PAPR Reduction using SLM & PTS
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Date
2014
Authors
\Rana Jawabry
Ghada Adnan
Sawsan Qasem
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Abstract
AbstractOFDM is an upcoming technique for high rate data transmission in both wire line and wireless communications. It provides great benefits in combating the multipath fading and Inter-Symbol-Interference (ISI). One of the major drawbacks of OFDM has been the high peak-to-average power ratio (PAPR) that is characteristic of signals with multiple sub-carriers. The high PAPR requires additional back off to achieve linear amplification at the transmitter end which results in inefficient power consumption. This inefficient power consumption is the major impediment in implementing OFDM in portable device. Previous efforts to address this problem have been principally directed at two areas, the reduction of signal PAPR and various methods of achieving linear and efficient power amplification (PA). However, all approaches suffer due to various deficiencies such as complexity, computational time, memory requirements, data rate loss and high distortion. Therefore, this report aimed at finding the solution of power control problem by reducing the PAPR of the signal. Two novel techniques are proposed in this report. One of the techniques is based on Selected Mapping (SLM) technique from probabilistic. Result obtained using second technique which is Partial transmit sequence (PTS). The performance of these reduction schemes are evaluated by using simulation software, we analyze the computational complexity and extensive simulations on the PAPR and show that our scheme considerably reduces the computational complexity while achieving similar PAPR reduction as SLM and better PAPR reduction than PTS. Its found that PTS reduce PAPR more effectively. When Space Time Block Coding (STBC) is added to the system it improves the PAPR reduction in OFDM system.Background of the Problem High PAPR is one of the most serious problems in MIMO-OFDM system. To transmit signals with high PAPR, it requires power amplifiers with very high power scope. These kinds of amplifiers are very expensive and have low efficiency-cost. If the peak power is too high, it could be out of the scope of the linear power amplifier. This gives rise to non-linear distortion which changes the superposition of the signal spectrum resulting in performance degradation. If there are no measures to reduce the high PAPR, MIMO-OFDM system could face serious restriction for practical applications. To combat high PAPR, one intuitive solution is to adopt amplifiers to have larger trade-off range. However, these types of amplifiers are generally expensive and have low efficiency-cost, and therefore are of no practical use. On the other side, certain algorithms were introduced and been proved have a good performance of high PAPR reduction. Hence, in this project, some currently promising PAPR reduction methods are studied and compared.There has been momentous progress in the field of wireless communication during last twenty years. The internet and digital communication evolution has resulted in enormous increase in methods of personal communication as well as commercial applications. The new paradigm of information access to everybody everywhere all the time is in making. To achieve the ever increasing demands of higher data transfer rates for new multimedia applications, the physical wireless link of wireless communication networks is constantly under trial. The phenomenon of multipath fading, mobility and the limited availability of bandwidth are major precincts. Lately, there have been many breakthroughs to triumph over these limitations. Many modulation techniques compete for new solutions and future applications. Modulation schemes can be broadly categorized in to single carrier and multi carrier. Wideband code division multiple access (W-CDMA) is single carrier modulation scheme. While OFDM, Multi Carrier Code Division Multiple Access (MC-CDMA) and multi carrier (MC-IDMA) are multi carrier schemes. W-CDMA which has been adopted by UMTS and it supports up to 2 [Mbit/s] at high mobility and large range. OFDM which is one of the multi-carrier techniques and digital broadcast systems like digital audio/video broadcasting (DAB/DVB) are already using this technique. It is also being used in wireless local area network (WLAN).OFDM is popular for high data rate (broadband) communications because it is immune to multipath delay spread, it results in low complexity equalizer, and it has high spectral efficiency. It is also immune to channel behavior and uses efficient modulation/demodulation. Amongst several disadvantages, high PAPR makes OFDM very sensitive to nonlinear components like HPA in the transmission path. The HPA causes additional in-band distortion and adjacent channel interference leading to low power efficiency which is the main impediment to execution of OFDM especially in low-cost applications. Although these algorithms that have been shown in this report add some enhancement in PAPR reduction in OFDM system, there are some constraints appear when these algorithms applied. the first one is complexity, SLM and PTS become not easy when data is divided to large number of sub-blocks, though when that done the reduction will increase more and more, and STBC also play rule in complexity but also when it is added the performance increase so it is important thing to make trade-off between complexity and the number of sub blocks.The Second problem was run-time of the system, when SLM & PTS a logarithm applied the simulation time increase which is directly increase delay in the system which represents a problem in real time application in telecommunication system. All the simulation results are acquired under ideal conditions, but in reality, OFDM system has lots of practical problems, such as synchronization, channel estimation. Hence, for establishing a more complete and credible simulation system, synchronization and channel estimation techniques can be added to OFDM system simulation platform. Besides, all these PAPR reduction methods can be applied to MIMO-OFDM system. But when these problems added to the system simulation it will be complex.