CiteULike: dcastro's Zhang

Compact Fully Integrated GaAs Left-Handed Bandpass Filter for Ultrawide Band Wireless Applications

W Tong — 2008-07-17T19:56:34-00:00

Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on (2007), pp. 1-6.

A GaAs MMIC technology of the novel compact left-handed bandpass filter consisting of one left-handed (LH) transmission line (TL) and one dual composite right/lefthanded (D-CRLH) TL is presented. The D-CRLH is the dual of the conventional CRLH in the sense that it consists of a LC parallel-tank impedance and of a LC series-tank admittance. In contrast to the conventional CRLH TL which has LH operation at low-frequency and RH one at high-frequency, the D-LH TL exhibits its LH band at high frequencies and its RH band at low frequencies. Thus, utilizing the high pass property of LH and low pass property of D-CRLH, a bandpass filter can be constructed. In this paper, this novel idea is realized by MMIC technology. The proposed filter exhibits a broad passband from 6.2 GHz to 20.8 GHz with a size of 1.43 mm<sup>2</sup>.

UMTS air interface voice/data capacity-part 1: reverse link analysis

Qinqing Zhang — 2008-07-17T13:39:39-00:00

Vehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd, Vol. 4 (2001), pp. 2725-2729 vol.4.

For pt.2 see ibid., p.2730-4. Universal Mobile Telecommunication System (UMTS) can offer large voice capacity for voice service and support high-speed data for Internet access and multimedia services. We evaluate the air interface capacity for voice, data and integrated voice and data services in UMTS. We present our analytical and simulation models for the reverse link only; the forward link analysis is presented in part 2. In our analytical model, different varying factors in a CDMA system are considered, such as the interference level, power control errors, soft handoff, required signal-to-interference ratio for different rates, etc. We propose a new approach to model the inter-cell interference under multiple cell condition. Furthermore, we apply different approximation methods to calculate the capacity based on voice and/or data traffic loading. Finally, we derive close form expressions of Erlang capacity for a single type of traffic and mixed types of traffic. We also develop a static system level simulator to evaluate capacity and coverage for UMTS. By comparing our analytical results with simulations, we show that our analytical approach has a very good match with simulations

Arrival paths in ultra wideband channels

Yongwei Zhang — 2008-07-10T19:27:30-00:00

Wireless Communications and Networking Conference, 2006. WCNC 2006. IEEE, Vol. 1 (2006), pp. 13-18.

Polyphase codes for uplink OFDM-CDMA systems

Yingming Tsai — 2008-06-27T10:53:50-00:00

Communications, IEEE Transactions on, Vol. 56, No. 3. (2008), pp. 435-444.

We propose a OFDM-CDMA system that employs polyphase codes to support variable spreading factors. A systematic approach for constructing the polyphase code sequences of variable spreading factors is developed. Polyphase codes exhibit better auto- and cross-correlation properties than Hadamard codes. When employed in OFDM-CDMA systems, polyphase codes result in certain structured multiple-access interference (MAI) caused by multipath. Analytical and numerical results show that OFDM-CDMA systems employing polyphase codes have better PAPR performance than those using Hadamard codes. The BER performance of the OFDM-CDMA system using polyphase codes is evaluated by numerical results and compared to that of the OFDM-CDMA system using Hadamard codes with and without clipping.

Orthogonal frequency division multiplexing with phase modulation and constant envelope design

Y Tsai — 2008-06-27T10:35:43-00:00

Military Communications Conference, 2005. MILCOM 2005. IEEE (2005), pp. 2658-2664 Vol. 4.

Constant envelope OFDM with phase modulation (CE-OFDM-PM) was proposed. The motivation of the CE-OFDM-PM system is to alleviate the high peak-to-average power ratio of conventional OFDM systems. In this paper, we explore more details of CE-OFDM-PM systems regarding bandwidth efficiency and performance under AWGN and multipath channels. A theoretical approach instead of Carson's rule to analyze bandwidth is proposed. It indicates that bandwidth requirement is determined by factors such as input data variance and modulation index. The analytical results show that the CE-OFDM-PM systems require the same bandwidth as conventional OFDM system when appropriate (low) modulation index is applied in CE-OFDM-PM system. Under the same multipath channel and bandwidth, the performance of CE-OFDM-PM systems is compared to conventional OFDM system with one tap equalizer. The uncoded BER performance of CE-OFDM-PM is getting close when OFDM applies clipping, but power efficiency of CE-OFDM-PM still outperforms OFDM since clipping cannot eliminate PAPR issue.

