METHODS AND APPARATUS FOR CELL SELECTION/RESELECTION IN MILLIMETER WAVE SYSTEM
Methods and apparatus for cell selection, cell reselection, and beam selection in MMW system are provided. The UE measures signal strength, or signal quality or both of them to get the best consolidation measurement result. During Cell Selection, the UE selects the cell with the best consolidation measurement result, or selects the cell containing the candidate control beam found firstly. In Cell Reselection, the serving cell and neighboring cells are ranked based on the consolidation measurement result. After camping on a cell, the UE selects one or more than one best control beams as the serving control beam to acquire system information and monitor paging message. Furthermore, the UE selects the best control beam or selects one control beam randomly among the serving control beams to initial access to the network.
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The disclosed embodiments relate generally to wireless communication, and, more particularly, to cell selection and cell reselection in a millimeter wave system.
BACKGROUNDThe bandwidth shortage increasingly experienced by mobile carriers has motivated the exploration of the underutilized millimeter wave (mmW) frequency spectrum between 3 G and 300 G Hz for the next generation broadband cellular communication networks. The available spectrum of mmW band is two hundred times greater than the conventional cellular system. The mmW wireless network uses directional communications with narrow beams and can support multi-gigabit data rate. The underutilized bandwidth of the mmW spectrum has wavelengths ranging from 1 mm to 100 mm. The very small wavelengths of the mmW spectrum enable large number of miniaturized antennas to be placed in a small area. Such miniaturized antenna system can produce high beamforming gains through electrically steerable arrays generating directional transmissions.
With recent advances in mmW semiconductor circuitry, mmW wireless system has become a promising solution for the real implementation. However, the heavy reliance on directional transmissions present particular challenges for the mobile stations in the mmW network, such as cell selection and cell reselection procedures during IDLE mode. Unlike the traditional cellular system, one mmW cell is covered by one or more than one directional beams. Therefore, the synchronization and broadcast signals for a cell are also directional and only cover a small area. The mobile stations need to san over a range of angles before a cell can be detected. The time latency would be even longer in standalone mmW system due to the lack of assistance information from the network. The frequent execution of finding a narrow beam to camp on during mobile movement is more complicated with more power consumption for measurement.
Improvements and enhancements are required for cell selection and cell reselection in the mmW network.
SUMMARYMethods and apparatus are provided for cell selection, cell reselection and beam selection in mmW system. In one novel aspect, consolidation measurements are used for cell selection and cell reselection for a UE in the mmW system. The UE measures signal strength, signal energy/power, signal quality, signal lifetime, signal error rate, signal angle of arrival (AoA)/direction of arrival (DoA) or a combination of the above to get the best consolidation measurement result. In one embodiment, the UE selects a set of control beams for each cell as qualified control beam to obtain the consolidation measurement. In one embodiment, the set of qualified control beams are multiple detected control beams associated with the cell. In another case, the set of qualified control beams are all the detected control beams associated with the cell. In another embodiment, the set of qualified control beams are multiple candidate control beams associated with the cell, where the candidate control beams is a subset of the detected control beams meeting a predefined criterion. In yet other embodiments, different consolidation rules are used to obtain the consolidation measurement.
In another novel aspect, during cell selection, the UE selects the cell with the best consolidation measurement result, or selects the cell containing the candidate control beam found firstly. In another embodiment, the UE selects one or more control serving beams from the control beams of the serving cell. The UE receives control information and system information on the serving control beams. In another embodiment, the UE selects an access control beam from the selected serving control beam(s) to initiate RRC connection.
In yet another novel aspect, during cell reselection, the serving cell and neighboring cells are ranked based on the consolidation measurement result. In one embodiment, the UE compares the serving-cell consolidation measurement with a set of measurement thresholds. The UE determines the measurement level based on the comparison. The measurement level includes measuring the serving control beams of the serving cell, measuring the serving and non- serving control beams of the serving cell, measuring the neighboring cells with the same frequency, and measuring the neighboring cells with different frequencies.
In one novel aspect, after the UE camps on a cell, the UE selects one or more than one best control beams as the serving control beam(s) to acquire system information and monitor paging message. Furthermore, the UE selects the best control beam or selects one control beam randomly among the serving control beams to initial access to the network.
The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.
Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Similarly, eNB 103 has an antenna 155, which transmits and receives radio signals. A RF transceiver module 153, coupled with the antenna, receives RF signals from antenna 155, converts them to baseband signals, and sends them to processor 152. RF transceiver module 153 is an example, and in one embodiment, the RF transceiver module comprises two RF modules (not shown), the first RF module is used for mmW transmitting and receiving, and another RF module is used for different frequency bands transmitting and receiving which is different from the module used for mmW. RF transceiver 153 also converts received baseband signals from processor 152, converts them to RF signals, and sends out to antenna 155. Processor 152 processes the received baseband signals and invokes different functional modules to perform features in eNB 103. Memory 151 stores program instructions and data 154 to control the operations of eNB 103. eNB 103 also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention. An mmW handler 161 handles mmW functions for eNB 103.
