WO2003103185A1

WO2003103185A1 - A receiving method based on mimo cdma

Info

Publication number: WO2003103185A1
Application number: PCT/CN2002/000368
Authority: WO
Inventors: Dandan Wang; Gang Wang; Yonghui Li
Original assignee: Linkair Communications,Inc.
Priority date: 2002-05-30
Filing date: 2002-05-30
Publication date: 2003-12-11
Also published as: AU2002313159A1; CN1555613A

Abstract

The present invention provides a receiving method based on MIMO CDMA,characterised in, the transmitting terminal sends separated signals by using at least two transmitting antennas; the rceiving terminal receives the signals transmitted from the transmitting terminal by using at least two receiving antennas,and resumes the signals transmitted from the transmitting terminal in the light of the maximum-likelihood criterion and the characteristic of MIMO CDMA in the Rayl-fading channel.The present invention is an algorithm with less complexity which performs receiving separately according to the characteristic of the spreaded signals in the multipath channel, and it is used for MIMO CDMA system, and it adapts to both simple carrier wave system and multi-carrier wave system of MIMO CDMA. This invention provides an algorithm with less operational complexity for the combination of MIMO and CDMA, and supports a condition for the application of this two techniques.

Description

A receiving method based on MIMO CDMA

TECHNICAL FIELD The present invention belongs to the field of communication technology, and specifically, it is a receiving method based on MIMO CDMA. BACKGROUND With the development of wireless communications, the status of data transmission has become increasingly prominent. In particular, 3G standards have paid special attention to data transmission. The service capabilities of the third generation of mobile communications will be significantly improved over the second generation. It should be able to support voice packet data to multimedia services; it should be able to provide bandwidth as needed. Among the minimum requirements of the third-generation mobile communication wireless transmission technology specified by the ITU (International Telecommunication Union), three requirements must be met in the following three environments. That is: fast moving environment, the highest rate is 144kbi t / s; indoor environment, the highest rate is 2Mbi t / s; outdoor to indoor or pedestrian environment, the highest rate is 384kbi t / s. It is predicted that the speed of the fourth generation mobile communication can reach more than 10 Mbps, and may even reach 30 Mbps to 100 Mbps.

However, due to the particularity of the medium of wireless communication in wireless communication, the tension of frequency band resources becomes increasingly prominent in the face of high-speed wireless data transmission. The frequency band of the first generation of analog mobile communications is several hundred megahertz, and the frequency band of the second generation of digital mobile phone systems is several hundred megahertz to gigahertz. The frequency band of the third generation of mobile communications in the future will be 2 gigahertz (2GHz )about. Although the expansion of new frequency bands has never stopped, in the face of spectrum tensions and data and the development of future multimedia services, improving spectrum utilization may be a better approach. If the wireless channel is rich in multipath scattering and the technology used can make full use of these multipath resources, the capacity of the channel will be huge. With the same bandwidth, the larger the capacity, the higher the frequency efficiency. In this way, the development of new technologies that can improve the utilization of the spectrum can transmit data at a higher rate based on the existing frequency band. Under this technical background, it is possible to use multiple antennas to transmit and receive. This has produced a multiple-input multiple-output system, MIMO (Mul t iple-Input Mul t iple- Output). MIMO technology There are multiple (N) antennas, in principle The peak capacity can be increased by N times, and the code reuse and small modulation constellation can be combined to obtain other intermediate rates. Later, someone combined MIM0 and CDMA (Code Division Multiple Access) and proposed the MIM0 CDMA system. Code division multiple access includes two basic technologies, one is code division technology, which is spread spectrum technology; the other is multiple access technology. Combining these two basic technologies and absorbing other key technologies has formed the technical support of today's CDMA mobile communication systems. The resources that a cellular system provides to users include time, frequency, and coding methods. Generally speaking, different systems can use different communication resources to distinguish communication objects. One such channel can only accommodate one user for communication, and many users who communicate at the same time are distinguished from each other in the form of different abstract channels. Site concept. The cellular mobile communication system is a system with multiple abstract channels working simultaneously, and has the characteristics of broadcasting and large-area coverage in the downlink direction. In the radio wave coverage area using the wireless communication environment, how to establish an infinite channel connection between users is a problem to be solved by the multiple access method. The method to solve the multiple access problem is called multiple access technology. Code division multiple access uses a set of orthogonal (or quasi-orthogonal) pseudo-random noise (PN) sequences (referred to as pseudo-random codes) through correlation processing to achieve the function of sharing frequency resources and simultaneous access to the network by multiple users. CDMA uses spread spectrum technology. The concept of spread spectrum technology is to transform the bandwidth of the original information into a much wider noise-like signal. At the transmitting end, the spectrum of the useful signal is broadened after being spread-spectrum processed; at the receiving end, the spectrum of the useful signal is restored to a narrow-band spectrum after being subjected to despreading processing using the correlation of the pseudo code. The wideband unwanted signal is not related to the local pseudocode, so it cannot be despread, and it is still a wideband spectrum; the narrowband unwanted signal is expanded by the local pseudocode into a wideband error. Since the unwanted interference signal is a wideband spectrum and the useful signal is a narrowband spectrum, we can use a narrowband filter to eliminate out-of-band interference levels, so the signal-to-noise ratio in the narrowband is greatly improved.

MIMO CDMA systems increase system capacity by sending independent spread-spectrum signals on different antennas. Signals on the same antenna are distinguished by orthogonal (or quasi-orthogonal) pseudo-random codes. However, due to the introduction of multiple antennas, under the Rayleigh fading channel model, the traditional RAKE reception scheme in CDMA technology is no longer applicable. However, a new scheme on how to use the characteristics of CDMA signals for reception under multipath channel conditions is not. Never appeared. Summary of the Invention

An object of the present invention is to provide a receiving method based on MIMO CDMA, which utilizes the characteristics of a MIM0 CDMA system under a Rayleigh fading channel, and proposes a MIMO CDMA system that is not only suitable for single carriers, but also according to the principle of maximum likelihood. The receiving scheme applicable to overlapping or non-overlapping multi-carrier receiving systems enables the transmission signals on different carriers of different antennas in a MIMO CDMA system to be recovered. The present invention provides an algorithm whose complexity is not high for the combination of two technologies, MIM0 and CDMA, and provides conditions for the application of these two technologies.

The technical solution of the present invention is: a receiving method based on MIMO CDMA, characterized in that the transmitting end uses at least two transmitting antennas to send signals independent of each other;

The receiving end uses at least two receiving antennas to receive the signal sent by the transmitting antenna, and according to the characteristics of MIMO CDMA under the Rayleigh fading channel, the signal sent by the transmitting antenna is recovered at the receiving end according to the maximum likelihood criterion.

The transmitting end uses at least two transmitting antennas to send signals independent of each other means that: the transmitting end may use more than two transmitting antennas to send signals; the receiving end uses at least two receiving antennas to send signals to the transmitting antennas Receiving means: The receiving end can use more than two receiving antennas to receive the signals sent by the transmitting antennas.

The transmitting terminal uses at least two transmitting antennas to send signals independent of each other means that: the transmitting terminal can use two transmitting antennas to send signals; the receiving terminal uses at least two receiving antennas to receive signals sent by the transmitting antennas It means: The receiving end can use two receiving antennas to receive the signal sent by the transmitting antenna.

The receiving step of the receiving end includes:

The receiving end uses at least two receiving antennas to receive the signals sent by the transmitting antennas; the receiving end obtains the differences received on different receiving antennas according to the characteristics of MIMO CDMA under the Rayleigh fading channel and the ideal autocorrelation and cross-correlation characteristics of the codeword Separation signal

Determining the merging coefficient of each separated signal;

The signal sent by the transmitting antenna is recovered at the receiving end according to the maximum likelihood criterion. When two transmitting antennas and two receiving antennas are used, the receiving step of the receiving end further includes:

The receiving end uses the receiving antenna 1 and the receiving antenna 2 to receive signals transmitted by the transmitting antenna 1 and the transmitting antenna 2;

Let bl and b2 be independent symbol information transmitted on two antennas, and H1, H2, H3, and H4 are transmitting antenna 1 and receiving antenna 1, transmitting antenna 2 and receiving antenna 1, transmitting antenna 1 and receiving antenna 2 respectively. A channel characteristic vector between the transmitting antenna 2 and the receiving antenna 2;

Let rl and ΐ2 be the signals received on receiving antenna 1 and receiving antenna 2, respectively; Take the 2-path Rayleigh fading channel as an example,

Hl = [h _u , h _u ], H2 = [h _2l , h ₂₂ ], H3 = [h ₃₁ , h ₃₂ ], H4 = [A ₄₁ , A ₄₂ ].

Here, c _i is a spread-spectrum pseudo-random code of the i-th user. It has ideal auto-correlation and cross-correlation characteristics within the scope of investigation, and can be obtained:

The above formula is despread, and the ideal auto-correlation and cross-correlation characteristics of the codeword are used to obtain:

It can be seen that „and ₁₂ , _Λι and: ^ are the first and second diameter separated signals received on the receiving antenna 1, and the receiving antenna 2, respectively;

Let G1 and G2 be the merging coefficients of ^ and ^, respectively, and then obtain according to the maximum likelihood criterion: and according to the maximum likelihood criterion, obtain:

The signals bl and b2 sent by the transmitting antenna are recovered at the receiving end.

The above steps can be analogized to MIMO CDMA that uses more than two transmitting antennas to send signals and uses more than two receiving antennas to receive signals sent by transmitting antennas. and,

^ Π 12 ^ _{2I 2} 2 is not limited to the inversion matrix in this example, as long as the separated multipath signals are obtained, they can be combined according to this method.

The beneficial effects of the present invention are as follows: The present invention is a receiving method designed according to the maximum likelihood maximum likelihood criterion using the characteristics of a MIMO CDMA system under a Rayleigh fading channel. The invention is used in a MIMO CDMA system, and uses the characteristics of spread-spectrum signals in a multipath channel to separate receive and then combine, which is a method with little computational complexity and is applicable to both MIMO CDMA single-carrier and multi-carrier systems. The invention provides a method with low computational complexity for the combination of the two technologies of MIMO and CDMA, and provides conditions for the application of these two technologies. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram of a MIMO CDMA system;

Figure 2 shows the simulation curves of MIM0, multipath, and bit error rate, where ML is: Maximum Likelihood Criterion and EGC is: Proportional Gain Merging. detailed description

Figure 1 is a block diagram of a MIMO CDMA system, where the transmitting end uses at least two transmitting antennas to send signals independent of each other; the receiving end uses at least two receiving antennas to receive signals sent by the transmitting antennas, and according to MIMO CDMA, the Rayleigh fading channel The characteristics, maximum likelihood criterion make the signal sent by the transmitting antenna recovered at the receiving end.

The calculation method of the present invention is described below by taking two transmitting antennas and two receiving antennas as examples. In other cases, the calculation method can be deduced by analogy. Let bl and b2 be independent symbol information transmitted on the two antennas. H1, H2, H3, and H4 are the transmitting antenna 1 and the receiving antenna 1, the transmitting antenna and the receiving antenna 1, the transmitting antenna 1 and the receiving antenna 2, respectively. Channel characteristic vector between transmitting antenna 2 and receiving antenna 1. Let rl and r2 be the signals received on receiving antenna 1 and receiving antenna 2, respectively. Take 2 trails Rayleigh An example of a fading channel:

Hl = [h _n , h ₁₂ ], H2 ^ [h _2l , h ₂₂ ], H3 = lh _zl , h _n l H4 = [h _4l , hJ.

Here, _C is a spread-spectrum pseudo-random code of the i-th user, which has ideal auto-correlation and cross-correlation characteristics in the scope of investigation, that is:

f constant il = i2

R winter

o zi ≠ find (l) multiply both sides by 2ι

The above formula is despread, and the ideal auto-correlation and cross-correlation characteristics of the codeword are used to obtain

It can be seen that, and; ₁₂ ; ₂₁ and: ^ are the first and second diameter separated signals received on the receiving antenna 1, and the receiving antenna 2, respectively.

And according to the maximum likelihood criterion: = y _n + y ₁₂

You get:

Figure 2 shows some simulation characteristics. The figure also shows the curve of proportional gain combining (EGC).

The invention is used in a MIMO CDMA system and uses the characteristics of a spread spectrum signal to receive separately in a multipath channel. It is an algorithm with little computational complexity and is applicable to both MIMO CDMA single-carrier and multi-carrier systems. The invention provides a low complexity algorithm for the combination of the two technologies of MIM0 and CDMA, and provides conditions for the application of these two technologies.

The above specific embodiments are only used to illustrate the present invention, but not intended to limit the present invention.

Claims

Rights request

1. A receiving method based on MIMO CDMA, characterized in that the transmitting end uses at least two transmitting antennas to send signals independent of each other;

The receiving end uses at least two receiving antennas to receive the signals sent by the transmitting antennas, and restores the signals sent by the transmitting antennas at the receiving end according to the characteristics of MIMO CDMA under the Rayleigh fading channel and the maximum likelihood criterion.

2. The method according to claim 1, wherein the transmitting end uses at least two transmitting antennas to send signals independent of each other, which means: the transmitting end can use more than two transmitting antennas to send signals;

The receiving end uses at least two receiving antennas to receive signals sent by the transmitting antennas means that the receiving end may use more than two receiving antennas to separate and receive signals sent by the transmitting antennas.

3. The method according to claim 1, wherein the transmitting end uses at least two transmitting antennas to send signals independent of each other, which means: the transmitting end can use two transmitting antennas to send signals;

The receiving end uses at least two receiving antennas to receive signals sent by the transmitting antennas means that the receiving end can use two receiving antennas to separate and receive signals sent by the transmitting antennas.

4. The method according to claim 1, wherein the receiving step of the receiving end comprises:

The receiving end uses at least two receiving antennas to receive the signals sent by the transmitting antennas; the receiving end obtains the differences received on different receiving antennas according to the characteristics of MIMO CDMA under the Rayleigh fading channel and the ideal autocorrelation and cross-correlation characteristics of the codeword. Separation signal

Determining the merging coefficient of each separated signal;

The signal sent by the transmitting antenna is recovered at the receiving end according to the maximum likelihood criterion.

5. The method according to claim 2, wherein the receiving step of the receiving end comprises:

Determining the merging coefficient of each separated signal;

6. The method according to claim 3, wherein the receiving step of the receiving end further comprises:

The receiving end uses receiving antenna 1 and receiving antenna 2 to receive signals sent by transmitting antenna 1 and transmitting antenna 2;

Let bl and b2 be independent symbol information transmitted on the two antennas, and H1, H2, H3, and H4 are the transmitting antenna 1 and the receiving antenna 1, the transmitting antenna 2 and the receiving antenna 1, and the transmitting antenna 1 and the receiving antenna 2 respectively. A channel characteristic vector between the transmitting antenna 2 and the receiving antenna 2;

Let rl and r2 be the signals received on receiving antenna 1 and receiving antenna 2, respectively; In a 2-path Rayleigh fading channel,

Hl = [h, h ₁

Here, it is the spreading pseudo-random code of the i-th user, which has ideal auto-correlation and cross-correlation characteristics in the survey range, and can be obtained:

It can be seen that: „and: ^ j ₂₁ and: ^ are received on the receiving antenna 1 and the receiving antenna 2 respectively. The first and second paths separate signals;

According to the maximum likelihood criterion, we get:

° 2-* 2 * 2 * 2 * The signals M and b2 sent by the transmitting antenna are recovered at the receiving end.

7. The method according to claim 6, wherein the steps can be analogized to MIMO CDMA using two or more transmitting antennas to transmit signals and using two or more receiving antennas to receive signals transmitted by the transmitting antennas.