CN109412995B - Multi-stream quasi-constant envelope multi-carrier transmission method based on variable sub-carrier bandwidth - Google Patents

Multi-stream quasi-constant envelope multi-carrier transmission method based on variable sub-carrier bandwidth Download PDF

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CN109412995B
CN109412995B CN201811446799.1A CN201811446799A CN109412995B CN 109412995 B CN109412995 B CN 109412995B CN 201811446799 A CN201811446799 A CN 201811446799A CN 109412995 B CN109412995 B CN 109412995B
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崔高峰
童建飞
张尚宏
李鹏绪
王卫东
胡欣
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Beijing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2614—Peak power aspects
    • H—ELECTRICITY
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Abstract

The invention provides a multi-stream quasi-constant envelope multi-carrier transmission method based on variable sub-carrier bandwidth, belonging to the technical field of wireless communication. The invention aims at the time of sending by the sending endThe length of the domain signal is N, N1,…,NP‑1P data streams of (1), wherein N > N is satisfied1+N2+…+NP‑1The bits of each data stream are mapped to form symbol data stream, the symbol data stream is mapped to different subcarriers, and the data stream 1 with the time domain signal length of N forms a constant envelope OFDM signal after phase modulation
Figure DDA0001885911010000016
Time domain signals of data streams 2,3, …, P are time division multiplexed and a guard interval is added to a length of N to form a composite time domain signal of length N
Figure DDA0001885911010000011
To pair
Figure DDA0001885911010000012
Phase modulation forming constant envelope OFDM signal
Figure DDA0001885911010000013
Will signal
Figure DDA0001885911010000014
And
Figure DDA0001885911010000015
and (4) performing item shifting and combining to obtain a final multi-flow quasi-constant envelope signal. The invention designs a quasi-constant envelope waveform with mixed waveform parameters, supports a plurality of service data streams with different subcarrier bandwidths and signal durations, and improves the transmission quality and the spectrum efficiency of a satellite mobile communication system.

Description

Multi-stream quasi-constant envelope multi-carrier transmission method based on variable sub-carrier bandwidth
Technical Field
The invention belongs to the technical field of wireless communication, and relates to a multi-stream quasi-constant envelope multi-carrier transmission technology based on variable sub-carrier bandwidth, which is applied to a satellite mobile communication system.
Background
In a wireless communication scenario, information is carried by electromagnetic waves and transmitted from a transmitter to a receiver through a wireless channel to realize communication. The communication quality is easily affected by channel factors such as noise and interference, so that the amplitude and the phase of a received signal are changed, and the communication quality is affected. Multicarrier transmission techniques modulate a signal onto a plurality of subcarriers to form a plurality of relatively flat subchannels. Orthogonal Frequency Division Multiplexing (OFDM) technology, one of the key technologies for terrestrial fourth and fifth generation mobile communications, is a typical multicarrier technology. A plurality of subcarriers of the OFDM signals are mutually orthogonal, and the frequency spectrum efficiency is obviously improved. However, the high peak-to-average ratio (PAPR) characteristic of OFDM makes it difficult to be directly applied to a satellite mobile communication system with limited power, and thus a low PAPR multi-carrier technology, such as a constant envelope OFDM (CE-OFDM) technology, is required. The CE-OFDM technology adopts a phase modulation mode, so that CE-OFDM signals have constant envelopes, the PAPR can be controlled to be 0dB, and the efficiency of satellite power amplification is improved. However, CE-OFDM signals require that the transmitting-end frequency domain signal be constructed as center conjugate symmetric data, and spectral efficiency is reduced to 50% of OFDM signals. In addition, the coverage area of the satellite communication system is wide, users in different areas have large-scale frequency offsets in different degrees, and the performance influence of the frequency offsets on the multi-carrier system depends on the size of the normalized frequency offset, so that the design of fixed subcarrier bandwidth cannot be well suitable for the satellite communication system with large-scale frequency offset difference, and the design of variable subcarrier bandwidth can be considered; on the other hand, due to the increasing number of ground user nodes and the abundant and diversified service demands, selecting a larger sub-carrier bandwidth for high-speed service can provide a higher transmission rate.
