University of Twente Student Theses
A Feasibility Study on PAPR Reduction through Signal Splitting in 5G NR Transmitters
Zanten, S. van (2020) A Feasibility Study on PAPR Reduction through Signal Splitting in 5G NR Transmitters.
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| Abstract: | The introduction of 5G NR enables mobile communications in many new domains. As the usage of telecommunication soars, the demand for more efficient implementations grows. A major bottleneck in the development of efficient 5G NR transmitters is the negative impact of a high PAPR on its analog hardware, which is a result of combining many subcarriers into an OFDM signal. The aim of this thesis is to investigate to what degree the negative impact of a high PAPR as a result of the use of OFDM modulation on the transmitter’s efficiency and linearity could be alleviated by making use of a combination of signal splitting and parallel hardware. Two system concepts have been explored. The first uses splitting in the frequency-domain through decomposition of the OFDM signal into groups of one or multiple subcarriers. Each is processed by its own analog hardware track of which the parallel outputs concurrently deliver power to the load. As these outputs can deliver power concurrently, also the possibility to omit the inefficient PA stage was investigated. The second concept uses time-domain splitting. Based on the magnitude of the baseband OFDM signal, it is processed by a particular hardware track, resulting in PAPR reduction for the signals in each of these tracks. For each of these concepts, the main research question has been answered through a combination of theoretical analysis and simulations. Statistical analysis on OFDM signal properties was used to evaluate PAPR reduction and the impact of this reduction on the transmitter’s hardware was considered through both literature studies and mathematical analysis. These theoretical components were verified with simulations on transmitter models in MATLAB/Simulink and LTSpice. Analysis on frequency-domain signal splitting showed that to profit from splitting in terms of PAPR, only few subcarriers may be combined for each hardware track. This proved problematic when attempting to profit from the PAPR reduction as excessive amounts of hardware are required for the number of subcarriers used in 5G NR. Also, the parallel DAC outputs drive the same load concurrently with orthogonal signals resulting in partial cancellation of the generated power in the load. Using frequency-domain splitting for PAPR reduction in 5G NR transmitters is therefore not recommended. Research also explored using frequency-domain splitting to omit the inefficient PA stage. Here, the strict linearity specifications complicate implementation. If the DACs would be used to provide the required output power of the transmitter, large signals in the mixers lead to problems with gain compression. Also, full power would be generated before upconversion leading to increased dissipation in the mixers, which is why this approach is also not recommended. Then, the feasibility of time-domain signal splitting to reduce PAPR was investigated. Here, significant PAPR reduction can be achieved with relatively little additional hardware. However, switching between hardware tracks was shown to introduce transient effects that degraded the signal’s linearity and the ACPR. Both the tough linearity requirements and the large signal bandwidths requiring fast switching complicate the implementation of functionality to disable or enable the unused hardware tracks. Based on the resemblance of this design problem to considerations in the design of envelope tracking PAs, the preliminary conclusion in this thesis is that the large bandwidths required prevent a feasible implementation of this transmitter concept. However, the limitations to this research should be recognized and more research into disabling hardware tracks is recommended to come to a well-considered final verdict. Considering the conclusions as presented in this thesis, the answer to the main research question is: no, the use of signal splitting and parallel hardware tracks does not benefit the negative impact of a high PAPR in 5G NR transmitters without significant degradation of other performance parameters. The identified root causes for the limitations that have surfaced in this thesis are the strict linearity requirements and the large signal bandwidth in 5G applications. |
| Item Type: | Essay (Master) |
| Faculty: | EEMCS: Electrical Engineering, Mathematics and Computer Science |
| Subject: | 50 technical science in general, 53 electrotechnology |
| Programme: | Electrical Engineering MSc (60353) |
| Link to this item: | https://purl.utwente.nl/essays/82596 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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