 it harder to deploy MIMO systems in its full capacity. However, CDMA networks do incorporate antenna receive diversity both at the base station and at the mobile station. Since MIMO gives higher capacities and better spectral efficiencies than the receive diversity technique, OFDMA systems are fundamentally superior to CDMA systems. 2.7.1.6 Spectral Efficiency When the operator has 10 MHz or more bandwidth, OFDMA based systems are more spectral efficient than CDMA systems. If bandwidth is less than 5 MHz, then CDMA provides higher spectral efficiency than OFDMA systems. Beyond high traffic metro areas, OFDM-based systems are not as such economical since the spectrum and network will most likely remain under utilized. 4 The Doppler effect (or Doppler shift) is the change in frequency of a wave for an observer moving relative to the source of the wave. OFDM and OFDMA 2.7.1.7 Higher Capacity In OFDMA, the influence of narrow-band interference is not the same for all users. The consequence of this is that some users can operate at higher interference values than others, and the number of users which can operate at a given performance level is an increasing function of the signal-to-interference ratio (SNR). The results indicated in [9] showed that OFDMA can accommodate a significant number of users at SNR values far below those which break TDMA and CDMA. 2.8 Summary Insights This chapter provided an overview of OFDM and OFDMA which are and expected to be used with Next Generation Networks. The principles of OFDM, pros and cons and remedies for the impairments were presented. The benefits of OFDMA over CDMA and TDMA were also provided. Both the Next Generation Mobile Technologies that is, 3G-LTE and WiMAX are based on OFDMA; the thing that industry is to waiting to see whether or not OFDMA in its current form will become part of IMT- Advanced (4G) networks or will the industry unveil a totally out of the box solution (access scheme) for futuristic 4G/5G networks. References 1. Wikipedia. available at http://en.wikipe