JP2008160237A - Wireless device and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless terminal or the like for efficiently transmitting an Ack signal. <P>SOLUTION: The wireless terminal 100 comprises an antenna 1 for receiving a wireless signal from a wireless base station 200, a transmission/reception switching part 2 for switching transmission/reception, an RF part 3 for converting the wireless signal into a prescribed frequency, and a base band part 4 for starting the transmission of an Ack signal of the wireless signal at timing that at least SIFS time has elapsed, and stopping the transmission of the Ack signal when an error is detected as a result of detecting an error in the wireless signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless device that transmits an Ack (Acknowledgment) signal when wireless signal communication is successful.

In recent years, wireless LANs based on the IEEE 802.11 standard have been increasingly used. Under this standard, for example, when wireless communication is successful between the receiving side and transmitting side terminals, the receiving side terminal is at the timing when SIFS (Short Interframe Space) time (16 μsec) has elapsed since the completion of reception. , Ack (acknowledgment response) signals are returned.
The IEEE 802.11n of the high-speed wireless LAN standard employs a MIMO (Multiple-Input Multiple-Output) transmission technology that simultaneously transmits and receives a plurality of transmission streams using a plurality of transmission and reception antennas. In this MIMO transmission technique, the received signal is repeatedly decoded (iterative decoding) in order to improve reception quality.

Under such circumstances, conventionally, the number of iterative decoding has been selected to improve reception quality (see, for example, Non-Patent Document 1).
Conventionally, when an FCS (Frame Check Sequence) is included in a radio signal, there has been a method in which iterative decoding is first completed and then an error due to FCS is detected. In this method, an Ack signal is transmitted when the SIFS time has elapsed. When an error is detected, the destination address of the Ack signal is changed to avoid returning the Ack signal (for example, Non-Patent Document 2).

"Characteristics of error correction coding MIMO-OFDM using parallel interference canceller", Shibahara, Nishimura, Ogane, Ogawa, IEICE RCS2004-81, IEICE "A Modified Medium Access Control Algorithm for Systems with Iterative Decoding", Inkyu Lee et al., IEEE Trans. On Wireless Communications, vol.5, no.2, Feb. 2006

However, in the method of Non-Patent Document 1, depending on the number of iterations, there is a possibility that the transmission of the Ack signal will be after the SIFS time has elapsed.
In the method of Non-Patent Document 2, although the Ack signal is transmitted when the SIFS time has elapsed, it is necessary to change the destination address of the Ack signal when an error is detected. This is because it is determined that the transmission of the Ack signal is successful unless the destination address of the Ack signal is changed. Here, the successful transmission of the Ack signal indicates that it has been determined that an already transmitted packet corresponding to the Ack signal has been received without error. For this reason, although the packet is originally retransmitted from the station corresponding to the destination address, the packet is not retransmitted.
Therefore, the present invention has been made under such circumstances, and an object of the present invention is to return an Ack signal with compatibility with the conventional communication standard and realize high-throughput communication.

  According to the present invention, it is possible to realize communication with high throughput by returning an Ack signal with compatibility with a communication standard.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, about the same part, it demonstrates using the same code | symbol (term).
First, a general Ack signal transmission procedure between the radio base station and the radio terminal will be described.
FIG. 1 is a time chart showing a general Ack signal transmission procedure. Here, description will be made on the assumption that the radio base station in FIG. 1A transmits a radio signal (packet) including data and FCS.
In this case, for example, according to FIG. 1 (b), the Ack signal d1 is the time when SIFS time (16 μsec: this is also referred to as a specified time) has elapsed from the time when reception of the radio signal is completed (at the start of transmission on the specified) The transmission has started. This is a case where the wireless terminal performs iterative decoding and does not detect an error due to FCS (when no error is detected).

  The Ack signal d1 is composed of a preamble part d11 and a data part d12. The preamble part d11 includes STS (Short Training Symbol) and LTS (Long Training Symbol). The data part d12 includes a SIGNAL, a MAC header, and an FCS.

  On the other hand, according to FIG. 1C, the transmission of the Ack signal d1 is started with a margin (about several μsec) secured from the completion of reception of the radio signal. This is a case where the wireless terminal does not perform iterative decoding (at the time of the first decoding).

