Development of High-capacity Protocol for M2M Services and Its Application to a Pallet Management System

1. Introduction

Machine to machine (M2M) communication systems have recently been attracting a lot of attention. The concept of the Internet of Things (IoT) involves connecting everything around us to the Internet. The information that comes from these multiple components will be collected and analyzed in a network. This information will then be utilized as big data and is expected to lead to the creation of new value services [1]. In addition, the infrastructure for M2M services is being improved. For example, the Association of Radio Industries and Businesses (ARIB) issued standard STD-T108 [2] for 920-MHz band use in 2012.

We have developed a high-capacity protocol that supports ARIB STD-T108. As a precursor of IoT/M2M, we applied the protocol to a pallet management system and completed initial trials.

2. M2M service requirements

M2M services create different wireless loads from those of personal communication devices such as cellular phones. Most M2M service terminals cannot move independently and thus remain stationary for long periods. M2M systems must therefore be designed in consideration of these attributes. The typical communication environment desired for M2M services is depicted in Fig. 1. We assume the environment has the following characteristics.

Fig. 1. Communication attributes desired for IoT/M2M service.

Various wireless systems have been developed for M2M services in consideration of these requirements. The characteristics of wireless systems that can be applied to M2M services are shown in Fig. 2. The IMS (Industrial, Scientific and Medical) bands are in very heavy use, for example, for passive radio frequency identification (RFID) tags, Bluetooth^*, and IEEE (Institute of Electrical and Electronics Engineers) 802.15.4/4g [3]/4e [4], the standards specifying the physical layer for low-rate wireless personal area networks.

Fig. 2. Wireless system characteristics.

Passive RFID tags have a short transmission distance, about 1 m, but they require no batteries. Thus, the usage scenario is to apply them as a substitute for barcodes in managing the logistics of goods. The Bluetooth transmission distance is about 10 m, and higher communication speeds are possible compared with other wireless systems used for M2M services, although the number of connected terminals is limited to 10. Bluetooth LE (low energy) specializes in low power consumption. Usage scenarios include applying it in wearable and healthcare related devices. IEEE 802.15.4/4g/4e specify a transmission speed of about 100 kbit/s, a maximum transmission distance of 1 km, and a capacity of about 1000 terminals. Unfortunately, the battery life is only about one year. Thus, the usage scenarios include metering devices, as stated in Wi-SUN (Wireless Smart Utility Network) alliance standards.

In contrast, the dotted line in Fig. 2 delineates the requirements of the pallet management system assumed here. This system must accommodate tens of thousands of pallets at a depot with only a few access points. Thus, the wireless distance is hundreds of meters, and the system capacity is more than 10,000 terminals. Moreover, the battery lifetime should be at least 10 years, roughly the lifetime of a pallet. In addition, rapid recognition of the loading and unloading of hundreds of pallets carried by trucks must be achieved, as indicated in Fig. 3. A new innovative wireless system is necessary to meet these requirements.

Fig. 3. Requirements of pallet management system.

3. High-capacity protocol technology

Our solution is a new high-capacity protocol that can connect tens of thousands of terminals and manage the movement of hundreds of terminals. Moreover, it enables a battery lifetime that can exceed 10 years. The protocol is outlined in Fig. 4.

Fig. 4. Outline of high-capacity protocol.

The terminal has two states, a resting state and a movement state. The resting state indicates that the terminal is stationary. The movement state is triggered by the terminal’s vibration sensor and indicates that the pallet is being transferred by a forklift or truck. The terminal transmits beacon packets consisting of a terminal ID, sequence number, and state information of the terminal. The transmission interval of the beacon packet is controlled by the state of the terminal. The beacon transmission interval is set very short in order to quickly identify the movement state. The resting state uses long time periods when transmitting beacon packets in order to accommodate many terminals.

In addition, the movement and resting states use different frequencies. For this reason, even if many resting state terminals are present, collision of beacon packets is minimized, and rapid recognition of terminals in the movement state becomes possible.

The protocol can be applied to a variety of M2M services with the use of different or additional sensors. For example, if the temperature exceeds or falls below a set threshold, rapid notification is sent. Furthermore, notification of sudden changes in water level, of a river, for example, can be sent quickly. Thus, our approach supports various M2M services by changing the sensor(s) and the beacon transmission interval.

4. Evaluation of pallet management system in practical use

We developed equipment that hosts the aforementioned high-capacity protocol. The key specifications of the wireless equipment are listed in Table 1. The frequency band, transmission power, and other radio specifications are based on STD-T108, the ARIB standard specifications for the 920-MHz band. The transmission speed and modulation method are based on the IEEE 802.15.4g specifications. The access point can handle multiple frequencies through the use of multiple wireless modules and antennas. The terminal is equipped with components including a wireless module, built-in antenna, vibration sensor, and a battery and is roughly the same size as a pack of cigarettes, so it is easy to mount on a pallet.

Table 1. Main specifications of wireless equipment.

We applied the protocol in a pallet management system and conducted tests at a depot of UPR Corporation, a collaborative partner. The system configuration is depicted in Fig. 5. Several terminals were installed on pallets, and the other terminals were put in the depot to replicate the resting state. The access point was placed in the depot and was able to connect to the terminals in all locations and at the depot entrance. The access point transferred the beacon packets to a cloud server for pallet management.

Fig. 5. System configuration of pallet management system.

Through these tests, we confirmed that the prototype system was able to accommodate more than 10,000 terminals. In addition, we confirmed that the reception probability reached 100% within 3 minutes when the terminal was in a movement state and within 100 m from the access point. Note that the number of terminals that one access point handles can be increased by enlarging the beacon packet interval in a resting state.

As a result of these successful tests, commercial operation of a pallet management system using this protocol was commenced at UPR Corporation in April 2015 [5, 6].

5. Conclusion

In the future, we will work on advancing our research to achieve higher capacity and lower power consumption. Our goal is to achieve an M2M service that offers higher capacity and longer battery life.

References

	Nobuaki Mochizuki Senior Research Engineer, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received his B.E. and M.E. from Tohoku University, Miyagi, in 1992 and 1994, respectively. He joined NTT in 1994 and engaged in R&D of a modulation/demodulation scheme for a broadband 5-GHz wireless access system and synchronization scheme for coded orthogonal frequency-division multiplexing. He is currently developing M2M wireless access systems. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE).
	Masashi Shimizu Senior Research Engineer, Supervisor, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received his B.E. and M.E. in mechanical engineering from Keio University, Yokohama, in 1986 and 1988, respectively. He joined NTT in 1988 and began researching pointing control for deployable space antennas and surface error compensation through feed distribution control. His recent interests include active RFID and its applications. He is a member of IEICE.
	Kenji Suzuki Senior Research Engineer, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received his B.E. and M.E. in electrical and electronic engineering from Tokyo Institute of Technology in 1999 and 2001, respectively. In 2001, he joined NTT Telecommunications Energy Laboratories, where he worked on a wireless transceiver LSI architecture for low power dissipation. His interests include analog and RFIC (radio frequency integrated circuit) design for wireless communications. He is currently developing M2M systems. He is a member of IEICE and IEEE.
	Kohei Mizuno Senior Research Engineer, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received his B.E. and M.E. in electrical engineering from Keio University, Kanagawa, in 1997 and 1999, respectively. In 1999, he joined NTT Network Innovation Laboratories, where he worked on a wireless multihop network, active RFID tag, and home information and communication technology network. He is currently working on the design of 5G and beyond networks. He is a member of IEICE and IEEE.
	Akihiro Yamagishi Senior Research Engineer, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received a B.E. and M.E. in electrical engineering from Toyama University in 1986 and 1988, respectively, and a Ph.D. in electrical engineering from Tohoku University, Miyagi, in 2005. In 1988, he joined NTT LSI Laboratories, where he engaged in R&D of frequency synthesizer ICs. From 2000 to 2004, he studied 1-V-operation CMOS (complementary metal-oxide-semiconductor) RF circuits for wireless systems. He is currently studying a wireless terminal for M2M communication services. He is a member of the Institute of Image Information and Television Engineers of Japan.
	Mitsuru Harada Senior Research Engineer, Supervisor, Group Leader of Wireless Communication Circuits Research Group, Smart Devices Laboratory, NTT Microsystem Integration Laboratories. He received a B.S. and M.S. in physics from Tsukuba University, Ibaraki, in 1985 and 1987, and a Ph.D. in electronic engineering from Tohoku University, Miyagi, in 2003. In 1990, he joined NTT Atsugi Electrical Communication Laboratories, where he engaged in research on thin-film semiconductor-on-insulator devices. Since 1997, he has been researching high-speed/low-power CMOS circuits for wireless terminals.
	Shuichi Yoshino Senior Research Engineer, Supervisor, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories. He received his B.E. and M.E. in mechanical engineering from Kanazawa University, Ishikawa, in 1990 and 1992, respectively. He joined NTT in 1992 and worked on satellite Internet system and wireless networking technology development. He is currently engaged in R&D on wireless technology for M2M wireless access services.