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General differential modulation scheme for quasi-orthogonal space-time block codes with partial or full transmit diversity

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IET COMMUNICATIONS 2007年第2期1卷 256-266页

作者： Song, L.-Y. Burr, A. G. Univ York Dept Elect Commun Res Grp York YO10 5DD N Yorkshire England

A general and simple differential modulation scheme that can be applied to both partial-diversity quasi-orthogonal space-time block codes and full-diversity quasi-orthogonal space-time block codes is reported. A new class of quasi-orthogonal coding structures is presented for various number of transmit antennas. Differential encoding and decoding can be simplified to differential Alamouti codes by grouping the signals in the transmitted matrix and decoupling the detection of data symbols, respectively. For the codes with partial transmit diversity, the new scheme can achieve constant amplitude of transmitted signals, and avoid signal constellation expansion;in addition, it has a linear signal detector with very low complexity. Simulation results show that these partial-diversity codes can provide very useful results at low signal-to-nose ratio for current communication systems. For codes with full transmit diversity achieved by constellation rotation, the proposed scheme has performance equal to the best full-rate quasi-orthogonal schemes previously described in the literature with the benefit of a simpler detector. Moreover, a simple linear detector is also presented for the case when two orthogonal ASK constellations are used. Extension to more than four transmit antennas is also considered.

关键词： diversity reception linear signal detector differential detection amplitude shift keying partial transmit diversity full transmit diversity modulation coding differential modulation scheme block codes space-time codes diversity transmission Alamouti codes matrix transmission ASK constellations quasiorthogonal space-time block codes transmitting antennas orthogonal codes decoding

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Effect of error in channel state information on the channel capacity with QAM signalling and the design of robust signal constellations

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IET COMMUNICATIONS 2007年第6期1卷 1118-1125页

作者： Al-Askary, O. Slimane, S. B. Royal Inst Technol Dept Informat & Commun Technol Stockholm Sweden

The effects of channel estimation errors on the channel capacity of a discrete time, discrete input, infinite output Rayleigh fading channel are investigated. The case of conventional modulation methods such as phase shift keying (PSK) and quatrature amplitude modulation (QAM) is investigated at first where it was observed that the capacity degrades rapidly with increasing channel estimation errors. The effect of error in the channel estimation is similar to the effect of higher noise in the channel that depends on the transmitted signal. A genetic algorithm is used to optimise the signal constellation in order to maximise the capacity for a given finite number of signal points. The aim of trying to maximise the capacity is to estimate the remaining gap in performance between a traditional modulation scheme such as QAM and the best possible constellation that is optimised for the channel. The constellations obtained from the genetic algorithm are, in general, not directly implementable. A method to design practical robust signal constellations that overcome the effect of channel state information (CSI) error is presented. The robust signal constellations obtained show a performance that is very close to the otimal constellations. In this work, the probability distribution of the error in CSI is assumed to be known.

关键词： telecommunication signalling Rayleigh channels decoding channel estimation modulation coding channel estimation errors genetic algorithm QAM signalling quatrature amplitude modulation decoding schemes quadrature amplitude modulation discrete time discrete input infinite output Rayleigh fading channel channel state information channel coding channel capacity signal constellations genetic algorithms

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Scheduling schemes for multimedia service in wireless OFDM systems

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IEEE WIRELESS COMMUNICATIONS 2007年第5期14卷 99-105页

作者： Zhu, Haiying Julie Hafez, Roshdy H. M. Carleton Univ Dept Syst & Comp Engn Ottawa ON K1S 5B6 Canada

Scheduling schemes play a key role in the system performance of broadband wireless systems such as WLANs/WMANs. Maximal SNR and Round Robin are two conventional scheduling strategies that emphasize efficiency and fairness, respectively. The Proportional Fair scheme provides a trade-off between efficiency and fairness, and has been well Studied in TDMA and CDMA systems. In this article we extended the PF scheduling scheme to OFDM-based BWSs (OPF). In addition, we propose three variations: Adaptive OPF (AOPF), Multimedia AOPF (MAOPF), and Normalized MAOPF (NMAOPF) in order to meet the QoS requirements for multirate services in multimedia systems. The adaptive modulation and coding schemes in time varying and frequency selective fading are considered. The system performances of the algorithms are compared in terms of efficiency (throughput and mean packet delay) and fairness (user satisfaction rate and average user rate). Joint physical and media access control layer simulation results show that AOPF and MAOPF can improve throughput at the cost of fairness, and NMAOPF can provide the highest throughput without losing fairness.

