Multiple Access Links Research Articles

Performance Analysis of Soft-Switching FSO/THz-RF Dual-Hop AF-NOMA Link Based on Cognitive Radio

This paper presents a promising solution to address the scarcity of spectrum resources and enhance spectrum efficiency in the context of cognitive radio (CR)-based soft-switching free-space optical (FSO)/terahertz (THz) radio frequency (RF) dual-hop amplify-and-forward (AF)–non-orthogonal multiple access (ROMANO) links. The impact of maximum tolerable interference power in the primary network, transmit power in the secondary transmitter, and maximum relay transmission power on the link are thoroughly studied. The numerical results ultimately validate the effectiveness of this link in improving performance, and a comparative analysis is conducted with the without-CR scheme, highlighting the distinctive characteristics of the proposed link.

Joint Link Scheduling and Routing in Two-Tier RF-Energy-Harvesting IoT Networks

This article considers routing and link scheduling in a two-tier wireless backhaul network. The first tier consists of routers and the second tier consists of radio frequency (RF)-energy-harvesting Internet-of-Things (IoT) devices that rely on routers for energy. Our aim is to derive the shortest time division multiple access (TDMA) link schedule that satisfies the traffic demand of routers and energy demand of IoT devices. We formulate a linear program (LP) to jointly derive a routing and link schedule solution. We also propose a heuristic link scheduler called transmission set generation (TSG) to generate transmission sets and to derive the transmit power allocation of routers. In addition, we present a novel routing metric that considers RF-energy-harvesting devices on a given path. TSG on average achieves 31.25% shorter schedules as compared to competing schemes. Finally, our novel routing metric results in link schedules that are at most 24.75% longer than those computed by LP.

Link Scheduling in Rechargeable Wireless Sensor Networks With Imperfect Battery and Memory Effects

This paper considers the novel problem of deriving a Time Division Multiple Access (TDMA) link schedule for rechargeable wireless sensor networks (rWSNs). Unlike past works, it considers: (i) the energy harvesting time of nodes, (ii) a battery cycle constraint that is used to overcome so called memory effects , and (iii) battery imperfections, i.e., leakage. This paper shows analytically that the battery cycle constraint and leaking batteries lead to unscheduled links. Further, it presents a greedy heuristic that schedules links according to when their corresponding nodes have sufficient energy. Our simulations show that enforcing the battery cycle constraint increases the link schedule by up to 1.71 (0.31) times for nodes equipped with a leaking (leak-free) battery. When nodes have a leaking battery, the derived schedules are on average 1.05 times longer than the case where nodes have a leak-free battery. Finally, the battery cycle constraint reduces the number of charge/discharge cycles by up to 47.41% (45.67)% when nodes have a leak (leak-free) battery. Between leak-free and leak battery scenarios, using the former produces up to 51.46% fewer cycles than the latter.

Multiple carrier frequency offset compensation for cooperative HAPS IoT systems

Due to the deployment flexibility and broad coverage capabilities, High Altitude Platform Station is an efficiency solution of communication access for underserved areas like remote areas. However, for some special scenarios, multiple platforms may need to collaborate to overcome the effects of terrain. But the interferences introduced by multiple carriers and access links may hinder the process and restrict its practicability. In order to eliminate these interferences, a proposal on multiple carrier frequency offsets (MCFO) compensation algorithm was provided in this paper. Furthermore, this paper analyzed the lower bound of bit error ratio (BER) for cooperative HAPS systems. Simulation was also carried out, and the results validate the correctness of our theoretical analysis results.

The Backbone Packet Radio Network coloring for Time Division Multiple Access link scheduling in Wireless Multihop Networks

A radio network consists of a set of transceiver nodes in space that communicate using broadcast radio. Since communication is done over a shared medium, transmissions are subject to collisions. Different Medium Access Control techniques are used to avoid such collisions and subsequent data loss. In this article, we study Time Division Multiple Access link scheduling in Wireless Multihop Networks. We generalize the packet radio network (PRN)‐coloring model that was used in previous works to obtain the Backbone PRN (BPRN)‐coloring. The BPRN‐coloring captures the fact that typically only a subset of links need to be scheduled, corresponding to the backbone network. We study the BPRN‐coloring and the corresponding BPRN‐chromatic index considering a rooted tree as backbone, motivated by applications in Wireless Sensor Networks. The BPRN‐chromatic index is determined when the whole graph is either a complete graph or a cycle, and we give partial results in the case of a bipartite graph. We show that determining the BPRN‐chromatic index is NP‐hard even when the network graph is bipartite, and the backbone is an oriented tree toward a root vertex. Finally, we model a ring topology as the power of a cycle graph and give an upper bound on the BPRN‐chromatic index. © 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 71(4), 403–411 2018

Design of a Novel Architecture Signaling Network to Provide Internet Multimedia Subsystem Services through Aeronautical Passenger Communication

This article describes a novel architecture signaling network so that an IP Multimedia Subsystem (IMS) user, flying in an aircraft, be able to register with his IMS network of origin and have access to personal services and multimedia, through a Wide-Band Code Division Multiple Access (W-CDMA) link. The proposed architecture integrates the Session Initialization Protocol (SIP), the Network Mobility Basic Support (NEMO BS) protocol and the Mobile Internet Protocol (MIPv6) to enable the usage of IMS services by passenger on board an aircraft, as a type of Aeronautical Passenger Communication (APC) services. In this novel architecture, NEMO and MIPv6 protocols are responsible for the mobility management of smartphones and user notebook and the SIP protocol is responsible for the register and the management of sessions of an IMS user. This novel architecture enables an Air Communication Service Provider (ACSP) be able to supply to an on-board passenger (The IMS user) some APC services through an Universal Mobile Telecommunication System (UMTS). The simulation results indicate the accuracy of the proposed architecture into aeronautical scenarios.

The Capacity Region of a Class of Z Channels With Degraded Message Sets

We study a two-transmitter two-receiver network where Receiver 1 can only hear the transmitted signal of Transmitter 1. Transmitter 1 has two messages, one of which is intended for Receiver 1 while both are intended for Receiver 2. Transmitter 2 has one message which is intended for Receiver 2. We call this channel model the Z channel with degraded message sets. When the multiple access link between the two transmitters and Receiver 2 satisfies certain conditions, we characterize the capacity region of the the Z channel with degraded message sets despite the presence of distributed encoding.

Adaptive yielding scheme for link scheduling in OFDM-based synchronous device-to-device (D2D) communication system

Compared to asynchronous contention-based random access, e.g., carrier sensing multiple access, synchronous and distributed link scheduling for orthogonal frequency-division multiplexing (OFDM) systems is a viable solution to improve system throughput for device-to-device (D2D) ad hoc network. In particular, spatial spectral efficiency can be improved by scheduling as many concurrent D2D links necessary to satisfy individual signal-to-interference ratio (SIR) requirements. In this paper, we propose an adaptive yielding mechanism that can further improve the spatial spectral efficiency by allowing for more concurrent D2D links whenever more interference can be accepted, e.g., when the instantaneous bandwidth efficiency requirement is less than the current link capacity. Even if the system throughput varies with the link density, it is shown that the average system throughput can be significantly improved by the proposed yielding mechanism.

Outage-Capacity Based Adaptive Relaying in LTE-Advanced Networks

In this paper, we investigate the benefits of relaying by comparing the transmission rates of both direct transmission (DT) and relaying. It is shown that relaying achieves SNR (signal-to-noise power ratio) gain over DT due to less pathloss, but with several relaying penalties, including a lower multiplexing gain (due to half-duplex), a lower transmit power and a higher outage requirement at each hop (due to multi-hop). We determine the conditions over which relaying outperforms DT, where the SNR gain is greater than the loss due to relaying penalties. The result is applied to the LTE-advanced networks (LTE-A) where the relay nodes (RNs) are implemented to relay information between the user equipment (UE) and the evolutional NodeB (eNB). The major difference between LTE-A and a general relay system lies in that the UE-RN hop consists of multiple frequency-division access links, while the RN-eNB hop is a point-to-point link. By investigating the effects of diversity gain on the transmission rate, we propose an outage-capacity based adaptive relaying (OCA-R) scheme to replace the conventional same-carrier relaying (SC-R). It is shown that the transmission rates of both SC-R and OCA-R are one half of the harmonic means between the outage-capacities for two hops, where the advantage of OCA-R over SC-R comes from a higher diversity gain in the RN-eNB link.

