53,131 research outputs found
The Poisson multiple access channel
Cover title. "Presented in part at IEEE Info Theory Workshop, June 9-13, Haifa, Israel."Includes bibliographical references (p. 29-32).Research supported by the Laboratory for Information and Decision Systems, Massachusetts Institute of Technology. DAAH04-95-1-0103Lapidoth, A., Shamai, Shlomo (Shitz)
Uplink Performance of Large Optimum-Combining Antenna Arrays in Poisson-Cell Networks
The uplink of a wireless network with base stations distributed according to
a Poisson Point Process (PPP) is analyzed. The base stations are assumed to
have a large number of antennas and use linear minimum-mean-square-error (MMSE)
spatial processing for multiple access. The number of active mobiles per cell
is limited to permit channel estimation using pilot sequences that are
orthogonal in each cell. The cumulative distribution function (CDF) of a
randomly located link in a typical cell of such a system is derived when
accurate channel estimation is available. A simple bound is provided for the
spectral efficiency when channel estimates suffer from pilot contamination. The
results provide insight into the performance of so-called massive
Multiple-Input-Multiple-Output (MIMO) systems in spatially distributed cellular
networks
Maximum Average Service Rate and Optimal Queue Scheduling of Delay-Constrained Hybrid Cognitive Radio in Nakagami Fading Channels
As a promising technique to improve achievable bandwidth efficiency, cognitive radio (CR) has attracted substantial research attention from both the academic and industrial communities. To improve the performance attained by the secondary user (SU), a novel hybrid CR system is proposed, which combines the conventional interweave and underlay paradigms to enhance the chance of the SU to access the spectrum. Queuing theory is invoked in this paper to analyze the impact of the primary user’s maximum tolerable delay on the performance of the SU. Multiple queues are assumed for the SU, which is engaged in video communication. Apart from the Poisson traffic generation,we also model the classic Nakagami-m fading channel as a Poisson service process by utilizing the outage probability in the presence of cochannel interference. We optimize both the hybrid interweave/underlay procedure to maximize the average service rate μ_S,max of the SU, as well as the queue’s scheduling scheme, for the sake of minimizing the overall average delay (OAD). As a result, the OAD of the SU is reduced by up to 27% and 20%, compared with the proportion and round-robin schemes, respectively
On the Asymptotic Behavior of Selfish Transmitters Sharing a Common Channel
This paper analyzes the asymptotic behavior of a multiple-access network
comprising a large number of selfish transmitters competing for access to a
common wireless communication channel, and having different utility functions
for determining their strategies. A necessary and sufficient condition is given
for the total number of packet arrivals from selfish transmitters to converge
in distribution. The asymptotic packet arrival distribution at Nash equilibrium
is shown to be a mixture of a Poisson distribution and finitely many Bernoulli
distributions.Comment: Proceedings of the 2008 IEEE International Symposium on Information
Theory, Toronto, ON, Canada, July 6 - 11, 200
Towards a Realistic Assessment of Multiple Antenna HCNs: Residual Additive Transceiver Hardware Impairments and Channel Aging
Given the critical dependence of broadcast channels by the accuracy of
channel state information at the transmitter (CSIT), we develop a general
downlink model with zero-forcing (ZF) precoding, applied in realistic
heterogeneous cellular systems with multiple antenna base stations (BSs).
Specifically, we take into consideration imperfect CSIT due to pilot
contamination, channel aging due to users relative movement, and unavoidable
residual additive transceiver hardware impairments (RATHIs). Assuming that the
BSs are Poisson distributed, the main contributions focus on the derivations of
the upper bound of the coverage probability and the achievable user rate for
this general model. We show that both the coverage probability and the user
rate are dependent on the imperfect CSIT and RATHIs. More concretely, we
quantify the resultant performance loss of the network due to these effects. We
depict that the uplink RATHIs have equal impact, but the downlink transmit BS
distortion has a greater impact than the receive hardware impairment of the
user. Thus, the transmit BS hardware should be of better quality than user's
receive hardware. Furthermore, we characterise both the coverage probability
and user rate in terms of the time variation of the channel. It is shown that
both of them decrease with increasing user mobility, but after a specific value
of the normalised Doppler shift, they increase again. Actually, the time
variation, following the Jakes autocorrelation function, mirrors this effect on
coverage probability and user rate. Finally, we consider space division
multiple access (SDMA), single user beamforming (SU-BF), and baseline
single-input single-output (SISO) transmission. A comparison among these
schemes reveals that the coverage by means of SU-BF outperforms SDMA in terms
of coverage.Comment: accepted in IEEE TV
- …