approach the performance limits. For maximizing the aggregate throughput (sum rate) in downlink, dirty paper coding is a theoretical concept to achieve capacity. However, sum rate maximizing is neither an appropriate objective in real systems with fairness requirements, nor is the algorithm for dirty paper coding practically realizable with a large number of users.Especially in the case where additional fairness constraints between users with different channel
Current UWB systems apply convolutional codes as their channel coding scheme. For next generation systems LDPC codes are in discussion due to their outstanding communications performance. LDPC codes are already utilized in the new WiMax and WiFi standards. Thus it is reasonable to investigate these codes as candidate LDPC codes for UWB. In this paper the authors present an implementation complexity and performance comparison of LDPC decoders. We will show that it is of great advantage to design new LDPC codes which are tailored to the special latency and throughput constraints of upcoming UWB systems. This new class of LDPC codes is named Ultra-Sparse LDPC codes. Synthesis results of WiMax, WiFi, and U-S LDPC decoders are presented based on an enhanced 65 nm CMOS process. We show that the implementation complexity of the new U-S LDPC decoders is 55% smaller, utilizing only 0.2 mm 2 instead of over 0.4 mm 2 , while the communications performance of all observed LDPC codes are almost identical under all the considered UWB simulation conditions.
In this paper, we propose an iterative SIC receiver architecture with pilot-and data-based channel estimation for efficient decoding of non-orthogonal superimposed signals. The non-orthogonal superposition concept on top of OFDMA is a promising technique to improve cell spectral efficiency. In the cellular case, where users with significant path loss are superimposed by an intelligent scheduler, the SIC multi-user receiver scheme is well adapted for user signal separation. Based on the proposed receiver, we show the performance by means of multi-link link-level simulations in a realistic OFDMA uplink system including channel estimation based on real pilot patterns.
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