In recent years, Wireless Local Area Networks (WLANs) are becoming more and more popular. The IEEE 802.11 protocol is one of the most widely deployed wireless access technologies. In order to minimize the collision probability due to multiple simultaneous transmissions, all stations compete for the wireless channel with a contention resolution method, namely the Binary Exponential Back off (BEB). In the BEB scheme, the contention window (CW) is doubled every time a station experiences transmission collision and decreases to its minimum value after a successful transmission. However, the performance degradation will be resulted from the aggressive reduction in the CW size. Accordingly, Exponential Increase Exponential Decrease (EIED) is proposed to suggest a slower reduction in a back off period after a successful transmission. Actually, the variation of CW causes unsteady system performance. In this paper, we proposed an Oneself Adjusts Back off (OAB) mechanism to improve system performance over contention-based Distributed Coordination Function (DCF) WLANs. In the OAB, the variation of CW state will be kept based on the number of the consecutive collision or successful transmission. The numerical results show that the OAB mechanism provides a better system throughput and collision rate than the related back off schemes.

Forward Error Correction (FEC) is one of the most common means of performing packet error recovery in data transmissions. FEC schemes typically tune the FEC rate in accordance with feedback information provided by the receiver. However, the feedback and FEC rate calculation processes inevitably have a finite duration, and thus the FEC rate implemented at the sender may not accurately reflect the current state of the network. Thus, this paper proposes an Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism to improve the quality of video transmissions over Wireless Local Area Networks (WLANs). In contrast to most FEC schemes, the FEC redundancy rate is calculated directly at the Access Point (AP). Moreover, the redundancy rate is tuned in accordance with both the wireless channel condition (as indicated by the number of packet retransmissions) and the network traffic load (as indicated by the AP queue length). The experimental results show that the proposed ERED-FEC mechanism achieves a significant improvement in the video quality compared to existing FEC schemes without introducing an excessive number of redundant packets into the network.

The IEEE 802.16j standard supports multihop relay function for WiMAX network. The relay technique could enhance the signal strength and help the devices to compete the shadow fading effect from buildings. How to allocate resource becomes an important issue in recent research. In this paper, we discuss the resource allocation with directional antenna in IEEE 802.16j networks. In prior study, the frequency is equally divided according to the number of sectors in a cell. However, the prior allocation schemes often result in waste resource or insufficient bandwidth if the user distribution is not even. The proposed dynamic resource allocation (DRA) scheme considers the user distribution and allocates resource blocks from users' bandwidth request. The simulation results show the improvements from the DRA scheme in terms of utilization of frequency bands and duration of transmission time.

Video streaming over wireless networks have many challenges due to the high error rate and burst packet error characteristic. Forward error correction (FEC) is a method commonly used to handle losses in real-time communication. Conventional FEC mechanisms provide redundancy by an averaged packet loss rate and performance decreases by burst packet losses. However, the average packet loss rate cannot give any indication of burst packet loss. Hence, the conventional FEC mechanisms cannot recover original source data over wireless networks. In this paper, we propose a burst-aware adaptive FEC (BAFEC) control mechanism to overcome burst packet losses. We will therefore be able to take account of average burst packet loss length. The sender can rely on this information in order to adjust the FEC redundancy. The experimental result shows that compared to the conventional FEC mechanisms, our proposed mechanism achieved better recovery performance in terms of packet loss rate and PSNR.

This paper proposes an improvement to the TCP ramp up behavior in slow-start. Current implementations of the TCP start-up procedure may result in an exponential growth of the congestion window, which results in the transmission of an excessive number of packets. Consequently, the network becomes congested and the self-clocking mechanism of the TCP fails. By estimating the number of packets that which can be in flight in the network from the viewpoint of the TCP source, this study develops an algorithm to suppress congestion before it becomes significant. The simulation results indicate that the proposed algorithm enhances the TCP performance by establishing a smoother transmission rate at the end of the slow-start phase and reducing the number of dropped packets significantly as a result.

Local area network (LAN) will be a hybrid network that includes wired and wireless links together. Nonetheless, the wired hosts always take the most bandwidth and bring about the bandwidth allocation unfairness. This problem is caused by the flow control mechanism that is dominated by the round-trip time (RTT). Among the connections on a share link, the ones with shorter RTT tend to acquire bandwidth easier and exhaust the link bandwidth eventually. The RTT of wireless transmission is much longer than wired transmission. Therefore, the protocol that implements flow control mechanism such as TCP suffers a severe low performance problem on wireless links. This paper proposed a new scheme called DFQ that works on gateway. It prevents the wired hosts from grabbing the bandwidth of share link too much and averts the unfairness or starvation of wireless connections. The experiment result shows that DFQ is practicable and makes wireless network to work with wired network seamlessly.

The paper presents an implementation of QoS library redirection (QLR) for DiffServ in Microsoft Windows systems. In the QLR method, the legacy application obtains packet pre-marking ability without any modification of source codes. We have upgraded the FTP and vic (video conferencing) applications by using QLR in our Microsoft Windows testing platform. Our experimental results show that this approach can use really effectively and provide high performance of the QLR in Microsoft Windows systems.

This paper proposes a transparent packet pre-marking method named QLR (QoS Library Redirection) for DiffServ. This method can upgrade legacy applications to obtain packet pre-marking ability without any modification of source codes. In this case, users are allowed to purchase high or low service quality according to their requirements. The major techniques of QLR include the dynamic linking of shared libraries and the function call redirection. We have upgraded the vic application by using QLR in our FreeBSD testing platform. The experimental results can show the effectiveness of the QLR.

The traditional slotted ring network is one of the high speed networks, however its transmission delay in heavy network load is too long. We propose a reservation mechanism to improve this drawback. The mechanism is particularly useful in the heavy network load to get a lower delay for high priority packet transmission. We compare it with a traditional slotted ring network by using simulations, and the results show that this mechanism provides the lower delay when the network traffic load is heavy.