Hiromasa Habuchi

Design of UWB pulses based on B-splines

The paper discusses the construction of UWB pulses on the basis of B-splines under the following conditions: (i) the B-splines are time-limited piecewise polynomials; (ii) the pulses are rectangular when their order is one and they converge to band-limited functions at the limit that their order tends to infinity; (iii) an analog circuit and a fast digital filter exist for the generation of B-splines. A constrained minimization technique is proposed for designing pulses so as to comply with the FCC spectral mask and satisfy basic requirements for UWB pulses.

Proposal of a Simple Synchronization Method for CSK/SS *

In this paper, a new tracking method for Code Shift Keying Spread Spectrum (CSK/SS) is proposed. In the CSK/SS systems, since the transmitted sequences vary at every frame, synchronization is difficult. In the proposed method, a pair consists of the Manchester-coded PN sequence and the non-Manchester-coded PN sequence as the synchronizing sequence. The cross-correlation characteristic of the pair is used instead of the S-curve of delay lock loop (DLL). The receiver can track the signal timing by using the characteristic. The proposed method is applied to the external synchronization system whose structure is simple. The following performance in channel with the Additive White Gaussian Noise (AWGN) is analyzed and evaluated; (1) the tracking error (jitter) performance and (2) the bit error rate (BER) performance that takes the jitter into account. As a result, the jitter of the proposed system is better than those of the conventional DLL systems as Eb/N0 increases. The jitter of the proposed system has less degradation than those of the conventional systems, even if the number of users increases. Moreover, BER of the proposed system is similar to that of the 1Δ-DLL system and superior to that of the 2Δ-DLL system.

Theoretical Analysis of Optical Wireless CDMA with Modified Pseudo Orthogonal M-Sequence Sets

In this paper, to increase Normalized throughput of the optical wireless code-division multiple-access (CDMA) system, modified pseudo orthogonal M-sequences (MPOMS) are considered as optical pseudo-Noise (PN) code. Moreover, the bit error rate (BER) performance of the optical wireless CDMA system using multi-pulse pulse position modulation (MPPM) is also derived in the presence of the scintillation, background-Noise, avalanche photo-diode (APD) Noise, thermal Noise and signal dependence Noise. Consequently, the BER performance in consideration of Normalized throughput of the MPPM system with MPOMS is superior to that of the MPPM system with conventional pseudo orthogonal M-sequences in the single-user case and multi-user case.

A Reasonable Throughput Analysis of the CSK/SSMA Unslotted ALOHA System with Nonorthogonal Sequences *

In this paper, the throughput performance of the CSK/SSMA ALOHA system with nonorthogonal sequences which combines the ALOHA system with Code Shift Keying using nonorthogonal sequences is analyzed. In this system, the nonorthogonal sequences are constructed by concatenating Mcon orthogonal sequences. The throughput performance of the CSK/SSMA ALOHA system with nonorthogonal sequences is analyzed in consideration that the number of packets changes at intervals of one orthogonal sequence. Moreover, the throughput performance of our system with Channel Load Sensing Protocol (CLSP) is also analyzed. We also examine the influence of unreachable control signal of CLSP. Consequently, it is found that the throughput performance of our system decreases significantly by this analysis. It is also found that the throughput performance of our system improves greatly by using CLSP. However, the unreachable control signal affects the throughput performance of this system, seriously.

Theoretical analysis of M-CSK/CDMA system in optical wireless channel

In this paper, M-CSK with extended prime code sequence to enhance a data transmission rate of CSK is considered. Moreover, the bit error rate (BER) performance of M-CSK/CDMA is evaluated by taking into account scintillation, background-noise, avalanche photo-diode (APD) noise, thermal noise, and signal dependence noise through theoretical analysis. It is shown that the data transmission rate of the M-CSK system is better than that of the CSK system using extended prime code sequences. However, the BER performance of the M-CSK system is degraded by increasing the number of selected extended prime code sequences.

Design of UWB Pulses in Terms of B-Splines

The present paper discusses a new construction of UWB pulses within the framework of soft-spectrum adaptation. The employed basis functions are B-splines having the following properties: (i) The B-splines are time-limited piecewise polynomials. (ii) The first-order B-splines are rectangular pulses and they converge band-limited functions at the limit that their order tends to infinity. (iii) There are an analog circuit and a fast digital filter for the generation of B-splines. Simple application of Gram-Schmidt orthonormalization process to the shifted B-splines results in a few basic pulses, which are well time-limited and have a broad band width, but do not comply with the FCC spectral mask. A constrained approximation technique is proposed for adaptively designing pulses so that they approximate target frequency characteristics. At the cost of using eleven shifted B-splines, an example set of four pulses comforting the FCC spectral mask is obtained.

Performance evaluation of the M-ary/SSMA ALOHA system with CLSP

The M-ary spread spectrum multiple access (M-ary/SSMA) ALOHA system applying channel load sensing protocol (CLSP) as the traffic control is evaluated by a theoretical analysis. In particular, the throughput performance and the delay property of the M-ary/SSMA slotted ALOHA system with CLSP under additive white Gaussian noise are analyzed. Moreover, the M-ary/SSMA slotted ALOHA system with CLSP is compared with the conventional direct sequence spread spectrum multiple access (DS/SSMA) slotted ALOHA system with CLSP. As a result, it is shown that the CLSP improves the performance of the M-ary/SSMA slotted ALOHA system. The M-ary/SSMA slotted ALOHA system with CLSP is superior to the conventional DS/SSMA slotted ALOHA system with CLSP.

Optical-wireless enhanced code-shift-keying with IM/DD

In this paper, the extended pseudo orthogonal M-sequence is proposed for the optical-wireless code-shift-keying (CSK) system. The extended pseudo orthogonal M-sequence is a new optical pseudo-noise (PN) code which consists of the modified pseudo orthogonal M-sequence sets (MPOMS) and the bi-orthogonal code. The performance of the CSK systems is enhanced by increasing the number of the optical PN codes. As the conventional optical PN code, the bi-orthogonal code and the pseudo-orthogonal extended prime code set can generate the number of the optical PN codes same as the code length. The extended pseudo orthogonal M-sequence can achieve the performance enhancement of the CSK systems because of its generation of the large number of the codes per the code length. The CSK system using the extended pseudo orthogonal M-sequence has better performance than the CSK systems using the conventional PN code.

Construction of hierarchical optical broadcasting systems for intelligent transport system

The local broadcast systems, that transmit both the wide-area information and the local-area information, are proposed. A nearby user, which is near to the broadcasting station, demodulates together the wide-area information and local-area information. Even if a distant user, which is far to the station, does not receive the local-area information, it is expected that he receives wide-area information only. In the proposed systems, the broadcast information is hierarchized by combining the two modulation scheme. In particular, the two proposed systems are described; the ASK-CSK system which combines amplitude-shift-keying(ASK) with code-shift-keying(CSK) and the CNK-CSK system which combines code-number-keying(CNK) with CSK. The CNK-CSK system is superior to the ASK-CSK system.

Effect of unequal transmission power allocation in turbo-coded optical wireless communication system

In this paper, the turbo coded on-off keying with unequal transmission power allocation (UTPA) in optical wireless communications is evaluated. The turbo coded with UTPA allocates the different power on the message bit and parity bits at the turbo encoder outputs with total transmission power fixed. In the additive white Gaussian noise (AWGN) channel, the turbo coded with UTPA can improve the frame error rate (FER) performance. However, in the optical wireless communications, the effect of UTPA is not investigated. In the paper, the FER performance of the turbo coded on-off keying with UTPA is analyzed in the presence an avalanche photodiode (APD) noise, thermal noise, scintillation, and signal dependence noise. Consequently, the FER performance of the turbo coded on-off keying with UTPA is better than that of the traditional turbo coded on-off keying. It is found that there is an optimum power ratio. When the average received laser power is −47.9[dBm] and there is not scintillation, the optimum power ratio, denoted R, is 1.7. The turbo coded on-off keying with UTPA system with R=1.7 is superior to the conventional system with R=1.0 significantly. It is found that the performance improvement of the turbo coded on-off keying with UTPA becomes small when increasing the variance of scintillation.