High-Performance Precoding Techniques for Advanced Communication Systems

When the transmitter knows the channel information, precoding is an effective way to overcome channel effect and achieve high throughput transmission. With this desirable feature, precoding techniques have been adopted by several advanced communication standards, such as IEEE 802.3an, IEEE 802.11n, IEEE 802.16e/m, and 3GPP-LTE. Depending on the type of channel information and how fast the channel changes, the required precoding techniques are different for different communication standards. The precoding techniques are Tomlinson- Harashima precoding, singular value decomposition, and codebook for wireline systems, WLAN systems, and WMAN/WWAN systems, respectively. The design challenges of each precoding technique are described as follows.
In the application of the IEEE 802.3an systems, the Tomlinson-Harashima (TH) precoders need to operate at a speed of 800MHz. However, the speed requirement is hard to meet since the TH precoders contain modulo devices and feedback loops. Therefore, we propose a two-time pipelining scheme to pipeline the TH precoders, which enables us to develop a generalized TH precoder architecture. The proposed scheme provides more degrees of freedom in designing high-speed pipelining TH precoders with build-in arbitrary speedup factors.
In the IEEE 802.11n systems, the use of the singular value composition (SVD) technique can greatly enhance the system throughput. However, the high computational complexity and high decomposing latency are the important issues in applying the SVD to the real-time applications. Hence, we propose a complete adaptive SVD algorithm, as well as a reconfigurable architecture design for high-throughput wireless systems. The main design features include low decomposing latency and supporting all antenna configurations in a multi-input multi-output (MIMO) system. The proposed design is implemented in 90nm technology for the application of IEEE 802.11n systems. The chip result shows that for an 802.11n system, the average latency of our SVD engine is only 0.33% of the WLAN coherence time. Therefore, the proposed SVD engine is very suitable for the high-throughput WLAN applications.
Due to the feedback delay constraint and limited feedback bandwidth, codebook-based precoding is a promising practical method in the WMAN/WWAN applications. According to the current channel condition, the receiver selects the optimal precoder from a codebook which consists of a finite set of precoders and sends the index of the chosen precoder over a limited-feedback channel. Conventional precoder selection criteria require high computational complexity. Besides, if the codebook is square, some precoder selection criteria are not feasible. Therefore, we propose a low-complexity precoder selection criterion which is applicable to any existing codebook. Compared with direct implementation, the proposed scheme has significant computational complexity reduction without performance loss.
In summary, we propose three high-performance precoding techniques with their own design considerations for the advanced communication applications in this thesis. We expect that the proposed precoding techniques can also be applied to future advanced communication systems.