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In this study, we analyze the CSMA Non-Persistent protocol with a finite number of nodes, providing more accurate results for applications like wireless sensor networks. The finite model addresses scenarios where the node count is moderate, capturing realistic system dynamics. Our analysis reveals a dependency on the node count, impacting system throughput. As the node count increases, throughput behavior aligns with Kleinrock's infinite model. We derive a complex closed-form throughput expression for a finite quantity of nodes in the system, solved numerically, and offer an approximate expression for specific conditions. These insights advance understanding of low-contention network performance, especially in scenarios where the infinite model becomes inadequate. [ABSTRACT FROM AUTHOR]

In nonsaturated 802.11 distributed coordination function (DCF) networks, existing studies had observed a salient phenomenon: the maximum stable throughput may be far higher than the saturation throughput and last for a long duration (say, months). Such a maximum stable throughput is called the presaturation throughput peak. The long-duration peak suggests that 802.11 DCF networks may provide a far higher stable throughput than what we generally believe, without worrying about a sudden deterioration of quality of service (QoS). This paper is devoted to developing a general theoretical framework to predict the peak. In the framework, we define a backoff entropy to quantify the uncertainty of the inherent random backoff process of 802.11 DCF networks, and then innovatively introduce a BackoffEntropy-Peak linearity property (i.e., the peak is linearly proportional to the backoff entropy) for the peak prediction. This framework is applicable for a general configuration of contention windows (CWs). It enables us to reveal the most essential dependency of the peak on the initial CW size and the number of network nodes. Further, we design peak-based call admission control (CAC) schemes that can be performed quickly and easily, without requiring network performance measurements and complex calculations. We verify our framework and CAC schemes via widely adopted 802.11 DCF ns2 and ns3 simulators (mostly with typical 802.11 standard settings). Extensive simulations show that our framework and CAC schemes trade within 9% peak prediction errors for making 802.11 DCF networks provide high stable throughput with good QoS (such as short delay and low collision probability). This paper is the first to propose applying the information entropy to study the throughput-stability problem. We believe that this study makes a crucial breakthrough in thoroughly investigating nonsaturated performance and network stability of random access wireless networks. [ABSTRACT FROM AUTHOR]

The in-band full-duplexing is a promising technique to boost wireless network throughput by allowing a node to transmit and receive simultaneously. This paper provides a comprehensive investigation on the hidden-node problem that arises in the full-duplex (FD) enabled carrier-sensing multiple-access (CSMA) networks. In particular, we first provide the fundamental conditions that guarantee successful receptions for all the FD transmission cases, and propose an ellipse interference model and an ellipse carrier-sensing model to capture the interference relations and the carrier-sensing mechanism in FD CSMA networks, respectively. We further establish the hidden-node-free design in FD CSMA networks. Specifically, we show the sufficient conditions on the carrier-sensing power threshold that can eliminate hidden-node collisions. We show that compared with half-duplex CSMA networks, the FD CSMA network needs a much smaller carrier-sensing power threshold to prevent hidden-node collisions, which leads to poor network spatial reuse. This motivates us to further propose a new medium access control (MAC) protocol with Full-duplex Enhanced Carrier-Sensing (FECS) mechanism. The FECS-MAC enables the secondary carrier-sensing before starting the secondary transmission. We show that with the secondary carrier-sensing design, the required carrier-sensing power threshold can be increased while keeping the network hidden-node free. Therefore, the network spatial reuse and throughput can be significantly improved. Simulation results demonstrate that the FECS-MAC can improve the throughput of dense three-node FD networks by more than 30 percent, compared with relay full-duplex (RFD) MAC protocol proposed in. [ABSTRACT FROM AUTHOR]

