JP5053200B2 - Communication system and communication method - Google Patents

Description

  The present invention relates to a communication system and a communication method capable of obtaining a high-quality decoding result in wireless communication such as a cellular phone system.

  In wireless communication such as a cellular phone system, a one-cell repetitive system that performs communication using the same channel between adjacent cells is used. FIG. 6 is a schematic diagram of a one-cell repetition system used for wireless communication such as a conventional cellular phone system. As shown in FIG. 6, when a terminal (receiving device) 601 and a base station (transmitting device) 602 communicate and transmit transmission data via a downlink 603, other downlink 605 of an adjacent base station 604 is transmitted. The transmission data to the terminal becomes an interference signal in the terminal 601.

As a technique to suppress inter-channel interference such as inter-cell interference, error detection is performed by calculating the channel value (likelihood of demapping output) taking into account the amplitude distribution of the interference signal during demapping. Techniques for improving decoding characteristics have been proposed. At this time, the amount of processing required for the likelihood calculation is greatly reduced by approximating the amplitude distribution of the interference signal to a simple distribution and calculating the likelihood (see Non-Patent Document 1).
Suzuki et al. “A study on log likelihood of MAP decoding in the presence of co-channel interference” IEICE, IEICE Technical Report, RCS 2002-226, January 2003

  However, since the above technique assumes that the phase distribution is random within the frame, the amplitude distribution of the actual interference signal is particularly in an environment where the phase distribution is not random, such as an environment where the propagation path fluctuation is small. And the approximate distribution may become large.

  Therefore, in view of such circumstances, the present invention calculates quality information with high accuracy in consideration of the amplitude distribution of the interference signal even in an environment where the phase distribution of the propagation path is not uniform. The present invention provides a communication system and a communication method that can obtain a high decoding result.

  In order to solve the above-described problems, the present invention is configured as follows and has the following characteristics.

A communication system according to the present invention is a communication system including a mobile phone communication system that performs communication using the same channel between adjacent cells,
A transmission data signal generation unit that generates a transmission data signal to be transmitted to a receiving device that is a communication partner, a modulation unit that modulates the transmission data signal to generate a modulation symbol, and a phase rotation amount specific to each modulation symbol. A transmission device comprising: a phase rotation unit that provides; and a transmission unit that transmits the modulation symbol to which the phase rotation amount is provided;
A reception unit that receives a signal transmitted from the transmission device; an interference amplitude calculation unit that calculates an amplitude of an interference signal transmitted from a transmission device that is not a communication partner from the reception signal that is the received signal; and the reception signal On the basis of the amplitude of the interference signal, a phase restoration unit that restores the phase rotation unit by applying a phase rotation amount opposite to the inherent phase rotation amount given to each modulation symbol by the phase rotation unit And a demapping unit that calculates likelihood information from the receiver.

  Further, in the communication system according to the present invention, the demapping unit of the receiving device is based on an approximate interference amplitude distribution obtained by approximating the occurrence probability distribution of the in-phase component or the quadrature component of the interference signal using the amplitude of the interference signal. And calculating likelihood information.

  Further, in the communication system according to the present invention, when the transmission data signal to be the interference signal is PSK modulated, the demapping unit of the receiving apparatus uses the amplitude of the interference signal to Likelihood information is calculated based on an approximate interference amplitude distribution obtained by approximating an occurrence probability distribution of an in-phase component or a quadrature component to a concave shape.

Further, in the communication system according to the present invention, the phase rotation unit performs φ _{i, k} = (2π × i × k) / K (k) with respect to the kth modulation symbol of the transmission data signal of the i-th base station. K is characterized by giving the amount of rotation (the number of modulation symbols in a frame).

