WO2002093861A1

WO2002093861A1 - A method of applying quadature amplitude modulation to a radio mobile communication system

Info

Publication number: WO2002093861A1
Application number: PCT/CN2001/000804
Authority: WO
Inventors: Yongzhong Zou; Liwen Shi; Daoben Li
Original assignee: Linkair Communications, Inc.
Priority date: 2001-05-17
Filing date: 2001-05-17
Publication date: 2002-11-21
Also published as: CN1443416A

Abstract

The present invention relates to a method of applying quadature amplitude modulation to a radio communication system, especially to a radio high-speed mobile communication system. The method comprises the steps of: (a) selecting a appropriate method of fading-reducing according the requirement of the radio mobile communication system, simultaneously selecting a Star QAM constellation and optimizing it; (b) according the interference degree of the system, improving the front end signal-to-interference ratio to reduce the interference of the system; (c) transmitter side using the QAM constellation selected and optimized in step (a) to modulate the signal to be transmitted with QAM; (d) receiver side using the QAM constellation selected, and optimized in step (a) and corresponding with transmitter side, to demodulate the received signal with QAM and judge receiving. Using this method, the fading-reducing capability of the mobile communication system and the adaptive ability of the mobile terminal are preferable, and the service of high quality and efficiency can be provided to different channel condition and different speed of mobile terminal can be provided.

Description

Method for applying quadrature amplitude modulation to wireless mobile communication system

The present invention relates to wireless mobile communication technologies, and in particular, to a method for digital transmission using a quadrature amplitude modulation (QAM, Quadrature Amplitude Modulation) in a wireless mobile communication system, especially a wireless high-speed mobile communication system. Background of the invention

With the advent of the information society and the era of personal communications, people have become more and more urgent to improve the spectral efficiency of wireless communication systems, because frequency resources are very limited. The so-called spectrum efficiency refers to the maximum number of users that the system can accommodate in a cell (sector) or sector (sector) when a user's transmission rate and system bandwidth are given. The measurement unit is per cell (or sector) per The total transmission rate supported by the unit bandwidth system. Obviously, the higher the spectral efficiency, the larger the system capacity.

Quadrature Amplitude Modulation (QAM) is a kind of amplitude modulation, which is a mature and efficient narrowband modulation method. With the development of mobile communications, high-speed, high-spectrum-efficiency digital transmission is required. QAM has attracted people's attention because of its characteristics of high spectral efficiency, especially the 16QAM and 64QAM modulation methods.

Generally, the expression of M-ary QAM modulation is:

y (t) = A _m cos ω _α ί + B _m sin oj 0≤t <T _{b In the} formula, 7; is the symbol width, and is the discrete amplitude value, m = l, 2, · ..,.

It can be seen from the above formula that the modulated signal is formed by superposing two mutually orthogonal carriers, and the two carriers are respectively modulated by two sets of discrete amplitudes {} and {,}. Amplitude modulation. Its amplitude 4, and ^ can be expressed as:

K-e _m A

Where A is a fixed amplitude and is related to the average power of the signal. (^, _E „,) represents the coordinates of the vector endpoints of the QAM modulation signal in the signal space, and is determined by the input information data. The process of determining the vector endpoint coordinates by the input information data is called constellation mapping, and the coordinate map formed by these vector coordinate mappings It can be called a constellation diagram. A typical rectangular QAM modulation constellation is shown in Figure 1.

It can be seen from FIG. 1 that the input information bit stream 0100 is mapped to a vector (3a, a) in the constellation map, and the input information bit stream 1011 is mapped to a vector (-a,-3a) in the constellation map. Where a is determined by the average power of the signal.

From the QAM modulation expression, it can be seen that the bandwidth of the QAM modulation signal is equal to the bandwidth of the multi-amplitude modulation, and in the case of occupying the same bandwidth, the QAM modulation has twice as many symbols as the multi-amplitude modulation. Transmission rate. It can be seen that QAM is a narrow-band modulation with high spectral efficiency.

The principle of QAM modulation is shown in Figure 2. Binary bit stream data is input into the modulator, and is divided into two channels through serial-to-parallel conversion, and then converted from two levels to L levels to form ^ and ^. Each AB _m (m = l ₅ 2 ₅ ..., V) corresponds to log ₂ binary bits. In order to suppress the out-of-band radiation of the modulated signal, 和 and ^ must pass through a pre-modulated low-pass filter, and then multiply them with the two carriers to form two ASK signals. Finally, the two signals are added to obtain a modulated QAM output signal.

The principle of QAM demodulation is shown in Figure 3. The input signal is divided into two channels, which are multiplied with two orthogonal carriers restored locally, and passed through low-pass filtering, multi-level decision, and L-level to two. Level conversion, and finally, receiving the data by parallel-serial conversion of the two signals. A more general QAM demodulation principle is shown in Fig. 4. After the received signal is multiplied by a locally restored orthogonal carrier, and then integrated sampling is performed, an estimate (d, e) of the modulated signal (, B _m ) can be obtained, Then, by calculating the distance between (d, e) and all possible signal points (A _m ,), the signal point with the smallest distance from (d, e) is the best output signal point obtained after the decision. This decision method is called the minimum Euclidean distance decision.

Measuring the performance of a modulation method can be performed by its constellation diagram.

Assume that the signal vector x „(m = 0, 1, 2, ... M) in the constellation diagram is transmitted, and the received signal vector is Y after channel transmission. Define the decision domain 1 and! :as follows:

If Ye i _m , it is determined that the transmitted signal is _X „, that is, a correct decision.

The signal is x „,, ('≠ m), which is a wrong decision.

As shown in Figure 15.

According to the theoretical proof and engineering practice, the error performance is related to | Υ- χ ² . Therefore, if the distance between the end points of each signal vector in the signal constellation diagram is larger, the anti-noise performance is better, and the bit error characteristic is better; the smaller the distance between each signal vector, the worse the anti-noise performance is, and the more the error characteristic is difference. The upper limit of the error performance is determined by the minimum distance between the endpoints of the signal vector in the constellation. A good signal constellation distribution should ensure a maximum distance between each signal constellation point.

As is known to all, wireless mobile communication, especially wireless high-speed mobile communication, has stronger random changes than wired communication, so its requirements for anti-fading performance during signal transmission and its adaptability to mobile speed are higher, as follows:

1) The mobile communication channel is a typical random time-varying channel. Random frequency spread by effects, and random time spread by multipath propagation effects. Random frequency diffusion will cause time-selective fading of the received signal, that is, the level of the received signal will have different random fluctuations over time; random time diffusion will cause frequency-selective fading of the received signal, that is, different spectral components of the received signal will There are different random fluctuations. In addition to severely degrading system performance, fading will also significantly reduce system capacity. The signal transmitted in the fading channel is not only affected by noise, but also by multiplicative interference such as flat fading or frequency selective fading, which causes the amplitude of the received signal to be attenuated and the phase to generate an additional phase shift. Frequency selective fading can also cause inter-symbol crosstalk. The Doppler spread due to motion also produces an irreducible BER. At this time, when constructing the signal constellation diagram, we must not only consider the minimum distance between the signal vectors, but also take into account that the signal vector has as few amplitude and phase types as possible to ensure that the constellation diagram has better anti-fading performance.

Existing mobile communication systems use binary phase-shift modulation (BPSK), four-phase phase shift keying / differential coding four-phase phase shift keying (QPSK / DQPSK), and Gaussian filtered minimum frequency shift keying (GMSK) modulation for voice services. With the development of mobile communications, high-speed, high-spectrum-efficiency digital transmission is required. For users with high-speed data services, these requirements are difficult to achieve with BPSK, QPSK / DQPSK, and GMSK. The existing QAM technology is mainly used in wired channel communications and wireless communications with slow channel changes. For mobile communications with fast channel changes, especially high-speed mobile communications Rayleigh fading channels, in order to make the bit error rate meet data services If the requirement is lower than 1.0e-6, the threshold signal-to-noise ratio required by QAM is high (such as John G. Proakis in his Digital Communications P788 to get the threshold signal required by 4QAM under the condition of Rayleigh fading channel with double diversity Noise ratio is 32dB), but due to intersymbol interference existing in existing mobile communication systems (ISI), adjacent cell and adjacent channel interference (ACI), multiple access interference (MAI) in CDMA systems, which makes it difficult for the carrier-to-interference ratio (C / I) to reach the threshold signal-to-interference ratio required for high-dimensional QAM .

2) The wireless mobile communication environment has a wide range of changes. For the same mobile terminal, it may communicate indoors and outdoors while standing still, or it may communicate at a walking speed of several kilometers, or it may be at a speed of tens of kilometers to several kilometers. Communication is performed at a speed of 100 km / h, which requires strong adaptability to the speed of movement. Summary of the Invention

It can be seen from the above analysis that the main object of the present invention is to provide a method for applying quadrature amplitude modulation to a wireless communication system, so that it has better anti-fading performance in mobile communication channels, especially high-speed mobile communication systems. At the same time, it has a good adaptability to the moving speed of the mobile terminal.

To achieve the above object, the technical solution of the present invention is implemented as follows:

A method for applying quadrature amplitude modulation to a wireless communication system. It is important that the method includes at least the following steps:

a. First select the appropriate anti-fading method according to the requirements of the wireless mobile communication system, at the same time select the star QAM modulation constellation map, and optimize the constellation map;

b. According to the degree of system interference, use appropriate technology to improve the front-end signal-to-interference ratio to reduce system interference;

c The sender uses the star QAM constellation selected and optimized in step a to perform QAM modulation on the signal to be transmitted;

d. The receiver uses the star QAM selected and optimized in step a and consistent with the sender. Constellation diagram, QAM demodulation and decision reception of the received signal.

Wherein, the optimization of the constellation diagram is to optimize the scaling coefficient of the amplitude of each signal in the constellation diagram.

The requirements of the wireless mobile communication system refer to the capacity and spectrum efficiency requirements of the wireless mobile communication system, or to the requirements of high-speed data transmission services and the fading environment of the system and the Doppler frequency shift range.

The anti-fading method is maximum ratio combining, or channel interleaving, or multipath (Rake) receiving anti-fading.

The system interference is determined by the size of multiple access interference (MAI), inter-symbol interference (ISI), or adjacent channel and adjacent cell interference (ACI).

The technology for improving the judgment front-end signal-to-interference ratio is equalization technology, or channel coding technology, or diversity technology, or spread spectrum technology.

The signal modulation described in step c above further includes the following steps:

1) First, the binary bit stream data input to the modulator is divided into two channels through serial-parallel conversion;

2) The two levels are then transformed from two levels to multiple levels to generate discrete amplitude values A _m and _Bra ;

3) the discrete amplitude values ₁ „and B _{m are} pre-modulated by the low-pass filter and multiplied with the two carriers to generate two ASK signals;

4) The sum of the two signals is output as the required QAM modulation signal.

Each discrete amplitude value corresponds to log ₂ binary bits.

The demodulation and decision described in step d further includes the following steps:

1) After the received signal is multiplied by the locally restored orthogonal carrier, and then subjected to integral sampling to obtain To estimate a modulation signal (A _{_m,} B _m) of (d, e);

2) The estimated value of the modulated signal is output after channel compensation and channel estimation remove multiplicative interference from the fading channel;

3) Calculate the distance between the output value and all possible signal points (A _m , B _m ), and obtain the signal point with the smallest distance from the output value as the optimal signal point output after the decision.

The channel estimation is a decision feedback channel estimation, a linear interpolation channel estimation, a Gaussian interpolation channel estimation, or a continuous pilot channel estimation.

The channel compensation is phase compensation, or amplitude compensation, or multipath (Rake) receiving channel compensation.

The star QAM modulation constellation diagram is a 16QAM star modulation constellation diagram, a 32QAM star modulation constellation diagram, or a 64QAM star modulation constellation diagram.

The 16QAM star modulation is two 8-phase star modulation constellation diagrams, or four 4-phase star modulation constellation diagrams, or other equivalent star QAM modulation constellation diagrams.

The 32QAM star modulation is two 16-phase star modulation constellation diagrams, or four 8-phase star modulation constellation diagrams, or eight 4-phase star modulation constellation diagrams, or other equivalent star QAM modulation constellation diagrams.

The 64QAM star modulation is two 32-phase star modulation constellation diagrams, or four 16-phase star modulation constellation diagrams, or eight 8-phase star modulation constellation diagrams, or other equivalent star QAM modulation constellation diagrams. Brief description of the drawings

FIG. 1 is a schematic diagram of a typical rectangular QAM modulation constellation; Figure 2 is a principle block diagram of QAM modulation;

Figure 3 is a principle block diagram of QAM demodulation;

Figure 4 is a block diagram of another QAM demodulation;

Figure 5 is a block diagram of QAM demodulation transmitted through a fading channel;

6 (a) is a schematic diagram of two 8-phase star 16QAM constellations used in the present invention;

FIG. 6 (b) is a schematic diagram of a general rectangular 16QAM constellation;

Figure 7 is a performance comparison chart of two 8-phase star 16QAM and rectangular 16QAM; Figure 8 is a schematic diagram of four 4-phase star 16QAM constellations used in the present invention; Figure; Figure 10 is a performance comparison of two 8-phase star 16QAM and rectangular 16QAM under AWGN channel;

FIG. 11 is a schematic diagram of a homogeneous random time-varying channel model;

Figure 12 Schematic diagram of three-path uniform delay power spectrum;

FIG. 13 is a structural frame diagram of a system used in the embodiment; FIG.

Figure 14 is a schematic diagram of a RAKE receiver;

Figure 15 is a schematic diagram of the decision domain;

Figure 16 is a schematic diagram of a universal rectangular 64QAM constellation;

Figure 17 shows four 16-phase star 64QAM (64qam4al6p) constellation diagrams; Figure 18 shows four 16-phase star 64QAM and rectangular 64QAM performance comparison diagrams at different vehicle speeds;

Figure 19 is a combination of four 16-phase star 64QAM and Turbo Coding technology. Schematic diagram of the error performance. Mode of Carrying Out the Invention

In the method of the present invention, selecting an optimized signal constellation diagram, that is, selecting a star QAM modulation model with good performance, is a key to QAM modulation applied to wireless mobile communication, especially wireless high-speed mobile communication. The maximum phase tolerance of traditional rectangular QAM modulation is not good, which leads to its unsatisfactory anti-fading performance in high-speed mobile communication channels. It can be proved that the improved star QAM modulation method has better performance in wireless communication systems. The traditional rectangular QAM modulation method has good anti-fading performance in a mobile communication channel, especially a high-speed mobile communication system, and has a good adaptability to the moving speed of a mobile terminal. Take 16QAM modulation as an example to compare the advantages of improved QAM modulation over traditional QAM modulation.

The improved 16QAM modulation method uses two 8-phase star constellation diagrams as shown in Figure 6 (a), and Figure 6 (b) is a 16QAM rectangular constellation diagram with the same minimum distance.

This star 16QAM can be considered as a combination of amplitude modulation and phase modulation. It differs from the rectangular 16QAM in that it has two amplitudes and eight phases. During modulation, the input information is divided into two parts: one part performs baseband amplitude modulation and the other part performs phase modulation. Two 8-phase star 16QAM signals. Each symbol consists of four bits. It is divided into two parts: the first bit and the last three bits. The former is used to determine the signal amplitude. When the input bit is "0", the signal amplitude is 2.6131a, and when the input bit is "1", the signal amplitude is 4.6131a, a is determined by the average power of the signal. The last three bits are used to select a signal phase: one of [0, π / 4, π / 2, 3 π / 4, π, 5/4, 3π / 2, 7π / 4].

The minimum signal distance of two 8-phase star 16QAM and rectangular 16QAM is 2a, then Their noise immunity is the same. When equal probability occurs at each signal point, the average signal transmission power is:

Rectangle 16QAM:

: 4 (α ² + ² ) + s [a ² + (3α) ² ] + 4 [(3a) ² + (3α) ² ] _ ₂

α ^{ν =} 16 star 16QAM:

₌ 8 «(2.6131α) ² + 8. (4.6131α) ² ₌

16 means that the average signal power differs by 1.47dB. It can be seen that in an additive white Gaussian noise (AWGN) channel, the signal-to-noise ratio required for two 8-phase star 16QAMs is higher than that of a rectangle under the same bit error rate 16QAM is 1.47dB higher. However, the optimal constellation map under the AWGN channel is not necessarily optimal under the fading channel. The star 16QAM improves the arrangement of the rectangular 16QAM constellation, reduces the number of amplitudes and phases, and increases the maximum tolerable phase error.

The traditional rectangular 16QAM constellation diagram has three amplitude values and twelve phase values, and its maximum tolerance phase error is only 13.3. As shown in Table 1.

Table 1 Comparison of maximum tolerable phase errors

Therefore, the anti-fading performance of two 8-phase star 16QAMs should be better than that of rectangular 16QAMs. The simulation results are shown in Figure 7.

The improved 16QAM modulation can also use four 4-phase star 16QAM constellations as shown in Figure 8. You can also use the two 8-phase constellations and four 4-phase constellations described above. The corresponding constellation diagram after the map is mathematically transformed, for example, the constellation diagram obtained by rotating each signal point of two 8-phase star 16QAM constellation diagrams by π / 8.

For other QAM modulations, corresponding improved QAM modulation methods can be similarly obtained. For example, for 64QAM, two 32-phase star 64QAM, four 16-phase star 64QAM, 8 8-phase star 64QAM, and so on can be used.

According to the technical solution and the description of the star QAM modulation, the basic steps of the present invention are as follows:

The first step is to adopt effective anti-fading methods, such as maximum ratio combining, Rake, according to the capacity and spectrum efficiency requirements of the wireless mobile communication system or the requirements of high-speed data transmission services and the fading environment and Doppler frequency shift range of the system. Receive, channel interleaving, and select a star QAM modulation constellation diagram with good performance and optimize it, such as the optimization of the radius of each circle (that is, the amplitude of each signal), the coefficient of proportionality, so that the system has better anti-fading performance, and It has good adaptability to different Doppler frequency shifts.

The second step is to improve the signal-to-interference ratio of the decision front-end by using technologies such as equalization, channel coding, diversity, and spread spectrum based on the interference of the system, such as MAI, ACI, and ISI, so that it can meet the threshold information required by the corresponding service requirements. Interference ratio.

In the third step, the sender modulates the signal to be transmitted according to the constellation diagram selected in the first step, as shown in FIG. 2.

In the fourth step, the receiver selects the star QAM constellation map consistent with the sender according to the first step to demodulate and judge the received signal. As shown in FIG. 5, FIG. 5 is a QAM solution transmitted through a fading channel. Tuning block diagram.

Because in wireless mobile communications, signals are subject to multiplicative interference when transmitted in fading channels. Interference, resulting in amplitude attenuation and additional phase shift. Therefore, in an absolute amplitude modulation or absolute phase modulation scheme, an amplitude reference or a phase reference is required when demodulating a decision. QAM modulation is quadrature amplitude modulation, so a channel estimation circuit and a channel compensation circuit need to be added to the QAM demodulation circuit to ensure that the QAM signal can be correctly judged after being transmitted through the fading channel.

The channel estimation can use channel estimation methods such as decision feedback, linear interpolation, Gaussian interpolation, and continuous pilot. The channel compensation can use channel compensation methods such as phase compensation, amplitude compensation, and RAKE reception.

The present invention will be further described in detail through three embodiments and the accompanying drawings.

The first and second embodiments are performed on the COSSAP simulation platform of SY OPSYS Company in the United States. All simulation work is based on the assumption that chip synchronization and carrier synchronization have been achieved on the uplink and downlink.

Embodiment one:

The simulation work of this embodiment is divided into two parts: AWGN channel and Rayleigh fading channel.

First compare the error performance of the two constellation diagrams in the AWGN channel. The system adopts LAS code spread spectrum, and adopts rectangular and star 16QAM modulation respectively. The channel model is additive white Gaussian channel. At this time, channel estimation and compensation loop are not needed. Only the adverse effects of additive white Gaussian noise exist in the channel. The minimum Euclidean distance decision scheme shown in Figure 5 is used for demodulation and decision, and the source information is Gray coded, as shown in Figure 9.

Figure 10 shows the error curves of the two constellation diagrams in the AWGN channel obtained by simulation.

Comparing the error result curve, it can be seen that in the AWGN channel, when the star 16QAM modulation and the rectangular 16QAM modulation reach the same bit error rate, the star 16QAM needs The signal-to-noise ratio is about 1.4dB higher than the rectangular 16QAM, which is consistent with the results obtained by the theoretical analysis in the previous article.

When simulating the fading channel, the simulation of the fading channel is generated using the three-path channel model in the IS95 library provided in COSSAP. The delay spread parameters and power allocation of the three-path channel are shown in Figure 11.

¾ (0, (0 is a three-path independent flat Rayleigh fading, its power spectrum is the Doppler frequency shift power spectrum, the average value is 0, and the variances are ^σ ., ^Σ 2, and let: '

The three-path Rayleigh fading is delayed at equal intervals and has equal power, that is, the simulation uses a uniform delay power spectrum as shown in Figure 12. This type of channel model is called a HRTVC Homogeneous Random Time Variable Channel (HRTVC) model. The purpose of LAS-CDMA system simulation using this channel model is to find the most unfavorable situation in the chip synchronization process to test the performance of the synchronization loop. It has no influence on the selection of modulation mode, the simulation of fading channel estimation and compensation.

The frame structure used by the system in this embodiment is shown in FIG. 13, where the broadcast channel

(Broadcast Channel) and Access Channel complete the initial synchronization of the uplink and downlink. The broadcast channel also has automatic gain control (AGC) and automatic power control.

(APC) and automatic frequency correction (AFC) fields to perform the coarse adjustment of gain control, power control, and carrier synchronization functions.

The service channel consists of nine service sub-frames, and each service sub-frame includes two parts, pilot and service data. The service channel uses 16QAM modulation (rectangular or star), and the pilot symbol sends a known signal bit stream "1000", that is, it is transmitted at the maximum power and is used to provide 16QAM The required starting amplitude and phase reference for demodulation.

The receiver uses a five-path RAKE receiver, as shown in Figure 14. The demodulated outputs of the three rakes (k == 0, k = l, k = 2 three paths) are used for symbol decision, and the energy output of the five rakes is used to form automatic power control (APC, automatic power control). Control signals for automatic gain control (AGC) and automatic delay control (ADC).

The I and Q correlators and channel estimation loops (IQC & CAE) on each rake of the RAKE receiver first compare the performance of rectangular 16QAM and star 16QAM under fading channels when using decision feedback channel estimation paths.

Using the above-mentioned channel model, system frame structure, RAKE receiver, decision feedback channel estimation loop, and maximum ratio combining, under three-path Rayleigh fading channels, at different vehicle speeds, rectangular 16QAM and star-shaped 16QAM modulation errors are used, respectively. The code curve is shown as 7.

It can be seen from the results in the figure that the performance of the star 16QAM modulation under fading channels is greatly improved than that of the rectangular 16QAM, and as the vehicle speed increases, the Doppler frequency shift increases, and the performance difference between the two becomes larger Big. When the vehicle speed reaches 180km / h, the rectangular 16QAM modulation can no longer work normally (see the error curve in the figure), while the star 16QAM modulation still has better performance, which is consistent with the results of the previous analysis. This example demonstrates that two 8-phase star 16QAM modulation methods have good anti-fading performance in mobile communication channels, especially in high-speed mobile communication systems, and have good self-adaptation to the mobile terminal's moving speed. '1 · Raw.

The first embodiment is mainly based on a large area synchronous CDMA (LAS-CDMA) system. This system uses LAS spreading code spreading.

Embodiment two:

Referring to FIG. 16 and FIG. 17, when the simulation on the fading channel is performed, the simulation of the fading channel is generated by using the three-path channel model in the IS95 library provided in COSSAP. The parameters of the channel delay extension and power allocation are used. Rec.ITU-RM.1225 Parameters specified in Vehicle environment A. Channel estimation uses a continuous pilot estimation method. The RAKE receiver, maximum ratio combining, and the like are the same as those in the first embodiment. In the three-path Rayleigh fading channel, the error curves of rectangular 64QAM and star 64QAM modulations at different vehicle speeds are shown in Figure 18.

It can be seen from the results in the figure that the performance of the star 64QAM modulation under fading channels is greatly improved compared to the rectangular 64QAM, and as the vehicle speed increases, the Doppler frequency shift increases, and the performance gap between the two becomes larger. Big. When the vehicle speed reaches 180km / h, the rectangular 64QAM modulation cannot reach the bit error rate required by the data service (see the error curve in the figure), while the star 64QAM modulation still has good performance. This embodiment takes four 16-phase star 64QAM modulations as an example, and confirms that the star QAM modulation method has good anti-fading performance in mobile communication channels, especially in high-speed mobile communication systems. The moving speed of the terminal is very adaptive.

The above two embodiments can fully prove that applying the star QAM modulation method to a wireless communication system not only has good anti-fading performance, but also has good adaptability to the moving speed of a mobile terminal.

To apply QAM modulation to wireless mobile communication channels, especially wireless high-speed mobile fading channels, two conditions should be met: (1) The system's decision front-end signal-to-interference ratio must be greater than the threshold signal-to-noise ratio of the required bit error rate of the corresponding service corresponding to QAM modulation (such as voice service 1.0e-3, data service 1.0e-6).

(2) The system has better anti-fading performance. For different channel environments and different vehicle moving speeds (which essentially correspond to different Doppler frequency shifts), the system can provide high-quality services.

The above two embodiments only satisfy the second condition. In actual engineering implementation, if the first condition is to be satisfied, the following two methods can be adopted: 1) Reduce interference. Reduce intersymbol interference (ISI), adjacent cell and adjacent channel interference (ACI), multiple access interference (MAI), etc., which are present in mobile communication systems. For example, the CDMA system uses a spreading code with a small MAI and ACI, such as a LAS-CDMA system; for example, equalization and other technologies are used to reduce inter-symbol interference (ISI). 2) Use channel coding, Rake receiver, diversity, spread spectrum and other technologies to improve the signal-to-noise ratio of the decision front end.

The following uses channel coding technology as an example to further describe the change of the signal-to-noise ratio of the system's decision front end after channel coding is added. This embodiment uses the Turbo Coding coding technology. Embodiment three:

This embodiment combines Turbo Coding technology with this improved QAM modulation technology to improve the signal-to-noise ratio (C / I) of the decision front end. Turbo Coding is a high-performance channel coding method proposed by Claude Berrou, Alain Glavieux, Punya Thitimajshima, etc. in "Near Shannon Limit Error Correcting Coding and Decoding: Turbo Codes" in 1993. This embodiment is implemented by a recursive encoder with feedback, and the polynomials used are as follows:

Where i / () = l + i) ² + £ » ³ , n (D) = \ + D + D ³ , and D is a delay unit.

The encoder has a coding efficiency of 1/2. The Turbo Coding internal interleaver uses a pseudo-interleaver (Pseudo-random interleaver). The interleaving length is 4096 bits. The input decoder is hard-decision information. The number of decoding iterations is 8 times. The four 16-phase QAM constellation diagrams shown in FIG. 17 are used, and the others are the same as those in the second embodiment. The obtained simulation results are shown in FIG. 19. From Figure 19, it can be seen that when the vehicle speed is 300km / h, 180km / h, 120km / h, when Eb / N0 = 18dB, the bit error rate is 0; when the vehicle speed is 60km / h, 30km / h, when Eb / When N0 = 21dB, the bit error rate is 0. The Eb / NO is the power of each bit, where N0 is the noise power spectral density. The lower the value, the better the channel performance. Compared with Figure 18, the coding gain of Turbo Coding exceeds 15dB, and the channel coding effectively improves the signal-to-noise ratio of the decision front end.

The above embodiments show that the method of the present invention adopts improved and optimized QAM modulation, which can improve its phase blur tolerance and amplitude blur tolerance, and have good adaptability to different Doppler frequency shifts, so that the system has Good anti-fading performance. For different channel environments and different moving speeds, the system can provide high-quality services. Especially after the channel coding technology is added, the signal-to-noise ratio of wireless communication transmission can be significantly improved, and the quality of wireless communication is higher.

Claims

Claim

1. A method for applying quadrature amplitude modulation to a wireless communication system, especially a wireless high-speed mobile communication system, characterized in that the method includes at least the following steps:

c The sender uses the QAM constellation selected and optimized in step a to perform QAM modulation on the signal to be transmitted;

d. The receiver uses the QAM constellation map selected and optimized in step a and consistent with the sender to perform QAM demodulation and judgment reception on the received signal.

2. The method according to claim 1, wherein the star QAM modulation constellation diagram is a 16QAM star modulation constellation diagram, a 32QAM star modulation constellation diagram, or a 64QAM star modulation constellation diagram.

3. The method according to claim 2, wherein the 16QAM star modulation is two 8-phase star modulation constellation diagrams, or four 4-phase star modulation constellation diagrams, or other equivalent star patterns. QAM modulation constellation diagram.

4. The method according to claim 2, wherein: the 32QAM star modulation is two 16-phase star modulation constellation diagrams, or four 8-phase star modulation constellation diagrams, or eight four-phase stars. Type modulation constellation diagram, or other equivalent star QAM modulation constellation diagram.

5. The method according to claim 2, wherein: the 64QAM star modulation is two 32-phase star modulation constellation diagrams, or four 16-phase star modulation constellation diagrams, Or 8 8-phase star modulation constellation diagrams, or other equivalent star QAM modulation constellation diagrams.

6. The method according to claim 1, wherein the optimization of the constellation map is an optimization of a scaling factor of the amplitude of each signal in the constellation map.

7. The method according to claim 1, wherein the signal modulation in step c further comprises the following steps:

a. First, the binary bit stream data input to the modulator is divided into two channels through serial-parallel conversion;

b. The two levels are then transformed from two levels to multiple levels to generate discrete amplitude values A „B _m ;

c. The discrete amplitude values of eight ₁ and B _{m are} pre-modulated by the low-pass filter and multiplied with the two carriers, respectively, to generate two ASK signals;

d. The sum of the two signals is output as the required QAM modulation signal.

8. The method according to claim 7, wherein each discrete amplitude value corresponds to ₂ binary bits of Iog.

9. The method according to claim 1, characterized in that the demodulation and decision in step d further comprises the following steps: a. After the received signal is multiplied by the locally restored orthogonal carrier, and then integrated sampling , to give estimates (d, e) a modulation signal (a _{_m,} B _m) of;

b. The estimated value of the modulated signal is output after channel compensation and channel estimation remove the multiplicative interference from the fading channel;

C. Calculate the distance between the output value and all possible signal points (A _m , B _m ), and obtain the signal point with the smallest distance from the output value as the best signal point after the decision Output.

10. The method according to claim 9, wherein the channel estimation is a decision feedback channel estimation, a linear interpolation channel estimation, a Gaussian interpolation channel estimation, or a continuous pilot channel estimation.

11. The method according to claim 9, wherein the channel compensation is phase compensation, or amplitude compensation, or multipath (Rake) receiving channel compensation.

12. The method according to claim 1, wherein: the requirements of the wireless mobile communication system refer to capacity and spectrum efficiency requirements of the wireless mobile communication system, or high-speed data transmission service requirements and a fading environment of the system. And Doppler shift range.

13. The method according to claim 1, wherein the anti-fading method is maximum ratio combining, channel interleaving, or multipath (Rake) receiving anti-fading.

14. The method according to claim 1, wherein: the system interference is caused by multiple access interference (MAI), inter-symbol interference (ISI), or adjacent channel and adjacent cell interference (ACI). Decide.

15. The method according to claim 1, wherein: the technology for improving the front-end signal-to-noise ratio of the decision is equalization technology, or channel coding technology, or diversity technology, or spread spectrum technology.