KR20050051746A - Ofdm symbol differential demodulation apparatus and method for digital audio broadcasting receiver - Google Patents

Abstract

The present invention relates to an OFDM symbol demodulation apparatus and method for use in a digital audio broadcasting (DAB) receiver. OFDM symbol demodulation in a digital audio broadcasting (DAB) receiver is achieved by the product, sum, and difference of the current and previous symbols of each of the I and Q symbols. In OFDM symbol demodulation, the maximum number of carriers in one symbol is 1,536, and in case of Mode-I having the maximum number of carriers, the required symbol (Z _k ) and the previous symbol (Z _k- ) are required for differential demodulation. ₁₎ by a shift operation of the 1,536 symbols are needed to obtain the number of carrier. The present invention performs a symbol shift operation using a pointer counter that controls the read / write of the OFDM symbol memory and the OFDM symbol memory. Therefore, the OFDM demodulation device can be implemented in a simple structure to reduce the chip size when implementing the ASIC, and it is possible to easily implement a digital audio broadcasting (DAB) receiver suitable for a mobile receiver by reducing power consumption.

Description

OFDM symbol differential demodulation apparatus and method for digital audio broadcasting receiver

The present invention relates to a digital audio broadcasting (DAB) receiver, and more particularly, to a differential demodulation apparatus and method for recovering OFDM symbols transmitted through a channel in an orthogonal frequency division multiplexing (OFDM) receiver It is about.

In general, a differential bit demodulation method is used in a digital audio broadcasting (DAB) system. In the differential demodulation method, a previous symbol value is calculated to calculate a differential demodulation equation between a current OFDM symbol and a previous symbol as shown in Equations 1 and 2 below. Shift register array) was used. That is, the conventional differential demodulation device is composed of a shift register array and a differential decoder of each of an I-channel and a Q-channel for delaying one symbol (Z ⁻¹ ).

However, in the differential demodulation method applied to a digital audio broadcasting (DAB) receiver, since the maximum number of carriers of one OFDM symbol is 1,536, a shift operation of 1,536 is required for a delay Z ⁻¹ of one symbol. Therefore, in order to implement this in hardware, a shift register array is required. When the ASIC is implemented using a plurality of registers, the chip area is increased and power consumption is increased.

Iout (k-1) = I (Z _k ) * I (Z _k-1 ) + Q (Z _k ) * Q (Z _k-1 )

Qout (k-1) = Q ( _k ) * I (Z _k-1 )-I (Z _k ) * Q (Z _k-1 )

Where k is an integer between 0 < k < 1537 when in the DAB maximum symbol transmission mode-I.

Accordingly, the present invention provides a digital audio broadcast receiver capable of solving the above-mentioned shortcomings by obtaining a previous symbol value necessary for differential demodulation through a symbol shift operation using an OFDM symbol memory and a pointer counter that controls the read / write of the OFDM symbol memory. An object of the present invention is to provide an OFDM symbol differential demodulation device and method.

An OFDM symbol differential demodulation device of a digital audio broadcasting receiver according to the present invention for achieving the above object is a read pointer counter and a write pointer counter initialized by a synchronization signal in an enabled state and countered by a valid signal in an enabled state. And first and second sequentially storing symbol data according to the write address outputted from the write pointer counter and delayed by one clock, or sequentially outputting the stored symbol data according to the read address outputted from the read pointer counter. And a differential demodulation calculation unit configured to receive a symbol memory and currently input symbol data and previous symbol data stored in the first and second symbol memories, and output a demodulated signal through a predetermined operation.

In addition, the OFDM symbol differential demodulation method of the digital audio broadcasting receiver according to the present invention for achieving the above object comprises the steps of initializing the read pointer counter and the write pointer counter when the synchronization signal is enabled, Incrementing the read pointer counter and the write pointer counter one by one when input to the enabled state, storing valid symbol data in a symbol memory according to the write address outputted from the write pointer counter and delayed by one clock, and reading And receiving a differential demodulation operation by receiving previous symbol data stored in the symbol memory and currently input symbol data according to a read address output from a pointer counter.

The synchronization signal has a predetermined period, and the valid signal has a period of one symbol unit.

The write address output from the write pointer counter is delayed by one clock through the delay register.

The symbol data of different channels are stored in the first and second symbol memories, respectively.

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

1 is a block diagram of a digital audio broadcasting receiver to which the present invention is applied.

The fast Fourier transform block (FFT) 100 demodulates a multi-carrier modulated OFDM symbol transmitted through a transmitter primarily into I-channel and Q-channel signals, respectively, and performs OFDM symbol differential demodulation according to the present invention. The apparatus 200 differentially demodulates the first demodulated signal. The frequency deinterleaver 300 deinterleaves the differential demodulated signal from the OFDM symbol differential demodulation apparatus 200 to the QPSK demapper 400, and the QPSK demapper 400 and the differential demodulated I-channel signal Q. -Combine the channel signals and restore the original signal.

FIG. 2 is a block diagram for explaining in detail the configuration and operation of the OFDM symbol differential demodulation apparatus 200 according to the present invention, and will be described with reference to FIGS. 3 to 5.

When a multicarrier modulated I-channel signal I in and a Q-channel signal Q in from the high frequency (RF) transmitter are input to the fast Fourier transform block (FFT) 100 of the digital audio broadcast receiver, the fast Fourier A conversion block (FFT) 100 first demodulates the signal to produce an FFT_I symbol signal and an FFT_Q symbol signal. In this case, the 2,048-point fast Fourier transform block (FFT) 100 and the FFT valid signal (FFT_Valid) to transmit only 1,536 valid symbol data required for transmission mode-I (transmission mode having the maximum number of carriers) of digital audio broadcasting. The OFDM symbol synchronization signal (Symb_sync), which is a synchronization signal having one OFDM symbol period, is simultaneously output.

The OFDM symbol synchronization signal (Symb_sync) and the FFT valid signal (FFT_Valid) are respectively input to the read pointer counter 210 and the write pointer counter 220 of the OFDM symbol differential demodulation device 200 according to the present invention. The FFT_I symbol signal is input to an I-channel 2536 × 8 OFDM symbol memory 230 and a differential demodulation calculator 250, and the FFT_Q symbol signal is a Q-channel 2536 × 8 OFDM symbol memory 240 and a differential demodulation. It is input to the calculator 250. For example, when 2,048 FFT_I data and FFT_Q data having 8 bits of FFT are output, the FFT_I data is input to the I-channel 2536 × 8 OFDM symbol memory 230 and the differential demodulation calculation unit 250, and the FFT_Q Data is input to the Q-channel 2536x8 OFDM symbol memory 240 and the differential demodulation calculator 250. Actually valid data among the data is 1,536 each of I and Q.

When the OFDM symbol synchronization signal (Symb_sync) is enabled (Enable), the read pointer counter 210 and the write pointer counter 220 is reset to the read address (Raddress) of the symbol memory (230 and 240) The write address W address is initialized to an arbitrary value (eg, 0x0000 address).

Referring to FIG. 3, the FFT_I symbol signal and the FFT_Q symbol signal are valid only when the FFT valid signal FFT_Valid is valid. Therefore, only when the FFT valid signal FFT_Valid is enabled, the read pointer counter 210 and the write pointer counter 220 increment by one according to the system clock, and thus the read pointer counter 210 The write pointer counter 220 sends an address to the write address terminals Waddress and the read address terminals Raddress of the symbol memories 230 and 240, and transmits the FFT_I symbol data and the FFT_Q symbol data to the symbol memories 230 and 240. FIG. Or read the stored data from the symbol memories 230 and 240. The FFT valid signal FFT_Valid is disabled when the addresses of the read pointer counter 210 and the write pointer counter 220 reach the last address (for example, 0 × 5FF (1,535)). The read pointer counter 210 and the write pointer counter 220 no longer increase.

At this time, since the same addresses of the symbol memories 230 and 240 cannot be accessed at the same time, the write address output from the write pointer counter 220 is delayed by one clock, and then the Send to the write address port (Waddress). Thus, the write address is delayed by one clock using the simple 11-bit delay register 221 as shown in FIG. 4, and data is stored in the symbol memories 230 and 240 according to the write address delayed by one clock.

Since the FFT valid signal FFT_Valid has a period of one symbol unit, a symbol memory Z _k is stored in the symbol memories 230 and 240, and only after the FFT valid signal FFT_Valid is enabled. Read the previous symbol value (Z _k-1 ) stored at (230 and 240). The previous symbol value Z _k-1 stored in the memories 230 and 240 is sequentially output when the read / write signal R / W is enabled.

The differential demodulation calculator 250 needs a current OFDM symbol value Z _k and a previous OFDM symbol value Z _{k-1 in} order to perform differential demodulation. Therefore, the differential demodulation calculator 250 receives FFT_I data and FFT_Q data from the fast Fourier transform block (FFT) 100 and stores previous symbol values Z _k-1 stored in the symbol memories 230 and 240. Read A differential demodulation operation is performed as shown in Equations 1 and 2 to finally output the demodulated signals I out and Q out. In this case, the differential demodulation calculation unit 250 includes a multiplier, an adder, and a subtractor for operations such as Equations 1 and 2 above.

The number of carriers per symbol according to the digital audio broadcasting (DAB) mode is as follows.

Mode-I: 1,536

Mode-II: 384

Mode-III: 192

Mode-IV: 768

Since the periods of the FFT data and the FFT valid signal FFT_Valid change according to each mode, the values of the read pointer counter 210 and the write pointer counter 220 are automatically increased according to the FFT valid signal FFT_Valid. Therefore, a separate memory control device according to the digital audio broadcasting (DAB) mode value is not required, and each 1,535, 384,192 and 768 delayed carrier values (Z _k-1 ) for differential demodulation according to each mode value are not required. Can be found using shift operation. By reading the previous symbol value stored in memory after one symbol period, the same result can be obtained as in the conventional method of obtaining the previous symbol value using the shift register array.

In the digital audio broadcasting system, the maximum number of carriers per symbol according to the mode during OFDM symbol demodulation is 1,536, and in case of Mode-I having the maximum number of symbol carriers, one symbol (Z _l ) and the previous symbol (for differential demodulation) are required. In order to obtain Z _l-1 ), shift operations of 1,536 carriers must be performed. The shift operation requires an array of 1,536 shift registers. Using multiple registers makes hardware difficult due to excessive power consumption and size problems. Therefore, the present invention implements an OFDM demodulator with a simple structure by processing a symbol shift operation using an OFDM symbol memory and a read / write (R / W) controller to reduce the chip size in an ASIC implementation and to reduce the power consumption. A digital audio broadcasting (DAB) receiver suitable for the receiver can be easily implemented.

1 is a block diagram for explaining a digital audio broadcasting (DAB) receiver to which the present invention is applied.

2 is a block diagram illustrating an OFDM symbol differential demodulation device according to the present invention.

3 is a timing diagram for explaining the operation of the Fourier fast conversion block (FFT) shown in FIG.

FIG. 4 is a block diagram illustrating the operation of a symbol memory, a read pointer counter, and a write pointer counter shown in FIG. 2; FIG.

5 is a timing diagram for explaining the operation of an OFDM symbol differential demodulation device according to the present invention;

<Explanation of symbols for the main parts of the drawings>

100: Fast Fourier Transform (FFT) Block

200: differential demodulation device

210: read pointer counter

220: write pointer counter

221: delay register

230 and 240: symbol memory

250: differential demodulation calculation unit

300: frequency deinterleaver

400: demapper

Claims (8)

A read pointer counter and a write pointer counter initialized by the enable signal in the enabled state and countered by the valid signal in the enabled state, First and second symbol memories sequentially storing symbol data according to a write address output from the write pointer counter and delayed by one clock, or sequentially outputting the stored symbol data according to a read address output from the read pointer counter Wow, And a differential demodulation calculator for receiving current symbol data and previous symbol data stored in the first and second symbol memories, respectively, and outputting a demodulated signal through a predetermined operation. Symbol differential demodulation device. The apparatus of claim 1, wherein the synchronization signal has a predetermined period and the valid signal has a period of one symbol unit. The OFDM symbol differential demodulation device of claim 1, wherein the write address output from the write pointer counter is delayed by one clock through a delay register. The OFDM symbol differential demodulation device of claim 1, wherein the symbol data of different channels are stored in the first and second symbol memories, respectively. The OFDM symbol differential demodulation device of claim 1, wherein the differential demodulation calculation unit comprises a multiplier, an adder, and a subtractor for the differential demodulation operation. Initializing the read pointer counter and the write pointer counter when the synchronization signal is enabled; Incrementing the read pointer counter and the write pointer counter by one when a valid signal is input in an enabled state; Storing valid symbol data in a symbol memory according to a write address output from the write pointer counter and delayed by one clock; And performing a differential demodulation operation by receiving previous symbol data stored in the symbol memory and currently input symbol data according to a read address output from the read pointer counter. Differential demodulation method. 7. The method of claim 6, wherein the synchronization signal has a predetermined period and the valid signal has a period of one symbol unit. 7. The method of claim 6, wherein the differential demodulation operation is performed by Equations 3 and 4 below. Iout (k-1) = I (Z _k ) * I (Z _k-1 ) + Q (Z _k ) * Q (Z _k-1 ) Qout (k-1) = Q ( _k ) * I (Z _k-1 )-I (Z _k ) * Q (Z _k-1 ) Where k is an integer between 0 < k < 1537 when in the DAB maximum symbol transmission mode-I.