Multiple-input Multiple-output Switching Research Articles

Wireless MIMO Switching With Imperfect CSI in Frequency and Time Division Duplex

This paper investigates the robust transceiver design in a wireless multiple-input multiple-output (MIMO) switching network in which multiple users exchange messages via a multi-antenna relay. Previous works assume that perfect channel state information (CSI) is known at the relay, which is intractable in practice. In this paper, channel uncertainty is considered in both frequency division duplex (FDD) and time division duplex (TDD) systems. Regarding different types of CSI imperfection of uplink and downlink transmission in FDD, a statistical and norm-bounded uncertainty models are adopted to characterize the imperfect CSI of uplink and downlink, respectively. In contrast to FDD, the uplink and downlink channels are reciprocal in TDD, and an identical statistical model is adopted for both uplink and downlink channel uncertainty. For each duplex system, an optimization problem is formulated by minimizing the worst-case mean square error (MSE) with respect to channel uncertainty in the constraint of the maximum transmit power of the relay. In FDD, since the problem is non-convex and difficult to solve, we divide the original problem into two subproblems in which the channel uncertainty of uplink and downlink are treated individually. For the uplink subproblem, we propose an iterative approach to determine a closed-form solution of the robust transceiver. In addition, a Sylvester equation is formulated which closed-form solution is provided explicitly for the downlink channel uncertainty subproblem. An overall iterative algorithm is proposed by combining the two algorithms for the subproblems, which can solve the original problem efficiently. Moreover, in TDD, the optimization problem is non-convex and difficult to solve as well. However, the involved channel uncertainty reduces to uplink only due to the reciprocity of uplink and downlink. We propose an iterative algorithm directly for the overall problem to determine the robust transceiver for TDD systems. The simulation results show that the proposed iterative algorithms reduce the sum MSE efficiently and outperform the existing schemes in the channel uncertain scenarios, which validate our conclusion.

Optical comb enabled flexible‐bandwidth single‐carrier frequency‐division‐multiplexed‐based intra‐data centre interconnect

In this study, the authors propose a novel intra-data centre network (DCN) architecture based on cascaded micro-electro-mechanical system switches for dynamic DCN connectivity provisioning. Through combining the single-carrier frequency-division-multiplexed with the proposed architecture, this structure can achieve unprecedented flexibility in dealing with both mice and elephant flow in the DCN. Multiple-input multiple-output switching is experimentally demonstrated through intra- and inter-data centre switching scenarios. A numerical investigation is also performed to evaluate the performance of the fixed-grid transceivers, flex-grid transceivers and mixed-fixed/flex grid transceivers in the same switching scenario. The results show that the flex-grid transceivers significantly reduced the service latency and blocking probability compared to the fixed-grid transceivers. The proposed architecture would be better applied in the field of all-optical DCNs.

Performance of adaptive MIMO switching for cognitive MC-CDMA system

The future 5G wireless network will be identified by flexibility design, high combination of services, and higher data rate. In this treatise, we present the performance evaluation physical layer design for multi-carrier code-division-multiple-access (MC-CDMA) system for cognitive radio network (CRN) employing link adaptive multiple-input multiple- output (MIMO). CRN in conjunction with MIMO promises to achieve massive amelioration in system bandwidth. We consider link adaption scheme (LAS) which will select modulation scheme and MIMO profile based on channel parameters. CRN is a device in wireless communication which can sense the idle unused spectrum and allocate the spectrum dynamically to base station. We utilize sub-band frequency of CRN for multi-carrier communication and to extract for user-specific spreader in CDMA system. Further, we realize iterative decoder at the receiver to achieve better error-rate performance for CRN based MIMO MC-CDMA system with less signal-to-noise ratio (SNR). Furthermore,We study the performance of adaptive MIMO scheme with CRN defined MC-CDMA for Stanford University Interim channel model specifications. We discern through computer simulations that CRN based MC-CDMA system with adaptive MIMO scheme achieves significant performance enhancement both in error-rate and data rate.

