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检索条件"主题词=Modulation coding"

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Cross-Layer Adaptive ARQ and modulation Tradeoffs

Cross-Layer Adaptive ARQ and Modulation Tradeoffs

引用

IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

作者： Alireza Kobravi Mohammd Shikh-Bahaei King''s College London UK

We investigate the tradeoff between uncoded adaptive modulation (AM) in the physical layer, and automatic repeat re-quest (ARQ) in the data link layer, on the system throughput. Most of the applicable research has assumed fixed maximum-number-of-retransmissions (MNR); however, we show that applying adaptive MNR (referred to as adaptive ARQ in this paper) based on channel condition, enhances the throughput performance of the system. In the second part of this paper the effect of finite length queuing, AM, and ARQ on system packet loss is studied. As today's networks and applications generate the traffics that are bursty and self-similar, using Poisson processes to model the packet arrivals proves to be an error-prone assumption. Instead, we will apply generalized exponential (GE) and Pareto distributions, which allow for the modeling of a wide range of bursty distributions, to model the packet arrivals. Closed form expressions for the packet loss and the packet dropping probabilities are derived as functions of MNR and transmission rate. We show that employing adaptive ARQ decreases the packet loss rate while improving the throughput.

关键词： Automatic repeat request Physical layer Throughput Traffic control Resource management Quality of service Telecommunication traffic Propagation losses modulation coding Delay

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On the Outage Capacity of a Practical Decoder Using Channel Estimation Accuracy

On the Outage Capacity of a Practical Decoder Using Channel ...

引用

IEEE International Symposium on Information Theory

作者： Pablo Piantanida Sajad Sadough Pierre Duhamel CNRS-LSS Supelec Gif-sur-Yvette France ENSTA CNRS LSS Paris France CNRS LSS Suprlec Gif-sur-Yvette France

ISBN: (纸本)9781424413973;1424413974

The optimal decoder achieving the outage capacity under imperfect channel estimation is investigated. First, by searching into the family of nearest neighbor decoders, which can be easily implemented on most practical coded modulation systems, we derive a decoding metric that minimizes the average of the transmission error probability over all channel estimation errors. This metric, for arbitrary memoryless channels, achieves the capacity of a composite (more noisy) channel. Next, according to the notion of estimation-induced outage capacity (EIO capacity) introduced in our previous work, we characterize maximal achievable information rates associated to the proposed decoder. The performance of the proposed decoding metric over uncorrelated Rayleigh fading MIMO channels is compared to both the classical mismatched maximum-likelihood (ML) decoder and the theoretical limits given by the EIO capacity (i.e. the best decoder in presence of channel estimation errors). Numerical results show that the derived metric provides significant gains, in terms of achievable information rates and bit error rate (BER), in a bit interleaved coded modulation (BICM) framework, without introducing any additional decoding complexity.

关键词： Channel estimation Maximum likelihood decoding Channel capacity modulation coding Information rates Maximum likelihood estimation Bit error rate Nearest neighbor searches Error probability Memoryless systems

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A Cross-Layer Approach of Link Adaptation in IEEE 802.16 Broadband Wireless Access Systems

A Cross-Layer Approach of Link Adaptation in IEEE 802.16 Bro...

引用

International Conference on Wireless Communications, Networking and Mobile Computing (WiCom)

作者： Yu-Ting Yu Hsi-Lu Chao Department of Computer Science National Chiao Tung University Taiwan

IEEE 802.16 Broadband Wireless Access system (BWA) is a promising emerging technology. In the IEEE 802.16 standard, multiple data transmission rates are defined by employing different modulation and channel coding schemes. How to select a proper mode affects the system performance significantly. In this paper, an efficient link adaptation scheme with QoS support is proposed. The proposed scheme takes both QoS demand and channel condition into consideration to determine a proper transmission mode. The QoS demand of a connection is represented as an expected packet error rate (PER). Based on this expected PER, the BS calculates the required signal-to-noise ratio (SNR) threshold of each mode. By comparing the measured SNR and all modes' SNR thresholds, the BS then suggests the SS a proper transmission mode. We evaluate the proposed scheme by simulations. The simulation results show that the link adaptation scheme improves the average system throughput and guarantees each connection's QoS demand.

关键词： Physical layer modulation coding Councils Data communication Channel coding System performance Error analysis Signal to noise ratio Throughput Delay

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A Multi-dimensional super-orthogonal modulation alternative to M-QAM WCDMA for next generation wireless applications

A Multi-dimensional super-orthogonal modulation alternative ...