Also, according to FIG. 1 (d), iterative decoding is completed after elapse of SIFS time. This is a case where the wireless terminal executes iterative decoding a plurality of times (when iterative decoding is performed).
However, in the case of FIG. 1 (d), the Ack signal d1 is transmitted after SIFS time (after the start of regular transmission), which is inconvenient.
Therefore, in the first embodiment of the present invention, the Ack signal d1 is transmitted according to the procedure shown in FIG.

FIG. 2 is a time chart showing an Ack signal transmission procedure according to the first embodiment of the present invention.
The radio base station in FIG. 2A transmits a radio signal including data and FCS.
Upon receiving this transmission, the wireless terminal that has received this wireless signal uniformly transmits the preamble part d11 of the Ack signal when the SIFS time has elapsed, as shown in FIG. 2 (b). When the wireless terminal detects an error due to FCS, the transmission of the data part d12 is stopped at that time. Thereby, even if the radio base station receives the preamble part d11, the data part d12 is not received, and the radio base station retransmits the radio signal to the radio terminal.

  When the wireless terminal does not detect an error due to FCS, the data part d12 is transmitted following the preamble part d11. In this case, the wireless terminal can transmit an Ack signal when the SIFS time has elapsed.

Next, the configuration of the wireless terminal in FIG. 2 will be described.
FIG. 3 is a diagram illustrating a configuration example of the wireless terminal 100 according to Embodiment 1 of the present invention.
In FIG. 3, the radio terminal 100 includes an antenna (reception unit) 1 that transmits and receives signals to and from the radio base station 200, a transmission / reception switching unit 2, an RF unit 3, a baseband unit 4, and a MAC unit 5. The signal processing unit 6 is included.
The transmission / reception unit 2 switches to the transmission or reception mode. For example, in the reception mode, each unit of the wireless terminal 100 functions as follows. The RF unit 3 converts the radio signal into a baseband frequency band, converts the radio signal into a digital signal, and outputs the digital signal to the baseband unit 4. Then, the baseband unit 4 decodes the converted digital signal and outputs it to the MAC unit 5. The MAC unit 5 extracts a predetermined signal from the decoded digital signal and outputs it to the signal processing unit 6. Thereby, the signal processing unit 6 performs a predetermined process based on the predetermined signal. The signal processing unit 6 is a processing device such as a CPU or a microcomputer.

  On the other hand, in the transmission mode, each unit of the wireless terminal 100 functions as follows. The MAC unit 5 converts the signal (data) output from the signal processing unit 6 into a predetermined signal and outputs the signal to the baseband unit 4. The baseband unit 4 converts the converted signal into an analog signal and outputs the analog signal to the RF unit 3. The RF unit 3 converts an analog signal into a radio signal in a radio frequency band, and outputs it to the antenna 1 via the transmission / reception switching unit 2. Thereby, a radio signal is radiated into the air through the antenna 1. The wireless terminal 100 is a computer such as a mobile phone or a notebook computer.

Next, characteristic functions of the wireless terminal 100 will be described.
The MAC unit (specified time counting unit) 5 counts the time length of the SIFS length (16 μsec: see FIG. 2A). Specifically, the MAC unit 5 counts the time length from when the reception of the radio signal output from the radio base station 200 is completed. In the first embodiment, the time when reception is completed refers to a time when a received packet is no longer observed by the receiving antenna 1. As a method of detecting the reception completion time, a method of counting the packet time length after detecting a synchronization signal for starting reception can be considered. The packet time length is described at the beginning of the packet.
Further, the MAC unit (specified time counting unit) 5 determines whether or not the count number from the completion of reception matches the SIFS length. Note that the value of the SIFS length is held in, for example, the internal memory of the MAC unit 5.

  The baseband unit (transmission start unit) 4 starts transmission of the Ack signal for the radio signal at the timing when the SIFS time has elapsed at the latest after the completion of reception of the radio signal (when transmission starts in FIG. 2A). To do. Further, the baseband unit (error detection unit) 4 detects whether or not there is an error in the received signal. The baseband unit (transmission stop unit) 4 stops transmission of the Ack signal when the error is detected.

