Yongtao Su

A blind CFO estimator based on smoothing power spectrum for OFDM systems

Carrier frequency offset (CFO) estimation is a critical problem in orthogonal frequency-division multiplexing (OFDM) systems. This letter proposes a blind CFO estimator based on smoothing the signal power spectrum. A closed-form CFO estimate is also presented, which greatly reduces the computational complexity of the proposed method. Analysis and simulation results show that the proposed estimator is very effective for OFDM systems.

A closed-form blind CFO estimator based on frequency analysis for OFDM systems

This letter proposes a blind carrier frequency offset (CFO) estimator for orthogonal frequency-division multiplexing (OFDM) systems based on the frequency analysis of the received signal, and derives a closed-form CFO estimate. Since only one OFDM symbol is utilized instead of multi-symbol averaging, the proposed method is effective even when the CFO is time varying. Finally, analysis and simulation results indicate the outstanding performance of the proposed estimator.

Joint time and frequency offset estimation in LTE downlink

Time and frequency synchronization is very critical in LTE downlink. This paper proposed a joint time and frequency synchronization algorithm to estimate the carrier frequency offset (CFO), including the integer frequency offset (IFO) and the fractional frequency offset (FFO), and the start position of a radio frame. The FFO is first estimated by maximum likelihood auto-correlation algorithm. After the FFO compensation, the received signal is cross-correlated with the nine possible primary synchronization signals (PSS) in time domain to obtain the start position and the IFO. Simulation results show that the performance of the proposed synchronization algorithm is more robust than the traditional algorithms especially in large CFO.

A method of PRACH detection threshold setting in LTE TDD femtocell system

Detection threshold is a crucial parameter in Physical Random Access Channel (PRACH) receiver and determines the detection performance and efficiency. A method of PRACH detection threshold setting in Long Term Evolution (LTE) Time Division Duplex (TDD) femtocell system is proposed in this paper based on theoretical analysis. This method uses the frequency domain correlation calculation results, and benefits from multiple antennas diversity combing to adjust the relative detection threshold, which is the ratio of absolute detection threshold and time varying noise level. Cumulative Distribution Function (CDF) of the relative threshold is modified to obtain the absolute threshold. Simulation results show that the proposed method fulfills the requirements of the system and gets a promotion in performance under certain false alarm probability and channel conditions.

A low-complexity sequential Monte Carlo algorithm for blind detection in MIMO systems

In statistical signal processing, the sequential Monte Carlo (SMC) method is powerful and can approach the theoretical optima. However, its computational complexity is usually very high, especially in multiple-input multiple-output (MIMO) systems. This paper presents a new low-complexity SMC (LC-SMC) algorithm for blind detection in MIMO systems, the main idea of which is to shrink the sampling space via channel estimation which is initialized using the first differentially modulated symbol and then updated using the Monte Carlo samples. Since the a posteriori probability of the transmitted symbols can be calculated separately by each transmit antenna, the proposed LC-SMC algorithm is not only computationally efficient, as compared to the original SMC whose complexity grows exponentially with the number of transmit antennas, but also makes blind turbo receiver more feasible for multilevel/phase modulations. Simulation results are presented to demonstrate the effectiveness of the LC-SMC algorithm

An efficient implementation of PRACH generator in LTE UE transmitters

An efficient hardware-optimized Physical Random Access Channel (PRACH) baseband signal generation algorithm and its ASIC implementation in the LTE user equipment (UE) transmitter are presented in this paper. A simplified DFT of the Zadoff-Chu (ZC) sequence as well as a phase computation are applied to the prime size DFT of the PRACH preamble and the large size IDFT is accomplished by groups of smaller size IFFTs. The optimized algorithm achieves significantly lower computational complexity compared with the original algorithm in the LTE specification and better performance compared to another publication. The ASIC architecture is also designed to reduce the memory size and logic complexity, which achieves a low hardware cost in terms of the cell area. The proposed design was implemented in 65nm CMOS and it was demonstrated that this design can satisfy the timing requirements of the LTE specification.

Letters: A fast NPCA algorithm for online blind source separation

This paper addresses the problem of blind source separation (BSS) and presents an optimum step size which makes the nonlinear principal component analysis (NPCA) cost function descend in the fastest way. By applying this step size in the self-stabilized NPCA algorithm, a fast NPCA algorithm is obtained. Computer simulations of online BSS show that the new algorithm works more efficiently than the existing least-mean-square (LMS)-type and recursive least-squares (RLS)-type NPCA algorithms.

Performance Analysis of a Nested RLS-Type Interference Suppression Algorithm for CDMA Systems in Dispersive Channels

For code division multiple access (CDMA) systems operating over dispersive channels, the nested recursive least-squares (RLS)-type algorithm, based on minimum output energy (MOE) criterion, attracts much attention as an efficient interference suppression scheme for its simple adaptive recursion. In this letter, we investigate its performance analysis. Special attention is paid to theoretical issues concerning the global convergence and convergence dynamics performance. It is shown that this algorithm exhibits a global minimum attained, and the convergence is immune to the eigenvalue spread of the correlation matrix of received signal vector. Simulation results demonstrate that the nested RLS-type algorithm has indeed the expected convergence performance

A system-level design approach for SDR-based MPSoC in LTE baseband processing

This paper presents a system-level design approach from application perspective for an SDR based MPSoC (Multi-Processor System-on-Chip) in LTE baseband processing. Based on a quantitative measurement, a 0-1 knapsack model is proposed for hardware-software partition to enhance flexibility by replacing ACC (ACCelerator) with ASIP (Application-Specific Instruction-set Processor). In order to reduce the power consumption of ASIP, a two-level frequency requirement is formed according to the characteristics of baseband processing. Under this approach, the complex symbol based calculation can be all realized on ASIP and the same MPSoC can serve the LTE-A application by software programming. Moreover, the frequency of the ASIPs can be scaled down according to the requirement to get a power reduction from 6% to 90%.

Robust Downlink Precoding in Multiuser MIMO-OFDM Systems with Time-Domain Quantized Feedback

We consider the robust linear precoding (LP) and Tomlinson-Harashima precoding (THP) schemes for multiuser MIMO-OFDM downlink channels with limited feedback. Benefiting from the correlation of spatial channels, the mobile terminal compresses and feeds back the time-domain channel vectors instead of the corresponding frequency-domain vectors to substantially reduce the feedback signalling overhead. A compression and restoration method and a codebook design for channel state information at the transmitter (CSIT) feedback are proposed in the time domain. By treating the partial CSIT as a random quantity, we develop the robust precoders to combat the truncation and quantization errors introduced in the feedback procedure. In comparison with the non-robust designs, both the robust LP and THP have better bit-error rate performance especially in high signal-to-noise ratio region.