We address the uplink small-cell access point (AP) placement problem for optimal throughput, while considering load balancing (LB) among the APs. To consider LB and consequently incorporate fairness in user spectral access, i.e., the frequency of user-to-AP communications, we modify the Lloyd algorithm from vector quantization so that delays incurred by the existence of a large number of users in a cell are accounted for in the AP placement process. Accordingly, we present two methods, the first of which involves the incorporation of weights proportional to the cell occupancy, hence called the Occupancy Weighted Lloyd algorithm (OWLA). The second method adds a new step to the Lloyd algorithm, which involves re-assigning users from higher to lower occupancy cells, and the adoption of a distance threshold to cap the throughput lost in the assignment process. This formulated Lloyd-type algorithm is called the Cell Equalized Lloyd Algorithm-α (CELA-α) where α is a factor that allows for throughput and spectrum access delay trade-off. Extensive simulations show that both CELA-α and OWLA algorithms provide significant gains, in comparison to the standard Lloyd algorithm, in 95%-likely user spectral access. For the α values considered in this paper, CELA-α achieves gains up to 20.83%, while OWLA yields a gain of 12.5%. Both algorithms incur minimal throughput losses of different degrees, and the choice of using one algorithm over the other for AP placement depends on system LB as well as throughput requirements.

In this paper, we explore the small-cell uplink access point (AP) placement problem in the context of throughput optimality and provide solutions while taking into consideration inter-cell interference (ICI). First, we briefly review the vector quantization (VQ) approach and related single user throughput-optimal formulations for AP placement. Then, we investigate the small-cell case with multiple users and expose the limitations of mean squared error based VQ for solving this problem. While the Lloyd algorithm from the VQ approach is found not to strictly solve the small-cell case, based on the tractability and quality of the resulting AP placement, we deem it suitable as a simple and appropriate framework to solve more complicated problems. Accordingly, to minimize ICI and consequently enhance achievable throughput, we design two Lloyd-type algorithms, namely the Interference Lloyd algorithm and the Inter-AP Lloyd algorithm, both of which incorporate ICI in their distortion functions. Simulation results show that both of the proposed algorithms provide superior 95%-likely rate over the traditional Lloyd algorithm and the Inter-AP Lloyd algorithm yields a significant increase of up to 36.34% in achievable rate over the Lloyd algorithm.

It is of great interest to develop larger scale multiple-input multiple-output (MIMO) technology based on frequency division duplexing (FDD) for backward compatibility with existing standards and already deployed cellular networks. One hindrance to the FDD approach is the complexity of the codeword search performed by the receiver, which is known to scale with the number of transmit antennas N in a system. The codeword search complexity does not scale linearly and soon becomes infeasible even for the not-so-massive MIMO systems expected in the very near future. We address this problem by proposing a natural sequence-based orthogonal codebook and an intra-array interference magnitude (IIM) framework for MIMO beamforming based on quantized equal gain transmission that altogether tremendously simplifies the codeword search problem. We also present an assessment on the quality of the codeword selected by the proposed framework that explains it's near optimal performance, and, provide detailed codeword search complexity quantification. Finally, we provide simulation analyses of beamforming gain under time selective fading channels and an FDD MIMO system transmit delay model. Our analyses indicate that despite significantly reducing complexity, the proposed IIM framework executed by already commercialized processors is capable of approaching the ideal performance of an static system even in the presence of time-selectivity inherent to high-speed mobile communications. Our analyses also quantify the impact of feedback delay on average beamforming gain of moderately large transmit arrays.

The shared resource access wireless communication system is regarded as a paradigm that allows the mobile network operators (MNOs) to have extended coverage and allows them to satisfy their subscribers' high capacity demands while keeping the capital and operational expenditure in check. On the other hand, dual connectivity (DC), a small cell enhancement feature, allows the subscribers to have two simultaneous connections increasing throughput and enhancing mobility robustness. For the DC mechanism, the user needs to be under the coverage of multiple BSs concurrently. Because of random nature of the wireless links and distribution of BSs in a network, the practicability/operability of DC for a typical user under such random operating conditions (both topological and wireless link randomness) needs to be properly evaluated. In this paper, we perform stochastic analysis of DC in shared resource access high capacity wireless networks. We consider a fading-averaged signal propagation loss process, where the selection of the serving BS is perturbed shadowing, not by fading. The DC coverage probability is analyzed in terms of tractable, integral expressions. We have observed that the DC coverage probability is greatly affected by the density of the small cell BSs and the variance of the log-normal shadowing.

