JPH0946271A - Spread spectrum transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve power efficiency and frequency using efficiency and to enable using a matched filter for a reception circuit by providing a means arranging a modulation signal at a prescribed signal point by the combination of the respective bit values of a symbol. SOLUTION: A delay circuit 2 delays a parallel data signal DP supplied from an S/P converter 1 by the part of one symbol clock to supply a delay signal DDP for a signal mapping circuit 3B. A prefetch circuit generates a prefetch signal P of a prescribed value corresponding to the combination of the bit values of the signal DP. A spreading code processing circuit 9 generates an inversion signal PB in response to the supply of the signal P to take AND of each of the signals P and PB and a spreading code PN to supply spreading signals APN and APNB for a quadratic spreading circuit 4. A 2<n> -phase shift keying means arranging the modulation signal at the signal point of 2<n> by the combination of the respective bits of the symbol is provided like this to realize a modulation system where the point of an amplitude 0 does not pass at the phase change in secondary spreading.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum transmitter, and more particularly to a direct spread spectrum spread spectrum transmitter for second spreading with a spread code.

[0002]

2. Description of the Related Art In recent years, in addition to various broadcasts and public communications, communications for personal use such as mobile phones and personal computers have spread, and in proportion to this, expansion of communication capacity of wired and wireless communication systems is desired. In particular, wireless communication is expected to be in great demand as a communication function of mobile devices. However, since wireless communication uses a limited resource called a frequency band, there are major problems in improving the efficiency of use and preventing interference by wireless communication in an adjacent area or an adjacent frequency band.

The digital multiplex communication system is an effective system for solving the above problems and improving the utilization efficiency of the frequency band, and includes a time division multiplexing (TDM) and a frequency division multiplexing (FD).
M) and code division multiplexing (CDM). In this C
DM is a so-called spread spectrum modulation method that spreads and despreads a data signal based on a predetermined code between a transmitter and a receiver.

Since the spread spectrum modulation method cannot demodulate unless the code used between the transmitter and the receiver is known, by properly selecting a plurality of codes, a plurality of communications can be performed simultaneously using the same frequency band. Therefore, the spread spectrum modulation method has characteristics such as high channel utilization efficiency, strong interfering waves, and excellent confidentiality among digital multiplex communication methods.

Generally, the spread spectrum modulation method is disclosed in Japanese Patent Laid-Open No. 60-148245 (reference 1) and Japanese Patent Laid-Open No. 3-76.
Direct diffusion (Dir) described in Japanese Patent No. 333 (reference 1).
ect sequence (DS) system and frequency hopping (FH) system. The DS system is a system that spreads the frequency band by ten to several hundreds by multiplying data by a code of ten to several hundreds, and the FH system defines a frequency band to be used by dividing it from ten to several hundred channels. This is a method of switching the used channel according to the code pattern.

Referring to FIG. 6 which is a block diagram showing a conventional first spread spectrum transmitter of the DS system described in Documents 1 and 2, the first conventional spread spectrum transmitter of the present invention uses a serial data signal DS as a serial signal. An S / P converter 1 that performs parallel conversion and outputs a parallel data signal DP, and the parallel data signal DP are mapped to IQ coordinates composed of an in-phase phase I and a quadrature phase Q to generate an I signal ID and a Q signal QD. A signal mapping circuit 3 and a secondary spreading circuit 4 for secondary spreading each of the I, Q signals ID, QD in response to the supply of the spreading code PN to generate spread data signals IP, QP,
An LPF circuit 5 including low pass filters (LPF) 51 and 52 for low-pass filtering and waveform shaping each of the spread data signals IP and QP to generate spread signals FI and FQ, and a predetermined spread signal FI and FQ. Modulate carrier signal and transmit signal TD
And a spread signal generation circuit 8 for generating a spread code PN.

