Optimum code rate in cellular systems using adaptive modulation

It is essential to find suitable modes (combinations of alphabet sizes and code rates) for transmission in cellular systems. Bad choices result in low spectrum efficiency. An analytical method is proposed to find the modes which give the highest spectrum efficiency when using adaptive modulation. It is demonstrated that data rates considerably higher than 271 and 384 kbps are feasible in GSM and EDGE systems by using adaptive modulation. It is further demonstrated that the spectrum efficiency can be improved more than 100% by using three modes in a GSM system.