Square Root Raised Cosine Research Articles

Rectangular Orthogonal Digital Filter Banks Based on Extended Gaussian Functions

Rectangular orthogonal digital filter banks (ODFBs) based on square-root-raised-cosine (SRRC) functions are widely utilised to realise flexible and elastic multi-channel aggregations for fixed and mobile networks. However, long digital filter lengths are required to minimize digital filtering-associated signal distortions. In this paper, based on the extended Gaussian function (EGF), a novel rectangular ODFB with excellent robustness against the short digital filter length-induced truncation effect is proposed. Optimum digital filter parameters of the EGF-based ODFBs are identified and verified in multi-channel hybrid OFDM-digital filter multiple access (DFMA) PONs based on intensity modulation and direct detection (IMDD). By making use of the identified optimum digital filter parameters, extensive comparisons of digital filter characteristics and corresponding multi-channel upstream PON performances are made between the EGF-based ODFBs and the SRRC-based ODFBs. It is shown that to achieve a similar aggregated upstream signal transmission capacity, the EGF-based ODFB reduces the digital filter DSP complexity by a factor of 4. For a digital filter length as short as 8, in comparison with the SRRC-based ODFB, the EGF-based ODFB introduces >1.5 dB (>0.8 dB) improvements in upstream receiver sensitivity for 5-bits (8-bits) DACs/ADCs, increases the aggregated upstream signal transmission capacity by >5.5%, enlarges the ONU launch power dynamic range by >2.5 dB and improves the frequency offset tolerance by a factor of >1.5. In addition, the EGF-based ODFB also enhances upstream performance robustness against ONU symbol timing offsets.

Adaptive Power Control with Selection Combiner over Nakagami-m Fading Channel

Acceptable Quality of Service (QoS) is of paramount importance in wireless communication system. However, QoS is affected by multipath propagation resulting in unreliable reception. Selection Combiner (SC) which is one of the techniques previously used to solve this problem is associated with poor performance due to fixed power level used in the technique. Hence, in this paper, an Adaptive Power Control (APC) technique using SC with a closed form expression over Nakagami-m Fading Channel is proposed. APC technique is developed using fixed power SC and Link Adaptation Algorithm (LAA). Ten thousand (10,000) bits are randomly generated and modulated using Quadrature Amplitude Modulation (QAM) scheme. The modulated signal is passed through the Square Root Raised Cosine (SRRC) filter for suitable transmission over the Nakagami-m fading channel. The faded signals at varying paths ‘L’ (2, 3, 4) are selected by Conventional Selection Combining (CSC) to instruct the transmitter for adjustment of power level based on the value of the received signal through LAA. Mathematical expression for the received signal using Probability Density Function (PDF) of Nakagami-m Fading Channel at varying paths is derived. The APC technique is simulated using MATLAB software and evaluated using Signal to Noise Ratio (SNR), Outage Probability (OP) and Bit Error Rate (BER) to determine the performance of the proposed technique. OP values of 0.0969 and 0.1069 are obtained for APC and CSC, respectively, at SNR of 6 dB with L of 4, while BER values of 0.0052 and 0.2599 are obtained for APC and CSC, respectively. The percentage reduction in OP and BER are 29.79% and 54.43%, respectively. The results obtained show that APC gives lower OP and BER values with increase in SNR when compared with fixed power SC due to self-adjustment of the allocated power. Therefore, the APC technique proposed can be used to enhance the performance of wireless communication systems. Keywords— Adaptive Power Control (APC), Selection Combiner (SC), Link Adaptation Algorithm (LAA), Bit Error Rate (BER), Outage Probability (OP), Probability Density Function (PDF) and Diversity Combiner (DC).

