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Abstract The paragraph introduces a proposed CP-free OFDM PDMA downlink transmission system. The main focus of the system is to address the capacity limitations caused by the overhead of cyclic prefix in traditional PDMA systems. The transmitter utilizes a pattern mapping unit before CP-free OFDM modulation to enhance system capacity and frequency efficiency. Decision feedback equalization (DFE) is employed in the receiver to eliminate intersymbol interference. The output signals from the DFE are then passed through a CP restoration unit to convert a linear-shifted signal into a cyclic-shifted signals. To assess the system's performance, simulations are conducted, investigating different key parameters such as overload rate, channel condition, and signal-to-noise ratio. The results indicate that, compared to CP OFDM PDMA systems, the proposed CP-free PDMA system significantly enhances system capacity under the same overload rate. Additionally, bit error rate is also evaluated during the simulations. Overall, the paragraph provides an overview of the proposed CP-free OFDM PDMA system, its components, and the simulation-based evaluation of its performance compared to traditional PDMA systems.

Underwater communication is one of the most important and difficult challenges facing researchers due to the high attenuation of the signal, communication with the surface because of the harsh medium of water, and data transmission performance degradation as a result of various effects. Underwater acoustic communication (UWA) has a low data rate, which describes the disadvantage of this type of communication. In addition, it has a low bandwidth range and high latency but has a long transmission range as an advantage. Multicarrier wireless transmission systems increase the data rate by sending the data using more than one carrier. We proposed a noncoherent orthogonal frequency division multiplexing (OFDM) method to increase the data rate in UWA communication systems. In addition, doubling the data rate in the OFDM using Subcarrier Power Modulation (OFDM-SPM) system can save half of the bandwidth. The MATLAB simulation program was used to implement the system in the underwater acoustic environment to increase its throughput. The proposed design uses Differential Phase Shift Keying (DPSK) with power control, and the data stream is transmitted through two-dimensional modulation schemes, the DPSK, and the power level of each subcarrier in the OFDM system with cyclic prefix (CP). The underwater channel was designed using a Rician fading multipath with a spreading loss formula as a function of distance and frequency. We designed an equalizer at the receiver side to recover the original signal as a function of three parameters which are: the channel effect as a rate between transmitting and receiving symbols, the Rician channel response, and the UWA spreading loss. OFDM-Subcarrier Power Modulation (OFDM-SPM) using the proposed equalizer performed better than the theoretical OFDM-SPM in the Rayleigh channel. The designed equalizer increased the performance of the OFDM-SPM system by 25% which helped to enhance the system's throughput and doubled the data rate compared with the OFDM system, doubling the data rate using OFDM-SPM had been validated in laboratory experiments in the Time domain. [ABSTRACT FROM AUTHOR]

The paragraph introduces a proposed CP-free OFDM PDMA downlink transmission system. The main focus of the system is to address the capacity limitations caused by the overhead of cyclic prefix in traditional PDMA systems. The transmitter utilizes a pattern mapping unit before CP-free OFDM modulation to enhance system capacity and frequency efficiency. Decision feedback equalization (DFE) is employed in the receiver to eliminate intersymbol interference. The output signals from the DFE are then passed through a CP restoration unit to convert a linear-shifted signal into a cyclic-shifted signals. To assess the system's performance, simulations are conducted, investigating different key parameters such as overload rate, channel condition, and signal-to-noise ratio. The results indicate that, compared to CP OFDM PDMA systems, the proposed CP-free PDMA system significantly enhances system capacity under the same overload rate. Additionally, bit error rate is also evaluated during the simulations. Overall, the paragraph provides an overview of the proposed CP-free OFDM PDMA system, its components, and the simulation-based evaluation of its performance compared to traditional PDMA systems. [ABSTRACT FROM AUTHOR]

In this manuscript we investigate the implications of adopting a double cyclic prefix in the orthogonal time-frequency space modulation. Our study first focuses on the analysis of the modulated signal and on the development of a useful model for the received signal in the presence of a doubly selective fading channel. On the one hand, our mathematical results allow us to accurately assess the impact of pulse shaping on the structure of the transmitted waveform and on its power spectral density, and to develop some simple rules for allocating multiple pilot symbols within each orthogonal time-frequency space symbol. On the other hand, they are exploited to develop a novel algorithm for pilot-aided channel estimation, whose output provides a detailed representation of the communication channel; for this reason, it can be used for sensing at the transmit side in integrated sensing and communication applications, or for channel equalization at the receive side in digital communications. Our numerical results evidence that our channel estimation & equalization algorithm outperforms the other related techniques available in the technical literature at the price of a limited increase in computational complexity.

The Non Line of Sight (NLOS) broadband wireless access provided by Worldwide Interoperability for Microwave Access (WiMAX) operating in 2-11 GHz frequency is susceptible to the effects of multipath propagation, diffraction fading, vegetation attenuation, shadowing loss etc. In order to overcome these effects effective fade mitigation techniques, have to be implemented. The Orthogonal Frequency Division Multiplexing- Multiple Input Multiple Output (OFDM-MIMO) is an efficient method that helps in combatting the fading and providing higher SNR to the WiMAX system. According to the IEEE 802.16 specification, for QPSK modulation, a threshold SNR of 6 dB is required for the link to operate. In the present work the use of OFDM-MIMO achieves a SNR above this operating threshold.

Abstract Orthogonal frequency division multiplexing (OFDM) technology has been increasingly applied to power line carrier communication (PLC). Discrete Fourier Transformation (DFT)‐based channel estimation algorithm is suitable for OFDM‐based PLC due to its low complexity. In view of the problem that the traditional DFT channel estimation does not consider the influence of noise inside cyclic prefix (CP), an improved DFT channel estimation based on signal‐to‐noise ratio (SNR) estimation is proposed. First, least‐square (LS) algorithm is performed and the frequency domain channel estimation is converted to the time domain through inverse DFT, and the average SNR of the system is estimated according to the pilot sequence. Second, the substitute SNR for each sample point inside CP is defined and used to filter impulse noise inside CP. Third, the average SNR is converted into the threshold of the useful signal energy inside CP, and the widespread background noise inside CP is filtered. The simulation results show that the proposed algorithm can obtain more accurate channel estimation than other DFT channel estimation algorithms because it can effectively filter out noise inside CP. In addition, compared with other similar algorithms, the proposed algorithm dose not result in a significant increase in complexity.

The next-generation of wireless local area network systems are being conceptualized with new applications, smart devices and use cases which mandate unprecedented levels of high data rates, spectral efficiency, reliability, low latency and high energy efficiency. The index modulated orthogonal frequency division multiplexing (OFDM-IM) stands out as the most endearing candidate for physical layer modulation technique which provides a smooth transit to green communications. However, OFDM-IM being a multicarrier technique similar to classical OFDM is also very sensitive to frequency synchronization errors and needs to be addressed on priority. In this article, a novel algorithm is proposed which estimates and corrects the carrier frequency offset at the receiver and the algorithm's performance is compared with two frequency domain variants of OFDM-IM and the classical OFDM under the same channel conditions and the simulation results show that our algorithm is not only capable of meeting the standard requirement of +/-20ppm but can handle higher offsets till +/-30ppm.

Pada penelitian ini dilakukan analisis performansi downlink LTE dan 5G dengan menggunakan MATLAB. Penelitian ini bertujuan untuk menganalisis perbandingan kinerja teknik modulasi QPSK, 16-QAM, dan 64-QAM yang digunakan pada downlink LTE dan teknik modulasi QPSK, 16-QAM, 64-QAM, dan 256-QAM pada downlink 5G yang melalui kanal AWGN untuk mengetahui nilai BER pada teknik modulasi yang digunakan. Teknik multiplexing yang digunakan adalah OFDM dan CP-OFDM untuk downlink LTE dan CP-OFDM untuk downlink 5G dengan variasi cyclic prefix yang digunakan adalah kategori ”normal”. Pada downlink LTE, kinerja modulasi QPSK lebih baik dari 16-QAM dan 64-QAM. Pada OFDM, BER QPSK diperoleh 10-19 pada Eb/No 16 dB, BER 16-QAM diperoleh 10-19 pada Eb/No 20 dB dan BER 64-QAM diperoleh 10-8 pada Eb/No 20 dB. Pada CP-OFDM, BER QPSK diperoleh 10-20 pada Eb/No 16 dB, BER 16-QAM diperoleh 10-19 pada Eb/No 20 dB dan BER 64-QAM diperoleh 10-9 pada Eb/No 20 dB. Pada downlink 5G CP-OFDM, kinerja modulasi QPSK lebih baik dari 16-QAM, 64-QAM dan 256-QAM, BER QPSK diperoleh 10-24 pada Eb/No 16 dB, BER 16-QAM diperoleh 10-23 pada Eb/No 20 dB, BER 64-QAM diperoleh 10-14 pada Eb/No 20 dB, dan BER 256-QAM diperoleh 10-7 pada Eb/No 20 dB.

