• Journal of Broadcast Engineering
• /
• v.13 no.1
• /
• pp.6-16
• /
• 2008

An instable wireless channel condition causes more packet losses and retransmissions due to interference, fading, station mobility, and so on. Therefore video streaming service over a wireless networks is a challenging task because of the changes in the wireless channel conditions and time-constraints characteristics of the video streaming services. To provide efficient video streaming over a wireless networks, QoS-enhanced MAC protocol, IEEE 802.11e, is standardized recently. Tn this paper, we propose a new network-adaptive H.264 video streaming mechanism in the IEEE 802.11e wireless networks. To improve the quality of video streaming services, video stream has to adapt to the changes in the wireless channel conditions. The wireless channel conditions are estimated by the packet loss probability and informed to the application layer by the cross-layering. According to the wireless channel information, the video streaming application filters out the low-priority data. This adaptation mechanism efficiently uses system resources because it drops the low-priority data in advance. Therefore, our cross-layer design can provide improved video streaming services to the end-user. Through the implementation and performance evaluation, we prove that the proposed mechanism improves the QoS of the video streaming by providing the smoothed playback.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.6
• /
• pp.342-349
• /
• 2019

We describe and anlayzes the methodology and implementation results of H / W configuration and signal characteristics analysis algorithm for analyzing equipment for analyzing OFDMA physical layer based on 802.16e. Recently, demand for signal analysis of instruments that analyze these signals with the development of digital communication signals is rapidly increasing. Accordingly, it is necessary to develop signal analysis equipment capable of analyzing characteristics of a broadband communication signal using a wideband digital signal processing module. In this paper, we have studied the basic theory of OFDMA in order to devise a device capable of analyzing characterisitcs of broadband communication signals. Second, the structure of OFDMA transmitter/receiver was examined. Third, a wideband digitizer was implemented. we design Wimax signal analysis algorithm based on OFDMA among broadband communication methods and propose Wimax physical layer analysis S/W implementation through I, Q signals. The IF downconverter used the receiver module and the LO generation module of the spectrum analyzer. Quantitative analysis result is obtained through the algorithm of Wimax signal analysis by I, Q data.

• Review of Korean Society for Internet Information
• /
• v.6 no.4
• /
• pp.7-12
• /
• 2005

• Journal of Information Processing Systems
• /
• v.10 no.1
• /
• pp.119-131
• /
• 2014

In recent literature on traffic scheduling, the combination of the two-dimensional discrete-time Markov chain (DTMC) and the Markov modulated Poisson process (MMPP) is used to analyze the capacity of VoIP traffic in the cognitive radio system. The performance of the cognitive radio system solely depends on the accuracy of spectrum sensing techniques, the minimization of false alarms, and the scheduling of traffic channels. In this paper, we only emphasize the scheduling of traffic channels (i.e., traffic handling techniques for the primary user [PU] and the secondary user [SU]). We consider the following three different traffic models: the cross-layer analytical model, M/G/1(m) traffic, and the IEEE 802.16e/m scheduling approach to evaluate the performance of the VoIP services of the cognitive radio system from the context of blocking probability and throughput.

• Journal of KIISE:Computing Practices and Letters
• /
• v.16 no.6
• /
• pp.717-721
• /
• 2010

In general, wireless MAC uses the ACK for reliability. Meanwhile, in wireless sensor network, data is delivered periodically and redundantly. In these situations, every ACK transmission causes the reliability flexible applications to waste some energy. IEEE 802.15.4 developed for energy efficiency has the option of using ACK or not, but there are no researches exploiting this peculiarity. In this paper, we proposed the selective unacknowledged transmission satisfying some requirements (e.g., end-to-end delivery) by removing the ACK when frames are delivered well and using the ACK when frames are delivered poorly. Also, we performed several evaluations exploiting the NS2 simulator.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2008.10a
• /
• pp.882-885
• /
• 2008

Recently, various types of wireless networks have been proliferated. Bluetooth, IEEE 802.11 WLAN, 802.16e Mobile WiMAX (or Wibro) and 3G celluar networks are some examples. Accordingly, research on seamless mobility support mechanisms among homogeneous or heterogeneous networks has drawn significant interests. This paper examines recent research efforts on seamless mobility support mechanisms from link to transport layer. Yet, no single solution meets all the requirements for supporting the seamless mobility and it seems hard to tell which layer is the most appropriate one for supporting mobility. This area is still wide open and needs further research.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.2
• /
• pp.363-371
• /
• 2013

This paper describes a multi-standard LDPC decoder which supports 19 block lengths(576~2304) and 6 code rates(1/2, 2/3A, 2/3B, 3/4A, 3/4B, 5/6) of IEEE 802.16e mobile WiMAX standard and 3 block lengths(648, 1296, 1944) and 4 code rates(1/2, 2/3, 3/4, 5/6) of IEEE 802.11n WLAN standard. To minimize hardware complexity, it adopts a block-serial (partially parallel) architecture based on the layered decoding scheme. A DFU(decoding function unit) based on sign-magnitude arithmetic is used for hardware reduction. The designed LDPC decoder is verified by FPGA implementation, and synthesized with a 0.13-${\mu}m$ CMOS cell library. It has 312,000 gates and 70,000 bits RAM. The estimated throughput is about 79~210 Mbps at 100 MHz@1.8v.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.3
• /
• pp.51-57
• /
• 2010

A dual-mode direct conversion receiver is developed in $0.13\;{\mu}m$ RF CMOS process for IEEE 802.11n based wireless LAN and IEEE 802.16e based mobile WiMAX application. The RF receiver covers the frequency band between 2.3 and 2.7 GHz. Three-step gain control is realized in LNA by using current steering technique. Current bleeding technique is applied to the down-conversion mixer in order to lower the flicker noise. A frequency divide-by-2 circuit is included in the receiver for LO I/Q differential signal generation. The receiver consumes 56 mA at 1.4 V supply voltage including all LO buffers. Measured results show a power gain of 32 dB, a noise figure of 4.8 dB, a output $P_{1dB}$ of +6 dBm over the entire band.

• Proceedings of the KIEE Conference
• /
• 2008.04a
• /
• pp.159-160
• /
• 2008

Initial Ranging Detection and Synchronization is suggested for IEEE 802.16e OFDMA Systems. However ranging is vulnerable to the channel selectivity and other user's interference at low SNR. This paper presents enhanced ranging scheme that improves ranging detection process using the combine multiple FFT blocks and cope with channel selectivity and other user's interference at low SNR. Based on the ranging detection timing offset is calculated for synchronization.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2007.11a
• /
• pp.195-203
• /
• 2007

In this paper, an analytic model of sleep model operation in the IEEE 802.16e is investigated. A mobile subscribe. station (MSS) goes to sleep mode after negotiations with the base station (BS) and wakes up periodically for a short interval to check whether there is downlink traffic to it. If the arrival of traffic is notified, an MSS returns to wake mode. Otherwise, it again enters increased sleep interval which is double as the previous one. In order to consider the situation more practically, we propose the sleep mode starting threshold, during which MSS should await packets before it enters the sleep mode. By modifying the M/G/1 with multiple vacations model, energy consumption ratio(ECR) and average packet response time are calculated. Our analytic model provides potential guidance in determining the optimal parameters values such as sleep mode starting threshold, minimal sleep and maximal sleep window.