SYSTEM LEVEL MODELING
signal frequency without aliasing. Digital filter models H(z) must be used
instead of analog ones H(s). This can increase the modeling error. Few
tools (for example MATLAB and Ptolemy) provide time continuous data
2. Signals instead of nodes: system level simulators use signals, which
cannot represent voltage and current as a conservative electrical node.
Therefore it is difficult to model impedance mismatch between connected
blocks. Often an ideal matching is assumed in system level simulation.
More realistic port behavior can be achieved with additional modeling
effort and parameters for port impedance.
3. No feedback between models: system level tools use a signal or data flow
based simulation algorithm in a specified direction. There are only output
and input ports; no bi-directional ports exist. A feedback between blocks
must be modeled with additional ports and signals. The feedback loop
must have a delay of at least one sample to enable correct simulation
scheduling. In contrast an analog simulator solves the complete system at
each step by iteration.
Complex Baseband Simulation
The very high value of the carrier frequency in wireless communication
systems is the major problem in system simulation. It implies a very high
sampling rate in simulation. The consequence is a low simulation
performance, which results from a large number of iterations. Complex
baseband modeling provides a more efficient simulation of RF subsystems.
Digital modulation techniques use magnitude r and phase of a carrier
signal to transmit information. This means that the information does not
depend on the carrier frequency value. The idea of baseband simulation is to
transform the carrier frequency to zero. The advantage is that the required
sampling rate now depends on signal bandwidth, not on carrier frequency
SYSTEM LEVEL MODELING 27 signal frequency without aliasing. No feedback between models: system level tools use a signal or data flow based simulation algorithm in a specified direction. 4.3 Complex Baseband Simulation The very high value of the carrier frequency in wireless communication systems is the major problem in system simulation.