Contents
- 1 How the signal is generated in OFDM?
- 2 How to add cyclic prefix in OFDM?
- 3 How is the baseband OFDM converted to the passband?
- 4 Why are narrowband carriers used in OFDM transmission?
- 5 Why is OFDM used?
- 6 What is a signal and its types?
- 7 How are the signals stored in the OFDM frame?
- 8 What are the subcarriers of an OFDM signal?
How the signal is generated in OFDM?
In OFDM the signal itself is first split into independent channels, modulated by data and then re-multiplexed to create the OFDM carrier. OFDM is a special case of Frequency Division Multiplex (FDM). As an analogy, a FDM channel is like water flow out of a faucet, in contrast the OFDM signal is like a shower.
How to add cyclic prefix in OFDM?
5.1. To combat the intersymbol interference (ISI) in a multipath channel, a cyclic prefix (CP) is inserted in the OFDM symbol. The CP refers to the cyclic extension of an OFDM symbol, that is, appending the last N c p samples of the OFDM symbol to the front of the symbol as illustrated in Fig. 5.6.
How are AC and F C ( T ) represented in OFDM?
Both Ac(t)and f c(t),the amplitude and phase of the carrier, can vary on a symbol by symbol basis. The values of the parameters are constant over the symbol duration period t . OFDM consists of many carriers. Thus the complex signals ss(t)(Fig. 4) is represented by:
How is OFDM used to modulate the data?
OFDM uses multiple carriers to modulate the data N carriers B Modulation technique A user utilizes all carriers to transmit its data as coded quantity at each frequency carrier, which can be quadrature-amplitude modulated (QAM).
How is the baseband OFDM converted to the passband?
Later edit 2: it seems that there are many ways to convert the baseband OFDM into the passband. Constant Envelope OFDM is one interesting way to do it, the baseband OFDM signal is phase modulating the carrier. This is in contrast to regular OFDM where the baseband is somesort of amplitude modulating the carrier.
Why are narrowband carriers used in OFDM transmission?
This allows us to see how the signal is generated and how receiver must operate, and it gives us a tool to understand the effects of imperfections in the transmission channel. As noted above, OFDM transmits a large number of narrowband carriers, closely spaced in the frequency domain.
What is the function of a signal generator?
A signal generator is one of the most essential pieces of technology in electronics and communication. It is used to produce different types of signals and frequencies for a variety of purposes such as testing, troubleshooting, and designing.
What are types of signal generator?
Types of signal generators
- Waveform or function generators.
- Arbitrary function generator.
- Arbitrary waveform generator.
- RF signal generator.
- RF vector signal generator.
Why is OFDM used?
The main advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without the need for complex equalization filters.
What is a signal and its types?
Two main types of signals encountered in practice are analog and digital. The figure shows a digital signal that results from approximating an analog signal by its values at particular time instants. Digital signals are quantized, while analog signals are continuous.
How does OFDM modulate a frequency domain signal?
For information, see OFDM Modulation. ofdmSig = ofdmmod (inSym,nfft,cplen,nullidx) inserts null subcarriers into the frequency domain input data signal prior to performing OFDM modulation. The null subcarriers are inserted at index locations from 1 to nfft, as specified by nullidx .
How are input data symbols created in OFDM?
Input data symbols to an OFDM modulator are typically created with a baseband digital modulator, such as qammod. FFT length, specified as an integer greater than or equal to 8. nfft is equivalent to the number of subcarriers used in the modulation process.
How are the signals stored in the OFDM frame?
There are five different signals that form the OFDM frame: SS, RS, Header, Pilots, and Data. SS, RS, and Pilots are same for every frame. They are stored in separate look up tables (LUT) and accessed whenever required. Header and Data vary based on the inputs given to the transmitter.
What are the subcarriers of an OFDM signal?
Individual OFDM subcarriers are allocated as data, pilot, or null subcarriers. As shown here, subcarriers are designated as data, DC, pilot, or guard band subcarriers. Data subcarriers transmit user data. Pilot subcarriers are used for channel estimation. Null subcarriers transmit no data.