Q&A: HSPA+
What is HSPA+?
What are the main goals and benefits of HSPA+?
What are the expected speeds of HSPA Evolution (HSPA+)?
What is MIMO and how is it related to HSPA+?
How does HSPA+ compare to WiMax?
Where does HSPA+ lie in the GSM evolutionary path?
What is HSPA+?
High Speed Packet Access Plus (HSPA+), also known as High Speed Packet Access Evolution, is a new work study item in 3GPP that is intended to be an upgrade to HSPA technology. HSPA+ is an effort to further improve the radio performance of HSPA (HSDPA and HSUPA combined) to create a highly optimized version of HSPA that employs both Release 7 features and other incremental features such as interference cancellation and optimizations to reduce latency as well as enable co-existence with and a smooth migration path towards LTE (Long Term Evolution) and SAE (System Architecture Evolution).
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What are the main goals and benefits of HSPA+?
The main goals of HSPA+ are to enhance HSPA (HSDPA and HSUPA combined) as well as enable co-existence with and a smooth migration path towards LTE and SAE. It is intended that HSPA+ will:
- Exploit the full potential of a CDMA approach before moving to an OFDM platform in 3GPP LTE.
- Achieve performance comparable to LTE in 5 MHz of spectrum.
- Provide smooth interworking between HSPA+ and LTE that facilitates operation of both technologies. As such, operators may choose to leverage the SAE planned for LTE.
- Allow operation in a packet-only mode for both voice and data.
- Be backward compatible with previous systems while incurring no performance degradation with either earlier or newer devices.
- Facilitate migration from current HSPA infrastructure to HSPA+ infrastructure.
HSPA will also provide increased cost savings as well as increases in performance via architectural enhancements. Ideally, existing infrastructure should only need a simple upgrade to support the features defined as part of HSPA+.
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What are the expected speeds of HSPA Evolution (HSPA+)?
The goal of HSPA+ is to match the performance of OFDMA systems in 5 MHz of
spectrum. HSPA+ will expand the capabilities of existing infrastructure
with minimal equipment upgrades and extend the life cycle of the current
HSPA equipment that is being used.
Currently, the standard is still being worked on at 3GPP. However, the
general objectives are:
- Reach peak theoretical network downlink speeds of 28 Mbps (using
2x2 MIMO and 16 QAM (Quadrature Amplitude Modulation)
- Reach peak theoretical network uplink speeds of 11.5 Mbps
- Evolve to a peak theoretical network downlink speed of 42 Mbps
using 2x2 MIMO and 64 QAM (when 64 QAM is available)
Evolution of TDMA, CDMA, and OFDM systems: 2006-2011 (PDF - 71 KB)
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What is MIMO and how is it related to HSPA+?
The term “MIMO” is an acronym for multiple-input, multiple-output, and it is used to refer to any wireless system with multiple antennas at the transmitter and receiver. At the transmitter, multiple antennas can be used to mitigate the effects of fading via transmit diversity and to increase throughput via spatial division multiple access (SDMA). Beamforming and sectorization are two examples of SDMA. At the receiver, multiple antennas can be used for receiver combining which provides diversity and combining gains. If multiple antennas are available at both the transmitter and receiver, then different data streams can be transmitted from each antenna, with each stream carrying different information but using the same frequency resources. This technique, known as spatial multiplexing (SM), can potentially increase a user's peak data rate compared to conventional single-stream transmission. The transmitter sends different data streams over each antenna. Whereas multipath impedes other radio systems, MIMO actually exploits multipath, relying on signals to travel across different communication paths. This results in multiple data paths effectively operating somewhat in parallel and, through appropriate decoding, in a multiplicative gain in throughput.
Tests of MIMO have proven very promising in wide local area networks (WLANs) operating in relative isolation, where interference is not a large factor. Spatial multiplexing MIMO should also benefit HSPA “hotspots” serving local areas such as airports, campuses, and malls, where the technology will increase capacity and peak data rates. However, in a fully loaded network with interference from adjacent cells, overall capacity gains will be more modest.
Although MIMO can significantly improve peak rates, other techniques such as Space Division Multiple Access (SDMA)—also a form of MIMO—may be even more effective than MIMO for improving capacity in high spectral efficiency systems using a reuse factor of 1. 3GPP has enhanced the system to support SDMA operation as part of Release 6.
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How does HSPA+ compare to WiMax?
Depending on the features implemented, HSPA+ could match, and possibly exceed, the potential performance capabilities of IEEE 802.16e-2005 (mobile WiMAX) in the same amount of spectrum.
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Where does HSPA+ lie in the GSM evolutionary path?
HSPA+ is part of a long, clearly defined, standards-based evolution. It is the next step after UMTS enhanced with HSPA (HSDPA and HSUPA combined). Operators typically will upgrade their networks to HSUPA even as they continue to upgrade their existing HSDPA infrastructure to support peak download speed of 3.6 Mbps, 7.2 Mbps and beyond. This approach means that HSPA devices and networks, expected to be deployed in 2007, will provide increasingly fast upload and download speeds.
That near-symmetry is important for users who send large files as often as they receive them and for bandwidth-intensive applications such as videoconferencing.
HSPA+ technology provides the operator with enhancements towards a packet core as an upgrade to HSPA. In addition, HSPA+ will enable a smooth transition to the next major technological step: Long Term Evolution (LTE), expected to be commercially available by 2009. LTE is being designed to support peak download rates of 100 Mbps and peak upload rates of 50 Mbps. LTE also will feature all-IP network infrastructure.
For more details about HSPA, HSPA+ and LTE, see the September 2006 white paper “Mobile Broadband: EDGE, HSPA and LTE” and the July 2006 white paper “Mobile Broadband: The Global Evolution of UMTS/HSPA – 3GPP Release 7 and Beyond.”
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