US20130010907A1 - Selecting from Among Plural Channel Estimation Techniques - Google Patents
Selecting from Among Plural Channel Estimation Techniques Download PDFInfo
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- US20130010907A1 US20130010907A1 US13/620,737 US201213620737A US2013010907A1 US 20130010907 A1 US20130010907 A1 US 20130010907A1 US 201213620737 A US201213620737 A US 201213620737A US 2013010907 A1 US2013010907 A1 US 2013010907A1
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- Prior art keywords
- reference signals
- channel estimation
- wireless receiver
- wireless
- selection indication
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- 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
- H04L25/022—Channel estimation of frequency response
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- 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
-
- 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
- H04L25/024—Channel estimation channel estimation algorithms
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
- H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
Abstract
Description
- Various wireless access technologies have been proposed or implemented to enable mobile stations to perform communications with other mobile stations or with wired terminals coupled to wired networks. Examples of wireless access technologies include GSM (Global System for Mobile communications) and UMTS (Universal Mobile Telecommunications System) technologies, defined by the Third Generation Partnership Project (3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies, defined by 3GPP2. CDMA 2000 defines one type of packet-switched wireless access network, referred to as the HRPD (High Rate Packet Data) wireless access network.
- Another more recent standard that provides packet-switched wireless access networks is the Long Term Evolution (LTE) standard from 3GPP, which seeks to enhance the UMTS technology. The LTE standard is also referred to as the EUTRA (Evolved Universal Terrestrial Radio Access) standard. The EUTRA technology is considered to be fourth generation (4G) technology, to which wireless network operators are migrating to provide enhanced services.
- In general, according to some embodiments, a wireless receiver receives reference signals over a wireless link. The wireless receiver calculates a selection indication based on the received reference signals, and the wireless receiver selects from among plural channel estimation techniques based on the selection indication, where the selected channel estimation technique is usable to perform channel estimation of the wireless link.
- Other or alternative features will become apparent from the following description, from the drawings, and from the claims.
- Some embodiments are described with respect to the following figures:
-
FIG. 1 is a block diagram of an example arrangement including a wireless communications network incorporating some embodiments; -
FIG. 2 illustrates a subframe structure having demodulation reference signals useable by a process according to some embodiments; -
FIG. 3 is a flow diagram of the process of selecting from among multiple channel estimation techniques to perform channel estimation, according to some embodiments; and -
FIGS. 4A-4B illustrate example demodulation reference signal responses. - Channel estimation of a wireless link is used to determine a channel response of a wireless link to allow for removal or reduction of interference effects in the wireless link. Accurate channel estimation allows for improved performance in wireless communications in a wireless communications network, such as in the form of higher data rates and/or reduced errors caused by interference.
- Multiple channel estimation techniques may be available to perform channel estimation. However, different channel estimation techniques may not be optimal under different conditions. For example, one type of channel estimation technique is based on use of a time-domain averaging algorithm, which works well when a mobile station is moving relatively slowly, but can underperform in high-velocity situations. Another type of channel estimation technique involves use of a time-domain linear interpolation algorithm, which performs well in high-velocity conditions (when the mobile station is moving at a relatively high velocity), but underperforms in low-velocity conditions and in high-noise conditions.
- In accordance with some embodiments, techniques or mechanisms are provided to allow for real-time estimation of wireless link conditions so that real-time switching between different channel estimation techniques can be used. Real-time switching between different channel estimation techniques refers to the ability to determine channel conditions during a particular time interval, and to switch between different channel estimation techniques based on the determined channel conditions during that same time interval.
- In accordance with some embodiments, the determination of channel conditions for the purpose of performing switching between channel estimation techniques is based on reference signals received over the wireless link. In some implementations, the reference signals are demodulation reference signals (DMRS), which are reference signals used to enable coherent signal demodulation at a wireless receiver. In some examples, the demodulation reference signals are associated with transmission of uplink data and/or control signaling (transmission of data and/or control signaling from the mobile station to the base station). The demodulation reference signals are time-multiplexed with uplink data. The demodulation reference signals assist in estimating channel responses for uplink data so as to effectively demodulate the uplink channel.
