WO2002080432A3 - Successive user data multipath interference cancellation - Google Patents

Successive user data multipath interference cancellation Download PDF

Info

Publication number
WO2002080432A3
WO2002080432A3 PCT/IB2002/000938 IB0200938W WO02080432A3 WO 2002080432 A3 WO2002080432 A3 WO 2002080432A3 IB 0200938 W IB0200938 W IB 0200938W WO 02080432 A3 WO02080432 A3 WO 02080432A3
Authority
WO
WIPO (PCT)
Prior art keywords
user data
interference cancellation
multipath interference
successive user
encoded
Prior art date
Application number
PCT/IB2002/000938
Other languages
French (fr)
Other versions
WO2002080432A2 (en
Inventor
Thomas J Kenney
Original Assignee
Nokia Corp
Nokia Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Corp, Nokia Inc filed Critical Nokia Corp
Priority to AU2002244894A priority Critical patent/AU2002244894A1/en
Publication of WO2002080432A2 publication Critical patent/WO2002080432A2/en
Publication of WO2002080432A3 publication Critical patent/WO2002080432A3/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H04B1/7107—Subtractive interference cancellation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/711—Interference-related aspects the interference being multi-path interference
    • H04B1/7113—Determination of path profile
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/711—Interference-related aspects the interference being multi-path interference
    • H04B1/7115—Constructive combining of multi-path signals, i.e. RAKE receivers
    • H04B1/712—Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/0848—Joint weighting
    • H04B7/0857—Joint weighting using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0891—Space-time diversity
    • H04B7/0897—Space-time diversity using beamforming per multi-path, e.g. to cope with different directions of arrival [DOA] at different multi-paths
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W28/00—Network traffic management; Network resource management
    • H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
    • H04W28/18—Negotiating wireless communication parameters

Abstract

A wireless receiver (113) stores (201) one or more frames of received data and, during an initial demodulation (210, 220, 230), resolves each individual path for the multipath channel and estimates (pilot) channel parameters in order to process the received traffic, then decodes (203) the processed traffic to produce an estimate of the transmitted data. The estimated data is re-encoded (204) exactly as encoded by the transmitter, then scaled and time-shifted utilizing complex weights and timing estimates garnered during the initial demodulation process.
PCT/IB2002/000938 2001-03-30 2002-03-26 Successive user data multipath interference cancellation WO2002080432A2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002244894A AU2002244894A1 (en) 2001-03-30 2002-03-26 Successive user data multipath interference cancellation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US09/822,897 US6580771B2 (en) 2001-03-30 2001-03-30 Successive user data multipath interference cancellation
US09/822,897 2001-03-30

Publications (2)

Publication Number Publication Date
WO2002080432A2 WO2002080432A2 (en) 2002-10-10
WO2002080432A3 true WO2002080432A3 (en) 2003-01-03

Family

ID=25237272

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2002/000938 WO2002080432A2 (en) 2001-03-30 2002-03-26 Successive user data multipath interference cancellation

Country Status (3)

Country Link
US (1) US6580771B2 (en)
AU (1) AU2002244894A1 (en)
WO (1) WO2002080432A2 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9172456B2 (en) 2005-04-07 2015-10-27 Iii Holdings 1, Llc Iterative interference suppressor for wireless multiple-access systems with multiple receive antennas
US9172411B2 (en) 2002-09-20 2015-10-27 Iii Holdings 1, Llc Advanced signal processors for interference cancellation in baseband receivers
US9270325B2 (en) 2005-04-07 2016-02-23 Iii Holdings 1, Llc Iterative interference suppression using mixed feedback weights and stabilizing step sizes

