Joel Joseph S. Marciano

Carrier suppression locked loop mechanism for UHF RFID readers

The receiver of a UHF RFID reader is exposed to strong carrier leakage signals due to antenna reflections and limited isolation of circulators and directional couplers. This strong interference limits the performance of the reader as the active components in the receiver become saturated. In this paper, an improvement on the front-end architecture of UHF RFID readers is presented to address this problem. An automatically-adjusted canceling signal is combined with the received signal to suppress the strong carrier leakage. The experiment results show that the constructed prototype can achieve high isolation and that the canceling signal can be routinely configured even during reader operations.

Application of MUSIC, ESPRIT and SAGE Algorithms for Narrowband Signal Detection and Localization

This study presents the experimental verification of multiple signal classification (MUSIC), estimation of signal parameters via rotational invariance techniques (ESPRIT) and space-alternating generalized expectation-maximization (SAGE) algorithms in estimating the direction-of-arrival (DoA) of a narrowband source. MUSIC and ESPRIT are subspace-based methods while SAGE is a maximum-likelihood technique. A BPSK signal was transmitted off-the-air and was received under varied system parameters. The three algorithms were then applied on the recorded data. The performance of the three algorithms was compared based on their capability to estimate the signals general DoA. The results showed that SAGE has an average deviation in signal localization of 3.5deg, followed by MUSIC 3.8deg and ESPRIT 9.7deg. Further tests show that SAGE can closely estimate the signal DoA with lower data samples than MUSIC and ESPRIT. For subspace-based methods, a 4-element antenna array gives better estimates than a 2-element array

Enhancing the accuracy of direction-of-arrival (DoA) estimates of passive UHF RFID tag signals using adaptive filtering

This paper discusses a means of enhancing the accuracy of the direction of arrival (DoA) estimates of backscattered signals from passive ultra high frequency radio frequency identification (UHF RFID) tags. The DoA estimation is carried out by using the root-MUSIC algorithm on a two-element receive antenna array, which is realized through a RFID reader configuration involving a mono-static (Tx/Rx) antenna and an additional receive-only antenna. We show that accurate DoA estimation of RFID tag signals is hampered by inherent self-interference in such RFID systems, which is caused by the high power transmission of the reader leaking into the receiver through imperfect isolation. The proposed enhancement involves utilizing a Least Mean Square (LMS) adaptive filter to successfully suppress the carrier leakage prior to DoA estimation. Simulation results show substantial reduction in the standard deviation of error of the estimated DoA.

Normalized adaptive minimum bit-error-rate beamformers

We address the convergence limitations of adaptive minimum bit-error-rate beamformers (AMBER) beamformers under fading channel environments by developing the normalized AMBER (NAMBER) beamforming algorithms. NAMBER beamformers make use of probability-of-bit-error cost functions that are normalized vs. input signal level. The NAMBER beamformers include the normalized MBER (NMBER), normalized block-adaptive-MBER (NBAMBER), normalized least-bit-err or-rate (NLBER) and normalized approximate least-bit-error-rate (NALBER). Simulation results show that the NMBER can achieve lower BERs compared to MBER and maximum-signal-to-interference-plus noise ratio (MSINR) under a fading channel environment.

Packet detection and acquisition at low SINR in spread-spectrum based wireless communications

A low signal to interference and noise ratio (SINR) wireless environment makes successful reception and accurate detection of packets a challenging task. We can combat a low SINR by using direct-sequence spread spectrum modulation with a sufficiently high processing gain, as well as by employing block codes for FEC on each packet. In this paper, we propose a packet detection and acquisition method for low SINR environments. The received waveform is processed using a non-linear filtering algorithm based on a maximum likelihood ratio calculation to detect the presence of transmitted packets. The algorithm uses the entire packet transmission for chip timing synchronization and code acquisition at the receiver. The performance of the algorithm is analyzed using simula- tions and real packet transmissions captured over the wireless medium. The algorithm is finally implemented on a FPGA which is a part of a wireless transceiver prototype. The experimental results are reported.

