Usability and Engineering Aspects of Competing RF Technologies for

Communication with Commercial Sports Sensors in Ubiquitous

Applications

Experimental Comparison of Power Consumption and Use Cases for ANT+

and Bluetooth Low Energy Sensor Devices

Hans Weghorn

Baden-Wuerttemberg Cooperative State University, Kronenstrasse 53A, 70174 Stuttgart, Germany

Keywords: Sports sensors, Ubiquitous Sports Tools, Body Sensor Networks, ANT+, Bluetooth Low Energy.

Abstract: the commercial market offers quite some time already personal electronic sports tools for control and

monitoring of physical workouts. With these units, body measures like movement speed, tread rates, and

heart rate are detected by tiny autonomous sensor units and their recordings are transmitted via RF for

further processing to a central handheld device. Since a while, also smartphone apps can be used as control

instance, if their ubiquitous host device supports one of the particular RF standards for coupling them to the

sports sensors. During the last decade, two competing wireless standards have evolved for this sensor air

link, which are called ANT+ and Bluetooth Low Energy. The key features of this remote communication

technology determine the usability within the various scenarios in personal sports, for instance the question

how many sensor devices can be operated closely to each other without interference. In this paper, the

specified and advertised properties are analysed on base of the definition of these RF standards, and they are

furthermore practically verified with experiments. In particular, measurements of power consumption are

shown for the two different RF systems, since life time of sensor battery has relevant impact on convenience

of daily use. Furthermore, practical observations of various spurious effects when using the two RF

standards are reported here, which seriously bring the reliability and accuracy of such commercial devices

into question.

1 INTRODUCTION

Aging societies and also overweight, which can be

nowadays observed often already for young

children, induce continuously increasing costs in

public healthcare. This kind of evolvement

especially applies to the developed countries

(Colagiuri et al., 2010). Accordingly, efforts are

gradually intensified for encouraging broader parts

of the citizenship to regularly perform more physical

activity (Valentín and Howard, 2013), because its

positive effect is known and verified already from

decades of scientific research (Wannamethee and

Shaper, 1992).

Addressing the application field of sports and

fitness tools, over a period of time a broader market

has evolved that supplies appropriate computerized

tools for this purpose. In particular, monitoring and

control of physical workouts can be performed on

base of sensing the activity situation and condition

of the human body, such as measuring heart rate,

body temperature, acceleration forces and movement

speed. Blood glucose level or blood pressure would

also be measurable by such commercialized devices,

but these are applied less commonly. In addition,

various sensors can be attached to sports machines

like cycloergometers for complementing the trace of

physical activity of sports people.

Such tools are also of interest for semi- and full-

professional sports, since the relation between the

easily measurable parameter of the heart rate and the

physical effort level has been verified already long

time ago in medicine (Hoppeler et al., 1985), and

later also in sports research (Arts and Kuipers,

1994). Certainly, heart rate monitors are the

overwhelmingly advertised commercial tool for

personal sports and fitness activities, but many

athletes complement this type of body sensor with

sensors for tread or stride rate and style for reaching

best sports performance.

Weghorn, H..

Usability and Engineering Aspects of Competing RF Technologies for Communication with Commercial Sports Sensors in Ubiquitous Applications - Experimental Comparison of Power

Consumption and Use Cases for ANT+ and Bluetooth Low Energy Sensor Devices.

In Proceedings of the 3rd International Congress on Sport Sciences Research and Technology Support (icSPORTS 2015), pages 263-270

ISBN: 978-989-758-159-5

263

Figure 1: Body sensors for tracing sports and fitness

activities. Upper left shows the circuit board of a footpod,

while the other three devices are heart rate sensors. A

works with the RF standard ANT+, while B and B+ are

using Bluetooth as printed on their plastics case.

The general construction concept of such

electronic toolsets for personal sports monitoring is,

that data is collected by autonomous body sensors

(Fig. 1), which transmit their measures to a central

control unit via any kind of near field RF link. As

typical control device a watch like computer is used

(Fig. 2), or other tiny constructions that can be either

worn easily by a sports person, or which can be

mounted on a sports apparatus like a bike or similar.

A blocking aspect is, that such control units work

with closed software systems, which can not be

easily modified or even replaced with any other

customized implementation. The situation is quite

similar to the first generations of mobile phones,

which also contained fixed operational software

systems.

Figure 2: Two commercial sports units and one Android

smart phone receiving the identical ANT+ signal from a

heart rate chest strap. The left most device is for bicycling,

the middle one is a Triathlon watch, and the smart phone

app was developed in a usability study on sports utilities.

Fortunately, some of the important vendors for

electronic sports devices agreed roughly a decade

ago with the so-called ANT+ system on a common

communication standard that shall provide seamless

interoperation (Dynastream Inc., 2011). Later, the

Bluetooth consortium also expanded its own

definitions towards the so-called Bluetooth Smart

standard (Bluetooth SIG, 2015), which stands for a

very low power consumption in the communicating

devices, and which makes it also feasible for the

battery cell operated sports sensors.

In former research, this opportunity was used to

investigate, how the user handling of the control

handheld can be made more convenient, in particular

for applications in semi-professional endurance

training (Weghorn, 2015.1). In the beginning of this

project, ANT+ had to be used for coupling the

sensors to the control software, which was realized

on Android smartphones (visible in Fig. 2).

Half a decade later Bluetooth LE experienced its

broad market introduction within the smart phone

segment. For a technological evaluation on software

engineering efforts for the two alternative systems

(Weghorn, 2015.2), a simplified heart rate monitor

for an Android smartphone was developed (Fig. 3).

Figure 3: Simplistic Bluetooth LE heart rate monitor

running on an Android smart phone. This was developed

earlier for exploring the software engineering process and

it was used in the experiments described here.

From this experience in developing heart rate

monitors and the observation with the sensor

systems using the two competing RF communication

standards, additional, new research questions arose,

because both RF consortia can be understood as

offering the "better" standard. One field of interest

are the possible use scenarios, where these sports

tools can be efficiently employed for best benefit of

workouts. This addresses personal use with one

single or with several sensors, as also the use within

a group of sports people. In this paper, these aspects

are discussed and the findings are complemented

with a helpful base of practical experiments. In

particular, during the many hours of experiments on

power consumption different spurious and critical

effects in the sensor operation have been detected. In

the end, this paper can report about features and

usability of commercial sports tool sets with special

scope on the two competing wireless standards for

sports sensors.

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2 ANALYSIS OF THE RF

SPECIFICATIONS

In a pre-investigation, the properties and features of

the two communication standards have been

analyzed already (Weghorn, 2015.2). According to

these, ANT+ works with a straight forward 32 bit

addressing concept for its nodes. Considering the

most typical sensor of a heart rate detector, this

device class broadcasts its measures automatically

after detecting source signal (what happens, when it

is attached properly to a human body via a chest

strap). Broadcast of sensor measures implies that the

information can be consumed by many devices in

parallel without mutual disturbance (Fig. 3).

This seamlessly maps to training cases like a

sports person using a sports apparatus, which is

connected to the personal heart rate sensors and at

the same time a recording to the personal device,

e.g. a smartphone, is running. Or even more, a coach

could easily surveil the activity of this sports person

remotely from another, additional control monitor.

In contradiction to that, Bluetooth LE follows in

its communication a master-slave principle. This

consequences, that the working of the sensor and the

RF link has to be initiated in a point-to-point

scheme, and the transferred information cannot be

consumed directly in parallel by other devices. A

parallel use of sensor information is not totally

excluded, but it would require that the control

device, which is talking to the sensor as master,

would have to register itself as a sensor slave for

other Bluetooth masters. In this sense, it needs to

work as repeater of the information to other so-

called micro network cells, which indeed can coexist

in Bluetooth. Of course, this will complicate the

programming design of the control device software

considerably, and the handling would be moreover

rather inconvenient, because a manual pairing

between two communication partners is mandatory

at least once for the operation of each of the parallel

Bluetooth link.

