DCH

A Dedicated Channel is a radio resource in UMTS (Universal Mobile Telecommunications System) networks allocated exclusively to a single user for the duration of a connection. Unlike shared channels that multiplex traffic from many users, a DCH reserves both uplink and downlink capacity on the cell, guaranteeing bandwidth and latency characteristics for the duration of the call or data session.

DCH operates at the physical layer and carries user traffic, signaling, or both. The channel occupies a specific code on the CDMA hierarchy and is maintained throughout the connection lifetime. Common data rates range from 64 kbit/s to 2 Mbit/s, though higher rates are possible with multi-code operation, where a single user occupies multiple spreading codes in parallel to increase throughput.

The DCH is established through the Radio Resource Control layer after connection setup and may be modified during an active session if bandwidth requirements change. This differs fundamentally from Shared Channels (DSCH, FACH), which allow multiple users to share the same physical resource through time-division or code-division multiplexing. The trade-off is efficiency: DCH guarantees quality at the cost of lower spectral utilization during periods of light load.

Variants and measurement

A DCH is defined by its configuration: code allocation, spreading factor, power level, and whether it carries data, control signaling, or both. Measurement of a DCH includes received signal code power (RSCP) and signal-to-interference ratio (SIR), which determine if the link remains viable. When SIR falls below the target threshold, power control increases transmit power or the base station initiates handover or soft handoff to adjacent cells.

DCH resources are finite on a given sector. When all DCH capacity is exhausted, new connection requests may be rejected or queued, making DCH admission control critical for network planning. This limitation is one reason modern networks transitioned toward HSPA and later LTE, which rely more heavily on shared channel resources and packet scheduling rather than circuit-like dedicated allocations.