JP3004147B2 - Frequency diversity transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for mobile communication. In particular, it relates to frequency diversity transmission for overcoming fading fluctuation.

[0002]

2. Description of the Related Art In wireless communication such as mobile communication, a diversity technique has conventionally been used to overcome fading fluctuation. As the diversity technology, space diversity and frequency diversity are widely known. Further, as a technique for obtaining the frequency diversity effect, a multicarrier transmission scheme and a frequency hopping (Frequency Hopping: FH) transmission scheme are known.
Further, the frequency hopping transmission method includes a high-speed frequency hopping (FFH: Fast FH) that performs one or more frequency hoppings for one symbol information, and a burst signal formed based on a signal of several symbols or more. Frequency hopping (SFH:
Slow FH). In particular, fast frequency hopping
Since a frequency diversity effect is obtained for each symbol, an extremely stable transmission path can be formed.

FIG. 20 is a block diagram showing a conventional example of a frequency diversity transmission apparatus using high-speed frequency hopping.

This device includes a transmitting device and a receiving device,
The transmission device includes a quadrature modulator 201, a frequency synthesizer 202, a frequency control circuit 203, and a band-pass filter 204. The quadrature modulator 201 modulates the input symbol sequence with the carrier frequency generated by the frequency synthesizer 202. The frequency generated by the frequency synthesizer 202 is controlled by the frequency control circuit 203, and K different frequencies are generated in a predetermined order during one symbol period of the input symbol sequence. Quadrature modulator 20
1 is transmitted from the antenna after passing through the band-pass filter 204. The transmitted modulated signal is a signal in which one symbol is composed of K chips. Here, K = 4.

[0005] The receiving device comprises a mixer 205, a local oscillator 206, a band-pass filter 207 and a square detection circuit 2
08 = K, and a combining circuit 209 for combining the signals of the four systems. The signal received by the antenna is 4
Are distributed to the mixers 205. These four mixers 20
5 is supplied with a local frequency from a local oscillator 206. The output of the mixer 205 is input to the band pass filter 207, and a chip signal of a high-speed frequency hopping signal is extracted. The extracted chip signal is square-detected by a square detection circuit 208 to extract a level, and a synthesis circuit 209 detects and outputs the sum of chip levels over one symbol.

As a demodulation method of high-speed frequency hopping, two methods of coherent detection and non-coherent detection are considered. Since the non-coherent detection does not look at the phase of the chip, the transmission characteristics are degraded as compared with the coherent type that performs detection including the phase. For example, BPSK
In the case of (Binary Phase Shift Keying), in non-coherent detection, a carrier-to-noise ratio (CNR) is obtained to obtain the same error rate as compared to coherent detection.
It is known that the ratio degrades by about 6 dB.
However, in actual mobile radio, carrier synchronization is difficult due to fast fading fluctuation of the transmission path, and the above-described non-coherent detection has been used.

The present inventors have invented a system capable of coherent detection of a frequency hopping signal,
A patent application has already been filed (Japanese Patent Application No. 4-313317, hereinafter referred to as "prior application").

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency diversity transmission apparatus which can obtain more excellent transmission characteristics and can simultaneously transmit a plurality of symbol sequences at the same frequency.

[0009]

A frequency diversity transmission apparatus according to the present invention is characterized in that chips obtained by dividing individual symbols are encoded and transmitted.

That is, a transmitting apparatus that modulates each symbol of an input symbol sequence with K kinds (K is an integer of 2 or more) of carrier frequencies and transmits the modulated signal, In a frequency diversity transmission device including a reception device that demodulates with K kinds of local frequencies synchronized with carrier frequencies, a transmission device divides each symbol of an input symbol sequence into a plurality of chips and codes the chip sequence. Encoding means for outputting K coded chip signals per symbol, and K kinds of carrier frequencies modulated by each of K kinds of carrier frequencies by the K coded chip signals. And a chip modulating means for generating a wave, and the receiving apparatus converts the K chip modulated waves per symbol into K rows. A quasi-synchronized detection means for extracting the K complex envelope signals by detecting each by Le frequency, characterized in that it comprises a determination means for determining transmission symbols from the K-number of the complex envelope signals.

The chip modulating means includes means for multiplying a plurality of sequences of input symbols by signals orthogonal to each other for each sequence, and the judging means multiplies K complex envelope signals by a complex conjugate of the orthogonal signals. It may include means for performing

The determining means includes means for multiplying each of the K complex envelope signals by a complex coefficient, means for synthesizing the complex envelope signal multiplied by the complex coefficient to determine a symbol, and determining the complex coefficient in advance. Means for setting in accordance with the determination result for the training signal of the determined pattern.

[0013] The determining means encodes the symbol candidate by the same logic as the chip encoding means, and means for obtaining an estimated value for each of the K complex envelope signals from the output of the encoder. Means for obtaining an estimation error by subtracting the estimated value from each of the K complex envelope signals; means for obtaining the sum of squares of the estimation error; transition from one point of time of the symbol pattern candidate to the next point of time A maximum likelihood estimating circuit that determines a path corresponding to, and selects a path that minimizes the sum of squares of the estimation error from the path and performs symbol determination;
A signal generator that outputs a symbol candidate corresponding to the path obtained by the maximum likelihood estimation circuit.

