KR101474231B1 - Method of cancelling interference in sounding reference signals to estimate utdoa - Google Patents

Abstract

The present invention provides a method of interference cancellation. Embodiments of the method include removing one or more first reference signals from a signal received by a first base station to form a modified signal. The signal may comprise a first reference signal (s) transmitted by a first user equipment served by a first base station and a second reference signal transmitted by a second user equipment served by a second base station Overlapping. The method also includes extracting a second reference signal (s) from the modified signal and extracting the second reference signal (s) from the second user equipment and the first base station Lt; RTI ID = 0.0 > a < / RTI >

Description

METHOD OF CANCELING INTERFERENCE IN SOUNDING REFERENCE SIGNALS TO ESTIMATE UTDOA < RTI ID = 0.0 >

Cross reference to related applications

This application claims priority from U.S. Provisional Patent Application No. 61 / 357,222 filed on June 22, 2010.

The present invention relates generally to communication systems, and more particularly to wireless communication systems.

Wireless communication systems implement networks of base stations or other access nodes to provide wireless connectivity to different geographical areas or cells. User equipment or other access terminals located within the cells may access the wireless communication system by establishing a wireless communication session with one or more access nodes. The user equipment may also move or roam between different cells, and thus the wireless communication system generally implements mobility functionality, which may be useful when the system handoffs user equipment between different access nodes, Lt; RTI ID = 0.0 > a < / RTI > serving access node. However, in some environments, the network may or may not need to determine a more accurate geographic location of the user equipment. For example, the network may provide location-dependent services that use the geographic location (e.g., coordinates such as latitude-longitude) of the user equipment to configure the services provided to the user equipment. As another example, the network may provide emergency services that, for example, allow user equipment to be placed in an emergency state in response to a 911 call from the user equipment.

Wireless communication devices, particularly mobile user equipment, often implement global location system (GPS) functionality to determine the geographic location of a device using multiple GPS satellite signals. However, GPS functionality consumes considerable battery power and therefore occasionally disables or turns off GPS functionality when users do not use certain location-dependent services that require geographic information. Disable GPS functionality can not provide required location information in emergency situations, enabling disabled GPS functionality and then obtaining the necessary satellite signals can result in significant time delays. Furthermore, GPS functionality may not work when the user equipment is hidden or shielded and it is impossible to obtain the required number of satellite signals.

The geographic locations of the user equipment may also be determined by triangulation or trilateration using distances between the user equipment and multiple base stations. For example, the user equipment can determine the geographical location using downlink observed time difference of arrival (OTDOA) measurements for signals transmitted by a group of neighbor base stations. The difference between the arrival times of the signals from the two different base stations can be used to determine the trajectory of the locations of possible user equipments. The locus generally includes one or more candidate locations and the redundancy / degradation may be decomposed using one or more additional trajectories determined using OTDOA for signals received from the other pair of base stations. However, the base stations that transmit positioning reference signals (PRS) may detect the downlink signals through a sufficiently high signal-to-noise ratio (SNR) or a signal-to-interference-plus-noise ratio (SINR) , It may be necessary to limit or mute the transmission at the same time as sending the OTDOA signals to reduce interference. This can have a significant impact on overall system performance. Moreover, OTDOA technologies require additional functionality and computational power in user equipment.

The disclosed subject matter relates to solving the effects of one or more of the problems described above. The following provides a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an overall overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to limit the scope of the disclosed subject matter. Its sole purpose is to provide some concepts in a simplified form as an introduction to a more detailed description that is discussed later.