Hybrid Coding and Filtering Technique for Optical IM-DD Link With Robustness to Multipath Interference and Bandwidth Limitation

In this work, a hybrid code division multiplexing (CDM) coding and digital filtering method for optical intensity modulation and direct detection (IM-DD) link is investigated to address multipath interference (MPI) and channel bandwidth limitation. CDM signaling already provides robustness to MPI through suppressing the unsynchronized paths by orthogonal (de)coding. As for digital filtering based on square root raised cosine (SRRC) waveforms, its advantage to IM-DD link includes robustness to channel bandwidth limitation due to pulse shaping. Additionally, matching filters achieve the best orthogonality only when they are synchronized well, thus robustness to MPI can be expected on the basis of CDM. We study the performance of such hybrid coding and filtering method over IM-DD link in the presence of MPI and bandwidth limitations through simulation. This is followed by experimental demonstrations of single point-to-point transmission with capacity at 112 Gbps. BER comparison between CDM only and hybrid filtering and coding method is performed by emulating MPI using a Mach-Zehnder interferometer. Furthermore, bidirectional transmission over a single fiber verifies its performance advantage and demonstrates potentials for reducing implementation costs of end-to-end optical communications.

Pulse shapings employed in an underwater visible-light communication system based on carrierless amplitude and phase modulation utilizing a complex deep neural network equalizer

We experimentally demonstrate the performance of a complex deep neural network (CDNN) equalizer in multi-band super-Nyquist carrier-less amplitude and phase (m-SCAP) modulation for underwater visible-light communications (UVLC). The in-phase and quadrature of the complex data after the match filter and down-sampling are combined as real number pairs and input to the CDNN, which outputs the real part and the imaginary part of the equalized complex data. We compare the different performances of three pulse shapings [better-than-Nyquist pulse shaping (BTN), square-root raised cosine (SRRC), and Xia] utilized in the m-SCAP UVLC system based on the CDNN. We demonstrate that the CDNN equalizer can outperform the traditional equalizer based on the Volterra series and least-mean-square algorithm. The experiments show that the low-roll-off BTN performs best, and the high-roll-off SRRC performs best in the m-SCAP system. In our experiment, the bit-error rate (BER) of the BTN system is 2.6 × 10 − 4, the BER of the SRRC is 3.6 × 10 − 4, and the BER of the Xia system is 7.3 × 10 − 4 when the spectral efficiency is 3.76 bit / s / Hz and the signal peak-to-peak voltage (Vpp) is 0.9 V.

IEEE 802.15.6 WBAN Standard Compliant IR-UWB Time-Hopping PPM Transmitter using SRRC signaling pulse

This paper develops the design of an IEEE 802.15.6 Impulse-Radio (IR) Ultra-Wideband (UWB) transmitter for Wireless Body Area Networks (WBAN) in 180-nm CMOS technology. The transmitter operates at the mandatory data rate of 0.487 Mbps and employs a pulse position controller (PPC) to place the Square Root Raised Cosine (SRRC) pulse for a time-hopping pulse position modulation (TH-PPM) scheme. This transmitter features a novel piece-wise linear approximation (PWLA) approach for generation of SRRC signaling pulse. It is found that the generated PWLA SRRC pulse is fully compliant with the WBAN spectral mask. The proposed PWLA approach has the potential to approximate an arbitrary signaling waveform with a high degree of accuracy and hence should be useful in transceiver realizations.

An Intrinsic Interference Mitigation Scheme for FBMC-QAM Systems

Quadrature amplitude modulation-based filter-bank multicarrier system (FBMC-QAM) is a promising new radio access technology for the upcoming 5G standalone standard (5G-NR SA). By way of highly localized prototype filters, FBMC-QAM system is able to achieve low out-of-band (OOB) radiation and high spectral efficiency without the cyclic prefix (CP), at the price of non-orthogonality between adjacent subcarriers, intrinsic interferences, and bit error rate (BER) degradation. As an attempt to mitigate these impairments, a precoding scheme is proposed in this paper, which aims to maximize signal-to-leakage-and-noise ratio (SLNR) while allowing pulse-shaping filters with superb spectral characteristics to be leveraged. To justify the efficacy, performance analysis is conducted for prototype filters such as square-root raised cosine (SRRC), isotropic orthogonal transform algorithm (IOTA), and Mirrabasi-Martin (same as suggested in the PHY-DYAS project) for both additive white Gaussian noise (AWGN) and time-dispersive channels. The computer simulation shows that SLNR-based FBMC-QAM system incurs low complexity overhead and is able to enhance BER performance effectively.

Study on frequency and impulse response of novel triple band notched UWB antenna in indoor environments

In this paper, a novel fork shaped structure backed plane is added to a simple UWB (ultra wideband) slot antenna to enhance the impedance bandwidth as well as create triple band notched characteristics for Impulse Radio (IR) UWB applications. This fork-shaped structure is connected to a rectangular radiating patch at four different points through the cylindrical pins. The proposed antenna with this fork-shaped structure shows a very wide impedance bandwidth which spans from 2.5 up to more than 20 GHz and offers triple band-notched properties in WiMAX, WLAN and X-band downlink satellite communication spectrums. Moreover, the proposed antenna shows good radiation features such as gain, radiation efficiency and radiation patterns. A comprehensive investigation on the antenna time domain performance is also performed throughout the paper, and the effect of the proposed antenna on the two popular excitation pulses including modulated Gaussian (MG) and square root raised cosine (SRRC) pulses is fully investigated. A frequency-domain measurement setup is applied to measure time domain characteristics of the proposed antenna. Also, the realistic indoor multipath propagation channel characteristics when the proposed antennas are applied as the transmitter and receiver antennas are studied. Sub-band divided ray tracing method is used to simulate channel characteristics.

New SRRC receiver filter design with reduced number of filter taps for wireless communication systems

In wireless communication systems, it is well known that inter-symbol interference (ISI) can be avoided by using a pair of matched square-root-raised-cosine (SRRC) filters in the transmitter and receiver. In an effort to find methods which minimise the number of filter taps in the matched filter, numerous studies have been done. However, in practise, when the communication specification is fixed by the standard, it is not possible to change the coefficients of the transmit filter. In this study, the authors propose a new SRRC filter design with the reduced number of filter taps for a receiver of a wireless communication system. The proposed design utilises a recursive steepest-descent algorithm when the filter coefficients of the transmitter are fixed. That is, relaxing the ISI criterion while maintaining the stopband attenuation, the proposed receiver filter has fewer filter taps than that in the conventional case without undergoing bit error rate performance degradation. The proposed receiver filter design with the reduced number of filter taps reduces the computational complexity and the detection delay in the receiver.

Orthogonal Multiband CAP Modulation Based on Offset-QAM and Advanced Filter Design in Spectral Efficient MMW RoF Systems

In this study, to the first time, we demonstrate an offset-QAM carrier-less amplitude and phase modulation (OQAM-CAP) technique for spectral efficient multi-user radio-over-fiber systems. In comparison with traditional QAM-based CAP modulation schemes, the digital filter for each channel in OQAM-CAP can be adaptively redesigned to obtain either higher spectral efficiency or lower computational complexity. Two kinds of digital filters, namely, square-root raised-cosine (SRRC) filters and isotropic orthogonal transform algorithm (IOTA)-based filters, are studied and applied to shape the frequency window of each channel in CAP systems. We compared the performances among SRRC-OQAM CAP, IOTA-OQAM CAP, and traditional SRRC-QAM CAP. It is experimentally demonstrated that SRRC-OQAM-CAP can achieve higher spectral efficiency, IOTA-OQAM-CAP can obtain higher computational efficiency, and SRRC-QAM-CAP can be used in uplink transmission with lower interchannel interference. Bidirectional experiments are conducted with around 2-GHz nine aggregated channels on 60-GHz optical millimeter wave. Less than 7% error vector magnitudes are realized over 15-km standard single-mode fiber and 1.5-m wireless channel.

