Support of multiuser detection in the downlink

[0001] This application claims priority to US Patent Provisional Application No. 60 / 180,402 filed February 4, 2000.

The present invention generally relates to a time division duplex (TDD / CDMA) wireless communication system using code division multiple access. More specifically, the present invention relates to determining a channelization code for multi-user detection in the downlink of a TDD / CDMA system.

Description: TECHNICAL FIELD [0003] A TDD / CDMA communication system is shown in FIG. The system 10 has a plurality of base stations 121 to 125. Each base station 121 has an operating range associated therewith. User devices (UE) 141 to 143 within the operating range of one base station communicate with that base station 121. The communication signal transmitted from the base station 121 to the UE 141 is called a downlink communication signal, and the communication signal transmitted from the UE 141 to the base station 121 is called an uplink communication signal.

[0004] In a wireless TDD / CDMA communication system, a plurality of communication signals are transmitted through a shared frequency spectrum. One of these types of systems has been proposed for the Third Generation Wideband CDMA (W-CDMA) standard. In a CDMA system, a plurality of communication signals are transmitted in the shared frequency spectrum, and the signals are distinguished from each other by a channelization code. In a TDD / CDMA system, the shared spectrum is time divided using, for example, a repeating frame having 15 fixed number of time slots. Each time slot is used to transmit an uplink communication signal or a downlink communication signal. Therefore, the communication signals are distinguished from each other by both the channelization code and the time slot. A single channelization code used for a single time slot is called a resource unit. Based on the communication signal bandwidth, the communication signal requires one or more resource units. Common data modulation techniques used in TDD / CDMA systems are quadrature phase shift keying (QPSK), binary phase shift keying (BPSK), and N quadrature amplitude modulation (QAM). Where N = 8, 16 or 64.

[0005] In this type of system, data is transmitted using the communication signal burst 16. The communication signal burst 16 carries data (in one resource unit) in a single time slot using a single channelization code. The normal communication signal burst 16 includes a mid amble 20, a guard period 18, and two data bursts 22 and 24, as shown in FIG. In the mid amble 20, the communication signal burst 16 is separated from each other so as to allow the difference in the arrival time of the burst 16 transmitted from the two transmitters. The two data bursts 22 and 24 contain the data of the communication signal burst. The mid amble 20 includes a mid amble code for estimating the channel response between the receiver and the transmitter.

[0006] Since a plurality of communication signal bursts may be transmitted in a single time slot, the receiver must be able to distinguish the data burst from the plurality of bursts. One method for reproducing received data is multi-user detection (MUD).

[0007] In the MUD, the receiver reproduces data of all communication signal bursts in one time slot, that is, all communication signal bursts including bursts transmitted to users other than its own station. In order to reproduce the data of all bursts, the MUD receiver must know all the channelization codes used for burst transmission. In the TDD mode proposed above for W-CDMA, each of UE141 to 143 only knows which channelization code and midamble code are used to carry information destined for its own station. To determine the entire channelization code and midamble code, a matched filter group is used to detect all possible channelization code / midamble code combinations. The output power from each of these matched filters is compared to the threshold to determine if a particular channelization code / midamble code combination is used. This technique is highly complex due to the high number of matching filters required. Also, if there is a high degree of correlation between the channelization codes, the performance of this method will be reduced. UK Pat. No. 2351422 discloses the association between training codes and channelization codes. The association between the training code and the channelization code is made so that each training code is associated with only one channelization code for a given diffusion rate. To facilitate this association, each training code sequence is associated with a branch of the DVSF tree. WO 99/40698 discloses the use of channel estimates extracted from the tracking sequence for the estimation of soft symbols in the received communication signal. Therefore, there is a need for a method that enables UE 141 to 143 to determine the channelization code that is actually in use.

[Summary of the Invention] A wireless time division dual communication system using code division multiple access has a base station and a plurality of user devices. This system communicates using a communication signal burst. Each of the communication signal bursts has a unique channelization code and midamble code. Map each of the midamble codes to at least one set of channelization codes. For each of the communication signal bursts to be transmitted from the base station in one time slot, the midamble code mapped to the channelization code of that burst is determined. A communication signal burst occurs and is transmitted within that time slot. Each burst has a determined midamble code for its own channelization code. The user device receives these bursts and determines each received mid amble. The user apparatus determines the channelization code of the transmitted communication signal burst based in part on the result of the determination of each received midamble code.

[Detailed Description of Preferred Examples] FIG. 3 shows a simplified base station transmitter 26 and a UE receiver 28 using multi-user detection (MUD). The data to be transmitted to the operating UEs 141-143 is generated by the data generators 321-32K. Each of these data generators 321 to 32K produces data to be sent in a particular communication signal burst. The generated data in each communication signal burst is formatted into a communication signal burst by spread spectrum and modulation devices 341 to 34K. These spread spectrum and modulation devices 341 to 34K add a mid amble and spread the generated data with a channelization code associated with the communication signal burst. Furthermore, the spread spectrum data is guided to an appropriate time slot for time multiplexing. All communication signal bursts are combined by combiner 52. The synthesized communication signal burst is converted into a modulated radio frequency signal by a mixer 36 or the like, radiated from the antenna 38, and transmitted to the radio channel 30. When transmission diversity is used in base station 141, radio frequency signals are transmitted from a plurality of antennas.

[0010] In the UE receiver 28, the radio frequency signal is received by the antenna 40. The received signal is converted into a baseband signal by a mixer 42 or the like. The channel estimation device 44 is used to estimate the channel that has transmitted the communication signal burst by using the transmission midamble code. The multi-user detection (MUD) device 46 signals the baseband signal using the channel estimation information and the active state channelization code to generate a hard symbol.

[0011] The flow diagram of FIG. 4 shows how to specify the channelization code in the active state. One technique that helps identify the active channelization code in UE141 is to provide a mapping between the midamble code (midamble code sequence) 541-54N and the channelization code 5611-56NM. Each of the midamble series 541-54N is associated with a set of channelization codes 5611-56NM, as shown in FIG. These pairs may include only a single channelization code, which is a one-to-one mapping between the midamble code and the channelization code. A burst transmitted from base station 121 with a channelization code for a set of midambles is formatted with that midamble code sequence (60, 62). When a burst is transmitted with channelization code 21, the mid-amble code series 2 is used for the burst.

[0012] In the UE receiver 28, after channel estimation, the transmission midamble code sequence is detected by the midamble code sequence detection device 48 (64). Based on the detected midamble, the logical block 45 uses the midamble code-to-channelization code mapping to determine a possible set of channelization codes. The channelization code detector 50 determines the received channelization code based on this determination (66). When a one-to-one mapping between the midamble code and the channelization code is used, the logical block 45 determines the channelization code. Therefore, the channelization code detector 50 is not used for one-to-one mapping. The MUD device 46 detects data from the entire burst using the determined channelization code and the response to the midamble code sequence associated with that channelization code.

[0013] An example of the channelization code detection device 50 is shown in FIG. Matching filters 821-82M are matched to the possible channelization code and the associated channel response determined by logical block 45. Since it is sufficient to check only the above-mentioned possible channelization codes, the number of matching filters 821 to 82M is significantly reduced, the configuration is simplified, and the performance of the receiver 28 is improved. The power of the soft symbol generated by each of the matching filters 821 to 82M is measured by the corresponding power measuring device 841 to 84M. The comparator 80 determines the received channelization code based on the power measurements for each channel. If the number of channelization codes transmitted is known, the comparator 80 selects the number of channels with the maximum power measurement. Otherwise, the comparator 80 compares the power level of each channel with the threshold to determine the channelization code that has been transmitted.

[0014] The channelization code information such as the transmitted channelization code and the number of the channelization codes can be transmitted to the UE 141 in order to help identify the channelization code. The transmitted information is available in connection with the channelization code / midamble code mapping or when the map is not used. These additional channelization code information enhances the accuracy of determining the active state channelization code in the UE receiver 28. Such additional information includes a Layer 1 signal, i.e. a Layer 1 signal associated with a midamble code or midamble shift. The mid amble code detection device 48 determines the received mid amble code, and the logic block 45 reproduces the channelization code information using the determination result of the mid amble code. Further, the channelization code detection device 50 uses the reproduced information to be useful for the channelization code determination. Another approach uses layer 2/3 signals to convey channelization code information. The signal is generated in a communication network circuit. Layer 2/3 signals can be used in association with Layer 1 signals or midamble code / channelization code mappings.

BRIEF DESCRIPTION OF THE DRAWINGS [Fig. 1] A schematic diagram of a time-division double code division multiple access communication system.

FIG. 2 is an explanatory diagram of a communication signal burst.

FIG. 3 is a simplified explanatory view of a base station transmitter and a user device receiver.

FIG. 4 is a flow diagram of a downlink channelization code specific flow diagram.

FIG. 5 is an explanatory diagram of mapping of a mid amble code series to a channelization code.

FIG. 6 is a block diagram of a channelization code detector.

[Code Description] 10 Time division dual (TDD / CDMA) communication system using CDMA 12 Base station 14 User equipment (UE) 16 Communication signal burst 18 Guard period 20 Mid amble 22, 24 Data burst 26 Base station transmitter 28 Users Device (UE) Receiver 30 Radio Frequency Channel 32 Data Generator 34 Spread Spectrum and Modulator 36, 42 Mixer 38, 40 Antenna 52 Combiner 44 Channel Estimator 45 Logical Block 46 Multi-User Detection (MUD) Device 48 Midamble Code Series Detection Device 49 Midamble code / channelization code mapping device 50 Channelization code detector 54 Midamble code sequence 56 Channelization code 58 Forming a mapping between midamble codes and channelization codes 60 Mapping the midamble code sequence to the channelization code of the burst to format the communication signal burst to be transmitted into time slots 62 Formatted Sending a burst from a base station 64 Determining the received midamble code in the UE 66 Determining the active channelization code using the received midamble code and mapping 68 Replaying data from the burst using the determined channelization code 82 Matching Filter Channelization Code 1 to M84 Power Measuring Device 90 Comparer