5G NR Spectral Efficiency vs. Energy Efficiency

This article explores the differences between 5G NR (New Radio) spectral efficiency and energy efficiency, providing formulas and explanations based on the 3GPP 5G NR standard.

What is 5G NR?

As we know, 5G NR technical specifications have been published by 3GPP release 15 and beyond. It operates in FR1 and FR2 frequency bands. FR1 has 450 to 6000 MHz range. FR2 has 24250 to 52600 MHz range in mmwave spectrum. A 5G NR frame has a duration of 10 ms.

Figure 1: 5G NR Overall Architecture

The figure above illustrates the 5G NR architecture and its components. There are two modes in 5G NR viz. non-standalone and standalone. In non-standalone mode, it utilizes the LTE network for control signaling. In standalone mode, the 5G network handles both control signaling and data transfer.

5G NR Spectral Efficiency

Spectral efficiency defines the amount of information, or how much data, can fit within a given bandwidth (BW). This limit is also known as the Shannon limit, as described in the equation below:

Shannon Channel Capacity Formula

From the Shannon-Hartley theorem, we can draw the following conclusions:

• Increasing the channel bandwidth can help increase network capacity.
• Increasing the number of channels can increase data rates and, consequently, capacity.
• Due to the Signal-to-Noise Ratio (SNR) in the equation, we can conclude that increasing output power from femtocells or eNBs can improve the energy efficiency of the network.

Spectral efficiency can be expressed as the ratio of net data rate to channel bandwidth, as shown in the following formula:

5G NR Spectral Efficiency Formula

Example of 5G NR Spectral Efficiency (Downlink):

• INPUTS: Net data rate = 2.31 Gbps, Bandwidth = 100 MHz
• Output: Spectral efficiency = 2.31 x 10⁹ / 100 x 10⁶ = 23 bits/second/Hz

Similarly, uplink spectral efficiency can also be calculated in a 5G NR system.

5G NR Energy Efficiency

In general, energy efficiency refers to using less energy to perform the same task or function. In other words, it means eliminating energy waste.

In traditional cellular networks, one base station is used to transmit energy throughout a wide area. Usually, a 120-degree angular region is covered by one BS (Base Station or eNB). In 5G NR, a single Base Station Antenna is often replaced by a 120 antenna array. This concept is known as Massive MIMO.

Massive MIMO helps achieve higher energy efficiency due to the concentration of radiated energy on the Mobile Subscriber (MS) or User Equipment (UE).

Figure 2: 5G NR energy efficiency

Image Courtesy: Microwave Journal

Theoretically, when a single antenna is replaced by a 120-antenna array to target energy to individual users, the required BS power is decreased to 0.1% of the original output power. However, practically, due to the efficiency and losses of RF components used in the BS, the output power decreases by only 30% of the original power for the same capacity.

Difference Between 5G NR Spectral Efficiency and Energy Efficiency

• Spectral Efficiency: Describes how much capacity can be provided. It is measured in bps/Hz (Bits per second per Hertz).
• Energy Efficiency: Characterizes how much it costs to run the 5G network for a given capacity.