The mobile system has been taking an important role as the infrastructure of the advanced information society. First, as the telecommunication infrastructure, it enabled us to communicate with anybody, anytime, and anywhere. Next, as the multimedia infrastructure, it enabled us to send, receive, and retrieve data. Now, as the IT infrastructure, it enables us to purchase commodities, transact business, and enjoy entertainment on-line. The mobile system has morphed into the third generation in almost two decades. Several mobile services have been introduced in each generation to feature the above infrastructures. This paper describes the authors' views on how mobile services have contributed to the advance of the information society in the past three generations. It also discusses what role the future mobile system should take in realizing the wealthier information society.

Emerging requirement for higher rate data services and better spectrum efficiency is the main driving force identified for the third generation mobile radio systems. Moreover, it needs the capability of providing predictable qualities of service (QoS) for different applications. To maintain different QoS requirements, mechanisms such as call admission control (CAC) and load control, etc. are needed to achieve the required services. In this paper, we propose a CAC algorithm based on channel assignment in a multi-chip rate direct-sequence CDMA (MCR-DS-CDMA) cellular system supporting multi-rate services. Five multi-MBC (mapping of information bit rates to chip rates) channel assignment schemes and corresponding channel selection rules are proposed herein. Computer simulation, where multimedia applications are considered, is used to evaluate the system performance (e.g., blocking probability and system capacity) with different channel assignment schemes. Numerical results demonstrate that scheme 5 (i.e., Minimum-influence scheme) performs better because it provides the highest system capacity and least blocking probability.

In this paper, the performance of multi-stage parallel interference cancellation receiver using forward-backward filtering channel estimation is evaluated for the W-CDMA uplink. The channel estimation employs a non-causal forward-backward-multiplication-method filter, which was originally proposed for the reception of W-CDMA random access. Results of link level simulations for data and voice traffic scenarios over Pedestrian A and Vehicular A channels are discussed in comparison with the conventional channel estimation methods of 1-slot pilot averaging, 1-slot averaging, and weighted multiple slot averaging. It is shown that the forward-backward filtering channel estimation improves performances of the interference cancellation receiver as well as that of the ordinary Rake receiver in both Pedestrian A and Vehicular A channels. With its features of short processing delay and low complexity, the forward-backward filtering channel estimation is suitable for practical implementations of multi-stage interference cancellation receivers.

Unlike in existing mobile networks, a variety of services having different quality requirements will be provided in future mobile networks, where any single group of service users can not characterize the whole traffic distribution in the system. Beginning at the mobile network design, the population of service subscribers is estimated and then base stations are located. As the service market evolves, the volume of users might grow or the population of users distributed between the multiple services as well as the located cells might change. In this case, two questions are of interest: how much growth in user population and what change in user distribution can be accommodated in the current cell configuration. If such shifts could not be admitted, current frequency and base station allocations should be expanded or reallocated. In this paper, we provide a framework that can decide whether the present network configuration is able to admit the changes of interest. Admissibility decision rules are addressed with proofs.

In this paper, we investigate two packet scheduling schemes over the downlink of DS/CDMA systems to support packet data service. These schemes are the code division multiplexing (CDX)-based packet scheduling and the time division multiplexing (TDX)-based packet scheduling. To evaluate each scheme more effectively, we derive the throughput gain of the downlink as a performance measure based on the power constraint equation. In addition, the packet transmission delay of each scheme is derived and compared each other when the packet lengths of the concurrent data users are independently and identically distributed according to the exponential distribution. As the downlink capacity is quite related to the orthogonality factor, our analysis shows from the results that the throughput gain and the transmission delay are highly dependent on this factor. Furthermore, it is shown that the TDX scheduling scheme in CDMA downlink affords better performances than the CDX scheduling scheme, except when the orthogonality factor is around 1.

An adaptive array antenna should be applied for suppression of CCI in the spatial domain. However, the adaptive array antenna has some problems as follows. Because the adaptive array antenna takes a long time to converge to the optimum antenna weights, it's hard to track in case of quick varying channel. On the other hand, processing burden increases with the number of elements in the array antenna. To solve these problems, we propose an adaptive array antenna using array antenna as element antennas, the so-called "Layered array antenna." At the 1st layer, sector area are defined. We can change the sector areas according to the DOA distribution, because the sector areas are defined by the antenna weights. At the 2nd layer, MMSE is performed. Interference that couldn't be suppressed at the 1st layer is suppressed at the 2nd layer. By the proposed system, we confirmed higher convergence speed while relieving processing complexity.

