CN1691562B - A Code Division Multiple Access Method in Orthogonal Time-Frequency Domain Based on Variable Spreading and Frequency Hopping - Google Patents

Abstract

The code division multiple access method in the orthogonal time-frequency domain based on variable spread spectrum and frequency hopping comprises the steps of: a) selecting an appropriate time-frequency unit group in the time-frequency domain of OFDM according to the frequency hopping pattern; b) from Selecting an orthogonal code in the orthogonal code group, adopting orthogonal spread spectrum in the selected OFDM time-frequency unit group by step a) to determine the sub-channel under the selected frequency hopping pattern; c) selecting from step a) In the group with the same time-frequency unit, the spread spectrum information in the SC-SFHP channel selected from step b) in the same time-frequency unit group to meet the orthogonal characteristics is multiplexed; d) from step c) The multiplexed data information obtained in the process is transmitted through the OFDM system. The invention meets the needs of future high data rate transmission. Due to the orthogonal spread spectrum, it can provide the function of system frequency diversity. At the same time, it provides system time diversity under high spreading factor and frequency hopping. The synchronization required for frequency hopping information and the despreading of the orthogonal codes can benefit from the synchronization and channel estimation/channel equalization of the OFDM system.

Description

A Code Division Multiple Access Method in Orthogonal Time-Frequency Domain Based on Variable Spreading and Frequency Hopping

technical field

The invention relates to information transmission and multiple access technology in a wireless communication system, in particular to a method for information transmission and multi-channel division using orthogonal frequency spread and frequency hopping technology in an Orthogonal Frequency Division Multiplexing (OFDM) system.

Background technique

In the field of wireless communication, multiple access technology is used to support multiple users to access the network, so as to achieve the effect of multi-user service multiplexing. With the expansion of business requirements in wireless communications, providing higher-speed data transmission and multiple access technologies has become a research hotspot. Code Division Multiplexing (CDMA) is an advanced wireless spread spectrum communication technology used in digital cellular mobile communications in recent years, and has been adopted by IS-95, Wideband Code Division Multiplexing (W-CDMA) and other standards and systems. Code Division Multiplexing (CDMA) systems employ Direct Sequence Spread Spectrum (DS-SS) to overcome frequency selective fading in the channel. But its capacity is limited by multiple access interference (MAI, multiple access interference), and MAI comes from the autocorrelation and cross-correlation characteristics of incomplete spreading codes. Zero cross-correlation orthogonal codes do not introduce MAI in flat fading channels and Gaussian channels, but in frequency selective fading channels, due to inter-chip interference, the orthogonality of orthogonal codes is not easy to guarantee, which will lead to system Reduced performance. A method to suppress inter-chip interference in frequency-selective fading channels is to combine CDMA technology with multi-carrier modulation, such as Orthogonal Frequency Division Multiplexing (OFDM) technology, to achieve higher spectral efficiency. Multi-Carrier-CDMA (Multi Carrier-CDMA, MC-CDMA) and Orthogonal Frequency and Code Division Multiplexing (OFCDM) are typical representatives of access methods that combine CDMA and OFDM technologies.

In the MC-CDMA mechanism, in the frequency domain, the spreading information obtained by multiplying the spreading code specified by the user with the copy of the same information symbol is mapped to different subcarriers, because the copy of the same information symbol is passed through multiple subcarrier transmission, so the frequency diversity effect is achieved, but the possibility of MAI still exists.

Based on the idea of MC-CDMA, S.Abeta et al. in "Performance of coherentmulti-carrier/DS-CDMA for broadband packet wireless access", IEICE Trans, Commun., E84-B, n0.3, pp406-414, Mar., Orthogonal Frequency and Code Division Multiplexing (OFCDM) technology was proposed in the 2001 reference. Like MC-CDMA, OFCDM also performs spread spectrum processing in the frequency domain, so OFCDM and MC-CDMA have the same transceiver model. However, OFCDM can change the spreading factor according to factors such as cell structure and channel, so as to adapt to the requirements of various communication environments. Subsequently, Noriyuki Maeda et al. referenced in "Variable spreading factor-OFCDM with two dimensional spreading that prioritizes time domain spreading for forward link broadband wireless access" Vehicular Technology Conference, 2003. VTC 2003-Spring, Volume 1, April, 2020-2 , the orthogonal spread spectrum technology in OFCDM is extended to the time-frequency domain, and in order to ensure the orthogonality of the orthogonal codes after the frequency-selective channel, the coherent bandwidth and the time-frequency combination within the coherent time are mainly studied.

Channels experiencing frequency selective fading will lead to inter-chip interference, so the orthogonality of the orthogonal codes is not easy to guarantee, which will lead to the degradation of system performance. One approach to suppress inter-chip interference in frequency-selective fading channels is to combine CDMA technology with multi-carrier modulation, such as Orthogonal Frequency Division Multiplexing (OFDM) technology, to achieve higher spectral efficiency.

In the MC-CDMA mechanism, in the frequency domain, the spreading code specified by the user is multiplied by an information symbol to obtain spreading information, which is then mapped to different subcarriers. Frequency diversity is achieved because copies of the same information symbol are transmitted over multiple subcarriers.

OFCDM can change the spreading factor according to the cell structure and channel conditions, so as to adapt to the requirements of various communication environments. Moreover, in order to ensure the orthogonality of the orthogonal codes after experiencing the frequency selective channel, the coherence bandwidth and the time-frequency combination within the coherence time are mainly studied.

But regardless of MC-CDMA and OFCDM systems, the receiver needs to benefit from channel estimation and channel equalization in decoding the spread spectrum information. Especially for the OFCDM system, the inconsistency of the channel estimation bias in the extended domain of an orthogonal code will destroy the orthogonality and introduce MAI. Even if the channel estimation is performed on the spread spectrum information within the coherence bandwidth and coherence time, it is difficult to maintain a consistent bias of the channel estimation.

Contents of the invention

The object of the present invention is to provide a code division multiple access method in the orthogonal time-frequency domain based on variable spread spectrum and frequency hopping.

In order to achieve the above object, a method for code division multiple access in the orthogonal time-frequency domain based on variable spread spectrum and frequency hopping, comprising steps:

a) Select an appropriate time-frequency unit group in the time-frequency domain of OFDM according to the frequency hopping pattern;

B) select the orthogonal code from the orthogonal code group, and adopt the orthogonal spread spectrum to determine the sub-channel under the selected frequency hopping pattern in the OFDM time-frequency unit group selected by step a);

c) In the group with the same time-frequency unit selected from step a), perform the spread spectrum information in the SC-SFHP channel that satisfies the orthogonality characteristic in the same time-frequency unit group from step b) reuse;

d) The multiplexed data information obtained in step c) is transmitted through the OFDM system.

The invention meets the needs of future high data rate transmission. Due to the orthogonal spread spectrum, it can provide the function of system frequency diversity. At the same time, it provides system time diversity under high spreading factor and frequency hopping. The synchronization required for frequency hopping information and the despreading of the orthogonal codes can benefit from the synchronization and channel estimation/channel equalization of the OFDM system. It is convenient for the system to flexibly adapt to various communication environments. When the variable spreading factor is 1, VSFH-OTFCDM is simplified to FH-OFDMA, which is suitable for single-cell systems. When the variable spreading factor is greater than 1, VSFH-OTFCDM will combine technologies such as orthogonal spread spectrum, frequency hopping and OFDM, and is suitable for multi-cell systems.

Description of drawings

Fig. 1 is the structural diagram of the sub-channel SC-SFHP under the selected frequency hopping pattern;

Figure 2 is the composition framework of VSFH-OTFCDM;

Fig. 3 is the schematic diagram of the time-frequency allocation of the orthogonal spread spectrum SC-SFHP channel of VSFH-OTFCDM;

Fig. 4 is the signal model of VSFH-OTFCDM;

Figure 5 is an example of allocation of SC-SFHP channel orthogonal codes.

Detailed ways

OFDM technology uses mutually orthogonal sub-carriers (sub-carrier frequencies) to transmit low-rate data in parallel to achieve high-data-rate communications. The receiving end utilizes the orthogonality of each sub-carrier to separate the data information transmitted in parallel. Based on OFDM technology, the present invention proposes an orthogonal time-frequency domain code division multiple access technology (VSFH-OTFCDM) based on variable spread spectrum and frequency hopping. VSFH-OTFCDM combines orthogonal spread spectrum, frequency hopping and OFDM technology. Pattern, SC-SFHP), the data information is orthogonally spread, and the spread information is mapped to the SC-SFHP channel in the time-frequency domain, and transmitted through the OFDM system.

Among them, SC-SFHP is the minimum resource allocated to services in the VSFH-OTFCDM system. An SC-SFHP channel is mapped to a time-frequency unit group composed of multiple time-frequency units TFC. Each TFC can be composed of a group of continuous subcarriers in the frequency domain with a number greater than or equal to 1. The subcarrier combination method in TFC can be frequency domain Consecutive subcarrier combination or combination by subcarrier index. The combination of TFCs in the SC-SFHP channel is determined by the assigned frequency hopping pattern. In the code domain of the same time-frequency unit group, multiple SC-SFHP channels satisfying the orthogonal characteristic can be superimposed, and the SC-SFHP channels superimposed in the code domain can be allocated to the same user or to different users.

According to the present invention, a plurality of OFDM symbols form the OFDM time-frequency domain, and the VSFH-OTFCDM system controls the allocation of its time-frequency domain resources and orthogonal code channels based on variable spread spectrum and frequency hopping. The system selects a frequency hopping pattern according to system requirements and business requirements, and selects an appropriate time-frequency unit (TFC) group in the OFDM time-frequency domain. Orthogonal spread spectrum is used in the unit group to determine the appropriate SC-SFHP channel. Code channels with the same time-frequency unit group and orthogonal characteristics can be multiplexed, and the multiplexed data information is transmitted through the OFDM system. Wherein, the orthogonality characteristic of the orthogonal code refers to that two different codes selected from the orthogonal code group are integrated in a given interval, and the result is 0. The mathematical description of the orthogonality property is assuming that W _j (t) and W _k (t) (j and k are integers, and 0 j, k N-1) are selected from the same code set {W _i (t); t∈ (0,T),i=0,1,...,N-1}

${\∫}_0^T{W}_j\left(t\right)W_k\left(t\right)\mathrm{dt}=\left\{\begin{array}{cc}0& j\≠k\\ m& j=k\end{array}\right.$ , M is a real number

After the OFDM system synchronization is completed and the allocated frequency hopping pattern and orthogonal code are known, the receiving end determines the time-frequency unit group allocated by the system in the OFDM time-frequency domain, and uses the correlation characteristics of the orthogonal code to analyze the allocated The spread spectrum symbol information in the SC-SFHP channel is despread to extract the original data information.

Fig. 1 is a structural diagram of a sub-channel SC-SFHP under a selected frequency hopping pattern. Under the control of the frequency hopping pattern selection module 102, the system completes the function of determining the time-frequency unit group module 104 composed of multiple TFCs in the OFDM time-frequency unit. The system uses the orthogonal code selection module 106 to select an appropriate orthogonal code from the orthogonal code group to complete the orthogonal spread spectrum. The data symbol (including modulated or unmodulated) signal is copied multiple times by the data symbol signal replication module 104, and the number of copies is the same as the length of the selected orthogonal code. The replicated data symbols passed through the data symbol replication module 104 and the orthogonal code selected by the orthogonal code module 106 are multiplied bit by bit in the multiplier module 110 to form a spread spectrum symbol signal. Subsequently, the spread spectrum symbol signal is mapped to a selected time-frequency unit group in the constructing SC-SFHP channel module 112, thereby constituting the SC-SFHP channel. In the same selected time-frequency unit group, using the SC-SFHP channel orthogonal superposition module 114, the spreading symbols from multiple SC-SFHP channels will complete the orthogonal superposition. The signals after orthogonal superposition will be transmitted via the OFDM system.

Figure 2 is the composition framework of VSFH-OTFCDM. In the VSFH-OTFCDM system model, the system will construct an SC-SFHP channel in the OFDM time-frequency unit, and the SC-SFHP channel will carry spread spectrum service data, and the spread spectrum symbols of multiple SC-SFHP channels can complete orthogonal superposition. The signals after orthogonal superposition will be transmitted via the OFDM system. In this mechanism, controlled by the selected variable spreading factor (VSF) and frequency hopping pattern, the data symbols are orthogonally spread to the orthogonal channels in the time-frequency domain, and the VSF of the selected orthogonal spreading code The spreading factor can be selected according to the network topology and system requirements. VSFH-OTFCDM supports the multiplexing of multi-user services. Assume that there are data of users A and B to be transmitted. The service data of user A is delivered to the information symbol decomposition module 204 through the modulation module 202. The information symbol decomposition module decomposes the user information into each SC-SFHP channel according to the service requirements. In this illustration, the information symbol decomposition module Decompose the service data of user A into the SC-SFHP channel 0 module 206 and the SC-SFHP channel K module 218 . In the K+1 SC-SFHP channels, all functional modules are the same. Among them, in the SC-SFHP channel 0 module 206, user information is input into the orthogonal spread spectrum module 208 to perform orthogonal spread spectrum, and the spread information completes the channel mapping through the SC-SFHP channel mapping module 210, and the orthogonal The spread spectrum module 208 and the SC-SFHP channel mapping module 210 are all controlled by the VSF module 214 and the frequency hopping pattern module 216, and the information after the SC-SFHP channel mapping is input to the TFC mapping module 212 to complete the mapping of the specified subcarriers . For downlink (base station to mobile station) data transmission, the SC-SFHP channel allocated by the system for multiple users can be superimposed in the base station transmitter. As shown in FIG. 2 , it is assumed that the service data from another user B can also pass through the modulation module 220 , the information symbol decomposition module 222 and the SC-SFHP channel mapping module 224 to complete the mapping to the designated subcarrier. Assuming that the above data are mapped to the same TFC, these data can be input into the chip-level accumulation module 226 to perform quadrature accumulation (indicated by the dotted line). For uplink (mobile station to base station) data transmission, the SC-SFHP channel assigned to the mobile station will be superimposed on the code channel in the mobile station transmitter. After the processing of the above business data is completed, it can be input to the IFFT module 228 in the OFDM system together with other channel information, such as control channel information, to complete the conversion from the frequency domain to the time domain. It is then transmitted via the OFDM system.

FIG. 3 is a schematic diagram of time-frequency allocation of an orthogonal spread spectrum SC-SFHP channel of VSFH-OTFCDM. In this example, TFC consists of multiple frequency domain subcarriers. Viewed from the time axis, the functional division includes the training sequence 34 and the service/control channel part composed of SC-SFHP channels; from the frequency domain axis, multiple TFC blocks 36 are included in the available sub-channels. In the code domain, multiple SC-SFHP channels 32 with the same frequency hopping pattern can be superimposed in the code domain. Since the SC-SFHP channels are mapped to TFCs in different time domains, the time period T _SC-SFHP of the SC-SFHP channel will be given by These time domains are determined by the time period of the TFC.

Shown in Fig. 4 is the signal model of VSFH-OTFCDM. In the transmitter 40, the signal is orthogonally spread after the modulation module 402, and the orthogonal spread is represented by the multiplier module 404. After that, the signal after the orthogonal spread can be completed by the adder module 406. Signal orthogonal addition, and mapped to the time-frequency domain. The signal then passes through the channel module 408 . In the receiver 42, the signal can be channel equalized 410 in the frequency domain, wherein the estimated channel information is provided by the channel estimation module 412; the equalized received signal can be restored to the quadrature signal by the multiplier module 414, and then sent to the solution The modulation module 416 performs demodulation. Under this model, it is assumed that the modulated signal is denoted by M _i , and there are N SC-SFHP channels superimposed. Assuming that the length of the orthogonal code is Q, the orthogonal code of the i-th SC-SFHP channel is represented by S _i ={S _i,1 ,S _i,2 ,...,S _i,Q }; the frequency domain channel is represented by H Indicates that the estimated channel parameters are expressed by express.

T is the accumulated signal in the frequency domain, expressed by formula (1), where j is the corresponding subcarrier number.

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>\begin{array}{cc}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}& \mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Q</span>}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

R _j is the received signal at subcarrier number j, expressed by formula (2)

R _j = T _j *H _j j = 1, . . . , Q (2)

Equation (3) expresses the process of equalizing and despreading the orthogonal codes, where S _P is the orthogonal code sequence of the i-th SC-SFHP channel

$\stackrel{<span\; class="notranslate">\; -</span>}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}{\stackrel{<span\; class="notranslate">\; -</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

可用公式(4)表示Let the channel estimate be biased, then the biased estimated channel parameter

It can be expressed by formula (4)

H _j =H _j *δ _j (4)

Substitute expression (4) into (3) to get:

${\stackrel{<span\; class="notranslate">\; -</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

When the estimated deviation of the experienced channel for an orthogonal code is the same value δ, the above formula can be expressed as:

${\stackrel{<span\; class="notranslate">\; -</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Then when S _i =S _P ,

${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

As mentioned above, what affects VSFH-OTFCDM orthogonal decoding is the deviation of channel estimation, and only when the estimated deviation of the channel experienced by an orthogonal code is consistent, it is easy to guarantee the orthogonality of the orthogonal code. In the case of orthogonal spread spectrum under frequency selective fading channel, its system performance will be a compromise between diversity effect and orthogonality preservation. From the above analysis, in the VSFH-OTFCDM system, the orthogonal spread spectrum information controlled by the VSF is allocated to the SC-SFHP channel, and the selection of TFC in the SC-SFHP channel is determined by the selected frequency hopping pattern. Corresponding to an orthogonal code, its allocation in the frequency domain can be in the coherent frequency domain or in the irrelevant frequency domain. As long as the channel estimation deviation does not change much, it is still easy for the receiver to restore the orthogonality of the orthogonal decoding. . In the VSFH-OTFCDM system, the selection of the frequency hopping pattern can make the orthogonal spread spectrum information be allocated in the coherent time and coherent frequency domain, and can also be allocated in the incoherent frequency domain and incoherent time domain.

Example

The following assumes that a TFC has 8 subcarriers, and a SC-SFHP is composed of 8 TFCs. The composition of the TFC in the SC-SFHP is controlled by the frequency hopping pattern, and the data information is controlled by the variable spreading factor VSF. The variable spreading factor VSF size Can be 1, 2, ..., 64. Orthogonal spread into the SC-SFHP channel. In this case, the same time-frequency unit group controlled by the frequency hopping pattern can be allocated to the same user, or can be allocated to different users. These users can use the same spreading factor, and the orthogonal codes of the same spreading factor are selected from nodes at the same level in the orthogonal code construction tree. For example, as shown in Table 1, the same spreading factor is used in the same time-frequency unit group. When the VSF is 2, the system supports 2 orthogonal code channels in the corresponding time-frequency unit, that is, the maximum number of SC-SFHP channels M _max-num = 2 supported in the same time-frequency unit, SC-SFHP channel The number of modulated data symbol signals that can be carried in N _SC-SFHP-cm =32. Then in the time-frequency unit group, the maximum number of information symbols that can be transmitted is N _SC-SFHP-cm *M _max-num =64.

VSFH-OFCDM also supports the superposition of signals with different spreading factors SF complying with certain specifications in the same time-frequency unit group. When using different VSF spreading factors for superposition, in order to ensure orthogonality, the selection of orthogonal codes with different spreading factors SF should come from different parent nodes in the orthogonal code construction tree. As shown in FIG. 5 , orthogonal codes numbered 1, 2, and 5 with different spreading factors SF can be used, and the number of data that can be transmitted is 8+16+32=56. Orthogonal codes with different spreading factors SF numbered 1, 2, 4, and 5 can also be used, and the number of data that can be transmitted is 64. Therefore, the total number of transmittable data is less than or equal to 64.

In order to maintain the orthogonality of the orthogonal codes, if different SFs are selected in the same time-frequency unit group, all the time-frequency subcarriers in the time-frequency unit group need to be filled after spreading with the orthogonal codes of these different SFs , but because SC-SFHP is the smallest allocation unit, when the service data of a certain SF has occupied a part of an SC-SFHP channel, especially for a channel with a low SF, the entire SC-SFHP channel needs to be filled even if there is no remaining data. This will result in a certain waste of system resources and an increase in processing time. And this waste of resources is more prominent for different SFs.

Table 1. SC-SFHP channel parameters with the same spreading factor

VSFfactor N_SC-SFHP-cm=The number of modulated data symbol signals that can be carried in the SC-SFHP channel M_max-num=The maximum number of SC-SFHP channels supported in the same time-frequency unit 1 64 1 2 32 2 4 16 4 8 8 8 16 4 16 32 2 32 64 1 64

Claims (9)

1. CDMA access method based on the quadrature time-frequency domain of variable spread spectrum and frequency hopping comprises step:

A), select suitable time frequency unit group at the time-frequency domain of orthogonal frequency division multiplex OFDM according to frequency hopping pattern;

B) from orthogonal code sets, select orthogonal code, in the OFDM time frequency unit group selected, adopt orthogonal spectrum expansion to determine the subchannel under the selected frequency hopping pattern by step a);

C) in group selected from step a), carry out multiplexing to the spread spectrum information in the subchannel SC-SFHP channel under the selected frequency hopping pattern of in identical time frequency unit group, from step b), selecting that satisfies orthogonal property with identical time frequency unit;

D) from step c), obtain multiplexing after data message carry out transfer of data by ofdm system.

2. in accordance with the method for claim 1, it is characterized in that the same time frequency unit group of described frequency hopping pattern control can be distributed to same subscriber and also can distribute to different user.

3. in accordance with the method for claim 1, it is characterized in that, described SC-SFHP channel is made up of a plurality of time frequency unit, each time frequency unit is made up of more than or equal to 1 frequency domain continuous sub-carriers one group of number, and the subcarrier combination mode in the time frequency unit can be frequency domain continuous sub-carriers combination or make up by the index of subcarrier.

4. in accordance with the method for claim 1, it is characterized in that the described SC-SFHP channel that superposes can adopt identical spreading factor or different spreading factors in the same time frequency unit group by frequency hopping pattern control.

5. in accordance with the method for claim 1, it is characterized in that in the multiplexing SC-SFHP channel, the orthogonal code of the same spread factor is selected from the brother of node in the orthogonal code structure tree in the same time frequency unit group by frequency hopping pattern control.

6. in accordance with the method for claim 1, it is characterized in that in the described SC-SFHP channel multiplexing in the same time frequency unit group by frequency hopping pattern control, the selection of the orthogonal code of different VSF spreading factors comes different father node in the self-orthogonal code structure tree.

7. one kind is utilized orthogonal spectrum expansion and frequency hopping to control the emitter that multichannel is divided in ofdm system, comprising:

The information code element decomposing module is used for user profile is decomposed subchannel SC-SFHP channel under each selected frequency hopping pattern;

The orthogonal spectrum expansion module is used for the user profile that spread spectrum is imported, and spread spectrum information is mapped to SC-SFHP channel Mapping module;

SC-SFHP channel Mapping module is used to shine upon information behind the spread spectrum to the SC-SFHP channel;

Frequency hopping pattern module and change spreading factor module are used at the described SC-SFHP channel of the common control of time-frequency domain;

The TFC mapping block is used to finish information after the SC-SFHP channel Mapping to the mapping of designate sub;

Cut general level laminating module, the SC-SFHP sub-channel signal that will have identical time-frequency domain distribution superposes, and the signal that will cut after the general level stack transmits by ofdm system.

8. according to the described device of claim 7, it is characterized in that the same time frequency unit group of described frequency hopping pattern module controls can be distributed to same subscriber, also can distribute to different user.

9. according to the described device of claim 8, it is characterized in that the described SC-SFHP channel that superposes can adopt identical spreading factor or different spreading factors in the same time frequency unit group by the frequency hopping pattern module controls.

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