Title of Invention

MULTI-PATH SEARCHING METHOD IN CODE-DIVISION MULTIPLE ACCESS COMMUNICATION SYSTEM

Abstract A method of multi-path search in code-division multiple access communication system is provided, which comprises the following steps: first, calculating the power delay profile of the received signal, and multiple peaks with comparatively higher energy are selected from the power delay profile, then performing threshold comparison and interpolation for the selected peaks to determine the multi-path delay position and energy, finally, determining the multi-path delay according to the results of interpolation. Compared with the prior art, the present invention can improve multi-path search precision greatly without increasing the complexity of calculation, specifically, the search precision can reach 1/4 chip, 1/8 chip, or even 1/16 chip; at the same time, early-late gate tracking module are not needed in the method of the present invention, thus complex tracking algorithm are also not needed, which greatly simplify the realization complexity of Rake receiver and the complexity of multi-path assignment management; Furthermore, the method of the present invention is applicable for base stations and mobile stations of various of code division multiple access communication system.
Full Text TECHNICAL FIELD
The present invention relates to the signal receiving technology in Code-Division Multiple
Access (CDMA is used for short) communication system, and particularly, to a method of
multi-path searching during the period of receiving a signal. The present invention is
applicable for any communication system that applies Code-Division Multiple Access
technology.
BACKGROUND OF THE INVENTION
Code-Division Multiple Access is a multiple access method based on the spread spectrum
technology, which has become another multiple access method applied in communication
system in recent years besides frequency-division multiple access (FDMA) and time-division
multiple access (TDMA). Compared with frequency-division multiple access and
time-division multiple access technologies, CDMA technology has a lot of advantages, such
as high utilization rate of frequency spectra, simple to plan and so on. The communication
system which applies CDMA technology includes: narrowband CDMA system, i.e. IS-95
system; wideband CDMA system, i.e. WCDMA system; CDMA 2000 system, TD-SCDMA
system and TD-CDMA systematic etc.
Above-mentioned communication systems all have adopted multi-code spread spectrum
technology, which is also called two-step spread spectrum code design technology. Thus, the
spread spectrum process of the reverse link from a mobile station to a base station can be
divided into two steps. The first step comprises making spread spectrum for the signal by
using the orthogonal function (such as Walsh function, OVSF code etc) whose
cross-correlation value is zero when the delay is aligned as channel code. The first step is
called spreading, and the recovering process occurring at the corresponding receiving side
(base station) is called de-spreading. The second step comprises multiplying pseudo-random
code (such as PN sequence, M sequence, Gold sequence etc.) uniquely assigned by each
mobile station, which has good performance of both auto-correlation and cross-correlation,
with signal. The second step is called scrambling, and the recovering process occurring at the
corresponding receiving side (base station) is called de-scrambling. And the above-mentioned
pseudo-random code is called scrambling code .In the second step, the scrambling code is
used to distinguish different mobile station. A value in the scrambling code sequence is also
called chip. Also, in these systems, the spread spectrum process of the forward link from base
station to mobile station is also divided into the same two steps, wherein the only difference
is that in the forward link scrambling code is used to distinguish the base station or cell, and
different base station or cell has different scrambling code.
In a general mobile communication system, signals between a base station and a mobile
station propagate along multiple paths between the transmitter and the receiver. This
phenomenon of multi-path transmission mainly results from the signal reflection caused by
the objects' surface around the transmitter and receiver. Because the propagation path is
different, the propagation delays of the different multi-path components' arriving at the
receiver are different, wherein the multi-path components are generated by the same signal
propagating along different path., which results in multi-path interference and signal fading.
The receiver in CDMA system is of multi-branches structure, wherein each branch is an
individual receiver element. The receiver is used to demodulate the component of the desired
received signal and combine the signals of different receiver element, which can improve the
quality of the received signal. Each branch is synchronized with the multi-path that has
almost the same propagation delay. This kind of receiver is also called Rake receiver, which
can add up the multi-path energy of different delay corresponding to the same mobile station
according to a certain rule, thus the receiver's performance is improved.
The synchronization of the local spread spectrum code and the spread spectrum code in the
received signal is a prerequisite for the CDMA system to realize a normal communication. If
code synchronization can't be realized, the de-spreading can't be performed correctly;
therefore the original information can't be demodulated correctly. The more accurate the code
synchronization is, the better the receiver's demodulation performance is. Multi-path
searching includes detecting the propagation delay of multi-path signal from signals received,
and then adjusting local spread spectrum code according to the transmission delay to make it
synchronize with the spread spectrum code of each multi-path signal of received signals. If
the multi-path delay can't be searched accurately by multi-path searching, then the
demodulation performance of the followed Rake receiver will suffer a loss.
Multi-path searching methods according to the prior art comprise the following steps: first,
performing slide correlation integral of the received signal with the scrambling code to obtain
the Complex Relation Function (CRF) of the expected user signal; then, the Power Delay
Profile (PDP) is obtained by getting the sum of the square of real part and the square of
imaginary part of CRF, that is, PDP is the module square of the correlation function of a
scrambling code and a received signal; And then, peaks having a comparatively larger profile
value (i.e. comparatively larger correlation value, comparatively larger power ) or having a
profile value which is larger than a predetermined threshold are picked out from the power
delay profile PDP, wherein the position of the peaks are just the positions of the multi-path
delays. Above-mentioned method is the traditional multi-path searching method, which has
been described in the following books and papers, "Modern Mobile Communication
Systems" (People's Post & Telecomm Press, by Qi Yusheng and Shao Shixiang), "CDMA:
Principles of Spread Spectrum Communication" (Addison-WeSley Publishing Company, by
Andrew J. Viterbi), "Optimal Decision Strategies for Acquisition of Spread-Spectrum Signals
in Frequency-Selective Fading Channels "(IEEE Transactions on communications Vol. 46.
No. 5, by Roland R. Rick and Laurence B. Milstein.).
Actually, multi-path searching is just equivalent to making de-scrambling for each different
delay of received signal by using scramble code to select real multi-path delay. Usually,
hundreds of delay positions are needed to be de-scrambled, while only several of them are the
real multi-path positions, which is usually less than ten. It's enough for the followed Rake
receivers to de-scramble only the selected real multi-path positions.
The wireless communication environment changes continuously, so multi-path search needs
to be carried out continuously in order to reflect the current channel environment in time. To
reduce the time of multi-path search, a parallel searching method is adopted. Therefore in the
receiver, the multi-path search takes a great proportion in operation quantity, the realization
of which is also complex. If the operation for multi-path searching is reduced, the
corresponding multi-path searching precision will be lowered than usual also, and the gap
between two adjacent delay points is usually equal to half of chip period, namely, the
precision is only 1/2 chip, while the demodulation needs a precision of 1/4 chip or even 1/8
chip. To improve the precision, a method called early-late gate tracking method is usually
applied, which comprises the following steps of: first, in every branch of Rake receiver,
demodulating the energy of the signal at the position of multi-path delay (called on-time path)
and also demodulating that of the signal which is half chip earlier (called early path) than the
multi-path delay as well as that of the signal which is half chip later (called late path) than the
multi-path delay at the same time ; then, comparing these three paths signals, that is, early
path signal, late path signal as well as on-time path signal, and sliding 1/8 chip or 1/4 chip of
the multi-path delay positions of these three channels in the direction of late path if the
signal energy of late path exceeds a predetermined threshold; or, sliding 1/8 chip or 1/4 chip
of the multi-path delay positions of these three channels in the direction of early path if the
signal energy of early path exceeds a predetermined threshold; or, considering the current
multi-path delay position as a relatively correct position and there is no need to slide, if the
signal energies of both early path and late path are almost equal. This process is called
early-late gate tracking. This method makes further fine adjustment for the searched result,
which functions like a searcher with a smaller searching window (only have three delay
positions) substantially. Although the receiver's demodulation performance can be improved
greatly by using the early-gate gate tracking method, it makes the complexity of the Rake
receiver doubled at the same time. In addition, in multi-path assignment method, the
multi-path search result and early-late gate tracking result usually need to be synthesized, and
the appropriate one of them should be chosen and assigned to the Rake receiver in order to
assign a relatively accurate delay position when carrying out the multi-path assignment. Also,
the method of early-late gate tracking has increased the complexity of multi-path assignment
management. The method of early-late gate tracking has already been described in detail in
the following book "CDMA: Principles of Spread Spectrum Communication"
(Addison-WeSley Publishing Company, by Andrew J. Viterbi).
To sum up, multi-path searching method according to the prior art can only offer a search
with relatively low precision. To improve the precision, the method of early-late gate tracking
is applied, but it is complicated.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a multi-path searching method
applied in code-division multiple access communication system, capable of improving the
precision of the result of the multi-path searching almost without increasing the complexity
of calculation, which overcomes the shortcoming of complicated realization of the early-late
gate searching, and at the same time simplifies the complexity of Rake receiver.
A multi-path searching method provided in the present invention comprises the following
steps: calculating the power delay profile; selecting multiple peaks from said power delay
profile which have comparatively higher energy; then, performing threshold comparison and
interpolation for the selected peaks to determine multi-path delay position as well as energy;
finally, determining the multi-path delay according to the interpolation result.
The multi-path searching method, wherein the step of calculating the power delay profile
further comprises: performing the matching correlation of a received signal with the local
scrambling code to obtain a correlation function; and calculating the module square of the
above-mentioned correlation function to obtain the power delay profile.
The multi-path searching method, wherein the step of threshold comparison and interpolation
further comprises: calculating the ratio of energy difference between the energy at the delay
position earlier than the selected peak and the energy at the delay position later than the
selected peak to the energy at the selected peak; comparing the ratio with a threshold to
determine a real number section where the ratio is located; then, determining the multi-path
delay position and multi-path energy of this peak value according to the value of the real
number section; finally, repeating above steps and completing the threshold comparison and
interpolation for all selected peaks.
The multi-path searching method, wherein the step of determining multi-path delay further
comprises: selecting multiple paths which have comparatively higher energy from the multi-
paths obtained by the step of threshold comparison and interpolation, and the corresponding
delay is the multi-path delay.
Compared with multi-path searching methods according to the prior art, the multi-path
searching method described in present invention can guarantee to improve multi-path search
precision greatly almost without changing the complexity of calculating, wherein the search
precision can reach 1/4 chip, 1/8 chip or even 1/16 chip. At the same time, the early-late gate
tracking module is not needed in the present invention, i.e. complicated tracking algorithm is
not needed also, which simplifies the complexity of the realization of the Rake receiver and
the complexity of multi-path assignment management. The method according to the present
invention is applicable for base stations and mobile stations in various code-division multiple
access communicate system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l is a schematic block diagram of a typical CDMA system;
Fig.2 is a schematic block diagram of the CDMA system that applies the multi-path searching
method according to the present invention;
Fig.3 is a flowchart of the multi-path searching method according to the present invention;
Fig.4 is a graph illustrating the ideal shape of multi-path peak value;
Fig.5 is a graph showing the relation between the deviation of real peak position to the
searched peak position and the ratio of the energy difference between the energy of the
sampling point earlier than the searched peak and the energy of the sampling point later than
the searched peak to the energy of the searched peak;
Fig.6 is a graph showing the relation between the energy deviation factor of the real peak
value and the searched peak value and the ratio of the energy difference between the energy
of the sampling point earlier than the searched peak and the energy of the sampling point later
than the searched peak to the energy of the searched peak.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Accompanying drawings and embodiments are combined to make further description
hereinafter, according to which, the present invention can be easily realized for those skilled
in the art.
Fig.1 is a schematic block diagram of an existing typical CDMA system. Referring to fig.1,
the transmitting apparatus includes signal source 101, transmitting filter 102, radio frequency
(RF) modulating module and antenna 104. Before being modulated by the radio frequency,
the signal first passes through a base-band transmitting filter 102, which is also called pulse
shaping filter, which converts the spread spectrum digital signal to a signal that is fit for RF
modulating Then the signal fit for RF modulating is modulated by the RF modulating module
103, which is then transmitted into the air by antenna 104. Generally, the characteristic of the
transmitting filter 102 is stable, for example, for mobile stations in WCDMA system, the
filter is a root raised cosine filter with its roll-off coefficient being 0.22. The receiving
apparatus includes antenna 105, RF channel 106, multi-path searching module 107,
multi-path management module 108 and Rake receiver 109. After the antenna 105 receives
the signal, this signal passes through RF channel 106 and enters multi-path searching module
107, in which the process of multi-path search is carried out, signal output through another
route from the RF channel 106 enters Rake receiver directly. The multi-path searching
module applies existing multi-path searching method, such as early-late gate tracking method,
and the multi-path delay is output to the multi-path management module 108, and then the
output of the multi-path management module 108 enters the Rake receiver. Rake receiver
includes multiple relatively independent receiving elements 109. Each receiving element 109
includes delay adjustment module 1091, early path demodulation module 1092, on-time path
demodulation module 1093 and late path demodulation module 1094. The signals from
multi-path management module 108 and RF channel 106 are received by the delay
adjustment module 1091, which then adjusts the delay of the signal and transmits the outputs
to the early path demodulation module 1092, on-time path demodulation module 1093 and
late path demodulation module 1094. The demodulated results of these three early, on-time
and late paths need to be fed back to the delay adjustment module 1091, which forms a
feedback loop. At the same time, the delay adjustment module 1091 also needs to receive
information from the multi-path management module 108, and feeds back the information
about the delay adjusting to the multi-path management module 108, which also forms a
feedback loop. While feedback loop will make the mufti-path searching method complex.
Fig.2 is the schematic block diagram of the CDMA system that applies the multi-path
searching method according to the present invention. Same as Fig.l, the transmitting
apparatus includes signal source 101, transmitting filter 102, RF modulator module 103 and
antenna 104. The receiving apparatus includes antenna 105, RF channel 106, multi-path
searching module 207 and Rake receiver. After the antenna 105 receives the signal, this
signal passes RF channel 106 and enters multi-path searching module 207, multi-path
searching module 207 applies the multi-path searching method according to the present
invention to carry out multi-path search. And the searched multi-path delay is output to the
Rake receiver. Signal output through another route from the RF channel 106 enters Rake
receiver directly. Rake receiver includes multiple relatively independent receiving elements
209. Wherein, each receiving element 209 only includes on-time path demodulation module
2091. Compared with Fig.l, the structure of the Rake receiving element has been simplified
greatly, the delay adjustment module, the early path demodulation module as well as the late
path demodulation module have been omitted, and the on-time path demodulation module
2091 is totally the same as the original on-time path demodulation module 1091. With the
present invention, a complex multi-path management module is also not needed in the
receiving system. Compared with Fig.l, there is no feedback loop in the receiving system,
The kernel idea of the multi-path searching method of the present invention comprises:
calculating the power delay profile PDP without changing the precision of the multi-path
searching correlative integral, then selecting peak data of PDP with comparatively higher
energy to perform interpolation based on the threshold decision, which specifically, i.e.
calculating the ratio of the energy difference between the energy of the sampling point earlier
than the searched peak and the energy of the sampling point later than the searched peak to
the energy of the peak, which is then compared with a predetermined threshold to calculate
more accurate multi-path delay position and energy . The peak herein and hereinafter is
defined to be the position, the energy of which is higher than the energy of the positions on
both sides thereof. The flowchart of the present invention is shown as Fig.3.
The method of the present invention is an interpolation method based on threshold decision,
so it is necessary to set the threshold. The setting of the threshold can be completed during
the period of system configuration, as shown in block 301 of Fig.3. The number and value of
the thresholds, the corresponding delay position deviation and energy deviation thereof can
be determined according to the search precision requirement of the system. According to the
requirement of search precision, 2N thresholds Th(n) are determined which are arranged by
size, wherein n=+1, ±2,"* +N, wherein N is a natural number , to make a easier
description, the number zero is excluded. The smaller the serial number is, the smaller the
corresponding threshold value is, i.e. the ranking order of the threshold is Th(-N),
Th(-N+1),....., Th(-1), Th(+1),......, Th(N). For instance, if the system needs to interpolate
the search precision from 1/2 chip to 1/8 chip, at least four thresholds are needed, so here N is
equal to 2. If system needs to interpolate the search precision from 1/2 chip to 1/4 chip, then
two thresholds are needed, so here N is equal to 1. 2N thresholds divides the real number into
2N+1 real number sections, with the sequence number for which is defined as following: -N,
-N+1, •••, 0, 1, •••, N. If the calculated ratio R obtained in current peak threshold
interpolation locates in the real number section between Th (-1) and Th(l), that is, it locates
in the NO. 0 real number section , then the current peak position can be considered to be the
real multi-path delay position and the energy of the current peak is the real multi-path energy.
For other real number section, if the section number is n, then the position deviation
corresponding to the real multi-path position is DeltaOffset(n), and the energy deviation
factor corresponding to the real peak is AlphaEnergy(n), wherein n=±l,±2,"-, ±N, n
represents the section number of the real number. Generally, the unit of the delay position is
1/2 chip. For example, during the operation of the current peak threshold interpolation, the
calculated ratio R locates in the section between threshold Th(1) and Th(2), i.e.real number
section 1, then the real peak position is obtained by adding up the current peak position and
DeltaOffset(1), the real peak energy is obtained by multiplying the current peak energy by
AlphaEnergy(1). Then, the position deviation DeltaOffset(n) and the energy deviation factor
AlphaEnergy(n) can be determined according to the ideal shape of peak , wherein the energy
deviation factor AlphaEnergy(n) is defined to be the ratio of the real peak energy to the
searched peak energy. For example, in the above-mentioned embodiment, which has 4
thresholds, the corresponding position deviations are DeltaOffset(-2)=-0.25 chip,
DeltaOffset(-1)=-0.125 chip, DeltaOffset(1)= +0.125 chip, DeltaOffset(2)=+0.25 chip. While
in the embodiment which has 2 thresholds, the corresponding position deviations are
DeltaOffset(-1)=-0.25 chip, DeltaOffset(1)=+0.25 chip.
The specific multi-path searching method based on the threshold interpolation is carried out
during the period of system's operation. First, the power delay profile PDP is calculated (as
shown in block 302), which is the basic step for multi-path searching. There are many
methods to calculate the power delay profile according to the prior art, but the integral length
adopted may be of some difference, which has little effect on the method of the present
invention. In the present invention, the correlation function is obtained by matching
correlating the received signal with the local scrambled code and then the power at different
delay can be obtained by calculating the module square of the correlation function, wherein
the module square is the sum of the square of real part and the square of imaginary part.
Then, the threshold interpolation is carried out (as shown in block 303). First, multiple peaks
with comparatively higher energy are selected according to the value of power delay profile
PDP. Usually, according to an energy threshold which is defined or calculated by the system
itself, the maximum number of selected multi-path the energy of which exceeds the energy
threshold is less than or equal to Mpath, wherein the value of Mpath can be defined or
calculated by each system, typically the value of Mpath is within the range from 4 to 16.Then
the ratio of the energy difference between the energy of the delay position earlier than the
searched peak and the energy of the delay position later than the selected peak to the energy
of the selected peak is calculated. If the energy of selected peak is PDP (k), wherein k is the
delay position, then the ratio R is obtained by the following formula: R =[PDP
(k-l)-PDP(k+l)]/PDP(k). Comparing the ratio R with the defined threshold to determine the
real number section where the ratio R locates in, then the real multi-path delay position and
the corresponding multi-path energy thereof can be determined according to the value of that
real number section. If the real number section where ratio R locates in is p, then the real
multi-path delay position is the sum of the delay position of the selected peak and the position
deviation DeltaOffset(p) of the real number section where the ration R is located, wherein the
multi-path energy thereof is obtained by multiplying PDP(k) by AlphaEnergy(p). All selected
peaks are performed said threshold comparison and interpolation operation according to the
above steps to obtain the corresponding real multi-path delay position and multi-path energy
thereof.
Finally, the multi-path delay is determined (as shown in block 304). After the
above-mentioned threshold interpolation operation, several real multi-path delay positions
and multi-path energies are obtained. The energy of the real multi-path delay are compared
and M multi-paths, the energy of which are comparatively higher, are selected from above
mentioned real multi-paths. The specific value of M can be decided by each system
independently, typically, M can be any value between 1 and 8. And the delay position tm
which is corresponding to the energy is the multi-path delay, wherein m= 1, 2,*-\ M.
By carrying out the above-mentioned steps, the entire process of multi-path search is
completed; therefore, the multi-path delay is obtained.
Fig.4 is a graph of the ideal shape of the multi-path peak value. This ideal peak is obtained by
using 256 chips as the correlation integral length and 1/8 chip as the sampling precision,
wherein the real peak position is 15 and the real multi-path energy is about 4600. If other
integral length is adopted, the shape of the obtained peak will be of some difference. In the
present embodiment, the coherent integral length with 256 chips will be described as
example.
Fig.5 is a graph showing the relation between the deviation of real peak position to the
searched peak position and the ratio of the energy difference between the energy of the
sampling point earlier than the searched peak and the energy of the sampling point later than
the searched peak to the energy of the searched peak. Taking 256 chips integral length as
example and assuming the multi-path search precision is 1/2 chip, then one point for every 4
adjacent points in the curve of Fig.4 should be selected as the sampling point position. If that,
the real peak position 15 may not be selected, thus the searched peak may deviate from the
real peak position. The position deviation and searched peak have following characteristics:
the larger the absolute value of the position deviation is, the larger the absolute value of the
ratio R of the energy difference between the early sampling point and the late sampling point
around the searched peak to the energy of the searched peak is, and the symbol of the ratio,
i.e. positive or negative, corresponds to the direction of the deviation. The specific relation is
shown as the curve in Fig.5. For instance, if the position deviation is 0, then the ratio R equals
to 0; if the position deviation is 1/8 chip, then the ratio R equals to 0.43; if the position
deviation is -1/8 chip, then the ratio R equals to -0.43; if the position deviation is 1/4 chip,
then the ratio R equals to 0.94.
If the search precision is required to be improved from 1/2 chip to 1/8 chip according to the
requirement of the system, then four thresholds can be defined based on the curve in fig.5,
which are -0.68, -0.21, 0.21 and 0.68 respectively, and the corresponding four delay position
deviations DeltaOffset thereof are -0.25, -0.125, 0.125 and 0.25.
Fig.6 is a graph showing the relation between the energy deviation factor of the real peak
energy to the searched peak energy and the ratio of the energy difference between the energy
of the sampling point earlier than the searched peak and the energy of the sampling point later
than the searched peak to the energy of the searched peak. Taking integral length of 256 chips
as an example and assuming the multi-path search precision is 1/2 chip, and one point for
every 4 adjacent points in the curve of Fig.4 should be selected as the sampling point position.
If that, the real peak position 15 may not be selected, thus the energy of the searched peak
may be lower than the energy of the real peak. And the relation between the size of the
energy deviation and the searched peak is of following characteristic: the larger the absolute
value of the energy deviation is, the larger the absolute value of the ratio R of the energy
difference between the energy of the early sampling point and that of the late sampling point
around the searched peak to the energy of the searched peak is. The real relation is shown as
the curve in Fig.6. For instance, if the position deviation is 0, then the energy deviation equals
to 0 and the ration R equals to 0; and if the position deviation is 1/8 chip, the energy of the
real peak is 1.06 times of the energy of the searched peak, and the ratio R equals to 0.43; and
if the position deviation is 1/4 chip, the energy of the real peak is 1.28 times of the searched
peak energy, and the ratio R equals to 0.94.
Supposing that the search precision is required by the system to be improved from 1/2 chip to
1/8 chip, then four thresholds can be defined according to the curve in fig.5, which are -0.68,
-0.21, 0.21 and 0.68 respectively, and the corresponding four delay position deviations
DeltaOffset are -0.25, -0.125, 0.125 and 0.25, and the ratio of the real energy to the searched
energy, i.e.AlphaEnergy is 1.28, 1.06, 1.06 and 1.28.
From the above-mentioned analysis, in the present embodiment, it is enough only to retain
two datas of the energy deviation factor AlphaEnergy, and among the four datas of the delay
position deviation DeltaOffset and threshold Th, if the sign is not considered, there are only
two different datas, which facilitates the specific realization.