Wireless MIMO Switching: Weighted Sum Mean Square Error and Sum Rate Optimization

This paper addresses joint transceiver and relay design for a wireless multiple-input multiple-output (MIMO) switching scheme that enables data exchange among multiple users. Here, a multiantenna relay linearly precodes the received (uplink) signals from multiple users and forwards the signal in the downlink, where the purpose of precoding is to let each user receive its desired signal with interference from other users suppressed. The problem of optimizing the precoder based on various design criteria is typically nonconvex and difficult to solve. The main contribution of this paper is a unified approach to solve the weighted sum mean square error (MSE) minimization and weighted sum rate maximization problems in MIMO switching. Specifically, an iterative algorithm is proposed for jointly optimizing the relay's precoder and the users' receive filters to minimize the weighted sum MSE. It is also shown that the weighted sum rate maximization problem can be reformulated as an iterated weighted sum MSE minimization problem and can, therefore, be solved similarly to the case of weighted sum MSE minimization. With properly chosen initial values, the proposed iterative algorithms are asymptotically optimal in both high- and low-signal-to-noise-ratio regimes for MIMO switching, either with or without self-interference cancellation (a.k.a., physical-layer network coding). Numerical results show that the optimized MIMO switching scheme based on the proposed algorithms significantly outperforms existing approaches in the literature.

Design and Evaluation of a Flexible-Bandwidth OFDM-Based Intra-Data Center Interconnect

Data center networks are facing growing challenges to deliver higher bandwidth efficiency, lower latency, better flexibility, and lower cost. Various optical interconnect schemes have been proposed to take advantage of the high bandwidth capacity and low power consumption offered by optical switching. However, these schemes cannot offer flexible bandwidth sharing due to the large granularity in optical circuit switching, and they require costly optical components. In this paper, we introduce a novel data center network architecture based on cyclic arrayed waveguide grating device and multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing technology with parallel signal detection (PSD). This architecture offers flexible bandwidth resource sharing at fine granularity. Other features include high-speed switching, low and uniform latency, and the ability to change the data rates dynamically. By eliminating costly optical components and keeping the core optical router passive and static, the power consumption, hardware cost, and operation cost are reduced. The fine granularity bandwidth sharing and MIMO switching through PSD are verified experimentally. We also propose and evaluate efficient subcarrier allocation schemes to achieve high bandwidth utilization. Finally, we present the implementation of an efficient scheduler for the bandwidth allocation of the proposed scheme.

Wireless MIMO switching: network‐coded MMSE relaying and user group selection

ABSTRACTA wireless relay that forms a one‐to‐one mapping from the inputs (uplinks) to the outputs (downlinks) is called a multiple‐input multiple‐output (MIMO) switch. The MIMO switch carries out precode‐and‐forward, where all users send their signals in the uplink, and then, the MIMO switch precodes the received vector signal for broadcasting in the downlink. Ideally, each user employs a receive filter to recover its desired signal from one other user with no or little interference from other users. We first propose a joint design of the precoder and the receive filters to achieve the minimum‐mean‐ square‐error (MMSE), where network coding technique is incorporated, assuming that full channel state information is available at the relay. When the number of relay antennas is smaller than the number of source users, that is, the users that need to transmit signals, we investigate user group selection algorithms for the proposed MMSE relaying schemes. Our results indicate that the proposed MMSE relaying scheme outperforms the existing zero‐forcing/MMSE schemes. In addition, the results validate the efficiency of the proposed user group selection algorithms. Copyright © 2012 John Wiley & Sons, Ltd.

