JPH10117157A - Rake receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the RAKE receiver that is used for the direct spread spectrum communication system and able to receive a multipath signal efficiently. SOLUTION: A path searcher 12 measures each path, selects paths whose number is equal to (n) of inverse spread devices in the order of a path with a higher amplitude and assigns each of inverse spread devices 10(1)-10(n) to respective paths so as to allow the inverse spread devices 10(1)-10(n) to apply inverse spread processing to each signal of the selected path. In the assignment of each of the inverse spread devices 10(1)-10(n) to each path, the path with a higher amplitude and the path with a smaller amplitude are assigned respectively to adjacent inverse spread devices so that their outputs are given to the same beforedetection synthesizer. Outputs of the inverse spread devices 10(1)-10(n) are synthesized by before-detection synthesizers 14(1)-14(m) and their outputs are detected by detectors 16(1)-16(m). The detected outputs from the detectors 16(1)-16(m) are subjected to RAKE-synthesis by an after-detection synthesizer 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a RAKE receiving apparatus used in a direct spread spectrum communication system and capable of efficiently receiving a multipath signal.

[0002]

2. Description of the Related Art In a spread spectrum communication system, a received signal is multiplied by a spread code having a band several to tens of thousands of times larger than the band, and the resulting signal is transmitted as a wideband signal. This is a communication system that reproduces narrowband information by generating a despreading code synchronized with the code and multiplying it by a received signal.

In recent years, the spread spectrum communication system has been applied to multiple access of mobile radio, and CDMA (Code Division M).
ultiple Access) method is drawing attention. Features of the spread spectrum communication method include noise resistance, interference resistance, and confidentiality.

[0004] In the case of a multipath transmission line, it is possible to separate the multipath with the resolution of the spreading code length in the despreading process. Since a plurality of multipaths arrive via different paths, they have independent amplitude and phase at the receiving point. In particular, in the case of a mobile transmission path, fading occurs because the transmission path characteristics fluctuate with movement. However, since each of the multipaths fluctuates independently, a path diversity effect can be obtained by appropriately receiving the multipaths.

[0005] This is called RAKE reception.

FIG. 6 shows a configuration example of a rake receiving apparatus according to the prior art. In FIG. 4, 10 is a despreader (1)-(n) corresponding to each multipath, 12 is a path searcher that detects the timing of the multipath and gives timing to each despreader 10, and 16 is each path. Detectors (1)-(n), 18 which detect each time, are combiners for combining the outputs of the detectors.

In general, the path searcher 42 is constituted by a sliding correlator capable of continuously sliding the timing of despreading, a matched filter matched with a spreading code, or the like.

The operation of the RAKE receiving device shown in FIG. 6 will be described. First, the path searcher 12 measures the multipath state of the transmission path. When the path searcher 12 detects a path, the despreader 10 detects the path at the detected timing.
(1) -10 (n) are sequentially operated. That is, each of the despreaders 10 (1) -10 (n) receives a different multipath. Since each multipath is subject to phase rotation and amplitude fluctuations, the detector 16
(1) Compensation of phase and amplitude is performed by -16 (n).

Each set of despreaders 10 (1) -10 (n) and detectors 16 (1) -16 (n) is also called a RAKE finger. Each finger output is synthesized by the synthesizer 18. The combined output receives and adds signals passing through a plurality of paths, rather than receiving only a reception signal passing through one path, so that it can be received efficiently, and a received signal with less deterioration due to fading is obtained.

As described above, by performing RAKE reception, multipath can be received, so that incoming power can be efficiently received. Further, a path diversity effect can be obtained.

[0011]

In the configuration of the RAKE reception shown in FIG. 6 described above, FIG.
If the multipath is buried with noise, as shown in
When signals from these paths are combined, characteristic degradation occurs.

FIG. 7A shows the relationship between the output of the despreader and the noise level of the signal received from each path, and how the output of the despreader is input to each detector.

In the above-mentioned RAKE reception, a synchronous detection method is often used as a detection method. this is,
The synchronous detection scheme, when operated ideally, requires a required signal power to noise power ratio (S / S) to obtain a certain average bit error rate.
N ratio) is the smallest.

However, this synchronous detection method is not shown in FIG.
When synchronous detection is performed on a path in which noise is buried as shown in (1), the characteristic is greatly deteriorated compared to the absolute phase estimation error.

When the number of multipaths is larger than the number of RAKE fingers as shown in FIG. 7A, the received power cannot be effectively combined. If the number of RAKE fingers is increased as a countermeasure, a path buried in noise will be synthesized.

FIG. 7B shows the relationship between the output of the despreader and the noise level of the received signal from each path and the output of the despreader to each detector as in FIG. 7A. It shows how it is. An output not connected to the detector indicates that there is no RAKE finger corresponding to the path.

It is an object of the present invention to provide a receiver that can perform RAKE combining by effectively using received power from a path even when there is a path buried in noise, and obtain reception with less reception deterioration due to noise.

[0018]

In order to achieve the above object, the present invention relates to a RAKE receiving apparatus used in a direct spread spectrum communication system, wherein a plurality of RAKE receiving apparatuses corresponding to each path and despreading a received signal of the path are provided. A despreader, a plurality of pre-detector combiners for combining at least two or more signals from the despreader, a detector for detecting an output of the pre-detector or the despreader, and the detector And a path searcher for detecting a multipath of a transmission path and allocating the despreader to a path.

In a RAKE receiving apparatus used for a direct spread spectrum communication system, a plurality of despreaders corresponding to each path and despreading a received signal of the path, and at least a signal from the despreader are used. A plurality of pre-detector combiners for combining two or more, a plurality of detectors for detecting an output from the pre-detector combiner or an output from the despreader, and an arbitrary output from the plurality of despreaders. A switch that can be connected to the inputs of the plurality of pre-detector combiners and that can connect the output from the despreader to the input of the detector, a post-detector combiner that combines signals from the detectors, A path searcher for detecting a multipath, assigning the despreader to the path, and setting a connection state of the switch.

In the RAKE receiving apparatus, the setting of the switch is dynamically set according to a multipath detection result.

In the RAKE receiving apparatus, at least one path having a large level and at least one path having a large level are connected.
It can be combined with two smaller paths before detection.

Also, a plurality of paths whose average level of a signal is smaller than a certain threshold may be combined before detection, and a signal whose average level is larger than a certain threshold may be combined after detection.

A first threshold level and a second threshold level are provided, and a path lower than the smaller second threshold level is not synthesized, and a level between the first threshold level and the second threshold level is not combined. Are combined before detection by combining the paths
Paths higher than the level may be combined after detection.

It is preferable to combine paths before detection so that the average level of each input synthesized by RAKE is equal.

The N paths from the higher average level may be combined after detection, and the remaining paths may be combined before detection.

With this configuration, RA with little deterioration
KE synthesis can be performed.

[0027]

Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of a rake receiving apparatus according to the present invention.

In FIG. 1, reference numeral 10 denotes n despreaders (1)-(n), 12 denotes a path searcher, 14 denotes m pre-detection combiners (1)-(m), and 16 denotes m Detectors (1)-(m), 18 are post-detection combiners. In general,
The path searcher 12 is configured by a sliding correlator capable of continuously sliding the timing of despreading, a matched filter matched with a spreading code, or the like. In addition, it has a function of measuring the amplitude and delay time of each path. In addition, each despreader 10
(1)-(n) may be set with a timing for performing despreading so as to correspond to a path. Pre-detection synthesizer 1
4 (1) -14 (m) can be constituted by a simple adder. The detector 16 also compensates for phase rotation caused by fading or a frequency shift between transmission and reception for each path. Thus, appropriate synthesis is performed by RAKE synthesis. After the detection, the synthesizer 18 outputs R
The AKE combiner weights and combines them so that the maximum ratio combination is obtained. Note that a configuration may be employed in which a part of the despreaders 10 (1) to (n) is directly connected to the detector 16.

