JP7746899B2 - Wireless communication method, wireless communication device, and wireless communication system - Google Patents

Description

The present invention relates to a wireless communication method, a wireless communication device, and a wireless communication system using a transmission amplifier.

For wireless communication devices equipped with a transmission amplifier that amplifies transmission signals, the smaller the roll-off factor α of the transmission amplifier, the narrower the transmission bandwidth that can be used. Furthermore, the peak to average power ratio (PAPR) of a wireless communication device is expressed as a function of the roll-off factor α and the compression factor τ.

For example, Non-Patent Document 1 discloses the contribution of square root raised cosine (SRRC) to PAPR for each roll-off rate α. Non-Patent Document 2 discloses the change in PAPR with respect to compression ratio for each roll-off rate α.

Furthermore, SC (single carrier)-FTN (faster-than-nyquist) transmission is known as one technology for optimizing the transmission capacity of wireless communication devices that wirelessly transmit transmission signals amplified using a transmission amplifier.

FTN transmission is a method of transmitting modulation symbols at a symbol rate that exceeds the clock frequency, and is expected to reduce PAPR more than higher-order QAM (Quadrature Amplitude Modulation) with the same number of transmission bits (see, for example, Non-Patent Documents 2 and 3).

Marco Baldi, et al., "A comparison between APSK and QAM inwireless tactical scenarios for land mobile systems", EURASIP Journal on Wireless Communications and Networking 2012 Jean-Alain Lucciardi, et al., "Trade-Off Between Spectral Efficiency Increase And PAPR Reduction When Using FTN Signaling: Impact Of Non Linearities", IEEE ICC 2016 SAC Satellite and Space Communications Fredrik Rusek, et al., "Constrained Capacities for Faster-Than-Nyquist Signaling", IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 55, NO. 2, FEBRUARY 2009

When a wireless communication device lowers the average transmit power taking into account the backoff and PAPR of the transmit amplifier, the signal-to-noise ratio (SNR) decreases. Therefore, in order to optimize communication capacity, it is necessary to adjust the roll-off rate α and compression rate τ to maintain communication quality.

In wireless communications, if the PAPR value exceeds the backoff value and distortion is allowed to occur, quality degradation equivalent to a drop in SNR occurs. Furthermore, in wireless communication devices that can switch modulation methods, the PAPR contribution and minimum Euclidean distance differ depending on the modulation method (e.g., 16QAM, 16APSK, etc.), and therefore the amount of SNR degradation also differs.

The present invention aims to provide a wireless communication method, wireless communication device, and wireless communication system that can optimize transmission capacity while maintaining transmission quality.

A wireless communication method according to one aspect of the present invention is a wireless communication method using a wireless communication device that includes a transmission amplifier and transmits signals via SC-FTN by switching modulation schemes, the method comprising: a tolerance calculation step of calculating a PAPR value for each of a plurality of modulation schemes that is allowed as a back-off by a difference from P1 dB for an average transmission power P amplified by the transmission amplifier; specifying roll-off rates for the calculated PAPRs of the plurality of modulation schemes using a relationship table in which PAPRs by SRRC for roll-off rates are predetermined for each modulation scheme ; and calculating a ratio of the amount by which the PAPR of the transmission amplifier exceeds the back-off to the minimum Euclidean distance for each modulation scheme. and a determination step of determining an optimum transmission capacity from the calculated transmission capacities based on a plurality of PAPR values while sequentially changing the average transmission power, and determining the roll-off rate that results in the optimum transmission capacity as the final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier.

According to another aspect of the present invention, there is provided a wireless communication device including a transmission amplifier, which transmits signals by switching modulation schemes via SC-FTN , and which includes a tolerance calculation unit that calculates a PAPR value for each of a plurality of modulation schemes that is allowed as a back-off by a difference from P1 dB for an average transmission power P amplified by the transmission amplifier, and a roll-off rate calculation unit that specifies roll-off rates for the PAPRs of the plurality of modulation schemes calculated by the tolerance calculation unit using a relationship table in which PAPRs by SRRC for roll-off rates are predetermined for each modulation scheme, and calculates a degraded SNR equivalent based on the amount by which the PAPR of the transmission amplifier exceeds the back-off and the minimum Euclidean distance for each modulation scheme. and a determination unit that determines an optimal transmission capacity from among the transmission capacities calculated by the capacity calculation unit based on a plurality of PAPR values while sequentially changing the average transmission power, and determines the roll-off rate that results in the optimal transmission capacity as the final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier.

Furthermore, a wireless communication system according to one aspect of the present invention is a wireless communication system that transmits signals via SC-FTN using a wireless communication device that has a transmission amplifier and switches modulation methods, the wireless communication system including: a tolerance calculation unit that calculates a PAPR value for each of a plurality of modulation methods that is allowed as a back-off, the difference from P1 dB for an average transmission power P amplified by the transmission amplifier; and a roll-off rate calculation unit that specifies roll-off rates for the PAPRs of the plurality of modulation methods calculated by the tolerance calculation unit using a relationship table in which PAPRs by SRRC against roll-off rates are predetermined for each modulation method, and a ratio of the PAPR of the transmission amplifier to a minimum Euclidean distance for each modulation method is calculated. and a determination unit that determines an optimal transmission capacity from among the transmission capacities calculated by the capacity calculation unit based on a plurality of PAPR values while sequentially changing the average transmission power, and determines the roll-off rate that results in the optimal transmission capacity as the final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier.

This invention makes it possible to optimize transmission capacity while maintaining transmission quality.

10 is a graph illustrating the contribution of SRRC to PAPR for each roll-off factor α. 10 is a graph illustrating a change in PAPR with respect to compression ratio for each roll-off ratio α. (a) shows a constellation of SC-64QAM, and (b) shows a distorted constellation of SC-64QAM. 1A shows a constellation for 16APSK, and FIG. 1B shows a constellation for 16QAM. 10 is a graph illustrating input/output characteristics of a transmission amplifier included in a wireless communication device according to an embodiment. 1 is a functional block diagram illustrating functions that a wireless communication device according to an embodiment has for optimizing transmission capacity while maintaining transmission quality. 10 is a flowchart illustrating an example of an operation of a wireless communication device according to an embodiment.

In one embodiment, a wireless communication system is configured such that a transmitting device (wireless communication device) equipped with a transmission amplifier transmits a signal to a receiving device, for example, using SC-FTN. Here, the roll-off factor α is calculated to optimize the transmission capacity of the wireless communication device.

First, let's explain the PAPR of SC-FTN transmission. PAPR is expressed as a function of the roll-off rate α and the compression rate τ.

Figure 1 is a graph illustrating the contribution of an SRRC to PAPR for each roll-off factor α. Figure 1 illustrates the increase in PAPR due to the SRRC as a function of the roll-off factor α (see Non-Patent Document 1).

Figure 2 is a graph illustrating the change in PAPR with respect to the compression ratio for each roll-off ratio α. Figure 2 shows that the PAPR changes due to signal overlap, which depends on the compression ratio τ (see Non-Patent Document 2).

Next, we will explain the transmission capacity of SC-FTN and distortion caused by the transmission amplifier. The transmission capacity C _FTN of FTN is expressed by the following equation (1), and is maximum when the following equation (2) holds (see Non-Patent Document 3).

where τ is the compression ratio of FTN, α is the roll-off rate, W is the bandwidth, T is the symbol duration, P is the received power, N ₀ is the noise power, SNR is the signal-to-noise ratio (P/N ₀ ), and H(·) is the frequency response of the communication channel.

Given the above equation (2), the transmission capacity C _FTN can be seen as a function of two variables: SNR and roll-off rate α.

However, if the average transmit power is lowered taking into account the transmit amplifier backoff and PAPR, the SNR will decrease.

For example, the SC-64QAM constellation shown in Figure 3(a) will be distorted as shown in Figure 3(b) if the PAPR value exceeds the backoff value of the transmit amplifier.

Therefore, in order to optimize communication capacity while maintaining transmission quality, it is necessary to adjust the roll-off rate α and compression rate τ to maintain communication quality.

For example, if the PAPR value is allowed to exceed the backoff value and distortion occurs, quality degradation equivalent to a decrease in SNR will occur, so parameters such as the roll-off rate α and compression rate τ must be adjusted.

Therefore, a wireless communication device according to one embodiment is configured to optimize transmission capacity while maintaining transmission quality, even when distortion may occur due to the transmission amplifier. The wireless communication device according to one embodiment is capable of transmitting signals by switching modulation methods, and is premised on the following three conditions (A) to (C).

(A): The wireless communication device maintains the relationship of the above equation (2) so that the transmission capacity C _FTN is maximized.

(B): The wireless communication device has a unique PAPR for each modulation scheme with respect to the roll-off factor α (a function of τ), and stores a table (e.g., a look-up table) of the relationship between PAPR and roll-off factor α for each modulation scheme (e.g., 16QAM and 16APSK).

Figure 4 illustrates constellations for different modulation schemes. Figure 4(a) illustrates a constellation for 16APSK. Figure 4(b) illustrates a constellation for 16QAM. As shown by comparing Figures 4(a) and 4(b), the PAPR contribution and minimum Euclidean distance differ for different modulation schemes.

(C) The wireless communication device allows distortion to occur when the PAPR value exceeds the backoff value of the transmit amplifier.

Figure 5 is a graph illustrating the input/output characteristics of a transmission amplifier included in a wireless communication device according to one embodiment. Here, the backoff is defined as the difference between P1dB (1dB compression point) and the average transmission power, which is the operating point. The PAPR value also exceeds the backoff value of the transmission amplifier.

The wireless communication device in one embodiment then performs the following processes (a) to (d) to select the optimal combination of FTN efficiency, roll-off rate, SNR (degraded SNR equivalent amount), and modulation method, thereby optimizing transmission capacity.

(a): The wireless communication device identifies the roll-off rate α for each PAPR of each modulation method (e.g., 16QAM and 16APSK) from a relationship table, calculates the degradation SNR equivalent amount based on the amount by which the PAPR of the transmitting amplifier exceeds the backoff and the minimum Euclidean distance for each modulation method, and selects the modulation method with the least degradation amount.

(b): The wireless communication device calculates the SNR for the PAPR using the following equation (3):

(c): The wireless communication device calculates the transmission capacity C _FTN by using the specified roll-off factor α and the calculated SNR according to the above formula (1).

(d): The wireless communication device determines an optimum _CFTN from a plurality of PAPR values, and determines the roll-off factor α that results in the optimum _CFTN as the final roll-off factor α for the transmitting amplifier.

Next, specific examples of functions provided in a wireless communication device according to one embodiment will be described. Figure 6 is a functional block diagram illustrating functions provided in a wireless communication device according to one embodiment for optimizing transmission capacity while maintaining transmission quality.

As shown in FIG. 6, the wireless communication device according to one embodiment includes a memory unit 10, a tolerance calculation unit 11, a modulation scheme selection unit 12, an SNR calculation unit 13, a capacity calculation unit 14, and a determination unit 15.

The storage unit 10 is a memory or the like that stores information necessary for the wireless communication device to optimize transmission capacity while maintaining transmission quality, such as the relationship table described above.

The tolerance calculation unit 11 calculates the allowable PAPR value for the average transmission power P of the transmission amplifier, using the difference from P1 dB as the backoff, and outputs the calculation result to the memory unit 10 and the modulation scheme selection unit 12.

In other words, the tolerance calculation unit 11 calculates the PAPR value for each modulation method that is acceptable as a backoff, using the difference from P1 dB for the average transmission power P amplified by the transmission amplifier.

The modulation scheme selector 12 determines the roll-off rate α for each PAPR of each modulation scheme, such as 16QAM or 16APSK, using a relationship table stored in the memory unit 10. It then calculates the SNR degradation equivalent amount based on the amount by which the PAPR of the transmitting amplifier exceeds the backoff and the minimum Euclidean distance for each modulation scheme, and selects the modulation scheme with the least degradation. The modulation scheme selector 12 then outputs information indicating the selected modulation scheme to the memory unit 10 and the SNR calculator 13.

In other words, the modulation scheme selector 12 uses a predetermined relationship table to determine the roll-off rate for each PAPR of each modulation scheme calculated by the tolerance calculator 11, calculates the degradation SNR equivalent amount based on the amount by which the PAPR of the transmitting amplifier exceeds the backoff and the minimum Euclidean distance for each modulation scheme, and selects the modulation scheme with the least degradation amount.

The SNR calculation unit 13 accesses the memory unit 10, calculates the SNR for the average transmission power P using the above equation (3), and outputs the calculated SNR to the memory unit 10 and the capacity calculation unit 14.

The capacity calculation unit 14 accesses the storage unit 10, calculates the transmission capacity C FTN according to the above formula (1) using each of the roll-off rates α specified by the modulation scheme selection unit 12 and the SNR calculated by the _SNR calculation unit 13, and outputs the calculation result to the storage unit 10 and the determination unit 15. For example, the capacity calculation unit 14 calculates the PAPR value of each modulation scheme allowed in SC-FTN transmission.

In other words, the capacity calculation unit 14 calculates the transmission capacity via the transmission amplifier using each roll-off rate identified by the modulation scheme selection unit 12 and the SNR calculated by the SNR calculation unit 13.

The determination unit 15 accesses the memory unit 10, and while sequentially changing the average transmission power P, determines the optimal transmission capacity C _FTN from multiple PAPR values, and determines the roll-off rate α that results in the optimal C _FTN as the final roll-off rate α for the transmission amplifier.

In other words, the determination unit 15 sequentially changes the average transmission power, determines the optimal transmission capacity from the transmission capacities calculated by the capacity calculation unit 14 based on multiple PAPR values, and determines the roll-off rate that results in the optimal transmission capacity as the final roll-off rate for the transmission amplifier.

In this way, the wireless communication device according to one embodiment realizes optimization of the transmission capacity C _FTN by selecting an optimal combination of FTN efficiency, roll-off rate α, SNR (degraded SNR equivalent amount), and modulation method.

Next, an example of the operation of a wireless communication device according to one embodiment will be described. Figure 7 is a flowchart showing an example of the operation of a wireless communication device according to one embodiment.

In step 100 (S100), the tolerance calculation unit 11 calculates the allowable PAPR value for the average transmission power P of the transmission amplifier, using the difference from P1 dB as the backoff.

In step 102 (S102), the modulation scheme selection unit 12 determines the roll-off rate α for each PAPR of each modulation scheme, such as 16QAM or 16APSK, using the relationship table stored in the storage unit 10, calculates the degradation SNR equivalent amount based on the amount by which the PAPR of the transmitting amplifier exceeds the backoff and the minimum Euclidean distance for each modulation scheme, and selects the modulation scheme with the least degradation amount.

In step 104 (S104), the SNR calculation unit 13 calculates the SNR for the average transmission power using equation (3) above.

In step 106 (S106), the capacity calculation unit 14 calculates the transmission capacity C FTN by the above equation (1) using each of the roll-off _factors α specified by the modulation scheme selection unit 12 and the SNR calculated by the SNR calculation unit 13.

In step 108 (S108), the determination unit 15 determines whether the C _FTN calculated by the capacity calculation unit 14 is greater than the C _FTN previously stored in the memory unit 10, and if it is greater (S108: Yes), proceeds to processing S110; otherwise (S108: No), proceeds to processing S112.

In step 110 (S100), the storage unit 10 stores the _CFTN last calculated by the capacity calculation unit 14.

In step 112 (S112), the decision unit 15 determines whether the average transmission power P is greater than Pmax (maximum transmission power value), and if it is greater (S112: Yes), the process ends; otherwise (S112: No), the process proceeds to S114.

In step 114 (S114), the determination unit 15 sets the average transmission power P _i to P _i+1 (where . . . < P _i-1 < P _i < P _i+1 < . . . ).

That is, the determination unit 15 determines the optimal transmission capacity C _FTN from multiple PAPR values while sequentially changing the average transmission power P, and determines the roll-off rate α that results in the optimal C _FTN as the final roll-off rate α for the transmission amplifier.

In this way, a wireless communication device equipped with a transmission amplifier that amplifies a transmission signal can determine the combination of roll-off rate α, SNR degradation equivalent amount, and modulation method, and optimize transmission capacity while maintaining transmission quality.

Note that some or all of the components constituting the wireless communication device described above may be configured using hardware, or may be configured by having a processor execute a program stored in memory or the like.

Furthermore, if some or all of the components of a wireless communication device are configured by having a processor execute a program, the program may be recorded on a recording medium and supplied, or may be supplied via a network.

10: Memory unit, 11: Tolerance value calculation unit, 12: Modulation method selection unit, 13: SNR calculation unit, 14: Capacity calculation unit, 15: Determination unit

Claims (3)

A wireless communication method using a wireless communication device that includes a transmission amplifier and transmits signals by switching modulation methods using SC-FTN ,
a tolerance calculation step of calculating a PAPR value for each of a plurality of modulation schemes, the difference from P1 dB being a back-off allowable for an average transmission power P amplified by the transmission amplifier;
a modulation scheme selection step of specifying a roll-off rate for each of the calculated PAPRs of the plurality of modulation schemes using a relationship table in which the PAPRs by the SRRC for the roll-off rates are predetermined for each modulation scheme, calculating an amount of degradation equivalent to an SNR based on the amount by which the PAPR of the transmission amplifier exceeds the back-off and the minimum Euclidean distance for each modulation scheme, and selecting a modulation scheme with a small amount of degradation;
an SNR calculation step of calculating an SNR for an average transmission power;
a capacity calculation step of calculating a transmission capacity through the SRRC and the transmission amplifier using each of the identified roll-off rates and the calculated SNR;
determining an optimal transmission capacity from the calculated transmission capacities based on a plurality of PAPR values while sequentially changing the average transmission power, and determining the roll-off rate resulting in the optimal transmission capacity as the final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier. A wireless communication device that includes a transmission amplifier and transmits signals by switching modulation methods using SC-FTN ,
a tolerance calculation unit that calculates a PAPR value for each of a plurality of modulation schemes, the difference from P1 dB being a backoff for an average transmission power P amplified by the transmission amplifier;
a modulation scheme selection unit that specifies roll-off rates for the PAPRs of the plurality of modulation schemes calculated by the tolerance calculation unit using a relationship table in which PAPRs by SRRC for each of the modulation schemes are predetermined relative to roll-off rates, calculates a degradation SNR equivalent amount based on the amount by which the PAPR of the transmission amplifier exceeds a back-off and the minimum Euclidean distance for each of the modulation schemes, and selects a modulation scheme with a small amount of degradation;
an SNR calculation unit that calculates an SNR for an average transmission power;
a capacity calculation unit that calculates a transmission capacity via the SRRC and the transmission amplifier using each roll-off rate specified by the modulation scheme selection unit and the SNR calculated by the SNR calculation unit;
and a determination unit that determines an optimal transmission capacity from the transmission capacities calculated by the capacity calculation unit based on multiple PAPR values while sequentially changing the average transmission power, and determines the roll-off rate that results in the optimal transmission capacity as a final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier. In a wireless communication system in which a signal is transmitted by a wireless communication device equipped with a transmission amplifier and capable of switching modulation methods,
a tolerance calculation unit that calculates a PAPR value for each of a plurality of modulation schemes, the difference from P1 dB being a backoff for an average transmission power P amplified by the transmission amplifier;
a modulation scheme selection unit that specifies roll-off rates for the PAPRs of the plurality of modulation schemes calculated by the tolerance calculation unit using a relationship table in which PAPRs by SRRC for each of the modulation schemes are predetermined relative to roll-off rates, calculates a degradation SNR equivalent amount based on the amount by which the PAPR of the transmission amplifier exceeds a back-off and the minimum Euclidean distance for each of the modulation schemes, and selects a modulation scheme with a small amount of degradation;
an SNR calculation unit that calculates an SNR for an average transmission power;
a capacity calculation unit that calculates a transmission capacity via the SRRC and the transmission amplifier using each roll-off rate specified by the modulation scheme selection unit and the SNR calculated by the SNR calculation unit;
a determination unit that determines an optimal transmission capacity from the transmission capacities calculated by the capacity calculation unit based on multiple PAPR values while sequentially changing the average transmission power, and determines the roll-off rate that results in the optimal transmission capacity as a final roll-off rate for SC-FTN transmission via the SRRC and the transmission amplifier.