05-05-2011, 04:27 PM
Reliable Multi-hop Routing with Cooperative Transmissions in Energy-Constrained Networks
Abstract
We present a novel approach in characterizing theoptimal reliable multi-hop virtual multiple-input single-output(vMISO) routing in ad hoc networks. Under a high node densityregime, we determine the optimal cardinality of the cooperationsets at each hop on a path minimizing the total energy cost pertransmitted bit. Optimal cooperating set cardinality curves arederived, and they can be used to determine the optimal routingstrategy based on the required reliability, transmission power,and path loss coefficient. We design a new greedy geographicalrouting algorithm suitable for vMISO transmissions, and demonstratethe applicability of our results for more general networks.Index Terms—virtual MIMO, energy-efficiency, space-timeblock codes
I. INTRODUCTION
In wireless networks, energy efficiency is a dominatingdesign criterion. It is well-known that for the same throughputrequirement multi input multi output (MIMO) systemsrequire less transmission energy than single input single output(SISO) systems in the presence of fading [1]. However, itis usually infeasible to mount multiple antennas on smallwireless devices due to the required minimum separation ofthese antennas. To achieve MIMO gains in wireless networks,cooperative (virtual) MIMO techniques have been proposed[2]. There is an increasing interest in translating the advantagesof using virtual MIMO at the physical layer into higherlayer performance benefits to maximize network throughput,or minimize total energy consumption and end-to-end delay[3] - [8]. In previous works, energy efficiency of cooperativetransmissions over a single hop was investigated and comparedto the traditional SISO transmissions [4], [5]. The capacityof a large gaussian relay network, where a source cooperateswith relay nodes to transmit to a sink node is investigated in[8]. In our work, we investigate energy efficient routing inmulti-hop wireless networks with cooperative transmissionswhen the channel is slowly-varying. Unlike [8], transmissionsare required to satisfy an outage probability requirement,which is a suitable metric for this channel model. Also, [8]includes unreliable transmissions between source and relaynodes, which is omitted in the present work.The key advantage provided by the cooperative transmissionsconsidered in this work is the increase in the transmissionrange due to diversity gain when all radios transmit at thesame fixed power level as in traditional SISO systems. Our objective is to determine in a multi-hop network, the optimalnumber of cooperating nodes per hop to minimize the endto-end total energy consumption while satisfying an outageprobability requirement at each hop. In order to identifythe effect of the number of cooperating nodes on energyconsumption, all other parameters, i.e., transmission power,rate and reliability are kept constant. The theoretical analysisof this problem is performed for networks with unlimited nodedensity. Our results indicate that cooperative transmission isespecially useful in multi-hop networks with low propagationloss coefficient, stricter outage probability requirement, andlower transmission power level. A new greedy geographicalrouting algorithm suitable for vMISO transmissions is designedto demonstrate the applicability of our results for moregeneral networks.The letter is organized as follows: In Section II, we discussthe system model and give the necessary background onvMISO systems. In Section III, we calculate and comparethe energy consumption of vMISO and SISO systems underhigh node density assumption. In Section IV, we developand analyze a greedy vMISO geographical routing algorithm.Finally, we conclude in Section V
.II. PRELIMINARIES
The channel is modeled as a Rayleigh flat-fading channel,where each node transmits with a fixed power level, P0.The receiver has the full channel state information (CSI),but the transmitters do not estimate the channel. Let N0 bethe one-sided noise spectral density and ®0 be the complexGaussian distributed random variable, Nc(0; 1), characterizingthe Rayleigh flat fading channel. The instantaneous signalto-noise-ratio (SNR) at a SISO receiver is, SNRSISO =P0N0j®0j2d¡¯0 , where ¯ is the path loss coefficient and d0 isthe transmission range.In vMISO systems, a set of cooperating nodes emulatethe antenna array of real MISO systems. vMISO systemscan provide diversity gain over SISO systems due to thetransmission of data over multiple independent channels. Weconsider decode and forward cooperation scheme, where initially,the head node transmits the original data to the relaynodes [2]. The cooperative transmission begins once all relaynodes receive, and correctly decode the original data. In orderto leverage the benefits of space-diversity, data is encoded bya space time block code (STBC) with code rate rn = kkn• 1.The head node and n¡1 relay nodes simultaneously transmitover kn time slots in order to transfer k information bits.
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http://research.sabanciuniv.edu/9616/1/L...7-0030.pdf
Abstract
We present a novel approach in characterizing theoptimal reliable multi-hop virtual multiple-input single-output(vMISO) routing in ad hoc networks. Under a high node densityregime, we determine the optimal cardinality of the cooperationsets at each hop on a path minimizing the total energy cost pertransmitted bit. Optimal cooperating set cardinality curves arederived, and they can be used to determine the optimal routingstrategy based on the required reliability, transmission power,and path loss coefficient. We design a new greedy geographicalrouting algorithm suitable for vMISO transmissions, and demonstratethe applicability of our results for more general networks.Index Terms—virtual MIMO, energy-efficiency, space-timeblock codes
I. INTRODUCTION
In wireless networks, energy efficiency is a dominatingdesign criterion. It is well-known that for the same throughputrequirement multi input multi output (MIMO) systemsrequire less transmission energy than single input single output(SISO) systems in the presence of fading [1]. However, itis usually infeasible to mount multiple antennas on smallwireless devices due to the required minimum separation ofthese antennas. To achieve MIMO gains in wireless networks,cooperative (virtual) MIMO techniques have been proposed[2]. There is an increasing interest in translating the advantagesof using virtual MIMO at the physical layer into higherlayer performance benefits to maximize network throughput,or minimize total energy consumption and end-to-end delay[3] - [8]. In previous works, energy efficiency of cooperativetransmissions over a single hop was investigated and comparedto the traditional SISO transmissions [4], [5]. The capacityof a large gaussian relay network, where a source cooperateswith relay nodes to transmit to a sink node is investigated in[8]. In our work, we investigate energy efficient routing inmulti-hop wireless networks with cooperative transmissionswhen the channel is slowly-varying. Unlike [8], transmissionsare required to satisfy an outage probability requirement,which is a suitable metric for this channel model. Also, [8]includes unreliable transmissions between source and relaynodes, which is omitted in the present work.The key advantage provided by the cooperative transmissionsconsidered in this work is the increase in the transmissionrange due to diversity gain when all radios transmit at thesame fixed power level as in traditional SISO systems. Our objective is to determine in a multi-hop network, the optimalnumber of cooperating nodes per hop to minimize the endto-end total energy consumption while satisfying an outageprobability requirement at each hop. In order to identifythe effect of the number of cooperating nodes on energyconsumption, all other parameters, i.e., transmission power,rate and reliability are kept constant. The theoretical analysisof this problem is performed for networks with unlimited nodedensity. Our results indicate that cooperative transmission isespecially useful in multi-hop networks with low propagationloss coefficient, stricter outage probability requirement, andlower transmission power level. A new greedy geographicalrouting algorithm suitable for vMISO transmissions is designedto demonstrate the applicability of our results for moregeneral networks.The letter is organized as follows: In Section II, we discussthe system model and give the necessary background onvMISO systems. In Section III, we calculate and comparethe energy consumption of vMISO and SISO systems underhigh node density assumption. In Section IV, we developand analyze a greedy vMISO geographical routing algorithm.Finally, we conclude in Section V
.II. PRELIMINARIES
The channel is modeled as a Rayleigh flat-fading channel,where each node transmits with a fixed power level, P0.The receiver has the full channel state information (CSI),but the transmitters do not estimate the channel. Let N0 bethe one-sided noise spectral density and ®0 be the complexGaussian distributed random variable, Nc(0; 1), characterizingthe Rayleigh flat fading channel. The instantaneous signalto-noise-ratio (SNR) at a SISO receiver is, SNRSISO =P0N0j®0j2d¡¯0 , where ¯ is the path loss coefficient and d0 isthe transmission range.In vMISO systems, a set of cooperating nodes emulatethe antenna array of real MISO systems. vMISO systemscan provide diversity gain over SISO systems due to thetransmission of data over multiple independent channels. Weconsider decode and forward cooperation scheme, where initially,the head node transmits the original data to the relaynodes [2]. The cooperative transmission begins once all relaynodes receive, and correctly decode the original data. In orderto leverage the benefits of space-diversity, data is encoded bya space time block code (STBC) with code rate rn = kkn• 1.The head node and n¡1 relay nodes simultaneously transmitover kn time slots in order to transfer k information bits.
Download full report
http://research.sabanciuniv.edu/9616/1/L...7-0030.pdf