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1.
In this paper we present a computationally efficient, suboptimal integer bit allocation algorithm that maximizes the overall
data rate in multiuser orthogonal frequency division multiplexing (OFDM) systems implemented in wireless networks. Assuming
the complete knowledge of a channel and allowing a subchannel to be simultaneously shared by multiple users we have solved
this data rate maximization problem in two steps. The first step provides subchannel assignment to users considering the users’
requests on quality of service (QoS) expressed as the minimum signal-to-noise ratio (SNR) on each subchannel. The second step
provides transmit power and bit allocation to subchannels in order to maximize the overall data rate. To reduce computational
complexity of the problem we propose a simple method which assigns subchannels to users and distributes power and bits among
them. We have analyzed the performance of our proposed algorithm by simulation in a multiuser frequency selective fading environment
for various signal-to-noise ratios and various numbers of users in the system. We have concluded that our algorithm, unlike
other similar algorithms, is suitable for OFDM wireless networks, especially when signal-to-noise ratio in the channel is
low. Also, the results have shown that the total data rate grows with the number of users in the system. 相似文献
2.
研究半双工正交频分复用(OFDMA)中继网络的资源分配。解决动态子信道分配,自适应功率分配,传输策略选择和中继选择的联合优化问题。为了公平利用中继用户的资源,把中继用户所能帮助的最大子信道数和每个子信道的功率设为常量。在此基础上,提出贪婪算法以最大化总效用。当算法每次分配资源时,把资源分配给潜在效用增长最大的用户。仿真结果表明所提算法与固定的资源分配策略相比,能更高效地利用资源,并且改善了用户间的公平性。 相似文献
3.
We obtain an analytical result for the symbol-error rate of a wireless orthogonal frequency-division multiplexing system employing Fischer's bit-loading algorithm. First we assume that the subchannel coefficients are statistically independent, then we extend the results to the case with dependent subchannel coefficients. Throughout the analysis, we assume that the number of subchannels is large, and that subchannels have Rayleigh-distributed coefficients. The comparison of analytical and simulated results shows that the approximation error is small, especially at low noise and high bit rate. 相似文献
4.
该文针对MU-MIMO下行(广播)信道提出一种基于空间子信道关联干扰的先验式调度算法。该方法将用户调度转换为子信道的选择问题,通过综合考虑候选子信道的传输增益,以及候选者与已选的和潜在的、将来可能被选中的子信道间的相互干扰,获得一组相互干扰较小的子信道。仿真结果表明,合理地选取关联干扰参数,该算法能够获得计算复杂度与传输性能的良好折中,有效改善系统和速率。 相似文献
5.
Adaptive resource allocation in multiuser OFDM systems with proportional rate constraints 总被引:12,自引:0,他引:12
《Wireless Communications, IEEE Transactions on》2005,4(6):2726-2737
Multiuser orthogonal frequency division multiplexing (MU-OFDM) is a promising technique for achieving high downlink capacities in future cellular and wireless local area network (LAN) systems. The sum capacity of MU-OFDM is maximized when each subchannel is assigned to the user with the best channel-to-noise ratio for that subchannel, with power subsequently distributed by water-filling. However, fairness among the users cannot generally be achieved with such a scheme. In this paper, a set of proportional fairness constraints is imposed to assure that each user can achieve a required data rate, as in a system with quality of service guarantees. Since the optimal solution to the constrained fairness problem is extremely computationally complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. In the proposed algorithm, subchannel allocation is first performed by assuming an equal power distribution. An optimal power allocation algorithm then maximizes the sum capacity while maintaining proportional fairness. The proposed algorithm is shown to achieve about 95% of the optimal capacity in a two-user system, while reducing the complexity from exponential to linear in the number of subchannels. It is also shown that with the proposed resource allocation algorithm, the sum capacity is distributed more fairly and flexibly among users than the sum capacity maximization method. 相似文献
6.
This paper investigates the Resource allocation problem in OFDMA-based decode-and-forward cooperative communication systems.
The objective is to maximize the sum throughput under the constraints of joint total transmission power and subchannels occupation,
while maintaining the maximum fairness among multiple relay nodes. Since the optimal solution to this combinatorial problem
is extremely computationally complex to obtain, we propose a low-complexity suboptimal algorithm that allocates subchannel
and power separately. In the proposed algorithm, subchannel allocation over the relay nodes is first performed under the assumption
of equal power distribution. Then, an optimal power allocation algorithm named multi-level water-filling is used to maximize
the sum rate. The simulation results show that the performance of the proposed algorithm can approach asymptotically to that
of the optimal algorithm while enhancing the fairness among all relay nodes and reducing computational complexity from exponential
to linear with the number of subchannels. It is also shown that the proposed equal power distribution algorithm with subchannel
permutation (SP) outperforms the one without SP. 相似文献
7.
