This paper reviews an approach to secret-key distribution based on the bounded observability (BO) model. First, the information-theoretic framework of secret-key agreement from a correlated random source is reviewed. Next, the BO model is introduced. In the context of this model, the BO condition is presented as a necessary and sufficient condition for the possibility of secret-key distribution. This condition describes limits on the information obtained by observation of a random object, and models the practical difficulty of completely observing random physical phenomena. Finally, an implementation of secret-key distribution based on BO in an optical fiber system is described.

We present a collective behavior in the optimal aggregation of noisy observations of a source. The quality of estimation of the source state involves a difficult tradeoff between sensing quality which increases by increasing the number of sensors, and aggregation quality which decreases if the number of sensors is too large. We analytically study the optimal strategy for large scale aggregation, and obtain an explicit and exact result by introducing a basic model. We show that larger scale aggregation always outperforms smaller scale aggregation at higher noise levels, while below a critical value of noise, there exist moderate scale aggregation levels at which optimal estimation is realized. We also examine the practical tradeoff between the above two aggregation strategies by applying an iterative encoding to linear codes.

Abstract We investigate the challenge of splitting a traffic flow over WiMAX and WiFi links. For traffic load distribution over heterogeneous RATs (Radio Access Technologies), heterogeneous link resources need to be commonly measured and fairly compared. To this end, an airtime cost model is considered as a common resource measure. The model can be used to estimate channel time consumed for a successful packet transmission. As a traffic split mechanism, an airtime‐balance method is proposed. Using the airtime cost model, the offered traffic load (in Mbps) is converted into airtime cost required for its transmission, and IP packets are distributed to multiple RATs so that airtime is equally balanced between RATs. We have implemented a practical test‐bed system, including both WiMAX and WiFi systems, and used it to conduct extensive experiments indoor and outdoor. Experimental results confirm that airtime‐balance can achieve an improved flow split to reduce the waiting packets at the reorder buffer of the receiver. Moreover, it could realize a more rapid adaptation to link variations with local measurements, when compared to the RTT‐based method, which also requires extra system overhead due to the use of probe packets. Copyright © 2010 John Wiley & Sons, Ltd.

This paper proposes a method of real-time seamless location cognition in WLAN systems based on monitoring, learning and recognizing the statistics of received data traffic. It uses the property that statistics such as average and variance of throughput are often correlated with the location. The method also uses a confidence parameter to quantify the confidence in the location identification, based on comparing matches with multiple candidates. The proposed method can support seamless location cognition by WLAN terminals, indoor and outdoor, without depending on any infrastructure service.

This paper proposes bidirectional packet aggregation and coding (BiPAC), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable VoIP sessions in wireless multi-hop networks. BiPAC applies network coding for aggregated VoIP packets by exploiting bidirectional nature of VoIP sessions, and largely reduces the required protocol overhead for transmitting short VoIP packets. We design BiPAC and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by VoIP transmission, such as delay and packet loss rate. Our computer simulation results show that BiPAC can increase the number of supportable VoIP sessions maximum by around 70% as compared with the case when the packet aggregation alone is used, and 450% in comparison to the transmission without aggregation/coding. We also implement BiPAC in a wireless testbed, and run experiments in an actual indoor environment. Our experimental results show that BiPAC is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.

A multi-player video game via wireless connections using portable devices is one of the most popular applications of ad-hoc networks. Broadcast transmissions can be used for many- to-many communications in multi-player games. However, reliable broadcast communications are hard to realize because of the lack of retransmissions in the medium access control (MAC) layer. In this paper, we propose a broadcast method using random linear network coding in order to enhance the reliability of many-to-many and real-time communications. Exploiting the periodic nature of game traffic as well as inherent robustness offered by random network coding, the proposed method can provide reliable packet deliveries between 2 nodes which have a link under constant fade or even under temporary loss. Our simulation results show that the proposed method can provide higher reliability than the other schemes using multi point relay (MPR) or redundant transmissions such as forward error correction (FEC). We also implement the proposed method in a wireless testbed, and show that the proposed method achieves high reliability in a real-world environment with practical degree of complexity when installed on current wireless devices.

In wireless communication networks, there is growing interest in using mobile terminals with multiple wireless interfaces in order to achieve increased throughput and reliability. However, the performance of communications using multiple wireless interfaces can be severely impaired by fluctuations in quality of the wireless links. We designed and implemented a novel interface status monitoring scheme which supports the detection of changes in wireless link characteristics for multiple wireless interfaces and proactive decision making about the status of interfaces which can be used for communication. The monitoring scheme acquires information about link quality parameters, such as signal strength, retries and rate, directly from the wireless device driver, which allows it to acquire a large amount of information about wireless transmissions available in the driver, and to reduce latency in deciding the status of interfaces. In this paper we describe the design of the scheme and demonstrate its application to sustaining throughput on aggregated Wi-Fi links.

We demonstrate a method for improving quality of ad-hoc multihop wireless communications between moving vehicles. This method is designed to overcome problems of high packet loss and route instability common in inter-vehicular communications. We implemented the proposed method as middleware supporting real-time packet transmissions such as VoIP, and evaluated the performance in experimental tests, including a 3-vehicle test on a public road. We obtained measurement results showing maximum packet loss lower than 5 %, compared to more than 80% with existing implementations of the ad hoc routing protocols OLSR and AODV. We also showed that it is possible to support good quality VoIP broadcasts at normal traffic speeds of from 40km/h to 60 km/h on open roads.

Secret key agreement is a procedure for agreeing on a secret key by exchanging messages over a public channel when a sender, a legitimate receiver and an eavesdropper have access to correlated sources. Maurer, IEEE Trans. Inf. Theory 1993 defined secret key capacity, which is the least upper bound of the key generation rate of the secret key agreement, and presented an upper and a lower bound for the secret key capacity. In this paper, the advantage distillation capacity is introduced and it is shown that this quantity equals to the secret key capacity. A naive information theoretical expression of the secret key capacity and the advantage distillation capacity is also presented. An example of correlated sources, for which an analytic expression of the secret key capacity can be obtained, is also presented

We consider the problem of distributed sensing in a noisy environment; the CEO problem. Here individual sensor readings are encoded and transmitted independently by multiple sensors with a limited combined data rate. We present a scaling analysis of a semi-practical system using the sparse matrix codes, and show that the analysis is consistent with a general argument based on an existence of the rate distortion function. This approach well describes the tradeoff between reducing errors due to environmental noise and increasing errors due to lossy coding as the number of sensors increases, showing threshold behavior for optimal number of sensors

Congestion bottlenecks at nodes where flows cross can severely limit the number of simultaneous flows in ad hoc wireless networks using 802.11 media access. We show how routing protocols and packet generation parameters can be modified to reduce congestion at such bottlenecks. We also present results of implementation tests which show dramatic reduction of packet error rate and delay, and increase in the number of VoIP sessions due to reduction in congestion

We demonstrate the use of ad hoc multi-hop flooding for sharing information among mobile terminals. PDA devices with 802.11 WLAN cards are used as mobile terminals which periodically broadcast position and other presence information. Each terminal relays packets broadcast by neighbors using ayooding algorithm which has been optimized for fast propagation of information over multiple hops. We also report results of systematic experiments using 50 terminals showing characteristic propagation time distributions for up to 5 hops.

Ad hoc wireless networks are expected to have many useful applications, such as emergency communications after accidents and natural disasters, distributed sensing in buildings and natural environments, versatile wireless monitoring in health care and support system, and to make our daily lives easier, more productive and more enjoyable. In order to fully realize the potential of wireless ad hoc networks, we need to be able to realize large-scale networks, which connect large numbers of ad hoc terminals over wide areas. Previous research on ad hoc networks has been based mainly on computer simulations and small-scale implementations, and there have been few successful implementations of large-scale ad hoc networks. We have made significant breakthroughs toward realizing real-world operation of large-scale ad hoc networks, by the testbed based approach. In this paper, we discuss the breakthroughs toward realizing large-scale ad hoc networks and inter-vehicle communications for vehicle safety, which is one of the promising applications of ad hoc networks.

Several positioning systems to obtain precise location information have been researched. However, they have scalability and flexibility problems because they need completely configured space with a large number of sensors. To avoid the problems, we have proposed a self-organizing location estimation method that uses ad hoc networks and Self- Organizing Maps and needs no prepared space with a large number of sensors. In this paper and our demonstration, the proposed method and its characteristic are presented.

This paper proposes a MAC protocol for information discovery in ubiquitous networks. The proposed protocol is based on proactive discovery in which wireless devices periodically send advertisement broadcasts. The objective of the protocol is to provide the specified discovery time of the single-hop neighbors in a mobile ad hoc network. Since collisions in wireless network degrade performance on the discovery time, a node selects an adequate broadcast rate considering the network topology. In this paper, we show that using information about the number of neighbors in combination with framed Aloha scheme can provide the specified discovery time. We also consider a simple basic power saving mechanism which allows significantly reduce the power consumption

The capacity for secret key agreement for permutation-invariant and symmetric sources under a sampling attack is investigated. The supremum of the normalized secret key capacity is introduced, where the supremum is taken over all permutation-invariant sources or all symmetric sources and the normalized secret key capacity is the secret key capacity divided by the description length of the symbol. It is proved that the supremum of the normalized secret key capacity bound under a sampling attack is close to 1/m for permutation-invariant sources and O(1/m) for symmetric sources, where and m is the number of Eve's sources

This paper considers the capacity for secret key agreement under a sampling attack. Given the number of the eavesdropper's sources, we evaluate the secret key capacity bound which is defined as the supremum of the secret key capacity divided by the description length of the alphabet, where the supremum is taken over a set of probability distributions corresponding to the correlated sources. In particular, we consider symmetric sources and permutation-invariant sources. We derive inequalities which show the scaling of the secret key capacity bound with the number of the eavesdropper's sources

We propose two methods for improving the stability of communication in ad hoc wireless networks - firstly, the selection of reliable neighbors for data relay based on monitoring signal strength variations and secondly, the synchronous update of routing tables. These methods were designed to overcome problems observed in recent large testbed experiments. We show the dramatic improvement in stability and reduction of packet error rate which was achieved when we introduced these methods to an implementation of the OLSR routing protocol. Specifically we evaluated performance in a 50-node ad hoc wireless network, and showed a reduction in the packet error rate from 12% to less than 1.

Abstract A brief description of the current field of Science and Technology Information Transfer clearly indicates that it suffers from a number of problems which cannot be solved unless a whole‐system perspective is adopted. A planning methodology is needed which would allow us to organize a cooperative effort of different stakeholders to design an image of the desired system. Idealized planning is such a methodology. It was applied in a large participative planning effort aimed at an idealized design of a Scientific Communication and Technology Transfer System. This design is briefly described. Various alternative strategies for implementing change in the field of science and technology information transfer are reviewed. Difficulties arising from incrementalist and rational‐comprehensive approaches are contrasted. The role of a planner in implementing change is also discussed. Finally, the experience generated with the idealized planning approach is used in order to build a typology of stakeholders in the field. They are categorized by personal traits and by institutional characteristics.