KR20050049140A - Method for embodying uplink fram of wireless communication system based on ofdma - Google Patents

Abstract

The present invention relates to a method for constructing an uplink frame in a wireless communication system using Orthogonal Frequency Division Multiple Access (OFDMA). The uplink frame configuration method divides the entire band of an uplink frame into a specific number of subcarrier groups, and then divides each subcarrier in the subchannels defined for a specific number of consecutive symbols defined as slots in the uplink frame. Allocates subcarriers within a group. Next, a pilot subcarrier is allocated in units of the predetermined number of symbols to enable channel estimation among the allocated subcarriers. According to the present invention, in order to enable channel estimation using a preamble and channel estimation in a cellular system, data subcarriers are allocated by minimizing collision with a specific user of a neighboring cell, and assigning a portion of data subcarriers to a pilot. By assigning, synchronous demodulation is enabled and the frequency reuse rate can be improved.

Description

How to configure uplink frame in wireless communication system using orthogonal frequency division multiple access method {METHOD FOR EMBODYING UPLINK FRAM OF WIRELESS COMMUNICATION SYSTEM BASED ON OFDMA}

The present invention relates to a method for configuring an uplink frame in a wireless communication system using an orthogonal frequency division multiple access scheme, and more particularly, to a wireless communication system using an orthogonal frequency division multiple access (OFDMA) scheme. In the uplink frame of the present invention relates to a method of configuring an uplink frame that can improve the frequency reuse rate while performing synchronous demodulation.

Recently, the US standardization organization, IEEE, has decided the IEEE 802.11a wireless LAN standard of the OFDM method having a transmission rate of 6 ?? 54 Mbps in the 5 GHz band, and the similar standard in the European Standardization Organization (ETSI). HiperLAN / 2 is defined as a standard for high-speed wireless LAN, and the physical layers of HiperLAN / 2 and IEEE 802.11a are variable rates from 6 to 54 Mbps using the same OFDM scheme in the 5 GHz band of the ISM band. To provide.

In addition, the Wireless MAN (Metropolitan Area Network), which covers the physical and MAC layers for the 10-66 GHz and 2-11 GHz frequency bands, has completed the IEEE 802.16 standard for the 10-66 GHz frequency band. The IEEE 802.16a standard has been advanced.

Meanwhile, when a signal is transmitted through a multipath channel, an inter-symbol interference ("ISI") is generated in the received signal by the multipath. In particular, in the case of high-speed data transmission, since the period of the symbol is smaller than the delay spread of the channel, the ISI becomes more severe, and a complex reception technique is required to compensate for the distortion caused by the ISI and accurately recover the transmission signal. In order to reduce the distortion of the signal caused by the ISI, the period of the symbol should be larger than the delay spread of the channel, and the OFDM method has been proposed as a modulation method that can simply compensate for the distortion in the multipath channel.

Unlike the transmission method using a single carrier, the OFDM method transmits data using a plurality of subcarriers having mutual orthogonality. That is, the OFDM scheme performs serial and parallel conversion on the input data by the number of subcarriers used for modulation, modulates the converted data using the corresponding subcarriers, and maintains the data rate as it is. Lengthens by the number of subcarriers. Since the OFDM method uses subcarriers having mutual orthogonality, bandwidth efficiency is better than conventional frequency division multiplex (FDM), and symbol periods are increased, and thus, the OFDM method has stronger characteristics than that of a single carrier modulation scheme.

In the OFDM system, modulation and demodulation processes of the transmitter and the receiver are performed by performing an Inverse Discrete Fourier Transform (IDFT) and a Discrete Fourier Transform (DFT), respectively. This is called an Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT). You can also use In addition, if a guard interval longer than the delay spread of the channel is inserted for each transmitted symbol period, orthogonality between subcarriers is maintained, thereby preventing inter-carrier interference (ICI) from occurring. OFDM symbols are not overlapped so that ISI between adjacent symbols can be completely removed.

In addition, in the OFDMA-based cellular system, a frequency hopping method is used to average the inter-cell interference, and by using a different frequency hopping pattern for each cell, one channel of one cell collides as uniformly as possible with several channels of another cell. A method of averaging inter-cell interference is widely used, and one of them is the aforementioned IEEE802.16a OFDMA scheme. However, in IEEE 802.16a, interference is averaged without distinction between channels, and the target received signal-to-noise ratio (required SNR) is mixed and averaged by different channels, making it difficult to control inter-cell interference easily.

The above-described OFDM systems such as IEEE 802.11a, HiperLAN type 2, and IEEE 802.16a use preambles in the uplink.

1 is a diagram illustrating an uplink data burst structure of HiperLAN type 2 of IEEE OFDM / TDMA and IEEE 802.11a, and includes a short preamble 11, a long preamble 13, and a payload 15.

FIG. 2 is a diagram illustrating an uplink frame structure of IEEE 802.16a of the general OFDMA, and includes a preamble 21, an uplink (UL) burst # 1 (23), an uplink (UL) burst # 2 (25), and an uplink frame structure. A link (UL) burst # 3 (27), and a ranging subchannel (29).

Referring to FIGS. 1 and 2, such systems may have difficulty in performing channel estimation using a preamble due to collision between preambles 11, 13, and 21 between cells according to a position distribution of users in a cell. Cell planning is needed to avoid collisions between cell preambles. In addition, the channel estimation using the preamble is possible at the time of stop, or can be used only in the case of a low speed satisfying the condition that the time for demodulation using the preamble is smaller than the channel change time due to the speed of the terminal. If the terminal has mobility of medium speed or more, an error occurs between a channel value estimated by the preamble and a channel value of a symbol after the preamble, and performance is degraded.

On the other hand, as a related technology, Korean Patent Application No. 1998-27484 (filed on July 8, 1998) discloses "method and apparatus for synchronizing orthogonal frequency division multiplexing receivers", and using one reference symbol, an OFDM signal Although the present invention provides an OFDM receiver synchronization method and apparatus for achieving symbol / frame timing synchronization, carrier frequency synchronization, and sampling clock timing synchronization, there is still a need for improvement in the frequency reuse problem.

An object of the present invention for solving the above problems is to provide a method of configuring an uplink frame that can improve the frequency reuse rate in a wireless communication system using the OFDMA scheme.

In addition, another object of the present invention is to provide a method for configuring an uplink frame that can estimate a channel even when mobility of a terminal exists in a wireless communication system using an OFDMA scheme.

Method for configuring an uplink frame of a wireless communication system according to an aspect of the present invention for achieving the above object,

a) dividing the entire band of the uplink frame into a specific number of subcarrier groups; b) assigning subcarriers in each of the divided subcarrier groups to subchannels defined for a specific number of consecutive symbols defined as slots in the uplink frame; c) allocating a pilot subcarrier by the specific number of symbol units to enable channel estimation among the allocated subcarriers.

Here, in step a), the subcarrier group divides an effective subcarrier corresponding to an entire band into eight groups, and in step b), the subchannel is defined by three orthogonal frequency division multiple access symbol units. Preferably, two subcarriers are selected from each of the eight subcarrier groups and allocated to the subchannels.

In addition, it is preferable that the subcarriers belonging to each group allocated to the subchannels are adjacent subcarriers.

In the step c), the pilot subcarriers are preferably allocated in units of three symbols by using two adjacent subcarriers for each symbol in the uplink.

In addition, the pilot subcarrier is preferably disposed in a symbol located in the middle of the symbols of the allocated unit.

In addition, the pilot subcarrier is preferably assigned to one of two adjacent subcarriers corresponding to the arranged symbol.

Preferably, the pilot subcarriers are arranged on even-numbered subcarriers when the sum of cell numbers and slot numbers is even among the two adjacent subcarriers, and on odd-numbered subcarriers when odd numbers are used.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

In the structure of an uplink frame of a wireless communication system using an OFDMA scheme, the present invention allocates data subcarriers in units of two adjacent subcarriers so that collision between specific users between adjacent cells is minimized and channel estimation is possible. A pilot is inserted and transmitted at each position.

