Spectral Efficiency Comparison Between FTN Signaling and Optimal PR Signaling for Low Complexity Detection Algorithm

Faster-than-Nyquist (FTN) signaling is an attractive transmission technique which accelerates data symbols beyond the Nyquist rate to improve the spectral efficiency; however, at the expense of higher computational complexity to remove the introduced intersymbol interference (ISI). In this work, we introduce a novel FTN signaling transmission technique, named coordinate interleaved FTN (CI-FTN) signaling that exploits the ISI at the transmitter to generate constructive interference for every pair of the counter-clockwise rotated binary phase shift keying (BPSK) data symbols. In particular, the proposed CI-FTN signaling interleaves the in-phase (I) and the quadrature (Q) components of the counter-clockwise rotated BPSK symbols to guarantee that every pair of consecutive symbols has the same sign, and hence, has constructive ISI. At the receiver, we propose a low-complexity detector that makes use of the constructive ISI introduced at the transmitter. Simulation results show the merits of the CI-FTN signaling and the proposed low-complexity detector compared to conventional Nyquist and FTN signaling.

The achievement of the boundary values of spectral efficiency is associated with the development of methods for generating and receiving signals with a compact spectrum. The reason is a constant increase in the capacity of existing communication channels caused by an increase in the volume of transmitted information. Moreover, the allocated frequency bandwidths have natural limitations, and they are almost all reached. The effective way to approach the boundary values of spectral efficiency is the application of spectrally efficient signals, such as FTN (Faster-Than-Nyquist) signals. This article proposes to synthesize optimal FTN signals that are more compact in the spectrum than RRC (root raised cosine) pulses-based signals. The criterion of maximum energy concentration in the occupied frequency bandwidth and the constraint on the cross-correlation coefficient are used to solve the optimization problem. The contribution of this work is the optimization of FTN signal shape. The obtained optimal FTN signals provide a 24% increase in spectral efficiency compared to the RRC pulses-based signals. At the same time, the energy loss stays almost unchanged. To the best of authors’ knowledge, this is the first case when the frequency bandwidth reduction is achieved at practically no energy loss. The simulation modeling in channels with additive white Gaussian noise and fading channels is done with regard to the FTN-SC-FDE (Faster-Than-Nyquist - Single Carrier system with Frequency Domain Equalization) structure. The optimal FTN signals presented in this work can be used to increase the spectral efficiency of satellite broadcasting systems, such as DVB-S2/S2X.

Numerous works are dedicated to Faster-than-Nyquist (FTN) signaling providing symbol rate higher than “Nyquist limit” without energy losses. It is necessary to use infinite pulses or pulses with rather long duration for FTN signaling. Using limited duration of FTN pulses allows to simplify the structure of transceiver but causes challenges with measurement of spectral efficiency. Finite time optimal pulses with controlled level of intersymbol interference (ISI) may be used for FTN signaling. In this work it is proposed to solve optimization problem taking into account limitation on Euclidean distance between different realizations of two random FTN signals. Obtained optimal FTN signals provide the gain in energy efficiency about 2 dB and 4 times higher spectral efficiency comparing to the known spectrally efficient signals based on RRC pulses.

With the exponential growth of cellular traffic in recent times, larger bandwidth and higher spectral efficiency (SE) have become indispensable for higher data rate applications. Discrete Fourier transform spreading orthogonal frequency division multiplexing (DFT-s-OFDM) waveform is being considered as one of the potential candidates for the next generation communications, because of its low peak to average power ratio (PAPR), which is more suitable for large bandwidth systems that are limited by inefficient power amplifiers. However, DFT-s-OFDM suffers from low SE, thus affecting the system throughput. Recently, faster than Nyquist (FTN) signaling combined with DFT-s-OFDM is being studied for its improved spectral efficiency with less PAPR. In this paper, we analyze the performance benefits of applying FTN signaling on DFT-s-OFDM waveform with 5G new radio uplink system. We show that the FTN combined with DFT-s-OFDM has 2% ∼ 75% more throughput than that of of DFT-s-OFDM for the same signal to noise ratio (SNR), using fading channel model. We further show through link adaptation method that the SE of DFT-s-OFDM waveform improves significantly when combined with FTN signaling. We also discuss about the implementation aspects and the performance trade-off with FTN integration into beyond 5G systems.

Faster-than-Nyquist (FTN) signaling is deemed a promising candidate for enabling high spectral efficiency in next-generation optical data center interconnects (DCIs). Trellis-based sequence detectors, such as maximum likelihood sequence estimation (MLSE) and maximum a posteriori (MAP) sequence estimation, operating with long memory lengths, are by far the most commonly adopted strategy for deciphering the original symbol from severe inter-symbol interference (ISI). Nevertheless, the inherent high complexity of this approach poses significant challenges to its practical implementation. In this paper, a partial-response decision feedback equalizer (PR-DFE) is proposed to realize ultra-low complexity and high-performance FTN signaling. The fundamental principle of the proposed scheme involves combining the transmitter-side precoding and receiver-side partial response equalization criteria, which significantly reduces the occurrence of the error propagation issue of the typical DFE in the FTN system. The effectiveness of the proposed scheme is experimentally verified in a 56Gbaud FTN 4-ary pulse amplitude modulation (PAM4) system with a compression factor of 0.8. According to the experimental results, PR-DFE achieves 2.4 dB and 1.5 dB receiver sensitivity improvement compared to the typical DFE and PR-FFE at a bit-error-rate (BER) of 4.5 × 10-3 (BER threshold of 6.7% overhead staircase hard-decision forward error correction code). Moreover, the implementation of the PR-DFE has successfully reduced the probability of two consecutive symbol errors from 4.83 × 10-3 to 0 compared to the typical DFE. According to experimental results, the proposed PR-DFE FTN signaling scheme is a promising candidate for ultra-low complexity and high spectral efficiency intra-datacenter interconnect (intra-DCI) applications.

Recently [16], we have proposed using faster than Nyquist (FTN) signaling to achieve transmission over continuous-time broadcast channels and shown that it can achieve the capacity region of the two-user Gaussian broadcast channel. Benefits of FTN broadcasting include separate encoding and explicit transmission of all users' data, i.e., unlike the previously proposed broadcast coding schemes, no joint encoding is needed. This paper presents a design of a Turbo-coded broadcast transmitter based on the FTN signaling. The proposed receiver architecture has a low implementation complexity and is based on Turbo decoding and successive cancellation of FTN-induced intersymbol interference. The presented simulation results indicate that the designed FTN broadcast architecture can be superior to the time-sharing broadcasting used in practice, and shows the potential to perform close to the capacity boundaries of the Gaussian broadcast channel.

The sparse code multiple access (SCMA) is a promising candidate for bandwidth-efficient next generation wireless communications, since it can support more users than the number of resource elements. On the same note, faster-than-Nyquist (FTN) signaling can also be used to improve the spectral efficiency. Hence in this paper, we consider a combined uplink FTN-SCMA system in which the data symbols corresponding to a user are further packed using FTN signaling. As a result, a higher spectral efficiency is achieved at the cost of introducing intentional inter-symbol interference (ISI). To perform joint channel estimation and detection, we design a low complexity iterative receiver based on the factor graph framework. In addition, to reduce the signaling overhead and transmission latency of our SCMA system, we intrinsically amalgamate it with grant-free scheme. Consequently, the active and inactive users should be distinguished. To address this problem, we extend the aforementioned receiver and develop a new algorithm for jointly estimating the channel state information, detecting the user activity and for performs data detection. In order to further reduce the complexity, an energy minimization based approximation is employed for restricting the user state to Gaussian. Finally, a hybrid message passing algorithm is conceived. Our Simulation results show that the FTN-SCMA system relying on the proposed receiver design has a higher throughput than conventional SCMA scheme at a negligible performance loss.

Time Division Multiple Access (TDMA) based protocols over Rician fading, have been analyzed and proposed by many researchers. However, these protocols need to be explored further in order to improve diversity order at destination. Therefore, this paper aims to propose TDMA amplify-and-forward based three time slot protocol over Rican fading channel with inter-relay communication. The proposed protocol is further investigated for various relay locations in order to optimize the bit error rate (BER) for different relay locations. It is concluded that the proposed amplify-and-forward (PAFP) three time slots protocol performs better in terms of low bit error rate values, as compared to previously proposed amplify-and-forward (PPAF) two time slot and three time slots protocols. Moreover, the PAFP also shows less BER values, as compared to DF three time slot protocol. Furthermore, the PAFP shows less BER values in case of minimum inter-relay distance.KeywordsCooperative inter-relay wireless communicationAmplify-and-forward (AF) protocolTDMABER

Faster than Nyquist (FTN) signaling has been studied as an alternative transmission technology in communication systems when information carrying symbols are sent faster than the Nyquist rate determined by the physical channel bandwidth. This paper presents analysis of the information rates of cyclostationary FTN signaling on AWGN and selected ISI channels. It also presents related numerical capacity results and discusses potential merits to the FTN signaling.

Provision of broadband communications services in High Altitude Platform Station (HAPS) is a new idea and worthy to be discussed. One is the application of OFDM transmission technique as a medium for digital modulation in HAPS. HAPS is a new technology in the telecommunications sector at an altitude of 18-50 km (the stratosphere) and used to serve the broadband wireless access (BWA) and other multimedia devices. HAPS technology has advantages that can cover the lack of terrestrial and satellite technology. Performance of OFDM transmission technique in which a HAPS channel Rician channel can be evaluated by looking at the effect of K-factor. K-factor is the dominant signal power ratio (Line Of Sight) with multipath signal power. In real conditions on the ground, the received power is a combination of the dominant signal power and multipath signal power. The increase in elevation angle between the HAPS platform with user terminals resulted in the increasing value of K-factor and the influence that affected the performance of OFDM systems multipath fading. Effect of K-factor can be identified by computer simulation. Effect of K-factor observed by looking at the value of Bit Error Rate (BER) on the system to the value of signal to noise ratio (SNR) by varying the bitrate and frequency doppler. The results showed that the increasing value of K-factor at the same bitrate the smaller the resulting BER. This shows the better performance of OFDM systems. Meanwhile, the OFDM system performance deteriorated over increasing Doppler frequency. This is because the increasing value of K-factor at the same Doppler frequency resulting more BER value. Keywords: HAPS, OFDM, K-factor, BER, bit rate, Doppler frequency.

