JPH0746180A - Cellular telephone system according to cdma system - Google Patents

Abstract

PURPOSE:To prevent system capacity from being reduced even in a mobile station disabled to deal with a power control instruction from a base station. CONSTITUTION:The base station 2 is provided with a signal intensity detecting means 30 which detects the signal intensity of reception signals from plural mobile stations 1a, 1b,..., 1n to which inverse diffusion processing is applied by using a proper code allocated to each mobile station, a mean value calculating means 31 which calculates the mean value of the signal intensity detected by the signal intensity detecting means 30, a disturbance reception signal detecting means 32 which detects a disturbance reception signal with signal intensity exceeding the mean value by a prescribed value, a demodulation means which demodulates the disturbance reception signal detected by the disturbance reception signal detecting means 32, a spread modulation means 33 which performs the spread modulation of a signal demodulated by the demodulation means, a level adjusting means 34 which adjusts the level of a spread signal obtained at the output side of the spread modulation means 33, and a subtractor means 35 which sets the level of the disturbance reception signal as the mean value by subtracting the spread signal from the disturbance reception signal.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a CDMA (Code Division Multiple Access) using spread spectrum technology.
System cellular telephone system.

[0002]

2. Description of the Related Art C using spread spectrum technology
A DMA type cellular telephone system has been proposed.

In this CDMA cellular telephone system, for example, as shown in FIG. 3, a plurality of mobile stations 1a, 1b ... 1n are used by users to communicate using the same frequency band, and communication is performed to distinguish the plurality of mobile stations. This is a system that uses a PN (pseudo noise) code unique to the channel. In this case, when the voice data is multiplied by the PN code and spread-modulated, the voice data is spread over a wider frequency band, and when demodulated, the same PN code is multiplied.

The cellular telephone system has several k service areas.
The cell is divided into about m cells, and each cell has one base station 2
Is a system in which a subscriber (mobile station) uses the base station 2 as an intermediary to communicate with other subscribers (mobile station).

As shown in FIG. 3, from the base station 2 to the mobile station 1a,
A line connection to 1b ... 1n is called a forward link,
The line connection from the mobile stations 1a, 1b ... 1n to the base station 2 is called a reverse link.

In this CDMA cellular telephone system, a forward link is used to transmit various signals such as a power control command signal from the base station 2 to each mobile station 1a, 1b ... The control signal of is transmitted.

The modulator of this forward link transmitter is constructed, for example, as shown in FIG. In FIG. 4, reference numeral 3 denotes a data input terminal to which various data to be transmitted such as audio compressed data of 9.6 Kbps is supplied. For example, 9.
1-bit transmission data of 6 Kbps via convolutional encoder 4
The transmission data of 9.2 Kbps is supplied to the multiplication circuit 5 which constitutes the spread modulation circuit.

Further, 6 is each mobile station (user) 1a, 1b.
.. shows a long code generator for generating user-specific spreading (PN) codes assigned (assigned) to 1n respectively. A PN sequence of a spreading code called a long code assigned to each user is generated by the generator polynomial shown below.

[0009]

[Formula 1] P _L (X) = X ⁴² + X ³⁵ + X ³³ + X ³¹ + X ²⁷ + X ²⁶ + X ²⁵ + X ²² + X ²¹ + X ¹⁹ + X ¹⁸ + X ¹⁷ + X ¹⁶ + X ¹⁰ + X ⁷ + X ⁶ + X ⁵ + X ³ + X ² + X ¹ +1

The clock frequency of this PN series is 1.22.
The frequency is 88 MHz, the code length is (2 ⁴² -1), and one cycle is about 999 hours. Only one type of this PN sequence is designated, and a long code mask is used for the purpose of enabling identification between users (mobile stations).

As shown in FIG. 5, the concrete configuration of the long code generator 6 includes a shift register 6a composed of 42 flip-flop circuits and a long code mask 6b composed of 42 AND circuits and a modulo-2 adder. In this configuration, the spread (PN) code assigned to each user is obtained at the output terminal 6d by the 42-bit long code mask signal supplied from the 42-bit long code mask signal input terminal 6C.

The long code generator 6 of the forward link transmitter is designed to generate a long code (spreading code) corresponding to a user (mobile station) who is going to transmit. The long code is supplied to the multiplication circuit 5 which constitutes the spread modulation circuit via the 1/64 thinning circuit 7.

19. The signal obtained at the output side of the multiplication circuit 5
The spread signal of 2 Kbps is supplied to one input terminal of each of the multiplying circuits 9i and 9q constituting the spread modulation circuit via the frequency conversion circuit 8 for converting the spread signal of 1.2288 MHz. The pilot spreading (PN) codes P _I (X) and P _Q (X) are supplied to the other input terminals 10i and 10q of the multiplying circuits 9i and 9q, respectively.

The pilot spreading codes P _I (X) and P _Q (X) are based on an M sequence generated by the generator polynomial shown in the following equation, and after "0" continues for 14 bits, "0" becomes 1 It is a PN sequence with bits inserted.

[0015]

## EQU2 ## P _I (X) = X ¹⁵ + X ¹³ + X ⁹ + X ⁸ + X ⁷ + X ⁵ +1

P _Q (X) = X ¹⁵ + X ¹² + X ¹¹ + X ¹⁰ + X ⁶ + X ⁵ + X ⁴ + X ³ +1

The clock frequency of this PN series is 1.22.
88 MHz, the code length is 2 ¹⁵ , and one cycle is 26.66.
It will be 66 msec. This pilot spreading code P
_{The I} (X) and P _Q (X) generators are composed of shift registers each composed of 15 flip-flop circuits as shown in FIGS. 6A and 6B.

The spread signals obtained at the output sides of the multiplying circuits 9i and 9q are supplied to the multiplying circuits 11i and 11q, which form the quadrature modulating circuit, respectively. Reference numeral 12 denotes a carrier signal generator, and this carrier signal generator 12
The carrier signal is supplied to the multiplication circuit 11i and the carrier signal is supplied to the multiplication circuit 11q via the π / 2 phase shifter 13.

A multiplication circuit 11 which constitutes this quadrature modulation circuit.
The output signals of i and 11q are added by the adder circuit 14, a transmission intermediate frequency signal is obtained at the output terminal 15 of the addition circuit 14, and the transmission intermediate frequency signal is high-frequency modulated and transmitted.

FIG. 7 shows an example of the modulator of the reverse link transmitter, and 16 shows a data input terminal to which various data to be transmitted such as voice compression data of 9.6 Kbps is supplied. For example, the convolutional encoder 17 converts the transmission data of 9.6 Kbps supplied to the input terminal 16 into the convolutional encoder 17.
28.8 Kbps transmission data via the
307.2 Kb via the 6 → 64 code conversion circuit 18 for increasing the bit rate of the transmission data of 8.8 Kbps
The ps transmission data is supplied to the multiplication circuit 19 which constitutes the spread modulation circuit.

Reference numeral 20 denotes a long code generator for generating a long code (spreading code) assigned to the mobile station (user), that is, the reverse link transmitter. The long code generator 20 is as shown in FIG. Although it is configured, a specific long code mask is assigned,
It is designed to generate a unique long code (spread code).

The 1.2288 MHz long code (spread code) obtained at the output side of the long code generator 20 is supplied to the multiplication circuit 19. The spread signal of 1.2288 MHz obtained at the output side of the multiplying circuit 19 is supplied to one input terminal of each of the one and the other multiplying circuits 21i and 21q constituting the spreading modulation circuit.

Pilot spreading codes P _I (X) and P _Q (X) as shown in equations 2 and 3 are respectively applied to the other input terminals 22i and 22q of the multiplication circuits 21i and 21q, respectively.
To supply. The spread signals obtained at the output sides of the multiplication circuits 21i and 21q are supplied to the multiplication circuits 23i and 23q, respectively, which form the quadrature modulation circuit.

Reference numeral 24 denotes a carrier signal generator,
The carrier signal from the carrier signal generator 24 is supplied to the multiplication circuit 23i, and the carrier signal is π / 2.
It is supplied to the multiplication circuit 23q via the phase shifter 25.

A multiplication circuit 23 which constitutes this quadrature modulation circuit
The output signals of i and 23q are added by an adder circuit 26, a transmission intermediate frequency signal is obtained at an output terminal 27 of the addition circuit 26, and the transmission intermediate frequency signal is high-frequency modulated and transmitted.

The characteristic of the CDMA cellular telephone system is that it has three types of PN sequences P _L (X), P _I (X) and P _Q.
This means that only (X) is used, and these three types of PN
The system timing is used to secure a large system capacity using the sequence. The system timing means the base station 2 and the mobile stations 1a, 1b ...
Multiple access is made possible by having a common time base in the entire system consisting of n and using this time as a reference.

