US 5,978,365 A · Communications system handoff operation combining turbo coding and soft handoff techniques

Abstract

Communication systems, including, for example, cell-based mobile communication systems, multiple satellite communication systems, or multibeam satellite systems, require reliable handoff methods between cell-to-cell, beam-to-beam, or satellite-to-satellite respectively. Recent measurement of a CDMA cellular system indicates that the system is in handoff about 30% to 50% of an average call period. Therefore, system reliability during handoff is one of the major system performance parameters and eventually becomes a factor in the overall system capacity. The present invention advantageously relates to novel and improved techniques for handoff in cellular communications, multibeam and multisatellite systems. The present invention combines the soft handoff mechanism wvith a code diversity combining technique (i.e., combining signals from multiple sources), a packet combining technique (i.e., combining multiple signals), and an iterative decoding algorithm (e.g., Turbo Coding).

Claims38

Dependent claims

A mobile communication system, comprising:

a source of digital data, for communication to or from a predetermined one of a plurality of mobile stations;
a first constituent encoder, coupled to the source, for encoding the digital data into a first code sequence;
an intierleaver, coupled to the source, for interleaving the digital data;
a second constituent encoder, coupled to the interleaver, for encoding the interleaved digital data into a second code sequence;
a first code puncturer, coupled to the first and second constituent encoders, for selectively replacing data in the first code sequence with selected data from the second code sequence to form a first punctured code sequence;
a second code puncturer, coupled to the first and second constituent encoders, for selectively replacing data in the second code sequence with selected data from the first code sequence to form a second punctured code sequence;
first and second transmitters for transmission of information on first and second logical channels assigned to the predetermined mobile station;
and
a control coupled to the first and second transmitters, wherein during a handoff operation, the control causes the first transmitter to broadcast the first channel carrying the digital data together with the first punctured code sequence, and concurrently causes the second transmitter to broadcast the second channel carrying the interleaved digital data together with the second punctured code sequence.

6 more elements

A mobile receiver for operation with a wireless communication system having a plurality of transmitters serving cells or segments of a geographic region, the mobile receiver comprising:

receiver circuitry for processing received modulated signals intended for the mobile receiver from one or more of the transmitters, wherein during a handoff from one transmitter to another transmitter the receiver circuitry is capable of processing received modulated signals intended for the mobile receiver from at least two of the transmitters, to obtain first and second forward data streams;
a first demultiplexer, coupled to an output of the receiver circuitry, for processing the first forward data stream received during handoff to recover digital data corresponding to digital information intended for the mobile receiver and a first coded sequence;
a second demultiplexer, coupled to an output of the receiver circuitry, for processing the second forward data stream received during handoff to recover digital data corresponding to interleaved digital information intended for the mobile receiver and a second coded sequence;
a code combiner, coupled to the first and second demultiplexers, for processing the first and second coded sequences during handoff, to recover a first constituent encoded sequence corresponding to the digital information intended for the mobile receiver and a second constituent encoded sequence corresponding to the interleaved digital information intended for the mobile receiver;
and
an intelligent decoder, coupled to the code combiner, for recovering an accurate representation of the digital information intended for the mobile receiver from the recovered digital data corresponding to the digital information intended for the mobile receiver, the first constituent coded sequence, the recovered digital data corresponding to the interleaved digital information intended for the mobile receiver, and the second constituent encoded sequence.

3 more elements

In a cellular communications system, a method for effectuating handoff of service for a mobile station between base stations, comprising the steps of:

communicating information between the mobile station and a first one of the base stations using a turbo coding/decoding scheme with respect to a first version of the information;
measuring the strength of transmitted pilot signals from the first base station and from a second one of the base stations which is not currently communicating with said mobile station to determine a need for handoff;
continuing the communication of the information between the mobile station and the first base station while establishing communications between the mobile station the second base station, the communications between the mobile station and the second base station using a turbo coding/decoding scheme with respect to a second version of the information;
and
terminating communications between the mobile station and the first base station when the pilot signal strength of the first base station falls below a predetermined level for a predetermined time period.

2 more elements

A method of receiving digital data from two base stations at a wireless receiver, comprising:

receiving a first transmission intended specifically for the wireless receiver, the first transmission containing a first data stream and a first code sequence, the first data stream consisting of a first one of (a) digital information and (b) an interleaved representation of the digital information;
processing the first data stream and the first code sequence to recover an accurate representation of the digital information;
initiating handoff;
continuing to receive the first transmission intended specifically for the wireless receiver if possible, and receiving a second transmission intended specifically for the wireless receiver, the second transmission containing a second data stream and a second code sequence, the second data stream consisting of the second one of (a) the digital information and (b) the interleaved representation of the digital information;
processing any two or more of the first and second data streams and the first and second code sequences to recover an accurate representation of the digital information;
ending reception of the first transmission intended specifically for the wireless receiver;
continuing to receive the second transmission intended specifically for the wireless receiver;
and
processing only the second data stream and the second code sequence to recover an accurate representation of the digital information.

6 more elements

Dependencies are inferred from the claim text.

Communications system handoff operation combining turbo coding and soft handoff techniques

Life of this patent

Communications system handoff operation combining turbo coding and soft handoff techniques

Life of this patent

Abstract

Claims38