Performance Analysis of Low-Complexity Simply-Differential Time Synchronization Approach for MTC over LTE Systems

A major challenge in low power sensor networks is collecting data from large number of nodes with low latency. Access point (AP) typically needs to poll large number of nodes individually and schedule transmission times for each of the nodes resulting in large latency. In this paper, we propose a physical layer technique that parallelizes the polling response from multiple nodes (so called parallel acknowledgment) in order to decrease the latency. Each node responds to the poll request of an AP by using the well-known Zadoff-Chu (ZC) sequences. By using the orthogonal properties of the ZC sequences, the AP is able to resolve the multiple signatures of different nodes simultaneously. We further develop low complexity transmission scheme for the ZC sequences in order to reduce the number of computations and complexity required by the low power sensor nodes. We also compare the performance of both time and frequency domain receivers.

In order to coexist with the WiFi systems in the unlicensed spectrum, Long Term Evolution (LTE) networks can utilize periodically configured transmission gaps. In this paper, considering a time division duplex (TDD)-LTE system, we propose a Q-Learning based dynamic duty cycle selection technique for configuring LTE transmission gaps, so that a satisfactory throughput is maintained both for LTE and WiFi systems. By explicitly taking the impact of IEEE 802.11n beacon transmission mechanism into account, we evaluate the coexistence performance of WiFi and LTE using the proposed technique. Simulation results show that the proposed approach can enhance the overall capacity performance by 19% and WiFi capacity performance by 77%, hence enabling effective coexistence of LTE and WiFi systems in the unlicensed band.

The fast growth of drone applications in industrial, commercial and consumer domains in recent years has caused great security, safety and privacy concerns. For this reason, a demand for solutions of drone detection and monitoring in consumer market can be foreseen in the near future. For detecting drones that employ Zadoff-Chu (ZC) sequences for synchronization, these ZC sequences can be used to determine their presence in the air. However, it is a great challenge to blindly detect thousands of unknown ZC sequences possibly used by the drones in real time. Existing solutions mainly developed for LTE systems cannot be directly applied to the blind detection of ZCs in drones without incurring huge cost. In this paper, a low-complexity cost effective blind ZC detection method based on double differential is proposed for low-cost drone detection and monitoring systems. Signal-to-noise ratio (SNR) lower bounds are analytically derived for low and high SNR regimes. Monte Carlo simulations show the proposed scheme performs well in moderate and high SNR.

Multiple input multiple output (MIMO) technique that requires multiple antennas at both transmitter and the receiver is a key technology to meet the peak data rates and spectral efficiency targets of long term evolution (LTE) systems. MIMO is a widely researched topic, and understanding of MIMO concepts have an interaction with other essential enhancement mechanisms in the system including link adaptation, resource scheduling, inter stream interference, rank of the channel, etc. This paper mainly aims to target the MIMO mode adaptation strategies in LTE systems by considering the rank and other key parameters like antenna correlation, doppler frequency, bit rate, throughput, etc. 3GPP LTE rel-8 has adopted seven MIMO modes and variable modulation and coding schemes (MCS) to effectively utilize the available resources for maximizing the throughput of the system. In this paper, new techniques for obtaining appropriate rank and a new MIMO mode switching algorithm to maximize data rate of the user equipment (UE) for a given channel consider at the receiver with reasonable complexity, and there by improving the average system throughput are proposed. The paper considers only four MIMO modes namely transmit diversity, open loop spatial multiplexing (OLSM), closed loop spatial multiplexing (CLSM) and beam-forming with different modulation levels. MIMO mode switching is done based on throughput value between open loop modes namely transmit diversity and OLSM for high mobility UE in the presence of co channel interference (CCI). Similarly, mode switching is done between closed loop modes namely CLSM and beam-forming for pedestrian UE in the presence of CCI. Simulation results are provided to illustrate the performance benefits of the proposed algorithm. The simulation results reveal that these new techniques improves the system throughput significantly.

Coexistence research for LTE systems is indispensable to ensure that the time division duplex (TDD) Long Term evolution (LTE) system can coexist with the frequency division duplex (FDD) LTE system operating at the adjacent frequency band within the same geographical area. Previous studies on this topic only focus on the throughput loss of the victim system from the data channel viewpoint. In this paper, the performance of control channels (CCHs) in the typical coexistence scenario is investigated, since the performance of communication systems is largely dependent on the quality of CCHs. The CCHs' interferences are analyzed in detail, including the coexistence issue for CCHs, Co-Channel Interference (CCI) analysis, and Adjacent Channel Interference (ACI) on CCHs. The simulation results indicate that the ACI generated by the Base Station (BS) of collocated LTE system degrades the performance of the uplink (UL) CCHs of the victim LTE system significantly.

This paper proposes a downlink synchronization and cell identity (CID) estimation technique for cellular systems based on orthogonal time-frequency space (OTFS). In the proposed technique, each base station (BS) transmits one detection preamble (DP) and two OTFS symbols (pilot and secondary-CID (SCID) signal (SS)). The DP based on a linear frequency-modulated (LFM) waveform, called proposed-LFM (pLFM), carries the primary-CID (PCID) for symbol timing (ST) synchronization, whereas the SS based on the Zadoff-Chu (ZC) sequence mapped in the delay-Doppler domain carries the SCID. The pLFM is obtained by discretizing the LFM waveform, increasing the frequency sweeping parameter beyond the limit of the operational bandwidth, and incorporating the PCID into the LFM waveform. The autocorrelation and cross-correlation functions of the pLFM are analyzed to examine its correlation properties under the influence of a high Doppler shift. To reduce the undesirable correlation properties (side peak and time ambiguity), a receiver processing (RP) scheme is developed for the pLFM. It is found that the pLFM with RP is suitable for the DP design because it can provide an accurate ST in high-mobility scenarios. In addition, the influence of OTFS modulation on the ZC sequence is derived and a low-complexity detection algorithm based on message passing is applied to detect SCID at the user equipment. The simulation results demonstrate that the proposed downlink synchronization and CID estimation techniques are suitable for OTFS-based cellular systems in high-Doppler environments.

The fifth-generation (5G) mobile network is facing severe challenges of the traffic demand surge and spectrum scarcity. To improve the network capacity and data rate, the deployment of Long Term Evolution (LTE) cellular system on unlicensed band is considered as one of the promising solutions. But the interference problem among LTE and WiFi system on the same unlicensed band hinders the deployment process, which is a critical issue unsolved for network operators. Therefore, a novel channel access scheme integrating the energy detection scheme and back-off mechanism in LTE system has been proposed in this paper, to minimize the interference to WiFi system. The throughput of both LTE and WiFi systems and the optimal sensing time and back-off time are theoretically analyzed with proofs. Furthermore, an efficient adaptive reconfiguration strategy of access parameters is proposed based on the channel occupancy cognition results. Simulation results verify that the proposed channel access scheme with optimal back-off time can double the throughput of WiFi system when coexisting with LTE system on unlicensed band.

In this paper, the truncated singular value decomposition expectation-maximization (TSVD-EM) based channel estimation on single transmit antenna transmission is extended to transmit diversity transmission. Particular attention is given to Long Term Evolution (LTE) systems. In order to obtain the received symbols for each transmit antenna, an approximation is proposed by using the soft symbols and channel estimates from the previous iteration. We prove that the mean square error (MSE) of TSVD-EM on transmit diversity transmission has almost the same constant value at high signal-to-noise ratio (SNR) as on single transmitter antenna case. Simulation results show that the proposed TSVD-EM channel estimation improves system performances remarkably and approaches the performance with perfect channel state information. Even without pilot boosting used in LTE systems, the TSVD-EM achieves the same performances as with pilot boosting.

Radar interference into LTE base stations in the 3.5 GHz band

A frequency-domain cepstrum correlation and temporal transient filtered radio frequency fingerprints (RFF) blind extraction method is proposed for long term evolution uplink device authentication in this work. With the merits of the constant-modulus nature of the Zadoff-Chu (ZC) sequence and the cyclic prefix (CP) structure of the physical random access channel (PRACH) frame, the device RFF integrated in both the frequency-domain ZC sequence and the transient ramp-on/ramp-off sequences are extracted. For the frequency-domain RFF extraction, the cepstrum of the ZC sequence is calculated to enlarge the gap between the constant RFF and the random fading effects, and the correlation between two cepstrum fragments is then calculated to mitigate the random fading components. For the temporal RFF extraction, the ramp-on and ramp-off features induced by the device-specific power amplifier are extracted by exploiting the CP structure of the PRACH frame, where the CP part and the duplicate part are adaptively filtered and the final adapted weight of the least mean square filter is used as RFF. No prior PRACH parameter knowledge is required in RFF extraction and both the frequency-domain and the temporal RFF are combined as the input of the convolutional neural network to enhance the classification accuracy. With four-months sampling of PRACH signals emitted from universal software radio peripheral devices, the experimental results show that the authentication accuracy of the proposed combined RFF can reach as high as 99.9% in the line-of-sight (LOS) scenario and 99.6% in the non-LOS scenario.

The new radio (NR) system is recently proposed to deploy alongside the long term evolution (LTE) system to improve the wireless communication capacity. The Vandermonde-subspace frequency division multiplexing (VFDM) is an efficient technique for such a two tier network, whereby the NR transmitter can reuse the frequency spectrum of LTE system meanwhile guaranteeing interference free to LTE. In this paper, we first investigate the robust rate-maximization problem in the VFDM system. In the condition of imperfect channel state information (CSI), the precoder is optimized to satisfy both non-interference to LTE system and rate-maximization in the NR system. To tackle the challenge in solving such a non-convex problem, an iterative algorithm is proposed based on the block coordinate descent (BCD) and penalty dual decomposition (PDD) methods. Finally, simulation results demonstrate the superiority of the proposed algorithm in terms of robustness and achievable rate over the conventional SVD-based VFDM technique.

In order to satisfy the requirement of reliability in the TD-LTE RF Conformance Testing Instrument, a method to achieve the synchronization of protocol and physical layer based on embedded system is imposed. According to the feature of the long term evolution (LTE) system, it highlights the details to enhance the synchronization between various aspects in the LTE system through General-Purpose Memory Controller (GPMC) from ARM. GPMC is a memory controller that helps achieve the primitive interaction between the protocol and physical layer and the application. What is more important is that GPMC achieves the coordination that means LTE works at the same time in the same frame of the same sub-frame. Verified multiple times this design achieves the synchronization of aspects in LTE as well as meets the requirement of hardware platform in TD-LTE RF Conformance Testing Instrument.

In this paper, a new preamble design technique that can increase the number of cell IDs (CIDs) and beam IDs (BIDs) significantly is proposed, using a preamble sequence constructed by a combination of two Zadoff-Chu (ZC) sequences. An efficient technique for the CID and BID (CBID) detection is also described for the proposed preamble. It is shown by simulations using a simple model of an mmWave cellular system that the proposed technique can obtain a significant reduction in the complexity of the CBID detection without a noticeable performance degradation, compared to the previous technique.

In this letter, new sets of non-orthogonal spreading sequences are constructed for uplink grant-free access of devices. Based on Golay complementary sequences and sets, the spreading sequences have theoretically bounded low peak-to-average power ratio (PAPR) for multicarrier transmission. Also, the corresponding spreading matrix has theoretically bounded low coherence, which guarantees the reliable performance of compressed sensing (CS) based joint channel estimation (CE) and multiuser detection (MUD). While the spreading sequence set accommodates up to 300% overloaded devices, a large number of distinct sequence sets can also be constructed for future applications. Simulation results demonstrate that the Golay-based sequences exhibit the PAPR of at most 4, which is lower than those for random bipolar, Gaussian, and Zadoff-Chu (ZC) sequences. We also observe that the Golay-based sequences provide the reliable performance for CS-based joint CE and MUD. Finally, the Golay-based sequences have fewer phases than ZC sequences, which can be more suitable for low cost devices in machine-type communications (MTC).

In Long Term Evolution (LTE) system the Tracking Area (TA) is a group of cells in which User Equipment (UE) may move freely without performing location update process. The TA scheme has many limitations such as ping-pong effect and massive mobility signaling congestion. To overcome the limitations of the TA scheme, Tracking Area List (TAL) scheme is introduced. TAL is a group of TAs and if a UE is registered to one TAL it will not perform TAL update. In LTE system mobility management techniques are used to keep track of the current location of the UE which are location update and paging techniques. These techniques induce system overhead in both system signals and bandwidth consumption. In this paper we will examine the effect of TAL design in reducing this signaling overhead, taking into account TAL overlapping which mean that a cell may be included in more than one TAL. For a given TA and TAL design the overall signaling overhead was calculated. Results obtained showed that the TAL scheme gives minimum signaling overhead when compared with the TA scheme.