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Packet acquisition for a time-frequency hopped asynchronous random multiple access (RMA) system is investigated. A novel analytical approach to performance evaluation is provided, which enables the waveform designer to quickly evaluate the network performance as various waveform design and RMA protocol parameters and are chosen. The results show that the network throughput is estimated and upper-bounded...
Frequency hopping provides some protection against multiple access interference in random-access ad hoc networks. Power control and the use of short routing hops can further reduce interference by promoting spatial reuse. If the network is fully connected, frequency hopping and power control alone may be sufficient to allow good throughput without the use of routing. This approach is particularly...
A typical military airborne networking scenario involves small groups of relatively closely-spaced aircraft which fly as a unit to perform a common mission. These aircraft need to maintain very long data links with other aircraft in the presence of strong interference from hostile jammers. Due to the physical separation of the aircraft, the time difference of arrival can often be greater than the...
The effects of adaptive-rate transmissions and routing on the total throughput of a slow-frequency-hop packet-radio network are considered. Adaptive rates are achieved through the use of error-control coding with perfect side information. Both fixed-length codes and variable-length codes are considered. Performance results are obtained for direct transmission (i.e., no routing), two-hop limited routing,...
This paper investigates packet acquisition in a random multiple access (RMA) environment. An analytical approach to performance evaluation is provided, which enables the waveform designer to set design parameters quickly such that the required performance is achieved without over-design. RMA is a medium access methodology used for time-frequency hopped signaling and has been widely considered in the...
The diversity provided by frequency-hop (FH) signaling can protect against jamming and multiple access interference (MAI). A FH transmission consists of two parts - an acquisition preamble and a data payload. The acquisition preamble allows the receiver to detect and synchronize with an incoming packet. Acquisition must be at least as robust as demodulation and decoding. If acquisition fails, the...
It has been shown that throughput in wireless networks is enhanced by using scheduled transmissions, low transmitter power, and multiple short hops to relay a packet from its source to its destination. There remain several difficulties with this approach. For example, relaying over many hops can cause large packet delays. The routing and slot assignment protocols can also incur a large overhead penalty...
For a frequency-hop (FH) spread-spectrum communication system, the packet error rate is dependent on both the performance of the error-correcting code and the ability of the receiver to detect and acquire timing of incoming packets. It is important that the error rate for one does not limit the overall error rate of the system. Turbo coding has been shown to be robust in the presence of partial-band...
Advances in analog-to-digital conversion and digital signal processing may allow new wideband receiver architectures to be built. For example, a receiver could sample a much wider bandwidth than is needed for a single user to communicate. This wideband receiver might be able to simultaneously demodulate the signals of multiple users that occupy different subbands. If a transmitted signal uses frequency...
Background. Guided percutaneous drainage (GPD) is used in the management of posttraumatic empyema thoracis; however, its equivalence to decortication has not been evaluated.Methods. We retrospectively reviewed the records of 12 patients who underwent GPD and nine who were treated with decortication.Results. No primarily GPD-managed empyemas necessitated a subsequent thoracotomy. The size and number...
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