Another exercise scenario is monitoring a group

of people during, e.g., indoor cycling. With ANT+,

it would be possible to supervise the activities from

a central device that is handled by a coach, while

Bluetooth limits the number of nodes within a micro

cell to 8, so the central device could only trace 7

people in parallel, and also only if each sports

person is using just one single sensor (e.g. for wheel

turning speed, or effort level). Again software

constructions of setting up parallel micro cells could

solve the problem, but it will also increase the

construction efforts for the central unit.

Doubtlessly, the most common use in sports will

be a 1:1 scenario, where a sports person is using the

personal body sensors together with one control unit,

e.g. a smartphone, in a rather private environment.

Both RF standards, ANT+ same as Bluetooth LE,

are clearly capable of serving such a scenario, while

the elaborated use cases are only reasonably

functioning with ANT+.

Discussing further the specifications shows that

ANT+ and Bluetooth LE are both transmitting their

information via radio in the royalty-free ISM band.

Both cocnepts are aiming towards very low power

consumption, which is primarily reflected by a low

sending level of 1mW. That the sending strength is

identical for both standards can be seen from the

measured signal strength in experiments with the

two standards (Fig. 4 and Fig. 5).

Figure 4: RF measurement of the ANT+ transmission

frame of a heart rate sensor. The oscilloscope was set into

accumulating mode for this measurement, the time scale is

50μs per display square unit.

The bits are modulated with a the GFSK scheme

(Gaussian frequency shift keying) in both RF

systems. According to the protocol for addressing

and node identification in ANT+, the minimum

frame size is here 175μs, which was verified by a RF

measurement of the sending signal (Fig. 4). Since

the used heart rate sensors add extra information (in

particular one extra byte for battery voltage) on top

of the minimum sensor frame definition, the

observed frame length is here 190μs.

Surprisingly, the frame length of the Bluetooth

LE measurement didn't map directly to the specified

frame size of 650μs (Fig. 5). Analysis of the

measurement yielded that the sensor device

transmits two sub-frames for each of its measures,

which sum up to a total air time of only 350μs. This

Bluetooth LE behavior was recorded for an

established and working life connection between the

heart rate sensor and the control unit, while it was

Usability and Engineering Aspects of Competing RF Technologies for Communication with Commercial Sports Sensors in Ubiquitous

Applications - Experimental Comparison of Power Consumption and Use Cases for ANT+ and Bluetooth Low Energy Sensor Devices

265

observed that after loss of this connection the sensor

indeed used the nominal RF transmission frame

length of around 650μs.

Another effect will increase Bluetooth

consumption on air further: in case of channel

collisions, re-transmission is invoked in Bluetooth,

while ANT+ ignores any channel collisions. ANT+

uses one single carrier frequency out of a set for one

particular sensor and tries to avoid collisions by a

gradual shifting of the sending time frame. Since 2

nodes can co-exist in the available band locally, the

likelihood of true collisions is rather low, which is

unlike for Bluetooth. It can be expected that in an

environment, where many sports user and by that

many active Bluetooth micro cells co-exist in the

same RF visibility range, there arises an increase in

power-consumption and sometimes an irresolvable

interference due to the much lower count of possible

independent air links.

What can be concluded here already from the

standards is that ANT+ consumes approximately

half of the energy than Bluetooth LE within the plain

air transmission.

Figure 5: RF measurement for Bluetooth LE.

3 EXPERIMENTS ON TOTAL

POWER CONSUMPTION

In practice, measuring the lifetime of a tiny battery

cell faces different difficulties, especially for pulsed

devices with very low average consumption. A

direct measurement of supply current during use of

the sensors is impossible, because the measuring

equipment can not be worn during sports (even a

miniaturized, remote controlled ampere meter

wouldn't be feasible because of the restriction to

local use). Therefore, an indirect measurement cycle

was selected:

1. Measure the battery voltage

2. Use the sensor device actively for a defined

period of time

3. Measure battery voltage again and detect by that

the discharging amount

According to the experience on battery lifetime

from sports exercises that was collected over many

years with ANT+ sensors, a usage time of 1 hour

was estimated to produce on the one hand side a

measurable effect, while remaining on the other side

in almost linear region of the discharge curve (Varta

Microbattery Inc, 2015).