In one embodiment, a method for interference cancellation is provided. Embodiments of the method may include removing one or more first reference signals from a signal received by the first base station to form a modified signal. The signal may comprise a first reference signal (s) transmitted by a first user equipment served by a first base station and a second reference signal transmitted by a second user equipment served by a second base station Overlapping. The method also includes extracting a second reference signal (s) from the modified signal and using the extracted second reference signal (s) to derive a timing delay between the second user equipment and the first base station And a step of determining the number

 In yet another embodiment, a method is provided for interference cancellation. Embodiments of the method may include modifying the signal received by the first base station using one or more estimated values of the one or more first channels received by the first base station. The signal comprises a superposition of one or more second channels transmitted by a first user equipment served by a first base station and a first channel (s) transmitted by a second user equipment served by a second base station. Embodiments of the method also include extracting a second channel (s) from the modified signal and determining a timing delay between the second user equipment and the first base station using the extracted second channel (s) can do.

The disclosed subject matter can be understood with reference to the following description, made with reference to the accompanying drawings, in which like reference numerals identify like elements.

1 conceptually illustrates a first exemplary embodiment of a wireless communication system;
Figure 2 conceptually illustrates a second exemplary embodiment of a wireless communication system;
Figure 3 conceptually illustrates one exemplary embodiment of an equivalent frequency domain channel (H (t)) for transmitting and receiving a sounding reference signal;
Figure 4 conceptually illustrates one exemplary embodiment of a location management unit;
5 is a conceptual illustration of one exemplary embodiment of a timing diagram;
Figure 6 conceptually illustrates one exemplary embodiment of a method for estimating the location of a user equipment using sounding reference signals;
Figures 7 and 8 illustrate the results of performing position estimation using UTDOA with and without the use of embodiments of sounding reference signal interference cancellation described herein.

While the disclosed subject matter may undergo various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.

 Exemplary embodiments are described below. For clarity, not all features of an actual implementation are described herein. Of course, in the development of any such actual implementation, it should be understood that many implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, will be. Moreover, it will be appreciated that these development efforts are complex and time-consuming, but nonetheless routine tasks for those of ordinary skill in the art having the benefit of this disclosure.

The disclosed subject matter will now be described with reference to the accompanying drawings. The various structures, systems, and devices are schematically illustrated in the figures, so as not to obscure the description for purposes of explanation and details that are well known to those skilled in the art. Nevertheless, the accompanying drawings are included to describe and describe illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have the same meaning as those skilled in the art understand these words and phrases. Any particular meaning of a term or phrase, i.e., any provision that is different from the ordinary and customary meaning understood by those skilled in the art, is not intended to be construed as being used herein through the consistent use of a term or phrase. As long as the term or phrase is intended to have a special meaning, that is to say a different meaning than those understood by those of ordinary skill in the art, this special provision is expressly set forth in the specification in a clear manner that provides a specific term or phrase specifically and explicitly will be.

In general, the present application describes embodiments of techniques that can be used to support position determination using uplink time delay of arrival (UTDOA) measurements. The location of the user equipment may be determined using uplink arrival time delay measurements for signals transmitted from the user equipment to its serving base station and two or more neighboring base stations (such as sounding reference signals). Because neighboring base stations are not selected as serving base stations, the user equipment is very likely to be located near the edges of neighboring base stations or even outside cell boundaries. Thus, the signal strength received at the neighboring base station from the user equipment is relatively weak compared to the signal strength received at the neighboring base station from the user equipment operating in the neighboring cell and / or served by the neighboring cell. As a result, the user equipment operating in the neighboring cell can generate strong interference to signals received from the user equipment associated with the serving cell. For example, cross-correlations between sounding reference signals generated using different root sequences may generate noise or interference between user equipment in a synchronized communication system. Although sequence hopping can be used to randomize interference, it has not been shown to provide sufficient uplink reach time delay performance.

