Deterministic access protocols for packet radio networks

In this paper, multiple-phase deterministic protocols for packet radio networks are introduced and analysed. Two modes of information transfer are considered, namely (a) broadcasting and (b) point-to-point transmission. We explore systematic ways of designing multiple-phase protocols and apply them on Manhattan networks. The proposed protocols are studied primarily from the point of view of throughput efficiency. Delay analysis is also presented.     

Multiple-packet forwarding protocols for frequency-hop packet radio networks

Reliable data distribution within multiple-hop spread-spectrum packet radio networks requires high performance from the network protocols. The high variability in quality among the links and the unique characteristics of frequency-hop spread-spectrum signaling impose special requirements for network protocols that are to be employed in frequency-hop packet radio networks. These features can be exploited in the forwarding protocols by allowing multiple packets to be included in each forwarding attempt. The use of multiple-packet transmissions exploits the capture property of frequency-hop signaling, and it reduces the overhead required for acknowledgments. A potential trade-off arises because the use of multiple-packet transmissions increases the throughput, but in some situations it can also increase the delay. Two new transmission protocols that employ multiple-packet transmissions are described, and their performance is evaluated.     

Future directions in packet radio architectures and protocols

The technology of packet switching over multihop, multiple-access channels has evolved to the point at which its protocols can now support internetwork operation of medium-size networks whose nodes possess some degree of mobility. As regards the needs and challenges of the future operating environment, it is clear that these can be met only by enhancing the packet radio architecture and its protocols. We discuss several enhancements that allow the organization of large, dynamic networks that can operate over multiple channels, adapt to varying conditions, and possess self-monitoring and self-control capabilities. As these areas are examined, the attendant issues and tradeoffs are discussed; in addition, some protocols and information regarding their performance are presented.     

A cellular packet radio data network

A new wide-area data network is described. The network employs packet switching techniques within a multi-access, narrowband cellular radio environment and provides a flexible alternative to copper wire telecommunications for short data message applications. Following a discussion of the network requirements, the paper describes the key design areas in terms of a layered model. A new data link layer protocol called dynamic slotted reservation Aloha is introduced. This protocol is optimised for the bidirectional communication of packets containing around 1000 bits of application data. The practical implementation is presented briefly before a number of the major applications are discussed     

Issues in packet radio network design

There are many design choices that must be made in the development of a packet radio network. There is usually no single correct choice, and the decisions are dependent on the environment that the network must work in, the requirements for performance and other functionalities, and the cost and other limitations, in addition, as new hardware and software technologies become available, the parameters governing the decisions change and often result in different selections. This paper outlines a number of design issues and choices available. The intent is to provide an overview of the design decisions that must be made so as to provide a context for the decisions made in a number of existing and developing packet radio networks. It is hoped that this will allow future designs to take advantage of both the wealth of experience available as well as new technologies. Three areas of design decisions are identified. The first area deals with the physical aspects of the network and concentrates on the radio connectivity and channel sharing. The second area deals with the automated management of the network and concentrates on issues such as link management and routing. The third area deals with the interface of the network to the users and some practical aspects of operating and maintaining a network.     

The low-cost packet radio

Research on packet switched radio networks requires reconfigurable testbeds with large numbers of readily deployable radios. This motivated the development of a small, low-cost packet radio (LPR) with the flexibility to support extensive network experiments, and to be amenable to tailoring to specific end-use applications. The LPR incorporates a digitally controlled direct sequence minimum shift keyed spread-spectrum radio and a microprocessor-based packet switch. Code changeable surface acoustic wave (SAW) matched filtering provides processing gain at burst symbol rates of 100k and 400k symbols per second in the presence of interference. Coherent recursive integration enhances synchronization performance, provides synchronous detection of the data, and serves the adaptive multipath accumulator. Forward error correction utilizing convolutional encoding and sequential decoding is incorporated at four different code rates for both burst symbol rates. The microprocessor runs the networking software. Requirements, design, and performance data for the LPR engineering model are presented.     

On improving throughput in packet mobile radio network

A novel random multiaccess protocol is proposed for a packet mobile-radio network employing an idle-signal casting multiple-access (ICMA) with/without collision detection scheme. The protocol takes advantage of the channel control scheme to reduce collisions. The authors show significant improvements in terms of maximum achievable throughput.<>     

Diversity reception in a multihop packet radio network

The performance improvement which results from the use of multiple antennas at each node in a multihop packet radio network is examined. Four transmission strategies based on three previously proposed routing schemes and one new routing scheme, MTP, are studied. It is found that the use of two antennas can improve the performance of all four transmission strategies by about 25% in a Rayleigh fading environment. The transmission strategy based on the MTP routing scheme is shown to be generally superior to those based on the other three routing schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Diversity reception in a multihop packet radio network

The performance improvement which results from the use of multiple antennas at each node in a multihop packet radio network is examined. Four transmission strategies based on three previously proposed routing schemes and one new routing scheme, MTP, are studied. It is found that the use of two antennas can improve the performance of all four transmission strategies by about 25% in a Rayleigh fading environment. The transmission strategy based on the MTP routing scheme is shown to be generally superior to those based on the other three routing schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Connectivity properties of a packet radio network model

A model of a packet radio network in which transmitters with range R are distributed according to a two-dimensional Poisson point process with density D is examined. To ensure network connectivity, it is shown that πR²D, the expected number of nearest neighbors of a transmitter, must grow logarithmically with the area of the network. For an infinite area there exists an infinite connected component with nonzero probability if π R²D>N₀, for some critical value N₀. It is shown that 2.195<N ₀<10.526     

On the capacity of an FFH-CDMA packet radio network

A packet radio network employing FFH-CDMA as multiple access technique is studied. We focus on the acquisition process and we examine the effect of multiple-access interference. The relationship between the maximum number of tolerable interfering transmissions and the number of frequencies used in frequency hopping is investigated. The bounds to the probability of acquisition as well as approximations to them are used. The effects of other system parameters, such as the length of the signal's preamble, the number of chips of the code (frequency shifts) per bit and the number of correlators are also studied     

Rule-based network design: application to packet radio networks

A heuristic, rule-based approach to network design is presented. The problem of designing high-performance packet radio networks by altering individual radio powers (i.e. by altering network connectivity) is considered. It is assumed that node locations, traffic requirements, and a multiaccess protocol are specified. The focus is on the dependence of capacity on connectivity for two reasons: connectivity is always a design parameter, whereas radio locations, protocol, and traffic may not always be; and the relationship between capacity and connectivity is well documented in the literature, even though the exact nature of this reliance remains unclear. Packet radio performance analysis models found in the literature are used for performance evaluation     

A buffered two-node packet radio network with product form solution

A packet radio network with two nodes, both of which access a single radio channel using the slotted ALOHA protocol, is discussed. This model results in a network of two interfering queues. Networks of interfering nodes normally do not have partial balance and thus seldom have product-form solution (PFSs). However, when certain assumptions are made on the network parameters, PFS-controls can be found that yield a PFS for the interfering two-node network. Three such cases are described. In the first two cases, PFS controls are found that control the new packet arrival rate. When operating under these PFS controls, the two-mode network has a simple, closed-form solution of the equilibrium probabilities, the expected throughput, and the expected packet delay. The throughput-delay performance closely approximates that of an exact two-node packet radio model. In the third case, a PFS control is found on one node's transmission probabilities. When operating under this PFS control, the transmission probabilities approach asymptotic values as the packet backlog increases. The network tends to adjust its transmission probabilities to reduce large unequal packet backlogs     

Optimum transmission ranges in a direct-sequence spread-spectrummultihop 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^α 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 α is related to the power loss law. The results obtained can be used in heuristics to determine optimum routing strategies in multihop networks     

Optimizing information efficiency in a direct-sequence mobile packet radio network

We consider a direct-sequence multihop packet radio network using slotted ALOHA in a Rayleigh fading environment. We are interested in optimally choosing the transmission range, code rate, and slotted ALOHA transmission probability to be used by each node. We use a new performance measure, information efficiency, to analyze the network and show that the information efficiency of the low-cost mobile packet radio network can be improved approximately 20 fold by using the optimum parameters. We suggest a practical trellis-coded modulation scheme which comes close to realizing the theoretic limits found.     

Performance evaluation for a quasi-synchronous packet radio network(QSPNET)

We propose a new media-access and connection-establishment protocol for an ad-hoc quasi-synchronous packet radio network (QSPNET). In the QSPNET, the bandwidth is partitioned into a data channel, used to transmit packets, and a control channel, used to make reservations. The transmitted waveforms in the QSPNET are made quasi-synchronous by using a local GPS clock. The QSPNET uses a novel linear decorrelator receiver for multiuser detection, which permits the reception of quasi-synchronous code division multiple access (QS-CDMA) waveforms. We initially describe the QSPNET and its connection and flow control protocols, giving the rules of transmission and reception followed by all mobiles. We also provide performance results for the case where connection requests are generated at each node of the QSPNET according to a random process over an infinite time horizon. In particular, we obtain results on the achievable throughput and the average delay as a function of the transmission radius, the quasi-synchronous uncertainty interval, the duration of the connections, and the buffer size per node     

On topology improvement of a packet radio network by power control

The packet radio network (PRN) is an attractive architecture for wireless data communication. The code assignment problem in PRN is a classical problem that has been extensively studied. However, we observe that the power control issue has been ignored by most works but may have significant impact on the PRN's performance. Given a set of PRN stations, the network topology can be changed by adjusting each station's transmission power. All existing works, nevertheless, assume that the network topology is given before solving the code assignment problem. We regard code assignment as an independent problem and show how to improve the network topology by power adjustment without violating the original code assignment. The improvement in topology (such as more links in the network) may result in improvement in network throughput. Through simulations, we demonstrate that, although the code assignment problem is NP-complete, our power adjustment schemes can easily improve the network performance by about 10% with polynomial costs.     

Run-away dynamics of CDMA channels in an adaptive packet radio network

Radio communication offers the great advantage of mobility for users. At least two important systems exploit this feature: packet radio networks and personal communication systems. Since their radio links are subject to rapid changes in quality, the ability to adapt to these changes has much to offer in improving throughput, delay, and robustness characteristics. This paper addresses three areas. First, it presents the design fundamentals of an adaptive link-gain control algorithm for a multiple access radio channel. Second, it develops a probabilistic model for a related family of algorithms, which includes models for the effects of code-division multiple access interference. Third, it uses two sample algorithms to explore the transient behaviour of the system. The two algorithms are chosen to compare the relative merits of designs that emphasize adapting to channel noise versus adapting to multiple access interference. Transient analysis is sparse in the literature and is an important contribution of this paper.     

Throughput-delay and stability analysis of an asynchronous spreadspectrum packet radio network

A continuous-time Markov chain model for an asynchronous spread spectrum packet radio network is presented. The network consists of N fully connected nodes and the radios in all nodes are identical. Packets arrive at each node and are retransmitted when lost, both according to Poisson processes with different rates, and packet lengths are exponential in distribution. A simple threshold approximation is used to account for the multiuser interference, and the preamble collision probability at receiving radios to account for the capture effect. The approximate analysis gives results which are very close to those obtained by simulations in most cases. The network stability conditions are discussed and the bistable behavior of the network is demonstrated. Results are given which show the effects on throughput and packet delay performance of the network according to the variations of the network size, the packet retransmission rate, the preamble collision probability at receiving radios, and the threshold value of the radio channel capacity     

Performance analysis of spread spectrum packet radio network withchannel load sensing

A continuous-time Markov-chain model for an asynchronous communication spread-spectrum code-division-multiple-access (CDMA) packet radio network is developed. The network is composed of mutually independent users. The receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model makes it possible to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread-spectrum packet radio networks due to channel-load sensing are shown. Steady-state results for throughput are obtained