Zadoff-Chu Matrix Transform Research Articles

Precoding-enabled OFDM-ROF transmission system with self-pumping structure

Precoding-enabled orthogonal frequency division multiplexing (OFDM) is proposed in radio-over-fiber (ROF) system based on a flexible self-pumping structure. Different from the use of two lasers, one laser-driven Mach-Zehnder modulator generates multiple spectra and forms self-pumping structures by selecting signal and pump light, which can effectively reduce the system cost and eliminate the laser phase conversion noise. The signal-to-noise ratio (SNR) of OFDM-ROF fluctuates wildly induced by non-ideal frequency response of optical/electrical devices and channel fading effects, and the BER performance is severely deteriorated. Therefore, seven common channel-independent precoding techniques are used and evaluated for the OFDM-ROF systems. The analysis of the results shows that seven precoding techniques can equalize uneven SNR on data subcarriers. Meantime, constant amplitude zero autocorrelation sequence-based matrix transform (CAZACT), Zadoff-Chu matrix transform (ZCT), discrete Fourier transform (DFT) have significant advantages in reducing the peak-to-average power ratio (PAPR). When the received optical power (ROP) is −3dBm, the BERs of the system under the seven precoding schemes are all lower than the hard decision - forward error correction threshold (HD-FEC). In addition, receiver sensitivity and comb flatness gain can also be achieved by the precoded OFDM compared to the conventional OFDM.

Experimental Demonstration of Zadoff–Chu Matrix Transform Precoding for MIMO-OFDM Visible Light Communications

Visible light communication (VLC) based on a light-emitting diode (LED) is considered to be a potential candidate for the next-generation communication. In this paper, a novel Zadoff–Chu matrix transform (ZCT) precoding is proposed to improve the performance of the traditional space-time block coding- (STBC-) based multiple-input multiple-output and orthogonal frequency division multiplexing (MIMO-OFDM) system. Compared with the existing orthogonal circulant matrix transform (OCT) precoding scheme, the proposed ZCT precoding achieves a much lower peak-to-average power ratio (PAPR) while maintaining the advantage of the uniform signal-to-noise ratio (SNR), which reduces the performance loss caused by LED nonlinearity. To study the system performance further, we set up an experimental demonstration to verify performance improvement under the condition of different driving peak-to-peak voltages (Vpps) and direct current (DC) offsets. Experimental results show that ZCT precoding gains the best bit error rate (BER) performance compared with the traditional and the OCT precoding MIMO-OFDM systems, whose BER is always below the 7% pre-forward error correction (pre-FEC) threshold of 3.8 × 10−3.

Comparison of Different Precoding Techniques for Unbalanced Impairments Compensation in Short-Reach DMT Transmission Systems

Channel independent precoding technique has been widely used in optical discrete multi-tone (DMT) transmission systems to compensate unbalanced impairments induced by bandwidth limitations and imperfect frequency responses of electrical/optical devices and various interferences. However, the comparison of different precoding techniques in terms of peak-to-average power ratio (PAPR) reduction, nonlinear distortion tolerance, implementation complexity, and bit error rate (BER) improvements has not been fully studied. In this article, we comparatively investigate seven most commonly used precoding techniques, i.e., discrete Fourier transform (DFT), orthogonal circulant matrix transform (OCT), constant amplitude zero autocorrelation sequence-based matrix transform (CAZACT), Zadoff-Chu matrix transform (ZCT), discrete cosine transform (DCT), discrete Hartley transform (DHT), and Walsh-Hadamard transform (WHT), through both numerical simulations and offline experiments. Simulations show that the ZCT can achieve the best PAPR reduction, and the OCT cannot reduce the PAPR. Besides, DFT, CAZACT, ZCT, DCT, and DHT precoded DMT signals have superior error vector magnitude performance after passing through nonlinear models. And the corresponding precoded QPSK-DMT signals have better BER performance than both OCT/WHT precoded and conventional ones in the distortion-limited scenarios. However, the precoded 16/64QAM-DMT signals, excluding OCT precoded one, are more sensitive to nonlinear distortions and provide minor BER improvement or even may degrade the BER performance. Complexity analysis exhibits the WHT precoding does not require multiplications and therefore has the lowest implementation complexity. In the inter-symbol interference-limited case, OCT precoding can still achieve a good signal-to-noise ratio (SNR) balance and provide the best BER performance. A simple timing synchronization point adjustment (TSPA) method is employed to enhance SNR balance. Simulated and experimental results exhibit that similar BER performance can be achieved by using these precoding techniques together with TSPA in noise-limited scenarios. Considering the implementation complexity, WHT precoding may be a good option to compensate unbalanced impairments in the short-reach DMT transmission system.

