Presence Of Carrier Frequency Offset Research Articles

A use-case efficient DFrFT-based index modulated-OFDM system in the presence of CFO

Index modulated orthogonal frequency division multiplexing (OFDM-IM) only utilizes partial resources to transmit signals according to use case requirement, it leads to higher energy efficiency and spectral efficiency than the classical OFDM. However, in the presence of inter-carrier interference (ICI) due to carrier frequency offset (CFO), the performance of index modulated OFDM system severely deteriorates. To mitigate this issue, a novel discrete fractional Fourier transform (DFrFT) based OFDM-IM scheme over Rayleigh frequency selective fading channel is proposed in this paper. The optimum DFrFT angle (αopt) for this new scheme at various CFO values has been calculated theoretically. Incorporating these estimated αopt, the proposed system achieves a gain of 8 dB over conventional FFT-based OFDM-IM at bit error rate (BER) = 10−3 in a high normalized CFO (ϵ) environment (ϵ=0.2). The system model is also verified for different user applications, i.e., high data rate and low data rate applications. Simulation and analytical results show that the proposed model has a robust and superior performance compared to the conventional FFT-based OFDM-IM, DFrFT-based OFDM, and classical OFDM. Moreover, the proposed DFrFT-OFDM-IM model achieves all these superiorities with the same complexity as the conventional FFT-based OFDM-IM system.

Impact of carrier frequency offset and in-phase and quadrature imbalance on the performance of wireless precoded orthogonal frequency division multiplexing

<p>Precoding in orthogonal frequency division multiplexing (OFDM) system proved to reduce the peak-to-average power ratio (PAPR), so that it improves BER. However, from the existing literature, the effect of carrier frequency offset (CFO), in-phase and quadrature (IQ) imbalance on precoded wireless OFDM systems has not been carried out. Therefore, this study evaluated the precoded OFDM (P-OFDM) system performance by considering the impact of CFO and IQ imbalance. P-OFDM performance evaluation is expressed in signal-to-interference noise ratio (SINR) and bit error rates (BER). The communication channels used are the additive white Gaussian noise (AWGN) channel and the frequency-selective Rayleigh fading (FSRF) channel, while the channel equalization process is considered perfect. The results of the analysis and simulation show that P-OFDM is greater affected by the presence of CFO and IQ imbalance than conventional OFDM system. In AWGN channel, P-OFDM experiences different SINR for each subcarrier. This is different from conventional OFDM system, where all SINRs are the same for all subcarriers. In the FSRF channel, both the POFDM system and the OFDM system experience different SINR for each subcarrier, where the SINRs fluctuation in the P-OFDM system is much larger than in the OFDM system.</p>

Joint CFO and channel estimation using pilot aided interpolation for high performance MIMO-OFDM

ABSTRACT Multiple Input Multiple Output (MIMO) system with orthogonal frequency division multiplexing (OFDM) is a promising physical layer candidate for the current and future wireless standards. MIMO increases system throughput while OFDM maximizes spectrum efficiency. To reduce the impacts of frequency selective fading and increase the capacity, MIMO requires precise channel state information (CSI). The presence of carrier frequency offset (CFO) introduces intercarrier interference (ICI) among the subcarriers which degrades the system performance. MIMO channel estimation is done under the assumption of perfect frequency synchronisation between the transmitter and receiver, or zero CFO. However, such an assumption is incorrect for time-varying and frequency-selective wireless channels, and the presence of CFO has an impact on channel estimation accuracy. In the existing methods, CFO and channel estimations are carried out independently using separate training sequences which reduces the spectral efficiency. As a result, the pilot aided interpolation approach is proposed in this paper for the joint estimate and compensation of CFO and channel effects using the same set of pilot tones. Theresults show that the proposed method offers precise CFO and channel estimation which improves the bit error rate performance and carrier to interference power ratio (CIR) of MIMO-OFDM system.

