Cell extender with timing alignment for use in time division multiple-access and similar cellular telephone systems

• US 5,541,979 A
• Filed: 03/08/1994
• Issued: 07/30/1996
• Est. Priority Date: 03/08/1994
• Status: Expired due to Term

• Current Assignee: Allen Telecom LLC (CommScope Holding Company, Inc.)
• Original Assignee: Allen Telecom Group, Inc. (CommScope Holding Company, Inc.)
• Inventors: Leslie, Samuel A., Gordon, Robert T., Evans, Michael W.
• Primary Examiner(s): Coles, Sr,, Edward L.
• Assistant Examiner(s): LEE, CHEUKFAN
• Application Number:
  US08/207,879
• Time in Patent Office: 875 Days
• Field of Search: 379/59, 379/60, 379/63, 455/11.1, 455/15, 455/16, 455/33.1, 455/33.2, 455/56.1, 455/51.1, 370/95.3, 370/108, 370/95.1, 370/97, 370/103, 375/356
• US Class Current: 455/436
• CPC Class Codes: H04B 7/2606 Arrangements for base station coverage control, e.g. by using relays in tunnels
• CPC Class Codes: H04B 7/2609 Arrangements for range control, e.g. by using remote antennas
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 16/26 Cell enhancers or enhancement, e.g. for tunnels, building shadow
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time

Abstract

A cell extender for use in digital cellular telephone systems comprises a control module, and scanning module, and several traffic modules. The control module bidirectionally repeats the donor cell site control channels. Voice modules therein bidirectionally repeat selected donor traffic channels for mobiles. The voice module amplifies and translates the Reverse Digital Traffic Channel RDTC (transmitted by the mobile). The voice module reframes the Forward Digital Traffic Channel, and advances its timing such that RDTC signals transmitted by the mobile and repeated by the cell extender arrive at the donor with the correct timing alignment. The timing advance compensates for RF path propagation delay between the donor and the cell extender, and for any additional delay through the cell extender. If the voice module determines that the mobile is leaving the cell extender coverage area, it sends a hand-off message returning the mobile to the assigned donor traffic channel.

Claims

1. For use with digital cellular telephone systems having at least one cell site and at least one subscriber terminal, said subscriber terminal adapted to receive a first forward digital traffic channel from said cell site and to transmit a first reverse digital traffic channel to said cell site, said subscriber terminal being responsive to the time at which a predefined element of said first forward digital traffic channel arrives to establish the timing of its transmission of said first reverse digital traffic channel;

a cell extender comprising;

means for fixing a selected delay to which radio-frequency signals between said cell site and said cell extender are subject;

first receiving means for receiving a first forward digital traffic channel signal from said cell site;

first transmitting means for transmitting a second forward digital traffic channel signal to said subscriber terminal;

second receiving means for receiving a first reverse digital traffic channel signal from said subscriber terminal;

second transmitting means responsive to said second receiving means for transmitting a second reverse digital traffic channel signal to said cell site;

and timing means responsive to said first receiving means and said means for fixing a selected delay for controlling the time at which said second forward digital traffic channel signal is transmitted to said subscriber terminal by said cell extender;

whereby a predefined element of said second reverse digital traffic channel signal arrives at said cell site at a predetermined shifted time.

2. The cell extender of claim 1 further comprising means for storing at least a portion of said first forward digital traffic channel signal received from said cell site.

3. The cell extender of claim 2 wherein said first transmitting means further comprises means for formatting said second forward digital traffic channel signal;

said formatting means being responsive to said storage means to include at least a part of said stored portion of said first forward digital traffic channel signal in said second forward digital traffic channel signal.

4. The cell extender of claim 1 wherein:

each of said digital traffic channels is formed as a periodically adjacent series of information frames;

each of said information frames is formed from a predefined number of periodically adjacent information slots having a predefined slot period; and

information corresponding to said subscriber terminal occupies at least one slot in each of said information frames of said received first forward digital traffic channel signal; and

said first transmitting means is responsive to said timing means for transmitting said information on said second forward digital traffic channel signal after a delay at least as long as said predefined slot period.

