What is HSPA network ?

The HSPA stands for High speed packet access, the network architecture mainly designed to support high speed data rate in the uplink and downlink. HSPA falls under categories which include HSDPA, HSUPA and HSPA+. All the HSPA standards follow different UMTS releases. HSDPA follows UMTS R5 release and supports about 14Mbps peak data rates (speed). HSUPA follows UMTS R6 release and supports about 5.76 Mbps uplink data rates. HSPA+ follows R7-R9 UMTS releases. HSPA supports spectral efficiency of about 2.9bits/sec/Hz.

It is a mobile communication technology that enhanced capabilities of 3G (Third Generation) networks. HSPA is also referred 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. These components work together to provide high speed data communication for mobile devices as well as voice calls. The HSPA architecture contains UE (User Equipment), NodeB (i.e. Base Station), RNC (Radio Network Controller), NodeB gateway and Core network.

UMTS network Architecture

User Equipment (UE) : Mobile devices such as mobile phones, smart phones, tablets and data cards are end point users of the HSPA network.
NodeB (i.e. base station) : It is the cell tower having HSPA radio interfaces and protocols which communicates with HSPA compliant UEs over the air interface. It is responsible for radio resource management, connection establishment and release, power control and handovers.
RNC (Radio Network Controller) : It is the central component in HSPA network which manages multiple NodeBs. It is responsible for various tasks such as handover between calls, RRM (radio Resource Management) and coordination of radio bearers.
NodeB Gateway (lub interface) : It is the interface which connects NodeBs to the RNC. It facilitates transmission of user data and control signaling between 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 Node) and CS (Circuit Switched ) domain : HSPA mainly operates in PS domain which allows efficient data transmission using IP protocols. It also supports circuit switched connections for voice calls.

HSDPA Overview

As mentioned HSDPA is mainly designed for high speed data rates in the downlink mainly for internet based applications and 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.

Silent features of HSDPA

-It supports asymmetric data transfer mode
-Bandwidth is about 5MHz same as WCDMA
-Supports both voice and data applications
-Turbo coding is used as FEC technique
-Adaptive coding and modulations based on channel conditions hence achieve better data rate under good channel conditions due to higher modulation-code rate assignment.
-utilizing maximum power for transmission
-minimizing use of redundant packets (under better channel conditions) in data transfer
-HARQ support for new channels introduced at PHY layer
-12 categories are available for UE; Category 10 is most commonly which supports 14 Mbps.

HSDPA Channels

In HSDPA HS-DSCH (High-Speed Downlink Shared Channel) is introduced as transport channel. This is supported by three physical layer channels viz. 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 UE that data will be carried on DSCH. DPCCH carries ACK/NACK and CQI.

HSPA+ overview

HSPA+ uses the same 5MHz band of WCDMA spectrum and hence great ease for operators. In the same 5MHz HSPA+ tries to increase data rate by using MIMO/higher order modulation techniques. Hence it roughly achieves 42.2 Mbps data rate and spectral efficiency of about 8.4 bits/sec/Hz.

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

HSDPA vs HSUPA | Difference between HSDPA and HSUPA

Following table mentions comparison between HSDPA and HSUPA with respect to various parameters.

Parameters HSDPA HSUPA
Full form High Speed Downlink Packet Access High Speed Uplink Packet Access
Direction Downlink (from network to device) Uplink (From device to network)
Technology Uses AMC (Adaptive Modulation and Coding) for efficient reception Techniques such as fast scheduling, adaptive modulation, HARQ are implemented for efficient uplink transmission.
Purpose Improves download speed Improves upload speed
Data rate or speed ~ 14.4 Mbps ~ 5.76 Mbps
Typical use cases Web browsing, streaming, downloadind Uploading photos, videos, files
3GPP release UMTS R5 UMTS R6

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.

Useful References

HSPA, HSDPA, UMTS refer following 3GPP link for detailed explanation.

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