JP2008022465A - Radio communication method in radio communication program and its base station equipment and reception program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication method in a radio communication system combined with the use of Hybrid ARQ for improving communication equality by achieving the signal processing of a frequency region for reducing multi-path interference and Co-channel interference and its base station device and a reception program. <P>SOLUTION: Base station devices 1A and 1B are provided with a virtual reception system created by using reception data when a decision error is caused and a plurality of reception systems, and when receiving an output from a radio communication terminal MS whose AC identifier is the same in the other communication cell different from the communication cell, it is subtracted from the plurality of reception systems, and an interference signal for removal is created by using a desired signal to be generated as the result of the composition of the signals of the virtual reception system and the plurality of reception systems, and removed from the reception signal of each reception system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a wireless communication system such as a MUI (Multi-User Interference) free access system in which orthogonality of signals in the same cell is guaranteed, for example, based on repetitive transmission of transmission signals such as CIBS-CDMA system and IFDMA system. The present invention relates to a radio communication method in a radio communication system, a base station apparatus thereof, and a reception program for reducing multi-cell interference using both error correction coding and hybrid automatic retransmission (Hybrid ARQ).

  In recent years, there have been proposals for MUI-free access wireless communication schemes based on repeated transmission of transmission information data, such as CIBS-CDMA (Chip-Interleaved Block Spread-Code Division Multiple Access) scheme and IFDMA (Interleaved Frequency Division Multiple Access) scheme. Many have been made. These are communication systems that satisfy the complete orthogonality between orthogonal codes used during spreading processing, and have better communication quality than existing multiple access systems such as the DS-CDMA (Direct Sequence-CDMA) system in a multi-user environment. Is possible.

  According to the conventional CIBS-CDMA system, although there is no interference between users, there is a problem that it is easily affected by multipath interference. This is because inter-user interference is replaced with multi-path interference of individual users in principle by interleaving transmission data on the transmission side and deinterleaving reception data on the reception side.

  In order to cope with this problem, a technique called frequency domain equalization (FDE) is used. In FDE, multipath interference can be removed while having a path diversity effect capable of synthesizing multipaths. Therefore, the effect is very large, and is likely to be adopted in 3.5 generation mobile communication.

US Patent Application Publication No. 2005/249269 Paper: StefanoTomasin, Nevio Benvenuto, “Frequency-DomainInterference Cancellation and Nonlinear Equalization for CDMA Systems,” IEEE Transactions on Wireless Communications, Vol.4, No.5, September 2005

  However, in the CIBS-CDMA system, there is no interference between users only when all users are recognized in advance and orthogonal codes are assigned to the recognized users. That is, unlike a cellular environment, users of other cells or sectors cannot be grasped, and when the same user identifier is used in an adjacent cell or sector, very large interference is received. Therefore, in order to avoid this problem, always grasp the user access status of neighboring cells and sectors, change the spreading factor instantaneously and adaptively, and always orthogonalize between all users, this problem can be solved. To do.

  However, this increases the load on the host station that manages the radio access, and even if a user identifier is assigned, the propagation distance differs between the desired wave and the interference wave, and it is received with a large attenuation. In some cases, it may not be necessary to assign an excessive spreading factor. Therefore, the effect was questionable despite the wastefulness.

  Conventionally, MUD (Multi-User Detection) and interference cancellers have been proposed in order to eliminate these inter-cell / sector interferences. MUDs and interference cancellers are so complex that they are unrealistic to implement and will not be described in detail, but will be outlined below. The core technology of MUD and interference canceller is to temporarily receive and provisionally decode all users (or users with high power), remodulate them, and subtract them from the received signal that has been delayed during that time. These one-time processes are called “stages”, and it has been confirmed that the characteristics are improved in multistage.

  Also, serial processing and parallel processing are being studied. Although it can be easily analogized from the above contents, “demodulate once, remodulate and subtract from the received signal” means that terminals corresponding to the total number of accommodated users are provided in one stage. Considering the scale and processing time, even if the reception performance is improved, the implementation involves considerable difficulty.

  In order to reduce this difficulty, a proposal has been made to implement these interference cancellers and MUDs in the frequency domain. As an example, there is [Non-Patent Document 1] in the paper, and [Patent Document 1] in the patent. However, in these papers / patents, the time domain interference cancellation, which has been complicated in the past, is simply converted onto the frequency axis, and there is no improvement with respect to the complexity of performing a tentative decision or remodulating. It was. Therefore, the hardware scale is also increased, and there are still questions about its implementation.

  In summary, although FDE (frequency domain equalizer) is effective as a multipath countermeasure, it does not provide feasible interference cancellation, but has a small circuit scale that uses both interference cancellation and multipath countermeasures. There was a problem that there was no.

  In addition, as an interference cancellation method that gives a practical circuit scale, linear processing is used to reduce the hardware scale to a level that can be realized, and a linear interference canceller that is effective when the number of interfering users is small is considered. It has been. However, such a linear interference canceller system has a problem that its interference removal performance is determined by the number of independent antennas (the number of receiving systems).

  The present invention has been made in consideration of the above points. In the frequency domain, multipath interference and inter-user interference from other cells and sectors (Co-channel interference) can be reduced. An object of the present invention is to provide a wireless communication method, a base station apparatus, and a reception program in a wireless communication system capable of improving communication quality with interference removal performance of orders exceeding the number of reception systems while realizing signal processing.

  In order to solve such a problem, in the present invention, a plurality of communication cells including a plurality of radio communication terminals and a base station apparatus accommodating each radio communication terminal are arranged, and the communication control apparatus determines the communication state in each communication cell. In such a manner, each wireless communication terminal in each communication cell modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and transmits a plurality of the transmission signals to the same communication. In a wireless communication method in which only a transmission signal having a desired orthogonal identifier is extracted and received by a base station apparatus in a cell, the base station apparatus in each communication cell receives transmission signals from a plurality of wireless communication terminals. A plurality of receiving systems that perform signal conversion from the time domain to the frequency domain, and when a bit error is detected when decoding a transmission signal after signal conversion received by each receiving system, the bit error is A first step of requesting retransmission to each wireless communication terminal, and re-modulating the transmission signal including a decoded bit error that is the basis of retransmission, A second step of constructing a virtual reception system for signal conversion from to the frequency domain in parallel with each reception system, and orthogonal identifiers in other communication cells in which each reception system and virtual reception system are different from their own communication cells When a transmission signal from a wireless communication terminal having the same signal is received, an interference signal for removal is created using the interference signal generated as a result of synthesis in each reception system and virtual reception system, and the transmission signal in each reception system is used. It is characterized by comprising a third step for removing each and a fourth step for performing transmission path fluctuation equalization on the transmission signals in each reception system and virtual reception system.

  According to the second aspect of the present invention, in the second step, when the transmission signal including a bit error after decoding is remodulated in the virtual reception system, redundant bits other than the transmission information bits included in the transmission signal However, when it is known in advance that there is a difference between before and after retransmission, a signal corresponding to redundant bits is removed from a transmission signal modulated again by the virtual reception system.

  According to a third aspect of the present invention, in the third step, in the virtual reception system and each reception system, different weighting processes are executed for the virtual reception system and each reception system according to the reliability of the received signal quality. It is characterized by doing.

  In the invention described in claim 4, a plurality of communication cells including a plurality of radio communication terminals and a base station apparatus accommodating each radio communication terminal are arranged, and the communication control apparatus determines a communication state in each communication cell. In such a manner, each wireless communication terminal in each communication cell modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and transmits a plurality of the transmission signals to the same communication. In the base station device in each cell in the wireless communication method in which only the transmission signal having a desired orthogonal identifier is extracted and received by the base station device in the cell, the transmission signals from a plurality of wireless communication terminals are received. When a bit error is detected at the time of decoding a plurality of reception systems that perform signal conversion from the time domain to the frequency domain and transmission signals that are signal-converted in each reception system, a transmission signal that includes the bit error is Retransmission request means for requesting retransmission to each wireless communication terminal, and transmission including a bit error after decoding that is constructed in parallel with each receiving system and is the basis for retransmission by the retransmission request means. A radio reception system that performs signal conversion from the time domain to the frequency domain after modulating the signal again, and wireless communication in which each reception system and virtual reception system have the same orthogonal identifier in another communication cell different from its own communication cell When receiving a transmission signal from a terminal, an orthogonalization process is performed in which an interference signal for removal is generated using an interference signal generated as a result of synthesis in each reception system and virtual reception system, and is removed from each transmission signal in each reception system And frequency domain compensation means for performing transmission path fluctuation equalization on transmission signals in each reception system and virtual reception system.

  The invention described in claim 5 is characterized in that each process in the orthogonalization processing means and the frequency domain compensation means can be executed by a circuit process having the same configuration in the frequency domain.

  According to the sixth aspect of the present invention, in a virtual reception system, when a transmission signal including a bit error after decoding is remodulated, redundant bits other than transmission information bits included in the transmission signal are different before and after retransmission. If this is known in advance, a signal corresponding to redundant bits is removed from the transmission signal modulated again by the virtual reception system.

  According to the seventh aspect of the present invention, the orthogonalization processing unit executes different weighting processes for the virtual reception system and each reception system in the virtual reception system and each reception system according to the reliability of the received signal quality. It is characterized by doing.

  In the invention described in claim 8, a plurality of communication cells including a plurality of radio communication terminals and a base station apparatus accommodating each radio communication terminal are arranged, and the communication control apparatus determines a communication state in each communication cell. In such a manner, each wireless communication terminal in each communication cell modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and transmits a plurality of the transmission signals to the same communication. Transmission signals from a plurality of wireless communication terminals are transmitted to the base station device in each communication cell in the wireless communication method in which only the transmission signal having a desired orthogonal identifier is extracted and received by the base station device in the cell. It has a plurality of receiving systems that receive and convert signals from the time domain to the frequency domain, and when a bit error is detected when decoding a transmission signal after signal conversion received by each receiving system, the bit error is detected. A first step of requesting retransmission to each wireless communication terminal, and re-modulating the transmission signal including a decoded bit error that is the basis of retransmission, A second step of constructing a virtual reception system for signal conversion from to the frequency domain in parallel with each reception system, and orthogonal identifiers in other communication cells in which each reception system and virtual reception system are different from their own communication cells When a transmission signal from a wireless communication terminal having the same signal is received, an interference signal for removal is created using the interference signal generated as a result of synthesis in each reception system and virtual reception system, and the transmission signal in each reception system is used. In a series of processes consisting of a third step for removing each and a fourth step for performing transmission path fluctuation equalization for transmission signals in each reception system and virtual reception system, the third and fourth steps Wherein the receiving program for determining a multiplication coefficient corresponding to the processing by the processing unit.

  According to the ninth aspect of the present invention, in the third step, in the virtual reception system and each reception system, a different weighting process is executed for each of the virtual reception system and each reception system according to the reliability of the received signal quality. It is characterized by doing.

  According to the present invention, it is possible to improve both communication quality by reducing both Co-channel interference and multipath interference. Further, according to the present invention, it is possible to reduce the required transmission power required until the radio wave reaches the receiving side, and it is possible to save power as the entire system. Furthermore, according to the present invention, it is possible to increase the spreading factor in anticipation of the presence of users in other cells / sectors in advance, that is, to perform communication without causing a decrease in transmission rate.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  Next, embodiments of a radio communication method and its base station apparatus in a radio communication system according to the present invention will be described in detail with reference to the accompanying drawings. Before the description, the present invention will be clarified. An example of operation in which is applied will be described, and then the difference from the prior art will be described.

(1) Example of system operation by conventional CIBS-CDMA system FIG. 1 shows an example of system operation by CIBS-CDMA system in the prior art. That is, in FIG. 1, two cells (Cell-A, Cell-B) are described, and Cell-A includes two users (MS # 0-A, MS # 1-) that are wireless communication terminals MS such as mobile terminals. A) is connected to Cell-B, and one user (MS # 0-B) is connected to each other, and is communicating with the base station apparatuses 1A and 1B. When limited to Cell-A, since User # 0 (MS # 0-A) and User # 1 (MS # 1-A) are assigned different orthogonal codes, base station apparatus 1A (2 ~ 9), these users can be orthogonalized without any problem.

  Here, the radio communication terminal MS includes a transmission data generation unit 10, a multiplier 11, an interleaver 12, a guard interval adding unit 13, and a transmission / reception radio unit (TRX) 14. The transmission data generation unit 10 is a block that generates data such as independent sounds and images. The multiplier 11 is a spread spectrum unit that provides an orthogonal variable spreading factor OVSF (Orthogonal Variable Spreading Factor) code that is an orthogonal identifier (hereinafter also referred to as a user identifier) that is also used in the current third generation wireless communication.

  The interleaver 12 changes the transmission order of transmission signals specific to the CIBS-CDMA communication system. The guard interval giving unit 13 is a guard interval (GI) giving unit for reducing an aperture effect generated when a time signal discontinuous in the frequency domain is converted into the frequency domain. The transmission / reception radio unit (TRX) 14 is a transmission / reception radio unit having an analog unit such as a D / A, an A / D converter, a frequency conversion unit, and a quadrature modulation / demodulation unit. Actually, although the base station apparatuses 1A and 1B and the radio communication terminal MS have slightly different configurations of the transmission / reception radio unit (TRX), the radio communication terminal MS and the base station apparatuses 1A and 1B are identical here because they have almost the same function The code | symbol is provided.

  The base station apparatuses 1A and 1B include a guard interval removing unit 3, a deinterleaver 4, a multiplier 5, an integrator 6, an FFT 7, a complex multiplier 8 and an iFFT 9. The guard interval removing unit 3 is a circuit that extracts the guard interval inserted by the guard interval providing unit 13. The deinterleaver 4 is a circuit that performs reverse processing of the transmission side interleaver 12 and converts it to the original signal order.

  The multiplier 5 is a multiplier that performs spectrum despreading, and is a user orthogonalization processing unit that identifies a desired signal based on the user identifier assigned by the multiplier 11 of the radio communication terminal MS. The integrator 6 is an integrator that performs spectrum despreading, and performs interval integration of one cycle (diffusion rate) of OVSF. FFT7 and iFFT9 are a time / frequency converter for converting to the frequency domain and a frequency / time converter for converting to the time domain, respectively.

  In FIG. 1, the user identifier OVSF # 0 used in Cell-A is assigned to the radio communication terminal MS # 0-B of Cell-B. Therefore, although the radio communication terminal MS # 0-B is communicating with the base station apparatus 1B, if the radio wave also arrives at the base station apparatus 1A (= may not arrive), it becomes an interference source. On the other hand, in a general MUI free access scheme such as CIBS-CDMA and IFDMA, interference does not occur due to the orthogonalization principle if the user identifier is different. Therefore, although MS # 0-B is an interference source for radio communication terminal MS # 0-A, MS # 0-B has an orthogonal user identifier for MS # 1-A. It will not be a source of interference.

  Based on the assumption that this principle is applied to MUI-Free access, a method of limiting the total number of users in the previous stage of equalization / interference removal can be considered. However, if user orthogonalization is performed in the previous stage of equalization / interference removal, only interfering users having the same user identifier (for example, OVSF code) as the desired user remain as interference. According to this configuration, it is possible to greatly reduce the circuit scale as compared with the case of handling signals of all assumed users, and the circuit scale can be realized.

  Incidentally, when handling the signals of all assumed users, the base station device is a large-scale circuit of User # 0 to User # N to transmit / receive to / from one wireless communication terminal in order to eliminate the influence of user interference. A configuration is necessary, and it is necessary to include a large number of virtual terminals in one stage.

  However, in the method of performing user orthogonalization in the previous stage of equalization / interference cancellation, as shown in FIGS. 2A and 2B, the interference cancellation performance depends on the number of independent reception systems. 2A shows a two-antenna reception system, and FIG. 2B shows a four-reception system. Obviously, the reception error rate characteristic is worse when receiving two antennas than the reception error rate characteristic when there is no interference. This is because, as the number of independent antenna systems (dimensions) increases, the accommodating user is identified by the difference in space (transmission path), as represented by space division multiple access (SDMA). This is because the interference removal capability is improved.

  In the present invention, paying attention to the expansion of the dimension, the automatic repeat request (Hybrid ARQ: Automatic Repeat reQuest) used in the wireless communication system is expanded and the dimension is expanded.

  The Hybrid-ARQ technique is a known technique and will not be described in detail, but is outlined as shown in FIG. In FIG. 3, a transmitter 20 (22 to 25) and a receiver 21 (26 to 30) are depicted. In the transmitter 20, the transmission information is once taken into the buffer 22, and error correction coding is performed. Here, a turbo encoder is used. In turbo coding, in general, two parity bits are output for one bit of transmission information. Since it is inefficient to transmit twice the non-information signal (Rate = 1/3) with respect to 1-bit transmission information, in general, parity bits are thinned out alternately, Rate = 1/2, That is, the information signal to the parity bit is output on a one-to-one basis (the rate may be further lowered or increased depending on the system).

