Kyungho Sohn

A novel multicast scheme for feedback-based multicast services over wireless networks

Recently, a point-to-multipoint transmission is a promising technology in the limitation of wireless resources and surging of subscribers, and an optimal to deliver real-time streaming service such as video/audio conference, digital live cast, and so on. There are two types of point-to-multipoint transmission; broadcast and multicast. Broadcast services deliver the information to all receivers in a cell and multicast services deliver the information to a multicasting group. Traditional approaches to multicast services operate by radiating transmission power with the lowest modulation level and coding rate which may be much lower than the lowest acceptable rate for all the multicast subscribers of a multicasting group. While such an approach has the advantage of simple implementation, this method may incur substantial performance penalties such as low spectral efficiency and a large amount of power consumption. To solve this issue, wireless multicasting with channel state information has been investigated in many research studies. However, the overhead of feedback information is a heavy drawback to the achievement of good network performance. In feedback-based multicast services, the system performance is also mostly dependent on the receivers with the lowest channel quality in a multicasting group. Hence, receivers who have better channel condition can receive multicast data successfully without channel quality indicator (CQI) feedback. In this point of view, the feedback-based multicast scheme should aim to achieve high resource efficiency by reducing unnecessary CQI feedback and transmission optimization by dynamically adapting modulation and coding selection (MCS) level according to the variations of the channel state. We show that the proposed scheme enhances the system throughput by dynamically adapting the MCS level according to variations of the CQI and also reduce CQI feedback by transiting from a feedback state to a non-feedback state according to a channel gain and recent frame error rate of each receiver. Finally, the proposed scheme does not need any additional control signaling overhead and also can be expanded and employed in any kind of systems, such as WCDMA, WiMAX, LTE, and LTE-Advanced.

A probabilistic transmission slot selection scheme for MC-CDMA systems using qos history and delay bound

In this paper, we propose an efficient transmission slot selection scheme for Band Division Multi-Carrier-CDMA (BD-MC-CDMA) systems under the constraints of packet loss and delay bound for each individual session. By utilizing channel dynamics together with the delay deadline and loss history, one can determine whether to transmit or not on each time slot, based on the prediction of future channel variations. In this way, one can enhance the chance for transmitting packets with the best channel quality. To validate the efficiency of the proposed algorithm, we model each sub-band as a discrete time Markov Chain using a finite state Markov channel (FSMC) and derive the criteria required for transmission decision. Simulation results show that our proposed scheme can satisfy quality of service (QoS) requirements for real-time traffic with a minimum use of power, while increasing throughput of non-real-time traffic with the power saved from real-time traffic.

Modeling and analysis of impatient packets with hard delay bound in contention based multi-access environments for real time communication

In this paper, we study problem of impatient packets in multimedia multi-access communication channel. Impatient users generally mean the users who leave the system if their service is not started before their respective deadlines. Their characteristic is perfect match to that of the packets with hard delay bound in real-time communication. In real-time communication, one of the most critical performance measure is the percentage of packets that are transmitted within hard delay bound. We assume contention based reservation ALOHA type MAC protocol, which is basic framework in next generation multimedia wireless LAN, and develop analytical model for the performance evaluation of defection probability of impatient packets. Our results show that proposed model is strong tool to evaluate packet loss probability due to expiration of deadline in contention based MAC protocols, which matches well with the simulation results.

Self-organized spatial reuse scheduling in multihop cellular systems

Multihop cellular systems using fixed relay stations are the most promising candidate in the next generation of cellular systems. In order to maximize multihop transmission gains, multihop cellular systems have to exploit an efficient multiple access scheme, which controls the interference of simultaneous transmission links. As one promising way of achieving the goal, we propose a spatial reuse scheduling algorithm that utilizes a self-organizing concept to maximize the system throughput in multihop cellular systems. In our proposed algorithm, each relay station (RS) can infer the buffer state of its neighbor RSpsilas, and determine its own action (a choice among receive, transmit, and shut down) based only on the preamble information from its base station (BS) without any centralized scheduling information. The proposed algorithm is self-organizing in the sense that only the local behavior of each RS is sufficient to maximize the system throughput, and it uses the implicit coordination of a RSpsilas action instead of aiming for perfect coordination. The proposed algorithm has the advantages of less complexity and a significantly smaller overhead when compared to centralized scheduling schemes, since the BS needs no information about the buffer states of RSs and channel qualities between RSs and users.

An Efficient Transmission Slot Selection Scheme for MC-CDMA Systems with Packet Loss and Delay Bound Constraints

In this letter, we propose an efficient transmission slot selection scheme for Band Division Multi-Carrier-CDMA (BD-MC-CDMA) systems under the constraints of packet loss and delay bound for each individual session. By utilizing channel dynamics together with the delay deadline and loss history, one can determine whether to transmit or not during each time slot, based on the prediction of future channel variations. To validate the efficiency of the proposed algorithm, we model each sub-band as a discrete time Markov Chain using a finite state Markov channel (FSMC) and derive the criteria required for transmission decision. Simulation results show that our proposed scheme can satisfy quality of service (QoS) requirements for real-time traffic with minimum use of resources, while increasing throughput of non-real-time traffic with the resources saved from real-time traffic.