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Cochannel interference is one of the inevitable deleterious components in designing and analyzing of a wireless network. The use of multiple antennas at both transmitting and receiving nodes is a promising technique to suppress and/or alleviate the effect of cochannel interference on capacity. In this paper, we assess the effects of both antenna correlation and cochannel interference on the ergodic capacity of multiple-input multiple-output channels with covariance feedback. In particular, we consider a general family of spatial fading correlation model-called unitary-independent-unitary -which encompasses most of zero-mean channels with arbitrary fading profiles including the popular separable correlation channel models. We derive the average minimum mean-square error and signal-to-interference-plus-noise ratio of the parallel spatial streams using Berezin’s supermathematics. We then put forth the structure of optimal input covariance matrix maximizing the mutual information connected with the necessary and sufficient conditions as a generalization of the noise-limited case, which is tested by a simple iterative algorithm. Together with the powerful supermathematical framework, the result in the paper enables us to quantify the multiuser MIMO interference effects on the capacity in terms of spatial correlation and interference power heterogeneity.

The use of multiple-antenna arrays has attracted much attention for the physical layer security of wireless systems, where the so-called artificial-noise solution can be applied to enhance the communication confidentiality. In the first part of this study, the authors consider secure communication over a multiple-input single-output Rayleigh-fading channel in the presence of a multiple-antenna eavesdropper - referred to as a multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel. Specifically, secure beamforming with artificial noise is treated when the transmitter has access to full channel state information (CSI) of a legitimate channel but only partial CSI of an eavesdropper channel. First, the optimal power allocation between the information-bearing signal and artificial noise (or simulated interference) is derived to maximise the achievable secrecy rate in the presence of a weak or strong eavesdropper. Then, the first-order optimal power allocation strategy is developed in a switched fashion by selecting the best of weak- and strong-eavesdropper solutions for a general eavesdropping attack, and a closed-form expression is derived for the ergodic secrecy rate achieved by secure beamforming with this switched power allocation in the MISOME wiretap channel. The numerical results show that the switched power allocation is a simple but effective approach that nearly achieves the optimal secrecy rate.

The authors consider secure beamforming with artificial noise in a multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel, where a transmitter has access to full channel state information (CSI) of a legitimate channel but only partial CSI of eavesdropper channels. In the second part of this study, the authors first put forth a new notion of symbol error probability (SEP) for confidential information – called the ‘δ-secrecy SEP’ – to connect the reliability and confidentiality of the legitimate communication in MISOME wiretap channels. For single-antenna colluding and non-colluding eavesdroppers, the authors then quantify the diversity impact of secure beamforming with artificial noise on the δ-secrecy SEP and show that the artificial -noise strategy with n t transmit antennas preserves the secrecy diversity of order n t − n e for n e colluding eavesdroppers and n t − 1 for n e non-colluding eavesdroppers, respectively. In addition, the authors determine the optimal power allocation between the information-bearing signal and artificial noise to minimise the δ-secrecy SEP in the presence of weak or strong eavesdroppers, and further develop the switched power allocation for general eavesdropping attacks.

Physical-layer multicast transmission, which seeks to deliver information messages to all users simultaneously, is becoming more important in wireless systems with demand for various multimedia mobile applications such as Multimedia Broadcast Multicast Services. The spatial randomness of communicating nodes in a wireless network is one of inevitable uncertainties in the design and analysis of network information flow and connectivity. The use of multiple antennas at both transmitting and receiving nodes is the most promising strategy to increase spectral efficiency and communication reliability as well as to enhance physical-layer confidentiality of wireless systems. In this paper, we characterize multicasting in such a stochastic multiple-input multiple-output (MIMO) network where a probe transmitter broadcasts confidential data with sectorized transmission to legitimate receivers sitting in a region R. We first put forth a measure of the total amount of information flow, called the space—time capacity, into R in a spatial random field of legitimate receivers without accounting for intrinsic confidentiality at the physical layer. We then derive the space—time capacity into the sectoral region R and the nth nearest ergodic capacity in a Poisson field to characterize the spatial average and ordering of MIMO ergodic capacity achieved by legitimate receivers in R. Using the Mar\u{c}enko—Pastur law, we further assess the asymptotic space—time capacity and the nth nearest ergodic capacity per receive antenna as the antenna numbers tend to infinity. In the presence of eavesdropping, we determine a total amount of confidential information flow per receive antenna, called the space—time secrecy rate, into R in Poisson fields of receiving equivalents—with asymptotic arguments. Using an asymptotic secrecy graph on R, we also characterize local confidential connectivity such as the secrecy range, out-degree, and out-isolation probability of the probe transmitter. The framework developed in this work enables us to quantify the local information flow in random MIMO wireless networks by averaging first small-scale fading processes over time and then large-scale path losses over space.

