Spelling suggestions: "subject:"dirtier coding"" "subject:"periopaper coding""
1 |
Interference Channel with State InformationZhang, Lili 2012 August 1900 (has links)
In this dissertation, we study the state-dependent two-user interference channel, where the state information is non-causally known at both transmitters but unknown to either of the receivers. We first propose two coding schemes for the discrete memoryless case: simultaneous encoding for the sub-messages in the first one and super-position encoding in the second one, both with rate splitting and Gel'fand-Pinsker coding. The corresponding achievable rate regions are established. Moreover, for the Gaussian case, we focus on the simultaneous encoding scheme and propose an active interference cancellation mechanism, which is a generalized dirty-paper coding technique, to partially eliminate the state effect at the receivers. The corresponding achievable rate region is then derived. We also propose several heuristic schemes for some special cases: the strong interference case, the mixed interference case, and the weak interference case. For the strong and mixed interference case, numerical results are provided to show that active interference cancellation significantly enlarges the achievable rate region. For the weak interference case, flexible power splitting instead of active interference cancellation improves the performance significantly.
Moreover, we focus on the simplest symmetric case, where both direct link gains are the same with each other, and both interfering link gains are the same with each other. We apply the above coding scheme with different dirty paper coding parameters. When the state is additive and symmetric at both receivers, we study both strong and weak interference scenarios and characterize the theoretical gap between the achievable symmetric rate and the upper bound, which is shown to be less than 1/4 bit for the strong interference case and less than 3/4 bit for the weak interference case. Then we provide numerical evaluations of the achievable rates against the upper bound, which validates the theoretical analysis for both strong and weak interference scenarios. Finally, we define the generalized degrees of freedom for the symmetric Gaussian case, and compare the lower bounds against the upper bounds for both strong and weak interference cases. We also show that our achievable schemes can obtain the exact optimal values of the generalized degrees of freedom, i.e., the lower bounds meet the upper bounds for both strong and weak interference cases.
|
2 |
Source-channel coding for robust image transmission and for dirty-paper codingSun, Yong 25 April 2007 (has links)
In this dissertation, we studied two seemingly uncorrelated, but conceptually
related problems in terms of source-channel coding: 1) wireless image transmission
and 2) Costa ("dirty-paper") code design.
In the first part of the dissertation, we consider progressive image transmission
over a wireless system employing space-time coded OFDM. The space-time coded
OFDM system based on a newly built broadband MIMO fading model is theoretically
evaluated by assuming perfect channel state information (CSI) at the receiver for
coherent detection. Then an adaptive modulation scheme is proposed to pick the
constellation size that offers the best reconstructed image quality for each average
signal-to-noise ratio (SNR).
A more practical scenario is also considered without the assumption of perfect
CSI. We employ low-complexity decision-feedback decoding for differentially space-
time coded OFDM systems to exploit transmitter diversity. For JSCC, we adopt a
product channel code structure that is proven to provide powerful error protection and
bursty error correction. To further improve the system performance, we also apply
the powerful iterative (turbo) coding techniques and propose the iterative decoding
of differentially space-time coded multiple descriptions of images.
The second part of the dissertation deals with practical dirty-paper code designs. We first invoke an information-theoretical interpretation of algebraic binning and
motivate the code design guidelines in terms of source-channel coding. Then two
dirty-paper code designs are proposed. The first is a nested turbo construction based
on soft-output trellis-coded quantization (SOTCQ) for source coding and turbo trellis-
coded modulation (TTCM) for channel coding. A novel procedure is devised to
balance the dimensionalities of the equivalent lattice codes corresponding to SOTCQ
and TTCM. The second dirty-paper code design employs TCQ and IRA codes for
near-capacity performance. This is done by synergistically combining TCQ with IRA
codes so that they work together as well as they do individually. Our TCQ/IRA
design approaches the dirty-paper capacity limit at the low rate regime (e.g., < 1:0
bit/sample), while our nested SOTCQ/TTCM scheme provides the best performs so
far at medium-to-high rates (e.g., >= 1:0 bit/sample). Thus the two proposed practical
code designs are complementary to each other.
|
3 |
Code design for multiple-input multiple-output broadcast channelsUppal, Momin Ayub 02 June 2009 (has links)
Recent information theoretical results indicate that dirty-paper coding (DPC)
achieves the entire capacity region of the Gaussian multiple-input multiple-output
(MIMO) broadcast channel (BC). This thesis presents practical code designs for
Gaussian BCs based on DPC. To simplify our designs, we assume constraints on
the individual rates for each user instead of the customary constraint on transmitter
power. The objective therefore is to minimize the transmitter power such that
the practical decoders of all users are able to operate at the given rate constraints.
The enabling element of our code designs is a practical DPC scheme based on nested
turbo codes. We start with Cover's simplest two-user Gaussian BC as a toy example
and present a code design that operates 1.44 dB away from the capacity region
boundary at the transmission rate of 1 bit per sample per dimension for each user.
Then we consider the case of the multiple-input multiple-output BC and develop a
practical limit-approaching code design under the assumption that the channel state
information is available perfectly at the receivers as well as at the transmitter. The
optimal precoding strategy in this case can be derived by invoking duality between
the MIMO BC and MIMO multiple access channel (MAC). However, this approach
requires transformation of the optimal MAC covariances to their corresponding counterparts
in the BC domain. To avoid these computationally complex transformations,
we derive a closed-form expression for the optimal precoding matrix for the two-user
case and use it to determine the optimal precoding strategy. For more than two users we propose a low-complexity suboptimal strategy, which, for three transmit antennas
at the base station and three users (each with a single receive antenna), performs
only 0.2 dB worse than the optimal scheme.
Our obtained results are only 1.5 dB away from the capacity limit. Moreover
simulations indicate that our practical DPC based scheme significantly outperforms
the prevalent suboptimal strategies such as time division multiplexing and zero forcing
beamforming. The drawback of DPC based designs is the requirement of channel state
information at the transmitter. However, if the channel state information can be
communicated back to the transmitter effectively, DPC does indeed have a promising
future in code designs for MIMO BCs.
|
4 |
Modulation for interference avoidance on the AWGN channelDu, Jinfeng January 2006 (has links)
Theoretic results have shown that the capacity of a channel does not decrease if the receiver observes the transmitted signal in the presence of interference, provided that the transmitter knows this interference non-causally. That is, if the transmitter has non-causal access to the interference, by using proper precoding this interference could be “avoided” (as if it were not present) under the same transmit power constraint. It indicates that lossless (in the sense of capacity) precoding is theoretically possible at any signal-to-noise-ratio (SNR). This is of special interest in digital watermarking, transmission for ISI channels as well as for MIMO broadcast channels. Recent research has elegantly demonstrated the (near) achievability of this “existence-type” result, while the complexity is notable. An interesting question is what one can do when very little extra complexity is permitted. This thesis treats such special cases of this problem in order to shed some light on this question. In the AWGN channel with additive interference, an optimum modulator is designed under the constraint of a binary signaling alphabet with binary interference.Tomlinson-Harashima precoding (THP), which is originally proposed for ISI channels, is improved by picking up optimized parameters and then taken as a benchmark. Simulation results show that the Optimum Modulator always outperforms the THP with optimized parameters. The difference in performance, in terms of mutual information between channel input and output as well as coded bit error rate with Turbo codes, is significant in many scenarios.
|
5 |
Coordinated Beamforming and Common Message Decoding for Intercell Interference Mitigation in Multicell NetworksDahrouj, Hayssam 15 February 2011 (has links)
Conventional multicell wireless systems operate with out-of-cell interference treated as background noise; consequently, their performance faces two major limitations: 1)Signal processing is performed on a per-cell basis; and 2)Intercell interference detection is infeasible as intercell interference, although significantly above the noise level, is typically quite weak. In this thesis, we consider a multicell downlink scenario, where base-stations are equipped with multiple transmit antennas, the remote users are equipped with a single antenna, and multiple remote users are active simultaneously via spatial division multiplexing. We propose solutions for the above limitations by considering techniques for mitigating interference.
The first part of the thesis proposes solutions for the first limitation. It considers the benefit of coordinating base-stations across multiple cells, where
multiple base-stations may jointly optimize their respective beamformers to improve the overall system performance. It focuses on the design criteria of minimizing either the total weighted transmitted power or the maximum per-antenna power across the base-stations subject to signal-to-interference-and-noise-ratio (SINR) constraints at the remote users. The main contribution of this part is an efficient algorithm for finding the joint globally optimal beamformers across all base-stations. The proposed algorithm is based on a generalization of uplink-downlink duality to the multicell setting using the Lagrangian duality theory. An important feature is that it naturally leads to a distributed implementation in time-division duplex (TDD) systems. Simulation results suggest that coordinating the beamforming vectors alone already provides appreciable performance improvements as compared to the conventional per-cell optimized network.
The second part of the thesis considers the transmission of both private and common messages for the sole purpose of intercell
interference mitigation. It solves the issues of the second limitation mentioned above. It considers the benefit of designing
decodable interference signals by allowing common-private message splitting at the transmitter and common message decoding by users in adjacent cells. It solves a network optimization problem of jointly determining the appropriate users in adjacent cells for
rate splitting, the optimal beamforming vectors for both common and private messages, and the optimal common-private rates to minimize the total transmit power across the base-stations subject to service rate requirements for remote users. Observe that for fixed user selection and fixed common-private rate splitting, the optimization of beamforming vectors can be performed using a semidefinite programming approach. Further, this part of the thesis proposes a heuristic user-selection and rate splitting strategy to maximize the benefit of common message decoding. This part proposes a heuristic algorithm to characterize the improvement in the feasible rates with common-message decoding. Simulation results show that common message decoding can significantly improve both the total transmit power and the feasibility region for cell-edge users when base-stations are closely spaced from each other.
|
6 |
Coordinated Beamforming and Common Message Decoding for Intercell Interference Mitigation in Multicell NetworksDahrouj, Hayssam 15 February 2011 (has links)
Conventional multicell wireless systems operate with out-of-cell interference treated as background noise; consequently, their performance faces two major limitations: 1)Signal processing is performed on a per-cell basis; and 2)Intercell interference detection is infeasible as intercell interference, although significantly above the noise level, is typically quite weak. In this thesis, we consider a multicell downlink scenario, where base-stations are equipped with multiple transmit antennas, the remote users are equipped with a single antenna, and multiple remote users are active simultaneously via spatial division multiplexing. We propose solutions for the above limitations by considering techniques for mitigating interference.
The first part of the thesis proposes solutions for the first limitation. It considers the benefit of coordinating base-stations across multiple cells, where
multiple base-stations may jointly optimize their respective beamformers to improve the overall system performance. It focuses on the design criteria of minimizing either the total weighted transmitted power or the maximum per-antenna power across the base-stations subject to signal-to-interference-and-noise-ratio (SINR) constraints at the remote users. The main contribution of this part is an efficient algorithm for finding the joint globally optimal beamformers across all base-stations. The proposed algorithm is based on a generalization of uplink-downlink duality to the multicell setting using the Lagrangian duality theory. An important feature is that it naturally leads to a distributed implementation in time-division duplex (TDD) systems. Simulation results suggest that coordinating the beamforming vectors alone already provides appreciable performance improvements as compared to the conventional per-cell optimized network.
The second part of the thesis considers the transmission of both private and common messages for the sole purpose of intercell
interference mitigation. It solves the issues of the second limitation mentioned above. It considers the benefit of designing
decodable interference signals by allowing common-private message splitting at the transmitter and common message decoding by users in adjacent cells. It solves a network optimization problem of jointly determining the appropriate users in adjacent cells for
rate splitting, the optimal beamforming vectors for both common and private messages, and the optimal common-private rates to minimize the total transmit power across the base-stations subject to service rate requirements for remote users. Observe that for fixed user selection and fixed common-private rate splitting, the optimization of beamforming vectors can be performed using a semidefinite programming approach. Further, this part of the thesis proposes a heuristic user-selection and rate splitting strategy to maximize the benefit of common message decoding. This part proposes a heuristic algorithm to characterize the improvement in the feasible rates with common-message decoding. Simulation results show that common message decoding can significantly improve both the total transmit power and the feasibility region for cell-edge users when base-stations are closely spaced from each other.
|
7 |
Transmission Strategies for the Gaussian Parallel Relay ChannelChangiz Rezaei, Seyed Saeed January 2010 (has links)
Cooperative wireless communication has received significant attention during recent years due to several reasons. First, since the received power
decreases rapidly with distance, the idea of multi-hopping is becoming of particular
importance. In multi-hopped communication, the source exploits some intermediate
nodes as relays. Then the source sends its message via those relays to the destination.
Second, relays can emulate some kind of distributed transmit antennas to form spatial
diversity and combat multi-path fading effect of the wireless channel.
Parallel Relay Channel is an information theoretical model for a communication system
whereby a sender aims to communicate to a receiver with the help of relay nodes. It represents the simplest model for a multi–hop wireless network and a full understanding of the limits of communication over such a channel can potentially shed light on the design of more efficient wireless networks. However, the capacity of the relay
channel has been established only for few special cases and little progress
has been made toward solving the general case since the early 1980s.
In this dissertation, motivated by practical constraints, we study the information theoretical limits of the half-duplex Gaussian Parallel Relay channel , as well as, the transmission strategies for the parallel relay channel with bandwidth mismatch between the first and the second hops.
Chapter 2 investigates the problem of communication for a network composed of two
half-duplex parallel relays with additive white Gaussian noise (AWGN).
There is no direct link between the source and the destination.
However, the relays can communicate with each other through the channel between them.
Two protocols, i.e., \emph{Simultaneous} and \emph{Successive} relaying, associated with
two possible relay scheduling are proposed. The simultaneous relaying protocol is based
on \emph{Broadcast-multiaccess with Common Message (BCM)} scheme. For the successive relaying protocol: (i) a \emph{Non-Cooperative}
scheme based on the \emph{Dirty Paper Coding (DPC)}, and (ii) a \emph{Cooperative}
scheme based on the \emph{Block Markov Encoding (BME)} are considered. The composite
scheme of employing BME in \emph{at most} one relay and DPC in \emph{at least} another
one is shown to achieve at least the same rate when compared to the \emph{Cooperative}
and \emph{Non-Cooperative} schemes. A \emph{``Simultaneous-Successive Relaying based
on Dirty paper coding scheme" (SSRD)} is also proposed. The optimum scheduling of the
relays and hence the capacity of the half-duplex Gaussian parallel relay channel in the
low and high signal-to-noise ratio (SNR) scenarios is derived. In the low SNR scenario,
it is revealed that under certain conditions for the channel coefficients, the ratio of
the achievable rate of the simultaneous relaying based on BCM to the cut-set bound tends
to be 1. On the other hand, as SNR goes to infinity, it is proved that successive relaying, based on the DPC, asymptotically achieves the capacity of the network.
Schein and Gallager introduced the Gaussian parallel relay channel in 2000.
They proposed the Amplify-and-Forward (AF) and the Decode-and-Forward (DF) strategies for this channel. For a long time, the best known achievable rate for this channel was based on the AF and DF with time sharing (AF-DF). Recently, a Rematch-and-Forward (RF) scheme for the scenario in which different amounts of bandwidth can be assigned to the first and second hops were proposed.
In chapter 3, we propose a \emph{Combined Amplify-and-Decode Forward (CADF)} scheme for the Gaussian parallel relay channel. We prove that the CADF scheme always gives a better achievable rate compared to the RF scheme, when there is a bandwidth mismatch between the first hop and the second hop. Furthermore, for the equal bandwidth case (Schein's setup), we show that the time sharing between the CADF and the DF schemes (CADF-DF) leads to a better achievable rate compared to the time sharing between the RF and the DF schemes (RF-DF) as well as the AF-DF.
|
8 |
Coding for Cooperative CommunicationsUppal, Momin Ayub 2010 August 1900 (has links)
The area of cooperative communications has received tremendous research interest
in recent years. This interest is not unwarranted, since cooperative communications
promises the ever-so-sought after diversity and multiplexing gains typically
associated with multiple-input multiple-output (MIMO) communications, without
actually employing multiple antennas. In this dissertation, we consider several cooperative
communication channels, and for each one of them, we develop information
theoretic coding schemes and derive their corresponding performance limits. We next
develop and design practical coding strategies which perform very close to the information
theoretic limits.
The cooperative communication channels we consider are: (a) The Gaussian relay
channel, (b) the quasi-static fading relay channel, (c) cooperative multiple-access
channel (MAC), and (d) the cognitive radio channel (CRC). For the Gaussian relay
channel, we propose a compress-forward (CF) coding strategy based on Wyner-Ziv
coding, and derive the achievable rates specifically with BPSK modulation. The CF
strategy is implemented with low-density parity-check (LDPC) and irregular repeataccumulate
codes and is found to operate within 0.34 dB of the theoretical limit. For
the quasi-static fading relay channel, we assume that no channel state information
(CSI) is available at the transmitters and propose a rateless coded protocol which
uses rateless coded versions of the CF and the decode-forward (DF) strategy. We
implement the protocol with carefully designed Raptor codes and show that the implementation suffers a loss of less than 10 percent from the information theoretical limit. For
the MAC, we assume quasi-static fading, and consider cooperation in the low-power
regime with the assumption that no CSI is available at the transmitters. We develop
cooperation methods based on multiplexed coding in conjunction with rateless
codes and find the achievable rates and in particular the minimum energy per bit to
achieve a certain outage probability. We then develop practical coding methods using
Raptor codes, which performs within 1.1 dB of the performance limit. Finally, we
consider a CRC and develop a practical multi-level dirty-paper coding strategy using
LDPC codes for channel coding and trellis-coded quantization for source coding. The
designed scheme is found to operate within 0.78 dB of the theoretical limit.
By developing practical coding strategies for several cooperative communication
channels which exhibit performance close to the information theoretic limits, we show
that cooperative communications not only provide great benefits in theory, but can
possibly promise the same benefits when put into practice. Thus, our work can be
considered a useful and necessary step towards the commercial realization of cooperative
communications.
|
9 |
Transmission Strategies for the Gaussian Parallel Relay ChannelChangiz Rezaei, Seyed Saeed January 2010 (has links)
Cooperative wireless communication has received significant attention during recent years due to several reasons. First, since the received power
decreases rapidly with distance, the idea of multi-hopping is becoming of particular
importance. In multi-hopped communication, the source exploits some intermediate
nodes as relays. Then the source sends its message via those relays to the destination.
Second, relays can emulate some kind of distributed transmit antennas to form spatial
diversity and combat multi-path fading effect of the wireless channel.
Parallel Relay Channel is an information theoretical model for a communication system
whereby a sender aims to communicate to a receiver with the help of relay nodes. It represents the simplest model for a multi–hop wireless network and a full understanding of the limits of communication over such a channel can potentially shed light on the design of more efficient wireless networks. However, the capacity of the relay
channel has been established only for few special cases and little progress
has been made toward solving the general case since the early 1980s.
In this dissertation, motivated by practical constraints, we study the information theoretical limits of the half-duplex Gaussian Parallel Relay channel , as well as, the transmission strategies for the parallel relay channel with bandwidth mismatch between the first and the second hops.
Chapter 2 investigates the problem of communication for a network composed of two
half-duplex parallel relays with additive white Gaussian noise (AWGN).
There is no direct link between the source and the destination.
However, the relays can communicate with each other through the channel between them.
Two protocols, i.e., \emph{Simultaneous} and \emph{Successive} relaying, associated with
two possible relay scheduling are proposed. The simultaneous relaying protocol is based
on \emph{Broadcast-multiaccess with Common Message (BCM)} scheme. For the successive relaying protocol: (i) a \emph{Non-Cooperative}
scheme based on the \emph{Dirty Paper Coding (DPC)}, and (ii) a \emph{Cooperative}
scheme based on the \emph{Block Markov Encoding (BME)} are considered. The composite
scheme of employing BME in \emph{at most} one relay and DPC in \emph{at least} another
one is shown to achieve at least the same rate when compared to the \emph{Cooperative}
and \emph{Non-Cooperative} schemes. A \emph{``Simultaneous-Successive Relaying based
on Dirty paper coding scheme" (SSRD)} is also proposed. The optimum scheduling of the
relays and hence the capacity of the half-duplex Gaussian parallel relay channel in the
low and high signal-to-noise ratio (SNR) scenarios is derived. In the low SNR scenario,
it is revealed that under certain conditions for the channel coefficients, the ratio of
the achievable rate of the simultaneous relaying based on BCM to the cut-set bound tends
to be 1. On the other hand, as SNR goes to infinity, it is proved that successive relaying, based on the DPC, asymptotically achieves the capacity of the network.
Schein and Gallager introduced the Gaussian parallel relay channel in 2000.
They proposed the Amplify-and-Forward (AF) and the Decode-and-Forward (DF) strategies for this channel. For a long time, the best known achievable rate for this channel was based on the AF and DF with time sharing (AF-DF). Recently, a Rematch-and-Forward (RF) scheme for the scenario in which different amounts of bandwidth can be assigned to the first and second hops were proposed.
In chapter 3, we propose a \emph{Combined Amplify-and-Decode Forward (CADF)} scheme for the Gaussian parallel relay channel. We prove that the CADF scheme always gives a better achievable rate compared to the RF scheme, when there is a bandwidth mismatch between the first hop and the second hop. Furthermore, for the equal bandwidth case (Schein's setup), we show that the time sharing between the CADF and the DF schemes (CADF-DF) leads to a better achievable rate compared to the time sharing between the RF and the DF schemes (RF-DF) as well as the AF-DF.
|
10 |
Genetic algorithms for scheduling in multiuser MIMO wireless communication systemsElliott, Robert C. 06 1900 (has links)
Multiple-input, multiple-output (MIMO) techniques have been proposed to meet the needs for higher data rates and lower delays in future wireless communication systems. The downlink capacity of multiuser MIMO systems is achieved when the system transmits to several users simultaneously. Frequently, many more users request service than the transmitter can simultaneously support. Thus, the transmitter requires a scheduling algorithm for the users, which must balance the goals of increasing throughput, reducing multiuser interference, lowering delays, ensuring fairness and quality of service (QoS), etc.
In this thesis, we investigate the application of genetic algorithms (GAs) to perform scheduling in multiuser MIMO systems. GAs are a fast, suboptimal, low-complexity method of solving optimization problems, such as the maximization of a scheduling metric, and can handle arbitrary functions and QoS constraints. We first examine a system that transmits using capacity-achieving dirty paper coding (DPC). Our proposed GA structure both selects users and determines their encoding order for DPC, which affects the rates they receive. Our GA can also schedule users independently on different carriers of a multi-carrier system. We demonstrate that the GA performance is close to that of an optimal exhaustive search, but at a greatly reduced complexity. We further show that the GA convergence time can be significantly reduced by tuning the values of its parameters.
While DPC is capacity-achieving, it is also very complex. Thus, we also investigate GA scheduling with two linear precoding schemes, block diagonalization and successive zero-forcing. We compare the complexity and performance of the GA with "greedy" scheduling algorithms, and find the GA is more complex, but performs better at higher signal-to-noise ratios (SNRs) and smaller user pool sizes. Both algorithms are near-optimal, yet much less complex than an exhaustive search. We also propose hybrid greedy-genetic algorithms to gain benefits from both types of algorithms.
Lastly, we propose an improved method of optimizing the transmit covariance matrices for successive zero-forcing. Our algorithm significantly improves upon the performance of the existing method at medium to high SNRs, and, unlike the existing method, can maximize a weighted sum rate, which is important for fairness and QoS considerations. / Communications
|
Page generated in 0.0548 seconds