Arc of WLAN coverage

With limited power condition (15-20dBm), the range of WLAN equipment is limited. Maximum range that can be achieved is that when the signal reaches the receiver sensitivity limit at the end over there. Actually, its calculation is simple, especially a rather complicated calculation process is the signal attenuation over the air (Free Space Loss) which the average size of about 100dBm depending on distance and frequency of use.

To give some idea, a WLAN connection with 15 dBi antenna and 15 dBm transmit power at both ends it will be able to reach a distance of about seven (7) taking into account the attenuation coax km 3 dBm. Quite normal for 2-11Mbps WLAN connectivity in many cities without having to use the power amplifier illegally.

Emission region is highly dependent on field conditions, location of buildings, location of obstructions, height, and shape antenna used. In the picture I try to show coverage (scope) emitted a WLAN base station in the form of spots.

For the planning / design of a Metropolitan Area Network (MAN) this beam shape we usually make an ideal into a hexagon shape as shown in the picture. This ideal form of coverage we will use later in further explanation below. Knowledge of the antenna will be very important in determining the coverage area that can form in service. In another section I describe the various forms of antenna and radiation pattern.

Example of calculation that is so can be obtained directly from me (onno@indo.net.id) in the form of Excel files for free. In Excel file I've also make some routine conversion from dBm to Watts scale to better show for us who are not familiar with the notation dBm. Alternatively, feel free to get in for free at http://www.bogor.net/idkf/ usually under the directory / physical / wireless.

Calculation of Operating Margin Systems Engineering (SOM)

Before further discussing the design Metropolotan Wireless Area Network (MAN) is good that we dive into how to calculate the power margin for operating the radio. One of the main keys to perform calculations is to understand the concept of magnitude as the magnitude dB power ratio. The formula used to convert dB to Watt or mW, are: dBm = (10 log (Power Watts)) + 30 Watts = 10 ^ ((dBm - 30) / 10) Milliwatts = 10 ^ (dBm/10) To give an idea 15 dBm transmit power is 30 mW, 20 dBm transmit power is 100 mW. A simple way to limit the scope of WLAN applications is to limit the transmit power. Legally signal transmit power in antenna dBmW allowed is 36, meaning that if you use a 24dBi parabolic antenna, you may only use WLAN equipment with a power of 15 dBm (about 30 mW only). Generally, existing WLAN equipment on the market have between 15-20 dBm transmit power (30-100 mW). Radiation emitted in antenna usually be measured with Effective Isotropic Radiated Power (EIRP), which is measured in dBm. In their agreement, IndoWLI colleagues seem inclined to agree allowable EIRP is 36dBm. EIRP which is a power in radiasikan at the end of the antenna, can be calculated from: EIRP (dBm) = TX Power - TX Cable Loss + TX Antenna Gain. With the batasinya EIRP of 36dBm, and the average loss in the coax cable & connectors at 5 dB. So if we use a 21 dBi parabolic antennas, transmit power that can be used only 20 dBm (100 mW). That is, the use of power amplifiers to be very in forbid, you might incur a fine of Rp. 600 million and or imprisonment of 6 years according to article 55 UU36/1999. To determine the System Operating Margin (SOM), we must see Free space loss-FSL, Margin Operating System, Sensitivity receiver (Rx), antenna gain and cable loss. The concept of attempted calculations are shown in the overview above system. Free Space Loss (FSL) is a loss (losses) that occur in communication connections via radio waves can be formulated as follows: FSL = 20 log 10 (Freq, in MHz) + 20 log10 (distance, in miles) + 36.6. From the simple calculation above, then for a distance of 5 km and the frequency of 2400 MHz (2.4 GHz), FSL = 114 dB Furthermore, the need to calculate is the Margin on Operating Systems (System Operating Margin - SOM) for the system to continue to work well. Formula to note is actually very simple which only requires the ability not only added, namely:
SOM = Rx signal level - Rx sensitivity. Rx signal level = Tx Power - Tx Cable Loss + Tx Antenna Gain - FSL + Rx Antenna Gain - Rx cable loss. To be safe from radio interference, such as fading, multipath, etc.. the margin of the operating system should be at least 15dB. IEEE 802.11b radio sensitivity in general have a Rx sensitivity = -77 dBm. If we use a dipole antenna, the Tx / Rx antenna gain is 3 dBi. Some colleagues, especially in WARNET many uses parabolic antennas to increase the Tx / Rx antenna gain to 24 dBi. For built-in antenna, the Tx / Rx cable loss = 0 dB. For installations in WARNET that are outside the building, then the Tx / Rx cable loss can reach 5 dB. From the above calculation, for nano-cell with Tx / Rx antenna cable loss 3dB and 0dB, it will be obtained Tx power 14 dBm or 25 mW. Thus the equipment-based 802.11b access point that there are now suitable / appropriate for the needs of nano cell above because most beroutput 25-50 mW. For the purposes of WARNET if counted correctly, then for a distance of 5-7 km we need a IEEE 802.11b equipment at 2.4 GHz with a power around 20 dBm or 100 mW.

 For those users WaveRider (http://www.waverider.com) calculation process is simplified by the tool facility in the form of excel file. In the tool we can easily calculate System Operating Margin (SOM), as shown in the picture. We just enter the type of antenna, type of equipment that we use Waverider, antenna length, distance etc then it will appear how SOM, Freshnel Clearence Zone (FZC) etc.. What a coincidence that not only provides a tool for SOM & FZC calculation, but also the calculation to determine the direction and elevation antenna of each node. This is very helpful, if we are equipped with Global Positioning System equipment (GPS) which provides location information (altitude, latitude and longitude), then by including information on the location, direction and elevation antenna antenna can be calculated directly. Other information was also brought by the software is the computation of antenna height, which is based on the calculation of FZC.

System Operating Margin (SOM) Calculation

Shown in the Figure is the System Operating Margin (SOM) calculation page. It has many input parameters with three (3) main output, namely,

            RX Signal Level (dBm)

            Free Space Loss (dB)

            Theoretical System Operating Margin (dB)

We need to make sure that we have about 10-15 dB of System Operating Margin (SOM) to give some space for any fading & multipath of the radio signal.

To be able to calculate these three (3) parameters, we need to provide the formula with data on

Frequency (MHz)

Distance (Miles)

TX Power (dBm), WLAN card transmitter power normally about 30-100mW range.

            TX Cable Loss (dB), depending on type of cable & length. It would be better to restrict the length to less then 10 meter.

            TX Antenna Gain (dBi),

            Free Space Loss

            RX Antenna Gain (dBi)

            RX Cable Loss (dB)

            RX Sensitivity

Most of the data needed can be found in the manual or specification of the equipments. Most of WLAN card will likely to have TX Power

Free Space Loss (FSL) Calculation

Shown in the figure is the Free Space Loss (FSL) calculation page provided by YDI.COM. As shown in the Figure, there are two (2) main parameters needed to calculate FSL, namely,

• Operating Frequency (in MHz)
• Distance Between Antennas (in Miles)

The output of the calculation is

• Free Space Loss (in dB)

The formula as shown clearly in the figure is

            Free Space Loss (dB) = 20 Log10 (MHz) + 20 Log10 (Distance in Miles) + 36.6

We will normally see a Free Space Loss in the range of 100 dB for radio signal operating in 2.4GHz frequency traveling in one (1) km distance.

Radio Link Calculation

 

Unlike Indoor usage, ability to calculate radio link budget & distances is very critical if one wants to use Wireless LAN equipments for bypassing Telco’s last mile. Those who has very minimal radio knowledge might having some difficulties in doing it. Fortunately, carries a simple radio link calculation accessible from the Internet. It includes all the formulas and, thus, anyone can always write their own routines in Excel. I would strongly suggest for accessing the site for playing with the radio link calculation.

There are several critical parameter needs to be calculate properly to make sure the system will correctly perform, namely,

• System Operating Margin (SOM), it correlates the transmitter power, type of antenna, length of coaxial cables and distance. We can make sure if our system has a sufficient power margin to reach such distance.
• Free Space Loss (FSL), loss in radio power in reaching certain distance.
• Fresnel Zone Clearance (FZC), to see the required antenna height needed to pass any obstacle.
• Antenna bearing, antenna down tilt, and antenna down tilt coverage radius are needed to know the exact point or area of your radio beaming into.

