A Hopfield neural-network-based dynamic channel allocation withhandoff channel reservation control

As channel allocation schemes become more complex and computationally demanding in cellular radio networks, alternative computational models that provide the means for faster processing time are becoming the topic of research interest. These computational models include knowledge-based algorithms, neural networks, and stochastic search techniques. This paper is concerned with the application of a Hopfield (1982) neural network (HNN) to dynamic channel allocation (DCA) and extends previous work that reports the performance of HNN in terms of new call blocking probability. We further model and examine the effect on performance of traffic mobility and the consequent intercell call handoff, which, under increasing load, can force call terminations with an adverse impact on the quality of service (QoS). To maintain the overall QoS, it is important that forced call terminations be kept to a minimum. For an HNN-based DCA, we have therefore modified the underlying model by formulating a new energy function to account for the overall channel allocation optimization, not only for new calls but also for handoff channel allocation resulting from traffic mobility. That is, both new call blocking and handoff call blocking probabilities are applied as a joint performance estimator. We refer to the enhanced model as HNN-DCA++. We have also considered a variation of the original technique based on a simple handoff priority scheme, here referred to as HNN-DCA+. The two neural DCA schemes together with the original model are evaluated under traffic mobility and their performance compared in terms of new-call blocking and handoff-call dropping probabilities. Results show that the HNN-DCA++ model performs favorably due to its embedded control for assisting handoff channel allocation     

Achievable Rates Over Time-Varying Rayleigh Fading Channels

This paper investigates achievable rates for a wireless communication system when neither the transmitter nor the receiver has a priori knowledge of the channel state information (CSI). The dynamics of the flat fading channel are characterized by a known Doppler spectrum. Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals and long data blocks. Expressions for the achievable rates include a lower bound on mutual information, and the achievable rates of pilot-aided systems with optimized resource allocation. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates in the low signal-to-noise ratio (SNR) regime, and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocation and duty cycle developed for Gaussian signals can also be applied to systems using other signaling formats.     

分布式双向中继选择算法及用户功率分配

针对放大转发的瑞利双向中继信道的节点选择问题,提出了基于部分信道信息的分布式双向中继选择算法。算法通过计算双向链路的接收信噪比,推导出满足目标接收信噪比的转发阈值,各中继节点根据该阈值决定是否参与转发,从而实现分布式选择。此外,考虑用户总功率受限的情况,在分布式中继选择基础上提出了优化功率分配策略,使双向信道的接收信噪比更加接近。仿真结果表明,分布式中继选择算法与最优多中继算法的系统传输速率相似,计算复杂度大大降低,尤其是在中继数目增大的情况下更加明显。优化功率分配策略能进一步提高系统能量效率,在相同性能下可节省7%左右的功率。     

Efficient power allocation for decentralized distributed space-time block coding

In this paper, we propose two ad-hoc, yet efficient, power allocation strategies for a decentralized distributed space-time block coding (Dis-STBC) system where knowledge about the channel state information (CSI) is not available at the transmitter(s). The first is an open-loop strategy which requires no control signaling; the second is a feedback-assisted strategy which requires some control signaling, but which can achieve better power-efficiency. Focusing on a particular decentralized Dis-STBC scheme (m-group), the asymptotic outage probability is derived and the power-efficiency advantages of the proposed strategies over a uniform-power strategy are illustrated by evaluating the outage and link failure probabilities.     

Optimized in-band control channel with channel selection scheduling and network coding in distributed cognitive radio networks

This article proposes an optimized in-band control channel scheme with channel selection scheduling algorithm and network coding based transmission paradigm in the distributed cognitive radio network (...     

Resource allocation for cellular radio systems

High terminal traffic densities are expected in urban multiuser radio systems. An efficient allocation of resources is the key to high system capacity. In this paper, a distributed dynamic resource allocation (DDRA) scheme based on local signal and interference measurements is proposed for multiuser radio networks. It offers “soft capacity” for time division multiple access (TDMA) and frequency division multiple access (FDMA) systems, bounded above by N per base station, where N is the total number of channels in the system. The decisions are made local to a terminal and its base and are essentially independent of the rest of the system. A distributed dynamic channel assignment scheme is used to assign channels to new calls. This scheme assigns a channel that offers the maximum carrier to interference ratio (CIR) to a new call. A distributed constrained power control (DCPC) scheme based on CIR measurements is used for power control. The channel assignment scheme and the power control scheme are coupled to obtain an interactive resource allocation scheme. We compare the capacity of a system which uses the distributed dynamic resource allocation scheme described above with the capacity of a system which uses the channel assignment scheme alone. The system capacity is measured by simulation as the number of terminals that can be served by the system with a CIR above an acceptable minimum. In a 1D cellular system, coupling the channel assignment scheme with power control is discussed. Simulations were also used to show the effect of varying the maximum transmitter power on system capacity     

