[Show abstract][Hide abstract] ABSTRACT: In this paper, we investigate the performance of a wireless relay network with multiple transmission sessions, in which multiple groups of source nodes communicate with their respective destination nodes via a shared wireless relay network. A multiple transmission session model with network code division multiplexing (NCDM) scheme is proposed to remove the intersession interference at each destination. The fundamental idea of the NCDM scheme takes advantage of the property of G⊙HT = 0 of the low-density generator matrix (LDGM) codes. Based on the analysis of the NCDM scheme, we investigate the relationship among the equivalent received signal vector, the number of sessions and the column weight of the generator matrix. New code design criteria for the construction of the generator matrix is proposed.We further evaluate the multiple transmission session model with the proposed NCDM scheme in terms of throughput and complexity. Our evaluation demonstrates that the proposed scheme not only has a linear computational complexity, but also shows a similar error performance in the AWGN case and a considerable throughput improvement compared with its counterpart, which is referred to as a serial session scheme, where groups of source nodes communicate with their respective destinations in a time division manner.
[Show abstract][Hide abstract] ABSTRACT: Despite intensive research in the area of network connectivity, there is an important category of problems that remain unsolved: how to characterize and measure the quality of connectivity of a wireless network which has a realistic number of nodes, not necessarily large enough to warrant the use of asymptotic analysis, and which has unreliable connections, reflecting the inherent unreliability of wireless communications? The quality of connectivity measures how easily and reliably a packet sent by a node can reach another node. It complements the use of capacity to measure the quality of a network in saturated traffic scenarios and provides an intuitive measure of the quality of (end-to-end) network connections. In this paper, we introduce a probabilistic connectivity matrix as a tool to measure the quality of network connectivity. Some interesting properties of the probabilistic connectivity matrix and their connections to the quality of connectivity are demonstrated. We demonstrate that the largest magnitude eigenvalue of the probabilistic connectivity matrix, which is positive, can serve as a good measure of the quality of network connectivity. We provide a flooding algorithm whereby the nodes repeatedly flood the network with packets, and by measuring just the number of packets a given node receives, the node is able to asymptotically estimate this largest eigenvalue.
IEEE Transactions on Mobile Computing 09/2015; 14(9):1765-1779. DOI:10.1109/TMC.2014.2366106 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we analytically derive an upper bound on the error in
approximating the uplink (UL) single-cell interference by a lognormal
distribution in frequency division multiple access (FDMA) small cell networks
(SCNs). Such an upper bound is measured by the Kolmogorov Smirnov (KS) distance
between the actual cumulative density function (CDF) and the approximate CDF.
The lognormal approximation is important because it allows tractable network
performance analysis. Our results are more general than the existing works in
the sense that we do not pose any requirement on (i) the shape and/or size of
cell coverage areas, (ii) the uniformity of user equipment (UE) distribution,
and (iii) the type of multi-path fading. Based on our results, we propose a new
framework to directly and analytically investigate a complex network with
practical deployment of multiple BSs placed at irregular locations, using a
power lognormal approximation of the aggregate UL interference. The proposed
network performance analysis is particularly useful for the 5th generation (5G)
systems with general cell deployment and UE distribution.
[Show abstract][Hide abstract] ABSTRACT: In heterogeneous networks (HetNets), the load between macro-cell base stations (MBSs) and small-cell BSs (SBSs) is imbalanced due to transmit power disparities and ad-hoc deployment of SBSs. This significantly impacts the system performance and user experience. Associating more users to the SBSs is an effective way to solve this problem. In this paper, we formulate the user-BS association problem as a distributed optimization problem with proportional fairness as the objective. Specifically, we propose a novel distribute algorithm based on the belief propagation (BP) method to solve the user-BS association problem via iteratively message passing between the users and BSs. Also, we develop an approximation calculation in the BP method to reduce the computational complexity and transmission overhead of message passing. Simulation results show that the proposed algorithm well approaches the optimal system performance (by exhausting search) with low complexity and fast convergence.
[Show abstract][Hide abstract] ABSTRACT: In this paper, for the first time, we analytically prove that the uplink (UL)
inter-cell interference in frequency division multiple access (FDMA) small cell
networks (SCNs) can be well approximated by a lognormal distribution under a
certain condition. The lognormal approximation is vital because it allows
tractable network performance analysis with closed-form expressions. The
derived condition, under which the lognormal approximation applies, does not
pose particular requirements on the shapes/sizes of user equipment (UE)
distribution areas as in previous works. Instead, our results show that if a
path loss related random variable (RV) associated with the UE distribution
area, has a low ratio of the 3rd absolute moment to the variance, the lognormal
approximation will hold. Analytical and simulation results show that the
derived condition can be readily satisfied in future dense/ultra-dense SCNs,
indicating that our conclusions are very useful for network performance
analysis of the 5th generation (5G) systems with more general cell deployment
beyond the widely used Poisson deployment.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we introduce a sophisticated path loss model into the
stochastic geometry analysis incorporating both line-of-sight (LoS) and
non-line-of-sight (NLoS) transmissions to study their performance impact in
small cell networks (SCNs). Analytical results are obtained on the coverage
probability and the area spectral efficiency (ASE) assuming both a general path
loss model and a special case of path loss model recommended by the 3rd
Generation Partnership Project (3GPP) standards. The performance impact of LoS
and NLoS transmissions in SCNs in terms of the coverage probability and the ASE
is shown to be significant both quantitatively and qualitatively, compared with
previous work that does not differentiate LoS and NLoS transmissions.
