US20180317143A1

US20180317143A1 - An rfid based arrangement for reducing wifi handoff latency

Info

Publication number: US20180317143A1
Application number: US15/531,076
Authority: US
Inventors: Luis Montalvo; Ali Louzir; Stephane Gouache
Original assignee: InterDigital CE Patent Holdings SAS
Current assignee: InterDigital CE Patent Holdings SAS
Priority date: 2014-11-26
Filing date: 2015-11-23
Publication date: 2018-11-01
Also published as: EP3224761A1; JP2017539154A; CN107004104A; EP3224760A1; WO2016083302A1; WO2016083306A1; US20170262672A1; KR20170087889A; EP3026596A1; US10049241B2

Abstract

A radio frequency identification (RFID) reader is contained in a mobile station. The RFID reader includes a transmitter for transmitting an interrogating radio frequency (RF) signal. It includes a receiver for receiving responding RF signals generated in corresponding pairs of RFID tags. Each responding RF signal contains information identifying a corresponding access point (AP). The RFID tag pairs are attached to corresponding regions of each location of corresponding locations. A processor of the RFID reader selects a responding RF signal based on signal strength and derives the information contained in the selected responding RF signal that identifies a corresponding AP among several access points that is the most appropriate one to associate with in a handoff operation.

Description

This application claims priority to European Patent Application entitled, SYSTEM FOR IDENTIFYING A LOCATION OF A MOBILE TAG READER, NO. EP14306895.5, filed on Nov. 26, 2014 and forms a continuation in part (CIP) of a corresponding to-be-filed United States Patent Application (PF140319-US-PCT.)

FIELD OF THE INVENTION

The present invention is directed to a radio frequency identification (RFID) tag system for reducing handoff delay in a wireless network and, in particular, for example, local area wireless computer networking (WiFi).

BACKGROUND

In the IEEE 802.11 standard, Extended Service Set (ESS) refers to two or more Basic Service Sets (BSS) whose respective Access Points (AP) communicate through a wired network, named Distribution System (DS). The BSS includes an AP antenna (ant). Its associated mobile stations communicate in the unlicensed Industrial Scientific and Medical (ISM) radio bands. When a mobile station (MS) moves beyond the radio range of an AP, and enters into a radio range of another BSS, the MS triggers a Handhoff process which can take from 200 ms and up to 1000 ms. Such a large delay range may be undesirable for delay sensitive applications, such as Voice over Internet Protocol (VoIP). VoIP is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP). For the purpose of VoIP the recommended maximum end-to-end latency is 150 ms.
In the IEEE 802.11 standard, the MS initiates the handoff process when the received signal strength and the signal-to-noise-ratio have decreased significantly. The MS can either passively or actively scan for new AP's to associate next. In the case of a fast active scan which is faster than a passive scan, the MS broadcasts probe frames and waits for responses for a minimum channel time (Tmin), and continues scanning until a maximum channel time (Tmax) has elapsed, if at least one response has been received within Tmin. Thus, the time to probe (Tprobe) n channels is given by: n*Tmin≤Tprobe≤n*Tmax. This information is processed by the MS to decide which BSS to join next. In general, Tprobe constitutes 90% of the handoff delay. It may be desirable to reduce the handoff latency. An article, Published in Wireless Communications and Networking Conference (WCNC), 2010 IEEE, entitled, Handoff Management relying on RFID Technology, in the names of Apostolia Papapostolou and Hakima Chaouchi proposes to predict the next point of attachment (PoA) of an RFID-enabled MS by using topology information provided by the network with the collaboration of an RFID system.
The use of an RFID reader is also described in, for example, a published patent application No. WO 2005/071597. There, an RFID tag array-based “smart floor” system for navigation and location determination for guiding individuals includes a plurality of spaced apart RFID tags. Each RFID tag has memory having information stored therein including positional information and attributes of objects or structures disposed in proximity to the tags. The tags convey radio frequency (RF) signals including the positional information and the attributes in response to received electromagnetic excitation fields.
Long range RFID tag systems operating in the ultra high frequency (UHF) band have a range that is typically 12 m in line of sight (LOS) conditions. This range could be drastically reduced by any blockage of the RFID tag or RFID reader caused by various kinds of obstacles such as people or furniture that results in a shadowing effect.
Because of multipath frequency selective fading, encountered in indoor environments, significant level variations of the received RF signal are experienced even within a distance of a few centimeters. FIG. 5 shows a graph presenting an example of variations of magnitudes of a received RF signal at UHF frequency within an indoor area having coordinates X and Y of 2 m×2 m, respectively. As shown in FIG. 5, variation of the RF signal of up to 40 dBm could be noticed over distances of a few tens of centimeters. Such fast fading signal could, disadvantageously, prevent the activation of one RFID tag even for a transmission from a close RFID reader, situated in the same area; whereas, another RFID tag, located in a nearby area could, disadvantageously, be activated and thus read by the RFID reader located in the area in which the one RFID tag is located. As illustrated in the graph of FIG. 6, a situation may happen in which an RFID tag located in a so-called fade at a region 66 with respect to a signal transmitted by an RFID reader situated in the same area. On the other hand, an RFID tag situated a different area might be located on a so-called crest 68.

SUMMARY

In accordance with an aspect of the disclosure, a mobile station is configured for performing a handoff operation in a wireless communication network. It includes a radio frequency (RF) identification (RFID) transmitter for transmitting an interrogating RF signal. An RFID receiver stage is capable of receiving, in response to the interrogating RF signal, a plurality of responding RF signals generated in a plurality of RFID tags, respectively, located in a plurality of locations. A processor is configured to select, in accordance with a selection criterion, at least one of the responding RF signals containing information identifying a corresponding access point (AP) and to select, in accordance with the identifying information, the identified AP from a plurality of access points (AP's) for the mobile station to associate with in the handoff operation.
In accordance with another aspect of the disclosure, a mobile station performs a handoff operation in a wireless communication. It includes a radio frequency (RF) identification (RFID) transmitter for transmitting an interrogating RF signal that is applied to RFID tags arranged in RFID tag pairs. A given RFID tag pair includes a first RFID tag and a second RFID tag separated from each other by a distance for reducing fading effect. The given RFID tag pair of the RFID tag pairs is capable of generating, in response to the interrogating RF signal, a first responding RF signal, if at all, and a second responding RF signal, if at all, respectively. A processor is configured to select, in accordance with a difference between a magnitude of the first responding RF signal that is received by the processor and a magnitude of the second responding RF signal that is received by the processor, one of the magnitudes, when both the first and second responding RF signals are generated, and to select the magnitude of one responding RF signal, when the given RFID tag pair generates merely the one responding RF signal. The processor is additionally configured to select a location from a plurality of locations. A given location of the plurality of locations contains a corresponding plurality of the RFID tag pairs, in a manner to reduce shadowing effect. The plurality of the RFID tag pairs contained in the given location generate at least a corresponding responding RF signal of a plurality of responding RF signals associated with the RFID tag pairs located in the given location. The selected location is selected in accordance with a sum of at least one selected magnitude of a plurality of selected magnitudes associated with the plurality of RFID tag pairs located in the selected location. The processor is further configured to select an access point (AP) from a plurality of access points (AP's) for the mobile station to associate with in the handoff operation in accordance with the selected location.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates an example of a building having, in each location, RFID attached tag pairs, embodying a preferred embodiment;

FIG. 2 illustrates a partial block diagram of an RFID tag pair of FIG. 1;

FIG. 3 illustrates a partial block diagram of a mobile device containing an RFID tag reader, embodying a preferred embodiment;

FIG. 4 illustrates a flow chart for explaining the operation of a processor of FIG. 3;

FIG. 5 illustrates a graph presenting an example of variations of magnitudes of a received RF signal; and

FIG. 6 illustrates a graph demonstrating a fading effect of a received RF signal.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a residential structure such as a building 100. Building 100 includes, for example, four locations, a Room 1, a Room 2, a Room 3 and a Room 4, respectively. In each of Rooms 1 and 3 in building 100 of FIG. 1, a corresponding wireless access point (AP) is installed, AP1 and AP3, respectively. Each of AP1 and AP3 allows wireless devices to connect to a network 200 using Wi-Fi, or related protocols. Each AP usually connects to a router (via a wired network) as a stand-alone device, but it can also be an integral component of the router itself.
In each room of residential building 100, for example, in Room 1, four identical radio frequency identification (RFID) tag sets, an RFID tag pair 11, an RFID tag pair 12, an RFID tag pair 13 and an RFID tag pair 14 are installed. RFID tag pairs 11, 12, 13 and 14 are spaced apart of each other so as to reduce the effect of shadowing. It should be understood that a set may include more RFID tags than a pair. However, in the preferred embodiment each set includes just a pair of RFID tags.
RFID tag pair 11 is embedded within or rigidly attached to a region 115-11 of a surface of a wall 50. Similarly, RFID tag pairs 12, 13 and 14 are embedded within or rigidly attached to a region 115-12 region, a region 115-13 and a region 115-14 of a surface of a wall 51, a ceiling 52 and a flooring 53, respectively. RFID tag pairs 11, 12, 13 and 14 are associated merely with Room 1 and with AP1 and none is associated with any other Room or with another AP. An RFID tag pair 21, an RFID tag pair 22, an RFID tag pair 23 and an RFID tag pair 24 are similarly installed in room 2 and are associated with Room 2 and with AP3 and none is associated with any other Room or with another AP. An RFID tag pair 31, an RFID tag pair 32, an RFID tag pair 33 and an RFID tag pair 34 are similarly installed in Room 3 and are associated with Room 3 and with AP3 and neither is associated with any other Room or with another AP. Lastly, an RFID tag pair 41, an RFID tag pair 42, an RFID tag pair 43 and an RFID tag pair 44 are similarly installed in room 4 and are associated with room 4 and with AP1 and none is associated neither with any other Room or with another AP. Being associated with a given room indicates that the corresponding RFID tag pair is contained in the given room. Being associated with a given AP indicates that the corresponding AP would be the preferred AP to associate or re-associate with in a handoff process.
Each RFID tag pair, for example, RFID tag pair 11 of FIG. 2, forms a set that includes an RFID tag 11 a and an RFID tag 11 b, each being of the passive type that does not require wired connection to a power supply for energization. Similar symbols and numerals in FIGS. 1 and 2 indicate similar items or functions. RFID tag 11 a, for example, of FIG. 2 is paper thin constructed on a flexible plastic substrate 115 with adhesive for its fixation. Substrate 115 may be optically transparent or may have the wall/ceiling color to be visually unobtrusive. RFID tag 11 a includes an etched directional antenna 110 having a hemispherical or half space radiation coverage, a tiny chip 114 which includes a memory 112 for storing data and a transceiver 113 that is coupled to antenna 110 in a conventional manner. The data in memory 112 may contain an identifier, not shown, identifying the room and region in which RFID tag 11 a is installed which, in this example, is room 1, region 115-11 and wall 50 of FIG. 1. It may also contain the RFID tag pair identifier which, in this example, identifies it as being included in RFID tag pair 11 and having an identification portion that differentiates it from the other RFID tag 11 b, of the same RFID tag pair 11. In addition, it may contain necessary information required by the protocol of Wi-Fi wireless network 200 for addressing and associating or re-associating the preferred AP in a handoff process, which, in this example, is AP1. RFID tag 11 b may be similarly constructed on flexible plastic substrate 115 as RFID tag 11 a but is attached to wall 50 of FIG. 1 at a distance, d, from RFID tag 11 a. RFID tag 11 a and RFID tag 11 b may be substantially identical except for the identifier, not shown, that differentiates RFID tag 11 b from RFID tag 11 a.
FIG. 3 illustrates a partial block diagram of a mobile device, for example, a smart phone 60 capable of communicating in, for example, a Wi-Fi wireless network 200 via AP1 and AP3 of FIG. 1. Smart phone 60 also includes an RFID tag reader 61 forming both an RF receiver and an RF transmitter, embodying an advantageous feature. Similar symbols and numerals in FIGS. 1, 2 and 3 indicate similar items or function. When smart phone 60 that contains Reader 61 of FIG. 3 is carried by a user, not shown, it can be used for identifying, for example, a room from among rooms 1-4 of FIG. 1 where mobile smart phone 60 is located and an AP that is most appropriate for association or re-association with smart phone 60 in a handoff process, when mobile smart phone 60 is located in such room.
RFID reader 61 of FIG. 3 includes a processor 64 which may be realized as a digital signal processor (DSP). Processor 64 is coupled to a bus 65 for coupling processor 64 to a memory 66 and to a motion detector 67 such as an accelerometer. Processor 64 is coupled via an RFID transceiver 62 to an antenna 63.