引用

AFRICON Conference

作者： Louis P. Linde Jacobus D. Vlok Department of Electrical Electronic and Computer Engineering University of Pretoria Pretoria South Africa University of Pretoria Pretoria South Africa

This paper presents bit-error-rate (BER) performance results of an upwards-expandable Multidimensional super-orthogonal modulation alternative to M-ary quadrature amplitude modulation wideband code- division-multiple-access (M-QAM WCDMA), suitable for application in next generation WLAN and wireless cellular systems. The unique combination of a M=4-dimensional WCDMA modem configuration and super-orthogonal families of quasi-complementary root-of-unity filtered (RUF) near constant-envelope generalized-chirp-like complex spreading sequences (SO-CE-GCL-CSS), renders a spectrally and power efficient output signal with a data throughput rate equivalent to that of M=16-ary quadrature amplitude modulated (16-QAM) WCDMA, but with the BER performance equivalent to that of BPSK/QPSK in both additive white Gaussian noise (AWGN) and fading multipath channel scenarios, given identical spreading factors and bandwidths.

关键词： Multiaccess communication Quadrature amplitude modulation AWGN Bit error rate Amplitude modulation Multidimensional systems modulation coding Wideband Wireless LAN Wireless cellular systems

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An Operation Scheme for T Hroughput Maximization and Fairness in CDMA Cellular Systems with AMC

An Operation Scheme for T Hroughput Maximization and Fairnes...

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IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

作者： Carlos E. Uc-Rios Domingo Lara-Rodriguez Electrical Engineering Department CINVESTAV Mexico Mexico

In this paper, the throughput maximization and fairness problems in the downlink of a sectored CDMA cellular system with AMC techniques are studied. We focus on maximizing the data rate for users on the cell border. An optimum data transmission with power control allocates the maximum allowable rate to only one user with the highest SINR. However, this throughput maximization rate allocation strategy causes high unfairness. On the other hand, if more service time or slots are assigned to the lower SINR users for fairness, system throughput will be decreased. Thus, we propose the operation of the system in a four time interval duty cycle that increases system throughput and fairness at the same time. In the first interval, users close to the base stations are served, one at a time in every sector. In the rest of the time intervals, for users close to the cell border, an On-Off Synchronous sectored operation is achieved. In this operation only one sector of each cell is allowed to transmit per each interval to only one user. Optimum durations of the time intervals are obtained. The results show that the average data rate at the cell border is increased 75% and the average data rate over the sector area is increased 9.7% relative to the traditional one-by-one transmission in each sector.

关键词： Multiaccess communication Throughput Signal to noise ratio Interference Downlink Data communication Base stations modulation coding Power control Cellular networks

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On Improving the Energy Efficiency of Wireless Sensor Networks under Time-Varying Environment

On Improving the Energy Efficiency of Wireless Sensor Networ...

引用

Conference on Local Computer Networks (LCN)

作者： Xiao-Hui Lin Yu-Kwong Kwok Hui Wang Faculty of Information Engineering Shenzhen University China Department of Electrical and Electronic Engineering University of Hong Kong Hong Kong China

The adaptive modulation and coding (AMC) schemes has long been adopted at physical layer to combat time-varying properties of the wireless channel. However, transmitting packet over deep fading channel can render extra energy expenditure, due to the incorporation of more error protection or usage of lower modulation mode, which is unaffordable for energy-limited wireless sensor device. To avoid such inefficient energy usage, a simple approach is to temporally buffer the packet when the channel is in deep fading, until the channel quality recovers. Nevertheless, buffering packet can lead to communication performance degradations - communication latency and packet overflow, which should be taken into consideration in sensing applications with QoS requirements. In this paper, by using previously proposed discrete time queuing model, we analyze the effects of Rayleigh fading on the sensor communication system, and propose a cross-layer design on power aware communication of sensor device. Specifically, in such channel adaptive system, each sensor can judiciously accesses the medium according to the channel condition, traffic load, and buffer variation. Simulation and analytical results indicate that, such cross-layer design can lead to energy conservation by as much as 30-40 per cent.

关键词： Energy efficiency Wireless sensor networks Sensor systems Rayleigh channels Cross layer design modulation coding Physical layer Fading Protection Degradation

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Multidimensional Coded modulation in Block-Fading Channels

Multidimensional Coded Modulation in Block-Fading Channels

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IEEE International Symposium on Information Theory

作者： Albert Guillen i Fabregas Giuseppe Caire Engineering Department University of Cambridge Cambridge UK Electrical Engineering Department University of Southern California Los Angeles CA USA

ISBN: (纸本)9781424413973

We study the problem of constructing coded modulation schemes over multidimensional signal sets in Nakagami-m block-fading channels. In particular, we consider the optimal diversity reliability exponent of the error probability when the multidimensional constellation is obtained as the rotation of classical complex-plane signal constellations. We show that multidimensional rotations of full dimension achieve the optimal diversity reliability exponent, also achieved by Gaussian constellations. Multidimensional rotations of full dimension induce a large decoding complexity, and in some cases it might be beneficial to use multiple rotations of smaller dimension. We also study the diversity reliability exponent in this case, which yields the optimal rate-diversity-complexity tradeoff in block-fading channels with discrete inputs.

