Improved Spatial Modulation Techniques for Wireless Communications

Transmission and reception methods with multiple antennas have been demonstrated to be very useful in providing high data rates and improving reliability in wireless communications. In particular, spatial modulation (SM) has recently emerged as an attractive transmission method for multiple-antennas systems due to its better energy efficiency and lower system complexity. This thesis is concerned with developing transmission techniques to improve the spectral efficiency of SM where antenna/subcarrier index involves in conveying information bits. In the first part of the thesis, new transmission techniques are developed for SM over frequency-flat fading channels. The first proposed scheme is based on a high-rate space-time block code instead of using the classical Alamouti STBC, which helps to increase the spectral efficiency and achieve a transmit diversity order of two. A simplified maximum likelihood detection is also developed for this proposed scheme. Analysis of coding gains and simulation results demonstrate that the proposed scheme outperforms previously-proposed SM schemes at high data transmission rates. Then, a new space-shift keying (SSK) modulation scheme is proposed which requires a smaller number of transmit antennas than that required in the bi-space shift keying (BiSSK). Such a proposed SSK-based scheme is obtained by multiplexing two in-phase and quadrature generalized SSK streams and optimizing the carrier signals transmitted by the activated antennas. Performance of the proposed scheme is compared with other SSK-based schemes via minimum Euclidean distance analysis and computer simulation. The third scheme proposed in this part is an improved version of quadrature SM (QSM). The main feature of this proposed scheme is to send a second constellation symbol over the in-phase and quadrature antenna dimensions. A significant performance advantage of the proposed scheme is realized at the cost of a slight increase in the number of radio-frequency (RF) chains. Performance comparisons with the most recent SM schemes confirm the advantage of the proposed scheme. The last contribution of the first part is an optimal constellation design for QSM to minimize the average probability of error. It is shown that, the error performance of QSM not only depends on the Euclidean distances between the amplitude phase modulation (APM) symbols and the energies of APM symbols, but also on the in-phase and quadrature components of the QSM symbols. The analysis of the union bound of the average error probability reveals that at a very large number of transmit antennas, the optimal constellations for QSM converge to a quadrature phase shift keying (QPSK) constellation. Simulation results demonstrate the performance superiority of the obtained constellations over other modulation schemes. In the second part of the thesis, the applications of SM in frequency-selective fading channels are studied. First, a new transmission scheme that employs SM for each group of subcarriers in orthogonal frequency-division multiplexing (OFDM) transmission is investigated. Specifically, OFDM symbols in each group are passed through a precoder to maximize the diversity and coding gains, while SM is applied in each group to convey more information bits by antenna indices. Performance analysis and simulation results are carried out to demonstrate the superiority of the proposed scheme over a previously-proposed combination of SM and OFDM. Next, the performance of OFDM based on index modulation and a flexible version of OFDM, knows as OFDM with multiple constellations, is compared for both case of "no precoding'' and "with precoding'' of data symbols. It is shown that the precoded OFDM with multiple constellations outperforms precoded-IM based OFDM systems over frequency-selective fading channels. The last part of the thesis investigates a multiuser downlink transmission system based on in-phase and quadrature space-shift keying modulation and precoding to reduce the minimum number of transmit antennas while keeping the complexity of the receiver low. In addition to the maximum likelihood (ML) detection, the low complexity zero forcing (ZF) receiver is also studied. Theoretical upper bounds for the error probabilities of both ML and ZF receivers are obtained and corroborated with simulation results

Spatial Modulation with Energy Detection: Diversity Analysis and Experimental Evaluation

In this paper, we present a non-coherent energy detection scheme for spatial modulation (SM) systems. In particular, the use of SM is motivated by its low-complexity implementation in comparison to multiple-input multiple-output (MIMO) systems, achieved through the activation of a single antenna during transmission. Moreover, energy detection-based communications restrict the channel state information to the magnitude of the fading gains. This consideration makes the design applicable for low-cost low-powered devices since phase estimation and its associated circuitry are avoided. We derive an energy detection metric for a multi-antenna receiver based on the maximum-likelihood (ML) criterion. By considering a biased pulse amplitude modulation, we develop an analytical framework for the SM symbol error rate at high signal-to-noise ratios. Numerical results show that the diversity order is proportional to half the number of receive antennas; this result stems from having partial receiver channel knowledge. In addition, we compare the performance of the proposed scheme with that of the coherent ML receiver and show that the SM energy detector outperforms its coherent counterpart in certain scenarios, particularly when utilizing non-negative constellations. Ultimately, we implement an SM testbed using software-defined radio devices and provide experimental error rate measurements that validate our theoretical contribution.Comment: This work has been submitted to an IEEE journal for possible publicatio