Next, the operation of the wireless terminal 100 will be described with reference to FIG. 4 and FIG.
FIG. 4 is a flowchart showing the overall operation of the wireless terminal 100.
First, in step S11, a packet including a FCS (radio signal: see FIG. 2A) is received from the radio base station 200. Specifically, the packet is received through the antenna 1 of the wireless terminal 100, and the baseband unit 4 receives the packet via the transmission / reception switching unit 2 and the RF unit 3.
Subsequently, the baseband unit 4 starts decoding the received packet (step S12). Thereby, the decoding process of FIG. 5 mentioned later is performed.

  Next, in step S13, the MAC unit 5 counts the SIFS length time length (16 μsec: see FIG. 2B). Specifically, when the baseband unit 4 receives a packet, the MAC unit 5 inputs a signal to that effect from the baseband unit 4. Then, the MAC unit 5 counts the time length from when the packet reception is completed (see FIG. 2B).

  Further, the MAC unit (specified time counting unit) 5 determines whether or not the count number matches the SIFS length (step S14). That is, the MAC unit 5 determines whether SIFS time has elapsed. As a result of the determination, if they do not match (No in step S14), the process returns to step S13, and the MAC unit 5 continues to count the time length of the SIFS length.

  On the other hand, if the result of the determination is a match (Yes in step S14), the baseband unit 4 proceeds to step S15 and starts transmitting the preamble portion d11 of the Ack signal (see FIG. 2B). As a result, the preamble part d11 is transmitted when the SIFS time has elapsed.

Thereafter, the baseband unit 4 starts transmission of the data part d12 of the Ack signal (see FIG. 2B).
Then, the baseband unit 4 determines whether or not an error has been detected in the error detection after the start of decoding in step S12 (FIG. 5 described later) (step S17). As a result of this determination, if no error is detected (No in step S17), the baseband unit 4 continues to transmit the data part d12 (step S18). Thereby, the Ack signal including the data part d12 and the preamble part d11 is radiated into the air through the antenna 1. Therefore, the radio base station 200 receives the Ack signal.

  On the other hand, if an error is detected in the error detection in step S17 (Yes in step S17), the baseband unit 4 stops transmission of the data unit d12 (step S19), and ends the process. As a result, the radio base station 200 cannot receive the data part d12 of the Ack signal d1, and retransmits the packet to the radio terminal 100.

  Note that the timing for stopping transmission is not limited to the data part d12, and even if the transmission is stopped instantaneously at the timing when an error is detected, the radio channel is not occupied excessively even in the middle of the preamble part d11. Furthermore, since the radio base station 200 can also cancel the reception state early, it is possible to shift to preparation for the next state early, which is preferable.

  Moreover, although FIG. 4 demonstrated step S17 as a step following step S16, you may insert between step S15 and step S16, for example. In this case, the baseband unit 4 starts transmitting the Ack signal preamble part d11 (step S15), and then determines whether an error is detected (step S17). If an error is detected as a result of this determination (Yes in step S17), the process proceeds to step S19, and the baseband unit 4 stops transmission of the data unit d12. On the other hand, if no error is detected (No in step S17), the process proceeds to step S16, and the baseband unit 4 stops the transmission of the data part d12 and proceeds to step S18.

FIG. 5 is a flowchart showing details of the decoding start process in step S12 of FIG.
When step S12 starts, in step S121, the MAC unit 5 first decodes and analyzes the MAC header of the received packet.

  Subsequently, the baseband unit 4 decodes the packet data (step S122) and counts the number of bits of the decoded data (step S123). Then, the baseband unit 4 determines whether or not the count number matches the packet length of the packet (step S124). That is, the baseband unit 4 determines whether or not bits for the designated packet length have been decoded.

  If the result of the determination is that they do not match (No in step S123), the process returns to step S122, and the baseband unit 4 decodes the data. On the other hand, if they match (Yes in step S123), the baseband unit 4 performs error detection based on the FCS of the packet (see FIG. 2A) (step S125). Thereby, it progresses to step S17 (refer FIG. 4) after that, and the baseband part 4 will judge whether the error was detected.

As described above, according to the present embodiment, the burst band unit 4 starts transmitting the Ack signal d11 at the timing when the SIFS time has elapsed from the completion of packet reception (see FIG. 2A).
Further, when an error due to FCS is detected, the baseband unit 4 stops transmission of the preamble part d11 or the data part d12 of the Ack signal.

