• Journal of the Korean Institute of Telematics and Electronics
• /
• v.23 no.5
• /
• pp.597-604
• /
• 1986

This paper describes various mismatch phenomena in differential pulse code modulation (DPCM) coding, such as the mismatch effects of probability density functin(pdf), signal variance, and correlation. At a high transmission rate(i.e., above 32 kbits/s), the performance of DPCM can be improved by matching the pdf shape between the input signal and the quantizer. However, the same gain cannot be obtained at a lower transmission rate. Also, it is shown that the gamma quantizer is realtively robust to the variation of pdf shaper and signal variance. Moreover, as the transmission rate increases, the performance of DPCM for the input signal with large variance is worse than that of DPCM for the signal with small variance due to the increase of overload noise. According to our simuladiton results, the mismatch effects of pdf shape and variance appear to yield more degradatin than that of correlation in a DPCM system.

• Journal of KIISE:Software and Applications
• /
• v.36 no.5
• /
• pp.396-400
• /
• 2009

During periods of large data transmission, routing selection methods are used to efficiently manage data traffic and improve the speed of transmission. One approach in routing selection is AntNet that applies the Ant algorithm in transmissions with uniform probability. However, this approach uses random selection, which can cause excessive data transmission rates and fail to optimize data This paper presents the use of the Genetic Algorithm (GA) to efficiently route and disperse data transmissions, during periods with "unnecessary weight increases for random selection". This new algorithm for improved performance provides highly accurate estimates of the transmission time and the transmission error rate.

• Journal of Communications and Networks
• /
• v.10 no.1
• /
• pp.28-37
• /
• 2008

In this paper, we investigate the problem of minimizing the average transmission power of users while guaranteeing the average delay constraints in time-varying uplink channels. We design a scheduler that selects a user for transmission and determines the transmission rate of the selected user based on the channel and backlog information of users. Since it requires prohibitively high computation complexity to determine an optimal scheduler for multi-user systems, we propose a low-complexity scheduling scheme that can achieve near-optimal performance. In this scheme, we reduce the complexity by decomposing the multiuser problem into multiple individual user problems. We arrange the probability of selecting each user such that it can be determined only by the information of the corresponding user and then optimize the transmission rate of each user independently. We solve the user problem by using a dynamic programming approach and analyze the upper and lower bounds of average transmission power and average delay, respectively. In addition, we investigate the effects of the user selection algorithm on the performance for different channel models. We show that a channel-adaptive user selection algorithm can improve the energy efficiency under uncorrelated channels but the gain is obtainable only for loose delay requirements in the case of correlated channels. Based on this, we propose a user selection algorithm that adapts itself to both the channel condition and the backlog level, which turns out to be energy-efficient over wide range of delay requirement regardless of the channel model.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.4 no.5
• /
• pp.691-708
• /
• 2010

An important issue of supporting multi-users with diverse quality-of-service (QoS) requirements over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resource while, at the same time, to meet each communication service QoS requirement. In this work, we study the problem of a variety of communication services over multi-media heterogeneous cognitive OFDM system. We first divide the communication services into two parts. Multimedia applications such as broadband voice transmission and real-time video streaming are very delay-sensitive (DS) and need guaranteed throughput. On the other side, services like file transmission and email service are relatively delay tolerant (DT) so varying-rate transmission is acceptable. Then, we formulate the scheduling as a convex optimization problem, and propose low complexity distributed solutions by jointly considering channel assignment, bit allocation, and power allocation. Unlike prior works that do not care computational complexity. Furthermore, we propose the FAASA (Fairness Assured Adaptive Sub-carrier Allocation) algorithm for both DS and DT users, which is a dynamic sub-carrier allocation algorithm in order to maximize throughput while taking into account fairness. We provide extensive simulation results which demonstrate the effectiveness of our proposed schemes.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.13 no.4
• /
• pp.17-22
• /
• 2013

In this paper, we propose a multi-hop cooperative transmission protocol over Rayleigh fading channels. In the proposed protocol, the multi-hop cooperative transmission is used to improve the system performance. Due to broadcast nature, we do not limit the receiving node to be only the next node, but the destination and all the nodes between the transmitting node and the destination. The proposed protocol can hence save the average transmit power, compared with multi-hop direct transmission protocol due to the skipped transmissions from some intermediate nodes or chosen relays. The proposed scheme is implemented and evaluated in mobile ad-hoc wireless networks.

• Journal of the Korea Society of Computer and Information
• /
• v.11 no.3
• /
• pp.49-56
• /
• 2006

A special feature of P2P distributed system isn't always the guarantee of online status for peers. In other words we want to download the file from the peer when we use the P2P system but it sometimes caused this system to fail the download. Many studies to resolve this problem depend on re-transmission method. It caused to lower performance so we have to resolve this problem. In this study, we analysis the average usage time of P2P application user and raise the resource transmission guarantee to apply the selection criteria of resource supplier. Moreover the combinations of distributed object replication techniques, the role to enhance the data transmission opportunity of high popularity resource. will cause this search algorithm to advance.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.10 no.6
• /
• pp.307-315
• /
• 2010

Although a substantial amount of studies have been carried out in order to improve the performance of IEEE 802.11, most of them focused on how to slowly decrease the Contention Window size, instead of resetting it to its initial value. Slow decreasing of the window size reduces the collision probability and increases the channel throughput. Therefore, it is difficult to achieve good results in a heterogeneous network which coexists with the original DCF. For instance, a Gentle DCF(GDCF) has good performance in a homogeneous environment, while it can hardly transmit frames in a heterogeneous environment including the original DCF. It is because the slow decreasing of the window size reduces the transmission probability. In this paper, we propose a Fast Recovery DCF(FRDCF) to solve this problem. In the FRDCF, the reset mechanism of the original DCF is maintained to keep the transmission probability high, while a new counter is used to enhance the performance of the wireless LAN. We prove that, compared with the GDCF, the FRDCF has better performance in a heterogeneous wireless LAN.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.11A
• /
• pp.853-860
• /
• 2011

In this paper, we proposed a transmission scheme for a full-duplex relay system that minimizes outage probability. A relay system with the full-duplex relay can mitigate resource inefficiency of a half-duplex relay system. However, the mobile station suffers from the interference because the base station and the relay station transmits signal simultaneously to the mobile station. First, we suggest a layered broadcasting for full-duplex relaying. Second, we derive an optimal power allocation for the layered broadcasting in terms of the outage probability minimization. The proposed algorithm shows better performance than a half-duplex relaying system with and without the diversity, and a conventional full-duplex relaying system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.5B
• /
• pp.530-538
• /
• 2011

In this paper, the feasibility of LEO(low earth orbit) satellite-based automatic identification system (SAT-AIS) for the coastal area of the South Korea is evaluated in the context of ship AIS transmission detection probability. We evaluate and compare AIS signal detection probability of ORBCOMM satellites and LEO-one satellites considering link budget, SOTDMA protocol and satellite's swath width. The simulation determines the total number of vessels served by those satellites according to satellite's swath width and thus, By simulation results, the ORBCOMM SAT-AIS system outperforms LEO-one SAT-AIS system. The suggested ORBCOMM based SAT-AIS system can be a solution to resolve the existing limited transmission distance problem of the conventional ship-to-shore AIS system.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.2
• /
• pp.80-87
• /
• 2013

This paper proposes a CW (Contention window) allocation scheme for real-time data transmission of emergency data on VANET (Vehicle to vehicle Ad hoc Network, V2V) protocol. The proposed scheme reduces the probability of packet collisions on V2V protocol and provides bandwidth efficiency with short delay of emergency sporadic data. In the case of high density traffic, the proposed scheme provides a decrease of recollision probability using dynamic CW adjustments. For the performance analysis, a throughput, end-to-end delays, and network loads were investigated on highway traffic. Simulation results show the performance enhancements in terms of the throughput, end-to-end delays, and network loads.