JP3886748B2 - Demodulator, demodulation method, and communication apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a demodulation device, a demodulation method, and a communication device that can reliably demodulate a baseband signal.
[0002]
[Prior art]
For example, in code division multiplexing (CDMA) communication used in communication systems such as IMT-2000, the same band can be shared by assigning different code sequences to a plurality of mobile terminal apparatuses.
[0003]
In direct spreading (DS) CDMA communication, for example, a primary modulation component corresponding to a baseband signal by QPSK (Quadri-Phase Shift Keying) or the like is spread by a different spreading code sequence for each channel. To do. The information transmission rate per channel is uniquely determined from the number and spreading factor of spreading sequences used for spreading, the multi-level number of temporary modulation, and the transmission rate of the spread spectrum transmission signal.
[0004]
The number of spreading code sequences, the spreading factor, and the modulation multi-value number can be changed as appropriate. By changing these values in the transmission band, it is possible to provide communication services with different transmission rates. It can be done.
[0005]
In such CDMA communication, as a technique for demodulating a multiplexed signal simultaneously with respect to a plurality of channels, for example, "" Zero Forcing and Minimum Mean-square-Error Equalization for Multicast Detection in Code-Division Multiple-Access Channels " "Joint Detection (JD) Method" as shown in ", Anja Klein, Ghassan Kawas Kaleh, Paul Walter Baier, IEEE TRANSACSION ON VHEICULAR TECHNOLOGY, VOL.45, No.2, MAY 1996, pp.276-287" It has been known.
[0006]
In this JD method, a system matrix A in which a sequence obtained by convolving a spread code sequence of each user and a channel impulse response is arranged as an element is obtained. Specifically, if the spreading code of user k is c (k) and the channel impulse response is h (k), h (k) = {h1 (k), h2 (k),..., HW (k)}^T[X^TIndicates a transposed matrix of the matrix X. ], C (k) = {c1 (k), c2 (k),..., CQ (k)}^T, K = 1, 2,..., K, Q: spreading factor, W: channel impulse response width, N: number of demodulated symbol sets for each user, the following b (k) is obtained.
[0007]
b (k) = (b1 (k), b2 (k),..., bQ + W−1 (k))^T= C (k) * h (k), k = 1, 2,..., K
When this equation is expanded, a matrix as shown in FIG. 26 is obtained.
[0008]
The system matrix A uses the elements of this matrix,
A = (A_ij), I = 1, 2,..., NQ + W−1, j = 1, 2,.
A_{Q (n-1) +1, n + N (k-1)}= Bl (k) {k = 1, 2, ..., K, n = 1, 2, ..., N, l = 1, 2, ..., Q + W-1}, 0 {k, n, l otherwise} expressed.
[0009]
Here, if the transmission data symbol is d and the noise is n, the received signal e is represented by e = Ad + n using this system matrix A. For simplification, if e = Ad, the received signal e is represented by a matrix as shown in FIG.
[0010]
Using this relationship, the transmission data symbol d is d = (A^HA) -1A^HDemodulated by e (ZF). Where A^HIs a complex conjugate transpose of the system matrix A.
[0011]
Therefore, in this JD method, the transmission data symbol d is estimated from the operation relating to the system matrix A.
[0012]
In addition, the self-interference due to the delayed wave component is canceled and synthesized from the convolutional component of the self-spread code and the channel estimation value (envelope of the received signal phase and amplitude variation due to fading). For example, "DATA DETECTION ALGORITHMS SPECIALLY DESIGNED FOR THE DOWNLINK OF CDMA MOBILE RADIO SYSTEMS", Anja Klein, IEEE 47^th Vehicular Technology Conference, pp.203-207, May 1997, "" Low Cost MMSE-BLE_SD Algorithm for UTRA TDD Mode Downlink ", ETSI STC SMEG Layer 1 Expert Group, Tdoc SMEG2 UMTS L1, Helsinki, Finland Sept. 1998, etc. A single user detection (SUD) method shown in FIG.
[0013]
In particular, in the downlink, since the channel estimation values between the spreading codes are the same, assuming that the same channel impulse response is H (hl) and the spreading code matrix is C (c (k)), between these and the received signal r Has a relationship of r = HCd + n. Here, Cd and H are matrices shown in FIGS. 28 and 29, respectively.
[0014]
In addition, since H is the same among the spreading codes and the orthogonality with other spreading codes is high, in this SUD method, only the own signal is considered as C, and only the own signal is estimated as d. It has become.
[0015]
Further, in this SUD method, Cd = (H^HH)^-1H^Hr (ZF), and the modulation data symbol d is d = C^HCd = C^H(H^HH)^-1H^HIt can be demodulated as r.