A fundamental difference between the two most representative random-access schemes, Aloha and carrier sense multiple access (CSMA), is sensing. There has been a common belief that the access efficiency can always be improved by the use of carrier sensing, which is indeed based on an implicit assumption that the packet length is much larger than the sensing time. For machine-to-machine (M2M) communications featured with short packets, the benefit of sensing may not overweigh the cost any more. It is therefore of paramount importance to identify the conditions for CSMA to outperform Aloha. In this paper, the sum rate performance of CSMA networks with two representative receiver structures, i.e., the collision model and the capture model, is characterized and optimized, based on which a comparative study of the optimal sum rate performance between Aloha and CSMA is conducted to establish criteria for beneficial sensing. The analysis shows that the maximum sum rates of CSMA with both receiver structures logarithmically increase with the mean received SNR $\rho $ at the high SNR region, and the rate gain of the capture model over the collision model is significant only when $\rho $ is small. The critical threshold for the ratio of the sensing time to the packet length for beneficial sensing is characterized under various scenarios, and found to be close to zero at the low SNR region when the capture model is adopted, indicating that the packet length needs to be extremely large for CSMA to outperform Aloha in that case. The analysis sheds important light on the access design of M2M communications, and suggests that Aloha could be a more favorable option when short packets are sent by a massive amount of low-power machine-type devices. [ABSTRACT FROM AUTHOR]

This paper proposes a carrier-sensing multiple access protocol for asynchronous multiple-packet reception (MPR), which enables wireless receivers to correctly decode partially time-overlapping packets. Unlike previous studies, which require back-off nodes to constantly monitor the channel, our design requires only that each node sense the number of transmitting nodes after the completion of the back-off period for determining whether to begin transmission in the next time slot. In addition, we develop an analytical model to evaluate relevant parameters and performance metrics of the proposed protocol. Our model relies on the channel-sensing probability of a node in a randomly chosen slot, rather than channel-accessing probability adopted in previous models for asynchronous MPR. The results are validated through numerical study under a variety of network conditions. We also show that the proposed protocol is quite robust to imperfect estimation in channel sensing, and is more energy-efficient than other similar threshold-based protocols.

Carrier sense multiple access (CSMA) is widely used as a medium access control (MAC) in wireless networks due to its simplicity and distributed nature. This motivated researchers to find CSMA schemes that achieve throughput optimality. In 2008, it has been shown that a simple CSMA-type algorithm is able to achieve optimality in terms of throughput and has been given the name “adaptive” CSMA. Later, new technologies emerged where a prolonged battery life is crucial such as environment and industrial monitoring. This inspired the foundation of new CSMA-based MAC schemes, where links are allowed to transition into a sleep mode to reduce the power consumption. However, the throughput optimality of these schemes was not established. This paper, therefore, aims to find a new CSMA scheme that combines both throughput optimality and energy efficiency by adapting to the throughput and power consumption needs of each link. This is done by controlling operational parameters, such as back-off and sleeping timers, with the aim of optimizing a certain objective function. The resulting CSMA scheme is characterized by being asynchronous, completely distributed and being able to adapt to different power consumption profiles required by each link while still ensuring throughput optimality. The performance gain in terms of energy efficiency compared with the conventional adaptive CSMA scheme is demonstrated through computer simulations. [ABSTRACT FROM AUTHOR]

The bidirectional transmission based-protocols have been proposed to resolve an uplink (UL)/downlink (DL) unfairness problem of an infrastructure mode WLAN. However, they do not guarantee the fairness in an error-prone channel. We propose two protocols enhancing the UL/DL fairness, named negative acknowledgement (NACK)-based channel reservation and hybrid automatic repeat request-based bidirectional media access control (MAC) (HyBiM). We analyze the throughput of the two protocols by proposing a new Markov chain model. The analytical and simulation results show that the HyBiM protocol guarantees the UL/DL fairness even in the error-prone channel. [ABSTRACT FROM AUTHOR]

