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Study and ideas for green wireless mobile communications

YOU Xiao-hu, WANG Jing, ZHANG Ping, LI Shao-qian, ZHU Jin-kang

2009, 39(10): 1009-1015.

Abstract:
To promote research on wireless and mobile communications, 2009 Huangshan Symposium on “Green Wireless Technology and System” was held during 12~13 June, 2009 in Huangshan, Anhui. At the symposium, five major speeches by professors from famous universities analyzed the cooperative distributed MIMO system to efficiently reduce transmitting power as a novel scheme of green networks, proposed an idea of green wireless network, especially content aware soft real time (CASoRT) transmission design, for reducing cost and saving energy, expounded on BS reconfiguration based on the cognitive technique for remarkably saving power, discussed the change from achieving highest transmitting data rate to seeking best power efficiency for future wireless and mobile communications, and advanced an environmentally friendly efficiency function for assessing cellular network design for green communications. These discussions reflect the research and development results and ideas for green wireless and mobile communications.

Soft real-time service and green communications

CHEN Ping-ping, ZHONG Xiao-feng, WANG Jing

2009, 39(10): 1016-1021.

Article Views:229 Full article PDF

Abstract:
The concept of “Green Communications” in broadband mobile soft real-time communication is discussed. The problems of how soft real-time service can save energy with delay and how to use threshold to have a balance between delay and energy are addressed. A power control algorithm, which is applicable to soft real-time service model, is introduced to optimize the power consumption of base stations.

A green resource allocation strategy for utilizing cooperative spatial multiplexing

LI Jian-dong, ZHANG Yan, SHENG Min, TIAN Ye, YAO Jun-liang

2009, 39(10): 1022-1026.

Article Views:182 Full article PDF

Abstract:
Building green communication systems is a part of building the harmonious society. A novel resource allocation algorithm was proposed to reduce the energy consumption of future communication systems by utilizing cooperative spatial multiplexing. In this algorithm, the number of cooperative nodes was determined by source power control and level of cooperation (LOC) adjustment to minimize the energy consumption of the system under the QoS constrains. Simulation results show that the performance of the scheme is superior to those of existing algorithms.

Sub-carrier allocation algorithm based on maximum likelihood ratio spectrum detection in cognitive radio

XU Xiao-rong, ZHENG Bao-yu, CUI Jing-wu

2009, 39(10): 1027-1033.

Article Views:192 Full article PDF

Abstract:
In cognitive radio (CR) systems with multi-carrier modulation, sub-carrier allocation is the premise for the realization of spectrum sharing for Primary Users (PUs) and Secondary Users (SUs). A sub-carrier allocation algorithm based on maximum likelihood ratio detection (MLD) in cognitive OFDM is introduced and studied. SUs detect the occurrence and spectrum gap of PU signals with MLD model in a distributive way, while the system allocates sub-carriers to SUs dynamically. Cognitive base station (CBS) makes the final decision by combining each sub-carriers local sensing result with special fusion rule. The upper and lower bound of the decision region, detection probability and false alarm probability of the MLD model are derived, and a performance comparison between MLD and energy detection (ED) is presented. Simulation results indicate that, compared with ED, the decision threshold of MLD is related to the average received SNR at the sub-carrier, and that the detection performance adapts to channel variation. Therefore, applied to sub-carrier allocation in CR multi-carrier modulation, MLD can enhance the cognitive OFDM sub-carrier spectrum sensing performance significantly and realize the utilization of limited spectrum resource efficiently, thus, meeting the requirements of “green communication” could be achieved effectively.

Optimal subchannel, rate and power allocation for OFDM-based two-tier Femtocell networks

ZHNAG Jian-min, ZHANG Zhao-yang, HUANG Ai-ping

2009, 39(10): 1034-1038.

