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To implement an AP it is either controller-based solution or without. When it is without a controller, the AP is configured separately, but with a controller-based architecture, the controller will automatically configure each access point based on global settings by logging in to the management console on the wireless controller (Geier, 2010). Based on this design as shown in Figure 6.15 and “H” of the block diagram, it is a controller based architecture. Therefore, all the configuration and management is achieved with the wireless controller (WC). The following are the configuration details:

6.6.1 Enabling the 802.11n mode:

This will enable IEEE 802.11n standard of WLAN

6.6.2 Selecting Frequency band:

The Cisco Aironet 1552E AP is equipped with both 2.4-GHz and 5-GHz radios, either can be selected or both. In most cases, it is advantageous to operate using both bands.

6.6.3 Defining the SSID:

The SSID (Service Set Identification) is the name given to the WLAN that the client radios must have to associate with the network. It is generally best to use a common SSID for all APs to improve roaming for client devices.

6.6.4 Setting of Beacon:

Beacon contains all the information about the network. Beacon frames are transmitted periodically to announce the presence of a wireless LAN. The default interval is 100 milliseconds, but it may be beneficial to increase the beacon interval to allow power-save modes to operate in a manner that is more effective at conserving battery power.

6.6.5 Transmit Power:

The transmit power setting has significant impact on the range and performance of the WLAN. It may be beneficial, however, to operate AP at relatively low transmit power to facilitate a microcell wireless architecture, which can dramatically improve the capacity of the WLAN. Similarly, instead of operating at fixed power levels, automatic assignment method can be selected and the controller automatically adjusts the transmit power levels of the APs as environmental conditions change.

6.6.6 Transmission Channel:

Transmission channels should be set to specific non overlapping channels to avoid inter- AP interference and avoid other interference sources, such as microwave ovens and neighbouring WLAN. Apart from fixed RF channel assignment for each AP, Cisco also implements dynamic channel assignment configuration that automatically sets the RF channels of the 2.4 - GHz access points associated with the controller to channels 1, 6, or 11 as environmental conditions change.

6.6.7 Data Rate:

By default, all data rates generally apply. Data rate settings can impact the range of a WLAN.

6.6.8 Antenna Diversity:

Most APs have diversity antennas, but it is necessary to ensure that the diversity setting in the AP is configured correctly so that diversity is actually implemented. It is not set by default in all cases, so it is best to check and enable diversity to maximize range and performance.

6.6.9 Channel Width:

The 802.11n allows configuration of 20-MHz or 40-MHz channels. 40-MHz channels offer the greatest performance, but it is wise to only use 40-MHz channels in the 5-GHz band. Most APs do not allow configuration of 40-MHz channels in the 2.4-GHz band

6.6.10 Fragmentation Threshold:

It may be beneficial to set the fragmentation threshold to a lower value if RF interference is present. However, lower fragmentation thresholds generate greater overhead. Therefore, setting a lower threshold may reduce overall throughput instead of make it better.

6.6.11 RTS/CTS Threshold:

Request-to-send / clear-to-send (RTS/CTS) can improve throughout when hidden nodes are present. RTS/CTS can be activated for different frame sizes by setting the threshold to a value lower than the default setting.

6.7 Conclusion

We designed the environmental radiation monitoring system of a nuclear facility which is an important component of nuclear accident emergency system. This chapter proposed radiation monitoring system based on IEEE 802.11n wireless mesh network solution which includes nuclear radiation dose collection terminal, wireless transmission system solutions and data processing centre. However, in the nuclear industry, even though, the controlled release of radionuclide’s to the atmospheric and aquatic environment is a legitimate waste management practice, its uncontrolled releases may occur as a result of nuclear or radiological accidents. Therefore, an important and essential element in the control of the

discharges is regular monitoring at the source of the discharge as well as the receiving environment thereby ensuring the protection of the public and the environment against the harmful effect of ionizing radiation.

CHAPTER SEVEN

MODELLING AND SIMULATION

Following the design of radiation monitoring system in the previous, this chapter focuses on the modelling and simulation of the radiation monitoring system models (Appendices A, B, C and D). Based on this, we established the minimum radiation level for these models by using the average background radiation level as shown in Table 6.6. However, in a nuclear environment, the radiation level will be a bit higher than the background radiation level due to the presence of nuclear activities. But according to Hall (2012), the design target for maximum radiation at the perimeter fence of a nuclear electricity generating station is 0.05 mSv/yr.

Thus, from Table 6.6, the maximum radiation reading per hour was 0.145µSv/hr

Converting it to per year = 0.145 x (Hours x Days x Months) (7.1)

= 0.145 x = (24x30x12) = 0.145 x 8640

= 1252.8µSv/hr

Converting to mSv =

= 1.25mSv/year

With the reading of 1.25mSv/year (0.145µSv/hr) indicated that the background radiation reading is higher than the recommended limit for the public by ICRP. Therefore, in proposing any limit for the design, it must not exceed the recommended dose limit by ICRP of 1mSv for public in mSv/year.

But with an average reading of 0.063µSv/hr as in Table 6.6, the converted value of 0.54mSv/year as shown below is hereby recommended as it is below ICRP dose limit.

Converting it to per year = 0.063 x 8640 (7.2)

= 544.32µSv/hr = 0.54mSv/year

Therefore, the minimum radiation level of 0.05 mSv/yr and maximum radiation level of 0.87mSv/year is hereby proposed for this system, with consideration to ALARA concept and ICRP recommendation of 1mSv/year allowable radiation exposure to the public.

Accordingly, based on the above factor and the significance of the research, it is necessary to investigate first the precautionary measures against external radiation sources which are time, distance and shielding that formed part of the design concepts and how they relate with the radiation monitoring system. Therefore, the following radiation intensities of 0.05 mSv, 2.5 mSv, 20 mSv, 250 mSv, 1000 mSv and 10000 mSv were subjected to various scenarios as shown below: