Partial Channel State Information Research Articles

On the Performance of Non-orthogonal Multiple Access Systems With Partial Channel Information

In this paper, a downlink single-cell non-orthogonal multiple access (NOMA) network with uniformly deployed users is considered and an analytical framework to evaluate its performance is developed. Particularly, the performance of NOMA is studied by assuming two types of partial channel state information (CSI). For the first one, which is based on imperfect CSI , we present a simple closed-form approximation for the outage probability and the average sum rate, as well as their high signal-to-noise ratio (SNR) expressions. For the second type of CSI, which is based on second order statistics (SOS) , we derive a closed-form expression for the outage probability and an approximate expression for the average sum rate for the special case two users. For the addressed scenario with the two types of partial CSI, the results demonstrate that NOMA can achieve superior performance compared to the traditional orthogonal multiple access (OMA). Moreover, SOS-based NOMA always achieves better performance than that with imperfect CSI, while it can achieve similar performance to the NOMA with perfect CSI at the low SNR region. The provided numerical results confirm that the derived expressions for the outage probability and the average sum rate match well with the Monte Carlo simulations.

밀리미터파 전 이중 시스템에서의 혼성 스케줄링

다중 경로 약한 산란 (poor scattering) 전 이중 (full-duplex) 시스템에서 혼성 스케줄링을 소개한다. 제안하는 시스템은 다중 안테나를 갖는 하나의 전 이중 기지국과 수 많은 단일 안테나 반 이중 (half-duplex) 단말로 구성된다. 혼성 스케줄링은 송신기에서의 부분적 채널 정보만을 활용한다. 특별히, 상향링크 및 하향링크에서 모두 기회적 송신 기술을 사용하는 기존 스케줄링 방법과는 달리, 제안하는 기술은 하향링크에서의 랜덤 송신 빔형성 및 상향링크에서의 간섭 제거 빔형성을 결합하여 사용한다. 주요 결과로써, 컴퓨터 모의실험을 통해 제안한 기술이 기존 스케줄링 방법보다 특정 신호 대 잡음비 영역 이상에서 훨씬 더 우수한 합 용량 성능을 가짐을 보인다. We introduce a hybrid scheduling in a multi-path poor scattering full-duplex (FD) system, which consists of one multi-antenna FD base station and a large number of single-antenna half-duplex mobile stations. Our hybrid scheduling utilizes partial channel state information at the transmitter. In particular, unlike the conventional scheduling method using opportunistic transmission for both uplink and downlink, the proposed scheme combines a random transmit beamforming for downlink and a zero forcing beamforming for uplink. As our main result, via computer simulations, it is shown that the proposed scheme has a superior sum-rate performance than that of the conventional scheduling method beyond a certain signal-to-noise ratio regime.

Achievable Rates of Cognitive Radio Networks Using Multi-Layer Coding with Limited CSI

In a cognitive radio (CR) framework, the channel state information (CSI) feedback to the secondary transmitter (SU_Tx) can be limited or unavailable. Thus, the statistical model is adopted to determine system performance using the outage concept. In this paper, we adopt a new approach using multilayer-coding (MLC) strategy, i.e., broadcast approach, to enhance spectrum sharing over fading channels. First, we consider a scenario where the SU_Tx has no CSI of both the link between the SU_Tx and the primary receiver (cross link) and its own link. We show that using MLC improves the cognitive rate compared with the rate provided by a single-layer coding (SLC). In addition, we observe numerically that two-layer coding achieves most of the gain for Rayleigh fading. Second, we analyze a scenario where SU_Tx is provided by partial CSI about its link through quantized CSI. We compute its achievable rate, adopting the MLC and highlight the improvement over SLC. Finally, we study the case in which the cross link is perfect, i.e., a cooperative primary user setting, and compare the performance with the previous cases. We present asymptotic analysis at the high-power regime and show that the cooperation considerably enhances the cognitive rate at high values of the secondary power budget.

On the Secrecy Rate Maximization with Uncoordinated Cooperative Jamming by Single-Antenna Helpers

A practical uncoordinated cooperative jamming (UCJ) scheme is proposed in this paper to enhance the physical layer security of the single-input-single-output (SISO) wiretap channel. Differing from the existing works, all the helpers in this UCJ scheme are uncoordinated single-antenna uplink users, and each helper transmits a jamming signal independently to confound the eavesdropper. The intended receiver plays the role of base station in the cellular systems as well as a control center to properly allocate the jamming power of each helper to maximize the secrecy rate. Two cases are addressed in solving the secrecy rate maximization problem, namely, the global channel state information (CSI) case and the partial CSI case. The optimal solution is obtained in the global CSI case, and a near-optimal solution is obtained under the secrecy outage probability constraint in the partial CSI case. Numerical results show that the performance of the proposed scheme is comparable with the existing works.

Distortion Outage Minimization in Distributed Estimation With Estimation Secrecy Outage Constraints

In this paper, we investigate a class of distortion outage minimization problems for a wireless sensor network in the presence of an eavesdropper. The observation signals transmitted from the sensors to the fusion center (FC) are overheard by the eavesdropper. Both the FC and the eavesdropper reconstruct minimum mean squared error estimates of the physical quantity observed. We address the problem of transmit power allocation to minimize the distortion outage at the FC, subject to an expected total transmit power constraint across the sensor(s) and a secrecy outage constraint at the eavesdropper. Applying a rigorous probabilistic power allocation technique, we derive power policies for the full channel state information (CSI) case. Suboptimal power control policies are studied for the partial CSI case in order to reduce the high computational cost associated with large numbers of sensors or receive antennas. Numerical results show that significantly improved performance can be achieved by adding multiple receive antennas at the FC. In the case of multiple transmit antennas, the distortion outage at the FC can be dramatically reduced and in some cases completely eliminated, by transmitting the observations on the null space of the eavesdropper's channel or deploying an artificial noise technique, in the full CSI and partial CSI cases, respectively.

Self-Organized Inter-Cell Interference Coordination Based on Partial CSI Sharing in Heterogeneous Networks Employing Cell Range Expansion

Self-Organized Inter-Cell Interference Coordination Based on Partial CSI Sharing in Heterogeneous Networks Employing Cell Range Expansion

Power allocation for two‐user cognitive multiple access channels under primary user outage constraint

SummaryWe consider a two‐user spectrum sharing cognitive radio multiple access channel (CR‐MAC) coexisting with a pair of primary users (PUs). Different from the existing works in CR‐MAC where the interference power constraint is applied to protect the PU transmission, a more advanced protection criterion over the interference power constraint, namely, PU outage constraint, is adopted in this paper not only to protect the PU transmission but also improve the performance of the CR‐MAC. Under such a constraint, as well as the transmit power constraint, and assuming that perfect channel state information (CSI) is available, two heuristic power allocation algorithms for the secondary users based on dual optimization are proposed. The objective is to maximize the ergodic sum capacity of the CR‐MAC without successive interference cancelation (SIC). One algorithm applies alternating direction optimization method to derive an iterative power allocation, while the other algorithm adopts exclusive transmission to determine the power allocation. Besides, we extend our results to the multi‐user and partial CSI scenarios. It is shown by extensive simulations that the proposed algorithm based on alternating direction optimization method always outperforms the existing algorithms based on the interference power constraint, while the proposed algorithm based on exclusive transmission outperforms the existing algorithms for medium and large values of the transmit power limit. Copyright © 2015 John Wiley & Sons, Ltd.

Robust Beamforming With Partial Channel State Information for Energy Efficient Networks

In this paper, we investigate robust beamforming to improve the energy efficiency (EE) of wireless networks when only imperfect or partial channel state information (CSI) is available at the transmitter. Due to CSI quantization errors and/or limited feedback information, CSI imperfections can be well modeled by a bounded uncertainty region. We focus on the worst case robust beamforming strategy to optimize the EE of downlink transmission under the deterministic bounded channel model, which merely assumes a maximal channel error magnitude. We start with a single-user single-cell MIMO system and obtain a closed-form design for robust beamforming. For a multicell network, robust beamforming is in a nonconvex fractional form, and the solution cannot be directly extended from the single-cell scenario. To solve this problem efficiently, we resort to a lower bound, instead of the primal problem, and cast it as a semidefinite program (SDP). The robustness and efficiency of the proposed beamforming design are confirmed by computer simulation results.

Resource Allocation for Secret Key Agreement Over Parallel Channels With Full and Partial Eavesdropper CSI

We consider the distillation phase of the secret key agreement (SKA) channel model for users connected through parallel additive white Gaussian noise fading channels. Alice sends binary phase shift keying modulated random bits to Bob who selects the subset of bits that have a log-likelihood ratio higher than a given threshold, i.e., they are sufficiently reliable. Alice has either full or partial channel state information (CSI) on her channel to the eavesdropper Eve. The main contributions of this paper are: 1) the derivation of the expression of outage probability when partial CSI is available; 2) the introduction of (outage) secret key throughput (SKT) as a metric in the full (partial) CSI scenario; 3) the derivation of SKT bounds; 4) the proposal of a new power allocation and threshold choice algorithm that maximizes the SKT under an outage probability constraint; and 5) the derivation of a suboptimal version of the allocation algorithm amenable for practical implementation obtained by approximating the objective functions with a closed-form expression. Moreover, we show that when power allocation and thresholds are optimized, per-channel and joint SKA are equivalent.

An Adaptive Threshold Based CQI Compression Scheme for LTE Cellular Networks

The frequency domain scheduling gain can be maximized when precise channel information is available at the eNodeB for the whole bandwidth. To compensate for the continuous variations of channel conditions in time and frequency domains, a huge undesirable amount of signaling overhead is required to report the channel quality indicator (CQI). On the contrary, partial channel state information detriments the downlink performances and does not guarantee the quality-of-service (QoS) when real-time multimedia services are applied. Thus, in this paper, the impact of CQI signaling overhead on the downlink performances is formulated. Then, an adaptive signal-to-interference-plus-noise ratio (SINR) threshold based CQI scheme is proposed by using multi-objective swarm intelligence to find the optimal feedback threshold. Based on an LTE system-level simulation, significant enhancements of 20% and 38% in throughput and packet loss ratio (PLR) respectively are obtained compared to a fixed threshold feedback with reasonable cost of feedback overhead. The proposed algorithm provides a high flexibility in responding to certain variations without complex modifications

Jamming partner selection for maximising the worst D2D secrecy rate based on social trust

AbstractDevice‐to‐device (D2D) communications have recently attracted broad attention, owing to its potential ability to improve spectrum and energy efficiency within the existing cellular infrastructure. Without sophisticated control, D2D users themselves are not powerful enough to resist eavesdropping or fight against security attacks. This work investigates how to select jamming partners for D2D users to thwart eavesdroppers by exploiting social relationship with the help of full channel state information (CSI) and partial CSI, respectively. We aim to maximise the worst‐case eavesdropping by selecting jammer node and allocating transmit power for both source and jammer nodes. We first present a heuristic genetic algorithm‐based solution to address the problem. We then propose low‐complexity optimisation solutions by considering the upper and lower bounds of power allocation. Numerical results show that the proposed schemes can achieve better performance through finding an appropriate partner. Copyright © 2015 John Wiley & Sons, Ltd.

On Quantization for Masked Beamforming Secrecy Systems

This study investigates how to quantize the masked beamforming systems to maximize the secrecy rate for MISOSE (multiple-input, single-output, single-eavesdropper) channels and assume that this eavesdropper equipped with only single antenna, where only partial channel state information (CSI) at the legitimate receiver is available to the transmitter. In this case, the artificial noise (AN) leaks to the legitimate receiver due to CSI quantization. In the literature, all quantization bits are used to quantize the beamforming vector. Then the null space of this quantized beamforming vector is used to transmit the AN. We find that such quantization schemes can result in serious interference at the legitimate receiver. To overcome this issue, we propose that the beamforming vector and the AN vector should be quantized separately, where the beamforming vector should be selected from a codebook to maximize the beamforming gain and the AN vector should be selected from another codebook to minimize the leakage (or interference). Theoretical results show that separate quantization can significantly reduce the AN leakage at the legitimate receiver. Furthermore, based on the proposed quantization scheme, we show how to allocate bits to separately quantize the beamforming vector and the AN vector to maximize the secrecy rate. By using the proposed quantization and bit allocation schemes, the secrecy rates of masked beamforming systems can be improved compared to the conventional quantization schemes. Simulation results corroborate the theoretical results.

Distributed Rate Adaptation and Power Control in Fading Multiple Access Channels

Traditionally, the capacity region of a coherent fading multiple access channel (MAC) is analyzed in two popular contexts. In the first, a centralized system with full channel state information at the transmitters (CSITs) is assumed, and the transmit power and data-rate can be jointly chosen for every fading vector realization. On the other hand, in fast-fading links with distributed CSIT, the lack of full CSI is compensated by performing ergodic averaging over sufficiently many channel realizations. Notice that the distributed CSI may necessitate decentralized power-control for optimal data-transfer. Apart from these two models, the case of slow-fading links and distributed CSIT, though relevant to many systems, has received much less attention. In this paper, a block-fading additive white Gaussian noise MAC with full CSI at the receiver and distributed CSI at the transmitters is considered. The links undergo independent fading, but otherwise have arbitrary fading distributions. The channel statistics and respective long-term average transmit powers are known to all parties. We first consider the case where each encoder has knowledge only of its own link quality, and not of others. For this model, we compute the adaptive capacity region, i.e., the collection of average rate-tuples under blockwise coding/decoding such that the rate-tuple for every fading realization is inside the instantaneous MAC capacity region. The key step in our solution is an optimal rate allocation function for any given set of distributed power control laws at the transmitters. This also allows us to structurally characterize the optimal power control for a wide class of fading models. Further extensions are also proposed for the case where each encoder has additional partial CSI about the other links.

Robust Interference Management via Linear Precoding and Linear/Non-Linear Equalization

This work studies the robust design of linear precoding and linear/ non-linear equalization for multi-cell MIMO systems in the presence of imperfect channel state information (CSI). A worst-case design approach is adopted whereby the CSI error is assumed to lie within spherical sets of known radius. First, the optimal robust design of linear precoders is tackled for a MIMO interference broadcast channel (MIMO-IBC) with general unicast/multicast messages in each cell and operating over multiple time-frequency resources. This problem is formulated as the maximization of the worst-case sum-rate assuming optimal detection at the mobile stations (MSs). Then, symbol-by-symbol non-linear equalization at the MSs is considered. In this case, the problem of jointly optimizing linear precoding and decision-feedback (DF) equalization is investigated for a MIMO interference channel (MIMO-IC) with the goal of minimizing the worst-case sum-mean squared error (MSE). Both problems are addressed by proposing iterative algorithms with descent properties. The algorithms are also shown to be implementable in a distributed fashion on processors that have only local and partial CSI by means of the Alternating Direction Method of Multipliers (ADMM). From numerical results, it is shown that the proposed robust solutions significantly improve over conventional non-robust schemes in terms of sum-rate or symbol error rate. Moreover, it is seen that the proposed joint design of linear precoding and DF equalization outperforms existing separate solutions.

Statistical Analysis of Multiantenna Relay Systems and Power Allocation Algorithms in a Relay With Partial Channel State Information

The performance of a dual-hop MIMO relay network is studied in this paper. The relay is assumed to have access to the statistical channel state information of its preceding and following channels and it is assumed that fading at the antennas of the relay is correlated. The cumulative density function (cdf) of the received SNR at the destination is first studied and closed-form expressions are derived for the asymptotic cases of the fully-correlated and non-correlated scenarios; moreover, the statistical characteristics of the SNR are further studied and an approximate cdf of the SNR is derived for arbitrary correlation. The cdf is a multipartite function which does not easily lend itself to further mathematical calculations, e.g., rate optimization. However, we use it to propose a simple power allocation algorithm which we call "proportional power allocation". The algorithm is explained in detail for the case of two antennas and three antennas at the relay and the extension of the algorithm to a relay with an arbitrary number of the antennas is discussed. Although the proposed method is not claimed to be optimal, the result is indistinguishable from the benchmark obtained using exhaustive search. The simplicity of the algorithm combined with its precision is indeed attractive from the practical point of view.

Rate–Interference Tradeoff in OFDM-Based Cognitive Radio Systems

In this paper, we investigate the tradeoff between increasing the secondary users' (SUs) transmission rate and reducing the interference levels at the primary users (PUs) for orthogonal-frequency-division-multiplexing-based cognitive radio systems. To achieve this target, we formulate a generalized multiobjective optimization (MOOP) problem that jointly maximizes the transmission rate of the SU and minimizes the cochannel interference (CCI) and adjacent channel interference (ACI) to existing PUs. We additionally constrain the allowed CCI and ACI to the PUs to guarantee the PUs' protection from harmful interference. The MOOP problem is solved by linearly combining the normalized competing objective functions—through weighting coefficients—into a single objective function. Prior work in the literature that maximizes the SU transmission rate can be considered as a special case of the generalized MOOP problem by setting the weighting coefficients associated with interference minimization to zero. Since estimating the full channel state information (CSI) of the links between the SU transmitter and the PU receivers is practically challenging, we assume only partial CSI knowledge of these links. Simulation results illustrate the performance of the proposed algorithm and quantify the SU performance loss due to incomplete CSI knowledge. Furthermore, the proposed algorithm is compared with state-of-the-art techniques, and our performance results show that the proposed algorithm is more energy aware, yet with reduced complexity.

Interference‐aware resource sharing in D2D underlaying LTE‐A networks

AbstractIn a device‐to‐device (D2D) underlaying cellular system, intra‐cell interference is no longer negligible, and such interference exists for sharing both uplink (UL) and downlink (DL) resources. This work presents a power and Physical Resource Blocks (PRBs) allocation algorithm to coordinate UL and DL interference in the D2D underlaying Long‐Term Evolution‐Advanced (LTE‐A) network. The objective is to find an effective and efficient mechanism to mitigate the interference between the two subsystems while maximising the weighted sum throughput. This optimisation problem is formulated as a mixed integer nonlinear programming, which is further decomposed into PRBs assignment and transmission power allocation. Analysis reveals that the proposed PRBs allocation strategy is energy‐efficient, and it suppresses the interference not only suffered by the LTE‐A system but also to the D2D users. In another side, the optimal power allocation is resolved by using a low‐complexity technique, and results show the optimal power resides in one of at most four feasible power vectors. Specifically, the scenario of applying partial channel state information (CSI) is also taken into account in our study. Simulations prove that the optimal power allocation combined with the proposed PRBs assignment achieves higher weighted sum throughput as compared with traditional algorithms, even when partial CSI is utilised. Copyright © 2015 John Wiley & Sons, Ltd.

Joint admission control and beamforming design for the interference cognitive radio network with partial channel state information case

In order to effectively utilise the spectrum of wireless network, secondary users (SUs) are often authorised to share spectrum with primary users (PUs) in cognitive networks. To guarantee effective transmission of PUs and SUs, the interference from the SUs to the PUs is limited and only the SUs that have the information rates (rates) than the corresponding thresholds are allowed to transmit their data. In order to select proper SUs to transmit and to maximise their achievable weighted sum rate (WSR) under rate requirement and interference constraint, the authors propose a joint admission control and beamforming design algorithm for partial channel state information (CSI) case. The WSR maximisation problem is first constructed by using approximation and convex relaxation, according to the statistical property of the CSI. Then a penalty factor is introduced to check the feasibility of such problem and instruct the admission of the SUs. Beyond the feasible SUs set, the WSR is maximised by updating the achievable rate of each user with rate profile technique and polyblock outer approximation method. Simulation results show that the proposed beamforming can achieve higher WSR than the beamforming of the existing baseline method.

On the Adaptive Sum-Capacity of Distributed Multiple Access with Individual CSI

In wireless communications, a fading multiple-access channel (MAC) is typically used to model the uplink communication. Conventional MACs assume a centralized system, where the transmission rate and power are chosen centrally for every fading vector realization. On the other hand, there is considerable interest in the performance of distributed multiple access systems, where the lack of global channel state information (CSI) demands novel communication strategies. We consider a block-fading MAC where each transmitter is aware only of its own link CSI, which we term as the individual CSI MAC. The receiver has access to the full CSI of all links. This model was recently introduced in the information theory literature, and naturally leads to a distributed access system with several applications. An important utility of interest for this model is known as the power-controlled adaptive sum-capacity, whose evaluation is an open problem. This is the main subject of the current paper. We present the power-controlled adaptive sum-capacity of a wide class of popular fading MAC models. In particular, we characterize the sum-capacity when the statistics of the channel are identical across users. The proposed schemes also allow a low-complexity successive-cancellation decoding using rate-splitting. Furthermore, the optimal schemes are extended to situations in which each transmitter has additional finite-rate partial CSI on the link quality of others.

Receiver Cooperation for MIMO Broadcast Channels With Finite-Rate Feedback

Receiver cooperation is an effective technique to improve the performance of multi-antenna Gaussian broadcast channels. In practical systems, the transmitter usually has partial channel state information (CSI) via the finite-rate feedback channel. How could receiver cooperation benefit the system performance in this case? In this letter, we propose a low complexity and effective cooperation scheme based on the principle of decode-and-forward (DF) relaying and successive interference cancelation (SIC) to mitigate the residual multiuser interference. Compared to non-cooperative systems, the proposed scheme brings a twofold benefit: improved chosen space of beamforming vectors and reduced multiuser interference terms. As a result, both degrees-of-freedom gain and power gain can be observed. The degrees-of-freedom gain leads to unbounded throughput with finite feedback rate. The power gain is significant such that the proposed scheme with partial CSI even outperforms the non-cooperative system with perfect CSI in low and moderate signal-to-noise ratio (SNR) region.