Transmission of a CCFI or of PCFICH in a wireless communication system

BACKGROUND OF THE INVENTION

Field of the Invention

0001The present invention relates to a method and apparatus for coding a CCFI (Control Channel Format Indicator) channel, also known as PCFICH (Physical Control Format Indicator Channel), and more particularly, to a method and apparatus for coding a CCFI channel using a concatenation of repeated (3,2) codewords and original CCFI bits, for the case where a total result coded length of CCFI is not an integer multiple of three.

Description of the Related Art

0002Orthogonal Frequency Division Multiplexing (OFDM) is a technology to multiplex data in frequency domain. Modulation symbols are carried on frequency sub-carriers. The total bandwidth in an OFDM system is divided into narrowband frequency units called subcarriers. The number of subcarriers is equal to the FFT/IFFT size N used in the system. In general, the number of subcarriers used for data is less than N because some of the subcarriers located at the edge of the frequency spectrum are reserved as guard subcarriers. In general, no information may be transmitted on guard subcarriers.

0003A typical cellular radio system includes a collection of fixed base stations (BS) that define a radio coverage area or a cell. Typically, a non-line-of-sight (NLOS) radio propagation path exists between a base station and a mobile station due to natural and man-made objects that are situated between the base station and the mobile station. As a consequence, the radio waves propagate via reflections, diffractions and scattering. The arriving waves at the mobile station (MS) in the downlink direction (at the BS in the uplink direction) experience constructive and destructive additions because of different phases of the individual waves. This is due the fact that, at high carrier frequencies typically used in the cellular wireless communication, small changes in the differential propagation delays introduces large changes in the phases of the individual waves. When the MS is moving or changes occur in the scattering environment, the spatial variations in the amplitude and phase of the composite received signal will manifest themselves as the time variations known as Rayleigh fading or fast fading. The time-varying nature of the wireless channel requires very high signal-to-noise ratio (SNR) in order to provide desired bit error or packet error reliability.

0004Diversity is widely used to combat the effect of fast fading. The idea is to provide the receiver with multiple faded replicas of the same information-bearing signal. On the assumption of independent fading of each of the antenna branches, the probability that the instantaneous SNR is below a certain threshold on each branch is approximately <i>P</i>^L where p is the probability that the instantaneous SNR is below the certain threshold on each antenna branch.

0005The methods of diversity generally fall into the following categories: space, angle, polarization, field, frequency, time and multipath diversity. Space diversity may be achieved by using multiple transmit or receive antennas. The spatial separation between the multiple antennas is chosen so that the diversity branches experience fading with little or no correlation. Transmit diversity uses multiple transmit antennas in order to provide the receiver with multiple uncorrelated replicas of the same signal. Transmit diversity schemes may further be divided into open loop transmit diversity and closed-loop transmit diversity schemes. In an open loop transmit diversity approach, no feedback is required from the receiver. In a known arrangement of a closed loop transmit diversity, the receiver computes the phase and amplitude adjustment that should be applied at the transmitter antennas to maximize the received signal power at the receiver. In another arrangement of the closed loop transmit diversity referred to as selection transmit diversity (STD), the receiver provides feedback information to the transmitter on antenna(s) to be used for transmission.

0006Dynamic Category 0 (Cat 0) bits are a LTE terminology used in 3GPP LTE standard body. The role of Cat0 is to support dimensioning (scaling) of the downlink control channel by indicating the number of downlink and uplink scheduling grants. The current working assumption is that the dynamic Cat0 bits have a maximum size of two bits, and the dynamic Cat0 bits should be transmitted once during every subframe where a control channel element (CCE) is present. The information conveyed by Cat0 bits includes, but not limited to, the number of OFDM symbols used for all control channels in the subframe. The transmit diversity of the Cat0 bits is not finalized, and it is the objective of the present invention to provide a simple and efficient transmit diversity scheme that captures both spatial and frequency diversity in the channel. Several approaches of coding and transmit diversity have been proposed for both the Category 0 bits and ACK/NACK channels. In the 3GPP standard RAN1 meeting in May 2007, the Category 0 bits have been renamed as CCFI (Control Channel Format Indicator). In the present invention, one additional coding method is proposed, as well as frequency domain resource mapping methods for the transmission of CCFI channel.

0007In addition, it was proposed to use a (3,2,2) binary linear code to map the 2 Cat0 bits into a 3-bit codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃<i>,</i> and this codeword belongs to a codebook of size four with a minimum Hamming distance two between any pairs of codewords. One example of the (3,2) codebook is <i>c</i>₁<i>c</i>₂<i>c</i>₃ ∈ C₁ = {111, 100, 010 001}.

0008Because the size of (3,2) codebook as above presented is three, merely repeating the 3-bit codeword may only be suitable for a case where the length of a coded CCFI is an integer multiple of three. Therefore, it is important to provide a CCFI coding method in a case where the length of a coded CCFI is not an integer multiple of three.

SUMMARY OF THE INVENTION

0009It is therefore one aspect of the present invention to provide an improved process and apparatus for solving the above mentioned problems.

0010It is another aspect of the present invention to provide a CCFI coding method in a case where the length of a coded CCFI is not an integer multiple of three.

0011In one embodiment of the present invention, it is proposed to code the CCFI channel using a concatenation of repeated (3,2) codewords and uncoded CCFI, bits, for the case where the total codeword length is not an integer multiple of three. Because the size of the (3,2) codebook as above presented is three and thus it is important to provide a CCFI coding method in a case where the length of a coded CCFI is not an integer multiple of three.

0012As shown in the table below, a mapping between the two bits CCFI and the component codewords in a (3,2) codebook is established. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" rowsep="0"><colspec colnum="1" colname="col1" colwidth="25mm" /><colspec colnum="2" colname="col2" colwidth="70mm" /><colspec colnum="3" colname="col3" colwidth="71mm" /><tbody><row rowsep="1"><entry>CCFI bits <i>b</i>₁<i>b</i>₂</entry><entry>Component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ (assuming (3,2) codebook C₂)</entry><entry>Component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ (assuming (3,2) codebook C₁)</entry></row><row rowsep="1"><entry align="center">00</entry><entry align="center">000</entry><entry align="center">111</entry></row><row rowsep="1"><entry align="center">01</entry><entry align="center">011</entry><entry align="center">100</entry></row><row rowsep="1"><entry align="center">10</entry><entry align="center">101</entry><entry align="center">010</entry></row><row rowsep="1"><entry align="center">11</entry><entry align="center">110</entry><entry align="center">001</entry></row></tbody></tgroup></table></tables>

0013The length-32 codewords are generated in the following procedures. <ol id="ol0001" compact="compact"><li>(1) A length-3 component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ is generated as shown in Table above;</li><li>(2) the component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ is repeated ten times to generate a length-30 sequence; and</li><li>(3) the length-30 sequence is concatenated with the original CCFI bits <i>b₁b₂.</i></li></ol>

0014The resulting four codewords of codebook A corresponding to each codeword of codebook C₂ are: <img file="EP2015504A2_D0001.tif" />

0015In another embodiment of the current invention, when the CCFI has only three states (i.e., CCFI is any three of "00", "01", "10" and "11"), then any of the three codewords in the above set may be used to carry the CCFI information.

0016In another embodiment of the present invention, the codebook generated above is column-wise permuted in order to fit the K 1x2 RU resource configuration, which has a total of 4K coded bits. In this permutation method, based on the sequential concatenation of the repeated codewords, K repetitions of 3-bit component codeword are assigned to the K RUs (leaving one bit open at each RU), and then the remaining K bits are mapped separately to the K RUs. Other codewords of codebook A may deviate in the same method. The resulting codebook deviated from codebook A is called Codebook B as shown below. The codebook B may be better than codebook A in fading channels, since a full repetition to an RU is mapped as much as possible. <img file="EP2015504A2_D0002.tif" />

0017In another embodiment of the current invention, a variation of the codebook A may obtained by mapping the CCFI bits to codebook C1, instead of codebook C2. The same repetition and concatenation used in generating this new codebook, called codebook C. <img file="EP2015504A2_D0003.tif" />

0018In another embodiment of the current invention, same column-wise permutation as stated above is applied to Codebook C in order to generate Codebook D. <img file="EP2015504A2_D0004.tif" />

0019In another embodiment of the current invention, when the CCFI has only three states, any three codewords in a given codebook (e.g, Codebook A, B, C, D, etc) may be used to carry the CCFI information.

BRIEF DESCRIPTION OF THE DRAWINGS

0020A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is an illustration of an Orthogonal Frequency Division Multiplexing (OFDM) transceiver chain having transmitter chain and receiver chain;</li><li><figref idref="f0002">Figure 2</figref> shows an Alamouti 2×1 space-time diversity scheme;</li><li><figref idref="f0002">Figure 3</figref> shows an Alamouti 2×1 space-frequency scheme;</li><li><figref idref="f0003">Figure 4</figref> shows an example of a method of a column-wise permutation; and</li><li><figref idref="f0004">Figures 5A</figref> and <figref idref="f0005">5B</figref> are flowcharts illustrating procedural steps of transmitting and receiving CCFI according to different embodiments of the present invention.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0021Several approaches of coding and transmit diversity have beeen proposed for both the Category 0 bits and ACK/NACK channels. In the 3GPP standard RAN1 meeting in May 2007, the Category 0 bits have been renamed as CCFI (Control Channel Format Indicator). In the practice of the principle of the present invention, a few additional coding methods as well as frequency domain resource mapping methods for the transmission of CCFI channel are disclosed. Here, the CCFI is also known as PCFICH (Physical Control Format Indicator Channel).

0022Orthogonal Frequency Division Multiplexing (OFDM) is a technology to multiplex data in frequency domain. Modulation symbols are carried on frequency sub-carriers. <figref idref="f0001">Figure 1</figref> illustrate of an Orthogonal Frequency Division Multiplexing (OFDM) transceiver chain having a transmitter chain and a receiver chain. A sample of Orthogonal Frequency Division Multiplexing (OFDM) transceiver chain is shown in <figref idref="f0001">Figure 1</figref>. At a transmitter chain 100, control signals or data signals are modulated by a modulator 101 and and the modulated signals are serial-to-parallel converted by a serial-to-parallel convertor 112. An Inverse Fast Fourier Transform (IFFT) unit 114 is used to transfer the modulated signal or data from frequency domain to time domain, and the modulated signals trasferred to the time domain is parallel-to-serial converted by a parallel-to-serial convertor 116. A cyclic prefix (CP) or zero prefix (ZP) is added to each OFDM symbol at a CP insertion stage 118 to avoid or alternatively, to mitigate the impact due to multipath fading at a multipath fading channel 122. Signals from cyclic prefix (CP) insertion stage 118 are applied to transmitter front end processing unit 120, RF amplifier 121 and then single or multiple antennas 123. Therefore, the signals transmitted by transmitter chain 100 are received by receiver chain 140. At a receiver chain 140, assuming that perfect time and frequency synchronization are achieved, signals received by receiving single or multiple antennas 125 is applied to receiver front end processing unit 124, are processed at a cyclic prefix (CP) removal stage 126 which removes the cyclic prefix (CP) of the received signal. Signals processed in cyclic prefix (CP) removal stage 126 are further serial-to-parallel converted by a serial-to-parallel convertor 128. A Fast Fourier Transform (FFT) unit 130 transfers the received signals from the time domain to the frequency domain for further processing, including parallel-to-serial conversion by a parallel-to-serial convertor 132 and being demodulation by signal demodulator 134.

0023The total bandwidth in an OFDM system is divided into narrowband frequency units called subcarriers. The number of subcarriers is equal to the FFT/IFFT size N used in the system. In general, the number of subcarriers used for data is less than N because some of the subcarriers located at the edge of the frequency spectrum are reserved as guard subcarriers. As a general rule, no information may be transmitted on guard subcarriers.

0024A typical cellular radio system includes a collection of fixed base stations (BS) that define a radio coverage area or a cell. Typically, a non-line-of-sight (NLOS) radio propagation path exists between a base station and a mobile station due to natural and man-made objects that are situated between the base station and the mobile station. As a consequence, the radio waves propagate via reflections, diffractions and scattering. The arriving waves at the mobile station (MS) in the downlink direction (at the BS in the uplink direction) experience constructive and destructive additions because of different phases of the individual waves. This is due the fact that, at the high carrier frequencies typically used in the cellular wireless communication, small changes in the differential propagation delays introduce large changes in the phases of the individual waves. Additionally, when the MS is moving or changes occur in the scattering environment, the spatial variations in the amplitude and phase of the composite received signal will manifest themselves as the time variations known as Rayleigh fading or fast fading. The time-varying nature of the wireless channel requires very high signal-to-noise ratio (SNR) in order to provide desired bit error or packet error reliability.

0025Diversity is widely used to combat the effects of fast fading. The idea is to provide the receiver with multiple faded replicas of the same information-bearing signal. On the assumption of independent fading of the signals broadcast by each of the antenna branches, the probability, that the instantaneous SNR is below a certain threshold on each branch is approximately <i>p</i>^L, where p is the probability that the instantaneous SNR is below the certain threshold on each antenna branch. L is the number of antenna branches. From a system operation viewpoint, "antenna branch" is also known as "antenna ports", and it indicates the number of antennas at the base station.

0026The methods of diversity that are suitable for use fall into the following categories: space, angle, polarization, field, frequency, time and multipath diversity. Space diversity may be achieved by using multiple transmit or receive antennas. The spatial separation between the multiple antennas is chosen so that the diversity branches experience fading with little or no correlation of the signals during the transit between the transmitting and receiving antennas. Transmit diversity uses multiple transmitting antennas in order to provide the receiver with multiple uncorrelated replicas of the same signal. Transmit diversity schemes may further be divided into open loop transmit diversity and closed-loop transmit diversity schemes. In an open loop transmit diversity approach, no feedback is required from the receiver. In one known arrangement of a closed loop transmit diversity, the receiver computes the phase and amplitude adjustment that should be applied at the transmitter antennas to maximize the received signal power at the receiver. In another arrangement of the closed loop transmit diversity referred to as selection transmit diversity (STD), the receiver provides feedback information to the transmitter on antenna(s) to be used for transmission.

0027An example of open-loop transmit diversity scheme is the Alamouti 2×1 space-time diversity scheme. <figref idref="f0002">Figure 2</figref> shows an Alamouti 2×1 space-time diversity scheme. In this approach during any symbol period, two data symbols are transmitted simultaneously from the two transmit antennas ANT 1 and ANT2. Suppose during the first symbol interval t1, the symbols transmitted from ANT1 and ANT2 are denoted as S₁ and S₂ respectively as shown in <figref idref="f0002">Figure 2</figref>. During the next symbol period, the symbols transmitted from ANT1 and ANT2 are -S₂^* and S₁^* respectively where x^* represents the complex conjugate of x. With certain processing at the receiver, original symbols S₁ and S₂ may be recovered. Here, the instantaneous channel gain estimates h1 and h2 on ANT 1 and ANT 2, respectively, are required for faithful recovery at the receiver. This requires separate pilot symbols on both of the antennas in order to provide channel gain estimation at the receiver. The diversity gain achieved by Alamouti coding is the same as that which may be achieved in Maximum Ratio Combining (MRC).

0028A 2 × 1 Alamouti scheme may also be implemented in a space -frequency coded form. <figref idref="f0002">Figure 3</figref> shows a 2X1 Alamouti scheme implemented in a space-frequency coded form. In this case, the two symbols are sent on two different frequencies, i.e., subcarriers f1 and f2, for example, on different subcarriers in an Orthogonal Frequency Division Multiplexing (OFDM) system as shown in <figref idref="f0002">Figure 3</figref>. When implemented in a space-frequency coded form in the open-loop transmit diversity scheme, the 2×1 Alamouti space-frequency diversity scheme illustrated by <figref idref="f0002">Figure 3</figref> shows an Alamouti 2×1 space-frequency diversity scheme in which during any symbol period, two data symbols are transmitted simultaneously from the two transmit antennas ANT1 and ANT2. If during the first frequency f1, the symbols transmitted from ANT1 and ANT2 are denoted as S₁ and S₂ respectively as shown in <figref idref="f0002">Figure 3</figref>. During the next symbol period, the symbols transmitted from ANT1 and ANT2 are -S₂^* and S₁^* respectively where x^* represents the complex conjugate of x. Original symbols S₁ and S₂ may be recovered by the receiver. Here, the instantaneous channel gain estimates h1 and h2 on ANT1 and ANT 2, respectively, are required for faithful recovery at the receiver. This requires separate pilot symbols on both of the antennas in order to provide channel gain estimation at the receiver. The diversity gain achieved by Alamouti coding is the same as that which may be achieved in Maximum Ratio Combining (MRC).

0029The received signals r₁ and r₂ at the mobile station in subcarrier f1, r1, and in subcarrier f2, r2, may be written as: <maths id="math0001" num="(1)"><math display="block"><mtable><mtr><mtd><msub><mi>r</mi><mn>1</mn></msub><mo>=</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>2</mn></msub><mo>+</mo><msub><mi>n</mi><mn>1</mn></msub></mtd></mtr><mtr><mtd><msub><mi>r</mi><mn>2</mn></msub><mo>=</mo><msub><mrow><mo>-</mo><mi>h</mi></mrow><mn>1</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>2</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>1</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>n</mi><mn>2</mn></msub></mtd></mtr></mtable></math><img file="EP2015504A2_D0005.tif" /></maths> where h1 and h2 are channel gains from ANT1 and ANT2 respectively. The assumption here is that the channel from a given antenna does not change between subcarriers f1 and f2. The mobile station performs equalization on the received signals and combines the two received signals (r1 and r2) in order to recover the symbols S1 and S2. <maths id="math0002" num="(2)"><math display="block"><mtable columnalign="left"><mtr><mtd><mtable><mtr><mtd><msub><mover><mi>s</mi><mo>^</mo></mover><mn>1</mn></msub><mo>=</mo><msup><msub><mi>h</mi><mn>1</mn></msub><mo>*</mo></msup><mo>⁢</mo><msub><mi>r</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msubsup><mi>r</mi><mn>2</mn><mo>*</mo></msubsup></mtd></mtr></mtable></mtd></mtr><mtr><mtd><mo>=</mo><msup><msub><mi>h</mi><mn>1</mn></msub><mo>*</mo></msup><mrow><mo>(</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>2</mn></msub><mo>+</mo><msub><mi>n</mi><mn>1</mn></msub><mo>)</mo><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msup><mfenced><mo>-</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>2</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>1</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>n</mi><mn>2</mn></msub></mfenced><mo>*</mo></msup></mrow></mtd></mtr><mtr><mtd><mo>=</mo><mfenced><msup><mfenced open="|" close="|"><msub><mi>h</mi><mn>1</mn></msub></mfenced><mn>2</mn></msup><mo>+</mo><msup><mfenced open="|" close="|"><msub><mi>h</mi><mn>2</mn></msub></mfenced><mn>2</mn></msup></mfenced><mo>⁢</mo><msub><mi>s</mi><mn>1</mn></msub><mo>+</mo><msup><msub><mi>h</mi><mn>1</mn></msub><mo>*</mo></msup><mo>⁢</mo><msub><mi>n</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msubsup><mi>n</mi><mn>2</mn><mo>*</mo></msubsup></mtd></mtr><mtr><mtd><mtable><mtr><mtd><mtable><mtr><mtd><msub><mover><mi>s</mi><mo>^</mo></mover><mn>2</mn></msub><mo>=</mo><msubsup><mi>h</mi><mn>2</mn><mo>*</mo></msubsup><mo>⁢</mo><msub><mi>r</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msubsup><mi>r</mi><mn>2</mn><mo>*</mo></msubsup></mtd></mtr></mtable></mtd></mtr><mtr><mtd><mo>=</mo><msup><msub><mi>h</mi><mn>2</mn></msub><mo>*</mo></msup><mrow><mo>(</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msub><mi>s</mi><mn>2</mn></msub><mo>+</mo><msub><mi>n</mi><mn>1</mn></msub><mo>)</mo><mo>+</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msup><mfenced><mo>-</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>2</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>h</mi><mn>2</mn></msub><mo>⁢</mo><msubsup><mi>s</mi><mn>1</mn><mo>*</mo></msubsup><mo>+</mo><msub><mi>n</mi><mn>2</mn></msub></mfenced><mo>*</mo></msup></mrow></mtd></mtr><mtr><mtd><mo>=</mo><mfenced><msup><mfenced open="|" close="|"><msub><mi>h</mi><mn>1</mn></msub></mfenced><mn>2</mn></msup><mo>+</mo><msup><mfenced open="|" close="|"><msub><mi>h</mi><mn>2</mn></msub></mfenced><mn>2</mn></msup></mfenced><mo>⁢</mo><msub><mi>s</mi><mn>2</mn></msub><mo>+</mo><msup><msub><mi>h</mi><mn>2</mn></msub><mo>*</mo></msup><mo>⁢</mo><msub><mi>n</mi><mn>1</mn></msub><mo>+</mo><msub><mi>h</mi><mn>1</mn></msub><mo>⁢</mo><msubsup><mi>n</mi><mn>2</mn><mo>*</mo></msubsup></mtd></mtr></mtable></mtd></mtr></mtable></math><img file="EP2015504A2_D0006.tif" /></maths>

0030It may be seen that both the transmitted symbols S1 and S2 achieve full spatial diversity.

0031The term Dynamic Category 0 (Cat 0) bits is a LTE terminology used by the 3GPP LTE standard body. The role of Cat0 is to support dimensioning (scaling) of the downlink control channel by indicating the number of downlink and uplink scheduling grants. The current working assumption is that the dynamic Cat0 bits have a maximum size of two bits, and should be transmitted during every subframe where a control channel element (CCE) is present. The information conveyed by Cat0 bits includes, but is not limited to, the number of OFDM symbols used for all control channels in the subframe. The transmit diversity of the Cat0 bits is not finalized, and it is one of the objectives of the present invention to provide a simple and efficient transmission and reception diversity scheme that is enable to capture both spatial and frequency diversity in the channel. Several approaches of coding and transmit diversity have been discussed for both the Category 0 bits and ACK/NACK channels. In the 3GPP standard RAN1 meeting in May 2007, the Category 0 bits have been renamed as CCFI (Control Channel Format Indicator). In the present invention, one additional coding method is proposed, as well as frequency domain resource mapping methods for the transmission of CCFI channel.

0032In addition, it was proposed to use a (3,2,2) binary linear code to map the two Cat0 bits into a 3-bit codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃, and to assign this codeword belongs to a codebook of size four with a minimum Hamming distance two between any pairs of codewords. A linear code (n,k,d) means a code with each codeword length of n coded bits, and each codeword correspond to a message with length k information bits. The minimum hamming distance of the codebook is d. Once the 3-bit codeword is specified, it will be repeated and rate-matched to fit the 2K channel symbols that are going to be used for the Cat0 bits. A (3,2) codebook is a short-hand notation of (3,2,2) code. One example of the (3,2) codebook is <i>c₁c₂c₃</i> ∈ C={111, 100, 010 001}.

0033In one embodiment of the present invention, it is proposed to code the CCFI channel using a concatenation of repeated (3,2) codewords and uncoded CCFI bits, for the case where the total codeword length is not an integer multiple of three. Because the size of (3,2) codebook as above presented is three and thus it is important to provide a CCFI coding method in a case where the length of a coded CCFI is not an integer multiple of three.

0034For example, when a total number of K 1x2 resource units (RU) are assigned to the CCFI channel, there are 2K channel symbols and 4K channel bits, assuming QPSK modulation on each channel symbol. Here, 1x2 RU occupies one OFDM symbol and two neighboring subcarriers. For example, when K=8 RUs, there are 2K=16 channel symbols and 32 coded bits. 32 is not an integer multiple of three.

0035As shown in Table 1, a mapping between the 2 bits CCFI and the component codewords in a (3,2) codebook is established. Table 1 is a mapping between CCFI bits and component codewords as shown above. Here, the (3,2) codebook is <i>c₁c₂c₃</i> ∈ C₂ = {000, 011, 101, 110}. Note the above shown (3,2) codebook is equivalent to <i>c₁c₂c₃</i> ∈ C₁ {111, 100, 010 001}. CCFI bits b₁ and b₂ are original CCFI bits. Component codewords of two (3,2) codebooks C₁ and C₂ corresponding to each state of CCFI bits are shown in Table 1. <tables id="tabl0002" num="0002"><table frame="all"><title><b>Table 1: Mapping between CCFI bits and component codewords.</b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="69mm" /><colspec colnum="3" colname="col3" colwidth="70mm" /><thead><row><entry valign="top">CCFI bits <i>b</i>₁<i>b</i>₂</entry><entry valign="top">Component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ (assuming (3,2) codebook C₂)</entry><entry valign="top">Component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ (assuming (3,2) codebook C₁)</entry></row></thead><tbody><row><entry align="center">00</entry><entry align="center">000</entry><entry align="center">111</entry></row><row><entry align="center">01</entry><entry align="center">011</entry><entry align="center">100</entry></row><row><entry align="center">10</entry><entry align="center">101</entry><entry align="center">010</entry></row><row><entry align="center">11</entry><entry align="center">110</entry><entry align="center">001</entry></row></tbody></tgroup></table></tables>

0036Four codewords with length of 32 generated for the CCFI bits <i>b</i>₁<i>b</i>₂ are shown as follows, for the example above. Here, (3,2) codebook C₂ are used. The length-32 codewords are generated by modulator 101 with the following procedural steps. <ol id="ol0002" compact="compact"><li>(1) A length-3 component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ is generated as shown in Table 1;</li><li>(2) the component codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ is repeated ten times to generate a length 30 sequence; and</li><li>(3) the length-30 sequence is concatenated with the original CCFI bits <i>b</i>₁<i>b</i>₂<i>.</i></li></ol>

0037Here, the codeword <i>c</i>₁<i>c</i>₂<i>c</i>₃ is repeated [4<i>K</i>/3] times, and the resulting sequence is concatenated with the original CCFI bits <i>b</i>₁<i>b</i>₂ . This concatenated bit sequence is the final channel bit sequence to be modulated and mapped into channel symbol.

0038The resulting four codewords of codebook A corresponding to each codeword of codebook C₂ are: <img file="EP2015504A2_D0007.tif" />

0039In another embodiment of the current invention, if the CCFI has only three states (i.e., CCFI is any three of "00", "01", "10" and "11"), then any of the 3 codewords in the above set may be used to carry the CCFI information.

0040In another embodiment of the present invention, the codebook generated above is column-wise permuted to fit the K 1x2 RU resource configuration, which has a total of 4K coded bits. <figref idref="f0003">Figure 4</figref> shows an example of a method of a column-wise permutation. In this permutation method, based on the sequential concatenation of the repeated codewords, K repetitions of 3-bit component codeword are assigned to the K RUs (leaving one bit open at each RU), and then the remaining K bits are mapped separately to the K RUs. The permutation of CW4 is illustrated in <figref idref="f0003">Figure 4</figref>. Other codewords of codebook A may be deviated in the same method. The resulting codebook deviated from codebook A is called Codebook B as shown below. The codebook B may be better than codebook A in fading channels, since a full repetition to an RU is mapped as much as possible. <img file="EP2015504A2_D0008.tif" />

0041In another embodiment of the current invention, a variation of the codebook A may obtained by mapping the CCFI bits to codebook C1, instead of codebook C2, as shown in Table 1. The same repetition and concatenation used in generating this new codebook, called codebook C. <img file="EP2015504A2_D0009.tif" />

0042In another embodiment of the current invention, same column-wise permutation as shown in <figref idref="f0003">Figure 4</figref> is applied to Codebook C and Codebook D is obtained. <img file="EP2015504A2_D0010.tif" />

0043In another embodiment of the current invention, when the CCFI has only three states, any three codewords in a given codebook (e.g, Codebook A, B, C, D, etc) may be used to carry the CCFI information.

0044<figref idref="f0004">Figures 5A</figref> and <figref idref="f0005">5B</figref> are flowcharts illustrating procedural steps of transmitting and receiving CCFI according to different embodiments of the present invention.

0045In <figref idref="f0004">Figure 5A</figref>, the procedure of generating Codebooks A and C are presented. When the CCFI is transmitted at a transmitter, two-bit CCFI is mapped to 3-bit codeword of codebook C1 or C2 as shown in Table 1 at step 201, the three-bit codeword is repeated for a predetermined times with the number of the predetermined time being a flooring of quotient [4<i>K</i>/3], where K is the number of resource units at step 203, the resulting bit sequence is concatenated with the original CCFI bits at step 205 and thus a final bit sequence is generated and transmitted at transmitting antennas. At the receiver side, the receiving antennas receive the transmitted resulting bit sequence from the transmitter at step 211, a demodulator of the receiver demodulates the received bit sequence at step 213, and the receiver achieves the information carried by CCFI at step 215 and thus the achieved information carried by the CCFI is utilized by the receiver.

0046In <figref idref="f0005">Figure 5B</figref>, the procedure of generating Codebooks B and D are presented. When the CCFI is transmitted at a transmitter, two-bit CCFI is mapped to three-bit codeword of codebook C 1 or C2 as shown in Table 1 at step 301, the three-bit codeword is repeated for a predetermined times with the number of the predetermined time being a quotient of 4K/3 where K is the number of resource units at step 303, the resulting bit sequence is concatenated with the original CCFI bits at step 305 and thus a bit sequence is generated. Here, the bit sequence may be illustrated as cw 4 shown in <figref idref="f0003">Figure 4</figref>. At step 307, leading K repetitions of the three-bit codeword as shown in Table 1 in the resulting bit sequence is mapped to the number of K resource units respectively with one bit of each of resource units being open, and the remaining K bits of the bit sequence are separately mapped to the open bit of each of the number of K resource units at step 309. Step 307 may be illustrated as the intermediate RU#1-RU#8 each having one bit open as shown in the intermediate bit sequence shown in <figref idref="f0003">Figure 4</figref>. Step 309 may be illustrated as the final RU#1-RU#8 each having four bits allocated as shown by the resulting bit sequence shown in <figref idref="f0003">Figure 4</figref>. The resulting mapped bit sequences are transmitted by the transmitting antennas. At the receiver side, the receiving antennas receive the transmitted resulting bit sequence from the transmitter at step 311, a demodulator of the receiver demodulates the received bit sequence at step 313, and the receiver achieves the information carried by CCFI at step 315 and thus the achieved information carried by the CCFI is utilized by the receiver.

0047Modulator 101 and IFFT 114 of transmitter 100 include microprocessors based controller. Demodulator. 134 and FFT 130 of receiver 140 include microprocessors based controller.