The typical urban (TU) channel model is a pdp-based channel model. You can find the implementation on +channel_gain_wrappers/pdpChannelFactory.m.
In the simulator it is possible to generate a channel trace for the first time and then reuse the same in other simulations by setting these parameters to
LTE_config.cache_network = true;
LTE_config.delete_ff_trace_at_end = false;
Otherwise you generate a new trace in each simulation run and delete it at the end of simulation.