Feedforward transmitter arrangement and method therein

Abstract

A transmitter arrangement (100) and method therein for amplifying and transmitting an input signal (X) are provided. The transmitter arrangement (100) comprises a first transmit path (110) configured to receive, process and amplify a first input signal (Y), and the first input signal (Y) is generated based on the input signal (X) to be transmitted. The transmitter arrangement (100) further comprises a second transmit path (120) configured to receive, process and amplify a second input signal (C), and the second input signal (C) is a cancellation signal generated based on the input signal (X) to be transmitted. The transmitter arrangement (100) further comprises a power combiner (130) configured to combine output signals from the first and second transmit paths (110, 120) to generate an output signal (Pout) for transmitting via an antenna (160). The transmitter arrangement (100) further comprises a transmitter observer path (150) configured to be connected to either the first or second transmit paths (110, 120) to generate a feedback signal (FB) from either the output signal of the first transmit path (110) or the output signal of the second transmit path (120) or the output signal of the power combiner (130). Publ.

Description

[0001] FEEDFORWARD TRANSMITTER ARRANGEMENT AND METHOD THEREIN

[0002] TECHNICAL FIELD

[0003] Embodiments herein relate to transmitter arrangement. In particular, they relate to a feedforward transmitter arrangement and method therein for amplifying and transmitting an input signal. Further, the embodiments relate to an electronic device comprising the transmitter arrangement.

[0004] BACKGROUND

[0005] The demand on high-speed mobile networks is continuously increasing nowadays. Besides new frequency bands and multi-antenna technology, improving spectral efficiency is still an effective way to boost throughput. In some scenarios, if the received signal-to-noise ratio (SNR) is good enough, high-order quadrature amplitude modulation (QAM) such as 256-QAM or 1024-QAM, can approximate the capacity as close as possible, resulting with higher throughput. In the meantime, high-order modulation also poses challenge on the network equipment, especially radio transmitter. As well known, to ensure a good power efficiency in power amplifier (PA), the transmit signal is clipped to reduce its peak to average power ratio (PAPR). This also introduces the clipping error that degrades the quality of transmit signal. Currently, under the target PAPR, it is difficult to meet the tough error vector magnitude (EVM) requirement set by the high-order modulation. The relevant topics including digital predistortion (DPD), PA and crest factor reduction (CFR) can be found for examples, in J. Joung, et.al, “A Survey on Power-Amplifier-Centric Techniques for Spectrum- and Energy-Efficient Wireless Communications’, IEEE Communications Surveys Tutorials, vol. 17, no. 1 , pp. 315-333, First Quarter 2015, Y. Rahmatallah et.al, “Peak-To-Average Power Ratio Reduction in OFDM Systems: A Survey and Taxonomy’, IEEE Communications Surveys Tutorials, vol. 15, no. 4, pp. 1567-1592, 2013. A conventional feedforward (FF) transmitter is presented in WQ2022203554A1 , “Method and arrangements for supporting intermodulation component suppression in a transmitter system with digital predistortion and feedforward linearization”. The goal of this conventional FF is complementary to DPD to correct the distortion that is not able to be corrected in DPD. The conventional FF extracts the residual distortion at the PA output. After amplification and phase / gain correction, the residual distortion is removed from the transmit signal by a coupler.

[0006] A straightforward way to guarantee EVM is by operating a transmitter in power backoff. However, this process leads to two major drawbacks. Firstly, the cell coverage of the transmitter is shrunken using this method and it is also noted that due to high SNR required by high-order modulation, the origin cell coverage is already quite small. After additional shrinking, the cell coverage will become too small to serve any user. Secondly, the efficiency of PA is decreased with this process. Normally, PA has higher efficiency for higher output power. Lower efficiency means higher heat dissipation and increased cooling cost. From sustainability perspective, power backoff is not a viable choice. There is still no other solution except power backoff that can meet the EVM requirement set by high-order modulation.

[0007] SUMMARY

[0008] Therefore, it is an object of embodiments herein to provide a transmitter arrangement with improved performance and efficiency.

[0009] According to one aspect of embodiments herein, the object is achieved by a transmitter arrangement for amplifying and transmitting an input signal X. The transmitter arrangement comprises a first transmit path configured to receive, process and amplify a first input signal Y. The first transmit path comprises a first digital predistortion (DPD) module, a first dig ital-to- analog converter (DAC) and a first power amplifier (PA). The first input signal Y is generated based on the input signal X to be transmitted.

[0010] The transmitter arrangement further comprises a second transmit path configured to receive, process and amplify a second input signal C. The second transmit path comprises a delay unit, an equalizer, a second DPD module, a second DAC and a second PA. The second input signal C is a cancellation signal generated based on the input signal X to be transmitted.

[0011] The transmitter arrangement further comprises a power combiner configured to combine output signals from the first and second transmit paths to generate an output signal for transmitting via an antenna.

[0012] The transmitter arrangement further comprises a transmitter observer path configured to be connected to either the first or second transmit paths to generate a feedback signal from either the output signal of the first transmit path or the output signal of the second transmit path or the output signal of the power combiner, for calculating coefficients of the first and second DPD modules and the equalizer.