Specific experimental configuration and results

For this first experimental set, one ANT+ heart

rate sensor and one Bluetooth LE heart rate sensor

were used, which were both operated from a lithium

cell of the identical standard type CR2032. For this

experimental series, two fresh cells were manually

selected out of a bigger lot from the same quality

vendor for providing an identical free starting

voltage (3.243 Volts for both). The two cells are

named here and in the following sections X and Y.

For such lithium battery cells many data sheets

exist, which display their capacity in dependence of

various parameters like, e.g., discharge current and

temperature. Unfortunately, no information is

available about the capacity tolerance. Since the

cells produce their electrical supply by a chemical

reaction process, which is similar to the one in other

electronic parts like electrolyte capacitors, it can be

expected that also such battery cells do suffer from

similar considerable variations in the order of at

least several percent. The starting voltage, of course,

doesn't state anything about the precise capacity, and

the following concept was worked out for

compensate this error factor during the comparison

of the sensor consumptions: For the two sensors

from Fig. 1 called here A (ANT+ sensor) and B

(Bluetooth LE sensor), the batteries were used in

alternation according to a balancing time slot

scheme (Tab. 1).

Table 1: Swapping plan for battery cells X and Y while

measuring after each hour (= time slot) of use their

discharge voltage caused by the sensors A and B.

slot 1 2 3 4 5 6 7 8 9 10

X A B B A A B B A A B

Y B A A B B A A B B A

According to the battery data sheet it is supposed

to keep in this plan all discharge voltage differences

at linear scale. While performing light physical

exercises during the hours of sensor use, the

discharge voltages were determined for four cycles

only (Tab. 2). The sensors were attached during the

time slots to the same person, so that there was no

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possibility for systematic error influence by different

sensor loads. The reason for completing the

experiments with less cycles than in Tab. 1 was, that

there was already a conclusive difference visible

between sensors A and B with fewer runs.

Additionally, it has to be regarded that the

Bluetooth sensor B was sending measures at varying

and at lower frequency of at maximum 1.8

seconds/samples, while the ANT+ sensor A was

broadcasting its measures at a fixed rate of 0.5

seconds/sample.

Table 2: Trace of the voltages while gradually discharging

and swapping batteries between sensors. Obviously, one

sensor is unloading the batteries considerably faster than

the other.

battery X battery Y

Vx dVx/dt Vy dVy/dt

t = 0h 3.243V 3.243V

t = 1h 3.206V -37μV/h 3.158V -85μV/h

t = 2h 3.129V -77μV/h 3.148V -10μV/h

t = 3h 3.051V -78μV/h 3.122V -26μV/h

t = 4h 3.022V -29μV/h 3.065V -57μV/h

From the record of the discharging voltages in

Tab. 2, the total load for the two sensors can be

resolved by the battery cell use as listed in Tab. 1.

The total discharge load within the four hours of use

for the ANT+ sensor is calculated to:

-Δ V

Atot

= 37μV + 10μV + 26μV + 29μV = 102μV

And the calculation for the Bluetooth LE sensor

yields as total sum:

-Δ V

Btot

= 85μV + 77μV + 78μV + 57μV = 297μV

Intermediate synopsis of discharge experiments

From this collection of experiments various

intermediate results can be derived: First, the time

slots of 1 hour appear long enough for detecting the

discharging effects. Second, the two battery cells

behave differently, hence the assumption that the

batteries are varying in capacity is also validated.

Third, the discharging steps show, that the

measurements do have bold error bars, so the

precision of the measurements appears limited.

Despite the the experimental restriction, it is

systematically visible, that the ANT+ sensor

consumes less energy than the Bluetooth LE one.

Despite that the ANT+ sensor is working more than

three times faster, it requires approximately three

times less electrical energy in average.

The measurements have also shown that it is

rather difficult to obtain systematic and reproducible

results with these electro-chemical power sources.

When not in use and removed from the sensors, the

cells use to recover within hours and days, so stable

voltages and differences in the order of μVolts

couldn't be validated in longer terms. Therefore, two

more experiments were conducted, in which the

ANT+ sensor was used for several hours and

without removing the battery and giving a chance

for self-recovery of this battery. Accounting for all

three experimental runs, the average discharge rate

of the ANT+ sensor at a sample rate of two heart

rate measures per second was found being

/dt = 18,83 μV/h ± 5,8μV/h

Estimation of total sensor battery lifetime

Under the assumption of a usable battery voltage

range from 3.3 Volts (fresh cell) down to 2.0 Volts

(cutoff limit for empty cell), a battery lifetime of

roughly full three days for the ANT+ sensor can be

estimated. The Bluetooth LE sensor will work only

for one single full day. All this is much behind the

advertisements of the consortia for these RF

standards, who advertise continuous work of sensors

for even several years with one single fresh battery.

It has to be stated that the Bluetooth LE

technology experienced its market introduction half

a decade latter than ANT+. The used Bluetooth LE

sensor B (Fig. 1) is one of the first generation that

was feasibly working with smartphones again of a

first device generation, which supported the

Bluetooth LE standard. On the other hand, the

description on the boxing wants to make suggest that

this is technology provides a long lifetime of sensor

battery, which is obviously misguiding.

Comparison of different product generations

At the end of the experiments, another Bluetooth

LE sensor was purchased (B+ in Fig. 1), which

stands for a recent product generation of a quality

vendor for electronic sports equipment. This sensor,

which shall be called B+ here, has got another type

of supply battery, therefore the discharging

experiments can not be applied in the same way like

described here, since a swap of batteries between the

sensors is impossible.

First investigations have shown that the

discharge rate ranges with approximately 28μV/h in

the similar order like the ANT+ sensor, so it is

considerably less than the Bluetooth LE sensor of

the first generation. Also the energy saving scheme

by automatic deactivation works reasonable for B+,

because it shuts the RF transmission down, when the

input signal is lost for more than 20 seconds. On the

other hand, it also comes also up with increased RF

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Applications - Experimental Comparison of Power Consumption and Use Cases for ANT+ and Bluetooth Low Energy Sensor Devices

267

activity, if no host Bluetooth connection is enabled,

or if such an air link is suddenly terminated despite

it was established and working before. The

construction of B+ suffers from a more bulky case

(20% thicker), 50% more mass, and this all despite a

smaller battery.

Summarizing the experimental findings here, it

can be stated that ANT+ appears as efficient as or

even better than Bluetooth LE, when targeting a

longer lifetime of sensor battery.

4 OBSERVATION OF SPURIOUS

SENSOR EFFECTS

Naturally, any body sensor for human activity has to

be operated under appropriate conditions before

reliable measurements can be expected. One base

requirement, of course, is sufficient power supply,

which implies for the sports sensors a battery that is

still sufficiently loaded and provides more than a

minimum, well defined supply voltage. For

acceleration sensors, the proper mounting, e.g. at a

running shoe, has to be ensured, for sensors

determining heart rate good and appropriately placed

electrical contacts to the human body are mandatory.

Observation of unpredictable distorted measures

During several years of practical use, various

problems have been observed many times, despite

such sensors were thoroughly attached and used.

Those disturbances couldn't be investigated, since

they arose unpredictably and intermediately only.

Suggestions for the reason may indeed be problems

with electrical contact quality, but also RF

interference from unknown other sources come into

question. With several, different ANT+ sensor

devices, spurious heart rate measures have been

recorded occasionally. Sometimes the disturbances

appeared only for a short period, sometimes some

kind of pattern could be interpreted into the data

(Weghorn, 2015.2).

The ANT+ sensors also produce wrong, much

too high measures, if battery life time is reaching its

end. Unfortunately, the sports computers do not

appropriately evaluate the battery information from

the ANT+ transmission package - an important

parameter that is a defined by standard - but the data

is processed further without any notification, also

disregarding that sometimes measurement values

appear even in a non-physiological range. Both

effects could be easily handled by adequate software

controls and algorithms; hence, the lack of such

mechanisms can be considered as serious deficiency,

which labels the commercial sports devices as not

elaborated to the state of technology and unreliable.

In Bluetooth there is not even a clear definition

for mandatory information about power supply

voltage of the sensor, and consequently such safety

checks are not necessarily available at all. This

represents also a clear defect in design of the

standard. Taking oscillograms of the RF packets

unveiled even further worse sensor effects.

