Hierarchical Cell Structures for FRAMES Wideband Wireless Access

To provide sufficient capacity in traffic hot spots, small micro cells are needed to complement macro cells providing low cost large area coverage. These problems can be solved by using a mixed cell structure with macro cells for coverage and micro cells for capacity. Such a scenario, where coverage is provided from both macro and micro cells in a large part of the service area, is often referred to as an HCS (Hierarchical Cell Structure). One common way to provide radio resource management in an HCS scenario is to divide the available spectrum between the two cell layers into one macro cell band and one micro cell band. The key problem in these scenarios is that due to the large dynamic range of received signals, the suppression of inter-band interference may not be sufficient to provide adequate Signal-to-interference ratios at all times. The unwanted radiation of high power macro cell terminals into the micro cell band may cause severe difficulties to the micro cell base station receivers, tuned to the low power micro cell terminals. In the paper, three candidate multi-access schemes proposed in the ACTS FRAMES project were studied using a simple macro/micro cell scenario in order to assess the width of these problems. Results indicate that there are no major performance differences between the different schemes for the up-link scenario. The down-link scenario was shown to yield much worse results than the up-link scenario and only the CATS2 and the narrowband SMA1 schemes were achieving acceptable performance at a very low noise floor.