Analysis of Spectral Degradation and Error Compensation in 5G NR Digital Polar Transmitters

Abstract

Cellular standards evolve to support increasingly higher bandwidths which results in strict in-and out-of-band requirements such as lower error vector magnitude (EVM) and/or adjacent channel leakage ratio (ACLR). Digital polar transmitters, which are showing the best performance in terms of power consumption, are challenged to fulfill these requirements. This work will show that even in case of ideal analog components and infinite digital resources, there are principle limitations in terms of out-of-band noise for digital polar transmitters. A typical polar modulation will be compared to a theoretical signal with continuous amplitude modulation. The analysis of the resulting error signal suggests a decomposition into two components which can be partially compensated in the amplitude and phase modulation paths. Based on that decomposition a compensation algorithm has been developed and evaluated with a 400 MHz 5G New Radio (NR) signal for Band n257 on Frequency Range 2 with carrier frequency of 26.5 GHz. The compensation results in an out-of-band noise reduction of 44 dB close to the carrier frequency. Furthermore, EVM improvements for NR signals are demonstrated.

Digital Polar Transmitters for Massive MIMO: Sum-Rate and Power Efficiency Analysis

“…In terms of power consumption, the digital polar architecture is the most promising transmitter architecture. It has been shown that polar architecture has an inherent power efficiency gain of up to 3 dB compared to the Cartesian architecture, due to the in-phase and quadrature (I/Q) signal summation in the latter [31]. Several successful designs and chip prototypes [32]- [36] have demonstrated the feasibility and superiority of the digital polar transmitters.…”

Dithering Concepts for Spur-Free Nonlinear DTC-Based Frequency Synthesizers

“…be the autocorrelation function (ACF) of the output signal which, without further assumptions, depends on both the absolute time t and the time displacement τ . Plugging (6) into (8) results to…”

“…Such phase shifters need to be able to operate in the GHz frequency range. Several works describe the construction of circuits capable of doing so, and their spectral effects [3]- [6]. These systems are using a digital input that describes a phase offset or time delay relative to a reference signal.…”

Quantized Polar Transmitters for Power Efficient Massive MIMO Systems

“…It also enables the whole transmitter to be integrated on a single chip, decreasing system cost and form-factor. In addition, the polar architecture has a power efficiency gain of up to 3 dB compared to the Cartesian, due to the omission of I/Q signal summation [9]. Moreover, a comprehensive analytical study followed by a CMOS implementation of a polar quantizer chip prototype demonstrated the superiority of signal-to-quantization-noise ratio improvement compared to rectangular (I/Q) quantizer [10].…”