In this paper, we present new important privacy goals for on-line matchmaking protocols, which are resistance to off-line dictionary attacks and forward privacy of users' identities and matching wishes. We enhance traditional privacy requirements (e.g., user anonymity, matching-wish authenticity) with our new privacy goals and define the notion of privacy-enhanced matchmaking. We show that previous solutions for on-line matchmaking do not satisfy the new privacy goals and argue that privacy-enhanced matchmaking cannot be provided by solutions to seemingly related problems such as secret handshakes, set intersection, and trust negotiation. We define an adversary model, which captures the key security properties of privacy-enhanced matchmaking, and show that a simple, practical protocol derived by a two-step transformation of a password-based authenticated key exchange counters adversary attacks in a provable manner (in the standard model of cryptographic security).

In classical routing protocols, geographical distances/locations are typically used as the metric to select the best route, under the assumption that shorter distances exhibit lower energy consumption and nodes within the communication range of the sender can receive packets with a certain success probability. However, in underwater acoustic sensor networks (UASNs), sound propagation in the ocean medium is more complex than that in the air due to many factors, including sound speed variations and the interaction of sound waves with the sea surface and floor, causing the sound rays to bend. Therefore, propagation of sound is anisotropic in water, and may cause a phenomenon called shadow zone where nodes in the communication range of the sender cannot hear any signal. This renders conventional routing protocols no longer energy-efficient. In this paper, we make use of the ray-model to account for the environment-dependent behavior of the underwater channel, re-define nodes' one-hop neighbors based on signal attenuation rather than geographical distance, and design a distributed energy-efficient routing protocol for UASNs. Results show that our ray-model-based routing policy consistently outperforms the shortest path policy, and performs very close to the optimal one in several scenarios.

As mobile multimedia services expand, user behavior will become more diverse and the control of service quality from the user's perspective will become more important in service design. The quality of the network is one of the critical factors determining mobile service quality. However, this has mainly been evaluated in objective physical terms, such as delay reduction and bandwidth expansion. It is less common to use a human-centered design viewpoint when improving network performance. In this paper, we discuss ways to improve the quality of web services using time-fillers that actively address the human factors to improve the subjective quality of a mobile network. A field experiment was conducted, using a prototype. The results of the field experiment show that time-fillers can significantly decrease user dissatisfaction with waiting, but that this effect is strongly influenced by user preferences concerning content. Based on these results, we discuss the design requirements for effective use of time-fillers.

Communication among isolated networks (clusters) in delay tolerant networks (DTNs) can be supported by a message ferry, which collects bundles from clusters and delivers them to a sink node. When there are lots of distant static clusters, multiple message ferries and sink nodes will be required. In this paper, we aim to make groups, each of which consists of physically close clusters, a sink node, and a message ferry. Our objective is minimizing the overall mean delivery delay of bundles in consideration of both the offered load of clusters and distances between clusters and their sink nodes. Based on existing work, we first model this problem as a nonlinear integer programming. Using a commercial nonlinear solver, we obtain a quasi-optimal grouping. Through numerical evaluations, we show the fundamental characteristics of grouping, the impact of location limitation of base clusters, and the relationship between delivery delay and the number of base clusters.

We have proposed a method of identifying superspreaders by flow sampling and a method of filtering legitimate hosts from the identified superspreaders using a white list. However, the problem of how to optimally set parameters of φ, the measurement period length, m^*, the identification threshold of the flow count m within φ, and H^*, the identification probability for hosts with m=m^*, remained unsolved. These three parameters seriously impact the ability to identify the spread of infection. Our contributions in this work are two-fold: (1) we propose a method of optimally designing these three parameters to satisfy the condition that the ratio of the number of active worm-infected hosts divided by the number of all vulnerable hosts is bound by a given upper-limit during the time T required to develop a patch or an anti-worm vaccine, and (2) the proposed method can optimize the identification accuracy of worm-infected hosts by maximally using a limited amount of memory resource of monitors.

We propose a simple and small phase shifter for a beam-steerable base-station antenna. This phase shifter has no metallic heterojunction, and the phase shift is controlled by moving an M-shaped dielectric plate between the strip conductor and the ground plane of a strip line. We derive a design equation from the condition that at the center frequency f₀, the reflection coefficient = 0. In this phase shifter, the reflection coefficient becomes minimum at f₀ regardless of the movement distance, r, of the dielectric plate, and the relationship between the phase shift and r is linear. These characteristics are verified by performing simulations and measurements. The size of the M-shaped dielectric phase shifter is 0.27λ₀0.12λ₀, where λ₀ is the free-space wavelength at f₀. The insertion loss is smaller than about 0.2 dB within a fractional bandwidth of 10%, and the phase shift can vary from 0 to about 80 degrees.

We design and fabricate a double-layer hollow-waveguide slot array antenna with wide bandwidth and high antenna efficiency for the 120 GHz band. The antenna is fabricated by diffusion bonding of laminated thin metal plates for high precision and perfect electrical contact. The 1616-element antenna shows more than 70% antenna efficiency over a 13 GHz bandwidth. Furthermore, it realizes error-free data transmission in 2.5 m distance at up to 10 Gbit/s. To our knowledge, this is the first report of the design and fabrication of a high-efficiency wideband planar antenna for the 120 GHz band.

In the next generation mobile network, the demand for high data rate transmission will require an increase in the transmission power if the current mobile cellular network architecture is used. Multihop networks are considered to be a key solution to this problem. However, a new resource allocation algorithm is also required for the new network architecture. In this paper, we propose a resource allocation scheme for a parallel relay 2-hop OFDMA virtual cellular network (VCN) which can be applied in a multiuser environment. We evaluate, by computer simulation, the ergodic channel capacity of the VCN using the proposed algorithm, and compare the results with those of the conventional single hop network (SHN). In addition, we analyze the effect of the location of the relay wireless ports on the ergodic channel capacity of the VCN. We also study the degree of fairness of the VCN, using the proposed scheme, compared with that of the SHN. For low transmission power, the simulation results show: a) the VCN can provide a better ergodic channel capacity and a better degree of fairness than the SHN, b) the distance ratio for which the ergodic channel capacity of the VCN is maximal can be found in the interval 0.20.3, c) the ergodic channel capacity of the VCN remains better than that of the SHN as the number of users increases, and d) as the distance between the relay WPs and the base station increases, the channel capacity of VCN approaches that of the SHN.

In this paper, we propose an efficient channel estimation scheme in bi-directional wireless orthogonal frequency division multiplexing (OFDM) relay systems applying analog network coding (ANC). In the relay systems applying ANC, channel separation is needed to estimate each of the bi-directional channels simultaneously from the combined received signal. In the conventional channel estimation schemes, relatively higher-ratio pilots are needed to obtain accurate channels. In contrast, we propose a channel estimation scheme with sparse pilots, while maintaining high accuracy for channel estimation. In the proposed scheme, Walsh codes are inserted as the pilot symbols at both end nodes, and the individual channels are obtained by correlation processing from the combined signals. The improved bit error rate (BER) and throughput performances of the proposed scheme are shown through computer simulations.

Multicode CDMA systems convert a high-rate serial data stream into low-rate parallel data streams prior to transmission, but reducing the peak-to-average-power-ratio (PAPR) is a prerequisite. In this paper, we propose constant amplitude coding schemes with forward error correction (EC) capability. The proposed schemes overcome the adverse nonlinear effects of the high power amplifier (HPA) by using the transmitted signal of constant amplitude and parity channel. In the first scheme, we add the EC capability to the previously reported constant-amplitude rate 4/4 (Suil's) scheme, which can transmit data without energy loss. Next, we propose a rate 12/16 decoder with EC capability, which is slightly different from the previous work through the addition of EC capability. Lastly, we propose a new high-rate EC capable 16/16 scheme without energy loss, which makes it superior to the conventional 12/16 scheme which experiences excessive energy loss due to redundancy. Computer simulation results confirm that new 4/4 decoder along with 12/16 decoder and 16/16 encoder/decoder can effectively reduce the inherent problem of high PAPR in the multicode CDMA signal transmission. Our methods also yield better BER performance than other constant amplitude coding schemes.

Multichannel MAC protocols with a single control channel in a cognitive radio ad hoc network (CRAN) suffer from the bottleneck problem. So a multichannel MAC protocol that can realize a virtual control channel on all available channels is preferred. Discontiguous-Orthogonal Frequency Division Multiplexing (D-OFDM) enables multiple data to be sent and received on discontiguous multiple channels. In this paper, we propose a new cooperative multichannel MAC (CM-MAC) protocol using D-OFDM in a CRAN. In the proposed CM-MAC protocol, a new approach utilizing multiple discontiguous control channels is presented and a remedy to tackle new collision types by the approach using D-OFDM is provided. The proposed mechanism mitigates the bottleneck problem of the protocol using single control channel, but does not need to share hopping patterns between a sender and a receiver. In addition, cooperative communications with relays reduce the time required to send the data of low-rate secondary users (SUs) by enabling relay SUs to relay the data of source SUs. The proposed CM-MAC protocol is shown to enhance throughput. Analysis and simulations indicate that throughput performance improves compared to the MAC protocol using the split phase control channel (SPCC) approach.

To provide robust wireless data transmission over fading channels, various schemes which involve the use of relays have been proposed. In some of those schemes, the relay chooses not to forward the received message if its reliability is deemed as too low. Some researchers refer to such schemes as selective decode-and-forward. Our work in this paper falls into such a category. More specifically speaking, the relay in our system is a censorial relay (a relay that performs censorial task). It evaluates the reliability, in terms of log likelihood ratio (LLR), of a received data bit (from the source). If its LLR magnitude is below some preset threshold, then it is censored (i.e. not sent to the destination). When the channel is Rayleigh faded, closed-form bit error rate (BER) expressions for the proposed system are derived for several scenarios. Those scenarios are differentiated by the availability of an energy detector (ED) and the various degrees of knowledge regarding the channel state information (CSI). Aided by those closed-form BER expressions, the system parameters can be efficiently optimized to achieve the minimum BER. Simulation results are observed to closely match theoretical values, as computed by the afore-mentioned closed-form BER expressions. As compared to some existing relay-assisted systems in which censoring is incorporated, the performance of our system is better in terms of BER when the same amount of CSI is exploited.

The 60GHz millimeter-wave (mmWave) wireless technology is a focus of increasing attention, since its ability to transmit more than Gbps PHY data rate makes it suitable for high-speed, short-range applications such as peer-to-peer synchronization and kiosk terminals. In the case of short-range communication with a range of several tens of centimeters, only terminals present in this communication range will be affect and communication is considered to be on a one-to-one basis. In one-to-one communication, a simpler and more efficient access mechanism is preferable. The ability of current CSMA/CA based MAC, for example MAC of IEEE 802.11 WLAN systems, to achieve high throughput is limited by the low MAC efficiency caused by high signal exchange overhead, such as interframe space (IFS) and acknowledgement. This paper proposes an ACK/NACK mechanism that enhances the throughput in short-range one-to-one communication. The ACK/NACK mechanism uses Negative ACK (NACK) as the acknowledgement policy to reduce the overhead of ACK and the transmitter switches the required acknowledgement policy to ACK based on a switchover threshold. It solves a problem arising from NACK, namely, that NACK has no mechanism for keeping alive. We evaluate the throughput of the ACK/NACK mechanism by both theoretical analysis and computer simulation. The proposed ACK/NACK mechanism is implemented in 65 nm CMOS process (BBIC); we connect this BBIC to a 60 GHz RFIC and exchange frames wirelessly. In this experiment, it is verified that the ACK/NACK mechanism enhances throughput.

MLPDA (Maximum Likelihood Probabilistic Data Association) has attracted a great deal of attention as an effective target track extraction method in high false density environments. However, to extract an accelerated target track on a 2-dimensional plane, the computational load of the conventional MLPDA is extremely high, since it needs to search for the most-likely position, velocity and acceleration of the target in 6-dimensional space. In this paper, we propose VG-MLPDA (Variable Gating MLPDA), which consists of the following two steps. The first step is to search the target's position and velocity among candidates with the assumed acceleration by using variable gates, which take into account both the observation noise and the difference between assumed and true acceleration. The second step is to search the most-likely position, velocity and acceleration using a maximization algorithm while reducing the gate volume. Simulation results show the validity of our method.