WO2001039531A1 - A digital communication receiver containing a channel tracker and a method for the operation thereof - Google Patents
A digital communication receiver containing a channel tracker and a method for the operation thereof Download PDFInfo
- Publication number
- WO2001039531A1 WO2001039531A1 PCT/SE2000/002300 SE0002300W WO0139531A1 WO 2001039531 A1 WO2001039531 A1 WO 2001039531A1 SE 0002300 W SE0002300 W SE 0002300W WO 0139531 A1 WO0139531 A1 WO 0139531A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- channel
- channel estimate
- received signal
- tracker
- digital communication
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0212—Channel estimation of impulse response
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0224—Channel estimation using sounding signals
- H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
- H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
Definitions
- a digital communication receiver containing a channel tracker and a method for the operation thereof.
- the present invention relates to digital communication receivers of the type, which is adapted to communicate with a digital communication transmitter across a communication channel and which comprises a channel estimator for providing a channel estimate of the communication channel based on a received signal, an equalizer for estimating a sequence of transmitted symbols and providing a sequence of decided symbols based on the received signal and the channel estimate, and a channel tracker for producing an up- dated channel estimate based on the received signal and the decided symbols and for supplying the updated channel estimate to the equalizer.
- the invention is also directed at a wireless communication device, for instance a radio telephone, incorporating such a digital communication receiver, for instance a TDMA receiver.
- the present invention relates to a method of operating a digital communication receiver, where a channel estimate of a communication channel between the receiver and a corresponding communication transmitter is produced from a received signal, and where a sequence of decided symbols is produced from the received signal and the channel estimate.
- Digital communication receivers as set out above are widely used m modern communication systems. For instance, most modern systems for mobile or cellular telecommunication are based on digital communication, GSM and EDGE being two well-known examples. In a digital communication system, the digital communication receiver necessarily requires a considerable level of complexity m order to be able to handle signal distortion, such as multi-path propagation, and still be able to decode data transmitted from a digital communication transmitter.
- the radio channel between the transmitter and the receiver is time-varying, the reason for this being either that the host communication device itself (the device in which the receiver is incorporated, such as a mobile telephone) is moving, or that external objects are moving (for instance cars or trains) and generate spurious reflections of the transmitted radio wave, which may reach the receiver.
- the host communication device itself the device in which the receiver is incorporated, such as a mobile telephone
- external objects for instance cars or trains
- TDMA Time Division Multiple Access
- GSM Global System for Mobile Communications
- the information is transmitted in bursts from the transmitter across the radio channel to the receiver.
- Each burst contains information-carrying data, the contents of which are unknown a priori to the receiver, as well as a known training sequence.
- the training sequence is used for the purpose of synchronization and channel estima- tion in order to perform coherent detection of the received signal .
- FIG 1 illustrates a TDMA receiver architecture of the prior art .
- the burst is received at an antenna 1 as a radio or microwave signal having a carrier frequency of e.g. 900 MHz or 1800 MHz.
- a front-end receiver 110 receives the signal from the antenna 1, processes it and converts it down to a baseband signal y t .
- the front -end receiver 110 comprises various well-known components, such as filters, amplifiers, mixers and local oscillators.
- the received baseband signal y c is fed to a synchronizer 120, which is arranged to correlate the known training sequence with the received signal y t , which contains the same training sequence, wherein the synchronizer 120 is able to locate a synchronization position.
- the received signal y t is then fed together with the located synchroni- zation position to a channel estimator 130.
- the channel estimator 130 is arranged to determine an estimate, H, of the radio channel.
- the received baseband signal y_, the channel estimate H and the synchronization position are all supplied to an equalizer 140, which - based on a predetermined channel model - demodulates the received signal y t in order to estimate the transmitted data.
- This channel model is further described in Digi tal Communica tions , by J. Proakis, Mc Graw-Hill, New York, 1995, which is fully incorporated herein by reference.
- the equalizer 140 is arranged to estimate the transmitted symbols, u c .
- the equalizer 140 provides as a first output a sequence of decided symbols ⁇ t and as a second output a qualitative information M_ (labeled Metric in FIG 1) , which is a measure of how close to the transmitted symbols the estimated symbols are. This qualitative information will be used when the received signal is processed further.
- FIG 2 A previously known TDMA receiver architecture with a channel tracker is shown in FIG 2.
- the burst received by the antenna 1 is converted to a received baseband signal y_ by a front-end receiver 210
- the received signal is correlated with the known training sequence by a synchronizer 220 m order to find the synchronization posi- tion, and then the channel is estimated by a channel estimator 230 m correspondence with what has been described above for channel estimator 130 of FIG 1.
- the channel estimate H 0 is an initial estimate, which is used to start up an equalizing process performed by an equalizer 240.
- the equalizer 240 estimates a sequence of decided symbols u t as well as qualitative information (Metric) .
- the channel estimate H t is subsequently fed back to the equalizer 240, which will use the updated channel estimate in order to demodulate ⁇ t+1 , and so on.
- channel tracker 250 By using a channel tracker 250, problems can be managed, that are otherwise associated with host communication devices travelling at high velocities.
- the channel tracker 250 of the prior art receiver shown in FIG 2 is used constantly during all operational times, which means that a lot of unnecessary data processing is performed by the receiver, even when the velocity of the host communication device is low and good performance may be obtained without using a channel tracker.
- the channel tracker 250 since the channel tracker 250 is used all the time, the current consumption is undesiredly high for a previously known receiver, like the one illustrated in FIG 2.
- the above object has been achieved by the provision of a controller, which determines and evaluates the momentary quality of the communication channel and in response generates a control signal, which is used for enabling or disabling the channel tracker in a way, so that the channel tracker is only active in circumstances, where so is needed (when the quality of the communication channel is degraded due to e.g. high-velocity movement of the digital communi- cation receiver) .
- the channel tracker is turned on or off based on the current radio channel conditions.
- the decision whether to turn the channel tracker on or off may be based on the qualitative information out- put from the equalizer.
- the decision may alternatively be based on a comparison between new channel estimates at the end and/or at the beginning of a burst and an initial channel estimate.
- FIGs 1 and 2 are illustrations of two communication receivers of the prior art
- FIG 3 is a schematic block diagram illustrating a digital communication receiver according to a preferred embodiment
- FIG 4 is a schematic block diagram illustrating a digital communication receiver according to an alternate embodiment
- FIG 5 is a triple-graph diagram illustrating the typical appearance of the qualitative information output from the equalizer of the receiver m three different situations .
- the behavior of the qualitative information output (M t , Metric) of the equalizer depends on which kind of distortion, that is affecting the received signal y .
- Three different typi- cal behaviors of the qualitative information are shown for a receiver without any channel tracker (i.e. like the one illustrated m FIG 1) for three different scenarios.
- the fact that the receiver has no channel tracker means that the channel estimate obtained during the training sequence will be used for the entire burst.
- the uppermost graph of FIG 5 illustrates a scenario, where white noise represents the dominating distortion. It appears that the qualitative information is quite constant during both the training sequence (TS) and the information sequence (Data) .
- the dominating distortion originates from a co-channel mterferer, i.e. a remote transmitter, which is transmitting on the same carrier frequency. Since the co-channel mterferer might not be synchronized with the desired signal, only some part of the burst may be distorted (m FIG 5, the rightmost portion of the second graph) .
- FIG 3 illustrates a digital communication receiver 300 according to a preferred embodiment of the invention.
- the digital communication receiver 300 is connected to an antenna 1 for receiving a radio or micro- wave signal transmitted by a digital communication trans- mitter.
- the radio or microwave signal is supplied to a front-end receiver 310, which converts the signal down to a received baseband signal y t , in similarity with what has been described above with reference to FIGs 1 and 2.
- the front-end receiver 310 comprises various components known per se, such as filters, amplifiers, local oscillators and mixers, all of which are well-known to a man skilled in the art. Consequently, the internal structure of the front-end receiver 310 is not dealt with further herein.