Optimizing Pulse Shaping Filter for DOCSIS Systems

This paper proposes a cost efficient nearly linear phase approximation to an square root raised cosine (SRRC) pulse shaping filter that satisfies the out-of-band spectral constraints of DOCSIS down-stream channels. A nearly linear phase filter structure is converted to an SRRC filter using a weighted and sampled least-squares criterion to fit the magnitude and phase responses. To ensure stability, the search for optimum coefficients is constrained using the Steigliz–McBride (SM) and Gauss–Newton (GN) methods, which unfortunately also eliminates sets of stable coefficients, one of which could be and probably is the optimum. To expand the sets of coefficients that produce stable filters in the SM and GN methods, the transfer function is parameterized in a special way. The effectiveness of the proposed filter is verified and compared with other approaches.

Implementation of SRRC Filter in Mobile WiMax with DWT Based OFDM System

Pulse shaping filter when applied to the symbols generated for transmission in a bandwidth limited systems allow for bandwidth containment that reduces the Inter-Symbol Interference (ISI) arising from multipath signal reflections which further minimizes the probability of errors at the receiver. Wavelets encompass the advantages of transforming and mapping data onto orthogonal subcarriers with optimal flexibility as well as less complexity which leads to increase the bandwidth efficiency of an Orthogonal Frequency Division Multiplexing (OFDM) system. In this paper Square Root Raised Cosine (SRRC) a pulse shaping technique when applied to Discrete Wavelet Transform (DWT) based OFDM system in mobile WiMax is simulated and its performance analysis in terms of Bit Error rate (BER) as a function of Signal to Noise Ratio (SNR) is investigated for various modulation schemes under AWGN channel. The results obtained show that SRRC filter offers to significantly improve BER for the given SNR and enhance the performance of physical layer in Mobile WiMax. The performance measurements and analysis is done in the simulation developed in MATLAB.

FTN 전송기법에서 최적의 필터 roll-off 값 및 탭수 설정

본 논문은 인접 심볼 간의 간섭이 발생하지 않는 최대 데이터 전송률인 Nyquist rate 보다 빠르게 데이터를 전송하여 전송량을 증가시키는 FTN(Faster than Nyquist) 기법을 이용하여 최적의 필터 roll-off 값과 탭 수를 설정한다. FTN 신호 전송 시 발생하는 ISI(Inter-Symbol Interference)를 최소화하기 위해 LDPC부호를 기반으로 하는 터보 등화 모델을 적용하였으며, FTN 신호의 필터 roll-off 값과 탭 수에 따라 시뮬레이션하여 성능을 향상시키고 최적의 값을 설정하였다. In this paper, to increase the throughput for wireless communication, FTN methods that is faster than Nyquist rate are used recently. To improve performance, turbo equalization algorithms that iteratively exchange probabilistic information between soft Viterbi equalizer and LDPC decoder to minimize ISI are applied in this paper. In FTN transmission, the performance depends on roll-off value and number of tabs of SRRC(Square Root Raised Cosine) filter. Therefore, Based on simulation, this paper present optimal number of filter coefficient and tab for various ISI factor of <TEX>${\tau}$</TEX>.

Square Root Raised Cosine Fractionally Delaying Nyquist Filter - Design and Performance Evaluation

Abstract In this paper we propose a discrete-time FIR (Finite Impulse Response) filter which is meant to be applied as a square root Nyquist filter and fractional delay filter simultaneously. The filter enables to substitute for a cascade of square root raised cosine (SRRC) Nyquist filter and fractional delay filter in one device/algorithm. The aim is to compensate for transmission delay in digital communication system. Performance of the filter in the role of a matched filter is evaluated using a newly defined energetic ISI (Intersymbol Interference) measure and ability of the filter to completely eliminate the ISI involved by fractional delay of symbol shaping filter in transmitter or by channel delay. Considerations and results of the contribution are documented by suitable eye-diagrams and the SRRC filter responses.

