Wireless communication device and wireless communication method

Abstract

An antenna active system (AAS) (10), according to the present disclosure, comprises: a signal processing unit (11); a transmitter (12) disposed downstream of the signal processing unit (11); and a transmission amplifier (13) disposed downstream of the transmitter (12). The signal processing unit (11) detects the presence / absence of a transmission signal, and if a transmission signal has been detected, a stabilization signal for stabilizing the characteristics of the transmission amplifier (13) is inserted into the time slot preceding the time slot of the transmission signal, thereby causing the stabilization signal to pass through the transmitter (12) and the transmission amplifier (13) before the transmission signal passes through the transmitter (12) and the transmission amplifier (13).

Description

Technical Field

[0001] The present disclosure relates to a wireless communication device and a wireless communication method.

Background Art

[0002] Compared with GaAs, GaN has advantages in that it has a large bandgap energy, can be made highly resistant to voltage and miniaturized, and has a high electron mobility. Therefore, RF (Radio Frequency) devices such as transmission AMPs using GaN FET (Field Effect Transistor) continue to be adopted in wireless communication devices such as base stations for Wide Area, macro base stations, and AAS (Antenna Active System) as high-output RF devices that exceed RF devices using GaAs FET. In addition, the two-dimensional electron gas structure of GaN / AlGaN FET has physical properties such as high mobility compared with Si FET. Therefore, RF devices using GaN / AlGaN FET are adopted and put into practical use particularly as high-output RF devices in the high-frequency band of RF. An example of GaN / AlGaN FET is GaN / AlGaN HEMT (High Electron Mobility Transistor).

[0003] FIG. 1 is a diagram showing a structural example of GaN / AlGaN HEMT. Further, FIG. 2 is a diagram showing a band structure example of GaN / AlGaN HEMT. As shown in FIGS. 1 and 2, GaN / AlGaN HEMT is realized by growing GaN / AlGaN on a sapphire substrate. In GaN / AlGaN HEMT, an electron layer called a two-dimensional electron gas generated at the boundary of different compound materials is used as a carrier, and the electron supply layer (AlGaN layer) and the electron traveling layer (GaN layer) are different. Therefore, GaN / AlGaN HEMT has the advantages that it can realize high electron mobility, can be used at high speed and high frequency, and can output high power with high efficiency.

[0004] When operating AlGaN / GaN HEMTs at high amplitude and high power, various parasitic phenomena must be addressed. Currently, various parasitic phenomena are known to occur in AlGaN / GaN HEMTs, stemming from the GaN semi-insulating substrate, surface energy levels, and deep impurity levels present at the substrate interface. These parasitic phenomena pose problems in terms of output power, strain characteristics, stability, and reliability of RF devices using AlGaN / GaN HEMTs. Regarding semiconductor surface energy levels, the energy levels are determined within the semiconductor crystal. However, at the semiconductor surface, if the continuity is interrupted, different energy levels (= surface energy levels) exist compared to those inside the crystal. These surface energy levels are formed by rearrangement at the crystal surface and adsorption of external atoms such as oxygen and hydrogen atoms, making theoretical analysis extremely complex. Therefore, overcoming parasitic phenomena caused by these surface energy levels is highly difficult.

[0005] Furthermore, among these parasitic phenomena, the phenomenon called current collapse is a phenomenon in which the drain current decreases as the drain voltage is applied. Current collapse is described, for example, in Patent Document 1. When aiming to increase the efficiency and power of the transmitting amplifier by changing the operating class of the transmitting amplifier from Class A to Class AB to Class C and so on, it is accompanied by an increase or decrease in the drain current in accordance with the amplitude of the transmitted signal. The increase or decrease in drain current is an unstable factor (memory effect) in which the current gain and output decrease and fluctuate due to the history of amplitude amplification operation in the past in time, and the difficulty of distortion improvement by DPD (Digital Pre-Distortion) increases.

[0006] Furthermore, transient phenomena such as drain lag and gate lag also pose problems for transmitting amplifiers. In Class C and above transmitting amplifiers, Class C amplification begins when drain current flows in response to a certain amplitude of the transmitted signal. The output of the transmitting amplifier is then matched by a matching circuit (a tank circuit that extracts and outputs only the fundamental wave from the harmonic group amplified signal, which includes the amplified signal as the fundamental wave), and the fundamental amplified signal is output. Drain lag is a phenomenon in which, when the drain voltage is abruptly turned off and then on to enable amplification of the transmitting amplifier, the drain current changes transiently and slowly until it reaches a steady voltage state. In addition, when a wireless communication device equipped with a transmitting amplifier is operating in TDD (Time Division Duplex) mode, the transmitting amplifier is turned off and on in accordance with the switching between UL (Up Link) and DL (Down Link). The On / Off startup of the transmit AMP involves switching the Vgs voltage from a pinch-off state (deep Vgs setting that results in Ids=0A) to a shallower Vgs voltage to achieve the desired Ids setting for the desired AMP performance. This sets the desired Ids and leads to the On operation of the transmit AMP, but a rapid change in gate voltage occurs at this time. Gate lag is a phenomenon in which the drain current changes transiently and slowly until it reaches a steady voltage state in response to this rapid change in gate voltage (Gate pinch-off setting results in Ids Off, the transmit AMP is completely Off → rapid change to the gate voltage that sets the Ids for the transmit AMP On). These Gate lag and Drain lag (hereinafter referred to as "Gate / Drain lag" as appropriate) can lead to transient response delay failures when a transmit AMP using AlGaN / GaN HEMT performs high-speed On / Off and burst operations to achieve TDD operation, until it reaches a normal state. A normal state means that the Gain, Output, and nonlinear distortion characteristics such as AM (Amplitude Modulation)-AM / AM-PM (Phase Modulation) are in a steady state.In this context, LTE (Long Term Evolution) and 5G (Fifth Generation Partnership Project) base stations, under TDD (Telegraphic Transfer Device) systems, perform low-power adaptive control by using burst operation to turn the transmit AMP on and off in time, or by frequently turning the transmit AMP on and off in response to the transmit symbol. However, due to the transient response delay mentioned above, a significant advancement of the transmit AMP's On control is required, resulting in a considerable amount of time being needed to stabilize the transmitted signal.