This paper proposes a channel monitor-based unequal error protection scheme using a dynamic OFDM subcarrier assignment technique for broadband video transmission systems in frequency selective fading environments. In the proposed system, to achieve stable regeneration of the received video, subcarriers with relatively high channel gain are assigned to the high priority data (HPD) in the MPEG data. To further guarantee a required transmission quality of the HPD, the proposed system also employs subcarrier transmission power control with delay profile information (DPI) feedback-type channel estimation technique. Computer simulation confirms that the proposed technique is effective in preventing quality degradation with about 20 dB lower transmission power than the conventional systems in frequency selective fading environments.

In this paper, three multiple access schemes, single carrier (SC)-CDMA, multicarrier (MC)-CDMA, and frequency & time spread (FTS)-CDMA, with space time transmit diversity (STTD) are presented for a broadband mobile communication system. In general, broadband communication systems are easily affected by severe frequency selective fading which results in the degradation of the system performance due to the multipath. In order to improve the system performance in such a fading environment, STTD is applied to these CDMA systems. Computer simulation is carried out to evaluate the system performance, and the BER results are compared with each other. From the simulation results, it is found that the performance of MC-CDMA with STTD is better than that of the other systems, and SC-CDMA cannot improve the system performance by using STTD.

A unified view of RAKE reception is proposed which models a RAKE receiver as an antenna array. This unified view provides valuable insight to the signal environment under RAKE reception. Based on this view, an optimum combining scheme for RAKE receivers is proposed for the downlink of multi-code W-CDMA systems. In multi-code scenarios, the presence of inter-code interference causes severe performance degradation. The antenna array model suggests that enhancement can be achieved by increasing the receiver's degrees of freedom which is defined as the number of RAKE fingers and employs an appropriate combining scheme. The conventional maximum-ratio combining scheme is excluded since it is not capable of exploiting the increased degrees of freedom. In contrast, the proposed combining scheme provides better interference suppression when the degrees of freedom are increased. Numerical results obtained show that the proposed scheme provides very promising performance.

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.

This paper presents an optimum antenna diversity combining method associated with despreading that employs Minimum Mean Square Error (MMSE) combining over the frequency domain in a frequency-selective fading channel for forward link Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access, in order to achieve the maximum radio link capacity. Simulation results considering various propagation channel conditions elucidate that the antenna diversity combining method with Equal Gain Combining (EGC) subsequent to the despreading employing MMSE combining based on pilot symbol-assisted channel estimation and interference power estimation can decrease the required average received signal energy per bit-to-background noise power spectrum density ratio (E_b/N₀) the most, taking into account the impact of the inter-code interference. Furthermore, we clarify that the required average received E_b/N₀ for the average packet error rate of 10^-2 employing the diversity combining scheme with EGC after despreading with MMSE combining is improved by approximately 0.3 dB compared to the diversity combining scheme with EGC before despreading with MMSE combining at the number of code-multiplexing of 24 for the spreading factor of 32 in a 24-path Rayleigh fading channel.

This paper investigates the problem of finding the optimal access point placement in simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for public access wireless LAN with micrometer or millimeter frequency band. We define our design criteria such that the quality of service is provided uniformly throughout a given service area. The optimal access point placement with a uniform quality of service was obtained by setting the cost function as the combination of a standard deviation of BER and the average of BER in a very fast simulated annealing algorithm. We applied the algorithm to the cases of fixed and mobile terminals, and obtained optimal access point placement results for both cases.

This paper addresses a novel scheme for variable rate error correction coding with interleavered puncturing serially concatenated convolutional code. In order to obtain a variable coding rate, the bits of the outer coder are perforated with a given puncturing pattern, and randomly interleaved. The effect of interleavered puncturing on the overall coding performance is analyzed, and the upper bound to the bit error probability of the proposed coder is derived. Moreover, to evaluate the effectiveness of the proposed scheme some simulation results are presented with the iterative decoding procedure, in which the channel models of Rayleigh fading and additive white Gaussian noises are assumed.

In this paper, a contention-based reservation MAC protocol is proposed for non-real-time burst traffic class in wireless ATM networks. The proposed protocol is characterized by the contention-based transmission of the reservation request and contention-free transmission of burst traffic. The design objective of the proposed protocol is to reduce contention delay during the contention phase of a connection. In order to reduce collision of reservation requests, the base station calculates the transmission probability based on the estimated load of reservation requests and the number of random access minislots, and broadcasts it over the frame header period of downlink channel. Wireless terminal, which has traffic burst, selects a random access minislot and transmits its reservation request with a received transmission probability. Based on the successfully received reservation, the scheduler allocates the uplink data slots to wireless terminal. Simulation results show that the proposed protocol can provide higher channel utilization, and furthermore, maintains constant delay performance in a heavy traffic environment.

