How does ofdm

If the symbol is long enough — i. In the second example lower part of the figure , we transmit faster i. The signal goes through the same channel, and its individual frequencies are multiplied by the corresponding elements in the channel frequency response, thus all the individual frequency components are modified according to the shape of the channel frequency response.

The resulting received signal shape is destroyed compared to the original signal frequency representation on the left side of the figure , and makes it hard to revoke the original shape without complex estimators and receiving algorithms. As a side comment, it is imporant to note that the long or short symbols are always with respect to the channel impulse response and its dispersion :. This is where OFDM comes as a solution. It, simply speaking, combines all requirements so that we get:.

When we transmit a wideband signal i. In contrary, multi-carrier transmission is analogous to shipment goods using several smaller cars, each carrying a single package right side of the figure.

This is analogical to a single deep fade, by which only one subcarrier part of data is destroyed i. IN addition to this other requirements needed to achieve error free data transmission in the presence of interference and selective propagation conditions. Initially the use of OFDM required large levels of processing and accordingly it was not viable for general use.

Some of the first systems to adopt OFDM were digital broadcasting - here OFDM was able to provide a highly reliable form of data transport over a variety of signal path conditions. Once example was DAB digital radio that was introduced in Europe and other countries. OFDM was also used for digital television. Later processing power increased as a result of rising integration levels enabling OFDM to be considered for the 4G mobile communications systems which started to be deployed from around OFDM is a form of multicarrier modulation.

An OFDM signal consists of a number of closely spaced modulated carriers. When modulation of any form - voice, data, etc. It is necessary for a receiver to be able to receive the whole signal to be able to successfully demodulate the data. As a result when signals are transmitted close to one another they must be spaced so that the receiver can separate them using a filter and there must be a guard band between them. This is not the case with OFDM. Although the sidebands from each carrier overlap, they can still be received without the interference that might be expected because they are orthogonal to each another.

This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. To see how OFDM works, it is necessary to look at the receiver. This acts as a bank of demodulators, translating each carrier down to DC.

The resulting signal is integrated over the symbol period to regenerate the data from that carrier. As a result when signals are transmitted close to one another they must be spaced so that the receiver can separate them using a filter and there must be a guard band between them. This is not the case with OFDM. Although the sidebands from each carrier overlap, they can still be received without the interference that might be expected because they are orthogonal to each another.

This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. To see how OFDM works, it is necessary to look at the receiver.

This acts as a bank of demodulators, translating each carrier down to DC. The resulting signal is integrated over the symbol period to regenerate the data from that carrier.

The same demodulator also demodulates the other carriers. As the carrier spacing equal to the reciprocal of the symbol period means that they will have a whole number of cycles in the symbol period and their contribution will sum to zero — in other words there is no interference contribution. One requirement of the OFDM transmitting and receiving systems is that they must be linear. Any non-linearity will cause interference between the carriers as a result of inter-modulation distortion.

We've mentioned before that WiFi 6 can handle more devices than any of its predecessors, but how exactly is this possible? The answer lies in OFDMA technology, a key feature that helped take device handling to a whole new level. These channels are important because they allow us to keep any devices on the same network separate with designated frequencies, preventing signal interference and helping you to achieve the most streamlined network experience possible.

Before OFDM came traditional FDM Frequency Division Multiplexing , a far less-developed technology that required any signals carrying data to be spaced in such a way that frequencies did not overlap. There were even empty spaces — guard bands — placed between frequencies to ensure there was no contact, but this relied on a much wider range of frequency with far less usability.

OFDM is the method by which these frequencies are placed more strategically, helping wireless access points differentiate data transmissions over channels. With OFDM, signals can overlap with each other as long as it's at just the right spot as seen in the image above. While one signal is at its peak, the other signals are at their zero-point, allowing the receiver to differentiate between each signal.

This technology has made it possible to pack more data into a lower range of frequency. Consider the receiver to be like a barista in a coffee shop. With previous technology like FDM, the barista could only handle one customer inside of the cafe at a time, forcing the other customers to wait outside to prevent overwhelm.

With OFDM, on the other hand, the barista can handle a line of people coming into the coffee shop at once, also allowing them to stand more closely together, take their orders sequentially, and use the space more efficiently.