Cooperative communications have been proposed to exploit the spatial diversity gains inherent in multiuser wireless systems without the need of multiple antennas at each node. This is achieved by having the users relay each others messages and thus forming multiple transmission paths to the destination. In resource constrained networks, such as wireless sensor networks, the advantages of cooperation can be further exploited by optimally allocating the energy and bandwidth resources among users based on the available channel state information (CSI) at each node. In the first part of this article, we provide a tutorial survey on various power allocation strategies for cooperative networks based on different cooperation strategies, optimizing criteria, and CSI assumptions. In the second part, we identify the similarities between cooperative networks and several sensor network applications that utilize collaboration among distributed sensors to achieve the system goal. These applications include decentralized detection/estimation and data gathering. The techniques developed in cooperative communications can be used to solve many sensor network problems

Cooperative Communications in Resource-Constrained Wireless Networks

We consider a two-hop MIMO-OFDM communication scheme with a source, an amplify-and-forward relay, and a destination. We examine the possibilities of power allocation (PA) over the subchannels in frequency and space domains to maximize the instantaneous rate of this link if channel state information at the transmitter (CSIT) is available. We consider two approaches: (i) separate optimization of the source or the relay PA with individual per node transmit power constraints and (ii) joint optimization of the source and the relay PA with joint transmit power constraint. We provide the optimal PA at the source (or the relay) with a node transmit power constraint that maximizes the instantaneous rate for a given relay (or source) PA. Furthermore, we show that repeating this separate optimization of the source and the relay PA alternately converges and improves the achievable rate of the considered link. Since the joint optimization of the source and the relay PA is analytically not tractable we use a high SNR approximation of the SNR at the destination. This approximation leads to rates which are quite tight to the optimum.

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Power Allocation Schemes for Amplify-and-Forward MIMO-OFDM Relay Links

Power allocation strategies are developed for amplify-and-forward cooperative relaying networks in fading channels. The average signal-to-noise ratio (SNR) and outage performances are optimized in some sense by maximizing the sum and product, respectively, of the average SNR of the direct link and an upper bound on the SNR of the relay link. The power allocation strategies require knowledge of only the mean strengths of the channels.

Power allocation for cooperative relaying in wireless networks

A wireless communication method in a system in which subscriber stations are each operable for communication with a base station is provided. The base station is capable of performing simultaneous communications with a plurality of the subscriber stations simultaneously by exchange of packets each conforming with a layered protocol of said system. The packets include a first portion for defining physical layer (PHY) parameters and a second portion for defining media access layer (MAC) parameters. Furthermore, communications between the subscriber stations and the base station are performed wholly or partly through at least one relay station. In this system, the method includes, in the relay station, receiving a plurality of packets from the subscriber stations, detecting the second portion of each of the packets, combining the detected second portions to form a second portion of at least one new packet, and transmitting the new packet to the base station.

Wireless communication systems

The present invention relates to relay supported wireless communication to enhance communication performance. In the wireless communication system according to the invention neighboring relay stations are arranged with substantially overlapping coverage. In the method according to the invention mobile stations makes soft association to relay stations. The mobile stations feed back the selection of relay stations and channel quality measures to the base station. The base station adapts the transmission to the relay stations based on each mobile stations reported soft associations and channel quality measures. In this way the control signaling to and from the relay stations can be very limited.

Method and system for wireless communication networks using cooperative relaying

Cooperative relaying is considered as an effective way to combat Rayleigh fading, to offer better quality of communication link or channel capacity. From the perspective of information theory, channel capacity depends on the SNR of the received signal, therefore, how to allocate transmit power between transmitter and relay to achieve maximum SNR at the receiver or maximum channel capacity is an important issue. In general, there are two types of relaying system, i.e. non-regenerative and regenerative systems. This paper puts emphasis on the power allocation (PA) of regenerative systems. Based on a 2-hop relaying channel suffering from Rayleigh fading, with and without diversity, an adaptive PA scheme is proposed, under transmit power constraints, to keep the system running at the optimum level. Numerical results indicate that with the proposed PA scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.

Power allocation for regenerative relay channel with Rayleigh fading

In order to combat fading in wireless networks and increase the capacity of a system, cooperation is allowed among the terminals in a network. The adaptive optimal power allocation (PA) scheme, based on a certain system performance, is an important issue for relaying routing and network operation. The paper analyzes the two-hop non-regenerative (NR) relaying channel with and without diversity, and investigates the optimal PA scheme between the source terminal (Tx) and the relaying terminal (RS) under power constraints. Since, in real relaying environments, the transmitter usually knows the instantaneous channel state information (ICSI) of the 1st hop and the statistical channel state information (SCSI) of the 2nd hop, the proposed PA schemes are based on two-hop ICSI and two-hop mixed channel state information (MCSI) respectively. With the adaptive scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.

Adaptive optimal transmit power allocation for two-hop non-regenerative wireless relaying system

In future wireless communication systems, an architecture introducing wireless relaying technologies into the cellular infrastructure seems a promising approach to enlarge the coverage area and enhance the system capacity. The paper describes a two-hop cellular system, based on time division multiple access (TDMA), incorporated with a nonregenerative relaying station (NRRS), or a regenerative relaying station (RRS), where the RS works in time division duplex (TDD) mode. A general analysis of the system performance is provided in a multi-cell environment, where two power allocation schemes, optimal power allocation (OPA) and uniform power allocation (UPA), between the base station (BS) and the RS, are compared. Simulation results show that, compared with the single-hop system, the relaying system not only can obtain diversity gain and improve the performance, but also, with the OPA scheme and the proper arrangement of RSs, the performance gains can be further improved.

Performance of a two-hop cellular system with different power allocation schemes

In a cooperative relaying system, multiple-input-multiple-output (MIMO) capacity enhancement techniques are applied to mobile terminals (MT) with a limited number of antenna elements. The adaptive optimal power allocation (OPA) scheme among the relay stations (RSs) is an important issue to achieve power efficiency and maximum performance improvement. The paper proposes a cooperative relaying system model based on MIMO technology, where the RSs are utilized to emulate the multi-antenna environment. In addition, an OPA scheme, through singular value decomposition (SVD) of the channel matrix, is developed among the RSs under a certain power constraint to achieve the maximum channel capacity. Numerical results indicate that, compared with the uniform power allocation (UPA) scheme, the OPA scheme improves the capacity significantly when the RSs are close to the transmitter (TX). However, if the RSs are close to the receiver (RX), there is almost no difference between these two schemes, which is similar to the case in the traditional MIMO system.

Optimal power allocation for multiple-input-multiple-output relaying system

In interference limited CDMA systems, call admission control plays a very important role because it directly controls the number of users. We introduce a interference-based CAC algorithm according to the characteristics of HCS. This algorithm adopts a global strategy in macro layer, while using a local strategy in the micro layer. Meanwhile, in order to make full use of resources in the macro layer, different threshold values in the two layers are used. Simulation results show that the performance has been greatly improved.

Zhang Jingmei

Papers

Power allocation for regenerative relay channel with Rayleigh fading

Adaptive optimal transmit power allocation for two-hop non-regenerative wireless relaying system

Performance of a two-hop cellular system with different power allocation schemes

Optimal power allocation for multiple-input-multiple-output relaying system

Call admission control in hierarchical cell structure