Particularly, our analysis demonstrates that when the density of small cells is
larger than a threshold, the network coverage probability will decrease as
small cells become denser, which in turn makes the ASE suffer from a slow
growth or even a notable decrease. For practical regime of small cell density,
the performance results derived from our analysis are distinctively different
from previous results, and shed new insights on the design and deployment of
future dense/ultra-dense SCNs.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we introduce a sophisticated path loss model incorporating
both line-of-sight (LoS) and non-line-of-sight (NLoS) transmissions to study
their performance impact in small cell networks (SCNs). Analytical results are
obtained on the coverage probability and the area spectral efficiency (ASE) for
two user association strategies (UASs) assuming both a general path loss model
and two special cases of path loss models recommended by the 3GPP standards.
The performance impact of LoS and NLoS transmissions in SCNs in terms of the
coverage probability and the ASE is shown to be significant both quantitatively
and qualitatively, compared with previous work that does not differentiate LoS
and NLoS transmissions. Particularly, our analysis demonstrates when the
density of small cells is larger than a threshold, the network coverage
probability will decrease as small cells become denser, which in turn makes the
ASE suffer from a slow growth or even a notable decrease. For practical regime
of small cell density, the performance results derived from our analysis are
distinctively different from previous results, and show that small cell density
matters. Therefore, our results shed new insights on the design and deployment
of future SCNs.
[Show abstract][Hide abstract] ABSTRACT: Cell association scheme determines which base station (BS) and mobile user
(MU) should be associated with and also plays a significant role in determining
the average data rate a MU can achieve in heterogeneous networks. However, the
explosion of digital devices and the scarcity of spectra collectively force us
to carefully re-design cell association scheme which was kind of taken for
granted before. To address this, we develop a new cell association scheme in
heterogeneous networks based on joint consideration of the
signal-to-interference-plus-noise ratio (SINR) which a MU experiences and the
traffic load of candidate BSs1. MUs and BSs in each tier are modeled as several
independent Poisson point processes (PPPs) and all channels experience
independently and identically distributed ( i.i.d.) Rayleigh fading. Data rate
ratio and traffic load ratio distributions are derived to obtain the tier
association probability and the average ergodic MU data rate. Through numerical
results, We find that our proposed cell association scheme outperforms cell
range expansion (CRE) association scheme. Moreover, results indicate that
allocating small sized and high-density BSs will improve spectral efficiency if
using our proposed cell association scheme in heterogeneous networks.
[Show abstract][Hide abstract] ABSTRACT: Raptor codes have been widely used in many multimedia broadcast/multicast
applications. However, our understanding of Raptor codes is still incomplete
due to the insufficient amount of theoretical work on the performance analysis
of Raptor codes, particularly under maximum-likelihood (ML) decoding, which
provides an optimal benchmark on the system performance for the other decoding
schemes to compare against. For the first time, this paper provides an upper
bound and a lower bound, on the packet error performance of Raptor codes under
ML decoding, which is measured by the probability that all source packets can
be successfully decoded by a receiver with a given number of successfully
received coded packets. Simulations are conducted to validate the accuracy of
the analysis. More specifically, Raptor codes with different degree
distribution and pre-coders, are evaluated using the derived bounds with high
[Show abstract][Hide abstract] ABSTRACT: Wireless communication in a network of mobile devices is a challenging and
resource demanding task, due to the highly dynamic network topology and the
wireless channel randomness. This paper investigates information broadcast
schemes in 2D mobile ad-hoc networks where nodes are initially randomly
distributed and then move following a random direction mobility model. Based on
an in-depth analysis of the popular Susceptible-Infectious-Recovered epidemic
broadcast scheme, this paper proposes a novel energy and bandwidth efficient
broadcast scheme, named the energy-efficient broadcast scheme, which is able to
adapt to fast-changing network topology and channel randomness. Analytical
results are provided to characterize the performance of the proposed scheme,
including the fraction of nodes that can receive the information and the delay
of the information dissemination process. The accuracy of analytical results is
verified using simulations driven by both the random direction mobility model
and a real world trace.
[Show abstract][Hide abstract] ABSTRACT: It is a great challenge to evaluate the network performance of cellular
mobile communication systems. In this paper, we propose new spatial spectrum
and energy efficiency models for Poisson-Voronoi tessellation (PVT) random
cellular networks. To evaluate the user access the network, a Markov chain
based wireless channel access model is first proposed for PVT random cellular
networks. On that basis, the outage probability and blocking probability of PVT
random cellular networks are derived, which can be computed numerically.
