Research On The Key Technology Of UMTS Heterogeneous Network

With rapid growth of Mobile Internet technology, the demand for high data rates and user experience is increasing as a consequence. Mobile operators have to build more NodeBs to meet the growing demand for larger systerm throughput. But when the demand for throughput increases in a geometical ratio, the method of building regular NodeBs becomes infeasible, and the Heterogenous Network technology arises at the historic moment. Heterogeneous network (HetNet) contains different transmission power NodeBs, including Macro NodeB, Micro NodeB, Pico NodeB, Femto NodeB and Relay NodeB. Researchers will add lower power NodeBs to the system according to interference condition and load condition, for the purpose of network optimization.HetNet has been researched extensively earlier in LTE system. Owing to the great improvement achieved by HetNet, UMTS HSPA HetNet is currently being standardized by3GPP working group. Simular to LTE, bringing in HetNet to HSPA may lead to some problems. In co-channel HSPA HetNet (CHH), Uplink-Downlink (UL-DL) imbalance caused by the hugely different power from different types of transmission nodes is a key problem leading to many undesirable conditions such as unbalanced load and severe interference. On the other hand, because of dense cell deployment in HetNet, fast moving UEs may encounter frequent handover. These two problems will be discussed in Section Two.3GPP has researched on UL-DL imbalance for a long time, and proposed many solutions. Range expansion scheme is a solution to solve UL-DL imbalance by enlarging the serving area of low power NodeBs, and E-DCH decoupling scheme is another solution by decoupling E-DCH transmissions of UEs in imbalance to low power NodeBs. Both of the two schemes will be introduced in Section Three.Traditional range expansion (RE) is to set a fixed cell individual offset (CIO) for each small cell, but configurations may differ from cell to cell, the best CIOs for cells may differ from each other. The main contribution of Section Five is to propose an adaptive range expansion (ARE) mechanism to mitigate the UL-DL imbalance in CHH. Our scheme tries to adaptively calibrate the parameter of RE by means of introducing an Imb value and using it as a reference to reflect the imbalance condition in the system. Simulation results will show the advantages of our proposed scheme.