14-04-2011, 03:56 PM
SUBMITTED BY,
P.J.KARTHIK
R.VENKATESH
[attachment=12216]
4G WIRELESS SYSTEM”
Abstract
The main aim of our paper is to bring forth the detail about the low cost wireless internet access for rural area through the 4G technology wi-fi (IEEE 802.11n).
Although a large number of Internet users now enjoy high-speed access, there are still vast geographic regions where broadband services are either prohibitively expensive or simply unavailable at any price. Researches and technology are more needed for rural areas where the development is lacking.
Hence our paper analyses the cost and effectiveness of all possible technologies such as Cisco Aeronet Bridge based system, tethered Aerostat based network, and mesh network to find the suitable broadband access technology for rural people in a bearable cost.
Introduction
The 4G technologies are all about improving the performance of today’s mobile networks, and also revolutionizing the model to create a truly ultra-broadband mobile experience.
The international telecommunications regulatory and standardization bodies are working for commercial deployment of 4G networks roughly in the 2012-2015 time scale.
Why move towards 4G
Limitation to meet expectations of applications like multimedia, full motion video, wireless teleconferencing
– Wider Bandwidth
Difficult to move and interoperate due to different standards hampering global mobility and service portability
Primarily Cellular (WAN) with distinct LANs’; need a new integrated network
Limitations in applying recent advances in spectrally more efficient modulation schemes
Need all digital network to fully utilize IP and converged video and data
What is 4G?
4G is a term used to describe the next complete evolution in wireless communications. A 4G system will be able to provide a comprehensive IP solution where voice, data and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at higher data rates than previous generations.
Objectives of 4G
1.4G will be a fully IP-based integrated system.
2. 4G will be capable of providing between 100 Mbit/s and 1 Gbit/s speeds both indoors and outdoors, with premium quality and high security.
3. 4G will use smart antennas.
4. It will be multiple inputs and multiple outputs (MIMO) system based
5.Dynamic packet asignment
6. Wideband orthogonal frequency division multiple access (OFDM)
Key 4G Technologies
Some of the key technologies required for 4G are described below:
1. OFDM technology
Orthogonal frequency division multiplexing (OFDM) is a modulation technique that divides the communication channel into a number of equally spaced frequency bands. A subcarrier carrying a portion of user information is transmitted in each Band. Each subcarrier is independent of each other.
OFDM transmits data simultaneously over a large number of channels at different frequency, enables to send a large data. Hence high speed information transmission occurs.
OFDM not only provides clear advantages for physical layer performance, but also a frame work for improving layer 2 performance by proposing an additional degree of freedom. Using OFDM, it is possible to exploit the time domain, the space domain, the frequency domain, even the code domain to optimize radio channel usage. It ensures very robust transmission in multi-path environments with reduced receiver complexity.
As shown in the fig. 2 the signal is split into orthogonal subcarriers, on each of which the signal is “narrowband” (a few kHz) and therefore immune to multi-path effects, providing a guard intervals is inserted between each OFDM symbol. OFDM also provides a frequency diversity gain, improving the physical layer performance. It is also compatible with other enhancement technologies, such as smart antennas and MIMO.
It can also be employed as a multi access technology (OFDMA). In this case, each OFDM symbol can transmit information to/from several users using a different set of flexibility for resource allocation (increasing the capacity) but also enables cross-layer optimization of radio page link usage.
OFDMA has being modulation technique for WLAN, digital audio broad cost systems, digital video broad cost systems and a candidate for future mobile systems.
2. MIMO system
The multiple input multiple output (MIMO) technology was decided to add to IEEE802.11n standards. MIMO is a family of technologies for multi antenna wireless transmission and reception that increases the achievable data throughput within the same occupied bandwidth, increases quality of communication, and allowing dramatically increased spectral efficiency, while offering sustainable benefits to system performance, it also increases the challenges in design and system evaluation and validation.
Multiple antennas at both the base station and terminal can significantly increases data rates with sufficient multipath. It uses signals multiplexing between multiple transmitting antennas (space multiplex) and time or frequency.
MIMO is well suited for OFDM, as it is possible to process independent time symbols as soon as the OFDM waveform is correctly designed for the channel. This process of OFDM greatly simplifies the process. The signal transmitted by m antennas is received by n antennas. Processing of received signals may deliver several performance improvements: range ,quality of received signals and spectrum efficiency
3. Smart antenna
Smart antennas are base station antennas that use digital signal processing to cancel interference. It provides sustainable interference suppression for enhanced performance.
A smart antenna combines multiple antenna elements with a signal-processing capability to optimize its radiation and/or reception pattern automatically in response to the signal environment .it amplifies the frequency to user who wants to communicate and it can be adopted to OFDM and SDR
4. Software Defined Radio
SDR technology is enabling frequencies and communication methods and to be changed flexible by means of software. It responses to internet protocol version 6 (IPV6). SDR benefits from today’s high processing to develop multi-band, multi-standard base stations and terminals.
Although in future the terminals will adapt the air interface to the available radio access technology, at present this is done by the infrastructure. Several infrastructure gains are expected from SDR.
For example to increase the network capacity at a specific time (eg. During sports event), an operator will reconfigure its network adding several modes at a given transceiver station (BTS). SDR makes this reconfiguration easy.
In the context of 4G systems, SDR will become an enabler for the aggregation of multi-standard Pico/micro cells. For the manufacture, this can be a powerful aid to providing multi-standard, multi-band equipment with reduced development effort and costs through simultaneous multi-channel processing.
