
I am currently a research scholar in Prof. John Cioffi's group at Stanford University. I am broadly interested in the application of mathematical and statistical tools such as convex optimization, information theory, graphical models, machine learning and statistical signal processing to wireless communications, solidstate storage devices, integrated circuits, big data classification and modeling. If you are a student (M.S./Ph.D.) or postdoc at Stanford University interested in collaborating with me in any of the fields of interest to me, contact me!
I completed my PhD at the
StarLab, Electrical Engineering department,
Stanford University.
My advisor was Prof. John Cioffi.
During my
PhD, I worked on the downlink wireless networks with limited feedback. My research was partly sponsored by research grants from Intel and LinkAMedia Devices.
I completed my undergraduate studies at the
Electrical Engineering department,
IIT Kanpur.


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Publications
Conference Publications
 Improving NAND Flash Read Performance Through Learning
Haleh Tabrizi, Borja Peleato, Rajiv Agarwal, Jeff Ferreira
IEEE ICC 2015
( Abstract 
Full Text 
Talk )
Two important performance metrics for a storage system are the latency associated with retrieving data from its storage medium and the effective lifetime of its storage medium. Both metrics are directly affected by the number of raw read errors (i.e. errors prior to exploiting errorcorrection mechanisms). This paper focuses on NAND flash memories, where a read is performed by comparing stored voltages with a threshold voltage. The unwanted variation of stored voltages causes read errors. This paper identifies number of flash programerase (PE) cycles, time elapsed between writing and reading, and the page number (physical location) as the main sources of voltage variations. It then proposes a method for learning how read thresholds should vary with these parameters such that the storage controller can dynamically vary thresholds and minimize read errors. Lab experiments show that at the flash endoflife, the proposed method lowers the raw biterrorrate by an order of magnitude, as compared to manufacturer's default read settings.
 Predicting Bad Pages in NAND Flash to Improve Read Time: A Dynamic Programming Approach
Haleh Tabrizi, Rajiv Agarwal
IEEE ICC 2015
( Abstract 
Full Text 
Talk )
On NAND Flash, a primary source of increased read time comes from the fact that in the presence of noise, the Flash medium must be read several times using different read threshold voltages to find the optimal read location, which minimizes biterrorrate. This paper proposes an algorithm to estimate the optimal read threshold in a fast manner using a limited number of rereads. Then it derives an expression for the resulting BER in terms of the minimum BER. It is also shown that minimizing BER and minimizing codeworderrorrate are competing objectives in the presence of limited number of allowed rereads, and a tradeoff between the two is proposed.
 BERbased wear leveling and bad block management for NAND flash
Borja Peleato, Haleh Tabrizi, Rajiv Agarwal, Jeff Ferreira
IEEE ICC 2015
( Abstract 
Full Text 
Talk )
On NAND Flash, a primary source of increased read time comes from the fact that in the presence of noise, the Flash medium must be read several times using different read threshold voltages to find the optimal read location, which minimizes biterrorrate. This paper proposes an algorithm to estimate the optimal read threshold in a fast manner using a limited number of rereads. Then it derives an expression for the resulting BER in terms of the minimum BER. It is also shown that minimizing BER and minimizing codeworderrorrate are competing objectives in the presence of limited number of allowed rereads, and a tradeoff between the two is proposed.
 Towards minimizing read time for NAND Flash
Borja Peleato, Rajiv Agarwal, John Cioffi, Minghai Qin, Paul Siegel
IEEE Globecom 2012
( Abstract 
Full Text 
Talk )
On NAND Flash, a primary source of increased read time comes from the fact that in the presence of noise, the Flash medium must be read several times using different read threshold voltages to find the optimal read location, which minimizes biterrorrate. This paper proposes an algorithm to estimate the optimal read threshold in a fast manner using a limited number of rereads. Then it derives an expression for the resulting BER in terms of the minimum BER. It is also shown that minimizing BER and minimizing codeworderrorrate are competing objectives in the presence of limited number of allowed rereads, and a tradeoff between the two is proposed.
 Analysis of Tradeoffs in V2PTable Design for NAND Flash
Borja Peleato, Rajiv Agarwal, John Cioffi
46th Asilomar Conference on Signals, Systems and Computers, Nov. 2012
( Abstract 
Full Text )
Flash memory uses relocateonwrite, also called outofplace
write for performance reasons. Data files from the host are
spread across several nonsequential NAND physical pages.
In order to retrieve host data at a later point a virtualtophysical address table mapping the files to their physical
addresses must be maintained. This process entails two basic
steps. The first is to divide the NAND physical space in a
hierarchical manner for efficiency of address lookup. The
second is to store the resulting address lookup table, also
called a virtualtophysical (V2P) table in an efficient manner
on the flash. This paper explores different architectures for
constructing such table and storing it, thereby characterizing
the tradeoff that they offer in terms of complexity, write
speed, and endurance of the flash memory.
 On the Distribution of Valid Pages with Greedy Garbage Collection for NAND Flash
Borja Peleato, Rajiv Agarwal, John Cioffi.
IEEE SSP 2012
( Abstract 
Full Text 
Poster )
Flash memory uses relocateonwrite, also called outofplace write for performance reasons. Relocateonwrite requires a garbagecollection process, which results in additional write operations referred to as writeamplification. The reclaiming policy that selects the blocks to garbagecollect is greedy if it is based only on the amount of free space to be gained. Write amplification is a critical factor limiting the write performance and endurance in solidstate drives and the greedy garbage collection policy minimizes it. In this paper, we derive an expression for the steadystate distribution of validpages using a novel probabilistic model for flashbased SSDs for a greedy reclaiming policy. This distribution lends itself directly to evaluation of writeamplification and gives insight into designing newer garbage collection policies, which would further reduce writeamplification. Numerical evaluation of the derived expression matches the distribution obtained via MonteCarlo simulation for several different drive configurations, thereby validating the derivation.
 Probabilistic Graphical Model for the Programming of a Flash Memory
Borja Peleato, Rajiv Agarwal, John Cioffi
IEEE SSP 2012
( Abstract 
Full Text 
Poster )
Flash memory presents significant advantages over hard
drives in terms of read speed and power efficiency; however
its lifetime can be several orders of magnitude smaller. Thus
increasing lifetime of flash memory via signal processing
techniques is an important research area. The first half of the
paper presents a statistical method for estimating the health of
the cells in a Flash memory, based on which a variable error
correction coding scheme can be used to increase lifetime.
The second half of the paper proposes a statistical approach
to increase lifetime when the flash controller can dynamically
vary the program and erase operation strategy. This approach
uses Markov Decision Processes (MDP) to choose the optimal program or erase strategy at any given point in the life
of a Flash memory based on its current state or health. From
a bigger picture standpoint, the paper presents a novel way
of flash management using a Markov model for health of the
memory at any given point in its lifetime.
 Maximizing MLC Nand lifetime and reliability in the presence of write noise
Borja Peleato, Rajiv Agarwal, John Cioffi
IEEE ICC 2012
( Abstract 
Full Text )
The aggressive scaling of the NAND flash technology has led to write noise becoming the dominant source of
disturbance in the currently shipping sub30 nm MLC NAND
memories. Write noise can be mitigated by reducing the magnitude of the voltage levels programmed into the cells, which
additionally translates to longer flash memory lifetime. However,
if all the target levels are small and close together, the probability
of error could become excessively high. It is therefore necessary
to optimize the target level placement in order to achieve a
tradeoff between flash lifetime and error probability. This paper
proposes a method to maximize flash lifetime subject to reliability
constraints, and vice versa. Simulation results show that the
proposed method doubles flash lifetime in comparison to a naive
scheme, for a 2% reliability constraint. It also comes very close
to the optimal solution obtained by brute force search, while
maintaining negligible computational complexity in comparison.
 A closedform expression for Write Amplification in NAND Flash
Rajiv Agarwal, Marcus Marrow
IEEE Globecom 2010
( Abstract 
Full Text )
The logstructured filesystems typically used in current solidstate drive’s (SSD) exhibit write amplification, whereby
multiple NAND writes are required for each host write. Write
amplification negatively affects the SSD endurance and write
throughput. This performance loss depends on the drive overprovisioning and the garbage collection method. This paper
presents a novel probabilistic model to analytically quantify
the impact of overprovisioning on write amplification under a
uniformlydistributed random workload and a greedy garbage
collection policy. The analysis shows write amplification approximately independent of NAND block size and number of blocks
in the SSD. The analysis is verified by full drive simulations.
 Optimal Resource Allocation in the OFDMA Downlink with Feedback of Buffer State Information
Rajiv Agarwal, Rath Vannithamby and John Cioffi
IEEE Globecom 2009
( Abstract 
Full Text )
With the advent of new applications, one of the
primary applications supported in downlink cellular systems is
streaming video. QoS for streaming video entails data transmission
to the mobile stations with limited latency and limited jitter.
This requirement on latency and jitter can be mapped to the
number of yettobeplayed packets in a mobile station’s buffer,
to always be above a certain minimum. Additionally, there should
be no overflow of finitesize user buffers. This paper solves the
problem of optimal resource allocation in a downlink OFDMA
system with buffer constraints for all downlink users. The optimal
strategy is shown to be a generalized version of waterfilling and
channelinversion. Specifically, with infinite buffer size and no
minimum constraint on buffer, it reduces to waterfilling; and
to channelinversion in the absence of a buffer. It is shown that
scheduling gains from the derived optimal strategy, in terms of
number of users that the system can support, can be an orderof
magnitude higher than that of heuristic scheduling schemes.
 Weighted SumRate Maximization using Weighted MMSE for MIMOBC Beamforming Design
S. S. Christensen, Rajiv Agarwal, Elisabeth de Carvalho, John Cioffi
IEEE ICC 2009 ( Abstract 
Full Text )
This paper studies linear transmit filter design
for Weighted SumRate (WSR) maximization in the Multiple
Input Multiple Output Broadcast Channel (MIMOBC). The
problem of finding the optimal transmit filter is nonconvex and
intractable to solve using low complexity methods. Motivated
by recent results highlighting the relationship between mutual
information and Minimum Mean Square Error (MMSE), this
paper establishes a relationship between weighted sumrate and
weighted MMSE in the MIMOBC. The relationship is used to
propose a low complexity algorithm for finding a local weighted
sumrate optimum based on alternating optimization. Numerical
results studying sumrate show that the proposed algorithm
achieves high performance with few iterations.
 User Profiling: A Method to Guarantee QoS in Limited Feedback OFDMA Systems
Rajiv Agarwal, V. Majjigi, Zhu Han, R. Vannithamby, John Cioffi
IEEE ICC 2009 (
Abstract 
Full Text )
In the OFDMA downlink, obtaining Channel State
Information (CSI) from users is necessary for the Base Station
(BS) to optimize network performance by intelligently allocating
resources and scheduling mobile stations (MS). However, the
overhead of obtaining CSI is a large burden and therefore,
schemes to reduce CSI are necessary for a realizable system.
By considering a MS’s coherence time Δt_{coh} and coherence
bandwidth B_{coh}, and exploiting this redundancy in the MS’s
CSI, the amount of feedback can be tailored to the specific user’s
profile and greatly decreased. Typically, reducing feedback results
in more uncertainty in CSIT and performance degradation.
However, in the proposed scheme, the CSIT’s deviation from
the true channel state is bounded, and thus can provide robust
scheduling. Specifically, two BS schemes are suggested that either
fix the average BER or the average outage probability regardless
of user mobility or delay spread.
 Beamforming Design for the MIMO Downlink for maximizing Weighted SumRate
Rajiv Agarwal, John Cioffi
IEEE ISITA 2008 (
Abstract 
Full Text )
This work studies linear transmit filter design for
Weighted SumRate (WSR) maximization in the Multiple
Input Multiple Output Broadcast Channel (MIMOBC).
The problem of finding the optimal transmit
filter is nonconvex and intractable to solve. Motivated
by the iterative algorithm that solves for the optimal
transmit and receive filters for minimizing sum
Mean Square Error (MSE), this paper suggests to use
Weighted Minimum Mean Square Error (WMMSE) optimization
in the MIMOBC. The paper presents an
iterative algorithm to maximize WSR. Numerical results
for sumrate using the derived filter are provided
under different system settings.
 Optimal Allocation of Feedback Bits for Downlink OFDMA
Systems
Rajiv Agarwal, Rath Vannithamby, John Cioffi
IEEE ISIT 2008 (
Abstract 
Full Text )
This paper studies the downlink Orthogonal Frequency
Division Multiplexing (OFDM) setup with a single Base
Station (BS) serving many users. The BS is assumed to have
limited Channel State Information (CSI) obtained by feedback
in a Time Division Duplexing (TDD) manner. Given that the
feedback rate and the coherence time of the channel are fixed,
the question asked in this paper is: how to allocate the feedback
resources optimally? Specifically, what is the optimal number
of tones grouped as a subchannel, the number of users that
feedback for any subchannel and the number of bits used for
quantization of CSI? Analytical expressions are derived for
the i.i.d. Rayleigh fading case and it is shown that there is a
definite hierarchy in the importance of the three design variables.
Feedback resources are first allocated to create the maximum
number of subchannels possible, then to allow for more users to
feedback for any subchannel and lastly to increase the precision
of the channel value. MonteCarlo simulations are performed to
verify the accuracy of the derived analytical expressions.
 Optimal ThroughputDelay Tradeoff in Mammalian Ad Hoc Networks
Rajiv Agarwal, John Cioffi
41st Asilomar Conference on Signals, Systems and Computers, Nov. 2007 (
Extended Abstract )
 Persistent Resource Allocation in OFDMA Networks for RealTime and NonReal Time Traffic
Vinay Majjigi, Rajiv Agarwal, Rath Vannithamby, John Cioffi 41st Asilomar Conference on Signals, Systems and Computers, Nov. 2007 (
Abstract 
Full Text )
We consider optimal allocation of resources to users
in a downlink OFDMA system to support heterogeneous applications
consisting of both deadlinesensitive (DS) and besteffort
(BE) users. Given the user raterequirements and longterm
statistics, the proposed persistent scheduling algorithm
allocates the minimum resources to ‘just’ meet the deadlines
for DS packets. The remaining resources are optimally split to
maximize a rate objective for BE users. We resort to a greedy tone
allocation algorithm to solve the optimization problem.
By considering persistent scheduling instead of instantaneous
scheduling, the proposed scheme’s complexity and required
feedback overhead is significantly reduced, hence a practical
algorithm for a realsystem.
 Efficient Scheduling for Heterogeneous Services in
OFDMA Downlink
Rajiv Agarwal, Vinay Majjigi, Rath Vannithamby, John Cioffi
IEEE Globecom 2007 (
Abstract 
Full Text )
We consider optimal allocation of resources to users
in a downlink OFDMA system to support heterogeneous applications
consisting of both deadlinesensitive (DS) and besteffort
(BE) data in a crosslayer manner. Given the user queuestates
and longterm channel statistics, the proposed persistent scheduling
algorithm allocates the minimum resources to ‘just’ meet
the deadlines for DS packets (QoS guarantee). The remaining
resources are optimally split between the users for their BE
data to maximize sumrate, minimize buffer holding cost or any
general utility function. We formulate the resource allocation
problem as a single geometric program (GP) that can be solved
using standard convex optimization software tools. Simulation
results are presented to compare the performance of different
objectives for the BE applications in presence of DS traffic.
 Opportunistic Feedback in OFDMA Downlink
Rajiv Agarwal, Vineet Abhishek, Rath Vannithamby, John Cioffi IEEE Globecom 2007 (
Abstract 
Full Text )
This paper presents an opportunistic feedback (OF)
protocol that reduces the amount of channelstateinformation
(CSI) feedback for the OFDMA downlink system. The OF
protocol associates a channel value instead of a user to each
feedback slot. The users access the slots opportunistically based
on their channel state measurement for each tone. This allows
the base station (BS) to deduce the channel state from the slot
index without explicit channelstate feedback, and also solve
the resource allocation problem on the fly. The OF protocol
is designed to support heterogeneous traffic, where users with
deadlinesensitive (DS) applications are prioritized over besteffort
(BE) users. The proposed OF protocol (a) requires finite
number of feedback slots upper bounded by a small number, (b)
is fully distributed, and (c) provides QoS to the DS applications.
 Opportunistic Feedback Protocol for Achieving SumCapacity of the
MIMO Broadcast Channel
Rajiv Agarwal, ChanSoo Hwang, John Cioffi
IEEE VTC Fall 2007 (
Abstract 
Full Text )
This paper presents an opportunistic feedback (OF)
protocol that achieves the asymptotic sumcapacity of the fading
broadcast channel (BC) with a limited amount of feedback. The
OF protocol associates a channel value instead of a user to
each feedback slot. The users access the slots opportunistically
based on their channel state measurement. This allows the
basestation to deduce the channel state from the slot index
without explicit channelstate feedback. This protocol is then
extended to the MIMO BC by using zeroforcing beamforming
and random beamforming. The OF protocol is analytically shown
to (a) require finite number of feedback slots upper bounded
by a small number, (b) be fully distributed, (c) need minimal
transmission energy during feedback and (d) asymptotically
achieve the sumcapacity of the MIMO BC. Comparison with
other opportunistic feedback schemes shows that the proposed
scheme has substantially larger sumrate with a lower feedback
overhead.
 Efficient Scheduling for Heterogeneous Traffic in
Downlink
Rajiv Agarwal, Vinay Majjigi, Rath Vannithamby, John Cioffi
IEEE VTC Fall 2007 (
Abstract 
Full Text )
This paper studies optimal allocation of resources
to users in a fading broadcast channel (BC) to support heterogeneous
traffic. Resource allocation is done in a crosslayer
manner for both deadlinesensitive (DS) and besteffort (BE) data
to provide users guaranteed Quality of Service (QoS). Given the
user queuestates, the proposed algorithm allocates the minimum
resource to `just' meet the deadlines for DS packets a fixed
% of time. The remaining resources are then optimally split
between the users for their BE data to maximize sumrate,
minimize buffer holding cost or any general utility function. The
resource allocation problem is formulated as a linear program
(LP) followed by a geometric program (GP) which can be solved
very efficiently. Simulation results are presented for Poisson
packet arrivals and exponentially distributed packet lengths on
a Rayleigh fading channel for both the DS and BE traffic.
 Opportunistic Feedback Protocol for Minimizing
Power in Uplink with Heterogeneous Traffic
Rajiv Agarwal, Vineet Abhishek, Rath Vannithamby, John Cioffi
IEEE VTC Fall 2007 (
Abstract 
Full Text )
This paper considers a wireless uplink, where some
users have deadlinesensitive (DS) traffic and others have besteffort (BE) traffic. The objective is to meet the deadlines for DS
packets a fixed percent of time (QoS guarantee), at the same time
minimizing the sumpower used for transmission in a distributed
manner without feedback from all users to the base station
(BS). Given each user’s channel state and rate requirement, the
optimal user ordering that minimizes sumpower is shown to
be independent of the rate requirements and depends solely on
the channel conditions. Based on this, using a limited amount
of feedback, the proposed opportunistic feedback (OF) protocol
guarantees QoS to DS data and minimizes sumpower. Numerical
results show that (i) the OF protocol provides deadlinemeeting
guarantees and (ii) minimizes sumpower with a greatly reduced
feedback overhead as compared to that of a central scheduler.
 Achieving SumCapacity of the MIMO BC with Large Transmit Array using OneShot
Scalable Feedback Protocol
Rajiv Agarwal, John Cioffi
IEEE VTC Spring 2007 (
Abstract 
Full Text )
We consider a MIMO broadcast channel (BC) with
large M and K, where M is the number of transmit antennas
and K is the number of singleantenna users; and propose a
scalable feedback protocol that achieves the sumcapacity with
limited feedback of channel state information (CSI). In our
earlier work, we showed that if feedback time slots correspond to
channel gains and not to users, the sumcapacity M log log K can
be achieved with feedback resources growing only as M log K,
unlike linearly as MK for conventional schemes. In this work,
we show that feedback requirement can further be reduced by
half or more, while still achieving the sumcapacity. A scalable
feedback (SF) protocol using Random Beamforming (RBF) is
proposed, which a) requires finite number of feedback slots
upper bounded by a constant, b) is fully distributed, c) needs
finite transmission energy during feedback and d) achieves the
sumcapacity. Numerical results show that feedback load is
substantially reduced as compared to conventional schemes, as
well as our own previously proposed SF scheme.
 Capacity of Fading Broadcast Channels with OneSided Feedback
Rajiv Agarwal, John Cioffi
40th Asilomar Conference on Signals, Systems and Computers, Nov. 2006 (
Abstract 
Full Text )
In this paper we study a 2user fast fading broadcast channel, in which instanta
neous channel state information at the transmitter (CSIT) is available for only one
of the users. We derive the achievable rate region using wellknown broadcast trans
mission strategies  1) dirty paper coding (DPC), 2) superposition coding (SPC)
and 3) timedivision multiplexing (TDM). For all three transmission strategies, we
¯nd closedform expressions for the boundary of the achievable region. It is shown
analytically that the achievable region with SPC contains that with DPC which in
turn contains the TDM region in general. We also give su±cient conditions on the
fading distribution under which the proposed achievable region with superposition
coding is the capacity region. Numerical results are provided for a Rayleigh fading
channel, where we compare the proposed achievable rate regions with the upper
bound  `capacity region with perfect CSIT', inner bound `achievable rate region
with no CSIT' and a recently proposed capacity region with transmitter ordering
information.
 Capacity of Fading Broadcast Channels with Limited Rate Feedback
Rajiv Agarwal, John Cioffi
Allerton 2006 (
Abstract 
Full Text )
In this paper, we study a fading broadcast channel
(BC) with perfect channel state information at the receiver
(CSIR) and only a quantized version of it at the transmitter
due to limitedrate links for channel feedback at each user.
We find an achievable region for the fading BC under this
condition using superposition coding and show that it is sumrate
optimal.We also derive a closedform expression for finding
channel partitioning, which turns out to be the same in form
as that for waterfilling of power over time in fading channels.
Using the derived closed form expression with temporal waterfilling
of power at the transmitter in an iterative manner, we
show numerically that a single iteration is adequate to achieve
most of the capacity. Thus the complexity of finding the optimal
(global maximum) or close to optimal (local maximum) channel
partitioning is greatly reduced as compared to using a searchbased
kmean clustering algorithm like Lloyd’s algorithm that
requires multiple iterations.
 Capacity of Fading Broadcast Channels with Transmitter Ordering
CSI
Rajiv Agarwal, Yifan Liang, Andrea Goldsmith
Allerton 2005 (
Abstract 
Full Text )
We derive the ergodic capacity region for a fading broadcast channel when
the transmitter knows only the channel ordering information of the users and the
receiver knows its transmitterreceiver channel gain and the ordering information
at any time instant. We show that superposition coding based on the ordering
information achieves the ergodic capacity region. Moreover, we prove that as the
number of users goes to infinity, the capacity region with just transmitter ordering
information is the same as the capacity region with perfect channel knowledge at
the transmitter. Numerical results are provided for a Rayleigh fading channel.
 Joint Rate Allocation and Routing for Multihop Wireless Networks with DelayConstrained Data
Rajiv Agarwal, Sanjay K. Bose
WNCG Symposium 2004 (
Abstract 
Full Text )
We develop a framework for optimal rate allocation and
routing in multihop wireless networks. Each node in the
network has delaysensitive data to send to a unique destination
and this data can be sent over a single (multihop) path
through the network or via multiple paths. Sending over
multiple paths can increase throughput and reduce congestion.
Our goal is to optimize the rate sent over each possible
sourcedestination path such that the average endtoend delay
per packet is minimized. We find that the optimal solution
is a modified waterfilling of rate relative to the number
of hops in each path towards the destination, where each
hop is weighted by its throughput.
 Geolocation using Transmit and Receive Diversity
Pulkit Grover, Rajiv Agarwal, Ajit K. Chaturvedi
IEEE Globecom 2004 (
Abstract 
Full Text )
Geolocation using received signal strength (RSS) has
large errors due to multipath fading, since fading results in high
variations in RSS. We show how and when spatial diversity
combined with channel knowledge at the receiver can be used to
combat fading effects to increase accuracy in location estimate. We
then propose a simple scheme for distance estimation, characterize
the channels for which improvement in distance estimates can
be thus obtained and prove that mean square error of distance
estimate converges to zero with increasing diversity order. It
is observed that the improvement can always be obtained for
Rayleigh channel, and for Nakagamim channel if the parameter
m remains the same regardless of the distance.
Journal Publications
 Low Complexity Resource Allocation with Opportunistic Feedback over Downlink OFDMA Networks
Rajiv Agarwal, Vinay Majjigi, Zhu Han, Rath Vannithamby, John Cioffi
IEEE JSAC Special Issue on Limited Feedback, Vol. 26,
No. 8, Oct. 2008, pp. 14621472 (
Abstract 
Full Text )
Optimal tone allocation in downlink OFDMA networks
is a nonconvex NPhard problem that requires extensive
feedback for channel information. In this paper, two constantcomplexity
limitedfeedback algorithms are proposed to achieve
nearoptimal performance. First, using opportunistic feedback,
the proposed schemes are shown to reduce feedback overhead by
requiring only users likely to be allocated resources to feed back.
There are differences between the two proposed schemes for
implementation of the feedback protocol. One scheme requires
less feedback but is contentionbased, while the other scheme is
sequential and thus avoids possible collisions leading to slightly
higher performance, but needs more feedback. Second, complexity
is reduced for resource allocation by solving the optimization
problem in a distributed manner, rather than centrally at the
base station. As shown both analytically and through numerical
results, these distributed algorithms reduce the required feedback
overhead significantly, and achieve constant computational
complexity with little performance loss compared to the optimal
solution.
 Weighted SumRate Maximization using Weighted MMSE for MIMOBC Beamforming Design
S. S. Christensen, Rajiv Agarwal, Elisabeth de Carvalho, John Cioffi
IEEE Transactions on Wireless Communication, Vol. 7, No. 12, Dec.
2008, pp. 47924799 (
Abstract 
Full Text )
This paper studies linear transmit filter design
for Weighted SumRate (WSR) maximization in the Multiple
Input Multiple Output Broadcast Channel (MIMOBC). The
problem of finding the optimal transmit filter is nonconvex and
intractable to solve using low complexity methods. Motivated
by recent results highlighting the relationship between mutual
information and Minimum Mean Square Error (MMSE), this
paper establishes a relationship between weighted sumrate and
weighted MMSE in the MIMOBC. The relationship is used
to propose two low complexity algorithms for finding a local
weighted sumrate optimum based on alternating optimization.
Numerical results studying sumrate show that the proposed
algorithms achieve high performance with few iterations.
Patents
 Blind and decision directed multilevel channel estimation in Nand Flash
Marcus Marrow, Jason Bellorado, Rajiv Agarwal
 Measure of health for writing to locations in Nand Flash
Rajiv Agarwal, Marcus Marrow
 Coding across data blocks to reduce write amplification in Nand Flash
Rajiv Agarwal, Marcus Marrow
 Solid state device coding architecture for chipkill and endurance improvement
Rajiv Agarwal, Marcus Marrow
Books
 Wireless Network Design: Utilizing Limited Feedback Resources Efficiently in Downlink Wireless Systems
Rajiv Agarwal
ISBN Nr 9783843393171 (Lambert Academic Publishing, February 2011)
( Link on Amazon )
Contact
Rajiv Agarwal
rajivag[AT]stanford.edu
