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`U8007599327B2
`
`(12) United States Patent
`Zhuang
`
`(in) Patent No.:
`(45) Date of Patent:
`
`US 7,599,327 82
`Oct. 6, 2009
`
`METI 10]) AND APPARATUS FOR ACCESSI .VG
`A WIRELESS COMMUNICATION SYSTEM
`
`Inventor: Xiangyang Zhuang. Hellman Estates.
`11., (US)
`
`Assignee: Motorola. Inc.. Schamnburg TL (US)
`
`Netiec:
`
`Subject to any disclaimer. the lerm oi‘ll'iis
`patent is exlcnded or adjusted under 35
`USC. l54(b) by 313 days.
`
`“(070,061
`
`Mar. 2. 2005
`
`(56)
`
`References Cited
`US. HNI'T‘ZN'I' DOCUMT‘ZN'T'S
`5.930.299 A
`7:1999 V’nnnattacta].
`6.l78.l58 Bl "
`l-'200|
`Stl'ztlki elnl.
`6.1T8.|9? Bl
`I'EOOI Freeiieh el‘al.
`6.738.728 Bl
`$2004 I’I'asadetall
`6.947.476 T32 ”‘
`932005 Sting
`2004:0[14504 Al"
`6-2004 Jung et Ell.
`2004001011 Al *
`T620043 Sande“ e1 :11.
`OTHER PUBLICATIONS
`
`370 '203
`
`375-149
`370203
`3703210
`
`Hey. V11; The Inlernnlitmnl Search Report or [he Decimalion. 18:15
`US. .-\lexaml.ria Virginia. completed Nov. 11.2005. mailed: Feb. 22.
`2006.
`
`* cited by examiner
`
`I’rimmj‘ Examiner {Seorge ling
`Assistant ExamineriMarcos L Torres
`
`Prior Publication Date
`
`(57)
`
`ABSTRACT
`
`US 200510286465 A1
`
`Dec. 29. 2005
`
`TRANSHIT THE ACCESS NAVEFORH
`
`Access to a wireless communication system (.100) by a sub-
`scriber station (101-103) is facilitated by selecting (705) an
`access sequence from a set of sequences that have been idenv
`lilicd [0 have a low average 01‘ peak-t0-averzlgc-pewer-rntios
`of access sigmils generated by the set n l‘ sequences and also
`based 011.: good cross—correlatinn ofthe access signals; form—
`ing (714) the access wavelbrm by generating an access signal
`using the access sequence and appending in the time domain
`a cyclic prefix to the access signal: and tramsmitting (715)1he
`access waveibrm. In some implementations. the access wave-
`form is cyclically shifted (820) before the cyclic prelix is
`appended, and in some implementalinns. the signal is trans-
`mitted (710. 81 D) in a randomly selected sebiband of an
`access interval.
`
`Related U.S. Application Data
`
`Provisional application Ne. 60582602. filed on Jun.
`24. 2004.
`
`Int. (7].
`HIMW 4/00
`
`(2006.01)
`
`370l329z370/203; 3701’210
`U.S.(.‘l.
`Field of Classification Search
`370/329,
`370f203. 208. 210. 330. 336. 394
`See application file for complete search history.
`
`IO
`
`2] Claims, 6 Drawing Sheets
`
`SELECT AH ACCESS SEQUENCE EROliI A SET OF Ne ACCESS SEDUENCES
`THAT HAVE BEEN IDENTIFIED TO HAVE A LON AVERAGE OF PEAK—TO-
`AVERACE—POH‘ER-RATIOS OF ACCESS SIGNALS GENERATED BY THE SET OF
`Ne ACCESS SEDUENCES AND TO HAVE A GOOD CROSS-CORRELATION OF
`THE ACCESS SIGNALS CENERATED BY THE SET O? Na ACCESS
`SEOUENDES. AND HHEREIN THE SET OF N: ACCESS SEDUENCES HAS
`BEEN CENERATED BY A CORRESPONDING SET OF SEOUENCES OF LENCTH
`K. NHEREIN K [S A OUANTITT OE CARRIERS IDENTIFIED FOR TRANSMITTING
`AN ACCESS NANEFORH
`
`SELECT A SOB—BAND
`
`FORH THE ACCESS NAVEFORH ET GENERATING AN ACCESS SIGNAL USING
`THE ACCESS SEQUENCE AND APPENDINC IN THE TIME DOMAIN A CTCLIC
`PREFIX TO THE ACCESS SIGNAL
`
`PETITIONERS 1062-0001
`IPR2016-00758
`
`