- the received signal y t is supplied to a synchronizer 320, which correlates a known training sequence with the received signal y c containing the same training sequence, wherein the synchronizer 320 is able to locate the synchronization position.
- the received signal y c is supplied to- gether with the synchronization position to a channel estimator 330, which estimates the channel, H, in a way essentially similar to what has been described with reference to FIGs 1 and 2.
- the received signal y_, the channel estimate H, and the synchronization position are then supplied to an equalizer 340, which modulates the received signal in order to obtain the transmitted data.
- the equalizer 340 provides a first output in the form of a sequence of decided symbols u t and a second output in the form of a qualitative information (Metric) .
- the updated channel estimate H t is then fed back to the equalizer 340 through a switch 360, on condition that the switch 360 assumes a closed position.
- the switch 360 is controllable through a controller 370. If an updated channel estimate H c is in fact fed back through the closed switch 360 to the equalizer 340, the equalizer 340 will use the updated channel estimate H c when demodulating u t+1 , and so on.
- a controller 370 is provided in the communication receiver 300 shown in FIG 3.
- the controller 370 has a first input for receiving an updated channel estimate H t from the channel tracker 350.
- the controller 370 also has a second input for reading the qualitative information Metric provided by the equalizer 340. Based on the qualitative information, the controller 370 determines and evaluates the quality of the communication channel in order to decide whether the channel tracker 350 needs to be used or not. To this end, the channel tracker 350 is enabled and disabled, respectively, via a control signal from the controller 370 (labeled "Tracker y/n?" in FIG 3) .
- this control signal is given a first value when the channel tracker 350 is to be enabled, and a second value when the channel tracker 350 is to be disabled.
- the controller 370 is coupled to an electronic memory 390 (preferably a non-volatile memory such as a flash memory, an (EE)PROM memory or an SRAM memory) for storing a predetermined threshold value, i.e. an upper limit, for the qualitative information (Metric) from the equalizer 350.
- This upper limit defines an acceptable limit for a difference, preferably a squared distance as described above, between symbols in the received signal (y c ) and symbols in a predicted received signal given the decided symbols ( ⁇ t ) .
- the qualitative information is representa- tive of a degree of correspondence between the received signal and the decided symbols
- the controller 370 uses the predetermined upper limit as a criterion for determining whether the qualitative information does not meet this criterion, and consequently, whether the control signal "Tracker y/n 7 " will have to be given its first value, indicating that the channel tracker 350 needs to be enabled.
- the controller 370 may be realized as a programmable microprocessor, a programmable logic array, other logic circuitry, discrete logic gates and components, etc.
- the controller 370 is also adapted to determine whether the channel tracker 350 may be disabled (turned off) In this case, it is less suitable to use the above qualitative information produced by the equalizer 340, since the channel tracker 350 will try to follow the variations m the communication radio channel, implying that the qualitative m- formation produced by the equalizer 340 will be approximately constant during the entire burst. Instead, tne channel estimates H_ are supplied to the control unit 370, which will use these for determining whether the channel tracker 350 may be turned off or not.
- H n » H scar , w H end where H 0 is the initial channel estimate and H ⁇ tart , H end are the channel estimates at the beginning and the end of the burst, respectively, then the quality of the radio channel is acceptable, and the controller 370 determines that the channel tracker 350 may be turned off or disabled by giving the control signal "Tracker y/n 9 " a second value, as previously described
- the controller 340 decides to continue using the channel tracker 350 and, consequently, gives the con- trol signal "Tracker y/n 9 " its first value, as previously described.
- the control signal "Tracker y/n 7 " is also supplied to the switch 360 for setting it to an open and closed position, respectively.
- the antenna 1, front -end receiver 410, synchronizer 420, channel estimator 430, equalizer 440, channel tracker 450 and memory 490 are all essentially identical to the antenna 1, front-end receiver 310, synchronizer 320, channel estimator 330, equal- izer 340, channel tracker 350 and memory 390 of FIG 3, and the description thereof is not repeated now.