Performance analysis of dual-cell HSDPA plus MIMO and LTE along with adaptive MIMO switching at the cellular level

The main target of this research work is to present the performance analysis of Dual-Cell High Speed Downlink Packet Access (DC-HSDPA) plus Multiple Input Multiple Output (MIMO) supported by sophisticated Power Control (PC) with Long Term Evolution (LTE) integrated with Adaptive MIMO Switching (AMS). A simple approach of power allocation for DC-HSDPA in the downlink direction is presented in this paper, in which power resources are dynamically allocated to the users, irrespective of the number of code utilizations. This paper also highlights the impact of efficient power allocation in DC-HSDPA compared to conventional DC-HSDPA without any PC. In addition to different Intersite Distance (ISD), the impact of serving variable numbers of users per Transmission Time Interval (TTI) was also analyzed in terms of average cell throughput, relative throughput gain, and user’s probability of no data transfer in a macrocellular environment.Simulation results revealed that at 500 m ISD LTE exhibits better performance with AMS compared to spatial multiplexing, and it offered an average cell throughput of around 47 Mbps with nearly 5.5% user’s probability of no data transfer. It was learned that DC-HSDPA performance improves by adopting a PC scheme in the Downlink (DL) direction. At small ISD, DC-HSDPA with MIMO provides an average cell throughput of around 19.5 and 13.7 Mbps with and without PC, respectively.

Very-large-scale integration hardware implementation of adaptive space–time coding/spatial multiplexing switching

Multiple input multiple output (MIMO) techniques are widely employed in modern wireless systems. The most prominent approaches to MIMO communication are space–time coding (STC) and spatial multiplexing (SM). Less studied is a hybrid technique called adaptive MIMO switching (AMS), which may be employed by fixing the transmission rate and selecting between space–time block coding and SM transmission modes based on instantaneous channel conditions to achieve the most efficient link. This study presents a hardware implementations of a selector algorithm and a detector employing it. The detector is designed for a 2×2 MIMO system and was implemented on an Altera Cyclone II FPGA. In addition, two transmission protocols with decision feedback from the receiver to the transmitter via a low-rate feedback channel are introduced and the feasibility of switching for high-data-rate transmissions is discussed.

A Pragmatic PHY Abstraction Technique for Link Adaptation and MIMO Switching

MIMO (multiple input multiple output) techniques are widely employed to improve the performance of wireless systems. These techniques are used to overcome multipath fading and/or improve the peak throughput of wireless systems. It is well known that there is a fundamental tradeoff between diversity gain and multiplexing gain [1]. Orthogonal space time codes such as the Alamouti code (also known as space time block codes (STBC)) exploit multiple antennas as a diversity source, and thus improve packet error rate (PER) and the average throughput. However, space time block codes are not designed to increase the peak data rate of the system. On the other hand, spatial multiplexing (SM) techniques offer higher peak throughput by transmitting parallel streams of data from different antennas. In order to successfully decode the parallel streams, the channel must exhibit a small eigenvalue spread. Otherwise, the streams will interfere with one another and it is difficult to decode the information data. The performance improvement from SM is therefore highly dependent on the channel characteristics. It is possible to use multiple encoders and rate control per layer to improve the SM performance. However, there are instances of channel where STBC is more beneficial than SM with a single encoder. In order to resolve the shortcomings of STBC and SM, a hybrid technique can be applied where depending on the instantaneous channel conditions either STBC or SM is selected. This technique is commonly referred to as adaptive MIMO switching (AMS) [5]-[11]. One important aspect of the technique is the switching criteria, namely the PHY abstraction method which estimates a packet error event as a function of the instantaneous channel condition, transmission profiles, and receiver characteristics. We show that the proposed algorithm outperforms other techniques such as determinant and Demmel condition number based techniques in flat fading channel. In selective fading channels where a codeword sees a finite number of multiple channel qualities, estimating the resulting PER is very challenging. Existing techniques rely on an estimate of the average of the channel qualities seen by each codeword. In this paper, we propose a PHY abstraction and switching algorithm hereby referred to by weighted sum of instantaneous qualities (WSIQ) whereby the channel qualities are ordered in order to reduce the variance of channel qualities and then a weighted sum of the qualities is applied. The weighting vector is chosen to minimize the variance of the linear sum. We have provided simulations to show the superiority of WSIQ even when channel statistics are unknown. In addition, computationally efficient techniques suited for practical implementation are proposed.