Presence Of Inter-cell Interference Research Articles

Optimum Base Station Antenna Tilt Angle for Inter-Cell Interference Limited Mobile Cellular System

This paper investigates the effect of base station (BS) antenna tilt angle on the performance of LTE-Advanced physical layer downlink channel in Inter-Cell Interference (ICI) limited scenario for five cell ranges, two carrier frequencies, and two BS antenna heights. The cellular system is deployed following the 3GPP hexagonal grid with a frequency reuse factor of one and three sectors per site. An urban based 3D ray-tracing tool is used to model the wireless channel for many BS and user equipment (UE) links. System performance is evaluated in terms of Signal power to Interference plus Noise power Ratio (SINR), received signal power, received interference power, achievable throughput (THR), Average Spectrum Efficiency (ASE) and UEs outage probability. The objective is to find the BS antenna tilt angle that provides the maximum ASE, minimum UEs outage probability, or optimum ASE and UE outage probability. The obtained simulation results unveil that the maximum ASE occurs at a tilt angle where the mean of the SINR is maximum and the mean of rms delay spread is minimum, while the minimum UEs outage occurs at a tilt angle where the received signal power is maximum. This is an important finding to facilitate the planning and the deployment of cellular system in the presence of ICI. Moreover it is found that the optimum tilt angles decrease as the cell range increase and BS antenna height decrease. The results also show that these optimum tilt angles are independent of the carrier frequency.

5G Cellular Networks: Coverage Analysis in the Presence of Inter-Cell Interference and Intentional Jammers

Intentional jammers (IJs) can be used by attackers for the launching of distributed denial-of-service attacks in 5G cellular networks. These adversaries are assumed to have adequate information about the network specifications, such as duration, transmit power and positions. With these assumptions, the IJs gain the ability to disrupt the legitimate communication of the network. Heterogeneous cellular networks (HetNets) can be considered a vital enabler for 5G cellular networks. Small base stations (SBSs) are deployed inside macro base station (MBS) to improve spectral efficiency and capacity. Due to orthogonal frequency division multiplexing assumption, HetNets’ performance is mainly limited by inter-cell interference (ICI). Additionally, there exist IJs-interference (IJs-I), which significantly degrades the network coverage depending on the IJs’ transmit power levels and their proximity with the target. The proposed work explores the uplink (UL) coverage performance of HetNets in the presence of both IJs-I and ICI. Moreover, to reduce the effects of ICI and IJs-I, reverse frequency allocation (RFA) is employed which is a proactive interference abating scheme. In RFA, different sub-bands of the available spectrum are used by MBS and SBS in alternate regions. The proposed setup is evaluated both analytically as well as with the help of simulation. The results demonstrate considerable UL coverage performance improvement by effectively mitigating IJs-I and ICI.

Interference Management in Ultra-Dense 5G Networks With Excessive Drone Usage

In fifth generation (5G) networks, the densification of small base stations in the coverage region of macro base station (MBS) leads to significant inter-cell interference (ICI). Similarly, drones (a.k.a. unmanned aerial vehicles) have a diverse scope in multifarious 5G assisted applications and, therefore, cause considerable drones interference (DI) as a result of excessive drone usage. This paper investigates the bottleneck uplink (UL) coverage performance of the MBS edge users in the presence of ICI and DI. To mitigate both ICI and DI, we use an efficient resource allocation scheme known as reverse frequency allocation (RFA). Moreover, we use decoupled association (DeCA) in place of coupled association to further improve UL signal-to-interference ratio. The results depict that RFA in conjunction with DeCA overpass all other techniques in terms of improved UL coverage performance because of effective DI and ICI mitigation.

A Green Coordinated Multi-Cell NOMA System With Fuzzy Logic Based Multi-Criterion User Mode Selection and Resource Allocation

We consider a multi-cell non-orthogonal multiple access (NOMA) system with coordinated base stations and investigate its downlink user coordination mode selection and resource allocation to green the system while maintaining high spectral efficiency, in the presence of inter-cell interference. To the best of our knowledge, this is the first work to consider multiple criteria in user coordination mode selection for coordinated NOMA systems, and a fuzzy logic (FL) based approach is proposed to balance among multiple criteria to achieve higher robustness against the combined effect of shadowing, fading and inter-cell interference, compared to the previous single-criterion-based user coordination mode selection methods. This is also the first known effort to investigate multi-subchannel resource allocation for coordinated NOMA where the previous work on coordinated orthogonal multiple access is not applicable. Two resource allocation algorithms are proposed: first, a serving channel gain based subchannel allocation (SCG-SA) algorithm, based on the theoretical proof that the total transmission power is mono-decreasing with respect to the SCG of the non-coordinated user in each cell with the highest channel gain on the shared subchannel; second, a low-complexity FL user ranking order based joint resource allocation algorithm, which requires no separate user ranking process in subchannel allocation, thanks to the FL ranking list generated from user coordination mode selection. Also, the effects of imperfect channel state information and successive interference cancellation are considered. Numerical results show that the proposed multi-criterion based schemes significantly outperform the previous schemes based on single-criterion user coordination mode selection, in terms of transmission power and energy efficiency, contributing to a greener system.

Coordinated Beamforming for Multi-Cell MIMO-NOMA

In this letter, two novel coordinated beamforming techniques are developed to enhance the performance of non-orthogonal multiple access combined with multiple-input multiple-output communication in the presence of inter-cell interference. The proposed schemes successfully deal with inter-cell interference, and increase the cell-edge users’ throughput, which in turn improves user fairness. In addition, they increase the number of served users, which makes them suitable for 5G networks where massive connectivity and higher spectral efficiency are required. Numerical results confirm the effectiveness of the proposed algorithms.

Distributed Beamforming for Macro Diversity and Power Control With Large Arrays in Spatial Correlated Channels

Downlink beamforming plays a key role in massive multiple-input multiple-output (MIMO) systems to provide reasonable signal-to-interference-plus-noise ratio (SINR) in the presence of intercell interference (ICI). Due to an excessive backhaul overhead, limited cooperative beamforming is usually desirable. In this paper, we consider distributed beamforming that can exploit macro diversity with limited cooperation for cell-edge users where multiple base stations (BSs) transmit signals to those users simultaneously. Bounds on the SINRs are derived to see the impact of the spatial correlation. Since distributed beamforming itself cannot guarantee quality of service (QoS) requirements for given target SINRs with limited cooperation, based on derived closed-form expressions for bounds on SINRs, joint power control is considered with two different approaches. One is optimal, but central processing is required. The other approach is suboptimal, while it can be implemented as a distributed power control algorithm.

Constrained Codes that Mitigate Inter-Cell Interference in Read/Write Cycles for Flash Memories

Inter-cell interference (ICI) is one of the main obstacles to precise programming (i.e., writing) of a flash memory. In the presence of ICI, the voltage level of a cell might increase unexpectedly if its neighboring cells are programmed to high levels. For q-ary cells, the most severe ICI arises when three consecutive cells are programmed to levels high - low - high, represented as (q-1)0(q-1), resulting in an unintended increase in the level of the middle cell and the possibility of decoding it incorrectly as a nonzero value. ICI-free codes are used to mitigate this phenomenon by preventing the programming of any three consecutive cells as (q-1)0(q-1). In this work, we extend ICI-free codes in two directions. First, we consider binary balanced ICI-free codes which, in addition to forbidding the 101 pattern, require the number of 0 symbols and 1 symbols to be the same. Using combinatorial methods, we determine the asymptotic information rate of these codes and show that the asymptotic rate loss due to the imposition of the balanced property is approximately 2%. Extensions to q-ary cells, for q>2 are also discussed. Next, we consider q-ary ICI-free write-once-memory (WOM) codes that support multiple writes of a WOM while mitigating ICI effects. These codes forbid the appearance of the (q-1)0(q-1) pattern in any codeword used in any writing step. Using properties of two-dimensional constrained codes and generalized WOMs, we characterize the maximum sum-rate of t-write ICI-free WOM codes or, equivalently, the t-write sum-capacity of an ICI-free WOM.