The 5th Generation (5G) systems demand a higher capacity, a lower latency, an ultra-reliability, a massive connectivity, and a higher energy efficiency. Especially, substantial improvement in energy efficiency of current 4G systems is highly required in 5G systems. High energy efficiency results in low operational cost and sustainable network deployment. In this paper, we propose a new receiver puncturing technique and a novel energy efficient dynamic resource allocation scheme for 5G systems. Improvements in BER performance and 20% transmit-energy expenditure reduction, as compared to conventional proportional fair resource allocation scheme, are shown by link/system level simulation. Finally, the complexity issues inherent to the proposed technique are evaluated as well.

We investigate an advanced two-phase shared spectrum access communication scheme as an efficient approach to enhance the spectral utilization of a network. In the first phase, we devise a spectrum-sharing policy based on demands, fairness, and so on, which utilizes a priority scheme in fulfilling operators' demands, and envision a secure operator-specific information sharing policy where no critical information is exchanged between the operators. In the second phase, a macro cell network (MCN) benefits through offloading services offered by small cell network (SCN). This allows the MCN to satisfy its users' capacity demands, improve its quality of services and coverage under Nakagami fading channel. As a repayment, the SCN is rewarded with licenses to share and operate on the spectrum originally owned by the MCN. We devise a density division-based shared spectrum access model, where the density of the licensee's SCN deployment is exploited as network resources. A fair division of the densities of the licensee operator's small cell base stations into fractions of licensed small cell base stations serving its own users and offloading small cells is presented. Unlike most of the previous research works that considered Poisson point process (PPP) to model the distribution of the network entities even when PPP modeling is not accurate for the networks, where the number of MCN/SCN base stations is definite and the number of MCN/SCN base stations in disjoint areas is not independent, we employ a more realistic network model known as binomial point process to perform an analytical analysis of the cumulative interference and performance of the system. Furthermore, we analyze the rate coverage and outage performances considering a wide range of values for path-loss exponent and fading severity parameter of Nakagami fading.

In this paper, we conceive an advanced small cells wireless network deployment framework within a managed space under shared spectrum access paradigm. We also conceive a complementary business model, referred to as neutral host micro operator (NH-μO), that leverages a single shared wireless infrastructure to mutually benefit μO (a third party service provider), the owner of the space/facility, and mobile network operators (MNOs). The model is composed of a μO slice, which delivers a venue with customized wireless services tailored to the its local service requirements, and an MNO slice, which facilitates improved wireless coverage to visitors/end-users with subscriptions to several different MNOs. The NH-μO is not biased to favor any specific client, which can be enforced through a concrete commercial agreement. A radio access network slicing concept is exploited to support and optimize both the slice instances (SIs) efficiently in a shared manner on a single physical network infrastructure. In addition, we devise an efficient architecture for the NH-μO small cell base station and dynamic spectrum assignment control unit, and their required functionalities supporting sustainable coexistence of different SIs in shared spectrum. We also devise both interSI and intra-SI dynamic spectrum allocation policies considering time-varying requirements of different SIs. These policies take care of application level priority by providing a proper mixture of users with guaranteed quality of service and best-effort users, while ensuring a healthy SI competition. The advantages of the proposed framework are twofold. It enables the venue owner to manage its wireless networks and consider its very specific requirements while capitalizing from the MNO slice. This, in turn, reduces the need for deployment of new infrastructure while providing improved wireless coverage and savings to MNOs. Finally, our proposed framework leverages efficient utilization of spectrum, physical infrastructure, and computational resources. The simulation results exhibit various important features of the proposed shared spectrum access policies.

