JP4773487B2 - Wireless communication terminal and communication control method - Google Patents

Description

  The present invention relates to a radio communication terminal and a radio communication method, and more particularly to a radio communication terminal and a radio communication method that reduce a load of error correction in a diversity radio communication terminal including a plurality of antennas.

  In general, in wireless communication such as mobile communication, data (signal) errors occur in a communication path due to fading and multipath effects. In recent years, turbo codes and LDPC (Low Density Parity Check) have been adopted as techniques for correcting this error. The turbo code is obtained by inputting data to be transmitted in different bit orders to a plurality of encoders on the transmission side. The receiving side (terminal side) includes a plurality of decoders, decodes the received data, feeds back the output of the decoder to the input, and performs iterative decoding. By performing iterative decoding in this way, the error correction accuracy of received data can be improved.

  As described above, it is necessary to perform iterative decoding in an error correction method using turbo code or LDPC, and the larger the number of times, the higher the data decoding characteristics. However, there is a limit to the reachable decoding characteristics, and there are times when the decoding characteristics do not further improve even if decoding is repeated a certain number of times. Therefore, in the prior art, the number of iterative decodings (hereinafter referred to as “convergence number”) at which the decoding characteristic sufficiently converges is obtained in advance, and the number of times of iterative decoding is performed.

  However, with the increase in the number of repeated decoding, there is a problem that the time required for the decoding process increases and the delay increases, and the power consumption further increases. As a technique for solving this problem, a technique has been proposed in the prior art in which the number of repetitive decoding is varied according to the reception quality (communication channel state) measured from the received pilot signal (see Patent Documents 1 and 2). I want to be.) FIG. 8 shows a schematic block diagram of a wireless communication terminal that controls the number of times of repeated decoding according to the prior art. In the figure, channel quality calculation section 230 calculates (estimates) reception quality from a pilot signal received by reception section 210 via antenna ANT3, and transmits the calculation result to repetition count calculation section 240. The iteration number calculation unit 240 controls the number of iteration decoding in the iterative decoder 220 according to the reception quality (channel quality). That is, when it is estimated that the channel quality is good and the received signal has few errors, the number of repetitive decoding is set to be more than the number of convergence with the recognition that good decoding characteristics can be obtained even if the number of times of decoding is small. Less.

  Note that recent wireless communication terminals are mainly provided with a plurality of antennas and performing communication by a diversity method. For example, spatial diversity utilizes the fact that, when reception is performed using a plurality of antennas located at spatially separated locations, the correlation of received signals generally becomes small and their fluctuations become independent. Therefore, the reliability of the received signal is improved by combining a plurality of received signals received by a plurality of antennas by a predetermined process or selecting a received signal with the best reception level.

  Note that in a wireless communication terminal including a plurality of antennas as described above, the relative positional relationship between the plurality of antennas may vary. For example, taking a mobile phone terminal as an example, in a foldable type in which two cases are connected by a hinge, or in a slide type consisting of two cases in which one case slides relative to the other case Some housings each have an antenna. Since the distance between antennas fluctuates by moving the casing, the diversity effect obtained differs depending on the shape of the casing. That is, when the distance between the antennas is large and the correlation between the antennas is small, the received signal quality is better than when the distance between the antennas is small and the signal is received by a single antenna. However, when using the above-mentioned error correction by iterative decoding for a wireless communication terminal having a plurality of antennas, the number of times of iterative decoding is controlled according to the reception quality obtained by the difference in relative distance between the plurality of antennas. No technique has been proposed.

JP 2001-230679 A JP 2002-152056 A

  Accordingly, an object of the present invention is to solve the above-described problems, and in a wireless communication terminal equipped with a plurality of antennas, control the number of decoding repetitions according to the distance between antennas, that is, the reception quality, and delay due to decoding processing. And a technique (a wireless communication terminal and a communication control method) for reducing power consumption.