The chip modulating means is provided with means for generating K chip modulated waves having different carrier frequencies in time series,
Frequency hopping type frequency diversity can be realized. In this case, it is preferable that the transmitting apparatus includes means for separately and continuously generating K types of carrier frequencies, and the chip modulating means include means for selecting the K types of carrier frequencies in time series.

The chip modulating means may be provided with means for simultaneously and in parallel generating K chip modulated waves having different carrier frequencies, so that multi-carrier type frequency diversity can be performed.

The transmitting apparatus includes means for generating carrier signals having substantially constant initial phases with respect to K encoded chip signals for each symbol as K kinds of carrier frequencies, and the receiving apparatus includes means for generating each carrier as a local frequency. It is desirable to include means for generating a local signal having a substantially constant initial phase for each of the K encoded chip signals. The means for generating the carrier signal and the means for generating the local signal may each include a memory table in which a sine waveform is recorded in advance, and a means for setting an output frequency by changing the address designation of the memory table. .

[0017]

The frequency diversity transmission apparatus according to the present invention divides each symbol into chips and further encodes the chips. Thereby, a plurality of symbol sequences can be transmitted simultaneously on the same frequency, and the frequency can be used effectively.

As an encoding method, for example, signals orthogonal to each other are multiplied for each symbol sequence. At this time, on the receiving side, the complex envelope signal obtained by quasi-synchronous detection of each of the K chip modulated waves is multiplied by the complex conjugate of the orthogonal signal, and further multiplied by a complex coefficient and synthesized.
A symbol is determined from the combined signal. As a complex coefficient to be multiplied, a coefficient obtained according to a determination result for a training signal having a predetermined pattern is used.

Further, the maximum likelihood determination can be performed on the receiving side. In that case, a symbol candidate is obtained on the receiving side, the same encoding as that on the transmitting side is performed on the symbol candidate, an estimated value of the complex envelope signal is obtained therefrom, and the received value is compared with the received complex envelope signal. In this case, decoding on the receiving side is unnecessary.

The present invention can also be used as frequency hopping type frequency diversity in which the carrier frequency for each symbol changes in a time-series manner. However, a multicarrier type in which the same symbol is simultaneously transmitted at a plurality of carrier frequencies is used. Frequency diversity can also be performed. In this case, signals obtained from the same symbol are transmitted at different frequencies from each other, but the signals, that is, the coded chip signals are coded, so that the same signal is transmitted as in the conventional multi-carrier type frequency diversity. It is not transmitted on multiple frequencies.

According to the present invention, coherent detection is preferably performed on the receiving side, as in the previous application. To this end, the transmitting side generates a carrier signal whose initial phase for the coded chip signal is substantially constant, and the receiving side has substantially the initial phase for the K coded chip signals for each symbol as the local frequency. It is preferable to use a fixed local signal for the control. Such a carrier signal and a local signal can be easily generated by using a direct digital synthesizer (DDS: Direct Digital Synthesizer).

[0022]

FIG. 1 is a block diagram showing a frequency diversity transmission apparatus according to a first embodiment of the present invention. In this embodiment, a frequency diversity effect is obtained by frequency hopping. The modulation method is quadrature phase modulation (QPSK), and shows a case where the number of chips K = 4.

The transmitting apparatus 1 of the present embodiment modulates and transmits K symbols (K is an integer of 2 or more) of individual symbols of an input symbol sequence.
And a receiving device 2 for receiving the transmission signal of the transmitting device 1 and demodulating the signal by K kinds of local frequencies synchronized with the K kinds of carrier frequencies.

The transmitting apparatus 1 includes chip encoding means for dividing each symbol of an input symbol sequence into a plurality of chips and encoding the chip sequence to output K encoded chip signals per symbol. And a quadrature modulator 1 as chip modulation means for modulating K types of carrier frequencies with the K coded chip signals to generate K chip modulated waves per symbol.
2. Frequency synthesizer 13 and frequency control circuit 14
Is provided. The output of the quadrature modulator 12 is the bandpass filter 1
5 and transmitted.

The receiver 2 includes a mixer 21 and a frequency synthesizer 22 as quasi-synchronous detection means for detecting K chip modulated waves per symbol at K local frequencies and extracting K complex envelope signals. , Frequency control circuit 23, band pass filter 24 and IQ detector 2
5 and a demodulation circuit 26 as determination means for determining a transmission symbol from the K complex envelope signals.

The symbol sequence b (t) input to the input terminal of the transmitter is represented by b (t) = b _i (t) + jb _q (t) (1), which is input to the encoder 11. You. Encoder 11
Divides this symbol sequence b (t) into K coded chips to generate coded chip signals. An orthogonal function such as a Walsh function is used for encoding. The coded chip signal is input to the quadrature modulator 12. The quadrature modulator 12 uses the carrier signal _ct (t) output from the frequency synthesizer 13 as a local carrier,
A chip modulation wave S (t) is generated. k-th (1 ≦ k ≦ K)
Assuming that the frequency of the carrier signal for the chip is ω _k and the initial phase is φ _k , c _t (t) becomes c _t (t) = exp [jω (t) t + φ (t)] (2) . _{However, ω (t) = ω k} , iT + (k-1) T / K ≦ t <iT + kT / K ... (3a) φ (t) = φ k, iT + (k-1) T / K ≦ t <iT + kT / K (3b). The frequency of the carrier signal _ct (t) is switched according to a control signal output from the frequency control circuit 14. The chip modulation wave S (t) is as follows: S (t) = b (t) _ct (t) (4) The frequency ω _{k of the} carrier signal changes for each chip in a predetermined order. Its value is distributed over the system bandwidth w _R and k ≠
In the case of k ', it is assumed that ω _k ≠ ω _k', and the more frequency separated, the more the diversity effect. Further, the phase for each hopping frequency is stored, and this phase control is also performed by the frequency control circuit 14.

