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We examine the integration of adaptive modulation and channel coding protocols with fountain coding in a packet radio system. We present three modes of operation for the adaptive transmission system, each of which adapts the channel code in a way that accommodates the fixed-length packets produced by the fountain encoder. Each mode works with the fountain coding system to mitigate the effects of time-varying fading on the radio links and provide high throughput.

Protocols that were proposed recently for adapting the error-control code from packet to packet in a frequency-hop packet radio network are evaluated for use on channels for which the fading distribution has fixed or slowly varying parameters. The protocols do not require channel measurements or pilot signals; instead, the receiver derives the necessary adaptation control information from its decoder during of the reception of each packet. The throughput achieved by each adaptive-coding protocol when it is used with a family of turbo product codes is compared with the capacity limit and with the throughput that is obtained from a hypothetical ideal protocol that is given perfect channel state information.

New distributed protocols for channel access and adaptive spreading are described and evaluated for use in direct-sequence spread-spectrum packet radio networks that have no central controllers, access points, or base stations. The protocols rely on demodulator statistics to provide the information needed for efficient sharing of the frequency band and compensation for changes in the communications environment in a network of half-duplex radios for which simultaneous two-way communications is not possible.

In this paper we design novel generalized likelihood ratio test (GLRT)-type packet-data detectors for general multiaccess/multiuser digital communication systems and we develop analytical performance evaluation tools for finite data packet sizes. For the known channel case, we derive a coherent GLRT packet-data detector while for the unknown channel case we derive both a coherent pilot assisted GLRT packet-data detector and a differential phase-shift-keying (DPSK) GLRT packet-data detector. Efficient suboptimum implementations of the above schemes that exhibit complexity linear in the packet size are also considered. Simulation studies evaluate the performance of the proposed schemes in the context of packet-data code-division multiple access (CDMA) communications.

This paper investigates the benefit of adaptive modulation based on channel state information (CSI) in direct-sequence/ code-division multiple-access (DS/CDMA) multihop packet radio networks. By exploiting varying channel conditions, adaptive modulation can be used in ad hoc networks to provide upper layers with higher capacity links over which to relay traffic. Using the /spl alpha/-stable interference model, the distribution of the signal-to-interference ratio (SIR) is obtained for a slotted system of randomly, uniformly distributed nodes using multilevel coherent modulation schemes. Performance is evaluated in terms of the information efficiency, which is a new progress-related measure for multihop networks. Three types of adaptivity are analyzed, differing in the level of CSI available: 1) full knowledge of the SIR at the receiver; 2) knowledge of only the signal attenuation due to fading; and 3) knowledge of only the slow fading component of the signal attenuation. The effect of imperfect channel information is also investigated. Sample results are given for interference-limited networks experiencing fourth-power path loss with distance, Ricean fading, and lognormal shadowing.

Wireless communication channels may change greatly from one transmission to the next, due to variations in propagation loss and interference. The use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of the power, code rate, and symbol rate reduces energy consumption and interference caused to other systems. Such adaptation requires information about the characteristics of the channel, which is more difficult to obtain in a packet radio network (PRN) or other mobile ad hoc network than in a typical cellular communication system. We develop methods for providing partial information about the channel state from three statistics that are derived by different subsystems in the receiving terminals of a direct-sequence spread-spectrum PRN. We present and evaluate a protocol that uses this information to adapt the transmission parameters in response to changes in interference and propagation conditions in the network. The performance of the new adaptive-transmission protocol is compared with a system with fixed transmission parameters and with an adaptive protocol that is furnished with perfect knowledge of the channel state at the completion of each transmission.

A fully connected frequency-hop packet radio network is considered. Four packet-combining techniques are presented, which significantly reduce the packet-error rate. An analytical model is used to offer insight into how system dynamics are affected by the error-control method and retransmission backoff policy. It is shown that enhancing the error-control method increases the maximum throughput of the network and alleviates the stability problem, but does not solve the problem. On the other hand, a good choice of retransmission backoff policy solves the stability problem, but does not alter the maximum throughput. These results suggest that in order to construct a stable network with large throughput, a good error-control method and retransmission backoff policy are both necessary.

