一种新颖的多用户OFDM资源分配算法

在多用户正交频分复用(OFDM)系统中设计一种新颖的子载波-功率分配方法来最大化用户数据传输速率.这个方案分成两部分,子载波分配和功率分配.其中,子载波分配方法是在信道容量矩阵中将信道容量最好的子载波首先进行分配,功率分配采用注水方法.研究和模拟结果表明,该算法在只改变各个子载波增益系数的基础上,基本保持了较低的复杂度,并且极大地提高了用户数据传输速率.     

Coding techniques for link adaptation in multicarrier systems

A novel technique for improving coding and diversity gains in orthogonal frequency division multiplexing (OFDM) systems is proposed. Multidimensional symbol design based on complex field codes with interleaving across frequency has been known for some time now. However, such symbols cannot be concatenated to convolutional codes owing to the prohibitive complexity of decoding. A novel way of designing multidimensional symbols that allow to concatenate them to convolutional codes while maintaining a low decoding complexity is shown. The proposed multidimensional symbols are based on tailbiting convolutional codes and the design of codes is discussed with desirable properties. Also the design of bit interleaved coded modulation-type and trellis-coded modulation-type codes over these multidimensional symbols is shown. Simulations show that the proposed coding scheme provides significant performance and/or complexity improvements over existing alternatives and also provides more degrees of freedom for channel-based link adaptation.     

On subchannel inversion for improvement of power efficiency in OFDM-based systems

The problem of power loading in orthogonal frequency division multiplexing (OFDM)-based systems that provides minimization of the bit-error rate (BER) performance under a fixed transmit power (or equivalently minimisation of the transmit power under a fixed value of the BER) is addressed in this work. A lemma about inversion of subchannel power gains is proved and examples that exhibit its utility are presented. As a result, a non-iterative adaptive power allocation technique is derived. The algorithm combines the recently proposed ordered subcarrier selection method with 'subchannel inversion'. Compared with the original technique, such a combination provides a power gain that depends on the channel statistics.     

Cross-layer design for block subchannel allocation and admission control in the IEEE 802.16 OFDMA networks

The flexibility of orthogonal frequency-division multiple access (OFDMA) technology necessitates a compromise between spectrum efficiency and quality of service (QoS) in IEEE 802.16 broadband wireless networks. This article proposes a complete solution with the nice feature of adaptive modulation and a coding scheme to provide both delay and loss rate guarantees for real-time services. The proposed method first determines the subframe boundary according to the current downlink and uplink backlogs. To comply with the IEEE 802.16 standard, the proposed method then groups contiguous subchannels and allocates them to proper connections based on the current loss rate and available modulation and coding schemes for each connection. By modeling the aggregated required subchannels as a Gaussian distribution, this study develops a simple admission control algorithm by checking if there are enough resources for a new connection. Simulation results show that the proposed solution can provide QoS guarantee with high spectrum efficiency.     

Comparison between wavelet-based and Fourier-based multicarrier UWB systems

The use of wavelet transform in multicarrier ultra wideband (UWB) systems is analysed and the results are compared with Fourier-based multicarrier UWB systems. It is well known that convolution in time domain is equivalent to multiplication in frequency domain; however, there is no closed-form expression in the literature for convolution's counterpart in the wavelet domain. A formula is derived to represent convolution's counterpart in the wavelet domain. Furthermore, the effects of choice and type of wavelet filters and different decomposition levels are investigated. Finally, a performance comparison of both techniques for IEEE 802.15.3a channel models using IEEE802.15.3a multiband-orthogonal frequency division multiplexing UWB specifications is provided.     

认知OFDM系统的一种公平有效的多用户资源分配方案

在可用子载波、干扰温度、次级用户功率预算及公平性等约束条件下,提出了一种适用于认知OFDM系统的公平有效的多用户资源分配方案.该方案将子载波和功率分配分为两个相继的步骤,以降低计算复杂度.第一步引入子载波分配的比例公平原则,保证每个用户都能满足一定的通信要求;第二步采用一种改进的快速迭代注水算法,通过选择适当的调整步长...     

