Field Guide · protocol

Also known as: HSPA, HSDPA, HSUPA, HSPA+, High Speed Packet Access, 3.5G

HSPA (High Speed Packet Access) is the 3.5G family of enhancements to UMTS/W-CDMA, combining HSDPA on the downlink and HSUPA on the uplink. It layers fast, shared, scheduled channels over the existing 5 MHz CDMA carrier and adds higher-order QAM plus hybrid ARQ to deliver true mobile-broadband speeds.1

scheduler 2 ms transmission-time intervals → best-placed user served each slot adaptive QPSK / 16-QAM / 64-QAM + hybrid ARQ retransmission shared high-speed channel over one 5 MHz W-CDMA carrier
HSPA adds a fast shared channel with a base-station scheduler that serves the best-placed user in each 2 ms interval, adapting modulation to radio conditions.

Overview

Plain UMTS gave every bearer a fixed dedicated channel, which was inefficient for the bursty traffic of web and app use. HSPA introduces a high-speed shared channel that a fast scheduler in the base station reallocates every 2 ms to whichever user currently has the best signal. It couples this with adaptive modulation (up to 64-QAM), hybrid ARQ that combines retransmissions rather than discarding them, and later MIMO — all on the same 5 MHz W-CDMA carrier.

Technical characteristics

Property Value
Generation 3.5G
Components HSDPA (down), HSUPA (up), HSPA+ (evolved)
Carrier spacing 5 MHz (as W-CDMA)
Modulation QPSK, 16-QAM, 64-QAM (down); QPSK, 16-QAM (up)
Scheduling 2 ms TTI, fast link adaptation
Retransmission Hybrid ARQ with soft combining
Peak (HSPA+) Tens of Mbit/s with MIMO / dual-carrier

Key rate gains come from moving scheduling and retransmission control from the core network down into the base station, cutting latency and reacting to fast fading.

History

3GPP introduced HSDPA in Release 5 (2002 spec, networks from about 2005) and HSUPA in Release 6, together branded HSPA. Later releases added HSPA+ (also called Evolved HSPA), bringing 64-QAM, MIMO, and multi-carrier operation that kept 3G competitive as LTE rolled out.

Deployment

HSPA became the workhorse of 3G mobile broadband worldwide, delivered through USB modems and smartphones alike, and HSPA+ let operators advertise “4G-like” speeds on upgraded 3G networks. It runs on the same UMTS carriers and core, so activation was largely a software and scheduler upgrade. HSPA is now being retired as carriers shut down 3G in favour of LTE and 5G.

Decoding it with GopherTrunk

GopherTrunk scans trunked land-mobile and utility signals; cellular broadband such as HSPA is out of scope and is not decoded. It carries private, authenticated, ciphered subscriber data on licensed W-CDMA spectrum. HSPA is included for reference as the high-speed evolution of 3G.

Sources

  1. High Speed Packet Access — Wikipedia, for the 3.5G HSPA family, its HSDPA/HSUPA components, fast shared-channel scheduling, and higher-order QAM. ↩

See also