Effect Of Outdated Channel State Information Research Articles

MIMO-Aided Nonlinear Hybrid Transceiver Design for Multiuser Mmwave Systems Relying on Tomlinson-Harashima Precoding

Hybrid analog-digital (A/D) transceivers designed for millimeter wave (mmWave) systems have received substantial research attention, as a benefit of their lower cost and modest energy consumption compared to their fully-digital counterparts. We further improve their performance by conceiving a Tomlinson-Harashima precoding (THP) based nonlinear joint design for the downlink of multiuser multiple-input multiple-output (MIMO) mmWave systems. Our optimization criterion is that of minimizing the mean square error (MSE) of the system under channel uncertainties subject both to realistic transmit power constraint and to the unit modulus constraint imposed on the elements of the analog beamforming (BF) matrices governing the BF operation in the radio frequency domain. We transform this optimization problem into a more tractable form and develop an efficient block coordinate descent (BCD) based algorithm for solving it. Then, a novel two-timescale nonlinear joint hybrid transceiver design algorithm is developed, which can be viewed as an extension of the BCD-based joint design algorithm for reducing both the channel state information (CSI) signalling overhead and the effects of outdated CSI. Moreover, we determine the near-optimal cancellation order for the THP structure based on the lower bound of the MSE. The proposed algorithms can be guaranteed to converge to a Karush-Kuhn-Tucker (KKT) solution of the original problem. The simulation results demonstrate that our proposed nonlinear joint hybrid transceiver design algorithms significantly outperform the existing linear hybrid transceiver algorithms and approach the performance of the fully-digital transceiver, despite its lower cost and power dissipation.

Secrecy Outage for Wireless Sensor Networks

This letter addresses physical layer security (PLS) for a wireless sensor network, in which multiple sensor nodes communicate with a single sink in the presence of an eavesdropper. Under the assumption of sink using outdated channel state information (CSI) of the eavesdropper link, the outage probability of achievable secrecy rate under Weibull fading is investigated and its analytical expressions are derived. Specifically, we consider sensor scheduling to enhance PLS, thereby, we quantify the degradation in outage probability due to outdated CSI under the best-node scheduling scheme and compare it with conventional round-robin scheduling. Finally, we analyze secrecy outage probability conditional on successful transmission and provide practical insights into the effect of outdated CSI of the eavesdropper. The derived theoretical results are validated through simulations.

Inter-vehicle cooperation channel estimation for IEEE 802.11p V2I communications

The impact of imperfect channel state information (CSI) is particularly serious in vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications. Considering the sparse characteristics of V2I channels, this paper proposes an inter-vehicle cooperation channel estimation (IVC-CE) method at the IEEE 802.11p physical layer, and the effects of outdated CSI can be mitigated by single or multiple vehicle measurements. With these assisted measurements, we can develop an interpolation-assisted channel estimation technique to obtain accurate CSI. To select optimum measurements from a group of channel estimates, we utilize the position and velocity of a vehicle as a priori information. We investigate the validity of the IVC-CE technique with the traditional linear minimum mean-squared error algorithm and present a scalable data transmission scheme at the physical layer. The performance of IVC-CE is analyzed by its mean squared error and bit error rate in a fast fading channel environment. Simulations and numerical results show the merits of the proposed techniques, which can significantly enhance estimation performance and support safety related data transmissions for vehicular ad hoc networks.

Outage performance and ergodic capacity of multiuser cognitive MIMO AF relaying systems with MUS/MRT/RAS over Nakagami‐m fading channels

AbstractTo improve the performance of cognitive spectrum‐sharing systems and to reduce the implementation complexity of multiple antenna systems, a cognitive multiple‐input multiple‐output (MIMO) amplify‐and‐forward relay cooperation (C‐MIMO AF‐RC) multiuser system is considered over Nakagami‐m fading channels by integrating maximum ratio transmission (MRT), multiuser selection (MUS) and receive antenna selection (RAS) techniques. In the C‐MIMO AF‐RC multiuser systems, all secondary users (SUs) are equipped with multiple antennas while the primary users (PUs), single antenna. The interested cognitive systems are investigated under the case where the systems have perfect or imperfect channel state information (CSI) of both the SUs–SUs and SUs–PUs links so that the effect of outdated CSI can be achieved. Specially, we first obtain the exact closed‐form expressions of the cumulative distribution function of end‐to‐end signal‐to‐noise ratio. Secondly, we perform a comprehensive comparison investigation on outage probability and ergodic capacity. Specially, based on moment generating function, the exact closed‐form expression of ergodic capacity is achieved. Finally, to highlight the insight of the effect of key system parameters, the high signal‐to‐noise ratio asymptotic analysis of outage probability is performed as well as diversity and coding gains, by considering the two cases where the systems have perfect or imperfect CSI of both the SUs–SUs and SUs–PUs links. The derivations clearly show that the CSI concerning SUs–PUs links only affects the coding gain, but not the diversity order. However, the CSI concerning the SUs–SUs links plays a key role on the achievable diversity order. In particular, when the CSI of SUs–SUs links is perfect, the C‐MIMO AF‐RC multiuser systems achieve the full diversity including not only MRT diversity but also MUS and RAS diversities. In contrast, when the CSI concerning secondary links is outdated, the MUS and RAS diversities disappear, and the MUS and RAS only improve coding gain. The remaining diversity is achieved through MRT.

Random Linear Network Coding Based on Outdated Channel-State Information

Scheduling based on random linear network coding is an effective way of improving system performance in a wireless network. In a time-varying channel environment, it is important to take the effects of outdated channel-state information (CSI) into consideration when scheduling because the CSI used may be different from the real CSI for data transmissions due to mobility and feedback delays. Here, we analyze the outage probability for scheduling based on random linear network coding in an outdated CSI environment. Practical scenarios are assessed so that the outage probability performance can be evaluated reliably.

Cooperative Distributed Beamforming With Outdated CSI and Channel Estimation Errors

This paper investigates the effect of imperfect channel state information (CSI) on the outage performance of cooperative distributed beamforming (DBF). The acquisition of perfect CSI is disturbed by outdated CSI and channel estimation errors. Decode-and-forward relays are considered with individual power constraints at each relay. Considering a training-and-feedback strategy to acquire CSI, a closed-form approximate expression for outage probability and the achievable diversity gain are first provided under Rayleigh fading channels. Numerical observations verify that the approximation is very tight. It is shown that outdated CSI seriously degrades the performance, and therefore, the outage probability is bounded and no diversity is achieved. Conversely, channel estimation errors cause slight performance degradation, and full diversity order is still achievable. However, even when CSI is outdated, it is shown that the asymptotic outage decreases as the number of relays $K$ increases, where the logarithm of the outage probability decreases at the rate of $K\log K$ . This paper shows that, when the destination re-estimates the current CSI for decoding, the effect of outdated CSI is greatly mitigated and consequently achieves a diversity gain of one. To re-estimate the current CSI with small overhead, the beamformed training sequence (BFTS) strategy is proposed, in which a new closed-form formula for minimum-mean-square-error estimation is presented using Gaussian approximation. Numerical results verify that the outage performance with the proposed BFTS scheme is close to that of a perfect estimation. A closed-form outage expression of DBF with the proposed BFTS scheme is also presented under an assumption of high-signal-to-noise ratio (SNR), but the expression is very tight even in low-to-moderate SNR regimes.

Impact of outdated channel state information on energy efficiency of co‐operative hybrid automatic repeat reQuest in wireless sensor networks

Co-operative communication has been shown to significantly improve energy efficiency in wireless sensor networks. The outdated channel state information (CSI) problem will result in severe performance degradation of co-operative communication systems including energy efficiency. In this study, the authors analyse the impact of outdated CSI on energy efficiency of amplify-and-forward co-operative hybrid automatic repeat reQuest system. The authors derive the expression of the average energy consumption per bit of data transmission under outdated CSI. Numerical results show the deteriorating effects of outdated CSI on the performance of energy efficiency and transmission reliability in co-operative communication system. It is also shown that energy efficiency can be improved by error correcting codes mechanism when end-to-end signal-to-noise ratio at the destination node is within a certain range.

Performance Analysis of TAS/MRC in MIMO Relay Systems With Outdated CSI and Co-Channel Interference

In this paper, we investigate the impact of outdated channel state information (CSI) and multiple co-channel interferers (CCI) on the performance of transmit antenna selection/receiver maximal-ratio combining (TAS/MRC) in a dual-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network. The tight lower bound and asymptotic expressions for the outage probability are derived. The diversity order of the system with/without outdated CSI in the presence of multiple CCI is further discussed. Numerical and simulation results are presented to validate our analysis and to demonstrate the effect of outdated CSI and multiple CCI on the system performance.

Relay Selection for Bidirectional AF Relay Network With Outdated CSI

Most previous works on relay selection (RS) of bidirectional relay networks typically assume perfect channel state information (CSI). However, outdated CSI, which is caused by the time variation of channels, cannot be ignored in the practical system, and it will deteriorate performance. In this paper, the effect of outdated CSI on the performance of bidirectional amplify-and-forward (AF) RS is investigated. The optimal single-RS scheme in minimizing the symbol error rate (SER) is revised by incorporating the outdated channels. The analytical expression of the end-to-end SER is derived in a closed form, along with the asymptotic SER expression in a high SNR. All the analytical expressions are verified by Monte Carlo simulations. The analytical and simulation results reveal that once CSI is outdated, the diversity order degrades to one from full diversity. Furthermore, a multiple-RS scheme is proposed, which is a feasible solution to compensate the diversity loss caused by outdated CSI.

On the Performance of AF Opportunistic Relaying over Non-identically Distributed Links with Outdated CSI

This paper presents an analysis of the performance of amplify-and-forward (AF) opportunistic relaying systems over independent and non-identically distributed (i.ni.d.) Rayleigh fading links with outdated channel state information (CSI). A closed-form expression is derived for the moment generating function (MGF) of the end-to-end SNR at the destination under outdated CSI conditions. Using that expression, closed-form expressions are derived for the average bit error rate (BER) performance of several M-ary modulations, and the average SNR gains obtained from AF opportunistic relaying. Asymptotic analyses for the BER and achievable diversity order of the system are also presented. Using the derived analytical expressions the deteriorating effects of outdated CSI and the differences over i.i.d. and i.ni.d. Rayleigh fading links are evaluated and discussed.

Interference-Aware Scheduling for Connectivity in MIMO Ad Hoc Multicast Networks

We consider a multicast scenario that involves an ad hoc network of cochannel multiple-input-multiple-output (MIMO) nodes in which a source node attempts to share a streaming message with all nodes in the network through some predefined multihop routing tree. The message is assumed to be broken down into packets, and the transmission is conducted over multiple frames. Each frame is divided into time slots, and each link in the routing tree is assigned one time slot in which to transmit its current packet. We present an algorithm for determining the number of time slots and the scheduling of the links in these time slots to optimize the connectivity of the network, which we define to be the probability that all links can achieve the required throughput. In addition to time multiplexing, the MIMO nodes also employ beamforming to manage interference when links are simultaneously active, and the beamformers are designed with the maximum connectivity metric in mind. The effects of outdated channel-state information are taken into account in both the scheduling and the beamforming designs. We also derive bounds on the network connectivity and sum transmit power to illustrate the impact of interference on network performance. Our simulation results demonstrate that the choice of the number of time slots is critical in optimizing network performance and illustrates the significant advantage provided by multiple antennas in improving network connectivity.

Symbol Error Rate of MIMO MRC Systems over Time-Varying Fading Channels

The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combining. Closed-form expressions for the cumulative distribution function of output signal-to-noise ratio and symbol error rate under time-varying channels are presented to evaluate the effect of outdated CSI. The analytical results are compared with Monte Carlo simulations and a good agreement is obtained.