The transmission circuit 6 includes a final stage amplifier 61 that outputs a transmission signal TD, a carrier signal oscillator 62 that generates a carrier signal C, and a π / 2 phase shifter 63 that shifts the carrier signal C by π / 2. Prepare

Next, the operation of the first conventional spread spectrum transmitter will be described with reference to FIG.
The data signal DS is serial-parallel converted by the S / P converter 1 and supplied to the signal mapping circuit 3 as a parallel data signal DP. The signal mapping circuit 3 maps the parallel data signal DP to the I-Q coordinate and outputs the I signal I
The D and Q signals QD are generated and supplied to the secondary diffusion circuit 4. The secondary diffusion circuit 4 is an exclusive OR circuit, and I, Q
Each of the signals ID and QD is secondarily spread in response to the supply of the spread code PN from the spread signal generation circuit 8, and spread data signals IP and QP are generated and supplied to the LPF circuit 5. The code normally used as the spreading code PN is a code having a strong orthogonality such as an M-sequence code represented by a Barker code. The LPF 5 low-pass filters and shapes each of the spread data signals IP and QP to generate spread signals FI and FQ, and supplies them to the transmission circuit 6. The transmission circuit 6 modulates the carrier signal from the carrier signal oscillator 62 in response to the supply of the spread signals FI and FQ, amplifies this modulated signal to a predetermined transmission power by the final stage amplifier 61, and transmits it as a transmission signal TD. .

Normally, in the secondary spreading circuit 4, I and Q signals I
Since each of D and QD is simultaneously multiplied by the secondary spreading code 0 or 1, the carrier phase is 1 by the secondary spreading code.
Invert by 80 °. That is, the second-order spreading modulation method is a method called binary phase shift keying (BPSK).

Referring to FIG. 7, which shows an example of a layout of coordinate points (signal points) of I and Q signals when the data signal 00 is transmitted, the data signal 00 is sent to a signal point (0, 0) by a signal mapping circuit. ), The signal is reciprocated between the signal points (0,0) and (1,1) by the secondary spreading circuit. The phase of the carrier changes by 180 ° in synchronization with this operation.

The demodulated signal is obtained by despreading the same spreading code as the transmitter at a cycle synchronized with the transmitter. On the contrary, it is possible to simultaneously realize a plurality of different communications on the same frequency band by using the fact that demodulation cannot be performed by despreading with different spreading codes and using different spreading codes.

Since the receiver normally operates with a clock different from that of the transmitter, in order to perform accurate demodulation, first, a function of reproducing / synchronizing the modulated clock of the data signal from the transmission signal is required. . Generally, a matched filter adapted to a secondary spread code is used for clock recovery of a DS spread spectrum signal. The matched filter uses a surface acoustic wave element (SAW) or a digital filter and outputs a match signal when a predetermined pattern is detected in the input signal. Specifically, when a DS spread spectrum signal is input to a matched filter that stores a secondary spreading code, a matching signal is output just at each synchronization with the secondary spreading code, and this is output as a symbol clock of the demodulator described later. Used for.

Here, the names of clocks and the like of the respective units used in the DS system spread spectrum modulation will be described. The transfer unit of input data is called a bit, and the clock for controlling this is called a bit clock. A cycle of an n-bit data signal is called a symbol, and a clock for controlling this is called a symbol clock. The signal mapping circuit 3 and the like in FIG. 7 are controlled by the symbol clock. A 1-bit cycle of the secondary spread signal is called a chip, and a clock for controlling this is called a chip clock. Spread signal generation circuit 8 of FIG.
Is controlled by the chip clock. Usually, the chip clock has a frequency that is (spread code number) times the symbol clock. That is, when data of 2 Mbps is secondarily spread by the primary modulation method of QPSK modulation, the spreading code of 11 chips, the bit clock is 2 MHz, the symbol clock is 1 MHz, and the chip clock is 11 MHz.

The modulation method used for the second spread of the DS system spread spectrum transmitter includes quadrature phase shift keying (QPSK) in addition to the above BPSK.

A drawback of the above-mentioned first conventional spread spectrum transmitter is that it passes through a point where the phase changes by 180 °, that is, the amplitude of the modulated wave becomes 0, as shown in FIG. A large change in the amplitude level of the modulated wave causes an increase in the frequency bandwidth due to the nonlinear distortion of the power amplifier of the transmitter. In order to suppress this, a power amplifier such as a linear power amplifier having a small non-linear distortion must be used, so that it is unavoidable to lower the power efficiency and the output level. Therefore,
A modulation method in which the amplitude of the secondary modulated wave does not become 0 is desired as a transmission method with excellent power efficiency.

The second conventional spread spectrum transmitter disclosed in Japanese Patent Laid-Open No. 6-232838 (reference 3) having a modulation method in which the amplitude of the secondary modulated wave does not become 0 is common to the constituent elements common to FIG. Referring also to FIG. 8, which is also shown in blocks with reference characters / numbers, the difference between this second conventional spread spectrum transmitter and the previously described first spread spectrum transmitter is that the input signal Between the secondary spreading circuit 4A that directly secondary-spreads the DP and the signal mapping circuit 3A, if the secondary spreading data is 0, it is turned counterclockwise if it is 1; A phase shift of the secondary modulation wave is changed by 180 ° by providing a diagonal point transition prohibition circuit 20 which inhibits the zero point passage of the modulation signal, that is, the diagonal point transition, and by shifting the transition time of each of the I and Q signals. Is avoiding

The diagonal transition prohibition circuit 20 inverts the secondary diffusion data and the exclusive OR circuits 21 and 22 to which one input is supplied with the secondary diffusion data and the inverted data thereof, and inverts the secondary diffusion data. Inverter I for generating data
21 and D flip-flops F21 and F22 for supplying outputs to the other inputs of the exclusive OR circuits 22 and 21, respectively.
And each of the exclusive OR circuits 21 and 22 transfers the right and left transition processing data to the signal mapping circuit 3A.
To supply. Therefore, the secondary spread signal is equivalently 1 /
Divided into two.

Referring to FIG. 9 showing the signal point transitions of the second conventional spread spectrum transmitter, the transitions corresponding to the changes in the I and Q signals are shown by a solid line and a dotted line, respectively. In this way, since the amplitude of the secondary modulated wave does not pass through the point where the amplitude is 0, it is less susceptible to the nonlinear distortion of the transmission power amplifier.

However, in this second conventional spread spectrum transmitter, the I and Q transition times are shifted to prevent the passage of the point where the amplitude becomes 0, so that the modulation signal is immediately preceding the transition. The information of the arrangement signal is multiplied. For this reason, the receiver also demodulates the modulation signal of the required current time by multiplying the arrangement signal immediately before the transition. Therefore, general clock recovery using a matched filter cannot be performed. The reason for this is that the first arrangement information is necessary for clock reproduction, and the clock reproduction is necessary for obtaining the arrangement information. Document 3 shows the demodulation method after synchronizing with the clock of the transmission signal, but does not show the clock recovery method required at the beginning.

In general, in wireless communication, preamble data is added before communication target data for clock recovery. The preamble data is simple data that is known in advance, and clock recovery and synchronization are performed on the receiving side within the transmission period of this data. The problem of difficulty in clock recovery in the example of Document 3 becomes a factor of increasing the transmission period of this preamble data. Since the original transmission data cannot be sent during this preamble data transmission period, the fact that this period is long means that the throughput of data communication is low.

In addition to these techniques, there are some modulation systems that do not pass through the point where the amplitude becomes zero. As such a modulation method, minimum phase shift keying (MSK), continuous phase frequency shift keying (CQPSK), offset QPSK (OP
QSK) and the like are known.

[0022]

In the above-mentioned first conventional spread spectrum transmitter, since the amplitude level of the modulated wave is largely changed by passing through the point where the amplitude of the modulated wave is 0, nonlinear distortion can be suppressed. Therefore, it is necessary to use a power amplifier having a small non-linear distortion such as a linear power amplifier, which has a drawback that power efficiency is lowered and output level is lowered.

In the second conventional spread spectrum transmitter that alleviates this drawback, the I and Q signals are multiplied by the secondary spread code and the preceding arrangement signal, so that a general matched filter in the receiver is used. It is difficult to reproduce the clock using the clock recovery circuit, the clock recovery circuit is complicated, and the transmission period of the preamble data for ensuring the clock recovery period is increased, and thus the throughput of data communication is reduced. there were. Further, since the secondary spread signal is divided into two, the spread rate of the transmission signal is 1 /
It becomes 2 and it is necessary to use double the clock frequency in order to maintain the same performance as other DS system spread spectrum transceivers using the same spreading code, which increases design difficulty and power consumption. However, there is a drawback that it becomes an increasing factor.

Furthermore, MSK, CPFSK, OQPSK, which is characterized in that the modulation method itself does not pass the point of zero amplitude
In each of the conventional spread spectrum transmitters of the above method, there is a drawback that clock recovery on the receiver side becomes complicated.

[0025]

A spread spectrum transmitter according to the present invention is a signal mapping circuit for mapping a data signal onto an in-phase quadrature coordinate system consisting of an in-phase phase and a quadrature phase to generate an in-phase data signal and a quadrature data signal. And a secondary spreading circuit for multiplying each of the in-phase data signal and the quadrature data signal and performing secondary spreading in response to the supply of the first and second spread signals to generate each of the in-phase and quadrature spread data signals. In a spread spectrum transmitter that generates a transmission signal by modulating each of the in-phase and quadrature spread data signals as a modulation signal so as not to pass through the origin of a modulation signal arrangement represented by the in-phase quadrature coordinate system, A continuous input data signal is divided into n-bit symbols, and the modulation signal is arranged by combining bit values of the symbols. 2 ⁿ to place the signal point of the definitive 2 ⁿ
The phase shift keying means is provided.

[0026]

Next, an embodiment of the present invention will be described with reference to FIG.
With reference to FIG. 1 in which components common to and are similarly denoted by blocks with common reference characters / numerals, the spread spectrum transmitter according to the present embodiment shown in FIG. Converter 1, secondary spreading circuit 4, and LPF circuit 5
In addition to the transmission circuit 6 and the spread signal generation circuit 8, a signal mapping circuit 3B for mapping to the signal coordinates corresponding to the QPSK system instead of the signal mapping circuit 3, and a delay for delaying the parallel data DP by one symbol clock. The circuit 2, the pre-fetch circuit 7 that outputs a pre-fetch (pre-read) signal P having a predetermined value corresponding to the combination of the bit values of the signal DP, the pre-fetch signal P and its inverted signal PB, and the logic of the spread code PN. AND and spread code A
A spread code processing circuit 9 for generating PN and APNB is provided.

The spread code processing circuit 9 takes the logical product of the inverter I91 which inverts the pre-fetch signal P to generate the inverted pre-fetch signal PB and the signals P and PB and the spread code PN, and outputs the signals APN and APNB. AND circuits G91 and G92 for generating are provided.

Next, the operation of this embodiment will be described with reference to FIG. 1. The S / P converter 1 performs parallel / serial conversion of the input data signal DP in units of 2 bits per symbol to generate a parallel signal. The data signal DP is supplied to the delay circuit 7 and the pre-fetch circuit 7. The delay circuit 2 delays the supplied signal DP by one symbol clock, that is, by two bits of the data signal DS to generate a delayed signal DDP and supplies it to the signal mapping circuit 3B. The signal mapping circuit 3B maps the delayed signal DDP to the signal coordinates of QPSK, generates I and Q signals IDP and IDQ, and spreads the spreading circuit 41 for each of I and Q of the secondary spreading circuit 4.
42. On the other hand, the pre-fetch circuit 7 generates a pre-fetch signal P by converting so as to output 1 in the case of 00 or 01 or 0 in the case of 11 or 11, depending on the combination of the bit values of the supplied data signal DP. The spread code processing circuit 9 responds to the supply of the pre-etch signal P by generating an inverted signal PB of the pre-etch signal P, and outputs these signals P, PB
And the spread code PN from the spread signal generating circuit 8 are taken to generate signals APN and APNB, respectively,
It is supplied to the diffusion circuits 41 and 42, respectively. Spreading circuit 4
1 and 42 are the signals IDP and APN, and the signal Q.
An exclusive OR operation is performed on DP and APNB to generate secondary spread signals IP and QP, respectively. The LPFs 51 and 52 waveform-shape these secondary spread signals IP and QP, and
P and QP are generated and supplied to the transmission circuit 6. Transmission circuit 6
In the same manner as in the prior art, in response to the supply of the spread signals FI and FQ, the carrier signal from the carrier signal oscillator 62 is modulated, and this modulated signal is amplified by the final stage amplifier 61 to a predetermined transmission power to be used as the transmission signal TD. Send.

Referring also to FIG. 2 showing an example of the signal point arrangement of the present embodiment, the data signal 00 indicated by the I and Q coordinates is arranged at the signal point (0, 0) in the signal mapping circuit 3B. Secondary diffusion is performed based on this signal point. This time,
When the next data signal is 00 or 01, the signal point (0,
The phase between 1) and the previous signal point (0,0) changes as shown by the dotted line. Similarly, the next data signal is 10 or 11
In the case of, the phase between the signal point (1,0) and the previous signal point (0,0) changes as shown by the solid line. That is, in both cases, the change in the co-phase does not pass through the point where the amplitude becomes 0, so that the change in the amplitude level of the modulated wave is small.

Further, the receiving circuit for receiving the transmission signal of the spread spectrum transmitter of the present embodiment does not need to change the receiving circuit of the conventional DS system spread spectrum transmitter. That is, the correlator using the conventional digital filter and the clock recovery circuit can be applied as they are, and the preamble data preceding the data transmission need not be changed.

Next, referring to FIG. 3, which is a block diagram of the second embodiment of the present invention, in which components common to those in FIG. Is different from the above-described first embodiment in that 8PSK is used as the primary modulation method, and each of 90 ° and −90 ° is controlled instead of the secondary diffusion circuit 4 using the exclusive OR circuit. The secondary diffusion circuit 4A using a 90 ° phase converter having a terminal is provided.

The operation of this embodiment will be described with reference to FIG. 3. The S / P converter 1 serially / parallel converts the input data signal DP in units of 3 bits per symbol to generate a parallel data signal DP. Is supplied to the delay circuit 7 and the pre-etch circuit 7. The delay circuit 7 receives the signal DP
Is delayed by one symbol clock (that is, three bit clocks), and the signal DPP is supplied to the signal mapping circuit 3B. The signal mapping circuit 3B outputs the signal DPP to 8PS.
The signals are mapped to the signal coordinates of K to generate signals IDP and QDP, which are supplied to the secondary diffusion circuit 4A. Secondary spreading circuit 4A
90 for each of the input mapping signals IDP and QDP
When the control terminal input value for each of ° and −90 ° is 1, it has a function of outputting a signal whose phase is rotated by + 90 ° and −90 °, respectively. On the other hand, the pre-fetch circuit 7 outputs 000,00 depending on the combination of bit values of the input data signal DP.
In the case of 1,010 or 011, the value 1 of the pre-etch signal P is converted, and in the case of 100, 101, 110 or 111, the value P of the signal P is converted to 0, respectively. The spread code processing circuit 9 responds to the supply of the pre-etch signal P by generating an inverted signal PB of the pre-etch signal P, and outputs these signals P, PB
And the spread code PN from the spread signal generating circuit 8 are taken to generate signals APN and APNB, respectively,
The signals are supplied to the 90 ° and −90 ° control terminals of the secondary diffusion circuit 4A, respectively. The secondary spreading circuit 4A uses the spread signal I
P and QP are generated, and then LP is generated similarly to the first embodiment.
The transmission signal TD is transmitted via the F circuit 5 and the transmission circuit 6.

Referring also to FIG. 4 showing an example of the arrangement of the signal points of the present embodiment, the data signal 000 indicated by the coordinates of I and Q is signal point (0, 0, 0) in the signal mapping circuit 3B.
0), and secondarily diffused based on this signal point.
At this time, when the next data signal is 000,001,010 or 011, the phase changes between the signal point (0,1,0) and the previous signal point (0,0,0) as shown by the dotted line. To do. Similarly, when the next data signal is 100, 101, 110 or 111, the phase changes between the signal point (1, 1, 0) and the previous signal point (0, 0, 0) as shown by the solid line. .

Similarly, according to the present invention, the primary modulation method is 2 ^n.
It is needless to say that the extension to use the phase shift keying modulation (2 ⁿ PSK) can be applied without departing from the gist of the present invention.

Referring also to FIG. 5 showing an example of the signal point arrangement when this 2 ⁿ PSK is used in the primary modulation method,
The data signals 000 ... 0 indicated by the coordinates of I and Q are arranged at signal points (0, 0, 0, ..., 0) in the signal mapping circuit 3B, and are secondarily diffused with reference to these signal points. At this time, when the next data is 000 ... 0000 ... 1, ..., 011 ... 1, the signal point (0,1,0, ..., 0) and the previous signal point (0,
The phase changes between 0, 0, ..., 0) as shown by the dotted line. Similarly, the next data is 100 ... 0, 100 ... 1,
…, 111… 1, signal points (1, 1, 0,…, 0)
And the signal point (0, 0, 0, ..., 0) described above, the phase changes as shown by the solid line.

In explaining the present invention, the primary diffusion I,
An example of selecting the phase change of 90 ° or −90 ° and performing the secondary spreading with the next data for one symbol clock pre-etched from the Q signal has been described. However, the spreading code for the secondary spreading is 90 °, −. It is also possible to use different spreading codes at 90 °.

