GB2510188A - Estimating noise covariance from signal covariance for use in PBCH intercell interference cancellation in systems with two interfering cells - Google Patents

Abstract

Signals including a PBCH (Physical Broadcast CHannel) are received from a wanted cell basestation and two interfering cell basestations. An estimate of the system noise covariance is derived from the signal covariance. The noise covariance estimate is used in the reduction of interference from the two interfering cells during recovery of the wanted PBCH. The cells may be heterogeneous (eg. a mixture of macro, pico and femto cells).

Description

Method and Apparatus for Reducing Contributions from Interfering Cells

Technical Field

A method, apparatus and computer program product are provided in accordance with an example embodiment for facilitating wireless communications and, more particularly, for detecting physical broadcast channel (PBCII) signals utilizing prevailing interference conditions.

Background

In order to support a non-uniform cell network, such as a network having overlapping macro cells and pico cells, enhanced inter-cell interference coordination (eICIC) was defined in the Long Term Evolution (LTETh) Release 10 specification.

eICIC provides network mechanisms to support overlapping macro cells and pico cells by defining almost blank subframcs (AJ3S) patterns to enable measurement and data transmission in instances in which the interference level created by the overlapping macro cells and pico cells may otherwise make network connection difficult or even impossible. During an ABS, user data transmitted via the physical downlink shared channel (PDSCII) is muted, either from the entire network or at least a portion of the network. Instead, only common reference signals (CRS) as well as other common control signals, such as primary synchronization signals (PSS), secondary synchronization signals (SSS) and/or broadcast control channel (BCCII) signals, are transmitted from the interfering cells during an ABS, thereby allowing legacy receivers, such as the receivers of one or more mobile terminals that are configured to support ITE Release 8 and/or 9, but not urn Release 10 and/or II, operating within the non-uniform network to stay connected.

The I 1'E Release II specification deflnes additional requirements for the detection and estimation capabilities of mobile terminals. Among the additional requirements is cell range expansion (CRE) which requires mobile temilnals to cope with higher interference levels, which enables extending the range of the cell to which certain mobile terminals are connected. In order to cope with higher interference levels, mobile terminals may include advanced receivers with more advanced

I

inlerierence cancellanon capabilities, such as downonk interference canceliation (IC), As a result of rang.e expansion and eiCLC, the effect of coverage holes caused by a non-uruforni network may he reduced. Additionally, more mohi k terminals may he transferred to the access points of lower powered riCO cells so as to improve the total network throughput.

in order to implement the performance requirements imposed by the LIft Release 11 specification, however, mobile ternThtals may implement CR5 cancellation an phystcal broadcast channel (PBCH) cam-ellation, With respect to CRS cancellation, the common reference signals of the interfering cells are cancelled mainly in order to Improve the ctiatmel estimation for thc desired cell. With rcs pect to PBCEI caneeliauon, PBCII is a channel utihi.ed to transmit a limited amount of essential system information, such as cell bandwidth, physical hybrid automatic repeat request (UARQ) indicator channel structure and the most significant bits of the system frame number (SUN). The PBCH signals am transmitted even during an ABS subframe, Thus, the PBCI-I signals can also experience interference, particularly in a range expansion si ftiation, As such, a mobile termnina may he required to cancel interfering PBCI I signals since a failure to decode a PBCII transmission from the desired cell may prevent a mobile terminal from connecting to the desired cell. In comparison to CR5 cancellation, however. PBC[l cancellation is different since the symbol sequence transmitted by an interfering cell is unknown.

Summary

A method, apparatus and computer program are provided according to an example emhouiment of the present invention in order to facilitate the detection of PBCH signals llroni a desired cell. In this regard, the method, apparatus and computer program product oF an example embodiment may cancel or otherwise reduce the contribution to the PBCH signals from the interfering ce]ls in order to permit the P13(11 signals front the desired cell to be received. As such, the method, apparatus and computer program product of an example embodiment may facilitate further enhanced inter-cell interference coordination (felCiC). such as within a non-uniform network including, for example, overlapping macro cells and pieo cells, By facilitating detection of the PUCE-I signals from a desired cell, a mobile terminal may he able to more reliably connect to the desired cell as a result of the method.

apparatus, and computer program product of an exampic. embodiment of the present nvent.on, In one embodiment, a method is provided for use, for example, in a mobile terminaL with the method including receiving a signal including PBCI I signals from a first cell and at least two imerferin cells. For example, the method may receive a signal from non-unilorm cells. such as a first cell and at least two interfering, cells operating in the same frequency band. In this regard, the method of one embodiment may receive a signal il-urn a combination of macro celLs and pi.co ceils, The method also includes approximating a noise covariance estimate for at least one of the intrierng cells utiiiting signal covariance, Ihe rneLhod further includes deteniiining a PBCI-i signal from the first cell based upon the signal that was received following reduction of contributions from the at least two interfering cells from the sig.nal that was reeeived In this regard, the reduction ol the coffin butions from the at least two interfering cells is at least irtiaily based upon the noise covarianec estimate for at least one of the interfering cells.

The at least Iwo inLerlenng cells may include first and second interfering cells.

in this embodiment, the method may approximate the noise covariance estimate by approximating the noise covariance estimate for the second interfering cell as

-

-r 1' In this regard, r may he defined as: rr-&-d =hd,. 4-Kd-1+n In this equation, r represents the signal vector that was received. h, liii and h are channel coefficient vectors for the first cell and the first and second interfering cells, respectively, d, du, and d i2 represent PUCIi data for the first cdl and the first and second interfering cells, respectively, n is a white noise vector, (A) notatton represents an estimated value and xT1 designates the complex conjugate transpose of a vector (or matrix) x, The method may also include approximating a noise covariance estimate for the first cell, utfliiing sianal covariance, In this embodiment, the reduction of contriliutions from the at least two interfering cells is also a.t least nartiafly base,d upon the noise covananee estimate br the first cell. In one embodiment, [he reduction of contnnutions from the at least two inter1erng cells is at least partially based upon noise covariance estimates for the second interfering cell and the first e.b In one embodiment, the method approximates the noise covariance estimate for the first cell s, -asCnn.T F'. inthisregard,r"isdefinedas"F =r In another embodiment, an apparatus is provided for use in a mobile terminal with the apparatus including a processing system, which may he embodied as at east one processor and at least one memory including computer program code, The processing system is arranged to cause the apparatus at least to perform receiving a 0 signal including PBCI-I signals from a first cell a'id at least two interfering cells. For example, the apparatus may receive a signal iron non--uniform cells, such as a first ccii arid at least two interfering cells operating in the same frequency hand. in tlu regard, the apparatus of one embodiment may receive a signal from a combination of niacro cells and ico cells. The processing system is arranged to cause the apparatus to approximate a noise covariance estimate for at least one of the interfering, cells utilizing signal covariance, The processing system is arranged to cause the apparatus to determine a FIlCH signal from the first cell based-cp()n the signal that was received following reduction of contributions from the a.t least two interfering cells from [Lie signal that was received. In this reaard, the reduction of the contributions from the at least two rntertenng cells is at least partially based upon the noise covarlance estimate for at east one of the interlering cells.

i*lie at least two interfering cells may include first and second interfering cells, In this embodiment, the processing system is arrtuieed to cause the apparatus to approximate the noise covariance estimate by approximating the noise covariance estimate for the second interfering cell isCm,ta = 1"FM In this regard, r may he defined as = .r -= hd + h2d2. The processing system is arranged to cause the apparatus to approXilTiate a noise covanance estimate for the first cell, utilizing signal covariance. In this embodiment, the reciucLion of contributions from the at least two interfering cells is also at least partially based upon the noise covariance estimate for the first cell. In one embodiment. the reduction of contributions from the at least two intertèring cells is at least partially based upon noise covariance estimates for the second interfering cell and the rt cell. In one embodiment, the processing system is arranged to cause the apparatus to approximate the noise covariance estimate for the first cell as nnu = r"r" In this regard, r "is defined " r" = -= hd1 + it In a further embodiment, a computer readable medium is provided that includes a set of instructions which, when executed on a mobile terminal causes the mobile terminal to perform receiving a signal including PBCH signals from a first cell and at least two interfering cells. For example, the signal may be received from non-uniform cells, such as a first ccli and at least two interfering cells operating in the same frequency band. In this regard, the signal may be received from a combination of macro cells and ptco cells. The set of instructions, when executed, also cause the mobile terminal to approximate a noise covariance estimate for at least one of the interfering cells utilizing signal covariance. The set of instructions, when executed, further cause the mobile terminal to determine a PBCH signal from the first cell based upon the signal that was mceived following reduction of contributions from the at least two interfering cells from the signal that was received. In this regard, the reduction of the contributions from the at least two interfering cells is at least partially based upon the noise covariance estimate for at least one of the interfering cells.

The at least two inLerfering cells may include first and second interlering cells.

In this embodiment, the set of instructions, when executed, may cause the mobile terminal to approximate the noise eovariance estimate by approximating the noise covariance estimate for the second interfering cell asessnaz = ?i'* In this regard, r' may be defined as r' = r-ItcL1 = l1⁄44+1kSia +". The set of instructions, when executed, may also cause the mobile terminal to approximate a noise covariance estimate for the first cell, utilizing signal covariance. In this embodiment, the iduction of contributions from the at least two interfering cells is also at least partially based upon the noise covariance estimate for the first cell. In one embodiment, the reduction of contributions from the at least two interlëring cells is at least partially based upon noise covariance estimates for the second interfering cell and the First cell. in one embodiment, the set ol instructions, when executed, may cause the mobile terminal to approximate the noise covariance estimate For the first U 13 ceiiascnn=r r inthisregard.r"isdefinedas"r =r In yet another embodiment, an apparatus is provided for ase. for example. in a mobile terminal. with the apparatus including means for receiving a signal including FIlCH signals from a first cell and at least two Interfering cells. For example. the signal may he received from nonuniform cells, such as a first cell and at least two interfering cells operating in the same frcqucncy hand. In this regard. the signal may be received in one embodiment from a combination of macro cells and pico cells.