`

`U.S. Patent
`
`'04
`
`BANDWIDTH
`
`Oct. 6, 2009
`
`Sheet 1 of6
`
`US 7,599,327 B2
`
`mum##—
`
`PETITIONERS 1062-0002
`IPR2016-00758
`
`

`

`Oct. 6, 2009
`
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`
`PETITIONERS 1062-0003
`IPR2016-00758
`
`

`

`Oct. 6, 2009
`
`(Df03tEehS
`
`US 7,599,327 B2
`
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`PETITIONERS 1062-0004
`IPR2016-00758
`
`

`

`US. Patent
`
`Oct. 6, 2009
`
`Sheet 4 of6
`
`US 7,599,327 B2
`
`602
`
`50!
`
`\
`" AA " CODES
`
`SAME CODES
`ASSIGNED 10 EACH
`SUB-BAND
`[A DIFFERENI CODE
`SET FOR A DIFFERENT
`sauna)
`
`SUBBAND#2SUBBAND#1
`
`"sh"cvcuc SHIFTS FOR EACH
`CODE (TIME 00mm):
`
`5‘”
`
`V
`
`1-31 SHIFT
`
`Zund SHIFT
`
`g'O'Q'Os:
`.
`
`aC
`L .
`.
`.
`.1)
`
`V
`
`:'O'.'O'.l".‘
`.
`
`3-rd SHIFT
`
`TRANSNIT THE ACCESS HAVEEORN
`
`SELECT AN ACCESS SEQUENCE FROM A SET OF Nc ACCESS SEQUENCES
`THAT HAVE BEEN IDENTIFIED TO HAVE A LON AVERAGE 0F PEAK—T0-
`AVERAGE-PGHER-RATIOS OF ACCESS SIGNALS GENERATED BY THE SET OF
`Nc ACCESS SEDUENCES AND TO HAVE A GOOD CROSS—CORRELATION OF
`THE ACCESS SIGNALS GENERATED BY THE SET OF N: ACCESS
`SEQUENCES, AND HHEREIN THE SET OF N: ACCESS SEOUENCES HAS
`BEEN CENERATED BY A CORRESPONDING SET OF SEOUENCES 0F LENGTH
`K. NHEREIN N
`IS A QUANTITY OF CARRIERS IDENTIFIED FOR TRANSMITTING
`AN ACCESS NANEFORN
`
`SELECT A SUB-BAND
`
`EDEN THE ACCESS HAVEFORN HT GENERATING AN ACCESS SIGNAL USING
`THE ACCESS SEQUENCE AND AFFENDING IN THE TIME DONAIN A CTCLIC
`PREFIX TO THE ACCESS SIGNAL
`
`PETITIONERS 1062-0005
`IPR2016-00758
`
`

`

`US. Patent
`
`Oct. 6, 2009
`
`Sheet 5 of6
`
`US 7,599,327 B2
`
`SELECTING AN ACCESS SEOUENCE FROM A SET OF Nc ACCESS SEOUENCES
`
`SELECTING A SUB-BAND
`
`GENERATING AN ACCESS SIGNAL USING THE SELECTED ACCESS SEQUENCE
`
`DECODING THE ACCESS SIGNAL
`
`IDENTIFYING IN A TRANSMITTED CONTROL SIGNAL ONE OR MORE SUB-BANDS
`IN AN ACCESS INTERVAL, EACH OF WHICH COHPRISES K SUB—CARRIERS AND
`FOR 'A'HICH EACH OF THE SUB—BANDS IS AVAILABLE FOR A SUBSCRIBER
`STATION TO USE TO TRANSNIT AN ACCESS SIGNAL
`
`CICLICALLT TINE SHIFTING THE GENERATED ACCESS SIGNAL BY A SHIFT
`VALUE THAT IS ONE OF A DEFINED SET OF A PLURALITY OF Nsh SHIFT VALUES
`
`FORMING AN ACCESS WAVEFORH BY APPENDING A CYCLIC PREFIX TO THE
`SELECTED ACCESS NAVEFORN
`
`TRANSMITTING THE ACCESS NAVEFORN
`
`FIG. 8
`
`RECEIVING AN ACCESS SIGNAL FROM THE SUBSCRIBER STATION IN ONE Of
`THE ONE OR MORE SUB-BANDS DURING THE ACCESS INTERVAL
`
`PETITIONERS 1062-0006
`IPR2016-00758
`
`

