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WIDEBAND DS - CDMA FOR 3RD GENERATION MOBILE COMMUNICATION SYSTEMS
Nobuo Nakajima,Fumiyuki Adachi 에스케이텔레콤 (주) 1997 Telecommunications Review Vol.7 No.2
This paper describes the features and technology of the wideband DS-CDMA system for next generation mobile communication system. The wider the bandwidth, the more the capacity increases. In addition, wide range of data rates from as low as about 4kbps to 2 Mbps can be accommodated by the wideband system, In order to flexibly offer data services with a variety of rates multi-rate codes are employed and four different bandwidths of 1.25, 5, 10, and 20 Mcps are adopted. The system operates in an inter cell asynchronous mode to allow flexible and continuous system deployment from outdoors into indoors. New technologies are developed to enhance the capacity and quality of the wideband DS-CDMA. They are the interference canceler and adaptive antenna array. Exensive measurements and evaluations of a 2-㎓ band DS-CDMA system were carried out under real multipath fading environments.
Application of Rate Compatible Punctured Turbo Coded Hybrid ARQ to MC-CDMA Mobile Radio
Deepshikha Garg,Fumiyuki Adachi 한국전자통신연구원 2004 ETRI Journal Vol.26 No.5
MC-CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC-CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC-CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC-CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space-time transmit diversity. In addition, the comparison of RCPT HARQ MC-CDMA, orthogonal frequency division multiplexing, and DS-CDMA shows that under similar conditions the throughput of MC-CDMA is the best in a frequency selective fading channel.
BER Performance of OFDM Combined with TDM Using Frequency-Domain Equalization
Gacanin, Haris,Takaoka, Shinsuke,Adachi, Fumiyuki The Korea Institute of Information and Commucation 2007 Journal of communications and networks Vol.9 No.1
Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM), in this paper called OFDM/TDM, can overcome the high peak-to-average-power ratio (PAPR) problem of the conventional OFDM and improve the robustness against long time delays. In this paper, the bit error rate (BER) performance of OFDM/FDM in a frequency-selective Rayleigh fading. channel is evaluated by computer simulation. It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays. It is also shown that the performance of OFDM/FDM designed to reduce the PAPR can bridge the conventional OFDM and single-carrier (SC) transmission by changing the design parameter.
Sojourn Time-Based Velocity Estimation in Small Cell Poisson Networks
Merwaday, Arvind,Guvenc, Ismail,Saad, Walid,Mehbodniya, Abolfazl,Adachi, Fumiyuki IEEE 2016 IEEE communications letters Vol.20 No.2
<P>Due to the increasing density of small cells, mobility management in heterogeneous networks has become a challenging task. One key challenge facing the development of advanced mobility management techniques is the accurate estimation of the users' velocity. One simple way to estimate a user's velocity is via the use of sojourn time samples. In this letter, the Cramer-Rao lower bound (CRLB) for the sojourn time-based velocity estimation is analyzed. Stochastic geometry is used for the spatial modeling of small cells, and the CRLB is derived using the tools from estimation theory. An asymptotically unbiased velocity estimator is also derived. Our analysis shows that the sojourn time-based velocity estimation exhibit a lower CRLB compared to the CRLB of classical velocity estimation using handover count.</P>
Decentralized Energy Allocation for Wireless Networks With Renewable Energy Powered Base Stations
Dapeng Li,Saad, Walid,Guvenc, Ismail,Mehbodniya, Abolfazl,Adachi, Fumiyuki Institute of Electrical and Electronics Engineers 2015 IEEE Transactions on Communications Vol. No.
<P>In this paper, a green wireless communication system in which base stations are powered by renewable energy sources is considered. This system consists of a capacity-constrained renewable power supplier (RPS) and a base station (BS) that faces a predictable random connection demand from mobile user equipments (UEs). In this model, the BS, which is powered via a combination of a renewable power source and the conventional electric grid, seeks to specify the renewable power inventory policy, i.e., the power storage level. On the other hand, the RPS must strategically choose the energy amount that is supplied to the BS. An M/M/1 make-to-stock queuing model is proposed to investigate the decentralized decisions when the two parties optimize their individual costs in a noncooperative manner. The problem is formulated as a noncooperative game whose Nash equilibrium (NE) strategies are characterized to identify the causes of inefficiency in the decentralized operation. A set of simple linear contracts are introduced to coordinate the system so as to achieve an optimal system performance. The proposed approach is then extended to a setting with one monopolistic RPS and N BSs that are privately informed of their optimal energy inventory levels. In this scenario, we show that the widely used proportional allocation mechanism is no longer socially optimal. To make the BSs truthfully report their energy demand, an incentive compatible (IC) mechanism is proposed for our model. Simulation results show that using the green energy can present significant traditional energy savings for the BS when the connection demand is not heavy. Moreover, the proposed scheme provides valuable energy cost savings by allowing the BSs to smartly use a combination of renewable and traditional energy, even when the BS has a heavy traffic of connections. Also, the results show that performance of the proposed IC mechanism will be close to the social optimal when the green energy production capacity increases.</P>