Practical aspects of using IMT-advanced channel models

A geometry-based stochastic channel model was adopted for IMT-advanced evaluations. The complexity of the channel model has been under discussion within ITU-R working groups as well as in industry and academia performing system level simulations of future B3G/4G systems. The complexity reduction is a key task to improve the model usability. However, the complexity reduction should be made without reducing the model accuracy and generality too much. The large scale propagation parameters are random variables with certain distribution. One set of large scale and small scale parameters is called a ldquodroprdquo. To obtain statistical confidence, the number of drops has to be sufficient. Also in each drop, the length of simulation should be long enough. Therefore it is necessary to investigate the required number of drops and impulse responses per drop. Even more important is to study if we need multiple drops at all. This paper presents several approximation steps from full multi-drop IMT-advanced model to simple AWGN. The main message of this paper is to introduce the different approximation steps and their impact on simulation complexity. Simplification of accurate model is always possible, and the methods are known, but doing vice versa is impossible without additional information. Another result is that average channel model is not sufficient, but multiple drops are needed. Additionally, this paper discusses practical aspects on network level simulations such as network layout, user types and penetration losses.