In order to solve the above-described problems, a wireless communication terminal (which can receive diversity) having a plurality of antennas with variable relative distances according to the present invention is provided.
(With a receiving unit for combining or selecting a plurality of received signals received by the plurality of antennas)
A decoder (turbo decoder) that repeatedly decodes a received signal including an error correction code received by the plurality of antennas;
An inter-antenna distance detector for detecting a distance between the plurality of antennas;
(A storage unit that stores a table of the number of repetitions of decoding in the decoder corresponding to the distance between the antennas)
And a control unit that controls to reduce the number of repetitions of the decoding when the detected distance between the antennas exceeds a predetermined value compared to when the distance between the antennas is below a predetermined value. .

Furthermore, other embodiments Diversity relative distance with a variable of the plurality of antennas by the possible wireless communication terminal of the present invention,
A channel quality calculation unit that calculates communication channel quality from received signals received by the plurality of antennas;
The controller is
When the communication channel quality calculated by the channel quality calculation unit exceeds a predetermined value when the distance between the antennas is lower than a predetermined value, the decoding channel is compared with a case where the quality of the communication channel is lower than a predetermined value . It is characterized by reducing the number of repetitions.

Furthermore, a wireless communication terminal (which can receive diversity) having a plurality of antennas with variable relative distances according to another embodiment of the present invention includes:
(A buffer for buffering received signals including error correction codes received by the plurality of antennas)
A determination unit (detection unit) for determining whether or not there is an error in the data decoded by the decoding unit;
A retransmission request unit that requests retransmission of data based on a determination result by the determination unit;
The controller is
The larger the number of retransmission requests of the retransmission request unit, the smaller the number of repetitions of decoding in the decoder.

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included. Note that each step of the method or program uses an arithmetic processing unit such as a CPU or a DSP as necessary in data processing, and the input data, processed / generated data, etc. are stored in an HDD, memory, etc. Is stored in the storage device.

For example, a communication control method of a wireless communication terminal capable of diversity reception provided with a plurality of antennas with variable relative distances, which is realized as a method of the present invention,
(Combining or selecting a plurality of received signals received by the plurality of antennas)
Repeatedly decoding a received signal including an error correction code received by the plurality of antennas with a decoder;
Detecting a distance between the plurality of antennas;
And a step of controlling so that the number of repetitions of the decoding is reduced when the distance between the antennas detected in the detecting step exceeds a predetermined value compared to a case where the distance between the antennas is lower than the predetermined value. Features.

  As described above, according to the present invention, in a wireless communication terminal having a plurality of antennas, it is possible to control the number of repetitions of decoding in accordance with the distance between antennas, that is, the reception quality, thereby reducing delay and power consumption due to decoding processing. It becomes possible.

  Hereinafter, a wireless communication terminal according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the wireless communication terminal is a portable electronic device such as a mobile phone terminal, a notebook computer, a PDA (personal digital assistance), a portable game machine, a portable audio player, a portable video player, a portable electronic dictionary, and a portable electronic book viewer. be able to.

  FIG. 1 is a schematic diagram of a wireless communication terminal according to an embodiment of the present invention. The radio communication terminal 100 is a foldable mobile phone terminal having two casings as shown in the figure, for example, and two antennas ANT1 and ANT2 are positioned in each casing. This wireless communication terminal can open and close two housings, and a state where the housings are separated from each other as shown in the figure is an open state, and a state where the housings (not shown) are in close contact with each other is a closed state. In the example shown in the figure, the two antennas ANT1 and ANT2 have a sufficiently long relative distance when the wireless communication terminal 100 is in an open state, have a small correlation between the antennas, and can obtain a sufficient diversity effect. And On the other hand, when the wireless communication terminal 100 is in the closed state, the relative distance between the two antennas ANT1 and ANT2 is short and substantially operates as one antenna. It should be noted that the present invention is not limited to a foldable mobile phone terminal, and can be applied to all wireless communication terminals that include a plurality of antennas and whose relative distances are variable. Moreover, although the number of antennas is two, the present invention is not limited to this and may have three or more antennas.

