Can mmWave 5G replace Wi-Fi? OpenSignal’s report says so.

For years, Wi-Fi has been the go-to choice of internet users that demand faster, reliable and uninterruptible service with consistent bandwidth. Although cellular is a popular alternative to Wi-Fi with LTE+ services getting cheaper, it still cannot be counted as a Wi-Fi replacement due to issues like bandwidth inconsistency and higher latency. However, as per the latest report from OpenSignal, with arrival of 5G mmWave, this is no longer the case. This post uses data from OpenSignal’s analysis.

Users connected to public Wi-Fi, can experience average download speeds of 21 Mbps. Public Wi-Fi already has limited availability. 5G experience may differ depending on the frequency being used to offer the service. For example, the users connected to widely available sub-6 5G may experience average download speeds of 64 Mbps. The same users, when connected to 5G mmWave with compatible hardware can experience whooping average download speeds of 640 Mbps, 10 times as high as sub-6 5G and almost 30 times as high as public Wi-Fi.

Data from OpenSignal for average download speeds of wireless interfaces

Public Wi-Fi, in its nature has its own limitations, which can explain the slower speeds experienced by users. As Wi-Fi uses unlicensed spectrum and unmanaged frequencies, its signal often suffers due to interference by competing signals. There are often multiple Wi-Fi networks in one place competing for non-abundant frequencies. Thus, public Wi-Fi is subject to interference, effectively slowing the network speed. On the other hand, 5G uses wireless spectrum that is licensed to only one carrier. Hence, there is no chance of interference. Standards like 5 GHz Wi-Fi and Wi-Fi 6 have been introduced solve this issue. However, their availability is very limited when it comes to public Wi-Fi. Since public Wi-Fi is often a free service, service providers may not have upgraded their access points. Public Wi-Fi is often a gateway to a wired broadband connection that might be using older technology (for example, ADSL) and is often not upgraded. Due to this, the network often has limited capacity and speeds suffer in case multiple users are connected. On the other hand, a 5G carrier uses a backhaul connection to a base station that is usually upgraded by the operator to ensure the best user experience.

Sub-6 and mmWave comparison (Image source: Qualcomm)

Though 5G mmWave offers promising high speeds and lowest possible latency, its current availability of is very limited. mmWaves aka Millimeter waves are extremely high frequencies and are subject to atmospheric attenuation, which significantly affects the coverage of a single 5G mmWave base station. The operator can overcome this limitation by installing multiple 5G mmWave base stations in public places to ensure seamless coverage. The number of 5G mmWave base stations to be installed is way more than that of sub-6 5G and 4G LTE base sations. These 5G mmWave base stations form small cells. The operator may deploy many of these at malls, cafes, restaurants, parks and so on. This makes makes a small cell of 5G mmWave very similar to a public Wi-Fi network and an mmWave base station similar to a Wi-Fi access point. Thus, unlike traditional cellular networks, 5G mmWave can be a perfect replacement to public Wi-Fi, whenever available.

However, Wi-Fi will still continue to play its role at home and work locations as it is free, cheap and often without any data cap. As almost all of existing devices support Wi-Fi or old cellular technologies and lack necessary 5G hardware, Wi-Fi and 5G mmWave will continue to complement each other for first few years. Slowly but steadily, users will get onboard 5G and use it as a preferred choice over the Wi-Fi. The operators can use this opportunity to offer significantly better connectivity to users in dense urban localities where Wi-Fi speeds suffer due to interference.

What are Network Functions (NFs) in 5G?

In 5G, the network architecture is changed to ‘Service-based Architecture’ (SBA). SBA allows 5G core solution vendors to move to software-based platform. Hence, eliminating the need to be dependent on proprietary software and hardware vendors. Each software unit in 5G core network is called as the ‘Network Function’. Every NF is entitled to a particular job and acts as a producer as well as consumer for every other NF. The communication is usually done over a software-based stateless interface. Services exposed by these network functions are invoked using a standard API. 5G Core architecture has introduced the concept of CUPS (Control and User Plane Separation).

Architectural diagram of 5G core network functions and interfaces

Following are different Network Functions in 5G and their functionalities:
1. AUSF (Authentication Server Function): Performs the UE authentication. It relies on a backend service for computation and keys. UEs get authenticated only with AUSF in the home network. When the device roams in a serving network a Security Anchor Function acts as the authentication gateway between the serving network and AUSF in the home network.

2. AMF (Access and Mobility Management Function): AMF is a control plane function in 5G core that is solely responsible for registration management, mobility management, reachability management and connection management. It performs registration and de-registration of the UE with 5G core. AMF also performs NAS (Non-Access Stratum) signaling with the UE via gNodeB. Function of AMF is much similar to MME (Mobility Management Entity) from 4G core. It ensures that UE is always reachable.

3. UDM (Unified Data Manager): UDM acts as a centralized repository of the data for authorization, user registration and subscriber profiles. Function of UDM is much similar to HSS (Home Subscriber Server) from 4G. A stateless UDM can store its data in external entity called UDR (Unified Data Repository).

4. PCF (Policy Control Function): PFC maintains the unified policy framework that controls the UE’s behavior with the network. It provides policy rules to other network functions for their enforcement. PCF is similar to PCRF (Policy and Charging Rules Function) from 4G core.