Nonsensical replication of sensor data samples

First of all, from the users point of view, it can

be observed that sensors keep on repeating the last

measures, in situations were the sensors is have lost

their input signal. For instance in Bluetooth LE, a

heart rate sample is passed to the control software

through the communication instances, despite there

is no input signal any more for a very longer while.

The continuation of replicated values applies for

Bluetooth sensors as also for ANT+ sensors at least

for a shorter while - the minimum time for detecting

signals loss was in the experiments 20 seconds -

while an older Bluetooth LW sensor kept on sending

information packets for three hours and further on

(Weghorn, 2015.2).

In a side experiment on the behaviour of the

Bluetooth communication it turned out, that spurious

measures were further replicated even within the

control unit, despite the fact that the air link was out

of range. A simultaneous observation of the sensor

behaviour with the oscilloscope showed in this

experiment, that the sensor well was capable of

detecting the loss of connection, but the

communication protocol stack on the handheld

control unit kept on producing spurious values.

A further effect was found as another side

observation during the comparative evaluation of the

power consumption. The Bluetooth LE device

followed the ANT+ measurements by a short delay,

sometimes this delay increased to a several seconds.

In heart rate monitoring this kind of behaviour may

not be too critical, because variations of heart rate

are physiological in the order of seconds. If the same

effect occurs with sensors for wheel turning or stride

rate and style in running, swimming or other

activities, it wouldn't be acceptable, because it

distorts any possible analysis. Additionally, the

impression was that the two heart rate measurements

taken simultaneously from the identical person by

both RF systems often didn't match exactly, even

when there was no variation in activity. This

suggests another conclusion, namely that the

measures are imprecise in general. From the

experiments so far it can not be decided, which

sensor system has which error strength, this would

be a research point for further detail investigations.

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In summary, these observations lead to the

impression that the technology is not handling

sensor problems reasonably, it even more arises the

suspicion that the sensor concept intentionally hides

recording as also communication problems.

Summarizing quality assessment of sensor data

This all guides in sum to the judge that

information from sports sensors is delivered

unreliable and that the measures can be disturbed

unpredictably at any time. Even worse appears the

fact, that intelligent processing itself often can not

recognize faulty situations, and therefore it is not

possible to develop appropriate software intelligence

that is able to inform the sports user accordingly.

Such system behaviour may in the end also easily

lead to misinterpretation of workouts.

5 CRITICAL REFLECTION ON

ENGINEERING

The tool sample of heart rate monitoring, which was

used in the experiments here solely, represents just

one particular application in sports, but it can be

considered of being representative as a common and

typical one for the investigated low energy RF

communication standards. The reason is that heart

rate monitoring is based exactly on the same scheme

like for other common sensors like foot pods, pedal

tread rate sensors and speedometers for bicycles.

In this sense, its operational scenario reflects the

use of just one autonomously operating sensor,

which is broadcasting its measures along the time

axis. Advertisements in the low price class market

for electronic sports tools show that heart rate

monitoring is exactly what is offered mostly in an

extremely broad price range for the end products,

and it is also a feature for any more elaborated sports

watch or computer. Evidently, bringing this

functionality to all-world devices like smartphones

will support even more customers to use it.

Use cases and limitations in sports scenarios

Very typical is also the role for the heart rate

sensor as network node: either it serves as source in

a point-to-point link – one sensor and one sports

computer – or as point-to-multipoint – one sensor

broadcasting at the same time its information to

many consumer devices, e. g. simultaneously to a

personal smartphone, a sports machine and the

surveillance monitor of a coach. Both modes should

work automatically, even more a seamless transition

between these modes can be expected according to

the current state of technology.

This investigation clearly shows the limits of the

Bluetooth LE system in comparison to the ANT+

concept. In particular the power consumption

measurement also shows the better performance of

ANT+, but it has to be stated here, that this can be

also effect of an old device generation as the first

experiments with the newer sensor indicate.

