Michal Lepiarz asked:


WLAN (Wireless Local Area Network) means technology which allows to build wireless data networks with satisfactory parameters and quite large ranges of operation at a comparatively low cost. Additional advantage of this technology is short time needed for its implementation.

Potentiality of WLANs

* wireless access to local network in home, office, business etc.

* wireless access to the Net in public space, e.g. in airports, stations, cafes etc. (hot-spot)

* wireless point-to-point links (connecting LAN networks, telemetry, remote control, remote monitoring)

* wireless access to the Internet (both in cities and in the country)

* emergency communications link (duplication of wired network)

WLAN standards

I will describe some solutions compliant to the next three standards:

* 802.11a – in 5 GHz band: 5.150 – 5.350 GHz and 5.470 – 5.725 GHz, transfer rate up to 54 Mbps;

* 802.11b – in 2.4 GHz band: 2.4 – 2.483 GHz, transfer rate up to 11 Mbps;

* 802.11g – in 2.4 GHz band: 2.4 – 2.483 GHz, transfer rate up to 54 Mbps;

However, there are also used other standards:

* 802.11f – IAPP – Inter Access Point Protocol – for cooperation between access points;

* 802.11i – standard defining new security methods in wireless networks;

* 802.11n – standard for transmitting multimedia in homes using MIMO technology, up to 300 Mbps;

* 802.11e – standard defining QoS – support for high quality of services;

* 802.16 – WiMax standard for backbone networks of high capacity

Wireless network range

It should be realized that the range of a wireless network depends on many factors; we can have an influence on some of them and the rest is unknown. The range of wireless network depends on:

1. Factors related to used devices:

* output power (it has been decided by the manufacturer),

* cable attenuation (depends on the cable and its length),

* gain of antennas (given by the manufacturer),

* sensitivity of devices (given by the manufacturer).

2. External factors:

* attenuation between antennas (can be estimated basing on FSL model);

* interferences from other devices (can’t be predicted – some additional margin of safety needs to be provided to compensate these interferences),

* influence of physical barriers (walls, floors, trees etc.)

So, if we want to know what would be the effective range of our network we have to gather the information mentioned above and carry out simple calculations showed in the further part of this self-help book.

Propagation of radio waves

Fresnel zone

Fresnel zone is one of the most important conceptions connected with propagation of electromagnetic waves, which is indispensable to assess parameters of wireless link. It is the area actively participating in transmission of radio signal energy. Shape of this area is an ellipse in longitudinal section, and circle in cross-section. Radius of this circle is a function of the ratio of distances between antennas – it has the maximum value in the middle of the link. The importance of first Fresnel zone comes from the fact that almost all energy of the signal is conveyed via this space.



The shape of Fresnel zone. R1 is the radius of the I zone.

[m]; where:

* dkm = d1km+d2km, is the distance between masts in km

* d1km – distance from the first antenna in km

* d2km – distance from the second antenna in km



Wrongly made installation. The installer didn’t secure mutual visibility of antennas. The radio link does not work.



Another example of wrongly made installation. Presence of barriers in the first Fresnel zone causes that radio link still doesn’t work properly.

… it is only the begining… full version of this text you can find on DIPOL library web site (free of charge, no login needed).

Hamid hameed asked:


This is a Wi-Fi age. Those who need can find Wi-Fi hotspots everywhere; in home, hotels, airport lounges and in the airplanes. Next thing on the offer is Wi-Fi in the cars.

Microsoft’s is going to offer Wi-Fi technology in the vehicle. They call it Vi-Fi – vehicle Wi-Fi and it is a Wi-Fi connection in vehicles. With the partnership of the University of Washington and the University of Massachusetts, Microsoft is working on a reliable and steady connection in the vehicles. This new system will allow multiple Wi-Fi signals to come in and out at any given time in order for the signal to remain strong and steer clear of “hand-offs”, which are known to fumble and lead to spotty service.