  First, a first embodiment of the present invention will be described. FIG. 2 is a schematic block diagram of a radio communication terminal according to the first embodiment of the present invention. The wireless communication terminal 100 includes a receiving unit 110, an iterative decoder 120, an iterative number control unit 130, an inter-antenna distance detection unit 140, a storage unit 150, and two antennas ANT1 and ANT2. The receiving unit 110 performs predetermined processing on the signals received from the two antennas ANT1 and ANT2. For example, the receiving unit 110 includes a demodulating unit, a switch (not shown), and the like, and selects a signal having a strong reception level from signals received from the two antennas ANT1 and ANT2. Or when the radio | wireless communication terminal 100 has three or more antennas, the receiving part 110 synthesize | combines a received signal, for example with a maximum ratio synthetic | combination system etc., and obtains the best received signal. Note that the signals received by the antennas ANT1 and ANT2 include a turbo code (error correction code) for error correction. Then, receiving section 110 transmits the processed data to iterative decoder 120. The iterative decoder 120 performs decoding using an error correction code included in the data transmitted from the receiving unit 110. The iterative decoder 120 includes two decoders, an interleaver and a deinterleaver, for example, similarly to a general turbo decoder, and performs iterative decoding based on an error correction method. Since iterative decoding using a turbo code is a known technique, details are omitted here.

  The inter-antenna distance detector 140 detects the distance between the two antennas ANT1 and ANT2. For example, in the case of a foldable mobile phone terminal, the inter-antenna distance detector 140 detects the distance between the antennas based on the opening angle of the housing (angle α in FIG. 1). Alternatively, when the mobile phone terminal is a slide type mobile phone and each of the two housings is provided with an antenna, the inter-antenna distance detection unit 140 detects the distance between the antennas depending on the sliding state. The iteration count control unit 130 determines the number of iterations of decoding in the iterative decoder 120 based on the inter-antenna distance detected by the inter-antenna distance detection unit 140. The number of repetitions is set according to the distance between the antennas, and the storage unit 150 stores a table of the number of repetitions with respect to the distance between the antennas.

  Next, processing of the wireless communication terminal 100 according to the present invention will be described using a flowchart. FIG. 3 is a flowchart showing an example of processing of the wireless communication terminal 100 according to the first embodiment of the present invention. First, in step S11, the inter-antenna distance detection unit 140 detects the inter-antenna distance between the two antennas ANT1 and ANT2, and transmits the detected inter-antenna distance to the repetition number control unit 130. The iteration count control unit 130 sets (controls) the decoding iteration count based on a table stored in the storage unit 150 and indicating the relationship between the iteration count and the distance between the antennas. An example of the table stored in the storage unit 150 is shown below.

  Based on the table shown in Table 1, when the distance between the antennas is below a certain threshold A, the repetition count control unit 130 sets the repetition count to “N2”. When the distance between the antennas is equal to or greater than the threshold A, the repetition count control unit 130 sets the repetition count to “N1” (steps S12 to S14). Here, if the distance between the antennas is equal to or greater than the threshold value A, the threshold A is set to such a value that there is little correlation between the antennas ANT1 and ANT2 and signals can be received by two antennas. The number of repetitions is N2 ≧ N1. This is based on the recognition that when the correlation between the antennas ANT1 and ANT2 is small, the quality of the received signal is good. The distance between the antennas is short, and the decoding is more effective than the state of receiving with a single antenna. This is because the number of repetitions can be reduced. In addition, when the distance between the antennas exceeds the threshold A, the reception quality becomes good, and therefore the number of repetitions N1 can be set to be smaller than the number of convergence times (the number of repetitions N2). After setting the number of repetitions in step S13 or S14, the receiving unit 100 receives data (step S15), and the iterative decoder 120 decodes the received data for the set number of times (step S16).

  According to the first embodiment described above, unlike the conventional technique in which the reception quality is good and the decoding characteristic converges quickly, unlike the conventional technique in which decoding is repeated by a predetermined number of convergence times, the advantage of the diversity method is utilized. When there is little correlation between them and the reception quality is good, the number of decoding iterations is reduced, so that the time and power consumption required for the decoding process can be reduced compared to the conventional case.

  Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram of a wireless communication terminal according to the second embodiment of the present invention. In the figure, the same reference numerals are given to the same functional units as those of the wireless communication terminal 100 of FIG. The radio communication terminal 100A further includes a channel quality calculation unit 160. Channel quality calculation section 160 calculates reception quality (channel quality) from signals received by antennas ANT1 and ANT2. For example, the reception quality is calculated by calculating an SIR (Signal to Interference Ratio) using a pilot signal included in the received signal. Alternatively, RSSI (Received Signal Strength Indicator), CIR (Carrier To Interference Ratio), CINR (Carrier to Interference plus Noise Ratio), SINR (Signal) to Interference plus Noise Ratio (signal-to-interference plus noise ratio) or the like can be used. The repetition count control unit 130A sets the number of repetitions of decoding based on the channel quality calculated by the channel quality calculation unit 160 together with the inter-antenna distance detected by the inter-antenna distance detection unit 140. Storage unit 150A stores a table of the number of repetitions for the distance between antennas and channel quality.

  Next, processing of the wireless communication terminal according to the second embodiment of the present invention will be described using a flowchart. FIGS. 5A and 5B are flowcharts showing an example of processing of the wireless communication terminal 100A according to the second embodiment of the present invention. First, in step S21, the inter-antenna distance detecting unit 140 detects the inter-antenna distance between the two antennas ANT1 and ANT2, and transmits the detected inter-antenna distance to the repetition number control unit 130A. The iteration count control unit 130A sets the decoding iteration count based on a table stored in the storage unit 150 and indicating the relationship between the iteration count and the inter-antenna distance. An example of the table stored in the storage unit 150 is shown below.

  Based on the table shown in Table 2, when the distance between the antennas is equal to or greater than a certain threshold A, the repetition count control unit 130A sets the repetition count to “N1” (step S23). If the distance between the antennas is below a certain threshold A, the repetition count control unit 130A proceeds to step S24, and performs the repetition count setting process based on the reception quality. FIG. 5B is a flowchart of an example of a process for setting the number of repetitions according to reception quality. First, in step S31, channel quality calculation section 160 determines whether or not reception quality is acquired, that is, whether or not data (pilot signal or the like) capable of calculating reception quality (channel quality) is acquired. When it is determined that the channel quality calculation unit 160 has not acquired the channel quality calculation unit 160, the process proceeds to step S33, and the repetition count control unit 130A sets the repetition count to “N5”. This “N5” is the number of times of convergence described above. When the distance between the antennas is short and the signal is received substantially by one antenna and the reception quality is not good, the number of times that the decoding characteristics converge sufficiently. Set. When it is determined in step S31 that the reception quality is acquired, the process proceeds to step S32, and the repetition count control unit 130A sets the repetition count according to the reception quality. This is performed based on the table shown in Table 2. That is, when the reception quality is equal to or higher than a certain threshold C, the number of repetitions is set to “N2”. When the reception quality is equal to or higher than a threshold value D and lower than the threshold value C, the number of repetitions is set to “N3”. When the reception quality is equal to or lower than the threshold value D, the number of repetitions is set to “N4”. Here, the threshold of reception quality has a relationship of C> D, and the number of repetitions has a relationship of N4 ≧ N3 ≧ N2 ≧ N1. This is also based on the recognition that the quality of the received signal is good when the correlation between the antennas ANT1 and ANT2 is small, as in the first embodiment. Further, in a state where the distance between the antennas is short and reception is substantially performed by one antenna, when the reception quality is good, the number of repetitions is made smaller than when the reception quality is not good. Note that when the distance between the antennas exceeds the threshold value A, the reception quality is good, and therefore the number of repetitions N1 can be set to be smaller than the number of convergence times described above. After setting the number of repetitions in step S32 or S33, the process returns to step S25 in FIG. 5A, and the receiving unit 100A receives the data. Thereafter, the iterative decoder 120 decodes the received data for the set number of times (step S26).

