Constant Amplitude Zero Autocorrelation Research Articles

Preamble-Based Symbol Timing Algorithms in OFDM Systems

In orthogonal frequency division multiplexing (OFDM) systems, a preamble is added at the start of the OFDM data frame in order to find the correct frame starting point. In the receiver, the symbol starting point is estimated by a correlation-based timing metric that uses the periodic properties of the preamble. In this study, a novel preamble structure using the constant amplitude zero autocorrelation (CAZAC) sequence is proposed. The performance of the timing synchronization algorithms has been compared with the proposed method in terms of mean squared error (MSE). The simulations are performed under additive white Gaussian noise (AWGN) and Rayleigh multipath fading channels. The simulation results indicate that our proposed method provides better timing MSE performance for the low signal-to-noise ratio (SNR) values.

Adaptive Modulation With CAZAC Preamble-Based Signal-to-Noise-Ratio Estimator in OFDM Cooperative Communication System

This paper presents an adaptive modulation in a single-input-single-output (SISO)-OFDM-based cooperative system that employs a Constant Amplitude Zero Autocorrelation (CAZAC) preamble-based SNR estimator. A novel CAZAC preamble-based SNR estimator that does not incur a throughput penalty is derived by exploiting a modified CAZAC preamble structure for the OFDM system. The proposed CAZAC SNR estimator is used to estimate the channel quality by finding the instantaneous SNR of the received cooperative data, which is sent to the transmitter via feedback channel. The modulation scheme is then changed according to the estimated SNR. The performance of the CAZAC preamble-based SNR estimator exhibits less than 0.02 dB and less than 0.2 dB bias when communicating over AWGN and SUI-5 channels, respectively. The proposed adaptive modulation scheme with the CAZAC SNR estimator significantly improved the channel throughput in comparison with the corresponding benchmarker scheme dispensing with adaptive modulation that invokes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PSK and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -QAM. More explicitly, the proposed adaptive modulation system with the CAZAC SNR estimator that invokes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PSK exhibits significant improvement by about 5 dB at BER=10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in comparison to its corresponding benchmarker scheme dispensing with adaptive modulation when communicating over the SUI-5 channel. On the other hand, the relay-aided cooperative transmission exhibited an approximately 6 dB SNR gain in terms of channel throughput in comparison to the corresponding non-cooperative benchmarker scheme, and benefited from spatial diversity.

Carrier frequency offset estimation for MIMO single-carrier FDMA system in wireless communication

Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems and Single-Carrier Frequency-Division Multiple Access (SC-FDMA) are so susceptible to carrier frequency offset (CFO) between transceivers. In this paper, a novel sequence called CAZBAR is proposed. The proposed CAZBAR sequence is based on constant amplitude zero autocorrelation (CAZAC) sequence and barker code. CAZBAR sequence shows better autocorrelation with higher peak at zero shift without ripples, which facilitates estimating carrier frequency offset in communication systems compared to other compensation methods in terms of mean square error (MSE). By applying CAZBAR sequence in MIMO SC-FDMA system 2 × 2 and 4×4, the bit error rate (BER) performance has improved significantly. At a BER=10-2, a SNR reduction of 11 dB is achieved for 2 × 2 system and 7 dB reduction for 4 × 4 system compared to other sequences. Which improves the performance of the whole system MIMO SC-FDMA. The CAZBAR sequence can be applied in 5G techniques, MIMO-OFDM, and MIMO SC-FDMA systems.

Cubic metric reduction for repetitive CAZAC sequences in frequency domain

In NR-based Access to Unlicensed Spectrum (NR-U) of 5G system, to satisfy the rules of Occupied Channel Bandwidth (OCB) of unlicensed spectrum, the channels of PRACH and PUCCH have to use some sequence repetition mechanisms in frequency domain. These repetition mechanisms will cause serious cubic metric(CM) problems for these channels, although these two types of channels are composed of Constant Amplitude Zero Auto-correlation(CAZAC) sequences.. Based on the characteristics of CAZAC sequences, which are used for PRACH and PUCCH (refer to PUCCH format 0 and format 1) in 5G NR, in this paper, we propose some new mechanisms of CM reduction for these two types of channels considering the design principles to ensure the sequence performance of the auto-correlation and cross-correlation. Then the proposed CM schemes are evaluated and the optimized parameters are further provided considering CM performance and the complexity.