The present application therefore describes embodiments of interference cancellation and / or noise cancellation techniques. In one embodiment, each neighbor cell extracts the reference signals transmitted by the user equipment served by the neighboring cell from the received signal. For example, a neighboring cell may decode sounding reference signal transmissions from a user equipment in a neighboring cell. The received signal may be a superposition of the reference signals from the user equipment served by the neighboring cell and the reference signals from the user equipment served by the serving cell. The extracted reference signals can be fed back so that they can be subtracted from the delayed form of the received signal. For example, the user equipment and sounding reference signals decoded from the neighboring cell may be subtracted from the received sounding reference signal symbol prior to performing decoding of the sounding reference signal symbol from the target user equipment for UTDOA measurements . The reference signals received from the user equipment served by the serving cell may then be extracted following the removal of the feedback signals. In some embodiments, the reference signals are accumulated for multiple subframes, for example, to increase signal-to-noise or signal-to-interference plus noise ratios. The accumulated signals can then be used to estimate timing delays between the user equipment and the receiving base station.

FIG. 1 conceptually illustrates a first exemplary embodiment of a wireless communication system 100. FIG. In the illustrated embodiment, the wireless communication system 100 includes a network of access nodes, such as base stations 105, that are used to provide wireless connectivity within corresponding geographic areas or cells. Alternate access nodes include access points, base station routers, evolved Node Bs, and so on. The base stations 105 may be configured to provide wireless connectivity in accordance with various standards and / or protocols. For clarity, only those aspects of the standards and / or protocols corresponding to the claimed subject matter will be discussed in detail herein. User equipment 110, 115, 120 may access wireless communication system 100 by establishing associations or connections with one or more base stations 105. Exemplary user equipment 110, 115, 120 may include devices that are generally referred to as mobile devices and which are freely movable, and / or devices that are commonly referred to as fixed devices and that are fixed or more difficult to move .

The base station 105 serves the access terminals of different cells that may or may not overlap in some areas. In the illustrated embodiment, base station 105 (1) is a serving access node for user equipment 110, as indicated by arrow 125. User equipment 115 is served by base station 105 (2) and user equipment 120 is served by base station 105 (3). For clarity, certain connections or associations between user equipment 115, 120 and base stations 105 (2-3) are not indicated by arrows. The base stations 105 (2-3) are capable of receiving signals from the user equipment 110, even if the user equipment 110 is not served by any of the base stations 105 (2-3) have. In the illustrated embodiment, the sounding reference signals transmitted by the user equipment 110 may be received at the base stations 105 (2-3) as indicated by the dashed arrows 130, 135. However, as discussed herein, the signals received at the base stations 105 (2-3) from the user equipment 110 are transmitted from the user equipment 115, 120 to the base stations 105 (2-3) May be relatively weak compared to the received signals. Moreover, the signals received from the user equipment 110 may be ambiguous by the interference or noise generated by the user equipment 115, 120 served by the neighboring base stations 105 (2-3). This interference may be achieved by extracting signals transmitted by the user equipment 115, 120 from the received signal, prior to attempting to decode the relatively weak signals received from the user equipment 110, as discussed herein Removed or canceled.

The user equipment 110 can be located using the uplink signals received at the base stations 105. [ In the illustrated embodiment, user equipment 110 may transmit sounding reference signals, which may be received by base stations 105, as indicated by, for example, arrows 125, 130, Channels. ≪ / RTI > If the timing errors and / or time offsets of the user equipment 110 are known accurately (e.g., within a particular tolerance), the timing of the received uplink signals may be compared to a timing reference, May be used to determine a timing delay that is indicative of the distances between the user equipment 110 and the base stations 105 by synchronizing the base station 105 with the user equipment 110. [ For example, each base station 105 may determine a corresponding timing delay indicative of the distance 140 between the base station 105 and the user equipment 110. Each base station 105 may thus determine that the user equipment 110 is located on a circle 145 defined by a corresponding distance or radius 140. The location of the user equipment 110 may be determined by combining information representative of the plurality of circles 145. Alternatively, if the timing errors and / or time offsets of the user equipment 110 are not known, a tridimensional metrology may be performed on the user equipment 110 based on the relative arrival time delays of the signals received at the different base stations 150. [ Can be used to determine the location. For example, the trilateration algorithm may be used such that unknown timing errors and / or time offsets associated with the user equipment 110 are at least partially offset by taking the difference of the two timing measurements for the user equipment 110 .

