Output-Controllable Partial Inverse Digital Predistortion for RF Power Amplifiers
02 Oct 2014-IEEE Transactions on Microwave Theory and Techniques (IEEE)-Vol. 62, Iss: 11, pp 2499-2510
TL;DR: The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization.
Abstract: In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to user's demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.
Citations
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TL;DR: In this paper, a novel decorrelation-based concurrent digital predistortion (DPD) solution is proposed for dual-band transmitters employing a single wideband power amplifier (PA), and utilizing only a single feedback receiver path.
Abstract: In this paper, a novel decorrelation-based concurrent digital predistortion (DPD) solution is proposed for dual-band transmitters (TXs) employing a single wideband power amplifier (PA), and utilizing only a single feedback receiver path. The proposed decorrelation-based parameter learning solution is both flexible and simple, and operates in a closed-loop manner, opposed to the widely applied indirect learning architecture. The proposed decorrelation-based learning and DPD processing can also be effectively applied to more ordinary single carrier/band transmissions, as well as generalized to more than two transmit bands. Through a comprehensive analysis covering both the DPD parameter learning and the main path processing, it is shown that the complexity of the proposed concurrent DPD is substantially lower compared with the other state-of-the-art concurrent DPD methods. Extensive set of simulation and RF measurement results are also presented, using base-station PAs as well as a commercial LTE-Advanced mobile PA, to evaluate and validate the effectiveness of the proposed DPD solution in various real world scenarios, incorporating both single-band and dual-band TX cases. The simulation and RF measurement results demonstrate excellent linearization performance of the proposed concurrent DPD, even outperforming current state-of-the-art methods, despite the significantly lower complexity.
24 citations
TL;DR: Experimental results demonstrated that excellent suppression performance can be achieved with very low implementation complexity by employing the proposed GDES distortion model structure.
Abstract: In this paper, a generalized dual-basis envelope-dependent sideband (GDES) distortion model structure is proposed to compensate the distortion induced by transmitter leakage in concurrent multi-band transceivers with non-contiguous carrier aggregation. This model has a generalized structure that is constructed via first generating a nonlinear basis function that maps the inputs to the target frequency band where the distortion is to be cancelled, and then multiplying with a second basis function that generates envelope-dependent nonlinearities. By combining these two bases, the model keeps in a relatively compact form that can be flexibly implemented in digital circuits such as field programmable gate array (FPGA). Experimental results demonstrated that excellent suppression performance can be achieved with very low implementation complexity by employing the proposed model.
20 citations
Cites background from "Output-Controllable Partial Inverse..."
...Because of low cost and great accuracy, digital predistortion (DPD) [4]–[10] in the transmitter has been widely employed to remove the sideband distortion....
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DOI•
22 Nov 2015TL;DR: A novel digital predistorter based on the Hammerstein structure has been proposed for linearization of radio frequency power amplifiers with memory effect and is implemented in Kintex FPGA using Vivado HLS and acceptable results have been obtained.
Abstract: Power amplifiers (PAs) are inherently nonlinear elements and digital predistortion is a highly cost- effective approach to linearize them. Although most existing architectures assume that the PA has a memoryless nonlinearity, memory effects of the PAs in many applications ,such as wideband code-division multiple access (WCDMA) or orthogonal frequency-division multiplexing (OFDM), can no longer be ignored and memoryless predistortion has limited effectiveness. In this paper, a novel digital predistorter based on the Hammerstein structure has been proposed for linearization of radio frequency power amplifiers with memory effect. Designing the Hammerstein model based digital predistorter has been done using an accurate Wiener model of the power amplifier. The proposed digital predistorter has many advantages such as low computational complexity, low memory space and simple implementation. The elimination of nonlinear effects and constructing accurate behavioral model, which is the exact inverse of a power amplifier characteristic, have been demonstrated by simulating 64 QAM constellation diagram in Matlab. In order to validate the proposed predistorter, it is implemented in Kintex FPGA using Vivado HLS and acceptable results have been obtained.
