Third generation advances, 3.5G

Third generation (3G) mobile systems have evolved from existing second-generation (2G) systems, that is, GSM and CDMA (IS-95).  The main 3G development criteria, brought together under the International Telecommunication Union (ITU)’s IMT-2000 project, were to provide a higher user capacity radio interface and to provide higher user speeds (in theory, 2Mbps), objectives achieved in the first release of specifications, known as Release 99.  It did not provide significant improvements in services, which has impacted user adoption of 3G technology.  Work has continued in 3GPP and 3GPP2 (organizations with responsibility for technical specification of 3G UMTS systems and cdma2000 systems, respectively) to evolve 3G systems, producing new releases (Releases 4, 5, and 6) that offer major improvements in terms of radio resource management (RRM), providing a new higher speed radio channel--High Speed Downlink Packet Access (HSDPA)--and a new IP multimedia communications domain (IP Multimedia Subsystem - IMS), which paves the way for new real-time service scenarios in the packet switched domain.  Specifications have also been completed for localization and security services, among others, and other access networks have been integrated, such as Low Chip Rate TDD (LCR-TDD), proposed by China, and Wireless LAN (WLAN).

Based on the cdma2000 and UMTS systems, current trends in 3G are to improve support for provision of multimedia services and bring them to up par with services offered over the terrestrial network.

As regards technical improvements, 3G networks are seeking to evolve in the following areas:

·     Implementation of systems providing multimedia services.  To that end, the Session Initiation Protocol (SIP) was chosen as the basis for the development of architecture enabling voice, data, video, instant messaging, etc. to be provided utilizing the same platform, and SIP-based mobile terminals to be designed and marketed.

The integration of different technologies (SIP, IP, WLAN, etc.) in 3G systems has altered the traditional standardization landscape, from organizations dedicated solely to specification of one system, to organizations which, in addition to specifying one system, define its interactions with other systems.  This change is simply the result of the convergence of information and communication technologies (ICTs).

IP multimedia systems are based on a series of SIP-based elements connected to the UMTS network through the PS domain (specifically, to the GGSN via Go and Mb interfaces), which provide multimedia services (voice, data, and video) to SIP-based UMTS terminals.  The figure below shows 3GPP’s IP Multimedia Subsystem (IMS) (Release 5).  A similar proposal exists in 3GPP2 for the provision of SIP multimedia services.

The IP multimedia system complements and, in fact, may replace, the UMTS network’s circuit-switched domain, as an SIP terminal is able to generate voice, data, and video calls via the IMS utilizing only the SIP protocol.  The IMS, and its 3GPP2 counterpart, are proposed as an alternative in the long-term to today’s traditional networks based on B-ISDN (SS7) signaling, and it is believed the some “greenfield” operators (new, not coming from GSM or CDMA) may establish IMS from the outset, although this depends on the availability of SIP terminals, which does not appear to be a difficulty.

Translation:  Nodo:  Node.

·       Integration with other access networks.  The objective here is to adopt other technologies (such as WLAN) to allow operators more flexibility in choosing the technology appropriate to each scenario.  For example, in places expected to have a great deal of traffic and where mobility is low (airports, terminals, cafés), less costly WLAN networks, providing greater bandwidth, may be implemented, and in places where high mobility is required, 3G cells may be implemented (UMTS or cdma2000).

In view of mobile operators’ growing interest in WLAN technologies (basically because of their potential for supporting high speeds (>10 Mbps) in low mobility environments, 3GPP is working on specification of the connectivity of UMTS systems with WLAN systems.

Connectivity is based on WLAN-UMTS dual mode mobile stations and, in addition (and optionally) on integration of WLANs and UMTS trunk networks.  This does not prevent (as is recognized) WLANs from being and continuing to be deployed independently by operators that do not have 3G licenses, and from such WLANs being or not being integrated with/connected to UMTS networks.

Unlicensed Mobile Access (UMA) technology provides access to GSM and GPRS mobile services via unlicensed spectrum technologies, such as Bluetooth and WLAN (802.11), and, subsequently, via cable accesses (Ethernet).  In deploying UMA technology, operators will enable subscribers (or UMA customers) to roam and make handovers between cellular networks and public and private wireless networks utilizing dual mobile stations.  With UMA, subscribers have the same user experience as with mobile voice and data services while moving between networks.

To promote mass adoption of UMA technology, a number of leading mobile industry companies have developed a series of specifications for development and deployment of interoperable solutions.

While it is true that the UMA specification was originally designed to be used with dual terminals, some router manufacturers are integrating UMA customers directly on the access router, providing an analog voice port (FXS) to connect a fixed telephony terminal, which communicates over the GSM network utilizing UMA as a fixed-mobile convergence mechanism.

·     Enhanced RRM. Its objective is to optimize spectrum use efficiency, thereby enabling operators to serve a larger number of users.  One example is assigning low-speed transmission users to 2G cells (GSM, cdmaOne) and high-speed transmission users to 3G cells.

·     Enhanced radio interface.  Both 3GPP and 3GPP2 are constantly working to improve radio interface efficiency with new technologies that permit a larger number of users and higher bit rate.  Examples are:  1X Evolution Data and Voice (1X-EVDV), HSDPA, and High-Speed Uplink Packet Access (HSUPA), which utilize, inter alia, adaptive modulation and coding to achieve speeds of the order of 10Mbps.

3GPP’s HSDPA and 1X-EVDV provide speeds up to five times (10 Mbps) the maximum speed of existing 3G networks (2 Mbps), without affecting the existing capacity of other channels in the cell.

Improvements or modifications of the architecture of HSDPA and 1X-EVDV channels

Translation:  Modulación y codificación adaptativa:  Adaptive modulation and coding.  Retransmisiones rápidas:  Fast retransmissions.  Scheduling en la EB:  Scheduling in the EB.

HSUPA is a data access protocol for networks with upload speeds of up to 5.76 Mbps.  Known as 3.5G, it is an HSDPA evolution technology.  Initially, the HSUPA solution will boost the UMTS uplink. At present, it is at an early stage of development.

HSDPA and HSUPA offer advanced voice and data features and will make it possible to develop a large mobile IP multimedia market.  HSUPA will enhance advanced person-to-person applications with higher and symmetric data rates, such as mobile e-mail and real-time person-to-person gaming.  Traditional business applications, as well as many consumer applications, will benefit from the higher connection speeds.

Alberto Montilla Bravo, MSc-DEA