Method, sa terminal and communication system for transmitting uplink data packets

Abstract

The present disclosure provides a method, a SA terminal and a communication system for transmitting uplink data packets. The method for transmitting uplink data packets comprises: searching, by a SA base station, n secondary link (SA) terminals whose load under a current cell is less than a preset threshold, n being a natural number greater than 1; establishing a communication link with the n SA terminals respectively; and transmitting, in a downlink time slot of a first frequency point, an i-th uplink data block to an i-th SA terminal through a second frequency point in sequence, wherein the i-th uplink data block comprises at least part of the uplink data packets, so that the i-th SA terminal transmits the i-th uplink data block to the SA base station in an uplink time slot of the first frequency point. The present disclosure can effectively improve the communication capability between the SA terminal and the SA base station, thereby effectively improving the user experience.

Description

Technical Field

[0001] This disclosure relates to the field of communications, and in particular to a method for sending uplink data packets, an SA terminal, and a communication system. Background Technology

[0002] Currently, in 5G SA (Standalone) communication, SA terminals and SA base stations use a single-link communication method. Summary of the Invention

[0003] The inventors noted that in 5G SA communication, because the communication capability (especially the uplink capability) is limited due to the single-link communication method between the SA terminal and the SA base station, the 5G SA user experience is severely affected.

[0004] Therefore, this disclosure provides an uplink data transmission method based on multi-link cooperation, thereby effectively improving the user experience.

[0005] According to a first aspect of the present disclosure, a method for sending uplink data packets is provided, executed by a primary link SA terminal, comprising: searching for n secondary link SA terminals in the current cell whose load is less than a preset threshold through an SA base station, where n is a natural number greater than 1; establishing communication links with the n secondary link SA terminals respectively; and sequentially sending the i-th uplink data block to the i-th secondary link SA terminal through a second frequency point in a downlink time slot at a first frequency point, wherein the i-th uplink data block includes at least a portion of the uplink data packet, so that the i-th secondary link SA terminal sends the i-th uplink data block to the SA base station in the uplink time slot at the first frequency point, where 1 ≤ i ≤ n.

[0006] In some embodiments, among the n secondary link SA terminals, at least one secondary link SA terminal is located at a distance less than the distance between the primary link SA terminal and the SA base station.

[0007] In some embodiments, the uplink data packet is divided into n uplink data blocks, and any two uplink data blocks are different.

[0008] In some embodiments, each uplink data block is the same as the uplink data packet.

[0009] In some embodiments, the (n+1)th uplink data block is sent to the SA base station in the uplink time slot of the first frequency point, wherein the (n+1)th uplink data block includes at least a portion of the uplink data packet.

[0010] In some embodiments, the uplink data packet is divided into n+1 uplink data blocks, and any two uplink data blocks are different.

[0011] In some embodiments, each uplink data block is the same as the uplink data packet.

[0012] In some embodiments, downlink data packets sent by the SA base station are received in the downlink time slot at the first frequency point.

[0013] According to a second aspect of the present disclosure, a main link SA terminal is provided, comprising: a memory configured to store instructions; and a processor coupled to the memory, the processor being configured to execute instructions stored in the memory to implement the method as described in any of the above embodiments.

[0014] According to a third aspect of the present disclosure, a communication system is provided, comprising: a primary link SA terminal as described in any one of claims 9; an SA base station configured to search for n secondary link SA terminals whose current cell load is less than a preset threshold, and to send the search results to the primary link SA terminal, where n is a natural number greater than 1; further configured to generate a receive data packet based on uplink data blocks sent by the n secondary link SA terminals; and an i-th secondary link SA terminal configured to receive the i-th uplink data block sent by the primary link SA terminal through a second frequency point in a downlink time slot at a first frequency point, wherein the i-th uplink data block includes at least a portion of the uplink data packet, and to send the i-th uplink data block to the SA base station in an uplink time slot at the first frequency point, where 1 ≤ i ≤ n.

[0015] In some embodiments, among the n secondary link SA terminals, at least one secondary link SA terminal is located at a distance less than the distance between the primary link SA terminal and the SA base station.

[0016] In some embodiments, the uplink data packet is divided into n uplink data blocks, and any two uplink data blocks are different; the SA base station is configured to merge the uplink data blocks sent by the n auxiliary link SA terminals to generate a received data packet.

[0017] In some embodiments, each uplink data block is the same as the uplink data packet; the SA base station is configured to concatenate uplink data blocks sent by n secondary link SA terminals to generate a received data packet.

[0018] In some embodiments, the SA base station is further configured to generate receive data packets based on uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals.

[0019] In some embodiments, the uplink data packet is divided into n+1 uplink data blocks, and any two uplink data blocks are different; the SA base station is configured to merge the uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals to generate a received data packet.

[0020] In some embodiments, each uplink data block is the same as the uplink data packet; the SA base station is configured to concatenate the uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals to generate a received data packet.

[0021] According to a fourth aspect of the present disclosure, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores computer instructions that, when executed by a processor, implement the method as described in any of the above embodiments.

[0022] Other features and advantages of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating a method for sending uplink data packets according to an embodiment of the present disclosure;

[0025] Figure 2 This is a flowchart illustrating a method for sending uplink data packets according to another embodiment of this disclosure;

[0026] Figure 3 This is a schematic diagram of the structure of a main link SA terminal according to an embodiment of the present disclosure;

[0027] Figure 4 This is a schematic diagram of the structure of a communication system according to an embodiment of the present disclosure;

[0028] Figure 5 This is a schematic diagram of the frame structure of an embodiment of the present disclosure;

[0029] Figure 6 This is a schematic diagram of the structure of a communication system according to another embodiment of the present disclosure;

[0030] Figure 7 This is a schematic diagram of the structure of a communication system according to yet another embodiment of the present disclosure. Detailed Implementation

[0031] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0032] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of this disclosure.

[0033] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0034] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0035] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0037] Figure 1 This is a flowchart illustrating a method for sending uplink data packets according to an embodiment of this disclosure. In some embodiments, the following method for sending uplink data packets is performed by the main link SA terminal.

[0038] In step 101, the SA base station searches for n auxiliary link SA terminals in the current cell whose load is less than a preset threshold, where n is a natural number greater than 1.

[0039] It should be noted that the value of n depends on the frame structure, SCS (Sub-Carrier Space), base station capabilities, terminal capabilities, and the number of idle or lightly loaded terminals in the cell.

[0040] In step 102, communication links are established with each of the n auxiliary link SA terminals.

[0041] In step 103, during the downlink time slot of the first frequency point, the i-th uplink data block is sequentially sent to the i-th auxiliary link SA terminal via the second frequency point. The i-th uplink data block includes at least a portion of the uplink data packet, so that during the uplink time slot of the first frequency point, the i-th auxiliary link SA terminal sends the i-th uplink data block to the SA base station, where 1 ≤ i ≤ n. Thus, the SA base station obtains the corresponding uplink data packet based on the received uplink data block.

[0042] In some embodiments, downlink data packets transmitted by the SA base station are received in the downlink time slot at the first frequency point.

[0043] In the method for sending uplink data packets provided in the above embodiments of this disclosure, by utilizing multi-link cooperation, the uplink transmission capability between the SA terminal and the SA base station can be improved, effectively enhancing the user experience.

[0044] In some embodiments, among the n secondary link SA terminals, at least one secondary link SA terminal has a distance from the SA base station that is less than the distance from the primary link SA terminal to the SA base station. This effectively improves the uplink coverage of the primary link SA terminal.

[0045] In some embodiments, uplink data packets are divided into n uplink data blocks, and no two uplink data blocks are identical. Accordingly, the SA base station merges the uplink data blocks sent by the n auxiliary link SA terminals to generate a received data packet. This effectively improves uplink transmission efficiency.

[0046] In some embodiments, each uplink data block is identical to an uplink data packet. Accordingly, the SA base station concatenates the uplink data blocks sent by the n secondary link SA terminals to generate a received data packet. This effectively improves uplink transmission reliability.

[0047] Figure 2 This is a flowchart illustrating a method for sending uplink data packets according to another embodiment of this disclosure. In some embodiments, the following method for sending uplink data packets is performed by the main link SA terminal.

[0048] In step 201, the SA base station searches for n auxiliary link SA terminals in the current cell whose load is less than a preset threshold, where n is a natural number greater than 1.

[0049] In step 202, communication links are established with each of the n auxiliary link SA terminals.

[0050] In step 203, in the downlink time slot of the first frequency point, the i-th uplink data block is sent to the i-th auxiliary link SA terminal sequentially through the second frequency point, wherein the i-th uplink data block includes at least a part of the uplink data packet, and 1≤i≤n.

[0051] In some embodiments, downlink data packets transmitted by the SA base station are received in the downlink time slot at the first frequency point.

[0052] In step 204, during the uplink time slot of the first frequency point, the (n+1)th uplink data block is sent to the SA base station, wherein the (n+1)th uplink data block includes at least a portion of the uplink data packet, and the i-th secondary link SA terminal sends the i-th uplink data block to the SA base station. Thus, the SA base station obtains the corresponding uplink data packet based on the received uplink data block.

[0053] In some embodiments, uplink data packets are divided into n+1 uplink data blocks, and no two uplink data blocks are identical. Accordingly, the SA base station merges the uplink data blocks sent by the primary link SA terminal and the n secondary link SA terminals to generate the received data packet. This effectively improves uplink transmission efficiency.

[0054] In some embodiments, each uplink data block is identical to an uplink data packet. Accordingly, the SA base station concatenates the uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals to generate a received data packet. This effectively improves uplink transmission reliability.

[0055] Figure 3 This is a schematic diagram of the structure of a main link SA terminal according to an embodiment of this disclosure. Figure 3 As shown, the main link SA terminal includes a memory 31 and a processor 32.

[0056] Memory 31 is used to store instructions, and processor 32 is coupled to memory 31. Processor 32 is configured to execute instructions based on memory storage, as shown in the example. Figures 1-2 The method involved in any of the embodiments.

[0057] like Figure 3 As shown, the main link SA terminal also includes a communication interface 33 for exchanging information with other devices. Additionally, the main link SA terminal includes a bus 34, through which the processor 32, communication interface 33, and memory 31 communicate with each other.

[0058] The memory 31 may include high-speed RAM, and may also include non-volatile memory, such as at least one disk storage device. The memory 31 may also be a memory array. The memory 31 may also be divided into blocks, and the blocks may be combined into virtual volumes according to certain rules.

[0059] Furthermore, processor 32 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present disclosure.

[0060] This disclosure also relates to a computer-readable storage medium storing computer instructions that, when executed by a processor, implement... Figures 1-2 The method involved in any of the embodiments.

[0061] Figure 4 This is a schematic diagram of the structure of a communication system according to an embodiment of this disclosure. The corresponding frame structure is as follows: Figure 5 As shown. In Figure 5 The following explanation uses a 2.5ms dual-cycle TDD frame structure as an example. This disclosed scheme is also applicable to other frame structures.

[0062] like Figure 4 As shown, the communication system includes a main link SA terminal 41, multiple auxiliary link SA terminals 42, and an SA base station 43. The main link SA terminal 41 is... Figure 3 The main link SA terminal involved in any of the embodiments.

[0063] SA base station 43 is configured to search for n secondary link SA terminals in the current cell whose load is less than a preset threshold, and send the search results to the primary link SA terminal, where n is a natural number greater than 1.

[0064] The auxiliary link SA terminal 42 is configured to receive uplink data blocks sent by the main link SA terminal 41 through the downlink time slot of the first frequency point via the second frequency point, wherein the uplink data block includes at least a portion of the uplink data packet, and send the uplink data block to the SA base station in the uplink time slot of the first frequency point.

[0065] SA base station 43 is also configured to generate receive data packets based on uplink data blocks sent by n secondary link SA terminals.

[0066] In some embodiments, among the n secondary link SA terminals, at least one secondary link SA terminal has a distance from the SA base station that is less than the distance from the primary link SA terminal to the SA base station. This effectively improves the uplink coverage of the primary link SA terminal.

[0067] In some embodiments, the uplink data packet is divided into n uplink data blocks, and any two uplink data blocks are different. Accordingly, the SA base station 43 merges the n uplink data blocks sent by the secondary link SA terminals 42 to generate the received data packet.

[0068] In some embodiments, each uplink data block is identical to an uplink data packet. Accordingly, the SA base station 43 concatenates the uplink data blocks sent by the n secondary link SA terminals 42 to generate a received data packet.

[0069] In some embodiments, the SA base station is further configured to generate receive data packets based on uplink data blocks sent by the primary link SA terminal 41 and n secondary link SA terminals 42.

[0070] For example, the uplink data packet is divided into n+1 uplink data blocks, and no two uplink data blocks are the same. Accordingly, the SA base station 43 merges the uplink data blocks sent by the primary link SA terminal 41 and the n secondary link SA terminals 42 to generate the received data packet. This effectively improves uplink transmission efficiency.

[0071] For example, each uplink data block is identical to an uplink data packet. Accordingly, the SA base station 43 is configured to concatenate the uplink data blocks sent by the primary link SA terminal 41 and n secondary link SA terminals 42 to generate a received data packet. This effectively improves uplink transmission reliability.

[0072] The above-mentioned scheme is illustrated below with specific examples.

[0073] Example 1:

[0074] like Figure 6 As shown, primary link SA terminal A searches for two idle or lightly loaded SA terminals B1 and B2 in the same cell through the SA base station. Primary link SA terminal A establishes channel links with the two secondary link SA terminals B1 and B2 respectively.

[0075] While the primary link SA terminal A transmits downlink data to the SA base station, it also sends uplink data blocks to each secondary link SA terminal B1 and B2. Specifically, during the downlink time slot at frequency F1, primary link SA terminal A receives downlink data from the SA base station at frequency F1. Simultaneously, it divides the uplink data packet TB into blocks and sends uplink data blocks TB1 and TB2 to the two secondary link SA terminals B1 and B2 at frequency F2 in a time-division manner. That is, TB = TB0 + TB1 + TB2, and TB0, TB1, and TB2 are all distinct. The two secondary link SA terminals B1 and B2 receive the uplink data blocks TB1 and TB2 in a time-division manner, parse them, and buffer them respectively.

[0076] During the uplink time slot of frequency F1, the main link SA terminal A and two auxiliary link SA terminals B1 and B2 simultaneously send uplink data blocks TB0, TB1 and TB2 to the SA base station on frequency F1 by utilizing the three links.

[0077] After receiving uplink data blocks TB0, TB1, and TB2 simultaneously from the primary and secondary link SA terminals, the SA base station merges the data blocks into a single large data block TB = TB0 + TB1 + TB2. Thus, the primary link SA terminal, with the help of two secondary link SA terminals B1 and B2, achieves primary and secondary multi-link collaborative transmission, improving the uplink transmission rate of the primary link SA terminal.

[0078] Example 2

[0079] like Figure 6 As shown, primary link SA terminal A searches for two idle or lightly loaded SA terminals B1 and B2 in the same cell through the SA base station. Primary link SA terminal A establishes channel links with the two secondary link SA terminals B1 and B2 respectively.

[0080] While the primary link SA terminal A transmits downlink data to the SA base station, it also sends uplink data blocks to each secondary link SA terminal B1 and B2. Specifically, during the downlink time slot at frequency F1, primary link SA terminal A receives downlink data from the SA base station at frequency F1, and simultaneously sends uplink data blocks TB1 and TB2 to the two secondary link SA terminals B1 and B2 at frequency F2 in a time-division manner, where TB = TB0 = TB1 = TB2. Upon receiving uplink data blocks TB1 and TB2 in a time-division manner, the two secondary link SA terminals B1 and B2 parse and buffer them respectively.

[0081] During the uplink time slot of frequency F1, the main link SA terminal A and two auxiliary link SA terminals B1 and B2 simultaneously send uplink data blocks TB0, TB1 and TB2 to the SA base station on frequency F1 by utilizing the three links.

[0082] After receiving uplink data blocks TB0, TB1, and TB2 simultaneously from the primary and secondary link SA terminals, the SA base station concatenates them to obtain the aforementioned data TB = TB0||TB1||TB2. Thus, the primary link SA terminal, with the help of two secondary link SA terminals B1 and B2, achieves primary and secondary multi-link coordinated redundant transmission, improving the uplink transmission reliability of the primary link SA terminal.

[0083] Example 3

[0084] like Figure 7 As shown, primary link SA terminal A searches for two idle or lightly loaded SA terminals B1 and B2 in the same cell through the SA base station. Primary link SA terminal A establishes channel links with the two secondary link SA terminals B1 and B2 respectively. Compared to primary link SA terminal A, secondary link SA terminals B1 and B2 are closer to the SA base station.

[0085] While the primary link SA terminal A transmits downlink data to the SA base station, it also sends uplink data blocks to each secondary link SA terminal B1 and B2. Specifically, during the downlink time slot at frequency F1, primary link SA terminal A receives downlink data from the SA base station at frequency F1, and simultaneously sends uplink data blocks TB1 and TB2 to the two secondary link SA terminals B1 and B2 at frequency F2 in a time-division manner, where TB = TB1 + TB2. After receiving the uplink data blocks TB1 and TB2 in a time-division manner, the two secondary link SA terminals B1 and B2 parse and buffer them respectively.

[0086] During the uplink time slot of frequency F1, two auxiliary link SA terminals B1 and B2 simultaneously send uplink data blocks TB1 and TB2 to the SA base station.

[0087] After receiving uplink data blocks TB1 and TB2 from the secondary link SA terminals, the SA base station concatenates them to obtain the aforementioned data TB = TB1||TB2. Thus, the primary link SA terminal, with the help of two secondary link SA terminals B1 and B2, achieves secondary multi-link collaborative redundant transmission, improving the uplink coverage range of the primary link SA terminal.

[0088] In some embodiments, the functional unit modules described above may be implemented as general-purpose processors, programmable logic controllers (PLCs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or any suitable combination thereof for performing the functions described herein.

[0089] By implementing the above embodiments of this disclosure, the following beneficial effects can be obtained:

[0090] 1) It effectively solves the problem of limited single-link communication capability (especially uplink capability) between SA terminals and SA base stations, and is highly targeted at 2C and 2B services with high requirements for uplink speed, reliability and coverage.

[0091] 2) Multi-link communication between SA terminals and SA base stations greatly improves uplink capability, enhances SA network performance, improves SA user experience, and reduces SA network operation and maintenance costs.

[0092] 3) It requires minimal system modifications, has low implementation complexity, and is easy to implement and promote.

[0093] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk.

[0094] The description in this disclosure is provided for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the disclosure to its forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of this disclosure and to enable those skilled in the art to understand this disclosure and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for sending uplink data packets, executed by a main link SA terminal, comprising: The system searches for n secondary link SA terminals in the current cell whose load is less than a preset threshold using the SA base station, where n is a natural number greater than 1. Establish communication links with each of the n auxiliary link SA terminals; In the downlink time slot of the first frequency point, the i-th uplink data block is sequentially sent to the i-th auxiliary link SA terminal through the second frequency point, wherein the i-th uplink data block includes at least a part of the uplink data packet, so that in the uplink time slot of the first frequency point, the i-th auxiliary link SA terminal sends the i-th uplink data block to the SA base station, 1≤i≤n.

2. The method according to claim 1, wherein, Among the n secondary link SA terminals, at least one secondary link SA terminal is located at a distance less than the distance between the primary link SA terminal and the SA base station.

3. The method according to claim 2, wherein, The uplink data packet is divided into n uplink data blocks, and no two uplink data blocks are the same.

4. The method according to claim 2, wherein, Each uplink data block is identical to the uplink data packet.

5. The method according to claim 1, further comprising: In the uplink time slot of the first frequency point, the (n+1)th uplink data block is sent to the SA base station, wherein the (n+1)th uplink data block includes at least a portion of the uplink data packet.

6. The method according to claim 5, wherein, The uplink data packet is divided into n+1 uplink data blocks, and no two uplink data blocks are the same.

7. The method according to claim 5, wherein, Each uplink data block is identical to the uplink data packet.

8. The method according to any one of claims 1-7, wherein, In the downlink time slot of the first frequency point, the downlink data packets sent by the SA base station are received.

9. A main link SA terminal, comprising: The memory is configured to store instructions; A processor, coupled to memory, configured to implement the method as described in any one of claims 1-8 based on memory-stored instruction execution.

10. A communication system, comprising: The main link SA terminal as described in claim 9; The SA base station is configured to search for n secondary link SA terminals with a load of less than a preset threshold in the current cell, and send the search results to the primary link SA terminal, where n is a natural number greater than 1; it is also configured to generate a receive data packet based on the uplink data blocks sent by the n secondary link SA terminals. The i-th auxiliary link SA terminal is configured to receive the i-th uplink data block sent by the primary link SA terminal through the downlink time slot at the first frequency point, wherein the i-th uplink data block includes at least a part of the uplink data packet, and send the i-th uplink data block to the SA base station in the uplink time slot at the first frequency point, where 1≤i≤n.

11. The system according to claim 10, wherein, Among the n secondary link SA terminals, at least one secondary link SA terminal is located at a distance less than the distance between the primary link SA terminal and the SA base station.

12. The system according to claim 11, wherein, The uplink data packet is divided into n uplink data blocks, and no two uplink data blocks are the same. The SA base station is configured to merge uplink data blocks sent by n secondary link SA terminals to generate a received data packet.

13. The system according to claim 11, wherein, Each uplink data block is identical to the uplink data packet; The SA base station is configured to concatenate uplink data blocks sent by n secondary link SA terminals to generate a received data packet.

14. The system according to claim 11, wherein, The SA base station is also configured to generate receive data packets based on uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals.

15. The system according to claim 14, wherein, The uplink data packet is divided into n+1 uplink data blocks, and no two uplink data blocks are the same. The SA base station is configured to merge uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals to generate a received data packet.

16. The system according to claim 14, wherein, Each uplink data block is identical to the uplink data packet; The SA base station is configured to concatenate uplink data blocks sent by the primary link SA terminal and n secondary link SA terminals to generate a received data packet.

17. A computer-readable storage medium, wherein, A computer-readable storage medium stores computer instructions that, when executed by a processor, implement the method as described in any one of claims 1-8.

Images