FIG. 2 shows the above modulation method when the number of chips K = 4. "1" every T symbol b _i is, "- 1, has been changed to" 1 ". These symbols are divided into four chips per symbol. For simplicity of description, it is assumed that encoding is performed using a DC Walsh function. Therefore, the encoded chip signal has the same waveform as the symbol. Next, the frequency and the initial phase are respectively assigned to the carrier signals of f ₁ and φ ₁ , f ₂ and φ ₂ , f ₃ and φ ₃ , f ₄ and φ ₄ , and modulation is performed. obtain. By repeating this operation for each symbol, a transmission wave of the high-speed frequency hopping method is generated.

The description will be continued with reference to FIG. The received wave received by the receiver is represented by r _x (t) = A (t) S (t) using a complex envelope fluctuation component A (t) due to fading of the transmission path and a thermal noise n (t). ) + N (t) (5) _{However, A (t) = A k} (t), iT + (k-1) T / K ≦ t <iT + kT / K ... (6a) A k (t) = | A k (t) | exp {jArg [A _k (t)] (6b). The received wave is input to the mixer 21, where it is reverse-hopped by the output _cr (t) of the frequency synthesizer 22. _cr (t) is the carrier signal c at the transmitter
with _t (t), represented by _{c r (t) = c t} (t) exp [j.phi ₀ (t)] ... (7). φ ₀ (t) is the phase difference between the frequency synthesizers 13 and 22 between transmission and reception. Here, it is assumed that the initial phase of the frequency synthesizers 13 and 22 is completely controlled, and φ ₀ (t) = φ ₀ ... (8) The frequency of the frequency synthesizer 22 for reception is
Switching is performed in synchronization with a hopping pattern on the transmission side by a control signal from the frequency control circuit 23. Mixer 2
The output of 1 passes through a band-pass filter 24 and is quasi-synchronously detected by an IQ detector 25. Quasi-synchronous-detected complex envelope signals r (t) _{is, r (t) = r x} (t) c r * (t) = A (t) S (t) c r * (t) + n (t) _cr ^* (t) = _Sr (t) + _nr (t) (9) At this time, S _r (t) = A (t) b (t) exp (−jφ ₀ ) (10) In the demodulation circuit 26, the complex envelope signal r (t)
, Channel identification is performed using the training signal in, and a symbol is determined based on the result to perform demodulation. A specific example of demodulation will be described later.

FIG. 3 shows the reception radio frequency f in the receiving apparatus.
_R , the received intermediate frequency f _IF , the system bandwidth W _R , and the intermediate frequency bandwidth W _IF . This figure shows the number of chips K =
4 shows an example. K band chips spread signal, the signal bandwidth when not diffuse When W _S, has its K times. Here, it is four times. Signals are hopping in this figure are evenly arranged in the band of the system bandwidth W _R. When converting this into an intermediate frequency band, and controls the frequency of the frequency synthesizer 22 so that the carrier frequency is all f _IF.

FIG. 4 is a block diagram showing an example of a high-speed frequency hopping frequency synthesizer used as the frequency synthesizers 13 and 22. This example uses a direct digital synthesizer (DDS: Direct Dig).
It uses a phase accumulator 41, a memory table 42, a digital
An analog converter 43 and a low-pass filter 44 are provided. The phase accumulator 41 specifies a read address of the memory table 42 in response to the frequency control input. The output of the memory table 42 is converted to an analog signal by a digital / analog converter 43 and output through a low-pass filter 44.

As the memory table 42, for example, a read-only memory storing a sine waveform is used, and a carrier signal of an arbitrary frequency is generated by a method of designating the read address. In the memory table 42, for example, sine waveform sample values as shown in FIG. 5 are written. In this figure, the number of sampling is simplified to 16 and
Addresses "0" to "15" correspond to each sample. This sample value is read at a constant clock cycle. When outputting a relatively low frequency waveform, for example, the addresses are designated as “0”, “2”, “4”, “6”,. This waveform is shown in FIG. To output a higher frequency waveform, for example, the addresses are designated as “0”, “4”, “8”, “12”,. By changing the addressing in this way, the frequency can be changed.

FIG. 7 shows another example of the structure of the chip modulating means. When the frequency of the carrier signal is instantaneously switched as shown in FIG. 2 at the time of frequency hopping, the phase and frequency of the chip modulation wave change rapidly. For this reason, the transmission spectrum includes many side lobes and requires a wide band. Therefore, it is desirable to narrow the transmission spectrum. FIG. 7 shows a configuration example for that purpose. Here, the description will be made on the assumption that K = 4.

In this configuration example, four systems of a low-pass filter 72 and a quadrature modulator 73 are provided as chip modulating means, and mutually different carrier frequencies are supplied to the quadrature modulator 73. Further, a switch circuit 71 for switching the system and a combining circuit 74 for combining are provided. The encoded chip signal is distributed by the switch circuit 71 to four branches for each chip. Each of these coded chip signals is shaped by the low-pass filter 72 to form a narrow band coded chip signal waveform. These coded chip signals whose waveforms have been shaped are modulated by the quadrature modulator 73, and are combined by the combining circuit 74.

FIG. 8 is a block diagram showing an example of the demodulation circuit 26. Here, an example using a linear demodulation method will be described.

This demodulation circuit includes a decoder 81 for decoding a signal encoded by the encoder 11 on the transmission side, and a switch 82 as means for multiplying each of the K complex envelope signals by a complex coefficient. , A memory 83 and complex multipliers 84-1 to 84-4, a synthesizing circuit 85 and a judging circuit 86 as means for synthesizing the complex envelope signal multiplied by the complex coefficient and judging a symbol. As means for setting according to the determination result for the training signal of a predetermined pattern, a subtracter 87 is used.
And a complex coefficient control circuit 88.

The decoder 81 performs decoding corresponding to the encoding on the transmitting side. As a result, a complex envelope signal of K chips corresponding to one symbol is obtained, and this is stored in the memory 83 via the switch 82. The switch 82 is controlled in synchronization with the operation of the frequency control circuit 23. Complex multiplier 87-1～87-4 performs multiplication of the complex coefficients w ₁ to w ₄ set by the complex envelope signal and a complex coefficient control circuit 88, which is stored in the memory 83, the combining circuit 85 is the multiplication Combine the signals. The determination circuit 86 determines the combined signal y _i output from the combining circuit 85 and demodulates the transmission symbol.

The complex coefficient w ₁ by the complex coefficient control circuit 88
Setting to w ₄ obtains a difference between the input and output signals of the decision circuit 86 by the subtractor 87, on the basis of the error is determined by the least squares method using a known training signal. The specific operation will be described below.

The complex multipliers 84-1 to 84-4 and the combining circuit 85 weight the complex envelope signal r (t) with the complex coefficient vector w _i-1 obtained at the time point [i-1]. Are combined to obtain a combined signal y _i . The combined signal y _i is expressed as _{y i = w i-1 r} i H ... (11). w _i-1, r _i ^H is a ^{_{vector, r i H = (r 1}} *, r 2 *, r 3 *, r 4 *) w i-1 = (w 1, w 2, w 3, w ₄ ) ... (12). A judgment of the combined signal y _i, a determination result d _i
Is output. The determination result by using the d _i and the synthetic signal y _i, for calculating an error e _i by _{e i = d i -y i ...} (13). The error e _i is input to the coefficient control circuit 88, and the complex coefficient vector w _i is calculated based on, for example, the least square method. Ideally, each component w _k of the complex coefficient vector w _i will be approximately equal to A _k ^* for the complex envelope component A _k . The complex signal y _{i + 1} at the next time point is obtained using the complex coefficient vector w _i . By repeating the above operation, symbol demodulation is performed.

FIG. 9 shows a signal format at the time of downlink transmission from the base station to the mobile station. In the frequency hopping method, a plurality of users use one frequency by time division at the time of downlink transmission from a base station to a mobile station. FIG. 9 shows a case where the number of chips K is 4 and the number of users M is 4;
The k-th (k = 1,...) Of the (m = 1,..., M) user
, K) are represented as mk. For example, 1
For the signal to the second user, use the frequency f ₁ to transmit the first coded chip signal,
To transmit the fourth and fourth encoded chip signals, the frequencies f ₂ , f ₃ and f ₄ are used, respectively.

FIG. 10 shows an example of the configuration of a chip modulating means for transmitting such a signal. This configuration example is TDMA
And a multiplexing circuit 101.
, A modulator 102 and an oscillator 103 in four systems, and a combiner 104 for combining the signals in the four systems. Four series of user signals b ₁ (t), b ₂ (t), b ₃ (t), b ₄ (t)
Are the frequencies f ₁ (t), f ₂ (t),
f ₃ (t), f ₄ (t) and separate modulators 10
2 modulated. At this time, the frequencies of the oscillator 103 may be fixed at f ₁ (t), f ₂ (t), f ₃ (t), and f ₄ (t), respectively, and there is no need to perform frequency hopping.

When high-speed frequency hopping of K chips is performed, the signal band becomes K times, so that the frequency use efficiency becomes 1
/ K. In order to improve the decrease in efficiency, a plurality of symbol sequences are simultaneously transmitted at the same frequency. That is, the same frequency is used simultaneously by a plurality of users. At this time, if the same frequency is simply used by a plurality of users, demodulation on the receiving side becomes difficult because signals of other users interfere. Therefore, in the encoder 11, signals orthogonal to each other in a symbol sequence using the same frequency are multiplied in advance by the chips of each symbol sequence.
As such an orthogonal signal, for example, a Walsh function is used.

FIG. 11 shows an example of the orthogonal function h _m (t) (where m = 1,..., 4) when the number of chips K = 4 and the number of users M using the same frequency = 4. An encoded chip signal is generated by multiplying each chip of the four symbol sequences by h _m (t) and multiplexed by adding them. Where h _m (t) is h _m (t) = hm _{, k} ... (14) when chip k, and Σhm _{, k} hm _{, k} ^* = 1 (15a) Σhm _{, k} h _{m ′, k} = 0 (15b) Where Σ is k =
Hm _{, k} ^* is the complex conjugate of hm _{, k} ,
k ′ ≠ k.

