Collision avoidance of rach signals in a TDMA satellite communication system
In a cellular mobile telephone system, a mobile station ( 4 d , 4 e ) requests allocation of a traffic channel by sending a request in a random access channel. Where there is a significant path length difference between locations in a cell and a network antenna, for instance on a satellite ( 3 ), not all of the available TDMA slots are used for random access signals. Instead, gaps of one to three time slots are left between valid random access time slots ( 103, 104 ) to avoid collision between random access bursts arriving at the network antenna along paths of different lengths.
1. A method of avoiding collision between random access channel signals in a TDMA mobile telephone system in which there is a significant difference between two locations in a cell and a network antenna, the method comprising operating a mobile station so to establish a local timebase at the mobile station on the basis of a received broadcast control information signal and disabling transmission on a random access channel frequency of random access channel signals during a subset of the time slots of said local timebase, wherein random access channel signal transmission on the random access channel frequency by the mobile station is enabled in time slots separated by n time slots, during which random access channel signal transmission is disabled, where n is a positive integer selected to avoid signal collisions between multiple random access channels in the cell having the largest mobile station-network antenna path length differential.
2. A method of avoiding collision between random access channel signals in a TDMA mobile telephone system in which there is a significant difference between two locations in a cell and a network antenna, the method comprising operating a mobile station so to establish a local timebase at the mobile station on the basis of a received broadcast control information signal and disabling transmission on a random access channel frequency of random access channel signals during a subset of the time slots of said local timebase, wherein random access channel signal transmission on the random access channel frequency by the mobile station is enabled in time slots separated by n time slots, during which random access channel signal transmission is disabled, where n is a positive integer communicated to the mobile station in a broadcast control signal to mitigate interchannel collisions.
3. A method according to claim 1 or 2 , wherein the network antenna is carried by a satellite.
4. A mobile station for a TDMA mobile telephone system configured for operation in a method according to claim 1 or 2 .