The apparatus also includes means for approximating a noise covariance estimate for at least one of the interfering cells utilizing signal covariance. [he apparatus further includes means for determining a P131'Il signal trout the first ccl] based upon the signal that was received following reduciion of conLihutions from the aL least Iwo interfering cells irom the signal that was received. In this regard, the reduction 01 tile contributions from the at least two interfcring cells is at icast partially based upon the noise covanance estimate for at least erie of the interfering cells, Ihe at least two inter!enng cells may include first and second interfering cells, In this embodiment, the means for approximating the noise covariance estimate may include means for approximating the noise eovariance estimate for the second

-

interFering cell as nt,i2 -r In this regard, rmay he defined as = r -= + h2d2 + . The apparatus may also include means for approximating a noise covariance estimate for the first cell, utilizing signal covanance. in this embodiment. the reduction of contributions from the at least two interfering, cells is also at least partially based upon the noise covanance estimale for the first cell. In one embodiment, the reduction of contributions from the at least two interfering cells is at least pardally based upon noise covariance estimates for the second interfering cell arid the first cell. In one embodiment, the means for approximating the noise covariance estimate includes means for approximating the "511 noise covariance estimate for the first cell as = r r. In this regard, r "is defined as" = -= hd + m

Brief Description of the Drawings

Having thus described example emhodiments of the invention in genera] terms, reference will now he made to the accompanying drawings. which are not necessarily drawn to scale, and wherein: Fig-tire I is a schematic representation of a non--un:form network inchiding a pair of macro cells and a pieo cell; Figure 2 is a block diagram of an apparatus that may he specifically configured in accordance with an example embodiment of the present invention; lO Figure 3 is a flow chart iLlustrating operations perlriried, such as by the apparatus of Figure 2, in accordance with an example embodiment of the present invention; and Figure 4 is a graphical representation of the PBCH block error rate.

Detailed Description

[ic present invention now will he described more fully hereinafte.r with reference to the accompanying drawings, in which some, hut riot all embodinients of the inventions are shown. Indeed, these inventions may he embodied in many different!brms and should not he construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will satisfy apphcab[c legal requIrements. Like numbers refer to like elements throughout.

As used in this application, the-term "circuitry" refers to all of the foUowing: (a)hardware-onlv circuit implementations (such as implementations in only analog anuror digital creuitry) and (T, to combinations of circuits and software (and/or firmware), such as (as applicable): U) to a combination of processor(s) or (ii) to portions of processor(s)/soitware (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a moNk phone or server, to perfonri various functions) and (c) to circuits. such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of "circuitry" applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or application specific integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

A method, apparatus and computer program product ace provided in accordance with an example embodiment of the present invention to facilitate the decoding of a PBCH transmission in order to increase the likelihood that a mobile terminal may successfully connect with a desired cell. In this regard, the method, apparatus and computer program product of an example embodiment may reduce the contributions from two or more interfering cells, such as by cancelling interfering PBCU signals from two or more interfering cells, so as to facilitate the successful decoding of the PBCH signals from the desired cell. By providing for PBCH cancellation, the method, apparatus and computer program product of an example embodiment may provide for further enhanced inter cell interference coordination.

While the method, apparatus and computer program product may operate in conjunction with an Lll or 14Th-Advanccd (l.TL-A) network, othcr networks may support the method, apparatus and computer program product of embodiments of the present invention including those configured in accordance with wideband code division multiple access W-CI)MA), CI)MA2000, global system for mobile communications (GSM), general packet radio service (CiPRS), IEEE 802.11 standard for wireless fidelity (WiPi). wireless local access network (WLAN), Worldwide interoperability for Microwave Access (WiMAX) protocols, and/or the like. For purposes of example, however, the method, apparatus and computer program product will be described in conjunction with a non-uniform network, such as a non-uniform network, e.g., a non-uniform universal mobile telecommunications systems (IJMTS) teaestrial radio access network (UTRAN) Lit network.

By way of example. hut not of limitation, I-i gure 1 depicts a non-uniform network that supports communications with a mobile terminal 10 and that includes one or more macro cells 14. and one or more pico cells 1 8 that at least partially overlap and that operate in the same frequency hand. In his regard, a pico cell is used aeneralIv herein to indicate a cell smaller than a maero cell, such as a pico cell, a ferrito cell or the Like, Each macro cell may include an access point 12, such as a base station, a Node B, an enhanced Node B (eNB), a macro eN'B, a coordination unil, a macro base station or the like. Similarly, each pico cell may include an access point 16, such as a base station, a secondary cell, a pico/femto eND, a home eNB. a remote radio head ( RRI-i), a coordination unit. a rmcro base statlon or the like. As shown, the macro cells partially overlap, and the pico cell is positioned at least partially and, in the illustrated err hodiment, ci tirely w thin the region of overlap netween the macro cells.

A mobile terminal 10 located within the overlapping portion of the cells is desirably connected to one of the cells so as to communicate with the respective access point, in the illustrated embodiment, for example, the mobile terminal is within the pico cell iX and, as such, is desirably connected te the access point 16 of the pico cell so as to reduce the overall power consumption and network congestion.

in order to connect to the destred cell, the mobile terminal must receive, among other signals, the PBCH signal. on the downlink from the desired cell. However, the overlapping cchs cause the mobile terminal to also receive interfering PIBC II signals Iron the other cells, also referred. to as the interfering cells herein. As uescnhed above, the. interfering PBCII signals may reduce the likelihood or. in some instances.

prevent the mobile terminal from successfully decoding the PI3CFI signals from the desired cell and., as a result, from properly-connecting to the desired cell.

the mobile terminal 10 may he a mobile communicatioii device such as, for example, a mobile telephone, smart phone, portable. digital assistant (PDA), pager.

laptop computer. tablet computer or any of mirnerot:is other hand held or potable communication devices, computation devices, content generation devices, content consumpi.ion devices, or combinations thereof. The mobile lerminal. may he embodied as or otherwise include an apparatus 20 as generically-represented by the in rilock diagram ol Figure 2. While the apparatus may be employed, br example. by a mohiie terminal, it should he noted that the components, devices or elements described below may not be mandatory and thus some may he omitted in certain embodiments, Additionally. some embodtments may include further or different components, iievices or elements beyond those shown and described herein.

As shown in Figure 2, the. apparatus 20 may include or otherwise be. in conrnxunication with processing circuitry 22 thaI is configurable to perform actions in accordance with example embodiments described herein. The Drocessing circuiiry may lie configured to perform data processing. application execution. PI3C1-4 signal processing, measurements and report generation, and/or otrier proccssng and management services according to an example embodiment of the present invention.

In sonic enihodinients, the apparatus or the processing circuitry may be embodied as a chip or chip set. In other words, the apparatus or the processing circuitry may comprise one or more physical packages (e.g., chips) including materials, components and/or wires on a structural assembly (e.g., a baseboard). The structural assembly may provide physical streneth. eonservat!on of size, and/or limitation of electrical Inltractlon for component circuitry included thereon. The apparatus or the processing circuitry may I erefore. in some cases, he configured to implement an embodiment of the present invention on a single chip or as a single "system on a chip." As such. in some cases, a chip or chipset may constitute means for perfOrming one or more operations for providing the. functionalities described herein. Alternatively or additionaLly, a processlng system may be embodied by or have similar functionality to the processing circuitry, In an example embodiment, the processing circuitry 22 may include a processor 24 and memory 26 that may he in communication with or otherwise control a communication interlace 30 and, in some cases, a user interlace 28.As such, the processing circuitry may be embodied as a circuit chip (e.g., an interrated circuit chip) configured (e.g., with hardware, software or a combination, of hardware and.

software) to perform operations described herein. however, in sonic embodiments, the processing circuitry may be embodied as a pori.ion of the mobile tenninai TO.

The user interlace 2.8 (ii' implemented) may be in communica on with the processing circuitry 22 to receive an indication of a user input at the user interlace ariuior to provide an audible, vsua] rnecharucal or other output to the user, In this regard, the user interface andlor the processing circuitry 22 may inctude user interface circuitry confiaured to facilitate user contro of at least some functions based upon user input. The user interface may include, for exmpie, a keyboard, a mouse, a traekhail, a display, a touch screen, a microphone. a speaker, and/or other input/output mechanisms. The arparatus 20 need not always include a user interface.

the communication interface 30 may include one or more interface mechanisms for enabling comniunicution with other devices andior networks. in sonic cases. [he communication inLerface may he any means such as a device or circuitry emh,or,hed in either hardware, or a combination of hardware and software thai is configured to receive andior transmit data Irornlto a network and/or any other device or module in comnmn ication with the process ng circuitry 22. Tn this regard, the communication interface may include, for example, an antenna (or multiple antennas) anu supporting hardware arid/or software for enabling communications with a wireless communication network and,or a comnnnication modem or other hardware/software for supporting communication via cable, digital subscriber line (DSL). universal serial bus (USB), Ethernet or other methods, In an example embodiment, the memory 26 may include one or more non-transltory memory devices such a.s, for example. volatile arid/or nonvoLaule memory that may be either fixed or removable, The memory may be configured to store information, data, applications, instructions or the like for enabling the apparatus 20 to carry out various functions iii accordance with example embodiments of the present invention. For example, the memory may be configured to buffer input data for processing by the processor 24. Additionally or alternatively, the memory could he configured to store instnictions for execution by the processor. As yet another alternative, the memory may include one of a plurality of databases that may store a variety of files, contents or data sets, Among the contents of the memory. applications may he stored for execution by the processor in order to carry out the functionality associated with each respective application. In some cases, the memory may be in communication with the processor via a bus for passing information among components ol' the apparatus.

The processor 24 ma.y he embodied in a number of different ways. For example, the processor may be embodied as various processing means such as one or more of a m!croprocessor or other processnig element, a coprocessor, a. control er or various other computing or processing devices including integrated circuits such as, for example. an application specific integrated circuit (ASIC), an field programmable gale array (IPGA1, or the like. in an example embodiment, the processor may be configured to execute instructions stored in the memory 26 o.r otherwise accessible to the processor. As such, whether corthaured by harthvare or by a conihnation of hardware and software, the processor may represent an entity (cg., physically emh,oded in circuilry -in the form of processing circuitry 22.) capable of perlbrming operations according to embodiments of the present invention while configured accordingly. Thus, for examnie. when the processor is embodied as an ASTC. FPOA or the like, the processor may be specifically configured hardware lbr conducting the operatic'ns described herein. Altcrnativey, as another example, when the processor is embodied as an executor of software instructions, the instructions may specmcaliy configure the processor to perform the operations described herein.

One technique to facilitate PBCH detection is to estimate the channel and noise covariance (applying CR5 cancellation) of an interfering celL to detect and decode the PBCI] signal from the interfering cell mid then to reconstruct the interfering PBCII signal using the detected symbols and channe]. estimates, Once reconstructed, the interfering PBCI-1 signal can be cancelled from the received signals.

l'his same procedure ma' he repeated for the interfering PRO-I signals from each interfering ccli such that die interfering PBCH signals are cancelled from the received.

signal samples such that PBCH detection of the PRCH signals from the desired eel] may lie performed. with improved rd ability.

By way of example, a mobile tennina! may include a single transmit antenna and two receive antennas, although the mohle ternvnal of other embodiments may include different antenna confguraUons. in tins lnstanee, the mobtle terminal may receive a signal, including PRCI-l signals, from a first cell, that is, the desired cell, and al least two interlering cells. namely. a first interfering cell and a second interftring cell. [he signal that is received may he defined as follows: r = h44,. ± hd1 + +n Following the removal of the interfering PBCH signals from the first S interfering cell, the resulting signal r' may he defined as foi]ows: = r-= h,d, +h,d2 + a Thereafter, following cancellatIon ot the intcifeiine PBEI-l signals from the sceond interfering cc!!, the rcsu]ting signal r" may he defined as: i'' = i' -= ± a In the foregoing equations. r is the received stanal vector tor a certain subcarrier containing samples for both receive antennas. h is the channel coefficient vector for the desired cell. h1 and li2 are the channel coeflicient vectors for the first and second interfering cells, respectively. d. d11 and d2 are the PBCH signals from the first cell and the first and second interlering cells, respectively. n is the vector representative of white noise. Additionally, (A) notation is used to represent a channel or data ectimate so as to u ifferentiate the channel or data. estimates from true sampes.

Since the channel estimation for the first cc] I and the interlhring cells is performed prior to PBCII cancellation, the noise covariance estimates may also he determined prior to PBC1I e»=mceilahon. In one approach, the noise covanance estimates may be determined by subtracting the known pilot signal to determine the interference Lerm, In this regard, the intertOrenee esd mate seen hy the first i ntertbring eel may be defined as: = r-hp1 =hd2 ±h2d2 ±n.

Sirrnlariy, the interference estimate seen by the secend interfering cell may be defined as: I =r-Lp,..,. =huSn ±n Finally, the interference estimate seen by the desired cell may be defined as loliows: =i- =hnd. ± +n En the toregomg equations, p represents a known reference signal. By comparing the foregoing interference estimates to those expected assuming perfect cancellation, the interference estimate seen by the First interfering cell has no cancellation gain is defined For i above. For the second interfering eel], flowevcr, the gain provided by cancellation of the interfering signals from the first inierfering cell may be defined as follows: Further, for the first cell, cancellation of the interfering signals [mm both the first and second interfering ceHs results in a signal containing only noise which may be defined as follows: = r-h,1p, -h Thus, from the foregoing interference terms, noise covariance may he determined by this oncshot noise. covanance estnaton approach approach as fol]ows: j2 -1x1r Based upon a comparison of the foregoing equations for 1i2 and I. the noise covanance estimates for the second interfering cell and the desired. first cell are different than those that would he expected assuming perfect cancellation since the noise covariance estimates do not reflect the cancellation effect. As such, thesc noise covanance estimates may create sonic erforrnance loss. Instead of estimating Qe interference terms and the resu]tine noise cc variance estimates for the second interfering cell and the desired first cell utilizing reference signals, eg., CRS pilot signals. and averaging techniques, the method, apparatus and computer program product of an example embodiment approximate the noise covariance estimates with the respective signal covarianees, By approximating the noise covarianee estimate with signal covarianee. the resulting calculations are simplified, and Lhe additional control is nunmtai to obtain the. interference samnies.

Referring now to Figure 3, the operations perfbrmed by an apparatus 20, such as shown n Figure 2. specifically configured in accordance with an example embodiment of the present invention are illustrated. In this regard., the apparatus may include means, such as the processing circuitry' 22., the processor 24. the communications interface 30 or the like, for receiving a signal including PBCI I signals from a First cell and at least two interfering cells. See block 40. As described above, the signal that is received may he a signal rom non-urn Form cells including the first cell and the at least two interfering cc] Is operating in the same frequency band.

As shown in Figure 1, for example. the signal that is received may be a signal from a combination of macro cells 14 arid pico cell 1$.

As shown in block 42 of Figure 3. the apparatus 20 may also include means.

such as the processing circuitry 22, the processor 24 or the like, for approximating the noise covariance estimate for at leasi one of the inurfering cells, such as the second inieriering cell, utilizing signal covariance. in this regard, the noise covariance estimate for the second interfering cell differs from the noise covariance estimate that would be ideally expecicu due to its own signal component, that is, the i2 term thai is represented in the noise covariance approximation, as follows: = r-= h,4. +n As viil be noted, this eqiwtion corresponds to the. foregoing equation that defines r' and can he utilized to determine the noise covariance estimate for the second interfbring cell as follows: = For a desired cell, the noise covariance may also he approximated with the signal covariance utilizing the received signal from which the contributions from the second interfering cell have been cancelled. As shown in block 44 of Figure 3, for example, the apparatus 2(1 may include means, such as the processing circuitry 22, the processor 24 or the like, for approximating a noise covariance estimate for the first cell utilizing, signal covarianee. More particularly, the noise covariance estimate for the first cell may differ from the noise covariance estimate that would he ideally expected (tue to the signal component of the first cell that is visible in the noise eovariance approximation as roHows: L =r-h, cL. -Ihd,,.=h,d,,-fn 4 & -\s will he noted, this equation corresponds to the foregoing equation that defines r" such that the noise covariance estimate for the desired first cell can he estimated as follows: C,..,rr The noise covariance estimate may be approximated by the signal covariance for at least two reasons, First, in a LeICIC scenario in which PBCH IC is utilized, them may be only one dominant interfering cell which, in the foregoing equations, corresponds to the first interfering cell that is detected with the appropriate noise covariance estimate. In the instances in which the noise covariance estimate is approximated with the signal covariance, such as in conjunction with the second interfering cell and the first cell, the noise and correct interference term are likely to dominate over the erroneous term. Additionally, a method, apparatus and computer program product of an example embodiment permit the complexity to be reduced as tv-estimation rounds for noise covariance using pilot signals and averaging techniques may be eliminated.

As shown in block 46 of Figure. 3, the apparatus 20 may also include means, such as the processing circuitry 22, the processor 24 or the like, for determining a PECH signal from the first cell based upon the signal that was received following reduction of contributions from the at least two interfering cells from the signal that was received. In this regard, the reduction of contributions from the at least two interfering cells is at least partially based upon the noise covariance estimate for at least one of the interfering cells, such as the second interfering cell. In an embodiment in which the noise covariance estimate for the first cell is also approximated utilizing signal covariance, the apparatus, such as the processing cirvuitry, the processor or the like, may also reduce the contributions from the at least two interfering cells in a manner that is also based upon the noise covarianee estimate for the first cell, Referring now to Figure 4, a graphical representation of the PBCH IC resulting from the cancellation of either one interfering ccli, namely, the first interfering cell, or two interfering cells, namely, both the first and second interfering cells, in an instance in which the first and second interfering cells have 6dB and 3dB powers, respectively, over the white noise level. In this regard, line 50 represents the PBCH block error rate (BLER) performance without any PBCII cancellation. Lines 52 and 54 illustrate the PBCH BLER performance utilizing a one-shot noise covariance estimation approach that cancels the first interfering cell and both the first 1 7 and second intericring cells, respechvely. Further, the PBCI-l BI YR perlormance utilizing the approximated noise covariance estimation approach of the method.

apparatus and computer program product of an example. embodiment is shown by lines 56 and. 58 in conjunction with the cancellatIon of the first interfering ccl and both the first and second interfering cells, respectively.

As can he seen, the one-shot noise covariance es ma on approach provides about 1 dB gain at 1% BLER compared to line 50 when the stronger interfering cell is cancelled as shown by line 52 and about 2 dB gain, at % BLER compared to line 50 when both interfering cells are cancded as shown by line 54. In contrast, the U) aporoxitn.tited noise covarian.ce estimation approach of the method, apparatus and computer program product of an example embodiment obtams almost 2. dB gain hi cancelling the stronger interfering cell as shown in line 56 and an additional dB of gain when also cancelling the second, weaker interfering cell as shown by line 58. It should he understood that Figure 4 is provided by of example and not ot lniitaton since Figure 4 depicts the results attrihutah]e to only certain example embodiments with other embodiments of the present nvention pro\'Iding other rewits.

l'he method, apparatus and computer program product of an example embodiment may also provide for simplified control, reduced latency and lower computatonai compiexty compared te other approaches that more fully-estimate the noise covanance. Additionally, the method, apparatus and computer program product of an example embodiment permit the. PDSC1 I and PBCII processing to be performed in parallel fol.[owir1g. such as immediately following, the channel and noise covanance estimate that may he performed in the first round of processing since there is no longer a connection or dependency between the PDSCI-i and PBCF-l processing and no riced for further estimation rounds. Additionally, the method, apparatus and.

computer program product of an example embodiment permit the noise covariance re-estimation to he reduced to vector multiplications with the samples already undergoing processing, as there is no reqi.urenient to fetch appropriate channel estimates and. corresponding reference symbols from memory in order to reconstruct the received pilot signal. A.s such, the method, apparatus and computer program.

product of an example embodiment may provide significantly improved performance in companson to a one-shot noise covariance estimation approacn or approximately the same performance, but with significantly lower complexity and delay and with more highly simplified control, in comparison to a successive interference cancellation (SIC) approaca.

Pigure 3 iflustrates example operations performed by a method, apparatus and computer prograrri product, such as apparatus 20 of Figure 2 it! accordance with one embodiment of Ihe present invention. It will he understood thai each blockS of the flowcharts, and combinations of'.iocks in the flowchart, may be mp1emented by various means. such as hardware, firmware, processor. circuitry and/or other device it) a.ssocated with c.xccuton of software includjng one or more computer program instruclions, For exampie, one or moie of the proceaures described above may he emh,odied by computer program instructions. In this regard. the computer program instructions which embody the procedures described above may he stored by a memory 26 of an apparatus employing an embodiment of' the present invention and executed by a processor 24 in the apparatLLs. .As will he appreciated, a'iy such compu.Ler program instructions may be loaded onto a computer or other programmable apparatus (e.g., hardware) to produce a machine, such that the resulting computer or other programmable apparatus provides for implementation of the functions specified in the flowchart's block(s). These computer program instructions may also he siored 21) in a non-transitory computer-readable storage memory that may direct a computer or other prow'ammabie. apparatus to hinction in a pamcutar manner, such that the insLuctions sLored in the computer-readable storage memory produce an article oF manufacture, the execution of which implements the function specified in the flowcharts block(s). The computer program instructions may also he loaded onto a computer or other programmable apparatus to cause a series of operations to he performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other piug mama hie apparatus pro\'icle operations for implementing the functions specified in the flowchar(s block(s). As such, the operations of Figure 3, when executed, convert a computer or processing circuitry into a particular machine configured to perform an example embodiment of the present invention, Accordingly.

the operations of 1:igLLre 3 deline an aigonthm br conhguring a computer or processing circuitry 22, e.g., processor. to perform an example embodiment. In some cases, a general puroe computer may he mvoeu with an instance or the processor which performs the algorithm of Figure 3 to transform the general purpose computer nto a particular mach inc configured to perform an example embodiment.

Accordingly, blocks of the flowcharts support combinations of means for performing the specified func Lions and combinations of operations for performing the snecified functions. it vviH also he understood that one or more blocks of the flowchart, and combinations of blocks in the flowchart, can be implemented by special purpose hardwarcbasc.d computer systems which perform the spccified functions. or combinations of special purpose hardware and computer instructions.

In some embodiments, certain ones o the operations above may be moifified or further amplified as described below. Moreover, in some embodiments additiona] optional or)crations may also be included. Tt should be aoprcciaLcd that each of the modmcations, optional additions or amphtications below may he incuded with the operations above either alone or in combination with any others among the features descnned herein.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these Invenuons pertain having the benefit o.f the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventIons are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended elairn. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments hi the context of certain example combinations of elements and/or functions, it should he appreciated that different combinations of elements and/or functions may he provided by alternative embodiments without departing from the scope of the appended claims. In this regard, fcr example, dfferenr combinattons of elements and/or functions than those exp]icitly described above are also contemplated as may be set forth in some of the appended claims. Although specific LeTms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (31)

1. Claims 1. A method for use in a mobiLe terminal, the method comprising: receiving a signal nciudi ng physca1 broadcast channel (PBCH) sgnais train a first cell and at least two interfering cells; approximating a noise covariance esiimaie for at least one of the interfering cells utilizing signal covariance; and determining a PBCF-L signal from the first cell based upon the signal that was ID received foLlowing reduction of contnbutions front the at iedst two interfering cells from the signal that was received, wherein the red uction of contributions from the at least two ml rlenng cells is at least partially based upon Lhe noise covanance estmate for at least one of the interfering cells.
2. 2. A method according to claim I wherein the at least two interfering cells comprise first and second interfering cells, wherein approximating the noise eovariance estimate comprises approximatIng the liaise eovartance estimate for the second interfering cell as: wheretn = r -iodn = h,d,, + hd5 + n and wherein r represents the signal vector that was received, h;j. h1, and h1 are channel coefficient vectors for the first cell and the first arid second interfering cells, respectively, d1], d0 and represent PBCH data for the first ccli and the first and second interfering cells, respectively, n is a white noise vector, (A) notation represents an estimated value and I-I designates a complex conjugate transpose operation.
3. 3. A method according to claim 2 further comprising approximating a 3D noise covariance estimate for the first cell utilizing signal covariance. and wherein the reduclion ol contrihutons from the at least two interlenng cells is also at least partially based upon the noise covarianee estimate for the first cell.
4. 4.. A method according to claim 3 wherein the reduction of contrihutions from the at least two nterlenng cells is at least partially based upon the muse eovariance estimates for the second intcrfering cell and the first cell.
5. 5. A method according to claims 3 or 4 wherein approximating the noise covariance estimate for the first cell comprises approximatin2 the noise covariance estimate for the first cell as: 1.0 = wherein = r' -= hd.. + i
6. 6. A method according to any one of claims I to 5 wherein receiving a signal comprises receiving a signal from nonnniforni cells including the first cell and at least two interfering cells operating in a same frequency band.
7. 7. A method according to claim 6 wherein receiving a signal from non-uniform cells comprises receiving a signal from a comnination of macro cells and pico cells
8. 8. An apparatus for use in a mobile terminal, the apparatus compnslng a processing system arranged to cause the apparatus to: receive a signal including physical broadcast channel (PBCII) signals from a First cell and at. least two interFering cells; approximate a noise eovananee estimate for at least one of the interfering cells utilizing signal covanancc; and determine a PBCI I signal from the first cell based upcn the signal that was received following reduction of contributions from the at least two interfering cells from the signal that was received, wherein the reduction of contributions from the at least two interfering cells is at least partially based upon the noise covariance estimate for at least one of the interfering cells.
9. 9. An apparatus acconiing to claim 8 wherein the at least two interfering cells comprise first and second interfering cells, wherein the processing system is arranged to cause the apparatus to approximate the noise covariance estimate by approximating the noise covariance estimate for the second interfering cell as: wherein = r -= + h2d2 ± n and wherein r represents the signal vector that was received, h, h,, and ha are channel coefficient vectors for the firsi. cell and the first and second interfering cells, respectively, d.,, d11 and dij represent PBCLI data for the first cell and the first and second interfering cells, respectively, n is a white noise vector. (A) notation represents an estimated value and H designates a complex conjugate transpose operation.
10. 10. An apparatus according to claim 9 wherein the processing system is further arranged to cause the apparatus to approximate a noise covariance estimate for the first cell utilizing signal covariance, and wherein the reduction of contributions from the at least two interfering cells is also at least partially based upon the noise covariance estimate for the first cell.
11. 11. An apparatus acconling to claim 10 wherein the reduction of contributions from the at least two interfering cells is at least partially based upon the noise covariance estimates for the second interfering cell and the first cell.
12. 12. An apparatus according to any one of claims 10 or 11 wherein the processing system is arranged to cause the apparatus to approximate the noise covariance estimate for the first cell by approximating the noise covariance estimate for the first cell as: p = r1.nH r wherein r"= r'hJa =hd2+n
13. 13. An apparatus according to any one of claims 8 to 12 wherein the processing system is arranged to cause the apparatus to receive a signal by receiving a signal from non-uniform cells including the first cell and at least two interfering cells operating in a same frequency band.
14. 14. An apparatus according to claim 13 wherein the processing system is arranged to cause the apparatus to receive a signal from non -uniform cells by receiving a signal from a combination of macrn cells and pico cells.
15. 15. An apparatus according to any one of claims 8 to 14 wherein the apparatus is embodied as a mobiie tenuinal.
16. 16. An apparatus according to any one of claims 8 to 15 wherein the apparatus is configured for use in an lMng Term Evolution (lit) or an lJI Advanced (Lit-A) system.
17. 17. An apparatus according to any one of claims 8 to 16 further comprising user interface circuitry configured to facifitate user control of at least some functions based upon user input.
18. 18. A computer readable medium comprising a set of instructions which, when executed on a mobile terminal, causes the mobile terminal to perform: receiving a signal including physical broadcast channel (PB( l I) signals from a first cell and at least two interfering cells; appmximating a noise covariance estimate for at least one of the interfering cells utili.eing signal covariance; and determining a PI3CH signal from the first cell based upon the signal that was received following reduction of contributions from the at least two interfering cells from the signal that was received, wherein the reduction of contributions from the at least two interfering cells is at least partially based upon the noise covariance estimate for at least one of the interfering cells.
19. 19. A computer readable medium accoitling to claim 18 wherein the at least two interfering cells comprise first and second interfering cells, wherein approximating the noise covariance estimate comprises approximating the noise covariance estimate for the second interfering cell as: tts,t2 -? wherein = r -= + h2d ± n and wherein r represents the signal vector that was received, h, h11 and h are channel coefficient vectors for the flrst cell and the first and second interfering cells, respectively, &. & and dz represent PBCH data for the first cell and the first and second interfering cells, respectively, n is a white noise vector, (A) notation represents an estimated value and H designates a complex conjugate transpose operation.
20. 20. A computer readable medium according to claim 19 further comprising instructions which, when executed on the mobile terminal, cause the mobile terminal to approximate a noise covariancc estimate for the first cell utilizing signal covariance, and wherein the reduction of contributions from the at least two interfering cells is also at least partially based upon the noise covariance estimate for the first cell.
21. 21. A computer readable medium according to claim 20 wherein the reduction of contributions from the at least two interfering cells is at least partially r)ased upon the noise covananee estimates for the second interfering cell and the first cell.
22. 22, A computer readable medium according to any one or claims 20 or 21 wherem approxiniating the noise covariance estimate br the first cell comprises approximating the nose covariance estimate for the first cell as: where in = r'- = h,4 + n
23. 23. A computer readable medium according to any one of c1ams 18 LU 22 wherein receiving a signal comprises receiving a signal from non--unuorni cells including the first cell and at least two inteiten.rmg cells operating In a same frequency hand,
24. 24. A computer readable medium according to claim 23 wherein receiving a. signal. from non-umfonn. cells comprises receiving a signal from a combnatiori of macro cells and pico cells.
25. 25. An apparatus for usc in a mobile terminal, the apparatus compnsing: means for receivIng a signal including physical broadcast. channel (PBC1 I) signals 1mm a first cell and at east two.interferng cells; means for approximating a noise covariarice estimate for at least one of the inierterrJg cells uti]izing signa] covariance; and means for determining a PBCH signal from the first cell based upon the signal that was received following reduction of contributions from the at least two interfering cells from the signal that was received, wherein the reduction of conLn.butions from the at least two interfering cells is at least partially based upon the noise covariance estimate for at least one of the interfering, cells.
26. 26. An apparatus according to claim 25 wherein the at least two interfering cells cornpnse first and second Interfering cells, wherein the means for approximatIng the noise covariancc estimate comprise means for approximating the noise covariance estimate for the second interfering cell as: = where in jr r?=r_ii =h,,d +hd<+n 1.L and wherein r represents the signal vector that was received. h, h1, and h12 arc channel coefficient vectors for the first ccii and the first and second interfering cells.respectjvely, d, do and d2 represent PBCI I data for the first cell and the first and second interlèring cells, respectively. n is a white noise vector. (A) nolation represents an esijniated value and II designates a complex conjugate transpose operatIon.
27. 27. An apparatus according to claim 26 Further comprising means for approximating a noise covariance estimate for the first cell utiliiing signal covariance, anU wherein the reduction of contributions from the at least two interfering cells is 2(1 also at least partially based upon the noise covariance estimate for the first cell.
28. 28. An ipparatus according to claim 27 wherein the reduction of contributions from the at least two interfering cells is at least partially based upon the noise covariance estimates for the second interfering cell and the first cell.
29. 29. An apparurus accordmg to ally one of claims 27 or 28 wherein the means For approximating the noise covanance estimate for the lirsI cell comprise means for approximating the noise covariance estimate for the first cell as: I, C,=rr wherein = -= hd.4 + i
30. 30. An apparatus accothing to any one of claims 25 to 29 wherein the means for receiving a signal comprise means for receiving a signal from non-uniform cells including the first cell and at least two interfering cells operating in a same frequency band.
31. 31. An apparatus according to claim 30 wherein the means for receiving a signal from non-uniform cells comprise means for receiving a signal from a combination of macro cells and pico cells.