Teong Chee Chuah

Recent advances in radio resource management for heterogeneous LTE/LTE-A networks

As heterogeneous networks (HetNets) emerge as one of the most promising developments toward realizing the target specifications of Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks, radio resource management (RRM) research for such networks has, in recent times, been intensively pursued. Clearly, recent research mainly concentrates on the aspect of interference mitigation. Other RRM aspects, such as radio resource utilization, fairness, complexity, and QoS, have not been given much attention. In this paper, we aim to provide an overview of the key challenges arising from HetNets and highlight their importance. Subsequently, we present a comprehensive survey of the RRM schemes that have been studied in recent years for LTE/LTE-A HetNets, with a particular focus on those for femtocells and relay nodes. Furthermore, we classify these RRM schemes according to their underlying approaches. In addition, these RRM schemes are qualitatively analyzed and compared to each other. We also identify a number of potential research directions for future RRM development. Finally, we discuss the lack of current RRM research and the importance of multi-objective RRM studies.

Game theoretic approach for channel assignment and power control with no-internal-regret learning in wireless ad hoc networks

In wireless ad hoc networks, co-channel interference can be suppressed effectively through proper integration of channel assignment (CA) and power control (PC) techniques. Unlike centralised cellular networks where CA and PC can be coordinated by base stations, the integration of CA and PC into infrastructureless wireless ad hoc networks where no global information is available is more technically challenging. The authors model the CA and PC problems as a non-cooperative game, in which all wireless users jointly pick an optimal channel and power level to minimise a joint cost function. To prove the existence and uniqueness of Nash equilibrium (NE) in the proposed non-cooperative CA and PC game (NCPG), the authors break the NCPG into a CA subgame and a PC subgame. It is shown that if NE exists in these two subgames, the existence of NE in the NCPG is ensured. Nonetheless, due to unpredictable network topology and diverse system conditions in wireless ad hoc networks, the NCPG may encounter the dasiaping-pongdasia effect that renders NE unattainable. By incorporating a call-dropping strategy and no-internal-regret learning into the NCPG, an iterative and distributed algorithm that ensures convergence to NE is proposed. It is shown through simulation results that the proposed approach leads to convergence and results in significant improvements in power preservation and system capacity as compared with the popular distributed dynamic CA technique incorporated with PC.

Robust adaptive spread-spectrum receiver with neural net preprocessing in non-Gaussian noise

Multiuser communications channels based on code division multiple access (CDMA) technique exhibit non-Gaussian statistics due to the presence of highly structured multiple access interference (MAI) and impulsive ambient noise. Linear adaptive interference suppression techniques are attractive for mitigating MAI under Gaussian noise. However, the Gaussian noise hypothesis has been found inadequate in many wireless channels characterized by impulsive disturbance. Linear finite impulse response (FIR) filters adapted with linear algorithms are limited by their structural formulation as a simple linear combiner with a hyperplanar decision boundary, which are extremely vulnerable to impulsive interference. This raises the issues of devising robust reception algorithms accounting at the design stage the non-Gaussian behavior of the interference. We propose a multiuser receiver that involves an adaptive nonlinear preprocessing front-end based on a multilayer perceptron neural network, which acts as a mechanism to reduce the influence of impulsive noise followed by a postprocessing stage using linear adaptive filters for MAI suppression. Theoretical arguments supported by promising simulation results suggest that the proposed receiver, which combines the relative merits of both nonlinear and linear signal processing, presents an effective approach for joint suppression of MAI and non-Gaussian ambient noise.

Fair power control for wireless ad hoc networks using game theory with pricing scheme

Resource allocation in wireless ad hoc networks is usually modelled in a non-cooperative game theoretic framework with the objective of maximising individual utility. However, the selfishness of autonomous users under such framework may lead to throughput unfairness which only benefits certain users. To alleviate this unfairness problem, the authors propose a payment-based power control scheme using game theory where each user announces a set of price coefficients that reflects different compensations paid by other users for the interference they produce. Users who generate higher interference are required to pay more by transmitting at a lower power to give other users a fairer chance of sharing the throughput. Without any incentive to play fairly, users could misbehave by broadcasting high price coefficients to force other users to transmit at a lower power. The authors treat this problem casting it into a price game which resembles a Prisoners Dilemma game. Users who play this game iteratively will behave cooperatively and broadcast the price coefficients truthfully. Together with analytical proof, the proposed approach is shown to converge to Nash equilibrium where at this point it is able to provide a fairer throughput share among users at the expense of a slight loss in total throughput.

