The wireless propagation environment between the transmitter and the receiver plays a major role in wireless communication. It is this environment that gives rise to the multipath. In contrast to the conventional wisdom, the impact of this multipath on wireless communication is now considered as something that can be changed. Instead of introducing foreign objects like "reflective surfaces" to physically alter the wireless environment, in this paper we study an emerging area of study known as "mediumband wireless communication", that can statistically manipulate the effect of the wireless propagation environment. The unique bimodal nature of the probability density function (PDF) of the desired fading factor in mediumband channels means this new class of channels have the potential to reduce the deep fading considerably. In this paper, we propose an accurate PDF in analytically convenient form to capture this bimodal nature, and analyse the extent of the effect of deep fading avoidance. The objective is to enable further analysis and simulation of mediumband channels and also to ease the study of the wider impact of mediumband wireless communication for future wireless communication.

Finding inventive and/or innovative ways to enhance the quality of wireless communication by altering the wireless channel is in the cutting edge of modern wireless communication research. Some looks in to ways to introduce foreign objects like "reflective surfaces" to manipulate the wireless environment. Deviating from this line of research, in this paper, a receiver architecture with a "feedback control loop" exploiting a "Lüneburg lens " and a dipole antenna array (but with a single RF chain) is proposed and studied. The proposed method iteratively modifies the relative permittivities of the antenna elements in order to alter the effect of gains and phase differences of different multipath components, thus enhancing the quality of wireless communication.

The fundamental phenomenon widely known as “multipath” is unavoidable in wireless communication, and affects almost every element of modern wireless communication systems. The impact of multipath on the received signal depends on whether the delay spread (i.e., spread of time delays associated with different multipath components) is large or small relative to the signalling period of the wireless communication system. In narrowband systems, the delay spread is about one tenth (or less) of the signalling period. The delay spread and the signalling period of broadband systems are in the same order of magnitude. In between these two extremes, there appears to exist an important, yet overlooked, class of systems whose delay spread is neither small nor large enough for them to fall into these two basic classes. In this paper, the effect of multipath on this class of systems denoted henceforth as “mediumband” is studied, and its channel is characterized in compact form in order to enable future research into this class of wireless communication systems.

Light-fidelity (LiFi) is recognised as a promising technology for next generation wireless access networks. However, limited research efforts have been spent on the uplink (UL) transmission system in LiFi networks. In this article, a wireless infrared (IR)-based LiFi UL system is investigated. In particular, we focus on the performance of a single static user under the influence of random device orientation and link blockage. Simulations and mathematical analysis have been used to evaluate the UL system performance. The analytical expressions for the UL optical wireless channel and signal-to-noise ratio (SNR) statistics under the effects of random device orientation and link blockage are derived. The results show that the effects of random orientation and link blockage may lead to a decrease in coverage probability by 10% - 40% with various SNR thresholds.

The co-channel interference (CCI) is one of the major impairments in wireless communication. CCI typically reduces the reliability of wireless communication links, but the "difficult" CCI which is no more or less stronger to the desired signals destroys wireless links despite having myriad of CCI mitigation methods. It is shown in this paper that M-QAM (Quadrature Amplitude Modulation) or similar modulation schemes which modulate information both in in-phase and quadrature-phase are particularly vulnerable to difficult CCI. Despite well-known shortcomings, it is shown in this paper that M-PAM or similar schemes that use a single dimension for modulation provides an important mean for difficult CCI mitigation.

Doppler effect is a fundamental phenomenon that appears in wave propagation, where a moving observer experiences dilation or contraction of the wavelength of a wave. It also appears in radio frequency (RF) wireless communication when there exists a relative movement between the transmitter and the receiver, and is widely considered as a major impairment for reliable wireless communication. The current paper proposes Doppler assisted wireless communication (DAWC) that exploits Doppler effect and uses kinetic energy for co-channel interference (CCI) mitigation. The proposed system also exploits the propagation environment and the network topology and consists of an access point (AP) with a rotating drum antenna. The rotating drum receive antenna is designed in such a way that it shifts the interfering signals away from the desired signal band. This paper includes a detailed system model, and the results show that under favorable fading conditions, CCI can be significantly reduced. Therefore, it is anticipated that more sophisticated wireless systems and networks can be designed by extending the basic ideas proposed herein.

Doppler effect is a fundamental phenomenon that appears in wave propagation, where a moving observer experiences dilation or contraction of wavelength of a wave. It also appears in radio frequency (RF) wireless communication when there exists a relative movement between the transmitter and the receiver, and is widely considered as a major impairment for reliable wireless communication. The current paper proposes a wireless receiver that carefully exploits Doppler effect for cochannel interference mitigation. The proposed system-termed as DAIM to stand for Doppler Assisted Interference Mitigation-exploits the propagation environment and the network topology, and consists of an access point with a rotating drum antenna. The rotating drum receive antenna is designed in such a way that it shifts the interference signals away from the desired signal band. This paper includes a detailed system model and a simulation study. The results show that under favorable fading conditions, co-channel interference can be significantly reduced if not eliminated. Therefore, it is anticipated that more sophisticated wireless systems and networks can be designed by extending the basic system proposed herein.

Light-fidelity (LiFi) extends visible light communication into high-speed and multiuser wireless networks. As in cellular networks, co-channel interference (CCI) stemming from other access points (APs) sharing the same transmission resources is the main limiting factor in the performances of the LiFi networks; therefore, it is important to study characteristics of CCI. This paper studies the statistical characteristics of aggregate signal interference iaggin downlink LiFi networks where LiFi-enabled APs are randomly deployed following a Poisson point process (PPP). One of the advantages of considering iaggcompared to the aggregate power interference is that parameters of modulation schemes and room dimensions can both be incorporated. The paper's key finding is that the energy of iaggis not monotonically decreasing as the vertical distance of user of interest and the AP increases. In addition, we show that the distribution of iaggrapidly approaches a Gaussian distribution as PPP intensity increases.

In this paper, a simple energy-efficient physical layer modulation scheme termed as random number modulation (RNM) is proposed. It is a class of new systems that harness the randomness of pseudo random number generators (RNGs) for efficient communication, and adds a new degree of freedom to digital communication systems. It is also highly adaptable to high-rate, low-latency, and low-rate, high-energy efficiency scenarios. This paper includes a detailed system model, preliminary performance analysis, and extended discussions. The performance of the proposed system is analyzed in terms of symbol and block error probabilities, energy efficiency, and latency. It is shown that there is a fundamental tradeoff between the energy efficiency and the latency of the proposed system, and they can be easily software programmable allowing devices to adapt to different circumstances and environments rapidly. Based upon the basic system model herein, it is anticipated that more sophisticated RNM systems can be developed.

In this paper, a hybrid radio frequency (RF) and visible light communication (VLC) system is considered. A hybrid system with multiple VLC access points (APs) and RF APs is designed and analyzed. In indoor environments, VLC APs provide very high data rates whilst proving illumination, and RF APs offer ubiquitous coverage with moderate data rates. Since VLC networks piggyback on existing lighting infrastructures, they may not always be able to provide full coverage despite supporting very high data rates in some areas. Hence in practical deployments, the standalone VLC networks should be augmented in order to improve the per user data rate coverage. In this context, RF APs can be used to improve the per user rate coverage of VLC networks as well as to provide the ubiquitous control functionalities. In this paper, a simple RF deployment is proposed in order to improve the per user outage data rate performance of standalone VLC networks. It is assumed that the VLC system resources are fixed, and this paper quantifies the minimum spectrum and power requirements for a RF system, which after introduction to the VLC system, the hybrid RF/VLC system achieves certain per user rate coverage performances.

