Karan Gumber

Bio: Karan Gumber is an academic researcher from Indian Institute of Technology Roorkee. The author has contributed to research in topics: Amplifier & Predistortion. The author has an hindex of 3, co-authored 6 publications receiving 37 citations. Previous affiliations of Karan Gumber include Indian Institutes of Technology.

Low-Cost RF in –RF out Predistorter Linearizer for High-Power Amplifiers and Ultra-Wideband Signals

Abstract: The 5G and beyond systems require the highly efficient linear power amplifier (PA) at the base station to deliver promised data rate in a power efficient manner. To facilitate higher data rates in future 5G communication, the demands for the wideband signals are continuously increasing, which creates adversity in employing digital predistortion (DPD) for the linearization of RF PA in ultra-wideband systems. System bandwidth constraint of the conventional DPD does not provide sufficient linearization of wideband signals. In this paper, we present two types of predistorter, first is RFin–RFout analog predistorter, in which linearization is performed by RF components in the analog domain, and the second is hybrid RF predistorter which takes the advantage of advanced DSP platform for improving the performance of RFin–RFout analog predistorter. The proposed predistorters eliminate the constraint on the system bandwidth of the conventional DPD. The requirements of data converters and reconstruction filters are relaxed in the analog predistorter (APD) architecture, whereas hybrid digitally controlled (HDC) APD eliminates the need of analog components by compensating the delay digitally. In order to validate this concept, a ZX60V-63+ PA from minicircuits is tested with 160-MHz eight-component carrier-long term evolution signal. The proposed APD architecture is able to deliver an adjacent channel power ratio (ACPR) of −46.4 dBc with an ACPR improvement of 13.4 dB at 1-dB back-off. Furthermore, with digital intervention, modified model, HDC-APD further provides a significant improvement in the linearization performance and delivers an ACPR of −53.5 dBc with an ACPR improvement of 20.5 dB.

A Modified Hybrid RF Predistorter Linearizer for Ultra Wideband 5G Systems

Abstract: The wide-bandwidth signal transmission is one of the requirements in upcoming 5G communication systems in its quest for high data rates. In this paper, a wideband hybrid RF/digital predistortion (HRF-DPD) linearization technique is reported to compensate for the nonlinearity of ultra-wideband power amplifier (PA) for 5G systems driven by carrier aggregated and wideband modulated signals. The proposed methodology is suitable for 5G PA design, since its power overhead and system bandwidth does not increase with an increase in signal bandwidth. Taking advantage of recent available digital signal processing solutions, the proposed method reduces hardware requirements of the conventional analog predistorter by alleviating the need of vector multiplier, branch line coupler, and delay lines. Such linear operations are controlled digitally, which provides flexibility in terms of digitally compensation of delay, gain and phase control of the signal. For establishing a proof of concept, HRF-DPD is implemented with ZX60V-82+ class AB PA and tested using a 100- and 50-MHz long term evolution-carrier aggregated (LTE-CA) signal at 2 GHz. Experimental results show that the wideband PA along with the proposed predistorter delivers an adjacent channel leakage ratio (ACLR) of −54 dBc with a cancellation of 30.6 dB for 100-MHz LTE-CA signal. With the proposed method PA, nonlinear distortion outside the 100-MHz band can be linearized leading to filter less architecture which provides 45-dBc ACLR performance.

Analogue predistortion lineariser control schemes for ultra-broadband signal transmission in 5G transmitters

Abstract: Analogue predistorter (APD) has gained a new significance due to the need for high bandwidth in the fifth generation (5G) communication. As predistorted signal is generated in the analogue domain, it is free from data converter bandwidth limitation and presents an attractive linearisation solution for power amplifier (PA) in the 5G base station. Furthermore, it also finds its application in the multicarrier repeater system for long-distance communication, where the baseband information is not readily available. However, the performance of the conventional APD is dependent on the appropriate control of gain and phase of the predistorted signal. The state-of-the-art work in analogue linearisation solutions mostly utilises vector multiplier for such a control. This work points out the limitations of such a scheme and proposes a novel control scheme (CS) that is capable of extracting better benefits of the APD. An experimental validation is carried out by linearising 10 W HMC8500 broadband GaN PA, excited by a eight-component carrier 160 MHz ultra-broadband long-term evolution signal. The proposed Type-II CS delivers an adjacent channel power ratio of −45.05 dBc with an improvement of 18 dB, which is 4 dB better than Type-I CS.

Digitally assisted analog predistortion technique for power amplifier

Abstract: This paper presents a digitally assisted analogpredistortion scheme for linearization of high power amplifier. Taking advantage of recent available digital signal processing solutions, the proposed method reduces hardware requirement of conventional analog predistorter by alleviating the need of Vector multiplier, hybrid 900 coupler and delay lines. Proposed method provides flexibility in terms of digitally compensation of delay, gain and phase control of signal. The proof-of-concept of method is presented for reducing odd-order intermodulation distortion (IMD). A better performance of 11-db reduction as compared to conventional analog predistorter in terms of 3rd IMD is achieved for two-tone test signal centered at frequency 2000 MHz and 2020 MHz.

Digital predistorter design using linear spline and its fixed point implementation

Abstract: This paper investigates digital predistorter design using linear splines polynomial (LSP) and its implementation in 16-bit fixed point FPGA The performance of memory polynomial model in fixed point implementation degrades, and LSP model has been proposed as a solution The performance is evaluated in terms of simulation and measured result It has been reported that we achieve numerically stable observation matrices using splines, hence accuracy level of coefficients is sufficient to cover full dynamic range in FPGA

Enabling Multi-Functional 5G and Beyond User Equipment: A Survey and Tutorial

Abstract: The fifth generation (5G) research and development has been fueled by many new breakthroughs in various areas. The recent progress in carrier aggregation (CA), licensed assisted access (LAA), massive MIMO (MaMi), beamforming techniques, cooperative spectrum sensing (CSS), compressive sensing (CS), machine learning, etc., has provided inspiring and promising approaches to address 5G and beyond challenges. However, at the user equipment (UE) end, limited design budget and hardware resources bring along a series of challenging implementation issues when delivering multi-standard and multi-functional wireless communications. In this paper, we first review recent advances in technical standards and critical enabling techniques, accompanied with several case studies of product developments. After the classification of typical 5G application and deployment scenarios, we propose and analyze a novel hardware reuse and multiplexing solution to facilitate cost-effective and energy-efficient UE design, followed by an investigation of state-of-the-art hardware development from the systems and circuits standpoint. Moreover, wireless UE hardware solutions, UE proof-of-concept (PoC) implementation and field test are proposed and discussed. Finally, the new trends of UE design and terahertz technologies for 5G and beyond applications are investigated and envisioned.

Multiband User Equipment Prototype Hardware Design for 5G Communications in Sub-6-GHz Band

Abstract: Verification of physical (PHY) layer and medium access control (MAC) layer procedures of the fifth-generation (5G) specifications with real hardware prototypes is important in the commercialization of 5G mobile communication systems and is challenging as well. In this paper, we propose a flexible software-defined-radio (SDR)-based prototype hardware design for user equipment (UE), which can be used to implement novel 5G communication concepts. The proposed hardware architecture is featured by using a flexible baseband signal processing module and two independent programmable wideband radio frequency (RF) front ends that, respectively, cover the lower and higher frequencies of sub-6-GHz band. The flexibility of the baseband signal processing module is ensured by using four powerful field-programmable gate arrays (FPGAs) running the PHY entities and a powerful FPGA-based system-on-chip running the MAC entities. The flexibilities of the RF front ends lay in the facts that: 1) the design covers three sub-6-GHz frequency bands, that is, 2.5, 3.5, and 4.9 GHz; 2) it can support dual connectivity for the upcoming 5G networks; and 3) it enables carrier aggregation (CA) over up to three carriers to achieve 300-MHz bandwidth. Accordingly, this prototype is capable of verifying the complicated scheduling procedures, evaluating the sophisticated signal processing algorithms in both PHY and MAC layers, and supporting the 100-MHz 4T4R multiple-input multiple-output (MIMO) or 200-MHz 2T2R MIMO techniques. Experiments have been performed on 256-QAM modulated waveforms to assess transmission power, error vector magnitude, adjacent channel leakage ratio from the UE side, and peak data rates between a base station and the UE.

Low-Cost RF in –RF out Predistorter Linearizer for High-Power Amplifiers and Ultra-Wideband Signals

Abstract: The 5G and beyond systems require the highly efficient linear power amplifier (PA) at the base station to deliver promised data rate in a power efficient manner. To facilitate higher data rates in future 5G communication, the demands for the wideband signals are continuously increasing, which creates adversity in employing digital predistortion (DPD) for the linearization of RF PA in ultra-wideband systems. System bandwidth constraint of the conventional DPD does not provide sufficient linearization of wideband signals. In this paper, we present two types of predistorter, first is RFin–RFout analog predistorter, in which linearization is performed by RF components in the analog domain, and the second is hybrid RF predistorter which takes the advantage of advanced DSP platform for improving the performance of RFin–RFout analog predistorter. The proposed predistorters eliminate the constraint on the system bandwidth of the conventional DPD. The requirements of data converters and reconstruction filters are relaxed in the analog predistorter (APD) architecture, whereas hybrid digitally controlled (HDC) APD eliminates the need of analog components by compensating the delay digitally. In order to validate this concept, a ZX60V-63+ PA from minicircuits is tested with 160-MHz eight-component carrier-long term evolution signal. The proposed APD architecture is able to deliver an adjacent channel power ratio (ACPR) of −46.4 dBc with an ACPR improvement of 13.4 dB at 1-dB back-off. Furthermore, with digital intervention, modified model, HDC-APD further provides a significant improvement in the linearization performance and delivers an ACPR of −53.5 dBc with an ACPR improvement of 20.5 dB.

Adaptive Dual-Input Analog RF Predistorter for Wideband 5G Communication Systems

Abstract: Advanced communication technologies like 5G focuses on the wideband signals and high data rate. The quality of wideband signal transmission deteriorates due to the nonlinear characteristics of the power amplifiers (PA). The digital predistortion (DPD) method reduces the distortion and spectrum regrowth, but the sampling speed of the converters restricts its operation to support 5 to 7 times the signal bandwidth. The analog predistortion (APD) method is not limited by the bandwidth of the distorted signal, but its linearization performance is inferior to the DPD. This paper presents an adaptive dual-input APD that establishes the benefit of digital control over the variable parameters to linearize the wideband signals. For the LTE signal with a bandwidth of 20 MHz and RF frequency of 3.5 GHz, the proposed method achieves an ACPR improvement of 24.01 dB. For another LTE-A signal with 100 MHz bandwidth, the proposed linearizer achieves an ACPR improvement of 9.2 dB and 15.7 dB over PA with and without conventional APD. Though the predistorter (PD) is designed for 3.5 GHz, it is reported that due to the wideband operation of APD, digital adaptation allows satisfactory performance for carrier frequency from 2 to 4 GHz.

Linearization as a Solution for Power Amplifier Imperfections: A Review of Methods

Abstract: Development of 5G networks requires a substantial increase to both spectral and power efficiency of transmitters. It is known that these two parameters are subjected to a mutual trade-off. To increase the linearity without losing power efficiency, linearization techniques are applied to power amplifiers. This paper aims to compare most popular linearization techniques to date and evaluate their applicability to upcoming 5G networks. The history of each respective linearization technique is followed by the main principle of operation, revealing advantages and disadvantages supported by concluding the latest research results. Three main groups of linearization methods currently known are feedforward, feedback, and predistortion, each with its own tradeoffs. Although digital predistortion seems to be the go-to method currently, other techniques with less research attention are still non-obsolete. A generalized discussion and a direct comparison of techniques analyzed are presented at the end of this paper. The article offers a systematic view on PA linearization problems which should be useful to researchers of this field. It is concluded that there are still a lot of problems that need to be addressed in every linearization technique in order to achieve 5G specifications.