Terminal control device and method for soft-handoff between terminals having different frequencies

• US 6,353,603 B1
• Filed: 07/22/1998
• Issued: 03/05/2002
• Est. Priority Date: 07/22/1998
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Joon-Lae
• Primary Examiner(s): Nguyen, Chau
• Assistant Examiner(s): TRAN, THIEN D
• Application Number:
  US09/120,921
• Time in Patent Office: 1,322 Days
• Field of Search: 370/331, 370/332, 370/334, 370/349, 370/335, 370/342, 455/436, 455/437, 455/439, 455/438, 455/442, 455/443, 455/525
• US Class Current: 370/335
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

An apparatus and method for providing a soft handoff between base stations using different operating frequencies. The apparatus includes a RAKE receiver having a plurality of main paths and an extra path, a first local oscillator for the main paths and a second local oscillator for the extra path. When the apparatus is located between two base stations using the different frequencies, both the first and second local oscillators are enabled and communication with the target base station is established using a demodulation signal output from the extra path. Thereafter, as the apparatus moves into coverage of a target base station, the oscillation frequency of the first local oscillator is adjusted for the frequency of the target base station. Upon stabilization of the first local oscillator, the extra path is disabled and communication with the target base station is established using modulation signals output from the main paths of the RAKE receiver.

Claims

1. An apparatus for providing soft handoff between a source base station using a first operating frequency signal in a first coverage area and a target base station using a second operating frequency signal in a second coverage area, wherein a portion of said first area and a portion of said second area overlap to form a common coverage area, said apparatus comprising:

first demodulating means for demodulating said first operating frequency signal of said source base station when said apparatus is located in one of said first coverage area and said common area, and for demodulating said second operating frequency signal of said target base station when said apparatus is located in said second coverage area;

second demodulating means for demodulating said second operating frequency of said target base station when said apparatus is located in said common area; and

processing means for simultaneously processing said demodulated first frequency and said demodulated second frequency when said apparatus is located in said common area.

2. The apparatus of claim 1, further comprising:

controlling means for controlling said first demodulation means, said second demodulating means and said processing means, such that when said apparatus moves into said second coverage area of said target base station from said common area, said controlling means disables said second demodulating means and causes said first demodulating means to demodulate said second operating frequency of said target base station and causes said processing means to process said demodulated second operating frequency of said target base station.

3. The apparatus of claim 1, wherein said first demodulation means comprises:

a first local oscillator for generating a first local oscillation signal;

a first mixer for mixing said first local oscillation signal with said first operating frequency signal of said source base station when said apparatus is located in one of said first coverage area and said common area, and mixing said first local oscillation signal with said second operating frequency signal of said target base station when said apparatus is located in said second coverage area;

a second local oscillator for generating a second local oscillation signal; and

a second mixer for mixing a signal output from said first mixer with said second local oscillation signal.

4. The apparatus of claim 3, wherein said second demodulation means comprises:

a third local oscillator for generating a third local oscillation signal;

a third mixer for mixing said third local oscillation signal with said second operating frequency signal of said target base station when said apparatus is located in said common area; and

a fourth mixer for mixing an output signal of said third mixer with said second local oscillation signal.

5. The apparatus of claim 2, wherein said processing means comprises:

a RAKE receiver having a plurality of main paths each receiving said demodulated signal from said first demodulating means, and an extra path for receiving said demodulated signal from said second demodulating means; and

a combiner, operatively connected to said RAKE receiver and having an output node associated therewith, for independently providing signals input from each of said plurality of main paths and said extra path to said output node; and

a decoder, operatively connected to said output node of said combiner, for decoding said signals provided by said combiner, whereby said controlling means enables said extra path when said apparatus moves into said common area and disables said extra path when said apparatus is one of located in said first coverage area and moves into said second coverage area from said common area.

6. An apparatus for controlling soft handoff between a source base station generating a first operating frequency signal and a target base station generating a second operating frequency signal, comprising:

a first local oscillator for generating a first local oscillation signal;

a first mixer for mixing said first and second operating frequency signals with said first local oscillation signal;

a second local oscillator for generating a second local oscillation signal;

a second mixer for mixing a signal output from the first mixer with said second local oscillation signal;

a third local oscillator for generating a third local oscillation signal;

a third mixer for mixing said first and second operating frequency signals with said third local oscillation signal;

a fourth mixer for mixing an output signal of said third mixer with said second local oscillation signal;

a RAKE receiver having a plurality of main paths for receiving an output signal of said second mixer, an extra path for receiving an output signal of said fourth mixer, and a combiner for independently providing said signals provided to said main paths and said extra path to an output node thereof;

a decoder for decoding a signal output from said combiner; and

a controller for controlling said first and third local oscillators, said RAKE receiver and said decoding means, such that when said apparatus moves from an operating area covered by said source base station into an operating area covered by both said source base station and said target base station, said controller causes said first local oscillator to generate said first local oscillation signal to demodulate said first operating frequency signal, enables said third local oscillator to generate said third local oscillation signal to demodulate said second operating frequency, enables said extra path for receiving said signal from said fourth mixer, and commands said combiner to receive a demodulation signal output from said extra path thereby allowing said apparatus to simultaneously process said first and second operating frequency signals from said source and target bases station, respectively.

7. The apparatus of claim 6, wherein when said apparatus moves from said operating area covered by both said source and target base stations to an operating area covered by said target base station, said controller causes said first local oscillator to adjust said first oscillation signal to demodulate said second operating frequency signal of said target base station and, upon stabilization of said adjusted first local oscillator, disables said extra path and commands said combiner to receive demodulation signals output from said plurality of main paths.

8. In a portable terminal having a first demodulating means, a second demodulating means, and a RAKE receiver having a plurality of paths, a method for controlling a soft handoff between a source base station generating a first operating frequency signal and a target base station generating a second operating frequency signal, comprising the steps of:

simultaneously enabling said first and second demodulating means, when said portable terminal moves into an operating area that is covered by both the source base station and the target base station, such that said first demodulation means is adapted to demodulate said first operating frequency signal of said source base station and said second demodulating means is adapted to demodulate said second operating frequency signal of said target base station;

simultaneously processing said demodulated first operating frequency signal and said demodulated second operating frequency signal;

adjusting said first demodulating means to demodulate said second operating frequency signal of said target base station when said portable terminal moves into an operating area covered by said the target base station; and

processing said demodulated second operating frequency of said target base station after said adjustment of said first demodulating means.

9. The method of claim 8, wherein the step of simultaneously processing includes the substep of:

providing said demodulated first operating frequency signal to a set of main paths of said plurality of paths of said RAKE receiver and providing said demodulated second operating frequency signal to an extra path of said plurality of paths of said RAKE receiver such that said demodulated first and second operating frequency signals can be processed independently of eachother.

10. The method of claim 8, wherein said step of processing said demodulated second operating frequency of said target base station after said adjustment of said first demodulating means comprises the substeps of:

disabling said extra path of said RAKE receiver; and

providing said demodulated second operating frequency signal of said target base station from said first demodulation means to said main paths of said RAKE receiver, such that communication with said target base station is achieved by processing said demodulation signals output from said main paths.