9 citations
Cites methods from "Output-Controllable Partial Inverse..."
...More recently, many of DPD models have been spread and the usage of the DPD linearization technique has been widely employed to linearize the power amplifier in the advanced radio transmitter [7]-[9]....
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...This method is one of the most wellknown digitally assistant analog approaches in the analog circuit design [7]....
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TL;DR: The experimental results for 30-W Class F PA and 40-W GaN Doherty PA with 40-MHz orthogonal frequency division multiplexing signal and 60-MHz long-term evolution signal have shown the superiority of the modified band-limited DPD.
Abstract: In this letter, a modified band-limited digital predistortion (DPD) technique is proposed to improve the performance of the conventional band-limited DPD method in wideband systems. The power amplifier’s (PA’s) spectral regrowth outside the passband of bandpass filter is unable to be compensated using the traditional band-limited DPD. To increase the overall linearized bandwidth and reduce the requirement for feedback signal path, this new technique introduced two modules of full-band model extraction and coefficient iteration based on the conventional structures of band-limited DPD. It provides higher linearization performance and also reduces the sampling rate of analog-to-digital converter. The experimental results for 30-W Class F PA and 40-W GaN Doherty PA with 40-MHz orthogonal frequency division multiplexing signal and 60-MHz long-term evolution signal, respectively, have shown the superiority of the modified band-limited DPD.
8 citations
Cites methods from "Output-Controllable Partial Inverse..."
...There is also an effective method for wideband DPD implementation to build a band-limited model (BLM) based on Volterra series [4], [5]....
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TL;DR: A new digital suppression model is proposed to cancel the TX leakage at baseband with a low sampling rate, based on the modified decomposed vector rotation model, and with the addition of cross-term products, the enhanced model is capable of eliminating the aliasing effect arising from the reduced sampling rate.
Abstract: The transmitter (TX)-induced interference due to power amplifier nonlinearities poses severe desensitization problems to the receiver chain in frequency-division duplexing transceivers. Due to nonlinear signal process involved, a high sampling rate is normally required in the existing digital suppression approaches, which can result in high cost and high power consumption in wideband systems. In this paper, a new digital suppression model is proposed to cancel the TX leakage at baseband with a low sampling rate. The cancellation model is based on the modified decomposed vector rotation model. With the addition of cross-term products, the enhanced model is capable of eliminating the aliasing effect arising from the reduced sampling rate. Theoretical analysis of aliasing elimination is presented, and the algorithm is subsequently verified by both simulation and experiment results, confirming the effectiveness and feasibility of the proposed cancellation technique for TX leakage suppression. Compared with conventional solutions, the new approach uses much less hardware resource and consumes much lower power while achieving comparable performance.
6 citations
References
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TL;DR: This paper relates the general Volterra representation to the classical Wiener, Hammerstein, Wiener-Hammerstein, and parallel Wiener structures, and describes some state-of-the-art predistortion models based on memory polynomials, and proposes a new generalizedMemory polynomial that achieves the best performance to date.
Abstract: Conventional radio-frequency (RF) power amplifiers operating with wideband signals, such as wideband code-division multiple access (WCDMA) in the Universal Mobile Telecommunications System (UMTS) must be backed off considerably from their peak power level in order to control out-of-band spurious emissions, also known as "spectral regrowth." Adapting these amplifiers to wideband operation therefore entails larger size and higher cost than would otherwise be required for the same power output. An alternative solution, which is gaining widespread popularity, is to employ digital baseband predistortion ahead of the amplifier to compensate for the nonlinearity effects, hence allowing it to run closer to its maximum output power while maintaining low spectral regrowth. Recent improvements to the technique have included memory effects in the predistortion model, which are essential as the bandwidth increases. In this paper, we relate the general Volterra representation to the classical Wiener, Hammerstein, Wiener-Hammerstein, and parallel Wiener structures, and go on to describe some state-of-the-art predistortion models based on memory polynomials. We then propose a new generalized memory polynomial that achieves the best performance to date, as demonstrated herein with experimental results obtained from a testbed using an actual 30-W, 2-GHz power amplifier
1,305 citations
TL;DR: A memory polynomial model for the predistorter is proposed and implemented using an indirect learning architecture and linearization performance is demonstrated on a three-carrier WCDMA signal.