The operation of processor 64 is explained in connection with a flow chart of FIG. 4. Similar symbols and numerals in FIGS. 1, 2, 3 and 4 indicate similar items or functions. In an operation block 400 of FIG. 4, processor 64 of FIG. 3 waits for a movement or motion indication, not shown, from motion detector 67. The movement indication is tested in a decision block 401 of FIG. 4 to determine whether smart phone 60 including RFID tag reader 61 has been moved. When motion detector 67 is indicative of a movement of portable RFID reader 61, the result is “yes” in decision block 401 of FIG. 4. Consequently, in a block 402, processor 64 of FIG. 3 is triggered to generate a transmission of an interrogation or selection RF signal 63 a that is modulated to contain an address for sequentially and selectively addressing each RFID tag, for example, RFID tag 11 a of FIG. 2 of tag pair 11 of FIG. 1. By not initiating the communication unless and until motion detector 67 becomes indicative of a movement of portable reader 61, current consumption of RFID reader 61 is, advantageously, reduced in a manner to conserve a charge in a battery, not shown, of smart phone 60.
It is known to use a variety of techniques to transmit and receive data to and from the corresponding RFID tag including amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). Furthermore, the data transmitted can be encoded using any of a variety of techniques, including frequency shift keying (FSK), pulse position modulation (PPM), pulse duration modulation (PDM), and amplitude shift keying (ASK).
In the example of FIG. 1, RFID tag 11 a of FIG. 2 is exposed to an RF field produced by antenna 63 of FIG. 3. Consequently, it absorbs energy from the RF transmissions of antenna 63 of reader 61 acting as transmitter and uses the absorbed energy for energizing chip 114 of FIG. 2 to perform data retrieval and data transmission. Upon decoding transmission of interrogation or selection RF signal 63 a of FIG. 3 that targets, for example, RFID tag 11 a, the aforementioned information stored in memory 112 of RFID tag 11 a of FIG. 2 is transmitted by antenna 110 and, in this example, a corresponding responding RF signal 111 a is received via antenna 63 of reader 61 of FIG. 3 acting as a receiver.
In an operational block 403 of FIG. 4, Processor 64 of FIG. 3 detects responding RF signal 111 a and stores in memory 66 a corresponding Receiver Signal Strength Indicator (RSSI) value that is indicative of a magnitude of responding RF signals 111 a received from RFID tag 11 a of FIG. 2 of tag pair 11. In addition, processor 64 of FIG. 3 stores in memory 66 the corresponding identifier information such as the room number that, in this example, is Room 1 and information capable of identifying the associated AP that, in this example, AP1 is associated with Room 1 including addressing information. Such addressing information may be required by smart phone 60 for communicating with the associated AP1 using the protocol of Wi-Fi network 200. Processor 64 of FIG. 3 also stores in memory 66 a number identifying RFID tag 11 a and RFID tag pair 11 from the information contained in responding RF signal 111 a. Similarly, RFID reader 61 of FIG. 3 communicates with RFID tag 11 b of FIG. 2 and with each of the remaining RFID tags of RFID tag pairs 12-14, 21-24, 31-34 and 41-44 of FIG. 1, during a sequence of time slots, respectively, not shown. The result is that the corresponding information for each responding RFID signal, if any, generated in RFID tag pairs 11-14, 21-24, 31-34 and 41-44 of FIG. 1 is stored, similarly to that stored for responding RF signal 111 a, is stored in memory 66 of FIG. 3.
If, in block 403, no responding RF signal is received by processor 64 of FIG. 3 from any of the targeted RFID tags of RFID tag pairs 11-14, 21-24, 31-34 and 41-44 of FIG. 1, represented by, T=0, in a decision block 404 of FIG. 4, processor 64 of FIG. 3 will keep sending transmission of interrogation, as suggested by the “yes” path of decision block 404. On the other hand, if at least one responding RF signal has been received, in the aforementioned sequence of time slots, the “no” answer of decision block 404 indicates that an operation block 405 will follow.
In operation block 405 of FIG. 4, processor 64 of FIG. 3 selects the largest (or larger, in the case of a pair of responding RF signals) stored RSSI value of each set of responding RF signal pairs generated in each responding RFID tag pair. For example, assume that a responding RF signal 111 a of FIGS. 1 and 2 happens to have a larger RSSI value than that of a responding RF signal 111 b, originated in RFID tags 11 a and 11 b, respectively, of FIG. 2 of RFID tag pair 11. In this case, the RSSI value of responding RF signal 111 a will be selected and stored. This would also be applicable in the special situation in which RF signal 111 a is received but no responding RF signal 111 b is detected. As indicated before, tag pair 11 is associated with region 115-11 of a portion of wall 50 of room 1 of FIG. 1 where substrate 115 of FIG. 2 is attached. RFID tag pair 11 is also associated with AP1. Similar communication process is applied with respect to each of the other responding RF signals originated in the corresponding RFID tag pairs 12-14, 21-24, 31-34 and 41-44 of FIG. 1. For example, a stored RSSI value associated with a larger responding RF signal 121 a of a set of responding RF signal pair that includes RF signal 121 a and an RF signal 121 b might be selected for representing tag pair 12 in further processing steps; whereas, in this example, a stored RSSI value of responding RF signal 121 b will not be selected or excluded from having any further effect. Similarly, a stored RSSI value associated with a responding RF signal 211 a might be selected for representing tag pair 21 in following processing steps; whereas, in this example, a stored RSSI value of a responding RF signal 211 b will not be selected. Likewise, a stored RSSI value associated with a responding RF signal 241 a might be selected for tag pair 24; whereas, in this example, a stored RSSI value of a responding RF signal 241 b will not be selected.
Thereafter, in an operation block 406 and a decision block 407, processor 64 of FIG. 3 determines, in accordance with the information stored in memory 66, whether each of the responding RF signals has originated in a single room or associated with a single AP. In this example, it could be just Room 1 or AP1 of FIG. 1, respectively.
