JPH10190522A - Direct spreading cdma transmission system receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide RAKE reception without requiring an RAKE synthetic (common-mode synthesization) multi-path search function in a CDMA transmission system. SOLUTION: A received signal is reversely spreaded by a matched filter 101 and a correlative detection value is outputted at every chip. The channels of respective multi-path signals separated at every chip cycle are estimated through the use of a pilot symbol at every multi-path by a channel estimating and compensating part 110. A matched filter output is inputted to respective average signal power measuring part 120 so as to generate an average delay profile. A threshold deciding part 140 decides the threshold of signal power for executing RAKE synthesization as against the max. signal power of the average delay profile. A synthetic path selecting part 150 selects the multi-path of signal power with the higher threshold and the channel estimating/ compensating part output of the selected multi-path is synthesized by a RAKE synthesizer 160.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver in a mobile communication system to which a direct spread CDMA (Code Division Multiple Access) transmission system for performing multiple access using spread spectrum in mobile communication is applied.

[0002]

2. Description of the Related Art The direct spread CDMA (DS-CDMA) transmission system is a system for transmitting information data by spreading a modulated signal into a wideband signal using a high-speed spreading code. In this system, a plurality of communicating parties perform communication using the same frequency band by assigning different spreading codes to each user.

FIG. 6 shows a configuration of a receiving apparatus in a conventional DS-CDMA transmission system. In the receiving apparatus shown in FIG. 6, the received spread modulated signal is amplified by a low noise amplifier 603, multiplied by a frequency from an oscillator 604 by a multiplier 605, passed through a band-pass filter (BPF) 606, The frequency is converted to a frequency (IF frequency) signal. Then, an automatic gain control amplifier (AGC amplifier) 6
At 07, linear amplification is performed. The amplitude envelope of the received signal is detected by the envelope detector 608, and the amplitude fluctuation is negatively fed back to the AGC amplifier 607 to compensate for the amplitude fluctuation caused by fading. The signal linearly amplified by the AGC amplifier 607 is quadrature-detected by the quadrature detector 609 into a baseband signal. The baseband in-phase (I) and quadrature (Q) components are converted into A / D converters 612 and 613.
To convert to digital value. The spread modulated signal converted to the digital value is subjected to despreading by the sliding correlator 632 using a spread code replica synchronized with the delay time of each multipath signal. Each of the despread multipath signals is subjected to delay detection or synchronous detection to perform data demodulation.

In this conventional example, a pilot symbol is inserted at a fixed period between information symbols in a transmission frame, and absolute synchronous detection demodulation is performed using the pilot symbol. The absolute synchronous detection demodulation method will be described.

[0005] In land mobile communications, the relative position of the base station and the mobile station moves, and the received signal undergoes amplitude and phase fluctuations called fading. In order to perform synchronous detection demodulation, it is necessary for a receiver to estimate a complex envelope due to the fading, that is, amplitude and phase fluctuations (also referred to as channels). For this reason, a known pilot symbol is inserted into the transmission information symbol at regular intervals. Using this known pilot symbol, a reception fading complex envelope can be obtained periodically. Using this value, a fading complex envelope at the information symbol position between pilot symbols can be obtained. As described above, the fading complex envelope fluctuation (channel fluctuation) of each information symbol can be compensated using the value obtained from the pilot symbol.

By performing in-phase synthesis (RAKE synthesis) of the plurality of multipath signals compensated for channel fluctuation,
The signal power ratio can be improved with respect to an interference signal or thermal noise.

Selection of a multipath signal to be RAKE-combined is performed by a sliding correlator called a search finger. In the search finger, the signal power of the despread signal is measured by the signal power measurement unit for each chip cycle, and a delayed wave having a large received signal level is selected on average.

FIG. 7 shows an example of a search finger algorithm when a conventional sliding correlator is used.

When one sliding correlator is used, one multipath correlation value (despread value) is obtained for each symbol, and the received signal power of the multipath signal is measured. Can be. As described above, selection of the RAKE combining path requires selection of a multipath signal having a large average signal level (after receiving a variation due to a distance variation between a base station and a mobile station and a variation due to shadowing). . On the other hand, in a land mobile communication environment, it is subject to instantaneous fluctuation due to Rayleigh fading. In a single measurement of the received signal level, the signal level of a certain multipath signal may be low due to the fact that the received signal level is dropped due to this Rayleigh fading variation, and this may be omitted from the selection of the RAKE combining path.

[0010] Therefore, in order to remove the influence of the instantaneous level fluctuation, it is necessary to measure the received signal level of a signal obtained by averaging the Rayleigh fading fluctuation. Therefore,
As shown in FIG. 7, the signal power measurement is repeated X times, and an average delay profile is created by the average signal power of X times. Then, the upper L RAKE combining multipaths are selected from the averaged delay profile.

When one sliding correlator is used, it takes N × X symbol times to create this one average delay profile.
Update the multipath signal to be combined. Therefore, when s sliding correlators (search fingers) are used, (N
× X) / s symbol time is required.

When the mobile station moves at a high speed with respect to the base station, the delay profile fluctuates quickly. Therefore, the multipath search using the sliding correlator takes time and cannot follow the delay profile fluctuation. There are cases.

On the other hand, in order to perform a high-speed multi-path search, the multi-path search range and the number of times of averaging may be reduced. However, if the search range is reduced, the time diversity effect of RAKE combining is reduced. In addition, if the number of times of averaging of the signal power is reduced, the RAKE combining multipath cannot be accurately selected.

[0014]

As described above, when the mobile station moves at a high speed with respect to the base station, the fluctuation of the delay profile also becomes high. In the conventional search finger using the sliding correlator, Multipath updating for RAKE combining cannot be performed quickly and accurately.

An object of the present invention is to provide a RAKE receiver that does not require a RAKE combining multipath search function by performing RAKE combining based on a matched filter.

[0016]

According to a first aspect of the present invention, there is provided a receiver for a direct spread CDMA transmission system, comprising:
A matched filter that despreads the digitized received spread signal, integrates the signal for a predetermined range, and outputs a correlation detection value, and outputs a matched filter output signal for all multipaths for each chip cycle in each slot. A channel estimator for estimating a channel, and a channel fluctuation for compensating for a channel fluctuation of each pulch path using a channel estimation value per slot for all multipaths output from the channel estimator for information symbols of a matched filter output signal. A compensating unit, an average signal power measuring unit for measuring an average received signal power of each multipath signal for each chip cycle of the matched filter output, a RAKE combining path threshold output unit for outputting a threshold, and a threshold. Each multipath signal from the channel fluctuation compensator is selected based on the output signal of the value output unit and the output signal of the signal power measuring unit. A RAKE combining path selector unit to output Te, RAKE synthesizing the RAKE combining path selector unit output
And a combining unit.

In the RAKE receiver of the present invention, a signal is selected from all the multipath signals in the multipath search range by using a threshold value by using a matched filter,
E synthesized. By using this configuration, all multipaths can be basically combined, and RAKE combining exclusion processing in a chip phase with a small signal level can be performed by threshold determination using an average delay profile.
Since the matched filter can generate a delay profile in a time series, it is possible to accurately perform RAKE combining with respect to a fast delay profile fluctuation.

Further, since all multipaths satisfying the threshold value within the search range are combined, the chip quality is particularly high, that is, the reception quality by the time diversity effect by RAKE is improved for direct spread CDMA. Can be realized.

[0019]

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

FIG. 1 shows a basic configuration of the present invention.

In FIG. 1, a received signal is input to a matched filter 101 as a baseband signal subjected to quadrature detection and A / D conversion. The input baseband signal is despread by the matched filter 101, and is demultiplexed by one within a RAKE combining path search range (P symbols).
A correlation detection value is output for each chip. The RAKE combining path search range needs to take a value sufficient for all delayed waves to arrive. N is the total number of chips in P symbols.

For each multipath signal output and separated for each chip period of the matched filter output, a channel (fading complex envelope) is estimated using a pilot symbol for each multipath. This is performed in the channel estimation / compensation unit 110, where channel variations of each multipath are compensated. The channel estimation and compensation unit 110 multiplies the complex conjugate signal of the channel estimation value of each information symbol obtained by the pilot symbol by the information symbol of the matched filter output,
Compensation is realized.

The output of the matched filter is input to each average signal power measurement section 120, and the average received signal power in all chip phases in the search range is measured to generate an average delay profile. The maximum signal power in the multipath search range is detected by the maximum power detection unit 130. In threshold value determination section 140, R
A threshold of signal power for performing AKE combining is determined. This threshold value can be obtained, for example, by multiplying the output of the maximum signal power detection unit 130 by a fixed threshold value determination gain.

