Modelling the time-varying cell capacity in LTE networks

In wireless orthogonal frequency-division multiple access (OFDMA) based networks like Long Term Evolution (LTE) or Worldwide Interoperability for Microwave Access (WiMAX) a technique called This work was partially supported by the Spanish Government through project TSI2005-07520-C03-03 and contract BES-2007-15030. Bart Sas PATS Research Group University of Antwerp/IBBT 2020 Antwerp, Belgium E-mail: [email protected] Elena Bernal-Mor GIRBA Research Group Universitat Politècnica de València/ITACA 46022 Valencia, Spain E-mail: [email protected] Kathleen Spaey PATS Research Group University of Antwerp/IBBT 2020 Antwerp, Belgium E-mail: [email protected] Vicent Pla GIRBA Research Group Universitat Politècnica de València/ITACA 46022 Valencia, Spain E-mail: [email protected] Chris Blondia PATS Research Group University of Antwerp/IBBT 2020 Antwerp, Belgium E-mail: [email protected] Jorge Martinez-Bauset GIRBA Research Group Universitat Politècnica de València/ITACA 46022 Valencia, Spain E-mail: [email protected] adaptive modulation and coding (AMC) is applied. With AMC, different modulation and coding schemes (MCSs) are used to serve different users in order to maximise the throughput and range. The used MCS depends on the quality of the radio link between the base station and the user. Data is sent towards users with a good radio link with a high MCS in order to utilise the radio resources more efficiently while a low MCS is used for users with a bad radio link. Using AMC however has an impact on the cell capacity as the quality of a radio link varies when users move around; this can even lead to situations where the cell capacity drops to a point where there are too little radio resources to serve all users. AMC and the resulting varying cell capacity notably has an influence on admission control (AC). AC is the algorithm that decides whether new sessions are allowed to a cell or not and bases its decisions on, amongst others, the cell capacity. The analytical model that is developed in this paper models a cell with varying capacity caused by user mobility using a continuous-time Markov chain (CTMC). The cell is divided into multiple zones, each corresponding to the area in which data is sent towards users using a certain MCS and transitions of users between these zones are considered. The accuracy of the analytical model is verified by comparing the results obtained with it to results obtained from simulations that model the user mobility more realistically. This comparison shows that the analytical model captures the varying cell capacity very accurately; only under extreme conditions differences between the results are noticed. The developed analytical and simulation models are then used to investigate the effects of a varying cell capacity on AC. The analytical and simulation models are also used to study an optimisation algorithm that adapts the parameter of the AC algorithm which de-