A new MAC protocol using the Adaptive Weighted Round Robin with Delay Tolerance (AWRR/DT) is presented. The proposed protocol is a type of centralized MAC protocol where the base station performs most operations. By using the AWRR/DT scheduler, we can guarantee delay QoS to different traffics without the heavy overhead induced by packet-based tagging techniques. In order to enhance the efficiency of random access systems, the proposed protocol employs three novel contention methods: slotted ALOHA with threshold, contention method using adaptive contention period, and traffic-specific contention method. Simulation results show that the proposed protocol guarantees delay bounds by using the AWRR/DT. The slotted ALOHA with threshold suffers less collisions than the regular slotted ALOHA when mobile terminals request slots. The method using adaptive contention period adjusts the length of contention period of each frame to relieve the performance degradation by collisions. The traffic-specific contention method provides a priority handling mechanism to contention-based systems. Experimental results of each contention method are provided.

IEEE 802.11ah is an emerging wireless LAN standard in the sub-1-GHz license-exempt bands for cost-effective and range-extended communication. One of the most challenging issues that need to be overcome in relation to IEEE 802.11ah is to ensure that thousands of stations are able to associate efficiently with a single access point. During network initialization, several thousand stations try to associate with the access point, leading to heavy channel contention and long association delay. Therefore, IEEE 802.11ah has introduced an authentication control mechanism that classifies stations into groups and only a small number of stations in a group are allowed to access the medium in a beacon interval. This grouping strategy provides fair channel access to a large number of stations. However, the approach to grouping the stations and determining the best group size is undefined in the draft of IEEE 802.11ah. In this paper, we first model the authentication/association in IEEE 802.11ah. Our analysis shows that there exists the best group size that results in minimal association delay. Consequently, the analytical model is extended to determine the best group size. Finally, an enhanced authentication control algorithm, which utilizes the best group size to provide the minimum association delay, is proposed. The numerical and the simulation results we obtained with the proposed method demonstrate that our method succeeds in minimizing the association delay.

Video quality generally suffers from packet losses caused by an unreliable channel when video is transmitted over an error-prone wireless channel. This quality degradation is the main reason that a video compression encoder uses error-resilient coding to deal with the high packet-loss probability. The use of adequate error resilience can mitigate the effects of channel errors, but the coding efficiency for bit reduction will be decreased. On the other hand, H.264/AVC uses multiple reference frame (MRF) motion compensation for a higher coding efficiency. However, an increase in the number of reference frames in the H.264/AVC encoder has been recently observed, making the received video quality worse in the presence of transmission errors if the cyclic intra-refresh is used as the error-resilience method. This is because the reference-block selection in the MRF chooses blocks on the basis of the rate distortion optimization, irrespective of the intra-refresh coding. In this paper, a new error-resilient reference selection method is proposed to provide error resilience for MRF based motion compensation. The proposed error-resilient reference selection method achieves an average PSNR enhancement up to 0.5 to 2dB in 10% packet-loss-ratio environments. Therefore, the proposed method can be valuable in most MRF-based interactive video encoding system, which can be used for video broadcasting and mobile video conferencing over an erroneous network.

Providing diverse Quality of Service (QoS) with ultra-low power consumption and support of mobility is the most important and challenging issue in wireless body area networks (WBANs). The IEEE 802.15.4 standard exhibits a desirable feature for WBAN, but its inability of mobility support makes it insufficient. In this paper, we show what is required for node mobility support and propose two strategies for the support. We observed that the amount of time required for the association process is the key reason IEEE 802.15.4 is unable to handle mobility. In this paper, we present a new fast association technique, which prevents nodes from scanning multiple channels. In the proposed scheme, by scanning just a single channel, a node can learn about all the coordinators working in different channels. The single channel scanning scheme is able to decrease the association time of IEEE 802.15.4 operating in 2.4GHz by 32 times. Furthermore, in this paper, a method to increase the node connectivity time with its coordinator in IEEE 802.15.4 beacon-enabled mode is introduced. The method tries to anticipate whether the node is moving towards or away from the coordinator by analyzing the signal strength of multiple beacons received from the same coordinator. Thus, the connectivity time is increased by choosing the coordinator with good signal strength, but located both furthest from the node and toward the direction which mobile node is moving. Our approach results in significant improvement by reducing the number of times the moving node switches coordinators. Experimental results have verified that our schemes work well in the mobile sensor network environment.

A new scheduling algorithm called the Adaptive Weighted Round Robin with Delay Tolerance (AWRR/DT) is presented. This scheme can adapt to the traffic fluctuation of networks with a small processing burden. The proposed scheme incorporates a cell discarding method to reduce the QoS degradation in high-loaded (or congested) period. Simulation results show that the proposed scheme can reduce the average delay of the non-real-time (NRT) class, especially in high-loaded conditions, while maintaining the QoS of real-time (RT) classes. Our scheme with the discarding method can also reduce both the mean waiting time and cell loss ratio of RT classes.

Current TCP-friendly congestion control mechanisms adjust the packet rate in order to adapt to wired network conditions and obtain a throughput not exceeding that of a TCP connection operating under the same conditions. However, these mechanisms can not be directly applicable to wireless network because there is no way to distinguish congestion losses from wireless channel losses. In this letter, a new loss differentiation algorithm for wired-to-wireless streaming service is described. The approach does not only adjust the sending rate according to the network status, but also provide the useful feedback to the video encoder.

IEEE 802.11ah is a new wireless standard for large-scale wireless connectivity in IoT and M2M applications. One of the major requirements placed on IEEE 802.11ah is the energy-efficient communication of several thousand stations with a single access point. This is especially difficult to achieve during network initialization, because the several thousand stations must rely on the rudimentary approach of random channel access, and the inevitable increase in channel access contention yields a long association delay. IEEE 802.11ah has introduced an authentication control mechanism that classifies stations into groups, and only a small number of stations in a group are allowed to access the medium at a time. Although the grouping strategy provides fair channel access to a large number of stations, the presence of several thousand stations and limitation that only a group can use the channel at a time, causes the association time to remain excessive. In this paper, we propose a novel block association method that enables simultaneous association of all groups. Our experiments verify that our block association method decreases the total association time by many folds.

Rate control regulates the coded bit stream to satisfy certain given bit rate condition while maintaining the quality of coded video. However, most existing rate control algorithms for low bit rate video can not handle scene change properly, so visual quality is consequently worsened. The test model TMN8 of H.263+ can be forced to skip frames after an abrupt scene change. In this letter, we propose a new frame-layer rate control which allocates bits to frames and controls the frame skipping adaptively based on the pre-analysis of future frames. Experimental results show that the proposed control method provides an effective alternative to existing frame skipping methods causing the motion jerkiness and quality degradation.

A real-time frame-layer rate control algorithm using sliding window method is proposed for low bit rate video coding over the Internet. The proposed rate control method performs bit allocation at the frame level to minimize the average distortion over an entire sequence as well as variations in distortion between frames. A new frame-layer rate-distortion model is derived, and a non-iterative optimization method is used for low computational complexity. In order to reduce the quality fluctuation, we use a sliding window scheme which does not require the pre-analysis process. Therefore, the proposed algorithm does not produce time delay from encoding, and is suitable for real-time low-complexity video encoder. Experimental results indicate that the proposed control method provides better visual and PSNR performance than the existing TMN8 rate control method.