How does a frequency selective channel behave in OFDM transmission?
One of the most important features in OFDM system is the division of the frequency selective channel into smaller subchannels. These subchannels can be considered to be equal to coherence bandwidth, in which the channel is behaving like flat fading channel, if the system has been correctly designed.
Does OFDM really prefer frequency selective fading channels?
OFDM (Orthogonal Frequency Division Multiplexing) scheme is robust to frequency selective fading in wireless channels, because it is insensitive to multipath delay spread within guard interval.
What is OFDMA and how it works?
OFDMA follows a set of rules created for the transmission of data between more than one terminal (any device at the end of a transmission channel, such as a computer or phone) over a transmission medium (such as a wireless network). An example of how OFDMA works is when two phones send data over the same phone line.
Why QAM is used in OFDM?
Each of the subcarriers is modulated using QAM. These modulated subcarriers can be used to support independent baseband signals but more typically they are combined to provide the maximum data throughput for one stream of data. Figure 2. An OFDM modulator sums signals of different frequencies.
What causes frequency selective fading?
Frequency selective fading occurs when the symbol length is shorter than the delay spread, or equivalently when signal bandwidth is larger than the channel bandwidth. Frequency selective fading is reduced by equalization, where a digital filter in the receiver counteracts the effects of the channel.
What are the effect of frequency selective fading?
The presence of frequency selective fading on the transmission channel causes intermodulation distortion to appear at the base-band output of frequency modulation systems. In addition this frequency selective fading causes phase and amplitude fluctuations to appear on demodulated subcarriers.
What is frequency selective fading?
Selective fading or frequency selective fading is a radio propagation anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by two different paths, and at least one of the paths is changing (lengthening or shortening).
What are OFDMA channels?
OFDMA stands for orthogonal frequency division multiplexing access. It is an extension of OFDM. The difference is that OFDMA is multi-user where OFDM is single-user. It has 3x higher throughput than single-user OFDM for short packets of data or multiple endpoints.
How is OFDMA used in frequency selective fading channel?
The comparison results for different schemes show that OFDM transforms the characteristics of the frequency selective fading channel to flat fading channel. This shows that OFDMA is a suitable data access technique of transforming wideband frequency selective channel into flat fading narrow bands at high data rate.
What is the difference between OFDMA and SC-FDMA?
For the Downlink, Orthogonal Frequency Division Multiple Access (OFDMA) is considered while Single Carrier Frequency Division Multiple Access (SC- FDMA) is for the Uplink 2 CHARACTERISTICS of WIRELESS CHANNELS IJOART
How is the performance of OFDM compared to flat fading channel?
The performance of OFDM for different modulation scheme on the channel was compared to the results obtained for flat fading channel. The comparison results for different schemes show that OFDM transforms the characteristics of the frequency selective fading channel to flat fading channel.