SERDP: Signature‐based and energy‐efficient relay discovery protocol for Internet of Things in cellular networks

SummaryWith the proliferation of Internet of Things (IoT), a large number of devices are expected to connect to the Internet over different networks due to various demands and characteristics of IoT devices (IoTDs). One of the networks that will connect IoTDs to the Internet is cellular networks. The 3rd Generation Partnership Project (3GPP) proposes a connectivity model for cellular networks in which IoTDs connect to the network via relay devices. In this model, discovering the relay devices is a challenging task due to energy budget constraints, mobility of devices, and collision of discovery messages. Since IoTDs are constrained devices, it is important that they perform discovery with the minimum energy consumption by intermittently sleeping and waking up. In this paper, we propose signature‐based and energy‐efficient relay discovery protocol (SERDP) using Zadoff–Chu sequences. Since Zadoff–Chu is a Constant Amplitude Zero Autocorrelation (CAZAC) sequence, we use the sequence for pointing the active slots of the devices within the proposed three‐stage original period structure. The probabilistic analysis and simulation results show that SERDP discovers more devices with less energy consumption as well as preventing collisions, as compared with the existing protocols.

Performance-enhanced indoor MIMO-OFDM visible light communications using individual/joint CAZAC precoding techniques

In this paper, efficient individual and joint constant amplitude zero auto-correlation (CAZAC) precoding schemes are proposed to improve the performance of an indoor multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM)-based visible light communication (VLC) system. By considering the proposed precoding scheme, a 3×3 MIMO-OFDM VLC system with symmetrical and asymmetrical structure is set up, whose peak-to-average-power ratio (PAPR) of transmitted signal, signal-to-noise ratio (SNR), and bit error rate performance are investigated. It is shown that both individual and joint CAZAC precoding schemes can reduce the PAPR of the transmitted signal and make the SNR uniform over data subcarriers, resulting in significant performance improvement compared to the system without precoding. It is demonstrated that there are similar performance improvements for the MIMO-OFDM VLC system using the individual CAZAC precoding and joint CAZAC precoding in a symmetric scenario. At the expense of higher implementation complexity, the joint CAZAC precoding has more performance benefits than the individual CAZAC precoding for the VLC system with asymmetrical MIMO.

Acquisition and Tracking Performance of Satellite Navigation System Signal using Tiered Differential Polyphase Code

Abstract In this paper, we analyze the acquisition and tracking performance of signal using a tiered differential polyphase code as the secondary code. The Zadoff-Chu sequence is known to have a CAZAC (Constant Amplitude Zero Auto-Correlation) characteristics. The secondary code generated by differential encoding of the Zadoff-Chu sequence also has the same characteristics as the Zadoff-Chu sequence. Therefore, long integration will give better correlation results. We compare signal acquisition and tracking performance when using the NH sequence and Zadoff-Chu sequence as the secondary code. Monte-carlo simulation is performed using MATLAB. We use the probability of detection and the mean acquisition time for signal acquisition performance and tracking jitter for signal tracking performance.

Efficient Channel Estimation for Aerial Wireless Communications

We present a technique to jointly estimate the channel taps and the frequency offset due to the Doppler effect of a special class of doubly dispersive aeronautical channels. The algorithm includes the use of pulse repetition techniques at the transmitter and the “power method” subspace iteration at the receiver. We show that transmitting constant-amplitude zero-autocorrelation sequences for channel sounding yields estimators with low computational complexity. Numerical simulations indicate performance comparable to the estimation-theoretic lower bound.

Performance Enhanced 256-QAM BIPCM-DMT System Enabled by CAZAC Precoding

In the paper, bit-interleaved polar-coded modulation discrete multi-tone (DMT) (BIPCM-DMT) with 256-QAM enabled by constant amplitude zero auto-correlation (CAZAC) precoding is proposed and experimentally demonstrated in a low-cost intensity-modulation and direct-detection (IM-DD) system. In order to conquer the fading effect on mapped bit-levels, two types of interleaver including quadratic polynomial permutation (QPP) interleaver and random interleaver are compared to optimize the system performance. However, for 256-QAM BIPCM-DMT system, the signal-to-noise ratio (SNR) fades dramatically as the data subcarrier index increases, it is difficult to match the well-designed operating point of Monte Carlo in the process of polar code construction. Thus, the precoding schemes including CAZAC and orthogonal circulant transform (OCT) are proposed to equalize the uneven SNRs in BIPCM-DMT system. Compared with the bit / power loading and pre-equalization schemes, it will greatly reduce the cost and complexity of the system because channel information obtained by the transmitter via round-trip feedback is not considered. In addition, CAZAC precoding is selected to optimize the BIPCM-DMT system because it is superior to OCT precoding in reducing PAPR. The experimental results show that aided by CAZAC precoding, 20.63 Gb/s BIPCM-DMT signal can be received with an error-free over 50-km standard single-mode fiber (SSMF). Furthermore, compared with BIPCM-free, only CAZAC precoding, and only random interleaver schemes, the proposed scheme can achieve Q-factor enhancement of 4.82 dB, 2.46 and 1.78 dB, respectively, at the received optical power (ROP) of −5 dBm.

An Anti-Interference Synchronization for OFDM Systems Based on Scrambling Sequence

To improve the performance of the synchronization in OFDM systems in the presence of interference, a new synchronization algorithm based on scrambling sequence is proposed in this paper, which redesigns the training sequence with the constant amplitude zero auto-correlation (CAZAC) sequence and an extra scrambling operation. Compared with the traditional scrambling sequence-based algorithm, the simulations carried out both in AWGN and COST 207 4-path rural area (RA) channel show that the proposed synchronization algorithm can still maintain the sharper correlation peak, and achieve accurate symbol timing estimation and carrier frequency offset (CFO) estimation in the interference environment, with a lower out-of-band energy of the spectrum due to a new scrambling sequence. Furthermore, owing to the particularity of the component elements from the scrambling sequence, a low complexity implementation structure is presented here to realize the correlation function of the proposed algorithm with fewer hardware resources.

Chromatic Dispersion Estimation Based on CAZAC Sequence for Optical Fiber Communication Systems

We propose a chromatic dispersion (CD) estimation method based on constant amplitude zero-autocorrelation (CAZAC) sequence and fractional Fourier transform (FrFT) algorithm for optical fiber communication systems, which extends the application of CAZAC sequence. By applying FrFT on the CAZAC sequence signal, the optimal order is searched and employed to estimate the accumulated CD because that the CAZAC sequence shares similar properties with chirp signal. We demonstrate the feasibility of the proposed method by the simulation of a 28 GBaud polarization-division-multiplexed (PDM) quadrature phase-shift keying (QPSK) optical fiber communication system. The error of CD estimation is less than 70 ps/nm for the standard single mode fiber (SSMF) link of 2000 km with OSNR in the range of 10–20 dB and the launch power in the range of 0–4 dBm per channel in a five channel system. It shows that the method is robust to ASE noise and optical fiber nonlinearity. Furthermore, the proposed method has been experimentally verified with the error of CD estimation less than 50 ps/nm after 100–900 km fiber link transmission.

Timing and Integer Frequency Offset Estimation for DLMT System over Time-Varying Rayleigh Fading Channel

In this paper, we study the timing and integer carrier frequency offset (ICFO) estimation problem for dynamic lattice multicarrier transmission (DLMT) system over time-varying Rayleigh fading channel. Firstly, a novel preamble structure based on two constant amplitude zero auto-correlation (CAZAC) sequences is designed for DLMT system. Then, by using the designed dual-CAZAC preamble, a discrete cross ambiguity function (DCAF) based timing and ICFO estimation algorithm is proposed. Simulation results show that the proposed DCAF based timing and ICFO estimation algorithm can mitigate the impact of time-varying multipath Rayleigh fading channel and outperforms traditional estimators on the correct estimation probability performance.

A Novel CAZAC Sequence Based Timing Synchronization Scheme for OFDM System

Several classical timing synchronization schemes have been proposed for the timing synchronization in OFDM systems based on the correlation between identical parts of OFDM symbol. These schemes show poor performance due to the presence of plateau and significant side lobe. In this paper we present a timing synchronization schemes with timing metric based on a Constant Amplitude Zero Auto Correlation (CAZAC) sequence. The performance of the proposed timing synchronization scheme is better than the classical techniques

A novel timing synchronization for CO-OFDM systems using CAZAC sequences

A novel symbol timing synchronization algorithm based on constant amplitude zero auto correlation (CAZAC) sequences is proposed for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The training symbol of the proposed algorithm is comprised of four different parts, utilizing even symmetry property of each part to accomplish timing synchronization. The performance of the proposed algorithm is demonstrated by means of simulations in OFDM and CO-OFDM systems. The proposed algorithm is shown to eliminate the timing sidelobes of Park’s algorithm and has a more accurate timing estimation. In the condition of chromatic dispersion (CD), the timing metric of the proposed method still maintains its peak value at the correct timing point, while the values are almost 0 at all the other positions. Meanwhile, the timing mean square error (MSE) of the proposed algorithm remains around 10-6.

High speed single-wavelength modulation and transmission at 2 μm under bandwidth-constrained condition.

The 2-μm optical band has gained much attention recently due to its potential applications in optical fiber communication systems. One constraint in this wavelength region is that the electrical bandwidth of components like modulators and photodetectors is limited by the immature manufacturing technologies. Here we experimentally demonstrated the high-speed signal generation and transmission under bandwidth-constrained scenario at 2-μm. It is enabled by the direct-detection optical filter bank multicarrier (FBMC) modulation technique with constant amplitude zero autocorrelation (CAZAC) equalization. We achieved a single wavelength 80 Gbit/s data rate using the 16-QAM FBMC modulation format which is the highest single channel bit rate at 2-μm according to our best knowledge. The signal is transmitted through a 100m-long solid-core fiber designed for single-mode transmission at 2-μm. The measured bit error rates of the signals are below the forward error correction limit of 3.8 × 10-3, and the 100m-fiber transmission brings negligible penalty.

Constructing Tight Gabor Frames Using CAZAC Sequences

The construction of finite tight Gabor frames plays an important role in many applications. These applications include significant ones in signal and image processing. We explore when constant amplitude zero autocorrelation (CAZAC) sequences can be used to generate tight Gabor frames. The main theorem uses Janssen’s representation and the zeros of the discrete periodic ambiguity function to give necessary and sufficient conditions for determining whether any Gabor frame is tight. The relevance of the theorem depends significantly on the construction of examples. These examples are necessarily intricate, and to a large extent, depend on CAZAC sequences. Finally, we present an alternative method for determining whether a Gabor system yields a tight frame. This alternative method does not prove tightness using the main theorem, but instead uses the Gram matrix of the Gabor system.

Synchronization Sequence Design for FBMC/OQAM Systems

In this paper, we propose a new sequence generation methodology to make a constant amplitude zero autocorrelation (CAZAC) preamble available in offset Quadrature Amplitude Modulation-based filter bank multicarrier (FBMC) synchronization. The role of the new sequence is to compensate the filtering and symbol overlap of the FBMC structure so as to finally be able to make a CAZAC preamble in time domain. To derive the new sequence, we formulate a symbol overlap model that shows the relation between the new sequence and a CAZAC preamble. On the other hand, the offset modulation format is a constraint that needs to be considered in the design of the new sequence. By using a property of this offset modulation constraint, we derive a closed-form expression of the new sequence from the symbol overlap model. In addition, we extend an advanced model to create a pseudo-CAZAC preamble that is not data-dependent, thus enabling convenience of implementation. Simulation results show the superiority of the proposed model with respect to synchronization accuracy, out-of-band radiation, and peak to average power ratio. Moreover, we verify that the proposed model is well-suited for use in the cellular environment through complexity and resource efficiency comparisons.

A PAPR Joint Optimization Algorithm in AF Cooperative Multicarrier System

In this paper, to reduce PAPR (Peak-to-Average Power Ratio) in AF (Amplify and Forward) cooperative multicarrier system, an SLM-TR (Selective Mapping-Tone Reservation) joint optimization algorithm based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence is proposed. In our proposed method, several carriers are reserved for tone candidates, and then SLM (Selective Mapping) algorithm is utilized for the remaining data carriers. In SLM procedure, CAZAC sequences are utilized as the initial phase vector candidates and phase vector optimization is further processed by using feedback phase rotation algorithm for data carriers. After that, in continued TR (Tone Reservation) operation, random sequence is considered as the initial tone sequence and further optimized and subtracted from the modified data signal for peak cancelling using cyclic transposition searching algorithm to further reduce PAPR. Finally, the signal with the lowest PAPR is transmitted. By doing so, not only exhausting searching for optimal phase vectors is avoided efficiently, but also additional PAPR reduction is achieved by tone sequence modification. Simulation results show that the proposed method can reduce PAPR considerably and improve BER (Bit Error Rate) performance effectively, with insurance of high spectrum efficiency, low complexity and low loss in power efficiency. The influences of several conditions such as HPA (High power Amplifier) type, initial phase vector number, tone carrier number and sequence type are discussed to improve system QoS(Quality of Service).

A Joint Timing Offset and Channel Estimation Using Fractional Fourier Transform and Cazac Sequences

This paper deals with symbol timing offset and channel estimation in OFDM (orthogonal frequency division multiplexing) system in fast varying channel. Symbol timing offset (STO) estimation is a major task in OFDM. Most of existing methods for estimating STO used cyclic prefix or training sequences. In this paper, we consider a new system for STO estimation using constant amplitude zero autocorrelation (CAZAC) sequences as pilot sequences in conjunction with fractional Fourier transform (FRFT). After STO estimation is done, timing compensation is made. Thereafter, channel is estimated to well recover the original transmitted signal. This method gives good results in terms of MSE in comparison with other known techniques, it estimated well the channel and it is important for fast varying channel. MATLAB Monte-Carlo simulations are used to evaluate the performance of the proposed estimator.

Joint timing and frequency synchronization based on weighted CAZAC sequences for reduced-guard-interval CO-OFDM systems.

A novel joint symbol timing and carrier frequency offset (CFO) estimation algorithm is proposed for reduced-guard-interval coherent optical orthogonal frequency-division multiplexing (RGI-CO-OFDM) systems. The proposed algorithm is based on a constant amplitude zero autocorrelation (CAZAC) sequence weighted by a pseudo-random noise (PN) sequence. The symbol timing is accomplished by using only one training symbol of two identical halves, with the weighting applied to the second half. The special structure of the training symbol is also utilized in estimating the CFO. The performance of the proposed algorithm is demonstrated by means of numerical simulations in a 115.8-Gb/s 16-QAM RGI-CO-OFDM system.