Per-station fairness is one of the important and challenging issues in wireless local area network based on a contention-based medium access control protocol. The unfairness problem among stations having different channel qualities is caused by the imbalance in access probability and outage probability among them. In this paper, we investigate the per-station fairness by resolving the imbalance in the above two factors through the enhanced distributed coordination function (DCF) adopting hybrid automatic repeat request (HARQ), named the DCF-H. We suggest adopting the HARQ with Chase combining as a solution for the imbalance in the outage probability on top of the loss differentiation mechanism which resolves the imbalance in the access probability. We also analyze the performance of the DCF-H by proposing a new Markov chain model and derive a closed-form expression of system throughput, delay, and outage probability. We compare the performance of the DCF-H with that of the conventional DCF protocols and find out that the DCF-H not only guarantees the near-perfect per-station fairness but also improves the whole system performance, such as throughput, delay, and outage probability. [ABSTRACT FROM AUTHOR]

The demand for extensive data rates in dense-traffic wireless networks has expanded and needs proper controlling schemes. The fifth generation of mobile communications (5G) will accommodate these massive communications, such as massive Machine Type Communications (mMTC), which is considered to be one of its top services. To achieve optimal throughput, which is considered a mandatory quality of service (QoS) metric, the carrier sense multiple access (CSMA) transmission attempt rate needs optimization. As the gradient descent algorithms consume a long time to converge, an approximation technique that distributes a dense global network into local neighborhoods that are less complex than the global ones is presented in this paper. Newton’s method of optimization was used to achieve fast convergence rates, thus, obtaining optimal throughput. The convergence rate depended only on the size of the local networks instead of global dense ones. Additionally, polynomial interpolation was used to estimate the average throughput of the network as a function of the number of nodes and target service rates. Three-dimensional planes of the average throughput were presented to give a profound description to network’s performance. The fast convergence time of the proposed model and its lower complexity are more practical than the previous gradient descent algorithm.

Game-theoretic approaches have provided valuable insights into the design of robust local control rules for the individuals in multi-agent systems, e.g., Internet congestion control, road transportation networks, and so on. In this paper, we introduce a non-cooperative medium access control game for wireless networks and propose new fully distributed carrier sense multiple access (CSMA) algorithms that are provably optimal in the sense that their long-term throughputs converge to the optimal solution of a utility maximization problem over the maximum throughput region. The most significant part of our approach lies in introducing novel price functions in agents’ utilities so that the proposed game admits an ordinal potential function with no price-of-anarchy. The game formulation naturally leads to game-based dynamics finding a Nash equilibrium, but they often require global information. Toward our goal of designing fully distributed operations, we propose new game-inspired dynamics by utilizing a certain property of CSMA that enables links to estimate their temporary throughputs without message passing. They can be thought of as stochastic approximations to the standard dynamics, which is a new feature in our work, not prevalent in other traditional game-theoretic approaches. We show that they converge to a Nash equilibrium, and numerically evaluate their performance to support our theoretical findings. [ABSTRACT FROM PUBLISHER]

Bidirectional transmission (BT)-based protocols have been proposed to achieve uplink/downlink fairness in IEEE 802.11 systems. To successfully guarantee the fairness in unsaturated carrier sensing multiple access (CSMA) systems, it is important to accurately estimate the number of backlogged nodes considering both of the uplink (UL) and downlink (DL) traffic. In this letter, we propose a backlog estimation mechanism for the bidirectional media access control to guarantee UL/DL fairness in an unsaturated CSMA environment. We derive the optimal transmit probability and the optimal DL transmit opportunity for BT as a function of the estimated backlog size. The proposed algorithm ensures the near-perfect UL/DL fairness while improving the overall system performance. [ABSTRACT FROM PUBLISHER]

