(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/014 1933 A1
`Smee et al.
`(43) Pub. Date:
`Jun. 29, 2006
`
`US 2006O141933A1
`
`(54) CHANNEL ESTIMATION FOR
`INTERFERENCE CANCELLATION
`
`(76) Inventors: John Edward Smee, San Diego, CA
`(US); Henry David Pfister, San Diego,
`CA (US); Jilei Hou, Carlsbad, CA
`(US); Stefano Tomasin, Venice (IT)
`
`Correspondence Address:
`QUALCOMM, INC
`S775 MOREHOUSE DR.
`SAN DIEGO, CA 92121 (US)
`
`(21) Appl. No.:
`
`11/192,503
`
`(22) Filed:
`
`Jul. 29, 2005
`
`Related U.S. Application Data
`(60) Provisional application No. 60/638,666, filed on Dec.
`23, 2004.
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04B I/00
`(52) U.S. Cl. ........................................ 455/63.1; 455/67.13
`
`(57)
`
`ABSTRACT
`
`A method and system for interference cancellation (IC). One
`aspect relates to traffic interference cancellation. Another
`aspect relates to joint IC for pilot, overhead and data.
`Another aspect relates to improved channel estimation.
`Another aspect relates to adaptation of transmit Subchannel
`gains.
`
`to
`PSTN/PDSN
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`Base Stations
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`Patent Application Publication Jun. 29, 2006 Sheet 1 of 33
`
`US 2006/014 1933 A1
`
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`Patent Application Publication Jun. 29,2006 Sheet 2 of 33
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`Patent Application Publication Jun. 29, 2006 Sheet 3 of 33
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`Patent Application Publication Jun. 29, 2006 Sheet 5 of 33
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`Patent Application Publication Jun. 29, 2006 Sheet 6 of 33
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`US 2006/014 1933 A1
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`Patent Application Publication Jun. 29, 2006 Sheet 8 of 33
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`US 2006/014 1933 A1
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`available Subpackets
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`Ex.1026 / Page 9 of 50Ex.1026 / Page 9 of 50
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`Patent Application Publication Jun. 29, 2006 Sheet 9 of 33
`
`US 2006/014 1933 A1
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`Means to Demodulate
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`FERAM for time segments
`stored
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`934
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`packets by Combining available
`subpackets
`from BERAM
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`936
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`946
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`Patent Application Publication Jun. 29,2006 Sheet 10 of 33
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`Patent Application Publication Jun. 29
`
`2006 Sheet 11 of 33
`
`US 2006/014 1933 A1
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 12 of 33
`
`US 2006/014 1933 A1
`
`Channel estimation for all users
`and perform power control
`
`1202
`
`Perform PC on all users
`
`- 1204
`
`Choose a group G of
`un-deCOded users
`
`12O6
`
`Attempt to decode overhead
`channels of users in G
`
`1210
`
`Attempt to decode traffic
`channels of users in G
`
`
`
`Perform OIC & TIC On users
`that successfully decoded
`
`FIG. 12A
`
`
`
`More users to
`be decoded ?
`
`
`
`1214
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 13 of 33
`
`US 2006/014 1933 A1
`
`Means to estimate channel for all 1230
`users and perform power control
`
`Means to perform PIC 1232
`On all users
`
`1234
`
`
`
`Means to choose a
`group G of
`un-decoded uSerS
`
`1236
`Means to attempt to decode
`Overhead channels of users
`in G
`
`1238
`
`Means to attempt to decode
`traffic channels of users in G
`
`Means to perform OlC & TIC
`on users that successfully
`deCOded
`
`
`
`
`
`
`
`
`
`1240
`
`1242
`
`FIG. 12B
`
`
`
`
`
`
`
`eanS to
`determine
`mOre USerS to
`be decoded?
`
`Means to terminate
`
`1244
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 14 of 33
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`US 2006/014 1933 A1
`
`
`
`Channel estimation for all users
`and perform power control
`
`1202
`
`Perform PIC On all users
`
`1210
`
`1204
`/
`
`Choose a group G of
`un-decoded users
`
`
`
`
`
`Attempt to decode overhead
`channels of users in G
`
`Attempt to decode traffic
`channels of users in G
`
`1210
`
`Perform OIC & TIC on users
`that successfully decoded
`
`
`
`
`
`Ore uSerS to
`be deCOded ?