`

`US. Patent
`
`Oct. 6, 2009
`
`Sheet 6 of6
`
`US 7,599,327 B2
`
`SYNCHRONIZATION INFORMATION
`
`ANALYZING THE ACCESS SIGNAL TO IDENTIFY AT LEAST ONE OF A CYCLIC
`SHIFT OF A DEFINED SET OF CYCLIC SHIFTS AND AN ACCESS SEQUENCE OF
`A SET OF ACCESS SEOUENCES
`
`RECEIVING AN ACCESS SIGNAL FROM A SUBSCRIBER STATION DURING
`AN ACCESS INTERVAL
`
`PROCESSING THE ACCESS SIGNAL TO EXTRACT SUBSCRIBER STATION
`
`PETITIONERS 1062-0007
`IPR2016-00758
`
`

`

`1
`METHOD AND APPARATUS FOR ACCESSING
`A WIRELESS COMM UN ICA'I'ION SYSTEM
`
`2
`for an efficient and flexible air interface mechanism that
`enables fast and reliable user access to the network.
`
`US 7,599,327 BZ
`
`FIELD OF THE INVENTION
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`CDMA.
`
`In a wireless conununication system. it is critical to design
`a mechanism for allowing a remote subscriber station (SS) to
`access the network by sending an access signal to a Base
`Station (BS). The access signal fulfills important functions
`such as requesting resource allocation from the BS. alerting
`[he BS ol‘tlle existence of the SS that is trying to enter the
`network, and initiating a process that allows the BS to mea—
`sure sotne parameters of the SS (e.g.. timing offset caused by
`propagation. transmit power. etc.) that must be maintained
`and adjusted constantly in order to ensure a non-interfering
`sharing of the uplinlc resource. Unlike ordinary data trafiic
`that is sent using scheduled resources that are allocated by the
`BS to the SS. such an access signal is often transmitted in an
`unsolicited trimmer. Therefore, this process is ofien referred
`to as a random access. Sometimes the process is also referred
`to as “ranging”. as used in the Institute of Electrical and .
`Electronic Engineers (llEEE) 302.16 standards. because the
`access signal can help the ES to measure the propagation
`distance from the SS (thus. its range). A parameter known as
`a timing advance offset is used by the SS to advance its
`transmission relative to the reference titning at the BS so that
`the signals horn all the 88's appear synchronized at the BS
`(i.e.. nplink timing synchroniralion). Once uplink timing syn-
`chronization is achieved. the SS orthogonality is ensured (i
`each SS occupies its own allocated sub-carriers widiout inter-
`fcringwith otherSS). In this specification. the terms"access",
`“random access“. and “ranging” will he usod interchangeably
`to describe these processes and also to describe the signal
`transmitted by the SS to initiate the access process.
`The random access or ranging process includes an initialtr
`handover ranging function for synchronizingan SS with a BS
`during the initial network entry or re-entry and during cell
`handoli‘. a periodic ranging function for maintaining SS syn-
`chronization. and a bandwidth request function that allows
`each SS to request uplink bandwidth allocation. These upiink
`ranging functions fulfill very important tasks that can signifi— _
`cantly influence the user experience. For example. the band—
`width request ranging perfomumce directly impacts the
`access latency perceived by a user. especially during committ—
`nication sessions (cg. HTTP) that consist ofsporadie packet
`lra [tie that requires fa st response. in which case high detection ..
`and low collision probabilities of the access request are very
`desirable. In another example. robust detection of an initial
`ranging signal is essential in order to allow a user to quickly
`enter the network or to be handed over to a new serving sector.
`Reliable extraction of the accurate timing offsets from the
`initial ranging signals is also critical for achieving uplink
`synchronization that ensures userotthogonality (i.e.. to make
`sure that each SS occupies its own allocated sub—carriers
`without interfering with other SS). Other important infon'na—
`tion that the BS needs to extract from ranging includes power
`measurement,
`frequency synchronization.
`and channel
`impulse response estimation. etc. Therefore. there is a need
`
`The present invention relates generally to corntnuniCation
`systems. and in particular, to a method and apparatus for
`randomly accessing a wireless communication system by a
`subscriber station in order to obtain or maintain such param-
`eters as uplinlt tinting. power control, channel estimation. and
`frequency alignment of the subscriber station.
`
`BACKGROUND OI“ THE INVENTION
`
`FIG. 1 is a block diagram of a conununication system. in
`accordance with some embodiments of the present invention
`FIG. 2 is a time-domain diagram oi'a “basic” dedicated
`basic ranging interval. in accordance with sortie embodiments
`ol‘the present invention.
`FIG. 3 is a time-domain diagram ofan extended dedicated
`ranging interval. in accordance with sortie embodiments of
`the present invention.
`FIG. 4 is a frequency-domain diagram ofa variation oftl’te
`extended dedicated ranging interval. in accordance with some
`embodiments ofthe present invention.
`FIG. 5 is a time-domain diagram ol‘an example design for
`an OFDM system such as the one defined by the IEEE 802.16
`standard.
`
`FIG. 6 is a block diagram of the division ofranging oppor—
`tunities in frequency. time. and code domains. in accordance
`with some embodiments of the present invention.
`FIGS. 7 and 8 are flow charts of methods of accessing a
`conununication system. in accordance with some embodi-
`ments of the present invention.
`FIGS. 9 and 10 are methods used by a base station in a
`wireless communication system for facilitating an access of
`the conununication system by a subscriber station= in accor—
`dance with some embodiments of the present invention.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Before describing in detail the particular communication
`system accessing teclulology in accordance with the present
`invention. it should be observed that the present invention
`resides primarin in combinations of method steps and appa-
`ratus components related to accessing a conununication sys-
`tem by a subscriber station. Accordingly. the apparatus com-
`ponents and method steps have been represented where
`appropriate by conventional symbols in the drawings. show-
`ing only those specific details that are pertinent to understand—
`ing the present invention so as not to obscure the disclosure
`with details that will be readily apparent to those of ordinary
`skill in the art having the benefit ot'the description herein.
`Turning now to the drawings. wherein like numerals. des-
`ignate like components. FIG. 1 is a block diagram of com-
`munication system 100. Communication system 100 com-
`prises a plurality ofcells 106 and 10? (only two shown) each
`having a base station (BS) 104, 105. The service area of the
`BS 104 covers a plurality of subscriber stations (SSS) 10L
`103, each at a time may be performing sortie type of ranging
`function. which is also called herein a random access finic—
`tion. For example. SS 10] may move out ol'the service area of
`BS 104 and enter into the service area of BS 105. in which
`case a handover occurs that often involves a handover access.
`In other examples, SS 102 makes a bandwidth request andfor
`SS 103 makes an initial entry access when it is first activated
`within the communication system. In one embodiment of the
`present
`invention. conununication system 100 utilizes an
`Orthogonal Frequency Division Multiplexed (OFDM) modu-
`lation or other variants of OFI)M such as nurlti-carrier
`CDMA (MC-C DMA), mttIti-carrier direct sequence C DMA
`(MC—DSCDMA).
`In other embodiments of the present
`invention. the multi—channei communication system 100 can
`use any arbitrary technology such as TDMA. FDMA. and
`
`PETITIONERS 1062-0008
`IPR2016-00758
`
`

