A.1 Requirements

Because of the very high license fees paid; the data rates achieved being on the order of 1 Mbits/s and a killer application not being yet found for their promotion, serious doubts have been raised about the success and, thus, the future of 3G systems. There is thus a scope and need for performance improvement of the 3G systems, and for the study of the beyond 3G systems in order to overcome these shortcomings.

In a global world, many networks of different characteristics will have to interoperate for the provision of very high data rate services by using different communication channels. These networks are required to be reconfigurable and sufficiently flexible to adapt themselves to new requirements. The integration and the management of services of different and heterogeneous media/networks will obviously be of critical importance. In view of the increasing mobility of the users, the increasing demand for higher data rates and the problems associated with global roaming, there are still many issues to be resolved in 3G and beyond 3G systems.

In addition to higher data rate requirements, the requirements for the quality of service (QoS) is getting more stringent, especially when higher user mobility is required. Consequently, higher data rates are needed with improved performance (e.g., better QoS, lower BER’s, better bandwidth and power efficiencies) for all users. This evidently imposes serious constraints on the system design.

It is a well-known fact from the Shannon capacity theorem that there is a trade-off between bandwidth efficiency, power efficiency and the system complexity, under the constraints on the QoS, connectivity, throughput and cost-effectiveness. One can use higher-order modulations as well as combined coding/modulation and diversity techniques to improve the bandwidth and power efficiencies.

In view of the increasing demand for the wireless services but, at the same time, the increased awareness against the hazardous effects of electromagnetic radiations to biological systems and the electromagnetic compatibility problems with other electronic systems impose serious restrictions on the transmitter power. The efficient utilization of the available bandwidth and the power should therefore be carefully considered.

On the other hand, the system implementation resulting as a trade-off between bandwidth and power should be practical, flexible, reproducible and cost-effective. The cost effectiveness of the systems under consideration, is obviously critical from the viewpoint of their implementability and the market success.

Broadband wireless access is a promising technology to connect the end users to the core network without an existing infrastructure, because not only wireless systems are quick to deploy but also they involve a low initial investment. Once in place, wireless networks are indeed easily upgraded to accommodate additional subscribers. However, the accommodation of the high-data services to be introduced seems to be difficult within the currently available bandwidth, by using the available technologies.

The performance improvement requires a careful consideration of the use of adaptive modulation and coding techniques; the frequency band of operation; the appropriate choice of the coverage and reuse factors; transmission (single carrier versus multicarrier) and access (e.g., OFDM/TDMA, OFDMA…) techniques; smart antenna technology; MIMO systems; ad-hoc networks, etc...

The wireless access is very important for increasing the user-friendliness of the system and for reducing the deployment and upgrade costs. Nevertheless, the mobile access and the core networks may be reconsidered for the provision of higher data rates. It may therefore be wise to develop techniques for combined improvement of the performances of the fixed and mobile parts of the system under consideration.

Currently different frequency bands are allocated to mobile communications, WLAN, Internet access and for broadcasting. This does not necessarily imply the most efficient usage of the available frequency bands. Using the opportunities offered by the digital technology, one may now consider the shared use of the frequency spectrum allocated to various services such as for communications and broadcasting only.

The frequency spectrum and transmitter power should be used efficiently, at every carrier frequency, geographical area, and time. Dynamic spectrum allocation, assignment and utilization needs to be considered seriously, to achieve higher overall spectral efficiencies and to provide better QoS under spectral and capacity restrictions as the traffic loads change over networks of different characteristics. Regulatory and system changes may be needed albeit with serious economic and market constraints. The technical means to dynamically assign and/or utilize the available spectrum and power involves, but not restricted to: