This book contains the information on Turbo Code System and suggested modifications to enhance the performance of the system.Research in coding theory has seen many proposals aimed at the construction of powerful codes using block and convolutional codes. Recently, a new forward error control code (FEC) known as Turbo Code is introduced. This new code combines simple component codes with iterative decoding process.Turbo code is adopted as FEC in 3rd Generation Wireless Communication System (UMTS). The name "Turbo" has been coined in analogy to the Turbo engine principle that brings the meaning of powerful. This book specifically describes the process of encoding and decoding turbo codes. A basic discussion of iterative decoding is presented. General turbo code performance issues are discussed and observed through simulations. Two novel approaches to enhance the performance of turbo codes are proposed: a new modified turbo encoder and new unequal power allocation (UPA) scheme for 3G system.