Two-Way Relaying Using Constant Envelope Modulation and Phase-Superposition-Phase-Forward

In this article, we propose the idea of phase-superposition-phase-forward (PSPF) relaying for 2-way 3-phasecooperative network involving constant envelope modulation with discriminator detection in a time-selectiveRayleigh fading environment. A semi-analytical expression for the bit-error-rate (BER) of this system is derived andthe results are verified by simulation. It was found that, compared to one-way relaying, 2-way relaying with PSPFsuffers only a moderate loss in energy efficiency (of 1.5 dB). On the other hand, PSPF improves the transmissionefficiency by 33%. Furthermore, we believe that the loss in transmission efficiency can be reduced if power isallocated to the different nodes in this cooperative network in an ‘optimal’ fashion. To further put the performanceof the proposed PSPF scheme into perspective, we compare it against a phase-combining phase-forwardtechnique that is based on decode-and-forward (DF) and multi-level CPFSK re-modulation at the relay. It wasfound that DF has a higher BER than PSPF and requires additional processing at the relay. It can thus beconcluded that the proposed PSPF technique is indeed the preferred way to maintain constant envelope signalingthroughout the signaling chain in a 2-way 3 phase relaying system

Cooperative Transmission Techniques in Wireless Communication Networks

Cooperative communication networks have received significant interests from both academia and industry in the past decade due to its ability to provide spatial diversity without the need of implementing multiple transmit and/or receive antennas at the end-user terminals. These new communication networks have inspired novel ideas and approaches to find out what and how performance improvement can be provided with cooperative communications. The objective of this thesis is to design and analyze various cooperative transmission techniques under the two common relaying signal processing methods, namely decode-and-forward (DF) and amplify-and-forward (AF). For the DF method, the thesis focuses on providing performance improvement by mitigating detection errors at the relay(s). In particular, the relaying action is implemented adaptively to reduce the phenomenon of error propagation: whether or not a relay’s decision to retransmit depends on its decision variable and a predefined threshold. First, under the scenario that unequal error protection is employed to transmit different information classes at the source, a relaying protocol in a singlerelay network is proposed and its error performance is evaluated. It is shown that by setting the optimal signal-to-noise ratio (SNR) thresholds at the relay for different information classes, the overall error performance can be significantly improved. Second, for multiple-relay networks, a relay selection protocol, also based on SNR thresholds, is proposed and the optimal thresholds are also provided. Third, an adaptive relaying protocol and a low-complexity receiver are proposed when binary frequency-shift-keying (FSK) modulation is employed and neither the receiver nor the transmitter knows the fading coefficients. It is demonstrated that large performance improvements are possible when the optimal thresholds are implemented at the relays and destination. Finally, under the scenario that there is information feedback from the destination to the relays, a novel protocol is developed to achieve the maximum transmission throughput over a multiple-relay network while the bit-error rate satisfies a given constraint. With the AF method, the thesis examines a fixed-gain multiple-relay network in which the channels are temporally-correlated Rayleigh flat fading. Developed is a general framework for maximum-ratio-combining detection when M-FSK modulation is used and no channel state information is available at the destination. In particular, an upper-bound expression on the system’s error performance is derived and used to verify that the system achieves the maximal diversity order. Simulation results demonstrate that the proposed scheme outperforms the existing schemes for the multiple-relay network under consideration

A Novel Chirp Slope Keying Modulation Scheme for Underwater Communication

A digital modulation method using Chirp-Slope Keying (CSK) is developed for coherent underwater acoustic communications. Effective signal detection is a critical stage in the implementation of any communications system; we will see that CSK solves some significant challenges to reliable detection. This thesis is primarily based on analyzing the effectiveness of CSK through simulations using Matlab\u27s Simulink for underwater communications. The procedure begins with modulating a chirp\u27s slope by random binary data with a linear-down-slope chirp representing a 0, and a linear-up-slope chirp representing a 1. Each received symbol is demodulated by multiplying it with the exact linear-up-slope chirp and then integrating over a whole period (i.e., integrate and dump). This slope-detection technique reduces the need for the extensive recognition of the magnitude and/or the frequencies of the signal. Simulations demonstrate that CSK offers sturdy performance in the modeled ocean environment, even at very low signal-to-noise ratio (SNR). CSK is first tested using the fundamental communication channel, Additive White Gaussian Noise (AWGN) channel. Simulation results show excellent BER vs. SNR performance, implying CSK is a promising method. Further extensive analysis and simulations are performed to evaluate the quality of CSK in more realistic channels including Rayleigh amplitude fading channel and multipath