Families Citing this family (79)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6650653B1 (en) * 2000-01-19 2003-11-18 Mitsubishi Electric Research Laboratories, Inc. Software-based digital receiver adaptable to multiple multiplexing schemes
US6819911B2 (en) * 2001-04-02 2004-11-16 General Dynamics Decision Systems, Inc. Active interference suppressor utilizing recombinant transmultiplexing
US8611311B2 (en) 2001-06-06 2013-12-17 Qualcomm Incorporated Method and apparatus for canceling pilot interference in a wireless communication system
US7218692B2 (en) * 2001-06-15 2007-05-15 Texas Instruments Incorporated Multi-path interference cancellation for transmit diversity
US6963727B2 (en) * 2001-07-26 2005-11-08 Time Domain Corporation Direct-path-signal detection apparatus and associated methods
US8085889B1 (en) 2005-04-11 2011-12-27 Rambus Inc. Methods for managing alignment and latency in interference cancellation
US7158559B2 (en) * 2002-01-15 2007-01-02 Tensor Comm, Inc. Serial cancellation receiver design for a coded signal processing engine
KR100415550B1 (en) * 2001-10-05 2004-01-24 한국전자통신연구원 Simplified Interference Canceller for Receiver of DS-CDMA System
US7430253B2 (en) * 2002-10-15 2008-09-30 Tensorcomm, Inc Method and apparatus for interference suppression with efficient matrix inversion in a DS-CDMA system
US20050101277A1 (en) * 2001-11-19 2005-05-12 Narayan Anand P. Gain control for interference cancellation
US7260506B2 (en) * 2001-11-19 2007-08-21 Tensorcomm, Inc. Orthogonalization and directional filtering
US20040146093A1 (en) * 2002-10-31 2004-07-29 Olson Eric S. Systems and methods for reducing interference in CDMA systems
SG114534A1 (en) * 2002-03-12 2005-09-28 Oki Techno Ct Singapore Pte Reduced-complexity multipath interference cancellation
US20040208238A1 (en) * 2002-06-25 2004-10-21 Thomas John K. Systems and methods for location estimation in spread spectrum communication systems
US7103094B2 (en) * 2002-08-29 2006-09-05 Broadcom Corporation Adaptive pilot interference cancellation in CDMA systems
US7876810B2 (en) 2005-04-07 2011-01-25 Rambus Inc. Soft weighted interference cancellation for CDMA systems
US7577186B2 (en) * 2002-09-20 2009-08-18 Tensorcomm, Inc Interference matrix construction
US20050180364A1 (en) * 2002-09-20 2005-08-18 Vijay Nagarajan Construction of projection operators for interference cancellation
US7463609B2 (en) * 2005-07-29 2008-12-09 Tensorcomm, Inc Interference cancellation within wireless transceivers
US7787572B2 (en) * 2005-04-07 2010-08-31 Rambus Inc. Advanced signal processors for interference cancellation in baseband receivers
US8761321B2 (en) 2005-04-07 2014-06-24 Iii Holdings 1, Llc Optimal feedback weighting for soft-decision cancellers
US20050123080A1 (en) * 2002-11-15 2005-06-09 Narayan Anand P. Systems and methods for serial cancellation
US8179946B2 (en) * 2003-09-23 2012-05-15 Rambus Inc. Systems and methods for control of advanced receivers
US8005128B1 (en) 2003-09-23 2011-08-23 Rambus Inc. Methods for estimation and interference cancellation for signal processing
US20040071197A1 (en) * 2002-10-10 2004-04-15 Jia-Chin Lin Modified PN code tracking loop for direct-sequence spread-spectrum communication over arbitrarily correlated multipath fading channels
AU2003286785A1 (en) * 2002-11-01 2004-06-07 Magnolia Broadband Inc. Processing diversity signals using a delay
WO2004073159A2 (en) * 2002-11-15 2004-08-26 Tensorcomm, Incorporated Systems and methods for parallel signal cancellation
FR2855342B1 (en) * 2003-05-20 2008-09-05 St Microelectronics Sa METHOD FOR DELAYING SYMBOLS WITHIN A "RAKE" RECEPTOR, AND CORRESPONDING "RAKE" RECEPTOR
US7477710B2 (en) * 2004-01-23 2009-01-13 Tensorcomm, Inc Systems and methods for analog to digital conversion with a signal cancellation system of a receiver
US20050169354A1 (en) * 2004-01-23 2005-08-04 Olson Eric S. Systems and methods for searching interference canceled data
US20050254590A1 (en) * 2004-05-11 2005-11-17 Ilari Kukkula Receiver, arrangement and method for decoding signal
KR100661335B1 (en) * 2004-07-14 2006-12-27 에스케이 텔레콤주식회사 Multi-path interference removing for wireless relay system apparatus and method using by same channel frequency
EP1659706A1 (en) * 2004-11-17 2006-05-24 Alcatel Method and system for improving the quality of a radio signal
US20060125689A1 (en) * 2004-12-10 2006-06-15 Narayan Anand P Interference cancellation in a receive diversity system
US8099123B2 (en) 2004-12-23 2012-01-17 Qualcomm Incorporated Adaptation of transmit subchannel gains in a system with interference cancellation
US8442441B2 (en) 2004-12-23 2013-05-14 Qualcomm Incorporated Traffic interference cancellation
US8406695B2 (en) 2004-12-23 2013-03-26 Qualcomm Incorporated Joint interference cancellation of pilot, overhead and traffic channels
US8422955B2 (en) 2004-12-23 2013-04-16 Qualcomm Incorporated Channel estimation for interference cancellation
US20060229051A1 (en) * 2005-04-07 2006-10-12 Narayan Anand P Interference selection and cancellation for CDMA communications
