WO2009133537A1

WO2009133537A1 - System and method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system

Info

Publication number: WO2009133537A1
Application number: PCT/IB2009/051792
Authority: WO
Inventors: Ni Ma; Xiaobo Zhang; Gang Wu
Original assignee: Nxp B.V.
Priority date: 2008-05-02
Filing date: 2009-05-01
Publication date: 2009-11-05

Abstract

A system and method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. The system includes a retransmission buffer and a processing unit. The retransmission buffer buffers an original data segment. The processing unit processes the original data segment into a plurality of symbols. The buffered original data segment is transmitted to the processing unit for processing in response to an error signal that is generated from a remote receiver in response to receiver processing of the symbols.

Description

SYSTEM AND METHOD FOR IMPLEMENTING A HYBRID

AUTOMATIC REPEAT REQUEST PROTOCOL IN A MULTIPLE INPUT

MULTIPLE OUTPUT WIRELESS COMMUNICATION SYSTEM

Embodiments of the invention relate generally to wireless communication systems and, more particularly, to techniques for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system.

In communication systems, if a data transmission fails, the receiver notifies the transmitter to retransmit the data segment by using a Negative Acknowledgement (NACK) feedback signal. On the contrary, if the data transmission is successful, the receiver validates the transmission by using an Acknowledgement (ACK) feedback signal. This type of acknowledgement scheme is referred to as Automatic Repeat Request (ARQ). Due to the potential for deteriorated channel characteristics in wireless communication systems,

Forward Error Correction (FEC) is often adopted to guarantee data transmission validity. However, FEC tends to depress the transmission efficiency. Conventionally, Hybrid Automatic Repeat Request (HARQ) combines ARQ and FEC schemes to improve the data retransmission efficiency. HARQ is one of the technologies of the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system for high throughput data transmission.

A multiple input multiple output (MIMO) wireless communication system utilizes at least one antenna in the transmitter and at least one antenna in the receiver and may achieve higher spectrum efficiency and link diversity. A MIMO wireless communication system may use more than one antenna in the transmitter and more than one antenna in the receiver, or one antenna in the transmitter and more than one antenna in the receiver, or more than one antenna in the transmitter and one antenna in the receiver, or one antenna in the transmitter and one antenna in the receiver. In the existing HARQ protocols in MIMO wireless communication systems, original data is processed into symbols and then buffered for retransmission. Because symbols contain complicated amplitude and phase data, buffering the symbols is a resource intensive operation. Embodiments of a system are described. In one embodiment, the system is a system to implement a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. The system includes a retransmission buffer and a processing unit. The retransmission buffer buffers an original data segment. The processing unit processes the original data segment into a plurality of symbols. The buffered original data segment is transmitted to the processing unit for processing in response to an error signal that is generated from a remote receiver in response to receiver processing of the symbols. Other embodiments of the system are also described. Embodiments of a method are also described. In one embodiment, the method is a method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. The method includes buffering an original data segment. The method also includes processing the original data segment into a plurality of symbols. The method also includes transmitting the buffered original data segment for processing in response to an error signal that is generated in response to receiver processing of the symbols. Other embodiments of the method are also described.

Embodiments of another method are also described. In one embodiment, the method is a method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. The method includes encoding an original data segment for error correction. The method also includes buffering the encoded data segment. The method also includes processing the encoded data segment into a plurality of symbols, wherein the processing comprises modulating the encoded data segment into a plurality of symbols and coding the symbols for data communication in a multiple input multiple output wireless communication system. The method also includes transmitting the buffered encoded data segment for processing into a new plurality of symbols in response to an error signal that is generated in response to receiver processing of the symbols. Other embodiments of the method are also described. Other aspects and advantages of embodiments of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. Fig. 1 depicts a schematic block diagram of one embodiment of a multiple input multiple output wireless communication system.

Fig. 2 illustrates a schematic block diagram of a system to implement a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system.

Fig. 3 illustrates an example embodiment of the retransmission buffer of the transmitter of Fig. 2.

Fig. 4 illustrates a schematic flow chart diagram of one embodiment of a method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system.

Throughout the description, similar reference numbers may be used to identify similar elements.

Fig. 1 depicts a schematic block diagram of one embodiment of a multiple input multiple output wireless communication system 100. The multiple input multiple output wireless communication system 100 includes a base station 102, also referred to as an evolved Node B (eNB), and multiple mobile stations 104, also referred to as user equipments (UEs). For description purposes, the eNB 102 also may be referred to generically as a transmitter and the UEs 104 may be referred to generically as the receivers. Alternatively, in some embodiments, the eNB also may be referred to generically as the receiver and the UEs may be referred to generically as the transmitters, depending on the direction of data communication within the wireless communication system. The multiple input multiple output wireless communication system utilizes at least one antenna in the transmitter and at least one antenna in the receiver. The multiple input multiple output wireless communication system may use more than one antenna in the transmitter and more than one antenna in the receiver, or one antenna in the transmitter and more than one antenna in the receiver, or more than one antenna in the transmitter and one antenna in the receiver, or one antenna in the transmitter and one antenna in the receiver. In the illustrated embodiment, the eNB 102 includes two antennas, although the eNB can include more than two antennas. In general, the eNB is responsible for coordinating communications between the eNB 102 and the UEs 104. In one embodiment, the UEs 104 are wireless communication mobile stations that support wireless operations as specified in the 3rd Generation Partnership Project (3 GPP) Long Term Evolution (LTE) system specification. The UEs may have one or two antennas, although the UEs are not limited to two antennas (e.g., the UEs can include more than two antennas). Other embodiments of the multiple input multiple output wireless communication system 100 may implement other wireless schemes such as the 3rd Generation Partnership Project (3GPP) Evolved High Speed Packet Access (HSPA+), WiMAX, IEEE 802.1 In, and other 3G standards or 4G standards. Fig. 2 illustrates a schematic block diagram of a system 190 that is configured to implement a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. The system includes a transmitter 200 and a receiver 216. Although the system includes several functional blocks described herein, other embodiments may include fewer or more functional blocks to implement more or less functionality.

Elements of the system 190 are described individually followed by a description of the system operation. Referring to Fig. 2, the transmitter 200 includes a forward error correction data encoder 202, a retransmission buffer 204, a retransmission manager 206, a processing unit 208, and an antenna unit 214, and the receiver 216 includes an antenna unit 218 and a data processor 220.

Referring to the transmitter side of the system 190, the forward error correction data encoder 202, located along the signal path that is before the retransmission buffer 204 and the processing unit 208, is responsible for encoding original data segments for error correction. The forward error correction data encoder utilizes, for example, block coding, convolutional coding, or both.

The retransmission buffer 204 is responsible for buffering the encoded data segments. The retransmission buffer may be implemented in software, hardware, or a combination of software and hardware. The retransmission buffer includes, for example, random access memory and disk drive. In an embodiment, the retransmission buffer buffers the encoded data segments in the same information storage format as the encoded data segments. For example, an eight bit original data segment is buffered as eight bits in the retransmission buffer. In another embodiment, the retransmission buffer buffers each encoded data segment in a plurality of blocks, according to a configuration in which the encoded data segment is organized for processing. An example of the retransmission buffer is described in more detail below with reference to Fig. 3.

The processing unit 208 is responsible for processing each of the encoded data segments into a plurality of symbols. The processing unit includes a data converter module 210 to convert each of the encoded data segments into a plurality of symbols and a multiple input multiple output encoder module 212 to code the symbols into antenna-specific symbols. In some embodiments, the data converter module modulates each of the encoded data segments into a plurality of symbols and the multiple input multiple output encoder module spatially codes the symbols into antenna-specific symbols of a multiple input multiple output coding structure, such as Alamouti space time block code. The processing unit may work according to one pattern, in which the output of the processing of the buffered encoded data segment is the same as the output of the processing of the encoded data segment. The processing unit may work according to different patterns, in which the output of the processing of the buffered encoded data segment is the different from the output of the processing of the encoded data segment. The pattern of the process unit includes the data conversion scheme of the data converter module and the coding scheme of the multiple input multiple output encoder module.

The retransmission manager 206 monitors for a Negative

Acknowledgement (NACK) feedback signal 222 that is generated in response to receiver processing of the symbols. The retransmission manager may be implemented in software, hardware, or a combination of software and hardware. The antenna unit 214 includes at least one antenna and sends the symbols to the receiver 216.

Referring now to the receiver side of the system 190, the antenna unit 218 includes at least one antenna and receives the symbols from the transmitter 200 and forwards the symbols to the data processor 220. The data processor processes the received data symbols and generates a Negative Acknowledgement (NACK) feedback signal 222 in response to an error that occurs in the processing of the symbols. For example, a NACK feedback signal is generated if the received data symbols fail a cyclic redundancy check. In response to correct processing of the symbols, an Acknowledgement (ACK) feedback signal is generated by the data processor and fed back to the transmitter. For example, a ACK feedback signal is generated if the received data symbols pass the cyclic redundancy check. The data processor may be implemented in software, hardware, or a combination of software and hardware.

In operation, the forward error correction data encoder 202 encodes original data segments for error correction. The retransmission buffer 204 buffers the encoded data segments. The processing unit 208 converts each of the encoded data segments into a plurality of symbols and codes the symbols into antenna- specific symbols. The retransmission manager 206 monitors for a Negative Acknowledgement (NACK) feedback signal 222 that is generated by the data processor 220 in response to a processing error of the symbols. If a NACK is detected, the retransmission manager triggers the retransmission of a buffered encoded data segment to the processing unit for processing. The processing unit converts the buffered encoded data segment into a plurality of symbols and codes the symbols into antenna-specific symbols, which can then be transmitted, referred to generally as "retransmitted" to the receiver 216.

In the existing HARQ protocols in MIMO wireless communication systems, original data is processed into symbols and then buffered for retransmission. In the scheme described herein, the original data segments, which are smaller than their corresponding symbols in terms of bits needed to represent the data, are buffered. Because symbols contain complicated amplitude and phase data, buffering the symbols is a resource intensive operation. Although in some embodiments, the number of symbols to be buffered may be smaller than the number of the corresponding original data segments to be buffered, the large size in terms of bits needed to represent the data of the symbols offset the number advantage of the symbols. Therefore, less memory is needed to buffer the original data segments than is needed to buffer the corresponding symbols.

Fig. 3 illustrates an example of the retransmission buffer 204 from Fig. 2. In an embodiment, the retransmission buffer buffers the encoded data segments in the same information storage format as the encoded data segments. In another embodiment, the retransmission buffer buffers each encoded data segment in a plurality of blocks, according to a configuration in which the encoded data segment is organized for processing. In Fig. 3, an example of an encoded data segment 300 having eight bits and two portions, labeled as Dl and D2, is shown. Each portion of the encoded data segment is four bits long and each four-bit portion will be individually processed by the processing unit 208. In one embodiment, the encoded data segment is buffered in the same form in which it is organized. That is, the encoded data segments organized in four-bit portions are buffered as four-bit blocks in the retransmission buffer. Fig. 3 depicts a retransmission buffer with two blocks labeled as B 1 and B2, with each block being four bits long. The contents stored in block B 1 are the same as the contents of Dl and the contents stored in block B2 are the same as the contents of D2. In response to a processing error signal, certain blocks of the retransmission buffer will be transmitted to the processing unit and individually processed into a new plurality of symbols.

Other embodiments of the retransmission buffer may use fewer or more blocks. Other embodiments of the retransmission buffer may use fewer or more portions. For example, four blocks and four portions may be used. Other embodiments may use bigger or smaller blocks or portions. For example, two bits or eight bits may be used. In some embodiments, the size requirement of the retransmission buffer depends on many factors, including modulation schemes, forward error correction code rates and retransmission buffer buffering scales. For example, if the modulation scheme is quadrature phase shift keying, the forward error correction code rate is 1/3, 1024 sub-carrier under OFDM transmission, and the buffering scale of the retransmission buffer corresponds to one symbol, the retransmission buffer size is 2* 1024*3=6144 bits. The labeling used herein for the blocks is merely exemplary and does not necessarily correspond to a particular order in which the corresponding encoded data segment is buffered. Additionally, the labeling used herein for the data portions is merely exemplary and does not necessarily correspond to a particular order in which the encoded data segment is organized. Fig. 4 depicts an example of a method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system. At block 402, an original data segment is buffered and processed into a plurality of symbols. At decision point 404, it is determined whether an error signal is received in response to receiver processing of the symbols. If an error signal is not received, then the process returns to decision point 404. If an error signal is received, then at block 406, the buffered original data segment is transmitted for processing. In addition to the embodiments described above, it may be helpful to review some mathematical analysis for the above-described scheme, in comparison with a conventional scheme. Original data segments are buffered in the current scheme and modulated symbols are buffered in the exemplary conventional scheme. For convenience, the mathematical analysis makes assumptions as follows. The size of a retransmitted symbol is the same as the size of an initial transmitted symbol. Buffering is in the scale of one codeword. The length of each original codeword is D bits, a modulated symbol corresponds to M original bits, a modulated symbol occupies N bits, and generally, a modulated symbol occupies more than ten bits and a modulated symbol corresponds to less than six original bits. The buffer requirement for the exemplary conventional scheme B_Symbol in bits is given by:

D x N

B Symbol M

Table 1 Table 1 includes the five columns. From left to right, the first column is the original codeword length, the second column is the modulation order M, the third column is the modulated symbol size N, the fourth column is the buffer requirement of the exemplary conventional scheme in bits, and the fifth column is the buffer requirement of the current scheme in bits. Table 1 illustrates that the buffer requirement of the current scheme is smaller than the buffer requirement of the exemplary conventional scheme. As illustrated by this comparison, embodiments of the current scheme can effectively conserve memory resources. It should be noted that, although limited combinations of the original codeword length D, the modulation order M, and the modulated symbol size N are considered above, the procedure of mathematical calculation above can be extended to the case of any suitable combination of codeword length, modulation scheme and modulated symbol size, and the same or a similar conclusion can be derived. Hence, embodiments of the current scheme can effectively conserve memory resources in other implementations.

Embodiments of the current scheme for implementing a hybrid automatic repeat request protocol can be applied to various MIMO wireless communication systems, including the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, the 3rd Generation Partnership Project (3GPP) Evolved High Speed Packet Access (HSPA+) system, WiMAX, IEEE 802.1 In, and other 3G systems or 4G systems.

Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

Claims

What is Claimed is:

1. A method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system, the method comprising: buffering an original data segment; processing the original data segment into a plurality of symbols; and transmitting the buffered original data segment for processing in response to an error signal that is generated in response to receiver processing of the symbols.

2. The method of claim 1, wherein buffering the original data segment comprises buffering the original data segment in the same information storage format as the original data segment.

3. The method of claim 1, wherein buffering the original data segment comprises buffering the original data segment in a plurality of blocks, according to a configuration in which the original data segment is organized for processing.

4. The method of claim 1, wherein: the original data segment is processed according to a first processing pattern; and the buffered original data segment is processed according to a second processing pattern, wherein the first processing pattern is different from the second processing pattern.

5. The method of claim 1, wherein: the original data segment is processed according to a first processing pattern; and the buffered original data segment is processed according to a second processing pattern, wherein the first processing pattern is the same as the second processing pattern.

6. The method of claim 1, further comprising monitoring for an error signal that is generated in response to receiver processing of the symbols.

7. The method of claim 1, wherein the original data segment is encoded for error correction before buffering and processing.

8. A transmitter configured to implement a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system, the transmitter comprising: a retransmission buffer to buffer an original data segment; and a processing unit to process the original data segment into a plurality of symbols; wherein the buffered original data segment is transmitted to the processing unit for processing in response to an error signal that is generated from a remote receiver in response to receiver processing of the symbols.

9. The transmitter of claim 8, wherein the retransmission buffer is further configured to buffer the original data segment in the same information storage format as the original data segment.

10. The transmitter of claim 8, wherein the retransmission buffer is further configured to buffer the original data segment in a plurality of blocks, according to a configuration in which the original data segment is organized for processing.

11. The transmitter of claim 8, wherein the processing unit comprises a data converter module to convert the original data segment into a plurality of symbols and a multiple input multiple output encoder module to code the symbols into antenna-specific symbols.

12. The transmitter of claim 8, wherein the processing unit is further configured to process the original data segment according to a first processing pattern and process the buffered original data segment according to a second processing pattern, wherein the first processing pattern is the same as the second processing pattern.

13. The transmitter of claim 8, wherein the processing unit is further configured to process the original data segment according to a first processing pattern and process the buffered original data segment according to a second processing pattern, wherein the first processing pattern is different from the second processing pattern.

14. The transmitter of claim 8, further comprising a forward error correction data encoder to encode the original data segment for error correction located along the signal path that is before the retransmission buffer and the process unit.

15. A method for implementing a hybrid automatic repeat request protocol in a multiple input multiple output wireless communication system, the method comprising: encoding an original data segment for error correction; buffering the encoded data segment; processing the encoded data segment into a plurality of symbols, wherein the processing comprises modulating the encoded data segment into a plurality of symbols and coding the symbols for data communication in a multiple input multiple output wireless communication system; and transmitting the buffered encoded data segment for processing into a new plurality of symbols in response to an error signal that is generated in response to receiver processing of the symbols.

16. The method of claim 15, wherein buffering the encoded data segment comprises buffering the encoded data segment in the same information storage format as the encoded data segment.

17. The method of claim 15, wherein buffering the encoded data segment comprises buffering the encoded data segment in a plurality of blocks, according to a configuration in which the encoded data segment is organized for processing.

18. The method of claim 15, wherein: the encoded data segment is processed according to a first processing pattern; and the buffered encoded data segment is processed according to a second processing pattern, wherein the first processing pattern is different from the second processing pattern.

19. The method of claim 15, wherein: the encoded data segment is processed according to a first processing pattern; and the buffered encoded data segment is processed according to a second processing pattern, wherein the first processing pattern is the same as the second processing pattern.

20. The method of claim 15, further comprising monitoring for an error signal that is generated in response to receiver processing of the symbols.