High Rate Packet Data

Description

High Rate Packet Data (HRPD), also known as CDMA2000 1xEV-DO (Evolution-Data Optimized), is a packet-switched radio access technology defined by the 3GPP2 standards body and subsequently integrated into 3GPP specifications for interworking. Architecturally, the HRPD access network comprises two key logical components: the evolved Access Network (eAN) and the Packet Control Function (PCF). The eAN is responsible for the radio resource management, mobility management, and the physical and link layer protocols over the air interface. The PCF acts as the interface between the eAN and the packet data core network, managing the setup and teardown of packet data sessions and relaying user data.

The technology operates on a separate carrier dedicated solely to packet data, employing advanced techniques like adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), and fast scheduling to maximize spectral efficiency and user throughput. The air interface uses Time Division Multiplexing (TDM) for the forward link, allowing the entire channel capacity to be allocated to a single user at any given moment, which is optimal for bursty, high-speed data traffic. The reverse link employs Code Division Multiple Access (CDMA). Key protocols within HRPD include the Radio Link Protocol (RLP) for link-layer reliability and the Radio Network Protocol (RNP) for control signaling between the terminal and the network.

Within the 3GPP ecosystem, HRPD's primary role is defined in the context of non-3GPP access interworking. It connects to the 3GPP Evolved Packet Core (EPC) via the S2a interface based on the Proxy Mobile IPv6 (PMIPv6) or GTP protocols, facilitated by an evolved Packet Data Gateway (ePDG) or directly through a Packet Data Network Gateway (PGW). This architecture allows User Equipment (UE) with dual-radio capabilities (e.g., LTE and HRPD) to perform handovers between the two technologies, a feature standardized as Optimized Handover (eHRPD). The HRPD network provides the UE with always-on IP connectivity, supporting a wide range of IP-based multimedia services.

Purpose & Motivation

HRPD was created to address the growing demand for mobile broadband data services beyond the capabilities of 2G and early 3G CDMA networks (like CDMA2000 1xRTT), which were primarily circuit-switched and voice-optimized. Its development was motivated by the need for a high-speed, efficient, packet-only air interface that could deliver internet-like experiences on mobile devices, supporting applications such as video streaming, large file downloads, and web browsing with low latency.

The integration of HRPD into 3GPP standards, starting with Release 8, was driven by the practical necessity of global mobility and seamless service. As 3GPP's LTE became the dominant 4G technology, many operators with existing CDMA/HRPD networks needed a clear migration path. Standardizing the interworking procedures between EPC and HRPD allowed these operators to leverage their existing radio investments while transitioning subscribers to LTE, ensuring data session continuity during handovers and a consistent user experience. This solved the critical problem of network fragmentation and enabled a smoother technology evolution for a significant portion of the global market.