| 1. |
- Luo, Yifei, et al.
(författare)
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Technology Roadmap for Flexible Sensors
- 2023
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 17:6, s. 5211-5295
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Forskningsöversikt (refereegranskat)abstract
- Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.
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| 2. |
- Xiao, Pei, 1968, et al.
(författare)
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A theoretical evaluation of parallel interference cancellation in M-ary orthogonal modulated asynchronous DS-CDMA system over multipath Rayleigh fading channels
- 2005
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 54:4, s. 1400-1414
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we tackle the problem of theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a direct-sequence code division multiple access (DS-CDMA) system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time varying multipath Rayleigh fading channel. By applying the Central Limit Theorem and some other approximations to multiple access interference (MAI) and intersymbol interference (ISI), as well as assuming identically distributed chips from a single interferer, the bit error rate (BER) performance of the PIC scheme at any stage can be recursively computed from the signal-to-noise ratio, number of users, the number of path per user, processing gain of the CDMA system, and the average received power of each path. For completeness, the BER expression is derived for chip synchronous and chip asynchronous systems over both equal and unequal power multipath channels. The proposed analysis is validated by the Monte Carlo simulations and proved to be reasonably accurate, and it gives insight into the performance and capacity one can expect from PIC-based receivers under different situations. For instance, the analytical results can be used to examine the convergence property, multipath diversity gains, and near-far resistance of the PIC scheme.
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| 3. |
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| 4. |
- Xiao, Pei, 1968, et al.
(författare)
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Applications of Maximum Likelihood Algorithm in Asynchronous CDMA Systems
- 2002
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Ingår i: 2002 IEEE SEVENTH INTERNATIONAL SYMPOSIUM ON SPREAD SPECTRUM TECHNIQUES AND APPLICATIONS, ISSSTA'2002, SEP 02-05, Prague, Czech Republic. ; 1, s. 208-213
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Konferensbidrag (refereegranskat)abstract
- In this paper, we treat the problems of propagation delay and channel estimation as well as data detection of orthogonally modulated signals in asynchronous DS-CDMA system over fading channels using the maximum likelihood (ML) approach. The overwhelming computational complexity of the ML algorithm makes it unfeasible for implementation. The emphasis of this paper is to reduce its complexity by some approximation methods. The derived approximative ML schemes are compared with conventional algorithms as well as some others, e.g., the PIC for data detection and the subspace-based algorithm for acquisition.
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| 5. |
- Xiao, Pei, 1968, et al.
(författare)
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BER Performance Analysis of Multistage PIC Scheme in An Asynchronous DS-CDMA System with Long Scrambling Codes
- 2004
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Ingår i: IEEE 59th Vehicular Technology Conference, 2004. VTC 2004-Spring, Milan, Italy, 17-19 May 2004. ; 2, s. 952 - 957
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Konferensbidrag (refereegranskat)abstract
- In this paper, we tackle the problem of theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a DS-CDMA system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time-varying multipath Rayleigh fading channel. By applying the Central Limit Theorem to multiple access interference (MAI) and intersymbol interference (ISI), as well as identically distributed chips from a single interferer, the bit error rate (BER) performance of the PIC scheme at any stage can be recursively computed from the signal-to-noise ratio, number of users, the number of paths per user, processing gain of the CDMA system, as well as the average received power of each path. The proposed approximative analysis is validated by the Monte-Carlo simulations and proved to be accurate, and it gives insight into the performance and capacity one can expect from the PIC based receivers under different situations.
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| 6. |
- Xiao, Pei, 1968, et al.
(författare)
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Delay Estimation and Data Detection in Long-Code DS-CDMA System
- 2003
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Ingår i: 9th Asia-Pacific Conference on Communications held in conjunction with the 6th Malaysia International Conference on Communications (MICC 2003). Penang, MALAYSIA. SEP 21-24, 2003. ; 2, s. 584-589
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Konferensbidrag (refereegranskat)abstract
- In this paper, we aim at solving the problem of joint delay estimation and data detection of the orthogonal modulated signals in the asynchronous DS-CDMA system employing aperiodic long spreading codes over fading channels. The general system requirement of low error rate in data demodulation necessitates the reliable synchronization mechanisms. Synchronization of CDMA signals with long spreading codes is a more challenging task than that of CDMA signals with short spreading codes. In this work, two algorithms are introduced to perform acquisition and tracking of orthogonal modulated signals with long spreading codes, followed by data detection. The numerical results show that when applying to the asynchronous system with random propagation delays, the proposed algorithm's approximate the performance that is attainable in the synchronized and chip-aligned system.
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| 7. |
- Xiao, Pei, 1968, et al.
(författare)
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Estimation of Time-Varying Multipath Rayleigh Fading Channels in Asynchronous DS-CDMA Systems
- 2004
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Ingår i: Proceedings IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Barcelona, SPAIN, SEP 05-08, 2004. ; 4, s. 2570 - 2575
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present channel estimation algorithms for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signalling formats and long scrambling codes. The performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigated channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of multipath propagation of the transmitted signal as well as multiple access interference (MAI). Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of the channel estimate and the bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems.
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| 8. |
- Xiao, Pei, 1968, et al.
(författare)
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Integrated Approach to Demodulation and Decoding of Convolutionally Coded and Orthogonally Modulated DS-CDMA Signals
- 2003
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Ingår i: WPMC'2003, Yokosuka, Japan. ; 1, s. 122-126
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Konferensbidrag (refereegranskat)abstract
- The system under study is a convolutionally coded and orthogonally modulated DS-CDMA system in time-varying frequency selective Rayleigh fading channels. After convolutional encoding and block interleaving, information bits are mapped to M- ary orthogonal Walsh sequences. In conventional systems, Mary symbol demodulation and convolutional decoding are conducted separately in the receiver, only hard decisions are passed between these two blocks. In this paper, we propose an integrated scheme based on some soft demodulation and decoding algorithms. Instead of making hard decision on the transmitted M-ary symbols from the received observations, we compute the reliability value for the code bits from which orthogonal symbols are formed. This soft information is then deinterleaved and decoded. The detected bits are fed back to demodulator for channel estimation and multiuser detection. For channel decoding, we use Log-MAP algorithm instead of VA (Viterbi algorithm) for better performance. Maximum achievable performance for the system is obtained by iterating this joint soft demodulation and Log-MAP decoding process. The performance of this strategy is evaluated numerically and proved to significantly outperform the conventional partitioned and hard decision based scheme.
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| 9. |
- Xiao, Pei, 1968
(författare)
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Iterative Detection, Decoding and Channel Parameter Estimation for Orthogonally Modulated DS-CDMA Systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, we study iterative detection, decoding and channel parameter estimation algorithms for asynchronous direct-sequence code division multiple access (DS-CDMA) systems employing orthogonal signalling formats and long scrambling codes. Multiuser detection techniques are widely used to combat the detrimental effects of multipath fading and multiple access interference (MAI), which are the major impairments in CDMA communication systems. Although the emphasis is placed on nonlinear interference cancellation schemes, several linear interference filtering techniques are also discussed in the first part of the thesis. The multistage parallel interference canceler (PIC) is evaluated analytically and compared with simulation results. To prevent performance degradation of PIC due to error propagation, some soft cancellation schemes using soft decision feedback are presented. Most multiuser detectors rely on accurate channel information, which needs to be estimated in practice. For the purpose of channel estimation, both classic and Bayesian methods are considered in this thesis, depending on whether prior knowledge about the parameters to be estimated is available or not. We focus on the decision directed approach when estimating the fading channel gains. That is, the receiver estimates the channel parameters based on the detected data, no training sequences are needed. The estimated channel coefficients are also used to regenerate the signal of each user for the purpose of interference cancellation. Another essential channel parameter to be estimated is the propagation delay. Many studies show that multiuser detectors need very accurate delay estimates to perform well. We propose some suboptimal synchronization algorithms that achieve good acquisition performance in presence of MAI and have reduced complexity compared to the optimum maximum likelihood estimator. In the second part of the thesis, we employ the turbo processing principle and study iterative demodulation and decoding of a convolutionally coded and orthogonally modulated asynchronous DS-CDMA system. Several iterative schemes based on soft demodulation and decoding algorithms are presented. The performance of different strategies are evaluated and proved to achieve substantial performance gains compared to the conventional hard decision based scheme, especially when the soft demodulator is assisted by decision directed channel estimation and interference cancellation techniques, and also when demodulation and decoding are performed jointly in an iterative manner. It is also shown that iterative decoding with properly corrected extrinsic information or with non-extrinsic/extrinsic adaptation enables the system to operate reliably in the presence of severe multiuser interference. Additional gain is noticed when soft information rather than hard decision feedback is used for channel estimation and interference cancellation.
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| 10. |
- Xiao, Pei, 1968, et al.
(författare)
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Multiuser Detection and Channel Estimation Algorithms for M-ary DS-CDMA Systems in Multipath Rayleigh Fading Channels
- 2003
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Ingår i: PIMRC'2003, Beijing, China, 7-10 Sept. 2003. - 0780378229 ; 2, s. 1829-1834
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present different linear and nonlinear iterative data detection schemes for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signalling formats and long scrambling codes. Compared to the conventional receiver and other noncoherent multiuser detectors, coherent multiuser detection schemes achieve much better performance provided that the channels are accurately estimated. To this end, we proposed several channel estimation algorithms to estimate multipath Rayleigh fading channels. Different data detection and channel estimation schemes are compared in terms of BER performance. Based on the numerical results, some recommendations are made on how to choose multiuser detectors and channel estimation algorithms in practical CDMA systems.
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