In this paper we propose a new algorithm for computing the optimal configuration of the Multiple Fractional Guard Channel (MFGC) admission policy in multiservice mobile wireless networks. The optimal configuration maximizes the offered traffic that the system can handle while meeting certain QoS requirements. The proposed algorithm is shown to be more efficient than previous algorithms appeared in the literature.

This paper proposes a scattered-pilot-OFDM reception scheme employing turbo inter-carrier interference (ICI) cancellation in the fast varying fading environments of mobile communications. In the OFDM transmission, the orthogonality among the subcarriers cannot hold due to large Doppler shift, and the OFDM signal suffers from severe degradation due to ICI. The proposed receiver carries out two modes: (i) a coherent detection (CD) mode, and (ii) a turbo ICI cancellation (TC) mode. Initially, the receiver performs the CD mode. When any decision errors are detected, it shifts from the CD mode to the TC one that carries out both the ICI cancellation and the channel estimation by using the decoder output (the log likelihood ratio). In addition, the iteration of the TC mode can improve the accuracy of the channel estimation and ICI cancellation ability. Computer simulations following specifications for the mobile reception mode in the digital terrestrial television broadcasting demonstrate that the receiver can effectively cancel ICI due to the fast varying fading, and that its average BER performance is much better than that of CD.

This paper studies a cellular system with mobile customers. The network system consists of cells, the tagged cell and the adjacent cells which surround the tagged one. Each cell has a finite number of channels that give calls to the mobile customers. The service (holding) time distribution of the calls is general. Customers in the adjacent cells inflow into the tagged cell according to a Poisson process. The sojourn time distribution of each customer in the tagged cell is general. Each customer without call in progress generates his call according to a Poisson process. It is proved that the steady state distribution in the tagged cell is the generalized Erlang loss formula which is the joint distribution of the number of customers with calls and the number of customers without calls. The distribution depends on the service time distribution and the sojourn time distribution only through their means.

In the mobile Internet, a handover brings significant performance degradation of TCP due to bursty packet losses during handover processing. In this paper, we propose a new bandwidth control for improving the TCP performance. In the proposed system, when a mobile node changes its accessing base station, an intermediate router suppresses an available bandwidth to the corresponding TCP flow. Because suppressing the bandwidth results in reducing mis-forwarded packets to the old base station, the bursty packet losses can be avoided. In the hierarchical mobile network structure, which is recently developed in order to realize micro-mobility protocol, all packets transferred to mobile nodes are converged to several gateways such as mobility anchor points (MAP) in hierarchical Mobile IPv6 (HMIPv6). Therefore, the proposed system is suited to the hierarchical structure because it can be easily implemented at such gateways. Computer simulation results show that the proposed system can improve the TCP performance degradation especially in a situation where handovers frequently occur.

In IP-based mobile networks, a few of mobility agents (e.g., home agent, foreign agent, etc.) are used for mobility management. Recently, Hierarchical Mobile IPv6 (HMIPv6) was proposed to reduce signaling overhead and handoff latency occurred in Mobile IPv6. In HMIPv6, a new mobility agent, called mobility anchor point (MAP), is deployed in order to handle binding update procedures locally. However, the MAP can be a single point of performance bottleneck when there are a lot of mobile node (MNs) performing frequent local movements. This is because the MAP takes binding update procedures as well as data packet tunneling. Therefore, it is required to control the number of MNs serviced by a single MAP. In this paper, we propose a load control scheme at the MAP utilizing an admission control algorithm. We name the proposed load control scheme proactive load control scheme to distinct from the existing load control schemes in cellular networks. In terms of admission control, we use the cutoff priority scheme. We develop Markov chain models for the proactive load control scheme and evaluate the ongoing MN dropping and the new MN blocking probabilities. As a result, the proactive load control scheme can reduce the ongoing MN dropping probability while keeping the new MN blocking probability to a reasonable level.

In multicarrier code division multiple access (MC-CDMA) systems, the orthogonality among the spreading codes is destroyed because the channels exhibit frequency-selective fading and the despreading stage performs gain control; that is, inter-code interference (ICI) can significantly degrade system performance. This paper proposes an optimum spreading code assignment method that reflects our analysis of ICI for up and downlink MC-CDMA cellular systems over correlated frequency-selective Rayleigh fading channels. At first, we derive theoretical expressions for the desired-to-undesired signal power ratio (DUR) as a quantitative representation of ICI; computer simulation results demonstrate the validity of the analytical results. Next, based on the ICI imbalance among code pairs, we assign specific spreading codes to users to minimize ICI (in short, to maximize the multiplexing performance); our proposed method considers the quality of service (QoS) policy of users or operators. We show that the proposed method yields better performance, in terms of DUR, than the conventional methods. The proposed method can maximize the multiplexing performance of a MC-CDMA cellular system once the channel model, spreading sequence, and combining strategy have been set. Three combining strategies are examined at the despreading stage for the uplink, equal gain combining (EGC), orthogonality restoring combining (ORC), and maximum ratio combining (MRC), while two are considered for the downlink, EGC and MRC.

The power system and the battery management of mobile phones used by NTT DoCoMo subscribers will be described. The energy requirements of the phones' AC-adaptors (chargers), their power-management systems, and trends in energy consumption will be focused on. The results of the new Li-ion batteries' safety tests, quick tests assessing battery capacity deterioration, and battery lifetime predictions will be also discussed.

This letter describes the current mechanism for IP address configuration in the wireless Internet and examines its drawbacks, and suggests a new mechanism of address configuration which provides a reduced message exchange for address configuration in the wireless Internet over the current 4-way message exchange when performing address configuration through DHCP. Analytic performance evaluation and comparison have shown that the proposed mechanism is faster in terms of delay than the existing mechanism including reduced packet loss when in motion.

In this paper, iterative adaptive soft parallel interference canceller (ASPIC) is proposed for turbo coded multiple-input multiple-output (MIMO) multiplexing. ASPIC is applied to transform a MIMO channel into single-input multiple-output (SIMO) channels for maximum ratio diversity combining (MRC). In the ASPIC, replicas of the interference are generated and subtracted from the received signals. For the generation of replicas with higher reliability, iterative ASPIC is proposed. It performs the iterative interference cancellation by feedback of the log-likelihood ratio (LLR) sequence obtained as the turbo decoder output. For iterative ASPIC, at the transmitter, the information sequence and parity sequence are transmitted from different antennas. In this paper, the achievable bit error rate (BER) performance, in a Rayleigh fading channel, for the turbo coded MIMO multiplexing with the proposed iterative ASPIC system is evaluated by computer simulation.

We have demonstrated radio-over-fiber transmission of wireless signals at millimeter-wave bands. The system incorporated 25 km of an optical intermediate frequency feeder and 60 GHz OFDM signal transmission at 155 Mbps with a BER of less than 10-6 was achieved within the system cell of a radius of 2.6 m under the channel condition of Line-of-Sight.

Mobile IP provides an efficient and scalable mechanism for host mobility within the Internet. Using Mobile IP, mobile nodes may change their point of attachment to the Internet without changing their IP address. In contrast to the advantages of Mobile IP, updating the location of a mobile node incurs high signaling costs if the mobile node moves frequently. Thus, IP paging schemes for Mobile IP have been proposed to avoid unnecessary registration signaling overhead when a mobile node is idle. However, they require the additional paging costs and delays associated with message delivery when a correspondent node sends packets to the idle mobile node. These delays greatly influence the quality of service (QoS) for multimedia services. Moreover, existing IP paging schemes do not consider a hierarchical mobility management scheme, which can reduce signaling costs by the significant geographic locality in user mobility pattern. Thus, we propose a novel IP paging protocol which can be used in hierarchical Mobile IPv6 networks. In addition, our proposal can reduce signaling costs for paging and delay using the concept of the anchor-cell. The cost analysis presented in this paper shows that our proposal has superior performance when the session-to-mobility ratio value of the mobile node is low.

The data throughput of wireless LAN of IEEE 802.11 g in mobile environment is measured according to the distance between AP and NIC, and the moving speed. It shows there is no degradation of the maximum data throughput of 20 Mbps due to the vehicle speed up to 160 km/h.

In this paper, we propose an optimal power control algorithm with fast convergence rate for CDMA cellular systems. The new power control algorithm is based on linear quadratic control theory (LQR). Using the state feedback control designed to minimize an objective function, each mobile performs a successful transmission with optimal power. Simulation results show a fast convergence rate to target SIR with less power consumption, and an augmented channel capacity through decreased outage probability.

To prevent performance degradation of TCP due to packet losses in the smooth handoff by the route optimization extension of Mobile IP standard, a few packet buffering methods have been proposed. The packet buffering at the BS recovers the packets dropped during an inter-subnetwork handoff, by forwarding the buffered packets at the previous BS to the new BS to which the mobile host is connected after handoff. However, when the mobile host user moves to a congested BS in a new foreign subnetwork, those buffered packets are likely to be dropped at the new BS. Thus, as well as the TCP connections of the mobile host which have moved into the new BS, the already existing TCP connections of the new BS experience severe performance degradation. This effect is due to the increased congestion by the forwarded burst packets; all of the TCP connections can initiate their congestion control algorithms simultaneously, i.e., global synchronization. This paper will consider a general case where a mobile host user moves into a congested BS of a new foreign subnetwork. We analyze the influence of the packet buffering on the TCP performance in the new BS, for the Drop-Tail and Random Early Detection (RED) buffers. Simulation results show that although the RED buffer gives better handoff performance than the Drop-Tail buffer, it cannot avoid a large decrease in the TCP throughputs due to global synchronization, when a TCP connection is added at the BS by an inter-subnetwork handoff. Finally, we discuss some methods that can address the negative effect of the packet buffering method.

To improve the DS-CDMA signal transmission performance in a frequency-selective fading channel, the frequency-domain equalization (FDE) can be applied, in which simple one-tap equalization is carried out on each subcarrier component obtained by fast Fourier transform (FFT). Equalization weights for joint FDE and antenna diversity combining based on maximal ratio combining (MRC), zero-forcing (ZF), and minimum mean square error (MMSE) are derived. The conditional bit error rate (BER) is derived for the given set of channel gains in a frequency-selective multipath fading channel. The theoretical average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation. Performance comparison between DS- and multi-carrier (MC)-CDMA both using FDE is also presented.

Europe has initiated research activity to analyse and prepare the floor for mobile communication beyond 3G. Very recently, around the beginning of 2004, the European commission started together with the main partners in the relevant industry special projects to realize this plan. The key objective of the WINNER (Wireless World Initiative New Radio) project is to develop an innovative concept in radio access in order to address high flexibility and scalability with respect to data rates and radio environments. The future converged wireless world requires in the long-term perspective a ubiquitous radio system instead of disparate systems for different purposes (cellular, WLAN, short-range access etc.). This concept will be derived by a systematic investigation of advanced radio technologies with respect to predicted user requirements and challenging scenarios. The project will contribute to the global research, regulatory and standardisation communities and processes.

This paper proposes two types of network architectures using UMTS Release 5 architecture and wireless LAN suitable for context-aware information delivery and personal communication services, and it reports on preliminary evaluations of their performance. The first type of network architecture is the NCA (network-centric architecture) and the second is the ECA (end-user-centric architecture). The two architectures are modeled with a queuing network and their response times are compared through theoretical analysis and simulation. The results indicate that with low-performance servers, the response times of the ECA are generally shorter or almost the same as those of the NCA. However with high-performance servers, the response times of the NCA are generally shorter except during high server utilization.

This paper presents a path compression protocol for on-demand ad hoc network routing protocols, which is called dynamic path shortening (DPS). In DPS, active route paths adapt dynamically to node mobility based on the "local" link quality estimation at each own node, without exchanging periodic control packets such as Hello messages. Each node monitors its own local link quality only when receiving packets and estimates whether to enter the "proximity" of the neighbor node to shorten active paths in a distributed manner. Simulation results of DPS in several scenarios of various node mobility and traffic flows reveal that adding DPS to DSR which is the conventional prominent on-demand ad hoc routing protocol significantly reduces the end-to-end packet latency up to 50-percent and also the number of routing packets up to 70-percent over the pure DSR, in heavy traffic cases. We also demonstrate the other simulation results obtained by using our two novel mobility models which generate more realistic node mobility than the standard random waypoint mobility model: Random Orientation Mobility and Random Escape Mobility models. Finally, simple performance experiments using DPS implementation on FreeBSD OS demonstrate that DPS shortens active routes in the order of milliseconds (about 5 ms).

Integrating Multi Protocol Label Switching (MPLS) and Mobile IP (MIP) protocols is a challenge to support Quality of Services (QoS) as well as mobility. Existing approaches may suffer from (1) high blocking rate and handover delay due to the path re-establishment, and (2) twice MPLS label PUSH and POP procedures due to the triangle routing. In this paper, we propose a novel approach to integrating MPLS and MIP. The proposed approach maintains an efficient QoS path and solves the above drawbacks. We also design a path extension procedure to reduce blocking probability and a path optimization procedure to maintain the shortest transmission path under delay constraints with the lowest cost. The simulation results show that the proposed approach reduces handover delay, connection dropping rate, and data loss rate comparing to the original MIPs over MPLS. Furthermore, we can also tune the system performance using an extension counter for the trade-off between management cost and data transmission delay.

In this paper, we propose the Synchronized Mobile Multicast (SMM) scheme for the real-time multimedia service to achieve three most important characteristics that the traditional Home Subscription (HS) and Remote Subscription (RS) mobile schemes cannot support. First, the SMM scheme supports the scalable one-to-many and many-to-many synchronized multimedia multicast on mobile IP networks to achieves seamless playback of continuous media streams even when both the mobile sender and receivers handoff simultaneously. Second, it analyzes the minimal buffer requirements of the mobile sender, the core router, the foreign agents and the mobile receivers in the multicast tree and formulates the initial playback delay within a handoff Guarantee Region (GR). Further, combined with the fine granularity scalability (FGS) encoding approach in the MPEG-4 standard, the SMM scheme achieves superior multimedia QoS guarantees and unlimited numbers of handoffs of the mobile sender and receivers only at the cost of degraded video quality for a short period after handoff with minimal extra bandwidth.