a2) United States Patent
`US 8,467,366 B2
`(0) Patent No.:
`
`Liet al. (45) Date of Patent:
`*Jun. 18, 2013
`
`US008467366B2
`
`(54) METHODS AND APPARATUS FOR RANDOM
`ACCESS IN MULTI-CARRIER
`COMMUNICATION SYSTEMS
`
`Inventors: Xiaodong Li, Kirkland, WA (US); Titus
`Lo, Bellevue, WA (US); Kemin Li,
`Bellevue, WA (US); Haiming Huang,
`Bellevue, WA (US)
`Assignee: Neocific, Inc., Bellevue, WA (US)
`to any disclaimer, the term ofthis
`Notice:
`Subject
`patent is extended or
`adjusted under 35
`U.S.C. 154(b) by 149 days.
`to a terminal dis-
`This patent is subject
`claimer.
`
`Appl. No.: 13/205,579
`Aug.8, 2011
`Filed:
`Prior Publication Data
`
`US 2011/0292881 Al
`
`Dec. 1, 2011
`
`Related U.S. Application Data
`Continuation of application No. 10/583,158, filed as
`application No. PCT/US2005/008169 on Mar. 9,
`now Pat. No. 7,995,967.
`2005,
`Provisional application No. 60/551,589, filed
`9, 2004.
`
`on Mar.
`
`(75)
`
`(73)
`
`(*)
`
`(21)
`
`(22)
`
`(65)
`
`(63)
`
`(60)
`
`(51)
`
`(52)
`
`(58) Field of Classification Search
`wiecesssesctesseseseseecssseecsnecensensseseeansentes
`USPC
`370/342
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`12/1990 Ballanceetal.
`4,977,593 A
`11/1999 Fuhrmannetal.
`5,991,308 A
`etal.
`6,519,449 Bl
`2/2003 Zhang
`7,995,967 B2
`8/2011 Lietal.
`wow.
`2010/0111017 Al*
`5/2010 Umetal.
`
`370/329
`
`KR
`KR
`KR
`
`FOREIGN PATENT DOCUMENTS
`20050015119 A
`2/2005
`100585233 Bl
`5/2006
`20060055636 A
`5/2006
`
`OTHER PUBLICATIONS
`
`International
`International Search Report and Written Opinion;
`Patent Application No. PCT/US05/08169; Filed Mar. 9, 2005; Appli-
`cant: Waltical Solutions, Inc.; Mailed Jun. 9, 2005; 9 pages.
`*
`
`cited by examiner
`—
`
`Primary Examiner
`(74) Attorney, Agent,
`
`—
`Ajibola Akinyemi
`or Firm
`Perkins Coie LLP
`
`ABSTRACT
`(57)
`Methods and apparatus in a multi-carrier cellular wireless
`network with random access
`improve receiving reliability
`and reduce interference of uplink signals of a random access,
`ofa basestation
`while improving the detection performance
`receiver by employing specifically configured ranging sig-
`nals.
`
`Int. Cl.
`H04Q 7/216
`(2006.01)
`US. Cl.
`cece cece sencnen ene enees
`USPC
`
`310
`Base
`Station
`
`370/342; 370/329
`
`24 Claims, 8 Drawing Sheets
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`US 8,467,366 B2
`
`1
`METHODS AND APPARATUS FOR RANDOM
`ACCESS IN MULTI-CARRIER
`COMMUNICATION SYSTEMS
`
`CROSS-REFERENCE TO RELATED
`
`APPLICATION(S)
`This application is a continuation of U.S. patent applica-
`tion Ser. No. 10/583,158, entitled “METHODS AND APPA-
`RATUS FOR RANDOM ACCESS IN MULTI-CARRIER
`COMMUNICATION SYSTEMS”,
`filed Aug. 27, 2008,
`which is a U.S. National Stage application of PCT/US05/
`08169, entitled “METHODS AND APPARATUS FOR RAN-
`DOM ACCESS IN MULTI-CARRIER COMMUNICA-
`TION SYSTEMS”, filed Mar. 9, 2005, which claims the
`benefit of U.S. Provisional Patent Application No. 60/551,
`589, entitled “METHODS AND APPARATUS FOR RAN-
`DOM ACCESS IN MULTI-CARRIER COMMUNICA-
`TION SYSTEMS”,filed Mar. 9, 2004.
