JP3452253B2 - CDMA receiver using adaptive array - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDMA receiving apparatus using an adaptive array, and more particularly to a CDMA receiving apparatus which adds adaptive array characteristics to a fixed directional CDMA receiving apparatus.

[0002]

2. Description of the Related Art By arranging a plurality of antenna elements in an array for each half-wavelength of a carrier frequency and independently controlling the amplitude and phase of a signal supplied from each transmitter to each antenna element, , It is possible to form a beam that strongly emits a radio wave in a specific direction, or to form a null that emits almost no radio wave in a specific direction. This array antenna can similarly control the reception directivity such as the beam direction and null direction of the antenna by connecting each antenna element to each receiver whose amplitude and phase can be controlled independently. .

This array antenna is used for CDMA (Code D
ivision Multiple Access (code division multiple access), which is used for the base station of cell-based mobile communication and uses orthogonal codes for communication with each mobile station or codes that do not correlate with each other. Even if the same frequency band is used, each communication can be independently established at the same time.
In addition, it is possible to direct a beam or direct a null toward each mobile station, further reducing the mutual interference of communication with mobile stations, and jumping the communication capacity that can be accommodated in one base station. Can be increased.

Regarding an algorithm for forming a beam toward a desired mobile station using this array-antenna or automatically directing a null toward a mobile station that causes interference, an antenna using this is an adaptive array antenna. Various algorithms have been proposed and researched and developed. For example, according to Nobuyoshi Kikuma, "Adaptive Signal Processing by Array Antenna," Science and Technology Publication (1998), the least square error method (MMSE: Minimum Mean Square Erro)
r), maximum SNR method (MSN: Maximum Signal-to-noise)
ratio), constrained output power minimization method (CMP: Constrai
ned Minimization of Power) and constant envelope signal algorithms (CMA: Constant Modulus Algorithm). The CMP includes a direction-constrained output power minimization method (DCMP: Directional-CMP) and a power inversion method (PI: Power Inversion) depending on the constraint conditions, and each has its own characteristics.

For a CDMA base station, the desired wave is not limited to a constant-envelope modulated wave, its arrival direction is undetermined, and there is no particular magnitude relationship between the power of the desired wave and the interference wave. MMSE is used. In particular, the LMS (Least Mean Square) algorithm based on the steepest descent method in MMSE is often used because an adaptive array can be realized with a simple configuration ([Reference 1] S. Tanaka,
M. Sawahashi, F. Adachi, `` Pilot Symbol-Assisted Decis
ion‐Directed Coherent Adaptive Array Diversity fo
r DS‐CDMA Mobile Radio Reverse Link 」ICICE Trans.
Fundamentals, Vol.E80-A, No.12, pp.2445-2454, 1997-1
2).

[0006] LMS Al Gore rhythm can be implemented by algorithms based on the steepest descent method for minimizing a signal a signal of each antenna element was synthesized by phase and amplitude weighting of the array, the error between the desired reference signal. Therefore,
A desired reference signal is required for beam forming and null generation by the LMS algorithm.

[0007] Here, in cell type mobile communication using CDMA, a known signal called a pilot symbol is sandwiched between data, or a communication signal is formed in parallel with the data and transmitted. The pilot symbol can be detected from the received communication signal, and the pilot symbol can be selected from a plurality of known pilot symbols and used as a reference signal. Further, the received communication signal may be demodulated based on the pilot symbol, and the demodulated signal or the signal after error correction may be used as the reference signal.

On the other hand, generally, in cell type mobile communication using CDMA, a RAKE receiver is used. FIG. 2 is a diagram showing a configuration of a RAKE receiver provided in the base station. Note that RAKE means “ku”, and is named for collecting received signal power that has been diffused, scattered, and arrived.

In FIG. 2, the fixed directional antenna 1
The signal from the mobile station received by the 1-F and the RF receiver 12-F is input to the RAKE branch 14. The RAKE branch 14 is a matched filter (MF) 1 for compressing, ie, despreading, the spread signal in time.
4-1, a channel estimator 14-2 that estimates the delay phase of the signal despread by the MF 14-1, and an MF 14-
1 for multiplying 1 and the output of the channel estimator 14-2
It is composed of 4-3. This RAKE branch 14
L sets are prepared according to the expected number of paths L (number of paths) of signals from mobile stations, and the despread and delayed phase matched outputs are combined by the combiner 15 and sent to the demodulator. And is demodulated into a signal from the mobile station.

As described above, when the RAKE receiver is used as the base station, the signal emitted from the mobile station passes through a plurality of propagation paths (paths) due to reflection from surrounding structures such as a building. Although it reaches the fixed directional antenna 11-F of the station, it is received as a superposition of signals having different delay times due to the difference in the propagation path length of each propagation path. Signals having a delay difference due to the multiple propagation paths are code-correlated, which is a unique technique of CDMA, to be separated into signals of each path, and the delay time difference is corrected and combined. In this way, fading existing in a signal from a single path is smoothed by synthesizing signals from a plurality of paths, and stable propagation can always be ensured.

Here, the adaptive array antenna and the RAKE receiver are simultaneously installed, and the adaptive array operation is performed for each path so that even signals from the same mobile station are focused on the respective paths in the arrival direction. The method of inputting these signals to the RAKE receivers after directing the beams and combining them is a CD using an adaptive array.
As an MA receiver, it is known as shown in FIG.

In FIG. 3, the antenna element 31
The signals received at -1 to 31-4 are matched filters (MF) 32-1 having codes corresponding to the respective mobile stations.
1 to 32-4, it is selected as a signal of the desired mobile station. The MFs 32-1 to 32-4 correspond to the despreading in the spread spectrum technique, and convert the wideband signal from the desired mobile station spread with the specific code into the original symbol rate (information band width).

The outputs of the MFs 32-1 to 32-4 are branched into L pieces corresponding to the number L of branches of the RAKE branch 34 at the subsequent stage, and are input to the L sets of beam formers 33.

The beam former 33 is composed of multipliers 33-11 to 33-14, a combiner 33-2, a weighting control circuit 33-3, an adder 33-4, and a multiplier 33-5 as shown in the figure. There is. Then, for the signal from each despread antenna element, the reference signal, each antenna
Based on the signal from the element and its own combined output signal,
The weighting control circuit 33-3 using MMSE weights and combines both the amplitude and the phase, beam-forms them, and inputs them to the L sets of RAKE branches 34.

In the RAKE branch 34, channel estimation is performed by the channel estimator 34-1 based on the pilot symbols contained in the received signal (eg PSA channel).
el estimator), signals corresponding to L multipaths are
The signals are weighted according to the intensity of the signal and are combined in phase by the combiner 35.

The combined signal is sent to the demodulator and also input to the temporary symbol determiner 36, and the received pattern is temporarily determined. The temporary symbol determiner 36 generates a reference signal based on the temporary determination data and known pilot symbols. This reference signal is supplied to the L sets of beam formers 33 after power distribution by the power distributor 37. Then, the beam former 33 obtains an error signal from the reference signal, the output of the channel estimator, and the output result of the beam former, and the weighting control circuit 3 using MMSE 3 is obtained.
3 is input and the directivity is sequentially updated.

In the method of FIG. 3, signals from the same mobile station are also regarded as different signals due to the delay difference based on the difference in propagation paths, and the signals of different paths interfere with each other in the L different units. It is regarded as a wave and operates to erase. That is, with respect to the arrival direction of the multipath signal, it is attempted to form directivity such that nulls are formed between the multipaths.

However, generally speaking, most of the multipaths are reflected signals from a reflector near the moving body, and therefore, when viewed from the base station, the direction of arrival of the multipath does not come from a significantly distant direction. In rare cases, the incoming waves come from almost the same direction, and even if you try to separate the desired wave and the signal (multipath signal) from different propagation paths using directivity, the separation is difficult because the angle difference is small, There was a problem that the operation became unstable.