In the current satellite mobile communication system, a CE-OFDM multi-carrier signal of a single data stream has a constant envelope, so that the PAPR can be effectively reduced, but the frequency spectrum efficiency is reduced by half of the original frequency spectrum efficiency. In addition, the multicarrier of a single waveform parameter cannot adapt to a wide range of channel parameter changes in the satellite mobile communication system, such as a large-scale frequency offset.
Disclosure of Invention
Aiming at the problem that the existing satellite communication multi-carrier transmission technology adopts a single waveform parameter and cannot adapt to large-scale frequency offset change and service transmission requirements in a satellite mobile communication system, the invention provides a multi-stream quasi-constant envelope multi-carrier transmission method based on variable subcarrier bandwidth, designs a novel multi-carrier transmission signal structure, and provides more flexible channel adaptability and spectrum utilization efficiency for the system through flexible and variable subcarrier bandwidth design and a multi-data stream transmission structure.
The invention relates to a multi-stream quasi-constant packet multi-carrier transmission method based on variable sub-carrier bandwidth,
p data streams are sent at a transmission sending end, and the time domain signal lengths of the P data streams are N and N respectively1,…,NP-1And satisfy N > N1+N2+…+NP-1(ii) a The method of the invention firstly forms symbol data stream by symbol mapping of each data stream bit, and then maps the symbol data stream to different sub-carriers; p is a positive integer;
the data stream 1 with the time domain signal length of N is subjected to phase modulation to form a constant envelope OFDM signal at N moments
Figure BDA0001885908990000021
N-0, 1, …, N-1; n is a positive integer;
Figure BDA0001885908990000022
n-0, …, N-1; wherein A is1Is amplitude, 2 π h1Is a modulation index;
time domain signals of data streams 2,3, …, P are time division multiplexed and a guard interval is added to a length of N to form a composite time domain signal of length N
Figure BDA0001885908990000023
Then the composite time domain signal
Figure BDA0001885908990000024
By phase modulationMaking constant envelope OFDM signals at n instants
Figure BDA0001885908990000025
Figure BDA0001885908990000026
N-0, …, N-1; wherein A is2Is amplitude, 2 π h2Is a modulation index;
will signal
Figure BDA0001885908990000027
And
Figure BDA0001885908990000028
performing item shifting combination to obtain a multi-stream quasi-constant envelope signal at a final time n
Figure BDA0001885908990000029
The invention has the advantages and positive effects that: the method of the invention can provide the system with the capability of dynamic adjustment based on the channel condition and the service requirement, and improves the transmission quality and the spectrum efficiency of the satellite mobile communication system. The method constructs the multi-carrier signal of the quasi-constant envelope in a multi-data stream time-frequency superposition mode. The invention provides a signal transmission system which has high spectrum efficiency and can adapt to the transmission requirement of satellite diversified services and large-scale frequency offset change under the condition of ensuring low PAPR, so that the quasi-constant envelope OFDM has feasibility of application in the actual satellite scene.
Drawings
Fig. 1 is a schematic flow chart of a multi-stream quasi-constant envelope multi-carrier transmission transmitting end according to the present invention;
fig. 2 is a schematic diagram of multi-stream time division multiplexing and guard interval addition according to the present invention;
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
In the existing satellite mobile communication system, data transmission with single service, single subcarrier bandwidth and fixed time length is considered, and the problem that the single waveform bears a plurality of data streams with mixed waveform parameters (with various subcarrier bandwidths and various signal time lengths) is not considered in the prior art, namely the problem that the large-scale frequency offset change and the service transmission requirement in the satellite mobile communication system cannot be met. The method designs a quasi-constant envelope waveform with mixed waveform parameters, and can support a plurality of service data streams with different subcarrier bandwidths and signal durations. For diversified services with different subcarrier bandwidths and signal durations in actual communication, the multiplexing mode designed by the method can be adopted to transmit according to the length of a specific data stream. The method is suitable for the satellite communication system with limited power.
