Shinsuke Hara

Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels

This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.

Propagation characteristics of IEEE 802.15.4 radio signal and their application for location estimation

IEEE standard 802.15.4 defines the physical (PHY) and medium access control (MAC) layers for low-cost and very low-power short-range wireless communications. One of the promising applications offered by the standard is wireless sensor networks. To begin with, this paper shows the propagation characteristics of the IEEE 802.15.4 radio signal in indoor environments such as power decay factor due to near/far effect and fading distribution. Then, the paper presents a wireless sensor network system for location estimation which utilizes only received signal strength indicator (RSSI) and discusses the location estimation performance.

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels. First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM. Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency. Finally, we propose a two-stage frequency offset compensation method.

Throughput performance of SAW-ARQ protocol with adaptive packet length in mobile packet data transmission

In a noncellular or large cell-size mobile radio communication system, log-normal shadowing as well as Rayleigh fading becomes the predominant source of system degradation. This paper proposes an efficient stop and wait automatic repeat request (SAW-ARQ) protocol with adaptive packet length to provide reliable mobile data packet transmission. The adaptive SAW-ARQ protocol controls the transmitting packet length according to the time-varying channel condition estimated with the number of ACK (acknowledgment packet) and NACK (negative-acknowledgment packet). Computer simulation results show that the proposed protocol can achieve high throughput and reduce the number of retransmission effectively for slow and fast Rayleigh fading/log-normal shadowing conditions.

A pre-FFT OFDM adaptive antenna array with Eigenvector Combining

This paper proposes a novel pre-FFT type OFDM adaptive array antenna called Eigenvector Combining. The eigenvector combining is a realization of a post-FFT type OFDM adaptive array antenna through a pre-FFT signal processing, so it can achieve excellent performance with less computational complexity and shorter training symbols. Numerical results demonstrate that the proposed eigenvector combining shows excellent bit error rate performance close to the lower bound just with two training symbols.

A novel OFDM adaptive antenna array for delayed signal and Doppler-shifted signal suppression

It is well known that OFDM scheme is robust to frequency selective fading in wireless channels. However, once delayed signals beyond the guard interval and Doppler-shifted signals are introduced in the channel, inter-subcarrier interference and inter-symbol interference give a severe degradation in the transmission performance. This paper proposes a novel OFDM adaptive antenna array which can suppress both delayed signals and Doppler-shifted signals. The proposed adaptive antenna array has a simple structure and by forcing virtual subcarrier outputs to be zero, it can steer its nulls toward incoming Doppler-shifted signals, even when they have no time delay. Computer simulation results show its excellent performance, for a case where four signals are incident on an eight-element circular array, such as one signal with no time delay, one Doppler-shifted signal with no time delay, one Doppler-shift signal with time delay within the guard interval, and one signal with time delay beyond the guard interval.

A new spatio-temporal equalization method based on estimated channel response

This paper proposes a new spatio-temporal equalization method, which simultaneously utilizes an adaptive antenna array and a decision feedback equalizer (DFE). For effective spatio-temporal equalization with less computational cost, how to split equalization functionality into spatial processing, and temporal processing is quite important. One of the answers which we have given is incoming signals with larger time delays should be cancelled at the spatial equalization part. The weights of both adaptive antenna array elements and taps of DFE are calculated only using the estimated channel impulse response, therefore, it requires no information on direction of arrival (DoA). We show the performance of the proposed system in multipath fading channels often encountered in indoor wireless environments and discuss the attainable bit error rate (BER), antenna patterns, and the computational complexity in comparison with other equalization methods such as spatial equalization and temporal equalization.

Optimum beamforming for pre-FFT OFDM adaptive antenna array

It is well known that orthogonal frequency-division multiplexing (OFDM) is robust to frequency-selective fading in wireless channels due to the exploitation of a guard interval that is inserted at the beginning of each OFDM symbol. However, once delayed signals beyond the guard interval are introduced in a channel with a large delay spread, intersymbol interference causes a severe degradation in the transmission performance. In this paper, we propose a novel pre-fast Fourier transform (FFT) OFDM adaptive antenna array, which requires only one FFT processor at a receiver, for suppressing such delayed signals. We derive the optimum weight set for beamformers based on the max- imum signal-to-noise-and-interference power ratio (Max-SNIR) and the minimum mean square error (mmse) criteria, respectively. In addition, we propose a novel mmse-criterion-based commuta- tive optimization scheme, which is more robust to the estimation error of the channel state information. Furthermore, we show the equivalence between the Max-SNIR-criterion-based scheme and the proposed commutative optimization scheme. Computer simu- lation results show its good performance even in channels where directions of arrival of arriving waves are randomly determined.

EACLE: Energy-Aware Clustering Scheme with Transmission Power Control for Sensor Networks

In this paper, we propose a new energy efficient clustering scheme with transmission power control named “EACLE” (Energy-Aware CLustering scheme with transmission power control for sEnsor networks) for wireless sensor networks, which are composed of the following three components; “EACLE clustering” is a distributed clustering method by means of transmission power control, “EACLE routing” builds a tree rooted at a sink node and sets the paths from sensor nodes taking energy saving into consideration, and “EACLE transmission timing control” changes the transmission timing with different levels of transmission power to avoid packet collisions and facilitates packet binding.With an indoor wireless channel model which we obtained from channel measurement campaigns in rooms and corridors and an energy consumption model which we obtained from a measurement of a chipset, we performed computer simulations to investigate the performance of EACLE in a realistic environment. Our simulation results indicate that EACLE outperforms a conventional scheme such as EAD (Energy-Aware Data-centric routing) in terms of communication success rate and energy consumption. Furthermore, we fully discuss the impact of transmission power and timing control on the performance of EACLE.

Performance comparison of MC-CDMA and cyclically prefixed DS-CDMA in an uplink channel [mobile radio]

This paper compares multi-carrier code division multiple access (MC-CDMA) with cyclically prefixed direct sequence CP-DS-CDMA in an uplink channel. For the CP-DS-CDMA scheme, we propose an MMSE-based multi-user detection (MUD) technique, which recovers code orthogonality among users destroyed by frequency-selective fading in the frequency domain. On the other hand, it is well known that the peak to power average ratio (PAPR) of a single carrier transmission scheme is lower than that of a multi-carrier transmission scheme. Thus, from the viewpoint of the PAPR issue, this paper studies the effect of resolution bits of the digital to analog converter (DAC) at the transmitter and the analog to digital converter (ADC) at the receiver on both schemes. Then, this paper evaluates the performance of the two schemes by computer simulations.