Joint Transceiver Design for Non-Concurrent MIMO Two-Way AF Relaying
We consider an amplify-and-forward infrastructure non-concurrent two-way relaying (ncTWR) scenario where a base station serves a transmit-only user TUE and a receive-only user RUE. Unlike conventional two-way relaying, the RUE in ncTWR experiences back-propagating interference (BI). Uniform channel decomposition and Tomlinson-Harashima precoding improve the bit error rate (BER) of multiple-antenna-multiple-output (MIMO) systems. Inspired by these techniques, we design a transceiver to reduce BER of both users in MIMO ncTWR. This transceiver cancels BI of the RUE and uses spatial noise whitening filters, designed herein, to uniformly decompose MIMO channels of both TUE and RUE. This letter quantifies the improved BER of the proposed transceiver.
Deploying IP multimedia subsystem (IMS) services over next generation networks (NGNs): The IU-ATC integrated test bed
The IP Multimedia Subsystem (IMS) is the Third Generation Partnership Project's (3GPP) standardized service platform that enables the deployment of rich and personalized services over fixed and mobile networks whilst allowing end-users ubiquitous access to services such as voice, video, presence and online gaming anytime and anywhere. However, the delivery of these services to the end-users is highly dependent on the available or preferred access network which could range from fixed broadband access to mobile 4G connections. Although the IMS was initially developed as the core network for Third Generation (3G) systems, it has now been adopted as the service platform for the Long Term Evolution (LTE) and System Architecture Evolution (SAE). As this transition of 3G to 4G and beyond evolves, there is an immediate need for a research testbed that facilitates the research, development and early trials of the integration of these technologies. This has motivated us to integrate the IMS based Advanced Next Generation Network (ANGN) testbed at the University of Surrey (UniS), U.K. with the 4G Access Network Testbed at IIT Madras, India via an academic transnational network link to form a fully functional telecommunications mobile network. In this paper, we discuss the rationales, motivations and objectives behind the integrated testbed whilst also investigating how it can be extended to support 4G and future technologies such as LTE/SAE and WiMAX. The testbed as a whole plays a key as role in the future of IMS development as it provides a fully functional platform similar to commercial networks for researchers to investigate and demonstrate the feasibility of their proposal in a realistic environment. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2011.
Linear precoders for nonregenerative asymmetric two-way relaying in cellular systems
In conventional two-way relaying (TWR), it is assumed that a user has data to send and receive simultaneously from the base station (BS) via a relay. In cellular systems, data flow between the BS and a user is usually not simultaneous, e.g., a transmit-only user (say, TUE) may have uplink data to send in the multiple access (MAC) phase, but may not have downlink data to receive in the broadcast (BC) phase. Such one-way data flow will reduce TWR to spectrally inefficient one-way relaying. The multiple-input-multiple-output (MIMO) asymmetric TWR (ATWR) protocol considered here restores the two-way data flow via a relay. In ATWR, the BC phase following the MAC phase of a TUE is used to send downlink data to a receive-only user (say, RUE). However, the RUE will not be able to cancel the back-propagating interference. We design a structured precoder at the relay to cancel this interference. The proposed precoder also triangularizes the end-to-end MIMO channels. The channel triangularization reduces the weighted sum-rate maximization and relay power minimization problems to power allocation problems, which are then cast as geometric programs. Simulation results illustrate the effectiveness of the proposed precoder when compared with conventional solutions.
Two-way MIMO DF relaying for non-simultaneous traffic in cellular systems
Two-way relaying (TWR) improves the spectral efficiency of cellular systems by enabling data exchange between two nodes via a relay station (RS) in two channel uses. It is assumed in TWR that a user has data to send and receive from the base station (BS) at the same time. This paper considers a non-simultaneous traffic scenario observed in cellular systems, where one user sends data to the BS and another user receives data from the BS. We consider a novel multiple-input multiple-output (MIMO) TWR protocol to enable communication between two users and the BS in two channel uses. By designing a linear precoder at the decode-And-forward RS, we maximize the sum-rate of this protocol by formulating a sequence of semidefinite programs. The sum-rate performance of this protocol is evaluated in two coverage-limited scenarios in a cellular framework by extensive numerical simulations. It is shown that the protocol results in a dramatic performance gain over conventional protocols.
Precoder design for asymmetric two-way AF shared relay
Two-way relaying (TWR) reduces the loss in spectral efficiency caused in a conventional half-duplex relay. TWR is possible when two nodes exchange data simultaneously through a relay. In the case of cellular systems, data exchange between base station (BS) and users is usually not symmetric, e.g., a user might have uplink data to transmit during multiple access (MAC) phase, but might not have downlink data to receive during broadcast (BC) phase. This asymmetry in data exchange will reduce the gains of TWR. With infrastructure relays, where multiple users communicate through a relay, the BC phase following the MAC phase of a transmitting user (UE1) can be used by the relay to transmit downlink data to a second user (UE2). This will result in the receiving user UE2 not being able to cancel the back-propagating interference in the usual way. Precoders are designed in [1] to mitigate the back-propagating interference at UE2 for an amplify-and-forward (AF) relay. The present work studies the asymmetric data-flow problem for a shared AF relay, wherein multiple BS and users communicate using a common relay with multiple antennas. In this case, UE2 will observe inter-user interference (IUI) in addition to the back-propagating interference. Also, BS will now observe the IUI. We propose a precoder to jointly mitigate the back-propagating interference for UE2 and IUI for BS and UE2. It is shown that the sum-rate performance is better for the proposed precoder than the conventional zero-forcing precoder. © 2013 IEEE.
Joint transceiver design for QoS-constrained MIMO two-way non-regenerative relaying using geometric programming
Transceiver designs for multiple-input multiple-output (MIMO) two-way relaying are being actively explored. Most of the state-of-the-art studies optimize a system-wide objective function subject to the transmit power constraints on the two source nodes and the relay. Transceiver designs with quality-of-service (QoS) constraints have lacked attention in two-way relaying literature. In this paper, we study a MIMO transceiver design, based on the generalized singular value decomposition, that allocates power at the source and relay nodes to optimize the following per-stream rate-constrained objectives: 1) network transmit power, and 2) sum-rate. In addition, we also maximize the rate of the transmit stream with the worst signal-to-noise ratio. Through extensive numerical evaluations, we demonstrate the superior performance of proposed design over the existing ones, not only with QoS constraints but also without them.
Precoder design for asymmetric multi-user two-way AF relaying in cellular systems
Two-way relaying reduces the loss in spectral efficiency caused in a conventional half-duplex relay due to two channel uses per data unit transmitted to the destination. Two-way relaying is possible when two nodes exchange data simultaneously through a relay. In the case of cellular systems, data exchange between base station (BS) and users (UE) is usually not symmetric, e.g., a user (UE1) might have uplink data to transmit during multiple access (MAC) phase, but might not have downlink data to receive during broadcast (BC) phase. This asymmetry in data exchange will reduce the gains of two-way relaying. In the case of infrastructure relays, where there are multiple users communicating through a relay, we propose that the BC phase following the MAC phase of UE 1 be used by the relay to transmit downlink data to a second user (UE2). Conventional two-way relaying with symmetric MAC and BC phases must now be modified to asymmetric MAC (BS → RS ← UE1) and BC phases (BS ← RS → UE2), respectively. This will result in UE2 not being able to cancel the back-propagating interference in the usual way. We design precoders using conventional zero-forcing and linear minimum-mean-square-error criteria to mitigate the back-propagating interference at UE2 for an amplify-and-forward (AF) relay. We also propose a novel precoder appropriate for the asymmetric two-way relaying. The sum-rate performance of the proposed precoder is shown to be better than the conventional precoders. © 2013 IEEE.
Transceiver Design for Nonconcurrent Two-Way MIMO AF Relaying with QoS Guarantees
We consider a cellular system with amplify-and-forward (AF) nonconcurrent two-way relaying (ncTWR), where a base station serves a transmit-only user and a receive-only user. Most of the state-of-the-art transceiver designs for AF multiple-input multiple-output (MIMO) ncTWR optimize a system-wide objective function subject to the transmit power constraints. Transceiver designs that incorporate quality-of-service (QoS) constraints are not well investigated in ncTWR literature. In this paper, we design a MIMO AF transceiver that maximizes weighted sum-rate (WSR) while guaranteeing the QoS constraints that are cast as per-stream rate required by two ncTWR users. The WSR maximization is a nonconvex problem due to its nonconvex objective. We solve this problem by separately approximating the objective at low and high signal-to-noise ratios (SNRs), with each approximation cast as a geometric program. With extensive numerical evaluations, we first demonstrate the improved performance of the proposed transceiver over existing designs without QoS constraints. We later investigate the effect of QoS constraints on the system WSR.
Diagonalized two-way MIMO AF relaying for non-simultaneous traffic in cellular systems
A novel multiple-input multiple-output (MIMO) channel-diagonalization design is proposed for non-simultaneous two-way relaying (NS-TWR). Unlike conventional TWR, the base station in NS-TWR serves two different users - a transmit-only user and a receive-only user. The receive-only user experiences back-propagating interference (BI). The proposed design, which uses linear receivers, cancels the BI and diagonalizes the end-to-end MIMO channels. The diagonalized NS-TWR overcomes the restrictive antenna configurations of existing designs and yields substantial sum-rate improvement over them.
Joint precoder and receiver design for AF non-simultaneous two-way MIMO relaying
We investigate a joint design of linear precoders and receivers for multiple-input multiple-output non-simultaneous two-way relaying (NS-TWR). Unlike conventional two-way relaying, the base station in NS-TWR performs two-way relaying with two different users - a transmit-only user and a receive-only user (RUE). The RUE experiences back-propagating interference (BI). The proposed design cancels this BI and provides beamforming gain over existing designs. For NS-TWR, we maximize the weighted sum-rate (WSR) through joint power allocation, by solving a sequence of geometric programs. The precoder and the receiver designs as well as the power allocation program are then extended for a multi-user system with multiple transmit-only and receive-only users. With exhaustive simulations, we show that the proposed design provides significantly better WSR than the existing ones. The proposed design is also evaluated in a cellular framework using realistic path loss models, to assess the system-level performance gain achievable.