Jihun Koo

An enhanced dual carrier modulation for performance improvement in WiMedia UWB systems

In this paper, we propose an enhanced dual carrier modulation algorithm to improve performance in WiMedia ultra-wideband (UWB) systems. The proposed algorithm, which is named as double dual carrier modulation (DDCM), uses additional precoding to the conventional DCM to transmit symbols over different subbands. By using DCM and additional precoding, the proposed algorithm exploits not only frequency diversity in one subband, but also frequency diversity between uncorrelated subbands, resulting in more diversity and better performance than DCM. We also propose the detection method of the proposed algorithm by sharing the modified dual carrier modulation (MDCM) detection block which is included in WiMedia UWB systems. The proposed detection method reduces hardware complexity by combining the MDCM detection and the proposed algorithm detection. Simulation results of applying the proposed algorithm to WiMedia UWB systems show that the performance was improved by 1.5 dB and transmission range increased by 0.5 m in CM1 at a PER of 1%, compared to DCM.

A parallel collaborative sphere decoder for a MIMO communication system

In this paper, we propose a parallel collaborative sphere decoder with a scalable architecture promising quasi-maximum likelyhood performance with a relatively small amount of computational resources. This design offers a hardware-friendly algorithm using a modified node operation through fixing the variable complexity of the critical path caused by the sequential nature of the conventional sphere decoder (SD). It also reduces the computational complexity compared to the fixed-complexity sphere decoder (FSD) algorithm by tree pruning using collaboratively operated node operators. A Monte Carlo simulation shows that our proposed design can be implemented using only half the parallel operators compared to the approach using an ideal fully parallel scheme such as FSD, with only about a 7% increase of the normalized decoding time for MIMO dimensions of 16×16 with 16-QAM modulation.

A low complexity soft-output detection algorithm for 2×2 multiple-input multiple-output multiband-ofdm systems using dual carrier modulation

This paper presents a low complexity soft-output detection algorithm for 2×2 multiple-input multiple-output (MIMO) multiband-orthogonal frequency division multiplexing (MB-OFDM) systems using dual carrier modulation (DCM) or modified DCM (MDCM). By detecting each symbol pair of DCM or MDCM separately, the proposed detection algorithm reduces the complexity of the partial Euclidean distance (PED) calculation and the preprocessing complexity, which is the complexity of QR decomposition and channel ordering. This paper also proposes an efficient candidate list extension method for soft-output MIMO detection by using the calculated PEDs. Because the proposed algorithm has a low complexity and can also be implemented in a fully-pipelined hardware, the proposed algorithm is suitable for MB-OFDM systems requiring high speed hardware. The simulation results of applying the proposed algorithm to 2×2 MIMO MB-OFDM systems using DCM or MDCM show that the performance of the proposed algorithm has near soft-output maximum likelihood detection performance. The hardware complexity of the proposed algorithm is approximately 40% of that of the existing algorithm with similar performance.

High diversity achievement algorithm for dual carrier modulation in MB-OFDM UWB systems

In this paper, we propose a high diversity achievement algorithm for dual carrier modulation (DCM) in multiband-orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) systems. The proposed algorithm uses additional precoding to the conventional DCM symbols with 25 subcarrier separation. The proposed algorithm exploits not only frequency diversity between 50 subcarrier separation by using DCM, but also frequency diversity between 25 subcarrier separation by using additional precoding, resulting in better performance than the conventional DCM. We also propose a method for detecting the proposed algorithm by sharing the modified dual carrier modulation (MDCM) detection block which is basically included MB-OFDM UWB systems. The proposed detection method prevents the increase in hardware complexity caused by additional precoding. Simulation results show that the performance of the proposed algorithm was improved by 3 dB in CM1 at an uncoded BER of 10-5, compared to DCM.

Enhanced WiMedia UWB system using antenna selection with reduced feedback

In this paper, we propose an antenna selection (AS) scheme with reduced feedback for enhanced WiMedia ultra-wideband (UWB) systems with multiple transmit and receive antennas. The proposed scheme groups several adjacent subcarriers and selects one transmit antennas per group. Only indexes for the selected antennas are transmitted to reduce the amount of feedback information. We also present a practical operating scenario for the proposed AS scheme. By following the scenario, the proposed scheme not only can prevent throughput loss due to feedback transmission but can also provide robustness against channel changes between several frames. From simulation results for 1024 Mbps transmission mode in the WiMedia UWB system, the proposed scheme showed that performance was improved by 7 dB and transmission range was extended to 4.7 m at 1% PER, compared to the orignal 1 × 1 WiMedia UWB standard.

Transmitter-leakage compensator of UHF RFID reader for mobile applications

This paper presents a new approach for reducing transmitter-leakage in UHF RFID readers for mobile devices. In the approach, it is possible to reduce the leakage dynamically by utilizing pilot signals for detecting the leakage and then applying reverse-phase signals for its compensation. Experimental results show more than 30dB of the leakage elimination and 25~600% of enhancement in the reading range when tested with a 8dBi stationary and a -3.5dBi mobile antennae in an anechoic chamber.