This paper considers constellation designs for 2×2 systems with a coherent dual-polarized antenna configuration. Such an architecture enables a four dimensional (4D) signal space that exploits polarization, and this paper considers hybrid constellations formed as a combination of amplitude/phase states and polarization states. For coherent detection, phase shift keying (PSK) is combined with polarization shift keying (PolSK) to produce constant-power PSK+PolSK constellations that consistently outperform PSK+PSK. Next, quadrature amplitude modulation (QAM) and amplitude phase shift keying (APSK) are combined with PolSK to construct hybrid QAM+PolSK and APSK+PolSK constellations, and constrained capacity results indicate the viability of coded modulation based on these signal spaces. For non-coherent detection, differential PSK (DPSK) is combined with PolSK to yield DPSK+PolSK signaling that does not require phase alignment at the receiver and outperforms DPSK+DPSK, both with and without the adverse effect of carrier frequency offset and symbol time offset. The methods are verified in over-the-air testing with universal software radio peripherals (USRPs) integrated in a dual-polarized testbed. Error performances of all proposed 4D hybrid constellations in an OFDM framework are analyzed under both quasi-AWGN and multipath fading scenarios.

An approach for associating signals from frequency-hopped (FH) emitters has recently been proposed that leverages polarization-frequency characterizations obtained from dual-polarized antenna architectures. An effective extension of these methods is considered here that incorporates multiple spatially separated dual-polarized antennas. Correlations in polarization-frequency responses, space-frequency responses, and hybrid combinations are leveraged to associate FH signals. The extended method is investigated using empirically informed simulations and over-the-air experiments to illustrate the efficacy of the approach. The over-the-air experiments involved four FH signals in a laboratory environment. A two-second interval was collected involving 2000 frequency hopping dwells. Results for a single manifold were found to experience misassociation errors, even at high SNR, due to similarities between polarization-frequency responses associated with the sources. When all manifolds are exploited, perfect association is achieved over the interval. Similar trends occur at low SNR, where increasing the number of available manifolds improves misassociation rates. It is concluded that additional diversities provided by a space-polarization architecture improve association performance.

This paper considers polarization shift keying (PolSK) modulation in wireless communication systems. The PolSK has previously been analyzed in additive white Gaussian noise (AWGN) for optical fiber and wireless communications. In our work, analytical results additionally focus on Rayleigh and Rician fading channels. It is shown that the dual-polarized signaling enjoys an ergodic capacity advantage over co-polarized signaling for a sufficiently large Rician K factor and signal-to-noise ratio. Specific PolSK constellations are formulated and analyzed in AWGN and Rayleigh fading channels. We examine the effect of the channel's polarization parameters on symbol error rates and achievable information. Also, considered are detection candidates to exploit statistical and instantaneous channel state information at the receiver. Over-the-air experiments were conducted to validate the principles. At higher modulation orders, uncoded PolSK shows an error rate advantage over unit symbol power constellations such as phase shift keying (PSK) and differential PSK with/without adverse carrier frequency offsets. The PolSK with dual-polarized antennas also outperforms the same modulation technique implemented with spatially separated co-polarized antenna elements in a line-of-sight (LoS) scenario. The proposed maximum likelihood PolSK detectors exploiting non-Gaussian statistics of the noise on the Poincaré sphere are validated to be superior to zero forcing and minimum mean square error equalization for a non-LoS scenario.

This paper considers the design of signal constellations for a 2 × 2 MIMO digital communication system with dualpolarized transmit and receive antennas. Specifically, it proposes four-dimensional “hybrid” constellations formed as the direct product of an absolute amplitude/phase state and a polarization state. We begin by imposing a constant symbol power constraint and combining phase shift keying (PSK) with polarization shift keying (PolSK) to produce hybrid constellations referred to as PSK+PolSK. As a motivating example, uncoded 8PSK+8PolSK is shown to enjoy a 1.1 dB gain over more conventional 8PSK+8PSK at a symbol error rate of 10-4in additive white Gaussian noise. When the power constraint is removed to form QAM+PolSK an APSK+PolSK constellations, the resulting performance suffers relative to comparable QAM+QAM and APSK+APSK constellations due to the polarization state's sensitivity to symbol power. Capacity calculations provide insight into the viability of coded modulation based on hybrid signaling. Particular hybrid constellations based on QAM+PolSK and APSK+PolSK were shown to provide a capacity advantage over comparable QAM+QAM constellations over a range of rates of practical value.

This paper explores fundamental properties of wireless communication using polarization-based modulation. Channel models for polarization shift keying (PolSK) are developed assuming additive white Gaussian noise (AWGN) and Rayleigh fading; the resulting analysis of a maximum likelihood receiver yields a bound on the symbol error rate (SER) for PolSK that is approximately 1.0 dB tighter than the previously published bound. In addition, insight into the fundamental performance of polarization-based modulation is gained by computing a bound on achievable rate derived from the channel's mutual information assuming equiprobable inputs. Finally, it is shown how statistical and instantaneous channel state information (CSI) can be exploited at the receiver to form asymmetric decision regions and improve SER performance.

This paper investigates fundamental properties of polarization-based modulation for wireless communication - and in particular the application of channel coding techniques to such systems. After developing appropriate channel models, bounds on achievable rates are computed, and the performance of exemplary LDPC codes are simulated; this is done for both additive white Gaussian noise channels as well as channels subject to i.i.d. Rayleigh fading. A novel “on/off” modulation scheme is developed that adaptively changes the information-bearing polarization states based on the singular value decomposition (SVD) of the realized channel; this scheme is shown to significantly outperform fixed-constellation schemes as well as adaptive-constellation schemes employing equal energy signals.

In this paper, we analyze packet-based energy efficiencies (EE) of battery-powered multiple-input multiple-output (MIMO) mobile radio communications over frequency-selective fading channels in the presence of cochannel interference (CCI). An efficient interference avoidance (IA) technique is proposed that relies on the conveyance of interference statistics derived at the receiver. Using the IA information, which incurs very small overhead, the transmitter selects the subchannels to be used for communications and on these subchannels, channel state information (CSI) derived from time-division duplexing (TDD) operation is applied in linear precoding strategies to minimize transmit energy consumption. The minimum energy solution is conditioned on various factors such as channel coding characteristics, linear precoding beams, interference avoidance schemes, and channel realizations. A method for identifying the transmit power leading to optimization is derived and simulation results show the effectiveness of the techniques over MIMO fading channels with different CCI conditions.

The transmit energy efficiency (EE) of space- polarization multiple-input multiple-output (SpPol-MIMO) architectures, dual-polarized MIMO architectures (DP-MIMO), and conventional co-polarized MIMO (CP-MIMO) schemes are compared for packet-based communication systems using full multiplexing without channel state information at the transmitter. We develop a closed-form approximation for assessing the EE of single-input single-output (SISO) and MIMO systems and show tradeoffs that exist between EE, spectral efficiency, modulation schemes, and packet designs. Using a hardware/software testbed, we also compare the EE among SISO, 2 × 2 CP-MIMO, 2 × 2 DP-MIMO, and 4 × 4 SpPol-MIMO architectures in frequency-selective MIMO channels. Emulation results from the testbed indicate that in the high SNR-regime, SpPol-MIMO provides the best EE performance in spatially uncorrelated channels, with EEs approximately four and two times better than SISO and 2 × 2 MIMO architectures, respectively. In Rician channels exhibiting either partial or high sAbstract-The transmit energy efficiency (EE) of space- polarization multiple-input multiple-output (SpPol-MIMO) architectures, dual-polarized MIMO architectures (DP-MIMO), and conventional co-polarized MIMO (CP-MIMO) schemes are compared for packet-based communication systems using full multiplexing without channel state information at the transmitter. We develop a closed-form approximation for assessing the EE of single-input single-output (SISO) and MIMO systems and show tradeoffs that exist between EE, spectral efficiency, modulation schemes, and packet designs. Using a hardware/software testbed, we also compare the EE among SISO, 2 × 2 CP-MIMO, 2 × 2 DP-MIMO, and 4 × 4 SpPol-MIMO architectures in frequency-selective MIMO channels. Emulation results from the testbed indicate that in the high SNR-regime, SpPol-MIMO provides the best EE performance in spatially uncorrelated channels, with EEs approximately four and two times better than SISO and 2 × 2 MIMO architectures, respectively. In Rician channels exhibiting either partial or high spatial correlation, DP-MIMO offers more than a 2× performance improvement relative to the other architectures at high SNR. At low SNR, SISO systems offer the best energy efficiency but also exhibit the lowest data rates. For all of the architectures, operating points are identified that provide near achievable data rates while operating at a local minimum in energy consumption.patial correlation, DP-MIMO offers more than a 2× performance improvement relative to the other architectures at high SNR. At low SNR, SISO systems offer the best energy efficiency but also exhibit the lowest data rates. For all of the architectures, operating points are identified that provide near achievable data rates while operating at a local minimum in energy consumption.

In this paper, we propose extending conventional co-polarized (CP) MIMO architectures for mobile-to-mobile communications to 4×4 space-polarized (SP) MIMO architectures. SP-MIMO systems employ spatially-separated dual-polarized antennas (where each dual-polarized antennas has two co-located orthogonally-polarized elements) in place of spatially separated CP antennas, effectively doubling the number of antenna ports without dramatically increasing the antenna system form factor. To analyze the potential gains that can be achieved with a SP-MIMO architecture, a mobile-to-mobile (M2M) wideband channel model is developed using a three-dimensional (3D) geometry-based stochastic channel model (GSCM). GSCM channel realizations are characterized by several parameters including the angular distributions of the scatterers, angles of arrival (AoA), angles of departure (AoD), antenna gain patterns, the Rician K-factor, the maximum Doppler frequency, the cross-polar discrimination (XPD), and the co-polar ratio (CPR). Using the SP-MIMO channel model, we study and quantify performance shifts that are possible when the CP antennas in a CP-MIMO systems are each replaced with a dual-polarized antenna, leading to a SP-MIMO system. Using simulation, we compare the performance of the resulting 4×4 SP-MIMO system relative to the conventional 2×2 CP-MIMO system in terms of capacity and diversity measures. Results show that, in the case of identical total transmit powers, 4×4 SP-MIMO systems dramatically outperform 2×2 CP counterparts in a variety of non-isotropic scattering and multipath fading propagation environments.

A 2times2 multiple-input multiple-output (MIMO) architecture using dual-polarized antennas (DPAs) is considered with orthogonal frequency division multiplexing (OFDM). The performance of DPAs is evaluated for adaptive polarization (AP) transmission techniques in time-varying multipath channels impaired by polarization mode dispersion (PMD) and polarization-dependent loss (PDL). AP transmission techniques considered include power gain maximization, polarization dispersion minimization for interference avoidance, polarization multiplexing with water-filling, and a suboptimal multiplexing strategy that enables direct recovery of the polarization multiplexed streams, thereby simplifying the design of the receiver. Measured time-varying dual-polarized channel realizations from mobile-to-mobile experiments are used to estimate the capacity, diversity, and interference avoidance performance of the adaptive approaches.

A three-dimensional (3-D) analytical model for mobile-to-mobile communications is presented. From the analytical model, the envelope level crossing rate and average fade duration are derived for a 3-D non-isotropic scattering environment. The obtained analytical results are compared with measured data. The close agreement between the analytical and empirical curves confirms the utility of the proposed model.

A three-dimensional reference model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles travelling along expressways in a metropolitan area. The measured data is processed and the channel statistics obtained from the reference model and from the empirical measurements are compared. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model.

In this paper, the optimal form of a channel matrix is derived to maximize the MIMO capacity in a LOS environment. Antenna response functions are proposed to achieve the optimal form and suboptimal results are considered. In designing an antenna to maximize the capacity, the objective is to increase the slope of the far-field phase response without sacrificing too much antenna gain. Such a constraint has not typically been considered in antenna design and should be further explored.

The performance of optimum combining is studied in a Rayleigh fading environment with arbitrary-power cochannel interferers and thermal noise. Based on the joint eigenvalue distributions of quadratic forms in complex Gaussian matrices, closed form expressions for exact moment generating function (MGF) of the output signal-to-interference-plus-noise ratio are derived. From the exact MGF, the moments of the output SINR and the symbol error rate of various M-ary moulation schemes are obtained. We verify the accuracy of our analytical results by 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 optimum combining.

The performance of multi-antenna receivers in co-channel interference is investigated for narrow-band links in a non-line-of-sight (NLOS) mobile-to-mobile channel. A novel architecture utilizing antenna down-selection is analyzed in simulation and compared with the performance of conventional architectures. Various down-selection criteria are proposed and analyzed. The simulation results show excellent performance enhancement when channel state information is available at the receiver for all of the co-channel sources. For many applications, such knowledge would be impractical, so suboptimal down-selection solutions are developed and results are compared in terms of estimated complementary cumulative distribution functions of output signal-to-interference-plus-noise ratio (SINR) derived from Monte Carlo simulations

Several new "sum-of-sinusoids" models have recently been introduced for the simulation of Rayleigh fading channels. These models are statistical in nature implying that their simulation parameters such as the Doppler frequencies are random. They have been shown to accurately reproduce some of the desired statistical properties of the faded envelope such as the time autocorrelation and the level crossing rate. However, a comparative analysis of these models, hitherto scattered throughout the literature, is not available. This paper compares these models in terms of their complexity and performance. The performance assessment is based upon the variance of the time average statistical properties from their ideal ensemble averages.

Mobile-to-mobile channels find increasing applications in futuristic intelligent transport systems, ad hoc mobile wireless networks, and relay-based cellular networks. Their statistical properties are quite different from typical cellular radio channels, thereby requiring new methods for their simulation. This paper proposes a "double-ring" model to simulate the mobile-to-mobile local scattering environment, and develops sum-of-sinusoids (SoS)-based models for simulating such channels. The proposed models produce waveforms having desired statistical properties with good accuracy, and also remove some drawbacks of an existing model derived by using the discrete line spectrum simulation method.

The paper proposes a simple cascade estimation method to detect both carrier frequency and sampling clock offsets for orthogonal frequency-division multiplex (OFDM) systems. The new approach needs much less computation than the typical maximum likelihood (ML) method and generates a satisfactory estimate, which is validated by simulation results.

The use of multiple input and multiple output (MIMO) antennas is a promising technique for increasing the capacity of wireless communication systems. Huge capacities are guaranteed only when channels between different transmitting and receiving antenna pairs are statistically independent. In this paper, we investigate the capacities of MIMO systems in a mobile-to-mobile environment by employing a "two ring" model which is simple extension of previous "one ring" model. With this model, we investigate the spatial correlation and information theoretic channel capacity of MIMO systems that use omni-directional antennas as well as MIMO systems with directional antennas. We show that MIMO systems with directional antennas yield good spatial decorrelation between antenna pairs even in a scarce scattering environment, while MIMO systems with omni-directional antennas suffer capacity degradation either when antennas are located closely each other, or when there is not enough multipath richness. Directional antennas guarantee the independence between different antenna pairs by not sharing scatterers, and the capacity is maximized by exploiting the independence between antenna pairs.

The BER degradation caused by imperfect channel estimation as well as the adverse effect of jamming on pilot symbols, which are used for the channel estimation (CE), is often neglected while analyzing OFDM und MC-CDMA systems leading to over-optimistic results. Therefore, to provide a more realistic analysis, we analyze the vulnerability of pilot symbol aided CE schemes for OFDM/MC-CDMA systems to narrowband and partial band jamming. We derive closed form BER expressions for studying the effect of imperfect CE for OFDMA/MC-CDMA in the absence of jamming in a frequency selective Rayleigh fading environment. We extend these results via simulations and theory (wherever permitted by mathematical tractability) to account for jamming. Some possible solutions such as the use of boosted pilots and the use of jamming side information, whenever available, to excise the jammed pilots or provide MMSE equalization are proposed to reduce the impact of jamming on the CE.

Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM.

This paper studies the statistical properties of the conventional frequency offset estimation algorithm. Analytical expressions describing the mathematic expectation and the variance are derived for both the integer and the fractional frequency offset estimation algorithms. The theoretical equations presented in this paper provide improved agreement with simulation results in comparison to those previously reported in the literature.