HK1196204A - Method and system for signaling in a heterogeneous network - Google Patents

Abstract

A method at a network element operating in a wireless network, wherein the network element is configured to transmit a default cell search signal at a default position in one or more subframes, the method comprising transmitting, by the network element, an auxiliary cell search signal in addition to the default cell search signal.

Description

Method and system for signaling in heterogeneous networks

RELATED APPLICATIONS

This application is a non-provisional application of U.S. provisional application No. 61/522,395, filed on 11/8/2011, the entire contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates to heterogeneous networks, and in particular, to communicating with a weaker cell in a heterogeneous network.

Background

The third generation partnership project (3GPP) long term evolution-advanced (LTE-a) working group has considered heterogeneous deployments as a technology that significantly improves system capacity and coverage. In heterogeneous deployments, low power network nodes such as pico evolved node bs (enbs) and femto enbs overlap with conventional high power enbs, which may be referred to as macro enbs. These macro, pico, and femto enbs form a macro, pico, and femto cell, respectively. The term "cell" refers to a coverage area for wireless transmissions by a network, such as an eNB. In some instances, each of the pico cells or femto cells may have a coverage that at least partially overlaps with a coverage of the macro cell. To efficiently utilize the radio spectrum, in one embodiment, the macro cell, pico cell, and femto cell are deployed on the same carrier. However, full frequency reuse among pico, femto and macro cells may introduce severe inter-cell interference.

In particular, to improve system capacity, range extensions have been introduced for pico enbs to which User Equipment (UE) may connect even when the signal from the macro eNB is stronger. Similarly, in a Closed Subscriber Group (CSG) femtocell, a UE may receive a stronger signal from the femtocell than a signal received from a macro eNB. However, if the UE is not part of a closed subscriber group, the UE may need to connect to the macro eNB. The weaker cell to which the UE is connected is referred to herein as an interfered (victim) cell. In this example, the stronger cell to which the UE is not connected may be referred to as an interference source (accumulator) cell in the context of this document.

An alternative way to reduce interference from interfered cells is enhanced inter-cell interference coordination (eICIC) based on Almost Blank Subframes (ABS). In this alternative, the higher power cell blanks out the transmission (blank) or reduces the transmit power on certain subframes, thereby enabling successful data transmission from the lower power (interfered) cell. However, almost blank subframes still contain cell-specific reference signals (CRS) and are transmitted in the ABS if Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS)/Physical Broadcast Channel (PBCH)/system information block 1(SIB 1)/paging/Positioning Reference Signal (PRS) coincide with the ABS, when SIB 1/paging is transmitted, the associated physical downlink control channel is transmitted.

However, due to interference from the interferer cell, the UE may not be able to reliably detect primary signals such as PSS, SSS, PBCH, etc. from the weaker cell.

Drawings

The disclosure will be better understood with reference to the accompanying drawings, in which:

figure 1 is a block diagram illustrating a conventional heterogeneous network having pico cells and macro cells, wherein the pico cells have a range extension area;

fig. 2 is a block diagram illustrating a conventional heterogeneous network with closed subscriber group femtocells and macrocells;

fig. 3 is a timing diagram of a conventional method of transmitting almost blank subframes in a pico-macro case;

fig. 4 is a timing diagram of a conventional method of transmitting an almost blank subframe in a femto-macro scenario;

fig. 5 illustrates a conventional radio frame with a cell selection signal for FDD;

fig. 6 shows a conventional radio frame with a cell selection signal for TDD;

FIG. 7 is a process diagram illustrating a process at a mobile device for detecting a PSS according to one embodiment;

figure 8 is a schematic diagram of a process at a legacy user equipment for detecting SSS, according to one embodiment;

figure 9 is a process diagram illustrating a process at an exemplary user equipment for detecting SSS according to one embodiment;

figure 10 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PSS and SSS according to one embodiment;

figure 11 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PSS and SSS in a different location than that of figure 10, in accordance with another embodiment;

figure 12 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PSS and SSS in a different location than that of figures 10 and 11, in accordance with another embodiment;

figure 13 is a block diagram illustrating a portion of a radio frame in FDD with the addition of multiple auxiliary PSS and SSS according to one embodiment;

fig. 14 is a block diagram illustrating a portion of a radio frame in TDD with the addition of an auxiliary PSS and SSS according to one embodiment;

figure 15 is a block diagram illustrating a portion of a radio frame in TDD with the addition of an auxiliary PSS and SSS in a different location than that of figure 14, in accordance with another embodiment;

fig. 16 is a block diagram illustrating a portion of a radio frame in TDD with the addition of an auxiliary PSS and SSS in a different location than that of fig. 14 and 15, in accordance with another embodiment;

fig. 17 is a block diagram illustrating a portion of a radio frame in TDD with the addition of an auxiliary PSS and SSS in a different location than that of fig. 14-16, in accordance with another embodiment;

figure 18 is a block diagram illustrating a portion of a radio frame in FDD with the addition of auxiliary PSS and SSS, where the location of the PSS and SSS are swapped, according to one embodiment;

figure 19 is a block diagram illustrating a portion of a radio frame in FDD with the addition of auxiliary PSS and SSS where the PSS and SSS are swapped and located differently from that of the embodiment of figure 18, in accordance with another embodiment;

figure 20 is a block diagram illustrating a portion of a radio frame in FDD with the addition of auxiliary PSS and SSS where the PSS and SSS are swapped and located differently from the embodiments of figures 18 and 19, according to another embodiment;

figure 21 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary SSS according to one embodiment;

figure 22 is a block diagram illustrating a portion of a radio frame in FDD with an auxiliary SSS added in a different location than that of figure 21, in accordance with another embodiment;

figure 23 is a block diagram illustrating a portion of a radio frame in FDD with an auxiliary SSS added in a different location than that of figures 21 and 22, in accordance with another embodiment;

figure 24 is a block diagram illustrating a portion of a radio frame in FDD with an auxiliary SSS added in addition to the auxiliary PSS and SSS pair, according to one embodiment;

figure 25 is a block diagram illustrating two radio frames in FDD with the addition of half-length auxiliary PSS and SSS, where the two radio frames may be frequency multiplexed, according to one embodiment;

fig. 26 is a block diagram illustrating two radio frames in TDD with half-length auxiliary PSS and SSS added, where the two radio frames may be frequency multiplexed, according to one embodiment;

figure 27 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PBCH, in accordance with one embodiment;

fig. 28 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PBCH in a location different from that of fig. 27, in accordance with another embodiment;

fig. 29 is a block diagram illustrating a portion of a radio frame in FDD with the addition of an auxiliary PBCH in a location different from that of fig. 27 and 28, in accordance with another embodiment;

fig. 30 is a block diagram illustrating two radio frames in which a secondary cell selection signal is located at different positions between two radio cells according to one embodiment;

FIG. 31 is a simplified block diagram of an exemplary network element according to one embodiment; and

FIG. 32 is a block diagram of an exemplary user device that can be used with the systems and methods in embodiments described herein.

Detailed Description

The present disclosure provides a method at a network element operating in a wireless network, wherein the network element is configured to transmit a default cell search signal at a default position in one or more subframes, the method comprising transmitting, by the network element, an auxiliary cell search signal at a position different from the default position in addition to the default cell search signal.

The present disclosure also provides a method at a user equipment ("UE") operating in a wireless network having a default cell search signal at a default position in one or more subframes, the method comprising: detecting, by the UE, an auxiliary cell search signal; and obtaining, by the UE, system information of the wireless network using the information in the auxiliary cell search signal.

The present disclosure also provides a network element operating in a wireless network, wherein the network element is configured to transmit a default cell search signal at a default position in one or more subframes, the network element comprising a processor; and a communication subsystem, wherein the processor and communication subsystem cooperate to transmit, by the network element, an auxiliary cell search signal to user equipment operating in the wireless network in addition to the default cell search signal.

The present disclosure also provides a user equipment operating in a wireless network having a default cell search signal at a default position in one or more subframes, the user equipment comprising a processor; and a communication subsystem, wherein the processor and the communication subsystem cooperate to detect an auxiliary cell search signal by the UE; and obtaining, by the UE, system information of the wireless network using the information in the auxiliary cell search signal.

The disclosure is described below with reference to the 3GPP LTE-a standard, and in some embodiments, with reference to release 11 of the 3GPP LTE-a standard. However, the present disclosure is not limited to this standard and may be applied to all versions of the LTE standard and other similar radio technologies.

In 3GPP LTE-a, heterogeneous deployments have been considered to improve system capacity and cell coverage. In heterogeneous deployments, low transmit power network nodes such as pico enbs and femto enbs are placed in conventional high transmit power macro cells. Further, for pico enbs, range extension may be used to offload traffic from a macro eNB to a pico eNB. Reference is now made to fig. 1.

In fig. 1, macro eNB110 has a coverage area shown by reference numeral 112. To offload UEs from macro eNB110, pico eNB120 may be introduced in area 112. The pico eNB has a coverage area shown by reference numeral 122.

To offload more UEs to the pico eNB120, a range extension may be utilized to increase the service area of the pico eNB120 from area 122 to the area shown by reference numeral 130. In the range extension area 132 between reference numerals 130 and 122, UE140 communicates with pico eNB120 even though the signal from macro eNB110 is stronger. While this offloads more UEs to pico than not using range extension, UEs connected to pico eNB120 in the range extension area may suffer severe interference from macro eNB 110.

Similarly, for femtocells with Closed Subscriber Group (CSG) access, an interference condition may exist. Reference is now made to fig. 2.

In fig. 2, a macro eNB210 serves an area shown by reference numeral 212. The CSG femto eNB220 serves an area shown by reference numeral 222. However, CSG femtocells are closed groups and allow communication only from designated or member UEs. If the non-member UE230 is in the area 222, the non-member 230 still needs to be served by the macro eNB 210. However, the non-member UE230 will experience severe interference from the femto eNB 220.

