Given the budget advantages, many operators have chosen HSPA+ over Long Term Evolution (LTE) as their short-term upgrade strategy.
As more data services are handled by mobile networks, network provision must change. For example, successive advances in technology and enhanced system specifications have provided higher cell capacity and consequent improvements in single-user data rates. Current High Speed Packet Access (HSPA) networks can deliver data rates to 14 Mb/s on downlinks and 5.8 Mb/s on uplinks. Evolved HSPA (HSPA+), in contrast, delivers data rates of 21 Mb/s on downlinks and 11 Mb/s on uplinks. In “Concepts and Measurements of HSPA+ Evolution,” Agilent Technologies notes that many operators have chosen HSPA+ over Long Term Evolution (LTE) as their short-term upgrade strategy. For networks based on 3GPP specifications, HSPA+ is simply a software upgrade—making it quite budget friendly.
The application note begins by laying out the major goals of HSPA+: to exploit the full potential of the Code-Division-Multiple-Access (CDMA) physical layer (PHY) before moving to LTE’s orthogonal-frequency-division-multiplexing (OFDM) PHY; to achieve performance that compares with LTE in a 5-MHz channel bandwidth; and to provide smooth interworking between HSPA+ and LTE. The standard also is tasked with enabling both technologies to coexist in one network. For both voice and data, HSPA+ will allow operation in packet-only mode. Finally, HSPA+ will of course be backward compatible with earlier user devices.
All current Wideband-CDMA (W-CDMA) systems are based on 5-MHz channel bandwidth. While 3.84 MHz of that bandwidth is used, the rest acts as a guardband between channels. Release 8 offers a dual-carrier option for High-Speed Downlink Packet Access (HSDPA). As a result, the system can aggregate the content of two contiguous channels to double downlink rates. If the HSPA+ network operates completely in packet mode for voice and data, the backhaul network is updated. This aspect will simplify future LTE deployment, as only the physical (base-station radio) layer would need a major upgrade.
The document clearly provides all of the important features of HSPA+ by release. For 3GPP Release 7, for example, the key aspects are the following: multiple-input multiple-output (MIMO) capability on downlink; higher-order modulation of 16-state quadrature amplitude modulation (16QAM) for uplink and 64-state QAM (64QAM) for downlink; and continuous packet connectivity (CPC). Release 8, in contrast, combines MIMO and 64QAM, reaching a peak rate of 42 Mb/s. It also provides CS over HSPA, which is a circuit-switched connection in a packet-based user network. The final new element in Release 8 is dual-carrier HSDPA (which, notably, cannot be combined with MIMO). In Release 9 and beyond, further multi-carrier capability will be added. While providing insight into the test and measurement tools that will be needed for successful HSPA+ deployment, this application note clearly explains why moving to HSPA+ may be a better move for carriers than jumping directly to LTE.
Agilent Technologies, 5301 Stevens Creek Blvd., Santa Clara, CA 95051; (877) 424-4536, www.agilent.com.