  According to the second embodiment, in addition to the advantages of the first embodiment, even when the distance between the antennas is short and the antenna is received with substantially one antenna, the number of decoding iterations depends on the reception quality. And the time and power consumption required for the decoding process can be reduced.

  Next, a third embodiment of the present invention will be described. FIG. 6 is a block diagram of a wireless communication terminal according to the third embodiment of the present invention. In the figure, the same reference numerals are given to the same functional units as those of the wireless communication terminal 100 of FIG. The radio communication terminal 100B further includes a packet synthesis unit 170, a buffer 172, a CRC detection unit 174, and a retransmission request generation unit 176. The radio communication terminal 100B performs error correction using a known HARQ (Hybrid Automatic Repeat reQuest: hybrid ARQ) technique. HARQ is an ARQ (Automatic Repeat reQuest) that is a control requesting the transmitting side to retransmit the data (wrong packet) when the receiving side receives wrong data (packet). For example, a technique to which a packet combining technique is applied. The packet combining technique is a technique for combining packets of previously received data and newly received data retransmitted from a communication partner apparatus (for example, a base station). In the third embodiment, the number of iteration decoding in HARQ is changed according to the distance between antennas and the number of retransmission requests. In the present embodiment, HARQ using the chase combining method will be described as an example, but the present invention is not limited to this. Also, since HARQ is publicly known, details are omitted.

  The repetition count control unit 130B in the wireless communication terminal 100B sets the number of decoding iterations based on the number of retransmission requests by the retransmission request generation unit 176 and the inter-antenna distance detected by the inter-antenna distance detection unit 140. Storage unit 150B stores a table of the number of retransmission requests by retransmission request generation unit 176 and the number of repetitions for the distance between antennas.

  Next, processing of the wireless communication terminal according to the third embodiment of the present invention will be described using a flowchart. FIG. 7 is a flowchart showing an example of processing of the wireless communication terminal 100B according to the third embodiment of the present invention. First, in step S41, the inter-antenna distance detection unit 140 detects the inter-antenna distance between the two antennas ANT1 and ANT2, and transmits the detected inter-antenna distance to the repeat count control unit 130B. The iteration count control unit 130B sets the decoding iteration count based on a table stored in the storage unit 150B and indicating the relationship between the iteration count and the distance between the antennas. This table can be, for example, the table shown in Table 1 above. When the distance between the antennas is below a certain threshold A, the repetition count control unit 130B sets the repetition count to “N2”. If the distance between the antennas is equal to or greater than the threshold A, the repetition count control unit 130 sets the repetition count to “N1” (steps S42 to S44). Note that the number of times of setting is the same as that in the first embodiment, and a description thereof will be omitted. Next, in step S45, the receiving unit 110 receives data. Thereafter, the repeat count control unit 130B decreases the repeat count according to the previous number of retransmission requests stored in the storage unit 150B (step S46). In HARQ, previously received data stored in the buffer 172 and newly retransmitted data are combined by the packet combining unit 170. Therefore, if the number of retransmissions increases, the quality of data transmitted to the iterative decoder 120 is improved by increasing the absolute amount of data. In this embodiment, the number of repetitions of decoding increases as the number of retransmissions increases. Decrease. Thereafter, in step S47, the iterative decoder 120 repeats decoding for the set number of times. The CRC detection unit 174 detects a CRC (Cyclic Redundancy Check) code of the data processed by the iterative decoder 120 and determines whether there is an error (step S48). If an error is detected, a retransmission request is transmitted by the retransmission request generation unit 176, and the process returns to step S41. If no error is detected, the process ends.

  The advantages of the present invention will be described again. As described above, according to the wireless communication terminal according to the present invention, unlike the conventional technique in which decoding is performed unnecessarily in advance when the reception quality is good and the decoding characteristics converge quickly, the advantage of the diversity method is When the reception quality is good with little correlation between antennas, the number of decoding iterations is reduced, so that the time and power consumption required for the decoding process can be reduced compared to the conventional case. Even when the distance between the antennas is short and reception is performed with substantially one antenna, the number of decoding iterations can be reduced according to the reception quality.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each component, each means, etc. can be rearranged so as not to be logically contradictory, and a plurality of components can be combined into one or divided. For example, the number of repetitions N1 to N4 shown in the table in each embodiment may be different in each embodiment. In the second embodiment, the reception quality thresholds are two, C and D, but further thresholds may be provided. In addition, the wireless communication terminal is not limited to the foldable type shown in FIG. 1, and the present invention can be applied to any wireless communication terminal that includes a plurality of antennas and whose relative distance changes between the antennas. . In the above-described embodiments, the turbo code is used. However, the present invention is not limited to this, and can be applied to an error correction system that performs iterative decoding such as LDPC.

1 is a schematic diagram of a wireless communication terminal according to an embodiment of the present invention. 1 is a schematic block diagram of a wireless communication terminal according to a first embodiment of the present invention. It is a flowchart which shows an example of the process of the radio | wireless communication terminal 100 by 1st Example of this invention. It is a block diagram of the radio | wireless communication terminal by the 2nd Example of this invention. It is a flowchart which shows an example of a process of 100 A of radio | wireless communication terminals by 2nd Example of this invention. It is a block diagram of the radio | wireless communication terminal by the 3rd Example of this invention. It is a flowchart which shows an example of a process of the radio | wireless communication terminal 100B by 3rd Example of this invention. It is a schematic block diagram of the radio | wireless communication terminal which performs control of the repetition decoding frequency by a prior art.

Explanation of symbols

100, 100A, 100B Wireless communication terminal 110 Receiving unit 120 Iterative decoder 130, 130A, 130B Iteration number control unit 140 Inter-antenna distance detection unit 150, 150A, 150B Storage unit 160 Channel quality calculation unit 170 Packet synthesis unit 172 Buffer 174 CRC Detection unit 176 Retransmission request generation unit ANT1 to ANT3 Antenna 200 Wireless communication terminal 210 Reception unit 220 Iterative decoder 230 Channel quality calculation unit 240 Number of repetitions calculation unit

Claims (4)

In a wireless communication terminal capable of diversity reception having a plurality of antennas with variable relative distances,
A decoder that repeatedly decodes a received signal including an error correction code received by the plurality of antennas;
An inter-antenna distance detector for detecting a distance between the plurality of antennas;
When the detected distance between the antennas exceeds a predetermined value, a control unit that controls to reduce the number of repetitions of the decoding compared to when the distance between the antennas is less than a predetermined value ;
A wireless communication terminal comprising: The wireless communication terminal according to claim 1 ,
A channel quality calculation unit that calculates communication channel quality from received signals received by the plurality of antennas;
The controller is
When the communication channel quality calculated by the channel quality calculation unit exceeds a predetermined value when the distance between the antennas is lower than a predetermined value, the decoding channel is compared with a case where the quality of the communication channel is lower than a predetermined value . Reduce the number of repetitions ,
A wireless communication terminal characterized by the above. In the wireless communication terminal according to claim 1 or 2 ,
A determination unit for determining whether or not there is an error in the data decoded by the decoding unit;
A retransmission request unit that requests retransmission of data based on a determination result by the determination unit;
The controller is
The reduced number of iterations of the decoding in the decoder the greater the number of retransmission requests of the retransmission request unit,
A wireless communication terminal characterized by the above. In a communication control method of a wireless communication terminal capable of diversity reception including a plurality of antennas with variable relative distances,
Repeatedly decoding a received signal including an error correction code received by the plurality of antennas with a decoder;
Detecting a distance between the plurality of antennas;
When the distance between the antennas detected in the detecting step exceeds a predetermined value, the step of controlling to reduce the number of repetitions of decoding compared to the case where the distance between the antennas is lower than a predetermined value ;
The communication control method characterized by including.

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