

  The above description of the embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiments, and various modifications can be made according to the design and the like as long as they do not depart from the technical idea of the present invention. .

  For example, the embodiment of the present invention is not limited to an adaptive modulation scheme that adaptively switches between a QPSK modulation scheme and a 16QAM modulation scheme in accordance with the quality of a wireless channel, and for example, a system that uses only a 16QAM modulation scheme. Applicable.

  Further, the mobile radio communication system of the embodiment of the present invention is not limited to a mobile phone system.

It is a block diagram which shows schematic structure of the mobile radio | wireless communications system of this Embodiment. It is a figure which shows the relationship between the downlink user data channel and downlink control channel in the mobile radio | wireless communications system of this embodiment. It is a quadrant arrangement diagram used for the conceptual explanation of 16QAM demodulation. It is a block diagram which shows the detailed structure of the demodulator with which the receiving side apparatus of this invention is provided. It is a figure which shows the lookup table of Doppler frequency and threshold value calculation frequency which SN fluctuation | variation estimation part has. It is a figure which shows an example of the measurement waveform of I and Q signal amplitude of a demodulator input signal in case a Doppler frequency is 6 Hz and 240 Hz. It is a figure which shows the lookup table of the number of Rake receiving paths and threshold value calculation frequency which a receiving path number detection part has. It is a timing chart of a demodulator when the threshold value 2α is calculated for each slot by the threshold value calculation unit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Transmission side apparatus, 2 Reception side apparatus, 11 Encoder, 12 Modulator, 13 Multiplexer, 14 Pilot signal generator, 21 Demodulator, 22 Decoder, 31 Input signal buffer, 32 Demodulator, 33 SN variation Estimator, 34 Threshold calculator

Claims (8)

A threshold value calculation means for calculating a threshold value necessary for amplitude demodulation of a received signal that is at least amplitude-modulated and wirelessly transmitted;
Calculation frequency control means for controlling the frequency of threshold calculation by the threshold calculation means based on the reception quality of the received signal transmitted wirelessly;
And a demodulating means for performing amplitude demodulation of the received signal using the threshold value calculated by the threshold value calculating means. The demodulator according to claim 1, comprising:
The calculation frequency control means obtains a fluctuation level per time of the amplitude of the received signal as the reception quality, estimates a Doppler frequency from the fluctuation level per time, and determines the Doppler frequency according to the Doppler frequency by the threshold calculation means. A demodulator that controls the frequency of threshold calculation. The demodulator according to claim 2,
The calculation frequency control means controls the frequency of threshold calculation by the threshold calculation means to be reduced as the Doppler frequency becomes lower. The demodulator according to claim 3, wherein
The calculation frequency control means has a correspondence table between the threshold frequency number in the threshold calculation means and the Doppler frequency. The demodulator according to claim 1, comprising:
The calculation frequency control means obtains the number of rake reception paths of the received signal as the reception quality, and controls the frequency of threshold calculation by the threshold calculation means according to the number of rake reception paths. apparatus. The demodulator according to claim 5,
The demodulator according to claim 1, wherein the calculation frequency control means controls the frequency of threshold calculation by the threshold calculation means to decrease as the number of rake reception paths increases. The demodulator according to claim 5,
The demodulating apparatus characterized in that the calculation frequency control means has a correspondence table between the threshold frequency number in the threshold calculation means and the rake reception path number. A step in which a threshold value calculation means calculates a threshold value required when amplitude-demodulating a received signal that is at least amplitude-modulated and wirelessly transmitted;
Based on the reception quality of the received signal transmitted wirelessly, the calculation frequency control means controls the threshold calculation frequency in the threshold calculation means;
A demodulation method, comprising: a step of demodulating the amplitude of the received signal using the threshold value calculated by the threshold value calculation unit.

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