CN1961510B - Method and apparatus for reducing multi-user processing in wireless communication systems - Google Patents

Abstract

A method and apparatus is disclosed for reducing multi-user processing at the receiver in wireless communication systems. Detected codes are grouped according to channel impulse response and a parent code is identified for each group of detected codes. A matrix A is constructed and joint detection is performed using the identified parent codes. Data symbols of the detected codes are obtained from the data symbols of the identified parent codes.

Description

Method and device for reducing multi-user processing in wireless communication system

technical field

The present invention relates to wireless communication systems. In particular, the present invention relates to reduced multi-user processing in wireless communication systems.

Background technique

In a Code Division Multiple Access (CDMA) communication system, multiple communications can be sent simultaneously by sharing a frequency spectrum. Each communication can be identified by the code that transmits the communication. The data symbol of the communication uses the encoding chip to spread the spectrum. The number of chips used to transmit a code for a particular symbol is called the spreading factor. A common spreading factor is sixteen (16), where sixteen chips are used to transmit one symbol. For example, typical spreading factors (SF) are 16, 8, 4, 2 and 1 in a TDD/CDMA communication system.

In some CDMA communication systems, in order to better utilize the shared spectrum, the spectrum can be divided into frames with a predetermined number of time slots, such as fifteen time slots. Such systems may generally be referred to as hybrid CDMA/Time Division Multiple Access (TDMA) communication systems. Time Division Duplex (TDD) communication systems are representative of such systems, in which both uplink and downlink communications are restricted to specific time slots.

One means of receiving multiple communications transmitted in a shared spectrum is joint detection. In joint detection, data from multiple communications is determined simultaneously. A joint detector can utilize encodings (known or determined) of multiple communications and estimate data from multiple communications as soft symbols. Some typical implementations of joint detectors utilize a zero-point forcing block linear equalizer (ZF-BLE), a Cholesky or approximate Cholesky decomposition, or a Fast Fourier transform.

The receiver receives communications with a particular spreading factor. When the spreading factor of the received communication is higher, the complexity of performing joint detection is also higher. In view of this, the main objective of the present invention is to provide a method and device for reducing the complexity of performing joint detection in a wireless communication system.

Contents of the invention

The present invention relates to a method and apparatus for reducing multi-user processing at a receiver in a wireless communication system. The detected codes are grouped according to the channel impulse response, and a parent code of each group of detected codes is identified. In addition, matrix A is established, and joint detection can be performed using the identified parent codes. The detected encoded data symbols may be obtained from the identified parent encoded data symbols.

Description of drawings

Figure 1 shows a transmitter and receiver with a reduced chip-level multiuser detection (MUD) processor and post-data converter;

Figure 2 is a block diagram representing components within a reduced chip-level MUD processor;

Fig. 3 represents the tree structure of Orthogonal Variable Spreading Factor (OVSF) coding; And

Figure 4 is a flow chart illustrating grouping of detected codes according to channel impulse response and performing joint detection with a parent code having a lower spreading factor for detected codes with the same channel impulse response .

Detailed ways

Although the features and components of the present invention have been described in detail using specific combinations of the preferred embodiments, individual features or components of the preferred embodiments of the present invention can also be used alone (without requiring other combinations of the preferred embodiments of the present invention). Features or components), or individual features or components of the preferred embodiments of the present invention can also form various compositions (without having or omitting other features or components of the preferred embodiments of the present invention).

In the preferred embodiment of the present invention, a wireless transmit/receive unit (WTRU) includes, but is not limited to, user equipment (UE), mobile workstation, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment . In addition, in the preferred embodiment of the present invention, a base station (BS) includes, but is not limited to, a Node B, a site controller, an access point (AP), or any other type of interface device in a wireless environment.

First, please refer to FIG. 1 , which shows a transmitter 20 and a receiver 22 . The transmitter may be set at a wireless transmit/receive unit (WTRU), or the multi-transmission circuit 20 may also be set at a base station (BS). The receiver may be located in a wireless transmit/receive unit (WTRU), a base station (BS), or both.

Receiver 22 includes a reduced chip-level multiuser detection (MUD) processor 44 and post-data converter 46 . In general, the MUD processor 44 can group detected codes according to channel impulse responses and perform joint detection using parent codes of the detected codes for detected codes with the same channel impulse response. (for example, a code in a downlink transmission or a code in an uplink transmission from the same user). Joint detection can be implemented on a single detected encoding. Post-data converter 46 is configured to convert the parent encoded data symbols back to respective originally detected encoded data symbols of the parent encoding.

Specifically, referring to FIG. 2 , the receiver 22 includes a code detector 32 , a code grouper 34 , a mother code locator 36 , and a multi-user detector (MUD) 44 . Code detector 32 may detect the transmitted code when the communication is received with a particular spreading factor. The code grouper 34 may then group codes having the same channel impulse response (that is, group codes for a single user). In general, a single incoming communication is from a single user, so all detected codes will usually have the same channel impulse response, resulting in a single group. Of course, there may be a situation where there are multiple groups. For each set of detected codes, parent code locator 36 may identify a parent code. As previously stated, a detected code can be considered as detected when it has a unique channel impulse response (i.e., the detected code does not have the same channel impulse response as any other detected code). The respective parent codes of the codes.

Once the mother code is identified, matrix A builder 40 of MUD 44 may use the mother code to build matrix A. A matrix A, such as a channel/coding convolution matrix known to those skilled in the art, can be constructed and provided to a joint detector 42 of a multiuser detector (MUD) 44 . The matrix A may be utilized by the joint detector 42 to estimate the soft symbols of the spread spectrum data. Performing joint detection using parent codes instead of detected codes can significantly reduce the complexity of the joint detector 42 . The soft symbols estimated by the joint detector 42 may be input to a post data converter 46 which converts the estimated soft symbols back to the originally detected encoded raw data symbols.

Please refer next to FIG. 3 , which shows an Orthogonal Variable Spreading Factor (OVSF) coding tree 300 . However, the inventors also appreciate that within each level of coding in the Orthogonal Variable Spreading Factor (OVSF) coding tree 300 with a particular spreading factor (SF), coding groups may also be based on a unique high-level coding (i.e.: codes with lower spreading factors (SF)). In a preferred embodiment of the present invention, a code group with a given level has the same parent code, if all codes in the group are based on the same parent code and no other codes with the given level are based on the parent code.

As an example, assume that a communication formed by four codes with the same channel impulse response is received with a spreading factor of 16. These four codes 302, 304, 306, 308 are detected and grouped together. The detected codes 302, 304, 306, 308 can then be backtracked as far as possible in the Orthogonal Variable Spreading Factor (OVSF) code tree 300 to identify the parent The parent code 310 of the code and only the parent code of these detected codes 302 , 304 , 306 , 308 . Mother code 310 is the parent code in Orthogonal Variable Spreading Factor (OVSF) code tree 300 that is the mother code for each detected code 302, 304, 306, 308 and only said detected code 302, 304, 306, The unique code of the parent code of 308.

For convenience, the parent code 310 (i.e., 1111) may be referred to as C, and the detected codes 302, 304, 306, 308 may be referred to as CCCC, CCC'C', CC'CC', CC'C'C, respectively , where C' is -1-1-1-1. The data symbols corresponding to the detected codes 302, 304, 306, 308 can be expressed as:

CCCC ←---→d ^{SF16, 1}

CCC'C'←---→d ^{SF16, 2}

CC'CC' ←---→d ^{SF16, 3}

CC'C'C ←---→d ^{SF16, 4}

Wherein, d ^SF16,i , i=1, 2, 3, 4 may represent the i-th coded data symbol in the four detected codes 302, 304, 306, 308, respectively.

In an Orthogonal Variable Spreading Factor (OVSF) coding tree 300, the number of associated data symbols for a particular code varies according to the coding spreading factor (SF). For example, during a 16-chip period, a code with a spreading factor (SF) of 16 can carry one data symbol, a code with a spreading factor (SF) of 8 can carry two data symbols, and a code with a spreading factor (SF) of 4 A code with a spreading factor (SF) of 2 can carry eight data symbols, and a code with a spreading factor (SF) of 8 can carry 16 data symbols. In addition, the parent codes and their sub-codes may carry the same data symbols, however, the data symbols carried by the parent codes are processed sequentially, while the data symbols carried by the sub-codes are processed in parallel.

In view of this, in FIG. 3 , the parent code 310 may include the information needed to decode the data symbols of the detected codes 302 , 304 , 306 , 308 . The first data symbol of the mother code 310 may comprise information for decoding the data symbols carried by the first four bits of the detected code 302 , 304 , 306 , 308 . The second data symbol of the parent code 310 may comprise information for decoding the data symbols carried by again four bits of the detected code 302 , 304 , 306 , 308 . The third data symbol of the mother code 310 may comprise information for decoding the data symbols carried by again four bits of the detected codes 302 , 304 , 306 , 308 . The fourth data symbol of the mother code 310 may comprise information for decoding the data symbol carried by the last four bits of the detected code 302 , 304 , 306 , 308 . The data symbols of the parent code 310 and the data symbols of the detected codes 302, 304, 306, 308 may have the following relationship:

d ₁ ^SF4 ＝d ^SF16,1 +d ^SF16,2 +d ^SF16,3 +d ^SF16,4

d ₂ ^SF4 =d ^SF16,1 +d ^SF16,2 -d ^SF16,3 -d ^SF16,4

d ₃ ^SF4 ＝d ^SF16,1 -d ^SF16,2 +d ^SF16,3 -d ^SF16,4

d ₄ ^SF4 ＝d ^SF16,1 -d ^SF16,2 -d ^SF16,3 +d ^SF16,4

Wherein, d _i ^SF4 , i=1, 2, 3, 4 may represent four data symbols of the mother code 310 respectively. As previously mentioned, the number of overall data symbols carried by the mother code 310 and the detected codes 302, 304, 306, 308 is the same, however, the data symbols carried by the mother code 310 are processed sequentially, while the detected codes The data symbols carried by 302, 304, 306, 308 are processed in parallel.

In a preferred embodiment of the present invention, the mother code 310 can be used to establish the matrix A and implement joint detection. As such, the Multi-User Detector (MUD) can significantly reduce its complexity relative to performing joint detection using detected codes 302,304,306,308. The original data symbols carried by the detected codes 302 , 304 , 306 , 308 can then be recovered using the post-data converter 46 . In a preferred embodiment of the present invention, raw data symbols can be calculated in the following manner:

d ^SF16, 1 = 1/4(d ₁ ^SF4 +d ₂ ^SF4 +d ₃ ^SF4 +d ₄ ^SF4 )

d ^SF16, 2 = 1/4(d ₁ ^SF4 +d ₂ ^SF4 -d ₃ ^SF4 -d ₄ ^SF4 )

^dSF16, 3 = 1/4(d ₁ ^SF4 -d ₂ ^SF4 +d ₃ ^SF4 -d ₄ ^SF4 )

d ^SF16, 4 = 1/4 (d ₁ ^SF4 -d ₂ ^SF4 -d ₃ ^SF4 +d ₄ ^SF4 )

As can be seen from the above relationship, converting back to the original data symbols requires only four additions and one multiplication for each of the four data symbols of the mother code 310 .

Subsequently, please refer to FIG. 4 , which shows a flow chart of a method 400 for grouping detected codes according to channel impulse responses and performing joint detection using a parent code, wherein Encoded lower spreading factor (SF). In the method 400 of the present invention, first, step 402 detects the transmitted code in the received communication. Subsequently, step 404 may determine whether there are any detected codes with the same channel impulse response. If there are any detected codes with the same channel impulse response, then step 406 groups the detected codes and the method 400 of the present invention may proceed to step 408 . Conversely, if there is no detected code with the same channel impulse response, the method 400 of the present invention proceeds directly to step 408 .

In step 408, a parent code for each set of detected codes is identified. Then, in step 410, the identified parent codes can be used to build matrix A. Then, in step 412, the matrix A is provided to a joint detector and joint detection can be performed. In step 414 , the demodulated data symbols may be converted back to the encoded original data symbols detected in step 402 .

It should be noted that in order to reduce the complexity of the receiver, the transmitter should use a lower spreading factor (SF) for coded transmission, and the receiver and transmitter should use the same spreading factor (SF) for despreading and demodulation. However, when the transmitter uses a higher spreading factor for coded transmission, the receiver can still use a lower spreading factor (SF) for despreading and demodulation, and utilize a post-data converter Data symbols with a low spreading factor (SF) are used to recover the original data symbols with a higher spreading factor (SF), thereby significantly reducing its complexity.

In addition, it should be noted that the present invention can also be implemented in any type of wireless communication system using orthogonal coding. For example, the present invention can be implemented in CDMA 2000, UMTS-TDD, UMTS-FDD, TD-SCDMA, wireless local area network (WLAN) system with any type of 802.XX system, or any type of wireless communication system. In addition, although the present invention has been described in detail using preferred embodiments, those skilled in the art may make various modifications and changes without departing from the scope of the following claims of the present application.

Claims (14)

1. A receiver for reducing the complexity of multi-user processing, the receiver comprising: a code detector to detect transmitted codes and identify a channel impulse response for each detected code; a code grouper for grouping codes with the same channel impulse response; a parent code locator, used to identify the parent codes of each group identified by the code grouper; a multi-user detector to build a matrix A using the identified parent code, and to perform joint detection using said matrix A using the identified parent code; and a post-data converter to obtain a plurality of data symbols from the multi-user detector. 2. The receiver of claim 1, wherein the multiuser detector is configured to perform multiuser detection on said identified mother code. 3. The receiver of claim 2, wherein a detected code with a unique channel impulse response is considered a mother code. 4. The receiver of claim 1, wherein the multiuser detector comprises a matrix A builder and a joint detector. 5. The receiver of claim 4, wherein the matrix A builder is configured to build matrix A using the identified mother code. 6. The receiver of claim 5, wherein a detected code having a unique channel impulse response is considered a mother code. 7. The receiver of claim 4, wherein the joint detector is configured to perform joint detection using the identified parent codes. 8. The receiver of claim 7, wherein a detected code having a unique channel impulse response is regarded as a mother code. 9. The receiver of claim 1, wherein the post-data converter is to convert the parent encoded data symbols into the detected encoded data symbols. 10. The receiver of claim 9, wherein a detected code having a unique channel impulse response is considered a mother code. 11. A method for reducing the complexity of multi-user processing in a receiver, the method comprising the steps of: detecting at least one transmitted code; Identify the channel impulse response for each detected code; group detected codes with the same channel impulse response; Identify the parent code of each set of detected codes; Establish matrix A by using the identified parent code; performing joint detection using said matrix A using said identified parent code; and A plurality of data symbols carried by at least one detected code is obtained. 12. The method of claim 11, wherein a plurality of transmitted codes are detected. 13. The method of claim 11, wherein a detected code having a unique channel impulse response is considered a parent code. 14. The method of claim 11, wherein said plurality of data symbols carried by said at least one detected code is obtained using a parent code of said detected code.

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