Orthogonal frequency division multiplexing (OFDM) technology has been increasingly applied to power line carrier communication (PLC). Discrete Fourier Transformation (DFT)‐based channel estimation algorithm is suitable for OFDM‐based PLC due to its low complexity. In view of the problem that the traditional DFT channel estimation does not consider the influence of noise inside cyclic prefix (CP), an improved DFT channel estimation based on signal‐to‐noise ratio (SNR) estimation is proposed. First, least‐square (LS) algorithm is performed and the frequency domain channel estimation is converted to the time domain through inverse DFT, and the average SNR of the system is estimated according to the pilot sequence. Second, the substitute SNR for each sample point inside CP is defined and used to filter impulse noise inside CP. Third, the average SNR is converted into the threshold of the useful signal energy inside CP, and the widespread background noise inside CP is filtered. The simulation results show that the proposed algorithm can obtain more accurate channel estimation than other DFT channel estimation algorithms because it can effectively filter out noise inside CP. In addition, compared with other similar algorithms, the proposed algorithm dose not result in a significant increase in complexity. [ABSTRACT FROM AUTHOR]

The Non Line of Sight (NLOS) broadband wireless access provided by Worldwide Interoperability for Microwave Access (WiMAX) operating in 2-11 GHz frequency is susceptible to the effects of multipath propagation, diffraction fading, vegetation attenuation, shadowing loss etc. In order to overcome these effects effective fade mitigation techniques, have to be implemented. The Orthogonal Frequency Division Multiplexing-Multiple Input Multiple Output (OFDM-MIMO) is an efficient method that helps in combatting the fading and providing higher SNR to the WiMAX system. According to the IEEE 802.16 specification, for QPSK modulation, a threshold SNR of 6 dB is required for the link to operate. In the present work the use of OFDM-MIMO achieves a SNR above this operating threshold. [ABSTRACT FROM AUTHOR]

Orthogonal Frequency Division Multiplexing (OFDM) is a modern and suitable modulation strategy for commercial high-speed broadband wireless communication systems. This is because wireless services and demands have grown so quickly in recent years. While creating wireless communication, the channel environment is crucial. A square grid with identical vertical and horizontal spacing is used for the constellation points in quadrature amplitude modulation (QAM). More bits can be transferred per symbol to higher-order modulation forms. This research has looked at how Orthogonal Frequency Division Multiplexing OFDM systems perform using different modulation techniques on channels with additive white Gaussian noise (AWGN). Using MATLAB software to do an experiment with different modulation methods and parameters such as FFT length and cyclic prefix findings showed that 64-QAM modulation sends the same amount of data faster and with fewer symbols than QPSK 16-QAM. Here, the 64- QAM modulation technique performs better. An extensive literature survey has been carried out. The work done here involved working on many parameters to improve the performance of OFDM, i.e., by reducing BER, changing modulation techniques, and analyzing the trade-off between cyclic prefix length and Bit Error Rate. Compared to the existing work, the proposed system provides better performance. [ABSTRACT FROM AUTHOR]

The next-generation of wireless local area network systems are being conceptualized with new applications, smart devices and use cases which mandate unprecedented levels of high data rates, spectral efficiency, reliability, low latency and high energy efficiency. The index modulated orthogonal frequency division multiplexing (OFDM-IM) stands out as the most endearing candidate for physical layer modulation technique which provides a smooth transit to green communications. However, OFDM-IM being a multicarrier technique similar to classical OFDM is also very sensitive to frequency synchronization errors and needs to be addressed on priority. In this article, a novel algorithm is proposed which estimates and corrects the carrier frequency offset at the receiver and the algorithm's performance is compared with two frequency domain variants of OFDM-IM and the classical OFDM under the same channel conditions and the simulation results show that our algorithm is not only capable of meeting the standard requirement of ±20ppm but can handle higher offsets till ±30ppm. [ABSTRACT FROM AUTHOR]

When dealing with the phenomenon of unexpected high peak-to-average power ratio (PAPR) caused by multicarrer techniques, it is rarely to find a proposed solution that addresses the most important challenges together, that are; reducing the PAPR, achieving performance identical, mostly, to the theoretical curve and a reasonable level of computational complexity. This paper presents a new proposal that is able to achieve these three criteria together as the following. First, reducing the PAPR curves through easy development in the selective mapping (SLM) structure. Second, identifying the original transmitted phase block by taking advantage of the cyclic prefix structure and its mechanism, without any explicit side information, while maintaining the system performance. Lastly, these achievements were obtained at low computational complexity comparing to the traditional methods of SLM PAPR reduction schemes. This proposed method is referred to as; Injected and Extracted Short-SLM to and from the Cyclic Prefix (IES-SLM-CP). The appropriate short phase sub-block is injected to a specific locations of CP, and at the receiver side, this sub-block can be extracted from the CP to reconstruct the whole original phase block.

This paper investigates the degradation caused by interference resulting from cyclic prefix violation and symbol timing offset in narrowband power line communication systems. In this sense, it presents a unified formulation from which Hermitian symmetric orthogonal frequency division multiplexing (HS-OFDM), orthogonal chirp division multiplexing (OCDM), single-carrier cyclic prefix (SCCP), and orthogonal time–frequency division multiplexing (OTFDM) can be easily derived. The paper then provides closed-form expressions for quantifying the aforementioned interference in the presence of a frequency domain equalizer. The numerical analyses exhibit the performances of these schemes under various data communication conditions, such as the availability of channel state information, the presence or absence of interference, modeling of additive noise as a white or colored Gaussian random process, frequency domain equalizer type, and the use of bit and power allocation techniques. The closed-form expressions and performance analyses regarding achievable data rate and bit error probability provide guidance for dealing with distinct constraints in narrowband power line communication (PLC) systems using the HS-OFDM, OCDM, SCCP, or OTFDM scheme. Lastly, the unified formulation and results obtained motivate the design of multi-scheme transceivers. [ABSTRACT FROM AUTHOR]

Sixth generation (6G) wireless networks are envisioned to provide global coverage for the intelligent digital society of the near future, ranging from traditional terrestrial to non-terrestrial networks, where reliable communications in high-mobility scenarios at high carrier frequencies would play a vital role. In such scenarios, the conventional orthogonal frequency division multiplexing (OFDM) modulation, which has been widely used in both the fourth generation (4G) and the emerging fifth generation (5G) cellular systems, is vulnerable to severe Doppler spread. A new two-dimensional modulation technique called Orthogonal Time Frequency Space (OTFS) modulation designed in the delay-Doppler domain is introduced. Through this design, which exploits full diversity over time and frequency, OTFS coupled with equalization converts the fading, time-varying wireless channel experienced by modulated signals such as OFDM into a time-independent channel with a complex channel gain that is roughly constant for all symbols. In this paper, we evaluate and analyze the performance of the OTFS receiver using four data detection algorithms: Single-tap frequency domain equalizer, Linear minimum mean-square error detection (LMMSE), Message passing detection (MP), and Maximum-ratio combining detection (MRC). Further, we extend our study to the variants of OTFS, where the waveform is transmitted with a cyclic prefix (CP) or zero padding (ZP) added to each OTFS frame or block. The simulation results show that the MRC detector can be improved the detection of the OTFS receiver. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) is an efficient multicarrier scheme that uses different types of guard intervals such as cyclic prefix (CP) and known symbol padding (KSP) (zero padding (ZP), unique word (UW), etc.) in block formation. Among these guard intervals, CP varies for each block, while other guard intervals remain fixed from block to block. These guard intervals efficiently perform channel estimation, synchronization and remove inter-block interference (IBI); nevertheless, none of the existing schemes develop any relationship between the guard interval (sequence) and the data symbols on different subcarriers of the OFDM block. We present a new idea of selecting the guard interval based on the data symbols of a subset of subcarriers in the block and exploit the high auto-correlation of the selected guard sequence to improve the bit error rate (BER) performance of the system. The results based on a fair comparison show that our enhanced orthogonal frequency division multiplexing (eOFDM) scheme inherits significant improvements in BER and the capacity of a multicarrier system as compared to the existing techniques. [ABSTRACT FROM AUTHOR]

OFDM is one of the most common multi-carrier modulation schemes implemented for a range of wireless standards. The key drawback of the OFDM method is its frequency offset sensitivity, which contributes to loss of orthogonality. In OFDM system, when the orthogonality is lost ICI occurs which decreases the System Output. The reason for occurrence of Inter Carrier Interference because of the arising carrier frequency offset from the doppler shift from lesser extent. Various methods of Inter Carrier Interference cancellation techniques idea has also been discussed. In this project, the ICI triple cancelation scheme was proposed to minimize inter-carrier interference in a quick time varying environments. In this process, at transmitter section the Inter Carrier Interference self-cancellation modulation is observed and LTV model is modeled for time varying channel to perform ICI dual cancellation scheme and thus ICI self-cancellation demodulation is done at the end of the receiver.. The basic scheme is performed through channel estimation which works more efficient in fast varying systems The outputs obtained by this technique and by comparing MSE in various channel estimations demonstrates that the latest scheme is certainly better than the current scheme and increases the efficiency of the program. [ABSTRACT FROM AUTHOR]

When dealing with the phenomenon of unexpected high peak-to-average power ratio (PAPR) caused by multicarrer techniques, it is rarely to find a proposed solution that addresses the most important challenges together, that are; reducing the PAPR, achieving performance identical, mostly, to the theoretical curve and a reasonable level of computational complexity. This paper presents a new proposal that is able to achieve these three criteria together as the following. First, reducing the PAPR curves through easy development in the selective mapping (SLM) structure. Second, identifying the original transmitted phase block by taking advantage of the cyclic prefix structure and its mechanism, without any explicit side information, while maintaining the system performance. Lastly, these achievements were obtained at low computational complexity comparing to the traditional methods of SLM PAPR reduction schemes. This proposed method is referred to as; Injected and Extracted Short-SLM to and from the Cyclic Prefix (IES-SLM-CP). The appropriate short phase sub-block is injected to a specific locations of CP, and at the receiver side, this sub-block can be extracted from the CP to reconstruct the whole original phase block. [ABSTRACT FROM AUTHOR]

In this paper, we propose novel reduced-complexity fast Fourier transform (FFT)-spread multicarrier faster-than-Nyquist (MFTN) signaling with power allocation for a frequency-selective fading channel. The information rate of the proposed MFTN signaling is derived by relying on the circulant approximation of the FTN-specific intersymbol interference matrix and noise covariance matrix. This allows us to constitute efficient calculations of precoding and weighting matrices. The power allocation coefficients are optimized such that the approximated information rate is maximized. Our simulation results demonstrate that the proposed scheme with power allocation achieves the bit error ratio (BER) performance close to the conventional eigenvalue-decomposition (EVD)-precoded FTN signaling counterpart that is optimal in terms of an achievable information rate while significantly reducing the computational complexity as low as the order of $\mathcal {O}(N\log N)$ . While the proposed scheme exhibits a high peak-to-average-power ratio similar to the conventional EVD-precoded counterpart due to the effects of FFT-based precoding, it achieves better BER performance than the conventional open-loop single-carrier FTN signaling scheme and the Nyquist signaling scheme, employing the same root-raised cosine shaping filter. It is also confirmed that the proposed MFTN signaling scheme does not suffer from any significant bandwidth broadening.

This paper proposes a novel method to improve the performance and reduce the implementation design complexity of the angular domain cyclostationary feature detection (CFD). This method implements Orthogonal Frequency Division Multiplexing (OFDM) signal detection for cognitive radio applications. The originality of this work is based on using a selective sampling process for the OFDM signal detection by using only samples related to the cyclic prefix (CP). Using only the first N C P (CP length) angles of the angular domain cyclic autocorrelation function and eliminating the remaining angles has significantly improved the detector sensitivity. Results from Matlab simulations revealed that the proposed method reaches a detection probability of 100% at an SNR (signal-to-noise ratio) equal to − 16 dB in the case of an additive white Gaussian noise (AWGN) channel. Moreover, the proposed method outperforms the other CFD methods with a performance range up to 5 dB. The proposed algorithm is coded using the VHDL language and implemented with the minimum of counters and comparators on Field-programmable gate array (FPGA) platform without using multipliers and DSP blocks. The proposed design requires a lesser power, logic and memory bits by 5.95, 60.96 and 87.5%, respectively, compared to the conventional angular domain CFD design. The proposed hardware architecture can be more efficient for spectrum sensing in many communication systems, such as LTE-Advanced and the L-band Digital Aeronautical Communication System (LDACS). • Angular Domain cyclostationary feature detection of OFDM signals. • A new selective sampling process is adopted to improve the detector's sensitivity. • An optimised design of the proposed method is delivered and hardware prototyped on an FPGA platform. [ABSTRACT FROM AUTHOR]

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Radar system environment is complex, and excessively high range sidelobes will cause weak targets to be lost and false targets. To solve this problem, a novel orthogonal frequency-division multiplexing(OFDM) radar low sidelobe waveform design method based on genetic algorithm(GA) is proposed. First, the OFDM waveform based on cyclic prefix(CP) is constructed. All sub carriers are modulated with m-sequence codes. Then, the main lobe and sidelobe ratio after pulse compression is taken as the objective function, and the phase parameter is taken as the optimization object. The objective function is transformed into an unconstrained optimization problem. Last, by using genetic algorithm to solve the optimization problem, the radar range sidelobe suppression is achieved. Theoretical analysis and simulation results show that this method can effectively suppress the range sidelobes.

In classical orthogonal frequency division multiplexing (OFDM) systems, inserting the cyclic prefix (CP) is necessary before each symbol to overcome the multi-path effect, which, however, occupies numerous time-frequency radio resources, resulting in hampered spectrum efficiency. To address this issue, in this paper, symbol repetition aware OFDM (SR-OFDM) is developed to lower the overhead of CP. In the proposed SR-OFDM, multiple symbols share the same CP with which we examine that the multi-path channels can also be overcome by a simple single-tap equalization without causing any interference. Moreover, after the discrete Fourier transform at the receiver, different symbols are proved to be separated in the time domain, which is beneficial for lowering the demodulation complexity. Furthermore, it is revealed that the above conclusions still hold even under timing synchronization errors, which makes the proposed SR-OFDM favorable in real systems. Extensive simulations validate the efficacy of our proposed SR-OFDM system under the multi-path channels with or without timing synchronization errors. [ABSTRACT FROM AUTHOR]

This paper investigates the degradation caused by interference resulting from cyclic prefix violation and symbol timing offset in narrowband power line communication systems. In this sense, it presents a unified formulation from which Hermitian symmetric orthogonal frequency division multiplexing (HS-OFDM), orthogonal chirp division multiplexing (OCDM), single-carrier cyclic prefix (SCCP), and orthogonal time–frequency division multiplexing (OTFDM) can be easily derived. The paper then provides closed-form expressions for quantifying the aforementioned interference in the presence of a frequency domain equalizer. The numerical analyses exhibit the performances of these schemes under various data communication conditions, such as the availability of channel state information, the presence or absence of interference, modeling of additive noise as a white or colored Gaussian random process, frequency domain equalizer type, and the use of bit and power allocation techniques. The closed-form expressions and performance analyses regarding achievable data rate and bit error probability provide guidance for dealing with distinct constraints in narrowband power line communication (PLC) systems using the HS-OFDM, OCDM, SCCP, or OTFDM scheme. Lastly, the unified formulation and results obtained motivate the design of multi-scheme transceivers.

Orthogonal frequency division multiplexing (OFDM) scheme has been widely employed in the wireless communication systems. However, the scheme suffers a limitation of high peak to average power ratio (PAPR). Carrier Interferometry (CI) codes proved to be an efficient PAPR reduction method but these CI codes when employed with OFDM (CI-OFDM), acts as a single-carrier modulation scheme. To retain the principle of multi-carrier modulation and gain the advantage of low PAPR using CI codes, a new efficient oversampled CI-OFDM scheme is proposed in this paper. Furthermore, the architecture for the oversampled CI-OFDM transceiver with two modulation schemes is proposed and prototyped on the commercially available virtex5 FPGA device in the laboratory experimental setup. The proposed scheme exhibits a PAPR reduction of minimum 4 dB, and a bit error rate (BER) of 10 − 4 is achieved for a signal to noise ratio (SNR) of 8.4 dB. To analyse the behaviour of the proposed scheme, various hardware performance parameters in terms of occupied bandwidth, channel power of main lobes and side lobes are measured, and the total bandwidth is found to be 240 KHz. The hardware resource utilization of the proposed architecture is also reported. [ABSTRACT FROM AUTHOR]

In this paper, we propose a sensing scheme based on energy detection, matched filter and cyclic prefix. Both Equal Gain Combining (EGC) and optimal combination of the aforementioned detectors are investigated in cooperative and non-cooperative spectrum sensing scenarios. In packet transmission systems such as OFDM (Orthogonal Frequency Division Multiple access) systems, the proposed scheme takes advantage of utilizing more samples than individual detectors, i.e., cyclic prefix, training or pilot samples, and data payload samples. The proposed combine-sensing scheme offers higher detection probability and lower false alarm probability, as compared with the performance of individual detectors over the same frame duration. Simulation results are congruent with the theoretical curves and confirm the validity of our derivations.

Orthogonal frequency division multiplexing (OFDM) is an efficient multicarrier scheme that uses different types of guard intervals such as cyclic prefix (CP) and known symbol padding (KSP) (zero padding (ZP), unique word (UW), etc.) in block formation. Among these guard intervals, CP varies for each block, while other guard intervals remain fixed from block to block. These guard intervals efficiently perform channel estimation, synchronization and remove inter-block interference (IBI); nevertheless, none of the existing schemes develop any relationship between the guard interval (sequence) and the data symbols on different subcarriers of the OFDM block. We present a new idea of selecting the guard interval based on the data symbols of a subset of subcarriers in the block and exploit the high auto-correlation of the selected guard sequence to improve the bit error rate (BER) performance of the system. The results based on a fair comparison show that our enhanced orthogonal frequency division multiplexing (eOFDM) scheme inherits significant improvements in BER and the capacity of a multicarrier system as compared to the existing techniques.

The upcoming fifth-generation (5G) systems needs to provide several services with short packets. Due to the property of short packet communication (SPC), reducing the length of cyclic prefix (CP) and length of pilot is an important study. In Darsea et al. [D. Darsea, G. Geli, and F. Verd, "Joint blind channel shortening and compensation of transmitter I/Q imbalances and CFOs for uplink SC-IFDMA systems," Phys. Commun., Vol. 11, pp. 25–35, Jun. 2014], a blind receiver with joint CFO (carrier frequency offset) compensation and channel shortening was proposed for the system with single transmitted antenna and single received antenna. In this paper, we extend the scheme in Darsea et al. (2014) to the multiuser multi-input multi-output (MU-MIMO) environment. We employ the blind system in the receiver which does not need pilot and reduce the length of CP as short as possible. The methods of channel shortening and CFO compensation had been proposed individually. If the duration of CP is not sufficient, we can use equalizer to shorten the channel. The proposed receiver is with four-stage structure. At first, the blind shortening of channel impulse responses (CIRs) is performed. Secondly, the joint estimation and compensation of the CFOs is derived. The third step of the receiver implements signal-to-noise ratio (SNR) maximization. Finally, the fourth stage performs blind detection with constant modulus algorithm (FLOS-CMA). [ABSTRACT FROM AUTHOR]