To overcome the interference problems associated with these heterogeneous deployments, an enhanced inter-cell interference coordination (eICIC) scheme based on almost empty self-subframes (ABS) has been adopted in release 10 of the LTE standard to address the interference problems. Reference is now made to fig. 3 and 4, wherein fig. 3 shows an ABS deployment for the embodiment of fig. 1 and fig. 4 shows an ABS deployment for the embodiment of fig. 2.

As shown in fig. 3 and 4, an ABS subframe is configured on an interferer cell. Specifically, referring to fig. 3, in the pico-cell RE case, the interference signal comes from the macro eNB, and therefore an ABS is configured on the macro eNB. Similarly, for the femto case of fig. 4, interference comes from the femto cell, so ABS is configured on the femto eNB.

During ABS, the aggressor cell blanks out the transmission of control and data, or transmits at a significantly lower power. However, during ABS, the aggressor cell may have some transmissions for vital signals, as explained below. The ABS provides interference-free or nearly interference-free resources to the interfered cell so that pico UEs in the RE area or interfered macro UEs in the femto coverage area may be scheduled to communicate with its serving node.

Thus, referring specifically to fig. 3, macro eNB310 and pico eNB320 communicate over subframes generally designated 330. Pico eNB320 utilizes subframes with normal transmissions, while macro eNB310 spreads almost blank subframes 350 in normal transmission subframes 352.

Similarly, for fig. 4, macro eNB410 transmits a subframe with normal transmission shown by reference numeral 412. Femto eNB420 transmits almost blank subframes or multicast/broadcast bearer single frequency network (MBSFN) subframes 422 interspersed among subframes 424 with normal transmissions.

However, as indicated above, almost blank subframes are not completely blank, but include some signaling. For example, a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a Physical Broadcast Channel (PBCH), a system information block 1(SIB1), a paging, or a Positioning Reference Signal (PRS) is transmitted in almost blank subframes if it coincides with the almost blank subframes. When the SIB1 or page is sent, the associated Physical Downlink Control Channel (PDCCH) is sent. In the embodiments described herein, the term "synchronization signal" may be used interchangeably with "synchronization sequence".

Cell-specific reference signals (CRS) are also transmitted on the ABS to avoid affecting release 8 or 9LTE standard UE channel estimation and Radio Resource Management (RRM), Radio Link Management (RLM), and channel quality indicator measurements for these UEs. To further reduce interference from CRS on the data region, the ABS may be configured as an MBSFN subframe (if possible). However, for Frequency Division Duplex (FDD), subframe numbers 0, 4, 5 and 9 cannot be MBSFN subframes due to PSS/SSS/PBCH/SIB 1/paging. Similarly, in Time Division Duplex (TDD), subframes 0, 1, 2, 5, and 6 cannot be MBSFN subframes.

Synchronization signal

As indicated above, PSS and SSS are basic signals transmitted by the eNB. These signals are used to assist cell search and are transmitted on the downlink.

Although the PSS and SSS signals have the same detailed structure, the time domain position of the synchronization signals within the frame may be slightly different depending on the mode of operation, i.e. Frequency Division Duplex (FDD) or Time Division Duplex (TDD).

In one embodiment, there are, for example, 504 individual physical layer cell identities. The physical layer cell identities are grouped into, for example, 168 unique physical layer cell identity groups, each group containing three unique identities. The grouping is such that each physical layer cell identity is part of a unique set of physical layer cell identities. Thus, physical layer cell identificationFrom numbers in the range 0 to 167(representing physical layer cell identity group) and numbers in range 0 to 2(representing the physical layer identities in the physical layer cell identity group) is uniquely defined.

The two PSS transmitted by the cell within the radio frame may be the same. The PSS of a cell may employ three different sequences, e.g., from the cellAnd (4) determining. Once the UE detects and identifies the PSS of the cell, the UE has identified at least two messages. The first message is the millisecond timing of the cell, thus also identifying the location of the SSS with a fixed offset relative to the PSS. The second message isWhich is the cell identity in the cell identity group.

Upon detection of the PSS, the UE mayIn an attempt to detect SSS. Each SSS may employ a different cell identification group than 168Corresponding 168 different sequences.

The set of sequences valid for the two SSSs (SSS1, SSS2) in a radio frame is different. Thus, upon detection of a single SSS, the UE may determine whether SSS1 or SSS2 has been detected, thus determining radio frame timing.

According to SSS, a terminal may find at least two messages. The first message is the radio frame timing, which has two different alternatives, taking into account the location of the PSS. The second message isWhich is a cell identification group and is one of 168 alternatives.

Once the terminal has acquired the radio frame timing and physical layer cell identity, it has identified the cell-specific reference signal and can start channel estimation. The cell may then decode the broadcast channel transport channel carrying the most basic set of system information.

With respect to synchronization signals for the FDD case, PSS may be transmitted in the last symbol of the first slot (which corresponds to slots 0 and 10) of subframes 0 and 5, while SSS may be transmitted in the second last symbol of the same slot. In other words, the SSS is transmitted in the symbol immediately before the PSS.

Referring now to fig. 5, fig. 5 shows a radio frame 500 having a plurality of subframes 502. Each subframe 502 has two slots. An enlarged first sub-frame 502 is shown in the example of fig. 5.

As shown in the example of fig. 5, the PSS510 is found in the last OFDM of slot 0, and the PSS510 is also found in the most significant OFDM symbol of slot 10. The PSS occupies the central 62 subcarriers.

The SSS512 immediately precedes the PSS510, so the SSS512 is found in the last but one OFDM symbol of slot 0 and the last but one OFDM symbol of slot number 10. Like PSS, SSS occupies the central 62 subcarriers.

In addition, PBCH514 occupies the first four OFDM symbols of slot number 1, and PDCCH516 occupies the first three OFDM symbols of each subframe 502. PBCH occupies the central 72 subcarriers.

For synchronization signals for TDD, the PSS is transmitted in the third OFDM symbol of subframes 1 and 6. SSS is transmitted in the last OFDM symbol of subframes 0 and 5. Therefore, SSS is transmitted three OFDM symbols before PSS. Both PSS and SSS occupy the central 62 subcarriers.

Referring now to fig. 6, fig. 6 shows a TDD radio frame 600 having a plurality of subframes 602.

As shown in fig. 6, the PSS610 is transmitted in the third OFDM symbol of subframe 1 (the third OFDM symbol of slot number 2) and the third OFDM symbol of subframe 6 (the third symbol of slot number 12).

The SSS612 is transmitted in the last symbol of subframe 0 (the last symbol of slot number 1) and the last symbol of subframe 5 (the last symbol of slot number 11).

Also, PBCH614 is transmitted in the first four symbols of slot number I, and PDCCH616 is transmitted in the first three symbols of each subframe except for the subframe in which PSS610 is transmitted, and for the subframe in which PSS610 is transmitted, only two symbols contain PDCCH. PBCH occupies the central 72 subcarriers.

As used herein, PSS, SSS, and PBCH may be collectively or individually referred to as cell search signals. In other embodiments, the term "cell search signal" may refer to any other signal suitable for use in cell search. Furthermore, PSS, SSS, or PBCH signals defined in release 8, 9, and 10 standards of LTE may be referred to as default or primary cell search signals, while new PSS, SSS, or PBCH signals specified in the present disclosure may be referred to as secondary cell search signals.

For network selection, in an LTE-a heterogeneous network, a UE may communicate with a weaker cell. Such communication may include, for example, communicating with the pico cell when the UE is in a range expansion area or a non-member UE is in a coverage area of a CSG cell. Although the aggressor cell blanks the transmission or minimizes the transmit power during the ABS, the PSS/SSS/PBCH/SIB 1/page/PRS is still transmitted during these ABS to avoid impact on legacy UEs.

Without subframe offset, the PSS/SSS/PBCH of the interfering source cell may collide with the PSS/SSS/PBCH of the interfered cell. In the present disclosure, an interferer cell is a cell with a stronger signal and an interfered cell is a cell with a weaker signal. Thus, PSS/SSS/PBCH transmissions from the interfering source cell degrade signal reception at UEs in the interfered cell (e.g., in the range extension area).

According to some embodiments, the present disclosure provides for inserting an auxiliary PSS in an interfered cell and/or an auxiliary SSS in an interfered cell. To avoid confusion with existing PSS and SSS, the present disclosure provides a number of alternatives. These alternatives include utilizing new Zadoff-Chu sequences in the auxiliary PSS to avoid confusion with the existing PSS. Furthermore, in some embodiments, confusion may be avoided by introducing new sequences to be used for auxiliary SSS. Furthermore, in some embodiments, a new relative position may be used between the auxiliary PSS and SSS.

According to one embodiment of the disclosure, an auxiliary PBCH is inserted in an interfered cell to provide Master Information Block (MIB) information.

Further, according to an embodiment, configuration information of auxiliary PSS/SSS/PBCH may be exchanged between neighboring cells via a backhaul or X2 interface.

In another embodiment, some of the resource blocks of the interfering source cell may be blanked to protect the auxiliary PSS/SSS/PBCH of the interfered cell.

Further, according to an embodiment, the configuration of auxiliary PSS/SSS/PBCH between neighboring cells may be coordinated to avoid mutual interference.

According to another embodiment, signaling from the eNB to the UE may be used to trigger the UE to perform cell search using the auxiliary PSS/SSS/PBCH.

It will be clear to those skilled in the art that the UE performs its initial cell search and cell selection using the same procedures as non-initial cell search or cell reselection. The UE not only performs cell search when powered on, but also can continuously search for, synchronize to, and estimate reception quality of a neighboring cell to support mobility. The reception quality of the neighbouring cell is then evaluated with respect to the reception quality of the current cell to take into account whether a handover or cell selection/reselection should be performed.

Various embodiments of the present disclosure take advantage of the following design considerations when creating auxiliary PSS/SSS/PBCH signaling. However, these design considerations are not meant to be limiting, and other options are possible.

