22 research outputs found
Spectrum optimization in multi-user multi-carrier systems with iterative convex and nonconvex approximation methods
Several practical multi-user multi-carrier communication systems are
characterized by a multi-carrier interference channel system model where the
interference is treated as noise. For these systems, spectrum optimization is a
promising means to mitigate interference. This however corresponds to a
challenging nonconvex optimization problem. Existing iterative convex
approximation (ICA) methods consist in solving a series of improving convex
approximations and are typically implemented in a per-user iterative approach.
However they do not take this typical iterative implementation into account in
their design. This paper proposes a novel class of iterative approximation
methods that focuses explicitly on the per-user iterative implementation, which
allows to relax the problem significantly, dropping joint convexity and even
convexity requirements for the approximations. A systematic design framework is
proposed to construct instances of this novel class, where several new
iterative approximation methods are developed with improved per-user convex and
nonconvex approximations that are both tighter and simpler to solve (in
closed-form). As a result, these novel methods display a much faster
convergence speed and require a significantly lower computational cost.
Furthermore, a majority of the proposed methods can tackle the issue of getting
stuck in bad locally optimal solutions, and hence improve solution quality
compared to existing ICA methods.Comment: 33 pages, 7 figures. This work has been submitted for possible
publicatio
Statistical Delay QoS Driven Energy Efficiency and Effective Capacity Tradeoff for Uplink Multi-User Multi-Carrier Systems
In this paper, the total system effective capacity (EC) maximization problem for the uplink transmission, in a multi-user multi-carrier OFDMA system, is formulated as a combinatorial integer programming problem, subject to each user?s link-layer energy efficiency (EE) requirement as well as the individual?s average transmission power limit. To solve this challenging problem, we first decouple it into a frequency provisioning problem and an independent multi-carrier linklayer EE-EC tradeoff problem for each user. In order to obtain the subcarrier assignment solution, a low-complexity heuristic algorithm is proposed, which not only offers close-to-optimal solutions, while serving as many users as possible, but also has a complexity linearly relating to the size of the problem. After obtaining the subcarrier assignment matrix, the multi-carrier link-layer EE-EC tradeoff problem for each user is formulated and solved by using Karush-Kuhn-Tucker (KKT) conditions. The per-user optimal power allocation strategy, which is across both frequency and time domains, is then derived. Further, we theoretically investigate the impact of the circuit power and the EE requirement factor on each user?s EE level and optimal average power value. The low-complexity heuristic algorithm is then simulated to compare with the traditional exhaustive algorithm and a fair-exhaustive algorithm. Simulation results confirm our proofs and design intentions, and further show the effects of delay quality-of-service (QoS) exponent, the total number of users and the number of subcarriers on the system tradeoff performance
Opportunistic Interference Alignment in MIMO Interference Channels
We present two interference alignment techniques such that an opportunistic
point-to-point multiple input multiple output (MIMO) link can reuse, without
generating any additional interference, the same frequency band of a similar
pre-existing primary link. In this scenario, we exploit the fact that under
power constraints, although each radio maximizes independently its rate by
water-filling on their channel transfer matrix singular values, frequently, not
all of them are used. Therefore, by aligning the interference of the
opportunistic radio it is possible to transmit at a significant rate while
insuring zero-interference on the pre-existing link. We propose a linear
pre-coder for a perfect interference alignment and a power allocation scheme
which maximizes the individual data rate of the secondary link. Our numerical
results show that significant data rates are achieved even for a reduced number
of antennas.Comment: To appear in proc. IEEE PIMRC 2008 - Workshop in Emerging Network
Perspectives in Multiuser and Cooperative MIMO (NWMIMO). 5 pages and 4
figure
Real-time dynamic spectrum management for multi-user multi-carrier communication systems
Dynamic spectrum management is recognized as a key technique to tackle
interference in multi-user multi-carrier communication systems and networks.
