Wide band digital predistortion using iterative feedback decomposition
01 Jul 2019-Analog Integrated Circuits and Signal Processing (Springer US)-Vol. 100, Iss: 1, pp 93-108
TL;DR: The proposed digital predistortion technique has almost the same performance as the other methods with an ACPR of − 60 dB and reduces considerably the constraints on the ADC and the power calculation resources.
Abstract: This paper presents a new digital predistortion (DPD) technique for wide band applications. Digital predistortion is the most useful linearization technique to reduce power amplifier (PA) nonlinearity effects due to its high flexibility and low complexity. However, this technique requires high performances ADC to digitize the feedback signal whose bandwidth is equal to several times the original bandwidth due to spectral regrowth generated by the PA nonlinearity. This point represents one of the main bottlenecks for the deployment of the wideband LTE-A standard. The method proposed in this paper calculates the DPD coefficients iteratively using an ADC with a fixed bandwidth equal to the original bandwidth. The proposed method has been simulated and compared with other methods using Matlab. Simulation results show that the proposed method has almost the same performance as the other methods with an ACPR of − 60 dB. Moreover, it reduces considerably the constraints on the ADC and the power calculation resources.
Citations
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TL;DR: The development of complex-valued three-layer perceptrons suitable for concurrent-dual band DPDs and the introduction of a modified indirect approach to improve the accuracy of previous direct and indirect learnings are contributions.
Abstract: Current radio communication systems that adopt amplitude and phase modulations demand high linearity and high efficiency. The cascade connection between digital baseband pre-distorter (DPD) and power amplifier (PA) can be a cost-effective solution to guarantee the required linearity without compromising the efficiency. In the design of a DPD for a single band PA, direct learning can be used to extract the pre-inverse parameters or, alternatively, indirect learning can be employed by exchanging the position of the system during the identification procedure to avoid the necessity of a PA model within a closed-loop process. The performance of direct learning is substantially dependent on the accuracy of the behavioral model that replaces the PA. Furthermore, in a practical environment where only an approximation to the inverse is achieved, the linearization capability of the indirect learning is affected by shifting the post-inverse placed after the PA to a pre-inverse located before the PA. For concurrent dual-band PAs, an additional advantage of the indirect approach is that the post-inverse identifications for each band are completely independent of each other. In an authors’ previous work, a comparative analysis between the two learning architectures applied to the linearization of concurrent dual-band PAs was performed based on DPDs modeled by polynomials with memory. This work contributions are the extension of such comparative analysis to DPDs modeled by artificial neural networks, the development of complex-valued three-layer perceptrons suitable for concurrent-dual band DPDs and the introduction of a modified indirect approach to improve the accuracy of previous direct and indirect learnings. Spectre-RF transient simulations are performed in the circuit-under-test described by a wideband 130 nm CMOS PA concurrently stimulated by 2.4 GHz Wi-Fi and 3.5 GHz LTE signals. Reported simulation results show that, in a comparison with the previous direct and indirect learnings with similar output mean powers of about 60 mW, the modified indirect approach provides a superior linearity performance. The modified indirect learning reduces the error vector magnitude (EVM) metric to 0.87% and 1.13% for Wi-Fi and LTE bands, respectively, whereas the indirect and direct learnings achieve EVM equal to or larger than 1.05% and 1.49% for Wi-Fi and LTE bands, respectively.
4 citations
TL;DR: Simulation results show that the proposed 3DIMP and 3DHIMP, in comparison with previous three-dimensional multi-band (3DMB) and three- dimensional harmonic memory polynomial (3DHMP) having the same amount of parameters, can improve the normalized mean square error by up to 8.3 dB and 16.6 dB, respectively, when applied to the PA inverse behavioral modeling.
Abstract: This paper presents the design and post-layout results of a 5G power amplifier (PA) in 130 nm CMOS technology. The circuit incorporates a pre-amplification stage that uses a current reuse technique followed by a power stage. The PA operates in the 2–5 GHz range, with a power gain of 16–20.9 dB, output saturation power of 19.1–21.7 dBm, an output compression point of 15.8–20.4 dBm and maximum power-added efficiency of 9.28–22.4%. A three-dimensional improved memory polynomial (3DIMP) and a three-dimensional harmonic improved memory polynomial (3DHIMP) are introduced to the behavioral modeling and digital baseband predistortion of the designed PA for the cases without and with multiplicity among carriers, respectively. Moreover, an ascendant factor algorithm is presented for selecting the truncation factors. Simulation results adopting IEEE 802.11n at channel 1, LTE at channel 2 and IEEE 802.11ac at channel 3 show that the proposed 3DIMP and 3DHIMP, in comparison with previous three-dimensional multi-band (3DMB) and three-dimensional harmonic memory polynomial (3DHMP) having the same amount of parameters, can improve the normalized mean square error by up to 8.3 dB and 16.6 dB, respectively, when applied to the PA inverse behavioral modeling. Additional reductions in error vector magnitude up to 0.39 p.p. and 1.23 p.p. are also achieved when the 3DIMP and 3DHIMP are responsible for the PA linearization instead of previous 3DMB and 3DHMP, respectively.
References
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TL;DR: A frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements and is shown to fit measured data very well.
Abstract: Simple two-parameter formulas are presented for the functions involved in the amplitude-phase and the quadrature nonlinear models of a TWT amplifier, and are shown to fit measured data very well. Also, a closed-form expression is derived for the output signal of a TWT amplifier excited by two phase-modulated carriers, and an expression containing a single integral is given when more than two such earriers are involved. Finally, a frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements.
1,442 citations
TL;DR: A brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network.
Abstract: Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogenous network deployment based on micro, pico and femtocells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technology.
1,163 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
TL;DR: In this paper, a three-tone test setup is constructed to measure the phase of third-order intermodulation distortion products, and the measured results for a bipolar junction transistor and a MESFET amplifier are presented.
Abstract: Memory effects are defined as changes in the amplitude and phase of distortion components caused by changes in modulation frequency. These are particularly important in cancelling linearizer systems, e.g., when distortion is reduced by similar distortion in the opposite phase. This paper begins by describing electrical and electrothermal causes for memory effects. A three-tone test setup is then constructed to measure the phase of third-order intermodulation distortion products. This paper also presents the measured results for a bipolar junction transistor and a MESFET amplifier.
400 citations
TL;DR: The DPD techniques are discussed in the context of linearizing nonlinear RF PAs to create more suitable RF transceiver architectures to provide wireless access with better user experience and less power waste.
Abstract: The RF PA, as one of the most essential components in any wireless system, suffers from inherent nonlinearities. The output of a PA must comply with the linearity requirement specified by the standards. Due to its satisfactory linearization capability, DPD has been widely accepted as one of the fundamental units in modern and future wideband wireless systems. With the help of this flexible digital technology, the inherent linearity problem of PAs operating in the saturation region can be significantly improved, which enables us, the wireless engineers, to create more suitable RF transceiver architectures to provide wireless access with better user experience (linearity perspective) and less power waste (power efficiency perspective). This moves us one more step towards the ultimate green communications. In this article, we discussed the DPD techniques in the context of linearizing nonlinear RF PAs. As the computing-horsepower and the transistor-density of digital IC increases while the cost per transistor decreases, the concept that uses digital enhancement techniques to eliminate active analog imperfects will gain more attention from both industry and academia.
169 citations