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.
Table 3.
3 GPP evolution (Release 5 - Release 8).
Basic HSDPA+HSUPA
HSPA evolution
Long-term evolution (LTE) + Further HSPA evolution
HSPA R5
HSPA R6
HSPA R7
3 GPP R8
HSDPA 14 Mbps
1. HSUPA 5.76 Mbps
2. MBMS
1. Enhanced FACH
2. Continuous packet connectivity
3. L2 optimization
4. Flat architecture
5. MIMO
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.
Table 4.
Comparison of retransmission and scheduling delays: R99 versus HSPA.
Release 99
HSPA
Retransmission delay
12 ms
Scheduling delay
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...
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