Sequans

About: Sequans is a company organization based out in Reading, United Kingdom. It is known for research contribution in the topics: Communication channel & MIMO. The organization has 73 authors who have published 126 publications receiving 1066 citations.

Fast varying channel estimation in downlink LTE systems

Abstract: This paper tackles the problem of fast varying channel estimation in LTE systems. Particular attention is given to downlink transmission where OFDMA is used as the multiple access technique for the air interface. In OFDMA, fast variation of the channel results in significant inter-carrier interference (ICI) which cannot be mitigated with conventional estimation and equalization techniques. In this paper, we investigate the polynomial modeling of rapidly time varying channels. Specifically, we propose a time-domain estimation method and a low-complexity frequency-domain estimation method both of which leverage the special structure of the approximated channel matrix to compute ICI channel components. It is shown by simulations that these two methods provide a considerable performance improvement over conventional methods by means of improved ICI mitigation. We further study the robustness of these two methods to both partial and full channel profile knowledge. It has been shown that the frequency-domain approach has much lower complexity and better robustness compared to the time domain approach.

Enhanced spatial modulation with multiple constellations

Abstract: Spatial modulation (SM) has recently drawn a great deal of attention, particularly due to the low complexity that it promises for both the transmitter and the receiver sides. However, this technique has a significant spectral efficiency loss with respect to spatial multiplexing (SMX) with the same number of transmit (Tx) antennas, and when the modulation order is increased to achieve the same spectral efficiency, it loses in terms of the bit error rate (BER). In this paper, a new type of SM (referred to as Enhanced SM) is proposed which increases the number of bits transmitted per channel use compared to conventional SM. Note that conventional MIσMO techniques including SMX and SM employ a fixed signal constellation. In our proposed technique, some information bits select not only the index(es) of the active antenna(s), but also the constellations to be transmitted from each of them. Both the closed-form analysis and the numerical results demonstrate that the proposed technique achieves better performance than conventional SM and that in most cases it also outperforms SMX.

Diversity, interference cancellation and spatial multiplexing in MIMO mobile WiMAX systems

Abstract: Multiple input multiple output (MIMO) techniques are an essential part of the IEEE 802.16e-2005 specifications, which form the basis of mobile WiMAX systems. In this paper, we first discuss the tradeoffs between diversity, interference cancellation and spatial multiplexing in MIMO systems, and we compare optimum combining (OC), maximum-ratio combining (MRC) and interference cancellation for different numbers of receive antennas. Then, we focus on the two mandatory MIMO profiles in the IEEE specifications (Alamouti's STC and the 2x2 spatial multiplexing scheme) and compare them when the first is combined with MRC at the receiver. The analysis obtained using the ITU pedestrian B channel in ideal conditions indicates that the two schemes lead to similar performance when they are operated at the same spectral efficiency

Method and system for synchronizing a base station of a wireless communication system and a subscriber communication equipment

Abstract: A method of synchronizing a base station of a wireless communication system and a subscriber communication equipment located in the coverage area of the base station by compensating a sampling frequency offset in the subscriber equipment by interpolating input and/or output signals of a radio frequency part of the communication equipment to generate samples corresponding to the original symbol timing of the base station, and compensating the carrier frequency offset from the estimate of the sampling clock error.

Full Frequency Reuse in Mobile WiMAX and LTE Networks with Sectored Cells

Abstract: Frequency reuse is an important topic in wireless communications systems. In this paper, we address the issue of frequency reuse in sectored cells which are subject to interfer-ence in the overlap regions of adjacent sectors. We propose to increase the number of sectors from 3 to 4 using conventional base station sector antennas with beam-width exceeding 120°, which purposely creates large overlap regions between adjacent sectors. Rather than treating the signals of adjacent sectors as interference, we investigate sector cooperation for communica-tion with users located in the overlap regions. Different scenarios are considered for user locations, and simulation results are given which illustrate the performance of the proposed schemes.