Method of and apparatus for selective resynchronization in a digital cellular communications system

Claim 2

In a digital communication system employing base stations and mobile stations exchanging ciphered digital data, a method for indicating cipher synchronization which comprises: transmitting from a base station to a mobile station a message over an old channel being received by said mobile station instructing said mobile station to acquire a new channel, said message including an indication of whether or not to resynchronize its cipher upon acquiring the new channel; receiving said message in said mobile station; and acquiring said new channel in said mobile station and resynchronizing or not resynchronizing said cipher at said mobile station in accordance with said indication.

Claim 3

A method according to claim 1, in which said message further includes an indication of which one of a plurality of different options for obtaining cipher resynchronization is to be selected by said mobile station when resynchronization of the cipher is required.

Claim 4

In a digital communication system employing base stations and mobile stations exchanging ciphered digital data, each of said base stations and said mobile stations including a block counter which is used in generating said ciphered data, a method for cipher synchronization which comprises: transmitting from a base station to a mobile station a message over an old channel at said base station being received by said mobile station instructing said mobile station to acquire a new channel at a target base station, said message including an indication for the mobile station to resynchronize its cipher; receiving said message in said mobile station; acquiring said new channel in said mobile station; setting the block counter in each of the mobile station and the target base station to a predetermined value; exchanging ciphered data between said mobile station and said target base station over said new channel with the block counter in each of said mobile station and said target base station being set to said predetermined value; transmitting from the target base station to the mobile station over said new channel a message containing a new value for the block counter in each of the mobile station and the target base station; receiving said block counter message in the mobile station; resetting the block counter in each of said mobile station and said target base station to said new value; and exchanging ciphered data between said mobile station and said target base station over said new channel with the block counter in each of said mobile station and said target base station being first reset to said new value and then incremented at predetermined intervals.

Claim 5

In a digital communication system employing base stations and mobile stations exchanging ciphered digital data, each of said base stations and said mobile stations including a block counter which is used in generating said ciphered data, a method for cipher synchronization which comprises: transmitting from a base station to a mobile station a message over an old channel at said base station being received by said mobile station instructing said mobile station to acquire a new channel at a target base station, said message including an indication for the mobile station to resynchronize its cipher; receiving said message in said mobile station; acquiring said new channel in said mobile station; setting the block counter in each of the mobile station and the target base station to a predetermined value; exchanging ciphered data between said mobile station and said target base station over said new channel with the block counter in each of said mobile station and said target base station being set to said predetermined value; transmitting from the target base station to the mobile station over said new channel a message containing a new value for the block counter in each of the mobile station and the target base station; receiving said block counter message in the mobile station; resetting the block counter in each of said mobile station and said target base station to said new value; and exchanging ciphered data between said mobile station and said target base station over said new channel with the block counter in each of said mobile station and said target base station being first reset to said new value and then incremented at predetermined intervals.

Claim 6

In a digital communication system employing base stations and mobile stations exchanging ciphered digital data, each of said base stations and said mobile stations including a block counter which is used in generating said ciphered data, a method for cipher synchronization which comprises: transmitting from a base station to a mobile station a message over an old channel at said base station being received by said mobile station instructing said mobile station to acquire a new channel at a target base station, said message including an indication for the mobile station to resynchronize its cipher; receiving said message in said mobile station; acquiring said new channel in said mobile station: starting a timer within said mobile station; exchanging unciphered data between said mobile station and said target base station; determining whether said mobile station has received from said target base station prior to the expiration of said timer a message containing a new value for the block counter in each of the mobile station and the target base station; providing a perceptible indication at the mobile station when said timer expires without the mobile station having received said block counter message; setting the block counter in said mobile station to said new value if said mobile station receives said block counter message prior to the expiration of said timer; and exchanging ciphered data between said mobile station and said target base station if said block counter has been set to said new value, and incrementing said block counter at predetermined intervals.

Claim 7

In a digital communication system employing base stations and mobile stations exchanging ciphered digital data, each of said base stations and said mobile stations including a block counter which is used in generating said ciphered data, a method for cipher synchronization which comprises: transmitting from a base station to a mobile station a message over an old channel at said base station being received by said mobile station instructing said mobile station to acquire a new channel at a target base station, said message including an indication for the mobile station to resynchronize its cipher; receiving said message in said mobile station; acquiring said new channel in said mobile station: starting a timer within said mobile station; exchanging unciphered data between said mobile station and said target base station; determining whether said mobile station has received from said target base station prior to the expiration of said timer a message containing a new value for the block counter in each of the mobile station and the target base station; providing a perceptible indication at the mobile station when said timer expires without the mobile station having received said block counter message; setting the block counter in said mobile station to said new value if said mobile station receives said block counter message prior to the expiration of said timer; and exchanging ciphered data between said mobile station and said target base station if said block counter has been set to said new value, and incrementing said block counter at predetermined intervals.

