# Patent

## Title
Method of transmitting scheduling request in a wireless communication system

## Abstract

A method of transmitting a scheduling request which is used to request a radio resource for uplink transmission includes configuring an uplink control channel for transmission of a scheduling request in a subframe, the subframe comprising two consecutive slots, a slot comprising a plurality of single carrier-frequency division multiple access (SC-FDMA) symbols, the scheduling request being carried by presence or absence of transmission of the uplink control channel, and transmitting the scheduling request on the uplink control channel.

## Background
The present application claims priority to Korean Application No. 10-2007-0069991, filed on Jul. 12, 2007, Korean Application No. 10-2007-0103661, filed Oct. 15, 2007, and to International Application No. PCT/KR2008/004087, filed Jul. 11, 2008, wherein the contents of these applications are fully incorporated by reference as if fully set forth herein.
TECHNICAL FIELD
The present invention relates to wireless communications, and more particularly, to a method of transmitting a scheduling request on an uplink control channel in a wireless communication system.
BACKGROUND ART
Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future.
An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference with a low complexity is taken into consideration as one of next generation (after 3G) systems. In the OFDM system, serial input data symbols are converted into N parallel data symbols and are carried and transmitted on separate N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users in a system using the OFDM as a modulation scheme.
One of primary problems of the OFDM/OFDMA system is that a peak-to-average power ratio (PAPR) can be significantly large. The PAPR problem is that a peak amplitude of a transmit (Tx) signal is significantly larger than an average amplitude. This is caused by the fact that OFDM symbols are N sinusoidal signals overlapping on different subcarriers. In particular, since the PAPR is related to battery capacity, the PAPR is problematic when a user equipment (UE) is sensitive to power consumption. The PAPR needs to be reduced to decrease power consumption.
A single carrier-frequency division multiple access (SC-FDMA) system is one of systems proposed to reduce the PAPR. An SC-FDMA is a combination of a single carrier-frequency division equalization (SC-FDE) and a frequency division multiple access (FDMA). The SC-FDMA has a similar characteristic with an OFDMA in that data is modulated and demodulated in a time domain and a frequency domain by using a discrete Fourier transform (DFT). However, the SC-FDMA is advantageous over the OFDMA in terms of Tx power saving due to a low PAPR of a Tx signal. In particular, regarding the use of batteries, the SC-FDMA is advantageous in uplink communication in which communication is made to a base station (BS) from a UE sensitive to Tx power.
A wide coverage is important when the UE transmits data to the BS. Although a bandwidth of Tx data is small, power can be concentrated in the wide coverage. The SC-FDMA system provides a signal with little variation, and thus has a wider coverage than other systems when the same power amplifier is used.
In order to implement various transmission or reception methods to achieve high-speed packet transmission, transmission of a control signal on time, spatial, and frequency domains is an essential and indispensable factor. A channel for transmitting the control signal is referred to as a control channel. An uplink control signal may be various such as an acknowledgement (ACK)/negative-acknowledgement (NACK) signal which is a response for downlink data transmission, a channel quality indicator (CQI) indicating downlink channel quality, a precoding matrix index (PMI), a rank indicator (RI), etc.
One example of the control signal is a scheduling request. The scheduling request is used when a UE requests a BS to allocate an uplink radio resource. The scheduling request is a sort of preliminary information exchange for exchanging uplink data. The UE first transmits the scheduling request and is allocated with an uplink radio resource. Thereafter, the UE transmits uplink data to the BS. When in an idle mode, the UE can transmit an uplink radio resource allocation request through a conventional random access process. However, when in a connected mode, a service may be delayed if the UE transmits the uplink radio resource allocation request through the conventional random access process. This is because the random access is a contention based process, and thus allocation of the uplink radio resource can be delayed. Therefore, when in the connected mode, the scheduling request may be transmitted through a control channel in order to provide effective resource allocation in a more reliable and rapid manner.
Compatibility with another control channel for transmitting another control signal has to be taken into consideration when the scheduling request needs to be transmitted on an uplink control channel. In addition, capacity of the control channel for transmitting the scheduling request has to be also taken into consideration.
Accordingly, there is a need for a control channel having an effective structure for transmitting a scheduling request.
DISCLOSURE OF INVENTION
Technical Problem
A method is sought for requesting a radio resource for uplink transmission on an uplink control channel in a wireless communication system.
A method is also sought for transmitting a scheduling request which is used to request a radio resource for uplink transmission in a wireless communication system.
Technical Solution
In an aspect, a method of transmitting a scheduling request which is used to request a radio resource for uplink transmission in a wireless communication system is provided. The method includes configuring an uplink control channel for transmission of a scheduling request in a subframe, the subframe comprising two consecutive slots, a slot comprising a plurality of single carrier-frequency division multiple access (SC-FDMA) symbols, the scheduling request being carried by presence or absence of transmission of the uplink control channel, and transmitting the scheduling request on the uplink control channel, wherein configuring the uplink control channel comprises dividing the plurality of SC-FDMA symbols in the slot into a first set of SC-FDMA symbols and a second set of SC-FDMA symbols, mapping each of first frequency domain sequences to each SC-FDMA symbol in the first set, the first frequency domain sequences being generated by cyclic shifts of a base sequence, mapping each of second frequency domain sequences to each SC-FDMA symbol in the second set, the second frequency domain sequence being generated by cyclic shifts of the base sequence, spreading the first frequency domain sequences in the first set with a first orthogonal sequence, the first orthogonal sequence having a length equal to the number of SC-FDMA symbols in the first set, and spreading the second frequency domain sequences in the second set with a second orthogonal sequence, the second orthogonal sequence having a length equal to the number of SC-FDMA symbols in the second set.
The two consecutive slots in the subframe may use different subcarriers. The length of the first frequency domain sequence and the length of the second frequency domain sequence may equal to the number of subcarriers in one SC-FDMA symbol.
In another aspect, a method of transmitting a scheduling request which is used to request a radio resource for uplink transmission in a wireless communication system is provided. The method includes configuring an uplink control channel for transmission of a scheduling request in a plurality of SC-FDMA symbols, the scheduling request being carried by presence or absence of transmission of the uplink control channel, and transmitting the scheduling request on the uplink control channel, wherein configuring the uplink control channel comprises dividing the plurality of SC-FDMA symbols into a first set of SC-FDMA symbols and a second set of SC-FDMA symbols, mapping each of first frequency domain sequences to each SC-FDMA symbol in the first set, the first frequency domain sequence being generated by cyclic shifts of a base sequence, mapping each of second frequency domain sequences to each SC-FDMA symbol in the second set, the second frequency domain sequence being generated by cyclic shifts of the base sequence, spreading the first frequency domain sequences in the first set with a first orthogonal sequence, the first orthogonal sequence having a length equal to the number of SC-FDMA symbols in the first set, and spreading the second frequency domain sequences in the second set with a second orthogonal sequence, the second orthogonal sequence having a length equal to the number of SC-FDMA symbols in the second set.
Advantageous Effects
A scheduling request can be transmitted without interference with a control channel transmitting another control signal, and thus the control channel can be effectively used.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a wireless communication system.
FIG. 2 is a block diagram of a transmitter according to an embodiment of the present invention.
FIG. 3 shows an exemplary structure of a radio frame.
FIG. 4 shows an exemplary structure of a subframe.
FIG. 5 shows an exemplary structure of a control channel in case of using two-dimensional spreading.
FIG. 6 shows another exemplary structure of a control channel in case of using two-dimensional spreading.
FIG. 7 shows a structure of an acknowledgement (ACK)/negative-acknowledgement (NACK) channel.
FIG. 8 shows an exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 9 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 10 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 11 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 12 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 13 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 14 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted.
FIG. 15 shows a structure of a channel quality indicator (CQI) channel.
FIG. 16 shows an example of a scheduling request channel.
FIG. 17 shows an example of a scheduling request channel.
FIG. 18 shows an example of resource allocation for a scheduling request channel.
FIG. 19 shows another example of resource allocation for a scheduling request channel.
FIG. 20 shows another example of resource allocation for a scheduling request channel.



