Soft handoff in OFDMA system

• US 8,331,324 B2
• Filed: 08/30/2011
• Issued: 12/11/2012
• Est. Priority Date: 06/22/2004
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Ma, Jianglei, Tong, Wen, Jia, Ming, Zhu, Peiying, Fong, Mo-Han, Zhang, Hang
• Primary Examiner(s): Doan, Phuoc
• Application Number:
  US13/221,535
• Publication Number:
  US 20110310846A1
• Time in Patent Office: 469 Days
• Field of Search: 455/442, 370/331, 370/311, 370/480, 375/267
• US Class Current: 370/331
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0691 using subgroups of transmit antennas
• CPC Class Codes: H04W 36/00692 using simultaneous multiple data streams, e.g. cooperative multipoint [CoMP], carrier aggregation [CA] or multiple input multiple output [MIMO] allocation of physical resources in CoMP or in CA H04L5/0035
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

Soft handoff in an OFDMA system is disclosed. If the pilot signal strength for a base station exceeds the defined threshold, the base station is added to an active set list. Subcarriers in a plurality of orthogonal frequency division multiplexing (OFDM) symbols are divided and allocated into subchannels. The OFDM symbols are divided and multiplexed. A soft handoff zone with a first dimension of the subchannels and a second dimension of the divided and multiplexed OFDM symbols is defined. The soft handoff zone has subcarriers with a subchannel definition, for example, an identical permutation.

Claims

1. A method for receiving data by a subscriber station in an orthogonal frequency division multiplexing access (OFDMA) system comprising:

a) receiving and downconverting a plurality of orthogonal frequency division multiplexing (OFDM) symbols, said plurality of OFDM symbols comprising a first plurality of subcarriers, said first plurality of subcarriers being defined in a soft handoff zone comprising a first dimension of subchannels, said first dimension of subchannels comprising said first plurality of subcarriers; and

a second dimension of divided and multiplexed OFDM symbols;

said first plurality of subcarriers in said soft handoff zone having a subchannel definition;

b) providing a Fourier Transform (FT) on each of said first plurality of subcarriers to generate a plurality of divided-multiplexed coded signals; and

c) providing division-multiplexing decoding on the plurality of divided-multiplexed coded signals to recover data from a base station.

2. The method of claim 1, wherein said first plurality of subcarriers is divided in a frequency domain.

3. The method of claim 1, wherein said subchannel definition is identical for each of said first plurality of subcarriers.

4. The method of claim 1, wherein said subchannel definition is a subcarrier permutation.

5. The method of claim 1, wherein said first plurality of subcarriers is divided and multiplexed using time division multiplexing.

6. The method of claim 1, wherein receiving and downconverting the plurality of OFDM symbols further comprises receiving and downconverting the plurality of OFDM symbols via a plurality of antennas;

said plurality of antennas receiving the first plurality of subcarriers from a first base station and a second plurality of subcarriers from one or more second base stations, wherein said first plurality of subcarriers and said second plurality of subcarriers are in said soft handoff zone and form a macro-diversity transmission.

7. The method of claim 6, wherein said macro-diversity transmission is a multi-input multi-output (MIMO) transmission, and said first base station and said one or more than one second base stations provide a plurality of antennas to form an antenna pool.

8. The method of claim 6, wherein said received first plurality of subcarriers is different from said received second plurality of subcarriers.

9. The method of claim 6, wherein said received first plurality of subcarriers is identical to said received second plurality of subcarriers, and all or some antennas in said antenna pool transmit said subcarriers in a same data region, achieving a combination of radio frequency (RF) signals from said first base station and said one or more than one second base stations.

10. The method of claim 6, wherein said received first plurality of subcarriers is in a first data region, and wherein said received second plurality of subcarriers is transmitted through a second set of antennas in a second data region of a same size, wherein the first plurality of subcarriers and the second plurality of subcarriers are soft-combined to achieve diversity combining and soft combining gain.

11. The method of claim 6, wherein said received first plurality of subcarriers is transmitted through a first set of antennas in a first data region, and said received second plurality of subcarriers is transmitted through a second set of antennas in a second data region, wherein said first plurality of subcarriers and said second plurality of subcarriers are separately decoded to achieve data rate increase.