Future ultrahigh-speed wireless communication systems face difficult challenges due to the fundamental limitations of current technologies working at microwave frequencies. Millimeter-wave (mmWave) technologies can offer large underutilized bandwidths and ease the implementation of large antenna arrays which are required to help overcome the severe signal attenuation that occurs at these frequencies. The high cost and power consumption of a fully digital mmWave precoder and combiner can be reduced by the adoption of hybrid analog/digital designs based on analog phase shifters. The implementation can be simplified even further if each transceiver is connected to an independent antenna subarray and if the phase shifters are replaced by switches, with the possible aid of inverters. In this paper we present an hybrid design algorithm for orthogonal frequency division multiplexing (OFDM) based mmWave MIMO systems, which can cope with different analog architectures that can be adopted at either the RF precoder or combiner, in order to achieve reduced complexity and power consumption. Numerical results show that using the proposed algorithm, all the architectures can achieve good trade-offs between spectral efficiency and simplified implementation.

Single carrier transmissions with frequency domain equalization (SC-FDE) have gained widespread use in emergent broadband wireless systems becoming an attractive alternative to popular Orthogonal Frequency Division Multiplexing (OFDM) schemes, particularly at the uplink. Since coherent receivers are usually employed with SC-FDE, accurate channel estimates are required so as to avoid substantial performance degradation. Several channel estimation strategies have been proposed for SC-FDE, but a thoroughly evaluation of the degradation caused by channel estimation errors and a comparison against OFDM is still lacking. In this paper we study the impact of imperfect channel knowledge on SC transmission with focus on the linear frequency domain equalizer (FDE) and on the Iterative Block Decision Feedback Equalizer (IB-DFE). We propose a modified IB-DFE which incorporates knowledge of the channel estimation error model and show that its performance becomes more robust against the presence of strong error components in the channel estimates. We also evaluate, analytically and through simulations, the degradation caused by imperfect channel estimation in SC-FDE and compare it against OFDM schemes (Orthogonal Frequency Division Multiplexing). It is shown that the channel estimation requirements for SC-FDE are higher than for OFDM unless a channel estimation error aware receiver is employed.

The Iterative Block Decision Feedback Equalizer (IB-DFE) is a promising technique for single carrier (SC) block transmissions whose performance can approach the matched filter bound in severely time dispersive channels. In this paper we evaluate analytically and through simulations the impact of imperfect channel estimation on the performance of this equalizer and propose a modified IB-DFE which is shown to be more robust against the presence of strong error components in the channel estimates.

Imperfect channel estimation can have a severe impact on the performance of coherent detection systems. In this paper we study the effect of imperfect channel knowledge in the performance of SC-FDE (Single Carrier with Frequency Domain Equalization). We propose a low complexity linear FDE which incorporates knowledge of the channel estimation error variance and derive analytical BER expressions. It is shown that its performance becomes more robust in the presence of strong channel estimation error components compared with a conventional FDE receiver. We also compare the degradation caused by imperfect channel estimation in SC-FDE and in OFDM schemes (Orthogonal Frequency Division Multiplexing) and show that the channel estimation requirements for SC-FDE are higher than for OFDM.

This study focuses on the negotiation in the financial markets, specifically in programming an algorithm to trade automatically (without human intervention) in the foreign exchange market (Forex). The platform used in this study was the Meta Trader (version 5), which allows for this kind of negotiation. The main objective was to conclude about the effectiveness of a newly developed strategy for automatic negotiation. The developed strategies must have the ability to identify situations with lucrative potential based on several types of trading strategies used around the world. Methods were created based on technical and fundamental analysis as well as correlations. Fundamental analysis, in particular, is a novelty in this type of algorithms since, most part of the times, it is hard to quantify the information necessary to make decisions based on this type of analysis. Moreover, some other functions were developed in order to optimize the overall performance of the implemented strategies.

Orthogonal frequency division multiplexing (OFDM) schemes are the choice modulation for broadband wireless broadcast and multicast systems. However, OFDM schemes have important limitations such as high-envelope fluctuation of the transmitted signals and its sensibility to carrier frequency errors. When these limitations prove critical the authors consider single-carrier frequency-domain equalisation (SC-FDE) schemes, that allow much higher power efficiency because of lower envelope fluctuations. The overall performance can be further improved if the conventional linear FDE is replaced by an iterative FDE such as an iterative block decision feedback equaliser (IB-DFE). Conventional IB-DFE are usually designed for a quadrature phase shift keying constellation. However, it is strongly recommended that broadcast and multicast systems employ hierarchical constellations with several classes of bits with different error protection. In this study the authors consider the use of SC-FDE schemes combined with IB-DFE receivers in broadband wireless broadcast and multicast systems. The authors emphasise the advantages of these schemes and the authors present IB-DFE designs suitable for hierarchical constellations with several classes of bits with different error protection.

The authors derive a lower bound on the performance of generalised multilevel quadrature amplitude modulations (M-QAM) in time-discrete multipath Rayleigh fading environments with imperfect channel estimation. The bound can be regarded as an extension of the well-known matched filter bound (MFB), taking into account the impact of imperfect channel knowledge. The analytical expressions derived allow the computation of the bit error rate for the different bit streams that can be mapped simultaneously onto M-QAM symbols using a hierarchical approach when unequal bit error protection is desired.

In this paper we consider SC-FDE schemes (Single-Carrier with Frequency-Domain Equalization) employing multi-resolution hierarchical constellations and we consider the design of turbo receivers, implemented in the frequency-domain, for systems where we have different error protections. We present a versatile method to design the receiver that is suitable to any constellation.

This paper considers the use of a code combining hybrid ARQ scheme (Automatic Repeat reQuest) on a TDMA (Time Division Multiple Access) system. A multi-rate turbo-code is proposed to implement the H-ARQ scheme, allowing improved performances. This paper analyzes the energy per packet successfully received, the packet delay and goodput performances for the TDMA system on a HAP (High Altitude Platform). Analytical models were used to define a constrained energy optimization problem, where the minimum transmission power is calculated based on the goodput and delay constraints. Analytical results were validated through simulations for a typical HAP Network uplink channel.

In this paper, we derive matched filter bound (MFB) expressions for the performance of hierarchical quadrature amplitude modulations (M-HQAM) over time-discrete multipath Rayleigh fading environments with diversity. The expressions are valid for multipath environments where different paths and antennas can be correlated. Since hierarchical constellations are usually employed to achieve unequal bit error protection, the MFB expressions are given in terms of the individual bit error rate (BER) for the different bit streams. Although typically the MFB is obtained assuming slow time varying channels, fast varying channels are also considered in this paper.

This paper presents a multipacket detection technique for dealing with packet collisions in OFDM schemes (orthogonal frequency division multiplexing). Instead of discarding collided packets as it is done in traditional MAC approaches (medium access control) additional packets are transmitted and separated using multiple input multiple output (MIMO) based techniques. Reliable detection and high throughputs can be achieved as long as different interleavers are used for different retransmissions. We also include a method for estimating the users involved in the collision.

In this paper we derive a lower bound on the bit error rate (BER) for the individual bit streams that can be mapped simultaneously in an hierarchical way onto generalized multilevel quadrature amplitude modulations (M-QAM). The expressions are valid for time-discrete multipath Rayleigh fading environments with imperfect channel estimation and can be regarded as an extension of the well-known matched filter bound (MFB).

Whenever there is a collision involving several transmitted packets, the traditional approach for MAC (Medium Access Control) protocols is to discard all packets involved and request their retransmission, with a consequent loss in the overall throughput. Based on conventional Multiple Input Multiple Output (MIMO) techniques, in this paper we propose a multipacket detector for OFDM schemes (Orthogonal Frequency Division Multiplexing) that allows an efficient packet separation in the presence of collisions and can achieve high throughputs. We show that reliable detection is possible as long as different interleavers are used for different retransmissions. We also include a method to estimate the users involved in the collision, as well as well as the corresponding channel characteristics.

In this paper we derive matched filter bound (MFB) bit error rate (BER) expressions for the individual bit classes of multilevel hierarchical quadrature amplitude modulations (M-HQAM). The expressions are valid for time-discrete multipath Rayleigh fading environments with diversity where the different paths can be correlated. Though typically MFB are obtained assuming slow-varying channels in this paper we also consider fast varying channels.

SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) are promising candidates for future broadband MIMO (Multiple Input, Multiple Output) wireless systems. These modulations allow excellent performances in severely time-dispersive channels, provided that accurate channel estimates and performing decoding algorithms are available at the receiver. For this purpose, pilot symbols and/or training sequences are usually multiplexed with data symbols. However, since this leads to overhead and some spectral degradation, the use of implicit pilots (i.e., pilots superimposed to data) should be considered. In this paper we consider MIMO SC-FDE systems where the channel estimation is based on either explicit or implicit pilots. Since the interference levels between data and pilots might be very high (for the implicit bits), we propose an iterative receiver with joint equalization, turbo decoding and channel estimation. Our performance results show that the use of implicit pilots, combined with the proposed receiver, allows performances close to the case with perfect channel estimation, even for severely time-dispersive channels.

The traditional approach for MAC protocols (Medium Access Control) is to discard all packets involved in a collision and request their retransmission, which precludes high throughputs. However, since the signals associated to collisions have important information concerning the packets involved, with proper retransmissions we can efficiently resolve collisions. In this paper we propose a multipacket detection technique for OFDM schemes (Orthogonal Frequency Division Multiplexing) that allows an efficient packet separation in the presence of collisions. This technique allows high throughputs, since the total number of transmissions can be equal to the number of packets involved in the collision. By using different interleavers for different retransmissions we can successfully separate packets involved in a collision even when the channel remains fixed for the retransmissions.

This paper focuses on the use of specific interleaving techniques for use in W-CDMA (wideband code division multiple access). The linear equalization algorithm usually performs a matrix inversion on a matrix with a high level of sparseness, and such sparseness shouldn't be compromised with the use of a random interleaver; specific interleaver designs should be employed in order to keep the complexity of the equalization algorithm down to an acceptable level. The used equalizer is based on the linear MMSE (minimum mean square error) algorithm and is tested using the UMTS (universal mobile telecommunications system) HSDPA (high speed downlink packet access) standard as a basis, including the reference UMTS environments.

In this paper we derive general expressions for the performance of hierarchical multilevel quadrature amplitude modulation constellations (M-QAM), over flat Rayleigh fading environments with imperfect channel estimation. Cases of diversity reception with identical channels and with dissimilar channels, employing maximal ratio combining (MRC) are considered. Since hierarchical constellations are usually employed to achieve unequal bit error protection, the individual bit error rate (BER) of each bit stream is analyzed and it is shown that poor channel estimation has a more severe impact in the performance of the least protected bit streams.

Among radio technologies, multiple-input multiple-output (MIMO) systems have attracted wide research interests in recent years. It is widely recognized that MIMO systems can be employed for achieving a high capacity and a high diversity order, for mitigating the effects of various types of interfering signals, and for supporting space-division multiple-access (SDMA). In this study a MIMO assisted cellular system using distributed antennas is proposed and investigated, where a big number of antennas are distributed in the area covered by the system. The proposed system is capable of providing a platform for possibly integrating the conventional cellular systems into the future advanced, high-flexibility, ad-hoc and cooperative wireless networks. This system is considered for MBMS (multimedia broadcast multicast service) that enables mobile operators to deliver rich multimedia to a huge number of subscribers by broadcasting over the radio frequencies assigned to WCDMA.

A coherent detection of OFDM signals (Orthogonal Frequency Division Multiplexing) allows good performances in severely time-dispersive channels. However, coherent receivers require good channel estimates, a difficult task when the channel impulse response is long and/or when space diversity techniques are employed. Usually, the channel estimates are obtained with the help of pilot symbols multiplexed with data symbols, which reduces the useful bit rate, decreasing the spectral efficiency of the systems. To avoid this, we consider the use of implicit pilots instead of multiplexed pilots. Since the interference levels between data and pilots might be very high, we propose an iterative receiver with joint detection and channel estimation. Our performance results show that our technique allows the use of low-power pilots, with performances close to the ones with perfect channel estimation, even when space diversity techniques are employed.

The LMMSE (linear minimum mean square error) algorithm is one of the best linear receivers for DS-CDMA (direct sequence-code division multiple access). However, for the case of MIMO/BLAST (multiple input, multiple output/Bell Laboratories layered space time) with high loading, the perceived complexity of the LMMSE receiver is taken as too big, and thus other types of receivers are employed, yielding worse results. In this paper, we investigate the complexity of the solution to the MIMO LMMSE receiver's equations using block-Fourier algorithms, for both steady and unsteady channel situations.

The analytical bit error rate of hierarchical quadrature amplitude modulation formats, which include uniform and nonuniform constellations, over flat Rayleigh fading environments is studied in this paper. The analysis takes into account the effect of imperfect channel estimation and considers diversity reception with both independent identically and nonidentically distributed channels, employing maximal ratio combining.

Abstract Low rate convolutional and turbo codes that output non‐linear cyclic (NLC) codewords of lengthn = 2m,mbeing a positive integer, are described. These codes have a very low coding rate, which makes them especially suitable for spread spectrum systems where they can be used for simultaneously achieving error correction and bandwidth expansion. Due to the cyclic properties and codeword length of the component codes, branch metrics can be efficiently computed using the fast Fourier transform (FFT), enabling simple implementation of the encoder and decoder. Among the possible NLC base codes, special attention is given to the Tomlinson, Cercas, Hughes (TCH) codes family due to their good autocorrelation properties. It is shown by simulation that the turbo codes schemes studied usually perform better than traditional turbo codes (in this paper the universal mobile telecommunications system (UMTS), rate 1/3 turbo code was used as a reference). This improvement is accomplished at the cost of bandwidth expansion. One of the advantages of the presented solutions over other low rate codes is their ability to improve the synchronization process at the receiver due to the good autocorrelation properties of the available NLC codes (especially TCH codes). A comparison of performance between the UMTS uplink connection and an equivalent system using the proposed codes for a multiuser scenario in a multipath fading channel is presented showing the possibility of capacity increase when using these codes. Copyright © 2006 John Wiley & Sons, Ltd.

This paper focuses on the usage of an enhanced equalization-based receiver for WCDMA (wideband code-division multiple access) MIMO (multiple input, multiple output) BLAST (Bell Labs layered space time)-type systems. The receiver is based on the MMSE (minimum mean square error) algorithm coupled with an IPC (iterative partial cancellation) scheme. The scheme is tested in both an uncoded and coded setting, using the UMTS (Universal Mobile Telecommunications System) HSDPA (high speed downlink packet access) standard as a basis, and the reference UMTS environments.

In this paper we describe parallel concatenations of two convolutional encoders based on nonlinear cyclic codes with codewords of length n=2m, m being a positive integer. The resulting turbo codes have a very low coding rate, which makes them especially suitable for spread spectrum systems where they can be used for achieving simultaneously error correction and bandwidth expansion. Due to the cyclic properties and codeword length of the component codes, branch metrics can be efficiently computed using the Fast Fourier Transform, which enables simple implementation of the encoder and decoder for the component convolutional coding schemes. Among the possible base nonlinear cyclic codes, special attention is given to the TCH (Tomlinson-Cercas-Hughes) codes family due to their good autocorrelation properties, which enables the resulting turbo codes to achieve good BER performance. These schemes, similarly to the superorthogonal turbo codes, usually perform better than the traditional turbocodes at the cost of bandwidth expansion. Simulation results are presented both for the AWGN and for the uncorrelated Rayleigh fading channels. One of the advantages of the presented solution over the traditional turbo superorthogonal codes is its ability to improve the synchronization process at the receiver due to the good autocorrelation properties of the available nonlinear codes (specially TCH codes).