Advance In Adaptive Modulation For Fading Channels
Authors: Hamamra Jehad 
Published: November 2013

Smart phones are becoming dominant handsets that are available to wireless technology users. Wireless access to internet is also becoming the default scenario with vast majority of internet users. The increasing demand for high speed wireless internet services makes current technologies meet their limit due to channel impairments. The conventional adaptive modulation technique (CAMT) is no longer helpful due to high data rate requirements of new technologies and wireless video streaming in addition to other applications such as downloading large files. The CAMT is one of the developed approaches that are considered a powerful techniques that are currently being used in advanced wireless communication systems such as long term evolution (LTE) technology. This technique is used to enhance energy efficiency and increase spectral efficiency of wireless communication systems over fading channels. The CAMT dynamically changes modulation schemes based on channel conditions to maximize throughput with minimum bit error rate (BER) based on channel state information of each user, which is sent back to transmitter by receiver side via reliable channel. The CAMT is based on predefined set of ranges signal to noise ratios (SNRs) for different orders of modulation schemes. The more increase in SNRs lead to higher level of ranges of SNRs set that lead to a higher modulation order. This will allow to higher transmission speed utilizing the good channel condition. In order to minimize BER, when channel condition degrades, modulation order is reduced, which result to lower spectral efficiency but more robust modulation scheme. The dynamicity of changing modulation order based on SNRs ranges of radio channel is the key part of CAMT to increase throughput and minimize the BER. However, this work proposes an advance in AMT that is based on utilizing more channel state information in addition to SNR ranges. The particular new information is related to how sever fading the channel experiences. The amount of severity in this work is measured with amount of fading (AF), which is computed by using the first and second central moments of envelope amplitude. This additional information helps to distinguish between different channel conditions that have same average set of SNR ranges but different levels of fading severity that may be utilized to increase performance of CAMT. The different levels of fading severity and similar sets of SNR ranges have been tested with Nakagami-m fading channels. The AF measure of fading severity is equal to 1/m in this radio fading channels. So, the investigation in this work is based on testing how to leverage the AF dimension in addition to the conventional approach used in CAMT. In this work we show that the BER of different modulation schemes depends on fading amount for every range of SNR defined by sets of AMT. Current results show dramatic improvements in BER performance and throughput when AF is leveraged with SNRs range set approach defined in CAMT. Utilization of AF with SNR ranges allow adapting higher modulation order in channel conditions that were not possible with conventional AMT.