Decoding Schemes for FBMC with Single-Delay STTC

Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.

This paper presents a correlation reduction precoding scheme for joint decoding in an overloaded multiple input multiple output (MIMO)- orthogonal frequency division multiplexing (OFDM) system. In the overloaded MIMO system, the number of receive antenna elements is less than that of transmit antenna elements. Through joint maximum likelihood (ML) decoding a frequency diversity suppresses the BER degradation owing to the spatial multiplexing of signal streams. On a Rician channel, the correlation among the coded symbols deteriorates the performance of the joint ML decoding. Thus, this paper proposes the precoding scheme that reduces the correlation on the Rician channel. Numerical results obtained through computer simulation show that the proposed scheme improves the BER by a factor of 1/10 on the Rician channel with the Rician factor of 10.

Orthogonal frequency division multiplexing(OFDM) is a multicarrier modulation(MCM) system that enables high-speed communications using multiple carriers and has advantages of power and spectral efficiency. Therefore, this study aims to complement the existing shortcomings and to design an efficient MCM system. The proposed system uses the inverse discrete wavelet transform(IDWT) operation instead of the inverse fast Fourier transform(IFFT) operation. The bit error rate(BER), spectral efficiency, and peak-to-average power ratio(PAPR) performance were compared with the conventional OFDM system through the OFDM system design based on wavelet transform. Our results showed that the conventional OFDM and Wavelet-OFDM exhibited the same BER performance, and that the Wavelet-OFDM using the discrete Meyer wavelet had the same spectral efficiency as the conventional OFDM. In addition, all systems of Wavelet-OFDM based on various wavelets confirm a PAPR performance lower than that of conventional OFDM.

Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

In this work, we proposed Offset-Quadrature Amplitude Modulation (OQAM) for Discrete Wavelet Transform (DWT) as alternative of Multi-Carrier Modulation (MCM) systems. Instead of the upsampler in the conventional DWT-MCM, OQAM is used in each level. In OQAM, each symbol will be separate into two components, in-phase and quadrature. With OQAM, maximum phase variation will decrease to its half value, which means that the performance of the RF power amplifier will improved. In addition, half symbols period will offset (stagger) the quadrature and in-phase components of the modulated signal to achieve low bit error rate. By contrast, in conventional orthogonal frequency division multiplexing (OFDM), without using the guard interval (Cyclic Prefix (CP)), inherent interferences cause degeneration in received symbols. In this paper, the proposed system model enhanced the spectrum efficiency and becomes more robust to the frequency selective environments. The simulation results illustrate that our proposed system model improves the system performance in terms of probability of errors compared with the OFDM system.

Filter bank based multicarrier systems (FBMC) offer a number of benefits over conventional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP). One benefit is the improved spectral efficiency by not using a redundant CP and by having much better control of out-of-band emission. Another advantage is the ease of accommodating multiple users in an FDMA fashion especially in the uplink, i. e. the multiple access channel (MAC). On the other hand, more elaborate equalization concepts are needed compared to the single-tap per-subcarrier equalizer sufficient in the OFDM with CP case. In this contribution we will present an efficient linear minimum mean square error (MMSE) equalization concept. Since FBMC systems employ offset-quadrature-amplitude-modulation (OQAM), a fractionally spaced per-subcarrier equalizer will be derived, which takes into account the inter-subcarrier interference due to frequency selective multipath fading. Still this is handled with decoupled per-subcarrier equalizers. Simulation results will show that OQAMFBMCs allow for savings in transmit power which have to be paid with a practicable amount of computational overhead.

Orthogonal frequency-division multiplexing (OFDM) with index modulation has been emerged as a promising technique for next-generation networks, where the specific activation pattern of the OFDM subcarriers is capable of conveying additional information implicitly without additional energy consumption, hence improving the system energy efficiency. In this paper, zero-padded tri-mode OFDM with index modulation (ZTM-OFDM-IM) is proposed, which is capable of achieving high spectral and energy efficiency. In ZTM-OFDM-IM, subcarriers are partitioned into subblocks. In each OFDM subblock, only a fraction of subcarriers are modulated by two distinguishable constellation alphabets, while the others remain empty, which reduces the energy consumption. With such an arrangement, extra information bits can be carried by the subcarrier activation pattern. At the receiver, a maximum-likelihood (ML) detector as well as a reduced-complexity two-stage log-likelihood ratio (LLR) detector are developed for signal demodulation. Theoretical performance analysis based on Euclidean distance metric and pairwise error probability are conducted. Besides, in order to attain better BER performance, the design strategies for the two distinguishable constellation alphabets are investigated, which is followed by brief discussions on generalization methods for the proposed ZTM-OFDM-IM. It is demonstrated via Monte Carlo simulations that ZTM-OFDM-IM is capable of enhancing the BER performance compared with the conventional OFDM and other conventional index-modulated OFDM benchmarks, which provides high-rate data transmission with low energy consumption. Moreover, the LLR detection of ZTM-OFDM-IM only suffers from slight performance loss in comparison with the ML detection and achieves significant complexity reduction.