关键词： Multimedia systems OFDM Throughput System performance Round robin Time division multiple access Multiaccess communication Adaptive systems modulation coding Fading

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Iterative low-complexity multi-user detection for asynchronous multi-sequence signalling based bit-interleaved coded modulation code division multiple access systems

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IET COMMUNICATIONS 2007年第4期1卷 628-637页

作者： Tseng, D-F. Lu, K-C. Natl Taiwan Univ Sci & Technol Dept Elect Engn Taipei 106 Taiwan

An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation (BICM) technique, a group of bits at the output of a bit-wise interleaver is mapped uniquely to a complex signalling vector belonging to an orthogonal plane sequence modulation signal space, which is constructed over a set of expanded signature sequences. This transmission system provides not only bandwidth efficiency offered by additional signal planes but also time diversity resulting from the BICM technique. It is observed that at high system traffic load error performance could degrade substantially due to user cross-correlations, multi-access asynchronism as well as channel frequency selectivity. The authors employ a 'turbo principle' receiver, consisting of a soft interference cancellation scheme, soft demappers and maximum a posteriori decoders, to avert this capacity loss by exploiting the serially concatenating structure at the transmitter. After simple mathematical manipulation, a soft space-time linear minimum mean-square error multi-user detector could even be explored on the basis of per signal plane per user. Both analytical performance-bound and computer simulation of the proposed framework in terms of bit-error rate (BER) are revealed. Further, performance comparisons with convolutionally coded and conventional bandwidth-efficient coded direct sequence code division multiple access systems under the same system conditions are illustrated. The authors have also investigated the impact of labelling maps on the BER performance.

关键词： multiuser detection space-time linear minimum mean-square error multiuser detector code division multiple access systems fading channels turbo principle receiver modulation coding telecommunication traffic system traffic load error code division multiple access least mean squares methods quasi-static frequency-selective fading channel direct sequence spread spectrum communications systems asynchronous multisequence signalling iterative low-complexity multiuser detection bit-interleaved coded modulation soft interference cancellation scheme interference suppression soft demappers error statistics bit-error rate bandwidth efficiency spread spectrum communication telecommunication signalling maximum a posteriori decoders

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Study of signal processing for optical multi-layer disk

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IEEE TRANSACTIONS ON MAGNETICS 2007年第2期43卷 840-844页

作者： Maeda, Taksehi Kondou, Masaharu Hitachi Ltd R&D Grp Cent Res Lab Tokyo 1858601 Japan

Research intended to increase the capacity of multi-layer optical disks has frequently applied to multi-layer disks the format for a single layer disk. However, when writing and reading data through non-readout layers, light intensity is fluctuated by data recorded on those layers. To solve this problem, we invented a modulation code, and studied a way to detect data from recorded marks. We report the results of this research here.

关键词： modulation coding optical memory optical recording signal processing

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Signal constellation design for symbol-level rate adaptation in AWGN channels

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IEEE COMMUNICATIONS LETTERS 2007年第11期11卷 836-838页

作者： Christensen, Soren Skovgaard Popovski, Petar Univ Aalborg Dept Elect Syst Aalborg Denmark

This paper considers rate adaptation for the Additive White Gaussian Noise (AWGN)-channel with unknown channel capacity. We show how multi-layer signal constellations can be optimized layer-wise for particular Signal-to-Noise Ratio (SNR)-points, to provide simple and efficient ARQ-based symbol-level rate adaptation with fine granularity. A turbo-coded system is used as an example showing that the proposed design provides actual communication rates that are close to the channel capacity.

关键词： automatic repeat request adaptive modulation modulation coding error correction coding

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An improved technique for suppression of intrachannel four-wave mixing in 40-Gb/s optical transmission systems

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IEEE PHOTONICS TECHNOLOGY LETTERS 2007年第2-4期19卷 67-69页

作者： Batshon, Hussam G. Djordjevic, Ivan B. Vasic, Bane V. Univ Arizona Dept Elect & Comp Engn Tucson AZ 85721 USA

This letter presents an efficient method for testing the efficiency of modulation techniques for countering the effects of intrachannel four-wave mixing by calculating the sum of all the contributors at a given resonance position (the position affected by the surrounding pulses). In addition to this method, we are proposing a modulation technique that shows a significant Q-factor improvement of up to 7.5 dB (depending on the number of spans and the phase sequence implemented) over the uncoded return-to-zero ON-OFF keying. Although the implementation of this phase modulation technique is simple, it is still very efficient in extending the nonlinearity tolerance and enhancing the performance of a high-speed optical transmission system.

