Showing papers on "Frequency-division multiplexing published in 2008"

An overview of limited feedback in wireless communication systems

Abstract: It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.

Multicarrier Communication Over Underwater Acoustic Channels With Nonuniform Doppler Shifts

Abstract: Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.

Experimental Demonstrations of Electronic Dispersion Compensation for Long-Haul Transmission Using Direct-Detection Optical OFDM

Abstract: We present experimental demonstrations using direct-detection and optical-orthogonal frequency division multiplexing (DD-OOFDM) for the compensation of chromatic dispersion in long-haul optical fiber links. Three transmitter designs of varying electrical and optical complexity are used for optical single sideband (OSSB) transmission and the theory behind each design is discussed. The data rates achieved for the three systems are 10, 12, and 20 Gbit/s for fiber distances between 320 and 400 km. A discussion of system overheads is provided together with simulations of the required optical signal-to-noise ratio (OSNR).

Single Carrier FDMA: A New Air Interface for Long Term Evolution

Abstract: Single Carrier Frequency Division Multiple Access (SC-FDMA) is a novel method of radio transmission under consideration for deployment in future cellular systems; specifically, in 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) systems. SC-FDMA has drawn great attention from the communications industry as an attractive alternative to Orthogonal Frequency Division Multiple Access (OFDMA). Introduction to Single Carrier FDMA places SC-FDMA in the wider context of wireless communications, providing the reader with an in-depth tutorial on SC-FDMA technology. The book introduces the reader to this new multiple access technique that utilizes single carrier modulation along with orthogonal frequency multiplexing and frequency domain equalization, plus its applications in communications settings. It considers the similarities with and differences from orthogonal frequency division modulation, multiplexing, and multiple access used extensively in cellular, broadcasting, and digital subscriber loop applications. Particular reference is made to the peak power characteristics of an SC-FDMA signal as an added advantage over OFDMA. Provides an extensive overview of the principles of SC-FDMA and its relation to other transmission techniques. Explains how the details of a specific implementation influence the tradeoffs among various figures of merit. Describes in detail the configuration of the SC-FDMA uplink transmission scheme published by 3GPP. Features link level simulation of an uplink SC-FDMA system using MATLAB. This is an essential text for industry engineers who are researching and developing 3GPP LTE systems. It is suitable for engineers designing wireless network equipment, handsets, data cards, modules, chipsets, and test equipment as well as those involved in designing LTE infrastructure. It would also be of interest to academics, graduate students, and industry researchers involved in advanced wireless communications, as well as business analysts who follow the cellular market.

Mixed-signal parallel compressed sensing and reception for cognitive radio

Abstract: A parallel structure to do spectrum sensing in cognitive radio (CR) at sub-Nyquist rate is proposed. The structure is based on compressed sensing (CS) that exploits the sparsity of frequency utilization. Specifically, the received analog signal is segmented or time-windowed and CS is applied to each segment independently using an analog implementation of the inner product, then all the samples are processed together to reconstruct the signal. Applying the CS framework to the analog signal directly relaxes the requirements in wideband RF receiver front-ends. Moreover, the parallel structure provides a design flexibility and scalability on the sensing rate and system complexity. This paper also provides a joint reconstruction algorithm that optimally detects the information symbols from the sub-Nyquist analog projection coefficients. Simulations showing the efficiency of the proposed approach are also presented.

Complex signal demodulation and random body movement cancellation techniques for non-contact vital sign detection

Abstract: A complex signal demodulation technique is proposed to eliminate the null detection point problem in non-contact vital sign detection. This technique is robust against DC offset in direct conversion system. Based on the complex signal demodulation, a random body movement cancellation technique is developed to cancel out strong noise caused by random body movement in non-contact vital sign monitoring. Multiple transceivers and antennas with polarization and frequency multiplexing are used to detect signals from different body orientations. The noise due to random body movement is cancelled out based on different patterns of the desired and undesired signals. Experiments by highly compact 5–6 GHz portable radar systems have been performed to verify these two techniques.

