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It was shown recently that carrier sense multiple access (CSMA)-like distributed algorithms can achieve the maximal throughput in wireless networks (and task processing networks) under certain assumptions. One important but idealized assumption is that the sensing time is negligible, so that there is no collision. In this paper, we study more pract...
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Citations
... It is well known that, while contention access (ALOHA, CSMA etc.) performs well at low contention, it can result in very large delays and possibly instability under high contention [Le84]. While attempts have been made to stabilize CSMA (see [JW12], [JW11] and [RSS09] for examples), the delay of these algorithms still remains prohibitively high. Polled access (e.g., 1-limited cyclic service [TK85], which we will call TDMA in this paper) on the other hand, shows the opposite behavior. ...
We consider a system of several collocated nodes sharing a time slotted wireless channel, and seek a MAC that (i) provides low mean delay, (ii) has distributed control (i.e., there is no central scheduler), and (iii) does not require explicit exchange of state information or control signals. The design of such MAC protocols must keep in mind the need for contention access at light traffic, and scheduled access in heavy traffic, leading to the long-standing interest in hybrid, adaptive MACs. We first propose EZMAC, a simple extension of an existing decentralized, hybrid MAC called ZMAC. Next, motivated by our results on delay and throughput optimality in partially observed, constrained queuing networks, we develop another decentralized MAC protocol that we term QZMAC. A method to improve the short-term fairness of QZMAC is proposed and analyzed, and the resulting modified algorithm is shown to possess better fairness properties than QZMAC. The theory developed to reduce delay is also shown to work in the presence of transmission errors and fast fading. Extensions to handle time critical traffic (alarms, for example) and hidden nodes are also discussed. Practical implementation issues, such as handling Clear Channel Assessment (CCA) errors, are outlined. We implement and demonstrate the performance of QZMAC on a test bed consisting of CC2420 based Crossbow telosB motes, running the 6TiSCH communication stack on the Contiki operating system over the 2.4GHz ISM band. Finally, using simulations, we show that both protocols achieve mean delays much lower than those achieved by ZMAC, and QZMAC provides mean delays very close to the minimum achievable in this setting, i.e., that of the centralized complete knowledge scheduler.
... Suppose the nodes in C i could determine the backlog of a node in C i each time it transmitted a packet 12 . Then, at the beginning of slot t, the information common to all nodes in C i would consist of the number of slots V i (t) since node i last transmitted 13 and its backlog Q i (t − V i (t)) at that instant. With this partial information structure, we have already shown, in [20], that exhaustively serving a nonempty queue minimizes mean delay. ...
... The backlog information could be quantized and contained in the packet header, for example.13 If the node were empty at this instant, it wouldn't have actually transmitted anything. ...
Motivated by medium access control for resource-challenged wireless Internet of Things (IoT), we consider the problem of queue scheduling with reduced queue state information. In particular, we consider a time-slotted scheduling model with $N$ sensor nodes, with pair-wise dependence, such that Nodes $i$ and $i + 1,~0 < i < N$ cannot transmit together. We develop new throughput-optimal scheduling policies requiring only the empty-nonempty state of each queue that we term Queue Nonemptiness-Based (QNB) policies. We propose a Policy Splicing technique to combine scheduling policies for small networks in order to construct throughput-optimal policies for larger networks, some of which also aim for low delay. For $N = 3,$ there exists a sum-queue length optimal QNB scheduling policy. We show, however, that for $N > 4,$ there is no QNB policy that is sum-queue length optimal over all arrival rate vectors in the capacity region. We then extend our results to a more general class of interference constraints that we call cluster-of-cliques (CoC) conflict graphs. We consider two types of CoC networks, namely, Linear Arrays of Cliques (LAoC) and Star-of-Cliques (SoC) networks. We develop QNB policies for these classes of networks, study their stability and delay properties, and propose and analyze techniques to reduce the amount of state information to be disseminated across the network for scheduling. In the SoC setting, we propose a throughput-optimal policy that only uses information that nodes in the network can glean by sensing activity (or lack thereof) on the channel. Our throughput-optimality results rely on two new arguments: a Lyapunov drift lemma specially adapted to policies that are queue length-agnostic, and a priority queueing analysis for showing strong stability.
... Performance of wireless networks has been enhanced in [5], [6] through spatial reuse time-division multiple access (STDMA) based scheduling. In [7], the throughput optimal scheduling algorithms were proposed for CSMA instead of STDMA. The proposed CSMA based link capacity mode is more practical since it includes the packet error occurred due to the collision. ...
... Similar to BP, also HD rests on a centralized scheduling with a computational complexity that can be prohibitive in practice. Fortunately, much progress has recently been made to ease this difficulty by deriving decentralized schedulers with the performance of arbitrarily close to the centralized version as a function of complexity [11,24,28]. ...