`
`
`
`
`
`
`
`DERIVE DATA BASED
`CHANNELESTIMATE
`
`1300
`
`PERFORM RESIDUAL
`PILOT INTERFERENCE
`CANCELLATION
`
`1302
`
`FIG. 13A
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 15 of 33
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`US 2006/014 1933 A1
`
`Means to estimate channel for all
`users and perform power Control
`
`
`
`
`
`
`
`
`
`
`
`
`
`Means to perform PIC
`On all users
`
`1232
`
`1234
`
`
`
`Means to choose a
`group G of
`un-deCOced users
`
`1236
`Means to attempt to decode
`Overhead channels of users
`in G
`
`1238
`
`
`
`
`
`Means to attempt to decode
`traffic channels of users in G
`
`Means to perform OlC & TIC
`on users that successfully
`decoded
`
`
`
`
`
`
`
`
`
`
`
`Means to
`determine
`more USerS to
`be decoded 2
`
`Means to terminate
`
`1310
`
`MEANS TO DERIVE
`DATA BASED
`CHANNELESTIMATE
`
`MEANS TO PERFORM
`RESIDUAL PILOT
`INTERFERENCE
`CANCELLATION
`
`
`
`1312
`
`FIG. 13B
`
`1244
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 16 of 33
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`US 2006/014 1933 A1
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`
`
`
`
`Channel estimation for all users
`and perform power control
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Choose a group G of
`un-deCOced users
`
`Re-estimate the Channel
`from pilots
`
`Attempt to decode overhead
`Channels of users in G
`
`Attempt to decode traffic
`Channels of USerS in G
`
`Perform PIC for all users and
`OIC & TIC for users that
`successfully decoded
`
`
`
`More users to
`be decoded ?
`
`
`
`
`
`
`
`Terminate
`
`FIG. 14A
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 17 of 33
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`US 2006/014 1933 A1
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`all users and perform power
`Control
`
`
`
`
`
`
`
`Means to choose a
`group G of
`un-decoded users
`
`Means to re-estimate the
`Channel
`from pilots
`
`Means to attempt to decode
`OVerhead channels of users
`in G
`
`Means to attempt to decode
`traffic channels of users in G
`
`Means to perform PIC for all
`uSerS and OC&TIC for
`users that successfully
`deCOded
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
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`
`Means to
`determine more
`USerS to
`be deCOded 2
`
`
`
`
`
`1436
`
`terminate
`
`FIG. 14B
`
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`Patent Application Publication Jun. 29, 2006 Sheet 18 of 33
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`1400
`
`Channel estimation for all users
`and perform power control
`
`1402
`
`Choose a group G of
`un-deCOded uSerS
`
`Re-estimate the Channel
`from pilots
`
`Attempt to decode overhead
`Channels of users in G
`
`Attempt to decode traffic
`Channels of users in G
`
`1404
`
`1406
`
`1408
`
`
`
`1410
`Perform PIC for all users and
`OIC & TIC for USerS that
`successfully decoded
`
`
`
`DERVE DATA BASED
`CHANNELESTIMATE
`
`1500
`
`OPTIONAL PERFORM
`RESIDUAL PILOT
`INTERFERENCE
`CANCELLATION
`
`
`
`More uSerS to
`be decoded ?
`
`1414
`
`FIG. 15A
`
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`Patent Application Publication Jun. 29, 2006 Sheet 19 of 33
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`US 2006/014 1933 A1
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`
`
`Means to channel estimation for 1422
`all users and perform power
`Control
`
`1424
`
`Means to choose a
`group G of
`un-decoded users
`
`
`
`
`
`
`
`Means to re-estimate the
`Channel
`from pilots
`
`Means to attempt to decode
`Overhead channels of users
`in G
`
`Means to attempt to decode
`traffic channels of users in G
`
`Means to perform PIC for all
`users and OIC & TIC for
`users that successfully
`decoded
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`determine more
`users to
`be decoded 2
`
`terminate
`
`
`
`
`
`MEANS TO DERVE
`DATA BASED
`CHANNELESTIMATE
`
`1510
`
`OPTIONAL MEANS TO
`PERFORMRESIDUAL
`PILOT INTERFERENCE
`CANCELLATION
`
`FIG. 15B
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 20 of 33
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`US 2006/014 1933 A1
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`:
`
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 21 of 33
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`US 2006/014 1933 A1
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`
`
`9
`
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`Patent Application Publication Jun. 29, 2006 Sheet 22 of 33
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`
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`Patent Application Publication Jun. 29, 2006 Sheet 23 of 33
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`US 2006/014 1933 A1
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`Ex.1026 / Page 24 of 50Ex.1026 / Page 24 of 50
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`Patent Application Publication Jun. 29, 2006 Sheet 24 of 33
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`
`
`
`
`
`
`
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`
`
`Despread Front-End
`Samples with Pilot
`PN Chips to get
`RAKE Finger Values
`
`
`
`
`
`Perform Data
`Demodulation
`
`2002
`
`Perform Data
`Decoding and
`Check CRC
`
`if CRC Passes,
`Determine Transmitted Data Chips by:
`Re-encoding
`Re-interleaving
`Re-modulating
`Re-spreading
`
`
`
`FIG. 20A
`
`2006
`
`
`
`
`
`Despread Front-End
`Samples with
`Transmitted Data
`Chips to get improved
`Channel Estimate at
`Each Rake Finger
`Dela
`
`2008
`
`Reconstruct User's Traffic
`and Overhead
`Contribution to Front-End
`samples with improved
`Channel Estimate
`
`
`
`
`
`
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 25 of 33
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`
`
`
`
`
`
`
`
`Means to Despread
`Front-End Samples
`with Pilot PN Chips
`to get RAKE Finger
`Values
`
`2020
`
`
`
`
`
`
`
`Means to
`Perform Data
`Demodulation
`
`2022
`
`Means to
`Perform Data
`Decoding and
`Check CRC
`
`2024
`
`FIG. 20B
`
`lf CRC Passes,
`Means to Determine Transmitted Data
`Chips by:
`Re-encoding
`Re-interleaving
`Re-modulating
`Re-spreading
`
`
`
`2026
`
`
`
`
`
`
`
`Means to Despread
`Front-End Samples
`With Transmitted Data
`Chips to get improved
`Channel Estimate at
`Each Rake Finger
`Delay
`
`2028
`
`Means to Reconstruct
`User's Traffic and
`Overhead Contribution to
`Front-End samples with
`Improved Channel
`Estimate
`
`2030
`
`
`
`
`
`
`
`
`
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`Patent Application Publication Jun. 29, 2006 Sheet 26 of 33
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`Patent Application Publication Jun. 29, 2006 Sheet 27 of 33
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`US 2006/014 1933 A1
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`Despread Front-End
`Samples with Pilot
`PN Chips to get
`RAKE Finger Values
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`2000
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`Perform Data
`Demodulation
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`2002
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`Perform Data
`Decoding and
`Check CRC
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`2004
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`if CRC Passes,
`Determine Transmitted Data Chips by:
`Re-encoding
`Re-interleaving
`Re-modulating
`R-espreading
`
`2006
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`Based on RAKE Finger
`Delays, Determine
`Time-Span for Uniform
`Reconstruction.
`
`2200
`
`Determine improved Channel
`Estimate by:
`Despreading Front-End
`Samples with Transmitted
`Data Chips at Uniform Delays
`for Appropriate Time-Span
`
`2202
`
`Reconstruct User's Traffic
`and Overhead
`Contribution to Front-End
`samples with improved
`Channel Estimate
`
`
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`
`
`FIG.22A
`
`2010
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`Patent Application Publication Jun. 29, 2006 Sheet 28 of 33
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`US 2006/014 1933 A1
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`Means to Despread
`Front-End Samples
`with Pilot PN Chips
`to get RAKE Finger
`Values
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`
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`
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`
`
`Means to
`Perform Data
`Demodulation
`
`Means to
`Perform Data
`Decoding and
`Check CRC
`
`2020
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`2022
`
`2024
`
`lf CRC Passes,
`Means to Determine Transmitted Data
`Chips by:
`Re-encoding
`Re-interleaving
`Re-modulating
`R-espreading
`
`
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`2026
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`Based on RAKE Finger
`Delays, Means to
`Determine Time-Span
`for Uniform
`Reconstruction.
