Multiple subcarrier passive communication is a new research area which enables a type of frequency division multiple access with wireless and batteryless sensor RF tags just by implementing RF switches to produce dedicated subcarriers. Since the mutual interference among subcarriers is unevenly distributed over the frequency band, careless allocations of subcarrier frequencies may result in degraded network performance and inefficient use of the frequency resource. In this paper, we examine four subcarrier frequency allocation schemes using MATLAB numerical simulations. The four schemes are evaluated in terms of the communication capacity and access fairness among sensor RF tags. We found that the subcarrier allocation scheme plays an important role in multiple subcarrier communication and can improves the communication capacity by 35%.

Wide area virtualization of wireless transceivers by centrally managed software radio systems is a way to efficiently share the resources for supporting a variety of wireless protocols. In order to enable wide-area virtualization of wireless transceivers, the authors have developed a mechanism to deliver the radio space information which is quantized broadband radio wave information including the radio signals to the transceivers. Delivery mechanism consists of a distribution server which distributes radio space corresponding to the request of the client such as the center frequency and the bandwidth and a client which uses the radio space information. Accumulation of the distribution servers which deliver radio space information simultaneously to a large number of clients will contribute to build an infrastructure for any clients ubiquitously distributed over the globe. In this paper, scale-out architecture of a distribution server is proposed to deliver unlimitedly broadband radio space information to unlimited number of clients. Experimental implementation indicates the architecture to be a scale-out solution, while the number of clients is restricted by the computer resources of the distribution server. The band pass filter processing for individual client in the distribution server consumes the dominant part of the processing power, and the number of CPU cores is the upper limit of clients supportable for the distribution server in the current operating system implementation. The logical increase of the number of CPU cores by hardware multithreading does not contribute to relax this limit. We also discuss the guidance architecture or building server derived from these conclusions.

This paper proposes a novel multiple access method that enables concurrent sensor data streaming from multiple batteryless, wireless sensor tags. The access method is a pseudo-FDMA scheme based on the subcarrier backscatter communication principle, which is widely employed in passive RFID and radar systems. Concurrency is realized by assigning a dedicated subcarrier to each sensor tag and letting all sensor tags backscatter simultaneously. Because of the nature of the subcarrier, which is produced by constant rate switching of antenna impedance without any channel filter in the sensor tag, the tag-to-reader link always exhibits harmonics. Thus, it is important to reject harmonics when concurrent data streaming is required. This paper proposes a harmonics rejecting receiver to allow simultaneous multiple subcarrier usage. This paper particularly focuses on analog sensor data streaming which minimizes the functional requirements on the sensor tag and frequency bandwidth. The harmonics rejection receiver is realized by carefully handling group delay and phase delay of the subcarrier envelope and the carrier signal to accurately produce replica of the harmonics by introducing Hilbert and inverse Hilbert transformations. A numerical simulator with Simulink and a hardware implementation with USRP and LabVIEW have been developed. Simulations and experiments reveal that even if the CIR before harmonics rejection is 0dB, the proposed receiver recovers the original sensor data with over 0.98 cross-correlation.

This paper proposes a method for deriving protocol specifications in a communicating processes model, in which protocol specifications are modeled by finite automata communicating through the LOTOS multirendezvous mechanism. Message sequence charts (MSCs) are used for the derivation inputs. MSCs are graphical representations of traces of protocols and are suitable for defining requirements. Since an MSC usually covers only partial behavior, several mechanisms for composing a large number of MSCs from element MSCs have been proposed. These mechanisms, however, are not adequate: Either their input language for MSCs is not powerful enough, or they need some information on protocol specifications (i.e., implementation specifications). This paper proposes the use of regular expressions over MSCs to fully define protocols. The proposed language is powerful enough to describe protocols in the communicating processes model. A derivation algorithm based on a finite automata construction algorithm that accept sets expressed by regular expressions is presented. Because the derived protocols sometimes include unrequired behavior, an algorithm for detecting unrequired behavior is also presented.

This paper proposes an algorithm for optimizing concurrent program specification generated by design automation techniques. Some of the information in automatically generated specifications can be modified for optimization. The proposed algorithm changes some signals between processes. The computational complexity of the algorithm is O(nlogn), where n is the number of states in a given process specification. Experimental application results demonstrate it useful not only to optimize individual process descriptions but also to change signals transferred between processes in the optimization.

An extended state transition model and verification algorithm are proposed for specification and verification of protocols. The state transition model is an extention of Zafiropulo's two process protocol model to specify protocols designed for communication between more than two processes. A concept of Reduced Implementation Sequence (RIS)" is introduced to establish a protocol verification algorithm. By using RIS, potential movements of modeled systems are compactly described and the computation time necessary for verification becomes much shorter than that required for the method based on the traditional reachability analysis.

Backscatter wireless communications offer advantages such as batteryless operations, small form factor, and radio regulatory exemption sensors. The major challenge ahead of backscatter wireless communications is synchronized multicarrier data collection, which can be realized by rejecting mutual harmonics among backscatters. This paper analyzes the mutual interferences of digitally modulated multicarrier backscatter to find interferences from higher frequency subcarriers to lower frequency subcarriers, which do not take place in analog modulated multicarrier backscatters, is harmful for densely populated subcarriers. This reverse interference distorts the harmonics replica, deteriorating the performance of the existing method, which rejects mutual interference among subcarriers by 5dB processing gain. To solve this problem, this paper analyzes the relationship between subcarrier spacing and reverse interference, and reveals that an alternate channel spacing, with channel separation twice the bandwidth of a subcarrier, can provide reasonably dense subcarrier allocation and can alleviate reverse interference. The idea is examined with prototype sensors in a wired experiment and in an indoor propagation experiment. The results reveal that with alternate channel spacing, the reverse interference practically becomes negligible, and the existing interference rejection method achieves the original processing gain of 5dB with one hundredth packet error rate reduction.

This paper presents a language called SAL (Service Addition Language) which is used to describe protocol-oriented service specifications for communications software. This language has the following features: (1) Formal representation of the message sequence diagram: An individual service can be specified in an algebraic form of message sequence diagrams which are widely used in service design. (2) Separate description of services: New services to be added can be specified without the necessity of referring to the existing services. The synthesizer utility for SAL is prepared to detect any inconsistent relationship between the new and existing services. (3) Transformability into CCITT SDL (Specification and Description Language) document: As new service specifications are integrated with existing ones, functional specifications in SDL are automatically extended to implement the new along with the existing services. This is also done by the synthesizer. The algorithm is presented, which detects inconsistent relations between services, and a considerable amount of effort for service addition is shown to be automatable by introducing SAL. SAL and its supporting utilities are intended to be integrated into a development and maintenance environment called a Systems Design Environment (SDE) for communications software. SDE has a utility which generates program codes for the processes defined by the SDL documents which are derived from SAL description.

Multiple Subcarrier Multiple Access (MSMA) enables concurrent sensor data streamings from multiple wireless and batteryless sensors using the principle of subcarrier backscatter used extensively in passive RFID. Since the interference cancellation performance of MSMA depends on the Signal to Interference plus Noise Ratio of each subcarrier, the choice of channel allocation scheme is essential. Since the channel allocation is a combinatorial problem, obtaining the true optimal allocation requires a vast amount of examinations which is impracticable in a system where we have tens of sensor RF tags. It is particularly true when we have variable distance and variable bandwidth sensor RF tags. This paper proposes a channel allocation scheme in the variable distance and variable bandwidth MSMA system based on a newly introduced performance index, total contamination power, to prioritize indecision cases. The performance of the proposal is evaluated with existing methods in terms of average communication capacity and system fairness using MATLAB Monte Carlo simulation to reveal its advantage. The accuracy of the simulation is also verified with the result obtained from the brute force method.

Many devices are expected to be networked with wireless appliances such as radio frequency identification (RFID) tags and wireless sensors, and the number of such appliances will greatly exceed the number of PCs and mobile telephones. This may lead to an essential change in the network architecture. This paper proposes a new network architecture called the appliance defined ubiquitous network (ADUN), in which wireless appliances will be networked without network protocol standards. Radio space information rather than individual appliance signals is carried over the ADUN in the form of a stream with strong privacy/security control. It should be noted that this is different from the architectural principles of the Internet. We discuss a network-appliance interface that is sustainable over a long period, and show that the ADUN overhead will be within the scope of the broadband network in the near future.

A service specification description method for communication control machines (CCM), called the multilogue-set method", is proposed. This method is well suited for the discussion of the CCM renewal in response to service addition requests.