The main difference from the conventional RAKE receiving apparatus shown in FIG. 4 is that the pre-detection combiner 14 is inserted between the despreader 10 and the detector 16. The pre-detection combiner 14 combines the outputs of the plurality of despreaders and inputs the combined output to the detector. In the example shown in FIG. 1, two paths are combined before detecting the despread signal. Therefore, the number n of despreaders and the number m of detectors are

[0031]

## EQU1 ## The relation is m = n / 2.

The operation of the RAKE receiver according to the present invention shown in FIG. 1 will be described. First, the path searcher 12 measures the amplitude and delay time of a multipath from a received signal for each path. Next, pass searcher 12
For example, each of the despreaders 10 (1) -10 (n) is selected such that the paths are selected by the number (n) of the despreaders in order from the path having the largest amplitude, and the selected paths are despread. Of each despreader 10 by setting the timing of
(1) -10 (n) is assigned to each path.

The assignment of the despreader 10 to the path is as follows:
In the above example, a path having a large amplitude and a path having a small amplitude are assigned to adjacent despreaders, and are input to the same pre-detection combiner.

The outputs of the despreaders 10 (1) -10 (n) are combined by the pre-detection combiners 14 (1) -14 (m) for each of two paths, a large amplitude path and a small amplitude path. , 16 (1) to 16 (m).
The detected outputs of the detectors 16 (1) to 16 (m) are combined by the combiner 18 after detection. As a result, RAK
E effect is obtained.

As described above, by combining the signals from the large amplitude path and the small amplitude path before detection,
Even when there is a path buried in noise, the power of the multipath can be used effectively.

In the above example, the outputs of two passes are combined, but the outputs of three or more despreaders can be combined. In this case, for example, a combination of a path having a large amplitude and two or more paths having a small amplitude can be considered.

The number n of the despreaders and how many outputs of the despreaders are combined before detection are determined by measuring the multipath state of the propagation path to be used, and determining the state and the degree of despreading. It can be determined in advance depending on whether a vessel can be prepared.

FIG. 2 shows the configuration of another embodiment of the RAKE receiving apparatus according to the present invention.

In FIG. 2, 10 is a despreader (1)-(n) corresponding to each multipath, 22 is a path searcher,
23 is a switch, 14 is a pre-detection combiner (1)-(m),
16 is a detector (1)-(m), and 18 is a post-detection combiner. The RAKE receiving device shown in FIG.
Is inserted between the despreader 20 and the pre-detector combiner 24. The switch 23
By the control of the searcher 22, the despreader 10 (1) -10
The output of (n) can be input to any of the pre-detection combiners 14 (1) to 14 (m) in any combination. Also, any output of the despreaders 10 (1) -10 (n) can be directly connected to any of the detectors 22 (1) -22 (n).

The operation of the RAKE receiver having the configuration shown in FIG. 2 will be described. The path searcher 22 detects and measures the multipath, determines the number of despreaders 10 to be used and the combination of pre-detection synthesis according to the number and amplitude of the multipaths, and determines the timing of the despreader 10. And the switch 23 are set.

One example of the combination of the number of despreaders 10 and the pre-detection combining performed by the path searcher 22 will be described below.

(1) The number N of paths whose amplitude is equal to or higher than a certain threshold level (for example, -6 dB) is obtained in comparison with the path having the largest amplitude among the multipaths.

(2) Select the despreader 10 twice as large as N, and select the despreader 10
Is assigned to each path.

(3) N path having an amplitude of -6 dB or more and -6
The switch 23 is set so that the outputs of the despreader 10 from the N paths of dB or less are combined and input to the pre-detection combiner 14.

In this case, two paths, a path with a large amplitude and a path with a small amplitude, are combined and input to the pre-detection combiner 14, and are combined. After that, the pre-detection synthesizer 1
The outputs of 4 are respectively detected by the detector 16, and the N-path RAKE combining is performed by the combiner 18 after the detection.

In this configuration, the output of the despreader 10 (1) -10 (n) is dynamically combined by the switch 23 in an arbitrary combination, and an arbitrary pre-detection combiner 14 (1) -14 (m).
Can be entered. Therefore, even if the multipath state of the propagation path fluctuates with time, a combination that reduces the combined power or a path that contains a lot of noise can be combined by dynamically changing the combination of paths. Therefore, an optimal RAKE synthesis can be performed.

As a combination of path selection and combination, for example, (1) A path having a large average signal level and a path having a small average level are combined before detection (the example described above).

(2) Combine a plurality of paths whose average level of a signal is smaller than a certain threshold before detection. Signals whose average level is greater than a certain threshold are combined after detection.

(3) The threshold of the average level of the signal is provided in two stages, and a path having a lower second threshold level or less is not synthesized (it cannot be distinguished from noise).
The paths are combined between the first threshold level and the second threshold level and are combined before detection. Paths at the first level or higher are combined with other paths after detection.

(4) Combine the effects so that the effect of RAKE combining is maximized, that is, the average level of each input combined by RAKE is equal.

(5) The N paths from the higher average level are combined after detection. The remaining paths are combined before detection.

There are various combinations.

The combination (4) will be described in detail with reference to FIG. As described above, the RAKE combining achieves the maximum effect when the average level of each input to the RAKE combining is equal. This is similar to the case of space diversity using a plurality of antennas, and is similar to the case where the gain of the antennas and the reception average level are not equal (unequal gain), and the diversity effect is reduced.

There are a plurality of combinations for equalizing the average of the inputs of the RAKE combining. One example will be described with reference to FIG. First, the average level of each path is obtained.
FIG. 3A shows this. The horizontal axis in FIG. 3A is a path, and the vertical axis is an average level. The obtained average level of each path is sorted in descending order. This is shown in FIG. 3 (b). Paths sorted by this average level
For example, the switch 23 is used to assign to the synthesizer 14 from (1) in descending order. When assignment is performed up to (n) of the combiner 14, from the path of the average level of (n + 1), conversely, assignment is performed in order of magnitude from (n) of the combiner 14 to (1) of the combiner 14. This is used for all paths
Repeat until assigned to. This is shown in FIG.
It is an arrow of (b). The assigned path is the synthesizer 1
4 yields approximately equal output levels.
This is detected and input to a RAKE combiner (combiner after detection) 18. With this configuration, the RAKE combiner 18
Will have approximately equal inputs. with this,
The effect of RAKE combining is maximized.

FIG. 4 is a block diagram of a receiver incorporating the RAKE combining shown in FIG. In FIG.
The signal received from the antenna 41 is converted into a baseband signal by the radio unit 42 and is converted into a digital signal by the A / D converter 43. The signal is input to the despreader 10 and also input to the path searcher 22. The signal input to the path searcher 22 is correlated while shifting the timing using the correlator 52 and the code generator 53, and the correlation value determination unit 54 determines whether the correlation has been obtained. If the correlation is obtained, a path has been found, and the timing is sequentially assigned to the code generators 45 (1) to 45 (n) of the inverse correlator 10 by the timing control unit 51. At this timing, by performing despreading by the code generator 45 and the correlator 44, a path is assigned to the path finger.

Now, in order to detect the average level of the signal for each path, the correlation value of the path is accumulated in the correlation value memory 55 provided for each path. By accumulating the correlation value for each path in the correlation value memory 55, the average level for each path is calculated. Thus, the composition using the average level described above can be performed. After that, the signal processing unit 19
Then, by decoding, the original transmitted signal is obtained.

When the present invention having the configuration shown in FIG. 1 is applied, 1 is required to obtain an average bit error rate (BER) of 10 ^-3 with respect to a normalized fading frequency (fDT).
Signal power to noise power density ratio per bit (E _b / N
₀ ) is shown in the graph of FIG. This is because there are four multi-paths, and in the conventional example, the four paths are RAKE-combined as they are, and when the present invention is applied, the four paths are divided into a path having a large amplitude and a path having a small amplitude. A combination of two is obtained by RAKE combining two output signals.

As can be seen from this graph, when the present invention is applied, about 0 to 0.5 dB when space diversity is not used, and about 0.3 to 0.5 dB when space diversity is used. The improvement of the signal power to noise power density ratio was obtained.

[0059]

As described above, according to the RAKE of the present invention,
According to the receiving apparatus, it is possible to effectively combine the powers of the received signals and suppress characteristic deterioration due to noise.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a rake receiving apparatus according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the RAKE receiving device of the present invention.

FIG. 3 is a diagram illustrating path selection and synthesis.

FIG. 4 is a detailed block diagram showing a rake receiving apparatus according to the present invention.

FIG. 5 shows a signal power to noise power density ratio per bit (E _b ) required to obtain an average bit error rate (BER) of 10 ⁻³ with respect to a normalized fading frequency (fDT).
/ N ₀ ).

FIG. 6 is a block diagram illustrating a configuration of a conventional RAKE receiving device.

FIG. 7 is a diagram illustrating a relationship between a multipath state, a noise level, and a RAKE finger.

[Explanation of symbols]

 Reference Signs List 10 despreader (1)-(n) 12 path searcher 14 pre-detector combiner (1)-(m) 16 detector (1)-(m) 18 post-detector combiner (RAKE combiner) 19 signal processing Unit 22 path searcher 23 switch 41 antenna 42 radio unit 43 A / D converter 44 correlator 45 code generator 51 timing control unit 52 correlator 53 code generator 54 correlation value determination unit 55 correlation value memory 56 path searcher control unit

Claims (8)

[Claims] 1. A rake receiving apparatus used in a direct spread spectrum communication system, comprising: a plurality of despreaders corresponding to each path for despreading a received signal of the path; and at least a signal from the despreader. A plurality of pre-detector combiners for combining two or more, a detector for detecting an output of the pre-detector or the despreader, a post-detector for combining a signal from the detector, and a transmission path. A path searcher for detecting multipath and assigning said despreader to a path.
AKE receiver. 2. A rake receiving apparatus used in a direct spread spectrum communication system, comprising: a plurality of despreaders corresponding to each path for despreading a received signal of the path; and at least a signal from the despreader. A plurality of pre-detection combiners for combining two or more; a plurality of detectors for detecting an output from the pre-detection combiner or an output from the despreader; and an arbitrary output from the plurality of despreaders. A switch that can be connected to the inputs of the plurality of pre-detector combiners, and that can connect the output from the despreader to the input of the detector; a post-detector combiner that combines signals from the detectors; A RAKE receiving apparatus comprising: a path searcher that detects a multipath, assigns the despreader to a path, and sets a connection state of the switch. 3. The RAKE receiving apparatus according to claim 2, wherein the setting of the switch is dynamically set based on a multipath detection result. 4. The R according to claim 1, wherein
In the AKE receiver, at least one large path and at least one
A RAKE receiving apparatus characterized in that the signal is combined before detection with a combination of two low-level paths. 5. The R according to claim 1, wherein
In the AKE receiver, RAK is characterized in that a plurality of paths whose average level of a signal is smaller than a threshold are combined before detection, and a signal whose average level is larger than a threshold is combined after detection.
E receiving device. 6. R according to claim 1, wherein
In the AKE receiver, a first threshold level and a second threshold level are provided, and a path smaller than the smaller second threshold level is not combined, and the path between the first threshold level and the second threshold level is not combined. A RAKE receiving apparatus characterized in that paths prior to detection are combined and combined before detection, and paths above the first level are combined after detection. 7. The R according to claim 1, wherein
An AKE receiving device, wherein paths before detection are combined so that the average level of each input synthesized by RAKE is equal. 8. The R according to claim 1, wherein
In the AKE receiving apparatus, the RAK is characterized in that the N paths are combined after detection from the higher average level and the remaining paths are combined before detection.
E receiving device.