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A major challenge of the heterogeneous network is the Radio Resource Management (RRM) strategy. Common RRM (CRRM) is proposed to jointly manage radio resources among different Radio Access technologies (RATs) in an optimized way. This paper does a comprehensive survey on CRRM and introduces it from different aspects. Two interaction functions (information reporting function and RRM decision support function) and four interaction degrees (from low to very high) between local RRM and CRRM entities are introduced. Possible CRRM topologies (CRRM server, integrated CRRM and CRRM in user terminals) are introduced. Different RAT selection algorithms for both of mixed GREAN/UTRAN and WWAN/WLAN scenarios are compared. Future research works on CRRM is also considered in the conclusion section.

Long term evolution (LTE) is the next generation wireless system that uses orthogonal frequency division multiple access (OFDMA) technology in the downlink. Packet scheduling becomes paramount as the wireless systems are moving towards all IP transmissions. Since LTE system is relatively new, very little work has been published to date that can precisely model and simulate the downlink LTE system environment. This paper provides detailed descriptions on modeling and simulation of packet scheduling in the downlink LTE system using a C++ simulation tool. The tool accurately modeled the wireless system parameters and can be used for study of optimization of the LTE system.Index Terms -LTE, packet scheduling, modeling and simulation, OFDMA.