Require Channel State Information Research Articles

Differential Spatial Modulation With BPSK for Two-Way Relay Wireless Communications

A differential spatial modulation (DSM) with binary phase shift keying (BPSK) scheme is designed for two-way relay (TWR) wireless communications that use the denoise-and-forward (DNF) protocol without requiring channel state information at the sources and relay. The key area to make this scheme work is a multiple-to-one mapping method for DSM at the relay, as well as the DSM matrix design at the sources, which are proposed and derived in this letter. Simulation results show that the proposed system achieves significant gains in BER performance over traditional differential modulation with BPSK in DNF-TWR systems when both operate at the same spectral efficiency.

A Novel Iterative OFDMA Channel Estimation Technique for DOCSIS 3.1 Uplink Channels

This paper presents an orthogonal frequency division multiple access (OFDMA) channel estimation technique that jointly considers the effects of coarse timing error and multipath propagation. Many conventional approaches only consider an optimistic scenario where timing synchronization is perfect and each of the channel delays is an integer number of system samples. In realistic scenarios timing offsets and echo delays are not integer multiples of the system’s sampling period. This leads to poor estimation and consequently reduces the system’s overall performance. This paper proposes a novel iterative channel estimation technique, which considers the practical scenario of fractional timing error and nonsample-spaced echo delays. The proposed method does not require channel state information (e.g., second-order statistics of the channel impulse responses or the noise power). Moreover, timing error can be conveniently obtained with the proposed technique. Simulation results show that, when comparing OFDMA channel estimation techniques under realistic data over cable service interface specification 3.1 channel conditions, the proposed algorithm significantly outperforms all conventional methods known to the authors.

Link Regimes Analysis for Partial Decode-Forward Two-Way Relay Transmission

We propose a composite decode-forward (DF) scheme for the two-way relay channel in the full-duplex mode by combining coherent, independent, and partial relaying strategies. The relay partially decodes each user’s information in each block and forwards this information coherently with the source user to the destination user in the next block as in block Markov coding. In addition, the relay independently broadcasts a binning index of both users’ decoded information parts in the next block as in independent network coding. Each technique has a different impact on the relay power usage and the rate region. We further consider the independent and partial DF scheme for its more practical channel state information requirements, and derive in closed-form link regimes when this scheme achieves a strictly larger rate region than just time sharing between its constituent techniques, direct transmission, and independent DF relaying, and when it reduces to a simpler scheme. The analytical approach is based on maximizing the weighted composite DF sum rate and comparing with the outermost time-sharing line connecting corner points of rate regions of the constituent techniques. Numerical results demonstrate significant rate gains by performing link adaptation of the composite scheme based on the identified link regimes.

Outage Probability Analysis for Energy Harvesting Cooperative Relays in a Clustered Environment

This paper presents the outage probability analysis of the energy harvesting (EH) decode and forward (DF) cooperative relay network when more than one relays are available to assist the communication between source and destination in the presence of the direct connection. The relays use power splitting (PS) protocol with adaptive PS ratio for EH. As wireless EH can be more beneficial over smaller distances therefore a clustered environment is considered in which the source, destination and relays are located in a small area. First, we analyze the performance of selection cooperation (SC) which requires channel state information (CSI) at the source. High signal to noise ratio approximation of the outage probability is provided for this case. Secondly, we present the performance of all relays cooperation (ARC) scheme which requires no CSI at the source. Lower and upper bounds of the outage probability are presented for smaller number of relays in ARC scheme whereas high signal to noise ratio approximation is provided for higher number of relays. Simulation results validate the analytical results and show that SC scheme outperforms ARC scheme at the expense of CSI requirement.

Hybrid Beamforming for Massive MIMO: A Survey

Hybrid multiple-antenna transceivers, which combine large-dimensional analog pre/postprocessing with lower-dimensional digital processing, are the most promising approach for reducing the hardware cost and training overhead in massive MIMO systems. This paper provides a comprehensive survey of the various incarnations of such structures that have been proposed in the literature. We provide a taxonomy in terms of the required channel state information (CSI), namely whether the processing adapts to the instantaneous or the average (second-order) CSI; while the former provides somewhat better signal-to-noise and interference ratio (SNIR), the latter has much lower overhead for CSI acquisition. We furthermore distinguish hardware structures of different complexities. Finally, we point out the special design aspects for operation at millimeter-wave frequencies.

Differential Space Time Frequency Codes for MIMO OFDM Systems

In general coherent detection, channel estimation requires huge number of symbols for transmission in Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wide Band (UWB) system, due to this bandwidth efficiency reduces. The proposed Differential Space-Time-Frequency Code (DSTFCs) for multiband-OFDM Ultra-WB communications is increases the efficiency of bandwidth. DSTFC system does not require Channel State Information (CSI). Due to this, the system bandwidth efficiency is possible to increase with DSTFCs. The proposed DSTFCs are derived both coding and decoding algorithms for 64 QAM (Quadrature Amplitude Modulation). The Simulation outcomes show that the use of DSTFCs can improve the coherent MB-OFDM (without STFC), differential MB-OFDM (without OFDM) bit error performance. The performance of DSTFCs almost reaches the STFCs performance even in the absence of channel state information.

Sequential Beamforming for Multiuser MIMO With Full-Duplex Training

Multiple transmitting antennas can considerably increase the downlink spectral efficiency by beamforming to multiple users at the same time. However, multiuser beamforming requires channel state information (CSI) at the transmitter, which leads to training overhead and reduces overall achievable spectral efficiency. In this paper, we propose and analyze a sequential beamforming strategy that utilizes full-duplex base station to implement downlink data transmission concurrently with CSI acquisition via in-band closed or open loop training. Our results demonstrate that full-duplex capability can improve the spectral efficiency of uni-directional traffic, by leveraging it to reduce the control overhead of CSI estimation. In moderate SNR regimes, we analytically derive tight approximations for the optimal training duration and characterize the associated respective spectral efficiency. We further characterize the enhanced multiplexing gain performance in the high SNR regime. In both regimes, the performance of the proposed full-duplex strategy is compared to the half-duplex counterpart to quantify spectral efficiency improvement. With experimental data [1] and 3D channel model [2] from 3GPP, in a 1.4 MHz 8X8 system LTE system with the block length of 500 symbols, the proposed strategy attains a spectral efficiency improvement of 130% and 8% with closed and open loop training, respectively.

HSSEC strategy for decode‐and‐forward‐relaying systems over Nakagami‐ m fading channels

Distributed switched diversity combining has drawn significant attention in the recent past due to its low-complexity nature in terms of channel state information requirement at the receiving end to achieve full diversity order. In this study, the authors propose a hybrid selection and switch-and-examine combining (HSSEC) scheme, which is a combination of selection combining and SEC schemes, for a multi-relay decode-and-forward system to improve the performance of distributed switched diversity combining schemes proposed in the literature. Furthermore, the performance of HSSEC scheme is investigated over non-identical Nakagami-m fading channels. Average end-to-end symbol error probability (SEP) expression is derived for M-ary phase-shift keying signalling, and in addition asymptotic SEP expression is also derived to analyse diversity order. From the derived asymptotic expression, it is inferred that the HSSEC scheme attains full diversity order over Nakagami-m fading channels, except for the case when threshold signal-to-noise ratio (SNR) is very much lesser than the average SNR. Furthermore, exact outage probability expression is derived for the HSSEC scheme. Finally, in the numerical results, the outage and SEP performances are compared with other schemes proposed in the literature.

Performance Analysis of Two Cooperative Multicast Schemes in Cellular Networks

This paper discusses multicast schemes in cellular networks based on rateless codes and cooperative relaying technologies. Unlike fixed-rate codes, rateless codes do not require channel state information at transmitters or feedback of successful reception of individual packets from recipient user equipment (UEs). Cooperative relaying among a group of multicast recipient UEs can further improve wireless multicast service. In the proposed cooperative multicast (CM) scheme, after part of the recipients have decoded the source message of the base station (BS), these recipients can act as cooperative relays (CRs) and simultaneously transmit the decoded information to other recipients. The CM process stops after all the recipients have reliably decoded the message. If the CRs use different fountain codes, the other recipients can accumulate the mutual information from the BS and the CRs. If the CRs use the same fountain code as used by the BS, the recipients can only accumulate the received energy. By comparing with the conventional direct transmission based multicast scheme, the transmission delay, the energy consumption, and the spectrum efficiency performances of the proposed CM schemes are evaluated. The simulation results show that the mutual information accumulation (MIA) based CM scheme outperforms the energy accumulation (EA) based CM scheme in the spectrum and energy efficiency. This is because the MIA approach acquires better time delay performance but consumes less energy than the EA approach.

Position-Based Limited Feedback Scheme for Railway MU-MIMO Systems

In future railway communications, the system architecture is highly likely to be based on the mobile relay structure. However, during the transition period, onboard passenger equipment can only directly connect to wayside public mobile networks to get wireless services. As an efficient technology to increase the capacity widely used in Long-Term Evolution (LTE) public mobile networks, multiuser multiple input–multiple output (MU-MIMO) requires channel state information (CSI) of users at base stations to suppress interuser interference, which poses a bandwidth burden on feedback links. Thus, how to reduce the MU-MIMO feedback load becomes an urgent problem. In railway scenarios, onboard passenger equipment of a user set almost has the same signal-to-noise ratio (SNR), which provides a new way to reduce the MU-MIMO feedback overheads. Accordingly, we propose a position-based limited feedback scheme for railway MU-MIMO systems, in which dedicated feedback resource positions are preassigned to codebook vectors. A resource position where users feed back channel quality indicators (CQIs) indicates a special codebook vector. Then, overheads due to precoding matrix index (PMIs) are saved. Even if bandwidth resources assigned to feedback positions may be insufficient to supply every user with a feedback chance, it still has little impact on the total capacity for whether the user with the largest CQI in an active user set is selected in highly populated railway scenarios. Moreover, a novel performance criterion called feedback efficiency is proposed. Simulation results demonstrate that the proposed scheme can achieve higher feedback efficiency compared with the conventional scheme.

Limited Rate Feedback in a MIMO Wiretap Channel With a Cooperative Jammer

We study strategies for enhanced secrecy using cooperative jamming in secure communication systems with limited rate feedback. A Gaussian multiple-input multiple-output (MIMO) wiretap channel with a jamming helper is considered. The transmitter and helper both require channel state information (CSI), which is quantized at the receiver and fed back through two sum-rate-limited feedback channels. The quantization errors result in reduced beamforming gain from the transmitter, as well as interference leakage from the helper. First, under the assumption that the eavesdropper's CSI is completely unknown, we derive a lower bound on the average main channel rate and find the feedback bit allocation that maximizes the jamming power under a constraint on the bound. For the case where statistical CSI for the eavesdropper's channel is available, we derive a lower bound on the average secrecy rate, and we optimize the bound to find a suitable bit allocation and the transmit powers allocated to the transmitter and helper. For the case where the transmitter and helper have the same number of antennas, we obtain a closed-form solution for the optimal bit allocation. Simulations verify the theoretical analysis and demonstrate the significant performance gain that results with intelligent feedback bit allocation and power control.

Adaptive Relay Selection and Data Transmission Scheme for Cooperative Communication

In this paper, an adaptive relay selection and transmission scheme are proposed for cooperative communication. As the conventional relay selection schemes, the best harmonic mean and the threshold-based relay selection scheme require channel state information (CSI) in advance at the source. By using CSI, they can select the optimal or the sub-optimal relay. But, the source does not know CSI as a priori information in general environment. Additionally, the conventional system uses the fixed maximum throughput regardless of channel state. The proposed relay selection scheme does not require a priori information at the source. It uses a characteristic of Reed---Solomon codes. By using it, the source can select the optimal relay for cooperative communication. Additionally, the proposed adaptive transmission scheme can change the maximum throughput according to the result of optimal relay selection. By using the proposed relay selection and adaptive transmission scheme, the proposed system is more reliable and adaptable according to selected relay.

Spatial Modulation Exploited in Non-Reciprocal Two-Way Relay Channels: Efficient Protocols and Capacity Analysis

In this paper, the concept of spatial modulation is exploited in two-way relay channels, where two single-antenna source terminals exchange information through an assisting multi-antenna relay node, and thereby two novel transmission strategies are proposed based on the decode-and-forward protocol, aiming to achieve high throughput. One strategy is to simply engage spatial modulation in the transmissions of the relay node, whereas the other is to develop transmit diversity with spatial modulation for further benefiting from the feature of two-way relaying. Neither of the strategies requires channel state information at the transmitter and, therefore, the assumption of channel reciprocity that is commonly used in two-way relay channels can be released herein. To evaluate the performance of both proposed strategies, their capacity behaviors are analyzed and numerical comparisons are established in the metrics of achievable rate region and sum-rate. Subsequently, the first strategy, simple spatial modulation, is generalized into the two-way relaying with multi-antenna source terminals to improve the flexibility in system design and demonstrate the tractability of spatial modulation. Illustrative discussions on bit error rate not only substantiate the validity of the proposed strategies but also provide useful tools for the two-way relaying layout without the restriction of channel reciprocity.

User Association and Interference Management in Massive MIMO HetNets

Two key traits of 5G cellular networks are much higher base station (BS) densities—especially in the case of low-power BSs—and the use of massive MIMO at these BSs. This paper explores how massive MIMO can be used to jointly maximize the offloading gains and minimize the interference challenges arising from adding small cells. We consider two interference management approaches: joint transmission (JT) with local precoding, where users are served simultaneously by multiple BSs without requiring channel state information exchanges among cooperating BSs, and resource blanking, where some macro BS resources are left blank to reduce the interference in the small cell downlink. A key advantage offered by massive MIMO is channel hardening, which enables to predict instantaneous rates a priori . This allows us to develop a unified framework, where resource allocation is cast as a network utility maximization (NUM) problem, and to demonstrate large gains in cell-edge rates based on the NUM solution. We propose an efficient dual subgradient based algorithm, which converges towards the NUM solution. A scheduling scheme is also proposed to approach the NUM solution. Simulations illustrate more than 2x rate gain for 10th percentile users vs. an optimal association without interference management.

Blind Compute-and-Forward

Compute-and-forward (C&F) is a promising new approach to interference management, enjoying several advantages over other information-theoretic schemes. C&F usually requires channel state information (CSI) at the receivers so that an “optimal” scaling factor can be computed for the purposes of decoding. In this paper, a blind C&F scheme—i.e., one not requiring CSI—is developed. Rather than attempting to compute the optimal scaling factor, this new scheme seeks one or more “good” scalars, i.e., scalars that allow correct decoding despite possibly being suboptimal. The region of all such good scalars is characterized. To find a good scalar, a computationally efficient scheme is proposed which involves error-detection, a hierarchically organized list, as well as a use of the smoothing lemma from lattice theory. Simulation results show that our blind C&F scheme achieves—for a class of nested lattice codes—the same throughput as its CSI-enabled counterpart at the expense of, approximately, a two-fold increase in computational complexity in the high-throughput region. Moreover, our blind C&F scheme can be applied to multisource multirelay networks with a good performance/complexity tradeoff.

Precoder Design With Incomplete Feedback for Joint Transmission

A centralized coordinated multipoint downlink joint transmission in a frequency division duplex system requires channel state information (CSI) to be fed back from the cell-edge users to their serving BS, and aggregated at the central coordination node for precoding, so that interference can be mitigated. The control signals comprising of CSI and the precoding weights can easily overwhelm the backhaul resources. Relative thresholding has been proposed to alleviate the burden; however, this is at the cost of reduction in throughput. In this paper, we propose utilizing the long-term channel statistics comprising of pathloss and shadow fading in the precoder design to model the statistical interference for the unknown CSI. In this regard, a successive second-order cone programming (SSOCP)-based precoder for maximizing the weighted sum rate is proposed. The accuracy of the solution obtained is bounded with the branch and bound technique. An alternative optimization framework via weighted mean square error minimization is also derived. Both these approaches provide an efficient solution close to the optimal, and also achieve efficient backhauling, in a sense that the precoding weights are generated only for the active links. For comparison, a stochastic approach based on particle swarm optimization is also considered.

Relay-Aided Successive Aligned Interference Cancellation for Wireless X Networks with Full-Duplex Relays

This paper proposes a novel relay-aided successive aligned interference cancellation (RaSAIC) method for a $\text{2}\times K$ $X$ channel with $L$ full-duplex relays, each of which is fully connected to the channel. The core idea of the RaSAIC is to apply a cooperative relays' precoding technique that aligns interference signals at unintended receivers while creating an Alamouti structure for the desired signals. With the proposed cooperative relay transmission technique, it is shown that both the optimal sum degree of freedom (sum-DoF) gain of $\text{2}K/(K+\text{1})$ and the diversity gain of two are achievable for both constant and time-varying channels when the numbers of relays' antennas are enough to meet the derived conditions, without requiring channel state information (CSI) at transmitters, but with global CSI at relays. Furthermore, it is demonstrated that the same sum-DoF and diversity gain are attainable, even in the presence of interrelay interference due to a full-duplex relaying operation if the memory at the relay nodes is exploited in the proposed manner.

Distributed Long-Term Base Station Clustering in Cellular Networks Using Coalition Formation

Interference alignment (IA) is a promising technique for interference mitigation in multicell networks due to its ability to completely cancel the intercell interference through linear precoding and receive filtering. In small networks, the amount of required channel state information (CSI) is modest and IA is, therefore, typically applied jointly over all base stations. In large networks, where the channel coherence time is short in comparison to the time needed to obtain the required CSI, base station clustering must be applied however. We model such clustered multicell networks as a set of coalitions, where CSI acquisition and IA precoding are performed independently within each coalition. We develop a long-term throughput model, which includes both CSI acquisition overhead and the level of interference mitigation ability as a function of the coalition structure. Given the throughput model, we formulate a coalitional game where the involved base stations are the rational players. Allowing for individual deviations by the players, we formulate a distributed coalition formation algorithm with low complexity and low communication overhead that leads to an individually stable coalition structure. The dynamic clustering is performed using only long-term CSI, but we also provide a robust short-term precoding algorithm, which accounts for the intercoalition interference when spectrum sharing is applied between coalitions. Numerical simulations show that the distributed coalition formation is generally able to reach long-term sum throughputs within 10% of the global optimum.

Power Control in D2D-Based Vehicular Communication Networks

This paper studies how to efficiently apply device-to-device (D2D) communications underlaying a cellular system to support vehicle-to-vehicle (V2V) connection (termed D2D-V). By considering the geographic features of the D2D-V system, we propose a D2D-V grouping, reuse channel selection (RS), and power control (PC) framework to achieve the optimal performance of the D2D-V system, in terms of either maximized sum rate or maximized minimally achievable rate. First, in a full channel state information (CSI) scenario, we apply difference of two convex functions (D.C.) programming to obtain the optimal PC. However, because the CSI between some terminals is hard to obtain and some interference can be appropriately inhibited by taking advantage of the vehicles' geographic features, we make a series of simplifications to the PC problem to reduce the requirement of full CSI, the dependence of centralized control, and the computational complexity. The suitable conditions of each simplification are elaborated. Each step of our simplifications are shown as a certain tradeoff between performance and complexity. Furthermore, we provide an investigation into the service quality that one vehicle can achieve when it passes through the covered segment of the highway and propose the location–service curve to portray this. We use numerical simulations to verify the accuracy and feasibility of each step of our suboptimal PC and specific features embedded in the location–service curve.

Optimization on semi-blind channel estimation for MIMO-OFDM systems

An orthogonal frequency division multiplexing (OFDM) is one of the effective techniques used in wireless communication. In OFDM systems, channel impairments due to multipath dispersive spreading can cause deep fades in wireless channels. Thus, the OFDM receiver requires channel state information when coherent detection is involved. Therefore, to overcome the impact of channel fades good channel estimation (CE) methods are needed in OFDM systems. And one of these CE methods is a semi-blind CE. However, the semi-blind method requires a large number of processing operations. In order to avoid the high computing complexity of the existing method, scaled least square (SLS) technique is applied to improve the performance of the semi-blind channel estimator which require less knowledge of the channel second-order statistics and have better performance than the least square (LS) which used in semi-blind CE. Simulation results shows, this proposed method of semi-blind CE has the capacity of elevating CE performance in multiple-input multiple-output (MIMO) OFDM systems.