Cooperative OFDM Channel Estimation in the Presence of Frequency Offsets
Cooperative OFDM Channel Estimation in the Presence of Frequency Offsets
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DOI：
10.1109/tvt.2009.2016345
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发表时间：
2009-02
影响因子：
6.8
通讯作者：
Zhongshan Zhang;Wei Zhang-;C. Tellambura
中科院分区：
文献类型：
--
作者：
Zhongshan Zhang;Wei Zhang-;C. Tellambura
存在频率偏移的情况下的信道估计是为协作正交频分复用 (OFDM) 系统而开发的。提出了一种两时隙协作信道估计协议。源将训练序列广播到中继和目的地（第一个时隙），并且中继重新传输训练序列（第二个时隙）。推导了放大转发（AF）和解码转发（DF）中继的导频设计。这些设计消除了由于同时中继重传而发生的中继间干扰 (IRI)，并最大限度地减少了均方误差 (MSE)。因此，AF 和 DF 中继的数量被限制为分别小于 lfloorN/(2L - 1)rfloor 和 lfloorN/Lrfloor，其中 N 是子载波总数，L 是信道阶数，lfloorarfloor 是 alpha 的最大整数部分。还评估了由于频率偏移和信道估计误差而导致的协作 OFDM 中正交空时编码的成对误差概率 (PEP)。为 AF 和 DF 中继导出源和中继之间的最佳功率分配比，以最小化 PEP。当 L < 16 时，DF 继电器在 PEP 方面优于 AF 继电器。对于 L = 4 和 16 个活动继电器，对于 10-3 的频偏误差方差，间隙为 9 dB，并且当方差增加到 10-2 时，该间隙增加到约 11.3 dB。
Channel estimation in the presence of frequency offsets is developed for cooperative orthogonal frequency-division multiplexing (OFDM) systems. A two-time-slot cooperative channel estimation protocol is proposed. The source broadcasts the training sequence to the relays and the destination (first time slot), and the relays retransmit the training sequence (second time slot). Pilot designs for amplify-and-forward (AF) and decode-and-forward (DF) relays are derived. These designs eliminate interrelay interference (IRI), which occurs due to the simultaneous relay retransmissions, and minimize the mean square error (MSE). Consequently, the number of AF and DF relays is constrained to be less than lfloorN/(2L - 1)rfloor and lfloorN/Lrfloor, respectively, where N is the total number of subcarriers, L is the channel order, and lfloorarfloor is the maximum integer part of alpha. The pairwise error probability (PEP) of orthogonal space-time coding in cooperative OFDM due to both frequency offset and channel-estimation errors is also evaluated. The optimal power allocation ratio between the source and the relays to minimize the PEP is derived for AF and DF relays. When L < 16, DF relays outperform AF relays in terms of PEP. With L = 4 and 16 active relays, the gap is 9 dB for a frequency offset error variance of 10-3, and this gap increases to about 11.3 dB when the variance increases to 10-2.