As promising copy networks of very large multicast switching networks for Broadband ISDN, multi-stage Recursive Copy Networks (RCN) have been proposed recently. In the multicast switch structure, the RCN precedes a point-to-point switch. At an RCN, all the copies of a master cell are generated recursively, i.e., a few copies of the master cell are made initially, and by considering each of these copies to be master cells, more copies are made which, in turn, are again considered to be master cells to make still more copies, the process thus progressing recursively till all the required copies are made. By this principle of recursive generation of copies, the number of copies that can be generated is independent of the hardware size of the RCN. A limitation of RCNs is that buffer sizes at all stages except the first stage have to be large so as to keep the cell loss due to buffer overflow within desired limits. This paper inspects a flow control scheme by which the probability of buffer overflow can be kept low, even though the buffer sizes at later stages are not large. Under this flow control procedure, a cell is not transmitted from a stage to the succeeding stage, if the occupancy level of the buffer of the succeeding stage exceeds a threshold. We study by simulation the performance aspects of such a flow control scheme in RCNs under cut-through switching scheme and under store-and-forward switching scheme. At high load intensities, the overflow probability can be reduced by an order of magnitude in 2-stage RCNs and by two orders of magnitude in 3-stage RCNs. To restrict the overflow probability within a given limit, the required buffer size is less under flow control than under no flow control. The implementation of the flow control is simple and the control overhead is small, thereby making the scheme attractive for implementation in high speed switching environments. Further, the proposed flow control scheme does not disturb the cell sequence.

In this paper, we derive spatial correlation functions of linear and circular antenna arrays for three types of angular energy distributions: a Gaussian angle distribution, the angular energy distribution arising from a Gaussian spatial distribution, and uniform angular distribution. The spatial correlation functions are investigated carefully. The spatial correlation is a function of antenna spacing, array geometry and the angular energy distribution. In order to emphasize the research and their applications in diversity reception, as an example, performance of the antenna arrays with MRC in correlated Nakagami fading channels is investigated, in which analytical formulas of average BER for the spatial correlation are obtained.

This paper compares three cell transfer quality control schemes, namely HPS, DAS and ORS, which integrate a preventive congestion control and a reactive congestion control in ATM switch. Simulation results showed that ORS achieves the largest network utilization, and HPS provides enough large throughput compared with DAS only when many VBR connections are multiplexed.

In this paper, we propose a modified scheme of MSODB and PMS, called Predictive User Mobility Behavior (PUMB) to improve performance of resource reservation and call admission control for cellular networks. This algorithm is proposed in which bandwidth is allocated more efficiently to neighboring cells by key mobility parameters in order to provide QoS guarantees for transferring traffic. The probability is used to form a cluster of cells and the shadow cluster, where a mobile unit is likely to visit. When a mobile unit may change the direction and migrate to the cell that does not belong to its shadow cluster, we can support it by making efficient use of predicted nonconforming call. Concomitantly, to ensure continuity of on-going calls with better utilization of resources, bandwidth is borrowed from predicted nonconforming calls and existing adaptive calls without affecting the minimum QoS guarantees. The performance of the PUMB is demonstrated by simulation results in terms of new call blocking probability, handoff call dropping probability, bandwidth utilization, call successful probability, and overhead message transmission when arrival rate and speed of mobile units are varied. Our results show that PUMB provides the better performances comparing with those of MSODB and PMS under different traffic conditions.

In order to serve traffic hot spots, the hierarchical cellular systems or the hybrid TDMA/CDMA have been proposed, recently. In order to depress the multi-user interference and increase capacity, the forward link power control strategy is adopted in the macrocell/microcell hierarchical cellular system using code division multiple access (CDMA). Its effects are estimated in this paper. Especially, the impact of -th distance power control laws on the forward link outage probability and capacity plane for the hierarchical cellular system are investigated. The coverage area user capacity of the overlaid macrocell/microcell cellular system is obtained. The numerical results and discussions with previous published results are presented in detail.

In this paper, we propose an approach to solve the power control issue in a DS-CDMA cellular system using genetic algorithms (GAs). The transmitter power control developed in this paper has been proven to be efficient to control co-channel interference, to increase bandwidth utilization and to balance the comprehensive services that are sharing among all the mobiles with attaining a common signal-to-interference ratio(SIR). Most of the previous studies have assumed that the transmitter power level is controlled in a constant domain under the assumption of uniform distribution of users in the coverage area or in a continuous domain. In this paper, the optimal centralized power control (CPC) vector is characterized and its optimal solution for CPC is presented using GAs in a large-scale DS-CDMA cellular system under the realistic context that means random allocation of active users in the entire coverage area. Emphasis is put on the balance of services and convergence rate by using GAs.