In this paper, we study a power allocation technique for Tomlinson-Harashima precoding (THP) in multi-user multiple input single output (MISO) downlink systems. In contrast to previous approaches, a mutual information based method is exploited for maximizing the sum rate of zero-forcing THP systems. Then, we propose a simple power allocation algorithm which assigns proper power level for modulo operated users. Simulation results show that the proposed scheme outperforms a conventional water-filling method, and it provides similar performance with near optimal method with much reduced complexity.

Various multiple-input multiple-output techniques have been introduced to improve performance of next-generation systems. In single-cell environments, closed-loop MIMO schemes increase the system capacity as well as cell coverage. In cellular networks where interference coming from other cells is usually a dominant factor, several multiple-base-station cooperation schemes have been introduced to mitigate the intercell interference. In this article, we first provide an overview of scenarios and technology categories for multi-BS MIMO cooperation schemes. Next we introduce closed-loop multicell MIMO techniques adopted in IEEE 802.16m, which do not require data forwarding among different base stations. In particular, this article explains the overall operations which minimize overhead. We also present simulation results that confirm the efficiency of the presented interference mitigation method.

As one of the candidate fourth-generation mobile communication systems, the IEEE 802.16 m-based WiMAX 2.0 system is required to provide up to 1 Gb/s peak transmission rate. The most efficient solution to achieve this challenging objective is to utilize wider channel bandwidth. Multicarrier is the technology to utilize wider bandwidth for parallel data transmission across multiple RF carriers, which is well agreed as one of the key technologies to satisfy ITU-R IMTAdvanced requirements. As the evolution of the IEEE 802.16 e-based WiMAX 1.0 system, IEEE 802.16 m specifies physical and MAC layers to enable multicarrier technology for the WiMAX 2.0 system. This can lead to more than 1 Gb/s peak transmission rate for low-mobility users and 100 Mb/s peak transmission rate for high-mobility users. By having the protocol structure with a common MAC entity to control transmission by multiple physical-layer connections over different RF carriers, the network operator can aggregate either contiguous or non-contiguous spectrum resources with higher deployment flexibility, user throughput, and spectrum efficiency. This article provides an overview of the multicarrier technology supported by the IEEE 802.16 m draft standard1 for WiMAX 2.0 system, including not only the general operation principle but also some details of physical layer and MAC layer support.

Femtocells are low-power base stations operating in licensed spectrum, which are typically installed indoors in a house, small office, or home office by end users to provide exclusive or preferential access to a designated group of users as configured by the femtocell subscriber and/or the access provider. Femtocells have gained a lot of attention recently due to their advantages in terms of infrastructure cost saving and improved user experience in indoor environments. Several standards bodies, such as 3GPP, WiMAX Forum, and IEEE 802.16, have started to develop standard solutions to enable and optimize femtocells operation. However, there are some technical challenges to the success of femtocell technologies that need to be overcome before they can be deployed on large scales. This article presents an overview of WiMAX femtocell requirements, deployment models, and solutions in the near and long terms.

The performance of multiple-input-multiple-output systems with optimum combining (OC) is studied in a Rayleigh fading environment with arbitrary-power cochannel interference and thermal noise. Based on the joint eigenvalue distributions of quadratic functions of complex Gaussian matrices, a closed-form expression for the exact distribution of the output signal-to-interference-plus-noise ratio (SINR) is derived. A closed-form expression for the exact moment-generating function (MGF) of the output SINR of single-input-multiple-output (SIMO) systems is also derived. From the exact MGF, the moments of the output SINR and the symbol error rate of various M-ary modulation schemes are obtained. We verify the accuracy of our analytical results with numerical examples. The new analytical framework provides a simple and accurate way to assess the effects of equal- and unequal-power cochannel interferers and thermal noise on the performance of OC.

In this paper, we investigate the effects of the spatial fading correlation on the performance of a multiple-input multiple-output (MIMO) adaptive antenna system with optimum combining (OC) in the presence of multiple cochannel interferers over a correlated Rayleigh fading channel. Based on the Khatri's distribution functions of quadratic forms in complex Gaussian random matrices, we develop a unified determinant representation of those joint eigenvalue distributions. Taking into account the spatial correlation among the antenna elements at the transmitter or receiver, we derive the closed-form formulas for the probability density function and outage probability of the maximum output signal-to-interference ratio (SIR) in an interference-limited MIMO-OC system. Furthermore, the average output SIR and error probability are also investigated. From numerical examples, we show that a new theoretical approach gives a simple and accurate way to assess the performance of the MIMO-OC system over arbitrarily correlated fading channels

This paper presents approximate error rates of M-ary phase shift keying (MPSK) for optimum combining (OC) with multiple cochannel interferers in a flat Rayleigh fading channel. For the first-order approximation, we derive the closed-form expression for ordered mean eigenvalues of the interference-plus-noise covariance matrix, which facilitates performance evaluation for the OC with arbitrary numbers of interferers and antenna elements without Monte Carlo simulation and multiple numerical integrals. We also derive the closed-form expressions for approximate error rates of MPSK for the OC in terms of the average error rate of MPSK for maximal ratio combining (MRC). From the simple evaluation of ordered mean eigenvalues, we show that the first-order approximation gives a simple and accurate way to analyze the performance of the OC.

In this paper, an infrared intervehicle ranging and vehicle-to-roadside communication systems are studied. A direct-sequence spread-spectrum (DS-SS) technology is employed to obtain the robustness against multiuser interference and ambient light noise. We compare the correlation properties for various optical spreading codes such as an optical orthogonal code (OOC), a prime code, an extended prime code, and a modified m-sequence. The performance of the infrared DS-SS ranging and communication system is evaluated by computer simulation over a channel in consideration of multipath dispersion, multiuser interference, and a background light noise. The infrared DS-SS intervehicle ranging system using an OOC has lower ranging error rate (RER) than ranging systems using a prime code, an extended prime code, and modified m-sequences even if there is the interference from other users and lightwave dispersion. In the infrared DS-SS vehicle-to-roadside communication system, L-ary pulse position modulation (L-PPM) is used as a modulation scheme due to high average power efficiency. It is shown that the proposed system achieves smaller BER performance as the modulation order L increases and the proposed system with a (361,6,1,1) OOC has a smaller BER than that with a (181,6,1,1) OOC.

As a next generation railroad communication technology, 3GPP has been considered to provide railroad communication using LTE, known as LTE-R, including railroad control, passenger services, wireless surveillance video, etc. International Union of Railways (UIC) has commenced to generate LTE-R requirements. There are some technical challenges for LTE to be used for today's railroad communications because of the mobility of train up to 430km/h. Since railroad communication is related to public safety, very tight reliability requirement also needs to be met. In this paper, some technical considerations of LTE-R in terms of the possible frequency bands are provided. Upper limit of frequency band for high-speed train up to 500km/h is suggested by investigating the Doppler spread of wireless channel and physical channel structure of LTE.

We study the performance analysis of optimum combiner for M-ary phase-shift keying (MPSK) with multiple interferers in a flat Rayleigh fading channel. The first-order approximation is considered for the dual-antenna diversity reception. We derive the analytical solutions for the ordered mean eigenvalues of interference-plus-noise covariance matrix and a simple closed-form expression for the average symbol error rate of MPSK in the case of multiple cochannel interferers.

Block diagonalization is one approach for linear preceding in the multiple-input multiple-output broadcast channel that sends multiple interference free data streams to different users in the same cell. Unfortunately, block diagonalization neglects other cell interference, which limits the performance of users at the edge of the cell. This paper presents an OCI-aware enhancement to block diagonalization that uses a whitening filter for interference suppression at the receiver and a novel precoder using the interference-plus-noise covariance matrix for each user at the transmitter. For complex Gaussian matrix channels, the asymptotic sum rate of the proposed system is analyzed under a large antenna assumption for isotropic inputs and compared to conventional block diagonalization.

In this paper, we propose a low-rank pilot-symbol-aided (PSA) channel estimator for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. Group-wise pilot patterns are also proposed for the low-rank channel estimator. We evaluate the performance of the proposed low-rank channel estimator for various mobile channel environments by computer simulation. It is shown than the proposed channel estimator has better performance than the conventional 2D PSA channel estimator without increase of computational complexity and pilot overhead.

We investigate an adaptive subcarrier, bit, and power allocation algorithm for the downlink MIMO-OFDMA system. Using the singular value decomposition, the MIMO fading channel of each subcarrier is transformed into an equivalent bank of parallel SISO sub-channels. For the efficient allocation of the banks of parallel sub-channels, we define the problem of minimizing total transmit power with constraints on BER and transmission rate for users. Using the simplified problem formulation, we propose a sub-optimal adaptive subcarrier, bit, and power allocation algorithm which outperforms the fixed subcarrier allocation in the MIMO-OFDMA system.

This paper investigates the adaptive subcarrier and bit allocation algorithm for OFDMA systems. To minimize overall transmit power, we propose a novel adaptive subcarrier and bit allocation algorithm based on channel state information, Moreover, the block-wise method is considered based on channel variation for adaptive subcarrier and bit allocation. It is shown that a near optimal solution is obtained by the proposed algorithm which has low complexity compared to that of other conventional algorithms. Also, it is shown that the block-wise method significantly reduces the complexity and the feedback or side information though has a slight transmit power increase.

This work presents the approximate symbol error rate (SER) of M-ary phase shift keying (MPSK) for optimum combining (OC) with multiple co-channel interferers in a flat Rayleigh fading channel. The closed-form expression for the ordered mean eigenvalues of interference-plus-noise covariance matrix is derived for the first-order approximation to avoid Monte Carlo simulation and multiple numerical integrals in the cases of arbitrary numbers of interferers and antenna elements. We also derive the closed-form expression for approximate SER of MPSK for OC in terms of the average SER of MPSK for maximal ratio combining (MRC). From the simple evaluation of ordered mean eigenvalues, the first-order approximation gives a simple and accurate way to analyze the performance of OC in the presence of the arbitrary number of interferers.

In this paper, the performance of M-ary signals for optimum combining with multiple co-channel interferers is analyzed in a flat Rayleigh fading channel. The closed-form expressions of average symbol error rates of M-ary phase shift keying and M-ary differential phase shift keying are derived by using the moment generating function-based approach and the orthogonal approximation which is employed to evaluate the eigenvalues of the covariance matrix of the received interference-plus-noise. This analysis is a convenient way of evaluating the performance of optimum combining and comparing it with that of maximal-ratio combining. In the cases of single and multiple interferer(s), the accuracy of the approximation is assessed through computer simulations.

A sequence inverse keyed (SIK) code-division multiple-access (CDMA) system is proposed for an indoor wireless infrared channel. The proposed system employs an m-sequence as a signature sequence. On-off keying (OOK) is used as a modulation scheme. The bit error rate of the proposed system is evaluated by analysis and computer simulation. It is shown that the SIK OOK-CDMA system is more robust against multi-user interference than the OOK-CDMA system with an optical orthogonal code (OOC) in an indoor environment and the former has lower complexity than the latter due to zero-valued threshold detector in the receiver.