To sum up, compared with the CDMA receiving system according to the prior art, the CDMA
receiving system applying the multi-path searching method according to the present invention
can reduce the complexity of the receiving system greatly without reducing the performance
of the system, which is easy to realize and is of obvious effect and is applicable for various
code division multiple access communication system.
It should be understood that the above-described embodiments are used to explain but not to
limit the present invention. Although the present invention has been explained in detail by
referring to the embodiments, it should be apparent to those skilled in the art that various
modifications and variations may be made in the present invention without departing from
the spirit or scope of the invention. Thus, it is intended that the present invention cover the
modifications and variations of this invention provided they come within the scope of the
appended claims and their equivalents.
WE CLAIM:
1. A method of multi-path searching in code-division multiple access communication
system comprising the steps of:
calculating power delay profile of a received signal;
selecting multiple peaks which have comparatively higher energy from said power
delay profile;
performing threshold comparison and interpolation for said selected peaks to
determine multi-path delay position;
determining the multi-path delay according to the results of said interpolation .
2. The method according to claim 1, wherein said step of performing threshold
comparison and interpolation further comprises performing threshold comparison and
interpolation to determine multi-path energy.
3. The method according to claim 2, wherein said step of calculating power delay profile
further comprises:
performing a matching correlation of said received signal with local scrambling
code to obtain a correlation function; and
calculating module square of said correlation function to obtain the power delay
profile.
4. The method according to claim 2, wherein said step of selecting multiple peaks
which have comparatively higher energy further comprises :
selecting no more than Mpath multi-paths according to an energy threshold
prescribed or calculated by the system, wherein the energy of the selected
multi-paths exceeds the energy threshold, wherein the maximum number of
selected multi-path Mpath is prescribed or calculated by the system.
5. The method according to claim 4, wherein said Mpath is within the range between 4
and 16.
6. The method according to claim 2, wherein said step of setting threshold further
comprises:
determining 2N threshold Th(n) ,which are arranged by size according to the
system requirement of the search precision, wherein N is a natural number and n is
expressed as: n=± 1,+2,"m, +N, and wherein the smaller the serial number is,
the smaller the value of the threshold is;
dividing the real number into 2N+1 real number sections by using the 2N
thresholds, and the sequence number for the sections are : -N, -N+1, •••, 0,1, ••,
N;
considering the peak locating in real number section 0 as the real multi-path delay
position, for other real number section n, the position deviation corresponding to
the real multi-path is DeltaOffset(n), and the energy deviation factor corresponding
to the real peak is AlphaEnergy(n);
determining the value of the position deviation and the energy deviation factor
according to an ideal peak shape.
7. The method according to claim 6, wherein said step of performing threshold
comparison and interpolation for the selected peaks further comprises :
calculating the ratio of the energy difference between the energy at the delay
position before the selected peak and the energy at the delay position after the
selected peak to the energy of the selected peak;
comparing said ratio with said threshold to determine the real number section
where said ratio locates;
determining the real multi-path delay position and the multi-path energy thereof
corresponding to the selected peak according to the value of the real number
section;
repeating above steps to complete the threshold comparison and interpolation for
all selected peaks.
8. The method according to claim 7, wherein said step of determining the real
multi-path delay position and the multi-path energy thereof corresponding to the
selected peak further comprises :
adding the position deviation of the real number section where the ratio of the peak
locates to the peak to get the real multi-path delay position;
multiplying the energy of the peak and the energy deviation factor of the real
number section where the ratio of the peak locates to get the real multi-path
energy.
9. The method according to claim 2, wherein said step of determining the multi-path
delay according to the results of said interpolation further comprises :
comparing the energy of the real multi-paths obtained by carrying out the step of
threshold comparison and interpolation ;
selecting M multi-paths from said real multi-paths, the energy of which are
comparatively higher, wherein M is determined by system ;
obtaining multi-path delays which are the delays corresponding to the M multi-paths.
10. The method according to claim 9, wherein said M can be any integer from 1 to 8.