FPGA implementation of a Time Domain Reflectometry (TDR) system for slope monitoring applications

A compact Time Domain Reflectometry (TDR) system was designed and implemented on a Field-Programmable Gate Array (FPGA). The implementation features potential reconfigurability and reprogrammability of important parameters such as pulse shape, pulse width, pulse repetition frequency, and sampling rate. Furthermore, the digital implementation minimizes the need for external analog components. Experimental results of the initial prototype were able to achieve a pulse width of 6.25 ns corresponding to a resolution of 6.67 ns/m in a free space filled cable. We showed that the performance of the system is limited by the conversion rate of the DAC and the maximum clock frequency of the FPGA. However, with advances in FPGAs, ADCs and DACs, this implementation shows tremendous promise in achieving a reconfigurable, flexible, and compact TDR system for slope monitoring.

Enhanced FM0 decoder for UHF passive RFID readers using duty cycle estimations

This paper proposes a novel FM0 decoding technique for EPC Class 1 Generation 2 (Gen 2) UHF RFID readers. The proposed decoder overcomes the limitations of current implementations, which focus on correlation based decoding and require complex synchronization schemes. New rectangular wave symbols are derived from the FM0 stream and mapped to corresponding bit sequences using duty cycle estimations. Since the duty cycle approximated is independent of the received data rate, the proposed decoder is unaffected by the large +/− 22% data rate deviation and can decode the whole data rate range of 40kHz to 640kHz without changing the decoder structure. Furthermore, the characteristics of the rectangular wave symbols allow for early bit error detection prior to CRC computation. The duty cycle based decoder is prototyped on a Xilinx Virtex 5 FPGA and subsequent FPGA utilization data are presented and compared with a correlation-based scheme. BER measurements show that higher performance gains are achieved as the number of samples per symbol used for duty cycle estimations is increased.

A simulation study of a Time Domain Reflectometry (TDR) cable with non-standard cross-section

Coaxial cables are used in Time Domain Reflectometry for geotechnical survey and slope stability monitoring. In this work, a cable model with a rectangular outer conductor and cylindrical inner conductor is subjected to shearing simulations, with shearing introduced from the edge and from the corner of the cable. We examine the profile of reflected pulses due to the shearing for the different cable configurations. Simulation results show that the magnitude of the TDR reflection spikes obtained from the edge shear differs from that of the corner shear by 8.00% to 209.09%, depending on the shear displacement. Since the TDR reflection signals vary with shear orientation, this can be exploited to provide additional information on orientation of movement or deformation. Such information may be useful for applications such as landslide detection and slope monitoring.

The Effect of Signal Distortion Techniques for PAPR Reduction on the BER Performance of LDPC and Turbo Coded OFDM System

Signal distortion techniques namely, peak windowing and clipping, are methods to address the high peak-to-average power ratio (PAPR) problem on OFDM systems. However, signal distortion technique introduces in-band and out-of-band distortion which may undermine the gain given by an error control code. This study investigated the effect of signal distortion techniques on the bit error rate (BER) performance of turbo and low density parity check (LDPC) coded orthogonal frequency division multiplexing (COFDM) communication system. It was found that LDPC-COFDM performs better than the turbo coded OFDM (T-COFDM) in an AWGN and exponentially decaying Rayleigh fade channel. Upon the application of signal distortion techniques, reduction in the coding gain was experienced by the LDPC-COFDM and T-COFDM. However, only a minimal loss was experienced by T-COFDM unlike the LDPC-COFDM. Thus, the effect of signal distortion to the T-COFDM systems performance is a good trade off, considering the reduced PAPR level

Performance of the differential space-time block code modulation for the wideband CDMA system

The differential space-time block code (DSTBC) modulation for DS-CDMA system Liu, J et al., (2002) combines the merits of differential detection based on space-time block codes and spread spectrum technology to improve the performance of CDMA systems in a fast time-dispersive fading channel. In this paper, the new modulation scheme is adapted to a wideband CDMA system operating at a chip rate of 3.84 Mchips/sec and an output data rate of 240 kbits/sec. Simulation results indicate a 13-dB loss in performance when compared to a DSTBC-CDMA system. This loss can be attributed to the high autocorrelation values of the spreading codes.