However existing dynamic spectrum management algorithms may not be suitable
when the available computation time and compute power are limited, i.e., when a
very fast responsiveness is required. In this paper, we present a new paradigm,
theory and algorithm for real-time dynamic spectrum management (RT-DSM) under
tight real-time constraints. Specifically, a RT-DSM algorithm can be stopped at
any point in time while guaranteeing a feasible and improved solution. This is
enabled by the introduction of a novel difference-of-variables (DoV)
transformation and problem reformulation, for which a primal coordinate ascent
approach is proposed with exact line search via a logarithmicly scaled grid
search. The concrete proposed algorithm is referred to as iterative power
difference balancing (IPDB). Simulations for different realistic wireline and
wireless interference limited systems demonstrate its good performance, low
complexity and wide applicability under different configurations.Comment: 14 pages, 9 figures. This work has been submitted to the IEEE for
possible publicatio
Subcarrier Allocation Algorithm Based on Greedy-Like in Multi Carrier Code Division Multiple Access Systems
One of the most important issues to be taken into consideration in multi carrier communication systems with multi users is the assignment of the available resources to the users efficiently. Thus, how to determine the number of subcarriers to be allocated to the users has an important role with regards to data rate and error performance of the system when active users are increased in multi carrier system. In this study by using Greedy-Like algorithm, the subcarriers in MCCDMA systems are optimal allocated to the users and the efficiency of this algorithm compared with other algorithms in terms of bit error and bit rate performance
Effective capacity based resource allocation for Rayleigh-fading parallel channels
International audienceWe address the problem of allocating different powers amongst parallel channels when effective capacity is the performance metric and sum-power is constrained. We assume that Chase-Combining-HARQ mechanism is applied. Closed-form expressions for the powers are exhibited. Numerical comparisons with other power allocations obtained through either ergodic capacity or throughput optimizations are done
Energy Efficient Communications in MIMO Wireless Channels: Information Theoretical Limits
ISBN : 978-1466501072This chapter is focused on defining and optimizing an energy-efficiency metric for MIMO systems. This metric, which expresses in bit per Joule, allows one to measure how much information is effectively transferred to the transmitter per unit cost of energy consumed at the transmitter. For a MIMO point-to-point communication (single user MIMO channels) this metric can be useful to determine what power level, precoding scheme, training length, or number of antennas have to be used for obtaining the maximum information that is effectively transferred per unit energy spent. Then, we move from a physical layer-type approach to a cross-layer design of energy-efficient power control by including the effects a queue with finite size at the transmitter. As a last step we study a distributed multiple user scenario (MIMO multiple access channels) where each user selfishly maximizes its energy-efficiency by choosing its best individual power allocation policy. Here, we present the most relevant results in this field in a concise and comprehensible manner
Link-Layer Capacity of NOMA Under Statistical Delay QoS Guarantees
In this paper, we study the achievable link-layer rate, namely, effective capacity (EC), under the per-user statistical delay quality-of-service (QoS) requirements, for a downlink nonorthogonal multiple access (NOMA) network with M users. Specifically, the M users are assumed to be divided into multiple NOMA pairs. Conventional orthogonal multiple access (OMA) then is applied for inter-NOMA-pairs multiple access. Focusing on the total link-layer rate for a downlink M-user network, we prove that OMA outperforms NOMA when the transmit signalto- noise ratio (SNR) is small. On the contrary, simulation results show that NOMA prevails over OMA at high values of SNR. Aware of the importance of a two-user NOMA network, we also theoretically investigate the impact of the transmit SNR and the delay QoS requirement on the individual EC performance and the total link-layer rate for a two-user network. Specifically, for delay-constrained and delay-unconstrained users, we prove that for the user with the stronger channel condition in a twouser network, NOMA prevails over OMA when the transmit SNR is large. On the other hand, for the user with the weaker channel condition in a two-user network, it is proved that NOMA outperforms OMA when the transmit SNR is small. Furthermore, for the user with the weaker channel condition, the individual EC in NOMA is limited to a maximum value, even if the transmit SNR goes to infinity. To confirm these insightful conclusions, the closed-form expressions for the individual EC in a two-user network, by applying NOMA or OMA, are derived for both users and then confirmed using Monte Carlo simulations