Here, by stopping the transmission of the Ack signal in the middle, data cannot be accurately demodulated on the receiving side, and the transmission of the Ack signal becomes unsuccessful. On the receiving side, when the Ack signal is not received, the packet is automatically retransmitted. As a result, the packet is retransmitted.
Thereby, when an error is detected, transmission of the Ack signal d11 is stopped without changing the destination address of the Ack signal. Therefore, the transmission stop of the Ack signal d11 is easily performed. Therefore, it is possible to efficiently transmit the Ack signal d11.

From the above, it is possible to reduce the probability of error occurrence by iterative iterative decoding, and to return the Ack signal within SIFS (predetermined time) defined in the IEEE 802.11 standard. Therefore, compatibility with the IEEE 802.11 standard is maintained.
Further, since transmission is stopped at the timing when an error is detected, a useless wireless channel is not occupied, and communication with high throughput can be realized.
Furthermore, since the wireless terminal can be realized by a relatively simple procedure (see FIGS. 4 and 5), the wireless terminal can be realized with a small and low power consumption circuit.

(Embodiment 2)
In the second embodiment, unlike the case of the first embodiment, it is assumed that there are a plurality of wireless terminals 100 (for example, two) and these wireless terminals 100 use the same wireless channel. explain. Each wireless terminal receives a spatially multiplexed signal according to the MIMO transmission scheme. Each wireless terminal 100 adopts an autonomous distributed access control method, for example, DCF (Distribute Coordination Function).
In this case, when two wireless terminals are close to each other, a certain wireless terminal 100 (hereinafter also referred to as wireless terminal 100A) transmits another preamble 100 (hereinafter referred to as wireless terminal 100A) by transmitting a preamble part d11 of the Ack signal. Wireless terminal 100B) receives the preamble part d11. For this reason, the radio terminal 100B determines that the radio channel is busy and refrains from transmitting a predetermined radio signal (packet).
Therefore, in the second embodiment, the total throughput of the radio channel is improved to facilitate data transmission of radio terminals existing on the same radio network.

FIG. 6 is a diagram illustrating a configuration example inside the baseband unit 4 of the wireless terminal 100 according to the second embodiment.
In FIG. 6, the baseband unit 4 includes a carrier sense unit 400, a preamble detection unit 401, a synchronization unit 402, a channel estimation unit 403, a determination unit 404, and an iterative decoding unit 405. Furthermore, the baseband unit 4 includes an S / N estimation unit 406, a throughput estimation unit 407, a usage state estimation unit 408, a first switching unit (comparison unit) 409, an error detection unit 410, and a second switching unit (transmission start unit). Part, transmission stop part) 411.
The carrier sense unit 400 performs carrier sense (comparison with the threshold level) of the signal from the RF unit 3 (including the Ack signal transmitted from the wireless terminal 100A). The comparison here is for confirming whether the radio channel is occupied or not.
Then, from the time when the other wireless terminal 100B completes transmission of a signal (data packet or the like) addressed to the wireless terminal 100A, a back-off time (based on a random value is used) in DIFS (Distributed Coordination Function Interframe Space) time (= 34 μsec). If the carrier sense result is below the threshold level when the time of adding the random time) has elapsed, the radio terminal 100 can start transmission.

The preamble detection unit 401 detects a preamble part (for example, one transmitted from the radio terminal 100A) for the signal from the RF unit 3.
The synchronization unit 402 performs frequency and time based on an output from the preamble detection unit 401 (a detection signal indicating that the preamble unit has been detected) and a signal from the RF unit 3 (for example, a signal transmitted from the wireless terminal 100A). Establish synchronization.
The channel estimation unit 403 estimates a radio channel based on the output (established frequency / time) of the synchronization unit 402. Channel estimation section 403 estimates channel characteristics from preamble section d11. Channel estimation section 403 then outputs the estimated value of the radio channel characteristic to each of determination sections 404, 4052a, 4052b, and 4052c.
The determination unit 404 determines decoding of the signal from the RF unit 3 based on the output of the synchronization unit 402 (frequency synchronization and time synchronization is established) and the output of the channel estimation unit 403.

The iterative decoding unit 405 repeatedly performs iterative decoding a preset number of times. In the present embodiment, the number of times is set to three times, for example, but may be changed.
In the present embodiment, the iterative decoding unit 405 includes an initial stage iterative decoding unit 405a, a middle stage iterative decoding unit 405b, and a final stage iterative decoding unit 405c.

The first-stage iterative decoding unit 405a includes a first-stage cancellation unit 4051a and a first-stage determination unit 4052a.
The cancel unit 4051a remodulates the signal output from the RF unit 3 through the determination unit 404, and extracts the other stream multiplexed in space by the MIMO transmission method, so that the signal before MIMO separation is extracted. The re-modulated replica signal is subtracted from this (this operation is called cancel operation).

  By executing this cancel operation for each stream, it is possible to extract multiplexed signals. It is preferable that diversity cancellation by receiving a plurality of antennas can be obtained by performing this cancellation on received signals from a plurality of antennas and combining the signals after cancellation with a maximum ratio.

  The first determination unit 4052a determines the output of the cancellation unit 4051a and decodes the binary digital signal. Each of the other iterative decoding units 405b and 405c also performs decoding determination on the target stream in the same manner as the first stage iterative decoding unit 405a.

  In addition, although the iterative decoding unit 405 of FIG. 6 has been illustrated for the cascade connection type, it may be configured as a recursive operation type.

  The S / N estimation unit 406 estimates the S / N ratio based on the output (modulation signal) of the cancellation unit 4052c at the final stage.

  The throughput estimation unit 407 estimates the throughput of the same wireless channel as the signal from the RF unit 3. At this time, the throughput estimation unit 407 uses the same wireless communication based on the estimated S / N ratio, the output (packet length) of the determination unit 404, and the output (usage status of a radio channel described later) of the usage status estimation unit 408. Estimate channel throughput.

Specifically, the throughput estimation unit 407 estimates the throughput using various tables stored therein. The S / N ratio table holds the S / N ratio and the estimated throughput value in association with each other in advance. The packet length table holds the packet length and the estimated throughput value in association with each other in advance. The usage status table holds the usage status of the radio channel and the estimated value of the throughput in association with each other in advance.
Then, the throughput estimation unit 407 reads throughput estimation values corresponding to the respective values from various tables. In the present embodiment, for example, the throughput estimation unit 407 specifies the lowest estimated value of the read throughput estimated values and outputs the lowest estimated value to the first switching unit 409. In the present embodiment, the lowest value among the estimated values of a plurality of throughputs is employed, but an average value thereof may be employed.

  Based on the output of carrier sense unit 400 (detected value of carrier sense), the output of preamble detector 401 (contents of the preamble part), and the output of MAC unit 5 (destination address), usage status estimating unit 408 The channel occupation state (for example, channel occupation rate) of the channel (for example, two wireless terminals 100A and 100B) is estimated. At this time, the usage status estimation unit 408 calculates the channel occupation status for each destination address (wireless terminal 100A or wireless terminal 100B), for example. In addition, the usage state estimation unit 408 calculates the busy time of the radio channel from the detected value of the carrier sense for each destination address.

  In this embodiment, the throughput estimation unit 407 estimates the estimated value of the throughput based on three types of information, that is, the S / N ratio, the packet length, and the usage status of the radio channel. The combination of types of information may be changed (for example, one type or two types may be used).

The first switching unit (comparison unit) 409 compares the throughput estimated by the throughput estimation unit 407 with a preset threshold value (allowable value) when the SIFS time has elapsed. The threshold is the throughput of the system including the wireless terminals 100A and 100B in communication when the terminal (wireless terminal 100B) transmits the preamble part of the Ack signal without waiting for the final iterative decoding result. The value does not decrease, and is held inside the first switching unit 409.
As a result of the comparison, if it is equal to or less than the threshold value, the first switching unit 409 starts the Ack signal to the second switching unit (transmission start unit) 411 described later at the timing when the specified time has elapsed at the latest. Let At this time, the first switching unit 409 outputs the determination result of the final determination unit 4052c to the subsequent error detection unit 410.

  On the other hand, when the value is larger than the threshold value, the first switching unit 409 outputs the determination result of the iterative decoding unit 405b in the middle stage to the error detecting unit 410 in the subsequent stage.

In this case, it is assumed that the iterative decoding unit 405b in the middle stage obtains a decoding result within the SIFS time. For example, if an error occurs in the final stage iterative decoding unit 405c under the condition that the estimated throughput is larger than the threshold value, a preamble signal of an Ack signal that does not need to be output is transmitted. Thus, although temporarily, the radio channel is occupied, the throughput of the system is reduced.
For this reason, the first switching unit 409 determines whether or not to send the Ack signal based on the iterative decoding result that can be processed within the SIFS time without waiting for the decoding result of the final stage iterative decoding unit 405c. to decide.

When the estimated throughput is equal to or less than the threshold value, the second switching unit (transmission start unit) 411 uses the error detection unit 410 when the decoding of the final iterative decoding unit 405c is completed (at the time of completion). If no error is detected, the Ack signal is transmitted as it is. On the other hand, when an error is detected by the error detection unit 410, the second switching unit (transmission stop unit) 411 immediately stops transmission of the Ack signal. As a result of such interruption processing, the packet is automatically retransmitted from the radio base station 200 side.
On the other hand, when the estimated throughput is larger than the threshold value, the second switching unit (transmission start unit) 411 generates an error in the error detection unit 410 based on the error detection result of the middle stage iterative decoding unit 405b. If not, an Ack signal is transmitted. On the other hand, if there is an error in the error detection unit 410, the second switching unit (transmission stop unit) 411 controls not to transmit anything. By such control, as a result, the packet is automatically retransmitted from the radio base station 200 side.

In this way, by limiting the number of times of iterative decoding in consideration of the channel usage situation, adjustment is made so that the frequency of outputting an originally unnecessary Ack signal is reduced.
When the transmission / reception switching unit 2 changes to the transmission mode, the Ack signal is transmitted to the radio base station 200.

Next, the operation of radio terminal 100B in Embodiment 2 will be described with reference to FIG.
FIG. 7 is a flowchart showing the operation of the wireless terminal 100B. Here, when the SIFS time (see FIG. 2B) has elapsed (when processing can be performed within the SIFS time), the final decoding result in the final stage determination unit 4052c is output according to the estimated throughput value. A case will be described in which transmission of the Ack signal is started before or transmission of the Ack signal is controlled based on the decoding result in the determination unit 4052b in the middle stage.
First, in step S21, the determination unit 404 (baseband unit) receives the packet from the RF unit 3 (including the Ack signal of only the preamble part), and proceeds to step S22. With this reception, the MAC unit 5 counts the SIFS length (see steps S13 and S14 in FIG. 4).

In step S22, the usage status estimation unit 408 (baseband unit) outputs the carrier sense unit 400 output (carrier sense detection value), preamble detection unit 401 output (preamble unit contents), and MAC unit 5 output (destination). Based on the address), the channel usage status of the same wireless channel (for example, two wireless terminals 100A and 100B) is estimated and output to the throughput estimated value 407, and the process proceeds to step S23.
In step S23, the determination unit 404 (baseband unit) detects the packet length of the received packet and outputs the packet length to the throughput estimation unit 407.

Next, the S / N estimation unit 406 (baseband unit) estimates the S / N ratio based on the output (cancellation output) of the cancellation unit 4051c (step S24), and proceeds to step S25.
In step S25, the throughput estimation unit 407 (baseband unit) determines the RF unit based on the channel usage state estimated in step S22, the packet length detected in step S23, and the estimated throughput value estimated in step S25. The throughput of the same radio channel as the signal from 3 (radio signal) is estimated. Then, the throughput estimation unit 407 outputs the estimated value to the first switching unit 409. This estimation is performed using various tables as described above.

Furthermore, the first switching unit 409 (baseband unit) compares the estimated value of the throughput from the throughput estimation unit 407 with a preset threshold value when the SIFS time has elapsed at the latest (step S26).
If the result of this comparison is below the threshold value (Yes in step S27), the second switching unit 411 starts transmission of the preamble portion of the Ack signal.

Thereafter, the error detection unit 410 determines whether there is an error in the final stage output, that is, the output of the final stage determination unit 4052c (step S29). If there is an error (Yes in step S29), the second switching unit 411 immediately stops the packet transmission and shifts to an idle state (step S34).
If there is no error in the error detection unit 410 (No in step S29), the second switching unit 411 continues transmission after the data portion of the Ack signal (step S31). Then, when the transmission is completed, the state shifts to the idle state (step S34).

On the other hand, if it is larger than the threshold value (No in step S27), error detection section 410 has an error in the output of middle stage output that can be completed until error detection within SIFS time, that is, the output of middle stage determination section 4052b. It is determined whether or not there is (step S32). If there is an error (Yes in step S32), the second switching unit 411 must not output the Ack signal, and thus shifts to the idle state (step S34) as it is. As a result, the packet is retransmitted from the base station side.
If there is no error (No in step S32), the second switching unit 411 transmits an Ack signal at the SIFS time (step S33).

  As described above, according to the present embodiment, when the SIFS time has elapsed (when the Ack signal can be transmitted within the SIFS time), the burst band unit 4 outputs the final stage according to the estimated value of the throughput. Switch to either error detection based on, or error detection based on middle stage output. Thereby, it is possible to control the timing of error detection in consideration of the throughput. Therefore, when an error occurs even if iterative decoding is repeated, it is possible to adaptively control whether or not to transmit the preamble part of the Ack signal that occupies an extra channel as a result. Therefore, the channel throughput does not decrease.

(Embodiment 3)
In Embodiment 3, the baseband unit performs error detection for each number of iteration decoding stages. When the baseband unit no longer detects an error for the first time, the baseband unit bypasses the subsequent iterative decoding result to the MAC unit. This will be described in detail below.
FIG. 8 is a diagram illustrating a configuration example inside the baseband unit 4 of the wireless terminal 100 according to the third embodiment.
The baseband unit 4 of FIG. 8 has four error detection units 410a, 410b, 410c, and 410d, unlike the case of the second embodiment having one error detection unit (see FIG. 6). Furthermore, unlike Embodiment 2, the baseband unit 4 in FIG. 8 includes a selection unit 312 and a third switching unit 413. Since the configuration of other wireless terminals is almost the same as that of the second embodiment, description of the same parts is omitted.

The first error detection unit 410a is provided on the output side of the determination unit 404, and the second error detection unit 410b is provided on the output side of the first stage iterative decoding unit 405a. The third error detection unit 410c is provided on the output side of the middle stage iterative decoding unit 405b, and the fourth error detection unit 410d is provided on the output side of the final stage iterative decoding unit 405c.
These error detection units 410a to 410d perform error detection by inputting the decoding results from the corresponding iterative decoding units 405a to 405c or the determination unit 404.

The selection unit 412 receives detection signals indicating the presence or absence of error detection from the error detection units 410a to 410d. Then, when a detection signal indicating an error is first input, the selection unit 412 selects an iterative decoding unit corresponding to the stage and notifies the third switching unit 413 of the selection. This notification is performed using the identification information assigned to the iterative decoding unit 405.
The third switching unit 413 receives the notification from the selection unit 412 and inputs the result of iterative decoding from the iterative decoding unit subsequent to the notified iterative decoding unit. Then, the third switching unit 413 outputs the result of the iterative decoding to the MAC unit 5. As a result, iterative decoding is terminated when there is no error.

(Embodiment 4)
In Embodiment 4, when transmitting a preamble part, a baseband part is transmitted by reducing its transmission power. This will be described in detail below.
FIG. 9 is a diagram illustrating a configuration example inside the baseband unit 4 of the wireless terminal 100 according to the fourth embodiment.
The baseband unit 4 in FIG. 9 is different from the second embodiment in that it further includes a power switching unit 414. Since the configuration of other wireless terminals is almost the same as that of the second embodiment, description of the same parts is omitted.
The power control unit 414 controls the error detection unit 410 to reduce the transmission power when error detection is not obtained within the SIFS time and the preamble part is transmitted.

In this case, the configuration of the signal from the RF unit 3 is studied, for example, according to the IEEE 802.11n standard of FIG. The signal in FIG. 10 includes a preamble part d111, SIGNAL2 for high speed of 2 symbols, and HT-STS (1 symbol) for automatic gain control. Further, this signal includes HT-LTS for demodulating high-speed mode data and HT (High Through-put) -DATA.
The preamble part d111 includes known STS, LST, SIGNAL0, and SIGNAL1. HT-DATAd 121 indicates high-speed mode data.

In the present embodiment, when the second switching unit 411 transmits signals from STS to SIGNAL 1 in FIG. 10, the second switching unit 411 instructs the power control unit 414 to transmit at low power (power lower than normal power). . Receiving this command, the power control unit 414 sends a signal to that effect to the RF unit 3. As a result, the RF unit 3 converts the signal from STS to SIGNAL 2 in FIG. 10 into a radio signal in the radio frequency band (based on the modulation scheme defined in SIGNAL 0, 1), and transmits the signal through the transmission / reception switching unit 2 Output to antenna 1 with electric power.
On the other hand, when transmitting the signal after HT-STS of FIG. 10, the second switching unit 411 instructs the power control unit 414 to transmit with high power (normal power). Receiving this command, the power control unit 414 sends a signal to that effect to the RF unit 3. As a result, the RF unit 3 converts the signal after HT-STS in FIG. 10 into a radio signal in the radio frequency band, and outputs the radio signal to the antenna 1 through the transmission / reception switching unit 2 with normal power.

  By configuring in this way, the preamble part d111 is transmitted with low power, so that it is difficult for other wireless terminals to receive. Therefore, the throughput as the system can be improved, and the Ack signal can be transmitted efficiently.

  The present invention is not limited to the first to fourth embodiments. The hardware configuration and operation procedure of the wireless device may be changed without departing from the spirit of the present invention. For example, in step S15 of FIG. 4, the case where transmission of the preamble portion is started when the SIFS length is reached has been described, but the preamble portion may be transmitted before the SIFS length (before the specified time). In step S16 in FIG. 4, the transmission of the data portion may be started before the SIFS length.

  The wireless device of the present invention ensures compatibility with a terminal compliant with the IEEE 802.11 standard and is useful as a MIMO wireless LAN device.

The time chart which shows the transmission procedure of a general Ack signal. The time chart which shows the transmission procedure of the Ack signal in Embodiment 1 of this invention. The figure which shows the structural example of the radio | wireless terminal in Embodiment 1 of this invention. 3 is a flowchart showing an overall operation of the wireless terminal according to Embodiment 1 of the present invention. The flowchart which shows the detail of the decoding start process in step S12 of FIG. The figure which shows the structural example inside the baseband part 4 of the radio | wireless terminal in this Embodiment 2. FIG. 9 is a flowchart showing the operation of a wireless terminal in the second embodiment. The figure which shows the structural example inside the baseband part of the radio | wireless terminal 100 in Embodiment 3 of this invention. The figure which shows the structural example inside the baseband part 4 of the radio | wireless terminal 100 in Embodiment 4 of this invention. The figure which shows the structural example of the signal in Embodiment 4 of this invention.

Explanation of symbols

1 Antenna (receiver)
2 Transmission / reception switching unit 3 RF unit 4 Baseband unit 5 MAC unit 6 Signal processing unit d1 Ack signal d11 Preamble unit d12 Data unit

Claims (7)

A receiver for receiving a radio signal;
A transmission start unit that starts transmission of the Ack signal of the radio signal at the timing when the specified time has passed at the latest;
An error detector for detecting an error in the radio signal;
A transmission stop unit for stopping transmission of the Ack signal when the error is detected;
Including a wireless device. An iterative decoding unit that performs iterative decoding of the wireless signal repeatedly a preset number of times;
A throughput estimation unit that estimates the throughput of the same wireless channel as the wireless signal;
The estimated throughput is compared with a preset allowable value. If the estimated value of the throughput is equal to or smaller than the allowable value as a result of the comparison, the transmission of the Ack signal is started at the timing when the specified time has passed at the latest. A comparison unit to be started by the unit,
The wireless device according to claim 1. The throughput estimation unit estimates the throughput using at least one of the usage status of the radio channel, the packet length of the radio signal, or the S / N ratio of the radio signal.
The wireless device according to claim 2. The transmission start unit continues to transmit the Ack signal when the error is not detected;
The radio | wireless apparatus of any one of Claim 1 thru | or 3. When the radio signal is composed of a preamble part and a data part,
A power switching unit that switches the transmission power of the preamble unit to be lower than the transmission power of the data unit;
The wireless device according to claim 1. Receiving a wireless signal;
Starting transmission of the Ack signal of the radio signal at the timing when the specified time has passed at the latest,
Detecting an error in the radio signal;
If the error is detected, stopping transmission of the Ack signal;
A wireless communication method. Repeatedly performing the iterative decoding of the radio signal a preset number of times;
Estimating the throughput of the same radio channel as the radio signal;
Comparing the estimated throughput with a preset tolerance,
In the step of starting the transmission, if the estimated throughput is equal to or less than the allowable value as a result of the comparison, the Ack signal is started at the timing when the specified time has passed at the latest.
The wireless communication method according to claim 6.

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