5. UPF (User Plane Function): UPF is the crucial component of the 5G core. It is directly connected to the Data Networks (DN) like internet or IMS. It is responsible for packet routing, packet forwarding, QoS handling and PDU session management. It handles the downlink (DL) and uplink (UL) rate enforcement. It also performs the downlink packet buffering for the UE.

6. NSSF (Network Slice Selection Function): As discussed in the previous post(s) earlier, 5G introduces the concept of ‘network slicing’, where a piece of 5G network is dedicated to a specific use case. NSSF assists AMF with selection of a network slice to serve a particular device. It determines the NS-SAI (Network Slice Selection Assistance Information) for the device.

7. NRF (Network Repository Function): NRF is the key network function in 5G core. It acts as an internal broker for all core network functions. It maintains an updated repository of all network functions along with services provided by them with NF discovery information in an entity called ‘NF Profile’. It allows consumer NFs to discover provider NFs and keep track of other NF instances.

8. NEF (Network Exposure Function): One of the biggest advantages of 5G SBA is that it emphasizes the use of HTTP/2 based stateless APIs for communication. NEF facilitates a third-party application function (AF) by securely exposing some of the services offered by 5G core network functions. It acts as an ‘external broker’ for third-party applications having access to 5G core network information. For example, an external application may try to request information such as UE reachability from AMF. NEF does the job of retrieving this information from AMF and provide it to the external application.

The Voice of 5G

Voice is the most fundamental and an essential service when it comes to mobile communication. In 2G and 3G, voice was a primary network service and was mainly handled in circuit-switched fashion. It was only until the network architecture was changed to all-IP in 4G, an alternative solution was needed to replace traditional circuit-switched voice calls with packet-switched fashion which could deliver more sophisticated IP-based voice service. This is how Voice over LTE (VoLTE) was emerged. VoLTE offered superior call quality with a significantly reduced connection delay. However, most 4G networks had chosen an option of CSFB (Circuit Switched Fall Back) to hand over voice calls to legacy networks (2G/3G) on the fly. Most of the operators went with the CSFB approach, skipping a much more sensible approach of VoLTE entirely. Hence, the adoption of IMS has been slower. According to data, VoLTE adoption in UK is around 60%. This is more or less the same with all operators across the globe. In contrast, India’s Jio has all-IP LTE network with 100% VoLTE adoption. There is another standard called Voice over Wi-Fi (VoWiFi, or simply Wi-Fi calling) that allows offloading of the VoLTE traffic to any Wi-Fi/WLAN network, thus ensuring the superior call quality even in areas where network coverage is low.

Using IMS for enabling packet-switched mobile voice

First introduced back in 2003 in 3GPP Release 5, IMS (IP Multimedia System) is an architectural framework that delivers multimedia services over a packet-switched network. IMS is the backbone of VoLTE and VoWiFi. It uses SIP (Session Initiation Protocol) as a signaling protocol for the initiation, maintenance and termination of real-time call sessions. It can offer various services such as voice calls, video calls and SMS messaging. Even though 3GPP had put an end to the circuit-switched era in Release 15 (5Gv1) mandating operators to use IMS for 5G voice, the legacy alternative was re-introduced in Release 16 (5Gv2). Irrespectively, operators should be opting for end-to-end packet-switched voice on their most advanced 5G infrastructures (With great power comes the great responsibility!)

Voice over 5G (Vo5G) aka Voice over NR (VoNR) will need some evolutionary upgrade over existing IMS implementation (if any). This upgrade is a must in order to support the new interfaces within the Service Based Architecture (SBA) of 5G. The enhanced IMS must be cloud-native, and thus utilizing containerized OS-level virtualization leveraging numerous benefits such as auto-scaling, improved security and faster deployment. This cloud-native IMS also provides numerous 5G-specific benefits such as network slicing. A dedicated network slice for IMS will effectively isolate the 5G voice from the rest of the data traffic, enabling highly reliable and optimized voice experience.

There is a makeshift solution called EPS fallback. In case the IMS and/or the core network is not upgraded to 5G by the operator, EPS fallback allows to make the voice call over VoLTE when connected to 5G. The same approach is being used by most of the current 5G operators operating non-standalone (NSA) mode.

Readiness of the market for Vo5G

Chipmakers like Qualcomm and Mediatek have introduced chipsets with native support of VoNR, with Mediatek’s Demensity 1000 chip and Qualcomm’s third generation Snapdragon X60 modem. Phone manufacturer Oppo supports 5G voice calls with the latest smartphone Reno 3. While the availability of VoNR is currently limited to a few ones among current 5G enabled smartphones, we can expect more and more devices in 2021. Most of the current 5G phones and network operators use EPS fallback for making voice calls over 5G. Talking about the equipment vendor’s contribution to 5G voice, Ericsson has put forward some pretty interesting use cases of 5G voice calls like interactive calling.

Although there is much work to be done to enable this next-gen voice technology – 5G, in its nature, opens a huge platform unleashing a bunch of possibilities for innovation and new monetization opportunities for carrier voice (and video) calls.