International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / This paper addresses a method to provide both secure and non-secure voice communications to a DS-1 network from a common keyset. In order to comply with both the electrical isolation requirements and the operational security issues regarding voice communications, an all-digital approach to the keyset was developed based upon the AD2101 DSP. Protocols that are handled by the keyset include: Multiple PTT modes, hot mike, telephone access, priority override, direct access, indirect access, paging, and monitor only. Special features that are addressed include: independent channel by channel assignment of access protocols, headset assignment, speaker assignment, and PTT assignment. Multiple microprocessors are used to implement the foregoing as well as down-loadable configurations, remote keyset control and monitoring, and composite audio outputs. Partitioning of the digital design provides RED to BLACK channel isolation and RED channel to AC power isolation of greater than 107 dB.

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / The Edwards Digital Switch (EDS) is a digital communication system that provides advanced voice networking capabilities to the Edwards Test Range. The EDS is a member of a new family of all-digital switching systems that internally handle data in digital form. To accommodate analog voice and data circuits, conversions between analog and digital formats occur at the system interfaces. The EDS consists of six groups of configuration items: System-level control and monitoring is centralized in the Control and Display Subsystem. Workstations provide subsystem-level control and monitoring. The Central Switching Subsystem, as the primary interface with the range environment, provides system connectivity to radios, telephone circuits, and communications links to other facilities. It integrates the EDS with links to the Control Room Switching Subsystems. Each Control Room Switching Subsystem connects individual user stations within a Mission Control Room or other localized area. The user equipment element consists of a Subscriber Terminal Unit, Channel Expander, and interface panels for headsets, foot switches, and speakers. The Remote Radio Control Unit optimizes usage of available frequencies, allowing control of tunable radios from the Control and Display Subsystem. *The original name, Edwards Communication Switching System (ECSS) was changed to Edwards Digital Switch (EDS) in 1990. The Site Selection Unit facilitates the handover of voice communications between receiver sites when a long-range test is monitored. The system architecture is based on a central system-level control element, a central switch, multiple subsystem-level control elements, multiple subsystem switches, and end-equipment items that are interconnected through the switch network. The EDS combines multiple voice communications applications in a single system. The system is being expanded to integrate voice and data switching. Its major function is support of multiparty networked voice communications within Mission Control Rooms and between other test participants. Other voice functions are an intercom capability including both Direct Access (hot line) and Indirect Access (dial-up), subscriber loop connections to the base-level telephone exchange, and the Public Switched Network System. Digital interfaces allow integration of ciphertext data and Time Space Position Information data switching functions. A system based on the EDS design has also been installed by the Air Force at Eglin AFB. Engineering studies for systems that make use of the EDS design are currently underway by the Navy at China Lake and the Army at White Sands Missile Range. The EDS project office has actively pursued promising program management concepts such as: specifying nondevelopmental items, requiring industry standard interconnectivity and interoperability, and using a multiyear fixed-price requirements-type contract to encourage multiservice participation.

Cognitive Radio Networks (CRNs) provide a solution for the spectrum scarcity problem facing the wireless communications community. However, due to the infancy of CRNs, further research is needed before we can truly benefit from CRNs. The basic concept of CRNs relies on utilizing the unused spectrum of a primary network, without interfering with the activity of primary users (PUs). In order to successfully achieve that, users in a CRN has to perform spectrum sensing, spectrum management, spectrum mobility, and spectrum sharing. The latter, which is the focus of our research, deals with how secondary users (SUs) share the unused spectrum. Furthermore, to be able to utilize CRNs in practical applications, a certain level of quality-of-service (QoS) should be guaranteed to SUs in such networks. QoS requirements vary according to the application. Interested in voice communications, we propose a packet scheduling scheme that orders the SUs' transmissions according to the packet dropping rate and the number of packets queued waiting for transmission. Two medium access control (MAC) layer protocols, based on the mentioned scheduling scheme, are proposed for a centralized CRN. In addition, the scheduling scheme is adapted for a distributed CRN, by introducing a feature that allows SUs to organize access to the available spectrum without the need for a central unit. Finally, extensive simulation based experiments are carried out to evaluate the proposed protocols and compare their performance with that of other MAC protocols designed for CRNs. These results reflect the effectiveness of our proposed protocols to guarantee the required QoS for voice packet transmission, while maintaining fairness among SUs in a CRN.

Cognitive Radio Networks (CRNs) provide a solution for the spectrum scarcity problem facing the wireless communications community. However, due to the infancy of CRNs, further research is needed before we can truly benefit from CRNs. The basic concept of CRNs relies on utilizing the unused spectrum of a primary network, without interfering with the activity of primary users (PUs). In order to successfully achieve that, users in a CRN has to perform spectrum sensing, spectrum management, spectrum mobility, and spectrum sharing. The latter, which is the focus of our research, deals with how secondary users (SUs) share the unused spectrum. Furthermore, to be able to utilize CRNs in practical applications, a certain level of quality-of-service (QoS) should be guaranteed to SUs in such networks. QoS requirements vary according to the application. Interested in voice communications, we propose a packet scheduling scheme that orders the SUs' transmissions according to the packet dropping rate and the number of packets queued waiting for transmission. Two medium access control (MAC) layer protocols, based on the mentioned scheduling scheme, are proposed for a centralized CRN. In addition, the scheduling scheme is adapted for a distributed CRN, by introducing a feature that allows SUs to organize access to the available spectrum without the need for a central unit. Finally, extensive simulation based experiments are carried out to evaluate the proposed protocols and compare their performance with that of other MAC protocols designed for CRNs. These results reflect the effectiveness of our proposed protocols to guarantee the required QoS for voice packet transmission, while maintaining fairness among SUs in a CRN.

Miscommunication between controllers and pilots, potentially resulting from a high pilot cognitive load, has been a causal or contributing factor in a large number of aviation accidents. In this context, failure to communicate can be attributed, among other factors, to an inadequate human-system interface design, the related high cognitive load imposed on the pilot, and poor performance reflected by a higher error rate. To date, voice radio remains in service without any means for managing pilot cognitive load by design (as opposed to training or procedures). Such an oversight is what prompted this dissertation. The goals of this study were (a) to investigate the utility of a voice-to-text transcription (V-T-T) of ATC clearances in managing pilot's cognitive load during controller-pilot communications within the context of a modern flight deck environment, and (b) to validate whether a model of variable relationships which is generated in the domain of learning and instruction would "transfer", and to what extend, to an operational domain. First, within the theoretical framework built for this dissertation, all the pertaining factors were analyzed. Second, by using the process of synthesis, and based on guidelines generated from that theoretical framework, a redundant verbal display of ATC clearances (i.e., a V-T-T) was constructed. Third, the synthesized device was empirically examined. Thirty four pilots participated in the study – seventeen pilots with 100-250 total flight hours and seventeen with > 500 total flight hours. All participants had flown within sixty days prior to attending the study. The experiment was conducted one pilot at a time in 2.5-hour blocks. A 2 Verbal Display Redundancy (no-redundancy and redundancy) X 2 Verbal Input Complexity (low and high) X 2 Level of Expertise (novices and experts) mixed-model design was used for the study with 5 IFR clearances in each Redundancy X Complexity condition. The results showed that the amounts of iii reduction of cognitive load and improvement of performance, when verbal display redundancy was provided, were in the range of about 20%. These results indicated that V-T-T is a device which has a tremendous potential to serve as (a) a pilot memory aid, (b) a way to verify a clearance has been captured correctly without having to make a "Say again" call, and (c) to ultimately improve the margin of safety by reducing the propensity for human error for the majority of pilot populations including those with English as a second language. Fourth, the results from the validation of theoretical models "transfer" showed that although cognitive load remained as a significant predictor of performance, both complexity and redundancy also had unique significant effects on performance. Furthermore, these results indicated that the relationship between these variables was not as "clear-cut" in the operational domain investigated here as the models from the domain of learning and instruction suggested. Until further research is conducted, (a) to investigate how changes in the operational task settings via adding additional coding (e.g., permanent record of clearances which can serve as both a memory aid and a way to verify a clearance is captured correctly) affect performance through mechanisms other than cognitive load; and (b) unless the theoretical models are modified to reflect how changes in the input variables impact the outcome in a variety of ways; a degree of prudence should be exercised when the results from the model "transfer" validation are applied to operational environments similar to the one investigated in this dissertation research.