Bin Tian

A method for PAPR reduction in MSE-OFDM systems

High peak to average power ratio (PAPR) of the transmitted signal is a major drawback of multicarrier transmission such as orthogonal frequency division multiplexing (OFDM). This work considers the problem of PAPR reduction in a multi-symbol encapsulated OFDM (MSE-OFDM) system. This paper employs the discrete cosine transform (DCT) to the data sequence. Not only can this method have the same bandwidth efficiency as that of the CP-reduced MSE-OFDM system, but also reduce the PAPR in the MSE-OFDM. Simulation shows that the proposed scheme can significantly reduce the PAPR in MSE OFDM system without increasing the symbol error rate.

A Time Slicing Adaptive OFDM System for Mobile Multimedia Communications

Multi-Symbol Encapsulated-Orthogonal Frequency Division Multiplexing (MSE-OFDM) is an adaptive OFDM system which was proposed earlier to meet the overwhelming needs of spectrum-efficient wireless communication systems. In this technique, one cyclic prefix (CP) is used for multiple OFDM symbols. The motivation for MSE-OFDM is to mitigate two major inherited disadvantages of OFDM system at the same time i.e., the sensitivity to carrier frequency offset (CFO) and high peak to average power ratio (PAPR). In this paper, we propose a new time slicing technique where the cyclic prefix is replaced with the precoded pseudo-random sequence for MSE-OFDM system. Therefore it is possible to multiplex multiple data streams using this technique with dynamic data rates for mobile multimedia communications. It also overcomes disadvantages with other techniques such as high sensitivity to frequency offset inherited with Orthogonal Frequency Division Multiple Access (OFDMA) system and complex equalization problem with conventional Single Carrier-Frequency Division Multiple Access (SC-FDMA). Therefore this technique can be used for both uplink and downlink transmissions of mobile multimedia communications with variable data rates. With those inherent advantages of proposed time slicing technique which is compatible to DVB-H standard, power saving for mobile receivers is enabled and therefore extended battery life can be guaranteed which is very important for the mobile users.

A Hybrid Domain Block Equalizer for Single-Carrier Modulated Systems

Poor performance in the presence of multipath with long delay spread has been considered as one of the main weaknesses of most single carrier modulated systems, including ATSC (advanced television systems committee) system. The introduction of distributed transmission network and single frequency network brings new challenges for the ATSC equalizer design, since the delay spread of a multipath channel under such scenarios becomes significantly longer than the traditional broadcasting practice of using one high power transmitter to cover a wide area, where the multipath distortion is mainly from reflected echoes. An iterative hybrid frequency-time domain equalizer for ATSC system is proposed in this paper based on our block-based interference analysis. The multipath distortion in the received ATSC signal is first tentatively removed with a frequency domain equalizer on a block-by-block basis. However, inter-block and intra-block interferences still exist due to the lack of cyclic structure in the received ATSC signal. A time domain interference cancellation algorithm is then used to cancel the inter-block interference and intra-carrier interference, based on the tentative decisions in time domain after the frequency domain equalization. These two steps are iterated until desired receiver performance is achieved. The proposed equalizer and the subsequent analysis are verified through numerical simulations.

PAPR Reduction of OFDM Signals With Minimized EVM via Semidefinite Relaxation

In this paper, we exploit convex optimization techniques for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) signals. Our optimization strategy is to minimize error vector magnitude (EVM) with constraints of PAPR and free carrier power overhead. Then, a nonconvex quadratic program is obtained, which is computationally difficult. By utilizing the semidefinite relaxation (SDR) technique, the optimization model is relaxed to a semidefinite program, which can be efficiently solved using polynomial time. On top of this, we use the rank minimization technique to improve the proposed model. Simulation results demonstrate that the optimized OFDM signals have quasi-constant PAPR values and are not sensitive to the nonlinear effects of the power amplifier in comparison with other approaches.

