Linearity of Power Amplification Essay

5.1 Linearity of Power Amplification

Linear curves transfer can easily be located over a range of varieties in input power generally in the practical power amplifiers. To measure the amplifications of nonideal power within the power amplifiers and the corresponding linearity a term is used which is so called the Compression Point or more specifically One [1] dB compression' point. The terminology one compression is best illustrated as

The above formula typically used to formulate the response curve for an amplifier of a nonideal power.

5.2 Clipping

Peak to average ratio [PAR] of OFDMs has a significant feature in which the symbols' percentages will have enough peak power and side by side there is a good significant percentage of decrement experienced whenever the subcarriers numbers got increased. Thus the feasible and the very simplest solution to avoid the problem of peak power is to restrict the amplitudes of the peak to a some maximum cap of power buffer level and this is so called the 'clipping'. This simple approach although have some of the limitation and weakness which are as

The very first disadvantage we would like to discuss with clipping technique is the bit error rate [BER] problem. It introduces some kind of self dependent interference and intrusion that would generally deteriorate the performance of BER.

The subsequent increment in the outofband radiations due to the distortions in the nonlinearity imposed by clipping.

5.3 ErrorControl Coding Technique

As discussed over in above point that clipping is more responsible for the BER degradation thus increasing pickup in noise. Not only this however, those symbols are more entitled to errors which are having a large amount of PAR' ratio. Now to overcome this effect a technique is usually be considered in practice known as FEC (forward error correction) and this can be applied to a large varieties of OFDM symbols. Application of forward error correction i.e. [FEC] technique in the surrounding symbols can rectify the defects and errors which are caused because of large PAR ratio.

5.4 Peak Termination

Another simple way for using this technique which helps out in OFDM signal to remove peaks is the subtraction of scaled reference and shift of time function so that the referenced subtracted functions will reduce the power peak of the sample by at least one. Thoroughly the recommendation has been followed that the signals which are approximately having the similar bandwidths with that of the transmitted signals need to be chosen. The desirable domain frequency characteristics are needed so SinC function can be commonly used for the peak cancellation. Now SinC can be windowed within limited time and can be multiplied with that of the windowed raisedcosine. It is proved that the technique of cancellation in the peak results in lesser interference in out of band signals than the techniques of clipping and window bases ones. An additional advantage of the peakcancellation technique is the fact that it can be digitally implemented, following to the IFFT in the transmitter