2.4 MODES OF WIRELESS TRANSMISSION

Unguided media transports electromagnetic waves without using a physical conductor and is often called wireless communication. Signals are broadcasted through air and received by all who have devices to receive them.

It can be categorized as follows:

1) Radio waves

2) Micro waves

3) Infrared

2.4.1 Radio Waves

Electromagnetic waves ranging in frequencies between 3 kilohertz and 1 gigahertz are Communication Devices normally called radio waves. Radio waves are easy to generate, can travel long distances and can penetrate buildings easily, therefore widely used for communication. They are omnidirectional meaning that they travel in all directions from the source, so the transmitter and receiver do not have to be carefully aligned physically.

Radio signals have been used for a long time to transmit analog information. They are particularly attractive for long distance communication over difficult terrain or across the oceans, where the cost of installing cables can be too prohibitive. A minimum radio system consists of a transmitter and a receiver.

Another increasinglypopular form of radio is cellular radio, which is currently being used by carriers for providing mobile telephone networks. These operate in the VHF (very high frequency) band and subdivide their coverage area into conceptual cells, where each cell represents a limited area which is served by a lowpower transmitter and receiver station. As the mobile user moves from one cell area to another, its communication is handed over from one station to another. Radio waves transmitted by one antenna are susceptible to interference by another antenna due to this Omnidirectional property. Radio waves can be received both inside and outside the building.

Radio waves are very useful in multicasting and hence used in AM and FM radios, cordless phones and paging.

2.4.2 Microwaves

Electromagnetic waves ranging from 1 to 300 gigahertz are called micro waves. Micro waves are unidirectional that is the sending and receiving antennas need to be aligned. 

Microwave is by far the most widely used form of radio transmission. It operates in the GHz range with data rates in order of 100s of mbps per channel. Telecommunication carriers and TV stations are the primary users of microwave transmission. 

An important form of microwave system is a satellite system, which is essentially a microwave system plus a large repeater in the sky as shown in Figure 8. The signals transmitted by earth stations are received, amplified, and retransmitted to other earth stations by the satellite. Like other microwave systems, the bandwidth is subdivided into channels of 10s of MHz each, providing data rates in order of 100s of mbps.

Because of their high bandwidths, satellites are capable of supporting an enormous number and variety of channels, including TV, telephone, and data. The satellite itself, however, represents a major investment and typically has a limited lifetime (at most a few decades).

Unidirectional property of microwave helps in avoiding interference by a pair of aligned antenna to another. High frequency micro waves cannot be received inside the building. Micro waves help in unicasting communication due to their unidirectional property and hence used in cell phones, satellite networks etc.


2.4.3 Infrared

Infrared signals range between 300 gigahertz to 400 terahertz. These can be used for short range communication. High range infrared rays cannot be used for long range communication as it cannot penetrate walls. This also helps in avoiding interference.

Infrared signals are generated and received using optical transceivers. Infrared systems represent a cheap alternative to most other methods, because there is no cabling involved and the necessary equipment is relatively cheap. Data rates similar to those of twisted pairs are easily possible. However, applications are limited because of distance limitations (of about one kilometer). One recent use of infrared has been for interfacing handheld and portable computing devices to LANs as shown in Figure 9.

It cannot be used outside building as rays of sun contain infrared which leads to interference in communication. Infrared having wide band width can be used to transmit digital data with a very high data rate. Infrared signals can be used for communication between keyboards, mouse and printers.




Comments

Post a Comment

Popular posts from this blog

3.8 SECURE NETWORK DEVICES

 In this unit, we have already learnt that the firewall is only one entry point to your network. Modems, if you allow them to answer incoming calls, can provide an easy means for an attacker to sneak around, your front door (or, firewall). Just as castlesweren't built with moats only in the front, your network needs to be protected at all of its entry points. Secure Modems, DialBack Systems If modem access is to be provided, this should be guarded carefully. The terminal server, or network device that provides dialup access to your network needs to be actively administered, and its logs need to be examined for strange behavior. Its passwords need to be strong not ones that can be guessed. Accounts that aren't actively used should be disabled. In short, it's the easiest way to get into your network from remote: guard it carefully. There are some remote access systems which have the feature of a twopart procedure to establish a connection. The first part is the remote user di...
Read more

3.5 SECURITY ISSUES FOR SMALL AND MEDIUM SIZED BUSINESSES

 Small and medium sized businesses use the Internet and networked applications to reach new customers and serve their existing ones more effectively. At the same time, new security threats and legislation puts increased pressure on business networks to be reliable and secure. Business Challenges According to recent studies, security is the biggest challenge facing small and mediumsized businesses. Everchanging security threats from both inside and outside the business network can wreak havoc on business operations, affecting profitability and customer satisfaction. Small and mediumsized businesses must also comply with new regulations and laws created to protect consumer privacy and secure electronic information. Security issues for small and medium – sized businesses are classified into 5 basic categories: Worms and Viruses As per research, Computer worms and viruses remain the most common security threat, with 75 percent of small and medium businesses affected by it.. Worms and v...
Read more

3.6 TOOLS FOR NETWORK SECURITY

There are many strong tools available for securing a computer network. Tools to protect your enterprise network have been evolving for the last two decades, roughly the same amount of time that people have been trying to break into computer networks. These tools can protect a computer network at many levels, and a wellguarded enterprise deploys many different types of security technologies. The most obvious element of security is often times the most easily overlooked: physical security—namely, controlling access to the most sensitive components in your computer network, such as a network administration station or the server room. No amount of planning or expensive equipment will keep your network secure if unauthorized personnel can have access to central administration consoles. Even if a user does not have evil intent, an untrained user may unknowingly provide unauthorized outside access or override certain protective configurations. Let us briefly discuss few of these network secur...
Read more