KR101460920B1 - Ranging channel structures and methods - Google Patents

Abstract

A periodic ranging channel used by a mobile terminal is defined to facilitate ranging between mobile terminals and the base station in a wireless communication network that uses orthogonal frequency division multiplexing (OFDM) for uplink data communication. The channel specifies a plurality of N blocks of subcarrier frequencies in the discontinuous OFDM frequency band within the OFDM frequency band. The channel also specifies a timeslot that spans one or more OFDM symbol periods within an OFDM subframe. The ranging transmission is periodically transmitted as a spread signal over the specified N blocks of subcarrier frequencies within the specified time slot. The duration of the ranging transmission may be less than the duration of the OFDM subframe. A conceptual grid of tiles representing time and frequency resources associated with the subframe may facilitate channel definition. A similar method can be used to define an initial access channel for initial access transmission.

Description

[0001] RANGING CHANNEL STRUCTURES AND METHODS [0002]

<Cross-reference of relevant technology>

This application claims priority to U.S. Provisional Application No. 61 / 223,108, filed July 6, 2009, which is hereby incorporated by reference in its entirety.

<Technical Field>

The present invention relates generally to wireless communication technologies, and more particularly to techniques relating to orthogonal frequency division multiplexing (OFDM).

In a wireless communication network, such as a cellular network, a plurality of mobile stations or mobile terminals (e. G., Cellular phones, smart phones, or other types of wireless communication devices) may communicate via uplink and / or downlink data communication via orthogonal frequency division multiplexing And can communicate with the base station. An orthogonal frequency division multiplexed network may facilitate cell-based high-speed services such as those provided under the IEEE 802.16 standard, which may be referred to as WiMAX or, less commonly, WirelessMAN or Air Interface Standard.

In a cellular network using OFDM, a cell's base station may be responsible for assigning OFDM frequency band subcarrier frequencies to mobile terminals in a cell for use in a particular timeslot. If the distance between the mobile stations and the base station changes over time, the transmission delay of the wireless data communication between the mobile stations and the base station may also change. Disadvantageously, therefore, misalignment of data communications received at the base station with respect to particular timeslots can occur. A similar problem may arise when the mobile terminal first communicates with the base station, for example, when the mobile terminal enters the cell or when the mobile terminal wakes from the idle period, It may not have been.

<Technology Related to the Application>

In the draft IEEE 802.16m system description document, IEEE 802.16m-08 / 003r1, dated April 15, 2008, the following description is provided:

This [802.16m] standard modifies the IEEE 802.16 WirelessMAN-OFDMA specification to provide an advanced air interface that operates in the licensed band. This meets the cellular layer requirements of IMT-Advanced next-generation mobile networks. These modifications provide continued support for legacy WirelessMAN-OFDM equipment.

This standard will address the following objectives:

i. The purpose of this standard is to provide the performance improvements needed to support future advanced services and applications such as those described by ITU in ITU-R M.2072.

More generally, the following embodiments may be applied in any communication system that uses multi-carrier or OFDM-type technology in the uplink.

In an aspect, there is provided a method of performing periodic ranging between a mobile terminal and the base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station, Defining a periodic ranging channel used by the mobile terminal, the periodic ranging channel including a plurality of N blocks of subcarrier frequencies of an OFDM frequency band, The channel is non-contiguous within the OFDM frequency band, and the channel is further subdivided into subcarriers within a particular OFDM subframe by using N blocks of subcarrier frequencies to transmit ranging transmissions from the mobile terminal to the base station, Wherein the time slot spans at least one OFDM symbol period, Less than the duration of the probe frame; And periodically transmitting a ranging transmission over the periodic ranging channel from the mobile terminal to the base station, the transmitting step comprising transmitting the ranging transmission as a spread signal in the timeslot, Spreading signal is spread over subcarrier frequencies of the N blocks and the duration of the ranging transmission is less than the duration of the OFDM subframe.

In another aspect, a method is provided for performing periodic ranging between a mobile terminal and the base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station, Defining a periodic ranging channel for the mobile terminal, the periodic ranging channel being represented as a plurality of N tiles in a notional grid of tiles representing OFDM time and frequency resources, The grid has a time dimension including a plurality of OFDM symbol periods of an OFDM subframe and a frequency dimension including a plurality of blocks of subcarriers of an OFDM frequency band, and each of the N tiles includes one or more OFDM symbol periods At least the subcarrier used by the mobile terminal Wherein the N tiles are discontinuous in the frequency dimension of the conceptual grid and each of the N tiles spans the same time slot in the time dimension of the conceptual grid, Is at least one OFDM symbol period but has a duration less than the duration of the OFDM subframe; And periodically transmitting a ranging transmission over the periodic ranging channel from the mobile terminal to the base station, the transmitting step comprising transmitting the ranging transmission as a spread signal in the timeslot, The spread signal is spread over subcarrier frequencies of the N tiles, and the duration of the ranging transmission is less than the duration of the OFDM subframe.

In yet another aspect, a method is provided for performing an initial access from a mobile terminal to the base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station, Defining an initial access channel used by the mobile terminal, the initial access channel comprising a plurality of N blocks of subcarrier frequencies in an OFDM frequency band, and N blocks of subcarrier frequencies in the OFDM frequency band Wherein the initial access channel further comprises a timeslot in which initial access transmissions are sent from the mobile terminal to the base station using N blocks of subcarrier frequencies in a particular OFDM subframe, But over one or more OFDM symbol periods, but the O Less than the duration of the FDM subframe -; And transmitting an initial access transmission on the initial access channel from the mobile terminal to the base station, the transmitting comprising transmitting the initial access transmission as a spread signal in the timeslot, Wherein the duration of the initial access transmission is less than the duration of the OFDM subframe, and the number of OFDM symbol periods including the timeslot is greater than the number of OFDM symbol periods including the time slot, And an estimated or determined maximum ranging delay between the base station and the base station.

