Firstly this paper researches present mobile communication technique of enhancing system capacity , next further researches basic principles of tdma and cdma system . based on these researches a new scheme is proposed that let broadband code division multiple access ( b - cdma ) system overlay on an existing narrowband digital cellular system ( i . e . gsm ) 本文首先研究了移动通信现有的扩容技术,其次深入研究了tdma系统和cdma系统的基本原理,在此基础上提出了利用gsm与宽带cdma系统同频传输实现系统扩容的方案。