KR100366288B1 - Optimal searching method of DS-CDMA signal composed of time multiplexed known symbols and unknown symbols - Google Patents

Abstract

In the present invention, the pilot symbol region and the control symbol region are time-divided, so that the pilot symbol and the control symbol are time-divided to maximize the performance of the receiver when searching for signals or measuring SIR using a direct sequence spread signal. The present invention relates to a method for optimally searching a DS-CDMA signal and a device therefor, and furthermore, when a receiver searches for the above-mentioned signal, it basically uses both energy of a pilot symbol and a control symbol, but coherent integration of two regions is performed. The present invention proposes a method of maximizing the searcher's performance by varying the lengths and adding weights to two parts when the coherent correlation value is finally added noncoherently, and relates to an effective SNR estimation method for each search path.

Description

Optimal searching method of DS-CDMA signal composed of time multiplexed known symbols and unknown symbols}

In the present invention, the pilot symbol region and the control symbol region are time-divided so that the pilot symbols and the control symbols are time-divided to maximize the performance of the receiver when searching for signals or measuring SIR using a direct sequence spread signal. The present invention relates to a method for optimally searching a DS-CDMA signal and a device thereof.

In addition, the present invention basically uses both the energy of the pilot symbol and the control symbol when the receiver searches for the above-mentioned signals, but varies the coherent integral lengths for the two regions, and finally, noncoherently the coherent correlation value. We propose a method of maximizing the searcher's performance by adding weights to two parts when adding it intently, and an effective SNR estimation method for each search path.

Recently, IMT-2000, a next generation mobile communication system that is attracting attention, is divided into a satellite communication area and a terrestrial communication area. As an exemplary diagram, a frame structure of a reverse DPCH (Dedicated Physical CHannel) of an asynchronous W-CDMA scheme currently being developed by a 3rd Generation Partnership Project (3GPP) is shown.

As shown in FIG. 1, one frame has a length of 10 msec and is divided into 15 slots. One slot is 0.667 msec, which corresponds to a 2560 chip length.

As shown in FIG. 1, the DPCH includes a Dedicated Physical Data CHannel (DPDCH) and a Dedicated Physical Control Channel (DPCCH). The DPDCH of FIG. 1 is used to carry the user's information bit 1 from the upper layer, and the data transmission rate may be variable in each frame, with a minimum spreading factor of 4 and a maximum of 256.

The DPCCH is a pilot region (2) which enables coherent demodulation when a base station demodulates a mobile station signal, and a control region carrying control information such as information on data rate and power control bits for data (1) of DPDCH. It consists of 3). This format is given identically in every slot.

In FIG. 1, the number of DPCCH symbols transmitted during one slot is 10 symbols in total, and this value does not always change. That is, the spreading factor of the DPCCH is always 256. Among the total 10 symbols, the number of symbols in the pilot area can be from 3 to 8, depending on the slot format specified in the W-CDMA standard. The slot format is determined at the initial call setup between the base station and the mobile station. The slot format may change during a call, such as when switching from compressed mode to compressed mode or vice versa.

Table 1 below shows the slot format of the reverse link DPCCH defined in the W-CDMA standard. In Table 1, A and B slot formats are used in compressed mode and the other formats are used in normal mode.

In FIG. 1, the pilot symbol 2 of the DPCCH is masked by a pilot pattern for frame synchronization confirmation. Since the W-CDMA standard defines a pilot pattern according to the number of pilot symbols per slot, a pilot symbol is a known symbol from a receiver side. On the other hand, since the control symbol 2 changes randomly every slot or every frame, it is an unknown symbol before demodulation from the receiver's point of view.

DPDCH and DPCCH are first spread with a quadrature code having a chip rate of 3.84 Mcps as shown in FIG.

In FIG. 2, Cd (4A) and Cc (4B) are orthogonal codes for distinguishing DPDCH and DPCCH, respectively. After spreading to the orthogonal code, the gain is multiplied by βd and βc as in block (5). And complex scrambled with a complex pseudonoise code of 3.84 Mcps as in block 6.

Complex pseudonoise codes are used to separate multiple mobile stations. The real and imaginary parts of the demodulated scrambled signal pass through a pulse shaping filter as shown in blocks 7A and 7B, respectively, and are modulated (8) and amplified and transmitted through the antenna.

After the call is established, the base station must continue to search for the multi-path component of the signal received from the mobile station using the aforementioned DPCCH for finger reassignment. Since the path of the received signal on the radio channel is continuously changed according to the change of mobile station and the surrounding environment, the receiver must continuously search the multipath and reallocate the finger to avoid disconnection.

In addition to the multi-path search mentioned above, the base station should also use the DPCCH when performing a handover search for a mobile station to perform a handover from an adjacent base station to the current base station.

In the above-mentioned example, a pilot sequence and a control symbol have been known in the present invention in searching for a received signal or measuring signal strength using a direct sequence spread spectrum signal (DPCCH in the above example) having a time division scheme. The receiver structure uses both the energy of the pilot symbol region and the control symbol region, but the coherent integral length of the two regions is the same, and the coherent integral value is simply added non-coherently without distinguishing the pilot symbol region from the control symbol region. to be. Since the conventional receiver structure is not an optimal receiver, there is a disadvantage in that the performance of the receiver is very degraded at a low signal to noise ratio.

An object of the present invention for solving the above problems is to configure the pilot symbol region and the control symbol region by time division to maximize the performance of the receiver when searching for signals or measuring SIR using a direct sequence spread signal. An apparatus and method are provided.

1 is a frame structure of the reverse DPCH of the asynchronous W-CDMA scheme

2 is a conceptual diagram of an asynchronous W-CDMA mobile station transmitter.

3 is a structure of a base station receiver to which the present invention is applied

4 is a multipath / handover searcher structure according to the present invention.

5 is a method for searching for a multipath searcher of the present invention in a base station including multiple sectors.

A feature of the present invention for achieving the above object is a searcher having the same structure and consisting of at least one correlator that maintains the number (M) of at least one and less than the size of the search window to be searched; A sector and antenna selection unit which receives a complex value to a reception control block of a base station receiver and selects a sector and an antenna received signal to be searched by a searcher; The partial search window of the M / 2 chip can be searched at a time when the search step size is 1/2 chip by receiving the received signal of the sector and antenna selected from the sector and antenna selection unit and receiving a complex value corresponding thereto. A decimator for transferring data to the searcher side so that the data may be transmitted to the searcher side; In the searcher, the energy of the pilot symbol and the control symbol is used, but the coherent integral lengths of the two regions are different, and when the coherent correlation value is finally noncoherently added, the weighted values are applied to the two parts to accumulate different values. And a determining device for performing any one of a function for multipath searching, a handover searching, and a function for detecting signal strength.

As an additional feature of the present invention for achieving the above object, the searcher includes a condenser for performing complex condensation by a symbol length of 256 chips using code phases for M hypotheses. ; A decimator for decimating the signal condensed in the condenser on a 256-chip basis, but differentiating a transmission path by distinguishing whether the decimated signal region is a pilot symbol region or a control symbol region; A coherent accumulator for receiving a signal divided into a pilot symbol region from the decimator and performing a coherent accumulation operation; A square combiner for receiving a signal divided into a control symbol region from the coherent accumulator output or the decimator and adding the squared real and imaginary parts, respectively; A multiplier that receives the output of the square combiner and bypasses when the current symbol corresponds to the control symbol region, and performs a multiplication operation to give a weight when the current symbol corresponds to the pilot symbol region; And a non-coherent accumulator for accumulating the values received from the multiplier or the square combiner according to the slot lengths controlled by the controller and transferring the accumulated values to the determination device.

The above object and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, the method of the present invention mentioned above will be described in detail with reference to the drawings.

3 illustrates an example of a base station receiver including a multipath searcher or a handover searcher using the method proposed by the present invention, which manages a plurality of sectors and has two receiving antennas per sector.

In FIG. 3, the signals received through the base station antennas 10A, 10A ', 10N, 10N' are down-converted by the RF processing and AD conversion blocks 11A, 11A ', 11N, 11N' and matched by a pulse matching filter. After filtering, A / D conversion. A / D converted signals have 4 or 8 sample values per chip.

Thereafter, the reception signal control block 12 serves to distribute signals received from the N sectors to the demodulator block 20 referred to by reference numeral 20 in the base station. In FIG. 3, only one demodulator block 20 is illustrated at the base station receiving end. In practice, multiple demodulator blocks may exist.

The demodulator block 20 basically consists of a plurality of fingers 15A and 15L, one combiner 17 and one multipath / handover searcher 16, each block being a controller 18. ) Is under control.

The multipath / handover searcher 16 has two roles, one for setting up a random search window for signals received from one or two sectors, and the other for continuously searching for multiple paths. Searching for a received signal from a mobile station that attempts to perform a soft or hard handover from a base station to a current base station.

4 shows an embodiment of the searcher of the present invention.

The searcher of the present invention according to the embodiment of FIG. 4 is composed of M active correlators 23A and 23M, and each of the M correlators has the same structure. In this case, the variable M is greater than or equal to 1 and less than or equal to the size of a search window to be searched by the searcher.

The M active correlators 23A and 23M may be implemented in the form of a code matching filter having a tap size of M, but this method does not depart from the scope of the present invention. The searcher of FIG. 4 shows an example of a searcher capable of searching the partial search window of the M / 2 chip at a time, assuming that the search step size is 1/2 chip.

In addition, the sector and antenna selector 21 selects a sector and an antenna received signal to be searched by the searcher under the control of the controller. The bold arrows in FIG. 4 mean passing a complex value, and the thin lines indicate passing real values.

The M despreaders 22 perform complex despreading by symbol (256 chips) length using code phases for M hypotheses. Each of the I and Q channel components of the condensed signal is decimated by the decimator 25 every 256 chips.

The decimator 25 output enters the coherent accumulator 26 when the area of the current respread signal is the pilot symbol area and bypasses the coherent accumulator 26 when it is the control symbol area.

The coherent integration length in the control symbol region cannot be larger than 256 chips because the control symbol value is not known until the receiver demodulates the control symbol. In the situation where the pilot symbols of the received signal are masked by the pilot pattern as in the example of FIG. 1, a pilot pattern remover is inserted into (or at the front of) the coherent integrator. (The pilot pattern remover is not shown in FIG. 4.)

The square combiner 27 squares the real part and the imaginary part of the coherent accumulator 26 output or the decimator output 25 and adds them. The output of the square combiner 27 becomes the input of the multiplier 28. If the current symbol corresponds to the control symbol region (control symbol region: 3), it bypasses the multiplier 28 for weighting and the current symbol pilot. If it corresponds to a symbol region (pilot symbol region: 2), it enters the input of the multiplier 28.

The multiplier 28 stores weight values corresponding to each slot format defined in Table 1 therein and multiplies a weight combiner output signal by a weight value corresponding to a slot format of a current mobile station transmission signal. This is discussed in detail below.

The non-coherent accumulator 29 accumulates the values received from the multiplier 28 or the square combiner 27 over several slot lengths. The accumulated slot length is controlled by the controller. The accumulated value becomes an input of the determination device 30. The determination device 30 may be a block for multipath search, a block for handover search, or a block for detecting signal strength.

Hereinafter, the receiver structure of the present invention described above will be described in detail through an example shown in Table 1.

First, consider slot format 0B of Table 1 as the first example. In this case, the number of pilot symbols per symbol of the DPCCH is 4 symbols and the number of control symbols is 6 symbols.

In this case, the maximum coherent integration length for the pilot symbol region (pilot region) may be a 4-symbol interval. If the integral section of the non-coherent accumulator 29 is 10 symbols (= 1 slot interval), the final decision variable 29 for the m (1 ≤ m ≤ M) th correlator is expressed by Equation 1 below. Can be given.

In the above Equation 1, the first part is a squared combination of the coherent accumulated values of the real part and the imaginary part, respectively, during the four symbol periods for the pilot symbol region, and the second part is the one symbol interval for the control symbol region ( The sum of the coherent integrals of the real part and the imaginary part during the 256-chip period is summed non-coherently during the six-symbol period. λ ^(0B) is a weighting value for slot format 0B, and the receiver of the present invention stores this value.

When the integral section of the non-coherent accumulator 29 of the present invention is 10 symbols (= 1 slot) or more, the process given by Equation 1 is repeated to accumulate. In the description of Equations 1 and 4 of the present invention, the weight corresponding to the portion corresponding to the pilot region is multiplied, but in the implementation, a method of weighting the control region may be considered. This method also does not depart from the scope of the present invention.

In an ideal channel environment, the larger the coherent integration interval of the coherent accumulator 26 for the pilot region, the better the receiver performance. However, when the Doppler frequency is large according to the speed of the mobile station in the wireless channel environment, the performance of the receiver may be degraded when the coherent integration section of the coherent integrator 26 for the pilot region is larger than the coherent section of the channel. Can be.

In this case, the present invention also proposes a method of dividing the coherent integration section into two or more. For example, consider slot format 1 in Table 1. In this case, the number of pilot symbols per symbol is eight. In this regard, the final decision variable may be given by Equation 2.

In Equation 2, the first two parts correspond to the integral value for the pilot region and the second part correspond to the integral value for the control symbol region. In Example 2 of the present invention, assuming that a coherent section of a channel is a 4-symbol region, an eight-symbol pilot region is divided into two regions and multiplied by the same weight. [lambda] ⁽¹⁾ is a weight value for slot format 1 of Table 1, and the receiver of the present invention stores this value. When the integral section of the non-coherent integrator 29 of the present invention is 10 symbols (= 1 slot) or more, the process given by Equation 2 is repeated and accumulated.

If the pilot symbol region is odd and larger than the coherent integration interval of the channel, as shown in slot format 3 of Table 1, the pilot region may be divided as follows.

In Equation 3, the first two parts are integral values for the pilot region and the second part correspond to the integral values for the control symbol region. In Example 3 of the present invention, when a coherent section of a channel is assumed to be a 4-symbol region, a 7-symbol pilot region is divided into 2 regions and multiplied by different weight values. λ ₁ ⁽³⁾ and λ ₂ ⁽³⁾ are weight values for slot format 3 in Table 1, and the receiver of the present invention stores these values.

The reason for multiplying different weight values as in Equation 3 is that the coherent integration lengths of the two regions are different. When the integral section of the non-coherent accumulator 29 of the present invention is 10 symbols (= 1 slot) or more, the process given by Equation 3 is repeated to accumulate.

Hereinafter, summarizing the examples 1, 2, and 3 can be summarized as shown in Table 2 below.

In the receiver of the present invention, as shown in Table 2, the coherent integral length and weight vector for each slot format are stored, and a value corresponding to the corresponding format is used when establishing a call.

When the multipath searcher of the present invention is used in a base station receiver including two or more sectors, if there is only one active sector of the reverse link talking to the mobile station, the time division (TDM) not only the current active sector but also the adjacent non-active sector (TDM) To search.

5 is an exemplary diagram illustrating an example of a six sector base station. In FIG. 5, the base station searcher of the present invention searches 32 sectors in a TDM manner including not only the current active sector but also two adjacent non-active sectors when there is one active sector (31). If there are two active sectors (33), the multi-path searcher searches for two active sectors in a TDM manner (34).

The greatest advantage of the direct sequence CDMA system is that the receiver's performance is maximized due to the path diversity effect caused by rake combining multiple multipath components. However, these multipaths are not fixed but continue to change on the time axis depending on the speed of the mobile station.

The multipath searcher sets up a random search window in such a time-varying channel situation to continue to search the multipath and pass information on each path to the controller. The multipath information includes signal strength (or SNR) information of each path as well as delay information of each path.

In the multipath searcher of the present invention, the SNR estimation method of an arbitrary path uses M noncoherent combiner outputs of the parallel correlator, but uses a ratio of the average value of the selected path and the remaining paths. This is described in detail below.

The decision device 30 of the multipath searcher of the present invention selects L in order from the larger of the M noncoherent combiner outputs. L is greater than or equal to 1 and less than M.

The multipath searcher estimates [Es / Io] values for each of the selected L paths and passes them to the controller using the ratio of the average of the outputs of the remaining ML non-coherent accumulators 29 except the L selected paths. .

Where Es is the energy per symbol of the received signal and Io is the total noise power density. To [Es / Io] value of the i-th path of the L paths release as [Es / Io] l _i [Es / Io] l _i value is given as in expression (4).

In Equation 4, N _c1 represents a primary coherent integration region in symbol units shown in Table 2, and λ ₁ represents a weighting factor for the primary coherent integration region. In addition, N _c2 represents a secondary coherent integration region in symbol units shown in Table 2 above, and λ ₂ represents a weighting factor for the secondary coherent integration region. 2 [Es / Io] l _i a l _i-th path of the car if the coherent integration length 0 days is as in equation (5).

In Equation 4 and Equation 5, Γ ^(li) is the output of the noncoherent accumulator 19 for the path l _i and the output of the noncoherent accumulator 19 for the ML paths except L selected paths. As an average, it is defined as in Equation 6.

The SNR measurement method of the multipath searcher of the present invention is based on Equation 6 and Equation 4 or Equation 5.

6 is a graph showing a false alarm probability versus a detection probability when the existing method and the present method are applied to a multipath searcher. The figure shows an example where five of the ten symbols are pilot symbols and the rest are control symbols. In the case of the method of the present invention, the coherent integral length for the pilot part was set to 5 symbol intervals, and the optimal weight factor at that time was used for the simulation for performance analysis. From the figure, it can be seen that the method of the present invention is much better in terms of signal detection probability than the conventional method.

While the invention has been shown and described in connection with specific embodiments thereof, it is well known in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

As described above, according to the present invention, the pilot symbol region and the control symbol region are time division multiplexing (TDM). When all of the energy of the control region is used but the correlation values for the two regions of the present invention are noncoherently added, the weight of the two portions can be simply changed to maximize the performance of the receiver.

The present invention also proposes a method for differently setting a weight value for a slot format. By using this method, there is an advantage of maximizing the performance of a receiver for each slot format.

Claims (9)

A searcher having the same structure and comprising at least one correlator for maintaining at least one number M less than or equal to the size of a search window to be searched; A sector and antenna selection unit which receives a complex value to a reception control block of a base station receiver and selects a sector to be searched by a searcher and a reception signal of an antenna; The partial search window of the M / 2 chip can be searched at a time when the search step size is 1/2 chip by receiving the received signal of the sector and antenna selected from the sector and antenna selection unit and receiving a complex value corresponding thereto. A decimator for transferring data to the searcher side to ensure that the data is transmitted; And In the searcher, the energy of both the pilot symbol and the control symbol is used, but the coherent integral lengths of the two regions are changed, and when the coherent correlation value is finally noncoherently added, the weighted values are applied to the two parts to accumulate the accumulated values. The pilot symbol and the control symbol are configured by time division, comprising a determination device for performing any one of a function for multipath search, a function for handover search, and a function for detecting signal strength. Optimal search device for DS-CDMA signals. The method of claim 1, The searcher comprises: a condenser for performing complex condensation by a symbol length of 256 chips using code phases for M hypotheses; A decimator for decimating the signal condensed in the condenser on a 256-chip basis, but differentiating a transmission path by distinguishing whether the decimated signal region is a pilot symbol region or a control symbol region; A coherent accumulator for receiving a signal divided into a pilot symbol region from the decimator and performing a coherent accumulation operation by applying a predetermined weight; A square combiner that receives a signal divided into a control symbol region from the coherent accumulator output or the decimator and squares a real part and an imaginary part, respectively, and adds them; A multiplier that receives the output of the square combiner and bypasses when the current symbol corresponds to the control symbol region, and performs a multiplication operation to give a weight when the current symbol corresponds to the pilot symbol region; And The pilot symbol and the control symbol are time-divided, comprising: a non-coherent accumulator for accumulating the values received from the multiplier or the square combiner according to the slot lengths controlled by the controller and transferring the accumulated values to the determination device. Optimal search device for DS-CDMA signals. In a method for optimal search of a signal in a searcher which consists of a pilot symbol region and a control symbol region in a time division manner and searches for a direct sequence spread signal with a pseudo noise code: A first step of using both energy of a pilot symbol region and a control symbol region of a received signal, and different coherent integration intervals for the two regions; Finally, when the coherent correlation values of the pilot symbol region and the control symbol region of the received signal are added non-coherently. And a second process of differently weighting the two parts, such as a pilot symbol and a control symbol, wherein the DS-CDMA signal has a time division. The method of claim 3, wherein The first process includes: a first step of dividing the coherent integration section of the pilot symbol region into two or more when the pilot symbol region of the received signal is larger than the coherent interval of the channel; When the coherent integration value for the pilot symbol region divided into two or more in the first step is finally noncoherently added A second step of assigning a weight of each part corresponding to an integral value for the control symbol region and a latter part for the pilot region as in the above equation; When the non-coherent addition of the coherent integral value for the pilot symbol region divided into two or more in the first step As shown in the above equation, the first two parts include an integral value for the pilot region, and the second part includes a third step of assigning a weight to each part corresponding to the integral value for the control symbol region. Optimal search method for DS-CDMA signals whose symbols are time-divided. The method of claim 3, wherein The second process includes a first step in which the receiver stores a weight value for each preset slot format; And a second step of using a coherent integration length and a weight value when the slot format of each frame is changed. 2. The method according to claim 3 or 4, When the multipath searcher is used in a base station receiver including two or more sectors, if there is only one active sector on the reverse link in communication with the mobile station, the present invention searches the adjacent active non-active sector as well as the current active sector in a time division manner. Optimal search method for a DS-CDMA signal in which a pilot symbol and a control symbol are composed of time division. The method according to claim 3 or 4, When the multipath searcher is used in a base station receiver including two or more sectors, the pilot symbol and the control symbol are characterized by searching two active sectors in a TDM manner when there are two active sectors of the reverse link talking to the mobile station. Optimal Searching Method for DS-CDMA Signal Composed of Time Division. The method according to claim 3 or 4, And a third process of using the M non-coherent accumulator output values, and using the ratio of the mean of the selected path to the rest of the path, the multipath searcher calculates a signal-to-noise ratio for any path. Optimal search method for a DS-CDMA signal having a pilot symbol and a control symbol consisting of time division. The method of claim 8, The third process includes a first step of selecting L in order from the largest of the M non-coherent accumulator outputs; For any of the L paths selected through the first step Obtaining a ratio of an average of the non-coherent accumulator outputs for the paths and the non-coherent accumulator outputs for the M-L paths except the selected L paths as in the above equation; The ratio of the non-coherent accumulator output calculated in the second step is or And a third step of calculating the result by substituting the subfields into the subfields of the DS-CDMA signal.