OFDMA Initial Ranging for IEEE 802.16e Based on Time-domain and Frequency-domain Approaches

Yue Zhou — 2008-06-09T14:43:03-00:00

Communication Technology, 2006. ICCT '06. International Conference on (2006), pp. 1-5.

In this paper, we propose and compare two ranging methods for the OFDMA uplink system prescribed by IEEE 802.16e, including multi-user ranging code detection, timing, frequency and power synchronization. In Method I, timing offset estimation is based on the auto-correlation and cross-correlation in time-domain, and an adaptive threshold is defined to detect transmitted ranging codes. The time-domain algorithm has a similar counterpart in the frequency-domain described in Method II, which is more accurate since it bears less interference by extracting the sub-carriers used for ranging from data sub-carriers. Moreover, Method II needs fewer computations since it shares the FFT calculations with the data demodulation process. However, Method I has the advantage of a flexible correlation window size. Simulations confirm that both methods perform well even in the condition of low SNR values and several simultaneous ranging users. To obtain the 90% probability of successful detection, Method II requires an SNR about 3.5dB less than Method I. Simulations also show that both methods are better, compared with some existing methods.

Bypass Decoding -- A Reduced Complexity Decoding Technique for LDPC Coded MIMO-OFDM Systems

Y Xin — 2008-05-18T12:37:12-00:00

, IEEE Transactions on Vehicular Technology (2007)

The Effect of Imperfect Carrier Frequency Offset Estimation on OFDMA Uplink Transmission

Zhongshan Zhang — 2008-05-16T12:02:08-00:00

Communications, 2007. ICC '07. IEEE International Conference on (2007), pp. 6281-6286.

Since carrier frequency offset destroys user's signal orthogonality in orthogonal frequency-division multiplexing access (OFDMA) uplink transmission, resulting in an interference-limited system, its estimation/correction is very important. The residual carrier frequency offset of each user contributes inter-carrier-interference (ICI) and multiple-user-interference (MUI) to other users. In this paper, the effect of the carrier frequency offset on OFDMA uplink is analyzed. We first analyze the average uplink capacity losses as well as the signal-to-interference-and-noise ratio (SINR) reduction due to the carrier frequency offsets, and then discuss the capacity increases by using adaptive power allocation. The averaged bit error rate (BER) performance with the carrier frequency offsets on OFDMA uplink is also analyzed.

Artificial neural networks for RF and microwave design - from theory to practice

Qi-Jun Zhang — 2008-05-15T15:11:13-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 51, No. 4. (2003), pp. 1339-1350.

Neural-network computational modules have recently gained recognition as an unconventional and useful tool for RF and microwave modeling and design. Neural networks can be trained to learn the behavior of passive/active components/circuits. A trained neural network can be used for high-level design, providing fast and accurate answers to the task it has learned. Neural networks are attractive alternatives to conventional methods such as numerical modeling methods, which could be computationally expensive, or analytical methods which could be difficult to obtain for new devices, or empirical modeling solutions whose range and accuracy may be limited. This tutorial describes fundamental concepts in this emerging area aimed at teaching RF/microwave engineers what neural networks are, why they are useful, when they can be used, and how to use them. Neural-network structures and their training methods are described from the RF/microwave designer's perspective. Electromagnetics-based training for passive component models and physics-based training for active device models are illustrated. Circuit design and yield optimization using passive/active neural models are also presented. A multimedia slide presentation along with narrative audio clips is included in the electronic version of this paper. A hyperlink to the NeuroModeler demonstration software is provided to allow readers practice neural-network-based design concepts.

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

Guangliang Ren — 2008-05-09T23:47:09-00:00

Circuits and Systems II: Express Briefs, IEEE Transactions on [see also Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions on], Vol. 52, No. 6. (2005), pp. 336-338.