Further, in the case of mobile communication, each path changes sequentially as the mobile moves, and the paths selected for RAKE reception (several paths with large signal power) are constantly updated. If the arrival direction is undecided each time it is updated, the adaptive array operation is initialized and started, and in actual operation, the adaptive array directivity is not always converged sufficiently, and the fixed path There was a problem that sufficient results could not be obtained unless there was.

In order to solve this problem, a plurality of paths from the same mobile station are often in substantially the same direction.
It is known to operate the adaptive array so that several paths selected in the AKE branch have the same directivity. ([Reference 2] Nakaminami, Ihara, Tanaka, Sawahashi, "Laboratory Experimental Characteristics of Adaptive Antenna Array Diversity Reception for Generating Common Path Antenna Weight for W-CDMA Uplink", IEICE Technical Report RCS2
000-46 (2000-06)).

As shown in FIG. 4, this method is configured such that a plurality of L beamformers 33 are operated by the same weighting control circuit 47 with respect to the circuit configuration of FIG. Therefore, compared to FIG. 3, a power divider is not required, a single weighting control circuit is sufficient, and other arrangements of adders and multipliers are replaced, but other points are shown in FIG. Since it is the same as that of 3, the description thereof will be omitted.

According to the method of FIG. 4, even if the path used for the RAKE receiver is changed, it is not necessary to initialize the array one by one to start the adaptive array operation, and it is possible to obtain a stable directivity in operation. There is.

[0023]

However, in the CDMA receiver using the adaptive array shown in FIGS. 3 and 4, the signal from each antenna element corresponds to the code of each mobile station. The signal after despreading through (MF) is used. Thus, despreading,
Since the processing unique to the CDMA receiver, such as RAKE reception, is intertwined with the functional circuit of the adaptive array, there is a problem that it is difficult to realize the adaptive array antenna and the CDMA receiver separately. Was there.

That is, when introducing an adaptive array antenna into a CDMA cell type mobile communication base station using a fixed directional antenna already installed as shown in FIG. 2, a despreading circuit (MF) is used. The configuration of the RAKE receiver that contains it must be changed, in fact
There was a problem that it was difficult to introduce an adaptive array antenna without replacing the main part as a base station.

Therefore, an object of the present invention is to provide a CDMA receiver using an adaptive array antenna, which is also applicable to a CDMA receiver using a fixed directional antenna.

[0026]

A CDMA receiver using an adaptive array according to claim 1 has received signals from a plurality of array antenna elements 11-1 to 11-n and input control signals. Based on e (t),
A beamformer 13 for forming a beam by combining the received signals by weighting the amplitude and the phase and combining them, and an output signal y (t) of this beamformer are input, and each has a matched filter (MF), Spread and RAKE
It outputs the output signal for receiving and
Spread code timings τ1 to τ4 in the cutt filter
A plurality of L RAKE branches 14 for outputting, and a combining means 15 for performing weighted combination of the output signals of the plurality of RAKE branches according to the signal strength and outputting the weighted RAKE branches.
The data-determined signal or the known pilot signal obtained based on the output O (t) of the synthesizing means is re- created with the corresponding code at the spread code timings τ1 to τ4 in each of the matched filters (MF). A replica generator 16 that obtains a reference signal d (t) by spreading and weighting and combining the re-spread signals, a reference signal d (t) from the replica generator, and an output signal y of the beamformer.
Subtracting means for taking the difference e (t) from (t) and supplying it as the control signal to the beamformer.

A CDMA receiver using the adaptive array according to a second aspect of the present invention is a CDMA receiver using the adaptive array according to the first aspect, wherein each re-signal when forming the reference signal e (t). The weighting ratio of the spread signal is determined based on the ratio of the output signal strengths of the plurality of L RAKE branches 14.

