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Presents information and current topics of interest to the global communications industry.

Crosstalk among different orbital angular momentum (OAM) states, mainly caused by the atmospheric turbulence and the misalignment between the transmitting and receiving antennas, leads to the increase of error probability of OAM transmission systems. Considering the OAM-based multiple-input multiple-output (OAM-MIMO) transmission system with unaligned antennas, the error probability model is derived under the non-Kolmogorov turbulence. Furthermore, a power allocation optimization algorithm is proposed to alleviate the crosstalk among different OAM states, thus effectively decreasing the error probability of the OAM-MIMO transmission system. Numerical results show that the error probability reduction of the OAM-MIMO transmission system by using the proposed optimization algorithm is up to 26.1 dB.

Efficiently scheduling various service classes while fulfilling performance targets is one of the main challenges in 3GPP Long-Term Evolution (LTE) communication systems. However, Quality of Service (QoS) and fairness provisioning for all different service classes are generally unstable due to insufficient radio resources, especially in heavily loaded states of the network, which leads to the deterioration of overall system performance. In this paper, we address these challenging issues by proposing a two-level downlink scheduling algorithm to deliver all traffic types while attempting to provide a compromise for the LTE performance targets. For the higher level of the algorithm, a coherent resource distribution approach is developed by applying a game theory model in a nested manner to provide per-class fairness. At the lower level, the greedy-knapsack algorithm is properly tailored to optimally allocate resources to the best potential bearers for QoS and throughput enhancement. The performance of the proposed algorithm was evaluated for normal and overload states of the network. The simulation results clearly demonstrate that the proposed scheduling algorithm, compared with the reference scheduling algorithms, provides the best tradeoff for fairness, throughput, and QoS performance in terms of packet loss rate and packet latency for different service classes.

This paper presents a novel low-complexity technique for reducing the Peak-to-Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) systems followed by an efficient hardware co-simulation implementation of this technique by using a Xilinx system generator on a Field Programmable Gate Array (FPGA). In this technique, each subblock is interleaved with the others, and a new optimisation scheme is introduced in which the number of iterations is equal only to the number of subblocks, which results in reduced processing time and less computation that, in turn, leads to reduced complexity. Furthermore, the proposed method focuses on simplifying the required hardware resources. Thus, it can be easily combined with other simplified techniques. The simulation results demonstrate that the new technique can effectively reduce the complexity up to 98.22% compared with the new existing Partial Transmit Sequence (PTS) techniques and yield a good Bit Error Rate (BER) performance. Through the comparison of performance between simulation and hardware, it is distinctly illustrated that the designed hardware block diagram is as workable as the simulation and the difference of the result is only 0.1 dB.

New mobility solutions are required for mobile environments characterised by an ever-increasing number of mobile devices and volume of internet data traffic. A single mobility anchor in the current Centralised Mobility Management (CMM) performs all mobility and routing functionalities. Distributed Mobility Management (DMM) paradigm is introduced recently to overcome scalability, reliability and non-optimal routing issues of the CMM. The DMM approach is proposed to flatten the network architecture by moving the mobility anchors closer to the users and separating the control and data planes at the network edge. In this paper, we develop and implement a network-based DMM model using NS2 simulation tool. Extensive simulations are performed to evaluate the performance of the DMM against that of the CMM. The simulation results indicate that the DMM approach outperforms the CMM approach under various mobility environments. Thus, this study verifies previous analytical studies and provides more accurate findings in DMM.

ABSTRACTOver the past few years, the wireless mesh network (WMN) with a multi-radio multi-channel (MR-MC) has attracted increasingly high attention because of its wider coverage area. The use of multiple radios and the function of multi-hop forwarding allows WMN to achieve a greater capacity and coverage area. MR-MC can be used to utilize the radio spectrum efficiently. However, the performance of WMN is highly affected by several radios operating at frequencies close to each other. This problem can be solved using one of the key techniques called channel assignment (CA). In this paper, we first present the six main constraints of CA algorithms, i.e., interference, delay, routing, connectivity, congestion, and link scheduling. Then, various CA techniques proposed in the literature to improve the performance of WMN are discussed in detail.

This article presents a novel peak-to-average power ratio (PAPR) reduction scheme based on the insertion of dummy random Gaussian (IDRG) subcarriers to the data constellation points in the frequency domain integrated with a partial transmit sequence (PTS) technique. The dummy signals are Gaussian random signals which have the same statistical distribution as that of the output signals of the conventional orthogonal frequency division multiplexing (OFDM) system. The integration of IDRG with PTS technique reduces the overall complexity of the OFDM system. Compared to the conventional PTS which requires several inverse fast Fourier transform (IFFT) operations, the proposed IDRG–PTS scheme requires only half as many IFFT operations with comparable PAPR performance. Simulation results have been examined with 16 quadrate amplitude modulation OFDM signals.

AbstractConventional design of cellular systems aims to maximize the system capacity and spectral efficiency due to sustainable growth of data rate requirements. As the energy consumption becomes relatively high, energy-efficient design for cellular systems is highly required to save energy as well as reducing the undesirable carbon dioxide emitted by these systems. However, reducing the energy consumption will degrade other system performances such as the data rate and quality of service. Therefore, joint optimization for overall system performances should be achieved. In this paper, the energy-efficient radio resource management (RRM) for Long Term Evolution (LTE) systems is addressed. After a brief introduction to LTE radio resource block and LTE frame, different types of energy efficiency metrics are defined to give a better understanding to the energy efficiency perspectives. The energy-efficient approaches related to link adaptation and RRM are explained. The state-of-the-art energy-efficient schedulers are also discussed, and a comprehensive comparison between them is adopted in this paper. Moreover, many trade-offs, challenges, and open issues are addressed to optimize the system performances.

AbstractHandover (HO) mechanism is one of the critical operations in mobile WiMAX. It takes place when a mobile station (MS) moves from a serving base station (BS) to another BS. However, the HO latency in mobile WiMAX is still an issue that may affect continuity of real-time application sessions such as Voice over Internet Protocol (VoIP). This paper presents performance comparison of some HO mechanisms for real-time applications in mobile WiMAX, including HO, cross-layer HO, pre-coordination HO, passport HO mechanisms and fast intra-network and cross-layer HO (FINCH). Each one of these mechanisms reduces HO latency, especially during downlink traffic; however, they still produce insufficient HO latency during uplink traffic. Except for FINCH, they do not consider the scenario of HO between BSs that belong to different access service network-gateways (ASN-GWs) or to different connectivity service networks (CSNs); these two cases cause extra layer 3 (L3) HO latency.

This paper proposes a new synchronous digital hierarchy (SDH) based forward error correction (FEC) scheme for wavelength division multiplexing (WDM) networks. In this scheme, a dedicated WDM channel is used to transport the FEC redundant bits. This paper also proposes the use of error location analysis of the FEC correctable bits to identify the pattern of errors, combined with the seriousness of errors obtained from B2-byte analysis to decide as to the suitable FEC code to be assigned to the payload channels. The proposed FEC scheme is studied not only under the typical Poisson errors but also the bursty errors. Simulation results show that the proposed FEC scheme performs significantly better than the existing FEC schemes. It is also shown that the performance of the proposed FEC scheme on bursty errors is independent of the line rates, whereas the existing FEC schemes either cannot support bursty errors or degrades with line rates.This paper proposes a new synchronous digital hierarchy (SDH) based forward error correction (FEC) scheme for wavelength division multiplexing (WDM) networks. In this scheme, a dedicated WDM channel is used to transport the FEC redundant bits. This paper also proposes the use of error location analysis of the FEC correctable bits to identify the pattern of errors, combined with the seriousness of errors obtained from B2-byte analysis to decide as to the suitable FEC code to be assigned to the payload channels. The proposed FEC scheme is studied not only under the typical Poisson errors but also the bursty errors. Simulation results show that the proposed FEC scheme performs significantly better than the existing FEC schemes. It is also shown that the performance of the proposed FEC scheme on bursty errors is independent of the line rates, whereas the existing FEC schemes either cannot support bursty errors or degrades with line rates.

This paper analyses and compares the performance of International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) recommended forward error correction (FEC) for the Synchronous digital hierarchy (SDH) system and the newly ratified Optical transport network (OTN) system. The analysis and comparison are based on simulation results using Poisson and bursty error patterns. While a Poisson error pattern is a commonly studied environment for these systems, a bursty error pattern is not. The simulation results show that the FEC for both SDH and OTN support Poisson errors well. However, for bursty errors, it is found that the FEC for SDH does not work well, while the FEC for OTN is working well for short burst length only.This paper analyses and compares the performance of International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) recommended forward error correction (FEC) for the Synchronous digital hierarchy (SDH) system and the newly ratified Optical transport network (OTN) system. The analysis and comparison are based on simulation results using Poisson and bursty error patterns. While a Poisson error pattern is a commonly studied environment for these systems, a bursty error pattern is not. The simulation results show that the FEC for both SDH and OTN support Poisson errors well. However, for bursty errors, it is found that the FEC for SDH does not work well, while the FEC for OTN is working well for short burst length only.

A switch architecture for ATM is described which uses a simple priority module to resolve input contention and a distributed design to permit transfer of input cells to the first free output buffer. The switch has been synthesised using VHDL software and a target generic library and can operate at speeds >400 Mbit/s.