JPH07231278A - Reke receiver by direct spread spectrum communication system - Google Patents

Abstract

PURPOSE:To form the REKE receiver in the direct spread spectrum communication system in which the reception characteristic is improved even when many multi-paths exist and low power consumption is realized. CONSTITUTION:Direct spread modulation signals S30 whose path number is N are received by 1st-N-th inverse spread means 501-50N and 1st-N-th spread series synchronously with the N-sets of signals S30 whose reception timing differs from each other apply inverse spread demodulation to each reception signal S30 and a multiplexer means 51 multiplexes demodulated data D401-D40N. Through the constitution above, a control means 52 obtains individually a level difference between a signal of a highest level and each of other signals among the levels of the N-sets of the signals $30 and controls an inverse spread means (e.g. 50N-2, 50N-1, 50N) to be inactive, which applies inverse spread demodulation to signals having a level difference more than a threshold level T with respect to the signal of a highest level when the level difference is a prescribed threshold level T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rake receiver using a direct spread spectrum communication system. In recent years, there is an increasing demand for "anytime, anywhere, with anyone" communication, and the number of subscribers of mobile communication phones such as car phones and mobile phones is increasing.

When it comes to car telephones, it is rare to communicate within the line of sight of radio waves, and in general, in buildings, etc.
Radio waves that have been diffracted and passed through various routes are received in an overlapping manner.
This is called multipath propagation, and the reception state greatly changes due to traveling, and fading occurs.

Particularly in a wide band communication system such as a direct spread spectrum spread communication system, it is necessary to take measures against frequency selective fading (fading in which the frequency characteristic of the propagation path is not flat in the band) due to the spread of the propagation delay time of multipath. Is.

However, in the direct sequence spread spectrum communication system, an ordinary analog or digitally modulated signal is converted into a special digital code sequence [PN (Pseudo Nois).
e) code: pseudo-noise code] is used to spread the spectrum 100 times or 1000 times by modulating with a spreading sequence. At the receiving side, a spreading sequence that is an arbitrary data sequence used for spreading at the transmitting side By demodulating with the same, the information power that has been spread and scattered is collected, and the original information can be obtained by analog demodulation or digital demodulation.

As a measure against frequency selective fading,
One of the well known systems is a system called REKE (rake) reception system. This is a method for improving performance by separating multipaths in time and despreading and demodulating the signals that have passed through the paths, and the rake receiver of the invention adopts that method. Is.

[0006] Incidentally, RAKE means "rake", and is named to collect radio waves separated by multipath.

[0007]

2. Description of the Related Art FIG. 3 shows a block diagram of a conventional rake receiver, which will be described. However, it is assumed that this rake receiver is used in a mobile phone.

In FIG. 3, 1 is an antenna, 2 is a mixer, 3 is an oscillator, 4 is a correlator, 5 is a PN generating circuit, 6 is a delay difference detecting circuit, 7 is a level detecting circuit, and 8, 9 and 10 are First to third mixers 11, 12, 13 are first to third demodulators, 14, 15, 16 are first to third delay correction circuits, 1
Reference numerals 7, 18 and 19 are first to third multipliers, and 20 is an adder circuit. However, although the first to third multipliers 17 to 19 are each composed of a mixer, here, the first to third mixers 8 to 10 are used.
The function is given as a name to clarify the distinction from.

The connection path of the first mixer 8, the first demodulator 11, the first delay correction circuit 14 and the first multiplier 17 is called the first branch, and the second mixer 9, the second demodulator 12 and the second branch are connected. The path of the second delay correction circuit 15 and the second multiplier 18 is called the second branch, and the path of the third mixer 10, the third demodulator 13, the third delay correction circuit 16 and the third multiplier 19 is called the third branch. To

The mixer 2 multiplies a direct spread modulated wave (DS modulated wave) R1 received by the antenna 1 and transmitted from a base station (not shown) by an oscillation signal S1 of a predetermined frequency output from the oscillator 3. The baseband signal S
Convert to 2 and output. However, it is assumed that the DS modulated wave R1 is a multipath signal.

