Patent Publication Number: US-2013251003-A1

Title: Systems and methods for indoor positioning

Description:
RELATED APPLICATION INFORMATION 
     This application claims priority to U.S. patent application Ser. No. 13/151,246 filed on Jun. 1, 2011, titled “Systems and Methods for Indoor Positioning,” which claims priority to U.S. Provisional Patent Application No. 61/350,434, filed Jun. 1, 2010, and entitled “Indoor Positioning System,” which is incorporated herein by reference in its entirety as if set forth in full. 
    
    
     BACKGROUND 
     1. Technical Field 
     The embodiments described herein are related to wireless communication and in particular to systems and methods for wireless indoor positioning. 
     2. Related Art 
     Wireless indoor positioning systems have become more popular in recent years. These systems are commonly used for asset tracking and inventory management. For example, these systems have been used for location detection of products in a warehouse, location detection of medical personnel or equipment in a hospital, location detection of firemen in a burning structure, and tracking of maintenance equipment scattered over a facility or compound. 
     Numerous wireless technologies have been developed or adapted for use in indoor positioning applications. These technologies include WLAN, RFID, UWB, ZigBee, Bluetooth, HomeRF, GPS, wireless assisted GPS, etc. In general, these technologies and systems based thereon tradeoff complexity and power requirements for range. In other words, the lower the power, the shorter the distance the over which the system will work effectively.  FIG. 1  is a diagram taken from “Survey of Wireless Indoor Positioning Techniques and Systems,” H. Lui et al., IEEE Transactions on Systems, Man, and Cybernetics—Part C: Applications and Reviews, Vol. 37, No. 6, November 2007, which is incorporated herein by reference. The systems on the left tend to be low power systems, while the systems on the right are high power systems. As can be seen, the low power systems work over a relatively short range. 
     While many systems and techniques for wireless indoor positioning have been developed, there are still several deficiencies that limit adoption and deployment. Ideally, an indoor positioning system would comprise tracking devices that require very little power to operate so that the devices can be made very small, very inexpensively, and so that the devices can last longer on a single battery. The consumer of power within a tracking device is the transceiver. The further a device must transmit, the higher the transmit power required, which translates directly into higher power consumption within the device. As a result, very low power systems, such as UWB systems have been deployed. A UWB system can, for example, transmit effectively at transmit powers as low as −1 Odb. 
     But in order to be effective, such low power systems typically require very precise timing. This requires a high quality crystal oscillator to control the devices timing, which drives up cost, size, and power requirements. Thus, conventional systems cannot provide the extremely low power operation, and accuracy that is required for many applications. 
     SUMMARY 
     Methods for low power indoor tracking systems are described herein. 
     According to one aspect, a positioning system comprises a plurality of controllers, each controller comprising a wideband receiver and a narrow band transmitter, the each controller configured to receive a wideband positioning frame using the wideband receiver from one or more devices and to transmit acknowledgement frames using the narrow band transmitter that include timing and control data for use by the devices to establish timing for transmission of the positioning frame; and at least one device comprising a wideband transmitter and a narrow band receiver, the device configured to transmit a positioning frame to the plurality of controllers using the wideband transmitter and to receive an acknowledgement frame from one or more controllers using the narrow band receiver, extract timing and control information from the frame, and adjust the timing and synchronization of the wideband transmitter using the timing and control information. 
     According to another aspect, A positioning system comprises a plurality of controllers, each controller comprising a wideband receiver and a narrow band transmitter, the each controller configured to receive a wideband positioning frame using the wideband receiver from one or more devices and to transmit acknowledgement frames using the narrow band transmitter that include timing and control data for use by the devices to establish timing for transmission of the positioning frame; at least one device comprising a wideband transmitter and a narrow band receiver, the device configured to transmit a positioning frame to the plurality of controllers using the wideband transmitter and to receive an acknowledgement frame from one or more controllers using the narrow band receiver, extract timing and control information from the frame, and adjust the timing and synchronization of the wideband transmitter using the timing and control information; and a server interfaced with the plurality of controllers, the server configured to maintain synchronization between the plurality of servers; 
     These and other features, aspects, and embodiments are described below in the section entitled “Detailed Description.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and embodiments are described in conjunction with the attached drawings, in which: 
         FIG. 1  is a diagram illustrating various indoor positioning systems in terms of range; 
         FIG. 2  is a diagram illustrating an example positioning system in accordance with one embodiment; 
         FIG. 3  is a block diagram illustrating an example tracking device that can be included in the system of  FIG. 2 ; 
         FIG. 4  is a block diagram illustrating an example controller that can be included in the system of  FIG. 2 ; 
         FIG. 5  is a diagram demonstrating the bandwidth and frequency ranges of UWB, narrow band, and spread spectrum systems; 
         FIG. 6  is a diagram illustrating how the UWB physical layer divides the spectrum; and 
         FIG. 7  is a diagram illustrating an example superframe of a UWB system. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein relate to dual band tracking systems in which an array of controllers is used to track the position of a plurality of devices. The controllers use a narrow band technology/protocol to communicate with the devices, while the devices use a low power, wide band technology/protocol to communicate with the controllers. The number of devices to be tracked can be relatively large, while a relatively small number of controllers can be required. 
     The controllers can be fixed, e.g., within a building or room. Power is generally not a concern, so the controllers can transmit at very high power, e.g., they can transmit at up to 1 W. Further, the receiver, which is a wideband receiver configured to receive the wideband transmissions from the devices, can be supplied with high power such that it can more easily detect and decode the very low power signals transmitted from the devices. 
     The high power, narrow band transmitter in the controllers can be used to transmit timing and synchronization information to the devices so that the devices themselves do not require a high precision crystal. Thus they can be very low power, low cost, small devices that last for a long time without the need to replace a battery or replace the tracking device. In fact, a printed battery can even be used in certain implementations. 
       FIG. 2  is a diagram illustrating an example embodiment of a positioning system  100  configured in accordance with one embodiment. System  100  includes several controllers  102  and a plurality of devices  104  that are being tracked. Devices  104  are attached to an item being tracked and are described in more detail below. Devices  104  can be configure to broadcast transmissions so that they can be received by multiple controllers  102 . In certain embodiments, triangulation techniques can be used to determine the position of a particular device  104 . Thus, each device  104  would need to communicate with at least three controllers  102 . 
     Controllers  102  can be interfaced with a server  106  that can be configured to maintain precise synchronization between controllers  104  and to process data received from devices  104 . Controllers  102  can be interfaced with server  106  via a wireless connection. But it can be preferable for the interface between controllers  102  and server  106  to be a wired connection, such as an Ethernet connection. 
       FIG. 3  is a block diagram illustrating an example tracking device  104  in more detail. Device  104  can comprise an antenna  302  configured to transmit wide band signals and receive narrow band signals. In certain embodiments, device  104  can comprise two antennae, one for receiving and one for transmitting. But because very precise timing can be used, device  104  does not need to transmit and receive at the same time. Thus, a single antenna can be used, reducing complexity, size, cost, etc. 
     Antenna  302  is then interfaced with wideband transmitter  304  and narrow band receiver  306 . It will be understood that transmitter  304  can comprise the circuitry required for transmission. For example, transmitter  304  can comprise the filters, pulse shapers, modulators, amplifiers, digital to analog converters, etc., required for a specific transmitter design. Of course, transmitter  304  is a very low power transmitter, thus there is no need for a high power amplifier. Moreover, low power, all digital ultra wideband transmitter designs exist. Similarly, receiver  306  can comprise all of the circuitry required to receive the narrow band communications from controllers  104 . 
     Transmitter  304  and receiver  306  can be interfaced with a processor or microcontroller  308  that can be configured to control the operation of device  104 , decode information included on signals received by receiver  306 , and generate information to be transmitted using transmitter  304 . Processor  308  can be interfaced with memory  310 , which can store instruction for processor  308  and data, such as an identifier. In many applications, a very limited amount of data is communicated, thus limiting the memory requirements. 
     A crystal  314  can also be included to control the timing of processor  308 . As noted above, the crystal  314  can be a very inexpensive, low power crystal as a result of the systems and methods described herein. 
     It should also be noted that device  104  does not require a lot of power in the receiver, because controllers  102  can transmit at very high power, which can aid the ability of device  104  to receive and effectively decode the received narrow band signals. 
     Additionally, a power source  312  can be included and can be configured to power the components included in device  104 . Power source  312  is often a battery, but because device  104  uses very low power for transmission, power source  312  does not have to have a large capacity in order to provide a relatively long lifetime. In fact, in certain embodiments, power source  312  can be a printed battery. 
     It should also be noted that antenna  302  can also be printed. In general, device  104  can be constructed as, or included in a sticker tag or label, similar to passive RFID transponders. Such tags typically comprise a base layer, a print layer on which the antenna, and in this case possibly power source, and other circuit interconnects and components are printed, a circuit layer on which integrated circuits are attached, and then a top layer. Often, many of these layers, such as the base layer, print layer, and circuit layer are combined into a single layer. Certainly, the ability to use a print battery allows for the reduction of potential layers and overall size of the device  104 . 
       FIG. 4  is a block diagram illustrating an example controller  102  according to one embodiment. As can be seen, the diagram of controller  102  is very similar to that of device  104 ; however, controller  102  includes a narrow band transmitter  404  configured to communicate with the narrow band receivers  306  included in devices  104 , and a wide band receiver  406  configured to receive signals from the wide band transmitters  304  included devices  104 . Again, controller  102  can include a single antenna  402  or dual antennae. In fact, since controllers  102  are less resource constrained, it may be feasible and preferable to include separate transmit and receive antennae. 
     Both processor  408  and memory  410  can be larger and more powerful than the corresponding processor  308  and memory  310  included in devices  104 ; however, because much of the processing and synchronization can occur on server  106 , there is not necessarily a need for large amount so of processing power and memory within controllers  104 . As such, controllers  102  can include a communications port  412 , such as an Ethernet port for communications with server  106  and possible with other controllers  102 . 
     Controllers  102  can also include a power input that can provide power from an external supply such as the building or enclosures power system. It will be understood that power input block  414  can include some or all of the power circuits required, such as power conversion, regulation, over voltage protection, etc. Because power is not a concern for controllers  102 , power input  414  can be configured to provide high power levels to both transmitter  404  and receiver  406 . This allows transmitter  404  to transmit with significantly high power such that low power devices  104  can still effectively receive the transmit signals even though they have very low power receivers. Similarly, receiver  406  can be supplied with very high power allowing it to receive and detect information included in the very low power signals received from low power transmitters  304 . 
     One of skill in the art will understand the basic techniques and designs required to implement a device and a controller as described, and in particular the receivers and transmitters circuits required. Although, specific coding and decoding algorithms, modulation techniques, etc., needed for optimum performance are not necessarily straight forward. 
     Thus, the system is a dual band system, i.e., a higher powered, narrow band system in the down link, and a low power, wide band system in the up link. Thus, a narrow band communication system/protocol, e.g., in the 2.4 GHz Industrial Scientific and Medical (ISM) band can be chosen for the down link portion. Ultra-WideBand (UWB) can be chosen for the uplink.  FIG. 5  is a diagram demonstrating the bandwidth and frequency ranges of UWB, narrow band, and spread spectrum systems. As can be seen, the UWB signal comprises a very wide bandwidth and very low power compared, e.g., to the narrow band signal. 
     Accordingly, in certain embodiments, devices  104  can comprise a low power low cost device comprising a UWB transmitter  304  and a narrowband ISM receiver  306 , and controllers  102  can comprise a UWB receiver  406  and a narrowband ISM transmitter  404 . The UWB frequency band is very wideband and is used for positioning whereas the narrowband spectrum is used for control and data communication. The controllers  102  are connected to a backbone network and are highly synchronized. This allows controllers  102  to provide timing to devices  104 , so that devices  104  do not require high cost, precision crystals. 
     Various implementations of UWB technology differ in frequency band and signal characteristics. The most common UWB technology is based on the WiMedia Alliance recommendations. WiMedia&#39;s UWB technology is an ISO-published radio standard for high speed wireless connectivity. UWB offers an unsurpassed combination of high data throughput and low energy consumption using bands within the frequency range of 3.1-10.6 GHz in the U.S. and many other parts of the world. 
     On the physical layer, the spectrum is divided into  14  bands and  6  band groups, each band group consisting of 3 bands as illustrated in  FIG. 6 . The WiMedia standard also specifies a multi-band orhtogonol frequency division multiplexing with or 110 sub-carriers per channel, i.e., 4.125 MHz bandwidth per sub-carrier, a channel bandwidth of 528 MHz and very low broadcast power that allows same channel coexistence with narrower band devices such as 802.11a/b/g/n radios. UWB&#39;s much high bandwidth results in higher data throughput, coupled with a very low RF output power. UWB typically offers a communication range of up to 30 feet. 
     The basic UWB timing for the network is the superframe. The superframe consists of a “beacon-period” and a “data period” that includes fixed duration time-slots as illustrated in  FIG. 7 . The beacon frame are transmitted by each UWB device  104  to ensure cooperative behavior among all devices. The beacon frame provides basic timing information such as superframe start time as well as convey reservation and scheduling information for medium access. 
     In certain embodiments, during a time slot in the data period, a device  104  can transmit a positioning frame in the UWB spectrum. This positioning frame can be used by system  100  to determine the position of the device  104 . For example, a device  104  can broadcast its positioning frame, which can be picked up by three or more controllers  102 . The positioning frame can include a time stamp that indicates when the frame was sent. By comparing the time stamp to the time when the frame was received, the controllers, or server  106  can determine how far the device  104  is from each controller  102 . If the frame is received by three controllers, then triangulation can be used to determine the position of the device. 
     As mentioned, the devices  104  can comprise low cost, low precision crystals. Accordingly, the crystals will drift and the timing on devices  104  will be off. But the controllers can transmit super frame timing information to the devices  104 , which can allow the devices  104  to reset their timing and eliminate any such timing skew or drift. 
     The basic protocol can include the devices  104  transmitting their positioning frame, using the UWB spectrum, and the controllers  102  transmitting acknowledgement frame m return, using the narrow band spectrum. The acknowledgment frame can comprise timing and other information that allows the devices  104  to reset their timing. In certain embodiments, a device  104  can receive acknowledgement from up to four controllers  102 . The acknowledgments can, depending on the implementation, be consolidated in a single acknowledgment sent from one of the controllers  102 , e.g., as dictated by server  106 . 
     If the acknowledgements indicate reception by less than three controllers  102 , then this can cause the device  104  to retransmit its positioning frame. 
     The positioning frame can comprise at least a preamble and a header, and an optional data portion depending on the implementation. The frame can be modulated using ternary modulation, i.e. +1, 0, and −1 with a predetermined PRF (Pulse Repetition Frequency). The header can comprise a device ID field, possibly a time stamp, and can be encoded and protected with a CRC. The preamble can comprise a sync field and a start frame delimiter field. Each of these two fields can comprise data spread using a common spreading sequence. The common spreading sequence may consist of a ternary sequence with good correlation properties such as Ipatov and Justesen ternary sequence. Different devices  104  can use a common ternary sequence or different ternary sequences depending on the implementation. 
     Further reductions in power can be achieved in devices  104  by turning-on the UWB transmitter  304  only during the time-slot where the device  104  is attempting the positioning and shutting down the transmitter  304  after finishing the frame transmission. Each controller  102  has a much higher complexity and has to be able to receive and demodulate frames sent from multiple devices  104  typically during different time slots. A more advanced controller  102  can be able to demodulate frames sent in the same timeslot as well. 
     In certain embodiments, after sending the positioning frame, the device  104  waits for a predetermined period and turns on its narrow-band receiver  306  and waits for an acknowledgment frame from one or more controllers  102 . In addition to successfully acknowledging successful reception of the frame, the acknowledgment frame can comprise control data and information data sent by the controller  102 . 
     If a device  104  does not receive an acknowledgment within a given timeout period, the device  104  can wait for a random time and attempt retransmission of the positioning packet in a different time-slot. The time-slot number can, e.g., be based on slotted-aloha protocol with exponential backoff. 
     As noted, timing can be established using a superframe structure established by the controllers  102  in the narrowband spectrum. The superframe is divided into two parts: A beacon period; and a time-slotted period. The beacon period can be divided into equal size time-slots. During a beacon time-slot, one of the controllers  102  can transmit a beacon frame comprising information about superframe timing and the structure of the superframe. Different controllers  102  can use different time-slots of the beacon and do not overlap with each other. The beacon frame can comprise as well time  0  of the UWB time axis that sets the time-slots boundary in the UWB spectrum. Thus, using this information, the devices  104  can maintain proper timing. Further, the acknowledgement frame sent by the controller  102  in a response to the positioning frame should be aligned with the boundary of a time-slot in the time-slotted narrowband superframe. 
     Server  106  can comprise one or multiple servers, routers, databases, application, programs, code, user interfaces, etc., to allow server  106  to decode the information received from controllers  102 , and ultimately devices  104 . Server  106  can, therefore, perform such tasks as tracking the location of devices  104 , tracking their movement, detecting the entry or exit of a device  104 , etc. 
     It will be understood that some or all of the functions of server  106  can be implemented by or included in one or more controllers  102 . 
     While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the systems and methods described herein should not be limited based on the described embodiments. Rather, the systems and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.