Patent Description:
In computer networking, a wireless Access Point (AP) is a networking hardware device that allows a Wi-Fi compatible client device to connect to a wired network and to other client devices. The AP usually connects to a router (directly or indirectly via a wired network) as a standalone device, but it can also be an integral component of the router itself. Several APs may also work in coordination, either through direct wired or wireless connections, or through a central system, commonly called a Wireless Local Area Network (WLAN) controller. An AP is differentiated from a hotspot, which is the physical location where Wi-Fi access to a WLAN is available.

Prior to wireless networks, setting up a computer network in a business, home, or school often required running many cables through walls and ceilings in order to deliver network access to all of the network-enabled devices in the building. With the creation of the wireless AP, network users are able to add devices that access the network with few or no cables. An AP normally connects directly to a wired Ethernet connection and the AP then provides wireless connections using radio frequency links for other devices to utilize that wired connection. Most APs support the connection of multiple wireless devices to one wired connection. APs are built to support a standard for sending and receiving data using these radio frequencies.

<CIT> is directed to an approach for identifying coverage holes in a radio access technology (RAT. In some examples, a network management (NM) apparatus may receive a first report, including one or more measurements taken by a first UE, in response to an event related to a handover of the first UE between a first RAT and a second RAT different from the first RAT. The NM apparatus may receive a second report including one or more measurements taken by a second UE in response to an event related to a handover of the second UE between the first RAT and a third RAT different from the first RAT. The NM apparatus may identify a hole in a coverage area of the first RAT based at least in part on the first and second reports.

<CIT> is directed to systems and techniques for coverage adjustment in evolved universal terrain radio access networks (E-UTRANs). In some examples, a network management (NM) apparatus may receive data representative of first and second radio link failure (RLF) reports including information related to respective disconnections of first and second user equipment (UEs) from an E-UTRAN. The NM apparatus may identify a hole in a coverage area of the E-UTRAN based at least in part on the first and second RLF reports, and may perform an automated coverage and capacity optimization (CCO) action to reconfigure cell resources of the E-UTRAN based on the identified hole.

A Quality of Service (QoS) based wireless coverage map may be provided. First, a station may be identified by an Access Point (AP) in a Wireless Local Area Network (WLAN). Next, a report request may be sent by the AP to the station in response to identifying the station. A report may then be received from the station in response to the report request. The report may comprise information. The information may comprise a location of the station and data indicating a strength of a signal from the AP at the station.

Both the foregoing overview and the following example embodiments are examples and explanatory only, and should not be considered to restrict the disclosure's scope, as described and claimed. Furthermore, features and/or variations may be provided within the scope of the appended claims in addition to those described. For example, embodiments of the disclosure may be directed to various feature combinations and sub-combinations described in the example embodiments, provided that they fall within the scope of the claims.

The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims.

Service providers may deploy extensive public Wireless Local Area Networks (WLANs) (e.g., Wi-Fi) in parallel with their cellular networks in spaces such as smart cities, campuses, and convention centers for example. However, due to the size and shape of these spaces, many WLAN coverage dead spots (i.e., holes) may exist in these public areas. Moreover, even where WLAN coverage exists, the WLAN coverage may not be suitable for certain applications, such as higher Quality of Service (QoS) applications like voice and video that may need a stronger signal strength. In other words, some areas may comprise a dead spot for real time applications such as voice service, but may not comprise a dead spot for applications that just exchange data. For service providers, it may be challenging to find these dead spots and mitigate them with new or additional APs to cover them. Accordingly, embodiments of the disclosure may provide a process to create a "dark map" that may show where these dead spots may be according to a QoS level.

<FIG> shows an operating environment <NUM>. As shown in <FIG>, operating environment <NUM> may comprise a Wireless Local Area Network (WLAN) <NUM>, a station <NUM>, and a mapping server <NUM>. WLAN <NUM> may comprise a first Access Point (AP) <NUM>, a second AP <NUM>, and a third AP <NUM>. First AP <NUM>, second AP <NUM>, and third AP <NUM> may provide wireless network access (e.g., access to WLAN <NUM>) for devices such as station <NUM>. Station <NUM> may comprise, but is not limited to, a smart phone, a personal computer, a tablet device, a mobile device, a cable modem, a cellular base station, a telephone, a remote control device, a set-top box, a digital video recorder, an Internet-of Things (IoT) device, a network computer, a mainframe, a router, or other similar microcomputer-based device. First AP <NUM>, second AP <NUM>, and third AP <NUM> may be compatible with specification standards such as the <NUM>. 11ax specification standard for example.

Consistent with embodiments of the disclosure, mapping server <NUM> may create a dark map for WLAN <NUM>. The dark map may comprise a map indicating coverage holes in the coverage area of WLAN <NUM>, for example, per access (e.g., QoS) category. A coverage hole may comprise an event where a station is outside the coverage boundaries of WLAN <NUM>'s APs. Embodiments of the disclosure may build a QoS aware dark map that may identify coverage areas of WLAN <NUM> based on the QoS from a station's view. For example, embodiments of the disclosure may identify holes (i.e., dead spots) for data services, voice services, and video services based on an AP density view from the station.

Embodiments of the disclosure may provide a dark map that may identify areas (i.e., dead spots) where WLAN <NUM> may be lacking coverage for basic data traffic. This may be accomplished, for example, by leveraging Wi-Fi Agile Multi-Band Operation (MBO). MBO may allow for dynamic monitoring of network (e.g., WLAN <NUM>) conditions where client (e.g., station <NUM>) and network infrastructure devices (e.g., first AP <NUM>) may exchange information about the network environment. This may result in efficient utilization of network resources, increased network and device performance, and better end user experiences. Embodiments of the disclosure may further extend MBO to have stations send beacon reports on-demand, based on the infrastructure request. For example, when station <NUM> roams away from WLAN <NUM> to a cellular network, first AP <NUM> may initiate a beacon report request. Similarly, based on the traffic load, first AP <NUM> may periodically request a non-associated (but visible) station to report its view of the network infrastructure (e.g., first AP <NUM>, second AP <NUM>, and third AP <NUM>).

In response to receiving the beacon report request, station <NUM> may scan its surrounding wireless medium and create a beacon report. In addition to the strength of a signal (e.g., the Received Signal Strength Indicator (RSSI)) from first AP <NUM>, second AP <NUM>, and third AP <NUM>), station <NUM> may also include in the beacon report, location information (e.g., Global Positioning System (GPS) coordinates) corresponding to its current location. A report <NUM> shown in <FIG> may illustrate an example beacon report. Because station <NUM> may be at the edge of WLAN <NUM>, <NUM> based Real-time locating systems (RTLS) may not be used.

Although station <NUM> may not be associated with an AP in WLAN <NUM>, the beacon report, including the location information of station <NUM>, may be reported (i.e., sent) to first AP <NUM>. First AP <NUM> may pass the beacon report for station <NUM> to mapping server <NUM>, noting that station <NUM> has roamed off WLAN <NUM>. In other embodiments where station <NUM> may not support MBO, station <NUM> may initiate its own beacon report and transmit it to mapping server <NUM> over the cellular network.

Periodically, (as long as station <NUM> may be visible by first AP <NUM>, but not associated with an AP in WLAN <NUM>) first AP <NUM> may continue to request a report (e.g., request an MBO Beacon Report) from station <NUM>. Thus, station <NUM> may continue to report its location (e.g., its GPS coordinates) along with the strength of signals of the APs in the beacon report to the mapping server <NUM> as station <NUM> moves.

The elements described above of operating environment <NUM> (e.g., station <NUM>, mapping server <NUM>, first AP <NUM>, second AP <NUM>, and third AP <NUM>) may be practiced in hardware and/or in software (including firmware, resident software, micro-code, etc.) or in any other circuits or systems. The elements of operating environment <NUM> may be practiced in electrical circuits comprising discrete electronic elements, packaged or integrated electronic chips containing logic gates, a circuit utilizing a microprocessor, or on a single chip containing electronic elements or microprocessors. Furthermore, the elements of operating environment <NUM> may also be practiced using other technologies capable of performing logical operations such as, for example, AND, OR, and NOT, including but not limited to, mechanical, optical, fluidic, and quantum technologies. As described in greater detail below with respect to <FIG>, the elements of operating environment <NUM> may be practiced in a computing device <NUM>.

<FIG> is a flow chart setting forth the general stages involved in a method <NUM> consistent with an embodiment of the disclosure for providing a Quality of Service (QoS) based wireless coverage map. Method <NUM> may be implemented using first access point <NUM> and mapping server <NUM> as described above with respect to <FIG>. Ways to implement the stages of method <NUM> will be described in greater detail below.

Method <NUM> may begin at starting block <NUM> and proceed to stage <NUM> where first AP <NUM> may identify station <NUM>. For example, station <NUM> may have roamed away from first AP <NUM> on WLAN <NUM> and may have roamed to a cellular network. Consistent with embodiments of the disclosure, first AP <NUM> may identify station <NUM> by determining that station <NUM> has roamed away from first AP <NUM>. In other embodiments, in order to identify station <NUM>, first AP <NUM> may periodically request a non-associated, but visible to first AP <NUM>, station to report its view of WLAN <NUM>'s infrastructure (e.g., first AP <NUM>, second AP <NUM>, and third AP <NUM>). In other words, during times of lower usage for example, first AP <NUM> may scan its surrounding wireless medium and see stations (e.g., station <NUM>) that may not be associated with first AP <NUM>. First AP <NUM> may identify these non-associated, yet visible stations as stations that could report their view of WLAN <NUM>'s infrastructure.

From stage <NUM>, where first AP <NUM> identifies station <NUM>, method <NUM> may advance to stage <NUM> where first AP <NUM> may send a report request to station <NUM> in response to identifying station <NUM>. For example, once identified as a station that could report its view of WLAN <NUM> infrastructure, first AP <NUM> may send a report request to station <NUM>. The report request may comprise, but is not limited to, an MBO beacon report request.

Once first AP <NUM> sends the report request to station <NUM> in response to identifying station <NUM> in stage <NUM>, method <NUM> may continue to stage <NUM> where first AP <NUM> may receive, from station <NUM> in response to the report request, a report <NUM> comprising information. The information may comprise a location of station <NUM> and data indicating a strength of a signal from first AP <NUM> at station <NUM>. For example, in response to receiving the report request, station <NUM> may scan its surrounding wireless medium and create a report. The report may comprise an MBO beacon report for example. In addition to the strength of a signal (e.g., an RSSI) from first AP <NUM>, second AP <NUM>, and third AP <NUM>, station <NUM> may also include in the beacon report, location information (e.g., GPS coordinates) corresponding to its current location.

<FIG> illustrates an example report <NUM> (e.g., beacon report). As shown in the example of <FIG>, station <NUM> may provide its current location as latitude <NUM> and longitude <NUM>. GPS coordinates are an example and station <NUM> may provide its current location using processes other than GPS and may use indicators other than coordinates. Also as illustrated in <FIG>, report <NUM> may include the strength of the signal from first AP <NUM>, second AP <NUM>, and third AP <NUM> as seen by station <NUM> at its current location. These strengths of the signals may comprise, for example, an RSSI of -<NUM> dBM for first AP <NUM> (i.e., AP1), an RSSI of -<NUM> dBM for second AP <NUM> (i.e., AP2), and an RSSI of -<NUM> dBM for third AP <NUM> (i.e., AP3). Although station <NUM> may not be associated with an AP in WLAN <NUM>, report <NUM>, including the location information of station <NUM>, may be reported to first AP <NUM>.

Periodically, (as long as station <NUM> may be visible by first AP <NUM>, but not associated with an AP in WLAN <NUM>) first AP <NUM> may continue to request a report (e.g., request an MBO Beacon Report plus location) from station <NUM>. Thus, station <NUM> may continue to report its location (e.g., its GPS coordinates) along with the strength of signals of WLAN <NUM>'s APs in beacon reports to first AP <NUM> as station <NUM> moves.

Consistent with embodiments of the disclosure, station <NUM> may send report <NUM> to first AP <NUM> that may forward it to mapping server <NUM> noting that station <NUM> has roamed off WLAN <NUM>. In other embodiments, station <NUM> may send report <NUM> to mapping server <NUM> over a network other than WLAN <NUM>, for example, a cellular network to which station <NUM> may have roamed. In other embodiments where station <NUM> may not support MBO, station <NUM> may initiate its own beacon report and transmit it to mapping server <NUM> over the cellular network.

After first AP <NUM> receives, from station <NUM> in response to the report request, report <NUM> comprising information in stage <NUM>, method <NUM> may proceed to stage <NUM> where mapping server <NUM> may create, based on received report <NUM>, a map. The map may indicate a hole or holes in the coverage of WLAN <NUM>. For example, mapping server <NUM> may create a dark map for WLAN <NUM> that may comprise a map indicating coverage holes in the coverage area of WLAN <NUM>, for example, per access (e.g., QoS) category. A coverage hole may comprise an event where a station is outside the coverage boundaries of WLAN <NUM>'s APs. Embodiments of the disclosure may build a QoS aware dark map that may identify coverage areas of WLAN <NUM> based on the QoS from a station's view. For example, embodiments of the disclosure may identify holes (i.e., dead spots) for QoS levels comprising, but not limited to, data services, voice services, and video (e.g., High Definition (HD) video) services based on an AP density view from the station.

<FIG> illustrates coverage for a plurality of QoS levels. As shown in <FIG>, acceptable strength of signals of the APs may vary with the type of service being consumed. For example, for HD video service <NUM>, -<NUM> dBM may be the lowest strength of signal. A lower strength of signal may be considered a hole for HD video service. For voice service <NUM>, -<NUM> dBM may be the lowest strength of signal. A lower strength of signal may be considered a hole for voice service. For data service <NUM>, -<NUM> dBM may be the lowest strength of signal. A lower strength of signal may be considered a hole for data service. Any strength of signal lower than -<NUM> dBM may be considered a hole for any service type <NUM>.

<FIG> illustrates a plurality of maps <NUM> (e.g., dark maps) corresponding to a plurality of QoS levels. For example, map <NUM> may correspond to HD video service, map <NUM> may correspond to voice service, map <NUM> may correspond to data service, and map <NUM> may comprise a floor plan for the area. The dark areas in plurality of maps <NUM> may indicate service holes for the given service type. As can be seen from <FIG>, the number of holes increase and grow larger as the QoS level increases from data to HD video. This may be because stronger signals may be needed for higher service quality.

In addition to the signal strengths reported by the station (e.g., station <NUM>), mapping server <NUM> may use the following network parameters in order to combine both an infrastructure view and a client (i.e., station) view for more accurate QoS aware coverage dark map production. These network parameters may comprise, but are not limited to: i) Received Signal to Noise Indicator (RSNI) and Radio Signal to Interference Noise Ratio (SiNR); ii) Enhanced Distributed Channel Access (EDCA); iii) backhaul channel quality state index; iv) network contention; v) histogram of transmit data rates; and vi) channel utilization QoS Enhanced Basic Service Set (QBSS).

Regarding RSNI and Radio SiNR, mapping server <NUM> may first generate a QoS aware dark map leveraging the beacon report based RSNI and the radio's SiNR readings. These parameters may quantify both Uplink (UL) and Downlink (DL) quality metrics that may influence QoS. With respect to EDCA, mapping server <NUM> may then evaluate contention backoff parameters CWmin, CWmax, and AIFSN, for example, mapped to individual QoS access categories. These EDCA parameters may influence the amount of TxOP from the station and radio (i.e., AP) and therefore may affect overall link capacity to meet minimum QoS for the station.

With respect to backhaul channel quality state index, in service provider segments, some sites operate in Wi-Fi Mesh mode. Mesh architecture supports multi-hop deployment where only a Root Access Point has wired backhaul and the rest of the Child Mesh APs (CMAPs) have wireless backhaul links over the <NUM> or <NUM> spectrum and are therefore more susceptible to network latency. Therefore, mapping server <NUM> may evaluate the Backhaul Channel Quality State Index by measuring backhaul capacity along with channel state information and the number of mesh hops from the Root Access Point. For example, any CMAPs with mesh hops greater than three may fail to handle latency requirements for Voice and Video traffic.

Regarding network contention, even when wireless (e.g., Wi-Fi) UL and/or DL RSSI is strong, a station's performance may be impacted due to the amount of Wi-Fi and non-Wi-Fi interference. Hence, mapping server <NUM> may evaluate the amount of co-channel contention induced by nearby wireless rogue devices and persistent devices. In the presence of a Spectrum Analysis Engine (SaGE), mapping server <NUM> may accurately measure Interference Severity Index (ISI) metrics to determine a level of contention present at a localized RF neighborhood.

With respect to histogram of transmit data rates, for active stations associated and passing traffic, mapping server <NUM> may monitor a network histogram of transmit rates from nearby stations. Based on this report, mapping server <NUM> may quantify an average Modulation and Code Scheme (MCS) index used at different network edges.

Regarding Channel Utilization (QBSS), mapping server <NUM> may measure average QBSS along with TxUtil and RxUtil on an AP and its immediate close neighbors to assess total channel utilization along with Receive (UL) and Transmit (DL) utilization in a localized cluster. QBSS along with TxUtil and RxUtil may dictate overall jitter and latency and thus may have an influence on the QoS level that may be offered at a local site.

Data for the beacon reports may be continually written to mapping server <NUM> and statistical inference processes may be used to correct stochastic variation in both the AP signal strength (e.g., RSSI) and station location (e.g., GPS location) measurements. GPS location accuracy may vary, however, using statistical methods over time, the location and relative RSSI estimates may converge with much better accuracy giving a clear picture of the dark map.

Over time, mapping server <NUM> may build both the dark map (showing the coverage holes / dead zones) and also the DL signal strength observed by clients (e.g., stations) that may be near to APs (e.g., by periodically querying beacon reports from these stations). Mapping server <NUM> may now be able to build a service-level dark map model leveraging historical data from these devices where it may estimate levels of service that the clients can handle.

In addition, the stations (e.g., station <NUM>) may passively forward association responses that are heard from its neighbors. Mapping server <NUM> may then compare these against beacon reports above, allowing it to further refine the transition maps to other wireless (e.g., Wi-Fi) systems. Based on the above information, mapping server <NUM> may be able to create statistical edges for WLAN <NUM> where different types of applications (e.g., video, voice, and data) may function to satisfaction. Once mapping server <NUM> creates the map (e.g., dark map) in stage <NUM>, method <NUM> may then end at stage <NUM>.

<FIG> shows computing device <NUM>. As shown in <FIG>, computing device <NUM> may include a processing unit <NUM> and a memory unit <NUM>. Memory unit <NUM> may include a software module <NUM> and a database <NUM>. While executing on processing unit <NUM>, software module <NUM> may perform, for example, processes for providing a Quality of Service (QoS) based wireless coverage map as described above with respect to <FIG>. Computing device <NUM>, for example, may provide an operating environment for station <NUM>, mapping server <NUM>, first AP <NUM>, second AP <NUM>, or third AP <NUM>. Station <NUM>, mapping server <NUM>, first AP <NUM>, second AP <NUM>, and third AP <NUM> may operate in other environments and are not limited to computing device <NUM>.

Computing device <NUM> may be implemented using a Wireless Fidelity (Wi-Fi) access point, a cellular base station, a tablet device, a mobile device, a smart phone, a telephone, a remote control device, a set-top box, a digital video recorder, a cable modem, a personal computer, a network computer, a mainframe, a router, a switch, a server cluster, a smart TV-like device, a network storage device, a network relay devices, or other similar microcomputer-based device. Computing device <NUM> may comprise any computer operating environment, such as hand-held devices, multiprocessor systems, microprocessor-based or programmable sender electronic devices, minicomputers, mainframe computers, and the like. Computing device <NUM> may also be practiced in distributed computing environments where tasks are performed by remote processing devices. The aforementioned systems and devices are examples and computing device <NUM> may comprise other systems or devices.

Embodiments of the disclosure may comprise a method for providing a Quality of Service (QoS) based wireless coverage map. The method may comprise identifying, by an Access Point (AP) in a Wireless Local Area Network (WLAN), a station; sending, by the AP, a report request to the station in response to identifying the station; and receiving, from the station in response to the report request, a report comprising information, the information comprising a location of the station and data indicating a strength of a signal from the AP at the station.

Identifying the station may comprise determining that the station has roamed away from the AP. Identifying the station may comprise determining that the station has roamed away from the AP to a cellular network. Identifying the station may comprise determining that the station is visible by the AP and not associated with the AP.

Receiving the report may comprise receiving the report by the AP over the WLAN. The method may further comprise forwarding the report to a mapping server.

Receiving the report may comprise receiving the report by a mapping server over a cellular network. Receiving the report may comprise receiving the report wherein the information further comprises data indicating a strength of a signal from another AP at the station.

The method may further comprise creating, based on the received report, a map wherein the map indicates a hole in the coverage of the WLAN. The method may further comprise creating, based on the received report, a plurality of maps wherein each of the plurality of maps indicates a hole in the coverage of the WLAN for a corresponding plurality of service levels.

Embodiments of the disclosure may comprise a system for providing a Quality of Service (QoS) based wireless coverage map. The system may comprise a memory storage and a processing unit disposed in an Access Point (AP), the processing unit coupled to the memory storage. The processing unit may be operative to determine that a station has roamed away from the AP, send a report request to the station in response to determining that the station has roamed away from the AP, and receive, from the station in response to the report request, a report comprising information, the information comprising a location of the station and data indicating a strength of a signal from the AP at the station.

The processing unit being operative to determine that the station has roamed away from the AP may comprise the processing unit being operative to determine that the station has roamed away from the AP to a cellular network. The report may be received over a Wireless Local Area Network (WLAN) in which the AP is disposed.

The processing unit may be further operative to forward the report to a mapping server. The information may further comprise data indicating a strength of a signal from another AP at the station.

Embodiments of the disclosure may comprise a method for providing a Quality of Service (QoS) based wireless coverage map. The method may comprise determining, by a station, that the station has roamed away from an Access Point (AP) in a Wireless Local Area Network (WLAN) to a cellular network; creating, by the station in response to determining that the station has roamed away from the AP, a report comprising information, the information comprising a location of the station and data indicating a strength of a signal from the AP at the station; and sending the report to a mapping server.

The method may further comprise creating the report wherein the information may further comprise data indicating a strength of a signal from another AP at the station. Sending the report to the mapping server may comprise sending the report to the mapping server over the cellular network.

Embodiments of the disclosure, for example, may be implemented as a computer process (method), a computing system, or as an article of manufacture, such as a computer program product or computer readable media. The computer program product may be a computer storage media readable by a computer system and encoding a computer program of instructions for executing a computer process on one or more processors so as to cause any of the method described herein to be carried out The computer program product may also be a propagated signal on a carrier readable by a computing system and encoding a computer program of instructions for executing a computer process. Accordingly, the present disclosure may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.). In other words, embodiments of the present disclosure may take the form of a computer program product on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. A computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

Embodiments of the disclosure may be practiced via a system-on-a-chip (SOC) where each or many of the elements illustrated in <FIG> may be integrated onto a single integrated circuit. Such an SOC device may include one or more processing units, graphics units, communications units, system virtualization units and various application functionality all of which may be integrated (or "burned") onto the chip substrate as a single integrated circuit. When operating via an SOC, the functionality described herein with respect to embodiments of the disclosure, may be performed via application-specific logic integrated with other components of computing device <NUM> on the single integrated circuit (chip).

Claim 1:
A method comprising:
identifying (<NUM>), by an Access Point, AP, (<NUM>) in a Wireless Local Area Network, WLAN, (<NUM>) a station (<NUM>) wherein identifying the station (<NUM>) comprises determining that the station (<NUM>) has roamed away from the AP (<NUM>);
sending (<NUM>), by the AP (<NUM>), a report request to the station (<NUM>) in response to identifying the station (<NUM>); and
receiving (<NUM>), from the station (<NUM>) in response to the report request, a report comprising information, the information comprising a location of the station (<NUM>) and data indicating a strength of a signal from the AP (<NUM>) at the station (<NUM>), the method further comprising creating (<NUM>), by a mapping server (<NUM>) based on the received report, a plurality of maps wherein each of the plurality of maps indicates a hole in the coverage of the WLAN (<NUM>) for a corresponding plurality of service levels.