SOFT HANDOFF IN OFDMA SYSTEM

• US 20110310848A1
• Filed: 08/30/2011
• Published: 12/22/2011
• Est. Priority Date: 06/22/2004
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Rockstar Bidco LP (Rockstar Consortium Inc.)
• Inventors: Ma, Jianglei, Tong, Wen, Jia, Ming, Zhu, Peiying, Fong, Mo-Han, Zhang, Hang
• Granted Patent: US 8,165,094 B2
• Time in Patent Office: Days
• 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

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. An orthogonal frequency division multiplexing access (OFDMA) system comprising:

a) a base station controller adapted to schedule data for a subscriber station during a soft handoff;

b) a plurality of base stations operatively associated with said base station controller, each base station participating in said soft handoff being adapted to receive at least a portion of the scheduled data from said base station controller, and to transmit a first plurality of subcarriers to said subscriber station;

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 divided in a frequency domain; and

a second dimension of divided and multiplexed orthogonal frequency division multiplexing (OFDM) symbols comprising said first plurality of subcarriers;

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

2. The OFDMA system according to claim 1, wherein said subchannel definition is identical for each of said first plurality of subcarriers.

3. The OFDMA system according to claim 1, wherein said subchannel definition is a subcarrier permutation.

4. The OFDMA system according to claim 1, wherein a first base station of said plurality of base stations transmits said first plurality of subcarriers, and one or more than one second base stations of said plurality of base stations transmits a second plurality of subcarriers in said soft handoff zone to said subscriber station concurrently, said first base station and said one or more than one second base stations forming a macro-diversity transmission.

5. The OFDMA system according to claim 4, wherein radio frequency (RF) signals from said macro-diversity transmission from said first base station and said one or more than one second base stations are combined at said subscriber station.

6. The OFDMA system according to claim 5, wherein said RF signals from said macro-diversity transmission from said first base station and said one or more than one second base stations are demodulated separately, and received data is combined at Log Likelihood Ratio (LLR) level at said subscriber station.

7. The OFDMA system according to claim 4, wherein said macro-diversity transmission is a multi-input multi-output (MIMO) transmission, and wherein 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 OFDMA system according to claim 7, wherein said first plurality of subcarriers and said second plurality of subcarriers are identical, and all or some antennas in said antenna pool transmit said subcarriers in a same data region, and wherein radio frequency (RF) signals from said first base station and said one or more than one second base stations are combined at the subscriber station.

9. The OFDMA system according to claim 7, wherein said first plurality of subcarriers is transmitted through a first set of antennas in a first data region, and said second plurality of subcarriers is transmitted through a second set of antennas in a second data region of a same size, wherein said first plurality of subcarriers and said second plurality of subcarriers are soft-combined to achieve diversity combining and soft combining gain.

10. The OFDMA system according to claim 7, wherein the first plurality of subcarriers is transmitted through a first set of antennas in a first data region, and the 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.

11. The OFDMA system according to claim 4, wherein said first plurality of subcarriers transmitted between said first base station and said subscriber station is different from said second plurality of subcarriers transmitted between said one or more than one second base stations and said subscriber station, thus achieving higher throughput.

12. The OFDMA system according to claim 1, wherein said first plurality of subcarriers is divided and multiplexed using time division multiplexing.

13. The OFDMA system according to claim 1, wherein said first plurality of subcarriers is divided and multiplexed using space-time code (STC).

14. The OFDMA system according to claim 1, wherein said first plurality of subcarriers is divided and multiplexed using spatial multiplexing.