[0013] According to some embodiments herein, the transmitter arrangement may further comprise a crest factor reduction (CFR) unit having a first output and a second output. The CFR unit is configured to generate the first and second input signals based on the input signal X. The CFR unit comprises a delay unit configured to delay the input signal X, a cancellation signal generator (CSG) configured to generate, at the second output of the CFR unit, the second input signal C based on the input signal X, the second input signal is a cancellation signal C. The CFR unit further comprises a combination unit configured to combine the delayed input signal X with the cancellation signal C to generate the first input signal Y at the first output of the CFR unit. The first input signal is a peak reduced signal compared to the input signal X.

[0014] According to some embodiments herein, the equalizer (EQ) may be a complex-valued finite impulse response filter, and the coefficient of the EQ is determined based on a difference between frequency responses of the first and second transmit paths to a training signal injected into the inputs of the first and second transmit paths during initializing of the transmitter arrangement or during time slots where no traffic data is transmitted by the transmitter arrangement.

[0015] According to some embodiments herein, the second transmitter path may be configured to be switched off for power saving when the input signal X to be transmitted does not contain 256-QAM or higher order QAM signal.

[0016] According to one aspect of embodiments herein, the object is achieved by a method performed by a transmitter arrangement for amplifying and transmitting an input signal X. The transmitter arrangement receives a first input signal Y from a CFR unit, by a first transmit path configured to process and amplify the first signal Y. The first transmit path comprises a first DPD module, a first DAC and a first PA. The first input signal Y is generated by the CFR unit based on the input signal X.

[0017] The transmitter arrangement receives a second input signal C from the CFR unit, by a second transmit path configured to process and amplify the second input signal C. The second transmit path comprises a delay unit, an equalizer, a second DPD module, a second DAC and a second PA. The second input signal C is a cancellation signal generated by the CFR unit based on the input signal X.

[0018] The transmitter arrangement generates, by a transmitter observer path configured to be connected to either the first or second transmit paths, a feedback signal from either an output signal of the first PA or an output signal of the second PA or an output signal of a power combiner configured to combine the output signals from the first and second PAs.

[0019] The transmitter arrangement calculates by a coefficient calculating unit, coefficient of the equalizer based on the feedback signal from the output signal of the power combiner and the input signals of the first or second transmit paths.

[0020] The transmitter arrangement calculates by the coefficient calculating unit, coefficients of the first and second DPD modules based on the feedback signals from the first and second PAs and the input signals of the first or second transmit paths. The transmitter arrangement generates an output signal by combining the output signals from the first and second PAs in the power combiner.

[0021] The transmitter arrangement transmits the output signal via an antenna.

[0022] In other words, the transmitter arrangement includes two transmit paths, i.e., the first path which is a main path and a second path which is an auxiliary path. The CFR unit outputs are not just the clipped signal, but also the cancellation signal. Then, these two signals are transmitted by the main path and the auxiliary path, respectively. After amplified by the two PAs, these two signals are combined, as a result the clipping error is largely mitigated. To obtain a superior performance, two transmit paths must be aligned perfectly. However, in the reality, the hardware impairments cannot be ignorable. To overcome this, an EQ is added at the auxiliary path to compensate the frequency-dependent differential errors. These errors include timing error, phase error and amplitude error. DPD modules are employed on both paths to remove the nonlinear distortions of the two PAs. To compute coefficients for the EQ and DPD modules, a shared transmitter observer path is used, which can reduce the hardware cost. Training signal is injected in the empty downlink (DL) slot and collected at the transmitter observer path. For example, in a first time slot, the training signal is injected at the main path and the transmitter observer path is connected to the main path, in a second time slot, the training signal is injected at the auxiliary path and the transmitter observer path is connected to the auxiliary path. The DPD modules are adapted in the normal downlink slot and their coefficients are calculated at the transmitter observer path. For examples, in a first time slot, the transmitter observer path is connected to the main path and the DPD module for the main path is updated, in a second time slot, the transmitter observer path is connected to the auxiliary path and the DPD module for the auxiliary path is updated. The auxiliary path can be turned on or off on demand, that results in lowest power consumption for additional function.

[0023] The proposed solution is proved by intensive lab experiments with real hardware implementation. The results show that with the proposed FF transmitter arrangement, the EVM measured at antenna port can meet the tough requirement set by the high-order modulation.

[0024] Embodiments herein provide some advantages, for examples:

[0025] Improving the signal quality to boost throughput of mobile networks.

[0026] Enabling high-order modulation without compromise to PA efficiency and output power. Add-on hardware cost is minimized.

[0027] Power consumption due to additional function is ignorable.