Recent large-scale deployments of wireless sensor networks have posed a high demand on network throughput, forcing all (discrete) orthogonal ZigBee channels to be exploited to enhance transmission parallelism. However, the interference from widely deployed WiFi networks has severely jeopardized the usability of these discrete ZigBee channels, while the existing CSMA-based ZigBee MAC is too conservative to utilize each channel temporally. In this paper, we propose ART (Adaptive fRequency-Temporal co-existing) as a framework consisting of two components: FAVOR (Frequency Allocation for Versatile Occupancy of spectRum) and P-CSMA ( Probabilistic CSMA), to improve the co-existence between ZigBee and WiFi in both frequency and temporal perspectives. On one hand, FAVOR allocates continuous (center) frequencies to nodes/links in a near-optimal manner, by innovatively converting the problem into a spatial tessellation problem in a unified frequency-spatial space. This allows ART to fully exploit the “frequency white space” left out by WiFi. On the other hand, ART employs P-CSMA to opportunistically tune the use of CSMA for leveraging the “temporal white space” of WiFi interference, according to real-time assessment of transmission quality. We implement ART in MicaZ platforms, and our extensive experiments strongly demonstrate the efficacy of ART in enhancing both throughput and transmission quality. [ABSTRACT FROM AUTHOR]

This letter investigates a queue-stabilizing backoff algorithm for slotted ALOHA and carrier-sense multiple access systems from game-theoretic perspective. Since queue stability of each user could be achieved when user’s throughput is greater than its mean packet arrival rate, every user tries to achieve its throughput up to a certain target level, by playing a non-cooperative game of determining a (re)transmission probability. We characterize Nash equilibrium points (NEPs) of this game and the convergence of a distributed backoff algorithm for users to employ to reach the NEPs. [ABSTRACT FROM PUBLISHER]

With the development of the times, in the wireless sensor networks, the increasing amount of information transmission requires more advanced transmission protocols. Especially accompanied by the arrival of the era of Big Data, the conflicts between traditional transport agreement and the sudden or large amount of data are increasingly prominent. The discrete time three-dimensional probability CSMA protocol with multichannel mechanism proposed solves these problems pretty well. By the new MAC protocol to control transmission of information, so that the agreement adapts various contingencies problems in the network better and has more controllable ability. Using simulation tool- MATLAB for the accuracy of the agreement is demonstrated. [ABSTRACT FROM AUTHOR]

Carrier sense multiple access (CSMA) based distributed algorithms can attain the largest capacity region as the centralized Max-Weight policy does. Despite their capability of achieving throughput optimality, these algorithms can either incur large delay and have large complexity or only operate over nonfading channels. In this letter, by assuming arbitrary backoff time, we first propose a fully distributed randomized algorithm whose performance can be pushed to the performance of the centralized Max-Weight policy not only in terms of throughput but also in terms of delay for completely connected interference networks with fading channels. Then, inspired by the proposed algorithm, we introduce an implementable distributed algorithm for practical networks with a reservation scheme. We show that the proposed practical algorithm can still achieve the performance of the centralized Max-Weight policy. [ABSTRACT FROM PUBLISHER]

In this paper, we study the transport capacity of large multi-hop wireless CSMA networks. Different from previous studies that rely on the use of a centralized scheduling algorithm and/or a centralized routing algorithm to achieve the optimal capacity scaling law, we show that the optimal capacity scaling law can be achieved using entirely distributed routing and scheduling algorithms. Specifically, we consider a network with nodes Poissonly distributed with unit intensity on a √n × √n square Bn ⊂ R2. Furthermore, each node chooses its destination randomly and independently and transmits following a CSMA protocol. By resorting to the percolation theory and by carefully tuning the three controllable parameters in CSMA protocols, i.e., transmission power, carrier-sensing threshold, and countdown timer, we show that a throughput of Θ(1/√n) is achievable in distributed CSMA networks. Furthermore, we derive the preconstant preceding the order of the transport capacity by giving an upper and a lower bound of the transport capacity. The tightness of the bounds is validated using simulations. [ABSTRACT FROM PUBLISHER]