[0037]

As described above, the spread spectrum transmitter of the present invention is provided with the 2 ⁿ phase shift keying means for arranging the modulated signal at the 2 ⁿ signal points according to the combination of each bit value of the symbol. As a result, it is possible to avoid passage of the point of amplitude 0 at the time of phase change in the second spreading and suppress the amplitude fluctuation of the modulated wave. Therefore, it is possible to use a power amplifier with large nonlinear distortion but high power efficiency. There is an effect that it is possible to improve the power consumption and increase the output level.

Further, since the transmission format is not changed, there is no need to change the conventional receiving system, and the correlator and clock recovery circuit using digital filters can be applied as they are.

Further, since the preamble data sent prior to the data transmission may be left as it is, there is an effect that there is no particular decrease in throughput due to the application of the present invention.

Furthermore, since there is no factor for lowering the spread spectrum ratio of the transmission signal as in the second conventional spread spectrum transmitter, the use of double the clock frequency, the difficulty of designing and the increase factor of power consumption are eliminated. There is an effect that is done.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a spread spectrum transmitter of the present invention.

FIG. 2 is a signal point arrangement diagram showing an example of operation in the spread spectrum transmitter according to the present embodiment.

FIG. 3 is a block diagram showing a first embodiment of a spread spectrum transmitter of the present invention.

FIG. 4 is a signal point arrangement diagram showing an example of the operation of the spread spectrum transmitter according to the present embodiment.

FIG. 5 is a signal point arrangement diagram showing an example of an operation when 2 ⁿ PSK is used for a primary modulation scheme.

FIG. 6 is a block diagram showing a first conventional spread spectrum transmitter.

FIG. 7 is a signal point arrangement diagram showing an operation in the first conventional spread spectrum transmitter.

FIG. 8 is a block diagram showing a second conventional spread spectrum transmitter.

FIG. 9 is a signal point arrangement diagram showing an operation in the second conventional spread spectrum transmitter.

[Explanation of symbols]

 1 S / P converter 2 Delay circuit 3, 3A, 3B Signal mapping circuit 4, 4A Two-time spreading circuit 5 LPF circuit 6 Transmitter circuit 7 Pre-fetch circuit 8 Spreading signal generating circuit 9 Spreading signal processing circuit 20 Diagonal line transition prohibition circuit 21, 22 Exclusive OR circuit 41,42 Spreading circuit 51,52 LPF 61 Final stage amplifier 62 Carrier wave signal oscillator

Claims (4)

[Claims] 1. A signal mapping circuit for mapping a data signal to an in-phase quadrature coordinate system consisting of an in-phase phase and a quadrature phase to generate an in-phase data signal and a quadrature data signal, and
And a secondary spreading circuit that multiplies each of the in-phase data signal and the quadrature data signal in response to the supply of the second spread signal and performs secondary spreading to generate each of the in-phase and quadrature spread data signals. In a spread spectrum transmitter that generates a transmission signal by modulating each in-phase and quadrature spread data signal as a modulation signal so that the carrier signal does not pass through the origin of the modulation signal arrangement represented by the in-phase quadrature coordinate system, continuous input data A signal is divided into n-bit symbols, and 2 ⁿ phase shift keying means for arranging the modulated signal at 2 ⁿ signal points in the modulated signal arrangement by combining the bit values of the symbols is provided. Spread spectrum transmitter. 2. A delay circuit, wherein said 2 ⁿ phase shift keying means delays said input data signal for one symbol period to generate said data signal, and said input data signal in response to supply of said input data signal. A pre-fetch circuit for outputting a pre-fetch signal having a predetermined value corresponding to a combination of bit values forming the pre-fetch signal, and an inversion of the pre-fetch signal and an inverted pre-fetch signal obtained by inverting the pre-fetch signal. The spread spectrum transmitter according to claim 1, further comprising a spread code processing circuit 9 that generates a second spread signal. 3. The secondary spreading circuit is responsive to the supply of the first and second spread signals to set the phase of each of the in-phase data signal and the quadrature data signal to either + 90 ° or −90 °. A spread spectrum transmitter as claimed in claim 1, comprising a 90 ° phase converter which is rotated to generate each of the in-phase and quadrature spread data signals. 4. The spread code processing circuit obtains an inverter that inverts the pre-fetch signal to generate an inverted pre-fetch signal, and ANDs each of the pre-fetch signal and the inverted pre-fetch signal with the spread code. First and second
3. The spread spectrum transmitter according to claim 2, further comprising: a first and a second AND circuit for generating the spread signal.