The multi-stream quasi-constant envelope multi-carrier transmission method based on the variable sub-carrier bandwidth supports the transmission of diversified service data streams, and meanwhile, the waveform has the characteristic of quasi-constant envelope. In order to improve the spectrum utilization efficiency, the multi-stream quasi-constant envelope transmission structure designed by the invention is shown in fig. 1.
As shown in fig. 1, first, P data stream bits to be transmitted are symbol mapped to form a plurality of symbol data streams; secondly, mapping each symbol data stream to different subcarriers; setting the time domain signal lengths of P data streams as N and N respectively1,…,NP-1And satisfy N > N1+N2+…+NP-1. P is a positive integer, and for the process of the invention P is greater than or equal to 2. Data stream 1 is subjected to an N-point IDFT (inverse discrete fourier transform), and data streams 2,3, …, P are subjected to N-point IDFT, respectively1,N2,…,NP-1IDFT of point, subcarrier bandwidth of different data flow is respectively delta f1,Δf2,…,ΔfP. And finally, multiplexing of multiple data streams is realized by different data streams through a shift superposition structure.
The sub-carrier bandwidth of data stream P in the P data streams is delta fpThe time domain OFDM signal of the data stream p at time n can be expressed as
Figure BDA0001885908990000031
The following were used:
Figure BDA0001885908990000032
where N is 0,1, …, N-1, and N is the number of points of the inverse discrete fourier transform. Time 0 represents an initial time.
Figure BDA0001885908990000033
Is a frequency domain conjugate symmetric, zero-filled data vector of data stream p, which can be represented as
Figure BDA0001885908990000034
Wherein the content of the first and second substances,
Figure BDA0001885908990000035
is a normalized M-QAM data symbol, the M-QAM data symbol is an M-ary QAM (quadrature amplitude modulation) symbol,
Figure BDA0001885908990000036
is 1 line NzpZero vector of column, N ═ Ns+Nzp+2, oversampling factor J ═ N/(2N)s+2)。NsRepresenting the number of M-QAM data symbols. N is a radical ofzpFor the length of the zero vector, change NzpThe oversampling factor may be adjusted.
Figure BDA0001885908990000037
Is a vector XmThe conjugate vector of (2).
Due to such a structure, the OFDM signal becomes a real-valued sequence, thereby constructing a constant-envelope OFDM (CE-OFDM) signal as follows:
Figure BDA0001885908990000038
wherein A isp2 π h as amplitude of data stream ppIs the modulation index of the data stream p, N-0, 1, …, N-1. Thus, the multi-carrier only affects the phase of the signal, and the PAPR can be effectively reduced. However, as can be seen from the formula (2), with respect toIn the case of single data stream transmission, the spectral efficiency is lower than 50% of the conventional OFDM signal due to the presence of the conjugate symmetric structure and the intermediate zero padding.
Data stream 1 with time domain signal length N may be phase modulated to form a CE-OFDM signal, as shown in the following equation:
Figure BDA0001885908990000039
the time domain signals of data streams 2,3, …, P may be time division multiplexed and a guard interval added to the length of N to form a composite time domain signal as shown in fig. 2. In fig. 2, the time domain lengths of data streams 2,3, …, P are N, respectively1,N2,…,NP-1The time domain symbols of a particular data stream p may be further written as
Figure BDA00018859089900000310
P ═ 2,3, …, P; in the figure 0 denotes the guard interval between the data streams, which together form a time domain signal of length N
Figure BDA00018859089900000311
n＝0,1,…,N-1。
The multiplexed data stream of length N after time division multiplexing of multiple data streams can be represented as
Figure BDA00018859089900000312
N is 1,2, …, N. The multiplexed data stream may be phase modulated to form a CE-OFDM signal as shown in equation (5), where 2 π h2Indicating the modulation index, A, of the multiplexed data stream2Representing the amplitude of the multiplexed data stream.
Figure BDA00018859089900000313
Further, as shown in fig. 1, the multiple data streams are subjected to term shift combination, and the final output signal can be represented by equation (6).
Figure BDA00018859089900000314
In the shift-term superposition structure in fig. 1, N-point time-domain symbols of data stream 1 form a CE-OFDM signal with length N by formula (4), data streams 2,3, …, P form a time-domain symbol with length N in a time-division multiplexing manner by adding a guard interval, and further form another CE-OFDM signal by phase modulation of formula (5), and multiply the time-domain symbol with length N by formula (5)
Figure BDA0001885908990000041
And linearly added with the signal of the data stream 1 to form a final multi-stream quasi-constant envelope signal.
The effect of time-frequency superposition is illustrated in the dashed box above fig. 1, taking three data streams as an example. In the figure, time is represented horizontally, frequency is represented vertically, and the lower symbol duration is T1Sub-carrier bandwidth Δ f1Is T with the upper left symbol duration2Sub-carrier bandwidth Δ f2And the symbol duration on the upper right side is T3Sub-carrier bandwidth Δ f3The data streams realize time-frequency superposition, the utilization efficiency of the frequency spectrum is improved, and the middle gap part of the two upper data streams is the guard interval between the subcarriers.
It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims (2)

1. A multi-stream quasi-constant packet multi-carrier transmission method based on variable sub-carrier bandwidth is characterized in that a transmission sending end is provided for sending P data streams, the time domain signal lengths of the P data streams are N, N1,L,NP-1And the condition is satisfied: n > N1+N2+L+NP-1(ii) a The method comprises the following steps: firstly, the bits of each data stream are mapped into symbol data streams through symbols, and then the symbol data streams are mapped onto different subcarriers;
subjecting a data stream 1 of time-domain signal length N to phase modulationThe formed constant envelope OFDM signal at n time is
Figure FDA0002421840380000011
N is 0,1, L, N-1; p, N are all positive integers;
time-domain signals of data streams 2,3, L and P are subjected to time-division multiplexing, and a guard interval is added to the length of N to form a composite time-domain signal with the length of N
Figure FDA0002421840380000012
Then the composite time domain signal
Figure FDA0002421840380000013
The constant envelope OFDM signal at n time formed by phase modulation is
Figure FDA0002421840380000014
Figure FDA0002421840380000015
Wherein A is2Is amplitude, 2 π h2Is a modulation index;
will signal
Figure FDA0002421840380000016
And
Figure FDA0002421840380000017
performing phase shift combination to obtain a final multi-stream quasi-constant envelope signal at n time
Figure FDA0002421840380000018
2. The method of claim 1, wherein the P data streams are represented by a time-domain OFDM signal with the data stream P at n time instants
Figure FDA0002421840380000019
Wherein the content of the first and second substances,
Figure FDA00024218403800000110
is a frequency domain conjugate symmetric, zero-padded data vector for data stream p, represented as follows:
Figure FDA00024218403800000111
wherein the content of the first and second substances,
Figure FDA00024218403800000112
for the normalized M-QAM data symbols,
Figure FDA00024218403800000113
is a vector XmThe conjugate vector of (1), NsRepresenting the number of M-QAM data symbols;
Figure FDA00024218403800000114
is 1 line NzpA zero vector of columns; N-Ns+Nzp+2, oversampling factor J ═ N/(2N)s+2)；
Then the constant envelope OFDM signal of n time instants formed by phase modulation
Figure FDA00024218403800000115
p＝1,2,…,P；
Wherein A isp2 π h as amplitude of data stream ppIs the modulation index of the data stream p.
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