Capacity of cellular dynamic channel assignment schemes employingadaptive modulation and coding

An investigation into the benefits of introducing adaptive modulation and coding techniques into a cellular system employing dynamic channel assignment is performed for the case of a fixed wireless access network conveying fixed-bandwidth information. It is shown that in the typical cases considered, the introduction of adaptive modulation and coding can actually reduce the capacity of the system     

Channel assignment algorithms satisfying cochannel and adjacent channel reuse constraints in cellular mobile networks

Improved channel assignment algorithms for cellular networks were designed by modeling the interference constraints in terms of a hypergraph. However, these algorithms only considered cochannel reuse constraints. Receiver filter responses impose restrictions on simultaneous adjacent channel usage in the same cell or in neighboring cells. We first present some heuristics for designing fixed channel assignment algorithms with a minimum number of channels satisfying both cochannel and adjacent channel reuse constraints. An asymptotically tight upper bound for the traffic carried by the system in the presence of arbitrary cochannel and adjacent channel use constraints was developed by Deora (1995). However, this bound is computationally intractable even for small systems like a regular hexagonal cellular system of 19 cells. We have obtained approximations to this bound using the optimal solutions for cochannel reuse constraints only and a further graph theoretic approach. Our approximations are computationally much more efficient and have turned out to track very closely the exact performance bounds in most cases of interest.     

Distributed dynamic channel assignment with violation to the reuse pattern for microcellular networks

In this paper, the frequency reuse and the distributed dynamic channel assignment for microcellular networks are studied. We show that it is possible to use carriers with violation to the frequency reuse pattern with an insignificant degradation of the quality of service. As a result, a new family of distributed dynamic channel assignment algorithms is presented: the DDCA with violation to the reuse pattern (DDCA with VRP) strategies. The DDCA with VRP schemes allow the use of carriers with at most one violation to the reuse pattern, under the restriction that both cells using simultaneously the same carrier must be the farthest cells of their interference neighborhoods. The results show that the use of carriers with VRP is an effective strategy to increase the system capacity at the expense of an insignificant degradation of the quality of service. This is due to the fact that the carriers are employed with VRP by short time intervals in the least harmful situations. We propose and evaluate five DDCA with VRP schemes and everyone overcomes the performance of the maximum packing (MP) algorithm, with limited carrier usage information and without the need of centralized coordination neither global carrier rearrangements.     

Achievable performance over the correlated Rician channel

The correlated Rician channel is a useful model for a slowly fading channel, in which the complex fading process is composed of two quadrature Gaussian processes with a given autocorrelation function. For slow fading the correlation between adjacent symbols is relatively high. The authors investigate the achievable error probabilities over the channel, employing coherent detection and ideal side information on the realization of the fading processes at the receiver. An underlying decoding delay constraint which precludes the use of (ideal) interleaving is assumed. Coded BPSK performance is addressed both with and without the piecewise constant approximation (according to which the fading value remains constant during the symbol duration). For the latter case, that is no piecewise constant approximation, the analysis relies on the Fredholm determinant associated with the fading process autocorrelation function. The authors focus on the exponentially correlated channel. The “worst case” pairs of codewords are identified. The exponential behavior of the error probability with random coding (and i.i.d. Gaussian inputs) is analyzed, and the behavior of the cut-off rate and capacity is addressed. The results enhance the insight to the effect of the basic parameters governing the performance and these are examined in view of previous works and compared to relevant performance results for the block-fading channel model     

Achievable performance of turbo codes over the correlated Rician channel

The performance of turbo codes is evaluated through analysis and simulation over the Rice multiplicative fading channel. The analysis is conducted extending the results presented by A.M. Viterbi and A.J. Viterbi (see Proc. ISIT'98, p.29, 1998) to the Rice multiplicative fading channel case. Simulation results are obtained using an extended version of the improved Jakes' channel simulator, first presented by M.F. Pop and N.C. Beaulieu (see IEEE Trans. Commun., vol.49, p.699-708, 2001).     