关键词： communication system nonlinearities forward-error correction (FEC) low-density parity-check (LDPC) codes modulation coding optical communications optical Kerr effect

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Characters of laser ranging on inter-satellite relative position measurement

Characters of laser ranging on inter-satellite relative posi...

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3rd International Conference on Recent Advances in Space Technologies

作者： Gao Peng You Zheng Tsinghua Univ Dept Precis Instruments & Mechanol Beijing 100084 Peoples R China

ISBN: (纸本)9781424410569

More and more technology innovation and evolution have been used on the small satellite for remote measurement, target searching and tracking missions being performed in space. To achieve relative navigation, relative control intelligently, or to implement some important missions, inter-satellite relative position must be known. In this paper, the measurement procedures of relative position are given. To get precise result of inter-satellite relative position under some specific conditions, laser ranging method should be considered. And the laser ranging method is one of the most valuable methods which should be considered. The principles of laser ranging means and characters of that in space are discussed. Some analysis of this mean is presented. Because of the laser ranging specific characters of application in small satellites formation-flying, some conclusion of laser ranging method will not be suitable for usage in space. The difference of the measurement in space and that in general condition is discussed. Then the modified laser ranging method using code modulation is presented. While, this laser ranging method may require help of other means to achieve the continuous measurement of relative position in some specific missions. Finally, the outlook of the inter-satellite relative position measurement is represented.

关键词： Position measurement Space technology Technological innovation Target tracking Performance evaluation Extraterrestrial measurements Space missions Satellite navigation systems Intelligent control modulation coding

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Evaluation of Welch-Costas frequency hopping pattern for OFDM cellular system

Evaluation of Welch-Costas frequency hopping pattern for OFD...

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18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication

作者： Wang Chenwei Zhang Xin Yang Dacheng Beijing Univ Posts & Telecommun Wireless Theories & Technol Lab WT&T Beijing 100876 Peoples R China

ISBN: (纸本)9781424411436

The performance of frequency hopped OFDM cellular system depends on the designing of frequency hopping sequences. This paper explores fast frequency hopped OFDM in the link level of a cellular communication system. Each user is assigned several sub-carriers by the base station in each cell in every time slot according to the predetermined hopping sequences. The frequency hopped OFDM technique based on orthogonal hopping sequences can improve communication performance in a cellular system since it could minimize intra-cell interference and average inter-cell interference. In this paper, Welch-Costas Array Pattern is derived under independent and cluster hopping schemes, which enable us to evaluate the system performance with the Turbo code modulation scheme. Examples of the frequency sequences and how they are assigned to users are also given. We also simulate and analyze the impacts of the channel environment and parameters, frequency diversity, and inter-cell interference diversity on the performance of the coded frequency hopped OFDM cellular system.

关键词： Interference Spread spectrum communication Frequency diversity Base stations System performance Turbo codes modulation coding OFDM modulation Analytical models Performance analysis

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Bit and Power Loading Approach for Broadband Multi-Antenna OFDM System

Bit and Power Loading Approach for Broadband Multi-Antenna O...

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IEEE Conference on Vehicular Technology (VTC)

作者： Muhammad Imadur Rahman Suvra Sekhar Das Yuanye Wang Flemming Bjerge Frederiksen Ramjee Prasad Center for TeleInFrastruktur (CTiF) Aalborg University Copenhagen Denmark

In this work, we have studied bit and power allocation strategies for multi-antenna assisted Orthogonal Frequency Division Multiplexing (OFDM) systems and investigated the impact of different rates of bit and power allocations on various multi-antenna diversity schemes. It is observed that, if we cannot find the exact Signal to Noise Ratio (SNR) thresholds due to different reasons, such as reduced Link Adaptation (LA) rate, Channel State Information (CSI) error, feedback delay etc., it is better to fix the transmit power across all sub-channels to guarantee the target Frame Error Rate (FER). Otherwise, it is possible to use adaptive power distribution to save power, which can be used for other purposes, or to increase the throughput of the system by transmitting higher number of bits. We also observed that in some scenarios and in some system conditions, some form of simultaneous bit and power allocations across OFDM sub-channels are required together for efficient exploitation of wireless channel.

关键词： OFDM Diversity methods modulation coding Signal to noise ratio Power distribution Throughput System performance Channel state information State feedback Delay

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