| Author | Gupta, Ajay Kumar |
| Call Number | AIT RSPR no.TC-12-01 |
| Note | A research study submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Telecommunications, School of Engineering and Technology
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| Publisher | Asian Institute of Technology |
| Abstract | OFDM is a multicarrier modulation technique because of the robustness in multipath fading channels. There are two main problems faced by the OFDM systems, the first one is its high sensitivity to synchronization errors and the second one is its high peak-to-peak average power ratio (PAPR). And because of high PAPR OFDM is more sensitive to nonlinear distortion than single carrier systems.
Out-of band distortion and in-band distortion are introduced because of the HPA non-linearity and as a result there is adjacent channel interference (ACI) and so the BER performance gets degraded. If there is an increase in the input power of the amplifier and is increased beyond the linear region of the amplifier, so there is a nonlinear increase in the output power due to reduction in the gain . The output power reaches saturation when input power exceeds certain power level. In the compression region the output of the amplifier is distorted.
One of the simplest way to manage the HPA distortion is to work on the linear region and operate the HPA far from the saturation point, this is known as power back-off technique but this technique decreases the efficiency of HPA to a large extent. HPA linearization can also be managed by many other technique such as linear amplification with non-linear component (LINC), feed-forward technique, cartesian feedback technique, digital adaptive pre-distortion technique and envelope elimination and restoration. All of these technique have their own advantages and disadvantages and at present memoryless digital predistortion technique at baseband is being used due to easy implementation capability and good adaptive performances. We envestigate our sytem with the ideal AWGN channel. In the initial stage we inserted a distortion that is the uncompensated system to show the non-linearity effect and to reduce this non-linearity we inserted a PD just before the TWT HPA so that it creates a pre-distorted signal and later on cancels with the distrorted signal and as a result overall system goes towards linearity. Later on we have adopted the Shadowed Rican channel with different parameter channel state such as heavy shadowing and moderate shadowing and analysed the performance of the system.
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| Year | 2012 |
| Type | Research Study Project Report (RSPR) |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Ahmed, Kazi Mohiuddin; |
| Examination Committee(s) | Teerapat Sanguankotchakorn ;Poompat Saengudomlert; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship; |