According to the present invention, an adaptive array
As a reference signal for determining the weighting of the antenna,
Since signals re-spread with a code corresponding to a desired mobile station delayed at the despreading timing of each RAKE branch are weighted and combined and used, C having an existing fixed directivity is used.
CDM using an adaptive array antenna by adding an adaptive array antenna to a DMA base station
The A base station can be easily configured.

In addition, the existing CDMA base station having fixed directivity is used as a CD using an adaptive array antenna.
It is possible to modify the base station having the MA receiving device by changing and updating the device configuration as much as possible.

When forming the reference signal e (t),
The weighting ratio of each respread signal is determined by the existing RAK.
Since it is obtained from the ratio of the output signal strength of the E branch 14, it is possible to optimally determine the antenna directivity weighted according to the signals passing through the respective paths without any extra burden.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, in a cell type mobile communication base station using CDMA, processing unique to a CDMA receiver and processing unique to an adaptive array antenna can be performed separately. It is a CDMA receiver using the adaptive array, and the adaptive array antenna section and the CDMA are provided by only a slight mutual signal exchange.
The receiver can be realized separately. This makes it possible to install the adaptive array antenna additionally by making the best use of the existing radio equipment of the CDMA base station having the fixed directional antenna, and to significantly reduce the cost for performance improvement by the adaptive array antenna of the base station. Reduce to.

An embodiment of the present invention will be described in detail below with reference to FIG. 1 showing the configuration of a CDMA receiver using the adaptive array of the present invention.

In FIG. 1, a portion surrounded by a chain line indicated by A is a CDMA having an existing fixed directional antenna.
This is a CDMA receiver provided in the base station, and its configuration is exactly the same as that shown in FIG.

That is, a fixed directional antenna 11-F and an RF receiver 12-F for receiving a signal from a mobile station,
A matched filter (MF) 14-1 for despreading an input spread signal at the same time and a channel estimator 14-2 for estimating a delay phase of the despread signal.
And a multiplier 14-3 that multiplies the outputs of the MF 14-1 and the channel estimator 14-2, and L sets are prepared according to the expected number L of paths (the number of paths) of signals from the mobile station. RAKE branch 14 and L sets of RAKE branch 1
It is composed of a combiner 15 for adding and combining the outputs of the four.

C having this existing fixed directional antenna
In order to add an adaptive array function to the DMA receiver, the fixed directional antenna 11-F and the RF receiver 12-F are removed, and a portion surrounded by a chain line indicated by B in the figure is newly added. to add.

The configuration of the newly added B in the figure will be described below. n array antenna elements 1
The spread signals from the mobile body side received by the 1-1 to 11-n and the RF receivers 12-1 to 12-n are supplied to the beam former 13, respectively.

The beam former 13 weights each received signal by the multipliers 13-1 to 13-n on the basis of the received signal and the input control signal e (t), and An output signal y (t) representing the beam formed and combined by the combiner 13-2 is generated and supplied to the existing L set of RAKE branches 14.

The replica generator 16 is the existing synthesizing means 1.
5 based on the output O (t) of the signal 5, a temporary symbol determiner 16-1 that outputs a signal whose data has been determined or a known pilot symbol that has been determined, and a temporary symbol determiner 16-1 using a predetermined code sequence. Output each timing τ
1-.tau.4 re-spreading L sets of spreaders 16-21 to 16-
24, and a combiner 16-3 for weighting and combining the output signals of the spreaders 16-21 to 16-24 and outputting as a reference signal d (t). In this example, L
Is 4.

The subtractor 17 takes the difference between the reference signal d (t) from the replica generator 16 and the output signal y (t) of the beam former 13 and sends it to the weighting control circuit 13-3 of the beam former 13. It is supplied as a control signal e (t).

C using the adaptive array of the present invention
The DMA receiver is configured as described above, and the processing unique to the CDMA receiver is performed by the existing RAKE branch 14 or the like.
In addition, the processing unique to the adaptive array antenna can be performed separately by the additional beam former 13, the replica generator 16 and the like.

The overall operation of the CDMA receiver using the adaptive array of the present invention will be described below in sequence.