`

`US 7,599,327 BZ
`
`well. Immediately after the special OFDMA symbol. there is
`
`3
`Definition of Dedicated Ranging Zone
`Referring to FIG. 2. a time-domain diagram shows a
`“basic” dedicated basic ranging zone 20] defined for an
`OFDM example system [the term "zone" is interchangeable
`herein with the tent] “interval” used in the figure). in accor-
`dance with some embodiments of the present invention. The
`duration ofthe dedicated basic ranging interval 201 consists
`ofan interval ofa special OFDM symbol 202 (denoted as
`“extended-CF" OFDM symbol) and a "dead interval" 204
`that is a tie-transmission interval equal to tlte maximum tim-
`ing delay to be accommodated in the cell. The special OFDM
`symbol 202 has a duration equal to the sum of the duration of
`a special Fast Fourier 'l'ransl‘orm (Fl-"1) window 209 and the
`duration ofan extended cyclic prefix (CP) 203 whereintbe C P
`represents the repeat ofa portion ofthe signal as commonly
`known in OFDM. I-lence. the special OFDM symbol is also
`referred to as an “extended-CF" OFDM symbol in FIG. 2.
`The special Fast Fourier Transform (FFT) window 209 may
`be chosen conveniently to be the same as a “regular” OFDM
`symbol period in an example deployment ol‘an OFDM sys-
`tem. or other designed value {discussed later). The duration of
`the extended CP 203 equals to the sum of the duration ol'a
`“regular” CP 205 and the maximum timing delay 206 to be
`accommodated. The maximum timing delay is chosen based
`on the possible timing difierences among all possible sub-
`scriber locations. This value directly relates to the round-trip
`propagation delay and the cell size. Meanwhile. the duration
`ofa “regular” C P 205 within the extended CP 203 is the same
`as the CP length defined for regular data transmissions if the
`invention is used for an OFDM system. For other systems. the .
`time duration of a regular ClJ is often chosen based on the
`excessive delay spread of the channels encountered in a
`deployment environment. which is also how the CP length is
`determined for OFDM systems. Lastly. as described above.
`the appended "dead" interval is chosen aocordingtothe maxi—
`mal tinting delay.
`A ranging signal is allowed to be transmitted only in the
`defined ranging interval. The ranging wavel‘on'n itself is con-
`structed as an OFDM symbol. i.e.. by appending a C? of a
`certain length to a ranging signal. For convenience. we will
`use the term “waveform” to refer to the (TP-included signal
`and the term “signal” for the CP—excluded portion only. The
`ranging waveform transmission starts from what the SS deter—
`mines to be the right timing. For initial ranging users. that
`transmission point (i.e.. the transmission start time) will be
`the beginning of the dedicated ranging interval according to
`the base reference plus the one-way propagation delay. The
`initial ranging SS should send at that point a waveform whose
`C1" portion is of the length of an extended CP. For other
`ranging 88‘s that have already synchronized with the BS. the _
`SS should have known the timing advance and transmit in
`advance to some reference point so that all the SS signals
`arriveat the BS at roughly the same time. In one embodiment.
`the non-initial ranging SS can either transmit a waveform
`with a regular (7P at a timing point in advance to the start of ..
`205 within 203 of FIG. 2. or transmit a wavefonn with an
`extended CP at a tinting point in advance to the start 0120).
`With the above definition of ranging interval, all types of
`ranging signals will not interfere with any transmission that
`precedes and follows the ranging interval, such as OFDM
`symbols 207 and 208 in an OFDM-based example system.
`The maximum timing delay should be large enough to accom-
`modate the maximum propagation delay for SSS that have not
`adjusted their timing (i.e.. initial ranging users). The maxi—
`mum timing delay is a parameter determined based on the cell
`sire.
`l-‘or the receiver processing at the BS. since the BS
`predefines the maximum timing delay and thus the extended
`
`4
`CP length. the BS should know how to adjust the sampling
`position accordingly in order to extract the special FF'I‘ win—
`dow 209. The special F FT window can be any size in theory
`A large special FFT window can reduce the proportion ofthe
`extended GP to the special FFT size (i.e.. reducing the over-
`head) and provide more ranging opportunities to reduce col-
`lision. Also. the time span of the transmission can also be
`extended so that there will be more signal power arriving at
`the [38 for the same average transmit power. However, with a
`large special FF'I‘ window. the overall overhead of a ranging
`signal as a portion of the uplink sub-frame increases and the
`ranging signal also becomes more susceptible to channel time
`variations (e.g. mobility) that results in inter-carrier interfe -
`ence caused by Doppler Sitifi. The choice of the special F FT
`size should also consider practical
`implementation. For
`example. in an OFDM system. making it an integer multiple
`ofthe regular Fl’T size may simplify the BS proceSsing.
`The total ranging overhead. which is the ratio of the dura-
`tion ofthe dedicated basic ranging interval to the entire uplink
`sub-frame. depends only on the uplink sub-frame. The longer
`the uplink. the lower is the overhead. If the overhead due to
`the “dead interval” 204 delay becomes too excessive. the
`“dead interval” 204 can be omitted at the price of generating
`inevitable interference to the next symbol.
`Referring to FIG. 3. a time-domain diagram shows an
`“extended” dedicated ranging interval 303 that is built upon
`the “basic” dedicated ranging interval 20.]. in accordance
`with some embodiments of the present invention. If more
`ranging opportunities are needed than what a basic ranging
`interval cent provide. an extended ranging interval 303 can be
`defined where one or more regular OFDM symbols 301 and
`302 with only a regulaGC length may be added in front ofthe
`extended-CF special symbol. Initial ranging transmission is
`allowed only during the extended-CF interval. but other rang-
`ing transmissions are allowed everywhere. This design is an
`alternative to the case in which the special FFT size is
`enlarged. as described with reference to FIG. 2.
`Referring to FIG. 4. a frequency-domain diagram of a
`variation of the extended dedicated ranging interval is shown.
`in accordance with some embodiments of the present inven-
`tion. In these embodiments. the ranging signal is allowed to
`occupy only a portion of the system bandwidth instead ofthe
`entire bandwidth as before. For example, for the extended-C P
`symbol 401 (that is the same as extended C P symbol 202 in
`FIG. 2). a portion of the bautdwidth 402 is dedicated to rang-
`ing. and the remaining bandwidth 403 is for data traffic. In
`fact. such a design in which the ranging and data traffic are
`multiplexed can be done using different dalafranging ratios
`for each symbol in the extended ranging interval such as that
`illustrated in FIG. 4. where the additional regular OFDM
`symbols 404 and 405 are used. The generic term “frequency—
`time ranging zone” is used for these cases.
`Referring to FIG. 5, a lime-domain diagram shows an
`exemplary ranging interval for an OFDM system similar to
`01" DM systems described by drafts and the published version
`of the IEEE 802.16 standard The ranging interval 501 is
`composed of one special OFDMA symbol with an extended
`CP that may be preceded by up to four regular OFDMA
`symbols each having a regular UP for providing moreranging
`opporttmitics ifneeded. The duration of the extended CP is
`signaled by the base in a control message sent from the BS
`(e.g.. the UL-MAP message defined in draft and published
`versions of lEEE 802.16 standards) as an integer multiple of
`the regular C P. Similarly.
`the special FFT size of the
`extended—CF symbol. which may also be an integer multiple
`of the regular F 1“‘1" size. is signaled in the control message as
`
`.
`
`PETITIONERS 1062-0009
`IPR2016-00758
`
`

`

`US 7,599,327 BZ
`
`5
`a “dead” interval that equals to the largest maximum timing
`difference. But it may be omitted to trade perfornuurce deg—
`radation for overhead reduction. The control message may
`indicate whetherthe dead interval is included. The duration of
`tlte dead interval is implicitly known to the SS and is equal to 5
`the difference between the extended-(“P symbol duration and
`the regular C P duration.
`
`Division of Ranging Opportunities in Frequency, Time, and
`Code Domains
`
`(for non-OFDM that does not definea (.‘P length. the duration
`
`Referring to FIG. 6. a block diagram shows the division of
`ranging opportunities in frequency. time. and code domains.
`in accordance with sotne embodiments of the present inven—
`tion. Each random access signal is generated based on a
`ranging sequence (interchangeable with “access sequence“
`and “ranging code" and “acce5s code") that is randomly cho-
`sen from a code group 601 allocated to the sector (the code
`group size is denoted herein as NC. an integer). The access
`sequences used in a code group and the allocation of code
`groups to different sectors are specified later. The ranging
`sequence may be used to generate an access signal by directly
`modulating the contiguous sub~carriers in a frequency block
`(sub-band) that is randomly chosen among N b] sub-bands
`602, wherein N b. is an integer including the value “1" known
`to both BS and SS. Nb, may be determined based on the
`system bandwidth and be made known to the BS and the SS.
`The timewdomain access signal is generated by performing an
`lFFT on the ranging sequence after modulating the chosen
`sub—band. Before a CP is inserted in front ofthe access signal
`to form a complete aceess wavct‘onn. the access signal may be _
`cyclically (circularly) shifted in time domain. where the shift
`is chosen randomly among Nd, allowed values 603 that are
`known to the BS and SS. wherein N5), is an integer. Lastly. a
`CP is added to form the final ranging waveform where the
`length ofthe C P is that of the extended CP for initial ranging
`and for other ranging. either the extended CP or the regular
`CP depending on the transmission point (discussed above).
`The duration of the waveform corresponds to the duration of
`one OFDM symbol
`in the extended ranging interval.
`in
`embodiments such as those described with reference to FIG.
`3 and FIG. 5 In embodiments such as those described with
`reference to FIG. 5. the ranging sequence may be used to
`generate an access waveform by appending data symbols to
`the ranging sequence and directly modulating the contiguous
`sub-carriers in the frequency block (sub—band) that is ran—
`dotuly chosen. using terms of the appended ranging
`sequence.
`More detail on lhe division of ranging opportunities in
`frequency. time. and code domains is as follows. Firstly, in the
`frequency domain, an entire frequency band is divided into _
`Nb1 frequency blocks 602 (Nb1 subnbands with K sub-carriers
`in each sub-band). A ranging signal may occupy only one
`sub-band. The reason for dividing the bandwidth into
`orthogonal blocks is for better flexibility. First. the number of
`ranging opportunities can be made adjustable to the band— ..
`width: larger bandwidth systems need to provide tnore opporw
`tunities than narrower bandwidth systems for a similar colli—
`sion rate. Second, transmitting on a narrow subsband allows
`power boost on that band to achieve a decent uplinlt SNR.
`even though narrowband transmission has lower timing reso-
`lution than wider bandwidth transmission (Nb. channel taps
`will collapse into one channel tap when only UN)” of the
`bandwidth is excited). On the other hand. the number of
`sub—carriers in each sub—baud, which equals to the length of
`the ranging sequence code, affects the cross-correiation char—
`acteristics. For example. halving the number of sub-carriers
`in a sub-band allows a 3 dB transmit power boost on that band.
`
`6
`but the potential interference from other co-channel ranging
`codes also increases by 3 dB. So the ntunber of sub-carriers in
`a sub-band involves a l'radeoif between SNR boost and inter-
`ference sacrifice. In summary. the parameter lily,j is specified
`by the BS based on the bandwidth (FFT size). uplink SNR
`requirement.
`timing precision requircnttntl.
`suppression
`capability to potential coachannel interferences. and the num
`ber of ranging opportunities that needs to be provided. It
`should also be specifiedjointly with the other two parameters
`NC and N“, described in more detail below.
`Secondly. in each sub-band. a number of ranging codes 601
`(i.e.. N, sequences) may be allowed. Since these ranging
`codes occupy the same band. they may interfere with each
`other even without any code collision. Sequences with good
`cross—correlation are much desired for better code detection
`and channel estimation. in addition. a low PAPRj of the
`time-domain ranging waveform is also much desirable in
`order to be able to boost the transmission power to improve
`the upliuk SNR. The details of the sequences that have these
`desirable properties will be discussed in the next section.
`Additionally. for cellular deployment. a number of sequence
`groups (each having NC. access sequences) are also required
`for allocating to difi'erent neighboring sectors. So when those
`codes are generated and grouped, any pair of codes from
`distinct groups needs to have good cross correlation, just like
`any pair of codes in the same group. In summary. the param-
`eter N‘, is determined by the BS based on the access needs and
`the maximally tolerable interference level at which the suc-
`cessful detection rate is still good.
`Thirdly. for each ranging code, NW cyclic time shifts 603 of
`the little-domain ranging signal (phase rotation in frequency
`domain) can be used to further increase the number o franging
`opporttuu'ties. Mathematically.
`the
`frequency
`domain
`sequence. after the_j"’ shift is
`
`IJ-tl' talkie PW “Wm.
`
`t I i
`
`where s(k) is the original (or t]m shift) sequence. L is the CP
`length (regular or extended CP. depending on the type of
`ranging) and NF”- is the FFT size. In essence. code separa-
`bility is achieved by the fact that the estimated channel is
`shified in time domain by some multiples of L. if L is large
`enough to cover most ofthe channel length. the access signals
`using distinct cyclic shifts will allow their corresponding
`channeis to be separated reasonably well.
`The initial ranging transmission may be used by any SS
`that wants to synchronize to the system chatutel for the first
`time. In one embodiment of llte invention. a control message
`from the BS may specify the sub~bands that an initial ranging
`signal can use. All sub—bands or. for example, a specified
`number of the sub-bands starting from the lowest frequency
`offset may be allowed for initial ranging. Maximally, only
`Nfl=LNWJLCMI shiftsare preferred for interference—free code
`separation among different shifts ofa ranging signal where
`[it] denotes the flooring function (Len, the maximum integer
`that is not greaterthan x). LEW is the length ofanextendedCP
`and NW isthe FFTsize ofthe special FFT symbol (209 of FIG.
`2) that may be multiples of the regular FFT size N. If some
`interference between estimated channels can be tolerated.
`that maximal number may be even increased.
`In general.
`more shifts can be used at the expense of increased interfer-
`ence. But a good practice is setting the number of shifts to
`NM'
`[Nsrj/L(_.,hjml so that a good estimation ofthe noise and
`interference level can be obtained from the “charmel—free"
`
`lFFT samples. Since LCPn can be significantly larger than the
`regular Cl’ length (denoted as Isa—P) used in an OFDM system
`
`PETITIONERS 1062-0010
`IPR2016-00758
`
`