The problem in such a CDMA cellular telephone system is that a plurality of mobile stations 1a and 1b in one cell are used.
... If all of the transmission signals as the reverse link that reach the base station 2 from 1n do not have the same power, a near-far problem occurs. The near-far problem is a problem of masking a transmission signal from a distant mobile station due to the cross-correlation of the strong transmission signal of the mobile station near the base station 2.

Therefore, first, in the base station 2, the mobile stations 1a and 1b.
After despreading the transmission signal from 1n, the signal strength is detected, and this base station 2 instructs each mobile station 1a, 1b, ... 1n to control the transmission power through this forward link. The power control instruction data to be transmitted is demodulated with the power control instruction data in each mobile station 1a, 1b ... 1n, and then the transmission power is controlled according to the instruction, which is repeated every predetermined period. Is proposed.

[0028]

However, the base station 2
1n, even though the power control instruction data is transmitted to the mobile stations 1a, 1b ... 1n, even one of the mobile stations 1a, 1b. There was a problem that the system capacity was reduced due to the perspective problem.

In view of the above point, the present invention improves the near-far problem even when there is a mobile station that cannot fully respond to the power control instruction from the base station among a plurality of mobile stations, and prevents the system capacity from decreasing. The purpose is to

[0030]

A CDMA cellular telephone system according to the present invention includes a base station 2 as shown in FIGS.
And a plurality of mobile stations 1a, 1b ...
In the cellular telephone system, the received signals from the plurality of mobile stations 1a, 1b ... 1n are despread to the base station 2 by using a unique code assigned to each mobile station. A signal strength detecting means 30 for detecting the signal strength, an average value calculating means 31 for calculating an average value of the signal strengths detected by the signal strength detecting means 30, and an average value from the average value calculating means 31 is a predetermined value. An interference reception signal detection means 32 for detecting an interference reception signal having a signal strength higher than the above, a demodulation means for demodulating the interference reception signal detected by the interference reception signal detection means 32, and a signal demodulated by the demodulation means From the spread modulation means 33 for spread modulation, the level adjustment means 34 for adjusting the level of the spread signal obtained at the output side of the spread modulation means 33, and the interference reception signal By subtracting the spread signal is one having a subtraction means 35 for the level of the interference reception signal with the average value.

[0031]

According to the present invention, a plurality of mobile stations 1a, 1b ...
Even if there is a mobile station out of n that cannot fully respond to the power control instruction from the base station 2, the base station 2 receives the average value of the reception signal (interference reception signal) from the mobile station. Since the signal is demodulated and then processed according to the data of the received signal in the base station 2, the near-far problem can be improved and the system capacity can be prevented from lowering.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the CDMA cellular telephone system of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of a receiver of the base station 2 according to this example.
In FIG. 1, reference numeral 70 denotes a receiving antenna of the base station 2 which receives received signals from a plurality of mobile stations 1a, 1b ... It is supplied to the mixing circuit 72.

Further, in FIG. 2, reference numeral 73 indicates a local oscillator, and the oscillation signal from the local oscillator 73 is mixed by the mixing circuit 7.
2, and the received intermediate frequency signal obtained at the output side of the mixing circuit 72 is passed through the series circuit of the intermediate frequency amplifying circuit 74 and the interfering received signal processing circuit 75 according to the present example to the demodulating circuit 76 including a despreading circuit. Supply.

In the base station 2, the transmission data from the mobile station, which is obtained at the output terminal 77 of the demodulation circuit 76, is sent to the public line network or the like according to the transmission data via the signal processing circuit or the like.

Interfering reception signal processing circuit 75 according to this embodiment
As shown in FIG. That is, in FIG. 1, reference numeral 36 denotes a reception intermediate frequency signal input terminal to which the reception intermediate frequency signal from the intermediate frequency amplifier circuit 74 is supplied. In this case, the reception intermediate frequency signal supplied to the reception intermediate frequency signal input terminal 36 is the same as the signal obtained at the output terminal 27 of the reverse link transmitter shown in FIG.

The reception intermediate frequency signal supplied to the reception intermediate frequency signal input terminal 36 is supplied to a memory 37 which constitutes a delay circuit for time adjustment, and is supplied to a carrier regenerator 38 which reproduces a carrier signal from a transmitter. . Further, the reception intermediate frequency signal supplied to the reception intermediate frequency signal input terminal 36 is supplied to one input terminal of each of the multiplication circuits 39i and 39q forming the quadrature demodulation circuit.

The carrier signal obtained at the output side of the carrier regenerator 38 is supplied to the other input terminal of the multiplication circuit 39i, and the carrier signal obtained at the output side of the carrier regenerator 38 is supplied to the π / 2 phase shifter 40. Multiplier circuit 3 via
It is supplied to the other input terminal of 9q.

The output signal of the multiplying circuit 39i is supplied to the multiplying circuit 41i which constitutes the despreading circuit, and the output signal of the multiplying circuit 39i is used for demodulating I channel data as shown in equation 2 for the pilot spreading code P _I (X ) Is supplied to the PN-I regenerator 42i for regenerating, and the pilot spreading code P _I (P _I (P) of the phase corresponding to the unique spreading code assigned to the transmitted mobile station, which is obtained at the output side of the PN-I regenerator 42i. X) is supplied to this multiplication circuit 41i.

I obtained at the output side of the multiplication circuit 41i
The channel data is supplied to the signal strength measuring circuit 30 via the low-pass filter 43i and also to the first I-channel data output terminal I ₁ .

The output terminal of the multiplying circuit 39q is supplied to the multiplying circuit 41q which constitutes the despreading circuit, and the output signal of this multiplying circuit 39q is a pilot spreading code P _Q (X ) Is supplied to the PN-Q regenerator 42q for regenerating, and the pilot spreading code P _Q (Phase corresponding to the unique spreading code assigned to the transmitted mobile station, which is obtained at the output side of the PN-Q regenerator 42q. X) is supplied to this multiplication circuit 41q.

Q obtained at the output side of the multiplication circuit 41q
The channel data is supplied to the signal strength measuring circuit 30 via the low pass filter 43q and also to the first Q channel data output terminal Q ₁ .

The signal strength measuring circuit 30 calculates the sum of squares of the I channel data and the Q channel data, and the base station 2 of the transmission signal from the first mobile station is output to the output side of the signal strength measuring circuit 30. The received signal strength of the received signal at is obtained.

The output signal of the signal strength measuring circuit 30 is supplied to the first input terminal 31 ₁ of the average value calculating circuit 31.
In the interference reception signal processing circuit 75 according to this example, the number N of mobile stations (users) for this base station 2 (for example, 30) is provided with the signal strength measurement block indicated by the broken line in FIG.

Therefore, the output signals from the N signal strength measuring circuits 30 are supplied to the average value calculating circuit 31. In the average value calculating circuit 31, the N received signal strength output signals are averaged, An average value signal is obtained.

In FIG. 1, reference numeral 32 denotes a channel in which the levels of the N received signal strength signals of the N channels supplied to the average value calculation circuit 31 exceed the level of the average value signal by a predetermined value or more. The intensity over-channel detection circuit for detecting is shown. The channel selection signal detected by the output signal of the intensity over-channel detection circuit 32 is I channel data selector circuit 44i, Q channel data selector circuit 44q, I channel pilot spread code selector circuit 45i. And Q channel pilot spreading code selector circuit 45q.

The intensity over-channel detection circuit 32 supplies the level control circuit 34 with a level control signal corresponding to the detected signal intensity of the channel. In this case, the level control circuit 34
The level control of the spread signal received from the spread signal described later from the level control circuit 34 is performed by the subtraction circuit 35.
When subtracted by, the output signal of the subtraction circuit 35 is set to the average value level.

Further, the I channel data selector circuit 44
On the input side of i, N I-channel data output terminals I ₁ ,
I ₂ ... I _n are connected to each other, and N Q channel data output terminals Q ₁ , Q _2, ... Q _n are connected to the input side of the Q channel data selector circuit 44 q.

Further, N I-channel pilot spreaders which are phase-modulated corresponding to the spreading codes assigned to the first to N-th mobile stations (users) on the input side of the I-channel pilot spread code selector circuit 45i. The code P _I (X) is supplied from the I-channel pilot spreading code generator 46i, and the first to the input side of the Q-channel pilot spreading code selector circuit 45q.
The Q channel pilot spreading code generator 46q supplies N Q channel pilot spreading codes P _Q (X) that are phase-modulated in accordance with the spreading code assigned to the Nth mobile station (user). .

The I channel data selected by the I channel data selector circuit 44i is supplied to one input terminal of the multiplication circuit 47i which constitutes the spread modulation circuit 33, and the I channel pilot spread code selector circuit 45 is provided.
I channel pilot spreading code P _I selected by i
(X) is supplied to the other input terminal of the multiplication circuit 47i, and the output signal of the multiplication circuit 47i is supplied to the multiplication circuit 48i forming the quadrature modulation circuit.

Further, the Q channel data selector circuit 44
The spread channel modulation circuit 33 converts the Q channel data selected by q.
And the Q channel pilot spreading code P _Q (X) selected by the Q channel pilot spreading code selector circuit 45q is supplied to the other input terminal of the multiplying circuit 47q. The output signal of the multiplication circuit 47q is supplied to the multiplication circuit 48q forming the quadrature modulation circuit.

The carrier reproduced by the carrier regenerator 38 is input to the carrier selector circuit 38a, the carrier signal selected there is supplied to the multiplication circuit 48i, and the carrier signal from the carrier selector circuit 38a is π / 2. The signal is supplied to the multiplication circuit 48q via the phase shifter 49, the output signals of the multiplication circuits 48i and 48q are added by the addition circuit 50, and the spread signal obtained at the output side of the addition circuit 50 is supplied to the level control circuit 34. The spread signal whose level is adjusted by the level control circuit 34 is supplied to the subtraction circuit 35, and the spread signal is supplied from the time-interlocked reception intermediate frequency signal from the memory 37 by the subtraction circuit 35. The subtraction circuit 35 is configured to always obtain a reception intermediate frequency signal having an average value level at the output side thereof.

The reception intermediate frequency signal of the average value level which is obtained at the output side of the subtraction circuit 35 is supplied to the demodulation circuit 76 which is a despreading circuit. Others are the same as those of the conventional CDMA cellular telephone system.

Since this example is configured as described above, even if there is a mobile station that cannot support the power control instruction from the base station 2 among the plurality of mobile stations 1a, 1b ... The received signal strength of the received signal (interfering received signal) at the base station 2 from
Since the demodulation circuit 76 demodulates the received intermediate frequency signal at the base station 2 after the reception intermediate frequency signal at the average value level, all the received intermediate frequency signals demodulated by the demodulation circuit 76 are signals at the average value level. There is an advantage that the system capacity can be improved and a decrease in system capacity can be prevented.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0055]

According to the present invention, even if there is a mobile station out of a plurality of mobile stations that cannot respond to the power control instruction from the base station, it is possible to improve the near-far problem and prevent a decrease in system capacity. Have a profit

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of an embodiment of a CDMA cellular telephone system of the present invention.

FIG. 2 is a block diagram showing an example of a base station receiver of an embodiment of the CDMA cellular telephone system of the present invention.

FIG. 3 is a configuration diagram showing an example of a CDMA cellular telephone system.

FIG. 4 is a configuration diagram showing an example of a forward link transmitter.

FIG. 5 is a configuration diagram showing an example of a long code generator.

FIG. 6 is a configuration diagram showing an example of a pilot spreading code generator.

FIG. 7 is a configuration diagram showing an example of a reverse link transmitter.

[Description of Codes] 1a, 1b ... 1n Mobile station 2 Base station 30 Signal strength measurement circuit 31 Average value calculation circuit 32 Strength over-channel detection circuit 33 Spreading modulation circuit 34 Level control circuit 35 Subtraction circuit 36 Reception intermediate frequency signal input Terminal 37 Memory 75 Interference reception signal processing circuit

Claims (1)

[Claims] 1. A CDM having a base station and a plurality of mobile stations.
In the A-system cellular telephone system, a signal for detecting the signal strength of each received signal after despreading the received signals from the plurality of mobile stations to the base station using a unique code assigned to each mobile station. Strength detecting means, average value calculating means for calculating an average value of the signal strengths detected by the signal strength detecting means, and detecting an interfering received signal having a signal strength exceeding the average value from the average calculating means by a predetermined value or more. Interference reception signal detecting means, demodulation means for demodulating the interference reception signal detected by the interference reception signal detecting means, spreading modulation means for spreading modulation of the signal demodulated by the demodulation means, and spreading modulation means of the spreading modulation means. Level adjusting means for adjusting the level of the spread signal obtained at the output side, and subtracting the spread signal from the interference received signal, the level of the interference received signal as the average value CDMA scheme cellular telephone system; and a subtraction unit that.