JP2005072810A - System, device, and method for wireless communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize spatial division multiple connection of downlink for communication from an access point to a terminal station, with an access point of narrow dynamic range. <P>SOLUTION: At an analogue part, the data for learning from each station is received in time division manner, and the waveforms of different electric power and dimension are standardized into a constant dimension for reception. In a digital part, a gain value based on a difference of required SN in such modulation method as allocated to each station is multiplied with each learning data for virtual gain re-adjustment. Using the learning data after the gain re-adjustment, the weight of an adaptive array antenna is calculated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, and a wireless communication method for realizing simultaneous communication with a plurality of counterparts by applying a multiple access technique and increasing a communication capacity, and in particular, includes a plurality of antenna elements. The present invention relates to a radio communication system, a radio communication apparatus, and a radio communication method for realizing space division multiple access by adaptively performing addition weighting and synthesis by appropriately weighting each antenna element in an adaptive array antenna.

  More particularly, the present invention relates to a radio communication system and a radio communication apparatus that realize space division multiple access without requiring a large dynamic range even when receiving a desired wave and an interference wave with a large power difference. In particular, in a wireless communication system in which an access point having a plurality of antennas communicates with a plurality of terminal stations having one antenna, a downlink space for communicating from the access point to the terminal station The present invention relates to a wireless communication system, a wireless communication apparatus, and a wireless communication method for realizing division multiple access with an access point having a narrow dynamic range.

  As a system for releasing a user from a wired LAN connection, a wireless LAN has attracted attention. According to the wireless LAN, most of the wired cables can be omitted in a work space such as an office, so that a communication terminal such as a personal computer (PC) can be moved relatively easily. In recent years, the demand for wireless LAN systems has increased remarkably with the increase in speed and cost. In particular, recently, in order to establish a small-scale wireless network between a plurality of electronic devices existing around a person and perform information communication, introduction of a personal area network (PAN) has been studied.

  In recent years, the prevalence of wireless LANs has increased, and in addition to information devices such as PCs and PDAs, they are also used in portable devices such as mobile phones and digital cameras. Examples of the application include uploading image data taken with a camera-equipped mobile phone or a digital camera to a PC via a wireless LAN.

  Here, in a wireless communication environment in which a plurality of communication stations exist within one communication range, a multiple access technique for detecting which signal belongs to which user and controlling access is necessary. In particular, it is an important issue in order to expand communication capacity with less resources.

  As one of multiple access technologies, a system that realizes space division multiplexing called SDMA (Space Division Multiple Access) has been developed. For example, in an adaptive array antenna constituted by a plurality of antenna elements, reception beam forming is adaptively performed by appropriately weighting and adding and combining received signals received by the respective antenna elements (that is, By changing the directivity adaptively, simultaneous communication with a plurality of opponents can be realized and the communication capacity can be increased (for example, see Non-Patent Document 1).

  A basic adaptive array antenna configuration is realized by having an RF unit independently for each antenna, and multiplying a signal from each RF unit by a weighting factor for each antenna.

  Each weighting factor is usually realized by a digital part, and its value is calculated by a digital signal processing part. As a specific weight calculation method, a least square method (RLS (Recursive Least Squares) algorithm) or the like is representative. When the RLS algorithm is operated, learning is performed by simultaneously receiving a desired wave and an interference wave as inputs and further inputting a known desired wave signal as a teacher signal of the RLS algorithm. The adaptive array antenna after learning changes to a characteristic that receives only a desired wave and does not receive an interference wave.

  In order to realize the space division multiplexing system as described above, it is necessary to have a desired wave transmitted from a desired terminal and an interference wave transmitted from a terminal serving as another interference source at the same time and received by a base station or the like. At this time, there is a possibility that there is a large power difference between the desired wave and the interference wave. When the desired station is nearby and the interfering station is far away, the desired wave is received with a large power, and the interference wave is received with a small power because of a large propagation loss.

  However, a large dynamic range is required in order to receive large power and small power at the same time, and to process in the digital section through the RF section (analog section). For example, in the case of an AD converter, if there is a power difference of 60 dB between each interference wave and the largest desired wave, the number of bits must be sufficient to represent the difference, which is costly. Disadvantageous.

  In addition to the AD converter, a high dynamic range must be maintained in all other components related to transmission and reception. When it is desired to mount an adaptive array antenna on a consumer product such as a wireless LAN, it becomes an obstacle in terms of cost.

  Here, if the transmission power on the transmitting terminal side is adjusted and power control is performed, this dynamic range problem can be solved, but a new problem is introduced. That is, if the modulation scheme is the same, it can be solved by power control at a relatively low cost, but it cannot cope with a different modulation scheme.

  For example, when a signal having a different modulation scheme is to be subjected to space division multiple access, one is a modulation scheme that requires SN of -20 dB (for example, 16QAM1 / 2), and the other is a modulation scheme that requires SN of -10 dB ( For example, QPSK1 / 2) is assumed. At this time, if power control is performed uniformly and the received power on the access point side where the adaptive array is mounted is made uniform, only -10 dB null is required at the downlink side where -20 dB null is required. The problem that it cannot be taken up arises. In short, to perform spatial division multiple access for multiple modulation schemes, a wide dynamic range is required for devices with an adaptive array, and even if the dynamic range is reduced by power control, it is a downlink. Space division multiple access on the side fails. In addition, it is unrealistic to install a power control function in consumer products.

Nobuyoshi Kikuma, “Adaptive signal processing by array antenna” (Science Description Publishing, ISBN 4-87653-054-8)

  An object of the present invention is to perform space division multiple access in an adaptive array antenna composed of a plurality of antenna elements by appropriately weighting and adding and combining each antenna element and performing beam forming adaptively. Is to provide an excellent wireless communication system, wireless communication apparatus, and wireless communication method.

  A further object of the present invention is that even when a desired wave and an interference wave are received with a large power difference, a space division multiple access can be suitably realized without requiring a large dynamic range. A wireless communication system, a wireless communication apparatus, and a wireless communication method are provided.

  A further object of the present invention is to provide a downlink space division multiple for communicating from an access point to a terminal station in a wireless communication system in which an access point having a plurality of antennas communicates with a plurality of terminal stations having a single antenna. An object of the present invention is to provide a wireless communication system, a wireless communication apparatus, and a wireless communication method for realizing connection with an access point having a narrow dynamic range.

The present invention has been made in consideration of the above problems, and a downlink for performing communication from an access point to a station in a wireless communication environment in which an access point having an adaptive array antenna communicates with a plurality of stations. A wireless communication system for space division multiple access,
Data for learning to calculate the weight of the adaptive array from multiple stations is transmitted in time division,
The access point receives learning data from each station in a time-sharing manner, normalizes waveforms with different power and different sizes in the analog part, and then assigns them to each station in the digital part. Each learning data is multiplied by a gain value based on the difference in required SN of the modulation scheme being used, the gain is readjusted, and the weight of the adaptive array antenna is calculated using the learning data after the gain readjustment To
This is a wireless communication system.

  However, “system” here refers to a logical collection of a plurality of devices (or functional modules that realize specific functions), and each device or functional module is in a single housing. It does not matter whether or not.

  Hereinafter, an apparatus equipped with an adaptive array composed of a plurality of antenna elements is referred to as an access point, and a terminal equipped with only one antenna is referred to as a station.

  From a plurality of stations, learning data for calculating the weight of the adaptive array is transmitted in a time division manner. Access points that receive these learning data in a time-sharing manner have different power levels by performing AGC (auto gain control) separately and adjusting the gain of the LNA (low noise amplifier). Waveforms of different sizes are normalized to a certain size and received. Here, since the waveform is received by AGC with a certain size, the dynamic range of the apparatus can be small.

  Next, the digital unit multiplies the learning data received in time division by a certain value of gain and virtually adjusts the gain. For example, the gain is readjusted by multiplying the learning data by a gain value based on the required SN difference necessary for the modulation scheme assigned in each station. Here, the gain readjustment method will be briefly described.

  Now, assume that station A and station B exist, and station B is far from the access point, so that the propagation loss is large. For example, it is assumed that the signal from station A can have an SN of 20 dB, and the signal from station B can have an SN of only 10 dB.

  The small signal from this station B is expanded by AGC at the time of reception. The magnitude of the signal is similar to that from station A, but the noise is also magnified together, so the SN is still 10 dB.

  Here, it is assumed that a modulation scheme requiring a required SN of 20 dB is assigned to the data of the station A, and a modulation scheme requiring a required SN of 10 dB is assigned to the data of the station B.

  The largest required SN is set as a reference SN. Here, the reference SN is 20 dB. Since the required SN of the station B is 10 dB smaller than the reference SN, the digital unit performs gain readjustment by multiplying the learning signal received for the station B by 0.1 times so that the learning signal is reduced by 10 dB.

  Thus, the weight of the adaptive array antenna can be calculated using the learning data after gain adjustment. In other words, the access point can obtain the weight vector for each station based on the readjusted gain value, thereby realizing downlink space division multiple access to the station.

  According to the present invention, in an adaptive array antenna constituted by a plurality of antenna elements, appropriate weighting is performed on each antenna element, and addition and synthesis is performed adaptively, thereby suitably realizing space division multiple access. An excellent wireless communication system, wireless communication apparatus, and wireless communication method can be provided.

  Further, according to the present invention, even when a desired wave and an interference wave are received with a large power difference, space division multiple access can be suitably realized without requiring a large dynamic range. A wireless communication system, a wireless communication apparatus, and a wireless communication method can be provided.

  According to the present invention, in a wireless communication system in which an access point having a plurality of antennas communicates with a plurality of terminal stations having a single antenna, downlink space division multiple access for communicating from the access point to the terminal station Can be realized with a narrow dynamic range access point.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

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

  The propagation path of communication assumed in the present invention is wireless, and a network is constructed between a plurality of communication stations by access control based on space division multiple access (SDMA). Further, the communication assumed in the present invention is a storage and exchange type traffic, and information is transferred in units of packets.

  FIG. 1 schematically shows a network configuration of a wireless LAN according to an embodiment of the present invention.

  The AP has a plurality of antennas, and the STA has one antenna. This is a system that communicates with a plurality of STAs using the same frequency from the AP at the same time. Hereinafter, communication from the STA to the AP is referred to as “uplink”, and communication from the AP to the STA is referred to as “downlink”. Communication using the same frequency at the same time is called space division multiple access (SDMA). In the industry, uplink space division multiple access and downlink space division multiple access are conceivable, but the present invention aims to realize downlink space division multiple access with a narrow dynamic range AP. .

  The access point may also be connected to a wired network such as Ethernet (registered trademark) to communicate with other access points.

  FIG. 2 schematically shows a functional configuration of a wireless communication apparatus that operates as an access point in the wireless network according to the present invention.

  The access point AP includes an analog unit including a plurality of antennas and a plurality of RF units. The analog part includes AGC and LNA. The digital unit also has a plurality of AD converters and DA converters. Signal processing is performed in the digital section. Although not shown, each station is configured as a normal terminal having one antenna.

  In the wireless network system according to the present invention, transmission control using a plurality of channels effectively is performed by a transmission (MAC) frame having a gradual time division multiple access structure, and each communication station is provided with a CSMA (Carrier). Information can also be directly and asynchronously transmitted in accordance with an access procedure based on Sense Multiple Access (carrier detection multiple access).

  In the case of the latter access procedure, at this time, the RTS / CTS method can be adopted as means for avoiding collision and improving communication quality.

  In this case, prior to transmission of the net information, the transmission source communication station transmits RTS (Request to Send), and if the reception destination communication station can receive the RTS and receive data, the response As CTS (Clear to Send). Then, data transmission is executed after a connection is established between the transmitting and receiving stations by exchanging RTS / CTS information.

  The peripheral station that has received either the RTS signal or the CTS signal refrains from data transmission processing during the data transmission period described in these packets. Therefore, the communication station that becomes a hidden terminal from the transmission side or the reception side avoids the data transmission collision by receiving either the RTS signal or the CTS signal, and thus the hidden terminal problem can be solved. In the following, an embodiment will be described in which data is transmitted by the RTS / CTS method in a space division multiple access wireless network.

  A data transmission / reception procedure in the wireless network according to the present invention will be described with reference to FIG.

  In the figure, an access point AP is a master station that mainly transmits a large amount of data, for example, a communication station such as a video server that performs streaming transmission of moving image data. On the other hand, the other communication stations STA1, STA2, and STA3 are slave stations that mainly receive data, and correspond to a content reproduction device such as a television / monitor that reproduces content such as moving image data received from the master station. Station. Here, consider a case where the access point AP transmits different data simultaneously to each of the slave stations STA1, STA2, and STA3.

  First, the access point AP transmits an RTS packet dedicated to spatial multiplexing transmission (SMT). This STS-dedicated RTS packet includes the addresses of the target slave stations (STA1, STA2, and STA3 in the illustrated example). The slave station that has received the RTS packet returns the CTS packet in a time division manner according to the address order described in the RTS packet.

  The CTS returned by each slave station in a time division manner is transmitted in a time division manner with an interval corresponding to the MIFS (Momentary IFS) time. The time interval is set to this value to ensure that the access point AP can receive these CTSs.

  When the access point AP receives these CTSs in a time division manner, the access point AP calculates a weight vector for space division multiple access of each slave station, sets the optimum transmission beam pattern for each, and sets the net data Send the frame (SMT).

  When each slave station receives a data frame from the access point AP, each slave station returns an ACK in the same manner as when returning a CTS packet.

  A Duration field is prepared in the MAC field of each RTS packet, CTS packet, data packet, and ACK packet or the header of the PHY frame, and the NAV is set based on this value.

  In the example shown in FIG. 2, in the RTS, the time between the end of transmission of the RTS and all the CTSs is set as the NAV.

  For CTS, the time until CTS, the subsequent data frame and all ACKs are transmitted is set as NAV. Therefore, the time when the set time of the NAV specified by the CTS ends is the same time in each of the slave stations STA1, STA2, and STA3.

  In the data frame, the time until all subsequent ACKs are transmitted is set as the NAV.

  In ACK (+ CTS), as in the case of CTS, the time until the subsequent data frame and all ACKs are completely transmitted is set. Therefore, the set value of the NAV designated by this ACK is the same time in each of the slave stations STA1, STA2, and STA3.

  The access point is adjusted so that a plurality of CTSs received from each station in a time division manner can be received at a constant size by adaptively setting the LNA gain of the analog unit.

  When receiving a plurality of CTSs in time division, the access point acquires a transfer function (also referred to as “direction vector”) for each station from the data received in these time divisions. The gain of each transfer function is adjusted again in the digital section.

  The required SN is determined for each station based on the assigned modulation scheme. In this specification, the station having the largest required SN among the stations capable of receiving the CTS is defined as a “reference SN”. Then, the difference between the reference SN and the required SN of the target CTS is obtained, and if the value is X dB, the digital unit adjusts the size of the CTS to be reduced by X dB. The weight of the adaptive array is obtained using this adjusted transfer function.

  One method of deriving weights from time-divided learning data is to obtain a transfer function from the learning data and use the transfer function to calculate the inverse matrix and directly calculate the array antenna weights. The method to ask is mentioned. This is an algorithm used in a system in which arrival direction estimation such as MUSIC is performed, and when a direction is detected, the direction vector (transfer function) is used to derive a weight, and “solution based on maximum likelihood method” is being called.

  The access point transmits a downlink data frame (DATA) using the obtained weight while performing space division multiple access. From each station side, an ACK is returned for checking that the data has been successfully received. This ACK is also returned in a time-sharing manner. The ACK is used to calculate the weight of the adaptive array antenna, similar to the CTS, and the weight acquired at the time of receiving the ACK is used at the access point when transmitting the next data.

  FIG. 4 shows signals from the stations STA1 to STA3 received by the access point in a time division manner. Since the noise component is determined by the characteristics of the RF section of the receiver, it is common to each station. In the illustrated example, each station is assigned a different modulation scheme, and the required SN is 30 dB for STA1, 20 dB for STA2, and 10 dB for STA3. The received signal level from each station is -60 dBm for STA1, -70 dBm for STA2, and -80 dBm for STA3. Each of the noise components based on the apparatus noise includes -90 dBm.

  In FIG. 5, the AGC (automatic gain control) is uniformly applied to the signals received from the stations shown in FIG. 4, and the LNA gain is adjusted so that the signals can be received as waveforms having substantially the same magnitude. This shows the state of the signal and noise when received. As shown in the figure, the received signal level from each station is uniformly normalized to 0 dB.

  FIG. 6 shows a signal obtained by adjusting the gain of the signal whose gain has been adjusted as shown in FIG.

  In the gain readjustment of the digital part, first, the one having the highest required SN is selected. In this case, the required SN of the station STA1 is the highest at 30 dB. This 30 dB is set as a reference SN. The gain is readjusted by multiplying the learning data by the gain value based on the difference between the reference SN and the required SN.

  In each STA, the following formula is calculated:

    Digital part adjustment gain value = -1 x (reference SN-required SN)

  That is, in the example shown in FIG. 6, the following formula is calculated for each station.

Digital part gain value of STA1 = -1 × (30 dB-30 dB) = 0 dB
Digital part gain value of STA2 = −1 × (30 dB−20 dB) = − 10 dB
Digital part gain value of STA3 = −1 × (30 dB−10 dB) = − 20 dB

  Using these values, the digital unit performs gain readjustment using the differences 0 dB, −10 dB, and −20 dB from the reference SN for each station. The result is as shown in FIG. That is, the received signal level from each station that has been adjusted to 0 dB after normalization by AGC becomes 0 dB, −10 dB, and −20 dB, respectively, after gain readjustment.

  These gain readjusted signals are used to calculate the weight of the adaptive array antenna. As a result, it is possible to form antenna directivity so that SNs (precisely SINR) of −30 dB, −20 dB, and −10 dB can be secured in the stations STA1, STA2, and STA3 at the time of downlink.

  The above-described gain readjustment and adaptive array antenna weight calculation method will be described more specifically with reference to FIGS.

Using the weight w ₂ with STA3 as the desired station, the signals of STA1 and STA2 are suppressed to below noise. That is, as shown in FIG. 8, the access point directs a -30 dB null to STA1 as an interfering station, and directs a -20 dB null to STA2. As a result, the STA3 can satisfy the required SN = 10 dB.

  That is, the access point learns to ensure a 10 dB SINR for STA3 in the uplink with each station, so that a -30 dB null beam is received for the STA1 signal, and a STA2 signal is received. An effect equivalent to directing a -20 dB null beam is obtained.

  FIG. 9 shows a state in which the access point performs space division multiple access in the downlink based on the learning result of SINR in the uplink.

  When the same weight is used in the downlink, the same antenna characteristics can be used. Therefore, it can be seen that the transmission signal for STA3 reaches STA1 at a level lower by −30 dB than the transmission signal for STA1. Similarly, the signal for STA3 reaches STA2 at a level that is -20 dB lower than the signal for STA2. Although not shown, the same applies to the case of the downlink signal for STA2.

  In other words, when the wireless communication apparatus according to the present embodiment is applied as an access point, the weight for each STA is set so as to satisfy the required SN required for each station after adjusting the gain of the digital unit. Can be calculated. Then, by performing downlink using the obtained weight, the required SN can be satisfied in the downlink direction.

  It should be noted that a method of calculating the weight without using the present invention as shown in FIG. 5 while keeping the signal uniformly controlled by the auto gain at each station is also conceivable. The following problems arise.

  For example, when calculating the weight with STA3 as the desired station, in order to satisfy SN = −10 dB, the STA1 signal is lowered by −10 dB, and the STA2 signal is also lowered by about −10 dB. In the uplink, the required SN = 10 dB of STA3 is satisfied, but the null beam to the signals of the interfering stations STA1 and STA2 is −10 dB. If the downlink is performed as it is, the STA3 signal (here, the interference signal) is only -10 dB lower than the STA1 signal (here, the desired signal), so that the required SN of STA1 = 30 dB is satisfied. I can't.

[Supplement]
The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention. That is, the present invention has been disclosed in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

FIG. 1 is a diagram schematically showing a network configuration of a wireless LAN according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a functional configuration of a wireless communication apparatus operating as an access point in the wireless network according to the present invention. FIG. 3 is a diagram showing an example of a data transmission / reception procedure in the wireless network according to the present invention. FIG. 4 is a diagram showing a signal and noise from each station received by the access point in a time division manner. In FIG. 5, AGC (auto gain control) is uniformly applied to the signals received from the stations shown in FIG. 4, and the gain of the LNA is adjusted so that it can be received as a waveform having substantially the same magnitude. It is the figure which showed the signal at the time of reception, and the mode of noise. FIG. 6 is a diagram illustrating a state of noise and a signal obtained by adjusting the gain of the signal whose gain has been adjusted again in the digital unit. FIG. 7 is a diagram for explaining a gain readjustment for each station and a weight calculation method for an adaptive array antenna. FIG. 8 is a diagram for explaining the gain readjustment and adaptive array antenna weight calculation method for each station. FIG. 9 is a diagram illustrating a state in which an access point performs space division multiple access in the downlink based on the learning result of SINR in the uplink.

Claims (13)

In a wireless communication environment in which an access point having an adaptive array antenna communicates with a plurality of stations, a wireless communication system that performs space division multiple access on a downlink that performs communication from the access point to the station,
Data for learning to calculate the weight of the adaptive array from multiple stations is transmitted in time division,
At the access point, the learning data from each station is received in a time-sharing manner, and after the waveforms with different power and different sizes are standardized to a certain size in the analog part, the gain is readjusted in the digital part. Calculating the weight of the adaptive array antenna using the learning data after the gain readjustment;
A wireless communication system. The analog section performs auto gain control separately on the learning data received in time division, and adjusts the gain of the low noise amplifier to make waveforms with different power and different magnitudes constant. Normalize,
The wireless communication system according to claim 1. The digital unit performs virtual gain readjustment by multiplying each learning data by a gain value based on the difference in required SN of the modulation scheme assigned at each station.
The wireless communication system according to claim 1. A wireless communication device comprising an adaptive array antenna and performing space division multiple access by giving weights to each antenna based on learning data transmitted in a time division manner from a plurality of communication stations,
Means for receiving learning data from each communication station in a time-sharing manner;
Normalization means for normalizing each learning data composed of waveforms with different power and different sizes,
Readjustment means for multiplying each learning data by a predetermined gain and readjusting the gain;
A weight calculation means for calculating a weight of the adaptive array antenna using the learning data after the gain readjustment;
A wireless communication apparatus comprising: The normalization means is configured as an analog circuit, and the readjustment means is configured as a digital circuit.
The wireless communication apparatus according to claim 4. The normalization means performs auto gain control separately on the learning data received in time division, and adjusts the gain of the low noise amplifier to obtain constant waveforms of different power and different sizes. Normalize to size,
The wireless communication apparatus according to claim 5. The readjustment unit performs virtual gain readjustment by multiplying each learning data by a gain value based on a difference between required signal state values of modulation schemes assigned by each communication station.
The wireless communication apparatus according to claim 5. The signal state value comprises a signal to noise ratio (SN);
The wireless communication apparatus according to claim 7. A wireless communication method for performing space division multiple access in a communication station equipped with an adaptive array antenna by assigning weights to each antenna based on learning data transmitted in a time division manner from a plurality of peripheral communication stations. There,
Receiving learning data from each peripheral communication station in a time-sharing manner;
A normalization step for normalizing each learning data composed of waveforms having different powers and different sizes to a certain size;
A readjustment step of multiplying each learning data by a predetermined gain and readjusting the gain;
A weight calculating step for calculating a weight of an adaptive array antenna using the learning data after the gain readjustment;
A wireless communication method comprising: The normalization step is configured as an analog process, and the readjustment step is configured as a digital process.
The wireless communication method according to claim 9. In the normalization step, auto-gain control is performed separately on the learning data received in time division, and the gain of the low-noise amplifier is adjusted, so that waveforms with different power and different sizes are fixed. Normalize to size,
The wireless communication method according to claim 10. In the readjustment step, virtual gain readjustment is performed by multiplying each learning data by a gain value based on a difference between required signal state values of the modulation schemes assigned in each communication station.
The wireless communication method according to claim 10. The signal state value comprises a signal to noise ratio (SN);
The wireless communication method according to claim 12.

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