... By allowing as many routes as possible, D-class routing policies tend to distribute traffic all over the network. This class includes all opportunistic max-weight schedulers that do not incorporate the Markov structure of topology process into their decisions, including BP [43] and most of its derivations [1,11,12,15,16,[20][21][22][23][24][30][31][32]38,39,41,46]. The class also encompasses all offline stationary randomized algorithms (possibly unfeasible) that make routing decisions as pure functions only of observed channel states, and so independent of queue occupancies, by typically using the knowledge of arrival statistics and channel state probabilities. ...
A dynamic routing policy, referred to as Heat-Diffusion (HD), is developed for multihop uniclass wireless networks subject to random traffic, time-varying topology and inter-channel interference.The policy uses only current condition of queue occupancies and channel states, with requiring no knowledge of traffic and topology.Besides throughput optimality, HD minimizes an average quadratic routing cost defined by endowing each channel with a time-varying cost factor. Further, HD minimizes average network delay in the class of routing policies that base decisions only on current condition of traffic congestion and channel states. Further, in this class of routing policies, HD provides a Pareto optimal tradeoff between average routing cost and average network delay, meaning that no policy can improve either one without detriment to the other. Finally, HD fluid limit follows graph combinatorial heat equation, which can open a new way to study wireless networks using heat calculus, a very active area of pure mathematics.
... Liew et al. [20] presented a simple and accurate method for computing throughput distributions among links in CSMA networks. Jiang and Walrand [21] proposed an elegant CSMA-based scheduling algorithm to approach the throughput-optimality. Bellalta et al. [22] analyzed the interactions between a group of neighboring WLANs that use the channel bonding technique and evaluated the impacts of those interactions on the achievable throughputs. ...
Full-duplex wireless communication has been recognized as an effective technique to improve the system throughput. This paper designs a CSMA-based utility-optimal scheduling scheme to fully explore the performance improvement brought by AP’s full-duplex capability. In particular, to keep the backwards compatibility of the legacy users, we allow users to compete to access the channel using the CSMA protocol in their uplink transmissions while let the AP select its downlink user to communicate with for completing the full-duplex transmission upon each uplink access. Moreover, to achieve the optimal system utility, we then formulate an optimization problem of maximizing the downlink aggregate utility subject to the uplink users’ data rate constraints. The formulated problem falls into a mixed integer nonlinear programming (MINLP) form, which is generally NP-hard to solve. To make the problem tractable, we divide it into user pairing and access-intensity adjustment subproblems. More specifically, we devise a user pairing criterion based on the signal-to-interference-plus-noise ratio (SINR) to reduce the uplink-downlink interference, and adopt the Hungarian algorithm to find the best matching between uplink and downlink users. After that, we adjust the access-intensity of users (i.e., the ratio of the mean packet transmission time to the mean backoff time) to maximize the downlink aggregate utility based on the geometric programming. Simulation results are presented to evaluate the performance of our scheduling design and demonstrate the downlink aggregate utility improvement compared to other scheduling schemes in full-duplex WLANs.
... It is worth mentioning that there are some studies on distributed schemes that consider not all the node pairs are in the interference range of each other [17][18][19][20]. In this case, several node pairs can transmit concurrently by exploiting the spatial diversity, and the networks usually involve multiple-channel or multiple-hop scenarios. ...
... where aðpÞ is given in (3). It can be seen from Fig. 2 that if the estimated network throughput ê k out is well below the maximum throughputk max , there is a large difference between aðe p 1 Þ and aðe p 2 Þ, implying that the estimated steady-state point can be readily chosen according to (18). ...
... To this end, we can see that each transmitter only needs to count the number of busy intervals and the ACK frames on the channel during an estimation interval T, and then obtains an estimated network steady-state pointp according to (12)(13)(14)(15)(16)(17)(18). The estimated optimal initial backoff window size can then be obtained as ...
For IEEE 802.11 DCF networks in ad-hoc mode, how to achieve the maximum throughput in a distributed manner draws much attention in previous studies. The problem becomes challenging for partially-saturated heterogeneous networks with multiple groups, as the optimal access parameters not only depend on the group size of saturated groups but also the aggregate input rate of all the unsaturated groups, both of which are hard to obtain without a central controller. In this paper, a novel distributive scheme is proposed for partially-saturated heterogeneous IEEE 802.11 DCF networks to achieve the maximum network throughput. With the proposed scheme, each saturated transmitter can obtain the optimal initial backoff window size distributively by two estimation rounds. In each estimation round, each saturated transmitter only needs to count the number of busy intervals and ACK frames on the channel. For fully-saturated networks, only one estimation round is needed. It is shown by extensive simulations that the proposed scheme can achieve the maximum network throughput in a distributive manner.
... Since [11], much work has been carried out in the field of adaptive CSMA based link scheduling. Ref. [13] study the scheduling algorithm when the sensing time cannot be negligible. Ref. [14] computes the desired link access intensity (ratio of its mean transmission time to its mean back-off time) for each link when the link is unsaturated. ...
