Transmission device, wireless communication system, transmission method, control circuit, and storage medium

Abstract

A transmission device (100) provided in a base station of a wireless communication system configured to include a plurality of base stations comprises: a modulation unit (10) that modulates a transmission bit sequence to generate a modulated symbol; a differential block coding unit (11) that differential block codes the modulated symbol to generate a differential block coded signal; and a precoding unit (12) that executes precoding processing including phase rotation on the differential block coded signal. The precoding unit (12) phase-rotates the differential block coded signal by a phase rotation amount different from that of phase rotation included in precoding processing executed by a precoding unit of a transmission device provided in another base station adjacent to the base station in which the transmission device is provided.

Description

Transmitting device, wireless communication system, transmission method, control circuit, and storage medium

[0001] This disclosure relates to a transmitting device, a wireless communication system, a transmitting method, a control circuit, and a storage medium.

[0002] In wireless communication, diversity technology is sometimes applied to prevent a decrease in communication performance due to fading. For example, in spatiotemporal block coding wireless communication, which is a type of transmit diversity, the transmitting device performs spatiotemporal block coding on the transmission sequence to generate multiple orthogonal sequences. The transmitting device then transmits these multiple sequences using different antennas. In spatiotemporal block coding wireless communication, full diversity gain can be obtained at the receiving end.

[0003] In spatiotemporal block coding wireless communication (hereinafter simply referred to as "spatiotemporal block coding"), multiple symbols are treated as a single transmission block. Generally, in spatiotemporal block coding, the number of antennas is associated with the number of symbols treated as a single transmission block. For example, in spatiotemporal block coding with two antennas, two symbols are treated as one transmission block. A receiver in spatiotemporal block coding needs to estimate the transmission path information in order to demodulate the received spatiotemporal block coding symbols.

[0004] Furthermore, there is a differential block coding scheme that performs differential coding on a per-transmission block basis in spatiotemporal block coding, which allows for the use of diversity effects through spatiotemporal block coding and eliminates the need to estimate transmission path information. For example, in a differential block coding scheme with two antennas, the transmitting device generates a 2x2 matrix with two symbols as one transmission block and performs differential coding between the matrices of two consecutive transmission blocks. The receiving device generates a 2x2 matrix with the two received symbols and performs demodulation by performing differential decoding between the two matrices (see Non-Patent Literature 1).

[0005] V. Tarokh and H. Jafarkhani, "A Differential Detection Scheme for Transmit Diversity," IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 18, NO. 7, JULY 2000.

[0006] When constructing a wireless communication system by installing a plurality of base stations, it is desirable to arrange each base station so that an area where the base station and the mobile station cannot communicate does not occur. In this case, at a location where communication areas, which are areas where each base station and the mobile station can communicate, overlap, there is a problem that the same signal at the same frequency transmitted from each base station reaches the mobile station in a state where they are combined with equal power and opposite phases, that is, so-called beat interference occurs where the power of the signal received by the mobile station decreases, and the communication performance deteriorates.

[0007] The present disclosure has been made in view of the above, and an object thereof is to obtain a transmission device capable of suppressing the occurrence of beat interference in a wireless communication system.

[0008] In order to solve the above-described problems and achieve the object, the present disclosure is a transmission device included in a base station of a wireless communication system including a plurality of base stations, the transmission device including: a modulation unit that modulates a transmission bit sequence to generate a modulation symbol; a differential block encoding unit that differentially block-encodes the modulation symbol to generate a differentially block-encoded signal; and a precoding unit that performs a precoding process including a phase rotation on the differentially block-encoded signal, wherein the precoding unit phase-rotates the differentially block-encoded signal with a phase rotation amount different from the phase rotation included in the precoding process performed by the precoding unit of a transmission device included in another base station adjacent to the base station provided with the own transmission device.

[0009] The transmission device according to the present disclosure has an effect that it can suppress the occurrence of beat interference in a wireless communication system.

[0010] Diagram showing a configuration example of the wireless communication system according to Embodiment 1, diagram showing a configuration example of the transmission device included in the base station according to Embodiment 1, flowchart showing an example of the operation of the transmission device included in the base station according to Embodiment 1, diagram showing an example of the precoding process by the precoding unit of the transmission device according to Embodiment 1, diagram showing a configuration example of the wireless communication system according to Embodiment 2, diagram showing a configuration example of the processing circuit when the processing circuit included in the transmission device according to Embodiments 1 and 2 is realized by a processor and a memory, diagram showing an example of the processing circuit when the processing circuit included in the transmission device according to Embodiments 1 and 2 is configured by dedicated hardware

[0011] Hereinafter, a transmission device, a wireless communication system, a transmission method, a control circuit, and a storage medium according to an embodiment of the present disclosure will be described in detail based on the drawings.

[0012] Embodiment 1. FIG. 1 is a diagram showing a configuration example of a wireless communication system 200 according to Embodiment 1. The wireless communication system 200 according to the present embodiment includes a control device 1 that controls a group of base stations, a base station 2 that covers a communication area 2a, a base station 3 that covers a communication area 3a, and a mobile station 4.

[0013] In the wireless communication system 200 shown in FIG. 1, the frequency of the signal transmitted by the base station 2 and the frequency of the signal transmitted by the base station 3 are the same. Also, a part of the communication area 2a of the base station 2 and the communication area 3a of the base station 3 overlap. In FIG. 1, as an example, a case is shown where the mobile station 4 exists in an area where the communication area 2a and the communication area 3a overlap, and the mobile station 4 can communicate with both the base station 2 and the base station 3.

[0014] The two base stations, the base station 2 and the base station 3, wirelessly transmit a transmission bit sequence, which is information received from the control device 1, based on the control from the control device 1. It is assumed that the base station 2 and the base station 3 receive the same transmission bit sequence from the control device 1 at the same timing.

[0015] The mobile station 4 receives the information transmitted from the base station 2 and the base station 3.

[0016] Here, base stations 2 and 3 transmit signals in synchronization. For example, base stations 2 and 3 transmit signals in synchronization based on GPS (Global Positioning System) time information. However, the method of synchronization between base stations 2 and 3 is not limited to this. For example, the control device 1 may transmit a synchronization signal to base stations 2 and 3, and base stations 2 and 3 may transmit signals in synchronization based on this signal.

[0017] Under the conditions described above, if base stations 2 and 3 transmit the same information as signals, at the location of mobile station 4 shown in Figure 1, the transmitted signals from base station 2 and base station 3 are attenuated by the same amount due to radio wave propagation, resulting in the same received power at the same time and being received at the antenna terminal of mobile station 4. This phenomenon, known as beat interference, occurs.

[0018] In Figure 1, the wireless communication system 200 is configured to include two base stations (base station 2 and base station 3) and one mobile station 4, but the number of base stations and mobile stations is not limited to this.

[0019] Figure 2 shows an example of the configuration of a transmitting device 100 provided by base stations 2 and 3 according to Embodiment 1. As shown in Figure 2, the transmitting device 100 according to this embodiment includes a modulation unit 10 that maps a sequence of transmitted bits onto the complex plane as modulation symbols, a differential block coding unit 11 that performs differential block coding on the modulation symbols and generates a differential block coded signal, and a precoding unit 12 that performs precoding processing with weighting and phase rotation on the differential block coded signal generated by the differential block coding unit 11. The transmitting device 100 also includes a transmission filter unit 13a that performs filtering processing for bandwidth limiting corresponding to a first transmitting antenna on the differential block coded signal precoded by the precoding unit 12, a transmission filter unit 13b that performs filtering processing for bandwidth limiting corresponding to a second transmitting antenna, a digital-to-analog conversion unit 14a that performs digital-to-analog conversion on the signal bandwidth limited by the transmission filter unit 13a, and a digital-to-analog conversion unit 14b that performs digital-to-analog conversion on the signal bandwidth limited by the transmission filter unit 13b. Furthermore, the transmitting device 100 includes a high-frequency unit 15a that modulates the analogized transmission signal by the digital-to-analog conversion unit 14a to the carrier frequency, a high-frequency unit 15b that modulates the analogized transmission signal by the digital-to-analog conversion unit 14b to the carrier frequency, a transmitting antenna 16a that transmits the high-frequency signal output from the high-frequency unit 15a, and a transmitting antenna 16b that transmits the high-frequency signal output from the high-frequency unit 15b.

[0020] Next, the processing of the precoding unit 12 of the transmitting device 100 will be explained. The precoding unit 12 performs the precoding processing shown in the following equations (1) and (2) on the differential block coded signal generated by the differential block coding unit 11.

[0021] y1(t) = w 11 ・θ1t・x1(t)+w 12 ・θ2t・x2(t) …(1) y2(t)=w 21 ・θ1t・x1(t)+w 22 ・θ2t・x2(t) …(2)

[0022] In equations (1) and (2), y1(t) and y2(t) represent signals corresponding to the first transmission antenna and the second transmission antenna in the output of the precoding unit 12. w 11 , w 12 , w 21 , w 22 represent weight coefficients for creating mixed components of the precoding output between the transmission antennas 16a and 16b. θ1t and θ2t represent phase rotation values of the first transmission antenna and the second transmission antenna. x1(t) and x2(t) represent signals corresponding to the first transmission antenna and the second transmission antenna in the input to the precoding unit 12.

[0023] Here, the weight coefficients w 11 , w 12 , w 21 , w 22 are weight coefficients for mixing and outputting the signal component transmitted from the first transmission antenna and the signal component transmitted from the second transmission antenna, and w 11 + w 12 = 1 and w 21 + w 22 = 1 are set under the constraint.

[0024] In this embodiment, for simplicity of explanation, w 11 = 1, w 12 = 0, w 21 = 0, w 22 = 1, and it is assumed that there is no component mixing between the transmission antennas 16a and 16b, and the following explanation will continue. In this case, the above equations (1) and (2) are simplified to equations (3) and (4).

[0025] y1(t) = θ1t · x1(t) … (3) y2(t) = θ2t · x2(t) … (4)

[0026] As shown in equations (3) and (4), the precoding process by the precoding unit 12 is a process that applies a phase rotation at fixed time intervals t. The resolution of t may be the unit of modulation symbols before differential block coding, a finer resolution (e.g., the unit of samples), or a coarser resolution (e.g., every block of differential block coding, every two blocks, etc.). In other words, the phase rotation may be applied in units of modulation symbols before differential block coding, in units of samples, or in units that are integer multiples of the blocks on which differential block coding is performed.

[0027] The y1(t) corresponding to the first transmitting antennas of base station 2 and base station 3 are respectively y 1a (t) and y 1b (t) The propagation channel information from the first transmitting antennas of base stations 2 and 3 to the receiving antenna of mobile station 4 is h 1a (t) and h 1b If (t) is the case, the received signal r1(t) of the mobile station 4 corresponding to the first transmitting antenna of each base station can be expressed as shown in equation (5) below.

[0028] r1(t) = h 1a (t)・y 1a (t) + h 1b (t)・y 1b (t) = (h 1a (t)・θ 1a t+h 1b (t)・θ 1b t)・x1(t) …(5)

[0029] Condition without precoding (θ 1a t = θ 1b At t=1), the propagation channel information between each base station and the mobile station 4 is in reverse phase (h 1a (t) = -h 1b At the point in (t), the transmitted information is lost. In environments where propagation channel information changes rapidly over time, the conditions under which the transmitted information is lost are limited. However, for example, if the mobile station 4 is in a stopped state and the propagation channel information is fixed, and the conditions under which the transmitted information is lost occur, a communication interruption will occur.

[0030] On the other hand, when precoding, h 1a (t)・θ 1a t = -h 1b (t)・θ 1b Under the condition t, the transmitted information disappears, but θ 1a t and θ 1b Since t is a value that changes over time due to precoding processing at each base station, it is possible to avoid a situation in which transmitted information is continuously lost, regardless of the communication environment of mobile station 4.

[0031] If we organize the above similarly for the second transmitting antenna, h 2a (t)・θ 2a t = -h 2b (t)・θ 2b Since the transmission information from the second transmitting antenna disappears under the condition t, when combined with the first transmitting antenna, h 1a (t)・θ 1a t = -h 1b (t)・θ 1b t katsuh 2a (t)・θ 2a t = -h 2b (t)・θ 2b The goal of precoding is to minimize the occurrence of conditions that result in t, which is the phase rotation value θ. 1a t, θ 1b t, θ 2a t, θ 2b This will be the key point when determining t.

[0032] The phase rotation value should be determined with two constraints: the first constraint is that the direction (positive or negative) of the phase rotation should be reversed between transmitting antennas 16a and 16b, and the second constraint is that different phase rotation values ​​should be used for each antenna transmitting the same information between base stations whose communication areas overlap. In other words, the phase rotation value θ 1a t, θ 1b t, θ 2a t, θ 2b For business, θ 1a t and θ 1b t means reversing the direction of phase rotation, and θ 2a t and θ 2b t means reversing the direction of phase rotation, and θ 1at≠θ 1b Let t be θ 2a t≠θ 2b Setting the phase rotation value to t is a condition for setting each phase rotation value.

[0033] In a transmitted signal subjected to transmission diversity processing using differential block coding, the receiving device (in this embodiment, the mobile station 4) can extract information from the received signal as long as the transmission information from either the first or second transmitting antenna is not lost. Therefore, in order to minimize the chances of the conditions for the loss of transmission information from the first or second transmitting antenna being the same, it is necessary to reduce the correlation between the signals of transmitting antennas 16a and 16b by "reversing the direction (positive or negative) of phase rotation between transmitting antennas 16a and 16b." In addition, since it is essential that the first and second transmitting antennas do not transmit the same information between base stations, it is important to "use different phase rotation values ​​for each antenna transmitting the same information between adjacent base stations whose communication areas overlap." Note that it is not essential to operate with fixed values ​​for the precoding matrix settings; for example, the mobile station 4 could specify (notify) the setting values ​​to each base station, and the settings could be changed according to the communication environment of the mobile station 4. Furthermore, when setting the precoding matrix for each base station, some base stations may not add any phase rotation values ​​at all.

[0034] Figure 3 is a flowchart showing an example of the operation of the transmitting devices 100 provided by base stations 2 and 3 according to Embodiment 1. Figure 3 shows the processing flow for one communication frame, which is commonly used as a processing unit in a communication system.

[0035] After processing begins, the transmitting device 100 first generates a modulation symbol (step S11). Specifically, the modulation unit 10 generates a modulation symbol by performing modulation processing on the transmission bit sequence, which is the transmission information.

[0036] The transmitting device 100 then performs differential block coding (step S12). Specifically, the differential block coding unit 11 performs differential block coding on the modulation symbols output from the modulation unit 10.

[0037] The transmitting device 100 then updates the precoding matrix and performs precoding (steps S13 and S14). Specifically, the precoding unit 12 updates the precoding matrix and uses the updated precoding matrix to perform precoding on the differential block coded signal output from the differential block coding unit 11.

[0038] Next, the transmitting device 100 performs filtering and other processing on the signal generated by the precoding process before transmitting it (step S15). Specifically, the transmitting filter units 13a and 13b filter the signal output from the precoding unit 12, the digital-to-analog conversion units 14a and 14b perform digital-to-analog conversion, the high-frequency units 15a and 15b perform frequency conversion to the carrier frequency, and the transmitting antennas 16a and 16b transmit the signal at the carrier frequency.

[0039] Next, the transmitting device 100 checks whether the transmission of one frame has been completed, that is, whether the transmission of the transmission bit sequence for one frame has been completed (step S16). If the transmission of one frame has been completed (step S16: Yes), the process ends. If the transmission of one frame has not been completed (step S16: No), the transmitting device 100 returns to step S11 and repeats the process from steps S11 to S16.

[0040] Note that Figure 3 shows an example in which a series of processes are looped in units of precoding matrix updates (the period during which the precoding matrix is ​​updated), but the system is not limited to this configuration. The transmitting device 100 may be configured to process each process by each component in a single frame. In other words, even if each process by each component is not looped, it is acceptable as long as the signal processing is equivalent to the process shown in the flowchart of Figure 3.

[0041] Figure 4 shows an example of precoding processing by the precoding unit 12 of the transmitting device 100 according to Embodiment 1. In Figure 4, the image of the precoding processing is represented using the complex plane.

[0042] Figure 4 visually shows examples of phase rotation amounts over three processing times on a complex plane, illustrating the precoding process for each transmitting antenna of base station 2 and base station 3 over three processing times. As shown in Figure 4, the precoding unit 12 performs a phase rotation by a positive phase rotation amount θ1 every processing time when precoding the signal transmitted from the first transmitting antenna of base station 2 (differential block coded signal), and a phase rotation by a negative phase rotation amount θ2 every processing time when precoding the signal transmitted from the second transmitting antenna. Furthermore, the precoding unit 12 performs a phase rotation by a positive phase rotation amount φ1 every processing time when precoding the signal transmitted from the first transmitting antenna of base station 3, which is different from the precoding corresponding to the first transmitting antenna of base station 2, and performs a phase rotation by a negative phase rotation amount φ2 every processing time when precoding the signal transmitted from the second transmitting antenna, which is different from the precoding corresponding to the second transmitting antenna of base station 2.

[0043] In this embodiment, for the sake of simplicity, an example was described in which the communication areas of two base stations partially overlap. However, even when the communication areas of three or more base stations partially overlap, the pre-coding process rotates the transmitted signal by a different phase rotation amount for each base station. For example, if there is an area where one mobile station can communicate simultaneously with three base stations (an area where three communication areas overlap), the transmitting devices 100 of each of the three base stations rotate the transmitted signal by a different phase rotation amount during the pre-coding process. Furthermore, although the case where the transmitting device 100 has two transmitting antennas was described, the number of transmitting antennas may be three or more. Similarly, even when the number of transmitting antennas is three or more, the pre-coding process rotates the transmitted signal by a different phase rotation amount for each transmitting antenna.

[0044] As described above, the transmitting device 100 according to this embodiment is applied to two or more base stations that perform the same modulation processing and the same differential block coding processing on the same transmission bit sequence and transmit the transmission signal simultaneously. In the precoding process after the differential block coding processing, the phase rotation is performed by a different amount for each antenna that transmits the same transmission signal for each base station. This makes it possible to suppress the occurrence of beat interference in the wireless communication system 200 and improve communication quality. In other words, it is possible to avoid a situation in which the transmission signal is continuously canceled out due to beat interference at the antenna terminal of the mobile station 4 that receives transmission signals from two or more base stations simultaneously, thereby improving communication quality.

[0045] Embodiment 2. Figure 5 shows an example of the configuration of the wireless communication system 201 according to Embodiment 2.

[0046] The wireless communication system 201 according to this embodiment includes a control device 41 for controlling a group of base stations, a base station 42 covering a communication area 42a, a base station 43 covering a communication area 43a, a base station 44 covering a communication area 44a, a base station 45 covering a communication area 45a, a base station 46 covering a communication area 46a, and a mobile station 47.

[0047] In the wireless communication system 201 shown in Figure 5, the frequencies of the signals transmitted by each of the base stations 42 to 46 are the same. Also, there is some overlap between the communication area 42a of base station 42 and the communication area 43a of base station 43. Similarly, there is some overlap between the communication area 43a and the communication area 44a, some overlap between the communication area 44a and the communication area 45a, and some overlap between the communication area 45a and the communication area 46a. Under these conditions, the mobile station 47 moves between areas in the following order: from the communication area 42a of base station 42, to the communication area 43a of base station 43, to the communication area 44a of base station 44, to the communication area 45a of base station 45, to the communication area 46a of base station 46, or from the communication area 46a of base station 46, to the communication area 45a of base station 45, to the communication area 44a of base station 44, to the communication area 43a of base station 43, and to the communication area 42a of base station 42.

[0048] Communication between the control device 41 and each base station (base stations 42 to 46) is the same as in Embodiment 1. Furthermore, the process and procedure for generating a transmission signal from the transmission bit sequence at each base station are the same as in Embodiment 1. That is, base stations 42 to 46 are equipped with the transmission device 100 described in Embodiment 1. Therefore, a detailed explanation of the operation of the control device 41 and base stations 42 to 46 is omitted.

[0049] Even under conditions such as those shown in this embodiment, where multiple base stations are synchronized and each base station transmits the same transmission information, the phase rotation value of the precoding matrix can be set according to the same constraints as in Embodiment 1, thereby avoiding situations in which beat interference continuously occurs.

[0050] In this embodiment, there are many base stations, and a different phase rotation value for the precoding matrix is ​​set for each base station. However, other setting methods may be applied. Another effective setting method is to set the phase rotation value of the precoding matrix to a different value for adjacent base stations whose communication areas overlap, while setting the same phase rotation value for the next adjacent base station (a non-adjacent base station two base stations away, for example, base station 44 relative to base station 42 in Figure 5). That is, in the wireless communication system 201 shown in Figure 5, base stations 42, 44, and 46 may set the phase rotation value of the precoding matrix to the same value (first value), while base stations 43 and 45 may set the phase rotation value of the precoding matrix to a different value (second value) (base stations 43 and 45 have the same setting value).

[0051] As described above, the wireless communication system 201 according to this embodiment sets the phase rotation amount (phase rotation value of the precoding matrix) in the precoding process to different values ​​for adjacent base stations (base stations whose communication areas partially overlap), and sets the phase rotation amount in the precoding process to the same value for non-adjacent base stations. According to this embodiment, similar to Embodiment 1, by preparing phase rotation values ​​for the precoding matrix for two base stations, it is possible to cover a very wide communication area while obtaining the same effects as Embodiment 1, namely, interference countermeasures against beat interference between base stations.

[0052] Next, the hardware configuration of the transmitting device 100 described above will be explained. In the transmitting device 100, the transmitting filter sections 13a, 13b, the digital-to-analog conversion sections 14a, 14b, the high-frequency sections 15a, 15b, and the transmitting antennas 16a, 16b are implemented by the transmitter. In the transmitting device 100, the other components, namely the modulation section 10, the differential block coding section 11, and the precoding section 12, are implemented by the processing circuit. The processing circuit may be a processor and memory that execute a program stored in memory, or it may be dedicated hardware. The processing circuit is also called a control circuit.

[0053] Figure 6 shows an example configuration of a processing circuit 90 when the processing circuit of the transmitting device 100 according to Embodiments 1 and 2 is implemented using a processor and memory. The processing circuit 90 shown in Figure 6 includes a processor 91 and a memory 92. Each function of the processing circuit 90, which is composed of the processor 91 and the memory 92, is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 92. In the processing circuit 90, each function is realized by the processor 91 reading and executing the program stored in the memory 92. That is, the processing circuit 90 includes a memory 92 for storing a program that will result in the processing of the transmitting device 100 being executed. This program can also be said to be a program that causes the transmitting device 100 to execute each function realized by the processing circuit 90. This program may be provided by a storage medium on which the program is stored, or by other means such as a communication medium.

[0054] Here, the processor 91 is, for example, a CPU (Central Processing Unit), processing unit, arithmetic unit, microprocessor, microcomputer, or DSP (Digital Signal Processor). The memory 92 is, for example, a non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), EEPROM (Registered Trademark) (Electrically EPROM), magnetic disk, flexible disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0055] Figure 7 shows an example of a processing circuit 93 when the processing circuit of the transmitting device 100 according to Embodiments 1 and 2 is configured with dedicated hardware. The processing circuit 93 shown in Figure 7 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The processing circuit of the transmitting device 100 may be partially implemented with dedicated hardware and partially implemented with software or firmware. In this way, the processing circuit can realize the above-mentioned functions with dedicated hardware, software, firmware, or a combination thereof.

[0056] The configurations shown in the above embodiments are examples only, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention.

[0057] 1, 41 Control device, 2, 3, 42-46 Base station, 2a, 3a, 42a-46a Communication area, 4, 47 Mobile station, 10 Modulation unit, 11 Differential block coding unit, 12 Precoding unit, 13a, 13b Transmitting filter unit, 14a, 14b Digital-to-analog conversion unit, 15a, 15b High-frequency unit, 16a, 16b Transmitting antenna, 100 Transmitting device, 200, 201 Wireless communication system.

Claims

1. A transmitting device provided in a base station of a wireless communication system comprising a plurality of base stations, comprising: a modulation unit that modulates a transmission bit sequence to generate a modulation symbol; a differential block coding unit that differentially blocks encodes the modulation symbol to generate a differential block coded signal; and a precoding unit that performs a precoding process including phase rotation on the differential block coded signal, wherein the precoding unit phase-rotates the differential block coded signal by a phase rotation amount different from the phase rotation included in the precoding process performed by the precoding unit of a transmitting device provided in another base station adjacent to the base station where the self-transmitting device is installed.

2. The transmitting device according to claim 1, characterized in that the precoding unit rotates the phase of the differential block coded signal transmitted from each of the plurality of transmitting antennas by a different phase rotation amount for each transmitting antenna.

3. The transmitting device according to claim 2, characterized in that the precoding unit rotates the phase of the differential block coded signal at intervals of integer multiples of the modulation symbol.

4. The transmitting device according to claim 2, characterized in that the precoding unit rotates the phase of the differential block coded signal on a sample-by-sample basis.

5. The transmitting apparatus according to any one of claims 1 to 4, wherein the precoding process further includes a weighting process that mixes the components of the differential block coded signal transmitted from each of the plurality of transmitting antennas.

6. The transmitting device according to any one of claims 1 to 5, characterized in that the amount of phase rotation when the precoding unit rotates the differential block coded signal is changed according to a specification from the mobile station.

7. A wireless communication system comprising a plurality of base stations each equipped with a transmitting device according to any one of claims 1 to 6, wherein the amount of phase rotation included in the precoding process performed by the precoding unit of the transmitting device provided at non-adjacent base stations is the same.

8. A transmission method for a base station of a wireless communication system comprising multiple base stations to transmit a transmission bit sequence, comprising: a modulation step of modulating the transmission bit sequence to generate a modulation symbol; a differential block coding step of differentially block coding the modulation symbol to generate a differential block coded signal; and a precoding step of performing a precoding process including phase rotation on the differential block coded signal, wherein in the precoding step, the differential block coded signal is phase-rotated by a different amount of phase rotation than that included in the precoding process performed by a transmission device of another base station adjacent to the base station where the self-transmitting device is provided.

9. A control circuit comprising a transmitting device of a base station in a wireless communication system comprising a plurality of base stations, the control circuit comprising: a modulation step of modulating a transmission bit sequence to generate a modulation symbol; a differential block coding step of differentially block coding the modulation symbol to generate a differential block coded signal; and a precoding step of performing a precoding process including phase rotation on the differential block coded signal, wherein in the precoding step, the differential block coded signal is phase-rotated by a phase rotation amount different from the phase rotation included in the precoding process performed by a transmitting device of another base station adjacent to the base station where the self-transmitting device is provided.

10. A storage medium for storing a program executed by a control circuit constituting a transmitting device of a base station in a wireless communication system comprising a plurality of base stations, wherein the program causes the control circuit to execute: a modulation step of modulating a transmission bit sequence to generate a modulation symbol; a differential block coding step of differentially block coding the modulation symbol to generate a differential block coded signal; and a precoding step of executing a precoding process including phase rotation on the differential block coded signal, wherein in the precoding step, the differential block coded signal is phase-rotated by a phase rotation amount different from the phase rotation included in the precoding process executed by a transmitting device of another base station adjacent to the base station where the self-transmitting device is provided.

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