tailieunhanh - Discrete Time Systems Part 14

Tham khảo tài liệu 'discrete time systems part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Half-overlap Subchannel Filtered MultiTone Modulation and Its Implementation 379 compiled and implemented on digital signal processor with the help of the Link for CCS toolbox. This way of generating code is fully functional and they allow measuring the proposed algorithm directly in the digital signal processor but they definitely cannot be considered optimized. It is convenient to use libraries that are optimized for a given processor and replace the standard Simulink blocks by optimized ones. It is also possible to replace the original number formats by formats corresponding to the processor. Also the filterbank can be designed in two ways. The first way is independent filtering in each branch of filterbank Sysel Krajsa 2010 . a b c Fig. 16. Efficient filterbank implementation The second one is described on Fig. 16 where hm is n-th coefficient of m-th filter X m is r -th IFFT symbol in m-th branch and o m is f-th output sample in m-th branch. We have three buffers one a for prototype coefficients one b for input symbols from IFFT and the last one c for output frame. Buffer b is FIFO buffer samples are written in frames of 2N samples. This way of filtering is more effective because we need only one for cycle for computing one output frame. Fig. 17. SNR for a DMT b Non-overlapped FMT c Half-overlapped FMT with narrowband noise 380 Discrete Time Systems In the term of testing and comparing the implementation on DSP is interesting for the possibility of power spectral density measurement and for its characteristics inside and outside of the transmission band of partial subchannels on real line. In Fig. 19 is measured PSD for the considered modulations. Fig. 18. FMT transmitter adjusted for implementation tone - Fig. 19. Measured power spectral densit It is clear that the implementation results confirm the theoretical assumptions about the properties of implemented modulations mainly about their spectral properties. For the halfoverlap FMT modulation the PSD measured