analysis of state-of-the-art approaches for “marking” during multi … · 2012-09-07 · pieps...

Analysis of State-of-the-Art approaches for “Marking” during multi-burial beacon search versus the aspects of fully maintaining the

EN300718 standard

Schober, Michael1 ; Eck, Markus

2; Rust, Michael

3

1Electronic Communications Engineer, PIEPS GmbH, Parkring 4 Lebring, Austria

2UIAGM Mountain Guide, PIEPS GmbH, Parkring 4 Lebring, Austria

3UIAGM Mountain Guide, Instructor of Austrian Mountain Guide Education, Krieglach, Austria

ABSTRACT Over the recent years most of the state-of-the-art beacons now support the search for multi-ple burials using signal analysis strategies. Due to this, new tests results have been published. Some of these tests have the focus on range and bandwidth (i.e. the support of the international beacon standard EN300718) while other tests are focused on solving multiple burial scenarios. From the technical point of view, there are several different strategies how to face these technical challenges. With this study, the authors analyse the different technical solutions and point out the advantages and disadvantages of each technical solution based on standardized, reliable and reproducible search scenarios in respect of cover-ing the allowed variability from the standard EN300718. Finally the strengths and weaknesses of each strategy and its impact on real burial scenarios are scope of this research.

1 INTRODUCTION

In the recent years the public knowledge of beacon technologies has been increased significantly. Everybody nowadays is aware of the impact of a third searching antenna to avoid misleading signal maximums (i.e. distance minimums) during fine search. Also, all the discussions about search strip with, range and receiving characteristics of several beacon technologies have one thing in common - simply said: RANGE MATTERS MOST - in the search of a first signal. Unfortunately the global technology discussion got a little off the subject in the recent past and is focused too much to the is-sue about multiple burial support. Accompanied by the questions about the feasibility of several multi-ple burials scenarios - which either can be seen as pretty high or likely not relevant - depending on the diversity of a decided weight of the distance be-tween the single victims. Fact is that there are several technical solutions to deal with these sce-narios. It’s the intentions of the authors to take a close view to the different approaches and to point out the interaction between the basic performance facts, range issues and receiving bandwidth in re-spect to the given EN300718 standard.

2 BACKGROUND

The European standard EN300718 – more or less threaded as the common international standard – defines the characteristics of a transmitted signal of any avalanche beacon. A range of given toler-ances is also defined within this standard.

Concerning the emitted signal, the allowed band-width, timing limitations and signal strengths are well determined. Also the fact that only A1A modu-lation is allowed, is regulated in this standard. Every manufacturer of avalanche transceivers has to maintain this standard – to ensure a maximum compatibility between all different devices to the end users benefit.

Fig. 1: Signal conform to EN300718, A1A-modulation, car-rier frequency 457.000 Hz +/- 80 Hz

*Corresponding author address: Michael Rust, UIAGM Mountain Guide Krieglach, Austria

Mail: [email protected]

Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska

314

In the real world, there is a certain level of variation transmitting characteristics out in the market - roughly 1 million beacons are in use. Several stud-ies and field tests from user groups (like alpine associations) do confirm this picture.

Following Schweizer/Genswein, ISSW2008, only 50% of the beacons are within 30Hz deviation from 457kHz. The other 50% (except the low number of defect beacons which are outside the +/-80Hz lim-it) are still correct transmitting beacons following the standard but have a 31Hz-80Hz deviation from 457kHz.

3 STUDY AND METHODOLOGY

At the first step, the authors did estimate the basic performance values of the tested beacons using a standardized range test. This test estimates both, the receiving characteristics of the different anten-nas and the bandwidth for a single victim. With this performance values (i.e. ranges for the first victim) a marking test for a second victim has been done. 3.1 INCLUDED TRANSCEIVERS Transceiver model Firmware Serial number

PIEPS DSP 8.2 11388825630371

PIEPS DSP Tour 8.2 11368835810873

PIEPS VECTOR 1.0.11 8855930387

MAMMUT Barryvox PULSE 3.2 N11394

MAMMUT Barryvox ELEMENT 1.0 1127803209

ORTOVOX S1 1.2.3488 B205261A

ORTOVOX 3+ 1.1 2161945920

ARVA LINK 3.10 L00996-1115

ARVA AXIS 3.00 AY00065-0916

BCA TRACKER II 03 11C08284

BCA TRACKER DTS ? 65508

3.2 RANGE TEST SETUP The basic range test was performed using a PIEPS 3-antenna-transmitter-box with adjustable settings for period, pulse, frequency. For this test the transmitter was setup with a pulse time of 100ms and a period time of 1080ms. This has been maintained during the complete test. Determined Ranges: 1. Range of receiving X-antenna RX to a coaxial

transmitting antenna TX (Fig. 3a) 2. Range of receiving Y-antenna RY to a coaxial

transmitting antenna TX (Fig. 3b) 3. Range of “weak” antenna (as a result of 1 and

2) to a vertical transmitting antenna TZ (Fig. 3c) All configurations have been measured with differ-ent transmitting frequencies: 457kHzM..+/-0 Hz, +40Hz, -40Hz, +80Hz, -80Hz This has been done using the following test stand-ard: • The entire place was ensured to have no inter-

ference. • For distance measurement a measuring tape

made of plastic was used. • The start took place from a point without receiv-

ing any signal. • All beacons were tested in the same way: same

pace and same height at approach. • The resulting range was the point of at least

one receiving signal per 3 seconds, which is a quite stable signal.

