Universal Mobile Telecommunication System (UMTS): Implementation and Issues

	ABOUT THE AUTHOR Vikrant Shinde received BSEE degree from the University of Pune, India. He worked on designing data networks for his capstone project and then for industrial applications. Currently working towards his MSEE degree at the University of New Brunswick, Canada; he is researching various Communication Protocols. He has interests in wireless communication.

The advances in wireless communications have not been always dependent on any one factor and, even today, are influenced by several factors, including consumer demand, corporate growth, technology inventions and their implementation, service-provider infrastructure, and the political agendas of various countries and regions.

The history of mobile wireless communications can be broadly divided into the different generations of technological advances and their consequent implementations. The different phases of growth in the wireless communication sector comprise various generations of systems.

• First-generation cellular systems (1G)
  These were the simplest communication networks deployed in the 1980s and were based on analog-frequency-modulation (FM) transmission technology. These systems had a host of problems including inconsistency, loss of signal, and low bandwidth, and could service a limited customer base.
  
  
• Second-generation cellular systems (2G and 2.5G)
  These systems were the first to apply digital transmission technologies such as Time Division Multiple Access (TDMA) for voice and data communication. The data transfer rate was on the order of tens of kbits/s. Other examples of technologies in 2G systems include Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA).
  
  The later advanced technological applications were defined as 2.5G. These systems, which included GSM (Global System for Mobile Communications) and GPRS (General Packet Radio Service), have a greater data transfer rate and bandwidth.
  
  
• Third-Generation cellular systems (3G)
  These systems are in operation today in some countries in Europe and the Far East. They have a maximum bit rate of 2 Mbits/s (Mbps) and offer packet-switched as well as circuit-switched voice services with a host of new features that are user-friendly and improved performance for transfer of data, voice, and video. Examples of 3G cellular-system technologies include Universal Mobile Communications System (UMTS), Wireless Application Protocol (3GWAP), and CDMA-2000.
  
  
• Fourth-Generation cellular systems (4G)
  These systems are currently under development and will be implemented somewhere in 2008-2015. They will not only connect people to people, but machines or houses to people.

where,

U is the fractional area with radius r and propagation parameters—path loss exponent 'n' and standard deviation 's'; P_edge is a good received signal at edge of cell; and Q is the probability function.

Figure 1:  UMTS architecture

This network architecture helps in distributing data traffic. Local traffic operates in the microcells and picocells (for example, a local cellular subscriber, slow-moving subscribers, and users in dense population areas) while highly mobile traffic operates in the large macrocells (such as a cellular subscriber travelling on a highway or by air). This greatly reduces the number of handoffs required for the fast-moving traffic. We see that in this 'overlaid architecture', the macrocells perform the dual function of covering areas not covered by smaller cells and avoiding the failures of the overlapped cells.

Figure 2:  Intermediate 2.5G technologies

In recent years, Europe has witnessed a massive growth of mobile communications, ranging from the more traditional analog-based systems to the current generation of 2G digital systems. The 2G systems include DCS-1800 (Digital Communication System at 1800 MHz), ERMES (European Radio Messaging System), DECT (Digital European Cordless Telephone), and TETRA (Trans European Trunked Radio). However, the 3G technologies such as UMTS and CDMA 2000 will, in a real sense, enable users to use full-fledged multimedia capabilities, a higher number of channels, larger data transfer rates, and a host of other features as the next section of this article discusses.

With an EU-mandated rollout date of January 1, 2002, a series of implementation steps have been planned to work towards expected UMTS speeds. Initially, data speeds will be in the 9.6 kbps range, with transfer rates as high as 115 kbps using GPRS. With the implementation of EDGE technology, speeds are expected to rise into the range of 384 kbps before finally reaching the UMTS plateau of 2 Mbps.

UMTS is designed with both terrestrial and global satellite components to be compatible with GSM 900 and 1800, building upon the older technology instead of supplanting it. The terrestrial units called UMTS Terrestrial Radio Access (UTRA) use two technologies for radio access: W-CDMA for paired spectrum bands and TD-CDMA for unpaired spectrum bands.

UMTS/UTRA will be providing much greater data-transmission rates than you have with current 2G networks using GSM. The rate breakdown is as follows:

• 144 Kbps for full outdoor mobility applications in all environments.
  
  
• 384 Kbps for limited-mobility outdoor applications in the macro and micro cellular environments (in urban/ suburban areas).
  
  
• 2.048 Mbps for low-mobility outdoor applications, particularly in the micro and pico cellular environments (in indoor urban areas).

The UMTS network architecture involving macrocells (outdoor environments), microcells (urban/ suburban areas) and picocells (urban/ local) is as described in the section, "What is UMTS?" The operator decides the best possible Cell Cluster Size, determined from the signal strength in the cell. Taking into view the adjacent interfering cells and assuming all base stations are equidistant from the base station in the cell under consideration, the operator will be able to approximate the Cluster Size from the signal to interference ratio as

where N is the cell cluster size, n is the path-loss exponent, and I₀ represents the number of interfering adjacent cells.

