US20140099946A1 - Smart antenna for interference rejection with enhanced tracking - Google Patents
Smart antenna for interference rejection with enhanced tracking Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/20—Selecting an access point
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/24—Cell structures
- H04W16/28—Cell structures using beam steering
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/16—Discovering, processing access restriction or access information
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
- H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/06—Testing, supervising or monitoring using simulated traffic
Definitions
- This invention is directed towards antenna systems for mobile devices.
- Wireless communication is extensively used in mobile or nomadic applications.
- FIG. 1 shows an example of a system used to support a mobile application.
- Mobile station 111 will try to establish a link with one of base stations 121 and 122 , as it travels along path 131 .
- Typical solutions for mobile or nomadic wireless devices use omnidirectional antennas that are isotropic or have similar properties, for example gain, in all directions of interest.
- FIG. 2 shows an example of the coverage 403 for base-station 401 and the coverage 404 for the base-station 402 when both base-stations use the same frequency channel, and the three mobile/nomadic devices 406 , 407 and 408 use omnidirectional antennas.
- Mobile device 406 receives coverage, that is, it can establish an operating link with better than threshold signal quality from base station 401 in area 403 .
- mobile device 407 receives coverage from base station 402 in area 404 .
- mobile device 408 cannot receive coverage from either base station 401 or 402 because the signal quality is not good enough. This is because the omnidirectional antenna captures signals from the two base-stations 401 and 402 and needs to be very close to one of them and very far from the other to obtain the needed signal quality.
- a smart antenna system for communicating wireless signals between a mobile device and a plurality of fixed base stations using one or more channels and one or more beams
- said smart antenna system comprising a control subsystem, a radio transceiver and an antenna subsystem coupled to each other and adapted to perform scanning of one or more combinations of base stations, channels and beams using one or more test links established with one or more of the fixed base stations and the test links use at least some of the channels and the beams.
- a first combination of base station, channel and beam is selected based on data obtained during scanning, and a first operating link is established for transmitting a wireless signal to the currently selected base station using the currently selected channel and beam.
- scanning is continued using one or more test links established with the currently selected base station, using one or more beams different from the currently selected beam and the currently selected channel, or with one or more combinations of base stations, channels and beams.
- the continued scanning is performed aperiodically, and the interval between consecutive continued scanning operations is pseudo-random.
- said control subsystem inserts a downtime and the continued scanning is performed during the downtime.
- control subsystem calculates the duration of the downtime before inserting the downtime.
- FIG. 1 shows an example of a system used to support a mobile application.
- FIG. 2 shows example coverage of a given area for a mobile/nomadic device or station with an omnidirectional antenna.
- FIG. 3 shows a smart antenna system
- FIG. 4 shows a radiation pattern for beam 200 .
- FIG. 5 shows an example radiation pattern for arrangement 300 .
- FIG. 6 shows a flowchart of the process when the smart antenna system 100 becomes active.
- FIG. 6A shows one embodiment for determining the operating channel and the best-performing beam from a candidate set of channels and beams.
- FIG. 6B is the flowchart of the process for another embodiment when the smart antenna system 100 becomes active.
- FIG. 6C shows a sequence of steps for the tracking process.
- FIG. 6D shows a situation where mobile device 904 uses beam 906 to connect to base station 901 to maximize signal to interference and noise ratio (SINR)
- SINR signal to interference and noise ratio
- FIG. 6E shows a situation where after travelling in direction 907 , mobile device 904 changes to beam 905 to connect to base station 901 to maximize signal to interference and noise ratio (SINR)
- SINR signal to interference and noise ratio
- FIG. 6F shows a situation where after further travel in direction 907 , mobile device 904 changes to beam 906 to maximize signal to interference and noise ratio (SINR)
- SINR signal to interference and noise ratio
- FIG. 6G shows beams 915 A- 915 E produced by mobile device 904 .
- FIG. 6H shows a sequence where tracking downtimes are inserted between data transmissions to allow switching between beam-channel combinations to occur.
- FIG. 7 shows an illustrative example of the advantage of making selections of base station, operating channel and beam based on signal quality over signal strength.
- FIG. 8 shows example coverage of a given area for a mobile/nomadic device or station with a smart antenna with the same base stations and the same area of interest as in FIG. 2 .
- FIG. 3 shows a smart antenna system 100 consisting of radio transceiver 101 to transmit over a wireless link; an antenna subsystem 102 ; and a control subsystem 103 .
- Information can be passed between the radio transceiver 101 , antenna subsystem 102 and control subsystem 103 .
- the control subsystem 103 can receive information, including, but not limited to wireless link quality information; and other information such as base station operating capacity and base station load/utilization; from either or both of the radio transceiver 101 and the antenna subsystem 102 .
- the control subsystem 103 can process this information and command either or both of the radio transceiver 101 and antenna subsystem 102 accordingly.
- the smart antenna system 100 is designed to be installed in, for example, a mobile/nomadic device or station which establishes a wireless link to a base station.
- the radio transceiver 101 performs several different functions, including but not limited to, for example, transmitting and receiving information on the available operating channels; obtaining data to compute signal quality measures such as signal to noise ratio (SNR), signal to interference and noise ratio (SINR) and bit error rate (BER); and computing these measures either by itself or together with the control subsystem 103 .
- the operating channel to be used for transmitting and receiving is set by the control subsystem 103 .
- the radio transceiver can transmit on more than one channel. This allows the smart antenna system to have “background” operation.
- control subsystem 103 can direct the radio transceiver 101 to transmit and receive on other channels used in, for example, test links which have been set up in the background.
- link quality measurements can also be computed. These include, for example, packet error rate (PER), packet jitter and throughput.
- PER packet error rate
- packet jitter packet jitter
- throughput packet error rate
- the antenna subsystem 102 provides multiple beams that can be selected by the control subsystem 103 .
- the multiple beams can be produced by independent antennas, by beam-steering or by beam-forming. These techniques are well known to one having skill in the art.
- FIG. 4 shows an example radiation pattern of such a beam 200 , where the main lobe 201 of the beam covers the 90° sector between lines 201 -A and 201 -B, while the lateral lobes 202 and 203 provide some attenuation and the back-lobe 204 provides very strong attenuation.
- FIG. 5 shows an example radiation pattern for such an arrangement 300 , where the beam 200 of FIG. 4 , with only main lobe 201 shown for simplicity, is repeated 8 times as beams 301 - 308 at 45° intervals for 360° coverage. Beams 301 - 308 are overlapping to ensure low ripple in omnidirectional coverage.
- the ripple 310 is the difference between maximum gain and the minimum gain obtainable using all available beams.
- the ability of the antenna subsystem 102 to provide multiple beams allows for “background” operation on other beams. This, together with the ability of the radio transceiver 101 , to transmit and receive on other channels, means that the control subsystem 103 can establish test links in the background on different channels and beams, to the channel and beam used by the current operating link running in the foreground.
- the control subsystem 103 is the controller of the smart antenna system 100 .
- the control subsystem 103 commands, controls, co-ordinates and manages the operation of the antenna subsystem 102 and radio transceiver 101 .
- the control subsystem 103 can receive information, such as wireless link status from either or both of the radio transceiver 101 and the antenna subsystem 102 .