Claim 8

In a radio communications system communicating speech or control data with a plurality of mobile stations over a plurality of radio channels, a method for synchronizing the encryption of said data by said mobile stations comprising the steps of: transmitting data from said system to a mobile station over a first channel in said system; transmitting from said system to said mobile station over said first channel an order to switch communications to a second channel in said system, along with an indication of whether synchronization is required for communicating encrypted data on said second channel; receiving said order and said synchronization indication at said mobile station; switching said mobile station to said second channel in accordance with said order; determining at said mobile station from said synchronization indication whether synchronization is required for communicating encrypted data on said second channel; synchronizing encryption at said mobile station prior to transmitting encrypted data on said second channel if synchronization is required according to said synchronization indication; and transmitting encrypted data from said mobile station to said system over said second channel if no synchronization is required, or if synchronization is required and said mobile station has synchronized encryption, on said second channel.

Claim 9

In a radio communications system communicating speech or control data with a plurality of mobile stations over a plurality of radio channels, a method for synchronizing the encryption of said data by said mobile stations comprising the steps of: transmitting data from said system to a mobile station over a first channel in said system; transmitting from said system to said mobile station over said first channel an order to switch communications to a second channel in said system, along with an indication of whether synchronization is required for communicating encrypted data on said second channel; receiving said order and said synchronization indication at said mobile station; switching said mobile station to said second channel in accordance with said order; determining at said mobile station from said synchronization indication whether synchronization is required for communicating encrypted data on said second channel; synchronizing encryption at said mobile station prior to transmitting encrypted data on said second channel if synchronization is required according to said synchronization indication; and transmitting encrypted data from said mobile station to said system over said second channel if no synchronization is required, or if synchronization is required and said mobile station has synchronized encryption, on said second channel.

Claim 10

The method of claim 5 wherein said first channel is a control channel, said second channel is a traffic channel and said order is contained in an initial traffic channel designation (ITCD) message.

Claim 11

The method of claim 6 wherein said synchronization indication is included in said ITCD message.

Claim 12

The method of claim 6 wherein said control channel is a digital control channel (DCCH) including a broadcast control channel (BCCH) which carries synchronization information for use by said mobile station in synchronizing encryption on said DCCH.

Claim 13

The method of claim 8 wherein said synchronization information is transmitted periodically on said BCCH.

Claim 14

The method of claim 8 wherein each of said system and said mobile station includes a counter which is used in encrypting said data and wherein said synchronization information comprises the value of the counter in said system.

Claim 15

The method of claim 5 wherein said first and second channels are traffic channels and said order is contained in a handoff message.

Claim 16

The method of claim 11 wherein said synchronization indication is included in said handoff message.

Claim 17

The method of claim 11 wherein said handoff message is transmitted in a fast associated control channel (FACCH) portion of said first traffic channel.

Claim 18

The method of claim 5 wherein said synchronization indication specifies one of a plurality of actions to be taken by said mobile station if synchronization is required on said second channel.

Claim 19

The method of claim 14 wherein each of said mobile stations includes a counter which is used in encrypting said data, said system including a corresponding counter, and wherein said actions include: abating data transmission on said second channel until said mobile station receives from said system a message to update the counter in said mobile station with the value of the corresponding counter in said system, and thereafter commencing transmission of encrypted data and incrementing of the counter using the updated counter value; defaulting the counter in said mobile station to a predetermined value and transmitting on said second channel encrypted data using this value until said mobile station receives from said system a message to update the counter in said mobile station with the value of the corresponding counter in said system, and thereafter continuing transmission of encrypted data and incrementing of the counter using the updated counter value; and disabling encryption and transmitting unencrypted data on said second channel until said mobile station receives from said system a message to update the counter in said mobile station with the value of the corresponding counter in said system, and thereafter resuming transmission of encrypted data and incrementing of the counter using the updated counter value.

Claim 20

The method of claim 15 wherein a timer is started in said mobile station at the time encryption is disabled, and said transmission of unencrypted data is terminated or said mobile station generates a perceptible alert, if said counter update message is not received by said mobile station prior to the expiration of said timer.

Claim 21

In a digital radio system communicating data with a plurality of mobile stations over a plurality of radio frequency (RF) channels, each of said RF channels being divided into a plurality of traffic channels, each of said mobile stations including a counter used in ciphering data transmitted to said system in one of said traffic channels, said system maintaining a corresponding counter, a method for controlling the transmission of ciphered data from said mobile stations to said system comprising the steps of: exchanging ciphered data between said system and one of said mobile stations over an old traffic channel, said counter in said one mobile station being synchronously incremented with the corresponding counter in said system; assigning a new traffic channel to said one mobile station; transmitting from said system to said one mobile station a message including a cipher synchronization code, said code being selectively set to one of a plurality of values including: a first value which indicates that said one mobile station is to continue incrementing its counter and continue transmitting ciphered data on said new traffic channel; a second value which indicates that said one mobile station is to inhibit transmission of any data on said new traffic channel until it receives from said system a new counter value whereupon it is to set its counter to said new counter value, begin incrementing its counter, and begin transmitting ciphered data on said new traffic channel; a third value which indicates that said one mobile station is to set its counter to a predetermined value and to continue transmitting ciphered data on said new traffic channel using said predetermined value until it receives from said system a new counter value whereupon it is to replace said predetermined value with said new counter value, begin incrementing its counter, and continue transmitting ciphered data on said new traffic channel; and a fourth value which indicates that said one mobile station is to transmit unciphered data on said new traffic channel until it receives from said system a new counter value whereupon it is to set its counter to said new counter value, begin incrementing its counter, and begin transmitting ciphered data on said new traffic channel; receiving said message at said one mobile station; and transmitting from said one mobile station to said system over said new traffic channel as indicated by said cipher synchronization code.

Claim 22

In a digital radio system communicating data with a plurality of mobile stations over a plurality of radio frequency (RF) channels, each of said RF channels being divided into a plurality of traffic channels, each of said mobile stations including a counter used in ciphering data transmitted to said system in one of said traffic channels, said system maintaining a corresponding counter, a method for controlling the transmission of ciphered data from said mobile stations to said system comprising the steps of: exchanging ciphered data between said system and one of said mobile stations over an old traffic channel, said counter in said one mobile station being synchronously incremented with the corresponding counter in said system; assigning a new traffic channel to said one mobile station; transmitting from said system to said one mobile station a message including a cipher synchronization code, said code being selectively set to one of a plurality of values including: a first value which indicates that said one mobile station is to continue incrementing its counter and continue transmitting ciphered data on said new traffic channel; a second value which indicates that said one mobile station is to inhibit transmission of any data on said new traffic channel until it receives from said system a new counter value whereupon it is to set its counter to said new counter value, begin incrementing its counter, and begin transmitting ciphered data on said new traffic channel; a third value which indicates that said one mobile station is to set its counter to a predetermined value and to continue transmitting ciphered data on said new traffic channel using said predetermined value until it receives from said system a new counter value whereupon it is to replace said predetermined value with said new counter value, begin incrementing its counter, and continue transmitting ciphered data on said new traffic channel; and a fourth value which indicates that said one mobile station is to transmit unciphered data on said new traffic channel until it receives from said system a new counter value whereupon it is to set its counter to said new counter value, begin incrementing its counter, and begin transmitting ciphered data on said new traffic channel; receiving said message at said one mobile station; and transmitting from said one mobile station to said system over said new traffic channel as indicated by said cipher synchronization code.

Claim 23

The method of claim 17 wherein said message is a handoff message.

Claim 24

The method of claim 3 wherein the target base station with said new channel is the same as the base station with said old channel.

Claim 25

The method of claim 4 wherein the target base station with said new channel is the same as the base station with said old channel.

Claim 26

A base station comprising: means for processing a first information bit stream; means for generating a first pseudorandom bit stream; means for combining said first information bit stream with said first pseudorandom bit stream to generate a first encrypted data stream; means for transmitting said first encrypted data stream over a first communication channel; means for processing a second information bit stream; means for generating a second pseudorandom bit stream; means for combining said second information bit stream with said second pseudorandom bit stream to generate a second encrypted data stream; means for transmitting said second encrypted data stream over a second communication channel; and means for transmitting an indication of whether said second pseudorandom bit stream is synchronized to said first pseudorandom bit stream.

Claim 27

A base station comprising: means for processing a first information bit stream; means for generating a first pseudorandom bit stream; means for combining said first information bit stream with said first pseudorandom bit stream to generate a first encrypted data stream; means for transmitting said first encrypted data stream over a first communication channel; means for processing a second information bit stream; means for generating a second pseudorandom bit stream; means for combining said second information bit stream with said second pseudorandom bit stream to generate a second encrypted data stream; means for transmitting said second encrypted data stream over a second communication channel; and means for transmitting an indication of whether said second pseudorandom bit stream is synchronized to said first pseudorandom bit stream.

Claim 28

The base station of claim 21 wherein said synchronization indication is transmitted over said first communication channel to a remote transceiver which is switching from said first communication channel to said second communication channel.

Claim 29

The base station of claim 22 wherein: said remote transceiver is a mobile station; said first communication channel is a digital control channel or a first digital traffic channel; and said second communication channel is a second digital traffic channel.

Claim 30

The base station of claim 23 wherein: said first pseudorandom bit stream is generated as a function of a first block counter value; and said second pseudorandom bit stream is generated as a function of a second block counter value.

Claim 31

The base station of claim 24 wherein: said first and second block counter values are the same; and said synchronization indication indicates that said second pseudorandom bit stream is synchronized to said first pseudorandom bit stream.

Claim 32

The base station of claim 24 wherein: said first and second block counter values are different; said synchronization indication indicates that said second pseudorandom bit stream is not synchronized to said first pseudorandom bit stream; and said second block counter value is transmitted from said base station to said mobile station.

Claim 33

A radio communication system comprising a plurality of base stations operating on a plurality of communication channels, each of said base stations comprising: means for processing an information bit stream; means for generating a pseudorandom bit stream; means for combining said information bit stream with said pseudorandom bit stream to generate an encrypted data stream; means for transmitting said encrypted data stream over one of said communication channels; and means for transmitting an indication of whether said pseudorandom bit stream is synchronized to the pseudorandom bit stream generated in another base station for use in transmitting an encrypted data stream over another communication channel.

Claim 34

A radio communication system comprising a plurality of base stations operating on a plurality of communication channels, each of said base stations comprising: means for processing an information bit stream; means for generating a pseudorandom bit stream; means for combining said information bit stream with said pseudorandom bit stream to generate an encrypted data stream; means for transmitting said encrypted data stream over one of said communication channels; and means for transmitting an indication of whether said pseudorandom bit stream is synchronized to the pseudorandom bit stream generated in another base station for use in transmitting an encrypted data stream over another communication channel.

Claim 35

The system of claim 27 wherein said pseudorandom bit stream is generated as a function of a block counter value stored in the base station.

Claim 36

The system of claim 27 wherein said synchronization indication is sent to a mobile station which is switching to the other communication channel.

Claim 37

The system of claim 29 wherein said synchronization indication is sent in a handoff message transmitted to said mobile station.

Claim 38

A mobile station comprising: means for processing an information bit stream; means for generating a pseudorandom bit stream; means for combining said information bit stream with said pseudorandom bit stream to generate an encrypted data stream; means for transmitting said encrypted data stream over any one of a plurality of communication channels; means for receiving an indication of whether to resynchronize the generation of said pseudorandom bit stream upon switching transmission from one to another of said channels; and means for resynchronizing said pseudorandom bit stream in response to the receipt of an indication to resynchronize upon switching transmission between said channels.

Claim 39

A mobile station comprising: means for processing an information bit stream; means for generating a pseudorandom bit stream; means for combining said information bit stream with said pseudorandom bit stream to generate an encrypted data stream; means for transmitting said encrypted data stream over any one of a plurality of communication channels; means for receiving an indication of whether to resynchronize the generation of said pseudorandom bit stream upon switching transmission from one to another of said channels; and means for resynchronizing said pseudorandom bit stream in response to the receipt of an indication to resynchronize upon switching transmission between said channels.

Claim 40

The mobile station of claim 31 wherein said pseudorandom bit stream is generated as a function of a block counter value stored in said mobile station and resynchronized by resetting said block counter value.

Claim 41

The mobile station of claim 32 wherein said synchronization indication comprises a code which is selectively set to one of a plurality of values including: a first value which indicates that upon switching to the other channel said mobile station is to continue incrementing its block counter value and continue transmitting encrypted data on the other channel; a second value which indicates that upon switching to the other channel said mobile station is to inhibit transmission of any data until it receives a new block counter value whereupon it is to reset its block counter value to the received value, begin incrementing its block counter value, and begin transmitting encrypted data on the other channel; a third value which indicates that upon switching to the other channel said mobile station is to reset its block counter value to a predetermined value and to continue transmitting encrypted data without incrementing its block counter value until it receives a new block counter value whereupon it is to reset its block counter value to the received value, begin incrementing its block counter value, and continue transmitting encrypted data on the other channel; and a fourth value which indicates that upon switching to the other channel said mobile station is to transmit unencrypted data until it receives a new block counter value whereupon it is to reset its block counter value to the received value, begin incrementing its block counter value, and begin transmitting encrypted data.

Claim 42

The mobile station of claim 33 wherein said code is contained in an initial traffic channel designation (ITCD) message transmitted from a base station to said mobile station.

Claim 43

The mobile station of claim 33 wherein said code is contained in a handoff message transmitted from a base station to said mobile station.