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Adaptive secure data transmission method for OSI level 1

by Lallo, Pauli, PhD


Page 11

Chapter I

1. Introduction

This chapter is organized into background, motivation of the work, evolution of telecommunications,
objectives and, outline of the thesis. The motivation includes earlier activities and work
experiences and contribution papers of this thesis. The evolution section gives a review of
other studies of telecommunications, standard modems and their performance, waveforms and
the idea of multi-carrier systems. Research methods and research problems are discussed in the
last section: objectives of the thesis and outline of the work. The objectives describe the aim of
the research. Formulation of the adaptive secure data communication method for OSI level one,
its potential applications and new knowledge of the use of discrete Fourier transform (DFT) in
generation and detection of waveforms is the expected benefits of this study. The outline of the
work defines the structure of the thesis.

1.1. Background

The most unfortunate things in the modern world awoke the world, the World Trade Center on
September eleven in 2001 and an earthquake followed by a tsunami in Asia on Boxing Day
26.12.2004, when we think of all the precautions against manmade catastrophes and convulsions
of nature. The former perfected a military transformation in USA. The latter made it clear
that an information system based on telecommunications could have saved most of the nearly
180 000 deaths. It is sad that a working alert system was not made there, in spite of the technology
known and used in most countries in the Pacific Basin. The Pacific Tsunami Warning Center
(PTWC), established in 1949, provides warnings for teletsunamis to the areas and US interests.

The communication system from the information source via radio waves (public broadcast,
mobile cellular, satellite service etc) to the people exists. The completing alternatives to public
broadcasting, for example messages with cellular phones, can serve as redundancy in securing
the authority made alerts. The motto of the Signal Regiment of the Finnish Defence Forces
(FDF) says “Denuntiatio solum translata valet”. The tsunami also reminds the author of the development
efforts within telemedicine in general as one of the most important issues. It is worth
all the efforts already made and those that will be made in the future. This encourages the author
in publishing some results of the secure adaptive data communication methods studied and
developed during several years and especially during 2000-2005 at the Tallinn University of
Technology. The results of this thesis will be presented on the following pages. An adaptive
data communication method (soft data generation and DFT detection method) will be presented
that can be included in public broadcasting systems all over the world. The idea is that broadcasting
stations are coupled in the alerting data sources and local authorities have standard receivers
equipped with a small additional audio circuit for detection of an alerting coded waveform.
For telemedicine communications the waveform will be proposed as a secure OSI level 1
wireless data transmission.

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1.2. Motivation of the Work

The public switched telephone network (PSTN) in Finland was in an early phase of the automatic
traffic during the time 1968-1970, when the author was an office engineer at the Post and
Telegraph Administration in Helsinki. The value of automatic telephone networks was well understood
during the automation projects in various places in Finland (Porvoo, Imatra, Keuruu,
Lieksa, Kristiinankaupunki, Saarijärvi, Kemijärvi etc). The author completed his M.Sc thesis in
1969 about the R2, which is a MFC signaling in the automatic PSTN. The result of that work is
described in reference [Par00].

During active military service in 1970-1977 the author was also involved in discussions
concerning the automation of the, at that time, manual tactical military telephone services
[Lei72]. The author’s first post-graduate thesis (Lic.Tech 1975) and a publication
in HUT (1987) was a result of the studies for the evaluation of the availability of a limited
network, papers [Lal75] and [Lal87]. For eleven years, 1977-1988, the author worked
at the vocational training centers at Jyväskylä leading a department and at Järvenpää as a
leader. Among several activities during that time he was also involved in the development of
training programs for numerically controlled (NC) machinery and microcomputers. At that time
the evolution of microprocessors and personal computers (PC) was intensive. The use of PCs in
education and small businesses with the idea of electronic sheet, Visicalc in 1978-1979
[Rad80], was started. The author also had the TRS-80 Model I at home.

The post of Assistant Professor of Applied Electronics at Lappeenranta University of Technology
was founded in 1989 and the author was its first holder conducting courses on “Microprocessors”
and “Machine language programming. The author published a textbook about microcomputers
used in vocational training centers and Lappeenranta University of Technology. At
Helsinki University of Technology the author has conducted courses on “Teleautomation” in
1984-1985 and 1988-1989, and “Digital systems” in 1990-1991 working at the Department of
Electrical and Communications Engineering.

The automation and digitization of military networks, both tactical (moving) and strategic
(fixed), and the start-up of the military information age with the Intranet and first personal
computers (PC) was established in about 1988. This time was his second military service in
1988-2004 (retired on 31.12.2004). The author designed training guides and planning methods
for new systems including modeling and simulation methods described in references [Cac93,
Mis98] and a robust simulation tool of his own [Lal04a-b]. Design methods for the tactical radio
links and wireless networks were one of the main efforts during 1998-2004. The network
planning system is based on modeling and computer simulations using cartographic data from
Finland (digital maps, elevation models, clutter and forest height information).

Oracular forecast is found in reference [Fdf03] about the roles and tasks of defense forces and
their mutual relations. International peace keeping forces are gaining a more significant role as
the threat of armored attack diminishes. Large-scale national disasters and defense against terrorism
necessitate the use of armed forces in support of Civil Society. The reference presents a
software radio program and its new adaptive wideband networking waveform for FDF [Fdf03].
Also the need of command and control (C2) systems with wireless communication networks
using (VHF, UHF) digital radios motivated into several studies of adaptive data communication
systems One result of the author’s studies in these areas was the concept of an adaptive modem
and later an adaptive security method for data communication [Lal99, Lal00, Lal02, Lal04b].
The adaptive modem was found as a novel solution in the PCT review in 1999. Both the adaptive
securing method for OSI level one (physical) data transmission and the adaptive modem itself
have been awarded with an invention prize of the FDF in 1999 and in 2002. This system is
the main result in this thesis, discussed in several references [Lal97a-b, Lal99, Lal00, Lal01,
Lal02, Lal04a-b].

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The background described above gave the motivating force for the academic work at the Tallinn
University of Technology during 2000-2005 with the results published in the following proceeding
of
- Eurocom conference 2000 in München “Adaptive modem” [Lal00].
- MILCOM conference 2001 in MacLean, USA with title “Adaptive modem techno logy”

[Lal01]
- MILCOM conference 2002 in Anaheim, CA, USA with title “Basic theory of adaptive data

transmission” [Lal02].
- ESM conference 2004 in Magdeburg, Germany with title “Modeling and simulation of

biomedical data networks” [Lal04a].
- MILCOM conference 2004 in Monterey, CA, USA with title “Robust simulation of wav e-

forms” [Lal04b].
The main contributions of this thesis are in the theory of adaptive data communications, a simulation
of telemedicine traffic, and the soft detection and generation method of adaptive bandlimited
waveforms based on the discrete Fourier transform (DFT), Appendix 1. The result of the
studies is defined in the proposal for secure telemedicine and biomedical information data
transmission method for OSI level 1.

1.3. Evolution of Telecommunications

A Shannon’s result is the concept that every communication channel had a speed limit, mea s-
ured in binary digits per second. The famous Shannon Limit is the familiar formula for the capacity
of a white Gaussian noise channel [Sha48]. In a paper [Mos02] a new paradigm called
“capability" is proposed, which gauges the effectiveness of a steganographic method. It includes
payload carrying ability, detectability, and robustness components. A demonstration is made
that a compressed image (JPEG) always has the potential to carry hidden information [Mos02].
In the adaptive data transmission method studied in this thesis hidden information will be carried
in the signal space. The use of zero-error capacity for channel analysis is discussed. The
error free channel capacity is one substance used in this thesis.

1.3.1. Studies of Telecommunication

Alec Reeves invented PCM in 1937 as a result of a research group in Paris [Alc92, Rob04].
Severe problems with noise and distortion were reported while bandwidth was large in radio
links. Technologically it was too early to use PCM in practice. The encoding of signals with 1-
bit code has been studied quite early 1946 [Del46]. The introduction of delta modulation (DM)
by de Jager was made in 1952 [deJ52]. Voice coding methods (PCM and DM) produce granular
noise. Bandwidth and signal-to-noise ratio (SNR) are important parameters used in evaluation
of a system’s pe rformance in this thesis.

Voice Grade Data Communication

At present, “capacity" is the prevailing paradigm for covert channels. Voice grade data tran s-
mission on wired channels has been studied by ITU-T as early as in March 1960 [Itt61, Itu60].
Modulation method of the first data transmissions was FSK and later MFSK. Modem development
is based on modulation method, bit rate and symbol rate, Table 1.1.

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Table 1.1. Standard modems [Lal97a]

Modem development is seen in the modulation method: phase difference, phase and amplitude
difference (QAM), and finally coding methods were used. The key idea was that the operations of
modulation and coding are combined. Limitations on conventional block and convolutional codes
on band-limited channels have motivated to introduce other coding methods TCM (Trellis-Coded
Modulation) scheme, discovered by G. Ungerboeck in 1976 [Ung82] and its several variants for
example iterative turbo BICM (Bit Interleaved Code Modulation) scheme [Big91 SNg03] for decreasing
error probabilities.

