A dynamic pre-allocated connection (DPC) scheme is proposed to support fast handoff and to effectively utilize wireline links in a multi-connection call environment. Handoff can be quickly executed in real-time with reduced connection overhead, since the proposed scheme uses pre-allocated switched virtual connections (PSVCs). This dynamic resource management scheme increases link utilization due to statistical multiplexing effects. A path-loop elimination algorithm can be applied to remove duplicate resource usages. The DPC scheme in an environment of multi-connection calls is analyzed to obtain three probabilities; 1) new multi-connection call blocking probability, 2) multi-connection handoff call blocking probability, and 3) fast handoff failure probability.

In the Mobile IP handoff procedure, mobile node movement is detected from advertisements of foreign agents that differ from previously received advertisement and the new "care-of" address is registered with the home agent. However, user packets are not forwarded to the new foreign agent until a registration is completed and this interruption may degrade the quality of service especially in real-time applications such as audio and video, or may lower the TCP throughput due to retransmission timeout. To tackle these issues, we propose a new low latency handoff method, where access points used in a wireless LAN environment and a dedicated MAC bridge are jointly used to alleviate packet loss without altering the Mobile IP specifications. In this paper, we present design architecture of the proposed method and evaluate its performance in an actual network environment to verify the effectiveness of our approach.

This paper assesses the performance of the handoff algorithm based on distance and RSSI measurements in a multi-cellular environment by computer simulation. The algorithm performs a handoff if handoff initiation conditions, handoff possible conditions, and handoff selective conditions are met. The performance criteria are based on the average number of handoffs, the crossover points and the average number of outages. Numerical results are presented to demonstrate the feasibility of the algorithm. The performance of the distance-assisted handoff algorithm is compared with that of a conventional algorithm that utilizes signal strength alone. Overall, the distance-assisted algorithm exhibits higher performance in average number of handoffs and the crossover points, yet exhibits a higher number of outages on average than the conventional algorithm.

In DS-CDMA (Direct Sequence-Code Division Multiple Access) mobile systems, soft handoff is recognized as reducing interference and increasing reverse link capacity, whereas from the radio channel resource viewpoint, soft handoff can make the system performance deteriorate significantly. This paper focuses on using the channel resources of soft handoff in a limited field environment for evaluating the performance of DS-CDMA mobile systems. Our traffic model is based on the mobile traffic environment with region overlap among multiple cells. The soft handoff rates are estimated by the mobility of mobiles, and simulation results show good agreement with the traffic model. The channel holding time distribution of the soft handoff traffic model, which does not have a closed-form solution, is derived by a numerical integration method. Computer simulations show promising results based on the non-closed-form application. We analyze the performance of DS-CDMA mobile systems with the proposed traffic model to see the effect of the soft handoff region on blocking probability. From the result, when the soft handoff region is extended with the given channels, both the handoff rate and the mean channel holding time are increased and these make the blocking probability increase a great deal. To maintain the required blocking probability as before, additional channel resources should be supplied according to the extended region. It is our belief that the proposed traffic model and the performance analysis presented in this paper are practically acceptable.

In this paper, we investigate the optimal assignment problem of cells in PCS (Personal Communication Service) to switches on a ATM (Asynchronous Transfer Mode) network. Given cells and switches on an ATM network (whose locations are fixed and known), the problem is to group cells into clusters and assign these clusters to switches in an optimum manner. This problem is modeled as a complex integer programming problem. Since finding an optimal solution of this problem is NP-hard, a heuristic solution model consists of three phases (Cell Pre-Partitioning Phase, Cell Exchanging Phase, and Cell Migrating Phase) is proposed. Experimental results show that Cell Exchanging and Cell Migrating Phases can really reduce total cost near 44% on average.