5. For use with digital cellular telephone systems having at least one cell site and at least one subscriber terminal, said subscriber terminal adapted to receive a first forward digital traffic channel from said cell site and to transmit a first reverse digital traffic channel to said cell site, said subscriber terminal being responsive to the time at which a predefined element of said first forward digital traffic channel arrives to establish the timing of its transmission of said first reverse digital traffic channel;

a cell extender comprising;

means for fixing a selected delay substantially corresponding to a radio-frequency propagation delay to which radio-frequency signals between said cell site and said cell extender are subject;

first receiving means for receiving a first forward digital traffic channel signal from said cell site;

first transmitting means for transmitting a second forward digital traffic channel signal to said subscriber terminal;

second receiving means for receiving a first reverse digital traffic channel signal from said subscriber terminal;

second transmitting means responsive to said second receiving means for transmitting a second reverse digital traffic channel signal to said cell site;

said first forward digital traffic channel signal and said second reverse digital traffic channel signal each experiencing a propagation delay between said cell extender and said cell site;

said second forward digital traffic channel having a timing alignment offset with respect to said first forward digital traffic channel;

and propagation delay compensation means for adjusting said timing alignment offset such that the effects of said propagation delay are minimized.

6. For use with digital cellular telephone systems having at least one cell site and at least one subscriber terminal, said subscriber terminal adapted to communicate with said cell site using digital messages using at least one traffic channel, said subscriber terminal receiving from said cell site an information signal having a predefined timing alignment;

a cell extender comprising;

receiver means for scanning a plurality of traffic channels assigned for use by said cell site;

activity detecting means for determining whether each of said traffic channels is in use to provide communications between said cell site and said subscriber terminal;

coverage detecting means responsive to said activity detecting means for determining, for each active traffic channel, whether the subscriber terminal using said traffic channel is within a predefined coverage region for said cell extender;

means responsive to said coverage detecting means for generating and transmitting a digital message to instruct said subscriber terminal to cease operating on said active traffic channel and to begin operating on a different traffic channel assigned for use by said cell extender;

and timing alignment means for controlling the time at which said digital message is transmitted to said subscriber terminal such that said message is actually received by said subscriber terminal with a timing alignment substantially identical to that of said cell site information signal.

7. The cell extender of claim 6 further comprising means for measuring the strength of a signal received from said subscriber terminal and wherein said coverage detecting means is responsive to said measuring means.

8. The cell extender of claim 6 further comprising means for determining approximately the distance between said subscriber terminal and said cell extender;

and wherein said coverage detecting means is responsive to said distance determining means.

9. The cell extender of claim 6 further comprising means for receiving information transmitted by said subscriber terminal relating to a measurement of the strength of a signal received by said subscriber terminal from said cell extender;

and wherein said coverage detecting means is responsive to said information.

10. The cell extender of claim 6 further comprising means for receiving information transmitted by said subscriber terminal relating to a measurement of the strength of a signal received by said subscriber terminal from said cell site;

and wherein said coverage detecting means is responsive to said information.

11. The cell extender of claim 6 further comprising means for measuring the strength of a signal received from said subscriber terminal and wherein said timing alignment means is responsive to said measuring means.

12. The cell extender of claim 6 further comprising means for determining approximately the distance between said subscriber terminal and said cell extender;

and wherein said timing alignment means is responsive to said distance determining means.

13. The cell extender of claim 6 further comprising means for receiving information transmitted by said subscriber terminal relating to a measurement of the strength of a signal received by said subscriber terminal from said cell extender;

and wherein said timing alignment means is responsive to said information.

14. The cell extender of claim 6 further comprising means for receiving information transmitted by said subscriber terminal relating to a measurement of the strength of a signal received by said subscriber terminal from said cell site;

and wherein said timing alignment means is responsive to said information.

15. The cell extender of claim 14 further comprising means for comparing the relative timing synchronization between a signal received from said base site and a signal received from said subscriber terminal;

and wherein said timing alignment means is responsive to said information.

16. A method of handing off a mobile radio telephone unit communicating on a donor site channel and under the control of and in direct communication with a donor site, said mobile unit receiving from said donor site an information signal having a predefined timing alignment, to a cell extender so that the mobile unit will communicate on a cell extender channel and will be under the control of and in direct communication with a cell extender, said mobile being responsive to messages from said cell extender exclusively during predefined time intervals within cyclically occurring time frames, comprising the steps of:

determining whether the mobile unit is a candidate for hand-off to, and control by, a cell extender by (1) measuring the strength of a mobile unit signal between the mobile unit and the donor site, and (2) when available, also examining signal strength measurements provided by the mobile unit for the donor site and for the cell extender;

generating a hand-off message instructing the mobile unit to use a cell extender channel; and

in response to the determining step, sending said hand-off message to said mobile unit from said cell extender, the timing of transmission of said message being arranged such that said message arrives at said mobile unit within one of said predefined time intervals, said message being received by said mobile unit with a timing alignment substantially identical to that of said donor site information signal.

17. The method of claim 16 wherein the message sending step further comprises the step of controlling the timing of said transmission of said message such that the beginning of said message arrives at said mobile unit aligned within one-quarter symbol of the beginning of said one predefined time interval.

18. For use in a cellular telephone system having at least one donor cell, at least one subscriber terminal, and at least one additional device;

said subscriber terminal being in direct communication with a donor cell over a radio channel assigned to said donor cell;

said subscriber terminal being under control of said donor cell;

said subscriber terminal receiving from said donor cell an information signal having a predefined timing alignment;

a method for instructing said subscriber terminal to begin communications over a different radio channel comprising the steps of;

determining whether the subscriber terminal is a candidate for using said different radio channel;

generating a message instructing the subscriber terminal to use said different radio channel; and

transmitting said message from said additional device to said subscriber terminal at a selected time such that said message is received by said subscriber terminal with a timing alignment substantially identical to that of said donor cell information signal.

19. The method of claim 18, wherein said determining step further comprises the steps of:

(1) measuring the strength of a signal transmitted by said subscriber terminal; and

(2) comparing measurements by said subscriber terminal of a signal transmitted by said donor cell and a signal transmitted by said additional device, when such measurements are available.

20. The method of claim 19, wherein said determining step further comprises the step of:

determining that said subscriber terminal is a candidate for using said different radio channel if the measured strength of the signal transmitted by the subscriber terminal exceeds a predetermined threshold.

21. The method of claim 19, wherein said determining step further comprises the step of:

determining that said subscriber terminal is a candidate for using said different radio channel if the measurements by said subscriber terminal indicate that the signal transmitted by said additional device is stronger than the signal transmitted by said donor cell.

22. The method of claim 18 wherein said transmitting step further comprises the step of:

comparing the timing of a signal received from said subscriber terminal with the timing of a signal received from said donor cell.

23. The method of claim 18 wherein said transmitting step further comprises the steps of:

measuring a difference in timing between a signal received from said subscriber terminal with the timing of a signal received from said donor cell; and

adjusting the time at which said signal is transmitted responsive to said measured timing difference.

24. The method of claim 18 wherein said transmitting step further comprises the steps of:

measuring a difference in timing between a signal received from said subscriber terminal with the timing of a signal received from said donor cell;

obtaining a timing parameter responsive to a known radio-frequency propagation delay between said donor cell and said additional device; and

adjusting the time at which said signal is transmitted responsive to said measured timing difference and said timing parameter.

25. For use in a radio system having at least one control station, at least one user station, and at least one auxiliary station;

said user station being in direct communication with said control station over a radio channel assigned to said control station;

said user station being under the control of said control station;

said user station receiving from said control station an information signal having a predefined timing alignment;

a method for instructing said user station to begin communications over a different radio channel comprising the steps of;

determining whether the user station is a candidate for using said different radio channel;

generating a message instructing the user station to use said different radio channel; and

transmitting said message from said auxiliary station to said user station at a selected time such that said message is received by said user station with a timing alignment substantially identical to that of said control station information signal.