[0016]
Further, a RAKE receiver is known as an apparatus that considers only its own spreading code and synthesizes its own delayed wave by multipath or the like into a direct wave (maximum ratio synthesis) to improve reception sensitivity.
[0017]
By the way, in CDMA communication, in order to select a channel to be received, a pilot different for each channel is added to the signal before spreading as shown in FIG. 30, or at a certain moment as shown in FIG. A common pilot is added to all channels. Such a pilot can be extracted from the despread output of the received spread signal.
[0018]
In particular, in the downlink (wireless) line, even if the spreading code is different, the propagation path to a specific mobile terminal device is the same. May be used as a pilot to indicate the channel of
[0019]
As a specific example, for example, a common pilot allocation using a common pilot in all the spreading codes shown in FIG. 6 described above (Common Pilot Allocation), and when one user has code multiplexing shown in FIG. A specific pilot allocation (UE Specific Pilot Allocation) and the like for assigning common pilots are known.
[0020]
In such cases, when a slot (time slot) having a fixed pattern common between spreading codes is received, a channel estimation value using the common fixed pattern is obtained.
[0021]
After obtaining the channel estimation value in this way, demodulation is performed by the above-described JD method, SUD method, and RAKE receiver using the obtained channel estimation value. By performing demodulation using the channel estimation results as described above, it is possible to reduce the processing load of the demodulation processing as compared with the case where demodulation is performed by obtaining the power of each channel.
[0022]
[Problems to be solved by the invention]
However, since the power of the fixed pattern common between different spreading codes is not the same as the power of each channel, the channel estimation value corresponding to the power of such a fixed pattern is used, for example, demodulation by the RAKE receiver described above. As shown in FIG. 17, the position of the demodulated symbol (black circle in the figure) is the modulation base point (white circle in the figure, (± 1 ± j) / (2 in the case of QPSK).^1/2)).
[0023]
The RAKE receiver performs maximum ratio combining according to the channel estimation result. In this maximum ratio combining, the received signal is simply multiplied by a real number in accordance with the channel estimation result, so that the demodulated symbols after combining deviate from the modulation base point.
[0024]
However, even if the demodulated symbol deviates from the modulation base point in this way, the symbol phase does not change and the demodulated symbol amplitude only changes. When QPSK is used, the demodulated symbol does not become a symbol of another phase.
[0025]
However, when QAM (Quadrature Amplitude Moduration) is used for primary modulation in order to improve the coding efficiency, if the distance from the origin of the demodulated symbol changes, as shown in FIG. It becomes impossible to perform accurate demodulation.
[0026]
The present invention has been made in view of the above-described problems, and provides a demodulation device, a demodulation method, and a communication device that can return a demodulated symbol to a modulation base point and can reliably demodulate a baseband signal. The purpose is to provide.
[0027]
[Means for Solving the Problems]
In order to solve the above-described problem, a demodulator according to the present invention has a channel multiplexed by a plurality of orthogonal spreading code sequences, and a pilot signal common to at least some channels is spread in each channel. Receiving means for receiving a signal spread by a code sequence and spreading a predetermined code (fixed code) common to all channels by a spreading code sequence; and a common pilot signal in the received signal received by the receiving means. The despreading means for despreading, the common channel estimation means for performing channel estimation according to the common pilot signal despread by the despreading means, and the fixed code amplitude for each channel according to the estimation output of the channel estimation means Depending on the amplitude detection means to be obtained, the estimated output of the common channel estimation means, and the fixed code amplitude for each channel obtained by the amplitude detection means. Characterized in that it comprises a restoring means for restoring the data in the signal unit received.
[0028]
The restoration of data by the restoration means includes, for example, demodulation of a despread received signal, decoding of the demodulated data, and the like.
[0029]
In addition, another demodulation apparatus according to the present invention has a channel multiplexed by a plurality of orthogonal spreading code sequences, and a pilot signal common to at least some channels is spread by the spreading code sequence of each channel. Receiving means for receiving a signal in which a predetermined code (fixed code) different for each channel is spread with a spreading code sequence; and despreading means for despreading a common pilot signal in the received signal received by the receiving means; A common channel estimation unit that performs channel estimation according to a common pilot signal despread by the despreading unit, and an amplitude detection unit that determines the amplitude of the fixed code for each channel according to the estimation output of the channel estimation unit, In the signal received by the receiving means according to the estimated output of the channel estimating means and the amplitude of the fixed code for each channel obtained by the amplitude detecting means Characterized in that it comprises a restoring means for restoring the data.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be applied to, for example, a mobile communication system that performs communication between a base station and a mobile terminal device.
[0031]
(First embodiment)
(Constitution)
The mobile communication system according to the first embodiment of the present invention includes, as shown in FIG. 1, for example, a base station 10 and a mobile terminal device 20 that perform communication by code division multiplexing (CDMA-DS) of direct spreading scheme. It has.
[0032]
The base station 10 is provided for each predetermined area (cell). The base station 10 is connected to a network 1 (hereinafter simply referred to as a wired telecommunications network) 1 such as a wired telecommunications network. The base station 10 provides services such as relay to the wired telecommunication network 1 or communication between the mobile terminal devices 20 to the mobile terminal device 20 in the cell.
[0033]
In addition, this mobile communication system includes a communication management device 2 connected to each base station 10 via a wired telecommunications network 1. The base station 10 that performs communication with a specific mobile terminal device 20 is selected by communication control by the communication management device 2.
[0034]
In this mobile communication system, communication between the base station 10 and the mobile terminal apparatus 20 is performed by so-called W-CDMA (Wideband-Code Division Multiple Access). In this W-CDMA, spreading codes having high orthogonality are assigned to a plurality of channels using the same band, and a transmission signal is spread with the spreading code assigned to each channel. On the receiving side, the received signal is despread using the same spreading code as that on the transmitting side to reproduce the received signal.
[0035]
As shown in FIG. 2, for example, the base station 10 includes a communication interface (I / F) 100 that performs communication with the wired telecommunication network 1, a downlink system 110 that transmits a signal to the mobile terminal device 20, and a mobile terminal device. And an uplink system 120 that receives a signal from 20.
[0036]
The downlink system 110 separates data received via the communication I / F 100 for each predetermined logical channel, and divides the data supplied from the separation unit 111 for each predetermined length and adds parity. , Interleaving or the like to form data to be transmitted to the mobile terminal apparatus 20 and a data configuration unit 112 that configures data to be transmitted to the mobile terminal apparatus 20 and, for example, quadrature phase modulation (QPSK), quadrature phase modulation (QPSK) The modulation unit 113 that performs modulation (primary modulation) by QAM (Quadrature Amplitude Modulation), the spreading unit 114 that spreads the modulation output with a different spreading code for each predetermined channel, and the output of the spreading unit 114 of each logical channel are combined And a transmission unit that drives the transmission antenna 117 according to signals of all channels spread according to the synthesized signal. And an amplifier 116.
[0037]
The modulation unit 113 is adapted to, for example, the primary modulation scheme (number of QAM symbols, etc.) by adapting to the QoS of the radio communication line with the mobile terminal device 20 detected separately. The modulation unit 113 can be configured by a DSP, for example, and can change the modulation method adaptively according to parameters such as QoS.
[0038]
The number of QAM symbols can be 16 values as shown in FIG. 3, for example. In this case, for example, when the QoS is reduced to a predetermined level, the number of QAM symbols is set to 8 values. When the QoS is improved to a predetermined level or more, the number of QAM symbols is set to 64 values as shown in FIG. You may comprise. The number of QAM symbols is not limited to these examples, and can be changed as appropriate.
[0039]
The uplink system 120 includes a reception amplifier 122 that amplifies a signal received via the reception antenna 121, a separation unit 123 that separates the reception signal for each channel, and a despreading unit that performs despreading for each spreading code. 124, a channel estimation unit 125 that performs channel estimation according to the despread output, a demodulation unit 126 that demodulates the despread output according to the channel estimation value of the channel estimation unit 125, and extracts received data from the demodulated data A data extraction unit 127 that combines the data extracted by each data extraction unit 127.
[0040]
In this embodiment, as shown in FIG. 2 described above, the case where the receiving antenna 121 is provided separately from the transmitting antenna 117 has been described. However, by using a device such as a duplexer or a circulator, the transmitting antenna and the receiving antenna are used. Can be shared.
[0041]
Further, as shown in FIG. 5, for example, the mobile terminal apparatus 20 includes an input / output I / F 200 for inputting / outputting voice signals or inputting / outputting data to be transmitted / received, and an uplink system 210 for transmitting signals to the base station 10 A downlink system 220 that receives a signal from the base station 10, a transmission / reception antenna 230, and a duplexer 240 that switches a signal to be transmitted / received.
[0042]
The uplink system 210 configures data to be transmitted to the base station 10 by performing processing such as division for each predetermined length, addition of parity, interleaving, etc. on data transmitted from data supplied from the input / output I / F 200 A data configuration unit 211 that performs modulation, modulation unit 212 that performs modulation by QPSK, QAM, or the like according to the configured transmission data, a spreading unit 213 that spreads the modulation output, and transmission that drives the transmission / reception antenna 230 according to the spread output And an amplifier 214.
[0043]
The downlink system 220 includes a reception amplifier 221 that amplifies the reception output supplied via the duplexer 240, a despreading unit 222 that despreads the received signal, and a channel estimation unit that performs channel estimation according to the despread output. 223, a demodulator 224 that demodulates the despread output according to the channel demodulated output of the channel demodulator 223, and a data extractor 225 that extracts received data from the demodulated output.