We consider a frequency-hopping multihop packet radio network using M-ary frequency-shift keying modulation in a Rayleigh fading environment. Each node transmits packets using an extended (n, k) Reed-Solomon code and the slotted ALOHA channel access protocol. For this network, we determine the optimum transmission range, optimum code rate, and optimum slotted ALOHA transmission probability to be used by each node in the network. Tradeoffs in choosing the transmission range and code rate, and the spectral efficiency of the network are captured in a new performance measure, information efficiency, which is analogous to expected forward progress. Maximizing the information efficiency yields the optimum desired network parameters.

The application of a type-II hybrid ARQ protocol in a slotted direct-sequence spread-spectrum multiple-access (DS-SSMA) packet radio system is investigated. Both the static performance and the dynamic performance of such a system are analyzed. In the physical layer, packet error and packet success probabilities are computed using the improved Gaussian approximation technique, which accounts for the bit-to-bit error dependence within a packet. In the data-link layer, two-dimensional Markov chains are employed to model the system dynamics. Based on this model, the performance of the type-II hybrid ARQ protocol is upper and lower bounded by considering, respectively, a superior scheme and an inferior scheme. Steady state throughput and delay performances of the two bounding schemes are obtained. Moreover, it is shown that for each fixed input load, there is an optimal retransmission probability under the finite user population assumption. Bounds on this optimal retransmission probability are also given.

This paper addresses Gaussian minimum-shift keyed (GMSK) receiver performance analysis for limiter discriminator detection with cochannel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD), which shares spectrum with cellular voice users; thus, the CDPD receiver will see both narrow-band frequency modulation (NBFM) voice and GMSK data interference. Previous studies investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend earlier work to multiple Rayleigh fading (Doppler spread) interferers having NBFM (f/sub dm/=12 kHz) analog modulation and/or GMSK modulation. Probability of bit-error expressions are derived for the frequency modulation (FM) and GMSK interferer cases assuming medium-to-high signal-to-noise ratio regions. For scenarios of from one to six NBFM interferers, having the same total power, a corresponding Gaussian approximation is within 1.5 dB. Simulation results are also presented for various combinations of FM and GMSK interference. FM interference is only slightly worse than GMSK interference. Delay spread representing an urban scenario resulted in only a slight increase in the error floor.

Capture phenomena in slotted ALOHA packet radio networks employing spread-spectrum modulation is considered. Probability of capture with both delay and power capture mechanisms are derived and compared with power- and delay-only capture models. Significant improvements in the capture probability is observed. The improvement over the delay-only capture model increases with decreasing arrival-time randomization overhead.

Throughput, delay, and stability for two slotted ALOHA packet radio systems are compared. One system is a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) network where each user employs a newly chosen random signature sequence for each bit in a transmitted packet. The other system is a multiple-channel slotted narrow-band ALOHA network where each packet is transmitted over a randomly selected channel. Accurate packet success probabilities for the code-division multiple-access (CDMA) system are computed using an improved Gaussian approximation technique which accounts for bit-to-bit error dependencies. Average throughput and delay results are obtained for the multiple-channel slotted ALOHA system and CDMA systems with block error correction. The first exit time (FET) is computed for both systems and used as a measure of the network stability. The CDMA system is shown to have better performance than the multiple-channel ALOHA system in all three areas.

Current portable and land-mobile radio systems employ frequency modulation which exhibits a distinct capture effect. Furthermore, multipath propagation, shadowing, and the spatial distribution of the terminal units create data packets with varying signal strength. We investigate the performance of nonpersistent inhibit sense multiple access (ISMA) applied to the forward channel of packet radio communication networks. We show that the aggregate capacity of ISMA substantially increases compared to the noncapture case for small capture ratios. The mean packet delay of ISMA is also reduced with capture. The effect of different signal strength distribution is explored, and the capacity and delay improvements discussed.

This paper considers the combination of multiple copies of a packet to improve the performance of a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) ALOHA packet radio system with coherent binary phase-shift keying (BPSK) modulation. Both slotted DS/SSMA ALOHA with and without forward error correction (FEC) are considered. For the case with FEC, maximum-likelihood decoding with code combining is used. Code combining allows for the combination of multiple copies of the same packet (which are typically discarded), to obtain a lower code rate for that specific packet, and therefore an improved probability of successful decoding. In both cases, combining multiple copies of the same packet results in a throughput which is an increasing function over a broad range of offered load, so that the system is more reliable from the point of view of stability. In addition, combining provides a higher throughput and a smaller time delay for packet transmission. This is illustrated by means of analytical and simulation results.

Multiple-access schemes are introduced and analyzed for the integration of voice and data traffic in packet radio networks using code-division multiple-access (CDMA). The multiple-access capability of the CDMA channel is used to accommodate several voice calls simultaneously, while the data users follow the ALOHA protocol with retransmission control and contend for the remaining (if any) multiple-access capability of that channel. The retransmission probabilities of the backlogged data users are

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. >

An important, yet difficult, problem in the design of a packet radio network is the determination of a conflict-free broadcast schedule at a minimum cycle length. We first formulate the problem via a within-two-hop connectivity matrix and then, by assuming a known cycle length, determine a conflict-free scheduling pattern using a centralized approach that exploits the structure of the problem via a modified genetic algorithm. This algorithm, called genetic-fix, generates and manipulates individuals with fixed size (i.e., in binary representation, the number of ones is fixed) and therefore, can reduce the search space substantially. We also propose a method to find a reasonable cycle length and shorten it gradually to obtain a near-optimal one. Simulations on three benchmark problems showed that our approach could achieve 100% convergence to solutions with optimal cycle length within reasonable time.

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.

Investigates the performance of direct-sequence spread-spectrum packet radio networks in the presence of the near/far problem. It is found that the maximum throughput of the network suffers degradation due to the near/far problem. However, analysis also shows that, under high traffic conditions, a network with the near/far problem delivers higher throughput than another without the near/far problem. This suggests that the direct-sequence spread-spectrum packet radio network with the near/far problem retains stability for heavier traffic conditions. Following these findings, a new adaptive power control scheme is suggested to enhance network throughput under both low and heavy traffic conditions. The mean and variance of the packet delay are derived and network stability and deadlock avoidance issues are discussed. The impact of channel fading on the network behavior is also studied. >

Adaptive protocols that specify the ways in which a radio is permitted to modify its normal forwarding procedures based on information obtained locally in the network are considered. A computer program has been developed to simulate a frequency-hop (FH) packet radio network with partial-band jamming and interference due to other FH and narrowband radios. The radios in the network use time-slotted, receiver-directed, FH spread-spectrum signaling. Results on throughput, delay, and end-to-end probability of success are presented, and comparisons between different forwarding protocols are given for a static network topology with both static and mobile network jamming. >

The authors consider the use of a multiple-beam adaptive array (MBAA) in a packet radio system. In an MBAA, a given set of antenna elements is used to form several antenna patterns simultaneously. When it is used in a packet radio system, an MBAA can successfully receive two or more overlapping packets at the same time. Each beam captures a different packet by automatically pointing its pattern toward one packet while nulling other, contending packets. It is shown how an MBAA can be integrated into a single-hop slotted ALOHA packet radio system, and the resulting throughput is analyzed for both finite- and infinite-user populations. >

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. >

The effect of frequency offset on the probability of miss for a packet radio modem, using the constant false alarm rate (CFAR) preamble detection scheme, is analyzed. The expression for the probability of miss for the general case, i.e., where there is a frequency offset, is derived. This general expression is then used to derive the expressions for the false alarm rate and the probability of miss for the special case where the frequency offset is negligible. Several graphs depicting the probability of miss for different values of signal-to-noise ratio and frequency offset are also included. >

The performance of a local/mobile radio communications system utilizing the slotted ALOHA multiple random access protocol is analyzed. The probability of correct packet capture is evaluated for a local/mobile packet radio system using ideal coherent binary phase-shift keying (BPSK) modulation. Both the near/far effect and the effect of Rayleigh fading on the probability of correct packet capture are taken into account, but the effect of thermal noise is neglected since the interference due to competing packets is dominant in practical systems. The probability of correct packet reception is evaluated for a system using spatial diversity. In addition, the effect on system performance of either convolutional coding with hard decision Viterbi decoding or binary linear block coding with hard decision decoding is evaluated. The pseudo-Bayesian algorithm that has been developed to stabilize a packet system based on the slotted ALOHA protocol at maximum channel throughput is found to be adaptable to the local mobile operating environment. For the system considered here, channel throughputs as high as 0.66 can be obtained. >

A new method for the exact calculation of the throughput of a centralized slotted ALOHA packet radio network over slow Rayleigh-fading channels is presented and the results are compared with the computer simulations. Also, upper and lower bounds on the performance are provided. The effects of capture on the throughput of the system are related to the modulation and coding technique, signal to noise ratio of the received signal, general terminal distribution in the area, and the length of the transmitted packets. The binary phase shift keying (BPSK), coherent and noncoherent binary frequency shift keying (FSK) modulations and BCH coding are considered for the exact calculations. The results of the analysis show that the maximum average throughput of the slotted Aloha packet radio network is around 60% rather than 36% predicted from the simplified analysis. In contrast with some previous reports, it is shown that the throughput of the system is not affected significantly by the use of coding or the change of packet lengths. >

The use of an adaptive antenna array as a means of improving the performance of a slotted ALOHA packet radio network is presented. An adaptive array creates a strong capture effect at a packet radio terminal by automatically steering the receiver antenna pattern toward one packet and nulling other contending packets in a slot. A special code preamble and randomized arrival times within each slot allow the adaptive array to lock onto one packet in each slot. The throughput and delay performance of a network with an adaptive array are computed by applying the standard Markov chain analysis of slotted ALOHA. It is shown that throughput levels comparable to carrier sense multiple access (CSMA) are attainable with an adaptive array without the need for stations to be able to hear each other. The performance depends primarily on the number of adaptive array nulls, the array resolution, and the length of the randomization interval within each slot. >

A novel mathematical method is presented to express the outage probability for a desired radio signal received from a mobile transmitter in the presence of multiple interfering signals with combined log-normal and Rayleigh fading. In contrast to previously reported analyses, this exact method avoids approximation of the PDF of the received powers of the various signals. This is useful in determining the spectrum efficiency and performance of (interference-limited) radio networks for high-capacity cellular telephony, two-way paging, packet radio and other mobile data networks. >

The probability of q/sub i/ of successful packet reception when i users transmit simultaneously in a mobile packet radio system is shown to decrease monotonically with i for a number of commonly used capture and spatial distribution models, with no fading. Examples of both noiseless and noisy systems in which q/sub i/ is not monotonically decreasing with i are also given. >

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. >

A comprehensive study of the problem of scheduling broadcast transmissions in a multihop, mobile packet radio network is provided that is based on throughput optimization subject to freedom from interference. It is shown that the problem is NP complete. A centralized algorithm that runs in polynomial time and results in efficient (maximal) schedules is proposed. A distributed algorithm that achieves the same schedules is then proposed. The algorithm results in a maximal broadcasting zone in every slot. >

