基于优先级信道预留的快速动态信道分配算法

针对TD-SCDMA系统现有快速动态信道分配算法的不足,提出了一种基于优先级信道预留的快速动态信道分配算法.该算法根据接力切换用户的移动台属性设定不同的优先级,为接力切换呼叫预留信道,结合小分组借用算法,增加了可移动边界动态信道分配(MB DCA)策略的灵活性.仿真结果表明,此算法相对于混合数据速率、小分组借用(MRG,mixed-data rate grouping borrowed)MB DCA算法,实现了VIP和快速移动切换用户的优先接入,有效地降低了切换呼叫的阻塞率,提高了数据业务性能和系统的信道利用率.     

Impact of radio resource allocation policies on the TD-CDMA systemperformance: evaluation of major critical parameters

This paper investigates the impact of major critical parameters and the effect of some radio resource allocation policies on the TD-CDMA system performance. Critical parameters are related either to the user behavior (e.g., user mobility, activity factors) or to processing techniques and algorithms implemented to control network performance and individual radio link quality (e.g., joint detection imperfection, handover margin, timeout for maintaining alive bad radio links). Network topology (e.g., distance between neighboring base stations) also undoubtedly influences capacity results. Analysis is carried out through accurate modeling of user behavior, interference scenarios, and power budget limitations at both terminals and infrastructure, allowing for proper implementation of radio resource allocation algorithms. Among these algorithms, power management (both at the initial channel assignment and during communication), dynamic channel allocation (DCA), and ongoing calls management are explored. An event-driven simulation approach was considered to model realistic system behavior and address system stability under various events generating traffic/interference fluctuations (e.g., call arrivals and departures, handovers, steps of power control loops). Such an approach is expected to offer a good estimate of the real conditions provided the propagation models are close to real life. As a consequence, measures to be taken to avoid/control overloading in a TD-CDMA (CDMA in general) environment can be naturally derived and tested with this methodology     

Interference-Adaptive Fast Dynamic Channel Allocation in TD-SCDMA System

This paper proposes a new priority metric for fast dynamic channel allocation (DCA) in TD-SCDMA system, which reallocates radio resource units (RUs) to bearer services in a cell. It allows for developing a new interference-adaptive fast DCA algorithm, which is more flexible with a non-uniform user distribution. It considers the relative transmission opportunities with respect to the residual capacity and co-channel interference levels for all users, which steadily varies in the real communication environment. The proposed fast DCA algorithm aims to fully utilize the physical resource available in the time-division duplexing (TDD)-based CDMA system subject to the various types of inter-cell interference, as opposed to most existing algorithms in which traffic load and quality of service cannot be jointly balanced among the multiple radio resource units in a flexible manner. The simulation results show that the proposed algorithm improves the outage performance while reducing the average system interference, achieving full utilization of the physical resource, i.e., 48 RUs in TD-SCDMA, over a wide range of acceptable outage performance.     

Performance of a cellular network based on frequency hopping with dynamic channel allocation and power control

A frequency- and time-division multiple-access (F-TDMA)-based mobile radio system using both dynamic channel allocation (DCA) and frequency hopping (FH) is investigated. We propose a new interference adaptive DCA (IA-DCA) algorithm that is suitably designed for a network implementing FH. The role played by the power control algorithm in this DCA-FH context is also investigated. We compare the performance of our proposal to that of fixed channel allocation (FCA) with and without FH and the well-known IA-DCA schemes investigated in the literature in the absence of FH. The performance results show that interesting synergic effects can be obtained in terms of forced termination and user satisfaction probability by using both DCA and FH. The results we show in the paper have been achieved by means of a system-level simulation tool which takes propagation, user mobility, interference, traffic, and channel allocation into account. The advantages of using FH are accounted for by using a suitable analytical model that gives the frame error rate as a function of the carrier-to-interference ratio and the number of hopping frequencies, at link level; this model is taken from the literature where it was presented for FCA, and here it is modified in order to be applicable to the DCA case.     

