The drive signal was generated offline in matlab with a 1024fft with 32point cyclic prefix cp. Adaptive subcarrier and power allocation in ofdm based on maximizing utility guocong song and ye geoffrey li the school of electrical and computer engineering georgia institute of technology, atlanta, ga 303320250 email. In addition, for a 300 gbs pdm qpsk co ofdm transmission, a performance improvement of around 0. Motivated by the above, in this paper we first derive the analytical expression of electrical power spectral density psd and show that it matches a system simulation including optical. Orthogonal subcarriers no intercarrierinterference ici. This paper discuss several phy layer aspects broadband mimo ofdm systems. A modification of pctw for coherent optical orthogonal frequency division multiplexing co ofdm exploring the demonstration of phaseconjugated subcarrier coding for fiber nonlinearity compensation in co ofdm transmission son thai le, mary e. The trick that makes ofdm a practical transmission system is to link the subcarrier modulation rate to the subcarrier spacing such that the nulls in the spectrum of. Ofdmsubcarrier index selection for enhancing security and.
Orthogonality is achieved by generating a rectangular subcarrier pulse. The insertion of a cyclic prefix cp is one of the critical steps that have to be implemented at the ofdm transmitter to reduce intercarrier interference ici caused by overlapping between symbols of an ofdm signal 3. The resulting subcarrier frequency spacing in the ieee 802. Sung, low complexity subcarrier and power allocation for utility maximization in uplink ofdma systems, ieee lds ofdm wf 0 0 0 0 0 0 transactions on wireless communications, vol. In the frequency domain, since the bandwidth of a subcarrier is designed to be smaller than the coherence bandwidth, each sub. Another null subcarrier is the dc direct current subcarrier. One simple way to achieve the centering is to use a 2nifft 2 and t2 as the elementary period. Sensitivity improvement and carrier power reduction in direct. Subcarrier multiplexing an overview sciencedirect topics. Orthogonal frequency division multiplexing with subcarrier.
There are still spectral nullsat other subcarrier frequencies. The idea of ofdm is to spread data across multiple overlapping subcarriers. The implementation of ofdm modulationdemodulation is done using the fft and ifft. Thus there exist no known algorithms that can provide optimal solutions for all instances of these problems in polynomial time. Time domain rectangular windowed ofdm signal time nt a time domain beforeafter windowing. Pdf multiuser subcarrier and power allocation algorithm for. In ofdm and ofdma phy layers, the dc subcarrier is the subcarrier whose frequency is equal to the rf centre frequency of the transmitting station. We consider two scenarios, where in one the total power per user and in the other total power per subcarrier is. Orthogonal frequency division multiplexing ofdm modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination.
Subcarrier equalization and pilot correction openofdm 1. Ber, iot, multipath rayleigh channel, ofdm, subcarrier power modulation, ofdm spm spec tral efficiency, throughput, wireless. Ofdm with subcarrier number modulation ieee journals. Resource allocation based on subcarrier exchange in multiuser. Theory and applications of ofdm, plenum publishing corporation. Ouahman abstractin this letter, the multiuser bit and power allocation we develop a new algorithm for ofdm oqam and we show problem for an orthogonal frequency division. May 22, 2018 a new modulation technique, named orthogonal frequency division multiplexing ofdm with subcarrier number modulation, is proposed for efficient data transmission. Multiuser ofdm with adaptive subcarrier, bit, and power allocation. Ofdm and ofdma subcarrier allocation with standard ofdm the subcarrier allocations are fixed for each user and performance can suffer from narrowband fading and interference. Ofdm and ofdma subcarriers what are the differences. More specifically, it relates to adding an additional dimension to the conventional twodimensional 2d amplitudephase modulation apm techniques, i.
Optimized null subcarrier selection for cfo estimation in ofdm over frequencyselective fading channels mounir ghogho1, ananthram swami2 and georgios b. Orthogonal frequency division multiplexing ofdm is a multicarrier modulation technique, in which a. As we can see in table 1, the ofdm symbol duration. That means, all other subcarriers are 0 at the evaluation point of a specific subcarrier. Pdf ofdm with subcarrier number modulation researchgate. The increase in the number of subcarriers tones also increases in the ofdm symbol duration from the maximum of 4. So now once use ofdm, you can that the channel coefficients across the subcarrier in the time domain are given by the n point fft in fact, 0 pared fft of the channel taps in the time domain. Pdf joint subcarrier pairing and power allocation for ofdm. Request pdf subcarrier and power allocation in ofdm noma vlc systems we propose a novel subcarrier and power allocation method to improve both the throughput and user fairness in orthogonal. Every subcarrier has an integer number of cycles within t. The proposed phaseconjugated coding scheme for co ofdm transmission, the numbers in red are the probabilities of symbols in the constellation set. The discussion about the theoretical performance of space time coded ofdm with transmit and receive antenna selection is provided and specifically, the performance of subcarrier group based joint antenna selection technique for convolutional coded ofdm and space time block coded ofdm systems are presented. Odd and even constellations from 256qam to 4096qam frame structure a frame consists of 128 4k fft and 64 8k fft subframes a subframe consists of 2 ofdm symbols pilots.
An 800 subcarrier system with 64qam mapped to each subcarrier can transmit 800 x 8 6400 bits per symbol. In ofdm a number of different frequency carriers are modulated with a signal from a scheme such as quadrature amplitude modulation qam. Mar 01, 2021 in this blog series, we will use both terms interchangeably. Is a composite of all ofdm subcarrier symbols and time. Ofdm channel estimation enhancement using null subcarriers. Pdf effect of subcarriers on orthogonal frequency division.
Pdf multiuser subcarrier and power allocation algorithm. The first technique is a phasing scheme for ofdm pilot symbols, which uses genetic algorithms to optimise the phase angle of each subcarrier. Orthogonal frequency division multiplexing ofdm is the modulation scheme chosen for the lte downlink. Ofdm introduction ee225c introduction to ofdm lbasic idea using a large number of parallel narrowband subcarriers instead of a single wideband carrier to transport information ladvantages very easy and efficient in dealing with multipath robust again narrowband interference ldisadvantages sensitive to frequency offset and phase. We propose an acoustic ofdm system for underwater communication, specifically for vertical link communications such as between a robot in the sea bottom and a mother ship in the surface. Multiuser mimoofdm systems using subcarrier hopping. Hence, the typical underwater acoustic communication channels can be expressed as. This technique achieves a lower cf than any previously published techniques, obtaining a cf as low as 0. Jun 29, 2012 cheong y w, cheng r s, lataief k b, et al.
The idea behind this scheme is inspired from the integration of ofdm with pulse width modulation, where the width. Furthermore, a closedform analytical bit error ratio ber of sim ofdm. The physical phy layer techniques described in this paper are intended to approach 10 bshz bandwidth efficiency. A typical ofdm transmitter and receiver structure is shown in figure 2. Pdf power allocation and subcarrier pairing in ofdmbased. Therefore, the received snr over the k th subcarrier of s d, s r and rd links can be gi ven by. In a singlecarrier system, the symbol length is closely related to the occupied bandwidth. The transmitted leaco ofdm consists of 4 layers, carrying 45, 22, 11 and 6 subcarriers. Ofdm is a combination of modulation and multiplexing. It corresponds to frequency zero direct current if the fft signal is not modulated. Phaseconjugated subcarrier coding for fibre nonlinearity. Pdf ofdm with transmit and receive antenna selection based. Ofdm that is orthogonal frequency division multiplexing basically overcomes the inter symbol interference, okay all right.
Multiplexing method of sharing a bandwidth with other independent data channels. Orthogonal frequency division multiplexing for wireless communications by ye geoffrey li editor, gordon l. Ofdm system is capable of a chieving a high frequency diversity, and hence exhibits a high robustness to mui. The main contributions are 1 estimation of time varying doppler shift using continual pilots in conjunction with monitoring the drift of power delay profile and 2 symbolbysymbol doppler compensation in. The source transmits in the first hop, and the relay transmits in the second hop. The rest of this paper has been organized as follows. The key idea of sim is to employ the subcarrier index to convey information to the receiver. As they are orthogonal it is still possible to demodulate them.
In this paper, the ofdm system was developed for orthogonal 32, 64, and 128 subcarriers at different mobile speeds of 30kmh, 60kmh and 120kmh over. Orthogonal frequency division multiplexing ofdm is a multicarrier modulation technique which uses orthogonal subcarriers to convey information. In the literature, substantial research efforts have been invested in designing subcarrier allocation algorithms for singleinputsingleoutput siso ofdm systems, which are subject to various design constraints, such as requiring. A transmitter includes a baseband modulator, subcarrier mapping, inverse fourier transform, cyclic prefix addi. William shieh, ivan djordjevic, in ofdm for optical communications, 2010. Each individual subcarrier is modulated at a low symbol rate with a conventional modulation format. In this scheme, the information bits are conveyed by changing the number of active subcarriers in each ofdm subblock. Ofdma incorporates elements of time division multiple access tdma so that the subcarriers can be allocated dynamically among the different users of the channel.
In the ofdm radcom system, xt, modulated by rf car. It is a digital multicarrier scheme that uses a large number of closelyspaced subcarriers to carry data and control information. With dsp techniques fft and ifft, subcarrier spacing can be reduced to. Among these schemes, ofdm with subcarrier number modulation ofdm snm introduces an extra signal modulation. Pdf a new modulation technique, named as orthogonal frequency division multiplexing ofdm with subcarrier number modulation snm.
Orthogonal frequency division multiplexing ofdm is a multicarrier modulation technique which is very much popular in new wireless networks of ieee standard, digital television, audio. Subcarrier modulation identification of underwater acoustic. Lte has chosen 15 khz subcarrier spacing, giving 66. The novel approach of sim ofdm tries to exploit an additional new dimension in the ofdm frame coming from the state of each. Mimo ofdm systems with bandwidth efficiencies on the order of 10 bshz are feasible for lanman environments. An acoustic ofdm system with symbolbysymbol doppler. Feb 01, 2021 where c n, k is the k th subcarrier modulation signal of the n th ofdm symbol mapped by subcarrier modulation, x n, l is the data on the l th subcarrier of the n th ofdm symbol. The key idea of sim is to employ the subcarrierindex to convey information to the receiver.
An introduction to orthogonal frequency division multiplex. A new transmission approach, referred to as subcarrier index modulation sim is proposed to be integrated with the orthogonal frequency division multiplexing ofdm systems. Subcarrier spacing is equal to the reciprocal of the symbol time. The obm ofdm could be realized using either subcarrier multiplexing 3 or wavelength multiplexing to patch multiple orthogonal bands into a complete ofdm spectrum see figure 8. The adaptation of the ofdm modulation scheme parameters, such as symbol duration and subcarrier spacing, to transmission properties of the. Stuber editor, isbn 0387290958 ahmad bahai and burton saltzberg, multicarrier digital communications. Assuming an ofdm system with subcarriers, a bandwidth of 6 hz and symbol length of 3 seconds, of. Pdf subcarrier and power allocation for ldsofdm system. This subcarrier has a baseband frequency f when the condition f. In this paper, a pointtopoint orthogonalfrequency division multiplexing ofdm system with a decodeand forward df relay is considered. Pdf adaptive subcarrier and power allocation in ofdm based. Ofdm and mitigate the high peaktoaverage power ratio papr problem, various frequencydomain sparsity modulation schemes without activating all available frequency resources have been proposed and analyzed in recent years 25.
Demonstration of phaseconjugated subcarrier coding for fiber. Subcarrier and power allocation in ofdmnoma vlc systems. Ber, iot, multipath rayleigh channel, ofdm, subcarrier power modulation, ofdmspm spec tral efficiency, throughput, wireless. An introduction to orthogonal frequencydivision multiplexing diva. The first task to consider is that the ofdm spectrum is centered on fc. Here, the 96 mhz channel bandwidth includes a 1 mhz guard band on each end of the channel, so the encompassed spectrum is 94 mhz.
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