The beauty of 5G phone is like being in your ear

[[352290]]

This article is reprinted from the WeChat public account "Wireless Deep Sea", written by Fei Caicai. Please contact the Wireless Deep Sea public account to reprint this article.

2020 is a critical year for China's 5G construction. Huawei predicts that by the end of this year, the number of 5G sites in China will reach 800,000 and the number of users will exceed 200 million, both accounting for more than 70% of the world's total.

Since the end of last year, 5G mobile phones have begun to appear on the market. Most of the new mobile phones released this year support 5G. In October, with the release of Apple iPhone 12, the fire of 5G has been even more intense.

At the same time, the three major mobile operators have spared no effort in promoting 5G packages. The selling points of 5G packages are naturally large data traffic, fast speed, and "good price". As for how many minutes of voice calls are included in the package, it has long been hidden in an inconspicuous corner and almost no one cares about it.

In this issue, I will talk about how to make calls on 5G network.

1. Voice service is the first priority

Making phone calls is everyone's most basic need and the original goal of the mobile communications industry. Just like ensuring sufficient supply of water and electricity, there is really no highlight in promoting voice services.

Moreover, few people care whether the network used for making calls is 5G, 4G, 3G or 2G. As long as you can make calls, it doesn’t matter how many Gigabits it is!

Besides, WeChat can be used for voice and video calls, and it doesn’t take up much data. Isn’t it great to use it?

It’s good, but although various OTT (Over The Top) voice services represented by WeChat are available, their status is completely incomparable to voice services.

As the most basic communication service, the operator's voice service has the highest priority. At a critical moment, it is even our only lifeline.

When you make a WeChat voice call and the other party is busy, don't worry, because this process proves a fact: at this moment, the other party is holding the phone. Then call her/his phone number directly, you will definitely hear the familiar ringback tone, and her/his WeChat connection will be cut off, and you will be stuck with the binary choice of whether to answer the call or not.

When the signal is poor, the Internet is slow, WeChat voice calls are stuck, and video calls cannot be connected at all. However, calls can definitely be connected, and although the sound quality may not be good, it can meet basic needs. This is the promise of basic service guarantee.

Even in an emergency, no matter if your phone has a signal or not, or even if your SIM card is not inserted, you can still make an emergency call. This is the social responsibility that wireless network operators must bear.

The reason for all this is as mentioned before. Voice service is the most basic service and has the highest indisputable priority. Not only do operators do their best to ensure smooth network operation, but other applications on the mobile phone also have to give way to it.

Therefore, 5G networks must support voice services.

How does 2.5G network support voice services?

How does the 5G network support voice? The most fundamental way is to do it yourself and have enough food and clothing. Directly support VoNR (Voice over New Radio) without relying on 4G or even 3G and 2G.

The 5G network architecture is actually inherited from 4G and only supports packet switching, not circuit switching. In other words, its own 5GC core network cannot support voice services and must rely on a system called IMS.

IMS, also known as IP Multimedia Subsystem, can implement voice services in packet switching networks. The wireless access part of 5G is called NR (New Radio). After combining with IMS, the problem of independent phone calls is perfectly solved. Therefore, the voice service based on 5G is called VoNR (Voice over NR).

This is exactly the same as 4G. The voice service of 4G supported by IMS is called VoLTE (Voice over LTE). VoLTE is currently widely supported in China.

If 5G does not support VoNR, then we can only rely on 4G's VoLTE, or even the circuit-switched domain voice services supported by 3G and 2G.

According to the network deployment mode, 5G can be divided into two categories: NSA (non-standalone networking) and SA (standalone networking). According to whether 5G supports VoNR and whether 4G supports VoLTE, it is divided into the following solutions.

2.1 Voice services under NSA:

Under NSA, the 5G network is called an auxiliary node. It serves as a traffic supplement to 4G and does not directly participate in voice services. All voice functions are completely completed by 4G. Therefore, 5G does not support VoNR.

If 4G supports the VoLTE function, voice calls will be made directly. When the coverage is poor, the call will be switched to 3G or 2G through SRVCC (Single Radio Voice Call Continuity).

If 4G does not support VoLTE, it will directly fall back to 3G or 2G when making a call (this function is called CS Fallback, circuit switched fallback).

2.2 Voice services under SA:

In SA mode, the 5G voice solution is relatively complex, with four scenarios. The general idea is that the 5G network gives priority to using VoNR. If it is not supported, it will fall back to 4G VoLTE, and finally 3G or 2G will be used as a backup.

Scenario 1: If the 5G network supports voice (VoNR), the call can be made directly on 5G, and then switched to 4G VoLTE when the 5G signal is poor. If the user goes to an area with poor 4G coverage, he can also switch to 3G or 2G through SRVCC.

Scenario 2: If the 5G network supports VoNR, you can directly make calls on 5G. When the 5G signal is poor and the 4G signal is also poor, the call can be switched directly from 5G to 3G through SRVCC.

5G to 3G SRVCC has just been standardized in the 3GPP R16 version and no mobile phone supports it yet.

Since you can switch from 5G to 3G, will there be support for switching to 2G in the future? In fact, there is no need for that, because in general, 3G coverage is good enough to provide a safety net. Besides, 2G will be decommissioned in a few years, so it is not worth investing any more money.

Scenario 3: If the 5G network does not support VoNR, the call will first fall back to 4G VoLTE through EPSFB (EPS Fallback), and then switch to 3G or 2G through SRVCC when 4G coverage is poor.

Scenario 4: The 5G network does not support VoNR, so when making a call, EPSFB is used to fall back to 4G. Unfortunately, 4G does not support VoLTE either, so the call can only be made by falling back to 3G or 2G through CSFB.

It can be seen that in these scenarios, the phone may switch from 5G to 4G, or even from 4G to 3G or 2G while making a call. After the call, will it continue to stay on 4G, or even 3G or 2G?

It is easy to go from frugality to luxury, but it is difficult to go from luxury to frugality. After getting used to the high speed of 5G/4G, the slow speed of 3G and 2G is unacceptable, so the mobile phone needs to return to the most powerful network as soon as possible. This process is called fast return.

What are the advantages of 3.5G VoNR?

As voice services based on IMS, what are the advantages of VoNR over VoLTE?

First of all, when the mobile phone is stationed in a 5G cell, using VoNR is simple and direct. Otherwise, it has to go through EPS Fallback to 4G. The signaling process increases and the latency will inevitably increase, affecting the user experience.

Then, VoNR requires mandatory support for a new voice codec solution that can effectively improve the sound quality of voice calls to the HiFi level. This is EVS (Enhanced Voice Services), also known as Super HD Voice.

[[352296]]

In fact, EVS was defined as early as 3GPP R12, when LTE was still developing rapidly. However, few mobile phones supported it because people did not pay enough attention to voice quality. This delay has brought us to the 5G era.

How does EVS improve sound quality?

Sound is generated by vibration, which forms sound waves when it propagates in the air. However, human ears can only hear sound waves within a limited frequency range, from 20Hz to 20,000Hz.

The frequency range that human vocal cords can produce is narrower, from 85Hz to 1100Hz.

In previous speech coding and decoding schemes, only a small part of the human auditory frequency range was included, and some did not even fully encode the human vocal bandwidth.

For example, the frequency range of the earliest standard voice coding is 300Hz to 3400Hz, while the frequency range of human voice is 85Hz to 1100Hz. That is to say, the sound from 85Hz to 300Hz is not transmitted at all.

This narrowband coding leads to a loss of timbre. The most intuitive feeling is that when making a phone call, although the other party's words can be recognized and the meaning can be understood, it is often difficult to tell who is speaking, as if the voice has been changed.

EVS directly realizes the encoding of the full bandwidth of the human auditory range. In addition to human voices, even the calls of dogs and cats in the background are real and comparable to the sound quality of CD.

Although 5G voice is not taken seriously, it has quietly achieved the best results.

Well, that’s all for this issue. I hope it will be helpful to you.