Each antenna element 11-1 to 11-
Each of the received signals received by the n and RF receivers 12-1 to 12-n is a signal spread by a specific code sequence on the mobile station side, and each received signal is input to the beamformer 13.

In the beam former 13, each of the input received signals is weighted by the multipliers 13-1 to 13-n with respect to the amplitude and the phase. This weighting value is a control signal e which is an error between the reference signal d (t) from the replica generator 16 and the output signal y (t) of the beam former.
(T) and the weighted control circuit 13-3 using the MMSE based on each received signal, and the multiplier 13-1
~ 13-n. Multipliers 13-1 to 13-n
Then, the received signal weighted with respect to the amplitude and the phase is combined by the combiner 13-2 by, for example, maximum ratio combining, and becomes the output signal y (t) of the beam former 13.

Output signal y (t) of the beam former 13
Is supplied to the subtractor 17 to obtain the difference from the reference signal d (t) from the replica generator 16, and L sets of R
It is supplied to the AKE branch 14.

In each RAKE branch 14, first, MF1
In 4-1 the data symbol is despread with a specific code sequence used for spreading on the side of the mobile station and at a timing corresponding to each path delay of the received signal, and converted into a data symbol. This MF14-
The channel estimator 14 calculates the delay phase of the signal despread by
-2 to estimate the MF 14-1 and the channel estimator 14-2.
14-3 multiplies the outputs of
The signals combined with the delay phases are combined in the combiner 15 by maximum ratio combining corresponding to the respective signal intensities to form the output signal O (t), which is sent to the demodulator and demodulated into the signal from the mobile station. .

Further, the output signal O (t) is supplied to the temporary symbol determiner 16-1 of the replica generator 16. The temporary symbol determiner 16-1 makes a data decision based on the output signal O (t), and outputs the data-decided signal or a corresponding pilot symbol from a plurality of known pilot symbols to use as a reference signal. To do.

The outputs of the temporary symbol determiner 16-1 are input to the spreaders 16-21 to 16-24, respectively, and RAK
It is re-spread at a specific code sequence used in the MF 14-1 of the E branch 14 and at timings τ1 to τ4 corresponding to each path delay, and further weighted and combined by the adder 16-3 to be used as a reference signal d (t). Is output.

Here, the re-spreading at the timings τ1 to τ4 of the spreading code corresponding to each path delay means that the signal spread from the mobile station with a specific code passes through each path and reaches the base station. At the same time, it means reconstructing the spread signal to be input in each path from the pilot symbol and the determination data at the same timing as the spread signal reaching this base station. Therefore, the reference signal d (t) is
The weighted sum is time-shifted with respect to each other by the delay difference of the estimated spread signal when passing through these plural paths.

Despreading timing τ1 required at this time
~ Τ4 is the M of each RAKE branch 14 for each path
Since it is a signal necessary for timing the code generation when performing despreading in F14-1, it can be easily output from the existing CDMA base station equipment.

Based on this reference signal d (t), the error e (t) of the output signal y (t) of the beam former 13 is detected and output to the weighting control circuit 13-3, and the MMSE
An adaptive array antenna using is constructed.

Further, in the above description, the fixed directional antenna 11-F and the RF receiver 12-F are added to the CDMA receiver having the existing fixed directional antenna in order to add the adaptive array function. Described as removing. However, the fixed directional antenna 11-F and RF
The receiver 12-F can be configured so as to be newly added to the part surrounded by the alternate long and short dash line indicated by B in the figure without removing the receiver 12-F. In this case, the received signals from the fixed directional antenna 11-F and the RF receiver 12-F are, as seen from the beam former 13, the received signals which are not weight-controlled, but the array antenna. -Beamforming control is possible by performing weighted control of the reception signals of the elements 11-1 to 11-n.

In the above description, the replica generator generates the reference signal based on the temporary decision value of the pilot symbol, but the decision data after error correction of the data may be used. In this case, although there is a disadvantage that the control delay increases, it can operate even in an environment with a poor S / N ratio.

