Jeng-Kuang Hwang

Highly efficient algorithm for joint ML estimation of carrier frequency offset and channel for OFDM transmissions

This paper investigates the problem of joint estimation of carrier frequency offset (CFO) and channel response for OFDM systems. In deriving the solution of the joint maximum likelihood (JML) estimator, the channel model absorbs the effects of the unknown carrier phase offset and symbol timing error. It is shown that a highly efficient JML algorithm can be cleverly obtained in two steps, consisting of a nonlinear JML-CFO estimator and a linear least squares channel estimator. Especially, the complexity of the JML-CFO estimation can be greatly reduced by exploiting the idempotent property of the projection matrix and using a polynomial approach to transform a brute-force searching into a simple coarse FFT peak finding operation. Finer CFO resolution can then be obtained by iterative zoom-FFT. Finally, simulation result shows that the JML-CFO estimate can approach the theoretical CRLB when the SNR exceeds a low threshold of 0 dB.

An iterative receiver with intercarrier interference cancellation for ofdm communication systems with carrier-frequency and timing offsets over multipath fading channels

A joint estimation and compensation algorithm of the carrier frequency offset (CFO) and sampling clock offset (SCO) is proposed for orthogonal frequency division multiplexing (OFDM) systems under multipath fading channels. First, we propose the joint weighted least-squares (JWLS) algorithm with intercarrier interference (ICI) cancellation to enhance the accuracy of the CFO and SCO estimation. Next, the partial parallel interference cancellation (PPIC) algorithm with maximal ratio combining (MRC) method is proposed to recover the synchronization errors and reconstruct the ICI interference. Finally, the iterative JWLS and PPIC algorithms are designed to overcome the serious ICI effect and improve the performance of OFDM systems. With computation simulation, it is shown that the proposed receiver is reliable and provides nearly the performance of the ideal receiver as iterations proceed.

Transceiver design and analysis of DS-CDMA ultra-wideband radio for next generation WPAN

This paper investigates a transceiver design and analysis of DS-CDMA Ultra-wideband radio, which is adapted from an 802.15.3a OWE draft proposal for WPAN. The system uses M-ary bi-orthogonal keying modulation with ternary spreading code. The 802.15.3a Saleh-Valenzuela CMI-CM4 channel models are specified for performance evaluation. For channel dispersion over many consecutive symbols, we use not only rake receiver to compensate the inter-chip interference, but also decision feedback equalizer to eliminate the post-cursor inter-symbol interference. Moreover, using the Gaussian approximation technique, analytic upper-bound error performance is derived for the rake-only and rake-DFE receiver. The result is well matched to the simulation result. It also shows that the Rake-DFE attains a significant performance gain as compared to the rake-only receiver.

A new /spl pi//4-DQPSK single carrier system with cyclic prefix and frequency domain equalizer: merits and applications

In this paper, a new single-carrier /spl pi//4-DQPSK system with frequency domain equalizer is proposed, which attempts to integrate the merits of differential signalling (/spl pi//4-DQPSK) and cyclic prefix (CP) aided frequency domain equalization (FDE). In the transmitter, this system possesses low computational complexity and has low peak-to-average power ratio (PAPR) of the transmitted signal. In the receiver, at the same time, this system can not only combat severe dispersion effects of multipath propagation as the famous OFDM system does, but it is also insensitive to carrier frequency offset (CFO) due to the use of differential signalling. Such features make it a good candidate for asymmetrical communication applications, such as high-speed unidirectional wireless multimedia transmission or wireless sensor network (WSN) which require low cost and low power consumption.

Constrained-beam amplitude monopulse technique for bearing estimation in passive radar with uniform circular dipole array

The paper presents an improved method for estimating the direction of arrival (DoA) of aircraft targets, based on a passive coherent location (PCL) equipped with uniform circular dipole array (UCDA). First, we use the dual-domain spatial-temporal processing (STP) for suppressing the direct path interference (DPI). Based on the STP, a constrained-beam amplitude monopulse (CBAM) technique is then developed. It is shown that the combined STP-CBAM technique has many merits, such as high bearing estimation accuracy, low complexity, and feasibility for hardware realization. Finally, the performance of the complete STP combined with CBAM bearing estimation scheme is validated using computer simulation.

An OFDM-based multipath channel sounding method with fractional delays resolution

In this paper, an OFDM-based high resolution CS method is proposed under T/2-spaced sampling. The proposed CS method consists of three iterative steps. In each iteration, it attempts to catch a new path with accurate fractional delay. Besides, it is equipped with EDC criterion for path order determination. The CFR-MSE performance can be greatly improved over the conventional LS method. Besides, the proposed CS method is robust enough for different settings of EDC penalty factor a. In addition, some algorithmic refinements could be added for decreasing the complexity in the future.

Slotted adaptive frequency hopping and rolling scheme for multi-net cognitive radio with experimental result

In this paper, we propose a slotted adaptive frequency hopping and rolling (SAFHR) scheme to realize the dynamic spectrum access for cognitive radio (CR). First, based on the CR spectrum sensing result and the quadratic prime code, an adaptive frequency hopping scheme is designed to avoid the frequency static interference due to primary user (PU). Secondly, adaptive frequency rolling scheme is incorporated to combat the frequency dynamic interference in the presence of multiple CR nets. As a whole, the SAFHR algorithm aims to maximize the frequency spectrum utilization and frequency diversity for each CR user, and to accommodate as many CR users as possible. By employing a so called Instruments-in-MATLAB software defined radio (IM-SDR) platform, experimental results of the SAFHR scheme is demonstrated under the scenario with two CR nets, five CR nodes, and one PU.

Transceiver design and implementation of a new dual-mode spread spectrum system with DQPSK-HCSOK modulation

Based on the newly proposed cyclic shift orthogonal keying (CSOK) scheme, this paper presents the top-down design and realization of a dual-mode single-carrier/multi-carrier (SC/MC) spread spectrum (SS) system, including a new DQPSK-HCSOK hybrid modulation scheme and associated differential receiver. Packet and preamble formats are also designed for packet detection, CFO compensation, and channel estimation. Compared to the ideally synchronized receiver, the overall receiver degrades by only 1 dB, showing that the proposed system is very robust against the residual CFO. Then, efficient FPGA implementation of the proposed system on Xilinx XtremeDSP platform is described. The hardware can run at 97.276 MHz, and suffers from a slight implementation loss of less than 0.1dB at 8% PLER, in comparison to the floating-point simulation. Under multipath fading channel, the SC and MC modes perform equally well but the SC transceiver can save a lot of FPGA resources than the MC transceiver.