AU758992B2 - Diversity combining receiver - Google Patents

Description

S F Ref: 471134

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

0000 00 0 0000 *000 00 0 Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: NEC Corporation 7-1, Shiba Minato-ku Tokyo

JAPAN

Motofumi Hanada Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Diversity Combining Receiver The following statement is a full description of this Invention, including the best method of performing it known to me/us:- 5845 DIVERSITY COMBINING RECEIVER BACKGROUND OF THE INVENTION 1. Technical Field of the Invention The present invention relates to a diversity combining method and a receiver with a plurality of receiving units using the diversity combining method.

2. Description of the Prior Art 10 Communication quality in mobile communication may be evaluated by, for example, an error rate of received data is degraded due to, for example, fading which is an interference phenomenon of radio signals which reach a receiving station through multiple paths of propagation.

The diversity is known as one of measures to cope with the fading. In selective diversity, a plurality of antennas is •go* employed to select the highest level as a received data.

Further, in diversity combining, a plurality of antennas is employed to combine signals from each antenna. The diversity combining is superior to selective diversity in the receiving quality.

One of the diversity combining receivers is shown in Figure 7. The receiver as shown in Figure 7 comprises four receiving units and diversity combining unit 29. Further, each receiving unit comprises an antenna, one of receiving subunits 20, to 204 one of phase detectors 21, to 214 and one of weight detectors 22, to 224. Receiving sub-units to 204 transform the frequency of received signals from each antennas into intermediate frequency.

Phase detectors 21, to 214 demodulate the intermediate frequency signals from receiving sub-units 20, to 204 and outputs them as received data D 1 to D4.

Weight detectors 22, to 224 output the received signal levels in receiving sub-units 20, to 204 as weight signals W1 to W4. Weight signals WI1 to W4 are the signal levels received by each of antennas.

Further, diversity combining unit 29 comprises multipliers 11 to 14, and adder 15. Multipliers 11 to 14 multiply received 10 data D1 to D4 by weight signals W1 to W4, respectively.

o Adder 15 adds the outputs from multipliers 11 to 14 and outputs the result of addition as combined output signal 33.

Thus, the above-mentioned conventional receiver executes multiplication and addition.

However, the conventional receiver has a disadvantage that a noise from a receiving sub-unit with, for example, a troubled antenna is multiplied and added, which results in a degradation of quality of combined output signal 33 from diversity combining unit 29.

20 The weight signal of the malfunctioned receiving sub-unit becomes naturally small but is not zero. Therefore, the quality of combined output signal 33 is degraded.

Such a disadvantage might be solved by equating the weight to be zero, when the weight W1 to W4 is smaller than a prescribed value. In this case, a part of the weight signals which contribute to improve the quality of combined output signal 33 may possibly be thrown away.

Therefore, a need exists to solve or ameliorate the abovementioned degradation of combined output signal quality due to the malfunctions of the receiving sub-units.

SUMMARY

Embodiments of the present invention provide a diversity combining receiver which can prevent or ameliorate the degradation of communication quality, even when one of the receiving sub-units of mobile communication receiver does not functions completely.

The diversity combining receiver of the present invention includes a plurality of receiving units, each of which SI comprises a receiving sub-unit for transforming a signal received by an antenna into an intermediate frequency signal, a demodulation unit for demodulating the intermediate signal to output it as a received datum, and a weight detector for outputting a weight corresponding to the level of the S:received signal.

The diversity combining receiver of the present inventionfurther includes an error rate detector which detects frame gO" 20 error rates of the received data from the receiving units, and outputs a notification signal which conveys that there exists at least one receiving unit of which frame error rate is greater than a prescribed rate.

The diversity combining receiver of the present invention further includes a diversity pre-processing unit which equates the weight of the receiving unit with high error rate to be zero, when the notification signal is inputted.

Further, the diversity combining receiver of the present invention includes a plurality of multipliers, each of which multiplies the weight and the received datum.

Furthermore, the diversity combining receiver of the present invention includes an adder which adds the outputs from the multipliers to obtain a combined output signal.

In short, the diversity combining receiver of an embodiment of the present invention identifies the false receiving unit on the basis of the frame error rates and the weights, and equates the weight of the identified false receiving unit to be zero. Accordingly, the data with noise from the false receiving unit is not used for diversity 1. 0 combining. Thus, the quality of communication is not S" "degraded.

Further, the notification signal may include information for identifying the receiving units of which error rates are greater than a prescribed rate. In this case, the diversity combining receiver has only to calculate the formula only for the receiving unit of which error rate is greater than a prescribed rate. Therefore, the quantity of calculation by the Sdiversity combining receiver is reduced, and its processing speed becomes high.

20 The present weight may be a threshold defined by the maximum weight multiplied by a constant which is greater than or equal to zero and smaller than unity.

Also, the error detector may detect the error rate of the Unique Word (UW) and the error rate by the Cyclic Redundancy Check (CRC) for each of the receiving unit.

Accordingly, the communication quality can be maintained, even when the receiving units in base stations or mobile stations are in bad conditions, because the false receiving unit can be detected, and the diversity combining is executed by equating the weight of the false unit to be zero.

BRIEF EXPLANATION OF THE DRAWUNGS Figure 1 is a block diagram of diversity combining unit 19 in the diversity combining receiver of the first mode of 10 embodiment of the present invention.

Figure 2 is a block diagram of diversity pre-processing unit 30 as shown in Figure 1.

Figure 3 is a flow chart for explaining the operation of the diversity combining receiver of the first mode of embodiment of the present invention.

Figure 4 is a block diagram of diversity combining unit 59 in the diversity combining receiver of the second mode of embodiment of the present invention.

Figure 5 is a block diagram of diversity pre-processing unit 70 as shown in Figure 4.

Figure 6 is a flow chart for explaining the operation of the diversity combining receiver of the second mode of embodiment of the present invention.

Figure 7 is a block diagram of a conventional diversity combining receiver.

Figure 8 is a block diagram of diversity combining unit 29 as shown in Figure 7.

PREFERRED EMBODIMENT OF THE INVENTION In the following, the modes of embodiment of the present invention are explained, referring to the drawings.

(First Mode of embodiment of the Present Invention A block diagram of the diversity combining unit 19 of the first mode of embodiment of the present invention, is shown in Figure 1. Reference numbers are used commonly in Figures 1,7, and 8. Conventional diversity combining unit 29 as shown in Figure 7 is replaced by diversity combining unit 10 19.

Diversity combining unit 19 includes diversity preprocessing unit 30 and error rate detector 35 which are not included in diversity combining unit 29.

Error rate detector 35 inputs received data D1 to D4 to determine the degradation of communication quality and starts up diversity pre-processing unit 30, when the 0o00 communication quality is recognized to be degraded.

The degradation of communication quality is determined on the basis of the following formulae and in the PHS personal handy phone) system which is practically used in Japan from 1995, utilizing time division duplex, 7 /4 shift QPSK (quadrature phase shift keying), and ADPCM (adaptive differential pulse code modulation).

In short, a frame error rate is determined by detecting an error of a unique word (UW) included in the received data.

Further, a cyclic redundancy ckeck (CRC) is executed.

UW is a signature for synchronization by detecting a coincidence between received UW and stored UW, and for identification of the other party.

CRC calculation is a calculation of error rate of information signature, using CRC signature included in the information signature. Here, CRC is a residue of the information signature divided by a generating polynomial.

Error rate ofUW a Formula (1) Error rate by CRC caluculation 0 Formula (2) Here, a is a critical error rate.

Further, diversity pre-processing unit 30 comprises false receiving unit detector 40 and weight correction unit 41 as shown in Figure 2.

False receiving unit detector 40 detects receiving units in bad conditions, on the basis of information from the receiving units 20, to 204.

Concretely, false receiving unit detector 40 selects the 15 maximum value among W1,W2,W3, and W4, and caluculates the following formula The receiving sub-unit which satisfyes the formula is determined to be in bad condition.

Wn/Wmax Formula (3) n 1 to4 Wmax maximum of WI to W4 3 a small number which is almost zero Here, 3 is put to be, for example, 0.01.

Weight correction unit 41 inputs weights W1 to W4 and outputs zero weight for the false receiving unit On the contrary, when any degradation is not found by error rate detector 35, the weight wl to W4 are transferred as they are without activating diversssity pre-processing unit Next, the operation of the diversity combining receiver of the first mode of embodiment of the present invention is explained, referring to Figure 3. First, the operation when any degradation is not found is explained.

Received data D1 to D4 are inputted into multipliers 11 to 14 and error rate detector 35, while weights W1 to W4 are inputted into diversity pre-processing unit Error rate detector 35 does not start up diversity preprocessing unit 30 (step 50), because error rate detector can not detect the degradation of the error rate. Accordingly, 10 diversity pre-processing unit 30 outputs weights W1 to W4 as they are inputted toward multipliers 11 to 14.

Multipliers 11,12,13,14 multiply received data D1 to D4 by weights W1 to W4 from diversity pre-processing unit respectively. Then, the output from multipliers 11 to 14 are 15 added by adder 15 and the result of addition is outputted as combined output signal 33.

Thus, the diversity combining receiver of the present invention operates similarly to the conventional diversity combining receiver, when no degradation is found in the receiving sub-units.

Next, the case when the receiving unit comprising receiving sub-unit 201, phase detector 211, and weight detector 221 is in bad condition is explained.

Also in this case, received data D 1 to D4 are inputted into multipliers 11 to 14 and error rate detector 35, while weights W1 to W4 are inputted into diversity pre-processing unit Error rate detector 35 starts up diversity pre-processing unit 30 (step 50), because error rate detector 35 detects the degradation of the error rate.

After starting up of diversity pre-processing unit 30, false receiving unit detector 40 selects the maximum value among W1,W2,W3, and W4(step51), and calculates the following formula to determine the false receiving unit (step 53).

Here, weight correction unit 41 outputs zero for WI (step 54).

When steps 53 and 54 are executed for all the receiving units (step 52), processing flow comes to the end.

Then, multipliers 11,12,13,14 multiply received data D 1 to D4 by weights W1 to W4 from diversity pre-processing unit 10 30, respectively. Here, the output from multipliers 11 becomes zero, because D1 is multiplied by zero weight W1.

Then, the outputs from multipliers 11 to 14 are added by 0 S"adder 15 and the result of addition is outputted as combined output signal 33. Here, the output from multipliers 11 does 15 not contribute the result of addition, because the output from multipliers 11 is zero.

Although antenna failure in the receiving units is taken up in the above-mentioned explanation, the present invention is applicable also to the failure of top amplifiers in the receiving units, because the output level from the malfunctioned receiving unit becomes quite small.

(Second Mode of embodiment of the Present Invention Next, the second mode of embodiment of the present invention is explained.

A block diagram of diversity combining unit 59 connected with the diversity combining receiver of the first mode of embodiment is shown in Figure 4. The reference numbers are used commonly in Figures 1,2, and 4.

Diversity pre-processing unit 30 in diversity combining unit 19 as shown in Figure 1 is replaced by diversity preprocessing unit 70, and error rate detector 35 is replaced by error rate detector Error rate detector 75 functions similarly to error rate detector 35 as shown in Figure 1. Further, error rate detector outputs notification signal 70 for indicating receiving units of which error rates are greater than a prescribed rate.

False receiving unit detector 40 as shown in Figure 2 is replaced by false receiving unit detector 80 as shown in Figure False receiving unit detector 80 selects the maximum value among W1,W2,W3, and W4(step51), and calculates the formula for the receiving unit indicated by notification signal 71. When the formula is satisfied, false receiving o• S unit detector 40 instructs weight correction unit 41 to equate the weight of the indicated receiving unit to be zero.

*fe Next, the operation of the second mode of the present invention is explained, referring to the flow chart as shown in Figure 6.

The operation when any fault is not detected is the same as shown in the flow chart as shown in Figure 3.

When a fault occurs, error rate detector 75 detects the receiving unit of which error rate becomes greater than the prescribed rate, starts up diversity pre-processing unit and send notification signal 71 to false receiving detector (step False receiving unit detector 80 selects the maximum value among W1 to W4 (step51), and calculates the following formula for the notified receiving unit(step 83). When the formula is satisfied, false receiving unit detector instruct weight correction unit 41 to equate the weight of the indicated receiving unit to be zero (step 84).

In the second mode of the present invention, false receiving unit detector 80 has only to calculate the formula only for the receiving unit of which error rate is greater than a prescribed rate, because notification signal 71 is sent to false receiving unit detector Therefore, the quantity of calculation by false receiving 10 unit detector 80 is reduced, and processing speed becomes *@e high.

The number of receiving units in the first and second S"modes of the present invention is not limited to four.

S:Further, not only phase shift keying (PSK), but also frequency shift keying (FSK) and amplitude shift keying (ASK) is employed preferably for the present invention.

The receiving unit is determined to be false, when its weight is smaller than a threshold /3 W max on the basis of the formula The threshold -W max may be replaced by a prescribed constant value.

Although the present invention has been shown and described with respect to the best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.

Claims (3)

1. A diversity combining receiver which comprises: a plurality of receiving units, each of which comprises a receiving sub-unit for transforming a signal received by an antenna into an intermediate frequency signal, a demodulation unit for demodulating said intermediate signal to output it as a received datum, and a weight detector for outputting a weight corresponding to the level of said signal received by said antenna; 10 an error rate detector which detects frame error rates of o..o the received data, and outputs a notification signal which conveys that there exists at least one receiving unit of which frame error rate is greater than a prescribed rate; a diversity pre-processing unit which equates said weight S 15 to be zero for the weight which is smaller than a prescribed weight, when the notification signal is inputted into said diversity pre-processing unit; a plurality of multipliers, each of which multiplies said weight and said datum; and an adder which adds the outputs from said multipliers to obtain a combined output signal.

2. The diversity combining receiver according to Claim 1, wherein said diversity pre-processing unit comprises: a false receiving unit detector which determines whether or not said weight is smaller than said prescribed weight, when the notification is received; and a weight correction unit which equates said weight to be zero, when said weight is determined to be smaller than said prescribed weight.

13- 3. The diversity combining receiver according to claim 1, wherein said notification signal includes information for identifying the receiving units of which error rates are greater than said prescribed rate. 4. The diversity combining receiver according to claim 1, wherein said prescribed weight is a threshold defined by the maximum of said weights multiplied by a constant which is greater than or equal to zero and smaller than unity. The diversity receiver according to claim 1, wherein said error detector detects error rates of the Unique Word (UW) and error rates by the Cyclic Redundancy Check (CRC) for each of said receiving units. 6. A diversity combining receiver substantially as herein described with reference to Figs. 1 to 3 or Figs. 4 to 6. 0 DATED this Eighth Day of July, 1999 *NEC Corporation Patent Attorneys for the Applicant @0.o SPRUSON FERGUSON o..o [R:\LIBT]055 3.doc: IAD