The statistical dependence of hits due to multiple-access interference in an asynchronous slow-frequency-hop packet radio network in which the radios employ memoryless hopping patterns is described. Models in which hits are conditionally independent given the number of interfering packets are investigated. It is shown that if the conditional probability of a hit is chosen appropriately, the distribution function for the number of hits in a packet for these models can be used to compute upper and lower bounds on the true distribution function for the number of hits. Conditions are described for which these models can be used to compute upper and lower bounds on the codeword and packet error probabilities. It is shown that if the ratio of the number of interfering packets to the number of frequency slots is held constant, hits in the asynchronous frequency-hop network are asymptotically independent in the limit as the number of frequency slots increases. This result suggests that when the number of frequency slots is large, error probabilities can be closely approximated by using the distribution for the number of hits that results from assuming that hits are independent. >

The packet error probability induced in a frequency-hopped spread-spectrum packet radio network is computed. The frequency spectrum is divided into q frequency bins. Each packet is exactly one codeword from an (M, L) Reed-Solomon code (M=number of codeword symbols (bytes); L=number of information symbols (bytes)). Every user in the network sends each of the M bytes of his packet at a frequency chosen among the q frequencies with equal probability and independently of the frequencies chosen for other bytes (i.e., memoryless frequency-hopping patterns). Statistically independent frequency-hopping patterns correspond to different users in the network. Provided that K users have simultaneously transmitted their packets on the channel and a receiver has locked on to one of these K packets, the probability that this packet is not decoded correctly is evaluated. It is also shown that although memoryless frequency-hopping patterns are utilized, the byte errors at the receiver are not statistically independent; instead they exhibit a Markovian structure. >

In the above-titled paper by M. Georgiopoulos (see ibid., vol.36, no.6, p.720-3, 1988), the packet error probability induced in a frequency-hopped spread-spectrum packet radio network is computed by using the Markovian property of the byte errors at the receiver. It is shown here that the byte errors at the receiver do not exhibit a Markovian structure. A correct analysis and numerical results are provided. >

While the use of radio technology for wireless data communications has increased rapidly, the wide variety of radio interfaces being used has made interference investigations hard to perform. With that in mind, we present a novel approach for analyzing packet radio communications, applicable to interfering heterogeneous networks, which leads to tractable analytical expressions. The core of the approach is an analytical framework modeling each network with individual properties for the packet types and the channel sets used, while taking path loss between all network nodes into account. Furthermore, we present a derivation of closed-form expressions for the throughput of the networks, thus allowing for the investigation of important mechanisms limiting network and system performance. The expressions enable fast and flexible analysis to be performed without extensive computer simulations or measurement campaigns. To illustrate the use of the framework and the strength of the closed-form expressions, we analyze a heterogeneous example system consisting of one IEEE 802.11b network and multiple Bluetooth networks that use multiple packet types. In the analysis, we also take the adjacent channel interference into account when calculating network throughput as functions of the number of interferers in the system.

We continue in this paper our study of two-hop centralized packet radio networks in view of understanding the behavior of these systems. Traffic originates at terminals, is destined to a central station, and requires for its transport the relaying of packets by store-and-forward repeaters. We consider here that all devices employ the nonpersistent carrier sense multiple-access mode. System capacity and through-put-delay tradeoffs are derived and compared to those obtained for slotted ALOHA in Part I [l].

Packet switching has found widespread application in computer communications because of its ability to efficiently handle high ratios of peak-to-average data rate. Packet radio is the application of packet switching techniques to radio channels. The resultant multiple-access problem requires novel approaches. Such approaches have been developed by others and have primarily been analyzed in steady-state behavior. This paper demonstrates and analyzes an important aspect of the dynamic characteristics of packet radio, namely, that of bistable behavior. That is, the system possesses two statistically stable equilibrium points, one in a desirable low-delay region, and the other in an undesirable high-delay region. Since the stability is only statistical in nature, the system oscillates between these two points. Even if the resultant steady-state behavior is very poor, this dynamic analysis frequently shows that system performance will be acceptable. This is due to quiet periods (such as at night) which allow the system to recover.