In total, the discharge experiments may be too

critical, because the recovery behaviour of the

lithium battery cells was not studied and by that

regarded in very detail. Three days lifetime for a

new battery in an ANT+ sensor appears really low

and doesn't map many days and weeks of personal

use of such sensors in sports, which was not

scientifically investigated. At least, the findings can

be considered as reliable infimum for the battery

durability.

Overcoming the need for sensor batteries

Looking at modern and future development in

tiny electronics, the research question about battery

lifetime has to be challenged anyway. It is not

appropriate any more to use batteries at all in the

very low power sensors, instead super capacitors

should be the first choice as energy source in such

devices. From the consumption measurements it can

be derived that a capacity of 3mF per operational

hour would be required. The capacity of low voltage

gold capacitors range in the order of 100 times this

value at a lower price than for lithium battery cell,

but at a similar size. The super capacitor can be

loaded contactlessly through a magnetic field. Or in

case of the heart rate sensors even the body contacts

can be used for DC injection during charging. This

would make the use of the sensors more comfortable

also in mechanical sense, since the exchange of the

tiny batteries with even more tiny screws is often not

easily possible without special mechanical tools.

6 CONCLUSIONS

Two different RF standards are nowadays available

and commercialized for wirelessly binding body and

activity sensors in sports applications to handheld

control units. Especially the use of smart phones for

the latter purpose may make sports exercises to a

regular part of the weekly life cycle also for average

people. Doubtlessly, if such workouts are monitored

and controlled properly - that is, what could render

possible because of the broad availability of the

before described devices - there can arise positive

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Applications - Experimental Comparison of Power Consumption and Use Cases for ANT+ and Bluetooth Low Energy Sensor Devices

269

effects on the average health and fitness level for

broader parts of the citizenships.

In this study, the usability and reliability of

sensors working with the two competing RF linking

standards ANT+ and Bluetooth have been

investigated. The results are not strictly positive;

instead there arise many problems in daily operation.

First of all, the battery life time is much lower than

what is promised by the promoting consortia of the

two RF standards. An early hardware

implementation of a Bluetooth LE sensor appears

much worse than ANT+, while newer Bluetooth

sensors may reach similar operational times.

ANT+ is the standard of the two that is basically

parameterized for lower energy requirements on the

air link, but the consumption measurements have

shown that the leverage of the sensor electronics is

much higher than just the contribution for the RF

transmission. Even more energy is wasted, if the

sensor sleep mode is not controlled properly by its

own firmware. In particular, the older Bluetooth LE

sensor kept on being active for hours despite control

link and body contact were lost. As RF

measurements show, Bluetooth produces an

increased air activity - and by that a much increased

energy expenditure - when the host control

connection is lost or shut down.

Directly notable by the sports user appears the

network node design in both standards. While ANT+

allows a lot of nodes being operated close to each

other, and while it furthermore enables a seamless

interoperation of one sensor with many parallel

consuming devices, these features are not available

with Bluetooth LE. Hence, it can be expected that

there are many interferences, when Bluetooth LE

sensors are operated in gym studios or in bigger

sports events like, e.g., city runs. Even worse

appears the fact, that the sensors and display units

hide communication problems by simply replicating

the last valid sensor measure. This effect may occur

even for several hours despite the sensors are

detached from the body.

Also other spurious measures have been

observed from time to time in various use situations.

In addition, it was found that measures from

Bluetooth LE sensors were displayed considerably

delayed compared to ANT+ sensors. Accordingly

further research is planed in this context here, where

professional instruments - e.g. a wired medical ECG

recorder - will be used to evaluate the precision and

time-axes accuracy of the commercial body sensors

feasible for RF linking to smart phones.

Summarizing the current situation of an average

sports user, who is not a technical expert and who

wants to apply the available commercial tools for the

best control and benefit of physical workouts, it has

to be stated that no clear recommendation for one

particular system can be given. ANT+ seems to be

the technology that is better appropriate for versatile

and professional sports applications, while Bluetooth

LE experiences a much broader support due to the

compatibility to almost any new smart phone.

Further research on the sensor data will unveil,

whether the Bluetooth LE combination can be

considered as a professional sports tool or just as a

nice-to-have rough measuring indicator that gives

some inspiration for sports activity.

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