JP3466797B2 - Coded Multi-level Modulation for Digital Mobile Communication System - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coded multilevel modulation system used in digital mobile communication systems such as digital mobile phones and digital satellite communications.

[0002]

2. Description of the Related Art In order to realize wireless multimedia communication, an information transmission system capable of transmitting a large amount of information such as data, images as well as voice with high reliability and at high speed is essential. In particular, when transmission is performed in a bad environment where multipath fading, shadowing, etc. occur, countermeasures against it are an important issue.

As one of the techniques for solving such a problem, there is an adaptive modulation system. This method transmits as much information as possible when the transmission path condition is good due to multipath fading, shadowing, etc., and conversely increases the error correction capability when the transmission path condition deteriorates. This is a method that strongly protects a small amount of information by doing so.

For example, SM Alamouti is a Pragmatic Trel
An adaptive MPSK method using the lis Coded Modulation method is proposed. In this system, the state of the transmission line is estimated by a transmission line state estimator, and the estimated value α (k LT) is given to an information buffer and an adaptive multilevel modulation mapping circuit. Then, in the information buffer, the estimated transmission line state value α (k LT)
Control the amount of information to be transmitted, and in the adaptive multilevel modulation mapping circuit, the transmission line state estimated value α (k LT)
According to the above, the modulation multi-value number is changed to perform the modulation. The information amount control and the modulation multi-value number control are performed as follows.

(1) When the transmission line condition deteriorates, that is, when α (k LT) is determined to be worse than a predetermined threshold value μ ₁ , the information to be transmitted is 1 bit and the coding rate is 1
/ 2 convolutional coding and interleaving are performed. Then, the output information is subjected to QPSK mapping by the adaptive multilevel modulation mapping circuit, and the modulated signal is wirelessly transmitted. As the mapping method, for example, a Double-Gray mapping method as shown in FIG. 7 is used.

(2) When the estimated transmission line state value α (k LT) is better than the threshold value μ ₁ and worse than the threshold value μ ₂ , the transmission information is set to 2 bits and 1 bit out of them is set. On the other hand, as in the case of the above (1), after performing convolutional coding with a coding rate of 1/2 and interleaving, it is input to the adaptive multi-level modulation mapping circuit, and the remaining bits are directly subjected to the adaptive multi-level without coding. Input to modulation mapping circuit. Then, in the adaptive multilevel modulation mapping circuit,
8PSK mapping is performed on each input information and the modulated signal is transmitted.

(3) In the case where the estimated transmission line state value α (k LT) exceeds the threshold value μ ₂ and the state is good, the transmission information is set to 3 bits, and 1 bit among them is (1) Similarly, the convolutional coding with a coding rate of 1/2 and interleaving are performed and then input to the adaptive multilevel modulation mapping circuit, and the remaining 2 bits are directly input to the adaptive multilevel modulation mapping circuit without encoding. Then, the adaptive multilevel modulation mapping circuit performs 16PSK mapping on the above 3-bit information and transmits the modulated signal.

Thus, the transmission line state estimated value α (k LT)
By changing the modulation multi-value number according to the value of, it is possible to transmit the information amount suitable for the transmission path state. For details of this method, see, for example, IEEE TRANSACTION.
S ON VEHICULAR TECHNOLOGY
"Adaptive Trellis Coded Multiple-Phase-Shift" by SMAlamouti, S. Kallel, Vol.
Keying for Rayleigh Fading Channels ”.

However, in the system such as SMAlamouti or the like, the amount of information that can be transmitted is uniquely determined by the number of modulation levels, and therefore the number of modulation levels must be increased to transmit a large amount of information. However, in a poor environment where multipath fading, shadowing, etc. exist, there is a limit to the maximum number of modulation levels that can be increased, which is not suitable for practical use.

On the other hand, one of the methods that has attempted to solve this problem is the coded multilevel modulation method proposed by Tanaka and Matsushima, which permits the expansion of the band. This method absorbs redundant components due to encoding at an arbitrary expansion rate when expanding the band, and it is possible to control transmission information relatively freely by setting the band expansion rate and the number of modulation levels. Is. For details of this method, see, for example, IEICE TRANSACTI.
ONS ON FUNDAMENTALS OF EL
ECTRONICS, COMMUNICATIONS
AND COMPUTER SCIENCES E7
Volume 7-A, Issue 8 by Tanaka and Matsushima, "Performance of
a Modified Symbol-Rate-Increased TC -2 m QA
M ”.

However, in this method, the band expansion rate and the modulation multi-valued number are preset when the system is designed, and therefore, once set, the band expansion rate cannot be changed. For this reason, it is not possible to cope with the deterioration of the quality of the transmission path, and it is required to transmit a large amount of information with high reliability and high speed in a bad environment where multipath fading, shadowing, etc. exist. It cannot be directly applied to multimedia communication.

[0012]

As described above, all the methods proposed so far attempt to wirelessly transmit a large amount of information in a poor environment where multipath fading, shadowing, etc. exist. It cannot be applied to a system as it is, and a coding multilevel modulation method suitable for such a system has been desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a large amount of information with high reliability even in a bad environment where multipath fading, shadowing and the like exist. In addition, it is to provide a coded multilevel modulation method suitable for wireless multimedia communication by enabling high-speed wireless transmission.

[0014]

In order to achieve the above object, the present invention provides a reception signal from a partner communication device during a period of wireless transmission with the partner communication device via a wireless transmission path. Based on the estimation result of the transmission path state, the number m of digital signal sequences to be transmitted and the multilevel modulation method are adaptively and variably set based on the estimation result of the transmission path state. Then, the value of i is calculated from the controlled m-bit digital signal sequence based on the estimation result of the transmission path state.
While variably setting, it is converted into a j-bit signal sequence satisfying j <m and an i-bit signal sequence satisfying i <m−j, and 1>r> for the j-bit signal sequence
Error correction coding is performed at a coding rate of (m−j−1) / (m−i) to output a m−i bit signal sequence, and the m−i bit signal sequence and the i-bit A 2m-value modulated signal is output by performing a mapping process on the signal sequence according to the selected multi-level modulation method.

Further, according to the present invention, in the error correction coding means, 1>r> (m-
It is characterized in that after convolutional coding is performed at a coding rate of (i-1) / (m-i), interleaving is performed.

Further, the adaptive multilevel modulation mapping means is characterized in that the mapping processing is performed according to the double-gray mapping method. Therefore, according to the present invention, in a radio transmission in accordance with a change in the state of the transmission path, a digital signal number m Toko to be transmitted
The number i of signal sequences used for error correction coding and the multilevel modulation method are adaptively and variably set, and the transmission data is coded and multivalued modulated by the variably set number of signal sequences and modulation method to perform wireless transmission. To be done. That is, the transmission information amount and the modulation method are adaptively switched based on the estimation result of the transmission path state. Therefore, even when wireless transmission is performed in a bad environment in which multipath fading, shadowing, etc. exist, it is possible to wirelessly transmit a large amount of information with high reliability and at high speed.

[0017]

1 is a circuit block diagram showing an embodiment of a transmitter / receiver section of a digital radio communication apparatus to which a coded multilevel modulation system according to the present invention is applied. In the figure, an information bit string output from a signal processing unit (not shown) is passed through an information buffer 1 to an encoding / modulation unit 2
Entered in. The encoding / modulating unit 2 includes a trellis encoder / interleaver 3 and an adaptive multilevel modulation mapping circuit 4, and in these circuits 3 and 4, error correction encoding and interleaving for the input information bit string,
And multi-level modulation mapping is performed, thereby generating a coded multi-level modulation signal. Then, the encoded multi-level modulated signal is input to the wireless transmission circuit 5, frequency-converted into a wireless channel frequency by the wireless transmission circuit 5, amplified to a predetermined transmission power, and then supplied to an antenna (not shown). Transmitted from the antenna to the wireless transmission path.

On the other hand, the radio signal transmitted through the radio transmission path is received by an antenna and a receiving circuit (not shown), and further frequency-converted to an intermediate frequency or a baseband frequency, and then input to the demodulator 6. The demodulator 6 demodulates the received signal. The demodulated signal is deinterleaved by the deinterleaver 7 and then decoded by the trellis decoder 8. After that, the data alignment circuit 7 rearranges the original information bit string and supplies it to a signal processing circuit (not shown).

By the way, the demodulator 6 has an amplitude detector for detecting the amplitude value of the received signal, and the received amplitude value IS detected by this amplitude detector is input to the transmission path state estimator 10. To be done. The transmission line state estimator 10 estimates the transmission line state of the wireless transmission line based on the reception amplitude value IS. At this time, as a wireless transmission method, TDD in which an upstream transmission path and a downstream transmission path are time-division multiplexed on the same frequency for transmission.
When using the (time division duplex) method, it is possible to estimate the transmission path state of the uplink transmission path with high accuracy by detecting the amplitude value of the received signal that has arrived through the downlink transmission path. Is. The transmission channel state estimation value FS obtained by the transmission channel state estimator 10 is the information buffer 1,
It is supplied to the trellis encoder / interleaver 3 and the adaptive multilevel modulation mapping circuit 4, respectively.

The information buffer 1 sets the number of bits m of information to be transmitted based on the above-mentioned transmission path state estimation value FS, and outputs a digital signal sequence having a transmission rate of mR ₀ [bps].

The trellis encoder / interleaver 3 includes a rate converter 31 and a convolutional encoder 3 as shown in FIG.
2 and an interleaver 33. Speed converter 31 Among First, the digital signal series of the mR ₀ [bps], j bits (j having a rate of R ₁ [bps] <
m) signal sequences b1 to bj and i bit (i <m-j) signal sequences a1 to ai having a speed of R ₂ [bps]. Then, the signal sequences a1 to ai are supplied to the adaptive multilevel modulation mapping circuit 4 as they are, while the signal sequences b1 to b1.
The bj is supplied to the convolutional encoder 32. Note that the value of i is variably set based on the transmission path state estimation value FS supplied from the transmission path state estimator 10.

The convolutional encoder 32 performs convolutional encoding on the signal sequences b1 to bj output from the rate converter 31 at a predetermined encoding rate r. Here, the coding rate r is set so as to satisfy the condition shown in the following equation.

[0023]

[Equation 1]

The signal sequences ci + 1 to cm convolutionally coded by the convolutional encoder 32 are interleaved by the interleaver 33 to become signal sequences di + 1 to dm, and then input to the adaptive multilevel modulation mapping circuit 4. To be done.

The adaptive multilevel modulation mapping circuit 4 receives the transmission line state estimation value F supplied from the transmission line state estimator 10.
The modulation method is adaptively set based on S, and the input signal series a1 to ai and signal series di + 1 to dm are subjected to mapping processing according to the set modulation method. Then, it outputs a 2 ^m- value modulated signal having a speed of mR ₂ [bps].

Here, the relationship between the signal velocities R ₀ , R ₁ and R ₂ is expressed as follows. That is, the j-bit signal sequence b1 to bj having a speed of R ₁ [bps] is an i-bit signal sequence c having a speed of R ₂ [bps] by convolutional coding.
Since it is converted to i + 1 to cm,

[0027]

[Equation 2] Holds. Further, the speed of the input data to the speed converter 31 and the signal sequences a1 to ai and b1 to bj after the speed conversion.
Since the sum with the speed of is equal,

[0028]

(J−i) R ₁ + iR ₂ = mR ₀ (3) holds. Therefore, from the above equations (2) and (3), R ₁ and R ₂ are respectively

[0029]

[Equation 4] It is expressed as. At this time, the band expansion rate is

[0030]

[Equation 5] Becomes

Next, the operation of the apparatus configured as described above will be described using a concrete example. In this example, the coding rate r in the convolutional encoder 32 is set to r = 3/4, the number j of signal sequences used for convolutional coding is supplied to j = 1, and the adaptive multilevel modulation mapping circuit 4 is supplied as it is. This is a case where the number i of signal sequences to be set is selected and set from 0, 1, and 2 based on the channel state estimated value FS.

During communication, the transmission line state estimator 10 obtains an estimated value SNR, β of the state of the wireless transmission line based on the amplitude value IS of the received signal. Then, the estimated value β is compared with preset threshold values μ ₁ and μ _2, and the comparison result is supplied to the speed converter 31 and the adaptive multilevel modulation mapping circuit 4 as the transmission path state estimated value FS.

A correspondence table as shown in FIG. 4 is stored in advance in the speed converter 31, and when the speed converter 31 is supplied with the transmission line state estimated value FS, the speed converter 31 uses the correspondence table to obtain the current value. The number i of signal sequences is selected according to the state of the transmission path. For example, if the transmission line state estimation value FS is β> μ ₂ , the transmission line state is good, and i = 2 is selected.

The adaptive multi-level modulation mapping circuit 4 also stores the correspondence table shown in FIG. 4, and the adaptive multi-level modulation mapping circuit 4 uses this correspondence table to perform modulation according to the current transmission path state. Select a method. For example, as described above, 16PSK is selected when the transmission path state estimation value FS is β> μ ₂ .

Therefore, when the transmission line condition is good, as shown in FIG. 3, the speed converter 31 outputs two system signal sequences a1 and a2 and one system signal sequence b1, respectively. The signal sequence b1 is convolutionally coded by the convolutional encoder 32 and then interleaved. Then, the signal sequences d3 and d4 obtained by this convolutional encoding and interleaving, and the speed converter 31
The other two-bit signal series a1 and a2 output from the adaptive multi-level modulation mapping circuit 4 have 16PSK.
It is transmitted after being mapped according to the system.

Therefore, the frequency utilization efficiency at this time is as follows: the signal sequence coded by the convolutional encoder 32 with the coding rate r = 3/4 and the 2-bit signal sequences a1 and a2 that are not coded. Will be sent, so 3.5
It becomes [bit / sec / Hz].

If the transmission line state is slightly deteriorated and the transmission line state estimation value FS becomes μ ₁ <β <μ ₂ , the speed converter 31 selects i = 1. In the adaptive multilevel modulation mapping circuit 4, the above μ
_The 8PSK method is selected as the modulation method corresponding to ₁ <β <μ ₂ .

Therefore, when the state of the transmission line is somewhat deteriorated, one signal sequence a from the speed converter 31 is obtained.
One and one system of signal sequences b1 are output, and one of these signal sequences b1 is convolutionally coded by the convolutional encoder 32 and then interleaved. Then, the signal sequences d2 and d3 obtained by the convolutional coding and interleaving and the other 1-bit signal sequence a1 output from the speed converter 31 are applied to the 8PSK system in the adaptive multilevel modulation mapping circuit 4. It is transmitted after being mapped according to.

Therefore, the frequency utilization efficiency at this time is that the signal sequence encoded by the convolutional encoder 32 with the encoding rate r = 3/4 and the 1-bit signal sequence a1 that is not encoded are transmitted. 2.5 [bit / s
ec / Hz].

On the other hand, it is assumed that strong multipath fading or the like occurs, and the state of the transmission line is significantly deteriorated by this. Then, the transmission line state estimation value FS of the transmission line state estimator 10 becomes β <μ1. Therefore, i = 0 is selected in the speed converter 31, and β <μ is selected in the adaptive multilevel modulation mapping circuit 4.
The QPSK method is selected as the modulation method corresponding to 1.

Therefore, when the state of the transmission path is significantly deteriorated, the rate converter 31 outputs only the signal sequence b1 for convolutional coding. This one-sequence signal sequence b1 is convolutionally coded by the convolutional encoder 32, interleaved, further mapped by the adaptive multilevel modulation mapping circuit 4 according to the QPSK system, and then transmitted. Therefore, the frequency utilization efficiency at this time is 1.5 because only the signal sequence encoded by the convolutional encoder 32 with the encoding rate r = 3/4 is transmitted.
It becomes [bit / sec / Hz].

As described above, in this embodiment, the state of the transmission path is continuously estimated by the transmission path state estimator 10 during communication, and the convolutional coding is performed based on the estimation result FS of the transmission path state. The number i of signal sequences to be used for mapping as it is, is adaptively variably set by the rate converter 31, and the modulation method according to the estimation result FS of the transmission path state is adapted by the adaptive multilevel modulation mapping circuit 4. Select and set. Then, the digital signal sequence in which the number of sequences is adaptively variably set in this way is mapped and transmitted according to the adaptively selected and set modulation scheme.

Therefore, according to this embodiment, according to the estimation result of the transmission path condition, when the transmission path condition is good, the transmission information is transmitted using the modulation method such as 16PSK or 8PSK, which has a large number of modulation levels. On the other hand, when the state of the transmission path is deteriorated due to fading or the like, the transmission information is transmitted by using a modulation method having a relatively small number of modulation levels such as QPSK. For this reason, multipath
It is possible to wirelessly transmit information at a high frequency utilization rate even in a bad environment where fading, shadowing, etc. exist, and this can be sufficiently applied to wireless multimedia communication.

The effects of this embodiment will be described below in comparison with the conventional system. That is, for example, the transmission line state estimation value β is now calculated as the instantaneous S at a predetermined timing.
If NR, β can be expressed by the following equation.

[0045]

[Equation 6] However, α represents the amplitude component of Rayleigh fading,

[0046]

[Equation 7] Suppose When the relationship between β and i in the correspondence table shown in FIG. 4 is rewritten using α from the above equation (7), it becomes as shown in FIG. From this Figure 5,

[0047]

[Equation 8] Required by. However,

[0048]

[Equation 9] It is represented by.

The average frequency utilization efficiency is 1 Hz 1 s.
It represents the number of bits that can be transmitted per ec. FIG. 6 is a characteristic diagram showing the average frequency utilization efficiency of the present invention specifically calculated by using the above equations (9) and (10) and comparing with the conventional method calculated under the same conditions. Is. In the figure, A shows the characteristics according to the present invention, and as shown in the figure, it can be seen that higher frequency utilization efficiency can be obtained as compared with B showing the conventional method.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the transmission line state is estimated based on the amplitude value of the received signal obtained by the demodulator 6, but the transmission line state is estimated based on the bit error rate BER obtained by the trellis decoder 8. It may be estimated.

In the above embodiment, the case where the coding rate r of the convolutional encoder 32 is set to r = 3/4 has been described, but the coding rate r falls within the range shown in the equation (1). Can be set arbitrarily, and can be set arbitrarily according to the system request. By changing the coding rate r, the band expansion rate can be easily changed.

Further, as the multi-level modulation method, for example, a QAM method may be applied in addition to the PSK method, and other error correction coding methods, transmission path state estimation methods, etc.
The present invention can be variously modified and implemented without departing from the scope of the present invention. The present invention also provides a digital radio communication device used in a satellite communication system for communicating between earth stations via a communication satellite that orbits in a low orbit, as well as a terrestrial radio communication system such as a digital mobile phone system. You may apply.

Further, the coding rate 1>r> (m-i-1)
As a means for realizing a convolutional encoder that satisfies / (m−i), a convolutional encoder with a coding rate of (m−i−1) / (m−i) that uses a punctured code is considered. To be

Further, as means for realizing the mapping, mapping based on set partitioning or mapping based on Sectorized-Gray mapping can be applied in addition to Double-Gray mapping.

