The MAC Layer of PLC

Software-defined/cognitive radio has recently made the jump from a purely research driven endeavor to one that is now being driven commercially. Such radios offer the promise of spectrum agility and re-configurability through flexibility at the MAC and physical layers. In the wireless domain, it has been shown that hybrid-MAC layer algorithms can lead to improved overall performance in varying network conditions. A hybrid MAC that uses CSMA in low-contention periods and switches to TDMA in high-contention periods can outperform CSMA or TDMA individually. However, such hybrid systems do not offer the flexibility and cognition required of dynamic spectrum networks. In this paper, we describe MultiMAC, a framework and experimental platform for evaluating algorithms that dynamically reconfigure MAC and physical layer properties. MultiMAC acts as a mediating MAC layer and dynamically reconfigures and/or selects from a collection of alternative MAC layers. As a result of monitoring current network metrics, MultiMAC chooses the MAC layer capable of achieving the best performance while ensuring that incoming frames are decoded using the correct MAC layer algorithm. MultiMAC incorporates decision processes to select the appropriate MAC component based on per-node and per-flow statistics. This engine will allow intelligent reconfiguration of the MAC and physical layers in response to changes in external conditions and/or requirements optimizing use of the available spectrum

In this paper, a new MAC and Network cross layer protocol for OFDMA-based Multi-hop Ad-hoc Networks is proposed. In wireless network, when a route is established, the radio resource allocation problems at MAC layer may decrease the end to end performance proportionally with the length of each route. The contention at MAC layer may causes routing protocol to respond by finding new routes and routing table updates. The cross layer protocol allows layers to exchange state information in order to solve the problem and obtain higher performance. The proposed MAC and Network optimized cross layer protocol based the dynamic Sub-channel Assignment Algorithm in [4] to ensure the performance of ad-hoc and multi-hop networks is significantly improved.

This paper analyses the very high system throughput of IEEE 802.11ac by taking into consideration the key features of MAC and PHY layers under a Multiple In Multiple Out (MIMO) channel. Throughput at the MAC layer is calculated from the transmission probability, contention window and transmission stage. Likewise, the new critical attributes of 802.11ac PHY (i.e. modulation and coding schemes, spatial streams, and channel bandwidth) are used to determine the throughput at the PHY layer. To this end, a theoretical model is formulated at the MAC and PHY layers followed by a system model of MIMO multipath fading channel for 802.11ac. The system model is verified by simulation analysis. The results compare theoretical and simulation findings for different sets of parameters. Furthermore, important trends and trade-offs are identified between system throughput and (MAC + PHY) features as a function of number of contending stations and payload size. The system throughput of 802.11ac networks is significantly improved due to the addition of new PHY features. However, the system may degrade upto 50% in terms of symbol reception in case of a high error-prone MIMO channel. The performance of 802.11ac systems is also analyzed under different MIMO TGn channel models in terms of Packet Error Rate (PER). Thus based on our simulation results, an appropriate channel model can be chosen for 802.11ac network under a given configuration to achieve a better performance.

Quality of Service (QoS) is considered as the standard check of a conveyance system to show provided services and its availability. For illustration application like video conferencing, voice over ip (VOIP), streaming videos, real time operation feel necessity for draconian assurance on jitter, packet loss, prioritization of services and end-to-end delay. So to overcome these issues a novel scheme employing MAC and Application Layer protocols with enhanced (MAP) is proposed. Improved black-burst protocol as well as prioritization of services is proposed at the MAC layer. An influential packet scheduling scheme for multimedia application in IEEE 802.11e has also been designed. At the Application layer level, real time protocols such as Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP) are adopted to support QoS. The performance of proposed MAP with enhanced Black Burst Protocol is studied with OPNET 14.5 simulator. The result shows that proposed MAP mechanism has better performance in QoS parameters considered, while maintaining fairness during channel allocation.

Wireless multimedia sensor networks (WMSNs) have got capacity to collect both scalar sensor data and multidimensional sensor data. It is the basis for the Internet of things (IoT). Quality of service (QoS) pointers like energy efficiency, reliability, bit error rate, and latency can be helpful in data collection estimation over a network. In this paper, we review a number of QoS strategies for WMSNs and wireless sensor networks (WSNs) in the IoT context from the perspective of the MAC and application layers as well as the cross-layer paradigm. Considering the MAC layer, since it is responsible for regulating the admittance to the shared medium and transmission reliability and efficiency through error correction in wireless transmissions, and for performance of framing, addressing, and flow control, the MAC protocol design greatly affects energy efficiency. We thus review a number of protocols here including contention-free and contention-based protocols as well as the hybrid of these. This paper also surveys a number of state-of-the-art machine-to-machine, publish/subscribe, and request/response protocols at the application layer. Cross-layer QoS strategies are very vital when it comes to system optimization. Many cross-layer strategies have been reviewed. For these QoS strategies, the challenges and opportunities are reviewed at each of the layers considered. Lastly, the future research directions for QoS strategies are discussed for research and application before concluding this paper.

The major issue in the design of any Wireless Sensor Network (WSN) is low power consumption that needs to be addressed at every layer of network to enhance the Lifetime. Research shows several Energy efficient protocols developed for Scheduling in MAC layer and Routing in Network layer independently with a traditional approach. This paper proposes a bio-inspired Energy efficient Scheduling & Routing algorithm by sharing the Energy data between MAC and Network layer with a cross-layer interaction. Swarm intelligence is a popular field where the collective behavior of insects and animals is used to address the design issues of WSN. The algorithm developed here incorporates the evolutionary behavior of Anuran species for Energy efficiency both in MAC and Network layer. NS2 is being used as the network simulator and the performance of the simulation results are compared with existing protocols to prove efficiency of the proposed evolutionary technique for Scheduling and Routing.

Hybrid Automatic Repeat Request is used as an error control and recovery mechanism in IEEE 802.16. Many different performance improvements over the standard error control mechanism have been proposed. One such improvement [1] considers the synergy between the MAC and PHY layers and proposes an adaptive fragmentation scheme, whereby the fragmentation is done only at the MAC layer at high bit error rates. This avoids duplicate fragmentations and enhances the throughput. In this paper, an enhancement over [1] is proposed by introducing a cross-layer decoding approach. In case of decoding failure at the PHY layer, the packets are not discarded rather passed on to the MAC layer along with the side information, i.e., the bit reliabilities, from the decoder at the PHY. MAC layer performs an additional decoding effort in the form of iterative decoding on such erroneous packets based on these bit reliabilities. Simulation results are presented showing a considerable coding gain at different values of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The packet error rate is improved with this method and therefore the retransmission of packets is reduced.

As broadband wireless channels become common, the performance of TCP over end-to-end paths containing such links is important. TCP SACK suffers substantially when residual packet error rates increase beyond a value of about 1%--5%(especially for longer RTTs). Recently we have proposed improvements to TCP (called LT-TCP) to make TCP loss-tolerant in heavy and bursty erasure environments. However, real world wireless systems do not just present bursty randomloss patterns to the transport layer. The PHY, MAC and transport layers all respond to errors, interacting in myriad ways. In this paper, we focus on one underlying source of packet erasure (non-congestion loss), namely interference in 802.11 environments (from Bluetooth and co-channel interferers), and the resulting interaction between the MAC and transport layer mechanisms. MAC layer mechanisms cannot fully mitigate the interference problem and tend to misinterpret interference as noise and aggressively respond with techniques like rateadaptation. Such aggressive responses lead to poor scheduling performance at the MAC layer (e.g., well-known unfairness and capture effects) and limit mitigation opportunities at the transport layer. We argue that aggressive rate adaptation is undesirable in these situations and show how a combination of reconfiguration of MAC layer mitigation options and increased buffering leads to significantly improved end-to-end performance.

Multi-rate capabilities are supported by the physical layers of most 802.11 devices. To enhance the network throughput of MANETs, transfer rate adaptation at MAC layer should employ the multi-rate capability at physical and the information of previous transmissions provided by MAC and physical layers. In this paper, we propose a transfer rate adaptation scheme plus back-to-back frame transmissions, and fragmentation at MAC layer, named TRAF. TRAF adopts a bi-direction-based approach with an extended option to select an appropriate rate for frame transmission under fast changing channel conditions. Consecutive back-to-back frame transmissions to fully utilize good channel quality during a coherent time interval and fragmentation algorithm to maintain high throughput under worse channel conditions are recommended in TRAF. Extensive simulation is experimented to evaluate the performance of TRAF. Regarding simulation results, frame delivery ratio, and network throughput of TRAF are significantly improved by comparing to that of other protocols.

