Abstract:
Physical layer structures and access schemes for use in such networks are described and in particular initial access channel (IACH) structures are proposed. A spectrum efficient downlink (DL) IACH design supports different types of User Equipment (UE) capabilities and different system bandwidths. An IACH includes the synchronization channel (SCH) and broadcast-control channel (BCH). A non-uniform SCH for all system bandwidths is provided, as well as scalable bandwidth BCH depending on system bandwidth. An initial access procedure is provided, as well as an access procedure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/759,388 filed Jan. 17, 2006, U.S. Provisional Patent Application No. 60/722,744 filed Sep. 30, 2005, and U.S. Provisional Patent Application No. 60/814,417 filed Jun. 16, 2006, which are each hereby incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to wireless mobile communication systems, and in particular to physical layer structures and access schemes for use in such networks. 
       BACKGROUND 
       [0003]    In OFDM (Orthogonal Frequency Division Multiplexing) and OFDMA (Orthogonal Frequency Division Multiple Access) wireless communication networks, data streams are typically transmitted in parallel using multiple orthogonal sub-carriers or tones within a single channel. The use of orthogonal sub-carriers allows the sub-carriers, spectra to overlap, thus achieving high spectrum efficiency. An OFDM system maps coded or modulated information symbols, QPSK (Quadrature Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) symbols for instance, to sub-carriers in the frequency domain, and then generates a time domain signal for transmission using such a transformation technique as IFFT (Inverse Fast Fourier Transform). At a receiver, a time-to-frequency transformation, such as an FFT (Fast Fourier Transform), is used to convert a received time domain signal into the frequency domain. In order to recover transmitted source symbols correctly, the receiver aligns an FFT window with a corresponding IFFT window used at the transmitter and compensates for any frequency offset between the transmitter and the receiver. 
         [0004]    Initial access to a communication network by a communication terminal involves a search operation to find available base stations and communication channels and a synchronization operation to synchronize the terminal to a base station. Dedicated physical channels, such as a downlink initial access channel (IACH) and a synchronization channel (SCH) for timing and frequency synchronization are used. A downlink IACH enables initial system access. 
         [0005]    In wireless communication systems, the Base Transceiver Station (BTS) and User Equipment (UE) may have different transmission bandwidth capabilities. For example, a BTS and a UE may each have scalable bandwidths from 1.25 MHz to 20 MHz. However, in prior art systems, the bandwidth of the IACH is equal to the system transmission bandwidth and is thus variable depending on the system transmission bandwidth. This assumes that the UE reception capability is always equal to or larger than the transmission bandwidth. In prior art systems, a UE finds the system transmission bandwidth by changing the receive bandwidth and FFT size. This approach requires longer access time and complexity. 
       SUMMARY OF THE INVENTION 
       [0006]    A downlink initial access channel is described to support different types of UE capabilities and different system bandwidths. 
         [0007]    According to one aspect of the present invention, there is provided a method of transmitting an access channel in a network having a system bandwidth, the access channel comprising a first channel and a second channel, the method comprising transmitting the access channel using a bandwidth less than the system bandwidth. 
         [0008]    According to another aspect of the present invention, there is provided a method of transmitting a communication signal, the communication signal comprising one or more frames being of the type that are regularly repeated, each frame comprising a plurality of time slots, each time slot comprising one or more OFDM symbols, the method comprising: inserting common pilot symbols in predetermined OFDM symbols; inserting a SCH over some or all of the predetermined OFDM symbols; transmitting the communication signal. 
         [0009]    According to still another aspect of the present invention, there is provided a method for decoding a BCH from a diversity transmitted signal comprising: receiving a plurality of time domain OFDM signals from a plurality of transmit antennas to provide a received signal; decoding from the received signal a basic BCH without any information regarding the number of transmit antennas; and decoding from the received signal an Extended BCH. 
         [0010]    According to yet another aspect of the present invention, there is provided a method of a UE performing initial access to a BTS comprising: performing initial timing and frequency synchronization based on a basic SCH; performing initial cell search based on the basic SCH; detecting the basic BCH; obtaining system parameters; decoding a basic BCH and an Extended BCH; entering a connected mode; and performing sync tracking and cell search based on both the basic SCH and the Extended SCH. 
         [0011]    According to a further aspect of the present invention, there is provided a base transceiver station in a communication network, the communication network having a system bandwidth, the base transceiver station comprising: a processor configured to select a bandwidth for an access channel less than the system bandwidth, and transmit the access channel. 
         [0012]    Other aspects and features of the present invention will become apparent, to those ordinarily skilled in the art, upon review of the following description of the specific embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will now be described in greater detail with reference to the accompanying diagrams, in which: 
           [0014]      FIG. 1  is a block diagram of a wireless communication network; 
           [0015]      FIG. 2  is a diagram of a known physical layer structure for a wireless communication network; 
           [0016]      FIG. 3A  is a diagram illustrating spectrum allocation for a Primary common Synchronization Channel (PSC) for 5 MHz, 10 MHz and 20 MHz transmission bandwidths; 
           [0017]      FIG. 3B  is a diagram illustrating spectrum allocation for a PSC for 1.25 MHz, and 2.5 MHz transmission bandwidths; 
           [0018]      FIG. 4  is a diagram illustrating various examples of SCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz transmission bandwidths, 
           [0019]      FIG. 5A  is a diagram illustrating various examples of SCH and Extended SCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHz transmission bandwidths, 
           [0020]      FIG. 5B  is a diagram illustrating other examples of SCH and Extended SCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHz transmission bandwidths, 
           [0021]      FIG. 5C  is a diagram illustrating yet other examples of SCH and Extended SCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHz transmission bandwidths, 
           [0022]      FIG. 6A  is a diagram illustrating a first example for spectrum allocation for a SCH for 20 MHz transmission bandwidth; 
           [0023]      FIG. 6B  is a diagram illustrating a second example for spectrum allocation for a SCH for 20 MHz transmission bandwidth; 
           [0024]      FIG. 7  is a diagram of the frequency domain structure of the broadcast-control channel (BCH) for system bandwidths of 5 MHz, 10 MHz and 20 MHz; 
           [0025]      FIG. 8  is a diagram of the frequency domain structure of the BCH for system bandwidths of 1.25 MHz and 2.5 MHz; 
           [0026]      FIG. 9A  is a diagram illustrating various examples of BCH and Extended BCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHz transmission bandwidths, 
           [0027]      FIG. 9B  is a diagram illustrating other examples of BCH and Extended BCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHz transmission bandwidths, 
           [0028]      FIG. 10  is a diagram illustrating a spectrum allocation for a BCH for 20 MHz transmission bandwidth; 
           [0029]      FIG. 11A  is a diagram of an example frame used in accordance with one embodiment of the invention; 
           [0030]      FIG. 11B  is a diagram of a time domain structure of a PSC; 
           [0031]      FIG. 11C  is a diagram of Secondary Cell specific Sync Channel (SSC) and PSC locations for a Time Division Multiplex (TDM) based pilot design; 
           [0032]      FIG. 11D  is a diagram of SSC and PSC locations for a scattered pilot design; 
           [0033]      FIG. 11E  is a diagram of a one antenna and a four antenna irregular diamond lattice scattered pilot pattern for OFDM symbols carrying a PSC; 
           [0034]      FIG. 12A  is a diagram of an example frame used in accordance with one embodiment of the invention; 
           [0035]      FIG. 12B  is a diagram of the time domain structure for two PSC locations used in accordance with one embodiment of the invention; 
           [0036]      FIG. 13  is a diagram of time domain SCH multiplexing; 
           [0037]      FIG. 14  is a flow chart of the possible steps that could be carried out in connection with an initial access procedure between a UE and a BTS; and 
           [0038]      FIG. 15  is a flow chart of the steps carried out by a UE to access the SCH and BCH in one embodiment, 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0039]      FIG. 1  is a block diagram of a wireless communication network. The communication network includes BTSs  10 ,  12 ,  14 , which provide communication network coverage to respective coverage areas or “cells”  20 ,  22 ,  24 . UE  16  is adapted to communicate with any of the BTSs  10 ,  12 ,  14  within whose coverage areas the UE  16  is located. 
         [0040]    The communication network shown in  FIG. 1  is intended solely for illustrative purposes, and that a communication network may include further or different components than those explicitly shown in  FIG. 1 . For example, most communication networks include more than three BTSs and provide communication services for many UEs. Such communication networks are also normally connected to other types of networks, including landline telephone networks, for instance. It should be further appreciated that BTS coverage areas and UE ranges are not normally purely hexagonal, and will include other areas of overlap. 
         [0041]    Each BTS  10 ,  12 ,  14  includes a transceiver, or alternatively a separate transmitter and receiver, for sending communication signals to and receiving communication signals from the UE  16  via an antenna system. An antenna system at a BTS may include a single antenna or a multiple antennas, such as in an antenna array, for example. The BTSs  10 ,  12 ,  14  may also communicate with each other, and with other communication stations or components, including components in other communication networks, through wireless or wired communication links. Communication functions of the BTSs may involve such operations as modulation and demodulation, coding and decoding, filtering, amplification, and frequency conversion. These and possibly other signal processing operations are preferably performed in the BTSs by digital signal processors (DSPs) or general-purpose processors that execute signal processing software. 
         [0042]    UE  16  is a wireless communication device such as a data communication device, a voice communication device, a multiple-mode communication device that supports data, voice, and possibly further communication functions, or a wireless modem that operates in accordance with a computer system. UE  16  receives communication signals from and/or sends communication signals to the BTSs  10 ,  12 ,  14  through a transceiver or a receiver and a transmitter, and an antenna system that may include a single antenna or multiple antennas. As in the BTSs  10 ,  12 ,  14 , such signal processing operations as modulation and demodulation, coding and decoding, filtering, amplification, and frequency conversion may be performed by a DSP or general-purpose processor in UE  16 . 
         [0043]    Communication signals between BTSs and UEs in a communication network are formatted according to a particular protocol or communication scheme for which the communication network is adapted. Such signal formats are also commonly referred to as physical layer structures. 
         [0044]    An IACH is an initial acquisition channel for a mobile terminal such as UE  16  of  FIG. 1  to access a communication network. For example, when UE  16  is turned on, the device first receives the IACH transmitted from a BTS such as BTS  10 . The IACH is used for one or more functions including initial access, synchronization, base station identification, and channel estimation. More particularly, an IACH comprises control information and includes an SCH and a BCH. An IACH can also be used for the synchronization tracking and cell search for UEs in the connected mode and idle mode. 
         [0045]      FIG. 2  illustrates prior art system bandwidths structure  200  for a wireless communication network in the frequency domain in an OFDMA network where system bandwidths are scalable from 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz generally indicated at  200 . Also illustrated at  202  is the bandwidth of the IACH which is equal to the system bandwidth for each of the 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz scenarios. 
         [0046]    Spectral efficiencies can be gained where the IACH is designed to have a bandwidth less than the system bandwidth for at least some system bandwidths. Fast initial access can be supported by reduce the blind bandwidth search time with reasonable overhead. 
       The Spectrum Arrangement of a Synchronization Channel (SCH) and an Extended Synchronization Channel (Extended SCH) 
       [0047]    An SCH is a logical channel used by mobile stations to achieve time/frequency synchronization with the network. An SCH enables (i) fast initial system access; (ii) timing and frequency synchronization and tracking, (iii) fast cell selection and re-selection; (iv) low complexity; (v) Downlink (DL) Continuous Quality Indicator (CQI) measurement; and (vi) channel estimation. 
         [0048]    An SCH is typically comprised of two channels, a Primary Synchronization Channel (PSC) and a Secondary Synchronization Channel (SSC). The synchronization process occurs when a UE is initially turned on and also thereafter when the UE moves from one cell to another. Synchronization is required because the UE does not previously have a set timing with respect to the BTS. The PSC is detected in a first acquisition stage, which provides the UE of the timing of the communications. The SSC is detected at a later acquisition stage, which provides the UE with more accurate timing information and a cell id. 
         [0049]    The PSC may be modulated with the Primary Sync Sequences (PSS). The same Pseudo-noise (PN) sequences across the whole network enable fast system access and cell search. 
         [0050]    An Extended SCH is used to improve ongoing cell search performance. 
         [0051]    A first implementation of the invention is shown in  FIGS. 3A and 3B  which illustrate two types of SCH (i) 
         [0052]    Type 1 in  FIG. 3A , for system bandwidths equal to or above 5 MHz, and (ii) Type 2 in  FIG. 3B , for system bandwidths below 5 MHz. As illustrated, the SCH bandwidth (as represented by PSC  508 ) is less than the system bandwidth where system bandwidth equals 20 MHz, 10 MHz and 2.5 MHz). In the cases of 5 MHz and 1.25 MHz, the SCH bandwidth equals the system bandwidth. This allows for fast blind initial access by a UE. 
         [0053]    BTS bandwidth information can be conveyed by the PSC for Type 1 and Type 2. For Type 1: Three common PN sequences corresponding to three possible system bandwidths: 5 MHz, 10 MHz and 20 MHz and (ii) Type 2: Two common PN sequences corresponding to two possible system bandwidths: 1.25 MHz and 2.5 MHz. The time domain repetition structure of PSC symbol(s) allows the fast coarse synchronization. In Type 1, only half of the sub-carriers are modulated (see bottom portion of  FIG. 3A ). In Type 2, there may be two identical PSC symbols (see bottom portion of  FIG. 3B ). 
         [0054]    As shown in  FIG. 3A , for Type 1, the PSC  508  is located in 5 MHz in the center of the available band. In the case of 20 MHz system bandwidth  502 , PSC  508  takes up only 5 MHz of bandwidth, leaving 15 MHz of leftover bandwidth  525 . In the case of 10 MHz system bandwidth  504 , PSC  508  takes up only 5 MHz of bandwidth, leaving 5 MHz of leftover bandwidth  525 . In the case of 5 MHz system bandwidth  502 , PSC  508  takes up all 5 MHz of bandwidth, leaving no leftover bandwidth. As illustrated in this Type 1 system, PSC  510  is modulated on half of the sub-carriers, leaving the other half of the sub-carriers to be null  512 . The spectrum allocation displayed in  FIG. 3A  for various system bandwidths is merely illustrative of one example of this embodiment. 
         [0055]    As shown in  FIG. 3B , for Type 2, the primary common SCH is located in 1.25 MHz in the center of the available band. In the case of 2.5 MHz system bandwidth  530 , PSC  508  takes up only 1.25 MHz of bandwidth, leaving 1.25 MHz of leftover bandwidth  525 . In the case of 1.25 MHz system bandwidth  532 , PSC  508  takes up all 1.25 MHz of bandwidth, leaving no leftover bandwidth. As illustrated in this Type 2 system, PSC  510  is modulated on all of the useful sub-carriers. The spectrum allocation displayed in  FIG. 3B  for various system bandwidths is merely illustrative of one example of this embodiment. 
         [0056]    A further embodiment of the invention is now described. The basic sampling frequency (fs) and FFT size (Nfft) can be defined according to the basic SCH bandwidth, which is chosen based on a trade-off of IACH detection performance and UE minimum implementation complexity as well as UE reception capability. The actual occupied bandwidth of the basic SC is determined by the basic SCH bandwidth, for example, around 4.5 MHz for 5 MHz of basic SCH bandwidth. 
         [0057]    Improved performance may be obtained from multiple basic SCHs when the system bandwidth and UE capacity is multiple times of the basic SCH bandwidth. Note that guard bands are used between basic IACHs to allow IACH acceptance by a UE with narrower than system bandwidth capacity. 
         [0058]    Common sequence or sequences are transmitted by the PSC. All cells (or sectors) transmit the same sequence or the selected sequence from the same sequence set. 
         [0059]      FIG. 4  is a diagram illustrating various examples of frequency domain IACH structures. In the case of 20 MHz system bandwidth  610 , SCH  602  is shown taking up intervals of approximately 4.5 MHz of bandwidth between guard bands  615 . As noted above, improved performance may be obtained from multiple basic SCHs when the system bandwidth and UE capacity is multiple times of the basic SCH bandwidth. 
         [0060]    In the 10 MHz bandwidth case  612 , SCH  602  takes up approximately 4.5 MHz leaving approximately 5.5 MHz of leftover system bandwidth  604 . In the case of 5 MHz system bandwidth  614 , SCH  602  takes up approximately 4.5 MHz leaving approximately 1 MHz of leftover system bandwidth  604 . In the case of 2.5 MHz system bandwidth  616 , SCH  602  takes up approximately 2 MHz leaving approximately 0.5 MHz of leftover system bandwidth  604 . In the case of 1.25 MHz bandwidth  618 , SCH  602  takes up approximately 1 MHz leaving approximately 0.25 MHz of leftover system bandwidth  604 . The spectrum allocation displayed in  FIG. 4  for various system bandwidths is merely illustrative of one example of this embodiment. The values of 4.5, 2 MHz and 1 MHz are only examples, the exact values are determined by the specific implementation. 
         [0061]      FIG. 5A  is a diagram illustrating the spectrum allocation of a basic SCH  1000  and an Extended SCH  1002 . During initial access, a UE has no information about the transmission bandwidth. To simplify the initial cell search, a basic SCH  1000  of fixed narrow bandwidth, for example 1.25 MHz, is used regardless of the overall transmission bandwidth. This basic SCH  1000  of fixed narrow bandwidth (in this case, 1.25 MHz) is shown in connection with the case of 1.25 MHz system bandwidth  1010 , 2.5 MHz system bandwidth  1012 , 5 MHz system bandwidth  1014 , and 10 MHz system bandwidth  1016 . 
         [0062]    To support mobility, a UE still needs to perform the cell search after initial access. At this stage, the UE already knows the transmission bandwidth of the serving BTS and even the neighbouring BTS through the broadcast-control channel. 
         [0063]    All useful sub-carriers in an SCH symbol are shared by the SCH and other data transmission. The basic SCH occupies the central  75  sub-carriers which in this example represents 1.25 MHz of bandwidth. For &gt;1.25 MHz transmission bandwidth scenarios, the leftover spectrum could be occupied by an Extended SCH and other data transmissions, depending on the overall SCH bandwidth and the overall transmission bandwidth. In the case where the Extended SCH does not occupy all of the leftover spectrum, other traffic, for example broadcast-control information, can also be transmitted by the same SCH symbol. 
         [0064]    Accordingly, an Extended SCH  1002  can be defined to enhance the cell search performance in the connected mode and idle mode. The whole SCH will therefore consist of two parts: (i) basic SCH  1000  used for initial access and occupied 1.25 MHz bandwidth, and (ii) Extended SCH  1002  which is used to enhance the cell search performance. 
         [0065]    The same SCH sequence with certain repetition or different SCH sequence can be used by Extended SCH  1002 . The advantage of this approach is low SCH overhead, especially when SCH is transmitted multiple times in each frame. 
         [0066]    In the case of 1.25 MHz system bandwidth  1010 , Extended SCH  1002  occupies 0 MHz of bandwidth as basic SCH  1000  has occupied the entirety of the spectrum. In the case of 2.5 MHz system bandwidth  1012 , Extended SCH  1002  occupies 1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth  1014 , Extended SCH  1002  occupies 3.75 MHz of bandwidth. In the case of 10 MHz system bandwidth  1016 , Extended SCH  1002  occupies 3.75 MHz of bandwidth. Other data traffic  1004  occupies 5 MHz of bandwidth. The spectrum allocation displayed in  FIG. 5A  for various system bandwidths is merely illustrative of one example of this embodiment. 
         [0067]    In another embodiment, basic SCH  1000  is transmitted through the central  75  sub-carriers in each band, and the Extended SCH  1002  is transmitted by all leftover spectrums. The advantage of this solution is that the low PAPR of a SCH symbol can be achieved when the cell common or cell specific waveform is defined with as low a PAPR as possible. The average transmission power of a SCH symbol can be higher than other OFDM symbols. This improves the cell search performance in some scenario, especially in the unsynchronized networks and for large cell size. The cell search performance is improved proportionally with the increase of the overall transmission bandwidth. More SCH overhead is introduced in each SCH symbol, especially for above 5 MHz transmission bandwidth cases. To reduce SCH overhead, SCH may be transmitted less frequently in each frame. The basic SCH sequence should be the central portion of the overall SCH sequence which has a low PAPR. The length of the total SCH sequence is equal to the overall length of basic SCH  1000  and the Extended SCH  1002 . 
         [0068]      FIG. 5B  is a diagram illustrating the spectrum allocation of basic SCH  1000  and Extended SCH  1002  in this alternative embodiment. In the case of 1.25 MHz system bandwidth  1010 , Extended SCH  1002  occupies 0 MHz of bandwidth as basic SCH  1000  has occupied the entirety of the spectrum. In the case of 2.5 MHz system bandwidth  1012 , basic SCH  1000  occupies 1.25 MHz of bandwidth with Extended SCH  1002  occupying the remainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth  1014 , basic SCH  1000  occupies 1.25 MHz of bandwidth, with Extended SCH  1002  occupying the remainder, or 3.75 MHz of bandwidth. In the case of 10 MHz system bandwidth  1016 , basic SCH  1000  occupies 1.25 MHz of bandwidth, with Extended SCH  1002  occupying the remainder, or 8.75 MHz of bandwidth. In this case, Extended SCH  1002  is transmitted by all leftover spectrums and therefore there is no leftover bandwidth for other data traffic as there was in connection with the embodiment shown in  FIG. 5A . The spectrum allocation displayed in  FIG. 5B  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. 
         [0069]    In another embodiment, a maximum SCH bandwidth, which is the total SCH bandwidth including the basic SCH and the Extended SCH, for example 5 MHz, is defined. In this embodiment, if the overall spectrum is broader than the maximum SCH bandwidth, the unoccupied spectrum will not be used. 
         [0070]      FIG. 5C  is a diagram illustrating the spectrum allocation of a basic SCH  1000  and an Extended SCH  1002  in this alternative embodiment. In the case of 1.25 MHz system bandwidth  1010 , Extended SCH  1002  occupies 0 MHz of bandwidth as basic SCH  1000  has occupied the entirety of the spectrum. In the case of 2.5 MHz system bandwidth  1012 , basic SCH  1000  occupies 1.25 MHz of bandwidth with Extended SCH  1002  occupying the remainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth  1014 , basic SCH  1000  occupies 1.25 MHz of bandwidth, with Extended SCH  1002  occupying the remainder, or 3.75 MHz of bandwidth. In the case of 10 MHz system bandwidth  1016 , basic SCH  1000  occupies 1.25 MHz of bandwidth, with Extended SCH  1002  occupying 3.75 MHz of bandwidth. In this case, leftover bandwidth  1020  is left unused. The spectrum allocation displayed in  FIG. 5C  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. 
         [0071]    In another embodiment, three options for SCH bandwidth and location for 20 MHz transmission bandwidth are described. It is currently assumed by persons skilled in the art that the maximum downlink transmission bandwidth is 20 MHz. However the maximum UE reception capability is 10 MHz. It is expected that a UE with 10 MHz reception capability will operate in either the lower part of upper part of the full 20 MHz transmission band. To avoid inter-frequency measurement during a neighbour-cell measurement, it is desired that cell search be performed by a UE without re-tuning the centre carrier frequency in connected mode and idle mode. 
         [0072]    The first option for this embodiment is shown in  FIG. 6A . In this embodiment, two identical SCHs, SCH A  1000 A and SCH B  1000 B are transmitted in the lower band and the upper band of a 20 MHz system bandwidth spectrum  1018  separately. For the sake of clarity, SCH A  1000 A and SCH B  1000 B are both being represented by SCH  1000  in the same shading. Other data traffic  1004  occupies the remainder of the spectrum in both the upper band and lower band. In the lower half of  FIG. 6A , a 10 MHz reception bandwidth  1025  for a UE is shown. The spectrum allocation displayed in  FIG. 6A  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. 
         [0073]    A second option for this embodiment is shown in  FIG. 6B . In this embodiment, a basic SCH  1000  is transmitted at the center of the 20 MHz system bandwidth spectrum  1018 . Two Extended SCHs, Extended SCH A  1002 A and Extended SCH B  1002 B are transmitted in the lower band and upper band separately though in different positions than as was shown in  FIG. 6A . Other data traffic  1004  occupies the remainder of the spectrum in both the upper band and lower band. In the lower half of  FIG. 6B , a 10 MHz reception bandwidth  1025  for a UE is shown. For the sake of clarity, Extended SCH A  1002 A and Extended SCH B  1002 B are both being represented by SCH  1000  in the same shading. The spectrum allocation displayed in  FIG. 6B  for various system bandwidths is merely illustrative of one example of this embodiment. For example, basic SCH  1000  and Extended SCH  1002 A,  1002 B could be transmitted alternatively in time. 
       The Spectrum Arrangement of a Broadcast-Control Channel (BCH) and an Extended Broadcast-Control Channel (Extended Broadcast-Control Channel) 
       [0074]    A BCH is a downlink channel including specific parameters needed by a UE in order that it can identify the network and gain access to it. Typical information includes the Location Area Code (LAC), Routing Area Code (RAC), and the Mobile Network Code (MNC), and other system parameters. 
         [0075]    A BCH can be located at any predetermined location in each frame. The overall BCH includes a basic BCH and an Extended BCH. A basic BCH is used to transmit the information to a UE with at least the same bandwidth capabilities as the minimum bandwidth supported by each type. The basic BCH transmits important system parameters, including antenna configuration, overall transmission bandwidth, the bandwidth of the Extended SCH, the bandwidth of the Extended BCH, and the cyclic prefix length. An Extended BCH transmits other broadcast-control signaling including the information for the UE above the available system bandwidth capabilities. 
         [0076]    The frequency domain arrangement of BCH is described as follows. The basic BCH originates at the left end of the spectrum. The Extended BCH occupies the leftover available spectrum. Guard bands may be required between the basic BCH and Extended BCH as well as between the Extended BCHs. 
         [0077]      FIG. 7  is a diagram of the frequency domain structure of the BCH in this embodiment for system bandwidths from 5 MHz to 20 MHz. In the case of 5 MHz system bandwidth  920 , basic BCH  902  takes up all of the available system bandwidth. In the case of 10 MHz system bandwidth  922 , basic BCH  902  takes up 5 MHz of bandwidth, and Extended BCH  904  takes up the remainder of the system bandwidth. Extended BCH  904  is designed to be used for a UE with receive capabilities over 5 MHz. In the case of a 20 MHz system bandwidth  924 , basic BCH  902  takes up 5 MHz of bandwidth, and Extended BCH  904  takes up an additional 5 MHz of system bandwidth. Extended BCH  906  is available to be used for the remainder of the system bandwidth. Extended BCH  906  is used for UE with receiving capabilities over 10 MHz. The spectrum allocation displayed in  FIG. 7  for various system bandwidths is merely illustrative of one example of this embodiment. 
         [0078]      FIG. 8  is a diagram of the frequency domain structure of the BCH in this embodiment for system bandwidths of 1.25 MHz and 2.5 MHz bandwidth. In the case of 1.25 MHz system bandwidth  954 , basic BCH  950  takes up all of the available 1.25 MHz of bandwidth. In the case of 2.5 MHz system bandwidth  956 , basic BCH  950  takes up 1.25 MHz of bandwidth, and Extended BCH  952  takes up an additional 1.25 MHz of system bandwidth. The spectrum allocation displayed in  FIG. 8  for various system bandwidths is merely illustrative of one example of this embodiment. 
         [0079]    In  FIG. 9A , one example of a spectrum arrangement for a BCH (i.e. basic BCH  1050  and an Extended BCH  1052 ) is shown. The bandwidth of the Extended BCH will vary depending on the overall system transmission bandwidth. The BCH bandwidth will increase with greater transmission bandwidth. 
         [0080]    In the case of 1.25 MHz system bandwidth  1010 , Extended BCH  1052  occupies 0 MHz of bandwidth as basic BCH  1050  has occupied the entirety of the spectrum. In the case of 2.5 MHz system bandwidth  1012 , basic BCH occupies 1.25 MHz of bandwidth with Extended BCH  1052  occupying the remainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth  1014 , basic SCH  1050  occupies 1.25 MHz of bandwidth, with Extended BCH  1052  occupying the remainder, or 3.75 MHz of bandwidth. In the case of 10 MHz system bandwidth  1016 , basic BCH  1050  occupies 1.25 MHz of bandwidth, with Extended BCH  1052  occupying the remainder, or 8.75 MHZ of bandwidth. In this case, Extended BCH is transmitted by all leftover spectrums and therefore there is no leftover bandwidth for other traffic. The spectrum allocation displayed in  FIG. 9A  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. 
         [0081]    In another example of this embodiment, all useful sub-carriers in a BCH symbol are shared by the broadcast-control channel and other data transmission. Therefore, a maximum BCH bandwidth is defined, which is the total BCH bandwidth (for example 5 MHz) including the basic BCH and the Extended BCH. In this example of 5 MHz BCH bandwidth, each BCH occupies the central  75  subcarriers. For &gt;1.25 MHz transmission bandwidth scenarios the leftover spectrum could be occupied by Extended BCH and other data transmission, depending on the overall BCH bandwidth and the overall transmission bandwidth. 
         [0082]      FIG. 9B  is a diagram illustrating the spectrum allocation of a basic BCH  1050  and an Extended BCH  1052  in this alternate example. In the case of 1.25 MHz system bandwidth  1010 , Extended BCH  1052  occupies 0 MHz of bandwidth as basic BCH  1050  has occupied the entirety of the spectrum. In the case of 2.5 MHz system bandwidth  1012 , basic BCH  1050  occupies 1.25 MHz of bandwidth with Extended SCH  1052  occupying the remainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth  1014 , basic BCH  1050  occupies 1.25 MHz of bandwidth, with Extended BCH  1052  occupying the remainder, or 3.75 MHz of bandwidth. In the case of 10 MHz system bandwidth  1016 , basic BCH  1050  occupies 1.25 MHz of bandwidth, with Extended BCH  1052  occupying 3.75 MHz of bandwidth. In this case, any leftover bandwidth is occupied by other data traffic  1004 . The spectrum allocation displayed in  FIG. 9B  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. 
         [0083]    In another example, BCH bandwidth and location for 20 MHz transmission bandwidth is described. To allow a 10 MHz capability UE to detect a BCH when directed at either side of the overall 20 MHz transmission band without a change of the carrier frequency, a BCH should be transmitted twice: once in the lower 10 MHz band and once upper 10 MHz band. Both the basic BCH and the Extended BCH are transmitted in the two 10 MHz bands. The same maximum BCH bandwidth can be used as in other transmission bandwidth scenarios described above. 
         [0084]    This example is shown in  FIG. 10  which is a diagram illustrating a spectrum allocation for a BCH for 20 MHz transmission bandwidth. In this embodiment, two identical BCHs, comprised of basic BCH A  1050 A and Extended BCH A  1050 A, and basic BCH B  1050 B and Extended BCH B  1052 B, are transmitted in the lower band and the upper band of a 20 MHz system bandwidth spectrum  1018  separately. For the sake of clarity, basic BCH A  1050 A and basic BCH B  1050 B are both being represented by basic BCH  1050  in the same shading. Likewise, Extended BCH A  1052 A and Extended BCH B  1052 B are both being represented by basic BCH  1052  in the same shading. Other data traffic  1004  occupies the remainder of the spectrum in both the upper band and lower band. In the lower half of the figure, a 10 MHz reception bandwidth  1025  for a UE is shown. The spectrum allocation displayed in  FIG. 10  for various system bandwidths is merely illustrative of one example of this embodiment of the invention. For example, basic BCH A  1050 A and Extended BCH A  1050 A, and basic BCH B  1050 B and Extended BCH B  1052 B could be transmitted alternatively in the lower band the upper band. 
       Time Domain Structure for SCH and BCH 
       [0085]    According to an embodiment of the invention common pilots may be used as a SCH or part of a SCH for OFDMA. According to one embodiment, the common pilots are used as a synchronization channel for DL communications as follows: 
         [0086]    Reuse some or all common pilot sub-carriers to transmit SCH, i.e. the PSC and the SSC. This reduces overhead and pilot density may be changed according to the channel condition. For TDM based pilot format, common pilot symbols may be modulated by primary common Sync sequence (PSS) and secondary cell specific Sync sequence (SSS) alternatively. For scattered pilot format, common pilot sub-carriers may be shared by PSC and SSC. 
         [0087]    In a first option, scattered pilots in each TTI may assigned to the PSC and SSC. For example, the pilot sub-carriers in the first symbol (or symbol pair) may be assigned to SSC and the pilot sub-carriers in the 4th (and 5th) symbols may be assigned to PSC. In a second option, the pilot sub-carriers in the 4th (and 5th) symbols in the last TTI per frame are used for PSC. To enable the fast system access, only half of the sub-carriers may be modulated. 
         [0088]      FIG. 11A  is a diagram of an example frame  302  for transmission used in accordance with one embodiment of the invention. More particularly,  FIG. 11A  illustrates a first embodiment where there are two types of SCH, a PSC and an SSC, in a system bandwidth greater than or equal to 5 MHz.  FIG. 11A  is only one example of a frame structure that can be used in accordance with this embodiment of the invention. 
         [0089]    Shown is frame  302  which in this example of 10 ms duration. Not shown is frame N−1 which precedes frame  302  and Frame N+1 which follows frame  302 . Frame  302  is comprised of a plurality of Transmission Time Intervals (TTI) TTI- 1   304 , TTI- 2   306 , TTI- 3   308 , TTI- 4   310 , TTI- 19   312  and TTI- 20   314 . For the sake of clarity, the TTIs between TTI- 4   310  and TTI- 19   312  are not shown. In this representative example, each TTI is of 0.5 ms duration, though 0.5 ms TTI is only an example. Therefore, in this example, there are a total of 20 TTIs in frame  302 . Each TTI comprises seven OFDM symbols 
         [0090]    In this embodiment, SSC  316  is transmitted in an OFDM symbol located at the beginning of each TTI in frame  302 . BCH  322  is transmitted in an OFDM symbol located at the end of TTI- 20   314 . PSC  320  is transmitted in an OFDM symbol located immediately preceding BCH  322  in TTI- 20   318 . Optionally, SSC  318  can also be transmitted in an OFDM symbol located in the middle of each TTI. 
         [0091]    One benefit to locating cell specific synchronization channel such as SSC  316  at the beginning of each TTI is that UE&#39;s for which there is no traffic in the remaining six symbols need not process these latter symbols. It is not necessary to locate synchronization information in the first OFDM symbol to realize a benefit. Instead, benefits can be achieved by locating such information in a dedicated OFDM symbol. The SSC can be used as pilots to assist channel estimation, channel quality measurement and cell search. There is a power saving feature for a UE which only needs to do the cell search and the channel quality measurement. 
         [0092]    In  FIG. 11B , the time domain structure of PSC  320  is shown. As illustrated, PSC  320  is comprised of prefix  324 , following by two identical parts  323  and  326 . Prefix  324  may be a cyclic prefix. This is only one embodiment and it is not absolutely necessary for PSC  320  to have two identical parts. 
         [0093]      FIG. 11C  illustrates another example of SSC and PSC locations for a TDM based pilot design. In this embodiment, SSC  316  is transmitted in the first OFDM symbol of each TTI in frame  302 . PSC  320  is transmitted in the first OFDM symbol of each TTI other than TTI- 1   304  (i.e. TTI- 2   306 , TTI- 3   308 , . . . TTI- 20   314 ). 
         [0094]      FIG. 11D  illustrates SSC and PSC locations for a scattered pilot design. In this embodiment, SSC  316  is transmitted in the first OFDM symbol of TTI- 1   304  and in the first OFDM symbol of TTI- 20   314  of frame  302 . PSC  320  is transmitted in the fourth and fifth OFDM symbols of TTI- 1   304  and TTI- 20   314 . 
         [0095]      FIG. 11E  is an example pilot pattern which can be used in accordance with one embodiment of the present invention. Pilot and data symbols are spread over an OFDM sub-frame in a time direction  120  and a frequency direction  122 . Most symbols within the OFDM sub-frame are data symbols  124 . Pilot symbols  126  are inserted into some of the OFDM symbols in each TTI. The PSC and SSC can be transmitted over these symbols. 
         [0096]      FIG. 12A  is a diagram of an example frame  402  used in accordance with one embodiment of the invention. More particularly,  FIG. 12A  illustrates a second embodiment, in a Type-2 system, i.e. a system bandwidth less than 5 MHz.  FIG. 12A  is only one example of a frame structure that can be used in accordance with this embodiment of the invention. 
         [0097]    Shown is frame  402  which in this example of 10 ms duration. Not shown is frame N−1 which precedes frame  402  and Frame N+1 which follows frame  402 . Frame  402  is comprised of TTI- 1   404 , TTI- 2   406 , TTI- 3   408 , TTI- 4   410 , TTI- 19   412  and TTI- 20   414 . For the sake of clarity, the TTIs between TTI- 4   410  and TTTi- 19   412  are not shown. In this representative example, each TTI is of 0.5 ms duration. Therefore, in this example, there are a total of 20 TTIs frame  402 . 
         [0098]    In this embodiment, SSC  416  is transmitted in a slot located at the beginning of each TTI in frame  402 . BCH  422  is transmitted in a slot located at the end of TTI- 20   414 . A first PSC  420  is transmitted in a slot located immediately preceding BCH  322  in TTI- 20   318 . A second PSC  421  is transmitted immediately preceding PSC  420 . Optionally, SSC  318  can also be transmitted in a slot in the middle of each TTI. 
         [0099]    In  FIG. 12B , the time domain structure of PSC  420  and PSC  421  is shown. As illustrated, PSC  420  and PSC  421  are both comprised of prefix  424 , following by part  425 . 
         [0100]      FIG. 13  is a diagram of time domain SCH multiplexing. As shown, SCH  575  is illustrated to be transmitted periodically. As illustrated, SCH  575  is transmitted in a slot at the beginning of each of Frame N  576  and Frame N+ 1   578 . For the sake of clarity, the preceding and succeeding frames are not illustrated. 
       Initial Access Procedure 
       [0101]    In general, the initial access procedure between a UE and a BTS comprises the following steps: 
         [0102]    1. Primary SCH bandwidth identification: SCH bandwidth selection based on UE&#39;s capability and/or system bandwidth. 
         [0103]    Option-1: 
         [0104]    UE determines the type of SCH according to its capability. UE then detects the Primary SCH using the bandwidth determined by the SCH type. 
         [0105]    Option-2: 
         [0106]    UE detects the Primary SCH using fs and Nfft determined by the basic SCH bandwidth. Multiple basic SCH may be detected if both the system bandwidth and UE capability are above certain multiples of bandwidth of the basic SCH. 
         [0107]    2. Frame acquisition. Coarse timing synchronization based on time domain repeated primary SCH structure. 
         [0108]    3. Timing acquisition 
         [0109]    4. Frequency acquisition 
         [0110]    5. System bandwidth identification 
         [0111]    6. BCH detection 
         [0112]    7. Cell identification and selection 
         [0113]    8. Fine frequency synchronization 
         [0114]    9. Fine timing verification 
         [0115]    Note that the order of steps 5 and 6 above can be exchanged. For example the system bandwidth information can be obtained from BCH if BCH can be decoded at first. 
         [0116]      FIG. 14  is a flow chart of the possible steps that could be carried out in connection with an initial access procedure between an UE and a BTS. At step  960 , a UE determines the type of SCH according to its capability. The UE detects the Primary SCH using the bandwidth (or sampling frequencies and FFT size (Nfft)) determined by the SCH type. Alternatively, the UE detects the Primary SCH using frequencies and Nfft determined by the basic SCH bandwidth. Multiple basic SCH may be detected if both the system bandwidth and UE capability are above certain times the bandwidth of the basic SCH. 
         [0117]    At step  962 , frame acquisition takes place. Coarse timing synchronization is based on time domain repeated primary SCH structure. At step  964 , system bandwidth detection and fine timing acquisition takes place. The system bandwidth information is carried by the Primary synchronization sequences, for example there are several sequences which corresponding to different system BW. At step  966 , coarse frequency synchronization in the time domain takes place. At step  968 , fine timing is the frequency domain is carried out based on selected PSS. At step  970 , the UE find the maximum of the cross correlation and performs cell correlation based on SSS. 
         [0118]    At step  972 , fine frequency synchronization is performed in the frequency domain. At step  974 , fine timing synchronization verification is performed (i.e. a correlation between the recovered and the original cell specific PN code corresponding to the selected cell). At step  976 , an evaluation is performed as to whether the correlation value is above a certain threshold. If not, the procedure is repeated at step  960 . If so, there is BCH detection according to system bandwidth and UE capability at step  980 . At step  982 , the fine sync and broadcast control information is output. 
         [0119]    In other embodiments, a spectrum arrangement of the SCH and BCH is set out. As noted above, a UE needs to detect the SCH and BCH during initial access. However, such connectivity is also required during the connected mode (i.e. there is an always-on connection between the UE and the BTS) and the idle mode (i.e. the UE is still connected to the BTS, but not receiving or demodulating any downlink signals during the packet transmission intermission interval, and thus power is saved). 
         [0120]    During initial access, the UE first detects the central part of the spectrum (i.e. center carrier frequency) regardless of the transmission bandwidth of the UE and that of the BTS. Transmission is then initiated using the assigned spectrum. 
         [0121]    In accordance with this embodiment, a UE can detect the SCH and BCH in the connected and idle mode without returning to the center carrier frequency. Transmit diversity can be applied to the SCH and BCH to improve the coverage when there are more than one transmit antenna present in BTS, though the transmit diversity scheme should be in some cases transparent to the UE, at least for the initial access. 
       Transmit Diversity Scheme for BCH 
       [0122]    In yet another embodiment, a transmit diversity scheme for a BCH is described. Transmit diversity can be applied by a BTS with more than one Tx antenna to improve the coverage. 
         [0123]    Candidate transmit diversity schemes include (i) 
         [0124]    Block code based transmit diversity. With this transmit diversity scheme, knowledge of the number of transmit antennas is needed by the UE, (ii) Frequency switched transmit diversity (sub-carrier based FSTD). With this transmit diversity scheme, there is no need for the UE to know the number of transmit antennas if the channel estimation is done based on SCH with the similar structure, and (iii) Cyclic delay diversity (CDD). Blind detection may be required for channel estimation if there is no antenna configuration information, and (iv) Time switched transmit diversity (symbol based TSTD). In this case, more than one BCH symbol is required to achieve the diversity. 
         [0125]    Usually, the UE has no a priori knowledge of the number of transmit antennas when decoding a BCH. It is desired that the transmit diversity scheme be transparent to UE, at least for the initial BCH detection. 
         [0126]    Two options for a Tx diversity scheme for BCH are preferred: (i) in Option 1: Either FSTD or CDD can be used to decode the basic BCH and the Extended BCH. (ii) In Option 2: Either of FSTD and CDD can be used to decode the basic BCH, and block code based transmit diversity is used to decode the Extended BCH. In Option 2, the UE will detect the number of transmit antennas from the basic BCH. The UE will decode the Extended BCH accordingly. 
         [0127]    Where the antenna configuration can be obtained before the decoding of BCH, in this case a block code based transmit diversity scheme can be applied to both the basic BCH and the Extended BCH. For FSTD, the sub-carriers used to transmit the data are mapped to different antennas alternatively on the sub-carrier base. For example, the odd indexed sub-carriers are mapped onto antenna-1 and the even indexed sub-carriers are mapped onto antenna-2. The mapping could be swapped between antennas in different transmission instances. 
       Access Procedure 
       [0128]    In another implementation, an access procedure is described. A flow chart of the steps carried out by a UE to access the SCH and BCH are set forth in  FIG. 15 . At step  1610 , a UE performs an initial timing/frequency synchronization based on the basic SCH. At step  1620 , the UE performs initial cell search based on the basic SCH. At step  1630 , the UE detects the basic BCH. At step  1640 , the UE obtains basic system parameters. At step  1650 , the UE decodes the Extended BCH. At step  1660 , the UE enters the connected mode. Finally, at step  1670 , the UE performs Sync tracking and cell search based on both the basic SCH and the Extended SCH. 
         [0129]    What has been described is merely illustrative of the application of the principles of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.