`
`2220
`
`Means to Determine Improved
`Channel Estimate by:
`Despreading Front-End
`Samples with Transmitted
`Data Chips at Uniform Delays
`for Appropriate Time-Span
`
`
`
`
`
`Means to Reconstruct
`User's Traffic and
`Overhead Contribution to
`Front-End samples with
`improved Channel
`Estimate
`
`2222
`
`2030
`
`FIG. 22B
`
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`Patent Application Publication Jun. 29, 2006 Sheet 29 of 33
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`US 2006/014 1933 A1
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`Patent Application Publication Jun. 29, 2006 Sheet 30 of 33
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`US 2006/014 1933 A1
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`Patent Application Publication Jun. 29, 2006 Sheet 31 of 33
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`US 2006/014 1933 A1
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`Patent Application Publication Jun. 29, 2006 Sheet 32 of 33
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`US 2006/014 1933 A1
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`Patent Application Publication Jun. 29, 2006 Sheet 33 of 33
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`US 2006/014 1933 A1
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`US 2006/014 1933 A1
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`Jun. 29, 2006
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`CHANNEL ESTMATION FOR INTERFERENCE
`CANCELLATION
`
`CLAIM OF PRIORITY UNDER 35 U.S.C. S 119
`0001. The present application claims priority to co-as
`signed U.S. Provisional Application No. 60/638,666,
`entitled TRAFFIC INTERFERENCE CANCELLATION
`AT THE BTS ON A CDMA REVERSE LINK, filed on
`Dec. 23, 2004, which is incorporated by reference.
`
`BACKGROUND
`
`0002) 1. Field
`0003. The present invention relates to wireless commu
`nication systems generally, and specifically to traffic inter
`ference cancellation in wireless communication systems.
`0004 2. Background
`0005. A communication system may provide communi
`cation between base stations and access terminals. Forward
`link or downlink refers to transmission from a base station
`to an access terminal. Reverse link or uplink refers to
`transmission from an access terminal to a base station. Each
`access terminal may communicate with one or more base
`stations on the forward and reverse links at a given moment,
`depending on whether the access terminal is active and
`whether the access terminal is in soft handoff.
`
`BRIEF DESCRIPTION OF DRAWINGS
`0006 The features, nature, and advantages of the present
`application may be more apparent from the detailed descrip
`tion set forth below with the drawings. Like reference
`numerals and characters may identify the same or similar
`objects.
`0007 FIG. 1 illustrates a wireless communication system
`with base stations and access terminals.
`0008 FIG. 2 illustrates an example of transmitter struc
`ture and/or process, which may be implemented at an access
`terminal of FIG. 1.
`0009 FIG. 3 illustrates an example of a receiver process
`and/or structure, which may be implemented at a base
`Station of FIG. 1.
`0010 FIG. 4 illustrates another embodiment of a base
`station receiver process or structure.
`0011
`FIG. 5 illustrates a general example of power
`distribution of three users in the system of FIG. 1.
`0012 FIG. 6 shows an example of a uniform time-offset
`distribution for frame asynchronous traffic interference can
`cellation for users with equal transmit power.
`0013 FIG. 7 illustrates an interlacing structure used for
`the reverse link data packets and a forward link automatic
`repeat request channel.
`0014 FIG. 8 illustrates a memory that spans a complete
`16-slot packet.
`0015 FIG. 9A illustrates a method of traffic interference
`cancellation for an example of sequential interference can
`cellation (SIC) with no delayed decoding.
`
`0016 FIG. 9B illustrates an apparatus to perform the
`method of FIG. 9A.
`0017 FIG. 10 illustrates a receiver sample buffer after
`arrival of successive subpackets of an interlace with inter
`ference cancellation of decoded subpackets.