Who needs to surf behind the wheel? Well, Wi-Fi- would be a good addition to technology in cars because it would replace satellite subscription services that are expensive, and it would allow users to have an unlimited amount of applications. With Wi-Fi in cars, the weather and movie times could be displayed, as well as Internet radio, live stock quotes, instant messaging, and pretty much anything else you could access on a laptop.

For this to be an option for the everyday driver, there will need to be a larger infrastructure for Wi-Fi, but Microsoft has proven they can produce terrific technology in cars with the Sync system. Just beware, with a road full of drivers surfing the Internet, you might need to be careful.

Kamlesh Patel asked:


s use encrypted technology that enables secure voice and data transfer during calls. GSM technology uses an algorithm to ensure the authenticity of the caller and the integrity of the channel, even when you are roaming in a foreign country.

The most interesting, and potentially contentious area of wireless security is that concerning wireless LANs or Wi-Fi networks, these are fast becoming the connection method of choice. Wireless signals do not recognize corporate or geographical boundaries and are only limited by the propagation configuration of the network. Even in an office environment you will find small areas or “blind spots” where the coverage is very weak or non-existent. So, it is possible for the random surfer to “happen upon” on someone else’s network. How can one protect against this happening?

Wireless local area networks use spread-spectrum technology – a technique that makes the radio signals difficult to intercept. Most Wi-Fi systems also include a form of user logon and password protection. Of course, the spread spectrum signals can be intercepted with a relatively simple wireless card and many networks do not properly set up the password feature and will allow ready access to anyone. The fact that “employees” have to go through some form of physical security before they can access the network only adds to the notion that wireless networks may not be as secure as equipment manufacturers would have us believe.

The problem with wireless security is essentially a technical issue with the way the signals are encrypted. The original wireless LANs (WLANs) used the Wireless Encryption Protocol (WEP). This was then replaced in late 2002 with the Wi-Fi Protected Access (WPA). Essentially, WPA offered improved data encryption through the use of temporal key integrity protocol (TKIP). The TKIP feature scrambles the keys using a hashing algorithm and ensures that the keys have not been tampered with. WEP only uses a static key that is seldom changed by users. This cryptographic weakness caused many of the security breaches in WLANs because intruders could, with relative ease, generate an encryption key and access a wireless network.

While WPA offers enhanced security features over WEP, not all industry observers are completely satisfied. A recent problem was highlighted with WPA concerning the use of poorly chosen passwords for a network. Criminals intent on compromising a WLAN can use simple dictionary software to overcome the system password. In fairness, this weakness only manifests itself when short, text-based keys are used and does not signify a fault in the WPA protocol. WLAN manufacturers can circumvent this problem by incorporating the ability to generate random keys across the network and putting in place user requirements concerning the length and style of passwords.

Microsoft responded to this potential threat by providing a Windows XP download that alters the way the operating systems communicates with the Wi-Fi network – using separately generated keys for each system user rather than one, albeit encrypted, key for the network connection

Alain Attias asked:


Bluetooth can be defined as a wireless form of communication that enables devices to send and receive communication. It is a global initiative set up by manufacturers such as IBM, Intel, Ericsson, Toshiba and Nokia to create a standard for linking up devices such as mobile phones, mobile PCs, handheld computers and other peripherals. Bluetooth relies on short-range radio technology to allow the wireless connectivity. The key features of Bluetooth are robustness, low power and low cost. Both data and voice transmissions can be handled simultaneously. Examples of innovative solutions which users can perform include printing or faxing capabilities, synchronising PDA, laptop or computer and making or receiving calls from a mobile phone, with many more applications available.

Wifi is short for ‘wireless fidelity’ and is a limited-range wireless networking code which is used in many airports, hotels or other services, who offer public access to Wifi networks, to allow people to log on to the Internet and receive emails whilst on the move. As Wifi is a reasonably fast method of transmitting information in wave form, it is often used in computers and also notebooks. In future, it will become possible to access the Internet from just about anywhere, without the use of any wires. The advantages of using Wifi are that the networks are fairly cheap and straight-forward to set up. Wifi is also quite inconspicuous and can hardly be noticed unless it is being looked for specifically, whilst in a Wifi ‘hotspot.’ For a wireless network to be created, communication is transferred like a two way radio, using radio waves.

Both Bluetooth and Wifi have both been in the news more especially in recent years. Both technologies are relatively new on the market and, with time, a trend may be seen favouring one or the other. As more and more Bluetooth devices become available, most people will own devices for Bluetooth and Wifi. There are several advantages for opting for Bluetooth networking over Wifi and vice-versa. WiFi and Bluetooth are actually very different technologies with very different reasons to exist. The question should not be Bluetooth versus Wifi but more how Bluetooth can work with Wifi.

Advantages of Bluetooth

Bluetooth can connect devices from point-to-point and probably better on security than Wifi, as it can cover shorter distances. In addition, Bluetooth offers an optional two levels of password protection. Up to seven devices can be connected at any one time which makes it easier to find and connect the device being searched for, as Bluetooth highlights itself to the other devices. Bluetooth technology is also more ideal for consumer electronics devices as it has a smaller power requirement. Microsoft have also recently announced that Bluetooth support will be built into a future version of windows XP. Another advantage is concerning voice communication. For an office or home environment, Bluetooth can be used in a cordless phone within a 10m range, without the need to be passed around. It is not likely that Wifi technologies will have a required voice-over-IP to support voice communication, within the near future. Bluetooth was also introduced much earlier in the market and is installed in much more user devices and products, in comparison to Wifi products.

Advantages of Wifi

The most prominent advantage which Wifi has over Bluetooth is that Wifi operates at a much faster rate – of about 11mbps, whereas Bluetooth only operates at a much slower rate of around 720kbps. This makes Bluetooth too slow for video transfers or for moving large amounts of large photo images from a digital camera. Wifi is also designed to link up entire networks, rather than computer to computer. Wifi can achieve this too but it is not its real purpose. Originally intended to be used for mobile computing devices, such as laptops, it is now often being used for increasingly more applications, such as Internet access, gaming and basic connectivity for home electronic appliances such as televisions or DVD players. Wi-Fi may be used by cars in highways, as standards rise in development, in support of an Intelligent Transportation System to increase safety, gather statistics, and enable mobile commerce.

Having taking in the advantages of both forms of communication, it can not be said that one is better than the other. The two wireless protocols can be used to perform separate things and it is not essential to opt for one, rather than the other. Bluetooth should be the first choice for when connecting single devices, only when speed is not an issue. It has a short range of approximately 30 to 60 feet and common applications can include sharing printers, syncing PDAs or using a mobile phone as a modem. As time goes by it will be very interesting to see how both Bluetooth and Wifi develop and what new uses they will have and for what devices.

Sophie Milch asked:


Uninterrupted power supply coupled with strong signals is the sole aim of any superior quality antennas. To help boost the strength of the antenna, antenna cables are used. Almost every other day a new product is initiated in the market which leaves behind the old redundant technology. This also holds true for antenna cables. The mere name of antenna cables conjures up an image of a giant steel grill attached to a black and white tube TV. But in a broad sense antenna cables are used in a wide array of antennas viz., tv antennas, rod based antennas, indoor and outdoor antennas, mobile phone and car antennas.

One of the foremost purposes of any antenna cable is to deliver a good international quality level output. As far as television signals are concerned these are distributed by way of coaxial or fibre-optic cables with antenna cables playing a vital role in transmitting the signals.

History behind Antenna Cables.



The history of pioneering antenna cables goes back to cable-TV systems which were introduced in the United States roughly in the 1940’s. The exclusive plan of introducing such a system was to enhance the reception of commercial and military networks, broadcasting systems in remote and hilly areas; through the application of antenna cables. With the passage of time during 1960s cable television systems was usurped in large metropolitan areas in an effort to improve the reception quality which was hindered by tall buildings.

Types of Antenna Cables.



Normally there are two types of major antennas which are utilized for cellular radio transmissions viz., Omni-directional and directional. Omni-directional antennas broadcast radio waves of identical strength in all directions and receive signals from all directions as well through the use of antenna cables, whereas directional antennas broadcast and receive signal strength only in one direction. These cables come in various shapes and sizes. For example, low-loss antenna cables recommend low loss at 2.4 GHz and come with reverse SMA connectors and a proffer standard connection which is being used in WLAN antennas.

RF or “F” type connectors which are attached to the coaxial cable are usually the oldest means of television signal transmissions.  It is through RF cables that both audio and video signals are combined into a single wire pair.  Unfortunately RF cables suffer heavy quality loss across great distances.

Then there are composite cables which are a triple wire pair of micro coaxial cables they contain RCA type connectors on each end.  They are usually color coded and come in yellow, red and white to provide a standard color code of understanding within audio and video enhancements.

Use of Antenna Cables today.

Now-a-days Digital Video Interface (DVI) and High Definition Multimedia Interface (HDMI) cables are being used by HD televisions which contain the highest quality cables. Both cables have indistinguishable video superiority, HDMI signals have been known to transmit superior quality audio levels comparatively.

Antenna Cables buying tips:

Ensure antenna cables are hand crafted and are waterproof. They bear the exclusive guarantee Make sure the cables come with a type N-Male connector. Choose the cable length aptly, did you know when you coil cables you get signal loss. Choose gold plated connectors for best quality signal strength.

Sophie Milch asked:


Uninterrupted power supply coupled with strong signals is the sole aim of any superior quality antennas. To help boost the strength of the antenna, antenna cables are used. Almost every other day a new product is initiated in the market which leaves behind the old redundant technology. This also holds true for antenna cables. The mere name of antenna cables conjures up an image of a giant steel grill attached to a black and white tube TV. But in a broad sense antenna cables are used in a wide array of antennas viz., tv antennas, rod based antennas, indoor and outdoor antennas, mobile phone and car antennas.

One of the foremost purposes of any antenna cable is to deliver a good international quality level output. As far as television signals are concerned these are distributed by way of coaxial or fibre-optic cables with antenna cables playing a vital role in transmitting the signals.

History behind Antenna Cables.



The history of pioneering antenna cables goes back to cable-TV systems which were introduced in the United States roughly in the 1940’s. The exclusive plan of introducing such a system was to enhance the reception of commercial and military networks, broadcasting systems in remote and hilly areas; through the application of antenna cables. With the passage of time during 1960s cable television systems was usurped in large metropolitan areas in an effort to improve the reception quality which was hindered by tall buildings.

Types of Antenna Cables.



Normally there are two types of major antennas which are utilized for cellular radio transmissions viz., Omni-directional and directional. Omni-directional antennas broadcast radio waves of identical strength in all directions and receive signals from all directions as well through the use of antenna cables, whereas directional antennas broadcast and receive signal strength only in one direction. These cables come in various shapes and sizes. For example, low-loss antenna cables recommend low loss at 2.4 GHz and come with reverse SMA connectors and a proffer standard connection which is being used in WLAN antennas.

RF or “F” type connectors which are attached to the coaxial cable are usually the oldest means of television signal transmissions.  It is through RF cables that both audio and video signals are combined into a single wire pair.  Unfortunately RF cables suffer heavy quality loss across great distances.

Then there are composite cables which are a triple wire pair of micro coaxial cables they contain RCA type connectors on each end.  They are usually color coded and come in yellow, red and white to provide a standard color code of understanding within audio and video enhancements.

Use of Antenna Cables today.

Now-a-days Digital Video Interface (DVI) and High Definition Multimedia Interface (HDMI) cables are being used by HD televisions which contain the highest quality cables. Both cables have indistinguishable video superiority, HDMI signals have been known to transmit superior quality audio levels comparatively.

Antenna Cables buying tips:

Ensure antenna cables are hand crafted and are waterproof. They bear the exclusive guarantee Make sure the cables come with a type N-Male connector. Choose the cable length aptly, did you know when you coil cables you get signal loss. Choose gold plated connectors for best quality signal strength.