JP7750156B2 - 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 by switching modulation indexes, the method comprising: a tolerance calculation step of calculating a PAPR value for each modulation index at which distortion is allowed beyond an average transmission power P amplified by the transmission amplifier, where the difference from P1 dB is used as a backoff; an SNR calculation step of specifying a roll-off rate for each calculated PAPR using a predetermined relationship table, calculating a degradation SNR equivalent amount based on the amount exceeding the backoff and the minimum Euclidean distance, and calculating an SNR by subtracting a propagation loss, noise power, and the degradation SNR equivalent amount from the average transmission power; and a step of calculating an SNR by subtracting the calculated SNR from the current modulation index. and a determination step of determining whether a predetermined required SNR for the transmission amplifier is satisfied, and lowering the modulation index if it is determined that the required SNR is not satisfied; a capacity calculation step of calculating a transmission capacity via the transmission amplifier using the modulation index based on the determination result, each of the specified roll-off rates, and the SNR; and a determination step of determining a maximum transmission capacity that maintains a predetermined transmission quality from the transmission capacities calculated in the capacity calculation step while sequentially changing the average transmission power, based on the PAPR value of each of the changed average transmission powers , and determining the roll-off rate that results in the maximum transmission capacity as a final roll-off rate for the transmission amplifier.

Also, according to one aspect of the present invention, a wireless communication device includes a transmission amplifier and transmits a signal by switching a modulation index, the wireless communication device including: a tolerance calculation unit that calculates a PAPR value for each modulation index where distortion is allowed beyond an average transmission power P amplified by the transmission amplifier, using a difference from P1 dB as a back-off; an SNR calculation unit that specifies a roll-off rate for each PAPR calculated by the tolerance calculation unit using a predetermined relationship table, calculates a degradation SNR equivalent amount based on an amount exceeding the back-off and a minimum Euclidean distance, and calculates an SNR by subtracting a propagation loss, noise power, and the degradation SNR equivalent amount from the average transmission power; and a tolerance calculation unit that calculates an SNR where the calculated SNR is the current modulation index, roll-off rate, and a minimum Euclidean distance. a capacity calculation unit that calculates a transmission capacity via the transmission amplifier using the modulation index based on the result of the determination by the determination processing unit, and each roll-off factor and SNR specified by the SNR calculation unit; and a determination unit that, while sequentially changing the average transmission power, determines a maximum transmission capacity that maintains a predetermined transmission quality from the transmission capacities calculated by the capacity calculation unit based on the PAPR value of each changed average transmission power , and determines the roll-off factor that results in the maximum transmission capacity as a final roll-off factor for the transmission amplifier.

Also, according to one aspect of the present invention, a wireless communication system includes a transmission amplifier and transmits a signal using a wireless communication device that switches a modulation index, the wireless communication system including: a tolerance calculation unit that calculates a PAPR value for each modulation index at which distortion is allowed to exceed an average transmission power P amplified by the transmission amplifier, the difference from P1 dB being a back-off; an SNR calculation unit that specifies a roll-off rate for each PAPR calculated by the tolerance calculation unit using a predetermined relationship table, calculates a degradation SNR equivalent amount based on the amount exceeding the back-off and the minimum Euclidean distance, and calculates an SNR by subtracting a propagation loss, noise power, and the degradation SNR equivalent amount from the average transmission power; and a signal processing unit that calculates an SNR by calculating the calculated SNR based on the current modulation index. a determination processing unit that determines whether a predetermined required SNR for a modulation index and a roll-off rate is satisfied, and that performs processing to lower a modulation index if it is determined that the required SNR is not satisfied; a capacity calculation unit that calculates a transmission capacity via the transmission amplifier using the modulation index based on the result of the determination by the determination processing unit, and each of the roll-off rates and SNRs specified by the SNR calculation unit; and a determination unit that, while sequentially changing average transmission power, determines a maximum transmission capacity that maintains a predetermined transmission quality from the transmission capacities calculated by the capacity calculation unit based on a PAPR value for each of the changed average transmission powers, and determines the roll-off rate that results in the maximum transmission capacity as a final roll-off rate for 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. FIG. 10 is a diagram illustrating a modulation index table used by the wireless communication device. 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 due to the transmission amplifier may occur. Note that the wireless communication device according to one embodiment can transmit signals by, for example, switching modulation indexes and switching between SC-FTN transmission and Nyquist transmission, and is based on the following three assumptions (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 roll-off factor α (a function of τ), and stores a table (e.g., a look-up table) that shows the relationship between the PAPR and the roll-off factor α for each modulation index.

Figure 4 shows an example of a modulation index table used by a wireless communication device. The modulation index table associates transmission bits and modulation methods with each modulation index.

(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 according to one embodiment then performs the following steps (a) to (f) to select either SC-FTN transmission or Nyquist transmission, which combines the optimal FTN efficiency, roll-off rate, SNR (degraded SNR equivalent amount), and modulation index, thereby optimizing transmission capacity.

(a): For average transmission power P, calculate the allowable PAPR by using the difference from P1 dB as the backoff, and determine the final roll-off rate based on the relationship between the allowable PAPR, the actual PAPR, the modulation method, and the roll-off rate α.

(b): The wireless communication device 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 method.

(c): The wireless communication device calculates the SNR for the average transmission power P using the following equation (3):

(d): If the wireless communication device determines that the required SNR for the current modulation index and roll-off rate α is not met, it lowers the modulation index and recalculates the actual PAPR.

(e): 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).

(f): The wireless communication device changes the average transmission power P and determines the average transmission power P, roll-off rate α, and compression rate τ that maximize the transmission capacity C _FTN .

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, an SNR calculation unit 12, a judgment processing 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 SNR calculation 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 SNR calculation unit 12 determines the roll-off rate α for each PAPR of each modulation method, such as 16QAM or 16APSK, using a relationship table stored in the memory unit 10. It calculates the SNR degradation equivalent amount and modulation index based on the amount by which the PAPR of the transmission amplifier exceeds the backoff and the minimum Euclidean distance. It then calculates the SNR for the average transmission power using equation (3) above, and outputs the calculated SNR to the memory unit 10 and the determination processing unit 13.

The determination processing unit 13 determines whether the required SNR for the current modulation index and roll-off rate α is met, and outputs the determination result to the memory unit 10, SNR calculation unit 12, and capacity calculation unit 14. For example, if the determination processing unit 13 determines that the required SNR is not met, it lowers the modulation index and, for example, causes the SNR calculation unit 12 to recalculate the actual PAPR.

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

The determination unit 15 accesses the memory unit 10, and while sequentially changing the average transmission power P, determines the optimal transmission capacity CFTN from multiple PAPR values, and determines the roll-off rate α that results in the optimal _CFTN 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 of one embodiment realizes optimization of the transmission capacity C FTN by selecting SC-FTN transmission or Nyquist transmission that combines the optimal _FTN efficiency, roll-off rate α, SNR (degraded SNR equivalent amount), and modulation index.

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 SNR calculation unit 12 identifies the roll-off rate α using the relationship table stored in the memory unit 10, calculates the SNR degradation equivalent amount and modulation index based on the amount by which the PAPR of the transmission amplifier exceeds the backoff and the minimum Euclidean distance for each modulation method, and calculates the SNR for the average transmission power.

In step 104 (S104), the determination processing unit 13 determines whether the required SNR for the current modulation index and roll-off rate α is met, and if it is determined that it is met (S104: Yes), proceeds to processing S108, and if it is determined that it is not met (S104: No), proceeds to processing S106.

In step 106 (S106), the determination processing unit 13 lowers the modulation index and returns to processing S102.

In step 108 (S108), the capacity calculation unit 14 calculates the transmission capacity C _FTN by the above formula (1) using the roll-off factors α and the SNR specified by the SNR calculation unit 12.

In step 110 (S110), 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 (S110: Yes), proceeds to processing S112, otherwise (S110: No), proceeds to processing S114.

In step 112 (S112), the storage unit 10 stores the _CFTN last calculated by the capacity calculation unit 14.

In step 114 (S114), the decision unit 15 determines whether the average transmission power P is greater than Pmax (maximum transmission power value), and if it is greater (S114: Yes), the process ends; otherwise (S114: No), the process proceeds to S116.

In step 116 (S116), the determination unit 15 sets the average transmission power P _i to P _i+1 (where . . . < P _i-1 < P _i < P _i+1 < . . . ).

In other words, if the required SNR is not met for a given roll-off rate α, the determination unit 15 lowers the modulation index and determines the roll-off rate α, etc.

In this way, when a wireless communication device equipped with a transmission amplifier that amplifies a transmission signal selects SC-FTN transmission, it can determine the combination of roll-off rate α, SNR degradation equivalent amount, and modulation index, 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: SNR calculation unit, 13: Judgment processing 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 indexes,
a tolerance calculation step of calculating a PAPR value for each modulation index where distortion is allowed to exceed a backoff value that is a difference from P1 dB with respect to an average transmission power P amplified by the transmission amplifier;
an SNR calculation step of specifying a roll-off rate for each calculated PAPR using a predetermined relationship table, calculating a degradation SNR equivalent amount based on the amount exceeding the back-off and the minimum Euclidean distance , and calculating an SNR by subtracting the propagation loss, noise power, and the degradation SNR equivalent amount from the average transmission power;
a determination process step of determining whether the calculated SNR satisfies a predetermined required SNR for the current modulation index and roll-off rate, and performing a process of lowering the modulation index when it is determined that the calculated SNR does not satisfy the required SNR;
a capacity calculation step of calculating a transmission capacity through the transmission amplifier using a modulation index based on the determined result, each of the specified roll-off factors, and an SNR;
a determination step of determining a maximum transmission capacity that maintains a predetermined transmission quality from the transmission capacities calculated in the capacity calculation step based on a PAPR value for each of the changed average transmission powers while sequentially changing the average transmission power, and determining a roll-off rate that results in the maximum transmission capacity as a final roll-off rate for the transmission amplifier. A wireless communication device including a transmission amplifier and transmitting a signal by switching a modulation index,
a tolerance calculation unit that calculates a PAPR value for each modulation index where distortion is allowed to exceed a backoff value that is a difference from P1 dB with respect to an average transmission power P amplified by the transmission amplifier;
an SNR calculation unit that specifies a roll-off rate for each PAPR calculated by the tolerance calculation unit using a predetermined relationship table, calculates a degradation SNR equivalent amount based on an amount exceeding the back-off and a minimum Euclidean distance, and calculates an SNR by subtracting a propagation loss, noise power, and the degradation SNR equivalent amount from an average transmission power;
a determination processing unit that determines whether the calculated SNR satisfies a predetermined required SNR for the current modulation index and roll-off rate, and performs processing to lower the modulation index when it is determined that the required SNR is not satisfied;
a capacity calculation unit that calculates a transmission capacity through the transmission amplifier using a modulation index based on the result of the determination by the determination processing unit, and each of the roll-off rates and the SNR specified by the SNR calculation unit;
a determination unit that determines a maximum transmission capacity that maintains a predetermined transmission quality from among the transmission capacities calculated by the capacity calculation unit based on a PAPR value for each of the changed average transmission powers while sequentially changing the average transmission power, and determines a roll-off rate that results in the maximum transmission capacity as a final roll-off rate for the transmission amplifier. In a wireless communication system in which a signal is transmitted by a wireless communication device that has a transmission amplifier and switches a modulation index,
a tolerance calculation unit that calculates a PAPR value for each modulation index where distortion is allowed to exceed a backoff value that is a difference from P1 dB with respect to an average transmission power P amplified by the transmission amplifier;
an SNR calculation unit that specifies a roll-off rate for each PAPR calculated by the tolerance calculation unit using a predetermined relationship table, calculates a degradation SNR equivalent amount based on an amount exceeding the back-off and a minimum Euclidean distance, and calculates an SNR by subtracting a propagation loss, noise power, and the degradation SNR equivalent amount from an average transmission power;
a determination processing unit that determines whether the calculated SNR satisfies a predetermined required SNR for the current modulation index and roll-off rate, and performs processing to lower the modulation index when it is determined that the required SNR is not satisfied;
a capacity calculation unit that calculates a transmission capacity through the transmission amplifier using a modulation index based on the result of the determination by the determination processing unit, and each of the roll-off rates and the SNR specified by the SNR calculation unit;
a determination unit that determines a maximum transmission capacity that maintains a predetermined transmission quality from among the transmission capacities calculated by the capacity calculation unit based on a PAPR value for each of the changed average transmission powers while sequentially changing the average transmission power, and determines a roll-off rate that results in the maximum transmission capacity as a final roll-off rate for the transmission amplifier.