[0055]

As described above in detail, in the present invention, the state of the wireless transmission line is estimated based on the received signal from the partner communication device during the wireless transmission, and the state of the transmission line state is estimated based on the estimation result. , The number m of digital signal sequences to be transmitted and
The number i of signal sequences used for error correction coding and the multilevel modulation method are adaptively variably set, and the information is coded by the adaptively variably set number m of digital signal sequences and the multilevel modulation method. By wirelessly transmitting the large amount of information, it is possible to wirelessly transmit a large amount of information with high reliability and speed even in a bad environment where multipath fading, shadowing, etc. exist. It is possible to provide a coded multilevel modulation method suitable for wireless multimedia communication.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a transceiver unit of a digital wireless communication apparatus to which a coded multilevel modulation system according to the present invention is applied.

FIG. 2 is a circuit block diagram showing a configuration of main parts of the device shown in FIG.

FIG. 3 is a circuit block diagram showing a specific operation example of the device shown in FIG.

FIG. 4 is a diagram showing a correspondence relationship between a channel state estimated value, a signal sequence number i, a modulation scheme, and frequency utilization efficiency.

FIG. 5 is a diagram showing another example of a correspondence relationship between a channel state estimated value, a signal sequence number i, a modulation scheme, and frequency utilization efficiency.

FIG. 6 is a diagram showing the effect of the system of this embodiment in comparison with the conventional system.

FIG. 7 is a diagram showing a constellation of a double gray code.

[Explanation of symbols]

1 ... Information buffer 2 ... Encoding / modulation section 3. Trellis coding / interleaver 4 ... Adaptive multilevel modulation mapping circuit 5 ... Wireless transmission circuit 6 ... Demodulator 7 ... Deinterleaver 8 ... Trellis decoder 9 ... Data alignment circuit 10 ... Channel condition estimator 31 ... Velocity converter 32 ... Convolutional encoder 33 ... Interleaver

Continuation of front page (51) Int.Cl. ⁷ identification code FI H04L 27/34 H04L 27/00 E (56) Reference JP-A-5-183439 (JP, A) JP-A-7-250116 (JP, A ) JP-A-6-14075 (JP, A) JP-A-2-288752 (JP, A) JP-A-7-288556 (JP, A) JP-A-5-327787 (JP, A) Siavash M. Alamout i, Samir Kallell, Ada ptive Trellis-Coded Multiple-Phase-Shift Keying for Rarayleigh Fading Chan Nels, IEEE TRANSUN SON COONS. 42, NO. 6, p. 2305-2314 (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 27/00-27/38 H03M 13/23

Claims (3)

(57) [Claims] 1. A coded multilevel modulation system in which 2m signal points are assigned to an m-bit digital signal sequence and one of the signal points is output as a modulation signal, and wireless transmission is performed with a partner communication device. And a transmission path state estimating means for estimating the state of the wireless transmission path based on a received signal from a partner communication device during a period in which wireless transmission is performed through the transmission path. Based on the estimation result of the transmission path condition, a sequence number control means for adaptively variably controlling the number m of digital signal sequences to be transmitted, and an m-bit digital signal sequence controlled by the sequence number control means , Obtained by the transmission line state estimation means
The value of i is variably set based on the estimation result of
And a signal sequence of j bits satisfying j <m and i <m−
Conversion means for converting to an i-bit signal sequence satisfying j
And error correction coding is performed on the j-bit signal sequence obtained by the conversion means at a coding rate of 1>r> (m−1) / (m−i) to obtain m−i bits. Error correction coding means for outputting a signal sequence of, and a modulation scheme is adaptively selected based on the estimation result of the transmission path condition obtained by the transmission path condition estimator, and output from the error correction coding means. Adaptive multi-level modulation for outputting a 2m-level modulated signal by performing mapping processing on the m-i-bit signal sequence and the i-bit signal sequence obtained by the converting means according to the selected modulation method. A coded multi-level modulation system for a digital mobile communication system, comprising: a mapping means. 2. The error correction coding means performs convolutional coding on a j-bit signal sequence at a coding rate of 1>r> (m−1) / (m−i), and then The coded multi-level modulation system for a digital mobile communication system according to claim 1, wherein interleaving is performed. 3. The coded multi-level modulation system for a digital mobile communication system according to claim 1, wherein the adaptive multi-level modulation mapping means performs a mapping process according to a double-gray mapping method.