Transmission Control Protocol Performance Comparison Using Piggyback Scheme In WLANS

The main problem at wireless networks is the overhead at MAC layer; when the data physical rate is increasing it causes increasing the overhead and decreasing at the MAC efficiency. In this study we study the performance comparison of TCP protocol in WLANs with and without using piggyback. The study of results concerning of implemented both mechanisms in NS2 simulator and find out the good performance from this comparison. Based on the results from our experiments show that the Piggyback scheme is one of the efficient ways to reduce the overhead at MAC wireless networks

Performance Improvement Of Mac Layer In Terms Of Reverse Direction Transmission Based On IEEE 802.11n

Medium access control (MAC) layer is one of the most prominent topics in the area of wireless networks. MAC protocols play a big role in improving the performance of wireless networks, and there are many challenges that have been addressed by the researchers to improve the performance of MAC layer in the family of IEEE 802.11. The physical data rate in IEEE 802.11n may reach 600 Mbps, this high data rate does not necessary transform into good performance efficiency, since the overhead at the MAC layer signifies that by augmenting PHY rates the effectiveness is automatically reduced. Therefore, the main objective of next generation wireless local area networks (WLANs) IEEE 802.11n is to achieve high throughput and able to support some applications such as TCP 100 Mbps and HDTV 20 Mbps and less delay. To mitigate the overhead and increase the MAC efficiency for IEEE 802.11n, one of the key enhancements at MAC layer in IEEE 802.11n is a reverse direction transmission. Reverse direction transmission mainly aims to accurately exchange the data between two devices, and does not support error recovery and correction; it drops the entire erroneous frame even though only a single bit error exists in the frame and then causes a retransmission overhead. Thus, two new schemes called (RD-SFF) Reverse Direction Single Frame Fragmentation and (RD-MFF) Reverse Direction Multi Frame Fragmentation are proposed in this study. The RD-SFF role is to aggregate the packets only into large frame, while RD-MFF aggregate both packets and frames into larger frame, then divided each data frame in both directions into subframes, Then it sends each subframe over reverse direction transmission. During the transmission, only the corrupted subframes need to be retransmited if an error occured, instead of the whole frame. Fragmentation method is also examined whereby the packets which are longer when compared to a threshold are split into fragments prior to being combined. The system is examined by simulation using NS-2. The simulation results show that the RD-SFF scheme significantly improves the performance over reverse direction transmission with single data frame up to 100%. In addition, the RD-MFF scheme improvers the performance over reverse direction transmission with multi data frames up to 44% based on network condition. These results show the benefits of fragmentation method in retransmission overhead and erroneous transmission. The results obtained by ON/OFF scheme takes into account the channel condition to show the benefits of our adaptive scheme in both ideal as well as erroneous networks. In conclusion, this research has achieved its stated objective of mitigation the overhead and increase the MAC efficiency for IEEE 802.11n. Additionally, the proposed schemes show a significant improvement over the reverse direction in changing network conditions to the current network state

Towards next generation WLANs: exploiting coordination and cooperation

Wireless Local Area Networks (WLANs) operating in the industrial, scientific and medical (ISM) radio bands have gained great popularity and increasing usage over the past few years. The corresponding MAC/PHY specification, the IEEE 802.11 standard, has also evolved to adapt to such development. However, as the number of WLAN mobile users increases, and as their needs evolve in the face of new applications, there is an ongoing need for the further evolution of the IEEE 802.11 standard. In this thesis we propose several MAC/PHY layer protocols and schemes that will provide more system throughput, lower packet delivery delay and lessen the power consumption of mobile devices. Our work investigates three approaches that lead to improved WLAN performance: 1) cross-layer design of the PHY and MAC layers for larger system throughput, 2) exploring the use of implicit coordination among clients to increase the efficiency of random media access, and 3) improved packets dispatching by the access points (APs) to preserve the battery of mobile devices. Each proposed solution is supported by theoretical proofs and extensively studied by simulations or experiments on testbeds

Reverse direction transmission using single data frame and multi data frames to improve the performance of mac layer based on IEEE 802.11N

Reverse direction transmission and block ACK are effective ways to improve the performance of MAC layer that reduces the overhead and increases the system throughput. As high as 600 Mbps of physical data rate is achieved in IEEE 802.11n where high data rate of the current MAC layer leads to a high performance overhead and low performance throughput. Further,designing the MAC layer is still ongoing to achieve high performance throughput. In this paper, we examine the performance enhancement of the proposed 802.11n MAC layer in terms of reverse direction transmission using a single data frame and multi data frames. We implemented these schemes in the NS2 simulator to show the results for TCP traffic and compared them with the literature

Reverse Direction Transmission in Wireless Networks: Review

Reverse direction mechanism is a promising significant development that may lead to promoting the accuracy of TXOP. The transfer, in conventional TXOP operation, is one way direction out of the station which holds the TXOP and which is not applied to some network services using two lane traffic namely VoIP and on-line gaming. Therefore, the conventional TXOP operation enhances only the forward direction transfer, but not the reverse direction transfer. Moreover, reverse direction mechanism makes it possible for the holder of TXOP to reserve unused TXOP time for its receivers which may improve the channel utilization as well as the performance of reverse direction traffic flows. It is well-known that the reverse direction transfer scheme aims mainly to improve the effectiveness and that plays a key role in reducing the overhead and increasing the system throughput. Thus, this paper provides an overview of a research progress in reverse direction transmission scheme over high speed wireless LANs. Moreover, it addresses the reverse direction mechanism that has been proposed for the next generation wireless networks and the ones adopted by IEEE 802.11n standard. Furthermore, it stresses the reverse issues that require to be dealt with in order to bring further progress to the reverse direction transmission

Cooperative Retransmissions Through Collisions

Interference in wireless networks is one of the key capacity-limiting factors. Recently developed interference-embracing techniques show promising performance on turning collisions into useful transmissions. However, the interference-embracing techniques are hard to apply in practical applications due to their strict requirements. In this paper, we consider utilising the interference-embracing techniques in a common scenario of two interfering sender-receiver pairs. By employing opportunistic listening and analog network coding (ANC), we show that compared to traditional ARQ retransmission, a higher retransmission throughput can be achieved by allowing two interfering senders to cooperatively retransmit selected lost packets at the same time. This simultaneous retransmission is facilitated by a simple handshaking procedure without introducing additional overhead. Simulation results demonstrate the superior performance of the proposed cooperative retransmission.Comment: IEEE ICC 2011, Kyoto, Japan. 5 pages, 5 figures, 2 tables. Analog Network Coding, Retransmission, Access Point, WLAN, interference, collision, capacity, packet los

Wireless broadband access: WiMAX and beyond - Investigation of bandwidth request mechanisms under point-to-multipoint mode of WiMAX networks

The WiMAX standard specifies a metropolitan area broadband wireless access air interface. In order to support QoS for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station can send request messages to a base station, and the base station can grant or reject the request according to the available radio resources. This article first compares two fundamental bandwidth request mechanisms specified in the standard, random access vs. polling under the point-to-multipoint mode, a mandatory transmission mode. Our results demonstrate that random access outperforms polling when the request rate is low. However, its performance degrades significantly when the channel is congested. Adaptive switching between random access and polling according to load can improve system performance. We also investigate the impact of channel noise on the random access request mechanism