Papers by Muhammad Nazmul Islam
This paper studies the optimal bit allocation for shape-gain vector quantization of wireless chan... more This paper studies the optimal bit allocation for shape-gain vector quantization of wireless channels in multiuser (MU) multiple-input multiple-output (MIMO) downlink systems based on linear precoding. Our design minimizes the mean squared-error between the original and quantized channels through optimal bit allocation across shape (direction) and gain (magnitude) for a fixed feedback overhead per user. This is shown to significantly reduce the quantization error, which in turn, decreases the MU interference. This paper makes three main contributions: first, we focus on channel gain quantization and derive the quantization distortion, based on a Euclidean distance measure, corresponding to singular values of a MIMO channel. Second, we show that the Euclidean distance-based distortion of a unit norm complex channel, due to shape quantization, is proportional to 2 − 2Bs 2M −1 , where, B s is the number of shape quantization bits and M is the number of transmit antennas. Finally, we show that for channels in complex space and allowing for a large feedback overhead, the number of direction quantization bits should be approximately (2M − 1) times the number of channel magnitude quantization bits.
Invited Paper at Conference on Information Science & Systems, Mar 2014
Small cells have been proposed as a vehicle for wireless networks to keep up with surging demand.... more Small cells have been proposed as a vehicle for wireless networks to keep up with surging demand. Small cells come with a significant challenge of providing backhaul to transport data to (from) a gateway node in the core network. Fiber based backhaul offers the high rates needed to meet this requirement, but is costly and time-consuming to deploy, when not readily available. Wireless backhaul is an attractive option for small cells as it provides a less expensive and easy-to-deploy alternative to fiber. However, there are multitude of bands and features (e.g. LOS/NLOS, spatial multiplexing etc.) associated with wireless backhaul that need to be used intelligently for small cells. Candidate bands include: sub-6 GHz band that is useful in non-line-of-sight (NLOS) scenarios, microwave band (6-42 GHz) that is useful in point-to-point line-of-sight (LOS) scenarios, and millimeter wave bands (e.g. 60, 70 and 80 GHz) that are recently being commercially used in LOS scenarios. In many deployment topologies, it is advantageous to use aggregator nodes, located at the roof tops of tall buildings near small cells. These nodes can provide high data rate to multiple small cells in NLOS paths, sustain the same data rate to gateway nodes using LOS paths and take advantage of all available bands. This work performs the joint cost optimal aggregator node placement, power allocation, channel scheduling and routing to optimize the wireless backhaul network. We formulate mixed integer nonlinear programs (MINLP) to capture the different interference and multiplexing patterns at sub-6 GHz and microwave band. We solve the MINLP through linear relaxation and branch-and-bound algorithm and apply our algorithm in an example wireless backhaul network of downtown Manhattan.
25th Queen's Biennial Symposium on Communications
We design an end-to-end linear transceiver in the downlink of
a multi-user (MU) multiple input s... more We design an end-to-end linear transceiver in the downlink of
a multi-user (MU) multiple input single output (MISO) system
with quantized channel state information at the transmitter
(CSIT). The design minimizes the sum mean squared error
(SMSE) under a sum power constraint. The contribution
of this paper is two-fold. First, unlike previous approaches,
we quantize the channels using mean squared inner product
(MSIP) vector quantization (VQ) and derive an SMSE-based
algorithm that considers MSIP quantization error as an integral
component of the whole system. This decreases the
bit error rate (BER) at high signal-to-noise ratio (SNR) and
outperforms previously derivedMUMISO linear transceivers
that exist in the limited feedback literature. Second, we show
analytically why the BER, in the high SNR regime, increases
if quantization error is not considered.
Submitted to Infocom 2014
Wireless transmission using non-contiguous chunks
of spectrum is becoming increasingly necessary... more Wireless transmission using non-contiguous chunks
of spectrum is becoming increasingly necessary due to: incumbent users in TV white space, anticipated spectrum sharing
between commercial and military systems, and uncoordinated
interference in unlicensed bands. Multi-Channel Multi-Radio
(MC-MR) platforms and Non-Contiguous Orthogonal Frequency
Division Multiple Access (NC-OFDMA) technology are the two
commercially viable transmission choices to access these noncontiguous spectrum chunks. Fixed MC-MR’s do not scale with increasing number of non-contiguous spectrum chunks due to their fixed set of supporting radio front ends. NC-OFDMA allows
nodes to access these non-contiguous spectrum chunks and put
null sub-carriers in the remaining chunks. However, nulling subcarriers increases the sampling rate (spectrum span) which, in
turn, increases the power consumption of radio front ends. Our
work characterizes this trade-off from a cross-layer perspective.
Specifically, we perform joint power control, spectrum span
selection, scheduling and routing to minimize system power of
multi-hop NC-OFDMA networks. Numerical simulations suggest
that our approach reduces system power by 4 12 dB over
classical water-filling based cross-layer algorithms
Published at International Conference on Communications 2013
"Wireless systems are getting deployed in many new
environments with different antenna heights, ... more "Wireless systems are getting deployed in many new
environments with different antenna heights, frequency bands
and multipath conditions. This has led to an increasing demand
for more channel measurements to understand wireless propagation in specific environments and assist deployment engineering. We design and implement a rapid wireless channel sounding system, using the Universal Software Radio Peripheral (USRP) and GNU Radio software, to address these demands. Our design measures channel propagation characteristics simultaneously from multiple transmitter locations. The system consists of multiple battery-powered transmitters and receivers. Therefore, we can set-up the channel sounder rapidly at a field location and measure expeditiously by analyzing different transmitters’ signals during a single walk or drive through the environment. Our design can be used for both indoor and outdoor channel measurements in the frequency range of 1 MHz to 6 GHz.
We expect that the proposed approach, with a few further
refinements, can transform the task of propagation measurement
as a routine part of day-to-day wireless network engineering."
Proc. Military Communications Conference (MILCOM) 2012, Oct 2012.
In this paper, we design and implement time exchange
(TE) based cooperative forwarding where nod... more In this paper, we design and implement time exchange
(TE) based cooperative forwarding where nodes use
transmission time slots as incentives for relaying. We focus
on distributed joint time slot exchange and relay selection in
the sum goodput maximization of the overall network. We
formulate the design objective as a mixed integer nonlinear
programming (MINLP) problem and provide a polynomial time
distributed solution of the MINLP. We implement the designed
algorithm in the software defined radio enabled USRP nodes of
the ORBIT indoor wireless testbed. The ORBIT grid is used as a global control plane for exchange of control information between the USRP nodes. Experimental results suggest that TE
can significantly increase the sum goodput of the network. We
also demonstrate the performance of a goodput optimization
algorithm that is proportionally fair.
Proc. 10th International Symposium on Modeling and Optimization in Mobile, Ad Hoc & Wireless Networks (WiOpt), pp. 192-199, May, 2012.
In this paper, we investigate joint optimal relay selection and resource allocation under bandwid... more In this paper, we investigate joint optimal relay selection and resource allocation under bandwidth exchange (BE)
enabled incentivized cooperative forwarding in wireless networks.
We consider an autonomous network where N nodes transmit
data in the uplink to an access point (AP) / base station (BS).
We consider the scenario where each node gets an initial amount
(equal, optimal based on direct path or arbitrary) of bandwidth,
and uses this bandwidth as a flexible incentive for two hop
relaying. We focus on alpha-fair network utility maximization (NUM) and outage reduction in this environment. Our contribution is two-fold. First, we propose an incentivized forwarding based
resource allocation algorithm which maximizes the global utility
while preserving the initial utility of each cooperative node.
Second, defining the link weight of each relay pair as the utility
gain due to cooperation (over noncooperation), we show that the
optimal relay selection in alpha-fair NUM reduces to the maximum
weighted matching (MWM) problem in a non-bipartite graph.
Numerical results show that the proposed algorithms provide 20-
25% gain in spectral efficiency and 90-98% reduction in outage
probability.
"We design an end-to-end linear transceiver in the downlink
of a multi-user multiple-input multi... more "We design an end-to-end linear transceiver in the downlink
of a multi-user multiple-input multiple-output (MIMO) system
with multiple data streams per user and quantized channel
state information at the transmitter. We minimize the sum
mean squared error (SMSE) under a sum power constraint
with quantization based on the mean squared inner product.
We make three contributions: (i) we remove dimensionality
constraints on the MIMO configuration and the resulting
feedback overhead scales linearly with the number of data
streams; (ii) we use the combination of eigenmode combining
and minimum mean square error receiver that makes user’s
feedback mutually independent; (iii) we analyze SMSE at
high signal-to-noise ratio and large number of transmit antennas
and derive an approximate SMSE floor."
"In the context of a time-varying multiuser multipleinput-
multiple-output (MIMO) system, we des... more "In the context of a time-varying multiuser multipleinput-
multiple-output (MIMO) system, we design recursive least
squares based adaptive predictors and differential quantizers to
minimize the sum mean squared error of the overall system.
Using the fact that the scalar entries of the left singular matrix
of a Gaussian MIMO channel becomes “almost” Gaussian
distributed even for a small number of transmit antennas,
we perform adaptive differential quantization of the relevant
singular matrix entries. Compared to the algorithms in the
existing differential feedback literature, our proposed quantizer
provides three advantages: first, the controller parameters are
flexible enough to adapt themselves to different vehicle speeds;
second, the model is backward adaptive i.e., the base station and receiver can agree upon the predictor and variance estimator
coefficients without explicit exchange of the parameters; third,
it can accurately model the system even when the correlation
between two successive channel samples becomes as low as 0.05. Our simulation results show that our proposed method can
reduce the required feedback by several kilobits per second for
vehicle speeds up to 20 km/h (channel tracker) and 10 km/h
(singular vector tracker). The proposed system also outperforms
a fixed quantizer, with same feedback overhead, in terms of bit
error rate up to 30 km/h."
"We investigate an incentive mechanism called Bandwidth
Exchange (BE) for cooperative forwarding... more "We investigate an incentive mechanism called Bandwidth
Exchange (BE) for cooperative forwarding where transmission
bandwidth is used as a flexible resource. We focus
on a network where two nodes, communicating with the base
station (BS) / access point (AP), initially get optimal amount of
bandwidth based on direct path transmission and then use their
individual bandwidths as flexible incentives for two hop relaying.
In our proposed scenario, the forwarder node sends its own data
along with the data of the sender in exchange for additional
transmission bandwidth, provided by the sender.We compare the
performance of the proposed mechanism with optimal bandwidth
and power allocation based direct transmission. We use sum rate, max-min rate and min-max power as the evaluation criteria and prove the convex/concave nature of the optimization problem
formulations. Our numerical analysis shows that the BE based
cooperative forwarding extends the coverage in wireless networks
when the far node falls in outage under direct transmission.
Further, BE significantly improves the max-min rate and minmax
power performance of the network."
IET Communications, Jan 1, 2011
The authors investigate quantisation and feedback of channel state information in a multiuser (MU... more The authors investigate quantisation and feedback of channel state information in a multiuser (MU) multiple-input multiple-output (MIMO) system. Each user may receive multiple data streams. The authors design minimises the sum mean squared error (SMSE) while accounting for the imperfections in channel state information (CSI) at the transmitter. This study makes three contributions: first, the authors provide an end-to-end SMSE transceiver design that incorporates receiver combining, feedback policy and transmit precoder design with channel uncertainty. This enables the proposed transceiver to outperform the previously derived limited feedback MU linear transceivers. Second, the authors remove dimensionality constraints on the MIMO system, for the scenario with multiple data streams per user, using a combination of maximum expected signal combining and minimum MSE receiver. This makes each user's feedback independent of the others and the resulting feedback overhead scales linearly with the number of data streams instead of the number of receiving antennas. Finally, the authors analyse the SMSE of the proposed algorithm at high signal-to-noise ratio (SNR) and large number of transmit antennas. As an aside, the authors show analytically why the bit error rate, in the high SNR regime, increases if quantisation error is ignored.
Thesis Chapters by Muhammad Nazmul Islam
Multi-user wireless systems with multiple antennas can drastically increase the capac-
ity while... more Multi-user wireless systems with multiple antennas can drastically increase the capac-
ity while maintaining the quality of service requirements. The best performance of these
systems is obtained at the presence of instantaneous channel knowledge. Since uplink-
downlink channel reciprocity does not hold in frequency division duplex and broadband
time division duplex systems, efficient channel quantization becomes important. This
thesis focuses on different quantization techniques in a linearly precoded multi-user wire-
less system.
Our work provides three major contributions. First, we come up with an end-to-end
transceiver design, incorporating precoder, receive combining and feedback policy, that
works well at low feedback overhead. Second, we provide optimal bit allocation across the
gain and shape of a complex vector to reduce the quantization error and investigate its
effect in the multiuser wireless system. Third, we design an adaptive differential quantizer
that reduces feedback overhead by utilizing temporal correlation of the channels in a time
varying scenario.
Uploads
Papers by Muhammad Nazmul Islam
a multi-user (MU) multiple input single output (MISO) system
with quantized channel state information at the transmitter
(CSIT). The design minimizes the sum mean squared error
(SMSE) under a sum power constraint. The contribution
of this paper is two-fold. First, unlike previous approaches,
we quantize the channels using mean squared inner product
(MSIP) vector quantization (VQ) and derive an SMSE-based
algorithm that considers MSIP quantization error as an integral
component of the whole system. This decreases the
bit error rate (BER) at high signal-to-noise ratio (SNR) and
outperforms previously derivedMUMISO linear transceivers
that exist in the limited feedback literature. Second, we show
analytically why the BER, in the high SNR regime, increases
if quantization error is not considered.
of spectrum is becoming increasingly necessary due to: incumbent users in TV white space, anticipated spectrum sharing
between commercial and military systems, and uncoordinated
interference in unlicensed bands. Multi-Channel Multi-Radio
(MC-MR) platforms and Non-Contiguous Orthogonal Frequency
Division Multiple Access (NC-OFDMA) technology are the two
commercially viable transmission choices to access these noncontiguous spectrum chunks. Fixed MC-MR’s do not scale with increasing number of non-contiguous spectrum chunks due to their fixed set of supporting radio front ends. NC-OFDMA allows
nodes to access these non-contiguous spectrum chunks and put
null sub-carriers in the remaining chunks. However, nulling subcarriers increases the sampling rate (spectrum span) which, in
turn, increases the power consumption of radio front ends. Our
work characterizes this trade-off from a cross-layer perspective.
Specifically, we perform joint power control, spectrum span
selection, scheduling and routing to minimize system power of
multi-hop NC-OFDMA networks. Numerical simulations suggest
that our approach reduces system power by 4 12 dB over
classical water-filling based cross-layer algorithms
environments with different antenna heights, frequency bands
and multipath conditions. This has led to an increasing demand
for more channel measurements to understand wireless propagation in specific environments and assist deployment engineering. We design and implement a rapid wireless channel sounding system, using the Universal Software Radio Peripheral (USRP) and GNU Radio software, to address these demands. Our design measures channel propagation characteristics simultaneously from multiple transmitter locations. The system consists of multiple battery-powered transmitters and receivers. Therefore, we can set-up the channel sounder rapidly at a field location and measure expeditiously by analyzing different transmitters’ signals during a single walk or drive through the environment. Our design can be used for both indoor and outdoor channel measurements in the frequency range of 1 MHz to 6 GHz.
We expect that the proposed approach, with a few further
refinements, can transform the task of propagation measurement
as a routine part of day-to-day wireless network engineering."
(TE) based cooperative forwarding where nodes use
transmission time slots as incentives for relaying. We focus
on distributed joint time slot exchange and relay selection in
the sum goodput maximization of the overall network. We
formulate the design objective as a mixed integer nonlinear
programming (MINLP) problem and provide a polynomial time
distributed solution of the MINLP. We implement the designed
algorithm in the software defined radio enabled USRP nodes of
the ORBIT indoor wireless testbed. The ORBIT grid is used as a global control plane for exchange of control information between the USRP nodes. Experimental results suggest that TE
can significantly increase the sum goodput of the network. We
also demonstrate the performance of a goodput optimization
algorithm that is proportionally fair.
enabled incentivized cooperative forwarding in wireless networks.