On the Optimal Alpha-

The alpha-k (alpha - k) curve is an important tool for real-time myriad filtering problems in channels with time-varying impulsiveness. In this letter, we use the asymptotic variance as the criterion to derive the optimal alpha - k curve. We then suggest a new expression for the optimal curve and compare it to the conjectured expression in earlier works.

k

Abstract-Recently, a robust version of the linear decorrelating detector (LDD) based on the Hubers M-estimation technique has been proposed. In this paper, we first demonstrate the use of a three-layer recurrent neural network (RNN) to implement the LDD without requiring matrix inversion. The key idea is based on minimizing an appropriate computational energy function iteratively. Second, it will be shown that the M-decorrelating detector (MDD) can be implemented by simply incorporating sigmoidal neurons in the first layer of the RNN. A proof of the redundancy of the matrix inversion process is provided and the computational saving in realistic network is highlighted. Third, we illustrate how further performance gain could be achieved for the subspace-based blind MDD by using robust estimates of the signal subspace components in the initial stage. The impulsive noise is modeled using non-Gaussian alpha-stable distributions, which do not include a Gaussian component but facilitate the use of the recently proposed geometric signal-to-noise ratio (G-SNR). The characteristics and performance of the proposed neural-network detectors are investigated by computer simulation.

Curve of the Sample Myriad

Achieving reliable high-speed communications over the power line requires robust modulation and equalization techniques to mitigate various hostile channel impairments. Multicarrier orthogonal frequency-division multiplexing (OFDM) has been proposed as the dominant modulation format for power-line communications (PLC). In this paper, we study a single-carrier cyclic prefix (SCCP)-assisted PLC system that employs block data transmission similar to OFDM and propose two frequency-domain equalizers based on the zero forcing and minimum mean-square error criteria. Performance comparisons with OFDM systems of identical system specifications are made via extensive computer simulations under different realistic channel parameters and data rates. The results show that the SCCP-assisted scheme outperforms the OFDM counterpart in most cases through higher frequency diversity exploitation while maintaining almost identical computational complexity. Other salient features of the SCCP technique for PLC applications are discussed. The proposed SCCP-assisted scheme is found to be an attractive alternative modulation technique for broadband PLC.

Robust CDMA multiuser detection using a neural-network approach

The problem of subcarrier allocation (SA) and power allocation (PA) for both the downlink and uplink of cognitive radio networks (CRNs) is studied. Two joint SA and PA schemes based on Blotto games are presented for orthogonal frequency-division multiple access (OFDMA)-based CRNs. In this work, the authors consider a more practical scenario by taking into account the correlation between adjacent subcarriers. In the proposed games, secondary users (SUs) simultaneously compete for subcarriers using a limited budget. In order to win as many good subcarriers as possible, the SUs are required to wisely allocate their budget subject to the transmit power, budget and interference temperature constraints. Two PA and budget allocation strategies are derived to enable fair sharing of spectrum among the SUs. It is shown that by manipulating the total budget available for each SU, competitive fairness can be enforced. In addition, the conditions to ensure the existence and uniqueness of Nash equilibrium (NE) in the proposed methods are established and algorithms which ensure convergence to NE are proposed. Simulation results show that the proposed methods can converge rapidly and allocate resources fairly and efficiently in correlated fading OFDMA channels.

Single-Carrier Cyclic Prefix-Assisted PLC Systems With Frequency-Domain Equalization for High-Data-Rate Transmission

The problem of data communications through impulsive power-line channels using Reed-Solomon (RS) codes combined with M-ary modulation is treated. It is shown that under the influence of impulsive interference, the seemingly robust algebraic RS decoder can suffer drastic performance degradation even with the aid of an interleaver. We attempt to elucidate the mechanism that leads to the breakdown of such coding schemes. It is found that in impulse channels, excessive random and burst errors can occur prior to RS decoding mainly due to the deficiency of the Gaussian-based demodulator. An impulse mitigation strategy derived from the myriad filtering framework is incorporated into the demodulator for efficient baseband filtering and RS decoding. Even without an interleaver, the proposed solution leads to substantial performance improvements over the conventional interleaved scheme in impulsive channels. Consequently, the delay caused by interleaving can be avoided, which has significant benefits for future broadband power-line communication systems supporting interactive applications.

Fair subcarrier and power allocation for multiuser orthogonal frequency-division multiple access cognitive radio networks using a colonel blotto game

Applications of video streaming and real-time gaming, which generate large amounts of real-time traffic in the network, are expected to gain considerable popularity in Long Term Evolution networks. Maintaining the QoS such as packet delay, packet loss ratio, median, and cell border throughput requirements in networks dominated by real time traffic, is critical. The existing dimensioning methodology does not consider QoS parameters of real-time traffic in network dimensioning. Moreover, exhaustive and time-consuming simulations are normally required to evaluate the performance and QoS of real-time services. To overcome this problem, we propose an improved radio network dimensioning framework that considers the QoS of real-time traffic in network dimensioning. In this framework, an analytical model is proposed to evaluate the capacity and performance of real-time traffic dominant Long Term Evolution networks. The proposed framework provides a fast and accurate means of finding the trade-off between system load, packet delay, packet loss ratio, required median, and cell border throughput. It also provides network operators with an analytical means for obtaining the minimum number of sites required by jointly considering coverage, capacity and QoS requirements. The accuracy of the proposed model is validated through simulations. Copyright