JP2012217114A - Ofdma system for long-time delay diffusion environments - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a design method for an OFDMA base system.SOLUTION: A system parameter including a channel bandwidth, an FFT size, a cycle prefix length, and a subcarrier interval is determined based on a long-time delay channel diffusion effect. A sign structure including data sign allocation and pilot sign of the subcarrier is defined by adjusting a fundamental tile structure and a cluster structure in both uplink and downlink systems. An interleave parameter is defined for helping reduction of burst error caused by a long-time channel delay high-frequency selective fading effect. In this design method, a packet overhead is effectively decreased and system data speed is improved. A bit error rate performance is maintained, even in the case of a long-time delay where a diffusion channel exceeds 10 microseconds.

Description

  The present invention relates generally to orthogonal frequency division multiple access (OFDMA) systems, and more particularly to OFDMA data and pilot symbol structure, system parameter selection, and interleaving techniques. The present invention can be used in public broadband network systems or other OFDMA based wireless communication systems. The time required for practical use is estimated to be less than half a year.

  An OFDMA system requires wireless channel information to recover data based on estimated channel parameters. The subcarrier of each OFDMA symbol is assigned to data and pilot signals. The received pilot signal is used to estimate the channel delay profile by comparing it with the original pilot message of the system transmitter. The determined channel profile is used to address channel equalization and multipath frequency selective fading. When the communication range is wide, the maximum channel delay spread rate is 10 ms. A typical OFDMA system, such as an IEEE 802.16e OFDMA system, cannot handle the long delay profile when operated with a bandwidth of 1.25 to 5 MHz due to the short cyclic prefix length (see FIG. 1). ). The data rate provided by OFDMA systems is also not sufficient to support high speed data transmission such as video streams.

号３個）と定義されるタイル構造になる。ダウンリンクシステムのパイロットパターンはクラスタ構造になる。パイロット記号４個が各クラスタに含まれ、クラスタは（副搬送波１４

ダウンリンクでそれぞれ２：１、６：１である。オーバーヘッドは高く、システムは、７Ｍｂｐｓ以上のアップリンク伝送速度を必要とする高品位テレビなどの高速データ伝送をサポートすることはできない。FIG. 2 illustrates the downlink and uplink defined in the wireless standard IEEE 802.16e.

No. 3)). The pilot pattern of the downlink system has a cluster structure. Four pilot symbols are included in each cluster, and the cluster (subcarrier 14

The downlink is 2: 1 and 6: 1 respectively. The overhead is high and the system cannot support high-speed data transmission such as high-definition television that requires an uplink transmission rate of 7 Mbps or higher.

  The present invention provides an OFDMA system design method for solving the high frequency selective fading effect. The present invention also provides an optimal OFDMA symbol structure to reduce overhead. The present invention can be used in the 170 MHz to 205 MHz frequency band of public broadband network systems and other OFDMA based wireless communication systems. The symbol structure is defined by placing data and pilot subcarriers in each OFDMA symbol. With this OFDMA symbol structure, the system data rate can be increased by nearly 30% for the same level of SNR and the packet overhead is reduced to 1/7.

FIG. 1 (Prior Art) illustrates OFDMA parameters used in WiMax PUSC. FIG. 2 (Prior Art) illustrates the downlink and uplink OFDMA symbol structures defined in the wireless standard IEEE 802.16e. FIG. 3 defines the proposed OFDMA system parameters. FIG. 4 shows an example of a proposed pilot pattern for uplink communication. FIG. 5 shows an example of proposed interleaving for uplink communication. FIG. 6 illustrates the prior art bit error rate performance. FIG. 7 shows the bit error rate performance of the proposed system.

  The present invention consists of a pilot pattern definition, an OFDMA system parameter design, and a corresponding interleaver. The system needs to employ subcarrier allocation, interleaving, FEC coding, subchannel permutation as defined in the IEEE 802.16e standard. By adopting the proposed system parameters, the proposed pilot pattern and interlouver are used. The system can provide high speed data transmission support for uplink transmission.

  High data rate support for uplink transmission is implemented by changing the pilot symbol pattern of the OFDMA symbol structure. The proposed symbol structure reduces the proportion of pilot symbols in each OFDM symbol, thereby reducing overhead and increasing data rate.

  The present invention defines an OFDMA symbol structure and supports an OFDMA system with a 5 MHz channel bandwidth. The proposed OFDMA parameters are defined in FIG. A 1024 FFT size is used, and the number of guard subcarriers is 184. The cyclic prefix length is 22.8 microseconds and can handle long channel delay profiles exceeding 10 microseconds.

記号７個）により形成される。データとパイロット副搬送波の比率はアップリンクで６：１であり、大きく改善され、提案される記号構造を使用することによりデータ速度を上げることができる。FIG. 4 is an example of a proposed pilot pattern for uplink transmission. Tiles

7 symbols). The ratio of data to pilot subcarrier is 6: 1 in the uplink, which is a significant improvement and can increase the data rate by using the proposed symbol structure.

このとき、ｋ＝０，１，・・・，Ｎ＿ｃｂｐｓ−１，ｄ＝１８．FIG. 5 is an example of proposed interleaving for uplink transmission. N_cbps is the length of the block to be encoded, d is the codeword length, k is the index of the data before replacement, and M_k is the index of the data after replacement. The substitution is defined by [Equation 1].

At this time, k = 0, 1,..., N_cbps-1, d = 18.

  6 and 7 show the bit error rate performances of the prior art and the present invention, respectively. From the examples, it can be seen that the present invention provides equivalent BER performance, reduces headers and increases data rate.

Claims (3)

In a method implemented in an orthogonal frequency division multiple access system,
(A) selecting channel bandwidth, subcarrier spacing, FFT size, cyclic prefix length;
(B) defining a pilot symbol pattern;
(C) defining a tile structure;
(D) defining a cluster structure;
(E) assigning subcarrier schemes for data and pilot symbols;
(F) defining interleaving techniques;
(G) defining a subcarrier replacement scheme;
(H) using a modulation and coating scheme. In the uplink transmission system,
(A) adjusting the symbol structure;
(B) reducing the number of pilot symbols in each tile structure;
2. The method of claim 1 comprising: (c) adjusting the interleaver depth. In the downlink transmission system,
(A) adjusting the symbol structure;
(B) changing the number of OFDMA symbols in each tile structure;
(C) changing the pilot symbol pattern;
The method of claim 1 comprising: (d) adjusting the interleaver depth defined in FIG.

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