A fast synchronization technique for DVB-H receiver using in-band pilots and cyclic prefix

A new fast time synchronization technique is proposed for DVB-H receiver in this paper. Only one DVB-H OFDM symbol is needed to achieve accurate time synchronization by using the correlation function of the received signal and four time-domain local references generated from the DVB-H scattered pilots. The computation complexity of the new algorithm is further reduced by limiting the range of correlation function, which is realized by exploiting the cyclic property of the OFDM signal

A Novel Hybrid CFO Estimation Scheme for UFMC-Based Systems

In this letter, a robust hybrid carrier frequency offset (CFO) estimation scheme based on training symbols is devised for universal-filtered multi-carrier (UFMC) based systems. In this scheme, the CFO estimator based on a least square (LS) criterion is first derived to acquire a coarse frequency offset estimation with the use of a large frequency searching step. And then, the residual frequency offset is accurately estimated through the auto-correlation operation of received signals, which have been compensated. This algorithm has the features of larger estimation range as well as higher estimation precision. Through numerical simulations, it is validated that the performance of the proposed algorithm is better than that of existing algorithms.

On the Computational Complexity of MSE-OFDM System using Pseudo Random Cyclic Prefix

A new multicarrier system, termed multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), was proposed earlier, in which one cyclic prefix (CP) is used for multiple OFDM symbols. The motivation of this proposal is to address the disadvantages of OFDM system, i.e., the high peak to average power ratio and sensitivity to carrier frequency offset at the same time. Although more robust performance and higher bandwidth efficiency are achieved, the implementation of the MSE-OFDM receiver is substantially more complicated than OFDM. In this paper, we propose a new cyclic prefix using pseudo random sequence for MSE-OFDM. With the new introduced cyclic prefix, the inter-symbol interference (ISI) within one MSE-OFDM frame can be easily canceled in time domain. It is shown that the implementation complexity of the MSE-OFDM receiver with the new cyclic prefix is comparable to the traditional OFDM. The performance of the proposed technique is also analyzed and verified through numerical simulations.

Quasi-Orthogonal Time Division Multiplexing and Its Applications under Rayleigh Fading Channels

Based on the principle that inserting N-l equally spaced zeros between each pair of samples is equivalent to sampling the original signal at rate of N times the Nyquist sampling rate. The representation of the quasi-orthogonal time division multiplexing (QOTDM) signal in both time and frequency domain was investigated for QOTDM system. The spectrum of QOTDM signal is the overlapping spectrum of each parallel signal which is rotated a certain angle in phase. Comparisons between QOTDM and orthogonal frequency division multiplexing (OFDM) was made in terms of bit error rate (BER) in Rayleigh fading channels. Simulation results indicate that the proposed QOTDM system does not have an error floor as OFDM does, and QOTDM is more robust against Rayleigh fading in high signal-to-noise ratio (SNR) region (larger than 14 dB) compared with OFDM.

A Frequency Domain Equalizer with Iterative Interference Cancellation for Single Carrier Modulation Systems

Recently, the growing popularity of low-complexity multi-carrier modulation techniques, such as orthogonal frequency division multiplexing (OFDM), has led researchers to consider equalization of single carrier (SC) transmissions in the frequency domain. However, existing frequency domain equalizers for single carrier modulation rely on the introduction of a cyclic prefix (CP), which are usually not available in the conventional SC based communications standards. In this paper, a frequency domain equalizer (FEQ) without cyclic prefix for single carrier system is proposed. An interference analysis is presented for the block equalization of SC system without CP. The cancellation of the inter-block interference and inter-carrier interference are based on the proposed iterative interference cancellation. The proposed equalizer and the subsequent analysis are also verified through numerical simulations.

An effective approach for parameter determination of the digital phase-locked loop in the z-domain

In digital communication systems, typical methodologies in determining loop parameters of the digital phase-locked loop (DPLL) are based on the mapping transformation from the analog domain to the digital domain. However, such transform based algorithms are relatively complicated and not straightforward, and they also cause the problem that loop parameters are affected by the pre-detection integration time greatly. To solve these issues, an effective direct method of determining loop parameters of the second-order DPLL in the z-domain is proposed in this paper. Through ascertaining specific positions of the closed-loop system functions poles inside the right-hand side of the z-planes unit circle, unknown parameters are calculated directly and flexibly in this method, which enables the DPLL to acquire good low-pass filtering characteristic and system stability. This novel method not only reduces the complexity of solving the parameters, but also eliminates the effect of the pre-detection integration time on loop parameters. Simulation results are provided to confirm the feasibility of the proposed method and to show that the DPLL obtained by this method achieves the similar tracking performance to the discretized PLL.