Device-to-Device (D2D) communications in this paper refer to autonomous direct communications among end devices without central control. Wireless networks based on autonomous D2D communications are of resiliency feature. We developed a lifelog gathering system using such autonomous D2D communications towards elderly health monitoring in depopulated area, where creating wireless networks with coverage over entire area is costly. The developed system consists of three types of terminals, i.e., sensing terminal (s-terminal), delivering terminal (d-terminal), and gathering terminal (g-terminal). The s-terminal collects lifelog at objective’s house. The d-terminal can be placed in a moving car and it receives lifelog data when running within communication range of the objective’s house. Moreover, the lifelog is forwarded to the g-terminal when the d-terminal enters the communication range of facilities where the g-terminal is in operation. We conducted field experiments in a mountainous village. The measured results show that the developed system can successfully gather lifelog data even under non line-of-sight environments. Examples of observation from the gathered lifelog data are also presented.

It is expected that IEEE 802.11ad is used as intra-vehicle communications for high-speed transmission. Currently, since motion detection by frequency modulated continuous wave (FMCW) signals in mmW has been available, issues on interference between IEEE 802.11ad and FMCW signals have been raised. To solve the issues, an interference mitigation method applicable into IEEE 802.11ad against FMCW signals has been proposed. In this method, FMCW signals are detected by summation of the energy in frequency domain of interfered received signals. Interference suppression is achieved by nulling the frequencies where it is determined that FMCW signals are detected. The method does not require any changes of IEEE 802.11ad specifications. Simulation results show that significant improvement on BER has been achieved by introducing the method over SIR range from 0 dB to 8 dB. Experiment on the method has been conducted to evaluate performance of the method in a vehicle. The results obtained by the experiment have shown that the method successfully suppresses FMCW signals.

IEEE 802.11ad is expected to be used as in-vehicle communications for high-speed transmission. Recently, radar systems using frequency modulated continuous wave (FMCW) signals in the 60 GHz band have been investigated for a child presence detection in a vehicle. Therefore, there is a concern that the in-vehicle radio communication system could be interfered with by the radar system. In this paper, transmission experiment of IEEE 802.11ad signals with existence of FMCW signals was conducted in a vehicle since the impact of the mutual interference has not been clarified. The results show that if the transmit antenna and the receive antenna face each other, the stable communication can be established in a vehicle even if the FMCW signal interferes. In addition, stable communications are confirmed by using reflection from the vehicle body as long as received signal power is beyond -33 dBm.

Decentralized synchronization among peer devices (PDs) for distributed device-to-device (D2D) wireless networks has been explored by many researches. A general way of performing decentralized synchronization is based on pulse-coupled methods. In which, all PDs are equal and each PD sends and receives synchronization packets as well as adjusts own clock accordingly to achieve mutual synchronization. A newly published standard of IEEE STD 802.15.8 (STD-15.8) provides a systematic process to achieve synchronization for distributed D2D. However, we find that the synchronization process of STD-15.8 may results in separated synchronization clusters. To solve this problem, we propose additional procedures to that of STD-15.8. Then, we conduct step-by-step simulations to reflect the lower MAC functions of real transceivers by employing multiagent model. The simulation results verify the effectiveness of our proposal on improving synchronization.

Our main aim is to develop and demonstrate energy saving technologies for mobile terminals (MTs) equipped with multiple wireless interfaces. We propose a new framework of device-to-device (D2D) cooperative virtual small-cell network in which a MT acts a virtual base station to take advantage of the good channel quality of long range link and the low energy consuming interface of short range link to save energy in MTs. In the proposed D2D cooperative virtual small-cell framework, how to select proxy MT which connects to the wide area network (WAN) and provides the local area network (LAN) connection to cooperated MTs is an important issue, and it is influenced by multiple factors such as channel quality both in WAN and LAN, throughput, battery lifetime, mobility of MTs. In this paper, the energy efficiency improvement is evaluated by a smartphone test-bed and the impacts of WAN channel condition and the number of cooperated MTs are discussed. The result shows that up to 66% improvement can be achieved by the proposal compared to the traditional systems without cooperation.

IR-UWB has been gaining attentions for its capability of providing high precision ranging and location-tracking. In responding to the changes of regulations, IR-UWB devices need to be implemented at UWB high band (6.0-10.6 GHz) instead of low band (3.14.9 GHz). To compensate the deficiency of high band in propagation, we propose an adaptive detection threshold at the receiver to improve receiving sensitivity. The proposed adaptive threshold is implemented by adding an additional circuit to a conventional detector. Evaluations are performed through measurements. The proposed structure improves receiving sensitivity by 7 dB compared to the conventional structure. Moreover, IR-UWB system with the proposed structure provides better positioning accuracy and precision than the conventional system.

We developed and deployed a testbed based on the concept of peer aware communication (PAC), where PAC is used to refer the fully distributed and self-coordinated device-to-device (D2D) wireless networks. The testbed was originally developed for information sharing at local community by employing in-operation community buses as main components. However, strong demands rise from the local community for obtaining bus location information. To enable the bus location features, a number of improvements are performed to the testbed such as increasing the robustness of wireless links, streamlining MAC frame format and data flow, etc. Examination is carried out on the improved testbed. The results show that the bus location information is obtained within acceptable time delay.

Wireless networks formed by peer devices or device-to-device communications are drawing more and more attention recently. In IEEE 802 Standardization Committee, TG15.8 was set up to develop a new standard for peer aware communication (PAC). PAC is expected to provide fast neighbor discovery, offload traffic for infrastructure-based networks, provide emergency links without fixed central control, etc. In this paper, we propose procedures and protocols for using common channel for discovery and for forming group in PAC. Computer simulations are carried out with various combinations of devices and various device densities. Simulation results show that the proposed method is efficient for fast initial discovery and for accommodation of large number of PDs.

Wireless body area network (WBAN) solution is an emerging technology to resolve the small area connection issues around human body, especially for the medical applications. Based on the integrated superframe structure of IEEE 802.15.4, this paper proposes a modified medium access control (MAC) protocol for WBAN with focus on the simplicity, dependability and power efficiency. Considering the support to multiple physical layer (PHY) technologies including ultra-wide band (UWB), the slotted ALOHA is employed in the contention access period (CAP) to request the slot allocation. Mini-slot method is designed to enhance the efficiency of the contention. Moreover, sufficient slot allocation in the contention-free period (CFP) makes the proposed protocol adaptive to the different traffic including the medical and non-medical applications. Simulation results show that the protocol effectively decreases the probability of collision in a CAP and extends the CFP slots to support more traffic with quality of service (QoS) guarantee.

Complementary WLAN and WPAN technologies, as well as other wireless technologies will play a fundamental role in the medical environments to support ubiquitous healthcare delivery. This paper investigates energy based carrier sensing and its impact on the coexistence of IEEE WLAN (802.11b) and WPAN (802.15.4) in the 2.4 GHz band. We derived closed-form expressions of energy based clear channel assessment (CCA) and qualified unequal sensing abilities between WLAN and WPAN in additive white Gaussian noise channel and fading channel. The asymmetric CCA is different from the traditional "hidden node" or "exposed node" issues in the homogeneous network. The WPAN is oversensitive to the 802.11b signals and the WLAN is insensitive to the 802.15.4 signals. Choosing an optimal CCA threshold requires some prior knowledge of the underlying signals. In the considered integrated medical environments, energy based CCA can effectively avoid possible packet collisions when they are close within the "heterogeneous exclusive CCA range". However, beyond this range, WPAN can still sense 802.11b signals, but WLAN lose its sense to 802.15.4 signals. This leads to WPAN traffic in a position secondary to the WLAN traffic.

Distance between a pair of UWB sensor nodes without common time reference can be obtained by measuring round trip time. Because of difficulties in synchronization and channel estimate, the response delay of impulse UWB node is the order of milliseconds. Comparing with the nanosecond propagation delay, relative crystal offset between UWB nodes introduces big error in two way ranging. This paper estimates relative crystal offset through measuring the ranging frame duration in the counting window after synchronization. Simulation shows the relative crystal offset can be reduced to less than plusmn2 ppm

Helicopter videoing is one of the most popular methods to acquire on scene information for disaster management and relief. We developed an on scene disaster information transmission system using Ku-band helicopter satellite communications. The main obstacle for a helicopter satellite communication link is the interruption by the rotating blades of the helicopter. To overcome the blade interruption, we use a time diversity transmission technique at the forward link and a blade-synchronized transmission technique at the return link. Furthermore, onboard position estimation is done for the on scene videoing pictures. Some primary field experiments have been done with satisfactory results.

A real time system for disaster information collection and transmission using ka-band aeronautical satellite communications has been developed. This system is composed of three subsystems: a Ka-band aeronautical satellite communication (KASC) subsystem, a position-estimation and data-processing (PEDP) subsystem, and an information-distributing Internet application subsystem. Experiments to examine the performance of the overall system have been carried out. In this paper, we'll outline the overall experimental system and present some experiment results.

This paper describes how block-coded modulation (BCM) and multiple BCM (MBCM) with Viterbi decoding can be designed for use in Rayleigh fading and severe Rician fading channels. New codes are developed by modifying known codes to increase the minimum symbol distance, which is one of the distances that has a strong effect on the bit error rate (BER) performance under fading channels. Combined with anti-fading techniques such as fading compensation, interleaving, and branch weighting, the new codes significantly improve BER performance. Computer simulations were used to confirm the code performance.

Researchers have studied two types of digital multi-carrier modulation, wavelet packet modulation (WPM), and fractal modulation. The advantage of WPM is that it allows signal time and frequency to be divided and multiplexed. Therefore the time and frequency of noise signals, e.g., tone and impulse noise, can be identified and effectively partitioned in packets. Using this advantage, we propose a class-coded modulation method for WPM that has good bit error rate (BER) performance when the length of the code constraint is extended and can select time and frequency noise signals simultaneously. This report describes the proposed method and the computer simulations carried out to test its effectiveness.

A variable data rate CDMA system is evaluated for personal multimedia random access satellite communications. This system utilizes a constant occupied bandwidth, and has variable data rates and processing gains to mitigate communication link impairments and interference as well as to provide variable data rates on demand. A conceptual hardware system is developed using MSK-type constant envelope direct sequence spread spectrum modulation and handles data rates from 4-64 kbps with FEC. The receiver structure provides variable data rates on demand during a call without the aid of system control earth stations. The proposed system is described, along with the CDMA performance of the prototype equipment with the non-geostationary ETS-VI satellite at the S-band (2.3/2.1 GHz) with Ka-band (30/20 GHz) feeder link. Both the IF loop back and satellite link test performance of the prototype equipment prove it has the potential for personal multimedia satellite applications. The experimental program of the next test satellite COMETS is also briefly described.

A two symbols/branch MBCM scheme is investigated under fading channels. Compared to a conventional BCM scheme, the two symbols/branch MBCM scheme produces better performances on either Gaussian or fading channels. The pilot symbol assisted technique as well as the techniques of interleaving and branch weighting are employed to combat the effect of channel fading. Through computer simulation, it is shown that large coding gains are obtained for both Rayleigh and Rician fading channels.

Pilot symbol assisted modulation (PSAM) has been proposed to overcome Rayleigh fading. However, as the fading rate becomes more rapid, it is difficult to provide an exact interpolation with conventional PSAM. To compensate for fast Rayleigh fading, a PSAM which calculates in the frequency domain rather than the time domain as in conventional PSAM is proposed. This PSAM provides an exact estimate in fast Rayleigh fading environments.