WO2014081421A1

WO2014081421A1 - Apparatus and method for robust sequence design to enable cross technology signal detection

Info

Publication number: WO2014081421A1
Application number: PCT/US2012/066165
Authority: WO
Inventors: Amitav Mukherjee; Sayantan Choudhury
Original assignee: Nokia Corporation; Nokia, Inc.
Priority date: 2012-11-20
Filing date: 2012-11-20
Publication date: 2014-05-30

Abstract

According to an example embodiment of this application, a method may include determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology; processing a data sequence of the first radio access technology by taking into account the at least one difference; and generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

Description

APPARATUS AND METHOD FOR ROBUST SEQUENCE DESIGN TO ENABLE CROSS TECHNOLOGY SIGNAL DETECTION TECHNICAL FIELD

The present application relates generally to an apparatus and a method for robust sequence design to enable cross technology signal detection.

BACKGROUND

This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application.

In wireless communication, different collections of communication protocols are available to provide different types of services and capabilities. Long term evolution, LTE, is one of such collection of wireless communication protocols that extends and improves the performance of existing universal mobile telecommunications system, UMTS, protocols and is specified by different releases of the standard by the 3^rd generation partnership project, 3GPP, in the area of mobile network technology. Other non-limiting example wireless communication protocols include global system for mobile, GSM, high speed packet access, HSPA, and wireless local area network WLAN, worldwide interoperability for microwave access, WiMAX.

In wireless communications typically coexistence problems occur when different systems operate by sharing the same communication resources, such as time and frequency resources. One recent area of study concerns license exempt spectrum such as television whitespaces TVWS in the VHF and UHF bands which is becoming available with the widespread adoption of digital television. In this unlicensed spectrum, typically devices access a whitespace database WSD to obtain a list of unoccupied spectrum in which these devices can transmit and receive data. The coexistence between WLAN and 802.15.4 radios deployed in the Industrial, Scientific, and Medical ISM 2.4GHz band has already been established. This sets a high probability that in the near future there will be coexistence between the long term evolution LTE and WLAN radio access technologies. However, LTE and WLAN are designed for different applications and are not compatible with each other. As a result, the two systems may cause mutual interference when they operate within the same frequency band. For instance, when LTE and WLAN are collocated and operating in the same time/frequency resources, LTE may dominate the medium. SUMMARY

Various aspects of examples of the invention are set out in the claims.

According to a first aspect of the present invention, there is provided a method comprising determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology; processing a data sequence of the first radio access technology by taking into account the at least one difference; and generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

According to a second aspect of the present invention, , there is provided an apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to determine, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology; process a data sequence of the first radio access technology by taking into account the at least one difference; and generate a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

According to a third aspect of the present invention, , there is provided a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code may include code for determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology; processing a data sequence of the first radio access technology by taking into account the at least one difference; and generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

According to a fourth aspect of the present invention, there is provided an apparatus comprising means for determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology; means for processing a data sequence of the first radio access technology by taking into account the at least one difference; and means for generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which: Figure 1 displays a framework of long term evolution LTE downlink physical channels, including the proposed physical heterogeneous coexistence channel according to an example embodiment;

Figure 2 illustrates ideal Zadoff-Chu sequence autocorrelation without impairments; Figure 3 illustrates Zadoff-Chu sequence autocorrelation with cross-technology impairments;

Figure 4 illustrates a robust sequence generation scheme at a LTE transmitter according to an example embodiment;

Figure 5 compares the probability of detection of interfering LTE signal for target of false-alarm rate 0.01 between the proposed method and the conventional method according to an example embodiment;

Figure 6 illustrates a flow diagram of operating a LTE transmitter according to an example embodiment.

Figure 7 illustrates a simplified block diagram of various example apparatuses that are suitable for use in practicing various example embodiments of this application.

DETAILED DESCRIPTON

When there is a traditional cellular wireless broadband base station (BS), such as for example, a long term evolution LTE evolved Node B eNB, operating in the unlicensed band, an underlying lower-power node of a second technology, such as for example, wireless local area network WLAN, operating on the same channel typically suffers from interference. Signal detection may be the first step for initiation of interference avoidance measures. Because different systems with different radio access technologies normally have dinstinct and incompatible characteristics, such as for example, sampling rate, orthogonal frequency-division multiplexing OFDM subcarrier spacing, synchronization sequence, frame structure, and so on, naively re -using existing synchronization sequences of one technology will suffer from poor signal detection performance due to the effect of the difference of characteristics. In an example embodiment, a new physical channel of a first radio access technology, such as for example LTE, dedicated to transmission of a coexistence frame in order to aid interference avoidance by a second technology, such as for example WLAN, is proposed. A robust sequence design and preprocessing techniques allows the devices of the second radio access technology to accurately detect the presence of co- channel signals of the first radio access technology in spite of the difference of characteristics of these two technologies.

In the illustration of various embodiments below, LTE and WLAN will be used as the non-limiting examples of the first and the second radio access technology, respectively. But they are non-limiting and presented for example only. In an example embodiment, a new downlink physical channel for LTE, denoted as physical heterogeneous coexistence channel PHCCH, is proposed for the transmission of a coexistence frame. A coexistence frame is designed to carry specially designed sequences that allow WLAN receiver to detect the presence of LTE transmitter. The design of the coexistence sequences accounts for the cross-technology incompatibility by intelligent pre-processing of sequence transmitted by LTE that are designed to improve the probability of signal detection at WLAN devices. In an example embodiment this is done without the need for modifying the conventional detection algorithm in place at WLAN nodes, while in other embodiments more sophisticated signal detection schemes can be utilized.

In an example embodiment, LTE eNB/user equipment UEs and WLAN devices share the same frequency band. WLAN operates under distributed coordination function DCF protocol, based on carrier sense multiple access/collision avoidance CSMA/CA mechanism. A new downlink physical channel PHCCH for LTE is defined to be used for the transmission of the coexistence frame. Figure 1 displays a framework of LTE downlink physical channels 101, including the proposed PHCCH 103 according to an example embodiment. As an example, the duration of each coexistence frame on the PHCCH may be the same as the time-span of the primary synchronization signal PSS and a secondary synchronization signal SSS.

In an example embodiment, the PHCCH is proposed to transmit a single-carrier signal instead of a conventional multi-carrier signal. Recall that LTE and WLAN have incompatible OFDM parameters, e.g., subcarrier spacings. By using a single-carrier signal, the reception of the coexistence frame by WLAN is made easier since it reduces the scope of frequency and sampling offsets. In an example embodiment, the single-carrier signal may be generated by reusing the uplink single carrier frequence division multiple access SC-FDMA architecture, or by bypassing inverse fast Fourier transform IFFT/fast Fourer transform FFT processing blocks in the OFDM subsystem. In another example embodiment, multi-carrier signals may be used for the PHCCH. Monitoring a predefined channel instead of searching over the entire spectrum for possible interferers significantly improves the energy efficiency of the WLAN receiver and simultaneously reduces complexity.

In an example embodiment, the proposed PHCCH periodically transmits coexistence frame that is designed for accurate reception at WLAN receiver. The proposed channel may be orthogonal to the existing LTE channels and may or may not be simultaneously transmitted with the other channels. For instance, PHCCH may be transmitted on certain symbols only and in those symbols, there can be no data transmission on those subcarriers. As an example, the traffic carried on the PHCCH may comprise a lengfh-N robust sequence x that is designed to be detected with high probability at WLAN receivers that use conventional auto-correlation algorithms, as described next. In LTE, the eNB broadcasts a PSS and a SSS that enables a UE to determine the cell ID and radio frame timing. The PSS is generated using a Zadoff-Chu ZC sequence that has ideal auto-correlation (delta function) and cross-correlation properties when received at a terminal of the same technology, i.e., when there are no sampling and frequency offsets, as shown in Figure 2. In Figure 2, the ideal auto-correlation of a ZC sequence has a peak 201 at lag of 0 and is 0 elsewhere.

When the LTE PSS is received by a terminal of a different technology such as WLAN, the ideal correlation properties of the ZC sequence no longer hold due to the dinstinct characteristics of different technologies, such as for example, the sampling and frequency offsets. Figure 3 describes the ZC sequence autocorrelation with cross-technology impairments. In Figure 3, besides the peak 301 at lag of 0, there are other smaller peaks, e.g., 302 at lag of -80. Since WLAN nodes generally use auto-correlation-based methods, e.g., energy detection, for signal detection, this phenomenon will degrade the signal detection accuracy and therefore impair interference avoidance capabilities. The autocorrelation-based detection process at the WLAN station STA works optimally when the received sequence has an autocorrelation with a single peak. However, in Figure 3 the effect of the cross-technology mismatch between LTE and WLAN leads to multiple peaks with 'sidelobes' of large amplitude in the received signal autocorrelation, which causes the degradation in detection performance.

WLAN assumes that the operating environment is interference-free once it has captured the medium after the CSMA/CA process, and therefore does not have intrinsic interference avoidance capabilities at the physical layer. The preamble section of every WLAN frame contains a short training field STF or legacy STF sequence for packet detection and coarse

synchronization. The overall STF is of 8μβ duration, consisting of 10 repetitions of a sequence that spans Ο.δμβ.

In an example embodiment, the sequence is sent by using a single carrier by LTE over a flat-fading channel. The incompatibility of LTE and WLAN at the physical layer leads to sampling time offset AT and carrier frequency offset Af , which are captured in the phase offset parameter φ as explained further below.

Let the LTE transmission symbol time be T and transmit sample clock rate be _; Hz. The received signal at a WLAN device in the time domain, when a sampling rate mismatch of factor (X

— exists between the LTE and WLAN, can be written as,

β

a

y ( k) = eⁱ*h ( t) x (t) + n (t) , t = k-,0≤k≤ 7—

a where x {t ) is the transmitted sequence sample at time t, h (t ) is the complex channel coefficient, n (t ) is additive complex Gaussian noise, and the cumulative sampling and frequency offset parameter φ is modeled as

Such a sequence y (k) carries the cross-technology impairments so it may not be proper for detection purpose.

Since the sampling time and carrier frequency offsets are generated due to the cross- technology incompatibility of LTE and WLAN, they can be assumed as deterministic parameters that can be obtained or estimated by LTE. In an example embodiment, a sequence generation method is proposed to take an arbitrary root sequence r generated at the LTE sample rate, and apply pre-filtering and frequency offset pre-compensation to generate the robust sequence that exihibits the autocorrelation property as shown in Figure 2.

Figure 4 illustrates a robust sequence generation scheme at a LTE transmitter according to an example embodiment. In the example embodiment of Figure 4, at a LTE transmitter 401, a transmit sequence 402 generated at the LTE samping rate, such as for example, an arbitrary root sequence r, is pre-filtered by a pre-filtering block 403 and pre-compensated for the frequency offset by a frequency offset pre-compensation block 405. In an example embodiment, the pre- filtering block 403 may be implemented as a zero-padding operation followed by a low-pass interpolation filter with finite impulse response, e.g., a linear-phase filter with a Kaiser window. In an example embodiment, the pre-compensation block may be implemented by multiplying by β^~1ψ e-jcp to remove the phase offset. Therefore, a robust transmit sequence 404 in the time domain is obtained as

x = e^~jip (c * r )

where * denotes the convolution operator and c stands for the pre-filter coefficients. The received signal at WLAN side can be given now by

y (k ) = h (t ) x (t ) + n (t ) , t s [θ, Τ )

In an example embodiment, the root sequence Γ can be a ZC sequence, a STF sequence, or taken from a new family of sequences such as Barker or Oppermann sequences that possess constant amplitude zero autocorrelation properties.

In an example embodiment, the detection scheme at WLAN receiver may be based on

(possibly normalized) auto-correlation with delayed version of received signal, e.g.,

R {t ) =∑y { i )y {i - d ) where ύΜ δμβ when the STF is used as the transmit sequence. Figure 5 shows the detection probability for the proposed method compared with conventional method, which is denoted as "Naive", according to an example embodiment. In the example embodiment of Figure 5, the target false-alarm rate is set to 0.01. Figure 5 shows that the proposed method 501 outperforms the naive case 502. The merits of the proposed invention also hold if conventional cross-correlation detection methods are used by WLAN.

A number of ways can be used to differentiate the LTE sequence from a packet transmitted by another WLAN device. For example, if LTE uses the STF as the transmit sequence. Then, instead of following the STF with the long training field as would be expected in a WLAN packet preamble, LTE can simply repeat the STF for another 8μβ, which alerts WLAN receiver that the sequence is non-WLAN, instead, it is for coexistence detection purpose.

Figure 6 illustrates a flow diagram of operating a LTE transmitter according to an example embodiment. At 601, a transmitter of a first radio access technology, such as for example, a LTE eNB transmitter, determines at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology, such as for example, WLAN. At 602, the LTE eNB transmitter processes a data sequence, such as for example an arbitrary root sequence r illustrated above. In an example embodiment, the process may comprise the pre-filtering and/or frequency offset precompensation of Figure 4. At 603, a second data sequence, such as for example, the sequence x described above, is generated based on the processing for transmission to an apparatus of the second radio access technology.

Reference is made to Figure 7 for illustrating a simplified block diagram of various example apparatuses that are suitable for use in practicing various example embodiments. In Figure 7, a network element NEl 701 of a first radio access technology, such as for example a LTE eNB, is adapted for communication with another network element NE2 711 of a second radio access technology, such as for example a WLAN device.

The NEl 701 includes a processor 705, a memory, MEM, 704 coupled to the processor 705, and a suitable transceiver, TRANS, 703 (having a transmitter, TX, and a receiver, RX) coupled to the processor 705. The MEM 704 stores a program, PROG, 702. The TRANS 703 is suitable for bidirectional wireless communications with the NE2 711. The NEl 701 is capable of being operably coupled to one or more external networks or systems, and/or communicating with one or more user equipment of the first radio access technology such as LTE terminals, which are not shown in this figure.

The NE2 711 includes a processor 715, a memory, MEM, 714 coupled to the processor 715, and a suitable transceiver, TRANS, 713 (having a transmitter, TX, and a receiver, RX) coupled to the processor 715. The MEM 714 stores a program, PROG, 712. The TRANS 713 is capable of bidirectional wireless communications with the NEl 701. The NE2 711 is capable of communicating with one or more devices of the second radio access technology such as WLAN devices, which are not shown in this figure

As shown in Figure 7, the NE1 701 may further include a robust sequence generation unit 706. The unit 706, together with the processor 705 and the PROG 702, may be utilized by the NE1 701 in conjunction with various example embodiments of the application, as described herein.

As shown in Figure 7, the NE2 711 may further include a sequence detection unit 716 for detecting the sequence transmitted from NE1 701 and distinguishing it from the conventional sequence sent from other device of the second radio access technology.

At least one of the PROGs 702 and 712 is assumed to include program instructions that, when executed by the associated processor, enable the electronic apparatus to operate in accordance with example embodiments of this disclosure, as discussed herein.

The example embodiments of this disclosure may be implemented by computer software or computer program code executable by one or more of the processors 705 and 715 of the NE1 701 and the NE2 711, or by hardware, or by a combination of software and hardware.

The MEMs 704 and 714 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as

semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. The memory may be non-transitory in nature. The processors 705 and 715 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors, DSPs, and processors based on single- or multi-core processor architecture, as non-limiting examples.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein may be generating a robust sequence that allows WLAN to correctly detect the presence of interfering LTE signals at the physical layer, without the need for explicit cross-technology control channels between LTE and WLAN or feedback from WLAN. This helps to reduce implementation complexity of WLAN devices and makes the invention a viable coexistence solution. Although LTE and WLAN are used throughout this document as examples, it is to be understood that the inventive principles described herein are not limited to a LTE- WLAN coexistence environment but are applicable to any suitable coexistence scenarios.

Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and/or hardware may reside on an apparatus such as a user equipment, a NodeB or other mobile communication devices. If desired, part of the software, application logic and/or hardware may reside on a macro eNodeB base station 701, part of the software, application logic and/or hardware may reside on a WLAN device 711, and part of the software, application logic and/or hardware may reside on other chipset or integrated circuit. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device. A computer-readable medium may comprise a computer-readable storage medium that may be any media or means that can contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device.

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

Further, the various names used for the described parameters are not intended to be limiting in any respect, as these parameters may be identified by any suitable names.

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

Claims

WHAT IS CLAIMED IS:

1. A method, comprising:

determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology;

processing a data sequence of the first radio access technology by taking into account the at least one difference; and

generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

2. The method of claim 1, wherein:

the at least one difference comprising at least one of the difference of sampling rates, the difference of carrier frequency offsets, and the difference of subcarrier spacings.

3. The method of any of claims 1 or 2, further comprising:

generating a dedicated channel, wherein the dedicated channel carries the second data sequence.

4. The method of claim 3, wherein the dedicated channel is generated as a single-carrier signal or as a multi-carrier signal.

5. The method of any of claims 1 to 4, wherein:

the first data sequence is a Zadoff-Chu sequence, a short training field sequence, a Barker sequence, an Oppermann sequence, or any sequence with ideal auto-correlation and cross- correlation property.

6. The method of any of claims 1 to 5, wherein:

the first radio access technology is long term evolution technology and the second radio access tehnology is wireless local area network technology, or vice versa.

7. An apparatus comprising:

at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: determine, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology;

process a data sequence of the first radio access technology by taking into account the at least one difference; and

generate a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

8. The apparatus of claim 7, wherein:

9. The apparatus of any of claims 7 or 8, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: generate a dedicated channel, wherein the dedicated channel carries the second data sequence.

10. The apparatus of claim 9, wherein the dedicated channel is generated as a single-carrier signal or as a multi-carrier signal.

11. The apparatus of any of claims 7 to 10, wherein:

the first data sequence is a Zadoff-Chu sequence, a short training field sequence, a Barker sequence, an Oppermann sequence, or any sequence with ideal auto-correlation and cross- corrleation property.

12. The apparatus of any of claims 7 to 11, wherein:

the first radio access technology is long term evolution technology and the second radio access tehnology is wireless local area network technology , or vice versa.

13. An apparatus, comprising:

means for determining, at a first radio access technology, at lease one difference between the characteristics of the first radio access technology and the characteristics of a second radio access technology;

means for processing a data sequence of the first radio access technology by taking into account the at least one difference; and

means for generating a second data sequence based on the processing for transmission to an apparatus of the second radio access technology.

14. The apparatus of claim 13, wherein:

15. The apparatus of any of claims 13 or 14, further comprising:

means for generating a dedicated channel, wherein the dedicated channel carries the second data sequence.

16. The apparatus of claim 15, wherein the dedicated channel is generated as a single-carrier signal or as a multi-carrier signal.

17. The apparatus of any of claims 13 to 16, wherein:

18. The apparatus of any of claims 13 to 17, wherein:

19. A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code includes code for:

20. The computer program product of claim 19, wherein:

21. The computer program product of any of claims 19 or 20, wherein the computer program code comprising:

code for generating a dedicated channel, wherein the dedicated channel carries the second data sequence.

22. The computer program product of claim 21, wherein the dedicated channel is generated as a single-carrier signal or as a multi-carrier signal.

23. The computer program product of any of claims 19 to 22, wherein:

24. The computer program product of any of claims 19 to 23, wherein: