(19)
(11)EP 2 790 368 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
06.05.2020 Bulletin 2020/19

(21)Application number: 14163515.1

(22)Date of filing:  04.04.2014
(51)International Patent Classification (IPC): 
H04L 27/26(2006.01)
H04J 11/00(2006.01)

(54)

Cyclic prefix based opportunistic transmission/reception scheme for interference cancelation

Auf zyklischen Präfixen basiertes opportunistisches Übertragungs-/Empfangsschema für Interferenzunterdrückung

Schéma de transmission/réception opportuniste à base de préfixe cyclique pour l'annulation d'interférence


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 09.04.2013 US 201313859252

(43)Date of publication of application:
15.10.2014 Bulletin 2014/42

(73)Proprietor: Nokia Technologies Oy
02610 Espoo (FI)

(72)Inventors:
  • Paiva, Rafael
    69093-415 Manaus - AM (BR)
  • Cavalcante, Andre Mendes
    69093-415 Manaus - AM (BR)
  • Domingos, Robson
    70397-900 Brasilia - DF (BR)
  • Chaves, Fabiano
    69093-415 Manaus - AM (BR)
  • Junior, Fuad
    69093-415 Manaus - AM (BR)
  • Sobrinho, Angilberto
    69093-415 Manaus - AM (BR)
  • Almeida, Erika
    69093-415 Manaus - AM (BR)

(74)Representative: Laine IP Oy 
Porkkalankatu 24
00180 Helsinki
00180 Helsinki (FI)


(56)References cited: : 
US-A1- 2012 106 372
  
  • STEFANO GALLI ET AL: "The inter-PHY protocol (IPP): A simple coexistence protocol for shared media", POWER LINE COMMUNICATIONS AND ITS APPLICATIONS, 2009. ISPLC 2009. IEEE INTERNATIONAL SYMPOSIUM ON, IEEE, PISCATAWAY, NJ, USA, 29 March 2009 (2009-03-29), pages 194-200, XP031453685, ISBN: 978-1-4244-3790-0
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

BACKGROUND:


Field:



[0001] Embodiments of the invention generally relate to communication networks, such as wireless networks. More specifically, embodiments may relate to interference cancelation in wireless networks.

Description of the Related Art:



[0002] Considerable research and development in wireless communications has been dedicated to cognitive radio and the coexistence of different wireless communications technologies. In these types of systems, a given frequency band may be shared between different wireless technologies. This sharing of frequency bands can result in interference among the different wireless technologies, or can even result in one system blocking the other. In order to enhance the spectrum usage, some coexistence strategy may be required so that different technologies are able to use the resources in an efficient manner.

[0003] Coexistence strategies are usually defined as cooperative or non-cooperative. The cooperative strategies often include some type of agreement between the systems in order to get a fair spectrum share. Cooperative strategies often result in one system giving away some of its resources to the other. As a result, the application of cooperative strategies may not result in benefits to the system that is mostly giving away its resources. On the other hand, non-cooperative strategies can be implemented without the consideration of one system sharing its resources with the other. Although non-cooperative technologies may result in smaller overhead and typically cheaper implementation, they will usually be less efficient than the cooperative strategies.

[0004] STEFANO GALLI ET AL: "The inter-PHY protocol (IPP): A simple coexistence protocol for shared media", POWER LINE COMMUNICATIONS AND ITS APPLICATIONS, 2009. ISPLC 2009. IEEE INTERNATIONAL SYMPOSIUM ON, IEEE, PISCATAWAY, NJ, USA, 29 March 2009 (2009-03-29), pages 194-200, XP031453685, ISBN: 978-1-4244-3790-0, discloses a Commonly Distributed Coexistence Function waveform obtained by repetition of baseband windowed OFDM signals for broadband Power Line Communications. Devices in PLC networks indicate their presence and requirements by transmitting simultaneously the CDCF waveform with an appropriate phase vector and in an appropriate time window (the CDCF window). CDCF detection means that a neighboring device is in interference range.

SUMMARY:



[0005] The invention is defined by the independent claims.

[0006] There is provided a method for interference cancellation according to claim 1, an apparatus according to claim 12 and a computer program according to claim 15.

[0007] Preferred embodiments are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS:



[0008] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

Fig. 1a illustrates an example of the time structure of an OFDM signal, according to an embodiment;

Fig. 1b illustrates an example of a cyclic prefix based opportunistic signal, according to one embodiment;

Fig. 2 illustrates an example of the cyclic prefix based opportunistic transmission scheme for two OFDM symbols, according to an embodiment;

Fig. 3 illustrates an example of an OFDM transmitter structure for cyclic prefix based opportunistic transmission, according to an embodiment;

Fig. 4 illustrates an example of a comb filter, according to one embodiment;

Fig. 5 illustrates an example of interference cancelation results, according to an embodiment;

Fig. 6a illustrates resulting throughput achieved according to certain embodiments;

Fig. 6b illustrates throughput gain achieved according to certain embodiments;

Fig. 7a illustrates an example of Shannon capacity analysis in interference conditions for certain embodiments;

Fig. 7b illustrates an example of Shannon capacity gain analysis in interference conditions for certain embodiments;

Fig. 7c illustrates an example of Shannon capacity gain analysis in interference conditions for certain embodiments;

Fig. 8 illustrates an apparatus, according to one embodiment; and

Fig. 9 illustrates a flow diagram of a method, according to an embodiment.


DETAILED DESCRIPTION:



[0009] It will be readily understood that the components of the invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of a system, a method, an apparatus, and a computer program product for interference cancellation, as represented in the attached figures, is not intended to limit the scope of the invention, but is merely representative of selected embodiments of the invention.

[0010] If desired, the different functions discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions may be optional or may be combined. As such, the following description should be considered as merely illustrative of the principles, teachings and embodiments of this invention, and not in limitation thereof.

[0011] One embodiment provides a non-cooperative coexistence strategy, based on exploring the OFDM symbols structure for interference cancelation purposes.

[0012] Uncoordinated spectrum sharing is a difficult task when technologies have different access schemes. As an example, if LTE and WiFi are deployed in the same spectrum and location, WiFi senses that the channel is busy due to a LTE transmission for most of the time, and, consequently, WiFi is blocked most of the time. On the other hand, if WiFi loosens its Carrier sense multiple access with collision avoidance (CSMA/CA) thresholds, the high interference caused by LTE could increase significantly the packet error rate of WiFi. Hence, it is highly desirable to obtain effective interference cancelation techniques that enable coexistence between different systems or technologies.

[0013] It should be noted that, while embodiments described herein use LTE and WiFi as examples of wireless technologies to which embodiments can be applied, embodiments of the invention are not limited to these example technologies. For example, embodiments may be applicable to wireless networks including, but not limited to, radio access networks such as the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) Long Term Evolution (LTE) and Evolved UTRAN (E-UTRAN) or LTE-A, High Speed Packet Access (HSPA) and HSPA+, wireless local area networks (WLAN) such as WiFi, and WiMAX, or any other legacy, current, or future wireless technology.

[0014] Certain embodiments provide a solution for interference cancellation, for example, when different technologies use the same spectrum band. In one embodiment, a non-cooperative interference cancellation transmit/receive scheme is provided, where the structure of orthogonal frequency-division multiplexing (OFDM) signals is considered. OFDM signals have a predefined symbols structure that may be used for interference cancelation. Fig. 1a illustrates an example of the time structure of an OFDM symbol. In particular, Fig. 1a depicts an overview of an OFDM symbol time structure, where B represents the cyclic prefix and its repetition, and A represents the symbol part without redundancy. In this structure, the time domain signal is created by processing the frequency domain OFDM symbol using an inverse fast Fourier transform (IFFT). Additionally, as depicted in Fig. 1a, the cyclic prefix is inserted repeating B at the beginning of the signal. Hence, Fig. 1a illustrates that an OFDM signal has a known redundancy which can be exploited for interference cancelation, according to certain embodiments discussed in detail below.

[0015] An objective of the transmit/receive scheme, according to one embodiment, is the transmission of data in an extreme non-cooperative interference condition where one technology would take over the channel while the other is completely blocked by interference. Additionally, certain embodiments may also be used in situations where simultaneous transmissions of two technologies are desirable.

[0016] Certain embodiments provide for the design of a signal structure that matches the structure of an OFDM symbol, as illustrated in Fig. 1b. For example, Fig. 1b illustrates an overview of the opportunistic scheme, where x1 and x3 are synchronized with the cyclic prefix and its repetition, and x2 is aligned with the rest of the symbol (e.g., A). In this embodiment, the transmitted signals x1 and x3 are respectively chosen in order to cancel the cyclic prefix and its repetition, and to reconstruct the desired signal in an optimum way. A general description of the solution, according to one embodiment, is described according to the following formulas:



where s1 and s2 are two data signals, and kn,m represents the mapping of data signal sm into the transmitted signal xn. The data signals sm may include OFDM symbols, or any other type of modulated signal with a symbol length smaller than the length of the cyclic prefix of the interfering technology.

[0017] Since embodiments take into consideration the cyclic prefix redundancy, some embodiments may be referred to as cyclic prefix based opportunistic transmission/reception (CPoTx). However, other naming conventions can be used according to other embodiments.

[0018] One implementation for Equation 1 and Equation 2 includes ignoring the second data signal s2, and making k1,1 = 1 and k1,2 = -1 in Equation 1 and Equation 2, which yields:



[0019] Once the result of Equation 3 is applied, the received signals y1 and y3 are obtained as:



where h and g represent the channel impulse response for the signal s and B, respectively, n represents the noise, and the symbol "∗" represents the time domain convolution. Given the received signals at Equation 4 and Equation 5, the effect of the interference over s and B can be removed by performing:



where rs is the received signal after canceling the interference B, and rb is the received signal after canceling s.]The result of Equation 6 shows that the interference of the cyclic prefix can be completely canceled at the receiver when choosing the transmission scheme of Equation 3. In other words, according to an embodiment, the cyclic prefix repetition of the interfering signal can be completely removed in the received signal. In the example of Equation 7, the term g*B of the LTE interference is completely removed since B is repeated twice and g is the same for both repetitions. Thus, certain embodiments provide a solution which can be used in extreme interference conditions with high interference level. In this embodiment, an interference with large power has known OFDM structure, with a symbol length which is larger than the symbol length of a second technology. Given this knowledge, certain embodiments are able to transmit a repeated version of the desired signal with opposite phase at the repeated version of the cyclic prefix, which enables perfect elimination of the interference as in Equation 6. As an additional advantage of the implementation of Equation 3, perfect elimination of the interference in the cyclic prefix of the interferer for estimation of B is enabled by Equation 7. This is an important result, since both technologies would have the means for interference cancellation once the structure of Fig. 1(b) is known. Additionally, the solutions of Equation 6 and Equation 7 provide an additional 3 dB signal-to-noise ratio_(SNR) gain, due to the averaging of the noise.

[0020] In another embodiment, one additional implementation of Equation 1 and Equation 2 is possible without repetition of the message, as:





[0021] In this embodiment, the data message is only transmitted at the repeated cyclic prefix. The received signal is the same as in Equation 5, and the interference over s can be removed as:



[0022] This embodiment yields smaller power consumption, since there is no repetition of the data message. However, this embodiment assumes that no other source of interference is present at the cyclic prefix, and any other source of interference will be included at the noise terms. Secondly, the 3 dB SNR gain will not be observed in this embodiment, since there is no averaging operation for estimating s.

[0023] Fig. 2 illustrates an example of the cyclic prefix based opportunistic transmission scheme for two OFDM symbols, according to an embodiment. In the example of Fig. 2, the DATA0 and DATA2 parts are repeated with opposite signals for optimum interference cancelation at the receiver.

[0024] Fig. 3 illustrates an example of the OFDM transmitter implementations for the CPoTx transmission scheme, according to one embodiment. In this implementation, only the cyclic prefix protected portion of the time is used. This implementation can be applied for interference scenarios where transmitting at the non-robust part is useless, or when it would be best used by another user.

[0025] According to one embodiment, both the transmitter and the receiver may be synchronized with the interfering technology. In an embodiment, this can be done using autocorrelation methods, or using the synchronization signals of the interfering technology. As an exemplary implementation, if the interferer technology is LTE, for example, the primary synchronization signal (PSS) and secondary synchronization signal symbol (SSS) can be used for synchronization. If the interference is from another technology, technology-specific synchronization signals can be used, or a simpler estimation of the beginning of symbol times can be obtained using autocorrelation metrics. Secondly, the transmitter can build the transmitted signal as in Fig. 3, where one part of the signal is repeated at the cyclic prefix of the interfering technology.

[0026] Changes at the medium access control (MAC) layer of both the transmitter and the receiver are also necessary. For instance, the receiver may need to be made aware of the use of CPoTx transmitting structure, and this indication can be implemented with special signaling between the transmitter and receiver. Examples of possible implementations of such signaling for WiFi include the access point (AP) notifying the stations (STAs) at network subscription and authentication stages, or using special Information Element (IE) fields at regular MAC protocol data unit (MPDU) headers. Additionally, if a WiFi network uses this technique, its AP may have a special field in its beacon indicating that this feature is enabled.

[0027] As an example of implementation for WiFi, when an AP detects it is blocked by LTE it can switch to an operation mode where it only transmits or receives MPDUs using CPoTx as the transmission structure, which includes Beacon transmission and regular MPDUs. Also, as part of this exemplary implementation, the AP might define that when CPoTx is used then all resource allocations are scheduled by the AP, which for that might use polling techniques like 802.11n power-save multi-poll (PSMP) for implementing such centralized scheduling. This exemplary implementation allows the AP to better utilize the scarce resources while coexisting with another technology.

[0028] Additionally, the receiver may need to combine the repetitions of the signal. This can be implemented using a comb filter that implements Equation 6, as illustrated in the example of Fig. 4, where the DELAY element may implement a fractional delay filter if the sampling frequencies of both technologies are not matched. On the interferer side no changes are required in order for this technique to work. In case of WiFi and LTE coexistence, for example, the required changes may need to be implemented only in WiFi Tx/Rx chain.

[0029] According to certain embodiments, one advantage is to guarantee a minimum throughput in extreme interference scenarios. One example of such a scenario is in which a WiFi (i.e., IEEE 802.11 standard) network coexists with an LTE network. In this example, the LTE network will block the WiFi network for most of the time. It has been shown that, in this scenario, the WiFi network usually remains in contention mode for at least 90% of the time and is nearly never able to access the channel, resulting in a decrease in WiFi user throughput of between 50% and 100% depending on the network scenario. However, when embodiments of the invention are applied, the WiFi network would be able to have additional channel access time

[0030] The performance of certain embodiments can be analyzed as discussed in the following. The maximum throughput of the CPoTx protected period is calculated as throughput when no interference is present, multiplied by an scaling factor βCPoTx given by:

where TCPoTx is the useful time inside the cyclic prefix of the interferer where the CPoTx signal can be transmitted, and TINTERF is the interference symbol length. It is noted that TCPoTx is bounded by the length of the cyclic prefix of the interference TCPoTx ≤ TCP, and will usually be an integer multiple of the symbol length of the transmitting technology.

[0031] The simulations presented below are based on the scenario where an IEEE 802.11ac network coexists with a LTE network. Although the results are shown for this case, they could be easily generalized for coexistence with other technologies and are, therefore not limited to this example. In this simulation scenario, a 20 MHz LTE interferer using long cyclic prefix interferes in a WiFi network with 4 µs symbol length. Since the LTE interferer has 16.67 µs cyclic prefix length, four WiFi symbols are transmitted at each cyclic prefix period. This results in 16 µs being used by WiFi for transmission of CPoTx signals, yielding a throughput factor βCPoTx = 0.19.

[0032] The interference cancelation results are illustrated as average power over 2000 iterations in Fig. 5. In the example of Fig. 5, an LTE interference which is 15 dB larger than the noise floor is analyzed. This interference is resampled to 20 MHz bandwidth, and is filtered by a 10 taps complex finite impulse response (FIR) filter emulating a channel impulse response. The interference cancelation test is performed by filtering the LTE interference by an FIR filter emulating the operation of Equation 6. In practice, this operation is likely performed only over the cyclic prefix repetitions, but it is shown here for illustrative purposes. When observing these results, one notices that the overall interference power is reduced 3 dB in most of the time due to the averaging operation, and that this interference is further reduced 3 dB below the noise floor level during the repetition of the cyclic prefix. This shows that the interference can be effectively cancelled during the CPoTx periods. Additionally, the same filtering process may be applied to a WiFi signal using the CPoTx scheme as presented in Equation 3 and Fig. 3. The results in Fig. 5 show that the power of the WiFi signal is kept constant at the CPoTx period while the interference is canceled, leading to an SINR improvement of 18 dB.

[0033] One additional conclusion can be taken from Fig. 5 with respect to the synchronization of WiFi with LTE. In some embodiments, the CPoTx technique may require synchronization with the interferer. When observing the curve of CPoTx interference+noise power in Fig. 5, it is possible to conclude that a simple FIR filtering process can be used for synchronizing the system using CPoTx with the interferer cyclic prefix if the symbol length of the interference is known. This illustrates the feasibility of this technique when the synchronization with the interference symbols is considered.

[0034] The throughput gain of the CPoTx method, according to certain embodiments, is illustrated in Fig. 6a. In the example results illustrated in Fig. 6a, the baseline WiFi throughput curves were obtained by link level simulations with LTE interference 5 dB over the noise floor level. The WiFi curves were generated with MCS 0, 4 and 8, and perfect link adaptation between them is assumed. The curves are presented in terms of signal to noise levels (SNR), hence the "LTE interference+noise" curve is shifted in comparison to the "noise only" curve. The CPoTx only of the scheme of Fig. 3 is labeled as "CP transmission", and is calculated by multiplying the "noise only" curve by the factor βCPoTx = 0.19, and shifting this curve by 3 dB to emulate the noise attenuation obtained with the averaging operation.

[0035] The "CP transmission" throughput results of Fig. 6a show significant gains when compared to the case where interference is present at low SNRs. These results illustrate that embodiments are capable of yielding some connectivity for users under extreme interference conditions. Overall, the throughput gain is illustrated in Fig. 6b, which may be significantly high for SNRs below 5 dB SNR. Additionally, the throughput gain is negative for SNRs larger than 5 dB. The reason for this behavior is that the maximum throughput obtained with the CPoTx is proportional to and limited by the effective time for data transmission, and above a certain level of SNR (about 5 dB in this example), the WiFi transmission without interference cancelation becomes reasonable. Thus, Fig. 6b illustrates that the CPoTx should not be used for large SNRs, and some adaptation procedure from CPoTx to/from normal mode could be used.

[0036] It should be also noted that the example results illustrated in Fig. 6 apply for an interferer 5 dB above the noise floor. However, if the interference is larger, the expected throughput gains according to certain embodiments of the CPoTx method are expected to yield even larger gains. In this case, the "LTE interference+noise" curve illustrated in Fig. 6a would be shifted further to the right hand side direction, while the "CP transmission" would remain unchanged.

[0037] Fig. 7 illustrates the generalization of the results in Fig. 6, according to an embodiment. In the example of Fig. 7, the Shannon theoretic capacity for a 20 MHz channel may be calculated as:

where p is the noise power with SNR = -10 log10(ρ), Pi is the interference power, and BW is the bandwidth. The capacity of Equation 12 is determined considering that the interference has the same effect as the noise in the channel capacity. Additionally, the noise and interference power are related by the interference to noise ratio (INR), INR = 10 log10(Pi/ρ). On the other hand, the capacity when using the CPoTx may be calculated as:



[0038] It is noted that the SNR term in Shannon's formula is increased by two and the interference term Pi is zero, since the CPoTx filter of Equation 6 decreases the noise power by 3 dB. However, the capacity using the CPoTx is never larger than the capacity in Additive white Gaussian noise (AWGN) channel with Pi = 0, since the factor βCPoTx is always smaller than 0.5. In an embodiment, βCPoTx is the throughput scaling factor, for example, used to obtain the CPoTx throughput when the throughput without CPoTx is available. Fig. 7 illustrates the results for LTE long CP length with βCPoTx = 0.19 and LTE short CP length with βCPoTx = 0.06.

[0039] The results in the example of Fig. 7b illustrate that when LTE's long CP length is used, embodiments of the CPoTx method provide gains when the interference to noise ratio (INR) is larger than 5 dB. Furthermore, the gains become significantly large for high INR values. As an example, the CPoTx gain at SNR=-15 dB is 4 for INR = 10 dB and 370 for INR = 30 dB. Additionally, the SNR range in which the CPoTx yields gains increases with the INR increase. The CPoTx results in gains larger than 1 when the SNR is smaller than 9, 16 and 23 for INR equal to 10, 15 and 20, respectively.

[0040] The theoretical gains for LTE's short CP length are illustrated in Fig. 7c. Even with the small amount of available resources, embodiments of the CPoTx method are capable of yielding significant capacity gains when the INR is large.

[0041] Fig. 8 illustrates an apparatus 10 according to one embodiment. Apparatus 10 may include a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. While a single processor 22 is shown in Fig. 8, multiple processors may be utilized according to other embodiments. In fact, processor 22 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[0042] In an embodiment, apparatus 10 may further include a memory 14, coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 14 can be comprised of any combination of random access memory ("RAM"), read only memory ("ROM"), static storage such as a magnetic or optical disk, or any other type of non-transitory machine or computer readable media. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 10 to perform tasks as described herein.

[0043] Apparatus 10 may also include one or more antennas (not shown) for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include a transceiver 28 that modulates information on to a carrier waveform for transmission by the antenna(s) and demodulates information received via the antenna(s) for further processing by other elements of apparatus 10. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly. According to one embodiment, apparatus 10 may include an OFDM transmitter structure for cyclic prefix based opportunistic transmission, as illustrated in Fig. 3 and discussed in detail above. In addition, in one embodiment, apparatus 10 may also include a comb filter for receiving a cyclic prefix based opportunistic transmission, as illustrated in Fig. 4 and outlined above.

[0044] According to an embodiment, processor 22 may perform functions associated with the operation of apparatus 10 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication resources.

[0045] In an embodiment, memory 14 stores software modules that provide functionality when executed by processor 22. The modules may include an operating system 15 that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules 18, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software.

[0046] According to certain embodiments, processor 22 and/or memory 14 may cause apparatus 10 to form a signal structure to match a structure of an orthogonal frequency-division multiplexing (OFDM) symbol of another wireless system, and to use the formed signal structure to completely eliminate interference caused by the OFDM symbol. For example, apparatus 10 may be caused to transmit the formed signal structure to cancel the interference caused by the OFDM symbol. As outlined above, the signal structure may include a first part (i.e., x1) synchronized to cancel a cyclic prefix of the OFDM symbol and a third part (i.e., x3) synchronized to cancel a repetition of the cyclic prefix of the OFDM symbol, and the signal structure may further include a second part (i.e., x2) synchronized with a remainder of the OFDM signal. Apparatus 10 may be configured to form and apply the signal structure as discussed above in connection with Equations 1-13 and Figs. 1-4, for example, to cancel interference.

[0047] Fig. 9 illustrates a flow diagram of a method for canceling interference, according to one embodiment. The method may include, at 900, forming, for example by a node in wireless system, a signal structure to match a structure of an orthogonal frequency-division multiplexing (OFDM) symbol of another wireless system. The method may further include, at 910, using the formed signal structure to completely eliminate interference caused by the OFDM symbol, for example, by transmitting the formed signal structure to cancel the interference caused by the OFDM symbol. The details of the formed signal structure and its application are as discussed above.

[0048] In some embodiments, the functionality of any of the methods described herein may be implemented by software stored in memory or other computer readable or tangible media, and executed by a processor. In other embodiments, the functionality may be performed by hardware, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software.

[0049] The computer readable media mentioned above may be at least partially embodied by a transmission line, a compact disk, digital-video disk, a magnetic disk, holographic disk or tape, flash memory, magnetoresistive memory, integrated circuits, or any other digital processing apparatus memory device.

[0050] The described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

[0051] Further, One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the scope of the appended claims.


Claims

1. A method, comprising:

forming (900), by a wireless system, a signal structure to match a structure of an interfering signal with repetitive time structure;

using (910) the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with repeated parts of the interfering signal structure to cancel interference caused by the repeated parts, and the signal structure further comprises another part synchronized with non-repeated parts of the interfering signal.


 
2. The method according to claim 1, wherein the interfering signal results from an orthogonal frequency-division multiplexing (OFDM) symbol of another wireless system, and a repetition of the interfering signal is a repetition of a cyclic prefix of the OFDM symbol.
 
3. The method according to claim 2, wherein the signal structure comprises a first part synchronized to the cyclic prefix for cancelling the cyclic prefix of the OFDM symbol and a third part synchronized to the repetition of the cyclic prefix for cancelling the repetition of the cyclic prefix of the OFDM symbol, and the signal structure further comprises a second part synchronized with a remainder of the OFDM signal.
 
4. The method according to any of claims 1 to 3, wherein the using (910) comprises transmitting the formed signal structure to cancel the interference caused by the interfering signal.
 
5. The method according to claim 3, wherein the first part of the signal structure is represented as x1, the second part of the signal structure is represented as x2, and the third part of the signal structure is represented as x3, and wherein x1 and x3 have the relationships:



where s1 and s2 are two data signals, and kn,m represents the mapping of data signal sm into transmitted signal xn.
 
6. The method according to claim 5, wherein the data signals sm comprise OFDM symbols, or any other type of modulated signal with a symbol length smaller than a length of the cyclic prefix.
 
7. The method according to claim 5, wherein the second data signal s2 is 0, and k1,1 = 1 and k1,2 = -1, such that:


 
8. The method according to claim 7, wherein the method comprises: observing at receivers signals y1 and y3, where y1 and y3 have the relationships:



where h and g represent the channel impulse response for signals s and B, respectively, and the symbol "*" represents a time domain convolution.
 
9. The method according to claim 8, further comprising:
removing an effect of interference over signals s and B, wherein rs represent the received signal after cancelling the interference signal B, and wherein rB represents the received signal after cancelling the interference signal s wherein rs and rB have the relationships with the observed signals y1 and y3:




 
10. The method according to claim 5, wherein:




 
11. The method according to claim 10, further comprising: removing the interference over s as determined by rs, where rs has the relationship:


 
12. An apparatus, comprising:

means (22,14) for forming a signal structure in a wireless system to match a structure of an interfering signal with repetitive time structure;

means (22,14) for using the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with the repeated parts of the interfering signal structure to cancel interference caused by the repeated parts, and the signal structure further comprises another part synchronized with the non-repeated parts of the interference signal.


 
13. An apparatus according to claim 12, comprising means (22, 14, 28) for performing a method according to any one of claims 2 to 11.
 
14. An apparatus according to any one of claim 12 -13, wherein the means (22, 14, 28)
for forming a signal structure in a wireless system to match a structure of an interfering signal with repetitive time structure and the means (22,14) for using the formed signal structure to eliminate interference caused by the interfering signal comprise:

at least one processor; and

at least one memory comprising computer program code.


 
15. A computer program, embodied on a computer readable medium, wherein the computer program, when executed by a processor, is configured to control the processor to perform a process, comprising:

forming (900) a signal structure in a wireless system to match a structure of an interfering signal with repetitive time structure;

using (910) the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with the repeated parts of the interfering signal structure to cancel interference caused by the repeated parts, and the signal structure further comprises another part synchronized with the non-repeated parts of the interference signal.


 


Ansprüche

1. Verfahren, umfassend:

Bilden (900), durch ein Drahtlossystem, einer Signalstruktur zum Angleichen an eine Struktur eines Störsignals mit sich wiederholender Zeitstruktur;

Verwenden (910) der gebildeten Signalstruktur zum Beseitigen der durch das Störsignal verursachten Störungen;

wobei die Signalstruktur Teile umfasst, die mit wiederholten Teilen der Störsignalstruktur synchronisiert sind, um die durch die wiederholten Teile verursachten Störungen zu unterdrücken, und die Signalstruktur ferner einen weiteren Teil umfasst, der mit nicht wiederholten Teilen des Störsignals synchronisiert ist.


 
2. Verfahren nach Anspruch 1, wobei sich das Störsignal aus einem Orthogonal Frequency-Division Multiplexing-(OFDM)-Symbol (dt. "Multiplexing durch Aufteilen auf orthogonale Frequenzen") eines anderen Drahtlossystems ergibt und eine Wiederholung des Störsignals eine Wiederholung eines zyklischen Präfixes des OFDM-Symbols ist.
 
3. Verfahren nach Anspruch 2, wobei die Signalstruktur einen ersten Teil umfasst, der mit dem zyklischen Präfix zum Unterdrücken des zyklischen Präfixes des OFDM-Symbols synchronisiert ist, und einen dritten Teil umfasst, der mit der Wiederholung des zyklischen Präfixes zum Unterdrücken der Wiederholung des zyklischen Präfixes des OFDM-Symbols synchronisiert ist, und die Signalstruktur ferner einen zweiten Teil umfasst, der mit einem Rest des OFDM-Signals synchronisiert ist.
 
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei das Verwenden (910) das Übertragen der gebildeten Signalstruktur zum Unterdrücken der durch das Störsignal verursachten Störungen umfasst.
 
5. Verfahren nach Anspruch 3, wobei der erste Teil der Signalstruktur als x1, der zweite Teil der Signalstruktur als x2 und der dritte Teil der Signalstruktur als x3 dargestellt wird und wobei für x1 und x3 die folgenden Beziehungen gelten:



wobei s1 und s2 zwei Datensignale sind und kn,m die Abbildung von Datensignal sm in übertragenes Signal xn darstellt.
 
6. Verfahren nach Anspruch 5, wobei die Datensignale sm OFDM-Symbole oder eine beliebige andere Art von moduliertem Signal mit einer Symbollänge kleiner als einer Länge des zyklischen Präfixes umfassen.
 
7. Verfahren nach Anspruch 5, wobei das zweite Datensignal s2 gleich 0 ist und k1,1 = 1 und k1,2 = -1, so dass gilt:


 
8. Verfahren nach Anspruch 7, wobei das Verfahren umfasst: Beobachten an Empfängern von Signalen y1 und y3, wobei für y1 und y3 die folgenden Beziehungen gelten:



wobei h und g die Kanalimpulsantwort für die Signale s und B darstellen und das Symbol "∗" eine Faltung im Zeitbereich darstellt.
 
9. Verfahren nach Anspruch 8, ferner umfassend:
Entfernen eines Effekts von Störungen über den Signalen s und B, wobei rs das empfangene Signal nach dem Unterdrücken des Störsignals B darstellt, und wobei rB das empfangene Signal nach dem Unterdrücken des Störsignals s darstellt, wobei rs und rB wie folgt mit den beobachteten Signalen y1 und y3 in Beziehung stehen:




 
10. Verfahren nach Anspruch 5, wobei gilt:




 
11. Verfahren nach Anspruch 10, ferner umfassend:
Entfernen der Störungen über s, wie durch rs bestimmt, wobei für rs gilt:


 
12. Vorrichtung, umfassend:

Mittel (22, 14) zum Bilden einer Signalstruktur in einem Drahtlossystem zum Angleichen an eine Struktur eines Störsignals mit sich wiederholender Zeitstruktur;

Mittel (22, 14) zum Verwenden der gebildeten Signalstruktur zum Beseitigen von Störungen, die durch das Störsignal verursacht werden;

wobei die Signalstruktur Teile umfasst, die mit den wiederholten Teilen der Störsignalstruktur synchronisiert sind, um die durch die wiederholten Teile verursachten Störungen zu unterdrücken, und die Signalstruktur ferner einen weiteren Teil umfasst, der mit den nicht wiederholten Teilen des Störsignals synchronisiert ist.


 
13. Vorrichtung nach Anspruch 12, umfassend Mittel (22, 14, 28) zum Durchführen eines Verfahrens nach einem der Ansprüche 2 bis 11.
 
14. Vorrichtung nach einem der Ansprüche 12-13, wobei die Mittel (22, 14, 28) zum Bilden einer Signalstruktur in einem Drahtlossystem zum Angleichen an eine Struktur eines Störsignals mit sich wiederholender Zeitstruktur und die Mittel (22, 14) zum Verwenden der gebildeten Signalstruktur zum Beseitigung von durch das Störsignal verursachten Störungen umfassen:

mindestens einen Prozessor; und

mindestens einen Speicher, der Computerprogrammcode umfasst.


 
15. Computerprogramm, das auf einem computerlesbaren Medium enthalten ist, wobei das Computerprogramm, wenn es von einem Prozessor ausgeführt wird, dafür ausgelegt ist, den Prozessor zum Ausführen eines Prozesses zu steuern, der Folgendes umfasst:

Bilden (900) einer Signalstruktur in einem Drahtlossystem zum Angleichen an eine Struktur eines Störsignals mit sich wiederholender Zeitstruktur;

Verwenden (910) der gebildeten Signalstruktur zum Beseitigen der durch das Störsignal verursachten Störungen;

wobei die Signalstruktur Teile umfasst, die mit den wiederholten Teilen der Störsignalstruktur synchronisiert sind, um die durch die wiederholten Teile verursachten Störungen zu unterdrücken, und die Signalstruktur ferner einen weiteren Teil umfasst, der mit den nicht wiederholten Teilen des Störsignals synchronisiert ist.


 


Revendications

1. Procédé comprenant :

la formation (900), au moyen d'un système sans fil, d'une structure de signal pour faire correspondre une structure d'un signal brouilleur avec une structure temporelle répétitive ;

l'utilisation (910) de la structure de signal formée pour éliminer un brouillage provoqué par le signal brouilleur ;

dans lequel la structure de signal comporte des parties qui sont synchronisées avec des parties répétées de la structure de signal brouilleur pour annuler un brouillage provoqué par les parties répétées, et la structure de signal comporte en outre une autre partie synchronisée avec des parties non répétées du signal brouilleur.


 
2. Procédé selon la revendication 1, dans lequel le signal brouilleur résulte d'un symbole de multiplexage par répartition orthogonale de la fréquence (OFDM) d'un autre système sans fil, et une répétition du signal brouilleur est une répétition d'un préfixe cyclique du symbole de multiplexage OFDM.
 
3. Procédé selon la revendication 2, dans lequel la structure de signal comprend une première partie synchronisée avec le préfixe cyclique pour annuler le préfixe cyclique du symbole de multiplexage OFDM et une troisième partie synchronisée avec la répétition du préfixe cyclique pour annuler la répétition du préfixe cyclique du symbole de multiplexage OFDM, et la structure de signal comprend en outre une deuxième partie synchronisée avec un reste du signal de multiplexage OFDM.
 
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel l'utilisation (910) comprend la transmission de la structure de signal formée pour annuler le brouillage provoqué par le signal brouilleur.
 
5. Procédé selon la revendication 3, dans lequel la première partie de la structure de signal est représentée sous la forme x1, la deuxième partie de la structure de signal est représentée sous la forme x2 et la troisième partie de la structure de signal est représentée sous la forme x3, et dans lequel x1 et x3 ont les relations :



s1 et s2 sont deux signaux de données et kn,m représente le mappage d'un signal de données sm dans un signal transmis xn.
 
6. Procédé selon la revendication 5, dans lequel les signaux de données sm comprennent des symboles de multiplexage OFDM ou n'importe quel autre type de signal modulé ayant une longueur de symbole plus petite qu'une longueur du préfixe cyclique.
 
7. Procédé selon la revendication 5, dans lequel le second signal de données s2 est 0 et k1,1 = 1 et k1,2 = -1 de telle sorte que :


 
8. Procédé selon la revendication 7, le procédé comprenant : l'observation, au niveau de récepteurs, des signaux y1 et y3, où y1 et y3 ont les relations :



où h et g représentent la réponse impulsionnelle de canal pour les signaux s et B, respectivement et le symbole « * » représente une convolution dans le domaine temporel.
 
9. Procédé selon la revendication 8, comprenant en outre :
la suppression d'un effet de brouillage sur les signaux s et B, dans lequel rs représente le signal reçu après l'annulation du signal brouilleur B et dans lequel rB représente le signal reçu après l'annulation du signal brouilleur s, dans lequel rs et rB ont les relations avec les signaux observés y1 et y3 :




 
10. Procédé selon la revendication 5, dans lequel :




 
11. Procédé selon la revendication 10, comprenant en outre : la suppression du brouillage sur s tel que déterminé par rs, où rs a la relation :


 
12. Appareil comprenant :

des moyens (22, 14) pour former une structure de signal dans un système sans fil pour faire correspondre une structure d'un signal brouilleur avec une structure temporelle répétitive ;

des moyens (22, 14) pour utiliser la structure de signal formée pour éliminer un brouillage provoqué par le signal brouilleur ;

dans lequel la structure de signal comporte des parties qui sont synchronisées avec les parties répétées de la structure de signal brouilleur pour annuler un brouillage provoqué par les parties répétées, et la structure de signal comporte en outre une autre partie synchronisée avec les parties non répétées du signal brouilleur.


 
13. Appareil selon la revendication 12, comprenant des moyens (22, 14, 28) pour réaliser un procédé selon l'une quelconque des revendications 2 à 11.
 
14. Appareil selon l'une quelconque des revendications 12 et 13, dans lequel les moyens (22, 14, 28) pour former une structure de signal dans un système sans fil pour faire correspondre une structure d'un signal brouilleur avec une structure temporelle répétitive et les moyens (22, 14) pour utiliser la structure de signal formée pour éliminer un brouillage provoqué par le signal brouilleur, comprennent :

au moins un processeur ; et

au moins une mémoire comprenant un code de programme d'ordinateur.


 
15. Programme d'ordinateur, incorporé sur un support lisible par ordinateur, le programme d'ordinateur, lorsqu'il est exécuté par un processeur, étant configuré pour commander le processeur pour réaliser un processus, comprenant :

la formation (900) d'une structure de signal dans un système sans fil pour faire correspondre une structure d'un signal brouilleur avec une structure temporelle répétitive ;

l'utilisation (910) de la structure de signal formée pour éliminer un brouillage provoqué par le signal brouilleur ;

dans lequel la structure de signal comporte des parties qui sont synchronisées avec les parties répétées de la structure de signal brouilleur pour annuler un brouillage provoqué par les parties répétées, et la structure de signal comporte en outre une autre partie synchronisée avec les parties non répétées du signal brouilleur.


 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Non-patent literature cited in the description