S e i m ONOE, J u n TAJIMA, T a k a n o r i UTANO a n d N a r u m i UMEDA NTT Radio Communication Systems Laboratories 1-2356, Take, Yokosuka, 238, J a p a n Abstract -This paper describes a control channel structure for TDMA mobile radio systems that must offer high system capacity a n d ISDN services. The optimum frequency assignment for control channels is clarified a n d the method to realize the assignment is presented. Furthermore, a n improved random access scheme is proposed, Idle-signal Casting Multiple Access with Partial Echo. This scheme has good throughput performance a n d achieves efficient a n d flexible signaling for radio link control and data services.