Performance Analysis

The performance analysis for a TCM system with a Viterbi decoder [Vit67] is derived in reference
[Ung82] as

The upper bound on the node error rate is

P

e

2
d E

free s

2
d E

⎜ ⎟
free s 4N
0

Q⎜ ⎟e T (D) (1.1)

2N

0

⎝ ⎠

with

E

s
4N0

=
D e (1.2)

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and the upper bound on BER is:

P

e

2
d E
free s
2 ⎜ ⎟

1 d

freeEs 4N
0


Q


m


2N

0


e


(D, I )

I (1.3)

with




Es
4N




0

D = e , I=1 (1.4)

Where T(D) is the generating function of the direct graph (state diagram of the trellis code).
T(D,I) is the augmented version of T(D)with components of the I terms denote the number of information
bits errors associated with each error event. N0 is the one sided noise spectral density
of AWGN, Es is the average energy of the signal constellation and m is the number of information
bits carried by each symbol.

The derivation of generating function is complicated as the number of states in the TCM increases.
At high S/N values an approximation is quite accurate without T(D,I) [Ung82]:

2
d freeEs
P ≈ ⎟

e N(d free )Q (1.5)

2N

0

⎝ ⎠

d
P m


Q


d

E





2

b
free free s

2N

0

(1.6)

Here the N(dfree) is the average number of sequences that are distance dfree from the transmitted
sequence.

For example, using TCM the error rate can be reduced by three orders of magnitude (from 1 in 10
to 1 in 10000). In a classical view the spectral efficiency as the number of bits per second transmitted
per one hertz of bandwidth is decreased due to the increased code rate. However, the
modulation symbol set could be enlarged when coding is used relative to that needed for uncoded
case [Ung82] and:
- If the signal set dimensionality per info bit is unchanged the power spectrum remains unchanged
(no BW expansion or change in spectral efficiency).
- The signaling rate does not change if coding and modulation is performed with respect to ED
(Euclidean distance) between coded modulation sequences.

TCM code is recommended by ITU-T with
V.32 for 9.6 kbps over two-wire telephone lines and 14.4 kbps one-wire lines.
V.17 for use with 64-QAM and 128-CROSS 14.4 kbps FAX traffic over standard phone lines.
V.33 14.4 kbps and V.34 28.8 kbps.

For evaluation of a modulation method a formula for BER versus S/N (bit error rate versus signal-to-noise
ratio) are generated.

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In general the Gaussian error integral, function Q(x), gives an approximation for error performance
Pe of sequences of transmitted symbols in signal space, where dmin minimum Euclidean distance
described in references [Vit67, Ung82]. At high signal-to-noise ratios [Ung87]:
dy
e
x
Q
x
y

∞ −
= 2
2
2
1
)
( π (1.7)






= σ
2
min
d
Q
P
e (1.8)








= σ
2
free
free
e
d
Q
N
P (1.9)
Where Nfree is the average number of sequences at dfree. In TCM the Euclidean distance dfree between
signal sequences is increased to get a lower error rate. The Euclidean distance between two
points p and q in N dimensions i=1…N as

=

=
N
i
i
q
p
d
1
2
1 )
( (1.10)
Formulae (1.11)-(1.12) for FSK and DPSK are proper references for other modems developed
later, reference [Car86].
2
2
1 γ

= e
P
b (1.11)
For FSK, envelope detection, and modulation speed 1
/ =
T
b B
r .
γ

= e
P
b 2
1 , (1.12)
For DPSK, phase-comparison detection and modulation speed 1
/ =
T
b B
r .
A comparison of modulation methods is presented in reference [Car86] pp. 553-554. The selection
of a modulation method is made at a common standard for comparison purposes
4
10
=
b
P .
For example, M-ary DPSK is a reference for modulation methods, formula (1.13). The performance
of 2-PSK…32-PSK is at
4
10
=
b
P about 5
...
1
/ =
T
b B
r bps/Hz and 21
...
8
=
γ dB.








= M
K
Q
K
P
b 2
sin
4
1 2 π
γ (1.13)

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Where bit error rate is Pb and χ is energy to signal ratio, data conversion factor is
K = log2 M K
and number of symbols in a M-ary system, for example M = 2 .

In this thesis FSK and DPSK are used as references in performance analysis.

Waveforms

The basic waveform is a simple sinusoidal signal as presented in formula (1.14)

s(t) = Asin(2π
mft + P) (1.14)

It has four information carrying parameters in it (A, f, t and P). These parameters are used in
data modulation methods. The multi-carrier or multi-channel signals are described Waveforms
as a Fourier presentation in formula (1.15)

∞ ∞

1
S(t) = c + an sin(2πnft) + bn cos(2πnft) (1.15)
2

n=1 n=1

Any signal can be presented as a Fourier series [Mar62]. An algorithm for the machine calculation
of complex Fourier series was first presented in 1965 [Coo65].

Digital Generation of Waveforms - A symbol-based approach

In present digital networks data transmission is virtually transmitted in digital form. The nature
itself is analog and also analog are the waveforms of Internet access circuits and radio waves
(presently called air interface, former name was ether). Thus the need for analog waveforms
and modeling methods still exists. However, the waveforms themselves can be made with digital
modulation methods. The present studies of waveforms are focused on wideband applications
(B-ISDN, UMTS, WNW etc) both in fixed wired and moving wireless systems. Several
applications are based on the OFDM waveform (Orthogonal Frequency Division Multiplexing)
scheme. The basic idea of multi-carrier modulation was introduced and patented in the mid 60s
by R.W.Chang [Cha66, Wei71]. The sampled waveform may be presented as x(t) in [Guo02]
formula (1.17). The analog signal at DAC output after quadrature modulation in a software radio
type modulator is

~ ))

j(ω
Ct+φ
(t
s (t) = R{x(t)e } (1.16)

With amplitude of the input signal to the RF transmitter

+∞ NS 1
2 2 TS
x(t) ∑ ∑ {[sI

(k) + sQ (k)]p(t k iTS )} (1.17)
N
=

i=0

k=0

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and the phase

~s (t)
1 Q
φ
(t) = tan ( ~ ) (1.18)
s (t)

I

where TS is the period of one time-domain OFDM symbol, NS is the number of samples in one
symbol after CP and p(t) is the pulse function of the symbols. The high peak-to-average-power
ratio (PAPR) of OFDM systems introduces non-linear distortion in the transmitter and causes
both in-band and out-of-band spectrum re-growth. Undesired effects are [Guo02]:
- Nonlinearities.
- Intermodulation among subcarriers.
- Undesired out-of-band radiation.
In general, the complexity of the equalizer grows with higher symbol rates because as the transmission
rate increases (symbol periods become shorter), the effects of ISI degradation are higher.
In the case of both DMT and OFDM, the channel is divided into many sub-channels situated in
different frequency bands, with each sub-channel utilizing a carrier with Quadrature Amplitude
Modulation (QAM). This allows a bit stream with a very high transmission rate to be sub-divided
into many bit streams with lower transmission rates, reducing the relative effect of ISI in each
symbol period (which is now longer) and allowing simplification of the equalizer. Therefore, both
OFDM and DMT systems can implement equalization in a simple fashion, due to their slower
symbol rates. The OFDM waveform is resistive against multi-path errors.

In this thesis band-limited multi-carrier waveforms are the main subject.

Channel Modeling

References of channel modeling [Sha48, Rum86, Agu03] and recommendations [Eur86, Itu88]
give a classification of channels:
AWGN used for theoretical modeling and reference in evaluations of modulation methods.
Granular noise channel is generated in the digitization process of analog signals.
Multi-path channel is a wireless (mobile cellular, radio broadcast) channel.
This classification is used in this thesis.

1.3.2. Evolution to Adaptive Communications

Adaptation is known as an adjustment by which a species improves its condition in relation to its
environment. Culture is the human adaptive system.

Idea of Multi-Carrier Modulation

The concept of Multi-Carrier Modulation (MCM) or Discrete Multi-Tone (DMT) has been known
for many decades. In the 1960s, a multi-carrier modulation technique known as Orthogonal Frequency
Division Multiplexing (OFDM) was invented, which utilized multiple sub-channels in the
frequency domain [Cha66, Wei71]. The basic idea of multi-carrier modulation was introduced
and patented in the mid 60’s by R.W.Chang. The channel is sliced up into narrow little bands and
multi-carrier modulation is used with individual modulation in each of the bands [Gal68, Gal01].
MCM techniques (OFDM and DMT) have evolved and have been adopted in various standard
bodies such as IEEE 802, American National Standards Institute (ANSI), European Telecommunications
Standards Institute (ETSI), and International Telecommunications Union (ITU). Multi-
Carrier Modulation (MCM) [Sta99], divides the data into a number of low rate channels that are
stacked in frequency and separated by 1/symbol rate. MCM, also called OFDM, is being proposed
for numerous systems including audio broadcasting (DAB), video broadcasting (DVB),
mobile wireless access (WLAN) and digital subscriber link systems (xDSL).

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Definition of OFDM

The recent OFDM method (sometimes called multi-carrier or discrete multi-tone modulation) is
the basis of several standardized systems for data networks and cellular radio communications. A
definition of OFDM systems [Eng03] describes it as: The available bandwidth W is divided into a
number Nc of subbands (subcarriers or subchannels) each of width f=W/Nc. Data symbols are
transmitted in parallel by modulating the Nc carriers. To assure a high spectral efficiency, the
subchannel waveforms must have overlapping transmit spectra. They need to be orthogonal for
enabling simple separation of these overlapping subchannels at the receiver. Multi-carrier modulations
that fulfill these conditions are called Orthogonal Frequency Division Multiplex (OFDM)
system.

OFDM System Model

A high-level block diagram [Ram02] is shown in Appendix 2. The system model of an OFDM
transmitter with RF is presented in reference [Guo02]. The information bits

[b1 b2 b3 … bM] (1.19)

are mapped into the I/Q channel baseband symbols using a modulation scheme such as phaseshift-keying
(PSK) or quadrature-amplitude-modulation (QAM). Then each group of N symbols
are packed into a parallel block

[ ]T
S S S ⋅⋅⋅ S

1 2 3N

(1.20)

at the input to the IFFT.

OFDM symbols in the time domain over time interval

[0 T ]

t , (1.21)

S

are generated by the IFFT operation as,

s(k) = 1

N

N


n=1

S

j knN
ne 2π( 1)( 1) /

(1.22)

for k=[1,2,…,N]

Then in Cyclic Prefix (CP) insertion, the first G coefficients are repeated after the original N coefficients
and made serial for quadrature modulation. The analog signal at DAC output after
quadrature modulation in a software radio type modulator is,

~ ))

j(ω
Ct+φ
(t
s (t) = R{x(t)e } (1.16)

with amplitude of the input signal to the RF transmitter

N 1
+∞ −

x(t) = ∑∑

i=0 k=0

{[s

2
I

(k) + s

2
Q

TS
(k)]p(t k N

iT

S

)} (1.17)

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and the phase
~s (t)
1 Q
φ
(t) = tan ( ~ ) (1.18)
s (t)

I

Where TS is the period of one time-domain OFDM symbol, N is the number of samples in one
symbol after CP and p(t) is the pulse function of the symbols.

1.3.3. Discussion of Broadband Evolution

The evolution to adaptive communications is due to many different factors including the development
of MCM in the 1960s. Advances in the design of new communication systems are
based, later in the 1970s, on the microprocessor, software memory, digital signal processing and
chip manufacturing technology. Methods for doing coding, waveform shaping and equalization
are still a developing area in communications. The terms “multilevel QAM digital radio sy s-
tem” or “variable rate QAM” or “symbol rate controlled modulation” were used i n the late
1980s. Self-adjusting adaptive systems and OFDM (Orthogonal Frequency Division Multiplex)
systems have been designed and used for many civil applications in the 1990s. The recent ubiquitous
OFDM method is the basis of several standardized systems for data networks and cellular
radio communications. In the 1990s also a new concept “adaptive modulation” is used.

Modeling and simulations have been used for telecommunication network planning since the
development of simulation programming and the first simulators in 1964. Simulations are important
in the evaluation and design of network structure, communication routes with traffic
calculations, link budgets, radio wave propagation and circuit level analysis. At about the same
time an algorithm for the machine calculation of complex Fourier series was presented in 1965.
In the 1970s Discrete Fourier Transform (DFT) was studied. Soft generation and detection of
waveforms with IFFT and FFT, Object-Oriented Analysis (OOA) were used in the 1990s.

Military applications will use new downloadable waveforms (a software algorithm) with Software
Defined Radios (SDR). WNW (Wideband Networking Waveform) waveforms will be
designed for military mobility and network access purposes according to some military development
plans during 2004-2007.

1.3.4. Discussion of Some Communication Problems

Biomedical Data Transmission Problems on Physical Level

Biomedical data transmission problems on the physical level of the OSI model are presented
according to reference [Var03]:
1. For the purposes of various databases and information systems off-the-shelf solutions are

available. There are already many standards for platform independent representation and interchange
of static or quasi-static medical records (patient data, insurance data, medical images
etc.). These communication standards are based on the upper layers of the OSI model,
and the lower layers, like the physical transmission, the media access and the routing methods
are not defined.
2. As it can be established, to fulfill all of these requirements we must define the lower layers

of the OSI model. Although many vendors are offering their monitoring systems, they lack
an open communication technology and so lack the ability of interchangeability between
devices of various vendors.

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