Broadband Wireless OFDM Systems

Doctoral thesis, 2002

While the readiness of the telecommunication market and the users' need for broadband mobile data are not currently noticeable, a set of presented megatrends and scenarios suggest that broadband mobile data access will develop quickly in the next ten years. Identification of the potential frequency bands offering cheap and trouble-free wireless infrastructure is therefore an important step towards the definition of new air interfaces. This thesis approaches many aspects of broadband wireless Orthogonal Frequency Division Multiplexing (OFDM) systems covering a limited list of topics such as market viewpoints, frequency allocation recommendations, channel models, propagation problems and related technical solutions. The goal is to prepare the grounds for next generation broadband mobile data systems, especially regarding the air interface, and gain a better knowledge of the numerous problems involved in their realization. Among several license-exempt frequency bands, we choose to give emphasis to the 60 GHz frequency band. The 60 GHz frequency band is identified as one of the potential very high bit-rate bands offering several GHz of licensed-exempt bandwidth in offces, shopping-malls and downtown areas. The properties of the radio propagation in this band is however still not completely understood. As part of this work, we aim to understand the fundamental issues inherent to the use of millimeter wave bands for wireless communication systems. Propagation, interference and shadowing issues are presented as major impediments at this frequency. Evaluation of OFDM-based air interfaces shows that many issues need to be addressed before one can build an entire 60 GHz infrastructure. We suggest network design solutions that solve some of the inherent channel problems at the price of a lower flexibility and higher network complexity. It seems however that this is the price to pay in order to guarantee proper coverage with good reliability and link performance. In addition, we evaluate 60 GHz system performance using Monolithic Microwave Integrated Circuit (MMIC) components developed at Chalmers and identify the need to develop further 60 GHz microelectronic components. Some results on research related to joint channel estimation and turbo (de)coding with OFDM are also covered.