The optimization of PAPR reduction in the OFDM-IM system
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In this paper, the main purpose is to study how to reduce PAPR in the OFDM-IM system. According to some methods used in the OFDM system, have a further exploration analysis in OFDM-IM system. Firstly, it is about the OFDM-IM system introduction and the effect of PAPR on the OFDM-IM system. Secondly, SLM and PTS are studied in many aspects in the direction of OFDM, like the choice of phase and subcarrier grouping patterns. When phase factor is {1, -1}, the method used in OFDM is borrowed in PTS to improve the calculation time of results in the OFDM-IM system. In addition, the comparative analysis of PAPR under the combination of SLM-PTS and SLM-PTS methods is also studied. It can be concluded that the new method combines the characteristics of both, and its running time is less than that of traditional PTS and the performance of PAPR is less than that of traditional single SLM.Space-division multiple access
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Clipping (morphology)
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Author(s): Batra, Arun | Abstract: This dissertation examines the effect of severe narrowband interference on wireless communication systems. In single- carrier systems, the interference causes the adaptive equalizer to have an extended convergence time, where convergence is considered in terms of the bit error rate (BER). Two techniques are proposed to improve the convergence. The first method, data-aided initialization (DAI), initializes the Wiener weights from estimates derived directly from the received data and training sequences. This technique is shown to substantially reduce the number of training symbols needed for convergence. Further, two methods for obtaining the DAI weights are investigated. The use of multistage Wiener filters (MSWF) is preferable to a parametric approach to direct matrix inversion in terms of BER performance and number of training symbols needed. The second method is a two-stage system that utilizes a prediction error filter (PEF) as a pre-filter to the equalizer. It is shown that the two- stage system reduces the number of training symbols required to reach a BER of 10⁻² by approximately two orders of magnitude without substantially degrading the steady-state BER performance as compared to the DFE-only case. In block-modulated multi-carrier systems the presence of a severe narrowband interference causes the degradation of a large number of subcarriers due to spectral leakage of the interference power after demodulation. Multi-carrier code division multiple access (MC-CDMA) obtains frequency diversity by spreading the data into every subcarrier, thus mitigating the effects of narrowband interference. On the other hand, orthogonal frequency division multiplexing (OFDM) requires the addition of coding and interleaving to obtain frequency diversity. The use of genie inserted erasures provides little to no improvement in BER performance, thus the PEF is proposed as an erasure insertion mechanism that notches out the tones located close to the interference, while leaving the remaining tones unaffected. This technique provides excellent results as compared to the case of no interference. This work was done at UCSD's Center for Wireless Communication, under the Bandwidth Efficient Communications project (CoRe research grant 06-10216) and supported by the Office of Naval Research, Code 313.
Narrowband
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Problem statement: Combining the properties of Multiple Input Multiple Output (MIMO) systems with those of Orthogonal Frequency Division Multiplexing (OFDM), MIMO-OFDM was considered to be a promising technique in the future of wireless communications. However, its sensitivity to frequency offsets which results in Inter-Carrier Interferences (ICIs) makes it necessary to use an exact frequency offset estimation method for data recovery in the MIMO-OFDM receiver. Approach: In this study, a new preamble-based frequency offset compensation method was introduced in frequency domain. In each block, two preambles are used to initially obtain the channel coefficients through LS channel estimation method. A polynomial curve fitting algorithm was then applied so that the frequency offsets experienced by every single data subcarrier are separately determined. Finally, to improve the compensating process, an iterative algorithm was applied. Results: Simulation results clearly showed that our proposed method was accurate in multipath fading channels and precisely recovered the transmitted data symbols. The BER performance of the iterative algorithm is within an acceptable distance of that in the ideal channel. Conclusion: In comparison with the conventional methods, our proposed scheme was less complex and showed better performance in lower SNRs. For further research, it can be investigated and improved while considering correlated antennas and spatial multiplexing.
Carrier frequency offset
Preamble
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Blind equalization
DPLL algorithm
Carrier frequency offset
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Orthogonal frequency division multiplexing is a promising technology for high data rate transmission in wide band wireless system for achieving high downlink capabilities in a future cellular system. This paper demonstrate, how to improve the capacity of the system and transmission quality of orthogonal frequency-division multiplexed (OFDM) along with multi-input multi-output (MIMO) used with adaptive modulation can effectively eliminate fading in wireless channels. To minimize the overall transmit power, greedy algorithm approach was proposed for the optimal bit and power allocation strategy, the performance of adaptive bit and power allocation MIMO-OFDM system based on greedy algorithm is completely studied and the performance comparison among greedy algorithm, chow algorithm and average algorithm is represented. The analysis and the simulation are considered in two stages. First stage involves single-input single-output (SISO) OFDM system. This is compared with the performance of fixed OFDM transmission where a constant rate is applied to each subcarrier. Second stage involves MIMO-OFDM and we compared the performance of MIMO-OFDM system under different antennas numbers.
Link adaptation
Transmitter power output
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FDMA, TDMA and CDMA are the well known multiplexing techniques used in wireless communication systems. While working with the wireless systems using these techniques various problems encountered are (1) multi-path fading (2) time dispersion which lead to intersymbol interference (ISI) (3) lower bit rate capacity (4) requirement of larger transmit power for high bit rate and (5) less spectral efficiency. The use of orthogonal frequency division multiplexing (OFDM) technique provides better solution for the above mentioned problems. The benefits of OFDM are high spectral efficiency, resiliency of RF interference, and lower multi-path distortion. OFDM is a powerful modulation technique that is capable of high data rate and is able to eliminate ISI. The use of FFT technique to implement modulation and demodulation functions makes it computationally more efficient.
Spectral Efficiency
Modulation (music)
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Abtract Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) is an attractive method which has gained significant interests as a promising candidate for the 4th Generation wireless communication. However, one of the main disadvantages of MIMO-OFDM is its high peak to average power ratio (PAPR). In this paper, Partial Transmit Sequences (PTS) method introduced in the MIMO-OFDM system is presented with various simulation results to verify its effectiveness. Results shows that PTS technique improves the performance of the MIMO-OFDM system, moreover, it can be shown that with increasing the value of the number of non overlapping sub-blocks, the PAPR performance becomes better. Different kinds of PTS schemes are also plotted. The Pseudo-random seems leading the better performance.
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