Distributed Algorithms for TDMA Link Scheduling in Sensor Networks

The paper is devoted to Time Division Multiple Access Link Scheduling Protocols in wireless sensor networks for full duplex (two-way) communication, where each sensor is scheduled on an incident link as a transmitter and as a receiver in two different time slots. We formulate the full duplex link scheduling problem (FDLSP) as distance-2 edge coloring in bi-directed graphs and prove tighter lower and upper bounds for the FDLSP problem. We formulate the FDLSP problem as an integer linear program (ILP). Then, we present two I”-approximation distributed algorithms for growth bounded graphs (GBG), for modeling the sensor networks, and for general graphs, I” being the maximum node degree in the network. The first algorithm is a synchronous $\Delta$-approximation algorithm based on finding maximal independent sets. The second is an asynchronous I”-approximation depth first search (DFS) based algorithm. The maximal independent set based algorithm requires only O(I” log * n) communication rounds (where n is the number of processors in the network) in growth bounded graphs. For general graphs, the maximal independent set based algorithm requires O(I” 4 +I” 3 log * n) communication rounds, improving upon the previous best known algorithm with O(nI” 2 + n 2 m) communication rounds (where m is the number of links in the network). The asynchronous DFS based algorithm requires only O(n) communication rounds for both general and growth bounded graphs. The simulations show that the proposed algorithms assign on average equal or fewer number of time slots compared to the best known distributed algorithm while being significantly faster.

Scheduling performance enhancement by network coding in wireless mesh networks

When a wireless mesh network accommodates interactive applications with quality of service requirements, schedule-based protocols are more suitable than contention-based protocols. In this paper, the problem of determining an appropriate schedule assignment for multiple group transmissions within a spatial time division multiple access link scheduling network is referred to as an integrated multiple-group communication and link scheduling problem. A polynomial-time scheduling algorithm, designated as a source-parallel-aware assignment (SPAA), is proposed to increase the spatial utilisation within each time slot in order to enhance the network throughput. Furthermore, an advanced version of SPAA, designated as joint source-parallel-aware assignment with network coding (JSANC), is proposed to reduce the effects of bottleneck paths on the schedule frame length by flexibly applying conventional or opportunistic network coding approaches. Simulation results show that the proposed algorithms achieve a better network throughput than existing flow-based or particular order-based scheduling schemes.

Mobile multipath cooperative network for real-time streaming

Access links are often times the bottlenecks of wireless wide area networks (WWAN). The prevalent use of multimedia applications on mobile devices introduces an ever increasing traffic load on WWAN access links, leading to traffic congestion and unsatisfactory user experiences. In this paper, we introduce a mobile multipath cooperative network. In the system, multiple paths are dynamically established among cooperative devices over WWAN and WLAN so that multiple descriptions of a multimedia stream can be transported over distinct end-to-end paths between two mobiles. As a result, the capacities of multiple wireless access links can be utilized to enhance quality of experience of a multimedia application. We also introduce a MDC rate adaptation algorithm that jointly adapts the source coding rates among multiple paths. Our lab experiments show that real-time streaming with multiple description coding benefits significantly from the proposed cooperative network and subsequently enhance the quality of user experience for multimedia applications.

On the Sum-Capacity of Degraded Gaussian Multiple-Access Relay Channels

The sum-capacity is studied for a K-user physically degraded Gaussian multiple-access relay channel (MARC). Decode-and-forward (DF) is shown to achieve the sum-capacity and capacity region for a subclass of degraded Gaussian MARCs in which the multiple-access link from the sources to the relay is the bottleneck link. For the remaining subclass, DF is shown to achieve the K-user sum-capacity when the sources are symmetric, i.e., they transmit with the same transmit power. The optimality of DF is conjectured for the case of asymmetric sources.

Computational Time-Division and Code-Division Channel Access Scheduling in Ad Hoc Networks

Using two-hop neighborhood information, we present the hybrid activation multiple access (HAMA) protocol for time-division channel access scheduling in ad hoc networks with omni-directional antennas. Different from other approaches, HAMA is a node-activation channel access protocol that also maximizes the chance of link activations using time- and code-division schemes. The throughput and delay characteristics of HAMA in randomly-generated multihop wireless networks are studied by analyses and simulations. The results of the analyses show that HAMA achieves higher channel utilization in ad hoc networks than previous similar works, namely, the node activation multiple access (NAMA), the link activation multiple access (LAMA) and pair-wise link activation multiple access (PAMA). In addition, HAMA achieves better throughout than an existing scheduling algorithm based on complete topology information, and much higher throughout than the ideal CSMA and CSMA/CA protocols. The main contribution of this work is to computationally derive channel access schedules according to local network topology information instead of on-demand negotiations or static global coordinations.

Code domain analysis of nonlinear links

The influence of nonlinearity on commercial code division multiple access links is considered. Nonlinearity corrupts the modulation of Walsh codes and generates modulation of new codes; a memoryless model and a Volterra model are presented to analyse this effect. The Volterra series requires only a few terms and can be applied to identify the channel nonlinearity from observations at the receiver.

Network architectures exploiting multiple HAP constellations for load balancing

This paper addresses network architectures in a constellation of high altitude platforms (HAPs) with overlapping coverage areas, focusing on the additional network elements/functionalities required...

On-the-fly TCP path selection algorithm in access link load balancing

Many enterprises install multiple access links for fault tolerance or bandwidth enlargement. Dispatching connections through good links is the ultimate goal in utilizing multiple access links. The traditional dispatching method is only based on the condition of the access links to ISPs. It may achieve fair utilization on the access links but poor performance on connection throughput. In this work, we propose a novel approach to maximize the per-connection end-to-end throughput by the on-the-fly round trip time (RTT) probing mechanism. The end-to-end RTTs through all possible links are probed by duplicating the SYN packet during the three-way handshaking stage of a TCP connection. The experiment results show that the ratio to choose the best outgoing access link is 79% on the average. If the second best link is chosen, it is usually very close to the best, thus averagely achieving 94% of the maximum possible throughput. The ratio of the traditional round-robin (RR) algorithm is only 35%, and the link selected by RR algorithm could provide 69% of throughput.

SINR estimation for power control in systems with transmission beamforming

This paper takes a unified approach to the downlink transmission power control, while a transmission beamforming is applied in the base station. The proposed scheme is based on the estimation of signal-to-interference-and-noise-ratios (SINRs) by antenna array measurement and using this estimate in transmission power control. Hence power control algorithms needing SINR-levels can be applied instead of the simple relay power control. The SINR estimation technique does not require any additional measurements compared to a separate adaptive beamforming and power control, since the required measurements are needed for the adaptive beamforming update. The estimation is based on the knowledge of the level of caused interference to the multiple access links in the same cell, and the utilization of relay power control commands in SINR estimation.

Data-aided channel estimation for wideband CDMA

The effect of channel estimation error on the performance of a wideband code division multiple access link using a pilot channel multiplexed with the data channel is analyzed. The gain achievable by improving the channel estimation algorithm is studied. Analysis and simulation results are presented for a data-aided channel estimation scheme that effectively extends the duration of the pilot signal. Using the maximum likelihood detection principle, it is shown that making tentative minimum mean-squared error decisions on the data bits using estimates obtained from the pilot channel can extend the number of samples used in the channel estimation, thus improving the channel estimate quality. Simulations show that a gain of up to 1.5 dB in block-error rate performance is achievable using the proposed channel estimation scheme for both Convolutional and Turbo codes. It is shown that the performance gain depends on the information bit rate, the channel characteristics, including the Doppler frequency, and the multipath fading channel power delay profile. Simulation results also show that for weak paths, data-aided channel estimation benefits significantly from diversity combining.

Robust image transmission over CDMA channels

The transmission of real-time images and video over wireless communication channels is a challenging problem. Digital compressed images are sensitive to bit errors which are typical in wireless communications. Moreover, the bandwidth at the air interface is currently a limiting factor because the first and second generation of mobile phone standards mainly support voice communications. We present a study of real-time image traffic over a radio link-the aim of this research is for videophone applications. We use the discrete wavelet transform (DWT) to compress images and a code division multiple access (CDMA) link to transfer images over wireless communications network. The experiment results indicate that it is possible to transfer 9-12 QCIF gray scale images per second over a CDMA link with graceful degradation in image quality.