Multi-Carrier High Speed Uplink Packet Access

Description

Multi-Carrier HSUPA (MC-HSUPA) is the uplink counterpart to MC-HSDPA, standardized from 3GPP Release 10 as part of the HSPA evolution. It allows a single User Equipment (UE) to transmit on multiple uplink WCDMA carriers concurrently, thereby aggregating the uplink bandwidth and increasing the peak uplink data rate. Similar to the downlink, one carrier typically serves as the Uplink Anchor Carrier, handling essential control signaling and dedicated channels, while additional Uplink Secondary Carriers are used for enhanced uplink data transmission via the E-DCH (Enhanced Dedicated Channel).

Operationally, for a UE configured with MC-HSUPA, the network assigns a primary uplink carrier which carries the DPCCH (Dedicated Physical Control Channel) for power control and pilot signals, as well as any associated DPDCH (Dedicated Physical Data Channel). The secondary uplink carrier(s) are configured with their own set of E-DPDCHs (Enhanced Dedicated Physical Data Channels) for high-speed data. The UE must manage its transmit power across multiple carriers, adhering to the maximum power limitation of the device. Scheduling grants, which control the UE's uplink transmission rate, are managed per carrier. The UE sends scheduling information (SI) and Happy Bits separately for each active E-DCH carrier, allowing the Node B's scheduler to control uplink resources independently on each.

The implementation requires enhancements in both the UE and the Node B. The UE must support multiple transmit chains and power amplifiers capable of simultaneous transmission on different frequencies, which has implications for device complexity and battery consumption. The Node B must be able to receive and demodulate the combined signal from the multiple uplink carriers. Key technical specifications for MC-HSUPA, including supported carrier combinations and UE categories, are detailed in 3GPP TS 25.102 and 25.319. For instance, Dual-Cell HSUPA (DC-HSUPA) in Release 10 aggregates two adjacent uplink carriers, potentially doubling the peak uplink rate from the single-carrier maximum of 11.5 Mbps to 23 Mbps, depending on the UE category and network configuration.

MC-HSUPA plays a crucial role in creating a symmetric high-speed experience in HSPA networks. While MC-HSDPA addressed the downlink bottleneck, many emerging applications (like video upload, cloud sync, and real-time communication) created demand for higher uplink capacity. By enabling uplink carrier aggregation, MC-HSUPA improves the overall balance of the radio link, reduces uplink latency for large data bursts, and increases the uplink capacity of a cell. It allows operators to make better use of their paired spectrum assets and provides a more complete broadband experience on HSPA networks, complementing the downlink capabilities and extending the technology's relevance in the era of increasing user-generated content and interactive services.

Purpose & Motivation

MC-HSUPA was developed to address the growing asymmetry between downlink and uplink capabilities in evolved HSPA networks. The prior focus had been on enhancing downlink speeds with features like MC-HSDPA and MIMO, leaving the uplink as a potential bottleneck. The rise of user-generated content, video calling, and cloud-based applications created a clear need for higher uplink throughput and lower latency. MC-HSUPA solved this by applying the multi-carrier aggregation principle to the uplink, directly increasing the peak data rate and spectral resources available for transmission from the UE.

It addressed the limitations of single-carrier HSUPA, which was constrained by the 5 MHz bandwidth and the UE's limited transmit power. By aggregating carriers, a UE could spread its transmission across a wider bandwidth, achieving higher rates without necessarily increasing peak power spectral density. This was more efficient and technically feasible than simply widening a single carrier. The technology also improved uplink cell capacity by allowing the scheduler to allocate resources across multiple carriers, serving more users simultaneously with high uplink data rates.

The creation of MC-HSUPA was motivated by the desire to provide a complete, high-performance HSPA evolution. It ensured that HSPA+ could deliver a balanced broadband experience, making it a more viable alternative or complement to LTE, especially in markets where LTE deployment was slower or where HSPA coverage was more extensive. By standardizing it in Release 10 alongside MC-HSDPA enhancements, 3GPP provided a clear roadmap for operators to upgrade their networks symmetrically, maximizing the utility of their existing UMTS spectrum investments and infrastructure.

Key Features

• Aggregates multiple 5 MHz WCDMA uplink carriers for a single UE
• Uses Uplink Anchor Carrier for control and Secondary Carriers for E-DCH data
• Increases peak uplink data rates proportionally to number of carriers
• Requires UE with multiple transmit chains and power amplifier support
• Features per-carrier uplink scheduling via E-AGCH and E-RGCH grants
• Improves uplink cell capacity and reduces latency for data bursts

Evolution Across Releases

Defining Specifications