When the signals re-spread by the spreaders 16-21 to 16-24 are weighted and combined with a delay corresponding to each path delay, the maximum ratio combination is performed according to the signal strength transmitted on each path. Weighted synthesis is preferable so that By combining in this way, in the case of MMSE, directivity in the direction corresponding to each path can be weighted according to the signal strength transmitted in each path.

As described above, the despreading timings τ1 to τ of the RAKE branch 14 are used as reference signals for determining the weighting of the adaptive array antenna.
Easily add an adaptive array antenna to an existing CDMA base station having fixed directivity by using a signal obtained by weighting and combining signals re-spread with a code corresponding to a desired mobile station delayed by 4. Therefore, a CDMA receiver using an adaptive array can be constructed.

[0055]

According to the present invention, as a reference signal for determining the weighting of an adaptive array antenna, re-spreading is performed with a code corresponding to a desired mobile station delayed at the despreading timing of each RAKE branch. Since these signals are weighted and combined and used, an adaptive array antenna can be added to an existing CDMA base station having fixed directivity to easily configure a CDMA base station using the adaptive array antenna. I can.

Further, the existing CDMA base station having a fixed directivity is used as a CD using an adaptive array antenna.
It is possible to modify the base station having the MA receiving device by changing and updating the device configuration as much as possible.

When forming the reference signal e (t),
The weighting ratio of each respread signal is determined by the existing RAK.
Since it is obtained from the ratio of the output signal strength of the E branch 14, it is possible to optimally determine the antenna directivity weighted according to the signals passing through the respective paths without any extra burden.

[Brief description of drawings]

FIG. 1 is a CDM using the adaptive array of the present invention.
The block diagram of an A receiver.

FIG. 2 is a configuration diagram of a RAKE receiver provided in a base station.

FIG. 3 CDMA using a conventional adaptive array
The block diagram of a receiver.

FIG. 4 is a CD using another conventional adaptive array.
The block diagram of MA receiving apparatus.

[Explanation of symbols]

A Existing fixed directional CDMA receiver B Additional adaptive array antenna section 11-F fixed directional antenna 12-F RF receiver 11-1 to 11-n array antenna element 12-1 to 12-n RF receiver 13 Beam former 13-1 to 13-n multiplier 13-2 Synthesizer 13-3 Weighting control circuit 14 RAKE branch 14-1 Matched filter (MF) 14-2 channel estimator 14-3 Multiplier 15 synthesizer 16 replica generator 16-1 Symbol temporary decision device 16-21 to 16-24 Diffuser 16-3 Combiner 17 Subtractor

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B ⁷ /02-7/12 H04L 1/02-1/06 H01Q 3/00-3/46 H01Q 21 / 00-25/04 H04B 1/69-1/713 H04J 13/00-13/06

Claims (2)

(57) [Claims] 1. A beamformer for forming a beam by weighting amplitude and phase of the received signals and combining the received signals based on received signals from a plurality of array antenna elements and an input control signal. , The output signal of this beamformer is input, each has a matched filter, and despreads to perform RAKE reception .
For outputting the output signal for
R to output spread code timing in
AKE branch and output signals of the plurality of RAKE branches are weighted and combined according to their signal strengths and output, and a signal for which data determination has been performed or a known pilot signal obtained based on the output of this combining means. On the other hand, a replica generator for re-spreading with a corresponding code at the spreading code timing in each matched filter, weighting and combining the re-spread signals to obtain a reference signal, and a replica generator from this replica generator And a subtraction unit that supplies a control signal to the beamformer by subtracting a difference between a reference signal and an output signal of the beamformer, and a CDMA receiving apparatus using an adaptive array. 2. The CDMA receiver using the adaptive array according to claim 1, wherein a weighting ratio of each respread signal when forming the reference signal is determined by an output signal strength of the plurality of RAKE branches. A CDMA receiver using an adaptive array, which is determined based on the ratio of