WO2006106589A1

WO2006106589A1 - Receiver and interference compensation method

Info

Publication number: WO2006106589A1
Application number: PCT/JP2005/006611
Authority: WO
Inventors: Yew Soo Eng; Shane Cw Chew
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2005-04-04
Filing date: 2005-04-04
Publication date: 2006-10-12

Abstract

A receiver of communication system using shared communication media. In this receiver, a power measuring part (320) measures the power of each of OFDM symbols. A weighting coefficient calculating part (322) calculates a power ratio weighting coefficient, which is a ratio of the power of each symbol to the total power of the received symbols, for each OFDM symbol. A time despreading part (324) multiplies each symbol by the power ratio weighting coefficient for that symbol, and thereafter sums up the symbols.

Description

Specification

Receiver and interference compensation method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a receiver and an interference compensation method for compensating for a symbol having a collision in a communication medium shared by a plurality of users.

Background art

[0002] In a communication system using a shared communication medium, there is a case where it is allowed to transmit information to two or more users at the same time in a certain state. For example, in a communication system using frequency hopping multiple access (FHMA), a symbol is transmitted to other symbols that are transmitted at the same time by other users in the same frequency band! Transmitted in different time slots on different frequency subbands according to a set of frequency hopping sequences or codes that reduce the possibility of interference or collisions.

[0003] Although channelization is obtained by these frequency hopping codes, inter-symbol interference or collision of other nearby piconets is not prevented. It is possible for two transmitters to transmit in the same frequency subband almost at the same time and interfere with each other throughout the transmission. At the receiver, such overlapping transmissions synthesize a composite signal that is described as a collision.

[0004] If collision between symbols is not repaired or compensated, multiple symbols may interfere with each other, preventing reception of some or all of the information of the symbols. Therefore, the received signal may be a superposition of overlapping symbols and becomes illegible, so that the transmission information is in a state referred to as lost.

[0005] In order to realize reliable communication, a technique for increasing the possibility of successful communication has been developed. For example, one such technique is to repeat the same information transmission multiple times in the time domain. This technique is referred to as time spreading in this context. Even if the interference prevents the reception of one or more information, the retransmitted information The likelihood that all transmissions of the report will collide or interfere is reduced. Therefore, the quality of the received symbol is improved.

[0006] In order to improve the overall link quality of the frequency / time spread communication system, weights are applied to the received signals before the received signals are subjected to time Z frequency despreading to compensate for the received signals. This improvement can be achieved.

[0007] A weight factor of 1 helps to reduce the contribution of collision symbols to the overall quality of the final despread symbol and increase the contribution of good symbols. The despread signal is obtained by averaging, and therefore, the despread signal is compared to the conventional method where the contribution of the collision symbol to the final despread signal and the contribution of the good symbol are equal U. The method of combining the signals is important for reducing the contribution of interference.

[0008] The prior art disclosed in Patent Document 1 uses the Walsh-Hadamard Transform (WHT) to spread data in the frequency domain and reduces the effects of interference. In this method, the received signal is weighted by the estimated signal-to-interference ratio (SIR).

Patent Document 1: U.S. Pat.No. 4,885,743

Disclosure of the invention

Problems to be solved by the invention

However, the prior art method estimates the SIR level by using null symbols periodically inserted in the spectrum of the desired signal during each frequency hopping slot at the transmitter side. That is what you need.

[0010] An object of the present invention is that it is simpler than the prior art because it does not require transmission of an extra null symbol in message communication that improves reception reliability by transmitting a message multiple times. It is an object of the present invention to provide a receiver and an interference compensation method capable of obtaining a better estimated value of transmission information and reducing the influence of interference.

Means for solving the problem

[0011] In order to solve the problem, the interference compensation method of the present invention includes (a) a step of receiving a plurality of symbols obtained by spreading one symbol at a communication partner, and (b) the received signal Measuring the power of each symbol; (c) the total power of the received symbol; Calculating a power ratio weighting factor that is a ratio of the power of each symbol to the power; (d) multiplying each received symbol by a power ratio weighting factor for the symbol; and (e) the power specific gravity. Adding a plurality of symbols multiplied by a coefficient.

[0012] Also, the receiver of the present invention is a receiving means for receiving a plurality of symbols obtained by spreading one symbol to a communication partner, and measures the power of each received symbol. Power measuring means, weight coefficient calculating means for calculating a power ratio weighting factor that is a ratio of the power of each symbol to the total power of the received symbol, and a power ratio weighting factor for the symbol for each received symbol And despreading processing means for summing up a plurality of symbols multiplied by the power ratio weighting factor.

The invention's effect

[0013] According to the present invention, the power ratio weighting coefficient for each of the received signals is calculated using the power of each of the received signals, and each signal is weighted with the power ratio coefficient, so that the collision symbol is obtained. Because it receives more contributions from good symbols than power, the overall quality of the despread signal can be improved.

Brief Description of Drawings

[0014] [Fig.1] Diagram showing time-frequency code

[Figure 2] Time-frequency map for symbol transmission on three frequency bands using time spreading factor of 2

FIG. 3 is a block diagram showing a configuration of a receiver according to an embodiment of the present invention.

FIG. 4 is a flowchart showing an interference compensation method according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Before describing embodiments of the present invention in detail, an exemplary environment in which the present invention can be used will be described. The present invention is directed to interference compensation for time spread shared media communication systems and is useful for many types of communication systems, particularly frequency hobbing multiple access and time spread communication systems. In time 'spread spectrum shared communication media, assume that one signal is communicated by sending the signal N multiple times, which also means that the signal is time spread N times . In order to facilitate the explanation of the present invention, the principle of the present invention in multiband UWB using OFDM will be described. However, the scope of the present invention can be applied to many types of communication systems as well.

[0017] FIG. 1 shows time-frequency codes for different piconets to realize channelization for different piconets in a multi-band UWB system. Multiple terminals (Devices) in the same piconet share the same time-frequency code, which is different from the time-frequency code of other terminals in another piconet. This allows multiple terminals in the same piconet to share a frequency band that does not interfere with other terminals in other piconets. For example, a piconet with channel number 1 transmits with a time-frequency code [123123], while a piconet with channel number 2 transmits with a time-frequency code [132132].

[0018] The time domain spreading operation is performed on the time domain subcarrier after the inverse Fourier transform (IFFT) operation. Time domain spreading processing is the power performed by spreading factor N = 2 This means that time domain spreading processing consists of transmitting the same information in two OFDM symbols. These two OFDM symbols are transmitted on different subbands to obtain frequency diversity using time-frequency codes.

[0019] For example, terminal A transmits an OFDM symbol message [Al, A2, A3 ···]! In this case, after performing the time spreading process with the spreading factor N = 2, the transmission message is [All, A12, A21, A22, A31, A32,...]. Here, A12, A22, and A32 are replicas of All, A21, and A31.

[0020] As shown in Fig. 1, when terminal A performs transmission using a time-frequency code [123123], information of the first OFDM symbol (All and A12) Information on the second OFDM symbol (A21 and A22) is transmitted on subbands F3 and F1, and further information on the third OFDM symbol (A3 1 and A32) is Retransmitted on subbands F2 and F3. Another terminal B in another piconet is also transmitting, and when these piconets are close to each other, as shown in Fig. 2, the symbol of terminal A and the symbol from terminal B A collision can occur between This collision causes the information in the symbols to overlap and damage this, eventually Affects the bit error rate.

[0021] The present invention is intended to compensate for the above problems of the prior art. The object of the present invention is to weight multiple symbols prior to performing time despreading, and multiply the symbols by a power ratio weighting coefficient, thereby affecting the error effect on the final despread symbol by the collision symbol. It is to reduce.

[0022] (One Embodiment)

FIG. 3 is a block diagram showing a configuration of a receiver according to an embodiment of the present invention. The receiver 300 includes a demodulator 350 and an interference compensator 352 connected to the demodulator 350.

[0023] The reception filter 306 of the demodulation unit 350 generates a baseband signal by filtering the input signal that has also received the shared communication media (not shown) power. This filtering removes unwanted spectral components from the sequence. Receive filter 306 may be a root 'raised' cosine filter.

The baseband signal output from the reception filter 306 is first sent to the interference compensation unit 352 before passing through the fast Fourier transform (FFT) unit 308.

The interference compensation unit 352 is connected between the reception filter 306 and the FFT unit 308. The interference compensation unit 352 performs interference compensation processing on the baseband signal. As shown in FIG. 3, the interference compensation unit 352 includes a power measurement unit 320, a weight coefficient calculation unit 322, and a time despreading processing unit 324.

[0026] Power measurement section 320 measures the power of each OFDM symbol using technical means including squaring processing and summation processing or averaging processing, and outputs the power to weighting coefficient calculation section 322. Such technical means are well known to those skilled in the relevant art. The power measuring unit 320 further includes a counter that counts the number of OFDM symbols. As an example, when multiple OFDM symbols (Al l, A12) with N = 2 are input, the power measurement unit 320 uses the power P (Al 1) and P (A12) for each OFDM symbol! taking measurement.

[0027] Weighting factor calculation section 322 calculates a power ratio weighting factor that is the ratio of the power of each symbol to the total power of the received symbol for each OFDM symbol! / The power ratio weighting coefficient is output to the time despreading processing unit 324. As an example, when symbols A1 and A12 are input, the power ratio weighting factor of the symbol A1 can be expressed as a ratio of the power of the symbol A12 to the total power of the symbols A1 and A12. On the other hand, the power ratio weighting factor of the symbol A12 can be expressed as the ratio of the power of the symbol All to the total power of the symbols Al1 and A12. That is, the power ratio weighting coefficient of the symbol All can be expressed by the equation [P (A12) / {P (A11) + P (A12)}], and the power ratio weighting coefficient for the symbol A12 is It can be expressed by the equation [P (A11) / {P (A11) + P (A12)}].

[0028] Time despreading processing section 324 multiplies each symbol by a power ratio weighting factor for the symbol. Thereafter, the time despreading processing unit 324 performs symbol summation and outputs the summed value to the FFT unit 308. For example, when the time despreading processing unit 324 performs processing on the symbols All and A12, [Α11χ {Ρ (Α12) / (Ρ (Α11) + P (A12))} +

Α12χ {Ρ (Α12) / (Ρ (Α11) + Ρ (Α12 >>)] is calculated as the sum of symbols.

[0029] The FFT unit 308 performs FFT conversion processing on the output signal of the time despreading processing unit 324.

The output signal of FFT section 308 is an OFDM demodulated symbol sequence in the frequency domain.

[0030] The advantage of the present invention in which the power ratio weighting factor is multiplied to the symbols before summing the symbols is that the contribution of the collision symbols to the overall quality of the despread signal is reduced, and the good symbols This is useful in increasing the degree of contribution. This increases the overall quality of the despread signal because it receives more contributions from good symbols than collision symbol power. If the power ratio weighting factor is not used, the contribution from the collision symbol force will be the same as the contribution from the good symbol.

The method begins at step 400 where an OFDM demodulator power OFD M symbol is received via a shared communication medium such as a wireless channel.

[0032] In step 402, power measurement is performed on the received OFDM symbols. In step 404! /, If the number of received OFDM symbols is not equal to the time spreading factor N! / ヽ, the process returns to step 400 to receive another OFDM symbol. It becomes. If the number of received OFDM symbols is equal to N! /, Processing proceeds to step 406.

[0033] Next, in step 406, a power ratio weighting factor is calculated. Then step 408 , Each OFDM symbol is multiplied by a power ratio weighting factor. Next, in step 410, the two OFDM symbols that have been multiplied by the power ratio weighting factor are added together.

[0034] Thus, according to the present embodiment, the power ratio weighting coefficient for each of the plurality of received signals is calculated, and each signal is weighted with the power ratio coefficient. As a result, the overall quality of the despread signal can be improved because more contribution is received from the good symbol than the collision symbol power.

[0035] Those skilled in the art will recognize that the present invention discloses numerous modifications within the scope of the inventive concept. Although the foregoing description is considered to be a preferred embodiment of the present invention, it will be understood that various modifications can be made thereto and that the present invention can be implemented in various forms and embodiments. Like. Therefore, the scope of the present invention is not limited to the embodiments disclosed herein, but is defined by the description of the claims presented below and further by their equivalents. Industrial applicability

[0036] The present invention is suitable for use in a receiver that compensates for a symbol having a collision in a communication medium shared among a plurality of users.

Claims

The scope of the claims

[1] The interference compensation method is

(a) receiving a plurality of symbols obtained by spreading one symbol to a communication partner; and

(b) measuring the power of each received symbol;

(c) calculating a power ratio weighting factor that is a ratio of the power of each symbol to the total power of the received symbols;

(d) multiplying each received symbol by a power ratio weighting factor for the symbol;

(e) adding a plurality of symbols multiplied by the power ratio weighting factor.

[2] The receiver

Receiving means for receiving a plurality of symbols obtained by spreading one symbol at a communication partner;

Power measuring means for measuring the power of each received symbol;

Weighting factor calculation means for calculating a power ratio weighting factor that is a ratio of the power of each symbol to the total power of the received symbol;

Despreading processing means for multiplying each received symbol by a power ratio weighting coefficient for the symbol and adding together a plurality of symbols multiplied by the power ratio weighting coefficient.