ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 2, August 2012
Comparative Study of Digital Modulation Techniques in WIMAX
Abstract: - The migration to 4G networks will bring a new level of expectation to wireless communications. As after digital wireless revolution made mobile phones available for everyone, the higher speeds and packet delivery of 4G networks will make high quality multimedia available everywhere. The key to achieving this higher level of service delivery is a new air interface. Orthogonal Frequency Division Multiplexing (OFDM) is an alternative wireless modulation technology to CDMA. OFDM is a digital modulation and multiplexing technique. In this paper, we have discussed various digital modulation techniques such as BPSK (2bits), QPSK (4 bits), QAM, 16 QAM and 64 QAM. We have designed simulation environment in MATLAB with various configurations of OFDM technique. The main objective of our work is to measure Bit Error Rate with different modulation schemes and come to the best configuration to achieve better utilization of bandwidth. We have studied existing configurations with analog and digital modulation techniques and compared the results. The driving force behind the need to satisfy this requirement is the explosion in mobile telephone, Internet and multimedia services coupled with a limited radio spectrum. Key Words:- OFDM; 3G; 4G; BPSK; QPSK; Bit Error Rate (BER); WIMAX; QAM.
I. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) is an alternative wireless modulation technology to CDMA. OFDM has the potential to surpass the capacity of CDMA systems and provide the wireless access method for 4G systems. OFDM is a modulation scheme that allows digital data to be efficiently and reliably transmitted over a radio channel, even in carriers. These carriers are regularly spaced in frequency, forming a block of spectrum. The frequency spacing and time synchronization of the carriers is chosen in such a way that the carriers are orthogonal, meaning that they do not cause interference to each other. This is despite the frequency (Frequency Division Multiplexing) and these carriers are orthogonal to each other, hence Orthogonal Frequency Division Multiplexing. In OFDM, usable bandwidth is divided into a large number of smaller bandwidths that are mathematically orthogonal using fast Fourier transforms (FFTs). Reconstruction of the band is performed by the inverse fast Fourier transform (IFFT). Carriers overlapping each other in the frequency domain. The name „OFDM‟ is derived from the fact that the digital data is sent using many carriers, each of a different Attenuation is drop in signal power when transmitting from one point to another which is caused due to shadowing /slow fading and it can be avoided by splitting the signal into many small bandwidth carriers like OFDM
does. This lead to small loss in carrier rather than complete loss. Delay spread is the time spread between the arrival of the first and last multipath signal seen by receiver. In digital system the delay spread can lead to inter-symbol interference. This can be minimized in many ways, one method is to reduce the symbol rate by reducing the data rate for each channel i.e. split the bandwidth into more channels by using frequency division multiplexing another is to use a coding scheme while is relevant to inter symbol interference such as CDMA. In this paper we have mainly focused on WIMAX technology and simulated it in Matlab (Simulink). Most users are keen to use wireless medium with greater speed and that is supported using the existing infrastructure. Many researches have been proved that WIMAX is answer for user‟s expectation and this paper will answer to all the questions regarding confusion on choosing the best modulation technique to use not only to get better utilization of available bandwidth but also how to minimize...
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