Slotted ALOHA Networks Research Articles

CLSP with channel clearance for spread slotted ALOHAnetwork

A new CLSP with channel clearance (CLSP/CC) is proposed for obtaining better network performances in spread slotted ALOHA networks. This protocol can decrease wasteful channel usage by prohibiting continuous transmissions of packets already destroyed in previous slot, with little added network complexities. To validate the performance improvements of our protocol, both simulation and analysis are considered. As a result, the network using the proposed CLSP/CC is superior to that with CLSP, and also to the conventional one, especially when the system capacity is half of the offered load, and improves as the threshold for CLSP increases to network capacity.

Retransmission control and fairness issue in mobile slotted ALOHA networks with fading and near-far effect

The effects of different retransmission control policies on the performance of a mobile data system employing the slotted ALOHA protocol are investigated, with the emphasis on the unfairness between close-in and distant users due to the near-far effect. An analytical multi-group model is developed to evaluate both the user and the network performance of the mobile slotted ALOHA network under two classes of retransmission control policies, namely the Uniform Policy and the Nonuniform Policy. The Uniform Policy requires that all users adopt the same retransmission probability, whereas the Nonuniform Policy allows more distant users to have larger retransmission probability in order to compensate for the unfairness caused by the near-far effect. The performance of a slotted ALOHA network with a linear topology in a Rician fading channel under the two policies is compared by the multi-group model and simulation. The Nonuniform Policy is found to be more effective in alleviating the unfairness of user throughput over a wider range of the data traffic load than the Uniform Policy, which is effective only when the data traffic load is very light. Thus, a mobile data network can enjoy the network performance improvement derived from the near-far effect while the unfairness between close-in and distant users can be greatly mitigated without resorting to power control.

Performance analysis of a slotted CDMA ALOHA network

ALOHA is a simple and efficient way of allowing many machines with bursty data streams to communicate with a central computer. For cases where machines are equally likely to transmit to one another, CDMA ALOHA, which allows for full connectivity, may be a better multiple access protocol than slotted ALOHA through a central machine. This paper first describes a model for a fully connected, full duplex, and slotted CDMA ALOHA network where the “receiver-based code” access protocol is used. The stations can send data to, and receive data from, different stations simultaneously. The model is analyzed using discrete-time Markov chain, and some numerical results are presented. For a system with a large number of users where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system and determine the throughput as well as the delay performance of the system when it is stable. It is shown that a CDMA slotted ALOHA network has a much better performance compared to simple slotted ALOHA networks.

Performance analysis of a fully-connected, full-duplex CDMA ALOHA network with channel sensing and collision detection

In cases where machines having bursty data are equally likely to transmit to one another, code-division multiple-access (CDMA) ALOHA which allows for an individual "virtual channel" for each receiving station may be a better multiple-access protocol than simple ALOHA. With the use of a "receiver-based code" multiple-access protocol, it is also possible for a station to listen to the channel of the intended receiver before transmission, and also abort transmission when it detects others transmitting on the same channel. This paper describes a model for a fully-connected, full duplex, and slotted CDMA ALOHA network where channel sensing and collision detection are used. The model is analyzed using a discrete time Markov chain and some numerical results are presented. For a system with a large number of users, where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system, and estimate the throughput as well as the delay performance of the system when it is stable. Finally, a comparison is made with a simple channel sense multiple-access with collision detection (CSMA-CD) network, showing that a substantial improvement in the performance is achieved by the proposed network.

On adaptive control of mobile slotted aloha networks

An adaptive control scheme for mobile slotted ALOHA is presented and the effect of capture on the adaptive control scheme is investigated. It is shown that with the proper choice of adaptation parameters the adaptive control scheme can be made independent of the effect of capture.

Recursive retransmission control for a two-station slotted-ALOHA network

Develops a first-order recursive retransmission control policy for a two-station slotted-ALOHA network. Under this policy, terminals adjust their retransmission probability at the end of each slot based on feedback from the current slot. The fundamental difference between a single-station and a two-station network is the interaction between the terminal groups. This interaction occurs because some terminals are in transmission range of both stations; when these terminals transmit to their station they also interfere with the other station. The retransmission control keeps the offered traffic levels near the maximum throughput point and divides the channel capacity fairly between the two terminal groups. The control is intuitively appealing: to acquire channel capacity in proportion to its arrival rate, each group balances efforts to increase its throughput with a certain backoff that permits channel use by the other group.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance analysis of slotted aloha over time‐varying channels

AbstractThis paper considers a slotted ALOHA network which consists of a central base station and many mobile terminals. In classical performance analyses of random access networks, a channel between the station and a terminal is assumed to be always in a good state. However, this is not the case in mobile radio networks since the channel suffers from many factors such as fading, shadowing, and so on. Moreover, the channel condition changes with the terminal location.In this paper, a simple channel model is used to consider the effects of time‐varying channels in a random access network. The channel model assumed in this paper has three states: shadowing, good, and bad. The transitions between the channel states are described by a Markov chain. The dynamic performance of a slotted ALOHA network over such time‐varying channels is evaluated by means of the equilibrium point analysis. Then the influence of the time‐varying channel on the throughput performance of a slotted ALOHA network is studied.

The analysis of the expected successful operation time of slotted ALOHA

It has been well-known for nearly 20 years that the bistable behavior of infinite population slotted ALOHA networks causes the unpleasant effect of eventually reaching an overloaded state, where the number of backlogged stations becomes larger and larger and the useful throughput reduces to zero. The detailed analysis reveals that this statement is true for any average offered load lambda >0, regardless of the retransmission probability p. A challenging, and to the best of the authors' knowledge, not sufficiently solved problem within this context concerns the time until this destabilization occurs. This question is successfully answered based on the fact that the operation of the system may be viewed as a sequence of consecutive busy periods, each starting from backlog 0 and return to backlog 0. It turns out that the whole period of successful operation S consists of a finite sequence of busy periods of finite lengths, which is terminated by an infinite busy period (which never returns to backlog 0). Further analysis of this simple renewal process leads to an infinite dimensional system of linear equations, which is shown to have only one meaningful solution. A pair of upper and lower asymptotic bounds for that solution eventually provide the key to the major result, an asymptotic formula for the average number of slots up to the beginning of the infinite busy period, uniformly for p to 0 and lambda to 0. >

Heterogeneous ALOHA networks: a sufficient condition for all equilibrium states to be stable

This paper models and analyzes the stability of a slotted-ALOHA network hosting heterogeneous users. The scheme is modeled by dividing the total user-population into groups of homogeneous users. The behavior of the system is represented by state equations. The stability analysis is carried out by Liapunov's indirect method, in association with the properties of M-matrix, to obtain the sufficient condition for the structural stability of the networks. The analysis also points out the method of hierarchical grouping of the heterogeneous users.

Stability of mobile slotted ALOHA network with Rayleigh fading, shadowing, and near-far effect

Dynamic network behavior is investigated using the classical ALOHA queueing model extended to mobile channels. The focus is on the assessment of receiver capture probabilities, based on a general propagation model for mobile radio communications. Queueing of packets in a mobile slotted ALOHA network with Rayleigh fading, shadowing, and UHF groundwave propagation is studied, using a finite Markov chain model. It is shown that receiver capture, assisted by all three propagation mechanisms, reduces bistability of the network substantially compared to the retransmission strategy. Results are presented for a uniform spatial distribution of the packet traffic ordered to the ALOHA channel. The near-far effect is highlighted, since the total network performance and the spatial distribution of the attempted traffic interact. >

A simple and versatile decentralized control for slotted ALOHA, reservation ALOHA, and local area networks

A simple, decentralized control for reducing the delays and stabilizing random-access channels is presented. The control, which is based on a computationally efficient recursive implementation of the minimum mean-squared error (MMSE) predictor of the channel backlog, applies to slotted ALOHA, to reservation ALOHA, and to local area networks (LANs) with carrier-sense multiple access (CSMA) or CSMA with collision detection (CSMA/CD) protocols. The MMSE predictor controller (MMSE-PC) can stabilize the slotted ALOHA for all traffic rates not exceeding e/sup -1/, and it can achieve stable throughput arbitrarily close to one with finite delays in the reservation ALOHA and in LANs. Extensive simulation has shown that the MMSE-PC performs extremely well in all three random-access environments. For the implementation of the MMSE-PC in LANs, synchronization of transmissions is not required but it is required in slotted ALOHA and reservation ALOHA. The MMSE-PC has been implemented in hardware and tested in asynchronous LANs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Capacity of Slotted ALOHA in Rayleigh-Fading Channels

Fading channels may improve the capacity of slottedALOHA networks. Rayleigh fading and spatially distributed packet transmitters diminish mutual packet interference and thus reduce the average blocking probability of a shared receiver. A transmission model, combining Poisson statistics of the offered data traffic with Rayleigh statistics for the fading channel, is developed. Analytical and numerical results are presented, indicating significant improvements to signaling in cellular mobile networks and in packet radio systems with fading radio channels.

Analysis of mobile radio slotted ALOHA networks

Given a mobile terminal transmitting a message to some receiver, the level at the receiver will be affected by path loss and by fading phenomena. Transmissions from different terminals will suffer different attenuations on their respective ways to the receiver and will therefore yield different levels at the receiver. Thanks to the capture effect, the receiver will now be able to read the message with the strongest signal, provided that it is sufficiently stronger than its contenders. In a mobile radio ALOHA network this means that a packet collision need not necessarily destroy all packets involved. A Markov model is developed for slotted ALOHA networks with capture and it is shown that the throughput in such a network can be markedly greater than the famous 1/e. Perhaps even more important is the result that such networks are very stable under overload.

Analysis of Mobile Radio Slotted ALOHA Networks

Given a mobile terminal transmitting a message to some receiver, the level at the receiver will be affected by path loss and by fading phenomena. Transmissions from different terminals will suffer different attenuations on their respective ways to the receiver and will therefore yield different levels at the receiver. Thanks to the capture effect, the receiver will now be able to read the message with the strongest signal, provided that it is sufficiently stronger than its contenders. In a mobile radio ALOHA network this means that a packet collision need not necessarily destroy all packets involved. A Markov model is developed for slotted ALOHA networks with capture and it is shown that the throughput in such a network can be markedly greater than the famous 1/e . Perhaps even more important is the result that such networks are very stable under overload.

On the Capacity of Single-Hop Slotted ALOHA Networks for Various Traffic Matrices and Transmission Strategies

In this paper we formulate a general model of the capacity of single-hop slotted ALOHA networks. We find that the capacity can be expressed as a function of the nodal degree (i.e., number of nodes within range of a transmitter). We than evaluate this model for various traffic matrices. In order to satisfy the requirements of a given traffic matrix, the transmission power is selected accordingly and this determines the degree of the nodes and, hence, the network performance. Finally we compare our results to simulation studies.

On the Capacity of Multihop Slotted ALOHA Networks with Regular Structure

In this paper we investigate the capacity of networks with a regular structure operating under the slotted ALOHA access protocol. We first consider circular (loop) and linear (bus) networks and then proceed to two-dimensional networks. For one-dimensional networks we find that the capacity is basically independent of the network average degree and is almost constant with respect to network size. For two-dimensional networks we find that the capacity grows in proportion to the square root of the number of nodes in the network provided that the average degree is kept small. Furthermore, we find that reducing the average degree (with certain connectivity restrictions) allows a higher throughput to be achieved. We also investigate some of the peculiarities of routing in these networks.

On the Capacity of Slotted ALOHA Networks and Some Design Problems

Packet switching over broadcast channels with random access schemes is of current interest for local distribution system and for satellite channels. This mode of operation is useful when the communicating devices are mobile and when the ratio of the peak to average data rate requirement of each device is high. Such systems have been analyzed for the case in which all communicating devices are within an effective transmission range of each other; either directly or through the satellite. In this paper, we address broadcast networks in which originating devices cannot directly reach the destination receiver. Thus, devices are introduced which receive these packets and repeat them to the destination. The capacity (maximum throughput) of such systems is determined, and design problems related to the number of repeating devices and the usefulness of directional antennas are resolved.