In a first embodiment, the auxiliary PSS/SSS and auxiliary PBCH may reside in the central 62 and 72 subcarriers, respectively, but in an Orthogonal Frequency Division Multiplexing (OFDM) symbol that is different from the default PSS/SSS/PBCH. When the UE performs a cell search for the first time, the UE does not know the cell bandwidth. Thus, the UE may assume a cell bandwidth equal to the smallest possible downlink bandwidth. This may be, for example, six resource blocks corresponding to 72 subcarriers. With the decoded MIB on PBCH, the terminal is then informed of the actual downlink cell bandwidth and can adjust the receiver bandwidth accordingly. Thus, in LTE, the PSS/SSS and PBCH may occupy the central 62 and 72 subcarriers, respectively (i.e., around the zero-frequency subcarriers). To allow the UE to continue operation regardless of the actual bandwidth, the auxiliary PSS/SSS and auxiliary PBCH may also reside in the center 62 and 72 subcarriers, respectively. However, in this case, since the PSS/SSS/PBCH resides in the same Resource Element (RE) as the default PSS/SSS/PBCH, the auxiliary PSS/SSS/PBCH may be transmitted at a different time instant than the default PSS/SSS/PBCH. This may be in different subframes or different OFDM symbols.

In a second embodiment, the auxiliary PSS and SSS are located in close proximity to each other, so that coherent detection of SSS is possible while SSS may be detected coherently and non-coherently. In some embodiments, using channel estimates obtained after the PSS is detected by coherent detection may result in less cell search time and higher accuracy. The above may be more relevant when the UE is moving fast.

In a third embodiment, the auxiliary PSS should not confuse legacy UEs with a timing (timing) of about five milliseconds. As used herein, the term legacy UE refers to a user equipment performing release 8, 9 or 10 of the LTE specification.

The UE performing the present embodiment will be aware of the auxiliary PSS used in conjunction with the existing PSS. However, legacy UEs may not be aware of this fact and therefore incorrectly identify the five millisecond timing from the secondary PSS.

In another embodiment, the secondary SSS should not confuse legacy UEs with radio frame timing. Similar to the issues with PSS, a UE performing the present embodiment may know to use an auxiliary SSS in conjunction with an existing SSS. However, legacy UEs may not be aware of the secondary SSS and should not erroneously identify radio frame timing from the secondary SSS in one embodiment.

In another embodiment, the auxiliary PSS and SSS may be located near the existing PSS and SSS so that UEs using a small search window may detect the synchronization signal.

In another embodiment, a Physical Downlink Shared Channel (PDSCH) may be controlled for transmissions of the same cell and neighboring cells, thereby protecting the auxiliary PSS/SSS/PBCH. For example, the PDSCH of a legacy UE may be scheduled on different resource blocks than those on which the auxiliary PSS, SSS and/or PBCH are transmitted, e.g., three resource blocks on either side of the zero-frequency subcarrier. One reason for not scheduling the entire Physical Resource Block (PRB) but suppressing (muting) resource blocks that overlap with the auxiliary PSS, SSS and/or PBCH is because legacy UEs expect data on the resource blocks assigned to the auxiliary PSS, SSS and/or PBCH.

In accordance with the above embodiments, a number of alternatives are presented herein.

Full size auxiliary PSS/SSS

In a first alternative, one way to avoid confusion between the auxiliary PSS/SSS and the existing PSS/SSS is to introduce a new Zadoff-Chu sequence for the auxiliary PSS. In this case, it may not be necessary to introduce a new sequence for SSS, since SSS may be detected after PSS is detected. Therefore, the introduction of new auxiliary PSS and SSS is unlikely to confuse legacy UEs.

Generating a length-N sequence for the default PSS from the frequency domain Zadoff-Chu sequence according to the following formula:

wherein the Zadoff-Chu routing sequence index u is given according to table 1 below.

Table 1: root index of PSS

According to Table 1, u is selected such that u₁+u₂N, where N =63 is the length of the Zadoff-Chu sequence. Using this relationship, therebyRaw time domain waveform PSS (u)₂) Is PSS (u)₁) Complex conjugation of (a). In other words, the sequence has time-domain complex conjugate symmetry. This allows to reduce the complexity of the PSS detection by about one third, since the correlation between the received signal and the third PSS can be obtained from the correlation with the second PSS, and thus a single correlator can be used to detect both PSS. Therefore, when selecting the auxiliary PSS, the root index may satisfy u₁+u₂N。

In another alternative, root indices 23, 40, and 41 may be used. These root indices have good auto-and cross-correlation properties. Furthermore, in one embodiment, the resulting sequences with new indices may have good cross-correlation properties with corresponding existing Zadoff-Chu sequences.

Referring now to Table 2, Table 2 shows three indices u' i, one for each u_iOne index u'_i. In other words, there is a one-to-one mapping between the existing Zadoff-Chu sequences and the auxiliary sequences of the PSS. Thus, for having an identifierUsing two PSS sequences, the existing PSS having an index u_iAuxiliary PSS with index u'_i。

In one embodiment, the cross-correlation between the auxiliary PSS with root index u ' and the existing PSS with root index u is made by selecting u ' such that | u ' -u | is a prime number of the length of the Zadoff-Chu sequence. For example, it may be 63. In one embodiment, u'₀、u′₁And u'₂May be 41, 40 and 23. These values are used as an example, and other values that provide sequences with good correlation properties may also be used.

Table 2: assisting root indexing of PSS

Alternatively, as long as there is only one interfered cell transmitting the auxiliary PSS in the coverage area, one auxiliary PSS sequence may be configured for the interfered cell. For example, if a pico cell is surrounded by a plurality of macro cells, the pico cell configures one auxiliary PSS. If existing PSS signaling can be relied upon to detect after providing correct time and frequency synchronizationOr if the interfered cell is a neighboring cell and the serving cell provides cell identifier information of the interfered cell such that the UE only needs to assist the PSS sequence to detect time and frequency synchronization. By using one sequence for the auxiliary PSS, the auxiliary PSS may provide only time and frequency synchronization. This helps to reduce the receiver complexity of any UE performing the present embodiment.

Any sequence with good properties other than the root indices 25, 29 and 34 from table 1 above may be used. In one embodiment, in cell j, the Zadoff-Chu sequence with root index u 'may be selected such that | u' -u_iI is a prime number of 63, where u is not equal for all i ≠ u_iIs a route index of the PSS transmitted by a cell which is a neighboring cell closest to the cell i. u. of_iMay include a root of Zadoff-Chu sequence used as the primary PSS and the auxiliary PSS. Further, on the UE side, the UE may monitor the auxiliary PSS sequence when certain conditions are met or the eNB may signal the UE. For example, in normal operation, the UE may perform legacy PSS/SSS detection. The UE may start detecting a new assistance sequence when the UE is close to the range expansion area or close to the femto cell. For initial access, e.g., when the UE is initially in idle mode, the UE may internally determine, based on implementation factors, whether to use the secondaryDetection of secondary PSS/SSS. For example, one implementation may be that a UE in idle mode always performs a search using the enabled auxiliary PSS/SSS.

Reference is now made to fig. 7. In fig. 7, the UE may sense low reliability of the PSS measurement during the initial cell. In these cases, the UE may attempt to detect the auxiliary PSS at a redefined location within the radio frame and combine the detection metrics after appropriate scaling. For example, the UE may combine correlation metrics collected at different time instants after scaling using the reliability values. The reliability value may for example depend on the signal to interference power ratio observed on the respective correlation measure. The frequency offset, slot boundary, and physical layer identifier may be determined from the combined metrics.

The process of fig. 7 starts at block 710 and proceeds to block 712 where, in block 712, the primary PSS is searched over K1 radio frames.

Then, the process proceeds to block 720 to check whether the reliability of the detected PSS is poor or whether the PSS is not detected.

If reliability is not poor and a PSS is detected, the process proceeds to block 722, where the UE searches for the primary SSS in block 722. The process then proceeds to block 724 and ends.

Conversely, if the reliability of the detected PSS is poor or if no PSS is detected, the process proceeds from block 720 to block 730, where the UE also searches for the auxiliary PSS in block 730.

From block 730, the process proceeds to block 740, where in block 740, detection metrics of the primary PSS and the secondary PSS are jointly evaluated over K2 radio frames.

The process then proceeds to block 742 where a check is made to determine whether the evaluated metric from block 740 is reliable in block 742. In other words, a check is made at block 742 to check whether the reliability of the detected PSS is poor or whether the PSS is not detected. If the reliability is poor or the PSS is not detected, the process proceeds to block 744, the PSS detection failure is recorded in block 744, and the process then proceeds to block 724 and ends.

Conversely, if the reliability of the PSS detected at block 742 is not poor and if the PSS is detected, the process proceeds to block 750 where the primary SSS is searched and optionally also the secondary SSS is searched in block 750.

From block 750, the process proceeds to block 724 and ends.

Therefore, according to fig. 7, the UE performing the present embodiment is aware of the secondary PSS transmission and may also search for the secondary PSS if it is determined that the detection of the primary PSS is not reliable. Alternatively, the UE attempts to detect the primary SSS with a timing and frequency offset derived based on the primary PSS detection before deciding whether to detect the secondary PSS. Based on the severity of the radio channel conditions, the PSS and SSS may be detected over multiple radio frames as described above. If the UE performing the present embodiment is searching for both the primary PSS and the auxiliary PSS, the number of radio frames on which the detection metric is observed, K2, may be reduced compared to K1.

Novel sequences for auxiliary SSS

In the embodiments discussed above, one way to avoid confusion between the auxiliary PSS/SSS and the existing PSS/SSS is to introduce a new Zadoff-Chu sequence for the auxiliary PSS. In an alternative embodiment, a new sequence may be defined for the auxiliary SSS to pair with PSS.

Currently, for eachSpecifying two SSS parameters (m)₀、m₁). Can be selected byAnd (m)₀、m₁) Different mapping tables between to define a new SSS sequence. For example, the set of physical layer cell identities may be based on a physical layer cell identity having an offset δ compared to an existing relationshipTo derive an index m₀And m₁. In makingIn the case of the offset δ, the parameter (m) can be generated according to the following equation₀、m₁)：

If δ is 1, it is provided in Table 3 belowAnd (m)₀、m₁) To be mapped between.

Table 3:and m₀And m₁To be mapped between

In one embodiment, where a new sequence is used for the auxiliary SSS, it may not be necessary to find a new sequence for the PSS. In other words, the root index of table 1 above may also be used in the auxiliary PSS. Since the auxiliary PSS uses the same sequence as the existing PSS, the same PSS for a given cell is simply repeated more times. With this arrangement, detecting the auxiliary SSS will fail assuming the existing SSS sequence. Thus, legacy UEs know that the timing from the auxiliary { SSS, PSS } pair is incorrect and continue to search at other times.

Referring now to fig. 8, fig. 8 illustrates a conventional UE detection procedure performed by a UE in accordance with the above. As shown, the UE attempts to detect the PSS over multiple frames. When the UE successfully detects PSS, SSS detection is initialized at a location adjacent to the selected PSS location. If not, the SSS detection process is repeated at the next moment of PSS.

Thus, the process of fig. 8 begins at block 810 and proceeds to block 812 where a search is conducted for the PSS in block 812.

The process then proceeds to block 814 where an average of the PSS detection metrics over K1 radio frames is found in block 814.

The process then proceeds to block 816 where, in block 816, the primary SSS is searched if the average PSS detection is successful. The search at block 816 is performed in a neighboring location of the selected PSS.

The process then proceeds to block 820 where a check is made to determine if the detection of SSS was successful in block 820. If not, the process returns to block 812 to continue searching for the primary PSS. Otherwise, if the search or detection for SSS is successful, the process proceeds from block 820 to block 822 and ends.

Referring now to fig. 9, fig. 9 illustrates a detection mechanism performed by a UE performing an embodiment of the present disclosure. The UE of fig. 9 attempts to detect the primary SSS and the secondary SSS in an attempt to acquire radio frame timing. To improve detection performance, the primary SSS detection metric and the secondary SSS detection metric may be combined. However, this may increase the detection delay for legacy UEs, since legacy UEs may have to perform more SSS detections than previously. One way to reduce the likelihood of increased detection delay is to place the location of the auxiliary PSS/SSS after the legacy PSS/SSS location, so that the legacy UEs are likely to detect the default PSS/SSS first. Thus, the UE will detect the auxiliary PSS only when the UE starts searching after the legacy PSS/SSS symbol. For a UE performing embodiments of the present disclosure, it may be difficult to detect the legacy PSS/SSS, and thus there may be no latency issue.

Referring to fig. 9, the process starts at block 910 and proceeds to block 912 where, in block 912, a search is made for the primary PSS and also for the secondary PSS.

The process then proceeds to block 914 where an average of the PSS detection metrics over K1 radio frames is found from the reliability value in block 914.

The process then proceeds to block 916 where a search is conducted for the primary SSS and the secondary SSS in block 916. At times adjacent to the detection time of the PSS, searching continues for the primary SSS and the auxiliary SSS. The best detection metric found by the search is selected.

The process then proceeds to block 920 to check if the detected reliability of the SSS is acceptable. If so, the process proceeds to block 922 and ends. Conversely, if the reliability of the detected SSS is not acceptable, the process proceeds to block 930 where a check is made to determine if the number of attempts is exhausted. It is appreciated that the number of attempts may be predetermined at the device. If the number of attempts is exhausted, the process proceeds to block 932 where the assertion detection fails and the process then proceeds to block 922 and ends.

Conversely, if at block 930 the number of attempts is not exhausted, the process returns to block 912 and continues to loop until the SSS is acceptably detected or there is a detection failure at block 932.

Auxiliary PSS/SSS placement

Because the distinction between the secondary synchronization signal and the existing synchronization signal (whether PSS, SSS, or both) is achieved by defining a sequence, the secondary synchronization signal can maintain the same relative position as the existing synchronization signal. Specifically, as shown in fig. 5, the default PSS and SSS locations in FDD are locations that have the SSS before the PSS. As shown in fig. 6, in TDD, the default PSS is three symbols before the default SSS.

Referring now to fig. 10, fig. 10 shows the secondary synchronization signal located in OFDM symbols 5 and 6 of slot number 1.

Specifically, in fig. 10, the auxiliary PSS1010 is shown as symbol 6 of slot number 1 and the auxiliary SSS1012 is shown as OFDM symbol number 5 of slot number 1.

Otherwise, referring to fig. 10, the primary PSS1020, primary SSS1022, PBCH1024, and PDCCH1026 remain the same.

Further, in the embodiment of fig. 10, cell-specific reference signals (CRSs) (although not shown) are provided in symbols 0, 1, and 4 of each slot.

For fig. 11-13, the primary PSS1020, primary SSS1022, PBCH1024, and PDCCH1026, and CRS remain the same.

Reference is now made to fig. 11. In the embodiment of fig. 11, the auxiliary PSS and SSS are located in OFDM symbols numbers 2 and 3 in slot number 11, as shown with reference numeral 1110 for the auxiliary PSS and 1112 for the auxiliary SSS.

Reference is now made to fig. 12. In the example of fig. 12, the auxiliary PSS and SSS are located in OFDM symbols 5 and 6 in slot number 11, as shown with reference numeral 1210 for the auxiliary PSS and 1212 for the auxiliary SSS.

Referring to fig. 10 to 12, although not shown in the drawings, a channel state information reference signal (CSI-RS) may occupy the same OFDM symbol as the secondary synchronization signal. Because the periodicity of the secondary synchronization signal is a multiple of five subframes, overlap may be avoided by configuring the CSI-RS to occupy a different subframe than the secondary synchronization signal.

The auxiliary PSS/SSS may occupy resource elements that typically contain PDSCH, and may adjust PDSCH transmission or reception based thereon. This may be achieved by replacing REs containing PDSCH with auxiliary PSS/SSS or by increasing the code rate of PDSCH data so that it adapts to the subframe without occupying REs containing auxiliary PSS/SSS. Thus, in a first example, this may be referred to as puncturing (puncturing) REs in PDSCH, and in a second example, this may be referred to as rate matching PDSCH near colliding REs.

UEs performing embodiments of the present disclosure may use the rate matching method because they may adjust the rate matching to use only the valid REs containing PDSCH. In contrast, legacy UEs may use a puncturing approach because the legacy UEs may not be aware of the auxiliary PSS/SSS. An eNB transmitting to a legacy UE may use a conservative Modulation and Coding Scheme (MCS) to achieve an acceptable error rate for such puncturing.

Further, as described above, the auxiliary PSS and SSS may maintain their relative positions, with the auxiliary SSS immediately preceding the auxiliary PSS. Further, the examples of fig. 10 to 12 show that the synchronization signal is located in the same subframe as the existing synchronization signal. Although in the embodiments of fig. 10 to 12 only one set of auxiliary PSS/SSS is added to one radio frame to reduce overhead, more instances of auxiliary PSS or SSS may be defined if high detection reliability is desired. For example, two new sets of auxiliary PSS/SSS may be defined for each radio frame.

Reference is now made to fig. 13, wherein the new sequences of auxiliary PSS and/or SSS provide a distinction from the existing PSS/SSS. In the example of fig. 13, the secondary synchronization signal may be located in OFDM symbol numbers 5 and 6 of slot number 1 and slot number 11. Thus, in fig. 13, the auxiliary PSS is shown with reference numerals 1312 and 1316, while the auxiliary SSS is shown with reference numerals 1310 and 1314.

The examples of figures 10 to 13 are meant only to illustrate the possibility of placement of the auxiliary PSS and SSS, and not to be limiting. Other examples are possible, such as different OFDM symbols in different slots, etc.

Furthermore, for TDD, similar arrangements may exist. This is illustrated with respect to fig. 14-17. In fig. 14, the secondary synchronization signal is located in OFDM symbol numbers 3 and 6 of slot 0. Specifically, the auxiliary PSS1410 is located in symbol number 6 of slot 0 and the auxiliary SSS1412 is located in symbol 4 of slot 0.

Similarly, in fig. 15, the secondary synchronization signal is located in OFDM symbol numbers 3 and 6 of slot 10. Thus, in fig. 15, the auxiliary PSS1510 is located in symbol number 6 of slot number 10 and the auxiliary SSS1512 is located in symbol number 4 of slot number 10.

Referring to fig. 16, the secondary synchronization signal is located in OFDM symbol number 6 of slot number 10 and OFDM symbol number 2 of slot number 11. This is illustrated by using reference numeral 1610 for the auxiliary PSS and 1612 for the auxiliary SSS.

Referring to fig. 17, the auxiliary synchronization signals are located in OFDM symbols number 2 and 5 of slot number 11, as shown with reference numeral 1710 for the auxiliary PSS and reference numeral 1712 for the auxiliary SSS.

Further, the auxiliary PSS and SSS may maintain their relative positions, with the auxiliary SSS three OFDM symbols before PSS. Maintaining the relative positions of the auxiliary PSS and SSS allows the UE to distinguish FDD and TDD during initial cell search as with existing designs.

Relative position between new auxiliary PSS and SSS

In another embodiment, one way to avoid confusion between the auxiliary PSS and SSS and the existing PSS and SSS is to place the auxiliary SSS in a different relative position to the auxiliary PSS than the existing PSS and SSS signaling. For FDD, this means that the auxiliary SSS is not located immediately before the auxiliary PSS. For TDD, this means that the auxiliary SSS is not located three OFDM symbols before the auxiliary PSS. In this way, it may not be necessary to introduce new sequences for PSS or SSS.

For legacy UEs, after detecting PSS, the legacy UEs may not be able to detect SSS. Therefore, detection will be attempted again. While this may increase the detection delay for legacy UEs, on the UE side, the delay impact may be affected by the UE implementation. On the network side, one way to reduce latency is to place the auxiliary PSS/SSS immediately after the legacy PSS/SSS, so that legacy UEs are likely to detect the legacy PSS/SSS first. For a UE performing embodiments of the present disclosure, because one scenario of interest is a high interference scenario, it may be difficult to detect the default PSS/SSS and thus there may be no latency issue.

Reference is now made to fig. 18 to 20. Fig. 18 to 20 show examples of various options for FDD, where the relative positions of SSS and PSS are selected such that SSS is immediately behind PSS. In other words, the relative positions are swapped compared to the embodiment of fig. 10-12.

Thus, in the embodiment of fig. 18, the auxiliary synchronization signals are located in OFDM symbols 5 and 6 of slot number 1, with the auxiliary PSS1810 immediately preceding the auxiliary SSS 1812.

In the embodiment of fig. 19, the auxiliary synchronization signals are located in OFDM symbols number 2 and 3 of slot number 11, where the auxiliary PSS1910 immediately precedes the auxiliary SSS 1912.

In the embodiment of fig. 20, the auxiliary synchronization signals are located in OFDM symbols 5 and 6 of slot number 11, where the auxiliary PSS2010 immediately precedes the auxiliary SSS 2012.

The examples of fig. 18-20 are not meant to be limiting and other relative positions will also be directly employed by those skilled in the art with reference to the present disclosure, e.g., SSS two OFDM symbols before or after PSS. Further, in some embodiments, the CRS may be punctured and this would provide an additional option for positioning assistance synchronization signals.

Similarly, for TDD, a similar location exchange may be applied. For example, the locations of the auxiliary SSS and PSS in fig. 14-17 may be swapped while reusing existing sequences of PSS and SSS.

Auxiliary SSS sequences only

In another embodiment, only an auxiliary SSS can be added to the interfered cell in one embodiment, because PSS has higher detection reliability than SSS due to the more hypotheses to test in SSS. By introducing only auxiliary SSS sequences, overhead is reduced and UE processing is simplified. The UE may detect the PSS using an existing PSS sequence.

For example, referring now to fig. 21, fig. 21 illustrates an exemplary FDD system in which only auxiliary SSS sequences are added instead of both auxiliary SSS and auxiliary PSS sequences. By adding only the auxiliary SSS sequence, the auxiliary SSS may be located in the same subframe as the default PSS and SSS sequences, so that the UE may quickly detect the auxiliary SSS after detecting the PSS.

In one embodiment, the location of the auxiliary SSS should not conflict with the PSS/SSS/PBCH of the interferer cell. Thus, if there is no data transmission in the interfering cell on the resource element where the secondary SSS sequence of the interfered cell is located, the secondary SSS will not be interference limited. Furthermore, if no reliable PSS is available, non-coherent detection techniques may be applied in high speed scenarios.

As shown in fig. 21, the auxiliary SSS2110 may be located at the fourth symbol of subframe 0, which is close to the existing PSS/SSS.

The auxiliary SSS2210 may also be placed in the second to last symbol of subframe 0, as shown in fig. 22.

Referring to fig. 23, an auxiliary SSS2310 may be placed at the fourth symbol of subframe 5, which is also close to the existing PSS/SSS.

Alternatively, an auxiliary SSS may be added along with the auxiliary PSS/SSS to further improve SSS detection probability. This is illustrated with respect to fig. 24. In particular, the auxiliary SSS2410 is located in the same subframe as the default PSS2412 and default SSS2416 and the auxiliary PSS2420 and the further auxiliary SSS 2422.

The use of the secondary SSS2410 may reduce the UE detection window. The above scheme has slightly less overhead than the two auxiliary PSS/SSS sets shown above with respect to fig. 13. For auxiliary SSS sequences, existing SSS sequences may be reused.

Furthermore, if multiple cells with overlapping coverage areas require auxiliary PSS/SSS, the cells may be both interferers and interfered. Thus, each cell may select a different location for the auxiliary PSS/SSS to avoid collisions. To avoid collisions between the auxiliary PSS/SSS/PBCH from the macro and pico in the presence of the femto cell, the macro and pico may choose to transmit the auxiliary PSS/SSS/PBCH in different locations, each using a different configuration than that shown in fig. 24.

Auxiliary PSS/SSS/PBCH in different bandwidths

Because the existing PSS/SSS/PBCH is transmitted in the center six Resource Blocks (RBs) of the system, one option is to transmit the auxiliary PSS/SSS/PBCH in the other RBs of the system. For example, the auxiliary PSS/SSS/PBCH may be transmitted in six consecutive RBs adjacent to the center six RBs. Alternatively, the auxiliary PSS/SSS/PBCH may be transmitted at positions adjacent to both sides of the existing PSS/SSS/PBCH. In other words, three RBs may be extended on either side of the existing PSS/SSS/PBCH.

By using different bandwidths, the impact on legacy UE synchronization and cell detection is minimized because there is no auxiliary PSS/SSS/PBCH that confuses legacy UE synchronization and cell detection. However, those RBs in which the auxiliary PSS/SSS/PBCH is transmitted will not be available for data transmission by legacy UEs, which may reduce the scheduling flexibility of legacy UEs. However, the eNB may still schedule these RBs for the UE performing the methods of the present disclosure. On the other hand, if the system bandwidth is small, e.g., 1.25MHz, there may not be additional frequency resources available for the auxiliary PSS/SSS sequence. For system bandwidths greater than a threshold, such as 1.25MHz, the auxiliary PSS/SSS sequence may be placed in the RBs immediately adjacent to the center six RBs in which the existing PSS/SSS is transmitted. For auxiliary PSS/SSS sequences, existing PSS/SSS sequences may be reused.

The frequency locations of the auxiliary PSS/SSS/PBCH are pre-configured and known to the UE performing embodiments of the present disclosure. Furthermore, by searching for PSS/SSS/PBCH sequences in the center six RBs, the UE performing this embodiment may also search for other preconfigured RBs to find the auxiliary PSS/SSS. If any auxiliary PSS/SSS is detected, the UE may add the cell to its measurement list for cell selection/reselection or handover.

To limit interference, in one embodiment, the interferer may not transmit any data on the REs in which the auxiliary PSS/SSS sequence is transmitted.

Half-size auxiliary PSS/SSS

In the LTE specifications of release 8 to release 10, the combination of two length-31 sequences defining the secondary synchronization signal is different between subframe 0 and subframe 5 according to the following equation:

wherein n is more than or equal to 0 and less than or equal to 30. According to physical layer cell identification groupWill index m₀And m₁The derivation is:

in order to keep the overhead of the auxiliary PSS/SSS low, in one embodiment, a half-size PSS/SSS may be introduced. Referring now to fig. 25, fig. 25 shows a first cell 2510 and a second cell 2520. In the cell 2510, the auxiliary PSS2512 may be frequency multiplexed with the auxiliary PSS2520 from the second cell 2520. Similarly, the auxiliary SSS2514 in the cell 2510 is placed such that it opposes the auxiliary SSS2524 of the cell 2520.

Fig. 26 shows the same case of TDD. Specifically, the first cell 2610 and the second cell 2620 utilize half-size PSS and SSS. Specifically, the auxiliary PSS2612 of the cell 2610 may be frequency multiplexed with the auxiliary PSS2622 of the second cell 2620. Similarly, the auxiliary SSS2614 may be frequency multiplexed with the auxiliary SSS2624 of the second cell 2620.

The equations for several alternative ways of SSS are shown below. Specifically, in a first alternative of the auxiliary sequence of the SSS, the cell may be represented as:

for a second alternative to the auxiliary sequence of SSS, the cell may be represented by:

in the above, a "null" indicates that the auxiliary SSS is not transmitted in the respective Resource Elements (REs) that would be occupied by the SSS if the SSS were transmitted in an OFDM symbol, and instead the REs are left unoccupied or occupied by other signals such as PDSCH or reference signals.

The half-size auxiliary PSS/SSS allows frequency resource sharing between two neighboring cells, thereby reducing overhead from the auxiliary PSS/SSS. Although the result of the half size PSS/SSS is a reduction of the autocorrelation peak by half in the UE detector, the degradation of the cell search performance may not be high because the interferer cell may blank out in the respective RE. In the absence of inter-cell interference, PSS and SSS may be performed with reduced length. This is because the existing full-size PSS/SSS is designed to operate without protection (and therefore with inter-cell interference from neighboring cells).

In another embodiment, overhead may be reduced by transmitting the auxiliary PSS/SSS less frequently. This results in a reduction of the time domain overhead and can be done by transmitting, for example, every other radio frame. This alternative may increase the detection delay by 10 milliseconds, but does not require the use of a new length to define the sequence.

Furthermore, in release 8, PSS is symmetric in the time domain, while SSS is not symmetric in the time domain. With the time domain symmetry property, the UE identifies the PSS position by comparing the signals in the first and second halves of the OFDM symbol duration. In the case of half-size auxiliary PSS, both the auxiliary PSS and SSS have this symmetric property in the time domain. To facilitate UE identification of PSS location, a UE performing embodiments of the present disclosure may need to buffer signals for the duration of two OFDM symbols. The second OFDM symbol is the PSS position if the signal length reveals symmetric properties in both OFDM durations.

Although in the examples of fig. 25 and 26, two OFDM symbols are adjacent in FDD and three OFDM symbols apart in TDD, this is meant as an example only and half the PSS and SSS lengths may be applied to the other embodiments described above.

Assisted PBCH

Without subframe offset, the PBCH from the interfered cell may be interfered by the PBCH from the interfering source cell. To allow the interfered cell to receive the MIB from the serving cell, the interfered cell may transmit an additional PBCH in a new location. To protect the secondary PBCH of the interfered cell, in one embodiment, the aggressor cell may send no RBs or low power RBs in the secondary PBCH location.

Thus, in accordance with the present disclosure, a UE performing embodiments herein decodes additional PBCH. The auxiliary PBCH may not affect legacy UEs.

Referring now to fig. 27, 28 and 29, examples of auxiliary PBCH for FDD and TDD are shown.

Similar to the default PBCH, in one embodiment, the auxiliary PBCH should not occupy the resource elements reserved for CRS antenna ports 0 to 3. The auxiliary PBCH may be located in any downlink subframe, but may typically occupy the same central six RBs as the central six RBs of the default PBCH. In one embodiment, the auxiliary PBCH and the default PBCH send the same MIB information on a given cell in a radio frame.

One auxiliary PBCH is simply to repeat the existing PBCH signal over the radio frame. However, other formats are possible. For example, different modulation or coding processes may be used to transmit the auxiliary PBCH in a more compact form. The auxiliary PSS/SSS may also provide channel estimates to facilitate decoding of the auxiliary PBCH if the auxiliary PBCH is close to the auxiliary PSS or SSS.

Referring to fig. 27, an auxiliary PBCH for FDD is shown. Specifically, in the embodiment of fig. 27, the auxiliary PBCH is located in symbols 0 to 3 of slot number 11, as shown by reference numeral 2710.

Referring to fig. 28, the auxiliary PBCH is shown in symbols 0 to 3 of slot number 3, as indicated by reference numeral 2810.

With respect to time domain duplexing, referring to fig. 29, fig. 29 shows an auxiliary PBCH in symbols 0 to 3 of slot 11, as indicated by reference numeral 2910.

The auxiliary PBCH occupies REs that typically contain PDSCH, and thus may need to adjust PDSCH transmission or reception. This can therefore be achieved by replacing the REs containing PDSCH with the secondary PBCH (puncturing the REs in PDSCH) or by increasing the code rate of the PDSCH data so that it adapts to new subframes (rate matching PDSCH around colliding REs) without occupying the REs containing the secondary PBCH.

UEs performing embodiments of the present disclosure may use the rate matching method because they may adjust the rate matching to use only the valid REs containing PDSCH. Legacy UEs may need to use the puncturing approach because they may not be aware of the auxiliary PBCH. If puncturing is used, the eNB may use the legacy MCS to achieve an acceptable reception error rate. To avoid impact on legacy UEs, in one embodiment, the eNB may schedule only UEs performing embodiments of the present disclosure on RBs containing the auxiliary PBCH.

Blanking to protect auxiliary PSS/SSS/PBCH

To ensure correct detection of auxiliary PSS/SSS in the context of inter-cell interference, in one embodiment, REs used for PSS/SSS/PBCH transmission in the interfered cell should not be used for data transmission by neighboring cells with strong interference.

In one example, in an interferer cell, subframes on which the auxiliary PSS/SSS/PBCH resides are designated as Almost Blank Subframes (ABS). Subframes of the auxiliary PSS/SSS/PBCH should be reconfigured or updated in the interfered cell, depending on the ABS configuration or reconfiguration of the neighboring interferer cell.

In another example, the subframe on which the auxiliary PSS/SSS/PBCH resides is not an ABS, but the eNB of the interfering source cell does not allocate any PDSCH to the center 6 RBs or allocates a PDSCH with low transmit power to the center 6 RBs. This provides the benefit of removing the impact on the auxiliary PSS/SSS/PBCH without losing RBs that does not conflict with the auxiliary PSS/SSS/PBCH.

In another embodiment, the eNB of the interfering source cell may know the RE locations of the auxiliary PSS/SSS/PBCH and may send data in other non-colliding REs while not sending any data on these REs. This may be achieved by replacing REs containing PDSCH with auxiliary PSS/SSS/PBCH (puncturing REs in PDSCH) or by increasing the code rate of PDSCH data so that data adapts to subframes (rate matching PDSCH around colliding REs) without occupying REs containing auxiliary PSS/SSS/PBCH.

On the UE side, for a UE performing an embodiment of the present disclosure, the UE may demodulate or decode data by receiving only valid REs containing PDSCH in the allocated RBs. For legacy UEs, all REs may be received in the allocated RBs to demodulate or decode the data. In this case, puncturing only REs is applicable. The eNB may use the legacy MCS to protect the data so the reception may still be successful or HAPRQ retransmission may be applied.

To enable appropriate blanking of the aggressor cells and configuration of the auxiliary PSS/SSS/PBCH, coordination information in both location and size may be sent from the victim cell to the aggressor cell via signaling such as X2 signaling. In another embodiment, the interfering source cell may request such information from the interfered cell.

Avoiding collisions of auxiliary PSS/SSS/PBCH between multiple cells

If multiple cells with overlapping coverage areas require auxiliary PSS/SSS/PBCH, each cell may select a different location for auxiliary PSS/SSS/PBCH to avoid collisions. For example, in the case of macro, pico, and femto deployments (where the pico and femto cells are in the coverage area of the macro cell and the coverage areas of the pico and femto cells do not overlap), the macro needs to send the auxiliary PSS/SSS/PBCH to facilitate macro UEs close to the CSG cell, and the pico needs to send the auxiliary PSS/SSS/PBCH to facilitate UEs in the range extension area as well.

To avoid collisions between the auxiliary PSS/SS/PBCH from the macro and pico, the macro and pico may choose to transmit the auxiliary PSS/SS/PBCH at different locations. For example, referring now to fig. 30, fig. 30 shows a radio frame 3010 for a picocell and a radio frame 3020 for a macrocell. In the radio frame 3010 of the pico cell, the auxiliary PSS3012 is in the sixth symbol of slot number 11 and the auxiliary SSS3014 is in the fifth symbol of slot number 11.

In addition, pico transmits the auxiliary PBCH3016 in symbols 0 to 3 of slot number 11.

On the macro cell, the macro cell transmits an auxiliary PSS3022 on the sixth symbol of slot number 1, an auxiliary SSS3024 on the fifth symbol of slot number 1, and an auxiliary PBCH on symbols 0 to 3 of slot number 3, as shown by reference numeral 3026.

To assist the UE in determining radio frame boundaries and auxiliary PBCH locations, different sequences may be used for auxiliary SSS at different locations. For example, the auxiliary SSS in subframes 0 and 5 will use different sequences. Furthermore, in one embodiment, the above new sequence may be used to assist the PSS. The auxiliary SSS in subframe number 0 will reuse the legacy SSS sequence of subframe number 0 and the auxiliary SSS in subframe number 5 will reuse the legacy SSS sequence of subframe number 5. In this case, when the UE detects a combination of the auxiliary PSS sequence and the SSS sequence of the legacy subframe number 0, the UE may know that it is currently at the last two OFDM symbols of subframe number 0 and the auxiliary PBCH is in the next subframe. If the UE detects a combination of the auxiliary PSS sequence and the SSS sequence of the legacy subframe number 5, the UE will know that it is currently at the last two OFDM symbols of subframe number 5 and the auxiliary PBCH is immediately before.

Alternatively, both the macro cell and the pico cell may have their own Physical Cell Identifier (PCI) space sent on the PSS/SSS. For example, the macro cell may transmit the auxiliary PSS/SSS in subframe number 0 and the auxiliary PBCH in subframe number I, and the pico may transmit the auxiliary PSS/SSS/PBCH in subframe number 5. According to this embodiment, the macro and pico will use the same sequence for the auxiliary SSS. After the UE detects the PCI from the auxiliary PSS/SSS, the UE will know whether it is from macro or pico, thus determining the radio frame boundary and auxiliary PBCH location accordingly.

Enabling detection of auxiliary PSS/SSS

In one embodiment, the UE may need to receive the PSS/SSS to search for a cell when it wishes to camp on the cell. Furthermore, the UE may need to receive the PSS/SSS for frequency or time acquisition needed for serving cell as well as neighbor cell measurements.

Thus, if a UE utilizing embodiments of the present disclosure is able to detect auxiliary PSS/SSS, the UE is able to detect auxiliary PSS/SSS for initial cell search and neighbor cell measurements. However, since the auxiliary PSS/SSS is not transmitted in all cells, this will increase UE battery power consumption if the UE performs detection on both the current PSS/SSS and the auxiliary PSS/SSS at all times.

To overcome the above problems and increase the possibility of using auxiliary PSS and SSS and reduce UE power consumption, a number of options are possible.

In a first embodiment, if the UE is able to receive the auxiliary PSS/SSS, the UE may always turn on detection of the auxiliary PSS/SSS for initial cell search and neighbor cell measurements for all cells.

In a second embodiment, an explicit indication may be signaled to the UE to indicate whether the UE needs to detect the auxiliary PSS/SSS. The explicit indication may be signaled using higher layer signaling. This may imply that the UE needs to be in a connected state to receive the signaling. This selection is not suitable for initial cell search in cell selection because the UE cannot receive higher layer signaling from the eNB before the UE finds a cell. However, explicit signaling may be included in the system information to enable the UE to detect neighboring cells for cell reselection purposes. Furthermore, dedicated signaling may be applied to neighbor cell measurements when the UE is in a connected state. The eNB may transmit dedicated Radio Resource Control (RRC) signaling to the UE to indicate that an auxiliary PSS/SSS is present, after which the UE may perform cell search using the auxiliary PSS/SSS. This may be included in a measurement configuration message, which is a type of Radio Resource Control (RRC) signal.

Although not strictly necessary, the frequency resources and timing of the PSS/SSS may be configurable if the auxiliary PSS/SSS is always used for UEs enabled by RRC signaling. Furthermore, if the eNB signals the cell identifier of the neighboring cell with detection of the auxiliary PSS/SSS enabled, it may not be necessary to identify the cell ID using PSS/SSS. In this case, PSS or SSS or any new sequence may be used for frequency and time acquisition purposes. If multiple cells require auxiliary PSS/SSS, the UE may need to receive PSS and SSS to identify to which cell the PSS and SSS are sent, although a cell ID is given. Alternatively, if a new sequence is used and a mapping between cell IDs and the new sequence is defined, a different sequence may be assigned to each cell in the neighbor cell list and the UE may use the sequence to detect the cell ID.

In a third option, an implicit indication may be used. When configuring measurements in restricted subframes, the UE may enable detection of the auxiliary PSS/SSS. More specifically, the UE may enable detection of the auxiliary PSS/SS when meassubframepatternconfigugneigh is received at the UE from the eNB and included in MeasObjectEUTRA transmitted to configure measurements. In release 10LTE, ABS is used to avoid interference in the context of heterogeneous network deployment. Therefore, limiting the measurement of subframes may occur because both features help to avoid interference in heterogeneous network scenarios. This selection may be applicable only to UEs performing neighbor cell measurements according to the present embodiment, considering that measurements in restricted subframes are configured when the UE is connected.

The above operations may be performed by any network element. A simplified network element is shown with respect to fig. 31.

In fig. 31, the network element 3110 includes a processor 3120 and a communication subsystem 3130, wherein the processor 3120 and the communication subsystem 3130 cooperate to perform the above-described methods.

Furthermore, the above method may be performed by any UE. An exemplary device is described below with respect to fig. 32.

The UE3200 is typically a two-way wireless communication device having voice and data communication capabilities. The UE3200 typically has the capability to communicate with other computer systems over the internet. Depending on the particular functionality provided, the UE may be referred to as, for example, a data messaging device, a two-way pager, a wireless e-mail device, a cellular telephone with data messaging capabilities, a wireless internet appliance, a wireless device, a mobile device, or a data communication device.

In the case where the UE3200 has two-way communication capabilities, it may have a communication subsystem 3211 including: a receiver 3212 and a transmitter 3214, and associated components, such as one or more antenna elements 3216 and 3218, a Local Oscillator (LO)3213, and a processing module, such as a Digital Signal Processor (DSP) 3220. As will be apparent to those skilled in the art of communications, the specific design of the communication subsystem 3211 will depend on the communication network in which the device is intended to operate.

Network access requirements may also vary depending on the type of network 3219. In some networks, network access is associated with a subscriber or user of the UE 3200. A UE may require a Removable User Identity Module (RUIM) or a Subscriber Identity Module (SIM) card to operate on a network. The SIM/RUIM interface 3244 is typically similar to a card slot into which a SIM/RUIM card can be inserted and ejected. The SIM/RUIM card may have memory and hold a number of key configurations 3251 and other information 3253, such as identification and subscriber related information.

Upon completion of the required network registration or activation procedures, the UE3200 may send and receive communication signals over the network 3219. As shown in fig. 32, the network 3219 may be comprised of multiple base stations communicating with the UE.

Signals received by the antenna 3216 through the communications network 3219 are input to a receiver 3212, and the receiver 3212 may perform conventional receiver functions such as signal amplification, frequency down conversion, filtering, channel selection, and so forth. Analog-to-digital (a/D) conversion of the received signal allows more complex communication functions, such as demodulation and decoding to be performed in the DSP 3220. In a similar manner, signals to be transmitted are processed, including modulation and encoding for example, by DSP3220 and are input to transmitter 3214 for digital to analog (D/a) conversion, frequency up conversion, filtering, amplification and transmission over the communication network 3219 via antenna 3218. DSP3220 not only processes communication signals, but also provides for receiver and transmitter control. For example, gains applied to communication signals in receiver 3212 and transmitter 3214 may be adaptively controlled through automatic gain control algorithms implemented in DSP 3220.

The UE3200 generally includes a processor 3238 that controls the overall operation of the device. Communication functions, including data and voice communications, are performed through the communication subsystem 3211. Processor 3238 also interacts with further device subsystems such as the display 3222, flash memory 3224, Random Access Memory (RAM)3226, auxiliary input/output (I/O) subsystems 3228, serial port 3230, one or more keyboards or keypads 3232, speaker 3234, microphone 3236, other communication subsystem 3240 (e.g., a short-range communications subsystem), and any other device subsystems generally designated as 3242. Serial port 3230 may include a USB port or other port known in the art.

Some of the subsystems shown in fig. 32 perform communication-related functions, whereas other subsystems may provide "resident" or on-device functions. It will be appreciated that some subsystems, such as keyboard 3232 and display 3222, for example, may be used for both communication-related functions, such as entering a text message for transmission over a communication network, and device-resident functions such as a calculator or task list.

Operating system software used by processor 3238 may be stored in a persistent store, such as flash memory 3224, which may also be a Read Only Memory (ROM) or similar storage element (not shown). It will be apparent to those skilled in the art that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile store such as RAM 3226. Received communication signals may also be stored in RAM 3226.

As shown, flash memory 3224 may be segregated into different areas for both computer programs 3258 and program data storage 3250, 3252, 3254 and 3256. These different storage types indicate that each program can allocate a portion of flash memory 3224 for its own data storage needs. The processor 3238, in addition to its operating system functions, may enable execution of software applications on the UE. A predetermined set of applications that control basic operations, including at least data and voice communication applications, for example, will typically be installed on the UE3200 during manufacture. Other applications may be installed subsequently or dynamically.

The applications and software may be stored on any computer-readable storage medium. The computer-readable storage medium may be a tangible or transitory/non-transitory medium such as optical memory (e.g., CD, DVD, etc.), magnetic memory (e.g., tape), or other memory known in the art.

One software application may be a Personal Information Manager (PIM) application having the ability to organize and manage data items relating to the user of the UE such as, but not limited to: e-mail, calendar events, voice mails, appointments, and task items. Naturally, one or more memory stores may be used on the UE to facilitate storage of PIM data items. Such PIM application may have the ability to send and receive data items via the wireless network 3219. Other applications may also be loaded onto the UE3200 through the network 3219, an auxiliary I/O subsystem 3228, serial port 3230, short-range communications subsystem 3240, or any other suitable subsystem 3242, and installed by a user in the RAM3226 or a non-volatile storage device (not shown) for execution by the processor 3238. Such flexibility in application installation increases the functionality of the device and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using the UE 3200.

In a data communication mode, received signals, such as text messages or web page downloads, will be processed by the communication subsystem 3211 and input to the processor 3238, which may be further processed by the processor 3228 for output to the display 3222 or alternatively to an auxiliary I/O device 3228.

A user of the UE3200 may also compose data items, such as e-mail messages, for example, using the keyboard 3232, which keyboard 3232 may be a full alphanumeric keyboard or telephone-type keypad, in conjunction with the display 3222 and possibly the auxiliary I/O device 3228. Such composed items may then be transmitted over a communication network through the communication subsystem 3211.

For voice communications, overall operation of the UE3200 is similar, except that received signals may generally be output to a speaker 3234 and signals for transmission may be generated by a microphone 3236. Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the UE 3200. While voice or audio signal output is preferably accomplished primarily through the speaker 3234, the display 3222 may also be used to provide indications regarding, for example, the identity of a calling party, the duration of a voice call, or other voice call related information.

Serial port 3230 in fig. 32 may typically be implemented in a Personal Digital Assistant (PDA) -type UE for which synchronization with a user's desktop computer (not shown) may be desired, although serial port 3230 is an optional device component. Such a port 3230 may enable a user to set preferences through an external device or software application and may extend the capabilities of the UE3200 by providing information or software downloads to the UE3200 other than through a wireless communication network. The alternate download path may be used, for example, to load an encryption key into the device through a direct and thus reliable and trusted connection to enable secure device communication. It will be clear to those skilled in the art that the serial port 3230 may also be used to connect the UE to a computer to act as a modem.

Other communication subsystems 3240, such as a short-range communication subsystem, is another optional component which may provide for communication between the UE3200 and different systems or devices, which need not necessarily be similar devices. For example, subsystem 3240 may include an infrared device and associated circuits and components or bluetooth^TMA communications module to provide communications with systems and devices having similar capabilities. Subsystem 3240 may also include non-cellular communications, such as WiFi or WiMAX.

The embodiments described herein are examples of structures, systems or methods having elements corresponding to elements of the technology of the present application. This written description will enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the technology of the present application. Accordingly, the intended scope of the technology of this application includes other structures, systems or methods that do not differ from the technology of this application described herein, and also includes other structures, systems or methods that do not differ from the technology of this application described herein.

Claims (85)

1. A method at a network element operating in a wireless network, wherein the network element is configured to transmit a default cell search signal at a default position in one or more subframes, the method comprising:

transmitting, by the network element, an auxiliary cell search signal in addition to the default cell search signal.

2. The method of claim 1, wherein the default cell search signal comprises a default synchronization signal and the auxiliary cell search signal comprises an auxiliary synchronization signal.

3. The method of claim 2, wherein transmitting the secondary cell search signal comprises: one or more of an auxiliary primary synchronization signal "PSS" or an auxiliary secondary synchronization signal "SSS" is transmitted.

4. The method of claim 3, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS once in a radio frame.

5. The method of claim 3, wherein transmitting the auxiliary PSS comprises: the auxiliary PSS is transmitted twice in a radio frame.

6. The method of claim 3, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS in the same subframe as the default cell search signal.

7. The method of claim 3, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS in a subframe adjacent to a subframe containing a default cell search signal.

8. The method of claim 3, wherein the auxiliary PSS comprises at least in part the same sequence as the default PSS.

9. The method of any of claims 2 to 7, wherein the auxiliary PSS comprises a Zadoff-Chu sequence generated from a different root index than the default PSS.

10. The method of any of claims 2 to 9, wherein the auxiliary PSS is placed in a predefined location in a radio frame, wherein the predefined location is different from the default location of the default PSS.

11. The method of claim 1, wherein the default cell search signal further comprises a default Secondary Synchronization Signal (SSS) and the auxiliary cell search signal further comprises an auxiliary SSS.

12. The method of claim 11, wherein the auxiliary PSS is adjacent to an auxiliary SSS in long term evolution frequency division duplex mode.

13. The method of claim 11, wherein, in a long term evolution time division duplex mode, the auxiliary PSS is separated from an auxiliary SSS by one or more orthogonal frequency division multiplexing, OFDM, symbols.

14. The method of claim 11, wherein the auxiliary PSS is in a different relative position to the auxiliary SSS than the default PSS is to the default SSS.

15. The method of claim 2, wherein the secondary cell search signal is transmitted on non-contiguous resource blocks.

16. The method of claim 2, wherein the auxiliary PSS occupies a different number of subcarriers than the default PSS.

17. The method of claim 16, wherein the auxiliary PSS is half as long as the default PSS.

18. The method of claim 17, wherein the auxiliary PSS is frequency division multiplexed with an auxiliary PSS from another cell.

19. The method of claim 1, wherein the default cell search signal is a default Secondary Synchronization Signal (SSS) and the auxiliary cell search signal comprises an auxiliary SSS.

20. The method of claim 19, wherein the auxiliary SSS utilizes a different sequence than the default SSS.

21. The method of claim 19, wherein transmitting the auxiliary SSS comprises: transmitting the auxiliary SSS once in a radio frame.

22. The method of claim 19, wherein transmitting the auxiliary SSS comprises: the auxiliary SSS is transmitted twice in a radio frame.

23. The method of claim 19, wherein transmitting an auxiliary SSS comprises: transmitting the auxiliary SSS in the same subframe as a default cell search signal.

24. The method of claim 19, wherein transmitting an auxiliary SSS comprises: transmitting the auxiliary SSS in a subframe adjacent to a subframe containing a default cell search signal.

25. The method of claim 19, wherein the auxiliary SSS is of a different length than the default SSS.

26. The method of claim 25, wherein the auxiliary SSS is half the length of the default SSS.

27. The method of claim 26, wherein the auxiliary SSS is frequency division multiplexed with an auxiliary SSS from another cell.

28. The method of claim 1, wherein the default cell search signal is a default Physical Broadcast Channel (PBCH) and the auxiliary cell search signal is an auxiliary PBCH.

29. The method of claim 28, wherein the auxiliary PBCH is a repetition of a default PBCH of a same radio frame.

30. The method of claim 28, wherein the auxiliary PBCH is formed by encoding a master information block "MIB" using any encoding technique such that combined decoding of default PBCH and auxiliary PBCH provides performance gain.

31. The method of claim 1, wherein the network element does not transmit on physical resources used by neighboring cells to transmit the secondary cell search signal in a particular subframe.

32. The method of claim 1, wherein the network element further exchanges information related to the auxiliary cell search signal with a neighboring network element.

33. The method of claim 1, wherein the network element further signals user equipment to enable or disable detection of the auxiliary cell search signal.

34. The method of claim 33, wherein the signaling is explicit through higher layer signaling.

35. The method of claim 33, wherein the signaling is implicit by a configuration that restricts measurements in subframes.

36. A method at a user equipment, UE, operating in a wireless network having a default cell search signal at a default position in one or more subframes, the method comprising:

detecting, by the UE, an auxiliary cell search signal; and

detecting, by the UE, a cell of the wireless network using information in the auxiliary cell search signal.

37. The method of claim 36, wherein the auxiliary cell search signal is at least one of an auxiliary Primary Synchronization Signal (PSS), an auxiliary Secondary Synchronization Signal (SSS), and an auxiliary Physical Broadcast Channel (PBCH).

38. The method of claim 36, wherein the auxiliary cell search signal is located at a predetermined position in a radio frame.

39. The method of claim 36, further comprising: detecting a cell of the wireless network using the detected auxiliary cell search signal and the default cell search signal for decoding.

40. The method of claim 36, wherein the detecting is performed only after receiving explicit signaling.

41. The method according to any of claims 36 to 40, wherein the explicit signalling is radio resource control signalling.

42. The method of claim 36, wherein the detecting is performed after receiving an implicit indication from the wireless network.

43. A network element operating in a wireless network, wherein the network element is configured to transmit a default cell search signal at a default position in one or more subframes, the network element comprising:

a processor; and

a communication subsystem for performing communication between a mobile station and a mobile station,

wherein the processor and the communication subsystem cooperate to:

transmitting, by the network element, an auxiliary cell search signal in addition to the default cell search signal.

44. The network element of claim 43, wherein the default cell search signal comprises a default synchronization signal and the auxiliary cell search signal comprises an auxiliary synchronization signal.

45. The network element of claim 44, wherein transmitting the secondary cell search signal comprises: one or more of an auxiliary primary synchronization signal "PSS" or an auxiliary secondary synchronization signal "SSS" is transmitted.

46. The network element of claim 45, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS once in a radio frame.

47. The network element of claim 45, wherein transmitting the auxiliary PSS comprises: the auxiliary PSS is transmitted twice in a radio frame.

48. The network element of claim 45, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS in the same subframe as a default cell search signal.

49. The network element of claim 45, wherein transmitting the auxiliary PSS comprises: transmitting the auxiliary PSS in a subframe adjacent to a subframe containing a default cell search signal.

50. The network element of claim 45, wherein the auxiliary PSS comprises, at least in part, the same sequence as the default PSS.

51. The network element of claim 45, wherein the auxiliary PSS comprises a Zadoff-Chu sequence generated from a different root index than the default PSS.

52. The network element of claim 45, wherein the auxiliary PSS is placed in a predefined location in a radio frame, wherein the predefined location is different from the default location of the default PSS.

53. The network element of claim 45, wherein the default cell search signal further comprises a default Secondary Synchronization Signal (SSS) and the auxiliary cell search signal further comprises an auxiliary SSS.

54. The network element of any of claims 43-52, wherein the auxiliary PSS is adjacent to an auxiliary SSS in Long term evolution frequency division Duplex mode.

55. The network element of any one of claims 43 to 52, wherein in Long term evolution time division Duplex mode, the auxiliary PSS is separated from auxiliary SSS by one or more Orthogonal Frequency Division Multiplexing (OFDM) symbols.

56. The network element of claim 45, wherein the auxiliary PSS is at a different relative position to an auxiliary SSS than the default PSS is to a default SSS.

57. The network element of claim 43, wherein transmitting the secondary cell search signal comprises: transmitting the secondary cell search signal on non-contiguous resource blocks.

58. The network element of claim 45, wherein the auxiliary PSS has a different length than the default PSS.

59. The network element of claim 45, wherein the reduced length auxiliary PSS has a length that is half of the default PSS length.

60. The network element of claim 45, wherein the auxiliary PSS is frequency division multiplexed with a second auxiliary PSS from another cell.

61. The network element of claim 43, wherein the default cell search signal is a default Secondary Synchronization Signal (SSS) and the auxiliary cell search signal comprises an auxiliary SSS.

62. The network element of claim 61, wherein the auxiliary SSS utilizes a different sequence than the default SSS.

63. The network element of claim 61, wherein transmitting the auxiliary SSS comprises: transmitting the auxiliary SSS once in a radio frame.

64. The network element of claim 61, wherein transmitting the auxiliary SSS comprises: the auxiliary SSS is transmitted twice in a radio frame.

65. The network element of claim 61, wherein transmitting an auxiliary SSS comprises: transmitting the auxiliary SSS in the same subframe as a default cell search signal.

66. The network element of claim 61, wherein transmitting an auxiliary SSS comprises: transmitting the auxiliary SSS in a subframe adjacent to a subframe containing a default cell search signal.

67. The network element of claim 61, wherein the auxiliary SSS is of a different length than the default SSS.

68. The network element of claim 67, wherein the auxiliary SSS is half the length of the default SSS.

69. The network element of claim 67, wherein the auxiliary SSS is frequency division multiplexed with a second auxiliary SSS from another cell.

70. The network element of claim 43, wherein the default cell search signal is a default Physical Broadcast Channel (PBCH) and the auxiliary cell search signal is an auxiliary PBCH.

71. The network element of any one of claims 43-70, wherein the auxiliary PBCH is a repetition of a default PBCH of a same radio frame.

72. The network element of claim 43, wherein the auxiliary PBCH is formed by encoding a Master Information Block (MIB) using any encoding technique such that combined decoding of default PBCH and auxiliary PBCH provides performance gain.

73. The network element of claim 43, wherein the network element is further coordinated with a neighboring network element to blank subframes for transmission.

74. The network element of claim 43, wherein the network element does not transmit on physical resources used by neighboring cells to transmit the secondary cell search signal in a particular subframe.

75. The network element of claim 43, wherein the network element further coordinates with a neighboring network element to determine a location of the auxiliary cell search signal.

76. The network element of claim 43, wherein the network element further signals user equipment to enable or disable detection of the auxiliary cell search signal.

77. The network element of claim 76, wherein the signaling is explicit through higher layer signaling.

78. The network element of claim 76, wherein the signaling is implicit by a configuration that restricts measurements in subframes.

79. A user equipment, UE, operating in a wireless network having a default cell search signal at a default position in one or more subframes, the user equipment comprising:

a processor; and

a communication subsystem for performing communication between a mobile station and a mobile station,

wherein the processor and the communication subsystem cooperate to:

detecting, by the UE, an auxiliary cell search signal; and

detecting, by the UE, a cell of the wireless network using information in the auxiliary cell search signal.

80. The user equipment of claim 79, wherein the auxiliary cell search signal is at least one of an auxiliary Primary Synchronization Signal (PSS), an auxiliary Secondary Synchronization Signal (SSS), and an auxiliary Physical Broadcast Channel (PBCH).

81. The user equipment of claim 79 or claim 80, wherein the auxiliary cell search signal is located at a predetermined position in a radio frame.

82. The user equipment of claim 79, further comprising: detecting a cell of the wireless network using the detected auxiliary cell search signal and the default cell search signal for decoding.

83. The user equipment of claim 79, wherein the detection is performed only after receiving explicit signaling.

84. The user equipment of claim 83, wherein the explicit signaling is radio resource control signaling.

85. The user equipment of claim 79, wherein the detecting is performed after receiving a configuration to limit measurements in subframes.