(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0075125A1
`(43) Pub. Date:
`Apr. 7, 2005
`Bada et al.
`
`US 20050075125A1
`
`(54) METHOD AND MOBILE STATION TO
`PERFORM THE INITIAL CELL SEARCH IN
`TIME SLOTTED SYSTEMS
`
`(76) Inventors: Anna Marina Bada, Milano (IT):
`Chiara Cavaliere, Rho (IT)
`Correspondence Address:
`BRCH STEWART KOLASCH & BRCH
`PO BOX 747
`FALLS CHURCH, VA 22040-0747 (US)
`(21) Appl. No.:
`10/498,521
`(22) PCT Filed:
`Jan. 21, 2002
`(86) PCT No.:
`PCT/IT02/00035
`
`Publication Classification
`
`(51) Int. Cl. .................................................... H04Q 7/20
`(52) U.S. Cl. .............................................................. 455/525
`(57)
`ABSTRACT
`A method is disclosed that a Mobile Station MS performs at
`Switch-on to search the most favorable target cell in UMTS
`systems like the 3GPP CDMA-LCR (Low Chip Rate)
`option at 1.28 Mcps-TDD (Time Division Duplex) mode
`and the equivalent TD-SCDMA (Time Division-Synchro
`nous CDMA). Signal at the MS antenna is the sum of
`different RF downlink frames coming from different carriers
`in the assigned frequency ranges. A DL Synchronization
`timeslot and a BCCH TSO are both transmitted with full
`power in the frames, the first one includes one out of 32
`
`SYNC codes assigned on cell basis. Following a conven
`tional approach the absence of a common downlink pilot and
`without prior knowledge of the used frequencies would
`force the MS, for all the frequencies of the channel raster
`stored in the SIM card, the correlation of the received frame
`with all the 32 SYNCs stored in the MS, in order to detect
`the BSIC of a cell to which associate the power measures.
`Following the two-step method of the invention the power
`measures are performed in two-step scan of the PLMN band
`without interleaved correlation Steps; once a final frequency
`is Selected the respective frame is the only correlated one. At
`least one frame duration about 5 ms long of the whole 15
`MHz bandwidth is acquired, IF converted, A/D converted
`and the digital Set is Stored. A rough Scan is performed
`multiplying the digital Set by a digital IF tuned in Steps wide
`as the channel band (1.6 MHz) along the 15 MHz band, and
`filtering the baseband signal with a Root Raise Cosine
`low-pass filter. The 5 ms baseband signal is Subdivided into
`15 blocks of half timeslot (337.5us) and the power of each
`block is measured. The power of the Strongest block indi
`cates the priority of the respective frequency. The Strongest
`power values are put in a Spectral Table together with
`respective frame load indicators. The load indicator is the
`percentage of timeslots in a frame almost equally loaded as
`the Strongest block. The three Strongest frequencies are
`Selected for the Successive Scan. The Second Step Search is
`performed like the first one but the IF steps are now 200 kHz
`wide and cover the only 1.6 MHz spectrum around a
`Selected frequency. A final frequency is Selected for the
`Successive correlation Step. Then the frequency error of the
`MS reference oscillator is corrected with data-aided tech
`niques and a calibration value Stored for Successive connec
`tions (FIG. 9).
`
`POSSIBLE SIMPLIFED RF SCENARIO
`EE
`= =
`
`CDMA FREQUENCY SUBSET (PLMN1)
`GSM FREQUENCY SUBSET (PLMN2)
`Ce3
`
`
`
`VWGoA EX1028
`U.S. Patent No. 10,965,512
`
`

`

`Patent Application Publication Apr. 7, 2005 Sheet 1 of 12
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`US 2005/0075125A1
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`Patent Application Publication Apr. 7, 2005 Sheet 2 of 12
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`Patent Application Publication Apr. 7, 2005 Sheet 3 of 12
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`Patent Application Publication Apr. 7, 2005 Sheet 7 of 12
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`US 2005/0075125A1
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`Patent Application Publication Apr. 7, 2005 Sheet 8 of 12
`
`US 2005/0075125 A1
`
`OUTLINE OF THE INITIAL CELL SEARCH METHOD
`
`Rough frequency scan
`15 MHz
`1.6 MHZ 1.6 MHZ 1.6 MHZ
`
`
`
`Finest frequency scan
`1.6 MHz
`200 kHz 200 kHz
`
`List of most
`probable
`frequencies
`
`
`
`
`
`SYNC DETECTION
`ALGORTHM
`
`Frequency error minimization
`algorithm and TCXO Calibration
`
`SYNC and carrier of the
`Selected Cell
`
`Fig. 9
`
`

`

`Patent Application Publication Apr. 7, 2005 Sheet 9 of 12
`
`US 2005/0075125 A1
`
`FREQUENCY SCAN WITH ROUGH STEPS
`RX Filter bandwidth
`
`Freq. rough step
`1.6 MHz
`
`Best Case
`
`
`
`Worst Case
`
`
`
`
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`frequency
`
`frequency
`
`POWer
`
`Fig.10a
`
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`Freq. rough step
`
`RX Filter bandwidth
`1.6 MHZ
`
`POWer
`
`Fig.10b
`
`freq.
`
`

`

`Patent Application Publication Apr. 7, 2005 Sheet 10 of 12
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`US 2005/0075125 A1
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`Patent Application Publication Apr. 7, 2005 Sheet 11 of 12
`
`US 2005/0075125A1
`
`SPECTRAL TABLE
`
`
`
`FINE SCAN TABLE
`
`ROUGH SCAN TABLE
`
`Fig. 12
`
`

`

`Patent Application Publication Apr. 7, 2005 Sheet 12 of 12
`
`US 2005/0075125A1
`
`TWO-STEP FREQUENCY ERROR WITHOUT CALIBRATION
`22000 Hz
`
`fideal
`Fig.13a
`
`fuE
`
`DETERMINATION OF THE CALIBRATION ERROR
`790 HZ
`-N-N
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`Calibration
`value
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`f_Bs
`fdoppler
`fuE
`-- VCXO UE offset: 21430 Hz -->
`Fig.13b
`
`FREQUENCY ERROR IN NORMAL OPERATION
`Calibration
`value
`
`absolute error:1360Hz + AE(f,T)
`relative error:
`790 Hz + Ae(f,T)
`
`
`
`
`
`fuE
`without Calibration
`
`fuE
`with calibration
`
`2_Bs
`
`Doppler
`
`2 ideal
`Fig.13c
`
`

`

`US 2005/0075.125 A1
`
`Apr. 7, 2005
`
`METHOD AND MOBILE STATION TO PERFORM
`THE INITIAL CELL SEARCH IN TIME SLOTTED
`SYSTEMS
`
`FIELD OF THE INVENTION
`0001. The present invention relates to the field of radio
`mobile Systems and more precisely to a method to perform
`the initial cell search in time slotted systems and Mobile
`Station (MS) architecture.
`
`BACKGROUND ART
`0002 Initial cell search is executed by the MS at Switch
`on time for the purpose of finding a cell from which the
`downlink data can be reliably decoded and that has high
`probability of communications on the uplink. Due to the
`next marketing of the new 3-th generation PLMNs (Public
`Land Mobile Network), which for a certain time add up their
`features to the existing PLMNs the initial cell search will be
`a very problematic task for the MS (Mobile Station) because
`of the presence of a lot of operating bands and different
`Synchronization requirements.
`0.003
`FIG. 1 schematizes a possible typical radiofre
`quency simplified scenario a Mobile Station MS1 is faced
`with. The depicted scenario includes three cells: Cell 1 in
`which the MS1 is located and two adjacent cells Cell 2 and
`Cell 3. A possible disturbing MS2 is located in Cell 3. The
`cells are served by respective BTSS (Base Transceiver
`Station) in corner-excited configuration (BTS1 and BTS2
`are the only visible). Two different PLMN systems, namely
`PLMN1 and PLMN2, share the same BTSs. The signal at the
`MS1 antenna is the sum of different RF frames coming from
`different carriers pertaining the two systems. PLMN1 is one
`of the 3GPP (3-rd Generation Partnership Project) UMTS
`(Universal Mobile Telecommunication System) systems
`based on CDMA (Code Division Multiple Access) tech
`nique. Relevant 3GPP documents are the ones Specifying an
`UTRA (Universal Terrestrial Radio Access) interface for the
`User Equipment (UE). UTRA's standardization establishes
`the minimum RF characteristics of the FDD (Frequency
`Division Duplex) and TDD (Time Division Duplex) mode.
`The FDD mode at 3.84 Mcps (Mega-chips-per-second) is
`known as W-CDMA (Wideband), while the TDD mode
`includes an HCR (High Chip Rate) option at 3.84 Mcps and
`a LCR (Low Chip Rate) option at 1.28 Mcps. Mostly
`features of the 1.28 Mcps standard has been jointly devel
`oped by the present Applicant and the CWTS (Chinese
`Wireless Telecommunication Standards) partner. The result
`ing system known as TD-SCDMA (Time Division-Syn
`chronous CDMA) Radio Transmission Technology (RTT)
`has been proposed to the 3GPP by CWTS committee, it
`adopts the same physical layers as UTRA-LCR-TDD, dif
`fering from the last mainly because of the Synchronization of
`the BTS between adjacent cells. PLMN2 could be one of the
`following PLMNs: GSM 900 MHz (Global System for
`Mobile communications), DCS 1800 MHz (Digital Cellular
`System) similar to the preceding one, GPRS (General Packet
`Radio Service) and EGPRS (Enhanced GPRS) added to the
`GSM for enabling it to manage packet data. In the PLMN2
`fBEac and face are two beacon carriers broadcasted by
`BTS1 and BTS2 respectively. Each beacon carrier is accom
`panied by the Subset of GSM carriers used in that cell in the
`observance of the known cluster's rule for the frequency
`assignment. In the PLMN1 three CDMA carriers per cell are
`
`considered without limitation. The GSM's cluster rules are
`not mandatory for PLMN1 which, differently from PLMN2,
`may use the same or different frequencies in adjacent cells,
`depending on the traffic planning. In the following part of the
`description MS and UE are synonyms so as BTS and BS
`(Base Station).
`0004. The national telecommunications Authorities usu
`ally assign the frequency bands to the various PLMNs in
`order to avoid overlap and reciprocal interferences.
`TABLES 1 to 4 of APPENDIX A include all the Standard
`ized frequency bands for the aforementioned PLMNS. The
`initial cell Search results in a list of acceptable cells of the
`selected PLMN (by hypothesis PLMN1 of FIG. 1) sorted by
`decreasing priority. If the list is not empty the MS chooses
`the cell of highest priority for indicating its presence to the
`network and access to the Services. Because of the different
`architectures of the radio interface among the different
`standards, the initial cell search performed by the MS takes
`Some peculiarities of the selected PLMN, despite the general
`criteria of filling in the priority list by decreasing power
`either of the received beacon carriers (GSM) or the beacon
`channels (CDMA). Power measures for initial cell search are
`generally performed by an MS which has not prior knowl
`edge of which carriers the System actually uses for broad
`casting the System information, So it shall Search all RF
`channels within the band of operation of each Selected
`PLMN. In order to speed up the search the MS can option
`ally store into the SIM card (Subscriber Identity Module),
`which is a non-volatile memory enabling the MS operation,
`a list of carriers used by the PLMN selected when it was last
`active (the carriers used are a Subset of the permissible
`carriers). For the sake of completeness, an MS already
`camped on a cell repeatedly executes the cell Selection and
`reselection procedure which take the place of the initial cell
`Search.
`0005. In order to properly set the technical problem
`Solved by the present invention a glance to the different
`physical layerS and the involved cell Search procedures are
`needed. FIGS. 2a and 2b concern GSM, FIG. 3 concerns
`UTRA-FDD, FIG. 4 concerns UTRA-TDD at 3.84 Mcps,
`and FIG. 5 concerns both UTRA-TDD at 1.28 Mcps and
`TD-SCDMA. While GSM is based on both FDMA (Fre
`quency Division Multiple Access) and TDMA (Time Divi
`Sion Multiple Access) techniques, the UTRA Systems add up
`CDMA which is quite a different approach to perform
`multiple access. AS known, CDMA is obtained by Summing
`up in baseband Kbit-Streams coming from K1 users, each of
`them being obtained multiplying (modulating) each over
`Sampled bit of the original Signal by a K2-th spread Sequence
`taken from an orthogonal set of K (being K1s K2 and
`K2s KSo that a single user can handle more than one code):
`the so-called OVSF (Orthogonal Variable Spreading Factor
`codes). The original channel band resulting by said modu
`lation is enlarged and the information is spread in the wider
`CDMA channel band. CDMA forces a different system
`philosophy for discriminating among the various cells,
`because, differently from GSM, adjacent CDMA cells may
`use the same frequencies. Various pilot Sequences associated
`with midambles and Scrambling code groups assigned on
`cell basis are used in the System for discriminating between
`adjacent cells. Cyclic shifts of the midambles and marked
`Synchronization Sequences are further used for more detailed
`discrimination inside a service cell. In FIG. 2a a possible
`GSM signalling multiframe for medium/small BTSS (Base
`
`

`

`US 2005/0075.125 A1
`
`Apr. 7, 2005
`
`Transceiver Station) is shown. The Signalling multiframe
`includes 51 basic frames as the one 4.615 ms long shown in
`FIG. 2b. Letters F. S., B, and C indicate, in the order, the
`following control channels carried by timeslot 0 of a rel
`evant beacon F0: FCCH (Frequency Correction CHannel),
`SCH (Synchronization CHannel), BCCH (Broadcast Con
`trol CHannel), and CCCH (Common Control CHannel). The
`physical bursts of FCCH and SCH downlink channels are
`depicted in FIG.2b. FCCH burst includes 142 useful bits at
`logic level “one” in order to allow the correction of the clock
`frequency of the MS oscillator when this burst is received
`(and easily recognized). The SCH burst includes a 64 bit
`“Synchronization Sequence” in midamble position and 2x39
`Encrypted bits. The SCH burst is always received by the MS
`with an 8 time slot delay (45.6 ms) from the FCCH burst,
`therefore the Mobile that has already corrected the fre
`quency of its own clock can discriminate with the due
`precision the correct position of the Synchronization
`Sequence within the received burst, and then the Starting
`instant of the time slot and the frame. Delay of 45.6 ms is
`reasonably short, in line with the Synchronization require
`ments of a GSM Mobile having access for the first time to
`the network, or remaining in Idle State. The Encrypted bits
`contain the information necessary to reconstruct the Frame
`Number FN for completing the synchronization procedure,
`and a BSIC field (Base Station Identity Code) useful to the
`Mobile to identify the BCCH carrier (beacon) of the serving
`cell from the BCCH carriers of the adjacent cells. The
`BCCH channel is used to diffuse downlink general use
`System information, Such as for instance: the configuration
`of channels within the cell, the list of BCCH carriers of the
`adjacent cells on which performing the level measurement,
`the identity of the Location Area and Some parameters for
`the Cell Selection and Reselection activity, the complete
`Cell Identity, parameters for the operation of the MS in Idle
`Mode and parameters for Random Access. The CCCH
`bi-directional channel includes three Subchannels: a first
`AGCH (Access Grant CHannel) and a second PCH (Paging
`CHannel) in downlink, and third RACH (Random Access
`CHannel) one shared in uplink. AS far as concerns the
`measures for initial cell Search, the MS Starts Searching for
`the FCCH channel, if this channel is found the Scanned
`frequency is a beacon frequency otherwise a frequency N+1
`is scanned. When the FCCH channel is detected the outlined
`frequency and frame Synchronization mechanism put into
`action by the two FCCH and SCH channels detects the
`beginning of time slot T0 and the frame. Power measure
`ments on the FCCH, SCH, and BCCH channel are possible
`consequently. These channels are continuously transmitted
`at full power from the BTSs just for the purposes of cell
`Search, cell Selection and reselection, and handover. Power
`measurements relevant to each beacon frequency enter the
`priority list. The selected cell is the one of whose BSIC is
`asSociated to the top carrier on priority list.
`0006. In FIG. 3 a basic radio synchronization frame of
`3GPP UTRA-FDD (W-CDMA) is shown (see 3GPP TS
`25.211, Version 4.2.0 (2001-09) Release 4). The downlink
`frame is 10 ms long and includes 38,400 chips belonging to
`15 timeslots TS0...TS14, each of 2560 chips. The first 256
`chips of each timeslot are assigned to a downlink Synchro
`nization Channel SCH used for cell search. The SCH
`channel consists of two Subchannels, the Primary and Sec
`ondary SCH, whose digital patterns are not orthogonal with
`the other spread channels and can be distinguished from
`
`them even in a noisy environment. The primary SCH
`consists of a modulated code of 256 chips, named Primary
`Synchronization Code (PSC), which is the same for every
`cell in the system. The secondary SCH consists of a modu
`lated code of 256 chips, named Secondary Synchronization
`Code (SSC), transmitted in parallel with the Primary PSC.
`The SSC code is denoted c.'', where i=0, 1,..., 63 is the
`number of the Scrambling code group, and k=0, 1, . . . , 14
`is the timeslot number. Each SSC code is chosen from a set
`of 16 different codes of length 256. This sequence on the
`Secondary SCH indicates which of the code groups the
`cell's downlink Scrambling code belongs to. Other important
`downlink control channels are the Primary Common Pilot
`Channel (P-CPICH) and the Primary Common Control
`Physical Channel (P-CCPCH). The P-CPICH channel has
`the following characteristics: there is one and only one
`P-CPICH per cell; it is broadcasted over the entire cell and
`is Scrambled by the primary Scrambling code assigned on
`cell basis. The P-CPICH channel is used to discriminate the
`scrambling code group of a cell. The P-CCPCH channel is
`a fixed rate physical channels (30 kbps, SF=256) used to
`carry the BCH transport channel. SCH, P-CPICH, and
`P-CCPCH channels are continuously transmitted at full
`power in the whole cell for initial cell Search, cell Selection
`and reselection, handover, and the reading of the System
`information. As far as cell search concerns (see 3GPP TS
`25.214, Version 4.2.0, 2001-09, Release 4) for each scanned
`frequency the cell Search is typically carried out in three
`Steps:
`0007 Step 1. Slot synchronization: During the first
`step the UE uses the SCH's primary synchronization
`code to acquire Slot Synchronization to a cell. This is
`typically done with a single matched filter (or any
`similar device) matched to the PSC code which is
`common to all the cells. The Slot timing of the cell can
`be obtained by detecting peaks in the matched filter
`output. The frequency of the UE's reference oscillator
`can be adjusted in the meanwhile to meet the Specifi
`cations.
`0008 Step 2. Frame synchronization and code-group
`identification: During the Second Step the UE uses the
`SCH's secondary synchronization code to find frame
`Synchronization and identify the code group of the cell
`found in the first step. This is done by correlating the
`received Signal with all possible SSC Sequences, and
`identifying the maximum correlation value. Since the
`cyclic shifts of the Sequences are unique the code group
`as well as the frame Synchronization is determined.
`0009 Step 3. Scrambling-code identification: During
`the third and last step the UE determines the exact
`primary Scrambling code used by the found cell. The
`primary Scrambling code is typically identified through
`symbol-by-symbol correlation over the CPICH with all
`code group identified in the Second step. After the
`primary Scrambling code has been identified, the Pri
`mary CCPCH can be detected and the system and cell
`specific BCH information can be read. If the UE has
`received information about which Scrambling codes to
`Search for, Steps 2 and 3 above can be Simplified.
`0010 Power measurements relevant to each scanned fre
`quency enter the priority list. The Selected cell is the one
`whose Primary Scrambling Code is associated to the top
`
`

`

`US 2005/0075.125 A1
`
`Apr. 7, 2005
`
`carrier on priority list. Power measurements can be usefully
`performed on the SCH, P-CPICH, and P-CCPCH channels.
`At the initial cell Search the measure of the received power
`in correspondence of the only Primary SCH channel could
`Speed-up the whole frequency Scan.
`0011. In FIG. 4 a basic radio synchronization frame of
`3GPP UTRA-TDD for 3.84 Mcps is shown (3GPP TS
`25.221, Version 4.2.0 (2001-09) Release 4). The frame is 10
`ms long and includes 38,400 chips belonging to 15 timeslots
`TS0...TS14, each of 2560 chips. The purposes of the SCH
`channel are near the same as UTRA-FDD of FIG. 3. SCH
`frame includes one or two SCH timeslots 8 positions spaced
`apart (i.e. TS0 and TS8). One Primary and three Secondary
`SCH are in parallel. Primary and Secondary SCH have a
`delay to
`from the beginning of the timeslot. A Primary
`Common Control Physical Channel (P-CCPCH) is located
`in a position (time slot/code) known from the Physical
`Synchronization Channel (PSCH). The Broadcast Channel
`(BCH) is a downlink common transport channel mapped
`onto the P-CCPCH channel to broadcast system and cell
`Specific information. For the purpose of measurements,
`physical channels at particular locations (timeslot, code)
`shall have particular physical characteristics, called beacon
`characteristics. Physical channels with beacon characteris
`tics are called beacon channels and are located in beacon
`locations. The beacon locations are determined by the SCH
`channel. The ensemble of beacon channels shall provide the
`beacon function, i.e. a reference power level at the beacon
`locations. Thus beacon channels must be present in each
`radio frame. Note that by this definition the P-CCPCH
`always has beacon characteristics. AS far as cell Search
`concerns, for each Scanned frequency the initial cell Search
`is typically carried out in three Steps similar to the ones valid
`for the preceding UTRA-FDD case, and also the top-list cell
`Selection criterion is the same.
`0012. In FIG. 5 a basic TD-SCDMA radio frame is
`depicted. The basic frame (see 3GPP TS 25.221, Version
`4.2.0 (2001-09) Release 4) has a duration of 10 ms and is
`divided into 2 subframes of 5 ms. The frame structure for
`each Subframe in the 10 ms frame length is the same. A
`multiframe is a module N number of frames. Each 5 ms
`subframe has 6,400 chips (T=0.78125us) Subdivided into 7
`timeslots for data (TS0, . . . TS6) of 864 chips, plus three
`special timeslots named DwPTS (Downlink Pilot Time
`Slot), GP (Main Guard Period), and UpPTS (Uplink Pilot
`Time Slot). TS-SCDMA can operate on both symmetric and
`asymmetric mode by properly configuring the number of
`downlink and uplink time slots and the Switching point
`consequently. In any configuration at least one time slot
`(time slotiiO) has to be allocated for the downlink and at least
`one timeslot has to be allocated for the uplink (time sloth 1).
`The burst of data at the bottom left of the Figure includes a
`central midamble and two identical data parts. The data parts
`are spread with a combination of channelisation code
`(OVSF 1, 2, 4, 8, or 16) and scrambling code. The scram
`bling code and the basic midamble code are constant within
`a cell. The K1 Simultaneous users which share an uplink
`timeslot are distinguishable each other at the BTS side by K1
`shifted versions of the basic midamble code. The DwpTS
`burst at the bottom right of the Figure includes a Guard
`Period GP and a 64-chips SYNC sequence used for down
`link frame synchronization. FIG. 6 schematizes the TD
`SCDMA criterion to share among different cells the 32
`available SYNC sequences characterizing the DwpTS pilot,
`
`the 32 associated Scrambling code groups, the midamble
`asSociations with the code groups, and the K=16 midamble
`shifts. From the diagram of FIG. 6 it can be argued that since
`the SYNC and the basic midamble code groups are related
`one-to-one, the UE knows which 4 basic midamble codes
`are used. Then the UE can determine the actually used basic
`midamble code using a try and error technique. The same
`basic midamble code will be used throughout the frame. As
`each basic midamble code is associated with a Scrambling
`code, the Scrambling code is also known by that time.
`0013 Primary Common Control Physical Channel
`(P-CCPCH1 and P-CCPCH2) is fixedly mapped onto the
`first two code channels of timeslot TS0 with fixed spreading
`factor of 16. The P-CCPCH channel is a beacon channel
`(like DwPTS) always transmitted with an antenna pattern
`configuration that provides whole cell coverage. The Broad
`cast Channel (BCH) is a downlink common transport chan
`nel mapped onto the P-CCPCH1 and P-CCPCH2 channels
`to broadcast system and cell-specific information. The BCH
`is transmitted in TS0 always with the midamble code
`obtained by the first time shift from the base midamble code.
`The location of the interleaved BCH blocks in the control
`multi-frame is indicated by the QPSK Quadrature Phase
`Shift Keying modulation of the DwpTS pilot with respect
`to midamble code. AS far as initial cell Search concerns the
`3GPP specifications (TS 25.224, Version 4.2.0, 2001-09,
`Release 4) say that is typically carried out in four steps:
`0014 Step 1. Search for DwPTS-During the first step
`of the initial cell search procedure, the UE uses the
`SYNC (in DwPTS) to acquire DwPTS synchronization
`to a cell. This is typically done with one or more
`matched filters (or any similar device) matched to the
`received SYNC-DL which is chosen from PN
`Sequences Set. A Single or more matched filter (or any
`Similar device) is used for this purpose. During this
`procedure, the UE needs to identify which of the 32
`possible SYNC sequences is used. The frequency of the
`UE's reference oscillator can be adjusted in the mean
`while to meet the specifications (0.1 ppm).
`0015 Step 2. Scrambling and basic midamble code
`identification-During the Second step of the initial cell
`search procedure, the UE determines the midamble for
`the k-th burst of data and the associated Scrambling
`code. According to the result of the Search for the right
`midamble code, UE may go to next step or go back to
`Step 1.
`0016 Step 3. Control multi-frame synchronization
`During the third Step of the initial cell Search procedure,
`the UE searches for the MIB (Master Indication Block)
`of multi-frame of the BCH. According to the result UE
`may go to next Step or go back to Step 2.
`0017 Step 4. Read the BCH-The (complete) broad
`cast information of the found cell in one or Several
`BCHS is read. According to the result the UE may move
`back to previous Steps or the initial cell Search is
`finished.
`0018. The wide presentation of the prior art includes the
`most digital PLMNs known up till now. Third generation
`cellular systems other than 3GPP have features widely
`referable to that Standardization.
`
`

`

`US 2005/0075.125 A1
`
`Apr. 7, 2005
`
`0019. Outlined Technical Problem
`0020. A sound procedure for the initial cell search shall
`take into account the worst case in which the mobile Station
`at Switch-on has not prior knowledge of which carriers the
`System actually uses for broadcasting the System informa
`tion, So it shall Scan all the permitted carriers within the band
`of operation of the selected PLMN. The sound procedure
`must give a reliable information about the pathloSS of a
`Scanned carrier, So that the priority list can be a useful tool.
`The mobile Station shall therefore carry out power measures
`in correspondence of at least one beacon channel, that
`should be necessarily detected in the meanwhile. The detec
`tion of a beacon channel means also detecting all the
`relevant physical entities building the beacon channel up in
`conformity with the selected PLMN. A first physical entity
`to consider is the frequency; a Second one is the temporal
`Subdivision of the baseband digital Signal into discrete time
`intervals (bursts, timeslots, Subframes, frames, multiframes,
`etc.); a third entity is the digital pattern transmitted in the
`beacon burst. The physical entities differently characterize
`the beacon channels used in the highlighted PLMN of the
`prior art. It's useful to remind that:
`0021 GSM makes use of FCCH and SCH frequency
`and time Synchronization patterns common to the
`whole system. Besides the SCH channel includes the
`BSIC for identifying the cell transmitting the
`received FCCH and SCH beacons.
`0022) 3GPP UTRA-FDD and 3GPP UTRA-TDD
`3.84 Mcps option make use in downlink of a Primary
`SCH subchannel common to the whole system for
`obtaining timeslot Synchronization, and Secondary
`SCH and CPICH channels to obtain cell-based
`Scrambling code group and Single Scrambling code.
`0023) 3GPP UTRA-TDD 1.28 Mcps option, or TD
`SCDMA, makes use of 32 DwPTS downlink syn
`chronization Sequences which are known by all the
`cells. One out 32 DwpTS sequence is assigned to the
`Single cell in order to obtain the respective Scram
`bling code group and the Single Scrambling code.
`0024. The procedure for initial cell search should consist
`of as many Scanning Steps as the permitted carriers. Each
`Scanning Step includes the Selection of a carrier, the detec
`tion of a beacon channel which conveys Suitable cell infor
`mation, the execution of a power measurement in the
`channel band at the occurrence of the beacon channel. The
`scanning raster is 200 kHz for all the above PLMNs. The
`channel band is quite different: 200 kHz for GSM; 5 MHz
`for 3GPP UTRA-FDD and 3GPP UTRA-TDD 3.84 Mcps
`option; 1.6 MHz for 3GPP UTRA-TDD 1.28 Mcps option
`and TD-SCDMA. While the selection of a carrier is imme
`diate, the detection of a beacon Sequence takes the time to
`calculate the correlation between the received Sequence and
`the known beacon pattern (or patterns). More in particular:
`0025. In case of GSM the search for a beacon
`channel is considerably sped up by the FCCH chan
`nel which points to the SCH channel 8-timeslots
`later. The detection of FCCH is very fast. The
`correlation with SCH is simplified from the short
`correlation window descending from the preceding
`FCCH detection. The detection of an SCH pattern
`allows frame Synchronization and consequent power
`
`measurement of the BCCH channel in correspon
`dence of timeslot TO of the next BCCH's frames.
`The initial cell search is fast and easy in GSM
`System.
`0026. In case of 3GPP UTRA-FDD and 3GPP
`UTRA-TDD 3.84 Mcps option the detection of pri
`mary SCH is more expensive than GSM due to the
`longer primary code (256 chips in comparison with
`64 bits) and the absence of a Frequency Correction
`Channel pointing to the SCH channel directly.
`Despite this complication the SCH detection can be
`completed in reasonably short time thanks to the
`singleness of the SCH patterns in the whole system,
`which needs a correlation only, jointly with the
`occurrence of the SCH sequence at each timeslot
`(2560 chips). Once timeslot synchronization is
`reached the other Steps leading to the acquisition of
`CPIC and CCPCH beacons of the specific cell are
`considerably simplified due to the short correlation
`window. Power measurements on CPIC and CCPCH
`for entering the priority list are consequent. It can be
`conclude that the initial cell Search is only moder
`ately expensive in respect of GSM.
`0027). In case of 3GPP UTRA-TDD at 1.28 Mcps
`and TD-SCDMA systems, for each frequency of the
`Initial cell Search procedure, the only Step "Search
`for DwPTS” requests the UE to correlate the whole
`6400 chips of the frame with each one of the 32
`SYNCs sequences 64 chips long. This formidable
`task (N-frequenciesx32 of Such long correlations)
`largely outperforms the calculation power of the UE
`making de-facto impossible a reasonably fast cell
`Search.
`
`OBJECTS OF THE INVENTION
`0028. The main object of th