Philippa A. Martin

Multiple serial and parallel concatenated single parity-check codes

Single parity-check (SPC) codes are applied in both parallel and serial concatenated structures to produce high-performance coding schemes. The number of concatenations or stages, M, is increased to improve system performance at moderate-to-low bit-error rates without changing the overall code parameters (namely, code rate and code block length). Analytical bounds are presented to estimate the performance at high signal-to-noise ratios. The SPC concatenated codes are considered with binary phase-shift keying and with 16-quadrature amplitude modulation bit-interleaved coded modulation on the additive white Gaussian noise channel and the independent Rayleigh fading channel. Simulations show that the four-stage serial or parallel concatenated SPC codes can, respectively, outperform or perform as well as 16-state turbo codes. Furthermore, decoding complexity is approximately 9-10 times less complex than that of 16-state turbo codes. The convergence behavior of both serial and parallel concatenated SPC codes is also discussed.

MIMO Cognitive Radios with Antenna Selection

In this paper, we propose two solutions to the problem of joint transmit-receive antenna selection in a multiple-input multiple-output (MIMO) cognitive radio (CR) system. Our objective is to maximize CR data rates and satisfy interference constraints at the primary user (PU) receiver(s). In the first we approximate the original non-convex optimization problem using an iterative approach solving a series of smaller convex problems. Second we present a novel, norm-based transmit receive antenna selection technique that simultaneously improves throughput while maintaining the PU interference constraints. We show that this approach yields near optimal results with massive complexity reductions. We make a performance comparison between the proposed approaches and the optimal exhaustive search approach. We provide an analysis of the exhaustive search and relate selection gains to system parameters such as the shadow fading standard deviation, the path loss exponent and the number of PUs per square kilometer. Our results establish that antenna selection is a promising option for future MIMO CR devices in sparse PU environments.

On multilevel codes and iterative multistage decoding

This paper develops an approach to iterative multistage decoding of multilevel codes. This involves passing reliability information to previous and subsequent decoders instead of only hard decisions to subsequent decoders. The paper also develops an adaptive version of the suboptimal soft output decoding algorithm of Picart and Pyndiah (1996). This adaptive algorithm provides a gain of approximately 0.24 dB at a bit error rate (BER) of 10/sup -5/ after four iterations and approximately 0.43 dB after ten iterations over the algorithm of Picart et al. If the adaptive algorithm is used in conjunction with iterative multistage decoding then a gain of approximately 0.62 dB is obtained at a BER of 10/sup -5/ after four iterations and approximately 0.9 dB after ten iterations over the algorithm of Picart et al.

Grouped multilevel space-time trellis codes

Space-time trellis codes (STTCs) generally provide coding and diversity gains, but only transmit one data symbol per time slot. Using higher order modulations incurs high decoding complexity and lengthy code searches. Multi-layer schemes using multiple STTCs over subgroups of antennas provide higher throughput, but require as many receive as transmit antennas and have reduced diversity gains. Here, we develop grouped multilevel STTCs that can provide the high throughput of multi-layered schemes while realizing larger diversity gains. Any number of receive antennas can be used. An example is shown that achieves 6 bits/sec/Hz using 16-QAM and 4 transmit antennas.

Distance based adaptive scaling in suboptimal iterative decoding

This article develops an alternative adaptive iterative Chase (1972) based decoding algorithm for block turbo/product codes. The decoder considers only a small subset of codewords, so that estimates of the extrinsic information are required in some cases. This article develops such an estimate based on code distance properties.

Differential Spatial Modulation for APSK in Time-Varying Fading Channels

We develop a novel differential spatial modulation (DSM) scheme for amplitude phase shift keying (APSK) modulation, which can either improve throughput or performance over DSM for PSK. Then we investigate the impact of time-varying fading on DSM. We find performance degrades if the fading is too fast due to differential detection. The impact of a long outer error control code (ECC) is also considered. Its performance is limited by the slowly varying channel required for differential detection. We consider using reconfigurable antennas to periodically change the channel conditions and hence significantly improve coded performance for DSM systems.

Wireless Communications: Algorithmic Techniques

This book introduces the theoretical elements at the basis of various classes of algorithms commonly employed in the physical layer (and, in part, in MAC layer) of wireless communications systems. It focuses on single user systems, so ignoring multiple access techniques. Moreover, emphasis is put on single-input single-output (SISO) systems, although some relevant topics about multiple-input multiple-output (MIMO) systems are also illustrated.Comprehensive wireless specific guide to algorithmic techniquesProvides a detailed analysis of channel equalization and channel coding for wireless applicationsUnique conceptual approach focusing in single user systemsCovers algebraic decoding, modulation techniques, channel coding and channel equalisation

Pilot Contamination Reduction Using Time-Shifted Pilots in Finite Massive MIMO Systems

Pilot contamination is an issue affecting massive MIMO systems. It is known that a time-shifted pilot method can be used to reduce pilot contamination from neighboring cells when the number of antennas at the base station is infinitely large [1]. In our research, we analyze the effect of a finite number of antennas on the sum rate of the time-shifted method. Numerical results show that the time-shifted pilot method can improve uplink and downlink transmission rate compared to time-synchronized method for small number of spatial multiplexing users. However, for higher number of spatial multiplexing users, the time-shifted method will need more antennas at the base station in order to have noticeable improvement over the time-synchronized method.

List-Based Group-Wise Symbol Detection for Multiple Signal Communications

Co-channel interference (CCI) occurs in a wireless receiver when multiple signals are present. The receiver experiences excessive CCI under overload which occurs when there are more signals than receive antennas. This makes separation and estimation of the transmitted data signals difficult. We develop a novel reduced-complexity receiver structure for the separation and symbol detection of multiple co-channel signals in frequency-flat Rayleigh fading channels. Moreover, we show that list-based group-wise processing can achieve better performance at low and moderate signal-to-noise ratios than existing group-wise soft information processing schemes. The receiver is equipped with multiple antennas and developed to work under overload. Its structure consists of a linear preprocessor followed by a nonlinear reduced-complexity symbol detector. The proposed list group-search detection (LGSD) algorithm relies on list feedback and reduces complexity by iteratively searching over groups of transmitted symbols. It outputs a list of likely data symbols which is well suited to further processing using soft input error control decoders. Simulation shows that LGSD can achieve near optimum joint maximum likelihood performance under overload at significantly lower complexity.

Extension of Quickest Spectrum Sensing to Multiple Antennas and Rayleigh Channels

In this letter, we study quickest spectrum sensing for cognitive radios with multiple receive antennas in Gaussian and Rayleigh channels. We derive the probability density function for the fading case and analytically compute the upper bound and asymptotic worst-case detection delay for both of the cases. The extension into multiple antennas allows us to gain insights into the reduction in detection delay that multiple antennas can provide. Although sensing in a Rayleigh channel is more challenging, good sensing performance is still demonstrated.