FIG. 2 conceptually illustrates a second exemplary embodiment of a wireless communication system 200. In the illustrated embodiment, wireless communication system 200 includes access nodes, such as base stations 205, that are used to provide wireless connectivity to one or more user equipments 210. For example, base station 205 (1) is a serving base station for user equipment 210, as indicated by arrow 215. User equipment 210 may therefore establish wireless communication links with serving base station 205 (1) over air interface channels. Signals transmitted by the user equipment 210 may be transmitted to the user equipment 210 in a direction indicated by the dashed arrows 220,225, although other neighboring base stations, such as the base stations 205 (2-3) May be received at these base stations 205 (2-3). Neighboring base stations 205 (2-3) may attempt to decode the signal received from user equipment 210 and use the decoded signals for various purposes, such as positioning.

In the illustrated embodiment, user equipment 210 transmits reference signals, such as pilot signals or sounding reference signals, over the air interface. By having the reference signals have a predetermined format, the base stations 205 can decode the signals and determine the time delay for the reference time used to synchronize the operation of the base stations 205 . In one embodiment, user equipment 210 may transmit constant amplitude zero autocorrelation (CAZAC) sequences of constant amplitude through the air interface on the channels assigned to the transmission of reference signals. For example, the user equipment 210 may generate a sounding reference signal sequence ( ^SRS ) using the circular movement of the root sequence:

S ^SRS (n) = e ^{j ? N} S _{?, V} (n)

In the above equation, S _{u , v} (n) is the root or base sequence, μ is the physical uplink control channel (PUCCH) sequence group number, and v is the basic sequence number. The cyclic shift (α) of the sounding reference signal is given by:

,

,

는 더 높은 기능 층들에 의해 각 이용자 장비를 위해 구성되고,

= 0, 1, 2, 3, 4, 5, 6, 7이다. 예시적인 CAZAC 시퀀스들은 Zadoff-Chu 시퀀스들을 포함하고, Zadoff-Chu 시퀀스들은 일정한 진폭의 전자기 신호를 생성하기 위해 무선 신호들에 인가될 수 있는 복소수-값의 수학적 시퀀스들이다. Zadoff-Chu 시퀀스는 시퀀스의 순환적으로 이동된 형태들이, 신호의 시간 도메인 내에서 보았을 때 각 순환 이동이 송신기와 수신기 사이에서 그 신호의 결합된 전파 지연 및 다중-경로 지연-분산보다 실질적으로 클 때, 서로에 대해 실질적으로 직교하는, 유용한 특성을 나타낸다.In the above equation

Are configured for each user equipment by higher functional layers,

= 0, 1, 2, 3, 4, 5, 6, 7. Exemplary CAZAC sequences include Zadoff-Chu sequences, and Zadoff-Chu sequences are mathematical sequences of complex-valued values that can be applied to wireless signals to produce an electromagnetic signal of constant amplitude. The Zadoff-Chu sequence indicates that the cyclically shifted forms of the sequence are such that each cyclic shift in the time domain of the signal is substantially larger than the combined propagation delay and multipath delay-variance of the signal between the transmitter and the receiver Exhibit useful properties that are substantially orthogonal to one another.

Figure 3 conceptually illustrates one exemplary embodiment of an equivalent frequency domain channel (H (t); 300) for transmitting and receiving a sounding reference signal (SRS). In the illustrated embodiment, the source signal S ^SRS is generated and provided to the front-end 305 of the transmitter. As discussed herein, the source signal may be an orthogonal sequence such as a CAZAC sequence. The front-end 305 of the transmitter includes a discrete Fourier transform (DFT) element 310 and an inverse fast Fourier transform (IFFT) element 315. The front-end 305 of the transmitter then provides a signal via the air interface channel h (t) 320 and the transmitted signal is received at the front-end 325 of the receiver, 325 includes a fast Fourier transform (FFT) element 330 and an inverse discrete Fourier transform (IDFT) element 335 for generating the received signal R ^SRS .