In order to receive a signal multiplexed by such encoding, it is necessary for the receiving device to perform complex multiplication with the complex conjugate h _m ^* (t) of the orthogonal function h _m (t) for decoding. .
The decoder 81 shown in FIG. 8, the complex envelope signal h _m ^*
(t) is complex-multiplied, and the multiplied signal is input to the switch 82. At this time, when the influence of fading is small and the level of each chip is substantially the same, the value of the complex envelope component A _k is substantially constant, and the complex coefficient w _k obtained by the least square method is substantially equal to A _k ^*. Become. Therefore, each complex envelope is synthesized with a constant weight, and the equation (1)
According to 5a), the m-th signal is extracted. The signals other than the m-th signal become zero according to the equation (15b). Further, when the influence of fading is large and there is a level difference between the complex envelope signals, a larger weight is applied to the complex envelope signal having a higher level by the least squares method.
In this case, since the levels of the complex envelope signals to be synthesized are not equal, the orthogonality condition is not satisfied, and it becomes impossible to completely cancel signals other than the m-th signal. However, the operation of weighting the complex envelope signal having a large level with a larger weight is substantially equivalent to the maximum ratio combining in the diversity reception, so that a diversity effect can be expected. Components of other channels that cannot be canceled because the orthogonality condition is not satisfied are suppressed by the diversity effect, so that desired channel components can be received.

As described above, multiplexing is possible in coherent combining, and it is possible to avoid a decrease in frequency use efficiency due to signal band expansion accompanying high-speed frequency hopping. Since this property is due to coherent processing, it is a feature not found in non-coherent high-speed frequency hopping.

When the same frequency is used by a plurality of users, it is preferable that, in downlink transmission from a base station to each mobile station, a signal of a user using the same frequency be encoded in baseband and multiplexed. FIG. 12 shows the configuration of such an encoding circuit. This encoding circuit includes a complex multiplier 121-
1 to 121-4 and a combiner 122. The user signals b ₁ (t) to b ₄ (t) are complex multipliers 121-1 to 121-1, respectively.
121-4, and orthogonal functions h ₁ (t) to b ₄ , respectively.
(t) is multiplied. These signals are combined by the combiner 122. By combining in the baseband in this manner, only one chip modulation means is required.

In the linear demodulation method shown in FIG. 8, when fading fluctuation is large, the complex envelope level is not constant, so that the cancellation of the signal of another user may be insufficient as described above, and the transmission characteristic may be reduced. Degradation. To perform demodulation while suppressing deterioration due to such fading fluctuation, a non-linear demodulation method using maximum likelihood determination is suitable. FIG. 13 shows an example of such a configuration.

The demodulation circuit shown in FIG. 13 includes an encoder 140 for encoding a symbol candidate by the same logic as the chip encoding means on the transmission side. From the output of the encoder 140, each of K complex envelope signals is output. The system includes K systems of complex multipliers 134 and a complex coefficient control circuit 135 as means for obtaining an estimated value of the signal, and subtracting the estimated value from the detected K complex envelope signals to obtain an estimation error. K subtractors 133 are provided, and K means of square operation circuits 136 and adders 137 are provided as means for calculating the sum of squares of the estimation error, and a path corresponding to a transition from one point of time of the symbol pattern candidate to the next point is determined. A maximum likelihood estimating circuit 138 for selecting a path in which the sum of squares of the estimation error is the smallest and performing symbol determination on the path. It includes a signal generator 139 for outputting a symbol candidate corresponding to. Further, a switch 131 and a memory 132 are provided for serial-to-parallel conversion of the detected K complex envelope signals.

Here, QPSK will be described as an example. However, it is assumed that one desired wave in which one's own signal is modulated and N interference waves in which only another user's signal is modulated,
It is assumed that a signal of another user [M-1] is multiplexed on the desired wave in addition to its own signal, and that M users are multiplexed on interference waves of the wave. In this case, the total number of signals of other users is [N + 1] M-1. In QPSK,
There are four possible transmission symbol patterns for one's own signal, four possible symbol patterns for another user's signal, and four ^{(N + 1) M-1} possible symbol patterns for another user's signal. In this demodulation method, the most probable pattern is estimated from these 4 × 4 ^{(N + 1) M−1} transmission symbol pattern candidates to determine the symbol.

First, the K-chip complex envelope signal subjected to quasi-synchronous detection is stored in the memory 132 via the switch 131. The switch 131 is controlled in synchronization with the operation of the frequency control circuit 23 (FIG. 1). In this demodulation method, the transmission symbol is not directly estimated by linearly converting the complex envelope, but is estimated by nonlinear processing. For this reason, the maximum likelihood estimating circuit 138 forms a path corresponding to the transition from one time point to the next time point of the symbol pattern candidates of the own and other users' signals, and performs symbol judgment by comparing the likelihoods of the paths. . The total number of paths is 4 × 4 ^{(N + 1) M−1} , which is the total number of symbol pattern candidates.

The signal generator 139 corresponds to the path information and indicates the total number of signals of itself and other users (N +
1) Output M sequence symbol candidates. Encoder 140
Encodes the symbol sequence candidates output from the signal generator 139 corresponding to the transmission side, and generates encoded chip signal candidates. The complex coefficient control circuit 135 calculates a carrier component estimated value of the complex envelope signal. This estimate is a complex coefficient. In addition, a training signal is used at the beginning of the estimation. By performing complex multiplication of the complex coefficient and the coded chip signal candidate by the complex multiplier 134, replicas of the own and other user's signals with respect to the complex envelope signals are generated.

Next, the subtraction of the replicas of the own and other user's signals and the complex envelope signal stored in the memory 132 is performed by the subtractor 133 to obtain an estimation error. Since this estimation error is obtained for each of the complex envelopes stored in the memory 132, K is performed in parallel with the number K of chips. As a result, K estimation errors are obtained. This estimation error is fed back to the complex coefficient control circuit 135 and used for updating the carrier component estimation value. Further, the square operation circuit 136 and the adder 137 provide K
Find the sum of squares of the estimation errors. This sum of squares of the estimation error is performed for all 4 × 4 ^{(N + 1) M−1} patterns that are the total number of paths.

The maximum likelihood estimating circuit 138 selects a path having the minimum sum of squares of the estimation error from among 4 × 4 ^{(N + 1) M−1} paths, and corresponds to the selected path. It is determined that the symbol candidate is most likely. Thereby, a transmission symbol is determined.

The difference between the above-described nonlinear demodulation system and the linear demodulation system shown in FIG. 8 is that the transmission path estimation is performed not only on the own signal but also on the other user's signal that is an interference component, and the received signal is estimated. A replica is being generated. In the linear demodulation method, signals of other users serving as interference components are treated the same as noise.Therefore, when the orthogonality between the own signal and the signal of another user becomes insufficient due to fading fluctuation, the equation The interference component remains in the estimation error shown in (13). For this reason, transmission path estimation performed based on the designated error cannot be performed with high accuracy, and transmission characteristics deteriorate. On the other hand, in the non-linear demodulation method, since the transmission path estimation is also performed for the signals of other users, the influence of interference due to the signals of other users is removed from the estimation error, and the accuracy of the transmission path estimation is improved. Therefore, the transmission characteristics are improved as compared with the linear demodulation method.

Here, the interference wave and the signal components of other users included in the desired wave are all canceled. However, since the circuit scale becomes large, only the other user signal of the desired wave is included in the own signal among the interference waves. Only other user's signals using the same orthogonal code as, or a combination of them,
Various simplifications are possible for the configuration of the canceller.

FIGS. 14 and 15 are block diagrams showing a frequency diversity transmission apparatus according to a second embodiment of the present invention. FIG. 14 shows a transmission apparatus and FIG. 15 shows a reception apparatus. Also in this embodiment, the number of chips K is set to four. In the first embodiment, the frequency diversity effect is obtained by frequency hopping, but in the present embodiment, the frequency diversity effect is obtained by a multicarrier method using a plurality of carrier signals simultaneously.

That is, the transmitting apparatus divides each symbol of the input symbol sequence into a plurality of chips and codes the chip sequence, thereby outputting K coded chip signals per symbol. , And K types of carrier frequencies are respectively modulated by the K coded chip signals to obtain K bits per symbol.
Quadrature modulators 142-1 to 142-4 and an oscillator 143-1 as chip modulation means for generating chip modulation waves
To 143-4. Quadrature modulators 142-1 to 142
-4 and the oscillators 143-1 to 143-4 simultaneously and in parallel generate K chip modulated waves having different carrier frequencies.

The encoder 141 adjusts the timing and outputs an encoded chip signal obtained by dividing one symbol into four chips. This encoded chip signal is shown in FIG. The encoded chip signals divided from the same symbol are output in parallel at substantially the same timing. Oscillator 143-1 to 14-14
3-4, respectively and outputs a carrier signal of frequency _{f 1, f 2, f 3} , f 4, the quadrature modulator 142-1～142-
4 performs modulation using each carrier signal. As a result, a multicarrier chip modulated wave is generated.

The receiving device includes a mixer 151, a local oscillator 152, a band-pass filter 153, and an IQ detector 15.
It is configured by arranging four receivers each consisting of four lines. The envelope signals detected by the four IQ detectors 154 are input to a demodulation circuit as shown in FIG. In the demodulation circuit in the frequency hopping shown in the first embodiment, since a complex envelope signal is input serially, a switch and a memory for converting the signal into parallel are required. However, in the case of multicarrier transmission, since the envelope signal is input to the demodulation circuit in parallel, a switch and a memory are unnecessary, and the encoding in the encoder is processed in parallel. In the present embodiment, unlike the frequency hopping method, signal transmission is performed using a plurality of frequencies at the same time, so that it is not necessary to switch the frequency of the synthesizer at high speed. However, a plurality of local oscillators 152 are required as shown in FIG.

[0059] In the signal shown in FIG. 16, although the chip length T _c and 1 / K times the symbol length _{T s, T s / K <} T
It may be used as the _c ≦ T _s. In that case, the band occupied by one chip modulation wave becomes narrow, and the operating frequency in modulation and demodulation also becomes low. Since the energy per bit increases, the operating frequency in transmission modulation / demodulation also decreases. Since the energy per bit increases, the transmission characteristics are also improved. Therefore, it is desirable to adaptively control the chip length together with the phenomenon of the number of simultaneous users.

