Digital radio communications

Abstract

An orthogonal frequency division multiplexing digital radio transmitter (110) is arranged to transmit a data packet (200) comprising a plurality of orthogonal frequency division multiplexing symbols (304). At least one of the symbols (304) comprises a plurality of demodulation reference signals (408) in a plurality of first frequency subcarriers (302) of the symbol (304). The transmitter (110) is arranged to transmit a physical control channel (406) at least partially distributed in the remaining frequency subcarriers (302) of the symbol (304) according to a calculated distribution. The transmitter (110) calculates the distribution by arranging the remaining frequency subcarriers (304) in a two-dimensional matrix so that the remaining frequency subcarriers (304) have consecutive indices in a first dimension and have a common increment in a second dimension, and sequentially allocating a plurality of second remaining frequency subcarriers (302) to the physical control channel (406) along a second direction.

Description

Technical Field

[0001] The present invention relates to low power digital radio communications and more particularly, but not exclusively, to allocating frequency subcarriers to different parts of a data packet in an Orthogonal Frequency Division Multiplexing (OFDM) radio system supporting a Multiple Input Multiple Output (MIMO) transmission mode. Background Art

[0002] OFDM is a form of radio transmission used in various radio protocols, such as Long Term Evolution (LTE), various IEEE 802.11 standards, DAB radio, DVB-T, and WiMAX. Instead of encoding data on a single carrier frequency, the data stream is spread over some or all of the radio channels containing multiple OFDM subcarriers. OFDM subcarriers are usually closely spaced at regular intervals across the spectrum, but this is not required. The subcarriers are orthogonal to avoid mutual interference. Therefore, OFDM can provide good resilience to multipath fading and external interference.

[0003] In some radio communication applications, the MIMO principle is used, whereby multiple antennas are provided for the transmitter and receiver, which can be exploited in various ways. MIMO communication relies on the fact that the transmit antennas are "separated" from each other and the receiver antennas are also separated from each other. This separation enables independent frequency selectivity between the transmit paths. The separation can be physical (distance) or polarization diversity (two antennas with orthogonal polarizations) or a combination thereof.

[0004] Radio systems that support MIMO modes of operation typically support a variety of different MIMO modes using different numbers of transmit antennas, including spatial multiplexing, space-time transmit diversity, space-time block coding, open-loop beamforming, and closed-loop beamforming. When operating using different MIMO modes and / or different numbers of transmit antennas, the OFDM frequency subcarrier allocations used to transmit different parts of a data packet may be different. Therefore, the transmitter and receiver need to be able to determine which subcarrier allocation to use in order to successfully encode, transmit, receive, and decode the data packet. Summary of the invention

[0005] When viewed from a first aspect, the invention provides an Orthogonal Frequency Division Multiplexing (OFDM) digital radio transmitter arranged to transmit a data packet comprising a plurality of OFDM symbols, at least one of said symbols comprising a plurality of Demodulation Reference Signals (DRS) in a plurality of first frequency subcarriers of said symbol, the transmitter being further arranged to transmit a Physical Control Channel (PCC) distributed at least in part in the remaining frequency subcarriers of said symbol according to a calculated distribution, wherein the transmitter is arranged to calculate the distribution by:

[0006] arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and

[0007] A plurality of second remaining frequency subcarriers are sequentially allocated to the PCC along the second direction.

[0008] The present invention extends to an Orthogonal Frequency Division Multiplexing (OFDM) digital radio receiver arranged to receive a data packet comprising a plurality of OFDM symbols, at least one of said symbols comprising a plurality of Demodulation Reference Signals (DRS) in a plurality of first frequency sub-carriers of said symbol, the receiver further being arranged to decode a Physical Control Channel (PCC) at least partly distributed in the remaining frequency sub-carriers of said symbol according to a calculated distribution, wherein the receiver is arranged to calculate said distribution by:

[0009] arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and

[0010] A plurality of second remaining frequency subcarriers are sequentially allocated to the PCC along the second direction.

[0011] The present invention also extends to a non-transitory computer-readable medium comprising instructions configured to cause a digital radio transmitter to transmit a data packet comprising a plurality of OFDM symbols, at least one of the symbols comprising a plurality of demodulation reference signals (DRS) in a plurality of first frequency subcarriers of the symbol, the instructions further configured to cause the transmitter to transmit a physical control channel (PCC) distributed at least in part in the remaining frequency subcarriers of the symbol according to a calculated distribution, wherein the instructions are configured to cause the transmitter to calculate the distribution by:

[0012] arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and

[0013] A plurality of second remaining frequency subcarriers are sequentially allocated to the PCC along the second direction.

[0014] The present invention also extends to a non-transitory computer-readable medium, comprising instructions configured to cause a digital radio receiver to receive a data packet comprising a plurality of OFDM symbols, at least one of the symbols comprising a plurality of demodulation reference signals (DRS) in a plurality of first frequency subcarriers of the symbol, the instructions further configured to cause the receiver to decode a physical control channel at least partially distributed in remaining frequency subcarriers of the symbol according to a calculated distribution, wherein the instructions are configured to cause the receiver to calculate the distribution by:

[0015] arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and

[0016] A plurality of second remaining frequency subcarriers are sequentially allocated to the PCC along the second direction.

[0017] Applicants have discovered that by the transmitter calculating the frequency subcarrier allocation for PCC according to the present invention, an optimal or near-optimal spread across the available subcarriers can be achieved, which can allow for maximum diversity from frequency selectivity compared to, for example, simply allocating subcarriers in sequence. This can help avoid adverse consequences from narrowband interference sources.

[0018] The first direction may be the rows of the matrix, and the second direction may be the columns. Thus, for example, the frequency subcarrier index may be continuous along each row, and the allocation of frequency subcarriers may be performed sequentially, preferably in order, along one or more columns. However, those skilled in the art will recognize that the designation of "rows" and "columns" of the matrix is ​​arbitrary and that they may be interchanged. In fact, it will also be recognized that the order referred to herein may be performed in either direction.

[0019] It will be appreciated that DRS allows a receiver to perform channel estimation.

[0020] This method of allocating subcarrier frequencies to PCCs is considered novel and inventive in itself, so when viewed from a second aspect, the present invention provides a method of allocating physical control channels (PCCs) to frequency subcarriers of OFDM symbols in an Orthogonal Frequency Division Multiplexing (OFDM) digital radio transmission system, the method comprising:

[0021] determining a plurality of first frequency subcarriers allocated to a demodulation reference signal (DRS);

[0022] Determining remaining frequency subcarriers of the frequency subcarriers of the symbol:

[0023] Arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension;

[0024] allocating a plurality of second remaining frequency subcarriers to the PCC in sequence along the second direction; and

[0025] The allocation of frequency subcarriers to the PCC is recorded.

[0026] In one set of embodiments, the frequency subcarrier index is also ordered in the second direction. For example, the index may run sequentially along each row (column), with each new row (column) continuing from the end of the previous row (column), so that there is a common increment between the elements in each column (row) and so that each element in a row (column) has a common increment relative to the corresponding element in the next row (column). According to the present invention, this can help ensure an optimal allocation when the allocation is read sequentially along the columns (rows).

[0027] In one set of embodiments, the transmitter or receiver is arranged to determine the total number of frequency subcarriers required to transmit the PCC, calculate a first number of remaining frequency subcarriers in a first symbol, compare the total number with the first number and perform the calculation of the allocation only if the total number is less than the first number. If the transmitter determines that the total number is greater than or equal to the first number, the transmitter may allocate all of the first remaining frequency subcarriers to the PCC, subtract the first number from the total number to produce an outstanding number of frequency subcarriers required to transmit the PCC, and compare the outstanding number with a second number of remaining frequency subcarriers in a second symbol. Such processing may be repeated until the outstanding number of frequency subcarriers is less than the number of remaining frequency subcarriers in the symbol, after which the transmitter may perform the calculation of the distribution. Thus, as a previous step, the transmitter is arranged to iterate through preferably consecutive symbols, allocating all available frequency subcarriers in each symbol to the PCC if the symbol does not include enough available subcarriers to fully allocate the remaining unallocated portion of the PCC. It will be appreciated that the receivers set out herein may include the same features.

[0028] In one set of embodiments, the size of the matrix in the second dimension, e.g., the number of rows, is equal to the greatest common factor of the maximum number of frequency subcarriers available in a single OFDM symbol (e.g., omitting subcarriers excluded to provide guard bands) and the number of separate frequency subcarriers required for PCC. It follows that the size of the matrix in the first dimension is preferably equal to the number of remaining frequency subcarriers divided by the size of the matrix in the first dimension. In one set of exemplary embodiments, the maximum number of frequency subcarriers available in a single OFDM symbol (determined by the size of the fast Fourier transform module used) is 56, and the number of separate frequency subcarriers required for PCC is 98, so the size of the matrix in the second dimension, e.g., the number of rows, is equal to 14, which is the greatest common factor of 56 and 98.

[0029] In another set of embodiments, the size of the matrix in the second dimension, e.g. the number of rows, is equal to a common factor of the maximum number of frequency subcarriers available in a single OFDM symbol (e.g. omitting subcarriers excluded to provide a guard band) and the number of separate frequency subcarriers required for the PCC, wherein the common factor is preferably selected so that each group of subcarriers with adjacent frequencies allocated to the PCC comprises an even number of subcarriers. By selecting the common factor in this way, in certain embodiments using multiple transmit antennas, a transmit diversity scheme can be used to transmit the PCC, such as Alamouti transmit diversity. It may be beneficial for the radio channel responses of the two subcarriers used for such transmit diversity to be as similar as possible, and since the radio channel response depends on frequency, it follows that pairs of subcarriers used for transmit diversity preferably have adjacent frequencies. Therefore, the groups of subcarriers with adjacent frequencies allocated to the PCC preferably have an even size.

[0030] Again, it follows that the size of the matrix in the first dimension is preferably equal to the number of remaining frequency subcarriers divided by the size of the matrix in the first dimension. In one set of exemplary embodiments set forth above, the maximum number of frequency subcarriers available in a single OFDM symbol (determined by the size of the Fast Fourier Transform module employed) is 56, and the number of separate frequency subcarriers required for the PCC is 98, and the size of the matrix in the second dimension, e.g., the number of rows, is equal to a common factor of 7 of 56 and 98, wherein symbols for which not all available subcarriers are allocated to the PCC include 7 groups of even (e.g., pairs) of adjacent frequencies.

[0031] In one set of embodiments, the size of the matrix in the second dimension, e.g., the number of rows, is equal to an even number (e.g., half) of the greatest common factor of the maximum number of frequency subcarriers available in a single OFDM symbol (e.g., omitting subcarriers excluded to provide guard bands) and the number of separate frequency subcarriers required for PCC, provided that the greatest common factor is an even number. In the set of these exemplary embodiments, the maximum number of frequency subcarriers available in a single OFDM symbol (determined by the size of the fast Fourier transform module used) is 56, and the number of separate frequency subcarriers required for PCC is 98, so the size of the matrix in the second dimension, e.g., the number of rows, is equal to 7, which is the greatest common factor of 56 and 98 (i.e., 14) divided by 2.

[0032] Applicants further recognize that it is particularly advantageous to have the transmitter and receiver apply a common algorithm to determine the subcarrier allocation for the PCC because it allows the transmission to adapt to changes in the available subcarriers without having to store and maintain lookup tables in all devices. For example, the available subcarriers will typically change due to changes in the MIMO transmission mode that change the allocation of subcarriers for DRS, or even due to changes in the communication protocol, such as to accommodate a different number of effective antennas. As used herein, the term "effective antenna" is used to refer to a single antenna from the perspective of the receiver. For example, if a transmit signal is beamformed using multiple different antennas (by changing the amplitude and phase of the signal sent from each antenna), the number of effective antennas is one, even though multiple physical antennas are used, because the receiver cannot distinguish between the signals sent by the separate antennas.

[0033] The applicant has recognised that the concept of having a common algorithm that can generate PCC allocations in both the transmitter and the receiver without the need to calculate, allocate and store values ​​in all devices is novel and inventive in itself and therefore, when viewed from a third aspect, the present invention provides a method of operating an OFDM digital radio communications system comprising a transmitter and a receiver according to a predetermined communications protocol, the method comprising:

[0034] Calculating a distribution of frequency subcarriers for transmitting the PCC using a predetermined algorithm;

[0035] the transmitter transmits a data packet comprising a plurality of OFDM symbols, at least one of said symbols comprising a plurality of DRSs in a plurality of first frequency subcarriers of said symbol, the transmitter being further arranged to transmit said physical control channel in accordance with an allocation of said frequency subcarriers;

[0036] A receiver receives the packet, determines the distribution of the frequency subcarriers of the PCC using the predetermined algorithm, and decodes the packet using the distribution of the frequency subcarriers.

[0037] In one set of embodiments the transmitter is further arranged to transmit a physical data channel (PDC) distributed in the remaining sub-carriers not allocated to DRS or PCC, wherein the PCC comprises information required to decode the PDC.

[0038] The transmitter may be arranged to transmit the data packets using multiple antennas. Thus, the transmitter may be arranged to encode at least a portion of the data packets using at least one of spatial multiplexing, space-time transmit diversity, and space-time block coding multiple-input multiple-output (MIMO) modes. The transmitter may also be arranged to perform beamforming on at least a portion of the data packets. In one set of embodiments, the transmitter is arranged to transmit multiple sets of DRS, wherein a set of DRS is transmitted for each effective antenna used by the transmitter.

[0039] In one set of embodiments the transmitter is arranged to transmit a synchronization training field (STF) distributed among the plurality of sub-carriers in at least one OFDM symbol preceding a symbol comprising the plurality of frequency sub-carriers allocated to the DRS. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0041] Figure 1 is a schematic diagram showing a first radio communication system according to the present invention;

[0042] Figure 2 is a schematic diagram showing a second radio communication system according to the present invention;

[0043] Figure 3 is a schematic diagram of a first data packet structure according to the present invention;

[0044] Figure 4 It is shown Figure 5 , Figure 8 , Figure 9a and Figure 9b An illustration of the different subcarrier allocation types shown in ;

[0045] Figure 5 is a schematic diagram showing the final subcarrier allocation for transmitting a data packet using a single effective antenna and two sub-time slots;

[0046] Figure 6a and Figure 6b A flow chart indicating a process of allocating subcarriers to a physical control channel (PCC) by a transmitter in a radio system according to the present invention is shown;

[0047] Figure 7a is a simplified view of the process of filling an empty matrix with available subcarriers by a transmitter in a radio system according to the present invention;

[0048] Figure 7b is a simplified view of the process by which a transmitter in a radio system according to the present invention selects subcarriers allocated to a PCC;

[0049] Figure 8 contains various schematic diagrams showing subcarrier allocations determined by the transmitter 100 at various stages during the PCC subcarrier allocation process; and

[0050] Figure 9a and Figure 9b Various diagrams are included that illustrate subcarrier allocations determined by transmitter 110 at various stages during the PCC subcarrier allocation process. DETAILED DESCRIPTION

[0051] Figure 1 A first radio communication system is shown including a first digital radio transceiver 100 and a second digital radio transceiver 102. The first radio transceiver includes one antenna 104 and the second radio transceiver includes two antennas 106a and 106b. As will be well understood by those skilled in the art, many standard modules such as processors, oscillators, filters, amplifiers, digital-to-analog converters and analog-to-digital converters are provided in the radio transceivers 100, 102, but their description is omitted for brevity.

[0052] Figure 1 Also shown is a possible signal path 108 through each of its antennas 106a, 106b to the second transceiver 102 acting as a receiver through its antenna 104 when the first transceiver 100 is acting as a transmitter. As will be appreciated by those skilled in the art, the transmitter of the transceiver 100 may include more than one antenna, but simply operate using only a single antenna 104. It will also be appreciated that the transmitter of the transceiver 100 may include more than one antenna but utilize a multi-antenna transmission mode, such as beamforming, such that the multiple antennas act as a single effective antenna 104. The transceiver is configured to operate using OFDM modulation as is known in the art.

[0053] Figure 2 A similar second radio communication system is shown comprising a first digital radio transceiver 110 and a second digital radio transceiver 112. However, in this case, the first transceiver 110 comprises two antennas or effective antennas 114a and 114b and the second transceiver comprises three antennas or effective antennas 116a, 116b and 116c.

[0054] Figure 2 Also shown is a possible signal path 118 from the first transceiver 110 through its antennas 114a, 114b when it is acting as a transmitter to the second transceiver 112 acting as a receiver through each of its antennas 116a, 116b, 116c.

[0055] Figure 3 An example structure of a data packet 200 according to the present invention is shown. The data packet comprises: a synchronization training field (STF) 204, a data field (DF) 206 and a guard interval (GI) 202. The lower part of the figure shows each of these fields in more detail.

[0056] The STF 204 forms the initial portion of the packet 200 and includes seven repeating signal patterns 208 for the purpose of achieving synchronization between the transmitter of the first transceiver 100, 110 and the receiver of the second transceiver 102, 112 by allowing the receiver of the second transceiver 102, 112 to correct receiver gain, frequency and timing errors relative to the transmitter of the first transceiver 100, 110.

[0057] Following the STF 204 is the DF 206, which includes a plurality of data field symbols 212, each preceded by a cyclic prefix 210, for the purpose of conveying the payload of the packet 200. The DF 206 is transmitted using OFDM, providing the ability to dedicate different subcarrier frequencies to different signals / channels, as will be described below with reference to Figure 5 Explain in more detail.

[0058] Following the DF 206 is the GI 202 , which provides separation between consecutive packets 200 .

[0059] Figure 4 It is shown Figure 5 6, showing the different shading and their corresponding subcarrier allocation types. Shown are the guard / blank field 202, the synchronization training field (STF) 204, the physical control channel (PCC) 406, the demodulation reference signal (DRS) 408, the physical data channel (PDC) 410, and the available / unallocated subcarriers 412. In this example, the PCC 406, DRS 408, and PDC 410 constitute Figure 3 Data field 206 is shown.

[0060] DRS 408 refers to a signal allowing a receiver of the second transceiver 102, 112 to perform channel estimation; PDC 410 is a data channel including a payload of the data packet 200; and PCC 406 is a control channel including various information bits required to decode the data channel (PDC 410). Figure 5 does not include any available / unassigned subcarriers, but Figure 8 , Figure 9a and Figure 9b Available / unallocated subcarriers are indeed included since these figures illustrate the progression when the transmitter of the first transceiver 100, 110 performs subcarrier allocation.

[0061] In order to ensure that the data packet 200 is successfully received by the receiver of the second transceiver 102, 112, a separate reference signal is provided for each active transmit antenna used, so as to allow the receiver to perform channel estimation for each active transmit antenna.

[0062] Figure 5An example of a subcarrier allocation 400 for a data packet 200 when transmitted by a transmitter of the first transceiver 100 using a two sub-timeslot transmission is shown. The rows correspond to the subcarriers 302 available to the transmitter of the first transceiver 100. The number of each subcarrier 302 corresponds to the index of the subcarrier, with index 0 corresponding to the center subcarrier frequency. Figure 5 In the example given, there are 64 subcarriers 302 available for the transceiver 100, i.e. the transmitted data packet 200 has a Fast Fourier Transform (FFT) of size 64. The columns correspond to the time evolution of the symbols 304 transmitted by the transmitter 100. The number of each symbol 304 corresponds to the index of the symbol, with index 0 being the first symbol transmitted by the transmitter 100.

[0063] The guard allocation 306 corresponds to the allocation of the guard / blank field 202. The STF allocation 308 corresponds to the subcarrier allocation for transmitting the synchronization training field 204. The DRS allocation 310 corresponds to the subcarrier allocation for transmitting the demodulation reference signal 408 for a single space-time stream with an index of 0. The PCC allocation 320 corresponds to the subcarrier allocation for transmitting the physical control channel 406. The PDC allocation 322 corresponds to the subcarrier allocation for transmitting the physical data channel 408.

[0064] The transmission of STF 204 is completed at the end of symbol index 0, and the subsequent symbols are used to transmit the data field 206. DF 206 includes the initial transmission of DRS 408 and PCC 406, each of which is assigned to a different subcarrier. Figure 6a and Figure 6b The process of allocating PCC subcarriers according to the present invention is described in more detail.

[0065] After the transmission of the PCC 406, the transmitter of the first transceiver 100 transmits the PDC 410. The second set of DRS allocations 310 is transmitted one subslot after the transmission of the first set of DRS allocations 310 to allow the receiver to perform an up-to-date channel estimation. The subcarriers at the band edge: subcarriers -32 to -29 and 29 to 31 are allocated to the GF 202 (i.e., no data is transmitted on these subcarriers) to protect adjacent radio channels. The center subcarrier (index 0) is also allocated to the GI 202 due to DC offset issues.

[0066] Now refer to Figure 6a and Figure 6b The process of allocating subcarriers to the PCC 406 by the transmitter of the first transceiver 100, 110 is described in more detail. At step 500, as Figure 6aAs shown, the transmitter of the first transceiver 100, 110 allocates subcarriers to DRS 408 according to the number of transmit antennas used as specified by the protocol. The transmitter of the first transceiver 100, 110 is required to allocate a group of 14 DRS allocations 310, which are evenly spaced along the frequency spectrum of symbol 1 to provide DRS 408 for each effective antenna used. Therefore, if a single effective antenna is in use (i.e., the transmitter 100), then 14 subcarriers of symbol 1 will be used to transmit DRS 408. If two effective antennas are in use (i.e., the transmitter of the first transceiver 110), then 28 subcarriers of symbol 1 will be used to transmit DRS 408.

[0067] The transmitter of the first transceiver 100, 110 then proceeds to step 502, where it sets OFDM symbol 1 = 1. Since OFDM symbol 0 is used to transmit the STF 204, symbol 1 is the first symbol available for transmitting the PCC 406. The transmitter of the first transceiver 100, 110 also sets the number of unallocated PCC 406 subcarriers Because 98 subcarriers are required to transmit the PCC 406 as specified in the protocol. It will be appreciated that 1 and The starting values ​​of are not limited to 1 and 98 respectively, but can be any number.

[0068] The transmitter of the first transceiver 100, 110 then proceeds to step 504, where it selects available subcarriers in symbol 1. Available subcarriers are subcarriers in symbol 1 that are not allocated to GI 202 and DRS 408. The number of available subcarriers in symbol 1 is equal to U. The U available subcarriers in symbol 1 are then denoted by the following notations: k (0,l) ,k (1,l) …k (U-1,l) .

[0069] Next, the transmitter of the first transceiver 100, 110 proceeds to step 506, where it compares the number U of available subcarriers in symbol l with the number of unallocated PCC 406 subcarriers. For comparison. The transmitter of the first transceiver 100, 110 proceeds to step 508; if Then the transmitter of the first transceiver 100, 110 proceeds to step 512. At step 508, the transmitter of the first transceiver 100, 110 converts the group k of U available subcarriers in symbol l to (0,l) ,k (1,l) ,…,k (U-1,l) The group k added to the subcarriers allocated to the PCC 408 PCC .

[0070] The transmitter of the first transceiver 100, 110 then proceeds to step 510, where it increments the OFDM symbol l by 1, i.e. the transmitter of the first transceiver 100, 110 sets l=l+1. The transmitter of the first transceiver 100, 110 also sets the number of unallocated PCC 406 subcarriers Decrement U (ie, the transmitter setting of the first transceiver 100, 110) ), since U subcarriers have now been allocated to the PCC 406. The transmitter of the first transceiver 100, 110 then returns to step 504, where it again selects U subcarriers available in the new symbol l.

[0071] As mentioned above, if Then the transmitter of the first transceiver 100, 110 proceeds to Figure 6b Step 514 is shown. At step 14, the transmitter of the first transceiver 100, 110 generates a signal having R PCC The blank matrix of the row and set R PCC =7. Specific selection R PCC =7 will be discussed below Figure 8 , Figure 9a and Figure 9b Next, the transmitter of the first transceiver 100, 110 proceeds to step 516, where it calculates the number of columns C of the blank matrix. PCC Set to:

[0072]

[0073] Select C PCC This value makes the number of elements in the blank matrix N matr =R PCC ·C PCC is equal to the number U of available subcarriers in symbol l.

[0074] The transmitter of the first transceiver 100, 110 then proceeds to step 518, where it uses the U available subcarriers k (0,l) ,k (1,l) ,…,k (U-1,l) Fill the blank matrix as follows, starting at the top-left element of the matrix, moving from left to right, then moving down to the next row, filling each row from top to bottom, as Figure 7a This will become clearer with reference to the matrix below, which shows the order in which the U available subcarriers are entered into the matrix. The numbers shown in the matrix below represent the available subcarrier k in symbol l. (i,l) The index i, that is, for subcarrier k (0,l) ,k (1,l) ,…,k (U-i,l), i=0,1…U-1.

[0075]

[0076] The transmitter of the first transceiver 100, 110 then proceeds to step 520, where it selects the remaining elements from the matrix starting at the top left element and moving from top to bottom, moving from left to right column by column. PCC 408 subcarriers, such as Figure 7b shown.

[0077] The transmitter of the first transceiver 100, 110 proceeds to step 522, where it transmits the selected The group of subcarriers is added to the group k of subcarriers allocated to PCC 408. PCC At this point, all 98 required subcarriers have been allocated to PCC 408.

[0078] Finally, at step 524, the transmitter of the first transceiver 100, 110 maps the modulated data of the PCC 408 to a group k of PCC subcarriers starting from the lowest OFDM symbol index l and the lowest subcarrier index available for that symbol. PCC The transmitter of the first transceiver 100, 110 then fills the subcarriers in the OFDM symbol with increased subcarrier frequencies before proceeding to the next OFDM symbol, resulting in a symbol mapping order that is independent of the allocation order.

[0079] Figure 7a A simplified view of the process of the transmitter of the first transceiver 100, 110 filling the matrix with U available subcarriers is shown, and Figure 7b The transmitter of the first transceiver 100, 110 selects the remaining FIG. 4 is a diagram showing the processing of a PCC 408 subcarrier. Figure 7a The arrow 700 of shows the direction in which the transmitter of the first transceiver 100, 110 fills the matrix with U available subcarriers, and Figure 7b Arrow 702 shows that the transmitter of the first transceiver 100, 110 selects the remaining The direction of the PCC 408 subcarriers.

[0080] Those skilled in the art will appreciate that the transmitter of the first transceiver 100, 110 may execute in real time Figure 6a and Figure 6bThe PCC 406 subcarrier allocation process is shown. The transmitter of the first transceiver 100, 110 may perform this process before transmitting each data packet; or the transmitter of the first transceiver 100, 110 may perform this process only when the subcarrier allocation changes from one packet to the next (i.e., the number of DRS 408 changes between packets due to the transmitter of the first transceiver 100, 110 changing operating modes).

[0081] It is also necessary for the receiver of the second transceiver 102, 112 to know the subcarrier allocation used by the transmitter of the first transceiver 100, 110 for the PCC 406 in order to be able to decode the data packet 200. Therefore, those skilled in the art will understand that the receiver of the second transceiver 102, 112 will perform the same Figure 6a and Figure 6b to determine the same PCC 406 subcarrier allocation as the transmitter of the first transceiver 100, 110 to allow successful reception of the data packet 200. Information about the MIMO transmission mode (which allows the receiver to infer the DRS allocation) may be predetermined or communicated in another manner.

[0082] Figure 8 , Figure 9a and Figure 9b shows how the above-mentioned subcarrier allocation is established and all use the same Figure 4 The same subcarrier allocation types as those shown in the legend, Figure 4 The different shadings and their corresponding subcarrier allocation types are shown. Figure 4 2, a guard / blank field 202, a synchronization training field (STF) 204, a physical control channel (PCC) 406, a demodulation reference signal (DRS) 408, a physical data channel (PDC) 410, and available / unallocated subcarriers 412. The same reference numerals are used to represent Figure 8 , Figure 9a and Figure 9b Different subcarrier allocation types shown in . Figure 8 The various stages during the PCC subcarrier allocation process are shown in FIG. Figure 1 The transmitter of the first transceiver 100 determines the various subcarrier allocations. Figure 9a and Figure 9b The various stages involved during the PCC subcarrier allocation process are Figure 2 The transmitter of the first transceiver 110 determines the various subcarrier allocations.

[0083] exist Figure 8, the subcarrier allocation 800 is determined by the transmitter of the first transceiver 100 before step 500: the transmitter of the transceiver 100 has allocated subcarriers for transmitting the STF 204, and as outlined above, it has allocated subcarriers at the edges of the frequency band (indexes -32 to -29 and 29 to 31) and the center subcarrier (index 0) to the GF 202. As can be seen from the allocation 800, this means that in each OFDM symbol l=1 and l=2 there are a total of 64 subcarriers, of which 56 are available / unallocated subcarriers.

[0084] The subcarrier allocation 802 is determined by the transmitter of the first transceiver 100 after step 500, where it has allocated the necessary subcarriers to the DRS 408. Since there is only one effective antenna, 14 of the 56 available subcarriers in OFDM symbol l=1 are required. This means that U=42 subcarriers in OFDM symbol l=1 are now available for PCC 406 allocation (not for DRS 408). As previously described, the transmitter of the first transceiver 100 then sets OFDM symbol l=1 at step 502 and sets

[0085] because The transmitter of the first transceiver 100 proceeds to the first iteration of step 508 , resulting in a subcarrier allocation 804 : all available subcarriers in the OFDM symbol l=1 have been allocated to the PCC 406 by the transceiver 100 .

[0086] The transmitter of the first transceiver 100 then proceeds to step 510, where it sets l=l+1=2 and There are U=56 available allocations in OFDM symbol 2.

[0087] In the second iteration, due to The transmitter of the first transceiver 100 proceeds to step 514, where it creates a PCC =7 rows of blank matrix. The transmitter of the first transceiver 100 selects R PCC =7, because it is U=56 and The transmitter of the first transceiver 100 then calculates the number of columns at step 516 as:

[0088]

[0089] The transmitter of the first transceiver 100 then populates the matrix with U=56 available subcarriers in OFDM symbol l=2 using the process outlined previously at step 518 .

[0090] The transmitter of the first transceiver 100 then selects from the matrix using the process previously outlined at step 520 subcarriers. In this case, Therefore the transmitter of the first transceiver 100 selects each subcarrier in the matrix. The transmitter of the first transceiver 100 then adds the selected subcarriers to the PCC 406 allocation, giving a final subcarrier allocation 806.

[0091] Figure 9a and 9b Shows when Figure 2 A specific example of a step-by-step PCC 408 subcarrier allocation occurs when the transmitter of the first transceiver 110 (ie, the transmitter having two effective antennas) performs the above process each iteration.

[0092] exist Figure 9a , the subcarrier allocation 810 is determined by the transmitter of the first transceiver 110 before step 500: the transmitter of the first transceiver 110 has allocated subcarriers for transmitting the STF 204, and as outlined above, it has allocated subcarriers at the edges of the band (indexes -32 to -29 and 29 to 31) and the center subcarrier (index 0) to the GF 202. As can be seen from the allocation 810, this means that in each OFDM symbol l=1, l=2 and l=3 there are a total of 64 subcarriers, of which there are 56 available / unallocated subcarriers.

[0093] Subcarrier allocation 812 follows step 500, where the transmitter has allocated the necessary subcarriers to the DRS 408. Since there are two active antennas, 28 of the 56 available subcarriers in OFDM symbol l=1 are needed. This means that now U=28 subcarriers in OFDM symbol l=1 are available for PCC 406 allocation (not for DRS 408). As previously described, the transmitter of the first transceiver 110 then sets OFDM symbol l=1 at step 502 and sets

[0094] because The transmitter of the first transceiver 100 proceeds to the first iteration of step 508 . Figure 9b The subcarrier allocation 814 in is determined by the transmitter of the first transceiver 110 after the first iteration of step 508 : all available subcarriers in OFDM symbol l=1 have been allocated to the PCC 406 by the transmitter of the first transceiver 110 .

[0095] The transmitter of the first transceiver 110 then proceeds to step 510, where it sets l=l+1=2 and There are U=56 available allocations in OFDM symbol l=2.

[0096] In the second iteration, due to The transmitter of the first transceiver 110 again proceeds to step 508 . The subcarrier allocation 816 is determined by the transmitter of the first transceiver 110 after the second iteration of step 508 : all available subcarriers in OFDM symbol l=2 have been allocated to the PCC 406 by the transmitter of the first transceiver 110 .

[0097] The transmitter of the first transceiver 110 proceeds to step 510, where it sets l=l+1=3 and There are U=56 available allocations in OFDM symbol 1=3.

[0098] In the third iteration, due to The transmitter of the first transceiver 110 proceeds to step 512, then 514, where it creates a PCC =7 rows of blank matrix. The transmitter of the first transceiver 110 selects R PCC =7, because it is U=56 and The transmitter of the first transceiver 110 then calculates the number of columns at step 516 as:

[0099]

[0100] The transmitter of the first transceiver 110 then populates the matrix with U=56 available subcarriers in OFDM symbol l=3 using the process outlined previously at step 518 .

[0101] The transmitter of the first transceiver 110 then selects from the matrix using the process previously outlined in step 520 subcarriers. In this case, due to The transmitter of the first transceiver 110 selects 7 subcarriers in the first column of the matrix and selects 7 subcarriers in the second column of the matrix. The transmitter of the first transceiver 110 then adds the selected subcarriers to the PCC 406 allocation, giving a final subcarrier allocation 818. As shown in the subcarrier allocation 818, the result is that the PCC 406 is allocated to 7 pairs of available subcarriers 414, 416, 418, 420, 422, 424 and 426 in OFDM symbol l=3, with 6 unallocated subcarriers between each pair. Therefore, each group 414, 416, 418, 420, 422, 424 and 426 of subcarriers with adjacent frequencies allocated to the PCC includes an even number, in this case two subcarriers, so the PCC can use transmit diversity to transmit the PCC using pairs of subcarriers with adjacent frequencies and therefore similar radio channel responses, as is known in the art.

[0102] Therefore, those skilled in the art will appreciate that, by following the PCC 406 subcarrier allocation process according to the present invention, the transmitter of the first transceiver 100, 110 allocates subcarriers to the PCC 406 so that the subcarrier frequencies are evenly distributed throughout the bandwidth, enabling good gain to be achieved based on frequency selectivity and preventing narrowband interference.

Claims

1. An Orthogonal Frequency Division Multiplexing digital radio transmitter arranged to transmit a data packet comprising a plurality of Orthogonal Frequency Division Multiplexing symbols, at least one of said symbols comprising a plurality of demodulation reference signals in a plurality of first frequency subcarriers of said symbol, said transmitter further arranged to transmit a physical control channel at least partially distributed in the remaining frequency subcarriers of said symbol according to a calculated distribution, wherein The transmitter is arranged to calculate the distribution by: arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and allocating a plurality of second remaining frequency subcarriers to the physical control channel in sequence along the second dimension; The size of the matrix in the second dimension is equal to a common factor of the maximum number of frequency subcarriers available in a single orthogonal frequency division multiplexing symbol and the number of separate frequency subcarriers required for the physical control channel, so that each group of subcarriers with adjacent frequencies allocated to the physical control channel includes an even number of subcarriers.

2. An OFDM digital radio transmitter according to claim 1, arranged to order the frequency subcarrier indices along the second dimension.

3. An orthogonal frequency division multiplexing digital radio transmitter according to claim 1, arranged to: determine the total number of frequency subcarriers required to transmit the physical control channel, calculate a first number of remaining frequency subcarriers in a first symbol, compare the total number with the first number, and perform the calculation of the distribution only if the total number is less than the first number.

4. The OFDM digital radio transmitter according to claim 3, wherein: When the transmitter determines that the total number is greater than or equal to the first number, the transmitter is arranged to: allocate all of the first remaining frequency subcarriers to the physical control channel, subtract the first number from the total number to produce a pending number of frequency subcarriers required to transmit the physical control channel, and compare the pending number with a second number of remaining frequency subcarriers in a second symbol.

5. The OFDM digital radio transmitter according to claim 1, wherein: The size of the matrix in the second dimension is equal to an even integer divided by the greatest common factor of the maximum number of frequency subcarriers available in a single OFDM symbol and the number of separate frequency subcarriers required for the physical control channel.

6. The OFDM digital radio transmitter according to any one of claims 1 to 5, wherein: The size of the matrix in the second dimension is equal to 14.

7. The OFDM digital radio transmitter according to any one of claims 1 to 5, further arranged to transmit a physical data channel distributed in the remaining subcarriers not allocated to the demodulation reference signal or the physical control channel, wherein: The physical control channel includes information required to decode the physical data channel.

8. An OFDM digital radio transmitter according to any one of claims 1 to 5, arranged to use multiple effective antennas to transmit the data packets and to transmit multiple sets of demodulation reference signals, wherein: One of the plurality of sets of demodulation reference signals is transmitted for each corresponding active antenna used by the transmitter.

9. An OFDM digital radio transmitter according to any one of claims 1 to 5, arranged to transmit a synchronization training field distributed in multiple subcarriers in at least one OFDM symbol, the at least one OFDM symbol preceding a symbol comprising multiple frequency subcarriers allocated to the demodulation reference signal.

10. An Orthogonal Frequency Division Multiplexing digital radio receiver arranged to receive a data packet comprising a plurality of Orthogonal Frequency Division Multiplexing symbols, at least one of said symbols comprising a plurality of demodulation reference signals in a plurality of first frequency subcarriers of said symbol, said receiver further arranged to decode a physical control channel at least partially distributed in the remaining frequency subcarriers of said symbol according to a calculated distribution, wherein The receiver is arranged to calculate the distribution by: arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and allocating a plurality of second remaining frequency subcarriers to the physical control channel in sequence along the second dimension; The size of the matrix in the second dimension is equal to a common factor of the maximum number of frequency subcarriers available in a single orthogonal frequency division multiplexing symbol and the number of separate frequency subcarriers required for the physical control channel, so that each group of subcarriers with adjacent frequencies allocated to the physical control channel includes an even number of subcarriers.

11. A non-transitory computer-readable medium comprising instructions configured to cause a digital radio transmitter to transmit a data packet comprising a plurality of orthogonal frequency division multiplexed symbols, at least one of the symbols comprising a plurality of demodulation reference signals in a plurality of first frequency subcarriers of the symbol, the instructions further configured to cause the transmitter to transmit a physical control channel distributed at least partially in the remaining frequency subcarriers of the symbol according to a calculated distribution, wherein The instructions are configured to cause the transmitter to calculate the distribution by: arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and allocating a plurality of second remaining frequency subcarriers to the physical control channel in sequence along the second dimension; The size of the matrix in the second dimension is equal to a common factor of the maximum number of frequency subcarriers available in a single orthogonal frequency division multiplexing symbol and the number of separate frequency subcarriers required for the physical control channel, so that each group of subcarriers with adjacent frequencies allocated to the physical control channel includes an even number of subcarriers.

12. A non-transitory computer-readable medium comprising instructions configured to cause a digital radio receiver to receive a data packet comprising a plurality of orthogonal frequency division multiplexed symbols, at least one of the symbols comprising a plurality of demodulation reference signals in a plurality of first frequency subcarriers of the symbol, the instructions further configured to cause the receiver to decode a physical control channel at least partially distributed in remaining frequency subcarriers of the symbol according to a calculated distribution, wherein The instructions are configured to cause the receiver to calculate the distribution by: arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; and allocating a plurality of second remaining frequency subcarriers to the physical control channel in sequence along the second dimension; The size of the matrix in the second dimension is equal to a common factor of the maximum number of frequency subcarriers available in a single orthogonal frequency division multiplexing symbol and the number of separate frequency subcarriers required for the physical control channel, so that each group of subcarriers with adjacent frequencies allocated to the physical control channel includes an even number of subcarriers.

13. A method for allocating physical control channels to frequency subcarriers of orthogonal frequency division multiplexing symbols in an orthogonal frequency division multiplexing digital radio transmission system, the method comprising: determining a plurality of first frequency subcarriers allocated to a demodulation reference signal; Determining remaining frequency subcarriers of the frequency subcarriers of the symbol: Arranging the remaining frequency subcarriers in a two-dimensional matrix such that the remaining frequency subcarriers have consecutive indices in a first dimension and have a common increment in a second dimension; allocating a plurality of second remaining frequency subcarriers to the physical control channel in sequence along the second dimension; as well as recording said allocation of frequency subcarriers to said physical control channel; The size of the matrix in the second dimension is equal to a common factor of the maximum number of frequency subcarriers available in a single orthogonal frequency division multiplexing symbol and the number of separate frequency subcarriers required for the physical control channel, so that each group of subcarriers with adjacent frequencies allocated to the physical control channel includes an even number of subcarriers.

14. A method of operating an orthogonal frequency division multiplexing digital radio communication system including a transmitter and a receiver according to a predetermined communication protocol, the method comprising: Using a predetermined algorithm to calculate a distribution of frequency subcarriers for transmitting a physical control channel; the transmitter transmitting a data packet comprising a plurality of orthogonal frequency division multiplexed symbols, at least one of the symbols comprising a plurality of demodulation reference signals in a plurality of first frequency subcarriers of the symbol, the transmitter being further arranged to transmit the physical control channel in accordance with a distribution of the frequency subcarriers; The receiver receives the packet, uses the predetermined algorithm to determine a distribution of the frequency subcarriers of the physical control channel, and uses the distribution of the frequency subcarriers to decode the packet.

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