Controller node and a method therein for selecting a network node in a heterogeneous network

Abstract

The exemplary embodiments herein relate to a controller node and a method in a controller node for selecting a network node in an heterogeneous network comprising a plurality of network nodes. The method comprises, receiving CQI values from a UE and based on those values selecting a network node for serving a UE.

Claims

1. A method in a controller node for selecting for a user equipment, UE, at least one network node in a heterogeneous network comprising a plurality of network nodes, each network node transmitting a primary pilot channel and a secondary pilot channel, the method comprising: receiving from the UE, channel quality indicator (CQI) values, each CQI value corresponding to a channel estimate estimated by the UE on the secondary pilot channel transmitted by a network node; processing the received CQI values, including storing the received CQI values; and deciding based on the stored CQI values which network node(s) in the heterogeneous network to select for serving the UE, wherein the deciding comprises comparing the received and stored CQI values with a CQI threshold and selecting the network node(s) associated with the CQI value having a value higher than the CQI threshold.

2. The method according to claim 1 wherein receiving comprises receiving each CQI value in a feedback channel being a high speed-dedicated physical control channel.

3. The method according to claim 2 further comprises combining the received feedback channels using maximum ratio combining or selection combining.

4. The method according to claim 1 wherein each individual secondary pilot channel transmitted by the network node is periodically transmitted by the network node.

5. A controller node for selecting for a user equipment, UE, at least one network node in a heterogeneous network comprising a plurality of network nodes, each network node transmitting a primary pilot channel and a secondary pilot channel, the controller node comprising: a receiver circuit configured to receive from the UE, channel quality indicator (CQI) values, each CQI value corresponding to a channel estimate estimated by the UE on the secondary pilot channel transmitted by a network node; and a processing circuit configured to process the received CQI values including storing the received CQI values, and the processing circuit further is configured to decide, based on the stored CQI values which network node(s) in the heterogeneous network to select for serving the UE, wherein the processing circuit is configured to decide by comparing the received and stored CQI values with a CQI threshold and to select the network node(s) associated with the CQI value having a value higher than the CQI threshold.

6. The controller node according to claim 5 wherein the receiver circuit is configured to receive each CQI value in a feedback channel being a high speed-dedicated physical control channel.

7. The controller node according to claim 6 wherein the controller node is further configured to combine the received feedback channels using maximum ratio combining or selection combining.

8. The controller node according to claim 5 wherein each individual secondary pilot channel transmitted by the network node is periodically transmitted by the network node.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating an example of a heterogeneous network comprising LPNs and a macro network node.

(2) FIG. 2 is another diagram illustrating an example of a heterogeneous network wherein the LPNs have different cell IDs as that of a macro node.

(3) FIG. 3 is another diagram illustrating an example of a heterogeneous network wherein the LPNs and the macro node use the same cell ID.

(4) FIG. 4 is diagram illustrating an example of a combined cell deployment of a heterogeneous network comprising a central node/controller connected to other network nodes

(5) FIG. 5 shows the configuration of spatial reuse between two network nodes A and B in a combined cell.

(6) FIG. 6 illustrates a method for selecting a network node in accordance with some exemplary embodiments herein.

(7) FIG. 7 illustrates messages exchanged between network nodes and a UE according to an exemplary embodiment.

(8) FIG. 8 illustrates messages exchanged between network nodes and a UE according to another exemplary embodiment.

(9) FIG. 9 illustrates messages exchanged between network nodes and a UE according to another exemplary embodiment.

(10) FIG. 10 illustrates results from link throughput simulations for combined cell deployment.

(11) FIG. 11 illustrates a block diagram depicting a network/controller node according to exemplary embodiments herein.

DETAILED DESCRIPTION

(12) Embodiments herein relate to heterogeneous networks in general and in particular to combined cell deployment of a heterogeneous network. The combined cell comprises a plurality of radio network nodes which may be a mix of network nodes which may be Low power Nodes (LPNs) and macro base stations. At least one of these network nodes may act as a central controller node or a central processing unit or a central scheduler unit. It should be mentioned that the network comprises one or more Radio Access Networks (RANs) and one or more Core Networks (CNs). The network may use access technologies such as Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (VVCDMA), High Speed Packet Access (HSPA) Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations.

(13) In the network one or more UEs are located and theses UEs may be legacy UEs or Rel. 12 UEs, as explained earlier. As previously mentioned, the UEs may be connected to one or more network nodes wirelessly. One method to identify which network node(s) is appropriate for transmitting to a particular UE is by transmitting probing pilots. For example probing pilots may either be continuously transmitted or transmitted periodically. Unfortunately, as explained before only UEs which can understand these pilots i.e. the UEs which are released after these pilots are standardized in third Generation Partnership Project (3GPP), Release 12; also called Rel-12 UEs; might be scheduled using probing pilots. The UEs which are already in the market; also called legacy UEs, may not benefit from these pilots. Hence when these UEs are present in the network or system, the central controlled node is not able to use spatial reuse scheme to improve the system capacity.

(14) Therefore, it is desirable to provide a method that allows any type of UE to be served by a network node upon selection by the controller node of that network node.

(15) Before describing exemplary embodiments of the present technology the main steps of the method performed by a network or controller node acting as a central network node for selecting at least network node for serving and a UE in a combined cell of a heterogeneous network are first presented in conjunction with FIG. 6.

(16) As shown the main steps comprise:

(17) (601) receiving from the UE channel quality indicator (CQI) values corresponding to channel estimates performed by the UE on individual pilots transmitted by network nodes in the combined cell;

(18) (602) processing, by said controller node, the received CQIs or CQI values; and

(19) (603) deciding based on the received and processed CQIs which network node(s) to select or schedule for serving the UE.

(20) The individual pilot or pilot channel transmitted from a network node and used for estimating the CQI value is a secondary pilot channel. The individual secondary pilot channel transmitted is periodically transmitted by the network node. As explained below, each network node may transmit both a primary pilot channel and a secondary pilot channel

(21) Referring to FIG. 7, there is shown a message sequence chart including channels such as a Primary Common Pilot Channel (P-CPICH); a High Speed Dedicated Physical Control Channel (HS-DPCCH); a High Speed-Shared Control Channel (HS-SCCH) and a downlink traffic channel High Speed-Physical Dedicated Control Channel (HS-PDSCH).

(22) In FIG. 7, four nodes (Node 1-4) are shown and a single UE is depicted. The embodiments herein are not restricted to any particular number of UEs or network nodes. Here is it assumed that the four nodes are included in a combined cell deployment. Each node is capable of serving one or more UEs. It is here also assumed that the UE under consideration is configured with a plurality of carries i.e. at least dual carries. During the cell setup, the UE may obtain radio configuration parameters from a RNC or any of the four nodes. This call set up is not shown in FIG. 7.

(23) Each network node is configured to transmit the P-CPICH. This primary carrier/pilot channel P-CPICH is transmitted continuously. In contrary, a secondary carrier/pilot channel denoted P-CPICH2 is transmitted from each network node periodically for a certain duration. Herein, and in accordance with an exemplary embodiment, the second carrier is used as a probing carrier or probing pilot. For example at one time instance denoted T1 in FIG. 7, the pilot channel belonging to this carrier P-CPICH2 is transmitted from Node 1; and at T2, the pilot belonging to P-CPICH2 is transmitted from Node 2; and at T3, the pilot belonging to P-CPICH2 is transmitted from Node 4; and at T4, the pilot belonging to P-CPICH2 is transmitted from Node 4. These pilots are transmitted to the UE. When the UE receives these pilot carriers, the UE estimates the channel quality in terms of CQI value(s) corresponding these carries based on individual pilots. The UE is then configured to report the estimated CQIs in an uplink feedback channel HS-DPCCH which channel is received by all four nodes as shown in FIG. 7.

(24) As mentioned earlier anyone of the nodes may act as a central controller node or as a central processing unit. Assume for example that Node 1 is acting as a central processing unit. Node 1 then processes each received signal HS-DPCCH from all nodes. This node may e.g. combine the received HS-DPCCH using maximum ratio combining or selection combining. Node 1 may process the received signals over a period of time say T_proc and then keeps note or stores of the CQI values of the above mentioned second carriers P-CPICH.sub.2. Based on the channel qualities stored or CQIs, the central controller Node 1 decides which node(s) is/are suitable for serving and transmitting data and control information to the UE. The same applies in case another network node Node 2, Node 3 or Node 4 is acting as a central controller node. In FIG. 7, it is Node 2 that is selected to serve the UE. This is indicated in time instance T5 by the transmission of HS-SCCH from Node 2 to the UE.

(25) Above was explained an embodiment wherein in a single network node is selected to serve the UE.

(26) FIG. 8 shows a message sequence chart where two nodes are selected in accordance to another embodiment herein. In that case, Node 2 and Node 3 are selected to serve the UE at time T5. This is indicated by the transmission of HS-SCCH from Nodes 2 and 3 respectively to the UE. Similarly to FIG. 7, the same channels and carries and pilots are shown. The process is repeated after some time interval. Here the central node may de-activate the secondary carrier once it decides on which network nodes to serve the UE. The secondary carrier may be re-activated after some time when it decides to probe the UE.

(27) It should be mentioned that by using the secondary carrier/pilot to determine the CQI, the central controller may distinguish which network node transmitting the secondary pilot/carrier is most suitable for serving the UE. However, if the primary carrier is used to determine the CQI, the central node may not distinguish between the network nodes. This is because the primary carrier P-CPICH is continuously transmitted while the secondary carrier P-CPICH.sub.2 is transmitted periodically for certain duration from each node. Hence the CQI of the secondary carrier of each network node is, in accordance with embodiments herein, used to select and decide on which network node to serve the UE.

(28) FIG. 9 illustrates an example of a message sequence chart when the central controller decides to select two carriers for data transmission or for serving the UE. Similarly to the previously described embodiments, the central controller node may be any of the network nodes in the combined cell scenario. The same process as shown and discussed with respect to FIGS. 7 and 8 are applicable for this exemplary embodiment up to time instance T5. Once the central node decides which node to serve the UE, it can de-activate the secondary carrier/probing and subsequently inform e.g. the RNC to send a RNC configuration message to configure a secondary carrier having a different frequency than that of the probing secondary carrier. As shown, in T5, Node 2 has been selected to serve the UE as Node 2 sends two carriers denoted here HS-SCCH.sub.1 and HS-SCCH.sub.2 to the UE.

(29) It should be noted that instead of de-activating the carrier used for probing, the central node may decide to schedule the UE on the secondary carrier in addition to the primary carrier P-CPICH. This means that in this example, the secondary carrier is used for probing as well as that of secondary carrier.

(30) In the following it is described on what basis the central controller node make a decision on which network node(s) to serve the UE. As previously described the central controller node processing unit or processing circuitry is configured to process received CQIs; and is further configured to decide based on the received and processed CQIs which network node(s) to select or schedule for serving the UE. The central node stores the CQI values and takes the decision based on e.g. a CQI threshold. For example, the central node selects the CQI having a value that is greater than the CQI threshold. Another example is to use the highest CQI of the secondary carrier and compare it with the threshold and if it is greater than the threshold, the network node associated with the highest CQI is selected to serve the UE. Another example is to base the decision on the CQI of the primary carrier.

(31) The CQI threshold may be determined by the central controller node as follows:

(32) Step 1: Pre-compute a signal to noise ratio (also known as geometry) from a CQI of each network node. This can be done by simulations.

(33) Step 2: Compute the geometry of the UE with respect to each network node.

(34) Step 4: Determine the geometry difference between the network node corresponding to the highest geometry and the remaining geometries of the other network nodes.

(35) Step 4: Select the network nodes whose difference is e.g. 5 dB or more compared to the node with the highest geometry.

(36) Step 5: Compute the CQI threshold based on the selection.

(37) FIG. 10 illustrates the performance when the UE performance is impacted by interference from a second network node. The graph shows the Link Throughput in Mbps as a function of the geometry denoted Ior/No. It can be seen that when the geometry of a second network node; being here a LPN; is 5 dB below the performance of a first node, the UE performance in terms of throughput is not impacted too much.

(38) Referring to FIG. 11 there is illustrated a network controller node 1100 for selecting at least one network node in a combined cell deployment of a heterogeneous network in accordance with embodiments herein. The controller network node 1100 comprises a receiver circuit or receiver unit 1101 configured to receive from the UE CQI values corresponding to channel estimates performed by the UE on individual pilots or carriers or pilot channels transmitted by the network nodes of the combined cell. The pilots or carriers being secondary carriers as previously described. The network node 1100 further comprising a processing circuit or processing unit 1102 configured to process the received CQIs. The processing circuit 1102 is further configured to decide based on the processed CQIs which network node(s) to select or schedule for serving the UE. The UE may be a legacy UE or a Rel. 12 UE. Hence the embodiments described herein are applicable independently on what type of UE is to be served in the combined cell. The network controller node 1100 may further comprise a transmitting circuit 1103 configured to transmit data or control signaling to the UE.

(39) The controller node 1100 may further comprise a memory 1104 for storing CQI values or any additional information e.g. the geometry of each network node or channel state information (CSI), muting patterns, UE speed etc. The network node may contain additional units circuits not illustrated such as one or several antennas, interfaces towards other network nodes etc.

(40) It should be mentioned that the embodiments herein for selecting a suitable network node may be implemented through one or more processors or processing units e.g. processing circuit or unit 1102 of the network node 1100 together with a computer program code for performing the functions and/or method steps of the embodiments. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing embodiments herein when being loaded into the network node. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network controller node 1100.

(41) Additional details on the method steps and functions performed by the network node acting as a central controller node have already been described in greater detail and therefore a repetition of the previous text is not considered necessary.

(42) Those skilled in the art will also appreciate that the various “circuits” described may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware (e.g., stored in memory) that, when executed by the one or more processors, perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC).

(43) Throughout this disclosure, the word “comprise” or “comprising” has been used in a non-limiting sense, i.e. meaning “consist at least of”. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. In particular, it should be noted that although terminology from 3GPP LTE of HSPA has been used in this disclosure to exemplify the invention, this should not be seen as limiting the scope of the invention to only the aforementioned system. Other wireless systems, including LTE-A (or LTE-Advanced), UMTS, WMax, and wireless LAN, may also benefit from exploiting the ideas covered within this disclosure.

REFERENCES

(44) [1] RP-121436, Study on UMTS Heterogeneous Networks [2]. R1-124512, Initial considerations on Heterogeneous Networks for UMTS, Ericsson, ST-Ericsson [3]. R1-124513, Heterogeneous Network Deployment Scenarios, Ericsson, ST-Ericsson.