Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions

Collaborative modulation multiple access for single hop and multihop networks

While the bandwidth available for wireless networks is limited, the world has seen an unprecedented growth in the number of mobile subscribers and an ever increasing demand for high data rates. Therefore efficient utilisation of bandwidth to maximise link spectral efficiency and number of users that can be served simultaneously are primary goals in the design of wireless systems. To achieve these goals, in this thesis, a new non-orthogonal uplink multiple access scheme which combines the functionalities of adaptive modulation and multiple access called collaborative modulation multiple access (CMMA) is proposed. CMMA enables multiple users to access the network simultaneously and share the same bandwidth even when only a single receive antenna is available and in the presence of high channel correlation. Instead of competing for resources, users in CMMA share resources collaboratively by employing unique modulation sets (UMS) that differ in phase, power, and/or mapping structure. These UMS are designed to insure that the received signal formed from the superposition of all users’ signals belongs to a composite QAM constellation (CC) with a rate equal to the sum rate of all users. The CC and its constituent UMSs are designed centrally at the BS to remove ambiguity, maximize the minimum Euclidian distance (dmin) of the CC and insure a minimum BER performance is maintained. Users collaboratively precode their transmitted signal by performing truncated channel inversion and phase rotation using channel state information (CSI ) obtained from a periodic common pilot to insure that their combined signal at the BS belongs to the CC known at the BS which in turn performs a simple joint maximum likelihood detection without the need for CSI. The coherent addition of users’ power enables CMMA to achieve high link spectral efficiency at any time without extra power or bandwidth but on the expense of graceful degradation in BER performance. To improve the BER performance of CMMA while preserving its precoding and detection structure and without the need for pilot-aided channel estimation, a new selective diversity combining scheme called SC-CMMA is proposed. SC-CMMA optimises the overall group performance providing fairness and diversity gain for various users with different transmit powers and channel conditions by selecting a single antenna out of a group of L available antennas that minimises the total transmit power required for precoding at any one time. A detailed study of capacity and BER performance of CMMA and SC-CMMA is carried out under different level of channel correlations which shows that both offer high capacity gain and resilience to channel correlation. SC-CMMA capacity even increase with high channel correlation between users’ channels. CMMA provides a practical solution for implementing the multiple access adder channel (MAAC) in fading environments hence a hybrid approach combining both collaborative coding and modulation referred to as H-CMMA is investigated. H-CMMA divides users into a number of subgroups where users within a subgroup are assigned the same modulation set and different multiple access codes. H-CMMA adjusts the dmin of the received CC by varying the number of subgroups which in turn varies the number of unique constellation points for the same number of users and average total power. Therefore H-CMMA can accommodate many users with different rates while flexibly managing the complexity, rate and BER performance depending on the SNR. Next a new scheme combining CMMA with opportunistic scheduling using only partial CSI at the receiver called CMMA-OS is proposed to combine both the power gain of CMMA and the multiuser diversity gain that arises from users’ channel independence. To avoid the complexity and excessive feedback associated with the dynamic update of the CC, the BS takes into account the independence of users’ channels in the design of the CC and its constituent UMSs but both remain unchanged thereafter. However UMS are no longer associated with users, instead channel gain’s probability density function is divided into regions with identical probability and each UMS is associated with a specific region. This will simplify scheduling as users can initially chose their UMS based on their CSI and the BS will only need to resolve any collision when the channels of two or more users are located at the same region. Finally a high rate cooperative communication scheme, called cooperative modulation (CM) is proposed for cooperative multiuser systems. CM combines the reliability of the cooperative diversity with the high spectral efficiency and multiple access capabilities of CMMA. CM maintains low feedback and high spectral efficiency by restricting relaying to a single route with the best overall channel. Two possible variations of CM are proposed depending on whether CSI available only at the users or just at the BS and the selected relay. The first is referred to Precode, Amplify, and Forward (PAF) while the second one is called Decode, Remap, and Forward (DMF). A new route selection algorithm for DMF based on maximising dmin of random CC is also proposed using a novel fast low-complexity multi-stage sphere based algorithm to calculate the dmin at the relay of random CC that is used for both relay selection and detection