`

`US 7,599,327 BZ
`
`5.,th = esp{ -j2Jru
`ut“ctass indefl = l
`
`Irtk+li
`}.k =t1...Nc;-| and
`3N6
`Na — 1
`
`3
`
`7
`ofa regular C‘P. orLCP. is ofien chosen based on the excessive
`delay spread of the charmcls encountered in a deployment. as
`discussed before).
`the allowed NS}, can be significantly
`reduced. To improve the number of shifts available for other
`non-initial ranging functions. the initial ranging can be con-
`lined to a certain number 0 f(say Nb 1 ') sub -hands on which the
`allowed number of shifts is. only for cxaittple. N_t,i'=LN_€pf
`Int-weld. But on the remaining NMANM' sub-bands. where
`only non-initial ranging is allowed. the number of shifts cart
`.3»
`be increased to NflfilN flit-Pf]. Often. the total ranging 1
`opportunities increases. if initial ranging is allowed on only
`Nb1'(<Nbl) sub~bands. the number ofinitial ranging oppomb
`11in is then N,;,'*NC*NM'. lf initial ranging is allowed on all
`sub-bands. the total number of all ranging opportunities is
`N_,,,'*Nl.*Nb 1. of which a portion may be assigned to initial
`ranging.
`Periodic-ranging transmissions are sent periodically for
`system periodic ranging. Bandwidth-requests transmissions
`are for requesting tlplink allocations from the BS. These .
`non-initial ranging transmissions may be sent only by 38::
`that have already synchronized to the system These trans-
`missions can also use the additional OFDM symbols if these
`symbols are allocated for ranging in a control message from
`the BS.
`
`desired length is chosen and the GC‘L sequence is cyclically
`
`where N6 is the length ofthe GCL sequence (a prime number
`is preferred as will be explained later) and u is referred to as
`the class index that is a non-zero integerchosen between I and
`NG—l. The GCL sequence has the following important prop—
`crties:
`Property 1 : The GCL sequence has constant amplitude. and
`its NG—point discrete Fourier Transform (DFT) has also con—
`stant amplitude.
`Property 2: The GCL sequences of any length have an
`“ideal” cyclic autooorrclation (i.c.. the correlation with the
`circularly shifted version ot‘itsclf is a delta function)
`Property 3: The absolute value ofthe cyclic cross-correla-
`tion [inaction between any two C'rCI . sequences is constant and
`equal to NVNZ. when Iul—uZl. 1.11. and u2 are all relatively
`prime to NC (a condition that can be easily guaranteed if NG
`is a prime number).
`The cross-correlation mentioned here is a sequence itself
`with each value corresponding to the correlation between two
`sequences where one ofthem is shifted by an integer number
`of elements (referred to as a “lag"). The cross-correlation If
`JET; at all lags (Property 3) actually achieves the optimal
`cross—correlation value for any two sequences that have the
`ideal autocorrelation property (meaning that the theoretical
`mininnun of the maximum value of the cross-correlation over
`all lags is achieved). The minimum is achieved when the cross
`correlations at all lags equal to 11’ This property is impor-
`tant since several interfering sequences are used in each sub-
`band and in each sector (more interferers if in a multi-sector
`environment). The cross correlation property allows the inter-
`fering signal be evenly spread in the time domain after cor-
`relating the received signal with the desired sequence. Hence.
`at least the significant taps of the desired channel can be
`detected more reliably.
`It should also be noted that an arbitrary scalar phase shift
`applied to a (iCL sequence also results in a GCI. sequence
`that has the optimal cyclic cross—correlation and ideal auto“
`correlation. Also, if an NG-point DF