JP3718403B2 - Rake receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum communication system and a rake receiver of a broadcasting system.
[0002]
[Prior art]
The spread spectrum wireless system using the direct spreading method has many advantages in terms of realizing path diversity due to the band expansion effect, ease of code channel allocation and frequency allocation, and is currently applied to mobile communication systems and broadcasting systems. Has been made. In particular, CDM (Code Division Multiplex) that performs multiplex transmission using orthogonal codes from one transmitting station transmits different data to different code channels while adaptively changing the transmission rate and maintaining orthogonality between channels. It is used in these systems because it can.
[0003]
By the way, there is a RAKE receiver (hereinafter referred to as RAKE receiver) as a path diversity realizing method in a direct spreading radio system. This receiver despreads each multipath signal at a timing suitable for each path, and synthesizes the result by weighting with the phase and amplitude to improve the SN ratio of the received signal. Here, multipath signals other than the desired signal are suppressed in the process of despreading the desired signal. However, when the number of multipath paths is very large, or when CDM with a large number of multiplexing is performed and the power of interference components becomes large, the interference signal is not sufficiently suppressed by despreading and the performance of the RAKE receiver. Deteriorate.
[0004]
[Problems to be solved by the invention]
As described above, in the conventional RAKE receiver, when the number of multipath paths is very large or when the power of the interference component is increased by performing CDM with a large number of multiplexing, the interference signal is sufficiently spread by despreading. There is a problem that the performance of the RAKE receiver is deteriorated without being suppressed.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the RAKE receiver according to claim 1 is a spread spectrum wireless communication system that performs spread modulation by direct spreading, means for measuring a transmission line response value in each propagation path of multipath propagation, Corresponding to each propagation path, an equalization unit that suppresses interference from signals other than the desired path using the transmission line response value, and a part of the multipath component using the equalization result by the unit It comprises means for removing, means for despreading corresponding to each propagation path, and means for synthesizing the despread signals of each propagation path obtained by this means.
As a result, it is possible to prevent characteristic deterioration due to an increase in multipath interference signals in the despreading process of the RAKE receiver.
[0006]
The RAKE receiver according to the second aspect of the present invention is characterized in that a transversal filter is used as an equalization means and the weighting coefficient is used to orthogonalize an interference signal with respect to a desired signal.
[0007]
The RAKE receiver according to the third aspect of the present invention is further characterized in that a transversal filter is used as the equalizing means, and the weight coefficient is used to suppress a main interference signal with respect to a desired signal. Thereby, it is possible to reduce the load of calculating the tap coefficient while suppressing the influence of large interference and improving the reception characteristics.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
FIG. 1 shows a configuration diagram of a RAKE receiver as a first embodiment according to the present invention, and FIG. 2 shows a generalized model of a multipath propagation path. The RAKE receiver of this embodiment includes an RF front end unit 11, a transmission path response estimator 12, variable delay units 114 to 116 for compensating for multipath delay and equalization delay, and the like for each desired path. Multipliers 13 to 15, means 117 to 118 for removing the previous equalization result from the received signal, despreaders 16 to 18 for despreading the respective propagation paths, and complex weights for RAKE combining. It includes multipliers 19 to 111, an adder 112 that synthesizes the weighted despread results, and a determiner 113.
[0010]
Next, the operation of this embodiment will be described with reference to FIGS. First, it is assumed that a direct spread spectrum spread signal is received through a multipath propagation path as shown in FIG. Here, each multipath h ₁ to h N _(complex notation) is a sample value of each arbitrary chip time, the signal intensity for simplicity of explanation it is assumed that _{h1>h2>...> h N} . The RF front end 11 performs frequency conversion on the baseband signal while sampling these multipath multiplexed waves and performs sampling. The transmission path response estimation unit 12 measures the complex delay profile (multipath delay time, amplitude, phase) of the multipath propagation path using the sampled signal, and the measurement result is sent to the equalizers 13 to 15, The complex conjugate of the transmission weight (amplitude, phase) of the desired path in the delay profile is transmitted to the multipliers 19 to 111 according to the desired path. The variable delay units 114 to 115 are installed for timing adjustment for removing the signal after the previous stage equalization from the received signal, and the subtracters 117 to 118 remove the equalized signal up to the previous stage. Incidentally, when the intensity of the preceding wave h ₁ is the strongest, the variable delay unit 114 for that path is not required. Here, it is assumed that the equalizer 13 and the despreader 16 are reception systems for the signal of the path h ₁ . In this h ₁ reception system, since the multipaths h _{2 to} h _N become interference signals, the equalizer 13 suppresses the signals h _{2 to} h _N. On the other hand, in the reception system of path h ₂ (assuming that the equalizer 14 and the despreader 17 are used), h ₁ and h _{3 to} h _N are interference signals, but the subtractor 117 performs a signal ( Since the received component for h ₁ is removed, the equalizer 14 performs processing so as to suppress the signals h _{3 to} h _N.
