WO2015133890A1

WO2015133890A1 - Method for adjusting transmission power in wireless network and system thereof

Info

Publication number: WO2015133890A1
Application number: PCT/MY2015/050008
Authority: WO
Inventors: Wahidah Hashim; Rajina M. RAJ
Original assignee: Mimos Berhad
Priority date: 2014-03-06
Filing date: 2015-02-27
Publication date: 2015-09-11
Also published as: MY184565A

Abstract

The present invention discloses a method for controlling transmission power in real time of a wireless communication system having at least one local access point and a plurality of remote access points. Preferably, the method involves calculating (101) the estimated RSS and scans (104) for the actual RSS. Consequently, the interference of each access point is defined through the comparison of the actual and estimated RSS. Also, the interference of each access point will be analyzed (200) and lastly followed by adjusting (300) the transmission power of each access point according to the interference analysis.

Description

METHOD FOR ADJUSTING TRANSMISSION POWER IN WIRELESS NETWORK AND SYSTEM THEREOF

FIELD OF INVENTION

The present invention relates to wireless network communication system and method. More particularly, the present invention relates to a method for adjusting the transmission power of access point to reduce the interference and system thereof. BACKGROUND OF THE INVENTION

Communication devices such as access points that include adaptive channel selection are known in the art. When a local access point detects the presence of other access points, the access point is configured to select a more efficient channel. Conventionally, 14 channels are available in 802.11b and 802. llg wireless networks. However, countries like the United State and Canada only utilize channels between the frequencies range of 2.4 GHz (channel 1) to 2.448 GHz (channel 11). As for other countries, channels 12 to 14 are employed. As shown in figure 1 , the channels are separated by 5 MHz having a bandwidth of 22 MHz. As a result, it is only possible to find at most 3 non-overlapping channels such as channel 1, 6, 11 or 2, 7, 12, or 3, 8, 13 or 4, 9, 14 or 5, 10.

Adjacent channel interference may arise due to the channels are only 5 MHz apart. In order to achieve non-overlapping channels in 802.11b/g/n, channels 1, 6, and 11 are used to provide 25 MHz channel separation or 20 MHz channel separation for Europe countries. Adaptive channel selection function that enables these access points to switch from one channel to another may not adhere to the limited 3 non-overlapping channel. The access point possibly switches into quieter channel which may be the neighboring of these non-overlapping channels. The harmonics of these neighboring channels could cause adjacent channel interference to non-overlapping channels as illustrated in figure 2.

Due to the limited numbers non-overlapping channels, frequency reuse of the channels follows a three-to-one pattern as shown in figure 3. If only three channels are available for a channel reuse pattern, the access point will be on the same channel within hearing distance of each other. For example, transmission of a communication device at point A can propagate into another cell using the same channel. This may induce co-channel interference which may affect the transmission from other access points on different cell but using the same channel. Transmission deferment occurs since Wi-Fi uses a listen-before-you-talk technology called the clear channel assessment (CCA) to ensure that only one radio can transmit on the same channel at any given time. During the transmission of an access point on a particular channel, the nearby access points and clients on the same channel will defer the transmission. Consequently, the transmission time of the nearby access points and clients is increased as a result of the turns taking by the mistaken interference. In addition, physical obstructions that cause multipath fading to the signals as well as the electronic magnetic effect of other devices is another crucial factor. There are a few patented technologies over the prior art attempt to solve the abovementioned drawbacks. Of interest in respect to a method and apparatus for reducing interference in wireless network is United State Patent No. 20110167291 Al. This patent provides a method and apparatus for reducing interference in wireless network comprising the steps of receiving, by a transmitter, a report from an associated client, setting and using a downlink or uplink transmit power level responsive to the report for data transmissions to the associated client, determining a downlink or uplink data loss rate and adjusting the downlink or uplink transmit power level responsive to the downlink or uplink data loss rate, wherein said report includes received signal strength, client transmit power level and one of link margin and receiver sensitivity. The patent relies on the communication between access point and station in order to obtain the wireless link data and performance. Access point to station communication is associated with the problem of using the medium on which control is performed, which is not always available. Furthermore, in response to occurrence of interference, most system either reduce the data transferring rate or increase the transmission power which will lead to other issues such as the signal-to- noise-interference ratio (SINR).

Therefore, an alternative method and system are needed to overcome the abovementioned drawbacks. The present invention provides such a method and system.

SUMMARY OF INVENTION The present invention provides a method for controlling transmission power in real time of a wireless communication system having at least one local access point and a plurality of remote access points comprises the steps of: calculating the expected relative signal strength (RSS) of each remote access points in relative to the local access points; scanning the actual RSS of each remote access points in relative to the local access points; analyzing the interference of each remote access point in relative to the local access points based on the comparison of the expected RSS and actual RSS; and adjusting the transmission power of the remote access points according to the interference analysis. In one embodiment of the invention, the interference analysis comprises the steps of: measuring the difference between the expected and actual RSS to compute an interference value for each remote access point; classifying interference threshold value into low, medium and high; and mapping each interference value to the threshold classification and indicating the corresponding access point as low, medium or high.

In another embodiment of the invention, the transmission power adjustment comprises the steps of: measuring the number of access point indicating as high or medium; measuring the number of access point indicating as low; classifying the transmission power into high, medium, or low; setting the transmission power into low if the number of access point indicating as high is more than low; and setting the transmission power into high or medium if the number of access point indicating as low is more than high.

Preferably, the expected RSS, actual RSS, interference value of each access point, classification of interference, time, and corresponding access point information are stored in a database. Furthermore, the interference threshold value is classified as low when the interference value is below noise level, medium when the interference value is in between the noise level and RSS of the corresponding access point, and high when the interference value is larger than RSS of the corresponding access point. The present invention also provides a system for controlling transmission power in real time of a wireless communication system having at least one local access point and a plurality of remote access points comprises: a power adjustment module incorporated with each access point, configured to execute the abovementioned method; wherein the power adjustment module comprises a monitoring unit for measuring and inspecting the expected and actual RSS between the local and remote access points; an assessment unit for analyzing and comparing the interference value of each access point to the interference threshold classification; and a decision unit for executing and performing the configured functions. In one embodiment of the invention, the system further comprises a database for storing the acquired data. An interference reduction technique is provided by calculating the communicated channel cost of interference. Once the cost of interference is determined, it will be compared with the noise level threshold. If the interference is above the noise level, the transmission power will be reduced instead of boosting the power further on.

One skilled in the art will readily appreciate that the invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated. Figure 1 shows the WLAN channels spectrum at 2.4 GHz Bandwidth.

Figure 2 shows the adjacent channel interference in neighboring WLAN channels. Figure 3 shows the co-channel interference in WLAN communication.

Figure 4 shows an example of how the transmission power adjustment process can be applied, in accordance to the preferred embodiment of the invention. Figure 5 is a flowchart illustrating an overall view of a transmission power controlling process, in accordance to the preferred embodiment of the invention.

Figure 6 is a flowchart of a signal strength measurement process, in accordance to the preferred embodiment of the invention.

Figure 7 is a flowchart of an interference analysis and evaluation process, in accordance to the preferred embodiment of the invention.

Figure 8 is a flowchart of a power adjustment process, in accordance to the preferred embodiment of the invention. Figure 9 is a schematic block diagram of a power adjustment module, in accordance to the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in greater detail, by way of example, with reference to the drawings.

The method and system of the invention can be implemented in a number of different ways, and incorporating a variety of different components and technologies. However, the various embodiments of the invention have some common elements. First, the devices or access points are immobile so that the physical distance is known. Second, the common transmission power is introduced per-cell basis and not per-client basis to avoid throughput starvation due to asymmetric links. Third, the interference is detected when there is a difference between expected RSS and actual RSS. And lastly, reducing the interference through adjusting the transmission power of the access points. Specifically, reducing the transmission power in a way such that the coverage overlapping is reduced and followed by increasing the transmission power whenever the dynamic interference is gone.

The invention faces the interference through decreasing the transmission power of the access point. The coverage of the access point will reduce as the transmission power decrease. In an example as shown in figure 4, if an interference source on the outer edge of the coverage area of an access point, the interference source can be eliminated by shrinking the coverage area. Assuming that an access point B is within the reduced coverage zone at point CI, this can significantly decrease the co-channel interference and improves the overall performance. However, if the access point B is at point C2 where the coverage may interfere by the interference source, power adjustment following the level of interference which creates an impact to the communication channel is needed. In this scenario, the access point B may calculate the interference of its own channel. If the interference is more than allowable noise threshold, the access point B decreases the transmission power. The decrement in transmission power reduces the coverage but at least the system does not have to deal with the interference which deteriorates the transmitted data.

As shown in figures 5, the method for controlling transmission power in wireless network comprises the steps of scanning and measuring (100) relative signal strength and updating information in the database; analyzing and evaluating (200) the interference; and adjusting (300) the transmission power based to the evaluation. The wireless network preferably is but not limited to a wireless LAN mesh network, wireless personal area network, wireless local area network, wireless metropolitan area network, wireless wide area network, and any cellular networks. Preferably, the first stage of the power controlling process (100) as illustrated in figure 6, involves measuring the physical distance between local and remote access points. The step will be performed in the beginning of set up or when there is any change in the floor plan and number of access points. Then, the expected path loss with respect to the physical distance can be calculated by using the standard free space path loss model with a constant value of 92.45. Next, the expected received power formula is determined through the transmit or receive antenna gain or losses and miscellaneous losses such as cable or connectors. The expected RSS of each remote access point is calculated (101) by using the well known expected received power formula thereof. Assuming all the remote access points are stationary and each location is known, the physical distance relative to the corresponding access point can be calculated for record. The expected RSS can be acquired as the free space path loss value is defined and the physical distance is known. Also, the signal attenuation (loss) relative to the physical distance can be estimated. The acquired information is preferably stored (102) in a centralized database (420). The acquired information can be transferred to the centralized database (420) through any suitable network protocol or transfer technology. Followed by the actual RSS of each remote access point is scanned (103) through incorporated received signal strength indicator (RSSI) reader such as receiving antenna in real time (104) and the acquired information is forwarded (105) to the centralized database (420) for comparison.

In one embodiment of the invention, the acquired information is stored in the information base table. One example of the information base table is shown in table 1. Alternatively, the information base table is updated based on a time schedule by a suitable program or module. Access Point A Access Point B Access Point C

Inventive Expected Actual Expected Actual Expected Actual

Access RSS RSS RSS RSS RSS RSS point XA ΧΆ XB X'B Xc X'c

Table 1, an example of the information base table in accordance to the preferred embodiment of the invention.

Referring to figure 7, the step of analyzing and evaluating (200) the interference comprises the steps of measuring (201) the difference between the expected and actual RSS for each access points and the interference value is defined by the degradation value of the RSS; classifying (202) the interference threshold value into low, medium, and high categories; setting (203) the interference threshold value as low when the interference value is below noise level; setting (204) the interference threshold value as medium when the interference value is greater than the noise level with an additional margin of X and less than the RSS of the corresponding access point, wherein X can be configured as 5 or 10 decibels depending on the sensitivity of the device, and setting (205) the interference threshold value as high when the interference value is larger than RSS of the corresponding access point; storing (206) the interference value, corresponding access point information, time, and classification into the centralized database (420); and mapping (207) each interference value to the threshold classification and indicating the corresponding access point by the classification.

In another embodiment of the invention, the interference threshold is defined as low when the difference between the expected and actual RSS is below 10% of the expected RSS, as medium when the difference between the expected and actual RSS is in between 10% and 25% of the expected RSS, and as high when the difference between the expected and actual RSS is more than 25% of the expected RSS. However, the percentage may vary as it depends on the range of tolerance of the system. If the system can tolerate low as the interference value up to 30% difference, it means that the system is very robust to withstand such high interference value.

Referring to figure 8, the step of adjusting (300) the transmission power involves ranking (301) the access point with the highest interference to the lowest interference; counting (302, 303) the number of access point of each classification (low, medium, and high); reducing (305) the transmission power of local access point if the number of access points indicated as high is more than low; increasing (304) the transmission power of local access point if the number of access point indicated as low is more than high. Since the system operates in real time, the transmission power can be increased until less high value interference access point is detected, or another way round. Preferably, the transmission power is categorized into low, medium, and high.

Figure 9 depicts a block diagram of the power adjustment module (400) according to the preferred embodiment of the invention. The module comprises a monitoring unit (410) responsible for measuring and inspecting the expected and actual signal strength between local and remote access point and store the information in a database (420), assessment unit (430) that analyzes and evaluates the signal power, interference, and mapping the interference with the configured thresholds classification, a decision unit (440) which regulates the access point transmission power with respect to the level of estimated interference. Preferably, the monitoring unit (410) includes a signal strength measurement inspector (411) connected to the centralized database (420), the inspectors (411) measures the expected and actual RSS and stores the information to the centralized database (420). The assessment unit (430) includes a signal power and interference analyzer (431) connected to the centralized database (420) for analyzing the interference through the described method and a signal power and interference evaluator (432) linked to the analyzer (431) for classifying and comparing interference threshold value. The decision unit (440) may comprise a transmission power self-regulator (441) coupled with the evaluator to perform the adjustment method as described.

The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.

Claims

1. A method for controlling transmission power in real time of a wireless communication system having at least one local access point and a plurality of remote access points comprising the steps of: calculating the expected relative signal strength (RSS) of each remote access points in relative to the local access points (101); scanning the actual RSS of each remote access points in relative to the local access points (104); analyzing the interference of each remote access point in relative to the local access points based on the comparison of the expected RSS and actual RSS (200); and adjusting the transmission power of the remote access points according to the interference analysis (300).

2. A method according to claim 1, wherein the interference analysis comprises the steps of:

measuring the difference between the expected and actual RSS to compute an interference value for each remote access point (201);

classifying interference threshold value into low, medium and high (202); and mapping each interference value to the threshold classification and indicating the corresponding access point as low, medium or high (207).

3. A method according to claim 1, wherein the transmission power adjustment comprises the steps of: measuring the number of access point indicating as high or medium (302);

measuring the number of access point indicating as low (303);

classifying the transmission power into high, medium, or low;

setting the transmission power into low if the number of access point indicating as high is more than low (305); and

setting the transmission power into high if the number of access point indicating as low is more than high (304).

4. A method according to claim 1, wherein the expected RSS, actual RSS, interference value of each access point, classification of interference, time, and corresponding access point information are stored in a database (420).

5. A method according to claim 2, wherein the interference threshold value is classified as low when the interference value is below noise level (203).

6. A method according to claim 2, wherein the interference threshold value is classified as medium when the interference value is in between the noise level and RSS of the corresponding access point (204).

7. A method according to claim 2, wherein the interference threshold value is classified as high when the interference value is larger than RSS of the corresponding access point (205).

8. A system for controlling transmission power in real time of a wireless communication system having at least one local access point and a plurality of remote access points comprising:

a power adjustment module (400) incorporated with each access point, configured to execute the method as claimed in claim 1 ;

wherein the power adjustment module (400) comprises a monitoring unit (410) for measuring and inspecting the expected and actual RSS between the local and remote access points;

an assessment unit (430) for analyzing and comparing the interference value of each access point to the interference threshold classification; and

a decision unit (440) for executing and performing the configured functions.

9. A system according to claim 8, further comprising a database (420) for storing the acquired data.