[0007] In a transmitting amplifier, when transient phenomena such as the gate / drain lag described above occur, the charging and discharging processes have a certain time constant due to the deep and surface energy levels of the AMP substrate (the substrate portion of the bare chip die inside the AMP). As a result, before the transmission signal is input to the transmitting amplifier, the time it takes for the drain current to reach the target steady-state drain current is significantly delayed due to the Off / On operation of the transmitting amplifier. Consequently, when the transmitting signal passes through the transmitting amplifier, the gain, output, and nonlinear distortion characteristics of the initial part of the transmitted signal do not reach a steady state. This means that, in the low-power adaptive control described above, stable characteristics of the transmitting amplifier cannot be ensured each time the transmitting amplifier is turned on.

[0008] Consequently, if LTE or 5G base stations employ a transmitting amplifier using GaN FETs, it becomes difficult to perform the aforementioned low-power adaptive control under a TDD system, resulting in numerous malfunctions in the system characteristics of the TDD system. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2012-227795 [Overview of the project] [Problems that the invention aims to solve]

[0010] The above-mentioned problem will be explained below with reference to the diagrams. Hereafter, an amplifier using a GaN FET will be referred to as "GaN AMP" as appropriate. Furthermore, hereafter, the wireless communication device on which the transmitting AMP is installed will be assumed to be an AAS that transmits DL signals as transmission signals to each UE (User Equipment: mobile terminal).

[0011] Figure 3 shows an example of the drain current Ids characteristics when the gate of a GaN AMP (transmitting amplifier) ​​is turned on from a pinch-off state. In Figure 3, the horizontal axis represents time, and the vertical axis represents the drain current Ids. Figure 4 is an enlarged view of the X portion of Figure 3. In Figure 4, the characteristics of Ids are shown when the Vgs setting is changed in four different ways.

[0012] As shown in Figure 3, when the gate is turned on from the pinch-off state, the gate voltage increases rapidly, causing the drain current Ids to change transiently and slowly until it reaches the desired Ids, resulting in gate lag. Furthermore, as shown in Figure 4, setting Vgs to a shallower value than the deep Vgs value in the pinch-off state and turning the gate on tends to shorten the time it takes for the drain current Ids to reach the desired Ids after the gate is turned on.

[0013] Figure 5 shows an example of how the drain current Ids characteristic decreases from the steady-state Ids value before impulse application when an impulse is input to a transmit amplifier with a poor drain lag GaN AMP. Figure 6 shows an example of the drain current Ids characteristic when an impulse is input to a transmit amplifier with a good drain lag GaN AMP. In Figures 5 and 6, the horizontal axis represents time and the vertical axis represents drain current Ids.

[0014] As shown in Figure 5, when an impulse is input to a transmit amplifier with poor drain lag, the drain current Ids drops by approximately 90% immediately after the input. Therefore, it takes a long time for the drain current Ids to recover to the desired level.

[0015] In LTE, the length of one symbol when the Subcarrier Space is 15kHz is approximately 64μsec. In 5G, the length of one symbol when the Subcarrier Space is 30kHz is approximately 36μsec, which is about half the length of one symbol in LTE mentioned above.

[0016] Therefore, in the case of a transmission amplifier with poor drain lag, it is difficult to restore the drain current Ids to the desired Ids within 1 Symbol length after the impulse input, whether in LTE or 5G.

[0017] On the other hand, as shown in Figure 6, when an impulse is input to a transmit amplifier with good drain lag, the decrease in drain current Ids immediately after the input is limited to approximately 40%. Therefore, the drain current Ids can be restored to the desired Ids in a short time.

[0018] Therefore, in the case of a transmit amplifier with good drain lag, the drain current Ids can be restored to the desired Ids within 1 Symbol length after the impulse input, whether in the case of LTE or 5G.

[0019] Figure 7 shows examples of drain current Ids characteristics when a transmitting amplifier with a good Gate / Drain Lag and a transmitting amplifier with a poor Gate / Drain Lag are turned ON. In Figure 7, the horizontal axis represents time and the vertical axis represents drain current Ids. Figure 8 is an enlarged view of the X portion of Figure 7. Note that in Figures 7 and 8, there is no RF modulation signal input to the transmitting amplifier.

[0020] As shown in Figures 7 and 8, for a transmit amplifier with good Gate / Drain Lag, the rise characteristics of the drain current Ids immediately after turning on the transmit amplifier are good. Therefore, the drain current Ids can be restored to the desired Ids in a short time. In contrast, for a transmit amplifier with poor Gate / Drain Lag, the drain current Ids immediately after turning on the transmit amplifier rises slowly. Therefore, it takes a long time for the drain current Ids to return to the desired Ids.

[0021] Figure 9 shows an example of the EVM (Error Vector Magnitude) characteristics when the transmit AMP is turned on in an AAS equipped with a transmit AMP that has poor Gate / Drain Lag (GaN AMP). Figure 10 shows an example of the EVM characteristics when the transmit AMP is turned on in an AAS equipped with a transmit AMP that has good Gate / Drain Lag (GaN AMP). In Figures 9 and 10, the horizontal axis represents Symbol and the vertical axis represents EVM. Note that in Figures 9 and 10, the transmit AMP is turned on and off twice.

[0022] As shown in Figure 9, in the case of an AAS equipped with a transmit amplifier with poor Gate / Drain Lag, the EVM of the leading Symbol 1 in the DL signal immediately after the transmit amplifier is turned on shows overshoot and degradation. In contrast, as shown in Figure 10, in the case of an AAS equipped with a transmit amplifier with good Gate / Drain Lag, the EVM from the leading Symbol 1 in the DL signal immediately after the transmit amplifier is turned on shows suppressed overshoot and no degradation.

[0023] FIG. 11 is a diagram showing an example of the constellation of the first symbol 1 of the DL signal immediately after turning on the transmission AMP in an AAS equipped with a transmission AMP which is a GaN AMP with poor Gate / Drain Lag. Further, FIG. 12 is a diagram showing an example of the constellation of the first symbol 1 of the DL signal immediately after turning on the transmission AMP in an AAS equipped with a transmission AMP which is a GaN AMP with good Gate / Drain Lag.

[0024] As shown in FIG. 11, in the case of an AAS equipped with a transmission AMP with poor Gate / Drain Lag, phase rotation occurs in the constellation of the first symbol 1 of the DL signal immediately after turning on the transmission AMP. Although not shown, it was confirmed that the constellations of symbols after symbol 1 are normal. On the other hand, as shown in FIG. 12, in the case of an AAS equipped with a transmission AMP with good Gate / Drain Lag, the DL signal immediately after turning on the transmission AMP has a normal constellation from the first symbol 1.

[0025] FIG. 13 is a diagram showing an example of the relationship between SNR (Signal-to-Noise Ratio) and Throughput for each of a plurality of MCSs (Modulation and channel Coding Scheme) in an AAS equipped with a transmission AMP which is a GaN AMP with poor Gate / Drain Lag. Further, FIG. 14 is a diagram showing an example of the relationship between SNR and Throughput for each of a plurality of MCSs in an AAS equipped with a transmission AMP which is a GaN AMP with good Gate / Drain Lag. In FIGS. 13 and 14, the horizontal axis represents SNR and the vertical axis represents Throughput.

[0026] As described above, in the AAS equipped with the transmission AMP which is a GaN AMP, when Gate / Drain Lag occurs, an Overshoot occurs in the EVM of the first Symbol of the DL signal immediately after turning on the transmission AMP. Therefore, when Gate / Drain Lag occurs, an Overshoot occurs in the EVM at the first Symbol of each DL Slot for each TDD DL / UL Configuration, or at any first Symbol in the DL Slot.

[0027] Therefore, as shown in FIG. 13, in the case of an AAS equipped with a transmission AMP with poor Gate / Drain Lag, particularly on the maximum direction (higher-order QAM (Quadrature Amplitude Modulation)) side of the MCS, the Max Throughput corresponding to the SNR cannot be achieved. As a result, an MCS with an SNR of about 20 dB or more cannot be achieved. On the other hand, as shown in FIG. 14, in the case of an AAS equipped with a transmission AMP with good Gate / Drain Lag, the Max Throughput corresponding to the SNR can be achieved up to the maximum MCS.

[0028] As described above, in a wireless communication device equipped with a transmission AMP with poor Gate / Drain Lag, due to the delay until the characteristics of the transmission AMP are stabilized, the communication quality of the leading portion of the transmission signal deteriorates, and as a result, there is a problem that many defects are generated.

[0029] An object of the present disclosure is to provide a wireless communication device and a wireless communication method capable of maintaining the communication quality of the leading portion of a transmission signal in view of the above-described problems.

Means for Solving the Problems

[0030] A wireless communication device according to one aspect includes: a signal processing unit, a transmitter provided at a subsequent stage of the signal processing unit, and a transmission amplifier provided at a subsequent stage of the transmitter. The signal processing unit, Detect the presence or absence of a transmission signal, When the aforementioned transmission signal is detected, a stabilization signal for stabilizing the characteristics of the transmission amplifier is inserted into the time domain preceding the time domain of the transmission signal, thereby causing the stabilization signal to pass through the transmitter and the transmission amplifier before the transmission signal passes through the transmitter and the transmission amplifier.

[0031] One aspect of wireless communication method is: A wireless communication method performed by a wireless communication device comprising a transmitter and a transmitting amplifier provided downstream of the transmitter, The step of detecting the presence or absence of a transmission signal in the preceding stage of the transmission amplifier, The method includes the step of, when the transmission signal is detected, inserting a stabilization signal for stabilizing the characteristics of the transmission amplifier into the time domain preceding the time domain of the transmission signal, thereby causing the stabilization signal to pass through the transmitter and the transmission amplifier before the transmission signal passes through the transmitter and the transmission amplifier. [Effects of the Invention]

[0032] According to the above-described embodiment, the effect is obtained that a wireless communication device and wireless communication method can be provided that can maintain the communication quality of the leading portion of the transmitted signal. [Brief explanation of the drawing]