[0028] Implementable for 5G and 5G beyond (6G) compliant mobile networks. Therefore, embodiments herein provide an improved transmitter arrangement regarding performance and efficiency.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Examples of embodiments herein are described in more detail with reference to attached drawings in which:

[0031] Figure 1 is a schematic block diagram illustrating a transmit arrangement according to embodiments herein;

[0032] Figure 2 is a schematic diagram illustrating an example training signal injecting schedule according to embodiment herein;

[0033] Figure 3 is a schematic diagram illustrating another example training signal injecting schedule according to embodiment herein;

[0034] Figure 4 is a flow chart showing a method for amplifying and transmitting a signal according to embodiments herein; and

[0035] Figure 5 is a block diagram illustrating an electronic device / apparatus in which embodiments herein may be implemented.

[0036] DETAILED DESCRIPTION

[0037] Figure 1 shows a schematic block diagram of a transmitter arrangement 100 for amplifying and transmitting an input signal X according to embodiments herein.

[0038] The input signal X contains multiple carriers from 1 to N. For an orthogonal frequencydivision multiplexing (OFDM) system, the input signal X has high PAPR, that is unfortunately not friendly for PA. To improve the efficiency of PA, CFR is employed to generate a cancellation signal C to cancel the peaks of the input signal X. The obtained signal Y, i.e. , Y = X - C, thus has lower PAPR than the input signal X. However, CFR also introduces clipping error that degrades EVM. Lower PAPR means higher EVM, or vice versa. This is known as EVM and PAPR tradeoff. For high-order modulation, a trade-off aiming to both low EVM and low PAPR is hard to be established. To overcome this problem, Feedforward is employed in the transmitter arrangement 100 that recovers EVM without compromise with respect to PAPR.

[0039] As shown in Figure 1 , the transmitter arrangement 100 comprises a first transmit path 110 configured to receive, process and amplify a first input signal Y. The first transmit path 110 comprises a first digital predistortion (DPD) module DPD1 , a first digital-to-analog converter DAC1 and a first power amplifier PA1. The first input signal Y is generated based on the input signal X to be transmitted and is a peak reduced signal compared to the input signal X. The transmitter arrangement 100 further comprises a second transmit path 120 configured to receive, process and amplify a second input signal C. The second transmit path 120 comprises a delay unit DL2, an equalizer EQ, a second DPD module DPD2, a second digital-to-analog converter DAC2 and a second power amplifier PA2. The second input signal C is a cancellation signal generated based on the input signal X to be transmitted.

[0040] The transmitter arrangement 100 further comprises a power combiner 130 configured to combine output signals from the first and second transmit paths 110, 120 to generate an output signal Pout for transmitting via an antenna 160.

[0041] The transmitter arrangement 100 further comprises a transmitter observer path 150 configured to be connected to either the first or second transmit paths 110, 120 to generate a feedback signal FB from either the output signal of the first transmit path 110 or the output signal of the second transmit path 120 or the output signal of the power combiner 130, for calculating coefficients of the first and second DPD modules DPD1 , DPD2 and the equalizer EQ.

[0042] As can be seen, the transmitter arrangement 100 comprises two paths, i.e., the first transmit path 110 which is a main path and a second transmit path 120 which is an auxiliary path, transmitting the clipped signal Y and the cancellation signal C, respectively. Two signals are then combined at the antenna port by a combiner or a coupler 130. The coupler 130 with different coupling factors will serve a purpose as well. The coupling factor can even be used as parameter to tune the dimensions of the PAs in the auxiliary and main paths, which will improve the system flexibility of the transmitter arrangement 100. Hence, the clipping error generated in CFR can be removed. Ideally, if two paths are identical, the clipping error can be removed thoroughly, leading to an EVM-free transmitter. However, in practice, the hardware impairments cannot be ignored. In the digital domain, the C will cancel the clipping error and restore the signal to limits of the system resolution. However, the signal waveform restoration at the antenna port depends on the hardware impairments and resource allocation, especially for a transmitter arrangement with a wide-band setup. The selection of the combiner 130 and the signal alignment over frequency are essential for the system performance. For this purpose, delay unit DL2 and equalizer EQ are added in the second transmit path 120. Some hardware impairment compensators must be considered, specifically, EQ is added to the second path to compensate the frequency dependent differential error, and DPDs are added to both paths to compensate the nonlinear memory distortion of the PAs.

[0043] To acquire the coefficients for the DPDs and EQ, a shared transmitter observer path

[0044] 150 is employed, which can get the signal from the outputs of the first and second PAs at different time slots. By adding switches, the transmitter observer path 150 can be shared by two transmit paths.

[0045] The coefficients may be computed in a module and applied to the DPDs and EQ, respectively. The coefficients are also adapted to track the time variant behaviour of hardware impairments.

[0046] Therefore, according to some embodiments herein, the transmitter observer path 150 may comprise a first switch S1 configured to connect the transmitter observer path 150 to either the input Pin1 of the first transmitter path 110 or the input Pin2 of the second transmitter path 120, and a second switch S2 configured to connect the transmitter observer path 150 to either the output of the first transmitter path 110 or the output of the second transmitter path 120 or the output of the power combiner 130.

[0047] The transmitter observer path 150 may further comprise a coefficient calculating unit CCU configured to calculate coefficients of the first DPD module DPD1 , the second DPD module DPD2 and the equalizer EQ.

