Capacity Improvement for OFDMA Systems Using ASB-ABL Techniques

Orthogonal frequency division multiplexing (OFDM) is a prominent multiplexing method for wireless system because of its high spectral efficiency and Efficient bandwidth usage. At the same time, it is also known for its susceptibility to frequency synchronization errors and inter-carrier interference (ICI) which degrades its performance to a large extent affecting the capacity of the system. It is proposed in this work to minimize these errors and to improve the capacity of the OFDMA systems in time varying channels by using variable sub-carrier bandwidths (VSB) technique, where as all conventional methods use static sub-carrier bandwidth. As ICI is inversely proportional to sub-carrier bandwidth, we can vary sub-carrier bandwidth (SCB) and reduce the ICI by developing an algorithm we can achieve the target of satisfying required bit error rate (BER) by maximizing the system capacity. We also used Adaptive Bit Loading technique where it senses the channel and determines whether the channel is good or bad and allocates the bits to the channel accordingly which minimizes the transmission errors therefore reducing the bit Error Rate and further enhance the system efficiency. Results show that VSB can provide higher capacity than its fixed sub-carrier bandwidth.