关键词： Multidimensional systems modulation coding Fading Decoding Constellation diagram Signal to noise ratio Rayleigh channels Error probability MIMO OFDM

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Improving Robustness of CDM Spread Spectrumwatermarking

Improving Robustness of CDM Spread Spectrumwatermarking

引用

International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： Joceli Mayer Jose Carlos M. Bermudez Department of Electrical Engineering Federal University of Santa Catarina Florianopolis Santa Catarina Brazil

This paper proposes improvements to the code division modulation and multiplexing (CDM) spread spectrum watermarking. The improved CDM technique exploits all the available information at the embedded and determines the required energy for the spreading sequences to achieve a specified bit error probability. This approach considers an additive noise in the channel and all the interferences from the host signal, cross-correlation between spreading sequences, perceptual masking and interferences from collusion attacks. We provide results to illustrate the improvements achieved and also comparisons with traditional CDM watermarking.

关键词： Robustness Watermarking Interference Spread spectrum communication modulation coding Code division multiplexing Additive noise Computational complexity Degradation Bit error rate

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Differential Super-Quasi-Orthogonal Space-Time Trellis Codes

Differential Super-Quasi-Orthogonal Space-Time Trellis Codes

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IEEE Conference on Vehicular Technology (VTC)

作者： Jun Wang Jing Qian Junhui Dou Shouyin Liu Seong-Hyun Jang Jong-Wha Chong The Department of Electrical & Information Eng Huazhong Normal University Wuhan China The College of Information & Communications Hanyang University Seoul South Korea

This paper proposes a new differential super-quasi- orthogonal space-time trellis codes (SQOSTTC) with single- symbol maximum-likelihood (ML) decoding. Firstly, a new joint constellation, which can be used to construct a unitary matrix for quasi-orthogonal space-time block code (QOSTBC), is designed. Secondly, based on the joint constellation and criterion of maximizing the coding gain distance (CGD), set-partitioning is done. Finally, we introduce the simple single-symbol maximum- likelihood (ML) decoding. Simulation results show that our differential SQOSTTC can get better performance than the differential super-orthogonal space-time trellis code (SOSTTC) [5] with four transmit antennas at the transmission rate of 1.5 bits/s/Hz and lower decoding complexity than the differential super-pseudo-orthogonal space-time trellis codes (SPOSTTC) [13] and the differential SOSTTC [14] at the transmission rate of 2 bits/s/Hz.

关键词： Convolutional codes modulation coding Maximum likelihood decoding Transmitting antennas Block codes Modular construction Space time codes Educational institutions Channel state information Transmitters

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On the Design of 2x2 Full-Rate Full-Diversity Space-Time Block Codes

On the Design of 2x2 Full-Rate Full-Diversity Space-Time Blo...

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IEEE GLOBECOM 2007 - IEEE Global Telecommunications Conference

作者： Alireza Ghaderipoor Mahdi Hajiaghayi Chintha Tellambura Department of Electrical and Computer Engineering University of Alberta Edmonton AB Canada

There has been considerable research on the design of space-time block codes (STBCs) that guarantee full diversity without sacrificing the data rate. The main challenge is to maximize the coding gain by maximizing the determinant criterion. It is shown that the most of previous STBCs with full rate and full diversity order (FRFD) (e.g. threaded algebraic space-time (TAST) codes) are constructed via a unitary generator matrix. However, the unitary matrix has been represented using only a small number parameters to enable algebraic code design. In this paper, for a 2 times 2 STBC, we use a more general unitary matrix with a large number of parameters for STBC design. We obtain an upper bound on the coding gain and show that the maximum coding gain is attainable only with PAM signaling. Since optimum parameters for the case of QAM signaling is analytically intractable, we search using the genetic algorithm (GA) method. We also use the union bound criterion for code parameter search by GA. Our simulation results show that with both criteria, the optimum code for QAM signaling is the Golden code. The proposed code significantly outperforms other existing STBCs with the gains about 2 dB at a symbol error rate of 10 for BPSK and 4-PAM. The proposed code performs identically to the Golden code for QAM.

关键词： Block codes Quadrature amplitude modulation modulation coding Upper bound Quadrature phase shift keying Performance gain Signal analysis Genetic algorithms Symmetric matrices Receiving antennas

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