Dynamic Channel Assignment with Flexible Reuse Partitioning in Cellular Systems

In cellular communications, one of the main research issues is how to achieve optimum system capacity with limited frequency spectrum. For many years, researchers have proposed and studied many dynamic channel assignment (DCA) schemes to increase the capacity of cellular systems. Another proposed technique, Reuse Partitioning (RP), is used to achieve higher capacity by reducing the overall reuse distance. In convention, when RP is exploited in network-based DCA, a portion of channels will be assigned permanently to each partitioned region. However, the number of channels assigned to each region may not be~optimum due to factors like the uneven and time-varying traffics. In this paper, a new network-based DCA scheme is proposed with the flexible use of RP technique, named as flexible dynamic reuse partitioning with interference information (FDRP-WI). In this scheme, channels are open to all incoming calls and no channel pre-allocation for each region is required. As long as the channel assignment satisfies the co-channel interference constraints, any user from any region can use any channel. The scheme aims to minimize the effect of assigned channels on the availability of channels for use in the interfering cells and to reduce overall reuse distance. Both FDRP-WI with stationary users and mobile users are investigated. Simulation results have confirmed the effectiveness of FDRP-WI scheme. In the case with stationary users, FDRP-WI exhibits outstanding performance in improving the system capacity under both uniform and non-uniform traffic distributions. Under the uniform traffic case, the scheme can provide over 100% capacity improvement as compared to conventional fixed channel assignment scheme with 70 system channels at 1% blocking probability. In the case with mobile users, the impact of mobility on the new call probability, P _b, and the call dropping probability, P _d, is evaluated. The effect on system capacity of reserving some channels for handoff calls is first studied. Then, we propose a new handoff scheme, called “Reverse Overflow” (RO), to improve the utilization of channels with smaller reuse distances under mobile environment. Simulation results show that, with RO handoff, the system capacity of FDRP-WI is effectively improved at the expense of higher handoff rates in the cellular system.     

Proportional-fairness resource allocation for uplink OFDM-based cognitive radio systems

This paper has proposed a proportional-fairness resource allocation algorithm, including both subcarrier assignment algorithm and power allocation algorithm, for uplink orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems. First, to get a better performance in the proposed system model, the influence factor (a,b,c) was introduced to realize the assignment of the subcarriers. Second, the transmit power of the secondary users (SUs) was allocated to the corresponding subcarriers in order to maximize the uplink capacity of the SUs subject to both power and interference constraints. With the appropriate influence factor in the subcarrier assignment, the loss of transmitted data rate arising from the fairness was minimized. Simulation results showed that the proposed algorithm can achieve a perfect fairness among the SUs while maximizing the system capacity simultaneously, and is of a low computation complexity.     

Multibeam cellular communication systems with dynamic channel assignment across multiple sectors

In cellular communication systems, directional multibeam antennas at cell sites can be used to reduce cochannel interference, increase frequency reuse and improve system capacity. When combined with dynamic channel assignment (DCA), additional improvement is possible. We propose a multibeam scheme using dynamic channel assignment across multiple sectors. A cell is divided into several sectors, each of which is covered by several directional beams. Specific channels are allocated to each sector as in fixed channel assignment (FCA). A channel of a sector is dynamically assigned to a wireless user who communicates through one of the several beams of the sector. The assignment is made so that constraints on the allowable cochannel interference are satisfied. Limitations due to cochannel interference are analyzed. A tractable analytical model for the proposed scheme is developed using multidimensional birth–death processes. Theoretical traffic performance characteristics such as call blocking probability, forced termination probability, handoff activity, carried traffic and channel rearrangement rate are determined. With the proposed scheme, call blocking probability can be reduced significantly for a fixed offered traffic. Alternatively, system capacity can be increased while blocking probability is maintained below the required level. Smaller forced termination probability is obtainable in comparison with corresponding FCA schemes.     

Adaptive channel assignment for different types of traffic in DS‐CDMA cellular systems

The link capacity of DS‐CDMA cellular systems is limited by the interference contained in the link. This link interference is affected by many environment factors and thus the link capacity varies with the environment. Since link capacity changes with the varying interference and different traffic types mutually interfere with each other, it is difficult to use link capacity efficiently. Static channel assignment (SCA) based on fixed link capacity is inefficient for DS‐CDMA cellular systems. To improve system capacity, channel assignments need to be adapted to variations in interference. In this paper, we propose an adaptive channel assignment (ACA) for different types of traffic. The proposed ACA is based on the reverse link power received at the base station and is adaptable to dynamically varying environments. It consists of two schemes: nonprioritized and prioritized. In the nonprioritized scheme, there is no difference in channel assignments between calls. In the prioritized scheme, however, the number of nonpriority calls acceptable is limited. In both schemes, a channel is assigned if the link power after assigning the channel is less than the power allowed in the link. The performance is evaluated in terms of link capacity and service grade. Utilizing the proposed algorithm yields more link capacity than using SCA in such environment changes as nonhomogeneous traffic load or varying path loss. Service grade is also improved by properly limiting the number of nonpriority channels. This revised version was published online in August 2006 with corrections to the Cover Date.     

