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It is well known that separate coding on each carrier is capacity-achieving in parallel Gaussian multiple-input multiple-output (MIMO) broadcast channels in the sense that the sum rate capacity under a sum power constraint is achievable with separate coding if the noise is independent on each carrier. In this paper, we generalize this statement by proving that the optimality of separate coding also...
We study opportunistic scheduling and the sum capacity of cellular networks with a full-duplex multi-antenna base station and a large number of single-antenna half-duplex users. Simultaneous uplink and downlink over the same band results in uplink-to-downlink interference, degrading performance. We present a simple opportunistic joint uplink-downlink scheduling algorithm that exploits multiuser diversity...
High Altitude Platform can provide mobile telecommuncication service to on-ground customers. This paper explains the behaviour of LTE network in a situation, where the service is being provided by HAP and eNodeB in a disaster scenario. In the disaster scenario, a set of adjacent eNodeB in the middle of Bandung city has been disabled. A HAP station has been launched to the disaster location to provide...
In wireless cellular networks, multiple scenarios involve the communication between devices located in the same vicinity. These links can be offloaded to a device to device (D2D) underlay which is controlled by the cellular infrastructure. Such an option alleviates the load on the base stations and saves spectrum resources for downlink connections. In this paper, we investigate the impact of D2D communications...
Optimization in mobile communications has mostly been performed based on spectral efficiency (SE). However, energy efficiency (EE) is fast becoming a key performance indicator, together with SE for designing future networks. In multi-cell communications, other-cell interference (OCI) coming from neighboring cells degrades both the SE and EE performances of the system. This paper presents an energy...
LTE (Long Term Evolution) is the last step towards the 4th generation of radio technologies designed to increase the capacity and speed of cellular networks. At present, current generation of cellular technology dominated by 3G (third generation), LTE is marked as 4G. The third generation partnership project (3GPP) currently work for developing the 3rd generation mobile and telecommunication system...
We consider the up- as well as downlink of a cellular network with multi-user multiple-input multiple-output (MIMO) communication and propose to turn the entire network into a two-hop network where a large amount of relays assist the bidirectional communication. To this end, many two-way relays are spread over the entire area of the network. In addition to introducing the concept of ubiquitous relaying,...
High capacity requirements in wireless systems can be met, at the network level, by using dense small cell deployments and, at the link level, by improving spectral efficiency via spectrum reuse. In this context, we consider a small-area radio system, e.g. a pico-or femtocell, where a full-duplex access point serves simultaneously two half-duplex devices, one in downlink and one in uplink direction...
In this paper, we investigate a downlink model for underlay cognitive radio networks (CRNs). In particular, we assume that the secondary transmitter (SU-Tx) sends common packets to secondary receivers (SU-Rx) under the outage constraint of a single primary user (PU) and the peak transmit power constraint of the SU-Tx. All channels undergo Rayleigh fading. Given these settings, an adaptive transmit...
Two-way relaying in wireless systems has initiated a large research effort during the past few years. In particular, structured codes and lattices are instrumental for achieving high rates when using Physical Layer Network Coding (PLNC). In an attempt to bring the gains of PLNC beyond the classical traffic pattern of two-way relaying, in this paper we consider a scenario with four-way relaying, where...
This paper deals with a cognitive approach used to reduce the co-channel interference arising from the coexistence of an LTE macrocell and an LTE femtocell sharing the same frequency band. Multiple-antennas technology is considered to exploit the angle dimension as a new spectrum opportunity: femtocell acts as a secondary system and inserts nulls in the directions of the UE connected to the macrocell...
We propose a time division duplex (TDD) based network architecture where a macrocell tier with a “massive” multiple-input multiple-output (MIMO) base station (BS) is overlaid with a dense tier of small cells (SCs). In this context, the TDD protocol and the resulting channel reciprocity have two compelling advantages. First, a large number of BS antennas can be deployed without incurring a prohibitive...
There are two basic principles used in wireless network coding to design throughput-efficient schemes: (1) aggregation of communication flows and (2) interference is embraced and subsequently cancelled or mitigated. These principles inspire design of Coordinated Direct/Relay (CDR) schemes, where each basic transmission involves two flows to a direct and a relayed user. Considering a scenario with...
Stochastic signal design is studied for the downlink of a multiuser communications system. First, a formulation is proposed for the joint design of optimal stochastic signals. Then, an approximate formulation, which can get arbitrarily close to the optimal solution, is obtained based on convex relaxation. In addition, when the receivers employ symmetric signaling and sign detectors, it is shown that...
Uncertainty in the spatial signature of interfering signals is a major source of performance degradation in the downlink of a MIMO network. In general, the exact transmit covariance matrix of the other transmitters can not be predicted correctly in advance as the optimal strategies mutually depend on each other. In this work, we investigate two approaches for optimizing downlink transmission that...
Block Diagonalization (BD) algorithm is a generalization of channel inversion scheme in multiuser multi-input multi-output (MIMO) broadcast channels. Although the BD algorithm is effective in removing interuser interference, it has a drawback that additional information should be delivered to the receiver. Recent work on BD with vector perturbation (VP) avoids the need for additional information and...
In this paper, we study a multi-user multi-antenna two-way relay system, where a multi-antenna base station (BS) exchanges uplink and downlink signals with multiple users via a multi-antenna amplify-and-forward relay station (RS). We jointly design the BS and RS transceivers, aiming to maximize the system bidirectional sum rate under inter-user interference free constraint. Since the optimization...
The information and communication technology (ICT) industry accounts for at least 2% of the world energy consumption [1], [2], and a considerable part of this energy is consumed by cell phone towers. Currently, resources are statically allocated to offer the best service during peak hours. Energy could be saved if the power is allocated adaptively, depending on the current users' demand. We provide...
This paper investigates the downlink system level performance for Layer-3 (L3) and Layer-1 (L1) relays with orthogonal frequency division multiple access (OFDMA) used in LTE-Advanced. Various practical factors are taken into account in the evaluations such as the processing delay and upper-bound of the amplifier gain of the L1 relay, capacity limitation of the backhaul channels, and empty buffer status...
We consider the role of independent single antenna relays in allowing for interference cancellation and for multiplexing of uplink and downlink communications, in the presence of multiple interfering users. For a specific practical scenario of interest, we construct interference neutralization schemes that are simple, distributed and which encode over both space and time, to achieve performance improvements...
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