Mutlu Koca

Performance Analysis of Spatial Modulation over Correlated Fading Channels

We present a general upper bounding framework for the average bit error probability of spatial modulation over correlated Rayleigh and Rician channels. The proposed approach provides a closed form upper bound for correlated Rayleigh fading conditions whereas for correlated Rician channels it leads to the numerical evaluation of a single integral formula. The framework is applicable to a general class of linear modulation alphabets and any number of transmit/receive antennas. Theoretical derivations are validated via simulation results.

Optical Spatial Modulation Over Atmospheric Turbulence Channels

We present a novel multiple-input multiple-output (MIMO) optical modulation method combining antenna shift keying with joint pulse position and amplitude modulations. The proposed approach, denoted optical spatial modulation (OSM), offers better power and spectral efficiencies than conventional MIMO optical modulation methods. We also provide a theoretical analysis framework for the performance of both uncoded and coded OSM in free space optical communication channels with weak-to-moderate and moderate-to-strong atmospheric turbulence. Theoretical derivations are validated with simulations, which illustrate the feasibility of the proposed transceiver in key design metrics, such as spectral efficiency, error performance, and robustness against scintillation effects.

Robust detection of ultra-wideband signals in non-Gaussian noise

A robust receiver is proposed for time-hopping pulse-position-modulation impulse radio systems transmitting over frequency-selective ultra-wideband channels, which aims to remove large-amplitude outliers that occur due to impulsive noise. The proposed system contains a rake structure for collecting the signal energy, which is dispersed over a large number of paths as a result of the wide channel bandwidth. Before the paths are merged via maximal ratio combining, they are passed through nonlinearities to trim the outlier noise components. The robust receiver so designed is shown to outperform the conventional linear rake receiver that consists of only matched filters at its fingers.

Cooperative Multiple Access under Energy Harvesting Constraints

We consider a cooperative multiple access channel (MAC) with two energy harvesting transmitters. The transmitters perform delay constrained transmission, i.e., every information block is encoded, transmitted and decoded between two consecutive energy harvests. We aim to maximize the achievable departure region over a finite transmission duration. We formulate the departure region maximization as a convex optimization problem. We propose an iterative algorithm which uses a directional waterfilling strategy to calculate the optimal power components. The departure region obtained by cooperation is shown to be significantly larger than that of a MAC without cooperation under the same energy arrival patterns. As a special case, we also analyze an energy harvesting relay channel with full duplex cooperation.

An Ultra Low-Power Dual-Band IR-UWB Transmitter in 130-nm CMOS

In this brief, a 0-960-MHz/3.1-5-GHz dual-band ultra low-power impulse-radio ultrawideband transmitter is presented. The pulse transmitter integrated circuit is fabricated using a 130-nm CMOS process with the core die area of 0.1 mm2. At 1-MHz pulse repetition frequency, the power consumption values are measured in the lower and the upper bands as 5.6 and 31 μW, respectively. The lower and the upper band “off-time” power consumptions of the transmitter are 0.36 and 1.7 μW, respectively. The dc-to-radio-frequency conversion efficiencies are 11.1% in the lower band and 4.8% in the upper band.

Bit-interleaved coded spatial modulation

We address coded spatial modulation (CSM) and present a novel approach denoted as bit-interleaved coded spatial modulation (BICSM) with iterative demodulation/decoding. The proposed transceiver architecture alleviates some drawbacks of the previously proposed CSM systems, such as being limited to a particular class of trellis codes or being effective only in limited channel scenarios. We specifically address the performance of BICSM over correlated Rayleigh and Rician fading channels and provide a general framework for the error performance analysis. Simulation results illustrate that BICSM provides not only significant performance improvements against channel fading in comparison to other CSM approaches but also higher robustness against antenna correlation effects.

Measurements of impulsive noise in broad-band wireless communication channels

Electrical and mechanical equipments can be major sources of interference for wireless systems. This paper presents the effects of both noise and interference in a wide frequency band between 100 kHz and 3 GHz. Electromagnetic field (EMF) strength measurements of the impulsive noise taken at various locations such as computer labs, TV stations and hospitals are presented. Measurement results are fitted into a mathematical model and it is shown that the amplitude probability distribution (APD) functions derived from the measurements can be described by the Middleton Class-A model.

Broadband beamforming with power complementary filters

This paper addresses the design of broadband finite impulse response (FIR) beamformers with a power complementarity property. The power complementarity requirement is needed to preserve the whiteness of the channel noise at the beamformer output, which allows the application of optimum trellis-based equalizers to the output signal. The power complementarity property imposes non-negative definite quadratic constraints on the beamforming filters so that the beamformer design is expressed as a constrained quadratic optimization problem. Two approaches are proposed to solve this problem. The first method is a Lagrangian relaxation technique, which exploits the fact that the dual mathematical problem reduces to the unconstrained minimization of a convex function over a convex domain. A second approach employs a cascaded lattice representation of the power complementary filterbank and performs the beamformer design incrementally, one lattice stage at a time.

Dual-Polarized Spatial Modulation Over Correlated Fading Channels

We address multiple-input multiple-output (MIMO) communication employing spatial modulation (SM) with dual-polarized (DP) antennas. The proposed architecture adds the polarization dimension to the conventional SM mappings and offers performances, which are comparable to or under certain conditions even better than those of the uni-polarized systems while occupying half as much space. We consider the generalized spatially correlated Rayleigh and Rician fading channel models and present an average bit-error probability upper bounding framework for the proposed DP SM-MIMO system. The theoretical error analysis is also extended to the case where the channel coefficients are estimated with Gaussian estimation errors. This upper bounding method is also used to determine the conditions in which the dual-polarized SM is better than equivalent systems with uni-polarized antennas. Theoretical derivations are also validated by extensive simulations, both corroborating that SM combined with dual-polarization forms an attractive alternative not only for its improved multiplexing gains and space efficiency but also for performance gains over correlated channels.

Doubly Iterative Equalization of Continuous-Phase Modulation

In this paper, a doubly iterative receiver is proposed for joint turbo equalization, demodulation, and decoding of coded binary continuous-phase modulation (CPM) in multipath fading channels. The proposed receiver consists of three soft-input soft-output (SISO) blocks: a front-end soft-information-aided minimum mean square error (MMSE) equalizer followed by a CPM demodulator and a back-end channel decoder. The MMSE equalizer, combined with an a priori soft-interference canceler (SIC) and an a posteriori probability mapper, forms a SISO processor suitable for iterative processing that considers discrete-time CPM symbols which belong to a finite alphabet. The SISO CPM demodulator and the SISO channel decoder are both implemented by the a posteriori probability algorithm. The proposed doubly iterative receiver has a central demodulator coupled with both the front-end equalizer and the back-end channel decoder. A few back-end demodulation/decoding iterations are performed for each equalization iteration so as to improve the a priori information for the equalizer. As presented in the extrinsic information transfer (EXIT) chart analysis and simulation results for different multipath fading channels, this provides not only faster convergence to low bit error rates, but also lower computational complexity.