In this paper, we study the problem of network utility maximization in a CSMA based multi-hop wireless network. Existing work in this aspect typically adopted continuous time Markov model for performance modelling, which fails to consider the channel conflict impact in actual CSMA networks. To maximize the utility of a CSMA based wireless network with channel conflict, in this paper, we first model its weighted network capacity (i.e., network capacity weighted by link queue length) and then propose a distributed link scheduling algorithm, called CSMA based Maximal-Weight Scheduling (C-MWS), to maximize the weighted network capacity. We derive the upper and lower bounds of network utility based on C-MWS. The derived bounds can help us to tune the C-MWS parameters for C-MWS to work in a distributed wireless network. Simulation results show that the joint optimization based on C-MWS can achieve near-optimal network utility when appropriate algorithm parameters are chosen and also show that the derived utility upper bound is very tight.
... Low-delay scheduling in queueing systems and, more re- cently, wireless sensor networks, has been an active area of research over the last few decades [1], [2], [3], [4], [5], [6]. While the early years of this area saw protocols that at- tempted to improve upon polling techniques already available, recent focus has been on proposing distributed variants of the MaxWeight algorithm [7], handle channel fading, delayed state information as in [8] and propose queue-length-based CSMA protocols [9], [10], [11], etc. ...
We consider the Medium Access Control (MAC)problem in resource-constrained ad-hoc wireless networks typical of the Internet of Things (IoT). Due to the delay-sensitive nature of emerging IoT applications, there has been increasing interest in developing medium access control (TDMA) protocols in a slotted framework. The design of such MAC protocols must keep in mind the need for contention access at light traffic, and scheduled access in heavy traffic (leading to the long-standing interest in hybrid, adaptive MACs.
In this paper, we consider the collocated node setting and require that each node acts autonomously only on the basis of locally available information. We propose EZMAC, a simple extension of ZMAC, and QZMAC which is designed using motivations from our extensions of certain delay-optimality and throughput-optimality theory from the literature. Practical implementation issues are outlined.
Finally, we show, through simulations, that both protocols achieve mean delays much lower than those achieved by ZMAC and indeed, QZMAC provides mean delays very close to the minimum achievable in this setting,i.e., that of the centralized complete knowledge scheduler.
... In [5], [4] the set of achievable throughput vectors of an ideal CSMA/CA network was identified and a dynamic algorithm to set the back-off rates was proposed that was proven to be throughput-optimal. Generalizations of this algorithm in a setting with packet collisions were considered in [21]. An simple approximate algorithm to set the back-off rates to achieve a given target throughput vector that requires only a single iteration was presented in [10]. ...
CSMA/CA networks have often been analyzed using a stylized model that is fully characterized by a vector of back-off rates and a conflict graph. Further, for any achievable throughput vector $\vec \theta$ the existence of a unique vector $\vec \nu(\vec \theta)$ of back-off rates that achieves this throughput vector was proven. Although this unique vector can in principle be computed iteratively, the required time complexity grows exponentially in the network size, making this only feasible for small networks. In this paper, we present an explicit formula for the unique vector of back-off rates $\vec \nu(\vec \theta)$ needed to achieve any achievable throughput vector $\vec \theta$ provided that the network has a chordal conflict graph. This class of networks contains a number of special cases of interest such as (inhomogeneous) line networks and networks with an acyclic conflict graph. Moreover, these back-off rates are such that the back-off rate of a node only depends on its own target throughput and the target throughput of its neighbors and can be determined in a distributed manner. We further indicate that back-off rates of this form cannot be obtained in general for networks with non-chordal conflict graphs. For general conflict graphs we nevertheless show how to adapt the back-off rates when a node is added to the network when its interfering nodes form a clique in the conflict graph. Finally, we introduce a distributed chordal approximation algorithm for general conflict graphs which is shown (using numerical examples) to be more accurate than the Bethe approximation.
... Future work may also explore physical layer design guidelines for minimizing delay when contention based random multiple access methods are employed. Here, the optimization strategy for minimizing the average packet delay must take into account the errors due to packet collision, other than errors at the receiver due to channel noise [45], [46]. ...
We consider a system where users are polled for transmission by a central server, and the link layer of each user employs automatic repeat request (ARQ) to ensure error-free delivery of packets. We present a cross-layer approach for reducing average packet delay (queuing delay plus service time). It is known that forward error correction (FEC) schemes can potentially lower the average packet delay by reducing the packet error probability (PEP) and, hence, the number of retransmissions. However, more precise results in the literature are few and far between. In this paper, we first establish that relative to an uncoded system, it is sufficient to reduce the average service time (AST) using FEC to achieve lower average packet delay. We then study and quantify the reduction in AST that can be achieved using the best possible FEC codes. The specific findings and contributions from our work are as follows: 1) We provide several bounds on the reduction in AST using the best possible FEC codes; 2) we give a sufficient condition when no FEC scheme can reduce the AST; 3) for Gaussian channels, we find that a relatively high PEP $(\sim\!\!\text{10}^{-2})$ , which is obtained using as high a coding rate as possible, typically results in sufficiently small AST; 4) the performance of optimum maximum-likelihood decoding can be approached by a lower complexity bounded distance decoder; and 5) average packet delay can be further reduced in certain cases by opportunistically combining and encoding several packets jointly.
