Method and apparatus for providing diversity in hard handoff for a CDMA system

• US 5,926,470 A
• Filed: 05/22/1996
• Issued: 07/20/1999
• Est. Priority Date: 05/22/1996
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tiedemann, Edward G. Jr.
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): NGO, RICKY QUOC
• Application Number:
  US08/651,430
• Time in Patent Office: 1,154 Days
• Field of Search: 370/328, 370/331, 370/332, 370/334, 370/335, 370/342, 370/441, 375/346, 375/347, 375/200, 455/436, 455/437, 455/504, 455/561, 455/562, 455/101, 455/65
• US Class Current: 370/334
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/2606 Arrangements for base station coverage control, e.g. by using relays in tunnels
• CPC Class Codes: H04W 16/26 Cell enhancers or enhancement, e.g. for tunnels, building shadow
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 52/0203 in the radio access network or backbone network of wireless communication networks
• CPC Class Codes: H04W 52/16 Deriving transmission power values from another channel
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

In a communications network, a network user communicates using a remote unit with another user via at least one base station. The communications network has a first base station having a first coverage area and a second base station having a second coverage area. In the situation where communication is not established between the second base station and the remote unit, in order to provide communication between the remote unit and the first base station when the remote unit is in the first coverage and simultaneously in the second coverage area, the first base station produces a first active communication signal at intended for the remote unit. The first base station transmits the first active communication signal from a first antenna. The base station delays the first active communication signal to produce a first delayed active communication signal and transmits it from a second antenna wherein the second antenna is oriented with respect to the first antenna such that the first active communication signal and the first delayed active communication signal fade independently as perceived by the remote unit. The first base station may measures a round trip delay of the first active communication signal in order to identify that the remote unit is located within the second coverage area.

Claims

1. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said communications network including a first base station having a first coverage area and a second base station having a second coverage area, the method providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit, wherein said first active communication signal is a spread spectrum signal which is spread with a series of pseudorandom noise chips each chip of which has a fixed duration;

transmitting from said first base station said first active communication signal from a first antenna;

delaying said first active communication signal to produce a first delayed active communication signal, said first active communication signal delayed by at least said fixed duration;

transmitting from said first base station said first delayed active communication signal from a second antenna wherein said second antenna is configured such that said first active communication signal and said first delayed active communication signal fade differently as perceived by said remote unit;

producing a second set of active communication signals at said second base station; and

transmitting from said second base station said second set of active communication signals;

transmitting said first active communication signal at an increased level compared to a set of other active signals transmitted from said first antenna because said remote unit is located in said second coverage area.

2. The method of claim 1 further comprising measuring at said first base station a round trip delay of said first active communication signal in order to identify that said remote unit is located in said second coverage area.

3. The method of claim 1 further comprising:

measuring at said remote unit a signal level of said first active communication signal;

reporting by said remote unit said signal level to said first base station; and

determining from said signal level that said remote unit is located in said second coverage area.

4. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said communications network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said first active communication signal from a first antenna, said first active communication signal transmitted at an increased level compared to a set of other active signals transmitted from said first antenna because said remote unit is located in said second coverage area;

transmitting from said first base station said first active communication signal from a second antenna;

coupling together said first and second antennas to create said first coverage area;

changing over time the phase of said second antenna relative to the phase of a first antenna at a rate sufficient to reduce a signal fading loss perceived by said remote unit;

producing a second set of active communication signals at said second base station; and

transmitting from said second base station said second set of active communication signals.

5. The method of claim 4 further comprising measuring at said first base station a round trip delay of said first active communication signal in order to identify that said remote unit is located in said second coverage area.

6. The method of claim 4 further comprising

measuring at said remote unit a signal level of said first active communication signal;

reporting by said remote unit said signal level to said first base station; and

determining from said signal level that said remote unit is located in said second coverage area.

7. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said communications network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said first active communication signal from a first antenna;

transmitting from said first base station said first active communication signal, a page and sync channel signal, and a pilot signal from a second antenna;

coupling together said first and second antennas to create said first coverage area;

changing over time the phase of said second antenna relative to the phase of a first antenna at a rate sufficient to reduce a signal fading loss perceived by said remote unit;

producing a second set of active communication signals at said second base station; and

transmitting from said second base station said second set of active communication signals at a substantially different power level from the power level at which the first active communication signal is transmitted.

8. The method of claim 7 further comprising transmitting said pilot signal from said second antenna at a different PN offset than a first pilot signal transmitted from said first antenna.

9. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit, wherein said first active communication signal is a spread spectrum signal which is spread with a series of pseudorandom noise chips, each chip of which has a fixed duration;

transmitting from said first base station said first active communication signal from a first antenna;

producing a second active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said second active communication signal from a second antenna wherein said second antenna is such that said first active communication signal and said second active communication signal fade independently as perceived by said remote unit and are separately receivable by said remote unit, and wherein said first and second active signals are separately receivable by said remote unit because said second active signal is offset in time from said first active signal by at least said fixed duration;

producing a set of active communication signals at said second base station none of which are intended for said remote unit; and

transmitting from said second base station said set of active communication signals.

10. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said first active communication signal from a first antenna;

producing a second active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said second active communication signal from a second antenna wherein said second antenna is such that said first active communication signal and said second active communication signal fade independently as perceived by said remote unit and are separately receivable by said remote unit, said second active communication signal transmitted because said remote unit is located in said second coverage area, wherein a round trip delay of said first active communication signal is measured at said first base station in order to identify that said remote unit is located in said second coverage area;

producing a set of active communication signals at said second base station none of which are intended for said remote unit; and

transmitting from said second base station said set of active communication signals.

11. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said first active communication signal from a first antenna;

producing a second active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said second active communication signal from a second antenna wherein said second antenna is such that said first active communication signal and said second active communication signal fade independently as perceived by said remote unit and are separately receivable by said remote unit said second active communication signal transmitted because said remote unit is located in said second coverage area;

measuring at said remote unit a signal level of said first active communication signal;

reporting by said remote unit said signal level to said first base station in order to identify that said remote unit is located in said second coverage area;

producing a set of active communication signals at said second base station none of which are intended for said remote unit; and

transmitting from said second base station said set of active communication signals.

12. A method for a communications network in which a network user communicates using a remote unit with another user via at least one base station, said network including a first base station having a first coverage area and a second base station having a second coverage area, a method for providing communications between said remote unit and said first base station when said remote unit is in said first coverage and simultaneously in said second coverage area and wherein communication is not established between said second base station and said remote unit, comprising the steps of:

producing a first active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said first active communication signal from a first antenna;

producing a second active communication signal at said first base station intended for said remote unit;

transmitting from said first base station said second active communication signal, a pilot signal, a page and sync channel signal from a second antenna wherein said second antenna is such that said first active communication signal and said second active communication signal fade independently as perceived by said remote unit and are separately receivable by said remote unit;

producing a set of active communication signals at said second base station none of which are intended for said remote unit; and

transmitting from said second base station said set of active communication signals.

13. The method of claim 12 wherein said pilot signal transmitted from said second antenna has a different PN offset than a first pilot signal transmitted from said first antenna.