Performance analysis of the low‐complexity adaptive channel estimation algorithms over non‐stationary multipath Rayleigh fading channels under carrier frequency offsets

The use of selective partial updating method for reducing computational complexity of adaptive algorithms has been proposed recently. However, its performance analysis has not been studied as extensively and exactly as LMS or RLS algorithms for time-varying channel estimation. This paper provides performance analysis of the low-complexity family of affine projection algorithms based on selective partial update method on the estimation of multipath Rayleigh fading channels in the presence of carrier frequency offsets (CFO) and random channel variations. The analysis is based on the calculation of the error correlation matrix of the estimation, the mean-square weight error (MSWE) and the mean-square estimation error (MSE) parameters. The analysis does not use strong assumptions like small or large step-size, and explicit closed-form expressions for the MSE of estimation are obtained only from common hypotheses in wireless communication context. In this paper, the optimum step-size parameters minimizing the MSE of estimation are analytically derived without any simplifying assumptions. For the sake of comparison with other analytical approaches, the performance of the introduced algorithms is also investigated using the energy conservation relation. Likewise, for exact performance analysis, all the moment terms that appear in closed form expressions for the MSE of estimation are evaluated. Simulations are conduced to corroborate the presented studies and show that the theoretical results agree well with the simulation results over non-stationary multipath Rayleigh fading channels.

Single carrier variable rate scheme and modified carrier allocation over a wireless channel with carrier frequency offset

SummaryCyclic Prefix Orthogonal Frequency Division Multiplexing (CP‐OFDM) is the backbone for the 5G, Internet of Things (IoT), and future generation wireless networks. However, OFDM is less localized in the frequency domain, and that's why more sensitive to carrier frequency offset (CFO). In this paper, different multicarrier variable rate schemes are evaluated in the presence of CFO. Additionally, variable rate schemes based on group orthogonal‐orthogonal frequency division multiple access (GO‐OFDMA) are discussed, and the effect of changing carrier allocation is examined. Different allocation schemes along with different variable rate schemes are verified in the presence of the CFO. Further for Up‐link variable rate application, single‐carrier scenario for the variable rate is proposed in this paper, and bit error rate (BER) performance is evaluated and compared with the variable rate GO‐OFDMA.

Analysis of Variable Bit Rate Spread FBMC-Based Integrated Satellite–Terrestrial Broadcast System

For the joint impact of carrier frequency offset (CFO) and phase noise (PHN), the exact closed-form signal-to-interference-noise ratio (SINR) expressions are derived for novel Walsh Hadamard (WH)-spread filterbank multicarrier (SFBMC) transmission scheme in integrated satellite–terrestrial broadcast system (ISTBS). For this evaluation, variable bit rates (VBR)s for WH-SFBMC are considered for transmission in 3-state Fontan land mobile satellite suburban environment. Further, symbol error rate (SER) and spectral efficiency are analyzed based on the obtained SINR expressions. Such analyses are conducted to support VBR quality of service (QoS) in orthogonal frequency division multiplexing (OFDM)-based digital video broadcasting standards utilizing ISTBS. Furthermore, pilot-based channel estimation error variance is evaluated for VBR WH-SFBMC. Later, block-by-block system computational complexity of VBR WH-SFBMC, perfect reconstruction (PR)-filterbank multicarrier (FBMC), and OFDM schemes are evaluated. It is shown that, VBR WH-SFBMC is rate-dependent and relatively more complex system than single rate PR-FBMC and OFDM. However, the SER performance of WH-SFBMC is illustrated to outperform PR-FBMC and OFDM significantly even for higher bit rates in presence of CFO and PHN. Moreover, simulation and analytic results are in close approximation with each other. Thus, a trade-off exists between achieved error performance and system complexity.

A Semi-Blind Multiuser SIMO GFDM System in the Presence of CFOs and IQ Imbalances

In this paper, we investigate an open topic of a multiuser single-input-multiple-output (SIMO) generalized frequency division multiplexing (GFDM) system in the presence of carrier frequency offsets (CFOs) and in-phase/quadrature-phase (IQ) imbalances. A low-complexity semi-blind joint estimation scheme of multiple channels, CFOs and IQ imbalances is proposed. By utilizing the subspace approach, CFOs and channels corresponding to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$U$ </tex-math></inline-formula> users are first separated into <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$U$ </tex-math></inline-formula> groups. For each individual user, CFO is extracted by minimizing the smallest eigenvalue whose corresponding eigenvector is utilized to estimate channel blindly. The IQ imbalance parameters are estimated jointly with channel ambiguities by very few subcarriers. The proposed scheme is feasible for a wider range of receive antennas number and has no constraints on the assignment scheme of subsymbols and subcarriers, modulation type, cyclic prefix length and the number of subsymbols per GFDM symbol. Simulation results show that the proposed scheme significantly outperforms the existing methods in terms of bit error rate, outage probability, mean-square-errors of CFO estimation, channel and IQ imbalance estimation, while at much higher spectral efficiency and lower computational complexity. The Cramér-Rao lower bound is derived to verify the effectiveness of the proposed scheme, which is shown to be close to simulation results.

