Spectral Efficiency and BER Analysis In 802.16e Standard

Abstract

Spectrum being nature’s gift; needs most wise use of it. OFDM system is an excellent way to utilize the spectrum. OFDM is a parallel data transmission system which promises the high data rate with minimum degradation of the quality of service relative to serial communication techniques. In OFDM, a single channel utilizes multiple sub-carriers on adjacent frequencies. In addition the subcarriers in an OFDM system are overlapping to maximize spectral efficiency. Ordinarily, overlapping adjacent channels can interfere with one another. However, sub-carriers in an OFDM system are precisely orthogonal to one another. Thus, they are able to overlap without interfering. As a result, OFDM systems are able to maximize spectral efficiency without causing adjacent channel interference. In order to obtain the orthogonality the subcarrier frequencies must be spaced by a multiple of the inverse of symbol duration. Other than spectral efficiency OFDM has many advantages, as immunity to impulse interference, resilient to RF interference, robustness to channel fading, resistance to multipath, much lower computational complexity(collectively, they reduces bit error rate ). Also, WiMAX being one of the standards which is using OFDM, has excellent spectral efficiency but there are no limits for researcher’s, that is inspiration for “spectral-efficiency and BER analysis in 802.16e”. As we know that with “differential -modulation” over either time samples (Doppler problem) or sub carrier (tone correlation & phase rotation problem) cause a problem. So the suitable modulation techniques are tradeoff between SPECTRAL EFFICIENCY & BER, in simple words as level of modulation is increased BER get degraded but spectral-efficiency get improved. However, an improvement in BER can be achieved using combinations of different FEC coding but at the cost of spectral-efficiency. In present work RS and CC combination has been implemented for BER improvement, without much loss in spectral efficiency. In wireless system, neither spectrum nor BER can be compromised at any cost. The tradeoff between modulation techniques and FEC is desirable. Hence, both the trade-off, the effect of modulation level and the effect of FEC have been analyzed in thesis work. Also, effect of CP addition has been analyzed. For this purpose different channels starting from ideal one i.e AWGN, after that Rayleigh and then finally Nakagami have been taken for analysis.