JPH098769A - Radio communication system using spread spectrum modulation - Google Patents

Abstract

PURPOSE: To effectively utilize frequency resources while keeping a speech enable state by making the band width of one radio signal among plural radio signals different from the band width of the other radio signals at least in a code division multiple access communication(CDMA) system. CONSTITUTION: In this radio communication system for the CDMA system for transmitting the plural radio signal individually subjected to spread spectrum modulation in the same transmission band, the band width of one radio signal among the plural radio signals is made different from the band width of the other radio signals at least. When communication channels CHa, CHb, CHc and CHd to be used in the same transmission band exist, for example, the signal band 1 width is made narrow for the communication channel CHd for which a carrier wave power/interference wave power ratio(CIR) is made excess. As a result, the CIR of the other communication channels CHa-CHc is improved. In this case, the central frequency of the respective communication channels CHa-CHd is identical but the central frequency can be made different for the respective communication channels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDMA (Code Division Multiple Access) type wireless communication system using spread spectrum modulation.

[0002]

2. Description of the Related Art In a wireless communication system such as a car phone and a mobile phone, a frequency division multiple access (FDMA) is used as a multiple access method.
Method, time division multiple access (TDMA: Time Division Mul)
tiple Access) method and code division multiple access (CDMA)
Each scheme is known. In the FDMA system, a predetermined frequency band is divided into a number of parts as shown in FIG. 1, and a plurality of users coexist by being distributed on the frequency axis so as to have different frequency channels. In the TDMA method, as shown in FIG. 2, the time used for each channel is divided within the same frequency band, and a plurality of users are dispersed on the time axis to coexist. In the CDMA system, as shown in FIG. 3, a code axis is provided as a third axis to allow a plurality of channels to communicate in a predetermined same frequency band at the same time. In a CDMA wireless communication system, an information signal such as a voice signal has a bandwidth (for example, 1
0 kHz) has a signal bandwidth (for example, 1
Since the spread spectrum spread to (MHz) is performed, FD
The number of channels per frequency bandwidth can be increased as compared with the MA method and the TDMA method, and the frequency utilization efficiency can be improved.

[0003]

By the way, in a CDMA wireless communication system, for example, in voice transmission, a BER (Bit Error Ratio) is 10 ^-2.
If you get a degree, you can talk. Therefore, a large amount of received input energy above a certain level at which the callable BER value is sufficiently secured is wasted. If the wireless device is
If the bit error rate characteristics shown in FIG. 4 are provided, the received input energy with which the CNR (Carrier-to-Noise power Ratio) is larger than 10 dB is not effectively used. It will be.

Therefore, an object of the present invention is to provide a CDMA radio communication system using spread spectrum modulation, which can effectively use frequency resources while ensuring a callable state.

[0005]

A radio communication system of the present invention is a CDMA radio communication system for transmitting a plurality of radio signals individually subjected to spread spectrum modulation within the same transmission band. The bandwidth of at least one of the wireless signals is different from the bandwidth of other wireless signals.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the wireless device using the wireless communication system of the present invention shown in FIG. 5, the antenna 1 is a transmitting / receiving antenna, and the terminal of the antenna 1 is either the receiving unit 3 or the transmitting unit 4 via the antenna switch 2. One of them is switched and connected. The selection of the antenna switch 2 on the receiving unit 3 side is in a steady state. In the receiving unit 3, the high frequency signal which is the received signal from the antenna switch 2 is band-limited by the band limiting filter (BPF) 5 and then supplied to the high frequency amplifier 6. The signal amplified by the high frequency amplifier 6 is supplied to the down converter 8 via the band limiting filter 7. The down converter 8 mixes the supplied high frequency signal with the local oscillation signal from the VCO 9 to generate an intermediate frequency signal. The level of the intermediate frequency signal is detected by the level detector 27 and supplied to the CPU (central processing unit) 19 as received electric field strength data. The intermediate frequency signal output from the down converter 8 is digitized by an A / D converter 10 and then supplied to a DSP (digital signal processor) 11. The DSP 11 detects the supplied digitized intermediate frequency signal, spreads and demodulates an information signal such as a voice signal and a control signal included in the received signal, and supplies the information signal to the channel coder / decoder 12.
The DSP 11 also performs a modulation operation according to a data signal, which is a digital information signal to be transmitted, supplied from the channel coder / decoder 12, and supplies the modulation result to the transmission unit 4.

