JP2004187270A - Cdma receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize circuit scale of a function part for removing multiple wave interference, to reduce power consumption and to shorten an arithmetic settlement time in a CDMA receiver for removing an influence of interference with present symbol data in a delay wave caused by multiple wave (multi-path). <P>SOLUTION: In the CDMA receiver of a single carrier system (a) or a multicarrier system (b), a received signal from an antenna is down-converted by a frequency converting part 6-1, a baseband signal is extracted through a low-pass filter 6-2, a despreading code is multiplied by a multiplier 6-3, and the signal is demodulated through an integrator 6-4. Delayed distributed waves are composed by a Rake composing part 6-5, the received signal after Rake composition is passed through a transversal filter 1-1, multiple waves except a desired wave of a receiving target are removed, and the data of the output are judged by a judgement part 6-6 and outputted. A tap coefficient of the transversal filter 101 is calculated by solving a decision theoretic operation expression. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a CDMA receiver that eliminates the influence of interference of a delayed wave caused by a multiplex wave (multipath) with its own symbol data. The third generation mobile communication system employs two types of direct sequence code division multiple access (DS-CDMA), one of which is 384 kbs when moving, and which is stationary. It is a system that can sometimes transmit data at 2 Mbps.

  Also in the fourth generation mobile communication system, the DS-CDMA system is a candidate for an effective access system, and realization of higher-speed data transmission is expected. Although the W-CDMA system is a transmission system using a single carrier, a multi-carrier DS-CDMA system using a plurality of carriers is regarded as a promising transmission system candidate as a next-generation system.

  The propagation path of the mobile communication is not necessarily a propagation path that can directly see through the base station, and is often a multiplex wave propagation path through which some reflected waves arrive. Even in the CDMA system which is considered to be resistant to interference, when high-speed data transmission is performed, the spreading factor becomes small, so that interference due to this multiplex wave cannot be ignored, and the quality of the received signal deteriorates.

  The present invention relates to a CDMA receiver that is suitably applied to a mobile communication device that performs high-speed data transmission in which the influence of interference caused by multiplex waves cannot be ignored, and that can eliminate the influence of interference caused by multiplex waves.

FIG. 6 shows a configuration of a conventional CDMA transmitter. FIG. 1A shows the configuration of a single-carrier CDMA transmitter, and FIG. 1B shows the configuration of a multi-carrier CDMA transmitter. The single carrier CDMA transmitter maps the transmission data (Source) to a predetermined modulation method by the mapping unit 6-1 and multiplies the transmission data by a spreading code, as shown in FIG. The signal is multiplied and spread by the unit 6-2, the spread signal is passed through a low-pass filter 6-3, and the frequency converter 6-4 carries the signal by carrying it on one carrier (e ^jwt ).

The multi-carrier CDMA transmitter converts the transmission data (Source) into, for example, the same number of parallel data as the number of carriers by a serial / parallel converter (S / P Converter) 6-5 as shown in FIG. The transmission data is mapped to a predetermined transmission frame corresponding to each carrier by the mapping unit 6-1. The transmission data corresponding to each carrier is multiplied by a spreading code by a multiplier 6-2 and spread. The spread signals are each passed through a low-pass filter 6-3, and are carried by a plurality of carriers (e ^{jw1t to} e ^jwmt ) by each frequency converter 6-4. Transmission signals of the plurality of carriers are combined by a combining unit 6-6. And send.

FIG. 7 shows a configuration of a conventional CDMA receiver. FIG. 1A shows the configuration of a single-carrier CDMA receiver, and FIG. 2B shows the configuration of a multi-carrier CDMA receiver. The single-carrier CDMA receiver ^performs down-conversion by multiplying the received signal from the antenna by the frequency signal (e ^jwt ) of the carrier by the frequency converter 7-1 as shown in FIG. 2 to extract the baseband signal.

  The baseband signal is multiplied by a despreading code by a multiplier 7-3, demodulated through an integrator 7-4, and rake-combined by a rake-combining receiving unit 7-5. The determination unit 7-6 performs data determination on the received data after the rake combination, and outputs the determination data. The rake combining receiver 7-5 combines the signal powers of the delay-dispersed received waves coming from a plurality of propagation paths into one.

The multicarrier CDMA receiver multiplies the received signal from the antenna by the frequency signals (e ^{jw1t to} e ^jwmt ) of each carrier by a plurality of frequency converters 7-1 as shown in FIG. The signal is converted, and a baseband signal is extracted through a low-pass filter 7-2 for each carrier.

  Each baseband signal is multiplied by a despreading code in a multiplier 7-3, demodulated through an integrator 7-4, and then rake-combined by a rake-combination receiving unit 7-5. Is performed in the determination unit 7-6 on each of the received data after the rake synthesis, and the parallel data of the determination data is converted into a parallel / serial converter (P / S Converter) 7-7. To convert the data into serial data and output.

FIG. 8 shows a configuration of a rake combining receiving unit. (A) of the figure shows a pilot detecting unit, and (b) of the figure shows a configuration of a rake combining receiving unit that performs rake combining using channel estimation values obtained from the pilot detecting unit. I have. Pilot detection section shown in the diagram (a) the received signal V _R, and input to a plurality of delay elements 8-1 for delay time in cascaded T _c, pilot symbol in the output signal of each delay element 8-1 multiplied by the multiplier 8-2 despreading code (pilot) of, and integrated by the integrator 8-3 demodulates pilot symbols to obtain channel estimates C ₀ ~C _L-1. It is to be noted that the delay element 8-1 gives a delay _Tc of one chip of the spread code and that the total number of assumed delay waves is L at the maximum, L-1 delay elements 8-1 and a multiplier 8-2 And L integrators 8-3 are provided.

Lake (Rake) Synthesis receiver of FIG. (B) the received signals V _R, similarly input to a plurality of delay elements 8-1 cascaded delay time T _c, the output of each delay element 8-1 The signal is multiplied by a despreading code of symbol data by a multiplier 8-2, integrated by an integrator 8-3 to demodulate transmission data, and the demodulated signal is added to the complex conjugate C of the above-described channel estimation value. ^After multiplying ^* _{0 to} C ^* _L-1 by the multiplier 8-4 to perform channel compensation on the propagation path, the combining unit 8-5 performs maximum ratio combining, and the determining unit 8-6 determines data. , And outputs the determination data.

In the DS-CDMA receiver for performing rake combining reception shown in FIGS. 7 and 8, as a conventional means for removing the influence of the interference of the delayed wave due to the multiplex wave (multipath) with the own symbol data. For example, the use of an interference canceller has been proposed as disclosed in the following Patent Document 1 or the like. However, the multi-wave interference canceller has a considerably large circuit scale in consideration of the current degree of integration of an LSI. Therefore, it is difficult to apply the method to moving objects and the like. In addition to the proposal of a multi-wave interference canceller having a large circuit scale, an interference canceller using a Viterbi equalizer which requires a large amount of computation and a large circuit scale has been proposed.
Japanese Patent No. 3024750

  The present invention is intended to improve the reception quality by eliminating interference caused by multiplex waves for high-speed transmission of wideband data in which the influence of frequency selective fading caused by interference of multiplex waves cannot be ignored. It is an object of the present invention to provide a CDMA receiver having a small circuit scale and power consumption of a functional unit for removing wave interference and having a short operation convergence time.

  According to the CDMA receiver of the present invention, (1) in a CDMA receiver for despreading a code division spread signal, performing rake combining and receiving and demodulating the rake combined signal, a delay element and a multiplier are provided after the rake combining and receiving section. And a transversal filter comprising an adder and an adder. A coefficient operation for calculating, as a tap coefficient of the transversal filter, a tap coefficient capable of obtaining an output obtained by removing a multiplex wave other than a desired wave to be received from the transversal filter. And a transversal filter, wherein the transversal filter multiplies each output of each delay element by a multiplier with a tap coefficient obtained from the coefficient operation unit, and adds each output of each delay element multiplied by the tap coefficient by an adder. And outputs the result.

(2) The tap coefficient of the transversal filter is calculated by using a first-order approximation equation expressed by the following equation (12).
(3) The tap coefficient of the transversal filter is calculated using an arithmetic expression that gives an exact solution according to Expression (14) described below.

  (4) The CDMA receiver is a receiver of a direct spreading code division multiple access system using a multicarrier, wherein the rake combining receiver and a transversal filter at a subsequent stage are provided for each carrier. This is provided for a received signal.

  (5) Quantizing the output of the transversal filter and feeding it back to the coefficient calculator, which updates the tap coefficient of the transversal filter using the fed back transversal filter output. Is what you do.

  According to the present invention, a transversal filter including a delay element, a multiplier, and an adder is provided at a subsequent stage of a rake combining receiver, and a tap coefficient of the transversal filter is calculated from a deterministic equation. The tap coefficient can be determined in a short time without performing repetitive calculations, and even when performing repetitive calculations by feeding back the calculation results, highly accurate multiplexed waves can be obtained with a very small number of repetitions of about 1 to 2 times. Interference cancellation can be performed.

  The circuit added in the CDMA receiver according to the present invention is only a transversal filter and a coefficient operation unit for tap coefficients thereof. The additional circuit having a small circuit size and low power consumption eliminates multi-wave interference and performs high-speed transmission. Data can be received with high accuracy.

  FIG. 1 shows the configuration of a CDMA receiver according to the present invention. FIG. 1A shows the configuration of a single-carrier CDMA receiver, and FIG. 1B shows the configuration of a multi-carrier CDMA receiver. In the CDMA receiver according to the present invention, a transversal filter 1-1 is arranged at a stage subsequent to a rake combining receiver 7-5 in the conventional CDMA receiver shown in FIG. , A multiplexed wave (delayed wave) other than the desired wave to be received is removed, and the influence of the multiplexed wave on its own symbol data is removed.

  The configuration of the CDMA receiver according to the present invention is the same as the configuration of the conventional CDMA receiver shown in FIG. 7 except that the transversal filter 1-1 is arranged at the subsequent stage of the rake combining receiver 7-5. Therefore, the same components are denoted by the same reference numerals, and duplicate description will be omitted.

  Hereinafter, the transversal filter 1-1 of the CDMA receiver according to the present invention will be described mainly for a multi-carrier system. The single carrier system corresponds to the case where the carrier number m in the multicarrier system is only 1.

  The multi-carrier scheme is used to reduce the influence of frequency selective fading, etc. The filter in the multi-carrier CDMA transceiver is a root Nyquist, and the frequency of each carrier does not overlap. That is, the carrier interval is set to Δω = 2π (1 + α) / T. Here, α is the roll-off rate, and T is the information bit width. Therefore, on the receiving side, only one carrier component is extracted by the receiving filter.

  In the calculation of the tap coefficient of the transversal filter 1-1 in the present invention, it is assumed that the channel estimation value and the spreading code of the propagation path are known, and the transversal filter 1-1 is optimized so as to optimize the channel impulse response of the transmission path. Set the coefficient of.

  Further, when trying to extract the signal of the user 1, the operation of multiplying the signal of the user 1 by the channel estimation value and the interference from the user 2 are multiplied by an independent Gaussian variable. The product of the variables has a Lorenthenian distribution. Although the sum of independent Lorentzian distributions approaches a Gaussian distribution, even when the diffusion ratio is as small as 4, it may be approximated to a Gaussian distribution if about two users communicate simultaneously. Therefore, the voice user's interference can be assumed to be additive white Gaussian noise (AWGN).

Here, the signal flow of the transmission signal will be described. The output signal v _S (t) of the CDMA transmitter is expressed as in equation (1).

Here, a _mn is the n-th transmission data of the m-th carrier, and b _mni is the i-th spreading code of the n-th transmission data of the m-th carrier. M is the total number of carriers, and N is the diffusion ratio. F _s (t) is the impulse response of the transmission filter.

The output signal v _S (t) of the transmitter undergoes Rayleigh fading in the propagation path, and the signal v ₂ (t) input to the receiver is represented by the following equation (2).

Here, z _ls = x _ls + ji _ls represents a channel estimation value, the first subscript 1 indicates a user number, and the next subscript s indicates a delay wave number. Note that x _ls and y _ls are independent Gaussian variables, and their envelopes have a Rayleigh distribution, and the phase is uniformly random. That is, a channel that receives Rayleigh fading has a two-dimensional Gaussian distribution obtained by reflecting radio waves from many obstacles and superimposing them. This is one manifestation of the central limit theorem. W ₁ ′ (t) in equation (2) is thermal noise. This includes voice user interference.

Next, the signal flow of the received signal will be described. The multi-carrier CDMA receiver extracts only the components of each carrier using a reception filter. The m-th carrier component v _3m (t) of the received signal is represented by the following equation (3).

