This letter proposes a novel intelligent dynamic channel assignment (DCA) scheme with small-cells to improve the system performance for uplink machine-type communications (MTC) based on OFDMA-FDD. Outdoor MTC devices (OMDs) have serious interference from indoor MTC devices (IMDs) served by small-cell access points (SAPs) with frequency reuse. Thus, in the proposed DCA scheme, the macro base station (MBS) first measures the received signal strength from both OMDs and IMDs after setting the transmission power. Then, the MBS dynamically assigns subchannels to each SAP with consideration of strong interference from IMDs to the MBS. Through simulation results, it is shown that the proposed DCA scheme outperforms other schemes in terms of the capacity of OMDs and IMDs.

This letter proposes a novel dynamic channel assignment (DCA) scheme to improve the downlink system capacity in heterogeneous networks (HetNets) with fractional frequency reuse (FFR). In the proposed DCA scheme, the macro base station (MBS) finds small-cell base stations (SBSs) that give strong interference to macro user equipments (MUEs) and then dynamically assigns subchannels to the SBSs to serve their small-cell user equipments (SUEs) according to the cross-tier interference information to MUEs. Through simulation results, it is shown that the proposed DCA scheme outperforms other schemes in terms of the total system capacity.

This paper proposes a novel dynamic channel assignment scheme named interference-aware dynamic channel assignment (IA-DCA) for the downlink of enterprise small-cell networks (ESNs) that employ orthogonal frequency division multiple access (OFDMA) and frequency division duplexing (FDD). In ESNs, a lot of small-cell access points (SAPs) are densely deployed in a building and thus small-cell user equipments (SUEs) have more serious co-tier interference from neighbor SAPs than the conventional small-cell network. Therefore, in the proposed IA-DCA scheme, a local gateway (LGW) dynamically assigns different numbers of subchannel groups to SUEs through their serving SAPs according to the given traffic load and interference information. Through simulation results, we show that the proposed IA-DCA scheme outperforms other dynamic channel assignment schemes based on graph coloring algorithm in terms of the mean SUE capacity, fairness, and mean SAP channel utilization.

This letter proposes a novel dynamic channel assignment (DCA) scheme with consideration of interference and fairness for the downlink of dense small-cell networks based on orthogonal frequency division multiple access-frequency division duplex. In the proposed scheme, a small-cell gateway fairly assigns subchannels to the small-cell user equipment (SUE) according to the co-tier interference from neighboring small-cell access points. From the simulation results, it is shown that the proposed DCA scheme outperforms other DCA schemes in terms of the fairness of each SUE capacity.

An interference-aware dynamic channel assignment scheme is proposed with consideration of co-tier interference for the downlink of an OFDMA/FDD based dense small-cell network. The proposed scheme adaptively assigns subchannels to the small-cell user equipment (SUE) according to the given traffic load and interference effect from neighbor small-cell access points. The simulation results show that the proposed scheme outperforms the other schemes based on the graph coloring algorithm in terms of the mean SUE capacity.

Recently, we proposed an interference-aware channel segregation based dynamic channel assignment (IACS-DCA). In IACS-DCA, each base station (BS) measures the instantaneous co-channel interference (CCI) power on each available channel, computes the moving average CCI power using past CCI measurement results, and selects the channel having the lowest moving average CCI power. In this way, the CCI-minimized channel reuse pattern can be formed. In this paper, we introduce the autocorrelation function of channel reuse pattern, the fairness of channel reuse, and the minimum co-channel BS distance to quantitatively examine the channel reuse pattern formed by the IACS-DCA. It is shown that the IACS-DCA can form a CCI-minimized channel reuse pattern in a distributed manner and that it improves the signal-to-interference ratio (SIR) compared to the other channel assignment schemes.

In dense femtocell networks (DFNs), one of the main issues is interference management since interference between femtocell access points (FAPs) reduces the system performance significantly. Further, FAPs serve different numbers of femtocell user equipments (FUEs), i.e., some FAPs have more than one FUE while others have one or no FUEs. Therefore, for DFNs, an intelligent channel assignment scheme is necessary considering both the number of FUEs connected to the same FAPs and interference mitigation to improve system performance. This paper proposes a two-stage dynamic channel assignment (TS-DCA) scheme for downlink DFNs based on orthogonal frequency division multiple access/frequency division duplex (OFDMA/FDD). In stage 1, using graph coloring algorithm, a femtocell gateway (FGW) first groups FUEs based on an interference graph that considers different numbers of FUEs per FAP. Then, in stage 2, the FGW dynamically assigns subchannels to FUE clusters according to the order of maximum capacity of FAP clusters. In addition, FAPs adaptively assign remaining subchannels in FUE clusters to their FUEs in other FUE clusters. Through simulations, we first find optimum parameters of the FUE clustering to maximize the system capacity and then evaluate system performance in terms of the mean FUE capacity, unsatisfied FUE probability, and mean FAP transmission energy consumption according to the different numbers of FUEs and FAPs with a given FUE traffic load.

A wireless multi-hop virtual cellular network (VCN) was recently proposed to avoid the large peak transmit power, resulting from the high transmission rates expected for future mobile communication systems. In VCN, calls hop through several links to reach the central port, which is the gateway to the network. With the use of a routing algorithm based on the total uplink transmit power minimization criterion, the total transmit power of all the multi-hop links between the mobile terminal and the central port can be significantly reduced, in comparison with the present (single-hop) cellular network. In this paper, an "on-demand" channel assignment strategy, using the channel segregation dynamic channel allocation (CS-DCA) algorithm, is proposed for multi-hop DS-CDMA VCN. Computer simulation is conducted to evaluate the blocking probability performance and make a comparison between the VCN and the present cellular network.

In this paper, the channel segregation dynamic channel allocation (CS-DCA) scheme is applied to a multi-hop DS-CDMA virtual cellular network (VCN). After all multi-hop routes are constructed over distributed wireless ports in a virtual cell, the CS-DCA is carried out to allocate the channels to multi-hop up and down links. Each wireless port is equipped with a channel priority table. The transmit wireless port of each link initiates the CS-DCA procedure and selects a channel among available ones using its channel priority table to check. In this paper, the channel allocation failure rate is evaluated by computer simulation. It is shown that CS-DCA reduces remarkably the failure rate compared to FCA. The impact of propagation parameters on the failure rate is discussed.

This work presents a novel channel assignment scheme for low earth-orbit (LEO) satellite-based mobile communication systems, in which any newly generated call will first be assigned an optimum channel and will no longer be reassigned even when it crosses the boundary of the cell. Thus, the compact reuse distance can be maintained and no handoff failure will occur owing to channel unavailability. Furthermore, a high quality service which guarantees successful handoff processes can be provided. The performance of the proposed strategy is analyzed and compared with the performances of the fixed channel assignment (FCA) scheme and dynamic channel assignment schemes.

In the current digital mobile communication that is used in the micro cellular system, a Self-Organized Dynamic Channel Assignment (DCA) Method has been proposed to use frequencies effectively. However, its characteristics and operational matters have not been reported yet. This paper takes up the TDMA/TDD system used in the current PHS system and also evaluates the characteristics and operational matters of this method through the actual operational tests. In addition, this paper aims to propose a new DCA method in order to speed up the Channel Segregation and evaluates its effects through the actual operational tests.

This paper discusses the teletraffic characteristics of cellular systems using Dynamic Channel Assignment. In general, it is difficult to exactly and theoretically analyze the teletraffic characteristics of Dynamic Channel Assignment. Also, it is not easy to theoretically evaluate influence of mobility on the traffic characteristics. This paper proposes approximate techniques to analyze teletraffic characteristics of Dynamic Channel Assignment considering mobility. The proposed techniques are based on Clique Packing approximation.

A new carrier based dynamic channel assignment for FDMA/TDMA cellular systems, called borrowing with directional carrier locking strategy, is proposed in this paper. When a call arrives at a cell and finds all voice channels busy, a carrier which consists of multiple voice channels can be borrowed from its neighboring cells for carrying the new call if such borrowing will not violate the cochannel interference constraint. Two analytical models, cell group decoupling analysis and phantom cell analysis, are constructed for evaluating the performance of the proposed strategy. Using cell group decoupling (CGD) analysis, a cell is decoupled together with its neigbors from the rest of the network for finding its call blocking probability. Unlike conventional approaches, decoupling enables the analysis to be confined to a local/small problem size and thus efficient solution can be found. For a planar cellular system with three-cell channel reuse pattern, using CGD analysis involves solving of seven-dimenional Markov chains. It becomes less efficient as the number of carriers assigned to each cell increases. To tackle this, we adopt the phantom cell analysis which can simplify the seven-dimensional Markov chain to two three-dimentional Markov chains. Using phantom cell analysis for finding the call blocking probability of a cell, two phantom cells are used to represent its six neighbors. Based on extensive numerical results, we show that the proposed strategy is very efficient in sharing resources among base stations. For low to medium traffic loads and small number of voice channels per carrier, we show that both analytical models provide accurate prediction on the system call blocking probability.

In this work, distributed dynamic channel assignment strategies with violation to the reuse pattern using vehicular mobility information for highway microcellular environments are proposed. It is shown that, when vehicular mobility information is included in the acquisition channel policy, the outage probability degradation because of the use of channels with one violation to the reuse pattern is negligible. Also, it is shown that, using different moving direction strategies it is possible to control the tradeoff between capacity and quality of service. The local packing algorithm (LP), was modified to allow the use of two different moving direction strategies with violation to the reuse pattern, resulting the VDLP1 and VDLP2 algorithms. The characteristics of user mobility are considered and a free-flowing vehicular traffic is assumed. Simulation results show that the use of vehicular mobility information in the distributed dynamic channel algorithms with violation to the reuse pattern, produce a considerable increase in the system capacity at the expense of an insignificant degradation of the quality of service. For a grade of service (GOS) of 0.1, the VDLP1 and VDLP2 carry 4% and 1.5% more traffic than the maximum packing algorithm, respectively. For the same GOS, the VDLP1 and VDLP2 carry 68% and 64% more traffic than the fixed channel assignment algorithm, respectively.

In cellular systems, autonomous reuse partitioning (ARP) is one of the channel assignment strategy which attains the high spectral efficiency. In the strategy, the movement of mobile stations (MSs) causes the disturbance of reuse partition. Furthermore the smaller cell size causes the spectral efficiency worse. In this paper, we propose a new ARP strategy with reuse partitioning reconstructing, named RP-reconstructing ARP strategy, for microcellular systems. We evaluate the performance of the proposed strategy with blocking rate and forced call termination rate by the computer simulation. The results show that the system with the proposed strategy accommodates 1.5 times as many users as the system with ARP does.

In this paper, the performance of dynamic channel assignment for cellular systems with an array antenna is evaluated assuming realistic beamformer. A new dynamic channel assignment algorithm is proposed to improve the performance by forming a directional beam pattern to cancel stronger co-channel interference with higher priority. Performance comparison is carried out by computer simulations. Conventional algorithm shows 2.7 fold capacity increase compared with an omni antenna system, whereas proposed algorithm shows around 3.3 fold capacity increase, at the point of 3 percent blocking probability. The simulation results also denote that a shorter reuse distance can be achieved by the proposed algorithm, which indicates a more efficient utilization of channel resource.

The feasibility of a dynamic zone configuration technique has been investigated. To make it easy to implement this technique in wireless communication systems, a simplified method for determining a suitable weight vector by using the least squares (LS) methods was developed. Simulations showed that the developed system is more effective than the present omni-directional zone system. Moreover, combining dynamic zone configuration technique with dynamic channel assignment strategy reduced blocking rate, forced call termination ratio, and required transmission power.

This paper proposes an intelligent and autonomous radio resource management scheme for a multi-layered cellular system with different assigned bandwidths to achieve flexible and high capacity wireless communication systems under any traffic conditions, especially under nonuniform traffic conditions. In the proposed system, terminals with lower mobility are connected to the wideband microcell systems to achieve higher system capacity, and terminals with higher mobility are connected to the narrowband macrocell systems to reduce intercell hand-off frequency. To flexibly cope with variations of traffic conditions, radio spectrum is adaptively and autonomously shared by both systems, and its control is conducted by each microcell base station. Moreover, at the existence of nonuniform traffic conditions , the proposed system introduces downlink power control for the microcells and graceful degradation thereby achieving high system capacity even under such extraordinary traffic situations . Computer simulation confirms that the proposed scheme can achieve lower blocking probability than the centralized scheme especially under nonuniform traffic conditions.

It is highly desirable to develop an efficient and flexible dynamic channel assignment algorithm in order to realize an integrated traffic TDMA mobile radio communication network. In this paper, an integrated traffic TDMA system is studied in which transmission of voice and data are assumed to occupy one and n time slots in each TDMA frame, respectively. In general, there are two types of channel (time slot) assignment algorithms: the partitioning algorithm and the sharing algorithm. However, they are not well-suited to the multimedia traffic consisting of various information sources that occupy different number of slots per frame. In this paper, assuming that voice is much more sensitive to transmission delay than data, an algorithm based on the sharing algorithm with flexible tima slot management scheme is proposed. Our method tries to vary the number of data slots adaptively so as to improve the quality of servive of voice calls and the system capacity. Computer simulations show the good performance of the proposed algorithm when compared to conventional channel assignment algorithms.

Dynamic Channel Assignment (DCA), which improves the efficiency of channel use in cellular mobile communication systems, requires finding an available channel for a new call after the call origination. This causes the delay which is defined as the time elapsing between call origination and completion of the channel search. For system planning, it is important to evaluate the delay characteristic of DCA because the delay corresponds to the waiting time of a call and influences service quality. It is, however, difficult to theoretically analyze the delay characteristics except its worst case behavior. The time delay of DCA has not been theoretically analyzed. The objective of this paper is analyzing the distribution and the mean value of the delay theoretically. The theoretical techniques in this paper are based on the techniques for analyzing the blocking rate performance of DCA.