Generalized Multicarrier Modulation with Pseudo Nonuniform Carrier Spaces
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In conventional orthogonal frequency division multiplexing (OFDM) technique, the subcarriers have uniform spaces. The channel gains of the subcarriers are the uniform samples of the channel frequency response. This method may not be efficient when the channel has variable gains in different subcarriers. In this paper we propose a new multicarrier modulation scheme based on generalized Fourier transform. In the new scheme the channel gains of the subcariers are the samples of the channel frequency response but with nonuniform sampling spaces, which is referred as ldquopseudordquo subcarrier spaces in this paper. When the channel information is available at the transmitter, it is possible to avoid the frequency null by adjusting the pseudo subcarrier space. Computer simulations give some demonstrative examples.Keywords:
Modulation (music)
Frequency-division multiplexing
Vehicle-to-Vehicle and Vehicle-to-Infrastructure (V2X) communication brings about stringent demand for robust and efficient communication techniques under sever Doppler effect and frequency-selective channel environments. Index Modulated Orthogonal Frequency Division Multiplexing with Interleaved grouping (IIM-OFDM), which utilizes the indices of active subcarriers in frequency domain interleaved subcarrier groups to carry information, is considered as a competitive candidate for its robustness against both Inter-Carrier Interference (ICI) and channel correlation. In this paper, we propose a novel revision of IIM-OFDM designed for V2X, namely Quadrature Index Modulated OFDM with Interleaved grouping (IQIM-OFDM), which performs index modulation independently for the inphase and quadrature components of the constellation symbols. Thanks to the increased index bits, IQIM-OFDM can work at smaller subcarrier group and constellation sizes compared with IIM-OFDM at the same data rate, and therefore boosts the performance under V2X channels. Monte Carlo simulations under measured V2X channels are conducted to verify the superiority of the proposed scheme against both IIM-OFDM and classical OFDM schemes.
Robustness
Quadrature (astronomy)
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Orthogonal frequency division multiplexing (OFDM) is the projected modulation of choice for fourth-generation broadband multimedia wireless systems. However, for mobile applications, channel variations during one OFDM symbol introduce intercarrier interference (ICI), which degrades the performance. This gets more severe as mobile speed, carrier frequency or OFDM symbol duration increases. We analyze ICI for mobile OFDM systems in terms of the complex weighting coefficients, which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Then, we propose a new cancellation method to reduce the effects of Doppler frequency shift. The results show that by using the proposed cancellation scheme, the ICI can be reduced significantly.
Adjacent-channel interference
Modulation (music)
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In today's communication scenario, high data rate single-carrier transmission may not be feasible due to too much complexity of the equalizer in the receiver. To overcome the frequency selectivity of the wideband channel experienced by single-carrier transmission, multiple carriers can be used for high rate data transmission. Orthogonal frequency division multiplexing (OFDM), is multicarrier system which has become a modulation in physical layer of next generation WiMAX, LTE system. In this paper effort is made to present challenges in OFDM and work done so far in channel equalisation and different transforms used in OFDM system.
Modulation (music)
Frequency-division multiplexing
Wideband
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Recently, orthogonal frequency division multiplexing (OFDM) has been considered as an irreplaceable and reliable technology. However, it is vulnerable to the frequency offsets, which may potentially cause intercarrier interference (ICI). Hence, in this paper, a general and efficient ICI self-cancellation scheme is proposed toward higher transmission efficiency. The scheme maps the data symbols to different subcarrier positions with the aid of scrambler or interleaver, so more adjacent subcarriers contribute to interference cancellation. The simulation in comparison to standard OFDM system demonstrates that the advantages offered by the presented scheme in the case of frequency offsets with no compromise in the attainable bit error rate (BER) performance.
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Abstract In 5G and beyond communication systems, distinct numerologies can coexist to serve diverse requirements for users and applications. However, the inter‐numerology interference (INI) is a main challenge that significantly impacts the system performance. Therefore, the performance under INI has become an essential evaluation metric for the suitability of the different transmission schemes in the future communication systems. This paper analyzes the impact of INI on the performance of orthogonal frequency division multiplexing with index modulation (OFDM‐IM) systems. Specifically, an analytical expression of the INI level in OFDM‐IM systems is presented as a function of the subcarrier activation ratio (SAR) and subcarrier activation probability (SAP). Furthermore, aiming at reducing the INI level, an adaptive subcarrier mapping scheme (SMS) is proposed based on the conventional combinatorial mapping scheme. Moreover, analysis and evaluation of SAR and SAP are performed regarding the requirements of 5G and beyond services. It is proved that the INI level in OFDM‐IM systems is highly dependent not only on the number of active subcarriers but also on their position in an OFDM block.
Adjacent-channel interference
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Stages of Development and Advantages of Orthogonal Frequency Division Multiplexing (OFDM) Technology
A review of stages of development of orthogonal frequency division multiplexing (OFDM) applied to different communication facilities and TV and sound broadcast systems is given. Advantages of application of the technology in conditions of various interferences in the channel are presented.
Frequency-division multiplexing
IEEE 802.11a-1999
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A novel subcarrier multiplexing based carrier sense technique called SCM-CS is proposed and is experimentally demonstrated. It can prevent the contention in optical frequency division multiple access networks that use an access protocol based on a fixed-wavelength transmitter and wavelength-tunable receiver. When two or more SCM signals on the same subcarrier frequency at different wavelengths simultaneously address the same destination node, SCM-CS detects the sum of the subcarrier frequencies by using RF heterodyne detection and denies the access. SCM-CS permits node access only if the carrier sense is negative which means that the destination node is idle. In the experiment, SCM-CS is successfully performed for 6.2 Mb/s SCM signals of the subcarrier frequency of 164 MHz with the frequency difference of the optical carriers up to 40 GHz.
Subcarrier multiplexing
Heterodyne detection
Frequency-division multiplexing
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Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2. In OFDM systems, the performance is very sensitive to subcarrier frequency errors (offset). This paper shows the analysis and derivations of intercarrier interference (ICI) complex gain that used in self-cancellation scheme and its dependence on subcarrier frequency offset. Simulation shows that better improvement in performance is achieved for systems that use this cancellation scheme. Moreover, analysis and simulation show that theoretical carrier-to-interference ratio (CIR) for OFDM with cancellation scheme is greater than conventional one by more than 14dB.
Carrier frequency offset
Adjacent-channel interference
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Multi-User Orthogonal Frequency Division Multiplexing (MU-OFDM) is an efficient technique for achieving high downlink capacity in high-speed communication systems. A key issue in MU-OFDM is the allocation of the OFDM subcarriers and power to users sharing the channel. In this paper, a proportional rate-adaptive resource allocation algorithm for MU-OFDM is presented. Subcarrier and power allocation are carried out sequentially to reduce the complexity. The low complexity proportional subcarriers allocation is followed by Greedy Power Allocation (GPA) to solve the rate-adaptive resource allocation problem with proportional rate constraints for MU-OFDM systems. It improves on the work of Wong et al. in this area by introducing optimal GPA that achieves approximate rate proportionality, while maximizing the total sum-rate capacity of MU-OFDM. It is shown through simulation that the proposed GPA algorithm performs better than the algorithm of Wong et al. by achieving higher total capacities with the same computational complexity, especially, at higher number of users.
Max-min fairness
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In this letter, the modulation and demodulation mechanisms of the discrete Fourier transform-based optical fast orthogonal frequency-division multiplexing (F-OFDM) scheme have been examined. Analysis shows that there exists an interference term between even and odd subcarriers in this F-OFDM scheme, which has severe impact on system performance, especially when the subcarrier number is small. We propose a zero-subcarrier-based method and numerically investigate the effectiveness of the method with different number of subcarriers. Simulation results show that the approach can greatly mitigate the interference in DFT-based F-OFDM scheme.
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Subcarrier multiplexing
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