Multihop Packet Radio Networks Research Articles

Broadcast scheduling in packet radio networks by Hopfield neural networks

A multihop packet radio network is a packet switching network where nodes communicate by radio signals. When used in real-time multimedia or military communication networks, it is very important to broadcast a packet from a source node to all other nodes as quickly as possible. Unfortunately, the problem of finding an optimal schedule to minimize the time needed to complete the broadcast for a general multihop packet radio network is NP-complete. We propose a Hopfield neural network solution for one-source-node broadcasting in a multihop packet radio network. The proposed neural network model always finds a good solution by trying to maximize the number of correctly receiving nodes in every time slot. Experiments indicate good results. The model requires n processing elements (neurons) for an n-node radio network.

Optimal transmission ranges for mobile communication in linear multihop packet radio networks

The analysis of multihop radio transmission for randomly distributed terminals in the plane has drawn a lot of attention in the literature. Several routing strategies have been investigated concerning throughput and normalized expected progress. Because of mathematically intractable problems all analyses use simulation studies as part of the derivation. In this paper we present a one-dimensional model to investigate the performance of multihop networks. This model seems to be more adequate for applications in road traffic information systems. Three routing strategies 'most forward with fixed transmission range', 'positively most forward with fixed transmission range', and 'positively most forward with variable transmission range' are analyzed on the basis of a complete mathematical description. We also consider directional antennas. The results are presented in closed formulae which are evaluated numerically and depicted in corresponding diagrams. It turns out that adjusted transmission ranges enlarge network performance. Furthermore, some interesting differences to the usual two-dimensional random model occur.

Determination of dependent and independent communication paths using neural networks.

Efficient and timely computation of routing algorithms is very important for proper operation of multihop packet radio networks. When a network operates in the presence of jammers (a hostile environment) additional constraints must be considered when computing the routing tables. Insertion of those constraints in routing algorithms enables the determination of dependent and independent paths between source and destination nodes, thus fixing lower limits on the number of external jamming sources required to sever a transmission. An important measure of network reliability is also provided. This paper proposes a solution to the routing problem through the implementation of a Hopfield network and demonstrates that by proper selection of an energy function we can solve the problem rapidly and reliably.

Multicluster, mobile, multimedia radio network

A multi-cluster, multi-hop packet radio network architecture for wireless adaptive mobile information systems is presented. The proposed network supports multimedia traffic and relies on both time division and code division access schemes. This radio network is not supported by a wired infrastructure as conventional cellular systems are. Thus, it can be instantly deployed in areas with no infrastructure at all. By using a distributed clustering algorithm, nodes are organized into clusters. The clusterheads act as local coordinators to resolve channel scheduling, perform power measurement/control, maintain time division frame synchronization, and enhance the spatial reuse of time slots and codes. Moreover, to guarantee bandwidth for real time traffic, the architecture supports virtual circuits and allocates bandwidth to circuits at call setup time. The network is scalable to large numbers of nodes, and can handle mobility. Simulation experiments evaluate the performance of the proposed scheme in static and mobile environments.

Optimum transmission ranges in multihop packet radio networks in the presence of fading

The evaluation of optimum transmission ranges in a packet radio network in a fading and shadowing environment is considered. It is shown that the optimal probability of transmission of each user is independent of the system model and is p/sub o//spl sime/0.271. The optimum range should be chosen so that on the average there are /spl chi/(G/b)/sup 2//spl eta// terminals closer to the transmitter than the receiver, where G is the spread spectrum processing gain, b is the outage signal-to-noise ratio threshold, /spl eta/ is the power loss factor and /spl chi/ depends on the system parameters and the propagation model. The performance index is given in terms of the optimal normalized expected progress per slot, given by /spl thetav/(G/b)/sup 1//spl eta// where /spl thetav/ is proportional to the square root of /spl chi/. A comparison with the results obtained by using deterministic propagation models shows, for typical values of fading and shadowing parameters, a reduction up to 40% of the performance index.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analyzing routing strategy NFP in multihop packet radio networks on a line

Presents a one-dimensional model to analyze routing strategy NFP (nearest with forward progress) for a multihop packet radio network. It is assumed that each station has adjustable transmission range to address target nodes, distributed on a line according to a nonhomogeneous Poisson process. NFP transmits to the nearest neighbor in the desired direction with transmission range as small as possible, to minimize the probability of collisions. This model is appropriate e.g. for road traffic information systems. The analysis is based on a complete mathematical description, the solution of certain differential equations is one of the key points to arrive at a closed form solution. Results are presented. Graphically, it turns out that NFP has uniformly largest throughput, while progress behaves comparably to other routing strategies proposed in the literature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A neural network approach to solving the link activation problem in multihop radio networks

We address the problem of link activation or scheduling in multihop packet radio networks. The objective is to determine a conflict-free schedule of minimum length that satisfies the specified end-to-end communication requirements. It is well known that this problem, in almost all of its forms, is a combinatorial-optimization problem of high complexity. We approach this problem by the use of a Hopfield neural network model in which the method of Lagrange multipliers is used to vary dynamically the values of the coefficients used in the connection weights. >

