2-hop Relay Network Research Articles

Tensor-Based Joint Channel Estimation and Symbol Detection for AF MIMO Relay Networks

A study on the joint channel and symbol estimation issue is provided for two hop relay networks which employ the amplify-and-forward (AF) relaying approach. The encoding scheme at the source node introduces the time-domain spreading with a time-varying linear constellation precoding. Then, a set of amplifying factors matrices is utilized by the relays to amplify and forward the received data to the destination. The received signal at the destination can be constructed as a fourth-order tensor model, which is referred to as the nested parallel factor (PARAFAC) model. And then, we present a novel Levenberg-Marquardt (LM) algorithm based on this tensor model. The proposed method does not require complex signal processing at the relay, which effectively reduces the burden of relay. As a semi-blind method, which does not require the pilot signal, the proposed receiver can jointly recover the channels and information symbols. Moreover, the proposed semi-blind receiver is robust as it can work in different wireless channel scenarios. Simulations are conducted to demonstrate the efficiency of the proposed semi-blind approach.

Analysis and Optimization Study of Antenna Selection in Dual Hop Relay Networks over Weibull Fading Channels

Field experiments show that Weibull distribution can be considered as the most suitable distribution to model weak to high signal power levels in indoor and outdoor environments. Recently, Exponentiated Weibull which is a special case of Weibull fading, have been widely adopted in free-space optical communication systems to model weak and high levels of turbulence effects. Motivated from the increasing use of Weibull distribution, this paper studies the popular dual-hop amplify-and-forward relay network with joint transmit and receive antenna selection where closed form ergodic capacity, symbol error rate and outage probability expressions are derived for Weibull fading channels. With the help of high SNR analysis, diversity gain, array gain and optimum relay location are obtained. Finally, theoretical findings are validated by simulation results.

New transmission scheme to enhance throughput of DF relay network using rate and power adaptation

ABSTRACTThis paper presents a new transmission scheme for a decode and forward (DF) relay network using continuous power adaptation while independent average power constraints are provisioned for each node. To have analytical insight, the achievable throughputs are analysed using continuous adaptation of the rates and the powers. As shown by numerical evaluations, a considerable outperformance is seen by continuous power adaptation compared to the case where constant powers are utilised. Also for practical systems, a new throughput maximised transmission scheme is developed using discrete rate adaptation (adaptive modulation and coding) and continuous transmission power adaptation. First a 2-hop relay network is considered and then the scheme is extended for an N-hop network. Numerical evaluations show the efficiency of the designed schemes.

Unified Performance Analysis of Multi-antenna Techniques in Dual Hop Networks over Nakagami-m Fading Channels

In this paper, various multi-antenna dual hop relay networks are studied over flat Nakagami-m fading channels. The studied scenarios include transmit diversity techniques such as orthogonal space-time block coding, maximal-ratio transmission, and transmit antenna selection techniques and receive diversity techniques such as selection combining and maximal-ratio combining, and hybrid versions of these transmit and receive diversity techniques. In order to study and analyze the performance of the multi-antenna relay networks, closed-form and exact expressions for the moment generating function, the signal-to-noise ratio moments, the outage probability, and the symbol error probability are derived. Besides, to provide further insight about the performance of the studied scenarios asymptotic expressions revealing the array and diversity gain are also derived. Theoretical results are approved by the Monte Carlo simulations.

Techniques to Enhance the Quality of Service of Multi Hop Relay Networks

Broadband internet access through the user equipment has become the hot research topic. The shadowing and multipath issues restrict the high performance nature of 4G cells. In Multi hop Relay (MHR) networks, Relay Stations (RS) are introduced to improve coverage and capacity of the system. There exist some issues like path selection and RSs deployment, which severely affects the Quality of Service (QoS) of the system. In this paper, to improve the QoS of MHR networks, Load Aware Routing Metric (LARM) based path selection and a low complex Burst Profile (BP) based RS deployment schemes are discussed.

Investigation on uplink collaborative contention-based bandwidth request for WiMAX three hop relay networks

This paper suggests a collaborative contention bandwidth request (BR) mechanism for worldwide interoperability for microwave access (WiMAX) three-hop relay networks. By complimenting message and code BR in three hops of a link, the proposed framework enables low block error rate (BLER), packet dropping and signaling overhead while preserving the connection throughput and access delay requirements of best effort (BE) services. With three hops between base station (BS) and mobile station (MS) via relay station 1 (RS1) and relay station 2 (RS2), there take place eight possible BR mechanisms with message and code BR. Among eight BR mechanisms, message-message-code (MMC) BR performs better with message dominant BR and code-message-code (CMC) BR performs better with code dominant BR. Further, with CMC BR, the BLER is reduced by 5.88%, packet dropping is reduced by 8.68%, medium access control (MAC) overhead is reduced by 7.6%, MAC wastage is reduced by 4.47%, connection delay is reduced by 28.30%, queuing delay is reduced by 8.65%, queue size is reduced by 15.25% and throughput is improved by 11.51% than MMC BR mechanism.

