KR20010025817A - Channel persumption apparatus of reverse direction link in the CDMA system - Google Patents

Abstract

PURPOSE: An apparatus for estimating channels in a reverse link of a CDMA(Code Division Multiple Access) system is provided to find out an amplitude and a phase of a channel in a state of a pilot signal not being transmitted, and to estimate the channel by using a maximum output correlation value only of an existing rake receiver, then to detect a synchronization by using estimated channel information. CONSTITUTION: Adders(S21,S22) add an I(In-phase) component(d_I(t)) and a Q(quadrature) component(d_Q(t) to a PN(Pseudo Noise) code of an I channel whose synchronization is adjusted with a transmission signal. Adders(S23,S24) add an output of the adder(S21) to a W¬1(t) and a W¬M(t). Adders(S25,S26) add an output of the adder(S22) to the W¬1(t) and the W¬M(t). Integral circuits(20-23) perform integral processes as many as 64 chips corresponding to one Walsh code period, from outputs of the adders(S23-S25). A maximum correlation value selector(24) selects a biggest value from 64 correlator outputs of the I channel from the integral circuits(20-23), and takes the value as a Z_ll¬k(m,l)''max. The selector(24) selects a biggest value from 64 correlator outputs of a Q channel, and takes the value as a Z_Ql¬k(m,l)''max. A channel estimator(25) estimates a size component and a phase component of a channel, by using the taken values.

Description

Channel persumption apparatus of reverse direction link in the CDMA system

The present invention relates to a CDMA system including an IS-95, and more particularly, to a channel estimating apparatus in a reverse link of a CDMA system that can easily find out the amplitude and phase of a channel in the absence of a pilot signal transmission.

In general, in wireless communication, a synchronous demodulator using information (phase and size information) of a channel on which a signal is transmitted has a performance improvement of 2-3 dB compared to an asynchronous demodulator that demodulates a signal without knowing the channel information.

However, in the reverse channel of the CDMA system which is the mainstream of mobile communication, the synchronous detection for channel information is impossible because the pilot signal is not transmitted due to power consumption.

Instead, asynchronous detection is used in the reverse channel, and 64-array orthogonality is currently applied in the reverse direction of IS-95 systems.

Here, the pilot signal is a signal promised at the transmitter and the receiver and is used when channel estimation or synchronization is performed in the system.

1 is a block diagram showing the configuration of a transmitting unit of a typical 64-array DS-CDMA system. An I-short code section 2 and a Q-short code section 3 for generating a PN code for spreading a band in a CDMA system, the output of the 64-array Walsh code sequence 1 and the I-short code section 2 And an adder (S1) (S2) for adding the output of the Q short code unit (3), a delay unit (4) for delaying the output of the adder (S2) for a predetermined time, and the output of the adder (S1) and cosωc ( A multiplier A1 for multiplying the output of t) and a multiplier A2 for multiplying the output delayed by the delay unit 4 and sinωc (t).

In the transmission unit of the conventional 64-array DS-CDMA system configured as described above, input data is grouped by 6 bits in the 64-array Walsh code sequence 1 to output corresponding Walsh codes.

The I-short code section 2 and the Q-short code section 3 generate a PN code for spreading the band in the CDMA system, and the output of the Q-short code section 3 is constant by the delay section 4. The delay unit 4 uses an offset quadrature phase shift keying (QPSK).

That is, six bits of information bit strings are grouped into symbols and mapped to one of 2 ⁶ orthogonal Walsh-Hadamard codes, and then each symbol is spread by the PN code.

Here, the transmission signal s _i (t) of the i-th user is expressed by Equation 1 below.

2 shows a configuration of a conventional rake receiver of an asynchronous detection method. The multiplier A3 multiplies the received signal {r (t)} and cosωc (t), the received signal {r (t)} and sinωc (t). A multiplier (A4) multiplying by, a low pass filter (LPF) 5 for filtering the output of the multiplier (A3), a low pass filter (LPF 6) for filtering the output of the multiplier (A4), and the LPF An adder S3 (S4) that adds the output of (5) and {a ^ i} _I (t) and {a ^ i} _Q (t), respectively, and the output of the LPF 6 and {a ^ i} _I (t), {a ^ i} _Q (t) adder (S5) (S6) and the output of the adder (S3) and W ^ 1 (t), W ^ M (t) An adder S7 (S8), an output of the adder S4, an adder S9 (S10) for adding W ^ 1 (t) and W ^ M (t), respectively, and an output of the adder S5, Adder (S11) (S12) that adds the outputs of W ^ 1 (t), W ^ M (t), the output of the adder (S6) and the outputs of W ^ 1 (t), W ^ M (t) To the adders S13 and S14, and to the outputs of the adders S7 to S14. An integrator circuit 7-14 that performs integration of 64 chips corresponding to a period of one Walsh code, an adder S15 that adds outputs of the integrator circuits 7 and 11, and the integrator circuit. (8) an adder (S16) for adding the outputs of (12), an adder (S17) for adding the outputs of the integrator circuits (9) and (13), and an adder for adding the outputs of the integrator circuits (10, 14) ( S18), a squarer 15-18 that takes the square of the integrated value to obtain energy from the adders S15-S18, and an adder S19 that adds the outputs of the squarers 15, 17, and And an adder (S20) for adding the outputs of the squarers (16) and (18), and a maximum value selector (19) for selecting the highest value from the outputs (S1-SM) of the adders (S19) and (S20). will be.

In this configuration, the base station uses a rake receiver for tracking the multipath component, Figure 2 shows the first branch of the rake receiver, the I channel low-pass component is represented by the following equation (2).

If it is assumed that the desired user is the k-th user, then tau_ {n_l} ^ k`` is the l-th multipath tracking component and tau_ {n_l} ^ k '' is correctly estimated by the synchronizer. You can define d_ {II} ^ {k, n_l} (t) '' as

d_ {II} ^ {k, n_l} ~ = ~ d_I (t) a_I ^ k (t-tau_ {n_l} ^ k)

Therefore, when Equation 2 is substituted into Equation 3, Equation 4 is obtained.

In FIG. 2, the output of the m th correlator of the l th receiver is defined as in Equation 5 below.

Where I_ {1, II} ^ {k, k} '' is the magnetic interference component due to the spread PN code of the Q channel, and I_ {2, II} ^ {k, k} '' is the receiver due to the multipath component. Is the magnetic interference component of the l-th branch of, and I_ {II} ^ {k, i} '' is the interference component by multiple users.

And N_ {II} ^ {k} '' are terms according to AWGN, and Z_IQ ^ k (m, l) ``, Z_QI ^ k (m, l) ``, Z_QQ ^ k (m, l ), And the output of the correlator gives the result as shown in Equation 6 below.

Where E _w is the symbol energy and E _W = PT _W. In the case of an equal gain combiner Rake receiver, the symbol decision variable of the k-th user is expressed by Equation 7 below.

Here, S_k (m, l) is as shown in Equation (8).

s_k (m, l) ~ = ~ [Z_ {II} ^ k (m, l) + Z_ {QQ} ^ k (m, l)] ^ 2 + [Z_ {IQ} ^ k (m, l)- Z_ {QI} ^ k (m, l)] ^ 2

The maximum ratio decision is applied to Equation 8 to determine the symbol at the receiving end. That is, selecting the maximum of the M correlator outputs has the best performance in the AWGN channel.

However, the multi-user environment is not AWGN, so it does not show optimal performance but is widely used due to its simplicity.

The present invention has been devised in response to this, and an object of the present invention is to provide a channel in a reverse link of a CDMA system for estimating a channel using only the maximum output correlation value of an existing rake receiver without adding a learning signal. The present invention provides an estimation apparatus.

According to the present invention as described above, by performing synchronous detection using estimated channel information, it is possible to improve performance and increase capacity of the system.

1 is a block diagram of a transmitter of a conventional 64-array DS-CDMA system.

2 is a block diagram of a conventional asynchronous detection method

3 is a block diagram of a channel estimating apparatus according to the present invention;

<Explanation of symbols for main parts of drawing>

S21-S26: Adder 20-23: Integrator Circuit

24: Maximum correlation value selector 25: Channel estimation

In order to achieve the above object, the present invention selects the largest value among the 64 correlator outputs of the I channel from the integrator circuit, takes Z_II ^ k (m, l) `` max, and selects the largest value among the 64 correlator outputs of the Q channel. Select a large value and have a maximum correlation value selection section taking Z_QI ^ k (m, l) `` max, and Z_II ^ k (m, l) `` max, Z_QI ^ k ( and a channel estimator for estimating a magnitude component and a phase component which are parameters of a channel using m, l) `` max.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a configuration diagram of the present invention, in which a low-pass in-phase component d_I (t) and an orthogonal component d_Q (t) of a received signal input to each branch of a rake receiver are synchronized with a transmission signal in phase channel Adder (S21) and adder (S22), respectively, and add the output of the adder (S21) and W ^ 1 (t), W ^ M (t) Adder (S23) (S24), the output of the adder (S22), adders (S25) (S26) to add W ^ 1 (t) and W ^ M (t), respectively, of the adders (S23-S25) An integrator circuit 20-23 that performs integration of 64 chips corresponding to a period of one Walsh code from the output and the largest value among 64 correlator outputs of I channels are selected from the integrator circuit 20-23. The maximum correlation value selector 24 taking Z_II ^ k (m, l) `` max and selecting the largest value among the 64 correlator outputs of the Q channel and taking Z_QI ^ k (m, l) `` max. And to the maximum correlation value selector 24. Consists of Z_II ^ k (m, l) `` max, Z_QI ^ k (m, l) `channel estimation unit 25 for estimating the channel parameter magnitude component and a phase component using the` max.

Referring to the operation of the present invention configured as described above is as follows.

First, d_I (t) and d_Q (t) are the low pass in-phase and quadrature components of the received signal input to each branch of the RAKE receiver. Is the coefficient estimate of the k-th user estimated at time t.

That is, the signal d_I (t), '' received through each path, is added to the PN code (a_I ^ k (t) ``) of the in-phase channel synchronized with the transmission signal and then correlated with 64 Walsh codes. In this case, the output of the correlator with the m th Walsh code is expressed by Equation 9 below.

In addition, multiplying the PN codes of the channels of the in-phase channel by d_Q (t), and correlating the M Walsh codes yields the output of the correlator with the m th Walsh code as shown in Equation 10 below. .

In Equations 9 and 10, the outputs of the correlators Z_II ^ k (m, l) `` and Z_QI ^ k (m, l) '' are m = j (that is, when the decision of the preceding symbol is a correct decision). ) The sum of the channel value and the interference signal to be estimated.

In general, since the probability of determining the correct symbol is large when the maximum value of the output values of the correlator is taken, the largest output value of the M correlator outputs is obtained, which can be selected as shown in Equations 11 and 12 below.

here, Omega_c and tau_ {n_l} are known values.

And I_ {II} ^ {k, k} (l) ``, I_ {II} ^ {k, i} (l) ``, N_ {II} ^ {k} (l) `` are all on average 0 Can be seen as a signal of a Gaussian distribution with Unbiased estimation based on

here, In addition to the information of the channel, since the influence of the additive noise is included, an adaptive method using the previous channel estimate can be used to eliminate the effect of the additive noise.

In addition, since the channel coefficient value to be estimated currently has a degree of correlation with the channel coefficient value of one symbol before, the accuracy of channel estimation can be improved by using the correlation.

That is, the value of the fading channel coefficient may be expressed as a "first-order Gauss-Markov process".

Using this relationship, we can estimate the channel as shown in Equation 13. First, multiply the previous channel estimate by beta, Multiply by (1-beta``).

Next, we add the two values to obtain an estimate of the channel coefficients, which are then removed from the effects of additive noise using the previous estimates.

here Is an estimate of the channel coefficient at time t of the k-th user, and beta `` is a forgetting factor.

And probability density functions of I_ {II} ^ {k, k} (l) ``, I_ {II} ^ {k, i} (l) ``, N_ {II} ^ {k} (l) `` Since are all Gaussian, the distribution of channel estimation error can be considered as Gaussian.

As described above, the present invention provides a channel estimator that finds the amplitude and phase of a channel in the absence of a pilot signal, and uses only the maximum output correlation value of an existing rake receiver without adding a learning signal. By estimating and using the estimated channel information for synchronous detection, the performance of the system can be improved and the capacity can be increased.

Claims (1)

The low-pass in-phase component d_I (t) and the orthogonal component d_Q (t) of the received signal input to each branch of the rake receiver are a_I ^ k (t) which is the PN code of the in-phase channel synchronized with the transmission signal. Adder (S21) and adder (S22), respectively, added to An adder (S23) (S24) for adding the output of the adder (S21) and W ^ 1 (t) and W ^ M (t), respectively; An adder (S25) (S26) for adding the output of the adder (S22) and W ^ 1 (t) and W ^ M (t), respectively, An integrator circuit 20-23 which performs integration of 64 chips corresponding to a period of one Walsh code from the outputs of the adders S23-S25; From the integrator circuit 20-23, select the largest value among the 64 correlator outputs of the I channel, take Z_II ^ k (m, l) `` max, and select the largest value among the 64 correlator outputs of the Q channel. The maximum correlation value selector 24, taking Z_QI ^ k (m, l) A channel for estimating a magnitude component and a phase component, which are parameters of a channel, using Z_II ^ k (m, l) `` max and Z_QI ^ k (m, l) `` max from the maximum correlation value selector 24. And an estimator (25). The apparatus for estimating a channel in a reverse link of a CD system.