A method of multi-path search in code-division multiple access communication system is
provided, which comprises the following steps: first, calculating the power delay profile of the
received signal, and multiple peaks with comparatively higher energy are selected from the
power delay profile, then performing threshold comparison and interpolation for the selected
peaks to determine the multi-path delay position and energy, finally, determining the multi-path
delay according to the results of interpolation. Compared with the prior art, the present invention
can improve multi-path search precision greatly without increasing the complexity of calculation,
specifically, the search precision can reach 1/4 chip, 1/8 chip, or even 1/16 chip; at the same
time, early-late gate tracking module are not needed in the method of the present invention, thus
complex tracking algorithm are also not needed, which greatly simplify the realization
complexity of Rake receiver and the complexity of multi-path assignment management;
Furthermore, the method of the present invention is applicable for base stations and mobile
stations of various of code division multiple access communication system.

Documents:

02075-kolnp-2006-abstract-1.1.pdf

02075-kolnp-2006-abstract.pdf

02075-kolnp-2006-assignment.pdf

02075-kolnp-2006-claims-1.1.pdf

02075-kolnp-2006-claims.pdf

02075-kolnp-2006-correspondence 1.2.pdf

02075-kolnp-2006-correspondence others-1.1.pdf

02075-kolnp-2006-correspondence others.pdf

02075-kolnp-2006-description (complete).pdf

02075-kolnp-2006-drawings-1.1.pdf

02075-kolnp-2006-drawings.pdf

02075-kolnp-2006-form-1.pdf

02075-kolnp-2006-form-2.pdf

02075-kolnp-2006-form-3.pdf

02075-kolnp-2006-form-5.pdf

02075-kolnp-2006-international publication.pdf

02075-kolnp-2006-international search authority report.pdf

02075-kolnp-2006-priority document-1.1.pdf

02075-kolnp-2006-priority document.pdf

2075-KOLNP-2006-ABSTRACT-1.1.pdf

2075-KOLNP-2006-CANCELLED PAGES.pdf

2075-KOLNP-2006-CLAIMS-1.1.pdf

2075-KOLNP-2006-CLAIMS.pdf

2075-KOLNP-2006-CORRESPONDENCE 1.4.pdf

2075-KOLNP-2006-CORRESPONDENCE-1.3.pdf

2075-KOLNP-2006-CORRESPONDENCE-1.5.pdf

2075-kolnp-2006-correspondence1.2.pdf

2075-KOLNP-2006-DESCRIPTION (COMPLETE)-1.1.pdf

2075-KOLNP-2006-DRAWINGS-1.1.pdf

2075-kolnp-2006-examination report.pdf

2075-KOLNP-2006-FORM 1-1.1.pdf

2075-kolnp-2006-form 18.pdf

2075-KOLNP-2006-FORM 2-1.1.pdf

2075-kolnp-2006-form 3.pdf

2075-kolnp-2006-form 5.pdf

2075-kolnp-2006-granted-abstract.pdf

2075-kolnp-2006-granted-claims.pdf

2075-kolnp-2006-granted-description (complete).pdf

2075-kolnp-2006-granted-drawings.pdf

2075-kolnp-2006-granted-form 1.pdf

2075-kolnp-2006-granted-form 2.pdf

2075-kolnp-2006-granted-specification.pdf

2075-kolnp-2006-pa.pdf

2075-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

2075-kolnp-2006-reply to examination report1.2.pdf

2075-kolnp-2006-translated copy of priority document.pdf

abstract-02075-kolnp-2006.jpg


Patent Number 245262
Indian Patent Application Number 2075/KOLNP/2006
PG Journal Number 02/2011
Publication Date 14-Jan-2011
Grant Date 11-Jan-2011
Date of Filing 24-Jul-2006
Name of Patentee ZTE CORPORATION
Applicant Address ZTE PLAZA, KEJI ROAD, SOUTH, HI-TECH INDUSTRIAL PARK, NANSHAN DISTRICT, SHENZHEN, GUANGDONG 518057
Inventors:
# Inventor's Name Inventor's Address
1 DING, JIEWEI ZTE PLAZA, KEJI ROAD, SOUTH, HI-TECH INDUSTRIAL PARK, NANSHAN DISTRICT, SHENZHEN, GUANGDONG 518057
PCT International Classification Number H04J 13/00
PCT International Application Number PCT/CN2003/001129
PCT International Filing date 2003-12-26
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA 2003-12-26 China