###### tags: `UNILA`

## Assigment 2 OFDM & Spectrum Performance

Nama : Hans Khalif Hafif
Student ID : 1915031078
Team : A-3

# 1. Study and modify the code to understand how to implement different FFT size as described in the table (FFT size = 128 and FFT size = 256). Explain the difference of the spectrum for each FFT size !

**CHART** :
- the spectrum of OFDM transmission with FFT size = 64

- the spectrum of OFDM transmission with FFT size = 128

- the spectrum of OFDM transmission with FFT size = 256

**EXPLANATION**

From the above simulation that included with different FFT of transimition spectrum (64,128 & 256) . When the size FFT 64 , power spectral density lower than the spectrum with size 128 . Has a same condition when we compare the transmition spectrum OFDM between 128 & 256 . So, it can be conclude that more things that it get , bigger size of the FFT , more interval guard that available which is used between OFDM symbol . If we make the guard interval bigger than spread multipath spread delay that expected , ISI can fully missed . Add guard interval however mean that power waste an decrease of bandwidth effisience . Total power that missed is depend on how big some of the time of OFDM symbol in guard time . It means that bigger the point mark & connect mark ; for particular data speed . This only means more subcarrier & dash ; smaller power miss and bandwidth effisience . FFT size from the OFDM desain should make a balancing beetwen the guard of moving doppler multipath & design cost . For particular bandwidth , choosing the bigger FFT size will decrease distance of subcarrier increasing symbol time . This make an easier way to protect from delay spread of multipath . But, decrease of distance of subcarrier also make the system more susceptible with interference between operator because the spread of Doppler in cellular application . The effect of delay and Doppler spread which is compete in OFDM design that need smart balancing . As we can see in each picture . The subcarrier distance is smaller after the FFT size decrease . So we can conclude that more FFT size given , little subcarrier distance given

# 2. Study and modify the code to understand how to implement different FFT size as described in the table (FFT size = 128 and FFT size = 256). Explain the difference of the BER performance for each FFT size!
**CHART **:
- the spectrum of OFDM transmission with FFT size = 64

- the spectrum of OFDM transmission with FFT size = 128

- the spectrum of OFDM transmission with FFT size = 256

**EXPLANATION**

Based on the above simulation, there are three results from the spectrum of OFDM transmission ( 64, 128 and 256 FFT) size. When FFT size is 64, the we can compare between theoretical bit and Bit Error Rate and the result is similar. It means that the ratio of data loss that because of the noise is more than the ratio of data loss from 128 FFT size. When FFT size is 128, Bit Error Rate is decreasing. So the probability of Bit Error Rate is also become lower. It contious to FFT which has 256 size. From the simulation , we can conclude that the bigger size FFT given, the less probability of Bit Error Rate that obtained and and the more data that can be transmitted too .