Number Of Free Channels Research Articles

Analysis of queuing system with calls of various width

In this paper, we study the mathematical model of a multi-channel queuing system in which Poisson flows of voice and data calls are served. It is assumed that narrow-band voice calls require only one free channel to service, while at the same time, number of free channels that required to service broadband data calls is b, b>1. The system adopts a widely used in practice, fully accessible access strategy to the common channel pool, according to which there are no differences between different types of speech and data calls. If upon arrival of a voice call (data call) there is one free channel (b>1 free channels), then it occupies free channel(s) of the system; otherwise the call is lost. The distribution functions of channel occupation time by heterogeneous calls are exponential with different average values. It is shown that the mathematical model of the system is a certain two-dimensional Markov chain with a finite set of states. An algorithm is proposed for constructing the generating matrix of this chain and it is proved that from any state of this chain in a finite number of steps it is possible to go to any other state. Using the Kolmogorov theorem, it is proved that the constructed two-dimensional Markov chain is reversible, and therefore the stationary probability distribution of the states of this Markov chain has a multiplicative form. An explicit form of the multiplicative representation is obtained. Explicit formulas have been developed for calculating the probabilities of the states of the Markov chain under study, and using these probabilities of states, explicit formulas have been proposed for calculating the indicators of service quality — call probabilities of each type calls and channel utilization. The developed formulas allow us to conduct numerical experiments in order to study the behavior of indicators of the quality of service of the system relative to changes in its parameters, as well as solve the problems of their optimization with respect to the selected quality criterion for the functioning of the system.

Performance Analysis of Channel-barrowing Hand-off Scheme in CDMA Cellular Systems

For cellular communication systems, mobility and limited radio coverage of a cell require calls to be handed over from one Base Station System (BSS) to another. Due to the limited band width available in various cells, there is a finite probability that an ongoing call, while being handed off, may get dropped. Minimizing the dropping of ongoing calls during hand off is an important design criterion. Some digital cellular systems, e.g., the Global System for Mobile Communications and the IS-136, use Mobile-Assisted Hand off (MAHO), in which a Mobile Terminal (MT) assists, it's BSS and a mobiles witching center in making hand off decisions. MAHO requires an MT to regularly report, back to its serving BSS, its current radio-link state (defined in terms of the Received Signal Strength Indicator (RSSI) and the Bit Error Rate (BER)) of transmissions received from neighboring BSSs. In the proposed technique, the MT reports back not only the RSSI and the BER but the number of free channels that are available for the hand off traffic as well. This will ensure that a handed-off call has acceptable signal quality as well as a free available channel. The performance of this hand off technique is analyzed using an analytical model whose solution gives the desired performance measures in terms of blocking and dropping probabilities.

Combined Guard Channel and Mobile-Assisted Handoff for Cellular Networks

For cellular communication systems, mobility and limited radio coverage of a cell require calls to be handed over from one base station system (BSS) to another. Due to the limited bandwidth available in various cells, there is a finite probability that an ongoing call, while being handed off, may get dropped. Minimizing the dropping of ongoing calls during handoff is an important design criterion. Some digital cellular systems, e.g., the global system for mobile communications and the IS-136, use mobile-assisted handoff (MAHO), in which a mobile terminal (MT) assists its BSS, and a mobile switching center in making handoff decisions. MAHO requires an MT to regularly report, back to its serving BSS, its current radio-link state [defined in terms of the received signal strength indicator (RSSI) and the bit error rate (BER)] of transmissions received from neighboring BSSs. Some researchers have suggested that a base station needs to give priority to the handoff calls over the new calls. This requires each cell to reserve a number of guard channels (GCs) to be used exclusively for processing of the handoff calls. Since MAHO makes handoff decisions based solely on RSSI/BER measurements, there is a finite probability that some handoff calls may get dropped due to the nonavailability of free channels in the neighboring cell to which the call is being handed off. Conversely, if a handoff decision is based solely on the availability of a free channel, without regard to the signal quality, it may result in some of the handed-off calls being dropped due to poor signal quality. In this paper, we propose a new handoff technique by combining the MAHO and GC techniques. In the proposed technique, the MT reports back not only the RSSI and the BER but the number of free channels that are available for the handoff traffic as well. This will ensure that a handed-off call has acceptable signal quality as well as a free available channel. The performance of this handoff technique is analyzed using an analytical model whose solution gives the desired performance measures in terms of blocking and dropping probabilities.

D-CAT: An Efficient Algorithm for Distributed Channel Allocation in Cellular Mobile Networks

We propose a distributed channel allocation algorithm based on a threshold scheme, called D-CAT, for cellular mobile networks. The algorithm employs two thresholds: (i) a heavy threshold for determining whether a cell is heavy, or overloaded, and for triggering the channel allocation algorithm; and (ii) a target threshold for indicating the target number of free channels that a heavy cell intends to acquire. Based on the two-threshold scheme, the D-CAT algorithm can determine the optimal number of free channels as well as the cell(s) from where a heavy cell should import channels in order to satisfy the required channel demand. Simulation experiments and analyses show that the proposed algorithm incurs lower overhead for channel allocation and is more efficient in terms of channel utilization than other distributed channel allocation algorithms. It also outperforms other centralized and distributed algorithms in terms of call blocking probability.

An adaptive quality of service channel borrowing algorithm for cellular networks

AbstractA multimedia call consists of three main sub‐streams (i.e. video, audio and data) each with its own distinct quality of service (QoS) requirements (e.g. packet loss rate, delay tolerance, and jitter). These requirements constitute a specific fixed QoS level. In contrast to static approaches, we propose an adaptive QoS platform in which each sub‐stream declares a preset range of acceptable QoS levels (e.g. maximum, acceptable, minimum) instead of just a single level. This range of QoS levels is pre‐defined in a user‐defined profile (UDP). In this paper, we propose a channel borrowing algorithm based on such adaptive QoS platform. In our proposed algorithm, an acceptor cell that has used all its channels can borrow from any neighbouring (donor) cell as long as this donor cell has some channels available after satisfying a minimum QoS (minQ) level defined in the UDP. A donor cell that is assigning QoS levels (to calls under its coverage) higher than the minQ levels will declare those channels as available for borrowing by other acceptor cells. The criteria for choosing the free channel include not only the number of free channels, but also the QoS levels in the donor cell. The criteria are also extended to include the effect of channel locking on the number of free channels, and the QoS levels on the locked cells. The algorithm is not triggered unless it does not cause any call dropping in either the donor cell, or the cells affected by call blocking. In the meantime, the call blocking rate is significantly decreased while the offered load increases. Copyright © 2003 John Wiley & Sons, Ltd.

Critical current in superconducting quantum point contacts

The quantization of the critical current I c in a quantum point contact is studied on varying the number of free channels (varying the constriction width d0 in 2DEG). It is shown that the shape of the quantum I c is not universal and depends on the parameters of the contact, in particular, on the properties of the 2DEG-S boundaries. Because of the effect of normal reflection from the S-2DEG boundaries, the quantum critical current nonmonotonically depends on d0 and may have a resonance structure. If E F coincides with a quasi-stationary level of the square potential well formed by the contact walls, the critical current has a local maximum (resonance) equal (in the first channel) to the ratio of the electron charge to its time of travel through the contact. The critical current at the maximum is determined by the lowest positive Andreev level (for the phase difference π).