[0033] [Figure 1] This figure shows an example of the structure of GaN / AlGaN HEMT. [Figure 2] This figure shows an example of the band structure of GaN / AlGaN HEMT. [Figure 3] This figure shows an example of the drain current Ids characteristics when the gate is turned on from a pinch-off state in a GaN amplifier (transmitting amplifier). [Figure 4] This is a magnified view of the X portion in Figure 3. [Figure 5]This figure shows an example of the drain current Ids characteristics when an impulse is input to a transmitting amplifier that is a GaN amplifier with poor drain lag. [Figure 6] This figure shows an example of the drain current Ids characteristics when an impulse is input to a transmitting amplifier that is a GaN amplifier with good drain lag. [Figure 7] This figure shows examples of drain current Ids characteristics when a transmitting amplifier with a good Gate / Drain Lag and a transmitting amplifier with a poor Gate / Drain Lag are turned ON. [Figure 8] This is a magnified view of the X portion in Figure 7. [Figure 9] This figure shows an example of EVM characteristics when the transmit amplifier is turned on in an AAS equipped with a transmit amplifier that has poor gate / drain lag (GaN AMP). [Figure 10] This figure shows an example of EVM characteristics when the transmit amplifier is turned on in an AAS equipped with a transmit amplifier that is a GaN AMP with good gate / drain lag. [Figure 11] This figure shows an example of a constellation of leading Symbols in a DL signal immediately after the transmit AMP is turned on, in an AAS equipped with a transmit AMP that has poor Gate / Drain Lag (GaN AMP). [Figure 12] This figure shows an example of a constellation of leading Symbols in a DL signal immediately after the transmit AMP is turned on, in an AAS equipped with a transmit AMP that is a GaN AMP with good Gate / Drain Lag. [Figure 13] This figure shows an example of the relationship between SNR and Throughput for each of multiple MCSs in an AAS equipped with a transmit AMP that has poor Gate / Drain Lag (GaN AMP). [Figure 14] This figure shows an example of the relationship between SNR and Throughput for each of multiple MCSs in an AAS equipped with a transmit amplifier that is a GaN AMP with good Gate / Drain Lag. [Figure 15] This figure shows examples of the drain current Ids characteristics when there is no RF modulation signal input, with a transmit amplifier that is a GaN AMP with good Gate / Drain Lag and a transmit amplifier that is a GaN AMP with poor Gate / Drain Lag turned ON. [Figure 16] This figure shows examples of the gain characteristics when an RF modulated signal is input along with an impulse for a transmitting amplifier that is a GaN AMP with good Gate / Drain Lag and a transmitting amplifier that is a GaN AMP with poor Gate / Drain Lag. [Figure 17] This figure shows an example of the drain current Ids deviation characteristics when a transmitting amplifier with a poor Gate / Drain Lag (GaN AMP) is turned on, and then RF modulated signals with different input levels are input to each other. [Figure 18] This figure shows an example of the arrangement of AMP stabilization signals in the time, frequency, and power directions. [Figure 19] This figure shows an example of the arrangement of AMP stabilization signals in the frequency and power directions. [Figure 20] This figure shows an example of the time and frequency arrangement of the AMP stabilization signal. [Figure 21] This figure shows an example of the data structure of an AMP-stabilized signal. [Figure 22] This figure shows an example of the time arrangement of an AMP stabilization signal. [Figure 23] This timing chart shows an example of how processing start timing changes in AAS due to AMP stabilization signal interrupts. [Figure 24] This figure shows an example of the configuration of the AAS according to the embodiment. [Figure 25] This figure shows an example in which an AMP stabilization signal is inserted into the time domain preceding the time domain of the DL signal in the AAS according to the embodiment. [Figure 26] This is a flowchart illustrating a general example of the operation of the AAS according to the embodiment. [Figure 27]This figure shows an example of the amplitude waveform of a DL signal in an AAS (Automatic Audio System) equipped with a transmitting amplifier that has poor gate / drain lag (GaN AMP) and no AMP stabilization signal. [Figure 28] This figure shows examples of amplitude waveforms for the AMP stabilization signal and DL signal in an AAS according to an embodiment in which a transmitting AMP is equipped with a GaN AMP with poor Gate / Drain Lag and an AMP stabilization signal is applied to the transmitting AMP. [Figure 29] This figure shows an example of EVM characteristics when the transmit amplifier is turned on in an AAS (Automatic Air System) equipped with a transmit amplifier that has poor gate / drain lag (GaN AMP) and no AMP stabilization signal is provided. [Figure 30] This figure shows an example of the EVM characteristics when the transmit AMP is turned on in an AAS according to an embodiment in which a transmit AMP is a GaN AMP with poor gate / drain lag and an AMP stabilization signal is applied to the transmit AMP. [Figure 31] This figure shows an example of a constellation of the leading Symbol of the DL signal immediately after the transmitting AMP is turned on, in an AAS according to an embodiment in which a transmitting AMP is a GaN AMP with poor Gate / Drain Lag and an AMP stabilization signal is applied to the transmitting AMP. [Figure 32] This figure shows an example of the relationship between SNR and Throughput for each of the multiple MCS in an AAS according to an embodiment in which a transmitting AMP is a GaN AMP with poor Gate / Drain Lag and an AMP stabilization signal is applied to the transmitting AMP. [Figure 33] This figure shows an example of a computer hardware configuration that implements some of the functions of the wireless communication device related to this disclosure. [Modes for carrying out the invention]

[0034] Embodiments of this disclosure will be described below with reference to the drawings. Note that the following description and drawings have been omitted and simplified as appropriate for clarity of explanation. Furthermore, the same elements are denoted by the same reference numerals in the following drawings, and redundant explanations have been omitted where necessary. Also, the specific numerical values ​​shown below are merely examples to facilitate understanding of this disclosure and are not limiting.

[0035] <Principle of the Embodiment> Before describing the details of this embodiment, the principle of this embodiment will be explained. In the following, the wireless communication device equipped with the transmitting AMP will be assumed to be an AAS that transmits a DL signal as a transmission signal to each UE.

[0036] The inventors of this disclosure have found that even with a transmit amplifier with poor gate / drain lag, inputting an RF modulated signal after inputting an impulse can shorten the time it takes for the characteristics of the transmit amplifier to stabilize.

[0037] Figure 15 shows examples of drain current Ids characteristics when no RF modulated signal is input, with a transmit amplifier having a good Gate / Drain Lag and a transmit amplifier having a poor Gate / Drain Lag, respectively. In Figure 15, the horizontal axis represents time and the vertical axis represents drain current Ids. Figure 16 shows examples of gain characteristics when an RF modulated signal is input along with an impulse, for both a transmit amplifier having a good Gate / Drain Lag and a transmit amplifier having a poor Gate / Drain Lag. In Figure 16, the horizontal axis represents time and the vertical axis represents gain.

[0038] As shown in Figure 15, in the case of a transmit amplifier with poor Gate / Drain Lag, the drain current Ids rises slowly immediately after the transmit amplifier is turned on, when there is no RF modulated signal input. Therefore, although not shown in Figure 15, it takes a long time of approximately 80 μsec for the drain current Ids to return to the desired Ids. As mentioned above, in 5G, the length of 1 Symbol when the Sub Carrier Space is 30 kHz is approximately 36 μsec. Therefore, the approximately 80 μsec required for the drain current Ids to recover corresponds to the time of approximately 2 Symbol lengths in 5G as described above.

[0039] In contrast, as shown in Figure 16, even with a transmission amplifier with poor Gate / Drain Lag, when an RF modulated signal is input along with an impulse, the time it takes for the gain to return to the level before the impulse input is approximately 10 μsec, thus shortening the time it takes for the gain to recover. The approximately 10 μsec for the gain to recover corresponds to the time of approximately 0.3 Symbols for 5G mentioned above.

[0040] Furthermore, the inventors of this disclosure have found that even with a transmit amplifier having poor gate / drain lag, a higher input level of the RF modulated signal input to the transmit amplifier after turning it on can shorten the time it takes for the characteristics of the transmit amplifier to stabilize.

[0041] Figure 17 shows an example of the drain current Ids deviation characteristics when a transmitting amplifier, which is a GaN amplifier with poor gate / drain lag, is turned on, and then RF modulated signals with different input levels are input to it. In Figure 17, the horizontal axis represents time, and the vertical axis represents the deviation of the drain current Ids. Here, the deviation of Ids on the vertical axis is expressed as the difference between Ids = Idq (idle current when no signal is applied) and Idq = 90mA, and then Ids during signal amplification at each time after the transmitting signal is input to the transmitting amplifier. Therefore, "0 (A)" on the vertical axis of the figure means that it matches Ids = 90mA before the transmitting signal was input. Note that in Figure 17, the drain current Ids is fixed at 90mA, and the input level of the RF modulated signal is varied within the range of 33.7dBm to 45.7dBm.

[0042] As shown in Figure 17, even with a poor Gate / Drain Lag in a transmit amplifier, a higher input level of the RF modulated signal input to the transmit amplifier after turning it on can shorten the time it takes to recover to the original drain current Ids (=90mA). In the example in Figure 17, the time it took to recover to the original drain current Ids was shortest when the input level of the RF modulated signal was set to the highest level of 45.7dBm.

[0043] Therefore, in this embodiment, based on the above-mentioned findings, a high-level AMP stabilization signal with as wide a bandwidth as possible (frequency can be extended up to the setting of each operational CC: Component Carrier) is inserted in the time domain preceding the time domain of the DL signal, so that the AMP stabilization signal passes through the transmitting AMP before the DL signal passes through the transmitting AMP. It is preferable to insert the AMP stabilization signal in the time domain immediately preceding the time domain of the DL signal.

[0044] In this way, by inputting an AMP stabilization signal to the transmitting AMP before the initial symbol of the DL signal is input to the transmitting AMP, the current collapse and gate / drain lag of the transmitting AMP are resolved early. This allows characteristic variations caused by the current collapse and gate / drain lag of the transmitting AMP to converge early, and the nonlinear distortion characteristics such as the gain, output, and AM-AM / AM-PM of the transmitting AMP can be stabilized. As a result, many problems caused by EVM overshoot of the initial symbol of the DL signal are avoided, and signal quality is guaranteed from the initial symbol of the DL signal and any initial symbol in the DL slot. Furthermore, since the AM-AM / AM-PM characteristics of the transmitting AMP in the initial symbol section of the DL signal are already stable when the initial symbol of the DL signal is input to the transmitting AMP, the initial symbol of the DL signal and subsequent symbols are stably distortion-compensated by the DPD in the transmitter (TX). This also contributes to the guarantee of signal quality from the initial symbol of the DL signal. The TX is located in the transceiver (TRX).

[0045] Figure 18 shows an example of the arrangement of the AMP stabilization signal in the time, frequency, and power directions. Figure 19 shows an example of the arrangement of the AMP stabilization signal in the frequency and power directions. Figure 20 shows an example of the arrangement of the AMP stabilization signal in the time and frequency directions. In Figures 18 to 20, the DL signal is assumed to be either a signal in the slot unit or a signal in the symbol unit.

[0046] As shown in Figures 18 to 20, the AMP stabilization signal is, for example, an OFDM (Orthogonal Frequency Division Multiplexing) format signal. Furthermore, the AMP stabilization signal has a Reighley distribution amplitude probability density with a PAPR (Peak to Average Power Ratio) of 14 dB. The AMP stabilization signal also passes through a CFR (Crest Factor Reduction) placed before the DPD in the TX, and then the PAPR of the AMP stabilization signal is soft-clipped to the CFR threshold (approximately 7-8 dB). The CFR is implemented to avoid the failure of uncompensated DPD, which occurs due to the significant high-order distortion caused by hard clipping in the transmitting AMP.

[0047] Furthermore, the AMP stabilization signal is placed in the time range before the first symbol of the DL Slot or any symbol within the DL Slot. For example, in a TDD system, a transient period called the Tx On Transient period is set as the period for switching TX from Off to On. Therefore, in a TDD system, the AMP stabilization signal will be placed in the time range within the Tx On Transient period before the DL signal. For example, in 3GPP (Third GPP) NR (New Radio) (3GPP TS 38.104 V15.16.0 (2021-12) and 3GPP TS 38.141 V15.11.0 (2021-12)), the Tx On Transient period is specified as 10 μsec. In this case, the time width of the signal with Ramp Up / Down added to the AMP stabilization signal is set to within 10 μs. Ramp Up / Down is a signal inserted to prevent the spread of the impulsive spectrum. The duration of the DL signal is approximately 36 μsec to several DL slots. Alternatively, the duration of the DL signal is 140 μsec when operating in SSB (SS (Synchronization Signal) / PBCH (Physical Broadcast Channel) Block) mode. Here, SSB is a synchronization signal / broadcast channel block composed of SS and PBCH. SSB is mainly transmitted periodically from the base station to enable terminals to detect cell ID and reception timing at the start of communication, but in 5G NR, it is also used to measure the reception quality of each cell.

[0048] Furthermore, as mentioned above, inputting an RF modulated signal in addition to the impulse signal promotes the early recovery of the transmit AMP's characteristics. Therefore, the frequency bandwidth of the AMP stabilization signal is set to a wide bandwidth equivalent to the frequency bandwidth of each component carrier used for transmitting the DL signal. The frequency bandwidth of each component carrier is approximately 20MHz to 100MHz. The frequency bandwidth of the DL signal is approximately 7.2MHz when operating in SSB mode, and the frequency bandwidth of each component carrier under actual DL signals such as PDSCH (Physical Downlink Shared Channel). Also, as mentioned above, increasing the input level of the RF modulated signal further promotes the early recovery of the transmit AMP's characteristics. Therefore, the power level of the AMP stabilization signal is set to a high level that is the same as the DL signal and at a power level at which the output of the transmit AMP reaches the maximum rated RMS (Root Mean Square) level.

[0049] As described above, according to this embodiment, by inserting a high-level and wide-bandwidth AMP stabilization signal in the time domain before the DL signal, the AMP stabilization signal passes through the transmitting AMP before the DL signal passes through the transmitting AMP.

[0050] In this way, by inputting an AMP stabilization signal to the transmitting AMP before the initial symbol of the DL signal is input to the transmitting AMP, the current collapse and gate / drain lag of the transmitting AMP are resolved early. This causes characteristic variations caused by the current collapse and gate / drain lag of the transmitting AMP to converge early, stabilizing the nonlinear distortion characteristics of the transmitting AMP, such as Gain, Output, and AM-AM / AM-PM. As a result, many problems caused by EVM overshoot of the initial symbol of the DL signal are avoided, and signal quality is guaranteed from the initial symbol of the DL signal and any initial symbol in the DL slot. Furthermore, since the AM-AM / AM-PM characteristics of the transmitting AMP in the initial symbol section of the DL signal are already stable when the initial symbol of the DL signal is input to the transmitting AMP, the initial symbol of the DL signal and subsequent symbols are stably distortion-compensated by the DPD in the TX. This also contributes to the guarantee of signal quality from the initial symbol of the DL signal.

[0051] Furthermore, for example, the AMP stabilization signal is placed within the time domain of the Tx On Transient period before the DL signal, but in 3GPP NR, the Tx On Transient period is specified as 10 μsec. Therefore, within the 10 μs of the Tx On Transient period, the nonlinear distortion characteristics such as AM-PM of the transmitting AMP are stabilized, and then the DL signal is subjected to distortion compensation by the DPD.

[0052] Therefore, by adopting the configuration of this embodiment, even in a transmitting amplifier that is a GaN AMP with poor current collapse and gate / drain lag, the maximum throughput corresponding to the SNR can be achieved for all symbols of the DL signal (including the leading symbol of the DL signal and any leading symbol in the DL slot), even for the maximum MCS. As a result, it is possible to maintain the highest system performance of the TDD system while also achieving optimal power consumption reduction according to user traffic.

[0053] The following provides a more detailed explanation of the AMP stabilization signal. Figure 21 shows an example of the data structure of an AMP-stabilized signal. As shown in Figure 21, the AMP-stabilized signal has a structure in which a Cyclic Prefix (CP) is added to the beginning of the data portion, Ramp up and Ramp down are added before and after it, and null is added at the end. Ramp up consists of 188 samples, CP consists of 8 samples, the data portion consists of 2048 samples, Ramp down consists of 188 samples, and null consists of 128 samples. The sum of Ramp up, CP, data portion, and Ramp down is 2432 samples, and the grand total including null is 2560 samples.

[0054] Other parameters of the AMP stabilization signal include, for example, the following: Transmission speed: 245.76 MSPS Frequency Bandwidth: Component Carrier Frequency Bandwidth Power level: The power level at which the output of the transmitting amplifier reaches its maximum rated RMS level. Modulation scheme: QPSK (Quadrature Phase-Shift Keying) ~ 256QAM PAPR: 14dB. After passing CFR: 7-8dB.

[0055] Figure 22 shows an example of the time arrangement of an AMP stabilization signal. As shown in Figure 22, the AMP stabilization signal is placed in a time domain within the Tx On Transient period, which is the period for switching TX from Off to On. The Tx On Transient period is specified as 10 μsec in 3GPP NR.

[0056] Figure 23 is a timing chart showing an example of the change in processing start timing associated with the AMP stabilization signal interrupt in AAS. As shown in Figure 23, in this embodiment, the AAS inserts the AMP stabilization signal into the time domain preceding the DL signal. Therefore, if the AMP stabilization signal is 10 μsec long, the AAS advances the timing of applying the control voltage TX_Enable On to TX to enable it in the TRX by 10 μsec. The AAS also advances the timing of applying the control voltage AMP On to the transmit AMP to turn it on by 10 μsec.

[0057] <Embodiment> The embodiments of the wireless communication device according to this disclosure will be described below. In the following description, the wireless communication device according to this embodiment will be described as an AAS that transmits a DL signal as a transmission signal to each UE.

[0058] Figure 24 shows an example configuration of the AAS10 according to this embodiment. Note that Figure 24 shows only the main components of the AAS10 according to this embodiment, and other components (for example, antennas, etc.) are omitted from the illustration.

[0059] As shown in Figure 24, the AAS10 according to this embodiment comprises a signal processing unit 11, a transmitter TX12, and a transmitting AMP13 which is a GaN AMP. The signal processing unit 11 also comprises a detection unit 111, an IFFT (Inverse Fast Fourier Transform) unit 112, a signal storage memory 113, and an adder 114.

[0060] The IFFT section 112 converts the DL signal from a frequency domain signal to a time domain signal. The detection unit 111 is located before the IFFT unit 112. The detection unit 111 autonomously detects the presence or absence of a DL signal in the frequency domain. For example, the detection unit 111 detects the presence or absence of a DL signal by performing a threshold determination in the frequency domain.

[0061] The signal storage memory 113 stores the AMP stabilization signal for stabilizing the characteristics of the transmitting AMP 13. Specifically, the AMP stabilization signal, when input to the transmitting AMP 13, causes the current collapse and Gate / Drain Lag of the transmitting AMP 13 to converge quickly, thereby stabilizing the gain, output, and nonlinear distortion characteristics of the transmitting AMP 13 early.

[0062] When the DL signal is detected by the detection unit 111, the adder 114 adds the AMP stabilization signal stored in the signal storage memory 113 to the time range preceding the time range of the DL signal after the DL signal has been output from the IFFT unit 112. In this way, the AMP stabilization signal is inserted into the time range preceding the time range of the DL signal. At this time, the adder 114 calculates the time when the DL signal exists by taking into account the processing time of TX12 from the radiation time of the DL signal from the antenna, and inserts the AMP stabilization signal at the beginning of that time. Figure 25 shows an example in which the AMP stabilization signal is inserted into the time range preceding the time range of the DL signal. This allows the AMP-stabilized signal to pass through TX12 and the transmit AMP13 before the DL signal passes through TX12 and the transmit AMP13.

[0063] In this case, during AAS10 TDD operation, the time period preceding the DL signal time period is, for example, the Tx On Transient period, which is the period for switching TX12 from Off to On. Therefore, the time width of the AMP stabilization signal is set within the time width of the Tx On Transient period. The Tx On Transient period is specified as 10 μsec in 3GPP NR.