- link status is active, the control subsystem 103 can collect information related to, for example, signal quality; and other information such as base station operating capacity and base station load/utilization; from the radio transceiver 101 , or both the radio transceiver 101 and antenna subsystem 102 .
- the control subsystem 103 can process this collected information and send commands and control instructions to either or both of the radio transceiver 101 and antenna subsystem 102 accordingly.
- the control subsystem 103 collects information related to signal quality. Various measures of signal quality can then be calculated. These measures include signal to noise ratio (SNR), signal to interference and noise ratio (SINR) and bit error rate (BER). As explained previously, in one embodiment the control subsystem 103 collects this information, and then together with the radio transceiver 101 calculates measures such as SNR, SINR and BER. In another embodiment, the radio transceiver 101 calculates these measures on its own. In a further embodiment, the control subsystem 103 together with the radio transceiver calculates a signal quality score for each base station based on a function which takes in one or more of signal quality measures such as SNR, SINR and BER as inputs, and produces the score as the output.
- SNR signal to noise ratio
- SINR signal to interference and noise ratio
- BER bit error rate
- control subsystem 103 calculates a weighted average based on SNR and SINR.
- a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score.
- the control subsystem 103 can store also store historical signal quality information, and other information for future use.
- link quality measurements can also be calculated. These measures include, for example, packet error rate (PER), packet jitter and throughput. Similar to signal quality, in one embodiment the control subsystem 103 collects this information, and then together with the radio transceiver 101 calculates measures such as PER, jitter and throughput. In another embodiment, the radio transceiver 101 calculates these measures on its own. In a further embodiment, the control subsystem 103 together with the radio transceiver calculates a link quality score for each base station based on a function which takes in one or more of link quality measures such as PER, jitter and throughput as inputs, and produces the score as the output.
- PER packet error rate
- the control subsystem 103 collects this information, and then together with the radio transceiver 101 calculates measures such as PER, jitter and throughput. In another embodiment, the radio transceiver 101 calculates these measures on its own. In a further embodiment, the control subsystem 103 together with the radio transceiver calculates a link quality
- control subsystem 103 calculates a weighted average based on PER and jitter.
- a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score.
- the control subsystem 103 can store also store historical link quality information, and other information for future use.
- control subsystem 103 is an independent module. In another embodiment, the control subsystem 103 is integrated with the other radio transceiver 101 control functions.
- the control subsystem 103 can be implemented in hardware, software, or some combination of hardware and software. In another embodiment, the control subsystem 103 is installed as software on, for example, the radio transceiver 101 .
- the smart antenna system When the smart antenna system becomes active, for example, when it is:
- FIG. 6 shows a flowchart of the process when the smart antenna system 100 becomes active.
- the control subsystem 103 selects a subset of the available beams and channels before the commencement of the scanning process, and then performs scanning using the selected subset.
- control subsystem 103 selects the subset based on historical signal quality.
- signal quality can be measured by, for example, one of SNR, SINR and BER.
- the control subsystem 103 together with the radio transceiver 101 calculates measures such as SNR and SINR. In another embodiment, the radio transceiver 101 calculates these measures on its own.
- control subsystem 103 together with the radio transceiver 101 calculates a signal quality score for each base station based on a function which takes in one or more of signal quality measures such as SNR and SINR as inputs, and produces the score as the output. For example, in one embodiment the control subsystem 103 calculates a weighted average based on SNR and SINR. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score.
- link quality measurements can also be calculated. These measures include, for example, packet error rate (PER), packet jitter and throughput. Similar to signal quality, in one embodiment the control subsystem 103 collects this information, and then together with the radio transceiver 101 calculates measures such as PER, jitter and throughput. In another embodiment, the radio transceiver 101 calculates these measures on its own. In a further embodiment, the control subsystem 103 together with the radio transceiver calculates a link quality score for each base station based on a function which takes in one or more of link quality measures such as PER, jitter and throughput as inputs, and produces the score as the output. For example, in one embodiment the control subsystem 103 calculates a weighted average based on PER and jitter. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score.
- PER packet error rate
- jitter packet jitter and throughput
- the control subsystem 103 uses geo-location information, for example, the location of the mobile/nomadic device relative to the base-stations, to select the subset of the available channels and beams.
- positional/motion information obtained, for example, from sensors in the mobile/nomadic device are used by the control subsystem 103 in optional step 601 to select the subset of the available channels and beams. Examples of positional/motion information include velocity of the device, acceleration of the device, direction of travel of the device, orientation of the device, angular velocity of the device, angular acceleration of the device and altitude of device.
- the subset of the available channels and beams is selected by control subsystem 103 based on user input and instructions.
- the subset of the available channels and beams is selected in optional step 601 based on at least one of historical signal quality, geo-location information, user input/instructions and positional/motion information.
- control subsystem 103 uses the fact that the beams are overlapping to select a subset of beams to perform scanning
- Steps 602 - 604 detail the scanning process.
- the control subsystem 103 determines the best-performing combination of base station, channel and beam. It does so by attempting to establish wireless test links to base stations, using a set of candidate channels and beams comprising at least some of the one or more available channels, and some of the one or more available beams.
- the candidate set is all available channels and beams.
- the candidate set is the subset of channels and beams selected using one of the methods outlined above.
- the control subsystem 103 For each wireless test link that the control subsystem 103 successfully establishes with a base station, the control subsystem 103 collects information relating to signal quality of the test link. As previously explained, signal quality can be measured by SNR, SINR or BER. In another embodiment, the control subsystem 103 uses the test link to collect information including, but not limited to, link quality, base station operating capacity; and base station load/utilization.
- the control subsystem 103 measures the performance for the combination of base station, channel and beam.
- performance is measured by signal quality.
- signal quality can be measured by SNR, SINR or BER.
- the control subsystem 103 together with the radio transceiver 101 calculates SNR, SINR and BER.
- the radio transceiver 101 calculates these measures on its own.
- the control subsystem 103 together with the radio transceiver 101 further calculates a signal quality score based on a function which takes in one or more of signal quality measures such as SNR and SINR as inputs, and produces the score as the output.
- a function is a weighted average.
- Another example of such a function is where a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score.
- performance can be measured by calculating a score for each combination based on a function which takes in one or more of signal quality measures such as SNR and SINR; link quality measures such as PER, jitter and throughput, base station operating capacity; and base station load/utilization as inputs, and produces the score as an output.
- signal quality measures such as SNR and SINR
- link quality measures such as PER, jitter and throughput, base station operating capacity
- base station load/utilization as inputs
- the control subsystem 103 calculates a weighted average based on SINR, base station operating capacity; and base station load/utilization; and selects the base station with the best weighted average.
- the control subsystem 103 first calculates the weighted average, then compares against a threshold, and uses the comparison to calculate a final performance score.
- FIG. 6A shows one embodiment to perform step 602 for a candidate set of channels and beams.
- control subsystem 103 scans all channels in the candidate set, and for each channel, all available beams in the candidate set.
- control subsystem 103 selects a first channel and a first beam from the candidate set.