Review of Recent Trends

This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe

Papr analysis and channel estimation techniques for 3GPP LTE system

High data rates and secured data communication has become an unavoidable need of every mobile users. 3G technology provided greater data speed and secured networks compared to its predecessor 2G or 2.5G. The highest bit rates in commercially deployed wireless systems are achieved by means of Orthogonal Frequency Division Multiplexing (OFDM) [1]. The next advance in cellular systems, under investigation by Third Generation Partnership Project (3GPP), also anticipates the adoption of OFDMA to achieve high data rates. But a modified form of OFDMA i.e. SCFDMA (Single Carrier FDMA) having similar throughput performance and essentially the same complexity has been implemented as it has an edge over OFDMA having lower PAPR (peak to average power ratio) [2]. SCFDMA is currently a strong candidate for the uplink multiple access in the Long Term Evolution of cellular systems under consideration by the 3GPP. In our project we have worked on PAPR analysis of OFDMA, SCFDMA and various other SCFDMA (with different subcarrier mapping). Though SCFDMA had larger ISI it has lower PAPR which help in avoiding the need of an efficient linear power amplifier. We have analyzed various modulation techniques and implemented various kinds of pulse shaping filters and compared the PAPR for IFDMA, DFDMA and LFDMA (kinds of SCFDMA). Like other communication systems, in SCFDMA we encounter many trade-offs between design parameters (such as roll-off factor) and performance. The project report also constitutes the channel estimation techniques implemented in OFDM systems. Due to multipath fading the channel impulse response fluctuates for different subcarriers in different time slots. But with channel estimation OFDM systems can use coherent detection instead of differential. For MIMO system like OFDM channel information is vital for diversity combining and interference suppression [3]. So we need to estimate the channel as accurately as possible. As we have taken a slow Rayleigh fading channel in our study we used block type pilot arrangement channel estimation which uses LS (least square), MMSE (minimum mean square error) estimator. Due to higher complexity of the MMSE estimator, modified MMSE is implemented where tradeoff is made with performance. Here we have compared various channel estimation techniques used in OFDM systems. There are various other adaptive estimation techniques like LMS and RLS for estimating blind channels and comb type pilot arrangement estimation techniques for fast fading channels

Semi-blind CFO estimation and ICA based equalization for wireless communication systems

In this thesis, a number of semi-blind structures are proposed for Orthogonal Frequency Division Multiplexing (OFDM) based wireless communication systems, with Carrier Frequency Offset (CFO) estimation and Independent Component Analysis (ICA) based equalization. In the first contribution, a semi-blind non-redundant single-user Multiple-Input Multiple-Output (MIMO) OFDM system is proposed, with a precoding aided CFO estimation approach and an ICA based equalization structure. A number of reference data sequences are carefully designed and selected from a pool of orthogonal sequences, killing two birds with one stone. On the one hand, the precoding based CFO estimation is performed by minimizing the sum cross-correlations between the CFO compensated signals and the rest of the orthogonal sequences in the pool. On the other hand, the same reference data sequences enable the elimination of permutation and quadrant ambiguities in the ICA equalized signals. Simulation results show that the proposed semi-blind MIMO OFDM system can achieve a Bit Error Rate (BER) performance close to the ideal case with perfect Channel State Information (CSI) and no CFO. In the second contribution, a low-complexity semi-blind structure, with a multi-CFO estimation method and an ICA based equalization scheme, is proposed for multiuser Coordinated Multi-Point (CoMP) OFDM systems. A short pilot is carefully designed offline for each user and has a two-fold advantage. On the one hand, using the pilot structure, a complex multi-dimensional search for multiple CFOs is divided into a number of low-complexity mono-dimensional searches. On the other hand, the cross-correlation between the transmitted and received pilots is explored to allow the simultaneous elimination of permutation and quadrant ambiguities in the ICA equalized signals. Simulation results show that the proposed semi-blind CoMP OFDM system can provide a BER performance close to the ideal case with perfect CSI and no CFO. In the third contribution, a semi-blind structure is proposed for Carrier Aggregation (CA) based CoMP Orthogonal Frequency Division Multiple Access (OFDMA) systems, with an ICA based joint Inter-Carrier Interference (ICI) mitigation and equalization scheme. The CFO-induced ICI is mitigated implicitly via ICA based equalization, without introducing feedback overhead for CFO correction. The permutation and quadrant ambiguities in the ICA equalized signals can be eliminated by a small number of pilots. Simulation results show that with a low training overhead, the proposed semi-blind equalization scheme can provide a BER performance close to the ideal case with perfect CSI and no CFO