WO2007038016A2 (en) * 2005-09-23 2007-04-05 Tensorcomm, Inc. An iterative interference canceller for wireless multiple-access systems with multiple receive antennas
US8472877B2 (en) * 2005-10-24 2013-06-25 Qualcomm Incorporated Iterative interference cancellation system and method
US8385388B2 (en) 2005-12-06 2013-02-26 Qualcomm Incorporated Method and system for signal reconstruction from spatially and temporally correlated received samples
US9113362B2 (en) * 2006-12-12 2015-08-18 At&T Mobility Ii Llc Method and apparatus to separate coverage limited and co-channel limited interferences
KR100833684B1 (en) * 2006-12-20 2008-05-29 에스케이텔레시스 주식회사 Interference cancellation method and apparatus for microwave repeaters
EP2273687B1 (en) * 2009-07-01 2016-12-07 Telefonaktiebolaget LM Ericsson (publ) Multi-path timing tracking and impairment modeling for improved grake receiver performance in mobility scenarios
US8787426B2 (en) * 2011-09-28 2014-07-22 Telefonaktiebolaget Lm Ericsson (Publ) Finger placement in multi-stage interference cancellation
US8761323B2 (en) 2011-09-28 2014-06-24 Telefonaktiebolaget Lm Ericsson (Publ) Impairment covariance and combining weight updates during iterative turbo interference cancellation reception
WO2014121290A1 (en) 2013-02-04 2014-08-07 Kumu Networks Signal cancellation using feedforward and feedback paths
US9698860B2 (en) 2013-08-09 2017-07-04 Kumu Networks, Inc. Systems and methods for self-interference canceller tuning
CN105556860B (en) 2013-08-09 2018-04-03 库姆网络公司 The system and method eliminated for non-linear, digital self-interference
US9054795B2 (en) 2013-08-14 2015-06-09 Kumu Networks, Inc. Systems and methods for phase noise mitigation
US10673519B2 (en) 2013-08-29 2020-06-02 Kuma Networks, Inc. Optically enhanced self-interference cancellation
JP6183939B2 (en) 2013-08-29 2017-08-23 クム ネットワークス インコーポレイテッドＫｕｍｕ Ｎｅｔｗｏｒｋｓ，Ｉｎｃ． Full duplex relay device
US9520983B2 (en) 2013-09-11 2016-12-13 Kumu Networks, Inc. Systems for delay-matched analog self-interference cancellation
US10230422B2 (en) 2013-12-12 2019-03-12 Kumu Networks, Inc. Systems and methods for modified frequency-isolation self-interference cancellation
US9774405B2 (en) 2013-12-12 2017-09-26 Kumu Networks, Inc. Systems and methods for frequency-isolated self-interference cancellation
US9712312B2 (en) * 2014-03-26 2017-07-18 Kumu Networks, Inc. Systems and methods for near band interference cancellation
US9521023B2 (en) 2014-10-17 2016-12-13 Kumu Networks, Inc. Systems for analog phase shifting
US9712313B2 (en) 2014-11-03 2017-07-18 Kumu Networks, Inc. Systems for multi-peak-filter-based analog self-interference cancellation
US9673854B2 (en) 2015-01-29 2017-06-06 Kumu Networks, Inc. Method for pilot signal based self-inteference cancellation tuning
US10027367B2 (en) * 2015-08-18 2018-07-17 Nokia Solutions And Networks Oy Quarter wavelength unit delay and complex weighting coefficient continuous-time filters
US9634823B1 (en) 2015-10-13 2017-04-25 Kumu Networks, Inc. Systems for integrated self-interference cancellation
US9742593B2 (en) 2015-12-16 2017-08-22 Kumu Networks, Inc. Systems and methods for adaptively-tuned digital self-interference cancellation
CN108370082B (en) 2015-12-16 2021-01-08 库姆网络公司 Time delay filter
US10666305B2 (en) 2015-12-16 2020-05-26 Kumu Networks, Inc. Systems and methods for linearized-mixer out-of-band interference mitigation
US9800275B2 (en) 2015-12-16 2017-10-24 Kumu Networks, Inc. Systems and methods for out-of band-interference mitigation
KR102129045B1 (en) * 2015-12-28 2020-07-02 주식회사 쏠리드 Removing apparatus and removing method for interference signal
US9979374B2 (en) 2016-04-25 2018-05-22 Kumu Networks, Inc. Integrated delay modules
US10454444B2 (en) 2016-04-25 2019-10-22 Kumu Networks, Inc. Integrated delay modules
US10142137B2 (en) 2017-03-02 2018-11-27 Micron Technology, Inc. Wireless devices and systems including examples of full duplex transmission
US10103774B1 (en) 2017-03-27 2018-10-16 Kumu Networks, Inc. Systems and methods for intelligently-tuned digital self-interference cancellation
EP3602776B1 (en) 2017-03-27 2021-04-21 Kumu Networks, Inc. Enhanced linearity mixer
WO2018183333A1 (en) 2017-03-27 2018-10-04 Kumu Networks, Inc Systems and methods for tunable out-of-band interference mitigation
US10200076B1 (en) 2017-08-01 2019-02-05 Kumu Networks, Inc. Analog self-interference cancellation systems for CMTS
US11941516B2 (en) 2017-08-31 2024-03-26 Micron Technology, Inc. Cooperative learning neural networks and systems
JP7096346B2 (en) 2018-02-27 2022-07-05 クム ネットワークス，インコーポレイテッド Configurable hybrid self-interference cancellation system and method
US10868661B2 (en) 2019-03-14 2020-12-15 Kumu Networks, Inc. Systems and methods for efficiently-transformed digital self-interference cancellation
US10979097B2 (en) * 2019-09-05 2021-04-13 Micron Technology, Inc. Wireless devices and systems including examples of full duplex transmission using neural networks or recurrent neural networks
FR3103658B1 (en) 2019-11-27 2022-09-02 Centre Nat Etd Spatiales Method for reducing multipath errors