A communication method according to the present invention is a communication method used in a communication system in which each of a plurality of transmitting devices communicates with a receiving device that is a communication partner,
Generating a transmission data signal to be transmitted to the receiving device that is a communication partner, generating a modulation symbol by modulating the transmission data signal, and providing a specific phase rotation amount for each modulation symbol; Transmitting the modulation symbol given the phase rotation amount, and transmitting by each of the transmitters,
A step of receiving signals transmitted from the plurality of transmission devices, a step of calculating an amplitude of an interference signal transmitted from a transmission device that is not a communication partner, from the reception signal that is the received signal; Te, a step of pre-symbol impart rotational amount of the reverse and the unique the phase rotation amount given to each modulation symbol, the method comprising: based on the amplitude of the interference signal, calculates the likelihood information from the received signal, And a receiving step by the receiving device.

  According to the communication system and the communication method of the present invention, the following excellent effects can be obtained.

  According to the communication system and the communication method of the present invention, by giving different phase rotation to the modulation symbol sequence of the transmission signal for each base station, in an environment where the phase distribution is not random, interference on the receiving side is prevented. The phase distribution can be made uniform, and the interference amplitude distribution can be approximated so as not to depend on propagation path fluctuations, greatly increasing the amount of processing when calculating likelihood information from the received signal based on the approximate interference amplitude distribution. In addition to being able to reduce, likelihood information with high accuracy can be calculated, and the quality of received data can be improved.

  Hereinafter, an embodiment of a communication system and a communication method according to the present invention will be described with reference to the drawings.

  1 to 5 are diagrams showing an example of an embodiment of a communication system and a communication method according to the present invention. In the drawings, the same reference numerals denote the same parts.

  First, a basic concept that a high-quality decoding result can be obtained by the communication system and the communication method according to the present invention will be described before a specific configuration / operation description.

  When demapping a received signal in an environment where there is co-channel interference from an adjacent base station, the likelihood information (likelihood, likelihood ratio, logarithmic likelihood ratio) with high accuracy is considered when the amplitude distribution of interference components is taken into account. However, a large amount of computation is required to calculate the likelihood information using the interference component amplitude distribution as it is. Therefore, likelihood information is calculated using a distribution approximating the amplitude distribution of interference components.

  Here, the amplitude distribution of the interference (signal other than the separation target) component will be described with reference to FIG. 1, taking a QPSK modulated signal as an example.

  FIG. 1 is a diagram showing a constellation distribution of received signals and an amplitude distribution of interference components when there is a phase rotation of a QPSK modulated signal.

  When the propagation path fluctuation is small in the frame, the constellation distribution of the received signal is affected by the propagation path, so that it becomes as shown in FIG. 1 (a) and FIG. The amplitude distribution of the in-phase component or the quadrature component is as shown in the lower diagrams of FIGS. Comparing the lower diagram of FIG. 1A and the lower diagram of FIG. 1B, it can be seen that the amplitude distribution of the in-phase component or the quadrature component of the signal is different when the phase variation due to the influence of the propagation path is different. On the other hand, when various phase rotations are given to the transmission signal in advance, the distribution of the constellation of the received signal is as shown in the upper diagram of FIG. 1C, and the amplitude distribution of the in-phase component or quadrature component of the signal at this time Is distributed as shown in the lower diagram of FIG. 1C regardless of the phase fluctuation due to the influence of the propagation path. In view of this, a process for bringing the amplitude distribution of the interference component on the reception side closer to the distribution used for approximation is performed by giving different phase rotation amounts to the modulation symbol sequences of the transmission signals for each adjacent base station.

  As described above, in the communication system and the communication method according to the present invention, by applying different phase rotations to the modulation symbol sequence of the transmission signal, the phase distribution of interference on the receiving side is made uniform, and the interference between the same channels is reduced. The amplitude distribution is approximated, and likelihood information is calculated from the received signal based on the approximated interference amplitude distribution. Thereby, likelihood information with high accuracy can be calculated, and the quality of received data can be improved.

  Next, specific embodiments according to the communication system and the communication method of the present invention will be described.

  In addition, this embodiment demonstrates the case where one interference cell exists besides the base station of the own cell which communicates.

  FIG. 2 is a block diagram illustrating a configuration of a transmission device (hereinafter referred to as a transmitter) used in the communication system and the communication method according to the present embodiment. The transmitter of the interference base station has the same configuration.

  As illustrated in FIG. 2, the transmitter 200 includes an encoding unit 201, a rate matching unit 202, a modulation unit 203, a phase rotation unit 204, a pilot generation unit 205, a multiplexing unit 206, a wireless transmission unit 207, and a transmission antenna unit 208. Prepare.

  Transmission data transmitted from the upper layer is subjected to error correction coding processing by the encoding unit 201, and a bit sequence (encoded bit sequence) is output. As the error correction code, it is preferable to use a code having a high error correction capability, such as a turbo code, a convolutional code, an LDPC (Low Density Parity Check) code, and a Reed-Solomon code.

  The encoded bit sequence output from the encoding unit 201 is adjusted to a bit length corresponding to the radio frame by processing such as puncturing, repetition, and bit padding in the rate matching unit 202.

  The bit sequence output from the rate matching unit 202 is modulated by the modulation unit 203 and converted into a modulation symbol sequence. As the modulation in the modulation unit 203, modulation schemes such as BPSK modulation, QPSK modulation, 8PSK modulation, 16QAM modulation, and 64QAM modulation can be used.

The modulation symbol sequence modulated by the modulation unit 203 is subjected to phase rotation by the phase rotation unit 204. The phase to be rotated preferably has no correlation between base stations. When the number of modulation symbols in a frame is K, for example, the following method is used.
(1) A rotation amount of φ _{i, k} = (2π × i × k) / K is given to the k th modulation symbol of the i th base station. Alternatively, a rotation amount obtained by performing an interleaving process on k with respect to this rotation amount is given.
(2) A rotation amount of uniform random numbers φ _{i, k} = Rand (i, k) is given to the k-th modulation symbol of the i-th base station. Note that Rand (i, k) can hold values set in advance as a table so as to be uniquely determined using at least i and k. For example, when a different value is used for each terminal device, the rotation amount may be uniquely determined from i, k, and a number unique to the terminal device.

で表されるＴ個の基地局の変調シンボルベクトルｓ_ｋ ^０に、

上記（２）式で定義される位相回転行列Φ_ｋを乗算することで、位相回転後の変調シンボルベクトルｓ_ｋは、

として得られる。ただし、回転させる位相回転量はこれに限るものではなく、信号の同相成分あるいは直交成分の振幅分布は伝搬路の影響による位相変動によらず一様となるように位相回転量を与える他の方法を用いることもできる。 In these cases,

In the modulation symbol vector s _k ⁰ of T base stations represented by

By multiplying the phase rotation matrix [Phi _k as defined above (2), the modulation symbol vector s _k after phase rotation,

As obtained. However, the amount of phase rotation to be rotated is not limited to this, and other methods for giving the phase rotation amount so that the amplitude distribution of the in-phase component or quadrature component of the signal is uniform regardless of the phase fluctuation due to the influence of the propagation path. Can also be used.

Further, if φ _{1, k} , φ _{2, k} ,..., Φ _{T, k} are not correlated with each other with respect to k (or if the correlation is low), 0 radians may be employed as the phase rotation amount.

  Pilot generation section 205 generates a pilot symbol sequence that is commonly known in transmitter 200 and receiver 300.

  Multiplexer 206 multiplexes the phase rotation-processed modulation symbol sequence output from phase rotator 204 and the pilot symbol sequence output from pilot generator 205, and the multiplexed signal is transmitted from radio transmitter 207. It is transmitted via the antenna unit 208.

  Subsequently, the configuration and operation of the receiver 300 used in the communication system and the communication method according to the present embodiment will be described.

  FIG. 3 is a block diagram illustrating a configuration of a receiver 300 used in the communication system and the communication method according to the present embodiment.

  As illustrated in FIG. 3, the receiver 300 includes a reception antenna unit 301, a radio reception unit 302, a propagation path estimation unit 303, a propagation path compensation unit 304, an interference amplitude calculation unit 305, a phase restoration unit 306, a demapping unit 307, A rate matching unit 308 and a decoding unit 309 are provided.

  A plurality of signals transmitted simultaneously from a plurality of transmitters (a base station of the own cell and a base station of an interfering cell) 200 are received by radio reception section 302 via reception antenna section 301. At this time, the signal received via the receiving antenna unit 301 includes a plurality of signals transmitted simultaneously from the plurality of transmitters 200.

  The propagation path estimation unit 303 refers to the pilot symbol included in the received signal received by the wireless reception unit 302, calculates a propagation path estimation value indicating the characteristics of the propagation path with the base station of the own cell, and generates noise power. Measure.

  The propagation path compensation unit 304 performs phase compensation of the received signal received by the wireless reception unit 302 by referring to the propagation path estimation value calculated by the propagation path estimation unit 303.

  The interference amplitude calculation unit 305 calculates the amplitude of the interference signal from the channel estimation value calculated by the channel estimation unit 303, the received signal, and the noise power. Specifically, the difference value between the transmission signal restoration value obtained from the propagation path estimation value and the reception signal may be averaged, and the expected value of the noise amplitude obtained from the noise power may be subtracted.

The phase restoration unit 306 rotates the received signal compensated for the propagation path in the propagation path compensation unit 304 so as to restore the phase. At this time, the phase is restored by rotating the phase rotation unit 205 in the transmitter 200 by the same rotation amount as the rotation amount rotated for each modulation symbol. The amount of phase rotation required for restoration is, for example,
(1) A common setting is made in advance between the transmitter and the receiver.
(2) Calculation is performed using a calculation method set in advance between the transmitter and the receiver.
(3) Information is shared by notifying the receiver of the amount of phase rotation rotated by the transmitter.
However, the present invention is not limited to this, and it is sufficient if the phase rotation amount rotated on the transmission side can be specified on the reception side.

と表すことができる。ここで、ｙは、受信信号、ｈは、伝搬路応答、ｓは、送信信号である。 Based on the noise power measured by the propagation path estimation unit 303 and the amplitude of the interference signal calculated by the interference amplitude calculation unit 305, the demapping unit 307 performs softening for each bit from the received signal subjected to the phase restoration process. A judgment value (or LLR) series is calculated. As a specific example, the likelihood is

It can be expressed as. Here, y is a received signal, h is a propagation path response, and s is a transmitted signal.

となるが、干渉振幅算出部３０５において算出された干渉成分の振幅に基づいた分布（干渉信号の同相成分または直交成分の生起確率分布）ｐ_Ｉを用い、

として尤度を算出することにより、干渉が存在する場合において、さらに確度の高いＬＬＲを算出することができるようになる。 If the error u is a Gaussian distribution based only on noise,

The distribution based on the amplitude of the interference component calculated by the interference amplitude calculation unit 305 (occurrence probability distribution of the in-phase component or quadrature component of the interference signal) p _I is used,

By calculating the likelihood as follows, it is possible to calculate an LLR with higher accuracy in the presence of interference.

  In the present embodiment, in the demapping process and the interference amplitude calculation process, it is assumed that the receiver side knows in what modulation method the transmission signal is modulated.

  The rate matching unit 308 supports puncturing, repetition, and bit padding processing in the rate matching unit 202 in the transmitter 200, such as depuncturing, soft decision value synthesis, and bit deletion for the soft decision value series. Processing is performed.

  In decoding section 309, error correction decoding processing is performed using the soft decision value sequence that has been subjected to rate matching processing in rate matching section 308, and received data is extracted. Here, the error correction decoding process in the decoding unit 309 uses a process corresponding to the error correction encoding process in the encoding unit 201 in the transmitter 200.

Next, with reference to FIG. 4, an example of the likelihood calculation using the distribution p _I, based on the amplitude of the interference components calculated in the interference amplitude calculating unit 305.

FIG. 4 is a graph showing the distribution of each component of the interference amplitude with the horizontal axis as the in-phase component or quadrature component of the interference amplitude and the vertical axis as the probability density when the amplitude is | y _{I, k} |. .

The solid line shows the distribution when the interference is QPSK modulated. Each component is distributed in a range from − | y _{I, k} | to | y _{I, k} |, and the probability density distribution is flat in the vicinity of each component being 0, and − | y _{I, k} | and | y _{I , K} | near the impulse distribution.

と表すことができる。実線の分布の代わりに点線の分布（近似干渉振幅分布）を用いて（６）式の尤度を計算することにより、確度の低下を抑制しつつ尤度演算の複雑性を大幅に低減することができる。なお、ε１とε２としては、確率密度の全領域における積分値が１となるように設定すればよい。例えば、

とすればよい。また、（６）式の尤度を計算する際のｐ_Ｎは、伝搬路推定部３０３から出力された雑音電力の測定値を用いることが好ましい。 The concave dotted line is a distribution that approximates the distribution of the solid line.

It can be expressed as. By calculating the likelihood of equation (6) using a dotted line distribution (approximate interference amplitude distribution) instead of a solid line distribution, the complexity of the likelihood calculation is greatly reduced while suppressing a decrease in accuracy. Can do. Note that ε1 and ε2 may be set so that the integral value in the entire probability density region is 1. For example,

And it is sufficient. Moreover, it is preferable to use the measured value of the noise power output from the propagation path estimation unit 303 as _PN when calculating the likelihood of the equation (6).

FIG. 5 is a diagram illustrating another example of likelihood calculation using the distribution p _I based on the amplitude of the interference component calculated by the interference amplitude calculation unit 305.

  In FIG. 5, the solid line is a distribution when the interference is 16QAM modulated, and the dotted line indicates a distribution that approximates the distribution of the solid line.

  In the example shown in FIG. 4, a distribution such as Equation (7) is used as a distribution that approximates the probability distribution of each component of amplitude, but the distribution is not limited to this distribution. Other distributions that facilitate the calculation of equation (6) while maintaining the correlation with the original probability distribution can also be used.

  As described above, the transmission side gives a different phase rotation amount for each modulation symbol sequence in advance to approximate the amplitude distribution of inter-channel interference such as inter-cell interference, and from the received signal based on the approximate interference amplitude distribution. Likelihood information is calculated. Thereby, it is possible to calculate likelihood information with high accuracy while suppressing the amount of calculation, and improve the quality of received data. In addition, a method of approximating the amplitude distribution of inter-channel interference such as inter-cell interference is performed in a MIMO system in which MIMO multiplexing is performed by providing a different phase rotation amount for each stream in advance on the transmission side, and MIMO separation is performed on the reception side. It can also be applied to the amplitude distribution of inter-stream interference.

  In the above embodiment, the likelihood distribution of each component of the interference amplitude is assumed to be a distribution approximated by a rectangle, so that the distribution when superimposed on the noise component distribution can be obtained analytically, and the likelihood is Although the case where calculation at the time of calculating information is facilitated has been described, the distribution used for approximation is not limited to a rectangle. Other distributions can be used, such as a distribution obtained by analytically obtaining a noise component distribution and superimposing a probability distribution of each component of the original interference amplitude.

  Further, the communication system and the communication method according to the present invention are not limited to the illustrated examples described above, and it is needless to say that various changes can be made without departing from the gist of the present invention.

