Yuping Zhao

In-band and out-band spectrum analysis of OFDM communication systems using ICI cancellation methods

This paper presents the in-band and out-band spectrum analysis of the previously proposed OFDM communication systems. The first part of the paper discusses the subcarrier spectrum of standard OFDM systems. It shows that the common understanding of the sinc(x) function OFDM spectrum is not relevant, and the OFDM spectrum should be represented as sinc(x)exp(-j/spl pi/x). The second part of the paper studies the spectrum of OFDM systems using intercarrier interference (ICI) cancellation methods. The ICI cancellation methods, known as the ICI self-cancellation scheme and using correlative coding in the OFDM frequency domain, have been proposed previously. This paper gives in-band and out-band spectrum analysis of the systems. It concludes that the proposed ICI cancellation methods not only reduce the ICI, but also make out-band spectrum roll-off much faster than the standard OFDM systems.

A Threshold-Based Hybrid Relay Selection Scheme

In this paper, in order to reduce error propagation for cooperative systems, we propose and analyze two new threshold-based hybrid relay selection schemes for the three-node cooperative relaying system, named as hybrid amplify-decode-forward relaying (HADF) and direct-amplify-forward relaying (HDAF). When the signal-to-noise ratio (SNR) is higher than the specific threshold, which is designed in HDAF, the relay chooses to transmit message in amplify-and-forward (AF) mode, otherwise, the source node deals with message in direct transmission (DT) mode without the relay. Similarly, in HADF scheme, a specific SNR threshold is derived to determine that the relay can choose to transmit message in decode-and-forward (DF) or AF mode. Closed-form expressions of the outage probability of the proposed HDAF and HADF schemes are derived. Theoretical analysis and simulation results show that the HADF scheme outperforms the AF and DF schemes, and the HDAF relaying scheme outperforms the DT and AF schemes. However, compared with HDAF scheme, the HADF scheme has a better outage probability in special channel condition.

Cross-layer design of AMC and truncated HARQ using dynamic switching thresholds

In this paper, we develop a cross-layer design incorporating adaptive modulation coding (AMC) and truncated hybrid automatic repeat request (HARQ). We define different packet error rate (PER) constraints for each (re)transmission, thus adopting dynamic switching thresholds correspondingly to fully exploit the combining gain in HARQ protocols. Analytical expressions for performance metrics are derived, based on which both multidimensional and simplified single-dimensional optimization problems are proposed to maximize the average spectral efficiency. Numerical results are obtained for analysis and our design has shown considerable performance improvement compared with conventional switching thresholds. Moreover, the single-dimensional optimization approach implies a suitable tradeoff between throughput and complexity.

Constellation Design for Odd-Bit Quadrature Amplitude Modulation

In this paper, we study the constellation design of quadrature amplitude modulations (QAMs) with odd number of bits per symbol. A square constellation, which adopts symmetrical Gray labeling, is proposed. Simplified mapping and demapping methods are also designed for it. Performance of the proposed square constellation is compared with that of conventional rectangular and cross constellations. As simulation results show, the proposed square constellation obtains better BER performance when channel coding is used in communication systems. Moreover, it achieves much lower realization complexity than cross constellation by using the proposed mapping and demapping method.

On Hybrid Multiple Access and Its Reuse Partitioning

The cyclic prefix comb spectrum code division multiple access (CP-CS-CDMA) has comb spectrum in frequency domain. Its different code groups can be separated with a simple hopping accumulator. In the paper, we combine OFDMA and CP-CS-CDMA, and propose a new multiple access scheme, hybrid multiple access (HMA). Then we propose a new reuse partitioning system with HMA. The cell of the system has two regions: the inner region with OFDMA and the outer region with CP-CSCDMA. The proposed system makes full use of the advantages of OFDMA and CDMA to improve the performance. Theoretical analysis and simulation results have verified that our HMA and the new reuse partitioning system significantly increase the capacity compared with the conventional OFDMA system.

Feedback compression for time-correlated MIMO block-fading channels using huffman coding

In this paper, we investigate feedback compression for a general multiple-input multiple-output (MIMO) system over time-correlated Rayleigh block-fading channels. With a channel state transition graph characterized by Markov chain, we first compress channel state information (CSI) feedback through Huffman coding. We then propose a threshold based approach by neglecting the states with small transition probabilities with slight performance loss to further reduce the feedback rate. Finally, we study the relationship between the channel ergodic capacity and feedback rate with water-filling precoding. Analysis and simulation show that the feedback rate can be significantly reduced by the proposed algorithms.

QRP08-6: A Novel Unicast based Multiplexing Scheme to Guarantee the QoS of VoWLAN

The mergence of VoIP and WLAN has created a new wireless platform for voice service delivery - VoWLAN. Focusing on the hot spot of WLAN research, we figure out the capacity bottleneck of VoWLAN and the QoS problem of the VoIP service existing in current solutions such as M-M (Multicast Multiplexing) scheme. A novel unicast multiplexing (U-M, Unicast Multiplexing) scheme to improve the voice capacity and guarantee the QoS of VoIP service in WLAN is proposed. Both theoretical and simulation results show that the U-M scheme doubles the number of VoIP users in VoWLAN as compared with traditional scheme and reduces the packet lost rate by nearly 10% as compared with M-M scheme. Meanwhile, U-M is also a power-saving scheme in the voice-dominant application typical of VoWLAN.