Frequency hopping is a radio communication technique in spread-spectrum modulation wherein information is transmitted using a sequence of carrier (or operating) frequencies that change at set times to produce a narrow band signal that bounces or hops around a center frequency over an available frequency spectrum.
In a centrally controlled multicellular mobile radio communication system based on slow frequency hopping, each cell has a base station that provides the necessary timing and control information received and used by all the remote stations that belong to the cell.
All stations belonging to a cell, the base station and all remote stations that belong to it, must hop in synchronism in order to communicate with each other at the same frequency. Different cells will typically operate on different frequency hopping patterns. The control information required for synchronized frequency hopping is broadcast by the base station. A key problem in the operation of a frequency-hopping based system is that of acquiring hop synchronization between one remote station and the base of a cell.
The following references are typical of the background art in the field of frequency hopping systems and synchronization techniques thereof.
U.S. Pat. No. 5,081,641 issued Jan. 14, 1992 to Kotzin et al. entitled "Interconnecting And Processing System For Facilitating Frequency Hopping" discloses a method and apparatus for facilitating communication of information in a system without the use of a baseband hopping unit, by sharing a common TDM bus between a plurality of radio communication units, processing units, and information links, where the processing units extract traffic channel information, packetize and/or unpacketize the information, and return same back to the common bus for retrieval by the information links or radio communication units.
In U.S. Pat. No. 4,850,036 issued Jul. 18, 1989 to Smith entitled "Radio Communication System Using Synchronous Frequency Hopping Transmissions" a frequency-hopping radio communication system is disclosed comprising a control unit which transmits to and receives from each of a plurality of slave stations using a frequency-hopping mode of operation. During a start-up mode, the control unit communicates a starting message to each slave station using a predefined frequency. The message identifies to each slave station a frequency-hopping sequence to be used to select the frequencies from a group of frequencies for transmission to and reception from the control unit. This message also specifies to each slave station unique starting frequencies in the frequency-hopping sequence at which to begin transmitting and receiving. All slave station transmission are synchronized to the control unit transmissions, thereby preventing any two stations from concurrently using the same frequencies for either transmitting to or receiving from the control unit.
EP 0658 023 A1 from IBM discloses a method for selecting a base station in a multicellular communication network system of the type having base stations and a plurality of remote stations. When a remote is first powered up it chooses randomly a frequency and searches for valid header messages from neighboring bases. After a fixed period of time which is equal to the length of a superframe (MAC protocol exchanges during the complete base station frequency hopping pattern) it randomly switches to another frequency and keeps on monitoring.
While the solutions of the prior art are efficient in their environment, they do not directly address the problem of shortening the procedure of radio environment listening. Moreover, the use of a signaling channel does not comply with the U.S. Federal Communications Commission (FCC) regulation in the 2.4 GHz Band, while the average and the maximum duration for selecting a base in the prior art does not comply with the fast base selection required for the actual hand-off systems.