[0048] The transmitter observer path 150 may further comprise an attenuator ATT configured to attenuate an analog signal received from either the output of the first transmitter path 110 or the output of the second transmitter path 120 or the output of the power combiner 130 to a required level.

[0049] The transmitter observer path 150 may further comprise an analog to digital converter ADC configured to convert the attenuated analog signal to a digital signal.

[0050] The transmitter observer path 150 may further comprise a compensation unit COMP configured to compensate phase and amplitude of the digital signal to generate the feedback signal FB.

[0051] To generate the clipped signal Y and the cancellation signal C, i.e. the first and second input signals, the transmitter arrangement 100 further comprises a CFR unit 140 having a first output and a second output. The CFR unit 140 is configured to generate the first and second input signals based on the input signal X.

[0052] The CFR unit 140 may comprise a delay unit DL1 configured to delay the input signal X.

[0053] The CFR unit 140 may further comprise a cancellation signal generator CSG configured to generate, at the second output of the CFR unit 140, the second input signal C based on the input signal X.

[0054] The CFR unit 140 may further comprise a combination unit 141 configured to combine the delayed input signal X with the cancellation signal C to generate the first input signal Y at the first output of the CFR unit 140. The first input signal is a peak reduced signal compared to the input signal X.

[0055] In the following, the generation of the first and second input signals, i.e. the clipped signal Y and the cancellation signal C, as well as the coefficients calculations for EQ and DPDs will be described respectively.

[0056] CFR is used to reduce the PAPR of an input signal X to be transmitted. In general, CFR function can be expressed as

[0057] Y = X - C,

[0058] Here, X, Y and C denote the input signal, the clipped signal, and the cancellation signal, respectively. A denotes the clipping threshold. |X| and (X) represent amplitude and phase of X, respectively. There are several CFR methods and any of them can be straightforwardly employed in the proposed FF transmitter arrangement 100.

[0059] In a traditional transmitter, only the clipped signal Y is needed from CFR. However, in the proposed FF transmitter arrangement 100, both signals are used. Due to that there are two outputs from the CFR unit 140, one connecting to the main transmit path for the clipped signal, another one connecting to the auxiliary transmit path for the cancellation signal.

[0060] To cancel the clipping error, two signals must be perfectly aligned at the combiner, even passing through two different paths. In reality, it is hard to build two paths that are exactly identical. The errors such as timing error, phase error and amplitude error between two paths are inevitable. Meanwhile, these errors are frequency-dependent, that means the errors are varying with different frequencies. To overcome this, an equalizer EQ is employed at the auxiliary path to compensate these frequency-dependent differential errors.

[0061] The EQ may be implemented by a complex-valued finite impulse response (FIR) filter. The coefficient of the equalizer EQ may be determined based on a difference between frequency responses of the first and second transmit paths 110, 120 to a training signal injected into the inputs of the first and second transmit paths 110, 120 during initializing of the transmitter arrangement 100 or during time slots where no traffic data is transmitted by the transmitter arrangement 100.

[0062] The FIR function can be expressed as

[0063] Here, c, z and wEQdenote the input, the output, and the coefficient of EQ, respectively. To compute the coefficient, injecting a training signal S at the output of the CFR unit 140, that is

[0064] Y = S at time slot TS1 ,

[0065] C = S at time slot TS2.

[0066] The training signal is injected at the inputs Pin 1 / Pin2 of the first and second transmit paths 110 / 120 during different time slots. The training signal is designed by OFDM with low PAPR, therefore no clipping occurs on it.

[0067] To avoid the interference from and to the DL traffic data, the training signal is injected when the traffic data is empty. The scheme of such training signal injection is illustrated in Figure 2. The training signal is injected at the input Pin 1 of the first transmit path 110 during a first time slot TS1 when the coefficient calculating unit CCU in the transmitter observer path 150 is connected to the input of the first transmit path 110, and the same training signal is injected at the input Pin2 of the second transmit path 120 during a second time slot TS2 when the coefficient calculating unit CCU in the transmitter observer path 150 is connected to the input of the second transmit path 120, and the output Pout of the power combiner 130 is coupled to the transmitter observer path 150 during the first and second time slots.

[0068] There are two signals received at the second switch S2 of the transmitter observer path 150 at the first time slot TS1 and the second time slot TS2, denoted by ffmainand RaUx, respectively. As shown in Figure 1 , the transmitter observer path 150 is employed to monitor any one of the outputs of PA1 , PA2 and the combiner 130, and provide a feedback signal for coefficient computation. The attenuator ATT is used to fit the input power of the ADC, the compensation unit COMP is used to compensate phase and amplitude of the digital signal of the ADC to generate the feedback signal FB.

[0069] Based on the injected training signal S and the received signals ffmainand RaUx, the frequency responses of two paths can be calculated by

[0070] Here, k represents the subcarrier index of the OFDM modulated training signal S. The bandwidth of S should be able to cover entire frequency region of interest. In EQ, the difference between two paths is

[0071] Once H(k) is obtained, the coefficient of EQ can be derived by minimizing the objective function of

[0072] The equation can be solved by least-squares (LS) method.

[0073] DPD is employed to compensate the nonlinearity and memory effects of PA. There are several DPD models, for sake of compactness, generalized memory polynomial (GMP) is used here as an example. The first DPD module for the main path can be expressed as

[0074] Here, at, dtrepresent address delay and data delay of filter tap i, respectively, p is the polynomial order and wPPDdenotes the coefficient of main DPD. Similarly, the second DPD module can be written as y(n) and y(n) are input and output of the first DPD module, z(n) and z(r) are input and output of the second DPD module.

[0075] The coefficients of DPDs are computed based on the traffic data. As shown in Figure 3, there are two time slots. In the first time slot TS1 , the transmitter observer path 150 is connected to the first path to derive the coefficient of first DPD module; In the second time slot TS2, the transmitter observer path 150 is connected to the auxiliary path to derive the coefficient of second DPD module.

[0076] The goal of DPD is to minimize the squared error between the input signal of DPD and the output signal of PA. These can be expressed as

[0077] Here, PA±and PA2represent the behavior of first PA and second PA, respectively. Similarly, the equations can be solved by LS method as well.

[0078] Therefore, according to embodiments herein, the coefficients of the first and second DPD modules DPD1 , DPD2 are determined during transmitting traffic data by the transmitter arrangement 100.

[0079] The coefficient of the first DPD module DPD1 is determined during a first time slot when the transmitter observer path 150 is connected to the first transmit path 110, and the coefficient of the second DPD module DPD2 is determined during a second time slot when the transmitter observer path 150 is connected to the second transmit path 120. The coefficients of the first and second DPD modules DPD1 , DPD2 are determined based on the input signals to the inputs of the first and second transmitter paths 110, 120 and the feedback signals from the outputs of the first and second transmitter paths 110, 120 respectively.

[0080] The second transmit path 120 may consume additional power in the transmitter arrangement 100, that may not be acceptable because power consumption becomes more important for radio products due to the target carbon emission. The second transmit path 120 can be turned on / off according to the traffic data. For instance, the second transmit path 120 can be enabled only if the OFDM symbol contains high-order modulation, e.g, 256-QAM or 1024-QAM. In the case of low-order modulation, the first transmit path 110 is good enough to meet the requirements. During this period, the second transmit path 120 can be turned off. Furthermore, the second transmit path 120 can be enabled only for high traffic mode. For low traffic mode, since there is no cancellation signal generated from the CFR 140, the second transmit path 120 can be turned off accordingly. Considering high traffic mode with high- order modulation does not occur frequently, with these features, the additional power consumption due to the second transmit path 120 is indeed trivial. In addition, to compute the coefficients of EQ and DPDs, the training signal may be injected. Note that the training signal is designed by OFDM with low PAPR, therefore it is not clipped and can be linearly amplified.

[0081] A method performed by the transmitter arrangement 100 for amplifying and transmitting an input signal X will be described with reference to Figure 4. The method comprises the following Actions or steps which may be performed in any suitable order and performed online during operating of the transmitter arrangement 100.

[0082] Action 410

[0083] The transmitter arrangement 100 receives a first input signal Y from the crest factor reduction (CFR) unit 140, by the first transmit path (110). The first input signal Y is generated by the CFR unit 140 based on the input signal X.

[0084] Action 420

[0085] The transmitter arrangement 100 receives a second input signal C from the CFR unit 140, by the second transmit path 120. The second input signal C is a cancellation signal generated by the CFR unit 140 based on the input signal X.

[0086] Action 430

[0087] The transmitter arrangement 100 generates by the transmitter observer path 150, a feedback signal FB from either an output signal of the first power amplifier PA1 or an output signal of the second power amplifier PA2 or an output signal of the power combiner 130. Action 440

[0088] The transmitter arrangement 100 calculates by the coefficient calculating unit CCU, coefficient of the equalizer EQ based on the feedback signal FB from the output signal of the power combiner 130 and the input signals of the first or second transmit paths 110, 120.

[0089] The calculating of the coefficient of the equalizer EQ may be performed during initializing of the transmitter arrangement 100 or during time slots where no traffic data is transmitted by the transmitter arrangement 100.

[0090] The calculating of the coefficient of the equalizer (EQ) may comprise the following actions:

[0091] Action 441 : connecting the transmitter observer path 150 to the output of the power combiner 130.

[0092] Action 442: connecting the coefficient calculating unit CCU comprised in the transmitter observer path 150 to the input of the first transmit path 110 during a first time slot.

[0093] Action 443: injecting a training signal to the input Pin 1 of the first transmit path 110 during the first time slot.

[0094] Action 444: calculating a frequency response of the first transmit path (110) to the training signal.

[0095] Action 445: connecting the coefficient calculating unit CCU comprised in the transmitter observer path 150 to the input of the second transmit path 120 during a second time slot.

[0096] Action 446: injecting the same training signal to the input Pin2 of the second transmit path 120 during the second time slot.

[0097] Action 447: calculating a frequency response of the second transmit path 120 to the training signal.

[0098] Action 448: calculating the coefficient of the equalizer EQ based on a difference between the frequency responses of the first and second transmit paths to the training signal.

[0099] Action 450

[0100] The transmitter arrangement 100 calculates by the coefficient calculating unit CCU, coefficients of the first and second DPD modules DPD1 , DPD2 based on the feedback signals FB from the first and second power amplifiers and the input signals of the first or second transmit paths 110, 120.

[0101] The calculating of the coefficients of the first and second DPD modules DPD1 , DPD2 may be performed during traffic data transmitting. The calculating of the coefficients of the first and second DPD modules DPD1 , DPD2 may comprise the following actions:

[0102] Action 451 : connecting the transmitter observer path 150 to the first transmit path 110 during a first time slot.

[0103] Action 452: calculating a difference between the input and output signals of the first transmit path 110.

[0104] Action 453: determining the coefficient of the first DPD module DPD1 based on the difference between the input and output signals of the first transmit path 110.

[0105] Action 454: connecting the transmitter observer path 150 to the second transmit path 120 during a second time slot.

[0106] Action 455: calculating a difference between the input and output signals of the second transmit path 120.

[0107] Action 456: determining the coefficient of the second DPD module DPD2 based on the difference between the input and output signals of the second transmit path 120.

[0108] Action 460

[0109] The transmitter arrangement 100 generates an output signal Pout by combining the output signals from the first and second power amplifiers in the power combiner 130.

[0110] Action 470

[0111] The transmitter arrangement 100 transmits the output signal Pout via the antenna 160.

[0112] To summarize, the transmitter arrangement 100 according to embodiments herein comprises two transmit paths 110, 120 and one transmitter observer path 150. The CFR unit 140 outputs two signals, one clipped signal and one cancellation signal. These two signals are transmitted by the two transmit paths, respectively. After amplified by the two PAs, these two signals are combined and as a result the clipping error is largely mitigated. The equalizer EQ is used to compensate the frequency-dependent differential errors between two transmit paths. DPD modules are employed on both paths to remove the nonlinear distortions of the two PAs. The transmitter observer path is shared which can reduce the hardware cost. The second transmit path can be turned on or off on demand, that results in lowest power consumption for additional function. Training signal is injected in the empty downlink (DL) slot and collected at the transmitter observer path 150 for calculating the coefficients of the EQ. The two DPD modules are adapted in the normal downlink slot.

[0113] It is verified by intensive lab experiments with real hardware implementation that by utilizing the proposed FF transmitter arrangement 100, the EVM can be significantly improved. The results show that with the proposed FF transmitter arrangement 100, the EVM measured at antenna port can meet the tough requirement set by the high-order modulation. The efficiency degradation due to the second transmit path is ignorable. The proposed method is suitable for scenarios which need high quality transmit signal, such as high throughput empowered by high-order modulation.

[0114] Embodiments herein provide some advantages, for examples:

[0115] Improving signal quality and therefore boost throughput of mobile networks using transmitter arrangement 100.

[0116] Enabling high-order modulation without compromise to PA efficiency and output power. Add-on hardware cost is minimized.

[0117] Power consumption due to additional function is ignorable.

[0118] Implementable for 5G and 5G beyond (6G) compliant mobile networks.

[0119] The transmitter arrangement 100 according to embodiments herein may be employed in various electronic devices or apparatus etc. Figure 5 shows a block diagram for an electronic device or apparatus 500. The electronic device or apparatus 500 comprises a transmitter arrangement 100 according to embodiments herein. The electronic device 500 may be a base station, a mobile device, a user equipment, a wireless communication device, a radar for a communication system. The electronic device 500 may comprise other units, where a memory 520, a processing unit 530 are shown. The memory 520 in the electronic device 500 may comprise one or more memory units and may be arranged to be used to store information, measurements, data, parameters, configurations to perform the methods herein when being executed in the electronic device 500.

[0120] The embodiments herein for amplifying and transmitting an input signal X may be implemented through one or more processors, such as the processing unit 530 in the electronic device 500, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product 540, for instance in the form of a data carrier carrying computer program code 550 for performing the embodiments herein when being loaded into the electronic device 500. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server or cloud and downloaded to the electronic device 500.

[0121] Therefore, according to some embodiments herein, it is provided a computer program product 540 comprising program code 550 which when the program is executed by a computer / processor in the the electronic device 500, cause the computer / processor to carry out the method for amplifying and transmitting an input signal X by the transmitter arrangement (100) according to embodiments herein.

[0122] The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Those skilled in the art will understand that the transmitter arrangement 100 according to embodiments herein may be implemented in Printed Circuit Board with discreate transistors or any semiconductor technology, e.g. Bi-polar, N-type Metal Oxide Semiconductor (NMOS), P-type Metal Oxide Semiconductor (PMOS), Complementary Metal Oxide Semiconductor (CMOS), Silicon on Insulator (SOI) CMOS, field-effect transistor (PET), MOSFET technology etc.

[0123] Those skilled in the art will also appreciate that the first and second transmitter paths 110, 120, the power combiner 130, the transmitter observer path 150, the CFR unit 140 described above for the transmitter arrangement 100, may be referred to as one circuit or one module, a combination of analog and digital circuits, one or more processors configured with software and / or firmware and / or any other digital hardware performing the function of each module. One or more of these processors, the combination of analog and digital circuits as well as the other digital hardware, may be included in a single application-specific integrated circuitry (ASIC), or several processors and various analog / digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

[0124] When using the word "comprise" or “comprising” it shall be interpreted as non-limiting, i.e. meaning "consist at least of". Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appended claims.

Claims

Claims1 . A transmitter arrangement (100) for amplifying and transmitting an input signal ( ), wherein the transmitter arrangement (100) comprises: a first transmit path (110) configured to receive, process and amplify a first input signal (T), wherein the first transmit path (110) comprises a first digital predistortion, DPD, module (DPD1 ), a first digital-to-analog converter (DAC1 ) and a first power amplifier (PA1 ), and wherein the first input signal (T) is generated based on the input signal ( ) to be transmitted; a second transmit path (120) configured to receive, process and amplify a second input signal (C), wherein the second transmit path (120) comprises a delay unit (DL2), an equalizer (EQ), a second DPD module (DPD2), a second digital-to-analog converter (DAC2) and a second power amplifier (PA2), and wherein the second input signal (C) is a cancellation signal generated based on the input signal (X) to be transmitted; a power combiner (130) configured to combine output signals from the first and second transmit paths (110, 120) to generate an output signal (Pout) for transmitting via an antenna (160); a transmitter observer path (150) configured to be connected to either the first or second transmit paths (1 10, 120) to generate a feedback signal (FB) from either the output signal of the first transmit path (110) or the output signal of the second transmit path (120) or the output signal of the power combiner (130), for calculating coefficients of the first and second DPD modules (DPD1 , DPD2) and the equalizer (EQ).

2. The transmitter arrangement (100) according to claim 1 , wherein the transmitter observer path (150) comprises: a first switch (S1 ) configured to connect the transmitter observer path (150) to either the input (Pin 1 ) of the first transmitter path (1 10) or the input (Pin2) of the second transmitter path (120); a second switch (S2) configured to connect the transmitter observer path (150) to either the output of the first transmitter path (1 10) or the output of the second transmitter path (120) or the output of the power combiner (130); a coefficient calculating unit (CCU) configured to calculate coefficients of the first DPD module (DPD1 ), the second DPD module (DPD2) and the equalizer (EQ); an attenuator (ATT) configured to attenuate an analog signal received from either the output of the first transmitter path (1 10) or the output of the second transmitter path (120) or the output of the power combiner (130) to a required level;an analog to digital converter (ADC) configured to convert the attenuated analog signal to a digital signal; a compensation unit (COMP) configured to compensate phase and amplitude of the digital signal to generate the feedback signal (FB).

3. The transmitter arrangement (100) according to any one of claims 1 -2, further comprises a crest factor reduction, CFR, unit (140) having a first output and a second output, and wherein the CFR unit (140) is configured to generate the first and second input signals based on the input signal (X), and wherein the CFR unit (140) comprises: a delay unit (DL1 ) configured to delay the input signal ( ); a cancellation signal generator (CSG) configured to generate, at the second output of the CFR unit (140), the second input signal (C) based on the input signal (X), wherein the second input signal is a cancellation signal (C); a combination unit (141 ) configured to combine the delayed input signal (X) with the cancellation signal (C) to generate the first input signal (T) at the first output of the CFR unit (140), wherein the first input signal is a peak reduced signal compared to the input signal (X).

4. The transmitter arrangement (100) according to any one of claims 1 -3, wherein the equalizer (EQ) is a complex-valued finite impulse response filter, and the coefficient of the equalizer (EQ) is determined based on a difference between frequency responses of the first and second transmit paths to a training signal injected into the inputs of the first and second transmit paths during initializing of the transmitter arrangement (100) or during time slots where no traffic data is transmitted by the transmitter arrangement (100).

5. The transmitter arrangement (100) according to claim 4, wherein the training signal is injected at the input (Pin 1 ) of the first transmit path (110) during a first time slot when the coefficient calculating unit (CCU) in the transmitter observer path (150) is connected to the input of the first transmit path (110), and the same training signal is injected at the input (Pin2) of the second transmit path (120) during a second time slot when the coefficient calculating unit (CCU) in the transmitter observer path (150) is connected to the input of the second transmit path (120), and the output (Pout) of the power combiner (130) is coupled to the transmitter observer path (150) during the first and second time slots.

6. The transmitter arrangement (100) according to any one of claims 1 -5, wherein the coefficients of the first and second DPD modules (DPD1 , DPD2) are determined during transmitting traffic data by the transmitter arrangement (100) and the coefficient of the first DPD module (DPD1 ) is determined during a first time slot when the transmitter observer path (150) is connected to the first transmit path (110), and the coefficient of the second DPD module (DPD2) is determined during a second time slot when the transmitter observer path (150) is connected to the second transmit path (120).

7. The transmitter arrangement (100) according to claim 6, wherein the coefficients of the first and second DPD modules (DPD1 , DPD2) are determined based on the input signals to the inputs of the first and second transmitter paths (110, 120) and the feedback signals from the outputs of the first and second transmitter paths (110, 120) respectively.

8. The transmitter arrangement (100) according to any one of claims 1 -5, wherein the second transmitter path (120) is configured to be switched off for power saving when the input signal (X) to be transmitted does not contain 256 or higher order Quadrature Amplitude Modulation, QAM, signal.

9. An electronic device (500) comprising a transmitter arrangement (100) according to any one of claims 1-8.

10. The electronic device (500) according to claim 9 is any one of a base station, a mobile device, a user equipment, a wireless communication device for a communication system.11 . A method performed by a transmitter arrangement (100) for amplifying and transmitting an input signal ( ), the method comprising: receiving (410) a first input signal (T) from a crest factor reduction, CFR, unit (140), by a first transmit path (110) configured to process and amplify the first signal (T), wherein the first transmit path (110) comprises a first digital predistortion, DPD, module (DPD1 ), a first digital-to-analog converter (DAC1) and a first power amplifier (PA1 ), and wherein the first input signal (T) is generated by the CFR unit (140) based on the input signal (X); receiving (420) a second input signal (C) from the CFR unit (140), by a second transmit path (120) configured to process and amplify the second input signal (C),wherein the second transmit path (120) comprises a delay unit (DL2), an equalizer (EQ), a second DPD module (DPD2), a second digital-to-analog converter (DAC2) and a second power amplifier (PA2), and wherein the second input signal (C) is a cancellation signal generated by the CFR unit (140) based on the input signal ( ); generating (430) by a transmitter observer path (150) configured to be connected to either the first or second transmit paths (110, 120), a feedback signal (FB) from either an output signal of the first power amplifier (PA1) or an output signal of the second power amplifier (PA2) or an output signal of a power combiner (130) configured to combine the output signals from the first and second power amplifiers; calculating (440) by a coefficient calculating unit (CCU), coefficient of the equalizer (EQ) based on the feedback signal (FB) from the output signal of the power combiner (130) and the input signals of the first or second transmit paths (110, 120); calculating (450) by the coefficient calculating unit (CCU), coefficients of the first and second DPD modules (DPD1 , DPD2) based on the feedback signals (FB) from the first and second power amplifiers and the input signals of the first or second transmit paths (110, 120); generating (460) an output signal (Pout) by combining the output signals from the first and second power amplifiers in the power combiner (130); and transmitting (470) the output signal (Pout) via an antenna (160).

12. The method according to claim 11 , wherein calculating (440) the coefficient of the equalizer (EQ) comprises: connecting (441) the transmitter observer path (150) to the output of the power combiner (130); connecting (442) the coefficient calculating unit (CCU) comprised in the transmitter observer path (150) to the input of the first transmit path (110) during a first time slot; injecting (443) a training signal to the input (Pin 1 ) of the first transmit path (110) during the first time slot; calculating (444) a frequency response of the first transmit path (110) to the training signal; connecting (445) the coefficient calculating unit (CCU) comprised in the transmitter observer path (150) to the input of the second transmit path (120) during a second time slot; injecting (446) the same training signal to the input (Pin2) of the second transmit path (120) during the second time slot;calculating (447) a frequency response of the second transmit path (120) to the training signal; calculating (448) the coefficient of the equalizer (EQ) based on a difference between the frequency responses of the first and second transmit paths to the training signal.

13. The method according to claim 12, wherein calculating (440) the coefficient of the equalizer (EQ) is performed during initializing of the transmitter arrangement (100) or during time slots where no traffic data is transmitted by the transmitter arrangement (100).

14. The method according to any one of claims 11 -13, wherein calculating (450) the coefficients of the first and second DPD modules (DPD1 , DPD2) comprising: connecting (451) the transmitter observer path (150) to the first transmit path (110) during a first time slot; calculating (452) a difference between the input and output signals of the first transmit path (110); determining (453) the coefficient of the first DPD module (DPD1 ) based on the difference between the input and output signals of the first transmit path (110); connecting (454) the transmitter observer path (150) to the second transmit path (120) during a second time slot; calculating (455) a difference between the input and output signals of the second transmit path (120); determining (456) the coefficient of the second DPD module (DPD2) based on the difference between the input and output signals of the second transmit path (120).

15. The method according to claim 14, wherein calculating (450) the coefficients of the first and second DPD modules (DPD1 , DPD2) is performed during traffic data transmitting.

16. A computer program product (540) comprising program code (550) which when the program is executed by a computer / processor, cause the computer / processor to carry out the method for amplifying and transmitting an input signal (X) by a transmitter arrangement (100) according to any one of the claims 11-15.

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