Uplink Cellular Networks Research Articles

On the Achievable Performance-Complexity Tradeoffs of Relay-Aided Space Shift Keying

Future cellular networks require transmission technologies and protocols that are energy-efficient, and that can meet the growing demands of mobile data traffic with the best performance versus complexity tradeoff. The recently proposed single-RF space shift keying (SSK-) multiple-input-multiple-output (MIMO) transmission scheme is one of such physical layer technology that satisfies these criteria. In general, SSK requires a large number of antenna elements (with only one of them active) at the transmitter for high data rate transmission. This makes SSK particularly useful for the downlink of cellular systems. In this paper, we exploit the virtual MIMO concept to design SSK transmission schemes for the uplink of cellular networks. The idea is to take advantage of nearby nodes to the mobile terminal as a “virtual spatial-constellation diagram,” where the information can be encoded and transmitted to the final destination. By taking into account the virtual nature of the spatial-constellation diagram, we develop advanced demodulation techniques, perform a comprehensive mathematical analysis, as well as analyze the system complexity and energy consumption. It is also shown that the proposed scheme is capable of outperforming certain state-of-the-art protocols.

Opportunistic Interference Alignment and Cancellation for the Uplink of Cellular Networks

In this letter, we propose an opportunistic interference alignment and cancellation (OIAC) scheme for cellular networks to exploit the multi-user diversity gain and the backhual resources among base stations. Particularly, an opportunistic user scheduling strategy is proposed by synthesizing opportunistic interference alignment (OIA) and successive interference cancellation (SIC). In the OIAC scheme, we propose a new user scheduling metric and a sequential user selection scheme based on the characteristics of SIC, and guarantee a target signal-to-interference-plus-noise ratio (SINR) for each selected user by performing user selection, decoder design and power control jointly in the user selection process. The OIAC scheme improves system performance by using SIC and keeps the low implementation complexity property of OIA. The simulation results show that the OIAC scheme can improve the achievable sum rate significantly compared to OIA and other schemes.

Multiuser Scheduling and Pairing With Interference Mitigation for LTE Uplink Cellular Networks

In this paper, we investigate multiuser scheduling with joint user pairing, resource allocation, and power control (PC) in Long-Term Evolution (LTE) uplink cellular networks. We first derive the received signal-to-interference-plus-noise ratio (SINR) in spatial multiuser single-carrier frequency-division multiple-access (SC-FDMA) systems with frequency-domain minimum mean square error (MMSE) equalization. Based on this, we formulate an optimization problem as joint multiuser pairing, resource allocation, and PC to maximize the weighted throughput of the system. We then divide it into a two-step optimization problem, which is suboptimal but significantly reduces the complexity. The two-step problem first performs optimal frequency resource allocation and user pairing for a given transmit power value and then adjusts the transmit power to maximize the weighted throughput when frequency resources are allocated and users are paired. With the help of high-interference indicators exchanged among multiple base stations (BSs), we develop an iterative distributed and low-complexity algorithm to further simplify the two-step problem. System-level simulation results show that the proposed algorithm can effectively mitigate interference and significantly outperforms the existing algorithms.

Analytical Modeling of Mode Selection and Power Control for Underlay D2D Communication in Cellular Networks

Device-to-device (D2D) communication enables the user equipments (UEs) located in close proximity to bypass the cellular base stations (BSs) and directly connect to each other, and thereby, offload traffic from the cellular infrastructure. D2D communication can improve spatial frequency reuse and energy efficiency in cellular networks. This paper presents a comprehensive and tractable analytical framework for D2D-enabled uplink cellular networks with a flexible mode selection scheme along with truncated channel inversion power control. The developed framework is used to analyze and understand how the underlaying D2D communication affects the cellular network performance. Through comprehensive numerical analysis, we investigate the expected performance gains and provide guidelines for selecting the network parameters.

Outage Analysis of Uplink Two-Tier Networks

Employing multi-tier networks is among the most promising approaches to address the rapid growth of the data demand in cellular networks. In this paper, we study a two-tier uplink cellular network consisting of femtocells and a macrocell. Femto base stations, and femto and macro users are spatially deployed based on independent Poisson point processes. We consider an open access assignment policy, where each macro user based on the ratio between its distances from its nearest femto access point (FAP) and from the macro base station (MBS) is assigned to either of them. By tuning the threshold, this policy allows controlling the coverage areas of FAPs. For a fixed threshold, femtocells coverage areas depend on their distances from the MBS; those closest to the fringes will have the largest coverage areas. Under this open-access policy, ignoring the additive noise, we derive analytical upper and lower bounds on the outage probabilities of femto users and macro users that are subject to fading and path loss. We also study the effect of the distance from the MBS on the outage probability experienced by the users of a femtocell. In all cases, our simulation results comply with our analytical bounds.

Stochastic optimization in cooperative relay networks for revenue maximization

In cellular networks, cooperative relaying is an economic and promising way to enlarge the network capacity and coverage. In the case that multiple users and multiple relays are taken into account, efficient resource allocation is important in such networks. In this paper, we consider the joint relay power control with amplify-and-forward (AF) strategy and dynamic pricing for uplink cellular networks in order to maximize the network administrator’s system revenue. The system revenue is associated with pricing strategies and mobile users’ random data request, which is supported by the relay assisted transmission. To deal with the problem of the coupling in pricing and relay resource allocation, we utilize Lyapunov optimization techniques to design online pricing and relay power control without any statistic information of random events in networks. Theoretical analysis shows that the proposed algorithm can achieve a near-optimal performance and simulation results also validate its effectiveness and robustness.

Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile charging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is applied to derive the tradeoffs between the network parameters including p, q, and the BS/PB densities under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product the BS density decreases with increasing p following a power law where the exponent is proportional to the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product between q, the PB density, and the BS density raised to a power proportional to the path-loss exponent has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, a similar result is obtained with the aforementioned product increased by the array gain. Last, similar results are derived for the case of mobiles having small energy storage.

Delay‐limited throughput analysis of cooperative hybrid automatic repeat request in asymmetric fading channels

This study analyses the delay-limited throughput performance of an uplink cellular relay network utilising hybrid automatic repeat request (HARQ) protocol in which one mobile station (MS) communicates with one base station (BS) with the aid of one amplify-and-forward relay station (RS). The authors’ analysis allows for a practical fading scenario where MS → RS and RS → BS channels undergo independent Rayleigh and Rician fading, respectively. Delay-limited throughput expressions for two HARQ protocols are derived, respectively, namely Repetition Time Diversity and Incremental Redundancy. Furthermore, the impact of different parameters on the achievable throughput, such as the maximum HARQ round number L, line-of-sight signal K, information rate R etc., is analysed. The authors’ analysis unveils that, for the presumed dual-hop cooperation model with the specified tolerable delay requirement and given channel condition, there exists an optimal information rate R* that achieves the maximum delay-limited throughput for the two HARQ protocols. Moreover, it is disclosed that, both HARQ protocols with the adaptive optimised information rate outperform the counterpart with the fixed information rate in low and moderate SNR regions, suggesting that an adaptive transmission scheme should be employed to achieve a better throughput performance.

Energy-Efficient Resource Allocation in OFDMA Networks

The widespread application of multimedia wireless services and requirements of ubiquitous access have triggered rapidly booming energy consumption at both the base station side and the user equipment (UE) side. Hence, energy-efficient design in wireless networks is very important and is becoming an inevitable trend. In this paper, we study the energy-efficient resource allocation in both downlink and uplink cellular networks with orthogonal frequency division multiple access (OFDMA). For the downlink transmission, the generalized energy efficiency (EE) is maximized while for the uplink case the minimum individual EE is maximized, both under certain prescribed per-UE quality-of-service (QoS) requirements. For both transmission scenarios, we first provide the optimal solution and then develop a suboptimal but low-complexity approach by exploring the inherent structure and property of the energy-efficient design. For the downlink case, by modifying the original problem, we also find a computationally efficient and numerically tractable upper bound on the EE, which indicates the performance limit and is demonstrated to be quite tight if the number of subcarriers is larger than that of UEs and motivates us to find a near-optimal approach relying on the quasiconcave relation between the modified EE and transmit power. Simulation results show that the energy-efficient design greatly improves EE compared with the conventional spectral-efficient design and the low-complexity suboptimal approaches can achieve a promising tradeoff between performance and complexity.

Iterative Mitigation of Intercell Interference in Cellular Networks Based on Gaussian Belief Propagation

The mitigation of 2-D intersymbol interference (ISI) has recently emerged as an important problem in the field of storage technology and wireless communications. Several solutions based on message passing have been proposed to perform equalization on 2-D channels with ISI. We present an algorithm based on Gaussian belief propagation (GaBP). We show that the proposed algorithm has interesting features compared with the corresponding message passing solutions available in the literature. First, the complexity of the proposed equalizer is independent of the size of the constellation used for modulation. Second, since the complexity is not exponential in the size of the state space, the computational burden is reduced for channels with long memory. As an application, we consider decentralized intercell interference mitigation in uplink cellular networks, where base stations communicate with their neighbors to recover their own users' signals.

A Statistical Inter-Cell Interference Model for Uplink Cellular OFDMA Networks Under Log-Normal Shadowing and Rayleigh Fading

The performance of uplink cellular OFDMA networks transmitting multiple QAM symbols per hop is evaluated under log-normal shadowing and Rayleigh fading without resorting to a Gaussian approximation of the inter-cell interference. The derived interference statistic is observed to deviate significantly from the Gaussian distribution which may be exploited to dramatically enhance the network performance. It is also observed that the network performance is highly dependent on the number and the geometry of the QAM symbols transmitted within a hop, especially for large code frame lengths.

A Comment on "Performance Analysis of Uplink Cognitive Cellular Networks with Opportunistic Scheduling"

An exact closed-form bit-error-rate (BER) expression is derived for the scheduled cognitive user (CU) in the uplink cellular networks with opportunistic scheduling considered by Li. Simulation results corroborate the theoretical analysis.

Reduced-Complexity Belief Propagation for System-Wide MUD in the Uplink of Cellular Networks

System-wide multiuser detection (MUD), in which all base stations (BSs) of a cellular system cooperate to detect the data of all mobile stations (MSs), has much promise. However, little is known at present about practical techniques or their performance. An attractive method is belief propagation (BP), with message exchange between nearby cooperating BSs over a backbone landline network, but its performance is known only for a greatly simplified network model and its computation load grows exponentially with the number of interfering MS symbols at each BS. In this paper, we present a reduced complexity variation of BP (RCBP) and show that its performance is close to or identical to that of BP in the simplified network. We also observe excellent performance by iterative multiuser detection and decoding of low-density parity check codes (LDPC). Furthermore, we examine RCBP performance in a realistic wireless network model, with path loss, shadowing, fading and power control. These results, though poorer than those of the simplified network, show that system-wide MUD with cooperating BSs provides great improvement compared with conventional systems.

Cross-layer feedback-based resilient coding for video transmission over uplink cellular network

Delivering real-time video over 3G cellular networks is an important component of mobile multimedia applications. Since hybrid coded video is very vulnerable to channel disturbances, the unavoidable burst frame losses when transmitting video over cellular network will cause severe quality degradation. It has been found that feedback channel combined multiframe is an effective tool to enhance error resilience for the wireless video communication. However, this method is affected by the long time delay of the feedback message greatly. In this paper, a novel error resilient video coding scheme for the uplink video applications over cellular networks is proposed. Unlike existing schemes, the proposed scheme adopts a radio link layer agent at the sender to implement the cross-layer feedback: get the frame losses information (by prediction or active time-out frame discarding) and send it to the application (APP) layer to adapt the encoder well to the varying channels. Experiments results show that the proposed scheme can improve both the coding efficiency and the error resilience of the uplink cellular video communication significantly.