A dynamic load balancing strategy for channel assignment using selective borrowing in cellular mobile environment

We propose a dynamic load balancing scheme for the channel assignment problem in a cellular mobile environment. As an underlying approach, we start with a fixed assignment scheme where each cell is initially allocated a set of channels, each to be assigned on demand to a user in the cell. A cell is classified as 'hot', if the degree of coldness of a cell (defined as the ratio of the number of available channels to the total number of channels for that cell), is less than or equal to some threshold value. Otherwise the cell is 'cold'. Our load balancing scheme proposes to migrate unused channels from underloaded cells to an overloaded one. This is achieved through borrowing a fixed number of channels from cold cells to a hot one according to a channel borrowing algorithm. A channel assignment strategy is also proposed based on dividing the users in a cell into three broad types – 'new', 'departing', 'others' – and forming different priority classes of channel demands from these three types of users. Assignment of the local and borrowed channels are performed according to the priority classes. Next, a Markov model for an individual cell is developed, where the state is determined by the number of occupied channels in the cell. The probability for a cell being hot and the call blocking probability in a hot cell are derived, and a method to estimate the value of the threshold is also given. Detailed simulation experiments are carried out in order to evaluate our proposed methodology. The performance of our load balancing scheme is compared with the fixed channel assignment, simple borrowing, and two existing strategies with load balancing (e.g., directed retry and CBWL), and a significant improvement of the system behavior is noted in all cases. This revised version was published online in June 2006 with corrections to the Cover Date.     

An innovative channel management strategy for highly reliable handoff in cellular networks

In this paper, we have resolved the problem of forced call termination that occurs when mobile traffic is concentrated on a hot‐spot cell in cellular networks. Enhanced Channel Management Scheme (ECMS) is an innovative way to increase the flexibility of channel usage over non‐uniform traffic distribution. ECMS exploits mobile hosts initiated or active in overlapping areas between cells. The scheme consists of three phases to monitor the status of channels on each base station and to make a channel reservation using the availability list maintained for the candidate‐MH selection. When the traffic load in a cell is intolerably high, ECMS invokes the load‐balancing procedure to distribute its traffic to adjacent cells. The reserved channels are used to support the safe and fast handoff. From the simulation, we observed that ECMS outperformed other compatible channel assignment schemes such as directed handoff schemes in blocking probability and channel utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

异构分层无线网络中的混合动态流量均衡算法研究

结合信道借用和流量转移技术提出了一种混合动态流量均衡算法。使用该算法热点小区可以向紧凑模式中的同类型轻负载小区借用信道，同时还可以按一定条件将呼叫转移到与热点小区重叠覆盖的异构轻负载小区中，每个流量周期借用的信道数和转移的呼叫数将根据热点小区的剩余可用信道数和新呼叫到达率来计算。仿真结果表明，该流量均衡算法能够显著降低热点小区系统和整个异构系统的新呼叫阻塞概率、切换呼叫掉线率，而且整个异构系统的利用率也得到了相应提高。     

Prioritized channel borrowing without locking: a channel sharingstrategy for cellular communications

We previously suggested a new channel sharing method for cellular communications. The method, called channel borrowing without locking (CBWL), allows real-time borrowing of channels from adjacent cells without the need for channel locking in co-channel cells. CBWL with cut-off priority for calls that arise in the cell is presented. This scheme discourages excessive channel lending and borrowing at high traffic load and promotes a more uniform grade of service throughout the service area. An analysis using macro-states and decomposition is devised to evaluate the performance of the scheme. The results are validated by simulation     

LTE网络多载波自动化智能均衡研究

网络负荷的增加,传统依靠人工调整负荷均衡已不能满足优化需求。自动化智能均衡方案通过穷举影响相邻两个小区覆盖性能的天馈、功率、互操作等类别参数,并进行归一化分析,自动输出负荷均衡调整方案。对无法通过覆盖均衡实现负荷均衡的小区,通过引入迭代算法,在优化边界范围内以固定步长自动输出负荷均衡调整建议,这有利于提高LTE网络容量、提高网络资源利用率、也有利于降低传输时延、降低人工和时间成本。     

CBWL: a new channel assignment and sharing method for cellularcommunication systems

A new scheme that allows cell gateways (base stations) to borrow channels from adjacent gateways in a cellular communication system is presented. Borrowed channels are used with reduced transmitted power to limit interference with cochannel cells. No channel locking is needed. The scheme, which can be used with various multiple access techniques, permits simple channel control management without requiring global information about channel usage throughout the system. It provides enhanced traffic performance in homogeneous environments and also can be used to relieve spatially localized traffic overloads (tele-traffic `hot spots'). Co-channel interference analysis shows that the scheme can maintain the same SIR as nonborrowing schemes. Analytical models using multidimensional birth-death processes and decomposition methods are devised to characterize performance. The results which are also validated by simulation indicate that significantly increased traffic capacity can be achieved in comparison with nonborrowing schemes     

Self‐organising cluster‐based cooperative load balancing in OFDMA cellular networks

Mobility load balancing (MLB) redistributes the traffic load across the networks to improve the spectrum utilisation. This paper proposes a self‐organising cluster‐based cooperative load balancing scheme to overcome the problems faced by MLB. The proposed scheme is composed of a cell clustering stage and a cooperative traffic shifting stage. In the cell clustering stage, a user‐vote model is proposed to address the virtual partner problem. In the cooperative traffic shifting stage, both inter‐cluster and intra‐cluster cooperations are developed. A relative load response model is designed as the inter‐cluster cooperation mechanism to mitigate the aggravating load problem. Within each cluster, a traffic offloading optimisation algorithm is designed to reduce the hot‐spot cell's load and also to minimise its partners’ average call blocking probability. Simulation results show that the user‐vote‐assisted clustering algorithm can select two suitable partners to effectively reduce call blocking probability and decrease the number of handover offset adjustments. The relative load response model can address public partner being heavily loaded through cooperation between clusters. The effectiveness of the traffic offloading optimisation algorithm is both mathematically proven and validated by simulation. Results show that the performance of the proposed cluster‐based cooperative load balancing scheme outperforms the conventional MLB. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of Scheduled Latency Insensitive Systems with Periodic Clock Calculus

Originally the Latency Insensitive Protocols (LIP) were invented to make a system elastic to the interconnect latencies using handshaking signals such as ‘valid’ and ‘stall’. Such protocols require extra signals leading to area overhead and may affect throughput of the system. To optimize away some of these overheads, scheduled LIPs were proposed which replaced the complex handshake control blocks by a central scheduling scheme. One can view a scheduled LIP based design as a system where within each strongly connected component of the system, the modules and the relay stations are scheduled by activation signals. These activation signals can be thought of as infinite sequence of ‘1’s and ‘0’s. If such sequences are periodic, one can view them as periodic clocks. Given the advances in periodic clock calculus in the synchronous programming context, in this paper, we analyze the LIP scheduling problem within the framework of periodic clock calculus. Such analysis provides straight forward algorithms to compute the throughput of scheduled LIP based systems. Within this framework, we also propose a method to synthesize fractional synchronizers. Fractional synchronizers are used to equalize cycles with different throughputs. Our method can determine the numbers and the scheduling sequences of such fractional synchronizers using the periodic clock calculus. In addition, we provide a static estimation of the required fractional synchronizers based only on the system’s structure which is fast and accurate.     

A STUDY OF METHODS FOR IMPROVING LEARNING VECTOR QUANTIZATION

Learning Vector Quantization(LVQ)originally proposed by Kohonen(1989)is aneurally-inspired classifier which pays attention to approximating the optimal Bayes decisionboundaries associated with a classification task.With respect to several defects of LVQ2 algorithmstudied in this paper,some‘soft’competition schemes such as‘majority voting’scheme andcredibility calculation are proposed for improving the ability of classification as well as the learningspeed.Meanwhile,the probabilities of winning are introduced into the corrections for referencevectors in the‘soft’competition.In contrast with the conventional sequential learning technique,a novel parallel learning technique is developed to perform LVQ2 procedure.Experimental resultsof speech recognition show that these new approaches can lead to better performance as comparedwith the conventional LVQ2     

蜂窝移动通信系统中一种热点业务分配算法

基于提出的最优组合业务量预测模型,对下一时刻的业务量进行预测,从而确定蜂窝系统中业务分布情况,据此将蜂窝小区分成冷点区域和热点区域,并提出一种优化的混合信道分配(OHCA)方案,分析并给出了该方案中动静信道比的定量关系。仿真结果证实了该最优组合预测模型较单一预测方法降低了预测误差、提高了预测精度,同时该优化分配算法较固定信道分配(FCA)和动态信道分配(DCA)方案,有较小的呼阻率和较高的频谱利用率,该策略可用来有效处理热点业务问题,有较好的应用前景。     

Load‐balancing channel assignment for dual‐band PCS networks

This paper investigates the channel assignment problem of dual‐band PCS systems where single‐band and dual‐band handsets co‐exist. Load‐balancing channel assignment schemes are proposed to improve the system performance. To balance the loads of both bands, the BSC selects a band to serve a call request of a dual‐band handset based on the loads of both bands. In addition, a channel re‐assignment scheme is used to further improve the system capacity. Analytic models and computer simulations have been developed to evaluate the performance of the load‐balancing schemes. The results indicate that both load‐balancing and channel re‐assignment techniques significantly increase the system capacity as the percentage of dual‐band handsets increases. Furthermore, the load‐balancing with channel re‐assignment scheme that combines both techniques achieves the best system performance even when the percentage of dual‐band handset is as low as 25%. In addition, we describe an approach to reduce the signal overhead of the load‐balancing schemes. Copyright © 2002 John Wiley & Sons, Ltd.     

A study of multi‐hop cellular networks

The number of cellular communication subscribers continues to grow, attesting to the great success of this technology. However, cellular networks have inherent limitations on cell capacity and coverage and shortcomings such as the dead spot and the hot spot problems. Multi‐hop cellular networks (MCNs) help enhance the cell capacity and coverage, while, at the same time, alleviating the dead spot and hot spot problems, increasing the utilization of radio resource, and reducing the power consumption of mobile terminals. In the past decade, more than a dozen of MCN architectures were proposed. In this paper, we study various types of MCN proposals. We identify and discuss the design decision factors and use these factors to classify most existing MCN proposals. Future research directions, including studies of capacity and energy consumption, and approaches addressing design issues such as cell size, routing, channel assignment, load balancing for MCNs are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Channel Borrowing Without Locking for Asynchronous Hybrid FDMA/TDMA Cellular Communications

The use of real time channel borrowing in digital cellular asynchronous hybrid FDMA/TDMA systems is considered. These systems, which are exemplified by North American digital cellular (IS-54), are asynchronous in the sense that time slots in different cells are not aligned. CBWL (channel borrowing without locking) techniques can be applied but (without cell-to-cell synchronization) borrowing individual time slots from adjacent cells would violate co-channel interference constraints. Instead, frequency carriers can be borrowed. In IS-54, a carrier supports three TDMA slots. So if only one TDMA slot is needed in the borrowing cell, two TDMA slots are unnecessarily transferred. We devised an appropriate carrier borrowing scheme and an analytical model to determine the traffic performance of TDMA/CBWL. Fast carrier returning is used to increase channel utilization by returning borrowed carriers as soon as possible. An efficient computational method that uses macro-states, decomposition, combinatorial analysis and the convolution algorithm is devised to find blocking probabilities. The results show that in comparison with FCA, the new CBWL scheme can significantly improve system performance of asynchronous TDMA cellular systems that use FDMA/TDMA multiplexing.     

