Slotted ALOHA System Research Articles

MIMO slotted ALOHA systems with collision resolution and truncated HARQ transmission and combining

In this paper, we investigate throughput and delay enhancement for two multi-user multiple-input multiple-output (MIMO) systems one with space-time block coding (STBC), the other with spatial multiplexing (SM) at the transmitter. Users operate using the slotted ALOHA (SA) protocol to access the wireless channel resulting in a high probability of collision. For both systems, we consider the uplink scenario, and we propose to recover the collided packets with spatial successive interference cancelation (SSIC) and a protocol for retransmission and combining of unsuccessfully received collided packets applying a truncated Hybrid Automatic Repeat reQuest (HARQ) scheme. For the first system, we propose to use channel realizations of collided packets as different signatures to separate them. Moreover, we propose a solution for the problem when the received powers are comparable. For this system, we note that the orthogonality of the STBC matrix allows the use of a simple linear processing step for the initialization of SSIC. For the SM multi-user system, the separation of collided packets is based on V-BLAST processing and SSIC. We also propose how to combine retransmitted packets. For both systems, we evaluate the block error rate, the throughput, and the delay. A comparison is done with the single-user case and with other receivers proposed in the literature.

The impact of stochastic resource availability on cognitive network performance: modeling and analysis

AbstractCognitive radio networks emerge as a promising solution for overcoming shortage and inefficient use of bandwidth resources by allowing secondary users (SUs) to access the primary users' (PUs) channel so long as they do not interfere with them. The dynamical spectrum availability makes SU's packet average delay one of the most important performance measures of a cognitive network. It is important to understand the nature of delay, as well as its dependence on PU behaviors. In this paper, we analytically model and analyze the dynamics of the spectrum availability and their impact on the SU's packet delay. The cognitive network is modeled as a discrete‐time queueing system. PU channel occupancy is modeled as a two‐state Markov chain. Our contribution in this paper is defining and characterizing the properties of the random process that describes the availability of the opportunistic resources. In addition, we apply the mean residual service time concept to achieve an analytical solution for the queueing delay. Moreover, inspired by the slotted Aloha system, we model the packet service mechanism and determine the manner in which it depends on the resource availability. The delay becomes unbounded if the spectrum availability dynamics are not carefully considered in network design. Copyright © 2015 John Wiley & Sons, Ltd.

Joint Routing and Medium Access Control in Fixed Random Access Wireless Multihop Networks

We study cross-layer design in random-access-based fixed wireless multihop networks under a physical interference model. Due to the complexity of the problem, we consider a simple slotted ALOHA medium access control (MAC) protocol for link-layer operation. We formulate a joint routing, access probability, and rate allocation optimization problem to determine the optimal max-min throughput of the flows and the optimal configuration of the routing, access probability, and transmission rate parameters in a slotted ALOHA system. We then also adapt this problem to include an XOR-like network coding without opportunistic listening. Both problems are complex nonlinear and nonconvex. We provide extensive numerical results for both problems for medium-size mesh networks using an iterated optimal search technique. Via numerical and simulation results, we show that: 1) joint design provides a significant throughput gain over a default configuration in slotted-ALOHA-based wireless networks; and 2) the throughput gain obtained by the simple network coding is significant, especially at low transmission power. We also propose simple heuristics to configure slotted-ALOHA-based wireless mesh networks. These heuristics are extensively evaluated via simulation and found to be very efficient.

A Terminal-Assisted Bayesian Broadcasting Algorithm for S-ALOHA Systems with Finite Population of Multi-Buffered Terminals

This letter proposes a backoff algorithm for slotted ALOHA (S-ALOHA) systems with multi-buffered terminals. According to the proposed algorithm, a base station (BS) broadcasts a retransmission probability based on estimated backlog size, while the terminals help the BS to estimate the backlog size by sending a one-bit backlog indication piggybacked on the information packet upon a successful random access. We present the performance of the proposed algorithm in terms of mean and variance of system response time, and compare them against existing algorithms and the optimal one. Results show that the proposed algorithm can improve the performance significantly especially for high packet arrival rates, small population size and asymmetric traffic cases.

Asymptotic Stability Region of Slotted Aloha

We analyze the stability of standard, buffered, slotted-Aloha systems. Specifically, we consider a set of $N$ users, each equipped with an infinite buffer. Packets arrive into user $i$ 's buffer according to some stationary ergodic Markovian process of intensity $\lambda_{i}$ . At the beginning of each slot, if user $i$ has packets in its buffer, it attempts to transmit a packet with fixed probability $p_{i}$ over a shared resource/channel. The transmission is successful only when no other user attempts to use the channel. The stability of such systems has been open since their very first analysis in 1979 by Tsybakov and Mikhailov. In this paper, we propose an approximate stability condition that is provably exact when the number of users $N$ grows large. We provide theoretical evidence and numerical experiments to explain why the proposed approximate stability condition is extremely accurate even for systems with a restricted number of users (even two or three).

Modeling and Estimation of One-Shot Random Access for Finite-User Multichannel Slotted ALOHA Systems

This paper presents a combinatorial model and approximation formulas to estimate the average number of successful and collided users for a one-shot random access in finite-user multichannel slotted ALOHA systems. The proposed model and approximation can be used to evaluate the performance of group paging for machine-type communication (MTC) in 3GPP LTE. Numerical results demonstrate the applicable range of the approximation formulas and the accuracy of the derived performance metrics.

An Exact Combinatorial Analysis for the Performance Evaluation of Framed Slotted Aloha Systems with Diversity Transmission Over Erasable Wireless Channels

Framed Slotted Aloha (FSA) protocols are widely used in various communication systems. This paper investigates the performance of FSA systems that employ diversity transmission (DT) techniques over...

Throughput Region of Random-Access Networks of General Topology

A random-access model is introduced and studied, which is a generalization of the classical slotted Aloha model. Unlike in the slotted Aloha, where two or more simultaneous transmissions on any subset of links collide and “erase” each other, a quite general interference structure is considered, where transmission on link <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> erases a simultaneous transmission on link <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</i> with some fixed probability φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ij</i> . In particular, it is allowed that φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ij</i> ≠ φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ji</i> , which captures possible asymmetric interference in real-most notably wireless-communication networks. Results characterizing the maximum achievable link throughput region and its Pareto boundary are derived. In some cases, the Pareto boundary characterization is almost as simple and explicit as that derived in prior work for the classical slotted Aloha system.

Estimating Collision Set Size in Framed Slotted Aloha Wireless Networks and RFID Systems

In wireless networks and RFID systems, a collision set is a group of nodes such that the simultaneous transmission of two or more nodes generates destructive interference at the receiver and, consequently, the loss of all transmitted packets. Knowing the number of nodes in the collision set, i.e., the collision set size, it is possible to design effective channel access strategies that minimize the time required to read all the tags or, more generally, collect the packets generated by each node in the set. However, the collision set size is often unknown and, then, needs to be estimated. In this paper we propose a novel estimation method for Framed Slotted Aloha systems that applies a maximum likelihood argument on a Poisson approximation of the packet arrivals process to the transmission channel, yielding an estimate with minimal mean error and mean square error, with respect to the best-performing estimate algorithms in the literature having similar complexity.

Hierarchy sustains partial cooperation and induces a Braess-like paradox in slotted aloha-based networks

This paper studies a hierarchical distributed choice of retransmission probabilities in slotted aloha. In particular, we consider a wireless system composed of one central receiver and several selfish mobile users communicating via the slotted aloha protocol. The set of mobile users is split into two classes: leaders and followers. We then study the induced non-cooperative hierarchical game based on the Stackelberg equilibrium concept. Using a 4D Markovian model, we compute the steady state of the system and derive the average throughput and the expected delay as well. We start by discussing the protocol design and propose a controlled slotted aloha using a virtual controller. The virtual controller can sustain partial cooperation among concurrent mobile users when accessing the channel by making the channel lossy. This leads us to identify a Braess-like paradox in which reducing capacity to the system may improve the performance of all mobile users. We then investigate the impact of hierarchy among mobile users in such a random access protocol and discuss how to distribute leader/follower roles. We show that the global performance of the system is improved compared to standard slotted aloha system. However, slight performances slow-down may be observed for the followers group when the total number of mobile users is relatively small.

Random Access Game in Fading Channels With Capture: Equilibria and Braess-like Paradoxes

The Nash equilibrium point of the transmission probabilities in a slotted ALOHA system with selfish nodes is analyzed. The system consists of a finite number of heterogeneous nodes, each trying to minimize its average transmission probability (or power investment) selfishly while meeting its average throughput demand over the shared wireless channel to a common base station (BS). We use a game-theoretic approach to analyze the network under two reception models: one is called power capture, the other is called signal to interference plus noise ratio (SINR) capture. It is shown that, in some situations, Braess-like paradoxes may occur. That is, the performance of the system may become worse instead of better when channel state information (CSI) is available at the selfish nodes. In particular, for homogeneous nodes, we analytically present that Braess-like paradoxes occur in the power capture model, and in the SINR capture model with the capture ratio larger than one and the noise to signal ratio sufficiently small.

Design and Analysis of Cross-Layer Contention Resolution Algorithms for Multi-Packet Reception Slotted ALOHA Systems

In this paper, we propose contention resolution algorithms for immediate and deferred first-transmission protocols in a multi-packet reception slotted ALOHA system based on code division multiple access. The system employs a central base station that broadcasts the retransmission probability for each slot to all mobile terminals within its coverage. The base station estimates the system backlog by exploiting cross-layer information on multiple access interference. Based on this information, the retransmission probability is chosen in order to maximize the expectation of the system throughput conditioned on the number of retransmitting terminals. The performance of our algorithms and the system stability are evaluated by theoretical analysis and compared to simulations. Under perfect power control it is shown that our algorithms are stable and their performance very closely approaches the analytical upperbound of the system throughput. Under imperfect power control, the simulation result shows that the algorithms remain robust in maintaining 50% throughput efficiency in a coded system with 2 dB in power control errors.

A self‐stabilized random access protocol against denial of service attack in wireless networks

AbstractOne of the main drawbacks of Slotted ALOHA is its throughput collapse at higher traffic load condition due to excessive collisions and known as stability problem. A random packet destruction Denial of Service (DoS) attack can increase the throughput collapse by increasing the collisions further. The current security protection techniques such as encryption, authentication and authorization cannot prevent these types of attacks, since the attacking packets destroy those packets by colliding those encrypted, authenticated and authorized packets. The maximum throughput of Slotted ALOHA can be achieved by the knowledge of the number of active mobile nodes and the average rate of the attacking packet arrival rate. However, the knowledge of these two parameters' current values are difficult and sometimes impossible to know. A self‐stabilized Slotted ALOHA system against the random packet destruction attacking noise packets is presented in this paper. Results show that the system provides nearly optimal stable throughput without the knowledge of current active number of mobile nodes and current attacking packets arrival rate. The proposed system is truly distributive in nature and can be easily implemented in wireless access systems without requiring any centralized control and can defend against random packet destruction DoS attack. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Partial Interference and Its Performance Impact on Wireless Multiple Access Networks

To determine the capacity of wireless multiple access networks, the interference among the wireless links must be accurately modeled. In this paper, we formalize the notion of the partial interference phenomenon observed in many recent wireless measurement studies and establish analytical models with tractable solutions for various types of wireless multiple access networks. In particular, we characterize the stability region of IEEE 802.11 networks under partial interference with two potentially unsaturated links numerically. We also provide a closed-form solution for the stability region of slotted ALOHA networks under partial interference with two potentially unsaturated links and obtain a partial characterization of the boundary of the stability region for the general M-link case. Finally, we derive a closed-form approximated solution for the stability region for general M-link slotted ALOHA system under partial interference effects. Based on our results, we demonstrate that it is important tomodel the partial interference effects while analyzing wireless multiple access networks. This is because such considerations can result in not only significant quantitative differences in the predicted system capacity but also fundamental qualitative changes in the shape of the stability region of the systems.

New approach for improving throughput in multi-channel packet radio systems

A new approach for improving the throughputs of multichannel packet radio systems is proposed. Based on the characteristics of multi-code CDMA technology, the scheme factitiously improves the transmission bit rate of a terminal by compressing the packet transmission time and thereby increases the number of the orthogonal spreading codes used by the terminal. By this means, the average interference level of the system is reduced and the system capacity is improved. Simulation results show that the proposed scheme exhibits larger throughput compared with the traditional multi-code CDMA slotted Aloha systems.

Random Access: An Information-Theoretic Perspective

This paper considers a random access system where each sender can be in two modes of operation, active or not active, and where the set of active users is available to a common receiver only. Active transmitters encode data into independent streams of information, a subset of which are decoded by the receiver, depending on the value of the collective interference. The main contribution is to present an information-theoretic formulation of the problem which allows us to characterize, with a guaranteed gap to optimality, the rates that can be achieved by different data streams. Our results are articulated as follows. First, we exactly characterize the capacity region of a two-user system assuming a binary-expansion deterministic channel model. Second, we extend this result to a two-user additive white Gaussian noise channel, providing an approximate characterization within $\sqrt{3}/2$ bit of the actual capacity. Third, we focus on the symmetric scenario in which users are active with the same probability and subject to the same received power constraint, and study the maximum achievable expected sum-rate, or throughput, for any number of users. In this case, for the symmetric binary expansion deterministic channel (which is related to the packet collision model used in the networking literature), we show that a simple coding scheme which does not employ superposition coding achieves the system throughput. This result also shows that the performance of slotted ALOHA systems can be improved by allowing encoding rate adaptation at the transmitters. For the symmetric additive white Gaussian noise channel, we propose a scheme that is within one bit of the system throughput for any value of the underlying parameters.