The handoff of in Mobile IP causes packet sequence disruption during packet forwarding procedure, which may result in degradation of network performance in higher layer protocol. In this paper, we investigate the impact of handoff on out-of-sequence packets in Mobile IP with Route-Optimization extension. To evaluate the handoff procedure, we use the unstable time period (UTP) when the packet sequence could be mis-ordered. The results show that the UTP mainly depends on queuing delay of old Foreign Agent (FA) and link capacity between old FA and new FA. Further, we propose that the priority queuing for the astray packets in the old FA can increase Mobile IP performance during handoff procedure by reducing the UTP.

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.

In this paper, we analyze the performance of a bulk handoff scheme for mixed traffic in integrated voice/data wireless mobile networks in which new and handoff voice/data calls are accepted based on prioritization of handoff requests. If fewer channels than handoff calls are available in the target cell, some handoff calls are terminated without queuing. A higher priority is given to voice handoff calls than to data handoff calls. A multidimensional birth-death process model is presented to analyze the bulk handoff performance of mixed traffic. A numerical analysis of system performance is presented to evaluate the blocking probabilities of new voice and data calls, handoff failure probabilities, and the forced termination probabilities of voice/data handoff calls.

In this paper, we propose an efficient algorithm of quick routing for private Wireless ATM (Asynchronous Transfer Mode) networks. This algorithm uses hierarchical source routing, which first establishes a connection between the sending node and the home node (which has the terminal location information), and then, partially releases the connection and reroutes it between the sending node and the receiving node. This results in less delay than found in other conventional routing methods, and avoids passing through congested nodes, because this algorithm uses traffic estimation based on queuing theory. We also show the effectiveness of this algorithm with the use of computer simulations.

Both tiers are assumed to share the same frequency band. Unlike a single tier cell environment, interference components to be considered in a hierarchical cell environment include the inter-tier interference as well as the intra-cell and the inter-cell interference. The numerical results show that the transmission power ratio between the macro cell and the micro cell affects the forward link capacity. And the results also show that the macro cell capacity increases as the mobile moves toward the edge of the macro cell. Moreover, soft handoff makes it possible to obtain a higher forward link capacity in the handoff region.

The soft handoff is widely adopted in code division multiple access (CDMA) systems for its many advantages mainly resulting from site diversity. However, in the forward link, other cell interference can be increased by soft handoff, decreasing system capacity. In future mobile systems, provision for the sufficient forward link capacity is very important since the forward link load is much higher than the reverse link load in mobile multimedia services such as Internet access. In this paper, we consider a combined handoff strategy in which voice services are provided with soft handoff whereas data services are supported with hard handoff. We analyze the effect of handoff method on the forward link performance. The performance measures we use are the outage probability of the bit energy to noise density ratio and the capacity based on the outage probability. As a result, we show that the combined handoff is very useful in CDMA cellular networks supporting both voice and data services simultaneously.

For ubiquitous computing and communication, a mobile node needs to change upon movements its network- and link-layer points of attachment to the Internet. Conventionally, the network-layer protocol is unaware of the link-layer changes, so IP datagrams to and from a moving node could be lost. Considerable system performance degradation might therefore result. This paper presents a scheme to integrate the handoff procedures of the two layers in the context of Mobile IP with route optimization. Experiment results show that our scheme is promising and can reduce packet loss due to host migrations substantially.

Mobile IP is a solution to support host mobility in the Internet. But, packets can be lost during the movement detection and registration periods of the Mobile IP. Regular TCP interprets theses packet losses as signs of network congestion, so it reduces its transmission rate by reducing its window size and slow start threshold. Besides, the multiple packet losses occurring during handoffs trigger successive retransmission timeouts at the TCP sender, causing a long communication pause even after handoff is completed. These together lead to significant throughput degradation. In this paper, we propose two new TCP schemes to reduce packet losses and to alleviate the effects of handoffs on TCP performance. TCP-MD (Movement Detection) is proposed to reduce packet losses by detecting a handoff earlier, and TCP-R (Registration) is designed to prevent packet losses by freezing data transmission during registration. The proposed schemes maintain end-to-end TCP semantics, making it possible to fully interoperate with the existing infrastructure. Only a small change is required in the mobile host, plus the implementation is simple because some Mobile IP messages are used to notify the handoff, eliminating the need for any additional messages. Simulations confirmed that the proposed schemes can give an excellent performance in an environment where the mobile host experiences frequent handoffs.

