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Reference Signals Designs for LTE-Advanced and Beyond

Reference signals are an integral part of the LTE and LTE-advanced, providing means for channel estimation and data demodulation. Reference signals are roughly uniformly assigned to subcarriers in frequency domain and to OFDM symbols in time domain. Compared to other radio access technologies (RATs), reference signal design presents an undesired trade-off for LTE pioneers. Too dense the reference signal, the precious resources, i.e., subcarriers and OFDM symbols, shrink for useful data. Too sparse the reference signal, the receiver is unable to get accurate channel estimation and demodulate the data satisfactorily. It can be said that the reference signals in LTE incur not only the power penalty (the power needed to transmit them), but also the resource penalty.

In comparison, reference signals in CDMA incur the power penalty but very little resource penalty. This can be seen from the fact that the resources in CDMA are in the form of the code channels. If 10 out of 2048 code channels are used to carry the reference signals, the impact on the resources is almost nonexistent. On the other hand, a single reference signal in LTE uses about 5% of the total resources. With advanced technologies such as MIMO and multipoint broadcasting, the number of LTE reference signals grows rapidly, resulting in fast disappearing of the available resources for useful data, which negates the benefits of those advanced technologies.

We have developed innovative reference signal designs for LTE-advanced and beyond that achieve zero or near-zero resource penalty regardless how many advanced technologies are incorporated, while ensuring the reference signals are sufficiently powerful for accurate channel acquisition and data demodulation.

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LTE-Advanced及后续技术中的参考信号设计

用来信道估计和数据解调的参考信号是LTE和LTE- advanced一个有机部分。参考信号基本上均匀地分布在频域上的子载波中和时域上的OFDM字符之间。相对于其它无线接入技术， 合理地设计参考信号对于LTE的设计者来说是个比较棘手的问题。太稠密的参考信号会减少输送有用数据的宝贵资源（即子载波和OFDM字符）。太稀疏的参考信号则使得接收器不能获得准确的信道估计，以及不能令人满意地解调数据。可以说，LTE中的参考信号不仅带来了功率损失（即发送参考信号所需的额外功率），还引入了资源损失。

作为比较，CDMA中的参考信号产生功率损失但只有极小的资源损失。这体现在作为CDMA资源的码道上。譬如，从2048条码道中选取10条承载参考信号，资源所受的影响可以忽略不计。而在LTE中，一条信道的参考信号就占去总资源的5% 左右。随着MIMO和多点传播等先进技术的应用，LTE中的参考信号的数量快速增长，用于有用数据的资源则不断流失，乃至抵消了这些先进技术的优势。

青山无线的创新技术克服了LTE-advanced 及后续技术中参考信号的难题。我们的解决方案的资源损失为零或接近零，满足了先进技术日益增长的对参考信号的需求，并保证了参考信号具有足够的功率以实现信道捕获和数据解调。