`0.018
`FIG. 11 illustrates an overhead channels structure.
`0.019
`FIG. 12A illustrates a method to first perform pilot
`IC (PIC) and then perform overhead IC (OIC) and traffic IC
`(TIC) together.
`0020 FIG. 12B illustrates an apparatus to perform the
`method of FIG. 12A.
`0021
`FIG. 13A illustrates a variation of the method in
`FIG. 12A.
`0022 FIG. 13B illustrates an apparatus to perform the
`method of FIG. 13A.
`0023 FIG. 14A illustrates a method to perform joint PIC,
`OIC and TIC.
`0024 FIG. 14B illustrates an apparatus to perform the
`method of FIG. 14A.
`0.025 FIG. 15A illustrates a variation of the method in
`FIG. 14A.
`0026 FIG. 15B illustrates an apparatus to perform the
`method of FIG. 15A.
`0027 FIG. 16 illustrates a model of transmission system.
`0028 FIG. 17 illustrates an example response of com
`bined transmit and receive filtering.
`0029 FIGS. 18A and 18B show an example of channel
`estimation (real and imaginary components) based on the
`estimated multipath channel at each of three RAKE fingers.
`0030 FIGS. 19 A-19B show examples of an improved
`channel estimate based on RAKE fingers and despreading
`with the data chips.
`0031
`FIG. 20A illustrates a method for despreading at
`RAKE finger delays with regenerated data chips.
`0032 FIG. 20B illustrates an apparatus to perform the
`method of FIG. 20A.
`0033 FIGS. 21A and 21B show an example of estimat
`ing the composite channel using uniformly spaced samples
`at chipX2 resolution.
`0034 FIG. 22A illustrates a method for estimating com
`posite channel at uniform resolution using regenerated data
`chips.
`0035 FIG. 22B illustrates an apparatus to perform the
`method of FIG. 22A.
`0036 FIG. 23 illustrates a closed loop power control and
`gain control with fixed overhead subchannel gain.
`0037 FIG. 24 is a variation of FIG. 23 power control and
`gain control with fixed overhead subchannel gain.
`0038 FIG. 25 illustrates an example of power control
`with fixed overhead subchannel gain.
`0.039
`FIG. 26 is similar to FIG. 24 except with overhead
`gain control.
`
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`US 2006/014 1933 A1
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`Jun. 29, 2006
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`0040 FIG. 27 illustrates a variation of FIG. 26 with
`DRC-only overhead gain control.
`
`DETAILED DESCRIPTION
`0041 Any embodiment described herein is not necessar
`ily preferable or advantageous over other embodiments.
`While various aspects of the present disclosure are presented
`in drawings, the drawings are not necessarily drawn to scale
`or drawn to be all-inclusive.
`0.042
`FIG. 1 illustrates a wireless communication system
`100, which includes a system controller 102, base stations
`104a-104b, and a plurality of access terminals 106a-106.h.
`The system 100 may have any number of controllers 102,
`base stations 104 and access terminals 106. Various aspects
`and embodiments of the present disclosure described below
`may be implemented in the system 100.
`0043. Access terminals 106 may be mobile or stationary
`and may be dispersed throughout the communication system
`100 of FIG. 1. An access terminal 106 may be connected to
`or implemented in a computing device. Such as a laptop
`personal computer. Alternatively, an access terminal may be
`a self-contained data device. Such as a personal digital
`assistant (PDA). An access terminal 106 may refer to various
`types of devices, such as a wired phone, a wireless phone,
`a cellular phone, a lap top computer, a wireless communi
`cation personal computer (PC) card, a PDA, an external or
`internal modem, etc. An access terminal may be any device
`that provides data connectivity to a user by communicating
`through a wireless channel or through a wired channel, for
`example using fiber optic or coaxial cables. An access
`terminal may have various names, such as mobile station,
`access unit, Subscriber unit, mobile device, mobile terminal,
`mobile unit, mobile phone, mobile, remote station, remote
`terminal, remote unit, user device, user equipment, handheld
`device, etc.
