Guangliang Ren

Synchronization method based on a new constant envelop preamble for OFDM systems

The synchronization method using the available constant envelop preamble is analyzed, and a new preamble weighted by pseudo-noise sequence is proposed, with which a novel timing and frequency offset estimation method is presented for orthogonal frequency division multiplexing (OFDM) systems in this paper. By the proposed method, the accuracy of the timing offset estimator is significantly improved, and the estimate range of the frequency offset estimator is greatly enlarged with no loss in accuracy. The performance of the proposed method is demonstrated by simulations.

SNR estimation algorithm based on the preamble for OFDM systems in frequency selective channels

We propose a new SNR estimation method based on the preamble for OFDM systems in frequency selective channels. The OFDM training symbols in the preamble are equalized by the known data in frequency domain and employed to estimate the noise variance. The second order moments of the received symbols are used to estimate the signal plus noise power in the OFDM packets. The SNRs on the subchannels and the average SNR of the packets can all be estimated. Simulation results show that the proposed method is robust to frequency selectivity in wireless channels, and its performance is considerably improved compared with the available methods.

A complementary clipping transform technique for the reduction of peak-to-average power ratio of OFDM system

A novel transform technique is proposed for reducing the peak-to-average ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. Large OFDM signals are replaced by small complementary signals according to the proposed method. It has a low SNR loss in bit error rate while achieving a significant reduction of PAPR. It is shown by computer simulations that the proposed method can outperform the well-known clipping filtering scheme and /spl mu/-law companding technique substantially.

A TDOA location scheme in OFDM based WMANs

A time difference of arrival (TDOA) location scheme for the orthogonal frequency division multiplexing (OFDM) based wireless metropolitan area networks (WMANs) is presented. A novel TDOA estimation algorithm for OFDM signals is proposed and adopted in this scheme. The algorithm enhances the location performance by utilizing the information in the time and frequency domains obtained from the received location OFDM signals. The simulations are implemented with an 802.16e configuration considering an outdoor wireless scenario. The simulation results show that the scheme can meet the E911 requirements in even complex multipath channel conditions, and outperform the location schemes with traditional correlation detection TDOA estimations.

An Efficient Frequency Offset Estimation Method With a Large Range for Wireless OFDM Systems

An efficient frequency offset estimation method is proposed for wireless orthogonal frequency-division multiplexing (OFDM) systems. In the proposed method, the received samples of the training symbol are processed by a novel envelop equalized processing method, and the estimation of the frequency offset in the OFDM systems turns out to be the frequency estimation of a complex tone. A novel frequency estimation method is employed to estimate the frequency offset. The estimation range of the proposed method is as large as the bandwidth of the OFDM signal, and the performance of the proposed method is independent of the structure of the training symbol.

A new SNR's estimator for QPSK Modulations in an AWGN channel

Signal-to-noise ratio (SNR) measurement is required in many receivers and systems of communications. In this brief, we derive a new SNRs estimator based on the second and fourth-order moments of the complex signals of quadrature phase-shift keying modulations. The mean square error of the estimated SNR by the proposed algorithm is smaller than that by other methods for a low SNR with limited samples.

A Novel Doppler Frequency Offset Estimation Method for DVB-T System in HST Environment

A novel Doppler frequency offset estimation method is proposed for the digital video broadcasting-terrestrial (DVB-T) system in the high-speed-train (HST) environment. Based on the analysis of the effect of the scattered components of the wireless channel on the accuracy of the Doppler frequency offset estimation, we separate the path with the Line-of-Sight(LOS) component from the multipath channel, and only use it to estimate the frequency offset caused by Doppler shift. Simulation results show that the mean square error (MSE) of the proposed scheme is far better than those of the available schemes.

Fast Time-Varying Channel Estimation Technique for LTE Uplink in HST Environment

A novel channel estimation technique is proposed for the time-division-duplex long-term evolution (TDD-LTE) single-carrier frequency-division multiple-access (SC-FDMA) system in the high-speed-train (HST) environment. In the new defined transform domain, the channel parameters of the two block pilots in the SC-FDMA subframe are first estimated, then the polynomial basis expansion model (P-BEM) is employed to estimate the channel parameters of the data symbols, and an autoregressive (AR) model is used to improve the estimation accuracy of the channel parameters of the data symbols out of the two block pilots. The symbol-by-symbol changes of the channel parameters can be effectively estimated by the proposed method. Simulation results show that the proposed method is robust to the fast time-varying channel in the HST scenario, and that the frame error rate (FER) performance of the system by using the proposed method can obtain a gain in the signal-to-noise ratio (SNR) of more than 10 dB compared with those of the available methods.

PAPR Reduction in Coded SC-FDMA Systems via Introducing Few Bit Errors

We propose a simple and flexible peak-to-average power ratio (PAPR) reduction scheme for coded single carrier frequency division multiple access (SC-FDMA) signals in the uplink of the Long Term Evolution (LTE). The proposed scheme is based on the introduction of few bit errors to modify the few complex modulated symbols of each data SC-FDMA symbol in a sub-frame, which cause peaks of the output signal samples to be larger than a predetermined threshold value. In addition, the effect on the bit error rate (BER) performance of the few deliberately corrupted bits can be greatly mitigated by using the channel decoding at the receiver. Computer simulations show that the proposed scheme can reduce the PAPR of SC-FDMA signals effectively with almost the same BER as the conventional SC-FDMA signals when the signal-to-noise ratio (SNR) is below 35 dB.

Beamforming Based Receiver Scheme for DVB-T2 System in High Speed Train Environment

In this paper, the received signal from the different base stations (BSs) of the second generation of Terrestrial Digital Video Broadcasting (DVB-T2) in the high-speed-train (HST) scenario is modeled as a fast time-varying signal with the multiple Doppler frequency offsets. The interference caused by the multiple Doppler frequency offsets and the channel variations, and the signal to interference plus noise ratio of the received signal, are derived for the DVB-T2 receiver. The results of the theoretical analysis show that the interference greatly degraded the performance of the DVB-T2 system. To suppress the interference, we proposed a beamforming based receiver scheme for DVB-T2 system. By using the new signal processing scheme for the received signal vector from the antenna array, one can separate the received signal with the multiple Doppler frequency offsets into the multiple signals, each of which is with a single Doppler frequency offset. The separated signals are compensated by the corresponding Doppler frequency offsets and equalized by the estimated channel responses respectively, then combined into a signal to be demodulated. The results of the simulation show that the proposed scheme can effectively suppress the interference and greatly improve the performance of the DVB-T2 system in the HST environment.