• Up to 2 Mbps data-transmission capacity in cellular networks.
  
  
• Support for wide-band network access with the integration of UMTS with Broadband Integrated Services Digital Network (B-ISDN) using an Asynchronous Transfer Mode (ATM) protocol.
  
  
• Support for a broad range of consumer services that user preferences, such as digital cable TV services, can customize.
  
  
• An open-source digital system to enable creation of new services and applications upon industry demand.
  
  
• Support for all services, along with greater compatibility with related terminal equipment (TE) associated with the future wired local-distribution networks.
  
  
• Dynamic channel allocation as well as frequency re-use, including 'on-demand'.
  
  
• Support for both public and proprietary services in a mutually non-destructive way.
  
  
• Quality of Service (QoS) at least equal to the fixed network, compatibility between the intelligent network procedures, and support for all wired and wireless systems.
  
  
• Convergence of present mobile systems, along with respect for a user's freedom in selecting services/applications according to individual requirements.
  
  
• Operating universally [at least intra-Europe], covering all environments and terrains so as to offer "roaming" facility throughout the world.
  
  
• The use of intelligent Subscriber Identity Module (SIM) cards with more memory, better encryption, faster CPU performance, and integrated operation. This feature would allow for e-commerce or e-ticketing as well as many B-to-B and B-to-C services.
  
  
• Sharing spectrum resources between network operators, both public and private, in city areas.
  
  
• Sharing spectrum resources between all applications, for example, one or many applications/services running simultaneously.
  
  
• Making UMTS consistent with the ITU's recommendations and regulations.

• Conversational class: This is related to voice telephony and related services. This class is expected to be high use.
  
  
• Streaming class: This is related more or less to the viewing or listening to real-time video or audio. Streaming class is primarily related to the reverse channel and is one-way.
  
  
• Interactive class: This class will using both forward and reverse channels, but will require a much lower bit error rate.
  
  
• Background class: Similar to the Interactive class, but will have a much lower priority than the Interactive class.

• Wideband-CDMA (W-CDMA), which will assume the role of the popular 3G transmission system
  
  
• TD-CDMA as an additional transmission mode.

W-CDMA is sometimes also referred to as FDD (Frequency Division Duplex), and TD-CDMA as TDD (Time Division Duplex). W-CDMA is a coded multiplex system whose greatest advantage is the ability to assign, quite flexibly, the transmission rates from the total available bandwidth according to the economic considerations of the service provider using the appropriate Quality-of-Service (QoS). Cellular-phone manufacturers are already manufacturing handsets that support both W-CDMA and TD-CDMA systems in keeping with their specific features and benefits. For example, you can use current cellular handsets in Europe as well as in Japan.

The frequency bands from 1920-1980 and 2110-2170 MHz will use Frequency Division Duplex (FDD, W-CDMA) technology. Paired uplink and downlink, channel, or carrier spacing can vary from 4.2 to 5.4 MHz and raster is 200 kHz. In addition, a "soft" handover or "inter-frequency" handover is possible using W-CDMA. An operator will need three or four channels (2x15 or 2x20 MHz) to be able to build a high-speed, high-capacity network having 1980-2010 MHz and 2170-2200 MHz satellite uplink and downlink capability.

Europe and Japan have agreed to have common frequency channels for UMTS applications. North America is yet to decide on the spectrum allocation and integration of UMTS with the present cellular systems in U.S. Spectrum negotiations still continue between telecom operators and the licensing federal monitoring body.

The summary of the frequency bands that UMTS will use is shown in Figure 3. The Satellite portion of the system will use the S-band Mobile Satellite Service (MSS) frequency allocations set aside for satellite IMT2000 and will provide services compatible with the terrestrial UMTS systems.

Figure 3:  UMTS frequency bands

A final objective after implementing 3G technologies such as UMTS is to develop a mobile wireless system for bit-rates of up to 155 Mbps throughput in the 40 or 60 GHz bands. Other objectives are to create the industrial capacity to produce the necessary system components (RF, Wireless/IF and baseband systems, antennas, terminals and, most importantly, the telecommunication products and equipment). All this and much more is currently being given shape in 4G technologies. The future path towards the 3G success and beyond is summarized as follows:

• Will involve a lot of Research and Development (R&D) in telecommunication-equipment integration leading to mobile-service "Convergence"
  
  
• Will define and develop common service standards with consistent transmission parameters and a radio interface between satellite and terrestrial implementations
  
  
• Will produce system integration that will be able to support handovers between land-based networks and satellite-mapped cells, such that the satellite effectively provides a large terrestrial cell.

Thus implementing the Universal Mobile Telecommunications System (UMTS) will be a stepping-stone in 3G technologies and a pathway towards global mobile convergence.