As OFDM (orthogonal frequency division multiplexing) technology has been considered for most next-generation mobile wireless networks, such as IEEE 802.16-WiMAX and 3G LTE (Long-Term Evolution), and these systems are susceptible to the inter-cell interference problem, there have been numerous approaches proposed to enhance the performance of cell-edge MSs. Recently, the 802.16m and 3G LTE Advanced standard groups proposed ways of supporting cell-edge MSs by deploying various network (multi-BS) MIMO antenna techniques as well as fractional frequency reuse schemes. In case fractional frequency reuse is adopted, the designated neighboring BSs of a cell to which a certain cell-edge MS is attached, should avoid concurrent transmission over the same set of channels. If macro-diversity or network MIMO is used, one or more neighboring BSs should serve a certain cell-edge MS at the same time, thus requiring concurrent transmissions over the same set of channels from multiple BSs to the same MS.
Such network-level radio resource coordination is easier to achieve, when there is an upper-level management entity like the ASN gateway. When BSs fulfill RRM in a flat architecture, the intercell RRM should be coordinated at least by one BS, rather than in a distributed way. Therefore, we present a simple solution of semi hierarchical cellular systems in Figure 1 where a super BS plays a role of a coordinator for intercell RRM. The super BS can be selected among a set of BSs in either a fixed or a dynamic way.
Figure 1: Semi hierarchical cellular systems
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