New data services, interactive TV and evolving Internet behavior will influence mobile data usage. Long sessions in always-on mode will force a re-think of radio access technology to achieve the required – but not easy to attain – capacity (Gbit/s/km_) at low cost. The ideas presented in this article can increase capacity by a factor of 500 with regard to expected cellular deployments. Coverage will be based on large umbrella cells (3G, WiMAX) and numerous pico cells interconnected to provide the user with seamless high data rate (several Mbit/s) sessions. Scalable and progressive deployments are possible while protecting the operator’s long-term investment. The 4G infrastructure operator will mix several technologies, each of which has its optimal usage. The connection to one of them will result in a real-time
trade-off which will offer the user the best possible service. Some tools that genuinely improve the user’s multimedia quality of experience (availability, response time, definition, etc) are also presented in this article.

D. Rouffet, S. Kerboeuf, L. Cai, V. Capdevielle

4G MOBILE

Voice was the driver for second-generation mobile and has been a considerable success. Today, video and TV services are driving forward third generation (3G) deployment. And in the future, low cost, high speed data will drive forward the fourth generation (4G) as short-range communication emerges. Service and application ubiquity, with a high degree of personalization and synchronization between various user appliances, will be another driver. At the same time, it is probable that the radio access network will evolve from a centralized
architecture to a distributed one. 4G will deliver low cost multi-megabit/s sessions any time, any place, using any terminal.

Service Evolution

The evolution from 3G to 4G will be driven by services that offer better quality (e.g. video and sound) thanks to greater bandwidth, more sophistication in the association of a large quantity of information, and improved personalization. Convergence with other network (enterprise, fixed) services will come about through the high session data rate. It will require an always-on connection and a revenue model based on a fixed monthly fee. The impact on network capacity is expected to be significant. Machine-to-machine transmission will involve two basic equipment types: sensors (which measure parameters) and tags (which are generally read/write equipment).
It is expected that users will require high data rates, similar to those on fixed networks, for data and streaming applications. Mobile terminal usage (laptops, Personal digital assistants, handhelds) is expected to grow rapidly as they become more user friendly. Fluid high quality video and network reactivity are important user requirements. Key infrastructure design requirements include: fast response, high session rate, high capacity, low user charges, rapid return on investment for operators, investment that is in line with the growth in demand, and simple autonomous terminals.
The infrastructure will be much more distributed than in current deployments, facilitating the introduction of a new source of local traffic: machine-tomachine. Figure 1 shows one vision of how services are likely to evolve; most such visions are similar.

Dimensioning targets

A simple calculation illustrates the order of magnitude. The design target in terms of radio performance is to achieve a scalable capacity from 50 to 500 bit/s/Hz/km2 (including capacity for indoor use), as shown in Figure 2.

As a comparison, the expected best performance of 3G is around 10 bit/s/Hz/km2 using High Speed Downlink Packet Access (HSDPA), Multiple-Input Multiple-Output (MIMO), etc. No current technology is capable of such performance.

Dimensioning objectives

Based on various traffic analyses, the Wireless World Initiative (WWI) has issued target air interface performance figures. A consensus has been reached around peak rates of 100 Mbit/s in mobile situations and 1 Gbit/s in nomadic and pedestrian situations, at least as targets. So far, in a 10 MHz spectrum, a carrier rate of 20 Mbit/s has been achieved when the user is moving at high speed, and 40 Mbit/s in nomadic use. These values will double when MIMO is introduced. Clearly, the bitrate should be associated with an amount of spectrum. For mobile use, a good target is a network performance of 5 bit/s/Hz, rising to 8 bit/s/Hz in nomadic use.

Multi-technology Approach

Many technologies are competing on the road to 4G, as can be seen in Figure 3. Three paths are possible, even if they are more or less specialized. The first is the 3G-centric path, in which Code Division Multiple Access (CDMA) will be progressively pushed to the point at which terminal manufacturers will give up. When this point is reached, another technology will be needed to realize the required increases in capacity and data rates.
The second path is the radio LAN one. Widespread deployment of WiFi is expected to start in 2005 for PCs, laptops and PDAs. In enterprises, voice may start to be carried by Voice over Wireless LAN (VoWLAN). However, it is not clear what the next successful technology will be. Reaching a consensus on a 200 Mbit/s (and more) technology will be a lengthy task, with too many proprietary solutions on offer.
A third path is IEEE 802.16e and 802.20, which are simpler than 3G for the equivalent performance. A core network evolution towards a broadband Next Generation Network (NGN) will facilitate the introduction of new access network technologies through standard access gateways, based on ETSI-TISPAN, ITU-T, 3GPP, China Communication Standards Association (CCSA) and other standards.
How can an operator provide a large number of users with high session data rates using its existing infrastructure? At least two technologies are needed. The first (called “parent coverage”) is dedicated to large coverage and real-time services. Legacy technologies, such as 2G/3G and their evolutions will be complemented by WiFi and WiMAX. A second set of technologies is needed to increase capacity, and can be designed without any
constraints on coverage continuity. This is known as pico-cell coverage. Only the use of both technologies can achieve both targets (Figure 4). Handover between parent coverage and pico cell coverage is different from a classical roaming process, but similar to classical handover. Parent coverage can also be used as a back-up when service delivery in the pico cell becomes too difficult.