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 this paper, we propose and evaluate a new channel assignment scheme for a micro-cellular network integrating data and conversational services. The channel assignment scheme combines handover processing depending on terminal speed with a preemptive scheme. High-speed terminals take over the channels of data terminals upon entering a full cell, while the data terminals are put in a queue until new resources are available. Simulating several variations of the scheme, allowing both fast moving data and voice terminals to preempt data terminals yielded the best result. Suspension time for fast moving data terminals was reduced dramatically, reducing the disadvantage caused by a high number of handovers. The cost was a small increase in blocking probability for new terminals.

This paper investigates the effect of fast cell selection (FCS) associated with fast packet scheduling methods and hybrid automatic repeat request (HARQ) with Chase combining, in which the optimum cell (or sector) transmitting a slot-assigned downlink shared channel (DSCH) is selected based on the received signal-to-interference power ratio (SIR), in high-speed downlink packet access (HSDPA). The Round robin (RR), Proportional fairness (PF) and Maximum carrier-to-interference power ratio (CIR) schedulers are used as the scheduling algorithm. The simulation results elucidate that although almost no additional diversity gain through FCS is obtained for the PF and Maximum CIR schedulers, the improvement in throughput by FCS coupled with the RR scheduler is achieved. Furthermore, we elucidate that the effect of FCS is small when only inter-sector FCS is performed; however, inter-cell FCS is effective in improving the radio link throughput for the access users with a lower received SIR near the cell edge. The radio link throughput at the cumulative distribution of 20% of soft handover users when both inter-sector and inter-cell FCS are performed is increased by approximately 20% and 60% for PF and RR schedulers, respectively, compared to that without FCS, i.e. with hard handover. We also show that when a traffic model such as the modified ETSI WWW browsing model is taken into account, the effect of FCS associated with the decreasing effect of fast packet scheduling is greater than that assuming continuous packet transmission. The user throughput at the cumulative distribution of 20% employing both inter-sector and inter-cell FCS is increased by approximately 60% compared to that without FCS.

A new error correction block based Hybrid ARQ protocol, in which PHY layer packets are composed of multiple error correction blocks, is devised together with a retransmission control scheme constructed on the basis of these error correction blocks. This protocol is designed dedicatedly for mobile AV stations to provide the high quality digital video transmission through a radio channel. To analyze the performance of this protocol, the frame loss rate vs. the uncorrectable error probability is simulated, in comparison with the ordinary packet based retransmission control. A wireless video transmission system using IEEE802.11b PHY is also described, which has been developed with the use of a Medium Access Control (MAC) LSI to perform the proposed protocol.

In this paper, the performance of HIPERLAN (HIgh PErformance Radio Local Area Networks) CAC (Channel Access Control) of ETSI (European Telecommunication Standards Institute) in Europe, as High speed wireless LAN, is analyzed mathematically. The CAC protocol of HIPERLAN is the EY-NPMA (Elimination Yield-Nonpreemptive Priority Multiple Access) in which data is transmitted after prioritization, elimination and yield phase. We analyzed channel contention phase composed of elimination and yield phase and then throughput is inspected by simulation. This result is useful to design and implement of Ad hoc wireless networks.

The plan of High Altitude Platform Station (HAPS) is considered as a revolutionary wireless system plan with several economic and technological advantages over both space- or ground-based counterparts. In this paper, we propose a joint system of terrestrial and HAPS cellular for Wideband-CDMA mobile communication. This system makes the conventional terrestrial W-CDMA cellular area smaller and the remainder area covered by HAPS to increase the total capacity. Furthermore in down link channel, we introduce the polarized wave and doughnut-like radiation. However, in the proposed system, the performance would be dependent on the terminal position especially near the boundary of doughnut-like cell zone. To overcome this, site diversity that uses both signals from terrestrial Base Station and HAPS Base Station is also introduced. To confirm the availability of the proposed system, we evaluate the system performance by computer simulation.

We developed a priority queueing method that can keep the loss ratio of high-priority packets at a target value. It regulates the number of input low-priority packets when the queue length exceeds the threshold that is adjusted so as to minimize the Lyapunov function of the system. We showed that the number of calculations for the optimum threshold is sufficiently small and derived a sufficient condition for the proposed method to be robust against unknown load fluctuations. From the viewpoint of guaranteeing the loss ratio of high-priority packets, we showed, by computer simulation and theoretical analysis, that the proposed method is superior to conventional methods such as the fixed-threshold method and the pushout method.

