WO2007074948A1

WO2007074948A1 - Apparatus for detecting frame preamble in wireless broadband system and method thereof

Info

Publication number: WO2007074948A1
Application number: PCT/KR2005/004521
Authority: WO
Inventors: Eun-Cheul Jeong; Ho-Joon You; Hyen-Bae Shin; Young-Sang Yoon; Chang-Rim Park; Seong-Choon Lee; Sang-Ho Yi; Yong-Joo Tcha
Original assignee: Kt Corporation; Ace Technology
Priority date: 2005-12-24
Filing date: 2005-12-24
Publication date: 2007-07-05

Abstract

Provided is an apparatus for detecting a frame preamble in a wireless broadband system and a method thereof . The apparatus includes a storage for storing a predetermined number of inputted samples; a correlation ratio operating unit for acquiring a correlation ratio of a first correlation value, which is obtained by reversely correlating a predetermined number of first samples and a predetermined number of last samples among samples stored in the storage, and a second correlation value, which is obtained by sequentially adding and autocorrelating a predetermined number of first samples and a predetermined number of last samples; and a preamble detecting unit for detecting a frame preamble as the correlation ratio acquired in the correlation ratio operating unit is located within a threshold section.

Description

APPARATUS FOR DETECTING FRAME PREAMBLE IN WIRELESS BROADBAND SYSTEM AND METHOD THEREOF

Description Technical Field

The present invention relates to an apparatus for detecting a frame preamble in a wireless broadband system and a method thereof; and, more particularly, to an apparatus for detecting a frame preamble in a wireless broadband system using a ratio of a first correlation value, which reversely correlates the predetermined number of first samples e.g., 256 samples among inputted samples, and another predetermined number of last samples, e.g., 256 samples among the inputted samples, and a second correlation value, which is obtained by sequentially summating and autocorrelating the predetermined number of first samples and the predetermined number of last samples among inputted samples, and a method thereof.

Background Art

As an example of a wireless broadband system in the present invention, a wireless broadband system based on an Orthogonal Frequency Division Modulation/Multiplexing

Access (OFDMA) /Time Division Duplex (TDD) methods will be described.

As personal mobility increases and diverse application services are introduced in addition that wired/wireless networks are connected to each other, demands for a service requiring a moving picture service, an Internet broadcasting service and a large-capacity database (DB) access technology increases. Therefore, a next-generation mobile communication system requires a high-quality, large-capacity and highspeed multimedia communication technology which can ultimately transmit/receive data at a transmission rate as high as hundreds of Mbps in bands ranging from 2 to 60 GHz, is efficiently adaptable to a time-varying wireless channel and can symmetrically or asymmetrically provide data according to traffic characteristics.

A wireless Internet service, which can be provided at a low price to anyone anytime and anywhere, attracts public attention as an initial model of the next- generation mobile communication. Since it takes a lot of costs to build a base station of a conventional mobile communication system, the service charge for using the wireless Internet is expensive. Also, since a terminal screen is small, there is a problem that contents are limitedly provided. Accordingly, there is a limit in providing of the very high-speed wireless Internet.

A wireless Local Area Network (LAN) technology using an Industrial Scientific and Medical (ISM) equipment band can be applied to a home LAN, but it has a limit in providing a public service due to electric wave interference and narrow coverage. Accordingly, it is required to develop a very high-speed mobile Internet system which has a cell larger than the wireless LAN system, supports medium or low-rate mobility and seamlessly provides a service.

A mobile Internet developed in response to the request is a service completed with merits of the wireless LAN and the mobile communication-based wireless Internet by being located in the middle of the wireless LAN and the mobile communication-based wireless Internet. The mobile Internet means a service which can acquire or apply diverse information and contents at a high transmission rate by accessing to the Internet in a medium or low-speed mobile state based on a portable wireless terminal anytime and anywhere.

It is expected that the mobile Internet stimulates formation of a new market except markets that the conventional wireless LAN and mobile communication form according to each service, or leading convergence of wired/wireless communication services in a future ubiquitous age.

In Korea, 2.3 GHz band used for a wireless local loop (WLL) will be used for the mobile Internet service. Accordingly, Telecommunications Technology Association (TTA) has progressed a work for standardizing a 2.3 GHz mobile Internet service.

Meanwhile, the concept of the mobile Internet service is to make it possible to transmit data at a high transmission rate by accessing to the wireless Internet anytime and anywhere in still and mobile states. A target of the mobile Internet service is supporting a transmission rate higher than 3Mbps for each subscriber both indoor and outdoor places. A research development tendency of a core technology is required in a system for providing the mobile Internet service as follows.

As for a duplex method, a Frequency Division Duplex (FDD) method requires a guard band ranging from 30MHz to 40MHz between an uplink band and a downlink band, whereas the Time Division Duplex (TDD) method requires a guard time for compensating the link budget decrease of 3dB and round trip latency between uplink (UL) and downlink (DL). According to the TDD method, since the uplink and the downlink use the same frequency, uplink and downlink channels are reversible. Accordingly, the TDD method can increase frequency use efficiency by efficiently introducing the concept of multiple input multiple output (MIMO) and a smart antenna. Also, there is a merit that the TDD method can be efficiently used in uplink and downlink asymmetric traffic according to the quantity for data required for packet communication.

As for modulating and coding methods, detailed technologies for adapting the modulating method such as Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (16QAM), and 64 Quadrature Amplitude Modulation (64QAM) are suggested as an Orthogonal Frequency Division Modulation (OFDM) method and a multi-code scheme (MCS) for each subcarrier forming an OFDM signal. Herein, the OFDM method is proper to broadband transmission for simplifying an equalizer by removing interference between neighboring symbols of the signal. It means an adaptive modulating method for adapting different modulating methods according to the channel circumstances. As for multiplexing access technology, Time Division Multiplexing Access (TDMA), Frequency Division Multiplexing Access (FDMA) and Orthogonal Frequency Division Multiplexing Access (OFDMA) adopting a frequency hopping method are comparatively researched, realized and tested. In the view of link budget and granularity, it is known that the OFDMA is more advantageous than the TDMA. A method adopting all of Space Division Multiplexing Access (SDMA), TDMA and FDMA in addition to a method for improving spectral efficiency based on a smart antenna is suggested. Also, a method for easily performing a cell planning according to the multiplexing access technology methods such as frequency hopping OFDMA and TDMA is researched and suggested.

To perform channel coding for reliable transmission of data, a coding method such as low density parity check (LDPC) and convolutional turbo code (CTC) and a hybrid Automatic Repeat Request (ARQ), which can improve performance of a system in combination of the modulating method and the coding method are researched and suggested. Also, when the high-speed Internet service is provided to a terminal moving at a high-speed, researchers are studying to develop a system for fast and exact mobile channel estimation and compensation in a physical layer, power control, and fast handoff in an upper layer.

In the respect of a service quality, a link budget improving method for supporting the transmission rate of the mobile Internet service in a hot spot region and outskirts of a downtown has been researched and suggested. Also, a method for supporting system throughput and Quality of Service (QoS) has been researched and suggested. The system throughput means the number of subscribers per cell which a system can simultaneously provide while supporting a Quality of Service designated in a multi-cell environment such as an IP-based wireless data service of diverse formats which are also provided in the wired Internet streaming video, file transfer protocol (FTP), mail, and chatting.

In the respect of a system technology, researchers are studying to provide a broadband packet data service at a price less expensive than the conventional cellular system. Considering that the broadband packet data service is an IP-based service, they are trying to develop a standard and a system that can reduce the cost for building base stations and a wireless network.

In the respect of supporting the mobile Internet service, the granular OFDMA based on a channel structure can efficiently and variably allocate wireless link resources of the OFDMA. The granular OFDMA quickly shifts the state of a terminal between a multiple states such as on, hold and sleep states, according to a QoS state. The granular OFDMA optimizes the system so that users do not collide with each other, provides fast ARQ and low latency to support interactive application services such as a game and VoIP. The granular OFDMA supports multiple scheduling which can easily perform fair constraint and QoS. Research on the media access control according to diverse multiplexing access channels except the OFDMA has been progressed. Also, researchers are studying a system additionally using a smart antenna (ANT) to improve high spectral efficiency, increase capacity and improve system capacity efficiency due to frequency reuse in a multiple input multiple output (MIMO) system and a neighboring cell. Meanwhile, in a wireless access system standard of Korean mobile Internet technology, a multiplexing method adopts the TDD method, has a 10MHz channel bandwidth and adopts the OFDMA method as a multiplexing access method. It necessarily requires a transmission rate per subscriber ranging from 128kbps to IMbps for uplink and a transmission rate ranging from 512kbps and to 3Mbps for downlink.

A frequency reuse factor is 1 and the maximum spectral efficiency is defined as 6bps/Hz/cell in downlink and 2bps/Hz/cell in uplink, respectively. Handoff is defined to be packet transmission cutoff time of 150ms and below, and the maximum mobile speed of 60km/h.

Also, the service coverage is defined 100m as a picocell, 400m as a micro cell, and lkm as a macro cell in a downtown region.

The TDD technology supports interactive transmission based on the same frequency band, which is different from the FDD technology using different frequency bands in uplink and downlink for interactive communication.

Theoretically, the TDD technology can support the same transmission rate by using smaller timeslots than that of the FDD technology and is proper to transmission of an asymmetric or bursty application by dynamic allocation of the timeslot. Also, the TDD technology can provide a service at 1/2 frequency and 1/2 price in comparison with the FDD technology. Accordingly, the TDD technology can be an attractive technology to communication service providers who plan to provide an inexpensive wireless Internet service.

Meanwhile, a preamble mapping method defined in Mobile Internet Standard inserts a preamble signal into even subcarriers among subcarriers, inserts a null signal into odd subcarriers, thereby performing Inverse Fast Fourier Transform (IFFT). As shown in Fig. 1, a pattern is repeated twice as a result.

Considering a conventional apparatus for detecting a frame preamble in a wireless broadband system with reference to Fig. 2, the conventional apparatus for detecting the frame preamble includes a storage 21, a correlation ratio operating unit 22, a signal/noise detecting unit 23, and a preamble detecting unit 24. The storage 21 stores the predetermined number of samples, e.g., 1024 samples, transmitted from a transmitting/receiving unit 20. The correlation ratio operating unit 22 operates a ratio of a first correlation value, which correlates the first 512 samples and the last 512 samples among 1024 samples from the storage 21, and a second correlation value autocorrelating last 512 samples. The signal/noise detecting unit 23 detects whether a sample operated in the correlation ratio operating unit 22 is a signal or noise. The preamble detecting unit 24 detects a preamble based on a correlation ratio operated in the correlation ratio operating unit 22 when it turns out that the operated sample is a signal.

A switch control unit 25 controls a switch 26 to synchronize frames according to the preamble detection signal from the preamble detecting unit 24. Also, the switch control unit 25 resets the frame preamble detecting apparatus in case that the switch control unit 25 does not receive the preamble detection signal from the preamble detecting unit 24 at a predetermined time interval. A method for detecting the frame preamble in the preamble detecting apparatus of the conventional mobile Internet system will be described with reference to Fig. 3. The samples, e.g., 1024 samples, are sequentially stored at step S301. The first correlation value is calculated by correlating the first 512 samples and the last 512 samples among 1024 samples based on Equation 1 below at step S302.

The second correlation value is calculated by autocorrelating the last 512 samples based on Equation 2 below at step S303.

A ratio of the first and second correlation values is calculated based on Equation 3 below at step S304.

The frame preamble is detected based on the calculated correlation ratio at step S305. A preamble detection result is as shown in Fig. 5. Herein, a horizontal part on a graph is created by cyclic prefix (CP) and an edge of the horizontal part is an ending point of the preamble.

511

P =∑R^*(n)-R(n+size_FFT/2)

«=o

30 Eq. 1

where n is a random integer and R(n) is a signal received in a random time n.

511

^{N =} Σ ^R* ( ^{n + size}FFτ / 2) ^• R ( n + size_FFT 12)

M = O

40 Eq . 2 Detect_value = P -P /N - N

Eq. 3

As shown in Fig. 4, there is a problem that the conventional apparatus for detecting the frame preamble in the wireless broadband system cannot normally detect the frame preamble even if there is a repeated pattern in case that a signal void transmission section is included between the uplink and downlink.

Also, since the conventional apparatus for detecting the frame preamble in the wireless broadband system detects the frame preamble based on many adders and multipliers as shown in Table 1 below, there is a problem that complexity increases.

Table 1

Disclosure

Technical Problem

It is, therefore, an object of the present invention to provide an apparatus for detecting a frame preamble in a wireless broadband system which can synchronize frames in a signal void transmission section by detecting the frame preamble based on a ratio of a first correlation value, which reversely correlates a predetermined number of first samples e.g., 256 samples among inputted samples, and a predetermined number of last samples, e.g., 256 samples among the inputted samples, and a second correlation value, which sequentially adds and autocorrelates the first samples and the last samples among inputted samples, and a method thereof.

Other objects and advantages of the invention will be understood by the following description and become more apparent from the embodiments in accordance with the present invention, which are set forth hereinafter. It will be also apparent that objects and advantages of the invention can be embodied easily by the means defined in claims and combinations thereof.

Technical Solution

In accordance with one aspect of the present invention, there is provided an apparatus for detecting a frame preamble in a wireless broadband system, including: a storage for storing a predetermined number of inputted samples; a correlation ratio operating unit for acquiring a correlation ratio of a first correlation value, which is obtained by reversely correlating a predetermined number of first samples and a predetermined number of last samples among samples stored in the storage, and a second correlation value, which is obtained by sequentially adding and autocorrelating a predetermined number of first samples and a predetermined number of last samples; and a preamble detecting unit for detecting a frame preamble as the correlation ratio acquired in the correlation ratio operating unit is located within a threshold section.

In accordance with another aspect of the present invention, there is provided a method for detecting a frame preamble in a preamble detecting apparatus of a wireless broadband system, including the steps of: a) sequentially storing a predetermined number of samples; b) calculating a first correlation value by reversely correlating a predetermined number of first samples and a predetermined number of last samples among the samples; c) sequentially adding the first samples and the last samples; d) calculating the second correlation value by autocorrelating the added samples; e) calculating a ratio of the first and second correlation values; and f) detecting a frame preamble as the calculated correlation ratio is located within a threshold section. Advantageous Effects

The present invention can synchronize frames in a signal void transmission section by detecting a frame preamble based on a ratio of a first correlation value, which reversely correlates the first 256 samples and the last 256 samples among inputted 1024 samples, and a second correlation value, which sequentially adds and autocorrelates the first 256 samples and the last 256 samples.

Also, since the present invention detects the frame preamble by using a small number of adders and multipliers, it is possible to detect the frame preamble at low complexity.

Description of Drawings

The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 shows an Inverse Fast Fourier Transform (IFFT) process result of a reception signal in a conventional wireless broadband system; Fig. 2 is a block diagram showing a conventional apparatus for detecting a frame preamble in the wireless broadband system;

Fig. 3 is a flowchart describing a frame preamble detecting method in the conventional apparatus for detecting the frame preamble in the wireless broadband system;

Fig. 4 shows a signal void transmission section existing between an uplink and a downlink in the conventional wireless broadband system; Fig. 5 is a graph illustrating a preamble detection result in the preamble detecting apparatus of the conventional wireless broadband system.

Fig. 6 shows a preamble symbol except cylic prefix (CP) which is applied to the present invention; Fig. 7 is a block diagram showing an apparatus for detecting a frame preamble in a wireless broadband system in accordance with an embodiment of the present invention;

Fig. 8 is a block diagram showing a correlation ratio operating unit of the frame preamble detecting apparatus in accordance with the embodiment of the present invention;

Fig. 9 shows a correlating procedure of a first correlater of the correlation ratio operating unit in accordance with an embodiment of the present invention;

Fig. 10 is a flowchart describing a method for detecting a frame preamble in the frame preamble detecting apparatus of the wireless broadband system in accordance with an embodiment of the present invention; and

Figs. 11 to 14 show output characteristics of the apparatus for detecting the frame preamble in the wireless broadband system accordance with an embodiment of the present invention.

Best Mode for the Invention

Other objects and advantages of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings. Therefore, those skilled in the field of this art of the present invention can embody the technological concept and scope of the invention easily. In addition, if it is considered that detailed description on a related art may obscure the points of the present invention, the detailed description will not be provided herein. The preferred embodiments of the present invention will be described in detail hereinafter with reference to the attached drawings .

5 Fig. 7 is a block diagram showing an apparatus for detecting a frame preamble in a wireless broadband system in accordance with an embodiment of the present invention.

As shown in Fig. 7, the frame preamble detecting apparatus according to the present invention includes a

10 storage 71, a correlation ratio operating unit 72, and a preamble detecting unit 73. The storage 71 stores a predetermined number of samples, e.g., 1024 samples, transmitted from a transmitting/receiving unit 70. The correlation ratio operating unit 72 operates a

15 correlation ratio of the first correlation value, which reversely correlates the first 256 samples and the last 256 samples among 1024 samples from the storage 71, and the second correlation value, which sequentially adds and autocorrelates the first 256 samples and the last 256

20 samples. The preamble detecting unit 73 detects the frame preamble as the correlation ratio operated in the correlation ratio operating unit 72 is located within a threshold section.

Herein, the threshold section X includes

„ _. 2* 1CT^B < X < 20 * lCf^s .

25 as an example.

Also, the switch control unit 74 controls a switch 75 to synchronize frames according to a preamble detection signal from the preamble detecting unit 73.

The switch control unit 74 resets the frame preamble

30 detecting apparatus in case that the switch control unit

74 does not receive the preamble detection signal from the preamble detecting unit 73 at a predetermined time interval .

As the correlation operation ratio from the 35 correlation ratio operating unit 72 is located within the threshold section, the preamble detecting unit 73 determines the 3^rd ratio among ratios within a threshold section where 6 ratios are generated in each frame as a start point of the preamble and determines the 6^th ratio as an end point of the preamble, thereby detecting the preamble .

Fig. 8 is a block diagram showing the correlation ratio operating unit of the frame preamble detecting apparatus in accordance with the embodiment of the present invention.

As shown in Fig. 8, the correlation ratio operating unit 72 of the frame preamble detecting apparatus includes a first correlater 81, an adder 82, a second correlater 83, and a correlation ratio operator 84. The first correlater 81 calculates a first correlation value by reversely correlating the first 256 samples and the last 256 samples among 1024 samples based on Equation 4. The adder 82 sequentially adds the first 256 samples and the last 256 samples based on Equation 5 below. The second correlater 83 calculates a second correlation value by autocorrelating 256 samples added in the adder 82 based on Equation 6 below. The correlation ratio operator 84 operates a ratio of the first correlation value and the second correlation value based on Equation 7 below.

Herein, the adder 82 prevents that Equation 6 becomes 0, which is a mathematical ^λ fault' in operating of the correlation ratio in Equation 7 below.

255

P = 2 ^R(n) * R(size_FFT - ^ή) ⁿ⁼¹ Eq . 4 size _FFT where the means 1024

k(i) =R(ι) +R(sizφ_FT/ 2+sizψ_FT/4+i) Eq . 5

Detect _value = power (P) / power (N)

= p-p*/N-N* Eq. 7

The complexity of the apparatus for detecting the frame preamble in the wireless broadband system according to the present invention is as shown in Table 2 below.

Table 2

A procedure that the first correlater 81 calculates a first correlation value by reversely correlating the first 256 samples and the last 512 samples among 1024 samples will be described in detail with reference to

Figs. 6 and 9.

As shown in Figs. 6 and 9, the first 512 samples among the inputted 1024 samples are repeated. Therefore, the first correlater 81 correlates a first inputted sample among the first 256 samples and a 256^th inputted sample c' among the last 256 samples. Also, the first correlater 81 correlates a 2^nd inputted sample b among the first 256 samples and a 255^th inputted sample b' among the last 256 samples.

The first correlation value is calculated by adding 256 result values correlated according to the above method.

Fig. 10 is a flowchart describing a method for detecting a frame preamble in the frame preamble detecting apparatus of the wireless broadband system in accordance with an embodiment of the present invention.

The predetermined number of samples, e.g., 1024 samples, is sequentially stored at step SlOOl. The first correlation value is calculated by reversely correlating the first 256 samples and the last 256 samples among 1024 samples at step S1002.

The first 256 samples and the last 256 samples are sequentially added at step S1003. The second correlation value is calculated by autocorrelating the added 256 samples at step S1004.

A ratio of the first and second correlation values is calculated at step S1005.

As the calculated correlation ratio is located within the threshold section, a frame preamble is detected at step S1006.

While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

What is claimed is:

1. An apparatus for detecting a frame preamble in a wireless broadband system, comprising: a storing means for storing a predetermined number of inputted samples; a correlation ratio operating means for acquiring a correlation ratio of a first correlation value, which is obtained by reversely correlating a predetermined number of first samples and a predetermined number of last samples among samples stored in the storing means, and a second correlation value, which is obtained by sequentially adding and autocorrelating a predetermined number of first samples and a predetermined number of last samples; and a preamble detecting means for detecting a frame preamble as the correlation ratio acquired in the correlation ratio operating means is located within a threshold section.

2. The apparatus as recited in claim 1, wherein the correlation ratio operating means includes: a first correlater for calculating and acquiring the first correlation value by reversely correlating the first samples and the last samples among the samples stored in the storing means; an adder for sequentially adding the first samples and the last samples; a second correlater for calculating and acquiring the second correlation value by autocorrelating the predetermined number of samples added in the adder; and a correlation ratio operator for acquiring the ratio of the first correlation value and the second correlation value .

3. The apparatus as recited in claim 1, wherein the preamble detecting means detects a preamble by determining a 3^rd ratio among ratios within a threshold section where 6 ratios are generated in each frame as a start point of the preamble and determining 6^th ratio as an end point of the preamble as a correlation operation ratio from the correlation ratio operating means is located within the threshold section.

4. The apparatus as recited in claim 1, wherein the storing means stores 1024 samples.

5. The apparatus as recited in claim 1, wherein the predetermined number of samples is 256.

6. A method for detecting a frame preamble in a preamble detecting apparatus of a wireless broadband system, comprising the steps of: a) sequentially storing a predetermined number of samples; b) calculating a first correlation value by reversely correlating a predetermined number of first samples and a predetermined number of last samples among the samples; c) sequentially adding the first samples and the last samples; d) calculating the second correlation value by autocorrelating the added samples; e) calculating a ratio of the first and second correlation values; and f) detecting a frame preamble as the calculated correlation ratio is located within a threshold section.

7. The method as recited in claim 6, wherein in the step f), a preamble is detected by determining a 3^rd ratio among ratios within a threshold section where 6 ratios are generated in each frame as a start point of the preamble and determining 6^th ratio as an end point of the preamble as a correlation operation ratio is located within the threshold section.

8. The method as recited in claim 6, wherein in the step a), 1024 samples are sequentially stored.

9. The method as recited in claim 6, wherein the predetermined number of samples is 256.