Generalized Multi-Carrier Waveforms in Two-Way Relay Systems

Generalized frequency division multiplexing (GFDM) and circular filter bank multicarrier (C-FBMC) are two contender waveforms with circular pulse-shaping that are recently proposed for the physical layer of the fifth generation of wireless communication networks (5G). This paper puts these waveforms under the microscope and conducts an analysis on their practical feasibility and performance. In addition, we present a transmitter structure for both GFDM and C-FBMC and show that this structure has the same complexity for both systems. In this paper, GFDM receiver with successive interference cancellation (SIC) is considered as it can get a performance close to that of OFDM (orthogonal frequency division multiplexing). Our bit error rate (BER) performance analysis reveals that GFDM has limitations in terms of the total number of symbols per data packet. When the number of symbols in a packet has an even value, GFDM suffers from a high error floor in BER. For the small constellation sizes, GFDM and C-FBMC reach the same BER performance as that of OFDM. As the constellation size increases, a gap between the BER curve of GFDM and OFDM starts to appear while C-FBMC keeps the same performance as OFDM. Finally, our computational complexity analysis reveals that C-FBMC receiver is simpler than GFDM.

In this paper, we assess the performance of a generalized frequency division multiplexing (GFDM) transceiver for underwater acoustic high data-rate transmission. We also present a comprehensive overview of the work done in the field of next generation multicarrier techniques beyond orthogonal frequency division multiplexing (OFDM) for underwater acoustic (UWA) channels. Since very little work has been done in determining the feasibility of acoustic GFDM, we evaluate the performance of proposed GFDM transceiver in terms of spectral efficiency, peak to average power ratio, error rates and complexity using simulations. We employ two types of receivers - matched filter and zero forcing and evaluate their performances for several system configurations. Results presented show that the zero forcing receiver outperforms the matched filter receiver at high SNR values for almost all the configurations; exceptions being the cases where 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> and 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> Xia pulse shapes are employed with higher values of the roll off factor. We also compare the performance of the proposed GFDM transceiver with that of OFDM and show that GFDM outperforms OFDM by almost 4 dB for a symbol error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . It is concluded that while GFDM is computationally more demanding than OFDM, it is still an appealing technique for future UWA communications due to its higher spectral efficiency, flexibility, and better error performance.

Generalized frequency division multiplexing (GFDM) and circular filter bank multicarrier (C-FBMC) are two contender waveforms with circular pulse-shaping that are recently proposed for the physical layer of the fifth generation of wireless communication networks (5G). This paper puts these waveforms under the microscope and conducts an analysis on their practical feasibility and performance. In addition, we present a transmitter structure for both GFDM and C-FBMC and show that this structure has the same complexity for both systems. In this paper, GFDM receiver with successive interference cancellation (SIC) is considered as it can get a performance close to that of OFDM (orthogonal frequency division multiplexing). Our bit error rate (BER) performance analysis reveals that GFDM has limitations in terms of the total number of symbols per data packet. When the number of symbols in a packet has an even value, GFDM suffers from a high error floor in BER. For the small constellation sizes, GFDM and C-FBMC reach the same BER performance as that of OFDM. As the constellation size increases, a gap between the BER curve of GFDM and OFDM starts to appear while C-FBMC keeps the same performance as OFDM. Finally, our computational complexity analysis reveals that C-FBMC receiver is simpler than GFDM.

The physical-layer network coding (PNC) can greatly improve the throughput of wireless network communications. However, critical synchronization in both time domain and frequency domain is required. Orthogonal frequency division multiplexing (OFDM) solves the problem of the synchronization in time domain while more critical synchronization in frequency domain is required. In this paper, we investigate the inter-channel interference (ICI) issue for OFDM-based physical-layer network coding (FPNC) over the two-way relay channel (TWRC). An approximate formula that calculates the ICI is derived. The compensation frequency, used by intermediate node to obtain minimal ICI power, has also been calculated. We find that average compensation is the optimal compensation method in the symmetric TWRC system while a different compensation method should be adopted in the asymmetric TWRC system. In addition, it is observed that bit error rate (BER) performance is not only decided by the power of the ICI but also by the distribution of it. At last, numerical results indicate that our approximate formula is accurate enough to calculate the ICI and can be applied to other OFDM systems.

DHT-based GFDM and STC-GFDM systems for beyond 5G wireless networks

Filter Bank Multicarrier and Generalized Frequency Division Multiplexing are being considered as the major candidates for the 5G modulation schemes. Orthogonal Frequency Division Multiplexing is used in 4G but owing to its Out of Band spectral leakage it is being replaced by these modified waveforms. Multicarrier Modulation schemes are sensitive to Carrier Frequency Offset which significantly degrades the Signal to Noise Ratio by introducing Inter Carrier Interference causing degradation in the Bit Error Rate performance. This paper provides an in-depth investigation and analysis on the effects of Carrier Frequency Offset on the performance of Filter Bank Multicarrier and Generalized Frequency Division Multiplexing under AWGN and fading environments. Results are compared with the Orthogonal Frequency Division Multiplexing to highlight the features of either modulation scheme under various static and dynamic environments.

Next generation networks (NGN) are required to fulfill a stringent set of requirements which include high data rate, spectral efficiency, low out-of-band (OOB) radiation and latency. Generalized frequency division multiplexing (GFDM) is one of the schemes proposed at physical layer for NGNs. GFDM is a block-based transceiver scheme consisting of non-orthogonal subcarriers which are individually filtered. The impulse response of this filter decides the characteristics of the signal. In GFDM, a block consists of a set of subcarriers and subsymbols, the block-based structure of GFDM is advantageous for low-latency applications. GFDM also increases spectral efficiency when compared with orthogonal frequency division multiplexing (OFDM) by reducing the overhead of cyclic prefix. Apart from these advantages of GFDM, individual filtering of subcarriers decides the overall performance of transmitter. In this paper, we study the characteristics of the transmitted GFDM signal such as peak-to-average power ratio and OOB radiation based on various filters. The proposed GFDM technique uses traditional Nyquist filters to perform subcarrier filtering, whereas we study the effect of improved Nyquist filters to do the same. We show that the use of improved Nyquist filtering improves the characteristics of the transmit signal.

When two wireless terminals exchange information through an intermediate relay, physical-layer network coding (PNC) improves the spectrum efficiency by allowing concurrent message transmission. In two-way relay systems, the performance gain of PNC under practical limits has been investigated. The results show that generally the performance would be significantly degraded by channel impairments like asymmetric channel gain at the multiple-access phase. As an alternative interference exploitation scheme, successive interference cancellation (SIC) works well when multiple sources’ signals have different power levels at the destination to successfully decoding. In this paper, an adaptive transmission scheme combing PNC and SIC is proposed for the two-way relay systems. Separate sum-rate simulation results for PNC and SIC show the opposite tendency with the channel impairment in two-way relaying, which means combining them would get a smooth sum-rate gain and let the system be more robust to dynamic scenarios.

In this paper, a new WHT-LWT-GFDM waveform obtained by combining Walsh–Hadamard Transform (WHT), Lifting Wavelet Transform (LWT), and Generalized Frequency Division Multiplexing (GFDM) is presented for use in next-generation wireless communication systems. The proposed approach meets the requirement of 5th-generation (5G) and beyond communication schemes in terms of low latency, low peak-to-average-power ratio (PAPR), and low bit-error rate (BER). To verify the performance of the presented waveform, PAPR and BER simulation results were obtained in additive white Gaussian noise (AWGN) and flat Rayleigh fading channels, and the performance of the proposed system was compared with conventional Orthogonal Frequency Division Multiplexing (OFDM), GFDM, and Walsh–Hadamard transform-based GFDM (WHT-GFDM). Simulation results show that the proposed waveform achieves the best BER and PAPR performances and it provides considerable performance gains over the conventional waveforms.

This paper proposes a new scheme to mitigate the effects of interference in generalized frequency division multiplexing (GFDM) systems. We take advantage of the tabu search (TS) process that was originally designed to find approximate solutions for combinatorial optimization problems. We find the initial solution through the application of conventional GFDM receivers such as matched filter and zero-forcing receivers. Starting from the initial solution, we apply the TS algorithm to find a new solution that has lower cost in terms of maximum likelihood costs. In this way, the proposed system can alleviate the interference inherent in GFDM systems. Simulation results show that the proposed system outperforms conventional GFDM systems and orthogonal frequency division multiplexing (OFDM) systems in a multi-path channel regardless of the roll-off factor of the prototype filter.

In this paper, we consider the two-way relay channel (TWRC) over which communication is performed using space-time block codes (STBC) with physical-layer network coding (PNC) protocol. The three-node two-way relaying (TWR) model consists of two end nodes (sources) simultaneously communicating with each other over a relay node where each node is equipped with two antennas and uses Alamouti's STBC to provide diversity. We consider non-reciprocal channels where fading channel coefficients are independent for opposite directions of the same link. We first derive closed form expressions for the outage probability of the STBC-TWR system and uncoded TWRC assuming equal transmit power at each node and decode-and-forward (DF) strategy at the relay. We show that the STBC-TWR system significantly improves the uncoded TWRC outage performance. Then, to further improve the performance, we propose an optimal power allocation in TWR scheme employing Alamouti's STBC and PNC protocol. The optimal power allocation is obtained by maximizing the sum-rate under the total power constraint. We show that the optimal power allocation considerably improve the outage performance as well as the sum-rate compared to the equal-power case.

Generalized frequency division multiplexing (GFDM) is a recent physical layer scheme proposed for next-generation cellular systems. Like orthogonal frequency division multiplexing (OFDM), it is based on multicarrier modulation, but the filter shape is no longer rectangular (roll off &#x2260; 0) and the orthogonality between subcarriers is lost. With higher flexibility, low peak to average power ratio (PAPR) and reduced out-of-band emissions compared with OFDM, GFDM modulation is an attractive candidate for 5G application scenarios. This paper explores the performance of 10 Gb&#x002F;s GFDM system over the optical link in terms of PAPR, quality factor (<italic>Q</italic> factor), and mean squared error using a third-order adaptive Volterra filter with 3 and 5 taps. The impact of linear impairments (chromatic dispersion, polarization mode dispersion), laser line width, and Mach&#x2013;Zehnder non-linearity have been addressed. The results of our simulations indicate that the transmitted 10 Gb&#x002F;s GFDM signal through an optical fiber can reach 930 Km and <italic>Q</italic> &#x003D; 11.9 dB after 700 Km at &#x2013;8 dBm of launch power using 5 taps third-order adaptive Volterra equalizer with an improvement of approximately 210 Km and 1.25 dB compared with the same equalizer with 3 taps.

One of the challenges of modulation techniques used in Fifth-Generation (5G) is their robustness in noisy environment. Conventional Orthogonal Frequency Division Multiplexing (OFDM) cannot be considered as a 5G waveform in its original form because of its certain limitations, such as performance degradation by impulsive noise (IN) and high peak to average power ratio (PAPR). Numerous modulation schemes proposed for 5G communications are able to overcome these drawbacks. Generalised Frequency Division Multiplexing (GFDM) is one of them. This paper analyses the performance of GFDM in presence of Additive White Gaussian Noise (AWGN), IN and Narrow Band Interference (NBI). It is found that GFDM is able to perform better than OFDM and Vector Orthogonal Frequency Division Multiplexing (VOFDM) in presence of noises, which can potentially be present in 5G applications. Simulation results show that GFDM achieve lower PAPR and Symbol Error Rate (SER) and an average of 10.73 dB and 4.73 dB gain in Signal to Noise Ratio (SNR) in presence of IN and combined IN and NBI respectively, as compared to OFDM and VOFDM.

PAPR analysis of wavelet based multitaper GFDM system

Generalized Frequency Division Multiplexing (GFDM) is a recently proposed multicarrier waveform which is being considered as one of the possible candidates for 5G wireless access technology. Key advantages of GFDM are flexibility and low spectral side-lobes which render it the ability of carrier aggregation and reduced adjacent channel interference. However due to its non-orthogonal nature GFDM suffers from the problem of self-inter-carrier interference (self-ICI) which occurs between time-slots of adjacent subcarriers in the signal. Due to self-ICI, the bit-error rate (BER) performance of GFDM is severely affected under low SNR regime. Moreover application of MIMO technique to GFDM further adversely affects the BER due to inter-antenna interference (IAI) between the transmit antennas. To mitigate this problem, spatial modulation has been applied to GFDM and its BER performance with respect to V-BLAST based GFDM is studied under flat Rayleigh fading channel condition through computer simulations.