[0044]
In this mobile communication system, for example, as shown in FIG. 6, pilot signals including a predetermined code (fixed pattern: m (x)) common to all channels from the base station 10 are transmitted at predetermined intervals. . The pilot signal of each channel is transmitted after being spread with a spreading code (Code 1, Code 2,..., Code n) assigned to each channel.
[0045]
Alternatively, for example, as shown in FIG. 7, a pilot signal including a fixed pattern (m (x),..., M (y)) common to some channels is transmitted, or as shown in FIG. The same fixed pattern (m (c)) may be spread on each channel by spreading code (Code 1, Code 2,..., Code n) of each channel and transmitted.
[0046]
In the downlink system 220 of the mobile terminal device 20, a part of the received transmission signal from the base station 10 is despread with a spreading code for each channel, and the above-described despread output is performed, for example, by a correlator operation or the like. The channel estimation is performed by calculating the correlation with the fixed pattern, and for example, the despread received signal is demodulated according to the result of the channel estimation as shown in FIG.
[0047]
Demodulation in the downlink system 220 performs despreading of the received signal for some symbols of the channel in which the received signal exists at the timing corresponding to the maximum peak in FIG. 9 described above, for example, and the power value per unit symbol Is obtained in accordance with the amplitude of a predetermined symbol (individual channel estimation value to be described later).
[0048]
By the way, in this mobile communication system, the signals of the individual channels code-multiplexed as described above are divided into time slots at predetermined time intervals as shown in FIG. 10 (A), for example. .
[0049]
In a time slot (for example, DPCH: Dedicated Physical Channel) frame with a downlink signal transmitted from the base station 10 to the mobile terminal apparatus 20, for example, as shown in FIG. , TPC (power control) bits and other control information are included.
[0050]
Further, as shown in FIG. 11, for example, the frames of other time slots include TFCI (channel format) bits arranged in a frame.
[0051]
Since these TFCI bits and TPC bits are set to predetermined values (symbols) in advance, it is appropriate to use them for obtaining the amplitude of the symbol corresponding to the power value per unit symbol.
[0052]
(Operation)
In the mobile communication system configured as described above, reception processing (channel estimation and demodulation) is executed by the procedure shown in FIG. 12, for example.
[0053]
First, before the communication between the base station 10 and the mobile terminal apparatus 20 is started, a spreading code determined in advance by a predetermined procedure is assigned from the base station 10 to the downlink line to the mobile terminal apparatus 20. . The spreading unit 114 spreads the modulation output from the modulation unit 113 according to the spreading code assigned to each mobile terminal device 20. The spread downlink transmission signal is amplified by the transmission amplifier 116 and transmitted to the mobile terminal apparatus 20 via the transmission antenna 117.
[0054]
The downlink transmission signal received by the transmission / reception antenna 230 of each mobile terminal apparatus 20 and amplified by the reception amplifier 221 is supplied to the despreading section 222. The despreading unit 222 despreads the supplied downlink transmission signal. The spreading code at this time is a spreading code assigned to each channel as described above.
[0055]
The channel estimation unit 223 performs channel estimation as described above according to the despread received signal and supplies a channel estimation value to the demodulation unit 224 (S1). Further, the channel estimation unit 223 despreads the common fixed pattern (for example, the above-described TFCI bits, TPC bits, etc.) (S2), and obtains the symbol amplitude corresponding to the power value per unit symbol as described above ( S3), and supplied to the demodulator 224.
[0056]
Further, the channel estimation unit 223 obtains an individual channel estimation result for each channel and supplies it to the demodulation unit 224 (S4 to S7).
[0057]
The demodulator 224 demodulates the despread received signal according to the supplied channel estimation value or the like (S8). The data extraction unit 225 extracts received data from the demodulated output, and outputs the extracted data via the input / output I / F 200, for example.
[0058]
Further, the channel estimation unit 223 obtains reception characteristics and the like based on the demodulation result and the like (S9), and uses it for controlling communication with the base station 10 and the like.
[0059]
・ (Channel estimation)
As described above, the channel estimation unit 223 performs channel estimation based on the correlation between the despread received signal and the fixed pattern (S1 in FIG. 12 described above). The estimation result of this channel has peaks at several timings as shown in FIG. 9 described above, for example. Among these, the channel estimation unit 223 performs despreading of the received signal for some symbols of the channel where the received signal exists at the timing corresponding to the maximum peak (S2), and corresponds to the power value per unit symbol. The amplitude of the symbol is obtained (S3).
[0060]
Specifically, for example, the received signals in a period corresponding to the above-described TFCI bits and TPC bits of all channels where the received signals exist at the timing corresponding to the maximum peak of the channel estimation value are despread, and these bits are The amplitude of the symbol corresponding to the power value per unit symbol corresponding to is obtained.
[0061]
In this case, the despreading may be performed by multiplying the scrambling code and the spreading code by one or a plurality of symbols. Alternatively, the despreading may be performed after the scrambling code is solved.
[0062]
In addition, although there is some degradation due to the influence of multipath, in the downlink channel, since the orthogonality of the spreading code of each channel is high, the accuracy of the amplitude per unit symbol obtained as described above is high. .
[0063]
The number of symbols for obtaining the amplitude by despreading may be one or plural. When obtaining the amplitude for a plurality of symbols, the average of the amplitudes of the plurality of symbols may be obtained.
[0064]
In addition, the period of the received signal for which the symbol amplitude is obtained by despreading is a symbol whose amplitude corresponds to the power value of the channel, such as the period corresponding to the TFCI bit and TPC bit described above.
[0065]
When the received signal is modulated by QAM, even if the received signal is despread, it is not known which symbol point the obtained symbol point corresponds to. However, even if a frame of normal data is modulated by QAM, a frame including control information such as the above-described TFCI bit and TPC bit is not compatible with conventional QPSK or the like from the viewpoint of maintaining compatibility. In some cases, modulation is performed by the modulation method.
[0066]
In such a case, the amplitude of the symbol corresponding to the power value per unit symbol can be obtained by despreading the control signal modulated and spread by QPSK in the same procedure as described above.
[0067]
Furthermore, for the other peaks of the channel estimation values shown in FIG. 9, the symbol amplitude corresponding to the power value per unit symbol of the received signal may be obtained as described above. However, since the downlink line is multiplexed orthogonally for each spreading code, the timing of the delayed wave on the time axis of channel estimation (received by the mobile terminal apparatus 20) is the same for all channels. Therefore, the symbol amplitude corresponding to the power value per unit symbol of each channel is multiplied by a real number according to the offset between the symbol amplitude of the common fixed pattern and the symbol amplitude of each channel.
[0068]
For this reason, for example, as shown in FIG. 13, the amplitude of the maximum peak of the channel estimation value by the common fixed pattern in FIG. 9 is normalized as 1 (S5), and further, as shown in FIG. By multiplying the symbol amplitude value for each channel (S6), a result similar to the case where the amplitude is obtained by performing despreading for each peak is obtained (S7).
[0069]
By using the individual channel estimation value obtained for each channel in this way, for example, demodulation using a JD method, SUD method, RAKE receiver, or the like (S8), the demodulated symbols are converted into modulation base points. Can be restored. As a result, the symbol can be reliably restored even when, for example, the above-described QAM is used as the primary modulation method in the modulation unit 113. Since the demodulated symbol can be returned to the modulation base point, even if another modulation method (for example, the above-described QPSK or the like) is used as the primary modulation, it contributes to improvement of the certainty of demodulation. can do.
[0070]
·(demodulation)
When performing demodulation according to the individual channel estimation result for each channel obtained as described above by combining multipath received signals by a RAKE receiver or the like, for example, the method shown in FIG. Modulation / demodulation).
[0071]
In this method, the individual channel estimation result (c) for each channel obtained as described above._n) Complex conjugate (c_n ^*) And determine the complex conjugate as the square of the individual channel estimate (| c_n｜²) Is multiplied by the spread output (c1, c2,...) Of each multipath received signal as a coefficient to obtain the components (d1, d2,...) Of each multipath. The multipath components thus obtained are combined to obtain a demodulated output d.
[0072]
Each multipath component is returned to the modulation base point because the value obtained by dividing the complex conjugate by the square of the individual channel estimation value is multiplied as a coefficient as described above. Therefore, the demodulated output d obtained by combining these components also returns to the modulation base point.
[0073]
In demodulation using a conventional RAKE receiver, for example, as shown in FIG. 16, values obtained by multiplying individual multipath components by complex numbers of channel estimation values as coefficients are combined (maximum ratio combining). Although the phase rotation due to fading or the like was corrected, the amplitude was not maintained. Thus, in demodulation using a conventional RAKE receiver, the amplitude changes as shown in FIGS. When phase modulation such as QPSK is used as the primary modulation as in the prior art, there is a problem because demodulation can be performed with the phase component even if the amplitude shifts from the modulation base point as shown in FIG. There wasn't. However, when a modulation method that requires an amplitude component such as QAM is used as the primary modulation as in this mobile communication system, the symbol point after demodulation is shifted from the modulation base point as shown in FIG. If it does, it will become impossible to demodulate correctly.
[0074]
For this reason, in the case of QAM, it is necessary to return to the modulation base point, for example, as shown in FIG. In order to satisfy such a need, for example, as described above, when a shared fixed code is transmitted between the channels as described above, for example, as a pilot signal, a common channel estimation value as in the past is used. Rather than using, detect the symbol width corresponding to the received signal power for each channel (power that takes into account the change in amplitude due to fading etc. in the transmission path to the transmitted signal power), and estimate the channel for each channel (spreading code) It is necessary to find a value.