[0011]
Performs the same operation until the receiving system for the signal follows the path h _N. In this way, each receiving system equalizes the multipath elementary waves and suppresses interference from other paths, and the despreaders 16 to 18 despread each of the equalized elementary wave signals. To output. The despreading results obtained in this way are weighted by the complex conjugate of the amplitude and phase of each path using the multipliers 19 to 111 and are in-phase synthesized by the adder 112. The determiner 113 performs bit determination on the combined symbol based on the information modulation method. By such processing, distortion of received signal quality due to multipath interference can be reduced, and communication quality can be improved.
[0012]
As another embodiment of the present invention, there is a RAKE receiver for a signal sampled at a fractional interval of a chip clock. In the receiver of this form, after performing waveform equalization according to the impulse response of the baseband filter with an equalizer, re-sampling is performed by re-sampling at the optimum sampling point of the desired signal. By using this method, waveform equalization can be executed with high accuracy, and reception characteristics can be further improved.
[0013]
Next, an embodiment of an equalizer used in the RAKE receiver of the present invention will be described with reference to FIG. The equalizer of the present embodiment is composed of a transversal filter type equalizer, and is composed of a tap coefficient calculator 31, a tapped shift register 32, weight coefficients 33 to 36, and an adder 37. . Here, for the sake of explanation, it is assumed that the equalizer corresponds to the reception system of h ₁ .
[0014]
Received signal samples are sequentially input from the left side of the shift register 32. In order to output the received signal h ₁ as it is, the weighting coefficient 33 (w ₁ ) is assumed to be a coefficient 1. First, in order to cancel the reception signal h ₂ delayed by one chip using the reception signal h ₁ , the weight coefficient 34 (w ₂ ) is set as follows.
[0015]
w ₂ = −h ₂ / h ₁
As a result, the interference component generated in the 3-chip delay time is a component in which w ₂ acts on the path of h ₂ in addition to the original h ₃ . Therefore, the weighting factor 35 (w ₃ ) is w ₃ = − (h ₃ + w ₂ h ₂ ) / h ₁
Similarly, the calculation is made up to the weighting factor 36 (w _L ).
[0016]
As another embodiment of the present invention, there is a method of performing the operations of the weighting multipliers 19 to 111 of the RAKE receiver with tap coefficients 33 to 36. In this method, for example, for the h ₁ reception system, all the tap coefficients obtained by the tap coefficient calculator are multiplied in advance by the complex conjugate of h ₁ . Thereby, in each receiving system, the phase of the output of the despreader is adjusted in phase, and weighting is performed according to the signal-to-noise ratio of the signal.
[0017]
As another embodiment of the present invention, there is a method of limiting interference waves to be suppressed by an equalizer to main interference sources. With this method, the load on the equalizer and the tap coefficient calculator can be reduced, and the power consumption and circuit scale of the receiver can be reduced.
[0018]
Next, another embodiment of the RAKE receiver of the present invention will be described with reference to FIG. The RAKE receiver according to the present embodiment measures a plurality of antennas (two antennas are shown in the figure), RF units 41 and 42 corresponding to each antenna, and multipath transmission path response for each antenna. Transmission path response measuring units 43 and 47, variable delay units 427 to 432 for compensating for multipath delay and equalization delay, and equalizers 44 to 46 for performing multipath waveform equalization on each desired wave 48 to 410, means 433 to 436 for removing the equalization result of the previous stage from the received signal, despreaders 411 to 413 and 414 to 416 for despreading the received signal, and multipath phase / amplitude weighting. Multipliers 417 to 419 and 420 to 422, adders 423 to 425 for performing RAKE combining of received signals, and a determiner 426 are included.
[0019]
The operation of this embodiment will be described with reference to FIGS. First, it is assumed that a direct spread spectrum spread signal is received through a multipath propagation path as shown in FIG. Here, it is assumed that the multipaths h _{1 to} h _N are the same as those described above. In the RF front ends 41 and 42, the received signals received by the individual antennas are subjected to frequency conversion to a baseband signal and sampled while the multipath multiplexed wave as shown in FIG. 2 is multiplexed. The transmission path response estimation units 42 and 47 measure the complex delay profile (multipath delay time, amplitude, phase) of the multipath propagation path using the signals sampled with respect to the respective antennas, and the measurement result is the equalizer 44. The complex conjugate of the transmission weight (amplitude, phase) of the desired path in the delay profile is transmitted to the multipliers 417 to 419 and 420 to 422 according to the desired path. Here, it is assumed that the equalizer 44 and the despreader 411 are reception systems for the signal of the path h ₁ received by the antenna on one side. The variable delay units 427 to 432 are installed for timing adjustment for removing the signal after the previous equalization from the received signal, and the subtracters 433 to 436 remove the equalized signals up to the previous stage. Incidentally, when the intensity of the preceding wave _{h 1} is the strongest, the variable delay device 427,430 for the path is not required. In the h ₁ reception system, since the multipaths h _{2 to} h _N become interference signals, the equalizer 44 suppresses the signals h _{2 to} h _N. On the other hand, in the reception system of path h ₂ (assuming the equalizer 45, the despreader 412 and the equalizer 49, and the despreader 415), h ₁ and h _{3 to} h _N are interference signals, but the subtractor Since the pre-equalized signal (received component for h ₁ ) is removed by 433 (435), the equalizer 45 (49) performs processing so as to suppress the signals h _{3 to} h _N. Performs the same operation until the receiving system for the signal follows the path h _N. In this way, each receiving system equalizes the multipath wave, suppresses interference from other paths, and the despreaders 411 to 413 and 414 to 416 convert the equalized wave signals to the equalized wave signals. On the other hand, despread processing is performed and output. The despreading results obtained in this way are weighted by the complex conjugate of the amplitude and phase of each path using the multipliers 417 to 419 and 420 to 422, and the in-phase synthesis is performed by the adders 423, 424 and 425. Is done. The determiner 426 performs bit determination on the combined symbol based on the information modulation method. With the above configuration, RAKE reception can be performed while reducing the influence of interference due to multipath, and the quality of the received signal can be improved by performing antenna diversity.
[0020]
A plurality of the above embodiments can be combined.
[0021]
【The invention's effect】
As described above, according to the RAKE receiver of the first embodiment of the present invention, each RAKE finger has an equalizer and a post-equalization signal removing means, so that the received signal quality is distorted by multipath interference. Communication quality can be improved. According to the equalizer in the RAKE receiver of the second embodiment of the present invention, the interference wave to be suppressed is limited to the main interference sources, the load on the equalizer and the tap coefficient calculator is reduced, and the receiver Power consumption and circuit scale can be reduced. Further, according to the RAKE receiver of the third embodiment of the present invention, it is possible to perform RAKE reception while reducing the influence of interference due to multipath, and it is possible to improve the quality of the received signal by performing antenna diversity. Become.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a configuration of a RAKE receiver according to the present invention.
FIG. 2 is a diagram showing an example of a delay profile of a multipath propagation path.
FIG. 3 is a diagram showing an embodiment of an equalizer in the RAKE receiver of the present invention.
FIG. 4 is a diagram showing another embodiment of the RAKE receiver of the present invention.
[Explanation of symbols]
11, 41, 42... RF front end 12, 43, 47... Transmission path response estimator 13, 14, 15, 30, 44, 45, 46, 48, 49, 410 ... Equalizer 16, 17, 18, 411 , 412, 413, 414, 415, 416 ... despreaders 19, 110, 111, 417, 418, 419, 420, 421, 422 ... multipliers 112, 37, 423, 424, 425, 119, 437, 438 ... Adders 113, 426... Determiners 114, 115, 116, 427, 428, 429, 430, 431, 432, variable delay devices 117, 118, 433, 434, 435, 436, subtractor 31, tap coefficient calculator 33 , 34, 35, 36 ... weighting factors

Claims (3)

In a spread spectrum wireless communication system that performs spread modulation by direct spreading,
Means for measuring a transmission line response value in each propagation path of multipath propagation;
Corresponding to each propagation path, equalization means for suppressing interference from signals other than the desired path using the transmission line response value ;
Means for removing a part of the multipath component using an equalization result by the means;
Means for despreading corresponding to each propagation path;
Means for synthesizing the despread signals of the respective propagation paths obtained by this means.   2. The receiver according to claim 1, wherein the equalizing means has a transversal filter format, and tap coefficients thereof are calculated from propagation coefficients of multipaths so as to orthogonalize a desired wave. Lake receiver.   2. The rake receiver according to claim 1, wherein the equalizing means suppresses only the main interference signal.

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