Currently, with the rapid development of Internet of Things (IoT), users demand more and more personalized and diversified business categories, radio spectrum increasingly tense. With the exploiting of Transmission Control Protocol/Internet Protocol (TCP / IP) protocol, network achieves the objects of the intelligent identifying, locating, tracking, monitoring and managing a network. Multichannel random access mechanism maximizes the utilization of constrained spectrum resources and allocating scarce channel resources to disparate hierarchical according to business priorities with various qualitiy of service (QoS) requirements. In this paper, we propose a MAC design combining them together in one unit system under three-dimensional probability CSMA (Carrier Sense Multiple Access) adopting the average cycle analysis method to analysis. Through the paper, precise mathematical value of system throughput is got by rigorous derivations under many circumstances. The correctness of the theory and model is demonstrated with simulation results and effectiveness illustrated. In the offline phase, simulation results verify that the proposed algorithm can improves the controllability of the system, the channel utilization, system security, and reliability of packet transmission and meet the different priorities of different QoS requirements.

In Ad Hoc networks,the net work of mobile nodes exchange information with their wireless transceiver equipment,the network throughput is in increased,compared to other such multiple hops network.Moreover along with the rapid development of modern information,communication business also will be increase.However,the access and adaptive of previous CSMA protocol are insufficient.According to these properties,this paper presents a kind of adaptive dual clock with monitoring function P-CSMA random multiple access protocol(ADNP-CSMA),and discusses two kinds of P-CSMA.ACK with monitoring function is introduced to maintain the stability of the whole system,and the introduction of dual clock mechanism reduces the channel of idle period.It calculate the system throughput expression through the method of average period,and the simulation results show that the system is constant in the case of high load throughput.

In the wireless sensor network, energy supply and consumption is the main factors to affect survival time. Introducing the three-dimensional probability CSMA protocol, the paper analyses the system throughput, system delay and energy efficiency with using the average cycle analysis methods. For this protocol, the system time is slotted into a time slot with high channel utilization realized by the choice of three parameters P1, P2 and P3. The correctness of the theory is verified through the simulation.

This paper considers random access protocols with multipacket reception (MPR), which include both slotted-Aloha and slotted $(\tau)$-persistent CSMA protocols. For both protocols, each node makes a transmission attempt in a slot with a given probability. The goals of this paper are to derive the optimal transmission probability maximizing a system throughput for both protocols and to develop a simple random access protocol with MPR, which achieves a system throughput close to the maximum value. To this end, we first obtain the optimal transmission probability of a node in the slotted-Aloha protocol. The result provides a useful guideline to help us develop a simple distributed algorithm for estimating the number of active nodes. We then obtain the optimal transmission probability in the $(\tau)$-persistent CSMA protocol. An in-depth study on the relation between the optimal transmission probabilities in both protocols shows that under certain conditions the optimal transmission probability in the slotted-Aloha protocol is a good approximation for the $(\tau)$-persistent CSMA protocol. Based on this result, we propose a simple $(\tau)$-persistent CSMA protocol with MPR which dynamically adjusts the transmission probability $(\tau)$ depending on the estimated number of active nodes, and thus can achieve a system throughput close to the maximum value. [ABSTRACT FROM PUBLISHER]

We consider extended wireless networks characterized by a random topology of access points (APs) contending for medium access over the same wireless channel. Recently, stochastic geometry has emerged as a powerful tool to analyze random networks adopting MAC protocols such as ALOHA and CSMA. The main strength of this methodology lies in its ability to account for the randomness in the nodes' location jointly with an accurate description at the physical layer, based on the SINR, that allows considering also random fading on each link. In this paper, we extend previous stochastic geometry models of CSMA networks, developing computationally efficient techniques to obtain throughput distributions, in addition to spatial averages, which permit us to get interesting insights into the impact of protocol parameters and channel variability on the spatial fairness among the nodes. Moreover, we extend the analysis to a significant class of topologies in which APs are not placed according to a Poisson process. [ABSTRACT FROM PUBLISHER]