In the majority of situations, it is more likely that all responding RF signals originate in a single room. Thus, if the answer in decision block 407 of FIG. 4 is “yes”, processor 64 of FIG. 3 determines, in an operation block 410 of FIG. 4, the room in which mobile station 60 of FIG. 3 is located. In the example of FIG. 1, processor 64 of FIG. 3 determines that mobile station 60 is located in Room 1. The same operation also determines the AP with which mobile smart phone 60 should preferably associate in a handoff process. In the example of FIG. 1, processor 64 determines that mobile smart phone 60 should preferably associate with AP1.
On the other hand, in rarely occurring situations, not all the responding RF signals originate in a single room or not all the responding RF signals are associated with a single AP, resulting in the answer, “no”, in the aforementioned decision block 407 of FIG. 4. Therefore, an operation block 408 will follow. Thus, operation block 408 follows when RFID reader 61 receives, in addition to, for example, responding RF signal 111 a that originated in Room 1 and associated with AP1 of FIG. 1, also, for example, a responding RF signal 211 a, a responding RF signal 211 b or both. Responding RF signals 211 a and 211 b have been generated in RFID tag 21 of room 2 that is outside Room 1 in which Mobile smart phone 60 is presently located. Similarly, responding RF signals 211 a and 211 b, in this example, are associated with AP3 located in room 3. RFID reader 61 might receive, in addition, for example, a responding RF signal 241 a or a responding RF signal 241 b originated from RFID tag pair 24 or both that are located in Room 2 and are also associated with AP3. As explained later on, in operation block 408 and in the following operation blocks 409 and 410, using the information contained in or derived from the responding RF signals, processor 64 of FIG. 3 determines the room number in which smart phone 60 is located and, similarly, the AP which Mobile smart phone 60 should preferably select to associate with in a handoff process.
A responding RF signal originated in, for example, tag pair 21 might be subject to the aforementioned multipath frequency selective fading problem encountered in indoor environments. Consequenltly and counter-intuitively, received responding RF signal 211 a that are generated in Room 2 and associated with AP3 might happen to be even larger than received responding RF signal 111 a generated in Room 1 of FIG. 1, in which Mobile smart phone 60 is presently located, and associated with AP1. This could have led to an identification error resulting in a false determination. Such false determination indicates, for example, that the room in which Mobile smart phone 60 is located is room 2 and the AP with which Mobile smart phone 60 should preferably select to associate would be AP3 instead of a correct determination of AP1 of Room 1, where it is actually located. To avoid such an error, the RFID tags of each RFID tag pair, for example, RFID tags 11 a and 11 b of the set of RFID tag pair 11 of FIG. 2 are separated from each other by the aforementioned distance, d.
Distance, d, is selected to be greater than a coherence distance, λ/4, associated with the frequency of the radiated RF signal which, at 900 MHz, is approximately 8 cm. However, distance, d, is also selected to be smaller than λ/2 which at 900 MHz is approximately 16 cm. Because distance, d, is greater than the coherence distance, λ/4, it is unlikely that, for example, both responding RFID signals 111 a and 111 b generated in RFID tags 11 a and 11 b, respectively, will simultaneously encounter the multipath frequency selective fading problem. Thus, the multipath frequency selective fading problem that may be encountered in indoor environment such as in Room 1-Room 4 of FIG. 1 is, advantageously, mitigated.
In the example referred to before, each selected responding RF signal 111 a, 121 a, 211 a and 241 a that was selected on the basis of having the larger RSSI value of the pair of responding RF signals generated in the corresponding RFID tag pair. In operation block 408 of FIG. 4, the stored RSSI values of all the selected larger responding RF signals from each tag pairs located in the corresponding room, for example, the magnitude or RSSI of each of RF signals 111 a and 121 a originated in Room 1 of FIG. 1, are combined to form an accumulative magnitude. The cumulative magnitude is formed by algebraically summed up RSSI of responding RF signals 111 a and RSSI of responding 121 a to produce a first sum associated with Room 1. Similarly, the stored RSSI values of each the selected larger responding RF signals, for example, of responding RF signals 211 a and 241 a, originated in Room 2 are also are combined to form an accumulative magnitude such as by being algebraically summed up to produce a second sum associated with Room 2. Similar operation is performed with respect to the stored RSSI values of all selected responding RF signals, if any, associated with each of Rooms 3 and 4 that are combined to form an accumulative magnitude of a third sum, if any, and an accumulative magnitude of a fourth sum, if any, respectively.
As shown in the example of FIG. 1, the number of RFID tag pairs in each of Rooms 1-4 is equal to that in each of the other rooms. Accordingly, processor 64 of FIG. 3 compares the first, second, third and fourth sums to one another for selecting the largest of the first, second, third and fourth sum, that is implemented in block 410 of FIG. 4. In block 410 of FIG. 4, processor 64 of FIG. 3 determines, among Rooms 1-4, the particular Room in which smart phone 60 is located by determining the room associated with the largest of the first, second, third and fourth sums. In the same way, as explained later on in more details, processor 64 of FIG. 3 determines the AP, AP1 or AP3, associated with the largest of the first, second, third and fourth sums, as being the most appropriate AP to be selected for associating with in a handoff process.
As represented in preceding block 409 of FIG. 4, processor 64 of FIG. 3 may, in addition, calculate the probability of such room as being the correct room to contain smart phone 60 and of such AP as being the most preferable one to associate with in a handoff process. This probability is equal to a fraction having the largest of the first, second, third and fourth sums, as a numerator, and a sum total of the first, second, third and fourth sums, as a denominator.
Each responding RF signal associated with the largest of the first, second, third and fourth sums may contain sufficient information to be included in the protocol for initiating the communication between smart phone 60 and the selected AP, AP1 or AP3 of FIG. 1, to associate with next in a handoff operation. As an alternative, memory 66 of RFID reader 61 of FIG. 3 may contain in a table, not shown, information of the AP to associate with next when mobile station 60 is present in a given room. In the above example, the table will indicate that AP1 is the appropriate AP to associate with when RFID reader 61 of FIG. 3 is located in either Room 1 or Room 2. In another alternative, each responding RF signal that originate in Room 1 or Room 2 will contain sufficient information to enable the selection of AP1 as the most appropriate AP to associate with in the handoff process.
In one embodiment, not shown, for each room in which Mobile smart phone 60 is located, the user can cause smart phone 60 to store in memory 66 information sufficient for enabling smart phone 60 to initiate Wi-Fi communication with the corresponding one AP, AP1 or AP3, of FIG. 1 which is the preferred AP to associate with next. For example, in a set-up or learning mode of operation, that can be initiated in response to a user command or automatically, smart phone 60 can determine by trial and error for a given room, in which Mobile smart phone 60 is located, the information required by smart phone 60 to initiate Wi-Fi communication with the applicable AP, AP1 or AP3, of FIG. 1 to associate with next. This information is then stored in a local table, not shown, that is contained in, for example, memory 66 for future operations.
Following operation box 410 of FIG. 4, when the determination of the next AP to associate with in a handoff operation has already been accomplished, smart phone 60 of FIG. 1 continues the handoff process in network 200 of an operation block 411 of FIG. 4.
Assume, for example, that smart phone 60 moves from Room 1, of FIG. 1 in which AP1 is the preferable AP to associate with, to Room 2, in which AP3 located in Room 3 is the preferable AP to associate with. For completing the handoff process, in order to verify that the aforementioned RFID-probe-response corresponds to AP3 of FIG. 1, mobile smart phone 60 of FIG. 3—can broadcast in Wi-Fi network 200 a New-AP-probe-request addressed to the next AP, AP3, of FIG. 1, in a manner similar to that defined in the IEEE 802.11 (WiFi) handoff process. Thus, the aforementioned RFID-probe-response will terminate when mobile smart phone 60 of FIG. 3 receives the New-AP-prove-response from AP3 of FIG. 1, in this example. Thereafter, the Authentication Phase defined in, for example, the IEEE 802.11 (WiFi) handoff process, will follow in a conventional manner. This phase involves the request and transfer of credentials and other state information from AP3 of FIG. 1 to mobile smart phone 60 of FIG. 3. After successfully receiving from AP3 of FIG. 1 the credentials and state information, mobile smart phone 60 of FIG. 3 sends a Re-association Request message to AP3 of FIG. 1, which, in turn, sends a Move Request message to the previous AP which, in this example, is AP1. Then, in a conventional manner, AP3 completes the handoff process by sending a Reassociation Response message to mobile smart phone 60 of FIG. 3.
Assume that the number of RFID tag pairs in different rooms of Rooms 1-4 of FIG. 1 is unequal in a manner not shown in FIG. 1. Accordingly, processor 64 of FIG. 3 divides each of the first, second, third and fourth sums or accumulative magnitudes by the number of RFID tag pairs in Rooms 1, 2, 3 and 4, respectively, to produce a first average value, a second average value, a third average value and a fourth average value associated with the responding RF signals originated in Rooms 1, 2, 3 and 4, respectively. Processor 64 of FIG. 3 compares the first, second, third and fourth average values to one another for selecting the largest of the first, second, third and fourth average values. The AP which is the most appropriate one to associate with in a handoff process would be the AP associated with the largest of the first, second, third and fourth aveage values. Similarly, the room in which mobile station 60 is located would be associated with the largest of the first, second, third and fourth average values.
In addition, processor 64 calculates in an operation block 409 of FIG. 4 the probability, P_k, that such AP is the most appropriate one to associate with in a handoff process and that such room is the room in which mobile station 60 is located. This is performed by calculating a fraction having the largest of the first, second, third and fourth average values, as a numerator, and a sum total of the first, second, third and fourth average values, as a denominator.
Let S_ijbe defined as the Maximum RSSI from a tag pair number j in room number i. Room number i assumes the value 1, 2, . . . or R, such that “R” is also the total number of rooms. Tag pair number j assumes the values 1, 2, 3, . . . or T, such that “T_i” is also the total number of tagged pairs in room i.

- 1. In case where all the rooms have the same number of tag pairs, for all i's T_iis equal to T.
  For each room k, RFID reader 61 of FIG. 3 calculates, a sum S_kof all Maximum RSSI obtained from the tag pairs situated in a room k. Let S_kjbe defined as the Maximum RSSI of tag pair number j in room k. It follows that S_k=Σ_jS_kj; j=1, . . . , T. Thus, the room where RFID reader 61 of FIG. 3 is most likely to be located is the room number for which the highest value S_kis obtained. Also, the probability P_kthat the user is located in room k could be estimated as P_k=S_k/S where S is the sum total of all the S_k's or S=Σ_kS_k. Similarly, the AP which Mobile smart phone 60 should preferably select to associate with is the AP associated with the RFID tags of room k for which the highest value S_kis obtained.
- 2. In case where the number of tag pairs is not the same in all the rooms, T_krepresent the number of tag pairs in a room k.
  For each room k, RFID reader 61 of FIG. 3 calculates the average value of the Maximum of RSSI from tag pairs j situated in room k, denoted as Sav_k. Thus, Sav_k=S_k/T_k; with S_k=Σ_jS_kj; j=1, 2, . . . , T_k.

The room where RFID reader 61 of FIG. 3 is located is the room number for which the highest value of Sav_kis obtained. The probability, P_k, that the user is located in room k could be estimated as P_k=Sav_k/Sav, where Sav is the sum of all Sav_kor Sav=Σ_kSav_k; k=1, 2, . . . , R. Similarly, the AP which Mobile smart phone 60 should preferably select to associate with is the AP associated with the RFID tags of room k for which the highest value Sav_kis obtained.

Claims

1. A mobile station configured for performing a handoff operation in a wireless communication network, comprising:

a long range RFID transmitter for transmitting an interrogating RF signal;

an RFID receiver stage capable of receiving, in response to said interrogating RF signal, a plurality of responding RF signals generated in a plurality of RFID tags, respectively, located in a plurality of locations, each responding RF signal containing information identifying a location of a RFID tag having generated the responding RF signal; and

a processor configured to select, in accordance with a selection criterion, at least one of said responding RF signals containing further information identifying a corresponding access point, and to select, in accordance with said identifying information, said identified access point from a plurality of access points for said mobile station to associate with in said handoff operation.

2. The mobile station according to claim 1, wherein said processor is configured to select said one of said responding RF signals (121 a), in accordance with signal strength.

3. The mobile station according to claim 1, wherein said further information contained in said selected responding RF signal that associates said selected responding RF signal with said selected access point is capable of being used by said mobile station in a protocol of said wireless communication network for performing the handoff operation.

4. The mobile station according to claim 1,

wherein the plurality of responding RF signals include a first plurality of sets associated with a first location of said plurality of locations and a second plurality of sets associated with a second location of said plurality of locations, each set of RF signals being generated by a given RFID tag pair including a first RFID tag and a second RFID tag separated from each other by a distance,

said processor being further configured to select, in accordance with the selection criterion, a first and a second magnitudes respectively of a first and a second responding RF signals in respectively a first and a second sets of said first plurality of sets, said processor being configured to combine said selected first and second magnitudes of said first plurality of sets,

said processor being further configured to select, in accordance with the selection criterion, a further first and a further second magnitudes respectively of a further first and a further second responding RF signals in respectively a first and a second sets of said second plurality of sets, said processor being configured to combine said selected further first and further second magnitudes of said second plurality of sets,

said processor being additionally configured to compare a value indicative of said combined first and second magnitudes of said first plurality of sets with a further value indicative of said combined further first and further second magnitudes of said second plurality of sets for selecting, in accordance with the comparison, the location corresponding to the selected at least one of said responding RF signals.

5. (canceled)

6. The mobile station according to claim 4, wherein said selected location is selected in accordance with a sum of each selected magnitude associated with a corresponding RFID tag pair of a plurality of RFID tag pairs that are located in said selected location.

7. The mobile station according to claim 6, wherein said selected location is selected in accordance with said sum that is larger than each other sum, similarly obtained, that is associated with each of the other locations of said plurality of locations.

8. The mobile station according to claim 4 wherein said mobile station is configured to apply a protocol applicable to said selected access point in accordance with information contained in at least a responding RF signal generated in a corresponding RFID tag pair located in said selected location.

9. The mobile station according to claim 4, further comprising a motion detector wherein said RFID transmitter is responsive to an output of said motion detector for transmitting said interrogating RF signal after said motion detector detects a motion of said mobile station.

10. The mobile station according to claim 4, wherein each of said RFID tag pairs is attached to a corresponding region of a plurality of regions of said given location, respectively.

11. The mobile station according to claim 4, wherein said distance is larger than or equal to λ/4 and smaller than or equal to λ/2 based on a frequency of a responding RF signal of said plurality of responding RF signals generated in said given RFID tag pair.

12. An RFID tag configured for transmitting a RFID signal in response to an interrogating RF signal according to claim 1, the RFID signal containing information identifying a location of the RFID tag, the RFID signal further containing further information identifying an access point for being selected among a plurality of access points, by a mobile station to associate with in a handoff operation.

13. A pair of RFID tags comprising a first RFID tag, and a second RFID tag, the first and the second RFID tags being according to claim 11, and being further separated from each other by a distance.

14. The pair of RFID tags, according to claim 12, wherein said distance is larger than or equal to λ/4 and smaller than or equal to λ/2 based on a frequency of the RF signal generated in response to the interrogating RF signal.

15. A computer-readable storage medium storing computer-executable program instructions to enable a computer to:

transmit by a long-range RFID transmitter an interrogating RF signal;

receive, in response to said interrogating RF signal, a plurality of responding RF signals generated in a plurality of RFID tags, respectively, located in a plurality of locations, each responding RF signal containing information identifying a location of a RFID tag having generated the responding RF signal; and

select, in accordance with a selection criterion, at least one of said responding RF signals containing further information identifying a corresponding access point, and to select, in accordance with said identifying information, said identified access point from a plurality of access points for said mobile station to associate with in said handoff operation.