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wireless mobile communications


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INTRODUCTION:

'The first operational cellular communication system was deployed in the Norway in 1981 and was followed by similar systems in the US and UK. These first generation systems provided voice transmissions by using frequencies around 900 MHz and analogue modulation.
The second generation (2G) of the wireless mobile network was based on low-band digital data signaling. The most popular 2G wireless technology is known as Global Systems for Mobile Communications (GSM). The first GSM systems used a 25MHz frequency spectrum in the 900MHz band.
Planning for 3G started in the 1980s. Initial plans focused on multimedia applications such as videoconferencing for mobile phones. When it became clear that the real killer application was the Internet, 3G thinking had to evolve. As personal wireless handsets become more common than fixed telephones, it is
clear that personal wireless Internet access will follow and users will want broadband Internet access wherever they go.



Migrating to 4G:
The fact that 4G mobile networks intend to integrate almost every wireless standard already in use, enabling its simultaneous use and interconnection poses many questions not yet answered. The research areas that present key challenges to migrate current systems to 4G are many but can be summarized in the following: Mobile Station, System and Service. To be able to use 4G mobile networks a new type of mobile terminals must be conceived.


GENERIC MIMO AND OFDM:

Increasing demand for high performance 4G broadband wireless mobile calls for use of multiple antennas at both base station and subscriber ends. Multiple Antenna technologies enable high capacities suited for Internet and multimedia services and also dramatically increase range and reliability. This design is motivated by the growing demand for broadband wireless Internet access.


OPENWIRELESSARCHITECTURE:

The 4G Mobile communications will be based on the Open Wireless Architecture (OWA) to ensure the single terminal can seamlessly and automatically connect to the local high-speed wireless access systems when the users are in the offices, homes, airports or shopping centers where the wireless access networks (i.e. Wireless LAN, Broadband Wireless Access, Wireless Local Loop, HomeRF

wireless mobile communications

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Mobile Radio Propagation

Large Scale Propagation Effects
Distance dependent loss
Reflection
Diffraction
Scattering
Useful in estimating radio coverage
Small Scale Propagation Effects
Rapid fluctuations of received signal strength over short durations or short distances
Multipath propagation – time dispersive
Mobility – frequency dispersive

Radio Propagation Mechanisms

Reflection
Propagating EM wave impinges on an object which is large as compared to its wavelength
- e.g., the surface of the Earth, buildings, walls, etc.
Conductors & Dielectric materials (refraction)
Diffraction
Radio path between transmitter and receiver is obstructed by a surface with sharp irregular edges
Waves bend around the obstacle, even when LOS (line of sight) does not exist
Fresnel zones
Scattering
Objects smaller than the wavelength of the propagating wave
- e.g. foliage, street signs, lamp posts
“Clutter” is small relative to wavelength

Diffraction

Diffraction occurs when waves hit the edge of an obstacle
“Secondary” waves propagate into the shadowed region
Water wave example
Diffraction is caused by the propagation of secondary wavelets into a shadowed region.
Excess path length results in a phase shift
The field strength of a diffracted wave in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.
Huygen’s principle: all points on a wavefront can be considered as point sources for the production of secondary wavelets, and that these wavelets combine to produce a new wavefront in the direction of propagation.

Signal Penetration into Buildings

RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency.
Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings.
Some devices to conduct the signals into the buildings