3 is a diagram illustrating a structure of an uplink frame in a wireless communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 3, the entire band is divided into subcarrier groups, and data subcarriers are allocated to minimize collisions with terminals of adjacent cells. Will be assigned.

In an OFDM frame structure according to an embodiment of the present invention, three OFDM symbols n (31, 33) given by consecutive (n = 0, 1, 2) defined as slots (slot t, slot t + 1), respectively. Define subchannels and assign data bursts. In this case, the division of the subcarriers into subchannels is performed in slot units (slot t, slot t + 1). The 1552 effective subcarriers of each OFDM symbol (31, 33) are divided into a total of eight groups (G ₀ ~ G ₇ ) consisting of 194 subcarriers in succession. In addition, one subchannel extracts two consecutive subcarriers from each of the eight groups G _{0 to} G ₇ to use 16 subcarriers per symbol equally during one slot.

At this time, the subcarriers constituting the subchannel are used as the subcarriers with a small subcarrier number among the subcarriers constituting each block, and their positions do not change in the same frame period.

In addition, a subchannel for data transmission is allocated in units of one slot and one subchannel, and a ranging channel for synchronizing synchronization of received signals of uplink terminals is 1 using the same subchannel in the same frame period. It is allocated in units of slots and six subchannels.

The subcarriers constituting the uplink (UL) subchannel are defined as follows for each symbol period belonging to each slot.

here, Is Composing the second subchannel The second subcarrier has a value of 0 to 1551. Also, Represents a subchannel number and has a value from 0 to 96. Also, Is a subcarrier index constituting the subchannel and has a value of 0 to 7. Also, Denotes a subcarrier index offset, = 8 × [(frame number) mod 12]. Also, Is the permutation permutation P ₀ Represents the j th element of the permutation shifted left to Indicates a cell number specified by MAC (Medium Access Control) and has a value of 0 to 96. here, Is the remainder after dividing a by b.

Hereinafter, to show an example of subchannel division, the cell number in frame 1 = 3, subchannel number The case of = 2 will be described with an example.

(1) First, P ₂ = {28, 43, 21, 8, 40, 6, 30, 53, 71, 64, 29, 48, 46, 36, 83, 27 , 38, 93, 77, 94, 82 , 22, 13, 65, 34, 73, 74, 79, 7, 35, 78, 2, 10, 50, 56, 86, 42, 16, 80, 12, 60, 9, 45, 31, 58, 96 , 92, 72, 69, 54, 76, 89, 57, 91, 67, 44, 26, 33, 68, 49, 51, 61, 14, 70, 59, 4, 20, 3, 15, 75, 84 , 32, 63, 24, 23, 18, 90, 62, 19, 95, 87, 47, 41, 11, 55, 81, 17, 85, 37, 88, 52, 66, 39, 1, 5, 25 }

(2) Subcarrier index offset because it is frame 1 Becomes 8 and uses only the 8th to 15th elements. That is, { 71, 64, 29, 48, 46, 36, 83, 27 } in P ₂ .

(3) Next, cell number = 3, so add 3 to all elements in the permutation and divide by 97 to find the remainder. That is, { 74, 67, 32, 51, 49, 39, 86, 30 }.

(4) Sixteen subcarriers are extracted from each symbol, two adjacent ones. Thus Carrier (2, m) = {148, 328, 452, 684, 874, 1048, 1336, 1418}, and the actual subcarriers used are {148, 149, 328, 329, 452, 453, 684, 685 , 874, 875, 1048, 1049, 1336, 1337, 1418, 1419}.

Here, reference numeral A denotes a pilot P allocated to a portion of the allocated data subcarriers to enable channel estimation, and a detailed pilot allocation method will be described with reference to FIGS. 4A and 4B below. .

4A and 4B are diagrams for explaining an uplink pilot allocation method according to an embodiment of the present invention. A diagram showing pilot allocation at mod 2 = 0, and FIG. 4B A diagram showing pilot allocation in mod 2 = 1.

4A and 4B, the pilot subcarriers of the uplink are allocated in units of three symbols for two consecutive subcarriers. The pilot subcarriers are arranged in symbol 1 corresponding to the center symbol of each slot. If the sum of the cell number and the slot number is even, as shown in FIG. 4A, the pilot subcarriers are arranged in the even numbered subcarriers. As shown, if the sum of the cell number and the slot number is an odd number, the cell number and the slot number are arranged in the position of the subcarriers of the odd number (see the shaded portions of FIGS.

Accordingly, the present invention minimizes the collision of a specific user of a neighboring cell with each data allocation so as to enable channel estimation using a preamble and channel estimation in a cellular system. In order to improve the performance, the entire band is divided into subcarrier groups, data subcarriers are allocated to minimize collisions between UEs between adjacent cells, and some positions of the data subcarriers are allocated as pilots to enable synchronous demodulation and frequency reuse rate. Can be improved.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

According to the present invention, synchronous demodulation is possible and the frequency reuse rate can be improved.

1 is a diagram illustrating an uplink data burst structure of HiperLAN type 2 of IEEE OFDM / TDMA and IEEE 802.11a.

2 is a diagram illustrating an uplink frame structure of IEEE 802.16a of general OFDMA.

3 is a diagram illustrating a structure of an uplink frame in a wireless communication system using an orthogonal frequency division multiple access scheme according to an embodiment of the present invention.

4A and 4B are diagrams for explaining an uplink pilot allocation method according to an embodiment of the present invention. A diagram showing pilot allocation at mod 2 = 0, and FIG. 4B A diagram showing pilot allocation in mod 2 = 1.

Claims (10)

A method of configuring an uplink frame in a wireless communication system using an orthogonal frequency division multiple access (OFDMA) method, a) dividing the entire band of the uplink frame into a specific number of subcarrier groups; b) assigning subcarriers in each of the divided subcarrier groups to subchannels defined for a specific number of consecutive symbols defined as slots in the uplink frame; c) allocating a pilot subcarrier by the specific number of symbol units to enable channel estimation among the allocated subcarriers The uplink frame configuration method of the wireless communication system comprising a. The method of claim 1, In step a), the subcarrier group divides the effective subcarriers corresponding to the entire band into 8 groups, In step b), the subchannels are defined in units of three orthogonal frequency division multiple access symbols, and two subcarriers are selected from each of the eight subcarrier groups and assigned to the subchannels. The uplink frame configuration method of the wireless communication system, characterized in that. The method of claim 2, The subcarriers belonging to each group allocated to the subchannels are subcarriers adjacent to each other. The method according to any one of claims 1 to 3, Subcarriers constituting the subchannel Is the relation here, Is Composing the second subchannel Subcarrier, Is the subchannel number, Is the subcarrier index constituting the subchannel, Is the subcarrier index offset, Is the permutation permutation P ₀ J th element of the permutation shifted left to Is the cell number specified by Medium Access Control (MAC), and The remainder being divided into a b. The uplink frame configuration method of the wireless communication system, characterized in that follows. The method of claim 4, wherein The subcarrier Has a value of 0 to 1551, The subchannel Has a value from 0 to 96, The subcarrier index Has a value of 0 to 7, The cell number Has a value of 0 to 96 The uplink frame configuration method of the wireless communication system, characterized in that. The method of claim 5, The subcarrier index offset Is 8 × [(frame number) mod 12]. The method of claim 1, In the step c), the pilot subcarriers are allocated in three symbol units by using two adjacent subcarriers for each symbol in the uplink. The method according to claim 1 or 7, And the pilot subcarrier is disposed in a symbol located in a center of symbols of an allocated unit. The method of claim 8, And the pilot subcarriers are allocated to one of two adjacent subcarriers corresponding to the arranged symbols. The method of claim 9, And wherein the pilot subcarriers are arranged on even-numbered subcarriers when the sum of cell numbers and slot numbers is even among the two adjacent subcarriers, and on odd-numbered subcarriers when odd numbers are used.