Hybrid channel gain prioritized access‐aware cell association with interference mitigation in LTE‐Advanced HetNets

LTE‐Advanced heterogeneous networks deployment is meant to address the increasing demand for quality of service, high data rates and coverage extension. Load balancing is among the primary challenges, especially when the user equipments (UEs) associate with diverse transmission power network tiers using received signal strength. The low‐power network tier's spectrum will be underutilized, and UEs associated with them will be inflicted by interference from the high‐power network tier. The proposed hybrid channel gain prioritized access (HCGPA)‐aware cell association scheme stresses the importance of combined metrics with interference mitigation to simultaneously achieve load balancing and enhance performance among the network tiers. The high‐priority UEs associate with the tier that gives the maximum channel gain being higher than a given threshold. While the low‐priority UEs association is based on the maximum joint metrics (channel gain, channel access probabilities of low‐priority UEs and high‐priority UEs). The HCGPA scheme has 1.72 times the number of UEs connected to low‐power networks, 8% better load balancing fairness, compared with the conventional reference signal receive power and RSRP + 6 dB bias cell associations. Although the susceptibility of HCGPA to interference led to the poor signal to interference to noise ratio (SINR) performance of the cell‐edge UEs, the cell‐centre UEs exhibited the best spectral efficiency performance. Copyright © 2016 John Wiley & Sons, Ltd.     

Hot-spot traffic relief in cellular systems

By analyzing mathematical models, it is shown that combining channel borrowing with a coordinated sectoring or overlying scheme provides effective ways to handle hot-spots in the system. Blocking probabilities with these arrangements are derived, and the dynamic sharing with bias (DSB) rule is suggested for increasing the trunking efficiency. A simple handoff model is formulated and analyzed for comparing the probabilities of additional handoffs due to sectoring and overlaying of cells. With the nominal allocation of 60 channels per cell and a donor cell having a load of 30 Erlangs, numerical results show that at a blocking requirement of 1%, the traffic load in the hot-spot cell can be increased from 47 to 63 Erlangs with the use of the channel borrowing with the cell sectoring scheme: while with the use of the DSB rule, the load can be increased further to 71 Erlangs. A slightly higher load can be carried in the hot-spot cell with the use of cell overlaying arrangement     

Acquisition of Soft Taxonomies for Intelligent Personal Hierarchies and the Soft Semantic Web

Information overload is a problem at an individual and a corporate level. Many solutions have been proposed, including knowledge management, data warehouses, service directories and digital libraries. The semantic Web aims to unify many of these approaches by appropriate markup and agreement on the meaning of the markup. At the individual's level, these techniques partially solve the problem by classifying documents within hierarchical structures and enabling searching and browsing of the documents. However, they also contribute to the problem as there is no unique categorisation and access structure that suits every individual. Finding the right document becomes a two-stage process — first find the right place in the categorisation scheme, then find the document within that class. In addition to enterprise-wide sources, individual information sources include e-mails, electronic documents in many formats, personal and group filespaces, notes, diary entries, etc. These are unlikely to conform to the enterprise categorisation but form useful resources nevertheless. The idea of an intelligent personal hierarchy for information (iPHI) is to auto-configure access to multiple sources of information based on personal categories. This entails fuzzy matching of meta-data structure as well as content. Metadata is a powerful tool in intelligent information management; however, it is not necessarily uniform, either in label or in content. One document's ‘author’ is another's ‘creator’; ‘John Smith’, ‘Smith, John’ and ‘J.Smith’ all refer to the same individual but are syntactically different. Fusion (or intelligent integration) of information takes place in an environment where the data may be of varying quality, and some may be incomplete or inconsistent. Combining metadata (and the associated data) is not possible without knowing (or learning) the mappings between their ontologies. Such mappings are likely to be soft, i.e. approximate — different sources arise from different designers with different world views. Soft computing is vital to tackle these problems. Frequently, data sources are organised implicitly, according to an internal ontology or taxonomy. Knowing this ontology or taxonomy is a necessary first step to using it in the fusion process. The work described in this paper extracts the implicit taxonomy and enables a user's interaction with the data (e.g. searching) to be expressed in their preferred terms rather than those used by the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance analysis of load balancing in OFDMA cellular networks with inter‐cell relay

To balance and improve the resource utilization of the orthogonal frequency division multiple access (OFDMA) cellular networks, we switch parts of the edge users in overloaded cell to the adjacent light‐loaded cells by using the inter‐cell relay. The efficiency of traditional load balancing method based on the cell switching is low and in some cases, will occur the collision load problem. In this paper, we propose a new load balancing scheme based on inter‐cell relay in downlink OFDMA cellular networks. Besides, we put forward a new spectrum division scheme to reduce interference and improve spectrum efficiency. According to the formulas derived from the model we established, we can obtain the signal interference ratio and further to calculate the amount of remaining subcarrier and the throughput of the system. Finally, through numerical calculation and simulation, the result shows that the load balancing and spectrum division schemes can remit the resource stress of the overloaded cell and improve the spectrum utilization in adjacent cells.     

An Adaptive Threshold Load Balancing Scheme for the End-to-End Reconfigurable System

In this paper, an adaptive threshold load balancing (ATLB) scheme is proposed for the joint load control (JOLDC) in the end-to-end reconfigurable system. The dynamic threshold based on heterogeneous load measurement is designed to adapt to varying load conditions for efficient resource utilization, while the network-initiated vertical handover (NIVHO) process is adopted for the timely control by exploiting the network-controlled reconfiguration management. Furthermore, considering terminal reconfigurability and the service variety, a multi-objective terminal selection algorithm is designed for NIVHO to minimize the system overhead and the impact on end-users. Simulation results show that the proposed scheme is effective in relieving congestion and improving system performance across the overlapped heterogeneous radio networks as well as the users’ satisfaction.     

Partial CRC Checksum of SCTP for Error Control over Wireless Networks

In the Stream Control Transmission Protocol (SCTP), when a portion of a packet is corrupted, the entire packet will be discarded at the receiver side. This may result in degradation of the throughput of SCTP over wireless networks with a high bit error rate. This paper proposes a new error control scheme of SCTP using a partial Cyclic Redundancy Check (CRC) checksum to enhance the throughput performance, in which a new ‘checksum chunk’ is introduced to effectively identify any corruptions of data chunks contained in the SCTP packet. In the proposed scheme, an SCTP data packet can carry one or more data chunks depending on the channel condition, and the newly defined ‘checksum’ chunk will contain the partial CRC checksums of the individual data chunks and/or the base header of the packet. By referring to these partial checksums, the receiver can discard only the corrupted data chunks, whereas the other available data chunks can be recovered. Simulation results show that the proposed scheme significantly provides better performance than the standard SCTP in the wireless networks.

A distributed implementation of mobility load balancing with power control and cell reselection in 4G network

We consider a self‐organizing network (SON) capability of mobility load balancing in a 4G network, which determines the transmission power level for individual base stations and cell reselection for individual mobile stations such that the network‐wide load is minimized while satisfying the minimum signal‐to‐noise and interference ratio (SINR) requirement of individual users. Both centralized and distributed schemes are proposed. The centralized scheme is based on the greedy algorithm, serving as a performance bound to the distributed scheme. The distributed scheme is to solve the system‐wide optimization problem in the flat network model, i.e. no central control node. Furthermore, it requires relatively low inter‐cell exchange information among neighboring cells over an inter‐cell channel, e.g. X2 interface in the LTE network. The proposed design objective is to minimize the number of mobile users that do not satisfy the specified average throughput, while distributing the user traffic load as uniformly as possible among the neighboring cells. Our simulation results for a uniform user distribution demonstrate that the proposed scheme can achieve up to almost 80% of a load balancing gain that has been achieved by a greedy algorithm in the centralized optimization. Copyright © 2014 John Wiley & Sons, Ltd.