Light fidelity (LiFi) uses light emitting diodes (LEDs) for high-speed wireless communications. Since an LED lamp covers a small area, a LiFi system with multiple access points (APs) can offer a significantly high spatial throughput. However, the spatial distribution of data rates achieved by LiFi fluctuates because users experience inter-cell interference from neighboring LiFi APs. In order to guarantee a quality of service (QoS) for all users in the network, an RF network is considered as an additional wireless networking layer. This hybrid LiFi/RF network enables users with low levels of optical signals to achieve the desired QoS by migrating to the RF network. With regard to moving users, the hybrid LiFi/RF system dynamically allocates either a LiFi AP or an RF AP to users based on their channel state information. In this paper, a dynamic load balancing scheme is proposed, which considers the handover overhead in order to improve the overall system throughput. Joint optimization algorithm (JOA) and separate optimization algorithm (SOA), which jointly and separately optimize the AP assignment and resource allocation, respectively, are proposed. Simulation results show that SOA can offer a better performance/complexity tradeoff than JOA for system load balancing.

One of the important issues in an indoor visible light communication (VLC) system is the multi-path (MP) effect due to reflections. Generally, the MP effect can be characterised by the channel impulse response (CIR). Methods based on ray-tracing/Monte Carlo simulations are primarily used to obtain these impulse responses, but this generally leads to time consuming computer simulations. In this study, an analytical approach is proposed to directly and accurately calculate the non-line-of-sight (NLOS) components of the CIR due to the interior surface reflections in a room. The proposed method could be used in system-level simulations of a networked VLC system (also referred to as a LiFi attocell network), which requires a large number of channels with different transmitter and receiver deployments to be generated in a computationally efficient manner.

This work studies the issue of access point selection (APS) in a hybrid wireless network accommodating visible light communication (VLC) and radio-frequency (RF) technologies. A hybrid network constructs multiple layers of coverage, and thus a user possibly acquires a high level of receiving signal strength (RSS) from more than one access point (AP). This fact undermines the effectiveness of conventional RSS-based APS methods. Another challenging factor is the dissimilarity between heterogeneous APs in terms of coverage area and capacity. In general, RF offers larger coverage area but lower capacity than VLC, and therefore the RF system is susceptible to overload. Although the issue of APS can be formulated as an optimisation problem, this approach requires a prohibitive amount of processing power. In this paper a two-stage APS method is proposed on the basis of fuzzy logic, with very low computational complexity. The new method first determines the users that should be connected to the RF system, and then assigns the remaining users as if in a stand-alone VLC network. Results show that when achieving the same amount of throughput, the proposed method can support up to 25% and 56% more users than the load balancing (LB) and signal strength strategy (SSS) methods, respectively.

In this paper, a promising wireless communication concept which is termed as Spatial Modulation (SM) is considered. In particular the focus is on an interference scenario between a SM multiple-input- multiple-output (MIMO) system and a conventional spatial multiplexing (SMX) MIMO system. It has been shown that the interference caused by SM has a peculiar behavior. Since SM exploits the spatial position of the active antenna as an additional dimension for data transmission, the interference caused by SM system has no fixed interference subspace which can not be estimated accurately. Hence, conventional interference suppression techniques can not be applied accordingly. In this paper, we discuss this unique problem generated by SM systems, and propose three methods to overcome the adverse effects caused by such interference.

In this paper, an optical space division multiple access (SDMA) scheme is proposed for optical attocell networks. In the system, a conventional single-element transmitter in each optical cell is substituted by an angle diversity transmitter which can simultaneously serve multiple active users at different positions. This type of configuration can increase the available bandwidth resource and also mitigate inter-cell interference (ICI) in optical attocell networks. The results indicate that the optical SDMA scheme significantly outperforms the conventional optical time division multiple access (TDMA) scheme. The SDMA schemes is shown to improve the average spectral efficiency of the system by a factor of 26 for a 37-element light-emitting diode (LED) angle diversity transmitter. Finally, the study is extended to account for user position errors. The Monte-Carlo simulation results show that the system is very robust to user position errors.