Effect of Rayleigh fading in a multihop mobile packet radio network with capture

We study the effect of Rayleigh fading in a multihop mobile packet radio network (PRN) with capture. Four transmission strategies based on two previously proposed routing schemes, most forward with fixed range (MFR) and nearest with forward progress (NFP), and two new routing schemes, minimal angular deviation (MAD) and angular deviation to transmission range ratio (ARR), are studied. Results show that the transmission strategy based on the ARR routing scheme is generally superior to those based on the other three routing schemes. It is found that all four transmission strategies perform worse in the presence of Rayleigh fading. This is in contrast to single-hop systems in which Rayleigh fading generally does not result in poorer performance. >

A distributed routing algorithm for multihop packet radio networks with uni- and bi-directional links

Multihop packet radio networks require routing algorithms which are distributed in nature and which have the ability to timely detect changes in the network topology. These changes are mostly changes in connectivity caused by link or node failures and by the relative motion of the nodes. This paper describes and analyzes an adaptive decentralized routing algorithm for packet radio networks. The network connectivity, as perceived by each node, is translated into a graph representation of the network. The proposed routing mechanism then uses a breadth-first search algorithm along the inbound links of such a graph. Unlike most of the algorithms found in the open literature the one proposed here can be used in networks having both uni- and bi-directional radio links. Examples are shown to illustrate the methodology. >

Code assignment for hidden terminal interference avoidance in multihop packet radio networks

Hidden terminal interference is caused by the (quasi-) simultaneous transmission of two stations that cannot hear each other, but are both received by the same destination station. This interference lowers the system throughput and increases the average packet delay. Some random access protocols that reduce this interference have been proposed, e.g., BTMA protocol. However, the hidden terminal interference can be totally avoided only by means of code division multiple access (CDMA) schemes. In the paper, the authors investigate the problem of assigning orthogonal codes to stations so as to eliminate the hidden terminal interference. Since the codes share the fixed channel capacity allocated to the network in the design stage, their number must not exceed a given bound. The authors seek assignments that minimize the number of codes used. They show that this problem is NP-complete, and thus computationally intractable, even for very restricted but very realistic network topologies. Then, they present optimal algorithms for further restricted topologies, as well as fast suboptimal centralized and distributed heuristic algorithms. The results of extensive simulation set up to derive the average performance of the proposed heuristics on realistic network topologies are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Throughput optimization in single commodity multihop packet radio networks

Abstract In this paper, we are interested in determining the maximum throughput that can be supported between a pair of nodes in a multihop packet radio network. To determine the maximum throughput between a pair of nodes, single commodity traffic is considered, that is, the only traffic in the network is that which is being transmitted from the source node to the destination node. We investigate two channel access protocols: perfect scheduling (spatial TDMA, link activation) and slotted ALOHA with the results of perfect scheduling serving as the upper bound of the maximum throughput achievable. For perfect scheduling, we show that the maximum throughput between a pair of nodes in a packet radio network is always 1 if there exist four or more independent paths between those two nodes. For the slotted ALOHA protocol, the optimization problem can be formulated as a nonlinear programming problem. We only consider the case where the flow from the source to destination is equally split among all the independent paths connecting them. For networks with three or more independent paths connecting the source and destination nodes, we are able to find a closed form expression for the maximum throughput and the optimum transmitting probabilities for each node. Comparison between the perfect scheduling and the slotted ALOHA channel access protocols is then made.

Making transmission schedules immune to topology changes in multi-hop packet radio networks

Transmissions scheduling is a key design problem in packet radio networks, relevant to TDMA and CDMA systems. A large number of topology-dependent scheduling algorithms are available, in which changes of topology inevitably require recomputation of transmission schedules. The need for constant adaptation of schedules to mobile topologies entails significant, sometime insurmountable, problems. These are the protocol overhead due to schedule recomputation, performance penalty due to suspension of transmissions during schedule reorganization, exchange of control message and new schedule broadcast. Furthermore, if topology changes faster than the rate at which new schedules can be recomputed and distributed, the network can suffer a catastrophic failure. The authors propose a robust scheduling protocol which is unique in providing a topology transparent solution to scheduled access in multi-hop mobile radio networks. The proposed solution adds the main advantages of random access protocols to scheduled access. Similarly to random access it is robust in the presence of mobile nodes. Unlike random access, however, it does not suffer from inherent instability, and performance deterioration due to packet collisions. Unlike current scheduled access protocols, the transmission schedules of the proposed solution are independent of topology changes, and channel access is inherently fair and traffic adaptive.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Topology control for multihop packet radio networks

A distributed topology-control algorithm has been developed for each node in a packet radio network (PRN) to control its transmitting power and logical neighbors for a reliable high-throughput topology. The algorithm first constructs a planar triangulation from locations of all nodes as a starting topology. Then, the minimum angles of all triangles in the planar triangulation are maximized by means of edge switching to improve connectivity and throughput. The resulting triangulation at this stage, the Delaunay triangulation, can be determined locally at each node. The topology is modified by negotiating among neighbors to satisfy a design requirement on the nodal degree parameter. Simulations show that the final topology is degree-bounded, has a rather regular and uniform structure, and has throughput and reliability that are greater than that of a number of alternative topologies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Maximum number of independent paths and radio connectivity

Methods for determining the network reliability of a multihop packet radio network in the presence of hostile jammers are discussed. A new connectivity parameter called radio connectivity is defined as the maximum number of disjoint communication paths that are still usable between given nodes s and d after the jammer is on or, more generally, the minimum number of jammers needed to disconnect s and d. A lower bound on the radio connectivity is computed by studying the number of jamming independent paths. The time complexity of obtaining the radio connectivity is analyzed and shown to be NP-hard except for some special cases. Greedy heuristics for developing approximate answers for general networks are described. Euclidean networks, in which the nodes and links correspond to points and line segments in the Euclidean geometry and satisfy Euclid's four fundamental axioms, are also discussed. It is found that the maximum number of independent paths between a pair of source and destination nodes that can possibly exist is five. An extension in which there is a protected zone of known size around the sender and receiver is studied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Jointly optimal routing and scheduling in packet ratio networks

A multihop packet radio network is considered with a single traffic class and given end-to-end transmission requirements. A transmission schedule specifies at each time instant the set of links which are allowed to transmit. The purpose of a schedule is to prevent interference among transmissions from neighboring links. Given amounts of information are residing initially at a subset of the network nodes and must be delivered to a prespecified set of destination nodes. The transmission schedule that evacuates the network in minimum time is specified. The decomposition of the problem into a pure routing and a pure scheduling problem is crucial for the characterization of the optimal transmission schedule. >

Design algorithms for multihop packet radio networks with multiple directional antennas stations

A protocol called the simple tone sense (STS) protocol is designed for multihop packet radio networks (PRNs) with multiple directional antennas stations. The protocol can minimize transmission interference by using a group of tones to identify the active neighbors. A variation of the STS protocol called the variable power tone sense (VPTS) protocol is also designed to further reduce interference. Algorithms for assigning tones and for determining the orientation and broadcasting angles of the directional antennas are designed. Design examples are given. Simulation result shows that the STS protocol gives better throughput-delay performance than the busy-tone multiple access protocol, especially when the traffic is heavy. The VPTS protocol gives still better throughput-delay performance than the STS protocol. >

Jamming in slotted ALOHA multihop packet radio networks

The properties of a packet radio network in the presence of active interference are discussed. Both the jammer and the network nodes are subject to an average power constraint. The network uses slotted ALOHA multiple access schemes and some simple fixed routing strategies with constant transmitter power. By using a game-theoretic approach the situation is considered as a two-person constant-sum game. The author defines network performance as the values of the game in terms of the expected forward progress of a packet. Both the performance and the optimum strategies for access and jamming are investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Slotted ALOHA multihop packet radio networks with directional antennas

The use of directional antennas in multihop packet radio networks using slotted ALOHA access is considered. Tractable approximations to the network performance in terms of expected forward progress are derived. Results show that packet collisions can be strongly reduced already with moderate gain antennas to allow for a substantial increase in network performance.

Optimum transmission ranges in a direct-sequence spread-spectrum multihop packet radio network

The authors obtain the optimum transmission ranges to maximize throughput for a direct-sequence spread-spectrum multihop packet radio network. In the analysis, they model the network self-interference as a random variable which is equal to the sum of the interference power of all other terminals plus background noise. The model is applicable to other spread-spectrum schemes where the interference of one user appears as a noise source with constant power spectral density to the other users. The network terminals are modeled as a random Poisson field of interference power emitters. The statistics of the interference power at a receiving terminal are obtained and shown to be the stable distributions of a parameter that is dependent on the propagation power loss law. The optimum transmission range in such a network is of the form CK/sup alpha / where C is a constant, K is a function of the processing gain, the background noise power spectral density, and the degree of error-correction coding used, and alpha is related to the power loss law. The results obtained can be used in heuristics to determine optimum routing strategies in multihop networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Decoupling link scheduling constraints in multi-hop packet radio networks

An aspect of the problem of constructing a minimal length link schedule for a PRN (packet radio network) is examined. Specifically, it is assumed that a PRN of unrestricted topology is given, including a set of users, a set of channels, a set of interference links, a frequency band assignment, and an initial link schedule. It is required that any link schedule satisfies two constraints. The first is the transmission/reception constraint, namely that users cannot transmit and receive simultaneously and cannot transmit/receive more than one packet at a time. The second is the interference-free constraint, namely that no user interferes with any other. It is assumed that the initial link schedule satisfies the transmission/reception constraint, but not necessarily the interference-free constraint. Then it is shown that a simple modification of the initial link is needed to satisfy the latter constraint as well, i.e. the two constraints can be decoupled. >