## 4 Simulated Results of the Overall DFE Architecture  
The frequency-domain signals at the outputs of individual building blocks are sketched in Figure 15. Adjacent channel selectivity (ACS) and 20 MHz + 20 MHz LTE CA were assumed. Signal (a) is the output of the ADC, where the blue line is for the signal and the red line is for the interference in ACS. Signal (b) is the output of the CIC filter or FIR1, which operates on the signal (a). Signal (b), which is decimated and filtered, is shown in Figure 15 in the spectral domain as well. Signal (c) is the output of FSRC, which is fed with signal (b). FSRC can filter the desired signal more sharply than the CIC filter or FIR1, which is plotted in Figure 15 [23]. Signal (c) that is the FSRC output is fed to the DM, which translates or relocates the carrier instead of suppressing interference. As is plotted, the carrier frequency of signal (d) is shifted in the minus direction (leftward) relative to that of signal (c). Signal (e) is the output of CAF1 where further suppression occurs with respect to signal (d) and the last-step decimation is conducted. Up to this point, however, the interference amplitude is as yet larger than the desired signal amplitude. The last building block, CSF1, of the receiver DFE attenuates the interference substantially, for signal (f). The DFE filter requirements are derived from various 4G LTE-A specifications. For instance, in case of LTE contiguous CA with an aggregate bandwidth of 40 MHz and for a 3 rd-order Butterworth-type analog lowpass filter with a 3 dB frequency of 20 MHz, prior to the ADC, the specification at the analog filter output is shown in the middle of Figure 16 and the specification at the DFE filter output is shown at the bottom of Figure 16. As shown at the top of Figure 16, wanted signals, adjacent channel blockers, inband blockers, intermodulation components, and narrowband blockers are all taken into account for the proposed DFE that is compliant with LTE-A. From Figure 16, the DFE filter requirements were readily derived. Namely, the DFE filter with a center frequency of 10 MHz and a 3 dB bandwidth of 20 MHz, the attenuations at 20.2075 MHz, 22.5 MHz, 27.5 MHz, 32.5 MHz, and 45 MHz were to be 39.1 dB, 39.0 dB, 46.4 dB, 44.4 dB, and 34.2 dB, respectively. The mean SNR was used as a performance measure, which was the SNR obtained at the 1-tap equalizer output in the terminal modem receiver. The output of the implemented DFE was fed to the Matlab-modeled OFDM receiver and the error between the receiver output and the original transmitted information was translated into the SNR on average. The performance of the proposed DFE was evaluated at the output of the OFDM receiver, which helped to capture the system impact of each design decision of the DFE. The OFDM receiver mainly consisted of cyclic prefix removal, FFT, and single-tap equalization. The synchronization and the channel estimation were assumed to be ideal. Our simulation results show that the frequency distortion introduced by the DFE (e.g., drooping) can be successfully removed by the standard OFDM receiver. Figure 14: Input and output of FIR5 (CSF) in the frequency domain in case of (20 MHz + 20 MHz) carrier aggregation (CA). Figure 17 displays the mean SNR for the desired signal only (blue), the SNR in the case of the inband blocker (IBB) coexists (black), the SNR in the case of the ACS with adjacent channel interference was assumed (pink), and the SNR in the case of the narrowband blocker (NBB) coexists (red). All the mean SNR values were obtained from simulation of the proposed DFE. The case numbers on the x axis, 1, 2, 3, 4, 5, 6, 10, 11, 12, and 13 represent ten frequency modes, 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz, 1.4 MHz, 20 MHz + 20 MHz (CA), 20 MHz + 15 MHz (CA), 20 MHz + 10 MHz (CA), and 5 MHz + 5 MHz (CA), respectively. Simulated results with IBB, ACS, and NBB were all exhibited to demonstrate that the proposed DFE was 3 GPP-compliant.