(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0155387 A1
`Li et al.
`(43) Pub. Date:
`Jul. 5, 2007
`
`US 20070 155387A1
`
`(54) TECHNIQUES FORSCHEDULING AND
`ADAPTATION TO COMBAT FAST EADING
`
`(76) Inventors: Qinghua Li, Sunnyvale, CA (US);
`Xintian E. Lin, Mountain View, CA
`(US)
`Correspondence Address:
`KACVINSKY LLC
`CFO INTELLEVATE
`P.O. BOX S2OSO
`MINNEAPOLIS, MN 55402 (US)
`
`(21) Appl. No.:
`
`11/322,525
`
`(22) Filed:
`
`Dec. 30, 2005
`
`
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04O 7/20
`(52) U.S. Cl. ............................................ 455/441; 375/141
`
`(57)
`
`ABSTRACT
`
`Techniques to perform scheduling and adaptation to combat
`fast fading are described. An embodiment is a scheduling/
`adaptation scheme for a communications system for which
`different Orthogonal Frequency Division Multiplexing
`(OFDM) symbol durations and subcarrier spacing are
`employed for slow and fast subscribers, respectively. Other
`embodiments are described and claimed.
`
`Detect speed of subscribers
`810
`
`Fast Subscribers?
`820
`
`Group fast subscribers and schedule
`transmission for each close in time and
`frequency
`830
`
`Increase Subcarrier spacing f decrease symbol
`duration
`840
`
`Decrease guard interval per symbol
`850
`
`inform subscribers of change
`860
`
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`Patent Application Publication Jul. 5, 2007 Sheet 1 of 8
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`US 2007/0155387 A1
`
`FIG. 1
`
`
`
`
`
`Wireless Shared Media
`160
`
`
`
`Component 140
`
`
`
`
`
`150
`
`Component 140
`
`150
`
`Component 140
`
`150
`
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`Patent Application Publication Jul. 5, 2007 Sheet 2 of 8
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`US 2007/0155387 A1
`
`FIG. 2
`
`Processor 210
`
`Module
`150
`
`Memory 260
`
`Component 140
`
`
`
`
`
`
`
`
`
`NetWork
`170
`
`150
`
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`Patent Application Publication Jul. 5, 2007 Sheet 4 of 8
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`US 2007/0155387 A1
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`FIG. 4
`
`1 2 3 4
`
`N
`
`f
`
`400
`
`INA-IN.INIA-AA.
`
`1
`
`3
`
`5
`
`N-1
`
`2 4
`
`N
`
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`Patent Application Publication
`
`Jul. 5, 2007 Sheet 5 of 8
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`US 2007/0155387 A1
`
`FIG. 5
`
`Frequency
`
`
`
`CXXXXXX
`XXXXXXX
`(XXXXX
`XXXXXXXX)
`CXXXXXXXXXXXXXXXXXX
`XXXXXXXXX
`SSXSRSXS&
`S&S
`XXXXXXXXXXXX X
`CXXXXXXX
`S&
`
`xx-SSSaxxxx's 3xxxxxx CCCC
`XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX 8X----
`OXXXXXXXXXX XXXXX
`CXXXXXXXXXXXXXX
`XXXXXXXXXXXXX OXXXXXXX) & OC Time
`
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`Patent Application Publication
`
`Jul. 5, 2007 Sheet 6 of 8
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`US 2007/0155387 A1
`
`F.G. 6
`
`Frequency
`
`
`
`Frequency
`
`Time
`
`Y
`al
`
`2 2
`Z
`
`XXX
`XXX XXX XX
`
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`Patent Application Publication Jul. 5, 2007 Sheet 7 of 8
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`US 2007/0155387 A1
`
`FIG. 7
`
`Frequency
`
`Pilot
`1 V
`
`
`
`Xxxxxxyyxxxxxxx
`XXXXXXXXXXXXXXXXX
`XXXXXXXXXXXXXXXXXX
`S&SR&S
`
`sa
`
`N
`
`sa
`
`
`
`N
`KXXXXXXXXXXXXXXXXs &S s
`s
`X
`s
`
`XXXXXXXXXXXXXXXXX &
`
`
`
`XXXXXXXXXXXXXxxxx
`XXXXXXXXXXXXXXXXX &
`d
`
`: & : : : : 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 : : 8
`
`Saxx-xx-xxxxxxxxx X8.
`XXXXXXXXXXXXXXXXXX
`
`Time
`
`
`
`
`
`Frequency
`
`Syyyyyy S&S S&S
`
`XXXX
`
`KX
`
`f
`
`xXxxxx &
`
`XXXXXXXX
`
`XX Sex
`XXXXXXXXX
`
`T
`
`XXXXX XXX & XXXXXXXX
`
`
`
`7 1 O
`
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`Patent Application Publication Jul. 5, 2007 Sheet 8 of 8
`
`US 2007/0155387 A1
`
`FIG. 8
`
`
`
`Detect speed of subscribers
`810
`
`Fast Subscribers?
`820
`
`Group fast subscribers and Schedule
`transmission for each close in time and
`frequency
`830
`
`Increase subcarrier spacing / decrease symbol
`duration
`840
`
`Decrease guard interval per symbol
`850
`
`inform subscribers of change
`860
`
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`US 2007/0155387 A1
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`Jul. 5, 2007
`
`TECHNIQUES FORSCHEDULING AND
`ADAPTATION TO COMBAT FAST EADING
`
`BACKGROUND
`0001 Modern wireless communication systems may
`operate according to Institute of Electrical and Electronics
`Engineers (IEEE) standards such as the 802.11 standards for
`Wireless Local Area Networks (WLANs) and the 802.16
`standards for Wireless Metropolitan Area Networks
`(WMANs). Worldwide Interoperability for Microwave
`Access (WiMAX) is a wireless broadband technology based
`on the IEEE 802.16 standard of which IEEE 802.16-2004
`and the 802.16e amendment are Physical (PHY) layer speci
`fications. In particular, IEEE 802.16 provides specifications
`for an air interface for fixed, portable, and mobile broadband
`wireless access systems. 802.16e aims to enhance the speci
`fications to the 802.16 standard to support both fixed and
`mobile Subscriber stations to accommodate, for example,
`Subscriber stations moving at vehicular speeds.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0002 FIG. 1 illustrates one embodiment of a wireless
`system.
`0003 FIG. 2 illustrates one embodiment of a wireless
`system node.
`0004 FIG. 3 illustrates one embodiment of an OFDMA
`frame.
`0005 FIG. 4 illustrates one embodiment of two OFDM
`signals.
`0006 FIG. 5 illustrates one embodiment of a time-fre
`quency location of a fast Subscriber.
`0007 FIG. 6 illustrates one embodiment of a time-fre
`quency location and grouping of multiple fast Subscribers.
`0008 FIG. 7 illustrates one embodiment of a pilot loca
`tion.
`0009 FIG. 8 illustrates one embodiment of a logic flow.
`
`DETAILED DESCRIPTION
`00.10 Embodiments of a system and method of Orthogo
`nal Frequency Division Multiple Access (“OFDMA)
`scheduling and adaptation to combat fast fading are
`described. One embodiment may comprise, for example, a
`scheduling/adaptation scheme for OFDMA for which dif
`ferent Orthogonal Frequency Division Multiplexing
`(“OFDM) symbol durations are employed for slow and fast
`subscribers respectively. In an embodiment, slow subscrib
`ers are scheduled with smaller subcarrier spacing while the
`fast Subscribers are grouped and scheduled with larger
`Subcarrier spacing. The grouping of subscribers according to
`their speed and apportionment of Subcarrier spacing accord
`ingly may reduce inter-subcarrier interference (“ICI) in
`OFDM and the corresponding OFDMA systems that support
`the subscribers.
`0011
`FIG. 1 illustrates an embodiment of a system. FIG.
`1 illustrates a block diagram of a communications system
`100. In various embodiments, the communications system
`100 may comprise multiple nodes. A node generally may
`comprise any physical or logical entity for communicating
`information in the communications system 100 and may be
`
`implemented as hardware, software, or any combination
`thereof, as desired for a given set of design parameters or
`performance constraints. Although FIG. 1 may show a
`limited number of nodes by way of example, it can be
`appreciated that more or less nodes may be employed for a
`given implementation.
`0012. In various embodiments, a node may comprise, or
`be implemented as, a computer system, a computer Sub
`system, a computer, an appliance, a workstation, a terminal,
`a server, a personal computer (PC), a laptop, an ultra-laptop,
`a handheld computer, a personal digital assistant (PDA), a
`set top box (STB), a telephone, a mobile telephone, a
`cellular telephone, a handset, a wireless access point, a base
`station (BS), a subscriber station (SS), a mobile subscriber
`center (MSC), a radio network controller (RNC), a micro
`processor, an integrated circuit such as an application spe
`cific integrated circuit (ASIC), a programmable logic device
`(PLD), a processor Such as general purpose processor, a
`digital signal processor (DSP) and/or a network processor,
`an interface, an input/output (I/O) device (e.g., keyboard,
`mouse, display, printer), a router, a hub, a gateway, a bridge,
`a Switch, a circuit, a logic gate, a register, a semiconductor
`device, a chip, a transistor, or any other device, machine,
`tool, equipment, component, or combination thereof. The
`embodiments are not limited in this context.
`0013 In various embodiments, a node may comprise, or
`be implemented as, software, a Software module, an appli
`cation, a program, a Subroutine, an instruction set, comput
`ing code, words, values, symbols or combination thereof. A
`node may be implemented according to a predefined com
`puter language, manner or syntax, for instructing a processor
`to perform a certain function. Examples of a computer
`language may include C, C++, Java, BASIC, Perl, Matlab,
`Pascal, Visual BASIC, assembly language, machine code,
`micro-code for a network processor, and so forth. The
`embodiments are not limited in this context.
`0014. The nodes of the communications system 100 may
`be arranged to communicate one or more types of informa
`tion, such as media information and control information.
`Media information generally may refer to any data repre
`senting content meant for a user. Such as image information,
`Video information, graphical information, audio informa
`tion, Voice information, textual information, numerical
`information, alphanumeric symbols, character symbols, and
`So forth. Control information generally may refer to any data
`representing commands, instructions or control words meant
`for an automated system. For example, control information
`may be used to route media information through a system,
`or instruct a node to process the media information in a
`certain manner. The media and control information may be
`communicated from and to a number of different devices or
`networks.
`0015. In various implementations, the nodes of the com
`munications system 100 may be arranged to segment a set of
`media information and control information into a series of
`packets. A packet generally may comprise a discrete data set
`having fixed or varying lengths, and may be represented in
`terms of bits or bytes. It can be appreciated that the described
`embodiments are applicable to any type of communication
`content or format. Such as packets, cells, frames, fragments,
`units, and so forth.
`0016. The communications system 100 may communi
`cate information in accordance with one or more standards,
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`such as standards promulgated by the IEEE, the Internet
`Engineering Task Force (IETF), the International Telecom
`munications Union (ITU), and so forth. In various embodi
`ments, for example, the communications system 100 may
`communicate information according to one or more IEEE
`802 standards including IEEE 802.11 standards (e.g.,
`802.11a, b, g/h, j, n, and variants) for WLANs and/or 802.16
`standards (e.g., 802.16-2004, 802.16.2-2004, 802.16e,
`802.16f, and variants) for WMANs. The communications
`system 100 may communicate information according to one
`or more of the Digital Video Broadcasting Terrestrial (DVB
`T) broadcasting standard and the High performance radio
`Local Area Network (HiperLAN) standard. The embodi
`ments are not limited in this context.
`0017. In various embodiments, the communications sys
`tem 100 may employ one or more protocols such as medium
`access control (MAC) protocol, Physical Layer Conver
`gence Protocol (PLCP), Simple Network Management Pro
`tocol (SNMP), Asynchronous Transfer Mode (ATM) proto
`col, Frame Relay protocol, Systems Network Architecture
`(SNA) protocol, Transport Control Protocol (TCP), Internet
`Protocol (IP), TCP/IP, X.25, Hypertext Transfer Protocol
`(HTTP), User Datagram Protocol (UDP), and so forth.
`0018. The communications system 100 may include one
`or more nodes (e.g., nodes 110-130) arranged to communi
`cate information over one or more wired and/or wireless
`communications media. Examples of wired communications
`media may include a wire, cable, printed circuit board
`(PCB), backplane, switch fabric, semiconductor material,
`twisted-pair wire, co-axial cable, fiber optics, and so forth.
`An example of a wireless communication media may
`include portions of a wireless spectrum, Such as the radio
`frequency (RF) spectrum. In Such implementations, the
`nodes of the system 100 may include components and
`interfaces suitable for communicating information signals
`over the designated wireless spectrum, Such as one or more
`transmitters, receivers, transceivers, amplifiers, filters, con
`trol logic, antennas and so forth.
`0019. The communications media may be connected to a
`node using an input/output (I/O) adapter. The I/O adapter
`may be arranged to operate with any suitable technique for
`controlling information signals between nodes using a
`desired set of communications protocols, services or oper
`ating procedures. The I/O adapter may also include the
`appropriate physical connectors to connect the I/O adapter
`with a corresponding communications medium. Examples
`of an I/O adapter may include a network interface, a network
`interface card (NIC), a line card, a disc controller, video
`controller, audio controller, and so forth.
`0020. In various embodiments, the communications sys
`tem 100 may comprise or form part of a network, Such as a
`WiMAX network, a broadband wireless access (BWA)
`network, a WLAN, a WMAN, a wireless wide area network
`(WWAN), a wireless personal area network (WPAN), a
`Code Division Multiple Access (CDMA) network, a Wide
`band CDMA (WCDMA) network, a Time Division Syn
`chronous CDMA (TD-SCDMA) network, a Time Division
`Multiple Access (TDMA) network, an Extended-TDMA
`(E-TDMA) network, a Global System for Mobile Commu
`nications (GSM) network, an Orthogonal Frequency Divi
`sion Multiplexing (OFDM) network, an Orthogonal Fre
`quency Division Multiple Access (OFDMA) network, a
`
`North American Digital Cellular (NADC) network, a Uni
`versal Mobile Telephone System (UMTS) network, a third
`generation (3G) network, a fourth generation (4G) network,
`a local area network (LAN), a wide area network (WAN), a
`metropolitan area network (MAN), the Internet, the World
`Wide Web, a cellular network, a radio network, a satellite
`network, and/or any other communications network config
`ured to carry data. The embodiments are not limited in this
`COInteXt.
`0021. The communications system 100 may employ vari
`ous modulation techniques including, for example: OFDM
`modulation, Quadrature Amplitude Modulation (QAM),
`N-state QAM (N-QAM) such as 16-QAM (four bits per
`symbol), 32-QAM (five bits per symbol), 64-QAM (six bits
`per symbol), 128-QAM (seven bits per symbol), and 256
`QAM (eight bits per symbol), Differential QAM (DQAM),
`Binary Phase Shift Keying (BPSK) modulation, Quadrature
`Phase Shift Keying (QPSK) modulation, Offset QPSK
`(OQPSK) modulation, Differential QPSK (DQPSK), Fre
`quency Shift Keying (FSK) modulation, Minimum Shift
`Keying (MSK) modulation, Gaussian MSK (GMSK) modu
`lation, and so forth. The embodiments are not limited in this
`COInteXt.
`0022. In various embodiments, the communications sys
`tem 100 may be arranged to schedule a scheme for OFDMA
`communication for multiple subscribers. More specifically,
`the communications system 100 may be arranged to employ
`different OFDM symbol durations and Subcarrier spacing for
`slow and fast subscribers respectively. In an embodiment,
`the communications system 100 is arranged to schedule
`slow Subscribers with Smaller Subcarrier spacing and longer
`OFDM symbol durations. The communications system 100
`is further arranged to schedule fast subscribers with larger
`subcarrier spacing and shorter OFDM symbol durations.
`Further, the communications system 100 of an embodiment
`may group multiple Subscribers in Substantially adjacent
`time-frequency locations of the OFDM frame based on their
`speed. The grouping of Subscribers according to their speed
`and apportionment of Subcarrier spacing accordingly may
`reduce inter-subcarrier interference (“ICI) in OFDM and
`the corresponding OFDMA systems that support the sub
`scribers.
`0023. As used herein, the terms “slow' and “fast may
`refer to the magnitude of an OFDM channel variation in time
`for the subscriber and the base station. The OFDM channel
`variation may be due to movement of the OFDM channel
`transmitter or receiver (e.g. the Subscriber or base station),
`objects moving in the wireless medium, and/or wireless
`medium change. For example, a reflective car moving
`around a stationary base may change a channel of the base
`station. Further, the reflectivity of a fluorescent light chang
`ing in time when on may cause a channel change. Further
`still, motion of the subscriber or base station relative to the
`other may cause OFDM channel variation.
`0024. Furthermore, speed is reciprocal. The speed is the
`same for the both devices (e.g., Subscriber and base station)
`for both uplink and downlink, for which the frequencies of
`downlink and uplink may be different. In addition to altering
`ODFM symbol duration, the base station and/or the sub
`scriber (e.g., a mobile station) can adaptively adjust their
`transmission scheme according to the Doppler spread
`detected from the reverse link. For example, a subscriber
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`may receive a downlink frame from the base station and
`detect an increased Doppler spread. The subscriber may in
`response employ more robust modulation (e.g., with a lower
`data rate) than that in its previous uplink transmission
`because the larger Doppler spread may cause degraded
`reception quality. Similarly, the base station can do the same
`thing upon detecting, for example, an increased Doppler
`spread. Further, the uplink and downlink between, for
`example, a Subscriber and a base station can occupy different
`frequency bands.
`0025. In one embodiment, communications system 100
`may include one or more wireless communication devices,
`such as nodes 110-130. Nodes 110-130 all may be arranged
`to communicate information signals using one or more
`wireless transmitters/receivers (“transceivers’) or radios,
`which may involve the use of radio frequency communica
`tion via 802.16 schemes (e.g., 802.16-2004, 802.16.2-2004,
`802.16e, 802.16f, and variants) for WMANs, for example.
`Nodes 110-130 may communicate using the radios over
`wireless shared media 160 via multiple inks or channels
`established therein. Although FIG. 1 is shown with a limited
`number of nodes in a certain topology, it may be appreciated
`that communications system 100 may include additional or
`fewer nodes in any type of topology as desired for a given
`implementation. The embodiments are not limited in this
`COInteXt.
`0026 Further, nodes 110 and 120 may comprise fixed
`devices having wireless capabilities. A fixed device may
`comprise a generalized equipment set providing connectiv
`ity, management, and control of another device. Such as
`mobile devices. Examples for nodes 110 and 120 may
`include a wireless access point (AP), base station or node B,
`router, Switch, hub, gateway, media gateway, and so forth. In
`an embodiment, nodes 110 and 120 may also provide access
`to a network 170 via wired communications media. Network
`170 may comprise, for example, a packet network Such as
`the Internet, a corporate or enterprise network, a voice
`network such as the Public Switched Telephone Network
`(PSTN), among other WANs, for example. The embodi
`ments are not limited in this context.
`0027. In one embodiment, system 100 may include node
`130. Node 130 may comprise, for example, a mobile device
`or a fixed device having wireless capabilities. A mobile
`device may comprise a generalized equipment set providing
`connectivity to other wireless devices, such as other mobile
`devices or fixed devices. Examples for node 130 may
`include a computer, server, workstation, notebook computer,
`handheld computer, telephone, cellular telephone, personal
`digital assistant (PDA), combination cellular telephone and
`PDA, and so forth.
`0028 Nodes 110-130 may have one or more wireless
`transceivers and wireless antennas. In one embodiment, for
`example, nodes 110-130 may each have multiple transceiv
`ers and multiple antennas to communicate information sig
`nals over wireless shared media 160. For example, a channel
`162, link, or connection may be formed using one or more
`frequency bands of wireless shared medium 160 for trans
`mitting and receiving packets 164. The embodiments are not
`limited in this context.
`0029 FIG. 2 more specifically illustrates node 110 of the
`communications system 100. As shown in FIG. 2, the node
`may comprise multiple elements such as component 140,
`
`module 150, processor 210, memory 260, switch 220, trans
`mitter 230, receiver 240, and antenna 250 to communicate
`packets 164 over wireless shared media 160. Transmitter
`230 and receiver 240 may also be collectively referred to as
`a transceiver. Antenna 250 may include an internal antenna,
`an omni-directional antenna, a monopole antenna, a dipole
`antenna, an end fed antenna or a circularly polarized
`antenna, a micro-strip antenna, a diversity antenna, a dual
`antenna, an antenna array, and so forth. Some elements may
`be implemented using, for example, one or more circuits,
`components, registers, processors, software Subroutines, or
`any combination thereof. Although FIG. 2 shows a limited
`number of elements, it can be appreciated that additional or
`fewer elements may be used in node 110 as desired for a
`given implementation. The embodiments are not limited in
`this context.
`0030. As noted, in an embodiment, node 110 may include
`a processor 210. Processor 210 may be connected to switch
`220 and/or the transceiver (e.g., transmitter 230 and receiver
`240). Processor 210 may be implemented using any proces
`sor or logic device. Such as a complex instruction set
`computer (CISC) microprocessor, a reduced instruction set
`computing (RISC) microprocessor, a very long instruction
`word (VLIW) microprocessor, a processor implementing a
`combination of instruction sets, or other processor device. In
`an embodiment, for example, processor 210 may be imple
`mented as a general purpose processor, Such as a processor
`made by Intel(R) Corporation, Santa Clara, Calif. Processor
`210 may also be implemented as a dedicated processor, such
`as a controller, microcontroller, embedded processor, a digi
`tal signal processor (DSP), a network processor, a media
`processor, an input/output (I/O) processor, a media access
`control (MAC) processor, a radio baseband processor, a field
`programmable gate array (FPGA), a programmable logic
`device (PLD), and so forth. The embodiments are not limited
`in this context.
`0031. In one embodiment, processor 210 may include, or
`have access to, memory 260. Memory 260 may comprise
`any machine-readable media. Memory 260 may be imple
`mented using any machine-readable or computer-readable
`media capable of storing data, including both volatile and
`non-volatile memory. For example, memory 260 may
`include read-only memory (ROM), random-access memory
`(RAM), dynamic RAM (DRAM), Double-Data-Rate
`DRAM (DDRAM), synchronous DRAM (SDRAM), static
`RAM (SRAM), programmable ROM (PROM), erasable
`programmable ROM (EPROM), electrically erasable pro
`grammable ROM (EEPROM), flash memory, polymer
`memory Such as ferroelectric polymer memory, ovonic
`memory, phase change or ferroelectric memory, silicon
`oxide-nitride-oxide-silicon (SONOS) memory, magnetic or
`optical cards, or any other type of media Suitable for storing
`information. It is worthy to note that some portion or all of
`memory 260 may be included on the same integrated circuit
`as processor 210, or alternatively some portion or all of
`memory 260 may be disposed on an integrated circuit or
`other medium, for example a hard disk drive, that is external
`to the integrated circuit of processor 210. The embodiments
`are not limited in this context.
`0032. When implemented in a node of communications
`system 100, node 110 may be arranged to communicate
`information over wireless communications media between
`the various nodes, such as nodes 120 and 130. The infor
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`mation may be communicated using in the form of packets
`164 over wireless shared media 160, with each packet 164
`comprising media information and/or control information.
`The media and/or control information may be represented
`using, for example, multiple Orthogonal Frequency Division
`Multiplexing (OFDM) symbols. A packet 164 in this context
`may refer to any discrete set of information, including a unit,
`frame, cell, segment, fragment, and so forth. The packet may
`be of any size suitable for a given implementation. The
`embodiments are not limited in this context.
`0033 FIGS. 3-7 more specifically describe, for example,
`a frame structure and the arrangement of the communica
`tions system 100 and/or node 110 to generate the frame
`structure. For example, FIG. 3 illustrates a frame 300
`according to the current IEEE 802.16e draft standard for
`which the Subcarrier spacing is constant for all Subscribers
`in the cell. Each block of frame 300 represents one QAM
`symbol carried by one subcarrier to a subscriber and differ
`ent fill patterns represent the frequency-time Zones assigned
`to multiple subscribers. For example, subscribers 310-340
`have frequency-time Zones assigned as illustrated. Further
`more, the frequency-time Zones have been assigned to the
`subscribers 310-340 regardless of their speed. Said alterna
`tively, while some subscribers may be mobile and other
`Subscribers may be stationary, that distinction does not
`determine the frequency-time Zone to which the subscribers
`310-340 respective symbols are assigned.
`0034. The mobility or speed of an individual subscriber
`(e.g., subscribers 310-340), however, may be an important
`feature of that subscriber. For example, high mobility, high
`speed, or fast fading causes ICI for OFDM and OFDMA
`systems that may limit their application to mobile channels
`and may increase the complexity of the receiver (e.g., by
`requiring computationally complex equalization or the like).
`Further, the mobile speeds of individual subscribers or
`groups of subscribers may be substantially different from
`other subscribers. Additionally, the mobile speed of a sub
`scriber relative to a base station may range from 0 to 250
`km/h as introduced above. Another Such example is a
`Subscriber traveling at Vehicular speed (e.g., in an automo
`bile, bus, taxi, train, etc) relative to a stationary base station.
`0035 FIG. 4 illustrates two OFDM signals. For example,
`for a given time slot T and Nadjacent subcarriers with total
`bandwidth Nf, an OFDM symbol of N subcarriers with
`subcarrier spacing f, can be transmitted as illustrated by
`OFDM signal 400. Alternatively, as illustrated by OFDM
`signal 410, for the same frequency and time resource, two
`OFDM symbols with N/2 subcarriers each can be transmit
`ted in two time slots with TF2 each for which the subcarrier
`spacing is 2?. Ignoring guard intervals to mitigate intersym
`bol interference (ISI), the same amount of data and data rate
`can be achieved by OFDM signal 400 and by OFDM signal
`410 respectively. More specifically, in general, a short
`OFDM symbol duration and larger subcarrier spacing
`reduces ICI but may simultaneously increase the overhead
`for additional guard intervals or larger cyclic prefix lengths.
`An increase in the overhead would reduce the data through
`put of the communication channel. However, as OFDM
`signal 410 may have a shorter delay spread, the guard
`interval for each symbol thereof may be shortened so that
`OFDM signal 410 has a total guard interval duration the
`
`same as OFDM signal 400. As will be described more fully
`below, the OFDM signal 410 of an embodiment may benefit
`fast subscribers.
`0036 FIG. 5 illustrates the time-frequency location of a
`fast subscriber of an embodiment for Band AMC of 802.16e.
`In an embodiment, a Subscriber is first categorized as to its
`speed. To do this, a base station detects subcarrier Doppler
`spread, delay spread, and/or ICI level of a mobile subscriber
`from its uplink signal. Based on the reciprocity between the
`uplink and downlink signals, the Doppler or delay spread of
`the uplink signals approximate the Doppler or delay spread
`that would be experienced by the downlink signal for each
`mobile subscriber. Further, since the Doppler spread is the
`same for the uplink signal and the downlink signal, no
`calibration is required for the Doppler estimation. In an
`embodiment, if the communications system and/or node 110
`detects that, based on the above or similar metrics, a
`subscriber exceeds a threshold speed, or a speed relative to
`other subscribers, the subscriber may be designated as a fast
`subscriber. Further, multiple fast subscribers may be
`grouped together as will be discussed more fully below.
`0037. In an embodiment, once subscribers have been
`designated as either fast or slow, the communications system
`100 and/or node 110 of an embodiment may schedule
`OFDM channel resources to accommodate both groups
`(e.g., fast and slow) of Subscribers. In an embodiment, the
`communications system 100 and/or node 110 of an embodi
`ment may employ two OFDM symbol durations and two
`subcarrier spacings (e.g., by utilizing OFDM signal 400 and
`OFDM signal 410 as illustrated by FIG. 4), one set assigned
`to the slow and fast subscribers respectively. In an embodi
`ment, the communications system 100 and/or node 110 of an
`embodiment assigns shorter symbol duration and larger
`subcarrier spacing (e.g., OFDM signal 410) to the fast
`Subscribers and longer symbol duration and Smaller Subcar
`rier spacing (e.g., OFDM signal 400) to the slow subscribers
`less prone to ICI.
`0038. In an embodiment, the communications system 100
`and/or node 110 of an embodiment assigns to a fast Sub
`scribera symbol duration that is half the duration of the slow
`Subscriber symbol duration. For example, and as introduced
`above, for a given time slot T and N adjacent subcarriers
`with total bandwidth Nf, the communications system 100
`and/or node 110 of an embodiment can transmit an OFDM
`symbol of N subcarriers with subcarrier spacing f, to slow
`Subscriber. Using the same frequency and time resource, the
`communications system 100 and/or node 110 of an embodi
`ment can transmit to the fast subscriber two OFDM symbols
`with N72 subcarriers each in two time slots with TF2 each,
`where the subcarrier spacing is 2?. In an embodiment, the
`communications system 100 and/or node 110 assigns the
`even OFDM subcarriers (e.g., N/2 nonadjacent subcarriers)
`to a fast subscriber and shortens the symbol duration from T
`to T/2. This embodiment minimizes the impact to MAC
`scheduling and may further simplify not only the system
`design, but also amendments made to the 802.16e standard.
`For an embodiment ignoring the guard interval for interSym
`bol interference (ISI) mitigation, the communications
`system 100 and/or node 110 of an embodiment may com
`municates the same amount of data with either Subcarrier
`spacing/symbol duration.
`0039. Further, the order of transmission by the commu
`nications system 100 and/or node 110 of an embodiment
`
`Intel Corporation Ex. 1016
`Intel Corp v. UNM Rainforest Innovations - IPR2020-01576
`Page 13 of 16
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`

`US 2007/0155387 A1
`
`Jul. 5, 2007
`
`may be altered. In general, in band AMC mode, one band
`consists of 36 physically contiguous Subcarriers. The total
`bandwidth of the band is comparable to coherent bandwidth
`of the channel. Therefore, frequency response roughly
`remains the same across the AMC band. In band AMC
`mode, a base station may ask a group of Subscribers to
`feedback channel qualities of the several AMC bands. The
`channel quality may be signal to interference-plus-noise
`ratios (SINRs) of the desired AMC bands or the indexes of
`the desired AMC bands, which may be sorted by channel
`quality. The feedback may also be the delta change of SINR.
`As the frequency response of each Subscriber's channel is
`usually different, the base station, according to multi-user
`diversity, can schedule dif