Nickolas J. LaSorte

Experimental assessment of wireless coexistence for 802.15.4 in the presence of 802.11g/n

Wireless coexistence is a growing concern, given the ubiquity of wireless technology. Although IEEE Standards have started to address this problem in an analytical framework, a standard experimental setup and process to evaluate wireless coexistence is lacking. Literature that reports experimental assessment of wireless coexistence places little emphasis on separation distance of wireless nodes under test or the spectrum occupancy of the interfering network, making comparisons difficult. This paper provides an extensive literature survey of 802.15.4 and 802.11 b/g/n wireless coexistence and demonstrates that in a higher wireless channel occupancy environment, ZigBee coexists with 802.11n better than with 802.11g. A reproducible, versatile, and practical test setup is presented to serve as a starting point toward establishing standard practice for wireless coexistence testing of wireless systems in general and wireless medical devices in particular. Experimental evaluations demonstrated consistency with results reported in the literature.

The History of Orthogonal Frequency Division Multiplexing

This paper depicts the development of Orthogonal Frequency Division Multiplexing from a historical perspective. A summary of major research milestones are noted that contributed to modern-day OFDM. These contributions include the use of discrete Fourier transforms replacing the analog implementation and addition of cyclic extensions to ensure orthogonality among the sub-channels. Also, channel equalization algorithms to suppress inter-symbol interference and inter-carrier interference, channel estimation through the insertion of pilot tones among data blocks, peak-to-average power ratio reduction, and synchronization techniques are discussed.

Characterization of the electromagnetic environment in a hospital and propagation study

This work presents the results of a survey of the electromagnetic environment from 30MHz-7GHz in St. Francis Hospital, in Tulsa, Oklahoma. Measurements were considered short term as the full spectrum was measured in twelve minutes. The results show the dynamic environment apparent in todays hospitals. There were no recorded cases in which the IEC immunity standard specifications, 3V/m, was exceeded. Another contribution by this paper was to show an example of cross-floor attenuation in a hospital.

An experimental method for evaluating wireless coexistence of a Bluetooth medical device

Medical device manufacturers are integrating wireless communication into medical devices at an increasing rate, specifically in the 2.4 GHz industrial, scientific, and medical (ISM) band. The increased use of the 2.4 GHz ISM band is fostered by the economic benefits of inexpensive wireless chipsets and the capability to communicate with other devices exploiting standard wireless technology.

Comparison of duty cycle measurement techniques of 802.11b/g in the frequency and time domain

Medical device manufacturers are evermore including wireless communication in their medical devices. Because most utilize common wireless standards such as ZigBee and Bluetooth that operate in the unlicensed 2.4 GHz industrial, scientific, and medical (ISM) band, the Food and Drug Administration (FDA) is asking medical device manufacturers to test for wireless coexistence. Coexistence among wireless devices is dependent on three factors, namely frequency, space, and time. Specific to time, the probability of coexistence in the 2.4 GHz ISM depends on channel occupancy (or duty cycle) of the interfering wireless network-the main source being WiFi (802.11b/g) for ZigBee and Bluetooth. This paper reports on the implementation of two dutycycle measurement systems for 802.11b/g utilizing a National Instruments 5663E vector signal analyzer. Measurement techniques were designed in the frequency and time domain, and then compared. Simulations of 802.11b/g duty cycles were also executed and compared with experimental measurements.

Experimental characterization of electromagnetic propagation of a hospital from 55–1950MHz

An examination of the electromagnetic environment and characteristics from 30MHz–7GHz in a hospital is discussed in this paper. Empirical propagation constants, building attenuation, floor height gain, and the CDF of the coverage, were calculated from 50–1950MHz. This is carried out to further understand the propagation of radio waves through hospitals. The understanding of wave propagation through hospitals will help advance the knowledge to control the electromagnetic environment of hospitals to decrease electromagnetic interference to medical devices. The understanding of the RF hospital environment is even more pressing given that many hospitals are implementing electronic medical records that would require the co-location and co-existence of many different types of RF emitters. The measurement parameters calculated are useful for propagation modelling.

Performance Evaluation of a Deployed WiMAX System Operating in the 4.9GHz Public Safety Band

This paper presents an evaluation of a deployed WiMAX system operating in the 4.9GHz Public Safety Band in the City of Tulsa. The study includes propagation analysis for the coverage and network performance tests to demonstrate the viability of a WiMAX system as a medium for public safety. We considered existing propagation models in the UHF band (300 MHz to 3 GHz) to be applied to 4.9 GHz and compared the characteristics predicted by the models with the measured data. The results show that of the three models presented, the Cost-231 Hata Model best predicts the characteristics of the deployed WiMAX system. Network performance tests were also conducted to measure the throughput of the system at various adaptive modulation rates.

802.11g channel characterization utilizing labview and NI-USRP

Medical device manufacturers have recently begun to incorporate wireless communication, such as ZigBee and Bluetooth operating in the unlicensed 2.4 GHz industrial, scientific, and medical (ISM) band, into their medical devices. Wi-Fi, however, is a major source of interference in the ISM band. With patient safety in mind, the FDA has mandated coexistence testing for wireless medical devices [1]. An initial step toward supporting this mandate is to be able to accurately characterize the interfering network in a typical environment. In this paper, a software defined radio (SDR) is employed to serve as a platform for measuring channel duty cycle, packet arrival rate, node distribution, and packet inter-arrival time distribution of 802.11g networks. Theoretical and technical concerns are discussed, and tests performed to assess system integrity are described. Experimental tests examining channel characteristics of an 802.11g network are also reported.

Creating an automated and emulated 802.11g wireless interfering network for wireless coexistence testing

Although the proliferation of wireless medical devices is mounting-partially due to benefits of wireless technology-associated risks must be evaluated. The Food and Drug Administration (FDA) is asking medical device manufacturers to quantify these by testing their wireless medical devices for coexistence. This can be a tedious and complicated chore. To streamline the process and to disseminate information about wireless coexistence testing, we are undertaking the task of automating the process. One of the most difficult steps in coexistence testing is setting up an interfering network. A major source of interference in the 2.4 GHz ISM band is Wi-Fi (802.11 b/g/n). This paper informs about tools developed to accurately characterize 802.11g and then emulate an 802.11g access point. Our previous work has shown that by employing a similar period and duty cycle, a signal generator can emulate an interfering 802.11g wireless network during wireless coexistence; however, the outcome performance of the wireless network under test is drastically different. An emulated interfering network must mimic channel characteristics of an actual network, as well as its influence on the wireless network under test. In response to previous findings, we performed wireless coexistence testing and compared the influence of an actual 802.11g wireless network with an emulated interfering 802.11g wireless network. A ZigBee network acted as the wireless network under test.

In vitro protocol to study the electromagnetic interaction of RFIDs and infusion pumps

The paper presents a generalized protocol to test and verify the reported results of EMI effects between RFID scanners and wearable infusion pumps. In addition, the protocol was created to more precisely evaluate the amount of interaction between RFID and medical devices, and identify those factors which had a significant influence on the level of interaction. Experimental EMI testing was conducted between three wearable infusion pumps and two RFIDs; no interference was observed.