Fast Fading Channel Environment Research Articles

Inter-vehicle cooperation channel estimation for IEEE 802.11p V2I communications

The impact of imperfect channel state information (CSI) is particularly serious in vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications. Considering the sparse characteristics of V2I channels, this paper proposes an inter-vehicle cooperation channel estimation (IVC-CE) method at the IEEE 802.11p physical layer, and the effects of outdated CSI can be mitigated by single or multiple vehicle measurements. With these assisted measurements, we can develop an interpolation-assisted channel estimation technique to obtain accurate CSI. To select optimum measurements from a group of channel estimates, we utilize the position and velocity of a vehicle as a priori information. We investigate the validity of the IVC-CE technique with the traditional linear minimum mean-squared error algorithm and present a scalable data transmission scheme at the physical layer. The performance of IVC-CE is analyzed by its mean squared error and bit error rate in a fast fading channel environment. Simulations and numerical results show the merits of the proposed techniques, which can significantly enhance estimation performance and support safety related data transmissions for vehicular ad hoc networks.

Two-Dimensional Interpolation-Assisted Channel Prediction for OFDM Systems

Channel prediction can provide up-to-date information about the state of a channel in OFDM systems at the expense of increasing the complexity of wireless systems. Therefore, this paper proposes a novel approach for optimizing the shape and intervals between samples in two-dimensions (2-D) for an orthogonal frequency-division multiplexing (OFDM) system to reduce the complexity of predicting the channel frequency response (CFR). Furthermore, the proposed prediction scheme has the flexibility to integrate with an adaptive algorithm which does not require any statistical prior knowledge and is able to track nonstationary channel statistics. The number of multipliers that are required to predict the CFR is reduced by predicting the CFRs at particular subcarriers and incorporating interpolation methods. This paper also deals with the proposal of a 2-D curve fitting (CF) interpolator to be used for predicting the CFR that allow improving the accuracy of the CFR prediction. Simulation and analysis results demonstrate that the 2-D CF interpolator combined with the proposed scheme has lower complexity than the other approaches to predicting CFR, without compromising the mean square error (MSE) or bit error ratio, even in a noisy and fast-fading channel environment.

Adaptive modulation based MC-CDMA systems for 4G wireless consumer applications

Adaptive modulation based MC-CDMA systems can play a vital role in future generation consumer communication electronics. Adaptive modulation, combined with MC-CDMA based transmission technology, is a promising way to increase the data rate that can be reliably transmitted over the wireless radio channels. For 4G wireless networks, which demand very high data rate up to 100 Mbits/s with the constraints limiting higher data rate being severe ISI due to multipath and limited spectrum, such kind of adaptive modulation based multi-carrier systems applied to a wide-area environment, can achieve very large average user throughputs. In this paper, adaptive modulation based M-ary PSK, M-ary QAM, M-ary CPM, M-ary MHPM and GMSK systems applied to a turbo coded MC-CDMA system in a Rayleigh fast fading channel environment have been investigated and the BER performance of all these digital modulation techniques have been compared. Results of the comparative study indicate that the continuous phase modulation schemes like CPM, MHPM, and GMSK gives better performance as compared to PSK and QAM schemes. At most of the time, the MHPM systems outperforms both GMSK and CPM. The PSK and QAM based systems perform well till the number of users are around 10. As a whole, the adaptive MHPM system is found to give the optimum performance among the considered digital modulation schemes for the MC-CDMA system in a 4G environment.

Performance limitation of closed-loop transmit antenna diversity over fast Rayleigh fading channels

Previously, transmit antenna diversity (TAD) has been considered as a key technique to improve the capacity of wireless systems over a fading channel. A type of TAD is closed-loop TAD, which utilizes channel conditions. Closed-loop TAD has a drawback caused by the feedback delay under a fast fading channel environment. If the channel information is outdated due to the feedback delay, the performance can be severely degraded. In this correspondence, we find the bit error rate (BER) of the closed-loop TAD with the feedback delay for a time-variant Rayleigh fading channel. For example, it is observed that there is about 2-dB degradation at the BER of 10-2 when four transmit antennas are used, and the feedback delay is 5 ms with the updating rate 400 Hz.