Experimental demonstration of a 10 Gb/s RSOA-based 16-QAM subcarrier multiplexed WDM PON

We experimentally demonstrate the performance of a 10 Gb/s subcarrier multiplexed (SCM) wavelength-division multiplexed (WDM) passive optical network (PON) using 2.5 Gbaud 16-QAM transmission signals. Digital signal processing (DSP) and square-root raised cosine (SRRC) pulse shaping enable both the uplink and downlink channels to achieve net spectral efficiencies up to 2.8 bit/s/Hz per channel using reflective semiconductor optical amplifier (RSOA)-based optical network units (ONUs) and economical 10 GHz intensity modulation and direct detection transceivers. We characterize the system's bit error rate (BER) performance over a 20 km single feeder PON with both remote continuous-wave (CW) seeding and full-duplex transmission scenarios, assuming standard forward error correction (FEC) codes.

The Design and FPGA Implementation of a Polyphase SRRC FIR Filter in DTMB

Polyphase FIR filters are applied in many practical Digital Signal Processing applications where the sampling rate needs to be changed. This paper focuses on the implementation of polyphase square root raised cosine (SRRC) FIR filter based on Field Programmable Gate Array (FPGA). The filter employs methods like filter's multiphase structure, symmetrical coefficients, I/Q channel multiplexing, pipeline addition and so on to design the SRRC filter. Compared with the traditional method, the designed FIR filter exhibits the advantages of high response speed and low hardware resource s consumption.

광대역 VHF 기저대역 모뎀의 효율적인 송·수신 기법

As an FMT (Filtered Multi-Tone) transmission method of Wideband VHF communication system specified by the ETS (European Telecommunications Standards) EN 300 392-2, this paper introduces three existing realization methods, i.e., the direct filtering method using different band SRRC (Square-Root Raised Cosine) filters for each subcarrier, the PPN-DFT method using the IDFT-PPN (Poly-Phase Network) and PPN-DFT at the transmitter and receiver, respectively, and the Extended DFT method. Then, it proposes the extended IDFT-SDFT (Sliding Discrete Fourier Transform) that computes the DFT values only for interested subcarriers every sample time, and shows that it has an advantage of blind symbol timing (using no training symbol) individually for each user signal (independently of other users` signals) in the multi-user environment where the subcarriers are assigned in contiguous or interleaved blocks to each user and each user signal possibly experiences different channels.

A New Peak Clipping Algorithm for PAPR Reduction in OFDM

The peak-to-average-power ratio (PAPR) is one of the major problems of Orthogonal Frequency Division Multiplexing (OFDM) systems. Various PAPR reduction techniques have been given in the past. Among these techniques, the clipping technique has been widely adopted as a practical scheme because of its low computational complexity and simplicity in implementation, while the pre-coding technique is known to provide good PAPR reduction with improved bit error rate (BER) performance. In this paper, a combination of clipping and pre-coding is proposed to reduce PAPR with almost same BER performance as given by individual pre-coding technique. The proposed technique gives good result because the clipping noise of combined scheme would be less than that of single clipping. Also the clipping used in this paper is not hard as used in conventional clipping. A new clipping algorithm is proposed which is based on averaging of high amplitude samples. In addition, an another pulse shape called modified Bartlett Hanning (MBH) is proposed to generate pre-coding matrix and its performance is compared with square root raised cosine (SQRC) pulse shape.dB.

DS-UWB 시스템에서 송신 필터에 따른 초기 동기 획득 성능 비교

본 논문에서는 DS-UWB 시스템에 사용되는 송신 필터에 따른 초기 동기 획득 성능을 모의 실험을 통해 비교하고, 칩 레이트가 1.32 Gchip/s인 DS-UWB 디지털 송신기에서 interpolation factor가 4인 제곱근 코사인 필터를 적용한 경우와 구형 필터를 적용한 경우 DS-UWB 수신기의 초기 동기 획득 성능은 AWGN 채널 환경뿐만 아니라 CM1/CM3 채널 환경하에서도 비슷한 성능을 냄을 실험을 통해 살펴 본다. 또한, 55 MHz의 시스템 클럭으로 동작하는 24 병렬 처리 상관 연산기 및 동기 획득기 구조에 대해 설명하고 초기 동기 획득 방법을 기술한다. 본 논문에서는 DS-UWB 시스템 설계시 구형 송신 필터를 사용하여 1.32 Gsample/s D/A 변환기 및 A/D 변환기를 적용할 수 있게 함으로써 DS-UWB 칩셋 개발시 현실적으로 고려할 수 있는 솔루션을 제시한다. In this paper, we compare the performance of initial timing acquisition in direct sequence ultra-wideband(DS-UWB) systems with different transmit pulse shaping filters through extensive computer simulations. Simulation results show that the timing acquisition performance of the DS-UWB system, whose chip rate is 1.32 Gchip/s, employing a rectangular transmit filter is similar to that employing a square root raised cosine(SRRC) filter with an interpolation factor of 4 in the realistic UWB channels(CM1 and CM3) as well as the additive white Gaussian noise(AWGN) channel. Additionally, we present both a 24-parallel digital correlator structure and a 24-parallel processing searcher operating at a 55 MHz system clock, and then briefly discuss the initial timing acquisition procedure. Because we can adopt an 1.32 Gsample/s digital-to-analog(D/A) converter and an 1.32 Gsample/s analog-to-digital(AID) converter in the DS-UWB system by employing the rectangular transmit filter, we have a realistic solution for the DS-UWB chipset development.

Modulation and Pre-Equalization Method to Minimize Time Delay in Equalization Digital On-Channel Repeater

This paper presents novel modulation and pre-equalization methods to minimize a signal processing time delay in the equalization digital on-channel repeater (EDOCR) for the ATSC terrestrial digital TV system. The proposed modulation method uses equi-ripple (ER) filter for vestigial side bands (VSB) pulse shaping instead of conventional square root raised cosine (SRRC) filter. And the proposed pre-equalization method calculates pre-equalizer filter coefficients by comparing a baseband signal as a reference signal and a demodulated repeater output signal, and then creates new VSB pulse shaping filter coefficients by the convolution of the ER filter and the pre-equalizer filter coefficients. The new VSB pulse shaping filter minimizes the time delay of EDOCR by adjusting the number of its pre-taps and also compensates the linear distortions due to the use of the ER filter and mask filter.

Performance of wavelet based Multi‐Chip Rate DS‐CDMA signals over multi‐path Nakagami‐m fading channels

AbstractMulti‐Chip Rate/Direct Sequence‐Code Division Multiple Access (MCR/DS‐CDMA) technique using scaled chip waveforms has been designed as an alternative to multi‐data rate DS‐CDMA techniques having constant chip rates. In this work, the probability of error (Pe) expression for MCR/DS‐CDMA signals is derived over multi‐path Nakagami‐m fading channels to investigate the effects of chip waveforms on it. This paper also proposes the use of orthogonal wavelets as chip waveforms of MCR/DS‐CDMA signals over the considered channel. For numerical calculations, Daubechies‐22 (D22) wavelet is used because its side lobes are 40 dB below its main lobe in frequency domain. D22 is compared with a Square Root Raised Cosine (SRRC) chip waveform. In the numerical calculations, only first four scales of the chip waveforms relating to four different chip/data rates are considered. The results for the Pe performance and the capacity (the number of user per Hertz for a same Pe level) show that D22 significantly outperforms the SRRC chip waveform at all data rates, due to low cross correlations among different scales of orthogonal wavelets. Besides, by increasing the number of scales, the advantage of the use of orthogonal wavelets will increase furthermore. Copyright © 2007 John Wiley &amp; Sons, Ltd.