574 research outputs found
Resource Allocation for Power Minimization in the Downlink of THP-based Spatial Multiplexing MIMO-OFDMA Systems
In this work, we deal with resource allocation in the downlink of spatial
multiplexing MIMO-OFDMA systems. In particular, we concentrate on the problem
of jointly optimizing the transmit and receive processing matrices, the channel
assignment and the power allocation with the objective of minimizing the total
power consumption while satisfying different quality-of-service requirements. A
layered architecture is used in which users are first partitioned in different
groups on the basis of their channel quality and then channel assignment and
transceiver design are sequentially addressed starting from the group of users
with most adverse channel conditions. The multi-user interference among users
belonging to different groups is removed at the base station using a
Tomlinson-Harashima pre-coder operating at user level. Numerical results are
used to highlight the effectiveness of the proposed solution and to make
comparisons with existing alternatives.Comment: 12 pages, 6 figures, IEEE Trans. Veh. Techno
MIMO Transceivers With Decision Feedback and Bit Loading: Theory and Optimization
This paper considers MIMO transceivers with linear precoders and decision feedback equalizers (DFEs), with bit allocation at the transmitter. Zero-forcing (ZF) is assumed. Considered first is the minimization of transmitted power, for a given total bit rate and a specified set of error probabilities for the symbol streams. The precoder and DFE matrices are optimized jointly with bit allocation. It is shown that the generalized triangular decomposition (GTD) introduced by Jiang, Li, and Hager offers an optimal family of solutions. The optimal linear transceiver (which has a linear equalizer rather than a DFE) with optimal bit allocation is a member of this family. This shows formally that, under optimal bit allocation, linear and DFE transceivers achieve the same minimum power. The DFE transceiver using the geometric mean decomposition (GMD) is another member of this optimal family, and is such that optimal bit allocation yields identical bits for all symbol streams—no bit allocation is necessary—when the specified error probabilities are identical for all streams. The QR-based system used in VBLAST is yet another member of the optimal family and is particularly well-suited when limited feedback is allowed from receiver to transmitter. Two other optimization problems are then considered: a) minimization of power for specified set of bit rates and error probabilities (the QoS problem), and b) maximization of bit rate for fixed set of error probabilities and power. It is shown in both cases that the GTD yields an optimal family of solutions
The Application of MIMO to Non-Orthogonal Multiple Access
This paper considers the application of multiple-input multiple-output (MIMO)
techniques to non-orthogonal multiple access (NOMA) systems. A new design of
precoding and detection matrices for MIMO-NOMA is proposed and its performance
is analyzed for the case with a fixed set of power allocation coefficients. To
further improve the performance gap between MIMO-NOMA and conventional
orthogonal multiple access schemes, user pairing is applied to NOMA and its
impact on the system performance is characterized. More sophisticated choices
of power allocation coefficients are also proposed to meet various quality of
service requirements. Finally computer simulation results are provided to
facilitate the performance evaluation of MIMO-NOMA and also demonstrate the
accuracy of the developed analytical results
Joint optimization of transceivers with decision feedback and bit loading
The transceiver optimization problem for MIMO
channels has been considered in the past with linear receivers as
well as with decision feedback (DFE) receivers. Joint optimization
of bit allocation, precoder, and equalizer has in the past been
considered only for the linear transceiver (transceiver with linear
precoder and linear equalizer). It has also been observed that
the use of DFE even without bit allocation in general results in
better performance that linear transceivers with bit allocation.
This paper provides a general study of this for transceivers
with the zero-forcing constraint. It is formally shown that when
the bit allocation, precoder, and equalizer are jointly optimized,
linear transceivers and transceivers with DFE have identical
performance in the sense that transmitted power is identical
for a given bit rate and error probability. The developments of
this paper are based on the generalized triangular decomposition
(GTD) recently introduced by Jiang, Li, and Hager. It will be
shown that a broad class of GTD-based systems solve the optimal
DFE problem with bit allocation. The special case of a linear
transceiver with optimum bit allocation will emerge as one of
the many solutions
Linear Precoders for Non-Regenerative Asymmetric Two-way Relaying in Cellular Systems
Two-way relaying (TWR) reduces the spectral-efficiency loss caused in
conventional half-duplex relaying. TWR is possible when two nodes exchange data
simultaneously through a relay. In cellular systems, data exchange between base
station (BS) and users is usually not simultaneous e.g., a user (TUE) has
uplink data to transmit during multiple access (MAC) phase, but does not have
downlink data to receive during broadcast (BC) phase. This non-simultaneous
data exchange will reduce TWR to spectrally-inefficient conventional
half-duplex relaying. With infrastructure relays, where multiple users
communicate through a relay, a new transmission protocol is proposed to recover
the spectral loss. The BC phase following the MAC phase of TUE is now used by
the relay to transmit downlink data to another user (RUE). RUE will not be able
to cancel the back-propagating interference. A structured precoder is designed
at the multi-antenna relay to cancel this interference. With multiple-input
multiple-output (MIMO) nodes, the proposed precoder also triangulates the
compound MAC and BC phase MIMO channels. The channel triangulation reduces the
weighted sum-rate optimization to power allocation problem, which is then cast
as a geometric program. Simulation results illustrate the effectiveness of the
proposed protocol over conventional solutions.Comment: 30 pages, 7 figures, submitted to IEEE Transactions on Wireless
Communication
Energy Efficient Reduced Complexity Multi-Service, Multi-Channel Scheduling Techniques
The need for energy efficient communications is essential in current and next-generation wireless communications systems. A large component of energy expenditure in mobile devices is in the mobile radio interface. Proper scheduling and resource allocation techniques that exploit instantaneous and long-term average knowledge of the channel, queue state and quality of service parameters can be used to improve the energy efficiency of communication.
This thesis focuses on exploiting queue and channel state information as well as quality of service parameters in order to design energy efficient scheduling techniques. The proposed designs are for multi-stream, multi-channel systems and in general have high computational complexity. The large contributions of this thesis are in both the design of optimal/near-optimal scheduling/resource allocation schemes for these systems as well as proposing complexity reduction methods in their design.
Methods are proposed for both a MIMO downlink system as well as an LTE uplink system. The effect of power efficiency on quality of service parameters is well studied as well as complexity/efficiency comparisons between optimal/near optimal allocation
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