无线多媒体DS—CDMA系统中的功率分配算法研究

本文提出一种基于信道特征（如业务量）的功率分配算法,并通过系统分析验证了该算法是能很好地在保证各业务的业务质量同时提高系统的容量。     

Performance limits for channelized cellular telephone systems

Studies the performance of channel assignment algorithms for “channelized” (e.g., FDMA or TDMA) cellular telephone systems, via mathematical models, each of which is characterized by a pair (H,p), where H is a hypergraph describing the channel reuse restrictions, and p is a probability vector describing the variation of traffic intensity from cell to cell. For a given channel assignment algorithm, the authors define T(r) to be the amount of carried traffic, as a function of the offered traffic, where both r and T(r) are measured in Erlangs per channel. They show that for a given H and p, there exists a function T_H,p(r), which can be computed by linear programming, such that for every channel assignment algorithm, T(r)⩽T_H,p(r). Moreover, they show that there exist channel assignment algorithms whose performance approaches T_H,p (r) arbitrarily closely as the number of channels increases. As a corollary, they show that for a given (H,p) there is a number r₀ , which also can be computed by linear programming, such that if the offered traffic exceeds r₀, then for any channel assignment algorithm, a positive fraction of all call requests must be blocked, whereas if the offered traffic is less than r₀, all call requests can be honored, if the number of channels is sufficiently large. The authors call r₀, whose units are Erlangs per channel, the capacity of the cellular system     

Efficient rate allocation,routing and channel assignment in wireless mesh networks supporting dynamic traffic flows

In this paper we address the issue of joint routing, channel re-assignment and rate allocation in multi-radio multi-channel Wireless Mesh Networks (WMNs) with the goal of optimizing the performance of the current set of flows in the WMN. The objective is to balance the instantaneous traffic in the network at the flow level, optimize link-channel assignment and allocate flow rates to achieve proportional fairness given the current traffic and network constraints, including the topology, interference characteristics, number of available channels and radios. Unlike prior work, we do not assume a priori knowledge of traffic, and instead take into account the instantaneous traffic conditions to optimize performance at the flow level, taking both throughput and fairness into account. In this work we analyze the problem and, due to its hardness, propose a fast heuristic algorithm (JRCAR) to solve it. We evaluate this algorithm through numerical experiments, including comparisons against optimal solutions. In addition, we show that JRCAR can be used in a highly responsive system in practical scenarios with time-varying traffic conditions. We implement such a system under the ns-3 simulator, where the simulation results obtained corroborate the behavior observed in the numerical experiments and show that JRCAR is effective in dynamic and practical conditions.     

Design of logical topology with K‐connected constraints and channel assignment for multi‐radio wireless mesh networks

In multi‐radio multi‐channel wireless mesh networks, the design of logical topology is different from that in single channel wireless mesh networks. The same channel assignment algorithm used for various logical topologies will lead to diverse network performance. In this paper, we study the relationship between k ‐connected logical topology and the maximum number of assigned channels. Meanwhile, we analyze the issues affecting channel assignment performance, and present the lower and upper bounds of the maximum allowable number of assigned channels for k ‐connected logical topology. We then develop a k ‐connected logical topology design algorithm based on shortest disjoint paths and minimum interference disjoint paths for each node‐pair. In addition, we propose a static channel assignment algorithm according to minimum spanning tree search. Extensive simulations show that our proposed algorithm achieves higher throughput and lower end‐to‐end delay than fault tolerant topology control algorithms, which validates the involved trade‐off between path length and nodal interference. Moreover, numerical results demonstrate that our proposed channel assignment further improves network performance under the context of limited radio interfaces. Copyright © 2014 John Wiley & Sons, Ltd.     

Power control supported dynamic channel assignment in cellular radio systems

Transmitter power control is an effective technique to reduce co-channel interference and increase system capacity for cellular radio networks. Dynamic channel assignment can also be used to improve spectrum efficiency and thus increases the system capacity. This paper investigates channel assignment algorithms which combine dynamic channel assignment with signal-to-interference ratio balanced power control and proposes a new algorithm. Simulation results show that this new scheme can greatly reduce the channel reassignment rate and still maintain satisfactory performance. It may thus be used as an effective channel assignment scheme in cellular mobile systems. © 1997 by John Wiley & Sons, Ltd.     

A novel phase noise compensation algorithm combining the DF algorithm with LCSC algorithm in CO-OFDM systems

A novel phase noise (PN) compensation algorithm based on the decision feedback (DF) algorithm and the linear combination self cancellation (LCSC) algorithm is proposed to improve the system performance degradation caused by laser linewidth in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. In this proposed LCSC-DF algorithm, the LCSC algorithm is used to precode the subcarrier information at the transmitter and decode the demodulation information and inter-carrier interference (ICI) related information at the receiver. And then the pilot information is used to obtain the final compensation signal by the improved DF algorithm. The simulation results show that the PN compensation performance of the proposed LCSC-DF algorithm is better than that of the DF algorithm. Furthermore, with the increase of the signal to noise ratio (SNR), its bit error rate (BER) performance approaches to that of the SC-DF algorithm at the larger PN linewidth. The subcarriers utilization ratio of the proposed algorithm is higher than that of the SC-DF algorithm. As a result, the proposed algorithm can effectively improve the performance of the system.     

Interference-based channel assignment for DS-CDMA cellular systems

Link capacity is defined as the number of channels available in a link. In direct-sequence code-division multiple-access (DS-CDMA) cellular systems, this is limited by the interference present in the link. The interference is affected by many environmental factors, and, thus, the link capacity of the systems varies with the environment. Due to the varying link capacity, static channel assignment (SCA) based on fixed link capacity is not fully using the link capacity. This paper proposes a more efficient channel assignment based on the interference received at the base station (BS). In the proposed algorithm, a channel is assigned if the corresponding interference margin is less than the allowed interference, and, thus, channels are assigned adaptively to dynamically varying link capacity. Using the proposed algorithm yields more channels than using SCA in such an environment changes with nonhomogeneous traffic load or varying radio path loss. The algorithm also improves service grade by reserving channels for handoff calls     

Incentive pricing in multiclass systems

In modern communication networks which offer multiple classes of services, an appropriate assignment of service classes to users (or applications) will have a key influence on the performance profile. Differentiated pricing is an important tool for guiding the user's choice. We consider a basic model for a multiclass system that offers multiclass services to multiple types of traffic, and propose a pricing framework which is based on the concept of nominal traffic assignment. Users (or their associated traffic) are categorized into a finite number of traffic types, which are distinct in their performance utilities at the different service classes. The system administrator specifies a required traffic assignment, which associates with each traffic type a nominal service class. Users, on the other hand, choose service classes so as to optimize their own performance. Optimal prices should provide incentives for the users to assign each traffic type to its nominal service class. Our goal is to implement a simple pricing scheme that provides such incentives. We establish necessary and sufficient conditions for the existence of optimal prices and provide an algorithm for their computation. We indicate that optimal prices can tolerate fluctuations in the various parameters. Next, we propose a distributed algorithm, which can be used by the system to compute optimal prices even when it does not have sufficient knowledge of traffic characteristics. We then generalize our analysis to an extended model, which explicitly includes congestion effects. This revised version was published online in June 2006 with corrections to the Cover Date.     

A pilot-based dynamic channel assignment scheme for wireless access TDMA/FDMA systems

We propose a control architecture for implementing a dynamic channel assignment (DCA) algorithm which optimizes two-way channel quality in a TDMA portable radio system. Computer simulations are used to evaluate the performance of this DCA method. A common control frequency, which is frame-synchronized among base stations, provides (1) beacons for portables to locate base stations and obtain DCA information, (2) broadcast channels for system and alerting information, and (3) pilot signals to permit portables to evaluate downlink interference. This allows low-complexity radio ports and portables to mutually select channels to avoid interference and avoid creating excessive interference. Results from computer simulations demonstrate the good spectrum efficiency of this method and its potential for handling nonuniform traffic demand. This work is targeted toward understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.A preliminary work with the same title was presented at the Second International Conference on Universal Personal Communications, October 12–15, 1993, Ottawa, Canada.     

An efficient channel assignment algorithm for multicast wireless mesh networks

Multicast can enhance the performance of wireless mesh networks (WMNs) effectively, which has attracted great attentions in recent years. However, multicast communication in WMNs requires efficient channel assignment strategy to reduce the total network interference and maximize the network throughput. In this paper, the concept of local multicast is proposed to measure interference and solve hidden channel problem in multicast communication. Basing on the concept, we propose a channel assignment algorithm considering the interference of local multicast and forwarding weight of each node (LMFW). The algorithm fully considers partially overlapped channels and orthogonal channels to improve the network performance. Simulations show that the proposed algorithm can reduce interference and improve network capacity of WMNs.     

Joint processing of topology control and channel assignment in wireless ad hoc networks

Network topology construction and its channel assignment for each node in the constructed network topology are two main problems in the initialization of topology building. Topology control is an effective way to solve the problem of topology building. To investigate the joint effect of topology control and channel assignment, we propose a joint processing scheme composed of a k‐Neighbor topology control algorithm and a greedy channel assignment (GCA) algorithm in this paper. Based on this joint processing scheme, the relationships between the energy consumption, the total required channel number and the network connectivity are discussed. We also discuss the impact of some parameters on the performance of networks in terms of the path loss factor, node density, maximum node degree, etc. Our main contributions in this paper is that we find that topology control has a good effect on improving the performance of channel assignment, and the proposed joint processing scheme can reduce the required channel number effectively, compared with its theoretical upper bound. In particular, if the node degree in a network is not more than k, various simulations indicate that the required channel number is not more than 2k + 1. Copyright © 2008 John Wiley & Sons, Ltd.     

Integrated predictive power control and dynamic channel assignment in mobile radio systems

It is known that dynamic allocation of channels and power in a frequency/time-division multiple access system can improve performance and achieve higher capacity. Various algorithms have been separately proposed for dynamic channel assignment (DCA) and power control. Moreover, integrated dynamic channel and power allocation (DCPA) algorithms have already been proposed based on simple power control algorithms. In this paper, we propose a DCPA scheme based on a novel predictive power control algorithm. The minimum interference DCA algorithm is employed, while simple Kalman filters are designed to provide the predicted measurements of both the channel gains and the interference levels, which are then used to update the power levels. Local and global stability of the network are analyzed and extensive computer simulations are carried out to show the improvement in performance, under the dynamics of user arrivals and departures and user mobility. It is shown that call droppings and call blockings are decreased while, on average, fewer channel reassignments per call are required.     

Uniform waveband assignment in optical mesh networks

The cost of an optical network in wavelength division multiplexing (WDM) networks can be reduced using optical reconfigurable optical add/drop multiplexers (ROADMs), which allow traffic to pass through without the need for an expensive optical-electro-optical (O-E-O) conversion. Waveband switching (WBS) is another technique to reduce the network cost by grouping consecutive wavelengths and switching them together using a single port per waveband. WBS has attracted the attention of researchers for its efficiency in reducing switching complexity and therefore cost in WDM optical networks. In this paper, we consider the problem of switching wavelengths as non-overlapping uniform wavebands, per link, for mesh networks using the minimum number of wavebands. Given a fixed band size b _s , we give integer linear programming formulations and present a heuristic solution to minimize the number of ROADMs (number of wavebands) in mesh networks that support a given traffic pattern. We show that the number of ROADMs (or number of ports in band-switching cross-connects) can be reduced significantly in mesh networks with WBS compared to wavelength switching using either the ILP or the heuristic algorithm. We also examine the performance of our band assignment algorithms under dynamic traffic.     

Resource management model and performance evaluation for satellite communications

Efficient resource management is mandatory to achieve maximum system capacity for next generation communications systems. Resource management deals with the available spectral band, time, power, and space for a transmission signal. It includes (i) the frequency planning, (ii) the selection of transmit power, and (iii) the assignment of the channels and access nodes to the users. The paper presents a generalized notation as well as graph algorithms for resource management problems. Impairment graphs can be used for frequency planning, whereas flow graphs are suitable for channel access problems. To evaluate the performance of the resource management, service criteria (such as blocking or the carrier to interference ratio C/I) or efficiency criteria (bandwidth requirements) can be derived from the graphs. The resource management techniques are applied to satellite networks with non‐geostationary orbits yielding time‐variant network topologies. As a simple example, the channel assignment and capacity optimization of the EuroSky Way system are shown. Furthermore, a comparison of fixed, dynamic and hybrid channel allocation schemes (FCA, DCA, HCA) for a typical MEO satellite scenario is given. Satellite diversity and its impact on bandwidth requirement and transmission quality is also examined. Finally, it is shown how spread spectrum systems can be investigated with the presented tools. Copyright © 2001 John Wiley & Sons, Ltd.     

DS-CDMA reverse link channel assignment based on interferencemeasurements

The authors propose a DS-CDMA reverse link channel assignment algorithm based on received interference. A new channel is assigned if the required power is less than the `current interference margin'. The proposed algorithm is adaptable to dynamically changing environments with the capability of assigning more channels than conventional channel assignment methods in nonhomogeneous traffic loads and path loss changes