Date Added: Mar 2011
Beyond 3G or 4G wireless networks will be based on the seamless coexistence and cooperation of heterogeneous radio access technologies with complementary technical characteristics. Despite continuous technical advances, traditional cellular architectures fail to offer homogeneous Quality of Service (QoS) levels throughout the coverage area as requested by the ITU recommendations for future 4G systems. This is the case because of the strong signal attenuation with the distance, and the highly variable propagation conditions caused by the presence of obstacles. Although reducing the cell size or augmenting the number of base stations can help increasing the user-perceived QoS levels, it also has a high economic and social cost.