Channel management in microcell/macrocell cellular radio systems

In this paper, we study spectrum management in a two-tier microcell/macrocell cellular system. Two issues are studied: micro-macro cell selection and frequency spectrum partitioning between microcells and macrocells. To keep the handoff rate in a two-tier cellular system at an acceptable level, low mobility users (with speed υ0 ) should undergo handoffs at microcell boundaries, and high mobility users (with speed υ>V₀) should undergo handoffs at macrocell boundaries. The mobile determines user mobility from microcell sojourn times and uses it for channel assignment at call origination and handoff. The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches. We investigate the optimal velocity threshold, V₀, and propose that it may be dynamically adjusted according to traffic load. Finally, we propose a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells. This partitioning is based on the traffic load and velocity distribution of mobiles in the system     

Performance analysis of dynamic channel assignment algorithms in cellular mobile systems with hand‐off

In this paper, the traffic performance of dynamic channel assignment (DCA) in cellular mobile system with hand‐off is investigated. A traffic model for cellular system incorporating hand‐off is established first. Under the framework of the model, a hand‐off priority scheme is developed to reduce the forced termination of calls in progress. This paper analyses and derives the traffic performance bound for DCA strategies with hand‐off by extending the maximum packing (MP) scheme to include the hand‐off procedure. For practical implementation, a distributed DCA algorithm (DDCA) is also proposed. A non‐priority scheme and the proposed priority scheme can be combined with either MP or DDCA. It is shown that the simulation results of DDCA scheme are comparable with the analytical bounds given by MP for both the non‐prioritized case and prioritized case. A reasonable trade‐off between the new call blocking probability and forced termination probability can be achieved by using the proposed prioritized scheme in DCA. Copyright © 2002 John Wiley & Sons, Ltd.     

Capacity analysis for underlaying CDMA microcell/macrocell systems

The CDMA system can provide more capacity than the conventional AMPS system and the hierarchical layer of cells is required for system design in the future. However, the problem is whether the same RF channels used in a CDMA underlaying macrocell/microcell structure also obtain high capacity as in the homogeneous structure. This paper investigates the interference of uplink and downlink from both the microcell and macrocell in a hierarchical structure. Downlink power control is also considered. The results show that the capacity of microcell in a hierarchical structure is 23 per cent less than in homogeneous cells. The capacity of macrocell in a hierarchical structure decreases dramatically in proportion to the number of microcells. The capacities of the microcell and macrocell are limited in downlink, and uplink, respectively. In addition, more efforts for microcell should be made, such as more power is transmitted by microcell basestation if the same RF channel is used in a hierarchical structure. The results suggest that different RF channels are used in a two‐tier cellular environment. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance analysis of a reuse partitioning technique for multi‐channel cellular systems supporting elastic services

For multi‐cell systems employing intra‐cell orthogonal communication channels, inter‐cell interference mitigation techniques are expected to be one of the key radio resource management functions. In this paper we propose and analyze a simple reuse partitioning technique (with random and coordinated resource block allocation in neighbor cells) that is able to reduce inter‐cell interference. We propose a model that is able to take into account that sessions dynamically enter and leave the system. Rigid sessions require a class‐specific fixed number of resource blocks, while elastic sessions can enter the system if a minimum number of resources are allocated to them. In this rather general setting (and using the example of a system employing frequency division for multiple access) we analyze the system performance in terms of the expected number of channel collisions, the session‐blocking probabilities, the signal‐to‐interference‐and‐noise ratio (SINR) and packet error rate performance. We present numerical results on the various trade‐offs between these measures (including the trade‐off between the reuse factor and the SINR performance) that provide insight into the behavior of multi‐channel cellular systems and help dimensionalize the parameters of a reuse partitioned system. Copyright © 2008 John Wiley & Sons, Ltd.     

Design aspects of satellite–cellular hybrid wireless systems

In this paper we investigate various issues related to the design of satellite–cellular hybrid systems. First, we review the fundamental problems of channel partitioning and call admission/assignment. Second, we study the impact of different frequency reuse constraints, in both layers, on the optimum channel partitioning. Third, we investigate, analytically and via simulation, the effect of reducing the cell size. We emphasize the blocking‐forced termination probabilities trade‐off for pure cellular and satellite–cellular hybrid systems. Accordingly, an optimization problem with respect to the cell size is formulated. Finally, we search for the optimum dynamic call re‐assignment policy that improves the system capacity at the expense of the complexity associated with tearing down a connection in one system and setting‐up an alternative one in the other system. For a small hybrid system, we characterized the optimum re‐assignment policies that minimize the blocking probability, dropping probability, and a weighted cost function of these probabilities. Copyright © 2002 John Wiley & Sons, Ltd.     

