• Title/Summary/Keyword: Bit-loading Problem

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Exact Algorithms of Transforming Continuous Solutions into Discrete Ones for Bit Loading Problems in Multicarrier Systems

  • Chung, Yong-Joo;Kim, Hu-Gon
    • Management Science and Financial Engineering
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    • v.16 no.3
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    • pp.71-84
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    • 2010
  • In this study, we present the exact methods of transforming the continuous solutions into the discrete ones for two types of bit-loading problem, marginal adaptive (MA) and rate adaptive (RA) problem, in multicarrier communication systems. While the computational complexity of existing solution methods for discrete optimal solutions depends on the number of bits to be assigned (R), the proposed method determined by the number of subcarriers (N), making ours be more efficient in most cases where R is much larger than N. Furthermore our methods have some strength of their simpler form to make a practical use.

An Efficient Bit Loading Algorithm for OFDM-based Wireless LAN systems and Hardware Architecture Design (OFDM 기반의 무선 LAN 시스템을 위한 효율적인 비트 로딩 알고리즘 및 하드웨어 구조 설계)

  • 강희윤;손병직;정윤호;김근회;김재석
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.41 no.5
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    • pp.153-160
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    • 2004
  • In this paper, we propose an efficient bit loading algorithm for IEEE 802.11a wireless LAN systems. While a conventional bit loading algorithm uses the SNR value of each subcarrier, it is very difficult to estimate the exact SNR value in wireless LAN systems due to randomness of AWGN. Therefore, in order to solve this problem our proposed algorithm uses the channel frequency response instead of the SNR of each subcarrier. Through simulation results, we can obtain the performance gain of 3.5∼8㏈ at PER of 10-2 with the proposed bit loading algorithm while the conventional one obtains the performance gain of 0.5∼5㏈ at the same conditions. Also, the increased data rate can be confirmed 63Mbps. After the logic synthesis using 0.3${\mu}{\textrm}{m}$ CMOS technology, the logic gate count for the processor with proposed algorithm can be reduced by 34% in comparison with the conventional one.

ABR Congestion Control for Signal Transmissions in ATM Networks (신호 전송을 위한 ATM 망에서의 ABR 체증제어)

  • 정준영;양현석;계영철;고인선
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.5B
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    • pp.448-456
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    • 2003
  • In this parer, an ABR (Available Bit Rate) congestion control algorithm for voice transmission in ATM networks was proposed. To deal with the network congestion problem, not only the buffer level of a switch but also the variation of the buffer level were considered. Also, to resolve the unfairness among sources where the bit transfer rates vary, a loading factor that is used to adjust the bit rate was introduced. To show the superiority of this paper over others, simulation was done with a network of 7 voice sources and 4 switches, which was represented by Petri net model. ExSpect was used for simulation. The simulation results showed that there was improvement in network utilization and that unfairness among sources were resolved a lot.

Design of Synchronous 256-bit OTP Memory (동기식 256-bit OTP 메모리 설계)

  • Li, Long-Zhen;Kim, Tae-Hoon;Shim, Oe-Yong;Park, Mu-Hun;Ha, Pan-Bong;Kim, Young-Hee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.12 no.7
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    • pp.1227-1234
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    • 2008
  • In this paper is designed a 256-bit synchronous OTP(one-time programmable) memory required in application fields such as automobile appliance power ICs, display ICs, and CMOS image sensors. A 256-bit synchronous memory cell consists of NMOS capacitor as antifuse and access transistor without a high-voltage blocking transistor. A gate bias voltage circuit for the additional blocking transistor is removed since logic supply voltage VDD(=1.5V) and external program voltage VPPE(=5.5V) are used instead of conventional three supply voltages. And loading current of cell to be programmed increases according to RON(on resistance) of the antifuse and process variation in case of the voltage driving without current constraint in programming. Therefore, there is a problem that program voltage can be increased relatively due to resistive voltage drop on supply voltage VPP. And so loading current can be made to flow constantly by using the current driving method instead of the voltage driving counterpart in programming. Therefore, program voltage VPP can be lowered from 5.9V to 5.5V when measurement is done on the manufactured wafer. And the sens amplifier circuit is simplified by using the sens amplifier of clocked inverter type instead of the conventional current sent amplifier. The synchronous OTP of 256 bits is designed with Magnachip $0.13{\mu}m$ CMOS process. The layout area if $298.4{\times}314{\mu}m2$.

An energy-efficiency approach for bidirectional amplified-and-forward relaying with asymmetric traffic in OFDM systems

  • Jia, Nianlong;Feng, Wenjiang;Zhong, Yuanchang;Kang, Hong
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.8 no.11
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    • pp.4087-4102
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    • 2014
  • Two-way relaying is an effective way of improving system spectral efficiency by making use of physical layer network coding. However, energy efficiency in OFDM-based bidirectional relaying with asymmetric traffic requirement has not been investigated. In this study, we focused on subcarrier transmission mode selection, bit loading, and power allocation in a multicarrier single amplified-and-forward relay system. In this scheme, each subcarrier can operate in two transmission modes: one-way relaying and two-way relaying. The problem is formulated as a mixed integer programming problem. We adopt a structural approximation optimization method that first decouples the original problem into two suboptimal problems with fixed subcarrier subsets and then finds the optimal subcarrier assignment subsets. Although the suboptimal problems are nonconvex, the results obtained for a single-tone system are used to transform them to convex problems. To find the optimal subcarrier assignment subsets, an iterative algorithm based on subcarrier ranking and matching is developed. Simulation results show that the proposed method can improve system performance compared with conventional methods. Some interesting insights are also obtained via simulation.

Circuit-Switched “Network Capacity” under QoS Constraints

  • Wieselthier, Jeffrey E.;Nguyen, Gam D.;Ephremides, Anthony
    • Journal of Communications and Networks
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    • v.4 no.3
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    • pp.230-245
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    • 2002
  • Usually the network-throughput maximization problem for constant-bit-rate (CBR) circuit-switched traffic is posed for a fixed offered load profile. Then choices of routes and of admission control policies are sought to achieve maximum throughput (usually under QoS constraints). However, similarly to the notion of channel “capacity,” it is also of interest to determine the “network capacity;” i.e., for a given network we would like to know the maximum throughput it can deliver (again subject to specified QoS constraints) if the appropriate traffic load is supplied. Thus, in addition to determining routes and admission controls, we would like to specify the vector of offered loads between each source/destination pair that “achieves capacity.” Since the combined problem of choosing all three parameters (i.e., offered load, admission control, and routing) is too complex to address, we consider here only the optimal determination of offered load for given routing and admission control policies. We provide an off-line algorithm, which is based on Lagrangian techniques that perform robustly in this rigorously formulated nonlinear optimization problem with nonlinear constraints. We demonstrate that significant improvement is obtained, as compared with simple uniform loading schemes, and that fairness mechanisms can be incorporated with little loss in overall throughput.