Adaptive systems in speckle-pattern interferometry

The concept of adaptivity in television holography is discussed, and various realizations of adaptivity are presented. In one possible variation, functions of the components of the optical arrangement may be changed to adapt them to measurement conditions. An additional peculiarity of the technique is that reference waves are produced by holographically reconstructed virtual images. A method, believed to be new, is introduced for synthesizing the phase front of the master object beam that is produced by a simple holographic optical element and is used as a smooth or a speckled reference beam in the electronic speckle-pattern interferometer. An adaptive interferometer is presented as a measuring device for various measuring tasks. Selected applications are shown, demonstrating different aspects of adaptivity.     

Multiple multi-level redundancy allocation in series systems

This paper deals with a multiple multi-level redundancy allocation problem (MMRAP) in which all available items for redundancy (system, module and component) can be simultaneously chosen. Due to a well-known principle that the redundancy at the component level (component redundancy) is more effective than the redundancy at the system level (system redundancy), the object of redundancy allocation has been limited to the component redundancy. In addition, multi-level redundancy allocation problems (MRAP) have been addressed, considering the redundancy at the subsystem level (modular redundancy). In this paper, the MMRAP is formulated and a GA algorithm is presented to solve the problem. Some numerical examples are illustrated.     

Power allocation in SVD- and GMD-assisted MIMO systems

Singular-value decomposition (SVD)-based multiple-input multiple-output (MIMO) systems have attracted a lot of attention in the wireless community where the whole MIMO channel is decomposed into a number of unequally weighted independent single-input single-output (SISO) channels. The unequal weighting of the SISO channels has led to intensive research on bit- and power allocation even in MIMO channel situations with poor scattering conditions identified as the antenna correlation effect. In this situation, the unequal weighting of the SISO channels becomes even much stronger. In comparison to the SVD-assisted MIMO transmission, geometric mean decomposition (GMD)-based MIMO systems are able to compensate for the drawback of weighted SISO channels when using SVD at the cost of remaining interferences which can be easily removed by using dirty paper precoding. Together with different QAM constellation sizes per layer, bit loading and power allocation can be helpful to balance the bit-error probabilities in the activated number of MIMO layers. The novel contribution of this paper is that optimal and suboptimal power allocation solutions are investigated under the assumption of unequal SISO channels as well as different QAM constellation sizes per MIMO layer. Our results show that GMD-based MIMO transmission has the potential to significantly simplify the process of bit and power loading and outperforms the SVD-based MIMO transmission as long as the same QAM-constellation size is used on all equally-weighted SISO channels.     

Simulation of the operation of multiuser distributed measurement and control systems

A computer simulation approach to the study of remote multiuser computer systems in educational and scientific research via the internet/intranet is proposed that offers the possibility of an extended analysis of their modes of operation. An example of algorithm and program execution of the proposed approach is discussed and analyzed.     

Optimal reliability and maintainability allocation in manufacturing systems

In this article an attempt has been made to solve an important task in the reliability management of manufacturing systems: the definition of reliability and maintainability specifications of parts, the general objective being to increase productivity while maintaining costs low. An analytical approach has been considered to evaluate an average index of production capability in series-parallel systems. A heuristic optimization procedure has been developed to solve the following problems: (a) determine the optimal reliability and maintainability allocation of parts to achieve the maximum production index at a given cost; and (b) determine the optimal reliability and maintainability allocation of parts which minimizes the total cost of investments, subject to the constraint of meeting a system production requirement. Numerical examples prove the effectiveness of the proposed procedure and show that the application of optimization analyses can provide large gains in terms of either productivity or total cost.     

Ant colony optimisation-based multiuser detection for direct-sequence CDMA systems with diversity reception

An ant colony optimisation (ACO)-based multiuser detector assisted by spatial diversity reception using direct-sequence CDMA is proposed. By taking advantage of heuristic values and the collective intelligence of ACO, the proposed detector offers almost the same bit error rate (BER) performance as the full-search-based optimum multiuser detector does, while greatly reducing the computational complexity. The near-far resistance of the ACO-based multiuser detector is also examined. The BER performance for a ten-user system deteriorates scarcely when the interfering users' energy is 12 dB higher than that of the desired user.     

Inspection allocation for multistage deteriorating production systems

The paper deals with the layout and operation of an inspection system used for detecting malfunctioning processors in a multistage production system. This problem involves three inter-related decisions: (i) the overall inspection capacity; (ii) the assignment of inspection tasks to inspectors; and (iii) the scheduling of the inspector's tasks. These decisions require a trade-off between the cost of inspectors and the loss associated with non-conforming products. A hierarchical heuristic solution procedure is proposed to support these three related decisions. Numerical experiments demonstrate the performance of the heuristic, showing that solution criteria are very close to their lower bounds. Although we use production terminology, the results might be applicable to any organization, which inspects and maintains a variety of characteristics of its branches or activities.     

Inspection allocation for multistage deteriorating production systems

The paper deals with the layout and operation of an inspection system used for detecting malfunctioning processors in a multistage production system. This problem involves three inter-related decisions: (i) the overall inspection capacity; (ii) the assignment of inspection tasks to inspectors; and (iii) the scheduling of the inspector's tasks. These decisions require a trade-off between the cost of inspectors and the loss associated with non-conforming products. A hierarchical heuristic solution procedure is proposed to support these three related decisions. Numerical experiments demonstrate the performance of the heuristic, showing that solution criteria are very close to their lower bounds. Although we use production terminology, the results might be applicable to any organization, which inspects and maintains a variety of characteristics of its branches or activities.     

A hybrid multiuser detector for DS-UWB systems with matched filter and error-bit recognizer

In this article, we propose a hybrid algorithm of multiuser detection (MUD) for direct sequence ultra-wideband (UWB) communication systems, based on matched filters (MF) and error-bit recognizers (ER). The ER embraces three steps: bit mapping, K-means clustering, and sign judgment. In this detector, we construct a mapping function and map the output base-band bits from MFs into a one-dimensional feature space to get the amplitude information. After that, we set an initial value and classify the bits into right bits and wrong ones by K-means clustering. Finally, we make the sign judgment to prevent some right bits being picked out as wrong bits and correct the wrong bits to reduce the bit error rate (BER) of the system. Compared to a conventional detector based on MFs and minimum mean square error detector, to a large extent, our detector can improve the BER performance of a system because of high recognition probability of the wrong bits in K-means clustering. What is more, the simulation results show that the proposed hybrid MUD is not sensitive to the number of users. It can achieve a good BER performance and low computational complexity when there are 20 UWB transmitters in the channel.     

放大转发中的最优功率分配与最佳中继选择

用最优功率分配与最佳中继选择相结合的方法实现了放大转发系统的误比特率最小化。为了使单中继非协作放大转发系统的误比特率最小,通过分析媒体接入控制(MAC)层的请求发送/允许发送(RTS/CTS)信息,获得候选中继前向信道和后向信道的增益,以信道增益为变量,得到最佳功率分配的闭合表达式。同时,以误比特率作为中继选择准则,实现分布式最佳中继选择。仿真结果表明,与同类算法相比,该功率分配与中继选择策略使系统的误比特率达到最小。     

基于改进粒子群算法的分布式天线系统跨层功率分配方案

结合数据链路层的队列状态信息和物理层的信道状态信息定义了系统的吞吐量系数和公平性系数,建立了分布式天线系统跨层功率分配的离散速率集优化模型。对粒子群优化算法的初始群体产生、粒子更新等步骤进行了改进,形成了改进粒子群算法(IMPSO)。利用IMPSO进行了动态功率分配和跨层优化。数值仿真结果表明,IMPSO能够取得很好的队列时延性能,选取不同的权重可对系统吞吐量性能和公平性性能产生重要影响,IMPSO获得的系统吞吐量性能和公平性性能较之功率固定分配算法(AP)均有较大幅度的提高。