Efficient signaling schemes for wideband space-time wireless channels using channel state information

An orthogonal decomposition of a general wideband space-time frequency selective channel is derived assuming antenna arrays at both the transmitter and receiver. Knowledge of channel state information is assumed at both the transmitter and receiver. The decomposition provides a framework for efficiently managing the degrees of freedom in the space-time channel to optimize any combination of bit-error rate and throughput in single-user or multiuser applications. The decomposition is used to derive efficient signaling schemes and receiver structures for a variety of scenarios. For a fixed throughput system, we investigate a power allocation scheme that minimizes the effective bit-error rate. In addition, a strategy to maximize the throughput under a worst-case bit-error rate constraint is proposed. For multiuser applications, we propose a signaling scheme that achieves orthogonality among users by exploiting the temporal channel modes which are common to all users. The effect of imperfect channel state information at the transmitter is also investigated.     

Robust H∞ Power Control for CDMA Systems in User‐Centric and Network‐Centric Manners

In this paper, we present a robust H_∞ distributed power control scheme for wireless CDMA communication systems. The proposed scheme is obtained by optimizing an objective function consisting of the user's performance degradation and the network interference, and it enables a user to address various user‐centric and network‐centric objectives by updating power in either a greedy or energy efficient manner. The control law is fully distributed in the sense that only its own channel variation needs to be estimated for each user. The proposed scheme is robust to channel fading due to the immediate decision of the power allocation of the next time step based on the estimations from the H_∞ filter. Simulation results demonstrate the robustness of the scheme to the uncertainties of the channel and the excellent performance and versatility of the scheme with users adapting transmit power either in a user‐centric or a network‐centric efficient manner.     

Traffic-adaptive aggregate channel allocation for future cellular communication systems

A fundamental problem in third-generation mobile systems is the adaptation of the channel allocation to the traffic volume variation. Traffic adaptation may be partly achieved by the following (aggregate channel allocation) problem: given the set of channels, the cell structure and the load to be accommodated in each cell within a certain time zone, find the optimal allocation of channels to cells subject to the restrictions arising from the minimum permissible distance of cells where the same channel can be used at the same time. In this paper the problem is optimally formulated and efficiently solved by a heuristic. In the sequel the performance of a combined channel management scheme that uses the above problem for handling major traffic variations and a distributed DCA scheme for handling local traffic variations is assessed. Finally, results are presented and some concluding remarks are made. © 1998 John Wiley & Sons, Ltd.     

Adaptive Self-Learning Resource Allocation Scheme for Unlicensed Users in High-Rate UWB Systems

In this paper, we investigate a dynamic sub-band allocation for spectrum sharing in the multiuser OFDM-UWB systems while respecting the system constraints and the distributed MAC architecture. The contribution of this work is twofold: first we propose a dynamic spectrum allocation scheme based on an analytical study by deriving a multiuser optimization problem to find the optimal allocation solution. Based on an adaptive and low-complexity approach, the proposed scheme shares the available resources among unlicensed UWB users while taking into consideration the QoS requirements and the channel conditions. Then we extend the proposed scheme to allow the coexistence of a maximum number of secondary users in one channel while maintaining all the constraints support. This leads to a time-frequency allocation approach that exploits information laying in different layers, allowing a cross-layer design. This new approach improves the system performance compared to WiMedia solution and offers a considerable gain for users that have strict QoS requirements.     

D-CAT: An Efficient Algorithm for Distributed Channel Allocation in Cellular Mobile Networks

We propose a distributed channel allocation algorithm based on a threshold scheme, called D-CAT, for cellular mobile networks. The algorithm employs two thresholds: (i) a heavy threshold for determining whether a cell is heavy, or overloaded, and for triggering the channel allocation algorithm; and (ii) a target threshold for indicating the target number of free channels that a heavy cell intends to acquire. Based on the two-threshold scheme, the D-CAT algorithm can determine the optimal number of free channels as well as the cell(s) from where a heavy cell should import channels in order to satisfy the required channel demand. Simulation experiments and analyses show that the proposed algorithm incurs lower overhead for channel allocation and is more efficient in terms of channel utilization than other distributed channel allocation algorithms. It also outperforms other centralized and distributed algorithms in terms of call blocking probability.     

