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HSDPA vs HSUPA: Key Differences Explained

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This article clarifies the differences between HSDPA and HSUPA technologies. Both are enhancements to WCDMA (Wideband Code Division Multiple Access), which initially supported downlink speeds of about 3.6 Mbps and uplink speeds of 384 Kbps. Devices compatible with these technologies are known as HSDPA modems and HSUPA modems. HSDPA and HSUPA both fall under the umbrella of HSPA (High-Speed Packet Access).

HSPA+ offers even higher speeds, reaching up to 84 Mbps in the downlink and approximately 23 Mbps in the uplink. It adheres to 3GPP Release 7, 8, and 9 standards. HSPA+ incorporates MIMO (Multiple-Input Multiple-Output), a more advanced modulation scheme using 64QAM (Quadrature Amplitude Modulation) for the downlink and 16QAM for the uplink, along with Layer 2 enhancements such as flexible PDU (Protocol Data Unit) sizes. HSPA+ also supports CPC (Continuous Packet Connectivity), enabling VOIP (Voice over Internet Protocol) and CS (Circuit Switched) voice services over the HSPA network.

Key Differences Between HSDPA and HSUPA

The following table summarizes the key differences between HSDPA and HSUPA:

Specification	HSDPA	HSUPA
Full Form	High-Speed Downlink Packet Access	High-Speed Uplink Packet Access
3GPP Standard	Release 5	Release 6
Applications	Video download, video conferencing	Big file upload
Direction	Downlink (from network to mobile device)	Uplink (from mobile device to network)
Modulation	QPSK, 16QAM (Older systems may only support QPSK)	QPSK
Data Rate	7.2 Mbps (previous) / 14.4 Mbps	About 5.76 Mbps
Physical Channel Additions	E-HICH, E-AGCH, E-RGCH, HS-PDSCH	E-DPDCH, E-DPCCH
MAC Layer	Supports MAC-hs (H-ARQ and rate adaptation)	Newly added E-DCH transport channel supports MAC-e/es sublayer
TTI (Transmission Time Interval)	2 ms (R99 supported 10ms as shortest TTI)	2 ms, 10 ms

Breakdown of the Specifications

HSDPA (High-Speed Downlink Packet Access): Focuses on improving the download speed from the network to the mobile device.
HSUPA (High-Speed Uplink Packet Access): Focuses on improving the upload speed from the mobile device to the network.

Physical Channel Additions Explained:

HSDPA:
- E-HICH (Enhanced Hybrid Indicator Channel): Carries ACK/NACK (acknowledgement/negative acknowledgement) signals for HARQ.
- E-AGCH (Enhanced Absolute Grant Channel): Assigns resources for HSDPA transmissions.
- E-RGCH (Enhanced Relative Grant Channel): Adjusts existing resource allocations.
- HS-PDSCH (High-Speed Physical Downlink Shared Channel): The main channel used for transmitting data in the downlink.
HSUPA:
- E-DPDCH (Enhanced Dedicated Physical Data Channel): Carries user data in the uplink.
- E-DPCCH (Enhanced Dedicated Physical Control Channel): Carries control information related to the uplink transmission.

MAC Layer Functionality:

HSDPA: Employs the MAC-hs protocol, which incorporates H-ARQ (Hybrid Automatic Repeat Request) for retransmitting erroneous data blocks and rate adaptation to optimize data throughput.
HSUPA: Introduces the E-DCH transport channel with MAC-e/es sublayers. MAC-e handles HARQ, demultiplexing, and fast scheduling, while MAC-es manages reordering, combining, and disassembly of PDUs.