Uplink-Downlink LTE Multi Cell Capacity: A Performance Analysis in the Presence of ICI, Imperfect Channel Information and Reuse-1 Plan

Long Term Evolution (LTE) technology is based on Orthogonal Frequency Division Multiple Access (OFDMA) technique in the downlink to support multiple users in the same cell at the same time. Such system is known to be susceptible to Inter Cell Interference (ICI) in the downlink. The uplink technology of choice, however, has been SC-FDMA due to low power consumption requirement by the mobile terminal. In order to deliver higher data rates anywhere in the cell in the downlink, especially at the cell edge; many algorithms have been proposed for interference mitigation and avoidance which impose additional complexity on the system and yields minimum capacity enhancements. MIMO techniques have proven to be more efficient than such algorithms. In this paper, a performance analysis of LTE cell capacity is conducted in the presence of several MIMO deployments, where multiple antennas at both the transmitter and the receiver are considered. A comprehensive simulation study of different multiple antenna configurations in the presence of uplink and downlink ICI and cell edge throughput is presented. We also provide insights into the MIMO deployment of choice based on users SINR.

A Multi-user Receiver for Inter-Cell Interference Reduction in LTE PUCCH Signaling

In 3rd generation partnership project (3GPP) long term evolution (LTE) systems, when no resources has been assigned in the uplink to a given user equipment (UE), the control information associated with layers 1 and 2 in the protocol stack is conveyed back to the base station through the so-called physical uplink control channel (PUCCH). In PUCCH, the data streams transmitted by multiple UEs are multiplexed in the time-domain and in the frequency-domain with the aid of spreading codes. Although the spreading codes associated with UEs within the same cell can be assumed to be orthogonal, the presence of inter-cell interference (ICI) in multi-cell scenarios severely limits receiver performance. In particular, the Format 1 of PUCCH, which is associated with the transmission of hybrid automatic repeat request acknowledgements (ACK/NACK) and scheduling requests, has a major impact on system performance, since an incorrectly decoded ACK/NACK message may introduce significant delay in data transmission. In this contribution, we propose a new multi-user receiver for ICI reduction in PUCCH LTE that operates both in cooperative and non-cooperative multi-cell architectures. The proposed receiver relies on a constrained tensor modeling of the received signal in PUCCH signaling, and affords an iterative joint channel estimation and symbol detection by simultaneously exploiting the energy of the data symbols and the pilot tones present in PUCCH. The formulation of the proposed algebraic receiver model incorporates symbol-basis hopping and slot-basis hopping signaling schemes, which are interference randomization techniques existing in the 3GPP specifications of LTE system. Computer simulation results show the remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver.

Exact outage probability analysis for cooperative AF relay network with relay selection in presence of inter-cell interference

Analysed is the outage probability of an amplify-and-forward relay network which adopts a relay selection policy to maximise end-to-end signal to interference plus noise (SINR) performance in the presence of inter-cell interference. The analysis considers the effect of adjacent cell interference, both at the relay and at the destination nodes, upon cooperative transmission. New exact analytical expressions for the probability density function, and cumulative density function of the received SINR are obtained and thereby closed form expressions for outage probability in the high signal-to-noise ratio region over Rayleigh frequency flat-fading channels are provided, which are verified by numerical simulation.

Multichannel Sharing and Joint Detection for Cell-Edge Users in Downlink Multicell OFDMA Systems

Cell-edge users in cellular systems suffer from intercell interference (ICI), and their data rates are usually lower than those of the users who are close to base stations (BSs). Since data rates cannot be improved by merely increasing transmission power in the presence of ICI, the interference management and alignment become crucial for cell-edge users. However, when channel state information (CSI) is not available at BSs, it is difficult to apply interference alignment techniques. In this paper, we consider a simple approach where each BS in coordination transmits signals to a dedicated user through multiple subcarriers shared by adjacent BSs, which results in an interference channel, so that higher diversity can be exploited for better performance. Using joint detection at users, we show that a reasonable performance can be achieved.

Degrees of Freedom of Multiple Broadcast Channels in the Presence of Inter-Cell Interference

In this paper, we provide lower and upper bounds for the number of degree of freedom (DOF) of B multiple-input single-output (MISO) broadcast channels (BC) where each base station (BS) equipped with M antennas supports its corresponding K single antenna users suffering from inter-cell interference. The sufficient and necessary condition for tightness of two bounds is presented. From the derived result, it can be observed that in-cell receiver cooperation does not help in most of the cases in a multiple-input multiple-output (MIMO) interference channel (IFC) except for one special case. Even for that special case, the DOFs with and without in-cell receive cooperation approach the same value for large K. Also, in a MIMO IFC with symmetric antenna settings (i.e., M = K), if both transmit and receive cooperations are removed to make it a single-input single-output (SISO) IFC, we show that the DOF is not affected. In addition, the DOF is studied for two mutually interfering broadcast channels in the presence of a cognitive BS. We obtain an interesting result that disabling in-cell receive cooperation of the MIMO IFC causes no DOF loss if at least one of two transmitters is a cognitive BS.

Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference

User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the core of high-rate data-oriented downlink schemes of the next-generation of cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users according to their channels vector directions and SINR levels. However, when scheduling is applied independently in each cell, the inter-cell interference (ICI) power at each user receiver is not known in advance since it changes at each new scheduling slot depending on the scheduling decisions of all interfering base stations. In order to cope with this uncertainty, we consider the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat reQuest (ARQ). We develop a game-theoretic framework for this problem and build on stochastic optimization techniques in order to find optimal scheduling and ARQ schemes. Particularizing our framework to the case of "outage service rates", we obtain a scheme based on adaptive variable-rate coding at the physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then, we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ) that is able to achieve a throughput performance arbitrarily close to the "genie-aided service rates", with no need for a genie that provides non-causally the ICI power levels. The novel HARQ scheme is both easier to implement and superior in performance with respect to the conventional combination of adaptive variable-rate coding and ARQ-LLC.

Chip-Interleaved Block-Spread CDMA Versus DS-CDMA for Cellular Downlink: A Comparative Study

A so-termed chip-interleaved block-spread (CIBS) code division multiple access (CDMA) system has been introduced for cellular applications in the presence of frequency selective multipath channels. In both uplink and downlink operation, CIBS-CDMA achieves multiuser-interference (MUI) free reception within each cell. This paper focuses on the cellular downlink configuration and compares CIBS-CDMA against the conventional direct-sequence (DS) CDMA system, which relies on a chip equalizer to restore code orthogonality and, subsequently, suppresses MUI by despreading. We provide a unifying framework for both systems and investigate their performance in the presence of intercell interference and soft-handoff operation. Extensive comparisons from load, performance, complexity, and flexibility perspectives illustrate the merits, along with the disadvantages, of CIBS-CDMA over DS-CDMA, and reveal its potential for future wireless systems.

A New Approach to High-Capacity Digital Mobile Radio

Space diversity (adaptive phased-array antennas) is an effective weapon against the cochannel interference encountered in cellular mobile radio systems. High-order diversity, and hence, strong interference suppression, can be achieved with modest hardware complexity by using time-division retransmission. With this technique, which is especially well-suited to digital modulation methods, the adaptive signal processing required for space diversity can be performed at just one end of the communication link, namely, the base station. At the other end (the mobile unit) only a single-element antenna is needed. Moreover, the use of coherent phase-shift keying in such a system allows simple RF circuity, because the adaptive processing is done at baseband. In the context of cellular mobile radio, the combination of space diversity, time-division retransmission and 120-degree corner illumination of each cell can yield a reliable communication channel even in the presence of intercell interference, Ray leigh fading (both flat and frequency-selective), and shadow fading. The use of these techniques allows approximately 130 two-way channels per cell (at 32 kb/s each) to be accommodated in the 40-MHz bandwidth of the 850-MHz mobile radio band.