Performance of Reuse Partitioning in Cellular Systems with Mobile Users

Reuse partitioning (RP) is a simple technique that can be used to increase the traffic capacity in a cellular system. With RP, a cell is divided into several concentric regions, each associated with a different cluster size. In this article, a traffic model is developed to analyze the impact of mobile users on a two-region RP system using fixed channel assignment. The influence of user speed and cell size on the new call blocking probability, P_b, and the call dropping probability, P_d, is investigated. A simpler model that can be used to estimate P_b and P_d in some cases is described. The effect on system capacity of reserving some channels for handoff calls is also studied. It is found that even though prioritized handoff can reduce P_d, it may also degrade the capacity. The accuracy of the analysis is verified using simulation for three mobility models.     

Uplink PID power control technique for TDMA‐based cellular radio systems

The efficient management of wireless resource is essential to the success of wireless systems. While power control is traditionally considered to be a means to counteract the detrimental effects of channel fading, it is also a flexible mechanism that achieves high link quality, high bandwidth utilization, and low power consumption, which are mainly driven in cellular radio systems. Once the power control algorithm provides a lower outage probability, the SUs experienced adequate link quality need not to competitively increase their transmission power. Spontaneously, the systems with lower power consumption and better bandwidth efficiency are achieved. In this paper, a novel power control based on the proportional‐integration‐derivative (PID) controller is proposed, and its performance with an autonomous closed‐loop uplink power control model under the time division multiple access (TDMA) systems is presented. Computer simulation is used to illustrate the performance of the proposed power control algorithm in a cellular radio system with Rayleigh fading channels. The results show that our proposed power control algorithm is remarkably superior to several previous power control methods, especially in a short power control period. Copyright © 2006 John Wiley & Sons, Ltd.     

Analytical evaluation of downlink interference mitigation in multi‐macrocell/femtocell networks with frequency & cell partitioning

In this paper, we propose an interference mitigation method to suppress the downlink interference in multi‐macrocell/femtocell networks, and analytically evaluate the interference mitigation and average rate performances. Specifically, the proposed interference mitigation method consists of three steps: frequency partitioning, cell partitioning, and sub‐band allocation. In the frequency partitioning step, the whole downlink frequency band is divided into nine non‐overlapping sub‐bands. In the cell partitioning step, each macrocell is divided into four macrocell regions and three femtocell regions for macrocells' and femtocells' communications, respectively. In the sub‐band allocation step, each macrocell or femtocell region is allocated a sub‐band to guarantee that any two neighboring macrocell/femtocell regions use different sub‐bands. Conducted simulation results show that the proposed method is effective in mitigating the downlink interference and improving the average downlink per‐channel rate in multi‐macrocell/femtocell networks. In summary, the major contribution of the proposed interference mitigation method is that the downlink interference can be mitigated without cooperation between macrocells and femtocells, while the full frequency utilization of the macrocell is achieved. Copyright © 2016 John Wiley & Sons, Ltd.     

Adjacent channel interference in a macrocell/microcell WCDMA system

This paper studies the impacts of adjacent channel interference (ACI) on uplink capacity in a multi‐macrocell/multi‐microcell wideband code‐division multiple access (WCDMA) system. A method is presented for computing ACI and deriving capacity limitation. This method is based on an interference analysis that accounts for shadow fading, and random distribution of mobile users. The results indicate that both the base station (BS) separation and adjacent channel interference power ratio (ACIR) strongly affect system capacity reduction. The proposed method in this paper is useful for measuring the impacts of ACI on uplink capacity. Copyright © 2008 John Wiley & Sons, Ltd.     

Capacity optimizing channel allocation schemes for multi‐service cellular systems with mobile users

In this paper, we study the blocking and dropping probability of mobile users in the multi‐service cellular systems with mobile users. Based on the idea that different services may require different signal‐to‐interference ratios and different reuse factors, we proposed a channel allocation scheme called channel partitioning to support different services using different reuse factors. Under channel partitioning scheme, the channels in each cell are divided into two or more sets of channels and each set of the channels supports certain service, depending on the required reuse factor of the service. We first apply this channel partitioning with fixed channel allocation scheme called fixed channel partitioning (FCP), where a three‐dimensional Markov chain is developed to analyze the impact of the mobile user. After that a simpler model, which can estimate the numeric result from the closed‐form solution, is presented to make the analysis easier. In order to cater for the traffic variation between services and between cells, a dynamic channel partitioning with flexible channel combination scheme, called FDCP, is proposed to support multiple services. This FDCP tries to minimize the effect of assigned channels on the availability of channels for use in the interfering cells. The analysis and the simulation results show that for equal arrival rate of two services, the proposed FCP and FDCP scheme can provide about 32% and 54% improvement, respectively, in terms of grade of service as compared with conventional FCA scheme using a single reuse factor to support two services for the mobile users. Copyright © 2006 John Wiley & Sons, Ltd.     

Energy‐efficient relay deployment in cellular systems using fractional frequency reuse and transmit antenna selection techniques

To cope with the steep surge in mobile traffic, network operators are now expanding their infrastructure for mobile access networks. However, since energy costs and greenhouse gas emissions are a large burden to network operators, they are making great efforts to improve the energy efficiency (EE) of their networks by promising techniques, including relaying and multiple‐input multiple‐output (MIMO). Relaying technique can considerably improve the EE when the interference between base stations (BSs) and relay stations (RSs) is effectively coordinated by an elaborate relay deployment using the fractional frequency reuse (FFR) technique. Also, MIMO techniques improve the radio channel quality through diversity gains, so the system capacity and the EE can be improved. Therefore, a combination of relaying/MIMO techniques can be considered to achieve the higher performance, particularly, if the system complexity and costs of using such techniques are low. Since the transmit antenna selection (TAS), one of MIMO techniques, can provide a sufficient transmit diversity gain and satisfy the requirements for low complexity and cost (thus, practical), the TAS is recommended for use with the relaying technique. In this paper, for an energy‐efficient relay deployment using FFR and TAS techniques, we derive the EE and the resource partitioning according to RS positions and the number of BS antennas by a mathematical analysis. Then, the optimal RS positions according to the number of antennas can be determined by an optimization approach. The numerical and simulation results indicate that the proposed analysis method can efficiently analyze the EE and locate the RSs.     

Sequential frequency reuse with power control for OFDMA systems

Orthogonal frequency division multiple access (OFDMA) is a promising technique for high data rate communications in future cellular systems. Since frequency resources are universally reused in every cell in a system, a typical OFDMA system tries to maximize the spectral efficiency. Users located near the cell‐edge tend to have the weakest signal strength. So they might experience severe inter‐cell interferences (ICIs). In this paper, we propose a sequential frequency reuse (SqFR) that reduces ICIs by a sequential sub‐channel allocation. By giving more power to sub‐carriers allocated to cell‐edge users, our SqFR significantly enhances the performance of cell‐edge users. The performance of the proposed SqFR is investigated via the analysis and simulations. Simulation results show that proposed SqFR improves the performance of cell‐edge users in an OFDMA system under both homogeneous and heterogeneous traffic conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance analysis of a P2P‐enabled TDD‐CDMA network with intra‐cell spatial resource reuse

In this paper a scheme of intra‐cell spatial resource reuse is proposed for a peer‐to‐peer (P2P) enabled TDD‐CDMA system to increase the system capacity via only software update. On account of the new interference scenario in our scheme, a more accurate model of signal to interference and noise ratio (SINR) is deduced and analyzed instead of using the conventional equation. As demonstrated by our system‐level simulations, the capacity is significantly improved by reusing the same radio resource among different P2P transmitters within a single cellular cell in the spatial domain. Furthermore, we employ critical values of SINR target observed from simulation results to indicate whether the P2P‐enabled system is resource‐restricted or interference‐restricted for a certain application scenario. By means of a hexagon‐padding plan, the relation between co‐channel reuse distance and single‐hop distance is also pointed out to help to apply our scheme to a real implementation. Copyright © 2008 John Wiley & Sons, Ltd.     

Optimal channel assignment in cellular networks

In this paper, we consider the problem of assigning frequencies to mobile terminals in a cellular network. We show that an optimal solution can be obtained by solving a sequence of alternating linear and quadratic maximization programming problems. We address co-channel constraints and adopt as an objective function the maximization of potentially established calls. Our algorithm is fairly general, and does not depend on any special network structure. This study indicates that mathematical programming can be used as an efficient technique for solving the aforementioned problem.     

Uplink channel assignment with balanced load for code division multiple access cellular systems

In a code division multiple access (CDMA) wireless communication system, each mobile handset must be power controlled such that the power received at the base station is roughly the same. Otherwise, the interferences between mobile handsets will degrade the performance and increase the error rate. When a mobile handset uses channels from the neighbouring cells, it will raise its power to meet the threshold of signal strength. This will also increase the interference in the home cell. Therefore, we do not want a mobile handset to use channels from other cells blindly. In this paper, we propose an uplink channel assignment method based on the directed retry concept for CDMA cellular systems. The purpose is to achieve load balancing between neighbouring cells and at the same time controlling the interference levels at the base stations such that it will not affect the performance. Furthermore, priorities are given to handoff calls when assigning channels. Copyright © 2002 John Wiley & Sons, Ltd.     

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.     

Combined code reuse scheme with two‐dimensional OVSF codes assignment algorithm for uplink multi‐user/multi‐rate block spread multi‐cellular CDMA

The two‐dimensional (2D) block spread code division multiple access (CDMA) can avoid the uplink multiple‐access interference with low‐complexity single‐user detection in a slow fading channel and, therefore, is very attractive. In the 2D spreading, orthogonal variable spreading factor (OVSF) is used for spreading; an important problem is how to efficiently assign the limited resource of OVSF codes to users with different data rates, while meeting the requirement of quality of service in a multi‐cell environment. In this paper, it is shown that the code reuse can improve the code reuse efficiency and the proposed code reuse scheme combined with code assignment algorithm can allow flexible multi‐rate uplink transmission. The computer simulation confirms that the proposed code assignment algorithm improves the code reuse efficiency while achieving lower blocking probability than traditional CDMA. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of CDMA cellular networks with channel sub‐rating

This paper presents the analysis of CDMA cellular networks with channel sub‐rating. From users' point of view, our considered scheme gives higher priority to handoff calls over new calls by sub‐rating the existing connections when handoff calls find no idle channels upon their arrivals. Therefore, it is considered that the disadvantage of the soft handoff which needs more channels than the hard handoff is made up for. Handoff calls can also wait in a queue while they are in handoff areas if all channels are sub‐rated in the cell of interest. We mathematically model this scheme by applying queueing theory. Then, we analyse its performance to derive the blocking probabilities of the new and handoff calls, the probability that handoff calls leave the handoff area without getting new channels, the degradation ratio of the voice quality by sub‐rating, mean and coefficient of variation of the waiting time of handoff calls. In numerical results, the analytical results are compared with the simulation ones to validate our analytical approach. Moreover, we compare the sub‐rating scheme with full‐rating one with respect to some characteristic values to show the effect of sub‐rating. Copyright © 2005 John Wiley & Sons, Ltd.     

Tree‐based channel assignment schemes for multi‐channel wireless sensor networks

Many sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a single radio channel for whole network, multiple channels can be utilized in a sensor network simultaneously to decrease overall network interference, which may help increase the aggregate network throughput and decrease packet collisions and delays. This method, however, requires appropriate schemes to be used for assigning channels to nodes for multi‐channel communication in the network. Because data generated by sensor nodes are usually delivered to the sink node using routing trees, a tree‐based channel assignment scheme is a natural approach for assigning channels in a WSN. We present two fast tree‐based channel assignment schemes (called bottom up channel assignment and neighbor count‐based channel assignment) for multi‐channel WSNs. We also propose a new interference metric that is used by our algorithms in making decisions. We validated and evaluated our proposed schemes via extensive simulation experiments. Our simulation results show that our algorithms can decrease interference in a network, thereby increasing performance, and that our algorithms are good alternatives for static channel assignment in WSNs. Copyright © 2015 John Wiley & Sons, Ltd.     

A compact dynamic channel assignment scheme based on Hopfield networks for cellular radio systems

In this paper, a new channel assignment strategy named compact dynamic channel assignment (CDCA) is proposed. The CDCA differs from other strategies by consistently keeping the system in the utmost optimal state, and thus the scheme allows to determine a call succeeding or failing by local information instead of that of the whole network. It employs Hopfield neural networks for optimization which avoids the complicated assessment of channel compactness and guarantees optimum solutions for every assignment. A scheme based on Hopfield neural network is considered before; however, unlike others, in this algorithm an energy function is derived in such a way that for a neuron, the more a channel is currently being allocated in other cells, the more excitation the neuron will acquire, so as to guarantee each cluster using channels as few as possible. Performance measures in terms of the blocking probability, convergence rate and convergence time are obtained to assess the viability of the proposed scheme. Results presented show that the approach significantly reduces stringent requirements of searching space and convergence time. The algorithm is simple and straightforward, hence the efficient algorithm makes the real‐time implementation of channel assignment based on neural network feasibility. Copyright © 2008 John Wiley & Sons, Ltd.