Vol. 71, n° 1-2, January-February 2016
Content available on Springerlink

A new C-RAN architecture based on RF signal soft-switching

Xiaoyuan Lu¹, Yunxiang Xu², Kejun Zhao², Wen Yang²
1 Fudan University, Shanghai, China
2 National Engineering Research Center for Broadband Networks and Applications, Shanghai, China

Abstract Coordinated multi-point (CoMP) is known to be one of the key technologies for long-term evolution (LTE)-advanced systems. CoMP technology can improve system capacity and the quality of wireless communication services for users in LTE networks. However, in practice, the actual performance of CoMP technology is limited by the switching capacity of the backhaul network among distributed base stations as well as its latencies. In this paper, we propose a new cloud radio access network architecture based on RF signal soft-switching to solve this problem. Furthermore, we introduce a narrow-band parallel processing technique on a common public radio interface in downlink and uplink to reduce the volume of data as well as the latencies in the transmission process among base band units and remote radio units. By combining theoretical analysis with computer simulations, we show that the technique is valid both for downlink and uplink, i.e., it does not degrade the performance of downlink and uplink propagation between BBU pool and user equipments. Moreover, the computational time of the narrow-band parallel processing technique is less than that of the standard technique.

Keywords CoMP – Backhaul – C-RAN architecture – RF signal soft-switching – Narrow-band signal – Parallel processing – Computer simulation

Spectrum efficiency evaluation of LMF channels under various adaptation policies with hybrid diversity schemes

Vidhyacharan Bhaskar^{1, 2}, Vivek G. Rajendran³
1 San Francisco State University, USA
2 Northwestern Polytechnic University, Fremont, USA
3 SRM University, Tamil Nadu, India

Abstract A single-input multiple-output (SIMO) system with lognormal multipath fading (LMF) channel is considered in this paper. The spectrum efficiency (capacity per unit bandwidth) of a LMF channel for various adaptation policies is studied. We obtain the closed-form expressions for various adaptation policies such as (i) optimal power and rate adaptation (OPRA) policy, (ii) channel inversion with fixed rate (CIFR) policy, and (iii) truncated channel inversion with fixed rate (TIFR) policy with hybrid diversity combining techniques like hybrid maximal ratio combining (MRC)-equal gain combining (EGC), hybrid EGC-MRC, and hybrid MRC-selection combining (SC) diversity. Numerical results show that the use of hybrid diversity combining techniques improves the spectrum efficiency over stand-alone diversity combining techniques. OPRA policy that provides the highest spectrum efficiency when compared to other policies is also shown.

Keywords Spectrum efficiency – Optimal power and rate adaptation (OPRA) policy – Channel inversion with fixed rate (CIFR) policy – Truncated channel inversion with fixed rate (TIFR) policy – Hybrid diversity

A novel channelized FB architecture with narrow transition bandwidth based on CEM FRM

Tao Chen, Pengchong Li, Wenxu Zhang, Yong Liu
Harbin Engineering University, China

Abstract The two key requirements of channelized filter bank in the design of a digital receiver are low computational complexity and reconfigurability. Modulated discrete Fourier transform (MDFT) filter bank permits sub-channel with linear phase characteristics and provides high degree of computational efficiency. However, with sub-channel exhibiting narrow transition bandwidth in MDFT filter bank, the length of the prototype filter becomes long prohibitively, which can reduce the computational efficiency. It is well known that the frequency response masking (FRM) provides an attractive technique for the realization of digital filters with very narrow transition bandwidth. In this paper, the FRM digital filter design technique and another important technique named complex-exponential modulation (CEM) are exploited and applied to the design of a novel cascaded channelized filter bank to realize selective sub-channel with very narrow transition bandwidth. A simulation is provided to illustrate the design of the proposed CEM filter bank. It is shown that the resulting filter bank entails less computational complexity substantially and reduces multiplier resource consumption comparing to the conventional MDFT filter bank.

Keywords Modulated DFT (MDFT) – Frequency response masking (FRM) – Complex-exponential modulation (CEM) – Channelized filter bank – Narrow transition bandwidth

Time-frequency localization as mother wavelet selecting criterion for wavelet modulation

Alexandru Isar, Marius Oltean
University of Timisoara, Romania

Abstract Throughout recent years, the discrete wavelet transform (DWT) was used in communications for wavelet modulation (WM). One of its features is the mother wavelets (MW) used. An important number of MW were already proposed in the literature. We investigate in this paper the selection of the MW for the WM, on the basis of its time-frequency localization. We prove, with the aid of Balian-Low theorem, that wavelets have better time-frequency localization than the elements of the bases which are used for signal decomposition in other orthogonal modulation techniques, as, for example, in orthogonal frequency division multiplexing (OFDM). A procedure for the evaluation of the time-frequency localization of MW belonging to Daubechies family is proposed. This procedure is next compared against the WM transmission on different channel types, which reveal the best MW to be used. This advantage of the WM versus OFDM is highlighted by simulation results in fading channels.

Keywords Time-frequency localization – Orthogonal modulation – Fading channels – Wavelets – Wavelet modulation

An interference cancellation scheme for D2D multi-link communication underlaying cellular network

Chithra R¹, Robert Bestak², Sarat Kumar Patra¹
1 National Institute of Technologies, Odisha, India
2 Czech Technical University in Prague, Czech Republic

Abstract Device-to-device (D2D) communication has attracted much attention in the field of mobile networks for local area connectivity due to its spectral efficiency, high bit rate support and low power consumption. A group of D2D capable devices, called a cluster, can be connected through multiple links by sharing common resources. This may however result in co-channel interference between them. In this paper, we propose a novel orthogonal precoding vector selection method for reducing co-channel interference and thus maximizing the achievable data rate for each device in the cluster. The proposed method can be employed for uplink and downlink transmissions of both cellular and D2D communications. The analysis of the proposed method is carried out for the case where the cellular channel resource is being shared by single and multiple D2D links. Initially, the results via simulations are compared with the theoretical analysis and the performance of the proposed method is evaluated and compared for different resource sharing modes. The results show that our proposed method enhance the system throughput when compared with the conventional precoding vector allocation method. Finally, the paper illustrates that the introduction of cluster head in a cluster can save battery life of devices.

Keywords Cluster – Device-to-device (D2D) communication – Long-term evolution-advanced (LTE-A) – Multiple input multiple output (MIMO) – Precoding

Hybrid GSADE algorithm for optimization of far-field radiation pattern of circular arrays

Gopi Ram, Durbadal Mandal, Rajib Kar, Sakti Prasad Ghoshal
National Institute of Technology Durgapur, India

Abstract In this paper, a design problem of non-uniform single-ring circular antenna arrays (CAA) and concentric circular antenna array (CCAA) for maximum side lobe level (SLL) by a hybridized method based on gravitational search algorithm with differential evolution (GSADE) is dealt with. The algorithm is used to determine an optimal set of current excitation weights and antenna inter-element spacing for CAA and an optimal set of current excitation weights for CCAA that provide a radiation pattern with maximum reduction of SLL. The same algorithm has been applied successively on CAAs of 8, 10, and 12 elements and two 3-ring CCAA, one having the set of 4, 6, and 8 elements and the other having 8, 10, and 12 elements with and without center element. Experimental results show a considerable improvement of SLL and some restricted improvement of first null beamwidth (FNBW) and 3-dB beamwidth as well with respect to the corresponding uniform cases and those of some recent literature reported in this paper.

Keywords Non-uniform circular arrays – First null beamwidth – Side lobe level – GSADE

Reliable and energy aware query-driven routing protocol for wireless sensor networks

Mawloud Omar¹, Souraya Yahiaoui¹, Abdelmadjid Bouabdallah²
1 Université de Bejaia, Algérie
2 Université de Technologie de Compiègne, France

Abstract Wireless sensor networks become very attractive in the research community, due to their applications in diverse fields such as military tracking, civilian applications and medical research, and more generally in systems of systems. Routing is an important issue in wireless sensor networks due to the use of computationally and resource limited sensor nodes. Any routing protocol designed for use in wireless sensor networks should be energy efficient and should increase the network lifetime. In this paper, we propose an efficient and highly reliable query-driven routing protocol for wireless sensor networks. Our protocol provides the best theoretical energy aware routes to reach any node in the network and routes the request and reply packets with a lightweight overhead. We perform an overall evaluation of our protocol through simulations with comparison to other routing protocols. The results demonstrate the efficiency of our protocol in terms of energy consumption, load balancing of routes, and network lifetime.

Keywords Routing – Energy preservation – Query-driven routing – Wireless sensor networks