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Adaptive secure data transmission method for OSI level 1

by Lallo, Pauli, PhD


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3. Clinical monitoring and intensive patient care mean a much different problem. In these applications
the various bedside medical equipment are to be networked at a lower level of
the communication hierarchy. This requires a dynamic, real-time, deterministic, faulttolerant,
and secure data exchange.

The 802.x standards lack some or more of these features. According to a survey in 1989 the
main requirements of bedside medical monitoring systems are:
1. Interconnecting bedside devices of one or more patients.
2. Real-time, deterministic, secure data exchange
3. Frequent reconfiguration of the network, plug & play features (ease-of-use)
4. Support a wide range of existing hospital information systems and databases

Address Resolution Protocol (ARP) Problem

Address Resolution Protocol (ARP) Problem is presented in reference [Noo99]. The Address
Resolution Protocol (ARP) is the protocol used to map 32-bit IP addresses to the address
scheme used by the data-link layer. The data-link layer (sometimes called the network link
layer), which consists of the operating system device driver and corresponding network interface
card, is responsible for dealing with the physical transport media. Each network interface
has a unique hardware address, typically assigned by the manufacturer. ARP is often referred to
as a “dynamic” protocol. This is due to the fact that its operation occurs automatically. The
protocol works in the background, without concern to the application user or even the network
administrator. It is the dynamic nature of ARP, which causes security issues.

1.4. Objectives of the Thesis

The investigation of analog (voice, image) data communication waveforms over band-limited
on voice grade circuits, soft modulation and detection methods in the mobile wireless or fixed
wired networks is a general objective in this thesis. The focus is not in the wide bandwidth applications
as in the general trend and in several other studies but in the limited base-band waveforms,
modulation methods, and the security on the physical level (OSI model level 1), which
has not been studied in the references. In summary the main objective of this study is the development
or evaluation of a new concept of soft adaptive multi-carrier data transmission over
band-limited wireless and fixed telephone channels especially for alert, telemedicine and authority
needs.

According to reference [Var03] medical communication standards only exist at the moment for
the higher level of medical care, like various databases and hospital information systems, and
not for low-level communication between various diagnostic devices. The main goals are to
ensure a real-time, deterministic and secure data exchange between the linked devices, and to
present a user-friendly visualization of the patient'state.

Our main goal is to present a secure adaptive communication method for a medical data communication
of OSI level 1. The method is also proposed for secure alarm signaling systems.

1.5. Outline of the Work

This study is an analysis and synthesis of an investigation of an adaptive data communication
method proposed for telemedicine and alert systems. The method is based on the present networks
and different channel types (AWGN, granular noise and multi-path). Biomedical data
processing and transmission are analyzed in Chapter 2. Transmission investigation methods are
measurements in Chapter 3, modeling and simulations in Chapter 4, and field tests with adaptive
data modem prototypes and new waveforms in Chapter 5.

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The study is organized as follows: This Chapter is an introductory chapter including a review
of adaptive communications. Chapter 2 provides an introduction to biomedical data processes
and data transmission based on the literature. Biomedical data processes and transmission
usually involves high quality biomedical images. Chapter 3 is an analysis and measurement
review. The basic investigation results in developing new waveforms and evaluating
their functionality in available transmission channels are presented in Chapter 4. Chapter 5
presents the theory of generation and detection of waveforms using a DFT based approach.
In summary Shannon’s, Fourier and Chang’s theories are used in the formulation of the final
results. A proposal and discussion of the adaptive secure data communication application is
included for telemedicine and alert system. Chapter 6 is a summary of the thesis.