Signal-to-noise ratio (SNR) measurement is required in many receivers and systems of communications. In this brief, we derive a new SNR's 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 lowpass microstrip filter using metal-loaded slots in the ground plane

R Zhang — 2008-05-09T15:46:49-00:00

Microwave Symposium Digest, 2004 IEEE MTT-S International, Vol. 3 (2004), pp. 1311-1314 Vol.3.

This paper presents a lowpass microstrip filter employing metal-loaded slots etched in the ground plane. The filter exhibits a superior RF performance in comparison with low pass filters that are based on electromagnetic band gap (EBG) structures. Several metal-loaded slot configurations have been proposed and theoretically investigated. A lowpass microstrip filter employing one of these slots is built and tested. The measured results are in good agreement with simulation demonstrating the validity of the proposed concept.

FDTD analysis of microwave active antenna including nonlinear model of FET transistor

Y Zhang — 2008-05-09T14:56:17-00:00

Microwave and Millimeter Wave Technology, 2002. Proceedings. ICMMT 2002. 2002 3rd International Conference on (2002), pp. 618-621.

In this paper, a non-linear circuit model of a FET has been incorporated into the finite-difference time-domain (FDTD) method when microwave active antennas are analysed. The FET, operating in class A mode, is biased and its non-linear properties (second harmonics) are investigated in a patch antenna configuration. The algorithm and the simulation results will be useful in the development of high power integrated active antenna modules.

Integration of a self-oscillating mixer and an active antenna

Jiazong Zhang — 2008-05-09T06:37:33-00:00

Microwave and Guided Wave Letters, IEEE [see also IEEE Microwave and Wireless Components Letters], Vol. 9, No. 3. (1999), pp. 117-119.

Current trends in commercial communication system developments have called for small-size and low-cost radio frequency (RF)/microwave circuits. One of the solutions is to design a circuit element such that it possesses multiple functionality. In other words, different parts of a circuit are integrated into a single element, and consequently fewer elements are required. In this work, a C-band self-oscillating mixer (SOM) integrated with an active antenna is presented. A dual-gate field-effect transistor (FET) is employed to facilitate the integration. The resultant unit was tested and experimental results are shown to demonstrate the feasibility of the design

A design for OFDMA receiver

Jianhua Zhang — 2008-04-23T18:38:14-00:00

Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st, Vol. 2 (2005), pp. 1268-1272 Vol. 2.

In this paper, a design for OFDMA receiver is given. Timing synchronization is achieved by ML algorithm with Gold sequence and then multipath delay estimate is achieved by the correlation operation between the local training sequence and the sampled received signal. In order to decrease the overhead for channel estimation, multiple users are combined as a group to share the pilot subcarriers and Walsh codes are used as pilots for different users. For such user group, LS algorithm with the forward estimated delay is adopted to estimate the channels of users. The simulation results show that this receiver can achieve the timing synchronization, multipath delay estimate at low SNR and good BER performance with accurate channel estimation.

Improved wide-band Schiffman phase shifter

Yong-Xin Guo — 2008-04-16T19:16:31-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 54, No. 3. (2006), pp. 1196-1200.

In this paper, one improved wide-band Schiffman phase shifter is presented by modifying the ground plane underneath the coupled lines. In this new design, with the ground plane under the coupled lines removed, the even-mode impedance will be increased substantially. Meanwhile, we propose that one additional isolated rectangular conductor is placed under the coupled lines to act as one capacitor so that the odd-mode impedance is decreased. The proposed new design was simulated by the full-wave electromagnetic software IE3D and validated by the measurement. Compared with the cascading microstrip multisection coupled-line configuration, our newly proposed planar one with a patterned ground plane is small in size and, meanwhile, has a good performance. As an example, one Schiffman phase shifter on a double-sided printed circuit board is designed, simulated, fabricated, and measured. The measured amplitude and phase imbalance between the two paths are within 0.5 dB and 5/spl deg/, respectively, over the frequency band from 1.5 to 3.1 GHz, or around 70% bandwidth. The measured return loss is found to be better than -12 dB over the operating frequency band.

