Proximity Services Communication

Description

ProSe Communication is a fundamental enabler for device-to-device (D2D) communication in 3GPP networks, introduced in Release 12. It allows two or more ProSe-enabled User Equipments (UEs) that are in proximity to communicate directly with each other, either via a direct radio link (using E-UTRA technology) or through a communication path that is routed via local eNodeBs (eNBs). This capability is part of the broader Proximity Services (ProSe) framework, which aims to enable discovery and communication between devices that are close to each other, without necessarily involving the core network for user-plane data.

Architecturally, ProSe Communication can be realized in several modes. In the direct communication mode, UEs establish a direct radio link using sidelink (PC5 interface) based on E-UTRA technology. This requires the UEs to be synchronized and to have the necessary radio resources, which can be allocated by the network (mode 1) or autonomously selected by the UEs (mode 2). In the locally-routed mode, the communication path goes through one or more local eNBs, which may forward user-plane data between the UEs without traversing the core network. This is particularly useful when the UEs are not able to establish a direct link but are still within the coverage of the same or nearby eNBs. The ProSe Communication path is thus flexible and can be adapted based on network conditions, UE capabilities, and operator policies.

Key components involved in ProSe Communication include the ProSe Function, which is a logical function in the core network that handles authorization, provisioning, and policy control for ProSe services. The ProSe Function interacts with the HSS (Home Subscriber Server) to authenticate and authorize UEs for ProSe Communication, and with the EPC (Evolved Packet Core) to manage mobility and session continuity. The UEs themselves must be ProSe-enabled, meaning they support the necessary protocols and procedures for discovery and communication. The radio access network (E-UTRAN) provides the sidelink resources and may assist in synchronization and resource allocation.

ProSe Communication operates in both network-covered and out-of-coverage scenarios. In network coverage, the network can control the communication, allocate resources, and provide security parameters. Out of coverage, UEs can still communicate directly using pre-configured parameters, which is essential for public safety and emergency scenarios. The communication can be one-to-one, one-to-many, or many-to-many, supporting various use cases such as group communication, relay, and broadcast.

Security is a critical aspect of ProSe Communication. The 3GPP specifications define security procedures for direct communication, including mutual authentication, key agreement, and privacy protection. The security architecture ensures that only authorized UEs can participate in ProSe Communication and that the user data is protected. The ProSe Function plays a central role in distributing security policies and credentials.

Overall, ProSe Communication represents a significant evolution in cellular networks, enabling new services and improving network efficiency by allowing direct communication between devices. It is a key technology for public safety, social networking, and IoT applications, and its continued development in later releases (e.g., 5G ProSe) ensures its relevance in future networks.

Purpose & Motivation

ProSe Communication was created to address the growing demand for direct device-to-device communication in cellular networks. Traditional cellular communication always routes user data through the core network, which can be inefficient for local communication, introduce latency, and consume network resources. ProSe Communication solves these problems by enabling UEs in proximity to communicate directly or via local eNBs, thereby offloading traffic from the core network, reducing latency, and enabling new applications such as public safety communication, social networking, and local content sharing.

Historically, direct communication between devices was not supported in 3GPP networks; all communication had to go through the network infrastructure. This limitation hindered the development of services that require low latency and high throughput for local interactions. The introduction of ProSe in Release 12 was motivated by the need for public safety agencies to have reliable communication even when network coverage is unavailable or congested. It also addressed the commercial demand for proximity-based services, such as finding friends nearby or sharing media locally.

ProSe Communication builds on the concept of proximity discovery, allowing devices to first discover each other and then establish a communication path. It leverages the existing E-UTRAN infrastructure and introduces new interfaces and procedures to support direct communication. The technology has evolved over releases to support more advanced features, such as relay, group communication, and integration with 5G. Its creation marked a shift towards more flexible and efficient use of network resources, paving the way for future device-centric communication paradigms.