Hybrid Zadoff‐Chu and multilateral piecewise exponential companding transform–based PAPR reduction technique in OFDM systems

SummaryThe orthogonal frequency‐division multiplexing (OFDM) is a multicarrier modulation system that is used to transmit the large volume of data to the receiver. Reducing the peak‐to‐average power ratio (PAPR) in OFDM system is one of the demanding and crucial task in recent days. For this reason, various precoding and companding mechanisms are developed in the traditional works, but it remains with the limitations of increased complexity, reduced performance, and nonlinear distortion. The reduction of PAPR is achieved by minimizing the companding distortion with the enhancement of the bit error rate (BER) performance significantly. Then, in order to avoid clipping in OFDM, a multilateral piecewise exponential companding transform (MPECT) method has been utilized rather than using piecewise exponential companding transform (PEC) where PAPR is getting reduced. The OFDM is very sensitive to synchronizing error. To overcome this sensitivity, employ the Zadoff‐Chu sequence to carrier frequency offsets. Zadoff‐Chu matrix transform (ZCMT) has numerous merits among the other ODFM systems such as the improvement in the performance of the channels that are fading away and provides an ideal periodic autocorrelation and a constant magnitude periodic cross correlation. Both of these techniques provide improvement in the ODFM systems. To get more efficiency, this paper aims to develop a hybrid technique by integrating the ZCMT and MPECT techniques for reducing the PAPR in OFDM systems. Further, convolutional encoding is applied for better BER and PAPR. The simulation results of the proposed ZCMT‐MPECT technique are evaluated and compared with the conventional OFDM and other precoding methods.

Chaotic reconfigurable ZCMT precoder for OFDM data encryption and PAPR reduction

A secure orthogonal frequency division multiplexing (OFDM) transmission scheme precoded by chaotic Zadoff–Chu matrix transform (ZCMT) is proposed and demonstrated. It is proved that the reconfigurable ZCMT matrices after row/column permutations can be applied as an alternative precoder for peak-to-average power ratio (PAPR) reduction. The permutations and the reconfigurable parameters in ZCMT matrix are generated by a hyper digital chaos, in which a huge key space of ∼10800 is created for physical-layer OFDM data encryption. An encrypted data transmission of 8.9 Gb/s optical OFDM signals is successfully demonstrated over 20 km standard single-mode fiber (SSMF) for 16-QAM. The BER performance of the encrypted signals is improved by ∼2 dB (BER@10−3), which is mainly attributed to the effective reduction of PAPR via chaotic ZCMT precoding. Moreover, the chaotic ZCMT precoding scheme requires no sideband information, thus the spectrum efficiency is enhanced during transmission.

Improved nonlinear tolerance in ultra-dense WDM OFDM systems

This paper demonstrates and experimentally validates the Zadoff–Chu matrix transform (ZCT) precoding as a peak-to-average power ratio (PAPR) reduction technique for coherent optical orthogonal frequency division multiplexing (OFDM) over ultra-dense wavelength division multiplexing (UDWDM). The work provides performance comparison between conventional and the precoded UDWDM–OFDM system. The system use case was implemented by 16-QAM–OFDM modulated channels among 3.5GHz, 7GHz, and 10GHz channel spacings scenarios. The ZCT precoding approach improves the nonlinear tolerance in UDWDM–PON systems. The performance in terms of error vector magnitude (EVM) and bit error rate (BER) is presented after transmission over 40km of standard single mode fiber (SSMF). The results show a significant EVM improvement considering the aforementioned channel spacings and for different number of UDWDM channel groups in the nonlinear regime operation. The implemented ZCT precoding system outperforms the non precoded approaches in terms of EVM and BER results.

Zadoff–Chu Matrix Transform Precoding-Based Orthogonal Frequency Division Multiple Access Uplink Systems: A Peak-to-Average Power Ratio Performance

High peak-to-average power ratio (PAPR) is one of the major drawbacks in orthogonal frequency division multiple access (OFDMA) systems. In this paper, we present two new Zadoff–Chu matrix transform (ZCMT) precoding-based OFDMA uplink systems, ZCMT precoding-based distributed OFDMA uplink system and ZCMT precoding-based localized OFDMA uplink system with reduced PAPR. The proposed systems are based on precoding the constellation symbols with the ZCMT precoder before subcarrier mapping to keep the PAPR low. The PAPR of the proposed systems is analyzed with root-raised-cosine pulse shaping to keep out of band radiation low and to meet the transmission spectrum mask requirement. Simulation results show that the proposed systems have better PAPR than the Walsh–Hadamard transform (WHT)precoded OFDMA uplink systems and the conventional OFDMA uplink systems.

BER Reduction in OFDM Systems using ZCT Matrix Transform

In recent years, Orthogonal Frequency Division Multiplexing (OFDM) is preferred for transmission over a dispersive channel. It is because of its several advantages such as high spectral efficiency, low implementation complexity, less vulnerability to echoes and non–linear distortion. However, it has few limitations such as peakto-average-power ratio (PAPR) and bit error rate (BER), which determines the system’s power efficiency. High PAPR is one of the major drawbacks in OFDM systems, which causes a significant level of signal distortions, when the modulated signals are amplified through high power amplifiers (HPAs). In particularly, high PAPR increases the complexity of Analogue to Digital (A/D) and Digital to Analogue (D/A) converters and also reduces the efficiency of HPAs. A high PAPR and high noise (e.g. AWGN) may significantly distort the signal, resulting in high BER on demodulation of the received signal. Therefore, PAPR & BER reduction is very essential. For this purpose, a Zadoff-Chu matrix Transform (ZCT) based precoding and postcoding techniques are quantitatively evaluated in this paper in terms of its parameters q and r. From the analysis, it is inferred that an optimum selection of q and r can lead to a significant level of reduction in BER.

PAPR reduction in mobile WiMAX: A new ZCMT precoded random interleaved OFDMA system

Mobile WiMAX (worldwide interoperability for microwave access) air interface adopts orthogonal frequency division multiple access (OFDMA) as multiple access technique for its uplink (UL) and downlink (DL) to improve the multipath performance. All OFDMA based networks, like mobile WiMAX, experience the problem of high peak-to-average power ratio (PAPR). The high PAPR increases the complexity of analog-to-digital (A/D) and digital-to-analog (D/A) convertors, and also reduces the efficiency of RF high-power-amplifier (HPA). In this work, a new zadoff-chu matrix transform (ZCMT) precoding based random interleaved orthogonal frequency division multiple access (OFDMA) system was proposed for PAPR reduction in mobile WiMAX system. The system is based on precoding the constellation symbols with the ZCMT precoder before subcarrier mapping. The PAPR of proposed system is analyzed with the root-raised-cosine (RRC) pulse shaping to keep out of band radiation low and meet the transmission spectrum mask requirement. Simulation results show that the proposed system has better PAPR gain than the hadamard transform (WHT) precoded random interleaved OFDMA systems and the conventional random interleaved OFDMA systems. Symbol-errorrate (SER) performance of the system is also better than the conventional random interleaved OFDMA systems and the random interleaved OFDMA systems with WHT. The good improvement in PAPR significantly reduces the cost and the complexity of the transmitter.

A ZCMT Precoding Based Multicarrier OFDM System to Minimize the High PAPR

This paper presents a Zadoff-Chu matrix transform (ZCMT) precoding based multicarrier orthogonal-frequency-division-multiplexing (OFDM) system to minimize the high peak-to-average power ratio (PAPR). In the proposed system, ZCMT kernel is applied to the constellation symbols which not only reduces PAPR but also improves bit-error-rate (BER) performance. The ZCMT precoded OFDM signals allow the radio-frequency high-power-amplifier (HPA) to operate near its saturation level, thus maximize the power efficiency. Extensive computer simulations have been performed to analyze the PAPR, BER and power-spectral-density (PSD). Simulation results show that the proposed system has excellent PAPR gain and BER performance with no spectral distortion.

A Novel Zadoff-Chu Matrix Transform Precoded Interleaved-OFDMA Uplink System for 4G Cellular Systems: Peak to Average Power Ratio Performance

High Peak to Average Power Ratio (PAPR) is one of the major drawbacks in the Orthogonal Frequency Division Multiple Access (OFDMA) systems. In this paper, we present a novel Zadoff-Chu Matrix Transform (ZCMT) precoding based Interleaved-OFDMA uplink system with improved PAPR for the upcoming 4G cellular systems. The proposed system is based on the precoding of constellation symbols with ZCMT precoder in such a way that the system becomes Constant Envelope OFDMA (CE-OFDMA). The CE-OFDMA signal allows the Radio-Frequency (RF) high power amplifier to operate near its saturation levels, thus maximize the power efficiency. However, even 0 db PAPR or CE-OFDMA systems must contend with pulse shaping to keep out of band radiation low and to meet the transmission spectrum mask requirement. Hence, the PAPR is analyzed with Root Raised Cosine pulse shaping. Simulation results show that proposed system has better PAPR gain than the walsh-hadamard transform (WHT) precoded Interleaved-OFDMA uplink systems and the conventional Interleaved-OFDMA uplink systems.

A Zadoff-Chu Matrix Transform Precoding Based Localized-Ofdma Uplink System: A Papr Analysis With RRC Pulse Shaping

High peak-to-average power ratio (PAPR) is one of the major drawbacks in the orthogonal frequency division multiple access (OFDMA) systems. In this paper, we present a zadoff-chu matrix transform (ZCMT) precoding based localized OFDMA uplink system with improved PAPR. The proposed system is based on precoding the constellation symbols with ZCMT precoder. Extensive computer simulations have been performed to analyze the PAPR of the proposed system with the root-raised-cosine (RRC) pulse shaping. Simulation results show that, the proposed system has better PAPR gain than the hadamard-transform (WHT) precoded Localized-OFDMA uplink systems and the conventional Localized-OFDMA uplink systems.