HSPA+ is expected to be commercially available in 2008 through [the introduction] of incremental investments and backward and forward compatible handsets. HSPA+ doubles the data capacity and increases voice capacity by three times enabling operators to offer mobile broadband at even lower cost" (Release 7 HSPA+, 2007, p. 3). Likewise, Housami (2008) reports that, "HSPA+ is a manifestation of the evolved HSPA philosophy where the existing HSPA implementation is pushed to its limits by introducing various improvements to increase the efficiency of the system while maintaining backward compatibility" (p. 2).
The term "HSPA+" is the name assigned to the set of HSPA enhancements that are defined in 3 GPP Release 7 (R7) and later; the enhanced downlink (HSDPA) was defined in 3 GPP R5 and provides three times the data capacity of WCDMA R99 (using a rake receiver and a single UE receive antenna) (Release 7 HSPA+).
Some of the more notable improvements included in the HSPA+ scheme are:
Higher order modulation;
The use of advanced receiver such as Equalizers and IC; and,
Possibly, the introduction of MIMO receivers and Receive diversity (Housami, 2008).
The main driver for HSPA+ is to capitalize on existing HSPA investment in infrastructure by focusing on backward compatibility and upgrade simplicity (Housami).
Long-Term Evolution (LTE) of 3 GPP. The main goal for the LTE of the 3 GPP is to enhance the 3 GPP standard to become a highly competitive packet-based radio access technology; to this end, 3 GPP provides a number of key advantages that promote enormous increases in performance and capacity with LTE. From a performance perspective, the main goals of LTE are:
Flexible spectrum usage with scalable system bandwidth from 1.25 MHz up to 20 MHz;
Increased spectrum efficiency and peak data rates at cell edge. Target peak rates of 100 Mbps/DL and 50 Mbps/UL; and,
Reduced latency for both user and control plane: less than 10ms round trip delay for user plane between UE and the serving RAN node, less than 100ms transition time for control plane between inactive state and active state (Housami).
According to this industry analyst, "LTE philosophy is more 'revolutionary' than HSPA+ in scope. In order to achieve the ambitious goals set for it, LTE takes a fresh look at system architecture and air interface access without the constraints of legacy systems. Therefore system architecture will noticeably change with a new radio access layer" (Housami, p. 2). While a number of features of LTE remain under development within 3 GPP, some of the main attributes are:
OFDM-based air interface (OFDM=Orthogonal Frequency Division Multiplexing).
Flat IP system architecture. (Often this is described as SAE: System Architecture Evolution, and is a separate study item in 3 GPP).
Higher level modulation and state of the art receiver technology (Housami).
R99 CS referring to 3GAmericas.com for R7 and R8.
According to Chiu and Lin (2004), "In order to avoid downlink channelization code shortage, a DSCH has been specified for WCDMA Release 99 system, and has been designed for enabling high data rate packet transmission. Further, WCDMA Release 5 introduces HSDPA to realize higher speed data rate together with lower round-trip times" (p. 1165). Indeed, HSPA+ provides three times more voice capacity through VoIP than R99 circuit-switched voice with the same quality and codec (Release 7 HSPA+). The enhanced uplink (HSUPA) was defined in R6 and doubles the uplink data capacity over WCDMA R99 (Release 7 HSPA+).
Figure 1. UMTS Evolution from Rel. 99 WCMDA.
Source: Release 7 HSPA+, p. 5.
Some of the key features involved in the evolution of the HSPA through its various permutations on the way to WiMAX are shown in Figure 2 below.
Figure 2. A single network element for user plane in radio and core network.*
Source: Khanna, p. 6.
Note: Same architecture in HSPA+, LTE and in WiMAX.
A description of the respective evolution phases of the 3 GPP from its Basic HSDPA+HSUPA configuration through its HSPA evolution to its Long-Term Evolution and Further HSPA evolution in shown in Table 3 below.
3 GPP evolution (Release 5 - Release 8).
Long-term evolution (LTE) + Further HSPA evolution
3 GPP R8
HSDPA 14 Mbps
1. HSUPA 5.76 Mbps
1. Enhanced FACH
2. Continuous packet connectivity
3. L2 optimization
4. Flat architecture
6. Higher order modulation
7. VoIP capacity
8. MBMS evolution
9. Evolved EDGE
1. LTE: New PS only radio
2. Further HSPA evolution
3. Uplink L2 optimization
4. Enhanced RACH
5. HSPA and I-HSPA carrier sharing.
Source: Khanna, 2008, p. 7.
Comparison of retransmission and scheduling delays: R99 versus HSPA.
Source: Khanna, p. 9.
According to Qualcomm, a number of UMTS operators are rapidly launching HSPA services to capitalize on its mobile broadband capabilities and increased data capacity. The enhanced downlink (HSDPA) had been launched commercially by 128 UMTS operators as of mid-2007, and deployment of the enhanced uplink (HSUPA) began during 2007; as indicated in Figure 3 above, HSPA+ is expected to be commercially available by the end of 2008 and represents the natural evolution of HSPA (Release 7 HSPA+). These authors also note that it further enhances the performance and capabilities of HSPA in the following ways:
HSPA+ doubles the data capacity over HSPA, thus reducing the cost of delivering data services and offering a better mobile broadband experience.
HSPA+ provides three times more voice capacity through VoIP than R99 circuit-switched voice with the same quality and codec.
HSPA+ VoIP frees up significant data capacity. The higher VoIP efficiency can also be used to free up significant data capacity in a mixed VoIP and data usage model. This helps to meet the increased demand for data services.
HSPA+ enhances the end-user experience through higher peak rates, lower latency, faster call set-up time, significantly longer talk time and a true "always-on" experience.
HSPA+ supports downlink peak rates up to 28 Mbps (42 Mbps in 3 GPP Release 8) and up to 11 Mbps in the uplink.
HSPA+ is the most economical evolution of HSPA, allowing UMTS operators to most efficiently use their existing assets and investments in network, spectrum and devices.
Like HSPA, HSPA+ is forward and backward compatible, allowing for a phased introduction of devices and a smooth upgrade to existing nodes.
HSPA+ is the optimal solution for a 5 MHz carrier, for existing, re-farmed 900 MHz, and for new spectrum; it provides similar data and voice performance as LTE in a 5 MHz block, using the same number of antennas.
The current HSPA deployment schedule is shown in Figure 3 below.
Figure 3. HSPA deployment schedule.
Source: Khanna, p. 8.
A graphic illustrating how HSPA pushes functionalities to base station is provided at Appendix a.
In sum, the following represent the key trends and features that can be expected based on the foregoing evolution from the R99 to the R7 and R8 formats:
HSDPA offers the highest peak data rates of any widely available wide area wireless technology, with peak user-achievable rates of over 1 Mbps
HSDPA today has the lowest latency of any widely available wide-area wireless technology
HSUPA will increase uplink speeds
HSPA+ will have peak network rates of 28 Mbps or higher, and in 5 MHz will match LTE capabilities
LTE will provide an extremely efficient OFDMA-based platform for future networks
EDGE/HSPA/LTE is one of the most robust portfolios of mobile broadband technologies and is an optimum framework for realizing the potential of the wireless-data market (Khanna).
The jury is in and the vote was not even close. The research showed that high speed packet access was shown to be evolving in important ways, with a number of innovations having already been implemented and other planned for deployment in the next few years. In addition, the research showed that the next-generation wireless systems such as Long-Term Evolution (LTE) and Ultra Mobile Broadband (UMB) will increasingly depend on VoIP and an IMS network for voice without supporting circuit-switched services. The research also showed that HSPA+ enables operators to offer these same high-capacity VoIP services to the end users without relying on the circuit-switched core network. In the final analysis, these innovations represent interim technological advances that bridge the gap between existing investments in telecommunications resources and infrastructure and the reality of ubiquitous computing envisioned by many authorities today.
Chiu, C.S. & Lin, C.C. (2004). Comparative downlink shared channel evaluation of WCDMA release 99 and HSDPA. IEEE International Conference on Networking, Sensing and Control, 2(2), 1165-1170.
Hazlett, T.W. (2006). Rivalrous telecommunications networks with and without mandatory sharing. Federal Communications Law Journal, 58(3), 477.
Herman, B.D. (2006). Opening bottlenecks: On behalf of mandated network neutrality. Federal Communications Law Journal, 59(1), 103.
Housami, H. (2007, January 4). Advanced cellular technologies episode…