High capacity multiuser multiantenna communication techniques

One of the main issues involved in the development of future wireless communication systems is the multiple access technique used to efficiently share the available spectrum among users. In rich multipath environment, spatial dimension can be exploited to meet the increasing number of users and their demands without consuming extra bandwidth and power. Therefore, it is utilized in the multiple-input multiple-output (MIMO) technology to increase the spectral efficiency significantly. However, multiuser MIMO (MU-MIMO) systems are still challenging to be widely adopted in next generation standards. In this thesis, new techniques are proposed to increase the channel and user capacity and improve the error performance of MU-MIMO over Rayleigh fading channel environment. For realistic system design and performance evaluation, channel correlation is considered as one of the main channel impurities due its severe influence on capacity and reliability. Two simple methods called generalized successive coloring technique (GSCT) and generalized iterative coloring technique (GICT) are proposed for accurate generation of correlated Rayleigh fading channels (CRFC). They are designed to overcome the shortcomings of existing methods by avoiding factorization of desired covariance matrix of the Gaussian samples. The superiority of these techniques is demonstrated by extensive simulations of different practical system scenarios. To mitigate the effects of channel correlations, a novel constellation constrained MU-MIMO (CC-MU-MIMO) scheme is proposed using transmit signal design and maximum likelihood joint detection (MLJD) at the receiver. It is designed to maximize the channel capacity and error performance based on principles of maximizing the minimum Euclidean distance (dmin) of composite received signals. Two signal design methods named as unequal power allocation (UPA) and rotation constellation (RC) are utilized to resolve the detection ambiguity caused by correlation. Extensive analysis and simulations demonstrate the effectiveness of considered scheme compared with conventional MU-MIMO. Furthermore, significant gain in SNR is achieved particularly in moderate to high correlations which have direct impact to maintain high user capacity. A new efficient receive antenna selection (RAS) technique referred to as phase difference based selection (PDBS) is proposed for single and multiuser MIMO systems to maximize the capacity over CRFC. It utilizes the received signal constellation to select the subset of antennas with highest (dmin) constellations due to its direct impact on the capacity and BER performance. A low complexity algorithm is designed by employing the Euclidean norm of channel matrix rows with their corresponding phase differences. Capacity analysis and simulation results show that PDBS outperforms norm based selection (NBS) and near to optimal selection (OS) for all correlation and SNR values. This technique provides fast RAS to capture most of the gains promised by multiantenna systems over different channel conditions. Finally, novel group layered MU-MIMO (GL-MU-MIMO) scheme is introduced to exploit the available spectrum for higher user capacity with affordable complexity. It takes the advantages of spatial difference among users and power control at base station to increase the number of users beyond the available number of RF chains. It is achieved by dividing the users into two groups according to their received power, high power group (HPG) and low power group (LPG). Different configurations of low complexity group layered multiuser detection (GL-MUD) and group power allocation ratio (η) are utilized to provide a valuable tradeoff between complexity and overall system performance. Furthermore, RAS diversity is incorporated by using NBS and a new selection algorithm called HPG-PDBS to increase the channel capacity and enhance the error performance. Extensive analysis and simulations demonstrate the superiority of proposed scheme compared with conventional MU-MIMO. By using appropriate value of (η), it shows higher sum rate capacity and substantial increase in the user capacity up to two-fold at target BER and SNR values

Design and evaluation of OFDM radio interfaces for high mobility communications

[Resumo] Nas dúas últimas décadas, as modulacións multiportadora emerxeron como una solución de baixa complexidade para combatir os efectos do multitraxecto en comuniacións sen fíos. Entre elas, Orthogonal Frequency Division Multiplexing (OFOM) é posiblemente o esquema de modulación máis estudado, e tamén amplamente adoptado como alicerce de estándares da industria como WiMAX ou LTE. Sen embargo, OFDM é sensible a canles que varian ca tempo, unha característica dos escenarios con mobilidade, debido á aparición da interferencia entre portadoras (ICI). A implementación de equipamento hardware para o usuario final faise normalmente en chips dedicados, afnda que entornos de investigación, prefírense solucións máis flexibles. Unha aproximación popular é a coñecida como Software Defined Radio (SOR), onde os algoritmos de procesado de sinal se implementan en hardware reconfigurable como Digital Signal Processors (OSPs) e Field Programmable Gate Arrays (FPGAs). O obxectivo deste traballo é dobre. Por un lado, definir unha arquitectura para implementacións de tempo real de capas físicas basadas en OFDM usando como referencia O estándar WiMAX, probada Dunha plataforma composta por OSPs e FPGAs. Por outra banda, estudar os efectos da selectividade en tempo no sinal OFDM, definindo métodos de estimación de canle que teñen en conta a ICI, e evaluándoos tanto en simulación como con medidas experimentais. Seguíronse dúas aproximacións para caracterizar o comportamento de formas de onda OFDM baixo condicións de mobilidade, unha basada nun emulador de canle que traballa en tempo real, e outra en inducir grandes ensanchamentos Doppler no sinal mediante a extensión da duración do símbolo OFOM.[Resumen] En las dos últimas décadas, las modulaciones multiportadora han emergido como una solución de baja complejidad para combatir los efectos del multitrayecto en comunicaciones iDalámbricas. Entre ellas, Orthogonal Frequency Division Mulriplexing (OFDM) es posiblemente el esquema de modulación más estudiado, y también ampliamente adoptado como fundamento de estándares de la industria como WiMAX o LTE. Sin embargo, OFDM es sensible a canales que varían con el tiempo, una característica de los escenarios coo movilidad, debido a la aparicióo de la interferencia entre portadoras (ICI). La implementación de equipamiento hardware para el usuario final se hace normalmente en chips dedicados, aunque eo entornos de investigación, son preferibles soluciones más Hexibles. Una aproximación popular es la conocida como Software Defined Radio (SDR), donde los algOritmos de procesado de señal se implementan en hardware reconfigurable como Digital Signa! Processors (DSPs) y Field Programmable Gate AIrays (FPGAs). El objetivo de este trabajo es doble. Por un lado. definir una arquitectura para implementaciones de tiempo real de capas ¡lSicas basadas en OFDM usando como referencia el estándar WiMAX, probada en una plataforma compuesta por DSPs y FPGAs. Por otro lado, estudiar los efectos de la selectividad en tiempo en la señal OFDM, definiendo métodos de estimacióo de canal que tengan eo cueota la ICI, y evaluándolos tanto en simulación como con medidas experimenta1es. Se han seguido dos aproximaciones para caracterizar el comportamiento de formas de onda OFDM bajo condiciones de mobilidad, una basada en un emulador de canal que trabaja en tiempo real. y otra en inducir grandes ensanchamientos Doppler en la señal mediante la extensión de la duración del símbolo OFDM.[Abstract] In Ihe last two decades, multicarrier modulations have emerged as a low complexity solulion to combal the effects of Ihe multipalh in wireless communicalions. Among Ihem, Orthogonal Frequency Division Mulliplexing (OFOM) is possibly Ihe mosl sludied modulation scheme, and has a1so been widely adopted as Ihe foundation of induslry standards such as WiMAX or LTE. However, OFOM is sensitive lo time selective channels, which are featured in mobility scenarlos, due lO Ihe appearance of Inler-Carrier Interference (ICI). Implemenlation of hardware equipmenl for Ihe end user is usually implemenled in dedicaled chips, bul in researeh environments, more flexible solutions are preferred. One popular approach is the so ealled Software Defined Radio (SOR), where the signal processing a1gorithms are implemented in reconfigurable hardware sueh as Digital Signal Processors (DSPs) and Field Prograrnmable Gate Arrays (FPGAs). The aim of Ibis work is two-fold. On the one hand, to define an architeclure for Ihe implementation of real-time OFOM-based physical layers, using as a reference Ihe WiMAX standard, and it is tested on a platform composed by DSPs and FPGAs. On the olher hand, to study Ihe effeets of !he time seleetivity on !he OFOM signal, defining channel estimation me!hods aware of !he ICI, and ils evaluation bo!h in simulation as well as experimental measuremenls. Two approaches have been followed to assess the behavior of OFOM waveforms under mobility conditions, one based on a real-time channel emulator, and the other on inducing large Doppler spreads in !he signal by extending the duration of Ihe OFDM symbols

Spectrally efficient Non-Orthogonal Multiple Access (NOMA) techniques for future generation mobile systems

With the expectation of over a 1000-fold increase in the number of connected devices by 2020, efficient utilization of the limited bandwidth has become ever more important in the design of mobile wireless systems. Furthermore, the ever-increasing demand for higher data rates has made it necessary for a new waveform design that satisfies not only throughput demands, but network capacity as well. One such technique recently proposed is the non-orthogonal multiple access (NOMA) which utilizes the distance-dependent power domain multiplexing, based on the principles of signal superposition. In this thesis, new spectrally efficient non-orthogonal signal techniques are proposed. The goal of the schemes is to allow simultaneous utilization of the same time frequency network resources. This is achieved by designing component signals in both power and phase domain such that users are precoded or preformed to form a single and uniquely decodable composite signal. The design criteria are based on maximizing either the sum rate or spectral efficiency, minimizing multi-user interference and detection ambiguity, and maximizing the minimum Euclidean distance between the composite constellation points. The design principles are applied in uplink, downlink and coordinated multipoint (CoMP) scenarios. We assume ideal channel state with perfect estimation, low mobility and synchronization scenarios so as to prove the concept and serve as a bound for any future work in non-ideal conditions. Extensive simulations and numerical analysis are carried to show the superiority and compatibility of the schemes. First, a new NOMA signal design called uplink NOMA with constellation precoding is proposed. The precoding weights are generated at the eNB based on the number of users to be superposed. The eNB signals the precoding weights to be employed by the users to adjust their transmission. The adjustments utilize the channel state information estimated from common periodic pilots broadcasted by the eNB. The weights ensure the composite received signal at the eNB belongs to the pre-known constellation. Furthermore, the users precode to the eNB antenna that requires the least total transmit power from all the users. At the eNB, joint maximum likelihood (JML) detection is employed to recover the component signals. As the composite constellation is as that of a single user transmitting that same constellation, multiple access interference can be viewed as absent, which allows multiple users to transmit at their full rates. Furthermore, the power gain achieved by the sum of the component signals maximizes the sum rate. Secondly, the constellation design principle is employed in the downlink scenario. In the scheme, called downlink NOMA with constellation preforming, the eNB preforms the users signal with power and phase weights prior to transmission. The preforming ensures multi-user interference is eliminated and the spectral efficiency maximized. The preformed composite constellation is broadcasted by the eNB which is received by all users. Subsequently, the users perform JML detection with the designed constellation to extract their individual component signals. Furthermore, improved signal reliability is achieved in transmit and receive diversity scenarios in the schemes called distributed transmit and receive diversity combining, respectively. Thirdly, the constellation preforming on the downlink is extended to MIMO spatial multiplexing scenarios. The first MIMO scheme, called downlink NOMA with constellation preforming, each eNB antenna transmits a preformed composite signal composed of a set of multiple users’ streams. This achieves spatial multiplexing with diversity with less transmit antennas, reducing costs associated with multiple RF chains, while still maximizing the sum rate. In the second MIMO scheme, a highly spectrally efficient MIMO preforming scheme is proposed. The scheme, called group layer MIMO with constellation preforming, the eNB preforms to a specific group of users on each transmit antenna. In all the schemes, the users perform JML detection to recover their signals. Finally, the adaptability of the constellation design is shown in CoMP. The scheme, called CoMP with joint constellation processing, the additional degrees of freedom, in form of interfering eNBs, are utilized to enable spatial multiplexing to a user with a single receive antenna. This is achieved by precoding each stream from the coordinating eNB with weights signalled by a central eNB. Consequently, the inter-cell interference is eliminated and the sum-rate maximized. To reduce the total power spent on precoding, an active cell selection scheme is proposed where the precoding is employed on the highest interferers to the user. Furthermore, a power control scheme is applied the design principle, where the objective is to reduce cross-layer interference by adapting the transmission power to the mean channel gain