We consider an autonomous network where N nodes transmit
data in the uplink to an access point (AP) / base station (BS).
We consider the scenario where each node gets an initial amount
(equal, optimal based on direct path or arbitrary) of bandwidth,
and uses this bandwidth as a flexible incentive for two hop
relaying. We focus on alpha-fair network utility maximization (NUM) and outage reduction in this environment. Our contribution is two-fold. First, we propose an incentivized forwarding based
resource allocation algorithm which maximizes the global utility
while preserving the initial utility of each cooperative node.
Second, defining the link weight of each relay pair as the utility
gain due to cooperation (over noncooperation), we show that the
optimal relay selection in alpha-fair NUM reduces to the maximum
weighted matching (MWM) problem in a non-bipartite graph.
Numerical results show that the proposed algorithms provide 20-
25% gain in spectral efficiency and 90-98% reduction in outage
probability.
of a multi-user multiple-input multiple-output (MIMO) system
with multiple data streams per user and quantized channel
state information at the transmitter. We minimize the sum
mean squared error (SMSE) under a sum power constraint
with quantization based on the mean squared inner product.
We make three contributions: (i) we remove dimensionality
constraints on the MIMO configuration and the resulting
feedback overhead scales linearly with the number of data
streams; (ii) we use the combination of eigenmode combining
and minimum mean square error receiver that makes user’s
feedback mutually independent; (iii) we analyze SMSE at
high signal-to-noise ratio and large number of transmit antennas
and derive an approximate SMSE floor."
multiple-output (MIMO) system, we design recursive least
squares based adaptive predictors and differential quantizers to
minimize the sum mean squared error of the overall system.
Using the fact that the scalar entries of the left singular matrix
of a Gaussian MIMO channel becomes “almost” Gaussian
distributed even for a small number of transmit antennas,
we perform adaptive differential quantization of the relevant
singular matrix entries. Compared to the algorithms in the
existing differential feedback literature, our proposed quantizer
provides three advantages: first, the controller parameters are
flexible enough to adapt themselves to different vehicle speeds;
second, the model is backward adaptive i.e., the base station and receiver can agree upon the predictor and variance estimator
coefficients without explicit exchange of the parameters; third,
it can accurately model the system even when the correlation
between two successive channel samples becomes as low as 0.05. Our simulation results show that our proposed method can
reduce the required feedback by several kilobits per second for
vehicle speeds up to 20 km/h (channel tracker) and 10 km/h
(singular vector tracker). The proposed system also outperforms
a fixed quantizer, with same feedback overhead, in terms of bit
error rate up to 30 km/h."
Exchange (BE) for cooperative forwarding where transmission
bandwidth is used as a flexible resource. We focus
on a network where two nodes, communicating with the base
station (BS) / access point (AP), initially get optimal amount of
bandwidth based on direct path transmission and then use their
individual bandwidths as flexible incentives for two hop relaying.
In our proposed scenario, the forwarder node sends its own data
along with the data of the sender in exchange for additional
transmission bandwidth, provided by the sender.We compare the
performance of the proposed mechanism with optimal bandwidth
and power allocation based direct transmission. We use sum rate, max-min rate and min-max power as the evaluation criteria and prove the convex/concave nature of the optimization problem
formulations. Our numerical analysis shows that the BE based
cooperative forwarding extends the coverage in wireless networks
when the far node falls in outage under direct transmission.
Further, BE significantly improves the max-min rate and minmax
power performance of the network."
Thesis Chapters by Muhammad Nazmul Islam
ity while maintaining the quality of service requirements. The best performance of these
systems is obtained at the presence of instantaneous channel knowledge. Since uplink-
downlink channel reciprocity does not hold in frequency division duplex and broadband
time division duplex systems, efficient channel quantization becomes important. This
thesis focuses on different quantization techniques in a linearly precoded multi-user wire-
less system.
