Q&A: HSPA+

 
 
What is HSPA+? 
High Speed Packet Access Plus (HSPA+), also known as HSPA Evolution and Evolved HSPA, was standardized in 3GPP Release 7 and Release 8. HSPA+ will apply some of the techniques developed for Long Term Evolution (LTE) and allow operators to extend the life of their HSPA networks. 4G Americas initiated proposals at 3GPP to lead the development of the HSPA+ standards which now have received wide scale commitment from operators.
 
HSPA+ is an affordable and incremental upgrade to existing HSPA networks. It provides a tremendous advantage to HSPA operators, which is not an option for CDMA operators who are already unable to compete with the higher data throughput performance of HSPA and have no future evolution commercially viable for enhancement to their EV-DO networks today. Because it offers impressive performance at an incremental cost, some HSPA operators plan to use HSPA+ as a companion to LTE.
 
 
 
Where does HSPA+ lie in the GSM evolutionary path? 
HSPA+ is part of a clearly defined, standards-based evolution. It is the next step after UMTS enhanced with HSPA.
 
 
 
Source: Mobile Broadband Explosion, The 3GPP Wireless Evolution, Rysavy Research, August 2012
 
Operators typically will upgrade their networks from 3GPP Release 5 (HSDPA) to Release 6 (HSUPA) to support peak theoretical download speeds from 3.6 Mbps, to 7.2 Mbps and beyond to 14.4 Mbps. In 3GPP Release 7 and later in Release 8, HSPA+ is standardized and the peak theoretical throughput rates continue to increase to 21 Mbps and later 42 Mbps. Each step or upgrade delivers additional benefits in addition to increased data rates.
 
Telstra in Australia, Starhub in Singapore, CSL in Hong Kong and Mobilkom Austria in Central and Eastern Europe were the first operators to launch commercial HSPA+ networks in early 2009, initially providing peak theoretical download speeds of 21 Mbps. Many operators such as T-Mobile USA and Telstra upgraded their HSPA+ networks to 42 Mbps.
 
 
 
What are the main goals 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
  • Provide backward-compatibility 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 need only a simple upgrade to support the features defined as part of HSPA+.
 
 
 
What are the expected speeds of HSPA Evolution (HSPA+)? 
HSPA+ exceeds the throughput performance of OFDMA systems (such as mobile WiMAX) in 5 MHz of spectrum and will deliver peak theoretical downlink speeds of 21 Mbps in the first phase with 64 QAM (Quadrature Amplitude Modulation). The second phase will include both 64 QAM and advanced antenna techniques such as 2X2 MIMO and can deliver 42 Mbps theoretical capability and 11.5 Mbps on the uplink. HSPA+ with MIMO became available in 2010. By 2011, operators were deploying dual carrier HSPA+ at peak theoretical downlink rates of 42 Mbps. There are standardization and commercial plans to lift this even further to 84 Mbps and beyond.
 
 
 
What are the strategic benefits for an HSPA operator to invest in HSPA+?
HSPA+ is an affordable and incremental upgrade to existing HSPA networks. It provides a strategic roadmap advantage to incumbent GSM-HSPA operators, which is not an option for CDMA EV-DO operators who are already unable to compete with the higher data throughput performance of HSPA today. CDMA operators have no future evolution commercially viable for enhancement to their EV-DO networks (UMB, the intended evolution to EV-DO, has been standardized by 3GPP2; however, it appears to lack commercial opportunity or operator uptake). Therefore, the need to deploy LTE as quickly as possible is more critical for CDMA operators like Verizon. HSPA operators have the option to upgrade to HSPA+ and choose the market timing that is best for their commercial strategies. Operators from the Americas that have already chosen HSPA+ include América Móvil, Rogers and T-Mobile USA.
 
HSPA+ protects an operator’s investment in the network. HSPA+ enhancements are backward-compatible with UMTS Release 99/Release 5/Release 6. HSPA+ will provide a bridge to LTE with smooth interworking between HSPA+ and LTE that will facilitate both technologies. As such, operators may choose to leverage the System Architecture Evolution/Evolved Packet Core (SAE/EPC) planned for LTE. Additionally, HSPA+ will significantly increase HSPA capacity as well as reduce latency below 50 milliseconds (ms). HSPA+ supports voice and data services on the same carrier and across all of the available radio spectrum and offers these services simultaneously to users.
 
 
 
What is MIMO? How is it related to HSPA+? 
Multiple-Input Multiple-Output (MIMO) is an antenna technology that is used both in transmission and receiver equipment for wireless radio communication. MIMO uses multiple antennas to send multiple parallel signals (from transmitter). MIMO is defined as, two or more unique radio signals, in the same radio channel, where each signal carries different digital information, or, two or more radio signals which use beamforming, receive combining and spatial multiplexing.
 
Operators affirm that the benefits envisioned from MIMO in LTE (Release 8) can also be obtained from MIMO in UMTS systems, starting in Release 7 HSPA. By using MIMO in the second phase of HSPA+, the theoretical peak throughput rates on the downlink are virtually doubled from 21 Mbps to 42 Mbps. Spatial Multiplexing MIMO will benefit HSPA hotspots serving local areas, such as airports, campuses and shopping 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  in the range of 20 to 33 percent over mobile-receive diversity. Relative to a standard 1x1 antenna system, however, 2x2 MIMO can deliver cell substantial throughput gains. 3GPP is standardizing spatial multiplexing MIMO in Release 7 using Double Transmit Adaptive Array (D-TxAA).
 
 
 
How does HSPA+ compare to WiMAX? 
Depending on the features implemented, HSPA+ could exceed the potential performance capabilities of IEEE 802.16e-2005 (mobile WiMAX) in the same amount of spectrum.
 
 
 
Which operators are expected to deploy HSPA+?
It is expected that virtually all HSPA operators will deploy the first phase of HSPA+. Some operators may choose to deploy LTE with MIMO technology rather than the second phase of HSPA+ with MIMO. This will clearly depend upon an operators’ strategy and market demands.
 
Telstra in Australia, Starhub in Singapore, CSL in Hong Kong and Mobilkom Austria in Central and Eastern Europe were the first operators to launch commercial HSPA+ networks in early 2009, initially providing theoretical peak download speeds of 21 Mbps. Several operators such as T-Mobile USA and Telstra launched HSPA+ networks to 42 Mbps.