`
`BACKGROUND
`
`a mobile station first
`In a wireless communication system,
`commu-
`a random access for establishing
`needs to
`perform
`nication with a base station. The random access
`typically
`includes twosteps: (1) Ranging and (2) Resource Request and
`Allocation. During Ranging, the mobile station sends a
`signal
`so that the base station can
`to the base station,
`identify the
`mobile station and measure the powerand time delay of the
`mobile station, and inform the mobile station for power
`adjustment and time advance. During Resource Request and
`Allocation, the uplink and downlink resources for communi-
`cation are
`andallocated. Ranging isa critical part of
`requested
`multi-carrier wireless communication system, and there are
`several important issues related to
`ranging:
`1. The bandwidth efficiency of the ranging signals
`2. The interference of ranging signal with other uplink
`signals
`3. The detection performance and complexity
`station receiver
`The ranging process typically involves an
`exchange of
`messages betweenthe base station and the mobile station by
`which the mobile station aligns itself with the start of each
`timeslot after compensating for propagation delay and other
`factors. One problem in a shared medium communication
`networkinvolves the ranging of many mobile stations. When
`many mobile stations attempt to
`perform the ranging simul-
`are forced to contendfor access to the shared
`taneously, they
`channel andit becomesdifficult for any ofthe mobilestations
`to
`complete the ranging process due to the large number of
`collisions. As a
`result, the time neededfor all of the mobile
`stations to
`complete the ranging process is excessive, and
`much bandwidth on the shared channelis wasted.
`
`at the base
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`a basic structure of a multi-carrier signal in
`FIG. 1 depicts
`the frequency domain, madeup of subcarriers.
`FIG. 2 showsa radio resource divided into small units in
`both the frequency domain (subchannels) and the time
`domain (timeslots).
`FIG. 3 showsacellular system with atleast one cell and one
`basestation.
`a
`FIG.4 depicts
`ranging subchannel composedofatleast
`one block of subcarriers.
`
`20
`
`25
`
`40
`
`45
`
`55
`
`60
`
`2
`FIG.5 illustrates a case of time misalignmentin a
`ranging
`signal, with a base station OFDM timeframe, due to uncer-
`at an initial stage
`tainty of a mobile station’s round
`trip delay
`of random access.
`a smeared spectrum of a subcarrier in a
`FIG. 6 depicts
`ranging subchannel whenthe rangingsignalis received using
`a
`regular OFDM timeframe.
`FIG. 7 illustrates a
`ranging sequence’s corresponding
`time-domain signal that can be approximated with a
`binary
`sequence.
`FIG. 8 shows a
`ranging subchannel arrangement in which
`spacing between subcarrier blocks in the frequency domain
`has no, or minimum,repetition.
`DETAILED DESCRIPTION
`
`In the following description, the invention is explained
`with respect to some of its various embodiments, and pro-
`vides specific details for a
`thorough understanding. However,
`one skilled in the art will understandthatthe invention may be
`practiced without such details. In other instances, well-
`known structures and functions have not been shown or
`described in detail to avoid obscuring aspects of the embodi-
`ments.
`Unless the context
`clearly requires otherwise, throughout
`the description and the claims, the words “comprise,” “com-
`prising,” and the like are to be construed in an inclusive sense
`as
`to an exclusive or exhaustive sense;
`that is to say,
`opposed
`in the sense of “including, but not limited to.” Words using the
`or
`or
`plural numberalso include the plural
`singular
`singular
`number
`the words “herein,”
`respectively. Additionally,
`“above,” “below” and words of similar import, when used in
`as a whole and
`this application, shall refer to this application
`not to any particular portions of this application. When the
`claims use the word “or” in reference to a list of two or more
`items, that word coversall of the following interpretations of
`the word: any of the itemsin thelist, all of the items in thelist
`and any combination of the itemsin thelist.
`The embodiments of this invention disclose methods and
`apparatus for random access in a multi-carrier system. In
`are
`to
`particular, ranging signals
`designed
`improvereceiving
`reliability and to reduce interference with other uplink sig-
`are described that
`nals. Furthermore, methods and apparatus
`at
`improve the detection performance
`the base station
`receiver.
`In a multi-carrier communication system such as multi-
`access
`carrier code division multiple
`(MC-CDMA) and
`access
`orthogonal frequency division multiple
`(OFDMA)
`systems, information data are
`on subcarriers that
`multiplexed
`are
`a
`mutually orthogonalin the frequency domain.In effect,
`a
`frequency selective channelis partitioned in frequencyinto
`numberof
`parallel, but small, segments that can be treated as
`flat fading channels and can
`employ simple one-tap equaliz-
`ers. The modulation/demodulation can be performed using
`the fast Fourier transform (FFT).
`In a multi-carrier communication system the physical
`media resource
`(e.g., radio or
`can be divided in both the
`cable)
`frequency and time domains. This canonical division pro-
`high flexibility and fine granularity for resource shar-
`vides a
`ing. A basic structure ofa multi-carriersignal in the frequency
`domain is made up of subcarriers, and within a
`particular
`spectral band or channelthere are a fixed numberof subcar-
`riers. There are three types of subcarriers:
`1. Data subcarriers, which carry information data;
`are pre-
`2. Pilot subcarriers, whose phases and amplitudes
`determined and made knownto all receivers and which
`
`10
`
`10
`
`

`

`US 8,467,366 B2
`
`4
`using the OFDM time window of regular signals. Therefore,
`misaligned subcarriers within a
`ranging subchannel will
`interfere with each other and with other data subchannels that
`are
`to them. In the following description, several
`adjacent
`methods are
`to address such problems.
`presented
`In one
`embodiment, the ranging subchannel is composed
`of multiple blocks of subcarriers. The subcarriers in each
`block are
`contiguous in frequency. The signal powerof the
`subcarriers towards the boundary (the lower ends and the
`higher ends in frequency) of a block is lower than that of the
`subcarriers towards the center of the block. In a
`special case,
`the powerlevels ofthe two subcarriers at both ends ofa block
`are set to zero.
`In yet another embodiment, each segment of a
`ranging
`sequence is a Hadamard sequence and a full ranging sequence
`is composed ofmultiple Hadamard sequences. Each segment
`to a block of contiguous subcarriers. In Table 1,
`corresponds
`a
`typical example is shown for two
`ranging sequences. Each
`segment is a 4-bit Hadamard sequence and each ranging
`sequence is composed of 4 segments. The two
`ranging
`sequences are
`segment-wise orthogonalto each other.
`
`TABLE1
`
`3
`are used for assisting system functions such as estima-
`tion of system parameters; and
`3. Silent subcarriers, which have no energy and are used for
`guard-bands and DCcarriers.
`The data subcarriers can be arranged into groups called
`subchannels to support scalability and multiple-access. The
`one subchannelare not
`carriers forming
`necessarily adjacent
`or all ofthe subchannels.
`to each other. Each user mayusepart
`The conceptis illustrated in FIG. 1 for the interleaved sub-
`channels at the base station transmitter. Data subcarriers can
`be grouped into subchannels in a
`particular way andthe pilot
`subcarriers are also distributed over the entire channel in a
`particular way. Thebasic structure ofa multi-carrier signal in
`the time domain is madeup oftime slots to support multiple-
`access. The resource division in both the frequency and time
`domains is depicted in FIG. 2.
`FIG.3 illustrates a
`typical cellular structure. In this illus-
`tration no distinction is made between a cell and a sector. Ifa
`cell is dividedinto sectors, from a
`system engineering point of
`view each sector can be considereda cell. In this context, the
`terms “cell” and “sector” are
`interchangeable. Both of them
`are
`generally called a cell. In the communication system of
`FIG.3 Base Station 310 is communicating with Mobile Sta-
`tions 301 and 302in Sector
`ofits cell site while Base Station
`320 is communicating with Mobile Stations 303, 304, and
`305 in Sector
`ofits cellsite.
`FIG.4 illustrates two
`ranging subchannels, each of which
`is composed of multiple blocks of subcarriers. The subcarri-
`ers in each block are
`contiguous in frequency. FIG. 4 sche-
`matically shows that the signal power of the subcarriers
`towards the boundary (the lower ends and the higher ends in
`frequency) of a block is lower than that of the subcarriers
`a
`towards the center of the block. (In
`special case, the power
`levels of the two subcarriers at both ends of a block are set to
`zero.) Because different factors may cause
`possible overlap of
`two subcarrier blocks from to different transmitters,
`the
`attenuated boundary subcarriers will minimize the resulting
`interference.
`In accordance with aspects of some
`embodiments, the
`ranging signalis carried over a
`ranging subchannelthat con-
`or
`tains multiple subcarriers. Either binary
`non-binary signals
`can be modulated on the subcarriers of a
`ranging subchannel.
`The sequence of modulating signals in a
`ranging subchan-
`nel is called a
`ranging sequence. Multiple ranging sequences
`are
`permitted in a cell. A mobile station chooses a
`ranging
`sequencefor random access and uses the sequenceto
`identify
`itself in the initial communication with a base station. The
`period of a
`ranging signal is called a
`ranging slot. A ranging
`slot may
`over one or
`multiple OFDM symbols. Multiple
`last
`ranging slots can be provided
`to increase the random access
`opportunity and reduce the collision probability.
`In one
`embodiment, different cells may have different sub-
`carrier configurations for their ranging subchannels. Differ-
`ent cells may
`also have different ranging sequencesets. These
`identify the association of a
`differences may be used to
`mobile station with a cell.
`FIG.5 illustrates the timing of regular uplink data signals
`a Guard Period G.P.). In the begin-
`and ranging signals (with
`ning of a random access
`the mobile station is
`attempt,
`unaware of its round-trip time to the base station. As a
`result,
`at the base station may be
`the arrival time of ranging signal
`misaligned with other signals which have been synchronized
`to the base station clock. As depicted in FIG. 5, the random
`access
`Ranging Signal does not coincide with the expected
`arrival time at the base station. As shown in FIG.6, time
`can cause
`misalignment ofregular signals and ranging signals
`to be smeared whenitis received
`spectrum of ranging signals
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`11
`
`Example of ranging sequences
`+1 414141
`+141-1-1 41-1-141
`Ranging +1-1+1-1
`Sequence
`1
`Ranging
`Sequence
`2
`
`+1-1-141
`
`+1 -141-1 4141-1-1
`
`+1 414141
`
`can be
`In addition, other properties in signal processing
`exploited in sequence design. In one embodiment of the
`implementation, the ranging sequence is designed such that
`its corresponding time-domain signal exhibits relatively low
`peak-to-average powerratio. This improves the powereffi-
`ciency of the mobile station transmission power amplifier.
`suchthat the time
`Furthermore, the ranging signal is designed
`can be approximatedwith a
`binary sequence(e.g., FIG.
`signal
`7), thereby reducing the complexityofthe receivercorrelator.
`While in theory, and even in practice, each modulating digit of
`a
`a
`ranging sequence can
`a range of logic levels,
`represent
`binary formatis practically the simplest representation and
`requires the simplest receiver components for its processing.
`FIG.7 illustrates a
`ranging sequence’s corresponding time-
`that can be approximated with a
`domain signal
`binary
`sequence.
`In another embodiment,the blocks ofa ranging subchannel
`can be distributed or allocated in such a way that the autocor-
`relation of a
`ranging sequence correspondingto the ranging
`subchannel, in time-domain, exhibits a set of desired proper-
`ties such as a narrow main peak and low sidelobes. For
`example, the blocks can be distributed in the frequency band
`of interest such that there is minimum redundancy in a co-
`sampling function. In other words, spacing between the
`blocks of a
`ranging subchannel in the frequency domain has
`as illustrated in FIG. 8, where the
`no or minimum repetition,
`spacing consists of the set
`{d, 2d, 3d, 4d, 5d, 6d}.
`an
`FIG. 8 is merely
`example of such possible arrange-
`ments, where an autocorrelation process only produces
`one
`major peak, regardless of the ranging sequence carried by the
`an autocorrelation pro-
`ranging subchannel blocks. During
`copies of a
`move in parallel with
`cess, two
`ranging signal
`respect to each other, in a
`step-wise manner, and at each step
`the sum of the multiplication of their corresponding valuesis
`computed and recorded. Note that in an interval of a
`ranging
`
`11
`
`

`

`US 8,467,366 B2
`
`5
`subchannel where there are no subcarriers, the ranging signal
`value is zero.
`Therefore, employing the proposed arrange-
`ments, at any step except for the step during which the two
`most of
`copiesof the ranging signalare substantially aligned,
`the non-zero values of either copy will correspondto the zero
`values of the other copy and the multiplication result of the
`corresponding values will be zero, which results in low side-
`lobe values.
`controlling the powersettings of a
`to
`With regard
`ranging
`signal, before a random access, a mobile station estimates the
`path loss from a base station, using the received downlink
`signal. It uses
`open-loop powercontrolto set the powerlevel
`of the ranging signal. In one
`embodiment, the mobile station
`adds a
`negative offset to the open-loop power setting and
`gradually ramps up the transmission power of the ranging
`as the number of random access failures andretrials
`signal
`increase.
`In one
`embodiment, the base station receiver detects the
`presence of each ranging signal, its time delay, and its power
`a
`or other
`level through the use of a matchedfilter,
`correlator,
`meansin the time domain, the frequency domain,or both.
`In another embodiment, when the ranging subchannelis
`composed of blocks of contiguous subcarriers, the base sta-
`first
`tion performs hierarchical detection:
`in frequency
`domain, then in time domain. The detection process is as
`follows:
`to a selected window ofthe received
`1. The FFT is applied
`time-domain signal, s(t).
`2. Fora particular ranging subchannel, its receivedversion,
`is correlated in the frequency domain with
`{r(x) }*,_,,
`the ranging sequencesassociated with the cell, in a seg-
`ment-wise fashion, where K is the total number of
`blocks in a
`ranging subchannel. If the m” sequence
`associated with the cell is denoted by {0,,,(k)}*;_,,
`the
`correlation value, P,,,, is computed by:
`
`m =
`
`K
`>) [AUD -Bm wl
`k=l
`
`where the dot-product is computed by:
`
`=
`
`N
`
`n=l
`D°
`
`(0) -Bm(K)
`
`xk, 0) Lem(k, I"
`
`and where N denotes the number of subcarriers in a
`block, x(k,n) denotes the received version of the n”
`subcarrier ofthe k” block in the given ranging subchan-
`nel, andc,,,(k,n) represents the value ofthe n” subcarrier
`of the k” block in the given ranging subchannel for the
`m” sequence. It is noted that that both
`and
`T(k)
`B,,(k)
`are vectors ofthe dimension sameas the segmentlength.
`If P,,, is greater than a
`given threshold, this indicates that
`a
`to the m” sequence has
`ranging signal corresponding
`been detected.
`a time-domain
`3. For the ranging signalidentified in Step 2,
`correlation of the full sequence of the ranging signal is
`a
`sliding-window fashion,to find the time
`performed,in
`delay of that ranging signal, that is:
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`12
`
`set 20
`
`forr=0,1,...
`
`,D
`
`T D
`
`t=0
`d
`
`=
`
`C(t)
`
`
`
`where T denotes the length of the time-domain ranging
`to the maximum time delay
`sequence, D corresponds
`allowed by the system, and z*(t) represents the time-
`domain signal of the detected ranging sequence. The
`maximum value of C(t) fort=0, 1,..., Dis the estimate
`of the powerofthe ranging signal and the corresponding
`value of t indicates the time delay associated with the
`ranging signal.
`In the case of ranging sequences composed of Hadamard
`sequences, the dot-products of the received signal and the
`ranging sequence in a
`particular segment in Step 2 can be
`a
`single Fast Hadamard
`evaluated simultaneously using
`Transform (FHT), thereby simultaneously detecting multiple
`ranging sequences.
`The above detailed description of the embodiments of the
`invention is not intended to be exhaustive or to limit the
`invention to the precise form disclosed above or to the par-
`ticular field of usage mentioned in this disclosure. While
`specific embodiments of, and examplesfor, the invention are
`described aboveforillustrative purposes, various equivalent
`modifications are
`possible within the scope of the invention,
`as those skilled in the relevant art will recognize. Also, the
`teachings of the invention provided herein can be applied
`to
`other systems, not
`necessarily the system described above.
`The elements andacts of the various embodiments described
`above can be combinedto provide further embodiments.
`All of the above patents and applications and otherrefer-
`ences, including any that may be listed in accompanying
`filing papers, are
`incorporated herein by reference. Aspects of
`the invention can be modified, if necessary, to
`employ the
`systems, functions, and concepts of the various references
`described above to
`provide yet further embodiments of the
`invention.
`can be madeto the invention in light of the above
`Changes
`“Detailed Description.” While the above description details
`certain embodiments of the invention and describes the best
`no matter how detailed the above
`mode contemplated,
`appears in text, the invention can be practiced in many ways.
`implementation details may vary considerably
`Therefore,
`while still being encompassed by the invention disclosed
`herein. As noted above, particular terminology used when
`describing certain features or
`aspects of the invention should
`not be taken to
`imply that the terminology is being redefined
`herein to berestricted to any specific characteristics, features,
`or
`aspects of the invention with which that terminology is
`associated.
`In general, the terms used in the following claims should
`not be construedto limit the inventionto the specific embodi-
`ments disclosed in the specification, unless the above
`Detailed Description section explicitly defines such terms.
`Accordingly, the actual scope of the invention encompasses
`not
`only the disclosed embodiments, but also all equivalent
`or
`ways of practicing
`implementing the invention under the
`claims.
`ofthe invention are
`presented below
`While certain aspects
`in certain claim forms, the inventors contemplate the various
`aspects of the invention in any number of claim forms.
`Accordingly, the inventors reserve the right
`to add additional
`to pursue such additional
`claimsafter filing the application
`claim formsfor other aspects of the invention.
`
`12
`
`

`

`US 8,467,366 B2
`
`7
`
`an
`
`Weclaim:
`1. In a multi-cell orthogonal frequency division multiple
`access
`(OFDMA)wireless communication system compris-
`a
`a mobile
`plurality of base stations and mobile stations,
`ing
`to communicate with a
`station configured
`serving base station
`in a cell via a communication channel, the mobile station
`comprising:
`an
`to transmit a data signal
`to the
`apparatus configured
`serving base station in the cell over a data subchannel,
`a
`wherein the data subchannel comprises
`plurality of
`or
`non-adjacent subcarriers within the commu-
`adjacent
`nication channel; and
`to transmit a
`ranging signalto the
`apparatus configured
`serving base station in the cell over a
`ranging subchannel
`for random access, wherein:
`the ranging signal is formed from a
`ranging sequence
`selected from a set of ranging sequences associated
`with the cell for identifying the mobile station;
`the ranging signallasts over a
`period of one or
`multiple
`orthogonal frequency division multiplexing (OFDM)
`symbols and the ranging signal exhibits a low peak-
`to-average powerratio in the time domain; and
`at least one block of
`the ranging subchannel comprises
`subcarriers within the communication channel and
`powerlevels of subcarriers at both endsof a block are
`set to zero.
`2. The mobile station of claim 1, wherein the subcarrier
`configuration of the ranging subchannelfor the cell is differ-
`ent from subcarrier configurations ofranging subchannels for
`other cells.
`3. The mobile station of claim 1, wherein theset ofranging
`is different from sets of ranging
`sequences for the cell
`sequencesfor othercells.
`4. The mobile station of claim 1, wherein subcarriers in a
`block are
`contiguous in frequency.
`an
`5. The mobile station of claim 1, further comprising
`to control a transmission powerof the
`apparatus configured
`an
`open-loop powercontrol method by:
`ranging signal using
`a
`path loss betweenthe serving base station and
`estimating
`the mobile station based on a received downlink signal;
`setting the transmission powerof the ranging signal based
`on the path loss; and
`increasing the transmission powerofthe ranging signal for
`retransmission.
`6. The mobile station of claim 1, wherein a powerlevel of
`subcarriers towards the high-end and low-end frequency
`boundaries of a block of subcarriers is lower than a power
`level of subcarriers towards the center of the block.
`7. The mobile station of claim 1, wherein boundary sub-
`carriers ofa block of subcarriers in the ranging subchannelare
`attenuated to reduce interference with other uplink signals
`occursat the basestation.
`whensignal time misalignment
`8. The mobile station of claim 1, wherein the ranging
`or
`sequenceis a
`non-binary sequence.
`binary
`9. In a multi-cell orthogonal frequency division multiple
`access
`a base
`(OFDMA) wireless communication system,
`to communicate with mobile stations in a
`station configured
`cell via a communication channel, the base station compris-
`ing:an
`apparatus configuredto receive a data signal from
`first
`mobile station in the cell over a data subchannel,
`a
`wherein the data subchannel comprises
`plurality of
`or
`non-adjacent subcarriers within the commu-
`adjacent
`nication channel; and
`to receive a
`ranging signal from a
`apparatus configured
`second mobilestation in the cell over a
`ranging subchan-
`nel for random access, wherein:
`
`an
`
`8
`the ranging signal is formed from a
`ranging sequence
`selected from a set of ranging sequences associated
`a mobile station;
`with the cell for identifying
`the ranging signallasts over a
`period of one or
`multiple
`orthogonal frequency division multiplexing (OFDM)
`symbols and the ranging signal exhibits a low peak-
`to-average powerratio in the time domain; and
`at least one block of
`the ranging subchannel comprises
`subcarriers within the communication channel and
`powerlevels of subcarriers at both endsof a block are
`set to zero.
`10. The base station of claim 9, wherein the subcarrier
`configuration of the ranging subchannelfor the cell is differ-
`ent from subcarrier configurations ofranging subchannels for
`othercells.
`11. The basestation of claim 9, wherein the set of ranging
`is different from sets of ranging
`sequences for the cell
`sequencesfor othercells.
`an
`12. The base station of claim 9, further comprising
`to detect the ranging sequence in the
`apparatus configured
`received ranging signal
`in the time domain,
`frequency
`or both time and frequency domain.
`domain,
`13. The base station of claim 12, wherein the apparatus
`to the received ranging signal
`to
`applies matchedfiltering
`detect the ranging sequence.
`14. The base station of claim 12, wherein the apparatus
`correlates the received ranging signal with a
`ranging
`sequence stored at the base station to detect the ranging
`sequence.
`an
`15. The base station of claim 9, further comprising
`to detect a time delay of the received
`apparatus configured
`ranging signal and to inform the second mobile station to
`adjust transmission time based on the detected time delay.
`an
`16. The base station of claim 9, further comprising
`to detect a powerlevel of the received
`apparatus configured
`ranging signal and to inform the second mobile station to
`a transmission power based on the detected power
`adjust
`level.
`access
`17. In an
`orthogonal frequency division multiple
`a method for
`(OFDMA) wireless communication system,
`a mobile station to a
`signal transmission by
`serving base
`station via a communication channel, the method comprising:
`a data signal
`over a data subchannel to the
`transmitting
`serving base station, wherein the data subchannel com-
`a
`or
`plurality of adjacent
`non-adjacent subcarriers
`prises
`within the communication channel; and
`a
`over a
`ranging subchannelto
`transmitting
`ranging signal
`the serving base station for random access, wherein:
`the ranging signal is formed from a
`ranging sequence
`selected from a set of ranging sequencesfor identify-
`ing the mobile station;
`the ranging signallasts over a
`period of one or
`multiple
`orthogonal frequency division multiplexing (OFDM)
`symbols and the ranging signal exhibits a low peak-
`to-average powerratio in the time domain; and
`at least one block of
`the ranging subchannel comprises
`subcarriers within the communication channel and
`powerlevels of subcarriers at both endsof a block are
`set to zero.
`18. The method of claim 17, wherein a power level of
`subcarriers towards the high-end and low-end frequency
`boundaries of a block of subcarriers is lower than a power
`level of subcarriers towards the center of the block.
`19. The method of claim 17, wherein boundary subcarriers
`ofa block of subcarriers in the ranging subchannelare attenu-
`ated to reduce interference with other uplink signals when
`occursat the basestation.
`signal time misalignment
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
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`
`60
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`65
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`13
`
`13
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`

`

`US 8,467,366 B2
`
`9
`20. The method of claim 17, wherein subcarriers in a block
`are
`contiguousin frequency.
`21. The method of claim 17, further comprising controlling
`an
`atransmission powerofthe ranging signal using
`open-loop
`powercontrol methodby:
`a
`path loss betweenthe serving base station and
`estimating
`the mobile station based on a received downlink signal;
`setting the transmission powerof the ranging signal based
`on the path loss; and
`increasing the transmission powerofthe ranging signal for
`retransmission.
`access
`22. In an
`orthogonal frequency division multiple
`a method for
`(OFDMA) wireless communication system,
`a base station from a
`plurality of mobile
`receiving signals by
`stations via a communication channel, the method compris-
`ing:
`over a data subchannel from a first
`a data signal
`receiving
`a
`mobile station, wherein the data subchannel comprises
`or
`plurality of adjacent
`non-adjacent subcarriers within
`the communication channel; and
`a
`over a
`ranging subchannel for
`receiving
`ranging signal
`random access
`a second mobile station, wherein:
`by
`
`10
`
`15
`
`20
`
`*
`
`10
`the ranging signal is formed from a
`ranging sequence
`selected from a set of ranging sequencesfor identify-
`ing the mobile station;
`period of one or
`the ranging signallasts over a
`multiple
`orthogonal frequency division multiplexing (OFDM)
`symbols and the ranging signal exhibits a low peak-
`to-average powerratio in the time domain; and
`at least one block of
`the ranging subchannel comprises
`subcarriers within the communication channel and
`powerlevels of subcarriers at both endsof a block are
`set to zero.
`a
`23. The method of claim 22, further comprising detecting
`time delay of the received ranging signal and informing the
`adjust transmission time based on
`second mobile station to
`the detected time delay.
`a
`24. The method of claim 22, further comprising detecting
`powerlevel of the received ranging signal and informing the
`a transmission power based on
`second mobile station to
`adjust
`the detected powerlevel.
`*
`
`*
`
`*
`
`*
`
`14
`
`14
`
`