Title

Enhancing Neighbor Cell List

Field of the invention The present invention relates to an apparatus, a method, a system, and a computer program product related to radio access technology, in particular to HSPA evolution. More particularly, the present invention relates to an apparatus, a method, a system, and a computer program product for heterogeneous networks. Background of the invention

Abbreviations

3GPP 3 ^rd Generation Partnership Project

AS Access Stratum

BCCH Broadcast Control Channel

BTS Base Transceiver Station

CDF Cumulative Distribution Function

CIO Cell Individual Offset

CPICH Common Pilot Channel

DCH Dedicated Channel

DL Downlink

DPCCH Dedicated Physical Control Channel

DRX Discontinuous Reception

Ec received Energy per bit information

eNB Evolved Node B

E-DCH Enhanced Dedicated Channel

E-UTRAN Evolved UTRAN

GSM Global System for Mobile Communication

HetNet Heterogeneous Network

HoF Handover Failure

HS-DPCCH High Speed-DPCCH

HSPA High Speed Packet Access

IE Information Element

lo Interference power density

L3 Layer 3 (call processing application)

LPN Low Power Node

LTE™ Long Term Evolution

LTE-A™ Long Term Evolution- Advanced

NBAP NodeB Application Protocol NCL Neighbor Cell List

PSC Primary Scrambling Code

RF Radio Frequency

RNC Radio Network Controller

RRC Radio Resource Control

RRM Radio Resource Management

RX Receive

SCH Synchronisation Channel

sec Serving Cell Change

SFN SubFrame Number

SHO Soft Handover

SIB System Information Block

SINR Signal to Interference and Noise Ratio

SIZ Strong Imbalance Zone

SON Self Organizing Networks

ToS Time of Stay

TS Technical Specification

1 1 1 Time to Trigger

TX Transmit

UE User Equipment

UL Uplink

UMTS Universal Mobile Telecommunication System

UTRA UMTS Radio Access

UTRAN UMTS Radio Access Network

WCDMA Wideband Code Division Multiplex Access

WiFi™ Wireless Fidelity

Mobile networks capacity enhancements is one of the key areas in current research driven by increasing data traffic demands. Such capacity enhancements can be fulfilled e.g. by add- ing more spectrum resources into the system (multicarrier for example) or by optimizing existing spectrum usage (e.g. multiflow). One of the proposed solutions to combat increased traffic is the use of so called small cells, also known as Low Power Nodes (LPNs). A deployment of small cells (pico or micro cells) together with macro cells is termed as Heterogeneous Network (HetNet).

In 3G system, small cells are basically low powered NodeBs (1 Watt to 5 Watts of maximum TX power) aimed at serving a specific concentration of data traffic especially in urban environments. Such deployments could be both indoor and outdoor. Indoor deployments are aimed at serving users located in public or private establishments with high traffic demands such as offices, airports, shopping malls etc.

On the other hand, outdoor deployments are envisioned for users in outdoor public places or, in some cases, for users with relatively higher mobility. Moving UEs at high speeds typically experience worse channel conditions than pedestrian or static UEs. Therefore, deploying small cells along the movement path of UEs especially in an urban setup is a plausible idea to improve their service experience.

Small cells due to their coverage limitations and overlapping service areas with macros are less robust against interference and varying power levels in the soft handover zones. This problem is known as UL/DL imbalance and has been a subject of extensive interest in 3GPP.

The detection of a neighbour cell is specified to be possible as long as signal strengths as low as Ec/lo of -20dB or higher is detected. In detail, 3GPP TS 25.133 defines:

A cell shall be considered detectable when

CPICH Ec/lo > -20 dB if DL_DRX_Active = 0, or CPICH Ec/lo ≥-17dB if DL_DRX_Active=1. In Hetnet environments a UE may present already a noticable level of interference in UL for an LPN even if the LPN DL power is close to or even below the above mentioned level.

Fig. 1 sketches the signal strengths between macro BTS and LPN BTS exemplarily. In Fig. 1 , the path between macro and LPN BTS (e.g. pico BTS), is divided into several zones. In Fig. 1 , it is assumed that the received UL/DL signal strength decreases linearly with the distance from the respective base station. However, linear decrease is only exemplary and not limiting. In Fig. 1 , DL coverage (thick dashed lines) of the macro BTS extends slightly larger than uplink coverage (thin dashed lines), but this is exemplary only, too. DL coverage of the small cell is much less than its UL coverage. No coverage means that the respective received power is below a certain threshold value, as defined e.g. in 3GPP TS 25.133.

The arrows at the bottom indicate zones at the boundary area between macro BTS and small BTS: In zone A (UL SHO zone), downlink of the macro BTS is stronger than downlink of LPN BTS. The UE is served by macro BTS. On the left side of zone A, UL to macro BTS is stronger than UL to LPN BTS, whereas this is different on the right side. The point with equal uplink SINR is marked by "same UL SINR". This zone is also called the SIZ because the UE acts as an interferer to the LPN uplink users. A notable characteristic of the SIZ is also that the LPN cannot reach the interfering UE in the DL and hence cannot control the UL Tx power of the interfering UE.

In zone B, the SINR of the UL to macro BTS becomes very small (below a threshold), but DL of the macro BTS is still higher than that of the LPN BTS. In this zone, conventional (DL) SHO may take place. This zone is shown extended compared to the conventional DL pilot boundary of the LPN because of application of an, optional, CIO.

In zone C, uplink and downlink of the LPN are stronger than those of the macro BTS. The UE is served by the LPN BTS.

