Showing papers by "Sequans published in 2019"

Multicast and Broadcast Enablers for High-Performing Cellular V2X Systems

Abstract: This paper focuses on capabilities enabled by 5G connectivity in the cooperative, connected and autonomous cars, and elaborates on two technical enablers. One of the technical enablers consists of a beamformed broadcast/multicast technology that builds on adaptive and robust beam management techniques at the air interface. The other proposed technical component aims to improve the end-to-end architectural design of 5G networks to enable efficient broadcast and multicast transmissions for vehicle-to-anything services. Finally, the key results of multicast and broadcast technical components are described and ongoing and future areas of work and research are detailed.

Bridging Spatial Modulation With Spatial Multiplexing: Frequency-Domain ESM

Abstract: Spatial modulation (SM) is a multi-input multi-output (MIMO) technique, which was originally introduced to reduce the number of radio frequency (RF) chains in a MIMO transmitter and thereby reduce cost and power consumption. Although it is very appealing in theory, this concept actually has two main problems: The first is that SM involves antenna switching, which degrades the spectral shaping and the Nyquist property of the transmitted signal. The second is the limited spectral efficiency due to the presence of silent antennas. In order to remedy the second problem, enhanced spatial modulation (ESM) was introduced in which multiple signal constellations are used, and information bits are conveyed not only by the transmitted symbols and the indices of the active antennas, but also by the constellation types activated. As for the problem of antenna switching, it actually disappears when SM is combined with OFDM, because the switching operation in frequency-domain SM (FD-SM) occurs at baseband. But the number of RF chains required becomes equal to the number of transmit antennas and the property of reduced number of RF chains, which was the original motivation for SM also disappears. FD-SM turns out to be a particular type of underloaded MIMO-OFDM system, which reduces the power requirements of the transmit power amplifiers rather than their number. In this paper, we introduce frequency-domain ESM (FD-ESM), which avoids both the spectral efficiency limitations and the antenna switching issues of the original SM. Exploiting the property that switching occurs at baseband and no savings in terms of the number of RF chains can be achieved in frequency-domain implementation, we design FD-ESM schemes in which the transmitted codewords do not include any zero-valued components. These designs bridge the concept of SM with spatial multiplexing, and they provide spectacular gains with respect to multi-stream SM (MSM) and also some significant gains compared to conventional spatial multiplexing.

Power-Domain NOMA or NOMA-2000?

Abstract: Non-Orthogonal Multiple Access (NOMA) has been a hot research topic in recent years, because it is widely advocated that this technique represents a promising technology for 5G cellular networks and beyond. The NOMA literature today is heavily based on the so-called Power-Domain NOMA (PD-NOMA), which requires a strong power imbalance between the signals assigned to different users. Also, the focus in the literature has been on the derivation of achievable rates, which represent an information theoretic measure. In contrast, the signal-to-noise ratio (SNR) degradation that is caused by multiuser interference at practical bit error rate (BER) values has not attracted much attention. In some recent papers, the present authors revived an early NOMA concept, which had been rather overlooked in the recent NOMA literature. This concept, which we refer to as NOMA-2000, consists of superposing the signals of two user groups with different signal waveforms rather than the signals of two users. In our earlier papers, performance of NOMA-2000 was investigated in various conditions, but no comparisons were provided with PD-NOMA. The purpose of this paper is to compare the BER performances of the two schemes using several values of the power splitting factor between users. The results confirm that PD-NOMA suffers a strong SNR degradation and that NOMA-2000 provides substantially better performance in general.

Signal Design for Frequency-Domain Enhanced Spatial Modulation

Abstract: Spatial Modulation (SM) was first introduced to reduce the number of radio frequency (RF) chains in a multiple-input multiple-output (MIMO) transmitter and thereby reduce cost and power consumption. Although it is very appealing in theory, this concept actually has two main problems, which are not sufficiently highlighted in the existing literature: The first is that the antenna switching involved destroys the spectral shaping of the transmitted signal, and the second is the limited spectral efficiency due to the presence of silent antennas. In order to remedy the second problem, Enhanced Spatial Modulation (ESM) was introduced. As for the problem of antenna switching, it actually disappears when SM is implemented in the frequency-domain, because the switching operation in Frequency-Domain SM (FD-SM) occurs at baseband. But the number of RF chains needed becomes equal to the number of transmit antennas. In this paper, we investigate Frequency-Domain ESM (FD-ESM), which avoids both the spectral efficiency limitations and the antenna switching of the original SM. Exploiting the property that switching occurs at baseband and no savings in terms of the number of RF chains can be achieved in frequency-domain implementation, we design FD-ESM schemes which provide spectacular gains with respect to conventional Multi-Stream SM (MSM) and also significant gains compared to spatial multiplexing.

Packet Recovery Latency of a Rate-less Polar Code in Low Power Wide Area Networks

Abstract: In this paper, we consider a Low Power Wide Area Networks (LPWAN) operating in a licensed-exempt band. In order to enhance the receiver sensitivity, low complexity repetition schemes that benefit from the time-varying channel condition are widely used. In this case, successful data recovery requires a significant channel variation from a bad to a good state depending on the data rate. This induces a relatively high decoding latency especially for slow time-varying channel. The main objective of this paper is to reduce the packet recovery latency by exploiting multiple channel states defined with respect to various transmission data rates, that are enabled by a rate-less polar code. We characterize the good channel sequence state of this code, and evaluate its latency performance in a slow and fast-time varying context.

LTE Channel Estimation

Abstract: A method for channel estimation in LTE, the method comprising decoding a received LTE signal comprising a message, and when a CRC of the decoder indicates successful decoding of a subframe, estimating the content of the message transmitted to the decoder, de-rotating the received LTE signal based on the estimated content of the message transmitted to the decoder to calculate pseudo pilot signals for all resource elements on which the corresponding physical downlink shared channel ‘PDSCH’ is mapped.

Messaging scheme for positioning

Abstract: A method of providing position assistance to a UE, the method comprising providing, by a location server, at least one unsolicited message, each message comprising one of data selected from a list comprising GNSS ephemeris assistance data, GNSS acquisition assistance data, OTDOA assistance data and eNB position data for a predefined area.

Performance Analysis of Reciprocity Calibration in Massive MIMO

Abstract: Time Division Duplexing (TDD) Massive MIMO (MaMIMO) relies on channel reciprocity to derive the channel state information at the transmit side (CSIT) from the uplink (UL) channel estimates. This reciprocity is impacted by the transmit and receive front ends which are non-reciprocal and hence a calibration is required to obtain the downlink (DL) channels from the UL channel estimates. The Cramer-Rao Bound (CRB) for reciprocity calibration and an optimal algorithm were derived in [1], [2] recently. In this work, we extend this and derive a generalized CRB that applies to both coherent and non-coherent calibration schemes (introduced in [1]). More importantly, we provide original mean squared error analysis for the commonly used Least-Squares (LS) estimator under different parameter constraints, and relate it to the CRB. Finally, we compare some antenna grouping strategies for calibration based on their CRB.