This article introduces a metric for performance evaluation of medium access schemes in wireless ad hoc networks known as local capacity. Although deriving the end-to-end capacity of wireless ad hoc networks is a difficult problem, the local capacity framework allows us to quantify the average information rate received by a receiver node randomly located in the network. In this article, the basic network model and analytical tools are first discussed and applied to a simple network to derive the local capacity of various medium access schemes. Our goal is to identify the most optimal scheme and also to see how does it compare with more practical medium access schemes. We analyzed grid pattern schemes where simultaneous transmitters are positioned in a regular grid pattern, ALOHA schemes where simultaneous transmitters are dispatched according to a uniform Poisson distribution and exclusion schemes where simultaneous transmitters are dispatched according to an exclusion rule such as node coloring and carrier sense schemes. Our analysis shows that local capacity is optimal when simultaneous transmitters are positioned in a grid pattern based on equilateral triangles and our results show that this optimal local capacity is at most double the local capacity of ALOHA based scheme. Our results also show that node coloring and carrier sense schemes approach the optimal local capacity by an almost negligible difference. At the end, we also discuss the shortcomings in our model as well as future research directions. [ABSTRACT FROM AUTHOR]

Full Duplex or Simultaneous transmission and reception (STR) in the same frequency at the same time can potentially double the physical layer capacity. However, high power transmit signal will appear at receive chain as echoes with powers much higher than the desired received signal. Therefore, in order to achieve the potential gain, it is imperative to cancel these echoes. As these high power echoes can saturate low noise amplifier (LNA) and also digital domain echo cancellation requires unrealistically high resolution analog-to-digital converter (ADC), the echoes should be cancelled or suppressed sufficiently before LNA. In this paper we present a closed-loop echo cancellation technique which can be implemented purely in analogue domain. The advantages of our method are multiple-fold: it is robust to phase noise, does not require additional set of antennas, can be applied to wideband signals and the performance is irrelevant to radio frequency (RF) impairments in transmit chain. Next, we study a few protocols for STR systems in carrier sense multiple access (CSMA) network and investigate MAC level throughput with realistic assumptions in both single cell and multiple cells. We show that STR can reduce hidden node problem in CSMA network and produce gains of up to 279% in maximum throughput in such networks. Moreover, at high traffic load, the gain of STR system can be tremendously large since the throughput of non-STR system is close to zero at heavy traffic due to severe collisions. Finally, we investigate the application of STR in cellular systems and study two new unique interferences introduced to the system due to STR, namely BS-BS interference and UE-UE interference. We show that these two new interferences will hugely degrade system performance if not treated appropriately. We propose novel methods to reduce both interferences and investigate the performances in system level. We show that BS-BS interference can be suppressed sufficiently enough to be less than thermal noise power, and with favorable UE-UE channel model, capacities close to double are observed both in downlink (DL) and uplink (UL). When UE-UE interference is larger than DL co-channel interferences, we propose a simple and "non-cooperative" technique in order to reduce UE-UE interference. [ABSTRACT FROM PUBLISHER]

A class of carrier sense multiple access (CSMA) protocols used in a broad range of wireless applications uses synchronized contention where nodes periodically contend at intervals of fixed duration. While several models exist for asynchronous CSMA contention used in protocols like IEEE 802.11 MAC, no model exists for synchronized CSMA contention that also incorporates realistic factors like clock drifts. In this paper, we introduce a model that quantifies the interplay of clock drifts with contention window size, control packet size, and carrier sense regulated by usage of guard time. Using a field programmable gate array (FPGA)-based MAC protocol implementation and controlled experiments on a wireless testbed, we evaluate the model predictions on the isolated and combined impact of these key performance factors to per-flow throughput and fairness properties in both single-hop and multihop networks. Our model and experimental evaluation reveal conditions on protocol parameters under which the throughput of certain flows can exponentially decrease; while at the same time, it enables solutions that can offset such problems in a predictable manner. [ABSTRACT FROM AUTHOR]

Aloha and Carrier Sense Multiple Access (CSMA) are two representative random-access protocols. Despite their simplicity in concept, the performance analysis of Aloha and CSMA networks has long been known as notoriously difficult. Numerous models and analytical approaches have been proposed in the past four decades. Yet how to integrate them into a coherent theory remains an open challenge. Toward this end, a unified analytical framework was recently proposed in , based on which a comprehensive study of throughput, delay and stability performance of Aloha networks was presented. In this paper, the framework is further extended to CSMA networks. The analysis shows that both CSMA and Aloha have the same bi-stable property, and the performance of both networks critically depends on the selection of backoff parameters. Different from Aloha, however, substantial gains can be achieved in CSMA networks by reducing the mini-slot length a and the collision-detection time x. The maximum throughput with CSMA is derived as an explicit function of a and x, and shown to be higher than that with Aloha if a

The problem of developing distributed scheduling algorithms for high throughput in multihop wireless networks has been extensively studied in recent years. The design of a distributed low-complexity scheduling algorithm becomes even more challenging when taking into account a physical interference model, which requires the SINR at a receiver to be checked when making scheduling decisions. To do so, we need to check whether a transmission failure is caused by interference due to simultaneous transmissions from distant nodes. In this paper, we propose a scheduling algorithm under a physical interference model, which is amenable to distributed implementation with 802.11 CSMA technologies. The proposed scheduling algorithm is shown to achieve throughput optimality. We present two variations of the algorithm to enhance the delay performance and to reduce the control overhead, respectively, while retaining throughput optimality. [ABSTRACT FROM AUTHOR]

Multipacket reception (MPR) refers to physical layers where receivers can decode multiple simultaneously transmitted packets. In this paper we investigate the resulting performance of conjoining carrier sense multiple access (CSMA) communications with MPR. We report on its maximum achievable stable throughput with decentralized control and show there can be throughput gain over slotted ALOHA (S-ALOHA), the non-channel-sensing protocol of choice. However, this gain diminishes as the physical layer's MPR strength increases, thereby diminishing the need for channel sensing. Nonetheless, for systems evolving from a single-user (SU) to a multiple-user (MU) channel, CSMA can furnish significantly more efficient utilization of MPR capacity than S-ALOHA. This is meaningful in practice because the emerging generation of the widely deployed IEEE 802.11 wireless local area networks (WLAN) — 802.11ac — is adapting MPR and will operate in said region. In that regard, we also discuss the effective usage of a channel's resources for MPR and highlight the advantages multiuser-MIMO (MU-MIMO), an MPR technique, can offer to WLANs. Using early design specifications of 802.11ac, we show that the existing SU-oriented 802.11 MAC parameters can under-utilize the MPR capacity offered by a MU-oriented physical layer. [ABSTRACT FROM PUBLISHER]

The release of IEEE 802.15.4 medium access control (MAC) and physical layer specifications represents a significant milestone in promoting deployment of wireless sensor networks. This paper first analyzes the performance of the contention access period (CAP) specified in the IEEE 802.15.4 standard by integrating the discrete-time Markov chain models of the node states and the channel states. Then a modified CAP is analyzed, which could significantly improve the performance of the system. Based on the theoretical analysis of the CAP and the effect of the modification, we have that in the saturated network of IEEE 802.15.4, the collision probability is large, and the throughput is small. The main reasons are the employment of slotted carrier sense multiple access-collision avoidance and the mechanism that if a frame transmission cannot be completed before the end of the CAP, it has to wait until the start of the next CAP. Thus an enhanced collision-avoidance MAC protocol, which achieves a better performance and is compatible with the IEEE 802.15.4 standard, is proposed to improve the performance of the system. Extensive simulations validate our conclusions. [ABSTRACT FROM AUTHOR]

Optimal CSMA (oCSMA) has been receiving extensive attentions for its provable optimality in throughput and fairness without message passing over wireless multi-hop networks. However, recent studies suggest that TCP over oCSMA performs poorly, hindering the deployment of oCSMA in real networks. In this letter, we show that just a simple, additional virtual queue at the MAC layer can significantly improve TCP performance when oCSMA is used as the underlying MAC. Through testbed-based experiments, we demonstrate that with our virtual queueing scheme, TCP flows achieve near-optimal throughput performance in various scenarios. [ABSTRACT FROM PUBLISHER]

Recent studies reveal that the main cause of the well-known unfairness problem in wireless networks is the ineffective coordination of CSMA-based random access due to topology asymmetry. In this paper, we take a modeling-based approach to understand and solve the unfairness problem. Compared to existing works, we advance the state of the art in two important ways. First, we propose an analytical model called the G-Model, which accurately characterizes the ineffective coordination of medium access in asymmetrical topologies. The G-Model can estimate network performance under arbitrary parameter configurations. Second, while previous works decompose a wireless network into embedded basic asymmetric topologies and study each basic topology separately, we go beyond the basic asymmetrical topology and design a model-driven optimization method called Flow Level Adjusting (FLA) to solve the unfairness problem for larger wireless networks. Through extensive simulations, we validate the proposed G-Model and show that FLA can greatly improve the overall fairness of wireless networks in which basic asymmetric topologies are embedded. [ABSTRACT FROM PUBLISHER]

“Belief propagation” (BP) is an efficient way to solve “inference” problems in graphical models, such as Bayesian networks and Markov random fields. It has found great success in many application areas due to its simplicity, high accuracy, and distributed nature. This paper is a first attempt to apply BP algorithms in CSMA wireless networks. Compared to prior CSMA optimization algorithms such as ACSMA, which are measurement-based, BP-based algorithms are proactive and computational, without the need for network probing and traffic measurement. Consequently, BP-based algorithms are not affected by the temporal throughput fluctuations and can converge faster. Specifically, this paper explores three applications of BP. 1) We show how BP can be used to compute the throughputs of different links in the network given their access intensities, defined as the mean packet transmission time divided by the mean backoff countdown time. 2) We propose an inverse-BP algorithm to solve the reverse problem of how to set the access intensities of different links to meet their target throughputs. 3) We introduce a BP-adaptive CSMA algorithm to find the link access intensities that can achieve optimal system utility. The first two applications are NP-hard problems, and BP provides good approximations to them. The advantage of BP is that it can converge faster compared to prior algorithms like ACSMA, especially in CSMA networks with temporal throughput fluctuations. Furthermore, this paper goes beyond BP and considers a generalized version of it, GBP, to improve accuracy in networks with a loopy contention graph. The distributed implementation of GBP is nontrivial to construct. A contribution of this paper is to show that a “maximal clique” method of forming regions in GBP: 1) yields accurate results; and 2) is amenable to distributed implementation in CSMA networks, with messages passed between one-hop neighbors only. We show that both BP and GBP algorithms for all three applications can yield solutions within seconds in real operation. [ABSTRACT FROM AUTHOR]

We consider the Medium Access Control (MAC) protocol design for nodes in a wireless LAN that use a wide-azimuth switched beam smart antenna system comprised of a multiple beam antenna array. The one-hop performance of Carrier Sense Multiple Access (CSMA) as well as Slotted Aloha for such a system is presented analytically and through simulation. The problem of synchronization of multiple beams in CSMA is investigated in our analysis. Our results show that, under heavy offered load conditions, CSMA is a good choice with nodes that have multiple-beam smart antennas, despite the performance loss due to the beam synchronization, providing a stable throughput that approaches unity and is invariant to fluctuations in the offered load. Slotted Aloha, on the other hand, is capable of higher peak throughput in a narrow range of offered loads as more switched beams are employed, but performance drastically reduces beyond optimum offered loads. We also introduce a method, Expanded Receive Rule (ERR), whereby the tight synchronization among different beams of a receiver node in CSMA is relaxed, which is observed to provide better throughput. Finally, we also present performance results for a 4-way-handshake-type carrier sense mechanism using multiple beam antennas. [ABSTRACT FROM AUTHOR]