Ofdm Systems Research Papers - Academia.edu (original) (raw)

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- by
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- Wireless Communications, Channel Coding, Information Theory and coding, OFDMA

– This paper aims to present an approximate location of a Mobile Station (MS) in Microcell zone concept in GSM system based on retrieving the Timing Advance (TA) from the Base Station (BS). In microcell concept, three or more zone sites are connected to a single BS and share the same radio equipment. Therefore, a MS travels within the cell uses the same frequency band assigned to the cell and served by the zone site with the strongest signal. Unlike sectoring, this method requires no additional hardware and a handoff procedure is not required at the Mobile Station Controller (MSC) when the MS travels between different zones within the same cell. The base station switches the channel to the next zone site. This algorithm is very useful for measuring the TA by the MSC while the MS is at the idle mode, since the BS can switch the channel to a different zone. By doing so and measuring the TA at each time the channel is switched to the next zone, a promising mobile positioning technique can be determined. Matlab simulation based location results and measurements statistics are also provided as MS coordinates, distances from the zone sites and the angles between the MS position and the zone site. These results using the direct solution approximated the error in calculating the distances between the MS and the zone sites to values between 100 – 133 meters.

- by Khalid G Samarah
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- Ofdm Systems, PAPR Reduction in OFDM systems
- by Maha George
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- Adaptive Filtering, Channel Estimation, Ofdm Systems

The current research trends towards mobile broadband communications highly focused on mitigating the power spectral analysis and frequency localization issues associated with Orthogonal Frequency Division Multiplexing namely OFDM signals. There are various existing research works have been found ensure less efficient communications strategies. Therefore to address various interference problems during transmission data filter, OFDM has been conceptualized and implemented. Most of the f-OFDM techniques have been designed without coding. The proposed study aims to develop a higher order modulations e.g. QAM/PSK based filtered OFDM system to mitigate the inter-symbol interference issues of channel properties. The proposed system has been configured and simulated in a real-time test bed (Matlab). The proposed system uses Root Raised Cosine (RRC) filter design specification and it also integrated the filter modules in the transmitter and the receiver side. The experimental outcomes of the proposed system show that it achieves very higher signal quality on less amount of bit error rates and the huge amount of power spectral density at the receiver end. It also achieves a high data transfer rate, well utilization of bandwidth as well as frequency localization factors as compared to the conventional OFDM models. Index Terms-Filtered Orthogonal Frequency Dvision Multiplexing (f-OFDM); Root Raised Cosine (RRC)Filter , PSK(Phase Shift Keying) , Frequency Localization.

- by Nextgen Research Publication
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- Communication, Wireless Communications, Ofdm Systems
- by Paolo Banelli
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- OFDM, Equalization, Channel Estimation, Ofdm Systems

Nonlinear distortions and impairments appear in multicarrier signal with high fluctuations when amplified by a Radio Frequency Power Amplifier (RF PA). This article is a contribution to improving the Tone Reservation (TR) method dedicated to reducing fluctuations in the Orthogonal Frequency Division Multiplexing (OFDM) modulation. This method exploits the null sub-carriers in communications standards in order to generate a correction signal used to reduce the Peak-to-Average Power Ratio (PAPR) with nevertheless limited performances due to the reduced number of these sub-carriers. For this purpose, our contribution is to combine the TR method with the Clipping (CL) method to improve the PAPR reduction without significantly impacting the quality of transmissions. We also show the gain provided by this strategy compared to the use of classical methods. Experiments using a simulated example on a complete WiMax 802.16e transmitter have been made in order to investigate the PAPR reduction performances on presence of the non-linear Power Amplifier model based on gain compression response and phase distortion.

- by International Journal of Electrical and Computer Engineering (IJECE) and +1
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- Ofdm Systems, Clipping, PAPR reduction, Conjugate Gradient
- by Paolo Banelli
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- OFDM, Ofdm Systems, Power Amplifiers
- by Paolo Banelli
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- OFDM, Ofdm Systems, Nonlinear Distortion

The next generation of mobile communication is based on OFDM technology. It is an efficient method of data transmission for high speed communication system. Orthogonal frequency division multiplexing (OFDM) systems have been proposed in the recent past years for providing high spectral efficiency, less vulnerability to echoes, low implementation complexity and resistance to non linear distortion .However the main drawback of OFDM system is high peak to average power ratio (PAPR) of transmitted signals due to inter-symbol interference between the subcarriers as a result the amplitude of such a signal can have high peak values. Thus a power amplifier must be carefully manufactured to have a linear input output characteristics or to have large input output back-off. Drawback of high PAPR is that dynamic range of power amplifier and Digital to Analog (D/A) converter during the transmission and reception of the signal is higher. As a result total cost of transceiver increases with reduced efficiency. Discrete Fourier Transform (DFT) Spreading is one of the schemes to reduce the PAPR problem in OFDM system by using different subcarrier mapping schemes. In this paper we proposed combination of DFT spreading technique with FEC coding to reduce PAPR in OFDM system. Performance evaluation carried out in terms of SNR (signal to noise ratio) BER (bit error rate).

- by Paolo Banelli
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- OFDM, Ofdm Systems, Ofdm Channel Estimation and Cfo, Time Varying Channels
- by Omar Al-Askary and +1
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- Coding Theory, Wireless Communications, Error control and Coding theory, Ofdm Systems
- by Hamza Kiani
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- Wireless Communications, ISI, OFDM, OFDMA

This paper focuses on the design of radio resource management policies for multicast service delivery in WiMAX networks. With the purpose of finding an alternative solution to the conventional multicast scheme that is conservative towards resource utilization, we propose to use a subgroup-based link adaptation technique that dynamically chooses the modulation and coding schemes based on the perceived channel conditions in each subgroup of multicast receivers. The main idea is to split the multicast destinations into different subgroups depending on the perceived channel quality, and to apply subgroup-based adaptive modulation and coding for a more efficient spectrum exploitation. The performance of different solutions for the subgroups formation will be analyzed and their effectiveness evaluated through simulations to show how the network can take advantage from the proposed subgrouping approach.

- by Khalid G Samarah
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- Ofdm Systems, PAPR Reduction in OFDM systems

To reduce the occurrence of high peak-to-average power ratio (PAPR), this paper introduces prolate-binary sequences, and their application in orthogonal frequency division multiplexing (OFDM) systems that implement selected mapping (SLM). Through computer simulation, it is shown that the proposed prolate-binary sequences offer combined improved PAPR reduction performance, and reduced computational complexity compared with Riemann-binary sequences.

- by Saheed Adegbite and +1
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- Computational Complexity, Orthogonal Frequency Division Multiplexing (OFDM), Long Term Evolution (LTE), Ofdm Systems

Beside the hard ware implementation problems in Cognitive Radio Networks (CRNs), some communication criteria’s are considering to generate CRN with improvement, reliability and motivation communication system. One of these criteria’s is how to maximize total throughput of the spectrum sharing CRNs to improve the Quality of Services (QOS) of Secondary Users (SUs), and adapt its communication parameters to communicate concurrent with primary system while assuring the QOS of primary users (PUs). In this paper, proposed optimization technique studies the power allocation strategies to maximize the total throughput of underlay CRN. This optimizing technique is based on Genetic Algorithm (GA) under the consideration of the maximum transmit power and interference constraints. Furthermore, this proposed technique will be applied on two different multicarrier modulation systems which are Orthogonal Frequency Division Multiplexing (OFDM) and Generalized Frequency Division Multiplexing (GFDM). Moreover, some OFDM problem will be solved such as cyclic prefix and subcarrier overlapping in CRNs. Finally, the performance of the proposed technique for maximization of throughput will be investigated by using different number of PUs, SUs, subcarriers M, noise levels and fully utilized system under maximum power and interference constraints while ensuring the QOS of PUs.

- by SDIWC Organization
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- Genetic Algorithms, Cognitive Radio Networks, Ofdm Systems, Spectrum Sharing
- by Paolo Banelli
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- OFDM, Ofdm Systems, Ofdm Channel Estimation and Cfo

In this paper, we have evaluated various methods of time-frequency-selective fading channels estimation in OFDM system and some of them improved under time varying conditions. So, these different techniques will be studied through different algorithms and for different schemes of modulations (16 QAM, BPSK, QPSK,…). Channel estimation gathers different schemes and algorithms, some of them are dedicated for slowly time
varying (such as block type arrangement insertion, Bayesian Cramer-Rao Bound, Kalman estimator, Subspace estimator,…) whereas the others concern highly time varying channels (comb type insertion,…) . There are others methods that are just suitable for stationary channels like blind or semi blind estimators. For this aim, diverse algorithms were used for these schemes such as Least Squares estimator LS, Least Minimum Squares LMS, Minimum Mean-Square-ErrorMMSE, Linear Minimum Mean-Square-Error LMMSE, Maximum Likelihood ML,…to refine estimators shown previously .

In coding theory, concatenated codes form a class of error-correcting codes that are derived by combining an inner code with an outer code. This is a solution to the problem of finding a code that has both exponentially decreasing error probability with increasing block length and polynomial-time decoding complexity. The work presented in this paper, provides link level performance analysis of non-line of sight (NLOS) QPSK-OFDM data transmission over Rayleigh fading channels. Two scenarios have been considered in this paper. Firstly, the performance of un-coded and coded 1024-pointOFDM over the AWGN channel was obtained. Secondly, using Jake's sum of sinusoids model, the link level performance of the system was obtained over the COST 207 Rayleigh fading channels (Typical Urban and Bad Urban) and the Winner vehicular NLOS (RS-MS-NLOS) channel. To the best of the authors' knowledge, this work is first in presenting the individual/compared contributions of CC, RS and RS-CC coded version of QPSK-OFDM over the COST 207 TU/BU channels.

- by Leonardo Iheme
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- Wireless Communications, Channel Coding, Fading Channel, Ofdm Systems