Distributed traffic adaptive channel allocation

Dynamic channel allocation (DCA) schemes adapt to the time variant demand for channels in cellular mobile telephony systems. In this paper we propose a DCA scheme that smoothly changes the channel allocation by solving the following problem. Given a cell structure, a collection of channels, the frequency reuse distance, an allocation of channels to cells, and the number of active connections per cell, accommodate a new call or a new handover by minimally reconfiguring the established allocation of channels to cells. First, this problem is formulated as 0–1 quadratic programming problem. Next, we present a distributed, heuristic solution to the problem, which is based on the observed behaviour of the optimal algorithm. Finally, we present some simulation results on the performance and the feasibility of the distributed algorithm. © 1997 John Wiley & Sons, Ltd.     

An Efficient and Adaptive Bandwidth Allocation Scheme for Mobile Wireless Networks Using an On-Line Local Estimation Technique

The next generation of mobile wireless networks has to provide the quality-of-service (QoS) for a variety of applications. One of the key generic QoS parameters is the call dropping probability, which has to be maintained at a predefined level independent of the traffic condition. In the presence of bursty data and the emerging multimedia traffic, an adaptive and dynamic bandwidth allocation is essential in ensuring this QoS. The paradox, however, is that all existing dynamic bandwidth allocation schemes require the prior knowledge of all traffic parameters or/and user mobility parameters. In addition, most proposals require extensive status information exchange among cells in order to dynamically readjust the control parameters, thus making them difficult to be used in actual deployment.In this paper, we introduce a novel adaptive bandwidth allocation scheme which estimates dynamically the changing traffic parameters through local on-line estimation. Such estimations are restricted to each individual cell, thus completely eliminating the signaling overhead for information exchange among cells. Furthermore, we propose the use of a probabilistic control policy, which achieves a high channel utilization, and leads to an effective and stable control. Through simulations, we show that our proposed adaptive bandwidth allocation scheme can guarantee the predetermined call dropping probability under changing traffic conditions while at the same time achieving a high channel utilization.     

Bounding the performance of dynamic channel allocation with QoSprovisioning for distributed admission control in wireless networks

We investigate the performance of distributed admission control with quality of service (QoS) provisioning and dynamical channel allocation for mobile/wireless networks where the co-channel reuse distance is considered as the only limiting factor to channel sharing. We first provide a QoS metric feasible for admission control with dynamically allocated channels. We then derive a criterion analytically using the QoS measure for distributed call admission control with dynamic channel allocation (DCA). When maximum packing is used as the DCA scheme, the results obtained are independent of any particular algorithm that implements dynamic channel assignments. Our results, thereby, provide the optimal performance achievable for the distributed admission control with the QoS provisioning by the best DCA scheme in the given setting     

Opportunistic multichannel access with decentralized channel state information

This paper considers multiaccess control for the uplink in orthogonal frequency division multiple access wireless networks. To avoid the extensive information exchange associated with centralized approaches, we formulate the decentralized access control problem with the contention power constraint as a Bayesian game, mapping time‐varying channel state information into contention strategies. By exploiting the problem structure, a strategy where users access the channels with probability one if the observed channel gain is above a predetermined threshold is shown to be optimal. It is also shown that the energy consumption of the threshold strategy will not exceed that of randomized strategies. The game is then equivalently reformulated as one of finding the threshold value in a distributed manner, and the existence and uniqueness of Bayesian Nash equilibria is established. A distributed algorithm based on Lagrange duality is proposed to approach the unique equilibrium, and the algorithm is shown to be globally stable. In a homogeneous system, the performance loss of the proposed scheme is proved to be bounded compared with a centralized channel allocation scheme. Contrary to other proposals, our method allows for heterogeneous channel state information and achieves a comparable throughput with reduced power. Copyright © 2013 John Wiley & Sons, Ltd.     

Capacity Performance of Polarized Distributed MIMO System on Rician Channel

The analytical upper bound and lower bound on the ergodic capacity of polarized distributed antenna system and their relation with antenna polarization on Rician channel are deduced by applying properties of complex non-central Wishart matrices and matrix-variate non-central quadratic forms. Compared to the related studies, our analysis is extended to account for the polarized distributed system with Rician fading where a line-of-sight component exists and both ends are affected by spatial correlation. The antenna polarization has some impacts on the capacity bounds according to the expressions of capacity bounds. Both the transmitter and the receiver are equipped with multiple polarization antennas, and the transmitters are of linear layout. A power allocation scheme based on the path loss fading is presented by maximizing the capacity upper bound. The power allocation scheme is feedback efficient compared with those power allocation schemes based on statistical parameters of the channel which need a large amount of feedback. In the simulations, the ergodic capacity of polarized distributed MIMO is analyzed. Comparisons are taken on the effects of angle spread, Rician factor and power on the ergodic capacity. The proposed power allocation scheme is superior to the equal power allocation scheme and has very close performance to the optimal power allocation scheme.     

5G室内密集立体覆盖的计算通信:架构、方法与增益

提出了一种新型的室内密集立体覆盖的计算通信一体化架构,通过挖掘信道计算、容量计算以及网络资源优化计算之间的内在联系,并利用基于云计算和雾计算的密集分布式接入网络的优势,该架构完成了计算电磁学、计算信息论与大规模优化理论到计算通信理论的深度融合.介绍了该架构的实现方法,即以密集异构分布式无线接入网络作为通信接入网络基础架构,利用分布式的计算资源结合计算电磁学理论实现并行化的信道计算,据此进一步依据计算信息论实现容量计算,并基于大规模优化理论完成多用户的网络资源优化计算,最终实现由传播环境到信道容量与资源分配的计算通信.     

Channel assignment and layer selection in hierarchical cellularsystem with fuzzy control

We consider a hierarchical cellular system, which consists of a macrolayer and a microlayer. The macrocells accommodate fast mobile users. However, if we direct too many mobile users to the macrocells, the system capacity is low. On the other hand, the microcells are designed to increase capacity, but they cause a large number of handoffs. The aim is to maximize the system capacity while keeping the amount of handoff small. We minimize the handoff rate by a fuzzy layer selection algorithm, which makes use of the past cell dwell times of a user and the channel occupancy of the target cell. To maximize the capacity, we propose a distributed channel assignment algorithm to dynamically allocate the channels among the two layers. Exchange of information is allowed between neighboring macrocells. The state of channel assignment in a macrocell and its interfering cells are tabulated in a channel allocation table, which provides all information required in the integrated resource allocation scheme. The performance is evaluated by simulation and compared with the popular layer selection scheme known as the threshold method     

分布式阵列系统中反馈比特的分配方法

在采用频分双工的通信系统中,基站通常需要用户反馈信道状态信息以进行预编码。对于分布式阵列系统,由于多个接入节点布置在小区的不同位置,用户与小区内不同接入节点之间的信道条件不同。当用于反馈信道状态信息的资源受限时,需要对反馈比特的分配方法进行优化,从而提高系统的整体性能。在多用户分布式阵列系统中,采用基于距离阈值的接入节点选择方法,并在此基础上结合随机矢量量化码本的量化特性以及泰勒展开法,对系统量化容量损失进行推导,并给出了近似表达式。基于该表达式,提出了反馈比特分配方法,与其他的分配方法相比,不限制用户选择的接入节点数目使本文的方法更加具有普遍性。仿真结果显示,在反馈资源有限的情况下,提出的策略优于传统的等比特分配方案,可以获得较好的性能。     

Spreading and power allocation for multiple antenna transmission using decorrelating receivers

We propose a new scheme for multiple antenna transmission in the context of spread-spectrum signaling. The new scheme consists of using shifted Gold sequences to modulate independent information on the multiple antennas. We show that this strategy of using multiphase spreading (MPS) on different antennas greatly improves the throughput over currently known spread-spectrum multiple-antenna methods. We also find the optimal power allocation strategy among multiple transmit antennas for a fixed rate of channel state information, which might be provided via a feedback link, at the transmitter. We demonstrate the differences in optimal power distribution for maximizing capacity and minimizing probability of outage. When the transmission from the two antennas uses orthogonal spreading, we find that optimizing the power does not give much gain over the equal power transmission. However, when the transmissions are not orthogonal as in the case of MPS, then allocating power to maximize throughput gives considerable gain over equal power transmission. We also consider the effect of imperfections in the feedback channel on the optimal power allocation and show that our power allocation scheme is robust to feedback errors.