KR100391292B1 - A channel estimation apparatus and method in time division duplexing system - Google Patents

Abstract

The present invention relates to a channel estimating apparatus and a channel estimating method in a time division bidirectional communication system.

In a time division bidirectional communication system according to an aspect of the present invention, a channel estimation method includes a frame configured by a timeslot including a first data unit, a midamble, a second data unit, and a guard interval (GP). CLAIMS 1. A method of estimating a channel of a signal received from a frame of a time division bidirectional communication system, comprising: obtaining an average value of a fading average in the midamble and a rate of change for each chip from at least one chip of the midamble; And estimating a channel from the fading average value and the average value of the rate of change.

The present invention uses a channel estimation method from a chip unit, a symbol unit, and a timeslot, thereby minimizing an error in channel estimation in a time division bidirectional communication system, and random FM by channel estimation error generated by using a simple averaging technique. This reduces the phenomenon of floor error.

Description

CHANNEL ESTIMATION APPARATUS AND METHOD IN TIME DIVISION DUPLEXING SYSTEM

The present invention relates to a communication apparatus and a communication method, and more particularly, to a channel estimating apparatus and a channel estimating method capable of reducing data detection error in a mobile communication system employing a time division bidirectional communication method.

With the development of the communication environment, IMT-2000 (International Mobile Telecommunications-2000) communication system, a third generation communication system, has emerged. The IMT-2000 communication system is characterized by the realization of global roaming, the world's most common design, the provision of services compatible with fixed networks, the provision of high-quality voice services such as fixed networks, and the high-speed communication services. do.

In the wireless transmission technology of the IMT-2000 communication system, code division multiple access (CDMA) is a spread spectrum code that is much faster than an information signal, and then modulates the signal by spectrum modulation to spread all the terminals. It allows simultaneous access at the same frequency and identifies the terminal by the difference in spreading codes.

There are two types of CDMA duplex schemes, FDD (FDD) and TDD (TDD). The FDD communicates by separating the transmission channel and the reception channel using different frequencies when the terminal and the base station transmit and receive signals.

TDD is a communication method in which a terminal and a base station use the same frequency (Unpaired band) when transmitting and receiving a signal, but they are separated by different usage times. A communication system adopting such a communication method is called a TDD system. That is, one frequency channel is divided into time slots, and a certain number of slots are allocated to the forward link between the base station and the terminal, and the remaining slots are allocated to the reverse link between the terminal and the base station. It is a communication method that enables bidirectional communication through a channel. For example, if the frequency channel is divided into eight timeslots T1 to T8, the terminal transmits to the base station at odd-numbered times T1, T3, and T5, and the base station at even-numbered times T2, T4, and T6. Only transmits to the terminal, resulting in separate transmission and reception channels. Since the TDD communication method can effectively use frequency when the amount of information sent by the terminal and the information received by the terminal, such as the Internet, is asymmetric, it is highly likely to be used as a high-speed data communication method.

1 is a diagram illustrating a frame and time slot structure in a general CDMA TDD system.

As shown in FIG. 1, one frame has a time of 10 ms (milli second) in a TDD communication scheme, and one frame includes 15 time slots (TSs). One timeslot consists of a data portion 1 (1), a midamble 2, a data portion 2 (3), and a GP (Guard Period).

In the TDD communication scheme, a midamble 2 for cell division is located in the center of all timeslots, and the channel is estimated through the midamble.

In general, a method for estimating a channel in a signal demodulation stage is a simple averaging technique in which fading values for all midamble chips are estimated, summed, and averaged. In other words, the length of the midamble used for channel estimation in the TDD mode is 512 chips and 256 chips. The simplest method for calculating the channel estimation value used for signal detection is the fading value for all the chips in the midamble. It is a method to average by adding. This simple averaging technique takes the average value of the fading of the midamble portion unconditionally without considering the rate of change of the fading.

However, in the conventional simple averaging technique, an error is generated between a phase applied to data located on both sides of the midamble and a phase estimated by the center midamble in a fast fading environment, and a random FM phenomenon (signal-to-noise ratio) caused by the estimation error is generated. Bit error rate (BER) performance does not improve even if (S / N) is increased, and there is a problem that an error becomes larger when data is detected.

In order to solve such a problem, the technical problem to be achieved by the present invention is to provide a method for minimizing the error that occurs during channel estimation in a time division bidirectional communication system.

1 is a diagram illustrating a frame and time slot structure in a general CDMA TDD system.

2 illustrates a channel estimator in a TDD system according to an embodiment of the present invention.

3A and 3B are diagrams illustrating a structure and an estimating method for estimating a fading value in units of chips according to a first embodiment of the present invention.

4A and 4B are diagrams illustrating a structure and an estimating method of estimating a fading value in symbol units according to a second embodiment of the present invention.

5A and 5B illustrate a structure and an estimation method for estimating a channel by combining an averaging technique and a fading estimation technique according to a third embodiment of the present invention.

6A and 6B are diagrams illustrating a structure and an estimation method for estimating a channel through linear interpolation using two or more consecutive time slots according to a fourth embodiment of the present invention.

Channel estimation method in a time division bidirectional communication system according to an aspect of the present invention for achieving the above object,

A method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP),

Obtaining an average value of the rate of change for each chip from the average value of fading in the midamble and at least one chip of the midamble;

Estimating a channel from the fading average value and the average value of the rate of change

It includes.

A channel estimation method in a time division bidirectional communication system according to another aspect of the present invention,

A method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP),

Calculating an average value for each chip from the number of chips in symbol units for at least two portions of the midamble; And

Calculating a rate of change of fading from the average value, and then estimating a channel from the calculated rate of change

It includes.

Channel estimation method in a time division bidirectional communication system according to another aspect of the present invention,

A method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP),

Detecting symbols of the first and second data units from channel estimates estimated by a simple averaging technique;

Estimating a channel by calculating a rate of fading from the detected symbols

It includes.

Channel estimation method in a time division bidirectional communication system according to another aspect of the present invention,

A method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP),

Calculating a fading change rate for at least two consecutive timeslots from the fading values obtained by the simple averaging technique;

Estimating a channel by predicting a fading value for the continuous timeslot from the calculated fading rate of change

It includes.

Channel estimation apparatus in a time division bidirectional communication system according to another aspect of the present invention,

If the carrier frequency is loaded after the modulation of the baseband midamble code and the complex signal of the communication signal is added and transmitted from the midamble modulation section, the time slot including the first data section, the midamble, the second data section, and the guard interval is included. A channel estimating apparatus for estimating a channel of a received signal based on one or more frames formed by

An arithmetic unit that calculates an average value of the in-phase and quadrature codes of the original signal received from the midamble modulator by the number of midamble chips or the length of the midamble from a midamble sequence; And

A channel estimation calculator for calculating an estimated value of a channel through one time slot or two consecutive time slots from an output value output from the calculator

It includes.

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

2 illustrates a channel estimator in a TDD system according to an embodiment of the present invention.

As shown in FIG. 2, a channel estimator in a TDD system according to an embodiment of the present invention is a quadrature pulse shift keying (QPSK) of a baseband midamble code from a midamble modulator (not shown). After the modulation, the carrier frequency is loaded and the complex part of the real part and the imaging part is added and transmitted, and the received RF signal r _I (t) is received to receive a sine wave ( a conversion unit 100 for converting the in-phase and quadrature baseband signals by cos (ω _c t)) and sin (ω _c t)); A matched filter (H * (f), 200) for filtering the signal converted by the converter 100; From the signal filtered through the matched filter 200, the signal sampled by the sampling period (mT _c ) of each chip unit is divided into mid-amble sequences for the I (in-phase) and Q (quad-phase) codes of the original signal. , Multiplication unit 300 to multiply); The midamble sequence by the multiplier 300 , An adder 400 which adds a signal by the number of all midamble chips from the signal multiplied by; An accumulator 500 which obtains an average value by dividing the signal by the adder 400 by the number of midamble chips (N or the length of the midamble); And a channel estimation calculator 600 for calculating an estimated value of the channel through one time slot or two consecutive time slots from the output values f _I and f _Q output from the accumulator 500.

The accumulator 500 obtains an average value by dividing the sum of the number of chips of the midamble by the product of the square root of the energy per chip Ec of all the midamble chips.

The channel estimation calculator 600 performs a complex operation on each chip ( , ) For calculating an estimated value _(I f, _Q f) through, the estimated value (thereby linear (change a channel estimation value by linear) with respect to at least one time slot from the _I f, _Q f).

Each functional unit of the channel estimator according to an embodiment of the present invention may be a program or a device that stores each function independently. In addition, the channel estimator according to the embodiment of the present invention describes the midamble length N of 512 chips, but the present invention is not limited to the embodiment.

Hereinafter, a channel estimation method according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3A and 3B are diagrams illustrating a structure and an estimating method for estimating a fading value in units of chips according to a first embodiment of the present invention.

As shown in FIG. 3A, in the structure of estimating a channel in a chip unit from the midamble, the midamble is located at the center and the data portions are located at both sides. In the description of the embodiment of the present invention, description of the GP (Guard Period) is omitted.

In general, fading depends on the speed of the terminal (or mobile station) but does not change much in one slot. Also, fading changes with very small differences when viewed at one chip intervals. Therefore, assuming that fading changes almost linearly in one slot, the fading in one slot can be estimated for all chips if the mean of the fading in the midamble and the rate of change between chips are known.

First, as shown in FIG. 3B, the accumulator 500 calculates a fading average in the midamble using a simple averaging technique (S100). Next, an average of fading change rates is obtained through each chip of the midamble (S110). Under the assumption that the fading changes linearly, the fading average of the midamble can be referred to as a reception value of a chip located in the center of the midamble, so that the channel estimation calculator 600 calculates an estimate of fading as shown in Equation 1 below. Can be.

i: number of chips in data part, d: total number of chips in data part 1

Lm is the length of the midamble,

Δ: average rate of change of fading for the calculated midamble or timeslot

s: number of symbol in data part

μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (cross-phase)

f: estimate for chip

The channel estimation method according to the first embodiment of the present invention is a channel estimation method that can be applied under the assumption that fading changes linearly in a timeslot. Therefore, when the speed is slower at 3 km / h, i.e., when fading changes almost linearly in the timeslot, performance-enhanced channel estimation can be performed. Even in the case of 30 km / h and 60 km / h, improved channel estimation can be performed.

By the way, the method of estimating the channel by calculating the rate of change of the fading value in units of chips according to the first embodiment of the present invention can perform the channel estimation with improved performance when white noise is not added. If white noise is considered, the accuracy of the transmission chip is low because the energy of the transmitting chip is small.

In order to secure such a problem, in the second embodiment of the present invention, the average value for a plurality of chips may be calculated in symbol units, and the accuracy of fading may be obtained by calculating the fading change rate using the calculated average value.

4A and 4B are diagrams illustrating a structure and an estimating method of estimating a fading value in symbol units according to a second embodiment of the present invention.

As shown in FIG. 4A, the structure of estimating the symbol unit fading value according to the second embodiment of the present invention is the same as the channel estimation structure of the first embodiment, and a description of overlapping portions will be omitted.

As shown in FIG. 4B, first, the adder 400 adds the start part and the end part of the reception midamble by the number of chips per symbol (S200). Next, the accumulator 600 calculates an average value for each chip (S210). When the average value is calculated, the rate of change of fading is calculated from the calculated average value (S220).

The channel estimation calculator 600 predicts a fading value for all symbols of the data unit 1 and the data unit 2 from Equation 2 from the rate of change of the fading (S230).

i: number of chips in data part, k: total number of symbols in data part 1

Lm is the length of the midamble,

Δ: average rate of change of fading for the calculated midamble or timeslot

s; Symbol number in data part

μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (cross-phase)

f: estimate of symbol

In the embodiment of the present invention, the channel was estimated by obtaining the average of the fading values for the three symbols and the last three symbols of the midamble from the beginning of the midamble, but the channel estimation for the symbol is limited to the embodiment of the present invention. It doesn't happen.

5A and 5B illustrate a structure and an estimation method for estimating a channel by combining an averaging technique and a fading estimation technique according to a third embodiment of the present invention.

As shown in FIG. 5A, the structure of estimating the channel by combining the averaging technique and the fading estimation technique according to the third embodiment of the present invention is the same as that of the channel estimation structures of the first and second embodiments, and overlaps thereafter. Description of the description is omitted.

As shown in FIG. 5B, the channel estimation calculator 600 roughly calculates an estimated value of the channel using a simple averaging technique (S300). The symbols of the data units 1 and 2 are detected using the calculated channel estimate (S310). At this time, instead of restoring all the data, only the first data of the data unit 1 and the last data of the data unit 2 are detected. Next, the fading value is estimated using the detected symbol (S320).

Using the calculated fading values of the first symbol of the data unit 1 and the last symbol of the data unit 2, the channel estimation calculator 600 calculates a fading change rate for one time slot length (S330).

The channel estimation calculator 600 predicts fading values for all symbols of the data unit as shown in Equation 3 by using an interpolation technique according to the calculated fading change rate (S340).

i: number of chips in data part, k: total number of symbols in data part 1

Lm is the length of the midamble,

Δ: average rate of change of fading for the calculated midamble or timeslot

s; Symbol number in data part

μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (cross-phase)

f: estimated value

6A and 6B are diagrams illustrating a structure and an estimation method for estimating a channel through linear interpolation using two or more consecutive time slots according to a fourth embodiment of the present invention.

As shown in FIG. 5, a channel estimating scheme using a linear interpolation technique using two consecutive time slots according to the fourth embodiment of the present invention is performed when two or more time slots are continuously allocated to the uplink. In addition, it is a structure for estimating a channel by looking at a channel change for two or more timeslots. This embodiment is also the same as the channel estimation structure in the first to third embodiments of the present invention, and the description of the same parts will be omitted below.

First, the accumulation unit 500 calculates an approximate value of a fading value for all chips of the midamble of each timeslot by a simple averaging technique (S400). At this time, the approximate value is calculated for both timeslots.

The channel estimation calculator 600 calculates a rate of change of fading for two timeslots using the calculated two values (S410).

The channel estimation calculator 600 predicts fading values for all symbols of the first timeslot and the second timeslot data units 1 and 2 from the equations 4a and 4b by using an interpolation technique to the calculated rate of change of fading ( S420).

First timeslot

Second timeslot

i: number of chips in data part, k: total number of symbols in data part 1

Lm is the length of the midamble,

Δ: average rate of change of fading for the calculated midamble or timeslot

s; Symbol number in data part

μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (cross-phase)

f: estimated value

Of course, the present invention is not limited to the embodiment as many modifications and variations are possible in the formula for obtaining the estimated value of the channel within the scope of the present invention without departing from the gist of the present invention.

As described above, the channel estimating apparatus and the channel estimating method in the time division bidirectional communication system of the present invention use the channel estimation method from the chip unit, the symbol unit, and the timeslot, thereby causing errors in channel estimation in the time division bidirectional communication system. By minimizing and minimizing the random FM phenomenon caused by the channel estimation error, the floor phenomenon of the error can be reduced.

Claims (13)

In the method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP), Obtaining an average value of the rate of change for each chip from the average value of fading in the midamble and at least one chip of the midamble; Estimating a channel from the fading average value and the average value of the rate of change Channel estimation method in a time division bidirectional communication system comprising a. The method of claim 1, wherein the channel estimating step , , (f: estimated value for chip, i: number of chips in data part, d: total number of chips in data part 1, Lm: length of midamble, Δ: average rate of change of fading relative to calculated midamble or timeslot) , s: symbol number in the data portion, μ: average division of fading for the entire midamble with respect to I (in-phase) and Q (cross-phase) Channel estimation method in the system. In the method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP), Calculating an average value for each chip from the number of chips in symbol units for at least two portions of the midamble; And Calculating a rate of change of fading from the average value, and then estimating a channel from the calculated rate of change Channel estimation method in a time division bidirectional communication system comprising a. 4. The method of claim 3, wherein the channel estimating step , , (f: estimated value for symbols, i: number of chips in data portion, k: total number of symbols in data portion 1, Lm: length of midamble, Δ: average rate of fading relative to calculated midamble or timeslot s; time division, characterized by calculating the rate of change of fading through the formula of the number of symbols in the data portion, μ: the average value of fading for the entire midamble with respect to I (in-phase) and Q (quad-phase) Channel Estimation Method in Bidirectional Communication Systems. In the method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP), Detecting symbols of the first and second data units from channel estimates estimated by a simple averaging technique; Estimating a channel by calculating a rate of fading from the detected symbols Channel estimation method in a time division bidirectional communication system comprising a. The method of claim 5, wherein the symbol detection step is And detecting symbols for the first data of the first data part and the last data of the second data part. 6. The method of claim 5, wherein the channel estimating step Fading values for all symbols of the first and second data units are determined through an interpolation technique according to the calculated fading change rate. , , (f: estimated value, i: number of chips in data portion, k: total number of symbols in data portion 1, Lm: length of midamble, Δ: average change rate of fading relative to calculated midamble or timeslot, s; Channel estimation in a time division bidirectional communication system, characterized by predicting the number of symbols in the data portion, μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (ortho-phase). Way. In the method of estimating a channel of a signal received from a frame of a time division bidirectional communication system in which one frame is constituted by a timeslot including a first data portion, a midamble, a second data portion, and a guard interval (GP), Calculating a fading change rate for at least two consecutive timeslots from the fading values obtained by the simple averaging technique; Estimating a channel by predicting a fading value for the continuous timeslot from the calculated fading rate of change Channel estimation method in a time division bidirectional communication system comprising a. In claim 8, The nth time slot (n is an integer) of the consecutive timeslots is , , (f: estimated value for symbols, i: number of chips in data portion, k: total number of symbols in data portion 1, Lm: length of midamble, Δ: average rate of fading with respect to the calculated midamble or timeslot) s; time division bidirectional communication, characterized in that the rate of fading change is calculated from a formula of the number of symbols in the data portion, μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (ortho-phase). Channel estimation method in the system. In claim 8, The n + 1 th time slot (n is an integer) of the consecutive timeslots , , (f: estimated value, i: number of chips in the data portion, k: total number of symbols in data portion 1, Lm: length of midamble, Δ: average rate of fading relative to the calculated midamble or timeslot, s; A time division bidirectional communication system, characterized in that the rate of change of fading is calculated by a formula of a symbol number in the data portion, μ: average value of fading for the entire midamble with respect to I (in-phase) and Q (ortho-phase). Channel estimation method in. 9. The method of claim 8, wherein the channel estimating step And estimating a fading value of all symbols of the data unit of the n th time slot and the n + 1 th time slot using an interpolation technique using the calculated fading change rate. If the carrier frequency is loaded after the modulation of the baseband midamble code and the complex signal of the communication signal is added and transmitted from the midamble modulation section, the time slot including the first data section, the midamble, the second data section, and the guard interval is included. In the channel estimating apparatus for estimating the channel of the received signal based on one or more frames formed by, An arithmetic unit that calculates an average value of the in-phase and quadrature codes of the original signal received from the midamble modulator by the number of midamble chips or the length of the midamble from a midamble sequence; And A channel estimation calculator for calculating an estimated value of a channel through one time slot or two consecutive time slots from an output value output from the calculator Channel estimation apparatus in a time division bidirectional communication system comprising a. The method of claim 12, wherein the operation unit A converter which receives the RF signal transmitted from the midamble modulator and converts the RF signal into a baseband signal in phase and quadrature by a sine wave; A matched filtering unit for filtering the signal converted by the conversion unit; A multiplier for multiplying the signal sampled by the sampling period of every chip from the signal filtered by the filtering unit with a midamble sequence for each in-phase and quadrature code of the original signal; An adder for adding signals from the signal multiplied by the multiambler to the number of all midamble chips; An accumulator for dividing the signal added by the adder by the number of midamble chips or the length of the midamble and obtaining an average value. Channel estimation apparatus in a time division bidirectional communication system comprising a.