Seungjae Bahng

QR-LRL Signal Detection for Spatially Multiplexed MIMO Systems

The performance of the ordered successive interference cancellation (OSIC) signal detection method is well known to depend on the successful detection of the first layer. In a previous work, in an effort to mitigate the error propagation effect, all the constellation points were tried as the first layer symbol, thereby achieving a better performance. In this letter, we show that the selection of the first layer impacts the error performance significantly, and based on the observation, we propose a novel signal detection method QR-LRL. In the proposed work, the least reliable layer (LRL) is chosen to be the first layer, which is shown to be the best choice in terms of noise enhancement in detecting the other layers. Also, we discuss Log Likelihood Ratio (LLR) computation when the proposed method is used. Computer simulations confirm the efficacy of the proposed method.

Enlarged QR-LRL based SM-MIMO detector for efficient soft output generation

An enlargement of candidate vector set of QR-LRL (QR - Least Reliable Layer) based MIMO detector for efficient soft output generation is proposed. Previous work [8] shows that QR-LRL based MIMO detector approaches hard decision output ML performance, but does not match the soft output ML performance due to empty candidate vector set problem. Performance degradation is more severe when modulation order is low. Some of the previous methods have provided solutions to mitigate Empty Vector Set (EVS) problem [4] [8] [9], but are not efficient in terms of performance or computation complexity. In this paper, we enlarged candidate vector set of QR-LRL detector by applying every constellation point at each layer. The proposed detector thus effectively removes EVS problem and achieves soft ML performance while keeping the computation complexity low, especially at low modulation order.

Non-orthogonal dual-polarization via polarization-domain rotation

In this paper, we focus on the effect of power gain imbalance between the H- and V-polarization components, which can boost the overall bit error rate (BER) of a dual-polarization transmission system. Thus, we propose a polarization-domain rotation scheme which rotates the axis of each polarization component such that their power gains are well balanced. In addition, we show that there exist optimal rotation angles which can minimize the BER. Throughout extensive simulation studies, we evaluate the effectiveness of the proposed polarization-domain rotation scheme for various scenarios.

BER minimization for dual-polarized wireless systems with polarization-domain rotation

We consider the problem of bit error rate BER degradation because of the power gain imbalance between horizontal H-polarization and vertical V-polarization components in an orthogonal dual-polarization transmission system. To alleviate the aforementioned BER degradation problem, we propose a non-orthogonal polarization-domain rotation scheme where the axes of H-polarization and V-polarization components are rotated with different angles at the transmitter and de-rotated at the receiver. In addition, in order to assess the effectiveness of the polarization-domain rotation scheme, we derive the closed-form BER expression under a practical dual-polarized channel model, which is represented by cross-polarization ratio and co-polarization ratio CPR. We also derive the approximated BER expressions for the two asymptotic values of CPR: balanced CPR and infinite CPR. With the derived BER expressions, we find the optimal rotation angles that jointly minimize the BER. According to the numerical results, it is shown that about 3dB Eb/N0 gain is obtained at the BER of 10-4 and the CPR of 10dB by the polarization-domain rotation scheme with optimal rotation angles compared with the conventional orthogonal dual-polarization transmission. Copyright

Uplink Packet Scheduling Schemes for Video Traffic in Wireless Communication Systems

We propose three different uplink packet scheduling algorithms for OFDMA-based wireless communication system through video traffic analysis and analyze their performances. The video traffic is assumed to be generated its packets according to the Pareto distribution parameters. The packet scheduler at the base station is able to do the priority-based resource allocation based on the information collected from the mobile stations. Defining the uplink scheduling classes according to the presence and the amount of the collected information, we propose, based on that, three kinds of uplink packet scheduling algorithm: BUS-DAP, PUS-DAP and AUS-PLR. Simulation results show the proposed AUS-PLF algorithm offers better channel capacity than the others.