HK1109290B - Wireless communication method and apparatus for optimizing access point channel selection - Google Patents

Description

Wireless communication method and apparatus for optimizing access point channel selection

Technical Field

The present invention relates to a wireless communication system. More particularly, the present invention relates to selecting the most appropriate operating channel for an Access Point (AP).

Background

The conditions of a radio link in 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 on its location.

The capacity of a communication system is sometimes limited due to bandwidth considerations. The bandwidth capacity of the communication channels available for the communication system to communicate data is limited and must be shared among a plurality of APs and portable WTRUs.

Several architectures are used today to increase the capacity of wireless communication systems. Channel (i.e., frequency) selection is one such architecture whereby one or more APs in a network select one or more channels to communicate with other associated WTRUs. The coordination of AP channel selection is typically done manually. However, it is highly impractical to manually coordinate channel selection in response to every small change in network configuration, as this may result in a redesign and reconfiguration of all APs. Unlicensed spectrum and external sources of interference can also cause problems that manual coordination cannot adequately address. Furthermore, it is difficult to assign channels by manual channel selection such that the traffic load of neighboring APs is amortized over the available channels in a manner that maximizes overall system capacity.

Another problem with existing architectures is that they suffer when multiple APs attempt to boot up simultaneously. When this occurs within a network, all APs attempt to make a channel selection at the same time. Therefore, the channel selection of APs may not be optimal because each AP does not take into account the channel selection of neighboring APs.

A method and apparatus that automatically optimizes channel selection to avoid the aforementioned problems associated with existing manual channel selection processes would be highly advantageous.

Disclosure of Invention

The present invention relates to a wireless communication method and apparatus for optimizing channel selection of an AP. The device may be an AP and/or an Integrated Circuit (IC).

The channel selection optimization process includes four sub-processes: 1) a measurement process; 2) a candidate channel determination process; 3) a channel selection process; and 4) a channel update procedure. Candidate channels for supporting communication by the AP are determined. The candidate channels are selected from an Allowable Channel Set (ACS) conditioned on the measured interference for each candidate channel being less than a determined maximum allowable interference.

Drawings

The invention will be described in detail below, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a wireless communication system in accordance with the present invention;

FIG. 2 is a flow chart of a channel optimization process according to an embodiment of the present invention; and

fig. 3A-3B fig. 3A and 3B are connected together and are a detailed flow chart of a channel selection process according to another embodiment of the invention.

Detailed Description

Hereinafter, the term "WTRU" includes, but is not limited to, a User Equipment (UE), a mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment.

Hereinafter, the term "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 implemented within a circuit comprising a plurality of interconnected components.

As described below, the present invention is generally applicable to Wireless Local Area Network (WLAN) technologies, such as IEEE 802.11 and ETSI HyperLAN specifications, but may also be applied to other interference-limiting wireless systems, such as IEEE 802.15 and IEEE 802.16.

Fig. 1 is a block diagram of a wireless communication system 100 in accordance with the present invention. The wireless communication system 100 includes an AP 105 and a plurality of WTRUs 110a-110 n. The AP 105 communicates with the WTRUs 110a-110n via an antenna 120 over a wireless link 115. The AP 105 includes a transceiver 125, a channel selector 130, a measurement unit 135, a power controller 140, a timer 145, and a memory 150. The transceiver 125 transmits signals 115a-115n to and receives signals 115a-115n from the WTRUs 110a-110n via the antenna 120.

The channel selector 130 selects a channel for contact with each of the WTRUs 110a-110 n. The measurement unit 135 measures operational parameters for supporting the AP 105. The measurement unit 135 is responsible for collecting, processing and storing channel measurements including, but not limited to: channel usage (i.e., the percentage of time the channel is busy), the level of external (non-802.11) interference, the received signal strength measured from the 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 for the AP 105 to perform certain operations. The memory 150 provides storage capability for the AP 105, including recording data such as measurement results.

Fig. 2 is a flow chart of a channel optimization process 200 in accordance with the present invention. Channel optimization refers to the process of selecting the best channel (i.e., frequency) for use by a particular AP or APs network under particular data transmission conditions. Channel optimization may be performed manually or automatically, and may be initiated at deployment or dynamically during operation. The channel optimization process 200 may be implemented in conjunction with a Wireless Local Area Network (WLAN) application, such as in accordance with IEEE 802.11.

As shown in fig. 2, the channel optimization process 200 begins at step 205. The channel optimization process 200 dynamically determines the best operating channel during normal system operation without causing the associated WTRUs in the BSS to experience a service outage. In step 210, the AP 105 periodically scans each of a plurality of channels for a short period of time to avoid service disruption to its associated users, and makes measurements on these channels. If it is determined in step 215 that the AP is operating during a low load period, i.e., no BSS traffic and/or no associated users, the AP 105 initiates the channel optimization process to determine whether a new channel is more suitable by calculating an "expected channel load" for each channel based on measurements taken during a high system load (step 220). In step 225, the AP 105 changes its operating channel to the channel with the lowest anticipated channel load.

In today's IEEE 802.11 networks, there is no mechanism (at least not in the underlying standard) for the AP 105 to inform the associated WTRU 110 of a change in the operating channel. If an AP 105 changes channels, each of its associated WTRUs 110 eventually understands that communication with the AP 105 has been lost and eventually begins searching for a new AP. It is likely to reselect the AP on the same AP's new operating channel. In any event, the problem is that WTRUs experience a service interruption from the time they lose communication with the AP to the time they re-associate with the AP on the new channel. To avoid service interruption, the channel optimization process 200 waits until there is no traffic in the BSS (cell) before changing channels. On the other hand, some versions of the IEEE 802.11 standard (i.e., IEEE 802.11h and possibly a future version of the standard) may allow an AP to signal to its WTRUs to change channels. In this case, the channel optimization process 200 does not have to wait until there is no BSS traffic. Thus, the channel optimization process 200 is run periodically and changes the operating channel whenever needed.

In all cases, the channel optimization process 200 scans a sequence of channels (e.g., a list of channels 1-11) to detect the best channel available. The channels may be scanned in a predetermined order, or the channels may be scanned randomly. The emphasis here is that channel scanning is not initiated when there is no BSS traffic. The channel scan occurs continuously throughout normal operation of the AP 105. For example, the AP 105 may take 5 milliseconds to listen to a different channel every 0.5 seconds. The AP may repeat this periodically, each time scanning a different channel. By doing so, the AP 105 steals 1% of the medium time (5 ms every 500 ms) to scan other channels with minimal impact on the associated users. The sequence of channels does not necessarily contain all available channels. Information about each AP detected on each channel is recorded. This information may include, but is not limited to, the identity of other APs operating on the scanned channel, an indication of whether other APs are part of the same ESS, the signal strength of APs, the amount of traffic on the channel, and whether there are any other sources of interference on the channel.

For each scanned channel, the process determines: 1) which other APs operate on the channel; 2) whether the APs are part of the same system (i.e., based on the ESS); 3) the signal strength of the APs; 4) traffic volume on the channel; and 5) whether there are any other interferers (e.g., non-802.11 interferers) on the channel. The amount of traffic on a channel is typically measured in terms of channel usage, which is equivalent to the percentage of time that the receiver is locked to a WLAN signal carrier.

The scanning occurs periodically and continuously. Once the channel optimization procedure is triggered (i.e., without BSS traffic and/or associated users, or simply a scheduled trigger mechanism, such as every 5 minutes), the AP 105 determines which channel provides the best performance. 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. Depending on whether the other APs detected are part of the same system, the AP can decide to be more aggressive or less aggressive with respect to the choice of channel to use.

In an alternative embodiment, the coordinated frequency selection may be accomplished by: 1) to have APs exchange information about their traits (e.g., load, capacity, or location); or 2) a centralized architecture that can obtain information from each AP and set the channels for all APs in the network. In the first case, each AP would still make a decision autonomously, but the information exchanged would allow a better decision (e.g., it could contain statistics that are difficult to observe externally by another AP). In the second case, information is collected from the different APs and communicated to a centralized unit or device, which makes a decision upon receipt of the information and communicates the decision back to the different APs.

The channel optimization process 200 is performed to select an optimal channel (e.g., a low-load channel) while a current channel is being used. The channel optimization process 200 may be triggered by one of the following conditions: 1) the last time the optimum channel selection was performed occurs is at least T_LastBefore second; 2) when there are no WTRUs currently associated with the AP; or 3) at the nearest T_FreeThere is no BSS traffic to and from the AP in seconds. Accordingly, T_LastIs the minimum elapsed time from the last activation of any channel selection process to the triggering of the channel optimization process 200; and T_FreeIs the minimum elapsed time from the last BSS packet transfer to or from the AP to trigger the channel optimization procedure 200.

By ensuring that there will be at least T before triggering the optimal channel selection in the aforementioned trigger conditions_FreeSecond without BSS traffic and then without WTRUs associated with the AP 105, the channel optimization process 200 does not interrupt any outgoing data transfers such as an incoming voice call, network download, and/or FTP transfer. On the other hand, if there is a way for the AP 105 to notify the associated WTRUs 110 that there is a change in the channel, the optimized channel selection process 200 may be run periodically without waiting for BSS traffic to be absent.

Fig. 3A and 3B are connected together and illustrate a detailed flow diagram of a channel optimization process 300 in accordance with the present invention. Channel selection optimization 300 includes four sub-processes: 1) a measurement process 305; 2) a candidate channel determination process 310; 3) a channel selection process 355; and 4) a channel update process 380.

In the measurement process 305, the average load of each neighboring BSS is calculatedIn one embodiment, the measurement unit 135 periodically estimates the load of each neighboring BSS. If any load estimate for a BSS is greater than L_MINThen the load of all neighboring BSSs for the estimation period is logged into memory 150. If all BSSs have less than L_MINThe load estimates are ignored. Only the most recent load estimate N is retained in memory 150_{load_est}And (4) collecting.

According to the preferred embodiment, the AP 105 listens to a particular channel of an ACS every Silence Measurement Period (SMP). The AP 105 listens to each channel in the wheel flow over successive SMPs and measures a separate set of measurements for each channel in the ACS. The measurement set contains as many SMPs as the number of channels in the ACS. In a known SMP, the Channel Usage (CU) of the channel is measured by a measurement unit 135. CU corresponds to the percentage of time that transceiver 125 is carrier locked. All packets that cause carrier lock of AP 105 are sourced from neighboring BSSs due to CU observation during an SMP. The CU measurements represent out-of-BSS channel usage. Processing individual CU measurements to obtain an average BSS load for each measured BSSNote that the BSS IDs for all BSSs on a channel are recorded along with each channel usage measurement.

Only high load measurements are recorded in order to avoid unnecessary history recording (logging). History recording corresponds to the recording or storage of measured values. As described earlier, the channel optimization process 300 only runs when there is no BSS traffic (i.e., not loaded). To reduce the number of logged measurements, the channel optimization process 300 only stores a predetermined number of high load measurements.

CU is less than C_MINAre excluded to ensure channel optimization based on measurements taken under a significant system load condition. In other words, if any of the CU measurements present in a measurement set is greater than C_MINThe entire measurement set is recorded. On the other hand, all channels are CU < C_MINThe measurement set of (3) is omitted. The measurement set may be the CU for each channel and the BSS IDs for all BSSs on the channel.

The channel optimization process 300 determines the best of its own BSSs based on individual channel utilization measurementsA good channel. Although the channel optimization should be based on measurements taken under significant system load conditions, the channel optimization process 300 may be performed only when the system load has been reduced. To avoid huge measurement history records, only the most recent measurement window N_SETIs retained in memory.

Referring back to fig. 3A, in the measurement process 305, the average load of each BSS is calculated based on the individual load of each BSS. The instantaneous load of BSS i operating on channel k during measurement set j is based on equation (1):

equation (1)

Where C (i, j) represents channel usage on channel k during measurement set j and N_BSS(i, j) represents the number of BSSs. The average load of BSS i is calculated as the average of the instantaneous loads in all recorded measurement sets according to equation (2):

equation (2)

Wherein N is_SETRepresenting the total number of recorded measurement sets. Plus a minimum average BSS load of 1%. The method of calculating the average load of each BSS is not limited to the above example.

Exemplary parameters for alternative measurement modes are listed in table 2 below. Those skilled in the art will appreciate that other parameters and values may be used in addition to or in place of these.

TABLE 2

In the candidate channel determination process 310, the AP 105 retrieves the maximum allowable interference I_MAX(step 315) the maximum allowable interference determined on any known channel based on a baseline range of an AP. Preferably, I for the candidate channel determination process 310_MAXIs calculated according to equation (3):

I_MAX＝P_MAX-(RNG_base+RNB_adj)-(C/I)_{req_high}-M_I

equation (3)

Wherein (RNG)_base+RNG_adj) Is the range covered by the AP 105; and (C/I)_{req_high}Is set to the required carrier to power interference ratio for a high rate packet (e.g., 11 Mbps). Subtract a margin M_ITo eliminate the possibility that the channel has an interference level that is too close to the actual maximum allowed level.

A first channel is selected from an ACS (step 320). Then, the interference I of the channel is measured and compared with the maximum allowable interference I_MAXA comparison is made (step 325). If the interference I of the channel is less than the maximum allowable interference I_MAXThe AP 105 logs the channel into a candidate list in the memory 150 (step 330). If the channel interference I is not less than the maximum allowable interference I_MAXThe AP 105 checks whether any channels are present in the ACS (step 335). If there are channels remaining in the ACS, the AP 105 selects the next channel from the ACS (step 340) and the process 300 returns to step 325. If there are no more channels within the ACS, the AP 105 checks if there are any available candidate channels (step 345). If it is determined in step 345 that there are no available candidate channels, the AP 105 will I_MAXΔ dB is increased (step 350) and the channel optimization process 300 returns to step 320. If it is determined in step 345 that at least one candidate channel exists, a channel selection process 355 is performed, as shown in fig. 3B.

Channel selection procedure 355 is the average load per measured BSSAnd the current BSS-channel map β (k). Calculating a predicted channel utilization C for all channels_PRED(k) (step 360). C_PRED(k) Representing the expected channel usage for channel k expected using load estimates from high load conditions. C_PRED(k) Possibly quite different from the most recent channel usage measurement for channel k. Preferably with C_PREDRather than merely selecting a channel based on the most recent channel usage measurements, because channel selection should be optimized for high load conditions.

For each channel k, the average load of all measured BSSs on channel k is summed according to equation (4):

equation (4)

Once C of all candidate channels is calculated_PREDSelecting channel k with the smallest expected channel usage according to equation (5):

K＝arg_kmin[C_PRED(k)]equation (5)

At which point the AP 105 checks whether the selected channel k is different from a current channel (step 370). If the selected channel k with the least anticipated channel usage is the same as the current channel, the channel selection process 355 ends. If channel k is selected to be different from the current channel, it is determined if there is a significant benefit to changing channels (step 375). A hysteresis criterionIt is of sufficient benefit to ensure that the channel is changed. Specifically, a new channel is adopted as long as it satisfies the following conditions:

equation (6)

Otherwise, the optimal channel selection is ended.

Exemplary parameters for optimizing channel selection are listed in table 3 below. Those skilled in the art will appreciate that other parameters and values may be used in addition to or in place of these.

TABLE 3

A simpler channel selection algorithm may be based solely on logged channel usage measurements (i.e., selecting the channel that observes the lowest channel usage under high load conditions). However, it is likely that a situation will occur where neighboring APs have changed operating channels before a known AP initiates optimal channel selection. There are recorded CU measurements that do not accurately represent the channel load during the next high load period. Thus, the channel selection is based on an expected value C of the channel usage_PREDOn the basis of C_PREDIs based on estimating the BSS load and the most recent BSS-channel mapping.

Once the channel selection process 355 is complete, the BSS channel is updated using a channel update process 380 if a new channel is selected. In the channel update process 380, a determination is made as to whether any WTRUs 110 are associated with the AP 105 via the current operating channel (step 385). If so, the AP 105 first has to send a disassociation message to each associated WTRU 110 (step 390). AP 105 then changes its operating channel to a new channel (step 395). If no WTRUs 110 are in contact with the AP 105 via the current operating channel, the AP 105 changes its operating channel to a new channel.

Preferably at least T has elapsed since the last time the channel optimization process 300 was performed_LastAnd second. Otherwise, the triggering criteria are disregarded. Thus, T_LastWill be the same as the value of the channel optimization process 300. Once T has elapsed since the channel change_LastI.e. per T_MEASTwo trigger conditions are periodically evaluated.

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.

Claims (9)

1. An access point, comprising:

a measurement unit configured for measuring operational parameters for each channel in an allowable channel set upon startup of the access point; and

a channel selector configured for selecting a channel for communication with a plurality of wtrus that is different from a current operating channel used by the ap, wherein the channel selector determines candidate channels based on the measured operating parameters, and selects a new operating channel from the candidate channels by performing the following optimized channel selection process:

calculating expected channel usage rates for all candidate channels;

selecting a channel having a minimum expected channel usage from the candidate channels;

determining whether the selected channel having the minimum anticipated channel usage is different from the current operating channel; and

determining whether the channel usage of the current operating channel is greater than the channel usage of the selected channel having the minimum anticipated channel usage by at least a predetermined threshold on a condition that the selected channel having the minimum anticipated channel usage is different from the current operating channel,

wherein the AP disassociates any of the WTRUs associated with the AP through the current operating channel in response to determining that the channel usage of the current operating channel is at least the predetermined threshold greater than the channel usage of the selected channel having the least anticipated channel usage.

2. The access point of claim 1, wherein the measurement unit and the channel selector are incorporated in an integrated circuit.

3. The access point of claim 1, the access point further comprising:

a memory configured to store the measured operational parameters.

4. The ap of claim 1 wherein the measurement unit measures an average load of each neighboring basic service set detected on a channel, and the channel selector selects candidate channels based on the interference levels detected on the candidate channels and selects a new channel from the candidate channels based on the average load.

5. The AP of claim 4 wherein the candidate channel is selected from the set of allowable channels on a condition that an interference level of the candidate channel is less than a maximum allowed interference on the candidate channel.

6. The access point of claim 1, wherein the optimized channel selection process ends on the condition that the selected channel with the minimum anticipated channel usage is the same as the current operating channel or on the condition that the channel usage of the current operating channel is not at least a predetermined threshold greater than the channel usage of the selected channel with the minimum anticipated channel usage.

7. A method for selecting at least one best channel for use by an access point having at least one operating channel, the method comprising:

determining a plurality of candidate channels for use by the access point;

selecting a channel from the plurality of candidate channels to use as a new operating channel by performing the following optimized channel selection procedure:

calculating expected channel usage rates for all candidate channels;

selecting a channel having a minimum expected channel usage from the plurality of candidate channels;

determining whether the selected channel having the minimum anticipated channel usage is different from a current operating channel;

determining whether the channel usage of the current operating channel is greater than the channel usage of the selected channel with the minimum anticipated channel usage by at least a predetermined threshold under conditions in which the selected channel with the minimum anticipated channel usage is different from the current operating channel; and

disassociating any WTRUs associated with the AP through the current operating channel in response to determining that the channel usage of the current operating channel is at least the predetermined threshold greater than the channel usage of the selected one of the channels having the least anticipated channel usage.

8. The method of claim 7, further comprising:

calculating an average load for each of a plurality of neighboring base service sets; and

information is recorded for neighboring basic service sets having an average load greater than a threshold.

9. The method of claim 7, wherein the optimized channel selection process is ended on a condition that the selected channel with the minimum anticipated channel usage is the same as the current operating channel or on a condition that the channel usage of the current operating channel is not at least a predetermined threshold greater than the channel usage of the selected channel with the minimum anticipated channel usage.