Fig. 2 shows a system level simulation performed by Nokia Siemens Networks, which shows a real situation in a typical Hetnet deployment with 4 LPNs dropped per Macro cell with 30 dBm LPNs. 21 macro cells (hence 84 LPNs and a total of 105 transmitting stations in total) were placed according to 3GPP simulation agreements for HetNet system level simulations (R1-125312: TP on Simulation Assumptions for Evaluation of HSPA Heterogeneous Networks). In detail, the CDF of the Ec/lo of the 3 strongest links in the strong UL/DL imbalance zone (also known as SIZ according to 3GPP terminology, UL SHO zone, or non AS region) are shown. Each curve represents a CDF of Ec/lo of a downlink from one of the 105 trans- mitting stations. The solid line curve on the rightmost part of Figure 2 represents the serving cell to a given UE. The curves to the left (the dashed curve and the curve with dots) are the 2 ^nd and 3 ^rd strongest DL contributors.

It can be seen from Fig. 2 that the Ec/lo of the two left curves (dashed curve and curve with dots) representing two of the links are quite below -20 dB. For the middle curve, the median value is close to -20 dB. Only the right curve representing the strongest link is well above -20 dB for substantially all points in the UL SHO zone. In reality, the situation may be worse than this because of shadowing and fast fading in a HetNet deployment. In 3G systems, NCL provides a means for a UE to look for potential cells to handover to if the signal strength from the current cell drops below an acceptable threshold. Neighbouring cells are defined on a cell-by-cell basis in the radio network configuration database. That is, each cell in the RAN can have an individual set of neighbouring cells. The NCL may be communicated to UEs in UTRAN by means of the commonly known System Information Block (SIBs) which is broadcasted or dedicated to the UE, e.g. by a RRC Measurement Control message. The NBAP system information update procedure is used to indicate to BTS the new information to be broadcasted on the BCCH and to control the state of the cell. Figure 3 shows an example of the former method described in the previous paragraph.

A principle of an NBAP system information update procedure is shown in Fig. 3. RNC sends a system information update request to the NodeB (as an example of a BTS). NodeB sends system information to UE based on the system information update request. This system information is repeatedly sent (continuously scheduled) by the NodeB. The receipt of a system information update by the NodeB is acknowledged by system information update response (or failure).

E.g., NCL information in the connected mode is contained in the SIB12 information block.

Conventionally, i.e. according to 3GPP WCDMA UTRAN Release 11 (3GPP TS 25.331 series describing the RRC protocol), the neighbour cell information which is transmitted to the mobile station for the intra-frequency measurements, includes the following L3 information elements:

• Cell Individual Offset is a value, which is added to the measured quantity (CPICH Ec/No) of the neighbouring cell before the UE compares the quantity with the reporting criteria.

• Primary CPICH Info information element contains the downlink scrambling code of the primary CPICH of the neighbouring cell.

• Read SFN Indicator information element (boolean) indicates whether the UE should read the SFN of the neighbouring cell or not.

• Tx Diversity Indicator information element (boolean) indicates downlink transmission diversity capability of the Node B that is controlling the neighbouring cell.

The neighbour cell information which is transmitted to the mobile station for the inter- frequency measurements, includes the following L3 information elements:

• Frequency Info information element contains the absolute UTRA RF channel number of the Primary CPICH of the inter-frequency neighbour cell. • Cell Individual Offset is an offset value, which is added to the measured quantity (CPICH Ec/No) of the neighbouring cell before the UE compares the Ec/No value with the reporting criteria. Conventionally, the value of the information element is always 0 dB.

• Primary CPICH Info information element contains the downlink scrambling code of the primary CPICH of the neighbouring cell.

• Read SFN Indicator information element (Boolean) indicates whether the UE should read the SFN of the neighbouring cell or not.

• Tx Diversity Indicator information element (Boolean) indicates downlink transmission diversity capability of the Node B that is controlling the neighbouring cell.

UE mobility classification (i.e. a determination of the approximate speed of the UE) is disclosed in prior art which is available through standards, products, patents and existing literature. UE classification is typically based on a number of cell-reselections in idle mode and number of active set updates in the connected mode.

Simulation studies for LTE (3GPP TS 36.839) and also for WCDMA (3GPP R2-131245: Mobility Performance in Hetnet) have shown that HO failure rate is directly proportional to the speed of a UE. A 30dBm cell can have a maximum coverage radius of around 50 meters in a coverage limited scenario not affected by other interferers. Therefore at a maximum diameter of 100 meters, a UE moving with 80 km/h will spend less than 5 seconds while passing through the cell. This leads to even smaller portion of time in the SHO region and therefore drastically compromising the HO success rate. UE speeds higher than 80 km/h shall have even higher impacts. Summary of the invention

It is an object of the present invention to improve the prior art. In detail, it is an object to overcome one or more of the problems related to HetNet deployments. According to a first aspect of the invention, there is provided an apparatus, comprising evaluating means adapted to evaluate an information received from an originating cell device, and applying means adapted to apply the evaluated information in at least one of measuring a radio link parameter of a selected neighbour cell and triggering reporting of a measurement report for the selected neighbor cell to the originating cell device; the information comprises at least one of 1. an indication of a timing offset of a first neighbor cell of the originating cell device;

2. an indication of a power class of a second neighbor cell of the originating cell device;

3. an indication of an uplink desensitization of a third neighbor cell of the originating cell device;

4. an indication of a power of a pilot channel of a fourth neighbor cell of the originating cell device;

5. an indication of a time to trigger specific for a fifth neighbor cell of the originat- ing cell device;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the originating cell device; and

7. an indication of a compensation factor for a seventh neighbor cell of the originating cell device; and

the selected neighbor cell is one of the first to seventh neighbor cells to which the information is related.

In the apparatus, the information may comprise the indication of the timing offset of the first neighbor cell; the selected neighbor cell may be the first neighbor cell; and the apparatus may be adapted to synchronize with the first neighbor cell based on the timing offset.

