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between telemedicine from wireless network for a general pur- pose. Besides that, we also need to ensure that the wireless net-
work is able to perform well under consistent heavy rain. Extra link margin is estimated mainly based on the transmitter design
and the site environment. In addition, if we maximize the link margin, it will ensure the system reliability to be maintained at
the optimum level.
5.1.5 Antenna Placement
It is tiresome to decide the location to place an antenna. Some- times a location offers the best performance is not feasible to be
used. Impedance matching is also one of the major elements to be considered to effectively transmit signals between antennas,
radios and cables. Also, cable connected between antennas and radios must be the same to prevent losses caused by mismatch.
As many antennas are not identical with cables connected, im- pedance matching circuitry is crucial to transform the antenna
impedance to the cable. To measure the impedance match, Voltage Standing Wave Ratio VSWR is applied. The optimal
value must be below the ratio of 2:1 so that more energy can be sent with minimum reflection. O the other hand, a VSWR with
high ratio shows that the power is either lost or retransmitted and the percentage of bandwidth relates to carrier frequency
ࢌ
ࢉ
:
ࢃ ൌ
ࢌ
ࡴ
ିࢌ
ࡸ
ࢌ
ࢉ
࢞Ψ
ࢌ
ࢉ
ൌ
ࢌ
ࡴ
ାࢌ
ࡸ
ࢌ
ࡴ
And ࢌ
ࡸ
represent the maximum and minimum band fre- quencies. Since most of the antenna does not support 360 de-
gree omni-directional coverage, the angle of coverage needs to
5.4
5.6
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be considered to place an antenna. Omni-directional coverage can be applied horizontally. The directivity of antenna is mainly
referred to the power focused when sending or acquiring signal from other antennas. Even though most of the wireless router
that we use at home provides cylindrical monopole antenna which can beam for 360°, many antennas are designed for only
high-focus beam in a few degrees. This is known as beam width. Antenna with narrow beam width is for longer coverage
to direct the energy. The concept is the same with the radiation from regular bulbs and spotlights with identical energy capacity.
Spotlights concentrate its lights in a more specific region with more intensity than bulbs. This difference shows the relative
strength of the radiated field in various directions from the an- tenna in the coverage area close to the antenna apart from that
of the pattern over long distance. The phenomena introduce the term near and far fields. A near-field refers to the induction
field and far-field refers to the radiation field. Far-field measures the radiated energy of an antenna. The measurement
use to determine this is:
ࢊ ൌ
Ǥ
ڊ
d represents the minimum distance and l represents the longest dimension while represents the wave length of the carrier fre-
quency. For antenna placement, near-field is not as significant as it only reduces the minimum safe distance which is normally
related to health issue.
5.2 Network Scalability for Network Development
The degree of the channel which can be expanded for a larger capacity, better performance and larger coverage area is termed
network scalability. In short, the degree of future expand is im- portant for any communication network. Network expansion
5.7
166
often involves setting up new hardware to the existing network and extending coverage area. During the expansion, the network
should not be interrupted as the availability of network is very important especially if that network supports life saving opera-
tions. In the case of telemedicine, availability is far more im- portant compared to the other purpose as accidents could be
happen and it will not wait until the network service resume. Therefore, a network should not be shut down temporarily. In
terms of wired network, expansion usually involves adding of new cables. On the other hand, in terms of wireless network, it
requires some adjustment of the infrastructure. Therefore, modi- fications are more feasible for wireless compared to wired net-
work. According to Fong 2004, the transmission path is hard to be altered. However, the transmitter can be enhanced to en-
sure receivers to process the incoming stream of data if there is an increase in data input. The main aim will be to maximise the
use of available resources in the system and minimize errors so that it is not necessary for re transmission.
5.2.1 Modulation
The conversion of digital signal to analog signal is termed mod- ulation. For example, a modem has the capability to transmit
computer digital signal into analog signal so that the signal could be transferred through the traditional phone line.
