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Energy detection is widely used by cognitive radios for spectrum sensing. During a silent period, secondary users (SUs) are kept silent so that the energy detector does not confuse SU signals for primary user (PU) signals. Due to imperfect coordination, an SU may transmit during a silent period and cause possible false alarms. We propose to leverage matched filters that already exist in many SUs to...
This paper proposes a cross-layer adaptive cooperative MAC protocol (CAC-MAC) based on IEEE 802.11 DCF, which forms a complete Application-MAC-PHY layer framework. The main feature of CAC-MAC protocol is an adaptive selection of data transmission scheme according to packet length and instantaneous wireless channel conditions. Simulation results show that the novel protocol significantly improves the...
IEEE- and ASTM-adopted Dedicated Short Range Communications (DSRC) vehicle safety-related communication services, which require reliable and fast message delivery, usually demand broadcast communications in vehicular ad hoc networks (VANETs). In this paper, we propose and justify a distributive robust scheme for DSRC one-hop safety-critical services. The new scheme enhances broadcast reliability using...
We propose an algorithm to choose a reasonable backoff window based on prediction of the congestion of downstream and upstream nodes. The algorithm listens to the number of consecutive idle slots of the wireless network, then calculates the congestion and feeds it back to the downstream node and upstream node. When sending packets, a reasonable backoff window is chosen, depending on downstream and...
802.11e HCCA (Hybrid coordination function Controlled Channel Access) exhibits good QoS provisioning for constant bit rate (CBR) video streams in a single collision domain. However, its performance degrades significantly for variable bit rate (VBR) video streams particularly in multi-collision domains. In addition, HCCA has the disadvantage of high complexity. In this paper, we introduce a deterministic...
IEEE 802.11s defines a new mesh data frame format and an extensibility framework for routing. The default routing protocol Hybrid Wireless Mesh Protocol (HWMP) is described. HWMP is based on Ad hoc On-demand Distance Vector Routing (AODV) and has a configurable extension for proactive routing. It uses MAC address with layer 2 routing and uses Radio-Aware as routing metric. We implemented HWMP on OPNET...
This paper first described the IEEE 802.11 MAC layer access control mechanism DCF. Next, we analysis the basic and improved DCF back-off algorithm, and then we proposed exponential-half DCF back-off algorithm MIEhD. This algorithm is easy to implement and has excellent performance when there is small scale of nodes and avoiding the shortcomings of basic algorithm when there is large scale of nodes.
Multi-hop wireless mesh networks (M-WMNs) have recently emerged as an alternative network infrastructure. For M-WMNs to serve as a network infrastructure, the protocol designs for M-WMNs should target a high network capacity. An efficient backoff algorithm is required to achieve a high network capacity. Most of existing works focused on backoff algorithms for infrastructure environment based on IEEE...
This paper first described the IEEE 802.11 MAC layer access control mechanism, that is, the DCF access control mechanism, analysis the basic DCF back-off algorithm BEB. Next, we study a variety of improved BEB algorithms, and then we proposed ZDCF back-off algorithm which is an exponential-based half back-off algorithm. ZDCF is flexible, easy to implement and has excellent performance as BEB algorithms...
In ad-hoc networks, the video quality of real-time services is greatly decreased when bandwidth reduction and channel access delay occur. In this paper, a dynamic frame rate adjustment of video transmissions is proposed in case of network congestion. Simulation results show that our approach improves the quality of real-time video over IEEE 802.11 based vehicular networks by guaranteeing a better...
In multi-channel wireless network, several nodes can transmit data simultaneously in different channels. Thus the overall network performance can be improved significantly compared to single channel network. Various multi-channel MAC protocols have been proposed to coordinate the usage of multiple channels. However, multi-channel MAC protocols that use dynamic channel selection can cause multi-channel...
Multi-channel MAC protocols are proposed to increase the capacity of wireless network. However, dynamic channel selection mechanism based on channel usage information from one-hop neighbor nodes causes multi-channel hidden node problems in a multi-channel multi-hop wireless network. In this paper, we propose a new approach of channel selection. Nodes snoop data channels during idle times and then...
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