[0075]
Accordingly, by performing demodulation according to the individual channel estimation values as described above as in this mobile communication system, the demodulated output can be returned to the modulation base point as shown in FIG. . Therefore, even a modulation method that requires an amplitude component such as QAM can be reliably demodulated.
[0076]
In this mobile communication system, as described above, the multipath components are synthesized by multiplying the received signal by the value obtained by dividing the complex conjugate of the channel estimation value by the square of the individual channel estimation value. Therefore, as shown in FIG. 19B and the like, the amplitude of the received signal is small. However, since the noise component included in the received signal is also small, the demodulated symbol can be returned to the modulation base point without changing the SN ratio.
[0077]
By the way, the demodulation according to the channel estimation value obtained as described above is not limited to the above-described demodulation using the RAKE receiver by the process as shown in FIG. 20, for example, the JD method by the process as shown in FIG. It can also be executed by the SUD method or the like by the process shown in FIG.
[0078]
By the way, a signal amplitude value corresponding to the power obtained individually for each spreading code is used as a modulation base point as a demodulated symbol returned to the modulation base point using an individual channel estimation value by the above processing. By obtaining the Euclidean distance using the multiplied value as a reference symbol point, the reception characteristic can be obtained with high accuracy.
[0079]
The reception characteristics that can be obtained include, for example, RSSI (Received Signal Strength Indicator), RSCP (Received Signal Code Power), ISCP (Interference Signal Code Power), SIR (Signal to Interference Ratio), and Eb / Io.
[0080]
These reception characteristics can be obtained with higher accuracy than the case where a common channel estimation value based on a fixed pattern is used also by the individual channel estimation value obtained for each channel as described above.
[0081]
By the way, it is not always necessary to return the received signal to the modulation base point using the individual channel estimation value obtained for each channel as described above in the demodulation stage. Specifically, for example, as shown in FIG. 23, individual channel estimation values (or power for each channel corresponding thereto) at the time of decoding by error correction or hard decision (processing for reproducing received data from modulated output) Error correction or decoding according to
[0082]
When performing such processing, first, as in S1 to S3 in FIG. 12 described above, after obtaining a common channel estimation value by a common fixed pattern and individual channel estimation values for each channel, Demodulation is performed using the common channel estimation value (S14).
[0083]
In this demodulation, for example, Ap is an amplitude of a fixed pattern common between spreading codes, Ad is a transmission amplitude of a channel, α is a complex fading channel, and γ is an estimated value of the common fixed pattern, as shown in FIG. The demodulated symbol Z is obtained according to the equation shown.
[0084]
After this, when obtaining a metric (for example, Euclidean distance) when performing error correction or hard decision decoding, a value including an amplitude corresponding to the channel power is used as a metric reference point (in the case of Euclidean distance) according to individual channel estimation values. Then, error correction or hard decision decoding is performed as the Euclidean reference point) (S15).
[0085]
In this decoding, for example, the amplitude for each individual channel corresponding to the channel estimation value obtained by a common fixed pattern is not used, but for example, according to the equation shown in FIG. A corresponding amplitude Ad ′ is obtained, and the decoded value (d_j) Is performed.
[0086]
Further, reception characteristics are measured using a value including an amplitude corresponding to the power of the channel according to an individual channel estimation value as a Euclidean reference point (S16).
[0087]
Note that when obtaining the metric at the time of decoding (S15), the coefficient to be multiplied by the modulation base point is determined in consideration of the processing at the time of demodulation, as shown in FIG.
[0088]
In order to accurately obtain the Euclidean distance as a metric at the time of decoding even when information is included in the amplitude of the signal as in QAM, the channel obtained individually for each channel as described above at the time of demodulation or decoding An estimate (or power for each channel) is required. For this reason, in this mobile communication system, as described above, processing is performed using individual channel estimation values obtained for each channel.
[0089]
As described above, decoding is performed by performing error correction or hard decision using an individual channel estimation value or the like for each channel, thereby contributing to improvement in the certainty of decoding of received data.
[0090]
(Second Embodiment)
(Constitution)
The mobile communication system according to the second embodiment of the present invention is configured in the same manner as the mobile communication system shown in FIG.
[0091]
In the first embodiment described above, the pilot signal used in each channel transmitted from the base station 10 to the mobile terminal apparatus 20 is transmitted for each channel as shown in FIGS. 6 to 8 described above. .
[0092]
In addition to this, in the mobile communication system according to the second embodiment, the base station 10 provides the mobile terminal device 20 with a specific value for each channel (for each spreading code), for example, as shown in FIG. A fixed pattern is being transmitted.
[0093]
Moreover, in this mobile communication system, the channel estimation unit 223 obtains a common channel estimation value by a common pattern between all or some of the channels, as described above.
[0094]
In the first embodiment described above, the received signal is despread for a predetermined number of symbols according to the common channel estimation result, and the amplitude of the symbol corresponding to the power value per unit symbol, The channel estimation value for each channel was obtained. In the first embodiment, for example, TFCI bits and TPC bits of all channels are used as predetermined symbols for this purpose.
[0095]
On the other hand, in the second embodiment, individual channel estimation values are obtained using a fixed pattern unique to each channel described above. The fixed pattern unique to each channel has a longer symbol than the above-described TFCI bits, TPC bits, and the like.
[0096]
(Operation)
When performing the above-described channel estimation, the channel estimation unit 223 performs channel estimation based on the correlation between the despread received signal and the fixed pattern, as in the first embodiment.
[0097]
After obtaining the common channel estimation value in this way, the channel estimation unit 223 despreads the received signal with respect to the above-described fixed pattern unique to each channel, and calculates the symbol corresponding to the power value per unit symbol. Find the amplitude. Further, the amplitude of such a symbol is obtained for each channel, and a unique channel estimation value is obtained for each channel.
[0098]
As described above, when a unique channel estimation value is obtained for each channel, the channel estimation unit 223 supplies the unique channel estimation value and the common channel estimation value obtained as described above to the demodulation unit 224.
[0099]
When these channel estimation values are supplied, the demodulator 224 demodulates the received signal as in the first embodiment described above.
[0100]
Thereby, similarly to the first embodiment described above, demodulation can be performed by returning the demodulated symbol to the modulation base point. Thereby, a baseband signal can be demodulated reliably.
[0101]
Furthermore, as described above, the fixed pattern unique to each channel has a longer symbol than the above-described TFCI bits, TPC bits, etc., and therefore, by using this, an individual channel estimation value is obtained for each channel. The accuracy of individual channel estimation values can be improved for each channel.
[0102]
For this reason, the demodulation accuracy can be improved by demodulating the received signal using such individual channel estimation values for each channel. Therefore, the certainty of demodulation can be improved.
[0103]
In addition, by using individual channel estimation values for each channel and obtaining the reception characteristics as in the first embodiment described above, it is possible to contribute to improving the accuracy of the reception characteristics.
[0104]
Alternatively, as in the first embodiment described above, decoding is performed by performing error correction or hard decision using an individual channel estimation value for each channel, thereby improving the reliability of decoding of received data. Can contribute.
[0105]
In the description of the second embodiment, a case has been described in which only a fixed pattern unique to each channel described above is used in order to obtain a channel estimation value unique to each channel. A unique channel estimation value may be obtained for each channel by the same procedure as in the first embodiment.
[0106]
As for the channel estimation value specific to each obtained channel, the average of these may be used for demodulation or the like, or only one of them may be used for demodulation or the like according to the reception situation such as QoS.
[0107]
【The invention's effect】
In the demodulation according to the present invention, the common pilot signal in the received signal received is despread, channel estimation is performed according to the despread common pilot signal, and the fixed code amplitude is set for each channel according to the estimated output. By restoring the data in the received signal according to the estimated output and the amplitude of the fixed code for each channel, the reliability of the restoration is improved compared to simply restoring the data with the estimated output. Can be made.
[0108]
In this demodulation, the demodulated symbol can be returned to the modulation base point by executing a predetermined process in data restoration.
[0109]
Thereby, for example, even when the QAM method is used as the primary modulation, the baseband signal can be reliably demodulated.
[0110]
In another demodulation according to the present invention, the common pilot signal in the received signal is despread, channel estimation is performed according to the despread common pilot signal, and fixed for each channel according to the estimation output. By obtaining the code amplitude and restoring the data in the received signal according to the estimated output and the fixed code amplitude for each channel, the restoration of the data is simply compared with the case of restoring the data by the estimated output. Certainty can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a mobile communication system according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a base station constituting the mobile communication system.
FIG. 3 is a diagram illustrating an example of QAM symbol points by a modulation unit configuring the base station.
FIG. 4 is a diagram illustrating an example of QAM symbol points by a modulation unit configuring the base station.
FIG. 5 is a block diagram showing a configuration of a mobile terminal apparatus constituting the mobile communication system.
FIG. 6 is a diagram illustrating an example of a pilot signal of each channel transmitted by the base station.
FIG. 7 is a diagram illustrating an example of a pilot signal of each channel transmitted by the base station.
FIG. 8 is a diagram illustrating an example of a pilot signal of each channel transmitted by the base station.
FIG. 9 is a diagram showing channel estimation results in a downlink system of mobile terminal devices constituting the mobile communication system.
FIG. 10 is a diagram showing the structure of a frame in a time slot in a signal of each channel.
FIG. 11 is a diagram showing the structure of a frame in a time slot in a signal of each channel.
FIG. 12 is a flowchart showing an example of reception processing in the mobile terminal apparatus.
FIG. 13 is a diagram illustrating an example of a normalized channel estimation value.
FIG. 14 is a diagram illustrating an example of an individual channel estimation value obtained by multiplying a normalized channel estimation value by a symbol amplitude value of each channel.
FIG. 15 is a diagram illustrating an example of demodulation by a RAKE receiver.
FIG. 16 is a diagram illustrating an example of demodulation by a conventional RAKE receiver.
FIG. 17 is a diagram illustrating an example of symbols after demodulation of a QPSK modulated wave by a conventional RAKE receiver.
FIG. 18 is a diagram illustrating an example of symbols after demodulation of a QAM modulated wave by a conventional RAKE receiver.
FIG. 19 is a diagram illustrating an example of demodulation for returning a demodulated symbol to a modulation base point;
FIG. 20 is a diagram illustrating an example of demodulation by a RAKE receiver.
FIG. 21 is a diagram illustrating an example of demodulation by the JD method.
FIG. 22 is a diagram illustrating an example of demodulation by the SUD method.
FIG. 23 is a flowchart showing an example of reception processing in the mobile terminal apparatus.
FIG. 24 is a diagram illustrating an example of a Euclidean distance obtained in the reception process.
FIG. 25 is a diagram illustrating an example of a pilot signal transmitted from the base station to the mobile terminal apparatus in the mobile communication system according to the second embodiment of the present invention.
FIG. 26 is a diagram for explaining a reception procedure according to a conventional JD method.
FIG. 27 is a diagram for explaining a reception procedure by a conventional JD method.
FIG. 28 is a diagram for explaining a reception procedure by a conventional SUD method.
FIG. 29 is a diagram for explaining a reception procedure according to a conventional SUD method.
FIG. 30 is a diagram illustrating an example of a pilot signal transmitted from a base station to a mobile terminal apparatus in a conventional mobile communication system.
[Explanation of symbols]
1 ... Wired telecommunication network
2. Communication management device
10 ... Base station
110 ... Downlink system
120 ... Uplink system
20 ... Mobile terminal device
210 ... Uplink system
220 ... Downlink system

Claims (4)

Receiving means for receiving a dedicated channel signal in which a pilot signal common to at least some channels and a fixed code including a TPC bit or a TFCI bit are spread by any one of a plurality of orthogonal spreading code sequences ;
Despreading means for despreading the common pilot signal in the received signal received by the receiving unit,
A common channel estimating means said despreading means have line channel estimation according to despread the common pilot signal, calculates the common channel estimates,
At a timing corresponding to the maximum peak of the common channel estimates, despreads the TPC bit or TFCI bits, determine the amplitude of the TPC bit or TFCI bits, you calculate the individual channel estimation value of the individual channel signal Amplitude detection means;
A demodulating device comprising: a restoring unit that restores data in the dedicated channel signal received by the receiving unit using the dedicated channel estimation value . Wherein in response to the TPC bit or the amplitude of the TFCI bits detected by the amplitude detection means, the demodulation device according to claim 1, characterized in that it comprises a reception state detecting means for determining the reception state by the reception means. A receiving step of receiving a dedicated channel signal in which a pilot signal common to at least some channels and a fixed code including a TPC bit or a TFCI bit are spread by any one of a plurality of orthogonal spreading code sequences ;
A despreading step of despreading the common pilot signal in the received received signal;
There line channel estimation according to the common pilot signal the despread common channel estimating step of calculating a common channel estimate,
At a timing corresponding to the maximum peak of the common channel estimates, despreads the TPC bit or TFCI bits, determine the amplitude of the TPC bit or TFCI bits, you calculate the individual channel estimation value of the individual channel signal An amplitude detection step;
A demodulation method comprising: a restoration step of restoring data in the received dedicated channel signal using the dedicated channel estimation value . Receiving means for receiving a dedicated channel signal in which a pilot signal common to at least some channels and a fixed code including a TPC bit or a TFCI bit are spread by any one of a plurality of orthogonal spreading code sequences ;
Despreading means for despreading the common pilot signal in the received signal received by the receiving unit,
A common channel estimating means said despreading means have line channel estimation according to despread the common pilot signal, calculates the common channel estimates,
At a timing corresponding to the maximum peak of the common channel estimates, despreads the TPC bit or TFCI bits, determine the amplitude of the TPC bit or TFCI bits, you calculate the individual channel estimation value of the individual channel signal Amplitude detection means;
A communication apparatus comprising: a restoring unit that restores data in the dedicated channel signal received by the receiving unit using the dedicated channel estimation value .

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