Waveform Design for Energy Efficient OFDM Transmission

*Homayoun Nikookar*

#### **Abstract**

In this chapter, a green radio transmission using the binary phase-shift keying (BPSK) modulated orthogonal frequency-division multiplexing (OFDM) signal is addressed. First, the OFDM transmission signal is clearly stated. For a specified performance of the system, the least transmit power occurs by the optimal OFDM shape, which is designed to minimize the average inter-carrier interference power taking into account the characteristic of the transmit antenna and the detection process at the receiver. The optimal waveform is obtained by applying the calculus of variations, which leads to a set of differential equations (known as Euler equations) with constraint and boundary conditions. Results show the transmission effectiveness of the proposed technique in the shaping of the signal, as well as its potential to be further applied to smart context-aware green wireless communications.

**Keywords:** green radio transmission, multicarrier, OFDM, signal design, optimization

#### **1. Introduction**

The advancements in the field of wireless communication have led to many exciting applications such as mobile internet access, health care and medical monitoring services, smart homes, combat radios, disaster management, automated highways, and factories. With each passing day, novel and advanced services are being launched even while existing ones continue to flourish. Wireless services have now found applicability in other sectors too including health care, transportation, security, logistics, education, and finance. Demand for wireless services is thus expected to grow in the foreseeable future. However, with the increasing popularity of wireless services (such as the 5G and the future 6G), the requirements on prime resources such as green transmission and radio spectrum are put to a great test. Recent studies have shown that the energy costs account for as much as half of a mobile service provider's annual operating expenses. Therefore, making the communication equipment more efficient in relation to its power consumption not only has implications with regard to environmental pollution and the level of CO2 emission, but also makes economic sense and can eventually reduce the cost of wireless services (for providers and users).

In this regard and given the 10% of the world's energy consumption due to the information and communication technology (ICT) industry [1], energy efficiency has become one of the key performance indicators (KPI) in the design and implementation of radio systems.

The theme of green radio communications is to design energy-efficient wireless communication techniques and protocols, which optimally utilizes available resources and minimize power consumption. Various strategies are employed for the design of energy-efficient wireless systems; among them are energy-efficient new radios [2, 3], minimization of interference [4], and optimal resource allocation [5]. In this chapter, we would like to design a signal for energy-efficient OFDM transmission. As can be seen from Section 4, we will reduce the power dissipation of the transmitter and consequently the level of CO2 emission of the radio system by optimal design of a waveform for transmission that minimizes inter-carrier interference of the OFDM system. In this way for reaching the same performance level of the provided communication services, a lower power level will be required for transmission, which leads to a green wireless radio system. As the reduction of the inter-carrier interference level is the basis for the optimization of OFDM signal, the approach explained in this chapter falls in the category of green radio by minimization of interference mentioned above.

The rest of the chapter is organized as follows. In Section 2, the basics of the OFDM transmission being provided. In Section 3, the data detection procedure in the receiver is mathematically explained. This procedure is further needed for the maximization of the detection performance of the system. Waveform design and the optimization procedure using calculus of variations and the Lagrange multiplier are detailed in Section 4, and the results are discussed. Conclusion remarks appear in Section 5.
