MANET techniques are critical to the success of emerging modern warfare concepts and are required to support communications for mobile military platforms, including ships, aircrafts, and ground vehicles operating in a highly dynamic and mobile tactical communications network without fixed infrastructure. Research in Mobile Ad Hoc Networking has increased dramatically over the last few years with significant work in hardware architectures, media access routing, and protocols. Until now, most of the work has been in simulation and small-scale laboratory demonstrations due to the significant resources required to implement an actual network with sufficient nodes to fully exercise the capabilities of both the hardware and software. Harris has built a flexible demonstration environment that enables the exercising of numerous network functions while still accomplishing research and development of the network protocols. The testbed, assumed in this paper, allows the system to be exercised in an outdoor environment that closely approximates the physical environment that the system will be operated in.

Researchers have proposed the core-based trees (CBTs) and protocol independent multicasting (PIM) protocols to route multicast data an internetworks. We compare the simulated performance of CBT and PIM using the OPNET network simulation tool. Performance metrics include end-to-end delay, network resource usage, join time, the size of the tables containing multicast routing information, and the impact of the timers introduced by the protocols. We also offer suggestions to improve PIM sparse mode while retaining the ability to offer both shared tree and source-based tree routing.

This paper provides performance results through analysis and simulation for key error control problems encountered in using wireless links to transport asynchronous transfer mode (ATM) cells. Problems considered include the forward-error correction (FEC) and interleaving at the physical layer, the impact of wireless links on the ATM cell header-error control (HEC) sand cell delineation (CD) functions, the application of data link automatic repeat-request (ARQ) for traffic requiring reliable transport, and the impact of the choice of end-to-end ARQ protocol for reliable service. We conclude that it is very important to make the physical layer as SONET-like as possible through the use of powerful FEC, interleaving, and ARQ. These additional error control measures are especially necessary for disturbed channels because of the degrading effects of the channel on higher-layer functions. A recommended error control architecture is given with tradeoffs.

Researchers have proposed the core based trees (CBT) and protocol independent multicasting (PIM) protocols to route multicast data on internetworks. The performance of these protocols is examined in the distributed interactive simulation (DIS) environment using the OPNET network simulation tool. The simulation results provide measures of important performance metrics including end-to-end delay, network resource usage, and join time. The size of the tables containing multicast routing information and the impact of the timers introduced by the protocols are also examined. Suggestions are offered to improve PIM Sparse while retaining the ability to offer both shared tree and source-based tree routing.

An adaptive link assignment algorithm for the distributed optimization of dynamically changing network topologies is presented. The algorithm is responsible for determining the network connectivity by controlling the selection of links to be established and disconnected. This algorithm is designed to recover from predictable link outages as well as massive unpredictable failures. To minimize computational time complexity as well as to improve transient response. Some known graph-theoretic algorithms are utilized.>

In this paper, we evaluate the performance of noninterleaved convolutional codes in the presence of Gaussian noise and periodic erasure bursts, with maximum likelihood (Viterbi) decoding. The results show that even for burst lengths that are a significant fraction of the code constraint length, the performance degradation is surprisingly small. It is then shown that in many of these cases the use of interleaving would provide very little performance gain. In addition, for burst lengths that are so long that interleaving is unavoidable, these results demonstrate the robustness of fixed periodic interleavers against variability in the parameters of the burst process.

The structure of punctured convolutional cedes is described, and it is indicated how their use simplifies the design of maximum likelihood decoders. The best codes of this class for rates 2/3 and 3/4 are tabulated and performance curves are given for these codes.

In this correspondence we analyze the error-propagation problem that is encountered in decoding noncatastrophic codes with feedback decoders. We show that if thc decoding depth is too short, unlimited error propagation will occur and that the depth can be chosen long enough so that unlimited error propagation does not occur when minimum-distance feedback decoders are used.

The use of feedback with concatenation is proposed as a technique for achieving the desired performance with less system complexity. Feedback can be used with the inner code, outer code, or both. The concatenation error exponents for several feedback schemes employing the Gaussian channel are determined analytically and found to be significantly better than those of the channel with no feedback.

The probability ofKor more zeros following a one and the covariance function of the output noise bits from the generalized Gilbert channel are determined. These probabilities are used in developing a method for calculating the probability distribution of burst lengths in a sequence ofnoutput bits from the channel. Several applications of the distribution are described.