SOFT HANDOFF FOR OFDM

• US 20140023046A1
• Filed: 09/25/2013
• Published: 01/23/2014
• Est. Priority Date: 03/22/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Ma, Jianglei, Jia, Ming, Zhu, Peiying, Tong, Wen, Yu, Dong-Sheng
• Granted Patent: US 9,414,279 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: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0025 Spatial division following the spatial signature of the channel
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

Various embodiments relate to soft handoffs in an OFDM system. Each mobile terminal measures pilot signal strengths of transmissions from adjacent base stations. If the pilot signal strength for a base station exceeds the defined threshold, that base station is added to an active set list. Each mobile terminal notifies the base stations of their active set lists. By providing the set list to the base station controller and the servicing base station, the mobile terminal identifies the sole servicing base station or triggers a soft handoff mode when multiple base stations appear on the active set list. The soft handoff mode uses a combination of scheduling and space-time coding to affect efficient and reliable handoffs.

Claims

1. A mobile terminal comprising:

receive circuitry adapted to receive and downconvert a plurality of orthogonal frequency division multiplexing (OFDM) signals, which were encoded using spatial encoding and transmitted using spatial diversity;

transform logic adapted to provide a transform on each of the plurality of OFDM signals to generate a plurality of spatially coded signals;

decoder logic adapted to provide spatial decoding on the plurality of spatially coded signals to recover scheduled data from servicing base stations;

processing logic configured to;

monitor signal strength from a plurality of base stations;

identify ones of the plurality of base stations having signal strength over a defined threshold; and

enter a mode in which the mobile terminal simultaneously communicates with two or more base stations, wherein more than one of the plurality of base stations have a signal strength over the defined threshold; and

transmit circuitry configured to transmit information identifying the ones of the plurality of base stations having signal strength over the defined threshold.