Spatial Performance Analysis and Design Principles for Wireless Peer Discovery

In wireless peer-to-peer networks that serve various proximity-based applications, peer discovery is the key to identifying other peers with which a peer can communicate and an understanding of its performance is fundamental to the design of an efficient discovery operation. This paper analyzes the performance of wireless peer discovery through comprehensively considering the wireless channel, spatial distribution of peers, and discovery operation parameters. The average numbers of successfully discovered peers are expressed in closed forms for two widely used channel models, i.e., the interference limited Nakagami-m fading model and the Rayleigh fading model with nonzero noise, when peers are spatially distributed according to a homogeneous Poisson point process. These insightful expressions lead to the design principles for the key operation parameters including the transmission probability, required amount of wireless resources, level of modulation and coding scheme (MCS), and transmit power. Furthermore, the impact of shadowing on the spatial performance and suggested design principles is evaluated using mathematical analysis and simulations.Comment: 12 pages (double columns), 10 figures, 1 table, to appear in the IEEE Transactions on Wireless Communication

Adaptive channel estimation in WCDMA STTD systems

The receiver performance with the use of a space time transmit diversity (STTD) scheme is more susceptible to the accuracy of channel estimate than that without the use of the STTD scheme since the despreading signals suffer from the effect of crosstalk and the transmit power is equally divided into multiple transmit antennas. As a result, the efficiency of channel estimation in the WCDMA STTD system becomes an important issue more than that in the non-STTD system. In this paper, an adaptive channel estimator (ACE) is designed to mitigate the performance degradation due to inaccurate channel estimation. Numerical results show that the performance improvement significantly increases with the use of the proposed ACE, particularly when the channel condition becomes worse

Optimum pilot pattern for channel estimation in OFDM systems

The performance of channel estimation in orthogonal frequency division multiplexing (OFDM) systems significantly depends on the pilot signal, which is usually scattered in time and frequency domains. For a given pilot density, the authors optimally design the pilot pattern so as to minimize the mean squared error (MSE) of the channel estimate with the use of a general interpolator. The analytic results are verified by computer simulation

Optimum pilot pattern for MMSE channel estimation in single-carrier MIMO systems

The minimum mean squared error (MMSE) channel estimator (CE) can provide receiver performance better than the least square (LS) CE. However, the MMSE CE usually uses a pilot pattern optimally designed for the LS CE. In this paper, we derive an optimum pilot pattern for the MMSE CE in single-carrier MIMO systems assuming that both the transmitter and receiver know the average channel information, such as the channel correlation matrix and signal to interference and noise power ratio. Analytic and simulation results show that the MMSE CE with the use of the proposed pilot pattern can reduce the MSE compared to the use of one optimized for the LS CEThis work was supported (in part) by the Ministry of Information & Communications, Korea, under the Information Technology Research Center (ITRC) Support Program

Design of a Channel-Aware OFDM Transceiver

The transmission performance of an OFDM system can significantly be improved by exploiting the channel characteristics. In this paper, we consider the design of a channel-aware OFDM transceiver whose parameters are adjusted in response to the change of channel condition. To this end, we first estimate the channel state information (CSI), such as the signal to interference power ratio, low order moments of Doppler spectrum and power-delay profile of the channel. The proposed CSI estimator can estimate these CSI parameters altogether in a unique manner by exploiting the autocorrelation properties of the channel impulse response (CIR). Then, we design a CIR estimator and adaptive OFDM modulator that adjust their parameters according to the estimated CSI. Finally, we verify the performance of the proposed OFDM transceiver by computer simulation.This work was in part supported by the Ministry of Information & Communications, Korea, under the Information Technology Research Center (ITRC) Support Program

Amplify-and-Forward Distributed Beamforming with Local CSI in the Presence of Interferences

This paper introduces an optimum amplify-and-forward (AF) distributed beamforming (DBF) in the presence of cochannel interference (CCI) when only local channel-state information (CSI) is available at each relay. It is shown that the proposed DBF closely achieves the performance obtained with global CSI when interference power toward relays is small or there are a large number of interferers but greatly reduces the complexity and overhead. The proposed DBF provides significant improvements over the conventional DBF designed without considering CCI at the cost of slightly increased complexity and overhead and achieves the capacity scaling of 1/2log⁡K through K relays, where 1/2log⁡K corresponds to the maximal capacity scaling when there is no CCI

A Hybrid Channel Estimation Scheme for OFDM Systems

Accurate channel information is indispensable for coherent reception of OFDM signal. Although a Wienertype channel estimation filter (CEF) is known optimum, it is not easily employable due to large implementation complexity. In practice, a moving average (MA)-type CEF is often employed, but it may not provide robust performance to the variation of channel condition. In this paper, we propose a hybrid CEF that takes advantages of both the Wiener and MA CEF, by alternatively employing the CEF according to the channel condition. Simulation results show that the proposed hybrid CEF scheme provides near optimum performance, while significantly reducing the implementation complexity compared to the long tap Wiener CEF