2, each of the illustrated embodiments of base stations 205 includes a location configured to generate location information using received signals, such as sounding reference signals received from user equipment 210 And a management unit (LMU) 230. For example, the LMUs 230 associated with the base stations 205 may be configured to measure a time delay for reference signals received from the user equipment 210 so that the location of the user equipment 210 may be determined have. Although LMUs 230 are shown as being implemented in base stations 205, those skilled in the art having the benefit of this disclosure should note that in alternative embodiments, LMUs 230 may be implemented in different locations For example, it should be appreciated that they can be stand-alone devices that are connected electronically and / or communicatively to base station 205. In the illustrated embodiment, each LMU 230 accesses the signal energy received over the reference channel and uses this information to attempt to decode the reference signals transmitted by the user equipment 210. The received signal energy may be a superposition of signals received from different user equipment. For example, the signal energy received by base station 205 (2) may be a superposition of reference signals transmitted by user equipment 210 and reference signals transmitted by other user equipment served by base station 205 . The LMUs 230 therefore receive the received signal by removing the estimated signals or channels for the user equipment served by the corresponding base station 205 before attempting to decode the reference signal transmitted by the user equipment 210. [ Can be modified.

Fig. 4 conceptually illustrates one exemplary embodiment of a portion of the location management unit 400. Fig. One function of the location management unit 400 is to identify and decode the reference signals transmitted by the user equipment that is not served by the base station associated with the location management unit 400. [ For example, the location management unit 400 may be used to measure time delays for reference signals transmitted by the target user equipment served by different base stations. The location management unit 400 may therefore remove or cancel the interference caused by the reference signals transmitted by the user equipment served by the base station associated with the location management unit 400. [ The reference signals from the target user equipment are then identified in the received signal after performing interference cancellation.

In the illustrated embodiment, the position management unit 400 includes a Discrete Fourier Transform (DFT) element 405, a Discrete Fourier Transform (DFT) element 405 receives signals transmitted over a reference signal channel And performs discrete Fourier transform on the received signals. The converted signals are then provided to the two branches 410. Signals transmitted on the first branch 410 (1) are provided to one or more time domain filters 415 and time domain filters 415 are provided to the user equipment To extract or extract reference signals received from the base station. In one embodiment, the reference signals for different user equipments are cyclically shifted forms of the root sequence, so that the different reference signals are shifted relative to each other in the time domain. The time domain filter 415 may thus be configured to filter and remove all reference signals except for the desired reference signal from the special user equipment served by the base station. The individual reference signals are then provided to a corresponding inverse discrete Fourier transform (IDFT) element 420 and are provided to multiplier elements 425 for multiplying these signals by the conjugate of the corresponding cyclically shifted root sequence, And generates a channel (H _i ) corresponding to the reference signal.

The second branch 410 (2) provides the received signals to the subtraction element 430 and the subtraction element 340 also receives the feedback signals from the IDFT element 420 of the first branch 410 (1) do. The feedback signals include signal energy for the reference signals transmitted by the user equipment served by the base station associated with the location management unit 400. The subtraction element 430 removes the signal energy for the feedback reference signals from the received signal. Delay elements 435 and 440 are used to delay signals in the first and second branches 410 so that the signals fed back for the particular symbol transmitted via the air interface are received Are synchronized with the same symbols of the signal. The modified signal is then provided to the time domain filter 445 and the time domain filter 445 filters or extracts the reference signal received from the target user equipment that is not served by the base station associated with the location management unit 400 . An individual reference signal is provided to a corresponding inverse discrete Fourier transform (IDFT) element 450 and is then provided to a multiplier element 455 for multiplying such a signal by the conjugate of the corresponding cyclically shifted root sequence, And generate a channel (H _i ) corresponding to the signal.