The reason why the threshold value of signal power for RAKE combining is determined is that even if a multipath signal with low signal power is combined, no improvement in characteristics due to an increase in signal power is expected.
This is because the cross-correlation and the thermal noise component of the reception signals of other users are combined, and the characteristics are deteriorated. Set a threshold to avoid combining signals with low signal power.
This is preventing this.

The combined path selecting section 150 compares the average received signal power of each multipath measured by the signal power measuring section 120 with a combined path selection threshold, and selects a multipath having a signal power higher than the threshold. The output of the selected multipath channel estimation / compensation unit is combined by the RAKE combiner 160.

The RAKE combining multipath selection and combining in the configuration shown in FIG. 1 will be described with reference to FIG.

In FIG. 2, the signal separated into N paths by matched filter 101 is subjected to channel estimation using a pilot symbol for each multipath in channel estimation / compensation section 110, and channel fluctuation compensation is performed (FIG. 2). d). Further, an average delay profile in the multipath search range is created (a), and the maximum signal power is detected from the average delay profile (b). Also, the threshold power of the RAKE combining path is determined for this signal power (b). The multipath signal power in each chip phase is compared with a threshold (c), and only multipath signals exceeding the threshold power are RAKE-combined (e).

As described with reference to FIGS. 1 and 2, in the above configuration, a signal is selected from all the multipath signals in the multipath search range by using a threshold value using a matched filter, and RAKE synthesis is performed. I have. By using this configuration, all multipaths can be basically combined, and RAKE combining exclusion processing in a chip phase with a small signal level can be performed by threshold determination using an average delay profile. Since a matched filter can generate a delay in a time series, it is possible to accurately perform RAKE combining with respect to a fast delay profile variation.

Further, since all multipaths satisfying the threshold value within the search range are combined, the chip quality is particularly high, that is, the reception quality by the time diversity effect by RAKE is improved for direct spread CDMA. Can be realized.

Referring to FIG. 3, an example of a channel estimation algorithm according to the present invention will be described.

The target signal has a frame configuration in which a pilot block composed of N _P pilot symbols is inserted for each of N _S information symbols (a). The matched filter output signal of the l-th multipath in the n-th slot is averaged to obtain the pilot symbol in the n-th slot of the l-th multipath.

[0032]

[Outside 1]

Is obtained as follows (b).

[0034]

(Equation 1)

Where

[0036]

[Outside 2]

Assume that: Similarly, the (n) of the l-th multipath
+1) in the pilot symbol of the slot

[0038]

[Outside 3]

Is expressed by the following equation (b).

[0040]

(Equation 2)

[0041]

[Outside 4]

There are three methods for estimating, for example, as shown below.

(1) A method of averaging fading complex envelope estimation values in pilot symbols of two slots.

[0044]

(Equation 3)

(2) In a 2-slot pilot symbol

[0046]

[Outside 5]

To perform primary interpolation on

[0048]

(Equation 4)

(3) Method of using fading complex envelope estimation value in pilot symbol of same slot Among them, method (3) uses only fading complex envelope of past pilot symbol, and therefore stores information symbols. No additional memory is required.

This estimated

[0051]

[Outside 6]

Is RAKE-combined as shown in the following equation.

[0053]

(Equation 5)

Here, * indicates a complex conjugate.

FIG. 4 shows an example of the matched filter used in FIG.

In FIG. 4, reference numeral 402 denotes a delay element for one chip, 403 denotes a multiplier, and 404 denotes a accumulator. In this configuration, when a received signal spread with a K-chip cycle spreading sequence is input to the matched filter, the matched filter correlates with the spreading sequence.

The input signal is supplied to the delay element 402
Is delayed one chip at a time to K chips. k (1 ≦ k ≦
K) The signal delayed by the chip is multiplied by the (K−k) th code of the spread sequence by the multiplier 403. In this way,
The product of each delay signal and the spreading code is combined and correlated.

In the matched filter, when the code of the input signal and the spread sequence are synchronized, the correlation is large, and when the code is not synchronized, the correlation is small. In a multipath environment, a large correlation is detected when a delayed wave arrives. Therefore, a delay profile is obtained from the output of the matched filter.

FIG. 5 shows an example in which the configuration of FIG. 1 is used to configure the receiving unit. The same reference numerals are given to components having the same functions as those in FIGS. 1 and 6.

In FIG. 5, a received spread modulated signal is amplified by a low noise amplifier 603, and then frequency converted to an IF frequency by an oscillator 604, a multiplier 605 and a BPF 606. Then, the amplitude fluctuation caused by fading is compensated by the AGC amplifier 607, and the quadrature is detected by the quadrature detector 609. The output baseband signal of the quadrature detector 609 is converted into a digital signal by A / D converters 612 and 613.

The signal converted into the digital value is despread by the matched filter 101, and is shifted N chips by one chip within the RAKE combining path search range (P symbol).
Components. Each of the despread multipath signals is compensated for channel fluctuation by a channel estimation and compensation unit 110. Further, the average received signal power in each chip phase is measured by the signal power estimation unit 120, an average delay profile is generated, and the maximum signal power of the obtained profile is detected by the maximum signal power detection unit 130. Using the maximum signal power and the threshold value determination gain, threshold value determination section 140 determines a threshold value for selecting a RAKE combining path. Combining path selecting section 150 selects a multipath having a signal power higher than a threshold value and performs RAKE combining.

The RAKE-combined signal is randomized in error by a deinterleave circuit 642 and decoded by a Viterbi decoder 643.

[0063]

As described above, in the receiving apparatus of the present invention, all multipath signals in the multipath search range are RAKE-combined by performing threshold control using a matched filter. RAKE combining can be performed accurately with respect to a large delay profile variation.

In addition, since all multipaths satisfying the threshold value within the search range are combined, RAK is particularly required for a high chip rate, that is, for wideband DS-CDMA.
It is possible to improve the characteristics of the reception quality by the time diversity effect by E.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram for explaining RAKE combining path component selection and combining in the present invention.

FIG. 3 is a diagram illustrating an example of channel estimation according to the present invention.

FIG. 4 is a block diagram illustrating a configuration of a matched filter.

FIG. 5 is a block diagram illustrating a configuration of a receiver according to the present invention.

FIG. 6 is a block diagram illustrating a configuration of a conventional DS-CDMA receiver.

FIG. 7 is a diagram illustrating a search algorithm when a conventional sliding correlator is used.

[Explanation of symbols]

 Reference Signs List 101 Matched filter 110 Channel estimation and compensation unit 111 Channel estimation unit using pilot symbols 112 Multiplier 120 Average signal power measurement unit 130 Maximum power detection unit 140 Threshold determination unit 150 Combination path selection unit 160 RAKE combination unit 601 Antenna 602 band Pass filter (BPF) 603 Low noise amplifier 604 Multiplier 605 Oscillator 606 Band pass filter (BPF) 607 Automatic gain control amplifier (AGC amplifier) 608 Envelope detector 609 Quadrature detector 610, 611 Low-pass filter (LPF) ) 612 613 A / D converter 620 RAKE path combining path finger 631 Spreading code generator 632 Sliding correlator 633 Channel estimator 634 Multiplier 641 RAKE combiner 642 Deinterleigh 643 Viterbi decoder 644 data judging unit 645 sliding correlator 646 power measuring section 647 RAKE combining path selector unit

Claims (3)

[Claims] 1. A receiver of a direct spread CDMA transmission system, comprising: a matched filter for despreading a digitized received spread signal, integrating over a certain range of time, and outputting a correlation detection value; A channel estimator for estimating all multipath channels for each chip period in each slot for the signal; and a slot for all multipaths of the channel estimator output for the information symbol of the matched filter output signal. A channel variation compensating unit that compensates for channel variation of each multipath by using the channel estimation value of the above, and an average signal power measuring unit that measures the average received signal power of each multipath signal for each chip cycle of the matched filter output A RAKE combined path threshold control unit that outputs a threshold value; and the RAKE combined path threshold control output. RA for selecting and outputting each multipath signal from the channel fluctuation compensating unit based on the signal and the output signal of the average signal power measuring unit.
A direct CDMA transmission system receiver, comprising: a KE combining path selecting unit; and a RAKE combining unit that combines outputs of the RAKE combining path selecting unit. 2. The receiver according to claim 1, wherein the channel estimator estimates a channel using pilot symbols. 3. The receiver according to claim 1, further comprising a maximum signal power detection unit that detects a maximum signal power from an output signal from the average signal power measurement unit, The control unit obtains a threshold value from the maximum power from the maximum signal power detection unit.