Young Yong Kim

Modeling multipath fading channel dynamics for packet data performance analysis

The multipath fading channel modeling traditionally focuses on physical level dynamics such as signal strength and bit error rate. In this paper we characterize multipath fading channel dynamics at the packet level and analyze the corresponding data queueing performance in various environments. The integration of wireless channel modeling and data queueing analysis provides us a unique way to capture important channel statistics with respect to various wireless network factors such as channel bandwidth, mobile speed and channel coding. The second order channel statistics, i.e. channel power spectrum, is found to play an important role in the modeling of multipath fading channels. The data queueing performance is largely dependent on the interaction between the channel power spectrum and the data arrival power spectrum; whichever has lower frequency power will have more impact on queueing performance. Note that the data arrival power spectrum provides a measure of burstiness and correlation behavior of data packet arrivals. Throughout the paper, we use the Markov chain modeling technique to match the measured important channel statistics for both channel modeling and queueing analysis.

Symbol-level random network coded cooperation with hierarchical modulation in relay communication

In order to effectively minimize packet error rate in error prone wireless networks, a novel cooperative communication strategy jointly using symbol-level random network coding and hierarchical modulation is proposed in this paper. The source broadcasts random network coded symbols with hierarchical modulation to the relays and the destination. In following time slots, the relays, which have successfully decoded the original packet, transmit additional random network coded symbols to the destination. When the proposed scheme is applied in multihop relay consumer device networks which comprise a set of consumer devices, error free transmission with high efficiency can be achieved. We show with simulation results that the proposed joint symbol-level random network coding and hierarchical modulation strategy achieves a substantial gain compared to the channel coded cooperation scheme.

Modeling fast fading channel dynamics for packet data performance analysis

The fast fading channel modeling traditionally focuses on physical-level dynamics such as signal strength and bit error rate. We characterize fast fading channel dynamics at the packet-level and analyze the corresponding data queueing performance in various environments. The integration of wireless channel modeling and data queueing analysis provides us a unique way to capture important channel statistics with respect to various wireless network factors such as channel bandwidth, mobile speed and channel coding. The second order channel statistics, i.e., channel power spectrum, is identified to play a dominant role in fast fading channel modeling. The data queueing performance is largely dependent on the interaction between the channel power spectrum and the data arrival power spectrum, whichever has a lower frequency power will have a dominant impact on the queueing performance. The data arrival power spectrum provides a measure of burstiness and correlation behavior of data packet arrivals. In queueing analysis, we use a Markov chain modeling technique to match the measured important channel statistics.

Proportional Fair Scheduling for Multicast Services in WIreless Cellular Networks

We propose a new multicast scheduling scheme which can achieve the proportional fair (PF) allocation in the wireless cellular systems. In case of multicast, the scheduler in the base station should select a group of users, instead of one user, among all users who request the multicast contents. Therefore, multicasting scheduling problem is equivalent to deciding a certain modulation and coding level and a group of users who have better enough channel quality to decode the multicast data. In this work, we first extend the PF metric to the extent that the scheduler can reflect the users time varying channel gain and fairness not only in the unicast case but also in the multicast transmission. Based on the extended PF metric, we propose a PF multicast scheduler and evaluate its performance. Our proposed algorithm outperforms other multicast scheduling schemes in terms of aggregated throughput as well as the fairness among all users.

Cross-layer multiuser resource allocation for video communication over OFDM networks

In this paper, we propose a resource allocation algorithm to transmit multiple video bitstreams over multiuser orthogonal frequency division multiplex (OFDM) networks. The proposed algorithm explores a low-complexity rate-distortion function and diversity of multiuser OFDM systems subject to constraints on delay and limited system resources. A set of relative importance is imposed in resource allocation to assure that each user can achieve the required data rate and the quality of service. We first present a simple and effective rate-distortion function including a temporal error propagation effect and relative importance. Then we propose the cross-layer multiuser resource allocation algorithm that consists of subcarrier assignment and power allocation for minimizing the overall video distortion. The proposed subcarrier assignment algorithm utilizes the subgradient method adopting a shadow price mechanism by assuming equal power distribution for each user. Based on the result of subcarrier assignment, the power allocation algorithm maximizes the sum of distortion reduction while the relative importance for each user is maintained. In simulation results, the proposed resource allocation algorithm outperforms the time division multiple access (TDMA) and the previous resource allocation algorithm maximizing the sum capacity in terms of the worst received video quality among users. The proposed algorithm achieves PSNR gain by 1.0-3.0dB, compared to the previous resource allocation algorithm considering rate-distortion function. It is shown that the proposed resource allocation algorithm distributes the video distortion among users more fairly with relative importance compared to the previous algorithms.

A Proportional Fair Scheduling for Multicast Services in Wireless Cellular Networks

We propose a new multicast scheduling scheme which can achieve the proportional fair (PF) allocation in the wireless cellular systems. In case of multicast, the scheduler in the base station should select a group of users, instead of one user, among all users who request the multicast contents. Therefore, multicasting scheduling problem is equivalent to deciding a certain modulation and coding level and a group of users who have better enough channel quality to decode the multicast data. In this work, we first extend the PF metric to the extent that the scheduler can reflect the users time varying channel gain and fairness not only in the unicast case but also in the multicast transmission. Based on the extended PF metric, we propose a PF multicast scheduler and evaluate its performance. Our proposed algorithm outperforms other multicast scheduling schemes in terms of aggregated throughput as well as the fairness among all users.

Packet loss resilience using unequal forward error correction assignment for video transmission over communication networks

Forward error correction (FEC) methods have been developed for packet loss resilience in application layer for real-time video transmission over communication networks. In this paper, an efficient packet loss resilience method is proposed using closed form solution for unequal FEC assignment based on a new packet distortion model. We first derive the packet distortion model by investigating the error concealment property and error propagation effect in H.264. To select the source and channel rate minimizing the overall distortion, we present a model-based rate allocation algorithm using the packet distortion model and rate-distortion function. Then we propose the closed form solution for unequal FEC assignment, which uses the packet distortion model and considers channel status information. Simulation results show that the proposed method gives substantial improvement for the received video quality in packet-lossy Internet and wireless network environments, while it requires much less computational complexity compared to the previous scheme.

Joint Reduction of Peak-to-Average Power Ratio, Cubic Metric, and Block Error Rate in OFDM Systems Using Network Coding

The reductions of peak-to-average power ratio (PAPR) and block error rate (BLER) are two challenges in wireless systems employing orthogonal frequency-division multiplexing (OFDM)/orthogonal frequency-division multiple access. High BLER renders the system unreliable, and high PAPR is associated with power inefficiency and nonlinearity of the system. These two issues have separately been studied in the literature, but few works have studied simultaneous reductions of PAPR and BLER. In this paper, we propose a new scheme to jointly reduce and tradeoff PAPR and BLER in OFDM systems using random network coding (NC). In our proposed scheme, different representations of the input information block are generated using a special form of NC matrices, for which we prove it achieves the minimum BLER. We then propose an additional step to our proposed scheme to tradeoff a further improvement in PAPR against degradation in BLER using encoded block puncturing. Simulation results show that the proposed scheme achieves the same PAPR as conventional selective mapping (C-SLM) schemes while achieving the minimum BLER. We also show through simulations the PAPR gains achieved by our proposed additional step over C-SLM and the tradeoff of this gain against BLER degradation. Simulations finally show that our proposed scheme achieves the same results for the recently developed cubic metric.

Fast Data Aggregation Algorithm for Minimum Delay in Clustered Ubiquitous Sensor Networks

We propose a time-efficient local data aggregation algorithm that aggregates delay-constrained data within a given time deadline in clustered wireless sensor networks. Our approach consists of two phases. First, we design a zone-based fast data aggregation tree (ZFDAT) to eliminate unnecessary packets being forwarded to many receiver nodes and avoid long detour paths until cluster-head, where cluster-head is local control center to coordinate the data transmissions in the cluster. Next, we propose optimal link scheduling algorithm to minimize aggregation time by given variable length of time slots for all links in the ZFDAT. Our simulation results show that our approach can minimize the aggregation time under energy constraint and outperforms the similar existing algorithms. In particular, our approach distributes the total aggregation time, then it can also reduce the heavy processing load at the cluster-head.

High quality, low delay foveated visual communications over mobile channels

Foveated video streams are created by selectively varying the spatio-temporal resolution of video data according to the assumed or measured fixation patterns of the intended viewers. The significant potential of foveated video lies in the considerable entropy reduction relative to the original video data while minimizing the loss of apparent visual information. By exploiting new human-machine interface techniques, such as visual eyetrackers, combined with foveated video compression and communication protocols, more efficient visual multimedia services operating over low bandwidths should become available in the near future. In this paper, we introduce a prototype foveated visual communication system suitable for implementation as a core element of an interactive multimedia wireless communication environment. We demonstrate the benefit of using foveation in noisy wireless low bandwidth applications, using measured fading statistics from the downtown area of Austin, Texas as an example. Based on a maximum source throughput criterion, the source and channel video transmission rates and the target video coding bit rate are adaptively decided according to the channel dynamics. In the simulations, we use the channel throughput, the spatial/temporal resolution, and the transmission delay as criteria to compare the performance of the foveated approach relative to normal (non-foveated) video. The results clearly underline the significant potential of foveated video communication protocols for wireless multimedia applications.