US 20090268671 A1
A startup process of an access point (AP) includes a discovery phase and an announcement phase. During the discovery phase, the AP detects neighboring APs from its own extended service set (ESS), neighboring APs from different ESSs, and external sources of interference. During the announcement phase, the AP transmits its beacon signals at maximum power in order to accelerate recognition by neighboring APs running the discovery phase. An automatic initialization channel selection process of an AP scans channels the AP will use to communicate. Information of each scanned channel is recorded and a best performance channel is determined for use by the AP.
1. A method of optimizing the selection of channels used by an access point (AP), the method comprising:
the AP determining a plurality of candidate channels, wherein the candidate channels are chosen from an allowable channel set (ACS) on a condition that a detected interference of each candidate channel does not exceed an established maximum allowed interference;
determining a number of beacons detected on each of the candidate channels; and
selecting at least one of the candidate channels on which a smallest number of beacons was detected and on a condition that there are at least two candidate channels which have an interference level that does not exceed a predetermined minimum interference level.
2. The method of
measuring an interference level on each of the selected candidate channels; and
selecting at least one of the selected candidate channels having an interference level that does not exceed the predetermined minimum interference level.
3. An access point (AP) comprising:
the AP configured to:
determine a plurality of candidate channels;
determine a number of beacons detected on each of the candidate channels; and
a channel selector configured to:
select at least one of the candidate channels on which a smallest number of beacons was detected; and
select at least one of the candidate channels randomly on a condition that there are at least two candidate channels which have an interference level that does not exceed a predetermined minimum interference level.
4. The AP of
a measuring unit configured to measure an interference level on each of the candidate channels selected by the channel selector on a condition that more than one candidate channel is selected; and
the channel selector is further configured to select at least one of the candidate channels having a measured interference level that does not exceed the predetermined minimum interference level.
This application is a continuation of U.S. patent application Ser. No. 12/256,521, filed Oct. 23, 2008, which issued as U.S. Pat. No. 7,558,571 on Jul. 7, 2009, which is a continuation of U.S. patent application Ser. No. 11/332,973, filed Jan. 17, 2006, which issued as U.S. Pat. No. 7,454,205 on Nov. 18, 2008, which is a continuation of U.S. patent application Ser. No. 10/978,956, filed Nov. 1, 2004, which issued as U.S. Pat. No. 7,016,684 on Mar. 21, 2006, which claims the benefit of U.S. Provisional Patent Application No. 60/526,134, filed on Dec. 1, 2003, U.S. Provisional Patent Application No. 60/535,019, filed on Jan. 8, 2004, and U.S. Provisional Patent Application No. 60/535,073, filed on Jan. 8, 2004, which are incorporated by reference as if fully set forth.
The present invention relates to a wireless communication system. More particularly, the present invention relates to initializing operating parameters and selecting the most appropriate operating channel for an access point (AP).
The conditions of a radio link under which a wireless communication system operates may change at any time. Since a wireless transmit/receive unit (WTRU) is mobile, the WTRU may be out-of-range, or within range of one or more APs depending upon the position of the WTRU. When an AP is newly established, or powers up again after powering down for some reason, the startup process of the AP must evaluate its radio resource environment. Typically, the startup process also provides a mechanism for announcing itself to other APs of its own extended service set (ESS) such that the other APs can self-adjust their own operating parameters accordingly.
There are several current schemes that are employed in order to increase the capacity of a wireless communication system. Channel, i.e., frequency, selection is one of such schemes, whereby one or more APs in a network select one or more channels to communicate with their associated WTRUs. Coordination of AP channel selection is usually performed manually. However, it is very impractical to manually coordinate channel selection in response to every small change in the network configuration since it may cause a redesign and reconfiguration of all APs. Unlicensed spectra and external sources of interference also raise problems that are not adequately addressed by manual coordination. Moreover, it is difficult for manual channel selection to assign channels such that the traffic loads of neighboring APs are shared among the available channels in a way that maximizes overall system capacity.
Another problem with prior art schemes is encountered when multiple APs attempt to power-up simultaneously. When this occurs within a network, all of the APs try to make a channel selection at the same time. Thus, the channel selection by the APs would not be optimal since each AP does not take into account the channel selection of neighboring APs.
A method and system which overcomes the above-mentioned problems would be greatly beneficial.
The present invention provides a method and apparatus for implementing startup and initial channel selection processes for an AP.
The startup process of the AP includes a path loss discovery phase and an announcement phase. During the path loss discovery phase, the AP detects neighboring APs from its own ESS, neighboring APs from different ESSs, and external sources of interference. During the announcement phase, the AP transmits a beacon signal in order to accelerate recognition by neighboring APs also running the path loss discovery phase. The startup process provides the AP with the ability to monitor and evaluate its radio environment, and therefore allows the AP to self-determine initial operating parameters.
An initialization channel selection process for an AP is automatically implemented when the AP's startup process begins.
A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein:
Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment.
Hereinafter, the terminology “AP” includes but is not limited to an access point, a base station, Node-B, site controller, or any other type of interfacing device in a wireless environment.
The features of the present invention may be incorporated into an IC or be configured in a circuit comprising a multitude of interconnecting components.
The present invention as described herein, is generally applicable to wireless local area network (WLAN) technologies, as applied to the IEEE 802.11 and ETSI HyperLAN specifications in general, but is envisaged to be applicable to other interference-limited wireless systems such as IEEE 802.15 and IEEE 802.16.
The channel selector 130 selects a channel which is used for communication with each WTRU 110 a-110 n. The measuring unit 135 measures operating parameters for supporting the AP 105. The measuring unit 135 is responsible for collecting, processing and storing channel measurements including, but not limited to: the channel utilization (i.e., percentage of time that the channel is busy), the level of external (non 802.11) interference, the received signal strength measured on received packets, and the like. The power controller 140 controls the transmission power of the AP 105. The timer 145 sets one or more predetermined periods during which the AP 105 performs certain operations. The memory 150 provides storage for the AP 105, including recording data such as results of the measurements.
In step 212 of the discovery phase 210, the measuring unit 135 measures the operating parameters by performing Nmeas
The duration of Tmpp
As a result of these measurements, the AP 105 can determine its radio environment, such as a detection of neighboring APs from its own ESS, a detection of neighboring APs from different ESSs, and a detection of external sources of interference.
Referring back to
During the discovery phase 210, the AP 105 remains silent (i.e., the AP 105 does not transmit any packets). Upon completion of the discovery phase 210, the AP 105 has gathered enough information to determine an optimal operating channel and select a transmission power setting.
After the discovery phase 210 ends, an announcement phase 220 follows. During the announcement phase 220, the AP configures its operating channel to the optimal channel determined at the end of the discovery phase 210. It should be noted that other processes may be performed in the interim as necessary. The purpose of the announcement phase 220 is to accelerate the detection of the AP by its neighboring APs. In the beginning of the announcement phase 220, various parameters, (e.g., Tdur Announce, Tbeacon Announce, PMax), and are initialized (step 221). During the announcement phase duration Tdur Announce, the AP 105 only transmits beacon frames having a maximum transmission power PMax with period Tbeacon Announce (step 222). This accelerates the detection of the AP 105 by other APs, because only maximum power packets are transmitted. During the announcement phase 220, WTRUs beyond the coverage range of the AP 105 may attempt to associate with the AP 105, because the AP 105 is transmitting at its maximum power. For this reason, all association requests from WTRUs are denied during the announcement phase 220 in order to avoid associating a WTRU that will be out of range during normal operation.
Once the announcement phase 220 ends, the startup of the AP 105 is complete. The AP 105 then configures itself for its normal operation (step 223) and begins normal operation (step 230). The AP 105 sets its transmission power to the setting determined by the power controller 140, after which the AP 105 begins normal operation and starts accepting association requests from the WTRUs 110.
The initialization channel selection process 300 is performed during the startup process 200 and determines the best operation channel. In the preferred embodiment, channels are being scanned during the discovery phase 210. At the end of the discovery phase 210, the channels selection process is invoked in step 214 to select the best channel based on the measurements observed on each channel during the discovery phase 210. In all cases, the initialization channel selection process 300 scans a plurality of channels (e.g., channels 1-11) to detect the best channel available. The sequence of scanned channels may be in a predetermined order, or it may be random. The channel sequence does not need to include all available channels. For each channel scanned, the process determines: (1) what other APs are operating on that channel; (2) whether the APs are part of the same system, (i.e., according to the ESS); (3) the signal strength of the APs; (4) the amount of traffic on the channel; and (5) if there are any other sources of interference on the channel (e.g., non-802.11 interference) and the received power level on non-WLAN interference. After the scanning is complete, the AP can calculate which channel would give the best performance (e.g., the channel that has the least amount of interference). The AP then retunes itself to that channel. Depending on whether the other APs detected are part of the same system, the AP can decide to be more or less aggressive in the choice of channel to use.
In an alternate embodiment, coordinated frequency selection may be accomplished by: (1) having APs exchange information with each other about their properties (e.g. load, capabilities or position); or (2) having a centralized scheme that can obtain information from each AP, and setting the channel of all APs in the network. For the first case, the decision is still made autonomously by each AP, but the information exchanged can allow a better decision (e.g., it can include statistics that are difficult to observe externally by another AP). For the second case, information is gathered from the different APs and communicated to a centralized unit or device, which upon reception of the information takes a decision and communicates the decision back to the different APs.
Referring still to
After the scanning is complete, the AP 105 determines which channel provides the best performance (step 325). This may be determined, for example, by measuring which channel has the least amount of interference or whether other APs are part of the same ESS. Once the channel having the best performance is determined, the AP 105 tunes itself to the best channel.
In the candidate channel determination process 405, the AP 105 retrieves the maximum allowed interference IMAX (step 410), which is the maximum allowed interference on any given channel determined based on the baseline range of an AP. IMAX may be obtained from the power control process. IMAX is calculated by the initialization channel selection process 400 using Equation (1) below. Some of the parameters that are used in Equation (1) are retrieved from the power control process. Specifically, power control will determine RNGbase. PMAX, (C/I)req
where PMAX is the maximum transmission power of the AP 105; RNGbase is the range covered by the AP 105; and (C/I)req
A first channel is selected from an ACS (step 415). Interference I of a channel is measured and compared with the maximum allowed interference IMAX (step 420). If the interference I of the channel is less than the maximum allowed interference IMAX, the AP 105 records the channel in a candidate list in the memory 150 (step 425). If the interference I of the channel is not less than the maximum allowed interference IMAX, the AP 105 checks whether any more channels in the ACS exists (step 430). If more channels in the ACS exist, the AP 105 selects next channel from the ACS (step 435) and the candidate channel determination process 405 then returns to step 420.
If no more channels exist in the ACS, the AP 105 checks whether any candidate channel is available (step 440). If, in step 440, it is determined that no candidate channel is available, the AP 105 increases IMAX by ΔdB (step 445) and the candidate channel determination process 405 returns to step 415. If, in step 440, it is determined that at least one candidate channel exists, the candidate channel determination process 405 is complete and the channel selection process 450 is then performed.
One criterion used by the channel selection process 450 is the number of neighboring BSSs that have been detected on each channel NB(k). Once the candidate channels are selected, the minimum number of detected beacons from different BSSs, among all candidate channels, NB MIN is determined (step 455). The number of neighboring BSSs that have been detected on channel k, NB(k), is compared with the minimum number of detected BSSs, NB MIN, and all channels for which NB(k)>NB MIN are removed from the list of candidate channels (step 460). In other words, only the channels with the minimum number of detected BSSs are retained. Alternatively, in steps 455 and 460, the number of detected neighbor BSSs on each channel could be replaced with the channel utilization on each channel. The channel utilization measurement corresponds to the percentage of time that the receiver is carrier locked by a WLAN signal. In this case, the channel selection process would favor channels that have lower channel utilization.
Another criterion used by the channel selection process is the minimum measured interference level, which is determined among all remaining candidate channels (step 465). The minimum measured interference level on channel k I(k) and the minimum interference level IMIN are compared, and all channels for which I(k)>IMIN from the list of candidate channels are removed (step 470). In other words, only the channels with the minimum interference level are retained.
If more than one candidate channel with the minimum interference level exists, a channel is randomly selected among the remaining candidate channels (step 475).
Exemplary parameters of the initialization channel selection process are listed in the following Table 2. As those of skill in the art would realize, other parameters and values may be used in addition, or in place of, these values.
Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone or in various combinations with or without other features and elements of the present invention.