3G versus WiMax

WITH CDMA taking the backseat, round one of the technology war in telecom has gone to the GSM platform. A second war for supremacy is brewing between the soon-to-be-launched 3G and WiMax technologies. Both are platforms for providing highspeed Internet on mobile, enabling video calls, movie downloads and other multimedia applications on mobiles.

The differences between the proponents of two technologies are heating up ahead of the spectrum auction next month. Ericsson – the biggest supporter and equipment vendor of 3G – is now laying claims even on 2.3 Ghz spectrum band, which is supposed to be used for WiMax in India. On the other hand, WiMax Forum, the international body supporting WiMax deployment, feels that it has products certified for use in that band, which is most spectral efficient for offering high-speed internet on mobile.

WiMax stands for Worldwide Interoperability for Microwave Access. It can be used to provide voice services too and is considered a rival of 3G since both platforms are used for similar applications. 3G, however, is said to be voice-centric and is expected to be used for easing network congestion before high-end data services can be offered.

As per the Department of Telecom (DoT), spectrum in the 2.1Ghz band will be used for 3G while 2.3 GHz and 2.5Ghz have been earmarked for Broadband Wireless Access (BWA), which is considered synonymous with WiMax. However, Ericsson CTO Hakan Eriksson said BWA is a family of technologies, which include 3G, HSPA (high speed packet access), LTE (long term evolution) as well as WiMax. “There is nothing that specifies it is only for WiMax,” he told ET.

WiMax Forum, however, feels otherwise. “2.3 and 2.5 Ghz bands are globally harmonized bands as per International Mobile Telecommunications (IMT)- 2000 standard. As a telecom professional, I have not seen a 3G network operational in these two bands anywhere in the world,” WiMax Forum India chapter chairman C S Rao said.

WiMAX, which can be fixed as well as mobile, mainly operates in the 2.3 – 2.7GHz range. Japan and the US are using both 2.3 and 2.5 for WiMax/OFDMA, said Mr Rao. Till now, several mobile WiMAX products operating between 2.3GHz and 2.5GHz have been certified by the WiMax Forum, allowing their commercial deployment, like by Sprint Nextel in the USA.

Ericsson, however, anticipates that by 2013, there will be two billion mobile broadband subscribers, with majority using 3G networks. “I don’t think WiMax will ever break the 10% market share,” said Mr Eriksson.
For BWA, the DoT auction will distribute two 20 MHz blocks in both the 2.3 and 2.5 GHz bands. In the 2.1 GHz 3G band, the auction will be for spectrum in blocks of 5 Mhz. The success of both 3G and WiMax will largely depend on the strength of ecosystem around them. The larger the number of equipment vendors, software suppliers and operators supporting a technology, the more widespread will be the usage. How each of them will span out in India will be visible only after the deployment of networks next year.

 

(Source: The Times Of India) 

 

 

GPS Functionality

What is GPS?
GPS or the Global Positioning System (GPS) is a space-based radio navigation system developed by the US Department of Defense, now available for civilian users worldwide. For anyone with a GPS receiver, the system provides location and time.

What are the components of the GPS?
The GPS is based on the Global Navigation Satellite System (GNSS), a constellation of 24-32 medium earth orbit satellites that transmit microwave signals to the GPS receiver. From these signals, the receiver calculates the latitude, longitude, altitude and time for the specific user. Its official name is NAVSTAR GPS. The GPS can be divided into three parts — satellites orbiting the earth; control and monitoring stations on earth; and the receivers.

What is the basic principle of GPS?
Suppose you are somewhere in India but don’t know exactly where. A passer by tells you that you are 115 km from Chittorgarh. You now know you are somewhere on a circle around Chittorgarh with a radius of 115 km. Another person tells you that you are 185 km from Mount Abu. Now you have two circles and mathematically two circles have two intersection points, so you know you are either in Udaipur or Rajsamand. Now a third person tells you that you are 262 km from Ahmedabad. Mathematically, three circles can intersect at only one point and hence you can deduce that you are in Udaipur. GPS uses a similar principle to locate positions.

How does it work?
The original GPS design consisted of 27 satellites, of which 24 were operational and 3 for backup purpose. Each of these was making two complete rotations of the earth every day. The satellites were so arranged that from any place on earth at least four were visible. A GPS receiver gets continuous feeds from the visible satellites. A receiver on earth getting feeds from the satellites can use trilateration to calculate the point of intersection of three spheres each centred at three satellites.

Why a minimum of four satellites?
Three satellites would be enough if only three variables latitude, longitude and altitude were involved. But a fourth variable is introduced since the satellites are moving at high speed and minor time lag between the received signals of two satellites can cause large positional error. Hence a fourth variable, which is the time of sending of the signal, is introduced and the receiver has to solve four equations to derive four variables and hence the need for a minimum of four satellites.

What are its applications?
Primarily developed for determining position, GPS has become a mainstay of transportation systems, providing navigation for aviation, ground, and maritime operations.

How reliable is the GPS?
GPS signals at terrestrial receivers tend to be relatively weak and hence the signals get distorted by other sources of electromagnetic radiation like solar flares, the earth’s magnetic field or man-made electromagnetic interfaces.

What are the other global navigation satellite systems?
At present, GPS is the only fully operational GNSS. The Russian GLONASS system was also operational for a short period but fell into disrepair with the collapse of the Russian economy. China is developing Beidou while EU with the help of India, China and Israel is developing Galileo. India is also developing Indian Regional Navigational Satellite System .