Article Views:201 Full article PDF

Abstract:
The problem of subchannel, rate and power allocation in OFDM-based two-tier Femtocell networks, which comprises a conventional macrocell and multiple Femtocells, is addressed. Our objective was maximizing the multiple Femtocell users weighted rate sum by jointly adjusting their subchannel, rate and power allocation under the constraints of cross-tier interference (CTI) between macrocell and multiple Femtocells and the cochannel interference (CCI) between multiple Femtocells. We formulated this optimization problem and solved it using the Lagrangian dual method and interpreted it from the angle of economics. Simulation results show that our system has better performance than the usually employed system, in which the Femtocells can only use the subchannels unoccupied by macrocell. Meanwhile, the utilization of spectrum can be improved significantly.

A novel resource-efficient cooperative sensing method

PENG Xiao, WU Su-wen, ZHU Jin-kang

2009, 39(10): 1039-1044.

Article Views:239 Full article PDF

Abstract:
Cognitive radio is a promising technology for its ability to overcome the insufficiency of available spectrums, and spectrum sensing is an important issue in cognitive radio research. Due to its ability to increase the reliability of sensing results and imitate hidden node problems, sensor cooperation in spectrum sensing has gained much attention. However, conventional cooperative method is usually resource inefficient for involving too many sensors. A novel iterative cooperative sensing method is proposed, which minimizes the quantity of cooperating sensors and resource consumption while satisfying the constraint of a given sensing accuracy. The simulation results show that our method can guarantee the target probability of detection and probability of false alarm and minimize the number of the sensors involved and resource consumed.

Distributed bayesian compressed spectrum sensing based on mutual information

WANG Zhen-xing, YANG Tao, HU Bo

2009, 39(10): 1045-1051.

Article Views:233 Full article PDF

Abstract:
When compressive sensing is applied in cognitive radio network, spectrum sensing precision by every cognitive radio user is greatly different due to different channel environments between them.Consequently information fusion methods in network and the efficient data processing manner by compressive sensing can be combined to improve sensing precision.First, CS (compressive sampling) is performed independently by every cognitive radio user for rough sensing, and then the sensing information between different users is exchanged for their spatial diversity. Here, mutual information is taken as a measure to evaluate the sensing difference between two cognitive radio users, and those users with large difference are related. The sensing information of every cognitive radio user will be shared under this kind of relationship. After sensing information is shared, Bayesian inference for CS construction in every cognitive radio user is re-built to update the local sensing. The simulation results show that the proposed scheme has advantage both in sensing accuracy and in sensing speed over the conventional scheme.

Energy-efficient spectrum sensing in wireless cognitive sensor networks

ZOU Dan, ZHONG Guo-hui, QU Dai-ming, CAO Yang

2009, 39(10): 1052-1058.

Article Views:201 Full article PDF

Abstract:
Two energy-efficient strategies are proposed to reduce the energy consumed in the spectrum sensing procedure for wireless cognitive sensor networks. One involves using confidence voting algorithm to reduce the detection number, the other is based on Partially Observable Markov Decision Process (POMDP). Simulation results show that both algorithms can reduce the energy consumed in the detection efficiently, and the combination of the two algorithms can save more than 30% energy compared with the general algorithm with system detection reliability requirement guaranteed.

A low complexity optimal number of secondary user selection algorithm through maximizing resource utility

WU Su-wen, PENG Xiao, ZHAO Ming, ZHU Jin-kang

2009, 39(10): 1059-1063.

Article Views:199 Full article PDF

Abstract:
Spectrum sensing is a key technology in Cognitive Radio (CR) and cooperative spectrum sensing is derived due to the effects of channel fading. We focus on the optimal number of secondary users in cooperative spectrum sensing to maximize the utility in CR networks. By considering both the detection error probability and the resource used by the secondary users in cooperation, we derive the analytical suboptimal number of secondary users in a special CR network where all the SUs have the same SNR. The simulation results show that the utility of suboptimal scheme is greater than that of other schemes and nearly the same as that of the optimal scheme with exhaust search. The energy cost of the fusion center is reduced and it is conducive to the realigation of the green energy-saving cognitive communication network.

Dynamic spectrum allocation in cognitive radio networks based on multi-auctioneer progressive auction

XU You-yun, GAO Lin

2009, 39(10): 1064-1069.

Article Views:226 Full article PDF

Abstract:
Dynamic spectrum access (DSA) is a promising paradigm to achieve efficient utilization of spectrum resources by allowing unlicensed users (i.e., secondary users, SUs) to access the licensed spectrums. A key issue in DSA is how to assign the idle spectrum bands of multiple primary spectrum owners (POs) among the SUs. A Multi-Auctioneer Progressive spectrum auction mechanism (MAP) based on the auction theory is proposed, where the POs act as the auctioneers and SUs act as the bidders. In MAP, each auctioneer systematically raises the price and each bidder subsequently chooses one auctioneer for bidding. Its shown analytically that MAP converges to an equilibrium where spectrum utilization is maximized. Its further shown that MAP dynamic spectrum access is low in complexity and traffic overhead.

Dynamic spectrum assignment based on FADM algorithm in cognitive networks

WU Guang-en, REN Pin-yi, Zhan Ming-hao

2009, 39(10): 1070-1075.

Article Views:213 Full article PDF

Abstract:
In order to improve auction effectiveness in dynamic spectrum assignment(DSA), a new assignment scheme based on FADM(fast auction with multiple goods and multiple winners) algorithm was given. The FADM algorithm transforms the traditional multiple goods auction into an integer 0/1 knapsack problem, whereby the optimal clearing vector can be found with dynamic programming. Our scheme restrains collusion with reservation price and discriminated price. Furthermore, the reservation price and bid price can be adjusted dynamically to spectrum supply and demand, which can balance revenue and social efficiency of spectrum auction. The results of performance analysis and simulation indicate that the FADM algorithm can make spectrum utilization close to demand and improve allocation revenue as high as possible.

An energy-saving scheduling scheme for two-hop relay networks

HUANG Gao-yong, FANG Xu-ming, CAO Jian-nong

2009, 39(10): 1076-1083.

Article Views:209 Full article PDF

Abstract:
An energy-saving proportional fair (ESPF) scheduling scheme for OFDMA-based two-hop relay networks is proposed. By defining a proportional fair factor which is based on the upper limit of delay for different types of services and the energy consumption per bit, a packet scheduling algorithm and a flexible resource allocation scheme are proposed to avoid the waste of resources. Simulation results show that the proposed scheduling scheme can effectively decrease system energy consumption and improve system throughput while still satisfying the QoS requirements for different types of services.

Joint routing and scheduling interactively in wireless mesh backbone networks

SUN Shao-feng, ZHANG Si-hai, WEI Guo, ZHOU Wu-yang

2009, 39(10): 1084-1090.

Article Views:214 Full article PDF

Abstract:
The problem of jointing routing and scheduling in TDMA based wireless mesh backhaul networks is studied. The objective is to maximize the spectrum efficiency. A novel routing algorithm is proposed, which jointly considers the traffic of nodes, the average capacity of paths, and the interference of links. Based on the correlation of the maximal clique at the bottleneck area, a novel link scheduling algorithm for the traffic pattern of Internet access is proposed. The joint optimization problem is solved by interactive feedback between two modules. Simulation results show that the proposed algorithms can significantly improve the system performance under various interference scenarios and save energy for effective communication.

Optimal antenna location for distributed antennas in DAS cells

HU Yu-lin, QIU Ling

2009, 39(10): 1091-1096.

Article Views:222 Full article PDF

Abstract:
The antenna location of the distributed antenna system (DAS) determines the systems performance. Under the condition of satisfying the users needs for QoS, the DAS antenna efficiency was first defined and then different methods were adopted to optimize the antenna position so as to reduce the number of antennas and/or minimize the average minimum access distance, thus improving the antenna efficiency and ultimately reducing the cost and the total transmission power of the system. The analysis and simulation results show that the methods have achieved excellent performance.

Analysis and comparison of transmission capacity for multiuser distributed and co-located antenna systems

CHEN Xiao-ming, ZHANG Zhao-yang, WANG Chao

2009, 39(10): 1097-1101.

Article Views:208 Full article PDF

Abstract:
In order to quantificationally compare the supported user distribution density and quality of service (QoS) by distributed antenna system (DAS) and co-located antenna system (CAS) under multiuser condition, a stochastic geometry based performance analysis method is proposed. When the users have a Poisson distribution in the cell, this method can obtain the exact expression of transmission capacity for the two multi-antenna systems. From the expression of transmission capacity for DAS, it is found that, given the user distribution density, in order to satisfy a certain QoS requirement, there is an upper bound of user access distance. Both theoretical analysis and simulation results show that, under the same condition, compared with CAS, DAS is able to admit more users and support higher QoS.

A power-saving single-carrier frequency domain equalization system

BAI Wen-ling, XIAO Yue, LI Shao-qian

2009, 39(10): 1102-1106.

Article Views:205 Full article PDF

Abstract:
Single-carrier frequency domain equalization (SC-FDE) systems, which offer comparable complexity and performance to orthogonal frequency division multiplexing (OFDM) systems with a lower peak-to-average power ratio (PAPR), is a promising technique in future generation of wireless communications. An improved SC-FDE system is proposed, in which the cyclic prefix (CP) is only inserted in front of even frames so that the proposed SC-FDE systems can enjoy higher power efficiency as well as save the sent power of the transmitter, compared to conventional SC-FDE systems. In the receiver, the even frames are detected using the conventional FDE technique while two approaches named overlap-save (OLS) FDE and overlap-add (OLA) FDE are proposed to detect the odd frames. Simulation results show that the proposed OLS FDE receiver can achieve the same symbol error rate (SER) as the conventional SC-FDE system.

A delay based dynamic discontinuous reception cycle adjusting scheme

HUANG Bo, TIAN Hui, XU Hai-bo

2009, 39(10): 1107-1113.

Article Views:215 Full article PDF

Abstract:
A novel dynamic configuration scheme for discontinuous reception (DRX) cycle based on the delay requirement of service is proposed for the LTE downlink system. First, the eNB configures the UEs with the power saving mechanism according to the DRX specifications. Then, the delay parameters are used to control the DRX cycle dynamically. Numerical analysis shows that, there is a close relationship between service delay and network load. Therefore, the configuration of the DRX cycle should be combined with the current network load. Simulation results show that the delay based dynamic cycle adjusting mechanism can adapt to the current network situation as well as their own requirements. Compared with the DRX mechanism with a fixed cycle, the performance of the proposed scheme has a great improvement in terms of user satisfaction and power efficiency.

Two-dimensional DCT-based channel estimation for OFDMA systems

JIANG Bin, WANG Hai-ming, GAO Xi-qi, YOU Xiao-hu

2009, 39(10): 1114-1118.

Article Views:243 Full article PDF

Abstract:
In orthogonal frequency division multiple access (OFDMA) systems, multiple access is achieved by assigning some time-frequency resource blocks to individual users. In this case, the conventional discrete Fourier transform (DFT)-based channel estimator suffers from an irreducible error floor. On the other hand, the DFT-based filtering and/or interpolation in time-domain also have performance degradation for systems with high Doppler frequency. In order to solve these two problems, a two dimensional discrete cosine transform (2-D DCT)-based channel estimator for OFDMA systems is proposed. Simulation results show that the performance of the proposed estimator can well approach the 2-D linear minimum mean square error (LMMSE) channel estimation with low implementation complexity. Furthermore, the proposed estimator can provide high accuracy channel estimation even in the low signal-to-noise ratio region, which contributes to the implementation of green communications.

Efficient time domain channel estimation for MIMO SC-FDMA systems

WANG Hai-ming

2009, 39(10): 1119-1124.

Article Views:194 Full article PDF

Abstract:
A two-sided comb-type pilot structure generated using Golay complementary sequence and time-domain channel estimation is proposed for MIMO SC-FDMA systems under time-varying frequency selective fading channels. Both left-shift and right-shift fast periodic Golay correlation lattices are combined as a symmetrical lattice. It can be used to efficiently implement periodic correlations of phase-shift and sequence orthogonal comb-type pilot blocks in the time domain. Employing this special lattice, computational complexities are significantly reduced. Low-complexity algorithm can reduce power consumption of a processor, which meets one of the requirements of green communications. Simulation results demonstrate the performance merits of the proposed scheme.

2009 Vol. 39, No. 10

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