MODE FOR THE INVENTION
FIG. 1 shows a wireless communication system. The wireless communication system can be widely deployed to provide a variety of communication services, such as voices, packet data, etc.
Referring to FIG. 1, the wireless communication system includes at least one user equipment (UE) 10 and a base station (BS) 20. The UE 10 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc. The BS 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another terminology, such as a node-B, a base transceiver system (BTS), an access point, etc. There are one or more cells within the coverage of the BS 20.
Hereinafter, downlink is defined as communication from the BS 20 to the UE 10, and uplink is defined as communication from the UE 10 to the BS 20. In the downlink, a transmitter may be a part of the BS 20, and a receiver may be a part of the UE 10. In the uplink, the transmitter may be a part of the UE 10, and the receiver may be a part of the BS 20.
FIG. 2 is a block diagram of a transmitter according to an embodiment of the present invention.
Referring to FIG. 2, a transmitter 100 includes a discrete Fourier transform (DFT) unit 110 that performs DFT and an Inverse fast Fourier transform (IFFT) unit 120 that performs IFFT. The DFT unit 110 performs DFT on data and outputs a frequency-domain symbol. The data input to the DFT unit 110 may be a control signal and/or user data. The IFFT unit 120 performs IFFT on the received frequency-domain symbol and outputs a transmit (Tx) signal. The Tx signal is a time-domain signal. A time-domain symbol output from the IFFT unit 120 is referred to as an orthogonal frequency division multiplexing (OFDM) symbol or a single carrier-frequency division multiple access (SC-FDMA) symbol. SC-FDMA is a scheme in which spreading is achieved by performing DFT in a previous stage of the IFFT unit 120. The SC-FDMA scheme is advantageous over an OFDM scheme in terms of decreasing a peak-to-average power ratio (PAPR).
FIG. 3 shows an exemplary structure of a radio frame.
Referring to FIG. 3, the radio frame includes 10 subframes. One subframe includes two consecutive slots. One slot can include a plurality of OFDM symbols in a time domain and at least one subcarrier in a frequency domain. The slot is a unit of radio resource allocation in the time domain. For example, one slot can include 7 or 6 OFDM symbols.
The radio frame structure is shown for exemplary purposes only, and thus the number of subframes included in the radio frame or the number of slots included in the subframe or the number of SC-FDMA symbols included in the slot may change variously.
FIG. 4 shows an exemplary structure of a subframe. The subframe may be an uplink subframe.
Referring to FIG. 4, the subframe can be divided into two parts, i.e., a control region and a data region. Since the control region and the data region use different frequency bands, frequency division multiplexing (FDM) has been achieved. The control region is a region allocated with a control channel. The data region is a region allocated with a data channel. The control channel may use one resource block in each of two slots in a subframe. A resource block includes a plurality of subcarriers. The control channel is a channel for transmitting a control signal. The data channel is a channel for transmitting the control signal and/or user data. The control channel is referred to as a physical uplink control channel (PUCCH). The data channel is referred to as a physical uplink shared channel (PUSCH). The control signal may have various types, such as, an acknowledgement (ACK)/negative-acknowledgement (NACK) signal, a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI), a scheduling request, etc.
The control channel transmits only the control signal. The data channel can transmit the user data together with the control signal. According to a single subcarrier property, one UE cannot transmit the control channel and the data channel simultaneously.
The control channel can be frequency-hopped in a slot unit on a subframe. The control channel uses different subcarriers for each slot on the subframe. A frequency diversity gain can be obtained by transmitting the control channel through slots allocated to different frequency bands. It will be assumed that one subframe consists of a 1st slot and a 2nd slot. In addition, the 1st slot is divided into a 1st region and a 2nd region in a frequency domain, and the 2nd slot is divided into a 1st region and a 2nd region in the frequency region. Then, the control signal is transmitted through the 1st region of the 1st slot and the 2nd region of the 2nd slot within one subframe.
Now, a structure of an uplink control channel will be described.
Frequency spreading and two-dimensional spreading of time-domain covering can be applied to the uplink control channel. A reference signal can be defined for coherent detection.
For clear explanation, it will be assumed hereinafter that one slot consists of 7 OFDM symbols, and thus one subframe including two slots consists of 14 SC-FDMA symbols in total. The number of SC-FDMA symbols included in one subframe or the number of SC-FDMA symbols included in one slot is shown for exemplary purposes only, and thus the technical scope of the present invention is not limited thereto.
FIG. 5 shows an exemplary structure of a control channel in case of using two-dimensional spreading.
Referring to FIG. 5, {s0, s1, . . . , s13} denotes a control signal sequence for SC-FDMA symbols, and {x0, x1, . . . , x13} denotes a time-domain sequence for SC-FDMA symbols. The time-domain sequence for time-domain spreading may use a well-known orthogonal sequence such as a Walsh code. {c0, c1, . . . , c11} denotes a frequency-domain sequence for frequency-domain spreading. The time-domain sequence is a sequence whose elements correspond to SC-FDMA symbols. The frequency-domain sequence is a sequence whose elements correspond to subcarriers.
A Zadoff-Chu (ZC) sequence is one example of a constant amplitude zero auto-correlation (CAZAC) sequence and is used as the frequency-domain sequence. A ZC sequence c(k) with a length of N can be generated as shown below:




  
    
      
        
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where 0≦k≦N−1, and M is a root index and is a natural number equal to or less than N, where N is a relatively prime number to M. This means that, once N is determined, the number of root indices is equal to the number of available ZC sequences. ZC sequences having different cyclic shift values are orthogonal to each other. Therefore, from a ZC sequence generated using one root index, a plurality of orthogonal sequences can be obtained through cyclic shift.
The ZC sequence is for exemplary purposes only. Thus, other sequences having an excellent correlation characteristic can also be used as the frequency-domain sequence.
The frequency-domain sequence can be undergone cyclic shift hopping for each SC-FDMA symbol. That is, although each SC-FDMA is spread through the same frequency-domain sequence in FIG. 5, each SC-FDMA can also be spread through a frequency-domain sequence having a different cyclic shift value. This is called cyclic shift hopping. When the cyclic shift hopping is carried out, a control channel characteristic can be prevented from rapid deterioration caused by a high correlation at a specific cyclic shift value.
FIG. 6 shows another exemplary structure of a control channel in case of using two-dimensional spreading.
Referring to FIG. 6, unlike the example of FIG. 5, a control signal sequence {s0, s1, . . . , s13} is spread over a frequency domain.
Now, a method of generating a scheduling request channel for transmitting a scheduling request will be described.
The scheduling request is used when a UE requests a BS to allocate an uplink radio resource. The scheduling request is a sort of preliminary information exchange for exchanging uplink data. In order for the UE to transmit uplink data to the BS, the uplink radio resource has to be first requested through the scheduling request. When the UE transmits the scheduling request on an uplink control channel, the BS transmits the allocated uplink radio resource to the UE on a downlink control channel. The uplink control channel for transmitting the scheduling request is referred to as a scheduling request channel.
Examples of a method of generating the scheduling request channel include a method in which a channel (i.e., an ACK/NACK channel or a CQI channel) for transmitting different control signals are reserved for the scheduling request and a method in which a dedicated channel is assigned for the scheduling request. In the former method, the channel is generated simultaneously with a different control channel, and compatibility with a different control signal needs to be maintained. Although the time-frequency resource is shared with the different control signal, the scheduling request can be identified by using a different sequence. In the latter method, a new time-frequency resource is allocated to transmit the scheduling request.
First, a method of transmitting a scheduling request signal by using an ACK/NACK channel and a CQI channel will be described. However, technical features of the present invention are not limited to the ACK/NACK channel or the CQI channel. Thus, the preset invention can be widely used in a control channel having a structure in which a second control signal (e.g., the scheduling request) can be transmitted on the control channel for transmitting a first control signal (e.g., the ACK/NACK signal, the CQI, etc.).
FIG. 7 shows a structure of an ACK/NACK channel. The ACK/NACK channel is a control channel on which an ACK/NACK signal is transmitted. The ACK/NACK signal is a reception confirm signal for downlink data for hybrid automatic repeat request (HARQ). When the control signal is transmitted within a pre-assigned band, frequency-domain spreading and time-domain spreading are simultaneously performed to increase the number of multiplexible UEs and the number of control channels.
Referring to FIG. 7, among 7 SC-FDMA symbols included in one slot, a reference signal (or simply RS) is carried on 3 consecutive SC-FDMA symbols in the middle portion of the slot and the ACK/NACK signal is carried on the remaining 4 SC-FDMA symbols. The RS is carried on the 3 consecutive SC-FDMA symbols located in the middle portion of the slot. The position and the number of symbols used in the RS may vary, and as a result, the position and the number symbols used in the ACK/NACK signal may also change.
A frequency-domain sequence is used to spread the ACK/NACK signal on a frequency domain. The aforementioned ZC sequence may be used as the frequency-domain sequence. ACK/NACK channels can be identified by using ZC sequences each having a different cyclic shift value. The number of available cyclic shifts may vary depending on channel delay spreading.
The ACK/NACK signal is spread in a frequency domain and is then subjected to IFFT processing. Thereafter, the ACK/NACK signal is spread again in a time domain by using a time-domain sequence (or an orthogonal sequence). The ACK/NACK signal is spread using 4 time-domain spreading codes w0, w1, w2, and w3 for 4 OFDM symbols. The reference signal is also spread using an orthogonal sequence with a length of 3.
Although it has been described that the frequency-domain spreading is performed before the time-domain spreading is performed, this is for exemplary purposes only. Thus, the present invention is not limited to the order of performing the frequency-domain spreading and the time-domain spreading. The time-domain spreading may be performed before the frequency-domain spreading is performed. The time-domain spreading and the frequency-domain spreading may be simultaneously performed by using a sequence having one combined format.
FIG. 8 shows an exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This is a case where at least one cyclic shift is reserved with the scheduling request in the ACK/NACK channel structure.
Referring to FIG. 8, in the ACK/NACK channel, ZC sequences maintain orthogonality with each other by using cyclic shifts, and one of the cyclic shifts is reserved by transmitting the scheduling request.
For example, if a total of 6 cyclic shifts can be used, one cyclic shift is used in transmission of the scheduling request. The number of possible cyclic shifts may vary, and two or more cyclic shifts may be reserved to transmit the scheduling request.
If a specific cyclic shift is used to transmit the scheduling request in the ACK/NACK channel, the ACK/NACK signal is transmitted using a cyclic shift unused in the transmission of the scheduling request.
If a reserved cyclic shift is used for the scheduling request, time-domain covering can be used for each SC-FDMA symbol in a time domain. In this case, for coherent detection, the number of times of performing time-domain spreading depends on min(the number of SC-FDMA symbols of an ACK/NACK signal, the number of SC-FDMA symbols of a reference signal). In the coherent detection, a constellation of a Tx signal (i.e., the ACK/NACK signal) is identified according to a defined reference signal. Since the number of SC-FDMA symbols of the ACK/NACK signal is 4 and the number of SC-FDMA symbols of the reference signal is 3, the time-domain spreading can be performed up to 3 times for the coherent direction. Therefore, if one cyclic shift is used as a scheduling request signal for the ACK/NACK channel in the coherent detection, a maximum of 3 scheduling request channels can be transmitted for each slot.
Although it has been described that the number of root indices of ZC sequences usable in one cell is one, more UEs can transmit the scheduling request when the number of root indices increases.
Cyclic-shift hopping may be used in a cyclic shift for the scheduling request channel. If the cyclic-shift hopping is used for each SC-FDMA symbol, a hopping pattern can be reserved in advance to be used.
The scheduling request channel is defined herein by using a cyclic shift when a ZC sequence is used as a frequency-domain spreading code in the ACK/NACK channel. However, if another sequence is used as the frequency-domain sequence, the scheduling request channel may be defined by reserving a part of a corresponding sequence set or by reserving a hopping pattern of the sequence.
FIG. 9 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This structure supports both cases of with and without the use of a reference signal.
Referring to FIG. 9, the number of SC-FDMA symbols of an ACK/NACK signal and the number of SC-FDMA symbols of a reference signal are compared, and a greater value of the two is defined as the number of times of performing time-domain spreading usable for each cyclic shift. When the number of times of performing time-domain spreading of the control signal is different from the number of times of performing time-domain spreading of the reference signal, a smaller value of the two is used for coherent detection, and the other value is used for non-coherent detection.
When the number of the SC-FDMA symbols of the control signal is 4 and the number of the SC-FDMA symbols of the reference signal is 3, the control signal has 4 time-domain spreading codes and the reference signal has 3 time-domain spreading codes. If the non-coherent detection is used, 4 time-domain sequences can be used as a spreading code. Three of the four time-domain sequences may be transmitted using non-coherent detection, and the remaining one may be transmitted using coherent detection.
FIG. 10 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This is a case where non-coherent detection is used.
Referring to FIG. 10, since there is no need to transmit a reference signal in non-coherent detection, sequences can be used in time-domain spreading, wherein the number of sequences corresponds to the number of all available SC-FDMA symbols. When the number of SC-FDMA symbols for each slot is 7, a length of a time-domain sequence is 7 and the number of all time-domain sequences is also 7.
FIG. 11 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. A time-domain sequence is reserved in the ACK/NACK channel and is used as a scheduling channel.
Referring to FIG. 11, at least one of time-domain sequences is reserved as a scheduling request channel for transmitting a scheduling request. A time-domain sequence with a length of 7 is used as the scheduling request channel. The scheduling request may be transmitted using an unused portion in a time-domain sequence of a control signal or a time-domain sequence of a reference signal.
As for a frequency-domain sequence, the same frequency-domain sequence of the control signal such as the ACK/NACK signal may be used. Another specific sequence may be dedicatedly used for the scheduling request.
The ACK/NACK signal and the scheduling request may be identified through a divided time-domain sequence. That is, a frequency-domain sequence assigned for ACK/NACK signal transmission is also used for the scheduling request, and the scheduling request and the ACK/NACK signal are identified through the time-domain sequence. In addition, when the same time-domain sequence is used for both the ACK/NACK signal and the scheduling request, the ACK/NACK signal and the scheduling request may be identified by assigning different frequency-domain sequences to the ACK/NACK signal and the scheduling request.
For example, in case of supporting coherent detection, a maximum of 3 time-domain sequences are present for 3 reference signals. At lease one of the three time-domain sequences is assigned to a scheduling request channel. In addition, a control signal's time-domain sequence associated with a reference signal's time-domain sequence assigned to the scheduling request channel may be assigned to another scheduling request channel. The scheduling request channel supports coherent detection.
FIG. 12 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This is a case where time-domain sequences are reserved for the ACK/NACK channel, wherein a time-domain sequence with a length of 3 and a time-domain sequence with a length of 4 are both used.
Referring to FIG. 12, in the ACK/NACK channel, a scheduling request channel is configured by spreading the time-domain sequence with a length of 3 in a reference signal region and the time-domain sequence with a length of 4 in a data region (i.e., an ACK/NACK signal part).
FIG. 13 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This is a case where time-domain sequences are reserved for the ACK/NACK channel, wherein a time-domain sequence with a length of 3 and a time-domain sequence with a length of 4 are separately used.
Referring to FIG. 13, in the ACK/NACK channel, the time-domain sequence with a length of 3 is used as a scheduling request channel in a reference signal region, and the time-domain sequence with a length of 4 is used as a scheduling request channel in a data region (i.e., an ACK/NACK signal part). By using two types of time-domain sequences for the scheduling request channel, a maximum of 7 scheduling request channels can be configured. In comparison with the example of FIG. 12, UE capability increases.
In addition, a combination of the example of FIG. 12 and the example of FIG. 13 can also be used. As described above, in the example of FIG. 12, the time-domain sequence with a length of 3 and the time-domain sequence with a length of 4 are simultaneously used in the time domain, and in the example of FIG. 13, the time-domain sequence with a length of 3 and the time-domain sequence with a length of 4 are separately used.
FIG. 14 shows another exemplary structure of an ACK/NACK channel on which a scheduling request is transmitted. This is a case where a time-domain sequence is reserved for the ACK/NACK channel to be used as a scheduling channel. Non-coherent detection is used herein.
Referring to FIG. 14, in case of supporting non-coherent detection, at least one of time-domain sequences with a length of 4 is assigned to a scheduling request channel. The four time-domain sequences correspond to four SC-FDMA symbols. Unused time-domain sequences of a remaining reference signal portion can be assigned to other scheduling request channels. That is, by identifying a time-domain sequence of a control signal from a time-domain sequence of a reference signal, the time-domain domain sequences are assigned to scheduling request channels supporting non-coherent detection. In case of supporting coherent detection, a time-domain spreading code of the control signal and a time-domain spreading code of the reference signal have to be paired to be transmitted simultaneously.
FIG. 15 shows a structure of a CQI channel. The CQI channel is a control channel for transmitting a CQI. To ensure a sufficient symbol space, time-domain spreading is not used in CQI transmission.
Referring to FIG. 15, among 7 SC-FDMA symbols included in one slot, a reference signal is carried on 2 SC-FDMA symbols spaced apart from each other by 3 SC-FDMA symbols, and the CQI is carried on the remaining 5 SC-FDMA symbols. This is for exemplary purposes only, and thus the position and the number of SC-FDMA symbols used in the reference signal or the position or the number of symbols used in the CQI may vary. When quadrature phase shift keying (QPSK) mapping is performed on one SC-FDMA symbols, a 2-bit CQI value can be carried. Therefore, a 10-bit CQI value can be carried on one slot. For one subframe, a maximum 20-bit CQI value can be carried. In addition to the QPSK, the CQI may use other modulation schemes, e.g., 16-quadrature amplitude modulation (QAM).
The CQI is spread over a frequency domain by using a frequency-domain sequence. The frequency-domain sequence may be a ZC sequence. Unlike the two-dimensional spreading in the ACK/NACK channel, the CQI channel uses only one-dimensional spreading and thus increases CQI transmission capacity. Although only the frequency-domain spreading is described herein as an example, the CQI channel may also use time-domain spreading.
In the CQI channel, cyclic shifts can be reserved to be assigned to a scheduling request channel. This is the same as the example of the ACK/NACK channel except for a difference in the number of SC-FDMA symbols of the reference signal. Unlike the ACK/NACK channel, in the CQI channel, in many cases, a less number of SC-FDMA symbols are assigned to the reference signal. This is because spreading is not necessary over a time axis since users can be identified with sequence identification on a frequency axis. Therefore, a function of the reference signal can be achieved with only at least one SC-FDMA symbol. In case of a high Doppler effect, about 2 SC-FDMA symbols may be assigned to the reference signal, but it is difficult to use time-domain spreading.
A time-domain sequence can be defined in order to define the scheduling request channel. In case of supporting coherence detection, similarly to the ACK/NACK channel structure, about 3 SC-FDMA symbols are assigned to the reference signal, and a control signal part and a reference signal part may be identified when transmitted. In case of supporting non-coherent detection, a time-domain spreading code can be defined using a long sequence with a total length of one slot. Also in this case, similarly to the ACK/NACK channel, a sequence set of mutually orthogonal sequences such as a cyclic shift of a ZC sequence can be defined to be used as a time-domain spreading code. The sequence set may be a set of sequences whose mutual cross-correlation is small.
Although it has been described above that the scheduling request channel is configured to have a compatibility with a structure of the ACK/NACK channel or the CQI channel, the scheduling request channel can be configured by reserving a new time-frequency resource. In case of configuring a dedicated scheduling request channel, non-coherent detection not requiring the reference signal may be used. This is because the scheduling request can be transmitted according to a presence/absence of transmission of the scheduling request channel since the scheduling request can be identified only with a presence/absence of the scheduling request channel. For example, transmission of the scheduling request channel can be regarded as transmission of the scheduling request. In addition, the presence/absence of the scheduling request can be toggled according to the presence/absence of the scheduling request channel.
FIG. 16 shows an example of a scheduling request channel.
Referring to FIG. 16, when the scheduling request channel is generated independently from other control channels, its design is not related to the control channels. Thus, in this case, an arbitrary structure can be selected. In addition, unlike a case where a scheduling request channel is configured to be compliant with a conventional control channel, all control channels can be used. Thus, UE capability for the scheduling request channel increases.
Similarly to the ACK/NACK channel, the scheduling request channel is configured by using two-dimensional spreading of a frequency domain and a time domain. That is, a slot is divided into two parts, and a first time-domain spreading is performed on a first part and a second time-domain spreading is performed on a second part. In other words, for 4 SC-FDMA symbols (i.e., a first set) corresponding to a data part of the conventional ACK/NACK channel with respect to one slot, a first frequency-domain sequence is mapped onto each SC-FDMA symbol. In this case, the first frequency-domain sequence may have the same cyclic shift for each SC-FDMA symbol belonging to the first set or may have different cyclic shifts. The first frequency-domain sequence is spread again through a first orthogonal sequence, that is, a time-domain sequence. In addition, for 3 SC-FDMA symbols (i.e., a second set) corresponding to a reference signal part of the conventional ACK/NACK channel with respect to one slot, a first frequency-domain sequence is mapped onto each SC-FDMA symbol. In this case, the second frequency-domain sequence may have the same cyclic shift for each SC-FDMA symbol belonging to the second set or may have different cyclic shifts. The second frequency-domain sequence is spread again through a second orthogonal sequence, that is, a time-domain sequence.
In the frequency-domain spreading and the time-domain spreading, different sequences may be used for each SC-FDMA symbol or each slot. That is, a cyclic shift of a frequency-domain sequence may change for each SC-FDMA symbol and/or for each slot. A method of using an independent scheduling request channel or a method of sharing the scheduling request channel with a different control channel may be used in combination. Information related to configuration of the scheduling request channel may be reported by the BS to the UE through a broadcast channel or the like. In a method of mapping resources for the scheduling request channel onto actual UEs, a range of a UE identifier (ID) may be determined so that UE IDs are mapped to resources for the scheduling request channel in a 1:1 manner according to the determined order. Although the scheduling request channel can be generated in every transmission time interval (TTI), waste of radio resources can be reduced by regulating a period generated according to an amount of radio resource usable in the scheduling request channel.
FIG. 17 shows an example of a scheduling request channel. This is a case where non-coherent detection is supported.
Referring to FIG. 17, in case of supporting non-coherent detection, time-domain spreading is carried out through a time-domain sequence with a length of 7 corresponding to one slot.
FIG. 18 shows an example of resource allocation for a scheduling request channel. A radio resource for the scheduling request channel is assigned to an outermost portion of a control region. FIG. 19 shows another example of resource allocation for a scheduling request channel. A radio resource for the scheduling request channel is assigned between a control region and a data region. The scheduling request channel may be assigned to a data region or may be assigned either one of the control region or the data region.
FIG. 20 shows another example of resource allocation for a scheduling request channel.
Referring to FIG. 20, the scheduling request channel is assigned to at least one SC-FDMA symbol. A resource block (or simply RB) is a unit of frequency domain resource allocation and includes a plurality of subcarriers. The scheduling request channel can be transmitted throughout the entire band similar to a sounding signal for uplink radio resource scheduling. The scheduling request channel may be transmitted alternately or simultaneously with the sounding signal.
In the scheduling request channel, resources can be allocated in a unit of resource blocks. A sequence used in each resource block may be a ZC sequence used in a control channel combined with a cyclic shift. In this case, a predetermined number of scheduling request channels can be configured, wherein the predetermined number corresponds to N cyclic shifts×X resource blocks.
One SC-FDMA symbol is used for a scheduling request channel. In detail, the scheduling request channel may be configured with one resource block, and a UE may be identified according to a sequence in use and a position of a resource block in use.
Instead of allocating all resource blocks to the scheduling request channel, some of the resource blocks may be allocated to the data channel.
Radio resource allocation information on the scheduling request channel can be reported by the BS through the broadcast channel. A scheduling request signal may be periodically transmitted by the UE or may be transmitted in an event-driven manner. A transmission period of a scheduling request may be reported by the BS to the UE.
A method of transmitting uplink data through a scheduling request related to uplink data transmission will now be described. A UE receives radio resource allocation information regarding a scheduling request channel from a BS. The scheduling request channel is an uplink control channel and is different from a random access channel which is used before synchronization between the BS and the UE is achieved yet. The UE configures the scheduling request channel by using the radio resource allocation information and transmits the scheduling request to the BS on the scheduling request channel. The BS transmits an uplink radio resource allocated according to the scheduling request to the UE on a downlink control channel. The UE transmits the uplink data by using the uplink radio resource.
A method of transmitting a scheduling request on a scheduling request channel is classified into non-coherent detection and coherent detection. However, the scheduling request can be detected in practice in more various manners. A method of analyzing the scheduling request by determining a presence/absence of a signal and a method of identifying the scheduling request by using modulated signal information may also be taken into consideration.
In the non-coherent detection, a presence/absence of a scheduling request is determined according to a presence/absence of transmission of a scheduling request channel. In the coherent detection, all UEs transmit scheduling request signals when scheduling request channels are allocated to the UEs. When binary phase shift keying (BPSK) modulation is used, a UE may transmit 1-bit information indicating whether a scheduling request is desired or not. When quadrature phase shift keying (QPSK) modulation is used, the UE may transmit additional 1-bit information together with the 1-bit information indicating whether the scheduling request is desired or not. In this case, the additionally transmitted information may be quality of service (QoS) information or buffer size information for facilitating a scheduling process.
Coherence detection and non-coherent detection can be used at the same time. This is referred to as partial coherent detection. In the partial coherent detection, only a UE desiring a scheduling request transmits the scheduling request rather than all UEs unconditionally transmit scheduling requests. The UE transmitting the scheduling request may transmit additional desired information. When the UE does not need scheduling, that is, when the UE does not require radio resource for uplink transmission, the UE ignores the scheduling request instead of transmitting the scheduling request. Then, a receiver first determines a presence/absence of the scheduling request according to a presence/absence of a signal. If the signal exists, it is determined that there is the scheduling request. In a case where a transmitter transmits the scheduling request, additional information can be transmitted as signal modulation information. When BPSK modulation is used, additional information related to the scheduling request may be carried using one bit. When QPSK modulation is used, additional information related to the scheduling request may be carried using two bits.
The present invention can be implemented with hardware, software, or combination thereof. In hardware implementation, the present invention can be implemented with one of an application specific integrated circuit (ASIC), a digital signal processor (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, other electronic units, and combination thereof, which are designed to perform the aforementioned functions. In software implementation, the present invention can be implemented with a module for performing the aforementioned functions. Software is storable in a memory unit and executed by the processor. Various means widely known to those skilled in the art can be used as the memory unit or the processor.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

## Claims

1. A method of transmitting a scheduling request in a wireless communication system, performed by a user equipment, the method comprising:
configuring an uplink control channel for transmitting the scheduling request, wherein the scheduling request is contained in a subframe comprising two consecutive slots, each slot comprising a first set of orthogonal frequency division multiplexing (OFDM) symbols and a second set of OFDM symbols; and
transmitting the scheduling request on the uplink control channel to a base station, wherein configuring the uplink control channel comprises, for the OFDM symbols in each slot:
mapping one of a plurality of first frequency domain sequences to each OFDM symbol in the first set of OFDM symbols, thereby generating a first set of mapped frequency domain sequences, wherein each of the plurality of first frequency domain sequences is cyclic shifted relative to each of the other first frequency domain sequences;
mapping one of a plurality of second frequency domain sequences to each OFDM symbol in the second set of OFDM symbols, thereby generating a second set of mapped frequency domain sequences, wherein each of the plurality of second frequency domain sequences is cyclic shifted relative to each of the other second frequency domain sequences;
spreading the first set of mapped frequency domain sequences with a first orthogonal sequence, the length of the first orthogonal sequence having a value equal to the number of OFDM symbols in the first set of OFDM symbols; and
spreading the second set of mapped frequency domain sequences with a second orthogonal sequence, the length of the second orthogonal sequence having a value equal to the number of OFDM symbols in the second set of OFDM symbols.

2. The method of claim 1, wherein the first orthogonal sequence is a time domain sequence, and wherein spreading the first set of mapped frequency domain sequences comprises:
applying each element associated with the first orthogonal sequence to a corresponding one of the OFDM symbols in the first set of OFDM symbols.

3. The method of claim 1, wherein the length of the first frequency domain sequences and the length of the second frequency domain sequences equal the number of subcarriers allocated to the OFDM symbols.

4. The method of claim 1, wherein the number of OFDM symbols in the first set of OFDM symbols is greater than the number of OFDM symbols in the second set of OFDM symbols.

5. The method of claim 4, wherein the number of OFDM symbols in one of the two consecutive slots is seven, the number of OFDM symbols in the first set of OFDM symbols is four and the number of OFDM symbols in the second set of OFDM symbols is three.

6. The method of claim 4, wherein the OFDM symbols in the second set of OFDM symbols are consecutive.

7. A method of transmitting a scheduling request in a wireless communication system, performed by a user equipment, the method comprising:
configuring an uplink control channel for transmitting the scheduling request using a plurality of OFDM (orthogonal frequency division multiplexing) symbols; and
transmitting the scheduling request on the uplink control channel to a base station, wherein configuring the uplink control channel comprises:
mapping one of a plurality of first frequency domain sequences to each of a first set of OFDM symbols, thereby generating a first set of mapped frequency domain sequences, wherein each of the plurality of first frequency domain sequences is cyclic shifted relative to each of the other first frequency domain sequences;
mapping one of a plurality of second frequency domain sequences to each of a second set of OFDM symbols, thereby generating a second set of mapped frequency domain sequences, wherein each of the plurality of second frequency domain sequences is cyclic shifted relative to each of the other second frequency domain sequences;
spreading the first set of mapped frequency domain sequences with a first orthogonal sequence, the length of the first orthogonal sequence having a value equal to the number of OFDM symbols in the first set of OFDM symbols; and
spreading the second set of mapped frequency domain sequences with a second orthogonal sequence, the length of the second orthogonal sequence having a value equal to the number of OFDM symbols in the second set of OFDM symbols.

8. The method of claim 7, wherein the length of the first frequency domain sequences and the length of the second frequency domain sequences are equal to the number of subcarriers allocated to the OFDM symbols.

9. The method of claim 7, wherein the number of OFDM symbols in the first set of OFDM symbols is larger than the number of OFDM symbols in the second set of OFDM symbols.

10. The method of claim 9, wherein the number of OFDM symbols in the first set of OFDM symbols is four and the number of OFDM symbols in the second set of OFDM symbols is three.

11. The method of claim 9, wherein the OFDM symbols in the second set of OFDM symbols are consecutive.

12. The method of claim 1, wherein the second orthogonal sequence is a time domain sequence, and wherein spreading the second set of mapped frequency domain sequences comprises:
applying each element associated with the second orthogonal sequence to a corresponding one of the OFDM symbols in the second set of OFDM symbols.

13. The method of claim 1, wherein the OFDM symbols are single-carrier frequency division multiple access (SC-FDMA) symbols.

14. The method of claim 7, wherein the first orthogonal sequence is a time domain sequence, and wherein spreading the first set of mapped frequency domain sequences comprises:
applying each element associated with the first orthogonal sequence to a corresponding one of the OFDM symbols in the first set of OFDM symbols.

15. The method of claim 7, wherein the second orthogonal sequence is a time domain sequence, and wherein spreading the second set of mapped frequency domain sequences comprises:
applying each element associated with the second orthogonal sequence to a corresponding one of the OFDM symbols in the second set of OFDM symbols.

16. The method of claim 7, wherein the OFDM symbols are single-carrier frequency division multiple access (SC-FDMA) symbols.