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.

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.

This paper proposes a bandwidth allocation scheme which improves degradation of communication quality due to handoffs in mobile multimedia networks. In general, a multimedia call consists of several component calls. For example, a video phone call consists of a voice call and a video call. In realistic environments, each component call included in one multimedia call may have different requirements for quality-of-service (QoS) from each other, and priorities among these component calls often exist with respect to importance for communications. When the available bandwidth is not enough for a handoff call, the proposed scheme eliminates a low priority component call and defers bandwidth allocation for a component call whose delay related QoS is not strict. Moreover, in the allocation, the scheme gives priority to new calls and handoff calls over a deferred call and also performs bandwidth reallocation to eliminated component calls. By computer simulation, we evaluate the performance such as call dropping probability and show effectiveness of the proposed scheme.

In this work, teletraffic performance of a hierarchically overlaid microcell and macrocell structure in a PCS environment is presented. In this system, each group of N microcells is overlaid exclusively by one macrocell. The microcell tier is dedicated to low-mobility users and the macrocell tier is dedicated to both high-mobility users and overflowed low-mobility users from microcells. In general, forced termination is considerably undesirable from the user's viewpoint compared with the occurrence of call blocking. Therefore, handoff calls are given access priority to channels at the macrocell tier. As a priority scheme at the macrocell tier, a partial buffer sharing (PBS) scheme is proposed. As performance measures, call blocking probability, forced termination probability, and carried traffic are derived. Effects of the sizes of a macrocell and of hierarchical cell structure on system performance are discussed. The performance of the PBS scheme is also compared with those of the no priority scheme (NPS) and the first-come-first-service (FCFS) queueing scheme. Numerical results show that the PBS scheme gives the best performance for handoff traffic among the three schemes.

Mobile IP can provide macro mobility for a mobile node (MN) instead of the original IP communication. Since the orignal Mobile IP does not consider micro mobility, it can not avoid handoff latency. The latency causes packets loss or large variations of the delivery times. To prevent it, several methods are proposed to improve the orignal Mobile IP handoff method. In our previous work, we proposed the fast registration method which enabled an MN to have two communication routes from the home agent (HA), and realized lower latency in the handoff procedures by the doublecasting on the two communication routes. But, the simulation results also show that the proposed method still has large overhead. This paper presents a seamless handoff method, which improves the fast registration method. In the method, the MN can know the first and second suitable base stations for the communications through information from the MAC media. The control helps for seamless handoff in case that the MN must frequently change its current base station (BS). The computer simulations for Constant Bit Rate (CBR) over real-time transport protocol (RTP) flow shows that the proposed method provides no handoff latency with low overhead even if the MN must occur frequent handoffs in a second.

In CDMA mobile cellular systems, wireless quality is improved by soft handoff techniques. However, it requires to hold multiple channels of cells, which is likely to increase call blocking at wired channels. It is therefore necessary to consider the entire system including the wired and wireless portions of systems for investigating an effectiveness of the soft handoff. In this paper, we also clarify the effect of interference power from mobile stations that are not in the soft handoff because of lack of wired channels. In the analysis, we model three-way soft handoff which has not been considered in past researches. We also show the effect of a call admission control to wireless quality.

The cellular-communication systems of the future will be required to provide multimedia services to users moving about in a variety of ways (on foot, in automobiles etc.). Different forms of motion have different characteristics. The characterization of the different forms of motion and their effects on telecommunications traffic is important in the planning, design and operation of mobile communication networks. The characterization of the motion of various platform types (inter-city buses, recreational vehicles, freight trucks, and taxis) based on measurements using Global Positioning System is presented in this paper. The measured characteristics of motion are then used to evaluate teletraffic statistics such as cell cross-over rate and cell dwell time by overlaying hypothetical cell systems on the measured loci of vehicles. Self-similarity was discovered in the cell dwell time characteristic of the taxis.