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Chapter II

2. Biomedical Data Processing and Transmission

Biomedical data processing uses image information. The importance and value of IMAC
systems is found in medicine. Image management and communication (IMAC) has been
developing since the First International Conference on IMAC held in June 1989 in Washington
D.C. New technological innovations, PACS, HDTV and ISAC, were discussed in the
second conference in 1991 in Kyoto. PACS is a picture archieving and communication system.
HDTV is a high definition TV. ISAC is an abbreviation of “Image Save and Carry”. A
medical image analysis and diagnosis system has been developed in Australia [Ead01] and a
system for patients as Patient-Centered Access to Secure Systems Online (PCASSO) in
USA. Biomedical data processes and standards are described in several references [Ima91],
[Bus02] e.g. European standardization in medical informatics is identified in a reference
[Ima91] pp. 230-234. Medical computing and data standards are introduced in [Bus02] pp.
85-98. The future and advances in telemedicine are surveyed in reference [Bus02] pp. 129-
136.

Security of biomedical or telemedicine data transmission on the OSI level, i.e. the physical
level, is not available as a standard [Har05]. Wireless mobile information transmission in
telemedicine is a new area of data transmission, legislation and studies. These areas and recent
needs brought about by tsunamis, e.g. warning systems, are the focus of this thesis.

2.1. Biomedical Information Systems

Development of E-Health and Telemedicine

Early days of and development of E-health, telemedicine applications and technologies are
described in references [Eads01, Mah01, Rat05] as:
- The 1990s brought advances in image digitization and data compression technology,

which enabled videoconferencing over lower bandwidth lines i.e. voice grade telephone
lines and present wireless mobile phone connections.
- The typical telehealth model involves a hub hospital with satellite hospitals and clinics.
- Benefits of health care telecommunication technologies are: a. Distribution of resources.

b. Access to resources. c. Cost of health care.
- Challenges: a. Professional practice. b. Guidelines. c. Malpractice issues. d. Reimbursement
and legislation. e. Staff training.
- The boundary between medical and communication technologies will increasingly blur.
An important issue is the image resolution as:
- High resolution is crucial to teleradiology.
- Images have to be ideally transmitted by using lossless compression methods.
Three important attributes of image transmission are:
- Fidelity: Resolution, linearity and noise.
- Informativeness: The image conveys clinically important information.
- Attractiveness: The aesthetic properties.

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Local Area Network

Several different systems are in relation and connected together with a Hospital Information
System (HIS) using a local area network (LAN). Systems are according to reference [Ima91]:
- Picture Archiving and Communications System (PACS).
- Radiological Information System (RIS).
- Hospital Information System (HIS).
HIS deals with patient identification, blood chemistry, diagnosis, medical history, infection and
accounting. RIS consists of exposure record, file management, label print, reservation of
examination and accounting. The main problems of large picture archieving and
communication systems (PACS) are the need for high speed local network (LAN) and a mass
storage device. Two major components of PACS are: the network and the data base.

Some conclusions about the hi-speed network for PACS were made in reference [Ima91] p.32-
35:
- At least 100 Mb/s transfer rate in a network is equal to the present performance of the filmbased
system.
- The rate of data generation with the paths that the information flows in hospital were

evaluated. ETHERNET had a signaling 10 MB/s but a transfer rate of about 200 kb/s. This
transfer rate is a limiting factor.
- The very high required transfer rate could be achieved by the signaling rate of PACS

network or the large efficiency of operation.
A prototype ETHERNET network XFT (eXtra Fast Transport) was designed in 1991 and is
described in reference [Ima91] p.32-35. The performance, 500 Mbit/s signaling and 450 Mb/s
fiber-optic serial point-to-point communication links, agrees with the specifications. In 1991
operating networks at gigabit per second speeds were demonstrated [Ste91].

Image Management and Communication

The image management and communication (IMAC) system has not been utilized as quicly as
expected since 1989 conference. Military operations (for example the Gulf War) is one area,
where IMAC systems were needed. The image management and communication system must
consist of [Ima91]:
- PACS (on-line).
- ISAC (off-line).
An Image Save and Carry (ISAC) committee was organised in 1989 supported by a foundation
established by the Japanese government.

An estimation of the annual data of an entire hospital in Japan during one year (1988) is given
in reference [Ima91] p. 67 as presented in Table 2.1.

Table 2.1. Annual data of a hospital [Ima91]
patients images data/image data volume
Plain study, CR 116,921+19,762 228,939+36,161 4.0 MB 916 MB+145 MB
Enhanced study 23,946 233,893 2.25 MB 526 MB
CT, MR, nuclear 29,556 361,289 0.5 MB 180 MB
Total 190,194 860,282
2.8 GB/disk
1.7 TB
680 disks

Another estimation of daily image volume in a hospital in Japan is also given in reference
[Ima91] p. 330 as presented in Table 2.2.

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Table 2.2. Daily image volume in a hospital [Ima91]
bits/image no of exposures bits

X-ray 2048x2048x12 900 4.0E10
CT 512x512x12 800 2.5E9
RI static
dynamic
256x256x8
64x64x8
10
50
0.3E8
2.5E6

DF 1024x1024x8 600 0.6E10
MRI 512x512x8 500 1.6E9
Total 2860 5.5E10

Another study evaluated the transfer speeds between neuroradiology network components.
Transfer rates versus times of a 60 images study varied from 171 kb/s versus 24.5 min to 677
kb/s versus 1.55 min. The low speed problem is disturbing in scanning images. However, the
lost images were reported to be even more of a disturbing problem, reference [Ima91] pp. 272-
277.

These results are interesting as a reference for this thesis.

Medical Diagnostic Imaging Support

The Medical Diagnostic Imaging Support (MDIS) system is a project of the U.S. Department of
Defense. The goal was to achieve filmless medical imaging operations in the 1990s throughout
the defense health care system.

A computerized analysis of lung textures for detection and characterization of interstitial
diseases in chest images based on the power spectrum is presented in reference [Ima91] pp.
280-283. A comparison of ROC analysis curves obtained from radiologists and by means of the
computerized method suggest that the computerized approach may provide perfornance similar
to human observers in distinguishing lungs with mild interstitial diseases from normal lungs.

Picture Archieving and Communication Systems

A simplified view of the Picture Archiving and Communications system (PACS) assumes that
it can be decomposed into the following classes of subsystems [Ima91] p.12:
- Acquisition.
- Distribution.
- Storage.
- Processing.
- Display.
Since 1983, in Personal Health Data Recording System (PHD-RS) Japan and Picture Archiving
and Communications system (PACS) in USA has started. The PHD-RS system is a personal
filing system to carry all medical information of a patient: medical images, laboratory findings
and past history under chronological editing. In the concept of PHD-RS in 1982, all personal
data concering medical information must be gatherted onto in one magnetic tape cassette and
carry with patient himself [Ima91] pp. 4-5.

A total information system using IBM 360 mainframe computer system was started in 1971 in
Kitasato University Hospital, Japan. Microfilm system was considered but cost performance
was not enough and they did not save manpower. Development in the 1980s based on computer
technology, information transfer technology and information media progress as:
- In the field of radiology.
- X-ray computed tomography (X-CT).
- Magnetic resonance imaging (MRI).

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- Single photon emission tomography (PET).
- Ultrasound tomography.
- Charge coupled device (CCD) camera for endoscopy.
All radiological images can be shown in digitalized patterns and recorded on optical disk. This
tendency leads the medical information system to be image save and carry system.

A Web-Based Collaborative System for Medical Image Analysis and Diagnosis

Reference [Ead01] explains the web-based collaborative system for medical image analysis and
diagnosis. The system uses computer and network technologies and the Internet, to provide and
support healthcare when distance separates the participants. There has been a lot of research
carried out to develop the electronic Picture Archiving and Communications system (PACS)
that is for a hospital wide network and for people to deal with medical image. The test results of
the client-server system is presented in reference [Ead01]:
- The client system consists of a chat system, image system, and a CGI based system.
- The chat system provides information on all the participants and actual messages between

them.
- The server was set up to test the consistency and feasibility of the system. The system’s ind e-

pendence was checked using different platform machines such as Microsoft windows,
Unix/x-windows, and Linux.
- It performed well in all kinds of operating systems but the performance depended on the network
bandwidth. For future work, a video-capturing function could be added to future work
to provide better presence of awareness.
- The image system consists of an image selector and drawing tools. The image selector

downloads medical images from a server’s database and displays a set of images. When a
user selects one image it creates a new image object with drawing tools to handle the image
and network connection to the server.

