Call blocking performance of distributed algorithms for dynamicchannel allocation in microcells

We determine the call blocking performance of channel-allocation algorithms where every channel is available for use in every cell and where decisions are made by mobiles/portables based only on local observations. Using a novel Erlang-B approximation method, together with simulation, we demonstrate that even the simplest algorithm, the timid, compares favorably with impractical, centrally administered fixed channel allocation. Our results suggest that an aggressive algorithm, that is, one requiring call reconfigurations, could provide a substantially reduced blocking probability. We also present some algorithms which take major steps toward achieving the excellent blocking performance of the hypothetical aggressive algorithm but having the stability of the timid algorithm     

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     

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     

Performance analysis of multihop cellular network with fixed channel assignment

Multihop cellular network (MCN) has been proposed to incorporate the flexibility of ad hoc networks into traditional single-hop cellular networks (SCNs). The performance analysis of MCN through analytical models is not trivial because the classic Erlang B formula no longer applies to MCN where multihop transmission is allowed. In this paper, we first propose a clustered MCN (cMCN) architecture with the use of dedicated information ports (DIPs), which are deployed wireless ports functioning as central controllers for multihop users. The proposed cMCN can be considered as a complement of the existing cellular network. Then, we study the feasibility of modeling time division multiple access (TDMA)-based cMCN with fixed channel assignment (FCA) scheme for uplink transmission. An exact multi-dimensional Markov chain model to analyze the performance of cMCN with FCA is developed. Furthermore, an approximated model which results in reduced complexity is also presented. The analytical results from both models are matched with the simulation results closely. The results show that cMCN with the proposed FCA scheme can reduce the call blocking probability significantly as compared to SCNs with either the conventional FCA or a dynamic channel assignment (DCA) scheme.     

Performance evaluation of distributed measurement-based dynamicchannel assignment in local wireless communications

The diverse environments emerging for wireless communication applications could render the centralized prediction-based channel assignment methodology, conventionally employed in cellular radio networks, impractical. The distributed measurement-based approach seems to be a more practical solution. We evaluate and compare several distributed measurement-based algorithms for dynamic channel assignment (DCA). Their performance is also compared with a centralized prediction-based algorithm. It is found that a simple aggressive algorithm with the use of a threshold, known as the least interference algorithm (LIA), performs the best     

Performance analysis of A dynamic channel allocation technique for satellite mobile cellular networks

This paper deals with an efficient dynamic channel allocation (DCA) technique suitable for applications in mobile satellite cellular networks. A cost function is defined to allow an optimum selection of channels to be allocated on demand. A mobility model suitable for low earth orbit (LEO) satellite systems is presented. The performance of the novel DCA technique in terms of call blocking probability has been derived by simulations. The obtained results are compared with those achieved by a fixed channel allocation (FCA) technique to show a better behaviour.     

Call-on-hold for improving the performance of dynamic channel-assignment strategies in cellular networks

Efficient use of the limited radio spectrum is of paramount importance to supporting the ever-increasing number of mobile terminals. There is a need for devising complementing techniques to improve the performance of dynamic channel-assignment (DCA) algorithms to increase the capacity of cellular systems. In this paper, we study the concept of call-on-hold to improve the performance of a class of DCA algorithms called coordinated assignment without measurement (CAWM). DCA algorithms such as the Geometric strategy, the Nanda-Goodman strategy, the borrowing with directional channel locking (BDCL) strategy, and the two-step dynamic priority (TSDP) strategy fall into the CAWM class. To gain insight into the CAWM DCA algorithms, we simulated those algorithms and monitored carrier availability and failure to assign a channel characteristics in a cell. After observing these characteristics, we formulated a hypothesis as follows: If a new or handoff call is put on hold for a short while in a cell in the absence of an available channel, it is highly likely that the local base station will soon find a channel for the call. In the proposed approach, a DCA algorithm is said to have failed to assign a channel to a call only if a waiting call is delayed for longer than a threshold period called maximum delay. Our simulation-based study shows that it is possible to significantly reduce failure rates of the CAWM class of DCA algorithms by putting those calls on hold which would otherwise be blocked or dropped. The impact of small values of maximum delay on the average delay suffered by all calls in a network is negligible, but the reduction in failure rate is significant. We have explained how the call-on-hold idea can be easily integrated with the GSM system.     

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.     

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.     

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     

Performance issues and algorithms for dynamic channel assignment

Using dynamic channel assignment (DCA) algorithms to select communications channels as needed, time-division multiple access (TDMA) or frequency-division multiple access (FDMA) systems can serve dynamic and nonuniform traffic demands without frequency planning as long as quality is sufficient and equipment is available. Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered. A fixed number of traffic servers (time slots) per radio port is assumed: therefore, the system capacity is hard-limited by the equipment availability, and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions     

Modeling resource management in cellular systems using Petri nets

Modeling and analysis tools are essential for the design and evaluation of complex systems. This is particularly true for cellular systems, where, for instance, a variety of handoff, channel allocation, and data-transmission algorithms have been proposed. The capabilities of Petri nets (PNs) are used as a novel approach in the analysis of handoff, dynamic channel allocation (DCA), and cellular digital packet data resource management problems. The generalized stochastic PN (GSPN) models are obtained and analyzed as continuous-time Markov chains (MCs) derived from the reachability graphs. Solution of the MC results in performance indicators, which show the impacts of different algorithms on the system behavior     

Near-optimality of distributed load-adaptive Dynamic Channel Allocation strategies for cellular mobile networks

In this paper we focus on the so-called load-adaptiveDynamic Channel Allocation (DCA) strategies for cellular mobile networks. Such strategies envisage the dynamic assignment of radio resources with the constraint that the outage probability (i.e. the probability that the carrier-to-interference power ratio be less than a given threshold) be less than a specified value, even in the worst foreseen propagation scenario. We identify a set of constraints to be satisfied in order that a DCA strategy belongs to the load-adaptive class. This provides a tight lower bound on traffic blocking and dropping performance such that: (i) it implies a dramatically lower computational effort than the known optimum strategy (based on the Maximum Packing algorithm); (ii) it is much tighter than the bound provided by the simple Erlang-B formula. A performance evaluation is carried out to compare the call blocking and dropping probabilities resulting from the tight bound above with those relevant to theFixed Channel Allocation and to some recently proposedDCA strategies, including theGeometric DCA. The simulations exploit a mobility model that provides different degrees of offered trafffic peakedness. It emerges that the Geometric DCA yields a practical way to attain near optimal performance in the load-adaptive class, leading a viable pathway to enhance the capacity of nowadays 2nd generation cellular networks in the short-medium term.     

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     

A Network-Based Dynamic Channel Assignment Scheme for TDMA Cellular Systems

Network-based dynamic channel assignment (DCA) schemes can be used to increase the capacity of TDMA cellular systems. In this paper, a new distributed network-based DCA scheme, known as DCA with interference information, DCA-WI, is proposed and its performance is studied. In this scheme, a base station (BS) assigns a channel in such a way as to minimize the effect on the availability of channels for use in its interfering cells. To accomplish this, each BS maintains an interference information table which contains information about the local cell and its interfering cells. DCA-WI does not require system-wide information. Channel reassignment for new and completed calls are used to further reduce the call blocking probability. Simulation results show that DCA-WI provides a lower call blocking probability compared to other existing schemes in both uniform and nonuniform traffic distributions.     

A deterministic channel access scheme for multimedia streaming in WiMedia networks

WiMedia MAC is an attractive transmission technology for high rate multimedia streaming and high quality consumer electronic devices in wireless personal area networks. In this paper, we propose a deterministic channel access (DCA), where all the devices determine their transmission orders in a distributed manner by exchanging beacon frames in the beacon period. Since all of the devices follow a deterministic transmission order, collision-free channel access can be achieved and thus the throughput can be significantly improved. In addition, the DCA addresses unfairness problems found in channel access by using circulating reference points. The trace-driven simulation results demonstrate that the DCA outperforms the existing channel access schemes in WiMedia MAC under different situations, especially under bursty traffic.     

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     

Modeling iCAR via Multi-Dimensional Markov Chains

iCAR is a new wireless system architecture based on the integration of cellular and modern ad hoc relaying technologies. It addresses the congestion problem due to limited channel access in a cellular system and provides interoperability for heterogeneous networks. The iCAR system can efficiently balance traffic loads and share channel resource between cells by using ad hoc relaying stations (ARS) to relay traffic from one cell to another dynamically. Analyzing the performance of iCAR is nontrivial as the classic Erlang-B formula no longer applies when relaying is used. In this paper, we build multi-dimensional Markov chains to analyze the performance of the iCAR system in terms of the call blocking probability. In particular, we develop an approximate model as well as an accurate model. While it can be time-consuming and tedious to obtain the solutions of the accurate model, the approximate model yields analytical results that are close to the simulation results we obtained previously. Our results show that with a limited number of ARSs, the call blocking probability in a congested cell as well as the overall system can be reduced.     

The geometric dynamic channel allocation as a practical strategy inmobile networks with bursty user mobility

We refer to a specific class of dynamic channel allocation (DCA) strategies, namely the interference-free, timid, not-conditioned class. The main concern of this work is to verify if and to what extent strategies belonging to this class can offer better performance than fixed channel allocation (FCA). The interest in this kind of strategies is motivated by their feasibility with current TDM technologies, the limited amount of information required to carry out channel assignments and their intrinsic stability. In this framework we present a simple, but very attractive DCA strategy, the so-called geometric DCA (GDCA). A performance evaluation is carried out to compare some representative DCA strategies of the considered class, by using a user mobility model that accounts for the large fluctuations of the number of users in a cell coverage area expected in a microcellular environment. The effect of the non-null propagation time required by the information exchange in the DCA strategies is also taken into account. It emerges that the proposed GDCA allows better performance than more sophisticated strategies already proposed, at the expense of a frequency planning carried out only at network configuration. This is due to the ability of GDCA to exploit the a priori information to maintain a tight geometric packing of used carriers. The reported results also show that DCA strategies in the considered class cope with large and sudden traffic fluctuations remarkably better than the FCA scheme does and that the advantage becomes more evident as the burstiness of the user mobility process (hence of the offered traffic) increases     

Performance of Channel Carrying for Handoff in a DCA Cellular Network

Channel carrying allows a mobile station to continue the use of its currently occupied channel when it hands off to a new cell. Since in a dynamic channel assignment (DCA) system, generally, any channel can be usedby any cell, channel carrying can be more easily implemented than in a fixed channel assignment (FCA) system which supports channel carrying through borrowing channels or extending channel reuse distance. Therefore, this paperinvestigates different channel carrying strategies maybe used in the distributed timid DCA scheme with the seamless handoff policy (DCA-DT/SLH), namely, channel carrying first (CCF) and channel carrying last (CCL). This study shows that (1) CCL generally outperforms CCF; (2) in DCA-DT/SLH without channel carrying,handoff calls may suffer higher dropping probabilities than new calls if no priority is given to handoff calls while channel carrying can easily avoidsuch undesirable situation; and (3) channel carrying in DCA-DT/SLH is comparableand even better than the guard channel (GC) in FCA and can also slightly improvethe performance of GC in DCA-DT/SLH.