CN115250125A - RAKE receiver of satellite communication system and improved receiving method - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention relates to the field of communication, in particular to a satellite communication system RAKE receiver and an improved receiving method. In the method, a transverse filter model for multipath propagation effect is modeled by using a reference signal p in a signal analysis unit, a filter coefficient C is solved, and each path of signal is multiplied by a corresponding coefficient C and then superposed to obtain an approximate service signal; the traffic signals are then diversity combined in a signal reconstruction unit using the same transversal filter model. The RAKE receiver comprises a signal analysis unit and a signal reconstruction unit; the signal parsing unit includes a FIR transversal filter. The invention avoids the problems of low resolution, error and leakage and the like in the prior art by using the signal modeling and reconstruction method based on the equivalence and approximation principles, and the problems of certain deviation in the delay and weighting links, thereby improving the communication capability of the covert satellite.
Description
Technical Field
The invention relates to the field of communication, in particular to a satellite communication system RAKE receiver and an improved receiving method.
Background
Covert communication technology:
the novel anti-interference Low-interception Low-detection LPI/LPD/LPE (Low reliability of detection/interrupt/extension) secure covert communication technology is a hotspot of current satellite communication research. A typical burst-oriented direct sequence spread spectrum receiver system and a carrier synchronization technology thereof are generally applied more mature, but are applied to a narrow-band satellite channel with large time delay and large time variation, and the global random access and fast acquisition and tracking requirements are difficult to meet. The novel safe covert communication technology is different from the traditional satellite communication technology and is characterized in that a wireless communication party can better conceal communication signals in a statistical sense by utilizing the thought of calculation communication and through novel signal waveform design and system technology; the method can not obtain the communication parameters of the party through the traditional communication signal detection methods such as long-term detection and complex calculation, cannot sense the existence of the wireless signals of the party, and is difficult to be intercepted in a targeted manner, thereby realizing stealth and effectively ensuring the survivability and the safety of satellite communication of the party.
The chaotic coding technology comprises the following steps:
at present, m sequences are widely used as pseudorandom sequences for constructing a spread spectrum system and providing hidden transmission and anti-detection capabilities. To further eliminate the signal characteristics, a large number of pseudo-random sequences with certain length and good auto/cross correlation properties need to be designed for spreading, and a large number of pseudo-random sequences with long period properties and good cross correlation properties need to be designed for communication parameter control in the randomization process. The traditional pseudo-random sequence generally has the defects of few primitive polynomials, short sequence periodicity and the like; the research adopts a chaotic sequence which has sensitive initial value, is bounded and is widely distributed as a pseudorandom spread spectrum and control sequence. Compared with the M sequence and the M sequence, the chaotic sequence not only has Gaussian statistical characteristics, but also has long-term unpredictability, and can bear complex decoding attacks. When the chaos sequence is adopted to carry out DSSS spread spectrum, the frequency spectrum has better balance characteristic and high detection resistance, so that the method has higher application prospect in the covert communication technology. But the corresponding receiving process becomes quite difficult due to the irregularity of the chaotic sequence. One of the problems is that orthogonality between spreading sequences is poor, resulting in a large loss of despreading performance, and adverse factors include despreading residues, low RAKE diversity accuracy, and the like.
1. Prior art close to the present invention
The basic architecture of a RAKE receiver is shown in fig. 1. In the figure, firstly, a correlator is used for determining the delay, amplitude and phase value of each path, then corresponding delay compensation is carried out, then despreading is carried out, weighting is carried out according to the measured amplitude and phase value, and finally, each path of signal is combined to complete RAKE processing.
The received spread spectrum signal may be represented as:
where x (k) is the transmitted baseband spread spectrum signal, a l ，θ l ，d l Respectively the amplitude, phase and delay of path i. In RAKE receiving process, each path has a corresponding Sinc-shaped curve through cross-correlation operation of local reference signal and r (k), and the position, amplitude and phase of the peak reflect a l ，θ l ，d l Processing in the manner shown in the figure based on these parameters can achieve a graded gain with maximized SNR.
2. Problems in the prior art
In practical application, the parameter estimation method based on cross-correlation operation has some defects, mainly including:
1. because the Sinc curve has a wider main lobe, the time delay resolution is not high, and paths with similar time delays are difficult to identify;
2. when d is l When the sampling period is not integral multiple, the Sinc curve has larger distortion, so that the a is difficult to measure l ，θ l ，d l ；
3. The cross-correlation curve has higher side lobes, so that curves corresponding to weaker multipath are easy to be mixed up, and wrong combination is caused.
For these reasons, the cross-correlation curve cannot accurately reflect the shape of the channel impulse response, and there is a relatively obvious difference between the two, as shown in fig. 2 and fig. 3, the cross-correlation curve at this time cannot accurately reflect the characteristics of the channel impulse response, and the corresponding RAKE processing gain is lower than the expected value, and the receiving performance is lower.
Therefore, when the parameters of the multipath channel are identified by the cross-correlation method, due to the influence of the main lobe width, the side lobe and the like of the Sinc-type curve, the problems of low resolution, error and leakage and the like exist, and certain deviation exists in the links of delay and weighting, so that the combination effect is lower than the expected value.
Disclosure of Invention
(I) technical problems to be solved by the invention
In order to improve the sensitivity of a hidden signal, the invention provides a RAKE receiver for improving diversity combining gain and an improved receiving method, and improves the communication capacity of a hidden satellite.
The technical scheme of the invention is as follows:
the invention provides an improved RAKE receiving method of a satellite communication system, which comprises the following steps:
1. modeling an FIR transverse filter model by using a reference signal p in a signal analysis unit, solving coefficients C of the FIR transverse filter, multiplying each path of signal by the corresponding coefficients C, and finally superposing the signals to obtain an approximate service signal;
1.1 divide y (k) into L paths through unit delay step by step, FIR transverse filter uses thisGround pilot reference signal y and filter polynomial coefficient C, C = [ C = [) 0 ,C 1 ,...,C L-1 ]Approximating the reference signal p in the received signal to generate a p', adjusting C by an algorithm 0 、C 1 、C 2 、……C L-1 Filter coefficients to make err as small as possible;
the effective component in p (k) is constructed by y (k), and the number of taps is L, and there are
Err (k) in the above formula is a portion of p (k) that cannot be modeled;
1.2 solving the coefficients C (k) of the FIR transverse filter in the above formula by a least square method, wherein k =0, 1, 2 … … L-1;
1.3, multiplying each path of signal by corresponding coefficient C (k), k =0, 1, 2, …, L-1, and finally superposing to obtain approximate service signal x (k).
2. The same model is used in the signal reconstruction unit to perform diversity combining on the service signals.
And dividing the subsequent service signal x (k) into L paths for time delay compensation and amplitude weighting, and finally superposing to complete RAKE processing. The time delay compensation method comprises the following steps: the delay compensation with large path delay is small, and the delay compensation with small path delay is large, so that the total delay of each path is the same after compensation.
A second aspect of the present invention provides a RAKE receiver including a signal analysis unit and a signal reconstruction unit; the signal analysis unit comprises an FIR transverse filter which is used for modeling a transverse filter model for multipath propagation effect by using a reference signal p, solving a filter coefficient C, multiplying each path of signal by a corresponding coefficient C and then superposing the signals to obtain an approximate service signal; and the signal reconstruction unit is used for performing diversity combination on the service signals by using the model constructed in the signal analysis unit.
A third aspect of the present invention provides a RAKE receiving system comprising a RAKE receiver.
The invention has the advantages that:
the method of the invention avoids the problems of low resolution, error and leakage and the like in the prior art by using the signal modeling and reconstruction method based on the equivalence and approximation principles, and the problems of certain deviation in the delay and weighting links, thereby improving the hidden communication capability.
Drawings
FIG. 1: the RAKE receiver structure principle in the prior art;
FIG. 2 is a schematic diagram: an impulse response of the channel;
FIG. 3: a cross-correlation curve;
FIG. 4 is a schematic view of: a Rake receiving system;
FIG. 5 is a schematic view of: the invention discloses a Rake receiver structure diagram;
FIG. 6: a schematic diagram of a signal analysis module structure;
FIG. 7 is a schematic view of: the structural diagram of the FIR filter is shown;
FIG. 8: a schematic diagram of a signal reconstruction module;
FIG. 9: an improved RAKE receiving unit.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 4, the invention provides a Rake receiving system for satellite communication, which comprises AGC, field strength detection, sampling unit, short code PNG, short code search, mapping, long code PNG, symbol synchronization, rake receiver, local pilot signal sequence transmitter, despreading, de-differentiating, de-interleaving, descrambling, decoding and other components.
After the code element synchronization is carried out on the received signal, the received multipath signal comprises a pilot frequency field p and effective information x. As shown in fig. 5, the signal analysis unit models the multipath propagation effect using the transverse filter model using the reference signal p to find the filter coefficient C, and the signal reconstruction unit performs diversity combining on the traffic signal using the same model to improve the reception sensitivity of the concealment signal.
The signal analysis unit structure is shown in fig. 6, where p is a reference signal in a received signal, and y is a local pilot reference signal. A FIR transversal filter is constructed in a signal analysis unit, which uses a local pilot reference signal y and a filter polynomial coefficient C (C = [ C ]) 0 ,C 1 ,...,C L-1 ]) Approximating a reference signal p in a received signal to generate a p', adjusting C by an algorithm 0 、C 1 、C 2 、……C L-1 The filter coefficients are equalized so that err is as small as possible. The FIR filter structure is shown in fig. 7.
The effective component in p (k) is constructed by y (k), taking the number of taps as L, there are
Err (k) in the above equation is a portion of p (k) that cannot be modeled.
