This paper proposes an algorithm managing the end-to-end video distortion of all users in multiuser orthogonal frequency division multiplex (OFDM) systems. The proposed algorithm mainly exploits the unequal importance of transmitted video packets and the diversity of multiuser existing in sub-carriers. We firstly induce model based rate-distortion function for measuring the amount of video quality degradation which a video packet affects in a group of picture (GOP). Based on the information of distortion in a packet to be transmitted, we propose the distortion management algorithm to allocate resources to users by balancing the subcarriers and power usages. Compared to the previous TDMA, simulation results show that substantial improvements of video quality are achieved.

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 RS’s, 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 RS’s 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.

In this paper, we present an analysis of various multicast schemes over IEEE 802.11 multi-hop. Analyzing performance of wireless multicasting communication is important because multicast communication is gaining more and more attention in wireless networks with numerous potential applications. The network coding has recently drawn people's attention and has proven to have benefits when it is applied to multicasting. Multi-hop wireless communication has been extensively investigated as a candidate of next generation wireless communication. When the network coding is used in multi-hop wireless network, we can expect network throughput to be enhanced. Because network coding is in theoretical stage, its performance in existing wireless communication system is not yet fully investigated. We used IEEE 802.11 MAC to apply various multicasting schemes including network coding and presented their performance.

This paper considers localized packet assignments and distributed packet assignments as joined in the transmission time interval (TTI) for downlink in multi-user OFDM systems. To enhance throughput, we propose an adaptive packet assignment using mode selection between the localized packet assignment and the distributed packet assignment. Moreover, we compare three types of localized packet assignment schemes and show the performance of GPA approaches to optimum performance by improving the spectral efficiency.

In this paper, we propose an adaptive time, frequency and code allocation algorithm to guarantee heterogeneous quality of service (QoS) of users in multicarrier code division multiple access (MC-CDMA) systems. It is separated into two stages. First, time slots and frequency bands are allocated based on the proposed signal-to-noise ratio (SNR) threshold which reflects channel information and the QoS requirements of each user. Next, we propose a cost function which represents sum delay of users and then the codes are allocated by minimizing the cost function while guaranteeing the required bit error rate (BER) of users. Simulation results show that the proposed algorithm yields lower outage probability and higher throughput compared with the existing algorithms.

We propose a predictive location based relaying for hybrid cellular and ad-hoc systems that can provide interference minimization to uplink transmission. Location Information Server (LIS) managed the mobile's routing information with centralized scheme. To maintain the routing correctness, mobile must send location information within a relatively short time period. However the tradeoff as the location-update period decreases is the increase in the overall cellular overhead. To overcome this problem, a predictive location-based routing scheme is proposed. Simulation results show that interference is greatly improved with very low cellular overheads.

We propose a new adaptive admission control scheme for multiuser OFDMA systems to allocate wireless resource with low complexity. In this adaptive admission control scheme, the number of users is estimated adaptively by using the required data rate, bit error rate (BER) and average channel gain of each user at frame by frame. The resource allocation complexity becomes lower since the proposed method estimates the approximate number of users to be supported and reduce the repetition of actual resource allocation. Simulation result shows that the proposed method has high accuracy when ACG (Adaptive Craving Greedy) is used as the resource allocation scheme.

We propose a novel multicast scheme that can provide quality-of-service (QoS) to multicast service over IEEE 802.11 wireless LANs by utilizing MAC layer relay. We develop the distributed relay node selection algorithm and the relay channel selection algorithm. The effectiveness of proposed scheme is examined by simulation. Simulation results show that the proposed relayed multicast significantly improves throughput and delay performance.

A scheduling scheme for MIMO systems which has the capability of obtaining multiuser diversity gain and controlling the link connection ratio among users simultaneously is proposed. Based on the Gaussian assumption of MIMO channel capacity which is fed back to the base station from each mobile, a Gaussian cost function with an appropriate mean and variance is used as a scheduling criteria. The mean and variance of the cost function permits the resources for the proposed scheduler to be controlled. We first consider the optimal scheduler, which maximizes overall system capacity with the desired link connection ratio(a priori desired ratio), and a method is proposed to obtain weights for the optimal scheduler using some properties of the Gaussian statistics. Although the optimal scheduler has the major impact on system capacity, the complexity associated with weight calculation is high. Thus, two types of suboptimal schedulers, weights of which are not dependent on the channel statistics, denoted as the Control Variance(CV) scheduler and the Control Mean(CM) scheduler, are proposed. The overall system capacity of the proposed schedulers, which is significantly enhanced by multiuser diversity, was evaluated analytically and verified by computer simulation. The simulation results show that the overall system capacity of the CM and the CV scheduler is above 99% that of the optimal scheduler. In addition, another result show that the proposed schedulers manage resources accurately, for a relatively small number of antennas.

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 user's 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.

The great potential of "foveated imaging" lies in the entropy reduction relative to the original image while minimizing the loss of visual information. Utilizing human foveation combined with video compression, as well as communication and human-machine interface techniques, more efficient multimedia services are expected to be provided in the near future. In this paper, we introduce a prototype for foveated visual communications as one of future human interactive multimedia applications, and demonstrate the benefit of the foveation over fading statistics in the downtown area of Austin, Texas. In order to compare the performance with regular video, we use spatial/temporal resolution and source transmission delay as the evaluation criteria.

We identify important characteristics of a fading/shadowing channel and present the work of measurement-based channel modeling for packet-level network queueing analysis. Our integration of wireless channel modeling and data queueing analysis at the packet-level provides a unique approach to study the effect of various channel dynamics on high-layer network performance, which otherwise cannot be captured through the traditional bit-level physical-layer channel modeling. In our study, the channel statistics are decomposed into three frequency regions [i.e., low (LF), mid (MF), and high (HF)]; the statistics in each frequency region is found to have significantly different impact on the queueing performance. While the HF statistics can be largely ignored in channel modeling due to their negligible impact on queueing performance, the LF statistics play the most important role in channel modeling because of substantial impact on queueing performance. Since the shadowing mainly represents the LF behavior of a channel, its dynamics are found to have a dominant effect on network performance as compared to the effect of multipath fading dynamics. In wireless networks, there are many other system factors which may change the channel dynamics, such as mobile user driving patterns, and forward-error-correction (FEC) coding (fixed or adaptive) using automated repeat request (ARQ) scheme. Our study further examines the individual impact of these factors on the network performance. In the measurement-based channel modeling, we use a Markov chain modeling technique to match the important channel statistics for queueing system analysis. The study shows an excellent agreement in queueing solutions between using the real original channel traces and using the sequences generated by the matched Markov chain models.

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.

We develop a Markov chain modeling framework for throughput/delay analysis of data services over cellular voice networks, using a dynamic channel stealing method. Some effective approximation techniques are also proposed and verified for simplification of the modeling analysis. Our study identifies the average voice call holding time as the dominant factor affecting the data delay performance. Especially in heavy load conditions, namely when the number of free voice channels becomes momentarily less, the data users will experience large network access delay in the range of several minutes or longer on average. We also examine the data performance improvement by using a priority data access scheme and speech silence detection technique.