`0044) The system 100 provides communication for a
`number of cells, where each cell is serviced by one or more
`base stations 104. A base station 104 may also be referred to
`as a base station transceiver system (BTS), an access point,
`a part of an access network, a modem pool transceiver
`(MPT), or a Node B. Access network refers to network
`equipment providing data connectivity between a packet
`Switched data network (e.g., the Internet) and the access
`terminals 106.
`0045 Forward link (FL) or downlink refers to transmis
`sion from a base station 104 to an access terminal 106.
`Reverse link (RL) or uplink refers to transmission from an
`access terminal 106 to a base station 104.
`0046) A base station 104 may transmit data to an access
`terminal 106 using a data rate selected from a set of different
`data rates. An access terminal 106 may measure a signal
`to-noise-and-interference ratio (SINR) of a pilot signal sent
`by the base station 104 and determine a desired data rate for
`the base station 104 to transmit data to the access terminal
`106. The access terminal 106 may send data request channel
`or Data rate control (DRC) messages to the base station 104
`to inform the base station 104 of the desired data rate.
`0047 The system controller 102 (also referred to as a
`base station controller (BSC)) may provide coordination and
`control for base stations 104, and may further control routing
`of calls to access terminals 106 via the base stations 104. The
`
`system controller 102 may be further coupled to a public
`switched telephone network (PSTN) via a mobile switching
`center (MSC), and to a packet data network via a packet data
`serving node (PDSN).
`0048. The communication system 100 may use one or
`more communication techniques, such as code division
`multiple access (CDMA), IS-95, High Rate Packet Data
`(HRPD), also referred to as High Data Rate (HDR), as
`specified in “cdma2000 High Rate Packet Data Air Interface
`Specification.” TIA/EIA/IS-856, CDMA 1x Evolution Data
`Optimized (EV-DO), 1xEV-DV. Wideband CDMA
`(WCDMA), Universal Mobile Telecommunications System
`(UMTS), Time Division Synchronous CDMA (TD
`SCDMA), Orthogonal Frequency Division Multiplexing
`(OFDM), etc. The examples described below provide details
`for clarity of understanding. The ideas presented herein are
`applicable to other systems as well, and the present
`examples are not meant to limit the present application.
`0049 FIG. 2 illustrates an example of transmitter struc
`ture and/or process, which may be implemented at an access
`terminal 106 of FIG. 1. The functions and components
`shown in FIG. 2 may be implemented by software, hard
`ware, or a combination of software and hardware. Other
`functions may be added to FIG. 2 in addition to or instead
`of the functions shown in FIG. 2.
`0050 A data source 200 provides data to an encoder 202,
`which encodes data bits using one or more coding schemes
`to provide coded data chips. Each coding scheme may
`include one or more types of coding, such as cyclic redun
`dancy check (CRC), convolutional coding, Turbo coding,
`block coding, other types of coding, or no coding at all.
`Other coding schemes may include automatic repeat request
`(ARQ), hybrid ARQ (H-ARQ), and incremental redundancy
`repeat techniques. Different types of data may be coded with
`different coding schemes. An interleaver 204 interleaves the
`coded data bits to combat fading.
`0051. A modulator 206 modulates coded, interleaved data
`to generate modulated data. Examples of modulation tech
`niques include binary phase shift keying (BPSK) and
`quadrature phase shift keying (QPSK). The modulator 206
`may also repeat a sequence of modulated data or a symbol
`puncture unit may puncture bits of a symbol. The modulator
`206 may also spread the modulated data with a Walsh cover
`(i.e., Walsh code) to form data chips. The modulator 206
`may also time-division multiplex the data chips with pilot
`chips and MAC chips to form a stream of chips. The
`modulator 206 may also use a pseudo random noise (PN)
`spreader to spread the stream of chips with one or more PN
`codes (e.g., short code, long code).
`0052 A baseband-to-radio-frequency (RF) conversion
`unit 208 may convert baseband signals to RF signals for
`transmission via an antenna 210 over a wireless communi
`cation link to one or more base stations 104.
`0053 FIG. 3 illustrates an example of a receiver process
`and/or structure, which may be implemented at a base
`station 104 of FIG.1. The functions and components shown
`in FIG.3 may be implemented by software, hardware, or a
`combination of software and hardware. Other functions may
`be added to FIG. 3 in addition to or instead of the functions
`shown in FIG. 3.