A Novel Architecture of Delta-Sigma Modulator Enabling All-Digital Multiband Multistandard RF Transmitters Design

Abstract: This paper proposes a new architecture of delta-sigma (DS) modulator suitable for RF digital transmitter design. This novel architecture considerably reduces the speed requirements of the digital signal processing block. The novelty lies in the implementation of a specific fully digital up-conversion in combination with a low-pass DS modulator to produce high-frequency digital-like signals, which can be used to drive highly efficient switching-mode power amplifiers. The proposed architecture is suitable for reconfigurable all-digital, multistandard and multiband wireless transmitters. The novel transmitter architecture has been validated using simulation and implemented on a field-programmable gate array development board for two different signals, code division multiple access and orthogonal frequency division multiplex.

The History of Orthogonal Frequency Division Multiplexing

Abstract: This paper depicts the development of Orthogonal Frequency Division Multiplexing from a historical perspective. A summary of major research milestones are noted that contributed to modern-day OFDM. These contributions include the use of discrete Fourier transforms replacing the analog implementation and addition of cyclic extensions to ensure orthogonality among the sub-channels. Also, channel equalization algorithms to suppress inter-symbol interference and inter-carrier interference, channel estimation through the insertion of pilot tones among data blocks, peak-to-average power ratio reduction, and synchronization techniques are discussed.

WDM extended reach passive optical networks using OFDM-QAM

Abstract: In order to reduce the cost for delivering future broadband services, network operators are inclined to simplify the network architectures by integrating the metro and access networks into a single system. Hence, extended reach passive optical networks (ER-PONs) have been proposed. ER-PON usually has four new features: high data rate in both upstream and downstream signals (>1 Gb/s); reach extension to >100 km; a high split ratio (>100); and using wavelength division multiplexing (WDM). In this work, we propose and demonstrate a highly spectral efficient ER-PON using 4 Gb/s OFDM-QAM for both upstream and downstream signals, while achieving a high split-ratio of 256. The ER-PON employs optical components optimized for GPON (bandwidth of ∼1GHz) and reaches 100 km without dispersion compensation. Numerical analysis using 16, 64 and 256-QAM OFDM are also performed to study the back-to-back receiver sensitivities and power penalties at different electrical driving ratios.

Joint CFO and Channel Estimation for Multiuser MIMO-OFDM Systems With Optimal Training Sequences

Abstract: This paper addresses the problem of joint carrier frequency offset (CFO) and channel estimation in multiuser multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. To choose the optimal training sequences with the goal of providing the smallest estimation mean square error (MSE), the asymptotic Cramer-Rao bounds (asCRBs) are derived. The optimal training sequences are designed that minimize the asCRBs for both CFO and channel estimation under the constraint that the asCRBs being channel independent. A joint CFO and channel estimator is derived based on the maximum likelihood (ML) criterion. A computationally efficient method using importance sampling technique is proposed to solve the highly demanding multidimensional exhaustive search required by the ML multi-CFO estimation. Simulation results illustrate the merits of the proposed training sequences and also verify the effectiveness of the proposed estimation scheme.

UWB Direct Chaotic Communication Technology for Low-Rate WPAN Applications

Abstract: The goal of this paper is to describe the design of an ultrawideband (UWB) system that is optimized for low-complexity, low-power, low-cost, and low-rate wireless personal area network applications. To this aim, we propose a system based on novel direct chaotic communication (DCC) technology, in which a 2-GHz-wide chaotic signal is directly generated into the lower band of the UWB spectrum. Based on this system, two simple modulation schemes, namely, chaotic on-off keying and differential chaos-shift keying, are studied, and the performance of both noncoherent and differential-coherent transceiver architectures is evaluated. Various system design parameters and tradeoffs are discussed throughout the paper, including frequency band plans, data throughput, and system scalability. In particular, the frequency-division multiplexing technique is proposed as a low-cost alternative to achieving simultaneous operating piconets for short-distance applications. The average power consumption for various operating data rates and the technical feasibility of implementing the DCC system as a low-cost integrated circuit are also addressed. Finally, Monte Carlo simulations are performed based on the IEEE 802.15.4a standard channel models to evaluate the performance of the two modulation schemes. In general, both schemes experience little degradation under multipath environments due to the self-inherent wideband characteristic of the chaotic signal.