26. The method of claim 25, wherein said determining step further comprises the steps of:

(1) measuring the strength of a signal transmitted by said user station; and

(2) comparing measurements by said user station of a signal transmitted by said control station and a signal transmitted by said auxiliary station, when such measurements are available.

27. The method of claim 26, wherein said determining step further comprises the step of:

determining that said user station is a candidate for using said different radio channel if the measured strength of the signal transmitted by the user station exceeds a predetermined threshold.

28. The method of claim 26, wherein said determining step further comprises the step of:

determining that said user station is a candidate for using said different radio channel if the measurements by said user station indicate that the signal transmitted by said auxiliary station is stronger then the signal transmitted by said control station.

29. The method of claim 25 wherein said transmitting step further comprises the step of:

comparing the timing of a signal received from said user station with the timing of a signal received from said control station.

30. The method of claim 25 wherein said transmitting step further comprises the steps of:

measuring a difference in timing between a signal received from said user station with the timing of a signal received from said control station; and

adjusting the time at which said signal is transmitted responsive to said measured timing difference.

31. The method of claim 25 wherein said transmitting step further comprises the steps of:

measuring a difference in timing between a signal received from said user station with the timing of a signal received from said control station;

obtaining a timing parameter responsive to a known radio-frequency propagation delay between said control station and said auxiliary station; and

adjusting the time at which said signal is transmitted responsive to said measured timing difference and said timing parameter.

32. For use by an auxiliary station in a radio system having at least one control station and at least one user station;

said user station being in direct communication with said control station over a radio channel assigned to said control station;

said user station being under control of said control station;

said user station receiving from said control station an information signal;

said user station being receptive to control information included in said information signal at a predefined time;

a method for capturing control of said user station comprising the steps of;

determining whether the user station is a candidate for capture;

said auxiliary station generating a message instructing the user station to begin receiving control information from said auxiliary station; and

said auxiliary station transmitting said message on said radio channel to said user station at a selected time such that said message is received by said user station at said predefined time and with adequate signal strength to substantially replace said control station information signal.

33. In a method for operating a digital cellular telephone system having at least one cell site, at least one cell extender, and at least one subscriber terminal in which said subscriber terminal is adapted to receive a first forward digital traffic channel from said cell site and to transmit a first reverse digital traffic channel to said cell site, said subscriber terminal being responsive to the time at which a predefined element of said first forward digital traffic channel arrives to establish the timing of its transmission of said first reverse digital traffic channel;

the steps comprising;

fixing a selected delay to which radio-frequency signals between said cell site and said cell extender are subject;

receiving a first forward digital traffic channel signal from said cell site;

transmitting a second forward digital traffic channel signal to said subscriber terminal;

receiving a first reverse digital traffic channel signal from said subscriber terminal;

in response to receipt of said first reverse digital traffic channel signal, transmitting a second reverse digital traffic channel signal to said cell site;

controlling the time an which said second forward digital traffic channel signal is transmitted to said subscriber terminal by said cell extender in response to said receipt of the first forward digital traffic channel signal from the cell site and to said selected delay,

whereby a predefined element of said second reverse digital traffic channel signal arrives at said cell site at a predetermined shifted time.

34. In a method for operating a digital cellular telephone system having at least one cell site, at least one cell extender, and at least one subscriber terminal in which said subscriber terminal is adapted to receive a first forward digital traffic channel from said cell site and to transmit a first reverse digital traffic channel to said cell site, and in which said subscriber terminal is responsive to the time at which a predefined element of said first forward digital traffic channel arrives to establish the timing of its transmission of said first reverse digital traffic channel;

comprising the steps of;

fixing a selected delay substantially corresponding to a radio-frequency propagation delay to which radiofrequency signals between said cell site and said cell extender are subject;

receiving a first forward digital traffic channel signal from said cell site;

transmitting a second forward digital traffic channel signal to said subscriber terminal, said transmission subject to a timing alignment offset with respect to said first forward digital traffic channel;

receiving a first reverse digital traffic channel signal from said subscriber terminal;

transmitting a second reverse digital traffic channel signal to said cell site responsive to receipt of said first reverse digital traffic channel signal; and

adjusting said timing alignment offset such that the effects of propagation delay experienced by said first forward digital traffic channel signal and said second reverse digital traffic channel signal during transit between said cell extender and said cell site are minimized.

35. In a method for controlling a digital cellular telephone system having at least one cell site, at least one cell extender, and at least one subscriber terminal in which said subscriber terminal is adapted to communicate with said cell site using digital messages over at least one traffic channel, said subscriber terminal receiving from said cell site an information signal having a predefined timing alignment;

the method comprising the steps of;

scanning a plurality of traffic channels assigned for use by said cell site;

evaluating whether each of said traffic channels is being used to provide communications between said cell site and said subscriber terminal;

responsive to said evaluating step, determining for each active traffic channel whether the subscriber terminal using said traffic channel is within a predefined coverage region for said cell extender;

responsive to said coverage determining step, generating and transmitting a digital message to instruct said subscriber terminal to cease operating on said active traffic channel and to begin operating on a different traffic channel assigned for use by said cell extender; and

controlling the time at which said digital message is transmitted to said subscriber terminal such that said message is actually received by said subscriber terminal with a timing alignment substantially identical to that of said cell site information signal.

36. In a cell extender for use in a digital cellular telephone system having at least one cell site and at least one subscriber terminal, said cell site being receptive to signals from said subscriber terminal only during predefined time slot intervals of cyclically recurring transmission frames, the method of controlling the relative timing of said signals received by said cell site from said subscriber terminal with respect to said intervals comprising the steps of:

providing said cell extender with a timing parameter corresponding to the known propagation delay of radio-frequency signals traveling between said cell site and said cell extender;

said cell extender applying a timing advance corresponding to said timing parameter to the transmissions of said cell extender to said subscriber terminal to compensate for said known propagation delay; and

said subscriber terminal timing its transmissions responsive to its observations of the transmissions of said cell extender such that said subscriber terminal transmissions arrive at said cell site during said predefined time slot intervals.

37. For use with digital-capable cellular telephone system having a cell extender, at least one cell site associated with said cell extender, and at least one subscriber terminal, said cell site being allocated a first set of channels, said cell extender being allocated a second set of channels, the method of enabling a subscriber terminal located within a predefined coverage area of said cell extender to engage in a telephone call through said cell site with said cell extender acting as a communications intermediary comprising the steps of:

said cell extender obtaining a timing adjustment parameter;

said cell extender observing a signal transmitted by said subscriber terminal to detect attempts by said subscriber terminal to begin a call;

said cell extender determining whether said subscriber terminal is capable of operating on a digital channel;

said cell extender observing a signal transmitted by said cell site to detect an instruction in said signal to assign said subscriber terminal to use one of said channels allocated to said cell site;

said cell extender translating said instruction to reassign said subscriber terminal to use one said channels allocated to said cell extender; and

said cell extender adjusting the timing of a signal transmitted to said subscriber terminal with respect to a signal received from said cell site according to said timing adjustment parameter.

38. The method of claim 37 further comprising the steps of:

said cell site measuring the timing of a signal transmitted by said subscriber unit retransmitted by said cell extender, with respect to signals transmitted by said cell extender;

said cell site transmitting an instruction to said subscriber unit to alter the timing of signals transmitted by said subscriber unit to arrive at said cell site within a desired timing interval.

39. The method of claim 37 wherein the step of said cell extender obtaining a timing adjustment parameter comprises the step of:

said cell extender obtaining a first timing advance parameter associated with a known distance between said cell extender and said cell site.

40. The method of claim 37 wherein the step of said cell extender obtaining a timing adjustment parameter comprises the step of:

said cell extender obtaining a second timing advance parameter corresponding to an estimated distance between said subscriber terminal and said cell extender, said estimated distance being a function of a measured strength of a signal transmitted by said subscriber terminal.

41. For use in a digital-capable cellular telephone system comprising at least one cell site;

a cell extender associated with the cell site; and

at least one subscriber terminal;

the cell extender acting as a communications intermediary between the cell site and the subscriber terminal during a call;

the cell site transmitting forward traffic on a first channel;

the cell extender receiving the forward traffic on the first channel and retransmitting it on a second channel;

the subscriber terminal receiving the forward traffic on the second channel;

the subscriber terminal transmitting reverse traffic on a third channel;

the cell extender receiving the reverse traffic on the third channel and retransmitting it on a fourth channel;

the cell site receiving the reverse traffic on the fourth channel;

the cell site transmitting information destined for the subscriber terminal only during predefined time slots assigned to that subscriber terminal within cyclically occurring transmit timing frames;

the cell site receptive to information from the subscriber terminal only during corresponding time slots assigned to said subscriber terminal within cyclically occurring receive timing frames;

the subscriber terminal timing its transmissions of reverse traffic responsive to the timing of the forward traffic as received thereby;

the method of controlling the cell extender comprising the steps of;

adjusting the timing of said cell extender transmissions on said second channel with respect to the timing of said cell site transmissions on said first channel by;

determining an effective additional propagation delay caused by the operation of said cell extender as a communications intermediary between said cell site and said subscriber terminal;

applying an effective timing advance to said cell extender transmissions on said second channel with respect to the timing of said cell site transmissions on said first channel to negate said effective additional propagation delay;

such that said reverse traffic transmitted by said subscriber terminal and retransmitted by said cell extender actually arrives at said cell site during said corresponding time slots.

42. For use in a digital-capable cellular telephone system comprising at least one cell site;

a cell extender associated with the cell site; and

at least one subscriber terminal;

the cell extender acting as a communications intermediary between the cell site and the subscriber terminal during a call;

the cell site transmitting forward traffic on a first channel;

the cell extender receiving the forward traffic on the first channel and retransmitting it on a second channel;

the subscriber terminal receiving the forward traffic on the second channel;

the subscriber terminal transmitting reverse traffic on a third channel;

the cell extender receiving the reverse traffic on the third channel and retransmitting it on a fourth channel;

the cell site receiving the reverse traffic on the fourth channel;

the cell site transmitting information destined for the subscriber terminal only during predefined time slots assigned to that subscriber terminal within cyclically occurring transmit timing frames;

the cell site receptive to information from the subscriber terminal only during corresponding time slots assigned to said subscriber terminal within cyclically occurring receive timing frames;

the subscriber terminal timing its transmissions of reverse traffic responsive to the timing of the forward traffic as received thereby;

the method of controlling the cell extender comprising the steps of;

adjusting the timing of said cell extender transmissions on said second channel with respect to the timing of said cell site transmissions on said first channel by;

determining a first delay parameter corresponding to an RF path propagation delay associated with the distance between said cell site and said cell extender;

determining a second delay parameter corresponding to an RF path propagation delay associated with an estimated distance between said cell extender and said subscriber terminal; and

applying an effective timing advance to said cell extender transmissions on said second channel with respect to the timing of said cell site transmissions on said first channel, said timing advance being responsive to said first and second delay parameters;

such that said reverse traffic transmitted by said subscriber terminal and retransmitted by said cell extender actually arrives at said cell site during said corresponding time slots.

43. The method of claim 42, wherein said step of applying an effective timing advance to said cell extender transmissions further comprises the step of delaying said cell extender transmissions on said second channel by an amount equivalent to the time between said predefined time slots less said timing advance to cause said reverse traffic transmission intended by said subscriber terminal to arrive at said cell site aligned with a particular corresponding time slot to actually arrive at said cell site aligned with a later time slot assigned to said subscriber terminal.