Multi-color visible light communication (MC-VLC) is able to achieve high date rate via multiple color channels. To separate different colors, optical filters have to be adopted. In conventional MC-VLC systems, the center wavelength (CWL) and bandwidth (BW) of optical filters is carefully designed for each transmitted color component at normal angles of incidence (AOIs). However, at non-normal AOIs, the CWL of optical filters shifts to shorter wavelength namely the filter CWL shift, leading to serious cross-color interference. In this paper, we propose a novel optical filter bank structure, which consists of a series of narrow-band optical filters, to address the issues caused by the CWL shift. We first establish the corresponding channel model for the VLC links based on optical filter bank, and then design the optimal combining receiver for different AOIs. Simulation results demonstrate that the proposed optical filter bank structure exhibits high and stable performance, and shows strong compatibility for different transmitter configurations.

Small-cell aided ultra-dense networks (UDNs) constitute an efficient solution to the ever-increasing thirst for more data. Thanks to the vast untapped high-frequency spectrum of visible light, visible light communications (VLCs) are a natural candidate for UDN. In this paper, layered asymmetrically clipped optical OFDM (LACO-OFDM) aided ultra-dense VLC (UD-VLC) is investigated in terms of its user association, multiple access (MA), and resource allocation. To handle the severe inter-cell interference (ICI) amongst the densely deployed access points, we propose a novel overlapped clustering technique relying on a hybrid non-orthogonal MA and orthogonal MA scheme for enhancing the performance, with the aid of our dynamic resource allocation conceived. Our simulations show that the proposed LACO-OFDM aided UD-VLC using our hybrid MA scheme is more robust against the ICI, at a price of modestly decreasing the sum throughput.

In this treatise, first of all, we conceive a generic multiple-symbol differential sphere detection (MSDSD) solution for both single- and multiple-antenna-based noncoherent schemes in both uncoded and coded scenarios, where the high-mobility aeronautical Ricean fading features are taken into account. The bespoke design is the first MSDSD solution in the open literature that is applicable to the generic differential space-time modulation (DSTM) for transmission over Ricean fading. In the light of this development, the recently developed differential spatial modulation and its diversity counterpart of differential space-time block coding using index shift keying are specifically recommended for aeronautical applications owing to their low-complexity single-RF and finite-cardinality features. Moreover, we further devise a noncoherent decision-feedback differential detection and a channel-state information estimation aided coherent detection, which also take into account the same Ricean features. Finally, the advantages of the proposed techniques in different scenarios lead us to propose for the aeronautical systems to adaptively: 1) switch between coherent and non-coherent schemes; 2) switch between single- and multiple-antenna-based schemes as well as; and 3) switch between high-diversity and high-throughput DSTM schemes.

Multi-class channel coded layered asymmetrically clipped optical orthogonal frequency-division multiplexing (LACO-OFDM) is proposed, where the achievable rate of the system is derived based on our mutual information analysis. We conceive a multi-class channel encoding scheme integrated with the layered transmitter. At the receiver, both the coded and uncoded likelihood ratios are extracted for inter-layer interference cancellation and symbol detection, respectively. Simulations are conducted, and the results show that our design approaches the achievable rate within 1.1 dB for 16-QAM fourlayer LACO-OFDM with the aid of a half-rate eight-iteration turbo code at BER = 10-3, outperforming its conventional counterpart by about 3.6 dB.

The next generation of Digital Subscriber Line (DSL) technologies seek to exploit frequencies beyond 106 MHz and up to 500 MHz where Far-End Crosstalk (FEXT) becomes excessive; for these frequencies effective crosstalk cancellation, also known as vectoring, is essential. This paper proposes a novel spatially adaptive linear precoder and explores its performance, alongside classical Zero-Forcing Precoding (ZFP) and Tomlinson-Harashima Precoding (THP) methods, under two distinct scenarios. In this paper, the objective function is set to maximise the aggregate capacity of the copper MIMO channel. All precoding methods benefit from a coordinated bitloading to maximise the spectra within a defined power spectrum density (PSD) mask. Results suggest that THP's superiority is substantial in the fixed cable length scenario whilst the proposed Spatially Adaptive Generalised ZFP (SA-GZFP) outperforms the latter marginally in the dendritic one. The paper further suggests that a spatially adaptive nonlinear precoder may have the potential of combining the gains of THP and Maximal Ratio Transmission (MRT) for greater system performance.

With an unprecedented amount of sensitive private data generated by mobile user equipment (UE), securing the emerging ultra-dense networks (UDNs) becomes critical. Although involving more access points (APs) is potentially capable of enhancing both the UE's throughput and security, the energy consumption becomes significant. In this paper, we investigate secure UDNs in the context of the user-centric clustering of UDNs from a secrecy energy efficiency perspective, while satisfying both the throughput and the security of each UE. We first propose a secure user-centric clustering architecture by introducing both a dedicated jamming strategy and an embedded jamming strategy, both of which degrade the overheard signals of the eavesdroppers and guarantee secure transmission relying on the different APs' involvement status. We formulate the secure user-centric clustering design for both known and unknown eavesdropper channel state information (CSI), whilst maximizing the secrecy energy efficiency with the aid of various secure transmission schemes. Since the problem formulated is a non-convex mixed integer non-linear programming problem, we develop a set of heuristic greedy secure user-centric clustering algorithms for diverse operating scenarios. Finally, our numerical results reveal the quantitative benefits of the proposed secure user-centric clustering architectures as a function of the network densities (i.e., AP, UE, and eavesdropper) and of both the throughput and the security constraints on the secrecy energy efficiency trade-off in different scenarios.

We are at the dawn of an era in information and communication technology with unprecedented demand for connected and automated everything. Both Shannon theories and industrial advances have clearly evidenced that more densely packed networks and a much wider operating bandwidth are key drivers for meeting the escalating wireless network demands. Recently, there have been substantial research efforts on the exploitation of higher frequency bands, in particular the millimetre wave and optical wireless bands. After a decade of active research and development, and along with the maturity of device technology, Visible Light Communications (VLC) has emerged as a very promising technology to enable next generation digital innovations and support wide range of applications. This special issue on VLC focuses on three core thrusts of the discipline:Localisation, CommunicationandNetworking. The overall aim of the special issue is to inspire multi-disciplinary international communities to work together in order to achieve further research advances. Indeed, a total of 96 high quality papers were received from both academia and industry. After a careful peer-reviewing process, 17 papers were selected based on their combined novelty, rigour, and impact. Owing to the highly selective nature of JSAC, many other interesting papers were not selected for the special issue, but we hope that these papers might appear elsewhere.

We propose a regularized zero-forcing transmit precoding (RZF-TPC)-aided and distance-based adaptive coding and modulation (ACM) scheme to support aeronautical communication applications, by exploiting the high spectral efficiency of the large-scale antenna arrays and link adaption. Our RZF-TPC-aided and distance-based ACM scheme switches its mode according to the distance between the communicating aircraft. We derive the closed-form asymptotic signal-to-interference-plus-noise ratio (SINR) expression of the RZF-TPC for the aeronautical channel, which is Rician, relying on a non-centered channel matrix that is dominated by the deterministic line-of-sight component. The effects of both realistic channel estimation errors and of the co-channel interference are considered in the derivation of this approximate closed-form SINR formula. Furthermore, we derive the analytical expression of the optimal regularization parameter that minimizes the mean square detection error. The achievable throughput expression based on our asymptotic approximate SINR formula is then utilized as the design metric for the proposed RZF-TPC-aided and distance-based ACM scheme. Monte-Carlo simulation results are presented for validating our theoretical analysis as well as for investigating the impact of the key system parameters. The simulation results closely match the theoretical results. In the specific example that two communicating aircrafts fly at a typical cruising speed of 920km/h, heading in opposite direction over the distance up to 740km taking a period of about 24 min, the RZF-TPC-aided and distance-based ACM is capable of transmitting a total of 77 GB of data with the aid of 64 transmit antennas and four receive antennas, which is significantly higher than that of our previous eigen-beamforming transmit precoding-aided and distance-based ACM benchmark.

In order to enhance the secrecy performance of the generalized space shift keying (GSSK) visible light communication (VLC) system, in this paper, an optical jamming-aided secrecy enhancement scheme is proposed, in which the source transmitter (S) simultaneously sends both the confidential desired signal and optical jamming signals under the amplitude and power constraints. The optical jamming signals obey the truncated Gaussian distribution for satisfying the constraints. Given the discrete set of channel inputs, the optical jamming-aided GSSK-VLC system's secrecy performance is analyzed. Explicitly, the average mutual information (AMI), the lower bound of AMI and its closed-form approximation as well as the achievable secrecy rate are formulated analytically. Furthermore, the optimal power sharing strategy of the proposed GSSK-VLC systems relying on optical jamming is derived. Closed-form expressions are provided for the optimal power sharing in both the low- and high-SNR regions. Finally, the extensive simulation results are presented to validate our analytical results.

The concept of amorphous-boundary-based user-centric cells invoked for visible light communication (VLC) was shown to offer extra throughput benefits over the conventional network-centric VLC. However, this improvement was quantified based on a number of idealized simplifying assumptions, such as operating exactly at the Shannon capacity. Also, the light emitting diode in VLC was assumed to have no non-linear distortion and no clipping distortion. Furthermore, greedily supporting all the user equipments in the system may in fact reduce the achievable throughput, when the transmit power is restricted. To provide more practical performance estimate, in this paper, the dynamic throughput maximization of user-centric VLC (UC-VLC) systems is investigated under a range of practical considerations, where the number of served UEs, the modulation-mode assignment and the power allocation strategy are all dynamically decided by our proposed heuristic dynamic-programming-based algorithm. Our simulations indicate that both the achievable throughput and the outage probability of the proposed UC-VLC system is better than that of the conventional NC-VLC system, under a range of practical constraints.

In this paper, a radically new anticipatory perspective is taken into account when designing the user-to-access point (AP) associations for indoor visible light communications (VLC) networks, in the presence of users' mobility and wireless-traffic dynamics. In its simplest guise, by considering the users' future locations and their predicted traffic dynamics, the novel anticipatory association prepares the APs for users in advance, resulting in an enhanced locationand delayawareness. This is technically realized by our contrived design of an efficient approximate dynamic programming algorithm. More importantly, this paper is in contrast to most of the current research in the area of indoor VLC networks, where a static network environment was mainly considered. Hence, this paper is able to draw insights on the performance tradeoff between delay and throughput in dynamic indoor VLC networks. It is shown that the novel anticipatory design is capable of significantly outperforming the conventional benchmarking designs, striking an attractive performance trade-off between delay and throughput. Quantitatively, the average system queue backlog is reduced from 15 to 8 [ms], when comparing the design advocated to the conventional benchmark at the peruser throughput of 100 [Mbps], in a 15 × 15 × 5 [m3] indoor environment associated with 8 × 8 APs and 20 users walking at 1 [m/s].

In order to meet the demands of “Internet above the clouds,” we propose a multiple-antenna aided adaptive coding and modulation (ACM) for aeronautical communications. The proposed ACM scheme switches its coding and modulation mode according to the distance between the communicating aircraft, which is readily available with the aid of the airborne radar or the global positioning system. We derive an asymptotic closed-form expression of the signal-to-interference-plus-noise ratio (SINR) as the number of transmitting antennas tends to infinity, in the presence of realistic co-channel interference and channel estimation errors. The achievable transmission rates and the corresponding mode-switching distance-thresholds are readily obtained based on this closed-form SINR formula. Monte-Carlo simulation results are used to validate our theoretical analysis. For the specific example of 32 transmit antennas and four receive antennas communicating at a 5-GHz carrier frequency and using 6-MHz bandwidth, which are reused by multiple other pairs of communicating aircraft, the proposed distance-based ACM is capable of providing as high as 65.928-Mb/s data rate when the communication distance is less than 25 km.

Visible light communication (VLC) may be expected to become a new member in the small-cell family of the next-generation heterogeneous network landscape for complementing the overloaded radio frequency band. In order to further improve the performance of our user-centric (UC) cluster formation design proposed in our previous work, the quality-of-service (QOS) metric in terms of statical delay requirements is considered, when constructing the UC clusters. Inspired by the concept of effective capacity (EC), we formulate the proportional-fairness-based utility function of each optical link, while satisfying the statistical delay requirement. Upon maximizing the sum utility of the system, the joint cluster formation and user association problem is solved by our proposed greedy algorithm, which is capable of providing an average user EC of about 90% of the optimal value found via exhaustive search. Furthermore, the performance of the UC cluster formation is superior than the traditional cellular designs in all scenarios considered.

In this paper, we design an energy efficient indoor visible light communications (VLC) system from a radically new perspective based on an amorphous user-to-network association structure. Explicitly, this intriguing problem is approached from three inter-linked perspectives, considering the cell formation, link-level transmission and system-level optimisation, critically appraising the related optical constraints. To elaborate, apart from proposing hitherto unexplored amorphous cells (A-Cells), we employ a powerful amalgam of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and transmitter pre-coding aided multi-input single-output (MISO) transmission. As far as the overall system-level optimisation is concerned, we propose a low-complexity solution dispensing with the classic Dinkelbach's algorithmic structure. Our numerical study compares a range of different cell formation strategies and investigates diverse design aspects of the proposed A-Cells. Specifically, our results show that the A-Cells proposed are capable of achieving a much higher energy efficiency per user compared to that of the conventional cell formation for a range of practical field of views (FoVs) angles.

Device-to-device (D2D) communication underlying cellular networks, allows direct transmission between two devices in each other's proximity that reuse the cellular resource blocks in an effort to increase the network capacity and spectrum efficiency. However, this imposes severe interference that degrades the system's performance. This problem may be circumvented by incorporating fractional frequency reuse (FFR) or soft frequency reuse (SFR) in OFDMA cellular networks. By carefully considering the downlink resource reuse of the D2D links, we propose beneficial frequency allocation schemes, when the macrocell has employed FFR or SFR as its frequency reuse technique. The performance of these schemes is quantified using both the analytical and simulation results for characterizing both the coverage probability and the capacity of D2D links under the proposed schemes that are benchmarked against the radical unity frequency reuse scheme. The impact of the D2D links on the coverage probability of macrocellular users (CUs) is also quantified, revealing that the CUs performance is only modestly affected under the proposed frequency allocation schemes. Finally, we provide insights concerning the power control design in order to strike a beneficial tradeoff between the energy consumption and the performance of D2D links.

Visible light communication (VLC) combined with advanced illumination may be expected to become an integral part of next-generation heterogeneous networks. In order to mitigate the performance degradation imposed by the intercell-interference (ICI), a user-centric (UC) cluster formation technique employing vectored transmission (VT) is proposed for the VLC down-link system, where multiple users may be simultaneously supported by multiple access points (APs). In contrast to the traditional network-centric (NC) design, the UC-VT cluster formation is dynamically constructed and adjusted, rather than remaining static. Furthermore, we consider the critical issue of multiuser scheduling (MUS) relying on maximizing the “sum utility” of this system, which leads to a joint cluster formation and MUS problem. In order to find a practical solution, the original problem is reformulated as a maximum weighted matching (MWM) problem relying on a user-AP distance-based weight and then a low-complexity greedy algorithm is proposed, which offers a suboptimal yet compelling solution operating close to the optimal value found by the potentially excessive-complexity exhaustive search. Our simulation results demonstrate that the proposed greedy MUS algorithm combined with the UC-VT cluster formation is capable of providing an average user throughput of about 90% of the optimal throughput, which is about three times the throughput provided by the traditional cellular design in some of the scenarios considered.

Developed from the recently emerged generalized pre-coding aided spatial modulation (GPSM) concept, a novel non-linear GPSM scheme based on the powerful vector perturbation philosophy is proposed, where a particular subset of receive antennas is activated and the specific activation pattern itself conveys useful implicit information in addition to the conventional modulated and perturbed symbols. Explicitly, both the infinite and finite alphabet capacities are derived for the proposed non-linear GPSM scheme. The associated complexity, energy efficiency, and error probability are also investigated. Our numerical results show that, as the only known non-linear realization within the spatial modulation family, the proposed scheme constitutes an attractive solution to the flexible design of green transceivers, since it is capable of striking a compelling compromise amongst the key performance indicators of throughput, energy consumption, complexity, and performance. In particular, in the challenging full-rank scenario, conveying information through receive antenna indices exhibits a lower complexity, a higher energy efficiency, and a better error resilience than that of the conventional arrangement.

Visible Light Communication (VLC) combined with advanced illumination has been expected to become an integral part of next generation heterogeneous networks at the time of writing, by inspiring further research interests. From both the Cell-Centric (CC) and the User-Centric (UC) perspectives, various VLC cell formations, ranging from fixed-shape regular cells with different Frequency Reuse (FR) patterns and merged cells employing advanced transmission scheme to amorphous user-specific cells are investigated. Furthermore, different Multi-User Scheduling (MUS) algorithms achieving Proportional Fairness (PF) are implemented according to different cell formations. By analysing some critical and unique characteristics of VLC, our simulation results demonstrate that, the proposed MUS algorithms are capable of providing a high aggregate throughput and achieving modest fairness with low complexity in most of the scenarios considered.

In echoing Varshney's seminal concept of jointly transmitting information and energy, we propose the concept of an energy pattern aided Simultaneous Wireless Information and Power Transfer (SWIPT) system, where in addition to power transfer, information is conveyed both by the specific Receive Antenna (RA) indices to which the power is delivered as well as by the particular intensity of the power assigned to that particular RA pattern. By embedding information into energy patterns rather than imposing it by modulating classic radio waveforms, our proposed solution is capable of operating both in an integrated receiver mode and in a power-split mode, while relying on a low-complexity two-stage non-coherent detection algorithm. Both our analysis and simulations show that our energy pattern aided SWIPT system exhibits a beneficial immunity to any potential performance degradation imposed by power-conversion. Moreover, the achievable rate versus power conversion trade-off bounds are characterized, demonstrating that our proposed energy pattern aided SWIPT system leads to a beneficial wireless information and power transfer convergence.

As a complementary extension of established Radio Frequency (RF) Wireless Local Area Networks (WLANs), Visible Light Communication (VLC) using commercially available Light-Emitting Diode (LED) transmitters offers a huge data rate potential in this license-free spectral domain, whilst simultaneously satisfying energy-efficient illumination demands. Various VLC cell formations, ranging from a regular cell-layout associated with different Frequency Reuse (FR) patterns to merged cells by employing advanced transmission scheme are investigated. Furthermore, a hybrid Down-Link (DL) offering full RF-coverage by a WLAN and additionally supported by the abundant spectral resources of a VLC network is studied. Cooperative Load Balancing (LB) achieving Proportional Fairness (PF) is implemented by using both centralized and distributed resource-allocation algorithms. The performance of this hybrid RF/VLC system is analysed both in terms of its throughput and fairness in diverse cell formation scenarios. Our simulation results demonstrate that, the VLC system advocated is capable of providing a high Area Spectral Efficiency (ASE) and our hybrid RF/VLC system achieves the highest throughput and the highest grade of fairness in most of the scenarios considered.

The resource-allocation (RA) problems of mobile terminals (MTs) are investigated in a heterogeneous wireless network, where both a visible light communication system and an RF femtocell system are deployed in a room. We consider diverse quality-of-service requirements in terms of the data rate, fairness, and statistical delay requirements. Inspired by the concept of effective capacity, we formulate our optimization problems applying α-proportional fairness while satisfying specific statistical delay constraints. Two types of MTs, namely, multihoming MTs and multimode MTs, are considered, where multihoming MTs have the capability of aggregating resources from different networks, whereas the multimode MTs always select a single network for their connection. Our optimization procedure solves the RA probability problem for multihoming MTs with the aid of a decentralized algorithm. By contrast, our optimization problem involves both network selection and RA probability optimization for multimode MTs, which may be regarded as a mixed-integer nonlinear problem. Since this problem is computationally intractable, a suboptimal decentralized method is proposed for solving it. Simulation results are also presented for clarifying the performance of the proposed algorithm. It is shown that the multimode MTs are capable of achieving similar performance to that of the multihoming MTs when the statistical delay requirements are loose. However, as expected, the multihoming MTs attain a better performance when we tighten the delay requirements.

The recently proposed multiple input multiple output (MIMO) transmission scheme termed as generalized pre-coding aided spatial modulation (GPSM) is analyzed, where the key idea is that a particular subset of receive antennas is activated and the specific activation pattern itself conveys useful implicit information. We provide the upper bound of both the symbol error ratio (SER) and bit error ratio (BER) expression of the GPSM scheme of a low-complexity decoupled detector. Furthermore, the corresponding discrete-input continuous-output memoryless channel (DCMC) capacity as well as the achievable rate is quantified. Our analytical SER and BER upper bound expressions are confirmed to be tight by our numerical results. We also show that our GPSM scheme constitutes a flexible MIMO arrangement and there is always a beneficial configuration for our GPSM scheme that offers the same bandwidth efficiency as that of its conventional MIMO counterpart at a lower signal to noise ratio (SNR) per bit.

Distributed Antenna Systems (DAS) and femtocells are capable of improving the attainable performance in the cell-edge area and in indoor residential areas, respectively. In order to achieve a high spectral efficiency, both the Distributed Antenna Elements (DAEs) and Femtocell Base Stations (FBSs) may have to reuse the spectrum of the macrocellular network. As a result, the performance of both outdoor macrocell users and indoor femtocell users suffers from Co-Channel Interference (CCI). Hence in this paper, heterogenous cellular networks are investigated, where the DAS-aided macrocells and femtocells co-exist within the same area. The outage probability is derived and the network is optimised for minimising the outage probability. Our analysis demonstrates that surprisingly, the Unity Frequency Reuse (UFR) based macrocellular system can be optimised in isolation, without considering the impact of femtocells. We found that the macrocells relying on hard-FFR as well as on soft-FFR tend to migrate to several small cells, illuminated by the DAEs, when the density of femtocells becomes high.

Femtocells constitute an economical solution conceived for improving the indoor coverage, which are capable of achieving a high network capacity. In order to guarantee a high Spectral Efficiency (SE), femtocells have to reuse the spectrum of macrocells. As a result, the performance of both the femtocells and macrocells may suffer owing to the near-far effects. In this paper, we study a twin-layer cellular networks, where the Macrocell Base Stations (MBSs) employing Fractional Frequency Reuse (FFR) host the Femtocell Base Stations (FBSs). This paper investigates the design, performance analysis and optimization problems of this FFR aided twin-layer network. We firstly assume that the femtocells opt for full spectrum access (FSA). The per-layer outage probability (OP) is derived and the network is optimized for maximizing the macrocell's throughput. We found that the advantage of FFR eroded in dense femtocell-scenarios and the optimized network tends to become a Unity Frequency Reuse (UFR) aided system. We then propose a spectrum swapping access (SSA) strategy for protecting the macrocell's performance and for overcoming the typical near-far problem. Our analysis demonstrates that both the OP of femtocell users in the Cell Centre Region (CCR) and that of the macrocell users in the Cell Edge Region (CER) will be reduced by the proposed SSA. The optimized network using our SSA is more robust to the detrimental impact of femtocells.

A new Multiple Input Multiple Output (MIMO) transmission scheme termed as Generalised Pre-coding aided Spatial Modulation (GPSM) is proposed, where the key idea is that a particular subset of receive antennas is activated and the activation pattern itself conveys useful information. This is in contrast to the previously proposed Spatial Modulation (SM) schemes, which operated by activating a specific subset of transmit antennas. We provide both analytical and numerical results characterizing the GPSM scheme proposed for both conventional as well as for large-dimensional MIMO configurations subject to both realistic imperfect Channel State Information at the Transmitter (CSIT) and to the low-rank approximation invoked for large-dimensional MIMO configurations. We also design a so-called reinforcement matrix for attaining substantial performance improvements for our proposed GPSM scheme. Our investigations show that the GPSM scheme constitutes a flexible alternative to the state-of-the-art MIMO transmission schemes, especially because it is capable of achieving a high throughput. Moreover, the benefits of mapping information to the spatial domain rather than relying on conventional modulation has substantial benefits in the medium to high Signal to Noise Ratio (SNR) region. Quantitatively, GPSM is capable of supporting the same throughput as the conventional full-multiplexing gain based MIMO arrangements at an SNR gain of about 1dB at the same receiver complexity. Furthermore, the reinforcement matrix aided GPSM scheme attains a further 3-4dB performance improvement as compared to the conventional GPSM scheme.

Coalition Network Elements (CNE) are proposed for Base Stations (BS) cooperation, where the CNEs carry traffic for the BS in support of its cell-edge MSs by exploiting the unused frequency bands of the BS network, while considering a range of practical impairments. We derive the coalition probability by taking into account both system loads of the primary network as well as the CNE's greediness. Our simulation results demonstrate that the proposed solution is capable of substantially increasing the attainable SINR in a wide range of scenarios and it is also robust to diverse practical imperfections.

Femtocells constitute an economical solution conceived for improving the indoor coverage, which are capable of achieving a high network capacity. In order to guarantee a high Area Spectral Efficiency (ASE), femtocells have to reuse the spectrum of macrocells. As a result, the performance of both the femtocells and macrocells may suffer owing to the near-far effects. In this paper, we investigate the Outage Probability (OP) of twin-layer cellular networks, where the Macrocell Base Stations (MBSs) employing Fractional Frequency Reuse (FFR) host the Femtocell Base Stations (FBSs). More explicitly, the frequency-swapping aided femtocell concept is proposed for overcoming the typical near-far problem. We derive the approximate closed-form expressions for the DownLink (DL) OP for both our benchmarker as well as for our proposed solution. Our analysis demonstrates that the OP of femtocell users in the Cell Centre Region (CCR) and that of the macrocell users in the Cell Edge Region (CER) will be reduced by the proposed swapped-spectrum access policy.

Cooperative Multiple Point (CoMP) transmission aided Distributed Antenna Systems (DAS) are proposed for increasing the received Signal-to-Interference-plus-Noise-Ratio (SINR) in the cell-edge area of a cellular system employing Fractional Frequency Reuse (FFR) in the presence of realistic imperfect Channel State Information (CSI) as well as synchronisation errors between the transmitters and the receivers. Our simulation results demonstrate that the CoMP aided DAS scenario is capable of increasing the attainable SINR by up to 3dB in the presence of a wide range of realistic imperfections.

A cooperative Medium Access Control (MAC) protocol employing auction-style relay selection combined with superposition coding is designed. In our proposed scheme, the source achieves its target throughput with the aid of cooperation. The potential candidate relays carry out autonomous decisions concerning whether to contend for a transmission opportunity to convey their traffic in the light of their individual energy requirements. Simulation results demonstrate that our scheme is capable of providing both considerable energy savings, as well as substantial throughput improvements for both the source and the relay in a 'win-win' cooperation regime.

The achievable throughput of the entire cellular area is investigated, when employing fractional frequency reuse techniques in conjunction with realistically modelled imperfect optical fibre aided distributed antenna systems (DAS). Given a fixed total transmit power, a substantial improvement of the cell-edge area's throughput can be achieved without reducing the cell-centre's throughput. The cell-edge's throughput supported in the worst-case direction is significantly enhanced by the cooperative linear transmit processing technique advocated. Explicitly, a cell-edge throughput of η = 5 bits/s/Hz may be maintained for a imperfect optical fibre model, regardless of the specific geographic distribution of the users.

In this paper, we design an energy-efficient cooperative Medium Access Control (MAC) protocol combined with physical layer power / rate control in order to minimize the energy consumption. Based on the Channel State Information (CSI) and relay-to-destination distance, the potential candidate relays carry out autonomous decisions for minimizing the transmission power required for forwarding their data, when relying on their cooperation. Simulation results demonstrate that our scheme is capable of providing considerable energy savings, while maintaining the target Frame Error Ratio (FER), which is achieved at the cost of introducing a modest additional MAC overhead.

Different-complexity Multi-Cell Processing (MCP) schemes employing Distributed Signal-to-Interference-Leakage-plus-Noise-Ratio (SILNR) precoding techniques are proposed, which require reduced back-haul data exchange in comparison to the conventional MCP structure. Our results demonstrate that the proposed structures are capable of increasing the achievable cell-edge throughput and offering different geographic rate profile distributions as well as meeting different delay requirements.

Multi-Source Cooperation (MSC) techniques, including conventional Code Division Multiplexing (CDM) and Classic Network Coding (CNC) are investigated. We adopt a soft sum-product decoding algorithm for the CNC technique and propose a flexible Variable-rate Network Coding (VNC) technique. The iterative decoding convergence of the multiple source computation methods is analysed with the aid of EXtrinsic Information Transfer (EXIT) charts.

A novel Multiplexed Hybrid Automatic Repeat reQuest (M-HARQ) scheme is proposed and compared to the conventional scheme in terms of its energy efficiency, while satisfying specific delay constraints. By employing the proposed scheme, the transmission rate and power can be reduced, while maintaining the maximum energy efficiency and meeting specific delay constraints. Alternatively, the cell-radius distance may be extended by about 10%, which results in a coverage area extension by a factor of 1.21.

In this paper, we consider coding schemes designed for two nodes communicating with each other with the aid of a relay node, which receives information from the two nodes in the first time slot. At the relay node we combine a powerful Superposition Coding (SPC) scheme with Iteratively-Decoded Self-Concatenated Convolutional Codes (SECCC-ID), which exchange mutual information between each other. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second time slot after re-encoding it, again, using a SECCC encoder. At the destination, an amalgamated SPC-SECCC block then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme's performance to a direct transmission link between the two sources having the same throughput. Additionally, the SPC-SECCC system achieves a low BER even for realistic error-infested relaying.

The achievable throughput of the entire cellular area is investigated, when employing fractional frequency reuse techniques in conjunction with realistically modelled imperfect optical fibre aided distributed antenna systems (DAS) operating in a multicell scenario. Given a fixed total transmit power, a substantial improvement of the cell-edge area's throughput can be achieved without reducing the cell-centre's throughput. The distributed antennas are connected by realistic lossy optical fibre associated with a pulse-broadening parameter of β ≤ 0.1. Quantitatively, the entire cell-edge throughput is better than η = 3bits/s/Hz, potentially reaching 4bits/s/Hz ≤ η ≤ 5bits/s/Hz in the best illuminated areas. The geographic throughput distribution is characterized with the aid of throughput contours.

Linear precoding techniques are designed for both joint and distributed Multi-Cell Processing (MCP), where both centralised and decentralised Channel State Information (CSI) exchange scenarios are considered. The outage rate of various linear precoding techniques is investigated in the cell-edge area of a practical three-cell based cooperative scenario under both fully-loaded and lightly-loaded system configurations, when encountering either no tier-one Co-Channel Interference (CCI) or full tier-one CCI. The numerical results demonstrate the superiority of the low-complexity, yet scalable decentralised Distributed Signal-to-Leakage-Noise-Ratio (DSLNR) based linear precoding technique under realistic CSI quantisation and channel-induced feedback error conditions when full tier-one CCI is considered.

A novel Multiuser Detection (MUD) scheme is proposed for DS-CDMA systems employing the so-called Harmony Search (HS) algorithm, which is a novel meta-heuristic optimisation method. We specifically design the HS aided MUD for the communications problem considered and apply it in an iterative joint Channel Estimation (CE), MUD and channel decoding framework. The simulation results demonstrate that a near-single-user performance can be achieved by the proposed algorithm while avoiding the excessive-complexity full-search-based optimum detection even in overloaded DS-CDMA systems. Moreover, the HS algorithm can be efficiently applied in the Expectation Maximisation (EM) based CE framework.

In this paper, we consider the co-channel interference mitigation capability of fixed relay aided wireless systems, where the relays are linked to the base station using realistic imperfect optical fibre. Three interference mitigation techniques are investigated, namely an appealing reduced-power transmission technique, the classic eigen-beamforming arrangement and their hybrid. The cellular model of Shamai and Wyner is used in conjunction with Fractional Frequency Reuse (FFR) and the tradeoffs between the cell-edge throughput and cell-centre throughput are characterised for the three interference mitigation techniques employed. Our simulation results demonstrate that the combination of the reduced-power transmission and the eigen-beamforming technique is capable of improving the achievable throughput for the MSs roaming close to the cell-edge without sacrifising the throughput of the cell-centre MSs.

We propose novel reconfigurable rateless codes, that are capable of not only varying the block length but also adaptively modify their encoding strategy by incrementally adjusting their degree distribution according to the prevalent channel conditions without the availability of the channel state information at the transmitter. In particular, we characterize a reconfigurable rateless code designed for the transmission of 9,500 information bits that achieves a performance, which is approximately 1 dB away from the discrete-input continuous-output memoryless channel's (DCMC) capacity over a diverse range of channel signal-to-noise (SNR) ratios.

In this paper, we consider coding schemes designed for energy efficient multi-source cooperation. More explicitly, we propose both a powerful superposition coding scheme and a physical-layer algebraic network coding scheme. The concept of generalised network coding is introduced and the relation between superposition coding and network coding is revealed. Our simulation results demonstrate that both of the proposed schemes are capable of performing close to the outage probability bound at the lower end of the target transmit power range. Moreover, compared to the superposition coding scheme considered, the proposed algebraic network coding arrangement imposes a lower complexity at the cost of a slight performance degradation, while maintaining the same throughput and delay.

In this paper, we consider coding schemes designed for multi-source cooperation, where a cluster of sources cooperatively communicates with the destination. More explicitly, we propose both a powerful superposition coding scheme and a physical-layer algebraic network coding scheme. Our simulation results demonstrate that both of the proposed schemes are capable of performing close to the outage probability bound. Compared to the superposition coding scheme considered, the proposed algebraic network coding arrangement imposes a much lower complexity at the cost of a slight performance degradation, while maintaining the same throughput and delay.

A novel random-guided optimization method is proposed for multiuser detection (MUD) in DS-CDMA systems employing the so-called harmony search (HS) algorithm. We specifically design the HS-aided MUD for the communications problem considered and apply it in an iterative joint MUD and channel decoding framework. Our simulation results demonstrate that a near-single-user performance can be achieved without the employment of the full-search-based optimum MUD even in extremely highly loaded DS-CDMA systems.

We propose novel reconfigurable rateless codes, that are capable of not only varying the block length but also adaptively modify their encoding strategy by incrementally adjusting their degree distribution according to the prevalent channel conditions without the availability of the channel state information at the transmitter. In particular, we characterize a reconfigurable rateless code designed for the transmission of 9,500 information bits that achieves a performance, which is approximately 1 dB away from the discrete-input continuous-output memoryless channel's (DCMC) capacity over a diverse range of channel signal-to-noise (SNR) ratios.

In this paper, we propose a novel distributed interleaved Random Space-Time Code (IR-STC) designed for Multi- Source Cooperation (MSC) employing various relaying techniques, namely Amplify-Forward, Decode-Forward, Soft-Decode-Forward and Differential-Decode-Forward. We characterise the achievable slot utilisation efficiency and introduce a two-phase communication regime for our IR-STC aided MSC. A matrix based formalism is used for describing our IR-STC scheme and a novel Structured Embedded (SE) random interleaver generation method is proposed. Furthermore, the Bit Error Ratio (BER) performance of our IR-STC is characterised in conjunction with various relaying techniques under different inter-source Nakagami-m fading channels.

In this paper, we propose the novel concept of Repeat Accumulate Code Division Multiple Access (RA-CDMA), which employs unique, user-specific channel code generator matrices (interleavers) for differentiating the users. We also suggest a Multilevel Structured (MLS) interleaver generation technique for the sake of reducing the memory storage requirements of our system and compare its correlation properties to those of the conventional random interleaver. A novel hybrid detector is designed for our system with the aid of Extrinsic Information Transfer (EXIT) charts. Furthermore, we also design a low-complexity unequal power allocation scheme, assigning a different power to each user of this near-capacity transmission scheme. It is shown that when a sufficiently high interleaver length is employed, the RA-CDMA system is capable of approaching the Gaussian channel's capacity.

In this paper, we introduce and outline the concept of channel code division multiple access (CCDMA) using a design example based on the proposed multilevel structured (MLS) LDPC codes. We succeeded in making the memory requirements of the multi-user transceiver to become practically independent of the total number of users supported by the system as well as ascertain that each user benefits from the same quality of service (QoS). Finally, we demonstrate that despite their beneficial compact structure, the proposed MLS LDPC codes do not suffer from any bit error ratio (BER) or block error ratio (BLER) performance degradation, when compared to an otherwise identical benchmarker scheme using significantly more complex LDPC codes having pseudo-random parity-check matrices.

With the advent of extrinsic information transfer (EXIT) charts, we are capable of analyzing, predicting and visually comparing the convergence behaviours of different turbo multi-user detectector (MUD)s. The different MUDs have diverse EXIT characteristics and hence their superposition allows us to create a combined EXIT curve, which closely matches that of the channel decoder. Hence a near-capacity operation is facilitated by combining the benefits of different MUDs and therefore to create a superior MUD. Thus in this contribution, we propose a novel hybrid MUD combining scheme, which combines the advantages of a high performance and low complexity in form of an advanced hybrid MUD solution. The transmitted bits are unknown at the receiver, hence it is not feasible to directly evaluate the mutual information gain of the iterative MUD in consecutive iterations, hence we propose a realistic algorithm for estimating this mutual information gain, which is then used for activating the most appropriate constituent MUD as and when it is necessary. The constituent MUDs are the matched filter (MF) based soft interference cancellation (SoIC) and the optimum Bayesian MUDs, which are invoked in the scenario of frequency-domain-spread chip- interleaved (FDSCI) multiple carrier code division multiple access (MC-CDMA). The resultant hybrid MUD is capable of outperforming both the MF-SoIC and Bayesian turbo MUDs in the terms of the attainable complexity and bit-error-rate (BER) performance.

In this paper, we design and investigate a novel Interleave Division Multiplexing based Space-Time Code (IDM-STC) in the context of cooperative communications. We outline the particular signalling scheme used for exchanging the necessary information amongst the cooperating MSs and suggest an efficient interleaver allocation scheme, which is capable of uniquely and unambiguously differentiating the different MSs' signals with the aid of their user and antenna-specific interleavers. We then characterize the achievable performance of our proposed IDM-STC design and compare it to that of the traditional G2and G4Space-Time Block Code (STBC) invoked for cooperative communications. Our cooperative IDM-STC scheme is flexible in terms of forming a cluster of cooperative users, it is power-efficient and capable of maintaining a high rate, in particular when combined with non-uniform power allocation.

In this paper, we consider the joint code-rate and spreading-factor optimisation of turbo-style iterative joint detection and decoding assisted single-carrier interleave division multiple access (SC-IDMA) systems using different-rate convolutional codes and extrinsic information transfer (EXIT) charts, when communicating over additive white Gaussian noise (AWGN) channels. More explicitly, we study the extrinsic information exchange between two serial concatenated components and maximise the number of users supported by the SC-IDMA system under the constraint of a fixed bandwidth expansion factor, while maintaining a predefined bit error ratio (BER) versus Eb/N0performance. We found that an optimum code-rate and spreading-factor combination can be found for the SC-IDMA system at low Eb/N0values, where maintaining a low BER inevitably requires the employment of channel coding. By contrast, at high Eb/N0the system performs best, when no channel coding is used, i.e. DS-spreading is the only means of bandwidth expansion.