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5553062A (en) * 1993-04-22 1996-09-03 Interdigital Communication Corporation Spread spectrum CDMA interference canceler system and method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5553062A (en) * 1993-04-22 1996-09-03 Interdigital Communication Corporation Spread spectrum CDMA interference canceler system and method

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9172411B2 (en) 2002-09-20 2015-10-27 Iii Holdings 1, Llc Advanced signal processors for interference cancellation in baseband receivers
US9172456B2 (en) 2005-04-07 2015-10-27 Iii Holdings 1, Llc Iterative interference suppressor for wireless multiple-access systems with multiple receive antennas
US9270325B2 (en) 2005-04-07 2016-02-23 Iii Holdings 1, Llc Iterative interference suppression using mixed feedback weights and stabilizing step sizes
US9425855B2 (en) 2005-04-07 2016-08-23 Iii Holdings 1, Llc Iterative interference suppressor for wireless multiple-access systems with multiple receive antennas

Also Published As

Publication number Publication date
WO2002080432A2 (en) 2002-10-10
US6580771B2 (en) 2003-06-17
US20020172265A1 (en) 2002-11-21
AU2002244894A1 (en) 2002-10-15

Similar Documents

Publication Publication Date Title
WO2002080432A3 (en) Successive user data multipath interference cancellation
WO2004112295A3 (en) Method and apparatus for estimating carrier frequency offset and fading rate using autoregressive channel modeling
IL170333A (en) Channel estimation of a receiver multipath cdma signal
WO2004073180A3 (en) System and method for interference cancellation in a wireless communication receiver
WO2003021795A3 (en) Method and apparatus for suppressing multipath interference usingprecoded pilots
WO2006069271A3 (en) Methods and apparatus for mitigating multi-antenna correlation effect in communication systems
WO2001071927A3 (en) Combined adaptive spatio-temporal processing and multi-user detection for cdma wireless systems
CA2437257A1 (en) Access channel structure for wireless communication system
EP1381172A3 (en) Adaptive transmit antenna diversity apparatus and method in a mobile communication system
EP1363406A4 (en) Mobile communication system, base station, and communication control method
WO2005101845A3 (en) Methods and apparatuses for minimizing co-channel interference
WO2007051206A3 (en) Method and apparatus for channel and noise estimation
WO2001086859A3 (en) Co-located frequency-agile system and method
WO2002019565A3 (en) Hopped delay diversity for multiple antenna transmission
WO2006121721A3 (en) Method and apparatus for estimating signal-to-noise ratio based on dedicated physical channel pilot symbols
MXPA05008763A (en) Communication receiver with an adaptive equalizer that uses channel estimation.
WO2006035292A3 (en) Parameter estimate initialization using interpolation after a change in one multipath delay
WO2002054614A3 (en) System, method and apparatus for wireless channel parameter estimation in spread spectrum communication systems
WO2004021580A3 (en) System and method for cdma communications
WO2003034677A1 (en) Transmitter and transmission control method, and receiver and reception control method
TW200501572A (en) Communication receiver with an adaptive equalizer length
WO2005053258A3 (en) Method and apparatus of frequency estimation for the downlink of td-scdma systems
WO2001067631A3 (en) Velocity-estimation-based transmission power gain tables
WO2003036891A3 (en) Channel estimation using a combination of correlation and least square error
EP1328080A4 (en) Method for improving channel estimation accuracy of wireless communication system

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NO NZ OM PH PL PT RO RU SD SE SG SI SK SL TJ TM TN TR TT TZ UA UG UZ VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
AK Designated states

Kind code of ref document: A3

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NO NZ OM PH PL PT RO RU SD SE SG SI SK SL TJ TM TN TR TT TZ UA UG UZ VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A3

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

REG Reference to national code

Ref country code: DE

Ref legal event code: 8642

122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP