Receiver Cooperation Research Articles

Generalized superimposed training for RIS-aided cell-free massive MIMO-OFDM networks

In this paper, a generalized superimposed training (GST) is proposed for an uplink cell-free multiple-input multiple-output orthogonal frequency-division multiplexing (mMIMO-OFDM) system, which is aided by reconfigurable intelligent surfaces (RISs) to enhance the spectral efficiency in the system. For the GST scheme, the pilots and data symbols are transmitted simultaneously in the coherence time. This scheme is different from traditional separate transmission methods, such as regular pilots (RP) transmission. In the OFDM multi-carrier case, a part of the subcarriers is based on the GST, whereas the other part of subcarriers is used for data transmission only. The channel and data estimations are carried out and the normalized mean-squared error (NMSE), bit error rate (BER), and sum-rate in different schemes are compared. Different receiver cooperation levels are analyzed in this case, including fully centralized processing and local processing. The distributed time processing and iterative process are also used to improve the performance of the data estimation in this system.

UAV Communications With WPT-Aided Cell-Free Massive MIMO Systems

Cell-free (CF) massive multiple-input multiple-output (MIMO) is a promising solution to provide uniform good performance for unmanned aerial vehicle (UAV) communications. In this paper, we propose the UAV communication with wireless power transfer (WPT) aided CF massive MIMO systems, where the harvested energy (HE) from the downlink WPT is used to support both uplink data and pilot transmission. We derive novel closed-form downlink HE and uplink spectral efficiency (SE) expressions that take hardware impairments of UAV into account. UAV communications with current small cell (SC) and cellular massive MIMO enabled WPT systems are also considered for comparison. It is significant to show that CF massive MIMO achieves two and five times higher 95%-likely uplink SE than the ones of SC and cellular massive MIMO, respectively. Besides, the large-scale fading decoding receiver cooperation can reduce the interference of the terrestrial user. Moreover, the maximum SE can be achieved by changing the time-splitting fraction. We prove that the optimal time-splitting fraction for maximum SE is determined by the number of antennas, altitude and hardware quality factor of UAVs. Furthermore, we propose three UAV trajectory design schemes to improve the SE. It is interesting that the angle search scheme performs best than both AP search and line path schemes. Finally, simulation results are presented to validate the accuracy of our expressions.

Impact of Channel Aging on Cell-Free Massive MIMO Over Spatially Correlated Channels

In this paper, we investigate the impact of channel aging on the performance of cell-free (CF) massive multiple-input multiple-output (MIMO) systems with both spatial correlation and pilot contamination. We derive novel closed-form uplink and downlink spectral efficiency (SE) expressions that take imperfect channel estimation into account. More specifically, we consider large-scale fading decoding and matched-filter receiver cooperation in the uplink. The uplink performance of a small-cell (SC) system is derived for comparison. The CF massive MIMO system achieves higher 95%-likely uplink SE than the SC system. In the downlink, the coherent transmission has four times higher 95%-likely per-user SE than the non-coherent transmission. Statistical channel cooperation power control (SCCPC) is used to mitigate the inter-user interference. SCCPC performs better than full power transmission, but the benefits are gradually weakened as the channel aging becomes stronger. Furthermore, strong spatial correlation reduces the SE but degrades the effect of channel aging. Increasing the number of antennas can improve the SE while decreasing the energy efficiency. Finally, we use the maximum normalized Doppler shift to design the SE-improved length of the resource block. Simulation results are presented to validate the accuracy of our expressions and prove that the CF massive MIMO system is more robust to channel aging than the SC system.

Signal-Aligned Network Coding for Multicell Processing With Limited Cooperation

In this paper, we propose a signal-aligned network coding (SNC) scheme for K-user time-varying multiple-input multiple-output (MIMO) interference channels with limited receiver cooperation. We assume that the receivers are connected to a central processor via wired cooperation links with individual limited capacities. Our SNC scheme determines the precoding matrices of the transmitters so that the transmitted signals are aligned at each receiver. The aligned signals are then decoded into noiseless integer combinations of messages, also known as network-coded messages, by physical-layer network coding. The key idea of our scheme is to ensure that independent integer combinations of messages can be decoded at the receivers. Hence the central processor can recover the original messages of the transmitters by solving the linearly independent equations. We prove that our SNC scheme achieves full degrees of freedom (DoF) by utilizing signal alignment and physical-layer network coding. Simulation results show that our SNC scheme outperforms the compute-and-forward scheme in the finite SNR regime of the two-user and the three-user cases. The performance improvement of our SNC scheme mainly comes from efficient utilization of the signal subspaces for conveying independent linear equations of messages to the central processor.

Efficient Receiver Design for Uplink Cell-Free Massive MIMO With Hardware Impairments

This paper investigates the effect of hardware impairments on the achievable performance of cell-free (CF) massive multiple-input multiple-output (MIMO) systems with four low-complexity receiver cooperation among the multiple antennas access points (APs), included large scale fading decoding (LSFD), simple LSFD, simple centralized decoding and small cell. Taking into account the joint hardware impairment (HI) effects brought by both APs and user equipments, we derive closed-form expressions for uplink spectral efficiency (SE) of CF massive MIMO systems. It is found that LSFD can achieve the largest SE. Furthermore, a novel hardware-quality scaling law is presented to reveal the relationship between the number of antennas and HI. Based on these results, we provide important insights into the practical impact of HI. For example, the impact of HI at the APs vanishes as the number of APs grows. Finally, numerical results validate our derived results.

Multiplexing Gains under Mixed-Delay Constraints on Wyner's Soft-Handoff Model.

This paper analyzes the multiplexing gains (MG) achievable over Wyner’s soft-handoff model under mixed-delay constraints, that is, when delay-sensitive and delay-tolerant data are simultaneously transmitted over the network. In the considered model, delay-sensitive data cannot participate or profit in any ways from transmitter or receiver cooperation, but delay-tolerant data can. Cooperation for delay-tolerant data takes place over rate-limited links and is limited to a fixed number of cooperation rounds. For the described setup, inner and outer bounds are derived on the set of MG pairs that are simultaneously achievable for delay-sensitive and delay-tolerant data. The bounds are tight in special cases and allow us to obtain the following conclusions. For large cooperation rates, and when both transmitters and receivers can cooperate, it is possible to simultaneously attain maximum MG for delay-sensitive messages and maximum sum MG for all messages. For comparison, in scheduling schemes (also called time-sharing schemes), the largest achievable sum MG decreases linearly with the MG of delay-sensitive messages. A similar linear decrease is proved for any coding scheme, not only for scheduling schemes, if only transmitters or only receivers can cooperate (but not both) and if delay-sensitive messages have moderate MG. In contrast, if the MG of delay-sensitive messages is small, the maximum sum MG can be achieved even with only transmitter or only receiver cooperation. To summarise, when cooperation rates are high and both transmitters and receivers can cooperate or when delay-sensitive messages have small MG, then transmitting delay-sensitive messages causes no penalty on the sum-MG. In other regimes, this penalty increases proportionally to the delay-tolerant MG in the sense that increasing the delay-sensitive MG by penalises the largest achievable delay-tolerant MG by and thus the sum MG by .

Sum-Rate Upper Bounds for the Gaussian X Channel with Limited Receiver Cooperation

In this paper, we propose sum-rate upper bounds in terms of the sum of 3 rates and the sum of 4 rates for the two-user Gaussian X channel with limited receiver cooperation. These upper bounds are derived by using the Fano's inequality, the data processing inequality and genie-aided techniques. Then, we explore the generalized degrees of freedom (GDoF) of the proposed upper bounds with a symmetric channel setting. By setting a certain set of parameters, the received results show that our results are identical to the existing results for both non-cooperation and limited receiver cooperation cases. Moreover, we obtain that the GDoF computed from our proposedupper bounds are greater than the GDoF of those in the non-cooperation case.

Achievable Rate Region for the Two-User Gaussian X Channel with Limited Receiver Cooperation: General Case

Achievable Rate Region for the Two-User Gaussian X Channel with Limited Receiver Cooperation: General Case

제주 정낭(錠木) 채널 Code Ⅲ

This paper presents 3-User NOR switching channel based on interference decoding with receiver in succession to Jong Nang channel code I, II. The Jeju Jong Nang code is considered as one of the earliest human binary coded communication (HBCC) in the world with a definite 1 or 0 binary symbolic analysis of switching circuits. In this paper, we introduce a practical example of interference decoding with receiver cooperation based on the three user Jong Nang NOR switching channel. The proposed system models are the three user Jong Nang (TUJN) NOR logic switching on-off, three-user injective deterministic NOR switching channel and Gaussian interference channel (GIC) with receiver cooperation. Therefore, this model is well matched to Shannon binary symmetric and erasure channel capacity. We show the applications of three-user Gaussian interference decoding to obtain deterministic channels which means each receiver cooperation helps to adjacent others in order to increase degree of freedom. Thus, the optimal sum rate of interference mitigation through adjacent receiver cooperation achieves 7 bits.

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.

Receiver Cooperation in Topology Control for Wireless Ad-Hoc Networks

We propose employing receiver cooperation in centralized topology control to improve energy efficiency as well as network connectivity. The idea of transmitter cooperation has been widely considered in topology control to improve network connectivity or energy efficiency. However, receiver cooperation has not previously been considered in topology control. In particular, we show that we can improve both connectivity and energy efficiency if we employ receiver cooperation in addition to transmitter cooperation. Consequently, we conclude that a system based both on transmitter and receiver cooperation is generally superior to one based only on transmitter cooperation. We also show that the increase in network connectivity caused by employing transmitter cooperation in addition to receiver cooperation is at the expense of significantly increased energy consumption. Consequently, system designers may opt for receiver-only cooperation in cases for which energy efficiency is of the highest priority or when connectivity increase is no longer a serious concern.

On the Sum-Rate of the Gaussian MIMO Z Channel and the Gaussian MIMO X Channel

In this paper, we study the Gaussian MIMO Z channel and the Gaussian MIMO X channel. The MIMO X channel (XC) consists of two multiple antenna transmit-receive pairs, where each transmitter communicates with both receivers. The MIMO Z channel (ZC) is obtained from the MIMO X channel by eliminating one of the links and its corresponding message. First, we derive a sum-rate upper bound for the MIMO Z channel and compare it with an existing bound in literature. Next, we consider the MIMO X channel and propose a new sum-rate upper bound by utilizing the sum-rate upper bound for the MIMO ZC. Subsequently, we derive another upper bound for the MIMO XC by assuming receiver cooperation and deriving the worst noise covariance matrix for the resulting two-user MAC. We compare the above two upper bounds for the MIMO XC with the MaddahAli-Motahari-Khandani (MMK) scheme. Then, we consider some consequences of the above results for the MIMO interference channel. Finally, we present some numerical results. The numerical results suggest that the proposed sum-rate capacity upper bounds are tighter than existing bounds.

The Degrees of Freedom of MIMO Networks With Full-Duplex Receiver Cooperation but no CSIT

The question of whether the degrees of freedom (DoF) of multiuser networks can be enhanced even under isotropic fading and no channel state information or output feedback at the transmitters (CSIT) is investigated. Toward this end, the two-user multiple-input multiple-output (MIMO) broadcast and interference channels are studied with no side-information at the transmitters and with receivers equipped with full-duplex radios. The full-duplex feature allows for receiver cooperation because each receiver, in addition to receiving the signals sent by the transmitters, can also simultaneously transmit a signal in the same band to the other receiver. Unlike the case of MIMO networks with CSIT and full-duplex receivers, for which DoF are known, it is shown that for MIMO networks with no CSIT, full-duplex receiver cooperation is beneficial to such an extent that even the DoF region is enhanced. Indeed, for important classes of two-user MIMO broadcast and interference channels, defined by certain relationships on numbers of antennas at different terminals, the exact DoF regions are established. The key to achieving DoF-optimal performance for such networks are new retro-cooperative interference alignment schemes. Their optimality is established via the DoF analysis of certain genie-aided or enhanced version of those networks. Taken together, the results of this paper show that full-duplex receiver cooperation can recover the DoF lost due to lack of CSIT. In particular, even without CSI and/or output feedback, it has the potential of yielding most, if not all, the gains promised by delayed CSIT, or even Shannon, feedback.

Network Anti-interference Technology Based on Hybrid Optimization Algorithm

According to the cooperation reception strategy and the hybrid optimization, an interference alignment algorithm is proposed. The algorithm can minimize leakage interference and maximize ideal receiption signal power. Firstly, according to the receiver cooperation technology, the pre-coding vectors of transmitter terminal can be estimated by receiver terminal, where these vectors need not be known in advance. In addition, the sum of interference covariance matrix is enough to describe the statistical features of interference alignment problem, which can quickly devise cooperation reception structure. Therefore, based on the bargaining process of cooperation game theory, the optimal full-cooperation mechanism of all the receivers can be selected. The simulation results show that compared with traditionary distributed interference alignment mechanism, our proposed interference alignment mechanism based on cooperation reception strategy and hybrid optimization technology has excellent feasibility under various transmission-power conditions.

The motion storage characteristics as the indicator of stability of internal combustion engine - receiver cooperation

In the article the attempt of using the motion stor-age characteristics was showed, to estimation of internal combustion engine - receiver cooperation. Basing on the external characteristics designated on chassis dynamome-ter, for various variants of power systems, it was tried to apply for applicability of proposed indicator. Initial analy-sis confirmed the usefulness of subjected characteristics, especially in the case of alternatively powered by LPG engines with extended adaptation cycle. Additionally, by using partial speed characteristics of the engine by various power degree, which simulated degrees of operational wear, the significant parameter of the motion storage char-acteristics was set with commonly used in engine - receiver analysis parameter, which is elasticity coefficient. The setting showed the legitimacy of designation the motion storage characteristics, whose the slope lets on one hand to evaluate the energetic parameters, on the other hand - to assess the engine - receiver cooperation stability. DOI: http://dx.doi.org/10.5755/j01.mech.20.1.6592

On the Capacity and Degrees of Freedom Regions of Two-User MIMO Interference Channels With Limited Receiver Cooperation

This paper gives the approximate capacity region of a two-user multiple-input multiple-output (MIMO) interference channel with limited receiver cooperation, where the gap between the inner and outer bounds is in terms of the total number of receive antennas at the two receivers and is independent of the actual channel values. The approximate capacity region is then used to find the degrees of freedom region. For the special case of symmetric interference channels, we also find the amount of receiver cooperation in terms of the backhaul capacity beyond, which the degrees of freedom do not improve. Further, the generalized degrees of freedom is found for MIMO interference channels with equal number of antennas at all nodes. It is shown that the generalized degrees of freedom improves gradually from a W curve to a V curve with increase in cooperation in terms of the backhaul capacity.

Achievable Rate Region for Gaussian MIMO MAC With Partial CSI

In this paper, we provide an information-theoretic analysis of a Gaussian multiple-input multiple-output multiple access channel (MIMO MAC) with imperfect channel knowledge at the receiver. In particular, we derive inner and outer bounds for the MIMO MAC rate region when the inputs are Gaussian. We then apply these bounds to a Gaussian interference network with receiver cooperation, in which a central processor with incomplete channel state information must jointly decode all the received signals. Then, in the case where the channel knowledge at the receiver is obtained through training signals, we derive the structure of the optimum training signals for all users under a definite and semidefinite rank constraint. Numerical results show that the bounds we derive can be quite tight, confirming the asymptotic analysis conducted for the finite case. Finally, we also investigate the low-SNR and high-SNR regimes, specifically analyzing the minimum required energy per information bit and the wideband slope region in the first case, and the high-SNR slope in the second.

New Inner and Outer Bounds for the Memoryless Cognitive Interference Channel and Some New Capacity Results

The cognitive interference channel is a two-user interference channel in which one transmitter is non-causally provided with the message of the other transmitter. This channel model has been extensively studied in the past years and capacity results have been proved for certain classes of channels. This paper presents new inner and outer bounds for the capacity region of the cognitive interference channel, as well as new capacity results. Previously proposed outer bounds are expressed in terms of auxiliary random variables for which no cardinality constraint of their alphabet is known. Consequently, it is not possible to evaluate such outer bounds explicitly for a given channel. The outer bound derived in this work is based on an idea originally devised by Sato for channels without receiver cooperation and results in an outer bound that does not contain auxiliary random variables, thus allowing it to be more easily evaluated. The inner bound presented in this work-which includes rate splitting, superposition coding, a broadcast channel-like binning scheme and Gel'fand Pinsker coding-is the largest known to date and is explicitly shown to include all previously proposed achievable rate regions. The novel inner and outer bounds are shown to coincide in certain cases. In particular, capacity is proved for a class of channels in the so-called “better cognitive decoding” regime, which includes the regimes in which capacity was known. Finally, the capacity region of the semi-deterministic cognitive interference channel, in which the signal at the cognitive receiver is an arbitrary deterministic function of the channel inputs, is established.

Interference Mitigation Through Limited Receiver Cooperation

Interference is a major issue limiting the performance in wireless networks. Cooperation among receivers can help mitigate interference by forming distributed MIMO systems. The rate at which receivers cooperate, however, is limited in most scenarios. How much interference can one bit of receiver cooperation mitigate? In this paper, we study the two-user Gaussian interference channel with conferencing decoders to answer this question in a simple setting. We identify two regions regarding the gain from receiver cooperation: linear and saturation regions. In the linear region, receiver cooperation is efficient and provides a degrees-of-freedom gain, which is either one cooperation bit buys one over-the-air bit or two cooperation bits buy one over-the-air bit. In the saturation region, receiver cooperation is inefficient and provides a power gain, which is bounded regardless of the rate at which receivers cooperate. The conclusion is drawn from the characterization of capacity region to within two bits/s/Hz, regardless of channel parameters. The proposed strategy consists of two parts: 1) the transmission scheme, where superposition encoding with a simple power split is employed and 2) the cooperative protocol, where one receiver quantize-bin-and-forwards its received signal and the other after receiving the side information decode-bin-and-forwards its received signal.

Degrees of Freedom of Multiple Broadcast Channels in the Presence of Inter-Cell Interference

In this paper, we provide lower and upper bounds for the number of degree of freedom (DOF) of B multiple-input single-output (MISO) broadcast channels (BC) where each base station (BS) equipped with M antennas supports its corresponding K single antenna users suffering from inter-cell interference. The sufficient and necessary condition for tightness of two bounds is presented. From the derived result, it can be observed that in-cell receiver cooperation does not help in most of the cases in a multiple-input multiple-output (MIMO) interference channel (IFC) except for one special case. Even for that special case, the DOFs with and without in-cell receive cooperation approach the same value for large K. Also, in a MIMO IFC with symmetric antenna settings (i.e., M = K), if both transmit and receive cooperations are removed to make it a single-input single-output (SISO) IFC, we show that the DOF is not affected. In addition, the DOF is studied for two mutually interfering broadcast channels in the presence of a cognitive BS. We obtain an interesting result that disabling in-cell receive cooperation of the MIMO IFC causes no DOF loss if at least one of two transmitters is a cognitive BS.