We consider joint optimization problems among link, MAC, and routing layers for wireless sensor networks with hetrogeneous nodes where battery lifetime maximization for a certain portion of nodes is more important than the maximization across all nodes in the network. For such applications, we propose two battery lifetime maximization schemes: a sequential joint link, MAC, and routing optimization, and a receive antenna selection for burst data applications. Numerical results show that proposed schemes greatly increase the battery lifetime for the node group regarded as more critical while the total energy consumption degradation maintains in a reasonable amount. I. INTRODUCTION Wireless sensor network (WSN) has been paid continuous attention due to its wide range of applications such as secu- rity, health, and disaster monitoring applications, etc. Recent advances in hardware technology make it easier to deploy the WSN by allowing more signal processing functionality to be integrated in a single chip. In such sensor networks, sensors are normally powered by small batteries and replacement of those batteries are expensive or nearly impossible in a certain case. Consequently, maximizing battery lifetime of sensors by reducing energy consumption for end-to-end transmissions has become a key design issue for the WSN. For sensor networks, component nodes are mainly designed to cooperate together for the end-to-end transmission. Thus the energy minimization should be jointly performed across all layers of protocol stack since all layers contribute to the energy consumption during the transmission. In (1) and (2), joint optimization between link and MAC layers are considered and optimal time slot lengths are computed based on time- division multiple aceess (TDMA) scheme by minimizing the total energy consumption. In such a cross-layer design, a constellation size or the number of data bits to be transmitted is determined by the link layer optimizations according to chan- nel capacity of physical links. MAC and routing layer compute time slot lengths of the TDMA scheme which minimize the total energy consumption with appropriate constraints such as a flow conservation (3). It is therefore of great benefit to jointly minimize the energy consumption over both date rates among links and link powers which affects the channel capacity. Throughout this paper, a scenario where nodes in the network have different energy property is considered. For this scenario, we classify entire nodes into two groups where one group is more difficult to access than the other. As a system of interest in this paper, we assume some nodes in the network are responsible for collecting information at a remote site where an approach to those nodes for maintenance operations takes a long time and is very expensive. Also some other nodes are responsible for relaying the information to the base station (BS) which can be approached for periodic maintenance purposes even though it is expensive. In such a system, the battery lifetime maximization for the information collecting node is much more important than the lifetime maximization across all nodes in the network. However, it is still required for relay nodes to minimize the energy consumption as much as possible to reduce the maintenance cost provided that the battery lifetime for information collecting nodes is minimal. In this paper, we consider joint optimization problems among link, MAC, and routing layers for the WSN with these hetrogeneous nodes and propose two energy minimiza- tion schemes. First scheme we propose is a successive joint optimization across two groups. In this scheme, the energy consumption of information collecting nodes is minimized over constraints such as the flow conservation (3) and the transmission deadline as a first stage optimization. This stage of the optimization produces modulation orders and time slot lengths among each link involving information collecting nodes. By doing so, as will be shown by simulations, the energy consumption for information collecting nodes can be greatly reduced. However, since the energy minimization for remaining relay nodes is not taken into account, the total energy consumption is much higher than the energy consump- tion optimized over total nodes in the networks. To combat such problem, at the second stage, the energy consumption of relay nodes will be minimized by jointly optimizing across remaining relay nodes and the BS provided that parameters for information collecting nodes optimized at the previous stage are preserved. As a result, the proposed scheme greatly reduces the energy consumption of information collecting node while the increase in the total energy consumption is maintained in a reasonable amount at the same time. The second scheme we propose in this paper employs an antenna selection scheme (4) at relay nodes. In certain applications, relay nodes can be easily treated by maintenance processes such as the battery replacement or location changes,

We propose an analytical cross-layer model to quantify tradeoffs between throughput and fairness. We study the effect of coding on the performance of the network while optimizing parameters that govern NETWORK, MAC and PHY layers. Indeed, the heart of our scheme is to code packets at MAC layer before transmitting them through the common lossy channel. To the best of our knowledge, we are the first to use Fountain codes at MAC layer. Indeed, coding packets is usually studied at APPLICATION or TRANSPORT layers. In standard IEEE 802.11, whenever a collision occurs the whole packet is lost and needs to be retransmitted. Our scheme uses an incremental combination of all previous copies of a backlogged packet to improve the decoding probability and therefore to correctly recover the original packet. Using Fountain coding increases the Jain's Fairness index over the network. It indeed improves the throughput on paths that suffer from high collision probability. However unfortunately, it may decrease the throughput on the other paths. This is due to the injected redundancy in coded packets and its negative effect on reducing the channel idle period seen by concurrent users.