Solving the coefficients C (k) of the FIR transverse filter by a least square method, wherein k =0, 1, 2 … … L-1. If L is larger than the delay spread range of the channel, the first term on the right side of the above equation will contain all the effective components in p (k) according to the orthogonality principle, and err (k) is the ineffective component such as noise.
According to the solved FIR transversal filter coefficient C and the structure of the FIR filter, it can be seen that the transmission process of the signal, that is, y (k) output by the transmitter passes through a multipath channel to form the effect of x (k) in the RAKE receiver, can be equivalent to the following operation, first divide y (k) into L paths through unit delays in stages, then multiply each path by the corresponding coefficient C (k), k =0, 1, 2, …, L-1, and finally superpose to obtain approximate x (k). I.e., an FIR filter that equates the multipath channel to L taps.
Therefore, when diversity and combination are performed on the subsequent traffic signal x (k), the inverse operation can be performed on x (k) based on the above model: and dividing the path into L paths for time delay compensation and amplitude weighting, and finally superposing to finish RAKE processing. The delay compensation method is that the delay compensation with large path delay is small, and the delay compensation with small path delay is large, so that after compensation, the total delay of each path is the same.
The principle of the corresponding signal reconstruction unit is shown in fig. 8, with improved RAKE processed output z (k), k =0, 1, 2, …, L-1.
The scheme for improving diversity combining gain proposed by the present invention is shown in fig. 9.
Firstly, modeling a transverse filter model for multipath propagation effect by using a reference signal p in a signal analysis unit, solving a filter coefficient C, multiplying each path of signal by a corresponding coefficient C, and finally superposing to obtain an approximate service signal; the traffic signals are then diversity combined in a signal reconstruction unit using the same model.
Claims (6)
1. An improved RAKE reception method in a satellite communication system, the method comprising the steps of:
(1) Modeling an FIR transverse filter model by using a reference signal p in a signal analysis module, solving coefficients C of the FIR transverse filter, multiplying each path of signal by the corresponding coefficients C, and finally superposing the signals to obtain an approximate service signal;
(2) And diversity combination is carried out on the service signals by using the same FIR transverse filter model in the signal reconstruction module.
2. The RAKE improved receiving method as set forth in claim 1, wherein said step (1) further comprises:
1.1 divide y (k) into L paths through unit delay step by step, FIR transversal filter utilizes local pilot reference signal y and filter polynomial coefficient C, C = [ C = [ ] 0 ,C 1 ,...,C L-1 ]Approaches a reference signal in the received signal,
p' is generated by the number p, C is adjusted by an algorithm 0 、C 1 、C 2 、……C L-1 Filter coefficients to make err as small as possible;
the effective component in p (k) is constructed by y (k), and the number of taps is L, and there are
Err (k) in the above formula is a portion of p (k) that cannot be modeled;
1.2 solving the coefficients C (k) of the FIR transverse filter in the above formula by a least square method, wherein k =0, 1, 2 … … L-1;
1.3, multiplying each path of signal by corresponding coefficient C (k), k =0, 1, 2, …, L-1, and finally superposing to obtain approximate service signal x (k).
3. The RAKE improved receiving method as set forth in claim 1, wherein said step (2) further comprises:
and dividing the subsequent service signal x (k) into L paths for time delay compensation and amplitude weighting, and finally superposing to complete RAKE processing.
4. The RAKE improved receiving method as set forth in claim 3, wherein the delay compensation method is: the delay compensation with large path delay is small, and the delay compensation with small path delay is large, so that the total delay of each path is the same after compensation.
5. A RAKE receiver implementing the RAKE improved receiving method of any one of claims 1 to 4, characterized in that the RAKE receiver comprises a signal analyzing unit and a signal reconstructing unit; the signal analysis unit comprises an FIR transverse filter which is used for modeling a transverse filter model for multipath propagation effect by using a reference signal p, solving a filter coefficient C, multiplying each path of signal by a corresponding coefficient C and then superposing the signals to obtain an approximate service signal; and the signal reconstruction module is used for performing diversity combination on the service signals by using the model constructed in the signal analysis unit.
6. A RAKE receiving system comprising the RAKE receiver of claim 5.
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Citations (4)
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| CN101188436A (en) * | 2006-11-10 | 2008-05-28 | 英飞凌科技股份公司 | Receiver |
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| CN107154813A (en) * | 2016-03-06 | 2017-09-12 | 南京理工大学 | Adaptive Rake receivers and method of reseptance |
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| CN101119130A (en) * | 1999-08-23 | 2008-02-06 | 高通股份有限公司 | Adaptive channel estimation in a wireless communication system |
| CN101188436A (en) * | 2006-11-10 | 2008-05-28 | 英飞凌科技股份公司 | Receiver |
| CN102111182A (en) * | 2009-12-25 | 2011-06-29 | 中国电子科技集团公司第五十研究所 | Self-adaptive UWB Rake receiver, self-adaptive UWB Rake receiving method and UWB wireless communication system |
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