Contention based bandwidth request with signaling analysis in IEEE 802.16 two hop relay networks

In this paper, we propose a joint contention-based bandwidth request mechanism for WiMAX two-hop relay networks. For this purpose, we considered contention by message and code mechanisms. These are normally deployed in single-hop networks. This message scheme suffers from low contention efficiency and higher access delay when the number of mobile stations (MSs) in the network increases. Conversely, this code technique undergoes transmission failure due to the inappropriate setting of the detection threshold at relay stations (RSs). However, these message and code mechanisms are advantageous when they are carried out at appropriate hops. Among the four possible options created by combining the message and code methods, the message requests from MS to RS and code requests from RS to base stations (BSs) performed better than other possible combinations. Using a comprehensive case study and simulation results, we generated signaling examples that confirmed the significance of the proposed method in terms of signaling overhead, network throughput, connection delay and queuing size.

Flow-based XOR Network Coding for Lossy Wireless Networks

A practical way for maximizing the throughput of a wireless network is to decompose the network into a superposition of small two-hop networks such that network coding can be performed inside these small networks to resolve bottlenecks. We call these networks 2-hop relay networks. Therefore, studying the capacity of 2-hop relay networks is very important. Most practical network coding protocols that perform the superposition ignore the diversity among the links by turning off coding when the channels are lossy. Other protocols deal with the packets separately - not as members of flows - which makes the network coding problem with lossy links intractable. In this paper, we use a different approach by looking at flows or batches instead of individual packets. We characterize the capacity region of the 2-hop relay network with packet erasure channels when the coding operations are limited to XOR. We derive our results by constructing an upper bound on the capacity region and then providing a coding scheme that can achieve the upper bound. The capacity characterization is in terms of linear equations. We also extend our 2-hop relay networks results to multihop wireless networks by providing a linear program that can perform the superposition optimally. We perform extensive simulations for both the 2-hop relay and large wireless networks and show the superiority of our protocols over the network coding protocols that deal with the packets separately.

A Survey on Technical Issues in IEEE 802.16j Mobile Multi-hop Relay Networks

In this paper, we have conducted a detailed survey on relay technologies for IEEE 802.16j mobile multi-hop relay networks, such as relay modes, relay transmission schemes, and relay pairing schemes. We have also conducted a detailed survey about the technical issues in the physical layer, medium access control-common part sub layer, and medium access control-security sub layer of IEEE 802.16j mobile multi hop relay networks. Technical issues such as data forwarding schemes, frame structure for transparent and non-transparent relay mode, link adaptation, modulation, and coding, belong to the physical layer. Other technical issues such as quality of service-scheduling services, bandwidth allocation and request, network planning, medium access control handover procedures, connection management, path management, and interference management belong to the medium access control- common part sub layer. Centralized security control and distributed security control belong to the medium access control--security sub layer. In this paper, we have also given how to integrated IEEE 802.16j (worldwide interoperability for microwave access) with IEEE 802.11(Wi-Fi).

Performance Evaluation of Multi Hop Relay Network for Oceanic Air Traffic Control Communication

This paper proposes a new kind of communication system for air traffic control over the oceans; it is particularly effective at handling high air traffic loads due to many oceanic flights. In this system, each aircraft position report is sent to its relevant ground station by forwardly relaying them via a multi hop ad-hoc network that is formed by the aircraft between this aircraft and the ground station. In addition, an effective multiple access scheme with optimal values is also proposed. This scheme enables the various aircraft involved in relaying the signal to operate autonomously in a flight-route airspace. Furthermore, two useful schemes are proposed for efficient timeslot reuse and timeslot assignment in cases of low aircraft densities: the position aided timeslot reuse (PATR) and distance based timeslot assignment (DBTA), respectively. Finally, another scheme is proposed to improve the achievable relayed packet rate under low aircraft densities, which is called interference-based node selection (IB-NS). In all, the proposed system combined with those three schemes show the availability to utilize this system for air traffic control communications, specifically on high traffic ocean routes.