Abstract: Power amplifiers (PAs) are inherently nonlinear devices and are used in virtually all communications systems. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored, and memoryless predistortion has limited effectiveness. In this paper, instead of focusing on a particular PA model and building a corresponding predistorter, we focus directly on the predistorter structure. In particular, we propose a memory polynomial model for the predistorter and implement it using an indirect learning architecture. Linearization performance is demonstrated on a three-carrier WCDMA signal.
1,160 citations
"Output-Controllable Partial Inverse..." refers methods in this paper
...The indirect learning [19], [20], also referred to as the th-order inverse [16], is based on the assumption that the th-order pre-inverse of the system is identical to its th-order post-inverse if linearized up to th-order nonlinearities....
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TL;DR: In this paper, memory effects in the power amplifier limit the performance of digital predistortion for wideband signals, and novel algorithms that take into account such effects are proposed to solve the problem.
Abstract: Memory effects in the power amplifier limit the performance of digital predistortion for wideband signals. Novel algorithms that take into account such effects are proposed. Measured results are presented for single and multicarrier UMTS signals to demonstrate the effectiveness of the new approach.
934 citations
"Output-Controllable Partial Inverse..." refers background in this paper
...Many DPD models have been developed in the past decades, and DPD is widely employed in modern wireless communication systems [1]–[5] today....
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TL;DR: This work presents a new Volterra-based predistorter, which utilizes the indirect learning architecture to circumvent a classical problem associated with predistorters, namely that the desired output is not known in advance.
Abstract: Nonlinear compensation techniques are becoming increasingly important. We present a new Volterra-based predistorter, which utilizes the indirect learning architecture to circumvent a classical problem associated with predistorters, namely that the desired output is not known in advance. We utilize the indirect learning architecture and the recursive least square (RLS) algorithm. Specifically, we propose an indirect Volterra series model predistorter which is independent of a specific nonlinear model for the system to be compensated. Both 16-phase shift keying (PSK) and 16-quadrature amplitude modulation (QAM) are used to demonstrate the efficacy of the new approach.
549 citations
"Output-Controllable Partial Inverse..." refers background or methods in this paper
...The indirect learning [19], [20], also referred to as the th-order inverse [16], is based on the assumption that the th-order pre-inverse of the system is identical to its th-order post-inverse if linearized up to th-order nonlinearities....
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...The nonlinearity injection function is directly related to the PA linearity and power efficiency....
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TL;DR: A software digital predistortion solution that enables closed-loop wideband linearization was briefly presented with excellent linearization capabilities when amplifying a 12-carrier 60-MHZ wide WCDMA signal.
Abstract: In this article, a thorough overview of behavioral modeling and predistortion of dynamic nonlinearities in RF PAs and transmitters was presented. The sensitivity of the DUT behavior to the characteristics of the stimulus was reviewed to ensure appropriate conditions for accurate observation. Nearly all state-of-the-art behavioral models were described and their relative performance and complexity discussed. Similarities and specifics of behavioral modeling and digital predistortion were presented. Thereby, digital predistortion can be seen as a behavioral modeling problem for which performance assessment is much more straightforward. For DUT behavioral modeling, there is no comprehensive metric that allows the model performance evaluation while taking into account the model accuracy in predicting all the three components of the DUT behavior (in-band distortion, static nonlinearity and memory effects). Finally, a software digital predistortion solution that enables closed-loop wideband linearization was briefly presented with excellent linearization capabilities when amplifying a 12-carrier 60-MHZ wide WCDMA signal.
467 citations