Understanding HSPA Network Architecture and Technologies

HSPA stands for High-Speed Packet Access. It’s a network architecture primarily designed to support high-speed data rates in both the uplink and downlink directions.

HSPA includes categories such as HSDPA, HSUPA, and HSPA+. These standards follow different UMTS (Universal Mobile Telecommunications System) releases.

• HSDPA follows the UMTS R5 release and supports peak data rates of about 14 Mbps.
• HSUPA follows the UMTS R6 release and supports uplink data rates of about 5.76 Mbps.
• HSPA+ follows the R7-R9 UMTS releases.

HSPA supports a spectral efficiency of about 2.9 bits/sec/Hz. It is a mobile communication technology that enhances the capabilities of 3G (Third Generation) networks. HSPA is also referred to as “3.5G” or “3.75G” due to its position between 3G and 4G mobile cellular technologies.

HSPA Architecture

The HSPA network consists of several components and technologies that work together to provide high-speed data communication for mobile devices as well as voice calls.

The HSPA architecture contains the following elements:

• UE (User Equipment)
• NodeB (Base Station)
• RNC (Radio Network Controller)
• NodeB Gateway
• Core Network

• User Equipment (UE): These are mobile devices such as mobile phones, smartphones, tablets, and data cards. They represent the end-point users of the HSPA network.
• NodeB (Base Station): This is the cell tower equipped with HSPA radio interfaces and protocols. It communicates with HSPA-compliant UEs over the air interface and is responsible for radio resource management, connection establishment and release, power control, and handovers.
• RNC (Radio Network Controller): This is the central component in the HSPA network, managing multiple NodeBs. It handles tasks such as handover between calls, RRM (Radio Resource Management), and coordination of radio bearers.
• NodeB Gateway (Iub interface): This interface connects NodeBs to the RNC, facilitating the transmission of user data and control signaling between the NodeBs and the core network.
• Core Network: It includes various components which enable communication between mobile devices and external networks such as PSTN (Public Switched Telephone Network) and internet (e.g. PSDN).The key components of the core network are MSC (Mobile Switching Center), SGSN (Serving GPRS Support Node), GGSN (Gateway GPRS Support Node), HLR (Home Location Register) and VLR (Visitor Location Register).
• PS (Packet Switched) and CS (Circuit Switched) domain: HSPA primarily operates in the PS domain, allowing efficient data transmission using IP protocols. It also supports circuit-switched connections for voice calls.

HSDPA Overview

As mentioned earlier, HSDPA is mainly designed for high-speed data rates in the downlink, primarily for internet-based applications, hence the name High-Speed Downlink Packet Access. As mentioned in UMTS tutorial, UMTS architecture composed of three main parts UE (User Equipment), RAN (Radio Access Network) and Core Network. In HSDPA changes are incorporated on air interface side and hence UE and RAN have been modified to take care of higher data rate requirements compare to its predecessor i.e. UMTS R99. No changes have been done on core network side.

Key features of HSDPA:

• It supports an asymmetric data transfer mode.
• The bandwidth is about 5MHz, the same as WCDMA.
• It supports both voice and data applications.
• Turbo coding is used as a FEC (Forward Error Correction) technique.
• Adaptive coding and modulation based on channel conditions achieves better data rates under good channel conditions due to higher modulation-code rate assignment.
• It utilizes maximum power for transmission.
• It minimizes the use of redundant packets (under better channel conditions) in data transfer.
• HARQ (Hybrid Automatic Repeat Request) support for new channels introduced at the PHY layer.
• 12 categories are available for UE; Category 10 is most commonly used, supporting 14 Mbps.

HSDPA Channels

In HSDPA, HS-DSCH (High-Speed Downlink Shared Channel) is introduced as a transport channel. This is supported by three physical layer channels:

• HS-PDSCH (High-Speed Physical Downlink Shared Channel)
• HS-SCCH (High-Speed Shared Control Channel)
• HS-DPCCH (High-Speed Dedicated Physical Control Channel)

PDSCH carries user information/data. SCCH informs the UE that data will be carried on DSCH. DPCCH carries ACK/NACK and CQI (Channel Quality Indicator).

HSPA+ Overview

HSPA+ uses the same 5MHz band of WCDMA spectrum, making it easier for operators to deploy. It tries to increase data rate by using MIMO (Multiple-Input Multiple-Output) and higher-order modulation techniques. It achieves roughly 42.2 Mbps data rate and spectral efficiency of about 8.4 bits/sec/Hz.

A significant achievement with HSPA+ is the reduced latency using a concept called CPC (Continuous Packet Connectivity). HSPA+ supports DC-HSDPA, which supports dual cell or dual carrier concepts where carrier aggregation of two nearby adjacent bands of 5MHz each are used for the same area of the cell to increase performance.

HSDPA vs HSUPA

Here’s a comparison between HSDPA and HSUPA:

Conclusion

In summary, the HSPA architecture combines NodeB, RNC, and core network (CN) components to provide high-speed data communication and voice services to mobile devices.