The orthogonal frequency division multiplexing (OFDM) technology is employed in the fourth-generation mobile communication. It has two disadvantages. The first is high peak-to-average power ratio, and the second is high out-of-band radiated power. With the advent of the fifth generation of mobile communications, it needs large data transmission rate, short time delay and flexible waveforms. In the future communication applications, the diversified scenarios such as Internet of Things, inter-machine communication and telemedicine make the fourth-generation mobile communication no longer applicable. The generalized frequency division multiplexing has a pulse-shaping filter, which has less out-of-band radiated power and peak-to-average power ratio and fewer cyclic prefixes than OFDM. In order to meet high- data-transmission rate, it is an inevitable trend to install massive multi-input multi-output (massive MIMO) antennas. As the number of antennas increases, so does its complexity. This paper employs time reversal technology to reduce the computational complexity. Although the number of base station antennas has increased to eliminate interference, there is still residual interference. In order to eliminate the interference one step further, we deploy a zero forcing equalization (ZF equalization) after the time reversal combination. [ABSTRACT FROM AUTHOR]

Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) is the pertinent waveform for current and next generation wireless systems, whose spectral efficiency can be potentially doubled by in-band full-duplex (IBFD) communication. However, in OFDM based IBFD systems, digital self-interference cancellation (DSIC) employed at baseband does not provide sufficient cancellation in the cyclic prefix (CP) region. When the propagation delay between two communicating radios is non-zero, the CP noise affects the data region of the desired signal. In this work, we propose CP noise reduction (CPNR) technique for OFDM based IBFD radios. We have evaluated CPNR with time and frequency domain DSIC schemes via both simulations and MATLAB and FPGA implementations on our Software Defined Radio based IBFD radio. In the laboratory tests, the total suppression of the IBFD radio is improved by 6 dB by employing CPNR in frequency-domain DSIC and EVM for bidirectional communication is improved by up to 5%, allowing realistic propagation delays. In addition to improving the total suppression and EVM performance, CPNR is also shown to enhance the multi-path resiliency of DSIC techniques. [ABSTRACT FROM AUTHOR]

The cyclic prefix (CP) is a prefix technique widely used in orthogonal frequency division multiplexing (OFDM) systems in order to eliminate the intersymbol interference (ISI) caused by the dispersion of wireless channels. However, CP reduces the number of symbols that can be transmitted in one OFDM symbol. Therefore, CP is one of the bottlenecks of OFDM systems limiting their spectral efficiency (SE). This limitation on the SE of the classical CP-based OFDM system is the main motivation for this work to introduce a novel method. In this paper, the design of a new CP structure, which is based on the generalized prefix (GP), is presented. In the proposed structure, extra bits are assigned to the GP structure to increase the SE of OFDM systems. Simulation results show that the proposed method has the same performance as conventional CP-based OFDM but higher spectral efficiency. Specifically, it is shown that the proposed method has 5.5% more spectral efficiency than the classical OFDM system. A simple algorithm is also proposed to detect the additional information bits conveyed by GP. As a result, the proposed method provides both high spectral efficiency and low computational complexity [ABSTRACT FROM AUTHOR]

This paper deals with Matlab simulation of Long Term Evolution system (Lte) to show data rate of the uplink layer from user equipment toward the tower with respect to the size of Desecrate Fourier Transform process (DFT) which will be increased from 2 to the size of Inverse Desecrate Fourier Transform process (IDFT). Also it shows the way of using Cyclic Prefix technique (CP) in Lte system and its types which effect on the data rate for uplink layer. Finally the results will show the value of Lte system data rate for different types of modulation and Cyclic Prefix which will be for many types of system bandwidth individually, and it will show the minimum and maximum values of (DFT) process size with the midpoint which is the best one.

In classical orthogonal frequency division multiplexing (OFDM) systems, inserting the cyclic prefix (CP) is necessary before each symbol to overcome the multi-path effect, which, however, occupies numerous time-frequency radio resources, resulting in hampered spectrum efficiency. To address this issue, in this paper, symbol repetition aware OFDM (SR-OFDM) is developed to lower the overhead of CP. In the proposed SR-OFDM, multiple symbols share the same CP with which we examine that the multi-path channels can also be overcome by a simple single-tap equalization without causing any interference. Moreover, after the discrete Fourier transform at the receiver, different symbols are proved to be separated in the time domain, which is beneficial for lowering the demodulation complexity. Furthermore, it is revealed that the above conclusions still hold even under timing synchronization errors, which makes the proposed SR-OFDM favorable in real systems. Extensive simulations validate the efficacy of our proposed SR-OFDM system under the multi-path channels with or without timing synchronization errors.