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Power Amplifier-Aware Transmit Power Optimization for OFDM and SC-FDMA Systems

Pawel Kryszkiewicz

TL;DR

This work addresses uplink sustainability and signal quality by accounting for nonlinear Power Amplifier (PA) effects in OFDM and SC-FDMA and by optimizing the PA operating point to maximize the receiver SNDR. It develops an analytic SNDR model for OFDM and a semi-analytic model for SC-FDMA under a soft-limiter PA, enabling transmit power adaptation via the input-back-off parameter $\gamma$. The key findings show that dynamic PA operation improves in-band SNDR for both waveforms, with SC-FDMA offering better performance due to lower envelope fluctuations, and that in-band distortion modeling yields different optimal operating points than time-domain distortion. The results support PA-aware transmit power control as a practical strategy to enhance efficiency and performance in future IoT and beyond-5G uplinks.

Abstract

The Single Carrier-Frequency Division Multiple Access (SC-FDMA) is a transmission technique used in the uplink of Long Term Evolution (LTE) and 5G systems, as it is characterized by reduced transmitted signal envelope fluctuations in comparison to Orthogonal Frequency Division Multiplexing (OFDM) technique used in the downlink. This allows for higher energy efficiency of User Equipments (UEs) while maintaining sufficient signal quality, measured by Error Vector Magnitude (EVM), at the transmitter. This paper proposes to model a nonlinear Power Amplifier (PA) influence while optimizing the transmit power in order to maximize the Signal to Noise and Distortion power Ratio (SNDR) at the receiver, removing the transmitter-based EVM constraint. An analytic model of SNDR for the OFDM system and a semi-analytical model for the SC-FDMA system are provided. Numerical investigations show that the proposed transmit power optimization allows for improved signal quality at the receiver for both OFDM and SC-FDMA systems. However, SC-FDMA still outperforms OFDM in this matter. Such a power amplifier-aware wireless transmitter optimization should be considered to boost the performance and sustainability of next-generation wireless systems, including Internet of Things (IoT) ones.

Power Amplifier-Aware Transmit Power Optimization for OFDM and SC-FDMA Systems

TL;DR

This work addresses uplink sustainability and signal quality by accounting for nonlinear Power Amplifier (PA) effects in OFDM and SC-FDMA and by optimizing the PA operating point to maximize the receiver SNDR. It develops an analytic SNDR model for OFDM and a semi-analytic model for SC-FDMA under a soft-limiter PA, enabling transmit power adaptation via the input-back-off parameter . The key findings show that dynamic PA operation improves in-band SNDR for both waveforms, with SC-FDMA offering better performance due to lower envelope fluctuations, and that in-band distortion modeling yields different optimal operating points than time-domain distortion. The results support PA-aware transmit power control as a practical strategy to enhance efficiency and performance in future IoT and beyond-5G uplinks.

Abstract

The Single Carrier-Frequency Division Multiple Access (SC-FDMA) is a transmission technique used in the uplink of Long Term Evolution (LTE) and 5G systems, as it is characterized by reduced transmitted signal envelope fluctuations in comparison to Orthogonal Frequency Division Multiplexing (OFDM) technique used in the downlink. This allows for higher energy efficiency of User Equipments (UEs) while maintaining sufficient signal quality, measured by Error Vector Magnitude (EVM), at the transmitter. This paper proposes to model a nonlinear Power Amplifier (PA) influence while optimizing the transmit power in order to maximize the Signal to Noise and Distortion power Ratio (SNDR) at the receiver, removing the transmitter-based EVM constraint. An analytic model of SNDR for the OFDM system and a semi-analytical model for the SC-FDMA system are provided. Numerical investigations show that the proposed transmit power optimization allows for improved signal quality at the receiver for both OFDM and SC-FDMA systems. However, SC-FDMA still outperforms OFDM in this matter. Such a power amplifier-aware wireless transmitter optimization should be considered to boost the performance and sustainability of next-generation wireless systems, including Internet of Things (IoT) ones.
Paper Structure (5 sections, 1 theorem, 37 equations, 4 figures)

This paper contains 5 sections, 1 theorem, 37 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. SNDR maximization by PA's operating point adjustment
  4. Numerical Results
  5. Conclusions

Key Result

Lemma 1

The linear scaling factor $\alpha$ for a soft-limiter PA is dependent on the IBO value, not the transmitted signal power itself for any input signal. The nonlinear distortion power is proportional to transmit signal power $\sigma^2$, with the proportionality coefficient dependent on IBO, not the tra

Figures (4)

  • Figure 1: Coefficients $\alpha$ and $D$ as a function of IBO for OFDM/SC-FDMA (QPSK, 64QAM modulations) considering in-band or time-domain signals.
  • Figure 2: Contour plot of SNDR (in-band or time-domain) for SC-FDMA and OFDM signals as a function of IBO and $SNR_{\mathrm{SAT}}$.
  • Figure 3: Optimal IBO as a function of $SNR_{\mathrm{SAT}}$ for SC-FDMA and OFDM signals, both in-band and time-domain distortion.
  • Figure 4: In-band SNDR for optimized IBO, with linear approximation, in comparison to a fixed IBO system as a function of $SNR_{\mathrm{SAT}}$ for SC-FDMA/OFDM.

Theorems & Definitions (2)

  • Lemma 1
  • proof