Positioning service is indispensable in next-generation mobile communications and is expected to have various applications. This paper proposes a positioning method using first path searching in the correlation between a received signal and the replica of the transmitted signal to calculate the TDoA (Time Difference of Arrival) and ToA (Time of Arrival) for W-CDMA (Wideband-Code Division Multiple Access) and OFDM (Orthogonal Frequency Division Multiplexing) in a broadband cellular mobile communication systems. W-CDMA and OFDM are both powerful modulation candidates in the next generation and are compared here in terms of positioning accuracy. The chip correlation in W-CDMA and the total signal correlation in OFDM are used. Uplink and downlink type positioning methods are also compared. Computer simulation shows that the proposed method gives good positioning performance in multi-path fading channels.

We propose a location management, 'Mobility/Traffic Adaptive Location Management,' that dynamically changes the Location Area (LA) in response to the terminal's mobility and traffic characteristics to reduce the location management traffic in the air. In this paper, we investigate the following subjects for realizing the proposed location management. First, we present a method of calculating the optimum LA size. Second, we present methods for dynamic LA set up. Third, we present the architecture of the proposed location management. Finally, we evaluate its performance.

We propose Concatenated Location Management (CLM), utilizing tendency for mobile terminals (MTs) to move as a group. When many MTs are on the same train, for example, they move together and share the same mobility characteristics. Therefore, we propose to concatenate the MTs and link them to the train for more efficient location management. CLM can reduce the number of location management signals because the train sends only one location registration signal on behalf of all of the individual MTs when a location registration area boundary is crossed. We discuss the key functions for CLM including location registration, paging, and location register configuration.

Hierarchical Mobile IPv6 (HMIPv6) has been proposed to accommodate frequent mobility of terminals within the Internet. It utilizes a router, named Mobility Anchor Point (MAP), so that networks can manage mobile terminals without floods of signaling message. Note here that, particularly in a wide area network, such as a mobile communication network, it is efficient to distribute several MAPs within the same network and make the MAP domains cover overlapped areas. This enables the network to manage the terminals in a flexible manner according to their different mobility scenarios. The method described in the Internet-Draft at the IETF, however, lets mobile terminals select its MAP. This may cause load concentration at some particular MAPs and/or floods of signaling messages, because the terminals may not select a feasible MAP in a desirable manner. In this paper, a MAP selection method in distributed-MAPs environment is proposed. It reduces signaling messages to/from outside networks without load concentration at any particular MAPs. Finally, we show that the proposed method works effectively by simulation experiments.

In this paper, how the new service of non-authenticated multicasting can be implemented on the AWA system is described. The AP is forced to send IGMP packets periodically in order to keep transmitting IP multicast data grams. The program tables of the non-authenticated multicast are transmitted as IP multicast data to allow the all clients to receive the material. Furthermore, the list of program tables which shows the pairs of the ID of the AP and the IP address of the program table are used so that different APs can offer different program tables and programs. Experiments on non-authenticated multicasting were successfully conducted and we confirmed that the proposed service works well.

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.

During TCP/IP communications, MobileIP routing optimization functions causes out-of-order TCP packet sequences. To solve this problem, we propose a dynamic delayed ACK control scheme in which the wireless link-state management part notifies the upper TCP/IP layer of base-station hand-over, and at this time the TCP/IP layer sends dynamic delayed ACKs in response by using two-level-timer (i.e., hard-timer and soft-timer) processing. Simulation results confirm that applying dynamic delayed ACK control to MobileIP networks improves average throughput.

In this paper, a multi-coded variable spreading gain (MC-VSG) CDMA system employing a binary transmission of MC signals by introducing a level clipper, termed MC-VSG BNet system, is proposed for a possible candidate of wireless personal area network (WPAN) and 3 G cellular applications. With an emphasis on the MC-VSG BNet physical layer and the system performance, we address the concise specification of the MC-VSG BNet system including the spreading code, level clipping, modulation, coding, and frame format. Especially, we focus on the level clipping of multi-level MC signals for both power- and cost-efficient implementation and the VSG code design fir high-rate transmissions. From the receiver performance based on simulation results, in addition to simple receiver structure, an acceptable performance degradation of the MC-VSG BNet system over the existing DS/CDMA system is observed, while guaranteeing an high bit rate transmission.