It is a figure which shows distribution of the constellation of the received signal, and amplitude distribution of an interference component in the case where there is a phase rotation of the QPSK modulated signal. It is a block diagram which shows the structure of the transmitter used for the communication system and communication method which concern on this embodiment. It is a block diagram which shows the structure of the receiver 300 used for the communication system and communication method which concern on this embodiment. When the amplitude is | y _{I, k} |, the horizontal axis is the in-phase component or the quadrature component of the interference amplitude, and the vertical axis is the distribution of each component of the interference amplitude with probability density. Another example of the likelihood calculation using the distribution p _I, based on the amplitude of the interference components calculated in the interference amplitude calculating unit is a diagram showing a. It is the schematic of the 1-cell repetition system used for radio | wireless communication, such as the conventional mobile telephone system.

Explanation of symbols

200 Transmitter 201 Encoding Unit 202 Rate Matching Unit 203 Modulation Unit 204 Phase Rotation Unit 205 Pilot Generation Unit 206 Multiplexing Unit 207 Radio Transmission Unit 208 Transmission Antenna Unit 300 Reception Unit 301 Reception Antenna Unit 302 Radio Reception Unit 303 Channel Estimation Unit 304 Propagation path compensation unit 305 Interference amplitude calculation unit 306 Phase restoration unit 307 Demapping unit 308 Rate matching unit 309 Decoding unit 601 Terminals 602 and 604 Base stations 603 and 605 Downlink

Claims (5)

A communication system including a mobile phone communication system that performs communication using the same channel between adjacent cells,
A transmission data signal generation unit that generates a transmission data signal to be transmitted to a receiving device that is a communication partner, a modulation unit that modulates the transmission data signal to generate a modulation symbol, and a phase rotation amount specific to each modulation symbol. A transmission device comprising: a phase rotation unit that provides; and a transmission unit that transmits the modulation symbol to which the phase rotation amount is provided;
A reception unit that receives a signal transmitted from the transmission device; an interference amplitude calculation unit that calculates an amplitude of an interference signal transmitted from a transmission device that is not a communication partner from the reception signal that is the received signal; and the reception signal On the basis of the amplitude of the interference signal, a phase restoration unit that restores the phase rotation unit by applying a phase rotation amount opposite to the inherent phase rotation amount given to each modulation symbol by the phase rotation unit A demapping unit that calculates likelihood information from
A communication system comprising:   The demapping unit of the receiving device calculates likelihood information based on an approximate interference amplitude distribution obtained by approximating an occurrence probability distribution of an in-phase component or a quadrature component of an interference signal, using the amplitude of the interference signal. The communication system according to claim 1.   When the transmission data signal to be the interference signal is PSK-modulated, the demapping unit of the receiver uses the amplitude of the interference signal to generate the occurrence probability distribution of the in-phase component or the quadrature component of the interference signal. 3. The communication system according to claim 2, wherein likelihood information is calculated based on an approximate interference amplitude distribution approximated to a concave shape.   The phase rotation unit has φi, k = (2π × i × k) / K (K is the number of modulation symbols in a frame) for the kth modulation symbol of the transmission data signal of the i-th base station. The communication system according to any one of claims 1 to 3, wherein a rotation amount is given. A communication method used in a communication system in which each of a plurality of transmitting devices communicates with a receiving device that is a communication partner,
Generating a transmission data signal to be transmitted to the receiving device that is a communication partner, generating a modulation symbol by modulating the transmission data signal, and providing a specific phase rotation amount for each modulation symbol; Transmitting the modulation symbol given the phase rotation amount, and transmitting by each of the transmitters,
A step of receiving signals transmitted from the plurality of transmission devices, a step of calculating an amplitude of an interference signal transmitted from a transmission device that is not a communication partner, from the reception signal that is the received signal; Te, a step of pre-symbol impart rotational amount of the reverse and the unique the phase rotation amount given to each modulation symbol, the method comprising: based on the amplitude of the interference signal, calculates the likelihood information from the received signal, Receiving step by the receiving device comprising:
A communication method characterized by comprising:

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