CN101753204B - Spread spectrum acquisition method in multi-path dense environment - Google Patents

Abstract

The invention discloses a spread spectrum acquisition method in a multi-path dense environment. The method comprises the following steps: dividing the entire uncertain region of a spread spectrum acquisition system into a plurality of continuous energy windows and accumulating the energy in all the windows. As long as the biggest energy window is found, the first accessible path is found. In the technical scheme of the method, a first accessible path position estimation method is added on the basis of the original spread spectrum acquisition, so that the demodulation bit error rate of the spread spectrum acquisition system is minimized, and the error performance of the system is improved.

Description

Spread spectrum acquisition method under the multi-path dense environment

Technical field

The present invention relates to wireless communication technology field, relate in particular to the spread spectrum acquisition method under a kind of multi-path dense environment.

Background technology

Simultaneous techniques is always the key technology of digital communication system.The quality of net synchronization capability is directly connected to the quality of spread spectrum system performance.Direct spread system just may with the spread-spectrum signal that synchronous PN sequence docking the is received despreading of being correlated with, become the WBSR wideband signal recovery of spread spectrum the narrow band signal of non-spread spectrum, to demodulate the information of transmission only after completing frequency expansion sequence synchronous.Spread-spectrum signal synchronously be divided into two stages: the tracking phase after initial acquisition and signal initial acquisition.Catching is thick synchronizing process, is thin synchronizing process and follow the tracks of.The working range of tracking cell has certain limit, is called as capture zone.Frequency expansion sequence catch (hereinafter to be referred as " spread spectrum acquisition ") when referring to that receiver begins receiving spread frequency signal, adjust and select the phase place of local frequency expansion sequence, the adjusting offset of transceiver frequency expansion sequence to capture zone, before tracking cell is opened, is obtained the thick synchronous of frequency expansion sequence.

Spread spectrum acquisition is one of the most key technology of spread spectrum system, also is called thick synchronous.The purpose of spread spectrum acquisition is the code sequence phase that rough estimate receives, in order to adjust the local code sequence phase, makes the difference of local code sequence phase and receiving code sequence phase within 1 chip.Whole uncertain phase place zone is by several in-phase phase places (H ₁) and out-of-phase phase place (H ₀) form.H ₁Phase place represents the local code sequence phase of difference within 1 chip with the receiving code sequence phase, and H ₀The difference of expression and receiving code sequence phase is greater than the local code sequence phase of 1 chip.Under the tradition Resistant DS Spread Spectrum System, it is generally acknowledged and only have a H in the uncertain region ₁Phase place, that remaining is all H ₀Phase place.But under multi-path environment, may there be a plurality of H ₁Phase place.For the spread spectrum acquisition system of reality, whole uncertain phase place zone is a chip sequence cycle N _cT _c, N wherein _cBe code sequence number of chips, T _cBe chip period, sample rate T _sBe the elementary cell of discrete phase, therefore uncertain phase place has N _s=N _cT _c/ T _sIndividual.

In general, the spread spectrum acquisition process is divided search phase and two stages of Qualify Phase.In the search phase, receiver is according to certain search strategy, searches in whole uncertain phase place zone, and step by step modulating local code phase place constantly is until search H ₁Phase place.The H that this searches ₁Phase place is temporary transient, remains further to be verified.Then at Qualify Phase, receiver is further verified the H that searches ₁Whether phase place is correct.Spread spectrum acquisition system for there is no Qualify Phase is called the single resident system; Spread spectrum acquisition system for Qualify Phase is arranged is called repeatedly resident system; For the system that only verifies at Qualify Phase once, be called two resident systems.Two resident systems are more extensive in actual applications.

Tradition spread spectrum acquisition method and some improved spread spectrum acquisition methods can capture a certain footpath preferably, yet lack the consideration to other footpaths.These class methods are worked in the additive white Gaussian noise situation well, but under the environment of multi-path dense, under the UWB indoor environment, these class methods will cause relatively poor system's error performance.Reason is that this class catching method has only captured a certain footpath in a lot of footpaths, and the footpath that captures is reached the footpath as head carries out follow-up demodulation process.

Fig. 1 is the schematic diagram of the traditional spread spectrum acquisition method under Dense Multipath Channels, as shown in Figure 1, the physical location in the footpath (hereinafter to be referred as " Shou Dajing ") that arrives first is dotted arrow first pulse pointed, and an actual bit duration is the time width that the dotted line four-headed arrow indicates.Yet according to present acquisition algorithm, might capture solid arrow position pointed, i.e. the 3rd pulse.Follow-up demodulation meeting reaches the position of estimating at the footpath as head, and subsequent demodulation thinks that a bit duration is the time width that the solid line four-headed arrow indicates like this.So previous bit is carried out multipath and merge to separate timing, can be by mistake front two energy larger footpaths of the rear bit information of carrying be merged into, thereby cause relatively poor error performance.

Summary of the invention

The technical problem that (one) will solve

For the defective that exists in prior art and deficiency, the purpose of this invention is to provide and a kind ofly can reduce system acquisition time, improve the spread spectrum acquisition method under the multi-path environment of the stability of a system, the method is particularly useful for Resistant DS Spread Spectrum System.

(2) technical scheme

For achieving the above object, the invention provides the spread spectrum acquisition method under a kind of multi-path dense environment, described method comprises step:

S1, for relevant spread spectrum system, the initial value of the position in the footpath that the position in the footpath that will capture in the spread spectrum acquisition process arrives in as multipath first, the energy window that a width is set is w sampling period, it is n=0 that energy window slip number of times is set, w sampled data in current energy window is R[0], R[1], R[w-1], this sampled data is from the matched filtering result of the search phase local code sequence that calculates and the code sequence that receives of spread spectrum acquisition, if the initial value of maximized window energy is 0, if it is 0 that head reaches the path position initial value, w, n is integer,

S2, calculate w the sampled data sum that drops in this energy window: $s=\underset{i=\mathrm{nw}}{\overset{(n+1)w-1}{\mathrm{\Σ}}}R\left[i\right],$ If s is updated to s with the maximized window energy greater than current maximized window energy, and the path position that arrives first in multipath is updated to nw; Otherwise the path position that does not upgrade the maximized window energy and arrive first;

Whether S3, judgement (n+1) w be less than the number N of the uncertain phase place in a chip sequence cycle in the spread spectrum acquisition process _sIf, less than, with energy window to front slide once, and n is added 1, then return to step S2; Otherwise the corresponding value in position in the footpath that arrives first after upgrading is the estimated value of the due in the footpath that arrives first.

Wherein, also comprised the step of spread spectrum acquisition before step S1, the step of described spread spectrum acquisition specifically comprises search phase and Qualify Phase;

In the search phase, the local code sequence is carried out related operation with the code sequence that receives, and operation result compares as judgement amount and the first thresholding, if less than the first thresholding, thinks that the local code sequence phase is H ₀Phase place, continue relatively after adjusting local sequence phase, until correlation is more than or equal to the first thresholding, more then each sampling interval enters Qualify Phase, keeps the local code sequence constant with the relative phase of the code sequence that receives, carry out the synchronous slide related operation, if correlation is less than the second thresholding, authentication failed, return to the search phase; Otherwise be proved to be successful, thereby capture a footpath in multipath.

Wherein, the size of described energy window satisfies wT _s/ τ _MAXLess than 1/2, wherein, τ _MAXBe the maximum excessive delay of multipath channel, T _sBe the sampling interval.

The present invention also provides the spread spectrum acquisition method under a kind of multi-path dense environment, and described method comprises step:

S1 ', for incoherent spread spectrum system, the initial value of the position in the footpath that the position in the footpath that will capture in the spread spectrum acquisition process arrives in as multipath first, the energy window that a width is set is w sampling period, it is n=0 that energy window slip number of times is set, w sampled data in current energy window is R[0], R[1], R[w-1], this sampled data is from the matched filtering result of the search phase local code sequence that calculates and the code sequence that receives of spread spectrum acquisition, if the initial value of maximized window energy is 0, if it is 0 that head reaches the path position initial value, w, n is integer,

S2 ', calculate the two norm sums that drop on w sampled data in this energy window: $s=\underset{i=\mathrm{nw}}{\overset{(n+1)w-1}{\mathrm{\Σ}}}\left\{R\right[i\left]\right\},$ If s is updated to s with the maximized window energy greater than current maximized window energy, and the path position that arrives first in multipath is updated to nw; Otherwise the path position that does not upgrade the maximized window energy and arrive first, wherein, R[i is asked in { R[i] } expression] two norms;

Whether S3 ', judgement (n+1) w less than the number Ns of the uncertain phase place in a chip sequence cycle in the spread spectrum acquisition process, if less than, with energy window to front slide once, and n is added 1, then return to step S2 '; Otherwise the corresponding value in position in the footpath that arrives first after upgrading is the estimated value of the due in the footpath that arrives first.

Wherein, also comprised the step of spread spectrum acquisition before step S1, the step of described spread spectrum acquisition specifically comprises search phase and Qualify Phase;

in the search phase, the local code sequence is carried out related operation with the code sequence that receives, operation result compares as judgement amount and the first thresholding, if less than the first thresholding, think that the local code sequence phase is the H0 phase place, continue relatively after adjusting local sequence phase, until correlation is more than or equal to the first thresholding, each sampling interval more once, then enter Qualify Phase, keep the local code sequence constant with the relative phase of the code sequence that receives, carry out the synchronous slide related operation, if correlation is less than the second thresholding, authentication failed, return to the search phase, otherwise be proved to be successful, thereby capture a footpath in multipath.

Wherein, the size of described energy window satisfies wT _s/ τ _MAXLess than 1/2, wherein, τ _MAXBe the maximum excessive delay of multipath channel, T _sBe the sampling interval.

(3) beneficial effect

Compared with prior art, the present invention can produce following beneficial effect: traditional spread spectrum acquisition method and some improved spread spectrum acquisition methods can capture a certain footpath preferably, but lack the consideration to other footpaths.These class methods under the UWB indoor environment, will cause relatively poor system's error performance under the environment of multi-path dense.The present invention has increased head and has reached path position estimation method on original spread spectrum acquisition basis, makes the demodulation bit error rate of spread spectrum system reach minimum, has improved system's error performance.

Description of drawings

Fig. 1 is the schematic process flow diagram of traditional spread spectrum acquisition method;

Fig. 2 is the schematic process flow diagram of the method for one embodiment of the invention;

Fig. 3 is the schematic process flow diagram of the method for another embodiment of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used for explanation the present invention, but are not used for limiting the scope of the invention.

Fig. 2 is the FB(flow block) of the spread spectrum acquisition method under Dense Multipath Channels of the present invention, and the method is based on the minimum bit-error rate criterion.Wherein to head reach path position method of estimation FB(flow block) as shown in Figure 3.Because near the footpath energy that head reaches the footpath wants large than the footpath that arrives later, therefore the whole uncertain region (being a code sequence period) of spread spectrum acquisition system can be divided into a plurality of continuous energy window, then the energy in each window is added up, find maximum energy window namely to find head to reach the footpath.In Fig. 2 and 3, R[0,1,2 ..., w-1] be R[0], R[1] ..., R[w-1].The method specific implementation step is described below:

S1, the energy window that a width is set is w sampling period, it is n=0 that energy window slip number of times is set, the sampled data in current energy window is (the matched filtering result of search phase) R[0], R[1] ..., R[w-1].It is 0 that maximized window energy initial value is set, and head is set, and to reach the path position initial value be 0;

S2, calculate and drop on sampled data sum in energy window: $s=\underset{i=\mathrm{nw}}{\overset{(n+1)w-1}{\mathrm{\Σ}}}R\left[i\right].$ If s is updated to s with the maximized window energy greater than current maximized window energy, and head reaches path position and is set to nw, otherwise do not upgrade the maximized window energy and head reaches path position.

Whether S3, judgement (n+1) w be less than the number N of the uncertain phase place in a chip sequence cycle in the spread spectrum acquisition process _sIf less than, with energy window to front slide once, and n is added 1, again begin to carry out from step S2; Otherwise the corresponding value in position in the footpath that arrives first after upgrading is the estimated value τ of the due in the footpath that arrives first.

Described above is coherent system, wherein, R[0], R[1] ..., R[w-1] and be real number; And for incoherent system, because I, Q two-way are arranged, so R[0], R[1] ..., R[w-1] be plural number, R[0 like this], R[1] ..., R[w-1] and carry out again the calculating of step S2 after needing first to ask two norms through two norm devices.Wherein, two norms are the quadratic sum of real part and imaginary part.

Need to prove, the selection of the size of energy window should be satisfied wT _sBe τ _MAXPart, as wT _s=τ _MAX/ 8, τ _MAXBe the maximum excessive delay of multipath channel, and wT _s/ τ _MAXShould be less than 1/2.

For illustrating the method for the embodiment of the present invention, can obtain a spread spectrum acquisition example that is applicable to the UWB indoor channel.Above-mentioned parameter can arrange as follows: T _s=T _c/ 4=1ns; N _c=31; N _s=128; wT _s/ τ _MAX=1/8; N _cBe the number of chips of local code sequence, T _cBe chip period, T _sBe the sampling interval.

As can be seen from the above embodiments, spread spectrum acquisition success means and is currently receiving preamble sequence, and captured wherein certain footpath.After the spread spectrum acquisition success, utilize the head based on minimum error code criterion of the present invention to reach path position estimation method and carry out the location estimation that head reaches the footpath.That is to say, the present invention to the basis in certain footpath, further estimates the first position that reaches the footpath at spread spectrum acquisition, thereby makes the error rate minimum of the demodulation of back.Tradition spread spectrum acquisition method and some improved spread spectrum acquisition methods can capture a certain footpath preferably, but lack the consideration to other footpaths.These class methods under the UWB indoor environment, will cause relatively poor system's error performance under the environment of multi-path dense.The present invention has increased head and has reached path position estimation method on original spread spectrum acquisition basis, makes the demodulation bit error rate of spread spectrum acquisition system reach minimum, has improved system's error performance.

The above is only embodiments of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the technology of the present invention principle; can also make some improvement and modification, these improve and modification also should be considered as protection scope of the present invention.