  On the receiver 21 side, user orthogonalization is performed, and frequency domain equalization / interference cancellation is performed by the frequency domain equalization / interference cancellation unit 27 in two-branch reception. The frequency domain equalization / interference cancellation unit 27 includes an FFT 31, a multiplier 32, an adder 33, and an iFFT 34. Of these, the FFT 31 and the iFFT 34 are a time / frequency conversion unit for converting to the frequency domain and a frequency for conversion to the time domain, respectively. -It is a time conversion part.

Thereafter, when turbo decoding is performed in the turbo decoder 29, if there is an error in the turbo decoding result unfortunately in the error presence / absence determination unit 30 (for example, detection by CRC: Cyclic Redundancy Check code), the transmitter 20 is instructed to transmit information again (NACK: Non ACKnoledgement). In the case of HARQ mode, for example, Chase-Combining, the transmitter 20 that has received NACK transmits exactly the same signal as before retransmission. Incremental
In Redundancy, as shown in FIG. 3, the parity bit switching initial phase is changed between the initial transmission and the retransmission. As a result, it is known that the incremental redundancy can perform decoding equivalent to R = 1/3 at the time of retransmission and improve the error correction capability.

(2) Configuration of Frequency Domain Equalization / Interference Canceling Unit According to this Embodiment Next, the first main point of the present embodiment will be described with reference to FIGS. 4 and 5, but this figure is only the first main point. Is not intended to illustrate the configuration of the present embodiment. FIG. 4, in which the same reference numerals are assigned to the parts corresponding to those in FIG. 3, shows how one interference user is canceled using the frequency domain equalization / interference cancellation unit 40.

The difference between the frequency domain equalization / interference cancellation unit 40 and the method of limiting the total number of users in the previous stage of equalization / interference removal described above is clearly the addition of a virtual reception system. This, in the upper part of FIG. 4 are represented by the output _{Y V} of FFT41, with its output is supplied to the multiplier 42, 43, 44, through the multiplier 42, 43 and 44, finally Is synthesized by an adder 45.

This configuration improves interference removal capability. The signal of the virtual reception system is the reproduced symbol data using the information sequence in which an error has occurred, which is the basis for the retransmission request, but has undergone error correction decoding, and most of the received bits are received normally. ing. For example, in the transmission / reception of an audio signal, a bit error rate of 10 ⁻² is the standard, which means that 1 bit out of 100 bits is incorrect. Therefore, most of the signal portion can be used as a desired wave removal signal for extracting and reproducing the interference signal.

  Further, although the frequency domain equalization / interference cancellation unit 40 of the present invention is a linear interference canceller, it is possible to improve a degradation factor lacking in noise reduction capability specific to the linear interference canceller by introducing a virtual reception system.

Next, the signal flow of the frequency domain equalization / interference cancellation unit 40 shown in FIG. 4 will be described. In FIG. 4, the desired wave extraction / reproduction stage and the interference wave extraction / reproduction stage are alternately repeated. Here, the multiplication coefficients W _DV , W _D1 , and W _D2 are MMSE (minimum mean square error) weights when there is no interference signal for each desired user of the virtual reception system and the two normal reception systems. A received signal in an n-th receiving system can be expressed as the following equation.
Y _n = H _Dn X _D + H _In X _I + Nn
W _Dn = H _Dn * / (Σ | H _Di | ² + SNR _D ⁻¹ )
W _In = H _In * / (Σ | H _Ii | ² + SNR _I ⁻¹ ) (1)

Here, * means a complex conjugate, and Σ means the sum between all related receiving systems, and the desired user signal is X _D and the interference user signal is X _I , respectively. Let the transfer function of the transmission line be H _D and H _I. Also, the MMSE weight for interfering signals and _{W I.} The desired signal-to-noise power ratio is SNR _D , the interference signal-to-noise power ratio is SNR _I , and the noise power is N. Note that X _D and X _I do not depend on the antenna number and are the same information, so there is no suffix n.

In FIG. 4, when the desired signal is synthesized by the multipliers 42, 46 and 47 with the multiplication coefficients W _DV , W _D1 and W _D2 , the output of the adder 48 includes the interference signal, A signal having an increased signal level is extracted. Thereafter, a transfer function of a transmission path for a desired signal that matches each receiving system is given by multipliers 49 and 50, and subtraction is performed from the receiving system by adders (subtracters) 51 and 52. Ideally, only the interference signal is extracted.

When the multipliers 53 and 54 receive and synthesize using the MMSE reception coefficients W _I1 and W _I2 for interference waves, the output of the adder 55 outputs an interference signal component from which a desired signal is deleted to some extent. By using this interference signal component and adding a transfer function for an interference wave in the multipliers 56 and 57 and performing subtraction from each normal reception system, the interference level for the desired wave signal can be reduced.

  By repeating these operations and subtracting the finally obtained interference signal by the subtracters 72 and 73, a normal reception system from which the interference signal is removed can be obtained.

  Thereafter, if the multipliers 44, 74, and 75 use the MMSE multiplication coefficient for each reception system and perform synthesis in the adder 45, a signal from which interference has been removed can be obtained.

  Since these are all linear processes, if simplified, as shown in FIG. 5, as a preferred embodiment, each of the complex multipliers 80, 81, and 82 has one interference multiplier and MMSE reception. it can.

It proves that FIG.4 and FIG.5 is the same. The FDE-IC output in FIG. 4, that is, the output of the adder 45 is
FDE output =
W _DV [Y _V ]
+ W _D1 [Y ₁ -HI ₁ {WI ₁ (Y ₁ -HD _{1 AD} ) + WI ₂ (Y ₂ -HD _{2 AD} )}]
+ W _D2 [Y ₂ −HI ₂ {W _I1 (Y ₁ −HD ₁ AD) + W _I2 (Y ₂ −HD _{2 AD} )}]
(2)
It can appear. Here, _AD is
_{A D = W DV Y V +} W D1 (Y 1 -H I1 B I) + W D2 (Y 2 -H I2 B I) ... (3)
And _BI is
_{B I = W I1 {Y 1} -H D1 (W DV Y V + W D1 Y 1 + W D2 Y 2)} + W I2 {Y 2 -H D2 (W DV Y V + W D1 Y 1 + W D2 Y 2)}
It is expressed in

_These, to put together the _{Y V,} Y _1, Y _2, respectively, will together before the _{B I.}
B _I =
Y _V {-W _I1 H _D1 W _DV -W _I2 H _D2 W _DV }
+ Y ₁ {W _I1 −W _I1 H _D1 W _D1 −W _I2 H _D2 W _D1 }
+ Y ₂ {W _I2 −W _I1 H _D1 W _D2 −W _I2 H _D2 W _D2 }
Here, if B = W _I1 H _D1 + W _I2 H _D2 ,
B _I =
Y _V {−W _DV B}
+ Y ₁ {W _I1 −W _D1 B}
+ Y ₂ {W _I2 −W _D2 B} (4)
It becomes.

Similarly for A _D , Y _V , Y ₁ , and Y ₂ are summarized as follows:
_{A D = W DV Y V +} W D1 (Y 1 -H I1 B I) + W D2 (Y 2 -H I2 B I)
_{= W DV Y V + W D1} Y 1 + W D2 Y 2 -B I (W D1 H I1 + W D2 H I2)
Here, A = W _D1 H _I1 + W _D2 H _I2
A _D = W _DV Y _V + W _D1 Y ₁ + W _D2 Y ₂ −B _I A

Substituting the result of equation (4) into this result,
_{A D = W DV Y V +} W D1 Y 1 + W D2 Y 2 -A {-Y V W DV B + Y 1 (W I1 -W D1 B) + Y 2 (W I2 -W D2 B)}
_{= Y V {W DV + AW} DV B} + Y 1 {W D1 -A (W I1 -W D1 B)} + Y 2 {W D2 -A (W I2 -W D2 B)} ... (5)

Similarly, for formula (2), Y _V , Y ₁ and Y ₂ are summarized as follows:
FDE output =
W _DV Y _V + W _D1 Y ₁ + W _D2 Y ₂
-Y ₁ {W _D1 H _I1 W _I1 + W _D2 H _I2 W _I1 }
-Y ₂ {W _D1 H _I1 W _I2 + W _D2 H _I2 W _I2 }
+ A _D {W _D1 H _I1 W _I1 H _D1 + W _D1 H _I1 W _I2 H _D2 + W _D2 H _I2 W _I1 H _D1 + W _D2 H _I2 W _I2 H _D2 }
= W _DV Y _V + W _D1 Y ₁ + W _D2 Y ₂
-Y ₁ {W _I1 A}
-Y ₂ {W _I2 A}
+ A _D {W _I1 H _D1 A + W _I2 H _D2 A}
= W _DV Y _V + W _D1 Y ₁ + W _D2 Y ₂
-Y ₁ {W _I1 A}
-Y ₂ {W _I2 A}
+ _AD {AB}
= W _DV Y _V
+ Y ₁ {W _D1 −W _I1 A}
+ Y ₂ {W _D2 −W _I2 A}
+ _AD {AB}

Substituting the result of equation (5) into this result,
FDE output =
W _DV Y _V
+ Y ₁ {W _D1 −W _I1 A}
+ Y ₂ {W _D2 −W _I2 A}
_{+ AB {Y V [W DV} + AW DV B] + Y 1 [W D1 -A (W I1 -W D1 B)] + Y 2 [W D2 -A (W I2 -W D2 B)]}
= W _DV Y _V
+ Y ₁ {W _D1 −W _I1 A}
+ Y ₂ {W _D2 −W _I2 A}
_{+ AB {W DV Y V [} 1 + AB] + Y 1 [W D1 -A (W I1 -W D1 B)] + Y 2 [W D2 -A (W I2 -W D2 B)]}
= Y _V {W _DV [1 + AB + A ² B ² ]}
+ Y ₁ {W _D1 −W _I1 A + AB [W _D1 −A (W _I1 −W _D1 B)]}
+ Y ₂ {W _D2 −W _I2 A + AB [W _D2 −A (W _I2 −W _D2 B)]}
= Y _V {W _DV [1 + AB + A ² B ² ]}
+ Y ₁ {W _D1 −A [W _I1 −B [W _D1 −A (W _I1 −W _D1 B)]]}
+ Y ₂ {W _D2 −A [W _I2 −B [W _D2 −A (W _I2 −W _D2 B)]]}

(6)

  This result is consistent with the coefficients in FIG. That is, it was shown that the multistage interference cancellation process shown in FIG. 4 can be expressed by a single multiplier (a complex multiplier in the case of handling complex signals) including the virtual reception system.

  From the above, as disclosed in the present embodiment, the desired signal is extracted and canceled in each of the virtual reception system using the decoded signal that is the basis of the retransmission request and the plurality of reception systems, and then By generating interference signals from a plurality of reception systems and subtracting each from the delayed reception signals, frequency domain compensation units that perform interference removal and transmission path equalization are each provided with one complex multiplier 80, 81, 82. It was shown that can be realized.

(3) Parity Removal Processing in Virtual Reception System Next, the operation of claim 2 of the present invention will be described with reference to FIG. In FIG. 6, the multiplication coefficient will be described in detail in claim 3 of the present invention. In addition, the blocks 25 and 26, which have been referred to as “user orthogonalization” in the drawings so far, will be expressed as IFDMA by giving a specific example.

  In the present embodiment, the virtual reception system includes a QPSK / 16QAM modulation unit 90, an FFT 41, and a multiplier 80. As will be described later, a weighting multiplication unit 91 may be provided between the multiplier 80 and the adder 45, and the weighting coefficient α may be changed to differentiate from the normal reception system.

  As described in the explanation of HARQ in claim 1, HARQ has a mode called “Incremental Redundancy” in which a parity bit to be transmitted is changed between initial transmission and retransmission. Also, even in Chase-Combining, the information sequence used for the virtual reception system is an information sequence in which an error has occurred, and when the turbo coding is performed on the receiver side based on this incorrect information, the result is The signal of the virtual reception system that is obtained automatically generates a completely different parity bit from the signal received at the time of retransmission, and when subtracting from the normal reception system, it causes an increase in interference (because a different signal is subtracted). It is highly possible that the desired signal is not deleted to extract the interference signal).

  Therefore, the second aspect of the present invention is characterized in that the parity bit is not incorporated as a desired signal when generating an interference signal.

Specifically, for example, QPSK (Quadrature Phase Shift Keying) is taken as an example. When turbo encoding is performed at Rate = 1/2, and transmission information bits and parity bits are symbol-mapped alternately, on the I and Q planes (Inphase, Quadrature phase), the QPSK symbol at a certain time t is It is shown as follows.
Symbol X (t) = D (t) + jP (t)
Here, j is an imaginary operator, D (t) takes a value of ± 1, and P (t) takes a value of ± 1.

Therefore, X (t) takes one of four types of “1 + j”, “−1 + j”, “+ 1−j”, and “−1−j”. In a normal reception system, information and parity are mapped according to these mapping rules. On the other hand, the virtual system uses only transmission information,
Playback symbol X ′ (t) = D ′ (t)
It becomes. D ′ (t) is a reproduction information sequence in which turbo decoding has been completed and an error has occurred (where it is unknown where).

  The reproduced symbol is used as an information signal of the virtual reception system. Obviously, although the signal is different from that of the normal reception system, interference cancellation can be performed for the information signal region, and at least the possibility of an increase in interference can be obtained for the parity region.

  Even in the case of a multi-level modulation system such as 16QAM or 64QAM (QAM: Quadrature Amplitude Modulation), it is possible to cope with this extension of the idea. Although it is not described in detail because it can be realized by simple extension, the same processing is possible if the signal power given by the parity part is set to 0 according to the mapping rule.

  From the above, as disclosed in the present embodiment, by forcibly deleting the parity bit part of the reproduced symbol, the present invention can be applied even when the signal at the time of retransmission in HARQ is different from that at the first transmission. It was shown to be possible.

(4) Differentiation method between virtual reception system and normal reception system Next, claim 3 of the present invention will be described. According to the third aspect of the present invention, the weighting coefficient α is changed based on the difference in reliability between the virtual reception system and the normal reception system. The processing image is a multiplication process by the weighting multiplication unit 91 shown in FIG. Note that the existence of this multiplication process is only a virtual one, and strictly speaking, it is not implemented in this place, but the transfer functions H _DV and H _{D1 of} each receiving system described in the description of claim 1 above. , Should be included in _HD2 .

  A transmission information sequence including an error used in a virtual reception system has been subjected to error correction processing although an error exists, and may have higher reliability than a normal reception system. For example, when the received signal level is very low compared to the noise power, the quality of the information signal sequence is higher when the error correction (turbo decoding) processing is performed than the received signal obtained in the normal receiving system. There is a case. In this case, the weight of the virtual reception system that has been subjected to the error correction process should be increased, and the dependence on the virtual reception system should be increased in the combined result of the virtual reception system and the normal reception system.

  On the other hand, although the received signal level is high, an error may occur unfortunately due to the interference level. In this case, it is not necessary to give a large weight to the virtual reception system, and a weight having a level equal to or lower than that of the normal reception system is required. Despite the better quality of the normal system, if the virtual reception system is heavily weighted, the normal reception system is neglected and optimal reception characteristics cannot be obtained.

  Therefore, it may be effective to perform different weighting between the virtual reception system and the normal reception system due to the difference in path / processing. Considering this weighting is a major point of claim 3 of the present invention.

A specific weighting method can be realized by giving each transfer function. The transfer function of the virtual reception system can be expressed as follows.
H _DV = G + j0
Here, G is a real constant, and as a result, it can be seen that the transfer function of the virtual reception system is a transfer function of a constant multiple giving a simple gain G. Since the virtual reception system is only modulated again and does not pass through the transmission line, it means that it is simply multiplied by a gain. Here, each frequency domain equalization / interference cancellation coefficient in MMSE reception of a desired signal can be expressed as follows.

If it is a virtual reception system,
_N
W _DV = H _DV ^* / (Σ | Hi | ² + | H _DV | ² + SNR ⁻¹ )
ⁱ
If it is a normal receiving system,
_N
W _DX = H _DX ^* / (Σ | Hi | ² + | H _DV | ² + SNR ⁻¹ )
ⁱ
It is expressed. From the above equation, it can be seen that the weight of the virtual reception system and the normal reception system can be changed by G.

  The optimum value of G depends on the modulation scheme used, such as QPSK, 16QAM, 64QAM, etc., and also changes depending on the state of transmission path fluctuation at the time of initial transmission and retransmission, so when constructing a system, It is desirable to investigate the optimum value in the expected range in advance.

  The effect of the IFDMA method according to this embodiment was confirmed by computer simulation. FIGS. 7A and 7B show the average packet error rate (PER) characteristics and the average throughput characteristics. In either case, there are usually two receiving systems. The transmission line model is a 6-pass exponentially damped static environment. It is assumed that one desired user and one interfering user exist near the cell or sector boundary, and the transmission path between the users is independent, but is received by the base station apparatus with equal power.

  The base station to be measured has a spreading factor of 4 and accommodates 4 users, and is in a so-called Fully Loaded state. In the figure, FDE-MMSE indicates a case where interference removal is not performed, and FDE-IC1 to FDE-IC4 are BER characteristics when interference removal / equalization of each stage is performed. Incremental redundancy was adopted, and the maximum number of retransmissions was set to 4 times. This means that if an error remains after four transmissions, the packet cannot be received.

  The characteristic using the disclosed technology of claims 1 to 3 is described as FDE-IC4 with Virtual Branch Addition (VBA). Eb / N0 (signal energy to noise power density ratio per bit of transmission information) on the horizontal axis indicates Eb / N0 per one when four antennas are employed, and is 3 [dB] so that they can be easily compared with each other. The left shift is processed.

  As is clear from FIG. 7A, the characteristic improvement of about 1.8 [dB] is made in the present invention compared with the FDE-IC4 at PER = 0.1 corresponding to the voice quality.

  Further, in FIG. 7B showing the average throughput characteristics, a throughput of 0.25 means a place where transmission power from the terminal is insufficient near the boundary of the cell (communication area), and retransmission is performed four times and reception is gradually possible. The improvement of about 1.2 [dB] can be confirmed.

  As described above in detail, in the frequency domain equalization / interference removal method in the receiver of the present invention, the orthogonal identifier unique to the wireless communication device assigned to each transmission device by the upper communication control device is used. In the wireless communication system that makes a retransmission request, the receiving apparatus creates a virtual reception system using the decoded sequence in which the error occurs, By having user orthogonalization means to perform user orthogonalization in the previous stage of frequency domain equalization, it has a plurality of normal reception systems, and unspecified many interference sources are emitted from different transmitters with the same user identifier The transfer function of the co-channel interference and the desired signal is obtained by taking into account that the different user signal is subtracted from the total received signal. A means for obtaining a demodulation coefficient optimum for the desired signal, a frequency domain conversion means for converting the total received signal into the frequency domain, and a coefficient optimum for the received signal to be demodulated are provided by at least one complex multiplier. Frequency domain compensation means for performing co-channel interference cancellation and multi-path interference cancellation of a desired signal at the same time.

  As a result, according to this receiver configuration, when performing multipath equalization of a user to be decoded in frequency domain equalization having a complex multiplier (only one in the optimal configuration) for each reception system, Co -Channel interference is reduced simultaneously, and reception characteristics can be improved by adding a virtual reception system even when the number of reception systems is small.

  Also, the equalization / interference removal method of the present invention eliminates interference or MMSE combining of redundant information areas other than transmission information in which mismatch is predicted in advance between the initial transmission and the retransmission in the HARQ mode. Is excluded.

  As a result, this equalization / interference removal method is characterized in that an interference level is not increased for a redundant information region and the interference removal performance is improved for transmission information.

Furthermore, the equalization / interference elimination method of the present invention gives a difference in reliability between the virtual reception system and the normal reception system by coefficient adjustment between retransmission and the previous transmission.
As a result, this equalization / interference removal method is characterized in that an optimum synthesis result is obtained when the reception quality differs depending on the path and processing included in each reception system.

  In addition, the equalization / interference removal method of the present invention can also include the concept of multi-stage processing of the prior art, and in multi-stage processing, by performing interference removal from a signal having a large received power, It is devised to improve the interference removal performance. As a result, this receiving apparatus is characterized in that the interference removal performance can be further improved.

It is a basic diagram which shows the operation example of the radio | wireless communications system by the CIBS-CDMA system in a prior art. It is a graph which shows the average error rate characteristic of 2 receiving systems and 4 receiving systems by a prior art. It is a block diagram with which it uses for description of system operation | movement at the time of introduce | transducing Hybrid ARQ. It is a block diagram which shows embodiment of the receiver applied to the base station apparatus in the radio | wireless communications system by this invention. It is a block diagram which shows embodiment of the receiver applied to the base station apparatus in the radio | wireless communications system by this invention. It is a block diagram with which it uses for description of system operation | movement at the time of introducing this invention to a HARQ environment. 4 is a graph illustrating average packet error rate characteristics and average throughput characteristics according to the present invention.

Explanation of symbols

  1A, 2A ...... Base station apparatus, 20 ... Transmitter, 21 ... Receiver, 27, 40 ... Frequency domain equalization / interference canceling unit, 29 ... Turbo decoder, 30 ... Error presence / absence determining unit, 31... FET, 32, 42 to 44, 46, 47, 49, 50, 53, 54, 56, 57, 60, 61, 63, 64, 67, 68, 70, 71, 74, 75. 33, 45, 48, 51, 52, 55, 58, 59, 62, 65, 66, 69, 72, 73 ... adder (subtractor), 34 ... iFET, 80-82 ... complex multiplier , 90... QPSK / 16QAM modulation unit, 91... Weighting multiplication unit.

Claims (9)

A plurality of communication cells each including a plurality of wireless communication terminals and a base station device that accommodates each wireless communication terminal are arranged, and the communication control device controls a communication state in each communication cell, so that each communication cell Each of the wireless communication terminals in the network modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and the base station apparatus in the same communication cell transmits a plurality of the transmission signals. In the wireless communication method for extracting and receiving only the transmission signal having the desired orthogonal identifier,
The base station device in each of the communication cells is
It has a plurality of reception systems for receiving transmission signals from a plurality of the wireless communication terminals and converting the signals from the time domain to the frequency domain, and bit errors are generated when decoding the transmission signals after signal conversion received by the respective reception systems. When detected, a first step of temporarily holding a transmission signal including the bit error and requesting retransmission to each wireless communication terminal;
Second step of constructing a virtual reception system for performing signal conversion from the time domain to the frequency domain in parallel with each of the reception systems after re-modulating the transmission signal including the bit error after decoding that is the basis of the retransmission When,
When each of the reception systems and the virtual reception system receives a transmission signal from the wireless communication terminal having the same orthogonal identifier in another communication cell different from its own communication cell, each of the reception systems and A third step of creating an interference signal for cancellation using an interference signal generated as a result of combining in the virtual reception system, and removing each interference signal from a transmission signal in each of the reception systems;
And a fourth step of performing transmission path fluctuation equalization on transmission signals in each of the reception systems and the virtual reception system. In the second step,
In the virtual reception system, when remodulating a transmission signal including a bit error after decoding, it is known in advance that redundant bits other than transmission information bits included in the transmission signal are different before and after retransmission. The radio communication method according to claim 1, wherein a signal corresponding to the redundant bit is removed from a transmission signal modulated again by the virtual reception system. In the third step,
In the virtual reception system and each of the reception systems, different weighting processes are executed for the virtual reception system and each of the reception systems, respectively, according to the reliability of received signal quality. The wireless communication method described in 1. A plurality of communication cells each including a plurality of wireless communication terminals and a base station device that accommodates each wireless communication terminal are arranged, and the communication control device controls a communication state in each communication cell, so that each communication cell Each of the wireless communication terminals in the network modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and the base station apparatus in the same communication cell transmits a plurality of the transmission signals. In the base station apparatus in each communication cell in the wireless communication method for extracting and receiving only the transmission signal having the desired orthogonal identifier,
A plurality of reception systems that receive transmission signals from a plurality of the wireless communication terminals and perform signal conversion from the time domain to the frequency domain;
When a bit error is detected at the time of decoding of a transmission signal that has been signal-converted in each reception system, a retransmission request means that temporarily holds a transmission signal including the bit error and requests retransmission to each wireless communication terminal When,
A virtual reception system that is constructed in parallel with each of the reception systems, re-modulates a transmission signal including a bit error after decoding that is a basis for retransmission by the retransmission request unit, and then performs signal conversion from the time domain to the frequency domain; ,
When each of the reception systems and the virtual reception system receives a transmission signal from the wireless communication terminal having the same orthogonal identifier in another communication cell different from its own communication cell, each of the reception systems and An orthogonalization processing means for creating an interference signal for removal using an interference signal generated as a result of combining in the virtual reception system, and removing each interference signal from a transmission signal in each of the reception systems;
A base station apparatus comprising: frequency domain compensation means for performing transmission path fluctuation equalization on transmission signals in each of the reception systems and the virtual reception system. 5. The base station apparatus according to claim 4, wherein each process in the orthogonalization processing unit and the frequency domain compensation unit can be executed by a circuit process having the same configuration in the frequency domain. In the virtual reception system,
When re-modulating a transmission signal including a bit error after decoding, it is known in advance that redundant bits other than transmission information bits included in the transmission signal are different before and after retransmission. The base station apparatus according to claim 4 or 5, wherein a signal corresponding to the redundant bit is removed from the re-modulated transmission signal. The orthogonalization processing means includes:
The said virtual receiving system and each said receiving system perform a different weighting process to said virtual receiving system and each said receiving system, respectively according to the reliability with respect to received signal quality, respectively. Or the base station apparatus in any one of 6. A plurality of communication cells each including a plurality of wireless communication terminals and a base station device that accommodates each wireless communication terminal are arranged, and the communication control device controls a communication state in each communication cell, so that each communication cell Each of the wireless communication terminals in the network modulates and transmits a transmission signal using a unique orthogonal identifier assigned by the communication control apparatus, and the base station apparatus in the same communication cell transmits a plurality of the transmission signals. Then, for the base station device in each communication cell in the wireless communication method for extracting and receiving only the transmission signal having the desired orthogonal identifier,
It has a plurality of reception systems for receiving transmission signals from a plurality of the wireless communication terminals and converting the signals from the time domain to the frequency domain, and bit errors are generated when decoding the transmission signals after signal conversion received by the respective reception systems. When detected, a first step of temporarily holding a transmission signal including the bit error and requesting retransmission to each wireless communication terminal;
Second step of constructing a virtual reception system for performing signal conversion from the time domain to the frequency domain in parallel with each of the reception systems after re-modulating the transmission signal including the bit error after decoding that is the basis of the retransmission When,
When each of the reception systems and the virtual reception system receives a transmission signal from the wireless communication terminal having the same orthogonal identifier in another communication cell different from its own communication cell, each of the reception systems and A third step of creating an interference signal for cancellation using an interference signal generated as a result of combining in the virtual reception system, and removing each interference signal from a transmission signal in each of the reception systems;
In a series of processes consisting of a fourth step of performing transmission path fluctuation equalization for transmission signals in each of the reception systems and the virtual reception system,
A receiving program for obtaining a multiplication coefficient corresponding to the processing of the third and fourth steps by an arithmetic processing unit. In the third step,
9. The virtual reception system and each of the reception systems execute different weighting processes for the virtual reception system and each of the reception systems, respectively, according to the reliability of received signal quality. Receiving program.