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We consider the downlink of Cell-Free Massive MIMO systems, where a very large number of distributed access points (APs) simultaneously serve a much smaller number of users. Each AP uses local channel estimates obtained from received uplink pilots and applies conjugate beamforming to transmit data to the users. We derive a closed-form expression for the achievable rate. This expression enables us...
A decoupled association scheme is considered based on instantaneous received power in downlink and uplink. Unlike traditional cellular networks where the associated base stations (BSs) in downlink and uplink are the same, in decoupled association the associated BSs in uplink and downlink can be different. The probability of user associations in co-channel BSs in finite multi-tier networks (with finite...
In this paper, we consider an energy harvesting multiple access channel (MAC) where the transmitters are powered by energy harvested from the ambient environment. We assume that the energy harvesting processes at the transmitters can be modeled as independent Bernoulli processes with parameters λis, and the channel states between the transmitters and the receiver are independent Bernoulli processes...
This paper addresses the problem of rate selection for the cooperative hybrid automatic repeat request with chase combination (HARQ-CC) system, where time correlated Nakagami-m fading channels are considered. To deal with this problem, the closed-form cumulative distribution function (CDF) for the combine SNRs through maximal ratio combining (MRC) is first derived as a generalized Fox's H̄ function...
In this article, we present a Cloud empowered Cognitive Inter-Cell Interference Coordination (C2-ICIC) scheme for small cellular networks. The scheme leverages a recently proposed cloud radio access network (C-RAN) architecture for enabling intratier coordination and relaxes the need for inter-tier coordination by adopting the phantom cell architecture. Employing tools from stochastic geometry, we...
The pilot reuse issue in massive multi-input multi-output (MIMO) antenna systems with interfering cells is closely examined. This paper considers scenarios where the ratio of the channel coherence time to the number of users in a cell may be sufficiently large. One such practical scenario arises when the number of users per unit coverage area cannot grow freely while user mobility is low, as in indoor...
We propose a rate-adaptive error-correction coding framework for transmission over finite-length block-fading channels, with causal channel state information at the transmitter. A dynamic programming optimization approach can be use to obtain the optimal rate adaptation strategy. A suboptimal rate adaptation strategy is developed for sequential random codes. Numerical results show that significant...
A new scheme for error-free transmission is presented which uses optimized combination of adaptive modulation and coding (AMC) and automatic repeat request (ARQ). Using conventional error correction codes with finite length, a limited value of packet error rate (PER) is inevitable. More powerful codes with more extra parity bits results in lower PER, however, at the cost of more transmit power per...
Pilot reuse in multiple cell Massive MIMO induces coherent inter-cell interference that does not disappear with large numbers of antennas. A simple way to mitigate pilot contamination is to use a pilot reuse factor that is greater than one, which surrounds the home cell by one or more rings of non-contaminating cells. The penalty for this measure is that training consumes an increasing fraction of...
Adaptive Modulation and cooperative Diversity are considered as two of the most commonly deployed techniques for wireless communication, which aims to compensate the performance degradation and enhance the capacity as much as possible. In this survey, several studies and research works that were introduced in the literature will be investigated, aided by the followed methodology and main concepts...
Mobile communication channels are frequently plagued by severe noise and disturbances such as multipath fading and doppler effects that severely degrade performance. Among the automatic-repeat-request (ARQ) protocols used to improve the communication channel reliability, the stop-and-wait (SW) is positively characterized by simple implementation and negatively by low throughputs. This work describes...
Vehicular ad-hoc network (VANET) is a new emerging type of mobile ad-hoc network that is characterized by high speed and extreme topology changes over short time. These two characteristics dramatically affect the performance of the routing protocols employed in these networks. The evaluation of different routing protocols for general VANET configuration provides great insight into the performance...
Wireless sensor networks (WSN) are used in many fields such as industrial control, building automation, environmental monitoring, etc. IEEE 802.15.4 standard defines the features of MAC layer and physical layer for WSN. Many analytical models studied the performance of the multihop IEEE 802.15.4 networks under the assumption of ideal wireless channel, and they did not consider the effect of imperfect...
The Quality of Service (QoS) on the traffic environment with high mobility, dynamic topology, and change trajectory is one of the challenges in the use of Vehicular Ad-Hoc Networks (VANET) Routing Protocols. PUMA routing protocol presents multicast work mechanism based on shared mesh topology. It always dynamically adapt to VANET traffic conditions. In this paper, we evaluated the PUMA routing protocol...
We present some preliminary results from our investigation of two forms of erasure-correction coding, fountain coding and network coding, when they are employed for file transfers in a distributed packet radio network. The radios adapt the modulation and channel coding of the transmitted signals in response to variations in fading on the links of the network. The control information for the adaptive...
In this paper, we consider the problem of relay placement and resource sharing among the relays and the base station in a cellular network. Specifically, we focus on the problem of deploying half duplex relays in cellular systems employing soft frequency reuse (SFR) and fractional frequency reuse (FFR) schemes. For both SFR and FFR schemes, we propose strategies for relay placement and assigning mobile...
In this paper, the problem of joint spectrum sensing and data transmission in a two-user cooperative cognitive radio network is studied. Tractable solution for optimal power allocation is proposed for cognitive sources for both sensing and data transmission slots with an aim to maximize sum throughput of the system while meeting the constraints of probability of detection of PU's signal and total...
A fading Multiple Access Channel with a jammer is considered and a non-cooperative game between the two users and the jammer is formulated. Here, both the user-receiver links as well as the jammer-receiver link are time-varying fading links. The decoder employed is a successive cancellation decoder. To begin with, the decoder announces a scheme where it shares with the users and the jammer their decoding...
In this paper performance of Image transmission with Space Time Block Coding (STBC) and Spatial Multiplexing (SM) and Hybrid MIMO with OFDM models are done. A Hybrid MIMO-OFDM is a combination of SM and STBC with OFDM. The performance of the above mentioned models are measured with respect to BER and Throughput and output image quality. The results demonstrate that Hybrid MIMO-OFDM provides low BER...
Recently, wireless LANs are utilized in various situations. However, inefficient channel utilization is still a serious problem. One of effective solutions is to prevent packet loss and to transmit packets at a higher rate. While the backoff algorithm in IEEE 802.11 avoids only the packet loss caused by collision, other existing works tackle the packet loss caused by channel fading by transmitting...
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