Distributed dynamic channel assignment for in-building microsystems

Several fully distributed measurement-based dynamic channel assignment (DCA) schemes are compared for the large-scale uncoordinated deployment of in-building microsystems: DCA based on the first quality of service (DCA-FQZOS) channel selection, DCA based on best QOS channel selection (DCA-BQOS), DCA-WO (channel) (DCA with weighted channel orderings), and DCA-WO (carrier) (DCA with weighted carrier orderings). The DCA schemes are evaluated in terms of their blocking probabilities and algorithm processing delay. We also investigate how the DCA performance depends on the number of radio ports per base station, asynchronous time-slot transmission, and propagation conditions. Of the proposed DCA schemes, the simulation results show that there are tradeoffs in selecting a DCA scheme. Finally, a new scheme called DCA with limited selection weighted ordering (DCA-LSWO) is proposed that combines some previous strategies to improve performance for in-building microsystems     

Worst-case performance of cellular channel assignment policies

Many cellular channel assignment policies have been proposed to improve efficiency beyond that resulting from fixed channel allocation. The performance of these policies, however, has rarely been compared due to a lack of formal metrics, particularly under nonhomogeneous call distributions. In this paper, we introduce two such metrics: the worst-case number of channels required to accommodate all possible configurations ofN calls in a cell cluster, and the set of cell states that can be accommodated withM channels. We first measure two extreme policies, fixed channel allocation and maximum packing, under these metrics. We then prove a new lower bound, under the first metric, on any channel assignment policy. Next, we introduce three intermediate channel assignment policies, based on commonly used ideas of channel ordering, hybrid assignment, and partitioning. Finally, these policies are used to demonstrate the tradeoff between the performance and the complexity of a channel allocation policy.Supported by the Ameritech Foundation.Supported by the National Science Foundation under grant CCR-9309111.     

Capacity allocation and channel assignment in cellular radio systems using reuse partitioning

Reuse partitioning is a technique for providing more efficient spectrum reuse in cellular radio systems. A cell in such a system is divided into concentric zones, each associated with an overlaid cell plan. For these schemes an optimum channel assignment strategy is proposed. Numeric examples show capacity improvements of about 50% compared to conventional systems.<>     

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     

Static and dynamic channel assignment using neural networks

We examine the problem of assigning calls in a cellular mobile network to channels in the frequency domain. Such assignments must be made so that interference between calls is minimized, while demands for channels are satisfied. A new nonlinear integer programming representation of the static channel assignment (SCA) problem is formulated. We then propose two different neural networks for solving this problem. The first is an improved Hopfield (1982) neural network which resolves the issues of infeasibility and poor solution quality which have plagued the reputation of the Hopfield network. The second approach is a new self-organizing neural network which is able to solve the SCA problem and many other practical optimization problems due to its generalizing ability. A variety of test problems are used to compare the performance of the neural techniques against more traditional heuristic approaches. Finally, extensions to the dynamic channel assignment problem are considered     

Greedy-based dynamic channel assignment strategy for cellularmobile networks

This letter proposes a greedy-based dynamic channel assignment (GDCA) strategy in cellular mobile communication networks. Its main feature is that it dynamically allocates the channels based on the greedy method. Instead of the regular hexagon cell shape considered by previous strategies such as BCO, BDCL, various CP-DCA, the new strategy can be applied to any irregular cell shape. In addition, it reuses channels in terms of C/I ratio criteria. By system simulation, the proposed strategy outperforms the still used FCA on call blocking probability, and even has better performance compared to BDCL and CPDCA, etc     

Handoff prioritisation with implicit channel reservation indistributed dynamic channel assignment algorithms

A new distributed dynamic channel assignment scheme with implicit channel reservation for handoff prioritisation is proposed. This scheme reduces the degree of computation and communications among base stations required for channel reservation and achieves a capacity similar to that of the maximum packing algorithm. For 40 total channels, the proposed algorithm achieves a 116% capacity increase relative to the nonprioritised fixed channel assignment (FCA) scheme and 93% relative to FCA with optimum channel reservation     

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.     

An aggressive dynamic channel assignment strategy for amicrocellular environment

A new aggressive distributed dynamic channel assignment strategy for microcellular telephone networks is proposed. Channels are assigned in carrier groups, where carriers are acquired and released according to a carrier acquisition and release criterion. Whenever a call is in jeopardy of a forced termination, or handoff failure, the serving cell may force a cell in the surrounding neighborhood to relinquish a carrier to service the call. This aggressive strategy actually improves the arrangement of carriers throughout the network. Simulations show this strategy to decrease the probability of forced termination at the expense of a slight increase in the probability of new call blocking over most ranges of offered traffic. Improvements are shown for two different channel selection criteria: one using simple carrier orderings, and a more complex one called dynamic resource acquisition     

Distributed dynamic channel assignment in TDMA mobile communication systems

Dynamic channel assignment (DCA) has been a topic of intense research for many years, and a variety of DCA algorithms have been proposed. Nonetheless, some important issues have been neglected because of the complexity involved in their study. In particular, the impact of user motion on the performance of DCA systems has not received enough attention. In this paper, we quantify the impact of motion on the capacity and cost-in terms of average number of reassignments per call-of a variety of representative distributed fixed-power DCA algorithms. A novel adaptive algorithm especially suited for mobility environments is proposed, which achieves high capacity while controlling the reassignment rate. We also prove that most of this capacity can be effectively realized with a reduced number of radio transceivers per base station. Finally, we evaluate the degradation associated with the use of estimates of local-mean signal and interference levels-obtained by averaging instantaneous measurements-instead of the actual local-mean values.     

Neural network-based dynamic channel assignment for cellular mobilecommunication systems

Conventional dynamic channel assignment schemes are both time-consuming and algorithmically complex. An alternative approach, based on cascaded multilayered feedforward neural networks, is proposed and examined on two cellular systems with different configurations. Simulation results showed that the blocking performance of our multistage neural network approach can match that of an example conventional scheme with less complexity and higher computational efficiency. The example scheme considered here is the ordered channel search, which can achieve a reasonably high spectral efficiency as compared to that of an ideal dynamic channel allocation algorithm. We conclude that our neural network approach is well-suited to the dynamic channel allocation problem of future cellular or microcellular systems with decentralized control     

Compact pattern based dynamic channel assignment for cellularmobile systems

A new compact pattern based dynamic channel assignment strategy called CP-based DCA is proposed. The strategy aims at dynamically keeping the cochannel cells of any channel to a compact pattern. A compact pattern of a channel is defined as the pattern with minimum average distance between cochannel cells. CP-based DCA consists of two phases: channel allocation and channel packing. Channel allocation is used to assign an optimal idle channel to a new call. Channel packing is responsible for the restoration of the compact patterns and is performed only when a compact channel is released. Simulation results indicate that the CP-based DCA always performs better than the borrowing with directional channel locking (BDCL) strategy. In the designed example, CP-based DCA is shown to have 2% more traffic-carrying capacity than that of the BDCL in case of uniform traffic, and 8% more traffic-carrying capacity in case of nonuniform traffic, both at a blocking rate of 0.02. Besides, the number of channels reassigned per released call in CP-based DCA is at most one and is, therefore, another advantage over BDCL     

Ordered dynamic channel assignment scheme with reassignment inhighway microcells

An ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed, and its performance is studied in a highway microcellular radio environment. Channels are assigned in an ordered basis in conjunction with a minimax algorithm under cochannel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure, at the expense of an increase in complexity and call switching requirements     

Phantom cell analysis of dynamic channel assignment in cellularmobile systems

In this paper, we propose phantom cell analysis for dynamic channel assignment. This is an approximate analysis that can handle realistic planar systems with the three-cell channel-reuse pattern. To find the blocking probability of a particular cell, two phantom cells are used to represent its six neighboring cells. Then, by conditioning on the relative positions of the two phantom cells, the blocking probability of that particular cell can be found. We found that the phantom cell analysis is not only very accurate in predicting the blocking performance, but also very computationally efficient. Besides, it is applicable to any traffic and channel-reuse patterns