Future radio systems: Impact of the air interface

In a radio network, the air interface connects the fixed network equipment and the subscriber units or directly the subscriber units. It includes the physical (PHY) layer and the medium access control (MAC) layer. A key requirement for high speed future systems is the MAC throughput, which, generally is a fraction of the PHY data rate, typically of the order of 50 %. Thus, there are two approaches to boost the throughput, first increase the data rate, second improve the efficiency of the MAC layer. However, the potential for MAC efficiency improvement is tightly related to some features of the PHY layer and, particularly, its robustness and flexibility. Clearly, the PHY layer is the key component of the air interface of future networks. In the talk, after a brief review of important features of future systems and the related requirements, the impact of the PHY layer is discussed, with emphasis on the new concept of cognitive radio. Turning to transmission techniques, multicarrier appears as the right approach to meet the requirements. With reference to the existing OFDM (orthogonal frequency division multiplexing) systems, future systems will require a more advanced modulation technique and FBMC (filter bank based multicarrier) modulation is proposed. The advantages of FBMC in terms of maximum PHY data rate, robustness to channel impairments, flexibity in the multiuser context are underlined. A critical issue is spectrum sensing for cognitive radio and the performance of FBMC in that respect is illustrated. Finally, some research topics in FBMC which are addressed by the European research project ldquoPHYDYASrdquo (physical layer for dynamic access and cognitive radio) are listed and commented. The progress made in that project so far confirms FBMC as a promising candidate technique for the air interface of future radio systems.