Hideyuki Torii

A new class of zero-correlation zone sequences

In this correspondence, two new methods for constructing sets of zero-correlation zone (ZCZ) sequences are proposed. These methods are based on perfect sequences and unitary matrices. Compared with previous methods, the proposed methods can generate sets of nonbinary ZCZ sequences having a longer zero-correlation zone. The sequences obtained by these methods are suitable for approximately synchronized code-division multiple-access (AS-CDMA) systems.

A New Class of Polyphase Sequence Sets with Optimal Zero-Correlation Zones

This paper proposes a new class of polyphase ZCZ (zero-correlation zone) sequence sets which satisfy a mathematical upper bound. The proposed ZCZ sequence sets are obtained from DFT matrices and unitary matrices. In addition, this paper discusses the cross-correlation property between different ZCZ sequence sets which belong to the proposed class.

Enhancement of ZCZ Sequence Set Construction Procedure*The material in this letter was presented at the 2nd International Workshop on Sequence Design and its Application in Communications, Shimonoseki, Oct. 2005. This work was supported by MEXT KAKENHI(17760321).

In our previous work, we have proposed a method for constructing ZCZ sequence sets. The method proposed by the previous work is based on perfect sequences and unitary matrices. This method can generate ZCZ sequence sets which possess a good feature concerning the length of zero-correlation zones. In this letter, we propose a new method for constructing ZCZ sequence sets by improving the previous method. The proposed method can generate new ZCZ sequence sets which can not be obtained from the previous method. These ZCZ sequence sets also possess the good feature concerning the length of zero-correlation zones.

Ternary phase shift keying and its performance

An important class of digital modulation is phase shift keying (PSK). Ternary phase shift keying (TPSK) has not been focused upon until now because it is not suitable for transmitting binary information signals. However, it has theoretically excellent features for mobile communication systems, that is, it has splendid error rate characteristics and minimum amplitude fluctuation among all of the PSK schemes. The latter feature is very appealing for usage in mobile terminals in which nonlinear amplifiers have to be used. A new class of convolutional codes is proposed in order to use the TPSK scheme in practical systems. The TPSK scheme with the new convolutional code is suitable for transmitting binary signals and it improves the error rate characteristics without bandwidth expansion.

General construction of periodic complete complementary codes composed of expanded modulatable orthogonal sequences

In this paper, we propose a construction of periodic complete complementary codes composed of the expanded modulatable orthogonal sequences. Because the number of the expanded modulatable orthogonal sequences of period N/sup 2/ is infinite, the number of the periodic complete complementary codes of period N/sup 2/ is also infinite. It is already proved that the proposed sequences are periodic complete complementary codes. In the meantime Suehiro (1998) has proposed a signal design method for approximately synchronized CDMA systems without co-channel interference. In this signal design method, we can assign the proposed periodic complete complementary codes as code words to each user so that the information transmission rate is increased.

Extension of family size of ZCZ sequence sets derived from perfect sequences and unitary matrices

The authors previously proposed a method for constructing ZCZ sequence sets. In this paper, we propose a method for expanding the family size. This extension can generate ZCZ sequence sets having a larger family size than the previous method generates, without losing the advantage of having a longer zero-correlation zone.

Quadriphase M-ary CDMA signal design without co-channel interference for approximately synchronized mobile systems

Suehiro (1985) has proposed a quadriphase signal design method for the uplink of the cellular CDMA mobile communication systems. The designed signals work without co-channel interference when the systems are synchronized approximately. The designed signals are free from the influence of multipath signals within some delay. The filters for the designed signals can be realized as SAW devices. We assign plural quadriphase signals as M-ary signals for each user so that the information-transmission rate is increased. The property of without co-channel interference remains the same, but the multipath property becomes a little bit worse. The filters for M-ary signals can also be realized as SAW devices.

Non-destructively reading out information embedded inside real objects by using far-infrared light

This paper presents a technique that can non-destructively read out information embedded inside real objects by using far-infrared-light. We propose a technique that can protect the copyrights of digital content for homemade products using digital fabrication technologies such as those used in 3D printers. It embeds information on copyrights inside real objects produced by 3D printers by forming fine structures inside the objects as a watermark that cannot be observed from the outside. Fine structures are formed near the surface inside real objects when they are being fabricated. Information embedded inside real objects needs to be read out non-destructively. We used a technique that could non-destructively read out information from inside real objects by using far-infrared light. We conducted experiments where we structured fine cavities inside objects. The disposition of the fine domain contained valuable information. We used the flat and curved surfaces of the objects to identify them. The results obtained from the experiments demonstrated that the disposition patterns of the fine structures appeared on the surface of objects as a temperature profile when far-infrared light was irradiated on their surface. Embedded information could be read out successfully by analyzing the temperature profile images of the surface of the objects that were captured with thermography and these results demonstrated the feasibility of the technique we propose.

Copyright Protection for 3D Printing by Embedding Information Inside 3D-Printed Objects

This paper proposes a technique that can protect the copyrights of digital content for 3D printers. It embeds the copyright information inside 3D-printed objects by forming a fine structure inside the objects as a watermark. Information on copyrights is included in the digital data for a real object before data are input into the 3D printer. This paper also presents a technique that can non-destructively read out information from inside real objects from a transparent image of the object using near infrared light. We conducted experiments using polylactide resin where we structured fine domains inside the objects. The domains have higher density than other regions. The disposition of the fine domains expressed binary code depending on whether or not they were at a designated position. The results obtained from the experiments demonstrated that the image of the fine domain inside the object can be captured by the near infrared camera and binary code could be read out successfully. These results demonstrated the feasibility of our technique showing that enough information can be embedded for copyright protection.

Nondestructive Readout of Copyright Information Embedded in Objects Fabricated with 3-D Printers

We studied a technique to protect the copyrights of digital data for 3-D printers to prevent illegal products from being fabricated with 3-D printers, which has become a serious economic problem. We previously proposed a technique that could be used to check whether illegal acts had been committed by embedding copyright information inside real objects fabricated with 3-D printers by forming fine cavities inside them and nondestructively reading the information out. We demonstrated that the proposed technique was feasible in practice. We examined a new method of nondestructive readout in this study by using thermographic movie files where the binary images of individual frames were summarized to amplify the signals of the cavity patterns and demonstrated the feasibility of automatic readout with 100 % accuracy in reading out embedded information.