In this paper, two major multiple-input-multiple-output (MIMO) transmission techniques such as spatial modulation (SM) and spatial multiplexing (SMX) are considered. In particular, the focus is on an interference scenario, where an SM MIMO system interferes with a conventional SMX MIMO system. The interference caused by SM has a peculiar behavior. In SMX MIMO networks, the interference subspace is fixed in a given coherence time interval. It can be estimated accurately, and interference suppression techniques can be applied accordingly. However, the interference caused by an SM system has no fixed interference subspace, and it changes in every single channel use. Therefore, SM interference could pose some unique challenges to SMX MIMO systems in some scenarios. In this paper, the effect of SM interference on SMX MIMO systems and methods to overcome/reduce the adverse effects caused by SM interference are studied. Furthermore, the effect of SMX interference on SM MIMO systems is also studied.

In this paper, the downlink signal-to-interference- plus-noise ratio (SINR) statistics are analysed in a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) based optical attocell network with a Poisson point process (PPP) cell deployment. An optical attocell system utilises existing lighting fixtures in an indoor environment to function as a small-cell cellular network. It uses each luminary as a base station (BS) to serve multiple nearby mobile users. Similar to a conventional radio frequency (RF) cellular system, the grid cell deployment is restricted by many practical issues in an optical attocell network. Therefore the performance of the system with PPP cell deployment is considered in this study in order to identify a lower bound for practical attocell networks with irregular cell deployment. An analytical framework is presented and compared with the computer simulations. Also the SINR statistics with different cell deployments are compared and discussed.

Multiple-input multiple-output (MIMO) systems can increase wireless link capacity without requiring additional bandwidth and power. On the one hand, MIMO systems heavily depend on channel state information (CSI) at the receiver. It has also been shown that CSI at the transmitter (CSIT) can improve the link capacity and reliability considerably but with the disadvantage of extra feedback and computational costs. On the other hand, energy efficiency of MIMO systems could adversely increase with the number of antennas in the link. Therefore, there are considerable interests in energy efficient practical transmission schemes for MIMO links without CSIT. In this study, an emerging wireless communication concept which is termed as spatial modulation (SM) is considered for large scale MIMO. The results show that in information-theoretic viewpoint, SM achieves capacity comparable to the open-loop MIMO capacity even though a subset of transmit antennas is activated in every channel use. The reason is both the channel coefficients and input symbols carry information in SM. As a result, SM regains (compensates) the loss of information capacity due to activating a subset of antennas by modulating information in the antenna index. This means that the sum information rate remains high.

A hybrid radio frequency (RF) and visible light communication (VLC) system is considered. A hybrid system with multiple VLC access points (APs) and RF APs is designed and compared. In indoor environments, VLC APs can provide very high data rates whilst satisfying illumination requirements, and RF APs can offer ubiquitous coverage. Even though very high throughput is supported by VLC APs, such coverage area may be spatially limited. This gives an opportunity to introduce a new small cell layer to current heterogeneous wireless networks, and it is referred as optical attocellular layer. However since VLC piggy-backs on the existing lighting infrastructure, it may not be possible to achieve full coverage. Hence in practical deployments, the spatial throughput distribution of standalone VLC systems should be augmented. In this context, RF APs can be used to improve the overall rate performance of the heterogeneous wireless system. In this study, the focus is on improving the per user average and outage throughput. It is assumed that the VLC system resources are fixed, and the study quantifies the spectrum and power requirements for a RF system, which after introduction to the VLC system, achieves better per user rate performance.

The cellular systems with base station (BS) coordination are known for increasing the cell edge user throughput considerably. They process signals captured by geographically distributed BSs coherently. In contrast, noncooperative BSs with large number of antennas are also known for achieving both high spectral and energy efficiency. The fully cooperative BSs have several drawbacks such as ideal backhaul requirements, need for BS synchronization, and channel state information (CSI). These drawbacks hinder fully cooperative cellular systems considerably. Therefore, in this paper, the prospect of designing noncooperative cellular systems with comparable performance in some sense to ideal cooperative cellular systems with no additional power or spectrum is systematically pursued. The approach is based on the information theoretic rate characterization for finite size systems. The size of systems is in terms of the number of BS antennas and users. We show in this paper that under certain conditions, such noncooperative cellular systems can be designed. We devise a framework to compare two systems and obtain necessary conditions for making the performance of two seemingly unrelated access technologies closely comparable.

The cellular systems with network coordination are known for increasing the cell edge user throughput by processing signals captured by geographically distributed base stations coherently. This concept is also known as macrodiversity or coordinated multipoint (CoMP) in the literature. It is now well known that large-scale fading has a significant influence on the link-level performance of users in multiuser (MU) multicell systems. In this paper, we investigate a channel distribution information (CDI)-based MU multiple-input-multiple-output (MIMO) power control problem in the uplink with joint processing to overcome the large-scale fading in macrodiversity systems. There are many power control algorithms for different variants of this problem, but the CDI-based problem in MU scenario has not been well addressed in the literature. Perhaps, the lack of understanding of the performance of macrodiversity MU systems, in terms of CDI, may have prohibited advanced power control solutions. Despite such analytical difficulties, we propose a simple algorithm for this uplink power control problem, and its accuracy is proved using Monte Carlo simulation.

In this paper, we propose a novel Virtual Multiple-Input-Multiple-Output (VMIMO) architecture based on the concept of Spatial Modulation (SM). Using a dual-hop and Decode-and-Forward protocol, we form a distributed system, called Dual-Hop Hybrid SM (DH-HSM). DH-HSM conveys information from a Source Node (SN) to a Destination Node (DN) via multiple Relay Nodes (RNs). The spatial position of the RNs is exploited for transferring information in addition to, or even without, a conventional symbol. In order to increase the performance of our architecture, while keeping the complexity of the RNs and DN low, we employ linear precoding using Channel State Information (CSI) at the SN. In this way, we form a Receive-Spatial Modulation (R-SM) pattern from the SN to the RNs, which is able to employ a centralized coordinated or a distributed uncoordinated detection algorithm at the RNs. In addition, we focus on the SN and propose two regularized linear precoding methods that employ realistic Imperfect Channel State Information at the Transmitter. The power of each precoder is analyzed theoretically. Using the Bit Error Rate (BER) metric, we evaluate our architecture against the following benchmark systems: 1) single relay; 2) best relay selection; 3) distributed Space Time Block Coding (STBC) VMIMO scheme; and 4) the direct communication link. We show that DH-HSM is able to achieve significant Signal-to-Noise Ratio (SNR) gains, which can be as high as 10.5 dB for a very large scale system setup. In order to verify our simulation results, we provide an analytical framework for the evaluation of the Average Bit Error Probability (ABEP).

The performance of maximal ratio combining (MRC) in Rayleigh channels with co-channel interference (CCI) is well-known for receive arrays which are co-located. Recent work in network MIMO, edge-excited cells and base station collaboration is increasing interest in macrodiversity systems. Hence, in this paper we consider the effect of macrodiversity on MRC performance in Rayleigh fading channels with CCI. We consider the uncoded symbol error rate (SER) as our performance measure of interest and investigate how different macrodiversity power profiles affect SER performance. This is the first analytical work in this area. We derive approximate and exact symbol error rate results for M-QAM/BPSK modulations and use the analysis to provide a simple power metric. Numerical results, verified by simulations, are used in conjunction with the analysis to gain insight into the effects of the link powers on performance.

