Mobile Originated Handover

Description

Mobile Originated Handover (MOHO) is a specific type of handover procedure in cellular networks where the initiative to trigger the handover comes from the mobile device (MS in GSM/UMTS, UE in LTE/5G), as opposed to the network (Network Originated Handover). The UE continuously performs measurements on the serving cell and neighboring cells as configured by the network via measurement control messages. When the UE's internal algorithms determine that a handover is necessary or beneficial—for instance, due to deteriorating signal quality from the current cell or a significantly stronger signal from a neighbor—it can send a measurement report to the network with a specific indication or, in some system implementations, explicitly request a handover.

The technical process involves the UE's physical and protocol layers. The UE's Layer 1 (physical layer) measures reference signal received power (RSRP), reference signal received quality (RSRQ) in LTE/5G, or received signal code power (RSCP) in UMTS. These measurements are processed by the UE's Radio Resource Control (RRC) layer. Based on configured thresholds and hysteresis parameters received from the network, the UE's RRC entity decides if an event-triggered measurement report should be sent. For a MOHO, this report may contain a recommendation for a specific target cell. Upon receiving this, the network's RAN node (e.g., eNodeB, gNB) makes the final decision, considering additional factors like network load and admission control, before executing the handover preparation and execution phases with the target cell.

MOHO is a critical component of UE-assisted, network-controlled handover schemes. It shifts part of the processing burden and decision-initiative to the UE, which has direct and immediate knowledge of the radio environment. This can lead to faster reaction times to rapid signal fading. The network maintains ultimate control to ensure overall stability and resource optimization. Key components enabling MOHO include the UE measurement capabilities, the RRC protocol for reporting, and the network's measurement configuration and handover decision algorithms. In advanced systems, MOHO principles are foundational for features like conditional handover (CHO) in 5G, where the UE is pre-configured with handover conditions.

Purpose & Motivation

MOHO was developed to improve the reliability and efficiency of handovers in dynamic radio environments. In early cellular systems, handovers were primarily network-originated based on measurements reported by the base stations, which might not fully capture the rapid signal variations experienced by a fast-moving mobile device. This could lead to dropped calls or suboptimal connectivity. MOHO empowers the UE, the entity directly experiencing the radio link, to proactively initiate the handover process, thereby reducing latency in responding to degrading conditions.

The technology solves the problem of handover lag and "ping-pong" effects in borderline areas. By allowing the UE to trigger based on its precise measurements, the handover can occur before the connection quality falls below a usable threshold, improving call drop rates. It is particularly valuable in scenarios with small cells or high user mobility, where radio conditions change quickly. MOHO also contributes to overall network performance by facilitating load balancing; a UE experiencing congestion in its current cell can request a handover to a less loaded neighbor, an aspect that has evolved in later standards.

Historically, handover was a tightly network-controlled process. The introduction of MOHO, particularly from GSM/UMTS eras, represented a shift towards more distributed mobility management. It acknowledged the UE as an intelligent agent in the network. This concept laid the groundwork for increasingly UE-centric mobility in 4G and 5G, such as UE-autonomous search and measurement, and ultimately conditional handover where the UE executes the handover itself upon meeting network-defined conditions, minimizing signaling delay and increasing robustness.

Key Features

• Handover trigger initiated by the User Equipment (UE)
• Based on UE-conducted measurements of serving and neighboring cells
• UE sends measurement reports with potential handover recommendations
• Final handover decision and execution authority remains with the network
• Reduces handover latency by leveraging UE's real-time radio awareness
• Foundation for advanced mobility schemes like conditional handover

Evolution Across Releases

Defining Specifications