Adaptive Transmission Bandwidth Based Packet Scheduling for LTE Uplink

Abstract: UTRAN long term evolution is currently under standardization within 3GPP with the aim of providing a spectral efficiency 2 to 4 times higher than its predecessor HSUPA/HSDPA release 6. Single carrier FDMA has been selected as multiple access for the uplink. This technology requires the subcarriers allocated to a single user to be adjacent. The consequence is a reduced allocation flexibility which makes it challenging to design effective packet scheduling algorithms. This paper proposes a channel aware packet scheduling algorithm which exploits the bandwidth flexibility offered by the system to perform an allocation which closely resembles the frequency domain envelope of the metric to be optimized. Compared to a fixed bandwidth approach, the proposed algorithm provides a greater flexibility given the inbuilt adaptation to different scenarios and loads, as well as an improvement in term of performance for the Macro 3 case. In this case the uplink capacity is increased by approximately 20% in average cell throughput and 10% in UE outage compared to a fixed bandwidth channel aware approach.

Least-Squares Channel Estimation for Mobile OFDM Communication on Time-Varying Frequency-Selective Fading Channels

Abstract: A least-squares (LS) channel estimation (CE) technique for mobile orthogonal frequency-division multiplexing (OFDM) communications over a rapidly time-varying frequency-selective fading channel is investigated in this paper. The proposed technique keeping the comb-type pilot arrangement can achieve a low error probability by accurately estimating channel impulse response (CIR) and effectively tracking rapid CIR time variations. The LS CE technique proposed here is conducted in the time domain (TD). Meanwhile, a generic estimator is serially performed block by block without assistance from a priori channel information and without increasing computational complexity. By taking advantage of linearly frequency-modulated (LFM) or pseudorandom signals transceived for jointly sounding pilot subchannels, the proposed LS CE can inherently perform pseudonoise (PN) matched filtering (MF) to suppress multipath interference (MPI) caused by frequency-selective fading and intercarrier interference (ICI) resulting from data subchannels. The optimality of the proposed technique is verified by taking Cramer-Rao lower bounds (CRLBs) into comparison both on noise- and interference-dominant signal-to-noise ratio (SNR) conditions. In addition, the dual optimality of the LFM and PN pilot symbols is verified for both TD and frequency-domain (FD) CEs. Furthermore, the proposed technique also exhibits good resistance against residual timing errors occurring with the discrete Fourier transform (DFT) demodulation. Extensive computer simulations in conjunction with statistical derivations show the superiority of the proposed technique.

Bit and Power Loading for OFDM-Based Three-Node Relaying Communications

Abstract: Bit and power loading (BPL) techniques have been intensively investigated for the single-link communications. In this paper, we propose a margin-adaptive BPL approach for orthogonal frequency-division multiplexing (OFDM) systems assisted by a single cooperative relay. This orthogonal half-duplex relay operates either in the selection detection-and-forward (SDF) mode or in the amplify-and-forward (AF) mode. Maximum-ratio combining is employed at the destination to attain the achievable distributed spatial diversity-gain. Assuming perfect channel knowledge is available at all nodes, the proposed approach is to minimize the transmit-power consumption at the target throughput (average number of bits/symbol) and the target link performance. With respect to various power-constraint conditions, we investigate two distributed resource-allocation strategies, namely flexible power ratio (FLPR) and fixed power ratio (FIPR). The FLPR strategy is proposed for scenarios without individual local power constraint. The source power and relay power have a flexible ratio for each subcarrier. The FIPR strategy is proposed for scenarios with individual local power constraint. The source power and relay power have a fixed ratio for each subcarrier. Computer simulations are carried out to evaluate the proposed approach with respect to the relay location. Significant performance improvement is observed in terms of both the symbol-error-rate and the transmit-power efficiency.

Beamforming of control information in a wireless communication system

Abstract: Techniques for sending traffic data and control information in a wireless communication system are described. In one design, a transmitter (e.g., a Node B or a UE) may perform beamforming to send traffic data on M layers based on a precoding matrix, where M may be one or greater. The transmitter may also perform beamforming to send control information on up to M layers based on the same precoding matrix used for the traffic data. The transmitter may send the beamformed traffic data on a first physical channel and may send the beamformed control information on a second physical channel. The transmitter may multiplex the beamformed traffic data and the beamformed control information using time division multiplexing (TDM) or frequency division multiplexing (FDM).

Optimized Dispersion Compensation Using Orthogonal Frequency-Division Multiplexing

Abstract: Orthogonal frequency-division multiplexing (OFDM) can compensate for linear distortions, such as group-velocity dispersion (GVD) and polarization-mode dispersion (PMD), provided the cyclic prefix is sufficiently long. Typically, GVD is dominant, as it requires a longer cyclic prefix. Assuming coherent detection, we show how to analytically compute the minimum number of subcarriers and cyclic prefix length required to achieve a specified power penalty, trading off power penalties from the cyclic prefix and from residual inter-symbol interference (ISI) and inter-carrier interference (ICI). We derive an analytical expression for the power penalty from residual ISI and ICI.

Vandermonde Frequency Division Multiplexing for Cognitive Radio

Abstract: We consider a cognitive radio scenario where a primary and a secondary user wish to communicate with their corresponding receivers simultaneously over frequency selective channels. Under realistic assumptions that the secondary transmitter has no side information about the primary's message and each transmitter knows only its local channels, we propose a Vandermonde precoder that cancels the interference from the secondary user by exploiting the redundancy of a cyclic prefix. Our numerical examples show that VFDM, with an appropriate design of the input covariance, enables the secondary user to achieve a considerable rate while generating zero interference to the primary user.

A blind carrier frequency offset estimation scheme for OFDM systems with constant modulus signaling

Abstract: This paper presents a new blind carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) systems with constant modulus (CM) signaling. Both single-input single-output (SISO) systems and multiple-input multiple-output (MIMO) systems with orthogonal space-time block coding are considered. The proposed scheme is based on the reasonable assumption that the channel frequency response changes slowly in the frequency domain, which implies that the channel frequency response on two consecutive sub- carriers is approximately the same. Based on this assumption, cost functions are derived in closed-form, which minimize the difference between the signal power of two neighboring subcarriers. The identifiability of the proposed scheme is mathematically proved, which implies that minimizing the derived cost function gives an approximate estimate of the CFO. We demonstrate that the proposed scheme provides an excellent trade-off between complexity and performance as compared to prominent existing estimation schemes.

Performance Analysis of OFDM Systems with Adaptive Sub Carrier Bandwidth

Abstract: Orthogonal frequency division multiplexing based wireless systems are spectrally efficient, but they are vulnerable to inter-carrier interference (ICI). In a wide area scenario, users will experience varying signal strength due to different individual path loss and also varying amount of Doppler spread because of their independent velocities. Therefore, the ICI among users will vary over a wide range. It is proposed in this work to use dynamically adaptive sub carrier bandwidth (ASB) along with adaptive bit loading to mitigate ICI in such conditions, which will keep receivers simple while maintaining maximum throughput in each situation. Results show that ASB can provide higher throughput than its fixed sub carrier bandwidth counterpart when both may use adaptive bit loading per sub carrier.

A Fast Subcarrier, Bit, and Power Allocation Algorithm for Multiuser OFDM-Based Systems

Abstract: In this paper, we propose a real-time subcarrier, bit, and power allocation algorithm for orthogonal frequency-division multiplexing-based multiuser communication systems in downlink transmission. Assuming that base stations know the channel gains of all subcarriers of all users, the proposed loading algorithm tries to minimize the required transmit power while satisfying the rate requirement and data error rate constraint of each user. The novel algorithm simultaneously determines subcarrier, bit, and power allocation by enhancing the suboptimal algorithm by Wong while having the same computational complexity. The proposed scheme offers better performance in terms of transmit power than that of Wong , as demonstrated in the simulation results, whereas the performance of the scheme in Wong was close to that of the optimal solution.

Optimal Cross-Layer Scheduling of Transmissions Over a Fading Multiaccess Channel

Abstract: We consider the problem of several users transmitting packets to a base station, and study an optimal scheduling formulation involving three communication layers, namely, the medium access control, link, and physical layers. We assume Markov models for the packet arrival processes and the channel gain processes. Perfect channel state information is assumed to be available at the transmitter and the receiver. The transmissions are subject to a long-run average transmitter power constraint. The control problem is to assign power and rate dynamically as a function of the fading and the queue lengths so as to minimize a weighted sum of long run average packet transmission delays.

Vandermonde frequency division multiplexing for cognitive radio

Abstract: We consider a cognitive radio scenario where a primary and a secondary user wish to communicate with their corresponding receivers simultaneously over frequency selective channels. Under realistic assumptions that the primary user is ignorant of the secondary userpsilas presence and that the secondary transmitter has no side information about the primarypsilas message, we propose a Vandermonde precoder that cancels the interference from the secondary user by exploiting the redundancy of the cyclic prefix and the frequency selectivity of the channel. Our numerical examples show that VFDM, with an appropriate design of the input covariance, enables the secondary user to achieve a non-negligible rate while generating zero interference to the primary user.

Method and apparatus for multiplexing cdm pilot and fdm data

Abstract: Techniques for sending control information in a wireless communication system are described. In an aspect, a user equipment (UE) may send data for control information in a resource block with frequency division multiplexing (FDM) and may send pilot in the resource block with frequency-domain code division multiplexing (CDM). The UE may determine multiple groups of subcarriers to use to send data in multiple symbol periods of the resource block based on a predetermined pattern or a pseudo-random hopping pattern. Each group may include consecutive subcarriers to support localized FDM. The multiple groups may include different subcarriers to provide frequency diversity and possibly interference averaging. The UE may send modulation symbols for data (e.g., in the time domain) on the multiple groups of subcarriers in the multiple symbol periods. The UE may send a reference signal sequence for pilot on multiple subcarriers in each symbol period for pilot.

OFDM Channel Estimation With Jammed Pilot Detector Under Narrow-Band Jamming

Abstract: This paper presents a channel estimation scheme using a new jammed pilot detection algorithm for orthogonal frequency-division multiplexing (OFDM) systems under narrow-band jamming (NBJ).signal-to-jamming ratio The jammed pilot subcarrier can be detected and excised by using the proposed algorithm after least squares estimation. The average mean square error (mse) on one OFDM symbol both under a jammed and a removed pilot subcarrier are derived analytically. Moreover, the symbol error rate (SER) performance for the channel estimation scheme using the proposed algorithm is evaluated by simulation. From the results, we can show that the channel estimator with the proposed algorithm improves the mse and SER performances at a low signal-to-jamming ratio.

Iterative frequency domain channel estimation for dft-precoded ofdm systems using in-band pilots

Abstract: We consider two techniques of in-band frequency domain multiplexed (FDM) pilots using interleaved frequency domain multiple access (IFDMA) signal with a Chu sequence for DFT-precoded OFDM (or single-carrier (SC)) systems. One, called frequency domain superimposed pilot technique (FDSPT), superimposes pilot tones onto scaled or deleted data tones, which preserves spectral efficiency at the expense of a slight performance loss. The other, called frequency expanding technique (FET), multiplexes pilot tones by displacing data tones, which slightly reduces spectral efficiency. Using FDM pilots in SC systems facilitates flexible and efficient assignment of signals to available spectrum. We propose an iterative frequency domain decision-directed interference cancellation technique to reduce the intersymbol interference level of SC signals with FDSPT pilots (resulting from the suppression of data tones). Moreover, we propose a low complexity frequency domain iterative decision-directed channel estimation (IDDCE) technique for SC systems using FDM pilots. Using IDDCE, the frame error rate (FER) performance for coded SC systems using FET and FDSPT pilots with interference cancellation is found to be about 0.2 dB and about 0.5 dB, respectively, away from the FER performance with known channel frequency response at FER=10-2. FDSPT pilots can also be used for OFDM systems with channel coding. It is found that an extra 1 dB of SNR is required at FER=10-2,compared with that using the conventional FET pilots for OFDM systems.

A Generalized Window Approach for Designing Transmultiplexers

Abstract: This paper proposes a computational, very efficient, approach for designing a novel family of M-channel maximally decimated nearly perfect-reconstruction cosine-modulated transmultiplexers. This approach is referred to as the generalized windowing method for transmultiplexers because after knowing the transmission channel a proper weighted sum of the inter-channel and inter-symbol interferences can be properly taken into account in the optimization of the window function, unlike in other existing windowing techniques. The proposed approach has also the following two advantages. First, independent of the number of subchannels and the common order of the subchannel filters, the number of unknowns is only four. Second, the overall optimization procedure is made considerably fast by estimating the above-mentioned sum in terms of two novel measures, namely, the signal to inter-symbol and the signal to inter-channel interferences, which are very easy to evaluate. Furthermore, when the transmission channel is not considered in the design, a table is provided, which contains the parameters for designing the prototype filter directly by using the windowing method without any time-consuming optimization. When comparing the resulting transmultiplexers with the corresponding perfect-reconstruction designs (the same number of subchannels and same prototype filter order), the levels of interferences are practically the same. However, when the system is affected by a strong narrowband interference, the proposed transmultiplexers outperform their PR counterparts. Design examples are included illustrating the efficiency of the proposed design approach over other existing techniques based on the use of the windowing method.

Scattered Pilots and Virtual Carriers Based Frequency Offset Tracking for OFDM Systems: Algorithms, Identifiability, and Performance Analysis

Abstract: In this paper, we propose a novel carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing (OFDM) systems by exploiting scattered pilot carriers and virtual carriers embedded in the existing OFDM standards. Assuming that the channel remains constant during two consecutive OFDM blocks and perfect timing, a CFO tracking algorithm is proposed using the limited number of pilot carriers in each OFDM block. Identifiability of this pilot based algorithm is fully discussed under the noise free environment, and a constellation rotation strategy is proposed to eliminate the c-ambiguity for arbitrary constellations. A weighted algorithm is then proposed by considering both scattered pilots and virtual carriers. We find that, the pilots increase the performance accuracy of the algorithm, while the virtual carriers reduce the chance of CFO outlier. Therefore, the proposed tracking algorithm is able to achieve full range CFO estimation, can be used before channel estimation, and could provide improved performance compared to existing algorithms. The asymptotic mean square error (MSE) of the proposed algorithm is derived and simulation results agree with the theoretical analysis.

Parallel Detection Algorithm Using Multiple QR Decompositions With Permuted Channel Matrix for SDM/OFDM

Abstract: Space division multiplexing (SDM)/orthogonal frequency division multiplexing (OFDM) systems transmit different data using the same frequency, so it is necessary to separate the simultaneously received signals in the receiver. Previous studies have shown that maximum likelihood detection (MLD) provides the best bit error rate (BER) performance. However, the complexity of MLD exponentially increases with the constellation size and the number of transmit antenna branches. Therefore, it is impractical to use a full MLD without reducing its computational complexity, because it would be prohibitively large for implementation. Recently, the use of QR decomposition with an M-algorithm (QRD-M) has been proposed to reduce the system complexity while maintaining the performance of the system. However, the QRD-M performance depends on the number of surviving symbol replica candidates. When QRD-M is used with a small number of surviving symbol replica candidates, the performance declines, but when there is a large number of surviving symbol replica candidates and the transmitter antenna branches, QRD-M requires a large memory to maintain their branch metrics, and a long latency time is also required. To reduce these problems, in this paper, we propose a parallel detection algorithm using multiple QR decompositions with permuted channel matrices for SDM/OFDM systems.

Pulse Shape Adaptation and Channel Estimation in Generalised Frequency Division Multiplexing Systems

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) is well known as an efficient technology for wireless communications and is widely used in many of the current and upcoming wireless and wireline c ...

Parallel operation of half- and full-duplex FDD in future multi-hop mobile radio networks

Abstract: There are two basic duplexing schemes for present and future mobile radio networks, frequency-division duplex (FDD) and time-division duplex (TDD). In general each of these methods has its benefits and drawbacks. However, both schemes have their scenarios where they perform best. In future mobile radio systems typical wireless data communication will not only occur in metropolitan area scenarios like hotspots in airports, city centres, exhibition halls, etc., but also in wide area environments, e.g. a moving car in a rural environment. In general TDD is more appropriate for dense metropolitan area scenarios whereas FDD has benefits in wide area environments. If an FDD terminal which transmitted and received simultaneously, it would need an expensive duplex-filter, in order to separate UL and DL channels. Half-duplex terminals do not need such a filter. Therefore, half-duplex FDD appears to be attractive in terms of cost. A Relay is a promising concept for next generation systems. It allows enlarging the cell coverage range and is increasing the total cell capacity. A relay is not connected by wire, but works in a decode-and-forward principle and consequently is a cost-efficient alternative to base stations. This paper introduces a protocol to support parallel operation of half- and full-duplex FDD terminals in a relay capable system.