Model Based Design of an Adaptive Transmission Module for Non-Line of Sight OFDM System (WiMAX)

摘要

In this article we present a specific application of a relevant trend due to the speed with which requirements and technologies change. The modeling of an adaptive transmission module for a non line of sight OFDM (Orthogonal Frequency Division Multiplexing) utilizing base don the IEEE802.16 Standard we employ module based design. This implementation approach allows for rapid creation of prototypes because model based design offers flexibility in the elaboration of systems. The adaptive transmission module is composed of two main parts: the SNR (Signal to Noise Ratio) estimator and the modulation mode selector. The designed module was created using model based design, which consists of the elaboration of systems by implementing blocks with previously established or constructed tunable parameters. We used Simulink from Matlab for this implementation because it's a software tool with ideal mathematical foundation for the design of digital signal processing solutions for communications systems. In order to estimate the SNR we used correlation to calculate the quantity of noised contained by the received signal. The mode selector module follows the IEEE802.16 standard and the capacity to transmit at 256QAM. The selected mode depends on the SNR and can also specify the (FEC) Forward Error Correction recommended for the next burst profile. The development of this module is tested with random data generated for several theoretic SNR levels. We proceeded to compare the estimated levels with the theoretic levels.