- control subsystem 103 attempts to establish a test link to a base station using the first channel and the first beam in the candidate set. If this is successful, (step 622 ) then in step 623 the control subsystem 103 records performance for every base station, channel and beam for which a test link is successfully established.
- step 624 the control subsystem 103 checks to see if all beams have been used. If not, then, in step 625 , the control subsystem 103 selects the next beam in the candidate set and returns to step 621 . If all beams have been used, then in step 626 the control subsystem 103 checks to see if all channels have been used. If not, then in step 627 , the control subsystem selects the next channel in the candidate set and returns to step 621 . If all channels have been used, the control subsystem 103 then moves to step 603 .
- control subsystem 103 scans beams in the candidate set, and for each beam, it scans all channels in the candidate set.
- step 603 the control subsystem 103 builds a list showing performance for all combinations of base station, channel and beam.
- step 604 the control subsystem 103 selects the best performing combination of base-station, channel and beam based on the information it collected in steps 602 and 603 .
- step 605 the control subsystem 103 then establishes an operating link to the selected base-station using the selected operating channel and beam. Communication over the operating link is carried out in step 606 .
- the control subsystem 103 establishes an operating link to the next best combination of base station, operating channel and beam, and communication over the operating link is carried out in step 606 .
- step 610 when the smart antenna system 100 becomes active, the control subsystem 103 configures the radio transceiver 101 first, and then the antenna subsystem 102 to connect with the base station and establish an operating link on the channel and with the beam on which an operating link was last established. If operating link establishment fails (step 610 A), then control subsystem 103 performs steps 612 - 616 , which are similar to steps 602 - 606 described above. In one embodiment, similar to as described previously for step 601 , control subsystem 103 may optionally perform step 611 , which is selecting a subset of the available channels and beams for the candidate set in step 612 .
- control subsystem 103 after the operating link is established the base station, channel and beam selection remain fixed until the operating link is lost. Once the operating link is lost, the control subsystem 103 performs steps 602 - 606 of FIG. 6 . In one embodiment, similar to as described previously, control subsystem 103 additionally performs step 601 .
- control subsystem 103 performs tracking, that is, the control subsystem 103 continues to search for a better combination of base station, channel and beam than the currently selected combination of base station, operating channel and beam. In one embodiment, the control subsystem 103 performs tracking in the background; while communication over the currently established operating link is ongoing.
- FIG. 6C shows a sequence of steps involved in tracking.
- FIGS. 6D-6F An example situation where tracking is useful is shown in FIGS. 6D-6F .
- FIG. 6D and 6E show an example of such a situation.
- the mobile device 904 uses beam 906 to connect to base-station 901 because doing so would avoid interference from base-stations 902 and 903 and therefore offers the best SINR.
- FIG. 6E shows the same mobile device 904 after it moved in direction 907 enough that the optimal beam is now beam 905 instead of beam 906 .
- FIG. 6F shows the same mobile device 904 after further moving in direction 907 enough that the optimum base-station is no longer base-station 901 on beam 905 but base-station 903 on beam 906 . In such a situation, tracking would be useful to select a beam with better performance.
- control subsystem 103 optionally performs step 631 of FIG. 6C , that is, it selects a new subset of channels and beams to be used in the tracking process using at least one of signal quality, geo-location and positional/motion information as outlined above.
- positional/motion information in step 631 , can be used together with geo-location information of the device to predict the path of the device, and orientation of the device along this predicted path. Based on this predicted path/orientation and other information such as geo-location information of the base stations; subsets of the base stations, beams and channels which are likely to provide better links in the future can be pre-loaded for tracking For example, with reference to FIGS.
- the control subsystem 103 determines performance for all combinations of base station, channel and beam other than the currently selected combination. In one embodiment, similar to step 602 , it does so by using a candidate set of channels and beams to establish test links to base stations.
- the candidate set is the subset of beams and channels previously selected in step 601 of FIG. 6 .
- the candidate set is the subset of beams and channels selected in optional step 631 .
- the candidate set is the set of all available channels and beams.
- step 632 the control subsystem 103 performs steps 620 - 627 of FIG. 6A for all combinations of base station, channel and beam other than the currently selected combination.
- control subsystem 103 searches for a better beam by testing the performance of other beams while the operating link is running on the currently selected beam. In one embodiment, the control subsystem 103 only tests the performance of difference beams, and keeps the base station and operating channel the same. In one embodiment, control subsystem 103 performs searching by periodically instructing the antenna subsystem 102 to switch between the currently selected beam and its neighbors to detect if any of the neighboring beams offer a better signal quality. In one embodiment, the control subsystem 103 alternates between adjacent beams. For example, in FIG. 6G , beam 915 A shown by the solid line is the currently used beam. Beams 915 B and 915 C are adjacent to 915 A.
- Beam 915 D is adjacent to beam 915 B, and 915 E are adjacent to beam 915 C. Then, testing will alternate between beam 915 B and beam 915 C. This switching can be carried out, for example, during a period between data transmissions such as for example, a gap between packets or bursts of packets. In another embodiment, these gaps or periods are inserted between data transmissions to specifically allow such switching to occur.
- FIG. 6H shows a sequence where these gaps or periods, or more specifically, tracking downtimes are inserted between data transmissions to specifically allow such switching to occur.
- the tracking downtime is fixed.
- control subsystem 103 calculates the duration of the impending tracking downtime.
- the duration of the period of tracking downtime is set such that it is short enough not to affect the latency of the user traffic.
- the utilization of the down-link and the up-link is first determined. Once this utilization is calculated, then using known formulas, the average latencies for different tracking downtime periods can be estimated. In one embodiment, in order to obtain the estimates, the average latency can be approximated by the sum of
- control subsystem 103 notifies, for example, the control subsystem of the current base-station of the impending tracking downtime.
- step 643 upon receiving the notification the control subsystem of the base-station ensures that it will not schedule any down-link (base-station to device) or up-link (device to base-station) transmission to or from the notifying mobile device during the tracking downtime.
- the base-station buffers all data packets that need to be delivered to the mobile device and any other previously scheduled downlink or uplink scheduled allocations that have been agreed with the mobile device.
- the mobile device buffers all data packets that need to be delivered to the base-station and any other previously scheduled downlink or uplink scheduled allocations that have been agreed with the base-station.
- the duration of the tracking downtime period is less than the minimum duration required to obtain a good measurement of signal quality for a single combination of base station, beam and channel; then data is acquired over several periods until a sufficient amount of data has been acquired to obtain a good measurement of signal quality for a single combination.
- the control subsystem 103 will test two or more combinations of base station, beam and channel. The number of combinations tested is given by:
- N C ⁇ Tracking ⁇ ⁇ downtime Minimum ⁇ ⁇ duration ⁇ ⁇ required ⁇ ⁇ per ⁇ ⁇ combination ⁇
- N C is the number of combinations tested in a given tracking downtime. For example, if it is determined that the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and the tracking downtime duration is 1.2 ms, then 2 channels are tested. If it is determined that the tracking downtime period is less than the minimum duration needed to obtain good measurements of signal quality for all the combinations within the candidate set of beams and channels, then data is acquired over several periods until a sufficient amount of data has been acquired to obtain good measurements of signal quality for all the combinations.