Comparative study of adaptive beam-steering and adaptivemodulation-assisted dynamic channel allocation algorithms

A range of dynamic channel allocation (DCA) algorithms, namely, distributed control and locally distributed control assisted DCA arrangements, are studied comparatively. The so-called locally optimized least interference algorithm (LOLIA) emerges as one of the best candidates for future mobile systems, supporting more than twice the number of subscribers in comparison to conventional fixed channel allocation (FCA). It can also cope with unexpected large increases in teletraffic demands while requiring no tedious frequency planning. This is achieved at the cost of more complex call setup and control, and the requirement of fast backbone networks for base station-base station signalling. Adaptive antennas are shown to significantly enhance the capacity of both the LOLIA and FCA-based networks, especially when used in conjunction with adaptive modulation techniques     

Dynamic channel allocation in interference-limited cellular systemswith uneven traffic distribution

Most recently proposed wireless dynamic channel allocation methods have used carrier-to-interference (C/I) information to increase the system performance. Power control is viewed as essential for interference-limited systems. However, the performance of such systems under an imbalance of load among cells, as may occur often in microcells, is largely unknown. Here, we study a typical interference-limited dynamic channel allocation policy. Calls are accepted if a channel can be assigned that will provide a minimum C/I, and power control and intracell handoffs are used to maintain this level. We focus on the relationship between system performance and the amount of imbalance in load among neighboring cells. Previous studies for systems that do not use C/I information have found that dynamic channel allocation (DCA) outperforms fixed channel allocation (FCA) in all but heavily loaded systems with little load imbalance. We present two principal new results. First, we find that with use of C/I information, the difference in performance between FCA and DCA (in terms of throughput or blocking probability) is increasing with load imbalance. DCA was found to be more effective in congestion control at the cost of a slightly lower call quality. Second, we find that use of power control to maintain a minimum C/I results in two equilibrium average power levels for both DCA and FCA, with DCA using a higher average power than FCA, and that while DCA's power is increasing with load imbalance, FCA's average power is decreasing with load imbalance     

Distributed dynamic fault-tolerant channel allocation for cellularnetworks

Efficient allocation of communication channels is critical for the performance of cellular systems. The centralized channel allocation algorithms proposed in literature are neither robust nor scalable. Several of these algorithms are unable to dynamically adjust to spatial and temporal fluctuations in channel demand (load). We present a distributed dynamic channel allocation (DCA) algorithm in which heavily loaded regions acquire a large number of communication channels, while their lightly loaded neighbors get assigned fewer channels. As the spatial distribution of channel demand changes with time, the spatial distribution of allocated channels adjusts accordingly. The algorithm described in this paper requires minimal involvement of the mobile nodes, thus conserving their limited energy supply. The algorithm is proved to be deadlock free, starvation free, and fair. It prevents cochannel interference and can tolerate the failure of mobile as well as static nodes without any significant degradation in service. Simulation experiments demonstrate that the performance of the proposed distributed dynamic algorithm is comparable to, and for some metrics, better than that of efficient centralized dynamic algorithms where the central switch has complete and latest information about channel availability. The major advantages of the proposed algorithm over its dynamic centralized counterparts are its scalability, flexibility, and low computation and communication overheads     

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     

TDD-CDMA系统的动态信道分配算法

TDD-CDMA系统由于上下行业务量的不对称,因此会产生严重的小区间干扰,需要使用动态信道分配算法(DCA)来适应上下行业务量的动态不平衡.文中提出了一种基于平均功率值的DCA算法.它通过采用平均功率控制的算法对功率进行处理,以提高信道利用率;并避免基站间的相互干扰来改善系统性能,从而提高系统容量.仿真结果表明,提出的算法能够显著地改善系统指标,达到优化效果.     

联合信号子空间和功率分配的认知干扰对齐传输方案设计

本文针对由一条授权通信链路和多条次用户干扰信道组成的认知多输入多输出（Multiple Input Multiple Output,MIMO）系统,首先提出了基于信号子空间的认知干扰对齐迭代优化算法,并且利用单调有界理论证明了该算法可以收敛到稳定点。为了进一步提升系统的和速率性能,提出了一种联合信号子空间和功率分配的增强认知干扰对齐算法。该算法通过在每个次用户的多个数据流之间进行自适应功率分配,解决了次用户的有用信号空间中总是有残余的干扰信号的问题。数值仿真结果表明,相对于传统的认知干扰对齐算法,所提的算法能够获得较为明显的性能提升。      

一种基于距离判决的HAPS通信无线DCA算法

本文提出一种基于距离判决的高空平台站(HAPS)通信的动态信道分配(DCA)算法,通过对无线链路功率到收发链路距离的转化,实时监测HAPS通信的收发链路距离来进行无线信道分配,解决HAPS通信中由于负载不均等造成的无线资源无法满足用户需求的问题.通过与随机信道分配算法及最差可接受信道分配算法的性能进行比较,本文提出的基于距离判决的算法能够在阻塞概率稍微增加的情况下解决系统连接中断问题,有效地提高了系统的整体性能.     

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     

Performance of autonomous dynamic channel assignment and powercontrol for TDMA/FDMA wireless access

We combine autonomous algorithms for dynamic channel assignment (DCA) and power control in a TDMA/FDMA wireless system as a medium access control (MAC) protocol. The DCA algorithm determines paired radio channels that experience the least interference and are least likely to cause interference. The power control algorithm uses local estimations of signal to interference ratio (SIR) at a receiver to iteratively command power adjustment on the desired transmitter. A common control frequency, which is frame-synchronized among base stations, provides all necessary information for DCA without blind slots. Computer simulations are used to evaluate system performance. Results from computer simulations demonstrate good spectrum efficiency and robustness. Although studied under a specific set of parameters, this type of MAC protocol can be applied in different wireless communications environments     

Handover and dynamic channel allocation techniques in mobilecellular networks

This paper deals with an efficient dynamic channel allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical fixed channel allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique     

Effective adaptive transmit power allocation algorithm considering dynamic channel allocation in reuse partitioning-based OFDMA system

This paper introduces an transmit power allocation (TPA) algorithm considering dynamic channel allocation (DCA) for a reuse-partitioning- based Orthogonal frequency division multiple access (OFDMA)/FDD cellular system. The proposed reuse partitioning-based DCA algorithm guarantees quality of service (QoS) by considering fairness among mobile stations in an OFDMA/FDD system. However, to improve the SINR values for users around the cell edge and increase the overall system throughput compared with the conventional OFDMA/FDD system of frequency reuse factor (FRF) 1, an effective TPA algorithm is also combined with the proposed DCA to adjust the transmit power per user according to the average received SINR value. Simulation results show that the proposed DCA algorithm increases the sector throughput by about 25% when compared with the conventional case that do not apply the proposed DCA algorithm. When the proposed TPA is combined with the proposed DCA algorithm, a further increase in the sector throughput of about 6% is achieved than when using just the proposed DCA algorithm.     

基于认知OFDM的子载波功率分配改进算法

在认知无线网络中,建立了基于认知OFDM多载波资源分配数学模型,在授权用户干扰受限条件下,以最大化传输速率为目标进行认知用户的子载波功率分配。传统注水法被证明是最优的单用户子载波功率分配算法,在传统注水法功率分配基础上,提出了两种可行的子载波功率分配改进算法,改进算法一是通过对水面值的粗略估计快速确定不分配功率子载波,改进算法二不需要通过迭代计算水面值,只通过线性计算就可以直接确定不分配功率的子载波,且对授权用户不产生干扰。仿真结果表明,在改进的两种子载波功率分配算法下,认知用户的数据传输速率优于传统注水法功率分配时认知用户的数据速率,所提改进算法具有自适应特性且计算复杂度大大降低。      

Mixed Power Control with Directed Assignment (MPCDA), a Method for Interference Reduction in Channelized Wireless Systems

Power control, often coupled with dynamic channel assignment, has been viewed as a promising answer to the challenge of reducing interference and increasing capacity. Indiscriminate use of power control, however, may exacerbate the near-far-end problem on the down link, and give rise to other complications when users are mobile. We propose a power control policy that can alleviate the near-far-end interference caused by the use of either the same channel or neighbor channels inside the same cell, while at the same time aiding in the reduction of interference from different cells through user matching. We present a heuristic algorithm for user matching, which is distributed and simple to implement. The method can be combined with an array of either fixed or dynamic channel assignment algorithms and applies to both circuit-based and packet-based traffic. It is ideal for fixed or slow circuit-based traffic and for packet-based traffic.A duality relationship is derived for the proposed power control policy between the signal-to-interference ratio of two interfering users experienced in the two communication directions. This relationship enables one to validate channel assignment decisions on both communication directions by analyzing only the decisions for one.     

Adaptive antenna array assisted dynamic channel allocationtechniques

The performance of base station adaptive antenna arrays (AAAs) is investigated in conjunction with fixed channel allocation (FCA) and dynamic channel allocation (DCA) schemes. Locally distributed DCA arrangements are studied and benchmarked against standard FCA, in the context of both line-of-sight (LOS) and multipath propagation environments. One-, two-, four-, and eight-element AAAs are employed using the sample matrix inversion (SMI) beamforming algorithm, in both the up- and the downlink. In most investigated scenarios, the locally optimized least interference algorithm (LOLIA) exhibited the best overall compromise in terms of a set of combined metrics, such as the forced termination probability, new call blocking probability, and the probability of a low quality access     

An uplink resource allocation scheme for OFDMA‐based cognitive radio networks

Cognitive radio makes it possible for an unlicensed user to access a spectrum unoccupied by licensed users. In cognitive radio networks, extra constraints on interference temperature need to be introduced into radio resource allocation. In this paper, the uplink radio resource allocation is investigated for OFDMA‐based cognitive radio networks. In consideration of the characteristics of cognitive radio and OFDMA, an improved water‐filling power allocation scheme is proposed under the interference temperature constraints for optimal performance. Based on the improved water‐filling power allocation, a simple subcarrier allocation algorithm for uplink is proposed. The subcarrier allocation rules are obtained by theoretical deduction. In the uplink subcarrier allocation algorithm, the subcarriers are allocated to the users with the best channel quality initially and then adjusted to improve the system performance. A cursory water‐filling level estimation method is used to decrease the complexity of the algorithm. Asymptotic performance analysis gives a lower bound of the stability of the water‐filling level estimation. The complexity and performance of the proposed radio resource allocation scheme are investigated by theoretical analysis and numerical results. Copyright © 2008 John Wiley & Sons, Ltd.     

Non-Uniform Traffic Issues in DCA Wireless Multimedia Networks

Wireless networks that utilize dynamic channel allocation (DCA) are known to perform better than those with fixed channel allocation, in terms of the call level QoS measures such as the handoff dropping probability. On account of this, the DCA networks are usually designed without the call admission control (CAC). However, given the decrease of cell sizes, together with ever increasing mobile phone and terminal population, dynamic channel allocation policies (such as channel borrowing) may not be sufficient to cope with the hot-spot area size and its traffic intensity. This paper analyses the performance of the DCA networks, both with and without the call admission control, under the hot-spot traffic regime. In such cases, the pure DCA approach fails to ensure sufficiently low level of QoS in both the hot-spot area and the surrounding cells. We propose a CAC policy that can stabilize the QoS under non-uniform traffic, whilst being easy to integrate in the distributed DCA policies.