Furthermore, taking into account the call arrival rate, the path loss exponent
and the base station (BS) density in random cellular networks, spatial spectrum
and energy efficiency models are proposed and analyzed for PVT random cellular
networks. Numerical simulations are conducted to evaluate the network spectrum
and energy efficiency in PVT random cellular networks.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we focus on one of the representative 5G network scenarios, namely multi-tier heterogeneous cellular networks. User association is investigated in order to reduce the down-link co-channel interference. Firstly, in order to analyze the multi-tier heterogeneous cellular networks where the base stations in different tiers usually adopt different transmission powers, we propose a Transmission Power Normalization Model (TPNM), which is able to convert a multi-tier cellular network into a single-tier network, such that all base stations have the same normalized transmission power. Then using TPNM, the signal and interference received at any point in the complex multi-tier environment can be analyzed by considering the same point in the equivalent single-tier cellular network model, thus significantly simplifying the analysis. On this basis, we propose a new user association scheme in heterogeneous cellular networks, where the base station that leads to the smallest interference to other co-channel mobile stations is chosen from a set of candidate base stations that satisfy the quality-of-service (QoS) constraint for an intended mobile station. Numerical results show that the proposed user association scheme is able to significantly reduce the down-link interference compared with existing schemes while maintaining a reasonably good QoS.
Mobile Networks and Applications 01/2015; 20(6). DOI:10.1007/s11036-014-0564-1 · 1.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wireless broadcast has been increasingly used to deliver information of common interest to a large number of users. There are two major challenges in wireless broadcast: the unreliable nature of wireless links and the difficulty of acknowledging the correct reception of every broadcast packet by every user when the number of users becomes large. In this paper, by resorting to stochastic geometry analysis, we develop a network coding based broadcast scheme that allows a base station (BS) to broadcast a given number of packets to a large number of users, without user acknowledgment, while being able to provide a performance guarantee on the probability of successful delivery. Further, the BS only has limited statistical information about the environment including the spatial distribution of users (instead of their exact locations and number) and the wireless propagation model. Performance analysis is conducted. On that basis, an upper and a lower bound on the number of packet transmissions required to meet the performance guarantee are obtained. Simulations are conducted to validate the accuracy of the theoretical analysis. The technique and analysis developed in this paper are useful for designing efficient and reliable wireless broadcast strategies.
[Show abstract][Hide abstract] ABSTRACT: Two-tier femtocell networks are an efficient communication architecture that significantly improves throughput in indoor environments with low power consumption. Traditionally, a femtocell network is usually configured to be either completely open or completely closed in that its channels are either made available to all users or used by its own users only. This may limit network flexibility and performance. It is desirable for owners of femtocell base stations if a femtocell can partially open its channels for external-user access. In such scenarios, spectrum and energy efficiency becomes a critical issue in the design of femtocell network protocols and structure. In this paper, we conduct performance analysis for two-tier femtocell networks with partially open channels. In particular, we build a Markov chain to model the channel access in the femtocell network and then derive the performance metrics in terms of the blocking probabilities. Based on stationary state probabilities derived by Markov chain models, spectrum and energy efficiency is modeled and analyzed under different scenarios characterized by critical parameters, including number of femtocells in a macrocell, average number of users, and number of open channels in a femtocell. Numerical and Monte Carlo (MC) simulation results indicate that the number of open channels in a femtocell has an adverse impact on the spectrum and energy efficiency of two-tier femtocell networks. Results in this paper provide guidelines for trading off spectrum and energy efficiency of two-tier femtocell networks by configuring different numbers of open channels in a femtocell.
[Show abstract][Hide abstract] ABSTRACT: In this article, a new framework of mobile converged networks is proposed for flexible resource optimization over multi-tier wireless heterogeneous networks. Design principles and advantages of this new framework of mobile converged networks are discussed. Moreover, mobile converged network models based on interference coordination and energy efficiency are presented, and the corresponding optimization algorithms are developed. Furthermore, future challenges of mobile converged networks are identified to promote the study in modeling and performance analysis of mobile converged networks.
[Show abstract][Hide abstract] ABSTRACT: Spectrum sharing between cellular and ad-hoc networks is studied in this work. Weak signals and strong interferences at the cell-edge area usually cause severe performance degradation. To improve the cell-edge users' performance quality while keeping high spectrum efficiency, in this paper, we propose a cooperative spectrum sharing scheme. In the proposed scheme, the ad-hoc users can actively employ cooperative diversity techniques to improve the cellular network downlink throughput. As a reward, a fraction of the cellular network spectrum is released to the ad-hoc network for its own data transmission. To determine the optimal spectrum allocation, we maximize the ad-hoc transmission capacity subject to the constraints on the outage probability of the ad-hoc network and on the throughput improvement ratio of the cellular network. Both the transmission capacity of the ad-hoc network and the average throughput of the cellular network are analyzed using the stochastic geometry theory. Numerical and simulation results are provided to validate our analytical results. They demonstrate that our proposed scheme can effectively facilitate ad-hoc transmissions while moderately improving the cellular network performance.