- the communication receiver 400 of FIG 4 does not use the qualitative information, Metric, when determining whether the channel tracker 350 is to be enabled or disabled. Instead, the decided symbols, u t , are supplied to a second channel estimator 480. Based on the decided symbols at the beginning and the end of the burst, new channel estimates, H_ Eart and H end , are obtained by the second channel estimator 480 and sub- mitted to the controller 470.
- the controller 470 decides to enable the channel tracker 450 by providing its control signal "Tracker y/n?" with a first value, wherein the channel tracker 450 will be ready to be used when the next burst is * received.
- the decision whether to turn the channel tracker 450 off is made in essentially the same way, as has been described above with reference to FIG 3.
- the digital communication receivers 300 and 400 shown in FIGs 3 and 4 are particularly well adapted to be incor- porated in a portable radio telephone, such as a GSM mobile telephone.
- a digital communication receiver according to the invention may very well be incorporated in a base station in a mobile telecommunication system, such as a GSM base station.
- the present invention is not limited to these examples, and the digital communication receiver according to the invention may be incorporated in virtually any host communication device.
- Other embodiments than the ones described above are equally applicable within the scope of the invention, as defined by the appended independent claims.
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
- Mobile Radio Communication Systems (AREA)
- Time-Division Multiplex Systems (AREA)
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00982006A EP1232660A1 (en) | 1999-11-25 | 2000-11-23 | A digital communication receiver containing a channel tracker and a method for the operation thereof |
JP2001540550A JP2003515997A (en) | 1999-11-25 | 2000-11-23 | Digital communication receiver including channel tracker and method of operation thereof |
AU19085/01A AU1908501A (en) | 1999-11-25 | 2000-11-23 | A digital communication receiver containing a channel tracker and a method for the operation thereof |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9904281A SE516962C2 (en) | 1999-11-25 | 1999-11-25 | Digital communication receiver with built-in control unit for switching on and off channel followers depending on the quality of the communication channel |
SE9904281-4 | 1999-11-25 |
Publications (1)
Publication Number | Publication Date |
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WO2001039531A1 true WO2001039531A1 (en) | 2001-05-31 |
Family
ID=20417862
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE2000/002300 WO2001039531A1 (en) | 1999-11-25 | 2000-11-23 | A digital communication receiver containing a channel tracker and a method for the operation thereof |
Country Status (7)
Country | Link |
---|---|
US (1) | US6888903B1 (en) |
EP (1) | EP1232660A1 (en) |
JP (1) | JP2003515997A (en) |
CN (1) | CN1169392C (en) |
AU (1) | AU1908501A (en) |
SE (1) | SE516962C2 (en) |
WO (1) | WO2001039531A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1427159A3 (en) * | 2002-08-16 | 2007-03-14 | Kabushiki Kaisha Toshiba | Channel estimation for use with MLSE |
Families Citing this family (8)
Publication number | Priority date | Publication date | Assignee | Title |
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JP3997890B2 (en) | 2001-11-13 | 2007-10-24 | 松下電器産業株式会社 | Transmission method and transmission apparatus |
US7221742B1 (en) * | 2002-06-26 | 2007-05-22 | Bellsouth Intellectual Property Corporation | Voicemail box with caller-specific storage folders |
US8073063B2 (en) * | 2005-08-23 | 2011-12-06 | Nortel Networks Limited | Methods and systems for orthogonal frequency division multiplexing (OFDM) multiple zone partitioning |
JP4606995B2 (en) * | 2005-10-28 | 2011-01-05 | Kddi株式会社 | Digital signal transmission method and transmitter |
US8059753B2 (en) * | 2006-09-21 | 2011-11-15 | Industrial Technology Research Institute | Adaptive channel estimator and adaptive channel estimation method |
TWI404378B (en) * | 2008-10-02 | 2013-08-01 | Mstar Semiconductor Inc | Channel estimator and channel estimation method |
TW201039574A (en) * | 2009-04-22 | 2010-11-01 | Ralink Technology Corp | Method of detecting transmission channel and a wireless communication system using the same |
GB2514174B (en) * | 2013-05-17 | 2015-12-02 | Cambium Networks Ltd | Improvements to adaptive modulation |
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WO1999062236A1 (en) * | 1998-05-27 | 1999-12-02 | Ericsson, Inc. | Apparatus and methods for variable delay channel tracking |
WO2000002328A1 (en) * | 1998-07-01 | 2000-01-13 | Ericsson Inc. | An equalizer with channel tracker switching |
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JPH03104329A (en) | 1989-09-19 | 1991-05-01 | Nippon Telegr & Teleph Corp <Ntt> | Mobile communication channel assignment control system |
JP3168610B2 (en) * | 1991-06-27 | 2001-05-21 | 日本電気株式会社 | Receiving machine |
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CA2083304C (en) * | 1991-12-31 | 1999-01-26 | Stephen R. Huszar | Equalization and decoding for digital communication channel |
US5577068A (en) * | 1992-06-08 | 1996-11-19 | Ericsson Ge Mobile Communications Inc. | Generalized direct update viterbi equalizer |
FR2706100B1 (en) * | 1993-03-03 | 1995-07-21 | Alcatel Mobile Comm France | Method for equalizing a block of data in reception in a time division multiple access communications system and receiver implementing this method. |
US5499272A (en) * | 1994-05-31 | 1996-03-12 | Ericsson Ge Mobile Communications Inc. | Diversity receiver for signals with multipath time dispersion |
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JPH0998465A (en) | 1995-09-29 | 1997-04-08 | Nec Corp | Portable radio telephone control method and portable radio telephone set |
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US6466616B1 (en) * | 1999-07-02 | 2002-10-15 | Telefonaktiebolaget Lm Ericsson (Publ) | Power efficient equalization |
-
1999
- 1999-11-25 SE SE9904281A patent/SE516962C2/en not_active IP Right Cessation
-
2000
- 2000-11-22 US US09/718,667 patent/US6888903B1/en not_active Expired - Fee Related
- 2000-11-23 JP JP2001540550A patent/JP2003515997A/en not_active Withdrawn
- 2000-11-23 AU AU19085/01A patent/AU1908501A/en not_active Abandoned
- 2000-11-23 CN CNB008162409A patent/CN1169392C/en not_active Expired - Fee Related
- 2000-11-23 WO PCT/SE2000/002300 patent/WO2001039531A1/en not_active Application Discontinuation
- 2000-11-23 EP EP00982006A patent/EP1232660A1/en not_active Withdrawn
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US5185764A (en) * | 1989-08-09 | 1993-02-09 | U.S. Philips Corporation | Receiver for time-varying distorted signals |
WO1999062236A1 (en) * | 1998-05-27 | 1999-12-02 | Ericsson, Inc. | Apparatus and methods for variable delay channel tracking |
WO2000002328A1 (en) * | 1998-07-01 | 2000-01-13 | Ericsson Inc. | An equalizer with channel tracker switching |
Cited By (2)
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EP1427159A3 (en) * | 2002-08-16 | 2007-03-14 | Kabushiki Kaisha Toshiba | Channel estimation for use with MLSE |
US7330505B2 (en) | 2002-08-16 | 2008-02-12 | Kabushiki Kaisha Toshiba | Equaliser apparatus and methods |
Also Published As
Publication number | Publication date |
---|---|
SE9904281D0 (en) | 1999-11-25 |
CN1399852A (en) | 2003-02-26 |
CN1169392C (en) | 2004-09-29 |
JP2003515997A (en) | 2003-05-07 |
SE516962C2 (en) | 2002-03-26 |
AU1908501A (en) | 2001-06-04 |
SE9904281L (en) | 2001-05-26 |
EP1232660A1 (en) | 2002-08-21 |
US6888903B1 (en) | 2005-05-03 |
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