JP2006211063A - Adaptive modulator, its method, and communication device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive modulation system for improving transmission efficiency by improving the ability of following a transmission state in a wireless communication system to which a multi-stage interference canceller is applied. <P>SOLUTION: The history of an SIR 1 which is calculated with ICUs 101a-101c in the first stage of the multi-stage interference canceller, and that of an SIR 2 calculated with reception parts 102a-102c after the interference cancellation, are held in memories 115 of MCS (Modulation and Code Scheme) decision parts 120a-120c. When the newest SIR in the first stage coincides with the SIR in the first stage held in the memories 115, a modulation parameter MCS is decided by using the held SIR 2 calculated with the reception parts. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an adaptive modulation apparatus and method and a communication apparatus using the same, and more particularly to an adaptive modulation system that adaptively determines a modulation scheme and a coding rate when a multistage interference canceller is applied.

  In mobile communication systems, there are a phase modulation method for changing the phase and a quadrature amplitude modulation method for changing the amplitude and the phase. Examples of the phase modulation method include BPSK (Binary Phase Shift Keying), QPSK (Quadrature PSK), and 8PSK. There are quadrature amplitude modulation schemes such as 16QAM (Quadrature Amplitude Modulation) and 64QAM. In these modulation schemes, transmission efficiency improves in the order of BPSK, QPSK, 8PSK, 16QAM, and 64QAM.

  On the other hand, if the transmission efficiency is improved, that is, the amount of data that can be transmitted with one symbol increases, it becomes more susceptible to multipath and fading, so redundant information is added to the transmission data to reduce the coding rate. By using an error correction code, reception errors can be reduced. However, if the coding rate decreases, redundant information increases, resulting in poor transmission efficiency.

  Therefore, the propagation state is estimated from the received signal, a modulation scheme with good transmission efficiency is achieved in a good propagation environment, and the coding rate is increased to increase the throughput, while in a poor propagation environment, the transmission efficiency is improved. By adopting an adaptive modulation method that enables reliable communication without errors by reducing the coding rate as a bad modulation method, overall transmission efficiency can be increased (Non-patent Document 1). reference).

  FIG. 6 is a diagram for explaining an operation example of uplink adaptive modulation in communication between the base station BS and the mobile station UE in the mobile communication system. The base station BS estimates the propagation state from the received uplink signal, determines MCS (Modulation and Code Scheme) according to the propagation state from the result, and notifies the mobile station UE using the downlink signal. The mobile station UE outputs an uplink signal by a modulation scheme according to MCS notified from the base station BS.

  Furthermore, in a CDMA (Code Division Multiple Access) mobile communication system, interference from other mobile stations due to cross-correlation between spreading codes caused by the non-synchronization between mobile stations, multipath interference occurs, These interferences are factors that reduce channel capacity and transmission quality of the mobile communication system. Therefore, a multi-stage interference canceller that removes such interference from the received signal and improves the propagation state estimation result, for example, SIR (Signal to Interference Ratio) is applied (Patent Document 1). reference).

  FIG. 7 is a block diagram showing a configuration example of an adaptive modulation apparatus using the conventional multistage interference canceller. There are two types of multistage interference cancellers, a parallel type and a serial type. Here, an example of a parallel type is shown. As shown in FIG. 7, the multi-stage interference canceller includes at least one cancellation stage (in the figure, first to third stages) in which processing for removing the interference signal is performed for each user signal. In addition, each user signal after passing through the cancel stage is generated with symbol information generated by the receiving units 102a to 102c, and decoded by the decoding units 103a to 103c, respectively. Also, the adaptive modulation is performed using the propagation state estimation result improved by removing the interference, for example, SIR.

  The multistage interference canceller processes a plurality of user signals with a plurality of stage configurations, but the multistage interference canceller shown in FIG. 7 is an example of three users and three cancellation stages.

  In this example, a plurality of ICUs (Interference Cancel Units) 101a to 101i that generate replica signals that are the same signal components as user signals, delay units 104a to 104c that delay received signals, and all replica signals First adding units 105a to 105c, subtracting units 106a to 106c for subtracting the output signals of the first adding units 105a to 105c from the delayed received signal, and output signals and replicas of the subtracting units 106a to 106c Output from the second adders 107a to 107i for adding the signals, the receivers 102a to 102c for generating the symbol signal and the SIR from the output signals of the second adders 107g to 107i, and the receivers 102a to 102c. Decoders 103a to 103c and receivers 102a to 102c for decoding the received symbol signals It has a MCS determination unit 120 a - 120 c to determine the MCS from SIR determined, and a downlink transmission portion 114a~114c for notifying the mobile station of MCS determined by the MCS determining unit 120 a - 120 c.

  The first stage includes ICUs 101a to 101c, a delay unit 104a, a first addition unit 105a, a subtraction unit 106a, and second addition units 107a to 107c. The second stage includes ICUs 101d to 101f, a delay unit 104b, a first addition unit 105b, a subtraction unit 106b, and second addition units 107d to 107f. Further, the third stage includes ICUs 101g to 101i, a delay unit 104c, a first addition unit 105c, a subtraction unit 106c, and second addition units 107g to 107i.

  In such a configuration, in the first stage, a replica signal of each user signal is generated from the received signal using a plurality of ICUs 101a to 101c connected in parallel, and each replica signal is synthesized by the first adder 105a. . The synthesized replica signal is input to the subtracting unit 106a, and the subtracting unit 106a subtracts the synthesized replica signal from the reception signal delayed by the delay unit 104a. The output signal of the subtracting unit 106a is a residual signal obtained by removing all users' replica signals from the received signal.

  The replica signals for each user are added to the residual signal by the second adders 107a to 107c, respectively, and the signals for each user from which other user signals are removed are output from the second adders 107a to 107c. The

  Thereafter, the same processing is performed on the output signals of the second adders 107a to 107c in the second stage, respectively, and the output signals of the second adders 107d to 107f of the second stage are executed on the third stage. Similar processing is performed, the output signals of the second adders 107g to 107i are input to the receivers 102a to 102c, the symbol information generated by the receivers 102a to 102c is input to the decoders 103a to 103c, Decoded signals are obtained by the decoding units 103a to 103c.

  Further, the MCS determination unit 120a determines the MCS using the SIR obtained by the reception unit 102a, notifies the determined MCS to the downlink transmission unit 114a, and the downlink transmission unit 114a notifies the mobile station of the notified MCS. . Similarly, the MCS determination unit 120b determines the MCS using the SIR obtained by the reception unit 102b, notifies the determined MCS to the downlink transmission unit 114b, and the MCS determination unit 120c uses the SIR obtained by the reception unit 102c. The MCS is determined, the determined MCS is notified to the downlink transmission unit 114c, and the downlink transmission units 114b to 114c notify the notified MCS to the mobile station.

JP 2000-13360 A IEICE Technical Report RCS2003-36 (2003-05) p.39 "Study on MC-CDMA Communication System Using Adaptive Modulation" Keiji Tachikawa, “W-CDMA mobile communication system”, Maruzen Co., Ltd., p. 56-59

  In the wireless communication system, when the above-described multistage interference canceller and adaptive modulation are applied, the MCS is determined using the propagation state estimation result obtained by the receiving unit after interference cancellation, for example, the signal power to interference power ratio (SIR). In this case, since it becomes difficult to follow the propagation state, there is a disadvantage that the transmission efficiency is deteriorated.

  The reason is that in the adaptive modulation method, it is ideal to determine and transmit the MCS while the propagation state does not change, but the multistage interference canceller has processing such as despreading in each stage, and the number of stages This is because the processing delay increases as the value increases, and if SIR after interference cancellation is used, it takes a long time to determine the MCS, and the propagation state changes during that time.

  The present invention has been made in view of the above points, and an object of the present invention is to improve transmission efficiency in a wireless communication system to which a multistage interference canceller is applied by improving the followability of propagation conditions. It is an object to provide an adaptive modulation apparatus and method capable of performing the above and a communication apparatus using the same.

  An adaptive modulation apparatus according to the present invention is an adaptive modulation apparatus that performs communication by changing MCS which is a parameter of a transmission signal modulation scheme and a coding rate in accordance with a propagation path state, and removes interference from a received signal. A plurality of stages of interference canceling means, a receiving means for receiving a signal after interference cancellation by the interference canceling means, and a first SIR (signal power to interference power ratio) obtained in the first stage of the interference canceling means And MCS determining means for determining the MCS based on the second SIR obtained by the receiving unit after interference.

  A communication apparatus according to the present invention uses the above-described adaptive modulation apparatus.

  Furthermore, the adaptive modulation method according to the present invention is an adaptive modulation method for performing communication by changing MCS, which is a parameter of a transmission signal modulation scheme and a coding rate, in accordance with a propagation path state. A plurality of stages of interference cancellation step to be removed, a reception step for receiving a signal after interference cancellation by the interference cancellation step, and a first SIR (signal power versus interference) obtained in the first stage of the interference cancellation step And an MCS determination step for determining the MCS based on the second SIR obtained in the reception step after interference.

  The operation of the present invention will be described. When the latest first SIR at the first stage in the multi-stage interference removing unit that removes interference from the received signal matches the past first SIR stored as the SIR history in the memory, or predetermined. If they match within the specified range, the MCS is determined using the past second SIR at the receiving unit corresponding to the matched first SIR. Thereby, the said objective can be achieved.

  The effect of the present invention is that transmission time is improved because the time until the MCS is determined is shortened and the followability of the propagation state is improved. The reason is that the SIR of the first stage obtained in the past and the SIR of the receiving unit after interference cancellation are held and used as a history, and without waiting for the output of the SIR of the receiving unit after interference canceling processing, This is because the MCS can be determined.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. The same parts as those in FIG. 7 are indicated by the same reference numerals, and this embodiment is adapted for uplink adaptation provided with an interference canceller having three users and three cancel stages. It is an example of a modulation apparatus.

  Referring to FIG. 1, a replica signal that is the same signal component as a user signal is generated, a propagation state is estimated, and a plurality of ICUs 101a to 101i for obtaining an SIR, and delay units 104a to 104c that delay received signals; First adders 105a to 105c that add all replica signals, subtractors 106a to 106c that subtract the output signals of the first adders 105a to 105c from the delayed received signals, and subtractors 106a to 106c Second adders 107a to 107i that add the output signal and the replica signal, respectively, and receivers 102a to 102c that generate symbol signals and obtain SIR from the output signals of the second adders 107g to 107i. .

  The first stage includes ICUs 101a to 101c, a delay unit 104a, a first addition unit 105a, a subtraction unit 106a, and second addition units 107a to 107c. The second stage includes ICUs 101d to 101f, a delay unit 104b, a first addition unit 105b, a subtraction unit 106b, and second addition units 107d to 107f. Further, the third stage includes ICUs 101g to 101i, a delay unit 104c, a first addition unit 105c, a subtraction unit 106c, and second addition units 107g to 107i.

  Further, using the SIR obtained by the ICU 104a to ICU 104c and the receiving units 102a to 102c, the MCS determination units 120a to 120c for determining the MCS for each user and the MCS determined by the MCS determination units 120a to 120c to the mobile station It is the structure which has downlink transmission part 114a-114c for notifying.

  All of the MCS determination units 120a to 120c have the same configuration, and in the figure, only the configuration of the MCS determination unit 120a is shown for simplification. Delay unit 110 that delays the first stage SIR (SIR1) output from any of ICU101a to ICU101c, and SIR (SIR2) that is output from any of SIR1 delayed by delay unit 110 and reception units 102a to 102c ) In the memory 115, the memory 115 holding the SIR1 and SIR2 written from the memory control unit 111, and the SIR1 and SIR2 and the SIR1a and SIR2a held in the memory 115 The SIR selecting unit 112 that selects the SIR to be output to the MCS determining processing unit 113, the MCS is determined using the SIR output from the SIR selecting unit 112, and the determined MCS is assigned to one of the downlink transmitting units 114a to 114c. The MCS determination processing unit 113 for outputting is configured.

  FIG. 2 is a configuration diagram of the ICUs 101a to 101c shown in FIG. As shown in FIG. 2, despreading units 21 a to 21 c that despread a received signal, a rake combining unit 22 that rake-combines signals despread by the despreading units 21 a to 21 c, and an output signal of the rake combining unit 22 SIR measurement unit 23 that measures SIR from the above, determination unit 24 that generates a symbol signal from the output signal of rake combining unit 22, and respreading unit 25a that re-spreads the symbol signal output from determination unit 24 for each path 25c and a combining unit 26 that combines all the signals for each respread path. The SIR obtained by the SIR measurement unit 23 is output to the delay unit 110 and the SIR selection unit 112 in FIG. 1 (SIR1).

  A plurality of despreading units 21a to 21c and respreading units 25a to 25c are provided according to the received delay wave number, that is, the number of paths, and FIG. 2 shows an example in which three paths are provided in parallel. The despreading units 21a to 21c are configured to include a despreading processing unit 21-1, which performs despreading for one path, a transmission path estimation unit 21-2, and a multiplication unit 21-3. The despreading processing unit 21-1 performs despreading for one wave among a plurality of reception delay waves. The transmission path estimation unit 21-2 calculates the transmission path estimation value ξ based on the method described in Non-Patent Document 2, for example.

  The multiplication unit 21-3 performs phase correction by multiplying the output signal of the despreading processing unit 21-1 by the complex conjugate ξ * of the transmission channel estimation value ξ obtained by the transmission channel estimation unit 21-2. Each of the re-spreading units 25a to 25c performs re-diffusion for one wave. A multiplier 25-2 that multiplies the symbol signal output from the determination unit 24 and the transmission path estimation value ξ output from the transmission path estimation unit 21-2, and respreading that respreads the output signal of the multiplication unit 25-2. And a processing unit 25-2.

  FIG. 3 shows the configuration of the receiving units 102a to 102c shown in FIG. As shown in FIG. 3, despreading units 31 a to 31 c that despread an input signal, a rake combining unit 32 that rake combines signals despread by the despreading units 31 a to 31 c, and an output signal of the rake combining unit 32 The SIR measuring unit 33 that measures SIR from the SIR.

  The SIR obtained by the SIR measurement unit 33 is output to the memory 111 of FIG. 1 (SIR2). The despreading units 31a to 31c have the same configuration as the despreading units 21a to 21c in FIG. The output signal of the rake combining unit 32 is output to one of the decoding units 103a to 103c.

  FIG. 4 shows the relationship between the frame numbers being processed by the ICUs 101a to 101c and the receiving units 102a to 102c. In the example, the receiving units 101a to 101c are processing with a delay of 4 frames compared to the ICUs 101a to 101c. is there.

  Next, the operation of the present embodiment will be described in detail. The SIR 1 input to the MCS determination units 120 a to 120 c is input to the SIR selection unit 112 and the delay unit 110. As shown in the example of FIG. 4, since a processing delay occurs between the paths from the ICUs 101a to 101c to the receiving units 102a to 102c, the delay unit 110 is set so that the SIR1 corresponds to the SIR2 obtained from the same received signal. The SIR1 is delayed by the time until the SIR2 obtained by the receiving unit 102a is output, and output to the memory control unit 111.

  In the example of FIG. 4, since the frame numbers processed by the receiving units 102a to 102c are delayed by about 4 frames compared to the frame numbers processed by the ICUs 101a to 101c, the delay unit 110 delays SIR1 by 4 frames. Let The SIR2 input to the MCS determination units 120a to 120c is distributed to the memory control unit 111 and the SIR selection unit 112.

  The memory control unit 111 writes the SIR 2 and the SIR 1 delayed by the delay unit 110 into the memory 115. At this time, the maximum number of SIR1 and SIR2 to be held in the memory 115 is determined in advance and written to the memory 115. The maximum number of SIR1 and SIR2 held in the memory 115 can be arbitrarily changed. Note that SIR1 and SIR2 held in the memory 115 are SIR1a and SIR2a, respectively.

  The memory control unit 111 deletes the oldest SIR1a and SIR2a in the memory 115 when the number of SIR1a and SIR2a held in the memory 115 has reached a predetermined maximum number, and then the delay unit 110 The SIR1 and SIR2 delayed by the above are written into the memory 115.

  The SIR selection unit 112 searches the SIR 1a that matches the inputted SIR1 from all the SIR1a held in the memory 115. If there is an SIR 1 a that matches SIR 1 in the memory 115, the SIR 2 a obtained from the same received signal as the matched SIR 1 a is output to the MCS determination processing unit 113.

  On the other hand, if there is no SIR 1 a that matches SIR 1 in the memory 115, the SIR 2 at the current time is output to the MCS determination processing unit 113. The MCS determination processing unit 113 determines the MCS using the SIR notified from the SIR selection unit 112, and notifies the determined MCS to any of the downlink transmission units 114a to 114c.

  Next, a specific operation example of the SIR selection unit 112 is shown. FIG. 5 is an example of SIR1a and SIR2a for 10 frames held in the memory 115 when the maximum quantity of SIR1a and SIR2a is 10 in the memory 115.

  The top is the oldest SIR1a and SIR2a, and newer as it goes down. In addition, SIR1a and SIR2a in each row are SIR values obtained from the same received signal. In this state, the operation of the SIR selection unit 112 will be described in the following cases (1) to (3).

(1) When SIR1 matches one SIR1a in the memory 115:
For example, when SIR1 = 7.9 dB, there is a matching SIR1a in the memory 115. In this case, the SIR selection unit 112 outputs SIR2a = 9.5 dB to the MCS determination processing unit 113.

(2) When SIR1 matches a plurality of SIR1a in the memory 115:
For example, when SIR1 = 10.3 dB, there are three matching SIR1a in the memory 115. In this case, the SIR 2a is selected based on a preset selection method. For example, when it is set to select the newest SIR 2 a, SIR 2 a = 12.0 dB is output to the MCS determination processing unit 113.

(3) When SIR1 does not match SIR1a in the memory 115:
For example, when SIR1 = 12.3 dB, since there is no matching SIR1a in the memory 115, the SIR selection unit 112 outputs the SIR2 at the current time to the MCS determination processing unit 113.

  As another modified example, when the SIR selection unit 112 searches for whether or not the SIR 1a that matches SIR1 exists in the memory 115, a range to be determined to match is set, and if within the range, it is determined to match. For example, if the integer parts of the SIR match, it can be determined that they match.

It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the structure of ICU of FIG. It is a block diagram which shows the structure of the receiving part of FIG. It is a figure for demonstrating operation | movement of the block of FIG. It is a figure which shows the example of the data currently hold | maintained at the memory 115 of FIG. It is a block diagram which shows schematic structure of the mobile communication system which employ | adopted the adaptive modulation system. It is a block diagram which shows the conventional structure of a multistage interference canceller and an adaptive modulation system.

Explanation of symbols

101a-101i ICU (interference cancellation unit)
102a to 102c Receiver 103a to 103c Decoder 104a to 104c, 110 Delay 105a to 105c, 107a to 107i Adder 106a to 106c Subtractor 111 Memory controller 112 SIR selector 113 MCS determination processor 114a to 114c Downlink transmitter 115 Memory 120a-120c MCS determination part

Claims (16)

An adaptive modulation apparatus that performs communication by changing MCS (Modulation and Code Scheme), which is a parameter of a modulation scheme and a coding rate of a transmission signal, adapted to a propagation path state,
A multi-stage interference removing means for removing interference from the received signal;
Receiving means for performing signal reception processing after interference removal by the interference removing means;
MCS determination for determining the MCS based on the first SIR (signal power to interference power ratio) obtained in the first stage of the interference canceling means and the second SIR obtained in the receiving unit after interference. Means,
An adaptive modulation device comprising:   The MCS determining means has memory means for storing a pair of the first SIR and the second SIR corresponding to the first SIR as a history, and based on the current first SIR, 2. The adaptive modulation apparatus according to claim 1, wherein the MCS is determined with reference to a memory means.   The MCS determination means determines the MCS using the second SIR paired with the first SIR when the current first SIR matches the first SIR in the memory means. The adaptive modulation apparatus according to claim 2, wherein:   If the current first SIR matches with the first SIR in the memory means within a preset range, the MCS determination means is the second SIR paired with the first SIR. The adaptive modulation apparatus according to claim 2, wherein the MCS is determined using SIR.   The MCS determination means determines the current second SIR when the current first SIR does not match the first SIR in the memory means, or does not match within the preset range. The adaptive modulation apparatus according to claim 3 or 4, wherein the MCS is determined by using the MCS.   6. The adaptation according to claim 2, wherein the retention history of the memory means is sequentially updated by a pair of the new first SIR and the second SIR corresponding to the first SIR. Modulation device.   The MCS determination means further comprises delay means for delaying the current first SIR by a time corresponding to a delay time caused by a path between the interference cancellation means and the reception means. 7. The adaptive modulation apparatus according to claim 2, wherein the SIR and the second SIR at that time are stored in the memory means as a pair.   A communication apparatus comprising the adaptive modulation apparatus according to claim 1.   The communication apparatus according to claim 8, wherein the communication apparatus is a base station in a mobile communication system. An adaptive modulation method in which communication is performed by changing MCS (Modulation and Code Scheme), which is a parameter of a modulation method and a coding rate of a transmission signal, adapted to a propagation path state,
A multi-stage interference cancellation step for canceling interference from the received signal;
A reception step that performs reception processing of the signal after interference cancellation by the interference cancellation step;
MCS determination for determining the MCS based on the first SIR (signal power to interference power ratio) obtained in the first stage of the interference cancellation step and the second SIR obtained in the reception step after interference Steps,
An adaptive modulation method comprising:   The MCS determination step stores a pair of the first SIR and the second SIR corresponding to the first SIR in a memory means as a history, and based on the current first SIR, 11. The adaptive modulation method according to claim 10, further comprising the step of determining the MCS with reference to a memory means.   The MCS determination step determines the MCS using the second SIR paired with the first SIR when the current first SIR matches the first SIR in the memory means. The adaptive modulation method according to claim 11, wherein:   In the MCS determination step, if the current first SIR matches the first SIR in the memory means within a preset range, the second SIR paired with the first SIR The adaptive modulation method according to claim 11, wherein the MCS is determined using SIR.   The MCS determination step determines the current second SIR when the current first SIR does not match the first SIR in the memory means, or does not match within the preset range. The adaptive modulation method according to claim 12 or 13, wherein the MCS is determined by using the MCS.   15. The method further comprises the step of sequentially updating the retention history of the memory means with a new pair of the first SIR and the second SIR corresponding to the first SIR. Any one of the adaptive modulation methods.   The method further includes a delay step of delaying the current first SIR by a time corresponding to a delay time occurring between the interference cancellation step and the reception step, and the delayed SIR and the second time at that time 16. The adaptive modulation method according to claim 11, wherein a pair of SIR is stored in the memory means.

Images