In this paper we define a broadcast channel access protocol called spatial TDMA, which is designed specifically to operate in a multihop packet radio environment where the location of the nodes of the network is assumed to be fixed. The defined protocol assigns transmission rights to nodes in the network in a local TDMA fashion and is collisionfree. Methods for determining slot allocations are developed, and an approximate solution is given for determining the assignment of capacities for the links of the network that minimizes the average delay of messages in the system.

In this paper we derive the probability of correct packet reception and the resulting channel throughput achievable in an asynchronous slow-frequency-hopped multiple user channel. Reed-Solomon coding is used to correct errors caused by other-user interference in an otherwise noiseless channel. We analyze and evaluate an M -ary FSK signaling scheme, which permits the discrimination against interfering signals that are present for a sufficiently small fraction of the hop duration, and results in substantial increases in channel throughput over previous models.

A two-hop packet radio network consisting of three nodes is considered. The three nodes have infinite buffers and share a common radio channel for transmitting their packets. Two of the nodes forward their packets to a third node that acts as a source of data as well as a relay that forwards all the packets entering the network to a main station. We assume that two of the nodes are granted full rights in accessing the channel while the third node uses a random access scheme. For this network we derive the condition for steady state and the generating function of the joint queue length distribution at the nodes in steady state. We also give several numerical examples and compare the performance of the network with and without a relay node.

A protocol that provides multiple access with two levels of priority to a common radio channel is described. A probabilistic model of the protocol is presented and its analysis yields the throughput-delay characteristics of the two classes of packets supported by that protocol, along with their interaction. The model is analyzed by a method similar to the one used in priority queues; this method allows consideration of each class separately, thus reducing the computational effort considerably.

Packet-switching broadcast radio networks are receiving considerable attention as a feasible solution for applications involving fast network deployment requirements, inaccessible physical environments, and mobile communication devices. Such networks also offer economic alternatives to traditional multiplexing schemes for local distribution. Most of the published papers relating to packet-switching broadcast radio networks address the case in which all communication devices are within an effective transmission range of the destination receiver, thus forming a single-hop network in which no packet routing is involved. In this paper, we address multihop networks. The problems encountered in packet transportation are identified and strategies to resolve these are proposed.

We consider a multiple-access broadcast communication channel which serves a network of terminals, each characterized by a distinct priority level. Higher priority terminals require, on the average, faster access across the communication channel than lower priority ones. We present a terminal priority contentionless access (TPCA) control scheme for sharing such a channel on a conflict-free basis. A ready terminal wishing to access the channel will wait for the channel to become idle, and then defer its access untill after higher priority terminals are given the opportunity to transmit. The model accounts for acquisition delays (including propagation and timearound delay components), idle detection times, multipacket message structures and different arrival intensities at different terminals, Analytical results are derived for the moments and transform of the message waiting-time distribution at each network terminal by relating the waiting times in our model to those in an appropriate M/G/1 queue with HOL (head of the line) priorities. Performance curves are presented under varirous system parameter conditions which correspond to applications involving digital radio local distribution systems and metropolitan-area, packet radio, and local-area communicatiton networks.

Virtual circuit and pure packet (datagram) based switching techniques are studied for future application to the integrated voice/data telecommunications. The coexistence of voice with both interactive and bulk data in an integrated network suggests the desirability of a mixed switching technique to allow the efficient sharing of both the switching and communications resources. Such a mixed packet switching scheme is also evaluated. It uses virtual circuit for regular traffic (voice and bulk data), and uses pure packet (datagram) for bursty traffic (interactive and query/response). It also adapts to changes in voice/ data input traffic mixture.

This paper describes the design and performance of a spread-spectrum medium frequency (MF) radio network. The network utilizes a simulcast time slotted transmission scheme in which radios that receive a data message in one time slot repeat the message in the next slot. Spread-spectrum radio designs that operate efficiently with simulcast under a variety of channel conditions are investigated. The performance of the radio network is characterized in terms of radio connectivity and message reaction time.