A power conversion calculation utility is also provided to convert dBm into Watt vice versa. The conversion is fairly simple, i.e.,

dBm                 = 30 + Log 10 (Watts)

Watts               = 10^((dBm - 30)/10)

MilliWatts         = 10^(dBm/10)

The calculations provided in YDI.COM is in miles and feet, and, thus, one need to convert into meter if needed. For your convenient, the following is the needed conversion table

            Meter   = Feet * 0.3048

            Km      = Miles * 1.609344

HOW TO SPEED INTERNET CONNECTION IN THE WINDOW

By default, windows limit bandwidth usage only 20% of the total obtained, to change it we must set parameters in the "Limit Reservable Bandwidth".
The steps are as follows:
1. Click start -> run, type "gpedit.msc", press "Enter ".
2. Select Computer Configuration -> Administrative Templates -> Network ->
    QoS Packet Scheduler.
3. Click 2 times the "Limit Reservable Bandwidth".
4. In the window "Limit Reservable Bandwidth Properties", select "Enabled"
    and set "Bandwidth Limit to " "0 ", click "OK".
5. Reboot

Hotspot Mikrotik Configuration

Setting Hotspot on Mikrotik Router OS is very easy to configure. Hotspot authentication system is usually used when we will provide Internet access in public areas, such as: Hotels, cafes, campus, airports, parks, malls etc.. Internet access technologies typically use wireless or wired network.
Usually provide free internet access using the hotspot or can also use the voucher for SASL authentication. When I open the web page then the router will check whether the user is in the authentication or not. If not perform authentication, the user will be directed to the hotspot login page that require username and password. If the login information entered is correct, then the router will insert the user into a hotspot and client systems can access web pages. Also a popup window will appear containing the status of the ip address, the byte rate and time live. Use of Internet access hotspots can be calculated based on time (time-based) and data in the download / upload (volume-based). Moreover, it can also be done melimit bandwidth based on the data rate, total data upload / download or can be in a long line based on usage.

An easy way of setting mikrotik hotspot is there are 2 (two) choice than to use the text mode we can also use the settings wizard by using Winbox Router OS, Step-Langkat following is the basic configuration mikrotik hotspot as a Gateway Server. First install Mikrotik Router OS on a PC or connect the DOM or if using immediately wrote Rouer Board Login = 'admin' while for your password blank for default.

Go to IP ==> Hotspot ==> Setup
Then specify the local IP hospot that there will be using, for example 192.168.10.1 and IP Set DHCP to clientnya that you will use, in this example is 192.168.10.2-192.168.10.255


For the SMTP server you should be blank, then adjust the DNS server you fill with your provider, in this example is DNS1 = 202.47.78.1 DNS2 = 202.47.78.9


NEXT local DNS hotspot you just then on your user Hotspot fill in the following example admin password admin123


Hotspot Server Profile used for setting up a server that will be frequently used for all users, such as authentication methods and data rate limitation. There are 6 types of authentication Hotspot mikrotik different in profile settings, autentikas types are: HTTP PAP, CHAP HTTP, HTTPS, HTTP cookies, MAC address, Trial




Authentication methods to be used, usually just use the HTTP method CHAP

Data rate limitation is used as the default setting for users that have not been in setting a limit bandwidth usage. Where is the Client upload RX and TX is the client download. For example the default settings in 64k/128k data rate (upload / download)


Hotspot user profile is used to store user data that will be made profilenya rule. Where in it can be set firewall filter chain for traffic entering or exiting, can also be for setting up the data rate limitation and in addition it can also be marking packets for each user who entered into the profile automatically.


Hotspot user ie user names that will be authenticated to the hotspot system. Some things can be done in the configuration of hotspot user: username and password, Restrict users based on time and package data to be used, only certain ip address dhcp ip address offered or simply allow the user to connect to the hotspot from specific MAC Address .


IP Bindings are used to allow certain ip to bypass authentication hotpot, is very useful when we want to run a server service, or IP telephony system under hotspot. For example, a PC or notebook that you can bypass the hotspot system, so you can browse without authentication