China Telecom Is the First Operator Worldwide to Launch a “Device-to-Device” Service on a Smartphone to Improve Coverage

On November 25, 2022, China Telecom launched a D2D service branded as “e-Mutual-Connect” (e-MC) by using its customer service app. The e-MC service is based on the idea of Proximity Radio Access Network (P-RAN), which is a distributed network integrating cellular networks with proximity links between smartphones. With this service, customers can use their smartphones to relay strong signals from Wi-Fi and cellular network to other nearby smartphone users. The preferred choice for China Telecom to provide the proximity link of P-RAN is sidelink technology defined by The 3rd Generation Partnership Project (3GPP) Rel-17/18 in terms of required authentication, security, and billing; however, it isn’t available at the current stage. China Telecom kicked off the D2D service using the Wi-Fi Direct technique at the initial stage with additional servers and N3IWF (i.e., a secure gateway to operators’ 5G network for non-3GPP access). In the future, the service is expected to migrate on sidelink once it is available in the consumer market.

China Telecom offers this service for free and compensates customers who use the P-RAN to share signals. For example, if customers shared via the P-RAN over 1.6 Gigabyte (GB), they could redeem another 2 GB P-RAN data package with rewards of extra “golden beans” to exchange for other services, e.g., voice minutes or value-added services. At the beginning, sharing signals may happen within a family or a group of friends with low security concern, as well as small businesses, e.g., convenience stores or restaurants to provide Internet connections to their customers. China Telecom also promotes using old smartphones as relays to save costs from purchasing indoor routers. Many of those smartphones with idle Central Processing Units (CPUs) are still powerful in computing resources and can be reused to build the proximity network to improve the coverage.

The benefit of a P-RAN is more to save costs for mobile operators instead of generating new revenue streams. For example, China Telecom estimates that indoor solutions with Distributed Antenna Systems (DASs) can cost at least twice the Capital Expenditure (CAPEX) of macro cell deployments for similar data usage. Therefore, the P-RAN with macro cells and smartphone relays for indoor coverage makes an attractive solution for mobile operators to save costs and ensure service quality.

In the future, 5G-Advanced/6G use cases, such as Extended Reality (XR) applications, 4K/8K videos, and hologram communications, could keep increasing the bandwidth requirements. Operators may have to move toward higher spectrum bands. The problem is that higher frequencies have a smaller cell radius coverage, and the radius will leave more small coverage holes with losses from wall penetration. Available technologies, such as multiple antennas, Reflecting Intelligence Surface (RIS), and repeaters, can mitigate coverage issues, but not adequately, especially regarding small coverage holes. The P-RAN using smartphone relay provides a potential solution targeting this issue.

ABI Research considers that sidelink is a valuable technology to support operators for coverage issues with enabling extra use cases, such as indoor location, public safety, and peer-to-peer gaming. 3GPP started standardization of sidelink from 4G; however, use cases are mainly for Internet of Thing (IoT), Vehicle-to-Everything (V2X), and public safety services. From Rel-17/18, 3GPP will extend sidelink technology to the User Equipment (UE) side, but the business model will be a major challenge, especially for how to encourage smartphone users to participate as relays. The scale of participating devices makes a substantial difference to the performance of the P-RAN for available relays. China Telecom is using a software solution to bring customers onboard with Wi-Fi Direct before upgrading its D2D proximity network on sidelink, which shows a proactive effort to explore the possible business models. Additionally, China Telecom has demonstrated that data rates can be possibly improved for a smartphone user with one additional hop choosing from several relay smartphones.

The industry needs to continue the remaining work for the P-RAN, including power efficiency, battery status, commercial network security, and more intelligent algorithms to optimize those concerns, which are all critical to its future business success. At the same time, 3GPP has approved the working item of “Multi-relay” based on the idea of P-RAN in Release 19, which is led by China Telecom and supported by more than 10 companies, including Qualcomm, Huawei, OPPO, LG Electricity, and Charter Communications. An article from China Telecom, “The Proximity Radio Access Network for 5G and 6G” was published in the IEEE Communications Magazine to illustrate the concept of P-RAN, with more articles to be published in 2023.