The prospect of base station cooperation leading to joint combining at widely separated antennas has led to increased interest in macrodiversity systems, where both sources and receive antennas are geographically distributed. In this scenario, analytical investigation of channel capacity is extremely challenging for finite-size systems since the channel matrices have a very general form where each path may have a different power. Hence, in this paper, we consider the ergodic sum capacity of a macrodiversity multiple-input multiple-output system with arbitrary numbers of sources and receive antennas operating over Rayleigh fading channels. For this system, we compute the exact ergodic capacity for a system with at most two transmit antennas and a compact approximation for the general system, which is shown to be very accurate over a wide range of cases. Finally, we compare our results with previous asymptotic results and bounds. Results are verified by Monte Carlo simulations and the impact on capacity of various channel power profiles is investigated.

Consider a multiuser system where an arbitrary number of users communicate with a distributed receive array over independent Rayleigh fading paths. The receive array performs minimum mean squared error (MMSE) or zero forcing (ZF) combining and perfect channel state information is assumed at the receiver. This scenario is well-known and exact analysis is possible when the receive antennas are located in a single array. However, when the antennas are distributed, the individual links all have different average signal to noise ratio (SNRs) and this is a much more challenging problem. In this paper, we provide approximate distributions for the output SNR of a ZF receiver and the output signal to interference plus noise ratio (SINR) of an MMSE receiver. In addition, simple high SNR approximations are provided for the symbol error rate (SER) of both receivers assuming M-PSK or M-QAM modulations. These high SNR results provide array gain and diversity gain information as well as a remarkably simple functional link between performance and the link powers.

The performance of linear receivers in the presence of co-channel interference (CCI) in Rayleigh channels is a fundamental problem in wireless communications. Performance evaluation for these systems is well-known for receive arrays which are co-located. In contrast, there are almost no analytical results available for macrodiversity systems (such as network MIMO) where both the sources and receive antennas are widely separated. In general, this appears to be an extremely difficult problem. However, progress is possible for the two-user scenario. In this paper, we derive closed form results for the probability density function (pdf) and cumulative distribution function (cdf) of the output signal to interference plus noise ratio (SINR) and signal to noise ratio (SNR) of minimum mean squared error (MMSE) and zero forcing (ZF) receivers in independent Rayleigh channels with arbitrary numbers of receive antennas. The results are verified by Monte Carlo simulations. The results enable further system analysis such as the evaluation of outage probabilities, bit error rate (BER) and capacity.

The prospect of base station cooperation has led to increased interest in macrodiversity systems, where both sources and receive antennas are geographically distributed. In this scenario, little is known about channel capacity since the channel matrices have a very general form where each path may have a different power. Hence, in this paper we consider the ergodic sum capacity of a macrodiversity MIMO system with arbitrary numbers of sources and antennas operating over Rayleigh fading channels. For this system, we compute a compact approximation to ergodic sum capacity, which is shown to be very accurate over a wide range of cases. Finally, we develop a highly simplified upper-bound which leads to insights into the relationship between capacity and the channel powers.

The performance of linear receivers in the presence of co-channel interference in Rayleigh channels is a fundamental problem in wireless communications. Performance evaluation for these systems is well-known for receive arrays where the antennas are close enough to experience equal average SNRs from a source. In contrast, almost no analytical results are available for macrodiversity systems where both the sources and receive antennas are widely separated. Here, receive antennas experience unequal average SNRs from a source and a single receive antenna receives a different average SNR from each source. Although this is an extremely difficult problem, progress is possible for the two-user scenario. In this paper, we derive closed form results for the probability density function (pdf) and cumulative distribution function (cdf) of the output signal to interference plus noise ratio (SINR) and signal to noise ratio (SNR) of minimum mean squared error (MMSE) and zero forcing (ZF) receivers in independent Rayleigh channels with arbitrary numbers of receive antennas. The results are verified by Monte Carlo simulations and approximations and high SNR analysis are also derived. The results enable further system analysis such as the evaluation of outage probability, bit error rate (BER) and capacity.