Cooperative Spatial Multiplexing Research Articles

Cooperative Spatial Multiplexing for CR Users Sharing a Common Channel with Primary Users*

To enable mobile stations (MSs) of secondary users (SUs) in cognitive radio (CR) networks sharing a common channel with MSs of primary users (PUs) is an important but challenging issue. In this paper, a cooperative spatial multiplexing (CSM) scheme is proposed, where base station (BS) in CR network has K antennas and each SU or PU has one antenna only, and BS supports PUs and SUs by K spatial channels. To ensure communication quality of the network, the paper applies LDPC as the channel coding for BS, PUs and SUs. Simulations verify the proposed scheme with good spatial multiplexing capacity and BER performance.

Network-Coded Cooperative Spatial Multiplexing in Two-Way Relay Channels

In this paper, for a two-way relay channel comprising two multi-antenna transceivers and $L$ single-antenna potential relay nodes, we propose three network-coded cooperative spatial multiplexing (CSM) schemes that effectively overcome the rate loss incurred due to the half-duplex limitation of the transceivers and the relay nodes and achieve high spectral efficiency. In the following, these three schemes are referred to as time-division broadcast (TDBC)-CSM , incremental (I)-TDBC-CSM and multiple-access broadcast (MABC)-CSM . We investigate these schemes in terms of the outage probability, the average transmission rate, the asymptotic behavior, and the diversity-multiplexing tradeoff. The analysis of the paper shows that, first, the I-TDBC-CSM scheme achieves the full diversity of order $L\min (M_1,M_2)+M_1M_2$ , where $M_1$ and $M_2$ are the numbers of antennas employed by the two transceivers; second, the TDBC-CSM and MABC-CSM schemes achieve the diversity of order $L\min (M_1,M_2)$ , where this quantity is the maximum achievable diversity gain in the absence of the direct link between the transceivers; third, the TDBC-CSM and I-TDBC-CSM schemes effectively overcome the rate loss incurred due to the half-duplex limitation of the relay nodes; fourth, the MABC-CSM scheme not only overcomes the half-duplex limitation of the relay nodes but also mitigates the spectral efficiency loss incurred due to the half-duplex limitation of the transceivers; and fifth, if one or both of the transceivers are equipped with a massive antenna array, the asymptotic average rate of the CSM-based schemes scales linearly with the number of potential relay nodes, as opposed to the conventional relaying schemes, in which the average rate is not scalable with $L$ . We provide extensive simulation results to confirm the theoretical analysis of the paper. The simulation results show that for a given outage probability, the proposed schemes outperform the conventional relaying schemes in terms of the average transmission rate.

Secure wireless multicasting with linear equalization

A confidential communication scenario is considered in which a base station (BS) transmits a common stream of information to a group of users in the presence of multiple eavesdroppers via multiple relays. Multiple relays are used to provide cooperative spatial multiplexing that significantly increases the spectral efficiency with the help of linear equalization at the users. In order to analyze the performance of proposed model showing the effect of fading and multiplexing gain, we derive the closed-form analytical expressions for the ergodic secrecy multicast capacity and the secure outage probability with and without equalization. Then, we study the effect of fading and shadowing, and the number of users, eavesdroppers and relays on the ergodic secrecy multicast capacity and the secure outage probability assuming channel state information at the receiver. The secure outage performances of the proposed model with zero-forcing (ZF) case are also compared without the case of ZF. In addition, we show the effect of the number of user and eavesdropper antennas and the distances from relays to users and eavesdroppers on the secure outage probability, and a comparison is shown between the composite and Rayleigh fading environments. Finally, the analytical expressions are verified via Monte Carlo simulation.

Diversity‐multiplexing tradeoff of opportunistic relay system with multiple‐antenna destination

In this study, the authors investigate the diversity-multiplexing tradeoff (DMT) of a wireless system in which user equipments (UEs) are equipped with only one antenna while the destination has multiple antennas. Each UE is assisted by M half-duplex cooperative users serving as relay nodes. They combine the opportunistic relaying scheme and the cooperative spatial multiplexing (C-SM) scheme to produce an opportunistic C-SM (OC-SM) scheme. The fraction of time allocated to the source–relay link and the relay–destination link is treated as a design parameter to minimise the outage probability of the system. At high signal-to-noise ratio regime, the optimal time allocated factor is obtained in a closed-form expression through DMT analysis. Based on the DMT result of the proposed OC-SM scheme, an adaptive OC-SM (AOC-SM) approach in which the system can switch between different C-SM models adaptively based on the rate transmitted is proposed. To reduce the complexity of the relay nodes, an AOC-SM scheme with relay selection (SAOC-SM) in which a constant number of relay nodes is selected from the set of relay nodes that have successfully decoded the source message is investigated. The DMT results of the SAOC-SM scheme and the AOC-SM scheme are obtained and compared.

Performance of Cooperative Spatial Multiplexing SISO/MIMO Communication Systems with Constellation Rearrangement technique

Cooperative spatial multiplexing technique proposed to simplify the transmitting and receiving process on the relay nodes while providing significant energy savings. This paper investigates the performance of constellation rearrangement scheme when used in conjunction with cooperative spatial multiplexing MIMO/SISO relaying networks. During the MIMO relaying process, instead of having a single antenna for relay we have multiple antennas for relay by using additional information from MAC layer. The idea is to use the optimized constellation so that minimum squared Euclidean distance between different branches is maximized. Through extensive numerical search, we obtain the best constellation rearrangement scheme. Maximum likelihood detector is required in the receiver but the computational complexity of the receiver does not change because the proposed constellation will be saved in a table at the transmitter this search done by using arrival information from MAC layer.

Design on Precoder in Cooperative Spatial Multiplexing Systems with Amplify-and-Forward Relaying

Simple half-duplex repetition-based relaying protocols can achieve spatial diversity at the expense of additional relaying signals in the time domain. In this paper, a linear unitary precoder based on a singular vector for cooperative systems with the amplify-and-forward (AF) relaying protocol is proposed in order to improve spectral efficiency. An exact expression of the precoder design is first derived for the case of equal power allocation. Then, water-filling power allocation is used in conjunction with the precoder to further increase the system capacity, where the precoder matrix is generated with an iterative process. From the implementation point of view, the channel state information (CSI) has to be estimated and quantized in systems, the detail of which is described in the sequel. The adaptive modulation and coding (AMC) technique with the proposed precoder is also discussed to achieve high throughput performance. Finally, numerical and simulation results are presented to demonstrate the effectiveness of the proposed technique in improving capacity and throughput.

셀 간 협동 CSM에서 상향 링크 용량 개선을 위한 자원 할당 알고리즘

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

Opportunistic and Cooperative Spatial Multiplexing in MIMO Ad Hoc Networks

With the fast progress of multiple-input-multiple-output (MIMO) technology and its growing applications in networks, it is important to develop techniques to enable more efficient MIMO network communications. However, it is very challenging to coordinate node transmissions in a MIMO-based ad hoc network. In this work, we propose schemes that take advantage of the meshed topology of ad hoc networks to fully exploit the multiuser diversity and spatial diversity in order to maximize the data rate of the network while supporting different transmission priorities, reducing transmission delay, and ensuring fair transmissions among nodes. We formulate a concrete physical model and present cross-layer centralized and distributed scheduling algorithms that exploit physical-layer channel information to opportunistically schedule cooperative spatial multiplexed transmissions between nodes. We also propose a new MAC scheme to support our distributed algorithm. The performance of our algorithms are studied through extensive simulations, and the results demonstrate that our algorithms are very effective and can significantly increase the network throughput while reducing the transmission delay.

Optimal decoding for hard-decision forwarding aided cooperative spatial multiplexing systems

In this letter, the optimal decoding strategy for cooperative spatial multiplexing (CSM) aided systems is derived. In CSM systems, the multiple relay stations (RSs), which compose a virtual antenna array (VAA), independently decode the packets received from the mobile stations (MS) and forward them to the base station (BS). When the BS decodes the signal forwarded from the RSs, the potential decoding errors encountered at the RSs will result in erroneous forwarding, but their effects are mitigated by the proposed solution. Our simulation results show that when the relay link has a significantly higher signal-to-noise ratio than the direct link, the proposed decoding algorithm achieves an approximately 3 dB better performance than conventional CSM, which does not consider the deleterious effects of erroneous forwarding from the RSs.

Cooperative spatial multiplexing for ad hoc networks with hybrid ARQ: system design and performance analysis

For a network where each node has multiple antennas, we propose a transmission mode and a cooperation protocol, with the aim of maximizing the network throughput. The distinctive feature of the work is that the focus in both the design and the evaluation is at the network level, rather than on a single link. To this end, we propose the use of spatial multiplexing and code division multiple access (CDMA) to increase the parallelism of transmissions in the network, thus improving throughput. Cooperation is also implemented by spatial multiplexing and CDMA, together with an adaptive hybrid automatic repeat request mechanism that adapts the retransmissions to the actual channel conditions. Spatial multiplexing allows frame-asynchronous transmissions and a flexible cooperation protocol that minimizes the signaling overhead. The resulting scheme is named layered coded cooperative system (LCCS). We propose an implementation of LCCS based on linear erasure packet codes, where cooperation is transparent to the receiver, and we assess the performance of LCCS both by analyzing a simple network with three nodes and by simulating a more complex network.