Claims (4)

1. the spread spectrum acquisition method under a multi-path dense environment, is characterized in that, described method comprises step:

S1, for relevant spread spectrum system, the position in the footpath that the position in the footpath that will capture in the spread spectrum acquisition process arrives in as multipath first, the energy window that a width is set is w sampling period, it is n=0 that energy window slip number of times is set, w sampled data in current energy window is R[0], R[1], R[w-1], this sampled data is from the matched filtering result of the search phase local code sequence that calculates and the code sequence that receives of spread spectrum acquisition, and the initial value of establishing the maximized window energy is 0, if it is that 0, w is integer that head reaches the path position initial value;

S2, calculate w the sampled data sum that drops in this energy window:

If s is updated to s with the maximized window energy greater than current maximized window energy, and the path position that arrives first in multipath is updated to nw; Otherwise the path position that does not upgrade the maximized window energy and arrive first;

Whether S3, judgement (n+1) w be less than the number N of the uncertain phase place in a chip sequence cycle in the spread spectrum acquisition process _sIf, less than, with energy window to front slide once, and n is added 1, then return to step S2; Otherwise the corresponding value in position in the footpath that arrives first after upgrading is the estimated value of the due in the footpath that arrives first;

The size of described energy window satisfies wT _s/ τ _MAXLess than 1/2, wherein, τ _MAXBe the maximum excessive delay of multipath channel, T _sBe the sampling interval.

2. the spread spectrum acquisition method under multi-path dense environment as claimed in claim 1, is characterized in that, also comprised the step of spread spectrum acquisition before step S1, the step of described spread spectrum acquisition specifically comprises search phase and Qualify Phase;

In the search phase, the local code sequence is carried out related operation with the code sequence that receives, and operation result compares as judgement amount and the first thresholding, if less than the first thresholding, thinks that the local code sequence phase is H ₀Phase place, continue relatively after adjusting local sequence phase, until correlation is more than or equal to the first thresholding, more then each sampling interval enters Qualify Phase, keeps the local code sequence constant with the relative phase of the code sequence that receives, carry out the synchronous slide related operation, if correlation is less than the second thresholding, authentication failed, return to the search phase; Otherwise be proved to be successful, thereby capture a footpath in multipath; Wherein, H ₀The difference of expression and receiving code sequence phase is greater than the local code sequence phase of 1 chip.

3. the spread spectrum acquisition method under a multi-path dense environment, is characterized in that, described method comprises step:

S1 ', for incoherent spread spectrum system, the position in the footpath that the position in the footpath that will capture in the spread spectrum acquisition process arrives in as multipath first, the energy window that a width is set is w sampling period, it is n=0 that energy window slip number of times is set, w sampled data in current energy window is R[0], R[1], R[w-1], this sampled data is from the matched filtering result of the search phase local code sequence that calculates and the code sequence that receives of spread spectrum acquisition, if the initial value of maximized window energy is 0, if it is 0 that head reaches the path position initial value, w is integer,

S2 ', calculate the two norm sums that drop on w sampled data in this energy window:

If s is updated to s with the maximized window energy greater than current maximized window energy, and the path position that arrives first in multipath is updated to nw; Otherwise the path position that does not upgrade the maximized window energy and arrive first, wherein, R[i is asked in { R[i] } expression] two norms; Described two norms are plural R[i] real part and the quadratic sum of imaginary part;

Whether S3 ', judgement (n+1) w be less than the number N of the uncertain phase place in a chip sequence cycle in the spread spectrum acquisition process _sIf, less than, with energy window to front slide once, and n is added 1, then return to step S2 '; Otherwise the corresponding value in position in the footpath that arrives first after upgrading is the estimated value of the due in the footpath that arrives first;

The size of described energy window satisfies wT _s/ τ _MAXLess than 1/2, wherein, τ _MAXBe the maximum excessive delay of multipath channel, T _sBe the sampling interval.

4. the spread spectrum acquisition method under multi-path dense environment as claimed in claim 3, is characterized in that, also comprised the step of spread spectrum acquisition before step S1, the step of described spread spectrum acquisition specifically comprises search phase and Qualify Phase;

In the search phase, the local code sequence is carried out related operation with the code sequence that receives, and operation result compares as judgement amount and the first thresholding, if less than the first thresholding, thinks that the local code sequence phase is H ₀Phase place, continue relatively after adjusting local sequence phase, until correlation is more than or equal to the first thresholding, more then each sampling interval enters Qualify Phase, keeps the local code sequence constant with the relative phase of the code sequence that receives, carry out the synchronous slide related operation, if correlation is less than the second thresholding, authentication failed, return to the search phase; Otherwise be proved to be successful, thereby capture a footpath in multipath; Wherein, H ₀The difference of expression and receiving code sequence phase is greater than the local code sequence phase of 1 chip.

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