• Three runs with each beacon led to an average range shown in table 1.

Fig. 3a – Range test, X-aligned

Fig. 3b – Range test, Y-aligned

Fig. 3c – Range test, vertical transmitter

Fig. 2: Transmit frequency deviation of beacons Schweizer/Genswein ISSW 2008


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3.3 MARK TEST SETUP After estimating the basic range performance characteristic the authors now developed a stand-ardized test setup for MARKING a first victim fol-lowed by estimating the range to a second victim. Whereby the answers to the following questions was most of interest:

• Is there any problem in general that occurs in a multiple burial situation?

• Do different coupling positions cause an ef-fect?

• Do different distances between the transmit-ters cause an effect?

• Does frequency deviation cause an effect?

The same beacons where tested for their marking performance except the BCA beacons (no marking function).

Two transmitters were placed along a measuring tape. The searcher started in a 10 meter distance to the first transmitter (TX1), followed the display indication to TX1, used MARK function to flag TX1, followed display indication to the second transmit-ter (TX2) and used MARK function to flag TX2. Tested coupling positions: RB = Receiving Bea-con, TX = Transmitters

Fig. 4a – Mark test, X-X

Fig. 4a – Mark test, X-Y

Fig. 4a – Mark test, Y-X

Again in this test PIEPS 3-antenna-transmitter-boxes with adjustable settings for period, pulse and frequency have been used as transmitters.

Parameter for TX1: pulse time = 100ms, period time = 850ms Parameter for TX2: pulse time = 100ms, period time = 1150ms Distance, coupling position and frequencies have been changed after each series. Distance between TX1 and Tx2 was changed after one distance series (e.g. 40m) was finished with all beacons. Frequency was changed after all distance series (40m, 30m, 20m, 10m, 5m) were finished – then the run started again with another frequency at 40m distance between TX1 and TX2. Standard and definitions used: Negative Results • No second transmitter (TX2) indicated on Dis-

play 10 seconds after MARK the first transmit-ter (TX1).

• No way to get to one of the transmitters by help of display indication.

Standard • The entire place was ensured to have no inter-

ference. • Frequency of transmitter was proved before

each test series. • Point of start: 10 meters in front of first transmit-

ter (TX1). • Any beacon was in send mode before it was

switched into search mode. • 10 seconds of waiting at the start point, before

starting the approach. • Searcher was following the display indication. • All beacons were tested in the same way: same

pace and same height at approach. • 3 seconds holding the receiver still before using

the MARK function. • 10 seconds waiting after MARK TX1 to wait for

TX2 appearing on display. • 10 seconds waiting after MARK TX2 to see if

something happens (e.g. loosing TX2). • 2nd or 3rd run was made if first run lead to un-

certain result.


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4 RESULTS

4.1 RANGE TEST RESULTS

Tab. 1: Range test results

4.2 MARK TEST RESULTS 4.2.1 LEGEND FOR RESULT TABLES y/n � test positiv x test negative - not performed TX2 oD I TX2 indicated within 5 seconds II TX2 indicated within 10 seconds III TX2 indicated on approach to TX1 IV TX2 indicated within 5 sec. after marking TX1 V TX2 indicated within 10 sec. after marking TX1 Notes 1 mark TX1 - more than one try 2 mark TX2 - more than one try 3 back to TX1 on TX2 approach 4 back to TX1 after TX2-mark 5 pendulum but successful TX2 approach 6 5 seconds or more calculation time 7 meandering approach to TX1 8 meandering approach to TX2 9 confusing approach to TX1 10 confusing approach to TX2 11 loss of TX2 12 abort after 5min approach attempt 13 TX1 indicated very late ! extreme effect of above effects


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4.2.2 RESULT DETAILS

Tab. 2a: Mark test result using X-X constellation with no frequency deviation

Tab. 2b: Mark test result using X-X constellation with frequency deviation +10Hz for TX1 and -10Hz for TX2

Tab. 2d: Mark test result using X-X constellation with frequency deviation +80Hz for TX1 and -80Hz for TX2

Tab. 3a: Mark test result using X-Y constellation with no frequency deviation


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Tab. 3b: Mark test result using X-Y constellation with frequency deviation +10Hz for TX1 and -10Hz for TX2

Tab. 3c: Mark test result using X-Y constellation with frequency deviation +80Hz for TX1 and -80Hz for TX2

Tab. 4a: Mark test result using Y-X constellation with no frequency deviation

Tab. 4b: Mark test result using Y-X constellation with frequency deviation +10Hz for TX1 and -10Hz for TX2


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Tab. 4c: Mark test result using Y-X constellation with frequency deviation +80Hz for TX1 and -80Hz for TX2

Tab. 4c: Mark test result using Y-X constellation with frequency deviation +40Hz for TX1 and -40Hz for TX2

Tab. 4c: Mark test result using Y-X constellation with frequency deviation 0Hz for TX1 and +80Hz for TX2

Tab. 4c: Mark test result using Y-X constellation with frequency deviation 0Hz for TX1 and -80Hz for TX2


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4.2.3 RESULT OVERVIEW

Tab. 5: Mark test result overview


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5 INTERPRETATION & OBSERVATIONS

As can be seen from the range test results (table 1) beacons show remarkable performance differ-ences in the way the two main antennas (X and Y) are measured. Beacons have either a good band-width for its analogue input filter or a good working FFT solution to eliminate the influence of frequen-cy deviation. Some beacons still show significant range decreases at the edge of the standard. When estimating the marking capabilities, several issues have significant impact to the result. Signal-overlapping This is a physical limitation – when two signals are overlapped the result quality of a result signal is more or less a pure coincident. For that reason, state-of-the-art beacons are using a small pulse time (about 100ms) and a randomly generated period time to have overlaps occurring more often but short in time. This results either in “WaitM” or “Stop...” readings or MARKING must be tried again. Coupling positions The different coupling positions from TX1 and TX2 have significant worse results with beacons having an elliptical receiving range (i.e. a much worse range on the Y-antenna). But this isn’t a surprise when you take a look at the range test results (see table 1). For most of the beacons not having the same range on X and Y the results are really get-ting worse with the different coupling positions (compare table 2 with table 3 and table 4). Digital filtering In general every beacon has to filter the receiving signal at first to separate the target frequency from all other electromagnetic noise. In the past this has been done with a narrow band analogue filter where a narrower filter characteris-tic did result in better range. Since the standard allows +/-80Hz deviation from the nominal frequency of 457 kHz, beacons meet-ing this standard have to support this bandwidth. This is the point where digital filtering came in to the game. Generally spoken, this means that the received signal is sampled into a logic/calculation unit and the result is calculated using several mathematic

algorithms (furthermore we just talk about this al-gorithms using the synonym ‘FFT’). In a single burial situation most beacons nearly perform according to this standard (see range test results in table 1). But the type of FFT-solution used by the different beacons becomes an important issue in case of mixed signals with frequency deviations. It’s a fact, that the marking quality directly depends on the time accuracy of the measured signal. For that reason you either can take this time infor-mation directly from the signal (which means a significant loss of range and bandwidth) or you can take the time-information from the calculated FFT result – which gives you the full range, the full bandwidth, but the accuracy is less than in the ‘di-rect’ case. This time inaccuracy is based on the fact, that the time context during a certain sample period - which the calculated result is based on – is lost. All com-pact beacon designs need to switch between the antennas (at least between the two main anten-nas) during transmit pulse which can be in worst case only 70ms. VECTOR Sliding FFT A significant improvement to this is done within the PIEPS Vector. With its unique antenna design, for the very first time both signals can be measured simultaneously – no switching is needed.

Due to this, a continuous sliding FFT is calculated, which now gives all information in the desired ac-curacy. Full performance, full range and best time accuracy for marking now is achieved.

6 CONCLUSIONS

When there is a standard, which allows all bea-cons to transmit within +- 80 Hz all manufacturers must meet this requirements also in their search performance. Simplifying algorithms by ignoring widely spread frequency deviations during multiple burials should be avoided. Essential beacon performance starts with the range-, bandwidth- and antenna characteristics.


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And when range is the most important issue for the first victim, why should it be less important for the second one? For the time being it is more or less the decision of a beacon manufacturer where to put the focus on. Either on pure performance (range to first and range to next victims) or on improved marking per-formance (which gives better results on multiple burials in very close proximity). Finally this leads back to statistics about ava-lanche accidents and the question which case may occur more likely?

7 LITERATURE

Genswein, M. and Schweizer, J., 2008. Numerical stimulation of the survival chance optimized search strip width. Genswein, Meilen, Schweiz and WSL Institute for Snow and Avalanche Reserach SLF, Davos, Switzerland.


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analysis of state-of-the-art approaches for “marking” during multi … · 2012-09-07 · pieps...

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