Antenna Research in China

WX Zhang — 2008-04-01T11:05:03-00:00

Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on (2007), pp. 1-6.

There have been great change and progress of antenna research and development in China in the past dozen of years. A brief review on huger and electrically-larger antennas, miniature and electrically-small antennas, printed antennas with multi-functions, array antennas with intelligent control, antennas with special materials etc. is presented in sequence.

Variable shortened-and-punctured Reed-Solomon codes for packet loss protection

Youshi Xu — 2008-02-26T20:04:21-00:00

Broadcasting, IEEE Transactions on, Vol. 48, No. 3. (2002), pp. 237-245.

Techniques using Reed-Solomon (RS) codes to recover lost packets in digital video/audio broadcasting and packet switched network communications are reviewed. Usually, different RS codes and their corresponding encoders/decoders are designed and utilized to meet different requirements for different systems and applications. We incorporate these techniques into a variable RS code and present encoding and decoding algorithms suitable for the variable RS code. A mother RS code can be used to produce a variety of RS codes and the same encoder/decoder can be used for all the derivative codes, with adding/detecting zeros, removing some parity symbols and adding erasures. A VLSI implementation for erasure decoding of the variable RS code is described and the achievable performance is quantitatively analyzed. A typical example shows that the signal processing speed is up to 2.5 Gbits/second and the processing delay is less than one millisecond, when integrating the decoder on a single chip. Therefore, the proposed algorithm and the encoder/decoder can universally be utilized for different applications with various requirements, such as transmission data rate, packet length, packet loss protection capacity, as well as layered protection and adaptive redundancy protection in DVB/DAB, Internet and mobile Internet communications.

High accuracy frequency offset correction with adjustable acquisition range in OFDM systems

Zhongshan Zhang — 2008-02-25T15:40:02-00:00

Wireless Communications, IEEE Transactions on, Vol. 4, No. 1. (2005), pp. 228-237.

A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) systems is proposed in this paper. Both the carrier frequency offset acquisition and tracking are based on a fixed-length training-symbol-block, which consists of multiple small identical training symbols. When each training symbol is shortened, the number of training symbols in the training-symbol-block should be increased accordingly to keep the total training-symbol-block length fixed. The proposed scheme extends Moose's estimator, where the estimation error is only dependent on total training symbol energy and cannot be reduced any more, once the total training symbol energy is determined. The proposed scheme can shorten each training symbol in a training-symbol block and select an appropriate estimator simultaneously, which can lead to further reduction of estimation error and increase of acquisition range, even with the total training-symbol-block energy being fixed. Performance analyzes for the proposed scheme in both the additive white Gaussian noise channel (AWGN) and the multipath channel are also presented in this paper. All estimators in the proposed scheme are conditionally unbiased, and simulation results demonstrate that they can work well both in the multipath channel and in the AWGN channel.

Joint frame synchronization and frequency offset estimation in OFDM systems

Zhongshan Zhang — 2008-02-25T15:27:23-00:00

Broadcasting, IEEE Transactions on, Vol. 51, No. 3. (2005), pp. 389-394.

A new joint frame synchronization and carrier frequency offset estimation scheme in orthogonal frequency division multiplexing (OFDM) systems is proposed in this paper, where both frame synchronization and carrier frequency offset estimation can be performed by using only ONE training symbol. Frame synchronization and carrier frequency offset acquisition are performed simultaneously in the proposed scheme. Reliable frame synchronization is obtained in the proposed scheme even in low SNR. The maximum carrier frequency offset acquisition range of the proposed scheme can be up to one half of the total signal bandwidth. The same training symbol can also be utilized to carrier frequency offset Fine Adjustment, which estimates the remaining carrier frequency offset after acquisition with higher accuracy. The performance comparison of the proposed Fine Adjustment algorithm and Schmidl's algorithm by using computer simulation illustrates and verify the superior performance of the proposed algorithm with regard to estimation accuracy.

On the Performance of IEEE 802.16 OFDMA System Under Different Frequency Reuse and Subcarrier Permutation Patterns

H Jia — 2007-12-06T16:50:46-00:00

Communications, 2007. ICC '07. IEEE International Conference on (2007), pp. 5720-5725.

Energy management in the IEEE 802.16e MAC

Y Zhang — 2006-12-07T16:33:53-00:00

Communications Letters, IEEE, Vol. 10, No. 4. (2006), pp. 311-313.

Energy management is an important component for the emerging standard IEEE 802.16e supporting mobility. In this paper, we characterize the standardized sleep mode in IEEE 802.16e. The comparison between our result and the simulation shows that our analytical model is accurate in evaluating the energy consumption and hence provides a potential guidance in efficiently managing energy.

Compact high-impedance surfaces incorporated with interdigital structure

Y Fu — 2007-11-27T10:26:41-00:00

Electronics Letters, Vol. 40, No. 5. (2004), pp. 310-311.

A novel compact high-impedance surface structure is presented. The periodic branched elements cross over like interdigital capacitors. This structure is adopted to increase the fringe capacitor in order to compress the overall size of the high-impedance surface. Measured results show that 30-40% size reduction could be obtained.

Internet Protocol Television (IPTV): The Killer Application for the Next-Generation Internet

Y Xiao — 2007-11-15T11:46:24-00:00

Communications Magazine, IEEE, Vol. 45, No. 11. (2007), pp. 126-134.

Frequency offset estimation with fast acquisition in OFDM system

Zhongshan Zhang — 2007-11-11T15:43:57-00:00

Communications Letters, IEEE, Vol. 8, No. 3. (2004), pp. 171-173.

A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) system is proposed. The carrier frequency offset estimation includes acquisition and tracking, and the acquisition range is as large as one half of overall signal bandwidth. The proposed tracking estimator is a maximum-likelihood estimator, and in AWGN channel, the Cramer-Rao lower bound is met at high signal-to-noise ratio (SNR); in multipath channel, the tracking algorithm works well at moderate SNR. Timing synchronization can be also performed during the course of acquisition.

Capacity enhancement for HSDPA in W-CDMA system

JH Horng — 2007-11-11T15:34:43-00:00

Vehicular Technology Conference, 2002. Proceedings. VTC 2002-Fall. 2002 IEEE 56th, Vol. 2 (2002), pp. 661-665 vol.2.

The upper bounds for SNR gains from several interference cancellation scenarios are calculated under different multipath environments and different power allocations for HSDPA (high speed downlink packet access) users. The simulation results show that cancellation of the intercell pilot has a larger gain than intracell pilot cancellation. When the power allocated to the HSDPA signal is reduced, the gains of canceling the interference from the intracell pilot and other HSDPA codes are also reduced, due to excessive MUI (multiple user interference). Further performance improvement based on the MPIC (multipath interference cancellation) technique is also studied, which includes intracell MUI cancellation.

Dual structure of composite right/left-handed transmission line

Xin Hu — 2007-11-07T07:53:03-00:00

Journal of Zhejiang University - Science A, Vol. 7, No. 10. (23 October 2006), pp. 1777-1780.

Abstract A dual structure of composite right/left handed (CRLH) transmission line (TL) is analyzed in which an inductance L R is in parallel with a capacitance C L and a shunt capacitance C R is in series with an inductance L L. Both the distributed and lumped cases are considered. The dispersion diagram and transmission properties of the dual CRLH TL are given and compared with those of a standard CRLH TL. Contrary to the frequency response of a standard CRLH TL, a dual CRLH TL has a left-handed (negative phase shift) band at higher frequencies and a right-handed (positive phase shift) band at lower frequencies. A novel dual-band balun is presented as an application.

Codirectional coupler and power divider mixed microstrip and metamaterials with lumped-elements L-C

Dongke Zhang — 2007-11-02T17:41:07-00:00

Microwave and Millimeter Wave Technology, 2004. ICMMT 4th International Conference on, Proceedings (2004), pp. 304-307.

A coupled-line backward coupler and a power divider, composed of the conventional microstrip line and the composite left-handed line with lumped-elements L-C, are presented. The coupler exhibits arbitrary coupling level and broad bandwidth. The power divider shows multi-ports, different coupling level output. The theoretical circuit-model simulated results are demonstrated by experiments. Both a 3-dB coupler and a trisecting power divider are demonstrated experimentally.