In one embodiment, location management unit 400 may be used to generate timing information for uplink arrival time difference (UTDOA) calculations. For example, the received SRS signals may be used to provide a reference received from a user equipment being served by a variety of different base stations when multi-cell SRS transmissions are adjusted, for example, using a common timing reference signal for transmissions in different cells Lt; / RTI > The received SRS signal can therefore be expressed as: < RTI ID = 0.0 >

In the above equation, subscripts j and k denote SRS transmissions from user equipment in neighboring measurement cells implementing the serving cell and location management unit 400, respectively.

The SRS signals received at the neighboring cell to perform the UTDOA measurements are combined with the SRS signals of the user equipment from all other cells including the measurement cell k and the target SRS signals from the user equipment associated with the serving cell j . ≪ / RTI > The primary interference to the SRS of the target user equipment is the SRS transmission from the user equipment of the neighboring measurement cell k. The SRS transmissions of user equipment from cells other than measurement cell k may be considered noise. The SRS interference cancellation scheme attempts to offset the SRS transmissions from the user equipment of the measurement cell. The interference cancellation can be expressed as:

는 수신된 심볼들로부터 제거될 수 있도록 피드백되는 채널을 나타낸다. UTDOA 측정들을 위한 타겟 SRS는 그 후 시간 도메인에서 제로-아웃 필터링을 통해 서빙 셀의 SRS 신호들로부터 추출될 수 있다. 필터링 절차는 다음과 같이 표현될 수 있다:In the above equation

Represents the channel being fed back so that it can be removed from the received symbols. The target SRS for UTDOA measurements can then be extracted from the SRS signals of the serving cell via zero-out filtering in the time domain. The filtering procedure can be expressed as:

는 UTDOA 측정을 위한 타겟 이용자 장비 이외의 서빙 셀의 이용자 장비를 위한 채널들을 나타낸다. 실제 채널들과 추정된 채널들 사이의 나머지 에러들은 매우 작다. SRS 간섭 상쇄 이후의 타겟 SRS는 그러므로 대략 다음과 같이 표현될 수 있다:In the above equation

Represents the channels for the user equipment of the serving cell other than the target user equipment for UTDOA measurements. The remaining errors between the actual channels and the estimated channels are very small. The target SRS after SRS interference cancellation can therefore be expressed approximately as:

In one embodiment, the SRS signals after the interference cancellation are accumulated over multiple SRS subframes, and then a timing offset estimation algorithm is applied to determine the timing delay associated with propagation between the target user equipment and the measurement cell .

Referring back to FIG. 2, the LMUs 230 may provide timing information for the reference signals to a central entity that can utilize the timing information to estimate the location of the user equipment 210. In the illustrated embodiment, the LMUs 230 send measured timing delays (for reference signals used by the base stations 205) to the signals received from the user equipment 210 to the serving mobile location center To a serving mobile location center (SMLC) 235. Embodiments of the illustrated SMLC 235 may be network elements of networks such as a European-style mobile communication (GSM) network. The SMLC 235 may be implemented in the base station controller and configured to calculate the network-based location of the user equipment, such as the user equipment 210. In the illustrated embodiment, the SMLC 235 utilizes the received timing information to determine a relative arrival time delay for signals received at different base stations 205. [

FIG. 5 conceptually illustrates one exemplary embodiment of a timing diagram 500. In the illustrated embodiment, the timing diagram shows reference signals 505, 510 received from the target user equipment by different base stations. These signals are synchronized to a common timing reference used by both base stations. A central entity such as eSMLC may collect timing information from different base stations and then use this information to determine relative arrival time delays 515 between signals received at different base stations from the target user equipment .

2, the eSMLC 235 may utilize the relative arrival time differences for the signals received by the pairs of base stations 205 to estimate the location of the user equipment 210. For example, For example, the relative uplink arrival time difference defines a hyperbola that includes the locus of points where the absolute value of the distance difference for two focuses (e.g., a pair of base stations) It is a constant determined by the difference. When the time difference of arrival is measured for signals received by three or more base stations, well known triangulation techniques may be used to identify the location of the user equipment 210, for example, using the intersections of various hyperbola Lt; / RTI >

Figure 6 conceptually illustrates one exemplary embodiment of a method 600 for estimating the location of a user equipment using sounding reference signals. In the illustrated embodiment, the target user equipment transmits sounding reference signals via the air interface, and the signals are received (at 605) in the serving cell and one or more neighboring cells. Neighboring cells may also receive sounding reference signals from user equipment being served by neighboring cells. The neighboring cell may therefore decode (at 610) the sounding reference signals received from the user equipment that the neighboring cell is serving. The energy associated with these user equipments can then be subtracted (at 615) from the received signal to form a modified signal. The sounding reference signals transmitted by the target user equipment may then be decoded (at 620) from the modified signal. The neighboring cell may then provide timing information to the central entity associated with the sounding reference signal of the target user equipment and the central entity may use the information provided by the serving and neighboring cells to provide uplink access to the relative timing delays By applying time delay techniques, this information can be used (at 625) to locate the target user equipment.

Figures 7 and 8 illustrate the results of performing position estimation using UTDOA with and without the use of embodiments of sounding reference signal interference cancellation described herein. Figures 7 and 8 illustrate the cumulative distribution function (CDF) of position errors (measured in meters) for different sets of simulation parameters. In both embodiments, the sounding reference signals are accumulated for 100 subframes before performing timing offset estimation. Performance requirements mandated by the US Federal Communications Commission (FCC) for ground positioning techniques require the system to locate user equipment with errors of at least 67% to less than 150m in frequency. US FCC regulations also require that the system be able to locate user equipment within an error of at least 95% to less than 300 m. Figure 7 shows the CDF of the position error when no interference cancellation is used. The results of FIG. 7 indicate that position errors of less than 150 m are achieved only at about 40-50% of the times and less than 90% of the times for cases where position errors of less than 300 m are considered. These results do not meet US FCC requirements. Figure 8 shows the CDF of the position error when embodiments of the interference cancellation techniques described herein are used. The results in FIG. 8 indicate that a position error of less than 150 m is achieved at approximately 95-97% of the times and a position error of less than 300 m is achieved at approximately 100% of the times. The results in FIG. 8 therefore meet the US FCC requirements.

Portions of the disclosed subject matter and corresponding detailed description have been presented in terms of software, or algorithms and symbolic representations of operations on data bits in computer memory. These descriptions and representations are those in which those skilled in the art effectively convey the gist of their work to others skilled in the art. As used herein, and as generally used, an algorithm is considered to be a self-matching sequence of steps leading to a desired result. Steps are those that require physical manipulations of physical quantities. Generally, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals that can be manipulated, stored, transferred, combined, compared, and otherwise manipulated. It has sometimes proven convenient to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, etc., for reasons primarily of common use.

It should be borne in mind, however, that all of these and similar terms will be associated with the appropriate physical quantities and are merely convenient labels adapted to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as "processing" or "computing" or "computing" or "determining" or " Which manipulates and transforms data represented as electronic quantities into other data similarly represented as physical quantities within computer system memories or registers or other such as information storage devices, transmission or display devices, , ≪ / RTI > or similar electronic computing device.

 It should also be noted that the software implemented aspects of the disclosed subject matter are typically encoded on some form of program storage medium or implemented on some type of transmission medium. The program storage medium may be magnetic (e.g., floppy disk or hard drive) or optical (e.g., compact disk read-only memory, or "CD-ROM") and may be read-only or random access. Similarly, the transmission medium may be twisted pair, coaxial cable, fiber optic, or some other suitable transmission medium known in the art. The disclosed subject matter is not limited to these aspects of any given implementation.

The particular embodiments disclosed above are by way of example only, since the disclosed subject matter can be modified and practiced in equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Moreover, no limitations are intended with respect to the details of construction and design shown in this specification, other than as described in the claims below. It is therefore to be understood that the particular embodiments disclosed above may be altered or modified and all such modifications are to be considered within the scope of the disclosed subject matter. Thus, the protection pursued herein is described in the claims below.

100, 200: Wireless communication system 105, 205: Base station
110, 115, 120, 210: user equipment 150: different base stations
305: TX front end 310, 405: DFT element
315: IFFT element 325: RX front end
330: FFT element
335, 420, 450: IDFT element
415, 445: Time domain filter

Claims (10)

Removing at least one first reference signal from a signal received by a first base station to form a modified signal, the signal being transmitted by a first user equipment served by the first base station, The at least one first reference signal and the at least one second reference signal transmitted by the second user equipment served by the second base station;
Extracting the at least one second reference signal from the modified signal; And
And using the at least one extracted second reference signal to determine a timing delay between the second user equipment and the first base station. The method according to claim 1,
Wherein removing the at least one first reference signal from the signal comprises filtering the at least one first reference signal from the signal using a time domain filter and filtering the at least one first reference signal from the signal received by the first base station Wherein subtracting the at least one first reference signal from the delayed form of the signal received by the first base station comprises subtracting at least one filtered first reference signal from the signal, Wherein subtracting the at least one second reference signal from the modified signal comprises subtracting the at least one second reference signal from the modified signal using a time domain filter, / RTI > The method according to claim 1,
Wherein determining the timing delay comprises comparing a time of arrival of the at least one reference signal with a reference time used by the first and second base stations, Accumulating the plurality of extracted second reference signals received through the subframes, and performing timing offset estimation using the accumulated plurality of extracted second reference signals. The method according to claim 1,
Providing information indicating a timing delay to the mobile location center so that a mobile location center can determine a plurality of relative timing delays between the user equipment, the first base station, the second base station and the at least one third base station, Wherein the mobile location center is capable of triangulating the location of the user equipment using the plurality of relative timing delays. The method according to claim 1,
Wherein the at least one first reference signal and the at least one second reference signal are sounding reference signals formed by cyclically shifting the root sequence. Modifying a signal received by a first base station using at least one estimated value of at least one first channel received by the first base station, 1 the at least one first channel transmitted by the user equipment and the at least one second channel transmitted by the second user equipment served by the second base station;
Extracting the at least one second channel from the modified signal; And
Determining a timing delay between the second user equipment and the first base station using the at least one extracted second channel. The method according to claim 6,
Determining the at least one estimated value of the at least one first channel by filtering the at least one first channel using a time domain filter, and extracting the at least one second channel Wherein filtering the modified signal comprises filtering the modified signal using a time domain filter and filtering the modified signal using a time domain filter to filter the modified signal by filtering the modified signal to remove channels transmitted by other user equipment served by the second base station. And filtering the filtered signal. The method according to claim 6,
Wherein determining the timing delay comprises comparing a time of arrival associated with the at least one first channel to a reference signal used by the first and second base stations, Accumulating energy associated with a plurality of second channels received over a plurality of subframes, and performing timing offset estimation using the accumulated energy. The method according to claim 6,
Providing information indicating a timing delay to the mobile location center so that a mobile location center can determine a plurality of relative timing delays between the user equipment, the first base station, the second base station and the at least one third base station, Wherein the mobile location center is capable of triangulating the location of the user equipment using the plurality of relative timing delays. The method according to claim 6,
Wherein the at least one first channel and the at least one second channel convey sounding reference signals formed by cyclically moving a root sequence.