A Game-Theoretic Approach for Exploiting Multiuser Diversity in Cooperative Slotted Aloha

Multiuser diversity gains can be achieved by assigning channels to users with better channel quality in multiuser systems. To avoid the extensive information exchange required for centralized approaches, we propose a distributed fair pricing strategy for a slotted Aloha system in which users act selfishly to improve their own utilities for both the collision model and the multipacket reception (MPR) model. Based on a game theoretic framework, we show that multiuser diversity gains can be achieved by appropriately designing the Nash equilibrium thresholds for the selfish users to preserve the throughput and revenue achieved in the classical slotted Aloha systems. The network enforces fairness among different users by employing a pricing policy that favors equal access probabilities. Our simulation results show that significant multiuser diversity gains are achieved in terms of energy consumption and/or spectral efficiency.

Communication Through Jamming Over a Slotted ALOHA Channel

This correspondence derives bounds on the jamming capacity of a slotted ALOHA system. A system with n legitimate users, each with a Bernoulli arrival process is considered. Packets are temporarily stored at the corresponding user queues, and a slotted ALOHA strategy is used for packet transmissions over the shared channel. The scenario considered is that of a pair of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">illegitimate</i> users that jam legitimate transmissions in order to communicate over the slotted ALOHA channel. Jamming leads to binary signaling between the illegitimate users, with packet collisions due to legitimate users treated as (multiplicative) noise in this channel. Further, the queueing dynamics at the legitimate users stochastically couples the jamming strategy used by the illegitimate users and the channel evolution. By considering various independent and identically distributed (i.i.d.) jamming strategies, achievable jamming rates over the slotted ALOHA channel are derived. Further, an upper bound on the jamming capacity over the class of all ergodic jamming policies is derived. These bounds are shown to be tight in the limit where the offered system load approaches unity.

Design and Analysis of Store-and-Forward Data Collection Network using Low-cost LEO Nanosatellite and Intelligent Terminals

[Abstract] There have been a lot of studies about Low Earth Orbit satellite constellations but very few have dealt with a single LEO satellite. The use of a single LEO satellite implies a complex hardware and software architectures both of the satellite payload and the ground terminals, especially when they are designed to be small, and economical. The Nanosatellite, as small as the Cubesat concept, requires employment of a simple store-and-forward payload whereas all the complexity is brought back to the terminals. This paper describes the design and analysis of store-and-forward data collection network using low-cost LEO Nanosatellite and intelligent ground terminals situated all over the world. The study will employ the Slotted-ALOHA multiple access in the uplink and will assess its efficiency in terms of the maximum number of ground terminals that can be served by the Nanosatellite along with the delays experienced in the packet transfer. In this work, we will establish a mathematical model for evaluating the performance of the slotted aloha system and then we will present a comparison between an analytical model and simulation results by using discrete event simulations. In such a system, two appropriate measures of the performance are the throughput and the average delay; thus, we will use these measures in this paper. A good correlation between analytical model and the discrete event simulations was found.

Opportunistic medium access for wireless networking adapted to decentralized CSI

Relative to a centralized operation, opportunistic medium access capitalizing on decentralized multiuser diversity in a channel-aware homogeneous slotted Aloha system with analog-amplitude channels has been shown to incur only partial loss in throughput due to contention. In this context, we provide sufficient conditions for stability as well as upper bounds on average queue sizes, and address three equally important questions. The first one is whether there exist decentralized scheduling algorithms for homogeneous users with higher throughputs than available ones. We prove that binary scheduling maximizes the sum-throughput. The second issue pertains to heterogeneous systems where users may have different channel statistics. Here we establish that binary scheduling not only maximizes the sum of the logs of the average throughputs, but also asymptotically guarantees fairness among users. The last issue we address is extending the results to finite state Markov chain (FSMC) channels. We provide a convex formulation of the corresponding throughput optimization problem, and derive a simple binary-like access strategy