This paper proposes likelihood function generation of complexity-reduced maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) suitable for soft-decision turbo decoding and investigates the throughput performance using QRM-MLD with the proposed likelihood function in multipath Rayleigh fading channels for orthogonal frequency and code division multiplexing (OFCDM) with multiple-input multiple-output (MIMO) multiplexing. Simulation results show that by using the proposed likelihood function generation scheme for soft-decision turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio (E/sub b//N/sub o/) at the average block error rate (BLER) of 10/sup -2/ at a 1-Gbps data rate is significantly reduced compared to that using hard-decision decoding in OFCDM access with 16 QAM modulation, the coding rate of 8/9, and 8-code multiplexing with a spreading factor of 8 assuming a 100-MHz bandwidth. Furthermore, we show that by employing QRM-MLD associated with soft-decision turbo decoding for 4-by-4 MIMO multiplexing, the throughput values of 500 Mbps and 1 Gbps are achieved at the average received E/sub b//N/sub o/ of approximately 4.5 and 9.3 dB by QPSK with the coding rate of R = 8/9 and 16 QAM with R = 8/9, respectively, for OFCDM access assuming a 100-MHz bandwidth in a twelve-path Rayleigh fading channel.

Wireless network is one of the most important things in the development of telecommunication. However, the existing wireless technology has not been able to efficiently create a very high data rate because it was very sensitive to fading. Therefore, Orthogonal Frequency Division Multiplexing (OFDM) technology combined with MIMO (Multiple Input Multiple Output) transceiver system was used to gain more diversity and bandwidth efficiency. The propagation performed on the OFDM MIMO system was multipath propagation. To reduce Intersymbol Interference (ISI) was used Zero Forcing (ZF) equalizer which works by combining channel response and equalizer response itself to eliminate ISI. This study aims to determine the effect of Zero Forcing Equalizer on OFDM MIMO system using rayleigh fading channel and compared the result with OFDM MIMO STBC system. The research method used was simulation using MatLab R2015a. The simulation results showed that the performance of OFDM MIMO ZF system was worse than OFDM MIMO STBC system i.e BER vs EbNo simulation, eye diagram simulation, and constellation diagram simulation. The OFDM MIMO ZF system was required an Eb / No value more than 25 dB to achieve BER 10-4 while the OFDM MIMO STBC system only required an Eb / No value of 10.5 dB to achieve BER 10-4. The eye pattern generated by the OFDM MIMO ZF system was more closed and the dispersion of constellation signals away from the ideal point while OFDM MIMO STBC system displayed a more open eye pattern and the dispersion of its constellation signal closer to the ideal point. It indicated more ISI occurs in the OFDM MIMO ZF system than that in OFDM MIMO STBC system.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the promising contendents in the race of very high data rate delivery, for 4G wireless systems. The conventional OFDM systems, so far deployed make use of Fast Fourier Transform (FFT) as their basic building block. Besides the numerous advantages, the restriction over the data rate imposed by the FFT in the form of cyclic prefix may be intolerable for the next generation OFDM systems. So, researches are on the way to replace FFT with a more suitable transform which is redundant free. DWT OFDM is one such system in which FFT in the conventional OFDM is replaced with Discrete Wavelet Transform (DWT). Using simulations, already it has been established that in ideal conditions, the performance of DWT OFDM is better than that of FFT OFDM. As phase noise can be considered as the major RF impairment and one of the leading performance limiting factors of the wireless systems, this paper analyses the Bit Error Rate (BER) performance of the DWT OFDM in presence of phase noise. BER performances of both DWT OFDM and FFT OFDM are analysed and compared in presence of phase noise. For this, Matlab Simulink model have been developed for both types of OFDM, and simulation is carried over in presence of phase noise for different modulation schemes. In all cases the BER performances of DWT OFDM is found to be fairly ahead that of FFT OFDM.

