CN1784865B - Method for measurement report time stamping to ensure reference time correctness - Google Patents

Abstract

A system and method is provided that resolves a possible ambiguity in WLAN measurement reports by having a measuring entity include timer values in returned measurement reports. The time a measurement was requested to be performed and the actual time it was done by a measuring entity can be compared by the receiver to ensure that no ambiguities occurred.

Description

The method used to measure the reported time stamp to ensure the correctness of the reference time

technical field

The present invention relates to local area network communications, and more particularly, to systems and methods for time stamping measurement reports to ensure reference time correctness. the

Background technique

In general, there are two variants of WLANs: infrastructure-based and ad hoc. In the former network, communication typically only takes place between wireless nodes called stations (STAs) and access points (APs), also STAs, which together form a Basic Service Set (BSS). In an ad hoc type network, communication takes place directly between wireless nodes that form an Independent Basic Service Set (IBSS). the

In WLAN, measurement and reporting of measurement values are requested between STAs capable of radio measurement. Measurements on non-serving channels are dedicated measurements, and the STA requiring the measurements interrupts its normal operation, switches channels and obtains radio measurements. Measurements on the serving channel are performed by STAs as concurrent measurements. Although a measurement-capable STA is responsible for decoding and interpreting each measurement report frame and evaluating its impact on its own performance, the execution of certain measurement requests is optional and would significantly degrade the STA's performance if performed , it can be ignored by the receiving STA. the

The STA itself may measure one or more channels or the STA may request other STAs in the same BSS or IBSS to measure one or more channels on its behalf. When requesting other STAs to measure one or more channels, the STA utilizes a measurement request frame in which at least one measurement request unit is specified. the

The Institute of Electrical and Electronics Engineers (IEEE) 802.11-1999 standard is a protocol standard for wireless LANs (WLANs) that focuses on the media access control (MAC) and physical (PHY) layers, incorporated herein by reference , as described in full here. In the IEEE 802.11(h) and 802.11(k) Draft Supplements to this Standard - incorporated herein by reference as if set forth in its entirety - a measurement request includes specifying when the requested measurements will begin time base. For example, as shown in FIG. 1A, a measurement deviation parameter 100 and a start delay parameter 101 together specify a reference time in IEEE TGh and TGk. Start Delay is the measured start delay in multiples of Target Beacon Transmission Time (TBTT), and Measure Offset is the measured offset in Timer Units (TU). Figure 1B shows the allowed measurement requests. the

Due to channel conditions, more than one attempt may be made to transmit the measurement request to the destination station (STA). At the receiving STA, if more than one copy of the same measurement request is received, the STA discards the newly received duplicate packet. It follows the protocol specified by the IEEE 802.11 standard. the

According to the IEEE 802.11 protocol, the discarding of duplicate frames at the receiving STA may result in the requesting and receiving STAs respectively having different reference beacons from which each reference measurement is timed. For example, if a measurement request is scheduled to be sent in one beacon period, and due to channel conditions, the frame is correctly received by the receiving STA but its ACK (acknowledgement) was not received at the sending STA, and if subsequent measurement If the request is successfully sent in another beacon period, the reference beacon is different at the sending station and the receiving station. the

Contents of the invention

Embodiments of the present invention provide a method and system for resolving ambiguity in WLAN measurement reports by including timer values in the measurement reports. The time at which the measurement was requested to be performed is compared by the requester with the time at which the measurement was actually taken to ensure that no ambiguity arises. In an embodiment of the invention for IEEE 802.11 WLAN, a Time Synchronization Function (TSF) timer value is included in the measurement report. the

In a preferred embodiment, by modifying the measurement reporting frames and cells to include fields with absolute time references. For IEEE 802.11 WLAN, the absolute time reference is the value of TSF time (or a fraction thereof) when the requested measurement starts. In all embodiments, a comparison is made between the scheduled (requested) time to start the measurement and the time when the measurement actually starts, to ensure that no protocol ambiguity arises. the

Description of drawings

Figure 1A shows the parameters of a service primitive requesting to send a measurement request to a peer entity in a WLAN;

Figure 1B shows the measurement requests allowed in WLAN;

Fig. 2 A is the simplified block diagram showing the structure of the Basic Service Set (BSS) wireless communication system wherein the embodiment of the present invention can be applied;

Fig. 2 B is the simplified block diagram showing the structure of the ad hoc type independent basic service set (IBSS) wireless communication system wherein the embodiment of the present invention can be applied;

Fig. 3 shows the simplified block diagram of access point (AP) and each station (STA) in specific basic service set (BSS) or independent basic service set (IBSS) according to an embodiment of the present invention;

Fig. 4 shows the measurement report frame format according to an embodiment of the present invention;

Figure 5A shows a measurement reporting unit format according to an embodiment of the invention; and

FIG. 5B shows a measurement reporting mode field of the measurement reporting unit shown in FIG. 5A according to an embodiment of the present invention. the

Detailed ways

In the following description, by way of illustration rather than limitation, specific details are set forth, such as specific structures, interfaces, techniques, etc., in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other wireless network embodiments that differ from these specific details. the

Figure 2A is a representative infrastructure Basic Service Set (BSS) wireless communication system in which embodiments of the present invention may be applied. As shown in FIG. 2A, an access point (AP) 200 is coupled to a plurality of mobile stations (STA _i ) 201 that communicate with each other via wireless links 202 and with the AP via a plurality of wireless channels. The key principle of the present invention is to provide a mechanism to time-stamp the reports of measurements taken by STA _i 201 so that protocol ambiguities can be avoided if they occur, thus making it possible to Take the right action. It should be noted that the network shown in Figure 2 is small for illustrative purposes. In practice, most networks will include a much larger number of mobile stations STA _i 201 . Figure 2B is a representative ad hoc type independent basic service set (IBSS) wireless communication system in which embodiments of the present invention may be applied. As shown in FIG. 2B, a plurality of mobile stations (STA _i ) 201 communicate with each other through a wireless link 202 without using any AP.

Referring to FIG. 3 , the AP 200 and each STA _i 201 in the WLAN of FIG. 2A may include a system having the structure shown in the block diagram of FIG. 3 . AP 200 and each STA _i 201 may include receiver 301 , demodulator 302 , measurement circuit 303 , memory 304 , control processor 305 , timer 306 , modulator 307 , and transmitter 308 . The example system 300 of FIG. 3 is for illustration purposes only. Although the description may use terminology commonly used in describing a particular mobile station, the descriptions and concepts are equally applicable to other processing systems, including systems having structures other than those shown in FIG. 3 .

In a preferred embodiment, a receiver 301 and a transmitter 308 are coupled to an antenna (not shown) to convert received measurement reports into corresponding digital data via a demodulator 302 and transmit desired measurements via a modulator 307, respectively. ask. The measurement acquisition circuitry operates under the control of the processor 305 to process received measurement report frames comprising measurements and corresponding time stamps, or to make requested or periodic measurements (autonomously), in which Values are conveyed in measurement report frames together with corresponding time stamps. Figure 1B shows possible supplicant and measurer combinations for the IBSS and BSS IEEE 802.11 WLAN embodiments of the present invention. The timer 306 is used to set a time stamp in the measurement report frame representing the reported start time of the measurement. the

FIG. 4 shows the format of a measurement report frame body 400 according to a preferred embodiment of the present invention. In the IEEE 802.11 WLAN embodiment of the present invention, the measurement report frame body 400 uses the action frame (Action Frame) body format, and is sent by the STA 201 in response to the measurement request frame, or by the STA 201 that provides measurement information autonomously. In all embodiments, the category field 401 is set equal to a value representing a radio measurement category or a spectrum management category. The action field 402 is set equal to a value indicating that a measurement report is contained therein. The dialog flag field 403 is set equal to the value in the corresponding measurement request frame. If the measurement report frame 400 was not sent in response to a measurement request frame, the dialog flag field 403 is set to zero. In a preferred embodiment, at least one of (1) the timestamp field 404 of the measurement report frame containing the absolute time reference value when the STA started measuring the first reported measurement and (2) the at least one measurement reporting unit 405, 500 One plus time stamp 504. The measurement reporting unit field 405 contains at least one measurement reporting unit 500, as shown in FIG. 5A. The number of measurement reporting units 500 and the length of the measurement reporting unit field 405 in the measurement reporting frame 400 are limited by the maximum allowed medium access control (MAC) management protocol data unit (MMPDU) size. the

Each measurement reporting unit 500 contains a measurement report of the measurements made by the STA 201. Figure 5B shows the format of the measurement reporting unit 500 of the preferred embodiment. The Unit ID field 501 is set to the identification number specified by the corresponding measurement request (eg it is 39 for measurement reports according to the IEEE 802.11 standard). The length field 502 is variable, depending on the length of the measurement report field 507 . The minimum value for the length field is 3 (eg, report measurement mode equal to not available or rejected, and use a zero length measurement report field). The measurement flag field 503 is set equal to the measurement flag in the corresponding measurement request. If the measurement record unit is sent autonomously by the STA, the measurement flag field 503 is set equal to zero. The time stamp field 504 is set to the value of the absolute timer when the requested measurement starts for each measurement unit reported in the measurement report frame 400, which is the TSF timer for the IEEE802.11 embodiment of the present invention. It should be noted that either or both of the timestamp fields 404 and 504 may appear in the measurement report. the

The confidence level of the measurement is increased due to the inclusion of the actual time 504 of the measurement unit 500, and this level of confidence is further increased when several STAs 201 report the same measurement at the actual time 504 at close but different times. improve. In addition, the frequency of the measurement reports sent and requested helps to guide the STA 201 when requesting and making measurement reports, for example, if the reports are received by the STA 201 at 1:00 and 1:05, the STA 201 may be at 1 :10 Request or report measurements, respectively get or provide reliable measurements for a given unit. the

While a preferred embodiment of the invention has been shown and described, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements of the embodiment without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation and the teachings of this invention without departing from its central scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. the

Claims (5)

1. A method for creating a measurement report between a plurality of stations in a wireless local area network WLAN, comprising the steps of: receiving, by a measurement-capable station of the plurality of stations, a request to perform a measurement of at least one measurement reporting unit at a given time, the given time being the time to start the measurement; recording said at least one measurement reporting unit by the measurement capable station; creating, by the measurement-capable station, a measurement report comprising said at least one measurement reporting unit as one of the measurement reporting units contained therein; time-stamping said at least one recorded measurement reporting unit and at least one of said measurement reports, respectively, with an absolute time reference; sending said created measurement report by the measurement capable station; and the station sending the measurement request receives said measurement report and compares the requested time to start the measurement with said time stamp, Wherein said time stamping step further comprises the step of setting, by the measurement capable station, each of said absolute time references to the value of a time synchronization function timer when the requested measurement is initiated. 2. The method of claim 1, further comprising the steps of: If at least one measurement reporting unit has been time-stamped with an absolute time reference, the earliest said absolute time reference of a measurement reporting unit is then determined by a station capable of measuring, and Said measurement report timestamp is set by a measurement capable station as the earliest absolute time reference of said determined measurement reporting unit. 3. The method of claim 1, wherein said creating step further comprises the step of including in said measurement report a plurality of fields formatted in one of the following formats: the type action conversation marker reserved Measurement Reporting Unit Octet: 1 1 1 1 8 8 variable and the type action conversation marker time stamp Measurement Reporting Unit Octets: 1 1 1 1 8 8 variable These fields are − the category field, set equal to a value representing the radio measurement category or the spectrum management category, Action field, set equal to a value indicating that a measurement report is included, the dialog flag field, set equal to the value in the corresponding measurement request, or zero if no measurement report was sent in response to the measurement request, the optional timestamp field contains the value of the absolute time reference when the measurement capable station performed the first measurement of the measurement reporting unit reported in the measurement report, and A Measurement Reporting Unit field comprising at least one Measurement Reporting Unit field having a combined length and a plurality of subfields and formatted as the Unit ID length measurement mark time stamp measurement mode measurement type measurement report Octets: 1 1 1 1 8 8 1 1 1 variable These subfields are − A unit ID subfield, set to the identification number assigned to the requested measurement report, length subfield, which is variable and has a minimum value of 3, the measurement flag subfield is set equal to the measurement flag in the corresponding measurement request element of the measurement request, or if the measurement report element is sent autonomously by a station capable of measurement, the measurement flag subfield is set equal to zero, The optional Timestamp field is set to the value of the absolute time base when the reported measurement started, The measurement mode subfield is a bit field describing the type of measurement request made, a measurement type subfield set to an identification number representing the type of measurement request, and a measurement reporting field comprising at least one measurement reporting element, Therein at least one of a measurement report timestamp and a measurement unit report timestamp is present. 4. The method of claim 3, wherein: WLAN is IEEE 802.11 WLAN; The unit ID is set to a unique identification number specified by the IEEE 802.11 standard; Each time stamp is a time synchronization function timer value; and The combined length of the MRUs is less than or equal to the maximum allowed MACMPDPDU size. 5. A method for creating autonomous measurement reports having at least one measurement reporting unit between stations in a wireless local area network, comprising the steps of: recording at least one predetermined measurement reporting unit by a measurement-capable station of the plurality of stations; time-stamping, by the measurement-capable station, said at least one recorded measurement reporting unit with an absolute time reference at the start of the requested measurement; creating, by the measurement-capable station, an autonomous measurement report comprising said at least one measurement reporting unit; time-stamping said autonomous measurement report with an absolute time reference of the earliest time of the measurement reporting unit contained therein; and sending said autonomous measurement report by a station capable of measurement, wherein at least one of said at least one measurement reporting unit time stamp and said autonomous measurement report time stamp is included in said autonomous measurement report, wherein each said time-stamping step further comprises the step of setting, by the measurement-capable station, each said time-stamp to a time synchronization function timer value when the requested measurement begins.

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