Assuming that the channel estimation in the rake combiner / receiver 7-5 is correct, the estimated value of the channel subjected to Rayleigh fading is multiplied by each carrier component v _3m (t) of the received signal, and is applied to each finger circuit. A rake synthesized output v _4m (nT _b ) obtained by despreading and synthesizing the output of each finger circuit is represented by the following equation (4).

However, in the equation (4), v _Imn and v _Qmn are an I channel component and a Q channel component, respectively, and are represented by the equations (5) and (6), respectively. In equations (5) and (6), the superscript ^{(i) of} a ⁽ⁱ⁾ _{m, n + p} indicates that (1) is the data of the I-channel component and (2) is the data of the Q-channel component. Represents. This notation applies to the spreading code b _mni as well. In other words, a subscript (1) added to a _mni and b _mni indicates an I channel component, and a subscript (2) indicates a Q channel component.

Further, the first n of the subscript of the coefficient X such as X ⁽¹¹¹⁾ _np in the equation (5) means that the n-th data of the data sequence is taken out as a desired signal, and the next subscript of p Indicates that the coefficient X ⁽¹¹¹⁾ _np is a coefficient for data at a point shifted by p data from the nth desired signal data.

The first superscript of the coefficient X such as X ⁽¹¹¹⁾ _np indicates whether it is the real part or the imaginary part of the parameter κ _r defined by equation (8), and 1 is the parameter κ _r Represents the real part Re (κ _r ) of the parameter κ _{r and} the imaginary part Im (κ _r ) of the parameter κ _r , and the second superscript indicates whether the spreading code used on the transmission side is that of the I channel. It indicates whether it is for the Q channel, and the third suffix indicates whether the despread code on the receiving side is for the I channel or the Q channel. 1 represents an I channel and 2 represents a Q channel.

The coefficient X ^(ijk) _np is represented by the following equation (7).

Note that W _Imn and W _Qmn in the equations (5) and (6) are thermal noises, and are respectively given by the following equation (9).

Next, the improvement of the channel impulse response by the transversal filter 1-1 will be described. The outputs v _Imn and v _Qmn of the rake combiner / receiver are added to the transversal filter 1-1 to improve the impulse response of the channel.

Tap coefficients for the I-channel and the Q-channel of the transversal filter 1-1 are distinguished by adding superscripts (I) and (Q) like α ^(I) and β ^(Q) , respectively. The outputs v _I and v _Q of the transversal filter 1-1 are represented by the following equation (10).

Here, the tap coefficient α _k is a coefficient for improving the impulse response of the channel, and the tap coefficient β _k is a coefficient for removing interference between the I channel and the Q channel. Here, the number of taps is 2K + 1, and K is a numerical value equal to or larger than the value on the right side of Expression (11). The subscripts of the tap coefficients α _k and β _k represent tap numbers. The right side of the equation (11) means an integer not exceeding (L-1) / N.

The tap coefficients α _k and β _k are calculated by substituting v _Imn and v _Qmn of equations (5) and (6) into equation (10). By the way, X ^(ijk) _np is maximum when p = 0, and has the largest value as compared with other cases. Therefore, the first-order approximation of the tap coefficient can be expressed by the following equation (12).

The channel impulse response is also improved by the transversal filter 1-1 using the first-order approximation of the tap coefficient. However, by calculating an exact solution and using an accurate tap coefficient, the improvement effect can be optimized. By substituting v _Imn and v _Qmn of Expressions (5) and (6) into Expression (10) and _rearranging the data a ⁽ⁱ⁾ _mn , the following Expression (13) is derived.

In order to output from the transversal filter 1-1 an ideal channel impulse response for outputting only a desired wave and removing a delayed wave within the tap range of the transversal filter 1-1, the following expression (14) is satisfied. What is necessary is just a tap coefficient.

In the above equation (14), δ _s0 is a Kronecker delta that becomes 1 when s = 0 and becomes 0 when s ≠ 0. s takes 2K + 1 values from -K to K. Each tap coefficient alpha _k by solving the simultaneous equations of formula (14), by calculating the beta _k, the tap coefficients to best channel impulse response alpha _k, can be obtained beta _k.

By solving a deterministic equation in which an arithmetic expression is determined in this way, unlike the convergence method such as the least squares error calculation method (MMSE), the tap coefficients α _k and β _k can be shortened in a short time without performing repetitive calculation. Can be determined, and by passing through a transversal filter using the tap coefficients α _k and β _k , the bit error rate of the received data can be significantly reduced.

FIG. 2 shows a configuration of a rake combining receiver and a transversal filter according to the present invention. The rake combining and receiving section includes a delay element 8-1, a multiplier 8-2 for multiplying a despreading code, an integrator 8-3, and complex conjugates C ^* _{0 to} C ^* _{L- of} channel estimation values. _It is composed of a multiplier 8-4 for multiplying by ₁ and a synthesizing unit 8-5, and these have the same configuration as that shown in FIG. 8B.

The transversal filter adds the output of the rake combining receiver to the plurality of delay elements 2-1 connected in cascade, and adds the tap calculated by the coefficient calculator 2-4 to the output of each delay element 2-1. multiplied by the coefficient gamma _-p to? _p by the multiplier 2-2, and outputs the tap output multiplied by the tap coefficient gamma _-p to? _p are added by the adder 2-3. Incidentally, For ease of illustration, but are not shown I channel component and the Q channel component in FIG. 2, are denoted as So tap coefficient alpha _k, collectively β _k γ _-p ~γ _p .

  FIG. 3 shows the configuration of an embodiment for feeding back the output of a transversal filter according to the present invention. In this embodiment, the output of the adder 2-3 of the transversal filter is quantized by the quantizer 3-1 to, for example, about eight levels, and the quantized output is fed back to the coefficient calculation unit 3-2, and the coefficient is calculated. The operation unit 3-2 updates the tap coefficient using the quantized output.

The output of the transversal filter is an accurate estimate of the transmitted data a ⁽ⁱ⁾ _mn . Therefore, the output of the transversal filter is soft-decisioned at about eight levels, stored in a buffer memory, used as an output of a rake combining receiver, and by changing tap coefficients, the own symbol by the delayed wave is obtained. Can be more accurately removed, and the bit error rate can be further improved.

  Further, by repeatedly performing the updating process of the tap coefficient, it is possible to more accurately remove the interference. Further, by using the soft decision output data of about eight levels of the transversal filter for the data decision of the subsequent decision section, the bit error rate can be reduced and the reception quality can be improved.

  In this case, as the initial coefficient of the tap coefficient, the tap coefficient calculated using the above equation (12) or (14) can be set. By setting it as an initial coefficient and then updating it by a feedback system, it becomes possible to simplify the arithmetic processing unit and calculate an accurate tap coefficient.

  On the other hand, when the tap coefficient calculated using the equation that gives the exact solution of equation (14) is set as the initial coefficient, the amount of calculation increases, but the tap coefficient is uniquely determined, and the convergence time is basically no. That is when all the previous assumptions are correct. However, there is a possibility that an error may be mixed in the channel estimation value. In such a case, by updating the taps by the feedback system, a more accurate tap coefficient can be obtained.

  Also, a coefficient calculation unit for a tap coefficient of a transversal filter in a multi-carrier CDMA receiver is provided only for a carrier close to the center frequency of the multi-carrier, and the tap coefficients calculated by the coefficient calculation unit are used for all carriers. , The circuit scale and the amount of calculation can be simplified.

  4 and 5 show an example of how the bit error rate of the CDMA receiver according to the present invention is improved. FIG. 4 shows a case in which the first-order approximation equation (12) is used, and FIG. 5 shows an improvement in the case of using the equation (14) for calculating an exact solution. In FIG. 4, the dotted line shows the bit error rate of a CDMA receiver not using a transversal filter, and the solid line shows the bit error rate of a CDMA receiver using a transversal filter.

The graph of FIG. 4 is measured under the following conditions. (1) Maximum bit rate: 20 Mbps, (2) Bandwidth: 100 MHz, (3) Number of carriers m: 16, (4) Delay dispersion range: 1 μs, (5) Processing gain (spreading factor) N: 4, (6) ) Number of users in cell: one user of 20 Mbps and several users of 64 kbps, (7) tap coefficient calculation condition: first-order approximation, (8) multipath interval: T _c , (9) multipath level: equal level

The graph shown in FIG. 4 uses tap coefficients calculated by first-order approximation (roughest approximation). For example, for a bit error rate of 10 ⁻² , a signal-to-noise ratio is obtained by using a transversal filter. It can be seen that a gain of about 5 dB can be obtained in (SNR).

  5A shows a graph of the bit error rate of the CDMA receiver not using the transversal filter, and FIG. 5B shows a graph of the bit error rate of the CDMA receiver using the transversal filter. . Comparing (a) and (b) in the figure, it can be seen that the bit error rate is significantly improved by using the transversal filter.

The graph of FIG. 5 is measured under the following conditions. (1) Maximum bit rate: 20 Mbps, (2) Bandwidth: 100 MHz, (3) Number of carriers m: 4, 8, 16, (4) Delay dispersion range: 1 μs, (5) Processing gain (spreading factor) N: 4. (6) Number of users in a cell: one user of 20 Mbps and several users of 64 kbps, (7) tap coefficient calculation condition ((b) in the figure): exact solution, (8) multipath interval: T _c , (9) Multi-pass level: Equal level

  Hereinafter, the features of the present invention will be described as additional notes.

  (Supplementary Note 1) In a CDMA receiver for despreading a code division spread signal and performing rake synthesis reception and demodulation, a transformer including a delay element, a multiplier, and an adder is provided downstream of the rake synthesis reception unit. A transversal filter, wherein the transversal filter is provided with a coefficient operation unit that calculates a tap coefficient as an tap coefficient of the transversal filter to obtain an output obtained by removing a multiplex wave other than a desired wave to be received from the transversal filter; The filter has a configuration in which each output of each delay element is multiplied by a multiplier with a tap coefficient obtained from the coefficient calculation unit, and each output of each delay element multiplied by the tap coefficient is added and output by an adder. CDMA receiver characterized by the above-mentioned.

  (Supplementary note 2) The CDMA receiver according to supplementary note 1, wherein a tap coefficient of the transversal filter is calculated by the above-described equation (12).

  (Supplementary note 3) The CDMA receiver according to supplementary note 1, wherein the tap coefficient of the transversal filter is calculated by the above-described equation (14).

  (Supplementary Note 4) The CDMA receiver is a receiver of a direct spreading code division multiple access system using multicarriers, and receives the rake combining receiver and a transversal filter at a subsequent stage for each carrier. 4. The CDMA receiver according to claim 1, wherein the CDMA receiver is provided for a signal.

  (Supplementary Note 5) The output of the transversal filter is quantized and fed back to the coefficient operation unit, and the coefficient operation unit updates the tap coefficient of the transversal filter using the fed back transversal filter output. The CDMA receiver according to any one of supplementary notes 1 to 4, wherein:

  (Supplementary note 6) The CDMA receiver according to Supplementary note 5, wherein a tap coefficient calculated by using the above equation (12) is used as an initial coefficient of the tap coefficient of the transversal filter.

  (Supplementary note 7) The CDMA receiver according to Supplementary note 5, wherein a tap coefficient calculated by using the above equation (14) is used as an initial coefficient of the tap coefficient of the transversal filter.

  (Supplementary note 8) The CDMA receiver according to any one of Supplementary notes 5 to 7, wherein a tap coefficient of the transversal filter is repeatedly updated using the fed back transversal filter output.

  (Supplementary Note 9) The coefficient calculation unit is provided only for a carrier close to the center frequency of the multicarrier, and the tap coefficients calculated by the coefficient calculation unit are used as the tap coefficients of the transversal filter for all the carriers. The CDMA receiver according to claim 4, characterized in that:

It is a figure showing the composition of the CDMA receiver of the present invention. FIG. 2 is a diagram illustrating a configuration of a rake combining receiver and a transversal filter according to the present invention. FIG. 5 is a diagram illustrating an embodiment of feeding back the output of a transversal filter according to the present invention. It is a figure which shows an example of the aspect of the improvement of the bit error rate of the CDMA receiver of this invention (when a 1st-order approximation solution is used). It is a figure which shows an example of the aspect of the improvement of the bit error rate of the CDMA receiver of this invention (when an exact solution is used). FIG. 3 is a diagram illustrating a configuration of a CDMA transmitter. FIG. 11 is a diagram illustrating a configuration of a conventional CDMA receiver. FIG. 3 is a diagram illustrating a configuration of a rake combining receiving unit.

Explanation of reference numerals

1-1 Transversal filter 7-1 Frequency conversion unit 7-2 Low-pass filter 7-3 Multiplier 7-4 Integrator 7-5 Rake (Rake) synthesis reception unit 7-6 Judgment unit 7-7 Parallel / serial converter (P / S Converter)

Claims (5)

In a CDMA receiver for despreading a code division spread signal and then performing Rake combining reception and demodulation,
A transversal filter including a delay element, a multiplier, and an adder is arranged at a stage subsequent to the rake combining and receiving unit.
As a tap coefficient of the transversal filter, a coefficient operation unit that calculates a tap coefficient from which an output obtained by removing a multiplex wave other than a desired wave to be received from the transversal filter is obtained,
The transversal filter multiplies each output of each delay element by a multiplier with a tap coefficient obtained from the coefficient calculation unit, and adds and outputs each output of each delay element multiplied by the tap coefficient by an adder. A CDMA receiver having a configuration. The CDMA receiver according to claim 1, wherein a tap coefficient of the transversal filter is calculated by the following equation (12).
Here, it is assumed that the output of the rake combining receiving unit is represented by the following equations (4), (5) and (6). In equations (5) and (6), each coefficient X is represented by equation (7). ) And (8), the thermal noise W is represented by equation (9), and the output of the transversal filter by the tap coefficients α _k and β _k (the subscript is the tap number and the number of taps is 2K + 1) is represented by equation (10). ), A _mn is transmission data, N is a spreading ratio, z _ls is a channel estimation value, the first suffix l is a user number, the next suffix s is a delay wave number, and In the term, the suffix I represents an I channel, the suffix Q represents a signal of a Q channel, m represents a carrier number, n represents a data sequence number, L represents a maximum number of assumed delay waves, and a coefficient X Is the data sequence number of the desired signal to be received. And the next lower suffix represents the number of data shifted from the data position of the desired reception wave, and the first upper suffix of the coefficient X is the real part of the parameter κ _r defined by equation (8). 1 indicates the real part, 2 indicates the imaginary part, and the second superscript indicates that the spreading code used on the transmitting side is of the I channel or of the Q channel. And the third superscript indicates whether the despreading code on the receiving side is for the I channel or the Q channel, and 1 indicates that the code is for the I channel and 2 indicates that the code is for the Q channel. .

The CDMA receiver according to claim 1, wherein a tap coefficient of the transversal filter is calculated by the following equation (14).
Here, it is assumed that the output of the rake combining receiving unit is represented by the following equations (4), (5) and (6). In equations (5) and (6), each coefficient X is represented by equation (7). ) And (8), the thermal noise W is represented by equation (9), and the output of the transversal filter by each tap coefficient α _k , β _k (the subscript is the tap number and the number of taps is 2K + 1) is represented by equation (10). ) And (13), a _mn is the transmission data, N is the spreading factor, z _ls is the channel estimate, the first suffix l is the user number, the next suffix s is the number of the delayed wave, In each equation, the suffix I represents an I channel signal, the suffix Q represents a Q channel signal, m represents a carrier number, n represents a data sequence number, and L represents the maximum number of assumed delayed waves. And the first subscript of the coefficient X is the data of the desired signal The sequence number and the following subscript represent the number of data shifted from the data position of the desired reception wave, and the first superscript of the coefficient X is the real part of the parameter κ _r defined by equation (8). And the imaginary part, 1 is the real part, 2 is the imaginary part, and the second suffix is the spreading code used on the transmitting side for the I channel or the Q channel. And the third suffix indicates whether the despreading code on the receiving side is for the I channel or the Q channel, where 1 is the I channel and 2 is the Q channel. _Where δ _s0 is 1 when s = 0 and 0 when s ≠ 0.

  The CDMA receiver is a receiver of a direct spreading code division multiple access system using a multicarrier, wherein the rake combining receiving unit and a transversal filter at a subsequent stage are used for a received signal for each carrier. The CDMA receiver according to any one of claims 1 to 3, wherein the CDMA receiver is provided.   Quantizing the output of the transversal filter and feeding it back to the coefficient operation unit, wherein the coefficient operation unit updates the tap coefficient of the transversal filter using the fed back transversal filter output. The CDMA receiver according to any one of claims 1 to 4.

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