These results are interesting as a reference for this thesis because the bandwidth requirements
will be simulated and new modulation methods will be evaluated. The goal of investigations is
to develop adaptive methods for use in data transmission over physical band-limited channels.

Patient-Centered Access to Secure Systems Online

At the time the project began, several prototypes existed, Web-based clinical data systems,
which were explicitly designed to serve only health professionals, and, the most used security
“firewalls” to filter queries originating from outside the organization’s private network times.
The Patient-Centered Access to Secure Systems Online (PCASSO) project was designed to apply
state-of-the-art security to the communication of clinical data over the Internet. The project
has completed its initial field test and is not open at this time for new participant enrolments.
Several references are made [Mas97, Mas98, Mas02].

The reported conclusion was: PCASSO applies state-of-the-art security technologies to the goal
of extending the current World-Wide Web so that it may be used by healthcare providers and
their patients to view person-identifiable health data. The project tests both the technology of
security and the sociology of healthcare in an era where patients are given online access to their
own medical data.

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2.2. Standards

The main goals are to ensure a real-time, deterministic and secure data exchange between the
linked devices, and to present a user-friendly visualization of the patient's state. Storage and
communication standards have been discussed since the 1980s (PACS, DICOM, JIRA, MIPS,
ACR/NEMA etc). Technical standards relating to image format and communication protocols, as
well as image processing including digital compression, have been the subject of discussions.
Issues of safety and security within these digital networks are emerging to be critical aspects of
medical multi-media data networks. Safety is usually defined in terms of hazards and risks as a
systems engineering concept. In certain medical environmental conditions, a hazard is a set of
conditions that can cause harm to a patient or other person. Safety is related to the reliable functioning
of hardware and software. Security deals with issues of protecting the system against:
- unauthorized access to multi-media medical records and
- malicious or accidental corruption of data.
OSI Security Architecture defines a number of mechanisms for authentication, access control,
data confidelity, data integrity, and non-repuditation. No standard mechanism exists or is likely to
be available in the near future, which guarantees perfect safety of medical information systems
and specially of IMAC systems [Ima91] p.183-185.

ACR-NEMA Standards

The first U. S. PACS meeting in Kansas City in 1982 acquired image and image descriptive data.
Different digitized video (often a loss of dynamic range) or magnetic tapes (different tape formats
and pixel packing technique) were used in the manufacturer’s systems. First a committee was
formed in 1983 by two bodies, the American College of Radiology (ACR) and the National Electrical
Manufacturers Association (NEMA). In 1985 the ACR-NEMA Standard was developed as
an interface standard for the interconnection of two pieces of imaging equipment. The standard
builds upon the OSI-ISO Reference Model but is not ISO compatible. Differences are in definitions
of layer-to-layer connections (interfaces in ISO terminology), reference [Ima91] pp. 235-
248.

Work items in ISO/TC 215 Work Group WG4

The working group experts identified the following areas as possible candidates for new work
items:
1. Definition of security terminology to be used in healthcare and in ISO/TC 215 standards in

particular.
2. Guideline to existing standards and to point out where the documents can be found and when

they may be applicable.
3. A framework document to show the scope of security standards for the healthcare field.
4. A standard for secure messaging (encapsulated objects with encryption for confidentiality and

digital signatures to provide proof of origin and integrity).
5. A standard for secure channeling, particularly for web applications.
6. Discussions were held concerning the selection of encryption algorithms. “Consensus was

almost reached that we should not make any restriction to the selection.... to draft a document
describing the business model and a proposed policy on encryption... possibly suggest a work
item on healthcare professional cards for authentication”.
7. The need for standards on a supporting infrastructure for cryptographic techniques was further
identified but not considered to be in the top priority for immediate action.