Nowadays, wireless demand is raised rapidly since the number of mobile‐cellular telephone and broadband internet are springing up. Thus, many base stations (BS) and a lot of money are needed to satisfy the demand. Radio over fiber (RoF) is the solution to this problem since it can operate a lot of BSs that connected to central station (CS) by using optical fiber, as well as offering cost‐effective solution. Due to some factors, received signals of RoF tend to be in a low quality. Those factors will lead to some problems such as high value of bit error rate (BER), low value of Q factor, and the receiver could not operate in high data rate network. Wavelength division multiplexing (WDM) network can be one of the solutions of those problems where different signals are transmitted through a single‐mode fiber. Bit error rate must be decreased to a certain value, and the Q factor should be increased. The design of RoF will be simulated by using Optisystem software. The performance of RoF’s receiver is measured and analyzed based on the obtained BER, value of Q factor and height of opening of eye diagram.

Several interference mitigation strategies can be used in LTE networks to meet the consumers' increasing need for faster data speeds. Dynamic Spectrum Allocation (DSA), which maintains spectrum in a converged radio system and distributes it across all participating radio terminals, is one of the most promising solutions. However, the fundamental obstacle to achieving increased network capacities is increased inter-cell interference. The aim of this paper is to analyse the effectiveness of a newly proposed DSA technique by comparing its bit error rate (BER) and throughput (TP) with a typical uplink LTE configuration. To maximise throughput in a heterogeneous network, the suggested DSA technique utilises the Nash Bargaining Solution (NBS) scheme, a cooperative game theory that could correlate with the bit error rate. The software tool GNU Radio, which offers signal-processing blocks to develop softwaredefined radios and signal-processing systems, was used to create the setups. After the simulations were performed, the BER values were recorded and compared, while the TP values were established and computed appropriately. According to the results, the uplink (UL-LTE) architecture with DSA has an improved TP and a lower BER value. As a result, spectral efficiency can also be improved.

Underwater wireless optical communication (UWOC) has been considered a promising technology for high-speed underwater transmission. Some Gb/s level UWOC systems applying visible light have been demonstrated with a transmission distance of several meters or more. Many of the previous works focus on the advanced technologies to push the systems’ capacity–distance performance. However, practical environmental factors issue such as flow turbulence and temperature variation are seldom studied through specific statistical/theoretical models. In this paper, a UWOC system using a 450 nm blue light laser source was set up using a 1.5-m water tank with mirrors located on both sides for single or multiple reflections corresponding to different transmission distances. The blue laser was modulated by a 1.25 Gbps NRZ-OOK format with PRBS of 7, 24 or 31, respectively, for system performance comparison. The bit error rate (BER) values were measured in 1.5, 3.0 and 6 m, respectively, for system evaluation. At room temperature, the BER value was down to 10 × 10−8 for a 1.25 Gbps data rate in a 6 m transmission. Then, the UWOC transmission system experiment was carried out under several environmental parameters such as temperature, turbulence, artificial seawater by adding salt to simulate practical application in river or sea. When a submerged motor with an output of 1200 L/h was used as a water flow turbulence source, the impact to BER and transmission quality was negligible. For the temperature change issue, the experiment shows that around the original temperature of 25 °C had the best BER as compared to other temperature ranges from 10 to 50 °C. For artificial seawater issues by adding salt to simulate the real seawater environment. The transmission distance was only 3-m instead of 6 m, mainly due to particle scattering and water disturbance. With the motor pump on, the power penalty was 1 dB at 10 × 10−8 BER when compared to the motor pump off.

We here consider utilizing faster-than-Nyquist (FTN) signaling to increase spectral efficiency in combination with using tight frequency roll-off, optimized signal constellations that have better energy efficiency, and allowing the satellite transponder to operate near its saturation. FTN provides a degree of freedom that allows for increasing the spectral efficiency without the need for introducing additional rings in the signal constellation, which is helpful in the presence of nonlinear transponders. Also, FTN allows for increasing the symbol rate without being adversely affected by the input multiplexing and output multiplexing (IMUX/OMUX) filters. This is because FTN does not alter the signal spectral shape. However, these advantages are gained at the expense of introducing distortion that needs to be compensated successfully. We then utilize an advanced Turbo Volterra receiver that compensates for FTN-induced distortion and nonlinear impairments. Through extensive simulations, we demonstrate substantial performance gains over a wide range of spectral efficiencies in nonlinear satellite systems with adjacent carriers.

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.