`0054) One or more antennas 300 receive the reverse link
`modulated signals from one or more access terminals 106.
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`Jun. 29, 2006
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`Multiple antennas may provide spatial diversity against
`deleterious path effects Such as fading. Each received signal
`is provided to a respective receiver or RF-to-baseband
`conversion unit 302, which conditions (e.g., filters, ampli
`fies, downconverts) and digitizes the received signal to
`generate data samples for that received signal.
`0055) A demodulator 304 may demodulate the received
`signals to provide recovered symbols. For CDMA2000,
`demodulation tries to recover a data transmission by (1)
`channelizing the despread samples to isolate or channelize
`the received data and pilot onto their respective code chan
`nels, and (2) coherently demodulating the channelized data
`with a recovered pilot to provide demodulated data.
`Demodulator 304 may include a received sample buffer 312
`(also called joint front-end RAM (FERAM) or sample
`RAM) to store samples of received signals for all users/
`access terminals, a rake receiver 314 to despread and process
`multiple signal instances, and a demodulated symbol buffer
`316 (also called back-end RAM (BERAM) or demodulated
`symbol RAM). There may be a plurality demodulated sym
`bol buffers 316 to correspond to the plurality of users/access
`terminals.
`0056. A deinterleaver 306 deinterleaves data from the
`demodulator 304.
`0057 Adecoder 308 may decode the demodulated data to
`recover decoded data bits transmitted by the access terminal
`106. The decoded data may be provided to a data sink 310.
`0.058
`FIG. 4 illustrates another embodiment of a base
`station receiver process or structure. In FIG. 4, data bits of
`Successfully decoded user are input to an interference recon
`struction unit 400, which includes an encoder 402, inter
`leaver 404, modulator 406 and filter 408. The encoder 402,
`interleaver 404, and modulator 406 may be similar to the
`encoder 202, interleaver 204, and modulator 206 of FIG. 2.
`The filter 408 forms the decoded user's samples at FERAM
`resolution, e.g., change from chip rate to 2x chip rate. The
`decoder user's contribution to the FERAM is them removed
`or canceled from the FERAM 312.
`0059 Although interference cancellation at a base station
`104 is described below, the concepts herein may be applied
`to an access terminal 106 or any other component of a
`communication system.
`Traffic Interference Cancellation
`0060. The capacity of a CDMA reverse link may be
`limited by the interference between users since the signals
`transmitted by different users are not orthogonal at the BTS
`104. Therefore, techniques that decrease the interference
`between users will improve the system performance of a
`CDMA reverse link. Techniques are described herein for the
`efficient implementation of interference cancellation for
`advanced CDMA systems such as CDMA2000 1xEV-DO
`RevA.
`Each DO RevA user transmits traffic, pilot, and
`0061
`overhead signals, all of which may cause interference to
`other users. AS FIG. 4 shows, signals may be reconstructed
`and Subtracted from the front-end RAM 312 at the BTS 104.
`The transmitted pilot signal is known at the BTS 104 and
`may be reconstructed based on knowledge about the chan
`nel. However, the overhead signals (Such as reverse rate
`indicator (RRI), data request channel or data rate control
`
`(DRC), data source channel (DSC), acknowledgement
`(ACK)) are first demodulated and detected, and the trans
`mitted data signals are demodulated, de-interleaved, and
`decoded at the BTS 104 in order to determine the transmitted
`overhead and traffic chips. Based on determining the trans
`mitted chips for a given signal, the reconstruction unit 400
`may then reconstruct the contribution to the FERAM 312
`based on channel knowledge.
`0062 Bits of a data packet from the data source 200 may
`be repeated and processed by the encoder 202, interleaver
`204 and/or modulator 206 into a plurality of corresponding
`“subpackets” for transmitting to the base station 104. If the
`base station 104 receives a high signal-to-noise-ratio signal,
`the first subpacket may contain sufficient information for the
`base station 104 to decode and derive the original data
`packet. For example, a data packet from the data source 200
`may be repeated and proces