Our work provides three major contributions. First, we come up with an end-to-end
transceiver design, incorporating precoder, receive combining and feedback policy, that
works well at low feedback overhead. Second, we provide optimal bit allocation across the
gain and shape of a complex vector to reduce the quantization error and investigate its
effect in the multiuser wireless system. Third, we design an adaptive differential quantizer
that reduces feedback overhead by utilizing temporal correlation of the channels in a time
varying scenario.
a multi-user (MU) multiple input single output (MISO) system
with quantized channel state information at the transmitter
(CSIT). The design minimizes the sum mean squared error
(SMSE) under a sum power constraint. The contribution
of this paper is two-fold. First, unlike previous approaches,
we quantize the channels using mean squared inner product
(MSIP) vector quantization (VQ) and derive an SMSE-based
algorithm that considers MSIP quantization error as an integral
component of the whole system. This decreases the
bit error rate (BER) at high signal-to-noise ratio (SNR) and
outperforms previously derivedMUMISO linear transceivers
that exist in the limited feedback literature. Second, we show
analytically why the BER, in the high SNR regime, increases
if quantization error is not considered.
of spectrum is becoming increasingly necessary due to: incumbent users in TV white space, anticipated spectrum sharing
between commercial and military systems, and uncoordinated
interference in unlicensed bands. Multi-Channel Multi-Radio
(MC-MR) platforms and Non-Contiguous Orthogonal Frequency
Division Multiple Access (NC-OFDMA) technology are the two
commercially viable transmission choices to access these noncontiguous spectrum chunks. Fixed MC-MR’s do not scale with increasing number of non-contiguous spectrum chunks due to their fixed set of supporting radio front ends. NC-OFDMA allows
nodes to access these non-contiguous spectrum chunks and put
null sub-carriers in the remaining chunks. However, nulling subcarriers increases the sampling rate (spectrum span) which, in
turn, increases the power consumption of radio front ends. Our
work characterizes this trade-off from a cross-layer perspective.
Specifically, we perform joint power control, spectrum span
selection, scheduling and routing to minimize system power of
multi-hop NC-OFDMA networks. Numerical simulations suggest
that our approach reduces system power by 4 12 dB over
classical water-filling based cross-layer algorithms
environments with different antenna heights, frequency bands
and multipath conditions. This has led to an increasing demand
for more channel measurements to understand wireless propagation in specific environments and assist deployment engineering. We design and implement a rapid wireless channel sounding system, using the Universal Software Radio Peripheral (USRP) and GNU Radio software, to address these demands. Our design measures channel propagation characteristics simultaneously from multiple transmitter locations. The system consists of multiple battery-powered transmitters and receivers. Therefore, we can set-up the channel sounder rapidly at a field location and measure expeditiously by analyzing different transmitters’ signals during a single walk or drive through the environment. Our design can be used for both indoor and outdoor channel measurements in the frequency range of 1 MHz to 6 GHz.
We expect that the proposed approach, with a few further
refinements, can transform the task of propagation measurement
as a routine part of day-to-day wireless network engineering."
(TE) based cooperative forwarding where nodes use
transmission time slots as incentives for relaying. We focus
on distributed joint time slot exchange and relay selection in
the sum goodput maximization of the overall network. We
formulate the design objective as a mixed integer nonlinear
programming (MINLP) problem and provide a polynomial time
distributed solution of the MINLP. We implement the designed
algorithm in the software defined radio enabled USRP nodes of
the ORBIT indoor wireless testbed. The ORBIT grid is used as a global control plane for exchange of control information between the USRP nodes. Experimental results suggest that TE
can significantly increase the sum goodput of the network. We
also demonstrate the performance of a goodput optimization
algorithm that is proportionally fair.
enabled incentivized cooperative forwarding in wireless networks.
We consider an autonomous network where N nodes transmit
data in the uplink to an access point (AP) / base station (BS).
We consider the scenario where each node gets an initial amount
(equal, optimal based on direct path or arbitrary) of bandwidth,
and uses this bandwidth as a flexible incentive for two hop
relaying. We focus on alpha-fair network utility maximization (NUM) and outage reduction in this environment. Our contribution is two-fold. First, we propose an incentivized forwarding based
resource allocation algorithm which maximizes the global utility
while preserving the initial utility of each cooperative node.
Second, defining the link weight of each relay pair as the utility
gain due to cooperation (over noncooperation), we show that the
optimal relay selection in alpha-fair NUM reduces to the maximum
weighted matching (MWM) problem in a non-bipartite graph.
Numerical results show that the proposed algorithms provide 20-
25% gain in spectral efficiency and 90-98% reduction in outage
probability.
of a multi-user multiple-input multiple-output (MIMO) system
with multiple data streams per user and quantized channel
state information at the transmitter. We minimize the sum
mean squared error (SMSE) under a sum power constraint
with quantization based on the mean squared inner product.
We make three contributions: (i) we remove dimensionality
constraints on the MIMO configuration and the resulting
feedback overhead scales linearly with the number of data
streams; (ii) we use the combination of eigenmode combining
and minimum mean square error receiver that makes user’s
feedback mutually independent; (iii) we analyze SMSE at
high signal-to-noise ratio and large number of transmit antennas
and derive an approximate SMSE floor."
multiple-output (MIMO) system, we design recursive least
squares based adaptive predictors and differential quantizers to
minimize the sum mean squared error of the overall system.
Using the fact that the scalar entries of the left singular matrix
of a Gaussian MIMO channel becomes “almost” Gaussian
distributed even for a small number of transmit antennas,
we perform adaptive differential quantization of the relevant
singular matrix entries. Compared to the algorithms in the
existing differential feedback literature, our proposed quantizer
provides three advantages: first, the controller parameters are
flexible enough to adapt themselves to different vehicle speeds;
second, the model is backward adaptive i.e., the base station and receiver can agree upon the predictor and variance estimator
coefficients without explicit exchange of the parameters; third,
it can accurately model the system even when the correlation
between two successive channel samples becomes as low as 0.05. Our simulation results show that our proposed method can
reduce the required feedback by several kilobits per second for
vehicle speeds up to 20 km/h (channel tracker) and 10 km/h
(singular vector tracker). The proposed system also outperforms
a fixed quantizer, with same feedback overhead, in terms of bit
error rate up to 30 km/h."
Exchange (BE) for cooperative forwarding where transmission
bandwidth is used as a flexible resource. We focus
on a network where two nodes, communicating with the base
station (BS) / access point (AP), initially get optimal amount of
bandwidth based on direct path transmission and then use their
individual bandwidths as flexible incentives for two hop relaying.
In our proposed scenario, the forwarder node sends its own data
along with the data of the sender in exchange for additional
transmission bandwidth, provided by the sender.We compare the
performance of the proposed mechanism with optimal bandwidth
and power allocation based direct transmission. We use sum rate, max-min rate and min-max power as the evaluation criteria and prove the convex/concave nature of the optimization problem
formulations. Our numerical analysis shows that the BE based
cooperative forwarding extends the coverage in wireless networks
when the far node falls in outage under direct transmission.
Further, BE significantly improves the max-min rate and minmax
power performance of the network."
ity while maintaining the quality of service requirements. The best performance of these
systems is obtained at the presence of instantaneous channel knowledge. Since uplink-
downlink channel reciprocity does not hold in frequency division duplex and broadband
time division duplex systems, efficient channel quantization becomes important. This
thesis focuses on different quantization techniques in a linearly precoded multi-user wire-
less system.
Our work provides three major contributions. First, we come up with an end-to-end
transceiver design, incorporating precoder, receive combining and feedback policy, that
works well at low feedback overhead. Second, we provide optimal bit allocation across the
gain and shape of a complex vector to reduce the quantization error and investigate its
effect in the multiuser wireless system. Third, we design an adaptive differential quantizer
that reduces feedback overhead by utilizing temporal correlation of the channels in a time
varying scenario.