In connected mode, consolidation measurements could be used for handover. In one embodiment, in idle mode, consolidation measurements are used for cell selection in the mmW system. When the UE starts cell selection, at step 211 the UE obtains signal measurements for multiple cells consisting of multiple control beams. The UE in the mmW system detects multiple control beams associated with one or more mmW cells. The signal measurement can signal strength, signal energy, signal power, signal quality, signal lifetime, signal error rate, signal AoA, or signal DoA. The signal measurement for each control beam can also be any combination of the above or other related measurements that can be obtain to indicate the control beam status. Based on the measurement, the UE can determine a set of candidate control beams of each cell of multiple cells. The candidate control beams are the subset of the detected control beams that meets a predefined criterion. For example, a candidate control beam is a candidate control beam whose signal measurement is greater than a predefine threshold. At step 212, the UE obtains the consolidation measurement results for each cell. The consolidation measurement result for each cell is to computes the measurement results based on a set of signal measurements of one or more control beams associated with the cell. At step 213, the UE applies cell selection criterion based on the obtained consolidation measurement results. At step 214, the UE performs cell selection and selects a cell to camp on.
Unlike traditional cellular system, once camped on a cell, the UE needs to perform beam selection in the serving cell. At step 221, the UE selects one or more serving control beams. The serving control beams are control beams in the serving cell on which the UE acquires system information, receives paging messages, and/or initial access to the network. The serving control beams are a subset of the candidate control beams of the serving cell. There can be one or more serving control beams for the UE. At step 222, the UE acquires system information through the serving control beams. At step 223, the UE monitors the paging message via the serving control beams. At step 224, the UE further selects the access control beam in the serving control beams. The access control beam is a serving control beam that meets a predefined criterion. For example, the access control beam is the serving control beam that has the best signal measurement. In another embodiment, the UE can randomly select one serving control beam as the access control beam.
The UE performs cell reselection in the IDLE state. At step 231, the UE performs priority selection. The UE prioritize different mmW frequencies or inter-RAT (radio access technology) frequencies. In one embodiment, the UE receives the priority configuration information in the dedicated message when the UE release RRC connection, or inherits from another RAT at inter-RAT cell selection or cell reselection. In another embodiment, the UE capable of supporting both EUTRAN and mmW will always consider the EUTRAN frequency as highest priority frequencies. At step 232, the UE obtains consolidation measurement results for the serving cell. At step 233, the UE applies the measurement rules based on the obtained serving cell consolidation-measurement result. If at step 233, the UE determines that neighbor cell measurement is need, the UE moves to step 234. At step 234, the UE measures neighbor cell control beams. At step 235, the UE obtains consolidation measurement results for multiple cells. At step 236, the UE applies cell reselection criterion based on the consolidation measurement results. At step 237, the UE performs cell reselection.
As an example, eNB 301 covers three cells #0 and cell #1 and cell #2. Similarly, eNB 302 covers three cells #3 and cell #4 and cell #5. UE 303 detects control beams for cell selection. As an example shown in
Once the UE selected the set of qualified control beams for consolidation measurement, the UE moves to step 411 wherein the UE obtains consolidation measurement for each cell. The UE obtains the consolidation measurement based on a consolidation rule 421. The consolidation rule can be configured or predefined. Different consolidation rules can be used. Each applied to the selected set of qualified control beams associated with the cell as determined in step 405. In one embodiment (method #1), the resulting consolidation measurement of the set of qualified control beams of the cell is the number of qualified control beams in the set. In other embodiments the resulting consolidation measurement of the set of qualified control beams of the cell is the maximum signal measurement of the set (method #2), or the minimum signal measurement of the set (method #3), or the mean value of signal measurements of the set (method #4), or the variance of signal measurements of the set (method #5), or the sum of the signal measurements of the set (method #6). Other consolidation methods can be used. In other embodiments, a combination of different methods may be used, for example, a combination of method #1 and method #2.
Once the consolidation measurements is determined for each cell, the UE moves to step 412 and finds the cell with the best consolidation result following a cell selection rule 422. Examples of the cell selection rule 422 includes determining the best cell being the cell whose consolidation measurement has the largest number of qualified control beams in the set, or has the largest maximum signal measurement of the set, or has the largest minimum signal measurement of the set, or has the largest mean value of signal measurements of the set, or has the smallest variance of signal measurement of the set, or has the largest sum of signal measurements of the set. Other cell selection rules can be used or combinations of the cell selection rules can be used.
Upon successfully selecting a serving cell, the UE moves to step 413 and finds one or more serving control beams of the serving cell using a beam selection rule 423. The UE receives control and signal information on the selected serving control beams.
In other embodiments, combinations of the above methods are used for the signal measurement of each cell. For example, the signal measurement results for each cell contains two measurements: a first weighted resulting consolidation measurement for each cell is the maximum signal measurement of the CB of the set (method #2) and a second weighted resulting consolidation measurement for each cell is the number of qualified control beams (method #1). The ranking of cells may be the same or may be different based on different measurements contained in the signal measurement. Providing a combination signal measurement for each cell presents a more complete picture of the cell condition such that the UE can select a better cell for cell selection, cell reselection, and/or handover. For example, using method #2, cell #2 may rank higher than cell #0 with a slightly higher maximum signal strength. However, using method #1, cell #0 may rank higher than cell #2 with a higher number of candidate control beams. In one embodiment, the UE uses an algorithm to select the target cell for cell selection, cell reselection, and/or handover. For example, a signal threshold is set such that the best-ranked cell using method #2 is selected if the maximum signal measurement is greater than the signal threshold; otherwise, the best-ranked cell using method #1 is selected. Similarly, a number threshold is set such that the best-ranked cell using method #1 is selected if the number of qualified control beams is greater than the number threshold; otherwise, the best-ranked cell using method #2 is selected. In other embodiments, a set of thresholds and/or a combination of thresholds are used for cell ranking Multiple signal measurements can be combined with corresponding cell ranking algorithms.
In the mmW system, the UE needs to monitor multiple beams in a cell to obtain the measurement result. The power consumption is a concern for frequent measurement. In one embodiment for cell reselection, the UE determines the set of control beams to measure based on a comparison between the consolidation measurement result of the serving cell and a set of thresholds.
Threshold_2 and Threshold_3 can be broadcasted in the system information.
At step 701, the UE compares the serving cell consolidation measurement RES_S, as shown in
For cell reselection measurement, the UE can use different sets of control beams for serving cell and neighbor cells.
At step 921, the UE determines if a cell of lower priority frequency fulfills a predefined condition for cell reselection. If step 921 determines yes, the UE moves to step 922 to check if a timer Ti has elapsed since the UE camped on the current serving cell. If step 922 determines yes, the UE moves to step 923 and performs a cell reselection to a cell of lower priority frequency. If at step 922, the UE determines no, or the UE determines no at step 921, the UE moves out of stage 920 and moves to step 931 of stage 930.
At step 931, the UE calculates serving cell consolidation measurement results Rs and neighboring cell consolidation measurement results Rn are based on RES_S and RES_N as shown in
Upon successful cell selection or cell reselection, the UE in the mmW system needs to select serving control beams. Further, while the UE camps on a serving cell, the UE performs beam selection to select better control beams to be serving control beams.
Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.
Claims
1. A method comprising:
- detecting multiple control beams in a millimeter wave (mmW) system by a user equipment (UE), wherein the mmW system has multiple cells each configured with multiple control beams;
- obtaining a signal measurement for each detected control beam; and
- calculating a consolidation measurement for each cell based on a set of qualified control beams associated with each corresponding cell using a consolidation rule, wherein at least one cell has more than one associated qualified control beams.
2. The method of claim 1, wherein the signal measurement of a control beam is obtained based on at least one of the measurements comprising: a signal strength measurement, a signal quality measurement, a signal lifetime measurement, signal error rate, and signal AoA/DoA.
3. The method of claim 1, wherein the set of qualified control beams of a cell consists of multiple detected control beams associated with the cell.
4. The method of claim 1, further comprising: determining one or more candidate control beams, wherein the signal measurement of each candidate control beam is greater a candidate threshold.
5. The method of claim 4, wherein the set of qualified control beams of a cell consists of multiple candidate control beams associated with the cell.
6. The method of claim 1, wherein the UE is camped on a serving cell and acquires system and control information through one or more serving control beams associated with the serving cell, and wherein the set of qualified control beams for the serving cell consists of multiple serving control beams.
7. The method of claim 1, wherein the consolidation rule determines the consolidation measurement for the set of qualified control beams is at least one selected from a group comprising: a number of qualified control beams in the set, a maximum signal measurement of the set, a minimum signal measurement of the set, a mean value of signal measurement of the set, a variance of signal measurement of the set, and a sum of the signal measurements of the set.
8. The method of claim 1, further comprising: performing a cell selection based on consolidation measurement results.
9. The method of claim 1, further comprising: performing a cell reselection based on consolidation measurement results.
10. The method of claim 1, further comprising: performing handover based on consolidated measurement results.
11. A method comprising:
- detecting multiple control beams in a millimeter wave (mmW) system by a user equipment (UE), wherein the mmW system has multiple cells each configured with multiple control beams;
- obtaining a signal measurement for each detected control beam;
- performing a cell selection to select a serving cell; and
- selecting one or more serving control beams associated with the serving cell, wherein the UE receives control information and system information on the serving control beams.
12. The method of claim 11, further comprising: determining one or more candidate control beams, wherein the signal measurement of each candidate control beam is greater a candidate threshold.
13. The method of claim 12, wherein the serving cell is selected upon detecting the first candidate control beam, and wherein the serving cell is the cell that the first detected candidate control beams is associated with.
14. The method of claim 11, further comprising: calculating a consolidation measurement for each cell based on a set of qualified control beams associated with each corresponding cell using a consolidation rule, wherein at least one cell has more than one associated qualified control beams, and wherein the serving cell is selected based on consolidation measurement results for each cell.
15. The method of claim 11, wherein the consolidation rule determines the consolidation measurement for the set of qualified control beams is one selected from a group comprising: a number of qualified control beams in the set, a maximum signal measurement of the set, a minimum signal measurement of the set, a mean value of signal measurements of the set, a variance of signal measurement of the set, and a sum of the signal measurements of the set.
16. The method of claim 11, wherein the selected serving control beams are detected control beams associated with the serving cell.
17. The method of claim 11, wherein the selected serving control beams are candidate control beams associated with the serving cell, and wherein each candidate control beam has its signal measurement greater than a threshold.
18. The method of claim 11, wherein the control beams of the serving cell are ranked based on the signal measurement and a predefined number of best control beams of the serving cell are selected based on the ranking as the serving control beams.
19. The method of claim 11, further comprising: performing a serving control beam selection based on multiple control beam measurements of the serving cell.
20. The method of claim 19, wherein the serving control beam selection involves:
- calculating a modified measurement for each serving control beam by adding an hypothesis value to the signal measurement of the corresponding serving control beam;
- ranking all control beams of the serving cell based on the modified measurement; and
- selecting one or more best ranked control beams as the new serving control beam candidate.
21. The method of claim 20, wherein the hypothesis value is obtained and configured by a system information.
22. The method of claim 20, wherein the hypothesis value is obtained and configured by a beam specific information.
23. The method of claim 11, further comprising: selecting an access control beam from the one or more selected serving control beams.
24. A method comprising:
- obtaining a consolidation serving cell measurement for cell reselection (Res_S) in a millimeter wave (mmW) system by a user equipment (UE), wherein the Res_S is calculated based on signal measurements of a set of control beams of the serving cell;
- determining a measurement level by comparing the Res _S with one or more thresholds in descending order comprising: a first threshold, a second threshold and a third threshold; and
- performing consolidation measurement for one or more cells based on the determined measurement level, wherein the consolidation measurement for a cell is calculated based on signal measurements of a set of control beams associated with the cell; and
- performing a cell reselection based on consolidation measurement results.
25. The method of claim 24, wherein the signal measurement of a control beam is obtained based on one or more UE measurements comprising: a signal strength measurement, a signal quality measurement, a signal lifetime measurement, signal error rate and signal AoA/DoA.
26. The method of claim 24, wherein the measurement level is a first level when the Res_S is greater than the first threshold, and wherein the consolidation measurement is only performed for the serving cell based on serving control beams on which the UE receives system and control information.
27. The method of claim 24, wherein the measurement level is a second level when the Res_S is smaller than the first threshold and larger than the second threshold, and wherein the consolidation measurement is performed on all detected control beams of the serving cell.
28. The method of claim 24, wherein the measurement level is a third level when the Res_S is smaller than the second threshold and larger than the third threshold, and wherein the consolidation measurement is performed on detected control beams in the serving cell and detected or configured neighbor cell control beams with a same frequency of the serving cell.
29. The method of claim 24, wherein the measurement level is a fourth level when the Res_S is smaller than the third threshold and wherein the consolidation measurement is performed on all detected control beams of detected control beams in the serving cell and detected or configured neighbor cell control beams with a different frequency of the serving cell.
Type: Application
Filed: Mar 5, 2015
Publication Date: Sep 8, 2016
Applicant: Mediatek (Beijing) Inc. (Beijing)
Inventors: Yuanyuan Zhang (Beijing), Aimin Justin Sang (San Diego, CA), Jiann-Ching Guey (Hsinchu City), Yu-Syuan Jheng (Taipei City), Ju-Ya Chen (Kaohsiung City)
Application Number: 14/655,727