In the transmitter 4, the digital signal output from the DSP 11 is supplied to the up converter 14 via the D / A converter 13. Upconverter 14
Mixes the modulated signal with the oscillation signal from the VCO 15 and frequency-converts it to a frequency to be transmitted. The oscillation signal is amplified by the pre-stage amplifier 16 and further amplified by the power amplifier 17 to become a transmission radio signal. This transmission radio signal is supplied to the antenna 1 via the antenna switch 2.

The modulation and demodulation operations of the DSP 11 are performed by the CPU 1
9. The switching operation of the antenna switch 2, the oscillation frequencies of the VCOs 9 and 15 and the amplification operation of the power amplifier 17 are controlled by the operating state of the DSP 11.
The CPU 19 is a DSP in response to an operation from the keyboard 20.
11 and controls a channel coder / decoder 1
2 and the operation modes of the voice CODEC (codec) 21 are controlled. The channel coder / decoder 12 operates as a coder that performs a predetermined code conversion on the digital audio signal supplied from the voice CODEC 21 or the digital data signal supplied from the data input / output interface 22, and the signal after the code conversion is performed. To D
Supply to SP11. Further, it operates as a decoder for decoding the demodulated digital signal supplied from the DSP 11 and supplies the decoded digital signal to the voice CODEC 21 or the data input / output interface 22. The voice CODEC 21 converts the analog audio signal from the microphone amplifier 23 into a digital audio signal of a predetermined format, converts the decoded digital audio signal from the channel coder / decoder 12 into an analog signal, and supplies it to the speaker amplifier 24. To do. A microphone 25 is connected to the microphone amplifier 23, and a speaker 26 is connected to the speaker amplifier 24.

The data to be transmitted is first supplied from the CPU 19 to the channel coder / decoder 12, and the voice CO
The data is converted into a data format according to the operation mode together with the communication data from the DEC 21 or the data input / output interface 22, and then supplied to the DSP 11. Communication data is not included until the link is established. As the operation mode, there are a normal mode and a thinning-out mode as described later, but the communication mode is set to operate in the normal mode. The DSP 11 performs data conversion on the supplied data signal by a modulation operation and supplies the data signal to the D / A converter 13. The data signal analogized by the D / A converter 13 is superimposed on the oscillation signal from the VCO 15 by the up converter 14. The oscillation signal including the data signal is amplified by the pre-stage amplifier 16 and further amplified by the power amplifier 17 to become a transmission signal, and the antenna switch 2
Is supplied to the antenna 1 via the. On the other hand, the signal received by the antenna 1 is supplied to the down converter 8 via the antenna switch 2, the band limiting filter 5, the high frequency amplifier 6 and the band limiting filter 7. Down converter 8
The supplied signal is mixed with the local oscillation signal from the VCO 9 to become an intermediate frequency signal, which is digitized by the A / D converter 10 and then supplied to the DSP 11. Spread demodulation is performed in the DSP 11, and the demodulated signal is supplied to the channel coder / decoder 12. The channel coder / decoder 12 sends control data to the CPU 1
9 and supplies communication data to the voice CODEC 21 or the data input / output interface 22. That is,
If the communication data is voice data, it is voice CODEC
21 is supplied to the data input / output interface 22.

As described above, the DSP 11 performs spread modulation operation during transmission and spread demodulation operation during reception. FIG. 6 is a block diagram showing an equivalent configuration during the spread modulation operation. That is, the data output from the channel coder / decoder 12 is supplied to the spread modulator 31 and spread-modulated by being multiplied by the spread code signal P1 indicating a spread code string consisting of a predetermined plurality of bits. The spread code signal P1 is generated from the spread code generator 32, and a clock signal that determines the bitwise generation timing of the spread code signal P1 is generated in the clock generator 33. The generation rate of the spread code signal P1, that is, the timing of the clock signal is much faster than the data rate, so that the band of the signal modulated is widened. The generation rate of the spread code signal is called the chip rate, and twice the rate is the spread band. The spreading band is selected to be about 10 to 1000 times the data band. The spread signal is supplied to the transmitter 4.

The equivalent configuration during the spread demodulation operation is configured as shown in the block diagram of FIG. The received data output from the receiving unit 3 is spread and demodulated by the spread demodulator 35. This demodulation is called despreading, and the received data is despread by the spreading code signal output from the spreading code selection generator 36. The spread code selection generator 36 stores the spread codes P1, P2, ..., Pn of all partner stations with which there is a possibility of communication as data in the internal memory 36a.
The same spreading code as the transmitting station to be received is selected from the plurality of spreading codes stored in a and is output as a spreading code signal in synchronization with the clock signal. The clock signal is generated from the clock generator 37. The spread demodulated data signal is supplied to the channel coder / decoder 12 via the filter 38. The filter 38 has the bandwidth of the despread data signal.

The clock generators 33 and 37 determine the frequency of the generated clock signal, that is, the chip rate, by the CPU 19
It is possible to change according to the command from. The spreading bandwidth can be changed by changing the chip rate. The larger the chip rate, the wider the diffusion bandwidth. Although the clock generators 33 and 37 are provided separately, they can be provided as a common clock generator during spread modulation and demodulation.

Further, in response to a command from the DSP 11, VC
Oscillation frequency of O9,15, output power of power amplifier 17,
The switching of the antenna switch 2 and the pass band of the BPF 7 are controlled. The wireless device having such a configuration is used in both the base station and the mobile station. At the time of calling or receiving a call, a transmission signal including control data for requesting link establishment is transmitted from the antenna 1 by operating the keyboard 20 in the mobile station. In response to a link channel establishment request from the mobile station to the base station on the control channel, the base station may transmit a transmission signal including control data of a link establishment response from the antenna 1 to perform link channel allocation to the mobile station. Done.

After shifting to the communication channel by the link establishment response, the CPU 19 in the wireless device of the base station.
For example, as shown in FIG. 8, the electric field strength of the communication channel CH1 is read from the output of the level detector 27 (step S1) every predetermined period, and it is determined whether the read electric field strength is larger than a threshold value. (Step S2). If the read electric field intensity is larger than the threshold value, the band adjustment subroutine is executed to obtain the optimum diffusion bandwidth (step S3). The operations of steps S1 to S3 are similarly performed for the other communication channels CH2 to CHn (n is the number of communication channels). Further, such an operation is repeated every predetermined period, and the optimum spreading bandwidth is always required for the communication channel in use.

In the bandwidth adjustment subroutine, as shown in FIG. 9, the current spread bandwidth is read (step S).
31). That is, since the current diffusion bandwidth for each communication channel is stored in the memory (not shown), the current diffusion bandwidth of the corresponding communication channel is read from the memory. Note that the maximum spreading bandwidth is used immediately after switching to the communication channel. Step S3
After executing 1, the optimum diffusion bandwidth is calculated from the electric field intensity read from the output of the level detector 27 and the current diffusion band (step S32). For this, a predetermined data table stored in the memory can be used, and the optimum diffusion bandwidth according to the read electric field strength and the current diffusion band is selectively set from the data table. In addition,
It is also possible to set the optimum diffusion bandwidth only in accordance with the read electric field strength. In this case, the larger the electric field strength, the smaller the optimum diffusion bandwidth is set. When the optimum spread bandwidth is obtained, a bandwidth change command to the optimum spread bandwidth is issued to the mobile station (step S33). Since the wireless signal in the communication channel contains the control data at a predetermined time interval in addition to the communication data as the information signal, the control data is used to move the bandwidth change command to the optimum spreading bandwidth. Transmitted to the station.

On the other hand, in the radio equipment of the mobile station, FIG.
As shown in 0, the CPU 19 determines whether or not the control data is received at every predetermined cycle (step S11), and if the control data is received, the bandwidth to the optimum spreading bandwidth is included in the control data. It is determined whether or not there is a change command (step S12). If there is a bandwidth change command, the DSP 11 is instructed to change the optimum spread bandwidth (step S13). The change to the optimum spreading bandwidth is carried out by changing the frequency of the clock signal emitted from the clock generator 33 as described above. C
For example, the PU 19 previously forms a data table indicating the relationship between the spread bandwidth and the frequency of the clock signal in an external memory (not shown), and uses the data table to determine the frequency of the clock signal corresponding to the optimum spread bandwidth. specify.

The spread spectrum processing gain Gp can be expressed by the following equation, where W is the signal bandwidth after spreading and B is the baseband signal bandwidth.

[0018]

[Equation 1] Gp = W / B That is, for example, when the gain Gp is compared for two types of the bandwidth W of 1 MHz and 10 MHz with the signal bandwidth B of the baseband being constant, the gain Gp is the bandwidth of 10 MHz. Bandwidth of 1MHz when W is 1 compared to when W
The gain is 0 times (10 dB).

Here, it is assumed that radio signals of the communication channels CHa, CHb, CHc, CHd that use the same transmission band exist as shown in FIG. The radio signal of each of those channels is W = 10 MHz, B = 16 kHz
When spread spectrum modulation is applied like
Is

[0020]

[Number 2] ^{Gp = (10 × 10 6)} / (16 × 10 3) = a 28 dB. Further, it is assumed that the energy density of each communication channel in the base station has the following values.

[0021]

(Equation 3)

In the base station, the desired reception channel is the communication channel CHa, and when the reception data signal obtained from the receiving unit 3 is despread using the spreading code corresponding to the radio signal, communication is performed as shown in FIG. Channel CH
Only the data signal received via a returns to the bandwidth of 16 kHz, and the data signals of the other communication channels are further spread to have the bandwidth of 20 MHz and the energy density is halved. The despread received data signal has a pass bandwidth of 16 kHz
z filter (corresponding to the filter 38 in FIG. 7). Therefore, the CIRa (Carrier to Interference Ratio) for the radio signal of the communication channel CHa is

[0023]

(Equation 4)

It is calculated as follows. Similarly, CIRb, CIRc, CIRd when the desired reception channel is the communication channel CHb, CHc, CHd is

[0025]

## EQU5 ## CIRb = Pb / Pn = 10.6 dB CIRc = Pc / Pn = 0.5 dB CIRd = Pd / Pn = 40.5 dB. In the communication channel CHc, the CIR is less than 1 dB and a sufficient BER value cannot be obtained.

According to the present invention, for the communication channel CHd having an excessively large CIR, the signal bandwidth, that is, the spreading bandwidth is narrowed as shown in FIG. At this time, the DSP 11 controls so that the signal bandwidth is changed but the power density per 1 Hz is not changed. Therefore, the communication channels CHa, CHb, C
For Hc,

[0027]

## EQU6 ## Gp = W / B (W = 10 MHz, B = 16 kHz), and for the communication channel CHd,

[0028]

## EQU00007 ## Gp '= W' / B (W '= 1 MHz, B = 16 kHz). The energy density of each communication channel in the base station has the following values.

[0029]

(Equation 8)

In the base station, the desired receiving channel is the communication channel CHa, and when the receiving data signal obtained from the receiving unit 3 is despread using the spreading code corresponding to the radio signal, communication is performed as shown in FIG. Channel CH
Only the data signal received via a returns to the bandwidth of 16 kHz, the data of the other communication channels CHb and CHc is further spread to have a bandwidth of 20 MHz, and the data of the communication channel CHd has a bandwidth of 11 MHz. In addition,
If the desired reception channel is the communication channel CHd, B is sent in response to a command from the CPU 19 before despreading.
The received signal is limited to a bandwidth of 1 MHz in PF7.

CIRa to CIRd for the radio signals of the communication channels CHa to CHd are

[0032]

[Equation 9]

It is calculated as follows. By narrowing the signal bandwidth of the communication channel CHd in this way, the CIR
Is 8 dB on channel CHa and 4d on channel CHb
It can be seen that B and channel CHc are improved by 5.8 dB. In the above-described embodiment, the center frequencies of the communication channels are the same, but the center frequencies may be different between the communication channels, and the DSP 11 controls the oscillation frequencies of the VCOs 9 and 15 to change the center frequency. Performed by. For example, as shown in FIG. 15, the signal bandwidths of the communication channels CHa and CHd are set to 1 MHz, and their center frequencies are the communication channels CHa and CHd.
The center frequencies of the communication channels CHb and CHc are also different. In this case, if the desired reception channel is the communication channel CHa, the reception signal of the communication channel CHd can be eliminated in the BPF 7 before despreading.

