Jumpei Taketsugu

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.

Saturation throughput of IEEE 802.11 using carrier sense mechanism in backoff intervals

Most modifications on IEEE 802.11 DCF (distributed coordination function) so far have focused on updating of the CW (Contention Window) value and the carrier sense mechanism during a backoff interval is not considered. In this paper, we propose two novel schemes for DCF, which effectively utilize the carrier sense mechanism during backoff interval. The proposed schemes can be applied to any conventional ones, such as DCF and SD (slow CW decrease). Saturation throughput of the proposed schemes is analyzed by means of Bianchis Markovian model. Computer simulation validates the accuracy of the analysis. Numerical results based on IEEE 802.11b show that up to 10-20% improvement of saturation throughput can be achieved by combining the proposed schemes with DCF or SD.

A Modification Strategy of Maximum Likelihood Method for Location Estimation Based on Received Signal Strength in Sensor Networks

This paper investigates a scheme to improve a location estimation method for higher estimation accuracy in sensor networks. For the location estimation method, we focus on the maximum likelihood method based on the measurements of received signal strength and its known probability distribution. Using some statistical properties of the estimate obtained by the maximum likelihood method in a simplified situation, we propose a modification of likelihood function in order to improve the estimation accuracy for arbitrary situation. However, since the proposed scheme is derived under a special assumption for the simplification, we should examine the impact of the proposed scheme in more general situations by numerical simulation. From the simulation results, we show the effectiveness of the proposed modification especially in the cases of small number of samples (namely, the measurements of received signal strength) and the channel model with exponential distribution.

Impact of transmission power control on appearance of traffic long-range dependence in DS-CDMA cellular system

Long-range dependence exists in the traffic fluctuations of wired communications systems, which has a bad influence on system performance. On the other hand, interdependence among system components (i.e., interference among users) can be a cause of long-range dependence in cellular system traffic. Moreover, the influence of the interference depends on the transmission power control scheme adopted in the cellular system. From the viewpoint of the long-range dependence caused by interdependence among system components, we analyze the influence of transmission power control schemes on the traffic long-range dependence in a DS-CDMA cellular system by computer simulation. From the simulation results, it is found that the long-range dependence is caused by some transmission power control schemes, and we investigate the cause of the long-range dependence by comparing several power control schemes.

Another cause of long-range time dependence in cellular system traffic

This paper discusses long-range dependence (self-similarity) in cellular network traffic, which is a phenomenon of complex systems. Assuming three kinds of cellular systems such as FCA-TDMA, DCA-TDMA and CDMA systems, we analyze the traffic intensity of the three systems by computer simulation. Our simulation results show that long-range dependence appears in DCA-TDMA system, and its cause is quite different from that of wired networks. Then, we propose a method for suppressing the long-range dependence which has a bad influence on the system performance, and show that the proposed method can effectively suppress the long-range dependence.

On stability of slotted-ALOHA systems with delay constraints and geometric transmission probability

It has been well-known that slotted ALOHA systems exhibit unfavorable bistable behavior, since 1970s. It was proved that we can eliminate bistable region by limiting the number of allowable transmission attempts per packet to eight or less. In this paper, we investigate bistable behavior of slotted ALOHA systems with delay constraints and geometric transmission probability in terms of the catastrophe theory. A lifetime of a packet is confined within D time-slots and packet transmission probability is determined based on geometric series depending on the number of elapsed time-slots after its generation. Let pd = pαd be the transmission probability in a slot for a packet with d-time-slot expiration after generation, d = 0, 1, …, D − 1. Then, we numerically indicate that bistable region may exist, if the sum p0 + p1 + … + pD−1 is greater than approximately 8.30, and that the system can operate with a unique stable equilibrium point, if the sum is less than approximately 8.30.

Application of random relaying of partitioned MDS codeword block to persistent relay CSMA over random error channels

We propose an incorporation of random relaying of MDS codeword blocks (RP-MDS), which has been proposed for multi-hop cooperative relay networks, to persistent relay CSMA (PRCSMA) over noisy channels. The proposed protocol elaborately employs the powerful error-correcting capability of MDS codes into cooperative communication systems and introduces the incremental redundancy concept to PRCSMA. A destination node can reinforce an error-correcting capability when it receives a new frame. The performance of the proposed protocol is compared to PRCSMA by means of computer simulation. Numerical results indicate that the proposed protocol can significantly reduce the duration of the cooperation phase and provide robust and stable performance against channel impairments.

A study on validity of random frame error assumption from the viewpoint of TCP performance in DS-CDMA cellular system

Many reports have investigated TCP performance over wireless links, where a high and time-invariant frame error rate is assumed for cellular systems. However, the frame error rate is temporally and geographically changeable by fading and interference in cellular systems. On the other hand, SINR-based transmission power control, which is employed for the randomization of frame errors in DS-CDMA cellular systems, can not always work properly depending on the control parameters or the channel characteristics. In this paper, we investigate the TCP performance over the wireless links in a DS-CDMA cellular system by computer simulation. From the simulation results, it has been found that the assumption of random frame error is valid only for a part of the TCP performance even in the system with an SINR-based transmission power control scheme.

Comparison between random frame error and SINR-based transmission power control in DS-CDMA cellular system from the viewpoint of TCP performance

Many reports have investigated TCP performance over wireless links, where a high and time-invariant frame error rate is assumed for the wireless link characteristic. However, the frame error rate is temporally and geographically changeable by fading and interference in cellular systems. On the other hand, SINR-based transmission power control, which is employed for randomization of the frame errors in DS-CDMA cellular systems, cannot always work properly depending on the control parameters or the channel characteristics. In this paper, we investigate TCP performance over wireless links in a DS-CDMA cellular system by computer simulation. From the simulation results, it has been found that the assumption of random frame error is valid only for a limited part of the TCP performance even in the system with an SINR-based transmission power control scheme.

Another Cause of Long-Range Time Dependence

Cellular communicationnetworks satisfy the very conditions required to be complex adaptivesystems,so it is expected thatinteresting phenomenaproper to themcan be observed in their behaviors.In this paper,assuming three kinds of cellular networkssuch as CDMA, FCA-TDMA and DCA-TDMA networks,we examine their traffic intensity dynamicsby computer simulation.We show thatDCA-TDMA network has a hidden cause to producea long-range time dependence in its traffic intensity dynamics,so self-similarity appears there,regardless of property of traffic source andservice generation rate.Furthermore,we reveal that the cause is a strong interdependency amongcells through inter-cell interference.