A simplified analysis is presented for the reverse link maximum capacity trade-offs between each layer, spectrum efficiency and its multi-rate features of TDMA/W-CDMA and N-CDMA/W-CDMA overlaid systems with the perfect power control based on the measurement of signal-to-interference ratio (CIR). In order to suppress the multi-cross interference, the other important techniques used in the analysis are the ideal notch filtering and the signal level clipper for W-CDMA system transmitters and receivers. We firstly propose the concepts of the notch filtering depth and signal level clipping depth in the paper. The numerical results can be adopted as a guideline in designing the overlaid systems in the various cases as well as a means to investigate the flexibility of sharing of the spread spectrum and their feasibility in the future mobile communication system.

In cellular networks, the system performance can be degraded because of the inefficient use of channels with the two types of traffic, that is, the new call traffic and handover call traffic. This problem can be alleviated if the channels are used efficiently for new call traffic and handover call traffic. In this paper, we consider the proper ratio of the number of channels for new calls to the number of total channels denoted as α. We introduce the new call channel limiting technique incorporating velocity of mobile user. We model one-dimensional cellular networks and evaluate the performance in terms of the blocking probabilities, the probability of call dropping and the probability of incomplete call. We show with numerical examples that the system performance can be improved by selecting the appropriate α for various velocities of mobile users.

In this paper, we consider a location management scheme using Limited Pointer forwarding from Commonly visited sites (LPC) strategy for Personal Communication Services (PCS) networks. The Commonly Visited Site (CVS) is defined as a site in which a mobile user is found with high probability. A feature of the strategy is that it skips updating location information of the mobile user, provided that the mobile user moves within its CVSs. Such a strategy is expected to significantly reduce the location update cost. We evaluate the location management cost of the LPC scheme by employing a Continuous-Time Markov Chain (CTMC) model. We show that the LPC scheme can reduce the location management cost of a highly mobile user who is found in its CVS with high probability.

In this paper, the co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. Overall rate, bit error ratio (BER) and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss in this system with cellular architecture, W-CDMA applying interference cancellation (IC) shows a substantial difference in spectrum efficiency, the overlaid system can provide a greater overall rate and higher spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system. The interference cancellation can significantly improve BER of the spectrum overlaid system.

In CDMA systems, power control strategy is the most important issue since the capacity of the system is only interference-limited. For a better understanding of the effects of Forward Link Power Control Strategy (FLPCS) on the outage probability in fading environments, this paper has presented a theoretical analysis of forward link in a CDMA cellular system by introducing the τ-th power of distance driven control strategy. Based on the power control, the capacity and outage probability of the system are estimated and discussed. In particular, we consider the impact of fading environments and investigate the "hole" phenomenon. Based on our numerical results, the "hole" points are at the upper bounds of where it is possible to ensure minimization of the maximum value of total Interference-to-Signal Ratio (ISR). At those upper bound points, at least, the power control strategy leads to approximately threefold the capacity compared to the case without power control strategy. It can be concluded that the forward link without power control strategy is a very heavy restriction for the capacity of the CDMA system, especially in environments of significant fading.

One of the remaining issues of Mobile IP is a mobile host (MH) needs to update its location each time it moves from one subnet to another, even when it is in dormant mode while roaming. This practice is apparently not efficient in terms of location update cost and power consumption. Recent research works have attempted to address that problem by extending Mobile IP with a layer 3 paging mechanism so-called IP paging. Particularly, IP Individual Paging schemes, which are customized to each MH, have attracted considerable interest of researchers. The employment of adaptability in some manner to MH parameters in order to enhance the efficiency of IP paging schemes is probably a promising approach. In this paper, we present an analysis on the effects of both host-adaptability and time-adaptability to MH parameters in Individual Paging schemes by comparing the signaling cost of an adaptive Individual Paging scheme to that of a non-adaptive counterpart. From our analysis, specifying the optimal paging area (PA) is critical in saving signaling cost of IP paging. Thus, our investigation is focused on the adaptability of PA to maintain its optimality.

In this paper, using a standard propagation model, the performance evaluation of a code-division-multiple-access (CDMA) cellular system with high data rate services for the reverse and forward links is investigated. In the approach, we propose "Equivalent Load" to estimate two cases of the system termed as the static analysis and the dynamic analysis. Performance measures of the static analysis obtained include the system capacity plane, outage probability and throughput. Performance measures of the dynamic analysis obtained include the allowed maximum data rate and the constraint set between the load situation and the data rate. We also estimate the effects of the power control on the system.

This paper proposes Channel Reservation for Ahead Cells (CRAC)" scheme for street micro-cellular systems. The scheme enables mobiles to reserve the same channel over several cells at once. This paper analyzes both CRAC and FCA (Fixed Channel Assignment) in a ring-shaped service area where high speed mobiles and low speed mobiles move. In the analysis, the priority control which prioritizes hand-off calls and reservation calls over new calls over new calls is also taken into account. Obtained results include the blocking rate, the forced call termination rate, the average number of channel changings and the system utilization. From numerical results, CRAC is found to perform better than FCA with regard to the average number of channel changings and the forced call termination rate.

For two-tier cellular network design, resource management between tiers is an important issue to be studied. In this paper, in order to use the network resources preciously, we considered sharing of the available spectrum between the tiers. We evaluate this sharing for two network architectures. In the first architecture, called System I, DS-CDMA is deployed in both tiers. In the second architecture, called System II, TDMA is deployed for users in the microcell tier and CDMA for macrocell users. Using analytically evaluated intercell interference for a two-tier cellular system, we will show the performance and the allowable system capacity for the above systems.

This paper is a study on the behavioral aspects of the input buffer limiting scheme whose basic feature is to award priority to the transit messages over the input messages so that congestion does not develop in the network. The numerical method employed in the analysis is that proposed in Ref.(7). The performance aspects are studied for different buffer capacities, different message handling capacities and different levels of reservation for transit traffic. The numerical method indicates that thrashing occurs at low levels of reservation for the transit messages, irrespective of the buffer size or the processor capacities of the node. This observation is supported by simulation results. With reference to the state-space of the model of our study, the congestion aspects are related to two Liapunov functions. Under the domain of one of the Liapunov functions, the evolution of the perturbed system is towards a congested state whereas, under the domain of the other Liapunov function, the evolution is towards a congestion-free state. Regardless of the configuration, it is found that the fundamental characteristic of the congestion under the input buffer limiting scheme is the characteristic of a fold catastrophe. In the systems with insufficient level of reservation for the transit traffic, the performance degradation appears to be inevitable, irrespective of the capacities of the nodal processor and output channel processor, and the size of the buffer pool. Given such an inevitability, the active life of a node under a typical node configuration is studied by simulation. A suitable performance index is suggested to assess the performance of deadlock-prone nodes.

For the connection request procedure in mobile communication systems, a previous study had shown that the 3-channel systems provide the haighest maximum of stable per channel throughput. In this paper, we propose and study a new algorithm, called the Parallel Collision Resolution Algorithm, which can be implemented in a Q-channel connection request environment, where Q3. For the implementation, the channels are arranged in R groups, where R is a positive integer. The collision resolution scheme distributes the collided messages over all the groups so that throughput and delay measures can be improved. At any point in time, there can be a maximum of R collision resolution schemes operational irrespective of the channel or the group number over which collisions occurred. The performance measures are estimated by computer simulation. Under the new algorithm, almost the same level of the perchannel stable throughput measure of a 3-channel network can be achieved in networks for which Q3. This feature allows freedom to the network designer to employ a higher number of connection request channels without forfeiting high channel utilization rates. When Q is an integral multiple of 3, the maximum stable per channel throughput level achieved can be the same as that achieved by the 3 channel system, if the grouping of channels is such that each group consists of 3 channels. When Q is not an integral multiple of 3, the intuitive strategy of organizing the channels in such a way that Q/3 groups consist of 3 channels each and one group consists of (Q mod 3) channels, may result in much degraded performance. It is found that, if the channels are so organised that no group is composed of (Q mod 3) channels, the performance levels can be substantially enhanced. Also, under the new algorithm, the delay measure is significantly improved, particularly in schemes like the mobile satellite systems with high propagation delays. We conclude that the new scheme presents a promising collision resolution methodology for connection request procedures.

This paper presents a new architecture of a copy network which employs the principle of recursive generation of copy cells. The proposed architecture achieves high utilization of the links and buffers of the copy network, and preserves the cell sequence. The architecture lends itself modularity so that large multicast ATM switches can be fabricated by employing the proposed copy network. Two different modular structures - one for reduced latency of the unicast cell and the master cell from which copies are made, and the other for reduced hardware overhead - for realizing large multicast ATM switches are configured. The hardware of functional elements of the copy network are the same as those of the functional elements of a modular point-to-point switch proposed earlier, thereby resulting in the modularity of functional elements as well. Simulation studies show that the proposed copy network achieves high throughput and low cell loss probability, and the required buffer sizes are small. The delay of cells is found to be very small for traffic loads up to 90%.

Transmit diversity, a key technique derived against multi-path mitigation in wireless communication system, is examined and discussed. Especially, we present an approach to investigate perfect/imperfect channel detection when the maximal ratio receiver combined scheme (MRRC) and a simple transmit diversity scheme (STD) are used in the wireless systems, which provide remarkable schemes for diversity transmission over Rayleigh-fading channels using multiple antennas. In order to effectively make use of the transmit diversity techniques, the same approach is extended to process the situation of one transmit antennas and N receive antennas in MRRC scheme (1 N MRRC) and two transmit antennas and N receive antennas in STD scheme (2 N STD). The effects of perfect/imperfect channel detection and the diversity reception with independent and correlated Rayleigh-fading signals are evaluated and compared carefully.