Further, in the above embodiment, the bandwidth of the radio signal is changed in the communication channel, but the bandwidth of the radio signal may be changed in the control channel.
Further, in the above-described embodiment, the bandwidth of the wireless signal is changed during communication, but the bandwidth of the wireless signal is set apart from the bandwidths of the wireless signals of other channels from the start of communication. May be.

[0035]

As described above, in the wireless communication system of the present invention, the bandwidth of at least one of the plurality of wireless signals individually subjected to spread spectrum modulation is equal to the bandwidth of other wireless signals. If the received energy of the one radio signal is excessive, the CIR of the other radio signal can be reduced by reducing the bandwidth of the one radio signal.
Will be improved. Therefore, it is possible to effectively use the frequency resource while ensuring a callable state.

[Brief description of drawings]

FIG. 1 is a diagram showing a multiplexing structure of an FDMA system.

FIG. 2 is a diagram showing a multiplexing structure of a TDMA method.

FIG. 3 is a diagram showing a multiplexing structure of a CDMA system.

FIG. 4 is a bit error rate characteristic diagram of a wireless device.

FIG. 5 is a block diagram showing a wireless device to which the present invention has been applied.

FIG. 6 is a block diagram showing an equivalent circuit realized by a DSP during transmission.

FIG. 7 is a block diagram showing an equivalent circuit realized by a DSP during reception.

FIG. 8 is a flowchart showing an operation of a CPU in the base station.

FIG. 9 is a flowchart showing a band adjustment subroutine.

FIG. 10 is a flowchart showing an operation of a CPU in a mobile station.

FIG. 11 is a diagram showing a multiplexing structure of radio signals of communication channels CHa to CHd.

FIG. 12 is a diagram showing a multiplexing structure of each radio signal including a spread and demodulated communication channel CHa.

FIG. 13 is a diagram showing a multiplexing structure of radio signals of channels CHa to CHd including a communication channel CHd whose bandwidth is changed.

FIG. 14 is a diagram showing a multiplexing structure of each radio signal including a spread and demodulated communication channel CHa.

FIG. 15 is a diagram showing a multiplexing structure of respective radio signals of communication channels CHa to CHd including a channel whose center frequency is changed.

[Explanation of symbols for main parts]

 1 Antenna 3 Receiver 4 Transmitter 11 DSP 12 Channel Coder / Decoder 19 CPU 21 Voice CODEC 22 Data Input / Output Interface

Claims (8)

[Claims] 1. A CDMA (code division multiple access) type wireless communication system for transmitting a plurality of wireless signals individually subjected to spread spectrum modulation in the same transmission band, wherein: A wireless communication system, wherein the bandwidth of at least one wireless signal is different from the bandwidths of other wireless signals. 2. The bandwidth of the radio signal is changed in a spread spectrum modulator.
A wireless communication system as described. 3. The spread code signal is obtained by generating a spread code signal composed of a code string of a plurality of bits and subjecting a data signal to be transmitted according to the spread code signal to spread spectrum modulation. The wireless communication system according to claim 2, wherein the bandwidth of the wireless signal is changed by changing the generation rate of the wireless signal. 4. A radio signal transmitted from one station of both stations in communication to the other station, when the reception level is higher than a threshold value, provides an appropriate bandwidth to the one station by radio signal. 2. The wireless communication according to claim 1, wherein the one station changes the bandwidth of the wireless signal to be transmitted according to the instruction of the appropriate bandwidth by the wireless signal from the other station. system. 5. The wireless communication system according to claim 4, wherein the bandwidth of the wireless signal is narrowed. 6. The wireless communication system according to claim 4, wherein the one station is a mobile station and the other station is a base station. 7. The wireless communication system according to claim 4, wherein the other station calculates the appropriate bandwidth from a received electric field strength of a wireless signal from the one station and a current bandwidth. . 8. The wireless communication system according to claim 1, wherein a center frequency of at least one of the plurality of wireless signals is different from a center frequency of other wireless signals.