In this paper, we focus on cross-layer (MAC and transport) design for variable-rate CDMA networks. First, we formulate the cross-layer rate assignment task as a constrained convex optimization problem. Next, we develop two sets of distributed feedback algorithms to solve this problem - one which merges the rate assignments at the MAC and transport layers (one-shot), and one which coordinates them (modular). We show that both sets of algorithms converge to the same equilibrium. In particular, we show that the addition of queues between the transport and MAC layers can actually facilitate the coordination required for the modular algorithm with only minimal modification to existing protocols. Practical distributed implementation and its impact on the convergence of both algorithms is addressed.

The neighborhood discovery and its maintenance are very important in wireless networks for any applications, especially for routing and every self-* algorithm. Neighbor nodes are usually discovered thanks to the use of the HELLO protocol. This makes this HELLO protocol very important for wireless networks especially for self-organizing the network. Most of layer-3 protocols assume an ideal MAC layer. In such a case, HELLO protocol parameters have no impact over the self-organization. But this is not the case when considering realistic MAC and physical layers. In this paper, we investigate the impact of the parameters of such a protocol over a self-organization structure when considering realistic a MAC layer. We analyze theoretically and by simulations, the joint effect of the HELLO protocol parameters and of the MAC layer characteristics over several network self-organizations.

This paper gives an insight into IEEE 802.11ac by analysing its performance in terms of system throughput taking into consideration the key features of MAC and PHY layers. Throughput at MAC layer is calculated from transmission probability, contention window and transmission stage. Likewise, the new critical attributes of 802.11ac PHY (i.e. modulation and coding schemes, spatial streams, and channel bandwidth) are used to determine the throughput. To this end, a theoretical model is developed followed by simulation analysis. The results compare theoretical and simulation findings for different set of parameters. Furthermore, important trends and tradeoffs are identified between system throughput and (MAC + PHY) features as a function of number of contending stations and payload size.

Many applications would require fast data transfer in Wireless Local Area Networks (WLANs). A representative example is that EAST experiment data are retrieved by some physics researchers using the Transmission Control Protocol (TCP). However, due to the high contention degree and the high error rate in wireless networks, the packets may be loss for wireless reasons but not for congestion. This will greatly degrade the TCP performance. On one hand, the wireless packet loss is not congestion, but the traditional TCP assumes that every packet drop is congestion and thus decreases its congestion window, which will degrade its performance. On the other hand, due to the MAC layer retransmission policy employed by the IEEE 802.11 DCF mechanism, the lost packets at the MAC layer will be retransmitted for some times. Thus the waiting time of the packets in the MAC layer queue will be increased. So if we ignore all the packet loss for wireless reasons as the other improved mechanisms do, the network work congestion will be aggravated and its performance will be degraded. To alleviate the impact of the wireless packet loss to TCP in WLANs, this paper proposes a MAC layer congestion control method which is implemented at the end wireless nodes based on IEEE 802.11b DCF mechanism. At first, we propose a concept of MAC layer congestion window which means the MAC layer will send all the packets in a window when it gets access to the wireless channel, other than just sends only one packet as the traditional DCF mechanism does. Then our congestion control mechanism adjusts the MAC layer congestion window based on the contention degree and the MAC layer packet loss rate. If the MAC layer contention degree or packet error rate is high, we will increase the congestion window to improve the successful transmission rate, and we will decrease the congestion window when the packet loss rate is lower than the average wireless packet loss rate. We also use a threshold to control the increase of the congestion window. The threshold is set according to the number of wireless nodes. By performing wireless congestion control at the MAC layer, our mechanism can mitigate the effect of wireless loss to TCP, and therefore improve the TCP performance. The simulation and experiment results show that our mechanism can have better performance than traditional MAC layer mechanisms in WLANs.