This study presents a new TEMPEST threat that an attacker can surreptitiously obtain original plain audio information from a distance by exploiting recently emerging unintentional electromagnetic (EM) radiations. As lightweight sensor-based Internet of things (IoT) services become widespread, a mixed-signal system on chip (MSoC) spontaneously integrates all components, such as digital, analog, and even power circuits, into a single chipset to minimize the size of IoT devices. Accordingly, we pay attention to the accelerated integration of a switching regulator (SWREG), which is one of the typical power circuits and may substantially increase the unintentional EM leakages, re-enabling the audio TEMPEST attack.

BACKGROUND: Since the development of sequencing technology, an enormous amount of genetic information has been generated, and human cancer analysis using this information is drawing attention. As the effects of variants on human cancer become known, it is important to find cancer-associated variants among countless variants. RESULTS: We propose a new filter-based feature selection method applicable for extracting cancer-associated somatic variants considering correlations of data. Both variants associated with the activation and deactivation of cancer's characteristics are analyzed using dual correlation filters. The multiobjective optimization is utilized to consider two types of variants simultaneously without redundancy. To overcome high computational complexity problem, we calculate the correlation-based weight to select significant variants instead of directly searching for the optimal subset of variants. The proposed algorithm is applied to the identification of melanoma metastasis or breast cancer stage, and the classification results of the proposed method are compared with those of conventional single correlation filter-based method. CONCLUSIONS: We verified that the proposed dual correlation filter-based method can extract cancer-associated variants related to the characteristics of human cancer.

This paper proposes an electric vehicle (EV) scheduling algorithm with fuzzy logic control in smart charging network in order to improve the charging performance of the network significantly. The fuzzy logic control helps that the EV scheduling algorithm determines the proper pair of charging station (CS) and EV logically. The fuzzy inference system determines a weight value by reflecting the multiple charging requirements such as distance between EV and CS, charging time, and charging speed. The weight value describes an EV charging priority, and is used in the scheduling algorithm. The proposed scheduling algorithm focuses on avoiding EV congestion at the CS by reducing the waiting time for charging and balancing charging request rate, which shows how the EV is distributed to the CS with balancing the number of available charging pads. In order to compare the performance of the proposed scheduling algorithm with that of conventional algorithms, the random and max weight scheduling algorithm are also considered. The simulation results show that the proposed scheduling algorithm can improve the performance of the smart charging network in view of waiting time for charging and balancing of charging request rate.

This paper presents a multi-mode transmission technique that can increase the T-R distance of UCA OAM systems. The proposed technique uses dual polarized UCA antennas to increase the number of simultaneously transmitable modes at a specific T- R distance by exploiting the two basis of the polarized dipole antenna elements, and further extends the reaching distance of the multi-mode signals by using the inter-mode spreading between the OAM modes belonging to the same polarization domain. Simulation results show that the proposed scheme improves the T-R distances by at least 2 times as much as the conventional scheme in transmitting the same number of OAM modes with the same symbol error rate, and also that the proposed technique can transmit twice as many modes as the conventional method with the SNR loss of less than 3 dB at the same T-R distance.

As the number of electric vehicles (EVs) is increasing, a balancing control is needed to decrease the charging delay for EV users and increase the overall number of charged EVs for a charging station (CS) service provider. This paper suggests the local pricing-based decentralized balancing control algorithm to balance the power demand and the number of EVs at each CS. The CSs choose the charging costs according to the power demand, and the probability of sending beacon message is controlled according to the queued ratio. When receiving the beacon messages, each EV chooses the CS with the lowest cost. Simulation results showed that the suggested algorithm could balance the parked pad ratio and the charging power ratio of multiple CSs. Furthermore, the number of completely charged EVs was increased and the quality of service was also increased due to the reduction of charging delay. In conclusion, the suggested algorithm can improve the overall performance at the local area from the perspective of both charging service provider and EV users.

Relay selection and random linear network coding are widely used and can improve the performance of wireless networks significantly. In this paper, random linear network coding which pre-forwards coding coefficients in cooperative communication system is proposed. Single relay selection and multiple relay selection are proposed for the relay selection schemes, which avoid collision problem in relay networks. Moreover, we consider channel correlation between coding coefficient and coded packet for practical environment since they are transmitted separately. We investigate the outage probability and diversity order for random linear network coding with two relay selection schemes.

This paper proposes a wireless ultra-wide area backhaul network consisting of fixed/mobile access points and a wireless backhaul switch with large scale array antenna for 5G mobile communication. We also consider a hybrid beamforming scheme for wireless ultra-wide area backhaul network. We designed an analog beamformer using the genetic algorithm for sum rate maximization, and conducted channel modeling for the proposed backhaul network by deterministic ray-tracing, which gives low path loss exponent of 3 due to the high position of wireless backhaul switch. In simulation results with zero-forcing (ZF) and maximum ratio transmission (MRT) precoding, we obtained the spectral efficiency over 900 bps/Hz with 99 downlink beams on 3 km radius cell, where 4 streams are supported per beam.

In this paper, a hybrid access system based on non- orthogonality and sparse code is proposed. Non- orthogonal multiple access (NOMA) applied to a communications network can exploit higher spectral efficiency than conventional orthogonal multiple access (OMA) scheme by using channel gain difference. Sparse code multiple access (SCMA) scheme can give massive connectivity by using sparsely spread code and message passing algorithm (MPA). Therefore, we propose a hybrid access system to use the advantages of two schemes which are mentioned above. The hybrid system supports near and far users simultaneously by using NOMA scheme and data for near users is transmitted by SCMA scheme. We present the results of two kinds of simulations, i.e., bit error rate simulation and throughput simulation, to verify the superiority of the proposed system.

The millimeter-wave (mm-wave) band will be a key component of fifth-generation (5G) wireless communication systems. This paper presents radio propagation measurements and analysis investigating the wideband directional channel characteristics of the mm-wave transmission for in-building and urban cellular communication systems in the 28-GHz band. Based on the measurements, we analyze and model the spatio-temporal channel characteristics such as multipath delay, angular statistics, and path loss. In particular we investigate the clustering of the multipath components, and investigate both the intra-cluster and inter-cluster distributions. Based on these investigations, we present a complete channel model suitable for system simulations in the in-building and urban environments.

In wireless broadcast environments, a system performance can be improved with random linear network coding (RLNC). In RLNC, a source transmits a set of coding coefficients and a coded packet together. The coded packet is a combination of the coding coefficients and uncoded packets. Using the key feature of RLNC, we herein propose a new RLNC scheme to minimize outage probability with a feedback channel. In addition, the outage probability of the proposed scheme is analyzed in a Rayleigh fading channel. Through the numerical analysis and Monte Carlo simulations, we demonstrate that the outage probability of the proposed scheme is lower than that of a conventional RLNC scheme.

Communication exploiting orbital angular momentum(OAM) was proposed recently to improve transmission performance while the method utilizing spin angular momentum(SAM) was researched actively already. A dual polarization antenna is a typical example using SAM. Taking advantage of OAM transmission, multiplexing gain can be achieved by transmitting multi-modes of OAM in line of sight(LOS) environment. To exploit OAM in radio frequency domain, uniform circular array(UCA) architecture assigning signals with different phase to each antenna was proposed to generate OAM carrying beam. However, only single polarization antenna was considered in existing research, so there is a limitation to increase channel capacity. Also, conventional research only considered ideal antennas that radiate isotropically, which are not much practical. In this paper, we propose a new system utilizing both OAM and SAM by using practical dual polarization antenna based UCA architecture to increase the channel capacity. Then, a receive array is located at off-axis to apply practical environment. The channel capacity according to the distance between transmit and receive array called T-R distance is investigated to analyze the performance of proposed system for three antenna configurations that are vertical polarization, horizontal polarization and dual polarization antenna configuration. Furthermore, bit error rate(BER) performances are observed for each antenna configuration.

A single-RF transmitter based on repetitive pulse width modulation (RPWM) was proposed for an alternative system of multiple-input multiple-output (MIMO) system. However, the RPWM transmitter system has demerits which are to require switch modules with high resolution and twice the number of antenna elements than the conventional system. In the previous works, the relation of the switch resolution and the performance of the RPWM transmitter system has not been analyzed and the practical antenna has not been considered. Also, it has not been also provided how to demodulate the received signal from the RPWM transmitter system. In this paper, we propose a compact 4-port antenna which can be applied for the RPWM transmitter system practically. We provide also a receiver architecture for the RPWM transmitter system. Then we will verify that the RPWM transmitter system achieves similar multiplexing gain compared to the conventional MIMO system practically by considering the proposed antenna, the practical switch modules, and the proposed receiver system.

Non-orthogonal multiple access (NOMA) has been viewed as a promising technology in future cellular network to increase channel capacity and frequency efficiency. This NOMA system utilizes power domain to improve the performance of multiple access. Signal detection of a near user is operated by successive interference cancellation (SIC). With SIC, the near user cancels out the signal of far user and decodes its own data. Thereafter, the near user drops the cancelled data if SIC is successful. On the other hand, the far user still needs that the far user data may be retransmitted in case of far user reception failure, i.e., no-acknowledgement. Therefore, retransmission to the far user via the near user is efficient when the near user reuses its cancelled data. In this paper, we investigate more efficient way to conduct hybrid automatic repeat request (HARQ) in NOMA. If the SIC procedure of near user is successful, there is an effective approach to recycle the interference-cancelled data. This concept contains full duplex MIMO technique on near user to support the far user. It is found that the proposed retransmission method provides improvements in view of outage probability, symbol error rate (SER), and throughput of far user.

Recently, many antennas are used to increase data rate in multiple input multiple output (MIMO) system to satisfy user's requirement. However, power consumption is increased significantly when many antennas are used. As importances of economic and environment benefits have arised, consumed power have to be handled through maximizing energy efficiency (EE). EE can be increased using antenna selection which can reduce power consumed in radio frequency (RF) chains. On the other hand, there is a limited space to integrate many antennas. Integrating many antennas in fixed space causes significant quantities of mutual coupling and spatial correlation between antennas. Therefore, mutual coupling and spatial correlation have to be considered when EE is maximized through antenna selection in practical system. In this paper, antenna selection algorithm is proposed considering mutual coupling and spatial correlation between antennas in the situation where antennas are integrated in fixed space. Mutual coupling and spatial correlation are reflected by electromagnetic (EM) simulation tool to consider more practical system. Then, performance of the proposed antenna selection algorithm is analyzed compared to three methods which are exhaustive search method, conventional algorithm and random selection method. Also, performances of the proposed algorithm are investigated in different environments where channel condition is different and minimum rate is required.

A single-RF transmitter based on repetitive pulse width modulation (RPWM) was proposed for an alternative system of multiple-input multiple- output (MIMO) system. However, the RPWM transmitter system has a demerit in view of requiring twice the number of antenna elements than the conventional MIMO transmitter. Then we propose an advanced RPWM transmitter which requires the same number of antenna elements compared to the conventional MIMO transmitter in this paper. We also verify that the proposed RPWM transmitter achieves similar multiplexing gain compared to the conventional MIMO system.

This study presents analyses of the feasibility for the 28 GHz band with a comprehensive overview of important channel parameters. A channel measurement system with a time synchronisation scheme is also introduced which is a sliding correlator channel sounder using 250 Mcps (Mega‐chips‐per‐second) pseudo‐random noise sequences. The system enables the observation of the behaviour of 28 GHz wave propagation not only to use of forming narrow beams in certain directions (classical narrow beam beamforming) but also omni‐likely. This novel synchronised system makes it possible to analyse the wideband channel characteristics. The outdoor channel measurements are conducted considering various features such as foliage effects, signal outage, path loss and outdoor‐to‐indoor conditions. Furthermore, the spatial channel modelling for omni‐like observations with temporal characteristics is firstly interpreted through analysing the essential channel modelling parameters, including the number of clusters, excess delay, root‐mean‐square (RMS) delay spread, power delay spectrum, and angular spread. In the authors’ measurements, the average number of clusters was 2.41 with standard deviation of 1.44. The average RMS delay spread was 36.06 ns with standard deviation of 46.73 ns. Furthermore, the mean values of the RMS azimuth spreads of the angle of departure and arrival were 6.65° and 24.04°, respectively.

We herein consider directional transmission based on adaptive beamforming in which multiple vehicles are served at the same time using multiple directional beams; this represents one promising technology that could improve the capacity of vehicle-to-infrastructure (V2I) communication. We propose an iterative resource-allocation method to maximize the capacity of V2I communication by taking into proper account the interference between directional beams, which reduces capacity. We also consider a heuristic resource allocation scheme, which has significantly less computational complexity than the iterative scheme and negligible performance degradation. We make use of computer simulations to show that the capacity of V2I communication can be improved using our proposed schemes.

Recently, self-healing has been actively investigated for mitigating an unforeseen network failure. In particular, to enable self-healing operations in indoor wireless communications systems, an autonomous mechanism to resolve unforeseen network failure problems should be considered. Therefore, we here address the issue of autonomous self-healing, in which continuous connectivity can be provided to users by resolving unexpected network failures. To overcome this problem, we propose a low-complexity resource allocation algorithm based on an optimization approach with reduced message passing. In the proposed algorithm, normal base stations perform subchannel and power allocations with a minimum amount of information sharing (NH(M-1) to provide reliable service to users in faulty cells autonomously. We also show that the proposed algorithm converges to a unique fixed point in the low-interference region by using a contraction mapping technique. Through simulation results, we demonstrate that the proposed algorithm achieves good performances with respect to the average cell capacity, user fairness, and outage probability while reducing the message passing overhead and computational complexity.

In heterogeneous networks, interference management is a crucial issue. Resource partitioning is one of the solution of enhanced intercell interference coordination (eICIC) in LTE-A. In this paper, we propose a bargaining-based resource partitioning. We model a net profit model considering service profit as well as operating expense, and analyze the Nash bargaining solution (NBS). For solving the NBS, we consider two algorithms: concurrent and sequential bargaining. In sequential bargaining, the NBS is dominated by a bargaining order. To mitigate this effect, we further study a bargaining power adaptation scheme. We verify the performance of the NBS and the bargaining power adaptation scheme by means of simulations. It is shown that proposed NBS can maintain fairness with little throughput degradation. Our results can be applied as a guideline for fair resource partitioning with economic efficiency.

In this paper, we propose a mobile AP system for an express bus that moves fast and includes many people densely. By using mobile AP, many users can be considered as one group and it supports high received signal strength for each UEs. In case of conventional wireless communication, we model the system as a multiuser MISO system. By using mobile AP, the model is changed to single user MIMO system with better received signal strength. For mobile AP system in express highway environment, we analyze the performances of mobile AP in view of handover failure probability, radio link failure probability, and user rate. Through simulations, we evaluate the performance of mobile AP system compared to conventional system.

Cell edge performance in the handover has been recently researched in the development of mobile network systems since it can cause the significant degradation of the quality of service (QoS). We consider a novel adaptive multi input multi output (MIMO) semisoft handover technique. Semisoft handover permits both hard and soft handover advantages for OFDM networks. In this paper, we analyze the semisoft handover combined with the adaptive MIMO mode switching scheme. The downlink spectral efficiency is studied for the adaptive MIMO semisoft handover compared to the adaptive MIMO hard handover. The simulation and numerical results for each handover of the cellular systems are computed to validate the effectiveness of adaptive MIMO semisoft handover in the femtocell networks. Finally, it is also shown that the influence of the correlation between the signal qualities of the source and target base station (BS).

In cellular networks, proximity users may directly communicate with each other without going through the base station. That is called Device-to-Device (D2D) communication. It has the advantages of improving the spectral efficiency and the power saving of a user equipment (UE). In D2D communication of cellular networks, multiple UEs work together to improve the overall throughput. We call this strategy user-cooperation. User-cooperation is useful method for multiple UEs using the same contents with the high data rate because they are capable of sharing information each other. However, these contents demand the high transmit power for a UE in uplink channel. Therefore, we study user-cooperation schemes based on clustering to minimize the average power consumption of UEs while guaranteeing the high data rate. In this paper, we develop an optimization problem that finds the optimal radius of the cluster to minimize the average power consumption of UEs. Numerical and simulation results show that user-cooperation of the proposed scheme can reduce a large amount of the average power consumption of a UE.

With the increase in indoor downlink traffic, the issue of supporting asymmetric traffic between uplink and downlink is gaining in importance. We consider the application of cross-subframe assigned femtocells, in which we add downlink femtocells to support asymmetric downlink traffic in an environment containing a pre-existing uplink macrocell and femtocells. Our objective is to maximize total capacity by allocating subchannels and power to the added downlink femtocells while limiting the induced interference to a certain level. Simulation results show that our proposed algorithm increases total capacity while guaranteeing the capacity of the pre-existing uplink for a macrocell and femtocells.

We compare the capacity of two most popular methods for acquiring the state of the spectrum in cognitive radio technology: geolocation-database-based schemes and spectrum-sensing-based schemes. For the comparison, we use a new Hidden Markov Chain based channel model, because recent measurements show that a conventional two-state model, which has been widely used, is not appropriate for modeling the behavior of channels in the cognitive environment. We also consider more generic cognitive environments in which each wireless system has its own licensed bands and uses unlicensed bands in addition to its licensed bands to increase its capacity. This type of wireless systems can comprise conventional cognitive radio systems by letting the number of licensed bands be zero. Moreover, we have derived the optimal number of unlicensed bands to be used for maximizing the capacity of wireless system by taking into account interference from neighboring wireless systems. Through simulations, we compare the capacity of wireless systems with two channel state acquisition schemes and show the counterbalancing relation between two schemes, which has never been investigated in previous works. To the best of our knowledge, this is the first work to compare the capacity of these two schemes for acquiring the state of the spectrum.

Since the beginning of a human genome project, 12 years have passed. There are many studies regarding the meaning of human genome sequences and the effort to identify the whole genome of other species. Although genes significantly affect phenotype, the importance of other factors have increased. In this paper, we propose an autocorrelation based method to arrange the repetitive elements which demonstrate a major part of the genomic sequences. The search for the entire genome based on a simple mathematical analysis will be given. The performance of our proposed self autocorrelation based method will be compared with that of conventional scheme for the human chromosome sequence. Fast scanning of the genome sequence based on our proposed scheme can give a clue to analyze the complex function of the genomic sequences.

Coordinated transmission among multiple base stations (BSs) is widely considered as an efficient method to mitigate inter-cell interference in a multi-cell network. When all BSs in the network join the coordinated transmission by generating a common precoding matrix, the inter-cell interference becomes controllable. However, the complexity involved in the feedback of channel information and the computation of the precoding matrix is significant. So, we propose a cell-clustering algorithm, in which a given network is divided into several cooperative groups of BSs. In the proposed scheme, the BSs in the same cluster periodically transmit a common pilot signal. Then, each user measures the common pilot signal and reports the SINR gain that is expected when its serving cluster merges with one of its neighboring clusters. Finally, a central controller calculates the total improvement in the SINR of all users, selects a pair of clusters that have the highest improvement, and merges them into a new cluster. Simulation results show that the proposed scheme outperforms a conventional static cell-clustering scheme since the proposed scheme adaptively generates a set of clusters for the various geographical distributions of users.

In this paper, we propose a cellular communication system in which base station (BS) uses smart antenna technology. In the system, BS can form multiple beams toward multiple mobile stations (MS) at the same time to serve those MS simultaneously. To support mobility, handover is the most important function. However, in this system, received pilot signal strength of neighbor BS changes according to the direction of the beam. Therefore, we cannot determine handover to the neighbor BS based on only the received pilot signal strength of the neighbor BS. To solve this problem, we propose an optimal handover scheme in which MS handovers directly from the serving beam of the serving BS to target beam of the target BS. However, this handover scheme requires much scanning time. It leads to much longer handover delay which may cause handover failure. Thus, we propose a new suboptimal handover scheme in which handover decision is made based on estimated received signal strength of target beams. Through analysis and simulation results, we show that the proposed suboptimal handover scheme could improve the outage probability performance of the system and require smaller scanning time.

In this paper, we introduce the basic principles of wireless power transfer using magnetic field resonance and describe techniques for the design of a resonant magnetic coil, the formation of a magnetic field distribution, and electromagnetic field (EMF) noise suppression methods. The experimental results of wireless power transfer systems in consumer electronics applications are discussed in terms of issues related to their efficiency and EMF noise. Furthermore, we present a passive shielding method and a magnetic field cancellation method using a reactive resonant current loop and the utilization of these methods in an online electric vehicle (OLEV) system, in which an OLEV green transportation bus system absorbs wireless power from power cables underneath the road surface with only a minimal battery capacity.

For the purpose of automating network management, self-organizing network (SON) technology is currently being investigated. There are three important issues in SON: self-configuration, self-optimization, and self-healing. This paper focuses on self-healing, in order to resolve the problem of unexpected network faults and improve network throughput simultaneously. To deal with this problem, we propose a healing channel selection and a cooperative beamforming-based iterative resource allocation algorithms. We utilize the cooperative beamforming in the healing channel based on phase pre-adjustment, and this cooperative beamforming can be performed without power cooperation between distributed nodes. Moreover, we derive the sub-optimality and convergence of the proposed algorithm in weak interference condition by using contraction mapping. Finally, simulation results demonstrate that the proposed algorithm improves average cell capacity and user fairness while repairing network failure effectively.

We solve a neighbor discovery problem for a wireless ad hoc network using directional antennae, in order to achieve k-connectivity. Highly connected network enables each node to transmit its data to any other nodes. In high density network, high connectivity is easily achieved since each node has sufficiently many neighbors. However, radio transmission range should be increased for high connectivity in low density network. To increase transmission range, we use directional antennae without increasing transmission power in this paper. We derive optimal beam width for the directional antennae to achieve a given connectivity in a random directional neighbor discovery algorithm. The required time to achieve a given connectivity is also considered. Results in this paper could be used to derive solutions that minimize the required time while achieving a given connectivity in the network.

In this paper, we focus on the network lifetime maximization in multiband cognitive radio systems. To deal with this problem, we formulate the optimization problem of an adaptive subchannel allocation and find an optimal solution. To reduce the computational complexity of the optimal solution, we also propose a heuristic algorithm. We use intensive simulations to verify the effectiveness of the proposed algorithm with respect to network lifetime and normalized throughput.

The directional transmission can be applied to wide range of wireless system, which ranges from indoor WPAN to outdoor cellular system. In the system which uses directional transmission, the interference estimation will be different from that with omni-directional transmission, because the interference from other cell will come from various directions. To solve this problem, we have proposed adaptive interference estimation scheme which uses directional transmission. Through the system level multi-cell simulation which is based on the actual wireless environment, we have shown that our proposed scheme can improve the performance of system in the view of spectral efficiency and fairness.

In this paper, we consider a time-varying ad hoc network where nodes communicate cooperatively based on adaptive clustering. When nodes having data become active, each active node wants to construct own cluster with neighboring non-active nodes for cooperative communication. If there exist multi-cluster in the network, each cluster gives (or takes) a different magnitude of interference to (or from) other clusters according to the position and the size of clusters in each time. Hence, each header needs to control the size of own cluster to improve total throughput of the network. To solve this problem, with considering time-varying interference between clusters, the adaptive clustering algorithm and frame structure are proposed to improve the performance.

In this paper, we propose a distributed topology control scheme in wireless mobile ad-hoc networks in which the transmit power of each node is adaptively adjusted based on both the number of its neighbor nodes and the amount of interference that the node generates to the neighbors.

This paper proposes a lifetime-aware routing using network coding scheme that provides the solution of lifetime maximization problems in the sensor networks with multiple sources and multiple destinations. In our proposed scheme, the relaying nodes select the route of each flow based on the node condition including remaining energy of adjacent nodes and achieve reduced flow bottleneck in the multicast system via network coding scheme. With lots of random topology simulations, we show that our proposed scheme obtains increased network lifetime performance compared to the conventional maximal lifetime routing scheme and the network coding based minimum distance routing scheme.

Sensors are embedded in dense mediums, such as walls of building and underground, for various applications. However, traditional wireless communication using electromagnetic (EM) waves does not operate well in this embedded sensor networks because the EM waves are attenuated severely in new propagation mediums including rock, soil, and water. Magnetic induction (MI) communication is rising as a promising technique for embedded sensor networks since the magnetic field experiences little attenuation in dense mediums. In this paper, we investigate the capacity maximization of MI communication. First, in strongly coupled scenario, we find the splitting coupling point from an equivalent circuit model to investigate frequency splitting problem. In loosely coupled scenario, optimal quality factor for maximizing the capacity is derived from the channel model of MI communication. Finally, we show the consistency of our analytic results and the effectiveness of the proposed algorithm through numerical results.

In a WSN (Wireless Sensor Network), cooperative communications can provide improved energy efficiency which is one of the most important metric given that sensors usually have constrained energy. In this paper, we consider a WSN where sensors operate selfish without centralized entity like as base station. The most of sensors do not tend to help spontaneously data transmission for others in a distributed WSN. We proposed the fair cooperative communication scheme which encourages sensors to participate in cooperative communication by giving some reward. In other words, sensors can participate in the same cluster and help each other to cooperatively transmit data if the following two conditions are satisfied: 1) sensors have a plan to transmit data to nearby area, and 2) sensors are able to decode message coming from a cluster representative. Hence, proposed scheme is more realistic and fair compared with existing scheme which makes sensors to participate in cooperative communication without reward. Moreover, simulation results show that the proposed scheme is more energy efficient than the existing schemes.

We propose a spectrum-sensing and data-transmission scheme that utilizes multiple-input and multiple-output (MIMO) technology to enable the spectrum to be sensed and data to be transmitted simultaneously. By using our proposed scheme, the degradation of quality of service (QoS) that is caused by spectrum sensing can be reduced and the system throughput of a cognitive radio (CR) system can be increased, while the accuracy of the spectrum sensing is unaffected. Even the CR system transmits data during the spectrum sensing, the interference to a primary user which is caused by the CR system will not increase compared to a conventional scheme. We also analyze the performance of the proposed scheme in the presence of channel estimation errors. Through performance evaluations, we show that the proposed scheme can increase the throughput and QoS of CR systems.

In this paper, we compare the performance of two major spectrum information acquisition schemes in cognitive radio system, which are geo-location database based scheme and spectrum sensing based scheme. Although these two schemes are the major spectrum information acquisition schemes which are mainly considered in current researches on cognitive radio system, the comparison of two schemes has not been considered in previous works. In the comparison, we propose a new channel model for the cognitive environment which has three states, because recent measurements show that two-state Markov Chain model which has been widely used is not appropriate to model the cognitive environment. And based on the new channel model, we propose a new spectrum sensing scheme to reduce sensing overhead. Through performance analysis and numerical results, we show that our analysis is accurate and that the number of spectrum sensing can be reduced by using our proposed scheme so that the throughput of a cognitive radio system can be improved. We also find that the throughput of a spectrum sensing based scheme is better than that of a geo-location database based scheme in general cognitive environment.

Femtocells are a promising technology for handling exponentially increasing wireless data traffic. Although extensive attention has been paid to resource control mechanisms, for example, power control and load balancing in femtocell networks, their success largely depends on whether operators and users accept this technology or not. In this paper, we study the economic aspects of femtocell services for the case of monopoly market, and aim to answer questions on operator's revenue, user surplus, and social welfare by considering practical service types and pricing strategies. We consider three user subscription services, that is, users can access only macro BSs (mobile-only), or deploy femto BSs in their house and open / exclusively use their femto BSs (open- / closed-femto). For pricing strategies, flat pricing and partial volume pricing are exploited. The main messages include the following: 1) open-femto service is beneficial to both users and providers; 2) in flat pricing, the impact on operator revenue of allowing or blocking the access of mobile-only users to open femto BSs is minor; and 3) compared with partial volume pricing, flat pricing is advantageous to the operator when users are sensitive to price.

This paper proposes a multi-channel MAC protocol that provides QoS for ad-hoc networks based on the IEEE 802.11 DCF mode. The IEEE 802.11 standard gives methodologies and examples for contention-based distributed coordination systems for only a single channel. To overcome this limited channel usage, many studies on how it works in multi-channel environment have been performed. The IEEE 802.11e has proposed the priority schemes that operate on the single channel. However, we combine this concept supporting QoS with multi-channel MAC protocol. Thus, we can achieve the advantage of multi-channel and provide QoS for real-time users.

The main objectives of a self-organizing network (SON) technology are autonomous network deployment, network performance optimization and real-time adaptation to environmental changes. There are three functionalities in SON, such as self-configuration, self-optimization and self-healing. In this paper, we focus on the self-healing issue with respect to abrupt network faults. In order to solve this problem, we design a healing channel (HC) and propose a collaborative resource allocation (CRA) algorithm based on a modified iterative water-filling (MIWF) algorithm. Through intensive simulations, we show that CRA efficiently supports users in disabled femtocell base stations (FBS) with the little degradation in system capacity.

The femtocell is an enabling technology to handle exponentially increasing wireless data traffic. Despite extensive attentions paid to resource control, e.g., power control and load balancing in femtocell networks, the success largely depends on whether operators and users accept this technology or not. In this paper, we study the economic aspects of femtocell services with game theoretic models between providers and/or users. We consider three services: users can access only macro BSs (mobile-only), or open/exclusively use their femto BS (open or closed-femto). The main messages include: 1) it is better off for the operator to provide just the open-femto service than a mix of closed and open-femto services; 2) two polices of allowing or blocking the access of mobile-only users to open femto BS are not significantly differentiated in the revenue.

In wireless network, a femtocell, a device with small coverage, becomes an inevitable technology due to the increasing demand for high data rate. However, at present, femtocells are not sufficiently reliable. Thus, it is a critical issue to provide good protocols for diagnosing and managing faults in femtocells. In this paper, we contribute to satisfying these requirements by suggesting a queuing model including faulty handover to analyze a dynamics of an indoor network and proposing an efficient cell selection algorithm that minimizes handover failure and achieves a load balancing between neighboring cells when the femtocell generates a fault. Simulation results reveal that mobile users of a faulty femtocell can handover successfully to neighboring cells when the proposed algorithm is used.

The concept of "Network MIMO" in which a set of access points (APs) form a cluster and cooperatively serve each user in the network has received much attention to enhance the performance of the users at cell boundary. Thus, in a network MIMO-based system, interference from neighboring clusters becomes a dominant factor to decide the spectral efficiency of the system. In this paper, we propose an efficient cell-clustering algorithm that can systematically determine a set of cooperative APs in the network. Through simulation, we observe the improved performance of the proposed cell-clustering algorithm in terms of the sum-rate and the outage probability compared with a non-adaptive cell-clustering algorithm.

An integrated cellular and short-range network, in which short-range communications among users are used as a mean of increasing the performance of a cellular system, is considered as a promising technology to support various multimedia services in an efficient manner. Especially for multicast service, this kind of network can provide a method to overcome a drawback of a conventional multicast, which is caused by applying a common data rate to multicast traffic. So, we study a cooperative multicast that utilizes the capability of the shortrange communications. In this case, the power consumption of a mobile device is unavoidable. Thus, we develop an optimization problem that finds the optimal data rates assigned to each user in a multicast group to minimize the power consumption of a mobile device. Simulation results show that the cooperative multicast based on the proposed rate control algorithm can reduce a large amount of transmit power of a base station while using a small amount of power of a mobile device.

In this paper, we propose a vehicle-to-vehicle-to-infrastructure (V2V2I) communication system which utilizes a smart antenna technology. In the proposed V2V2I communication system, both an infrastructure and a vehicle can form multiple directional beams by using multiple antennae in order to transmit multiple data streams simultaneously. Since vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications exist together in the V2V2I communication system, the co-channel interference between V2I and V2V communications causes severe system performance degradation. To solve this problem, we propose a downlink resource allocation scheme for the smart antenna based V2V2I system by considering the interference between V2I and V2V communications so that overall system capacity can be improved. Through simulation results, we show that our proposed scheme can contribute to increase the overall capacity of V2V2I communication system.

The power saving mechanisms of the current IEEE 802.16e system are designed to take no consideration of the harmonization between power saving classes (PSCs) I and II. Hence, we propose a harmonized power saving mechanism between PSC I and PSC II to increase unavailability interval when a mobile station (MS) uses PSCs. The proposed mechanism adjusts the timing of the sleep window of PSC I to maximize the unavailability interval of the MSs. As a result, the proposed mechanism achieves power saving of the MSs. Through the simulation, we show that the proposed mechanism can reduce the power consumption of the MSs considerably compared with conventional mechanisms.

In this paper, we propose a group handover scheme in multi-access networks, which utilizes adjusted delay to prevent handover blockings caused by a group handover. In the group handover, a lot of users try to initiate a handover at the same time, which causes network congestion and increases the probability that the handover would be blocked. In our proposed scheme, to prevent these problems of a group handover, each user which participates in the group handover, optimally selects an access point(AP) based on the remaining resources of the AP, and each user initiates a handover after adjusted delay to prevent network congestion. To find an optimal AP selection strategy, we formulate an optimization problem whose objective is to minimize handover blocking probability, and derive an optimal solution by using the Karush-Kuhn-Tucker (KKT) condition. Through performance analysis and simulation results, we show that our proposed scheme can reduce handover blocking probability in a group handover compared to a conventional scheme and keep handover blocking probability to be less than the maximum allowable value of handover blocking probability.

In wireless communication system, power saving mechanism is a key issue since a mobile station operates depending on limited power. Hence, the IEEE 802.16e system provides three types of power saving classes (PSC I, PSC II and PSC III) for the mobile station (MS) to reduce power consumption. Many models have been made to analyze the performance of power saving mechanism (PSM) of the IEEE 802.16e system. Although many researches have been studied about the PSC I and PSC II, no work has conducted the performance of PSM considering the coexistence of the PSC I and PSC II. Hence, in this paper, when the PSC I and PSC II are used simultaneously, we model the power saving mechanism (PSM) using a discrete-time Markov chain (DTMC) technique. We develop an analytical model considering the characteristics of the PSC I and PSC II. Using the model, we analyze the performance of the PSM by using several metrics such as power consumption and response delay. Then, by comparing numerical analysis with simulation results, we validate a proposed model.

In this paper, we focus on the guarantee of inter-cell fairness in OFDM femtocell systems. To solve this problem, we formulate an optimization problem to maximize the summation of logarithmic cell capacity. Based on analytic results, we propose an enhanced modified iterative water-filling algorithm which improves inter-cell fairness compared to a modified iterative water-filling algorithm. The key feature of the proposed algorithm is that each cell performs power allocation to minimize the interference that it causes to a heavy traffic cell to ensure the inter-cell fairness. We verify the effectiveness of the proposed algorithm with respect to fairness improvement and the little degradation of sum capacity by intensive simulations.

In wireless cellular networks, indoor coverage is a problem from the perspective of the service provider. A femto Access Point, also known as femto AP, is utilized to solve the problem. Generally, the femto AP is deployed in a home to support indoor users. Since there might be a small number of users in the home, it could be expected that the traffic load of the femto AP is lower than its wireless channel capacity. Though the femto AP could support indoor users, it also causes interference problems. In this paper, we proposed a power control algorithm for the femto AP that will help reduce the interference. The proposed scheme reduces the transmission power when the traffic density of the femto AP is low, so that the femto AP could avoid any throughput loss. In order to evaluate the performances of the proposed scheme, we use an finite state markov chain (FSMC) model. Then, we show some numerical results of the proposed scheme.

In multi-hop relaying systems, a cognitive radio (CR) technique can enhance system performance by an efficient resource sharing between relay stations (RSs). In this paper, the performance of a selective repeat (SR) ARQ mechanism in the CR systems is analyzed by Markov chain and matrix signal flow graph (MSFG) techniques. The proposed analytical model considers unreliable feedbacks, retransmission timer and roundtrip delay. A priority based resource allocation scheme is also proposed to prevent performance degradation caused by unstable resources obtained by the CR technique. The proposed analytical model and resource allocation scheme are verified by comparing numerical analysis with simulation results.

Wireless multi-hop relaying has been attracting considerable attention as a promising technique for future communication systems. The multi-hop relaying technique has many benefits, but many problems must be overcome if it is to be used successfully. One of the biggest is a degradation of system reliability that is caused by data being transmitted through many wireless links. Many automatic repeat request (ARQ) mechanisms have been proposed to improve system reliability. We propose an analytical model of hop-by-hop ARQ mechanisms and analyze performances using a discrete-time Markov chain (DTMC) technique. The proposed analytical model considers Poisson packet arrival, packet error rate, and channel capacity in a two-hop chain topology. In addition, we propose a rate control algorithm to compensate the weak point of the hop-by-hop ARQ mechanism. We evaluate the performance of the proposed ARQ mechanism with the rate control algorithm by comparing numerical analysis with simulation results.

In this paper, we propose a downlink power control scheme for a wireless system which utilizes a smart antenna technology for space division multiple access(SDMA). In the wireless system which we consider, an access point (AP) forms multiple beams by using multiple antennae and the users of wireless systems get services at the same time by using these beams. By doing so, the spectral efficiency of the wireless system can be increased because multiple data streams can be transmitted at the same time. In this paper, we propose a downlink power control scheme in which the transmission power of each beam is allocated by considering the interference to neighboring APs so that overall system throughput can be improved. Through performance analysis and simulation results, we show that our proposed scheme can increase overall system throughput. We also show that our proposed scheme can improve the throughput even though the information of neighboring APs is inaccurate, which implies that our proposed scheme is robust to errors.

In wireless sensor network (WSN), scheduling and power management schemes have been researched as key techniques to extend a network lifetime. In conventional studies, it has commonly been assumed that sensors with the same sensing range would gather the same amount of data. Hence, the sensors consume the same amount of energy when transmitting the collected data, regardless of how many targets they observed. In this paper, we address a multiple target coverage problem (MTCP) of WSN in which different sensors will monitor different numbers of targets and a sensor that monitors more targets would gather more data; hence it will consume more transmission energy. In addition, in the MTCP, there exist overlapped targets that are monitored by more than two sensors at the same time. This results in energy being wasted by the sensors due to the overlapped targets. In this paper, we propose energy efficient sensor scheduling schemes for multiple target coverage (MTC) which maximize the network lifetime by considering both the number of targets covered by the sensor and the redundancy of overlapped targets. This paper introduces two sensor scheduling schemes: optimization scheme and heuristic scheme and verifies power saving results through simulation.

Hierarchical cellular networks (HCNs), in which femtocells are deployed in the coverage of a conventional macrocell, offer a cost effective solution to achieve high user capacity and extended service coverage. Since a large number of femtocells can be installed by users without cell planning, interference between macrocells and femtocells causes a severe problem. Especially, the macro MS which is located near femtocells or transmits uplink data with large power may make strong uplink interference to neighbor femtocells. This uplink interference results in decreasing the system capacity of femtocells. In this paper, we propose novel resource allocation schemes which minimize the uplink interference from macro MSs to femtocells in TDMA (time division multiple access) based HCNs. This paper introduces two resource allocation schemes: optimization scheme and heuristic scheme. The simulation results show that our proposed schemes can contribute to increase the system capacity of femtocells. In addition, the heuristic scheme is more practical than the optimization scheme in view of computational time.

Since a large number of femtocells may coexist in one macrocell area, interference management becomes a major issue in the deployment of femtocells, and therefore has been researched actively. In the IEEE 802.16m, one way to mitigate interference is Low Duty Operation (LDO) Mode for femtocells. Femtocell in the LDO mode changes alternately between available interval and unavailable interval. During available interval, femtocell may become active on air interface by transmitting control messages, while during unavailable interval, femtocell becomes inactive on air interface. However, the operation of femtocell in the LDO mode is not efficient, since it still has available intervals even though there are no MSs will access the femtocell in anytime soon. In this case, the available intervals may not be necessary and can further cause interference to neighbor cells. In this paper, we propose an interference mitigation scheme based on the grouping of femtocells in one neighborhood area. The unnecessary available intervals in LDO can be decreased by the proposed scheme and results in decreasing interference to neighbor cells. The analysis and simulation results show that the proposed scheme has superior advantages compared to the conventional LDO scheme in IEEE 802.16m, in terms of interference reduction and energy saving aspects.

One of the important issues in hierarchical cellular networks is to assign a user to a proper cell. If the user is located in the overlapping area of a macrocell and a microcell, both cells can be candidates as a serving cell. Thus, a cell selection should be carefully performed to increase performance in view of users as well as networks. In this paper, we propose a cell selection algorithm based on competition among a group of users. Through the competition, each user in the group decides its serving cell that causes the reduction of total transmit power required to achieve a given target SINR. Simulation results show that a proposed algorithm has performance improvement in terms of the maximum number of supportable users compared with a conventional algorithm, in which a user is assigned to a cell that requires smaller transmit power to achieve the target SINR.

Hierarchical macro/femto-cell networks are considered as a promising technology for the improvement of indoor coverage and network capacity. In these emerging networks, handoff procedures for a mobile station moving from a macrocell to a femtocell should be provided to maximize the advantages of femtocells with respect to user satisfaction and system performance. Therefore, we propose an efficient handoff decision algorithm that can be utilized in the situation where a user enters the coverage area of the femtocell. The main idea of the proposed algorithm is to combine the values of received signal strength from a serving macro BS and a target femto BS in the consideration of large asymmetry in their transmit powers. Numerical results show that there is a significant gain in view of the probability that the user will be assigned to the femtocell while keeping the same level of the number of handoffs.

In the wireless LAN (WLAN), when a node transmits PS.POLL packet to receive downlink packet from an access point during a beacon transmission interval, the transmission order of PS.POLL packet is determined competitively without any policy. This results in needless power exhaustion of nodes. Therefore, we propose a battery-aware power efficient downlink scheduling in the WLAN. The proposed scheme differentiates PS_POLL packet transmission according to remaining battery quantity. Simulation results show that the proposed scheme consumes the power of overall node uniformly and increases life time of node compared with conventional scheme.

We propose a new distributed power control scheme for closed access femtocell networks. Since femto APs can be deployed unpredictably in a macro cell area, interference to macro users and interference between femto APs in down-link (DL) cause a severe problem. In this paper, we describe the system model using a noncooperative game model. We formulate a payoff function to provide fairness and to minimize interference. At the same time, we prove that this function can be appeared as a supermodular type. Our power control algorithm based on the game model can be applied to the decentralized environment. This novel power control algorithm leads transmission power to reach a steady state condition, i.e. Nash Equilibrium (NE). Through mathematical analysis and numerical results, we show that our proposed power control algorithm has several good characteristics.

Prior to performing handoffs for indoor services, a mobile station (MS) needs to scan for an accessible femtocell in hierarchical cellular networks. The longer scanning time denotes the higher power consumption for the femtocell and gives an extra burden to the MS as well. Using adaptive thresholds with a margin for received signal strength indicator (RSSI) of adjacent macrocells, we propose a new scanning scheme to minimize unnecessary scanning procedures for an accessible femtocell. Also, it is shown that the proposed scheme outperforms a conventional scheme through analysis and simulations. The proposed scheme can be a reasonable solution to lessen power usage and processing burdens in scanning procedures.

Femtocell system is expected to bring significant improvement of system performance with low cost. However, when a number of femto BSs are installed by users without cell-planning, the femtocell system will be in dense environment, in which many femto co-cells exist in a small region and a great portion of the femto cell is overlapped by other femto cells. Femtocell system in dense environment is exposed to strong inter-cell interference problem which is critical to system capacity. In this paper, we derive a joint power and subchannel allocation scheme in dense environment. The simulation and numerical results show that our proposed scheme simply finds a better solution compared to the conventional scheme in dense environment.

Relay based cellular system, which includes Relay Nodes (RNs) to relay transmitters' signal to receivers for coverage extension and capacity improvement, has been recently emerging as one of the candidates for next generation mobile communication system. However, Mobile Stations (MSs) in relay based cellular system suffer a problem of data loss when they move out of the coverage of the serving RN and perform handover to base station (BS) or other RNs. To prevent this behavior, this paper proposes a pre-buffering scheme that BS performs multicast transmission to the handover candidate RNs. After the MS detects a nearby RN and regards it as a candidate for the handover target, the MS requests BS to multicast the MS's traffic to the serving and the candidate RN. The numerical and simulation results show that the proposed scheme brings performance improvement in view of data loss and handover interruption time.

In wireless communication system, power saving mechanism is a key issue since the mobile station operates depending on limited power. Hence, the IEEE 802.16e system provides three types of power saving classes (PSC I, PSC II and PSC III) for mobile station (MS) to reduce the power consumption. When the MS is using two or more power saving classes, the MS reduces the power consumption only during time interval that does not overlap with any listening window of active PSC called the unavailability interval. Therefore, in this paper, based on the IEEE 802.16e standard, we propose a dynamic power saving mechanism (DPSM) that increases unavailability interval when the MS is using two or more power saving classes (PSCs). The proposed mechanism adjusts sleep window of PSC I (III) to match the start point of listening window in PSC I (III) with that of listening window in PSC II. By doing so, the MS can reduce the listening time, and can increase the unavailability interval. Through analysis and simulation results, we show that the proposed DPSM can reduce the power consumption of MS with two or more PSCs considerably compared with conventional scheme.

We propose a new neighbor discovery scheme for cellular communication systems that utilizes the azimuth spread (AS), delay spread (DS) and shadow fading of a mobile station (MS). Given that the AS, DS and shadow fading are spatially correlated, MSs that are close to each other will have similar AS, DS and shadow fading values. In our proposed scheme, we use the AS, DS and shadow fading of an MS to find its neighbor MSs. The proposed scheme filters out MSs that are unlikely to be neighbor MSs and uses the Kolmogorov-Smirnov (K-S) test for more refined neighbor discovery. Through analysis and simulation, it is shown that we can effectively find neighbor MSs.

We propose a new velocity estimation scheme for cellular communication systems that utilizes the azimuth spread (AS), delay spread (DS) and shadow fading of a mobile station (MS). Since the AS, DS and shadow fading are spatially correlated, the variation of the AS, DS and shadow fading of an MS is related to the velocity of the MS. In our proposed scheme, we use the AS, DS and shadow fading of an MS to estimate the velocity of the MS. Through analysis and numerical results, we show that we can accurately estimate the velocity.

In the context of the IEEE 802.16e standard, a dual power-saving mode (DPSM) algorithm for voice over IP (VoIP) traffic whose voice codec supports voice activity detection is proposed. The proposed algorithm utilises the inactivity of the voice codec of each conversing party during mutual silence periods. Using the suggested method, the length of the sleep intervals varies during mutual silence periods, while during talk-spurt periods it is fixed according the VoIP packet generation ratio. The performance of the proposed DPSM algorithm for the average packet-buffering delay in the base station (BS) and the energy consumption of a mobile station (MS) is evaluated numerically and validated with the aid of computer simulation. The results show that when the proposed combined method is used, the energy consumption of an MS is considerably less when a PSM that only uses sleep intervals of a fixed length is operating. This improvement in performance comes at the cost of greater packet-buffering delay in the BS.

An advanced MAP transmission scheme for improving media access control (MAC) overhead in the IEEE 802.16e systems is proposed. In the IEEE 802.16e system, when a base station (BS) broadcasts a MAP message, which is a control message about scheduling information, it applies a robust modulation and coding scheme (MCS) level and allocates a large amount of radio resources, which induce a huge MAP overhead. Our proposed scheme utilizes piggybacked MAP IEs, in which control messages are concatenated with data packets and transmitted with the MCS level applied to data transmission. Due to the fact that the rate at which data is transmitted is generally higher than the rate at which broadcasting messages are transmitted, the proposed scheme can increase average data rate of a MAP transmission and consequently reduce the amount of resources allocated to the MAP transmission. Numerical analysis and simulations are presented to show that the MAP overhead is critical to system performance and can be improved by the proposed scheme.

A new algorithm is proposed for wireless voice over IP (VoIP) codecs that allocates radio resources in consideration of the variations in packet size and packet-generation period. This algorithm allows resources to be utilized more efficiently in mobile-WiMAX systems. The outstanding performance of our proposed algorithm with respect to average throughput and average packet dropping probability is demonstrated through intensive numerical analysis and simulations. VoIP capacity is compared with respect to the application of different VoIP codecs (G.729B, adaptive multirate (AMR)) and VoIP header compression schemes (payload header suppression (PHS) and robust header compression (ROHC)).

In next generation wireless networks, not only wide area cells to provide moderate data rate with full mobility but also local area cells to support high data rate with local mobility will be deployed. In addition, numerous local area cells may be located within the coverage of wide area cells to increase overall network capacity and offer high quality services. In this circumstance, a scanning operation to detect suitable local area cells for handoff can degrade the performance of a mobile station since repeated trials of scanning are likely to cause service disruption and considerable power consumption. To solve these problems, we propose a hierarchical scanning algorithm that enables the mobile station to obtain the neighbor cell information corresponding to its own situation. We present an analytical model for the proposed algorithm and evaluate its efficiency in terms of the time spent in the scanning operation. Simulation results show that the proposed algorithm requires much less time to detect suitable local area cells for handoff than a non-hierarchical scanning algorithm, which is conventionally used.

We review previous resource allocation algorithms for voice over IP (VoIP) services in Mobile WiMAX based on the IEEE 802.16e-2005 standard, and propose a new algorithm that allocates radio resources in the consideration of packet-size and packet-generation period variations of wireless VoIP codecs; hence, we can improve the efficiency of resource utilization in Mobile WiMAX. Through simulations, we demonstrate the outstanding performance of our proposed algorithm with respect to packet dropping probability and VoIP capacity for various VoIP codecs, such as adaptive multi-rate wideband (AMR-WB) codec, enhanced variable rate codec (EVRC), and G.729B codec. In addition, we compare VoIP capacity of each algorithm according to the application of VoIP header compression schemes, such as payload header suppression (PHS) and robust header compression (ROHC).

Multi-hop relaying has attracted considerable attention recently as a key technique for improving cell coverage and throughput in wireless communication. We modelled various ARQ mechanisms that have been proposed for wireless multi-hop relay systems based on a Discrete Time Markov Chain(DTMC) technique. We analyzed the performance of the ARQ mechanisms with respect to delay and throughput. We also validated the proposed ARQ model and the performance analysis by comparing the analysis with simulation results.

In the IEEE 802.16 system, a relay station (RS) is required for the purpose of coverage extension and throughput improvement. However, if we use the RS, original bandwidth request mechanism is not applied to subscriber station (SS) which is connected to RS since the bandwidth request mechanism is optimized for single-hop environment. Therefore, we propose an efficient contention based CDMA bandwidth request mechanism for SS located in RS region in the IEEE 802.16 MMR system. In the proposed scheme, an SS can receive the uplink resource very well wherever an SS is located. Through the analysis, we show that the proposed bandwidth request mechanism reduces the signaling cost and delay of system.

In OFDMA systems, channel quality information (CQI) feedback is used to determine the modulation and coding level of a mobile station (MS). When the MS uses diversity, it transmits the CQI feedback information which contains channel condition which is averaged over all the sub-bands allocated to itself. In conventional CQI feedback scheme, every MS should send its own CQI feedback. So, as the number of MSs in the system increases, the amount of CQI feedbacks increases too, and it results in the reduction of system throughput. To solve this problem, we have proposed a new CQI feedback scheme. In our CQI feedback scheme, MSs which are close each other make a CQI feedback group. And only one representative CQI feedback per one CQI feedback group is transmitted because MSs which are in the same CQI feedback group have similar channel condition. In this paper, we also have derived the PER equation of MSs when the MSs use a representative CQI feedback. And also, through simulations and numerical results, we have shown that by using our proposed scheme, CQI feedbacks can be reduced.

To support dynamic traffic-asymmetry property in future wireless communication systems, we propose a hybrid- TDD scheme, combination of static-TDD and dynamic-TDD. By using adaptive power control, inner/outer scheduling and hybrid-link for guaranteeing safe downlink/uplink time-slots, we can effectively solve the interference problems of the dynamic- TDD scheme. Especially, an adaptive downlink power control strategy in hybrid-link region can efficiently reduce severe BS- BS interference compared with other conventional schemes. Through numerical analysis and simulation results, we prove that our proposed scheme has the best performance compared with other conventional schemes in view of spectral efficiency and downlink/uplink outage probability.

Recent broadband wireless access systems apply voice over Internet protocol (VoIP) for their voice services, so a mobile station (MS) requires an efficient energy-saving algorithm for VoIP services to prolong its battery lifetime. The IEEE 802.16e system calledMobileWiMAXprovides the power saving class (PSC) of type II as an energy-saving algorithm for VoIP service, but it is not originally designed to consider silent periods of VoIP traffic. Therefore, we propose a new hybrid energy-saving algorithm suitable for VoIP services with silence suppression, which basically follows PSC II during talk-spurt periods, but uses the truncated binary exponential algorithm of PSC I during silent periods. The analysis and simulation results show that the proposed hybrid scheme reduces power consumption effectively during silent periods while satisfying the maximum allowable end-to-end delay and low packet drop probability constraints with respect to the quality of service (QoS) of VoIP.

In sensor networks with mobile access points (MAs), distant sensor nodes cannot communicate directly with the MA when it is path-constrained and sensor area is very wide. For these nodes, we propose a relaying operation based on overhearing, which is very simple and compatible with the conventional operation of MAs. The simulation results show that it enhances coverage and energy efficiency.

A Mobile Multi-hop Relay (MMR) Task Group was created to achieve coverage extension and throughput enhancement by introducing a relay station (RS) in the IEEE 802.16 system. If the RS is introduced in the 802.16 system, the reliability of data transmission is worsen, since data transmission failures occur more frequently due to several wireless links establishing end-to-end connection and an ARQ mechanism used in the 802.16 system is not optimized for multi-hop environment. In this paper, we propose an ARQ mechanism focused on the 802.16 MMR system. The proposed ARQ mechanism introduces a new ARQ feedback message made by the RS for fast and efficient data transmission. The numerical analysis and simulation results show that transmission delay is reduced and transmission efficiency is enhanced by the aid of the RS with the proposed ARQ mechanism.

To improve system throughput and extend coverage, multi-hop relaying is a promising technology in wireless communication systems. Thus, multi-hop relaying is world-widely gaining huge attention as a key research item. Nevertheless, it may cause longer delay and degrade resource efficiency at the cost of the benefits due to multi-hop relaying. In this paper, we propose a traffic adaptive uplink scheduling algorithm for relay station, which could be applied to the centralized multi-hop system such as IEEE 802.16 MMR efficiently. The proposed algorithm can overcome those defects of multi-hop relaying technology and enhance system performance.

This paper analyzes Media Access Control(MAC) overhead of the IEEE 802.16e systems and shows that it causes to degrade system performance critically. MAP, a control message about resource allocation, is broadcasted with high robustness and uses a great amount of radio resource for it. This paper also proposes an advanced scheme which transmits MAP IE, a component of MAP, piggybacked on data packets, and uses fast feedback to conserve the transmission reliability of the MAP IE. Then, MAP IEs can be transmitted with high data rate, and the amount of radio resource for transmitting MAP IEs becomes extremely small. Numerical analysis and simulation results show that the proposed scheme can significantly improve the MAC overhead.

This paper proposes novel resource allocation schemes which minimize power consumption of Mobile Stations(MSs) in Orthogonal Frequency Division Multiple Access(OFDMA) systems. The conventional resource allocation schemes focus on maximizing throughput or mitigating inter cell interference. The proposed schemes allocate resource units assembled in an OFDM symbol to each MS for minimizing the total number of Orthogonal Frequency Division Multiplexing(OFDM) symbols that MSs receive. As a result, MSs can decode their own data with consuming less power for processing OFDM symbols. This paper introduces two schemes : Optimization Approached Scheme and Heuristic Approached Scheme. The simulation results in this paper show that the proposed schemes can contribute to reduce the power consumption of MSs and Heuristic Approached Scheme is more practical than Optimization Approached Scheme in view of computational time.

To reduce handover overhead such as signaling overhead and latency, optimal handover algorithm is needed for mobile multi-hop relay (MMR) systems. This article proposes a novel handover method that reduces inter-cell handover but increases intra-cell handover events, because inter-cell handover has more overhead in view of the system and gives more latency time to users rather compared to intra-cell handover. Therefore, in the proposed scheme, intra-cell handover is encouraged instead inter-cell handover using adaptive hysteresis level. Intra-cell handover performs based on higher hysteresis level than inter-cell handover. This paper also presents hierarchical relay station ID (RS ID) concept for IEEE 802.16j standard. And, additional method using MOB_NBR-ADV message is proposed in case that hierarchical ID could not be used. This proposed algorithm can decrease handover signaling overhead, latency, and unnecessary handovers called ping-pong effect as well. Also, the proposed algorithm is backward compatible with mobile station (MS). Performance analysis and simulation validate the efficiency of the proposed algorithm.

Current PS mechanisms in the IEEE 802.11 infrastructure mode cause reductions in system throughput because additional PS control packets induce more collisions. In this paper, we propose a new PS mechanism that offsets the defect of general PS schemes. The proposed scheme, which we call an arranged PS scheme, reduces the transmissions of redundant control packets and takes a load off the system. The analysis and simulation results show that with the arranged PS scheme, the number of collisions are greatly reduced and system throughput is enhanced in comparison with normal PS scheme without any degradation of power efficiency.

There are several scheduling algorithms for Voice over IP (VoIP) services in IEEE 802.16 systems, such as unsolicited grant service (UGS), real-time polling service (rtPS), UGS with Activity Detection (UGS-AD), and Lee's algorithm using Grant-Me bit of the generic MAC header. However, these algorithms have some problems of a waste of uplink resources, additional access delay, and MAC overhead for supporting VoIP services with variable data rates and silence suppression. To solve these problems, we propose a novel uplink scheduling algorithm (Extended-rtPS) for the VoIP services in IEEE 802.16 systems. Through the performance analysis and simulation results of resource utilization, VoIP capacity, total throughput, and packet transmission delay, we show that our proposed algorithm can solve the problems of the conventional algorithms, and has the best performance among these algorithms. In addition, with simulation results of packet transmission delay, we prove that our proposed algorithm can support more 74%, 24%, and 9% voice users compared with the UGS, rtPS, and UGS-AD (Lee's) algorithms, respectively.

In this paper, we investigate the adaptive resource allocation problem in multiuser multihop OFDM systems. Assuming that base station(BS) knows all channel information, we formulate capacity maximization problem(CMP) and fairness constrained capacity maximization problem(FCMP) for adaptive resource allocation. The CMP considers joint subchannel, power and path allocation problem for maximizing the system capacity, while the FCMP considers the same problem with guaranteeing a minimum number of subchannels for each user. The proposed optimization problems are productive, because BS can allocate the subchannel, power and routing path to MSs by solving one optimization problem. Since these optimizations should be performed in real time, we propose two efficient heuristic algorithms, one of which considers CMP and the other considers FCMP. In the heuristic algorithms, we separate the optimization problem into three steps, namely subchannel allocation, load balancing, and power distribution to reduce computational complexity. The proposed heuristic algorithms are simple in that the iterative computations are removed, and accurate in that two heuristic algorithms achieve a similar performance compared with optimum solution.

In multihop cellular network environments, the mobility is a major factor that disturbs finding a reliable routing path between mobile node (MN) and access node (AN). In order to minimize the effect of mobility, we propose fast route discovery protocols, which decrease the variation of link costs during the route discovery period and so achieve the reliable route setup. The proposed schemes use inhibit access control, priority access control, or hybrid control for the fast and reliable route discovery in view of cross-layer design. Simulation results show that the proposed route discovery protocols can decrease route discovery time and increase total received power compared with the conventional scheme.

HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and supports quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. In the current specification of HSDPA, each UE must periodically report to Node B the CQI. Hence, UE must report the same CQI value repeatedly when the channel quality is unchanged. Obviously, this is the waste of the UE's battery power. To solve this problem, we propose channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently using information about channel quality. With the proposed schemes, the battery capacity of UEs can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports.

In high speed downlink packet access (HSDPA), packet scheduler is a key element for high-speed and efficient transmissions. In this paper, we propose an enhanced packet scheduling algorithm which computes the priority according to the proportional fair algorithm. That is, for users to need hybrid ARQ retransmission in case of erroneous packets, the priority of the proportional fair algorithm is elegantly modified to reduce the transfer delay without degradation of system throughput.

When a WLAN station has low battery-power, a normal power-saving mechanism is not desirable and sparse wake-up should be used. In that case, the station cannot remain awake throughout every delivery-traffic-indication-message (DTIM) interval, which results in the loss of broadcast and multicast packets. In this paper, we propose a double-buffering power-saving mechanism for stations with low battery power. Broadcast and multicast packets can be delivered to stations with low battery power more reliably with the new scheme.

This paper introduces a resource allocation strategy which focuses on minimizing power consumption in orthogonal frequency division multiplexing (OFDM) systems. In case of multicasting systems, it is appropriate to allocate resource with power saving strategy, since the effect of frequency selective channel is ignorable. By this strategy, the number of OFDM symbols MSs receive is minimized. A great amount of power can be saved, because the radio frequency and baseband processes are the dominant factors of power consumption. This paper also proposes a heuristic algorithm for finding the suboptimal solution of resource allocation with low complexity. By this algorithm, resource allocation process requires O(n3) computations with little performance degradation. The numerical analysis and simulation results show that the performance of this algorithm is close to the optimum.

In wireless LAN, power saving is the essential issue to the node since the node has the limited battery. Hence, the nodes can use the Power Saving (PS) mode unless transmitting or receiving packet exists for the certain period. For the PS node to receive the buffered packet in Access Point (AP), the PS nodes periodically check the Traffic Indication Map (TIM) field in the beacon frame that contains the information about buffered packet. If the buffered packet exists, they must transmit the PS. POLL to the AP. The AP transmits the buffered packet to the node that succeeds to transmit the PS_POLL. However, when the node transmits the PS-POLL, the transmission order is determined without any priority. Therefore, we propose the efficient power management scheme to support inter-user QoS and reduce the power consumption in wireless LAN. In the proposed scheme, the node with high priority transmits PS_ POLL earlier than that with low priority, so the node with high priority receives the buffered packet faster than that with low priority, and reduces the power consumption by converting the mode from Active Mode (AM) to Power Saving (PS) for remaining beacon interval (BI). Through the analysis and simulation, we show that the proposed scheme reduces power consumption and guarantees inter-user QoS compared to conventional scheme.

At present, mobile multimedia services such as sports information and mobile TV services have been delivered over point-to-point connections. But it is clear that the point-to-multipoint connections can support these mobile multimedia services more efficiently because they can simultaneously transmit data packets from a single source to multiple destinations in a multicast group. Recently, the simulcast scheme for multimedia broadcast and multicast service (MBMS) in which the same signal is transmitted from all the cells within the system, has been proposed, but, in order to adopt this technology, the same channel bands or time slots for only broadcast/multicast service should be reserved at all cells. The reservation of these resources may not be suitable for services in a local region, and some operators may also not be easy to reserve these resources. So, in this paper, we propose multicast strategies which make multicast resources easily multiplex with unicast resources and enhance cell-capacity by improving the performance of cell-boundary users. In addition, we mathematically analyze the link-level performance and cell throughput of conventional and proposed schemes, and discuss their numerical results

The previous approach to the multicast problem for ad hoc networks is to resolve at networks layer. As a result, there are many multicast routing protocols based on multicast delivery structure in mobile ad hoc networks. In order to improve cross-layer optimization, we propose a collision free multiple access scheme by combining RTS/CTS with scheduling algorithms to support the multicast routing protocol. The benefit of proposed scheme, such as power saving, reliable data transmission and higher channel utilization compared with CSMA or multiple unicast, enables the efficient support of multicast services in mobile ad hoc networks.

The reverse link traffic in the cdma2000 ixEV-DO standard is controlled by a distributed rate control scheme in a probabilistic way. In this paper, a new reverse-link rate control scheme that controls the maximum possible data rate by considering traffic load and cell region is proposed. The simulation results show that the proposed cell region based rate control scheme significantly improves the reverse link capacity in multi-cell environments.

There are several scheduling algorithms for voice over IP (VoIP) services in IEEE 802.16e systems, such as unsolicited grant service (UGS), real-time polling service (rtPS), and extended real-time polling service (ertPS). The ertPS is a new scheduling algorithm for VoIP services with variable data rates and silence suppression, and this algorithm is recently proposed and accepted in the IEEE 802.16e standard. In this paper, we analyze and discuss the performance of the scheduling algorithms recommended in IEEE 802.16e systems including the ertPS algorithm. Through the analysis of resource utilization efficiency and VoIP capacity, we show that the UGS and rtPS algorithms have some problems, which are the waste of uplink resources in the UGS algorithm, and additional access delay and MAC overhead due to bandwidth request process in the rtPS algorithm, to support the VoIP services. In addition, for analysis of VoIP capacity, we utilize OPNET simulation, and show that the ertPS algorithm can support more 21% and 35% voice users compared with the UGS and rtPS algorithms, respectively

Handover has been the most important thing for supporting the mobility and has been researched in various wireless communication systems. Handover schemes in systems with multiple antennas, the technology highlighted for 4G wireless communications to increase the capacity, have frequently been made and considered to be very important. However, handover decision method using the number of multiple antennas has not been researched. In this paper, we propose a new handover decision method using the number of detected antennas and list requirements and distinctive features for this scheme. Simulation results show that our proposed scheme and conventional scheme trigger handovers at the almost same point. Since our proposed scheme is simpler than the conventional scheme, it has the better performance in view of feedback quantity.

The introduction of multi-hop relaying to cellular networks can enhance system performances. It supports not only the high data rate but also the service coverage extension while maintaining the deployment cost down. The primary advantage of the multi-hop relaying comes from the reduction in the overall path loss between base station and mobile station. On the other hand, the redundancy resource is needed for relay because the relay station cannot receive and transmit with the same resource concurrently. That is, there is a tradeoff between the path loss reduction and the increase in required resource for relay. This paper proposes a new serving node selection method which can be used in systems with fixed relay station. The proposed algorithm enables a mobile station to be connected with the node (base station or relay station) which supports the highest data rate. It is based on least-cost criterion, which minimizes the estimated service time. To evaluate the performance of the proposed algorithm, we analyze the performances of proposed scheme numerically. The results of analysis show that our proposed scheme enhances the system performances in view of throughput and fairness.

Code division multiple access (CDMA)-based radio-on-fiber road-vehicle communication systems were proposed to support real-time streaming services in intelligent transportation systems (ITSs). Soft handoff should be provided for real-time streaming services because these services are required to guarantee real-time property and quality of service (QoS). However, soft handoff of real-time streaming services causes the shortage of resource in view of the system. In this paper, the double-adjustment soft-handoff (DASH) scheme is proposed to support seamless service regardless of the shortage of resource and maximize the resource efficiency when real-time streaming services are served in CDMA-based ITSs. The DASH scheme adjusts the data rate of a call when it starts and finishes soft handoff. The performance of the DASH scheme is evaluated by analytical and simulation methods. Performances are evaluated with respect to the blocking probability, the handoff failure probability, and the carried traffic. Numerical results show that the proposed scheme can give relative good maintenance of calls and good throughput.

The distributed coordination function (DCF) scheme of IEEE 802.11 MAC protocol does not support any concepts of quality of service (QoS) but the enhanced distributed channel access (EDCA) scheme in IEEE 802.11e standard provides QoS according to access categories using different access parameters. However, the legacy DCF stations may be used together with EDCA stations. In this letter, we investigate and analyze the performance discrimination when EDCA and DCF stations operate simultaneously

In this paper, we present a practical UMTS-WLAN interworking architecture based on 3GPP standards, and propose a seamless handoff scheme that guarantees low delay and low packet loss during UMTS-WLAN handoff. For low handoff delay, the proposed handoff scheme performs pre-registration and pre-authentication processes before the layer 2 handoff. Moreover, it uses packet buffering and forwarding functions in order to reduce packet loss during the handoff period. Numerical and simulation results show that the proposed scheme performs well with respect to signaling cost, handoff delay, and packet loss compared with conventional schemes.

When the cells in a location area are paged sequentially based on the specific information such as last registered area or mobile speed, paging load may be nonuniformly distributed among the cells. This nonuniform paging traffic causes additional paging delay due to the increase of waiting time in the cell with high paging load. In this paper, we introduce a new paging strategy in which the paging sequence in a location area is optimized based on both the location probability of a mobile terminal and paging load distribution among the cells. From numerical results, we show that the paging cost of our proposed scheme is very close to the optimal one. In addition, we observe the effects of the paging load distribution and the location probability distribution on the paging cost.

The IS-856 standard provides bandwidth-efficient and high-speed wireless internet services to mobile subscribers. It can provide a maximum data rate of 2.4 Mbps on the forward link and 153.6 kbps on the reverse link by adopting advanced techniques. On the reverse link, there is a distributed rate control algorithm, which is based on a probabilistic model. Each mobile determines its data rate at the beginning of a new frame using a reverse activity bit and persistence probabilities. In this paper, the performance of the rate control is analyzed by modeling it as a Markov process. The results show that there is a trade-off between the reverse link throughput and the outage probability. In addition, the performance of the rate control is highly dependent on system parameters of IS-856.

The HiperLAN type2 is one of the representative wireless LAN and supports high speed transmission with mobility. Its MAC protocol is based on TDMA/TDD and provides access control and resource allocation schemes. These schemes are very important to prevent waste of resources and to improve the MAC performance in various traffic conditions. In this paper, we propose a scheme that provides adaptive random access and resource allocation according to traffic load. The proposed scheme supports the efficient resource allocation and the effective access control by using access probability. The analysis and simulation results show that the proposed scheme performs better than the conventional scheme and supports priority service easily.

To support multimedia services in intelligent transportation systems (ITS), CDMA based radio-on-fiber road-vehicle communication systems were proposed. Soft handoff should be provided for multimedia services because these services are required to guarantee real-time property and quality of service (QoS). The performance evaluation of soft handoff is important in view of system management such as determination of optimal resource allocation, cell configuration, and admission strategy. But, the performance evaluation of soft handoff when multimedia services are serviced has not been previously researched, even though there have been some previous works for voice-call service. In this paper, we develop a new analytical model of soft handoff when multimedia services are served in CDMA based ITS. We evaluate the performance of soft handoff scheme by analytical and simulational method. Blocking probability, handoff failure probability and carried traffic are obtained.

The great increase of the number of users requires efficient management of the spectrum. In hierarchical cellular systems based on CDMA, the frequency borrowing resource allocation (FBRA) algorithm is proposed to allocate frequency spectrum more efficiently. This algorithm lends frequency spectrum of macrocell to microcells when mass hot spot occurred. We analyze the interference to signal ratio and reverse link capacity in case of using the proposed algorithm. Based on the result, the algorithm performance is evaluated in view of blocking, the handoff refused probability, and the spectrum efficiency. The numerical result shows that the proposed algorithm can increase the capacity and solve the mass hot spot problem.

The need for wireless high speed data transmission is increasing. HIPERLAN type 2 is an ETSI broadband wireless access network standard operating in license-exempt 5 GHz band. The MAC protocol of HIPERLAN type 2 is based on TDMA/TDD and resources in one MAC frame can be allocated dynamically by the access point (AP). We propose a dynamic random channel allocation scheme for HIPERLAN type 2. The AP scheduler controls the number of random channels (RCH) in a MAC frame according to transmission results of the previous MAC frame. The simulation results show that the proposed scheme achieves higher efficiency of resource and lower access delay than fixed RCH allocation schemes.

One of main issues in 1/spl times/EV-DV systems is how to support and satisfy various QoS requirements of data services and voice service simultaneously. Another main issue in 1/spl times/EV-DV systems is how to increase throughput of data services without sacrificing voice service QoS requirements. The main motivation for our proposed architecture, MQC (multiple quality control), is to use per-stream buffers in the physical layer and to fully utilize air resources. The problem of existing architectures is that PDUs from only one stream can be transmitted and those PDUs may not fill out the allocated time slots. In contrast to existing architectures, MQC can multiplex several streams into one PLP (physical layer packet) because MQC utilizes per-service buffers in the physical layer. We also introduce a multiplexing scheme that minimizes queueing delays of real-time traffic and maximizes cell throughputs.

The access scheme is required to have fast access and reliable transmission in satellite communications because of the long propagation delay and different channel characteristics. In this paper we propose a hybrid access scheme based on one phase preamble and channel monitoring/allocation for satellite communications. For fast access, we use an access scheme of 3GPP2 using one phase preamble instead of 3GPP using two phase preambles, and for more reliable transmission, the CM/CA scheme of 3GPP is applied. We investigate the performance of these proposed schemes through simulation. According to the simulation results, we could improve the random access scheme and could support smaller delay in satellite environments.

In this paper, we propose an enhanced reverse link transmission procedure for 1xEV-DV which is an evolution of the cdma2000 1x for the support of circuit-switched voice and data as well as packet-switched high speed data on the same spectrum. The proposed scenario controls all mobile terminals separately. To dedicate control of each user, this scenario induces rate control (RC), MT status indication (MSI), and rate variation indication (RVI). It supports a large variance of the data rate due to the estimation of the mobile location and speed. To verify the performance of the proposed scenario, we investigated a portion of overshoot, goodput and delay. The results shows that the proposed scenario can utilize the reverse link resource efficiently by providing a rapid adaptation and accurate control of the data rate.

To efficiently support mobility of users on transportation systems, we propose a distributed group location tracking (DGLT) scheme based on several virtual visitor location registers (VVLRs) and representative identities. We analyze the DGLT scheme in view of the database (DB) access cost and the signaling cost under a one-dimensional network architecture. Compared with the IS-41 scheme, the DGLT scheme using distributed group management has a lower signaling cost as well as a lower DB access cost. As the user mobility-increases or the number of users on a TS increases, the outperformance of the DGLT scheme increases. Generally, the DGLT scheme in which a corresponding home location register selects an optimum VVLR among several VVLRs has a lower signaling cost, although a DB access cost is increased slightly compared with the GLT scheme.

In this paper, we propose a new algorithm that aids the recovery of lost packets by generating additional duplicate ACK. It is shown that by adopting this algorithm the response time and throughput of short term bursty traffic can be improved in a wireless link with high error rate.

In satellite communication systems, channel capacity is limited because of the limited number of satellites. In particular, uplink channel capacity is relatively low due to low-power handheld terminals, collision of many terminals, and fading by long propagation time. Also long propagation delay limits the number of data-retransmissions for real time traffic, and small capacity limits the number of data-retransmissions for non real time traffic. For these reasons, comparative studies are required in order to identify the most appropriate satellite-based RLC (radio link control) protocol for global mobile multimedia communication via LEO satellite networks. In this paper we consider two kinds of traffic, real time traffic and non real time traffic. For real time traffic, a class of adaptive error-control schemes using both the code rate of FEC and frame length based on the estimated channel state/condition are used as an RLC protocol with transparent mode or unacknowledged mode. Also, for non real time traffic, a hybrid ARQ type II/III protocol is used as an RLC protocol with acknowledged mode.

We propose access control protocols based on a prediction of the residual capacity available for data users. These protocols provide constant-bit-rate (voice), variable bit rate (video), and low priority data services in integrated voice/data/video code division multiple access (CDMA) systems. Three different access control protocols such as scheduled access of constant bit rate (CBR) data users, random access of CBR data users, and scheduled access of variable bit rate (VBR) data users are compared.

While traffic volume of real-time applications is rapidly increasing, current routers do not guarantee minimum QoS values of fairness and they drop packets in a random fashion. If routers provide a minimum QoS, resulting a less delay, reduced delay-jitter, more fairness, and smooth sending rates, TCP-friendly rate control (TFRC) can be adopted for real-time applications. We propose a dynamic buffer management scheme that meets the requirements described above, and can be applied to TCP flow and to data flow for transfer of real-time applications. The proposed scheme consists of a virtual threshold function, an accurate and stable per-flow rate estimation, and a per-flow exponential drop probability. We discuss how this scheme motivates real-time applications to adopt TCP-friendly rate control.

Energy efficiency is an important issue in wireless ad-hoc networks since the battery power of terminals is limited. The energy efficient MAC algorithm is based on reservation and scheduling for wireless ad-hoc networks. In this paper, we drive the optimal threshold energy level for the Pseudo Base Station (PBS) reselection in the energy efficient MAC through mathematical analysis.

A new resource allocation scheme is proposed for data services in an integrated voice/data CDMA system. After delay-sensitive voice users are first allocated, residual resources are then allocated to data users. To allocate data users fairly, we apply WFQ (weighted fair queueing) to a CDMA system with consideration of a generalized processor sharing (GPS) fluid-flow model. In order to implement this fair resource allocation scheme, a virtual clock and a credit table method are used. The throughput and delay of the data service under burst error conditions are shown. Numerical results show that the throughput of each data user has the same characteristics under burst error conditions.

CPCH (common packet channel) is an uplink common channel made by 3GPP to support rather a reliable packet transport. In this paper, we propose a new access scheme to provide a prioritized service. Discrimination of the backoff timer is applied and the channel characteristic is described. We also present a simple system model of CPCH for EPA and use it to get a mathematical result. The results show that the multi-class service with different priorities can be, effectively and easily, served by the proposed scheme.

Two distributed heuristic clustering schemes are proposed which will minimize the required transmission power in two-tiered mobile ad-hoc networks. Both schemes can be implemented and executed in real-time and can be adopted for periodic or event-driven cluster reconfiguration. Scheme performance is simulated and compared with optimum configurations based on the mean transmission power and the call drop rate as performance measures. Numerical results show that the proposed schemes deliver performance similar to optimum results.

We propose a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with two user classes and analyze the throughput of the proposed system. Mobile stations (MSs) are divided into two classes according to payment or traffic characteristics, such as delay-intolerant and delay-tolerant. Different permission probabilities are assigned to each class so that the appropriate quality of service can be provided. We assume that the generation of class 1 and 2 messages are Poisson distributed and the message is divided into several packets before transmission. The system is modeled as a two-dimensional Markov chain under the assumption that the number of packets transmitted immediately by both user classes is geometrically distributed and the packet length is constant. We calculate the packet success probability and the throughput as a function of the signal-to-noise ratio (SNR) during packet transmission, considering the number of overlapped class 1 and 2 messages and the amount of their time overlap. Moreover, we show that the proposed system differentiates user packets according to class and maintains a high throughput even under heavy traffic conditions using access control based on the channel load.

Increasing demands in various data services need high speed data transmission. The conventional system cannot support these needs and the 1xEV-DO and 1xEV-DV systems, which are optimized for high-speed packet data services, was proposed. To support high speed transmission in the reverse link in these systems, an efficient data rate control scheme is needed. We propose an enhanced reverse link data rate control scheme for increasing reverse link utilization. The proposed scheme enables both dedicated control and group control with consideration of the location of the access terminal. The proposed scheme is validated through simulation. The result shows that the proposed scheme can increase the average data rate and total amount of transmitted data. Also, the delay can be diminished.

A location tracking scheme called as a group location tracking (GLT) is proposed to reduce the location update cost for terrestrial transportation systems (TSs) in personal communication networks. To provide user mobility in a TS, we introduce two new concepts, virtual visitor location register (VVLR) and representative identity (RID). A VVLR is used to provide current location of a TS and an RID of a TS is used to represent a TS and the group of all users on the TS. When a TS moves into a new registration area, the GLT scheme based on an RID of the TS and a VVLR updates location information by a group location update request message instead of individual location update request messages generated by each user in the TS. We analyze the performance of our proposed scheme in view of the signaling load and call delivery failure. Compared with the IS-41 location tracking scheme, the GLT scheme significantly reduces frequent location updates caused by the high mobility of a TS and a large number of users in a TS.

We propose a distributed rate control scheme for throughput maximization and different QoS support of each user in the 3GPP WCDMA system using the variable spreading factor of physical channel specification. We focus on the uplink rather than downlink for the reason that the uplink resource is not used effectively by the multiple access. The base station transmits rate command bits and persistence value p considering current load and number of users with each transmission rate. And each mobile station performs the persistence test and changes transmission rate. The performance of the proposed scheme is compared with other conventional methods by simulation. The simulation results show that the proposed scheme has high throughput and supports proper differentiation according to the user's QoS.

We analyze the throughput of a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with variable length data traffic. The system is analyzed for two cases: (1) systems without a channel load sensing protocol (CLSP) and (2) systems with a CLSP. The bit-error probability and the throughput are obtained as a function of the signal-to-noise ratio (SNR) during message transmission, considering the number of overlapped messages and the amount of time overlap. We assume that the generation of data messages is Poisson distributed and that the messages are divided into packets before transmission. The system is modeled as a Markov chain under the assumption that the number of packets in a message is geometrically distributed with a constant packet length. The throughput variance of the DS/SSMA unslotted ALOHA system with variable length data traffic is obtained as the Reed-Solomon code rate varies. Results show that a significant throughput improvement can be obtained by using an error-correcting code.

We propose an adaptive redundancy control method for erasure-code-based real-time data transmission over the Internet. The loss rate is an important quality of service (QoS) parameter for real-time data transmission. However, real-time data transmission over best-effort networks, such as the Internet, suffers from a frequent packet loss due to traffic congestion. Erasure-code-based loss recovery scheme is widely used for loss recovery on the Internet. We propose a redundancy estimation algorithm which considers consecutive losses since the loss recovery rate depends on the amount of redundancy data. A continuous time Markov chain is used for modeling the loss process and adjusting the number of redundant packets. Measurements and simulation results show that the proposed scheme can be used as an efficient loss recovery algorithm for real-time data transmission over the Internet.

In the case of providing a high data-rate service, a capacity analysis of the CDMA forward link is required to allocate optimally high data-rate users. To solve this problem, we first analyze the capacity of the CDMA forward link based on optimal power control. In a multi-cell environment, the intracell interference and intercell interference are derived. To show the capacity impact of high data-rate users, we introduce a location dependent factor, which is the ratio of intercell interference to intracell interference. Considering the location dependent factor, we propose a coordinated allocation scheme, which can be used to allocate high data-rate users in sectorized cells. As a result, we show the capacity impact of high data-rate users according to the location variation. It is also shown that the outage probability can be decreased, when the coordinated allocation scheme is applied.

CDMA cellular systems use soft handoff. Although the capacity of CDMA systems is interference-limited in nature, channel shortages may occur because soft handoff uses several channels simultaneously. To cope with this problem, we propose an improved handoff method which borrows channels from stationary calls participating in soft handoff and allocates the borrowed channels to handoff requests by moving calls when a channel shortage occurs. Borrowing from stationary calls is possible because these calls do not undergo fast-fading and do not require receiver diversity. The proposed method is designed to avoid increased interference resulting from channel-borrowing. The proposed channel-borrowing handoff scheme is analyzed in a situation involving both moving and stationary calls. A comparison is made between the performances of the typical IS-95-based handoff scheme and the proposed scheme. Numerical results show that the proposed scheme is better than the IS-95 scheme in view of the handoff refused probability, the handoff queuing delay.

In these days, a mobile communication service has high-speed and multimedia characteristics. Due to the high error ratio of wireless link environments, a DLC protocol that is optimized for a wire network could not be used in wireless link environments. Thus, the DLC protocol that is suitable for mobile communication environments is required. To solve these problems, we propose an efficient WATM DLC layer protocol. The proposed DLC protocol could support various traffic attributes of high-speed multimedia services. That is, the proposed DLC layer protocol provides a piggyback response, the multiple-ack, and a multiple retransmission mechanism based on SR-ARQ. Also, an outband retransmission scheme using dynamic bandwidth is provided for the delay sensitive service and multi-copy transmission is applied in seriously faded radio environments such as handover. According to the simulation results, the suggested schemes show a better performance than the conventional SR-ARQ protocol in view of the cell transmission delay and throughput.

In the mobile ad-hoc network, there can exist two categories of terminals, the battery-powered and the outlet-plugged terminals. A new scheme for the power-saving of battery-powered terminals in mobile ad-hoc networks is proposed. Based on this scheme, the battery-powered terminals page the traffic with minimum power to the nearest outlet-plugged terminal, and only the outlet-plugged terminals are used as the routing terminals. The simulation results show that the mean radius of the battery-powered terminal's paging area are much smaller than that of the other conventional schemes.

The cdma2000, a candidate submission to ITU-R for IMT-2000 radio interface, has many MAC states such as control hold state (CHS), active state (AS), suspended state (SS), and dormant state (DS) for packet data services. A mobile station consumes the power differently as these MAC states and many timer objects called normal hold timer, slotted hold timer, virtual traffic timer, and slotted suspended timer, determine the MAC transition time of packet data. We show the relationship between the achieved power saving gain and the mean packet delay degradation.

We propose an adaptive redundancy control scheme for a systematic erasure coding scheme to transmit real time data in the Internet. Since the recovery rate of packet loss depends on the amount of redundancy data, we use the redundancy estimation algorithm which considers the loss burstiness. The Gilbert model is used for modeling the loss process and adjusting the number of redundant packets. Analysis and experimental results show that the proposed scheme is efficient for loss recovery in a consecutive loss environments like the Internet.

To support efficiently the high-speed service and the multimedia service in mobile communication environments, network architecture is generally based on small cell radius structure to increase the wireless channel capacity. In a small cell radius structure based mobile network environment, a mobile station with large mobility should perform frequent handover. Thus, an advanced handover mechanism should be provided, and must be done quickly. For these reasons, we suggest an efficient handover mechanism based on the forward handover method in this paper. The proposed handover mechanism could support a fast handover procedure, and is performed by using an optimized path. Also, the proposed handover mechanism could support QoS (quality of service) attribute of multimedia traffic during the handover procedure. We evaluated the performance of the proposed handover mechanism, and analysis results show that the suggested forward handover mechanism has less blocking ratio and lower delay than the conventional backward handover mechanism.

In this paper, we propose a new channel access mechanism for effective transmission of signal and data in the IMT-2000 W-CDMA system proposed by NTT DoCoMo. In the proposed mechanism, the base station broadcasts channel status information to prevent the mobile station from unnecessary transmission collision. That is, the proposed mechanism uses the competition mechanism for the transmission of first radio frame and utilizes the reservation mechanism for the transmission of other following continuous radio frame. According to the performance analysis, the proposed mechanism has better performance than slotted-ALOHA because of using contention and reservation in the case where signal and data messages are transmitted.

In this paper, we consider the link fault tolerance and error correction mechanisms of conventional signaling protocols to provide reliable services in a mobile multimedia telecommunication network based on ATM (asynchronous transfer mode) technology. Also, we propose efficient and optimized reliability support methods based on MTP-3 and SAAL layer for the ATM based IMT2000 system and WATM network. The first method is an end-to-end link fault detection and traffic rerouting method using the fast detection and rerouting scheme of SAAL as well as the reliable retransmission method of MTP-3. The second methodology is localized fault detection and rerouting between the IWF (inter-working function) and ATM network. By using these methods, the wormhole problem in the ATM network can be avoided between IWFs and ATM switches without notification of end-stations. Besides, we evaluate the performance of the proposed method through computer simulation. According to simulation results,the proposed signaling architecture shows efficient and fast fault restoration characteristics compared to the conventional MTP-3/3b based network. The functional signaling protocol stack and network architecture of the proposed fast rerouting mechanism provide reliable and efficient restoration performance in view of interworking between the SS7 based IMT2000 system and ATM networks.

In this letter, we propose a frequency-weighted block LMS (FWBLMS) algorithm that is based on minimization of the frequency-weighted block mean-squared error. The FWBLMS algorithm has an important advantage over the time-domain LMS algorithm in that it can be designed with different frequency weighting on error signal depending on the relative significance of various frequency bands. Application of the FWBLMS algorithm in adaptive linear prediction of speech is discussed.

Hybrid companding delta modulation (HCDM) is known to be superior in performance to other instantaneous or syllabic companding delta modulation systems [1]. To improve its performance or to reduce the bit rate further in coding speech, we propose to use a variable-rate sampling scheme in the HCDM system. The proposed system employs several different sampling rates but transmits the output binary signal at a fixed rate using a buffer. By using the variable-rate scheme, one can improve its performance by 3 to 4 dB in signal-to-quantization noise ratio (SQNR) over the fixedrate HCDM. Detailed algorithm and computer simulation results are presented. Buffer behavior and its control are also discussed. In addition, it is shown that the performance gain of a DM system with variable-rate sampling depends on the degree of variation of the input signal.