Patent Application
20120231807
1. Field
The present application relates generally to wireless communications, and more specifically to methods and systems for frequency and time synchronization of a femtocell with a wireless network.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A wireless communication network may include a number of network entities, such as base stations, that can support communication for a number of mobile entities/devices, such as, for example, access terminals (ATs) or user equipments (UEs). A mobile entity may communicate with a base station via a downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the AT, and the uplink (or reverse link) refers to the communication link from the AT to the base station.
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) represents a major advance in cellular technology as an evolution of Global System for Mobile communications (GSM) and Universal Mobile Telecommunications System (UMTS). The LTE physical layer (PHY) provides a highly efficient way to convey both data and control information between base stations, such as an evolved NodeBs (eNBs), and mobile entities, such as UEs. In addition, a new class of small base stations has emerged, which may be installed in a user's home and provide indoor wireless coverage to mobile units using existing broadband Internet connections. Such a base station is known as a femto Base Station (fBS), but may also be referred to as a femtocell, a Home NodeB (HNB) unit, Home evolved NodeB unit (HeNB), femto access point, or base station transceiver system. Typically, the femtocell is coupled to the Internet and the mobile operator's network via a Digital Subscriber Line (DSL), cable internet access, T1/T3, or the like, and offers typical base station functionality, such as Base Transceiver Station (BTS) technology, radio network controller, and gateway support node services. This allows an cellular/mobile device or handset (e.g., AT or UE), to communicate with the femtocell and utilize the wireless service.
With the deployment of femtocells in numerous environments, often times in indoor locations with limited or no macro signals from macro base stations and/or weak Global Positioning System (GPS) signal strength, there is a growing need to facilitate frequency and/or timing synchronization of femtocells with a wireless communication network. In a synchronous network, for example, it would be desirable to detect and prioritize the use of the available reference signals to tune a clock generator of the femtocell, and thereby achieve frequency and timing control for the femtocell.
The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.
In accordance with one or more embodiments and corresponding disclosure thereof, various aspects are described in connection with methods for synchronization with a network by a small base station. The method may involve detecting a macro signal of a macro base station. The method may involve setting a frequency reference based at least in part on the macro signal, in response to the macro signal being available in a different band than that for the small base station.
In related aspects, the method may further involve setting the frequency reference based at least in part on a Global Positioning System (GPS) signal, in response to detecting that the different band macro signal is not available. The method may further involve setting the frequency reference based at least in part on a same band macro signal, in response to detecting that the different band macro signal and the GPS signal are not available. In further related aspects, the method may further involve setting a timing reference based at least in part on the different band macro signal, in response to the network comprising a synchronous network. In yet further related aspects, an electronic device may be configured to execute the above described methodology.
In accordance with one or more embodiments and corresponding disclosure thereof, various aspects are described in connection with a small base station synchronization method. In one embodiment, the method may involve determining a signal strength of a GPS signal. The method may involve setting the frequency reference based at least in part on the GPS signal, in response to the GPS signal strength meeting a defined minimum strength.
In related aspects, the method may further involve setting the frequency reference based at least in part on a different band macro signal, in response to the GPS signal strength failing to meet the defined minimum strength. The method may further involve setting the frequency reference based at least in part on a same band macro signal, in response to detecting that the different band macro signal and the GPS signal are not available. In further related aspects, the method may further involve setting a timing reference based at least in part on the GPS signal, in response to the network comprising a synchronous network. In yet further related aspects, an electronic device may be configured to execute the above described methodology.
To the accomplishment of the foregoing and related ends, the one or more embodiments comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the one or more embodiments. These aspects are indicative, however, of but a few of the various ways in which the principles of various embodiments may be employed and the described embodiments are intended to include all such aspects and their equivalents.
Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other wireless networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA), Time Division Synchronous CDMA (TD-SCDMA), and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in both FDD and TDD, are new releases of UMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies.
Referring to
Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access point. In the embodiment, antenna groups each are designed to communicate to ATs in a sector, of the areas covered by the access point 100.
In communication over the forward links 120 and 126, the transmitting antennas of the access point 100 utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different ATs 116 and 124. Also, an access point using beamforming to transmit to ATs scattered randomly through its coverage causes less interference to ATs in neighboring cells than an access point transmitting through a single antenna to all its ATs.
It is noted that an access point may be a fixed station used for communicating with the terminals and may also be referred to herein as a base station, a NodeB, an eNB (e.g., in the context of an LTE network), or the like. An AT may also be referred to herein as a mobile entity, a user equipment (UE), a wireless communication device, terminal, or the like.
In an embodiment, each data stream is transmitted over a respective transmit antenna. The TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.
The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QSPK), M-ary Phase-Shift Keying (M-PSK), or Multi-Level Quadrature Amplitude Modulation (M-QAM)) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by a processor 230, which may be in operative communication with a memory 232.
The modulation symbols for the data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor 220 then provides NT modulation symbol streams to NT transmitters (TMTR) 222a through 222t. In certain embodiments, the TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.
Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NT modulated signals from transmitters 222a through 222t are then transmitted from NT antennas 224a through 224t, respectively.
At the receiver system 250, the transmitted modulated signals are received by NR antennas 252a through 252r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.
An RX data processor 260 then receives and processes the NR received symbol streams from the NR receivers 254 based on a particular receiver processing technique to provide NT “detected” symbol streams. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor 260 is complementary to that performed by the TX MIMO processor 220 and the TX data processor 214 at the transmitter system 210.
A processor 270 periodically determines which pre-coding matrix to use, discussed further below. The processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion, and may be in operative communication with a memory 272.
The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor 238, which also receives traffic data for a number of data streams from a data source 236, modulated by a modulator 280, conditioned by transmitters 254a through 254r, and transmitted back to the transmitter system 210.
At the transmitter system 210, the modulated signals from the receiver system 250 are received by the antennas 224, conditioned by the receivers 222, demodulated by a demodulator 240, and processed by a RX data processor 242 to extract the reserve link message transmitted by the receiver system 250. The processor 230 then determines which pre-coding matrix to use for determining the beamforming weights then processes the extracted message.
In related aspects, the owner of the HNB 410 may subscribe to mobile service, such as, for example, 3G mobile service, offered through the mobile operator core network 450, and the AT 420 may be capable of operating both in a macro-cellular environment and a residential small scale network environment. Thus, the HNB 410 may be backward compatible with any existing AT 420.
In further related aspects, in addition to the macrocell mobile network 450, the AT 420 can be served by a given number of HNBs 410, namely the HNBs 410 that reside within the user's residence 430, and cannot be in a soft handover state with the macro network 450. The AT 420 can communicate either with the macro network 450 or the HNBs 410, but not both simultaneously. As long as the AT 420 is authorized to communicate with the HNB 410, within the user's residence it is preferable that the AT 420 communicate with the associated HNBs 410.
In accordance with aspects of the particular subject of this disclosure, there are provided methods and apparatuses for frequency and timing synchronization of a femtocell with a wireless communication network. An inherent challenge in achieving such synchronization is that femtocells are typically deployed indoors, and sometimes in environments where Global Positioning System (GPS) signals and/or macro signals are weak or not available at all.
It is desirable for femtocells to have accurate time synchronization with the wireless network, as well as accurate frequency reference information for the generation of radio frequency carrier(s) and sampling clocks. The frequency and time synchronization of the femtocell can be obtained by using a GPS receiver unit within the femtocell. However, the GPS signal may not be available in certain environments, such as, for example, deep indoors or in a basement. In a scenario where the GPS signal is not available, the femtocell should utilize the available macro signal to achieve frequency and/or time synchronization.
The timing functionality of modem chipsets used in femtocells, such as, for example, CDMA and UMTS modem chipsets, such as, for example, Mobile Station Modem (MSM), which derives the timing reference for the modem, provides a candidate solution for femtocell timing control using available macro signals. However, the timing derived from the timing functionality is based on the earliest arrival finger, which has a propagation delay between the base station and the receiver. The propagation delay should to be properly calibrated to satisfy the femtocell's time synchronization requirement (e.g., 3-10 μsec with respect to the GPS time). In addition, since the reference timing update is based on the earliest finger among the fingers that are in lock and tracking the pilot signals from the base stations, timing reference jitter may be present when the earliest finger position changes abruptly due to fading. For example, the femtocell modem may update its timing reference every 160 ms. Specifically, every 160 msec, the modem slews its clock by ⅛ of a chip towards the earliest finger (i.e., the modem timing slew rate is ⅛ of a chip every 160 ms.).
The frequency control of the femtocell using the macro signal may be achieved using an Automatic Frequency Control (AFC) design or the like, modified for the specific operation of femtocells. Specifically, when the femtocell is operating at the same band as the macro, it should shut down its transmission when it listens to the macro signal. Therefore, the frequency control method of the femtocell, when using the macro signal, should be short and less frequent in order to avoid interrupting the femtocell transmission. Described in further detail below are the timing and frequency control schemes that may be implemented in the femtocell when the macro signal is used as the primary reference signal.
With reference to
With respect to frequency and timing source selection, the reference signal selection of the femtocell may be based on numerous factors and criteria, including, for example, the operation band, signal availability, etc. With reference to
In another approach to reference signal selection for a 1x/DO femtocell or the like, shown in
In another embodiment (not shown), the femtocell, at 730, simply determines whether the different band macro signal is available, and then, at 732, uses the different band macro signal for the frequency and/or timing reference if available. In the alternative, or in addition, the femtocell, 740, simply determines whether the same band macro signal is available, and then, at 742, uses the same band macro signal for the frequency and/or timing reference if available.
With reference to
With continued reference to
In another approach to reference signal selection for a GSM/UMTS femtocell or the like, shown in
As explained above with reference to
For example, when femtocell operates at the same band as the macrocell, the femtocell may shut down its transmission in order to receive the macro signal for VCTCXO stabilization, such as for example, in Discontinuous Transmission (DTX) mode. However, the DTX mode may not be desirable for the femtocell user since it may introduce frame loss or other performance degradation. Therefore, when the femtocell is in the DTX mode, a slotted idle mode operation may be adopted to discipline the VCTCXO. In normal operation of a modem chipset, the settling time (e.g. four times the time constant of the loop) of the AFC may be longer than a defined time period, such as, for example, 20 msec. In such a scenario, the femtocell transmission shut down period should to be longer than 20 msec in order to discipline the VCTCXO. The table in
In related aspects, there is provided a method for disciplining a clock generator, such as a VCTCXO or the like, by using a higher gain for a rotator to reduce settling time, and/or using the last few msec (TRot) of rotator measurements. In addition, the method may involve using the proper filter to smooth the fluctuations in the rotator measurements in the feedback loop. The feedback loop may involve making use of frequency error measurements over a multiple number of slots (NDTX) to further reduce the effect of fluctuations due to noise, etc.
With reference to
In accordance with one or more aspects of the embodiments described herein, for stationary environments, including, for example, femtocell deployment scenarios, the strongest finger is believed to be more stable in terms of timing jitter than the earliest fingers. Accordingly, the timing control protocol may utilize the strongest fingers of the Pseudo-Noise (PN) to generate the timing reference for the femtocell, and/or may utilize the strongest available finger measurement(s) to reduce the effect of clock slew.
In related aspects, there is provided a timing control technique for continuous tracking mode, when the femtocell utilizes a different band macro signal as the timing reference (i.e., when the femtocell and the macrocell are in different bands). With reference to
With reference to
In further related aspects, after 1340, the average position(s) and Ec/Io estimate(s) may be sent to block 1230 of
where U is the current path positions measurement sets (including the finger measurements and searcher measurements with Ec/Io>THsearch), P is the timing reference for femtocell, Pi are the strongest finger positions and the strongest path positions of the useful PNs from the searcher output,
After the timing reference (e.g., the clock rate and the eclock offset) is updated, the average finger positions and the Ec/Io of the strongest finger, as well as the average positions and the Ec/Io of the strongest paths corresponding to useful PNs may be updated.
In yet further related aspects, there is provided a timing control technique for when the femtocell utilizes a same band macro signal as the timing reference. When femtocell operates in the same band as macrocell, the DTX can be used to generate the timing reference for the femtocell. It may be assumed that during the DTX, the femtocell operates in slotted idle mode, and that the modem chipset tracks one PN, and that the earliest finger of that PN is used as the timing reference for the modem chipset. In such a scenario, the timing control method may accommodate the different operation of the modem chipset of the femtocell or the like.
When the slotted idle mode is used, the average path positions and the Ec/Io may be estimated using the searcher and finger output of the previous predefined number of NDTX slots. After such estimations are completed, the timing reference may be updated at each slot according to the method 1400 shown as a flow diagram in
With reference to
In view of exemplary systems shown and described herein, methodologies that may be implemented in accordance with the disclosed subject matter, will be better appreciated with reference to various flow charts. While, for purposes of simplicity of explanation, methodologies are shown and described as a series of acts/blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the number or order of blocks, as some blocks may occur in different orders and/or at substantially the same time with other blocks from what is depicted and described herein. Moreover, not all illustrated blocks may be required to implement methodologies described herein. It is to be appreciated that functionality associated with blocks may be implemented by software, hardware, a combination thereof or any other suitable means (e.g., device, system, process, or component). Additionally, it should be further appreciated that methodologies disclosed throughout this specification are capable of being stored on an article of manufacture to facilitate transporting and transferring such methodologies to various devices. Those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram.
With reference to
With reference to
In related aspects, the method 1600 may involve, at 1614, setting a timing reference based at least in part on the different band macro signal, in response to the network comprising a synchronous network (e.g., a 1x/DO network). The method 1600 may involve, at 1616, setting the timing reference based at least in part on the GPS signal, in response to detecting that the different band macro signal is not available. The method 1600 may involve, at 1618, setting the timing reference based at least in part on the same band macro signal, in response to detecting that the different band macro signal and the GPS signal are not available.
With reference to
In related aspects, the network may include an asynchronous network, such as, for example, a GSM/UMTS network. The method 1600 may involve, at 1624, generating the frequency reference based as least in part on a XO of at least 250 ppb. The method 1600 may involve, at 1626, stabilizing a VCTCXO based at least in part on the frequency reference.
In further related aspects, setting the frequency reference based at least in part on the same band macro signal may involve, at 1628, shutting down transmission by the small base station for a shutdown period in order to receive the same band macro signal. The method 1600 may involve, at 1630, estimating frequency jitters and defining the shutdown period based at least in part on the estimated frequency jitters.
With reference to
With reference to
In related aspects, the method 1900 may involve, at 1914, setting a timing reference based at least in part on the GPS signal, in response to the network comprising a synchronous network. The method 1900 may involve, at 1916, setting the timing reference based at least in part on the different band macro signal, in response to the GPS signal strength failing to meet the defined minimum strength. The method 1900 may involve, at 1918, setting the timing reference based at least in part on the same band macro signal, in response to detecting that the different band macro signal and the GPS signal are not available.
With reference to
In accordance with one or more aspects of the embodiments described herein, there are provided devices and apparatuses for frequency and timing synchronization of a small base node, as described above with reference to
For example, the apparatus 2200 of
In related aspects, the apparatus 2200 may optionally include a processor component 2210 having at least one processor, in the case of the apparatus 2200 configured as a network entity, rather than as a processor. The processor 2210, in such case, may be in operative communication with the components 2202-2204 via a bus 2212 or similar communication coupling. The processor 2210 may effect initiation and scheduling of the processes or functions performed by electrical components 2202-2204.
In further related aspects, the apparatus 2200 may include a radio transceiver component 2214. A stand alone receiver and/or stand alone transmitter may be used in lieu of or in conjunction with the transceiver 2214. The apparatus 2200 may optionally include a component for storing information, such as, for example, a memory device/component 2216. The computer readable medium or the memory component 2216 may be operatively coupled to the other components of the apparatus 2200 via the bus 2212 or the like. The memory component 2216 may be adapted to store computer readable instructions and data for effecting the processes and behavior of the components 2202-2204, and subcomponents thereof, or the processor 2210, or the methods disclosed herein. The memory component 2216 may retain instructions for executing functions associated with the components 2202-2204. While shown as being external to the processor 2210, the transceiver 2214, and the memory 2216, it is to be understood that one or more of the components 2202-2204 can exist within the processor 2210, the transceiver 2214, and/or the memory 2216.
In accordance with one or more aspects of the embodiments described herein, there are provided devices or apparatuses configured for synchronization of a small base station, as described above with reference to
Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or non-transitory wireless technologies, then the coaxial cable, fiber optic cable, twisted pair, DSL, or the non-transitory wireless technologies are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