[0064] Furthermore, the frequency bandwidth of the AMP stabilization signal is set to the frequency bandwidth of the Component Carrier used for transmitting the DL signal. Furthermore, the power level of the AMP stabilization signal is set to a power level at which the output of the transmitting AMP13 reaches its maximum rated RMS level, and is the same power level as the DL signal.

[0065] TX12 is located downstream of the signal processing unit 11 and converts the DL signal or AMP stabilized signal output from the signal processing unit 11 from an IQ (In-Phase / Quadrature-Phase) signal to an RF signal, which is then output to the transmitting AMP 13. TX12 is located within a transceiver (TRX) not shown. Furthermore, as mentioned above, TX12 includes components such as a DPP and a CFR located before the DPD, but these are not shown in the diagram.

[0066] The transmitting AMP13 is located downstream of the TX12 and amplifies and outputs the DL signal or AMP stabilized signal output from the TX12. The DL signal or AMP stabilized signal output from the transmitting AMP13 is transmitted to each UE via an antenna (not shown).

[0067] Figure 26 is a flowchart illustrating a schematic operation example of the AAS10 according to this embodiment. As shown in Figure 26, the detection unit 111 detects the presence or absence of a DL signal (step S11). If the detection unit 111 detects a DL signal (Yes in step S12), the adder 114 inserts an AMP stabilization signal into the time domain preceding the time domain of the DL signal (step S13). Therefore, the AMP stabilization signal first passes through TX12 and the transmitting AMP13 (step S14), thereby stabilizing the gain, output, and nonlinear distortion characteristics of the transmitting AMP13. Then, the DL signal passes through TX12 and the transmitting AMP13 (step S15).

[0068] As described above, according to this embodiment, when the signal processing unit 11 detects a DL signal, it inserts an AMP stabilization signal into the time period preceding the time period of the DL signal, and allows the AMP stabilization signal to pass through TX12 and the transmit AMP13 before the DL signal passes through TX12 and the transmit AMP13.

[0069] In this way, by inputting an AMP stabilization signal to the transmitting AMP13 before the leading symbol of the DL signal is input to the transmitting AMP13, the current collapse and gate / drain lag of the transmitting AMP13 are resolved early. This causes characteristic variations caused by the current collapse and gate / drain lag of the transmitting AMP13 to converge early, stabilizing the nonlinear distortion characteristics of the transmitting AMP13, such as Gain, output, and AM-AM / AM-PM. This suppresses overshoot in the EVM of the leading symbol of the DL signal, maintaining the communication quality of the leading symbol of the DL signal. As a result, many problems caused by overshoot in the EVM of the leading symbol of the DL signal are avoided, and signal quality is guaranteed from the leading symbol of the DL signal and any leading symbol in the DL slot. Furthermore, since the AM-AM / AM-PM characteristics of the transmitting AMP13 in the leading symbol section of the DL signal are already stable when the leading symbol of the DL signal is input to the transmitting AMP13, the leading symbol of the DL signal and subsequent symbols are stably distortion-compensated by the DPD in TX12. This also contributes to the fact that DL signals have guaranteed signal quality from the leading symbol.

[0070] The effects of this embodiment will be described in detail below with reference to the drawings. Figure 27 shows an example of the amplitude waveform of the DL signal in an AAS equipped with a transmitting AMP that has poor Gate / Drain Lag (GaN AMP) and no AMP stabilization signal is provided. Figure 28 shows an example of the amplitude waveforms of the AMP stabilization signal and the DL signal in an AAS10 according to this embodiment, equipped with a transmitting AMP13 that has poor Gate / Drain Lag (GaN AMP) and to which an AMP stabilization signal is provided. In Figures 27 and 28, the horizontal axis represents time and the vertical axis represents amplitude. The difference in amplitude waveforms in Figures 27 and 28 will appear as the difference in EVM characteristics in Figures 29 and 30, which will be described later.

[0071] Figure 29 shows an example of EVM characteristics when the transmit AMP is turned on in an AAS equipped with a transmit AMP that has poor Gate / Drain Lag (GaN AMP) and no AMP stabilization signal is provided. Figure 30 shows an example of EVM characteristics when the transmit AMP 13 is turned on in an AAS 10 according to this embodiment, which is equipped with a transmit AMP 13 that has poor Gate / Drain Lag (GaN AMP) and an AMP stabilization signal is provided to the transmit AMP 13. In Figures 29 and 30, the horizontal axis represents Symbol and the vertical axis represents EVM. Note that in Figures 29 and 30, the transmit AMP is turned on and off only once.

[0072] As shown in Figure 29, in the case of an AAS equipped with a poor-quality transmit AMP in the Gate / Drain Lag and without an AMP stabilization signal, the EVM of the leading Symbol 1 in the DL signal immediately after the transmit AMP is turned on is degraded due to overshoot. In contrast, as shown in Figure 30, in the case of the AAS10 according to this embodiment, equipped with a poor-quality transmit AMP 13 in the Gate / Drain Lag and with an AMP stabilization signal applied to the transmit AMP 13, the EVM from the leading Symbol 1 in the DL signal immediately after the transmit AMP 13 is turned on shows suppressed overshoot and no degradation.

[0073] Figure 31 shows an example of the constellation of Symbol 1, the leading element of the DL signal, immediately after the transmitting AMP 13 is turned on, in an AAS 10 according to this embodiment, which is equipped with a transmitting AMP 13 that is a GaN AMP with poor Gate / Drain Lag and is provided with an AMP stabilization signal. Note that in an AAS equipped with a transmitting AMP with poor Gate / Drain Lag and without an AMP stabilization signal, the example of the constellation of Symbol 1, the leading element of the DL signal, immediately after the transmitting AMP is turned on is the same as that shown in Figure 11.

[0074] As shown in Figure 11, in the case of an AAS equipped with a poor-quality transmit AMP for Gate / Drain Lag and without an AMP stabilization signal, the constellation of Symbol 1, the leading element of the DL signal immediately after turning on the transmit AMP, exhibits phase rotation. In contrast, as shown in Figure 31, in the case of the AAS10 according to this embodiment, equipped with a poor-quality transmit AMP 13 for Gate / Drain Lag and with an AMP stabilization signal applied to the transmit AMP 13, the constellation of the DL signal immediately after turning on the transmit AMP is normal from Symbol 1.

[0075] Figure 32 shows an example of the relationship between SNR and Throughput for each of the multiple MCS in an AAS10 according to this embodiment, in which a transmitting AMP13 is a GaN AMP with poor Gate / Drain Lag and an AMP stabilization signal is applied to the transmitting AMP13. In Figure 32, the horizontal axis represents SNR and the vertical axis represents Throughput. Note that in an AAS equipped with a transmitting AMP with poor Gate / Drain Lag and without an AMP stabilization signal, the example of the relationship between SNR and Throughput for each of the multiple MCS is the same as shown in Figure 13.

[0076] As shown in Figure 13, in the case of an AAS equipped with a poor-quality transmit AMP for Gate / Drain Lag and without an AMP stabilization signal, the Max Throughput corresponding to the SNR cannot be achieved, especially on the maximum direction (higher-order QAM) side of the MCS. As a result, MCSs with an SNR of approximately 20 dB or higher become unusable. In contrast, as shown in Figure 32, in the case of the AAS10 according to this embodiment, equipped with a transmit AMP13 which is a poor-quality GaN AMP for Gate / Drain Lag and with an AMP stabilization signal applied to the transmit AMP13, the Max Throughput corresponding to the SNR can be achieved up to the maximum MCS.

[0077] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be understood by those skilled in the art within the scope of the present disclosure.

[0078] For example, the embodiments described above illustrate an example of using the wireless communication device according to this disclosure in an AAS, but this disclosure is not limited thereto. The wireless communication device according to this disclosure can be used in any wireless communication device equipped with a transmission function for transmitting transmission signals (e.g., a base station for wide areas, a macro base station, etc.).

[0079] Furthermore, some functions of the wireless communication device related to this disclosure can also be realized by having a processor such as a CPU (Central Processing Unit) execute a program. Figure 33 is a diagram showing an example of the hardware configuration of a computer 20 that implements some of the functions of the wireless communication device according to this disclosure. As shown in Figure 33, the computer 20 includes a processor 21 and memory 22.

[0080] The processor 21 may be, for example, a microprocessor, a CPU, or an MPU (Micro Processing Unit). The processor 21 may include multiple processors.

[0081] Memory 22 is composed of a combination of volatile and non-volatile memory. Memory 22 may also include storage located away from the processor 21. In this case, the processor 21 may access memory 22 via an I(Input) / O(Output) interface, which is not shown.

[0082] A program is stored in memory 22. This program includes a set of instructions (or software code) that, when loaded into the computer 20, causes the computer 20 to perform some of the functions of the AAS 10 according to the above-described embodiment. The components of the AAS 10 described above may also be realized by the processor 21 loading and executing the program stored in memory 22. Furthermore, the components of the AAS 10 that have storage functions described above may also be realized by memory 22.

[0083] Furthermore, the programs described above may be stored on non-temporary computer-readable media or tangible storage media. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drives (SSDs) or other memory technologies, CD-ROMs, digital versatile discs (DVDs), Blu-ray® discs or other optical disc storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices. The programs may also be transmitted over temporary computer-readable media or communication media. Examples, but not limited to, include electrical, optical, acoustic, or other forms of propagating signals. [Explanation of Symbols]

[0084] 10 AAS 11 Signal Processing Unit 111 Detection Unit 112 IFFT section 113 Signal storage memory 114 Adder 12 TX 13 Send AMP 20 Computers 21 processors 22 memory

Claims

1. Signal processing unit, A transmitter is provided downstream of the signal processing unit, The transmitter is further configured with a transmitting amplifier located downstream of the transmitter. The signal processing unit, Detect the presence or absence of a transmission signal, When the aforementioned transmission signal is detected, a stabilization signal for stabilizing the characteristics of the transmitting amplifier is inserted into the time domain preceding the time domain of the transmission signal, thereby causing the stabilization signal to pass through the transmitter and the transmitting amplifier before the transmission signal passes through the transmitter and the transmitting amplifier. Wireless communication device.

2. The signal processing unit, A signal storage memory for storing the aforementioned stabilization signal, The aforementioned transmission signal is converted from a frequency domain signal to a time domain signal by an IFFT (Inverse Fast Fourier Transform) unit, A detection unit is provided prior to the IFFT unit and detects the presence or absence of the transmission signal in the frequency domain, The system includes an adder that, when the transmission signal is detected by the detection unit, adds the stabilization signal stored in the signal storage memory to the time period preceding the time period of the transmission signal output from the IFFT unit. The wireless communication device according to claim 1.

3. When the wireless communication device performs TDD (Time Division Duplex) operation, the time width of the stabilization signal is set to be within the time width of the period required to switch the transmitter from Off to On. The wireless communication device according to claim 1.

4. The frequency bandwidth of the stabilized signal is set to the frequency bandwidth of the component carrier used for transmitting the transmitted signal. The wireless communication device according to claim 1.

5. The power level of the stabilization signal is set to a power level at which the output of the transmitting amplifier reaches the maximum rated RMS (Root Mean Square) level, and is the same power level as the transmitting signal. The wireless communication device according to claim 1.

6. The stabilization signal, when input to the transmitting amplifier, generates a current collapse and gate lag / drain lag in the transmitting amplifier, thereby stabilizing the gain, output, and nonlinear distortion characteristics of the transmitting amplifier. The wireless communication device according to claim 1.

7. The aforementioned transmitting amplifier is an amplifier that uses a GaN FET (Field Effect Transistor). A wireless communication device according to any one of claims 1 to 6.

8. A wireless communication method performed by a wireless communication device comprising a transmitter and a transmitting amplifier provided downstream of the transmitter, The step of detecting the presence or absence of a transmission signal in the preceding stage of the transmission amplifier, The process includes, when the aforementioned transmission signal is detected, inserting a stabilization signal for stabilizing the characteristics of the transmitting amplifier into the time domain preceding the time domain of the transmission signal, thereby allowing the stabilization signal to pass through the transmitter and the transmitting amplifier before the transmission signal passes through the transmitter and the transmitting amplifier. Wireless communication method.

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