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explain the proper ways to handle the dumbbells so that the us- ers can follow every step closely.
Figure 3.12 Block diagram of a gymnasium network
FONG et al 2011 Different users can be recognized in a lot of ways. The easier
ways are either to install the user’s subscription card with a pas- sive tag or to set a RFID sticker on the shoe with readers on the
mats that are connected to each equipment. It works in a very simple way; a particular identification number will be saved
when a user steps on the mat and all data collected will be marked as belonging to the particular user when the equipment
is used by that user. Besides being used to monitor health, it can also be used for billing purposes if the user is charged based on
usage. When the user completes a session he or she has two choices. The user has a choice to either download the data and
save it in his or her removable storage device or to sent to his or her respective home using the networking system of gymna-
sium. The identification procedure used can make sure the pri- vacy of the data of each user is not compromised and there is
not mix up.
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3.5.3 Swimming pools and beaches
As explained before in section 3.3.1, underwater wireless com- munication always poses a big problem since the transmitter has
to be immersed under water. Despite significant challenges, life can be saved beyond and above the capabilities of health as-
sessment by using wireless communication like in a gym. This is an advantage to lifeguards on the beach who may not able to
keep track of all the swimmers. A tiny waterproof transmitter can be useful to seek for help should an accident occurs. We
also can use waterproof receiver that can accept signals from the shore if any emergency occurs for example the presence of a
shark. However, a system that permits a swimmer to take along tiny transceivers can only function normally at a distance of not
more than a few hundred meters as the radio waves are not to- tally block off by water absorption. An important matter here is
the material to be used in the waterproof cover because it will effect signal absorption. Besides, the wave penetration proper-
ties in salt water and effect of bleach in swimming pool are dif- ferent. Underwater Wireless Acoustic Network UWAN can
also help since the data rate is usually not more than a kilobyte per second. A possible propagation delay that can be a second
each kilometer is a big disadvantage of this kind of network. This major drawback should be considered while in the system
design phase. It can be difficult to install an UWAN since the swimmers will be on the move and the transceiver will not be
stationary. Below is a basic calculation that can explain the ef- fect of changing speed. The total speed of swimming and water
flow v is at an angle relative to the acoustic signal propagation direction
θ, resulting in the effective acoustic propagation speed v’ which is:-
3.1
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Rationally, if the combined speed v is moving towards the same direction as the signal propagation, effective propagation speed
v’ will rise. However, if v moves in the opposite direction of propagation, v’ will decrease. As the result of water flow, a nar-
row acoustic beam will bend slightly in the same direction. Nevertheless, the resulting effect is not significant. The propa-
gation speed will change significantly if going through a differ- ent medium, for example from air into water or vice versa. This
happen because of dielectric constant changes result in refrac- tion just as light bends from air through glass or water. Thus,
the direction of propagating signal will be changed by refrac- tion. On a light note, in optometry the term ‘refraction’ refers to
eye examination in the process of determining whether a pre- scription for spectacle improves a person’s vision. This applica-
tion is known as refractometry. Figure 3.13 shows that reflection also occurs when the signal touches the boundary be-
tween two media, then a part of the signal will be reflected back directly from the surface into water without going through the
air. Reflection from the bottom of shallow water as with most swimming pools and beaches will also cause multipath effect
Figure 3.13 Water surface causes refraction and reflection
FONG et al 2011 In mathematics, the accepted signal rt can be written as:
