Abstract
Femtocell is a promising solution for enhancing the indoor coverage and capacity in wireless networks. However, for the small size of femtocell and potentially frequent power on/off, existing handover schemes may not be reliable enough for femtocell networks. Moreover, improper handover parameters settings may lead to handover failures and unnecessary handovers, which make it necessary to enhance the mobility robustness for femtocells. In this article, we propose a gradient method and cost function-based mobility robustness optimization scheme for long term evolution (LTE) femtocell self-organizing networks. Moreover, signalling overhead of the scheme is analyzed. Simulation results show that the proposed scheme has a better performance than the fixed parameters method in terms of reduced the number of handover failures and unnecessary handovers with limited signalling modifications.
Highlights
As macrocells have limited indoor coverage, while above 50% of the voice services and 70% of the data traffics happen indoors [1], offloading the traffics from macrocells is badly needed
We develop a handover parameter adjusting-based mobility robustness optimization scheme, which aims to reduce unnecessary handovers and radio link failures (RLFs) caused by too late handover, too early handover, or wrong handover in open access femtocells
3.1 Cost function In order to reduce RLFs and unnecessary handovers in femtocells, we propose a cost function based algorithm, which is defined as follows: C = αiNi i=1 where N1, N2, N3, N4, and N5 denote the numbers of pingpong handover, continuous handover, too late handover, too early handover and wrong handover, respectively, and Algorithm 1 Detection of RLF and Unnecessary
Summary
As macrocells have limited indoor coverage, while above 50% of the voice services and 70% of the data traffics happen indoors [1], offloading the traffics from macrocells is badly needed. In [3], a cost function based handover parameter optimization scheme incorporating cell load, UE’s velocity and service type, is proposed for 3GPP LTE macrocells. We develop a handover parameter adjusting-based mobility robustness optimization scheme, which aims to reduce unnecessary handovers and RLFs caused by too late handover, too early handover, or wrong handover in open access femtocells. In order to realize the mobility robustness optimization, a cost function incorporating the unnecessary handovers and wrong handovers is introduced, and a MRO scheme based on gradient algorithm [18,19] is proposed for femtocell networks. 3.1 Cost function In order to reduce RLFs and unnecessary handovers in femtocells, we propose a cost function based algorithm, which is defined as follows:.
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