Kazushi Muraoka

Channel Estimation using Differential Model of Fading Fluctuation for EM Algorithm Applied to OFDM MAP Detection

This paper proposes a new channel estimation method for the expectation-maximization (EM) algorithm applied to an OFDM receiver. Conventional schemes using the EM algorithm assume the random walk model as a process equation of a channel impulse response, and thus have insufficient tracking ability to fading fluctuation over fast fading channels. To improve the tracking ability, the proposed channel estimation method employs the differential model having the first and higher order differentials of the channel impulse response with respect to time. Computer simulations under the fast fading condition demonstrate that the proposed method is much superior in packet error rate to the conventional schemes employing the random walk model.

Iterative Signal Detection of EM-Based Receivers with Multiple Antennas for OFDM Communications

Joint signal detection and channel estimation based on the expectation-maximization (EM) algorithm has been investigated for orthogonal frequency-division multiplexing (OFDM) mobile communications over fast- fading channels. In order to make the signal detection suitable for the iterative EM-based receiver with multiple antennas, this paper proposes spatial removal from the perspective of a message- passing algorithm on factor graphs. The spatial removal performs the channel estimation of a targeted antenna by using detected signals that are obtained from the received signals of all antennas other than the targeted antenna. It can avoid the repetitive use of unreliable received signals for consecutive signal detection and channel estimation. Computer simulations under fast-fading conditions demonstrate that appropriate application of the spatial removal can exploit such a removal effect and the spatial diversity, resulting in improvement of the packet error rate (PER).

Interleaved Resource Mapping for Autonomous Device-to-Device Discovery in Public Safety LTE

Device-to-device (D2D) discovery is an important function for public safety long term evolution (PS-LTE) to detect user equipment (UE) located in proximity. When many UEs are gathered at a disaster site or an incident command post, in-band emission (IBE) of discovery signals can cause significant interference resulting in discovery errors. In order to reduce the effect of IBE, a radio resource mapping method is proposed for autonomous D2D discovery in a PS-LTE system configured to repeatedly transmit discovery signals over different subframes. The proposed method interleaves discovery resources so that retransmission on resources with a certain frequency gap follows transmission on adjacent resources. Simulation results revealed that the proposed method takes 10% less time to detect UEs than a conventional method does.

Scheduling for Device-to-Device Communication Considering Spatial Reuse and User Fairness in Public Safety LTE

Public safety networks are desired to meet increasing demands for sharing images or videos among first responders and incident commanders. Long term evolution (LTE) is considered a candidate to achieve such broadband services. However, in the case of a disaster or a big sporting event, the traffic suddenly increases sharply as the number of active public safety users increases. This paper reports methods for allocating radio resources for device-to-device (D2D) communication as a means to enhance system capacity of the public safety LTE (PS-LTE). The methods allow spatial reuse of the resources among D2D communicating public safety users satisfying certain sharing conditions. Two practical scheduling algorithms that take into account both spatial reuse of the resources and fairness between the D2D communicating users are described. System level simulation results reveal that the methods can increase the number of users that satisfy the throughput requirement for video transmission.

Iterative MAP Channel Estimation Based on Factor Graph for OFDM Mobile Communications

To maintain good transmission performance of orthogonal frequency-division multiplexing (OFDM) mobile communications over fast-fading channels, iterative maximum a posteriori (MAP) receivers that iterate channel estimation and signal detection on the basis of the expectation-maximization (EM) algorithm have been investigated. In order to make such a MAP receiver more robust against time-variant channels, this paper derives channel estimation with subcarrier removal from the perspective of a message-passing algorithm on factor graphs. The subcarrier removal estimates the channel frequency response by using the detected signals of all subcarriers other than that of a targeted subcarrier. This modification can avoid the repetitive use of incorrectly detected signals for the channel estimation. Computer simulations under fast-fading conditions demonstrate that the EM-based MAP receiver performing the subcarrier removal can improve the packet error rate (PER) drastically.