Recently, demand for multimedia service applicable with wireless ad hoc networks is increasing. Many protocols which support QoS (Quality of Service) defined by ITU H.323 are suitable for the system with a central coordinator (ex. access point), and are not applied to ad hoc networks. Since each mobile station sends a packet randomly in a wireless network, it is necessary to avoid a packet collision which results in the decrement of the channel throughput. IEEE 802.11 is a standard for wireless LANs. The basic access mechanism in its media access control (MAC) protocol is the distributed coordination function (DCF) based on carrier sense multiple access with collision avoidance (CSMA/CA). However, this mechanism does not have QoS control, and packet collision may occur frequently with the increase of the number of mobile stations. In this paper, the two queues, voice over IP (VoIP) queue and DATA queue, are set in each mobile station, and we propose a novel MAC protocol using multiple queues for QoS. Our scheme consists of carrier sensing, packet scheduling and collision avoidance, and improves the contention window in DCF. We use two kinds of packet scheduling. One is the scheduling in a mobile station, and the other is the scheduling among mobile stations. We called the proposed scheduling among mobile stations D²VTS (Distributed Double Virtual Time Scheduling). Simulations are conducted to analyze the proposed scheme. The simulation results show that our scheme is able to carry multimedia traffic with a higher performance compared with the conventional DCF.

VoIP (Voice over IP) is one of the real time applications that demand wireless LAN systems meet severe quality requirements which commonly involve delay time, jitter, and packet loss. However, it is difficult for CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to achieve the service quality demanded by VoIP if voice and data traffic coexist, so some form of priority control is needed. This paper proposes a novel multiple access protocol based on autonomous distributed control that allows wireless LANs to satisfy the VoIP requirements. This new protocol suits both VoIP and data traffic and executes priority control dynamically according to whether the VoIP packet collides with a data packet or another VoIP packet. The results of a theoretical analysis and computer simulations indicate its excellent performance. This proposed protocol reduces the delay time of VoIP packets by 54 to 70% compared with conventional CSMA/CA even if the traffic load increases provided that the packet loss probability is less than 3%.

In this paper, we propose a new resource management scheme for multiple video stream transmission in a wireless environment. The proposed scheme adaptively determines transmission parameters such as the number of assigned time slots, modulation format, and forward error correction (FEC) code rate according to the required bit rate and error sensitivity of the video stream as well as the channel state. The computer simulation results show that the proposed scheme drastically improves the image quality degradation due to channel errors.

In this paper, we propose an efficient requantization method for INTRA-frames in MPEG-1/MPEG-4 transcoding. The quantizer for an MPEG-1 INTRA block usually uses a quantization weighting matrix, while the quantizer for an MPEG-4 simple profile does not. As a result, the quantization step sizes of the two quantizers may not be the same even for the same quantization parameter. Due to this mismatch in the quantization step size, a transcoded MPEG-4 sequence can suffer from serious quality degradation and the number of bits produced by transcoding increases from the original MPEG-1 video sequence. To solve these problems, an efficient method is proposed to identify a near-optimum reconstruction level in the transcoder. In addition, a Laplacian-model based PDF (probability distribution function) estimation for the original DCT coefficients from an input MPEG-1 bitstream is presented, which is required for the proposed requantization. Experimental results show that the proposed method provides a 0.3-0.7 dB improvement in the PSNR over the conventional method, even at a reduced bit-rate of 3-7%.

Today, many audiovisual delivery systems, including video streaming and video conferencing, are being developed for use over a range of networking technologies, the differing characteristics of which pose problems for service level interoperability. Multimedia transcoding is one means to provide interoperability between different types of audiovisual terminals and between terminals that connect to different networks. In this paper, we will present a multimedia transcoder system, which provides interoperability between video conferencing terminals on IP networks and mobile terminals on mobile networks.

Network-oriented car navigation systems (off-board navigation systems) have become a hot topic cause of the expanding car navigation and active wireless communication markets. This paper examines the map downloading architecture, which realizes practical off-board navigation systems. We focus on practical technologies for present low speed wireless communication networks, such as with a 9.6 kbps transfer speed. We propose a new off-board navigation architecture, which combines a cost-effective map downloading system and a guide information downloading system. The proposed architecture can reduce the download data size to within about 50-100 kbytes for destination setting and route guidance. It has about a 1-2 minutes response time and about a 30-60 yen communication cost for a PDC (Personal Digital Cellular) wireless communication network in Japan. We consider this communication cost has a potential for a commercial off-board navigation system.

