Kamis, 28 Mei 2015

Wireless Power Transmission Using Satellite Based Solar Power System

Electricity is the most versatile and widely used form of energy. The global demand for electricity is continuously growing. Of the total generation worldwide, more than 60 percent of energy is generated using coal-fired station resulting in carbon dioxide emission threatening the global warming. To mitigate the consequence of the climate change, the generation systems need to undergo significant changes. The installed capacity over the last century is a clear picture of growing economy. To satisfy the increasing demand for power and reducing CO2 emission, the future generation system must meet the demand, reliability, efficiency and sustainability. This has accelerated the generation using solar, wind, tidal, and many more. The objective of such initiative is to investigate on the feasibility, financing and development of new plans [1]. According to the “Load Generation Balance Report 2013-2014” of India, the energy requirement registered a growth of 6.5% during the year 2012-2013 against the projected growth of 5.1% [2]. This is due to increasing population, advancement in living standard of the people, discovery of new power consuming yet comfort providing devices/appliances and improvement in the life style of the masses. The conventional methods for generating electrical power are insufficient for providing the increasing demand of electrical power. Thus, there is an urgent need to supplement the conventional sources. Solar power generation with its associated technologies has advanced few steps ahead in last several decades. It has been believed and investigated since last four decades that solar energy in space free from the weather conditions is quite different from that on the earth. The SPS system has great potential to harness solar power using bulk photovoltaic (PV) array in space and transmit it to the earth using microwave.

 2. Design of The Satellite Based System
    The complete assembly of the satellite based system is shown in figure 1. The solar panels are connected on either sides of the satellite. These solar panels are the main source of DC power. Microwaves are generated using a device called magnetron powered by DC supply.

 3. Ground Based Model
    The design considerations for the ground based model of the proposed SPS system differs from that used in space. Starting from the DC power source, for space based system; the DC power source is the solar energy. As stated earlier, DC power produced by solar energy in geosynchronous orbit is approximately 3 to 4 times more that can be produced on earth’s surface for same duration. The number of solar panels required for ground based model would be more. For an experimental setup, the power supply for the ground based system may be taken from the voltage doubler/multiplier circuit to supply the DC power to magnetron. Instead of this, the magnetron extracted from microwave oven along with its power supply circuit may also be used. The waves generated by magnetron are passed through a waveguide. Further the microwaves from waveguide are guided to the antenna. Horn antenna attached with the waveguide is readily available. Once the microwaves are emitted from antenna, they are free to travel in space along with its assigned direction. This is the complete assembly of the transmitting section.

 4. Components Specifications and Operation
     The components required are:
4.1 Power Supply
In ground based model, for attaining better efficiency, the DC power that is to be transferred should be 1 kW or more. The source of DC power can be a transformer linked with voltage doubler/multiplier circuit or the magnetron extracted from microwave oven along with its power supply components may be an appropriate alternative.
4.2 Magnetron
Magnetron is a high powered vacuum tube device that generates microwaves owing to the motion of clouds of electrons in a crossed electric and magnetic fields. Magnetron originally developed in 1916 as an alternative to grid control in vacuum tubes. It was discovered during the DEO/NASA study of SPS that the microwave oven magnetron along with the external passive circuitry can perform as phase locked high gain of 30dB amplifier for direct use in the transmitting section. For ground based transmitter, the microwave oven magnetron can be used directly [5]. However for space use, based on the same principle, special space magnetron is required.
4.2.1 Construction
Figure 3 shows the cut view of magnetron. It consists of a cathode which is placed at the centre. A ring shaped anode surrounds the cathode. In anode structure, there are resonant cavities. A permanent magnet is placed beneath the anode which produces magnetic field along the length of the cathode. The resonant cavities present in anode structure are channelled at one end of the magnetron where the produced microwaves are collected. This channelled section is called as a waveguide.
4.2.2 Working
Generally, in microwave magnetron the maximum anode voltage is 4.5kV and the maximum cathode filament voltage is 3.75 V AC. There is a heated cathode at the centre. Hence electrons are released from it by the process called ‘Thermo Ionic Emission’
4.5 Receiving Section
    The rectenna assembly is designed for a frequency of 2.45 GHz. The word rectenna is derived from two individual words, namely rectifier and antenna. The microwaves from the antenna are rectified and filtered. The block diagram of receiving section is shown in figure 5.
5. Experimental Results
   W. C. Brown was the pioneer in the field of microwave power transmission (MPT) [8]. Based on the discovery of the magnetron tubes, W. C. Brown started the research on microwave power transmission and developed rectenna. He succeeded in developing wired helicopter in 1964 and to free-flied the helicopter in 1968. The photograph in figure 6 shows the laboratory experiment of MPT.
6. Conclusion
    The solar powered satellite transmitting power to the earth wirelessly is expected to be the central attraction of space and technology in coming decades. This concept promises to bridge the gap between the existing power generation and demand. The use of solar cells in space achieves 24 hour sunlight and are unaffected by atmosphere and clouds. The power generated is estimated to be approximately 3 to 4 times more that that can be produced on ground. It needs further study to explore its applications and biological impacts. These technologies will be verified in the ground demonstration within several years and will be fully verified in the space experiments within 10 years.

Jumat, 22 Mei 2015

Wireless Networking Security

         "Wireless Networking Security"

Wireless Internet access technology is being increasingly deployed in both office and public environments, as well as by the Internet users at home. We begin by outlining some of the basic technologies of wireless network systems.

    Wi-Fi Protected Access (WPA) is a wireless security protocol designed to address and fix the known security issues in WEP. WPA provides users with a higher level of assurance that their data will remain protected by using Temporal Key Integrity Protocol (TKIP) for data encryption. 802.1x authentication has been introduced in this protocol to improve user authentication.
    Wi-Fi Protected Access 2 (WPA2), based on IEEE 802.11i, is a new wireless security protocol in which only authorised users can access a wireless device, with features supporting stronger cryptography (e.g. Advanced Encryption Standard or AES), stronger authentication control (e.g. Extensible Authentication Protocol or EAP), key management, replay attack protection and data integrity.
    Shared key authentication can easily be exploited through a passive attack by eavesdropping on both the challenge and the response between the access point and the authenticating client. Such an attack is possible because the attacker can capture both the plaintext (the challenge) and the ciphertext (the response).
    WEP uses the RC4 stream cipher as its encryption algorithm. A stream cipher works by generating a keystream, i.e. a sequence of pseudo-random bits, based on the shared secret key, together with an initialisation vector (IV). The keystream is then XORed against the plaintext to produce the ciphertext. An important property of a stream cipher is that if both the plaintext and the ciphertext are known, the keystream can be recovered by simply XORing the plaintext and the ciphertext together, in this case the challenge and the response. The recovered keystream can then be used by the attacker to encrypt any subsequent challenge text generated by the access point to produce a valid authentication response by XORing the two values together. As a result, the attacker can be authenticated to the access point.
How to Configure My Wireless Broadband Router Securely?

1. User name and Password
Change the default user name and password because they are often easily guessed. Some manufacturers might not allow you to change the username, but at least the password should be changed.
2. Encryption (WEP/WPA/WPA2)
Whenever possible, WEP should be avoided. Instead, use WPA2/AES or WPA/AES if it is supported on the device.
3. Authentication Type (Open Authentication or Shared Key Authentication)
The shared key mechanism should never be used. Instead, a stronger mutual authentication as defined in the 802.11i standard should be considered.
3. Wireless Network Name / SSID
The default SSID should be changed. The new SSID should not be named to refer the network products being used, reflect your name or other personal information, otherwise the information could aid an attacker in collecting reconnaissance information about you and your wireless network.
4. Broadcast Network Name / SSID
Users may consider disabling SSID broadcasting or increasing the “Beacon Interval” to the maximum. Suppress SSID broadcasting could not prevent sophisticated attackers to steal SSID by sniffing the management frames between the communication of access points and clients, however it could able to stop casual wireless clients from discovering the wireless network or attempting to access.
5. MAC Address Filtering
Enabling MAC address filtering is recommended as another layer of protection.
6. Dynamic Host Configuration Protocol (DHCP)
Disabling the DHCP feature, if possible, is recommended, as DHCP makes it easier for malicious attackers to access a wireless network.