Method of frequency synchronization in a wireless communications system and configuration for implementing the method
View Patent ↗The wireless communications system synchronizes the current frequency and permits communication under the DECT protocol between a mobile unit and a fixed base station with rapid and frequent changes in frequency, as defined for example in the ADCT protocol. For this purpose a key is derived from the identification code transmitted by the base station. Lists containing random or pseudo-random frequency sequences are specified, and one of the lists is selected depending on the key transmitted, and the corresponding frequencies are used for the frequency change.
1. A frequency-synchronizing method in a wireless communications system, which comprises:
communicating between a mobile unit and a stationary base station over a defined number of frequencies;
transmitting a message containing a code identifying the base station during a time slot within a time frame;
deriving a key from the identification code;
specifying a defined number of different, unique frequency sequences each containing all the frequencies of the defined number of frequencies;
setting the defined number of different, unique frequency sequences to be 40 frequency sequences, and calculating the frequency sequence with the following algorithm: f x+1 =mod(75[f x +Y]); Y=1, 2, 4, 7, 8, 11, 13, 14, 16, . . . , 68, 71, 73, 74; wherein f x is a frequency in the frequency sequence;
assigning one of the frequency sequences to the key and selecting the one frequency sequence with the key; and
consecutively changing to the frequencies contained in the assigned frequency sequence in the defined sequence by the base station and the associated mobile unit.
2. The method according to claim 1 , which comprises calculating each of the frequency sequences with different algorithms, and thereby determining each subsequent frequency on a basis of an immediately preceding frequency.
3. The method according to claim 1 , which comprises retaining a frequency for a defined number of time frames before changing the frequency, and transmitting an item of information specifying how many times a current frequency will be used for transmission.
4. The method according to claim 1 , which comprises, in the mobile unit, checking the message transmitted from the base station for errors, and adopting the receiver key and make a frequency change only after an error-free message is received.
5. A configuration for synchronizing a frequency between a base station and a mobile unit each configured to implement the method according to claim 1 , the configuration comprising a frequency-change computation unit provided in the base station and in the mobile unit, a key register for storing the key, and a frequency register defining a current frequency, said frequency-change computation unit having an input receiving the contents of said key register and the contents of said frequency register, and having an output connected to said frequency register.
6. The configuration according to claim 5 , which comprises an update register controlled by a time-frame counter connected between said frequency register and said output of said frequency-change computation unit.
7. A frequency-synchronizing method in a wireless communications system, which comprises:
communicating between a mobile unit and a stationary base station over a defined number of frequencies;
transmitting a message containing a code identifying the base station during a time slot within a time frame;
deriving a key from the identification code;
specifying a defined number of different, unique frequency sequences each containing all the frequencies of the defined number of frequencies, each frequency sequence having several different, unique frequency subsequences specified by subkeys derived from the message;
assigning one of the frequency sequences to the key and selecting the one frequency sequence with the key; and
consecutively changing to the frequencies contained in the assigned frequency sequence in the defined sequence by the base station and the associated mobile unit.
8. The method according to claim 7 , which comprises, once a frequency subsequence has been run through completely, using another frequency subsequence.
9. A configuration for synchronizing a frequency between a base station and a mobile unit each configured to implement the method according to claim 7 , the configuration comprising a frequency-change computation unit provided in the base station and in the mobile unit, a key register for storing the key, and a frequency register defining a current frequency, said frequency-change computation unit having an input receiving the contents of said key register and the contents of said frequency register, and having an output connected to said frequency register.
10. The configuration according to claim 9 , which comprises an update register controlled by a time-frame counter connected between said frequency register and said output of said frequency-change computation unit.
11. A configuration for synchronizing a frequency between a base station and a mobile unit, the configuration comprising:
a key register for storing a key;
a frequency register defining a current frequency; and
a frequency-change computation unit provided in the base station and in the mobile unit, said frequency-change computation unit having an input receiving contents of said key register and contents of said frequency register, and having an output connected to said frequency register;
said configuration programmed to:
communicate between the mobile unit and the base station over a defined number of frequencies;
transmit a message containing a code identifying the base station during a time slot within a time frame;
derive the key from the identification code;
specify a defined number of different, unique frequency sequences each containing all the frequencies of the defined number of frequencies;
set the defined number of different, unique frequency sequences to be 40 frequency sequences, and calculate the frequency sequence with the following algorithm: f x+1 =mod(75[f x +Y]); Y=1, 2, 4, 7, 8, 11, 13, 14, 16, . . . , 68, 71, 73, 74; wherein f x is a frequency in the frequency sequence;
assign one of the frequency sequences to the key and select the one frequency sequence with the key; and
consecutively change to the frequencies contained in the assigned frequency sequence in the defined sequence by the base station and the associated mobile unit.
12. A configuration for synchronizing a frequency between a base station and a mobile unit, the configuration comprising:
a key register for storing a key;
a frequency register defining a current frequency; and
a frequency-change computation unit provided in the base station and in the mobile unit, said frequency-change computation unit having an input receiving contents of said key register and contents of said frequency register, and having an output connected to said frequency register;
said configuration programmed to:
communicate between the mobile unit and the base station over a defined number of frequencies;
transmit a message containing a code identifying the base station during a time slot within a time frame;
derive the key from the identification code;
specify a defined number of different, unique frequency sequences each containing all the frequencies of the defined number of frequencies, each frequency sequence having several different, unique frequency subsequences specified by subkeys derived from the message;
assign one of the frequency sequences to the key and select the one frequency sequence with the key; and
consecutively change to the frequencies contained in the assigned frequency sequence in the defined sequence by the base station and the associated mobile unit.