This paper describes a novel mobile video monitoring system. The receiver is a PDA (Personal Digital Assistant) with a PHS (Personal Handy Phone system) card. The sender is a PC-based video encoding system, which is connected to an ISDN line by ISDN-TA. Functions such as camera selection, remote camera control and high-resolution snap shot are implemented. In this paper, details of the system are explained and a practicability assessment is performed. An experiment was conducted to measure the upward and downward transmission delay. From the results, the system performs consistently to a theoretical behavior. Furthermore, the performance of this system is quite practical for mobile video monitoring.

The objective of this paper is to evaluate the impacts of impulsive class-A noise, co-channel interference due to other piconet, Rician fading on the packet error rate (PER), and throughput performance in the Bluetooth scatternet. Simulation results illustrate the significant difference in performance between synchronous and asynchronous Bluetooth systems. The paper also provides the insights on how to design Bluetooth scatternet for minimal PER and maximum throughput performance.

In this paper, we have analyzed transmission time for WAP (Wireless Application Protocol) over Bluetooth using a multi-slot segmentation scheme. In order for SAR to improve the transfer capability, the transmission of messages have been simulated using a fragmentation scheme that begins with the total package and incremental fragmentation for each layer using the WTP (Wireless Transaction Protocol) to define the resultant packet size and the level of fragmentation for each proceeding layer. The data is divided into individual packets at the baseband level. This scheme decreases transmission time of L2CAP (Logical Link Control And Adaptation Protocol) baseband packets by sending packets that span multiple slots. From the results, we were able to obtain packet transmission time and optimal WTP packet size for WAP over Bluetooth in a Rician fading channel.

We propose a new adaptive FEC scheme combined with ELN (Explicit Loss Notification) that was proposed for improving TCP performance in wireless cellular networks. In our method, transmission errors on the wireless link are measured at the packet level and the error status is notified the TCP sender with ELN. According to this information, an appropriate FEC code is determined in order to maximize the TCP performance. We first compare the TCP performance using Snoop Protocol, ELN and the fixed FEC, through which we find the appropriate FEC code against given BER (bit error ratio). We then show how the adaptive FEC can be realized using our solution, and also examine the appropriate observation period of measuring BER enough for the fading speed on the noisy wireless link. We finally demonstrate that our method can achieve better performance than the conventional fixed FEC by using the Gilbert model as a wireless error model.

Mobile terminals with Internet services such as i-mode are in wide use, and communication bandwidths are growing even further under 3G technology. However, displays of mobile terminals will remain small in view of their portable size and power consumption. In this paper, we propose a "ubiquitous display" that can be used in combination with mobile terminals. The user operates the mobile terminal and the ubiquitous display shows any content that requires a large screen space.

This paper presents an iterative algorithm for decoding product codes based on syndrome decoding of component codes. This algorithm is devised to achieve an effective trade-off between error performance and decoding complexity. A simplified list decoding algorithm, which uses a modified syndrome decoding method, for linear block codes is devised to deliver soft outputs for iterative decoding of product codes. By adjusting the size of the list, the decoder can achieve a proper trade-off between decoding complexity and performance. Compared to the other iterative decoding algorithms for product codes, the proposed algorithm has lower complexity while offers at least the same performance, which is demonstrated by analyses and simulations. The proposed algorithm has been simulated for BPSK and 16-QAM modulations over both the additive white Gaussian noise (AWGN) and Raleigh fading channels. This paper also presents an efficient scheme for applying product codes and their punctured versions. This scheme can be implemented with variable packet size and channel data block.

Recently, neural networks (NNs) have been extensively applied to many signal processing problem due to their robust abilities to form complex decision regions. In particular, neural networks add flexibility to the design of equalizers for digital communication systems. Recurrent neural network (RNN) is a kind of neural network with one or more feedback loops, whereas self-organizing map (SOM) is characterized by the formation of a topographic map of the input patterns in which the spatial locations (i.e., coordinates) of the neurons in the lattice are indicative of intrinsic statistical features contained in the input patterns. In this paper, we propose a novel receiver structure by combining adaptive RNN equalizer with a SOM detector under serious ISI and nonlinear distortion in QAM system. According to the theoretical analysis and computer simulation results, the performance of the proposed scheme is shown to be quite effective in channel equalization under nonlinear distortion.

This paper presents a comprehensive investigation of three optical wavelength-division multiplexed (WDM) mesh network protection approaches, namely minimal cost, single link basis and disjoint path approaches. The operation of each approach is described and their performances are extensively evaluated and compared. Key aspects that are taken into the consideration and comparison of the designs include a spare capacity requirement, ease of operation and practical feasibility. A mathematical model based on integer linear programming is introduced to obtain a lower bound on the spare capacity requirement for full protection against all single link failures. Two heuristic algorithms have also been developed to perform wavelength resource allocation under both normal and failure conditions for both systems with and without wavelength conversion capability. It is shown that the minimal cost approach can accomplish the lowest extra cost requirement for protection, but this approach is considered not appropriate for practical applications due to complicated restoration and management. The single link basis scheme is on the other hand more practical and very cost efficient. For the disjoint path technique, the cost for spare capacity is generally slightly greater than that of the single link basis scheme. Its main advantages lie in the simple re-configuration and inherent protection against node failure for in-transit traffic. Finally, a new framework for obtaining a good spare capacity cost estimate of a mesh restorable network is presented.

In this paper, we propose an improved CDMA/PRMA protocol named CDMA/CAC (Code Assignment Control). In the proposed protocol, each terminal can be assigned spreading code by simple control before packet transmission. We introduce the permission probability for code request. The permission probability for code request restricts the number of terminals requesting code in order to avoid the collision of request signal adaptively to traffic load. In the proposed protocol with enhanced mode, the voice terminals have priority in initial access by setting the permission probability to 1. Also in this protocol, the data terminals can transmit packets continuously if necessary. We carry out the performance evaluation of the protocols by computer simulation and confirm their validity.

This paper presents the transmission performance of a class-IV partial-response signaling SSB system and proposes a method that can improve its power efficiency. A line code that has no dc component has been used in the SSB transmission of digital signals. The type of line code, such as a partial-response signaling, increases the modulation states, and as a result, decreases the power efficiency. To overcome this obstacle, a new demodulation method called "re-filtering and combining" is proposed on the assumption of orthogonal phase detection. The demodulated quadrature channel is re-filtered by a Hilbert filter and is combined with the in-phase channel. It is confirmed by computer simulations that the new demodulation method improves the BER performance and a 3 dB improvement of the power efficiency is obtained.

The objective of this paper is to generate a wideband and temporal response from three-dimensional conducting structures. This is accomplished through the use of a hybrid method that involves generation of early time and low frequency information. These two are mutually complementary and contain all the necessary information for a sufficient record length. Utilizing orthogonal polynomials, time domain signal of scattering electromagnetic field could be expressed in an efficient way as well as the corresponding frequency domain responses. The available data is simultaneously extrapolated in both domains. Computational load for electromagnetic analysis, the Method of Moment (MOM), can be significantly reduced.

In mobile computing environments, a problem may exist between loss recovery mechanisms employed by the TCP (transmission control protocol) and RLP (radio link protocol). It is because that local retransmissions performed by the RLP could interfere with the TCP end-to-end error recovery when there are long and correlated packet losses due to bursty channel errors. That is, a spurious timeout would occur at the transport layer. In this paper, a new method is proposed to effectively suppress the occurrence of TCP spurious timeouts. In this new method a small number of ACKs (acknowledgements) is buffered at the base station prior to the emergence of every bad state period in the wireless channel, and these ACKs are henceforth released by the base station one at a time to reset the TCP sender's retransmission timer. Comprehensive comparisons between the proposed method and a baseline method are conducted through simulations to show that the improvement in throughput performance can be as large as 22%.

The pre-Rake system is known as a technique in TDD DS/CDMA system to reduce the mobile complexity and achieve the same BER performance like Rake receiver. The pre-Rake system itself is not optimum, since the channel impulse responses of uplink and downlink are slightly different in TDD system, so the signal- to-noise ratio (SNR) can be maximized with a matched filter based Rake receiver, which has not been considered in the conventional pre-Rake system. Furthermore pre-Rake system is sensitive to the Doppler frequency. Even though the pre-Rake system has the ability to suppress other user interference, it is not efficient to maximize the received signal in high Doppler frequency. However, Rake combiner is utilized for the detection method in our proposed system. So the maximized signal can keep the orthogonality better than the pre-Rake system and our proposed system can compensate the Doppler frequency effect. From these reasons, our system achieves better BER performance than that of the pre-Rake system with increasing the number of users in high Doppler frequency.

In this paper, we propose an equalizer for indoor infrared wireless systems using on-off keying code-division multiple-access (OOK-CDMA). The proposed equalizer has a decision-feedforward filter to mitigate the effects of inter symbol interference (ISI) at the previous chip position of the sampling instant. We evaluate the performance of indoor infrared wireless systems using OOK-CDMA with three kinds of equalizers: the decision-feedback qualizer (DFE), the feedforward equalizer (FE), and the proposed equalizer. To estimate the impulse response, we use the training sequence that alternates '1' and '0' sequentially. Among three kinds of equalizers, we show that the system with the proposed equalizer can achieve the best bit error rate (BER) performance at high bit rate, while the system with the FE achieves the best BER performance when the bit rate is low.

It is very important to accurately and effectively track the movement of each mobile terminal in the personal communications networks. Accordingly, various dynamic location update schemes reflecting the mobile terminal's moving pattern are proposed in the literature. Important schemes include time-based, movement-based, distance-based, and direction-based location update schemes. In this paper, we intend to improve the performance of the movement-based location update scheme which is simple to implement and shows good performance. The proposed location update scheme reflects each mobile terminal's movement characteristics and reduces the number of unnecessary location updates. The performance of the proposed scheme is evaluated and compared with the previously proposed movement-based location update scheme through simulation. The proposed location update scheme requires three memory elements to maintain the movement history in the mobile terminal. The simulation results show that the location management cost is significantly reduced especially for the case with small call-to-mobility ratio by minimizing the unnecessary location updates intrinsic in the movement-based location update scheme.

Emerging real-time and multimedia applications in IP over ATM networks are becoming an indispensable part of the networking world. Considering the different and essential natures of IP and ATM, it seems that they complement each other. Although several approaches have been proposed for IP and ATM integration, so far a key problem (i.e., Quality of Service support) in foreseeable future networking applications remains unsolved. This paper describes a new extension to Classical IP and ARP over ATM (CLIP) protocol, Real-time and Multimedia services using CLIP (RMCLIP), providing ATM service classes to the IP end users. It defines that different service classes are mapped to the associated IP addresses. It enables different IP end user applications (e.g., real-time video, voice and data) to obtain their own dedicated VCs.

The ranging algorithm allows active stations to measure their distances to the headend for synchronization purpose in Hybrid Fiber Coax (HFC) networks. A practicable mechanism to resolve contention among numerous stations is to randomly delay the transmission of their control messages. Since shorter contention cycle time increases slot throughput, this study develops three mechanisms, fixed random delay, variable random delay, and optimal random delay, to minimize the contention cycle time. Simulation demonstrates that the optimal random delay effectively minimizes the contention cycle time and approaches the theoretical optimum throughput of 0.18 from pure ALOHA. Furthermore, over-estimation reduces the impact on contention cycle time more than under-estimation through sensitivity analysis, and both phenomenon damage slot throughput. Two estimation schemes, maximum likelihood and average likelihood, are thereby presented to estimate the number of active stations for each contention resolution round. Simulation proofs that the proposed estimation schemes are effective even when the estimated number of active stations in initial contention round is inaccurate.

In this paper, the analysis, design and experimental results of active array applicator are presented. The injection-locking technique is used to alter the magnitude of the microwave sources so that the steering of near fields can be achieved. This technique can be applied for microwave hyperthermia cancer treatment to provide the large uniform temperature distribution. The complexity of the system can be reduced by using this technique. The study shows that the temperature distribution can be controlled by varying the modulation index, modulating frequency and initial phase of modulating signal. The temperature distribution is also affected by applicator configuration, spacing between applicators, and heating time. The Spectral Domain approach is used to analyze the near field and then the near field data are used to find the temperature distribution by using the Finite Difference method. The study is carried out at frequency of 2,450 MHz. This design is useful for implementation of the low cost steerable applicator.

In this letter, we describe an adaptive hybrid SR ARQ scheme using punctured TCM and code combining. Numerical results show that the proposed scheme yields better throughput efficiency than the scheme using TCM at the values of E_s/N_o smaller than 9 dB.

It has been established that the criteria for space-time convolutional code (STCC) are based on the maximization of the minimum rank and the minimum determinant of distance matrix over quasistatic flat Rayleigh fading channel. This letter presents a new criterion, i.e., modified trace criterion which maximizes both the minimum trace and the average trace of distance matrix for a new STCC. A new STCC is systematically searched so as to maximize the minimum trace and the average trace, and shown to be superior to other known codes in quasistatic flat Rayleigh fading channel.

The electromagnetic wave scattering from ocean-like lossy dielectric random rough surfaces is numerically analyzed by using FVTD method. We have investigated the problem of low-grazing-angle (LGA) scattering in order to gain a better understanding of experimental data for the microwave backscattering from ocean-like surfaces. It is indicated that the FVTD results are in good agreement with the experimental data.