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77
Iterative Waterfilling for Gaussian Vector Multiple Access Channels
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2001
"... This paper characterizes the capacity region of a Gaussian multiple access channel with vector inputs and a vector output with or without intersymbol interference. The problem of finding the optimal input distribution is shown to be a convex programming problem, and an efficient numerical algorithm ..."
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Cited by 313 (12 self)
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This paper characterizes the capacity region of a Gaussian multiple access channel with vector inputs and a vector output with or without intersymbol interference. The problem of finding the optimal input distribution is shown to be a convex programming problem, and an efficient numerical algorithm is developed to evaluate the optimal transmit spectrum under the maximum sum data rate criterion. The numerical algorithm has an iterative waterfilling int#j pret#4968 . It converges from any starting point and it reaches with in s per output dimension per transmission from the Kuser multiple access sum capacity af t#j just one it#4 at#49 . These results are also applicable to vector multiple access fading channels.
An overview of limited feedback in wireless communication systems
 IEEE J. SEL. AREAS COMMUN
, 2008
"... It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channe ..."
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Cited by 205 (41 self)
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It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finiterate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, singleuser, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
Designing Structured Tight Frames via an Alternating Projection Method
, 2003
"... Tight frames, also known as general WelchBoundEquality sequences, generalize orthonormal systems. Numerous applicationsincluding communications, coding and sparse approximationrequire finitedimensional tight frames that possess additional structural properties. This paper proposes an alterna ..."
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Cited by 87 (10 self)
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Tight frames, also known as general WelchBoundEquality sequences, generalize orthonormal systems. Numerous applicationsincluding communications, coding and sparse approximationrequire finitedimensional tight frames that possess additional structural properties. This paper proposes an alternating projection method that is versatile enough to solve a huge class of inverse eigenvalue problems, which includes the frame design problem. To apply this method, one only needs to solve a matrix nearness problem that arises naturally from the design specifications. Therefore, it is fast and easy to develop versions of the algorithm that target new design problems. Alternating projection will often succeed even if algebraic constructions are unavailable. To demonstrate
Transceiver optimization for multiuser MIMO systems
 IEEE Tran. on Signal Processing, 52(1):214 – 226
, 2004
"... Abstract—We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the systemwide mean squared error as the performance measure a ..."
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Cited by 76 (10 self)
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Abstract—We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the systemwide mean squared error as the performance measure and propose algorithms to find the jointly optimum linear precoders at each transmitter and linear decoders at the receiver. We first work with the case where the number of symbols to be transmitted by each user is given. We then investigate how the symbol rate should be chosen for each user with optimum transmitters and receivers. The convergence analysis of the algorithms is given, and numerical evidence that supports the analysis is presented. Index Terms—MMSE receivers, multiuser MIMO system, receiver beamforming, transmitter beamforming.
Cooperative Algorithms for MIMO Interference Channels
, 2010
"... Interference alignment is a transmission technique for exploiting all available degrees of freedom in the frequencyor timeselective interference channel with an arbitrary number of users. Most prior work on interference alignment, however, neglects interference from other nodes in the network not ..."
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Cited by 69 (13 self)
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Interference alignment is a transmission technique for exploiting all available degrees of freedom in the frequencyor timeselective interference channel with an arbitrary number of users. Most prior work on interference alignment, however, neglects interference from other nodes in the network not participating in the alignment operation. This paper proposes three generalizations of interference alignment for the multipleantenna interference channel with multiple users that account for colored noise, which models uncoordinated interference. First, a minimum interferenceplusnoise leakage (INL) algorithm is presented, and shown to be equivalent to previous subspace methods when noise is spatially white or negligible. This algorithm results in orthonormal precoders that are desirable for practical implementation with limited feedback. A joint minimum mean squared error design is then proposed that jointly optimizes the transmit precoders and receive spatial filters, whereas previous designs neglect the receive spatial filter. Finally, a maximum signaltointerferenceplusnoise ratio (SINR) algorithm is developed that is proven to converge, unlike previous maximum SINR algorithms. The sum throughput of these algorithms is simulated in the context of a network with uncoordinated cochannel interferers not participating in the alignment protocol. It is found that a network with cochannel interference can benefit from employing precoders designed to consider that interference, but in extreme cases, such as when only one receiver has a large amount of interference, ignoring the cochannel interference is advantageous.
Adaptation, coordination, and distributed resource allocation in interferencelimited wireless networks.
 Proceeding of the IEEE,
, 2007
"... ABSTRACT  A sensible design of wireless networks involves striking a good balance between an aggressive reuse of the spectral resource throughout the network and managing the resulting cochannel interference. Traditionally, this problem has been tackled using a Bdivide and conquer[ approach. The ..."
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Cited by 34 (3 self)
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ABSTRACT  A sensible design of wireless networks involves striking a good balance between an aggressive reuse of the spectral resource throughout the network and managing the resulting cochannel interference. Traditionally, this problem has been tackled using a Bdivide and conquer[ approach. The latter consists in deploying the network with a static or semidynamic pattern of resource reutilization. The chosen reuse factor, while sacrificing a substantial amount of efficiency, brings the interference to a tolerable level. The resource can then be managed in each cell so as to optimize the per cell capacity using an advanced air interface design. In this paper, we focus our attention on the overall network capacity as a measure of system performance. We consider the problem of resource allocation and adaptive transmission in multicell scenarios. As a key instance, the problem of joint scheduling and power control simultaneously in multiple transmitreceive links, which employ capacityachieving adaptive codes, is studied. In principle, the solution of such an optimization hinges on tough issues such as the computational complexity and the requirement for heavy receivertotransmitter feedback and, for cellular networks, celltocell channel state information (CSI) signaling. We give asymptotic properties pertaining to ratemaximizing power control and scheduling in multicell networks. We then present some promising leads for substantial complexity and signaling reduction via the use of newly developed distributed and game theoretic techniques.
The Feasibility of Interference Alignment Over Measured MIMOOFDM Channels
 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
, 2010
"... Interference alignment (IA) has been shown to achieve the maximum achievable degrees of freedom in the interference channel. This results in sum rate scaling linearly with the number of users in the high signaltonoiseratio (SNR) regime. Linear scaling is achieved by precoding transmitted signals ..."
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Cited by 29 (7 self)
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Interference alignment (IA) has been shown to achieve the maximum achievable degrees of freedom in the interference channel. This results in sum rate scaling linearly with the number of users in the high signaltonoiseratio (SNR) regime. Linear scaling is achieved by precoding transmitted signals to align interference subspaces at the receivers, given channel knowledge of all transmitreceive pairs, effectively reducing the number of discernible interferers. The theory of IA was derived under assumptions about the richness of scattering in the propagation channel; practical channels do not guarantee such ideal characteristics. This paper presents the first experimental study of IA in measured multipleinput multipleoutput orthogonal frequencydivision multiplexing (MIMOOFDM) interference channels. Our measurement campaign includes a variety of indoor and outdoor measurement scenarios at The University of Texas at Austin. We show that IA achieves the claimed scaling factors, or degrees of freedom, in several measured channel settings for a 3 user, 2 antennas per node setup. In addition to verifying the claimed performance, we characterize the effect of Kronecker spatial correlation on sum rate and present two other correlation measures, which we show are more tightly related to the achieved sum rate.
Signature Optimization for CDMA with Limited Feedback
 IEEE TRANS. INFORM. THEORY
, 2005
"... We study the performance of joint signaturereceiver optimization for Direct Sequence (DS)Code Division Multiple Access (CDMA) with limited feedback. The receiver for a particular user selects the signature from a signature codebook, and relays the corresponding B index bits to the transmitter over ..."
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Cited by 27 (9 self)
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We study the performance of joint signaturereceiver optimization for Direct Sequence (DS)Code Division Multiple Access (CDMA) with limited feedback. The receiver for a particular user selects the signature from a signature codebook, and relays the corresponding B index bits to the transmitter over a noiseless channel. We study the performance of a Random Vector Quantization (RVQ) scheme in which the codebook entries are independent and isotropically distributed. Assuming the interfering signatures are independent, and have independent, identically distributed elements, we evaluate the received SignaltoInterference plus Noise Ratio (SINR) in the large system limit as the number of users, processing gain, and feedback bits B all tend to infinity with fixed ratios. This SINR is evaluated for both the matched filter and linear Minimum Mean Squared Error (MMSE) receivers. Furthermore, we show that this large system SINR is the maximum that can be achieved over any sequence of codebooks. Numerical results show that with the MMSE receiver one feedback bit per signature coefficient achieves close to singleuser performance. We also consider a less complex and suboptimal reducedrank signature optimization scheme in which the user's signature is constrained to lie in a lower dimensional subspace. The optimal subspace coefficients are scalarquantized and relayed to the transmitter. The large system performance of the quantized reducedrank scheme can be approximated, and numerical results show that it performs in the vicinity of the RVQ bound. Finally, we extend our analysis to the scenario in which a subset of users optimize their signatures in the presence of random interference.
game theory perspective on interference avoidance
 in Proc. IEEE Globecom
"... Abstract – We show that the fixed power, synchronous Interference Avoidance (IA) scheme of [3] employing the (greedy) eigeniteration can be modeled as the recently developed potential game of [10]. Motivated by the fact that receivers can make small mistakes, we consider the convergence of the eige ..."
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Cited by 23 (7 self)
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Abstract – We show that the fixed power, synchronous Interference Avoidance (IA) scheme of [3] employing the (greedy) eigeniteration can be modeled as the recently developed potential game of [10]. Motivated by the fact that receivers can make small mistakes, we consider the convergence of the eigeniteration when noise is added in a manner similar to [2]. Further, we restrict ourselves to a class of signal environments that we call levelable environments. Applying gametheory, we obtain a convergence result similar to that of [2] for levelable environments: arbitrarily small noise assures that the eigeniteration almost surely converges to a neighborhood of the optimum signature set. I.
Iterative transmitter and receiver optimization for CDMA networks
 IEEE Trans. Wireless Commun
, 2004
"... Abstract—Optimization of the capacity of a singlecell codedivision multipleaccess (CDMA) system, both from the perspective of the maximum number of users that can be served at a required quality of service level and from the information theoretic perspective, has been recently shown to be achieve ..."
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Cited by 18 (4 self)
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Abstract—Optimization of the capacity of a singlecell codedivision multipleaccess (CDMA) system, both from the perspective of the maximum number of users that can be served at a required quality of service level and from the information theoretic perspective, has been recently shown to be achieved by the same joint transmit and receive strategies. In this paper, we propose an alternating minimization based iterative algorithm that updates the transmitters and the corresponding receivers of the users. The algorithm is suitable for online implementation, and the objective function is suitable for extension to multicell networks, both of which are in contrast with the previously proposed algorithms. We show that the algorithm is provably convergent to the optimum signature sequences and the corresponding receivers. Index Terms—Alternating minimization, codedivision multiple access (CDMA), mean squared error (MSE), optimum signature sequence sets, sum capacity, Welch bound equality (WBE) sequences. I.