The correlator 4 detects signals (referred to as correlator output signals) S3, S4, S5 of three paths having a large received power from the baseband signal S2, and outputs the first to third correlator outputs thereof. The signals S3, S4 and S5 are output together with the reception timing. First to third correlator output signals S3, S4, S
FIG. 4 shows an example of 5 levels and reception timing. In FIG. 4, it is assumed that the first correlator output signal S3 is a direct wave, and the other correlator output signals S4 and S5 are signal waves that have been reflected and diffracted by a building or the like and have gone through various paths. To do.
Further, it is assumed that the time lag of each correlator output signal S3, S4, S5 is within 1 bit of the system clock signal of the mobile communication system.

The PN generating circuit 5 is a PN signal synchronized with each of the correlator output signals S3, S4 and S5, that is, a PN signal P1 having the same code as the PN signal used for spread demodulation in the base station.
Output P2 and P3.

The delay correction circuit 6 includes a first correlator output signal S
3 and the delay differences between the second and third correlator output signals S4 and S5 are calculated and output. A delay difference between the first correlator output signal S3 and the second correlator output signal S4 is defined as a first delay difference signal DS2, and the first correlator output signal S3 and the third correlator output signal S5
And the delay difference between and is the second delay difference signal DS3.

The level detection circuit 7 is provided for each correlator output signal S.
The levels of 3, S4 and S5 are detected and output. The level of the first correlator output signal S3 is the first level signal L1, the level of the second correlator output signal S4 is the second level signal L2, and the third level
The level of the correlator output signal S5 is the third level signal L3.

The first to third mixers 8 to 10 are composed of the first to third mixers.
Despreading is performed by multiplying the PN signals P1, P2, P3 and the baseband signal S2, and the first to third despreading signals S6, S7, S8 are output.

The first to third demodulators 11 are provided for each despread signal S.
By demodulating S6, S7 and S8, the data D1, D2 and D3 of each path are reproduced. First delay correction circuit 14
Outputs the data D1 as data D4 by delaying the data D1 by one bit of the system clock signal. For example, the delay time for one bit is assumed to be the delay time from time t1 to t4 shown in FIG. 4, and will be referred to as fixed delay time t5.

As shown in FIG. 4, the second delay correction circuit 15 subtracts the delay time t6 corresponding to the delay difference signal DS2 from the fixed delay time t5, and the data D2 corresponding to the first delay time t7 obtained by this subtraction. Are delayed and output as data D5.

As shown in FIG. 4, the third delay correction circuit 16 subtracts the delay time t8 corresponding to the delay difference signal DS3 from the fixed delay time t5, and the second delay time t9 obtained by this subtraction, the data D3. Are delayed and output as data D6.

By this delay processing, the phases of the multipath signals (correlator output signals) S3, S4 and S5 become in phase. The first to third multipliers 17, 18 and 19 are configured to output the data D
4, D5, D6 and the first to third level signals L1, L2
By multiplying by L3, weighting according to the reception level of each path is performed on the data of each path. By weighting in this way, the data of the component with a large SN ratio becomes clearer. Also, the weighted data are defined as D7, D8, and D9.

The adder circuit 20 adds the data D7, D8, D9 at the final stage of each branch to add them and outputs them as combined data D10.

[0021]

In the rake receiver as described above, it is known that the rake gain improves as the number of branches increases. However, from the viewpoints of hardware scale and low power consumption, 3 branches were considered to be optimal as in the above-mentioned conventional example.

However, according to a recent survey, 3 branches are sufficient in the suburbs, but in urban areas, the symbols S10 to S10 in FIG.
Since the number of multi-paths is large as shown in 15 as an example, the result is obtained that the number of branches is insufficient in 3 branches.

The reason for this is that in the case of the 3-branch lake, the three paths with high power in the received signal are combined, but the other paths cause interference, and therefore the number of multipaths is large. And the reception characteristics will deteriorate.

However, when the number of branches of the rake receiver is increased to cope with a large number of multipaths, there is a problem that the power consumption becomes large. This becomes a problem especially in mobile phones whose demand is increasing year by year. This is because the demands for mobile phones are miniaturization and low power consumption.

The present invention has been made in view of the above points, and is capable of improving reception characteristics even when the number of multipaths is large, and direct diffusion capable of realizing low power consumption. An object is to provide a rake receiver in a spread spectrum communication system.

[0026]

FIG. 1 shows the principle of the present invention. In this figure, 50 ₁ to 50 _N are first to Nth despreading means, and the direct spread modulation signal S30 having N paths
Is received, and each of the received direct spread modulation signals S30 is subjected to despread demodulation with the first to Nth spreading sequences synchronized with the N direct spread modulation signals S30 having different received timings.

[0027] 51 is a synthesizing means is for combining the output data D40 ₁ ~D40 _N of the first to N despreading means 50 ₁ to 50 _N. Reference numeral 52 is a control means of a characteristic element of the present invention, and among the levels of the N direct spread modulation signals S30, the level difference between the highest level signal and the other signals is individually calculated, and the calculated individual Despreading means for despreading and demodulating a signal having a level difference equal to or higher than the threshold T with respect to the highest level signal when the level difference is equal to or higher than a predetermined threshold T (for example, 50 _N-2 , 50 _N-1 , 50 _N ) is controlled to an off state.

The threshold value T is the direct spread modulation signal S30.
Among these, it is preferable to set the value to a value corresponding to the level difference between the signal in which the path diversity effect due to synthesis is not obtained and the highest level signal.

[0029]

According to the present invention described above, when the direct spread modulation signal S30 having the number of paths N is subjected to the despread demodulation for each path, the control means 52 produces a signal for which the path diversity effect by combining cannot be obtained. Since the despreading means for despreading demodulation (for example, 50 _N-2 , 50 _N-1 , 50 _N ) is turned off, it is possible to improve the reception characteristic even when the number of paths is large, and to reduce the reception characteristic. It is possible to realize power consumption.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of a rake receiver according to a direct spread spectrum spread communication system according to an embodiment of the present invention. However, in the embodiment shown in FIG. 2, the portions corresponding to the respective portions of the conventional example shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

The rake receiver shown in FIG. 2 is provided with N stages of branches capable of processing a large number of multipath signals, and the branches are operated according to the number of multipaths. Is a power control circuit 30.

The power control circuit 30 includes a level detection circuit 7
Among the level signals L1 to LN detected in step 1, the level difference between the highest level signal (this is the main path signal, for example, L1) and the other signals L2 to LN is individually calculated, and each of them is calculated. When the level difference is a threshold level value (for example, 10 dB) SR or more, the first to Nth control signals C2 to CN for turning off the components of the branch are output to the corresponding branch to turn off the corresponding branch. Is.

The reason why the branch component is turned off is that the path diversity effect due to the combination cannot be expected when the level difference from the main path is a predetermined value or more.

The branches are the first to Nth branches, and the constituent elements of each branch are as described in the conventional example of FIG. 3. However, in FIG. 2, the reference numerals assigned to the respective elements are changed.

That is, the constituent elements of the first branch are the first mixer 31 ₁ , the first demodulator 32 ₁ , and the first delay correction circuit 33.
₁ and the first multiplier 34 ₁ , and the components of the second branch are the second mixer 31 ₂ , the second demodulator 32 ₂ , the second delay correction circuit 33 ₂ and the second multiplier 34 ₂ ,. The components of the Nth branch are the Nth mixer 31 _N and the Nth demodulator 32.
_N Nth delay correction circuit 33 _N and Nth multiplier 34 _N.

Further, the control signal C2 is adapted to be output to the second demodulator 32 ₂ and the second delay correction circuit 33 _{2 of} the second branch, and the Nth control signal CN is the Nth branch. Nth demodulator 32 _N and Nth delay correction circuit 33 _N
It is designed to be output to.

This is because the demodulators 32 _{1 to} 32 _N and the delay correction circuits 33 _{1 to} 33 _N are digital circuits.
This is because the other mixers 31 _{1 to} 31 _N and the multipliers 34 _{1 to} 34 _N are composed of analog circuits, but if all the constituent elements of the branch are composed of digital circuits, control signals will be sent to all the constituent elements. Is configured to supply.