FIGS. 17 and 18 are block diagrams showing a frequency diversity transmission apparatus according to a third embodiment of the present invention. FIG. 17 shows a receiving apparatus, and FIG. 18 shows a demodulation circuit. In this embodiment, an example of a configuration for further improving transmission characteristics by combining frequency diversity with space diversity will be described. Here, an example of the configuration of a receiving apparatus when the number of antennas L = 2, which is frequently used in mobile communication, is shown. Number of chips K = 2
And

The receiving device has two antennas 171, 172
Is provided. The signal received by the antenna 171 is
1-1, band-pass filter 24-1 and IQ detector 2
The signal is input to the demodulation circuit 173 via 5-1. The signal received by the antenna 172 is similarly transmitted to the mixer 21-
2. Bandpass filter 24-2 and IQ detector 25-
2, and is input to the demodulation circuit 173. Mixer 21
The local carrier is input from the frequency synthesizer 22 to -1, 21-2. The output frequency of the frequency synthesizer 22 is switched by a control signal from the frequency control circuit 23. With this configuration, the signals received by antennas 171 and 172 are subjected to frequency conversion and quasi-synchronous detection, respectively, to obtain a complex envelope signal. Demodulation circuit 1
73 demodulates these complex envelope signals.

The demodulation circuit 173 includes two decoders 81-1 and
81-2 and two switches 82-1 and 82-2. The decoder 81-1 decodes the complex envelope signal of the signal received by the antenna 171 and outputs the signal to the switch 82-1.
, And is stored in the first and second areas of the memory 83. The decoder 81-2 decodes the complex envelope signal of the signal received by the antenna 172, and
And accumulates in the third and fourth areas of the memory 83. Using these stored complex envelope signals, a complex envelope signal is synthesized by the same operation as in the case of K = 4 described with reference to FIG.

Here, an example using two antennas has been described. However, the present invention can be similarly implemented when a plurality of antennas are used.

FIG. 19 is a block diagram showing the configuration of a frequency diversity transmission apparatus according to a fourth embodiment of the present invention, and shows an example of the configuration of a transmission apparatus. The number of chips K is four. This embodiment includes a serial / parallel converter 191 that distributes a signal of one user to a plurality of channels, and distributes the signal of one user as if the signals are used by a plurality of users. In this example, it is divided into four. In this case, the transmission speed is reduced to 1/4. The divided four signals are divided into chips by the encoding circuit shown in FIG. 12, for example, to generate encoded chip signals. The operation of the transmitting apparatus after the encoding is the same as the case where the same frequency is used by a plurality of users. For reception, demodulation circuits shown in FIG. 8 may be provided by the same number as the number of distributions on the transmission side to perform demodulation.
Demodulation may be performed using the demodulation circuit shown in FIG. FIG.
In the demodulation circuit shown in FIG. 3, since the signal pattern is estimated and demodulated not only for the desired signal but also for the interference signal, the signal which was regarded as the interference signal in the first embodiment is regarded as the desired signal. Can be demodulated.

[0065]

As described above, the frequency diversity transmission apparatus according to the present invention divides each symbol into chips and further encodes the chips, thereby simultaneously transmitting a plurality of symbol sequences at the same frequency. Frequency can be used effectively.

Further, when coherent detection is performed on the receiving side, interference cancellation is possible, and superior transmission characteristics can be obtained as compared with the conventional non-coherent detection.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a frequency diversity transmission apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a modulation method, and is a diagram illustrating an example of a chip modulation waveform.

FIG. 3 is a diagram _showing a relationship among a reception radio frequency f _R , a reception intermediate frequency f _IF , a system bandwidth W _R , and an intermediate frequency bandwidth W _{IF in} the reception device.

FIG. 4 is a block diagram illustrating an example of a high-speed frequency hopping frequency synthesizer.

FIG. 5 is a diagram showing an example of sample values written in a memory table.

FIG. 6 is a diagram showing an example of an output waveform.

FIG. 7 is a diagram showing another configuration example of the chip modulation means.

FIG. 8 is a block diagram showing an example of a demodulation circuit.

FIG. 9 is a diagram showing a signal format at the time of downlink transmission from a base station to a mobile station.

FIG. 10 is a diagram showing a configuration example of a chip modulating means for transmitting such a signal.

FIG. 11 is a diagram showing an example of an orthogonal function.

FIG. 12 is a diagram illustrating a configuration example of an encoding circuit that encodes and multiplexes a signal of a user using the same frequency in a baseband when the same frequency is used by a plurality of users.

FIG. 13 is a block diagram illustrating an example of a demodulation circuit that performs demodulation by a non-linear demodulation method based on maximum likelihood determination.

FIG. 14 is a block diagram illustrating a frequency diversity transmission device according to a second embodiment of the present invention, and is a diagram illustrating a configuration of a transmission device.

FIG. 15 is a block diagram illustrating a frequency diversity transmission device according to a second embodiment of the present invention, and is a diagram illustrating a configuration of a reception device.

FIG. 16 is a diagram showing an encoded chip signal in the case of a multicarrier system.

FIG. 17 is a block diagram illustrating a frequency diversity transmission device according to a third embodiment of the present invention, and is a diagram illustrating a configuration of a reception device.

FIG. 18 is a block diagram showing a configuration of a demodulation circuit.

FIG. 19 is a block diagram illustrating a frequency diversity transmission device according to a fourth embodiment of the present invention, and is a diagram illustrating a configuration example of a transmission device.

FIG. 20 is a block diagram showing a conventional example of a frequency diversity transmission apparatus using high-speed frequency hopping.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitting device 2 Receiving device 11 Encoder 12 Quadrature modulator 13 Frequency synthesizer 14 Frequency control circuit 15 Bandpass filter 21, 21-1, 21-2 Mixer 22 Frequency synthesizer 23 Frequency control circuit 24, 24-1, 24-2 Band-pass filters 25, 25-1, 25-2 IQ detector 26 Demodulation circuit 41 Phase accumulator 42 Memory table 43 Digital / analog converter 44 Low-pass filter 71 Switch circuit 72 Low-pass filter 73 Quadrature modulator 74 Synthesis Circuits 81, 81-1, 81-2 Decoders 82, 82-1, 82-2 Switches 83 Memory 84-1 to 84-4 Complex multipliers 85 Synthesis circuits 86 Judgment circuits 87 Subtractors 88 Complex coefficient control circuits 101 Multiplexing Circuit 102 modulator 103 oscillator 104 synthesis 121-1 to 121-4 Complex multiplier 122 Synthesizer 131 Switch 132 Memory 133 Subtractor 134 Complex multiplier 135 Complex coefficient control circuit 136 Square operation circuit 137 Adder 138 Maximum likelihood estimation circuit 139 Signal generator 140 Encoder 141 Code 142-1 to 142-4 Quadrature modulator 143-1 to 143-4 Oscillator 151 Mixer 152 Local oscillator 153 Band-pass filter 154 IQ detector 171, 172 Antenna 173 Demodulation circuit 191 Serial / parallel converter 201 Quadrature modulator 202 Frequency synthesizer 203 frequency control circuit 204 band-pass filter 205 mixer 206 local oscillator 207 band-pass filter 208 square-law detection circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-164537 (JP, A) JP-A-61-159837 (JP, A) JP-A-62-179234 (JP, A) JP-A-62-179234 283735 (JP, A) JP-A-62-204633 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/00 H04B ⁷ /02-7/12 H04B ⁷ /24- 7/26 113 H04J 1/00-1/20 H04J 4/00-15/00 H04L 1/02-1/06 H04L 5/00-5/12 H04L 27/00-27/30 H04Q 7/00-7 / 04

Claims (9)

(57) [Claims] 1. A transmitting apparatus for modulating each symbol of an input symbol sequence with K kinds (K is an integer of 2 or more) of carrier frequencies and transmitting the modulated signals, And a receiving device for demodulating with K kinds of local frequencies synchronized with the respective carrier frequencies. The transmitting device divides each symbol of the input symbol sequence into a plurality of chips, Chip encoding means for outputting K encoded chip signals per symbol by encoding the above. K carrier frequencies are modulated by the K encoded chip signals to obtain K signals per symbol And a chip modulating means for generating chip modulated waves of the following formula: Quasi-synchronous detection means for detecting each of the K local frequencies to extract K complex envelope signals, and determining means for determining a transmission symbol from the K complex envelope signals. Frequency diversity transmission equipment. 2. The chip modulating means includes means for multiplying a plurality of sequences of input symbols by signals orthogonal to each other for each of the sequences, and the determining means comprises: 2. The frequency diversity transmission apparatus according to claim 1, further comprising means for multiplying the complex conjugate by: 3. The means for multiplying each of the K complex envelope signals by a complex coefficient, means for synthesizing the complex envelope signal multiplied by the complex coefficient to determine a symbol, 3. The frequency diversity transmission apparatus according to claim 1, further comprising: means for setting the complex coefficient in accordance with a result of determination on a training signal having a predetermined pattern. 4. An encoder for encoding a symbol candidate with the same logic as that of the chip encoder, and an estimated value of each of the K complex envelope signals is obtained from an output of the encoder. Means for subtracting the estimated value from each of the K complex envelope signals to obtain an estimation error; means for calculating the sum of squares of the estimation error; A path corresponding to the transition to the time point is determined, and a path that minimizes the sum of squares of the above estimation error is selected from the paths, and a maximum likelihood estimation circuit that performs symbol determination is performed. 2. The frequency diversity transmission apparatus according to claim 1, further comprising: a signal generator that outputs the symbol candidate. 5. The frequency diversity transmission apparatus according to claim 1, wherein said chip modulating means includes means for generating K chip modulated waves having different carrier frequencies in time series. 6. The transmitting apparatus includes means for separately and continuously generating K kinds of carrier frequencies, and the chip modulating means includes means for selecting the K kinds of carrier frequencies in time series. 6. The frequency diversity transmission device according to 5. 7. The frequency diversity transmission apparatus according to claim 1, wherein said chip modulating means includes means for simultaneously and in parallel generating K chip modulated waves having different carrier frequencies. 8. The transmitting apparatus includes means for generating carrier signals having substantially constant initial phases for K encoded chip signals for each symbol as the K kinds of carrier frequencies, and the receiving apparatus includes: 8. The frequency diversity transmission apparatus according to claim 1, further comprising means for generating local signals having a substantially constant initial phase for each of the K encoded chip signals for each symbol as a local frequency. 9. The means for generating the carrier signal and the means for generating the local signal each include a memory table in which a sine waveform is recorded in advance and a means for setting an output frequency by changing the address designation of the memory table. The frequency diversity transmission apparatus according to claim 8, comprising: