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DOI： 10.1587/transcom.E98.B.1640

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

DOI： 10.1109/VETECF.2005.1558154

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DOI： 10.1587/transcom.E96.B.3163

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DOI： 10.1587/transcom.E96.B.2112

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DOI： 10.1587/transcom.E92.B.1786

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DOI： 10.1109/VETECF.2009.5378922

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DOI： 10.1093/ietfec/e91-a.7.1589

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DOI： 10.1093/ictcom/e91-b.5.1568

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DOI： 10.1109/VETECF.2008.399

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DOI： 10.1002/wem.507

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DOI： 10.1109/VTCF.2006.522

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

DOI： 10.1109/vetecs.2006.1682917

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

DOI： 10.1093/ietcom/E88-B.1.1

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

DOI： 10.1109/vetecf.2003.1286156

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CiNii Research

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In order to realize high speed data transmissions in mobile communication networks, there exists a transmit power problem. To reduce the transmit power, while increasing the transmission data rate, authors proposed a wireless multi-hop virtual cellular network (VCN). The authors have been studied on routing and channel allocation schemes in multi-hop VCN. And the relationship among throughput, channel capacity, and transmission power in multi-hop VCN is also evaluated. In this paper, we introduce the multi-hop VCN for high speed wireless network.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

A 2-hop Virtual Cellular Network (VCN) is a promising network architecture for extending the coverage of a base station without increasing the transmit power in high speed data transmissions. In this paper an efficient routing with subcarrier allocation for multi-route parallel packet transmission in OFDMA 2-hop VCN, in order to increase the expected throughput, has been studied. Moreover, throughput performance of uneven packet transmission protocol in which more packets are sent through routes with better channel conditions is evaluated by computer simulation. It is shown that better throughput performance can be achieved in the multi-route parallel packet transmission than in the conventional single-route parallel packet transmission and that uneven packet transmission protocol further improves throughput performance at higher transmission rates.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Recently, we proposed a random transmit power control (TPC) to increase the uplink capacity of Direct Spread Code Division Multiple Access (DS-CDMA) wireless packet access using Rake combining. Furthermore, we evaluated the combined effect of random TPC and inter-path interference (IPI) cancellation and showed that a significant throughput improvement can be achieved if the IPI can be sufficiently suppressed. It is known that frequency-domain equalization (FDE) is a well-known technique to suppress the IPI. In this paper, we derive an expression for the received signal-to-interference plus noise power ratio (SINR) for a DS-CDMA wireless packet access using FDE and random TPC and evaluate its system throughput by numerical computation. We also compare the system throughput when using Rake combining with that using FDE to discuss the IPI suppression effect of FDE.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In OFDMA cellular network, if all the sub-carriers are used in all cells, the transmission performance of the user around the cell edge may be degraded due to the interference from the adjacent cells. If all the sub-carriers are divided into several sub-carrier groups, the sub-carrier group is allocated adaptively in each cell and the allocated sub-carriers are arranged to each user using a scheduling algorithm, the degradation of the transmission performance of the user around the cell edge may be improved since it can avoid the large interference from the adjacent cells. In this paper, OFDMA cellular network that has the above-mentioned feature is introduced, and the channel capacity is evaluated by the computer simulation.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

A multi-hop virtual cellular network (VCN) was proposed for future mobile communication systems. We have studied the multi-hop channel allocation for direct sequence code division multiple access (DS-CDMA) VCN. In DS-CDMA, although the same channel can be reused at different links in a VC by allocating the different spreading codes, a strong interference may be received from the adjacent wireless port. In this paper, we apply orthogonal frequency division multiple access (OFDMA) to VCN. In OFDMA, if the different subcarriers are allocated, interference from adjacent wireless port can be avoided. We study channel configuration methods for the downlink 2-hop OFDMA VCN. We evaluate, by numerical computation method, the Shannon's channel capacity when the block, equidistance and adaptive channel configuration methods are used. We compare 2-hop VCN and 1-hop CN.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Recently, we proposed a random transmit power control (TPC) and showed that it can increase the uplink capacity of DS-CDMA packet mobile communications by computer simulation. However, to the best of our knowledge, theoretical analysis of the effect of the random TPC to the throughput on DS-CDMA packet mobile communications has not been done yet. In this paper, we derive the numerical expression of the average packet error rate and system throughput. We also derive the optimal value of the fluctuation probability which is an important parameter of random TPC. The Monte Carlo numerical computation is also done to compare with the theoretically evaluated system throughput of DS-CDMA packet mobile communications using random TPC.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In the next mobile communication systems, high speed and high quality data transmission is demanded. In the high speed data transmission, throughput degrades seriously due to large inter-path interference (IPI). Recently, we proposed a random transmit power control (TPC) to increase the uplink capacity of DS-CDMA packet mobile communications. In this paper, we consider the application of IPI cancellation in addition to the random TPC. We evaluate, by computer simulation, the combined effect of IPI cancellation and random TPC on the uplink throughput of DS-CDMA packet mobile communications.

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DOI： 10.1093/ietcom/e90-b.4.918

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DOI： 10.1093/ietcom/e90-b.4.904

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In future mobile communication systems, there will be a big need to increase the transmit power. However, as the transmit power is limited, keeping the same transmit power will lead to decrease in the coverage area of the present cellular system. In order to overcome this problem, a multi-hop virtual cellular network (VCN) was proposed. In VCN, the coverage area can be extended using multi-hop communication technique, and the blocking probability can be reduced compared to the single hop conventional cellular network. In this paper, we focus on the 2 hop VCN and evaluate its blocking probability using computer simulation. We propose channel assignment using maxSINR algorithm and make comparison with when using channel segregation algorithm.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

There have been strong demands for higher speed data transmissions in mobile communications. To reduce the peak transmit power while increasing the data transmission rates, authors proposed a wireless multi-hop virtual cellular network (VCN). In order to shift from an existing cellular system easily, the number of hops may be limited to 2. The throughput performance may be degraded compared to the conventional single hop cellular network, since the delay time increases in the multi hop communication. ARQ is indispensable in packet transmission. In this paper, the throughput performance of 2-hop VCN with stop-and-wait (SW) or selective repeat (SR) ARQ is theoretically evaluated and compared to the conventional single hop case.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

A wireless multi-hop virtual cellular network (VCN) was recently proposed to avoid the large peak transmit power, resulting from the high speed data transmissions expected in next generation mobile communication systems. In a multi-hop VCN, a central port (CP) which is a gateway to the core network, communicates with a mobile terminal (MT) via wireless ports (WPs) in the downlink. In this paper, 2-hop VCN, which is a special case the of multi-hop VCN where a CP communicates with MT directly or via one WP using 2 hops only, is proposed. The impact of the distribution of WPs on the outage probability is evaluated by numerical analysis and computer simulation.

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DOI： 10.1109/IWAT.2007.370115

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DOI： 10.1093/ietcom/e89-b.12.3483

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DOI： 10.1093/ietfec/e89-a.7.1875

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A multi-hop virtual cellular network (VCN) was proposed for future mobile communication systems. In VCN, there are two methods of channel assignment; the pre-assignment and on-demand channel assignment. In this paper we will give a simple comparison of the two methods and give a reason why we will focus our research on the on-demand channel assignment from now-on. In a multi-hop VCN using on-demand channel assignment, increasing the number of hops leads to a less transmit power of the multi-hop links and hence to a decreased interference to other users, this can decrease the call blocking probability. On the other hand, increasing the number of the call links might increase the blocking probability of this call. In this paper, we give an analysis about this tradeoff and show the impact of the number of hops on the blocking probability of a DS-CDMA multi-hop VCN. Simulation results are presented to show that there is an optimum value of number of hops depending on some network conditions.

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A multi-hop virtual cellular network (VCN) was proposed for future mobile communication systems. In VCN, the transmitted signal from a mobile terminal is relayed via multi-hop links to the central port, which is a gateway to the core network. In the conventional multi-hop VCN, a call is blocked when there is no channel available at one link over the multi-hop route. In this paper, we propose a relay skipping method to avoid the call blocking in a DS-CDMA VCN. Computer simulation is conducted to evaluate the impact of the proposed method on the blocking probability of the multi-hop VCN and make comparison with the present cellular network as well.

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Adaptive antenna array is attractive for uplink signal transmission in mobile communication systems since it can suppress the multiaccess interference. Adaptive antenna array in OFDM systems is classified into Pre- and Post-FFT type. It is well known that the Pre-FFT type achieves faster weight convergence than Post-FFT type because Pre-FFT type can update weight at each received sampling. On the other hand, we showed that frequency-domain updating also could achieve a fast weight convergence so that it could update weight the number of subcarriers times per OFDM symbol under ideal channel estimation. However, this proposal needs channel state information for reference signal and channel estimation error may degree the BER performance. In this paper, we show by computer simulation that a fast weight convergence can be achieved and a good tracking ability against fading can be obtained using delay time-domain channel estimation.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

W-CDMA receiver with adaptive 4-element array antenna is developed. The adaptive algorithm is programmed and loaded in DSP which can be changed for the investigation of effects of various adaptive algorithms. The effects of RF circuit, adaptive algorithm and array antenna configuration on the performance of W-CDMA receiving system without fading are investigated.

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DOI： 10.1093/ietcom/e88-b.9.3643

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DOI： 10.1093/ietcom.e88-b.6.2525

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In DS-CDMA, all users can share the same frequency band. Since large other-cell interference is produced, site diversity must be used. If the available frequency bandwidth is divided into several narrow frequency bands and each user transmits a signal using one of divided frequency bands, the interference from adjacent cells can be avoided. In this paper, we propose a DS-CDMA slotted ALOHA using frequency-band division and random transmit power control (TPC). Its link capacity and throughput are evaluated by computer simulation to show that the use of the frequency-band division and random TPC can increase the throughput and link capacity.

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DOI： 10.1093/ietcom/e88-b.5.2202

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DOI： 10.1093/ietcom/e88-b.4.1613

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In high-speed mobile communication, the transmission performance is degraded by frequency selective fading channel, but in DS-CDMA it can be improved by employing the Rake receiver. In the reverse link of DS-CDMA, transmit power control (TPC) is an indispensable technique to mitigate the near-far problem. Independent shadowing losses are often assumed for evaluating the link capacity of DS-CDMA cellular systems. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and interfering signals. In this paper, we investigate how the shadowing correlation impacts the reverse-link capacity in DS-CDMA cellular system, by computer simulation.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

In virtual cellular network (VCN), proposed for high-speed packet mobile communications, the signal transmitted from a mobile terminal is received by wireless ports distributed in each virtual cell and relayed to the central port that acts as a gateway to the core network. In this paper, multi-hop maximal ratio combining (MHMRC) diversity is presented for the VCN to reduce the transmit power while achieving the required communication QoS. The transmit power efficiency is evaluated by computer simulation for a DS-CDMA VCN.

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DOI： 10.1093/ietcom/e88-b.4.1613

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DOI： 10.1093/ietcom/e88-b.6.2525

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In DS-CDMA cellular communications systems, the single frequency reuse is utilized and hence large co-channel interference is produced. Recently, authors proposed to divide the available wide frequency band into several narrow frequency bands and to assign the different frequency bands to adjacent cells using channel segregation algorithm, so as to avoid the large other cell interference. In conventional DS-CDMA cellular systems, the soft hand-off can be applied to increase the link capacity (this is only possible when the single frequency reuse is utilized). In this paper, we compare by computer simulation the link capacity of DS-CDMA using band division and channel segregation algorithm and that of conventional DS-CDMA using soft hand-off.

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In this paper, the theoretical analysis of system-throughput and user-throughput of slotted ALOHA DS-CDMA with random TPC is presented and the impact of random TPC parameters on their relationship is discussed. The link capacity is defined as the number of maximum users accommodated in the system while keeping the user-throughput above a prescribed value. It is found that the link capacity may not necessarily be maximized when the system-throughput is maximized.

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In DS-CDMA cellular communications systems, the single frequency reuse is utilized and hence large co-channel interference is received from other cells. If the single frequency reuse is not utilized to reduce the other-cell interference, we will face the frequency allocation problem, similar to FDMA systems. In this paper, we divide the available wide frequency band into several narrow frequency bands and try to assign the different frequency bands to adjacent cells so as to avoid the large other cell interference. For the assignment of the frequency bands, we propose to apply the channel segregation algorithm. We evaluate the link capacity by computer simulation to show that the link capacity can be increased by using band division and channel segregation algorithm.

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In this paper, it is theoretically shown that the optimal solution to maximize the DS-CDMA forward link capacity under the condition of constant total transmit power is to transmit only from the best base station (BS) that has the maximum channel gain (this is called site selection diversity transmit (SSDT)). This theoretical analysis is confirmed by the Monte-Carlo computer simulation of an instantaneous SSDT which is based on instantaneous channel gain. In addition we also consider the case of average power based SSDT to study the difference of these two types of SSDT and their effects on forward link capacity.

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It is known that in wireless packet communications the so called capture effect can be expected if the received signal is given certain power variations. Previously we have proposed a random TPC method. In this method, since received signal power variations are intentionally given in order to obtain capture effect, the link capacity is much larger than that of the conventional fast and slow TPC schemes irrespective of the number of propagation paths. In this paper, the link capacity of DS-CDMA/TDD packet cellular system with random TPC is evaluated by computer simulation and the impacts of various propagation parameters are discussed. The results show that the proposed random TPC scheme provides larger link capacity than the conventional fast and slow TPC schemes under any propagation condition.

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In DS-CDMA packet mobile communications, slow transmit power control (TPC) was found to provide a link capacity larger than fast TPC. This is because, with slow TPC, the received signal power variations due to fading remain intact and this results in a larger capture effect. This paper proposes a new fast TPC that changes TPC target randomly in order to obtain the capture effect. It is confirmed by computer simulation that proposed TPC achieves larger link capacity than conventional slow TPC.

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Independent shadowing losses are often assumed for computing the frequency reuse distance in a cellular system. For high mobile antenna heights, such an assumption is reasonable. However, shadowing losses may be partially correlated for low antenna heights, since the obstacles surrounding a mobile station can block similarly the desired signal and interfering signal. This paper investigates, by computer simulation, how the shadowing correlation impacts the frequency reuse distance in a power controlled FDMA cellular system.

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In this paper, we study DS-CDMA delay transmit diversity that transmits the time-delayed versions of the same signal from weighted multiple antennas in a frequency selective fading environment. At a receiver, multiple receive antennas are used and the received delayed signals are coherently combined by Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) is theoretically derived to show that the optimum solution is to transmit only from the best antenna that has the maximum equivalent channel gain after Rake combining. The improvement of the BER performance from conventional delay transmit diversity is theoretically analyzed and confirmed by computer simulations. The combined effect of transmit diversity and transmit power control (TPC) is also evaluated.

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It is known that there exists a so-called capture effect in the packet mobile communication; that is, a packet with large receiving power can be correctly received even when the packet collision has occurred. In the DS-CDMA packet mobile communication, the link capacity is decreased by the near-far problem and multi-path fading. Therefore, it is necessary to suppress the resulting fluctuation in the receiving power. The effective solution techniques to solve this problem are the transmit power control (TPC) and Rake combining. However, there is a tradeoff between the suppression of receiving power fluctuation and the capture effect. This paper presents an evaluation of the effect of TPC and Rake combing for the link capacity by computer simulation. The result has shown that in the slow TPC there are an optimum number of paths that maximize the link capacity which is larger than that in the fast TPC. The reason behind this is as follows. In the fast TPC no capture effect is obtained for a constant receiving power whereas in the slow TPC there is a certain receiving power fluctuation that yields the capture effect. This is because the multi-path fading fluctuation has not been perfectly suppressed. In addition, it is found that the link capacity does not depend on the number of paths both in the fast TPC and without TPC; moreover the link capacity without TPC is apparently smaller than those with the fast and slow TPC.

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For adaptive antenna array, the antenna weights are updated adaptively so that mean square error between a reference and an array output can be minimized. In mobile communications, the propagation channel state varies rapidly because of multipath fading. Therefore, the tracking ability of adaptive algorithm to the fading is an important issue. In the case of normalized LMS algorithm used in the adaptive antenna array, the choice of reference signal determines the tracking ability. In this paper, we consider three reference signals for the normalized LMS algorithm: (a)fixed pilot, (b)instant pilot of array output, and (c)mean pilot of array output. We evaluate the convergence property, the tracking performance, and the BPSK transmission performance when the above three reference signals are used in the adaptive algorithm.

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In this paper, we study multi-channel transmit diversity, with multiple transmit antennas and single receive antenna, for DS-CDMA. A transit diversity we consider is to transmit the weighted and time-delayed versions of the same signal from multiple antennas. At the receiver, Rake reception is performed using a single receive antenna. The optimum antenna weights for maximizing the received SNR, thus minimizing the average bit error rate, is theoretically derived to show the optimum weight is to transmit from one antenna that have the maximum channel gain. This transmit diversity is equivalent to selection combining (SC) receive diversity. The combined effect of transmit diversity and transmit power control (TPC) is also theoretically analyzed. The BER performance with SC transmit diversity in a frequency non-selective Rayleigh fading environment is evaluated by computer simulations.

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In this paper, the bit error rate (BER) of the OFDM-CDMA down-link in the presence of pure impulsive interference with antenna diversity in a frequency selective fading channel is theoretically derived and is numerically obtained by a Monte-Carlo integration method. Minimum mean square error combining (MMSEC) and orthogonal restoring combining (ORC) are considered for frequency-domain equalization. It is found that the error floor due to impulsive interference becomes larger as the area of impulse increases, and that the antenna diversity reception does not help to reduce the error floor. Almost no difference is observed between the MMSEC and the ORC with respect to the impulsive interference influence on the BER performance. Furthermore, the impulsive interference impacts ODFM-CDMA transmission similarly to DS-CDMA transmission.

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DOI： 10.1109/25.938566

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In this paper, we propose a new multi-channel Polling/CSMA protocols for wireless multi-hop networks and evaluate its perforamance by computer simulation. As proposed protocol changes its access method by traffic wariance autonomously, proposed protocol is suitable for multi-hop wireless networks where traffic is inclined, and can guarantee QoS from End-to-End. Comuputer simulation shows that proposed MAC protocol improves a throughput by about 60% compared to the conventional DCF, and lower delay and blocking rate are achived,

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DOI： 10.1109/ISCAS.2001.922375

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DOI： 10.1109/25.820708

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DOI： 10.1109/VETECF.1999.797152

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In DS-CDMA, Transmission Power Control performance is closely related to received Power distribution characteristics. It is found that the total reseived power distribution is concemed with the product of the rms delay spread and chip rate for specific distribution model. We investigate the relation between the total received power distribution and the product in any propagation model by means of a theoretical analysis. As a result, we found that the larger the product becomes the smaller the fluctuation level of the total received power becomes, and that if the product is larger than the specific value, the fluctuation level of the total received power becomes minimum.

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Language：English  

Web of Science

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CiNii Research

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

researchmap

CiNii Research

researchmap

researchmap

CiNii Research

researchmap

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

researchmap

researchmap

researchmap

Language：English  

Web of Science

researchmap

CiNii Research

researchmap

researchmap

CiNii Research

researchmap

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Web of Science

researchmap

Language：English  

DOI： 10.1049/el:19890847

Web of Science

CiNii Research

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3250199

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特開平5-22213

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特開平4-177934

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3208650

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3208643

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3223403

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特開平6-334575

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特開平6-252801

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特開平6-132880

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特開平5-37490

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特開平5-22211

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特開平4-10723

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3209629

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3343103

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3312718

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3337109

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3210949

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3199341

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3180651

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3163528

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3159235

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3154462

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3033860

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2977107

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2877243

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28686105

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特開2001-320224

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特開2001-320217

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特開2001-309442

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特開2002-077976

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特開2002-064546

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特開2002-051002

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特開2001-352578

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特開2001-345749

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特開2001-343244

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特開2001-320218

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特開2002-247088

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特開2002-124953

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特開平11-239080

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特開平8-223640

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特開平6-335050

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特開平8-223113

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特開平8-172390

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特開平7-212830

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特開平7-50612

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特開平6-343067

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特開平6-343066

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特開平6-338870

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特開平6-334598

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特開平10-224293

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特開平9-116946

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特開2001-237764

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特開2001-237761

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特開2001-237875

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特開2000-69037

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特開2000-13289

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特開2000-13268

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特開平11-252205

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超高速無線ネットワークのためのマルチホップバーチャルセルラネットワークに関する研究

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超高速無線ネットワークを構築するためのマルチホップバーチャルセルラネットワークに関する研究

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Country/Region：Japan

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Country/Region：Japan

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