7 research outputs found
Limits on the Capacity of In-Band Full Duplex Communication in Uplink Cellular Networks
Simultaneous co-channel transmission and reception, denoted as in-band full
duplex (FD) communication, has been promoted as an attractive solution to
improve the spectral efficiency of cellular networks. However, in addition to
the self-interference problem, cross-mode interference (i.e., between uplink
and downlink) imposes a major obstacle for the deployment of FD communication
in cellular networks. More specifically, the downlink to uplink interference
represents the performance bottleneck for FD operation due to the uplink
limited transmission power and venerable operation when compared to the
downlink counterpart. While the positive impact of FD communication to the
downlink performance has been proved in the literature, its effect on the
uplink transmission has been neglected. This paper focuses on the effect of
downlink interference on the uplink transmission in FD cellular networks in
order to see whether FD communication is beneficial for the uplink transmission
or not, and if yes for which type of network. To quantify the expected
performance gains, we derive a closed form expression of the maximum achievable
uplink capacity in FD cellular networks. In contrast to the downlink capacity
which always improves with FD communication, our results show that the uplink
performance may improve or degrade depending on the associated network
parameters. Particularly, we show that the intensity of base stations (BSs) has
a more prominent effect on the uplink performance than their transmission
power
Modeling and Analysis of Cellular Networks Using Stochastic Geometry: A Tutorial
This paper presents a tutorial on stochastic geometry (SG)-based analysis for cellular networks. This tutorial is distinguished by its depth with respect to wireless communication details and its focus on cellular networks. This paper starts by modeling and analyzing the baseband interference in a baseline single-tier downlink cellular network with single antenna base stations and universal frequency reuse. Then, it characterizes signal-to-interference-plus-noise-ratio and its related performance metrics. In particular, a unified approach to conduct error probability, outage probability, and transmission rate analysis is presented. Although the main focus of this paper is on cellular networks, the presented unified approach applies for other types of wireless networks that impose interference protection around receivers. This paper then extends the unified approach to capture cellular network characteristics (e.g., frequency reuse, multiple antenna, power control, etc.). It also presents numerical examples associated with demonstrations and discussions. To this end, this paper highlights the state-of-the-art research and points out future research directions
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Simultaneous Transmit and Receive (Star) Antennas for Geo-Satellites and Shared-Antenna Platforms
This thesis presents the analysis, design, and experimental characterization of antenna systems considered for shipborne, airborne, and space platforms. These antennas are innovated to enable Simultaneous Transmit and Receive (STAR) at same time and polarization, either at the same, or duplex frequencies. In airborne and shipborne platforms, developed antenna architectures may enhance the capabilities of modern electronic warfare systems by enabling concurrent electronic attack and electronic support operations. In space, and more precisely at geostationary orbit, designed antennas aim to decrease the complexity of conventional phased array systems, thereby increasing their capabilities and attractiveness. All antennas researched are first designed as a standalone radiator, then as entity of a platform having multiple different antennas.An ultrawideband, lossless cavity-backed Vivaldi antenna array for flush-mounting applications is first investigated. Eigen-mode analysis is used to analyze antenna-cavity interaction and to show that the entire structure may resonate within the band of interest resulting in a significant degradation of antenna performance. A simple approach based on connecting the array’s edge elements in E-plane to the cavity walls is proposed to eliminate the deleterious impact of these cavity resonances. The designed antenna is a 3 × 4 array with 3 elements in E-plane and 4 elements in H-plane, fabricated using stacked all-metal printed circuit board technique. Scan performance of the proposed cavity-backed antenna is investigated in two principal planes and is shown to have similar performance compared to its free-standing counterpart. A simplified version of this single-polarized antenna, when used for broadside only applications is developed. This antenna, excited with a single coaxial feed is shown to have a smaller aperture than the 3 × 4 array. Isolations between two of these antennas when mounted on a compact shared-antenna platform are investigated through computation and experiments.To extend the capability of systems relying on these designed antennas, frequency reuse is enabled through dual-polarized functionality. A dual-polarized, flush mounted, Vivaldi antenna, directly integrated with an all-metal cavity is introduced as an alternative to coax-fed quad-ridge horns. An approach based on shaping the side walls of the cavity is used to eliminate the occurrence of resonances. The proposed dual-polarized resonant-free antenna has two orthogonal 2 × 1 arrays with two elements in the E-plane, one element in the H-plane. It is fed using two 2-way power dividers that can be easily designed to maintain low amplitude and phase imbalances. The antenna is fabricated as a single piece and experimentally shows a monotonic gain increase with low cross-polarization over 4:1 bandwidth.Phased array antennas operating at geostationary orbit are required to scan within Earth’s field of view, without any grating lobe appearance. For dual-polarized applications, this requirement has limited the widespread and attractiveness of these systems at frequencies such as X-band. The narrow 150 MHz guard range between transmit and receive bands, leads to impractical diplexers in conventional dual-polarized systems. This research introduces a dual-polarized subarray architecture for X-band phased array systems which enables high isolation between closely separated TX and RX bands. The proposed approach either eliminates the need for diplexers, or significantly decreases their required complexity
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Wideband Monostatic Co-Channel Simultaneous Transmit and Receive (C-STAR) Antenna and Array Systems
Most modern wireless communication systems operate either at different times or frequencies to avoid self-interferences. With these duplexing techniques, more resources are required due to the increased demand for higher data rate. Therefore, alternative solutions not involving more use of the time or frequency spectrum are needed. One of the possible solutions that has been recently gaining increased interest is often referred to as co-channel simultaneous transmit and receive (C-STAR). C-STAR is considered by many as a key enabling technology for the next-generation wireless networks operating in spectrum congested environments. C-STAR allows transmitting (TX) and receiving (RX) at the same time and over the same frequency channel which may result in significant improvements in throughput and spectral efficiency. The chief challenge associated with these C-STAR systems is the required very high TX/RX isolation (110-140 dB) to suppress the self-interference. To obtain the necessary isolation over any bandwidth, a C-STAR transceiver is typically divided into several self-interference cancellation stages. Specifically these include antenna, analog, and digital layers. Clearly, the antenna array layer plays an important role in maximizing the overall system isolation since ~30-50% of the required isolation is achieved with a well-designed C-STAR antenna subsystem, then the overall system becomes feasible. In this Ph.D. thesis, several novel wideband co-polarized circulator and circulator-less monostatic antenna and array designs are presented. Developed theoretical concepts are validated with full-wave simulations and measurements. The monostatic C-STAR apertures utilizing multi-arm spiral antennas are first demonstrated where a set of arms is used for transmitting and the other set for receiving. Then, different novel omnidirectional and broadside C-STAR arrays utilizing closely-spaced spiral, monocone, or discone antennas are introduced. Phase mode orthogonality principle, antenna orientation, and beam-former cancellation are all combined to achieve the desired performance. All proposed C-STAR configurations have theoretically infinite isolation between TX and RX ports. Practically, the achieved isolation is limited by the electrical asymmetries of the used components. Overall, consistent wideband operation, high measured isolation, and good far-field performance are achieved for all proposed C-STAR antenna array sub-systems without taking advantages of any time-, frequency-, polarization-, pattern-, antenna-, and spatial-multiplexing