We consider a cognitive radio (CR) network consisting of a primary cellular system and a secondary cognitive machine-to-machine (M2M) system, and study the throughput enhancement problem of the latter system employing universal-filtered orthogonal frequency division multiplexing (UF-OFDM) modulation. The downlink transmission capacity of the cognitive M2M system is thereby maximized, while keeping the interference introduced to the primary users (PUs) below the prespecified threshold, under total transmit power budget of the secondary base station (SBS). The performance of UF-OFDM-based CR system is compared to the performances of OFDM-based and filter bank multicarrier (FBMC)-based CR systems. We also propose a near-optimal resource allocation method separating the sub-band and power allocation. The solution is less complex compared to optimization of the original combinatorial problem. We present numerical results that show that for given interference thresholds of the PUs and maximum transmit power limit of the SBS, the UF-OFDM-based CR system exhibits intermediary performance in terms of achievable capacity compared to OFDM- and FBMC-based CR systems. Interestingly, for a certain degree of robustness of the PUs, the UF-OFDM performs equally well as FBMC. Furthermore, the percentage rate-gain of UF-OFDM-based CR system increases by a large amount when UF-OFDM modulation with lower sidelobes ripple is employed. Numerical results also show that the proposed throughput enhancing method despite having lower computational complexity compared to the optimal solution achieves near-optimal performance.

Driven by the progress of regulations of TVWS worldwide, IEEE 802.11 started a new Task Group af (TGaf) to pursue extension of traditional Wi-Fi to TV White Spaces (TVWS). Wi-Fi in TVWS offers longer distance and broader bandwidth; while maintaining the same user experience of traditional Wi-Fi systems. It is therefore regarded as one of most promising technologies to exploit the market derived from the new regulations of VHF/UHF bands. In this paper, we present the world's first prototype system of Wi-Fi in TVWS based on the TGaf draft specification. The prototype system verifies the PHY and MAC design of TGaf and the database query protocols that is needed for TVWS operation but not in the scope of TGaf. It is demonstrated that, with sufficiently defined MAC protocol and PHY that meets sharp transmission spectrum mask, the developed prototype supports video streaming on single TV channel while well coexisting with primary TV services in the vicinity.

Following the standard approach envisioned by the Federal Communication Commission (FCC), we consider database as a tool to plan the utilization of VHF/UHF spectrum by White Space (WS) radios. Our approach, however, differs from the one adopted by the aforementioned regulatory body in the sense that the algorithms loaded into the database are not limited to processing broadcaster information, i.e., effective antenna height, effective isotropic radiated power (EIRP), and simplistic terrain information, i.e., antenna height above average terrain (HAAT). We utilize detailed regional topography data in order to predict the primary contour and WS radios service area in a more realistic fashion through Fresnel diffraction theory. The contour calculated based on our algorithms are overlaid on Google Earth software, therefore, creating a very flexible and interactive tool for TVWS prediction.

Moving forward based on the current spectrum regulations and industrial standardization for unlicensed usage of TV white space, we postulate a potential deployment scenario and describe the management procedure of coexisting secondary user (SU) networks under the interference constraints to the primary user (PU) receivers. For the quantitative evaluation of coexistence we first introduce a new parameter named quality of coexistence (QoC), which is utilized to measure the benefits achieved by a novel coexistence scheme also proposed in this paper, namely, interference-constrained time slot splitting and allocation. Furthermore, on the basis of a system model we obtain the optimal SU networks time slot allocation ratios by maximizing the aforementioned QoC, therefore, leading to an efficient spectrum usage by SUs without incurring harmful interference to the PUs. Finally, we simulate a coexistence scenario in TV white space in order to compare the proposed scheme with other schemes that select a single SU network to operate based on simplistic criteria. It can be seen that when the SU network employs adaptive transmit power control (TPC), the medium value of QoC is doubled by using the optimal time slot allocation, resulting in significant improvement in coexistence.

In cognitive radio networks, secondary users need to conduct spectrum sensing to properly detect the presence of primary signals that may have much lower power than noise plus interference power. In such a case, time-varying noise plus interference, which is briefly called noise uncertainty in this paper, can substantially degrade the sensing reliability of hard information combining (HIC) and soft information combining (SIC). To improve the sensing reliability in the circumstance with heavy noise uncertainty, we propose an adaptive two thresholds based energy detection and a two stage HIC based cooperative decision for cooperative spectrum sensing. The proposed sensing technique has shown better performance than conventional HIC and comparable performance with SIC when a small number of sensing nodes are used in spectrum sensing.