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Medical Instrumentation Bus of IEEE

Since 1992 IEEE had a draft proposal of the Medical Instrumentation Bus (MIB). The final
standard has not yet been approved. Bridge MIB modules approved 802.1 technologies. IETF
was in progress in 2004. IETF Bridge WG Transition is to IEEE 802.1 WG. The schedule is
presented in reference [Har05]:
- November 2004: RFC1493 update, RFC2674 update, and RSTP-MIB.
- In 2005: Bridge WG documents to proposed standard and MIB module in some 802.1xx.

802.3 Ethernet

Due to its economical price lots of hospitals and medical centers used and use the commercial
802.3 Ethernet to interconnect their departments, [Var03].

2.3. Conclusions

There are many PACS, RIS and HIS in the market but they are seldom connected to each other
and integrated. The reason has been lack of information exchange standards. Lack of standards
for communication between health care applications is still one of the primary reasons holding
up the wider use of information technology in health care. Movement of the standards towards
alternate lower layer connections, TCP/IP protocol (de facto standard) and ISO-OSI stacks will
contribute to the use of standards for network connection of devices [Ima91].

Today medical communication standards exist only for the higher level of medical care, like
various databases and hospital information systems, and not for low-level communication between
various diagnostic devices, see references [Sen95], [Var03] and [Rat05].

Transfer speed between network components and the problem of lost images are disturbing
effects in PACS implementation.

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Chapter III

3. Analysis and Measurements

Security of biomedical or telemedicine data transmission on the OSI level, i.e. the physical
level, is not available as a standard [Har05]. Thus the basic investigation problem is to find solutions
and proposals to this problem formulation. Firstly the quality of data transmission over
the present voice communication channels was investigated using measurements. Present networks
are based on digital hierarchy and digital channels. Analysis and data transmission methods
over these channels are discussed in the original papers written in 1997-2004. The papers
are listed at the end of this thesis. Earlier networks were analog networks and used FDM. These
networks and data transmission on their analog channels are discussed in the original papers
[Lal75] and [Lal87].

3.1. Definition of Measurement Objects

Based on the different standards in military and public telecommunication networks the attenuation
distribution requirements are different, Figures 3.1-3.2. In Figure 3.1 one can find that
delta modulation using 16 kbps bit rates have no requirements for frequencies higher than 2600
Hz.

Fig. 3.1 Attenuation distortion requirements of 32 kbps ADM and PCM [Eur86],
[Itu89]

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Fig. 3.2 Attenuation distortion requirements of 16 and 32 kbps ADM [Eur86]

On the other hand the 32 kbps delta modulation is quite near to the ITU-T speech channel,
[Eur86, Itu89]. The following problems with analog data transmission using standard ITU-T
modems over delta-modulated channels have been found in networks:
- Modern high-speed modems (telefax or 9600 bps) do not work.
- Low speed (1200-2400 bps) FSK V.23 and PSKV.26 modems have high BER.
- Packet switching does not work properly (long message delays).
There were problems in finding a proper standard modem or modems capable for use in 16
kbps networks defined in [Eur86]. The voice grade modems are optimized for use in the analogue
speech channel of the public telecommunication network. The results of these measurements
are discussed in the next sections.

3.2. Measurements

The measurements include ADM (adaptive delta-modulated) channel investigations and tests
for analog data transmission over the ADM-channel. Data transmission performance in a delta
modulated voice channel is limited by the channel performance. Thus the effect of several limiting
factors and physical parameters are investigated in the measurements:
- Attenuation and attenuation distortion versus frequency.
- Phase characteristics and distortion.
- Total harmonic distortion (THD).
- Input level of the channel.
- Signal-to-Noise (S/N) ratio.
- Bit rate of delta modulation.
- Bandwidth of the channel.

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