Aspects and features of the present invention will become apparent to those skilled in the art upon examination of the following description of specific embodiments of the invention, along with the accompanying drawings and appended claims.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.
1 is a block diagram of a cellular communication system.
2 is a block diagram of an example base station that may be used to implement some embodiments of the present invention.
3 is a block diagram of an example wireless terminal that may be used to implement some embodiments of the invention.
4 is a block diagram of an exemplary relay station that may be used to implement some embodiments of the present invention.
5 is a block diagram of a logical breakdown of an exemplary OFDM transmitter architecture that may be used to implement some embodiments of the present invention.
6 is a block diagram of a logical breakdown of an exemplary OFDM receiver architecture that may be used to implement some embodiments of the present invention.
Figures 7 and 8 illustrate conceptual grids that represent time and frequency resources associated with OFDM subframes, which may facilitate the definition of ranging channels.
The same reference numerals are used to denote like elements in the different figures.

Wireless Systems Overview

Referring to the drawings, FIG. 1 shows a base station controller (BSC) 10 that controls a plurality of cells 12 - wireless communications within these cells - services received by corresponding base stations (BSs) 14 . In some arrangements, each cell is further divided into a plurality of sectors 13 and zones (not shown). In general, each base station 14 facilitates communications using OFDM with the mobile and / or wireless terminals 16 within the cell 12 associated with the corresponding base station 14. The movement of the mobile terminals 16 to the base stations 14 causes the channel conditions to vary greatly. As illustrated, base station 14 and mobile terminals 16 may comprise a plurality of antennas providing spatial diversity for communication. In some arrangements, relay stations 15 may assist in the communication between base stations 14 and wireless terminals 16. The wireless terminals 16 may receive information from any cell 12, sector 13, region (not shown), base station 14 or relay station 15 to another cell 12, sector 13, (18) to base station (14) or relay station (15). In some arrangements, base stations 14 communicate with each other and with other networks (not shown, such as the core network or the Internet, etc.) through a backhaul network 11. In some configurations, the base station controller 10 is not needed.

Referring to FIG. 2, an example of a base station 14 is illustrated. Base station 14 generally includes a control system 20, a baseband processor 22, a transmit circuit 24, a receive circuit 26, a plurality of antennas 28, and a network interface 30. The receiving circuit 26 receives a radio frequency signal carrying information from one or more remote transmitters provided by the mobile terminals 16 (illustrated in FIG. 3) and the relay stations 15 (illustrated in FIG. 4). A low noise amplifier and filter (not shown) can cooperate to amplify and remove the broadband interference from the signal for processing. A downconversion and digitization circuit (not shown) is then filtered to downconvert the received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams.

The baseband processor 22 digitizes and processes the received signal to extract the information or data bits carried in the received signal. This process typically includes demodulation, decoding, and error correction operations. Thus, the baseband processor 22 is typically implemented with one or more digital signal processors (DSPs) or an application specific integrated circuit (ASIC). The received signal is then transmitted across the network interface 30 to the other mobile terminal 16 that is transmitted across the wireless network or served by the base station 14 or with the aid of the relay station 15.

On the transmitter side, the baseband processor 22 receives digitized data under the control of the control system 20, which can represent voice, data, or control information from the network interface 30 and transmits the data &Lt; / RTI &gt; The encoded data is output to a transmit circuit 24, where it is modulated by one or more carrier signals having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to an appropriate level for transmission and deliver the modulated carrier signal to antennas 28 via a matching network (not shown). The details of modulation and processing are described in more detail below.

Referring to FIG. 3, an example of a mobile terminal 16 is illustrated. Similar to the base station 14, the mobile terminal 16 includes a control system 32, a baseband processor 34, a transmit circuit 36, a receive circuit 38, a plurality of antennas 40, (42). The receiving circuit 38 receives radio frequency signals carrying information from one or more base stations 14 and relay stations 15. A low noise amplifier and filter (not shown) can cooperate to amplify and remove the broadband interference from the signal for processing. A downconversion and digitization circuit (not shown) is then filtered to downconvert the received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams.

The baseband processor 34 digitizes and processes the received signal to extract the information or data bits carried in the received signal. This process typically includes demodulation, decoding, and error correction operations. The baseband processor 34 is typically implemented with one or more digital signal processors (DSPs) and an application specific integrated circuit (ASIC).

For transmission, the baseband processor 34 receives digitized data that may represent voice, video, data, or control information from the control system 32 and encodes the data for transmission. The encoded data is output to a transmit circuit 36, where it is used by the modulator to modulate one or more carrier signals at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to an appropriate level for transmission and deliver the modulated carrier signal to antennas 40 via a matching network (not shown). Various modulation and processing techniques are available to those skilled in the art for signal transmission between the mobile terminal and the base station, either directly or via a relay station.

In OFDM modulation, the transmission band is divided into a plurality of orthogonal carriers. Each carrier is modulated according to the digital data to be transmitted. Since OFDM divides the transmission band into a plurality of carriers, the bandwidth per carrier decreases and the modulation time per carrier increases. Since a plurality of carriers are transmitted in parallel, the transmission rate for digital data, or symbols, on any given carrier is lower than when one carrier is used.

OFDM modulation utilizes the performance of an Inverse Fast Fourier Transform (IFFT) on the information to be transmitted. For demodulation, performing fast Fourier transform (FFT) on the received signal restores transmission information. In practice, the IFFT and FFT are provided by digital signal processing, which performs inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT), respectively. Thus, a characteristic feature of OFDM modulation is that orthogonal carriers are generated for a plurality of bands within a transmission channel. Modulated signals are digital signals that have a relatively low transmission rate and can stay within their respective bands. Individual carriers are not directly modulated by their digital signals. Instead, all carriers are simultaneously modulated by IFFT processing.

In operation, OFDM may be used for downlink transmissions from at least the base stations 14 to the mobile terminals 16. Each base station 14 has "n" transmit antennas 28 (n> = 1) and each mobile terminal 16 has "m" receive antennas 40 (m> = 1) . In particular, each antenna is marked for clarity only, as it can be used for reception and transmission using an appropriate duplexer or switch.

OFDM can be used for downlink transmissions from base stations 14 to relay stations 15 and from relay stations 15 to mobile terminals 16 when relay stations 15 are used.

Referring to FIG. 4, an example of relay station 15 is illustrated. Similar to base station 14 and mobile terminal 16, relay station 15 includes a control system 132, a baseband processor 134, a transmit circuit 136, a receive circuit 138, a plurality of antennas 130 ), And a relay circuit (142). The relay circuit 142 enables the relay station 15 to facilitate communication between the base station 14 and the mobile terminals 16. Receive circuit 138 receives radio frequency signals carrying information from one or more base stations 14 and mobile terminals 16. A low noise amplifier and filter (not shown) can cooperate to amplify and remove the broadband interference from the signal for processing. A downconversion and digitization circuit (not shown) is then filtered to downconvert the received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams.

The baseband processor 134 digitizes and processes the received signal to extract the information or data bits carried in the received signal. This process typically includes demodulation, decoding, and error correction operations. The baseband processor 134 is typically implemented with one or more digital signal processors (DSPs) and an application specific integrated circuit (ASIC).

For transmission, the baseband processor 134 receives digitized data that may represent voice, video, data, or control information from the control system 132 and encodes the data for transmission. The encoded data is output to the transmit circuitry 136, where it is used by the modulator to modulate one or more carrier signals at the desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a suitable level for transmission and deliver the modulated carrier signal to antennas 130 via a matching network (not shown). As described above, various modulation and processing techniques are available to those skilled in the art for signal transmission between a mobile terminal and a base station, either directly or indirectly through a relay station.

With reference to FIG. 5, a logical OFDM transmission architecture will be described. Initially, the base station controller 10 will transmit the data to be transmitted to the various mobile terminals 16 directly or to the base station 14 with the help of the relay station 15. The base station 14 may use channel quality indicators (CQIs) associated with mobile terminals to schedule the data for transmission and also to select the appropriate coding and modulation to transmit the scheduled data. The CQIs may be obtained directly from the mobile terminals 16 or may be determined at the base station 14 based on the information provided by the mobile terminals 16. In any case, the CQI for each mobile terminal 16 is a function of the degree to which the channel amplitude (or response) varies over the OFDM frequency band.

Scheduled data 44, which is a stream of bits, is scrambled using scrambling logic 46 to reduce the peak-to-average power ratio associated with the data. A cyclic redundancy check (CRC) for the scrambled data is determined and added to the scrambled data using the CRC add logic 48. [ Channel coding is then performed using the channel encoder logic 50 to effectively add redundancy to the data to facilitate recovery and error correction at the mobile terminal 16. Again, channel coding for a particular mobile terminal 16 is based on CQI. In some implementations, the channel encoder logic 50 utilizes known turbo encoding techniques. The encoded data is then processed by the rate matching logic 52 to compensate for the data expansion associated with the encoding.

The bit interleaver logic 54 systematically rearranges the bits in the encoded data to minimize the loss of consecutive data bits. The resulting data bits are systematically mapped to corresponding symbols according to the baseband modulation selected by the mapping logic 56. [ Preferably, quadrature amplitude modulation (QAM) or quadrature phase shift keying (QPSK) modulation is used. The degree of modulation may be selected based on the CQI for a particular mobile terminal. The symbols may be reordered systematically to further enhance the immunity of the transmitted signal to periodic data loss caused by frequency selective fading using symbol interleaver logic 58. [

At this point, the bit groups have been mapped to symbols representing positions in amplitude and phase constellation. When spatial diversity is desired, the symbol blocks are processed by the space-time block code (STC) encoder logic 60, which allows the transmitted signals to better tolerate interference, The symbols are modified in such a way that they are easily decoded. The STC encoder logic 60 will process the input symbols to provide "n" outputs corresponding to the number of transmit antennas 28 of the base station 14. The control system 20 and / or the baseband processor 22 as described above with respect to FIG. 5 will provide a mapping control signal to control the STC encoding. At this point, it is assumed that the symbols for the "n" outputs represent the data to be transmitted and can be recovered by the mobile terminal 16.

In this example, it is assumed that the base station 14 has two antennas 28 (n = 2) and the STC encoder logic 60 provides two output symbol streams. Thus, each of the symbol streams output by the STC encoder logic 60 is transmitted to a corresponding IFFT processor 62, which is separately illustrated for ease of understanding. Those skilled in the art will appreciate that more than one processor may be used to provide such digital signal processing, either alone or in combination with the other processes described herein. The IFFT processor 62 will preferably act on each symbol to provide an inverse Fourier transform. The output of the IFFT processor 62 provides symbols in the time domain. The time domain symbols are grouped into frames, which are associated with the prefix by the prefix insertion logic 64. Each of the resulting signals is upconverted from the digital domain to an intermediate frequency and converted to an analog signal via a corresponding digital up-conversion (DUC) and digital-to-analog (D / A) conversion circuit 66. The resulting (analog) signals are then modulated, amplified and transmitted at the desired RF frequency through the RF circuit 68 and antennas 28 at the same time. In particular, the pilot signals known to the intended mobile terminal 16 are distributed among subcarriers. The mobile terminal 16, which will be described in detail below, will use its pilot signals for channel estimation.

Now, referring to FIG. 6, it is described that the mobile terminal 16 receives the transmission signals either directly from the base station 14 or with the aid of the relay station 15. When the transmission signals arrive at each of the antennas 40 of the mobile terminal 16, the respective signals are demodulated and amplified by the corresponding RF circuit 70. For brevity and clarity, only one of the two receive paths is described and illustrated in detail. An analog-to-digital (A / D) converter and down conversion circuit 72 digitizes and downconverts the analog signal for digital processing. The resulting digitized signal can be used by the automatic gain control circuit (AGC) 74 to control the gain of the amplifiers in the RF circuit 70 based on the received signal level.

Initially, a digitized signal is provided to synchronization logic 76, which includes coarse synchronization logic 78, which buffers several OFDM symbols and produces autocorrelation between two consecutive OFDM symbols ). The resulting time index corresponding to the maximum value of the correlation determines a fine synchronization search window that allows the fine synchronization logic 80 to determine an exact framing start position based on the headers . The output of the fine synchronization logic 80 facilitates frame acquisition by the frame alignment logic 84. Proper framing alignment is important for subsequent FFT processing to provide accurate conversion from the time domain to the frequency domain. The fine synchronization algorithm is based on a correlation between the received pilot signals conveyed by the headers and a local copy of known pilot data. Once the frame alignment acquisition has occurred, the prefix of the OFDM symbol is removed by the prefix control logic 86 and the resulting samples are sent to the frequency offset correction logic 88, To compensate for the system frequency offset caused by the mismatched local oscillators in the system. Preferably, the synchronization logic 76 includes a frequency offset and clock estimation logic 82, which frequency offset and clock estimation logic 82 helps to estimate such effects on the transmitted signal based on the headers And provides the estimates to the correction logic 88 to properly process the OFDM symbols.