Yakun Sun Honig M.L. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(7):2879-2902
We study the capacity of multicarrier transmission through a slow frequency-selective fading channel with limited feedback, which specifies channel state information. Our results are asymptotic in the number of subchannels . We first assume independent and identically distributed (i.i.d.) subchannel gains, and show that, for a large class of fading distributions, a uniform power distribution over an optimized subset of subchannels, or on-off power allocation, gives the same asymptotic growth in capacity as optimal water filling, e.g., with Rayleigh fading. Furthermore, the growth in data rate can be achieved with a feedback rate as . If the number of active subchannels is bounded, the capacity grows only as with the feedback rate of . We then consider correlated subchannels modeled as a Markov process, and study the savings in feedback. Assuming a fixed ratio of coherence bandwidth to the total bandwidth, the ratio between minimum feedback rates with correlated and i.i.d. subchannels converges to zero with , e.g., as for Rayleigh-fading subchannels satisfying a first-order autoregressive process. We also show that adaptive modulation, or rate control schemes, in which the rate on each subchannel is selected from a quantized set, achieves the same asymptotic growth rates in capacity and required feedback. Finally, our results are extended to cellular uplink and downlink channel models. 相似文献
8.
《Signal Processing, IEEE Transactions on》2005,53(9):3572-3582
We consider the design of biorthogonal, as opposed to orthonormal, discrete multitone (DMT) systems supporting multiple services in a single antennae setting. The services may have differing quality of service (QoS) requirements, quantified by bit rate and symbol error rate specifications. Different users on the system can be potentially assigned different number of subchannels. Our goal is to minimize the transmitted power given the QoS specifications for the different users, subject to the knowledge of the channel and colored interference at the receiver input of the DMT system. We find an optimum bit loading scheme that distributes the bit rate transmitted across the various subchannels, where the precise subchannels are assigned to each user, and an optimum transceiver. Key conclusions are i) relaxing the orthonormality constraint yields no performance improvement; ii) the optimum transceiver is unaffected by changing service characteristics, and depends only on the channel and interference conditions; iii) the QoS requirements, the number of users, and the number of subchannels assigned to the different users only affect bitloading and subchannel assignment. 相似文献
9.
In this paper, we propose to apply a simple superposition coding strategy for downlink of OFDMA systems. The novelty of this
paper consists on allowing at most two users to share the same subchannel. The main idea is to consider the subchannels allocated
to the users with the weakest link, and allow these subchannels to be shared by some potential users who can transmit some
number of bits with only a small amount of power. To decrease the overhead of the proposed OFDMA system, we restrict to use
a predetermined superposition encoding|decoding scheme. We address the problem of resource allocation, which consists on finding
the optimal subchannel assignment in the OFDMA system. A low complexity algorithm, denoted Share Specific Subcarrier Allocation
(SSSA) is then proposed. It offers a fairness allocation among users. This can be done by taking into account all user’s buffer
states information. Simulation results confirm that the proposed technique outperforms the classical algorithms in terms of
total throughput and dropping probability. 相似文献
10.
Joint subchannel and power allocation in multiuser OFDM systems with minimal rate constraints 下载免费PDF全文
In this paper, we study the adaptive resource allocation in multiuser orthogonal frequency division multiplexing (OFDM) systems. We try to maximize the sum capacity of an OFDM system with given transmission power budget, while meeting users' minimal rate requirements. Unlike other resource allocation schemes, which generally separate subchannel allocation and power distribution into independent procedures, our proposed algorithm implements joint subchannel and power allocation. Given a set of subchannels, the required power to satisfy a user's minimal rate constraint is calculated by water‐filling policy. Then, the user who requires the maximum power to meet the rate requirement has a priority to obtain an additional subchannel. The procedure continues until all subchannels are consumed, by which time the consumed power to meet all users' rate requirements is also worked out. Finally, the margin power is allocated among all subchannels in an optimal manner to maximize the sum capacity of the OFDM system. Simulation results show that our proposed algorithm performs better than other existing ones. The solution produced by our proposed algorithm is close to the upper bound, while its complexity is relatively lower compared with other methods, which makes it attractive for applications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
OFDM中自适应比特及功率分配的分析 总被引:1,自引:0,他引:1
在宽带移动OFDM(正交频分复用)系统中,不同的子信道经受不同的信道衰落,因此具有不同的传输能力。根据子信道的增益对子信道上加载的比特数进行自适应分配,可在满足一定误码率(BER)性能要求下使系统的总传输功率达到最小。本文研究了一种在一定传输速率下的自适应比特及功率分配算法。该算法可适用于多径频率选择性衰落信道。仿真结果表明,采用自适应技术可大大提高OFDM系统的性能。 相似文献
12.
Yun Hee Kim Iickho Song Seokho Yoon So Ryoung Park 《Vehicular Technology, IEEE Transactions on》1999,48(5):1428-1436
Multicarrier transmission schemes have been introduced into code-division multiple access (CDMA) systems to gain advantages for high data rate transmission. One of the methods is to transmit identical narrowband direct-sequence (DS) waveforms in parallel over a number of subchannels using frequency diversity. In this paper, we propose a multicarrier CDMA system with an adaptive subchannel allocation method for forward links. In the proposed system, instead of identical DS waveforms being transmitted over a number of subchannels in parallel, each user's DS waveform is transmitted over the user's favourite subchannel which has the largest fading amplitude among all the subchannels. We analyze the performance characteristics of the system when orthogonal and random signature sequences are used. The proposed system is shown to have performance gain over the conventional multicarrier CDMA system. We also investigate how the performance is influenced when the signal is not perfectly allocated into the best subchannel 相似文献
13.
In this paper, the problem of resource allocation in an Orthogonal Frequency Division Multiple Access-based Cognitive Wireless
Mesh Network (CWMN) is addressed. The objective is to maximize the total utilities in a CWMN, which is defined as any increasing,
concave and twice differentiable function of the end-to-end flow rate, by jointly allocating each link’s rate, power and subchannels
under the constraints of multiple primary users’ Interference Temperature and multiple access interference. First, a centralized
resource allocation algorithm is developed based on the Column Generation approach, and shown to be optimal. So it can perform
as a criterion for designing other algorithms. Secondly, considering the applicability of algorithm in distributed system,
a near-optimal distributed algorithm is proposed, which allocates subchannel based on routing information at first, and then
jointly allocates the resource of rate and power. Finally, the simulation results validate the centralized and distributed
algorithms, and show that better performance can be achieved than the conventional algorithm. 相似文献
14.
Lingling Pu Michael W Marcellin Ivan Djordjevic Bane Vasic Ali Bilgin 《IEEE transactions on image processing》2007,16(8):2016-2022
A fast rate-optimal rate allocation algorithm is proposed for parallel transmission of scalable images in multichannel systems. Scalable images are transmitted via fixed-length packets. The proposed algorithm selects a subchannel, as well as a channel code rate for each packet, based on the signal-to-noise ratios (SNRs) of the subchannels. The resulting scheme provides unequal error protection of source bits and significant gains are obtained over equal error protection schemes. An application of the proposed algorithm to JPEG2000 transmission shows the advantages of exploiting differences in SNRs between subchannels. Multiplexing of multiple sources is also considered, and additional gains are achieved by exploiting information diversity among the sources. 相似文献
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17.
基于多用户MIMO-OFDM系统的子信道和功率分配算法 总被引:4,自引:2,他引:2
在多用户MIMO-OFDM系统中,当总功率受限时,为了使整个系统的数据传输速率最大.已有的最优算法的计算十分复杂,这里采用了一种次最优算法。在发射端,基于已知信道状态信息。应用奇异值分解将MIMO信道转化为并行的子信道,并将表征信道增益的信道特征值用于子信道自适应调制优化设计中。在自适应过程中.用到了子信道和功率联合分配算法。仿真结果表明,这种算法能使系统的性能明显提高。 相似文献
18.
Yanyan Shen Gang Feng Bo Yang Xinping Guan 《Wireless Communications and Mobile Computing》2014,14(2):269-283
We address the problem of subchannel and transmission power allocation in orthogonal frequency division multiple access relay networks with an aim to maximize the sum rate and maintain proportional rate fairness among users. Because the formulated problem is a mixed‐integer nonlinear optimization problem with an extremely high computational complexity, we propose a low‐complexity suboptimal algorithm, which is a two‐step separated subchannel and power allocation algorithm. In the first step, subchannels are allocated to each user, whereas in the second step, the optimal power allocation is carried out on the basis of the given subchannel allocation and the nonlinear interval Gauss–Seidel method. Simulation results have demonstrated that the proposed algorithm can achieve a good trade‐off between the efficiency and the fairness compared with two other existing relevant algorithms. In particular, the proposed algorithm can always achieve 100% fairness under various conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
19.
本文提出一种适用于多径频率选择性衰落信道中多用户OFDM系统的自适应分配算法.算法根据信道瞬时估计值,自适应地为多用户分配子信道和传输比特数,在给定误比特率的条件下,使系统总的发送功率达到最小.作者根据时分复用的基本思想,提出多用户最佳子信道和比特分配算法,导出系统最小发送功率的下限,并在此基础上,进一步提出次佳自适应分配算法.数值模拟表明:次佳算法所需的发送功率比下限值高约1dB;与等比特分配方案相比自适应分配算法可节省功率约3-4dB;与静态信道分配方案相比,自适应分配算法可节省功率6-8dB. 相似文献