The operation when the rake receiver having such a configuration is used in an urban area where the number of signal paths is large will be described. However, it is assumed that the number of paths is the number of branches N or less.

First, the DS modulated wave R1 received by the antenna 1 is converted into a baseband signal S2 by the mixer 2, and the correlator 4 and the first to Nth mixers 31 _{1 to} 31 _{N are used.}
Is output to.

In the correlator 4, the signals S1 to SN of the number corresponding to the number N of branches are detected in the order of reception timing in descending order of received power. Based on the detected correlator output signals S1 to SN, PN signals P1, P2, ..., PN for despreading are generated in the PN generation circuit 5, and delay difference signals DS2 ,. Is detected and the level signal L1,
L2, ..., LN are detected.

The level signals L1, L2, ..., LN are input to the power control circuit 30. In the power control circuit 30, the level signal L1 detected by the level detection circuit 7
.. LN, the level difference between the level signal L1 of the main path having the highest level and the other level signals L2 to LN is individually calculated, and the calculated individual level difference is compared with the threshold level value. In this comparison, if the level difference between the sixth level signal L6 and the main path level signal L1 (not shown) is equal to or more than the threshold level value SR, the demodulation of the sixth to Nth branches for processing the sixth and subsequent received signals is performed. The _sixth to Nth control signals C1 to CN are supplied to the devices 32 ₆ (not shown) to 32 _N and the delay correction circuits 33 ₆ (not shown) to 33 _N to be turned off.

As a result, of the first to Nth signals S _{a1 to} S _aN despread by the mixers 31 _{1 to} 31 _N , the first to fifth signals S _{a1 to} S _a5 are processed by the branch circuit in the _subsequent stage. Then, finally, the addition circuit 35 performs addition and outputs the synthesized data DD.

As described above, according to the rake receiver of the embodiment, even if the number of paths is large, it is possible to combine only received signals of effective levels to obtain data, so that the receiving characteristics can be improved. In addition, it is possible to reduce the power consumption by suppressing an increase in the power consumption due to the N paths.

[0044]

As described above, according to the present invention,
Even when the number of multipaths is large, there is an effect that the reception characteristic can be improved and the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of a rake receiver using a direct spread spectrum spread communication system according to an embodiment of the present invention.

FIG. 3 is a block diagram of a rake receiver according to a conventional direct spread spectrum communication system.

FIG. 4 is a correlator output time waveform diagram.

FIG. 5 is another correlator output time waveform diagram.

[Explanation of symbols]

50 ₁ to 50 _N 1st to Nth despreading means 51 Combining means 52 Control means S30 Direct spread modulation signal D40 _{1 to} D40 _N Data after spread demodulation

Claims (2)

[Claims] 1. A first to N-th spreading sequence synchronized with N direct-spread modulation signals (S30), each of which receives a direct-spread modulation signal (S30) with N paths and has different received timings. First to Nth despreading means (50 ₁ to 50 _N ) for despreading demodulation
And the output data of the _first to _N-th despreading means (50 ₁ to 50 _N ).
In a rake receiver by a direct spread spectrum communication system comprising a combining means (51) for combining (D40 ₁ to D40 _N ), the highest of the levels of the N direct spread modulation signals (S30) If the level difference between the level signal and each of the other signals is individually calculated, and the calculated level difference is equal to or greater than a predetermined threshold value (T), the threshold value (T )
It is characterized in that a control means (52) for controlling the despreading means (for example, 50 _N-2 , 50 _N-1 , 50 _N ) for performing despreading demodulation of signals having the above level differences to an off state is provided. Rake receiver using direct sequence spread spectrum communication. 2. The direct spread modulation signal is defined as the threshold (T).
The direct spread spectrum spread communication system according to claim 1, wherein a value corresponding to a level difference between a signal in which a path diversity effect due to synthesis is not obtained in (S30) and the signal of the highest level is set. Rake receiver.