At this point in time, the OFDM symbols in the time domain are ready to be transformed into the frequency domain using the FFT processing logic 90. The results are frequency domain symbols, which are transmitted to the processing logic 92. [ Processing logic 92 extracts the scattered pilot signal using scattered pilot extraction logic 94 and determines the channel estimate using channel estimation logic 96 based on the extracted pilot signal and provides channel reconstruction logic 98 ) To provide channel responses for all subcarriers. In order to determine the channel response for each of the subcarriers, essentially the pilot signal is a plurality of pilot symbols spread across the data symbols over the OFDM subcarriers in a known pattern in both time and frequency. Continuing with FIG. 6, the processing logic compares the received pilot symbols with the pilot symbols expected at predetermined subcarriers at a given time to determine the channel response for the transmitted subcarriers. The results are interpolated to estimate the channel response for most, if not all of the remaining subcarriers for which pilot symbols are not provided. The actual and interpolated channel responses are used to estimate the overall channel response, including channel responses for most, if not all, of the subcarriers of the OFDM channel.

The frequency domain symbols and channel reconstruction information obtained from the channel responses for each receive path are provided to the STC decoder 100 which performs STC decoding on both receive paths to recover the transmitted symbols to provide. The channel reconstruction information provides equalization information to the STC decoder 100 sufficient to eliminate the effect of the transmission channel when processing each frequency domain symbol.

The recovered symbols are arranged in-place using the symbol deinterleaver logic 102 corresponding to the symbol interleaver logic 58 of the transmitter. The deinterleaved symbols are then demodulated or demapped into a corresponding bitstream using demapping logic 104. [ The bits are then deinterleaved using the bit deinterleaver logic 106 corresponding to the bit interleaver logic 54 of the transmitter architecture. The deinterleaved bits are then processed by rate dematching logic 108 to provide the channel decoder logic 110 to recover the initially scrambled data and the CRC checksum. Accordingly, the CRC logic 112 may perform descrambling to descramble the known base station descrambling code to recover the originally transmitted data 116, by removing the CRC checksum, checking the scrambled data in a conventional manner, Logic 114. &lt; / RTI &gt;

In parallel with restoring the data 116, information sufficient to generate the CQI or at least the CQI at the base station 14 is determined and transmitted to the base station 14. [ As discussed above, the CQI may be a function of the degree of the channel response varying across the various subcarriers of the OFDM frequency band, as well as the carrier to interference ratio (CR). In this embodiment, the channel gains for each subcarrier in the OFDM frequency band used to transmit information to determine the degree to which the channel gain varies over the OFDM frequency band are compared against each other. One technique is to calculate the standard deviation of the channel gain for each subcarrier over the entire OFDM frequency band used to transmit the data, although many techniques are available to measure the degree of change.

In some embodiments, the relay station may operate in a time division fashion using only one radio, or alternatively may comprise a plurality of radios.

Figures 1-6 provide one specific example of a communication system that may be used to implement the embodiments of the present application. It should be appreciated that embodiments of the present application may be implemented using communication systems having architectures that operate in a manner consistent with the implementation of the embodiments described herein, which differ from this particular example.

FIG. 7 illustrates a conceptual grid 700 illustrating allocatable time and frequency resources for one OFDM subframe for the exemplary sector 18 of FIG. The grid 700 may alternatively be referred to as a "resource block ". In some embodiments, conceptual grid 700 may be stored in memory (not explicitly shown) of base station 16 of associated exemplary sector 18 or cell 14 (Fig. 1), such as a table or two- Can be represented as a corresponding data structure. The base station may be responsible for allocating the represented time and frequency resources among any mobile terminals operating within the sector. The OFDM subframe whose time and frequency resource allocation is represented by conceptual grid 700 includes an F subcarrier comprising OFDM frames in uplink data communication with base station 16 originating from various mobile terminals in a cell or sector Frame, where F is an integer greater than one.

As illustrated, conceptual grid 700 has a time dimension and a frequency dimension, which are shown on the horizontal and vertical axes, respectively. Other representations of the grid 700 are possible. It will be appreciated that the grid 700 is conceptual and may in fact not be represented logically or physically in some embodiments (either by the grid itself or otherwise).

Each column in the time dimension of the grid 700 represents one OFDM symbol period. This OFDM symbol period may be a predetermined duration, depending on the operating standard (e.g., IEEE 802.16m), for transmitting OFDM symbols. In the illustrated example, the time dimension of the grid 700 includes six columns labeled a-f. The number of columns 6 reflects the fact that the represented OFDM subframe has a duration of six OFDM symbol periods. In alternate embodiments, the number of OFDM symbol periods in the time dimension may be less than six or greater than six.

The frequency dimension of the exemplary conceptual grid 700 includes sixteen rows labeled 701-716. The number of rows 16 reflects the fact that subcarrier frequencies (or simply "subcarriers") of the operating OFDM frequency band are divided into 16 blocks. Each of the 16 blocks of subcarriers may be assigned to different mobile terminals; In addition, two or more blocks of subcarriers may be assigned to one mobile terminal. In alternate embodiments, the number of blocks in the frequency dimension may be less than 16 or greater than 16.

Each block in the frequency dimension comprises (and spans) a plurality of orthogonal subcarrier frequencies and the number is, for example, 6, 9 or 18. The range of subcarrier frequencies within each block may be such that the change in gain from the highest subcarrier to the lowest subcarrier frequency in the sub-range is minimized. That is, the range of subcarrier frequencies within each block may span frequencies less than the coherence bandwidth of the channel. Each subcarrier frequency may be used to modulate one modulation symbol. Thus, each subcarrier represents one bit during one OFDM time period and may represent more than two bits if properly modulated.

Each intersection between the rows and columns of the grid 700 forms a tile. A tile represents an allocation of blocks of subcarriers represented by rows for use during OFDM symbol periods represented by columns. 7, a tile containing an alphanumeric identifier means that time and frequency resources are assigned to the channel identified by the alphanumeric identifier. An empty tile may mean that the time and frequency resources associated with that tile have not been allocated or that they have been allocated for use not related to the present invention (i.e., not related to periodic ranging).

Based on the above rules, it can be seen that FIG. 7 shows the 21 allocated tiles of the grid 700. Specifically, tiles 701a, 708a, and 715a are collectively assigned as a first channel whose identifier is "A "; Tiles 701b, 708b, and 715b are collectively assigned as a first channel whose identifier is "B "; Tiles 701c, 708c, and 715c are collectively assigned as a first channel whose identifier is "C "; Tiles 701d, 708d, and 715d are collectively assigned as a first channel whose identifier is "D "; Tiles 701e, 708e and 715e are collectively assigned as a first channel whose identifier is "E "; Tiles 701f, 708f, and 715f are collectively assigned as a first channel whose identifier is "F "; Tiles 702a, 709a and 716a are collectively assigned as a first channel whose identifier is "G ". As described, the assignments may be organized centrally by the base station 14 or the base station controller 10. Let M be the number of possible separate channels in the grid. For example, if the entire grid of the 96 tiles in FIG. 7 is used for periodic ranging and assuming N = 3 (i.e., there are three tiles per channel), M would be 96/3 or 32 . Generally, M is configurable.

As described above, a plurality of tiles assigned to a particular one are collectively referred to as a "channel" in the grid 700 (or alternatively, a "location" or "transmission opportunity"). In the illustrated embodiment, the number of tiles defining each channel is three. That is, in FIG. 7, each set of three tiles with a common channel identifier defines one channel for use by a particular mobile terminal 16 to which the channel is assigned. Thus, a total of seven periodic ranging channels are defined in FIG. 7 (i.e., the number of channels presented in the subframe is 7 (A-G)). In general, the number of tiles allocated per channel is N, where N is an integer greater than one. The number of tiles per channel may be different between different mobile terminals, even in the same cell 12 or sector 13 (FIG. 1), and may be dynamically configurable, perhaps as described.

The relationship between channels and mobile terminals is one-to-one or one-to-many. In the latter case, each mobile terminal that uses the same channel may transmit a plurality of orthogonal or mutually orthogonal sequences, as described below, in order to allow its signal to be acknowledged at the base station among a plurality of signals simultaneously transmitted by a plurality of mobile terminals via the same channel. A different one of the low correlation sequences may be used.

For clarity, it should be noted that the identifiers A-G used to identify distinct mobile terminals in FIG. 7 have nothing to do with the identifiers a-f used to identify the columns of the grid 700. [ It should also be noted that the mobile terminals identified using the identifiers A-G are not necessarily explicitly illustrated in FIG. It should also be noted that the assignments illustrated in FIG. 7 are of a particular moment in time. When the mobile terminals 16 are activated or deactivated, or when they enter or leave the sector 18 to which they are associated, the assigned channels may change.

The channels defined in the grid of Figure 7 are periodic ranging channels (or simply "ranging channels"). Such channels are specifically intended to carry transmissions used for ranging. Ranging refers to estimating or determining the degree of timing offset of wireless transmissions from predetermined uplink subframe timing due to transmission delays between the mobile terminal and the base station. The periodic can, for example, cause the data communication between the mobile terminal and the base station to be aligned as needed to account for the movement of the mobile terminal within the relevant cell, sector or zone. For example, if it is determined that the mobile terminal 16 is now far from the base station 14, the mobile terminal 16 is configured to transmit its transmission slightly earlier in time to account for the relatively large MS-BS transmission delay (Forward time shift). In contrast, if it is determined that the mobile terminal 16 is close to the current base station 14, then the mobile terminal 16 is configured to send its transmission at some later time in order to account for the minimum MS-BS transmission delay in that case (Backward time shift). This may allow the transmissions originating from the various mobile terminals within the cell, sector or zone to occur substantially simultaneously with each other when arriving at the base station. Thus, interference between transmissions originating from different mobile terminals in adjacent OFDM symbol periods of a subframe can be minimized.

Generally, each ranging transmission, periodically transmitted from the mobile terminal to the base station via the periodic ranging channel, may comprise a known signal or a known signal in a set of known signals. The message or signal is for estimating or determining the arrival timing of the mobile transmission with respect to the timing of the uplink subframes defined at the base station. For example, the message or signal may cause a timing offset between the received radio transmission originating from the mobile terminal and an OFDM subframe tie slot (e.g., one or more OFDM symbol periods) to be estimated or determined. The message or signal may be, for example, a Walsh sequence, a gold sequence, or an orthogonal or low correlation sequence, such as a Zadoff-chu sequence. When a sequence is assigned by a base station, the base station may assign a unique sequence to each mobile terminal using the same channel (e.g., channel A of FIG. 7). For example, the sequence assigned to the first mobile terminal using channel A may be separate from the sequence assigned to the second mobile terminal using channel A, and may be orthogonal thereto or have a low correlation with the sequence. The base station may reuse sequences between channels. The content of the ranging transmission can be defined in either or both of standard IEEE 802.16e and / or standard IEEE 802.16m, which is hereby incorporated by reference.

For clarity, the ranging transmission is separate from the pilot symbols that may be used in OFDM data communication. The ranging transmission represents a known message or signal, such as a sequence, transmitted over a plurality of subcarriers defining a channel and used for ranging purposes. A pilot symbol is a known symbol transmitted for channel estimation purposes.

The periodic ranging channel can be defined as follows. First, one of the F subframes containing an OFDM frame is initially selected for defining a periodic ranging channel therein. The selection of the subframe is typically done by the mobile terminal 16, but this is not necessarily applied in all embodiments (e.g. it can be done by the base station 14). In some embodiments, the selection of OFDM subframes is unnecessary since the subframe to be used for periodic ranging is predetermined.

A conceptual grid representing the time and frequency resources of a selected or predetermined OFDM subframe may be used to facilitate channel definition. As described above, an exemplary grid 700 is shown in FIG.

Thereafter, time and frequency resources of the associated subframe are selected for the channel. This can be accomplished through the selection of a plurality of N tiles from the conceptual grid 700. The selection is typically made by the base station and then delivered to the mobile terminal 16 in accordance with, for example, the mechanisms defined in the IEEE standard 802.16e and / or 802.16m, no. For the purpose of minimizing contention between periodic ranging channels defined for different mobile terminals within the same cell, sector or zone, the selection of the OFDM subframe and / or the N tiles may optionally be performed in whole or in part Can be extracted randomly. In some embodiments, for example, tiles for which N tiles are selected are limited to a total number of tiles in the grid, if certain grid tiles are reserved for other uses or are already in use.

In some embodiments, N blocks of selected frequency subcarriers and / or selected OFDM symbol blocks may be dynamically selected by mobile terminal 16 based on the average power estimate of the synchronization channel. For clarity, the synchronization channel is the channel used by the mobile terminal for the initial acquisition of the base station's signal and for the initial downlink timing. The mobile station can estimate the received power of the synchronization channel from the base station. If the estimate implies a higher power indicating that the user is close to the base station, a short duration ranging channel is used (e.g., the duration of one OFDM symbol period as in FIG. 7). A longer channel duration may be used if the estimate has lower power, which may imply that the mobile terminal is not in proximity to the base station (e.g., as shown in FIG. 8, for two OFDM symbol periods Duration). Estimates of received power may result from a number of downlink messages transmitted by the base station, such as broadcast messages, signaling channels, and the like.

Each of the N tiles selected during the definition of one periodic ranging channel spans the same time period of the subframe (i.e., is located in the same column of the conceptual grid 700). This reflects the fact that the ranging transmission will be transmitted simultaneously using the subcarriers of each of the selected subcarrier blocks. The selected time period (i.e., the column (s) selected in this example) may be referred to herein as the "time slot" of the channel. For the sake of clarity, assuming that each tile of the grid 700 has a fixed width of one OFDM symbol period, it is assumed that the channel spanning multiple OFDM symbol periods has a number of tiles that is a multiple of N (For example, if the number of OFDM symbol periods spanned is 2, the number of tiles may be considered to be 2N). Alternatively, if it is assumed that a plurality of contiguous OFDM symbol periods of one subcarrier frequency block form one "wide" tile, then the number of tiles containing a multi-column-wide channel is assumed to be N . Regardless of these semantics, the selected tiles will be discontinuous at the frequency dimension of the conceptual grid 700. In other words, no two selected tiles will be adjacent to one another in the associated column (s) of the grid 700. This is to introduce frequency diversity for each ranging transmission to prevent frequency-selective fading.

For example, three tiles 701a, 708a, and 715a in FIG. 7 that are selected for channel "A" are all in the same column (column a) of grid 700, Lt; RTI ID = 0.0 &gt; OFDM &lt; / RTI &gt; Also, they are discontinuous in column a.

As a further aspect of the channel definition in at least some embodiments, a sequence for use as a ranging transmission over the channel is assigned (e.g., by a base station) or otherwise selected. As described above, the sequence for a given channel will be unique to the mobile terminal. That is, as long as a particular channel (e.g., channel "A" in Figure 7) is used for ranging transmissions by two or more mobile terminals, each mobile terminal using that channel may use a different sequence One of the orthogonal or low correlation sequences of &lt; RTI ID = 0.0 &gt; However, the sequence used for one channel may be used for another channel including a distinct set of N tiles. In this embodiment, the sequence has a length L greater than one. In some embodiments, the ranging transmission may be a predetermined message or signal rather than a sequence (e.g., if each channel is used by only one mobile terminal).

In some embodiments, the base station may determine, via communication on the downlink connection from the base station, which N tiles will define the channel and / or for the sequence to be used in that channel and / It is possible to notify the mobile terminal of the sequence to be used. The mechanism for this communication may be defined in standard IEEE 802.16e and / or 802.16m.

When the mobile terminal knows the tiles defining the channel and the sequence to be used on the channel, the mobile terminal can periodically transmit the ranging transmission to the base station through the channel, for example, as described above. In this embodiment, the transmission of the ranging transmission includes spreading the allocated or selected sequence of length L over the subcarrier frequencies of N blocks within the selected timeslot of the OFDM subframe, . In general, the transmission includes transmitting a message or components of a signal (e.g., portions of a sequence or bits) over each subcarrier frequency of N blocks within a selected timeslot. If the channel duration spans more than one OFDM symbol period, the OFDM symbol may be transmitted only during a portion of the channel duration, with the aim of reducing the probability of interference with data transmitted on the same subcarrier frequencies in adjacent timeslots . Each ranging transmission at base station 14 may then be used to estimate or determine the current timing offset of transmissions originating at the mobile terminal with respect to the timing of the OFDM subframe.

In some embodiments, the number of OFDM symbol periods used by each ranging transmission (e.g., the number of columns spanned by the channel) may be determined, for example, by a base station or mobile terminal, Based on the estimated or determined maximum ranging delay between the base stations. For example, as the estimated or determined maximum ranging delay increases, the number of OFDM symbol periods including the periodic ranging channel may be increased. The duration of the ranging transmission will generally be less than the duration of the OFDM subframe. However, in some cases, for example, if the range between the mobile station and the base station is large, the duration of the ranging transmission may coincide with the duration of the OFDM subframe.

In some embodiments, a subset of tiles in the conceptual grid for a subframe in which a periodic ranging channel is defined for use in defining periodic ranging channels may be reserved. The N tiles selected for the periodic ranging channel may be selected only from a subset of the tiles. For example, in FIG. 7, a subset of reserved tiles may be all tiles in rows 701, 702, 708, 709, 715, and 716 of grid 700. The subset of these reserved tiles is called the "periodic ranging region ". The base station can inform each mobile terminal in the relevant sector or cell about the range of the periodic ranging area through the downlink communication. The region may be represented either through the identifiers of the included tiles, or through the identifiers of the contained subcarrier frequency blocks and / or OFDM symbol periods.

In some embodiments, the periodic ranging region defined for a particular sector may be aligned to the periodic ranging region of the neighboring sector, both in time and frequency. For example, if the conceptual grids for a particular OFDM subframe are the same for two sectors in close proximity to each other, then the subset of reserved tiles in the conceptual grids may be made intentionally the same. In other embodiments, the periodic ranging region defined for a particular set may not be aligned to the periodic ranging region of other sectors in time or frequency.

Once a periodic ranging region is defined, the size of the periodic ranging region, i. E. The range of subsets of reserved tiles in the grid, may be sector specific or cell specific. If the size of the periodic ranging regions is different for different sectors, at least one sector of the region reserved for possible use by the mobile terminals of the cell edge users is sorted in frequency and time, such as between neighboring sectors or cells. . As is known in the art, cell edge users are users whose mobile terminals are away from their base stations and are approaching the boundaries of other cells. A mobile terminal of a cell edge user generally transmits at high power to be received at the base station. This may interfere with the reception of desired signals at other base stations. For example, for cell edge users, the alignment of periodic ranging regions allows the transmission of these high power signals simultaneously in different cells. This means that data or other sensitive signals that may be using time and frequency resources other than those used for ranging may be protected from the high power ranging transmissions of the cellular users.

FIG. 8 illustrates the definition of three periodic ranging channels for the exemplary cell or sector of FIG. 1, which are different from any of the seven periodic ranging channels defined in FIG. The rules used in Fig. 8 are the same as those used in Fig. As conceptual grid 700, conceptual grid 800 includes sixteen rows 801-816 and six columns (a-f). The sixteen rows indicate that the active OFDM frequency band is equally divided into sixteen blocks as shown in FIG. 7, and six columns (a-f) indicate that the duration of the represented OFDM subframe is six OFDM symbol periods.

As shown in Fig. 8, three periodic ranging channels are defined. The first channel labeled "A " is defined as tiles 801a-801b, 808a-808b, and 815a-815b. A second channel labeled "B " is defined as tiles 801c-801d, 808c-808d, and 815c-815d. A third channel labeled "C" is defined as tiles 801e-801f, 808e-808f, and 815e-815f. For clarity, the identifiers "A ", " B ", and" C "in FIG. 8 do not represent the same channels represented by the identifiers" A ", "B" The three periodic ranging channels defined in FIG. 8 differ from those of FIG. 7 in that each channel typically spans two OFDM periods rather than one OFDM period. Ranging transmissions (e. G., Sequences) transmitted over these channels are not necessarily transmitted during the entire duration of the ranging channel. For example, each may be configured to occupy the "center" of a timeslot defined by two columns defining a channel (i. E., A leading buffer interval preceding the entity of a ranging transmission in a timeslot, (E.g., having a trailing buffer interval subsequent to the entity of the ranging transmission within the intervals, and not transmitting any data by the mobile terminal over the relevant subcarriers during the intervals) And may be transmitted during the duration of the period. The duration of the buffer intervals (i. E. The sum of their persistent intervals) may be substantially equal to the duration of the message, signal or sequence comprising the entity of the ranging transmission. By transmitting the sequence with the leading and trailing buffers, it is possible to prevent or limit interference with any data that can be transmitted in the preceding or subsequent timeslots of the subframe. Considering that the time / frequency resources of the channels do not overlap, the same sequence may be used for ranging transmission of each channel.

In general, it should be noted that various methods and techniques relating to the definition and use of periodic ranging channels, as described above, may be used for the definition and use of the initial access channels. The initial access channels are used to transmit initial access transmissions that are initial communications from the mobile terminal to the base station when the mobile terminal enters an associated cell or sector or wakes up from an idle period. The initial access typically consists of a known message from the mobile station to the base station for the purpose of estimating the arrival timing of the mobile transmission with respect to the defined uplink subframe timing at the base station, or transmission of one known signal in a set of known signals. As with the ranging transmissions, the message or signal may be, for example, a sequence such as a Walsh sequence, a Gold sequence, or a Zadoff-Chu sequence. The sequence assigned to the first mobile terminal using the specific channel may be independent of the sequence assigned to the second mobile terminal using the same channel and may be orthogonal thereto or have a low correlation with the sequence. In the initial access, the timing offset of the mobile transmission with respect to the subframe may be significantly greater than in the case of periodic ranging. For initial access, the channel to be used can generally be randomly selected from among a predetermined set of time / frequency resources available or reserved for this purpose.

Annex A describes aspects of the above-described embodiments.

The various methods and techniques described above may be accomplished with hardware, firmware, software, or combinations thereof. In the case of firmware and / or software, processor executable instructions may be loaded into a memory of a computing device, such as a mobile terminal, base station or base station controller, from a computer readable or machine readable medium, such as a magnetic or optical disk And may be executed by one or more processors in the apparatus to achieve a related method or technique.

The foregoing embodiments of the present invention are intended to be illustrative only. Modifications, modifications and variations to the specific embodiments may be accomplished by those skilled in the art without departing from the scope of the present invention.

<Appendix A>

Claims (20)

A method of performing periodic ranging between a mobile station and a base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station,
Wherein the periodic ranging channel includes a plurality of (N) blocks of subcarrier frequencies of an OFDM frequency band, and the N blocks of the subcarrier frequencies are The channel is non-contiguous in the OFDM frequency band, and the channel uses N blocks of the subcarrier frequencies in a specific OFDM subframe to transmit a time slot to which ranging transmissions are to be transmitted from the mobile terminal to the base station Wherein the time slot spans at least one OFDM symbol period but is less than a duration of the OFDM subframe; And
Periodically transmitting a ranging transmission over the periodic ranging channel from the mobile terminal to the base station, the transmitting comprising transmitting the ranging transmission in the timeslot as a spread signal, Wherein the spreading signal is spread over subcarrier frequencies of the N blocks and the duration of the ranging transmission is less than the duration of the OFDM subframe,
Lt; / RTI &gt;
Wherein the number of OFDM symbol periods comprising the timeslot is configurable based on an estimated or determined maximum ranging delay between the mobile terminal and the base station. 2. The method of claim 1, wherein the number of OFDM symbol periods comprising the timeslot is configurable based on a size of cells served by the base station. 2. The method of claim 1, wherein the number of OFDM symbol periods comprising the timeslot increases as the estimated or determined maximum ranging delay increases. 2. The method of claim 1, wherein the ranging transmission comprises a message or a signal, and wherein the transmitting comprises configuring the message or signal on each subcarrier frequency of the N blocks in the timeslot of the OFDM subframe And transmitting the elements. 5. The method of claim 4, wherein the timeslot spans a plurality of contiguous OFDM symbol periods of the subframe, the ranging transmission comprising a leading buffer interval in the timeslot and a trailing buffer &lt; RTI ID = 0.0 &gt; Wherein the mobile terminal refrains from transmitting the message or the components of the signal during the leading buffer interval and the trailing buffer interval. 2. The method of claim 1, wherein the mobile terminal is a first mobile terminal, the ranging transmission is a first ranging transmission, and the periodic ranging channel is also used for a second mobile terminal to transmit a second ranging transmission Wherein each of the first and second ranging transmissions comprises sequences that are orthogonal to each other. 2. The method of claim 1, wherein the periodic ranging channel is associated with a sector of a cell of the base station, N blocks of the subcarrier frequencies and the time slot are collectively referred to as a periodic ranging region for the sector. A predetermined subset of OFDM symbol periods of a subframe and a predetermined subset of subcarrier frequency blocks of the OFDM frequency range, and wherein the periodic ranging region for the sector is selected from a period of a near sector The method comprising the steps of: 2. The method of claim 1, wherein the periodic ranging channel is associated with a sector of a cell of the base station, N blocks of the subcarrier frequencies and the time slot are collectively referred to as a periodic ranging region for the sector. A predetermined subset of OFDM symbol periods of a subframe and a predetermined subset of subcarrier frequency blocks and wherein a predetermined subset of the subcarrier frequency blocks and a predetermined subset of the OFDM symbol periods Each of a subset of subcarrier frequency blocks and a subset of OFDM symbol periods in a periodic ranging region of a neighboring sector. 9. The method of claim 8 wherein the section of the periodic ranging region for the sector is intended to define periodic ranging channels for cell edge users, Are arranged to be aligned with sections of the periodic ranging region of the neighboring sector intended to define periodic ranging channels for the neighboring sectors. 3. The method of claim 1, wherein the time slot defining the periodic ranging channel and / or the N blocks of subcarrier frequencies are used for initial acquisition of the base station signal and for synchronization channels used for initial download timing Wherein the average power estimate of the mobile terminal is dynamically selected by the mobile terminal. A method for performing periodic ranging between a mobile terminal and a base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station,
Defining a periodic ranging channel for the mobile terminal, the periodic ranging channel being represented as a plurality (N) of tiles in a notional grid of tiles representing OFDM time and frequency resources, The conceptual grid has a time dimension including a plurality of OFDM symbol periods of an OFDM subframe and a frequency dimension including a plurality of blocks of subcarriers of an OFDM frequency band, and each of the N tiles includes at least one of the OFDM symbol periods Wherein the N tiles are discontinuous in the frequency dimension of the conceptual grid, and each of the N tiles represents an allocation of one of the blocks of subcarriers used by the mobile terminal during an OFDM symbol period, Span the same time slot in the time dimension, An OFDM symbol period of the OFDM subframe but less than a duration of the OFDM subframe; And
Periodically transmitting a ranging transmission from the mobile terminal to the base station over the periodic ranging channel, the transmitting comprising transmitting the ranging transmission in the timeslot as a spread signal, Wherein the spread signal is spread over subcarrier frequencies of the N tiles and the duration of the ranging transmission is less than the duration of the OFDM subframe,
Lt; / RTI &gt;
Wherein the number of OFDM symbol periods comprising the timeslot is configurable based on an estimated or determined maximum ranging delay between the mobile terminal and the base station. 12. The method of claim 11, wherein the number of OFDM symbol periods comprising the timeslot is configurable based on a size of a cell served by the base station. 12. The method of claim 11, wherein the number of OFDM symbols comprising the ranging transmission increases as the estimated or determined maximum ranging delay increases. 12. The method of claim 11 wherein the periodic ranging channel is associated with a sector of a cell of the base station and the N tiles are selected from a predetermined subset of tiles of the grid called periodic ranging region for the sector Wherein the periodic ranging region for the sector is aligned with a periodic ranging region of a neighboring sector in a time dimension and a frequency dimension. 12. The method of claim 11 wherein the periodic ranging channel is associated with a sector of a cell of the base station and the N tiles are selected from a predetermined subset of tiles of the grid called periodic ranging region for the sector Wherein the periodic ranging region for the sector is different in size from the periodic ranging region for a neighboring sector. 16. The method of claim 15, wherein the section of the periodic ranging region for the sector is for defining periodic ranging channels for cell edge users, the section comprising: Wherein the section of the periodic ranging region is aligned with a section of the periodic ranging region. 12. The method of claim 11 wherein the N tiles defining the periodic ranging channel are dynamic by the mobile terminal based on an average power estimate of the synchronization channel used for initial acquisition of the base station signal and for initial download timing, &Lt; / RTI &gt; 12. The method of claim 11, wherein the conceptual grid comprises six OFDM symbol periods in the time dimension, the plurality (N) tiles are three tiles, and each of the three tiles comprises two adjacent OFDM symbol periods How to Spread. 19. The method of claim 18, wherein the periodic ranging channel is a first periodic ranging channel, the ranging transmission is a first ranging transmission,
The method comprises:
Defining a second periodic ranging channel and a third periodic ranging channel, each of said second and third periodic ranging channels being represented as a distinct set of three tiles of said conceptual grid, Wherein each set of three tiles is discontinuous in the frequency dimension of the grid and spans two adjacent OFDM symbol periods in a time dimension of the grid and wherein each set of three tiles comprises a first periodic lane Comprising the same subcarriers as the corresponding three tiles of the ranging channel; And
Periodically transmitting second and third ranging transmissions, respectively, from the mobile terminal to the base station via the second and third periodic ranging channels, the transmitting comprising transmitting the ranging transmission as a spread signal, Wherein the spreading signal is spread over subcarrier frequencies of the N tiles as the two OFDM symbols during two OFDM symbol periods and the duration of the ranging transmission is sustained in the duration of the OFDM subframe Less than duration -
&Lt; / RTI &gt; A method for performing an initial access from a mobile terminal to the base station in a wireless communication network using orthogonal frequency division multiplexing (OFDM) for uplink data communication between mobile terminals and a base station,
Wherein the initial access channel comprises a plurality (N) of subcarrier frequencies of an OFDM frequency band and N blocks of subcarrier frequencies are allocated to the OFDM frequency band Wherein the initial access channel further comprises a timeslot within which the initial access transmissions are to be transmitted from the mobile terminal to the base station using N blocks of the subcarrier frequencies in a particular OFDM subframe, Is over one or more OFDM symbol periods but less than the duration of the OFDM subframe; And
Transmitting an initial access transmission on the initial access channel from the mobile terminal to the base station, the transmitting comprising transmitting the initial access transmission in the timeslot as a spread signal, Wherein the duration of the initial access transmission is less than the duration of the OFDM subframe,
Lt; / RTI &gt;
Wherein the number of OFDM symbol periods comprising the timeslot is configurable based on an estimated or determined maximum ranging delay between the mobile terminal and the base station.

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