- the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and there are 2 combinations within the candidate set of beams and channels
- the minimum duration needed to obtain good measurement for both combinations is 2 ms.
- the tracking downtime duration is 1.2 ms, then data must be acquired over 2 durations to ensure that a good measurement of signal quality can be obtained.
- the duration of the tracking downtime period is greater than the minimum duration required to test a single combination of base station, beam and channel; then the number of combinations tested is given by:
- N C ⁇ Tracking ⁇ ⁇ downtime Minimum ⁇ ⁇ duration ⁇ ⁇ required ⁇ ⁇ per ⁇ ⁇ combination ⁇
- N C is the number of combinations tested in a given tracking downtime. For example, if it is determined that the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and the tracking downtime duration is 1.2 ms, then only one channel can be tested to ensure that a good measurement of signal quality can be obtained. Similar to as previously explained, if it is determined that the tracking downtime period is less than the minimum duration needed to obtain good measurements of signal quality for all the combinations within the candidate set of beams and channels, then data is acquired until a sufficient amount of data is recorded, to obtain good measurements of signal quality for all the combinations.
- control subsystem 103 tests the signal quality on the neighboring beam using normal data packets on the neighboring beam. In another embodiment, the control subsystem 103 instructs the antenna subsystem 102 to switch from the currently selected beam to a neighboring beam during a period between data transmissions, and then tests the signal quality on the neighboring beam, using special channel sounding packets on the neighboring beam. Control subsystem 103 then instructs the antenna subsystem 102 to switch back to the currently selected beam and resumes transmission of normal data packets. This is done to ensure that the delivery of data packets is not affected in case the signal quality on the neighboring beam is very poor.
- the interference experienced may be periodic.
- some base stations operate periodically, alternating between short “busy” periods and long “quiet” periods. If tracking is performed periodically, there is a chance that tracking will only occur during the “quiet” periods, and the base station will be “missed”.
- the mobile device performs tracking at aperiodic intervals to remove the impact of this periodic interference on the SINR measurements.
- the aperiodic intervals are pseudo-random.
- the control subsystem 103 builds a list showing performance for all combinations of base stations, channels and beams in step 633 .
- performance may be measured by signal quality or other measures, or a combination of signal quality and other measures.
- signal quality can be measured by, for example, SNR, SINR, BER, or a score calculated from a function which takes in measures such as SNR and SINR as inputs, and produces the score as an output.
- the control subsystem 103 finds a better combination of base station, channel and beam than the currently selected combination of base station, channel and beam (step 633 A), then it moves to select the better combination in step 634 . For example, in the embodiment described above with reference to FIG. 6G , if beam 915 B offers better performance than 915 A, then control subsystem 103 selects beam 915 B. If not, then beam 915 C is tested. If 915 C is found to be better, then control subsystem 103 selects beam 915 C. In another embodiment, the control subsystem 103 selects the better combination in step 634 , only if the control subsystem 103 determines that the improvement in signal quality persists for a predefined period.
- control subsystem 103 continues searching for a better combination of base station, operating channel and beam. In one embodiment, this involves selecting a new subset of available channels and beams (step 631 ).
- step 635 the control subsystem 103 establishes a new operating link to the selected base station using the new channel and beam.
- step 636 communication over the newly established operating link begins.
- the candidate set of beams and channels will also be updated. For example, with reference to FIG. 6G , if control subsystem 103 communicates using beam 915 B, then in the next tracking downtime, beams 915 D and 915 A will be tested. If control subsystem 103 communicates using beam 915 C, in the next tracking downtime, beams 915 E and 915 A will be tested.
- control subsystem 103 searches for a standby combination of base station, channel and beam, in case the current operating link fails. In one embodiment, the control subsystem 103 periodically performs steps 631 - 633 of FIG. 6C in the background. If the current operating link fails, then the control subsystem 103 selects the best combination of base station, channel and beam identified; establishes a new operating link over this combination; and communicates over this newly established operating link.
- FIG. 7 which shows a mobile device 701 containing a smart antenna system, with wireless test links to base stations 702 and 703 .
- Device 701 determines that base station 702 provides better signal quality than base station 703 .
- Device 701 then has to select a beam. It decides to select beam 712 over beam 711 , for the following reason: Device 701 can establish a test link to base station 702 with either beam 711 or 712 because it is in the area 713 in which the two beams overlap.
- the signal strength for base station 702 using beam 711 is stronger than beam 712 because base station 702 is closer to the center of beam 711 .
- the control subsystem 103 selected beam 711 , then it would have to contend with interference from base station 703 , and therefore the SINR would be lower.
- Control subsystem 103 chooses beam 712 because it offers lower interference, and consequently a better signal quality, than with beam 711 .
- FIG. 8 shows the coverage for the base stations 401 and 402 of FIG. 2 but with the mobile/nomadic devices 511 and 513 using smart antennas.
- the coverage 503 for the base-station 401 and the coverage 504 for the base-station 402 are much larger, almost covering the entire area of interest 405 .
- Mobile device 511 selects beam 512 that provides good signal strength from base station 401 and provides good isolation from (rejection of) base station 402 , which means good SINR and therefore signal quality.
- mobile device 513 selects beam 514 that includes base station 402 but excludes base station 401 .
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Abstract
Description
- This application is a continuation of and claims priority to U.S. application Ser. No. 13/899,787, filed May 22, 2013, which is a continuation of Ser. No. 13/682,540, filed Nov. 20, 2012, now allowed, which is a continuation-in-part of U.S. application Ser. No. 13/644,852, filed Oct. 4, 2012, now allowed, the entire contents of which are incorporated herein by reference.
- This invention is directed towards antenna systems for mobile devices.
- Wireless communication is extensively used in mobile or nomadic applications.
- In a typical mobile/nomadic application, a mobile or nomadic wireless device or mobile station will try to establish a link with a fixed base station, so as to transmit information to the base station. To achieve coverage of the desired area, multiple base-stations must be used.
FIG. 1 shows an example of a system used to support a mobile application.Mobile station 111 will try to establish a link with one ofbase stations path 131. - Typical solutions for mobile or nomadic wireless devices use omnidirectional antennas that are isotropic or have similar properties, for example gain, in all directions of interest.
- While mobile/nomadic devices use omnidirectional antennas, strict separation between base-stations covering adjacent areas is required to avoid harmful self-interference. Separation can be achieved through:
-
- Time, that is, the base stations do not transmit and receive at the same time,
- Frequency, that is, the base stations transmit and receive on different frequencies, or
- Code, that is, the base stations transmit and receive using different codes.
- All these methods reduce the total system capacity.
-
FIG. 2 shows an example of thecoverage 403 for base-station 401 and thecoverage 404 for the base-station 402 when both base-stations use the same frequency channel, and the three mobile/nomadic devices stations interest 405 is not adequately covered.Mobile device 406 receives coverage, that is, it can establish an operating link with better than threshold signal quality frombase station 401 inarea 403. Similarlymobile device 407 receives coverage frombase station 402 inarea 404. However,mobile device 408 cannot receive coverage from eitherbase station stations - In order to solve the problem shown in
FIG. 2 , there is a need for a system that has omnidirectional coverage, but is able to focus on one sector so as to optimize signal quality to enable communications with the highest reliability. Until now, systems have focused on optimizing signal strength, which may not result in enabling communications with the highest reliability. - In accordance with one embodiment, a smart antenna system for communicating wireless signals between a mobile device and a plurality of fixed base stations using one or more channels and one or more beams, said smart antenna system comprising a control subsystem, a radio transceiver and an antenna subsystem coupled to each other and adapted to perform scanning of one or more combinations of base stations, channels and beams using one or more test links established with one or more of the fixed base stations and the test links use at least some of the channels and the beams. A first combination of base station, channel and beam is selected based on data obtained during scanning, and a first operating link is established for transmitting a wireless signal to the currently selected base station using the currently selected channel and beam. After establishment of the first operating link, scanning is continued using one or more test links established with the currently selected base station, using one or more beams different from the currently selected beam and the currently selected channel, or with one or more combinations of base stations, channels and beams. The continued scanning is performed aperiodically, and the interval between consecutive continued scanning operations is pseudo-random.
- In one implementation, before the continued scanning is performed, said control subsystem inserts a downtime and the continued scanning is performed during the downtime.
- In one implementation, the control subsystem calculates the duration of the downtime before inserting the downtime.
- The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings.
-
FIG. 1 shows an example of a system used to support a mobile application. -
FIG. 2 shows example coverage of a given area for a mobile/nomadic device or station with an omnidirectional antenna. -
FIG. 3 shows a smart antenna system. -
FIG. 4 shows a radiation pattern for beam 200. -
FIG. 5 shows an example radiation pattern forarrangement 300. -
FIG. 6 shows a flowchart of the process when thesmart antenna system 100 becomes active. -
FIG. 6A shows one embodiment for determining the operating channel and the best-performing beam from a candidate set of channels and beams. -
FIG. 6B is the flowchart of the process for another embodiment when thesmart antenna system 100 becomes active. -
FIG. 6C shows a sequence of steps for the tracking process. -
FIG. 6D shows a situation wheremobile device 904 usesbeam 906 to connect tobase station 901 to maximize signal to interference and noise ratio (SINR) -
FIG. 6E shows a situation where after travelling indirection 907,mobile device 904 changes to beam 905 to connect tobase station 901 to maximize signal to interference and noise ratio (SINR) -
FIG. 6F shows a situation where after further travel indirection 907,mobile device 904 changes tobeam 906 to maximize signal to interference and noise ratio (SINR) -
FIG. 6G shows beams 915A-915E produced bymobile device 904. -
FIG. 6H shows a sequence where tracking downtimes are inserted between data transmissions to allow switching between beam-channel combinations to occur. -
FIG. 7 shows an illustrative example of the advantage of making selections of base station, operating channel and beam based on signal quality over signal strength. -
FIG. 8 shows example coverage of a given area for a mobile/nomadic device or station with a smart antenna with the same base stations and the same area of interest as inFIG. 2 . - Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
- Turning now to the drawings and referring first to
FIG. 3 ,FIG. 3 shows asmart antenna system 100 consisting ofradio transceiver 101 to transmit over a wireless link; anantenna subsystem 102; and acontrol subsystem 103. Information can be passed between theradio transceiver 101,antenna subsystem 102 andcontrol subsystem 103. For example, thecontrol subsystem 103 can receive information, including, but not limited to wireless link quality information; and other information such as base station operating capacity and base station load/utilization; from either or both of theradio transceiver 101 and theantenna subsystem 102. Thecontrol subsystem 103 can process this information and command either or both of theradio transceiver 101 andantenna subsystem 102 accordingly. Thesmart antenna system 100 is designed to be installed in, for example, a mobile/nomadic device or station which establishes a wireless link to a base station. - The
radio transceiver 101 performs several different functions, including but not limited to, for example, transmitting and receiving information on the available operating channels; obtaining data to compute signal quality measures such as signal to noise ratio (SNR), signal to interference and noise ratio (SINR) and bit error rate (BER); and computing these measures either by itself or together with thecontrol subsystem 103. In one embodiment, the operating channel to be used for transmitting and receiving is set by thecontrol subsystem 103. The radio transceiver can transmit on more than one channel. This allows the smart antenna system to have “background” operation. For example, while transmitting and receiving on a channel used in a current operating link in the foreground, thecontrol subsystem 103 can direct theradio transceiver 101 to transmit and receive on other channels used in, for example, test links which have been set up in the background. - In another embodiment, in addition to the signal quality measures described above, link quality measurements can also be computed. These include, for example, packet error rate (PER), packet jitter and throughput.
- The
antenna subsystem 102 provides multiple beams that can be selected by thecontrol subsystem 103. The multiple beams can be produced by independent antennas, by beam-steering or by beam-forming. These techniques are well known to one having skill in the art. - Each beam provides nulls (directions in which signal is strongly attenuated) that can be used to eliminate interference.
FIG. 4 shows an example radiation pattern of such a beam 200, where the main lobe 201 of the beam covers the 90° sector between lines 201-A and 201-B, while the lateral lobes 202 and 203 provide some attenuation and the back-lobe 204 provides very strong attenuation. - The sum of the coverage of all beams provides omnidirectional coverage.
FIG. 5 shows an example radiation pattern for such anarrangement 300, where the beam 200 ofFIG. 4 , with only main lobe 201 shown for simplicity, is repeated 8 times as beams 301-308 at 45° intervals for 360° coverage. Beams 301-308 are overlapping to ensure low ripple in omnidirectional coverage. The ripple 310 is the difference between maximum gain and the minimum gain obtainable using all available beams. - The ability of the
antenna subsystem 102 to provide multiple beams allows for “background” operation on other beams. This, together with the ability of theradio transceiver 101, to transmit and receive on other channels, means that thecontrol subsystem 103 can establish test links in the background on different channels and beams, to the channel and beam used by the current operating link running in the foreground. - The
control subsystem 103 is the controller of thesmart antenna system 100. Thecontrol subsystem 103 commands, controls, co-ordinates and manages the operation of theantenna subsystem 102 andradio transceiver 101. As explained previously, thecontrol subsystem 103 can receive information, such as wireless link status from either or both of theradio transceiver 101 and theantenna subsystem 102. When link status is active, thecontrol subsystem 103 can collect information related to, for example, signal quality; and other information such as base station operating capacity and base station load/utilization; from theradio transceiver 101, or both theradio transceiver 101 andantenna subsystem 102. - The
control subsystem 103 can process this collected information and send commands and control instructions to either or both of theradio transceiver 101 andantenna subsystem 102 accordingly. - As previously explained, the
control subsystem 103 collects information related to signal quality. Various measures of signal quality can then be calculated. These measures include signal to noise ratio (SNR), signal to interference and noise ratio (SINR) and bit error rate (BER). As explained previously, in one embodiment thecontrol subsystem 103 collects this information, and then together with theradio transceiver 101 calculates measures such as SNR, SINR and BER. In another embodiment, theradio transceiver 101 calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with the radio transceiver calculates a signal quality score for each base station based on a function which takes in one or more of signal quality measures such as SNR, SINR and BER as inputs, and produces the score as the output. For example, in one embodiment thecontrol subsystem 103 calculates a weighted average based on SNR and SINR. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score. Thecontrol subsystem 103 can store also store historical signal quality information, and other information for future use. - In another embodiment, in addition to the signal quality measures described above, as previously explained, link quality measurements can also be calculated. These measures include, for example, packet error rate (PER), packet jitter and throughput. Similar to signal quality, in one embodiment the
control subsystem 103 collects this information, and then together with theradio transceiver 101 calculates measures such as PER, jitter and throughput. In another embodiment, theradio transceiver 101 calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with the radio transceiver calculates a link quality score for each base station based on a function which takes in one or more of link quality measures such as PER, jitter and throughput as inputs, and produces the score as the output. For example, in one embodiment thecontrol subsystem 103 calculates a weighted average based on PER and jitter. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score. Thecontrol subsystem 103 can store also store historical link quality information, and other information for future use. - In one embodiment, the
control subsystem 103 is an independent module. In another embodiment, thecontrol subsystem 103 is integrated with theother radio transceiver 101 control functions. Thecontrol subsystem 103 can be implemented in hardware, software, or some combination of hardware and software. In another embodiment, thecontrol subsystem 103 is installed as software on, for example, theradio transceiver 101. - When the smart antenna system becomes active, for example, when it is:
-
- powered up;
- returned from sleep; or
- turned active by the user;
thecontrol subsystem 103 then performs scanning of combinations of base stations, channels and beams, that is, it establishes test links to base stations with different channels and beams using theradio transceiver 101 and theantenna subsystem 102, and performs analysis of results obtained from these test links to select the best combination of base station, channel and beam.
-
FIG. 6 shows a flowchart of the process when thesmart antenna system 100 becomes active. Inoptional step 601, thecontrol subsystem 103 selects a subset of the available beams and channels before the commencement of the scanning process, and then performs scanning using the selected subset. In one embodiment,control subsystem 103 selects the subset based on historical signal quality. As previously explained, signal quality can be measured by, for example, one of SNR, SINR and BER. As explained previously, in one embodiment thecontrol subsystem 103 together with theradio transceiver 101 calculates measures such as SNR and SINR. In another embodiment, theradio transceiver 101 calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with theradio transceiver 101 calculates a signal quality score for each base station based on a function which takes in one or more of signal quality measures such as SNR and SINR as inputs, and produces the score as the output. For example, in one embodiment thecontrol subsystem 103 calculates a weighted average based on SNR and SINR. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score. - In another embodiment, in addition to the signal quality measures described above, as previously explained, link quality measurements can also be calculated. These measures include, for example, packet error rate (PER), packet jitter and throughput. Similar to signal quality, in one embodiment the
control subsystem 103 collects this information, and then together with theradio transceiver 101 calculates measures such as PER, jitter and throughput. In another embodiment, theradio transceiver 101 calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with the radio transceiver calculates a link quality score for each base station based on a function which takes in one or more of link quality measures such as PER, jitter and throughput as inputs, and produces the score as the output. For example, in one embodiment thecontrol subsystem 103 calculates a weighted average based on PER and jitter. In another embodiment, a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score. - In another embodiment, in
optional step 601, thecontrol subsystem 103 uses geo-location information, for example, the location of the mobile/nomadic device relative to the base-stations, to select the subset of the available channels and beams. In yet another embodiment, positional/motion information obtained, for example, from sensors in the mobile/nomadic device are used by thecontrol subsystem 103 inoptional step 601 to select the subset of the available channels and beams. Examples of positional/motion information include velocity of the device, acceleration of the device, direction of travel of the device, orientation of the device, angular velocity of the device, angular acceleration of the device and altitude of device. In yet another embodiment, the subset of the available channels and beams is selected bycontrol subsystem 103 based on user input and instructions. - In yet another embodiment, the subset of the available channels and beams is selected in
optional step 601 based on at least one of historical signal quality, geo-location information, user input/instructions and positional/motion information. - In yet another embodiment, in
optional step 601 thecontrol subsystem 103 uses the fact that the beams are overlapping to select a subset of beams to perform scanning - Steps 602-604 detail the scanning process. In step 602, the
control subsystem 103 determines the best-performing combination of base station, channel and beam. It does so by attempting to establish wireless test links to base stations, using a set of candidate channels and beams comprising at least some of the one or more available channels, and some of the one or more available beams. In one embodiment, the candidate set is all available channels and beams. In another embodiment, the candidate set is the subset of channels and beams selected using one of the methods outlined above. - For each wireless test link that the
control subsystem 103 successfully establishes with a base station, thecontrol subsystem 103 collects information relating to signal quality of the test link. As previously explained, signal quality can be measured by SNR, SINR or BER. In another embodiment, thecontrol subsystem 103 uses the test link to collect information including, but not limited to, link quality, base station operating capacity; and base station load/utilization. - The
control subsystem 103 then measures the performance for the combination of base station, channel and beam. In one embodiment, performance is measured by signal quality. As previously explained, signal quality can be measured by SNR, SINR or BER. In one embodiment thecontrol subsystem 103 together with theradio transceiver 101 calculates SNR, SINR and BER. In another embodiment, theradio transceiver 101 calculates these measures on its own. In an alternative embodiment, thecontrol subsystem 103 together with theradio transceiver 101 further calculates a signal quality score based on a function which takes in one or more of signal quality measures such as SNR and SINR as inputs, and produces the score as the output. One example of such a function is a weighted average. Another example of such a function is where a weighted average is first calculated, then compared against a threshold, and used to calculate a performance score. - In another embodiment, performance can be measured by calculating a score for each combination based on a function which takes in one or more of signal quality measures such as SNR and SINR; link quality measures such as PER, jitter and throughput, base station operating capacity; and base station load/utilization as inputs, and produces the score as an output. For example, in one embodiment, the
control subsystem 103 calculates a weighted average based on SINR, base station operating capacity; and base station load/utilization; and selects the base station with the best weighted average. In another embodiment, thecontrol subsystem 103 first calculates the weighted average, then compares against a threshold, and uses the comparison to calculate a final performance score. -
FIG. 6A shows one embodiment to perform step 602 for a candidate set of channels and beams. InFIG. 6A ,control subsystem 103 scans all channels in the candidate set, and for each channel, all available beams in the candidate set. Instep 620,control subsystem 103 selects a first channel and a first beam from the candidate set. Instep 621,control subsystem 103 attempts to establish a test link to a base station using the first channel and the first beam in the candidate set. If this is successful, (step 622) then instep 623 thecontrol subsystem 103 records performance for every base station, channel and beam for which a test link is successfully established. - In
step 624, thecontrol subsystem 103 checks to see if all beams have been used. If not, then, instep 625, thecontrol subsystem 103 selects the next beam in the candidate set and returns to step 621. If all beams have been used, then instep 626 thecontrol subsystem 103 checks to see if all channels have been used. If not, then instep 627, the control subsystem selects the next channel in the candidate set and returns to step 621. If all channels have been used, thecontrol subsystem 103 then moves to step 603. - In another embodiment in step 602, the
control subsystem 103 scans beams in the candidate set, and for each beam, it scans all channels in the candidate set. - Once this is complete, then in
step 603 thecontrol subsystem 103 builds a list showing performance for all combinations of base station, channel and beam. - In
step 604 thecontrol subsystem 103 selects the best performing combination of base-station, channel and beam based on the information it collected insteps 602 and 603. - At the end of the scanning process, in step 605, the
control subsystem 103 then establishes an operating link to the selected base-station using the selected operating channel and beam. Communication over the operating link is carried out instep 606. In a further embodiment, if the operating link is not successfully established in step 605, then thecontrol subsystem 103 establishes an operating link to the next best combination of base station, operating channel and beam, and communication over the operating link is carried out instep 606. - In one embodiment, as shown in
FIG. 6B , in step 610, when thesmart antenna system 100 becomes active, thecontrol subsystem 103 configures theradio transceiver 101 first, and then theantenna subsystem 102 to connect with the base station and establish an operating link on the channel and with the beam on which an operating link was last established. If operating link establishment fails (step 610A), then controlsubsystem 103 performs steps 612-616, which are similar to steps 602-606 described above. In one embodiment, similar to as described previously forstep 601,control subsystem 103 may optionally performstep 611, which is selecting a subset of the available channels and beams for the candidate set in step 612. - In one embodiment, after the operating link is established the base station, channel and beam selection remain fixed until the operating link is lost. Once the operating link is lost, the
control subsystem 103 performs steps 602-606 ofFIG. 6 . In one embodiment, similar to as described previously,control subsystem 103 additionally performsstep 601. - In another embodiment, after the operating link is established, the
control subsystem 103 performs tracking, that is, thecontrol subsystem 103 continues to search for a better combination of base station, channel and beam than the currently selected combination of base station, operating channel and beam. In one embodiment, thecontrol subsystem 103 performs tracking in the background; while communication over the currently established operating link is ongoing. -
FIG. 6C shows a sequence of steps involved in tracking. - An example situation where tracking is useful is shown in
FIGS. 6D-6F . As a mobile device changes its position relative to the base-station to which is connected, it is possible that the currently selected beam might no longer be the optimum one.FIG. 6D and 6E show an example of such a situation. InFIG. 6D , themobile device 904 usesbeam 906 to connect to base-station 901 because doing so would avoid interference from base-stations 902 and 903 and therefore offers the best SINR. - However, as the mobile device moves in
direction 907 thebeam 906 will, at a certain point, offer worse SINR than beam 905 because of interference from base-station 903.FIG. 6E shows the samemobile device 904 after it moved indirection 907 enough that the optimal beam is now beam 905 instead ofbeam 906.FIG. 6F shows the samemobile device 904 after further moving indirection 907 enough that the optimum base-station is no longer base-station 901 on beam 905 but base-station 903 onbeam 906. In such a situation, tracking would be useful to select a beam with better performance. - In a further embodiment, the
control subsystem 103 optionally performs step 631 ofFIG. 6C , that is, it selects a new subset of channels and beams to be used in the tracking process using at least one of signal quality, geo-location and positional/motion information as outlined above. - In another embodiment, in step 631, positional/motion information, examples of which have been previously detailed, can be used together with geo-location information of the device to predict the path of the device, and orientation of the device along this predicted path. Based on this predicted path/orientation and other information such as geo-location information of the base stations; subsets of the base stations, beams and channels which are likely to provide better links in the future can be pre-loaded for tracking For example, with reference to
FIGS. 6D-6F , if the positions ofbase stations device 904, the direction ofmotion 907 ofdevice 904, and the beam patterns, it is possible to determine the regions of coverage, and the interference which is likely to be experienced if the device continues on the same path. A prediction is then made that either one of beam 905 andbeam 906 will be used. The candidate subset of beams and channels can be narrowed to either beam depending on which one is being used. For example, if beam 905 is being used, then the candidate subset of beams and channels is narrowed tobeam 906. If the velocity and acceleration ofdevice 904 is also known, then the instant at which the beam switch should occur can also be predicted. In another embodiment, predicted path and orientation are calculated by a subsystem external to the smart antenna, and this information is communicated to the smart antenna to be pre-loaded for the tracking process. - In
step 632, thecontrol subsystem 103 determines performance for all combinations of base station, channel and beam other than the currently selected combination. In one embodiment, similar to step 602, it does so by using a candidate set of channels and beams to establish test links to base stations. In one embodiment, the candidate set is the subset of beams and channels previously selected instep 601 ofFIG. 6 . In another embodiment, the candidate set is the subset of beams and channels selected in optional step 631. In yet another embodiment, the candidate set is the set of all available channels and beams. - In one embodiment, in
step 632 thecontrol subsystem 103 performs steps 620-627 ofFIG. 6A for all combinations of base station, channel and beam other than the currently selected combination. - In another embodiment, in
step 632,control subsystem 103 searches for a better beam by testing the performance of other beams while the operating link is running on the currently selected beam. In one embodiment, thecontrol subsystem 103 only tests the performance of difference beams, and keeps the base station and operating channel the same. In one embodiment,control subsystem 103 performs searching by periodically instructing theantenna subsystem 102 to switch between the currently selected beam and its neighbors to detect if any of the neighboring beams offer a better signal quality. In one embodiment, thecontrol subsystem 103 alternates between adjacent beams. For example, inFIG. 6G , beam 915A shown by the solid line is the currently used beam. Beams 915B and 915C are adjacent to 915A. Beam 915D is adjacent to beam 915B, and 915E are adjacent to beam 915C. Then, testing will alternate between beam 915B and beam 915C. This switching can be carried out, for example, during a period between data transmissions such as for example, a gap between packets or bursts of packets. In another embodiment, these gaps or periods are inserted between data transmissions to specifically allow such switching to occur. -
FIG. 6H shows a sequence where these gaps or periods, or more specifically, tracking downtimes are inserted between data transmissions to specifically allow such switching to occur. In one embodiment, the tracking downtime is fixed. In another embodiment, instep 641,control subsystem 103 calculates the duration of the impending tracking downtime. In one embodiment, the duration of the period of tracking downtime is set such that it is short enough not to affect the latency of the user traffic. In one embodiment, the utilization of the down-link and the up-link is first determined. Once this utilization is calculated, then using known formulas, the average latencies for different tracking downtime periods can be estimated. In one embodiment, in order to obtain the estimates, the average latency can be approximated by the sum of -
- the average time from which a given packet arrives in the buffer until the end of the downtime; and
- the average time taken to clear all the packets which are ahead of the given packet.
Both these average times can be calculated using formulas known to one of skill in the art. Then, the estimated average latency for each tracking downtime duration can be compared to a threshold latency. The tracking downtime duration can be chosen such that the estimated average latency is less than the threshold.
- In
step 642,control subsystem 103 notifies, for example, the control subsystem of the current base-station of the impending tracking downtime. - In step 643, upon receiving the notification the control subsystem of the base-station ensures that it will not schedule any down-link (base-station to device) or up-link (device to base-station) transmission to or from the notifying mobile device during the tracking downtime. During the same period of time, the base-station buffers all data packets that need to be delivered to the mobile device and any other previously scheduled downlink or uplink scheduled allocations that have been agreed with the mobile device. Also, the mobile device buffers all data packets that need to be delivered to the base-station and any other previously scheduled downlink or uplink scheduled allocations that have been agreed with the base-station.
- In one embodiment, if the duration of the tracking downtime period is less than the minimum duration required to obtain a good measurement of signal quality for a single combination of base station, beam and channel; then data is acquired over several periods until a sufficient amount of data has been acquired to obtain a good measurement of signal quality for a single combination.
- In another embodiment, if the duration of the tracking downtime period is greater than the minimum duration required to test a single combination of base station, beam and channel; then the
control subsystem 103 will test two or more combinations of base station, beam and channel. The number of combinations tested is given by: -
- where NC is the number of combinations tested in a given tracking downtime. For example, if it is determined that the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and the tracking downtime duration is 1.2 ms, then 2 channels are tested. If it is determined that the tracking downtime period is less than the minimum duration needed to obtain good measurements of signal quality for all the combinations within the candidate set of beams and channels, then data is acquired over several periods until a sufficient amount of data has been acquired to obtain good measurements of signal quality for all the combinations. Using the example above, if it is determined that the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and there are 2 combinations within the candidate set of beams and channels, then the minimum duration needed to obtain good measurement for both combinations is 2 ms. However, if the tracking downtime duration is 1.2 ms, then data must be acquired over 2 durations to ensure that a good measurement of signal quality can be obtained.
- In another embodiment, if the duration of the tracking downtime period is greater than the minimum duration required to test a single combination of base station, beam and channel; then the number of combinations tested is given by:
-
- where NC is the number of combinations tested in a given tracking downtime. For example, if it is determined that the minimum duration needed to obtain good measurement of signal quality for a single combination is 1 ms and the tracking downtime duration is 1.2 ms, then only one channel can be tested to ensure that a good measurement of signal quality can be obtained. Similar to as previously explained, if it is determined that the tracking downtime period is less than the minimum duration needed to obtain good measurements of signal quality for all the combinations within the candidate set of beams and channels, then data is acquired until a sufficient amount of data is recorded, to obtain good measurements of signal quality for all the combinations.
- In one embodiment, the
control subsystem 103 tests the signal quality on the neighboring beam using normal data packets on the neighboring beam. In another embodiment, thecontrol subsystem 103 instructs theantenna subsystem 102 to switch from the currently selected beam to a neighboring beam during a period between data transmissions, and then tests the signal quality on the neighboring beam, using special channel sounding packets on the neighboring beam.Control subsystem 103 then instructs theantenna subsystem 102 to switch back to the currently selected beam and resumes transmission of normal data packets. This is done to ensure that the delivery of data packets is not affected in case the signal quality on the neighboring beam is very poor. - In certain cases, the interference experienced may be periodic. Furthermore, some base stations operate periodically, alternating between short “busy” periods and long “quiet” periods. If tracking is performed periodically, there is a chance that tracking will only occur during the “quiet” periods, and the base station will be “missed”.
- To overcome these problems, in another embodiment, the mobile device performs tracking at aperiodic intervals to remove the impact of this periodic interference on the SINR measurements. In one embodiment, the aperiodic intervals are pseudo-random.
- In one embodiment, in optional step 633, the
control subsystem 103 builds a list showing performance for all combinations of base stations, channels and beams in step 633. As previously explained, performance may be measured by signal quality or other measures, or a combination of signal quality and other measures. As has also been previously explained, signal quality can be measured by, for example, SNR, SINR, BER, or a score calculated from a function which takes in measures such as SNR and SINR as inputs, and produces the score as an output. - If, for example, using the list built in step 633, or otherwise, the
control subsystem 103 finds a better combination of base station, channel and beam than the currently selected combination of base station, channel and beam (step 633A), then it moves to select the better combination instep 634. For example, in the embodiment described above with reference toFIG. 6G , if beam 915B offers better performance than 915A, then controlsubsystem 103 selects beam 915B. If not, then beam 915C is tested. If 915C is found to be better, then controlsubsystem 103 selects beam 915C. In another embodiment, thecontrol subsystem 103 selects the better combination instep 634, only if thecontrol subsystem 103 determines that the improvement in signal quality persists for a predefined period. - If not, then control
subsystem 103 continues searching for a better combination of base station, operating channel and beam. In one embodiment, this involves selecting a new subset of available channels and beams (step 631). - After the
control subsystem 103 has selected the better combination instep 634, in step 635 thecontrol subsystem 103 establishes a new operating link to the selected base station using the new channel and beam. - In
step 636, communication over the newly established operating link begins. Optionally, the candidate set of beams and channels will also be updated. For example, with reference toFIG. 6G , ifcontrol subsystem 103 communicates using beam 915B, then in the next tracking downtime, beams 915D and 915A will be tested. Ifcontrol subsystem 103 communicates using beam 915C, in the next tracking downtime, beams 915E and 915A will be tested. - In another embodiment, the
control subsystem 103 searches for a standby combination of base station, channel and beam, in case the current operating link fails. In one embodiment, thecontrol subsystem 103 periodically performs steps 631-633 ofFIG. 6C in the background. If the current operating link fails, then thecontrol subsystem 103 selects the best combination of base station, channel and beam identified; establishes a new operating link over this combination; and communicates over this newly established operating link. - The process outlined above to select base station, operating channel and beam based on signal quality offers advantages over making decisions based on signal strength. An illustrative example of these advantages is shown in
FIG. 7 .FIG. 7 which shows a mobile device 701 containing a smart antenna system, with wireless test links tobase stations 702 and 703. Device 701 determines that base station 702 provides better signal quality thanbase station 703. Device 701 then has to select a beam. It decides to selectbeam 712 overbeam 711, for the following reason: Device 701 can establish a test link to base station 702 with eitherbeam beam 711 is stronger thanbeam 712 because base station 702 is closer to the center ofbeam 711. However, if thecontrol subsystem 103 selectedbeam 711, then it would have to contend with interference frombase station 703, and therefore the SINR would be lower.Control subsystem 103 choosesbeam 712 because it offers lower interference, and consequently a better signal quality, than withbeam 711. -
FIG. 8 shows the coverage for thebase stations FIG. 2 but with the mobile/nomadic devices 511 and 513 using smart antennas. Compared toFIG. 2 the coverage 503 for the base-station 401 and the coverage 504 for the base-station 402 are much larger, almost covering the entire area ofinterest 405. Mobile device 511 selects beam 512 that provides good signal strength frombase station 401 and provides good isolation from (rejection of)base station 402, which means good SINR and therefore signal quality. Similarly mobile device 513 selects beam 514 that includesbase station 402 but excludesbase station 401. - While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (16)
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US20160182163A1 (en) * | 2014-12-18 | 2016-06-23 | Mediatek Inc. | Method for determining an optimum set of transmitting/receiving beams and a communications device utilizing the same |
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GB0102384D0 (en) * | 2001-01-31 | 2001-03-14 | Secr Defence | Signal detection using a phased array antenna |
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US20160344445A1 (en) * | 2015-05-22 | 2016-11-24 | Qualcomm Incorporated | Coefficient determination for digital subscriber line vectoring |
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US8706109B1 (en) | 2014-04-22 |
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