Combining IST-Based CFO Compensation and Neural Network-Based Demodulation for Eigenvalue-Modulated Signal

Eigenvalue-based communication technologies using inverse scattering transform (IST) have gained attention as a new transmission strategy in optical fiber communications. In recent years, several studies on artificial neural network (ANN)-based equalization and demodulation schemes for eigenvalue-modulated signal have been conducted to enhance the receiver sensitivity. However, in the case of a presence of a carrier frequency offset (CFO) at receiver, the effects of the CFO on ANN receiver of eigenvalue-modulated signal is yet to be reported. In this study, we numerically and experimentally investigated the generalization performances of eigenvalue domain ANN-based demodulator on CFO. Furthermore, we propose to combine an ANN-based demodulator with a CFO compensation method based on IST and a relation between frequency and eigenvalue shifts. The proposed method, based on an appropriate soliton pulse, achieves a high CFO estimation accuracy of submegahertz order even if the CFO reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 2.5 GHz under the noiseless condition. In the presence of noise and a large CFO of 2.5 GHz, the method attains a CFO estimation accuracy below 60 MHz for OSNR = 10 dB with a low pilot pulse rate, such as 0.064%. We show the simulation results obtained after applying the proposed CFO compensation to the ANN demodulator, which is valid for 2.5 GHz CFO and long-haul transmission over 5000 km. Experiments performed in this study demonstrate successful demodulation of an eigenvalue-modulated signal with OSNR penalty <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 1 dB in the presence of CFO within 1 GHz at 2.5 Gb/s.

New Satellite Random Access Preamble Design Based on Pruned DFT-Spread FBMC

Next generation satellite payload technology is expected to provide digital processing capabilities. This will pave the way to regard satellites as flying base stations. However, the initial access procedure must be improved. In this work we focus on non-geostationary earth orbit (NGEO) satellite networks. In this scenario, the random access preamble signal and the detection must be robust to large carrier frequency offsets (CFOs). Towards this end, we investigate the adoption of the pruned discrete Fourier transform spread filter bank multicarrier waveform. The proposed design is suitable for the access scheme of forthcoming 5G-based NGEO satellite communications. The reason is twofold. First, it improves the spectral confinement with respect to the standard single-carrier frequency-division multiplexing (SC-FDM) waveform. Second, it achieves a high level of commonality with 5G new radio, by keeping unchanged the subcarrier spacing, the slot duration and the preamble sequence. Remarkably, the new design allows the straightforward application of non-coherent post detection integration (NCPDI) techniques, which divide the correlation in blocks. Numerical results show that the proposed solution reduces out-of-band emissions and the missed detection probability in presence of CFO, with respect to the conventional approach based on SC-FDM and preamble detection with full-length correlation.

Fractional Fourier domain equalization for DCT based OFDM system with CFO

Discrete fractional Fourier transform (DFRFT) based orthogonal frequency division multiplexing (OFDM) system significantly outperforms the conventional discrete Fourier transform (DFT) based OFDM system in the presence of carrier frequency offset (CFO). DFRFT based OFDM system fundamentally involves the use of fractional transform at both transmitter and receiver. For DFRFT-OFDM, the angle of rotation (or chirp rate) should be made available to the transmitter through the feedback channel for multicarrier modulation using inverse DFRFT or IDFRFT. On the other hand, the discrete cosine transform (DCT) based OFDM system with frequency domain equalization (FDE) separately performs the task of multicarrier modulation/demodulation and channel equalization using different orthogonal transforms. In this paper, we have proposed fractional Fourier domain equalization (FFDE) for such DCT based OFDM system in the presence of CFO using DFRFT/IDFRFT replacing DFT/IDFT at the receiver. Unlike the DFRFT-OFDM, the proposed OFDM configuration is easily feasible without any chirp rate feedback to the transmitter side by replacing FDE with FFDE at the receiver. The proposed OFDM configuration significantly outperforms the conventional DCT-OFDM with FDE without any significant increase in the computational complexity.

Carrier Frequency Offset Effects on OFDM System over Rayleigh Fading Channel

Orthogonal Frequency Division Multiplexing (OFDM) system showed the use of Discrete Fourier Transform (DFT) and Inverse Discrete Fourier Transform (IDFT) to perform the baseband modulation and demodulation. So that, it can increase and improve the efficiency of the modulation and demodulation. Currently, the OFDM is being utilized in the field of broadband wireless communication, which transmit signals orthogonally, that increases speed of information transmission. It also has high proficiency with high bandwidth and provide large data rates and robust against the multipath delay spread. On the other hand, there are some issues faced OFDM system which are high Peak Average Power Ratio (PAPR), and sensitive to Phase Noise (PN) and Carrier Frequency Offset (CFO). This paper presents Orthogonal Frequency Division Multiplexing (OFDM) performance evaluation in the presence of CFO with two different environment scenarios were used: an AWGN channel and a Rayleigh fading channel. The simulation was performed to evaluate the effects of CFO based on Bit Error Rate (BER) vs. Energy Bit per Noise Ratio (Eb/No). The results showed that for BER degradation caused by CFO effects have presented in our simulation for both AWGN and Rayleigh fading channel.

Multi-Gigabit/s OFDM real-time based transceiver engine for emerging 5G MIMO systems

This paper presents a highly scalable multi-Gigabit/s Real-Time (RT) Wideband (WB) Orthogonal Frequency Division Multiplexing (OFDM) processing chain for 5G applications. It is aimed to significantly reduce the Hardware (HW) footprint of Multiple Input Multiple Output (MIMO) systems. In this context, implementation complexity results for MIMO configurations of 2 × 2, 4 × 4 and 8 × 8, enabled at sampling rates of 245.76, 122.88, 61.44 and 30.72 MHz, respectively, are compared with the ones from conventional MIMO architectures. For example, for a 8 × 8 MIMO–OFDM configuration implementation, savings of up to 87% are achieved when compared with conventional design methods, in terms of DSP48E1 slices. Moreover, in a Xilinx Virtex 7 XC7VX485T, it is shown that a second processing branch might be implemented, leading to a 5 Gbps (using 1024 Quadrature Amplitude Modulation (QAM)) Single-Input Single-Output (SISO) link or a 16 × 16 MIMO configuration. Finally, in order to validate the proposed architecture, the impact of its inclusion on a complete Field Programmable Gate Array (FPGA) 8 × 8 OFDM system, at LTE’s highest sampling rate of 30.72 MHz, is evaluated. Subsequently, it is demonstrated that this does not affect the performance of OFDM, even in the presence of Carrier Frequency Offset (CFO).

Analysis of Variable Bit Rate SOFDM Based Integrated Satellite-Terrestrial Broadcast System in Presence of CFO and Phase Noise

In this paper, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the joint effect of carrier frequency offset (CFO) and phase noise (PHN) is derived for integrated satellite-terrestrial broadcast system (ISTBS), employing Walsh–Hadamard (WH) based spread orthogonal division multiplexing (SOFDM) transmission scheme at the satellite terminal. To examine that, three-state Fontan land mobile satellite (LMS) suburban environment is considered for S-band transmission. Additionally, bit error rate (BER) and spectral efficiency is analyzed based on the obtained SINR expression. Variable bit rates (VBRs) are assumed for SOFDM. This analysis is performed to support VBR quality of service (QoS) at the physical layer of digital video broadcast satellite handheld (DVB-SH)-A based ISTBS. The results disclose a continuous performance deterioration under both assessment measures with increasing doppler frequency shift or PHN. Moreover, simulation and analytical results illustrate a close match for various values of normalized CFO and PHN. Further, pilot-based channel estimation technique is carried out and the estimated error variance is evaluated for VBR WH-SOFDM.

A Robust Transceiver for Narrow-Band Communications in Presence of Carrier Frequency Offset

We address narrow-band communications in presence of large and time-varying carrier frequency offset (CFO) at the receiver. This is a general assumption which includes the condition due to the Doppler effect where the transmitter and/or receiver are moving with a relative time-varying speed. A robust transceiver system is proposed to dynamically estimate and compensate the CFO. The proposed system is particulary attractive for low data-rate communications (e.g., voice service) where the CFO is significantly larger than the data bandwidth. A two-step carrier recovery scheme is developed with large acquisition range and fast frequency tracking. The proposed method provides accurate CFO estimation with affordable complexity. We also devise a robust frame synchronization scheme to provide accurate timing in presence of CFO. Furthermore, non-coherent detection with soft-decision decoding is employed to provide a low-complexity receiver with acceptable sensitivity. The proposed transceiver design is implemented on FPGA and real-time experiments are conducted on a Xilinx ZC706 evaluation base board along with AD-FMCOMMS3 daughterboard. After validating the experiments compared to the simulation results, the design was optimized for implementation on XC7Z020 and further integrated with the analog front-end on a board with smaller footprint.

Blind digital modulation classification for STBC‐OFDM system in presence of CFO and channels estimation errors

Here, the authors propose a robust blind digital modulation classification (BDMC) algorithm for space time block coding (STBC)-based MIMO-OFDM system in the presence of carrier frequency offset (CFO) and channel estimation errors. Previous papers published on the topic of modulation identification were limited to single-carrier systems operating over frequency-flat channels. The problem of joint channel and CFO estimation in conjunction with blind digital modulation classification for STBC-OFDM in frequency selective channel and in the presence of the impulsive noise has not been addressed before to the best of their knowledge. To cope with performance degradation of BDMC due to CFO and channels errors, they propose joint semi-blind CFO and channels estimation methods. Higher order statistics (HOS), used for feature extraction, are combined with pattern recognition methods to solve the modulation identification problem. The main contribution of their work is the development of estimators, the study of their impacts on the blind classification capability, and the use of simulations to demonstrate the superior performance of the proposed algorithms.

Trigonometric transforms and precoding strategies for OFDM‐based uplink hybrid multi‐carrier nonorthogonal multiple access

AbstractAn uplink hybrid nonorthogonal multiple access (h‐NOMA) scheme utilizing power domain multiplexing is adopted in this paper for orthogonal frequency–division multiplexing (OFDM)–based systems. The OFDM‐based NOMA systems can achieve high spectral efficiency with resilience to wireless multipath fading. The h‐NOMA maintains a low interference level per resource block or low complexity of multiuser detection (MUD) implementation at the receiver and also achieves consistent fairness performance by restricting the maximum number of users per resource block. An improved user clustering algorithm for OFDM‐based h‐NOMA system under the assumption of user's distinct data rate requirement is presented here. The proposed algorithm takes into consideration both the channel gain of all activated users and the different data rate requirements of weak channel gain users. High peak‐to‐average power ratio (PAPR) and performance degradation due to strict frequency synchronization requirements are the main drawbacks of such an OFDM‐based uplink h‐NOMA system. High PAPR of multicarrier NOMA is addressed here with precoding techniques. An enhanced minimum mean square error (MMSE) receiver performing joint equalization and carrier frequency offset (CFO) compensation using low‐complexity banded‐matrix implementation is proposed to cancel interference in the frequency domain. The MUD is implemented with low‐complexity successive interference cancellation (SIC) using bandedmatrix approximation of the interference matrix in the presence of CFO. Moreover, the possibility of utilizing efficient trigonometric transforms to implement OFDM‐based NOMA is studied with CFO and estimation errors. For OFDM‐based h‐NOMA system, an efficient combination of different trigonometric transform configurations to constitute the multicarrier basis for OFDM with a suitable precoding strategy for PAPR reduction is studied.

Performance Analysis of Precoded Wireless OFDM With Carrier Frequency Offset

Precoding is proved to be highly efficient to improve the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. Nevertheless, most of the work reported in the literature ignores the radio frequency impairments such as carrier frequency offset (CFO), which is known to be of significant impact on OFDM. Consequently, this paper considers the performance evaluation of precoded OFDM (P-OFDM) in the presence of CFO. The performance of the considered P-OFDM is evaluated in terms of the signal-to-interference plus-noise-ratio (SINR) and BER. Various channel models are considered and closed-form analytical expressions are derived for the exact SINR. The obtained analytical results, corroborated by simulation, show that P-OFDM is substantially more sensitive to CFO compared with conventional OFDM. Generally speaking, if the normalized CFO is about 18%, then OFDM will outperform P-OFDM for most practical channel models. It is also interesting to note that the subcarriers in P-OFDM may experience different SINRs, which is not the case for conventional OFDM. The paper also considers the SINR of OFDM after the equalization process. The obtained results show that ignoring the impact of the equalization process results in inflated SINR degradation.

Analysis of Variable Bit Rate SOFDM Transmission Scheme Over Multi-Relay Hybrid Satellite-Terrestrial System in the Presence of CFO and Phase Noise

In this paper, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the joint impact of carrier frequency offset (CFO) and phase noise (PHN), is derived for each channel link in a multi-relay hybrid satellite-terrestrial broadcast system, employing the Walsh Hadamard (WH) based spread-orthogonal frequency multiplexing (S-OFDM) and OFDM transmission scheme at satellite terminal and terrestrial repeaters (relays) respectively. Additionally, bit error rate and spectral efficiency are analyzed for such hybrid system with $M$ -relay, based on the obtained SINR expressions. To examine that, an adaptive decode and forward (ADF) strategy is employed at relay terminals. Also, three-state Fontan Land Mobile Satellite and six-path typical urban terrestrial channel models are considered. This analysis is performed to support variable bit rate (VBR) quality of service at the physical layer of Digital Video Broadcast Satellite Handheld (DVB-SH)-A architecture, the provision of which is absent in the DVB-SH standard. VBRs are assumed for S-OFDM. The results illustrate that both single-relay and three-relay ADF-based VBR WH-SOFDM yield an identical performance in the presence of the combined effect of CFO and PHN, under both performance measures. However, the improvement in performance for the three-relay strategy is observed in the presence of CFO only. Further, a pilot-based channel estimation technique is performed at the receiver, and the estimated error variance is evaluated for every channel link. Later, the block-by-block system computational complexity of single-relay and $M$ -relay ADF-based VBR WH-SOFDM is evaluated. It is shown that the complexity of the $M$ -relay ADF strategy is rate dependent and almost $M-1$ times the single-relay strategy. Hence, an increase in the number of relays would not yield any significant performance gain, but would enhance the system computational complexity considerably. Therefore, for high data rate transmission, the single-relay ADF-based WH-SOFDM scheme could be a suitable candidate for hybrid satellite-terrestrial communication systems in future.

Enhanced OFDM-NOMA for next generation wireless communication: A study of PAPR reduction and sensitivity to CFO and estimation errors

Orthogonal Frequency Division Multiplexing (OFDM) based on Non-Orthogonal Multiple Access (NOMA) has been previously studied to fulfil the demands of high spectral efficiency, massive connectivity and resilience to frequency selectivity for the upcoming fifth generation (5G) wireless communication and beyond. NOMA enables spectrum overlapping and allows distinct users to simultaneously operate over the same frequency band, and thus enables massive connectivity. High Peak-to-Average Power Ratio (PAPR) and sensitivity to Carrier Frequency Offset (CFO) are significant demerits to deploy such a multicarrier system for 5G and beyond applications. This paper studies the problem of high PAPR and the presence of CFO with efficient pre-coding techniques and a very simplified receiver design. An improved Minimum Mean Square Error (MMSE) receiver is proposed for low-complexity Joint Equalization and CFO Compensation (JECC) in frequency domain using Banded-Matrix Implementation (BMI). Moreover, we have investigated the sensitivity of different pre-coding techniques to channel and CFO estimation errors.

Multimedia transmission in MC-CDMA using adaptive subcarrier power allocation and CFO compensation

ABSTRACTMulticarrier code division multiple access (MC-CDMA) system is one of the most effective techniques in fourth-generation (4G) wireless technology, due to its high data rate, high spectral efficiency and resistance to multipath fading. However, MC-CDMA systems are greatly deteriorated by carrier frequency offset (CFO) which is due to Doppler shift and oscillator instabilities. It leads to loss of orthogonality among the subcarriers and causes intercarrier interference (ICI). Water filling algorithm (WFA) is an efficient resource allocation algorithm to solve the power utilisation problems among the subcarriers in time-dispersive channels. The conventional WFA fails to consider the effect of CFO. To perform subcarrier power allocation with reduced CFO and to improve the capacity of MC-CDMA system, residual CFO compensated adaptive subcarrier power allocation algorithm is proposed in this paper. The proposed technique allocates power only to subcarriers with high channel to noise power ratio. The performance of the proposed method is evaluated using random binary data and image as source inputs. Simulation results depict that the bit error rate performance and ICI reduction capability of the proposed modified WFA offered superior performance in both power allocation and image compression for high-quality multimedia transmission in the presence of CFO and imperfect channel state information conditions.