We experimentally demonstrate and numerically investigate a discrete-Fourier-transform (DFT) based offset quadrature-amplitude-modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) system. We investigate the scheme using a set of square-root-raised-cosine functions and a set of super-Gaussian functions as signal spectra. It is shown that offset-QAM OFDM exhibits negligible penalty for all investigated spectra, in contrast to rectangular-function based Nyquist FDM (N-FDM) and sinc-function based conventional OFDM (C-OFDM). The required guard interval (GI) length for dispersion compensation in offset-QAM OFDM is analyzed and shown to scale with twice the subcarrier spacing rather than the full OFDM bandwidth. Experimental results show that 38-Gb/s offset-16QAM OFDM supports 600-km fiber transmission with negligible penalty in the absence of GI while a GI length of eight is required in C-OFDM. Further numerical simulations show that by avoiding the GI, 112-Gb/s polarization multiplexed offset-4QAM OFDM can achieve 23% increase in net data rate over C-OFDM under the same transmission reach. We also discuss the design of the pulse-shaping filter in the DFT-based implementation and show that when compared to N-FDM, the required memory length of the filter for pulse shaping can be reduced from 60 to 2 in offset-QAM OFDM regardless of the fiber length.

Filter bank multi-carrier with offset QAM(FBMC/OQAM) is a multi-carrier modulation technique that can be an alternative to conventional orthogonal frequency division multiplexing(OFDM) with cyclic prefix (CP) in wireless network. FBMC has a higher spectrum efficiency and effective emission power without CP. Because the orthogonality only exists in real domain, the channel estimation in FBMC/OQAM system is more challenging. In this paper, the IAM preamble-based method and the DFT-based channel estimation are combined to do the estimation. And two improved DFT-based channel estimation methods are proposed to remove the noise in the channel impulse response(CIR) of conventional DFT-based method. The proposed are proved to have a better performance than the conventional DFT-based.

Rapidly growing demand for high data rates in wireless communication systems is the cause of the merging of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques. MIMO-OFDM technique needs Radio Frequency (RF) front end in each antenna, which is not effective for large dimensional antenna size. Therefore, RF front end on the receiver side will be simplified using a single RF technique based on the Electrically Steerable Parasitic Array Radiator (ESPAR) antenna. In real life, a channel cannot be ideal. Therefore, before the signal is transmitted, that signal must be coded to minimized errors when the data transmission process. Convolutional code is a coding technique that can detect and correct error bit (error control coding) and that it is expected to reduce the quantity of Bit Error Rate (BER). In this research, a simulation is designed to analyze single RF performance on the MIMO-OFDM system using Vertical Bell Laboratories Space-Time (VBLAST) detection for convolutional code encoder and Viterbi decoder. The result simulation shows that the channel estimation technique works well on the MIMO-OFDM system using single RF, which is shown in the magnitude and phase curves against the subcarrier index between the theory channel and the estimated channel are at almost the same points. VBLAST-ZF detector performance is shown in the BER curve against SNR, where the difference BER value for SNR value 10 dB between the theory channel and the estimated channel is 0.001499. Channel coding technique using convolutional code encoder and Viterbi decoder with a rate of ½ works well on the MIMO-OFDM system using single RF which is shown in the BER curve against SNR, where BER value with coding technique is smaller than BER value without coding technique.

This chapter extensively presents the most popular multicarrier modulation techniques such as, orthogonal frequency division multiplexing (OFDM), FilterBank MultiCarrier modulation with Offset QAM (FBMC-OQAM), universal Filtered Multicarrier (UFMC), and generalized frequency division multiplexing (GFDM). It investigates waveforms that helps to achieve the 5th-generation (5G) goals, that is, to propose modulation schemes with exceptional spectral efficiency, low out-of-band emissions (OOB), robustness against interference and synchronization errors and suitable for use in a fragmented radio spectrum. The cyclic extension has a special, beneficial role for the OFDM functionality. Besides its operation as a guard band, the cyclic prefix transforms the linear convolution of the signal with the channel response, to circular convolution. In frequency selective channels, the cyclic prefix reduces spectral efficiency even more. UFMC or Universal Filtered OFDM (UF-OFDM) focuses on the drastic reduction of OFDM side lobes. The main concept behind UFMC is to divide an OFDM waveform into components and filter each component individually.

This paper relates to the application method of channel state information (CSI) to the Viterbi (maximum likelihood) decoder in the digital terrestrial television broadcasting system. The proposed Viterbi decoder uses the CSI derived from the pilots inserted in the transmitter of the COFDM (coded orthogonal frequency division multiplexing) system. The CSI is calculated by interpolation using the pilots in the receiver. The active real (I) and imaginary (Q) data after equalization are transferred to the branch metric calculation block that decides the euclidean distance for soft decision decoding and also the estimated CSI values are transferred to the same block. After calculating the euclidean distance for the soft decision decoding, the euclidean distance of the branch metric is multiplied by CSI. To do so, new branch metric values that consider each carrier state information are obtained. We simulated this method in Rayleigh fading defined in the ETSI standard. From the simulation, this method has better performance of about 0.15 dB to 0.7 dB and 2.2 dB to 2.9 dB in the Rayleigh channel than that of conventional soft decision Viterbi decoding with or without a bit interleaver where the constellation is QPSK, l6-QAM and 64-QAM.