In the apparatus, the information may comprise at least one of the indication of the power class of the second neighbor cell, the indication of the uplink desensitization of the third neighbor cell, the indication of the power of the pilot channel of the fourth neighbor cell and the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be one of the second, third, fourth and seventh neighbor cells to which the information is related; and the apparatus may be adapted to estimate an uplink/downlink imbalance based on the evaluated information. In the apparatus, the information may comprise the indication of the power of the pilot channel; the selected neighbor cell may be the fourth neighbor cell; and the apparatus may further comprise detecting means adapted to detect the pilot channel using the indicated power of the pilot channel. In the apparatus, the information may comprise the indication of the power class of the second cell and an indication that the second cell is on a different carrier than the originating cell device; and the apparatus may further comprise first control means adapted to control measuring related to the second cell based on the indicated power class and the different carrier.

In the apparatus, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; the selected neighbor cell may be the fifth neighbor cell; and the apparatus may comprise checking means adapted to check if a measurement result of a measurement remains in a predefined range for a waiting time; triggering means adapted to trigger an event reporting of the measurement result if the measurement result remains in the predefined range for the waiting time; prohibiting means adapted to prohibit the event reporting of the measurement result if the measurement result does not remain in the predefined range for the waiting time; wherein the waiting time is the time to trigger if the measurement is related to the fifth neighbor cell; and the waiting time is different from the time to trigger if the measurement is related to a cell different from the fifth neighbor cell.

In the apparatus, the information may comprise at least one of the indication of the handover probability and the indication of the time of stay for the sixth neighbor cell; the selected neighbor cell may be the sixth neighbor cell; and the apparatus may comprise second control means adapted to control a measurement reporting related to the sixth neighbor cell based on the at least one of the handover probability and the time of stay indicated in the information. In the apparatus, the second control means may be further adapted to control the measurement reporting based on a mobility classification of the apparatus.

In the apparatus, the information may comprise the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be the seventh neighbor cell; and the apparatus may further comprise calculating means adapted to calculate a link imbalance based on the compensation factor; and reporting means adapted to report the link imbalance to the originating cell device.

In the apparatus, the information may be received in a neighbor cell list from the originating cell device. The neighbor cell list may comprise a neighbor cell list of a long term evolution network. According to a second aspect of the invention, there is provided an apparatus, comprising evaluating processor adapted to evaluate an information received from an originating cell device, and applying processor adapted to apply the evaluated information in at least one of measuring a radio link parameter of a selected neighbour cell and triggering reporting of a measurement report for the selected neighbor cell to the originating cell device; the information comprises at least one of

1. an indication of a timing offset of a first neighbor cell of the originating cell device;

2. an indication of a power class of a second neighbor cell of the originating cell device;

3. an indication of an uplink desensitization of a third neighbor cell of the originating cell device;

4. an indication of a power of a pilot channel of a fourth neighbor cell of the originating cell device;

5. an indication of a time to trigger specific for a fifth neighbor cell of the originating cell device;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the originating cell device; and

7. an indication of a compensation factor for a seventh neighbor cell of the originating cell device; and

the selected neighbor cell is one of the first to seventh neighbor cells to which the information is related.

In the apparatus, the information may comprise the indication of the timing offset of the first neighbor cell; the selected neighbor cell may be the first neighbor cell; and the apparatus may be adapted to synchronize with the first neighbor cell based on the timing offset.

In the apparatus, the information may comprise at least one of the indication of the power class of the second neighbor cell, the indication of the uplink desensitization of the third neighbor cell, the indication of the power of the pilot channel of the fourth neighbor cell and the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be one of the second, third, fourth and seventh neighbor cells to which the information is related; and the apparatus may be adapted to estimate an uplink/downlink imbalance based on the evaluated information. In the apparatus, the information may comprise the indication of the power of the pilot channel; the selected neighbor cell may be the fourth neighbor cell; and the apparatus may further comprise detecting processor adapted to detect the pilot channel using the indicated power of the pilot channel.

In the apparatus, the information may comprise the indication of the power class of the second cell and an indication that the second cell is on a different carrier than the originating cell device; and the apparatus may further comprise first control processor adapted to control measuring related to the second cell based on the indicated power class and the different carrier.

In the apparatus, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; the selected neighbor cell may be the fifth neighbor cell; and the apparatus may comprise checking processor adapted to check if a measurement result of a measurement remains in a predefined range for a waiting time; triggering processor adapted to trigger an event reporting of the measurement result if the measurement result remains in the predefined range for the waiting time; prohibiting processor adapted to prohibit the event reporting of the measurement result if the measurement result does not remain in the predefined range for the waiting time; wherein the waiting time is the time to trigger if the meas- urement is related to the fifth neighbor cell; and the waiting time is different from the time to trigger if the measurement is related to a cell different from the fifth neighbor cell.

In the apparatus, the information may comprise at least one of the indication of the handover probability and the indication of the time of stay for the sixth neighbor cell; the selected neighbor cell may be the sixth neighbor cell; and the apparatus may comprise second control processor adapted to control a measurement reporting related to the sixth neighbor cell based on the at least one of the handover probability and the time of stay indicated in the information. In the apparatus, the second control processor may be further adapted to control the measurement reporting based on a mobility classification of the apparatus.

In the apparatus, the information may comprise the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be the seventh neighbor cell; and the apparatus may further comprise calculating processor adapted to calculate a link imbalance based on the compensation factor; and reporting processor adapted to report the link imbalance to the originating cell device. In the apparatus, the information may be received in a neighbor cell list from the originating cell device. The neighbor cell list may comprise a neighbor cell list of a long term evolution network.

According to a third aspect of the invention, there is provided a user equipment, comprising an apparatus according to any of the first and second aspects.

According to a fourth aspect of the invention, there is provided an apparatus, comprising providing means adapted to provide an information, wherein the information comprises at least one of

1. an indication of a timing offset of a first neighbor cell of the apparatus;

2. an indication of a power class of a second neighbor cell of the apparatus;

3. an indication of an uplink desensitization of a third neighbor cell of the apparatus;

4. an indication of a power of a pilot channel of a fourth neighbor cell of the apparatus;

5. an indication of a time to trigger specific for a fifth neighbor cell of the apparatus;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the apparatus; and

7. an indication of a compensation factor for a seventh neighbor cell of the apparatus.

In the apparatus, the information may comprise the indication of the power of the pilot channel of the fourth neighbor cell; and the apparatus may comprise pilot controlling means adapted to control the power of the pilot channel of the fourth neighbor cell according to the indicated power.

In the apparatus, the information may comprise an indication of a cell individual offset of the fourth neighbor cell; wherein the apparatus may further comprise calculating means adapted to calculate the cell individual offset based on the power of the pilot channel.

In the apparatus, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; wherein the apparatus may further comprise determining means adapted to determine the time to trigger based on a size of the fifth neighbor cell. In the apparatus, the information may comprise plural indications of respective times to trigger specific for the fifth neighbor cell related to respective mobility classifications of a terminal device; and the determining means may be adapted to determine each of the times to trigger based on the size of the neighbor cell and the respective mobility classification.

In the apparatus, the information may comprise the indication of the compensation factor for the seventh neighbor cell; and the apparatus may comprise deciding means adapted to decide if a handover to the seventh neighbor cell takes place based on a received link imbalance.

In the apparatus, the providing means may be adapted to provide the information in a neighbor cell list. The neighbor cell list may comprise a neighbor cell list of a long term evolution network.

According to a fifth aspect of the invention, there is provided an apparatus, comprising providing processor adapted to provide an information, wherein the information comprises at least one of

1. an indication of a timing offset of a first neighbor cell of the apparatus;

2. an indication of a power class of a second neighbor cell of the apparatus;

3. an indication of an uplink desensitization of a third neighbor cell of the apparatus;

4. an indication of a power of a pilot channel of a fourth neighbor cell of the apparatus;

5. an indication of a time to trigger specific for a fifth neighbor cell of the apparatus;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the apparatus; and

7. an indication of a compensation factor for a seventh neighbor cell of the apparatus.

In the apparatus, the information may comprise the indication of the power of the pilot chan- nel of the fourth neighbor cell; and the apparatus may comprise pilot controlling processor adapted to control the power of the pilot channel of the fourth neighbor cell according to the indicated power. In the apparatus, the information may comprise an indication of a cell individual offset of the fourth neighbor cell; wherein the apparatus may further comprise calculating processor adapted to calculate the cell individual offset based on the power of the pilot channel. In the apparatus, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; wherein the apparatus may further comprise determining processor adapted to determine the time to trigger based on a size of the fifth neighbor cell.

In the apparatus, the information may comprise plural indications of respective times to trig- ger specific for the fifth neighbor cell related to respective mobility classifications of a terminal device; and the determining processor may be adapted to determine each of the times to trigger based on the size of the neighbor cell and the respective mobility classification.

In the apparatus, the information may comprise the indication of the compensation factor for the seventh neighbor cell; and the apparatus may comprise deciding processor adapted to decide if a handover to the seventh neighbor cell takes place based on a received link imbalance.

In the apparatus, the providing processor may be adapted to provide the information in a neighbor cell list. The neighbor cell list may comprise a neighbor cell list of a long term evolution network.

According to a sixth aspect of the invention, there is provided a base station or base station controller, comprising an apparatus according to any of the fourth and fifth aspects.

According to a seventh aspect of the invention, there is provided a method, comprising evaluating an information received from an originating cell device, and applying the evaluated information in at least one of measuring a radio link parameter of a selected neighbour cell and triggering reporting of a measurement report for the selected neighbor cell to the origi- nating cell device; the information comprises at least one of

1. an indication of a timing offset of a first neighbor cell of the originating cell device;

2. an indication of a power class of a second neighbor cell of the originating cell device;

3. an indication of an uplink desensitization of a third neighbor cell of the originating cell device; 4. an indication of a power of a pilot channel of a fourth neighbor cell of the originating cell device;

5. an indication of a time to trigger specific for a fifth neighbor cell of the originating cell device;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the originating cell device; and

7. an indication of a compensation factor for a seventh neighbor cell of the originating cell device; and

the selected neighbor cell is one of the first to seventh neighbor cells to which the information is related.

In the method, the information may comprise the indication of the timing offset of the first neighbor cell; the selected neighbor cell may be the first neighbor cell; and the method may further comprise synchronizing with the first neighbor cell based on the timing offset.

In the method, the information may comprise at least one of the indication of the power class of the second neighbor cell, the indication of the uplink desensitization of the third neighbor cell, the indication of the power of the pilot channel of the fourth neighbor cell and the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be one of the second, third, fourth and seventh neighbor cells to which the information is related; and the method may further comprise estimating an uplink/downlink imbalance based on the evaluated information.

In the method, the information may comprise the indication of the power of the pilot channel; the selected neighbor cell may be the fourth neighbor cell; and the method may further comprise detecting the pilot channel using the indicated power of the pilot channel.

In the method, the information may comprise the indication of the power class of the second cell and an indication that the second cell is on a different carrier than the originating cell device; and the method may further comprise controlling measuring related to the second cell based on the indicated power class and the different carrier.

In the method, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; the selected neighbor cell may be the fifth neighbor cell; and the meth- od may comprise checking if a measurement result of a measurement remains in a prede- fined range for a waiting time; triggering an event reporting of the measurement result if the measurement result remains in the predefined range for the waiting time; prohibiting the event reporting of the measurement result if the measurement result does not remain in the predefined range for the waiting time; wherein the waiting time is the time to trigger if the measurement is related to the fifth neighbor cell; and the waiting time is different from the time to trigger if the measurement is related to a cell different from the fifth neighbor cell.

In the method, the information may comprise at least one of the indication of the handover probability and the indication of the time of stay for the sixth neighbor cell; the selected neighbor cell may be the sixth neighbor cell; and the method may comprise controlling a measurement reporting related to the sixth neighbor cell based on the at least one of the handover probability and the time of stay indicated in the information. In the method, the controlling may be further adapted to control the measurement reporting based on a mobility classification of an apparatus performing the method.

In the method, the information may comprise the indication of the compensation factor for the seventh neighbor cell; the selected neighbor cell may be the seventh neighbor cell; and the method may further comprise calculating a link imbalance based on the compensation factor; and reporting the link imbalance to the originating cell device.

In the method, the information may be received in a neighbor cell list from the originating cell device. The neighbor cell list may comprise a neighbor cell list of a long term evolution network. According to an eighth aspect of the invention, there is provided a method, comprising providing an information, wherein the information comprises at least one of

1. an indication of a timing offset of a first neighbor cell of an apparatus performing the method;

2. an indication of a power class of a second neighbor cell of the apparatus;

3. an indication of an uplink desensitization of a third neighbor cell of the apparatus;

4. an indication of a power of a pilot channel of a fourth neighbor cell of the apparatus;

5. an indication of a time to trigger specific for a fifth neighbor cell of the apparatus;

6. at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the apparatus; and 7. an indication of a compensation factor for a seventh neighbor cell of the apparatus.

In the method, the information may comprise the indication of the power of the pilot channel of the fourth neighbor cell; and the method may comprise controlling the power of the pilot channel of the fourth neighbor cell according to the indicated power.

In the method, the information comprises an indication of a cell individual offset of the fourth neighbor cell; wherein the method may further comprise calculating the cell individual offset based on the power of the pilot channel.

In the method, the information may comprise the indication of the time to trigger specific for the fifth neighbor cell; wherein the method may further comprise determining the time to trigger based on a size of the fifth neighbor cell.

In the method, the information may comprise plural indications of respective times to trigger specific for the fifth neighbor cell related to respective mobility classifications of a terminal device; and the determining may be adapted to determine each of the times to trigger based on the size of the neighbor cell and the respective mobility classification.

In the method, the information may comprise the indication of the compensation factor for the seventh neighbor cell; and the method may comprise deciding if a handover to the seventh neighbor cell takes place based on a received link imbalance. In the method, the providing may be adapted to provide the information in a neighbor cell list. The neighbor cell list may comprise a neighbor cell list of a long term evolution network.

Each of the methods according to the seventh and eighth aspects may be a method of enhancing neighbor cell related information.

According to a ninth aspect of the invention, there is provided a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any one of the seventh and eighth aspects. The computer program product may be embodied as a computer-readable medium or may be directly loadable into the apparatus. According to some embodiments of the invention, at least one of the following advantages may be achieved:

- seamless user experience is improved;

- one or more problems related to HetNet deployments are overcome;

- synchronization is improved;

- UE can estimate the UL/DL imbalance;

- power consumption for dual carrier UEs is reduced;

- handover times are optimized;

- serving cell change is improved; and

- further dynamic information is considered in serving cell change.

It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as ex- eluding alternatives.

Brief description of the drawings

Further details, features, objects, and advantages are apparent from the following detailed description of the preferred embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein

Fig. 1 sketches UL and DL powers in different zones between a macro BTS and a LPN; Fig. 2 shows a simulation of a cumulative distribution function of three strongest links in the SIZ zone;

Fig. 3 shows a principle of NBAP system information update procedure;

Fig. 4 shows an apparatus according to an embodiment of the invention;

Fig. 5 shows a method according to an embodiment of the invention;

Fig. 6 shows an apparatus according to an embodiment of the invention; and

Fig. 7 shows a method according to an embodiment of the invention.

Detailed description of certain embodiments

Herein below, certain embodiments of the present invention are described in detail with ref- erence to the accompanying drawings, wherein the features of the embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain embodiments is given for by way of example only, and that it is by no way intended to be understood as limiting the invention to the disclosed details.

Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described.

According to embodiments of the invention, more parameters than according to a conven- tional NCL are sent to a UE. The additional parameters may enable a UE to detect, measure, and report neighbours with improved sensitivity so that the RAN could benefit from this information in advance and potential steps could be taken in advance to circumvent many of the issues related to HetNet deployments. In some embodiments, in order to ensure a seamless user experience, the content of a NCL is specific for the cell providing the NCL. That is, if a cell A is a neighbour of both cells B and C, the content of the neighbour cell list in cell B related to cell A may be different to the content of the neighbour cell list in cell C related to cell A. The enhancements of NCL according to some embodiments of the invention are inter alia applicable to connected mode of transmission in CELL_DCH state.

The deployment of HetNets in same frequency band raises new challenges which have to be addressed to ensure a successful network operation. The main issue is the difference be- tween macro base station and LPN downlink transmission power, which implies different coverage ranges for UL and DL. From the uplink perspective, the strength of the signal received at each node is not directly dependent on its DL transmission power. This leads to UL/DL imbalance, in the sense that cells other than the serving cell could receive a stronger signal from the UE than the serving cell. Such an imbalance also affects the reception of HS- DPCCH in the SHO zone when Multiflow is enabled. Multiple solutions are being studied to address UL/DL imbalance such as range expansion, receiver desensitization and power boosting. Some embodiments of the invention also aim to simplify UL/DL imbalance estimation at the UE side. According to some embodiments of the invention, one or more of the following information elements are included in the NCL. In general, these additional lEs may be provided for any cell (macro cells and small cells). However, in some embodiments, one or more of these information elements may be provided for an LPN only and not for a macro BTS. In these em- bodiments, the presence or absence of a corresponding IE indicates to the UE whether or not the cell belongs to a LPN.

The information elements are as follows: 1 ) LPN's Timing Offset

When a UE is provided with a neighbour list, it also receives the timing offset for LPN cells. This allows the UE to speed up synchronization as the step of looking for the primary synchronization channel (PSC) can be skipped or narrowed down.

It further enables the UE to detect the neighbour cell at lower signal strength, as it can average the measurements of the CPICH without prohibitive computational burden as would be the case otherwise. In legacy systems, during the first step of the cell search procedure the UE uses the SCH's primary synchronisation code to acquire slot synchronisation to a cell. This is typically done with a single matched filter (or any similar device) matched to the primary synchronisation code, which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output. By providing timing offset directly in the NCL, search for PSC can be optimized or skipped altogether. That is, synchronization is improved.

2) LPN's Power Class. By providing the LPN power class (transmit power), the UE can be informed if the target cell within its macro serving cell is a small cell. Such information can be utilized at the UE side to anticipate and estimate a UL/DL imbalance. Providing the power class in inter- frequency scenarios with dedicated deployments is also helpful for UE based cell detection. In an Inter-Frequency scenario, a UE served on one frequency may be required to periodically measure the second carrier using its second receiver chain. If the cell power class is provided through NCL, UE may independently optimize the periodicity and the need for activating its second receiver thus potentially lowering the power consumption.

3) LPN's UL desensitization.

If desensitization is applied at the receiver of the LPN, this information can be provided to the UE to estimate UL/DL imbalance.

4) LPN's CPICH Power.

If LPN's CPICH power is sent to the UE, it will enable tuning CPICH levels on per cell basis. This enables the LPN to use less power for CPICH, while UEs can still detect CPICH and estimate the UL/DL imbalance. Legacy UEs which cannot evaluate LPN's CPICH power may be affected by a lower CPICH level such that they cannot detect CPICH easily. This adverse effect may be mitigated by using range expansion in the form of Cell Individual Offset (CIO). CIO is provided in the legacy NCL. In some embodiments, the additional lEs may be different for intra-frequency NCL and inter- frequency NCL. For example, in case of intra-frequency NCL, the list may comprise one or more of timing offset for LPN, LPN power class, LPN's UL desensitization, LPN's CPICH Power. On the other hand, since UL/DL imbalance is not an issue for inter-frequency handover, the inter-frequency NCL according to some embodiments of the invention comprises one or more of timing offset for LPN and LPN power class only.

In particular, LPN power class in inter-frequency NCL can tell the UEs about the presence of potential small cells on a different carrier while they are in CELL_DCH state through the macro. Assume that an UE is required to measure inter-frequency neighbours in order to offload to a different carrier. In single carrier UEs, this is accomplished using Compressed Mode which is initiated by the network. Dual Carrier capable UEs however do not need compressed mode and can measure a different carrier independently without affecting the transmission from the first carrier. When the NCL provides information to the UE regarding the power class of the neighbouring LPNs, UE can control the measurements performed on the second carrier. For example, if there are multiple dedicated carrier LPNs in the vicinity pro- vided by the NCL, UEs can increase the measurement frequency. If no such neighbouring cells are provided in NCL, UE can decide to turn off its second receiver in order to save power. LPN power class is particular useful because the UE may derive therefrom a density of the LPN distribution. However, other indicators of a LPN, such as specific values of timing offset or uplink desensitization may be used to control measurements performed on the second carrier, instead of or in addition to LPN power class.

If the UE detects an UL/DL imbalance (e.g. based on one of LPN's CPICH power, LPN's power class, and LPN's UL desenistization) and reports it, it will help RNC in deciding how to tackle the mobility procedure when imbalance is high. RNC can take a decision early compared to later triggers. E.g. it can take the decision to initiate a SCC at event 1A instead of event 1 D. Typically, delaying mobility procedure such as SCC into the future makes it more vulnerable to failures in challenging radio environments because serving cell quality may drop quite quickly.

In particular (but not only) for high speed UEs, it is important to optimize handover times. For prohibitively higher speeds, it may be even appropriate to discourage handovers to small cells. In some embodiments, UE mobility classification is carried out by UE itself in order to avoid any corresponding additional signalling from the network.

According to some embodiments of the invention, one or more of the following lEs are provided in the NCL, which are in particular (but not only) useful for fast UEs:

5) LPN's time to trigger (TTT).

Mobility actions between two cells are carried out by a series of measurement and reporting events defined and standardized by 3GPP. Currently TTT values are not defined to be cell specific but are global parameters. They may have a granularity definition at event level. By adding a cell specific TTT to the NCL, TTT may be optimized separately for small cell and users depending on their mobility state.

In general, the TTT value (both the global TTT and the cell specific TTT) is set with the intention that a user should not unnecessarily trigger handovers upon receiving sufficient signal from a new cell while its own serving cell's signal is below a certain threshold. By allowing some time to pass for which it is necessary for the measurement event to report consistent results, it can be ensured that handovers are not initiated excessively often. Such excessive back and forth handovers are termed as ping pongs and they are likely at the cell edge where the signal level from two cells may fluctuate. TTT values are set to ensure that false alarms are avoided.

On the other hand, in small cells, a user with fast mobility relies on faster, more efficient handovers for a truly seamless experience. A user passing through a cell at considerable speed (e.g. higher than pedestrian velocity) is not likely to cause ping pongs at the same level as a static or pedestrian UE. Therefore TTT requirements can be relaxed (i.e. TTT can be shortened) which leads to faster handover times. In another scenario, if TTT is quite large and the source cell quality drops pretty quickly, this may cause handover failures, which can be avoided by cell specific shorter TTT.

Also, at too high speeds, it makes sense to avoid handover to a small cell entirely while maintaining a connection to the serving macro. Setting a large value for TTT can ensure that UE will pass through the cell before the handover is triggered.

According to some embodiments of the invention, conventional NCL (reported through SIB 12) includes additionally a new field named e.g. Time_To_T rigger' (or similarly) which would allow the operators to configure and report this value individually in dependence of at least one of different mobility classifications and cell sizes. The new field may be applied in particular in CELL_DCH state.

That is, TTT may vary dependent on the cell size. Furthermore, at a given cell size, sev- eral TTTs for respective mobility classifications may be indicated to the UE. Then, the UE may select a TTT value dependent on its mobility classification. In some embodiments, TTTs may be set globally (i.e. for all cells except for those where a cell specific TTT is set) dependent on the mobility classification. In the context of the present application, dependence on mobility classification is included in the term "cell specific", too, if not other- wise made clear from the context.

In some embodiments of the invention, the cell specific time-to-trigger (TTT) parameter is used for intra frequency measurement events such as event 1A, 1 B, 1 C, 1 D and can be suitably extended to events 1 E and 1 F. As specified in 3GPP TS 25.331 , these events are as follows: - event 1 A: A Primary CPICH enters the reporting range; addition of a radio link.

- event 1 B: A primary CPICH leaves the reporting range; removal of a radio link.

- event 1 C: A non-active primary CPICH becomes better than an active primary CPICH; replacement of the worst cell in AS.

- event 1 D: Change of best cell.

- event 1 E: A Primary CPICH becomes better than an absolute threshold.

- event 1 F: A Primary CPICH becomes worse than an absolute threshold.

The advantage of a lower TTT is that SCC is initiated faster. The TTT may be adjusted to the cell size of the LPN. A smaller cell would require a lower TTT in case the UE is meant to be offloaded to the LPN. On the other hand, if the UE is fast enough to traverse through the LPN's cell while staying connected to the macro, the TTT may be set to larger values. A lower TTT may also be chosen when it is known, for e.g. by SON specific data, that the radio conditions in a given HetNet deployment at particular spots degrades quickly. In such a case, the network may set a lower value of TTT based on cell specific parameterization. In some embodiments of the invention, the cell specific TTT may not be set for all the cells in the NCL and/or not for all UE mobility classifications. If a cell specific TTT is not indicated for a particular cell and/or a particular mobility classification, the global parameter takes precedence. 6) HOF probability and/or ToS values

Dynamic parameters such as Handover Failure Rate and Time of Stay in a cell can also be passed on to a UE through NCL. Thus, the UE may appropriately adjust and fine tune its device's performance based on the received parameters.

According to some embodiments of the invention, for some or each of the neighbour cells, the RAN sends at least one of HOF failure probability and median ToS values for the UE. Median ToS value is just an example of an aggregation value of several ToS values but other aggregations such as mean ToS, maximum ToS, minimum ToS may be used instead or in addition. An UE, such as a high speed UE, may take advantage of these parameters e.g. based on its mobility classification and may suitably change its measurement behaviour on the given cells in the NCL.

E.g., the UE may calculate a bias factor internally and use it in the measurement report equations. In some embodiments, the UE may sort the list of cells based on decreasing HOF probability OR may sort the list of cells based on increasing ToS. It may then filter the top cells only, and report events for only those filtered cells.

7) Compensation factor

According to some embodiments of the invention, NCL comprises information about a compensation factor to be used by the UE while calculating the UL boosting factor for HS-DPCCH channel. The boosting factor may be reported back to the network as part of the RRC measurement report, e.g. at event 1A. The network may then favourably use this parameter to decide if the HO would succeed into the new cell. The boosting factor is an example of a parameter indicating a link imbalance.

In some embodiments of the invention, the value of the boosting factor (reported back to the network) may also be used by the network in an RRM algorithm to configure Multiflow for the UE.

The Compensation Factor takes into account many or even all UL parameters in macro and small cell which contribute to UL imbalance. The following parameters are most important: RX diversity usage, receiver sensitivity, UL Noise Rise, RX equalization gain. Compensation Factor is calculated in RNC and included in NCL. Based on this information and desensitization parameter in NCL, UE may calculate initial boosting factor for UL channels.

UE may also, based on Compensation Factor and DL Path Loss difference measurement between macro and small cell, calculate UL/DL imbalance and send this information to RNC. RNC based on this knowledge may plan appropriate actions to minimize impact of DL/UL imbalance for improving robustness of channel decoding and HO performance. A UE may receive some of the lEs 2) to 4) and 6) (i.e. LPN's power class, LPN's UL desensi- tization, LPN's CPICH power, HOF probability, and ToS values) for all or for only some of the cells in the NCL. In order to decide if a measurement report to trigger handover should take place, the UE may give different weights to these parameters. E.g., LPN's power class may have prevalence over the other parameters such that a high LPN power class is favourably selected. Also, a small UL desensitization may be favourable because the UL/DL imbalance is not too large. Hence, this parameter may have prevalence over other parameters. Depending on the needs, other prevalence rules may be applied.

Fig. 4 shows an apparatus according to an embodiment of the invention. The apparatus may be a terminal device such as a UE, or an element thereof. Fig. 5 shows a method according to an embodiment of the invention. The apparatus according to Fig. 4 may perform the method of Fig. 5 but is not limited to this method. The method of Fig. 5 may be performed by the apparatus of Fig. 4 but is not limited to being performed by this apparatus.

The apparatus comprises evaluating means 10 and applying means 20.

The evaluating means 10 evaluates an information (S10). The information is received from an originating cell device. The originating cell device is typically the cell serving the apparatus. Typically, the information is received in a neighbor cell list from the originating cell device. The neighbor cell list may be included in a system information block broadcasted by the originating cell device. However, in some embodiments, the information may be received separately from a neighbor cell list. The information may also be received by dedicated signaling to the apparatus.

The information comprises at least one of the following:

8. an indication of a timing offset of a first neighbor cell of the originating cell device;

9. an indication of a power class of a second neighbor cell of the originating cell device;

10. an indication of an uplink desensitization value of a third neighbor cell of the originating cell device;

1 1 . an indication of a power of a pilot channel of a fourth neighbor cell of the originating cell device;

12. an indication of a time to trigger specific for a fifth neighbor cell of the originating cell device; 13. at least one of an indication of a handover failure probability and an indication of a time of stay for a sixth neighbor cell of the originating cell device; and

14. an indication of a compensation factor for a seventh neighbor cell of the originating cell device.

The first to seventh neighbor cells may be different from each other, or some or all of the first to seventh neighbor cells may be the same. The information may comprise the same indications for all neighbor cells, or it may comprise some of the indications for a subset of the neighbor cells only.

The respective indications may be specific for the respective neighbor cell. In addition, globally valid indications may be received for some of the parameters. In the evaluation, cell specific parameters may have prevalence over globally valid parameters. The applying means 20 applies the evaluated information to measuring a radio link parameter of a selected neighbor cell and/or triggering reporting of a measurement report for the selected neighbor cell to the originating cell device. The respective cell is the cell of the first to seventh neighbor cells to which the indicated parameter in the information is related. The measurement report may be based on the measuring of the radio link parameter mentioned hereinabove in this paragraph or may be based on a measuring of a different parameter such as a different radio link parameter.

Fig. 6 shows an apparatus according to an embodiment of the invention. The apparatus may be a base station device such as a NodeB or eNodeB, or a base station controller such as a RNC, or an element thereof. Fig. 7 shows a method according to an embodiment of the invention. The apparatus according to Fig. 6 may perform the method of Fig. 7 but is not limited to this method. The method of Fig. 7 may be performed by the apparatus of Fig. 6 but is not limited to being performed by this apparatus. The apparatus comprises providing means 1 10.

The providing means 1 10 provides an information (S1 10). The information comprises at least one of

8. an indication of a timing offset of a first neighbor cell of the apparatus;

9. an indication of a power class of a second neighbor cell of the apparatus; 10 an indication of an uplink desensitization of a third neighbor cell of the apparatus;

1 1 an indication of a power of a pilot channel of a fourth neighbor cell of the apparatus;

12 an indication of a time to trigger specific for a fifth neighbor cell of the apparatus;

13 at least one of an indication of a handover probability and an indication of a time of stay for a sixth neighbor cell of the apparatus; and

14 an indication of a compensation factor for a seventh neighbor cell of the apparatus. Typically, the information is provided by broadcasting, e.g. in a neighbor cell list of a system information block. However, in some embodiments, the information may be provided separately from a neighbor cell list.

The first to seventh neighbor cells may be different from each other, or some or all of the first to seventh neighbor cells may be the same. The information may comprise the same indications for all neighbor cells, or it may comprise some of the indications for a subset of the neighbor cells only.

The respective indications may be specific for the respective neighbor cell. In addition, glob- ally valid indications may be provided for some of the parameters.

Instead of in LTE or LTE-A, embodiments of the invention may be employed in other radio networks where neighbour lists are transmitted by base stations, such as CDMA, EDGE, UMTS, WiFi networks, etc.. A terminal (device) or a user equipment may be a mobile phone, a smart phone, a PDA, a laptop or any other terminal which may be attached to networks of the respective technologies such as LTE, LTE-A or UMTS. A base station (device) may be any base station (BTS) of the respective technology such as a NodeB, an eNodeB, an access point, etc., irrespective of its coverage area, such as macro cell, pico cell, femto cell. In particular, in the present application, NodeB and eNodeB are considered to e equivalent to each other if not otherwise stated or clear from the contect.

Embodiments of the invention are explained with special emphasis on LPNs. However, the embodiments may be applied not only to LPNs but to any type of cells including macro cells. The provided/received information may comprise one or more pieces of information related to different meanings. It is independent from the realization. Hence, it may comprise a single value (which may have several meanings, e.g. each bit or byte of the value may be related to a different meaning), plural fields of an array, plural information elements, etc.. One infor- mation may be transmitted in one or plural messages.

Names of network elements, protocols, and methods are based on current standards. In other versions or other technologies, the names of these network elements and/or protocols and/or methods may be different, as long as they provide a corresponding functionality.

If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they are differently addressed. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware.

According to the above description, it should thus be apparent that exemplary embodiments of the present invention provide, for example a terminal device such as a user equipment, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). Furthermore, it should thus be apparent that exemplary embodiments of the present invention provide, for example a base station device such as an eNB, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). Furthermore, it should thus be apparent that exemplary embodiments of the present invention provide, for example a radio network controller such as an RNC, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program^) and forming computer program product(s).

Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non limiting examples, implementations as hardware, software, firm- ware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It is to be understood that what is described above is what is presently considered the pre- ferred embodiments of the present invention. However, it should be noted that the description of the preferred embodiments is given by way of example only and that various modifications may be made without departing from the scope of the invention as defined by the appended claims.