57 research outputs found
Sum-rate Maximizing in Downlink Massive MIMO Systems with Circuit Power Consumption
The downlink of a single cell base station (BS) equipped with large-scale
multiple-input multiple-output (MIMO) system is investigated in this paper. As
the number of antennas at the base station becomes large, the power consumed at
the RF chains cannot be anymore neglected. So, a circuit power consumption
model is introduced in this work. It involves that the maximal sum-rate is not
obtained when activating all the available RF chains. Hence, the aim of this
work is to find the optimal number of activated RF chains that maximizes the
sum-rate. Computing the optimal number of activated RF chains must be
accompanied by an adequate antenna selection strategy. First, we derive
analytically the optimal number of RF chains to be activated so that the
average sum-rate is maximized under received equal power. Then, we propose an
efficient greedy algorithm to select the sub-optimal set of RF chains to be
activated with regards to the system sum-rate. It allows finding the balance
between the power consumed at the RF chains and the transmitted power. The
performance of the proposed algorithm is compared with the optimal performance
given by brute force search (BFS) antenna selection. Simulations allow to
compare the performance given by greedy, optimal and random antenna selection
algorithms.Comment: IEEE International Conference on Wireless and Mobile Computing,
Networking and Communications (WiMob 2015
Acknowledgment procedures at radio link control level in GPRS
In this paper, we investigate the acknowledgment procedures used at radio link control level in General Packet Radio Service (GPRS). The GPRS is a new GSM service, which is currently being standardized by ETSI for GSM Phase 2+ and it provides packet switched data services over GSM network resources. The role of acknowledgment procedures is to assure the delivery of packets on GPRS radio interface. This paper gives a brief description of GPRS radio interface with a special attention to the Radio Link Control and Medium Access Control (RLC/MAC) layer procedures. Particularly, the acknowledgment parameters and operations are described and their performance is evaluated. The delay introduced by acknowledgment procedures is studied analytically. In order to ameliorate the performance of RLC acknowledgment mechanism, we propose and describe a new additional hybrid FEC/ARQ mechanism, which can operate with the current one. The purpose of new mechanism is to decrease the number of control blocks used for RLC acknowledgment mechanism and thus reduces the delay requested for a packet delivery. After presenting the channel models used, we evaluate by simulation the performance of acknowledgment procedures presented in ETSI specifications and the proposed one over a stationary channel model and over a noisy wireless channel model affected by burst of errors
Impact of Spatial Correlation on the Finite-SNR Diversity-Multiplexing Tradeoff
The impact of spatial correlation on the performance limits of multielement
antenna (MEA) channels is analyzed in terms of the diversity-multiplexing
tradeoff (DMT) at finite signal-to-noise ratio (SNR) values. A lower bound on
the outage probability is first derived. Using this bound accurate finite-SNR
estimate of the DMT is then derived. This estimate allows to gain insight on
the impact of spatial correlation on the DMT at finite SNR. As expected, the
DMT is severely degraded as the spatial correlation increases. Moreover, using
asymptotic analysis, we show that our framework encompasses well-known results
concerning the asymptotic behavior of the DMT.Comment: Accepted for publication to IEEE Transaction on Wireless
Communication on June 4th 200
User-Base Station Association in HetSNets: Complexity and Efficient Algorithms
This work considers the problem of user association to small-cell base
stations (SBSs) in a heterogeneous and small-cell network (HetSNet). Two
optimization problems are investigated, which are maximizing the set of
associated users to the SBSs (the unweighted problem) and maximizing the set of
weighted associated users to the SBSs (the weighted problem), under
signal-to-interference-plus-noise ratio (SINR) constraints. Both problems are
formulated as linear integer programs. The weighted problem is known to be
NP-hard and, in this paper, the unweighted problem is proved to be NP-hard as
well. Therefore, this paper develops two heuristic polynomial-time algorithms
to solve both problems. The computational complexity of the proposed algorithms
is evaluated and is shown to be far more efficient than the complexity of the
optimal brute-force (BF) algorithm. Moreover, the paper benchmarks the
performance of the proposed algorithms against the BF algorithm, the
branch-and-bound (B\&B) algorithm and standard algorithms, through numerical
simulations. The results demonstrate the close-to-optimal performance of the
proposed algorithms. They also show that the weighted problem can be solved to
provide solutions that are fair between users or to balance the load among
SBSs
Performance Comparison between Adaptive and Fixed Transmit Power in Underlay Cognitive Radio Networks
In this paper, we compare the performance in terms of symbol error probability, data rate and power consumption of the use of fixed transmit power (FTP) and adaptive transmit power (ATP) in underlay cognitive radio networks. The use of FTP alleviates the signaling requirements of underlay cognitive radio networks compared to the ATP. Nevertheless, the use of FTP influences the performances of the underlay cognitive radio networks. To study this influence, we consider three relay selection schemes using FTP: opportunistic decode and forward with FTP (O-DF with FTP), opportunistic amplify and forward with FTP (O-AF with FTP) and partial relay selection with FTP (PR with FTP). We compare the performances of these schemes in terms of symbol error probability, data rate and power consumption with three relay selection schemes using ATP: opportunistic decode and forward with ATP (O-DF with ATP), opportunistic amplify and forward with ATP (O-AF with ATP) and partial relay selection with ATP (PR with ATP). We provide exact and/or lower bound expressions of the symbol error probabilities of O-DF, O-AF and PR with FTP. The analytical study for the data rate and the power consumption is also provided. Our comparison study shows that FTP has a positive impact on the data rate and power consumption performance while it deteriorates the symbol error probability performance
Opportunistic Adaptive Relaying in Cognitive Radio Networks
Combining cognitive radio technology with user cooperation could be
advantageous to both primary and secondary transmissions. In this paper, we
propose a first relaying scheme for cognitive radio networks (called "Adaptive
relaying scheme 1"), where one relay node can assist the primary or the
secondary transmission with the objective of improving the outage probability
of the secondary transmission with respect to a primary outage probability
threshold. Upper bound expressions of the secondary outage probability using
the proposed scheme are derived over Rayleigh fading channels. Numerical and
simulation results show that the secondary outage probability using the
proposed scheme is lower than that of other relaying schemes. Then, we extend
the proposed scheme to the case where the relay node has the ability to decode
both the primary and secondary signals and also can assist simultaneously both
transmissions. Simulations show the performance improvement that can be
obtained due to this extension in terms of secondary outage probability.Comment: 5 pages, 4 figures. Accepted for publication in Proc. IEEE
International Communications Conference (ICC), Ottawa (ON), Canada, June 201
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