- Although reference is made to demodulation reference signals in this discussion, it is noted that techniques or mechanisms according to some embodiments can be used with other uplink reference signals. More generally, a “reference signal” refers to a control signal that contains information to allow a wireless receiver to better process information received over a wireless link. Note also that although reference is made to uplink reference signals, in alternative implementations, other types of reference signals can be sent on the downlink (from the base station to the mobile station). Techniques or mechanisms according to some embodiments that allow for switching between different channel estimation techniques based on determined channel conditions can be applied to the uplink or downlink.
-
FIG. 1 illustrates an example arrangement that includes a wireless communications network, which includes an EUTRA (Evolved Universal Terrestrial Radio Access)wireless access network 102. The EUTRA standard, also referred to as the LTE standard, is defined by the Third Generation Partnership Project (3GPP). The EUTRAwireless access network 102 includes abase station 103, which in the context of the EUTRA is referred to as an enhanced node B (eNodeB). Thebase station 103 is able to perform wireless communications with amobile station 108 over awireless link 104. Although just onebase station 103 and onemobile station 108 are depicted inFIG. 1 , it is noted that there typically are multiple base stations and mobile stations in a wireless communications network. - A base station can perform one or more of the following tasks: radio resource management, mobility management for managing mobility of mobile stations, routing of traffic, and so forth. Generally, the term “base station” can refer to a cellular network base station or access point used in any type of wireless network, or any type of wireless transmitter/receiver to communicate with mobile stations. The term “base station” can also encompass an associated controller, such as a base station controller or a radio network controller. It is contemplated that the term “base station” also refers to a femto base station or access point, a micro base station or access point, or a pico base station or access point. A “mobile station” can refer to a telephone handset, a portable computer, a personal digital assistant (PDA), or an embedded device such as a health monitor, attack alarm, and so forth.
- As depicted in
FIG. 1 , themobile station 108 connects wirelessly to thebase station 103. Thebase station 103 is in turn connected to various components, including aserving gateway 110 and a mobility management entity (MME) 112. The MME 112 is a control node for the EUTRAaccess network 102. For example, the MME 112 is responsible for idle mode mobile station tracking and paging procedures. The MME 112 is also responsible for choosing the serving gateway for a mobile station at initial attach and at time of handover. The MME 112 is also responsible for authenticating the user of the mobile station. - The serving
gateway 110 routes bearer data packets. Theserving gateway 110 also acts as a mobility anchor for the user plane during handovers between different access networks. Theserving gateway 110 is also connected to a packet data network (PDN)gateway 114 that provides connectivity between themobile station 108 and the packet data network 116 (e.g., the Internet, a network that provides various service, etc.). - Reference to the EUTRA standard is intended to refer to the current EUTRA standard, as well as standards that evolve over time. It is expected that future standards evolve from EUTRA may be referred by different names. It is contemplated that reference to “EUTRA” is intended to cover such subsequently evolved standards as well.
- Although reference is made to EUTRA, note that techniques or mechanisms according to some embodiments are applicable for systems employing other types of wireless protocols.
- As further depicted in
FIG. 1 , thebase station 103 includes awireless receiver 120 to receive wireless information (bearer data and control signaling) over thewireless link 104. Thewireless receiver 120 includes channel estimation logic 122 (to perform channel estimation of the wireless uplink), and channel estimation technique switching logic 124 (to perform switching between channel estimation techniques in accordance with some embodiments). In some implementations, eachlogic mobile station 108 also includes a wireless receiver, which can also include channel estimation logic and channel estimation technique switching logic similar to those in thewireless receiver 120. -
FIG. 2 illustrates an exampleuplink subframe structure 200, which corresponds to a TTI (transmission time interval) according to EUTRA. The uplink subframe structure is defined by time along one axis and frequency along the other axis. The different frequencies correspond to different subcarriers (“SC”), starting withSC 0 and ending with SC n−1. The white rectangles in theuplink subframe structure 200 carry data, whereas the hashedrectangles DMRS symbol 202 occurs atsymbol position 3 in thesubframe structure 200, while theDMRS symbol 204 occurs atsymbol position 10 in thesubframe structure 200. - To determine channel conditions for the purpose of switching between channel estimation techniques, channel information received in the two
DMRS symbols uplink subframe structure 200 ofFIG. 2 ), real-time channel conditions can be determined and switching among multiple channel estimation techniques can be performed on a per-TTI basis. -
FIG. 3 is a flow diagram of a process performed by the channel estimationtechnique switching logic 124 ofFIG. 1 . The channel estimationtechnique switching logic 124 receives the twoDMRS symbols FIG. 3 ). Based on the DMRS symbols, DMRS processing is performed to calculate (at 304) a selection indication. In accordance with some example implementations, a selection indication is in the form of a parameter, referred to as Z in the discussed examples. The channel estimationtechnique switching logic 124 determines (at 306) the state of the parameter Z. If Z has a first value (e.g., Z=1), then frequency domain noise suppression is performed (at 308), and the linear interpolation algorithm is selected (at 310) to perform channel estimation. - On the other hand, if it is determined that Z has a second state (e.g., Z=0), then
tasks task 312 involves frequency domain noise suppression, andtask 314 involves selection of the averaging algorithm to perform channel estimation. - As depicted in
FIG. 3 , estimated channel response values are output (at 316), after application of the selected one of the linear interpolation algorithm and the moving average algorithm, to provide the channel estimation output. Although just two different types of channel estimation algorithms are noted in the described embodiments, it is noted that alternative or additional channel estimation algorithms can be used in other embodiments. - The frequency domain noise suppression performed at 308 or 312 in some examples can be based on frequency-domain moving averaging. Noise suppression is used to reduce noise to provide superior channel estimation results. As depicted in
FIG. 3 , the logic involved in performing the frequency domain moving averaging is represented generally as 320, where the input to the frequency domain moving averaging is represented as “IN” and the output of the frequency domain moving averaging is represented as “OUT.” The blocks “D” represent delay blocks, and the “X” circles represent multipliers (which in the example shown inFIG. 3 is multiply-by-⅕). The five multiplied signals are provided to a summer to produce the output. In the example ofFIG. 3 , the frequency domain moving averaging chooses N=2, which results in a filter order of 5. In other examples, other values of N can be used to provide other types or orders of filters. - The parameter Z is calculated as follows:
-
Z=sgn(F(dmrs1,dmrs2)−Delta), (Eq. 1) -
where -
sgn(x)=1 if x>0, or 0 if x<0, (Eq. 2) - and F(*) is a function of dmrs1 and dmrs2 (e.g.,
DMRS symbols FIG. 2 ) each including M tones, respectively, as shown below: -
dmrs1={h10 ,h11 , . . . , h1M-1}, -
dmrs2={h20 ,h21 , . . . , h2M-1}, (Eq. 3) - and Delta is a design parameter determined from simulation or testing.
- According to some examples, two DMRS symbols each can provide channel frequency response with noise added at a particular time instant in a subframe. The real relationship between channel frequency response and noise can be complicated but for analytical simplicity, one can assume that this relationship can be approximated by a summation of the channel frequency response at the ith subcarrier denoted as hi and the corresponding noise sample ni, i.e.,
-
d i k =h i k i=0,1 . . . , M; and k=a for DMRS1 or b for DMRS2, - where M is the number of used subcarriers and each quantity here is a complex number.
-
FIGS. 4A and 4B show example frequency responses of DMRS 202 (DMRS1) and DMRS 204 (DMRS2), respectively. As depicted, it is apparent that the two DMRS1 and DMRS2 responses are different—the differences between the two DMRS symbols are used to indicate the channel conditions such that selection between channel estimation techniques can be performed, in accordance with some embodiments. - In the wireless environment, channel frequency response varies with time due to the mobility of a mobile station. Since there is a time offset between DMRS1 and DMRS2 in each subframe, this time variation can be reflected by the difference between two received DMRS symbols (such as depicted in
FIGS. 4A-4B ). If a quantity (e.g., Z) can be selected to measure this difference, the quantity can be used to recognize how large the channel variation is along the time axis. - In some implementations, the mean of each DMRS sequence is chosen as the quantity to measure the status of each DMRS as a whole, and the status difference between two DMRS symbols is chosen as the quantity to measure the change of DMRS2 relative DMRS1 due to channel frequency response variation across the time period between two DMRS symbols. Therefore, according to some examples, the function, F(*), given previously can be expressed as:
-
- It should be pointed out that the second items in Eqs. 4 and 5 reflect noise suppression effect due to averaging, resulting in noise power reduction from its original power and an improvement of mean estimate of each DMRS. The larger the value of M, the more accurate the estimation will be.
- In the foregoing description, numerous details are set forth to provide an understanding of the subject disclosed herein. However, implementations may be practiced without some or all of these details. Other implementations may include modifications and variations from the details discussed above. It is intended that the appended claims cover such modifications and variations.
Claims (20)
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US13/620,737 US20130010907A1 (en) | 2009-07-15 | 2012-09-15 | Selecting from Among Plural Channel Estimation Techniques |
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US22566509P | 2009-07-15 | 2009-07-15 | |
PCT/IB2010/002070 WO2011007258A2 (en) | 2009-07-15 | 2010-07-15 | Selecting from among plural channel estimation techniques |
US201213383721A | 2012-01-12 | 2012-01-12 | |
US13/620,737 US20130010907A1 (en) | 2009-07-15 | 2012-09-15 | Selecting from Among Plural Channel Estimation Techniques |
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US201213383721A Continuation | 2009-07-15 | 2012-01-12 |
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US13/620,737 Abandoned US20130010907A1 (en) | 2009-07-15 | 2012-09-15 | Selecting from Among Plural Channel Estimation Techniques |
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EP (1) | EP2454901A4 (en) |
JP (1) | JP5712212B2 (en) |
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CA (1) | CA2768150C (en) |
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US9986388B2 (en) * | 2010-10-06 | 2018-05-29 | Unwired Planet International Limited | Method and apparatus for transmitting and receiving data |
US9071473B2 (en) | 2011-09-09 | 2015-06-30 | Telefonaktiebolaget L M Ericsson (Publ) | Method and system for wireless communication channel estimation |
KR102140298B1 (en) * | 2012-03-27 | 2020-07-31 | 삼성전자주식회사 | Method and apparatus for transmitting beam information in wireless communication system |
CN107332798B (en) * | 2016-04-29 | 2020-07-17 | 北京紫光展锐通信技术有限公司 | Terminal demodulation method and device for L TE system |
KR102017823B1 (en) * | 2016-08-30 | 2019-09-03 | 한국전자통신연구원 | Method and apparatus for estimating channel in terminal for narrow band Internet of things |
EP3340553B1 (en) * | 2016-12-22 | 2020-01-01 | Airbus Defence and Space GmbH | A method and apparatus for providing a channel response of a channel of interest |
CN110690951A (en) * | 2018-07-06 | 2020-01-14 | 维沃移动通信有限公司 | Information transmission method, network equipment and terminal |
US11283652B2 (en) * | 2019-05-08 | 2022-03-22 | National Taiwan University | Communication system and method |
KR20210037240A (en) * | 2019-09-27 | 2021-04-06 | 삼성전자주식회사 | Apparatus and method for reconstrucing downlink channel in wireless communication system |
WO2023068686A1 (en) * | 2021-10-18 | 2023-04-27 | 엘지전자 주식회사 | Method and device for transmitting/receiving wireless signal in wireless communication system |
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KR20120062693A (en) | 2012-06-14 |
KR101591635B1 (en) | 2016-02-03 |
CN102498734A (en) | 2012-06-13 |
JP2012533257A (en) | 2012-12-20 |
WO2011007258A2 (en) | 2011-01-20 |
JP5712212B2 (en) | 2015-05-07 |
EP2454901A2 (en) | 2012-05-23 |
CN102498734B (en) | 2015-04-15 |
RU2542732C2 (en) | 2015-02-27 |
WO2011007258A3 (en) | 2011-04-28 |
EP2454901A4 (en) | 2016-08-17 |
KR20150040321A (en) | 2015-04-14 |
CA2768150A1 (en) | 2011-01-20 |
US20120115470A1 (en) | 2012-05-10 |
KR20150001087U (en) | 2015-03-11 |
BR112012001022A2 (en) | 2016-03-15 |
US9131515B2 (en) | 2015-09-08 |
RU2012103504A (en) | 2014-01-20 |
CA2768150C (en) | 2016-09-20 |
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