Research Letters in Communications 

About: Research Letters in Communications is an academic journal. The journal publishes majorly in the area(s): Hybrid automatic repeat request & Matrix (mathematics). It has an ISSN identifier of 1687-6741. It is also open access. Over the lifetime, 26 publications have been published receiving 297 citations.

Multiuser scheduling on the downlink of an LTE cellular system

Abstract: The challenge of scheduling user transmissions on the downlink of a long-term evolution (LTE) cellular communication system is addressed. In particular, a novel optimalmultiuser scheduler is proposed. Numerical results show that the system performance improves with increasing correlation among OFDMA subcarriers. It is found that only a limited amount of feedback information is needed to achieve relatively good performance. A suboptimal reduced-complexity scheduler is also proposed and shown to provide good performance. The suboptimal scheme is especially attractive when the number of users is large, in which case the complexity of the optimal scheme is high.

The distribution of path losses for uniformly distributed nodes in a circle

Abstract: When simulating a wireless network, users/nodes are usually assumed to be distributed uniformly in space. Path losses between nodes in a simulated network are generally calculated by determining the distance between every pair of nodes and applying a suitable path loss model as a function of this distance (power of distance with an environment-specific path loss exponent) and adding a random component to represent the log-normal shadowing. A network with N nodes consists of N(N - 1)/2 path loss values. In order to generate statistically significant results for system-level simulations, Monte Carlo simulations must be performed where the nodes are randomly distributed at the start of every run. This is a time-consuming operation which need not be carried out if the distribution of path losses between the nodes is known. The probability density function (pdf) of the path loss between the centre of a circle and a node distributed uniformly within a the circle is derived in this work.

Design LDPC codes without cycles of length 4 and 6

Abstract: We present an approach for constructing LDPC codes without cycles of length 4 and 6. Firstly, we design 3 submatrices with different shifting functions given by the proposed schemes, then combine them into the matrix specified by the proposed approach, and, finally, expand the matrix into a desired parity-check matrix using identity matrices and cyclic shift matrices of the identity matrices. The simulation result in AWGN channel verifies that the BER of the proposed code is close to those of Mackay's random codes and Tanner's QC codes, and the good BER performance of the proposed can remain at high code rates.

Modeling distance and bandwidth dependency of TOA-based UWB ranging error for positioning

Abstract: A statistical model for the range error provided by TOA estimation using UWB signals is given, based on UWB channel measurements between 3.1 and 10.6 GHz. The range error has been modeled as a Gaussian random variable for LOS and as a combination of a Gaussian and an exponential random variable for NLOS. The distance and bandwidth dependency of both the mean and the standard deviation of the range error has been analyzed, and insight is given in the different phenomena which affect the estimation accuracy. A possible application of themodel to weighted least squares positioning is finally investigated. Noticeable improvements compared to the traditional least squares method have been obtained.

Precoded DOSTBC over Rayleigh channels

Abstract: Differential orthogonal space-time block codes (DOSTBC) sent over correlated Rayleigh fading channels are considered in this paper. Approximate expressions for the symbol error rate (SER) are derived for DOSTBC with M-PSK, M-PAM, and M-QAM constellations assuming arbitrary correlation between the transmit and receive antennas. A full memoryless precoder is designed to improve the performance of the DOSTBC over correlated Rayleigh MIMO channels. The proposed precoder design differs from the previous work: (1) our precoder design considers arbitrary correlation in the channels, whereas the previously proposed precoder design considers only transmit correlations in the Kronecker correlation model; (2) the proposed precoder is based on minimizing proposed SER, whereas the previously proposed precoder is based on minimizing the Chernoff bound of approximate SER; (3) we propose precoder design for DOSTBC with M-PSK, M-PAM, and M-QAM constellations, whereas the previously proposed precoder works for DOSTBC with M-PSK only. Additionally, the proposed precoded DOSTBC outperforms the conventional eigenbeamforming-based precoded DOSTBC for the Kronecker model with only transmit correlation.