It is challenging to design effective scheduling algorithms for multimedia transmissions over wireless channels that employ adaptive modulation and coding (AMC). On the one hand, it is desirable for the overall system throughput to be enhanced by taking advantage of multi-user diversity. On the other hand, fairness or QoS guarantees need to be maintained for individual users, especially in the case of multimedia applications that have strict delay requirements. In this paper, we propose a novel scheduling algorithm called QoS-based cross-layer scheduling (QoS-CLS) to achieve a good design tradeoff. To maximize the system throughput, the algorithm takes into account the information on both the physical layer and the data link layer to schedule user transmissions. Using cross-layer information, the scheduling problem is formulated as a Markov Decision Process and the optimal decision policy (based on the channel status, traffic state, and buffer status of each traffic flow) is pre-calculated by linear programming. This policy is then stored in the system for scheduling in real-time. Simulation results show that QoS-CLS can greatly enhance the channel throughput compared to existing algorithms because of its cross-layer QoS consideration and the optimization method. Moreover, it can provide QoS guarantees while achieving efficient resource sharing among different traffic flows.

Most previous work on code division multiple access (CDMA) considers the bit error ratio (BER) at the physical layer and the frame drop ratio (FDR) at the medium access control layer separately. However, a better system performance, e.g., in terms of a lower overall frame loss ratio (FLR), can be achieved if BER and FDR are jointly optimized. In this paper, we propose a cross-layer optimization scheme called traffic-adaptive scheme for multicode CDMA operating over a time division multiple access (TDMA) channel. Based on the traffic condition and buffer status, this scheme employs a Markov Decision Process (MDP) to determine the optimal value of the maximum number of simultaneous data frames that can be transmitted in each time slot of a TDMA frame so as to minimize the overall FLR of the system. To facilitate implementation, we also propose an approximation scheme named the rate-adaptive scheme to reduce the computation cost. Simulation and analytical results show that both the traffic-adaptive scheme and rate-adaptive scheme can significantly reduce FLR, increase the system throughput, and optimize the packet access delay of the system. Furthermore, the rate-adaptive scheme can achieve a performance close to the traffic-adaptive scheme when the traffic load in the system is high.

Communication systems are becoming more complicated to support different types of services. How to coordinate different services around a user in a flexible and customized way is a new and interesting challenge. Service providers have proposed solutions such as the Universal Communication Identifier

It is a big challenge to design an effective scheduling algorithm for multimedia transmissions over a wireless channel that employs adaptive modulation and coding (AMC). On one hand, the scheduling algorithm needs to schedule user transmissions by taking advantages of the channel diversity so that the overall system performance can be improved. On the other hand, the algorithm also needs to maintain fairness among users and to provide QoS guarantee based on user requirements. In this paper, we propose a novel scheduling algorithm called QoS-based cross-layer scheduling algorithm (QoS-CLS) to address the aforementioned issues. To maximize the system throughput, the algorithm takes into consideration both the physical layer and data link layer information to schedule user transmissions. Using the cross-layer information, the scheduling problem is formulated into a Markov Decision Process (MDP) and the optimum decision policy (based on the channel status, traffic state and buffer status of each traffic flow) is pre-calculated by linear programming and stored in the system for scheduling in real-time. Results show that QoS-CLS can greatly enhance the channel throughput compared to the opportunistic scheduling algorithm because of its cross-layer QoS consideration and the optimization method. Moreover, it can provide QoS guarantee and facilitate resource sharing among different traffic flows.

Previous work on code division multiple access (CDMA) often considers the bit error ratio (BER) at the physical layer and the frame drop ratio (FDR) at the medium access control (MAC) layer separately. However, better system performance (e.g., lower overall packet loss ratio (PLR)) can be achieved if BER and FDR are jointly optimized. This paper, the authors first set up a Markov chain model to evaluate the performance of transporting multimedia traffic over a multi-code CDMA network. Then, the authors propose two novel cross-layer optimization methods that dynamically adjust the maximum number of simultaneous transmissions according to the traffic arrival rate and the queue status, respectively. Simulation and analytical results show that these two methods can significantly reduce PLR and increase the system throughput.

We present MAGICS, a mobile agent-based system for supporting business-to-consumer electronic commerce (e-commerce) or mobile commerce (m-commerce) applications. To use the system, consumers first provide their buying requirements to a proxy/agent server through a Web browser or a wireless application protocol (WAP) terminal. Having obtained the requirements, mobile agents are generated to carry out tasks for the consumers including getting offers from merchants, evaluating offers, and even completing purchases. In the case of mobile commerce, consumers can generate a mobile agent to conduct a search and evaluation in the digital marketspace before making a purchase in the physical marketplace. To make it possible to choose an offer that best satisfies the consumer's requirement(s), we present a mathematical model for evaluating multiple decision factors. To test the basic functions of the mobile agent-based Internet commerce system (MAGICS), we have built a prototype system. To minimize the average cost of a product (including the cost of sending agents), we have also developed an analytical model that can determine how many agents should be sent to compare prices. Four different price distributions and some real price information are analyzed based on the model. The analysis provides valuable insights into the design of mobile agent-based shopping applications for m-commerce, in particular, and for e-commerce, in general.

Recent advances in signal processing techniques have enabled wireless networks to have multi-packet reception (MPR) capability at the physical layer, where it is possible to receive more than one packets when concurrent transmissions occur. In this paper, we propose a novel multi-reservation multiple access (MRMA) scheme for future wireless multimedia networks based on such an MPR channel model. MRMA can fully exploit the channel's MPR capacity while fulfilling the quality of service requirements of different multimedia traffic. Similar to many existing reservation protocols, MRMA guarantees (i) bounded access delay for real-time traffic by dropping packets not transmitted within the required delay bound, and (ii) satisfaction of the required packet loss ratio when applied in conjunction with a connection admission control method to limit the number of admitted traffic streams. MRMA further incorporates a priority control mechanism to differentiate guaranteed and best-effort services for real-time voice/video and connectionless data, respectively. Analytical and simulation results are presented to illustrate the effectiveness of MRMA in service differentiation and increasing the number of admitted traffic streams

In this paper, we propose a dynamic reservation protocol for the low earth orbit (LEO) mobile satellite system. Based on an analytical model, the dynamic reservation protocol enhances system performance by dynamically varying both the access probability and reservation bandwidth. To implement the protocol, a novel contention-pattern-analysis method is proposed to estimate the number of contending terminals at the start of a frame. The reservation protocol is employed to integrate connection-oriented and connectionless traffic over a satellite channel. Simulation and theoretical results are presented to analyze the performance of the protocol and illustrate its benefits.