In orthogonal frequency division multiplexing
based wireless system, a pilot signal is often
employed to estimate channel state information
(CSI). However, the received pilot signal is
interfered by other cell interference in multi-cell
environments. We consider the estimation of CSI by
utilizing orthogonal preambles and channel
correlation.Seoul R&BD Progra

Ban, Dae-Seung

Kim, Cheong-Hwan

Lee, Yong-Hwan

SNU Open Repository and Archive

2008년도 대한전자공학회 하계종합학술대회 제31권 제1호This research was supported by Seoul R&BD Program (10544)모바일 와이맥스 시스템에서인접 셀 간섭 완화를 위한 채널 추정김정환, 반 승, 이용환서울 학교 기컴퓨터공학부e-mail : kkins@ttl.snu.ac.kr, qks83@ttl.snu.ac.kr, ylee@snu.ac.krChannel Estimation for OCI Mitigationin Mobile WiMAX SystemsCheong-Hwan Kim, Dae-Seung Ban, Yong-Hwan LeeSchool of Electrical Engineering and INMCSeoul National UniversityAbstract  In orthogonal frequency division multiplexing based wireless system, a pilot signal is often employed to estimate channel state information (CSI). However, the received pilot signal is interfered by other cell interference in multi-cell environments. We consider the estimation of CSI by utilizing orthogonal preambles and channel correlation.I. Introduction   Orthogonal frequency division multiplexing (OFDM) can provide high spectral efficiency and mitigate inter-symbol interference in frequency selective channel. However, this requires the use of accurate channel state information (CSI), which is not easily obtainable. In OFDM based wireless systems such as the mobile-WiMAX, a pilot signal is employed to estimate the CSI. The received pilot signal is interfered by other cell interference, making it difficult to the CSI estimation. In this paper, we consider the use of orthogonal preamble and channel correlation to improve the CSI estimation performance.II. System modeling  We consider a three-cell three-sector OFDM based wireless system. Define the target channel and the -th interference channel between the target base station (TBS) and the mobile station (MS), and the -th interfering base station (IBS) and the MS, respectively. Received pilot signal corresponding to the -th OFDM symbol and the -th subcarrier can be represented as     (1)where   and   are respectively the target channel and pilot signal transmitted from the TBS,   and   are respectively the -th interference channel and the pilot signal transmitted from the -th IBS, and   is a zero-mean complex Gaussian noise with variance .  Preambles are transmitted through different frequency bands according to the sectors at time  . Received preambles transmitted from the TBS and the -th IBS can be represented as                (2)       (3)where   and    denote the 2912008년도 대한전자공학회 하계종합학술대회 제31권 제1호preambles transmitted from the TBS and the -th IBS, respectively. Let   and   be the correlation between the channel of the pilot signal and the preamble transmitted from the TBS and the -th IBS, respectively.Ⅲ. Proposed channel estimation  The target CSI can be estimated as                    (4)where   and   are estimated target CSI at pilot signal and preamble by using LS method, respectively. Also,    is a weight vector to be determined. Let   and   be the auto-covariance matrix and cross-covariance vector of the target channel respectively defined by [1]        (5)                        (6)where  and  are the gains of the target and the -th interference channel, respectively.  and   are  the average transmit power of preamble and pilot signal, respectively. The optimum weight vector   can be determined by [1]                                       (7)  Since the target channel behaves as noise to the estimation of the interference CSI, the interference CSI can be estimated by using the estimated target CSI as         ′           (8)The interference channel can further be re-estimated as      ′        (9)where    and   are the estimated the -th interfering CSI by using LS method and a weight vector for the -th interfering CSI, respectively. The auto-covariance   matrix and cross-covariance vector   of the -th interference channel can respectively be represented as [1]          (10)               (11)where   is mean square error of the target CSI estimation. Similarly, the optimum weight vector   for the -th interfering CSI is determined by [1]                                      (12)Ⅳ. Performance evaluation  The performance of the proposed scheme is verified by computer simulation. Fig. 1 depicts the packet error rate (PER) of the proposed scheme. It can be seen that the performance of the LS scheme is significantly degraded. It can also be seen that the proposed scheme outperforms the LS scheme.Ⅴ. Conclusion  In this paper, we have proposed a channel estimation scheme that utilizes the preamble and channel correlation. Simulation result shows that the proposed scheme is quite effective.Reference[1] S. Haykin, Adaptive Filter Theory, Prentice Hall, fourth edition, 2002.-5 -4 -3 -2 -1 010-210-1100SINR [dB]PER  IdealLS schemeProposed schemeMobility: 60km/hFig. 1. PER according to the SINR292

모바일 와이맥스 시스템에서 인접 셀 간섭 완화를 위한 채널 추정

https://s-space.snu.ac.kr/bitstream/10371/7076/1/%ed%95%98%ea%b3%84%ec%a2%85%ed%95%a9%ed%95%99%ec%88%a0%eb%b0%9c%ed%91%9c08_%ea%b9%80%ec%a0%95%ed%99%98_%eb%aa%a8%eb%b0%94%ec%9d%bc%20%ec%99%80%ec%9d%b4%eb%a7%a5%ec%8a%a4%20%ec%8b%9c%ec%8a%a4%ed%85%9c%ec%97%90%ec%84%9c%20%ec%9d%b8%ec%a0%91%20%ec%85%80%20%ea%b0%84%ec%84%ad%20%ec%99%84%ed%99%94%eb%a5%bc%20%ec%9c%84%ed%95%9c%20%ec%b1%84%eb%84%90%20%ec%b6%94%ec%a0%95.pdf

모바일 와이맥스 시스템에서 인접 셀 간섭 완화를 위한 채널 추정

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